What is the purpose of the Aviation Maintenance Technician Handbook–General?

The handbook provides basic information on principles, fundamentals, and technical procedures for those preparing for mechanic certification with airframe or powerplant ratings.

What topics are covered in this handbook?

Topics include mathematics, aircraft drawings, weight and balance, aircraft materials, processes and tools, physics, electricity, inspection, and FAA regulations.

Is this handbook intended to replace manufacturers' instructions?

No, the handbook is not intended to replace or supersede official regulations or manufacturers' instructions.

Where can I download the handbook?

The handbook is available for download in PDF format from the FAA website at www.faa.gov.

What is new in this edition of the handbook?

This edition includes a section addressing how aviation maintenance technicians incorporate knowledge and awareness of ethics, professionalism, and human factors in their work.

FAA-H-8083-30B — Aviation Maintenance Technician Handbook

Section 1

Chapter 1 False or Hung Start ....................................... 1-17 Safety, Ground Operations, & Servicing ........... 1-1 Engine Fails to Start ...................................... 1-17 Shop Safety ........................................................... 1-1 Towing of Aircraft .............................................. 1-17 Electrical Safety ................................................. 1-1 Taxiing Aircraft .................................................. 1-19 Physiological Safety ........................................ 1-1 Taxi Signals ................................................... 1-20 Fire Safety ....................................................... 1-1 Servicing Aircraft .................................................. 1-20 Safety Around Compressed Gases ................... 1-2 Servicing Aircraft Air/Nitrogen Oil & Fluids ....... 1-20 Safety Around Hazardous Materials .................. 1-2 Ground Support Equipment ............................ 1-21 Safety Around Machine Tools ............................. 1-2 Electric Ground Power Units ......................... 1-21 Flight Line Safety ................................................... 1-4 Hydraulic Ground Power Units ...................... 1-22 Hearing Protection ............................................. 1-4 Ground Support Air Units .............................. 1-23 Foreign Object Damage (FOD) .......................... 1-4 Ground Air Heating and Air Conditioning ..... 1-24 Safety Around Airplanes ..................................... 1-4 Oxygen Servicing Equipment ........................... 1-24 Safety Around Helicopters .................................. 1-4 Oxygen Hazards .............................................. 1-25 Fire Safety .......................................................... 1-5 Fuel Servicing of Aircraft ...................................... 1-25 Fire Protection ....................................................... 1-5 Types of Fuel and Identification ....................... 1-25 Requirements for Fire to Occur .......................... 1-5 Contamination Control ..................................... 1-25 Classification of Fires ......................................... 1-5 Fueling Hazards .............................................. 1-26 Types and Operation of Shop and Flight Line Fueling Procedures .......................................... 1-26 Fire Extinguishers .............................................. 1-5 Defueling .......................................................... 1-28 Inspection of Fire Extinguishers ......................... 1-7 Identifying Fire Extinguishers ............................. 1-8 Chapter 2 Using Fire Extinguishers .................................... 1-8 Regulations, Maintenance Forms, Records, & Tie-Down Procedures ............................................ 1-8 Publications ......................................................... 2-1 Preparation of Aircraft ........................................ 1-8 Overview — Title 14 of the Code of Federal Tie-Down Procedures for Land Planes .............. 1-8 Regulations (14 CFR) ............................................ 2-1 Securing Light Aircraft ..................................... 1-8 Title 14 CFR Part 3—General Requirements ..... 2-1 Securing Heavy Aircraft .................................. 1-8 Maintenance-Related Regulations ..................... 2-3 Tie-Down Procedures for Seaplanes ................. 1-8 14 CFR Part 1—Definitions and Tie-Down Procedures for Ski Planes ................ 1-9 Abbreviations ................................................. 2-3 Tie-Down Procedures for Helicopters .............. 1-10 14 CFR Part 21—Certification Procedures Procedures for Securing Weight-Shift-Control .. 1-11 for Products and Articles ................................. 2-3 Procedures for Securing Powered Parachutes . 1-11 14 CFR Part 23—Airworthiness Standards: Ground Movement of Aircraft ................................ 1-11 Normal, Utility, Acrobatic, and Commuter Category Airplanes .......................................... 2-4 Engine Starting and Operation .......................... 1-11 Reciprocating Engines ...................................... 1-11 14 CFR Part 25—Airworthiness Standards: Transport Category Airplanes ......................... 2-5 Hand Cranking Engines ................................... 1-13 Extinguishing Engine Fires ............................... 1-14 14 CFR Part 27—Airworthiness Standards: Normal Category Rotorcraft ............................ 2-5 Turboprop Engines ........................................... 1-14 Turboprop Starting Procedures ........................ 1-15 14 CFR Part 29—Airworthiness Standards: Transport Category Rotorcraft ....................... 2-5 Turbofan Engines ............................................. 1-15 Starting a Turbofan Engine .............................. 1-15 14 CFR Part 33—Airworthiness Standards: Aircraft Engines ............................................... 2-8 Auxiliary Power Units (APUs) ........................... 1-16 Unsatisfactory Turbine Engine Starts .............. 1-17 14 CFR Part 35—Airworthiness Standards: Propellers ........................................................ 2-8 Hot Start ........................................................ 1-17 iv 14 CFR Part 39—Airworthiness Directives ..... 2-8 records (except inspection performed in accordance with parts 91 and 125, and 14 CFR Part 43—Maintenance, Preventive sections 135.411(a)(1) and 135.419 of this Maintenance, Rebuilding, and Alteration ........ 2-8 chapter) ......................................................... 2-16 14 CFR Part 45—Identification and Section 43.10—Disposition of Life-Limited Registration Marking ....................................... 2-8 Aircraft Parts ................................................. 2-16 14 CFR Part 47—Aircraft Registration .......... 2-10 Section 43.11—Content, form, and 14 CFR Part 65—Certification: Airmen disposition of records for inspections Other Than Flight Crewmembers .................. 2-10 conducted under parts 91 and 125, and 14 CFR Part 91—General Operating and sections 135.411(a)(1) and 135.419 of this Flight Rules ................................................... 2-10 chapter .......................................................... 2-17 14 CFR Part 119—Certification: Air Section 43.12—Maintenance Records: Carriers and Commercial Operators ............. 2-10 Falsification, Reproduction, or Alteration ...... 2-17 14 CFR Part 121—Operating Section 43.13—Performance Rules Requirements: Domestic, Flag, and (General) ....................................................... 2-17 Supplemental Operations ............................. 2-11 Section 43.15 — Additional Performance 14 CFR Part 125—Certification and Rules for Inspections .................................... 2-18 Operations: Airplanes Having a Seating Section 43.16 — Airworthiness Limitations .... 2-18 Capacity of 20 or More Passengers or Section 43.17—Maintenance, preventive a Maximum Payload Capacity of 6,000 maintenance, or alterations performed Pounds or More; and Rules Governing on U.S. aeronautical products by certain Persons on Board Such Aircraft ................... 2-12 Canadian persons ......................................... 2-18 14 CFR Part 135—Operating Appendix A—Major Alterations, Major Requirements: Commuter and On-Demand Repairs, and Preventive Maintenance .......... 2-18 Operations and Rules Governing Persons on Board Such Aircraft ................................. 2-12 Appendix B—Recording of Major Repairs and Major Alterations .................................... 2-20 14 CFR Part 145—Repair Stations ............... 2-13 Appendix C—(Reserved) .............................. 2-20 14 CFR Part 147—Aviation Maintenance Technician Schools ....................................... 2-13 Appendix D—Scope and Detail of Items To Be Included in Annual and 100-Hour 14 CFR Part 183—Representatives of the Inspections .................................................... 2-20 Administrator ................................................. 2-13 Appendix E—Altimeter System Test and Explanation of Primary Regulations (Parts 43 Inspection ...................................................... 2-20 and 91) ................................................................ 2-14 Appendix F—ATC Transponder Tests and 14 CFR Part 43—Maintenance, Preventative Inspections .................................................... 2-20 Maintenance Rebuilding, and Alteration .......... 2-14 Section 43.1—Applicability ........................... 2-14 14 CFR Part 91—General Operating and Flight Rules ...................................................... 2-21 Section 43.2—Records of Overhaul and Subpart A—General ..................................... 2-21 Rebuilding ..................................................... 2-14 Subpart E—Maintenance, Preventive Section 43.3—Persons authorized Maintenance, and Alterations ........................ 2-21 to perform maintenance, preventive maintenance, rebuilding, and alterations ...... 2-14 Civil Air Regulations (CAR) .................................. 2-23 Section 43.5—Approval for return to CAR 3—Airplane Airworthiness—Normal, service after maintenance, preventive Utility, Aerobatic, and Restricted Purpose maintenance, rebuilding, and alterations ...... 2-15 Categories ........................................................ 2-23 CAR 4a—Airplane Airworthiness ..................... 2-23 Section 43.7—Persons authorized to approve aircraft, airframes, aircraft Suspected Unapproved Parts (SUP) ................... 2-24 engines, propellers, appliances, or Other FAA Documents ......................................... 2-24 component parts for return to service after Advisory Circulars (AC) .................................... 2-24 maintenance, preventive maintenance, The AC Numbering System .......................... 2-26 rebuilding, or alteration ................................. 2-16 Types of Airworthiness Directives (AD) ......... 2-26 Section 43.9—Content, form and AD Content ................................................... 2-26 disposition of maintenance, preventive AD Number ................................................... 2-26 maintenance, rebuilding, and alteration v Applicability and Compliance ........................ 2-27 Addition of Decimal Numbers ............................. 3-4 Subtraction of Decimal Numbers ....................... 3-4 Alternative Method of Compliance ................ 2-27 Multiplication of Decimal Numbers ..................... 3-5 Special Airworthiness Information Bulletin Division of Decimal Numbers ............................. 3-6 (SAIB) ............................................................... 2-27 Rounding Off Decimal Numbers ......................... 3-6 Aircraft Specifications ....................................... 2-27 Converting Decimal Numbers to Fractions ........ 3-6 Supplemental Type Certificates (STC) ............. 2-27 Converting Fractions to Decimals ...................... 3-7 Type Certificate Data Sheets (TCDS) .............. 2-30 Decimal Equivalent Chart ................................... 3-7 FAA Handbooks & Manuals ................................. 2-30 Ratio ...................................................................... 3-7 Non-FAA Documents ........................................... 2-30 Aviation Applications .......................................... 3-7 Air Transport Association ATA iSpec 2200 ...... 2-30 Proportion .............................................................. 3-8 Manufacturers’ Published Data ........................ 2-30 Extremes and Means ......................................... 3-8 Airworthiness Limitations ................................. 2-33 Solving Proportions ............................................ 3-8 Service Bulletins (SB) ...................................... 2-33 Percentage .......................................................... 3-10 Structural Repair Manual (SRM) ...................... 2-33 Expressing a Decimal Number as a Forms .................................................................. 2-33 Percentage ....................................................... 3-10 Airworthiness Certificates ................................. 2-33 Expressing a Percentage as a Decimal Aircraft Registration .......................................... 2-37 Number ............................................................ 3-10 Radio Station License ..................................... 2-38 Expressing a Fraction as a Percentage ........... 3-10 FAA Form 337—Major Repair and Alteration .. 2-38 Finding a Percentage of a Given Number ....... 3-10 Records ............................................................... 2-39 Finding What Percentage One Number is of Making Maintenance Record Entries ............... 2-39 Another ............................................................. 3-10 Temporary Records—14 CFR Part 91 Finding a Number When a Percentage of it is Section 91.417(a)(1) and (b)(1) ........................ 2-39 Known ............................................................... 3-11 Permanent Records—14 CFR Part 91, Positive & Negative Numbers (Signed Numbers) 3-11 Section 91.417(a)(2) and (b)(2) ........................ 2-39 Addition of Positive & Negative Numbers ......... 3-11 Electronic Records .......................................... 2-39 Subtraction of Positive & Negative Numbers .... 3-11 Light Sport Aircraft (LSA) .................................... 2-40 Multiplication of Positive & Negative Numbers .. 3-11 Maintenance ..................................................... 2-40 Powers .................................................................. 3-11 Aircraft Maintenance Manual (AMM) ................ 2-44 Special Powers ............................................... 3-12 Line Maintenance, Repairs, & Alterations ........ 2-45 Squared ....................................................... 3-12 Major Repairs & Alterations .............................. 2-45 Cubed ........................................................... 3-12 Chapter 3 Power of Zero ............................................... 3-12 Mathematics in Aviation Maintenance ............... 3-1 Law of Exponents ............................................. 3-12 Introduction ............................................................ 3-1 Powers of Ten ................................................... 3-12 Whole Numbers ..................................................... 3-1 Roots ................................................................ 3-12 Addition of Whole Numbers ............................... 3-1 Square Roots ................................................... 3-12 Subtraction of Whole Numbers .......................... 3-1 Cube Roots ...................................................... 3-13 Division of Whole Numbers ................................ 3-1 Fractional Powers ............................................ 3-13 Fractions ................................................................ 3-2 Functions of Numbers Chart ................................ 3-13 Finding the Least Common Denominator ......... 3-2 Scientific Notation ................................................ 3-13 Addition of Fractions .......................................... 3-2 Converting Numbers from Standard Notation Subtraction of Fractions ..................................... 3-2 to Scientific Notation ........................................ 3-13 Multiplication of Fractions ................................... 3-3 Converting Numbers from Scientific Notation to Standard Notation ........................................ 3-16 Division of Fractions ........................................... 3-3 Addition, Subtraction, Multiplication, and Reducing Fractions ............................................ 3-3 Division of Scientific Numbers .......................... 3-16 Mixed Numbers ..................................................... 3-3 Algebra ................................................................ 3-16 Addition of Mixed Numbers ................................ 3-4 Equations ......................................................... 3-16 Subtraction of Mixed Numbers ........................... 3-4 Algebraic Rules ................................................ 3-16 The Decimal Number System ................................ 3-4 Solving for a Variable ....................................... 3-16 Origin and Definition .......................................... 3-4 vi Use of Parentheses .......................................... 3-17 Assembly Drawing ............................................. 4-2 Order of Operation ........................................... 3-17 Installation Drawing ............................................ 4-2 Order of Operation for Algebraic Equations ..... 3-18 Sectional View Drawings .................................... 4-2 Computing Area of Two-Dimensional Solids ....... 3-18 Full Section ..................................................... 4-2 Rectangle ......................................................... 3-18 Half Section ..................................................... 4-2 Square .............................................................. 3-18 Revolved Section ............................................ 4-2 Triangle ............................................................ 3-18 Removed Section ............................................ 4-3 Parallelogram ................................................... 3-18 Title Blocks ............................................................ 4-3 Trapezoid ......................................................... 3-18 Drawing or Print Numbers .................................. 4-3 Circle ................................................................ 3-19 Reference and Dash Numbers ........................... 4-3 Ellipse ............................................................... 3-19 Universal Numbering System ................................ 4-3 Units of Area ..................................................... 3-20 Drawing Standards ................................................ 4-7 Computing Volume of Three-Dimensional Solids 3-20 Bill of Material ........................................................ 4-7 Rectangular Solid ............................................. 3-20 Other Drawing Data ............................................... 4-8 Cube ................................................................. 3-21 Revision Block .................................................... 4-8 Cylinder ............................................................ 3-21 Notes .................................................................. 4-8 Sphere .............................................................. 3-22 Zone Numbers ................................................... 4-8 Cone ................................................................. 3-23 Station Numbers & Location Identification on Units of Volume ................................................ 3-23 Aircraft ................................................................ 4-8 Computing Surface Area of Three-Dimensional Allowances & Tolerances ................................... 4-9 Solids ................................................................... 3-23 Finish Marks ....................................................... 4-9 Rectangular Solid ............................................. 3-24 Scale .................................................................. 4-9 Cube ................................................................. 3-24 Application .......................................................... 4-9 Cylinder ............................................................ 3-24 Methods of Illustration ........................................... 4-9 Sphere .............................................................. 3-24 Applied Geometry .............................................. 4-9 Cone ................................................................ 3-24 Orthographic Projection Drawings .................. 4-9 Trigonometric Functions ...................................... 3-24 Pictorial Drawings .......................................... 4-11 Right Triangle, Sides, and Angles .................... 3-24 Diagrams ........................................................ 4-11 Sine, Cosine, and Tangent ............................... 3-25 Flowcharts ..................................................... 4-13 Calculator Method: ........................................ 3-25 Lines and Their Meanings ................................... 4-16 Trigonometry Table Method: ......................... 3-25 Centerlines ....................................................... 4-16 Pythagorean Theorem ...................................... 3-25 Dimension Lines ............................................... 4-17 Measurement Systems ........................................ 3-26 Extension Lines ................................................ 4-17 Conventional (U.S. or English) System ............ 3-26 Sectioning Lines ............................................... 4-17 Metric System .................................................. 3-26 Phantom Lines ................................................. 4-17 Measurement Systems & Conversions ............ 3-26 Break Lines ...................................................... 4-18 The Binary Number System ................................ 3-27 Leader Lines .................................................... 4-18 Place Values ..................................................... 3-27 Hidden Lines .................................................... 4-18 Converting Binary Numbers to Decimal Outline or Visible Lines ..................................... 4-18 Numbers ........................................................... 3-27 Stitch Lines ....................................................... 4-18 Converting Decimal Numbers to Binary Cutting Plane and Viewing Plane Lines ........... 4-19 Numbers .......................................................... 3-27 Drawing Symbols ................................................. 4-19 Material Symbols .............................................. 4-19 Chapter 4 Shape Symbols ................................................ 4-19 Aircraft Drawings ................................................. 4-1 Electrical Symbols ............................................ 4-19 Introduction ............................................................ 4-1 Reading and Interpreting Drawings ..................... 4-19 Computer Graphics ............................................... 4-1 Drawing Sketches ................................................ 4-22 Purpose & Function of Aircraft Drawings ............... 4-1 Sketching Techniques ...................................... 4-22 Care & Use of Drawings ........................................ 4-2 Basic Shapes ................................................... 4-22 Types of Drawings ................................................. 4-2 Repair Sketches ............................................... 4-22 Detail Drawing .................................................... 4-2 Care of Drafting Instruments ............................... 4-22 vii Graphs & Charts .................................................. 4-23 Acceleration ..................................................... 5-15 Reading & Interpreting Graphs & Charts ......... 4-23 Newton’s Law of Motion ................................... 5-16 Nomograms ...................................................... 4-23 First Law ....................................................... 5-16 Microfilm & Microfiche ......................................... 4-23 Second Law .................................................. 5-16 Digital Images ...................................................... 4-23 Third Law ...................................................... 5-17 Circular Motion ................................................. 5-17 Chapter 5 Heat ..................................................................... 5-18 Physics for Aviation ............................................ 5-1 Heat Energy Units ............................................ 5-18 Matter ................................................................... 5-1 Heat Energy and Thermal Efficiency ................ 5-19 Characteristics of Matter ................................... 5-1 Heat Transfer ................................................... 5-19 Mass & Weight ................................................ 5-1 Conduction .................................................... 5-19 Attraction ......................................................... 5-1 Convection .................................................... 5-20 Porosity ........................................................... 5-1 Radiation ....................................................... 5-20 Impenetrability ................................................. 5-1 Specific Heat .................................................... 5-21 Density ........................................................... 5-2 Temperature ..................................................... 5-21 Specific Gravity .............................................. 5-2 Thermal Expansion/Contraction ....................... 5-22 Energy ................................................................... 5-2 Pressure .............................................................. 5-22 Potential Energy ................................................. 5-2 Gauge Pressure ............................................... 5-23 Kinetic Energy .................................................... 5-3 Absolute Pressure ............................................ 5-23 Force, Work, Power, & Torque ............................... 5-4 Differential Pressure ......................................... 5-23 Force .................................................................. 5-4 Gas Laws ............................................................. 5-23 Work ................................................................... 5-4 Boyle’s Law ...................................................... 5-24 Friction & Work ................................................... 5-4 Charles’ Law ..................................................... 5-25 Static Friction .................................................. 5-5 General Gas Law ............................................. 5-25 Sliding Friction ................................................ 5-5 Dalton’s Law ..................................................... 5-25 Fluid Mechanics ................................................... 5-26 Rolling Friction ................................................ 5-6 Buoyancy ......................................................... 5-26 Power ................................................................. 5-6 Fluid Pressure .................................................. 5-27 Torque ................................................................ 5-6 Pascal’s Law .................................................... 5-27 Simple Machines ................................................... 5-7 Bernoulli’s Principle .......................................... 5-29 Mechanical Advantage of Machines ................... 5-7 Sound .................................................................. 5-30 The Lever ........................................................... 5-8 Wave Motion .................................................... 5-30 First Class Lever ............................................. 5-8 Speed of Sound ............................................... 5-31 Second Class Lever ........................................ 5-9 Mach Number ................................................... 5-31 Third Class Lever ............................................ 5-9 Frequency of Sound ......................................... 5-31 The Pulley .......................................................... 5-9 Loudness .......................................................... 5-32 Single Fixed Pulley ......................................... 5-9 Measurement of Sound Intensity ..................... 5-32 Single Movable Pulley ..................................... 5-9 Doppler Effect ................................................... 5-32 Block and Tackle ........................................... 5-10 Resonance ....................................................... 5-32 The Gear .......................................................... 5-10 The Atmosphere .................................................. 5-32 Inclined Plane .................................................... 5-11 Composition of the Atmosphere ....................... 5-33 Stress .................................................................. 5-12 Atmospheric Pressure ...................................... 5-34 Tension ............................................................. 5-12 Atmospheric Density ........................................ 5-34 Compression .................................................... 5-13 Water Content of the Atmosphere .................... 5-34 Torsion .............................................................. 5-13 Absolute Humidity ......................................... 5-35 Bending ............................................................ 5-13 Relative Humidity .......................................... 5-35 Shear ................................................................ 5-13 Dew Point ...................................................... 5-36 Strain ................................................................ 5-14 Vapor Pressure ............................................. 5-36 Motion .................................................................. 5-14 Standard Atmosphere ...................................... 5-36 Uniform Motion ................................................. 5-14 Aircraft Theory of Flight ....................................... 5-36 Speed and Velocity .......................................... 5-14 viii Four Forces of Flight ........................................ 5-36 Maximum Weight ................................................ 6-3 Bernoulli’s Principle and Subsonic Flow ........... 5-37 Empty Weight ..................................................... 6-4 Lift and Newton’s Third Law ............................. 5-37 Empty Weight Center of Gravity (EWCG) .......... 6-4 Airfoils .............................................................. 5-38 Useful Load ........................................................ 6-4 Camber ......................................................... 5-38 Minimum Fuel ..................................................... 6-4 Tare Weight ........................................................ 6-5 Chord Line ..................................................... 5-38 Procedures for Weighing an Aircraft ...................... 6-5 Relative Wind ................................................ 5-38 General Concepts .............................................. 6-5 Angle of Attack ............................................... 5-38 Weight and Balance Data ................................... 6-6 Boundary Layer Airflow ................................... 5-39 Manufacturer-Furnished Information .................. 6-6 Boundary Layer Control ................................ 5-39 Weight and Balance Equipment ........................... 6-7 Wingtip Vortices ............................................... 5-40 Scales ................................................................ 6-7 Axes of an Aircraft ............................................ 5-40 Spirit Level .................................................... 6-11 Aircraft Stability ............................................... 5-40 Hydrometer ................................................... 6-12 Static Stability ............................................... 5-40 Preparing an Aircraft for Weighing ................... 6-12 Dynamic Stability .......................................... 5-40 Fuel System .................................................. 6-13 Longitudinal Stability ..................................... 5-41 Oil System ..................................................... 6-13 Lateral Stability ............................................. 5-42 Miscellaneous Fluids ..................................... 6-14 Directional Stability ....................................... 5-42 Flight Controls ............................................... 6-14 Dutch Roll ..................................................... 5-42 Other Considerations .................................... 6-14 Flight Control Surfaces ..................................... 5-42 Weighing Points ............................................ 6-14 Flight Controls & the Lateral Axis .................. 5-42 Jacking the Aircraft ........................................... 6-14 Flight Controls and the Longitudinal Axis ...... 5-43 Leveling the Aircraft .......................................... 6-14 Flight Controls and the Vertical Axis ............. 5-43 Safety Considerations ...................................... 6-15 Tabs .............................................................. 5-44 CG Range ........................................................ 6-15 Supplemental Lift-Modifying Devices ............ 5-45 Empty Weight Center of Gravity (EWCG) High-Speed Aerodynamics ............................... 5-46 Range ........................................................... 6-15 Compressibility Effects .................................. 5-46 Operating CG Range .................................... 6-16 The Speed of Sound ..................................... 5-46 Standard Weights Used for Aircraft Weight Subsonic, Transonic, and Supersonic Flight . 5-47 and Balance ..................................................... 6-16 Shock Waves ................................................ 5-47 Example Weighing of an Airplane .................... 6-16 High-Speed Airfoils ....................................... 5-48 EWCG Formulas .............................................. 6-16 Aerodynamic Heating .................................... 5-49 Datum Forward of the Airplane–Nosewheel Landing Gear ................................................... 6-16 Helicopter Aerodynamics ................................. 5-49 Datum Aft of the Main Wheels–Nosewheel Helicopter Structures and Airfoils .................. 5-49 Landing Gear ................................................... 6-17 Helicopter Axes of Flight ............................... 5-52 Location of Datum ............................................ 6-17 Helicopters in Flight ...................................... 5-54 Datum Forward of the Main Wheels–Tail Weight-Shift Control, Flexible Wing Aircraft Wheel Landing Gear ........................................ 6-17 Aerodynamics .................................................. 5-56 Loading an Aircraft for Flight ................................ 6-19 Powered Parachute Aerodynamics .................. 5-58 Example Loading of an Airplane ................... 6-19 Adverse-Loaded CG Checks ........................... 6-20 Chapter 6 Example Forward & Aft Adverse-Loaded CG Aircraft Weight & Balance .................................. 6-1 Checks ............................................................. 6-20 Introduction ............................................................ 6-1 Equipment Change & Aircraft Alteration .............. 6-21 Requirements for Aircraft Weighing ....................... 6-1 Example Calculation After an Equipment Weight & Balance Terminology .............................. 6-2 Change ......................................................... 6-21 Datum ................................................................. 6-2 Use of Ballast ................................................... 6-22 Arm ..................................................................... 6-2 Temporary Ballast ......................................... 6-22 Moment .............................................................. 6-2 Permanent Ballast ......................................... 6-23 Center of Gravity (CG) ....................................... 6-3 Loading Graphs & CG Envelopes ....................... 6-24 ix Helicopter Weight & Balance ............................... 6-25 Behavior of Steel During Heating & Cooling . 7-16 General Concepts ............................................ 6-25 Hardening ..................................................... 7-17 Helicopter Weighing ......................................... 6-25 Hardening Precautions ................................. 7-19 Weight and Balance—Weight-Shift Control Tempering ..................................................... 7-19 Aircraft and Powered Parachutes ........................ 6-26 Annealing ...................................................... 7-19 Weight-Shift Control Aircraft ............................. 6-27 Normalizing ................................................... 7-19 Powered Parachutes ........................................ 6-28 Case Hardening ............................................ 7-20 Built-In Electronic Weighing ............................. 6-28 Heat-Treatment of Nonferrous Metals .............. 7-20 Mean Aerodynamic Chord ................................ 6-28 Aluminum Alloys ............................................ 7-20 Weight & Balance Records .................................. 6-31 Alclad Aluminum ........................................... 7-21 Solution Heat-Treatment ............................... 7-21 Chapter 7 Quenching ..................................................... 7-22 Aircraft Materials, Hardware, & Processes ...... 7-1 Properties of Metals ........................................... 7-1 Lag Between Soaking & Quenching ............. 7-22 Hardness ......................................................... 7-1 Reheat-Treatment ......................................... 7-22 Strength .......................................................... 7-1 Straightening After Solution Heat-Treatment .... 7-22 Density ............................................................ 7-1 Precipitation Heat-Treating ............................... 7-22 Precipitation Practices .................................. 7-23 Malleability ...................................................... 7-1 Annealing of Aluminum Alloys .......................... 7-23 Ductility ........................................................... 7-1 Heat-Treatment of Aluminum Alloy Rivets ........ 7-24 Elasticity .......................................................... 7-1 Heat-Treatment of Magnesium Alloys .............. 7-24 Toughness ....................................................... 7-1 Solution Heat-Treatment ............................... 7-24 Brittleness ....................................................... 7-1 Precipitation Heat-Treatment ........................ 7-24 Fusibility .......................................................... 7-2 Heat-Treatment of Titanium .............................. 7-25 Conductivity .................................................... 7-2 Stress Relieving ............................................ 7-25 Thermal Expansion ......................................... 7-2 Full Annealing ............................................... 7-25 Ferrous Aircraft Metals ....................................... 7-2 Thermal Hardening ....................................... 7-25 Iron .................................................................. 7-2 Case Hardening ............................................ 7-25 Steel and Steel Alloys ..................................... 7-2 Hardness Testing .............................................. 7-25 Electrochemical Test .......................................... 7-4 Brinell Tester ................................................. 7-26 Nonferrous Aircraft Metals .................................. 7-5 Rockwell Tester ............................................. 7-26 Aluminum & Aluminum Alloys ......................... 7-5 Barcol Tester ................................................. 7-27 Wrought Aluminum .......................................... 7-7 Forging ............................................................. 7-27 Effect of Alloying Element ............................... 7-7 Casting ............................................................. 7-28 Hardness Identification ................................... 7-7 Extruding .......................................................... 7-28 Magnesium & Magnesium Alloys .................... 7-8 Cold-Working/Hardening .................................. 7-29 Titanium and Titanium Alloys .......................... 7-9 Nonmetallic Aircraft Materials .............................. 7-29 Copper and Copper Alloys ............................ 7-10 Wood ................................................................ 7-29 Nickel & Nickel Alloys ..................................... 7-11 Plastics ............................................................. 7-29 Substitution of Aircraft Metals ............................ 7-11 Transparent Plastics ......................................... 7-29 Metalworking Processes .................................. 7-12 Composite Materials ........................................ 7-30 Hot-Working .................................................. 7-12 Advantages/Disadvantages of Composites .. 7-30 Internal Structure of Metals ........................... 7-14 Composite Safety .......................................... 7-31 Heat-Treating Equipment .............................. 7-14 Fiber Reinforced Materials ............................ 7-31 Heating .......................................................... 7-15 Laminated Structures .................................... 7-31 Soaking ......................................................... 7-15 Reinforced Plastic ......................................... 7-31 Cooling .......................................................... 7-16 Rubber ............................................................. 7-32 Quenching Media .......................................... 7-16 Natural Rubber .............................................. 7-32 Quenching Equipment .................................. 7-16 Synthetic Rubber .......................................... 7-32 Heat-Treatment of Ferrous Metals ................... 7-16 Shock Absorber Cord ....................................... 7-33 x Seals .................................................................... 7-33 Material ......................................................... 7-58 Packings ........................................................... 7-34 Head Styles ................................................... 7-59 O-Ring Packings ........................................... 7-34 Diameters ...................................................... 7-59 V-Ring Packings ............................................ 7-35 Grip Length ................................................... 7-59 U-Ring Packings ........................................... 7-35 Rivet Identification ......................................... 7-59 Gaskets ............................................................ 7-35 Special Shear and Bearing Load Fasteners .... 7-60 Wipers .............................................................. 7-35 Pin Rivets ...................................................... 7-60 Sealing Compounds ......................................... 7-35 Taper-Lok ...................................................... 7-61 One Part Sealants ......................................... 7-36 HI-LOK™ Fastening System ......................... 7-61 Two Part Sealants ......................................... 7-36 HI-TIGUE™ Fastening System ..................... 7-63 Aircraft Hardware ................................................. 7-36 HI-LITE™ Fastening System ........................ 7-64 Identification ..................................................... 7-37 Captive Fasteners ......................................... 7-64 Threaded Fasteners ......................................... 7-37 Turn Lock Fasteners ..................................... 7-64 Classification of Threads ............................... 7-37 Dzus Fasteners ............................................. 7-64 Aircraft Bolts ..................................................... 7-37 Camloc Fasteners ......................................... 7-65 General Purpose Bolts .................................. 7-37 Airloc Fasteners ............................................ 7-66 Close Tolerance Bolts ................................... 7-38 Screws ............................................................. 7-66 Internal Wrenching Bolts ............................... 7-38 Structural Screws .......................................... 7-66 Identification and Coding .............................. 7-38 Machine Screws ............................................ 7-67 Special-Purpose Bolts ................................... 7-39 Self-Tapping Screws ..................................... 7-67 Aircraft Nuts ..................................................... 7-41 Identification & Coding for Screws ................ 7-67 Non-Self-Locking Nuts .................................. 7-41 Riveted & Rivetless Nut Plates ........................ 7-68 Self-Locking Nuts .......................................... 7-42 Nut Plates ..................................................... 7-68 Sheet Spring Nuts ......................................... 7-45 Rivnuts .......................................................... 7-68 Internal & External Wrenching Nuts .............. 7-45 Dill Lok-Skrus and Dill Lok-Rivets ................. 7-69 Identification & Coding .................................. 7-45 Deutsch Rivets .............................................. 7-70 Aircraft Washers ............................................... 7-46 Sealing Nut Plates ........................................ 7-70 Plain Washers ............................................... 7-46 Hole Repair & Hole Repair Hardware .............. 7-70 Lock Washers ............................................... 7-46 Repair of Damaged Holes with Acres Special Washers ........................................... 7-47 Fastener Sleeves .......................................... 7-71 Installation of Nuts, Washers, & Bolts .............. 7-47 Control Cables & Terminals ........................... 7-72 Bolt & Hole Sizes .......................................... 7-47 Push-Pull Tube Linkage ................................ 7-72 Installation Practices ..................................... 7-48 Safetying Methods ........................................... 7-75 Safetying of Bolts & Nuts ................................. 7-48 Pins ............................................................... 7-75 Repair of Damaged Internal Threads ............ 7-48 Safety Wiring .................................................... 7-77 Fastener Torque ............................................... 7-49 Nuts, Bolts, & Screws ................................... 7-77 Torque ........................................................... 7-49 Oil Caps, Drain Cocks, & Valves ................... 7-77 Torque Wrenches ......................................... 7-49 Electrical Connectors .................................... 7-79 Torque Tables ................................................ 7-50 Turnbuckles ................................................... 7-79 Cotter Pin Hole Line Up ................................ 7-50 General Safety Wiring Rules ............................ 7-80 Aircraft Rivets ................................................... 7-51 Cotter Pin Safetying ...................................... 7-80 Standards and Specifications ....................... 7-51 Snap Rings ................................................... 7-80 Solid Shank Rivets ........................................ 7-52 Identification .................................................. 7-54 Chapter 8 Blind Rivets ................................................... 7-56 Cleaning & Corrosion Control ............................ 8-1 Mechanically-Expanded Rivets ........................ 7-57 Corrosion ............................................................... 8-1 Self-Plugging Rivets (Friction Lock) .............. 7-57 Factors Affecting Corrosion ................................ 8-1 Pull-Thru Rivets ............................................ 7-57 Pure Metals ..................................................... 8-1 Self-Plugging Rivets (Mechanical Lock) ....... 7-58 Climate ............................................................ 8-2 xi Geographical Location .................................... 8-2 Treatment of Wrought Magnesium Sheet & Forgings ........................................................... 8-19 Foreign Material .............................................. 8-2 Treatment of Installed Magnesium Castings .... 8-19 Micro-organisms ............................................. 8-2 Treatment of Titanium & Titanium Alloys ............. 8-20 Manufacturing Processes ............................... 8-2 Protection of Dissimilar Metal Contacts ............... 8-20 Types of Corrosion ............................................. 8-2 Contacts Not Involving Magnesium .................. 8-20 Direct Chemical Attack .................................... 8-2 Contacts Involving Magnesium ........................ 8-20 Electrochemical Attack .................................... 8-3 Corrosion Limits ................................................... 8-20 Forms of Corrosion ............................................ 8-5 Processes & Materials Used in Corrosion Surface Corrosion ........................................... 8-5 Control ................................................................. 8-21 Filiform Corrosion ........................................... 8-5 Metal Finishing ................................................. 8-21 Pitting Corrosion ............................................. 8-6 Surface Preparation ......................................... 8-21 Dissimilar Metal Corrosion .............................. 8-6 Chemical Treatments ........................................... 8-22 Concentration Cell Corrosion .......................... 8-6 Anodizing ......................................................... 8-22 Intergranular Corrosion ................................... 8-7 Alodizing ........................................................... 8-22 Chemical Surface Treatment and Inhibitors ..... 8-22 Exfoliation Corrosion ....................................... 8-7 Chromic Acid Inhibitor ...................................... 8-22 Stress-Corrosion/Cracking .............................. 8-7 Sodium Dichromate Solution ............................ 8-23 Fretting Corrosion ........................................... 8-9 Chemical Surface Treatments .......................... 8-23 Fatigue Corrosion ........................................... 8-9 Protective Paint Finishes ..................................... 8-23 Galvanic Corrosion ....................................... 8-10 Aircraft Cleaning .................................................. 8-23 Common Corrosive Agents .............................. 8-10 Exterior Cleaning .............................................. 8-23 Preventive Maintenance ...................................... 8-10 Interior Cleaning ............................................... 8-24 Inspection ............................................................. 8-11 Types of Cleaning Operations ....................... 8-24 Corrosion Prone Areas ......................................... 8-11 Nonflammable Aircraft Cabin Cleaning Exhaust Trail Areas ........................................... 8-11 Agents & Solvents ......................................... 8-25 Battery Compartments and Battery Vent Flammable & Combustible Agents ................ 8-25 Openings .......................................................... 8-12 Container Controls ........................................ 8-25 Bilge Areas ....................................................... 8-12 Fire Prevention Precautions .......................... 8-25 Lavatories, Buffets, & Galleys .......................... 8-12 Fire Protection Recommendations ................ 8-26 Wheel Well and Landing Gear ......................... 8-12 Water Entrapment Areas .................................. 8-12 Powerplant Cleaning ........................................... 8-26 Engine Frontal Areas & Cooling Air Vents ........ 8-13 Solvent Cleaners ................................................. 8-27 Wing Flap & Spoiler Recesses ......................... 8-13 Dry Cleaning Solvent ....................................... 8-27 External Skin Areas .......................................... 8-13 Aliphatic and Aromatic Naphtha ....................... 8-27 Electronic & Electrical Compartments .............. 8-13 Safety Solvent .................................................. 8-27 Miscellaneous Trouble Areas ........................... 8-13 Methyl Ethyl Ketone (MEK) .............................. 8-27 Corrosion Removal .............................................. 8-14 Kerosene .......................................................... 8-27 Surface Cleaning and Paint Removal .............. 8-14 Cleaning Compound for Oxygen Systems ....... 8-27 Fairing or Blending Reworked Areas ................ 8-15 Emulsion Cleaners .............................................. 8-28 Corrosion of Ferrous Metals ................................ 8-15 Water Emulsion Cleaner .................................. 8-28 Mechanical Removal of Iron Rust .................... 8-15 Solvent Emulsion Cleaners .............................. 8-28 Chemical Removal of Rust ............................... 8-16 Soaps & Detergent Cleaners ............................... 8-28 Chemical Surface Treatment of Steel .............. 8-16 Cleaning Compound, Aircraft Surfaces ............ 8-28 Removal of Corrosion from Highly Stressed Nonionic Detergent Cleaners ........................... 8-28 Steel Parts ........................................................ 8-17 Mechanical Cleaning Materials ............................ 8-28 Corrosion of Aluminum & Aluminum Alloys .......... 8-17 Mild Abrasive Materials .................................... 8-28 Treatment of Unpainted Aluminum Surfaces .... 8-18 Abrasive Papers ............................................... 8-28 Treatment of Anodized Surfaces ...................... 8-19 Chemical Cleaners .............................................. 8-29 Treatment of Intergranular Corrosion in Phosphoric-citric Acid ....................................... 8-29 Heat - Treated Aluminum Alloy Surfaces ............ 8-19 Corrosion of Magnesium Alloys ........................... 8-19 xii

Next: Chapter 9 Clearance ...................................................... 9-21 →

Section 2

Chapter 9 Clearance ...................................................... 9-21 Fluid Lines & Fittings .......................................... 9-1 Hose Clamps .................................................... 9-22 Introduction ............................................................ 9-1 Rigid Fluid Lines .................................................... 9-1 Chapter 10 Tubing Materials ................................................. 9-1 Inspection Concepts & Techniques ................. 10-1 Copper ............................................................ 9-1 Basic Inspection ................................................. 10-1 Techniques/Practices ....................................... 10-1 Aluminum Alloy Tubing .................................... 9-1 Preparation ....................................................... 10-1 Steel ................................................................ 9-1 Aircraft Logs ........................................................ 10-1 Titanium 3AL–2.5V .......................................... 9-1 Checklists ............................................................ 10-2 Material Identification ......................................... 9-1 Publications ......................................................... 10-3 Sizes .................................................................. 9-2 Manufacturers’ Service Bulletins/Instructions ... 10-3 Fabrication of Metal Tube Lines ......................... 9-2 Maintenance Manual ........................................ 10-3 Tube Cutting .................................................... 9-2 Overhaul Manual .............................................. 10-4 Tube Bending .................................................. 9-2 Structural Repair Manual ................................. 10-4 Alternative Bending Methods ............................. 9-3 Illustrated Parts Catalog ................................... 10-4 Tube Flaring .................................................... 9-3 Wiring Diagram Manual .................................... 10-4 Instructions for Rolling-Type Flaring Tools ......... 9-4 Code of Federal Regulations (CFRs) .............. 10-4 Double Flaring .................................................... 9-5 Airworthiness Directives (ADs) ......................... 10-4 Double Flaring Instructions ............................. 9-5 Type Certificate Data Sheets (TCDS) .............. 10-4 Fittings ............................................................ 9-5 Routine/Required Inspections ............................. 10-5 Flareless Fittings ............................................. 9-5 Preflight/Postflight Inspections ......................... 10-5 Beading ........................................................... 9-7 Annual/100-Hour Inspections ........................... 10-5 Fluid Line Identification ...................................... 9-7 Progressive Inspections ................................. 10-12 Fluid Line End Fittings ........................................ 9-7 Continuous Inspections .................................. 10-12 Universal Bulkhead Fittings ............................ 9-8 Altimeter & Transponder Inspections ............. 10-12 AN Flared Fittings ........................................... 9-8 Air Transport Association iSpec 2200 ................ 10-12 MS Flareless Fittings .......................................... 9-9 Special Inspections ............................................ 10-12 Swaged Fittings .............................................. 9-9 Hard or Overweight Landing Inspection ........ 10-14 Severe Turbulence Inspection/Over “G” ........ 10-14 Cryofit Fittings ................................................. 9-9 Lightning Strike .............................................. 10-16 Rigid Tubing Installation and Inspection ........... 9-10 Bird Strike ...................................................... 10-16 Connection & Torque ..................................... 9-10 Fire Damage .................................................. 10-16 Flareless Tube Installation ............................ 9-12 Flood Damage ................................................ 10-16 Rigid Tubing Inspection & Repair .................. 9-14 Seaplanes ...................................................... 10-16 Flexible Hose Fluid Lines .................................... 9-16 Aerial Application Aircraft ............................... 10-16 Hose Materials & Construction ......................... 9-16 Special Flight Permits ........................................ 10-16 Buna-N ......................................................... 9-16 Nondestructive Inspection/Testing ..................... 10-17 Neoprene ..................................................... 9-16 Training, Qualification, & Certification ............ 10-17 Butyl ............................................................. 9-16 Advantages & Disadvantages of NDI Hose Identification ........................................ 9-16 Methods ......................................................... 10-17 Flexible Hose Inspection .................................. 9-18 Visual Inspection ............................................ 10-17 Fabrication & Replacement of Flexible Hose ... 9-18 Surface Cracks ........................................... 10-18 Flexible Hose Testing .................................... 9-19 Borescope ................................................... 10-18 Size Designations ............................................ 9-19 Interpretation of Results .............................. 10-18 Hose Fittings .................................................... 9-21 False Indications ......................................... 10-20 Installation of Flexible Hose Assemblies .......... 9-21 Eddy Current Inspection ................................. 10-20 Slack ............................................................. 9-21 Basic Principles ........................................... 10-20 Flex ............................................................... 9-21 Principles of Operations ................................. 10-21 Twisting ......................................................... 9-21 Eddy Current Instruments .............................. 10-21 Bending ......................................................... 9-21 Ultrasonic Inspection ...................................... 10-21 xiii Pulse Echo .................................................. 10-22 Care and Use ............................................... 11-10 Through-Transmission ................................ 10-23 Most Commonly Used Files ......................... 11-10 Resonance ................................................. 10-24 Care of Files ................................................. 11-12 Ultrasonic Instruments ................................... 10-26 Drills ................................................................ 11-12 Reference Standards ..................................... 10-26 Twist Drills .................................................... 11-12 Couplants ....................................................... 10-26 Reamers .......................................................... 11-13 Inspection of Bonded Structures ....................... 10-26 Countersink ..................................................... 11-14 Types of Defects ............................................ 10-28 Taps and Dies ..................................................... 11-14 Acoustic Emission Inspection ......................... 10-28 Layout and Measuring Tools ............................... 11-14 Magnetic Particle Inspection .......................... 10-29 Rules ............................................................... 11-14 Development of Indications ......................... 10-29 Combination Sets ............................................ 11-17 Types of Discontinuities Disclosed .............. 10-29 Scriber ............................................................. 11-18 Dividers and Pencil Compasses ..................... 11-19 Preparation of Parts for Testing ................... 10-30 Calipers ........................................................... 11-19 Effect of Flux Direction ................................ 10-30 Micrometer Calipers ........................................ 11-19 Effect of Flux Density .................................. 10-30 Micrometer Parts ............................................. 11-19 Magnetizing Methods .................................. 10-31 Reading a Micrometer ..................................... 11-22 Identification of Indications .......................... 10-31 Vernier Scale ................................................... 11-23 Magnaglo Inspection ...................................... 10-32 Using a Micrometer ......................................... 11-24 Magnetizing Equipment .............................. 10-32 Slide Calipers .................................................. 11-25 Indicating Mediums ..................................... 10-33 Demagnetizing ............................................ 10-33 Chapter 12 Standard Demagnetizing Practice .............. 10-34 Fundamentals of Electricity & Electronics ...... 12-1 Radiographic ............................................... 10-34 Introduction .......................................................... 12-1 Radiographic Inspection ................................. 10-34 General Composition of Matter ............................ 12-1 Preparation and Exposure .......................... 10-34 Matter ............................................................... 12-1 Radiographic Interpretation ......................... 10-35 Element ............................................................ 12-1 Compound ........................................................ 12-1 Radiation Hazards ...................................... 10-36 Molecule ........................................................... 12-1 Inspection of Composites .................................. 10-36 Atom ................................................................. 12-1 Tap Testing ..................................................... 10-36 Electrons, Protons, & Neutrons ........................ 12-1 Electrical Conductivity .................................... 10-37 Electron Shells & Energy Levels ...................... 12-2 Thermography ................................................ 10-37 Valence Electrons ......................................... 12-2 Inspection of Welds ........................................... 10-38 Ions ............................................................... 12-2 Chapter 11 Free Electrons ............................................... 12-2 Hand Tools & Measuring Devices .................... 11-1 Electron Movement .......................................... 12-2 General Purpose Tools ......................................... 11-1 Conductors, Insulators, and Semiconductors 12-2 Hammers & Mallets ........................................... 11-1 Conductors .................................................... 12-3 Screwdrivers ..................................................... 11-1 Insulators ...................................................... 12-3 Pliers & Plier-Type Cutting Tools ....................... 11-3 Semiconductors ............................................ 12-4 Punches ............................................................ 11-3 Metric Based Prefixes Used for Electrical Wrenches .......................................................... 11-4 Calculations ......................................................... 12-4 Special Wrenches ............................................. 11-5 Static Electricity ................................................... 12-4 Torque Wrench .................................................. 11-5 Attractive and Repulsive Forces ...................... 12-4 Strap Wrenches ................................................ 11-6 Electrostatic Field ............................................. 12-5 Impact Drivers ................................................... 11-6 Electrostatic Discharge (ESD) Considerations . 12-5 Metal Cutting Tools ............................................... 11-8 Magnetism ........................................................... 12-6 Hand Snips ........................................................ 11-8 Types of Magnets ................................................ 12-9 Hacksaws .......................................................... 11-8 Electromagnetism .............................................. 12-12 Chisels .............................................................. 11-9 Conventional Flow & Electron Flow ................... 12-14 Files ................................................................... 11-9 Conventional Flow .......................................... 12-14 xiv Electron Flow ................................................. 12-14 Relays ......................................................... 12-33 Electromotive Force (Voltage) ........................... 12-14 Series DC Circuits ............................................. 12-33 Current ............................................................... 12-16 Voltage Drops & Further Application of Ohm’s Ohm’s Law (Resistance) ................................... 12-17 Law ................................................................. 12-35 Resistance of a Conductor ................................ 12-18 Voltage Sources in Series .............................. 12-36 Factors Affecting Resistance .......................... 12-18 Kirchhoff’s Voltage Law .................................. 12-36 Resistance and Relation to Wire Sizing ......... 12-20 Voltage Dividers ............................................. 12-37 Circular Conductors (Wires/Cables) ........... 12-20 Determining the Voltage Divider Formula ...... 12-38 Parallel DC Circuits ........................................... 12-40 Rectangular Conductors (Bus Bars) ........... 12-20 Voltage Drops ................................................. 12-40 Power and Energy ............................................. 12-20 Total Parallel Resistance ................................ 12-40 Power in an Electrical Circuit ......................... 12-20 Resistors in Parallel ....................................... 12-40 Power Formulas Used in the Study of Two Resistors in Parallel ................................ 12-40 Electricity ....................................................... 12-21 Current Source ............................................... 12-41 Power in a Series & Parallel Circuit ............... 12-22 Kirchhoff’s Current Law .................................. 12-41 Energy in an Electrical Circuit ........................ 12-22 Current Dividers ............................................. 12-41 Sources of Electricity ...................................... 12-22 Series-Parallel DC Circuits ................................ 12-42 Pressure Source ......................................... 12-22 Determining the Total Resistance ................... 12-42 Chemical Source ......................................... 12-23 Alternating Current (AC) & Voltage .................... 12-43 Thermal Sources ......................................... 12-23 AC and DC Compared ................................... 12-44 Light Sources .............................................. 12-23 Generator Principles .......................................... 12-44 Schematic Representation of Electrical Generators of Alternating Current .................. 12-44 Components ................................................... 12-23 Position 1 .................................................... 12-45 Conductors .................................................. 12-23 Position 2 .................................................... 12-45 Types of Resistors ............................................. 12-24 Position 3 .................................................... 12-45 Fixed Resistor ................................................ 12-24 Position 4 .................................................... 12-46 Carbon Composition ...................................... 12-24 Position 5 .................................................... 12-46 Resistor Ratings ............................................. 12-24 Color Code .................................................. 12-24 Cycle and Frequency ..................................... 12-46 Cycle Defined .............................................. 12-46 Color Band Decoding ..................................... 12-25 Wire-Wound ................................................... 12-26 Frequency Defined ...................................... 12-46 Variable Resistors .......................................... 12-26 Period Defined ............................................ 12-47 Rheostat ...................................................... 12-26 Wavelength Defined .................................... 12-47 Potentiometer .............................................. 12-27 Phase Relationships ...................................... 12-47 Thermistors .................................................... 12-27 In Phase Condition ...................................... 12-48 Photoconductive Cells .................................... 12-27 Out of Phase Condition ............................... 12-48 Circuit Protection Devices ................................. 12-27 Values of Alternating Current .......................... 12-48 Fuse ............................................................... 12-28 Instantaneous Value .................................... 12-48 Current Limiter ............................................... 12-29 Peak Value .................................................. 12-49 Circuit Breaker ............................................... 12-29 Effective Value ............................................ 12-49 Arc Fault Circuit Breaker ............................. 12-29 Opposition to Current Flow of AC ................... 12-49 Thermal Protectors ......................................... 12-29 Capacitance ....................................................... 12-50 Control Devices .............................................. 12-30 Capacitors in Direct Current ........................... 12-50 Switches ...................................................... 12-30 The Resistor/Capacitor (RC) Time Constant .. 12-50 Toggle Switch .............................................. 12-30 Units of Capacitance ...................................... 12-50 Microswitches ............................................. 12-31 Voltage Rating of a Capacitor ........................ 12-51 Rotary Selector Switches ............................ 12-31 Factors Affecting Capacitance ........................ 12-51 Pushbutton Switches .................................. 12-31 Types of Capacitors ....................................... 12-51 Lighted Pushbutton Switches ...................... 12-32 Fixed Capacitors ......................................... 12-51 Dual In-Line Parallel (DIP) Switches ........... 12-33 Ceramic .......................................................... 12-51 Electrolytic ...................................................... 12-52 Switch Guards ............................................. 12-33 xv Tantalum ......................................................... 12-52 Precautions ................................................. 12-69 Polyester Film ................................................ 12-52 The Voltmeter .................................................... 12-70 Oil Capacitors ................................................. 12-53 Voltmeter Sensitivity ....................................... 12-70 Variable Capacitors ..................................... 12-53 Multiple Range Voltmeters ............................. 12-70 Trimmers ........................................................ 12-53 Voltmeter Circuit Connections ........................ 12-71 Varactors ........................................................ 12-53 Influence of the Voltmeter in the Circuit ......... 12-71 Capacitors in Series ....................................... 12-53 The Ohmmeter .................................................. 12-71 Capacitors in Parallel ..................................... 12-54 Zero Adjustment ............................................. 12-71 Capacitors in Alternating Current ................... 12-54 Ohmmeter Scale ............................................ 12-71 Capacitive Reactance Xc ............................... 12-54 The Multirange Ohmmeter ............................. 12-72 Sample Problem: ............................................ 12-55 Megger (Megohmmeter) ................................ 12-72 Solution: ......................................................... 12-55 AC Measuring Instruments ................................ 12-73 Capacitive Reactances in Series and in Electrodynamometer Meter Movement .......... 12-74 Parallel .......................................................... 12-55 Moving Iron Vane Meter ................................. 12-74 Phase of Current and Voltage in Reactive Inclined Coil Iron Vane Meter ......................... 12-75 Circuits .......................................................... 12-55 Varmeters ....................................................... 12-75 Inductance ......................................................... 12-56 Wattmeter ....................................................... 12-76 Characteristics of Inductance ......................... 12-56 Frequency Measurement/Oscilloscope .......... 12-76 The RL Time Constant ................................... 12-56 Horizontal Deflection ...................................... 12-77 Physical Parameters ...................................... 12-56 Vertical Deflection .......................................... 12-77 Self-Inductance .............................................. 12-57 Tracing a Sine Wave ...................................... 12-77 Types of Inductors .......................................... 12-57 Control Features on an Oscilloscope ............. 12-77 Units of Inductance ........................................ 12-58 Flat Panel Color Displays for Oscilloscopes .. 12-78 Inductors in Series ......................................... 12-58 Digital Multimeter ........................................... 12-78 Inductors in Parallel ........................................ 12-58 Basic Circuit Analysis & Troubleshooting .......... 12-78 Inductive Reactance ....................................... 12-58 Voltage Measurement .................................... 12-79 AC Circuits ......................................................... 12-59 Current Measurement .................................... 12-80 Ohm’s Law for AC Circuits ............................. 12-59 Checking Resistance in a Circuit ................... 12-80 Series AC Circuits .......................................... 12-59 Continuity Checks .......................................... 12-81 Solution: ...................................................... 12-60 Capacitance Measurement ............................ 12-81 Solution: ...................................................... 12-61 Inductance Measurement ............................... 12-81 Solution: ...................................................... 12-62 Troubleshooting Open Faults in a Series Circuit ............................................................ 12-82 Parallel AC Circuits ........................................ 12-62 Tracing Opens with the Voltmeter .................. 12-82 Solution: ...................................................... 12-62 Tracing Opens with the Ohmmeter ................ 12-82 Solution: ...................................................... 12-62 Troubleshooting Shorting Faults in a Series Resonance ..................................................... 12-63 Circuit ............................................................. 12-83 Power in AC Circuits ...................................... 12-64 Tracing Shorts with the Ohmmeter ................. 12-83 True Power Defined ....................................... 12-64 Tracing Shorts with the Voltmeter .................. 12-84 Apparent Power Defined ............................. 12-64 Troubleshooting Open Faults in a Parallel Solution: ...................................................... 12-65 Circuit ............................................................. 12-84 Transformers .................................................. 12-65 Tracing an Open with an Ammeter ................. 12-85 Current Transformers ..................................... 12-67 Tracing an Open with an Ohmmeter .............. 12-85 Transformer Losses ....................................... 12-67 Troubleshooting Shorting Faults in Parallel Power in Transformers ................................... 12-67 Circuits ........................................................... 12-85 DC Measuring Instruments ................................ 12-67 Troubleshooting Shorting Faults in Series- D’Arsonval Meter Movement .......................... 12-68 Parallel Circuits .............................................. 12-86 Current Sensitivity and Resistance ................ 12-68 Logic in Tracing an Open ............................ 12-86 Damping ......................................................... 12-69 Tracing Opens with the Voltmeter .................. 12-86 Electrical Damping ......................................... 12-69 Batteries ............................................................ 12-87 Mechanical Damping ...................................... 12-69 Primary Cell .................................................... 12-87 A Basic Multirange Ammeter .......................... 12-69 xvi Secondary Cell ............................................... 12-87 Filtering Characteristics of Capacitors .......... 12-111 Battery Ratings ............................................... 12-89 Filtering Characteristics of Inductors ............. 12-111 Life Cycle of a Battery .................................... 12-89 Common Filter Configurations ...................... 12-111 Lead-Acid Battery Testing Methods ................ 12-90 Basic LC Filters ............................................. 12-112 Lead-Acid Battery Charging Methods ............ 12-91 Low-Pass Filter .......................................... 12-112 Nickel-Cadmium Batteries ................................. 12-91 High-Pass Filter (HPF) ............................... 12-112 Chemistry and Construction ........................... 12-91 Band-Pass Filter ........................................ 12-112 Operation of Nickel-Cadmium Cells ............... 12-92 Band-Stop Filter ......................................... 12-112 General Maintenance and Safety Amplifier Circuits ............................................... 12-113 Precautions ................................................. 12-92 Classification ................................................. 12-113 Sealed Lead Acid (SLA) Batteries .................. 12-92 Class A ....................................................... 12-114 Lithium-Ion Batteries .......................................... 12-93 Class AB .................................................... 12-114 Inverters ............................................................. 12-93 Class B ....................................................... 12-114 Rotary Inverters .............................................. 12-94 Class C ...................................................... 12-114 Permanent Magnet Rotary Inverter ................ 12-94 Methods of Coupling ..................................... 12-115 Inductor-Type Rotary Inverter ........................ 12-94 Direct Coupling .......................................... 12-115 Static Inverters ............................................... 12-94 RC Coupling ............................................... 12-115 Semiconductors ................................................. 12-95 Impedance Coupling .................................. 12-116 Doping ............................................................ 12-96 Transformer Coupling ................................ 12-116 PN Junctions & the Basic Diode .................... 12-98 Feedback ...................................................... 12-116 Forward Biased Diode .................................... 12-98 Operational Amplifiers (OP AMP) .................. 12-116 Reverse Biased Diode ................................... 12-99 Applications ................................................ 12-117 Rectifiers .......................................................... 12-100 Half-Wave Rectifier ...................................... 12-101 Magnetic Amplifiers .......................................... 12-118 Full-Wave Rectifier ....................................... 12-102 Saturable-Core Reactor ................................ 12-119 Dry Disk ........................................................ 12-102 Logic Circuits .................................................... 12-119 Types of Diodes ........................................... 12-103 Logic Polarity ................................................ 12-120 Power Rectifier Diodes ............................. 12-103 Positive ..................................................... 12-120 Zener Diodes ............................................ 12-103 Negative .................................................... 12-120 Special Purpose Diodes ............................ 12-103 Pulse Structure ............................................. 12-120 Basic Logic Circuits ...................................... 12-121 Light-Emitting Diode (LED) ....................... 12-103 The Inverter Logic ..................................... 12-121 Liquid Crystal Displays (LCD) ................... 12-104 The AND Gate ........................................... 12-121 Photodiode ................................................ 12-104 The OR Gate ............................................. 12-122 Varactors ................................................... 12-104 The NAND Gate ........................................ 12-122 Schottky Diodes ........................................ 12-105 The NOR Gate .......................................... 12-122 Diode Identification ....................................... 12-105 Exclusive OR Gate .................................... 12-122 Introduction to Transistors ............................... 12-105 Classification ................................................ 12-105 Exclusive NOR Gate ................................. 12-122 Transistor Theory ......................................... 12-106 The Integrated Circuit ................................... 12-122 PNP Transistor Operation ............................ 12-107 Microprocessors ........................................... 12-123 Identification of Transistors .......................... 12-107 DC Generators ................................................ 12-123 Field Effect Transistors ................................. 12-107 Theory of Operation ..................................... 12-123 Metal-Oxide-Semiconductor FET (MOSFET) Generation of a DC Voltage ......................... 12-125 12-108 Position A .................................................. 12-125 Common Transistor Configurations .............. 12-108 Position B .................................................. 12-126 Common-Emitter (CE) Configuration ........ 12-108 Position C .................................................. 12-126 Common-Collector (CC) Configuration ..... 12-109 Position D .................................................. 12-127 Common-Base (CB) Configuration ........... 12-109 The Neutral Plane ..................................... 12-127 Vacuum Tubes .................................................. 12-110 Construction Features of DC Generators .... 12-128 Filtering ............................................................. 12-111 Field Frame ............................................... 12-128 xvii Armature ...................................................... 12-130 Synchronous Motor ...................................... 12-151 Gramme-Ring Armature ............................ 12-130 AC Series Motor ........................................... 12-152 Maintenance of AC Motors ........................... 12-153 Drum-Type Armature ................................. 12-130 Alternators ....................................................... 12-154 Commutators ................................................ 12-130 Basic Alternators & Classifications ............... 12-154 Armature Reaction ....................................... 12-131 Method of Excitation ..................................... 12-154 Compensating Windings .............................. 12-131 Number of Phases ....................................... 12-154 Interpoles ..................................................... 12-132 Armature or Field Rotation ........................... 12-155 Types of DC Generators .............................. 12-132 Single-Phase Alternator ............................ 12-155 Series Wound DC Generators .................. 12-132 Two-Phase Alternator ................................ 12-156 Shunt Wound DC Generators ................... 12-133 Three-Phase Alternator ............................. 12-156 Compound Wound DC Generators ........... 12-134 Wye Connection (Three-Phase) ................... 12-156 Generator Ratings ........................................ 12-134 Delta Connection (Three-Phase) ................. 12-156 Generator Terminals ..................................... 12-135 Alternator Rectifier Unit ................................ 12-156 DC Generator Maintenance ............................. 12-135 Brushless Alternator ..................................... 12-157 Inspection ..................................................... 12-135 Alternator Frequency .................................... 12-158 Condition of Generator Brushes ................... 12-136 Starter Generator ......................................... 12-158 DC Motors .................................................... 12-137 Alternator Rating .......................................... 12-158 Force Between Parallel Conductors ............. 12-138 Alternator Maintenance ................................ 12-159 Developing Torque ....................................... 12-138 Regulation of Generator Voltage .................. 12-159 Basic DC Motor ............................................ 12-138 Voltage Regulation with a Vibrating-Type Position A .................................................. 12-139 Regulator ...................................................... 12-159 Position B .................................................. 12-139 Three Unit Regulators .................................. 12-161 Position C .................................................. 12-139 Differential Relay Switch .............................. 12-162 Position D .................................................. 12-139 Overvoltage & Field Control Relays ............. 12-163 DC Motor Construction .................................... 12-140 Generator Control Units (GCU) ....................... 12-164 Armature Assembly ...................................... 12-140 Basic Functions of a Generator Control Unit Field Assembly ............................................. 12-141 (GCU) ........................................................... 12-164 Brush Assembly ........................................... 12-141 Voltage Regulation ....................................... 12-164 End Frame ................................................... 12-141 Overvoltage Protection ................................. 12-164 Types of DC Motors ......................................... 12-141 Parallel Generator Operations ..................... 12-164 Series DC Motor ........................................... 12-141 Over-Excitation Protection ........................... 12-164 Shunt DC Motor ........................................... 12-142 Differential Voltage ....................................... 12-164 Compound DC Motor ................................... 12-142 Reverse Current Sensing ............................. 12-164 Counter Electromotive Force (emf) ................. 12-142 Alternator Constant Speed Drive System ........ 12-164 Types of Duty ............................................... 12-143 Hydraulic Transmission ................................... 12-165 Reversing Motor Direction ............................ 12-144 Voltage Regulation of Alternators .................... 12-171 Motor Speed ................................................. 12-145 Alternator Transistorized Regulators ............ 12-172 Energy Losses in DC Motors .................... 12-145 Inspection and Maintenance of DC Motors .. 12-146 Chapter 13 AC Motors ........................................................ 12-147 Mechanic Privileges & Limitations .................. 13-1 Types of AC Motors ...................................... 12-147 Introduction .......................................................... 13-1 Three-Phase Induction Motor ....................... 12-148 Mechanic Certification: Subpart A—General (by Rotating Magnetic Field ............................... 12-148 14 CFR Section) .................................................. 13-1 Construction of Induction Motor ................... 12-148 Section 65.3, Certification of Foreign Airmen Induction Motor Slip ..................................... 12-149 Other Than Flight Crewmembers ..................... 13-1 Single-Phase Induction Motor ...................... 12-149 Section 65.11, Application and Issue ................ 13-1 Shaded Pole Induction Motor ....................... 12-149 Section 65.12, Offenses Involving Alcohol Split-Phase Motor ......................................... 12-150 and Drugs ......................................................... 13-1 Capacitor Start Motor ................................... 12-150 Section 65.13, Temporary Certificate ............... 13-1 Direction of Rotation of Induction Motors ..... 12-150 Section 65.14, Security Disqualification ........... 13-1 xviii

Next: Section 65.15, Duration of Certificates ............. 13-1 Elements of Human Factors ............................. 14-2 →

Section 3

Section 65.15, Duration of Certificates ............. 13-1 Elements of Human Factors ............................. 14-2 Section 65.16, Change of Name: Clinical Psychology ....................................... 14-3 Replacement of Lost or Destroyed Certificate . 13-2 Experimental Psychology .............................. 14-3 Section 65.17, Test: General Procedure .......... 13-2 Anthropometry .............................................. 14-4 Section 65.18, Written Tests: Cheating or Computer Science ........................................ 14-4 Other Unauthorized Content ............................ 13-2 Cognitive Science ......................................... 14-4 Section 65.19, Retesting After Failure .............. 13-2 Safety Engineering ....................................... 14-4 Section 65.20, Applications, Certificates, Medical Science ............................................ 14-4 Logbooks, Reports, and Records: Organizational Psychology ........................... 14-4 Falsification, Reproduction, or Alteration .......... 13-2 Educational Psychology ............................... 14-5 Section 65.21, Change of Address ................... 13-2 Refusal to Submit to a Drug or Alcohol Test ..... 13-2 Industrial Engineering ................................. 14-5 Mechanic Certification: Subpart D—Mechanics History of Human Factors .................................... 14-6 (by 14 CFR Section) ............................................ 13-3 Evolution of Maintenance Human Factors ....... 14-7 Section 65.71, Eligibility Requirements: The Pear Model ................................................... 14-9 General ............................................................ 13-3 People .............................................................. 14-9 Section 65.73, Ratings ..................................... 13-3 Environment ..................................................... 14-9 Section 65.75, Knowledge Requirements ........ 13-3 Physical ....................................................... 14-10 Section 65.77, Experience Requirements ....... 13-3 Organizational ............................................. 14-10 Section 65.79, Skill Requirements ................... 13-3 Actions ........................................................... 14-10 Section 65.80, Certificated Aviation Resources ...................................................... 14-10 Maintenance ..................................................... 13-4 Human Error ...................................................... 14-13 Technician School Students ............................. 13-4 Types of Errors ............................................... 14-13 Section 65.81, General Privileges and Unintentional ............................................... 14-13 Limitations ........................................................ 13-4 Intentional .................................................. 14-13 Section 65.83, Recent Experience Active & Latent ........................................... 14-13 Requirements ................................................... 13-4 The “Dirty Dozen” .............................................. 14-13 Section 65.85, Airframe Rating: Additional Lack of Communication .................................. 14-13 Privileges .......................................................... 13-4 Complacency ................................................. 14-14 Section 65.87, Powerplant Rating: Additional Privileges .......................................................... 13-4 Lack of Knowledge ......................................... 14-14 Section 65.89, Display of Certificate ................ 13-4 Distraction ...................................................... 14-15 Inspection Authorization (IA) (by 14 CFR Lack of Teamwork .......................................... 14-16 Section) ............................................................... 13-5 Fatigue ........................................................... 14-16 Section 65.91, Inspection Authorization ........... 13-5 Lack of Resources ......................................... 14-18 Section 65.92, Inspection Authorization: Lack of Assertiveness .................................... 14-22 Duration ............................................................ 13-5 Stress ............................................................. 14-24 Section 65.93, Inspection Authorization: Physical Stressors ..................................... 14-24 Renewal ........................................................... 13-5 Psychological Stressors ............................. 14-24 Section 65.95, Inspection Authorization: Physiological Stressors .............................. 14-25 Privileges and Limitations ................................ 13-6 Lack of Awareness ......................................... 14-26 Ethics .................................................................. 13-6 Norms ............................................................. 14-26 A Scenario ........................................................ 13-6 Example of Common Maintenance Errors ..... 14-28 Final Observation .......................................... 13-7 Where to Get Information .................................. 14-29 Federal Aviation Administration (FAA) ............ 14-30 Chapter 14 FAA’s Maintenance Fatigue Section ........... 14-30 Human Factors .................................................. 14-1 FAA Safety Team ......................................... 14-31 Introduction .......................................................... 14-1 Other Resources ............................................ 14-31 FAA Involvement .............................................. 14-1 System Safety Services .............................. 14-31 Importance of Human Factors .......................... 14-1 Human Factors & Ergonomics Society Definitions of Human Factors ........................... 14-1 (HFES) ........................................................ 14-31 What are Human Factors? .................................. 14-2 International Ergonomics Association (IEA) 14-31 xix Glossary .............................................................. G-1 Index ...................................................................... I-1 xx

Next: Chapter 1 →

Chapter 1

Safety, Ground Operations, &

Servicing

Aviation maintenance technicians (AMTs) devote a portion of Electrical Safety their aviation career to ground handling and operating aircraft.

Physiological Safety Technicians also need to be proficient in operating ground Working with electrical equipment poses certain physiological support equipment. The complexity of support equipment and safety hazards. When electricity is applied to the human body, the hazards involved in the ground handling of aircraft require it can create severe burns in the area of entrance and at the that maintenance technicians possess a detailed knowledge of point of exit from the body. In addition, the nervous system is safety procedures used in aircraft servicing, taxiing, run-up, affected and can be damaged or destroyed. To safely deal with and in the use of ground support equipment. The information electricity, the technician must have a working knowledge provided in this chapter is intended as a general guide for of the principles of electricity and a healthy respect for its safely servicing and operating aircraft.

capability to do both work and damage.

Introducing human factors to aircraft maintenance personnel Wearing or use of proper safety equipment can provide a makes them aware of how it affects maintenance performance.

psychological assurance and physically protect the user Although there are many human factors involved when at the same time. The use of rubber gloves, safety glasses, dealing with maintenance performance, several areas can be rubber or grounded safety mats, and other safety equipment considered. Some of these include fatigue, deadline pressure, contributes to the overall safety of the technician working stress, distractions, poor communication skills, complacency, on or with electrical equipment.

and lack of information. Maintenance technicians need to understand how human factors can impact their performance Two factors that affect safety when dealing with electricity are and safety while completing maintenance tasks.

fear and overconfidence. These two factors are major causes of accidents involving electricity. While a certain amount of Shop Safety respect for electrical equipment is healthy and a certain level Keeping the shop, hangars, and flight line clean is essential of confidence is necessary, extremes of either can be deadly.

to safety and efficient maintenance. The highest standards of orderly work arrangements and cleanliness must be observed Lack of respect is often due to lack of knowledge. Personnel during the maintenance of aircraft. Where continuous who attempt to work with electrical equipment and have work shifts are established, the outgoing shift removes and no knowledge of the principles of electricity lack the skills properly stores personal tools, rollaway boxes, work stands, to deal with electrical equipment safely. Overconfidence maintenance stands, hoses, electrical cords, hoists, crates, leads to risk taking. The technician who does not respect and boxes that were needed for the work to be accomplished. the capabilities of electricity will, sooner or later, become a victim of electricity’s power.

Signs are posted to indicate dangerous equipment or hazardous conditions. Additionally, there are signs that provide the Fire Safety location of first aid and fire equipment. Safety lanes, pedestrian Anytime current flows, whether during generation or walkways, and fire lanes are painted around the perimeter transmission, a by-product is heat. The greater the current inside the hangars. This is a safety measure to prevent accidents flow, the greater the amount of heat created. When this heat and to keep pedestrian traffic out of work areas.

becomes too great, protective coatings on wiring and other electrical devices can melt, causing shorting. That in turn Safety is everyone’s business. However, technicians and leads to more current flow and greater heat. This heat can supervisors must watch for their own safety and for the become so great that metals can melt, liquids vaporize, and safety of others working around them. Communication is flammable substances ignite.

key to ensuring everyone’s safety. If other personnel are conducting their actions in an unsafe manner, communicate An important factor in preventing electrical fires is to keep with them, reminding them of their safety and that of others the area around electrical work or electrical equipment around them.

1-1 clean, uncluttered, and free of all unnecessary flammable within the associated container and, if used properly with substances. Ensure that all power cords, wires, and lines the tags, indicate what personal safety equipment to use.

are free of kinks and bends that can damage the wire. Never place wires or cords where they may be walked on or run The most observable portion of the Safety Data Sheets (SDSs) over by other equipment. When several wires inside a power (formerly known as Material Safety Data Sheet (MSDS)) cord are broken, the current passing through the remaining label is the risk diamond. It is a four-color segmented wires increases. This generates more heat than the insulation diamond that represents flammability (red), reactivity coatings on the wire are designed to withstand and can (yellow), health (blue), and special hazard (white). In the lead to a fire. Closely monitor the condition of electrical flammability, reactivity, and health blocks, there is a number equipment. Repair or replace damaged equipment before from 0 to 4. Zero represents little or no hazard to the user, further use. while 4 means that the material is very hazardous. The special hazard segment contains a word or abbreviation to represent Safety Around Compressed Gases the specific hazard. Some examples are RAD for radiation, ALK for alkali materials, Acid for acidic materials, and Compressed air, like electricity, is an excellent tool when it is under control. A typical nitrogen bottle set is shown CARC for carcinogenic materials. The letter W with a line through it stands for high reactivity to water. [Figure 1-2] in Figure 1-1 . The following “dos and don’ts” apply when working with or around compressed gases: The SDS is a more detailed version of the chemical safety • Inspect air hoses frequently for breaks and worn spots.

issues. These forms have the detailed breakdown of the Unsafe hoses must be replaced immediately.

chemicals, including formulas and action to take if personnel • Keep all connections in a “no-leak condition.” come in contact with the chemicals. All sheets have the same information requirements; however, the exact location of the • Maintain in-line oilers, if installed, in operating information on the sheet may vary depending on the SDS condition.

manufacturer. These forms are necessary for a safe shop that • Ensure the system has water sumps installed and meets all the requirements of the governing safety body, the drained at regular intervals.

U.S. Department of Labor Occupational Safety and Health • Filter air used for paint spraying to remove oil and Administration (OSHA).

water.

Safety Around Machine Tools • Never use compressed air to clean hands or clothing.

Hazards in a shop increase when the operation of lathes, drill Pressure can force debris into the flesh leading to presses, grinders, and other types of machines are used. Each infection.

machine has its own set of safety practices. The following • Never spray compressed air in the area of other discussions are necessary to avoid injury.

personnel.

• Straighten, coil, and properly store air hoses when not The drill press can be used to bore and ream holes, to do in use.

facing, milling, and other similar types of operations. The following precautions can reduce the chance of injury: • Many accidents involving compressed gases occur during aircraft tire mounting. To prevent possible • Wear eye protection.

personal injury, use tire dollies and other appropriate • Securely clamp all work.

devices to mount or remove heavy aircraft tires.

• Set the proper revolutions per minute (rpm) for the material used.

When inflating tires on any type of aircraft wheels, always use tire cage guards. Extreme caution is required to avoid • Do not allow the spindle to feed beyond its limit of over inflation of high-pressure tires because of possible travel while drilling.

personal injury. Use pressure regulators on high-pressure air • Stop the machine before adjusting work or attempting bottles to eliminate the possibility of over inflation of tires.

to remove jammed work.

Tire cages are not required when adjusting pressure in tires • Clean the area when finished.

installed on an aircraft.

Safety Around Hazardous Materials Lathes are used in turning work of a cylindrical nature.

This work may be performed on the inside or outside of the Material safety diamonds are important with regard to cylinder. The work is secured in the chuck to provide the shop safety. These diamond-shaped labels are a simple rotary motion, and the forming is done by contact with a and quick way to determine the risk of hazardous material 1-2 during milling.

• Select the proper tools for the job.

• Do not change the feed speed while working.

• Lower the table before moving under or away from the work.

• Ensure all clamps and bolts are passable under the arbor.

Grinders are used to sharpen tools, dress metal, and perform other operations involving the removal of small amounts of metal. The following precautions can reduce the chance of injury: • Wear eye protection, even if the grinder has a shield.

• Inspect the grinding wheel for defects prior to use.

• Do not force grinding wheels onto the spindle. They fit snugly but do not require force to install them. Placing side pressure on a wheel could cause it to explode.

• Check the wheel flanges and compression washer.

They should be one-third the diameter of the wheel.

• Do not stand in the arc of the grinding wheel while operating in case the wheel explodes.

Welding must be performed only in designated areas. Any part that is to be welded must be removed from the aircraft, if possible. Repair would then be accomplished in a controlled environment, such as a welding shop. A welding shop must be equipped with proper tables, ventilation, tool storage, and Figure 1-1. A typical nitrogen bottle.

fire prevention and extinguishing equipment.

securely mounted tool. The following precautions can reduce the chance of injury: • Wear eye protection.

• Use sharp cutting tools.

• Allow the chuck to stop on its own. Do not attempt to stop the chuck by hand pressure.

• Examine tools and work for cracks or defects before starting the work.

• Do not set tools on the lathe. Tools may be caught by 3 2 the work and thrown.

• Before measuring the work, allow it to stop in the lathe.

Milling machines are used to shape or dress; cut gear

teeth, slots, or key ways; and similar work. The following precautions can reduce the chance of injury: • Wear eye protection.

• Clean the work bed prior to work.

• Secure the work to the bed to prevent movement Figure 1-2. A risk diamond.

1-3 Foreign Object Damage (FOD) Welding on an aircraft should be performed outside, if Foreign object damage (FOD) is any damage to aircraft, possible. If welding in the hangar is necessary, observe personnel, or equipment caused by any loose object. These these precautions: loose objects can be anything, such as broken runway concrete, shop towels, safety wire, etc. To control FOD, keep • During welding operations, open fuel tanks and work ramp and operation areas clean, have a tool control program, on fuel systems are not permitted.

and provide convenient receptacles for used hardware, shop • Painting is not permitted.

towels, and other consumables.

• No aircraft are to be within 35 feet of the welding operation.

Never leave tools or other items around the intake of a turbine engine. The modern gas turbine engine creates a low-pressure • No flammable material is permitted in the area around area in front of the engine that causes any loose object to the welding operation.

be drawn into the engine. The exhaust of these engines • Only qualified welders are permitted to do the work.

can propel loose objects great distances with enough force to damage anything that is hit. The importance of a FOD • The welding area is to be roped off and placarded.

program cannot be overstressed when a technician considers • Fire extinguishing equipment of a minimum rating the cost of engines, components, or a human life.

of 20B must be in the immediate area with 80B rated equipment as a backup.

Safety Around Airplanes • Trained fire watches are to be present in the area As with the previously mentioned items, it is important to around the welding operation.

be aware of propellers. Technicians cannot assume the pilot of a taxiing aircraft can see them and must stay within the • The aircraft being welded must be in a towable pilot’s view while on the ramp area. Turbine engine intakes condition, with a tug attached, and the aircraft parking and exhaust can also be very hazardous areas. Smoking or brakes released. A qualified operator must be on the open flames are not permitted anywhere near an aircraft in tug and mechanics available to assist in the towing operation. Be aware of aircraft fluids that can be detrimental operation should it become necessary to tow the to skin. When operating support equipment around aircraft, aircraft. If the aircraft is in the hangar, the hangar be sure to allow space between it and the aircraft, and secure doors are to be open.

it so it cannot roll into the aircraft. All items in the area of operating aircraft must be stowed properly.

Flight Line Safety Hearing Protection Safety Around Helicopters The flight line is a place of dangerous activity. Technicians Every type of helicopter has different features. These who perform maintenance on the flight line must constantly differences must be learned to avoid damaging the helicopter be aware of what is going on around them. The noise on a or injuring the technician. When approaching a helicopter flight line comes from many places. Aircraft are only one while the blades are turning, adhere to the following source of noise. There are auxiliary power units (APUs), fuel guidelines to ensure safety.

trucks, baggage handling equipment, and so forth. Each has its own frequency of sound. Combined all together, the noise • Observe the rotor head and blades to see if they on the ramp or flight line can cause hearing loss. are level. This allows maximum clearance when approaching the helicopter.

There are many types of hearing protection available.

• Approach the helicopter in view of the pilot.

Hearing protection can be external or internal. Earmuffs or • Never approach a helicopter carrying anything with headphones are considered external protection. The internal a vertical height that the blades could hit. This could type of hearing protection fits into the auditory canal. Both cause blade damage and injury to the individual.

types reduce the sound level reaching the eardrum and reduce the chances of hearing loss.

• Never approach a single-rotor helicopter from the rear.

The tail rotor is invisible when operating.

Hearing protection is essential when working with • Never go from one side of the helicopter to the other pneumatic drills, rivet guns, or other loud tools. Even short by going around the tail. Always go around the nose duration exposure to these sounds can cause hearing loss of the helicopter.

because of their high frequency. Continued exposure will cause hearing loss.

When securing the rotor on helicopters with elastomeric 1-4 bearings, check the maintenance manual for the proper by a Class A, B, or C fire. Usually Class D fires involve method. Using the wrong method could damage the bearing. magnesium in the shop, or in aircraft wheels and brakes, or are the result of improper welding operations.

Fire Safety Performing maintenance on aircraft and their components Any one of these fires can occur during maintenance on or around, or operations involving aircraft. There is a particular requires the use of electrical tools that can produce sparks, heat-producing tools and equipment, flammable and type of extinguisher that is most effective for each type of fire.

explosive liquids, and gases. As a result, a high potential Types and Operation of Shop and Flight Line Fire exists for fire to occur. Measures must be taken to prevent a Extinguishers fire from occurring and to have a plan for extinguishing it.

Water extinguishers are the best type to use on Class A fires.

Water has two effects on fire. It deprives fire of oxygen and The key to fire safety is knowledge of what causes a fire, how to prevent it, and how to put it out. This knowledge must be cools the material being burned.

instilled in each technician, emphasized by their supervisors through sound safety programs, and occasionally practiced. Since most petroleum products float on water, water-type fire extinguishers are not recommended for Class B fires. Extreme Airport or other local fire departments can normally be called upon to assist in training personnel and helping to caution must be used when fighting electrical fires (Class C) with water-type extinguishers. All electrical power must be establish fire safety programs for the hangar, shops, and flight line. removed or shut off to the burning area. Additionally, residual electricity in capacitors, coils, and so forth must be considered Fire Protection to prevent severe injury or possibly death from electrical shock.

Requirements for Fire to Occur Never use water-type fire extinguishers on Class D fires. The Three things are required for a fire. Remove any one of these cooling effect of water causes an explosive expansion of the things and the fire extinguishes: metal, because metals burn at extremely high temperatures.

1. Fuel—combines with oxygen in the presence of heat, releasing more heat. As a result, it reduces itself to Water fire extinguishers are operated in a variety of ways.

other chemical compounds.

Some are hand pumped, while others are pressurized. The pressurized types of extinguishers may have a gas charge 2. Heat—accelerates the combining of oxygen with fuel, stored in the container with the water, or it may contain a in turn releasing more heat.

“ soda-acid” container where acid is spilled into a container 3. Oxygen—the element that combines chemically with of soda inside the extinguisher. The chemical reaction of another substance through the process of oxidation.

the soda and the acid causes pressure to build inside the fire Rapid oxidation, accompanied by a noticeable release extinguisher, forcing the water out.

of heat and light, is called combustion or burning.

[Figure 1-3] Carbon dioxide (CO ) extinguishers are used for Class A, B, and C fires, extinguishing the fire by depriving it of oxygen.

Classification of Fires [Figure 1-4] Additionally, like water-type extinguishers, CO For commercial purposes, the National Fire Protection cools the burning material. Never use CO on Class D fires.

Association (NFPA) has classified fires into three basic types: As with water extinguishers, the cooling effect of CO on Class A, Class B, and Class C.

the hot metal can cause explosive expansion of the metal.

1. Class A fires involve ordinary combustible materials, such as wood, cloth, paper, upholstery materials, and When using CO fire extinguishers, all parts of the so forth.

extinguisher can become extremely cold, and remain so for a short time after operation. Wear protective equipment 2. Class B fires involve flammable petroleum products or take other precautions to prevent cold injury, such as or other flammable or combustible liquids, greases, frostbite. Extreme caution must be used when operating CO solvents, paints, and so forth. 2 fire extinguishers in closed or confined areas. Not only can 3. Class C fires involve energized electrical wiring and the fire be deprived of oxygen, but so too can the operator.

equipment.

CO fire extinguishers generally use the self-expelling A fourth class of fire, the Class D fire, involves flammable method of operation. This means that the CO has sufficient metal. Class D fires are not commercially considered by pressure at normal operating pressure to expel itself. This the NFPA to be a basic type of fire since they are caused 1-5 acts rapidly on fires by producing a heavy blanketing mist that It takes three things to start a fi re: eliminates oxygen from the fire source. More importantly, it OXYGEN, HEAT, FUEL interferes chemically with the combustion process of the fire.

Furthermore, it has outstanding properties in preventing re- flash after the fire has been extinguished.

Oxygen Bromotrifluoromethane (Halon 1301), chemical formula CF Br, is also a liquefied gas and has a UL toxicity rating of Fuel 3 Friction (heat) 6. It has all the characteristics of Halon 1211. The significant difference between the two is Halon 1211 forms a spray Figure 1-3. Three elements of fire.

similar to CO , while Halon 1301 has a vapor spray that is more difficult to direct.

pressure is held inside the container by some type of seal or frangible disk that is broken or punctured by a firing Note: The EPA has restricted Halon to its 1986 production mechanism, usually a pin. This means that once the seal or level due to its effect on the ozone layer.

disk is broken, pressure in the container is released and the fire extinguisher is spent, requiring replacement. [Figure 1-5] Dry powder extinguishers, while effective on Class B and C fires, are best for use on Class D fires. The method of Halogenated hydrocarbon extinguishers are most effective operation of dry powder fire extinguishers varies from gas on Class B and C fires. They can be used on Class A and D cartridge charges, stored pressure within the container that fires, but they are less effective. Halogenated hydrocarbon, forces the powder charge out of the container, to scooping commonly called Freon™ by the industry, are numbered pails or buckets of the powder from large containers or barrels according to chemical formulas with Halon™ numbers.

to toss on the fire.

Carbon tetrachloride (Halon 104), chemical formula CCl , has an Underwriters Laboratory (UL) toxicity rating of 3. As such, it is extremely toxic. [Figure 1-6] Hydrochloric acid vapor, chlorine, and phosgene gas are produced whenever carbon tetrachloride is used on ordinary fires. The amount of phosgene gas is increased whenever carbon tetrachloride is brought in direct contact with hot metal, certain chemicals, or continuing electrical arcs. It is not approved for any fire extinguishing use. Old containers of Halon 104 found in or around shops or hangars should be disposed of in accordance with Environmental Protection Agency (EPA) regulations and local laws and ordinances.

Methyl bromide (Halon 1001), chemical formula CH Br, is a liquefied gas with a UL toxicity rating of 2. It is very toxic and corrosive to aluminum alloys, magnesium, and zinc. Halon 1001 is not recommended for aircraft use.

Chlorobromomethane (Halon 1011), chemical formula CH ClBr, is a liquefied gas with a UL toxicity rating of 3. Like methyl bromide, Halon 1011 is not recommended for aircraft use. Dibromodifluoromethane (Halon 1202), chemical formula CBr F , has a UL toxicity rating of 4. Halon 2 2 1202 is not recommended for aircraft use.

Bromochlorodifluoromethane (Halon 1211), chemical formula CBrClF , is a liquefied gas with a UL toxicity rating of 5. It is colorless, noncorrosive, and evaporates rapidly leaving no residue. It does not freeze or cause cold burns and does not harm fabrics, metals, or other materials it contacts. Halon 1211 Figure 1-4. Carbon dioxide fire extinguisher.

1-6 • Safety seals unbroken Dry powder is not recommended for aircraft use, except • All external dirt and rust removed on metal fires, as a fire extinguisher. The leftover chemical • Gauge or indicator in operable range residues and dust often make cleanup difficult and can damage electronic or other delicate equipment.

• Proper weight • No nozzle obstruction Inspection of Fire Extinguishers • No obvious damage Fire extinguishers need to be checked periodically utilizing a checklist. If a checklist is unavailable, check the following Airport or other local fire departments can usually help in as a minimum: preparing or providing extinguisher checklists. In addition, • Proper location of appropriate extinguisher these fire departments can be helpful in answering questions Classes of Fire Extinguishing Materials Cylinder Hand Pump Stored Pressure N Cartridge of Self-Expelling A B C D Self-Generating Water and antifreeze X X X X X Soda-acid (water) X X Wetting agent X X Foam X X X Loaded stream X X X X+ Multipurpose dry chemical X+ X X X X Carbon dioxide X+ X X Dry chemical X X X X Bromotri fl uoromethane — Halon 1301 X X X Bromochlorodi fl uoromethane — Halon 1211 X X X Dry powder (metal fi res) X X X + Smaller sizes of these extinguishers are not recognized for use on these classes of fi re.

Figure 1-5. Extinguisher operation and methods of expelling.

Group De fi nition Examples Gases or vapors in concentrations up to 20% by volume, for durations of Bromotri fl uoromethane 6 (Least toxic) (Halon 1301) exposure of up to approximately 2 hours, do not appear to produce injury.

Gases or vapors much less toxic than Group 4, but more toxic than Group 6. 5a Carbon dioxide Gases or vapors in concentrations of the order of 2 to 2 ½%, for durations Dibromodi fl uormethane of exposure of up to approximately 2 hours are lethal or produce serious injury. (Halon 1202) Bromochloromethane (Halon 1011) Gases or vapors in concentrations of the order of 2 to 2 ½%, for durations of exposure of the order of 1 hour are lethal or produce serious injury.

Carbon tetrachloride (Halon 104) Gases or vapors in concentrations of approximately ½ to 1%, for durations Methyl bromide of exposure of up to approximately ½ hour are lethal or produce serious injury. (Halon 1001) Figure 1-6. Toxicity table.

1-7 and assisting in obtaining repairs to or replacement of fire Tie-Down Procedures for Land Planes extinguishers.

Securing Light Aircraft Light aircraft are most often secured with ropes tied only at Identifying Fire Extinguishers the aircraft tie-down rings provided for securing purposes.

Fire extinguishers are marked to indicate suitability for a Rope is never to be tied to a lift strut, since this practice can particular class of fire. The markings on Figure 1-7 must be bend a strut if the rope slips to a point where there is no slack.

placed on the fire extinguisher and in a conspicuous place Since manila rope shrinks when wet, about 1 inch (1") of in the vicinity of the fire extinguisher. When the location is slack needs to be provided for movement. Too much slack, marked, however, take extreme care to ensure that the fire however, allows the aircraft to jerk against the ropes. Tight extinguisher kept at that location is in fact the type depicted tie-down ropes put inverted flight stresses on the aircraft and by the marking. In other words, if a location is marked for a many are not designed to take such loads.

Class B fire extinguisher, ensure that the fire extinguisher in that location is in fact suitable for Class B fires.

A tie-down rope holds no better than the knot. Anti-slip knots, such as the bowline, are quickly tied and are easy to untie.

Markings must be applied by decalcomanias (decals), [Figure 1-10] Aircraft not equipped with tie-down fittings painting, or similar methods. They are to be legible and as must be secured in accordance with the manufacturer’s durable as necessary for the location. For example, markings instructions. Ropes are to be tied to outer ends of struts on used outside need to be more durable than those in the hangar high-wing monoplanes and suitable rings provided where or office spaces.

structural conditions permit, if the manufacturer has not already provided them.

When markings are applied to the extinguisher, they are placed on the front of the shell, if one is installed, above or below the Securing Heavy Aircraft extinguisher nameplate. Markings must be large enough and The normal tie-down procedure for heavy aircraft can be in a form that is easily seen and identifiable by the average accomplished with rope or cable tie-down. The number of person with average eyesight at a distance of at least 3 feet.

tie-downs are governed by anticipated weather conditions.

When markings are applied to wall panels, and so forth, in Most heavy aircraft are equipped with surface control locks the vicinity of extinguishers, they must be large enough and that are engaged or installed when the aircraft is secured.

in a form that is easily seen and identifiable by the average Since the method of locking controls vary on different person with average eyesight at a distance of at least 25 feet.

types of aircraft, check the manufacturer’s instructions for [Figure 1-8] proper installation or engaging procedures. If high winds are anticipated, control surface battens can also be installed Using Fire Extinguishers to prevent damage. Figure 1-11 illustrates four common tie- When using a fire extinguisher, ensure the correct type is down points on heavy aircraft.

used for the fire. Most extinguishers have a pin to pull that allows the handle to activate the agent. Stand back 8 feet and The normal tie-down procedure for heavy aircraft includes aim at the base of the fire or flames. Squeeze the lever and the following: sweep side to side until the fire is extinguished.

1. Head aircraft into prevailing wind whenever possible.

Tie-Down Procedures 2. Install control locks, all covers, and guards.

Preparation of Aircraft 3. Chock all wheels fore and aft. [Figure 1-12] Aircraft are to be tied down after each flight to prevent 4. Attach tie-down reels to aircraft tie-down loops, tie- damage from sudden storms. The direction that aircraft are down anchors, or tie-down stakes. Use tie-down stakes to be parked and tied down is determined by prevailing or for temporary tie-down only. If tie-down reels are not forecast wind direction.

1 1 available, ⁄ 4 " wire cable or 1 ⁄ 2 " manila line may be used.

Aircraft are to be headed into the wind, depending on the locations of the parking area’s fixed tie-down points.

Tie-Down Procedures for Seaplanes Spacing of tie-downs need to allow for ample wingtip Seaplanes can be moored to a buoy, weather permitting, or clearance. [Figure 1-9] After the aircraft is properly tied to a dock. Weather causes wave action, and waves cause located, lock the nosewheel or the tail wheel in the the seaplane to bob and roll. This bobbing and rolling while fore-and-aft position.

1-8 ORDINARY ORDINARY FLAMMABLE COMBUSTIBLES 1. Water FLAMMABLE ELECTRICAL COMBUSTIBLES LIQUIDS ELECTRICAL COMBUSTIBLE LIQUIDS EQUIPMENT 2. Carbon Dioxide, Dry Chemical Bromochlorodi fl uoromethane, and Bromotri fl uoromethane ORDINARY FLAMMABLE ELECTRICAL EQUIPMENT METALS COMBUSTIBLES LIQUIDS EQUIPMENT Figure 1-8. Identification of fire extinguisher type location.

3. Multipurpose Dry Chemical ELECTRICAL FLAMMABLE 2' Major axis + CAPABILITY EQUIPMENT LIQUIDS 10' 4. Multipurpose Dry Chemical (Insu ff icient Agent for ‘A’ Rating) COMBUSTIBLE 6' 6' 3' 3' METALS 5. Dry Powder Figure 1-7. Typical extinguisher markings.

3' 3' tied to a dock can cause damage.

Figure 1-9. Diagram of tiedown dimensions.

When warning of an impending storm is received and it is Tie-Down Procedures for Ski Planes not possible to fly the aircraft out of the storm area, some Ski planes are tied down, if the securing means are available, compartments of the seaplane can be flooded, partially in the same manner as land planes. Ski-equipped airplanes sinking the aircraft. Tie down the aircraft securely to anchors.

can be secured on ice or in snow by using a device called a Seaplanes tied down on land have been saved from high-wind dead-man. A dead-man is any item at hand, such as a piece damage by filling the floats with water in addition to tying of pipe, log, and so forth, that a rope is attached to and buried the aircraft down in the usual manner. During heavy weather, in a snow or ice trench. Using caution to keep the free end if possible, remove the seaplane from the water and tie down of the rope dry and unfrozen, snow is packed in the trench.

in the same manner as a land plane. If this is not possible, the If available, pour water into the trench; when it is frozen, tie seaplane could be anchored in a sheltered area away from down the aircraft with the free end of the rope.

the wind and waves.

1-9 Operators of ski-equipped aircraft sometimes pack soft snow around the skis, pour water on the snow, and permit the skis to freeze to the ice. This, in addition to the usual tie-down procedures, aids in preventing damage from windstorms.

Caution must be used when moving an aircraft that has been secured in this manner to ensure that a ski is not still frozen to the ground. Otherwise, damage to the aircraft or skis can occur.

Aft fuselage tiedown ring Nose landing gear tiedown loop Tie-Down Procedures for Helicopters Helicopters, like other aircraft are secured to prevent structural damage that can occur from high-velocity surface winds.

Helicopters are to be secured in hangars, when possible. If not, they must be tied down securely. Helicopters that are tied down can usually sustain winds up to approximately 65 mph. If at all possible, helicopters are evacuated to a safe area if tornadoes or hurricanes are anticipated. For added protection, helicopters can be moved to a clear area so that they are not damaged by Underside of wing tiedown loop Main gear wheel tiedown loop flying objects or falling limbs from surrounding trees.

If high winds are anticipated with the helicopter parked in the Figure 1-11. Common tie-down points.

open, tie down the main rotor blades. Detailed instructions for securing and mooring each type of helicopter can be found in length of time the aircraft is expected to remain on the ground, the applicable maintenance manual. [Figure 1-13] Methods and location and characteristics of the aircraft. Wheel chocks, of securing helicopters vary with weather conditions, the control locks, rope tie-downs, mooring covers, tip socks, tie- This one must be under Up through and Back down around back through Tying a Bowline Knot A Over Over Under Under Tying a Square Knot B Figure 1-10. Knots commonly used for aircraft tie-down.

1-10 down assemblies, parking brakes, and rotor brakes are used Procedures for Securing Powered Parachutes When securing powered parachutes, pack the parachute in a bag to prevent the chute from filling with air from the wind and dragging the seat and engine. The engine and seat can also be secured if needed.

Ground Movement of Aircraft Engine Starting and Operation The following instructions cover the starting procedures for reciprocating, turboprop, turbofan, and APU. These procedures are presented only as a general guide for familiarization with typical procedures and methods. Detailed instructions for starting a specific type of engine can be found in the manufacturer’s instruction book.

Before starting an aircraft engine: Figure 1-12. Wheels chocked fore and aft.

1. Position the aircraft to head into the prevailing wind to ensure adequate airflow over the engine for cooling to secure helicopters.

purposes.

Typical mooring procedures are as follows: 2. Make sure that no property damage or personal injury 1. Face the helicopter in the direction that the highest occurs from the propeller blast or jet exhaust.

forecast wind or gusts are anticipated.

3. If external electrical power is used for starting, ensure 2. Spot the helicopter slightly more than one rotor span that it can be removed safely, and it is sufficient for distance from other aircraft.

the total starting sequence.

3. Place wheel chocks ahead of and behind all wheels 4. During any and all starting procedures, a “fireguard” (where applicable). On helicopters equipped with equipped with a suitable fire extinguisher shall be skids, retract the ground handling wheels, lower stationed in an appropriate place. A fireguard is the helicopter to rest on the skids, and install wheel someone familiar with aircraft starting procedures.

position lock pins or remove the ground-handling The fire extinguisher should be a CO extinguisher wheels. Secure ground-handling wheels inside the of at least 5-pound capacity. The appropriate place is aircraft or inside the hangar or storage buildings. Do adjacent to the outboard side of the engine, in view of not leave them unsecured on the flight line.

the pilot, and also where they can observe the engine/ 4. Align the blades and install tie-down assemblies aircraft for indication of starting problems.

as prescribed by the helicopter manufacturer.

5. If the aircraft is turbine-engine powered, the area in [Figure 1-14] Tie straps snugly without strain, and front of the jet inlet must be kept clear of personnel, during wet weather, provide some slack to avoid the property, and/or debris (FOD).

possibility of the straps shrinking, causing undue stress 6. These “before starting” procedures apply to all aircraft on the aircraft and/or its rotor system(s).

powerplants.

5. Fasten the tie-down ropes or cables to the forward 7. Follow manufacturer’s checklists for start procedures and aft landing gear cross tubes and secure to ground and shutdown procedures.

stakes or tie-down rings.

Reciprocating Engines Procedures for Securing Weight-Shift-Control The following procedures are typical of those used to start There are many types of weight-shift-controlled aircraft— reciprocating engines. There are, however, wide variations engine powered and non-powered. These types of aircraft are in the procedures for the many reciprocating engines. Do not very susceptible to wind damage. The wings can be secured attempt to use the methods presented here for actually starting in a similar manner as a conventional aircraft in light winds.

an engine. Instead, always refer to the procedures contained In high winds, the mast can be disconnected from the wing in the applicable manufacturer’s instructions. Reciprocating and the wing placed close to the ground and secured. This engines are capable of starting in fairly low temperatures type of aircraft can also be partially disassembled or moved into a hangar for protection.

1-11 Before starting a radial engine that has been shut down for more than 30 minutes, check the ignition switch for off. Turn the propeller three or four complete revolutions by hand to detect a hydraulic lock, if one is present. Any liquid present in a cylinder is indicated by the abnormal effort required to rotate the propeller or by the propeller stopping abruptly during rotation. Never use force to turn the propeller when a hydraulic lock is detected. Sufficient force can be exerted on the crankshaft to bend or break a connecting rod if a lock is present.

To eliminate a lock, remove either the front or rear spark plug from the lower cylinders and pull the propeller through.

Never attempt to clear the hydraulic lock by pulling the propeller through in the direction opposite to normal Figure 1-13. Example of mooring of a helicopter.

rotation. This tends to inject the liquid from the cylinder into the intake pipe. The liquid is drawn back into the cylinder without the use of engine heating or oil dilution, depending with the possibility of complete or partial lock occurring on the grade of oil used.

on the subsequent start.

The various covers (wing, tail, flight deck, wheel, and To start the engine, proceed as follows: so forth) protecting the aircraft must be removed before 1. Turn the auxiliary fuel pump on, if the aircraft is attempting to turn the engine. Use external sources of so equipped.

electrical power when starting engines equipped with electric starters, if possible or needed. This eliminates an excessive 2. Place the mixture control to the position recommended burden on the aircraft battery. Leave all unnecessary electrical for the engine and carburetor combination being equipment off until the generators are furnishing electrical started. As a general rule, put the mixture control in power to the aircraft power bus.

the “idle cut-off” position for fuel injection and in the Align the blades Figure 1-14. Securing helicopter blades and fuselage.

1-12 “full rich” position for float-type carburetors. Many temperature gauge, and fuel flow gauge.

light aircraft are equipped with a mixture control pull Hand Cranking Engines rod that has no detent intermediate positions. When such controls are pushed in flush with the instrument If the aircraft has no self-starter, start the engine by turning the panel, the mixture is set in the “full rich” position. propeller by hand (hand propping the propeller). The person Conversely, when the control rod is pulled all the who is turning the propeller calls: “Fuel on, switch off, throttle way out, the carburetor is in the “idle cut-off” or “full closed, brakes on.” The person operating the engine checks lean” position. The operator can select unmarked these items and repeats the phrase. The switch and throttle must intermediate positions between these two extremes not be touched again until the person swinging the prop calls to achieve any desired mixture setting.

“contact.” The operator repeats “contact” and then turns on the switch. Never turn on the switch and then call “contact.” 3. Open the throttle to a position that provides 1,000 to 1 1 1,200 rpm (approximately ⁄ 8 " to ⁄ 2 " from the “closed” A few simple precautions help to avoid accidents when hand position).

propping the engine. While touching a propeller, always 4. Leave the pre-heat or alternate air (carburetor air) assume that the ignition is on. The switches that control the control in the “cold” position to prevent damage magnetos operate on the principle of short-circuiting the and fire in case of backfire. These auxiliary heating current to turn the ignition off. If the switch is faulty, it can devices are used after the engine warms up. They be in the “off” position and still permit current to flow in improve fuel vaporization, prevent fouling of the the magneto primary circuit. This condition could allow the spark plugs, ice formation, and eliminate icing in engine to start when the switch is off.

the induction system.

5. Move the primer switch to “on” intermittently (press Be sure the ground is firm. Slippery grass, mud, grease, or loose gravel can lead to a fall into or under the propeller. Never allow to prime by pushing in on the ignition switch during the starting cycle), or prime with one to three strokes any portion of your body to get in the way of the propeller. This applies even when the engine is not being cranked.

of priming pump, depending on how the aircraft is equipped. The colder the weather, the more priming Stand close enough to the propeller to be able to step away is needed.

as it is pulled down. Stepping away after cranking is a 6. Energize the starter and after the propeller has made safeguard in case the brakes fail. Do not stand in a position at least two complete revolutions, turn the ignition that requires leaning toward the propeller to reach it. This switch on. On engines equipped with an induction throws the body off balance and could cause a fall into the vibrator (shower of sparks, magneto incorporates a blades when the engine starts.

retard breaker assembly), turn the switch to the “both” position and energize the starter by turning the switch In swinging the prop, always move the blade downward by to the “start” position. After the engine starts, release pushing with the palms of the hands. Do not grip the blade the starter switch to the “both” position. When starting with the fingers curled over the edge, since “kickback” may an engine that uses an impulse coupling magneto, break them or draw your body in the blade path. Excessive turn the ignition switch to the “left” position. Place throttle opening after the engine has fired is the principal the start switch to the “start” position. When the cause of backfiring during starting. Gradual opening of the engine starts, release the start switch. Do not crank throttle, while the engine is cold, reduces the potential for the engine continuously with the starter for more than backfiring. Slow, smooth movement of the throttle assures 1 minute. Allow a 3- to 5-minute period for cooling correct engine operation.

the starter (starter duty cycle) between successive attempts. Otherwise, the starter may be burned out Avoid over priming the engine before it is turned over by the due to overheating.

starter. This can result in fires, scored or scuffed cylinders 7. After the engine is operating smoothly, move the and pistons, or engine failures due to hydraulic lock. If the mixture control to the “full rich” position if started in the engine is inadvertently flooded or over primed, turn the “idle cutoff” position. Carbureted engines are already ignition switch off and move the throttle to the “full open” in the rich mixture position. Check for oil pressure.

position. To rid the engine of the excess fuel, turn it over by hand or by the starter. If excessive force is needed to turn 8. Instruments for monitoring the engine during over the engine, stop immediately. Do not force rotation of operation include a tachometer for rpm, manifold the engine. If in doubt, remove the lower cylinder spark plugs.

pressure gauge, oil pressure gauge, oil temperature gauge, cylinder head temperature gauge, exhaust gas 1-13 Immediately after the engine starts, check the oil pressure and access plates are secured. Check sumps for water. Inspect indicator. If oil pressure does not show within 30 seconds, air inlet areas for general condition and foreign material.

stop the engine and determine the trouble. If oil pressure is Check the compressor for free rotation, when the installation indicated, adjust the throttle to the aircraft manufacturer’s permits, by reaching in and turning the blades by hand.

specified rpm for engine warm up. Warm up rpm is usually between 1,000 to 1,300 rpm. The following procedures are typical of those used to start turboprop engines. There are, however, wide variations in Most aircraft reciprocating engines are air cooled and the procedures applicable to the many turboprop engines.

depend on the forward speed of the aircraft to maintain Therefore, do not attempt to use these procedures in the actual proper cooling. Therefore, particular care is necessary when starting of a turboprop engine. These procedures are presented operating these engines on the ground. During all ground only as a general guide for familiarization with typical running, operate the engine with the propeller in full low procedures and methods. For starting of all turboprop engines, pitch and headed into the wind with the cowling installed to refer to the detailed procedures contained in the applicable provide the best degree of engine cooling. Closely monitor manufacturer’s instructions or their approved equivalent.

the engine instruments at all times. Do not close the cowl flaps for engine warm-up, they need to be in the open Turboprop engines are usually fixed turbine or free turbine.

position while operating on the ground. When warming up The propeller is connected to the engine directly in a fixed the engine, ensure that personnel, ground equipment that may turbine, resulting in the propeller being turned as the engine be damaged, or other aircraft are not in the propeller wash. starts. This provides extra drag that must be overcome during starting. If the propeller is not at the “start” position, difficulty Extinguishing Engine Fires may be encountered in making a start due to high loads. The propeller is in flat pitch at shut down and subsequently in flat In all cases, a fireguard should stand by with a CO fire extinguisher while the aircraft engine is being started. This pitch during start because of this.

is a necessary precaution against fire during the starting procedure. The fireguard must be familiar with the induction The free turbine engine has no mechanical connection between the gas generator and the power turbine that is system of the engine so that in case of fire, they can direct the CO into the air intake of the engine to extinguish it. A connected to the propeller. In this type of engine, the propeller remains in the feather position during starting and only turns fire could also occur in the exhaust system of the engine from liquid fuel being ignited in the cylinder and expelled during as the gas generator accelerates.

the normal rotation of the engine.

Instrumentation for turbine engines varies according to the type of turbine engine. Turboprop engines use the normal If an engine fire develops during the starting procedure, the operator should continue cranking to start the engine and instruments—oil pressure, oil temperature, inter-turbine temperature (ITT), and fuel flow. They also use instruments extinguish the fire. If the engine does not start and the fire continues to burn, discontinue the start attempt. The fireguard to measure gas generator speed, propeller speed, and torque produced by the propeller. [Figure 1-15] A typical turboprop then extinguishes the fire using the available equipment. The fireguard must observe all safety practices at all times while uses a set of engine controls, such as power levelers (throttle), propeller levers, and condition levers. [Figure 1-16] standing by during the starting procedure.

Turboprop Engines The first step in starting a turbine engine is to provide an adequate source of power for the starter. On smaller turbine The starting of any turbine engine consists of three steps that engines, the starter is an electric motor that turns the engine must be carried out in the correct sequence. The starter turns through electrical power. Larger engines need a much the main compressor to provide airflow though the engine. At more powerful starter. Electric motors would be limited by the correct speed that provides enough airflow, the igniters current flow and weight. Air turbine starters were developed are turned on and provide a hot spark to light the fuel that that were lighter and produced sufficient power to turn the is engaged next. As the engine accelerates, it reaches a self- engine at the correct speed for starting. When an air turbine sustaining speed and the starter is disengaged.

starter is used, the starting air supply may be obtained from an APU onboard the aircraft, an external source (ground air The various covers protecting the aircraft must be removed.

cart), or an engine cross-bleed operation. In some limited Carefully inspect the engine exhaust areas for the presence cases, a low-pressure, large-volume tank can provide the air of fuel or oil. Make a close visual inspection of all accessible for starting an engine. Many smaller turboprop engines are parts of the engines and engine controls, followed by an started using the starter/generator, that is both the engine inspection of all nacelle areas to determine that all inspection 1-14 starter and the generator. • The engine fails to ignite by 4,500 rpm or maximum motoring rpm.

While starting an engine, always observe the following: • Abnormal vibration is noted or compressor surge • Always observe the starter duty cycle. Otherwise, the occurs (indicated by backfiring).

starter can overheat and be damaged.

• Fire warning bell rings. (This may be due to either an • Assure that there is enough air pressure or electrical engine fire or overheat.)

capacity before attempting a start.

Turbofan Engines • Do not perform a ground start if turbine inlet Unlike reciprocating engine aircraft, the turbine-powered temperature (residual temperature) is above that aircraft does not require a preflight run-up unless it is specified by the manufacturer.

necessary to investigate a suspected malfunction.

• Provide fuel under low pressure to the engine’s fuel pump.

Before starting, all protective covers and air inlet duct covers are removed. If possible, head the aircraft into the wind to Turboprop Starting Procedures obtain better cooling, faster starting, and smoother engine To start an engine on the ground, perform the following performance. It is especially important that the aircraft be operations: headed into the wind if the engine is to be trimmed.

1. Turn the aircraft boost pumps on.

The run-up area around the aircraft is cleared of both 2. Make sure that the power lever is in the “start” personnel and loose equipment. The turbofan engine intake position.

and exhaust hazard areas are illustrated in Figure 1-17 .

3. Place the start switch in the “start” position. This starts Exercise care to ensure that the run-up area is clear of all the engine turning.

items, such as nuts, bolts, rocks, shop towels, or other loose debris. Many very serious accidents have occurred involving 4. Place the ignition switch on. (On some engines, the personnel in the vicinity of turbine engine air inlets. Use ignition is activated by moving the fuel lever.)

extreme caution when starting turbine aircraft.

5. The fuel is now turned on. This is accomplished by moving the condition lever to the “on” position.

Check the aircraft fuel sumps for water or ice. Inspect the 6. Monitor the engine lights of the exhaust temperature.

engine air inlet for general condition and the presence of If it exceeds the limits, shut the engine down.

foreign objects. Visually inspect the fan blades, forward compressor blades, and the compressor inlet guide vanes for 7. Check the oil pressure and temperature.

nicks and other damage. If possible, check the fan blades for 8. After the engine reaches a self-sustaining speed, the free rotation by turning the fan blades by hand. All engine starter is disengaged.

controls must be operational. Check engine instruments and 9. The engine continues to accelerate up to idle. warning lights for proper operation.

10. Maintain the power lever at the “start” position until Starting a Turbofan Engine the specified minimum oil temperature is reached.

The following procedures are typical of those used to start 11. Disconnect the ground power supply, if used.

many turbine engines. There are, however, wide variations in the starting procedures used for turbine engines, and no If any of the following conditions occur during the starting attempts are to be made to use these procedures in the actual sequence, turn off the fuel and ignition switch, discontinue starting of an engine. These procedures are presented only as the start immediately, make an investigation, and record a general guide for familiarization with typical procedures the findings.

and methods. In the starting of all turbine engines, refer • Turbine inlet temperature exceeds the specified to the detailed procedures contained in the applicable maximum. Record the observed peak temperature. manufacturer’s instructions or their approved equivalent.

• Acceleration time from start of propeller rotation to Most turbofan engines can be started by either air turbine stabilized rpm exceeds the specified time.

or electrical starters. Air-turbine starters use compressed air • There is no oil pressure indication at 5,000 rpm for from an external source as discussed earlier. Fuel is turned on either the reduction gear or the power unit.

either by moving the start lever to “idle/start” position or by opening a fuel shutoff valve. If an air turbine starter is used, • Torching (visible burning in the exhaust nozzle).

1-15 the engine “lights off” within a predetermined time after the fuel is turned on. This time interval, if exceeded, indicates a malfunction has occurred and the start must be discontinued.

0 0 TORQUE 26 TORQUE 26 2 2 24 24 Most turbofan engine controls consist of a power lever, 4 4 22 22 reversing levers, and start levers. Newer aircraft have replaced 6 6 20 20 FTLB X 100 FTLB X 100 8 8 18 18 the start levers with a fuel switch. [Figure 1-18] Turbofan 10 10 16 16 12 12 14 14 engines also use all the normal instruments speeds, (percent of total rpm) exhaust gas temperature, fuel flow, oil pressure, and temperature. An instrument that measures the amount 0 0 of thrust being delivered is the engine pressure ratio. This 23 23 5 5 measures the ratio between the inlet pressures to the outlet PROP PROP 22 22 pressure of the turbine.

10 21 10 21 20 20 13 13 RPH X 100 RPH X 100 19 19 14 14 The following procedures are useful only as a general guide 18 18 15 15 16 16 17 17 and are included to show the sequence of events in starting a turbofan engine.

1. If the engine is so equipped, place the power lever in the “idle” position.

6 6 2. Turn the fuel boost pump(s) switch on.

5 5 FUEL FLOW FUEL FLOW 3. A fuel inlet pressure indicator reading ensures fuel is 4 4 being delivered to engine fuel pump inlet.

0 3 0 3 RPH X 100 RPH X 100 4. Turn engine starter switch on. Note that the engine 1 2 1 2 rotates to a preset limit. Check for oil pressure.

5. Turn ignition switch on. (This is usually accomplished by moving the start lever toward the “on” position.

OIL OIL A micro switch connected to the leveler turns on the 140 140 200 200 ignition.)

150 150 100 100 60 60 6. Move the start lever to “idle” or “start” position, this 100 100 starts fuel flow into the engine.

20 20 50 50 0 0 0 -20 0 -20 7. Engine start (light off) is indicated by a rise in exhaust °C PSI °C PSI gas temperature.

8. If a two-spool engine, check rotation of fan or N1.

Figure 1-15. Typical examples of turboprop instruments.

9. Check for proper oil pressure.

10. Turn engine starter switch off at proper speeds.

Prop levers P 11. After engine stabilizes at idle, ensure that none of the P O W E R R engine limits are exceeded.

O P E 12. Newer aircraft drop off the starter automatically.

L RUN L E R I F Auxiliary Power Units (APUs) D GA E L A E T S APUs are generally smaller turbine engines that provide H T R E E O R V P E compressed air for starting engines, cabin heating and R S E cooling, and electrical power while on the ground. Their Condition levers Power levers operation is normally simple. By turning a switch on and up to the start position (spring loaded to on position), the engine starts automatically. During start, the exhaust gas temperature must be monitored. APUs are at idle at 100 percent rpm with no load. After the engine reaches its operating rpm, it can be used for cooling or heating the Figure 1-16. Engine controls of a turboprop aircraft.

1-16 cabin and for electrical power. It is normally used to start the main engines. Some types of tow bars available for general use can be used for many types of towing operations. [Figure 1-20] These Unsatisfactory Turbine Engine Starts bars are designed with sufficient tensile strength to pull most aircraft, but are not intended to be subjected to torsional or Hot Start twisting loads. Many have small wheels that permit them to be A hot start occurs when the engine starts, but the exhaust drawn behind the towing vehicle going to or from an aircraft.

gas temperature exceeds specified limits. This is usually When the bar is attached to the aircraft, inspect all the engaging caused by an excessively rich air-fuel mixture entering the devices for damage or malfunction before moving the aircraft.

combustion chamber. This condition can be caused by either Additionally, some aircraft have tow steering turn limits.

too much fuel or not enough airflow. The fuel to the engine must be shut off immediately.

Some tow bars are designed for towing various types of aircraft. However, other special types can be used on a False or Hung Start particular aircraft only. Such bars are usually designed and False or hung starts occur when the engine starts normally, but built by the aircraft manufacturer.

the rpm remains at some low value rather than increasing to the normal starting rpm. This is often the result of insufficient When towing the aircraft, the towing vehicle speed must be power to the starter or the starter cutting off before the engine reasonable, and all persons involved in the operation must be starts self-accelerating. In this case, shut the engine down.

alert. When the aircraft is stopped, do not rely upon the brakes of the towing vehicle alone to stop the aircraft. The person in Engine Fails to Start the flight deck must coordinate the use of the aircraft brakes The engine failing to start within the prescribed time limit with those of the towing vehicle. A typical smaller aircraft can be caused by lack of fuel to the engine, insufficient or tow tractor (or tug) is shown in Figure 1-21 .

no electrical power to the exciter in the ignition system, or incorrect fuel mixture. If the engine fails to start within the The attachment of the tow bar varies on different types of prescribed time, shut it down.

aircraft. Aircraft equipped with tail wheels are generally towed forward by attaching the tow bar to the main landing In all cases of unsatisfactory starts, the fuel and ignition must be gear. In most cases, it is permissible to tow the aircraft in turned off. Continue rotating the compressor for approximately reverse by attaching the tow bar to the tail wheel axle. Any 15 seconds to remove accumulated fuel from the engine. If time an aircraft equipped with a tail wheel is towed, the tail unable to motor (rotate) the engine, allow a 30-second fuel wheel must be unlocked or the tail wheel locking mechanism draining period before attempting another start.

may damage or break. Aircraft equipped with tricycle landing gear are generally towed forward by attaching a tow bar to the Towing of Aircraft axle of the nosewheel. They may also be towed forward or Movement of large aircraft about the airport, flight line, backward by attaching a towing bridle or specially designed and hangar is usually accomplished by towing with a tow towing bar to the towing lugs on the main landing gear. When tractor (sometimes called a “tug”). [Figure 1-19] In the case an aircraft is towed in this manner, a steering bar is attached of small aircraft, some moving is accomplished by hand to the nosewheel to steer the aircraft.

pushing on the correct areas of the aircraft. Aircraft may also be taxied about the flight line but usually only by certain The following towing and parking procedures are typical of qualified personnel.

one type of operation. They are examples and not necessarily suited to every type of operation. Aircraft ground-handling Towing aircraft can be a hazardous operation, causing personnel must be thoroughly familiar with all procedures damage to the aircraft and injury to personnel, if done pertaining to the types of aircraft being towed and local recklessly or carelessly. The following paragraphs outline operation standards governing ground handling of aircraft.

the general procedure for towing aircraft. However, specific Competent persons that have been properly checked out instructions for each model of aircraft are detailed in the direct the aircraft towing team.

manufacturer’s maintenance instructions and are to be 1. The towing vehicle driver is responsible for operating followed in all instances.

the vehicle in a safe manner and obeying emergency stop instructions given by any team member.

Before the aircraft to be towed is moved, a qualified person must be in the flight deck to operate the brakes in case the 2. The person in charge assigns team personnel as wing tow bar fails or becomes unhooked. The aircraft can then be walkers. A wing walker is stationed at each wingtip, in stopped, preventing possible damage.

such a position that they can ensure adequate clearance 1-17

Air intake idle Air intake takeo ff

Distance in feet 30 feet 100º 35 K Velocity in knots = K Temperature in °F 125° 60 K Exhaust 12 feet 150° 100 K 100° 25 K 200° 200 K 125° 40 K 300 K 150° 60 K 300° 200° 100 K 500 K 500° 300° 200 K 900 K 700° 25 feet 25 feet Figure 1-17. Engine intake and exhaust hazard areas.

1-18 towed into position.

7. The aircraft brake system is to be charged before each towing operation. Aircraft with faulty brakes are towed into position only for repair of brake systems, and then personnel must be standing by ready with chocks for emergency use. Chocks must be immediately available in case of an emergency throughout any towing operation.

8. To avoid possible personal injury and aircraft damage during towing operations, entrance doors are closed, ladders retracted, and gear-down locks installed.

9. Prior to towing any aircraft, check all tires and landing gear struts for proper inflation. (Inflation of landing gear struts of aircraft in overhaul and storage is excluded.)

Figure 1-18. Turbofan engine control levers.

10. When moving aircraft, do not start and stop suddenly.

For added safety, aircraft brakes must never be applied of any obstruction in the path of the aircraft. A tail during towing, except upon command by one of the walker is assigned when sharp turns are to be made tow team members in an emergency situation.

or when the aircraft is to be backed into position.

11. Aircraft are parked in specified areas. Generally, 3. A qualified person occupies the pilot’s seat of the towed the distance between rows of parked aircraft is great aircraft to observe and operate the brakes as required.

enough to allow immediate access of emergency When necessary, another qualified person is stationed to vehicles in case of fire, as well as free movement of watch and maintain aircraft hydraulic system pressure.

equipment and materials.

4. The person in charge of the towing operation verifies 12. Wheel chocks are placed fore and aft of the main that, on aircraft with a steerable nosewheel, the landing gear of the parked aircraft.

locking scissors are set to full swivel for towing. The locking device must be reset after the tow bar has 13. Internal or external control locks (gust locks or blocks) been removed from the aircraft. Persons stationed are used while the aircraft is parked.

in the aircraft are not to attempt to steer or turn the 14. Prior to any movement of aircraft across runways nosewheel when the tow bar is attached to the aircraft.

or taxiways, contact the airport control tower on the 5. Under no circumstances is anyone permitted to walk appropriate frequency for clearance to proceed.

or to ride between the nosewheel of an aircraft and the 15. An aircraft parked in a hangar must be statically towing vehicle, nor ride on the outside of a moving grounded immediately.

aircraft or on the towing vehicle. In the interest of safety, no attempt to board or leave a moving aircraft Taxiing Aircraft or towing vehicle is permitted.

As a general rule, only rated pilots and qualified airframe 6. The towing speed of the aircraft is not to exceed that and powerplant (A&P) technicians are authorized to of the walking team members. The aircraft’s engines start, run up, and taxi aircraft. All taxiing operations are usually are not operated when the aircraft is being Figure 1-19. Example of a tow tractor.

Figure 1-20. Example of a tow bar.

1-19 a minimum number of the most commonly used signals.

Whether this set of signals or a modified set is used is not the most important consideration, as long as each flight operational center uses a suitable, agreed-upon set of signals.

Figure 1-25 illustrates some of the most commonly used helicopter operating signals.

The taxi signals to be used must be studied until the taxi signalman can execute them clearly and precisely. The signals are to be given in such a way that the pilot cannot confuse their meaning. Remember that the pilot receiving the signals is always some distance away and often look out and down from a difficult angle. Thus, the signalman’s hands must be kept well separated, and signals are to be over-exaggerated rather than risk making indistinct signals. If there is any Figure 1-21. Typical smaller aircraft tow tractor.

doubt about a signal, or if the pilot does not appear to be following the signals, use the “stop” sign and begin the series performed in accordance with applicable local regulations.

of signals again.

Figure 1-22 contains the standard taxi light signals used by control towers to control and expedite the taxiing of aircraft.

The signalman is to always try to give the pilot an indication The following section provides detailed instructions on taxi of the approximate area that the aircraft is to be parked.

signals and related taxi instructions.

The signalman must glance behind himself or herself often when walking backward to prevent backing into a propeller Taxi Signals or tripping over a chock, fire bottle, tie-down line, or Many ground accidents have occurred as a result of improper other obstruction.

technique in taxiing aircraft. Although the pilot is ultimately responsible for the aircraft until the engine is stopped, a Taxi signals are usually given at night with the aid of taxi signalman can assist the pilot around the flight line. In illuminated wands attached to flashlights. [Figure 1-26] Night some aircraft configurations, the pilot’s vision is obstructed signals are made in the same manner as day signals with the while on the ground. The pilot cannot see obstructions close exception of the stop signal. The stop signal used at night is to the wheels or under the wings and has little idea of what the “emergence stop” signal. This signal is made by crossing is behind the aircraft. Consequently, the pilot depends upon the wands to form a lighted “X” above and in front of the head.

the taxi signalman for directions. Figure 1-23 shows a taxi signalman indicating his readiness to assume guidance of Servicing Aircraft the aircraft by extending both arms at full length above his Servicing Aircraft Air/Nitrogen Oil & Fluids head, palms facing each other.

Checking or servicing aircraft fluids is an important maintenance function. Before servicing any aircraft, consult The standard position for a signalman is slightly ahead of the specific aircraft maintenance manual to determine the and in line with the aircraft’s left wingtip. As the signalman proper type of servicing equipment and procedures. In faces the aircraft, the nose of the aircraft is on the left.

general, aircraft engine oil is checked with a dipstick or a sight [Figure 1-24] The signalman must stay far enough ahead gauge. There are markings on the stick or around the sight of the wingtip to remain in the pilot’s field of vision. It is a gauge to determine the correct level. Reciprocating engines good practice to perform a foolproof test to be sure the pilot are to be checked after the engine has been inactive, while can see all signals. If the signalman can see the pilot’s eyes, the turbine engine must be checked just after shutdown. Dry the pilot can see the signals.

sump oil systems tend to hide oil that has seeped from the oil tank into the gearcase of the engine. This oil does not show up Figure 1-24 shows the standard aircraft taxiing signals on the dipstick until the engine has been started or motored.

published in the Federal Aviation Administration (FAA) If serviced before this oil is pumped back into the tank, the Aeronautical Information Manual (AIM). There are other engine overfills. Never overfill the oil tank. Oil foams as it standard signals, such as those published in Advisory Circular is circulated through the engine. The expansion space in the 00-34, as revised, and by the International Standards (ICAO) oil tank allows for this foaming (oil mixing with air). Also Annex 2, Appendix 1 and the Armed Forces. Furthermore, the correct type of oil must be used for the appropriate engine operation conditions in many areas may call for a modified being serviced. Hydraulic fluid, fuel, and oil, if spilled on set of taxi signals. The signals shown in Figure 1-24 represent clothes or skin, must be removed as soon as possible because 1-20 of fire danger and health reasons.

When servicing a hydraulic reservoir, the correct fluid must be used. Normally, this can be determined by the container or by color. Some reservoirs are pressurized by air that must be bled off before servicing. Efforts must be made to prevent any type of contamination during servicing. Also, if changing hydraulic filters, assure that the pressure is off the system before removing the filters. After servicing the filters (if large amounts of fluids were lost) or system quantity, air must be purged and the system checked for leaks. While servicing tires or struts with high-pressure nitrogen, the technician must use caution while performing maintenance. Clean areas before connecting filling hose and do not overinflate.

Ground Support Equipment Electric Ground Power Units Ground support electrical APUs vary widely in size and type. However, they can be generally classified by towed, stationary, or self-propelled items of equipment. Some units are mainly for in-hangar use during maintenance. Others are designed for use on the flight line, either at a stationary gate area or towed from aircraft to aircraft. The stationary type can be powered from the electrical service of the facility.

The movable type ground power unit (GPU) generally has an onboard engine that turns a generator to produce power.

Some smaller units use a series of batteries. The towed power units vary in size and range of available power.

The smallest units are simply high-capacity batteries used Figure 1-23. The taxi signalman.

to start light aircraft. These units are normally mounted on wheels or skids and are equipped with an extra-long electrical Figure 1-27 .

line terminated in a suitable plug-in adapter.

Self-propelled power units are normally more expensive than Larger units are equipped with generators. Providing a the towed units and, in most instances, supply a wider range wider range of output power, these power units are normally of output voltages and frequencies. The stationary power unit, designed to supply constant-current, variable voltage DC shown in Figure 1-28, is capable of supplying DC power in electrical power for starting turbine aircraft engines and varying amounts, as well as 115/200-volt, 3-phase, 400-cycle constant-voltage DC for starting reciprocating aircraft AC power continuously for 5 minutes.

engines. Normally somewhat top-heavy, large towed power units are towed at restricted speeds, and sharp turns are When using ground electrical power units, it is important to avoided. An example of a large power unit is shown in position the unit to prevent collision with the aircraft being serviced, or others nearby, in the event the brakes on the unit Lights Meaning fail. It must be parked so that the service cable is extended to near its full length away from the aircraft being serviced, Flashing green Cleared to taxi but not so far that the cable is stretched or undue stress is placed on the aircraft electrical receptacle.

Steady red Stop Flashing red Taxi clear of runway in use Observe all electrical safety precautions when servicing an Flashing white Return to starting point aircraft. Additionally, never move a power unit when service cables are attached to an aircraft or when the generator Alternating red and green Exercise extreme caution system is engaged.

Figure 1-22. Standard taxi light signals.

1-21 Signalman directs towing Signalman's position Flagman directs pilot to signalman if traffic conditions require Stop Come ahead Emergency stop Cut engines Start engines Slow down Pull chocks Insert chocks All clear (O.K.) Left turn Right turn Night operation Figure 1-24. Standard FAA hand taxi signals.

Hydraulic Ground Power Units • Drain the aircraft hydraulic systems.

Portable hydraulic test stands are manufactured in many sizes • Filter the aircraft hydraulic system fluid.

and cost ranges. [Figure 1-29] Some have a limited range of • Refill the aircraft hydraulic system with clean fluid.

operation, while others can be used to perform all the system • Check the aircraft hydraulic systems for operation tests that fixed-shop test stands are designed to perform.

and leaks.

Hydraulic power units, sometimes called a hydraulic mule, provide hydraulic pressure to operate the aircraft systems This type of portable hydraulic test unit is usually an during maintenance. They can be used to: electrically-powered unit. It uses a hydraulic system 1-22 Stop Engage rotor Start engine Stop rotor Move back Move forward Move right Move left Take o ff Go down Landing direction Go up Swing tail to right Swing tail to left Figure 1-25. Helicopter operating signals.

capable of delivering a variable volume of fluid from zero (preferably wound on a reel) and kept clean, dry, and free to approximately 24 gallons per minute at variable pressures of contaminants.

up to 3,000 psi.

Operating at pressures of 3,000 psi or more, extreme caution Ground Support Air Units must be used when operating hydraulic power units. At 3,000 Air carts are used to provide low-pressure (up to 50 psi high psi, a small stream from a leak can cut like a sharp knife.

volume flow) air that can be used for starting the engines Therefore, inspect lines used with the system for cuts, frays, and heating and cooling the aircraft on the ground (using the or any other damage, and keep them free of kinks and twists.

onboard aircraft systems). It generally consists of an APU When not in use, hydraulic power unit lines are to be stored 1-23 outside hangars.

Oxygen used on aircraft is available in two types: gaseous and liquid. The type to use on any specific aircraft depends on the type of equipment in the aircraft. Gaseous oxygen is stored in large steel cylinders, while liquid oxygen (commonly referred to as LOX) is stored and converted into a usable gas in a liquid oxygen converter.

Oxygen is commercially available in three general types: aviator’s breathing, industrial, and medical. Only oxygen marked “Aviator’s Breathing Oxygen” that meets Federal Specification BB-0-925A, Grade A, or its equivalent is to be used in aircraft breathing oxygen systems. Industrial oxygen may contain impurities that could cause the pilot, crew, and/ or passengers to become sick. Medical oxygen, although pure, contains water that can freeze in the cold temperatures found at the altitudes where oxygen is necessary.

Figure 1-26. Night operations with wands.

built into the cart that provides bleed air from the APU’s compressor for operating aircraft systems or starting engines.

[Figure 1-30] Ground Air Heating and Air Conditioning Figure 1-27. A mobile electrical power unit.

Most airport gates have facilities that can provide heated or cooled air. The units that cool or heat the air are permanent installations that connect to the aircraft’s ventilation system by use of a large hose. Portable heating and air conditioning units can also be moved close to the aircraft and connected by a duct that provides air to keep the cabin temperature comfortable.

Oxygen Servicing Equipment Before servicing any aircraft, consult the specific aircraft maintenance manual to determine the proper types of servicing equipment to be used. Two personnel are required to service an aircraft with gaseous oxygen. One person is stationed at the control valves of the servicing equipment, and one person is stationed where they can observe the pressure in the aircraft system. Communication between the two people is required in the event of an emergency.

Do not service aircraft with oxygen during fueling, defueling, or other maintenance work that could provide a source of Figure 1-28. A stationary electrical power unit.

ignition. Oxygen servicing of aircraft is to be accomplished 1-24 Oxygen Hazards 100, 100LL, or 115. AVGAS can also be identified by a color code. The color of the fuel needs to match the color band on Gaseous oxygen is chemically stable and is nonflammable.

piping and fueling equipment. [Figure 1-31] However, combustible materials ignite more rapidly and burn with greater intensity in an oxygen-rich atmosphere. In Turbine fuel/jet fuel is used to power turbojet and turbo- addition, oxygen combines with oil, grease, or bituminous shaft engines. Three types of turbine fuel generally used material to form a highly-explosive mixture that is sensitive in civilian aviation are JET A and JET A-1, made from to compression or impact. Physical damage to, or failure kerosene, and JET B, a blend of kerosene and AVGAS.

of, oxygen containers, valves, or plumbing can result in an While jet fuel is identified by the color black on piping and explosive rupture with extreme danger to life and property.

fueling equipment, the actual color of jet fuel can be clear It is imperative that the highest standard of cleanliness be or straw colored.

observed in handling oxygen and that only qualified and authorized persons be permitted to service aircraft gaseous Before mixing AVGAS and turbine fuel, refer to the Type oxygen systems. In addition to aggravating the fire hazard Certificate Data Sheet for the respective powerplant. Adding and because of its low temperature (it boils at −297 °F), jet fuel to AVGAS causes a decrease in the power developed liquid oxygen causes severe “burns” (frostbite) if it comes by the engine and could cause damage to the engine (through in contact with the skin.

detonation) and loss of life. Adding AVGAS to jet fuel can cause lead deposits in the turbine engine and can lead to Fuel Servicing of Aircraft reduced service life.

Types of Fuel and Identification Two types of aviation fuel in general use are aviation gasoline, Contamination Control also known as AVGAS, and turbine fuel, also known as JET Contamination is anything in the fuel that is not supposed to A fuel.

be there. The types of contamination found in aviation fuel include water, solids, and microbial growths. The control of Aviation gasoline (AVGAS) is used in reciprocating engine contamination in aviation fuel is extremely important, since aircraft. Currently, there are three grades of fuel in general contamination can lead to engine failure or stoppage and the use: 80/87, 100/130, and 100LL (low lead). A fourth grade, loss of life. The best method of controlling contamination 115/145, is in limited use in the large reciprocating-engine is to prevent its introduction into the fuel system. Some aircraft. The two numbers indicate the lean mixture and rich forms of contamination can still occur inside the fuel system.

mixture octane rating numbers of the specific fuel. In other However, the filter, separators, and screens remove most of words, with 80/87 AVGAS, the 80 is the lean mixture rating the contamination.

and 87 is the rich mixture rating number. To avoid confusing the types of AVGAS, it is generally identified as grade 80, Water in aviation fuels generally take two forms: dissolved (vapor) and free water. The dissolved water is not a major problem until, as the temperature lowers, it becomes free water. This then poses a problem if ice crystals form, clogging filters and other small orifices.

Figure 1-30. Aircraft air start unit.

Figure 1-29. A portable hydraulic power unit.

1-25 Free water can appear as water slugs or entrained water.

Water slugs are concentrations of water. This is the water Breathing the vapors from fuel can be harmful and must that is drained after fueling an aircraft. Entrained water is be limited. Any fuel spilled on the clothing or skin must be suspended water droplets. These droplets may not be visible removed as soon as possible.

to the eye but give the fuel a cloudy look. The entrained water settles out in time. Fueling Procedures The proper fueling of an aircraft is the responsibility of the Solid contaminants are insoluble in fuel. The more common owner/operator. This does not, however, relieve the person types are rust, dirt, sand, gasket material, lint, and fragments doing the fueling of the responsibility to use the correct type of shop towels. The close tolerances of fuel controls and of fuel and safe fueling procedures.

other fuel-related mechanisms can be damaged or blocked by particles as small as ⁄ 20 the diameter of a human hair.

There are two basic procedures when fueling an aircraft.

Smaller aircraft are fueled by the over-the-wing method.

Microbiological growths are a problem in jet fuel. There This method uses the fuel hose to fill through fueling ports are a number of varieties of micro-organisms that can on the top of the wing. The method used for larger aircraft is live in the free water in jet fuel. Some variations of these the single point fueling system. This type of fueling system organisms are airborne, others live in the soil. The aircraft uses receptacles in the bottom leading edge of the wing to fuel system becomes susceptible to the introduction of fill all the tanks. This decreases the time it takes to refuel these organisms each time the aircraft is fueled. Favorable the aircraft, limits contamination, and reduces the chance conditions for the growth of micro-organisms in the fuel of static electricity igniting the fuel. Most pressure fueling are warm temperatures and the presence of iron oxide and systems consist of a pressure fueling hose and a panel of mineral salts in the water. The best way to prevent microbial controls and gauges that permit one person to fuel or defuel growth is to keep the fuel dry. any or all fuel tanks of an aircraft. Each tank can be filled to a predetermined level. These procedures are illustrated in The effects of micro-organisms are: Figures 1-32 and 1-33 .

• Formation of slime or sludge that can foul filters, Prior to fueling, the person fueling must check the following: separators, or fuel controls.

1. Ensure all aircraft electrical systems and electronic • Emulsification of the fuel.

devices, including radar, are turned off.

• Corrosive compounds that can attack the fuel tank’s 2. Do not carry anything in the shirt pockets. These items structure. In the case of a wet wing tank, the tank is could fall into the fuel tanks.

made from the aircraft’s structure. They can also have offensive odors. 3. Ensure no flame-producing devices are carried by anyone engaged in the fueling operation. A moment Fueling Hazards of carelessness could cause an accident.

The volatility of aviation fuels creates a fire hazard that has 4. Ensure that the proper type and grade of fuel is used.

plagued aviators and aviation engine designers since the Do not mix AVGAS and JET fuel.

beginning of powered flight. Volatility is the ability of a liquid 5. Ensure that all the sumps have been drained.

to change into a gas at a relatively low temperature. In its liquid state, aviation fuel does not burn. It is, therefore, the 6. Wear eye protection. Although generally not as critical vapor or gaseous state that the liquid fuel changes that is not as eye protection, other forms of protection, such as only useful in powering the aircraft, but also a fire hazard.

rubber gloves and aprons, can also protect the skin from the effects of spilled or splashed fuel.

Static electricity is a byproduct of one substance rubbing against another. Fuel flowing through a fuel line causes a certain amount of static electricity. The greatest static Color Grade electricity concern around aircraft is that during flight, the Red 80 aircraft moving through the air causes static electricity to build in the airframe. If that static electricity is not dissipated Green 100 prior to refueling, the static electricity in the airframe attempts Blue 100LL to return to the ground through the fuel line from the servicing unit. The spark caused by the static electricity can ignite any Purple 115 vaporized fuel.

Figure 1-31. Aviation gasoline color and grade reference.

1-26 Ground wire Figure 1-32. Refueling an aircraft by the over-the-wing method.

7. Do not fuel aircraft if there is danger of other aircraft in When using mobile fueling equipment: the vicinity blowing dirt in the direction of the aircraft 1. Approach the aircraft with caution, positioning the being fueled. Blown dirt, dust, or other contaminants fuel truck so that if it is necessary to depart quickly, can enter an open fuel tank, contaminating the entire no backing needed.

contents of the tank.

2. Set the hand brake of the fuel truck, and chock the 8. Do not fuel an aircraft when there is lightning within wheels to prevent rolling.

5 miles.

3. Ground the aircraft and then ground the truck. Next, 9. Do not fuel an aircraft within 500 feet of operating ground or bond them together by running a connecting ground radar.

wire between the aircraft and the fuel truck. This may be done by three separate ground wires or by a “Y” 1-27 cable from the fuel truck. is necessary to have a method of collecting the fuel. When the pumping method is used, care must be taken not to 4. Ensure that the grounds are in contact with bare damage the tanks, and the removed fuel cannot be mixed metal or are in the proper grounding points on the with good fuel.

aircraft. Do not use the engine exhaust or propeller as grounding points. Damage to the propeller can result, General precautions when defueling are: and there is no way of quickly ensuring a positive bond between the engine and the airframe. • Ground the aircraft and defueling equipment.

5. Ground the nozzle to the aircraft, then open the fuel • Turn off all electrical and electronic equipment.

tank.

• Have the correct type of fire extinguisher available.

6. Protect the wing and any other item on the aircraft from • Wear eye protection.

damage caused by spilled fuel or careless handling of the nozzle, hose, or grounding wires.

7. Check the fuel cap for proper installation and security before leaving the aircraft.

8. Remove the grounding wires in the reverse order. If the aircraft is not going to be flown or moved soon, the aircraft ground wire can be left attached.

When fueling from pits or cabinets, follow the same procedures as when using a truck. Pits or cabinets are usually designed with permanent grounding, eliminating the need to ground the equipment. However, the aircraft still must be grounded, and then the equipment must be grounded to the aircraft as it was with mobile equipment.

Defueling Defueling procedures differ with different types of aircraft.

Before defueling an aircraft, check the maintenance/service manual for specific procedures and cautions. Defueling can be accomplished by gravity defueling or by pumping the fuel out of the tanks. When the gravity method is used, it Figure 1-33. Single point refueling station of a large aircraft.

1-28

Next: Chapter 2 →

Chapter 2

Regulations, Maintenance Forms,

Records, & Publications

sequential number and has no relevance to the regulation it Overview — Title 14 of the Code of Federal Regulations (14 CFR) is addressing or attached to.

A viation-related regulations that have occurred from 1926– The remainder of this handbook focuses only on those 1966 are reflected in Figure 2-1 . Just as aircraft continue to regulations relative to airworthiness certification. There evolve with ever improving technology, so do the regulations, are 30 of these listed in Figure 2-4 , and they are shown publications, forms, and records required to design, build, graphically in Figure 2-5 . A significant benefit of this chart and maintain them.

is the visual effect showing the interaction of the regulation with other regulations and the placement of the regulation The Federal Aviation Administration (FAA) regulations that relative to its impact on airworthiness. It is fundamentally govern today’s aircraft are found in Title 14 of the Code important that the definition of the term “airworthy” be of Federal Regulations (14 CFR). [Figure 2-2] There are clearly understood.

five volumes under Title 14, Aeronautics and Space. The first three volumes containing 75 active regulations address Only recently did the FAA actually define the term “airworthy” the Federal Aviation Administration. The fourth volume in a regulation. (Refer to the 14 CFR part 3 excerpt following deals with the Office of the Secretary of the Department this paragraph.) Prior to this definition in part 3, the term could of Transportation (Aviation Proceedings) and Commercial be implied from reading part 21, section 21.183. The term was Space Transportation, while the fifth volume addresses the defined in other non-regulatory FAA publications, and could National Aeronautics and Space Administration (NASA) and also be implied from the text found in block 5 of FAA Form Air Transportation System Stabilization.

8100-2, Standard Airworthiness Certificate. This certificate is required to be visibly placed on board each civil aircraft.

These regulations can be separated into the following three (Refer to “Forms” presented later in this chapter.)

categories: 1. Administrative Title 14 CFR Part 3—General Requirements 2. Airworthiness Certification Definitions. The following terms have the stated meanings when used in 14 CFR part 3, section 3.5, Statements about 3. Airworthiness Operation products, parts, appliances and materials.

Since 1958, these rules have typically been referred to as • Airworthy means the aircraft conforms to its type design and is in a condition for safe operation.

“FARs,” short for Federal Aviation Regulations. However, another set of regulations, Title 48, is titled “Federal • Product means an aircraft, aircraft engine, or aircraft Acquisitions Regulations,” and this has led to confusion propeller.

with the use of the acronym “FAR.” Therefore, the FAA • Record means any writing, drawing, map, recording, began to refer to specific regulations by the term “14 CFR tape, film, photograph or other documentary material part XX.” Most regulations and the sections within are odd by which information is preserved or conveyed in any numbered, because the FAA realized in 1958 when the Civil format, including, but not limited to, paper, microfilm, Aeronautics Regulations were recodified into the Federal identification plates, stamped marks, bar codes or Aviation Regulations that it would be necessary to add electronic format, and can either be separate from, regulations later.

attached to or inscribed on any product, part, appliance or material.

Over the years, the FAA has sometimes seen the need to issue Special Federal Aviation Regulations (SFAR). [Figure 2-3] Airworthiness can be divided into two areas: original These are frequently focused very specifically on a unique airworthiness as depicted in Figure 2-5, and recurrent situation and are usually given a limited length of time airworthiness as depicted in Figure 2-6. There are three for effectiveness. Note that the SFAR number is purely a primary regulations that govern the airworthiness of an aircraft: 2-1 HISTORICAL BACKGROUND OF 14 CFR PARTS 23, 25, 27, AND 29 Event Regulating Agency Rules and Regulations Department of Bulletin 7 1926 Commerce Air Commerce Act Aeronautics Branch Bulletin 7-A Civil Air Regulation Bureau of Air Consolidation of CAR Part 04 Commerce Functions CAR 4T CAR 04 1935 Transport <12,500 lb Cutting Air Crash CAR 4b CAR 4a Civil Aeronautics 1938 Large A/C Small A/C Administration Civil Aeronautics Act CAR 3 CAR 4b CAR 4a-T CAR Part 6 Rotorcraft First Helicopter >12,500 lb Certificated Part 7 Part 6 Federal Aviation Transport Normal CAR 4b CAR 3 CAR 4a-T Federal Aviation Act Agency Rotorcraft Rotorcraft >6,000 lb 1956 SR 422 Jets Codification of CARs to FARs SR 422A SR 422B Federal Aviation Agency becomes PART 25 PART 29 PART 27 PART 23 Administration Administration under DOT Comment: Civil Aeronautics Manual (CAMs) contain both regulations and advisory material in the same document.

Figure 2-1. FAA historical background of aircraft airworthiness regulations.

1. 14 CFR part 21—Certification Procedures for Products discusses the FAA as if it was a single unit, it is important to and Parts understand that there are various subgroups within the FAA, and each have different responsibilities of oversight in the 2. 14 CFR part 43—Maintenance, Preventive Maintenance, aviation industry. These may vary by organizational chart or Rebuilding, and Alterations geographic location.

3. 14 CFR part 91—General Operating and Flight Rules The maintenance technician interacts mostly with FAA Note that the chart in Figures 2-5 and 2-6 show most of the personnel from the Flight Standards Service (AFS) and the other airworthiness certification regulations link to one of Flight Standards District Office (FSDO) but may also have these regulations.

some interaction with FAA personnel from the Aircraft Certification Service (AIR).

Although the history section that opens this chapter 2-2 Title 49 Transportation Congressional Act (Acts of Congress are Public Law) Code of Federal Regulations (CFR) (50 Titles) Public Law Basis for Title 14 is PL 103-272 Title 14 Aeronautics and Space (Five Volumes) Volume 3 Volume 4 Volume 5 Volume 1 Volume 2 Chapter I Chapter I Chapter I Chapter II Chapter V Parts 1–59 Parts 60–109 Parts 110–199 Parts 200–399 Parts 1200–1299 FAA, DOT FAA, DOT FAA, DOT O ff ice of Secretary, DOT NASA Subchapter D Subchapter G Subchapter A Subchapter A Chapter VI Airmen Air Carriers and Operators Economic Regulations De fi nitions and Parts 1300–1399 Parts 60, 61, 63, 65, 67, 68 Parts 110, 117, 119, 120, Parts 200–298 Abbreviations Air Transportation 121, 125, 129, 133, 135, Parts 1, 3, 5 System Stabilization Subchapter E 136, 137, 139 Subchapter B Airspace Procedural Regulations Subchapter B Subchapter A Parts 71, 73, 75, 77 Subchapter H Parts 300–331 Procedural Rules O ffi ce of Management Schools and Other Parts 11, 13, 14, 15, 16, and Budget Subchapter F Certi fi cated Agencies Subchapter C 17 Part 1300 Air Tra ff ic and General Parts 141, 142, 145, 147 Reserved Operating Rules Subchapter C Subchapter B Parts 91, 93, 95, 97, 99, Subchapter I Subchapter D Aircraft Air Transportation 101, 103, 105, Airports Special Regulations Parts 21, 23, 25, 26, 27, Stabilization Board 107 Parts 150, 151, 152, 153, Parts 372–383 29, 31, 33, 34, 35, Parts 1310–1399 155, 156, 157, 158, 36, 39, 43, 45, 47, 161, 169 Subchapter E 48, 49 Organization Subchapter J Parts 385, 389 Navigational Facilities Parts 170, 171 Subchapter F Policy Statements Subchapter K Parts 398, 399 Administrative Regulations Chapter III Parts 183, 185, 187, 189, Parts 400–1199 Commercial Space Transportation, FAA Subchapter L–M Reserved Subchapter A Subchapter N General War Risk Insurance Parts 400, 401 Parts 198, 199 Subchapter B Procedure Parts 404, 405, 406 Subchapter C Licensing Parts 411–1199 Figure 2-2. Title 14 of the Code of Federal Regulations.

1.2, Abbreviations and Symbols, tends to be highly focused Maintenance-Related Regulations on those abbreviations related to flight.

14 CFR Part 1—Definitions and Abbreviations This section is a very comprehensive, but certainly not all 14 CFR Part 21—Certification Procedures for inclusive, list of definitions that both pilots and mechanics Products and Articles must become familiar with. Many regulations often provide This regulation, the first of the three, identifies the additional definitions that are unique to their use and requirements of and the procedures for obtaining type interpretation in that specific part. Title 14 CFR part 1, section 2-3 Special Federal Aviation Regulations SFAR No Title Appears in 14 CFR Table of Contents Part 25 13 Special Federal Aviation Regulation No. 23 Part 23 23 Fuel venting and exhaust emission requirements for turbine engine powered airplanes. Part 11 27-5 Special Flight rules in the Vicinity of the Grand Canyon National Park, AZ Part 91 50-2 Removal of this SFAR e ff ective 10/8/2004 - Prohibition Against Certain Flights Between Part 91 65-1 the United States and Libya Special Operating Rules for Air Tour Operators in the State of Hawaii Part 91 71 Robinson R-22/R-44 Special Training and Experience Requirements Part 61 73 Prohibition Against Certain Flights Within the Territory and Airspace of Iraq Part 91 77 Prohibition Against Certain Flights Within the Flight Information Region of the Democratic Part 91 79 People's Republic of Korea Prohibition Against Certain Flights within the Territory and Airspace of Sudan Part 91 82 Prohibition Against Certain Flights Within the Territory and Airspace of Serbia-Montenegro Part 91 84 Airspace and Flight Operations Requirement for the Kodak Albuquerque International Part 91 86 Balloon Fiesta; Albuquerque, NM Fuel Tank System Fault Tolerance Evaluation Requirements Parts 21, 25, 91, 121, 125, 129 88 Special Federal Aviation Regulation No. 97 - Special Operating Rules for the Conduct of Parts 71, 91, 95, 121, 125, 129, 135 97 Instrument Flight Rules (IFR) Area Navigation (RNAV) Operations using Global Positioning Systems (GPS) in Alaska Construction or Alteration in the Vicinity of the Private Residence of the President of the Part 77 98 United States Relief for U.S. Military and Civilian Personnel Who Are Assigned Outside the United States Parts 61, 63, 65 100-2 in Support of U.S. Armed Forces Operations Process for Requesting Waiver of Mandatory Separation Age for Certain Federal Part 65 103 Aviation Administration (FAA) Air Tra ffi c Control Specialists Prohibition Against Certain Flights by Syrian Air Carriers to the United States Part 91 104 Special Federal Aviation Regulation No. 108 - Mitsubishi MU-2B Series Airplane Special Part 91 108 Training, Experience, and Operating Requirements Special Requirements for Private Use Transport Category Airplanes Parts 21, 25, 119 109 Prohibition Against Certain Flights Within the Tripoli (HLLL) Flight Information Region (FIR) Part 91 112 Figure 2-3. Special Federal Aviation Regulations From 14 CFR.

certificates (TCs), supplemental type certificates (STCs), technician in maintaining that part of the aircraft that has been production certificates, airworthiness certificates, and altered since it was new. This ICA is comprised of 16 specific import and export approvals. [Figure 2-5] Some of the subjects. [Figure 2-7] An ICA developed in accordance with other major areas covered in this part are the procedures this checklist should be acceptable to the Aviation Safety for obtaining a Part Manufacture Approval (PMA) or an Inspector (ASI) reviewing a major alteration.

authorization related to producing a Technical Standard Order (TSO) part. Note that part 21’s greatest significance 14 CFR Part 23—Airworthiness Standards: is in the original airworthiness phase, although it has minor Normal, Utility, Acrobatic, and Commuter Category application in recurrent airworthiness. [Figure 2-5] One Airplanes of the most important sections of this regulation is section Aircraft certificated under 14 CFR part 23 represent the 21.50, “Instructions for continued airworthiness and greatest portion of what the industry refers to as “general manufacturer’s maintenance manuals having airworthiness aviation.” These aircraft vary from the small two-place piston limitations sections.” When an aircraft is delivered new from engine, propeller-driven trainers that are frequently used the manufacturer, it comes with maintenance manuals that for flight training, to turbine-powered corporate jets used define the inspection and maintenance actions necessary to to transport business executives. Seating capacity is limited maintain the aircraft in airworthy condition. Also, any STC to nine or less on all aircraft, except the commuter aircraft modification that was developed after 1981 must have, as part where the maximum passenger seating is 19, excluding the of the STC documentation, a complete set of instructions for pilot and copilot seats.

continued airworthiness (ICA). This ICA contains inspection and maintenance information intended to be used by the This part specifies the airworthiness standards that must 2-4

Next: Part 1 De fi nitions and Abbreviations →

Section 6

criteria for the design of these aircraft. The first, subpart A, Part 1 De fi nitions and Abbreviations defines the applicability of this regulation. The others are: Part 13 Investigative and Enforcement Procedures Part 21 Certi fi cation Procedures for Products and Parts • Subpart B—Flight Part 23 Airworthiness Standards: Normal, Utility, Acrobatic, and • Subpart C—Structures Commuter Category Airplanes Part 25 Airworthiness Standards: Transport Category Airplanes • Subpart D—Design and Construction Part 27 Airworthiness Standards: Normal Category Rotorcraft • Subpart E—Powerplant Part 29 Airworthiness Standards: Transport Category Rotorcraft • Subpart F—Equipment Part 31 Airworthiness Standards: Manned Free Balloons Part 33 Airworthiness Standard: Aircraft Engines • Subpart G—Flightcrew Interface and Other Information Part 34 Fuel Venting and Exhaust Emission Requirements for Turbine Engine Powered Airplanes Within each of these subparts are numerous sections that Part 35 Airworthiness Standards: Propellers specify details, such as center of gravity (CG), gust load Part 36 Noise Standards: Aircraft Type and factors, removable fasteners, the shape of certain flight Airworthiness Certi fi cation deck controls, engine and propeller requirements, fuel tank Part 39 Airworthiness Directives markings, flight deck instrumentation marking and placards, Part 43 Maintenance, Preventive Maintenance, Rebuilding, and cabin aisle width, and flammability resistant standards.

Alteration Part 45 Identi fi cation and Registration Marking 14 CFR Part 25—Airworthiness Standards: Transport Part 47 Aircraft Registration Category Airplanes Part 48 Registration and Marking Requirements for Small Unmanned Aircraft The standards in 14 CFR part 25 apply to large aircraft with Part 61 Certi fi cation: Pilots, Flight Instructors, and Ground a maximum certificated takeoff weight of more than 12,500 Instructors pounds. This segment of aviation is usually referred to as Part 63 Certi fi cation: Flight Crewmembers Other Than Pilots “commercial aviation” and includes most of the aircraft Part 65 Certi fi cation: Airmen Other Than Flight Crewmembers seen at a large passenger airport, except for the commuter Part 68 Requirements for Operating Certain Small aircraft included in 14 CFR part 23. However, the ability to Aircraft Without a Medical Certi fi cate carry passengers is not a requirement for aircraft certified Part 91 General Operating and Flight Rules to 14 CFR part 25. Many of these aircraft are also used to Part 107 Small Unmanned Aircraft Systems transport cargo. This chapter is subdivided into similar design Part 119 Certi fi cation: Air Carriers and Commercial Operators subpart categories and the same sequence as the requirements Part 121 Operating Requirements: Domestic, Flag, and specified in 14 CFR part 23.

Supplemental Operations Part 125 Certi fi cation and Operations: Airplanes Having a 14 CFR Part 27—Airworthiness Standards: Normal Seating Capacity of 20 or More Passengers or a Maximum Payload Capacity of 6,000 Pounds or More; Category Rotorcraft and Rules Governing Persons on Board Such Aircraft This regulation deals with the small rotor wing aircraft and is Part 135 Operating Requirements: Commuter and On Demand consistent with 14 CFR part 23 with limiting the passenger Operations and Rules Governing Persons on Board Such Aircraft seating to nine or less. However, the maximum certificated weight is limited to 7,000 pounds. It contains similar design Part 145 Repair Stations Part 147 Aviation Maintenance Technician Schools subparts identified in 14 CFR part 23 that provide the details for designing the aircraft.

Part 183 Representatives of the Administrator Figure 2-4. List of FAA regulations relative to airworthiness 14 CFR Part 29—Airworthiness Standards: Transport certification.

Category Rotorcraft This section specifies those standards applicable to helicopters be met in order for a manufacturer to receive a TC and with a maximum certified weight greater than 7,000 pounds.

for the aircraft to receive an airworthiness certificate.

However, it also includes additional parameters based upon Part 23 aircraft are those aircraft that have a maximum seating capacity and an additional weight limit. Those certificated takeoff weight of 12,500 pounds or less, except parameters are passenger seating, (nine or less, ten or more) for those aircraft in the commuter category. The maximum and whether the helicopter is over or under a maximum certificated takeoff weight limit rises to 19,000 pounds or weight of 20,000 pounds. The design subparts of part 29 are less for these aircraft.

similar to those in 14 CFR parts 23, 25, and 27.

Part 23 has seven subparts, six of them providing detailed 2-5

Aircraft

Original Airworthiness

Certi fi cation

Aircraft Certi fi cation Certi fi cate Management Manufacturing Inspection

O ffi ce (ACO) O ffi ce (CMO) District O ffi ce (MIDO) Service (AIR)—

General Operating and Flight Rules 14 CFR §91.319 14 CFR §91.409 Investigative and Enforcement 13 Procedures Manufacturer 43.3(j) Airworthiness Standards: Normal, Utility, Acrobatic, and Commuter Category Airplanes 8110.42 PMA Parts Manufacturing Certi fi cation Approval Procedures for Airworthiness Standards: 25 Products and Parts TC Transport Category Airplanes STC Continued Airworthiness and Safety Improvements for TSOA Transport Category Airplanes §21.8(d) Airworthiness Standards: Normal Category Rotorcraft Identi fi cation and Registration Marking §21.9(a)(5) Owner Operator Built Parts Airworthiness Standards: Transport Category Rotorcraft Airworthiness Standards: Manned Free Balloons DMIR 8110.37 Aircraft Registration DER Guidance DER Airworthiness Standards: Handbook Aircraft Engines DAR Fuel Venting and Exhaust Emission DAS Requirements for Turbine Engine Powered Airplanes DAR Representatives of the Administrator Airworthiness Standards: DPE 35 Propellers DME 8100.8 Noise Standards: Designee Management Handbook Aircraft Type and DPRE Airworthiness Certi fi cation 8130.2 Airworthiness Certi fi cation Airworthiness Directives 8132.2 Designee Airworthiness Certi fi cation Suspected Unapproved Parts Program FAA ORDERS: 8100.7, ACSEP 2150.3 8110.4, Type Certi fi cation Compliance & Enforcement 8120.2, Production Approvals Figure 2-5. Graphic chart of FAA regulations.

2-6

Recurrent Airworthiness

Flight Standards

Certi fi cate Management Flight Standards International

Service (AFS)—

O ff ice (CMO) District O ffi ce (FSDO) Field O ffi ce (IFO) Certi fi cation Certi fi cation: Procedures for 61 Pilots and Flight Instructors Products and Parts Subpart H, L, K Certi fi cation: Flight Crewmembers Other Than Pilots § 43.5 No person may Certi fi cation: Airmen Other Than Flight approve for return Crewmembers to service, unless...

91 43

§ 43.5 A&P IA Dispatcher Maintenance General Operating Maintenance, record entry and Flight Rules Preventive Parachute Rigger Repairman required by §43.9 Maintenance, or §43.11, as Rebuilding, and Alteration appropriate Certi fi cation: Air Carriers and Commercial Operators 14 CFR 43 Appendix B § 43.13a FAA Form 337 Certi fi cation and Operation: Methods, techniques, Domestic, Flag, and Identi fi cation and and practices in Supplemental Air Carriers and Registration Marking Commercial Operators of current manufacturer’s § 43.13b Large Aircraft maintenance manuals Work and materials of such a quality that condition will be at least Certi fi cation and Operations: equal to the original or Airplanes Having a Seating property altered 125 Capacity of 20 or More condition Passengers or a Maximum Payload Capacity of 6,000 Aircraft Registration DMIR Pounds or More 8110.37 DER Guidance DER 8400.10 Deviation Handbook DAR Air Taxi Operators and ODA Representatives of Commercial Operators the Administrator DAR 9 or Less 10 or More DPE 8100.8 Designee Management Handbook DME Repair Stations 8130.2 Airworthiness Certi fi cation DPRE 8132.2 Operating Repair Station Designee Airworthiness Certi fi cation Speci fi cations Manual Suspected Unapproved Parts Program Drug and Alcohol 2150.3 FAA ORDERS: Testing Program Compliance & Enforcement 8900.1 FSIMS Figure 2-6. Graphic chart of FAA regulations (continued).

2-7 14 CFR Part 33—Airworthiness Standards: Aircraft in this handbook.

Engines 14 CFR Part 45—Identification and Registration Each of the four preceding 14 CFR regulations require that the Marking engine used in the aircraft must be type certificated. Title 14 CFR part 33 details the requirements for both reciprocating Title 14 of the CFR part 45 includes the requirements for and turbine style aircraft engines. It not only specifies the the identification of aircraft, engines, propellers, certain design and construction requirements, but also the block test replacement and modification parts, and the nationality and requirements that subject the engine to extremely demanding registration marking required on U.S.-registered aircraft. All testing in order to prove its capability of enduring the stresses type-certificated products must have the following information of powering the aircraft. on a fireproof dataplate or similar approved fireproof method.

1. Builder’s name 14 CFR Part 35—Airworthiness Standards: Propellers 2. Model designation Just as each engine used on an aircraft must have a TC, the 3. Builder’s serial number propeller must also be type certificated. This part is arranged the same way that 14 CFR part 33 is, in that subpart B 4. TC number (if any) specifies design and construction while subpart C covers 5. Production certificate number (if any) tests and inspections.

6. For aircraft engines, the established rating Since regulations change over the years, not every aircraft 7. Reference to compliance or exemption to 14 CFR Part presently flying meets the current design regulations 34, Fuel Venting and Exhaust Emission Requirements as printed this year. When regulations are revised, they for Turbine Engine Powered Airplanes are printed in the Federal Register and released with an 8. Any other information that the FAA determines to be amendment number that ties them to the regulation being appropriate revised. Aircraft are required to meet only the specifications in force at the time the aircraft is built. Note: The preceding Replacement and modification parts are produced in statement does not apply to the mandatory requirements accordance with a Parts Manufacturer Approvals (PMA) (14 imposed by Airworthiness Directives (AD), as these usually CFR part 21, section 21.303) and must have the following have a compliance date included in the AD note.

information permanently and legibly marked: 14 CFR Part 39—Airworthiness Directives 1. The letters “FAA-PMA” In spite of all the emphasis on proper design and certification 2. The name, symbol, or trademark of the holder of the testing, sometimes the actual day-to-day use of the aircraft PMA causes unanticipated wear or failure to occur. When that 3. The part number happens, if the FAA determines that the wear or failure 4. The name and model designation for each type represents an unsafe condition and that the condition is likely certificated product it can be installed on to exist in other products of the same type of design, it issues an AD. Actual AD notes are not included in 14 CFR part 39, If a part has a specified replacement time, inspection interval, but rather are printed in the Federal Register and are linked or other related procedure specification in the maintenance to this part as amendments to 14 CFR part 39, section 39.13.

manual or ICA, that part must have a part number and a serial AD notes are legally enforceable rules that apply to aircraft, number (or the equivalent of each).

aircraft engines, propellers, and appliances.

The manufacturer of a life-limited part must either provide 14 CFR Part 43—Maintenance, Preventive marking instructions for that part, or state that the part cannot Maintenance, Rebuilding, and Alteration be marked without a compromise to its integrity. Exceptions This regulation represents the heart of aviation maintenance are made for the identification of parts that are too small to and is one of the three major regulations previously identified.

be practical to mark the required data.

The 13 rules and 6 appendices contained within 14 CFR part 43 provide the standard for maintaining all civilian aircraft Nationality and registration marks (commonly known as currently registered in the United States. Note that 14 CFR the N-number for U.S.-registered aircraft) can vary in size, part 43 has a significant relationship with part 91 and other depending on the year that the aircraft was built and whether parts in maintaining continued airworthiness. [Figure 2-6] A or not the aircraft has been repainted. The most common size more detailed explanation of this regulation is presented later is at least 12 inches in height. Small aircraft built at least 30 2-8 ITEM SUBJECT 1. Introduction: Briefly describes the aircraft, engine, propeller, or component that has been altered. Include any other information regarding the content, scope, purpose, arrangement, applicability, definitions, abbreviations, precautions, units of measurement, list of parts used, referenced publications, and distribution of the ICA, as applicable.

2. Description: Of the major alteration and its functions, including an explanation of its interface with other systems, if any.

Control, operation information: Or special procedures, if any.

4. Servicing information: Such as types of fluids used, servicing points, and location of access panels, as appropriate.

Maintenance instructions: Such as recommended inspection/maintenance periods in which each of the major alteration components are inspected, cleaned, lubricated, adjusted, and tested, including applicable wear tolerances and work recommended at each scheduled maintenance period. This section can refer to the manufacturers’ instructions for the equipment installed where appropriate (e.g., functional checks, repairs, inspections). It should also include any special notes, cautions, or warnings, as applicable.

6. Troubleshooting information: Describes probable malfunctions, how to recognize those malfunctions, and the remedial actions to take.

7. Removal and replacement information: Describes the order and method of removing and replacing products or parts, and any necessary precautions. This section should also describe or refer to manufacturer’s instructions to make required tests, checks, alignment, calibrations, center of gravity changes, lifting, or shoring, etc., if any.

8. Diagrams: Of access plates and information, if needed, to gain access for inspection.

Special inspection requirements: Such as X-ray, ultrasonic testing, or magnetic particle inspection, if required.

10. Application of protective treatments: To the affected area after inspection and/or maintenance, if any.

11. Data: Relative to structural fasteners such as type, torque, and installation requirements, if any.

12. List of special tools: Special tools that are required, if any.

13. For commuter category aircraft: Provide the following additional information, as applicable: A. Electrical loads

B. Methods of balancing flight controls SAMPLE

C. Identification of primary and secondary structures D. Special repair methods applicable to the aircraft 14. Recommended overhaul periods: Required to be noted on the ICA when an overhaul period has been established by the manufacturer of a component or equipment. If no overhaul period exists, the ICA should state for item 14, “No additional overhaul time limitations.” 15. Airworthiness limitation section: Includes any “approved” airworthiness limitations identified by the manufacturer or FAA Type Certificate Holding Office (e.g., An STC incorporated in a larger field-approved major alteration may have an airworthiness limitation). The FAA inspector should not establish, alter, or cancel airworthiness limitations without coordinating with the appropriate FAA Type Certificate Holding Office. If no changes are made to the airworthiness limitations, the ICA should state for item 15, “No additional airworthiness limitations” or “Not Applicable.” 16. Revision: Includes information on how to revise the ICA. For example, a letter will be submitted to the local FAA Office with a copy of the revised FAA Form 337 and revised ICA.

The FAA inspector accepts the change by signing block 3 and including the following statement: “The attached revised/new Instructions for Continued Airworthiness (date______) for the above aircraft or component major alteration have been accepted by the FAA, superseding the Instructions for Continued Airworthiness (date______).” After the revision has been accepted, a maintenance record entry will be made, identifying the revision, its location, and date on the FAA Form 337.

Figure 2-7. Instructions for Continued Airworthiness (ICA) Checklist.

2-9 expiration date of the new battery. years ago, or replicas of these, or experimental exhibition or amateur-built aircraft may use letters at least 2 inches in height.

2. Section 91.213—Inoperative Instruments and Only a few aircraft are authorized to display registration Equipment markings of at least 3 inches. Note that this regulation sits Paragraph (a)(2)—a letter of authorization from the directly on the vertical line in Figure 2-5 indicating that it FSDO authorizing the operation of the aircraft under applies to both original and recurrent airworthiness.

a Minimum Equipment List (MEL) constitutes a STC and must be carried in the aircraft during flight.

14 CFR Part 47—Aircraft Registration This regulation provides the requirements for registering Subpart E—Maintenance, Preventive Maintenance, and aircraft. It includes procedures for both owner and dealer Alterations (Sections 91.401 through 91.421) registration of aircraft.

This is the section of most interest to the technician. They must be familiar with it, because it does carry some (indirect) 14 CFR Part 65—Certification: Airmen Other Than responsibility for the technician. Note that the 14 CFR part 91 Flight Crewmembers icon in Figure 2-6 has a direct line to 14 CFR part 43. This Pilots, flight instructors, and ground instructors are is because section 91.403(b) states, “No person may perform certificated under 14 CFR part 61. Flight crew other than maintenance, preventive maintenance, or alterations on an pilots are certificated under 14 CFR part 63. However, aircraft other than as prescribed in this subpart and other many other people are also required to be certificated by applicable regulations, including part 43 of this chapter.” the FAA for the U.S. aviation fleet to operate smoothly and A more complete discussion of this regulation, especially efficiently. Title 14 CFR part 65 addresses many of those Subpart E—Maintenance, Preventive Maintenance, and other people.

Alterations is presented later in this chapter.

• Subpart B—Air Traffic Control Tower Operators 14 CFR Part 119—Certification: Air Carriers and • Subpart C—Aircraft Dispatchers Commercial Operators • Subpart D—Mechanics In order to better understand the next three regulations • Subpart E—Repairmen discussed here (14 CFR parts 121, 125, and 135) a brief • Subpart F—Parachute Riggers overview of 14 CFR part 119 is beneficial. [ Figure 2-8] There are more than 50 Advisory Circulars (ACs) in the 120 A more detailed discussion of this chapter with a special series alone providing additional non-regulatory information concerning the variety of procedures involved with these emphasis on mechanics is included in Chapter 15, The Mechanic Certificate.

operations. There are basically three different criteria that must be analyzed in order to properly determine the Note: SFAR 100-2. Relief for U.S. Military and Civilian regulation that applies. These are: Personnel who are assigned outside the United States in 1. Is the service provided for Private Carriage or support of U.S. Armed Forces Operations is a good example Common Carriage?

of the specific nature and limited time frame that are part of 2. Is the aircraft For Hire or is it Not for Hire?

a SFAR.

3. Is it a large or small aircraft?

14 CFR Part 91—General Operating and Flight Rules AC 120-12, as revised, provides the following definition This is the final regulation of the three major regulations regarding this criterion: A carrier becomes a common carrier identified earlier in this chapter. Note its interaction in when it “holds itself out” to the public, or to a segment of the Figure 2-6 with other regulations visually indicating its public, as willing to furnish transportation within the limits “operational” involvement or “recurrent airworthiness.” of its facilities to any person who wants it. There are four Although it is an operational regulation that is focused elements in defining a common carrier: toward the owner, operator, and/or pilot of the aircraft, the maintenance technician must have an awareness of this 1. A holding out of a willingness to regulation. Two examples of these maintenance related 2. Transport persons or property issues are: 3. From place to place 1. Section 91.207—Emergency Locator Transmitters 4. For compensation Paragraph (c)(2)—battery replacement interval and requirement for a logbook entry indicating the 2-10 This “holding out” that makes a person a common carrier can 9. Parachute operations on nonstop flights within 25 NM be done in many ways, and it does not matter how it is done.

from the departure airport Signs and advertising are the most direct means of “holding 10. Fractional ownership in accordance with 14 CFR part out,” but are not the only ones.

91, subpart K Carriage for hire which does not involve "holding out" is 14 CFR Part 121—Operating Requirements: private carriage. Private carriers for hire are sometimes Domestic, Flag, and Supplemental Operations called “contract carriers,” but the term is borrowed from the Title 14 CFR part 121 establishes the operational rules for air Interstate Commerce Act and legally inaccurate when used carriers flying for compensation or hire. A domestic operation in connection with the Federal Aviation Act. Private carriage is any scheduled operation (within the 48 contiguous states, for hire is carriage for one or several selected customers, the District of Columbia, or any territory or possession) generally on a long-term basis. The number of contracts conducted with either a turbo-jet aircraft, an airplane having must not be too great; otherwise, it implies a willingness to 10 or more passenger seats, or a payload capacity greater make a contract with anybody. A carrier operating pursuant than 7,500 pounds.

to 18 to 24 contracts has been held to be a common carrier, because it held itself out to serve the public generally to the A “flag” operation means any scheduled operation (operating extent of its facilities. Private carriage has been found in in Alaska or Hawaii to any point outside of those states, or cases where three contracts have been the sole basis of the to any territory or possession of the United States, or from operator’s business.

any point outside the United States to any point outside the United States) conducted with either a turbo-jet aircraft, an Operations that constitute common carriage are required to airplane having 10 or more passenger seats, or a payload be conducted under 14 CFR part 121 or 135. Private carriage capacity greater than 7,500 pounds.

may be conducted under 14 CFR part 91 or 125.

“Supplemental” operation means any common carriage The term “for hire” is not defined in any of the FAA documents operation conducted with airplanes having more than 30 but is generally understood to mean that compensation for passenger seats (if less than 30, the airplane must also be both direct and indirect expenses associated with the flight, listed on the operations specifications of domestic and flag as well as a profit margin for the operator, are collected from carriers), with a payload capacity of more than 7,500 pounds.

the person or persons benefiting from the flight operation.

Part 121 operators are required by 14 CFR part 119 to have The determination of whether the aircraft is large or small is the following personnel: based upon the definition provided in 14 CFR part 1. If the • Director of Safety aircraft has maximum certificated takeoff weight of 12,500 pounds or more, it is a large aircraft. All aircraft less than 12,500 maximum certificated takeoff weight are considered 14 CFR Part 119 Applicability of Regulations to be small aircraft.

91, 125, 135, 121 It may also help the reader understand when 14 CFR parts 121, 125, and 135 regulations apply, by taking a brief look at a list of flight operations where 14 CFR part 119 does not apply.

CFR Part 91, CFR Part 119, Section 119.5 Section 91.501(b)(5) 1. Student instruction 2. Nonstop sightseeing flights with less than 30 seats and Common Carriage Private Carriage less than 25 nautical miles (NM) from the departure airport For Hire Not for Hire 3. Ferry or training flights Large A/C Large A/C Small A/C Small A/C Large A/C Large A/C 4. Crop dusting or other agricultural operations 5. Banner towing All Other A/C 6. Aerial photography or surveying 135 121 125 91 7. Fire fighting 8. Powerline or pipeline patrol Figure 2-8. Applicability of regulations.

2-11 • Director of Operations • Any other item that the administrator determines is necessary • Director of Maintenance • Chief Pilot Just as in 14 CFR part 121, subpart E identifies special airworthiness requirements dealing mostly with the • Chief Inspector mechanical devices of the aircraft.

There are 28 subparts and 16 appendices in this regulation.

However, only subparts J and L are of concern for the mechanic. 14 CFR Part 135—Operating Requirements: Subpart J—Maintenance, Preventive Maintenance, and Commuter and On-Demand Operations and Rules Alterations, identifies Special Airworthiness Requirements Governing Persons on Board Such Aircraft that deals with many of the mechanical aspects of a passenger As the title of this section states, this regulation is applicable or cargo aircraft. Subpart L—Maintenance, Preventive to short distance commercial aircraft operations or Maintenance, and Alterations, requires that a part 121 “commuters” and nonscheduled carriers that operate “on- operator have an operational manual that contains the demand.” These aircraft are frequently referred to as air taxi following information: or air charter aircraft.

• Organizational chart Aircraft operated under 14 CFR part 135 must be operated • List of individuals who may perform required and maintained in accordance with the certificate holder’s inspections operations manual. This manual, when accepted by the • Company maintenance, preventive maintenance, or FAA, specifies how the flight crew, ground personnel, and alterations maintenance technicians conduct their operations.

• A system to both preserve and retrieve maintenance A pivotal portion of this regulation is the first section in and inspection related information subpart J, 14 CFR part 135, section 135.411, Application.

This section specifies that having a type certificated passenger Also, 14 CFR part 121, section 121.1105, establishes the seating configuration of nine or less may be maintained in requirement for conducting inspections on aging aircraft.

accordance with the maintenance manual provided by the aircraft manufacturer. Those aircraft having a type certificated 14 CFR Part 125—Certification and Operations: passenger seating configuration of 10 or more seats must be Airplanes Having a Seating Capacity of 20 or More maintained in accordance with a maintenance manual written Passengers or a Maximum Payload Capacity of 6,000 by the air carrier and must then be submitted to the FAA for Pounds or More; and Rules Governing Persons on approval. The requirements for the maintenance manual are Board Such Aircraft specified in 14 CFR part 135, section 135.427. 14 CFR part This regulation applies to private and noncommon carriage 135, sections 135.415 through 135.417 and 135.423 through when such operations are conducted in airplanes having 135.443 specify additional maintenance requirements. 14 20 or more seats (excluding crewmembers) or having a CFR part 135, sections 135.415 and 135.417 are applicable payload capacity of 6,000 pounds or more. There must also regardless of the number of seats in the aircraft.

be “operations specifications” issued to the operator that include the following information: A major change in the “nine or less” aircraft maintenance • Kinds of operations authorized requirements occurred in February of 2005 when section 135.422, Aging Aircraft, was incorporated into 14 CFR part • Types of aircraft and registration numbers of the 135. This new subpart (note the even number) to 14 CFR airplanes authorized for use 135 specifically prohibits a certificate holder from operating • Approval of the provisions of the operator’s manual certain aircraft unless the Administrator has completed the relating to airplane inspections, together with the aging aircraft inspection and records review. This inspection necessary conditions and limitations requires the certificate holder to show the FAA that the maintenance of age sensitive parts and components has been • Registration numbers of the airplanes that are to be inspected under an approved airplane inspection adequate to ensure safety.

program (AAIP) under 14 CFR part 125, section 125.247 This section only applies to multi-engine aircraft in scheduled operation with nine or fewer passenger seats. It does not • Procedures for the control of weight and balance of apply to aircraft operating in Alaska. The required record airplanes review start date varies depending on the age of the aircraft.

2-12 However, once initiated, the repetitive inspection intervals • Procedures governing work done at another location are not to exceed 7 years.

• Procedures for working on air carrier aircraft • Description of the required records and record keeping The certificate holder must make both the aircraft and the records available to the FAA for inspection and review. The • Procedures for revising the repair station manual certificate holder must notify the Administrator at least 60 • Description of the system to identify and control the days in advance of the availability of the aircraft and the sections of the manual records for review.

All records from repair station maintenance activity must The records must include the following information: be kept a minimum of 2 years. Domestic repair station 1. Total years in service of the airplane certificates are effective until they are surrendered, suspended, or revoked. The certificates of foreign repair stations expire, 2. Total time in service of the airframe usually after 1 or 2 years and must be renewed.

3. Date of the last inspection and records review required by this section 14 CFR Part 147—Aviation Maintenance Technician 4. Current status of life-limited parts Schools Title 14 CFR part 147 defines the requirements for obtaining 5. Time since the last overhaul of all structural a maintenance training certificate. This certificate may be for components required to be overhauled on a specific either airframe, powerplant, or a combination of the two. The time basis minimum number of curriculum hours for conducting either 6. Current inspection status of the airplane, including the airframe or powerplant training independently is 1,150.

time since the last inspection required by the inspection program that the airplane is maintained under If both A&P ratings are offered, the combined total curriculum 7. Current status of applicable ADs, including the date hours are 1,900. This is because of the 1,150 hours specified and methods of compliance, and, if the AD involves to obtain either the airframe or the powerplant rating, 400 recurring action, the time and date when the next hours are devoted to general studies. Only one set of general action is required studies hours is applicable to the combined total. Therefore, 400 hours can be subtracted from the implied total of 2,300 8. A list of major structural alterations hours (1,150 × 2) to obtain the reduced figure of 1,900 hours.

9. A report of major structural repairs and the current Requirements are detailed as follows: inspection status of those repairs • Appendix A—Curriculum Requirements 14 CFR Part 145—Repair Stations • Appendix B—General Curriculum Subjects This regulation underwent a major rewrite released in 2004 • Appendix C—Airframe Curricular Subjects and was the most comprehensive change in nearly 20 years.

• Appendix D—Powerplant Curriculum Subjects It may be of interest to note an airframe and powerplant (A&P) certificate is not necessary to be employed at a repair 14 CFR Part 183—Representatives of the Administrator station. The repair station may also employ both repairmen As the aviation industry grows and the design, manufacture, (under 14 CFR part 65, subpart E) and non FAA-certificated and testing of aircraft gets more complex, the FAA faces personnel. All work that is signed off is done so using the both budget constraints and personnel shortages. As early repair station certificate number and must be done only by as 1962, the FAA began a program to allow private sector persons authorized by 14 CFR part 65 to approve an article persons in various areas of industry to be “designees” or for return to service (RTS). Just as other certificate holders “representatives of the FAA Administrator.” These people must have an operations manual, the repair station must have are NOT FAA employees, but rather are designated by the a repair station manual that contains the following: FAA to act on their behalf. Regular doctors may serve as • An organizational chart “aviation medical examiners,” skilled pilots can become • Procedures for maintaining rosters “pilot examiners,” and experienced airframe and/or powerplant mechanics can become “designated mechanic • Description of housing, facilities, and equipment examiners (DME)” to administer the oral and practical • Procedures for revising the capability list and portion of the FAA testing.

conducting a self-evaluation (audit) • Procedures for revising the training program Other lesser known designees are the designated engineering 2-13 representatives (DER), the designated manufacturing • Inspected inspection representatives (DMIR), and the designated • Repaired, as necessary airworthiness representatives (DAR).

• Reassembled • DERs approve data based upon their engineering • Tested training and their knowledge of FAA regulations.

• DMIRs make conformity inspections only at their The key difference between the two terms is in determining employer. They are similar to “designated repairmen” how the item is tested. If it is “tested in accordance with because they are only authorized to inspect parts at approved standards acceptable to the Administration that their employers’ facility.

have been developed and documented by the manufacturer, • DARs conduct aircraft certification and aircraft the item is said to be overhauled.” This is basically another inspection functions on behalf of the FAA depending way of describing “service limits,” a term frequently used to on specific functions they are authorized. They may describe manufacturer specified acceptable limits for used perform work for either manufacturing facilities or parts. A “rebuilt item, on the other hand, must be tested to maintenance entities depending on their designation. the same tolerances and limits as a new item.” Explanation of Primary Regulations (Parts 43 Section 43.3—Persons authorized to perform and 91) maintenance, preventive maintenance, rebuilding, and alterations 14 CFR Part 43—Maintenance, Preventative Maintenance Rebuilding, and Alteration There are nine different persons who may perform Section 43.1—Applicability maintenance: (Reminder: Per 14 CFR part 1, the FAA definition of a person is “an individual, firm, partnership, Paragraph (a) states quite clearly that aircraft (whether U.S.- corporation, association, joint-stock association, or or foreign-registered operating under 14 CFR part 121 or governmental entity. It includes a trustee, receiver, assignee, 135) and component parts thereof must be maintained in or similar representative of any of them.”) accordance with the rules set forth in this part. Although paragraph b states quite clearly the type of aircraft that this 1. Certificated mechanic, per 14 CFR part 65 part does not apply to, it seems to have led to considerable 2. Certificated repairman, per 14 CFR part 65 confusion within the aviation industry. If an aircraft is flying 3. Person working under the supervision of a certificated with a Special Airworthiness—Experimental Certificate mechanic or repairman (FAA Form 8130-7, Special Airworthiness Certificate—pink color certificate) and that is the only airworthiness certificate 4. Holder of repair station certificate this aircraft has ever had, then 14 CFR part 43 does not apply.

5. Holder of an air carrier certificate Conversely, sometimes during maintenance (especially STC 6. Except for holders of a sport pilot certificate, the modification—the STC is addressed later in this chapter), holder of a pilot certificate issued under part 61 it becomes necessary to temporarily place the aircraft into may perform preventive maintenance on any aircraft Special Airworthiness—Experimental. This is done to show owned or operated by that pilot which is not used compliance with federal regulations. These aircraft must under 14 CFR part 121, 129, or 135. The holder still be maintained in accordance with 14 CFR part 43, of a sport pilot certificate may perform preventive because the aircraft had a different kind of airworthiness (in maintenance on an aircraft owned or operated by that this example a Standard) prior to being issued the Special pilot and issued a special airworthiness certificate in Airworthiness Certificate. the light-sport category.

7. Pilot of a helicopter (when operated under 14 CFR Section 43.2—Records of Overhaul and Rebuilding part 135 and in remote areas) may perform specific These terms are not defined in 14 CFR part 1 and are given preventive maintenance actions. These actions may full explanation in this subpart. Each term states that it may only be accomplished under the following conditions: not be used to describe work done on an aircraft, airframe, • The mechanical difficulty or malfunction aircraft engine, propeller, appliance, or component part unless occurred en route to or in the remote area.

that item has been: • The pilot has been satisfactorily trained and is • Disassembled • Cleaned 2-14 authorized in writing by the certificate holder to work that to be performed constitutes a major or a minor perform the required maintenance. maintenance action. A “major” action is typically one that might appreciably affect weight, balance, structural strength, • There is no certificated mechanic available.

performance, powerplant operation, flight characteristics, • The certificate holder has procedures to evaluate or other qualities affecting airworthiness and that are not the work performed when a decision for done according to accepted practices or cannot be done airworthiness is required. The work done is listed by elementary operations. This is a much more complex in paragraph (c) of Appendix A of this chapter.

question, but it is extremely important as it drives the final question concerning the substantiating documentation. Please 8. Holder of part 135 certificate may allow pilots of refer to 14 CFR part 1 and part 43, appendix A, for additional aircraft with nine or less passenger seats to remove and clarification and examples.

reinstall cabin seats and stretchers and cabin mounted medical oxygen bottles. These actions may only be The third question deals with the type of documentation accomplished under the following conditions: required to substantiate the work performed. Minor repairs • The pilot has been satisfactorily trained and is and alterations need only to refer to “acceptable” data, such authorized in writing by the certificate holder to as manufacturers’ maintenance manuals or AC 43.13-1.

perform the required maintenance.

The maintenance action can simply be recorded in the • The certificate holder has written procedures maintenance record as a logbook entry. Major repairs and available to the pilot to evaluate the work alterations require “approved data.” Some examples of performed.

approved data are AD notes, STCs, TCDS, DER-specific delegations, and FAA-approved manufacturer Service 9. Manufacturer may inspect and rebuild any item it has Bulletins (SB).

manufactured.

Sometimes the repair or alteration being performed does not Section 43.5—Approval for return to service after have previously-approved data. In that case, the technician maintenance, preventive maintenance, rebuilding, may request that the FAA accomplish a “Field Approval.” and alterations In this procedure, the technician completes the front side of Approving an aircraft component for return to service Form 337 through block 6 (leaving block 3 open for later after maintenance, preventive maintenance, rebuilding, FAA approval) and then indicates in block 8 on the back what or alteration must be done by creating an appropriate work is to be done and what the substantiating reference data maintenance record entry as required by either 14 CFR part is. Form 337 is then submitted to the local FAA FSDO office 43, section 43.9 or 43.11. This may include the use of FAA for review and approval by an ASI. If necessary, this ASI may Form 337, Major Repair and Alteration, if the maintenance seek input from other ASIs or FAA specialists to assist in the action was a major repair or a major alteration. Whenever review of the data. If the data is found to comply with FAA a maintenance action is being planned, it is critical that the regulations, the ASI enters one of the following statements technician understands exactly: in block 3, depending on whether the ASI has performed 1. What he/she is going to do.

a review of the data only or has physically inspected the aircraft: 2. How that work is classified by the FAA.

• “The technical data identified herein has been found 3. What type of documentation is required to support to comply with applicable airworthiness requirements this activity.

and is hereby approved for use only on the above described aircraft, subject to conformity inspection by First consider whether this a repair or an alteration. This a person authorized in 14 CFR part 43, section 43.7.” should be a relatively simply decision since a repair basically returns the aircraft to its previous or unaltered or condition (i.e., replacing magnetos, an exhaust system, tires, • “The alteration or repair identified herein complies or brakes). Even replacing an entire engine (although it is with the applicable airworthiness requirements and a big job) is still a repair if it is the one properly specified is approved for use only on the above described for that aircraft. An alteration on the other hand, always aircraft, subject to conformity inspection by a person changes or modifies the aircraft from its previous state (i.e., authorized in 14 CFR part 43, section 43.7.” installing winglets, new avionics, or an engine that is not listed in the aircraft TCDS).

The second question to consider is whether or not the 2-15

Next: Section 43.7—Persons authorized to approve aircraft, other than the person who approves the RTS →

Section 7

Section 43.7—Persons authorized to approve aircraft, other than the person who approves the RTS airframes, aircraft engines, propellers, appliances, —the signature, certificate number, and type of or component parts for return to service after certificate of the person who is approving the maintenance, preventive maintenance, rebuilding, work for RTS or alteration There are seven different persons listed in this section who Note: Frequently, logbooks have a statement entered that ends may sign RTS documentation: something like this: “ … and is hereby returned to service. Joe Fixer A&P, Certificate #123456789.” As this section of the 1. Certificated mechanic or holder of an inspection regulation currently reads, that part of the record entry is not authorization (IA).

required. Title 14 of the CFR part 43, section 43.9 clearly states 2. Holder of a repair station certificate.

that “the signature constitutes the approval for return to service only for the work performed.” Furthermore, the technician 3. Manufacturer.

is only signing off the work they have done. Later, 14 CFR 4. Holder of an air carrier certificate.

part 43, section 43.11 explains that an inspection write-up 5. Certificated private pilot.

usually carries a broader scope of responsibility. This section is very clear that the entry completed in accordance with this 6. Repairman certificated with a maintenance rating for section only holds the technician responsible for the service light sport aircraft (LSA) only.

maintenance action they entered.

7. Certificated sport pilot for preventive maintenance on an aircraft owned and or operated by them.

If the maintenance accomplished was a major repair or alteration, the work must be documented on FAA Form 337 Note that although a certificated repairman is authorized and requires supporting approved data. If the maintenance to work on a product undergoing maintenance, preventive action was a major repair and it was done by a certificated maintenance, rebuilding, or alterations (refer to 14 CFR repair station, a signed copy of the completed customer work part 43, section 43.3), they are not authorized to approve order accompanied by a signed maintenance release may be that product for RTS. They must make the appropriate used in lieu of the FAA Form 337.

maintenance record entry per the requirements of 14 CFR part 43, section 43.9 or 43.11.

Section 43.10—Disposition of Life-Limited Aircraft Parts Section 43.9—Content, form and disposition of (Note the even number again. This regulation became part maintenance, preventive maintenance, rebuilding, of 14 CFR part 43 in 2002.)

and alteration records (except inspection performed in accordance with parts 91 and 125, and sections This section presents two terms not previously defined in 135.411(a)(1) and 135.419 of this chapter) 14 CFR: The first observation is that this section specifically 1. Life-limited part means any part that has specified a excludes inspection entries (those are covered in 14 CFR mandatory replacement limit.

part 43, section 43.11). This section deals exclusively with maintenance record entries.

2. Life status means the accumulated cycles, hours, or any other mandatory limit of a life-limited part.

The next observation is that the list of maintenance actions includes “preventive maintenance.” As stated in the This section then goes on to specify what to do with parts explanation of 14 CFR part 43, section 43.3, a certificated that are temporarily removed from and then reinstalled on pilot is authorized to perform preventive maintenance on the a type-certificated product; what to do with parts that are aircraft they own or operate. Therefore, remember that the removed from a type certified product and not immediately pilot must make a record entry of the preventive maintenance reinstalled; and how to transfer life-limited parts from one they have accomplished. There are three distinct issues to type-certificated product to another.

be addressed in the maintenance entry and they answer the questions of “what?, when?, and who?” When a life-limited part is removed, the person removing it from the type-certificated product must control the part and • What—a description of the work performed ensure proper tracking of the life-limiting factor. This is to • When—the date the work was completed prevent the installation of the part after it has reached its life • Who—the name of the person who did the work if limit. There are seven possible methods the technician or repair facility may choose from to comply with this requirement.

2-16 1. Recordkeeping “routine inspection” and a “detailed inspection.” Refer to explanatory text of 14 CFR part 43, section 43.15 for 2. Tagging a definition of these terms. Inspections accomplished in 3. Non-permanent marking accordance with other inspection program requirements must identify that particular program and that part of the 4. Permanent marking program the inspection completed.

5. Segregation 6. Mutilation Section 43.12—Maintenance Records: Falsification, Reproduction, or Alteration 7. Any other method approved or accepted by the FAA The aviation community relies heavily on trust and honesty When a life-limited part is transferred, the information in both oral and written communication. The maintenance concerning the life status of that part must be transferred log entries described in 14 CFR part 43, sections 43.9 with it. Although regulations already did exist that required and 43.11 provide the documentation trail relied upon the tracking of life-limited parts when they were installed by aircraft owners, pilots, and technicians regarding the on an aircraft, this regulation was generated to govern the aircraft’s maintenance history. Falsification of these records disposition of such parts when they were removed from is potentially dangerous to the personnel who rely on the the aircraft.

accuracy of these records.

Section 43.11—Content, form, and disposition of This section identifies that fraudulent entries are unacceptable.

records for inspections conducted under parts 91 If someone commits such an act, that action is the basis for and 125, and sections 135.411(a)(1) and 135.419 of suspension or revocation of the appropriate certificate, authorization, or approval. A technician who is encouraged this chapter by their employer, or by anyone else, to falsify records in This section deals exclusively with inspection record any way should remember this comment: “Companies come entries; however, the requirements are similar to 14 CFR and go, but my signature lasts a lifetime. I will not use it part 43, section 43.9 in that information of what, when, and inappropriately.” who is required.

• What—type of inspection, including a brief description Section 43.13—Performance Rules (General) • When—date of the inspection and the total time in This section deals with the specific requirements for service conducting maintenance. ( Note: This section best reflects the relationship between the FAA’s numbering of ACs and • Who—the signature, certificate number, and kind of the regulations they are related to.) Paragraph 3 on the cover certificate of the person approving or disapproving page of AC 43.13-2B, Acceptable Methods, Techniques, and the RTS Practices—Aircraft Alterations, dated March 3, 2008 states: Since this is an inspection write-up and not a maintenance “Title 14 of the Code of Federal Regulations (14 CFR) part entry, it is quite possible that the inspecting technician could 43, section 43.13(a) states that each person performing reject or disapprove the item being inspected for the RTS.

maintenance, alteration, or preventive maintenance on When that situation occurs, the regulation states in paragraph an aircraft, engine, propeller, or appliance must use the (b) that a list of discrepancies must be given to the owner.

methods, techniques, and practices prescribed in the current A reference to this list and its delivery to the aircraft owner manufacturer’s maintenance manual or Instructions for must be reflected in the record entry. Although the regulation Continued Airworthiness prepared by its manufacturer, or neither specifies how those discrepancies can be cleared, nor other methods techniques or practices acceptable to the who may do them, any appropriately-rated repair station or Administrator, except as noted in section 43.16.” [Figure 2-9] certificated technician can perform the required maintenance actions. When they are completed and the proper maintenance Although not all ACs are linked this directly, there is a definite record entries are generated in accordance with 14 CFR part relationship between ACs and companion regulations. Refer 43, section 43.9, the aircraft is approved for RTS. It is neither to this chapter on ACs for additional information.

necessary to have an additional inspection, nor is it necessary to contact the disapproving inspector.

Aircraft maintenance technicians (AMTs) are highly skilled personnel, because aviation maintenance work requires great If the aircraft is on a progressive inspection program, the attention to detail. The complexity of technology on today’s inspection statement changes slightly from the statement aircraft demands a significant level of communication to referenced earlier by adding the reference to both a 2-17 is the result of breaking down the large task of properly accomplish maintenance, preventive maintenance, conducting a major inspection into smaller tasks that rebuilding, or alteration. This communication frequently can be accomplished periodically without taking the comes in written form (i.e., manufacturer’s maintenance aircraft out of service for an extended period of time.)

manuals or ICA). If neither of these documents provide the Two new definitions are also presented: “routine” and guidance the technician needs to perform maintenance, either “detailed.” A routine inspection is a visual examination AC 43.13 (AC 43.13-1 or AC 43.13-2) contain examples or check of the item, but no disassembly is required.

of “other methods, techniques, or practices acceptable to A detailed inspection is a thorough examination of the Administrator” that may be sufficient. However, these the item, including disassembly. The overhaul of a ACs specifically state that the information is applicable to component is considered to be a detailed inspection.

non-pressurized areas of civil aircraft weighing 12,500 lb gross weight or less.

If the aircraft is away from the station where inspections are normally conducted, an appropriately In addition to the documentation, the technician must also use rated mechanic, a certificated repair station, or the the proper tools, equipment, and test apparatus that ensures manufacturer of the aircraft may perform inspections that the work complies with accepted industry practices.

in accordance with the procedures and using the If the test equipment specified by the manufacturer is not forms of the person who would otherwise perform available, equipment that is determined to be equivalent and the inspection.

acceptable to the Administrator may be used. The technician should be cautious, however, as “proving” the equivalence of Section 43.16 — Airworthiness Limitations test equipment may not be as simple as it seems.

The technician performing inspection or maintenance actions on an aircraft must be certain they have all appropriate data Air carriers (commercial—“scheduled” airlines operating available. Each person performing an inspection or other under 14 CFR part 121, the “commuter/on demand” aircraft maintenance specified in an Airworthiness Limitations section operating under 14 CFR part 135, and foreign air carriers of a manufacturer's maintenance manual or Instructions for and operators of U.S.-registered aircraft under 14 CFR Continued Airworthiness shall perform the inspection or part 129) may use the maintenance manual required by the other maintenance in accordance with that section, or in operations specifications to comply with the requirements accordance with operations specifications approved by of this section. The operator must provide a continuous the Administrator under part 121 or 135, or an inspection airworthiness maintenance and inspection program program approved under 14 CFR part 91, section 91.409(e).

acceptable to the Administrator.

ICAs, as required by 14 CFR part 21, section 21.50, must also be consulted when available. Since 1998, the FAA Section 43.15 — Additional Performance Rules for has required ICAs to be generated for all major alterations Inspections that are accomplished by the field approval process. This This section presents general comments concerning the section specifies that the technician is responsible to perform responsibility of conducting an inspection and then provides inspections or maintenance specified in an airworthiness details of three separate conditions. They are rotorcraft, limitation in accordance with all the preceding instructions.

annual and 100-hour inspections, and progressive inspections.

Section 43.17—Maintenance, preventive maintenance, 1. Rotorcraft—If a rotorcraft is being inspected, specific items, such as rotor transmissions and drive shafts, or alterations performed on U.S. aeronautical must be inspected. products by certain Canadian persons This section was significantly revised in 2005, as the result 2. Annual and 100-hour inspections—When performing of a Bilateral Aviation Safety Agreement (BASA) between an annual or 100-hour inspection, a checklist must the United States and Canada. This section of 14 CFR be used. This checklist may be a personal one or one part 43 defines some terms and gives specific limitations from the manufacturer. Either way, it must include as to what an Aircraft Maintenance Engineer (AME is the scope and detail of the inspection in Appendix D.

the Canadian equivalent to the U.S. A&P) may do to Specific engine performance is also required to be maintain U.S.-registered aircraft located in Canada. It also tested (or monitored) as part of RTS for an annual or provides similar limitations for an Approved Maintenance 100-hour inspection. This applies whether the aircraft Organization. (AMO is the Canadian equivalent to the U.S.- is reciprocating or turbine powered.

certified repair stations.)

3. Progressive inspection—If a progressive inspection is being conducted, it must be preceded by a complete Appendix A—Major Alterations, Major Repairs, and aircraft inspection. ( Note: A progressive inspection 2-18

Advisory

U.S. Department of Transportation Federal Aviation Administration

Circular

Subject: Acceptable Methods, Date: 3/3/08 AC No: 43.13-2B Techniques, and Practices – Aircraft Initiated by: AFS-300 Alterations 1. PURPOSE. This advisory circular (AC) contains methods, techniques, and practices acceptable to the Administrator for the inspection and alteration on non-pressurized areas of civil aircraft of 12,500 lbs gross weight or less. This AC is for use by mechanics, repair stations, and other certificated entities. This data generally pertains to minor alterations; however, the alteration data herein may be used as approved data for major alterations when the AC chapter, page, and paragraph are listed in block 8 of FAA Form 337 when the user has determined that it is: a. Appropriate to the product being altered, b. Directly applicable to the alteration being made, and c. Not contrary to manufacturer’s data.

2. CANCELLATION. AC 43.13-2A, Acceptable Methods, Techniques, and Practices ― Aircraft Alterations, dated January 1, 1977, is canceled.

3. REFERENCE. Title 14 of the Code of Federal Regulations (14 CFR) part 43, § 43.13(a) states that each person performing maintenance, alteration, or preventive maintenance on an aircraft, engine, propeller, or appliance must use the methods, techniques, and practices prescribed in the current manufacturer’s maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer, or other methods, techniques, or practices acceptable to the Administrator, except as noted in § 43.16. FAA inspectors are prepared to answer questions that may arise in this regard. Persons engaged in the inspection and alteration of civil aircraft should be familiar with 14 CFR part 43, Maintenance, Preventive Maintenance, Rebuilding, and Alterations, and part 65, subparts A, D, and E of Certification: Airmen Other than Flight Crewmembers, and applicable airworthiness requirements under which the aircraft was type-certificated.

4. COMMENTS INVITED. Comments regarding this AC should be directed to DOT/FAA: ATTN: Aircraft Maintenance Division, 800 Independence Ave., SW., Washington, DC 20591, FAX (202) 267-5115.

ORIGINAL SIGNED By James J. Ballough Director Flight Standards Service Figure 2-9. AC 43.13-2B Excerpt.

2-19

Next: Appendix C—(Reserved) →

Section 8

Preventive Maintenance Appendix C—(Reserved) This appendix provides a comprehensive, but not exclusive, list of subjects. For instance, paragraph (a) is titled Major Appendix C is reserved for future use and therefore currently Alteration, and is further subdivided as follows: contains no information.

• Airframe Appendix D—Scope and Detail of Items To Be • Powerplant Included in Annual and 100-Hour Inspections • Propeller Some important items to consider in this appendix are: • Appliance 1. The list of items and areas to be inspected are exactly the same for an annual as a 100-hour inspection.

This same subdivision is used in paragraph (b), Major The difference between the inspections is in who is Repairs. Paragraph (c), Preventive Maintenance, identifies authorized to perform and approve the aircraft for RTS those maintenance actions that are defined as preventive following the inspection. Refer to 14 CFR part 65, maintenance, provided the maintenance does not involve section 65.95(a)(2) that states that an IA must perform complex assembly operations. Preventive maintenance work an annual inspection.

may be accomplished by the holder of at least a private pilot 2. The aircraft and engine must be cleaned prior to certificate provided they are the owner or operator of that conducting the inspection.

aircraft, and it is not operated under 14 CFR part 121, 129, 3. Any miscellaneous item not covered in the detailed or 135.

list provided must also be inspected for improper installation and operation.

Appendix B—Recording of Major Repairs and Major Alterations 4. There are eight specific areas identified for detailed In most cases when a major repair or alteration is inspection. They are the fuselage hull group, cabin/ accomplished, FAA Form 337, Major Repair or Alteration, flight deck group, engine/nacelle group, landing is completed at least in duplicate with the original going gear group, wing/center section group, empennage to the aircraft owner and a copy sent to the FAA Aircraft assembly, propeller group, and the radio group.

Registration Branch in Oklahoma City where all civil aircraft information is compiled and retained. Note: Historically, Appendix E—Altimeter System Test and Inspection the second copy was sent to the local FAA FSDO within 48 This is commonly referred to as “the 411 test.” Refer to 14 CFR hours after RTS. This copy is reviewed by an ASI and then part 91, section 91.411 that requires that no person may operate forwarded by the FSDO to FAA records in Oklahoma City.

an aircraft in controlled airspace under IFR unless the aircraft However, in the fall of 2005, the FAA made a significant has had this test completed successfully within the preceding change to this submittal process and now requires the 24 months.) This section requires detailed testing of the static technician to submit the Form 337 directly to the Aircraft pressure system, the altimeter, and the automatic pressure Registration Branch in Oklahoma City. Although a third altitude reporting equipment, and that the test information be copy is not required, it makes good business sense for the recorded in the maintenance logs and on the altimeter.

technician or certified repair station to keep a copy of the work that was accomplished.

Appendix F—ATC Transponder Tests and Inspections However, if a certificated (part 145) repair station completes This is commonly referred to as “the 413 test.” (Refer to 14 a major repair, it may provide the customer with a signed CFR part 91, section 91.413, which requires that no person copy of the work order and a maintenance release signed may use a transponder unless it has had this test completed by an authorized representative of the repair station, instead successfully within the preceding 24 months.)

of the FAA Form 337. If the major repair or alteration was done by an AME or AMO, the copy normally provided This section specifies complex sets of tests, which may be to the FAA-FSDO is sent directly to the FAA Aircraft accomplished either as a bench test or by using portable Registration Branch.

test equipment. Major categories of the testing required are radio reply frequency, suppression, receiver sensitivity, radio However, if extended range tanks are installed in either frequency peak output power, and mode S (when applicable).

passenger or cargo compartments, the technician must Upon completion of testing, proper entries must be made in generate a third FAA Form 337 for the modification. This the maintenance record.

copy must be placed and retained in the aircraft. (Refer to 14 CFR part 91, section 91.417(d).)

2-20

Next: Subpart A—General →

Subpart A—General

14 CFR Part 91—General Operating and Flight Rules have been approved for RTS and a proper entry made in the maintenance records. If the maintenance that was done Subpart A—General could have appreciably changed the flight characteristics, an As mentioned in the brief overview of the regulation portion appropriately rated pilot must perform an operational flight earlier in this chapter, this part is actually addressing the check of the aircraft and must make an entry of the flight in operation of the aircraft. For example, 14 CFR part 91, section the maintenance records. If ground testing and inspection can 91.7(a) states “no person may operate a civil aircraft unless it show conclusively that the maintenance has not adversely is in an airworthy condition.” We learned earlier that this term affected the flight characteristics, no flight test is required.

means that the aircraft conforms to its approved type design and is in condition for safe operation. When the pilot performs Section 91.409—Inspections a preflight inspection, they are making a determination This paragraph identifies various types of inspection concerning the “condition for safe operation.” The pilot does applicable to the civilian aircraft fleet. Paragraph (a) defines not usually determine “conformity to type design” unless the requirement for an annual inspection. However, there are they perform a review of the maintenance records. However, certain exceptions to this regulation: since that is fundamental to the definition of airworthy, it is still part of their responsibility. Therefore, a professional 1. An aircraft that carries a special flight permit, a current and ethical technician wants to help the customer understand experimental certificate, or a light-sport or provisional their responsibilities in maintaining and documenting the airworthiness certificate; airworthiness of the aircraft.

2. An aircraft inspected in accordance with an approved aircraft inspection program under part 125 or 135 Subpart E—Maintenance, Preventive Maintenance, of this chapter and so identified by the registration and Alterations number in the operations specifications of the Section 91.401—Applicability certificate holder having the approved inspection Although this subpart describes in general the rules regarding program; maintenance, preventive maintenance, and alteration, certain 3. An aircraft subject to the requirements of paragraph sections do not apply if the aircraft is operated in accordance (d) or (e) of this section; or with 14 CFR part 121, 125, 129, or 135.

4. Turbine-powered rotorcraft when the operator elects to inspect that rotorcraft in accordance with paragraph Section 91.403—General (e) of this section.

The owner/operator holds the primary responsibility for maintaining the aircraft in airworthy condition. This Annual inspections are usually the inspection method includes compliance with all applicable ADs and is the associated with small “general aviation” aircraft. If this same reason that the FAA sends new AD notes to the registered aircraft is used for hire (including flight instruction for hire), owners of the affected aircraft. All maintenance performed then the aircraft must also be inspected every 100 hours of must be accomplished in accordance with 14 CFR part 43.

time in service. This requirement for a 100-hour inspection Compliance with the appropriate manufacturer maintenance to be conducted on an aircraft may be exceeded by as much manuals and ICA is also required. Mandatory replacement as 10 hours if the aircraft is en route to reach a facility that times, inspection intervals, and related procedures as outlined will be conducting the inspection. Any time accrued between in the FAA - approved operations specifications must also be 100 and 110 hours is subtracted from the hours remaining complied with.

before the next 100-hour inspection.

Since aircraft used for hire only generate revenue when they Section 91.405—Maintenance Required are flying, any time that the aircraft is “down for inspection” The owner/operator is required to have the appropriate can result in a loss of income for the owner/operator.

inspections made, and to have discrepancies repaired in Therefore, the FAA has made provision to minimize the accordance with part 43. They are also required to ensure that impact of the 100-hour and annual inspection requirement.

the appropriate entries have been made in the maintenance The owner/operator may petition the local FSDO for approval records. Any inoperative instruments or equipment must be of a progressive inspection program. This program breaks properly placarded as inoperative.

the complete inspection of the aircraft into smaller, less time-consuming steps. (Refer to 14 CFR part 43, Appendix Section 91.407—Operation after maintenance, preventive D.) This inspection may be either performed or supervised maintenance, or alteration by a technician holding an IA. The program must ensure at Whenever the aircraft has undergone maintenance, all times that the aircraft is airworthy. The owner/operator preventive maintenance, rebuilding or alteration, it must must submit an inspection schedule with their application 2-21 to the FAA. This schedule must identify the time intervals that the system was tested is the maximum altitude that (hours or days) when routine and detailed inspections are to the aircraft can be flown instrument flight rules (IFR) in be accomplished. (Refer to 14 CFR part 43, section 43.15.) controlled airspace.

Just as with the 100-hour inspection, a 10-hour maximum extension of a specified inspection interval is allowed if the Section 91.413—ATC Transponder Tests and Inspections aircraft is en route. A change in the inspection interval is also This “413 test” is the other test required every 24 months.

allowed for changes in service experience. If the progressive Whenever the ATC transponder is installed or has undergone inspection is discontinued, the aircraft is again subject to the maintenance, the complete system must be tested and inspected traditional annual and 100-hour inspections.

in accordance with Appendix E of 14 CFR part 43. The transponder itself must be tested and inspected in accordance Other inspection programs that may be applicable to other with Appendix F of 14 CFR part 43. As with the 411 test, aircraft are a continuous airworthiness inspection program only certain persons are authorized to conduct the tests. They and an approved aircraft inspection program (AAIP).

are the manufacturer of the aircraft, a properly certificated The former program is applicable to either a part 121 or repair station, or the holder of a continuous airworthiness 135 carrier, but the latter program is limited to part 135 maintenance program under 14 CFR part 121 or 135.

operators only. Finally, the owner/operator may use either a current inspection program recommended by the aircraft Section 91.415—Changes to Aircraft Inspection Programs manufacturer or one established by the owner/operator and If the FAA determines that the inspection program established approved by the local FSDO. Any subsequent changes to that and approved under either 14 CFR part 91, section 91.409 program must also be approved by the local FSDO.

or 91.1109 must be revised to ensure continued safety and adequacy of the program, the owner/operator must make There may be an instance when the operator of an aircraft the necessary changes as identified by the Administrator.

wishes to change from one type of inspection program to If the owner/operator desires to contest this request, they another. In that case, the time in service, calendar times, or must petition the FAA to reconsider their request to change cycles of operation from the current program must be carried the program within 30 days of receiving the change request over to the subsequent program.

from the FAA.

Section 91.411—Altimeter System and Altitude Reporting Section 91.417—Maintenance Records Equipment Tests and Inspections The understanding and implementation of this section Commonly referred to as “the 411 test,” this section specifies is fundamental to the aircraft industry, in general, and the requirements for testing the static pressure system, each the aircraft owner/operator, in specific. A professional altimeter instrument, and each automatic pressure altitude maintenance technician must be knowledgeable of this reporting system every 24 calendar months. The static system section and be able to help the owner/operator understand it.

must also be tested any time it has been “opened and closed,” [Figure 2-10] This section identifies four types of records— except for the normal use of the system drain and alternate two are quite specific (paragraphs a and d) and two are more static system pressure valves. If the automatic pressure general: (a)(1) and (a)(2). Paragraph (a) refers to the 411 and altitude reporting system of the air traffic control (ATC) 413 testing that requires testing every 24 months. Therefore, transponder is either installed or subjected to maintenance records must be kept for that length of time. Paragraph (d) actions, the system must also be tested per Appendix E of refers to the installation of fuel tanks in the cabin or cargo 14 CFR part 43.

area. The FAA Form 337 authorizing this installation must be kept on board the aircraft all the time.

Due to the inherent design and accuracy of this system, only the aircraft manufacturer, a properly-rated repair station, or a Note: Other than this paragraph, there is no requirement certificated airframe mechanic may perform these tests. The that the maintenance records of the aircraft be carried on the airframe technician may only perform the inspection and test aircraft. In fact, there are very logical reasons to not do so in of the static pressure system. Calibration and maintenance most cases. The two biggest concerns are damaged or lost of related instruments is specifically prohibited to the records. It is much safer to retain the logs in a filing system technician by the language of 14 CFR part 65, section 65.81 in the office. It is also a very wise idea to have the logbook and specifically allowed in 14 CFR part 145, section 145.59 copied or scanned and retained at a separate location should for repair stations holding an instrument rating.

a catastrophic event (fire, flood, tornado, hurricane, and so forth) occur at the site the original records are retained.

TSO’d items are considered to be “tested and inspected” as of the date they were manufactured. The maximum altitude Subparagraph (a)(1) then lists those records that are later 2-22 defined in (b)(1) as being retained for 1 year or until the The Civil Air Regulations (CARs) were part of the original work is repeated or superseded. Subparagraph (a)(2) specifies certification basis for aircraft first certified in the 1940s, the records that are permanent records and are identified 1950s, and 1960s by the Civil Aviation Authority (CAA).

in subparagraph (b)(2) as those that must be transferred Therefore, the CARs may still be needed as a reference for with the aircraft. Refer to the chart for further clarification. these older aircraft or as a standard for minor changes to older [Figure 2-10] aircraft designs. [Figure 2-11] Paragraph (c) requires that all of the maintenance records CAR 3—Airplane Airworthiness—Normal, Utility, Aerobatic, and Restricted Purpose Categories mandated by this section be made available upon request to the Administrator or any authorized representative of As the name implies, this specific regulation is the basis for the NTSB. Furthermore, the owner/operator must provide the current 14 CFR part 23 regulation [ Figure 2-1 ]. It has the Form 337 required to be aboard the aircraft whenever the following subpart categories: additional fuel tanks are installed in either the passenger • A—Airworthiness Requirements compartment or the baggage compartment, per paragraph • B—Flight Requirements—General (d), to any law enforcement officer upon request.

• C—Strength Requirements—General Section 91.419—Transfer of Maintenance Records • D—Design and Construction—General When an aircraft is sold, it is logical that the records are • E—Powerplant Installations—Reciprocating Engines transferred with it. They may be either in plain language or coded. The purchaser may elect to permit the seller to retain • F—Equipment the actual records; however, if that occurs the purchaser (now the current owner/operator) must still make these records Some examples of CAR 3 aircraft are Piper PA 22, PA 28, available to either the FAA or the NTSB upon request. PA 32, and Cessna 182, 195, and 310.

Section 91.421—Rebuilt Engine Maintenance Records Note: The “CAR” acronym actually has two interpretations: Civil Air Regulations and Canadian Aviation Regulations.

This section presents the term “zero time.” Although not The technician must clearly understand the difference and truly given as a definition, the wording of the regulation is recognize when one or the other is appropriate.

very clear that an aircraft engine, when rebuilt by the engine manufacturer or an agency approved by the manufacturer, CAR 4a—Airplane Airworthiness may be given a new maintenance record showing no This regulation was originated in 1936 and last amended on previous operating history. This new record must include a December 15, 1952. The subparts included in this regulation signed statement with the date it was rebuilt, any changes are: incorporated by compliance with AD notes, and compliance with any of the manufacturer’s SB.

• A—Airworthiness Requirements • B—Definitions Civil Air Regulations (CAR) • C—Structural Loading Conditions, General Structural Prior to 1926, access to flying was uncontrolled. No licensing Requirements or certification was required. By the middle of the 1920s, it became obvious that unregulated private and commercial • D—Proof of Structure flying was dangerous. There was a growing awareness • E—Detail Design and Construction and acceptance that regulation could improve safety and • F—Equipment encourage growth in aviation. Therefore in 1926, the aviation industry requested Congress to enact federal legislation to • G—Powerplant Installation regulate civil aviation. Thus, the Air Commerce Act of 1926 • H—Performance provided for the: • I—Miscellaneous Requirements 1. Establishment of airways.

2. Development of aviation aids.

Initially, this regulation was the basis for establishing the design requirements for virtually all produced aircraft in the 1930s, 3. Investigation of aviation accidents.

1940s, and 1950s. Eventually CAR 3 evolved as the regulatory 4. Licensing of pilots.

material specific to small aircraft, and CAR 4a and b focused on 5. Certification of aircraft.

regulatory requirements for large aircraft.

2-23 It is very important to review the TCDS for each aircraft. Current contact information for submitting a SUP Notification For example, The Cessna 140 was certified as a landplane can be found at www.faa.gov.

under CAR 3, but under CAR 4a as a ski-plane or seaplane.

Another example of a more current and larger aircraft is the Other FAA Documents Gulfstream 1159 and 1159A. The former is certified under Advisory Circulars (AC) CAR 4b, but the latter is certified to 14 CFR part 25.

AC refers to a type of publication offered by the FAA to provide guidance for compliance with airworthiness Suspected Unapproved Parts (SUP) regulations. They provide guidance such as methods, There are four types of aircraft parts: procedures, and practices acceptable to the Administrator for complying with regulations. ACs may also contain 1. Good parts with good paperwork.

explanations of regulations, other guidance material, best 2. Good parts with bad paperwork.

practices, or information useful to the aviation community.

3. Bad parts with “good” (bogus) paperwork. They do not create or change a regulatory requirement. The AC system became effective in 1962. It provides a single, 4. Bad parts with bad paperwork.

uniform, agency-wide system that the FAA uses to deliver advisory material to FAA customers, industry, the aviation The first of those listed represents properly authorized parts that, community, and the public.

when properly installed, are approved parts, and the aircraft can be returned to service. The last of those listed represent Unless incorporated into a regulation by reference, the unauthorized and unapproved parts. The technician should content of ACs are not binding on the public. ACs are be alert for these and must never install them on an aircraft.

issued in a numbered-subject system corresponding to the subject areas of the FARs (14 CFR, Chapter 1, Federal The center two categories of parts represent suspected Aviation Administration) and Chapter 3, Commercial Space unapproved parts. If either the physical part or the paperwork Transportation, Federal Aviation Administration, Department associated with the part is questionable, it is best to contact of Transportation, Parts 400–450. An AC is issued to provide the shop foreman, shift supervisor, or the assigned quality guidance and information in a designated subject area or to individual to discuss your concerns. Suspected unapproved show a method acceptable to the Administrator for complying parts (SUPs) should be segregated and quarantined until with a related federal aviation regulation.

proper disposition can be determined. Contacting the manufacturer of the product is a good way to start gathering Because of their close relationship to the regulations, ACs are the facts concerning the product in question. Refer to the arranged in a numbered system that corresponds to the subject current version of AC 21-29, Detecting and Reporting areas of the CFRs. In some series, consecutive numbers may Suspected Unapproved Parts, for additional information.

14 CFR 91.417 Maintenance Records Sections 91.411 and 91.413. Paragraph (d): FAA Form 337 for extended range paragraph (a): Retain for 2 years. fuel tanks in cabin or cargo. Keep on board A/C.

Paragraph (a)(1): Maintenance, Paragraph (a)(2): Records of total time in Paragraph (b)(3) List of defects Preventive Maintenance, service for A/F, each engine, each propeller furnished to the Owner/Operator Alterations and all Inspections. and each rotor. Currents status of life-limited in accordance with Section 43.11.

parts of A/F engine, prop, rotor, or app.

Time since last overhaul for items that are Description of work. Retained until defects are required to overhaul.

Date of completion. repaired and the A/C is approved Current inspection status.

Signature and Certi fi cate Number for RTS.

Current status of applicable ADs.

of person approving RTS.

Copies of Form 337.

Paragraph (b)(2): Retain and transfer with A/C.

Figure 2-10. Maintenance records.

2-24 Predecessor Regulations to the Federal Aviation Regulations (14 CFR) Aeronautical Bulletins 7A Airworthiness Requirements for Aircraft 7F Airworthiness Requirements for Aircraft Components and Accessories 7G Airworthiness Requirements for Engines and Propellers 7H Alteration and Repair of Aircraft 7J Special Requirements for Air Line Aircraft 14 Relative Lift Distribution in Any Biplane Requirements for Approved Type Certi fi cates 26 Design Information for Aircraft Civil Air Regulations (CAR) CAR 1 Certi fi cation, Identification, and Marking of Aircraft and Related Products CAR 2 Aircraft Identi fi cation Mark CAR 3 Airplane Airworthiness—Normal, Utility, Acrobatic, and Restricted Purpose Categories CAR 4a Airplane Airworthiness CAR 4b Airplane Airworthiness: Transport Categories CAR 6 Rotorcraft Airworthiness: Normal Category CAR 7 Rotorcraft Airworthiness: Transport Categories CAR 8 Aircraft Airworthiness: Restricted Category CAR 9 Aircraft Airworthiness: Limited Category CAR 10 Certi fi cation and Approval of Import Aircraft and Related Products CAR 13 Aircraft Engine Airworthiness CAR 14 Aircraft Propeller Airworthiness Maintenance, Repair, and Alteration of Certi fi cated Aircraft and of Aircraft Engines, Propellers and Instruments CAR 18 CAR 40 Scheduled Interstate Air Carrier Certi fi cation and Operation Rules Special CAR 425-C Provisional Certi fi cation and Operation of Aircraft Special CAR 406 Application of Transport Category Performance Requirements to C-46 Type Aircraft Civil Aeronautics Manual (CAM) Certi fi cation, Identification, and Marking of Aircraft and Related Products CAM 1 CAM 2 Production Certi fi cates CAM 3 Airplane Airworthiness: Normal, Utility, and Acrobatic Categories CAM 4a Airplane Airworthiness CAM 4b Airplane Airworthiness: Transport Categories CAM 6 Rotorcraft Airworthiness CAM 7 Rotorcraft Airworthiness: Transport Categories CAM 8 Aircraft Airworthiness: Restricted Category CAM 9 Aircraft Airworthiness: Limited Category Certi fi cation and Approval of Import Aircraft and Related Products CAM 10 CAM 13 Aircraft Engine Airworthiness CAM 14 Aircraft Propeller Airworthiness CAM 18 Maintenance, Repair, and Alteration of Airframes, Powerplants, Propellers, and Appliances Figure 2-11. Predecessor Regulations to the Federal Aviation Regulations (14 CFR).

2-25 be missing. These numbers were either assigned to ACs all substantive comments received with the rule perhaps being still in preparation that will be issued at a later date or were changed as warranted by the comments. The preamble to the assigned to ACs that have been canceled. final rule AD provides response to the substantive comments or states there were no comments received.

The AC Numbering System In certain cases, the critical nature of an unsafe condition There are three parts to an AC number, as in 25-42-C.

may warrant the immediate adoption of a rule without prior • The first part of the number identifies the subject notice and solicitation of comments. This is an exception to matter area of the AC. This corresponds to the part the standard process. If time for the terminating action to of the FAA’s regulations. In the above example, this be accomplished is too short to allow for public comment would be part 25.

(that is, less than 60 days), then a finding of impracticability • The second part of the number, beginning with the is justified for the terminating action, and it can be issued dash, is a sequential number within each subject area.

as an immediately adopted rule. The immediately adopted In the above example, this would be the 42nd AC rule is published in the Federal Register with a request for relating to part 25.

comments. The Final Rule AD may be changed later if substantive comments are received.

• The third part of the number is a letter assigned by the originating office showing the revision sequence An Emergency AD is issued when an unsafe condition exists if an AC is revised. The first version of an AC does that requires immediate action by an owner/operator. The not have a revision letter. In the above example, this is intent of an Emergency AD is to rapidly correct an urgent third revision, as designated by the “C.” [Figure 2-12] safety deficiency. An Emergency AD may be distributed by fax, letter, or other methods. It is issued and effective to Airworthiness Directives (AD) only the people who actually receive it. This is known as In accordance with 14 CFR part 39, the FAA issues ADs in “actual notice.” All known owners and operators of affected response to deficiencies and/or unsafe conditions found in U.S.-registered aircraft, or those aircraft that are known to aircraft, engines, propellers, or other aircraft parts. ADs require have an affected product installed, are sent a copy of an that the relevant problem must be corrected on all aircraft or Emergency AD. To make the AD effective to all persons, a aircraft parts using the same design. ADs are initiated as either follow up publication of the Final Rule AD in the Federal proposed, corrective, or final (telegraphic) via the Federal Register is critical. This Final Rule AD must be identical to Register. The Federal Register is the official daily publication the Emergency AD and is normally published in the Federal of the United States Government. It is the printed method of Register within 30 days of the Emergency AD issue.

informing the public of laws that are enacted or will be enacted.

Electronic versions of ADs are available from the Federal AD Content Register and from the Regulatory and Guidance Library. You can search by manufacturer, model, or AD number. All ADs Generally, ADs include: are “incorporated by reference” into part 39 and are considered • A description of the unsafe condition final. ADs must be followed to remain in compliance with • The product that the AD applies to the FAA. Once an AD has been issued, a person/company is authorized to use the affected aircraft or part only if it has been • The required corrective action or operating limitations corrected in accordance with the AD. or both • The AD effective date Types of Airworthiness Directives (AD) • A compliance time Three types of ADs are issued: • Where to go for more information • Notice of Proposed Rulemaking (NPRM), followed • Information on alternative methods of compliance by a Final Rule with the requirements of the AD • Final Rule; Request for Comments • Emergency ADs AD Number ADs have a three-part number designator. The first part is the The standard AD process is to issue an NPRM followed calendar year of issuance. The second part is the biweekly by a Final Rule. After an unsafe condition is discovered, period of the year when the number is assigned. The third part a proposed solution is published as an NPRM and solicits is issued sequentially within each biweekly period.

public comment on the proposed action. After the comment period closes, the final rule is prepared, taking into account 2-26 Applicability and Compliance 1. Group I—Type Certificate Aircraft, Engines, and Propellers. Covering standard, restricted, and limited The AD subject line specifically identifies the TC holder types issued for domestic, foreign, and military surplus of the aircraft or products affected by the AD. The specific products.

models affected and any special considerations, such as specific installed part numbers or modifications, are listed 2. Group II—Aircraft, Engine, and Propeller Approvals.

in the AD applicability section. In order to find all applicable Covering domestic, foreign, and military surplus ADs for a specific product, you must search for ADs on products constructed or modified between October 1, the product, aircraft, engine(s), propeller, or any installed 1927, and August 22, 1938. All have met minimum appliance. If there are multiple series under the aircraft or airworthiness requirements without formal type engine model, you must also search for ADs applicable certification. Such products are eligible for standard to the model, as well as the specific series of that model.

airworthiness certification as though they are type- The final determination of ADs applicable to a particular certificated products.

product can only be made by a thorough examination of the 3. Group III—Aircraft, Engine, and Propeller Approvals.

ADs and the product logbooks. No person may operate a Covering domestic products manufactured prior to product that an AD applies to, except in accordance with the October 1, 1927, foreign products manufactured prior requirements of the AD. Furthermore, the owner or operator to June 20, 1931, and certain military surplus engines of an aircraft is required by 14 CFR part 91, section 91.403 and propellers. All have met minimum airworthiness to maintain the aircraft in compliance with all ADs. The requirements of the Air Commerce Act of 1926 and AD specifies a compliance time that relates to the effective implementing Air Commerce Regulations without date of the AD. That compliance time determines when the formal type certification. Such products are eligible actions are required.

for standard airworthiness certification as though they are type-certificated products.

Alternative Method of Compliance 4. Group IV—Engine Ratings. Covering unapproved Different approaches or techniques that are not specified in engines rated for maximum power and speed only, an AD can, after FAA approval, be used to correct an unsafe their use being limited to specific aircraft with condition on an aircraft or aircraft product. Although the maximum gross weights less than 1,000 pounds. Such alternative was not known at the time the AD was issued, engines are not eligible for independent airworthiness an alternative method may be acceptable to accomplish the certification. These ratings are no longer issued.

intent of the AD. A compliance time that differs from the requirements of the AD can also be approved if the revised 5. Group V—Engine Approvals. Covering military time period and approved alternative method provides an surplus engines meeting CAR 13 design requirements acceptable level of safety as the requirements of the AD.

without formal type certification. Such engines are eligible for airworthiness certification as though they Special Airworthiness Information Bulletin (SAIB) are type-certificated engines.

A Special Airworthiness Information Bulletin (SAIB) is an information tool that the FAA uses to alert, educate, and make Supplemental Type Certificates (STC) recommendations to the aviation community. SAIBs contain When an aircraft is designed and that design is formally non-regulatory information and guidance that does not meet approved for manufacturing, the manufacturer is issued the criteria for an AD. [Figure 2-13] a Type Certificate (TC). The TC is issued by the FAA to signify the airworthiness of an aircraft design and may not Aircraft Specifications be changed except by formal authorization of the FAA.

Specifications were originated during implementation of This formal authorization supplements the original TC the Air Commerce Act of 1926. Specifications are FAA and is called the Supplemental Type Certificate (STC).

recordkeeping documents issued for both type-certificated Therefore, the STC issued by the FAA approves a product and non-type-certificated products that have been found (aircraft, engine, or propeller) modification. [Figure 2-14] eligible for U.S. airworthiness certification. Although they The STC defines the product design change, states how the are no longer issued, specifications remain in effect and will modification affects the existing type design, and lists serial be further amended. Specifications covering type-certificated number effectivity. It also identifies the certification basis products may be converted to a TCDS at the option of the listing specific regulatory compliance for the design change.

TC holder. However, to do so requires the TC holder to Information contained in the certification basis is helpful for provide an equipment list. A specification is not part of a those applicants proposing subsequent product modifications TC. Specifications are subdivided into five major groups and evaluating certification basis compatibility with other as follows: STC modifications. Refer to Figure 2-15 for a listing of how 2-27 Advisory Circular Numbering System 1. General. The advisory circular numbers relate to the FAR subchapter title and correspond to the Parts, and when appropriate, to the specific sections of the Federal Aviation Regulations.

2. General and specific subject numbers. The subject numbers and related subject areas are as follows: General Specific General Specific Subject Subject Subject Subject Number Number Number Number Subject Subject (1) (2) (1) (2) 00 GENERAL 90 AIR TRAFFIC AND GENERAL OPERATING RULES 1 Definitions and Abbreviations 91 General Operating and Flight Rules 10 PROCEDURAL RULES 93 Special Air Traffic Rules and Airport Traffic 11 General Rule-Making Procedures Patterns 13 Investigation and Enforcement Procedures 95 IFR Altitudes 20 AIRCRAFT 97 Standard Instrument Approach Procedures 21 Certification Procedures for Products and 99 Security Control of Air Traffic Parts 101 Moored Balloons, Kites, Unmanned 23 Airworthiness Standards: Normal, Utility, Rockets and Unmanned Free Balloons and Acrobatic Category Airplanes 103 Ultralight Vehicles 25 Airworthiness Standards: Transport Category Airplanes 105 Parachute Jumping 27 Airworthiness Standards: Normal Category 107 Airport Security Rotorcraft 108 Airplane Operators Security 29 Airworthiness Standards: Transport 109 Indirect Air Carrier Security Category Rotorcraft 119 CERTIFICATION: AIR CARRIERS AND 31 Airworthiness Standards: Manned Free COMMERCIAL OPERATORS Balloons 120 AIR CARRIERS, AIR TRAVEL CLUBS, AND 33 Airworthiness Standards: Aircraft Engines OPERATORS FOR COMPENSATION OR 34 Fuel Venting and Exhaust Emission HIRE: CERTIFICATION AND OPERATIONS Requirements for Turbine Engine Powered 121 Certification and Operations: Domestic, Airplanes Flag, and Supplemental Air Carriers and 35 Airworthiness Standards: Propellers Commercial Operators of Large Aircraft 36 Noise Standards: Aircraft Type and 125 Certification and Operations: Airplanes Airworthiness Certification Having a Seating Capacity of 20 or More Passengers or a Maximum Payload 39 Airworthiness Directives Capacity of 6,000 Pounds or More 43 Maintenance, Preventive Maintenance, 127 Certification and Operations of Scheduled Rebuilding and Alteration Air Carriers with Helicopters 45 Identification and Registration Marking 129 Operations of Foreign Air Carriers 47 Aircraft Registration 133 Rotorcraft External-Load Operations 49 Recording of Aircraft Titles and Security 135 Air Taxi Operators and Commercial Documents Operators 60 AIRMEN 137 Agricultural Aircraft Operations 61 Certification: Pilots and Flight Instructors 139 Certification and Operations: Land Airports 63 Certification: Flight Crewmembers Other Serving CAB-Certificated Air Carriers Than Pilots 140 SCHOOLS AND OTHER CERTIFICATED 65 Certification: Airmen Other Than Flight AGENCIES Crewmembers 141 Pilot Schools 67 Medical Standards and Certification 143 Ground Instructors 70 AIRSPACE 145 Repair Stations 71 Designation of Federal Airways, Area Low 147 Aviation Maintenance Technician Schools Routes, Controlled Airspace, and Reporting Points 150 AIRPORT NOISE COMPATIBILITY PLANNING 73 Special Use Airspace 151 Federal Aid to Airports 75 Establishment of Jet Routes and Area High Routes 152 Airport Aid Program 77 Objects Affecting Navigable Airspace Figure 2-12. List of advisory circular numbers.

2-28 Advisory Circular Numbering System General Specific General Specific Subject Subject Subject Subject number Number number Number Subject Subject (1) (2) (1) (2) 155 Release of Airport Property from Surplus 187 Fees Property Disposal Restrictions 189 Use of Federal Aviation Administration 156 State Block Grant Pilot Program Communication System 157 Notice of Construction, Alteration, 190 WITHHOLDING SECURITY INFORMATION Activation, and Deactivation of Airports 191 Withholding Security Information from 158 Passenger Facilities Charges Disclosure Under the Air Transportation Security Act of 1974 159 National Capital Airports 198 Aviation Insurance Program 159/10 Washington National Airport 210 FLIGHT INFORMATION 159/20 Dulles International Airport 211 Aeronautical Charts and Flight Information 161 Notice and Approval of Airport Noise and Publications Access Restrictions 212 Publication Specification: Charts and 169 Expenditures of Federal Funds for Publications Nonmilitary Airports or Air Navigational Facilities Thereon 400 COMMERCIAL SPACE TRANSPORTATION 170 NAVIGATIONAL FACILITIES 440 Financial Responsibility 170 Establishment and Discontinuance Criteria for Airport Traffic Control Tower Facilities 1—Based on Federal Aviation Regulation Subchapter Titles 171 Non-Federal Navigation Facilities (Excluding the 210 series).

180 ADMINISTRATIVE REGULATIONS 2—Based on Federal Aviation Regulation Part Titles (Excluding the 210 series).

183 Representatives of the Administrator 185 Testimony by Employees and Production of Records in Legal Proceedings 3. Within the General Subject Number Areas, Specific selectivity in advisory circular mail lists is available corresponding to the applicable FAR Parts. For example: under the 60 general subject area, separate mail lists for advisory circulars issued in the 61, 63, 65, or 67 series are available. An AC numbered “ 60 ” goes to all numbers in the 60 series. When the volume of circulars in a series warrants a sub-subject breakdown, the general number is followed by a slash and a sub-subject number. Material in the 150 series, Airports, is issued under the following sub-subjects: 150/5000 Airport Planning. 150/5240 Civil Airports Emergency Preparedness.

150/5020 Noise Control and Compatibility Planning 150/5325 Influence of Aircraft Performance on Aircraft Design.

for Airports.

150/5335 Runway, Taxiway, and Apron Characteristics.

150/5100 Federal-aid Airport Program.

150/5340 Airport Visual Aids.

150/5150 Surplus Airport Property Conveyance Programs.

150/5345 Airport Lighting Equipment.

150/5190 Airport Compliance Program.

150/5360 Airport Buildings.

150/5200 Airport Safety–General.

150/5370 Airport Construction.

150/5210 Airport Safety Operations (Recommended 150/5380 Airport Maintenance.

Training, Standards, Manning).

150/5390 Heliports.

150/5220 Airport Safety Equipment and Facilities.

150/5230 Airport Ground Safety System.

4. Individual circular identification numbers. Each circular has a subject number followed either by a dash and a consecutive number (135-15) or a period with a specific FAR section number, followed by a dash and a consecutive number (135.169-2) identifying the individual circular. This consecutive number is not used again in the same subject series. Revised circulars have a letter A, B, C, etc., after the consecutive number to show complete revisions. Changes to circulars have Chg. 1, Chg. 2, Chg. 3, etc., after the identification number on pages that have been changed. The Date on a revised page is changed to the date of the Change transmittal.

Figure 2-12. List of advisory circular numbers (continued).

2-29 Non-FAA Documents TCs and STCs are numbered.

Air Transport Association ATA iSpec 2200 Possession of the STC document does not constitute rights to To standardize the technical data and maintenance activities the design data or installation of the modification. The STC on large and therefore complex aircraft, the ATA e-Business and its supporting data (drawings, instructions, specifications, Program has established a classification of maintenance and so forth) are the property of the STC holder. You must related actions. These are arranged with sequential numbers contact the STC holder to obtain rights for the use of the STC.

assigned to ATA chapters. These chapters are consistent regardless of the large aircraft that is being worked on.

Type Certificate Data Sheets (TCDS) [Figure 2-19] The TCDS is a formal description of the aircraft, engine, or propeller. It lists limitations and information required for type Manufacturers’ Published Data certification including airspeed limits, weight limits, thrust The original equipment manufacturer (OEM) is usually limitations, and so forth.

the best source of information for the operation of and maintenance on a particular product. If the product is a TC’d TCDSs and specifications set forth essential factors and or STC’d item, 14 CFR part 21, section 21.50 requires the other conditions that are necessary for U.S. airworthiness holder of the design approval to provide one set of complete certification. Aircraft, engines, and propellers that conform ICAs. Additional requirements for ICAs are specified in to a U.S. TC are eligible for U.S. airworthiness certification sections 23.1529, 25.1529, 27.1529 and 29.1529. These when found to be in a condition for safe operation and sections further refer the reader to 14 CFR part 23, Appendix ownership requisites are fulfilled. [Figure 2-16] A; part 25, Appendix H; part 27, Appendix A; and part 29, Appendix A. Regardless of the appendix referred to, the TCDSs were originated and first published in January 1958.

requirements in the appendix for the ICA are as follows: Title 14 of the CFR part 21, section 21.41 indicates they are • General: The aircraft ICA must contain instructions part of the TC. As such, a TCDS is evidence the product has for continued airworthiness for each engine, propeller, been type certificated. Generally, TCDSs are compiled from or appliance and the interface of those appliances and details supplied by the TC holder; however, the FAA may products with the aircraft.

request and incorporate additional details when conditions warrant. [Figure 2-17] • Format: The ICA must be in the form of a manual or manuals appropriate to the data being provided.

Under federal law, no civil aircraft registered in the United • Content: The manual contents must be in English and States can operate without a valid airworthiness certificate.

must include the following: This certificate must be approved and issued by the FAA; • Introductory information, including an explanation and it is only issued if the aircraft and its engines, propellers, of the airplane’s features and data as necessary to and appliances are found to be airworthy and meet the perform maintenance or preventive maintenance requirements of an FAA-approved TC. The FAA issues a TC when a new aircraft, engine, propeller, and so forth, is found • A description of the aircraft and its systems, to meet safety standards set forth by the FAA. The TCDS including engine, propeller, and appliances lists the specifications, conditions, and limitations that the • Basic operating information describing how the airworthiness requirements were met under for the specified aircraft and its components are controlled product, such as engine make and model, fuel type, engine • Servicing information with such detail as servicing limits, airspeed limits, maximum weight, minimum crew, parts, tank capacities, types of fluid to be used, and so forth. TCDSs are issued and revised as necessary applicable pressures for the various systems, to accommodate new models or other major changes in the access panels for inspection and servicing, certified product. TCDSs are categorized by TC holder and lubrication points, and types of lubricants to be product type.

used FAA Handbooks & Manuals The maintenance instructions must include the following The FAA publishes handbooks and manuals for beginners and data: aviation professionals. Publications are updated periodically • Recommended schedule for cleaning, inspecting, to reflect new FAA regulations and technical developments.

adjusting, testing, and lubricating the various parts Figure 2-18 shows a list of aircraft and aviation handbooks and manuals available on the FAA website ( www.faa.gov ).

• Applicable wear tolerances 2-30

SPECIAL AIRWORTHINESS

FAA Aviation Safety

INFORMATION BULLETIN

SAIB: CE - 15 - 13 SUBJ: FUSELAGE – Seat Belt Mounting Bracket April 15, 2015 Date: This is information only. Recommendations aren’t mandatory.

Introduction This Special Airworthiness Information Bulletin is to alert owners, operators, and maintenance technicians of an airworthiness concern with aluminum seat belt mounting brackets affecting all Cessna Models 120 and 140 airplanes. Textron Aviation has issued Service Bulletin SEB-25-03, dated February 17, 2015, to address this concern.

At this time, the airworthiness concern is not an unsafe condition that would warrant airworthiness directive (AD) action under Title 14 of the Code of Federal Regulations (14 CFR) part 39.

Background On July 5, 2014, an accident occurred in Parma, New York where the pilot seat belt mounting bracket, part number (p/n) 0425132, failed after the airplane overturned following departure from the runway. Although cause of the failed bracket has not been determined and the investigation is ongoing, it was noted that the original Cessna seat belt installation had been replaced with a four- point Aero Fabricators harness per Supplemental Type Certificate (STC) SA1429GL in 2003. The failed bracket was made of aluminum. However, Cessna now only provides steel brackets as a replacement part for the aluminum brackets.

SAMPLE

Recommendations The FAA recommends that owners, operators, and maintenance personnel of the affected airplanes replace aluminum brackets with steel brackets following Cessna Service Bulletin SEB-25-03 dated February 17, 2015. To make the determination as to whether the bracket is made of aluminum or steel, a magnet may be used or look for evidence of iron oxide (rust).

For Further Information Contact Gary D. Park, Aerospace Engineer, ACE-118W phone: (316) 946-4123; fax: (316) 946-4107; e-mail: gary.park@faa.gov.

For Related Service Information Contact Cessna Aircraft Company, Customer Support Service, P.O. Box 7706, Wichita, Kansas; telephone: (316) 517-5800; fax: (316) 517-7271.

Figure 2-13. Special Airworthiness Information Bulletin (SAIB).

2-31 United States Of America Department of Transportation - Federal Aviation Administration

Supplemental Type Certificate

Number SA7855SW

This Certificate issued to Commander Premier Aircraft Corporation 20 Stanford Drive Farmington, CT 06032 certifies that the change in the type design for the following product with the limitations and conditions therefor as specified hereon meets the airworthiness requirements of Part 23 of the Federal Aviation Regulations .

A12SO Original Product Type Certificate Number : Commander Make : Model : Description of Type Design Change: Installation of McCauley B3D32C419/82NHA-5 Propeller on Commander Model 114 airplane in accordance with Commander Aircraft Co., Installation Instructions dated July 13, 1990, Revision A dated August 22, 1990, or later FAA approved revision.

Limitations and Conditions: FAA approved Commander Aircraft Co. Flight Manual Supplement dated August 23, 1990, must accompany this modification. The installer must determine whether this design change is compatible with previously approved modifications.

If the holder agrees to permit another person to use this certificate to alter a product, the holder must give the other person written evidence of that permission.

SAMPLE

This certificate and the supporting data which is the basis for approval shall remain in effect until surrendered, suspended, revoked or a termination date is otherwise established by the Administrator of the Federal Aviation Administration.

Date reissued : March 03, 2006 Date of application : February 09, 1990 Date amended : Amd. 1, September 10, 1990 Date of issuance : August 23, 1990 By direction of the Administrator _______________________________________________________ ( Signature ) Michele M. Owsley, Manager Airplane Certification Office, Southwest Region _______________________________________________________ ( Title ) _____________________________________________________________________________________________________________________________________ Any alteration of this certificate is punishable by a fine of not exceeding $1,000, or imprisonment not exceeding 3 years, or both.

_____________________________________________________________________________________________________________________________________ FAA Form 8110-2(10-68) Page 1 of 1 T his certificate may be transferred in accordance with FAR 21.47.

Figure 2-14. Supplemental type certificate (STC).

2-32 After 1978, the POHs generally took on both roles. • Recommended overhaul periods • Maintenance Manuals—These manuals are often • Details for an inspection program that identifies referred to as Aircraft Maintenance Manual (AMM) both the frequency and the extent of the inspections or Component Maintenance Manual (CMM). necessary to provide for continued airworthiness • Troubleshooting information The AMM is focused on the entire aircraft and provides the “big • The order and method for proper removal and picture” for the maintenance technician. It provides information replacement of parts concerning the maintenance, including troubleshooting and repair, of the aircraft and systems on the aircraft.

• Procedures for system testing during ground operations The CMM, on the other hand, is focused on a specific • Diagrams for structural access plates item or component, such as hydraulic pump, generator, or • Details for application of special inspection techniques thrust reverser. It provides the bench mechanic with detail troubleshooting information and usually serves as an overhaul • Information concerning the application of protective manual giving details for disassembly, cleaning, inspection, treatments after inspection repair as necessary, reassembly, and testing in accordance • Information relative to the structural fasteners with approved standards and technical data accepted by • List of any special tools needed the Administrator. Refer to 14 CFR part 43 section 43.2(a).

When maintenance is done according to the CMM, the Airworthiness Limitations technician must always include the appropriate references The ICA must contain a separate and clearly distinguishable in the maintenance record entry required by 14 CFR part 43, section titled “Airworthiness Limitations.” Within this section section 43.9 or 43.11.

are mandatory replacement times, structural inspection Service Bulletins (SB) interval, and related inspection procedures.

Throughout the life of a product (whether TC’d or not), All of this is included in the initial release of documents manufacturing defects, changes in service, or design when the aircraft is delivered. However, over the course of improvements often occur. When that happens, the OEM the life of an aircraft, various modifications can and often do frequently uses an SB to distribute the information to the occur. Whether these are as simple as a new cabin to galley operator of the aircraft. SBs are good information and should sliding door, or as complex as a navigation related STC, any be strongly considered by the owner for implementation to major alteration requires that this type of maintenance data the aircraft. However, SBs are not required unless they are be provided to the owner, so that subsequent maintenance, referred to in an AD note or if compliance is required as a inspection, and repair can be properly accomplished. As part of the authorized inspection program. Refer to section aircraft and their systems become more and more complex, 14 CFR part 39, 39.27.

and society continues its preoccupation with litigation for every incident, it is imperative that the technician have the right Structural Repair Manual (SRM) information, that it is current, and that they have the proper As the name implies, this manual carries detail information tools, including those required for any special inspection, and for the technician concerning an aircraft’s primary and correct replacement parts. If any one of these items is required, secondary structure, criteria for evaluating the severity of and the technician does not have it accessible, they are in the detected damage, determining the feasibility of a repair, violation of 14 CFR sections 65.81(b), 43.13(a), and 43.16 if and alignment/inspection information. This manual is usually they attempt to return the aircraft to service.

a separate manual for large aircraft. On small aircraft, this information is often included in the AMM.

Manufacturers may provide this required information in a variety of different manuals: Forms • Operating Instructions—The Airplane Flight Manual Airworthiness Certificates (AFM) or the Pilot’s Operating Handbook (POH) In addition to the registration certificate that indicates the provides the pilot with the necessary information ownership of an aircraft, an airworthiness certificate indicates to properly operate the aircraft. These manuals are the airworthiness of the aircraft. AC 21-12, Application usually listed in the aircraft TCDS, and therefore for U.S. Airworthiness Certificate, FAA Form 8130-6, is a are a required item for the aircraft to be considered comprehensive guide for the completion of the application airworthy. Note that the AFM is generally serial form for this certificate. There are two certificates: standard number specific, whereas the POH is model specific.

2-33 FAA Project Numbering and Designators FAA Project Numbers will use the following format: AAnnnnnYY-X Where: • AA is the two-letter designator for Project Type – see table 1 below • nnnnn is the integer sequential number for the specif i ed ACO; e.g., 00146 • YY is the two-letter designator for the Aircraft Certification Office (ACO) – see Table 2 below • X is the one-letter designator for the Product Type – see Table 3 below As an example, TC00125AT-A would be a TC project assigned by the Atlanta ACO on a small airplane with the assigned number 00125.

Table 3–Product Type Designators Table 1–Project Type Designators Code Description Code Description A Small Airplane TC New Type Certi f icate (TC) B Balloon ST New Supplemental Type Certif i cate (STC) E Engine AT Amended Type Certif i cate G Glider SA Amended Supplemental Type Certif i cate P Propeller SP Special Project (e.g. approval under section 21.305 project) R Rotorcraft PM Parts Manufacturer Approval (PMA) S Airship Table 2–Aircraft Certi fic ation Office (ACO) Designators T Transport Airplane I Experimental Q Other, or not product Branch Description Code AC ASW-150 Ft. Worth Airplane Certi fi cation O ffi ce AK ACE-115N Anchorage Aircraft Certi fi cation O ffi ce Table 4–Directorate Designators AT ACE-115A Atlanta Aircraft Certi fi cation Office Code Description BA ANM-100B Boeing Aviation Safety Oversight O ffi ce (BASOO) EPD Engine-Propeller BO ANE-150 Boston Aircraft Certi fi cation Office RCD Rotorcraft CE ACE-112 Small Airplane Directorate SAD Small Airplane CH ACE-115C Chicago Aircraft Certi fi cation O ffi ce TAD Transport Airplane DE ANM-100D Denver Aircraft Certi fi cation O ffi ce EN ANE-140 Engine Certi fi cation Office GU ACE-100G Gulfstream Aviation Safety Oversight Of fi ce (GASOO) IB ANM-116 Transport Airplane Directorate International Branch Table 5–Aircraft Evaluation Group Designators LA ANM-100L Los Angeles Aircraft Certi fi cation O ffi ce Code Description MC ACE-100M Military Certi fi cation O ffi ce BOS-AEG Boston AEG NY ANE-170 New York Aircraft Certif i cation Off i ce FTW-AEG Fort Worth AEG RC ASW-170 Ft. Worth Rotorcraft Certif i cation Office MKC-AEG Kansas City AEG SC ASW-190 Ft. Worth Special Certif i cation Office LGB-AEG Long Beach AEG SE ANM-100S Seattle Aircraft Certif i cation Office SEA-AEG Seattle AEG WI ACE-115W Wichita Aircraft Certif i cation Office As an example, TC00125AT-A would be a TC project assigned by the Atlanta ACO on a small airplane with the assigned number 00125.

Figure 2-15. Numbering system for type certificates (TCs) and supplemental type certificates (STCs).

and special. FAA Form 8100-2, Standard Airworthiness • Special classes Certificate, may be issued to allow operation of a type- certificated aircraft in one or more of the following categories: FAA Form 8130-7, Special Airworthiness Certificate, may be [Figure 2-20] issued to authorize the operation of an aircraft in the following categories: [Figure 2-21] • Normal • Primary • Utility • Restricted • Acrobatic • Multiple • Commuter • Limited • Transport • Light-sport • Manned free balloon 2-34

SAMPLE

Figure 2-16. Type certificate.

2-35 DEPARTMENT OF TRANSPORTATION FEDERAL AVIATION ADMINISTRATION A24CE Revision 1 1 1 Beechcraft 200 A100 - 1 (U - 21J) 200C A200 (C - 12A) 200CT A200 (C - 12C) 200T A200C (UC - 12B) B200 A200CT (C - 12D) B200C A200CT (FWC - 12D) B200CT A200CT (C - 12F) B200T A200CT (RC - 12D) 300 A200CT (RC - 12G) 300LW A200CT (RC - 12H) B300 A200CT (RC - 12K) B300C A200CT (RC - 12P) B300C (MC - 12W) A200CT (RC - 12Q) B300C (UC - 12W) B200C (C - 12F) 1900 B200C (UC - 12M) 1900 C B200C (C - 12R) 1900C (C - 12J) B200C (UC - 12F) 1900D B200GT B200CGT Ju ly 2 1 , 201 5 TYPE CERTIFICATE DATA SHEET NO. A24CE This data sheet which is part of Type Certificate No. A24CE prescribes conditions and limitations under which the product for which the type certificate was issued meets the airworthiness requirements of the Federal Aviation Regulations.

Type Certificate Holder: Beechcraft Corporation 10511 E. Central Wichita, Kansas 67206 Type Certificate Holder Record: Beech Aircraft Corporation transferred to Raytheon Aircraft Company on April 15, 1996 Raytheon Aircraft Company transferred to Hawker Beechcraft Corporation on March 26, 2007 Hawker Beechcraft Corporation transferred to Beechcraft Corporation on April 12, 2013 I. Model 200, Super King Air (Normal Category), Approved December 14, 1973 (See NOTES 10 and 11) Model A200C (UC-12B), Super King Air (Normal Category), Approved February 21, 1979 (See NOTE 11) Model 200C, Super King Air (Normal Category), Approved February 21, 1979 (See NOTE 11) Model B200, Super King Air (Normal Category), Approved February 13, 1981 (See NOTES 10 and 11) Model B200C, Super King Air (Normal Category), Approved February 13, 1981 (See NOTES 10 and 11 ) Model B200C (C-12F), (UC-12F), (UC-12M) and (C-12R), Super King Air (Normal Category), Approved February 13, 1981, (See NOTES 10, 11, and 12) For Notes, refer to Data Pertinent to All Model 200 Series Engine Two United Aircraft of Canada, Ltd., or Pratt & Whitney PT6A-41 (turboprop) per Beech Specification BS 22096 (200, 200C, A200C) Page No 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Rev. No. 111 101 104 97 82 97 82 99 97 101 111 104 96 101 101 110 Page No 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 Rev. No. 111 101 82 95 91 108 111 101 101 101 101 101 100 78 101 1 1 0 Page No 33 34 35 36 37 38 39 40 41 42 43 Rev. No. 104 111 110 110 111 108 111 96 100 101 101 Figure 2-17. Type Certificate Data Sheet.

2-36 Aircraft Aviation Aircraft Weight and Balance Handbook (FAA-H-8083-1A) Balloon Safety Tips: Powerlines & Thunderstorms ( FAA-P-8740-34) Airplane Flying Handbook (FAA-H-8083-3A) Banner Tow Operations ( FAA/fs-i-8700-1) IR-M 8040-1C, Airworthiness Directives Manual Flight Navigator Handbook ( FAA-H-8083-18) Amateur-built Aircraft & Ultralight Flight Testing Handbook Helicopter Flying Handbook ( FAA-H-8083-21A) Aviation Maintenance Technician Handbook – General Helicopter Instructor’s Handbook ( FAA-H-8083-4) (FAA-H-8083-30) Instrument Flying Handbook ( FAA-H-8083-15B) Aviation Maintenance Technician Handbook – Airframe Instrument Procedures Handbook ( FAA-H-8083-16) (FAA-H-8083-31) International Flight Information Manager Aviation Maintenance Technician Handbook – Powerplant (FAA-H-8083-32) MC-4 Ram Air Free-fall Personnel Parachute System Technical Manual Balloon Flying Handbook (FAA-H-8083-11A) Pilot Safety Brochures Glider Flying Handbook (FAA-H-8083-13A) Pilot’s Handbook of Aeronautical Knowledge ( FAA-H-8083-25A) Parachute Rigger Handbook (FAA-H-8083-17) Plane Sense–General Aviation Information ( FAA-H-8083-19A) Rotorcraft Flying Handbook (FAA-H-8083-21) Risk Management Brochures Risk Management Handbook ( FAA-H-8083-2) Aviation Safety Risk Management Advanced Avionics Handbook (FAA-H-8083-6) Seaplane, Skiplane, and Float/Ski Equipped Helicopter Operations Aerodynamics for Navy Aviators (NAVAIR 00-80T-80) Handbook ( FAA-H-8083-23) Aeronautical Information Manual Student Pilot Guide ( FAA-H-8083-27A) Air Quality Handbook Tips on Mountain Flying ( FAA-P-8740-60) Airship Pilot Manual Weight-Shift Control Aircraft Flying Handbook ( FAA-H-8083-5) Airship Aerodynamics Technical Manual Examiner and Inspector Aviation Instructor’s Handbook (FAA-H-8083-9A) Balloon Safety Tips: False Lift, Shear, and Rotors ( FAA-P-8740-39) Flight Standards Information Management System (FSIMS) (FAA Order 8900.1) Designee Management Handbook Guide for Aviation Medical Examiners General Aviation Airman Designee Handbook Figure 2-18. FAA handbooks and manuals.

• Experimental Aircraft Registration Aircraft must be registered in the United States if the • Special flight permit aircraft is not registered under the laws of a foreign country • Provisional and is owned by either a citizen of the United States, a foreign citizen lawfully admitted to the United States, Airworthiness certificates may be issued by either FAA or a corporation organized in and doing business under personnel or FAA designees. Refer to 14 CFR part 183, U.S. laws and primarily based in the United States. This sections 183.31 and 183.33. The certificate must not only registration is accomplished by using FAA Form 8050-1, be on board the aircraft (14 CFR part 91, section 91.203(a) Aircraft Registration Application. The aircraft registration (1)), but must also be “displayed at the cabin or flight deck form is available online at www.faa.gov. The aircraft owner entrance so that it is legible to the passengers or crew” 14 can mail in completed copy, and keep a copy of the form as CFR part 91, (section 91.203(b)). Since the ability to obtain temporary authority to operate the aircraft after the fee and this certificate is based upon the requirement to inspect the evidence of ownership have been mailed or delivered to the aircraft to determine that it conforms to type design and is Registry. When carried in the aircraft with an appropriate in condition for safe operation, it can also be revoked by current airworthiness certificate or a special flight permit, the FAA if either of those two requirements ceases to exist.

a copy of this completed application provides authority to operate the aircraft in the United States for up to 90 days.

2-37 Joint Aircraft Systems Component (JASC)/ATA Code Table Aircraft Powerplant System 35 Oxygen 11 Placards and Markings 36 Pneumatic 71 PowerPlant 12 Servicing 37 Vacuum 72 Turbine/Turboprop Engine 14 Hardware 38 Water/Waste 73 Engine Fuel and Control 18 Helicopter Vibration 74 Ignition 45 Central Maintenance System (CMS) Airframe Systems 49 Airborne Auxiliary Power 75 Air 21 Air Conditioning 51 Standard Practices/Structures 76 Engine Control 22 Auto Flight 77 Engine Indicating 52 Doors 23 Communications 78 Engine Exhaust 53 Fuselage 24 Electrical Power 54 Nacelles/Pylons 79 Engine Oil 25 Equipment/Furnishings 55 Stabilizers 80 Starting 26 Fire Protection 81 Turbocharging 56 Windows 27 Flight Controls 57 Wings 82 Water Injection 28 Fuel Propeller/Rotor Systems 83 Accessory Gearboxes 29 Hydraulic Power 61 Propellers/Propulsors 85 Reciprocating Engine 30 Ice and Rain Protection 62 Main Rotor 31 Instruments 63 Main Rotor Drive 32 Landing Gear 64 Tail Rotor 33 Lights 65 Tail Rotor Drive 34 Navigation 67 Rotors Flight Control Figure 2-19. Maintenance classification.

years. This is not an FAA requirement. FAA inspectors who In addition to the completed application form, the owner must conducted ramp inspections and detected an expired radio also submit evidence of ownership (such as a bill of sale) station license were not required to notify the FCC, nor and a registration fee. A successful review of the application could they issue a violation to the owner/operator. Simply results in the issuance of AC Form 8050-3, Certificate of informing the operator of the expired radio station license Aircraft Registration. (Note the AC prefix.) was their only responsibility.

14 CFR section 91.203(a)(2) requires that either the pink copy FSGA 96-06, a Flight Standards Information Bulletin (FSIB) of the application or the actual certificate of registration be for General Aviation (FSGA) titled “Elimination of Aircraft on board the aircraft during its operation. Radio Station Licenses” became effective on July 8, 1996.

Although that FSIB had an effectivity of only 1 year, the If the registration is ever lost or damaged, it may be replaced elimination of the requirement for aircraft used only in by contacting the FAA Aircraft Registration Branch and domestic operations continues.

providing them with the aircraft specific data, including make, model, N-number, and serial number. A replacement FAA Form 337—Major Repair and Alteration certificate fee and an explanation of the reason for the Refer to the current issue of AC 43.9-1, Instructions for replacement certificate are also required.

Completion of FAA Form 337 for help completing FAA Form 337, Major Repair and Alteration (Airframe, Powerplant, Radio Station License Propeller, or Appliance). [Figure 2-22] A radio station license is required if the aircraft is equipped with radios, and the aircraft is planned to be flown outside As the name clearly states, this form is to be used whenever the boundaries of the United States. A radio station license major repairs or alterations are accomplished on an aircraft.

is not required for aircraft that are operated domestically. The only exception would be that 14 CFR part 43, Appendix (A major change occurred on February 8, 1996, when the B, allows for a certificated repair station to RTS an aircraft telecommunications Act of 1996 was signed into law.) after a major repair by using a signed and dated work order and a signed maintenance release.

The Federal Communications Commission (FCC) formerly • Information in item 1 comes directly from the aircraft required that any communication transmitter installed in dataplate, except for the tail number. That is to be aircraft be licensed. These FCC licenses were valid for 5 compared to the aircraft registration form.

2-38 • Information in item 2 reflects the name and address with this requirement cannot be overemphasized. Complete listed on AC Form 8050-3, Certificate of Registration. and organized maintenance logs for an aircraft can have significant (and usually positive) effect during the buy/ • Item 3 is used when there is no existing approved data sell negotiations of an aircraft. On the other hand, poorly for the intended repair or alteration. In that case, the organized and incomplete logs can have a detrimental effect technician can request that the local FSDO Principal upon the selling price of an aircraft.

Maintenance Inspector (PMI) review the data and then grant a field approval, shown by completing and Temporary Records—14 CFR Part 91 Section signing this area. In many cases, this block is blank 91.417(a)(1) and (b)(1) because the technician has found, used, and made These are records that must be kept by the owner until reference to data already approved by the FAA.

the work is repeated, superseded, or 1 year has transpired • Item 4—If the repair or alteration is being done since the work was performed. These are typically records to the aircraft airframe, no entry is required since referring to maintenance, preventive maintenance, alteration, the data is identical to that in item 1. However, and all inspections. They include a description of the work if the repair or alteration is being done to an performed (or reference to the FAA-accepted data); the date engine, a propeller, or other appliance, entries must of completion; and the name, signature and certificate number include the appropriate make, model, and serial of the person doing the RTS.

number information.

Permanent Records—14 CFR Part 91, Section • Item 5 should have “X” marked in either the “Repair” 91.417(a)(2) and (b)(2) or the “Alteration” column.

These records must be retained by the owner during the time • Item 6—Enter appropriate data as specified and check they operate the aircraft. They are transferred with the aircraft the proper box in B. The technician is encouraged to at the time of sale. Typically, these are documents relating to carefully read the preprinted statement in subparagraph total time in service, current status of life-limited parts, time D prior to signing this section.

since last overhaul, current inspection status, current status of • Item 7 must be completed by the IA or authorized applicable AD notes, and major alteration forms as required individual from the repair station.

by 14 CFR part 43, section 43.9.

• Item 8 (on the reverse side) is for the description of Electronic Records the work accomplished. It must include a reference During the last 25 years, the field of aviation maintenance has to the approved data used to conduct the required seen a significant change in the documentation requirements maintenance.

for aircraft and related parts. Nowhere is that change seen as revolutionary as the introduction of electronic data and record The form must be completed at least in duplicate, with the retention. Just as the arrival of the personal computer placed original provided to the owner/operator and a copy to the local the possibility of the power and versatility of a computer in FSDO within 48 hours of completing the maintenance and the hands of the average person, it made it available to the RTS. If the FAA Form 337 is used to document additional maintenance technician. Initially some technicians developed fuel tanks in the cabin or cargo, then an additional copy their own programs for listing data (TCDS, AD notes, and must be signed and in the aircraft at all times. Maintenance so forth), but soon commercially available programs were facilities and mechanics are encouraged to make a copy for developed. Basically, these were developed by either one of their own records.

the following two groups: Records 1. Computer literate persons who felt the aviation Making Maintenance Record Entries industry could benefit from the computer Title 14 of the CFR part 43, sections 43.9 and 43.11 require 2. Aviation professionals who felt the aviation industry the technician to make appropriate entries of maintenance must benefit from the computer actions or inspection results in the aircraft maintenance record. How long those records must be kept is defined in Some of those initial programs were either not very 14 CFR part 91, section 91.417.

user friendly (if developed by computer wizards) or not “very sophisticated” (if developed by the maintenance Whenever maintenance, preventive maintenance, rebuilding, technician). Today, there is a mixture of these various or alteration work occurs on an aircraft, airframe, aircraft database programs. A review of the advertisement section engine, propeller, appliance, or component part, a maintenance in any current aviation maintenance magazine offers record entry must be created. The importance of compliance 2-39 ure 3-1. Sample FAA Form 8100-2, Standard Airworthiness Certificate,

New Aircraft (Face Side)

UNITED STATES OF AMERICA DEPARTMENT OF TRANSPORTATION-FEDERAL AVIATION ADMINISTRATION

STANDARD AIRWORTHINESS CERTIFICATE

1 NATIONALITY AND 2 MANUFACTURER AND MODEL 3 AIRCRAFT SERIAL 4 CATEGORY REGISTRATION MARKS NUMBER

N12345 Boeing 787 43219

Transport

5 AUTHORITY AND BASIS FOR ISSUANCE This airworthiness certificate is issued pursuant to 49 U.S.C. 44704 and certifies that, as of the date of issuance, the aircraft to which issued has been inspected and found to conform to the type certificate therefore, to be in condition for safe operation, and has been shown to meet the requirements of the applicable comprehensive and detailed airworthiness code as provided by Annex 8 to the Convention on International Civil Aviation, except as noted herein.

Exceptions:

None

6 TERMS AND CONDITIONS Unless sooner surrendered, suspended, revoked, or a termination date is otherwise established by the FAA, this airworthiness certificate is effective as long as the maintenance, preventative maintenance, and alterations are performed in accordance with Parts 21, 43, and 91 of the Federal Aviation Regulations, as appropriate, and the aircraft is registered in the United States.

DATE OF ISSUANCE FAA REPRESENTATIVE DESIGNATION NUMBER

9 Jan 2015 NE - XX

E.R. White E.R. White

Any iteration, reproduction, or misuse of this certificate may be punishable by a fine not exceeding $1,000 or imprisonment not exceeding 3 years or both.

SAMPLE

THIS CERTIFICATE MUST BE DISPLAYED IN THE AIRCRAFT IN ACCORDANCE WITH APPLICABLE FEDERAL AVIATION REGULATIONS.

FAA Form 8100-2 (04-11) Supersedes Previous Edition Figure 2-20. FAA Form 8100-2, Standard Airworthiness Certificate.

the reader numerous options for electronic maintenance the Internet?

ure 3-2. Sample FAA Form 8100-2, Standard Airworthiness Certificate, records. Many of these programs offer a combination of • What is the maximum number of aircraft that the the data research, such as ADs, SBs, STCs, and TCDSs,

ft Assembled from Spare and Surplus Products and Articles (Face Side)

system can handle?

required to conduct proper maintenance, inspections, and • Can the system handle both single- and multi-engine data recording (logbook entries, AD compliance history, aircraft? Fixed and rotary wing? Piston and jet?

length of component time in service, and so forth) desired UNITED STATES OF AMERICA to improve the efficiency of the technician.

• Can an item removed from an aircraft be tracked?

DEPARTMENT OF TRANSPORTATION-FEDERAL AVIATION ADMINISTRATION • Is the data from this system exportable to other Although some large shops and certified repair stations may

STANDARD AIRWORTHINESS CERTIFICATE

electronic formats?

1 NATIONALITY AND 2 MANUFACTURER AND MODEL 3 AIRCRAFT SERIAL 4 CATEGORY have a separate group of people responsible for “records and REGISTRATION MARKS NUMBER • Can it forecast items due for maintenance or research,” the professional maintenance technician must

N54321 Jackson 47G - 4 3191HG

Normal

inspection?

be aware of the benefits of these systems. Some factors to 5 AUTHORITY AND BASIS FOR ISSUANCE consider when reviewing a system are: This airworthiness certificate is issued pursuant to 49 U.S.C. 44704 and certifies that, as of the date of issuance, the aircraft to which issued has been inspected and found to conform to the type certificate therefore, to be in condition for safe operation, and has been Since no program can be considered the best, the technician shown to meet the requirements of the applicable comprehensive and detailed airworthiness code as provided by Annex 8 to the • What is the typical size of the aircraft that maintenance Convention on International Civil Aviation, except as noted herein. must learn all they can about the numerous systems that exist.

is being done on? (i.e., less than 12,500 pounds, more Exceptions: Exposure to the pros and cons of these different systems than 12,000? Mixed?)

can be one of the benefits of attending various trade shows,

None

• Does the program have built-in templates for the maintenance seminars, or IA renewal sessions. Continuous aircraft being worked on?

learning and personal improvement is the goal of every 6 TERMS AND CONDITIONS professional maintenance technician.

• What FAA forms (if any) are available in the program?

Unless sooner surrendered, suspended, revoked, or a termination date is otherwise established by the FAA, this airworthiness certificate Light Sport Aircraft (LSA) is effective as long as the maintenance, preventative maintenance, and alterations are performed in accordance with Parts 21, 43, and • Does it have a user-friendly template to enter the data 91 of the Federal Aviation Regulations, as appropriate, and the aircraft is registered in the United States.

Maintenance for the form or must data be directly entered onto the DATE OF ISSUANCE FAA REPRESENTATIVE DESIGNATION NUMBER The light sport aircraft (LSA) category includes gliders,

9 Feb 2015 SW - XX form?

E.J. Smith E.J. Smith

airplanes, gyroplanes, powered parachutes, weight-shift and Any iteration, reproduction, or misuse of this certificate may be punishable by a fine not exceeding $1,000 or imprisonment not exceeding 3 years or both.

• Can it calculate weight and balance data?

THIS CERTIFICATE MUST BE DISPLAYED IN THE AIRCRAFT IN ACCORDANCE WITH APPLICABLE FEDERAL AVIATION REGULATIONS.

lighter-than-air aircraft. There are two general types of LSAs: FAA Form 8100-2 (04-11) Supersedes Previous Edition • Does it have adequate word search capabilities?

Special (SLSA) and Experimental (ELSA). The SLSA are factory built and the ESLA are kit-built. This new category of • Is it networkable?

aircraft was added to the regulations in 2004. (Refer to 14 CFR • Are the updates sent via U.S. mail or downloaded from sections 21.190, 65.107, and 91.327, all dated July 27, 2004.)

2-40

Figure 4-1. Sample FAA Form 8130-7, Special Airworthiness Certificate

Front

UNITED STATES OF AMERICA DEPARTMENT OF TRANSPORTATION - FEDERAL AVIATION ADMINISTRATION

SPECIAL AIRWORTHINESS CERTIFICATE

CATEGORY/DESIGNATION

PURPOSE MANU - NAME

FACTURER ADDRESS FROM FLIGHT

TO N - SERIAL NO.

BUILDER MODEL DATE OF ISSUANCE EXPIRY OPERATING LIMITATIONS DATED ARE PART OF THIS CERTIFICATE SIGNATURE OF FAA REPRESENTATIVE DESIGNATION OR OFFICE NO.

Any alteration, reproduction or misuse of this certificate may be punishable by a fine not exceeding $1,000 or imprisonment not exceeding 3 years, or both. THIS CERTIFICATE MUST BE DISPLAYED IN THE AIRCRAFT IN ACCORDANCE WITH APPLICABLE TITLE 14, CODE OF FEDERAL REGULATIONS (CFR).

FAA Form 8130-7 (04-11) Previous Edition 07/04 May be Used until Depleted SEE REVERSE SIDE NSN: 0052-00-693-4000

Back

This airworthiness certificate is issued under the authority of Public Law 104-6, 49 United States Code

(USC) 44704 and Title 14 Code of Federal Regulations (CFR).

The airworthiness certificate authorizes the manufacturer named on the reverse side to conduct

SAMPLE

production fight tests, and only production flight tests, of aircraft registered in his name. No person may

conduct production flight tests under this certificate: (1) Carrying persons or property for compensation or hire: and/or (2) Carrying persons not essential to the purpose of the flight.

This airworthiness certificate authorizes the flight specified on the reverse side for the purpose shown in

Block A.

This airworthiness certificate certifies that as of the date of issuance, the aircraft to which issued has been inspected and found to meet the requirements of the applicable CFR. The aircraft does not meet the requirements of the applicable comprehensive and detailed airworthiness code as provided by Annex 8 to the Convention On International Civil Aviation. No person may operate the aircraft described on the

reverse side: (1) except in accordance with the applicable CFR and in accordance with conditions and limitations which may be prescribed by the FAA as part of this certificate; (2) over any foreign country without the special permission of that country.

Unless sooner surrendered, suspended, or revoked, this airworthiness certificate is effective for the

duration and under the conditions prescribed in 14 CFR, Part 21, Section 21.181 or 21.217.

Figure 2-21. FAA Form 8130-7, Special Airworthiness Certificate.

AS 9100 and AS 9110 as auditing standards for aerospace Just as industry standard specifications have replaced many facilities and specifically repair stations. Likewise, ISO 9001 of the military standards to define products that are destined is being adopted by the FAA as a system of measuring their to be part of the Department of Defense (DoD) inventory, performance. Therefore, it was logical that when the FAA so too have industry standards come into the FAA sights for looked to develop the standards for this newest category of documenting certain information. Quality is one example. aircraft, they again looked to industry, and this time it was The Society of Automotive Engineers (SAE) has developed the American Society for Testing and Materials (ASTM).

2-41 Federal Aviation Administration (As shown on registration certificate) 2. Owner 3. For FAA Use Only 5. Unit Identification 4. Type (As described in Item 1 above)

SAMPLE

6. Conformity Statement 7. Approval for Return to Service FAA Form 337 (10/06) Figure 2-22. FAA Form 337, Major Repair and Alteration.

2-42 8. Description of Work Accomplished

SAMPLE

FAA Form 337 (10/06) Figure 2-22. FAA Form 337, Major Repair and Alteration (continued).

2-43 • Heavy maintenance—any maintenance, inspection, The ASTM developed a comprehensive list of consensus repair, or alteration a manufacturer has designated that standards for use by manufacturers, regulators, maintenance requires specialized training, equipment, or facilities.

facilities, LSA owners, and service providers. It is unique that • Line maintenance—any repair, maintenance, these standards are the first ones in over 100 years to solely scheduled checks, servicing, inspections, or alterations address the issue of recreational aircraft use. It is also the not considered heavy maintenance that are approved by first complete set of industry consensus standards covering the manufacturer and is specified in the manufacturer’s the design, manufacture, and use of recreational aircraft that maintenance manual.

was developed by a non-government agency. The ASTM • LSA repairman–inspection—a U.S. FAA-certified committee that developed these LSA standards did so to LSA repairman with an inspection rating per 14 CFR ensure the quality of products and services to support both the part 65. This person is authorized to perform the 100- national and the international regulatory structures for LSAs.

hour/annual inspection of the aircraft that they own.

Over 20 standards have been generated, and more are being developed to cover this diversity of aircraft. This handbook • LSA repairman–maintenance—a U.S. FAA-certified only incorporates a review of F2483-05, “Standard Practice LSA repairman with a maintenance rating per 14 CFR for Maintenance and the Development of Maintenance part 65. This person is allowed to perform the required Manuals for Light Sport Aircraft (LSA)” a six-page document maintenance and can also accomplish the 100-hour/ comprised of the following 12 sections: annual inspection.

1. Scope • Major repair, alteration, or maintenance—any repair, alteration, or maintenance where instructions to 2. Referenced Documents complete the task are excluded from the maintenance 3. Terminology manual.

4. Significance and Use • Minor repair, alteration, or maintenance—any repair, 5. Aircraft Maintenance Manual alteration, or maintenance where instructions to complete the task are included in the maintenance 6. Line Maintenance, Repairs, and Alterations manual.

7. Heavy Maintenance, Repairs, and Alterations The 100-hour inspection is the same as the annual inspection, 8. Overhaul except for the interval of time. The requirements for whether 9. Major Repairs and Alterations or not the 100-hour inspection is applicable are exactly the 10. Task-Specific Training same as the criteria for the standard 100-hour/annual required of non-LSA aircraft.

11. Safety Directives 12. Keywords Aircraft Maintenance Manual (AMM) Although these manuals do not require any FAA approval, The scope of that document is basically twofold: the regulations do require that the manual be developed in • To provide guidelines for the qualification necessary accordance with industry standards. This ASTM sets that to accomplish various levels of maintenance on LSA.

standard by requiring: • To provide the content and structure of maintenance • General specifications to be listed, include capacities, manuals for aircraft and their components that are servicing, lubrication, and ground handling operated as LSAs.

• An inspection checklist for the annual condition or 100-hour inspection Some additional definitions from section 3, Terminology, • A description of and the instructions for the that help to better explain the LSA concepts are: maintenance, repair, and overhaul of the LSA engine • Annual condition inspection—defined as a detailed • A description of and the instructions for the inspection accomplished once a year in accordance maintenance, repair, and alteration of the aircraft’s with instructions provided in the maintenance manual primary structure supplied with the LSA. The purpose of this inspection is to look for any wear, corrosion, or damage that Other items that maintenance procedures must be provided would cause the LSA not to be in condition for for are: safe operation.

• Fuel systems 2-44 • Propeller • Structural repairs • Utility system • Recovering of a dope and fabric • Instruments and avionics Heavy alterations of components can be accomplished when • Electrical system instructions are provided in the maintenance manual or other service directed instructions. Examples of this activity are • Structural repair initial installation of skis and installation of new additional • Painting and coatings pitot static instruments.

The Inspection, Repair, and Alterations section must Overhaul of components can be performed only by the specifically list any special tools and parts needed to complete manufacturer (or someone authorized to perform) of the the task, as well as the type of maintenance action (line, LSA or the component to be overhauled. An overhaul heavy, or overhaul) necessary to accomplish the activity.

manual is required and must be a separate manual from Directly associated with that information is the requirement the manufacturer’s maintenance manual. Items typically to specify the level of certification needed to do the job (i.e., considered for overhaul are engines, carburetors, starters, LSA repairman, A&P, or repair station). The manual may generators, alternators, and instruments.

refer to existing FAA ACs.

Major Repairs & Alterations Line Maintenance, Repairs, & Alterations Another major difference between LSA maintenance and The minimum level of certification necessary to accomplish traditional aircraft maintenance is that FAA Form 337, line maintenance is LSA inspection. Some typical tasks Major Repair and Alteration, is not required to document considered to be line maintenance are: major repairs and alterations. Instead, any major repair or • 100-hour/annual condition inspection alteration that is accomplished after the LSA has gone through production acceptance testing must be evaluated relative to • Servicing of fluids the applicable ASTM requirements. After this evaluation has • Removing and replacing components when instructions been accomplished (either by the manufacturer or an entity to do so are provided in the maintenance manual approved by them), a written affidavit must be provided – Batteries attesting that the LSA still meets the requirements of the applicable ASTMs.

– Fuel pump – Exhaust The manufacturer (or other approved entity) must provide – Spark plugs and wires written instructions defining the level of certification necessary to perform the maintenance and also include any – Floats and skis ground test or flight testing necessary to verify that the LSA • Repair or alteration of components when specific complies with the original LSA acceptance test standards, instructions are provided in the maintenance manual and is in condition for safe operation. Proper documentation – Patching a hole in the fabric of this maintenance activity is required to be entered in the LSA records and is also defined by the manufacturer.

– Installation of a strobe light kit Task specific training is not required to be FAA approved.

Heavy maintenance, repairs, and alterations must be This is solely the responsibility of the manufacturer. Some accomplished by either a certified mechanic (A or P or examples of this are an engine manufacturer’s overhaul A&P) or an LSA repairman—maintenance who has received school or the EAA Sport Air fabric covering school.

additional “task specific” training. Some examples of this would be the removal and replacement of complete engine, Safety directives are issued against an LSA or component cylinder, piston and valve assemblies; primary flight controls; and are not issued by the FAA, but rather by the original and landing gear.

aircraft manufacturer. Note: If the LSA includes a product that is TC’d by the FAA, the manufacturer is required to Heavy repair of components or structure can be accomplished issue a safety directive. Typical instructions within a safety when instructions are provided in the maintenance manual directive include: or other service directed instructions. A few examples of • List of tools required for the task this activity are: • List of parts needed • Repainting of control surfaces 2-45 • Type of maintenance (line, heavy, overhaul) • Level of certification needed • Detailed instructions and diagrams • Inspection and test methods Safety directives are mandatory, except for experimental use LSAs.

2-46

Next: Chapter 3 →

Chapter 3

Mathematics in Aviation

Maintenance

97,578 Introduction Mathematics is woven into many areas of everyday life.

Therefore, 97,578 is the sum of the four whole numbers.

Performing mathematical calculations with success requires an understanding of the correct methods, procedures, Subtraction of Whole Numbers practice, and review of these principles. Mathematics may Subtraction is the process where the value of one number be thought of as a set of tools. The aviation mechanic needs is taken from the value of another. The result is called the these tools to successfully complete the maintenance, repair, difference. When subtracting two whole numbers, such as installation, or certification of aircraft equipment.

3,461 from 97,564, align them into columns according to place value and then subtract.

Many examples of using mathematical principles by the aviation mechanic are available. Tolerances in turbine engine 97,564 components are critical, making it necessary to measure – 3,461 within a ten-thousandth of an inch. Because of these close tolerances, it is important that the aviation mechanic can 94,103 make accurate measurements and mathematical calculations.

An aviation mechanic working on aircraft fuel systems The difference of the two whole numbers is 94,103.

also uses mathematical principles to calculate volumes and Multiplication of Whole Numbers capacities of fuel tanks. The use of fractions and surface Multiplication is the process of repeated addition. For example, area calculations are required to perform sheet metal repair 4 × 3 is the same as 4 + 4 + 4. The result is called the product.

on aircraft structures.

Example: How many hydraulic system filters do you have Whole Numbers if there are 35 cartons in the supply room and each carton contains 18 filters?

Whole numbers are the numbers 0, 1, 2, 3, 4, 5, and so on.

Whole numbers can be thought of as counting numbers.

× 35 Addition of Whole Numbers Addition is the process where the value of one number is added to the value of another. The result is called the sum. When working with whole numbers, it is important to understand the principle of the place value. The place value in a whole number is the value of the position of each Therefore, there are 630 filters in the supply room.

individual digit within the entire number. For example, in the number 512, the 5 is in the hundreds column, the 1 is in the Division of Whole Numbers tens column, and the 2 is in the ones column. Examples of Division is the process of finding how many times one place values of three whole numbers are shown in Figure 3-1 .

number (called the divisor) is contained in another number (called the dividend). The result is the quotient, and any When adding several whole numbers, such as 4,314, 122, amount left over is called the remainder.

93,132, and 10, align them into columns according to place value and then add.

quotient divisor dividend 4,314 Example: 218 landing gear bolts need to be divided between 93,132 7 aircraft. How many bolts will each aircraft receive?

+ 10 3-1 31 simplest form.

7 218 A common denominator can also be found for any group of − 21 fractions by multiplying all the denominators together. This number is not always the LCD, but it can still be used to add − 7 or subtract fractions.

2 3 4 Example: Add ⁄ 3 + ⁄ 5 + ⁄ 7 by finding a common denominator.

In this case, there are 31 bolts for each of the seven aircraft with one extra remaining.

A common denominator can be found by multiplying the denominators 3 × 5 × 7 to get 105.

Fractions N 2 3 4 70 63 60 193 88 A fraction is a number written in the form ⁄ D where N is + + = + + = = 1

( ) ( )

3 5 7 105 105 105 105 105 called the numerator and D is called the denominator. The fraction bar between the numerator and denominator shows Addition of Fractions that division is taking place.

In order to add fractions, the denominators must be the same 17 2 5 , , number. This is referred to as having “common denominators.” Some examples of fractions are: 18 3 8 1 3 Example: Add ⁄ 7 to ⁄ 7 The denominator of a fraction cannot be a zero. For example, the fraction ⁄ 0 is not allowed, because dividing 1 3 1 + 3 4 by zero is undefined.

+ = = 7 7 7 7 An improper fraction is a fraction in which the numerator is If the fractions do not have the same denominator, then one or equal to or larger than the denominator. For example, ⁄ 4 or all the denominators must be changed so that every fraction ⁄ 8 are examples of improper fractions.

has a common denominator.

Finding the Least Common Denominator Example: Find the total thickness of a panel made from To add or subtract fractions, they must have a common 3 1 ⁄ 32 - inch thick aluminum, that has a ⁄ 64 -inch thick paint denominator. In math, the least common denominator (LCD) coating. To add these fractions, determine a common is generally used. One way to find the LCD is to list the denominator. The LCD for this example is 1, so only the multiples of each denominator and then choose the smallest first fraction must be changed since the denominator of the number that they all have in common (can be divided by).

second fraction is already in 64ths.

1 1 Example: Add ⁄ 5 + ⁄ 10 by finding the LCD.

3 1 3 × 2 1 6 1 6 + 1 7 + = + = + = =

( ) ( ) ( ) ( )

32 64 32 × 2 64 64 64 64 64 Multiples of 5 are: 5, 10, 15, 20, 25, and so on. Multiples of 10 are: 10, 20, 30, 40, and so on. Notice that 10, 20, and 30 Therefore, ⁄ 64 is the total thickness.

are in both lists, but 10 is the smallest or LCD. The advantage of finding the LCD is that the final answer should be in the Subtraction of Fractions To subtract fractions, they must have a common denominator.

Place Value 2 10 Example: Subtract ⁄ 17 from ⁄ 17 10 2 10 – 2 8 – = = 17 17 17 17 Ten Thousands Thousands Hundreds Tens Ones If the fractions do not have the same denominator, then one or 3 5 35 shown as all the denominators must be changed so that every fraction 2 6 9 269 shown as has a common denominator.

1 2 7 4 9 12,749 shown as Figure 3-1. Example of place values of whole numbers.

3-2 Example: The tolerance for rigging the aileron droop of an 7 1 airplane is ⁄ 8 inch ± ⁄ 5 inch. What is the minimum droop to Then, divide each improper fraction by 2 to find the center which the aileron can be rigged? To subtract these fractions, of the plate.

first change both to common denominators. The common denominator in this example is 40. Change both fractions to 87 2 87 1 87 inches ÷ = × = ⁄ 40 , as shown, then subtract.

16 1 16 2 32 7 1 7 × 5 1 × 8 35 8 35 – 8 27 29 2 29 1 29 – = – = – = = inches ÷ = × =

( ) ( ) ( ) ( )

8 5 8 × 5 5 × 8 40 40 40 40 8 1 8 2 16 Therefore, ⁄ 40 is the minimum droop. Finally, convert each improper fraction to a mixed number: Multiplication of Fractions 87 23 inches = 87 ÷ 32 = 2 32 32 Multiplication of fractions does not require a common denominator. To multiply fractions, first multiply the 29 13 numerators. Then, multiply the denominators.

inches = 29 ÷ 16 = 1 16 16 Example: Therefore, the distance to the center of the hole from each of 23 13 the plate edges is 2 ⁄ 32 inches and 1 ⁄ 16 inches.

3 7 1 3 × 7 × 1 21 × × = = Reducing Fractions 5 8 2 5 × 8 × 2 80 A fraction needs to be reduced when it is not in the simplest The use of cancellation when multiplying fractions is a form or “lowest terms.” Lowest term means that the numerator and denominator do not have any factors in common. That helpful technique. Cancellation divides out or cancels all common factors that exist between the numerators and is, they cannot be divided by the same number (or factor).

To reduce a fraction, determine what the common factor(s) denominators. When all common factors are cancelled before the multiplication, the final product is in the simplest form. are and divide these out of the numerator and denominator.

For example, when both the numerator and denominator are Example: even numbers, they can both be divided by 2.

2 1 14 3 2 × 1 2 Example: The total travel of a jackscrew is ⁄ 16 inch. If the 14 3 × = × = =

( ) ( ) ( )

15 7 15 7 5 × 1 5 travel in one direction from the neutral position is ⁄ 16 inch, 5 1 what is the travel in the opposite direction?

Division of Fractions 13 7 13 – 7 6 – = = 16 16 16 16 Division of fractions does not require a common denominator.

To divide fractions, first change the division symbol to The fraction ⁄ 16 is not in lowest terms because the numerator multiplication. Next, invert the second fraction. Then, (6) and the denominator (16) have a common factor of 2. To multiply the fractions.

reduce ⁄ 16 , divide the numerator and the denominator by 2.

7 4 The final reduced fraction is ⁄ 8 as shown below.

Example: Divide ⁄ 8 by ⁄ 3 6 6 ÷ 2 3 7 4 7 3 7 × 3 21 = = ÷ = × = =

( ) ( ) ( )

16 16 ÷ 2 8 8 3 8 4 8 × 4 32 Therefore, the travel in the opposite direction is ⁄ 8 inch.

Example: In Figure 3-2 , the center of the hole is in the center of the plate. Find the distance that the center of the hole is Mixed Numbers from the edges of the plate. To find the answer, the length and width of the plate should each be divided in half. First, A mixed number is a combination of a whole number and change the mixed numbers to improper fractions: a fraction.

7 87 5 ⁄ 16 inches = ⁄ 16 inches 5 29 3 ⁄ 8 inches = ⁄ 8 inches 3-3 Addition of Mixed Numbers 1 5 2 5 18 5 13 3 1 3 1 2 1 1 – = – = – = 8 16 16 16 16 16 16 To add mixed numbers, add the whole numbers together. Then add the fractions together by finding a common denominator.

Therefore, the grip length of the bolt is 1 ⁄ 16 inches.

The final step is to add the sum of the whole numbers to the sum of the fractions for the final answer.

( Note: The value for the overall length of the bolt was given in the example, but it was not needed to solve the Example: The cargo area behind the rear seat of a small problem. This type of information is sometimes referred to airplane can handle solids that are 4 ⁄ 4 feet long. If the rear as a “distracter,” because it distracts from the information seats are removed, then 2 ⁄ 3 feet is added to the cargo area.

needed to solve the problem.)

What is the total length of the cargo area when the rear seats are removed?

The Decimal Number System 3 1 3 1 9 4 13 Origin and Definition 4 2 (4 + 2) + + + 6 + = = 6 + = =

( ) ( )

4 3 4 3 12 12 12 The number system that we use every day is called the decimal system. The prefix in the word decimal, dec, is a 7 feet of cargo room Latin root for the word “ten.” The decimal system probably originated from the fact that we have ten fingers (or digits).

Subtraction of Mixed Numbers The decimal system has ten digits: 0, 1, 2, 3, 4, 5, 6, 7, 8 and To subtract mixed numbers, find a common denominator 9. The decimal system is a base 10 system and has been in use for the fractions. Subtract the fractions from each other. It for over 5,000 years. A decimal is a number with a decimal may be necessary to borrow from the larger whole number point. For example, 0.515, 0.10, and 462.625 are all decimal when subtracting the fractions. Subtract the whole numbers numbers. Like whole numbers, decimal numbers also have from each other. The final step is to combine the final whole place value. The place values are based on powers of 10, as number with the final fraction.

shown in Figure 3-4 .

Example: What is the length of the grip of the bolt shown Addition of Decimal Numbers in Figure 3-3? The overall length of the bolt is 3 ⁄ 2 inches, To add decimal numbers, they must first be arranged so that the shank length is 3 ⁄ 8 inches, and the threaded portion is the decimal points are aligned vertically and according to 1 ⁄ 16 inches long. To find the grip, subtract the length of the place value. That is, adding tenths with tenths, ones with threaded portion from the length of the shank.

ones, hundreds with hundreds, and so forth.

1 5 3 ⁄ 8 inches – 1 ⁄ 16 inches = grip length Example: Find the total resistance for the circuit diagram shown in Figure 3-5 . The total resistance of a series circuit is To subtract, start with the fractions. Borrowing is necessary equal to the sum of the individual resistances. To find the total 5 1 2 because ⁄ 16 is larger than ⁄ 8 (or ⁄ 16 ). From the whole number resistance, R , the individual resistances are added together.

T 3, borrow 1, which is actually ⁄ 16 . After borrowing, the first 18 1 2 mixed number is now 2 ⁄ 16 . This is because, 3 ⁄ 8 = 3 ⁄ 16 = 2 R = 2.34 + 37.5 + 0.09 T 2 16 2 18 + 1 + ⁄ 16 = 2 + ⁄ 16 + ⁄ 16 = 2 ⁄ 16 .

Arrange the resistance values in a vertical column so that the decimal points are aligned and then add.

2.34 37.5 + 0.09 39.93 Therefore, the total resistance, R = 39.93 ohms.

T Subtraction of Decimal Numbers To subtract decimal numbers, they must first be arranged so that the decimal points are aligned vertically and according Figure 3-2. Center hole of the plate.

to place value. That is, subtracting tenths from tenths, ones 3-4 from ones, hundreds from hundreds, and so forth.

Place Value Example: A series circuit containing two resistors has a total resistance (R ) of 37.272 ohms. One of the resistors (R ) T 1 has a value of 14.88 ohms. What is the value of the other resistor (R )?

Millions Hundred Thousands Ten Thousands Thousands Hundreds Tens Ones Tenths Hundredths Thousandths Ten Thousandths R = R – R = 37.272 – 14.88 2 T 1 1 6 2 3 0 5 1 1,623,051 Arrange the decimal numbers in a vertical column so that the 0 0 5 3 1 0.0531 decimal points are aligned and then subtract.

3 2 4 32.4 37.272 Figure 3-4. Place values.

–14.88 the answer is 1.206.

22.392 6.03 2 decimal places Therefore, the second resistor, R = 22.392 ohms.

× 0.2 1 decimal place Multiplication of Decimal Numbers 1.206 3 decimal places To multiply decimal numbers, vertical alignment of the decimal point is not required. Instead, align the numbers to Example: Using the formula watts = amperes × voltage, what the right in the same way that whole numbers are multiplied is the wattage of an electric drill that uses 9.45 amperes from a (with no regard to the decimal points or place values) and 120-volt source? Align the numbers to the right and multiply.

then multiply. The last step is to place the decimal point in the correct place in the answer. To do this, count the number After multiplying the numbers, count the total number of of decimal places in each of the numbers, add the total, and decimal places in both numbers. For this example, 9.45 has 2 then assign that number of decimal places to the result.

decimal places and 120 has no decimal place. Together there are 2 decimal places. The decimal point for the answer is Example: To multiply 0.2 × 6.03, arrange the numbers placed 2 decimal places from the right. Therefore, the answer vertically and align them to the right. Multiply the numbers, is 1,134.00 watts, or simplified to 1,134 watts.

ignoring the decimal points for now.

9.45 2 decimal places 6.03 × 120 no decimal place × 0.2 1206 (ignore the decimal points, for now) + 945 After multiplying the numbers, count the total number of 1,134.00 2 decimal places decimal places in both numbers. For this example, 6.03 has 2 decimal places and 0.2 has 1 decimal place. Together there are a total of 3 decimal places. The decimal point for the answer is placed 3 decimal places from the right. Therefore, 2.34 Ohms Shank Grip 37.5 Ohms M .09 Ohms Overall length Figure 3-5. Circuit diagram.

Figure 3-3. Bolt dimensions.

3-5 Division of Decimal Numbers accuracy desired determines the number of digits to be retained. When the digit immediately to the right of the last Division of decimal numbers is performed the same way as retained digit is 5 or greater, round up by 1. When the digit whole numbers, unless the divisor is a decimal.

immediately to the right of the last retained digit is less than 5, leave the last retained digit unchanged.

quotient divisor dividend Example: An actuator shaft is 2.1938 inches in diameter.

Round to the nearest tenth.

When the divisor is a decimal, it must be changed to a whole number before dividing. To do this, move the decimal in the The digit in the tenths column is a 1. The digit to the right divisor to the right until there are no decimal places. At the of the 1 is a 9. Since 9 is greater than or equal to 5, “round same time, move the decimal point in the dividend to the right up” the 1 to a 2. Therefore, 2.1938 rounded to the nearest the same number of places. Then divide. The decimal in the tenth is 2.2.

quotient is placed directly above the decimal in the dividend.

Example: The outside diameter of a bearing is 3.1648 Example: Divide 0.144 by 0.12 centimeters. Round to the nearest hundredth.

1.2 The digit in the hundredths column is a 6. The digit to the 0.12 0.144 = 12. 14.4 right of the 6 is a 4. Since 4 is less than 5, do not round up – 12 the 6. Therefore, 3.1648 to the nearest hundredth is 3.16.

– 24 Example: The length of a bushing is 3.7487 feet. Round to 0 the nearest thousandth.

Move the decimal in the divisor (0.12) two places to the right. The digit in the thousandths column is an 8. The digit to The result is 12.0. Next, move the decimal in the dividend the right of the 8 is a 7. Since 7 is greater than or equal to (0.144) two places to the right. The result is 14.4. Now divide. 5, “round up” the 8 to a 9. Therefore, 3.7487 to the nearest The result is 1.2. thousandth is 3.749.

Example: The wing area of an airplane is 262.6 square feet Converting Decimal Numbers to Fractions and its span is 40.4 feet. Find the mean chord of its wing To change a decimal number to a fraction, “read” the decimal using the formula: area ÷ span = mean chord.

out loud, and then write it into a fraction just as it is read as shown below.

6.5 Example: One oversized rivet has a diameter of 0.52 inches.

40.4 262.6 = 404. 2626.0 – 2424 Convert 0.52 to a fraction. The decimal 0.52 is read as “fifty-two hundredths.” – 2020 52 “fifty-two” 0.52 = 100 “hundredths” Move the decimal in the divisor (40.4) one place to the In the above fraction of ⁄ 100 , we can divide 4 into each number right. Next, move the decimal in the dividend (262.6) one resulting in a fraction of ⁄ 25 .

place to the right. Then divide. The mean chord length is 6.5 feet.

A dimension often appears in a maintenance manual or on a blueprint as a decimal instead of a fraction. To use the Rounding Off Decimal Numbers dimension, it may need to be converted to a fraction. An Occasionally, it is necessary to round off a decimal number aviation mechanic frequently uses a steel rule that is calibrated to some value that is practical to use. For example, a in units of ⁄ 64 of an inch. To change a decimal to the nearest measurement is calculated to be 29.4948 inches. To use this equivalent common fraction, multiply the decimal by 64. The measurement, we can use the process of “rounding off.” A product of the decimal and 64 is the numerator of the fraction decimal is “rounded off” by keeping the digits for a certain and 64 is the denominator. Reduce the fraction, if needed.

number of places and discarding the rest. The degree of 3-6 Example: The width of a hex head bolt is 0.3123 inches.

3 3 Convert the decimal 0.3123 to a common fraction to decide = 3 ÷ 8 = 8 3.000 Therefore, = 0.375 8 8 which socket would be the best fit for the bolt head. First, – 24 multiply the 0.3123 decimal by 64: – 56 0.3123 × 64 = 19.9872 – 40 Next, round the product to the nearest whole number: 19.98722 ≈ 20.

Calculator tip: numerator (top number) ÷ denominator Use this whole number (20) as the numerator and 64 as the (bottom number) = the decimal equivalent of the fraction.

denominator: ⁄ 64 .

Some fractions when converted to decimals produce a 20 5 Now, reduce ⁄ 64 to ⁄ 16 as 4 is common to both the numerator repeating decimal.

and denominator. Therefore, the correct socket would be the 5 20 ⁄ 16 inch socket ( ⁄ 64 reduced).

Example: Example: When accurate holes of uniform diameter 0.33 are required for aircraft structures, they are first drilled = 1 ÷ 3 = 3 1.00 = 0.3 or 0.33 approximately ⁄ 64 inch undersized and then reamed to the – 9 This decimal can be final desired diameter. What size drill bit should be selected represented with a bar, or can for the undersized hole if the final hole is reamed to a diameter be rounded. (A bar indicates – 9 of 0.763 inches? First, multiply the 0.763 decimal by 64.

that the number(s) beneath it are repeated to infinity.)

0.763 × 64 = 48.832 Other examples of repeating decimals: Next, round the product to the nearest whole number: 0.212121… = 0.21 48.832 ≈ 49.

0.6666… = 0.7 or 0.67 0.254254… = 0.254 Use this number (49) as the numerator and 64 as the denominator: ⁄ 64 is the closest fraction to the final reaming Decimal Equivalent Chart diameter of 0.763 inches. To determine the drill size for the Figure 3-6 is a fraction to decimal to millimeter equivalency initial undersized hole, subtract ⁄ 64 inch from the finished chart. Measurements starting at ⁄ 64 inch and up to 3 inches hole size.

have been converted to decimal numbers and to millimeters.

49 1 48 3 Ratio – = = 64 64 64 4 A ratio is the comparison of two numbers or quantities. A ratio may be expressed in three ways: as a fraction, with a Therefore, a ⁄ 4 -inch drill bit should be used for the initial colon, or with the word “to.” For example, a gear ratio of 5:7 undersized holes.

can be expressed as any of the following: Converting Fractions to Decimals ⁄ 7 or 5:7 or 5 to 7 To convert any fraction to a decimal, simply divide the top number (numerator) by the bottom number (denominator).

Aviation Applications Every fraction has an approximate decimal equivalent.

Ratios have widespread application in the field of aviation.

Example: Example: Compression ratio on a reciprocating engine is the ratio of the volume of a cylinder with the piston at the bottom 0.5 of its stroke to the volume of the cylinder with the piston at 1 1 = 1 ÷ 2 = 2 1.0 Therefore, = 0.5 the top of its stroke. For example, a typical compression ratio 2 2 – 1.0 might be 10:1 (or 10 to 1).

Aspect ratio is the ratio of the length (or span) of an airfoil to 0.375 3-7 its width (or chord). A typical aspect ratio for a commercial Therefore, the ratio of cruising speed to maximum speed is 4:5.

airliner might be 7:1 (or 7 to 1).

Another common use of ratios is to convert any given ratio Air-fuel ratio is the ratio of the weight of the air to the to an equivalent ratio with a denominator of 1.

weight of fuel in the mixture being fed into the cylinders of a reciprocating engine. For example, a typical air-fuel ratio Example: Express the ratio 9:5 as a ratio with a denominator might be 14.3:1 (or 14.3 to 1). of 1.

9 ? 9 1.8 Glide ratio is the ratio of the forward distance traveled to R = = Since 9 ÷ 5 = 1.8, then = 5 1 5 1 the vertical distance descended when an aircraft is operating without power. For example, if an aircraft descends 1,000 feet while it travels through the air for two linear miles (10,560 Therefore, 9:5 is the same ratio as 1.8:1. In other words, 9 feet), it has a glide ratio of 10,560:1,000 which can be reduced to 5 is the same ratio as 1.8 to 1.

to 10.56: 1 (or 10.56 to 1).

Proportion Gear ratio is the number of teeth each gear represents when A proportion is a statement of equality between two or more two gears are used in an aircraft component. In Figure 3-7 , ratios. For example, the pinion gear has 8 teeth and a spur gear has 28 teeth. The 3 6 gear ratio is 8:28. Using 7 as the LCD, 8:28 becomes 2:7.

= or 3:4 = 6:8 4 8 Speed ratio is when two gears are used in an aircraft This proportion is read as, “3 is to 4 as 6 is to 8.” component; the rotational speed of each gear is represented Extremes and Means as a speed ratio. As the number of teeth in a gear decreases, The first and last terms of the proportion (the 3 and 8 in the rotational speed of that gear increases, and vice-versa.

this example) are called the extremes. The second and third Therefore, the speed ratio of two gears is the inverse (or terms (the 4 and 6 in this example) are called the means. In opposite) of the gear ratio. If two gears have a gear ratio of any proportion, the product of the extremes is equal to the 2:9, then their speed ratio is 9:2.

product of the means.

Example: A pinion gear with 10 teeth is driving a spur gear In the proportion 2:3 = 4:6, the product of the extremes, with 40 teeth. The spur gear is rotating at 160 rpm. Calculate 2 × 6, is 12; the product of the means, 3 × 4, is also 12. An the speed of the pinion gear.

inspection of any proportion shows this to be true.

Teeth in Pinion Gear Speed of Spur Gear Solving Proportions = Teeth in Spur Gear Speed of Pinion Gear Normally when solving a proportion, three quantities are known, and the fourth is unknown. To solve for the unknown, 10 teeth 160 rpm multiply the two numbers along the diagonal and then divide = 40 teeth S (speed of pinion gear) P by the third number.

To solve for S , multiply 40 × 160, then divide by 10. The P Example: Solve for X in the proportion given below.

speed of the pinion gear is 640 rpm.

65 X = 80 100 Example: If the cruising speed of an airplane is 200 knots and its maximum speed is 250 knots, what is the ratio of First, multiply 65 × 100: 65 × 100 = 6500 cruising speed to maximum speed? First, express the cruising Next, divide by 80: 6500 ÷ 80 = 81.25 speed as the numerator of a fraction whose denominator is Therefore, X = 81.25.

the maximum speed.

Example: An airplane flying 300 miles used 24 gallons of Ratio = gasoline. How many gallons will it need to travel 750 miles?

Next, reduce the resulting fraction to its simplest form.

The ratio here is: “miles to gallons;” therefore, the proportion is set up as: 200 4 Ratio = = 250 5 300 750 Miles = Gallons G 3-8 Fraction Decimal MM Fraction Decimal MM Fraction Decimal MM 1/64 0.015 0.396 1 1/64 1.015 25.796 2 1/64 2.015 51.196 1/32 0.031 0.793 1 1/32 1.031 26.193 2 1/32 2.031 51.593 3/64 0.046 1.190 1 3/64 1.046 26.590 2 3/64 2.046 51.990 1/16 0.062 1.587 1 1/16 1.062 26.987 2 1/16 2.062 52.387 5/64 0.078 1.984 1 5/64 1.078 27.384 2 5/64 2.078 52.784 3/32 0.093 2.381 1 3/32 1.093 27.781 2 3/32 2.093 53.181 7/64 0.109 2.778 1 7/64 1.109 28.178 2 7/64 2.109 53.578 1/8 0.125 3.175 1 1/8 1.125 28.575 2 1/8 2.125 53.975 9/64 0.140 3.571 1 9/64 1.140 28.971 2 9/64 2.140 54.371 5/32 0.156 3.968 1 5/32 1.156 29.368 2 5/32 2.156 54.768 11/64 0.171 4.365 1 11/64 1.171 29.765 2 11/64 2.171 55.165 3/16 0.187 4.762 1 3/16 1.187 30.162 2 3/16 2.187 55.562 13/64 0.203 5.159 1 13/64 1.203 30.559 2 13/64 2.203 55.959 7/32 0.218 5.556 1 7/32 1.218 30.956 2 7/32 2.218 56.356 15/64 0.234 5.953 1 15/64 1.234 31.353 2 15/64 2.234 56.753 1/4 0.25 6.35 1 1/4 1.25 31.75 2 1/4 2.25 57.15 17/64 0.265 6.746 1 17/64 1.265 32.146 2 17/64 2.265 57.546 9/32 0.281 7.143 1 9/32 1.281 32.543 2 9/32 2.281 57.943 19/64 0.296 7.540 1 19/64 1.296 32.940 2 19/64 2.296 58.340 5/16 0.312 7.937 1 5/16 1.312 33.337 2 5/16 2.312 58.737 21/64 0.328 8.334 1 21/64 1.328 33.734 2 21/64 2.328 59.134 11/32 0.343 8.731 1 11/32 1.343 34.131 2 11/32 2.343 59.531 23/64 0.359 9.128 1 23/64 1.359 34.528 2 23/64 2.359 59.928 3/8 0.375 9.525 1 3/8 1.375 34.925 2 3/8 2.375 60.325 25/64 0.390 9.921 1 25/64 1.390 35.321 2 25/64 2.390 60.721 13/32 0.406 10.318 1 13/32 1.406 35.718 2 13/32 2.406 61.118 27/64 0.421 10.715 1 27/64 1.421 36.115 2 27/64 2.421 61.515 7/16 0.437 11.112 1 7/16 1.437 36.512 2 7/16 2.437 61.912 29/64 0.453 11.509 1 29/64 1.453 36.909 2 29/64 2.453 62.309 15/32 0.468 11.906 1 15/32 1.468 37.306 2 15/32 2.468 62.706 31/64 0.484 12.303 1 31/64 1.484 37.703 2 31/64 2.484 63.103 1/2 0.5 12.7 1 1/2 1.5 38.1 2 1/2 2.5 63.5 33/64 0.515 13.096 1 33/64 1.515 38.496 2 33/64 2.515 63.896 17/32 0.531 13.493 1 17/32 1.531 38.893 2 17/32 2.531 64.293 35/64 0.546 13.890 1 35/64 1.546 39.290 2 35/64 2.546 64.690 39341 0.562 14.287 1 9/16 1.562 39.687 2 9/16 2.562 65.087 37/64 0.578 14.684 1 37/64 1.578 40.084 2 37/64 2.578 65.484 19/32 0.593 15.081 1 19/32 1.593 40.481 2 19/32 2.593 65.881 39/64 0.609 15.478 1 39/64 1.609 40.878 2 39/64 2.609 66.278 5/8 0.625 15.875 1 5/8 1.625 41.275 2 5/8 2.625 66.675 41/64 0.640 16.271 1 41/64 1.640 41.671 2 41/64 2.640 67.071 21/32 0.656 16.668 1 21/32 1.656 42.068 2 21/32 2.656 67.468 43/64 0.671 17.065 1 43/64 1.671 42.465 2 43/64 2.671 67.865 11/16 0.687 17.462 1 11/16 1.687 42.862 2 11/16 2.687 68.262 45/64 0.703 17.859 1 45/64 1.703 43.259 2 45/64 2.703 68.659 23/32 0.718 18.256 1 23/32 1.718 43.656 2 23/32 2.718 69.056 47/64 0.734 18.653 1 47/64 1.734 44.053 2 47/64 2.734 69.453 3/4 0.75 19.05 1 3/4 1.75 44.45 2 3/4 2.75 69.85 49/64 0.765 19.446 1 49/64 1.765 44.846 2 49/64 2.765 70.246 25/32 0.781 19.843 1 25/32 1.781 45.243 2 25/32 2.781 70.643 51/64 0.796 20.240 1 51/64 1.796 45.640 2 51/64 2.796 71.040 13/16 0.812 20.637 1 13/16 1.812 46.037 2 13/16 2.812 71.437 53/64 0.828 21.034 1 53/64 1.828 46.434 2 53/64 2.828 71.834 27/32 0.843 21.431 1 27/32 1.843 46.831 2 27/32 2.843 72.231 55/64 0.859 21.828 1 55/64 1.859 47.228 2 55/64 2.859 72.628 7/8 0.875 22.225 1 7/8 1.875 47.625 2 7/8 2.875 73.025 57/64 0.890 22.621 1 57/64 1.890 48.021 2 57/64 2.890 73.421 29/32 0.906 23.018 1 29/32 1.906 48.418 2 29/32 2.906 73.818 59/64 0.921 23.415 1 59/64 1.921 48.815 2 59/64 2.921 74.215 15/16 0.937 23.812 1 15/16 1.937 49.212 2 15/16 2.937 74.612 61/64 0.953 24.209 1 61/64 1.953 49.609 2 61/64 2.953 75.009 31/32 0.968 24.606 1 31/32 1.968 50.006 2 31/32 2.968 75.406 63/64 0.984 25.003 1 63/64 1.984 50.403 2 63/64 2.984 75.803 1 1 25.4 2 2 50.8 3 3 76.2 Figure 3-6. Fractions, decimals, and millimeters.

3-9 the denominator), and then convert the decimal number to a percentage by multiplying by 100 as shown earlier.

Example: Express the fraction ⁄ 8 as a percentage.

= 5 ÷ 8 = 0.625 = 62.5% Finding a Percentage of a Given Number This is the most common type of percentage calculation.

2:7

Here are two methods to solve percentage problems: using algebra or using proportions. Each method is shown next to find a percent of a given number.

Figure 3-7. Gear ratio.

Example: In a shipment of 80 wingtip lights, 15% of the lights were defective. How many of the lights were defective?

Solve for G: (750 × 24) ÷ 300 = 60 Algebraic Method: Therefore, to fly 750 miles, 60 gallons of gasoline is required.

15% of 80 lights = N (number of defective lights) 0.15 × 80 = N Percentage 12 = N Percentage means “parts out of one hundred.” The Therefore, 12 defective lights were in the shipment. percentage sign is “%.” Ninety percent is expressed as 90% (= 90 parts out of 100). The decimal 0.90 equals ⁄ 100 , or 90 Proportion Method: out of 100, or 90%.

N 15 Expressing a Decimal Number as a Percentage = 80 100 To express a decimal number in percent, move the decimal To solve for N: N × 100 = 80 × 15 point two places to the right (adding zeroes if necessary) and N × 100 = 1,200 then affix the percent symbol.

N = 1,200 ÷ 100 N = 12 Example: Express the following decimal numbers as a percent: or N = (80 × 15) ÷ 100 0.90 = 90% N = 12 0.5 = 50% 1.25 = 125% Finding What Percentage One Number is of Another 0.335 = 33.5% Example: A small engine rated at 12 horsepower is found to be delivering only 10.75 horsepower. What is the motor Expressing a Percentage as a Decimal Number efficiency expressed as a percent? Sometimes it may be necessary to express a percentage as a decimal number. To express a percentage as a decimal Algebraic Method: number, move the decimal point two places to the left and N% of 12 rated horsepower = 10.75 actual horsepower drop the % symbol.

N% × 12 = 10.75 N% = 10.75 ÷ 12 For example: Express the following percentages as decimal N% = 0.8958 numbers: N = 89.58 90% = 0.90 50% = 0.50 Therefore, the motor efficiency is 89.58%.

5% = 0.05 150% = 1.5 Proportion Method: Expressing a Fraction as a Percentage 10.75 N = To express a fraction as a percentage, first change the 12 100 fraction to a decimal number (by dividing the numerator by 3-10 To solve for N: N × 12 = 10.75 × 100 are removed from the aircraft. What is the new weight? For N × 12 = 1,075 weight and balance purposes, all weight removed from an N = 1,075 ÷ 12 aircraft is given a minus sign, and all weight added is given N = 89.58 a plus sign.

or N = (1,075 × 100) ÷ 12 2,000 + −3 + −10 = 2,000 + −13 = 1,987 N = 89.58 Therefore, the new weight is 1,987 pounds.

Therefore, the motor efficiency is 89.58%.

Subtraction of Positive & Negative Numbers Finding a Number When a Percentage of it is Known To subtract positive and negative numbers, first change the Example: Eighty ohms represents 52% of a microphone’s “–” (subtraction symbol) to a “+” (addition symbol), and total resistance. Find the total resistance of this microphone. change the sign of the second number to its opposite (that is, change a positive number to a negative number or vice Algebraic Method: versa). Finally, add the two numbers together.

52% of N = 80 ohms 52% × N = 80 Example: The daytime temperature in the city of Denver N = 80 ÷ 0.52 was 6° below zero (−6°). An airplane is cruising at 15,000 N = 153.846 feet above Denver. The temperature at 15,000 feet is 20° colder than in the city of Denver. What is the temperature The total resistance of the microphone is 153.846 ohms. at 15,000 feet?

Proportion Method: Subtract 20 from −6: −6 – 20 = −6 + (−20) = −26 = The temperature is −26°, or 26° below zero at 15,000 feet N above the city.

To solve for N: N × 52 = 80 × 100 N × 52 = 8,000 Multiplication of Positive & Negative Numbers N = 8,000 ÷ 52 The product of two positive numbers is always positive. The N = 153.846 ohms product of two negative numbers is always positive. The or product of a positive and a negative number is always negative.

N = (80 × 100) ÷ 52 N = 153.846 ohms Examples: 3 × 6 = 18 −3 × 6 = −18 −3 × −6 = 18 3 × −6 = −18 Positive & Negative Numbers (Signed Numbers) Division of Positive & Negative Numbers The quotient of two positive numbers is always positive. The Positive numbers are numbers that are greater than quotient of two negative numbers is always positive. The zero. Negative numbers are numbers less than zero.

quotient of a positive and negative number is always negative.

[Figure 3-8] Signed numbers are also called integers.

Examples: Addition of Positive & Negative Numbers 6 ÷ 3 = 2 −6 ÷ 3 = −2 −6 ÷ −3 = 2 6 ÷ −3 = −2 The sum (addition) of two positive numbers is positive. The sum (addition) of two negative numbers is negative. The Powers sum of a positive and a negative number can be positive or negative, depending on the values of the numbers. A good The power (or exponent) of a number is a shorthand method way to visualize a negative number is to think in terms of of indicating how many times a number, called the base, debt. If you are in debt by $100 (or, −100) and you add $45 is multiplied by itself. For example, 3 is read as “3 to the to your account, you are now only $55 in debt (or −55). power of 4.” That is, 3 multiplied by itself 4 times. The 3 is the base and 4 is the power.

Therefore: −100 + 45 = −55.

Examples: Example: The weight of an aircraft is 2,000 pounds. A radio 2 = 2 × 2 × 2 = 8 rack weighing 3 pounds and a transceiver weighing 10 pounds 3-11 Read “two to the third power equals 8.” When dividing numbers with powers, the powers can be subtracted as long as the bases are the same.

10 = 10 × 10 × 10 × 10 × 10 = 100,000 Example: Read “ten to the fifth power equals 100,000.” 10 × 10 × 10 × 10 10 × 10 × 10 × 10 4 2 2 10 ÷ 10 = = =10 × 10 =10 10 × 10 10 × 10 Special Powers 4 2 (4 – 2) 2 or 10 ÷ 10 = 10 = 10 Squared When a number has a power of 2, it is commonly referred to Powers of Ten as “squared.” For example, 7 is read as “seven squared” or Because we use the decimal system of numbers, powers of “seven to the second power.” To remember this, think about ten are frequently seen in everyday applications. For example, how a square has two dimensions: length and width.

scientific notation uses powers of ten. Also, many aircraft drawings are scaled to powers of ten. Figure 3-9 gives more Cubed information on the powers of ten and their values.

When a number has a power of 3, it is commonly referred to as “cubed.” For example, 7 is read as “seven cubed” or Roots “seven to the third power.” To remember this, think about A root is a number that when multiplied by itself a specified how a cube has three dimensions: length, width, and depth.

number of times produces a given number.

Power of Zero The two most common roots are the square root and the cube Any non-zero number raised to the zero power always equals 1.

root. For more examples of roots, see Figure 3-10 .

Example: Square Roots 0 0 0 7 = 1 181 = 1 (–24) = 1 The square root of 25, written as 25, equals 5. That is, when the number 5 is squared (multiplied by itself), it produces the Negative Powers number 25. The symbol is called a radical sign. Finding A number with a negative power equals its reciprocal with the square root of a number is the most common application the same power made positive.

of roots. The collections of numbers whose square roots are whole numbers are called perfect squares. The first ten -3 Example: The number 2 is read as “2 to the negative 3rd perfect squares are: 1, 4, 9, 16, 25, 36, 49, 64, 81, and 100.

power,” and is calculated by: The square root of each of these numbers is 1, 2, 3, 4, 5, 6, 1 1 1 7, 8, 9, and 10, respectively.

-3 2 = = = 2 2 × 2 × 2 8 For example, 36 = 6 and 81 = 9 When using a calculator to raise a negative number to a power, always place parentheses around the negative number To find the square root of a number that is not a perfect (before raising it to a power) so that the entire number gets square, use either a calculator or the estimation method. A raised to the power.

longhand method does exist for finding square roots, but with the advent of calculators and because of its lengthy Law of Exponents explanation, it is no longer included in this handbook. The When multiplying numbers with powers, the powers can be estimation method uses the knowledge of perfect squares to added as long as the bases are the same.

approximate the square root of a number.

Example: Example: Find the square root of 31. Since 31 falls between 2 4 6 3 × 3 = (3 × 3) × (3 × 3 × 3 × 3) = 3 × 3 × 3 × 3 × 3 × 3 = 3 the two perfect roots 25 and 36, we know that must be 2 4 (2+4) 6 or 3 × 3 = 3 = 3 between 25 and 36. Therefore, 31 must be greater than 5 and less than 6 because 25 = 5 and 36 = 6. If you estimate the square root of 31 at 5.5, you are close to the correct −5 −4 −3 −2 −1 0 +1 +2 +3 +4 +5 answer. The square root of 31 is actually 5.568.

Figure 3-8. A scale of signed numbers.

3-12 Cube Roots Powers Expansion Value of Ten The cube root of 125, written as 125 , equals 5. That is, when the number 5 is cubed (5 multiplied by itself then Positive Exponents multiplying the product (25) by 5 again), it produces the number 125. It is common to confuse the “cube” of a number 10 1,000,000 10 x 10 x 10 x 10 x 10 x 10 with the “cube root” of a number.

10 100,000 10 x 10 x 10 x 10 x 10 10 10,000 10 x 10 x 10 x 10 For clarification, the cube of 27 = 27 = 27 × 27 × 27 = 19,683.

10 1,000 10 x 10 x 10 3 However, the cube root of 27 = 27 = 3.

10 100 10 x 10 Fractional Powers 10 10 10 Another way to write a root is to use a fraction as the power 10 1 (or exponent) instead of the radical sign. The square root of a Negative number is written with a ⁄ 2 as the exponent instead of a radical Exponents sign. The cube root of a number is written with an exponent -1 10 1/10=0.1 1/10 1 1 of ⁄ 3 and the fourth root with an exponent of ⁄ 4 and so on.

-2 10 1/100=0.01 1/(10 x 10) -3 1 1 1 10 1/1,000=0.001 1/(10 x 10 x 10) ⁄ 3 ⁄ 4 ⁄ 2 3 4 Example: 31 = 31 125 = 125 16 = 16 -4 10 1/10,000=0.0001 1/(10 x 10 x 10 x 10) -5 Functions of Numbers Chart 10 1/100,000=0.00001 1/(10 x 10 x 10 x 10 x 10) -6 10 1/1,000,000=0.000001 1/(10 x 10 x 10 x 10 x 10 x 10) The Functions of Numbers chart found in Figure 3-10 is included in this chapter for convenience in making Figure 3-9. Powers of ten.

computations. Each column in the chart is listed below, with new concepts explained.

2 2 Area = π × r = 3.1416 × 1.5 = 3.1416 × 2.25 = • Number (N) 7.0686 square inches.

• N squared (N ) Scientific Notation • N cubed (N ) Scientific notation is used as a type of shorthand to express very • Square root of N ( N) large or very small numbers. It is a way to write numbers so • Cube root of N ( N) that they do not take up as much space on the page. The format of a number written in scientific notation has two parts. The • Circumference of a circle with diameter = N.

first part is a number greater than or equal to 1 and less than Circumference is the linear measurement of the 10 (for example, 2.35). The second part is a power of 10 (for distance around a circle. The circumference is example, 10 ). The number 2,350,000 is expressed in scientific calculated by multiplying the diameter of the circle notation as 2.35 × 10 . It is important that the decimal point by 3.1416 (3.1416 is the number referred to as pi, is always placed to the right of the first digit. Notice that very which has the symbol π). If the diameter of a circle is large numbers always have a positive power of 10 and very 10 inches, then the circumference would be: small numbers always have a negative power of 10.

10 × 3.1416 = 31.4160.

• Area of a circle with diameter = N. Area of a circle is Example: The velocity of the speed of light is over 186,000 the number of square units of measurement contained miles per second (mps). This can be expressed as 1.86 × 10 mps in the circle with a diameter of N. The area of a circle in scientific notation. The mass of an electron is approximately equals π multiplied by the radius squared. This is 0.000,000,000,000,000,000,000,000,000,911 grams. This can -28 calculated by the formula: A = π × r . Remember that be expressed in scientific notation as 9.11 × 10 grams.

the radius is equal to one-half of the diameter.

Converting Numbers from Standard Notation to Example: A flight deck instrument gauge has a round Scientific Notation face that is 3 inches in diameter. What is the area of Example: Convert 1,244,000,000,000 to scientific notation the face of the gauge? From Figure 3-10 for N = 3, the as follows. First, note that the decimal point is to the right answer is 7.0686 square inches. This is calculated by: of the last zero. (Even though it is not usually written, it is If the diameter of the gauge is 3 inches, then the assumed to be there.)

D 3 radius = ⁄ 2 = ⁄ 2 = 1.5 inches.

3-13 Number Square Cube Square Root Cube Root Circumference Area Circumference Area of a Square Root Cube Root 2 3 Number (N) N Squared (N ) N Cubed (N ) of a circle with circle with of N ( √ N ) of N ( √ N ) diameter = N diameter = N 1 1 1 1.000 1.000 3.142 0.785 2 4 8 1.414 1.260 6.283 3.142 3 9 27 1.732 1.442 9.425 7.069 4 16 64 2.000 1.587 12.566 12.566 5 25 125 2.236 1.710 15.708 19.635 6 36 216 2.449 1.817 18.850 28.274 7 49 343 2.646 1.913 21.991 38.484 8 64 512 2.828 2.000 25.133 50.265 9 81 729 3.000 2.080 28.274 63.617 10 100 1,000 3.162 2.154 31.416 78.540 11 121 1,331 3.317 2.224 34.558 95.033 12 144 1,728 3.464 2.289 37.699 113.01 13 169 2,197 3.606 2.351 40.841 132.73 14 196 2,744 3.742 2.410 43.982 153.94 15 225 3,375 3.873 2.466 47.124 176.71 16 256 4,096 4.000 2.520 50.265 201.06 17 289 4,913 4.123 2.571 53.407 226.98 18 324 5,832 4.243 2.621 56.549 254.47 19 361 6,859 4.359 2.668 59.690 283.53 20 400 8,000 4.472 2.714 62.832 314.16 21 441 9,261 4.583 2.759 65.973 346.36 22 484 10,648 4.690 2.802 69.115 380.13 23 529 12,167 4.796 2.844 72.257 415.48 24 576 13,824 4.899 2.885 75.398 452.39 25 625 15,625 5.000 2.924 78.540 490.87 26 676 17,576 5.099 2.963 81.681 530.93 27 729 19,683 5.196 3.000 84.823 572.55 28 784 21,952 5.292 3.037 87.965 615.75 29 841 24,389 5.385 3.072 91.106 660.52 30 900 27,000 5.477 3.107 94.248 706.86 31 961 29,791 5.568 3.141 97.389 754.77 32 1,024 32,768 5.657 3.175 100.531 804.25 33 1,089 35,937 5.745 3.208 103.672 855.30 34 1,156 39,304 5.831 3.240 106.814 907.92 35 1,225 42,875 5.916 3.271 109.956 962.11 36 1,296 46,656 6.000 3.302 113.097 1017.88 37 1,369 50,653 6.083 3.332 116.239 1075.21 38 1,444 54,872 6.164 3.362 119.380 1134.11 39 1,521 59,319 6.245 3.391 122.522 1194.59 40 1,600 64,000 6.325 3.420 125.664 1256.64 41 1,681 68,921 6.403 3.448 128.805 1320.25 42 1,764 74,088 6.481 3.476 131.947 1385.44 43 1,849 79,507 6.557 3.503 135.088 1452.20 44 1,936 85,184 6.633 3.530 138.230 1520.53 45 2,025 91,125 6.708 3.557 141.372 1590.43 46 2,116 97,336 6.782 3.583 144.513 1661.90 47 2,209 103,823 6.856 3.609 147.655 1734.94 48 2,304 110,592 6.928 3.634 150.796 1809.56 49 2,401 117,649 7.000 3.659 153.938 1885.74 50 2,500 125,000 7.071 3.684 157.080 1963.49 Figure 3-10. Functions of numbers.

3-14 Number Square Cube Square Root Cube Root Circumference Area Circumference Area of a Square Root Cube Root 2 3 Number (N) N Squared (N ) N Cubed (N ) of a circle with circle with of N ( √ N ) of N ( √ N ) diameter = N diameter = N 51 2,601 132,651 7.141 3.708 160.221 2042.82 52 2,704 140,608 7.211 3.733 163.363 2123.71 53 2,809 148,877 7.280 3.756 166.504 2206.18 54 2,916 157,464 7.348 3.780 169.646 2290.22 55 3,025 166,375 7.416 3.803 172.787 2375.83 56 3,136 175,616 7.483 3.826 175.929 2463.01 57 3,249 185,193 7.550 3.849 179.071 2551.76 58 3,364 195,112 7.616 3.871 182.212 2642.08 59 3,481 205,379 7.681 3.893 185.354 2733.97 60 3,600 216,000 7.746 3.915 188.495 2827.43 61 3,721 226,981 7.810 3.937 191.637 2922.46 62 3,844 238,328 7.874 3.958 194.779 3109.07 63 3,969 250,047 7.937 3.979 197.920 3117.24 64 4,096 262,144 8.000 4.000 201.062 3216.99 65 4,225 274,625 8.062 4.021 204.203 3318.30 66 4,356 287,496 8.124 4.041 207.345 3421.19 67 4,489 300,763 8.185 4.062 210.487 3525.65 68 4,624 314,432 8.246 4.082 213.628 3631.68 69 4,761 328,509 8.307 4.102 216.770 3739.28 70 4,900 343,000 8.367 4.121 219.911 3848.45 71 5,041 357,911 8.426 4.141 223.053 3959.19 72 5,184 373,248 8.485 4.160 226.194 4071.50 73 5,329 389,017 8.544 4.179 229.336 4185.38 74 5,476 405,224 8.602 4.198 232.478 4300.84 75 5,625 421,875 8.660 4.217 235.619 4417.86 76 5,776 438,976 8.718 4.236 238.761 4536.46 77 5,929 456,533 8.775 4.254 241.902 4656.62 78 6,084 474,552 8.832 4.273 245.044 4778.36 79 6,241 493,039 8.888 4.291 248.186 4901.67 80 6,400 512,000 8.944 4.309 251.327 5026.54 81 6,561 531,441 9.000 4.327 254.469 5152.99 82 6,724 551,368 9.055 4.344 257.610 5281.01 83 6,889 571,787 9.110 4.362 260.752 5410.60 84 7,056 592,704 9.165 4.380 263.894 5541.76 85 7,225 614,125 9.220 4.397 267.035 5674.50 86 7,396 636,056 9.274 4.414 270.177 5808.80 87 7,569 658,503 9.327 4.431 273.318 5944.67 88 7,744 681,472 9.381 4.448 276.460 6082.12 89 7,921 704,969 9.434 4.465 279.602 6221.13 90 8,100 729,000 9.487 4.481 282.743 6361.72 91 8,281 753,571 9.539 4.498 285.885 6503.88 92 8,464 778,688 9.592 4.514 289.026 6647.60 93 8,649 804,357 9.644 4.531 292.168 6792.90 94 8,836 830,584 9.695 4.547 295.309 6939.77 95 9,025 857,375 9.747 4.563 298.451 7088.21 96 9,216 884,736 9.798 4.579 301.593 7238.22 97 9,409 912,673 9.849 4.595 304.734 7389.81 98 9,604 941,192 9.900 4.610 307.876 7542.96 99 9,801 970,299 9.950 4.626 311.017 7697.68 100 10,000 1,000,000 10.000 4.642 314.159 7853.98 Figure 3-10. Functions of numbers (continued).

3-15 1,244,000,000,000 = 1,244,000,000,000.0 Equations To change to the format of scientific notation, the decimal Algebraic equations are frequently used in aviation to show point must be moved to the position between the first and the relationship between two or more variables. Equations second digits. In this case, it is between the 1 and the 2. Since normally have an equals sign (=) in the expression.

the decimal point must be moved 12 places to the left to get there, the power of 10 is 12. Remember that large numbers Example: The formula A = π × r shows the relationship always have a positive exponent. Therefore, 1,244,000,000,000 between the area of a circle (A) and the length of the radius = 1.244 × 10 when written in scientific notation. (r) of the circle. The area of a circle is equal to π (3.1416) times the radius squared. The larger the radius, the larger the Example: Convert 0.000000457 from standard notation to area of the circle.

scientific notation. To change to the format of scientific notation, the decimal point must be moved to the position Algebraic Rules between the first and second numbers, which in this When solving for a variable in an equation, you can add, case is between the 4 and the 5. Since the decimal point subtract, multiply, or divide the terms in the equation (you do must be moved 7 places to the right to get there, the the same to both sides of the equals sign) to get the variable power of 10 is −7. Remember that small numbers (those onto one side of the equals sign.

less than one) have a negative exponent. Therefore, -7 0.000000457 = 4.57 × 10 when written in scientific notation.

Examples: Solve the following equations for the value N.

Converting Numbers from Scientific Notation to 3N = 21 Standard Notation To solve for N, divide both sides by 3.

Example: Convert 3.68 × 10 from scientific notation to 3N ÷ 3 = 21 ÷ 3 standard notation, as follows. To convert from scientific N = 7 notation to standard notation, move the decimal place 7 places to the right. 3.68 × 10 = 36,800,000. Another way to think about N + 17 = 59 the conversion is 3.68 × 10 = 3.68 × 10,000,000 = 36,800,000.

To solve for N, subtract 17 from both sides.

N + 17 – 17 = 59 – 17 -10 Example: Convert 7.1543 × 10 from scientific notation N = 42 to standard notation. Move the decimal place 10 places to -10 the left: 7.1543 × 10 =.00000000071543. Another way N – 22 = 100 -10 to think about the conversion is 7.1543 × 10 = 7.1543 × To solve for N, add 22 to both sides.

0.0000000001 = 0.00000000071543 N – 22 + 22 = 100 + 22 N = 122 When converting, remember that large numbers always N have positive powers of ten and small numbers always have = 50 negative powers of ten. Refer to Figure 3-11 to determine To solve for N, multiply both sides by 5.

which direction to move the decimal point.

N × 5 = 50 × 5 N = 250 Addition, Subtraction, Multiplication, and Division of Scientific Numbers Solving for a Variable To add, subtract, multiply, or divide numbers in scientific Another application of algebra is to solve an equation for a notation, change the scientific notation number back to given variable.

standard notation. Then add, subtract, multiply or divide the standard notation numbers. After the computation, change the Example: Using the formula given in Figure 3-12 , find the final standard notation number back to scientific notation.

total capacitance (C ) of the series circuit containing three T capacitors with Algebra C = 0.1 microfarad C = 0.015 microfarad Algebra is the branch of mathematics that uses letters or 2 C = 0.05 microfarad symbols to represent variables in formulas and equations. 3 First, substitute the given values into the formula: For example, in the equation d = v × t, where distance = velocity × time, the variables are: d, v, and t.

3-16 1 1 1 C = = = Order of Operation T 10 + 66.66 + 20 1 1 1 1 1 1 + + + + In algebra, rules have been set for the order in which 0.05 C C C 0.1 0.015 1 2 3 operations are evaluated. These same universally accepted Therefore, C = ⁄ 96.66 = 0.01034 microfarad. The microfarad T rules are also used when programming algebraic equations in -6 (10 farad) is a unit of measurement of capacitance. This is calculators. When solving the following equation, the order discussed in greater length in Chapter 12, Electricity.

of operation is given below: 2 2 Use of Parentheses N = (62 – 54) + 6 – 4 + 3 × [8 + (10 ÷ 2)] + 25 + (42 × 2) ÷ 4 + ⁄ 4 In algebraic equations, parentheses are used to group numbers or symbols together. The use of parentheses helps us to 1. Parentheses. First you must do everything in parentheses, identify the order in which we should apply mathematical ( ), starting from the innermost parentheses. If the operations. The operations inside the parentheses are always expression has a set of brackets, [ ], treat these exactly performed first in algebraic equations.

like parentheses. If you are working with a fraction, treat the top as if it was in parentheses and the denominator Example: Solve the algebraic equation X = (4 + 3) .

as if it were in parentheses, even if there is none shown.

First, perform the operation inside the parentheses, which From the equation above, completing the calculation in is, 4 + 3 = 7. Then complete the exponent calculation parentheses gives the following: X = (7) = 7 × 7 = 49.

2 2 N = (8) + 6 – 4 + 3 × [8 + (5)] + 25 + (84) ÷ 4 + ⁄ 4 , When using more complex equations, which may combine then several terms and use multiple operations, grouping the 2 2 N = (8) + 6 – 4 + 3 × [13] + 25 + 84 ÷ 4 + ⁄ 4 terms together helps organize the equation. Parentheses, ( ), 2. Exponents. Next, clear any exponents. Treat any roots are most commonly used in grouping, but you may also see (square roots, cube roots, and so forth) as exponents.

brackets, [ ]. When a term or expression is inside one of these Completing the exponents and roots in the equation grouping symbols, it means that any operation indicated to gives the following: be done on the group is done to the entire term or expression.

N = 64 + 36 – 4 + 3 × 13 + 5 + 84 ÷ 4 + ⁄ 4 Example: 3. Multiplication and Division. Evaluate all of the Solve the equation N = 2 × [(9 ÷ 3) + (4 + 3) ]. Start with multiplications and divisions from left to right. Multiply the operations inside the parentheses ( ), then perform the and divide from left to right in one step. A common operations inside the brackets [ ].

error is to use two steps for this (that is, to clear all of the multiplication signs and then clear all of the division N = 2 × [(9 ÷ 3) + (4 + 3) ] signs), but that is not the correct method. Treat fractions N = 2 × [3 + (7) ] as division. Completing the multiplication and division First, complete the operations inside the parentheses ( ).

in the equation gives the following: N = 2 × [3 + 49] N = 2 × [52] N = 64 + 36 – 4 + 39 + 5 + 21 + ⁄ 4 Second, complete the operations inside the brackets [ ].

4. Addition and Subtraction. Evaluate the additions and N = 104 subtractions from left to right. Like above, addition and subtraction are computed left to right in one step. Completing the addition and subtraction in the equation gives the following: X = 161 ⁄ 4 Large Numbers Small Numbers with Positive with Negative Conversion Powers of 10 Powers of 10 A commonly used acronym, PEMDAS, is used for remembering the order of operation in algebra. PEMDAS From standard Move decimal Move decimal is an acronym for parentheses, exponents, multiplication, notation to scientific place to the right place to the left notation From scientific C = T Move decimal Move decimal 1 1 1 + + notation to standard C C C place to the left place to the right 1 2 3 notation Figure 3-12. Total capacitance in a series circuit.

Figure 3-11. Converting between scientific and standard notation.

3-17 division, addition, and subtraction. To remember it, many use side measures 25 inches? First, determine the known value the sentence, “Please Excuse My Dear Aunt Sally.” Always and substitute it in the formula.

remember, however, to multiply/divide or add/subtract in one sweep from left to right, not separately. a = l × w = 25 inches × 25 inches = 625 square inches Order of Operation for Algebraic Equations Triangle A triangle is a three-sided figure. The sum of the three angles 1. P arentheses in a triangle is always equal to 180°. Triangles are often 2. E xponents classified by their sides. An equilateral triangle has 3 sides of equal length. An isosceles triangle has 2 sides of equal 3. M ultiplication length. A scalene triangle has three sides of differing lengths.

4. D ivision 5. A ddition Triangles can also be classified by their angles. An acute triangle has all three angles less than 90°. A right triangle 6. S ubtraction has one right angle (a 90° angle). An obtuse triangle has one angle greater than 90°. Each of these types of triangles Computing Area of Two-Dimensional Solids is shown in Figure 3-16 .

Area is a measurement of the amount of surface of an object.

Area is usually expressed in such units as square inches or The formula for the area of a triangle is square centimeters for small surfaces or in square feet or square meters for larger surfaces.

1 1 area = ⁄ 2 × (base × height) = ⁄ 2 × (b × h) Figure 3-13 summarizes the formulas for computing the area Example: Find the area of the obtuse triangle shown in of two-dimensional solids.

Figure 3-17 . First, substitute the known values in the area formula.

Rectangle A rectangle is a four-sided figure with opposite sides of 1 1 a = ⁄ 2 × (b × h) = ⁄ 2 × (2'6" × 3'2") equal length and parallel to each other. [Figure 3-14] All of the angles are right angles. A right angle is a 90° angle. The Next, convert all dimensions to inches: rectangle is a very familiar shape in mechanics. The formula for the area of a rectangle is: 2'6" = (2 × 12") + 6" = (24 + 6) = 30 inches 3'2" = (3 × 12") + 2" = (36 + 2) = 38 inches area = length × width = l × w Now, solve the formula for the unknown value: Example: An aircraft floor panel is in the form of a rectangle having a length of 24 inches and a width of 12 inches. What a = ⁄ 2 × (30 inches × 38 inches) = 570 square inches is the area of the panel expressed in square inches? First, determine the known values and substitute them in the formula.

Parallelogram A parallelogram is a four-sided figure with two pairs a = l × w = 24 inches × 12 inches = 288 square inches of parallel sides. [Figure 3-18] Parallelograms do not necessarily have four right angles.

Square A square is a four-sided figure with all sides of equal length The formula for the area of a parallelogram is: and opposite sides are parallel to each other. [Figure 3-15] All angles are right angles. A right angle is a 90° angle. The area = length × height = l × h formula for the area of a square is: area = length × width = l × w Trapezoid A trapezoid is a four-sided figure with one pair of parallel Since the length and the width of a square are the same value, sides. [Figure 3-19] The formula for the area of a trapezoid is: the formula for the area of a square can also be written as: area = ⁄ 2 (base + base ) × height 1 2 area = side × side = s Example: What is the area of a square access plate whose 3-18 Object Area Formula Figure Rectangle 3-14 a = l × w length × width Square 3-15 a = l × w or a = s length × width or side × side a = ½ (l × h) or ½ × (length × height) or 3-16 Triangle a = ½ (b × h) or ½ × (base × height) or 3-17 a = (b × h) ÷ 2 (base × height) ÷ 2 Parallelogram 3-18 a = l × h length × height Trapezoid 3-19 a = ½ b + b × h ½ base + base × height ( ) ( ) 1 2 1 2 2 2 Circle 3-20 a = π × r π × radius Ellipse 3-21 a = π × a × b π × semi-axis A × semi-axis B Wing area 3-22 a = s × c span × mean chord Figure 3-13. Formulas to compute area.

2 2 Example: What is the area of a trapezoid in Figure 3-19 whose area = π × radius = π × r bases are 14 inches and 10 inches, and whose height (or altitude) is 6 inches? First, substitute the known values in Example: The bore, which is “inside diameter,” of a certain the formula. aircraft engine cylinder is 5 inches. Find the area of the cross a = ⁄ 2 (b + b ) × h section of the cylinder.

1 2 = ⁄ 2 (14 inches + 10 inches) × 6 inches First, substitute the known values in the formula: a = ⁄ 2 (24 inches) × 6 inches = 12 inches × 6 inches = 72 square inches a = π × r Circle The diameter is 5 inches, so the radius is 2.5 inches.

(diameter = radius × 2) A circle is a closed, curved, plane figure. [Figure 3-20] Every point on the circle is an equal distance from the center of the a = 3.1416 × (2.5 inches) = 3.1416 × 6.25 square circle. The diameter is the distance across the circle (through inches = 19.635 square inches the center). The radius is the distance from the center to the edge of the circle. The diameter is always twice the length Ellipse of the radius. The circumference, or distance around, a circle An ellipse is a closed, curved, plane figure and is commonly is equal to the diameter times π.

called an oval. [Figure 3-21] In a radial engine, the articulating rods connect to the hub by pins, which travel in circumference = c = d π the pattern of an ellipse (i.e., an elliptical or orbital path).

The formula for the area of a circle is: s = 25 l = 24 w = 12 Figure 3-15. Square.

Figure 3-14. Rectangle.

3-19 Triangles Based on Sides Equilateral Isosceles Scalene Height Length of all sides Length of two sides Length of all sides are di ff erent are equal are equal Triangles Based on Angles Acute Right Obtuse Length Figure 3-18. Parallelogram.

Each angle is < 90° One angle is = 90° One angle is > 90° Figure 3-16. Types of triangles.

Units of Area A square foot measures 1 foot by 1 foot. It also measures 12 inches by 12 inches. Therefore, one square foot also equals Wing Area 144 square inches (that is, 12 × 12 = 144). To convert square To describe the shape of a wing [Figure 3-22] , several terms feet to square inches, multiply by 144. To convert square are required. To calculate wing area, it is necessary to know inches to square feet, divide by 144.

the meaning of the terms “span” and “chord.” The wingspan, S, is the length of the wing from wingtip to wingtip. The A square yard measures 1 yard by 1 yard. It also measures 3 chord is the average width of the wing from leading edge feet by 3 feet. Therefore, one square yard also equals 9 square to trailing edge. If the wing is a tapered wing, the average feet (that is, 3 × 3 = 9). To convert square yards to square feet, width, known as the mean chord (C), must be known to find multiply by 9. To convert square feet to square yards, divide the area. The formula for calculating wing area is: by 9. Refer to Figure 3-23 , Applied Mathematics Formula Sheet, for a comparison of different units of area.

area of a wing = span × mean chord Example: Find the area of a tapered wing whose span is 50 Computing Volume of Three-Dimensional feet and whose mean chord is 6'8". First, substitute the known Solids values in the formula.

Three-dimensional solids have length, width, and height.

There are many three-dimensional solids, but the most a = s × c common are rectangular solids, cubes, cylinders, spheres, = 50 feet × 6 feet 8 inches and cones. Volume is the amount of space within a solid.

( Note: 8 inches = ⁄ 12 feet = 0.67 feet) Volume is expressed in cubic units. Cubic inches or cubic = 50 feet × 6.67 feet centimeters are used for small spaces and cubic feet or cubic = 333.5 square feet meters for larger spaces.

Rectangular Solid A rectangular solid is a three-dimensional solid with six rectangular-shaped sides. [Figure 3-24] The volume is the b = 10" Height = 2 ft 6 in Height = 6" b = 14" Base = 3 ft 2 in Figure 3-17. Obtuse triangle. Figure 3-19. Trapezoid.

3-20 e c n e r e f b m u c r i C Diameter (d) Radius (r) a 2 2 a + b Circumference = c = 2π π = 3.1416 a = Length of one of the semi-axes Figure 3-20. Circle.

b = Length of the other semi-axis Area = a = π x a x b number of cubic units within the rectangular solid. The Figure 3-21. Ellipse.

formula for the volume of a rectangular solid is: = 27 cubic feet of volume in the volume = length × width × height = l × w × h large carton In Figure 3-24 , the rectangular solid is 3 feet by 2 feet by Since each of the smaller boxes has a volume of 1 cubic foot, 2 feet.

the large carton holds 27 boxes.

The volume of the solid in Figure 3-24 is = 3 ft × 2 ft × Cylinder 2 ft = 12 cubic feet.

A solid having the shape of a can, a length of pipe, or a barrel is called a cylinder. [Figure 3-26] The ends of a cylinder are Example: A rectangular baggage compartment measures 5 feet identical circles. The formula for the volume of a cylinder is: 6 inches in length, 3 feet 4 inches in width, and 2 feet 3 inches in height. How many cubic feet of baggage will it hold? First, 2 2 volume = π × radius × height of the cylinder = π r × h substitute the known values into the formula.

One of the most important applications of the volume of v = l × w × h a cylinder is finding the piston displacement of a cylinder = 5'6" × 3'4" × 2'3" in a reciprocating engine. Piston displacement is the total = 5.5 ft × 3.33 ft × 2.25 ft volume (in cubic inches, cubic centimeters, or liters) swept = 41.25 cubic feet by all of the pistons of a reciprocating engine as they move in one revolution of the crankshaft. The formula for piston Cube displacement is given as: A cube is a solid with six square sides. [Figure 3-25] A cube is just a special type of rectangular solid. It has the same Piston Displacement = formula for volume as does the rectangular solid, which is π × (bore divided by 2) × stroke × (# cylinders) volume = length × width × height = L × W × H. Because all of the sides of a cube are equal, the volume formula for a cube can also be written as: volume = side × side × side = S c Example: A large, cube-shaped carton contains a shipment of smaller boxes inside of it. Each of the smaller boxes is s 1 ft × 1 ft × 1 ft. The measurement of the large carton is a = Wing area, ft.

3 ft × 3 ft × 3 ft. How many of the smaller boxes are in the large c = Average chord, ft.

carton? First, substitute the known values into the formula.

s = Span, ft.

v = l × w × h = 3 ft × 3 ft × 3 ft Figure 3-22. Wing planform.

3-21 The bore of an engine is the inside diameter of the cylinder. inches. For an eight-cylinder engine, then the total engine The stroke of the engine is the length the piston travels inside displacement would be: the cylinder. [Figure 3-27] Example: Find the piston displacement of one cylinder in a Total displacement for 8 cylinders = 8 × 128.29 = multi-cylinder aircraft engine. The engine has a cylinder bore 1026.32 cubic inches of displacement of 5.5 inches and a stroke of 5.4 inches. First, substitute the Sphere known values in the formula.

A solid having the shape of a ball is called a sphere.

2 2 v = π × r × h = (3.1416) × (5.5 ÷ 2) × (5.4) [Figure 3-28] A sphere has a constant diameter. The radius (r) of a sphere is one-half of the diameter (d). The formula v = 23.758 × 5.4 = 128.29 cubic inches for the volume of a sphere is given as: The piston displacement of one cylinder is 128.29 cubic Conversion Factors Length Area 2.54 centimeters 25.4 millimeters 1 inch 6.45 square centimeters 1 square inch 12 inches 30.48 centimeters 1 foot 144 square inches 0.093 square meters 1 square foot 3 feet 0.9144 meters 1 yard 9 square feet 0.836 square meters 1 square yard 5,280 feet 1,760 yards 1 mile 43,560 square feet 1 acre 0.0394 inches 1 millimeter 640 acres 2.59 square kilometers 1 square mile 0.62 miles 1 kilometer 0.155 square inches 1 square centimeter 1.195 square yards 1 square meter 0.384 square miles 1 square kilometer Volume 1 fluid ounce 29.57 cubic centimeters 1 cup 8 fluid ounces 1 pint 2 cups 16 fluid ounces 0.473 liters 1 quart 2 pints 4 cups 32 fluid ounces 0.9463 liters 1 gallon 4 quarts 8 pints 16 cups 128 ounces 3.785 liters 1 gallon 231 cubic inches 1 liter 0.264 gallons 1.057 quarts 1 cubic foot 1,728 cubic inches 7.5 gallons 1 cubic yard 27 cubic feet 1 board foot 1 inch x 12 inches x 12 inches Weight Temperature 1 ounce 28.350 grams °F to °C Celsius = ⁵⁄9 × (°F − 32) 1 pound 16 ounces 453.592 grams 0.4536 kilograms °C to °F Fahrenheit = ⁹⁄5 × (°C + 32) 1 ton 2,000 pounds 1 milligram 0.001 grams 1 kilogram 1,000 grams 2.2 pounds 1 gram 0.0353 ounces Figure 3-23. Applied mathematics formula sheet.

3-22 Formulas for Area of Two-Dimensional Objects Order of Operation for Algebraic Equations L = 3 Solid Volume Surface Area Figure W=2 1. P arentheses H = 2 2. E xponents 1-24 l × w × h 2 × [(w × l) + (w × h) + Rectangle 3. M ultiplication (l × h)] Solid 4. D ivision 3 2 1-25 s 6 × s Cube 5. A ddition 6. S ubtraction 2 2 1-26 π × r × h 2 × π × r + π × d × h Cylinder Use the acronym PEMDAS to remember the order of H 3 2 1-28 ⁄ × π × r 4 × π × r Sphere operation in algebra. PEMDAS is an acronym for parentheses, 2 2 2 ½ exponents, multiplication, division, addition, and subtraction.

1-29 ⁄ × π × r × h π × r × [r + (r + h ) ] Cone To remember it, many use the sentence, “Please Excuse My W Dear Aunt Sally.” Names and Symbols for Metric Prefixes L Prefix Means Trigonometric Equations exa (10 ) One quintillion times peta (10 ) One quadrillion times Figure 3-24. Rectangular solid.

B tera (10 ) One trillion times giga (10 ) One billion times 4 3 4 34 3 v = ⁄ 3 × π × radius = ⁄ 3 × (3.1416) × ( ⁄ 2 ) mega (10 ) One million times 3 = 1.33 × 3.1416 × 17 = 1.33 × 3.1416 × 4,913 kilo (10 ) One thousand times c a hecto (10 ) One hundred times v = 20,528.125 cubic inches deca (10 ) Ten times −1 deci (10 ) One tenth of Cone −2 centi (10 ) One hundredth of A C A solid with a circle as a base and with sides that gradually −3 b milli (10 ) One thousandth of taper to a point is called a cone. [Figure 3-29] The formula −6 micro (10 ) One millionth of −9 for the volume of a cone is given as: nano (10 ) One billionth of opposite side (side a) Sine (sin) of angle A = −12 pico (10 ) One trillionth of hypotenuse (side c) 1 2 1 2 v = ⁄ 3 × π × radius × height = ⁄ 3 × π × r × h Powers of Ten adjacent side (side b) Cosine (cos) of angle A = Powers Expansion hypotenuse (side c) Value Units of Volume of Ten Since all volumes are not measured in the same units, it is opposite side (side a) Positive Tangent (tan) of angle A = necessary to know all the common units of volume and how adjacent side (side b) Exponents they are related to each other. For example, the mechanic 10 1,000,000 10 x 10 x 10 x 10 x 10 x 10 may know the volume of a tank in cubic feet or cubic inches, 10 100,000 10 x 10 x 10 x 10 x 10 Pythagorean Theorem but when the tank is full of gasoline, they are interested in 10 10,000 10 x 10 x 10 x 10 how many gallons it contains. Refer to Figure 3-23 , Applied 10 1,000 10 x 10 x 10 Mathematics Formula Sheet, for a comparison of different 2 units of volume.

10 100 10 x 10 c 10 10 10 a Computing Surface Area of Three- 10 1 Dimensional Solids Negative The surface area of a three-dimensional solid is the sum of Exponents b the areas of the faces of the solid. Surface area is a different -1 10 1/10=0.1 1/10 -2 10 1/100=0.01 1/(10 x 10) 2 2 2 a + b = c -3 10 1/1,000=0.001 1/(10 x 10 x 10) Figure 3-23. Applied mathematics formula sheet (continued). -4 10 1/10,000=0.0001 1/(10 x 10 x 10 x 10) s -5 10 1/100,000=0.00001 1/(10 x 10 x 10 x 10 x 10) -6 10 1/1,000,000=0.000001 1/(10 x 10 x 10 x 10 x 10 x 10) 3 3 3 4 4 1 v = ⁄ 3 × π × radius = ⁄ 3 × π × r or v = ⁄ 6 × πd Example: A pressure tank inside the fuselage of a cargo s s aircraft is in the shape of a sphere with a diameter of 34 inches. What is the volume of the pressure tank?

Figure 3-25. Cube.

3-23 concept from that of volume. For example, surface area is the amount of sheet metal needed to build a rectangular fuel tank d d while volume is the amount of fuel that the tank can contain.

Rectangular Solid piston The formula for the surface area of a rectangular solid H=stroke [Figure 3-24] is given as: Surface area = cylinder 2 × [(width × length) + (width × height) + (length × height)] piston = 2 × [(w × l) + (w × h) + (l × h)] Cube The formula for the surface area of a cube [Figure 3-25] is given as: Surface area = 6 × (side × side) = 6 × s Example: What is the surface area of a cube with a side measure of 8 inches?

Piston at top center Piston at bottom center Surface area = 6 × (side × side) Figure 3-27. Cylinder displacement. 2 2 = 6 × S = 6 × 8 = 6 × 64 = 384 square inches Sphere Cylinder The formula for the surface area of a sphere [Figure 3-28] is The formula for the surface area of a cylinder [Figure 3-26] is given as: given as: 2 2 Surface area = 4 × π × radius = 4 × π × r Surface area = 2 × π × radius + π × diameter × height = 2 × π × r + π × d × h Cone The formula for the surface area of a right circular cone [Figure 3-29] is given as: 2 2 Surface area = π × radius × [radius + √(radius + height )] 2 2 = π × r × [r + √(r + h )] r Figure 3-30 summarizes the formulas for computing the volume and surface area of three-dimensional solids.

Trigonometric Functions Trigonometry is the study of the relationship between the angles and sides of a triangle. The word trigonometry comes h from the Greek trigonon, which means three angles, and metro, which means measure.

Right Triangle, Sides, and Angles In Figure 3-31 , notice that each angle is labeled with a diameter capital letter. Across from each angle is a corresponding bore side, each labeled with a lower case letter. This triangle is a right triangle because angle C is a 90° angle. Side “a” is Figure 3-26. Cylinder.

3-24 Pythagorean Theorem The Pythagorean Theorem is named after the ancient Greek mathematician, Pythagoras (~500 B.C.). This theorem is used to find the third side of any right triangle when two sides are 2 2 2 known. The Pythagorean Theorem states that a + b = c .

[Figure 3-32] Where “c” = the hypotenuse of a right triangle, “a” is one side of the triangle and “b” is the other side of the triangle.

Example: What is the length of the longest side of a right triangle, given the other sides are 7 inches and 9 inches?

The longest side of a right triangle is always side “c,” the hypotenuse. Use the Pythagorean Theorem to solve for the Figure 3-28. Sphere.

length of side “c” as follows: opposite from angle A and is sometimes referred to as the 2 2 2 a + b = c “opposite side.” Side “b” is next to, or adjacent to, angle 2 2 2 7 + 9 = c A and is therefore referred to as the “adjacent side.” Side 49 + 81 = c “c” is always across from the right angle and is referred to 130 = c as the “hypotenuse.” c = 130 = 11.4 inches Sine, Cosine, and Tangent Therefore, side “c” = 11.4 inches.

The three primary trigonometric functions and their Example: The cargo door opening in a military airplane is abbreviations are: sine (sin), cosine (cos), and tangent a rectangle that is 5 ⁄ 2 feet tall by 7 feet wide. A section of (tan). These three functions can be found on most scientific square steel plate that is 8 feet wide by 8 feet tall by 1 inch calculators. The three trigonometric functions are actually thick must fit inside the airplane. Can the square section of ratios comparing two of the sides of the triangle as follows: steel plate fit through the cargo door? It is obvious that the opposite side (side a) square steel plate will not fit horizontally through the cargo Sine (sin) of angle A = hypotenuse (side c) door. The steel plate is 8 feet wide and the cargo door is only 7 feet wide. However, if the steel plate is tilted diagonally, adjacent side (side b) will it fit through the cargo door opening?

Cosine (cos) of angle A = hypotenuse (side c) The diagonal distance across the cargo door opening can be opposite side (side a) calculated using the Pythagorean Theorem where “a” is the Tangent (tan) of angle A = adjacent side (side b) cargo door width, “b” is the cargo door height, and “c” is the diagonal distance across the cargo door opening.

Example: Find the sine of a 30° angle.

2 2 2 a + b = c Calculator Method: Using a calculator, select the “sin” feature, enter the number 30, and press “enter.” The calculator should display the answer as 0.5. This means that when angle A equals 30°, then the ratio of the opposite side (a) to the hypotenuse (c) equals 0.5 to 1, so the hypotenuse is twice as long as the opposite side for a 30° angle. Therefore, sin 30° = 0.5.

s h Trigonometry Table Method: When using a trigonometry table, find 30° in the first column.

Next, find the value for sin 30° under the second column r marked “sine” or “sin.” The value for sin 30° should be 0.5.

Figure 3-29. Cone.

3-25 today. Its standardization and decimal features make it well- Solid Volume Surface Area Figure suited for engineering and aviation work.

3-24 l × w × h 2 × [(w × l) + (w × h) + Rectangle (l × h)] Solid The metric system was first envisioned by Gabriel Mouton, 3 2 3-25 s 6 × s Cube Vicar of St. Paul’s Church in Lyons, France. The meter is the unit of length in the metric system, and it is equal to one 2 2 3-26 π × r × h 2 × π × r + π × d × h Cylinder ten-millionth of the distance from the equator to the North 3 2 3-28 ⁴⁄3 × π × r 4 × π × r Sphere Pole. The liter is the unit of volume and is equal to one cubic decimeter. The gram is the unit of mass and is equal to one 2 2 2 3-29 ¹⁄3 × π × r × h π × r × [r + √ (r + h )] Cone cubic centimeter of water.

Figure 3-30. Formulas to compute volume and surface area.

All of the metric units follow a consistent naming scheme, 2 2 2 (7 ft) + (5.5 ft) = c which consists of attaching a prefix to the unit. For example, since kilo stands for 1,000, one kilometer equals 1,000 meters.

49 + 30.25 = c 79.25 = c Centi is the prefix for one hundredth, so one meter equals one hundred centimeters. Milli is the prefix for one thousandths c = 8.9 ft and one gram equals one thousand milligrams. Refer to Figure 3-33 for the names and definitions of metric prefixes.

The diagonal distance across the cargo door opening is 8.9 feet, so the 8-foot wide square steel plate fits diagonally Measurement Systems & Conversions through the cargo door opening and into the airplane.

The United States primarily uses the conventional (U.S.

Measurement Systems or English) system, although it is slowly integrating the metric system (SI). A recommendation to transition to the Conventional (U.S. or English) System metric system within ten years was initiated in the 1970s.

Our conventional (U.S. or English) system of measurement is However, this movement lost momentum, and the United part of our cultural heritage from the days when the thirteen States continues to use both measurement systems. Therefore, colonies were under British rule. It started as a collection information to convert between the conventional (U.S.

of Anglo-Saxon, Roman, and Norman-French weights and or English) system and the metric (SI) system has been measures. For example, the inch represents the width of the included in Figure 3-23 , Applied Mathematics Formula thumb and the foot is from the length of the human foot.

Sheet. Examples of its use are as follows: Tradition holds that King Henry I decreed that the yard should be the distance from the tip of his nose to the end of his thumb.

To convert inches to millimeters, multiply the number of Since medieval times, commissions appointed by various inches by 25.4.

English monarchs have reduced the chaos of measurement by setting specific standards for some of the most important Example: 20 inches = 20 × 25.4 = 508 mm units. Some of the conventional units of measure are: inches, feet, yards, miles, ounces, pints, gallons, and pounds. Because To convert ounces to grams, multiply the number of ounces the conventional system was not set up systematically, it by 28.35.

contains a random collection of conversions. For example, 1 mile = 5,280 feet and 1 foot = 12 inches.

Example: 12 ounces = 12 × 28.35 = 340.2 grams Metric System The metric system, also known as the International System of Units (SI), is the dominant language of measurement used B c a c a b 2 2 2 A C a + b = c b Figure 3-31. Right triangle. Figure 3-32. Pythagorean Theorem.

3-26 The Binary Number System Example: Convert the binary number 10110011 to a decimal The binary number system has only two digits: 0 and 1. The number. Using the place value chart in Figure 3-35 , add up prefix in the word “binary” is a Latin root for the word “two” the place values of the ‘1s’ in the binary number (ignore the and its use was first published in the late 1700s. The use of place values with a zero in the binary number).

the binary number system is based on the fact that switches or valves have two states: open or closed (on/off).

The binary number 10110011 = 128 + 0 + 32 + 16 + 0 + 0 + 2 + 1 Currently, one of the primary uses of the binary number = 179 in the decimal number system system is in computer applications. Information is stored as a series of 0s and 1s, forming strings of binary numbers. An Converting Decimal Numbers to Binary Numbers early electronic computer, ENIAC ( Electronic Numerical To convert a decimal number to a binary number, the place Integrator and Calculator), was built in 1946 at the University values in the binary system are used to create a sum of of Pennsylvania and contained 17,000 vacuum tubes, along numbers that equal the value of the decimal number being with 70,000 resistors, 10,000 capacitors, 1,500 relays, 6,000 converted. Start with the largest binary place value and manual switches and 5 million soldered joints. Computers subtract from the decimal number. Continue this process obviously have changed a great deal since then, but are still until all of the binary digits are determined.

based on the same binary number system. The binary number system is also useful when working with digital electronics Example: Convert the decimal number 233 to a binary number.

because the two basic conditions of electricity, on and off, can be represented by the two digits of the binary number Start by subtracting 128 (the largest place value from the system. When the system is on, it is represented by the digit 8-bit binary number) from 233.

1, and when it is off, it is represented by the digit 0.

233 – 128 = 105 A “1” is placed in the first binary digit space: 1XXXXXXX.

Place Values The binary number system is a Base-2 system. That is, Continue the process of subtracting the binary number the place values in the binary number system are based on place values: powers of 2. An 8-bit binary number system is shown in Figure 3-34 .

105 – 64 = 41 A “1” is placed in the second binary digit space: 11XXXXXX.

Converting Binary Numbers to Decimal Numbers To convert a binary number to a decimal number, add up the 41 – 32 = 9 A “1” is placed in the third binary place values that have a 1 (place values that have a zero do digit space: 111XXXXX.

not contribute to the decimal number conversion).

Multiplier Multiplier Prefix Meaning Symbol (Exponential) (Numerical) Greater Than 1 exa (10 ) quintillion 1,000,000,000,000,000,000 E peta (10 ) quadrillion 1,000,000,000,000,000 P tera (10 ) trillion 1,000,000,000,000 T giga (10 ) billion 1,000,000,000 G mega (10 ) million 1,000,000 M kilo (10 ) thousand 1,000 k hecto (10 ) hundred 100 h deca (10 ) ten 10 da unit 1 Less Than 1 −1 deci (10 ) tenth 0.1 d −2 centi (10 ) hundredth 0.01 c −3 milli (10 ) thousandth 0.001 m −6 micro (10 ) millionth 0.000,001 μ −9 nano (10 ) billionth 0.000,000,001 n −12 pico (10 ) trillionth 0.000,000,000,001 p −15 femto (10 ) quadrillionth 0.000,000,000,000,001 f −18 atto (10 ) quintillionth 0.000,000,000,000,000,001 a Figure 3-33. Names and definitions of metric prefixes.

3-27 Since 9 is less than 16 (the next binary place value), a “0” is placed in the fourth binary digit space, 1110XXXX.

9 – 8 = 1 A “1” is placed in the fifth binary digit space: 11101XXX Since 1 is less than 4 (the next binary place value), a 0 is placed in the sixth binary digit space: 111010XX.

Since 1 is less than 2 (the next binary place value), a 0 is placed in the seventh binary digit space: 1110100X.

1 – 1 = 0 A “1” is placed in the eighth binary digit space: 11101001.

The decimal number 233 is equivalent to the binary number 11101001, as shown in Figure 3-36 .

Three additional decimal number to binary number conversions are shown in Figure 3-36.

Place Value 7 6 5 4 3 2 1 0 2 2 2 2 2 2 2 2 or 128 or 64 or 32 or 16 or 8 or 4 or 2 or 1 1 0 0 1 1 0 0 1 10011001 shown as =153 0 0 1 0 1 0 1 1 00101011 shown as =43 Figure 3-34. Binary system.

Place Value 7 6 5 4 3 2 1 0 2 2 2 2 2 2 2 2 or 128 or 64 or 32 or 16 or 8 or 4 or 2 or 1 1 0 1 1 0 0 1 1 10110011 shown as 128 + 0 + 32 + 16 + 0 + 0 + 2 + 1 =179 Figure 3-35. Place value chart.

Place Value 7 6 5 4 3 2 1 0 2 2 2 2 2 2 2 2 or 128 or 64 or 32 or 16 or 8 or 4 or 2 or 1 0 0 1 0 0 0 1 1 35 shown as 0 1 1 1 1 1 0 0 124 shown as 0 1 1 0 0 0 0 0 96 shown as 1 1 1 1 1 1 1 1 255 shown as 1 1 1 0 1 0 0 1 233 shown as Figure 3-36. Conversion from decimal number to binary number.

3-28

Next: Chapter 4 →

Chapter 4

Aircraft Drawings

• Computer Aided Design (CAD)—where a computer Introduction is used in the design of a part or product The exchange of ideas is essential to everyone, regardless of • Computer Aided Design Drafting (CADD)—where a their vocation or position. This exchange is usually carried on computer is used in the design and drafting process by oral or written word; but under some conditions, the use of these alone is impractical. The aviation industry discovered • Computer Aided Manufacturing (CAM)—where a that it could not depend entirely upon written or spoken computer is used in the manufacturing of a part or words for the exchange of ideas, because misunderstanding product and misinterpretation arose frequently. A written description • Computer Aided Engineering (CAE)—where a of an object can be changed in meaning just by misplacing computer is used in the engineering of a part or product a comma, and the meaning of an oral description can be completely changed by using a wrong word. To avoid these As computer hardware and software continue to evolve, a possible errors, drawings are used to describe objects. For greater amount of CAE is completed in less time, at lower this reason, drawing is the draftsman’s language.

cost. In addition to product design, some of the other uses of CAE are product analysis, assembly, simulations, and Drawing, in the aviation industry, is a method of conveying maintenance information. [Figure 4-1] ideas concerning the construction or assembly of objects.

This is done with the help of lines, notes, abbreviations, and CATIA, ProEngineer, Solid Works, and Unigraphics are some symbols. It is important that the aviation mechanic who is of the more popular CAD software packages used for aircraft to make or assemble the object understands the meaning of design and manufacturing. Most airframe manufacturers use the different lines, notes, abbreviations, and symbols that CATIA software to design their aircraft. The complete aircraft are used in a drawing. (See the “Lines and Their Meanings” is designed and assembled in the software package before section of this chapter.)

it is manufactured. Drawings of all parts of the aircraft are available and can be accessed using the computer software.

Computer Graphics Drawings are no longer limited to 1, 2, or 3 views. Drawings From the early days of aviation, development of aircraft, from every angle can easily be accessed by using the aircraft engines, and other components relied heavily on computer model of the part or product. Technicians can access th aircraft drawings. For most of the 20 century, drawings drawings and aircraft manuals on laptops or even mobile were created on a drawing “board” with pen or pencil and devices when performing maintenance on the shop floor.

paper. With the introduction and advancement of computers th in the later decades of the 20 century, the way drawings Purpose & Function of Aircraft Drawings are created changed dramatically. Computers were used Drawings and prints are the link between the engineers who not only to create drawings, but they were being used to design an aircraft and the workers who build, maintain, and show items in “virtual reality,” from any possible viewing repair it. A print may be a copy of a working drawing for angle. Further development of computer software programs an aircraft part or group of parts, or for a design of a system allowed for assembling of separately created parts to check or group of systems. They are made by placing a tracing of for proper fit and possible interferences. Additionally, with the drawing over a sheet of chemically-treated paper and nearly instantaneous information sharing capability through exposing it to a strong light for a short period of time. When computer networking and the Internet, it became much easier the exposed paper is developed, it turns blue where the light for designers to share their work with other designers and has penetrated the transparent tracing. The inked lines of the manufacturers virtually anytime, anywhere in the world.

tracing, having blocked out the light, show as white lines Using new computer-controlled manufacturing techniques, on a blue background. With other types of sensitized paper, it became possible to design a part and have it precisely prints may have a white background with colored lines or a manufactured without ever having shown it on paper. New colored background with white lines.

terms and acronyms became commonplace. The more common of these terms are: Drawings created using computers may be viewed on the • Computer Graphics—drawing with the use of a computer monitor or printed out in “hard copy” by use of an computer 4-1 ink jet or laser printer. Larger drawings may be printed by use of a plotter or large format printer. Large printers can print drawings up to 42 inches high with widths up to 600 inches by use of continuous roll paper. [Figure 4-2] Care & Use of Drawings Drawings should be handled carefully as they are both expensive and valuable. Open drawings slowly and carefully to prevent tearing of the paper. When the drawing is open, smooth out the fold lines instead of bending them backward.

To protect drawings from damage, never spread them on the floor or lay them on a surface covered with tools or other objects that may make holes in the paper. Hands should be free of oil, grease, or other unclean matter that can soil or smudge the print.

Figure 4-1. Computer graphics work station.

Never make notes or marks on a print, as they may confuse Installation Drawing others and lead to incorrect work. Only authorized individuals An installation drawing is one that includes all necessary are permitted to make notes or changes on prints, and they information for a part or an assembly in the final installed must sign and date any changes they make.

position in the aircraft. It shows the dimensions necessary for the location of specific parts with relation to the other When finished with a drawing, fold and return it to its proper parts and reference dimensions that are helpful in later work place. Prints are folded originally in an appropriate size for in the shop. [Figure 4-5] filing. Care should be taken so that the original folds are always used.

Sectional View Drawings A section or sectional view is obtained by cutting away part Types of Drawings of an object to show the shape and construction at the cutting Drawings must give information such as size and shape of plane. The part or parts cut away are shown by using section the object and all its parts, specifications for material to be (crosshatching) lines. Types of sections are described in the used, how the material is to be finished, how the parts are to following paragraphs.

be assembled, and any other information essential to making and assembling the object. Drawings may be divided into Full Section three classes: detail, assembly, and installation.

A full section view is used when the interior construction or hidden features of an object cannot be shown clearly by Detail Drawing exterior views. For example, Figure 4-6 is a sectional view A detail drawing is a description of a single part, describing of a cable connector and shows the internal construction of bylines, notes, and symbols the specifications for size, shape, the connector.

material, and methods of manufacture to be used in making the part. Detail drawings are usually rather simple. When Half Section single parts are small, several detail drawings may be shown In a half section, the cutting plane extends only halfway on the same sheet or print. [Figure 4-3] across the object, leaving the other half of the object as an exterior view. Half sections are used with symmetrical objects Assembly Drawing to show both the interior and exterior. Figure 4-7 is a half An assembly drawing is a description of an object made up sectional view of a Capstan servo.

of two or more parts. [Figure 4-4] It describes the object’s size and shape. Its primary purpose is to show the relationship Revolved Section of the various parts. An assembly drawing is usually more complex than a detail drawing and is often accompanied by A revolved section drawn directly on the exterior view shows detail drawings of various parts. the shape of the cross section of a part, such as the spoke of a wheel. An example of a revolved section is shown in Figure 4-8 .

4-2 Drawing or Print Numbers All prints are identified by a number that appears in a number block in the lower right corner of the title block. It may also be shown in other places—such as near the top border line, in the upper right corner, or on the reverse side of the print at both ends—so that the number shows when the print is folded or rolled. The purpose of the number is quick identification of a print. If a print has more than one sheet and each sheet has the same number, this information is included in the number block, indicating the sheet number and the number of sheets in the series. [Figure 4-4B] Reference and Dash Numbers Reference numbers that appear in the title block refer you to the numbers of other prints. When more than one detail Figure 4-2. Large format printer.

is shown on a drawing, dash numbers are used. Both parts would have the same drawing number plus an individual Removed Section number, such as 40267-1 and 40267-2.

A removed section illustrates parts of an object. It is drawn like revolved sections, except it is placed at one side and In addition to appearing in the title block, dash numbers often drawn to a larger scale than the view indicated to bring may appear on the face of the drawing near the parts they out pertinent details.

identify. Dash numbers are also used to identify right-hand and left-hand parts.

Figure 4-9 is an illustration of removed sections. Section A-A shows the cross-sectional shape of the object at cutting In aircraft, many parts on the left side are like the plane line A-A. Section B-B shows the cross-sectional shape corresponding parts on the right side but in reverse. The left- at cutting plane line B-B. These sectional views are drawn hand part is always shown in the drawing. The right-hand to the same scale as the principal view.

part is called for in the title block. Above the title block a notation is found, such as: 470204-1LH shown; 470204-2RH Title Blocks opposite. Both parts carry the same number, but the part called for is distinguished by a dash number. Some prints Every print must have some means of identification.

have odd numbers for left-hand parts and even numbers for This is provided by a title block. [Figure 4-4A] The title right-hand parts.

block consists of a drawing number and certain other data concerning the drawing and the object it represents. This Universal Numbering System information is grouped in a prominent place on the print, usually in the lower right-hand corner. Sometimes the title The universal numbering system provides a means of block is in the form of a strip extending almost the entire identifying standard drawing sizes. In the universal distance across the bottom of the sheet.

numbering system, each drawing number consists of six or seven digits. The first digit is always 1, 2, 4, or 5 and indicates Although title blocks do not follow a standard form as far the size of the drawing. The number 1 indicates a drawing of as layout is concerned, all of them present essentially the 8½" × 11"; number 2 indicates an 11" × 17" drawing; number following information: 4 represents a drawing of 17" × 22"; and 5 indicates a width of between 17 and 36 inches but on a continuous roll. Letters 1. A drawing number to identify the print for filing are also used (and becoming more prevalent) with the most purposes and to prevent confusing it with any common letters being A through E. The letter A is 8½" × 11", other print.

B is 11" × 17", C is 17" × 22", D is 22" × 34" and E is 34" 2. The name of the part or assembly × 44". There are additional letters, such as D1 at 24" × 36", 3. The drawing scale E1 at 30" × 42" and additional sizes unique to even larger formats but generally reserved for inter-company operations.

4. The date 5. The name of the firm The remaining digits identify the drawing. Many firms have 6. The name of the draftsmen, the checker, and the person modified this basic system to conform to their needs. The letter or number depicting the standard drawing size may be approving the drawing 4-3 B D A C 3 OF 3 SHEET SWorks Drawing No.: SIZE REVISIONS FOR REVISION HISTORY SEE SHEET 1 FLAT PATTERN FOR REFERENCE ONLY 4 4 5 5 -03 7 7 D A B C Figure 4-3. Detail drawing.

4-4 D A C B 1 OF 3 S-TEC S-TEC S-TEC S-TEC S-TEC S-TEC SHEET Drawing Number B Drawing No.: SIZE TITLE: REVISIONS Scale H - -03 -02 -01 6 5 3 2 1 ITEM 8 1 1 -01 Revision Block C. Bill of Materials 4 4 C D Allowances and Tolerance Title Block G A 5 5 EC130T2 6 6 7 7 Notes F E Zone Numbers FORM (SWorks) 86359 REV - A B C D CWHITWORTH Figure 4-4. Assembly drawing.

4-5 B D A C REV 3 OF 3 SHEET REF SWorks Drawing No.: REF SIZE REVISIONS FOR REVISION HISTORY SEE SHEET 1 9 11 4 4 REF 5 5 C 7 7 REF REF (REF) FORM 86359 REV - D A B C Figure 4-5. Installation drawing.

4-6 Figure 4-6. Sectional view of a cable connector.

prefixed to the number, separated from it by a dash. Other Drawing Standards numbering systems provide a separate box preceding the Drawing standards cover such items as paper sizes, notes, drawing number for the drawing size identifier. In another numbering systems, geometric dimensions and tolerances, modification of this system, the part number of the depicted abbreviations, welding symbols, roughness symbols, and assembly is assigned as the drawing number.

electrical symbols. These standards cover metric and inch measurements, as well as computer-drafting standards.

Different standards for drawings are used in industry and some of the more common ones are published by the International Organization for Standardization (ISO) and the American National Standards Institute (ANSI).

Bill of Material A list of the materials and parts necessary for the fabrication or assembly of a component or system is often included on the drawing. The list is usually in ruled columns that Figure 4-7. Half section of a Capstan servo. Figure 4-8. Revolved sections.

4-7 to the changes by lettering or numbering them and listing those changes against the symbol in a revision block. [Figure 4-4D] The revision block contains the identification symbol, the date, the nature of the revision, the authority for the change, and the name of the draftsman who made the change.

To distinguish the corrected drawing from its previous version, many firms are including, as part of the title block, a space for entering the appropriate symbol to designate that the drawing has been changed or revised.

B B

Notes Notes are added to drawings for various reasons. Some of these notes refer to methods of attachment or construction. Others give alternatives, so that the drawing can be used for different styles of the same object. Still others list modifications that are available. Notes may be found alongside the item that SECTION B-B they refer to. If the notes are lengthy, they may be placed elsewhere on the drawing and identified by letters or numbers.

Notes are used only when the information cannot be conveyed in the conventional manner or when it is desirable to avoid crowding the drawing. Figure 4-4E illustrates one method A A of depicting notes.

When the note refers to a specific part, a light line with an arrowhead leads from the note to the part. If it applies to more than one part, the note is worded to eliminate ambiguity as SECTION A-A to the parts it pertains to. If there are several notes, they are generally grouped together and numbered consecutively.

Zone Numbers Zone numbers on drawings are like the numbers and letters printed on the borders of a map. They help locate a point.

Figure 4-9. Removed sections.

To find a point, mentally draw horizontal and vertical lines from the letters and numerals specified; the point where these provide the part number, name of the part, material the part lines intersect is the area sought. Figure 4-4F shows the zone is to be constructed of, the quantity required, and the source numbers on a drawing.

of the part or material. A typical bill of material is shown in Figure 4-4C . On drawings that do not have a bill of Use the same method to locate parts, sections, and views material, the data may be indicated directly on the drawing.

on large drawings, particularly assembly drawings. Parts On assembly drawings, each item is identified by a number numbered in the title block can be located on the drawing in a circle or square. An arrow connecting the number with by finding the numbers in squares along the lower border.

the item assists in locating it in the bill of material.

Zone numbers read from right to left.

Other Drawing Data Station Numbers & Location Identification on Revision Block Aircraft Revisions to a drawing are necessitated by changes in A numbering system is used on large assemblies for aircraft dimensions, design, or materials. The changes are usually to locate stations, such as fuselage frames. Fuselage station listed in ruled columns either adjacent to the title block or at 185 indicates a location that is 185 inches from the datum of one corner of the drawing. All changes to approved drawings the aircraft. The measurement is usually taken from the nose must be carefully noted on all existing prints of the drawing.

or zero station, but in some instances, it may be taken from the firewall or some other point chosen by the manufacturer.

When drawings contain such corrections, attention is directed Just as forward and aft locations on aircraft are made by 4-8 reference to the datum, locations left and right of the aircraft’s block indicates the bracket assembly is for a Roll Servo longitudinal axis are made by reference to the buttock line installation for an S-Tec Auto Pilot installation. If this and are called butt stations. Vertical locations on aircraft are drawing pertained to a B95 Aircraft equipped with an Aero- made in reference to the waterline. Tech air conditioning system and the bracket illustrated was unique to that installation, the title block would provide that The same station numbering system is used for wing and application information. The title block may indicate Bracket stabilizer frames. The measurement is taken from the Assy., Roll Servo, with Aero-Tech air conditioner (Model centerline or zero station of the aircraft. Figure 4-10 shows AT103-1) installed.

use of the fuselage stations (FS), waterline locations (WL), and left and right buttock line locations (RBL and LBL). Methods of Illustration Applied Geometry Allowances & Tolerances Geometry is the branch of mathematics that deals with When a given dimension on a print shows an allowable lines, angles, figures, and certain assumed properties in variation, the plus (+) figure indicates the maximum, and the space. Applied geometry, as used in drawings, makes use minus (−) figure the minimum allowable variation. The sum of these properties to accurately and correctly represent of the plus and minus allowance figures is called tolerance.

objects graphically. In the past, draftsmen utilized a variety [Figure 4-4G] For example, using 0.225 + 0.0025 − 0.0005, the of instruments with various scales, shapes, and curves to plus and minus figures indicate the part is acceptable if it is not make their drawings. Today, computer software graphics more than 0.0025 larger than the 0.225 given dimension, or not programs show drawings at nearly any scale, shape, and curve more than 0.0005 smaller than the 0.225 dimension. Tolerance imaginable, outdating the need for additional instruments.

in this example is 0.0030 (0.0025 max plus 0.0005 min).

Several methods are used to illustrate objects graphically.

If the plus and minus allowances are the same, you will find The most common are orthographic projections, pictorial them presented as 0.225 ± 0.0025. The tolerance would then drawings, diagrams, and flowcharts.

be 0.0050. Allowance can be indicated in either fractional or decimal form. When very accurate dimensions are necessary, Orthographic Projection Drawings decimal allowances are used. Fractional allowances are To show the exact size and shape of all the parts of complex sufficient when precise tolerances are not required. Standard objects, several views are necessary. This is the system used tolerances of –0.010 or − ⁄ 32 may be given in the title block in orthographic projection.

of many drawings, to apply throughout the drawing.

In orthographic projection, there are six possible views of Finish Marks an object, because all objects have six sides—front, top, Finish marks are used to indicate the surface that must bottom, rear, right side, and left side. Figure 4-11A shows be machine finished. Such finished surfaces have a better an object placed in a transparent box, hinged at the edges.

appearance and allow a closer fit with adjoining parts. During The projections on the sides of the box are the views as seen the finishing process, the required limits and tolerances must looking straight at the object through each side. If the outlines be observed. Do not confuse machined finishes with those of of the object are drawn on each surface of the box, and the paint, enamel, chromium plating, and similar coating.

box is then opened [Figure 4-11B] to lay flat [Figure 4-11C] , the result is a six-view orthographic projection.

Scale Some drawings are made the same size as the drawn part; It is seldom necessary to show all six views to portray an reflecting a scale of 1:1. Other scales may be used. However, object clearly; therefore, only those views necessary to when drawings are made on a computer, drawing sizes may illustrate the required characteristics of the object are drawn.

be easily increased (zoom in) or decreased (zoom out). Some One-, two-, and three-view drawings are the most common.

electronic printers have the same capability. Furthermore, Regardless of the number of views used, the arrangement when a 1:1 copy of a print is made, the copy size may differ is generally as shown in Figure 4-11 , with the front view slightly from that of the original. For accurate information, as principal view. If the right-side view is shown, it will be refer to the dimensions shown on the drawing. [Figure 4-4H] to the right of the front view. If the left-side view is shown, it will be to the left of the front view. The top and bottom Application views, if included, will be shown in their respective positions When shown near or in the title block, application may relative to the front view.

refer to a specific aircraft, assembly, sub-assembly or unique application. For example, in Figure 4-4A the title One-view drawings are commonly used for objects of 4-9 WATER FS 350.2 LINE (WL) WL 165.5 FS 222.0 FS 100.0 FS 55.6 150.0 FS 38.3 WL100.0 NOTE Reference datum located 50.0 at fuselage station 0.0 FS 157.5 FUSELAGE STATION (FS) 0.0 50.0 100.0 150.0 200.0 250.0 300.0 350.0 LEMAC BUTTOCK LINE (BL) FS 133.1 RBL 229.5 230.0 200.0 150.0 100.0 RBL 87.7 MAC 47.7" TYPICAL LBL RBL 77.3 RBL 63.1 50.0 BL 0.0 BL 0.0 50.0 LBL 63.1 LBL 77.3 100.0 150.0 200.0 230.0 BUTTOCK LINE (BL) LBL 229.5 Figure 4-10. Station numbers and location identification on aircraft.

4-10 uniform thickness, such as gaskets, shims, and plates. A Oblique Drawings dimensional note gives the thickness as shown in Figure 4-12 .

An oblique view is like an isometric view, except for one One-view drawings are also commonly used for cylindrical, distinct difference. In an oblique drawing, two of the three spherical, or square parts if all the necessary dimensions can drawing axes are always at right angles to each other.

be properly shown in one view. When space is limited and [Figure 4-16C] two views must be shown, symmetrical objects are often represented by half views, as illustrated in Figure 4-13 .

Exploded View Drawings An exploded view drawing is a pictorial drawing of two or Aircraft drawings seldom show more than two principal or more parts that fit together as an assembly. The view shows complete views of an object. Instead, there will be usually one the individual parts and their relative position to the other complete view and one or more detail views or sectional views.

parts before they are assembled. [Figure 4-17] Detail View Exploded view drawings are often used in IPCs that are used A detail view shows only a part of the object, but in greater to order parts. The exploded view drawing has numbers and detail and to a larger scale than the principal view. The the numbers correspond to a list of part numbers. Exploded part that is shown in detail elsewhere on the drawing is views are also used in Maintenance Instruction Manuals usually encircled by a heavy line on the principal view.

(MIM) for the assembly and repair of aircraft components.

[Figure 4-14] The principal view shows the complete object, These drawings are often accompanied by notes that explain while the detail view is an enlarged drawing of a portion of the assembly process.

the object.

Diagrams Pictorial Drawings A diagram may be defined as a graphic representation of A pictorial drawing is like a photograph. [Figure 4-15] an assembly or system, indicating the various parts and It shows an object as it appears to the eye, but it is not expressing the methods or principles of operation. There are satisfactory for showing complex forms and shapes. Pictorial many types of diagrams; however, those that the aviation drawings are useful in showing the general appearance mechanic is concerned with during the performance of their of an object and are used extensively with orthographic job may be grouped into four classes or types: installation, projection drawings. Pictorial drawings are used in Aircraft schematic, block, and wiring diagrams.

Maintenance Manuals (AMM), Structural Repair Manuals (SRM), and Illustrated Parts Catalogues (IPC). Four types Installation Diagrams of pictorial drawings used frequently by aircraft engineers Figure 4-18 is an example of an installation diagram.

and technicians are: perspective, isometric, oblique, and This is a diagram of the installation of the flight guidance exploded view.

control components of an aircraft. It identifies each of the components in the systems and shows their location in the Perspective Drawings aircraft. Each number (1, 2, 3, and 4) on the detail shows the A perspective view shows an object as it appears to an location of the individual flight guidance system components observer. [Figure 4-16A] It most closely resembles the way within the flight deck of the aircraft. Installation diagrams are an object would look in a photograph. Because of perspective, used extensively in aircraft maintenance and repair manuals, some of the lines of an object are not parallel and therefore and are invaluable in identifying and locating components the actual angles and dimensions are not accurate.

and understanding the operation of various systems.

Isometric Drawings Schematic Diagrams An isometric view uses a combination of the views of an Schematic diagrams do not indicate the location of the orthographic projection and tilts the object forward so individual components in the aircraft nor do they show that portions of all three views can be seen in one view.

the actual size and shape of the components, but rather [Figure 4-16B] This provides the observer with a three- locate components with respect to each other within the dimensional view of the object. Unlike a perspective drawing system. Schematics show the principle of operation of an where lines converge and dimensions are not true, lines in aircraft system and are often used for troubleshooting and an isometric drawing are parallel and dimensioned as they training purposes.

are in an orthographic projection.

Figure 4-19 illustrates a schematic diagram of an aircraft air conditioning system. High-speed bleed air from the engine is 4-11 A OBJECT B ROTATED TOP FRONT LEFT SIDE RIGHT SIDE REAR C FLAT BOTTOM Figure 4-11. Orthographic projection.

the lines that lead into and out of the unit. Schematic combined with cold air in the mixing chamber and distributed diagrams and installation diagrams are used extensively in via a manifold to various parts of the aircraft.

aircraft manuals.

Note that each line is coded for ease of reading and tracing Block Diagrams the flow. Each component is identified by name, and its location within the system can be ascertained by noting Block diagrams are used to show a simplified relationship of a Figure 4-12. One-view drawing.

4-12 Figure 4-13. Symmetrical object with exterior half view.

more complex system of components. [Figure 4-20] Individual components are drawn as a rectangle (block) with lines Figure 4-15. Pictorial drawing.

connecting it to other components (blocks) that it interfaces with during operation.

technicians involved with electrical repairs and installations, a thorough knowledge of wiring diagrams and electrical Wiring Diagrams schematics is essential.

Wiring diagrams show the electrical wiring and circuitry, coded for identification, of all the electrical appliances and Flowcharts devices used on aircraft. [Figure 4-21] These diagrams, even Flowcharts are used to illustrate a sequence or flow of for relatively simple circuits, can be quite complicated. For events. There are two types of flow charts most frequently 8 7 6 5 4 3 2 1 REF REVISIONS FOR REVISION HISTORY SEE SHEET 1 D D REF REF REF REF C C E E B B A A VIEW C SWorks Drawing No.: REV SIZE - SHEET 4 OF 5 FORM 86359 REV - 1 2 3 4 5 6 7 8 Figure 4-14. Detail view.

4-13 A B C PERSPECTIVE ISOMETRIC OBLIQUE Figure 4-16. (A) Perspective, (B) isometric, and (C) oblique drawings.

used in the aviation industry: troubleshooting flowcharts Troubleshooting Flowchart and logic flowcharts.

Troubleshooting flowcharts are frequently used for the detection of faulty components. They often consist of a 6 5 4 2 7 3 1 series of yes or no questions. If the answer to a question D C B A TITLE: Drawing No.: SIZE SHEET 1 OF 2 1 2 3 4 5 6 7 Figure 4-17. Exploded view drawing.

4-14 is yes, one course of action is followed. If the answer is flowchart. [Figure 4-23] A logic flowchart uses standardized no, a different course of action is followed. In this simple symbols to indicate specific types of logic gates and their manner, a logical solution to a problem may be achieved. relationship to other digital devices in a system. Since digital Figure 4-22 shows a flow chart to determine the repair systems make use of binary mathematics consisting of 1s and options for a composite structure. 0s, voltage or no voltage, a light pulse or no light pulse, and so forth, logic flowcharts consist of individual components Logic Flowchart that take an input and provide an output that is either the same as the input or opposite. By analyzing the input or multiple Another type of flowchart, developed specifically for analysis inputs, it is possible to determine the digital output or outputs.

of digitally-controlled components and systems, is the logic LEGEND 1. Screw 2. Cable Connector 3. Altitude/Vertical Speed Selector 4. Flight Guidance Program/Computer A Serials 1005 thru 1336 and 1337 and subs FWD w/o PFD ALTITUDE TRANSDUCER (REF) Figure 4-18. Example of an installation diagram (flight guidance components).

4-15 Lines and Their Meanings Most drawings use three widths, or intensities, of lines: thin, medium, or thick. These lines may vary somewhat Every drawing is composed of lines. Lines mark the on different drawings, but there is a noticeable difference boundaries, edges, and intersection of surfaces. Lines are between a thin and a thick line, with the width of the medium used to show dimensions and hidden surfaces and to indicate line somewhere between the two.

centers. Obviously, if the same kind of line is used to show these variations, a drawing becomes a meaningless collection Centerlines of lines. For this reason, various kinds of standardized lines Centerlines are made up of alternate long and short are used on aircraft drawings. [Figure 4-24] Examples of dashes. They indicate the center of an object or part of an correct line uses are shown in Figure 4-25 .

object. Where centerlines cross, the short dashes intersect Figure 4-19. Schematic diagram of an air conditioning system for a B737 NG.

4-16 symmetrically. In the case of very small circles, the holes, the angle of countersinking and the diameters are centerlines may be shown unbroken. given. [Figure 4-26] Dimension Lines The dimensions given for tolerances signify the amount A dimension line is a light solid line, broken at the midpoint of clearance allowable between moving parts. A positive allowance is indicated for a part that is to slide or revolve for insertion of measurement indications, and having opposite pointing arrowheads at each end to show origin and termination upon another part. A negative allowance is one given for a force fit. Whenever possible, the tolerance and allowances for of a measurement. They are generally parallel to the line that the dimension is given for, placed outside the outline of the desired fits conform to those set up in the American Standard for Tolerances, Allowances, and Gauges for Metal Fits. The object, and between views if more than one view is shown.

classes of fits specified in the standard may be indicated on assembly drawings.

All dimensions and lettering are placed so that they read from left to right. The dimension of an angle is indicated by placing Extension Lines the degree of the angle in its arc. The dimensions of circular parts are always given in terms of the diameter of the circle Extensions are used to extend the line showing the side or and are usually marked with the letter D or the abbreviation edge of a figure for placing a dimension to that side or edge.

DIA following the dimension. The dimension of an arc is They are very narrow and have a short break where they given in terms of its radius and is marked with the letter R extend from the object and extend a short distance past the following the dimension. Parallel dimensions are placed so arrow of the dimensioning line.

that the longest dimension is farthest from the outline and the shortest dimension is closest to the outline of the object. On Sectioning Lines a drawing showing several views, the dimensions are placed Sectioning lines indicate the exposed surfaces of an object in upon each view to show its details to the best advantage.

a sectional view. They are generally thin full lines, but may vary with the kind of material shown in section.

In dimensioning distances between holes in an object, dimensions are usually given from center to center rather than Phantom Lines from outside to outside of the holes. When several holes of Phantom lines indicate the alternate position of parts of the various sizes are shown, the desired diameters are given on a object or the relative position of a missing part. They are leader followed by notes indicating the machining operations composed of one long and two short evenly spaced dashes.

for each hole. If a part is to have three holes of equal size, equally spaced, this information is explicitly stated. For AC Input Signal Reference Phase A Conditioning Voltage and Balancing PU DO AC Input Signal Voltage Power Phase B Comparator Conditioning Selector Ampli fi er and Balancing Output Relay AC Input Signal Phase C Conditioning and Balancing Figure 4-20. Block diagram.

precision work, sizes are given in decimals. Diameters and 4-17 depths are given for counterbored holes. For countersunk DIGITAL FLIGHT GUIDANCE J3A COMPUTER-1 S1 22-01-01 UIO - 212 33 J2A 93 50 J1A 37 FLIGHT DIRECTOR BOTH ON 2 C J3A J1A J2A E J3A M N BOTH ON 1 69 T NORMAL R J3A A BOTH ON 2 J2A L J4A WIRING DIAGRAM J1 44 1A P 34 – 25 – 12 J2A J4A J1 S1 R 34 – 51 – 01 J1A O J1 J2A 1B C 31 35 34 – 16 – 12 E J1 J2A 48 S M 34 – 24 – 01 S J1A NORMAL O J4A R AIR DATA L ON AUX INST J4A ATTITUDE SWITCHING SWITCHING UNIT UNIT 34 - 23 34 - 14 UIO - 228 J4A UIO - 207 R ON AUX C J4A E NORMAL J1A N M J1 45 J2B T 79 R J1 2A A J2B J1A L J2B S2 J1 J4A 64 2B P 33 48 J2B R J1 J4A BOTH ON 1 O J3A C NORMAL E BOTH ON 2 S J3A M S J3A J2A O J1B FLIGHT DIRECTOR BOTH ON 1 93 37 R J1B J3A J2A DIGITAL FLIGHT GUIDANCE S2 COMPUTER-2 22-01-01 UIO - 213 Figure 4-21. Wiring diagram.

referred to as dash lines.

Break Lines Outline or Visible Lines Break lines indicate that a portion of the object is not shown on the drawing. Short breaks are made by solid, freehand The outline or visible line is used for all lines on the drawing lines. For long breaks, solid ruled lines with zigzags are used. representing visible lines on the object. This is a medium-to- Shafts, rods, tubes, and other such parts that have a portion wide line that represents edges and surfaces that can be seen of their length broken out have the ends of the break drawn when the object is viewed directly.

as indicated in Figure 4-25 .

Stitch Lines Leader Lines Stitch lines are used to indicate the stitching or sewing lines Leader lines are solid lines with one arrowhead. They on an article and consists of a series of very short dashes, indicate a part or portion that a note, number, or other approximately half the length of dash or hidden lines, evenly reference applies. spaced. Long lines of stitching may be indicated by a series of stitch lines connected by phantom lines.

Hidden Lines Hidden lines indicate invisible edges or contours. Hidden lines consist of short dashes evenly spaced and are frequently 4-18 indicated symbolically if its exact specification is shown elsewhere on the drawing. In this case, the more easily drawn symbol for cast iron is used for the sectioning, and DAMAGE EXCESSIVE the material specification is listed in the bill of materials or ASSESSMENT indicated in a note. Figure 4-27 illustrates a few standard material symbols.

SCRAP Shape Symbols Symbols can be used to excellent advantage when needed to COMPLEX REPAIR EASY REPAIR show the shape of an object. Typical shape symbols used on REPAIR TYPE aircraft drawings are shown in Figure 4-28 . Shape symbols are usually shown on a drawing as a revolved or removed section.

SUBMIT/ CHECK Electrical Symbols SCHEME WITH MANUFACTURER Electrical symbols represent various electrical devices /OEM rather than an actual drawing of the units. [Figure 4-29] Having learned what the various symbols indicate, it TEMPORARY REPAIR becomes relatively simple to look at an electrical diagram and determine what each unit is, what function it serves, and how it is connected in the system.

IMPROVISE Reading and Interpreting Drawings AND APPROVED RETURN TO Aircraft technicians do not necessarily need to be accomplished TEMPORARY REPAIR REPAIR in making drawings. However, they must have a working WORKSHOP knowledge of the information that is to be conveyed to them.

They most frequently encounter drawings for construction PERMANENT COMPOSITE REPAIR and assembly of new aircraft and components, during ACCORDING TO APPROVED GUIDELINES modifications, and for making repairs.

A drawing cannot be read all at once any more than a whole page of print can be read at a glance. Both must be read QUALITY CHECK / NDT one line at a time. To read a drawing effectively, follow a systematic procedure.

RETURN TO SERVICE Upon opening a drawing, read the drawing number and the description of the article. Next, check the model affected, Figure 4-22. Troubleshooting flowchart.

the latest change letter, and the next assembly listed. Having determined that the drawing is the correct one, proceed to Cutting Plane and Viewing Plane Lines read the illustration(s).

Cutting plane lines indicate the plane where a sectional view of the object is taken. In Figure 4-25 , plane line A indicates In reading a multiview drawing, first get a general idea of the plane that section AA is taken. Viewing plane lines the shape of the object by scanning all the views. Then select indicate the plane from where a surface is viewed.

one view for a more careful study. By referring back and forth to the adjacent view, it is possible to determine what Drawing Symbols each line represents.

The drawings for a component are composed largely of Each line on a view represents a change in the direction of symbols and conventions representing its shape and material.

a surface, but another view must be consulted to determine Symbols are the shorthand of drawing. They graphically what the change is. For example, a circle on one view may portray the characteristics of a component with a minimal mean either a hole or a protruding boss, as in the top view amount of drawing.

of the object in Figure 4-30 . Looking at the top view, we see two circles. However, the other view must be consulted to Material Symbols Section line symbols show the kind of material from which the part is to be constructed. The material may not be 4-19 CLOSE TARGET • LOGIC "1" • LOW VOLTAGE (TEST POINTS ONLY) R PROXIMITY 27 1 DETECTOR U TEST DIM L2-632 G CC 18 29 3 2 B5 - 76 30 LANDING GEAR DIM & TEST UNIT 3 POSITION 33 - 11 29 INDICATOR 32 - 61 - 04 NOSE GEAR WARNED LIKE MAIN PRIOR TO 1,024 R UNSAFE R2-262 11 28 27 DIM HDL GEAR B HOT INTERLOCK D DD TEST ON 26 32-62 UNIT-2 B5-75 27 SI-412 32-35 33-11 HDL ON C G SAFE E 29 3 2 D 10 B 30 G NOSE GEAR POS INTLK SHIP 1,024 & SUBS LEFT SWITCH OR S832 - 17B LEFT NOSE RIGHT SEE 00 - 04 Z R 14 9 27 1 15 28 TEST DIM G B 8 30 29 2 3 B5 - 74 DIM & TEST UNIT-1 33 - 11 32-61-03 A I 20 2 1 34 33 GEAR DOOR L2-265 OPEN FDAU Y UIO-206 31 - 31 LANDING GEAR WARNING 18 PROXIMITY 2B VDC - L DETECTOR B1 - 187 R MAIN 51 CENTRAL AURAL 47 GROUND IS WARNING UNIT NOSE 50 34 AUTOSPOILER B5 - 71 DOWN B LOCKED 12B D SWITCHING UNIT SEE 32 - 63 L MAIN 49 46 6B B5 - 70 27 - 61 A9 S A 19 R GEAR UP & LATCHED RETARDED THROTTLE TURNS ON RED LIGHT WIRING DIAGRAM L GEAR UP & LATCHED 61 32 – 61 – 00 ONE GEAR 27 – 61 – 11 NOT J1A HDL 62 P WIRED OTHER PROXIMITY ON O UNIT SCHEMATICS 27 – 02 27 – 83 32 – 62 LANDING GEAR 27 – 23 27 – 84 32 – 63 HANDLE SWITCH 1 27 – 60 31 – 51 52 – 61 UP S1 - 89 DN 27 – 61 32 – 15 52 – 70 32 - 62 ALTERNATE GEAR DOWN A LEVER SWITCH POWER UP PROXIMITY SWITCH ELECTRONICS UNIT S1 - 466 SUPPLY 32 - 61 - OI B5 - 80 F 32 - 62 RIGHT AFT RADIO RACK - SHELF 1 Figure 4-23. Logic flowchart.

determine what each circle represents. views are given, all three must be consulted to be sure the shape has been read correctly.

A glance at the other view tells us that the smaller circle represents a hole, and the larger circle represents a protruding After determining the shape of an object, determine its size.

boss. In the same way, the top view must be consulted to Information on dimensions and tolerances is given so that determine the shape of the hole and the protruding boss. certain design requirements may be met. Dimensions are indicated by figures either with or without the inch mark. If no It can be seen from this example that one cannot read a print inch mark is used, the dimension is in inches. It is customary by looking at a single view when more than one view is given. to give part dimensions and an overall dimension that gives Two views do not always describe an object and when three the greatest length of the part. If the overall dimension is 4-20 Center line Thin Dimension Thin Extension line Thin Break (long) Thin Break (long) Thick Phantom Thin Sectioning Thin Hidden Medium Stitch line Medium Visible line Thick ³⁄16 DRILL 0.3125 DRILL 3 HOLES Datum line Thick 0.3217 REAM EQUALLY Cutting plane Extra thick SPACED ³⁄16 DRILL Cutting plane Extra thick 80 ° C’SK ¹⁄4 DRILL TO ⁵⁄16 DIA ⁷⁄16 C’BORE ¹⁄8 DEEP Complex cutting plane Extra thick 2 HOLES 80° Figure 4-24. The meaning of lines.

missing, it can be determined by adding the separate part dimensions. Many drawings used for new aircraft and components are now using the metric system and millimeter (mm) is the unit used for these drawings.

0.2560 DRILL ¹⁄4 DRILL, ³⁄6 C’BORE ¹⁄8 DEEP, 3 HOLES Drawings may be dimensioned in decimals or fractions. This Figure 4-26. Dimensioning holes. is especially true about tolerances. Instead of using plus and minus signs for tolerances, many figures give the complete dimension for both tolerances. For example, if a dimension is A print tolerance (usually found in the title block) is a 2 inches with a plus or minus tolerance of 0.01, the drawing general tolerance that can be applied to parts where the would show the total dimensions as: dimensions are noncritical. Where a tolerance is not shown on a dimension line, the print tolerance applies.

2.01 1.99 To complete the reading of a drawing, read the general notes and the content of the material block, find the various changes incorporated, and read the special information given in or Phantom line Extension line Center line Dimension line Sectioning line A Break line Section AA Cutting plane line Outline Hidden line Figure 4-25. Correct use of lines.

4-21 The rules and conventional practices for making mechanical drawings are followed to the extent that all views needed to portray an object accurately are shown in their proper relationship. It is also necessary to observe the rules for CAST IRON MAGNESIUM, correct line use and dimensioning. [Figures 4-24 and 4-25] ALUMINUM, AND ALUMINUM ALLOYS Sketching Techniques To make a sketch, first determine what views are necessary to portray the object. Then block in the views using light construction lines. Next, complete the details, darken the object outline, and sketch extension and dimension lines.

Complete the drawing by adding notes, dimensions, title, STEEL RUBBER, PLASTIC date, and when necessary, the sketcher’s name. The steps in ELECTRICAL making a sketch of an object are illustrated in Figure 4-31 .

INSULATION Basic Shapes Depending on the complexity of the sketch, basic shapes may be drawn in freehand or by use of templates. If the sketch is quite complicated or the technician is required to make frequent sketches, use of a variety of templates and other BRASS, BRONZE, BABBITT, LEAD, drafting tools is highly recommended.

AND COPPER ZINC, AND ALLOYS Repair Sketches A sketch is frequently drawn for repairs or for use in manufacturing a replacement part. Such a sketch must provide all necessary information to those who must make the repair or manufacture the part.

WOOD—ACROSS WOOD—WITH GRAIN GRAIN The degree that a sketch is complete depends on its intended use. Obviously, a sketch used only to represent an object pictorially need not be dimensioned. If a part is to be manufactured from the sketch, it should show all the necessary construction details.

CORK, FELT, FABRIC, ASBESTOS, LEATHER, Care of Drafting Instruments AND FIBER Good drawing instruments are expensive precision tools.

Reasonable care given to them during their use and storage Figure 4-27. Standard material symbols.

can prolong their service life.

near views and sections.

T-squares, triangles, and scales should not be used or placed where their surfaces or edges may be damaged. Use a drawing Drawing Sketches board only for its intended purpose and not in a manner that A sketch is a simple rough drawing that is made rapidly can mar the working surface.

and without much detail. Sketches may take many forms— from a simple pictorial presentation to a multi-view Compasses, dividers, and pens provide better results with less annoyance, if they are correctly shaped and sharpened orthographic projection.

and are not damaged by careless handling. Store drawing instruments in a place where they are not likely to be damaged Just as aircraft technicians need not be highly skilled in creating drawings, they need not be accomplished artists. by contact with other tools or equipment. Protect compass and divider points by inserting them into a piece of soft rubber or However, in many situations, they need to prepare a drawing to present an idea for a new design, a modification, or a repair similar material. Never store ink pens without first cleaning and drying them thoroughly.

method. The medium of sketching is an excellent way of accomplishing this.

4-22 SQUARE SECTION ( METAL ) SQUARE SECTION ( WOOD ) ROUND SECTION ( SOLID ) ROUND SECTION ( TUBULAR ) ANGLE SECTION ( METAL ) CHANNEL SECTION ( METAL ) I - BEAM ( METAL ) SQUARE SECTION ( TABULAR ) Figure 4-28. Shape symbols.

Microfilm & Microfiche Graphs & Charts The practice of recording drawings, parts catalogs, and Graphs and charts are frequently used to convey information maintenance and overhaul manuals on microfilms was graphically or information given certain conditions. They utilized extensively in the past. Microfilm is available as often utilize values shown on the “x” and “y” axes that can regular 16 mm or 35 mm film. Since 35 mm film is larger, be projected up and across to arrive at a specific result. Also, it provides a better reproduction of drawings. Microfiche is when data is entered into a computer database, software a card with pages laid out in a grid format. Microfilm and programs can create a variety of different bar graphs, pie microfiche require use of special devices for both reading charts, and so forth, to graphically represent that data.

and printing the information.

Reading & Interpreting Graphs & Charts Most modern aircraft manufacturers have replaced microfilm When interpreting information shown on graphs and charts, and microfiche with digital storage methods utilizing CDs, it is extremely important that all the notes and legend DVDs, and other data storage devices. A great deal of service information be carefully understood to eliminate any and repair information for older aircraft has been transferred misinterpretation of the information presented.

to digital storage devices. However, there may still be a need to access information using the old methods. A well-equipped Nomograms shop should have available, both the old microfilm and A nomogram is a graph that usually consists of three microfiche equipment, as well as new computer equipment.

sets of data. Knowledge of any two sets of data enables the interpreter to obtain the value for the third unknown Digital Images corresponding value. One type of nomogram consists of three Though not a drawing, a digital image created by a digital parallel scales graduated for different variables, so that when camera can be extremely helpful to aviation maintenance a straight edge connects any two values, the third can be read technicians in evaluating and sharing information concerning directly. Other types may use values on the “x” and “y” axes the airworthiness or other information about aircraft. Digital of a graph with the third corresponding value determined by images can be rapidly transmitted over the World Wide Web the intersection of the “x” and “y” values with one of a series as attachments to e-mail messages. Images of structural of curved lines. Figure 4-32 is an example of a nomogram fatigue cracks, failed parts, or other flaws, as well as desired that shows the relationship between aviation fuels, specific design and paint schemes, are just a few examples of the types weight, and temperature.

of digital images that might be shared by any number of users over the Internet. Figure 4-33 is a digital image of damage to a composite structure taken with a simple digital camera.

4-23 CONDENSERS LAMPS − RED, GREEN, WHITE R L G W CONDUCTORS OR INTERSECTING CROSSING OVER SINGLE SOLENOID TRANSFORMER ELECTRICALLY EACH OTHER MOTORS GENERATORS + + OR OR M G M G M G − − AC DC AC DC METERS V A AMMETER VOLT RHEOSTAT RESISTOR RELAYS CONNECTORS P S S P FIXED REMOVABLE A A B B C C NOT ALL ALL PINS D D SPST SPDT NORMAL OR MPDT NORMAL PINS SHOW SHOW E MOMENTARY MOMENTARY OR MOMENTARY CONTACTS CONTACTS ON P DESIGNATED PINS CIRCUIT BREAKERS S DESIGNATED SOCKETS AUTOMATIC PUSH PUSH RESET SWITCH MOMENTARY CURRENT RESET RESET PULL OFF TYPE SWITCH TYPE BUS BATTERY LIMITER SWITCHES SPDT CENTER SPST SPDT SPDT SPDT BIMETALIC OFF NORMAL OR SPST MOMENTARY CENTER MOMENTARY SPDT NORMAL OR PRESSURE THERMAL MOMENTARY ON OFF ON MOMENTARY CUT-OUT CONTACTS CONTACTS PUSHBUTTON TYPE NORMAL POSITION MOMENTARY POSITION NORMAL OR MOMENTARY NORMAL MPDT CENTER MOMENTARY MPST MECHANICAL LINKAGE ON ON OFF CONTACTS FUSE SPLICE POLARITY GROUND DC − BASIC + 10A ELECTRICAL DISCONNECT POSITIVE NEGATIVE Figure 4-29. Electrical symbols.

4-24 Block in Add Detail Darken Views Add Dimensions 1¼" 1¼" 1" 1½" ¾" 3" 1-27-06 WEDGE RJA Figure 4-31. Steps in sketching.

Figure 4-30. Reading views.

To provide information about the extent of the damage, a measurement scale, or other object, such as a coin, can be placed near the area of concern before the picture is taken.

Also, within the text of the e-mail, the technician should state the exact location of the damage, referenced to fuselage station, wing station, and so forth.

4-25 Density Variation of Aviation Fuel Based on Average Specif i c Gravity Average Speci fi c Fuel Gravity at 15 °C (59 °F) Aviation Kerosene 0.812 Jet A and Jet A1 Jet B (JP-4) 0.785 AV Gas Grade 100/130 0.703 NOTE: The fuel quantity indicator is calibrated for correct indication when using Aviation Kerosene Jet A and Jet A1.

When using other fuels, multiply the indicated fuel quantity in pounds by 0.99 for Jet B (JP-4) or by 0.98 for Aviation Gasoline (100/130) to obtain actual fuel quantity in pounds.

7.5 Aviation Kerosene Jet A & Jet A1 7.0 Jet B (JP-4) 6.5 c Weight (lb/US gal) fi Speci Aviation Gasoline Grade 100/130 6.0 5.5 −40 −30 −20 −10 0 10 20 30 40 Temperature (°C) Figure 4-32. Nomogram.

Figure 4-33. Digital image of damage.

4-26

Next: Chapter 5 →

Chapter 5

Physics for Aviation

Physical science, which is most often called physics, is a very Mass = Weight ÷ Acceleration due to gravity interesting and exciting topic. For an individual who likes technical things and is a hands-on type of person, physics The acceleration due to gravity here on earth is 32.2 feet is an invaluable tool. Physics allows us to explain how per second per second (32.2 fps/s). An object weighing 32.2 engines work, both piston and gas turbine; how airplanes pounds (lb) here on earth is said to have a mass of 1 slug.

and helicopters fly; and countless other things related to the A slug is a quantity of mass that will accelerate at a rate of field of aviation and aerospace. In addition to allowing us to 1 ft. /s when a force of 1 pound is applied. In other words, explain the operation of the things around us, it also allows under standard atmospheric condition, which is that gravity is us to quantify them. For example, through the use of physics equal to 32.2 fps/s, a mass of one slug would be equal to 32.2 lb.

we can explain what the concept of thrust means for a jet engine, and then follow it up by mathematically calculating Weight is a measure of the pull from gravity acting on the the pounds of thrust being created. mass of an object. The more mass an object has, the more it will weigh under the earth’s force of gravity. The only way for Physics is the term applied to an area of knowledge regarding an object to be weightless is for gravity to go away, because the basic and fundamental nature of matter and energy. It does it is not possible for the mass of an object to disappear. When not attempt to determine why matter and energy behave as we view astronauts on the space shuttle, it appears that they they do in their relation to physical phenomena, but rather are weightless. Even though the shuttle is far from the surface how they behave. The people who maintain and repair aircraft of the earth, the force of gravity has not completely gone should have knowledge of basic physics, which is sometimes away, and the astronauts are not weightless. The astronauts called the science of matter and energy. and the space shuttle are actually in a state of free fall, so relative to the shuttle the astronauts appear to be weightless.

Matter Mathematically, weight can be stated as follows: Matter is the foundation, or the building blocks, for any Weight = Mass × Gravity discussion of physics. According to the dictionary, matter is what all things are made of; whatever occupies space, has Attraction mass, and is perceptible to the senses in some way. According Attraction is mutual force acting between particles of matter, to the Law of Conservation, matter cannot be created or which tends to draw them together. Sir Isaac Newton called destroyed, although it is possible to change its physical state.

this the “Law of Universal Gravitation.” Newton showed When liquid gasoline vaporizes and mixes with air, and then how each particle of matter attracts every other particle, burns, it might seem that this piece of matter has disappeared how people are bound to the earth, and how the planets are and no longer exists. Although it no longer exists in the state attracted in the solar system.

of liquid gasoline, the matter still exists in the form of the gases given off by the burning fuel.

Porosity Characteristics of Matter Porosity means having pores or spaces where smaller Mass & Weight particles may fit when a mixture takes place. This is sometimes referred to as granular—consisting or appearing Mass is a measure of the quantity of matter in an object. In to consist of small grains or granules.

other words, how many molecules are in the object, how many atoms are in the object, or to be more specific, how Impenetrability many protons, neutrons, and electrons are in the object. The mass of an object does not change regardless of where you Impenetrability means that no two objects can occupy the take it in the universe, or with a change of state. The only same place at the same time. Thus, two portions of matter way to change the mass of an object is to add or take away cannot at the same time occupy the same space.

atoms. Mathematically, mass can be stated as follows: 5-1 Density Density of the substance Specific Gravity = The density of a substance is its weight per unit volume.

Density of water The unit volume selected for use in the English system of measurement is 1 cubic foot (ft ). In the metric system, it The same formulas are used to find the density of gases by is 1 cubic centimeter (cm ). Therefore, density is expressed 3 substituting air or hydrogen for water.

in pounds per cubic foot (lb⁄ft ) or in grams per cubic centimeter (g⁄cm ).

Specific gravity is not expressed in units, but as pure numbers.

For example, if a certain hydraulic fluid has a specific gravity To find the density of a substance, its weight and volume must 3 3 of 0.8, 1 ft of the liquid weighs 0.8 times as much as 1 ft be known. Its weight is then divided by its volume to find of water: 62.4 times 0.8, or 49.92 lb.

the weight per unit volume. For example, the liquid which fills a certain container weighs 1,497.6 lb. The container Specific gravity and density are independent of the size of is 4 ft long, 3 ft wide and 2 ft deep. Its volume is 24 ft 3 the sample under consideration and depend only upon the (4 ft. × 3 ft. × 2 ft.). If 24 ft of liquid weighs 1,497.6 lb, then substance of which it is made. See Figure 5-1 for typical 1 ft weighs 1,497.6 ÷ 24, or 62.4 lb. Therefore, the density 3 values of specific gravity for various substances.

of the liquid is 62.4 lb/ft . This is the density of water at 4 °C (Centigrade) and is usually used as the standard for comparing A device called a hydrometer is used for measuring specific densities of other substances. In the metric system, the density gravity of liquids. This device consists of a tubular glass float of water is 1 g⁄cm . The standard temperature of 4 °C is used contained in a larger glass tube. [Figure 5-2] The larger glass when measuring the density of liquids and solids. Changes tube provides the container for the liquid. A rubber suction in temperature will not change the weight of a substance, bulb draws the liquid up into the container. There must be but will change the volume of the substance by expansion or enough liquid raising the float to prevent it from touching the contraction, thus changing its weight per unit volume.

bottom. The float is weighted and has a vertically graduated scale. To determine specific gravity, the scale is read at the The procedure for finding density applies to all substances; surface of the liquid in which the float is immersed. An however, it is necessary to consider the pressure when finding indication of 1000 is read when the float is immersed in pure the density of gases. Pressure is more critical when measuring water. When immersed in a liquid of greater density, the float the density of gases than it is for other substances. The rises, indicating a greater specific gravity. For liquids of lesser density of a gas increases in direct proportion to the pressure density, the float sinks, indicating a lower specific gravity.

exerted on it. Standard conditions for the measurement of the densities of gases have been established at 0 °C for An example of the use of the hydrometer is to determine temperature and a pressure of 76 cm of mercury (Hg), which the specific gravity of the electrolyte (battery liquid) in an is the average pressure of the atmosphere at sea level. Density aircraft battery. When a battery is discharged, the calibrated is computed based on these conditions for all gases.

float immersed in the electrolyte will indicate approximately 1150. The indication of a charged battery is between 1275 Specific Gravity and 1310. The values 1150, 1275, and 1310 represent 1.150, It is often necessary to compare the density of one substance 1.275, and 1.310. The electrolyte in a discharged battery is with another substance. For this purpose, a standard is 1.15 times denser than water, and in a charged battery 1.275 needed. Water is the standard that physicists have chosen to to 1.31 times denser than water.

use when comparing the densities of all liquids and solids.

For gases, air is most commonly used, but hydrogen is also Energy sometimes used as a standard for gases. In physics, the word Energy is typically defined as something that gives us the “specific” implies a ratio. Thus, specific gravity is calculated capacity to perform work. As individuals, saying that we by comparing the weight of a definite volume of the given feel full of energy is an indicator that we can perform a lot substance with the weight of an equal volume of water. The of work. Energy can be classified as one of two types: either terms “specific weight” or “specific density” are sometimes as potential energy or kinetic energy.

used to express this ratio.

Potential Energy The following formulas are used to find the specific gravity Potential energy is defined as being energy at rest, or energy of liquids and solids.

that is stored. Potential energy may be classified into three Weight of the substance groups: (1) energy due to position, (2) energy due to distortion Specific Gravity = Weight of an equal volume of water of an elastic body, and (3) energy which produces work or 5-2 through chemical action. Examples of the first group are Speci fi c Speci fi c Speci fi c Liquid Solid Gas water in an elevated reservoir or an airplane raised off the Gravity Gravity Gravity ground with jacks; a stretched bungee cord on a Piper Tri- Gasoline Ice Hydrogen 0.917 0.0695 0.72 Pacer or compressed spring are examples of the second group; Jet Fuel Aluminum Helium 2.7 0.138 0.785 Jp-4 and energy in aviation gasoline, food, or storage batteries are examples of the third group.

Ethyl Titanium Acetylene 4.4 0.898 0.789 Alcohol To calculate the potential energy of an object due to its Jet Fuel Zinc Nitrogen 7.1 0.967 0.82 Jp-5 position, as in height, the following formula is used: Kerosene Iron Air 7.9 1.000 0.82 Potential Energy = Weight × Height Lube Oil Brass Oxygen 8.4 1.105 0.89 Synthetic Carbon Copper 8.9 1.528 0.928 A calculation based on this formula will produce an answer Oil Dioxide that has units of foot-pounds (ft-lb) or inch-pounds (in-lb), Water Lead 11.4 1.000 which are the same units that apply to work. Work, which Sulfuric is covered later in this chapter, is described as a force being Gold 19.3 1.84 Acid applied over a measured distance, with the force being pounds Mercury Platinum 21.5 13.6 and the distance being feet or inches. Potential energy and work have a lot in common.

Figure 5-1. Specific gravity of various substances.

Example: A Boeing 747 weighing 450,000 pounds needs to be raised 4 feet in the air so maintenance can be done on the 1,275 Charged 1,150 Discharged landing gear. How much potential energy does the airplane possess because of this raised position?

Potential Energy = Weight × Height PE = 450,000 lb × 4 ft PE = 1,800,000 ft-lb As previously mentioned, aviation gasoline possesses potential energy because of its chemical nature. Gasoline has the potential to release heat energy, based on its British thermal unit (BTU) content. One pound of aviation gas contains 18,900 BTU of heat energy, and each BTU is capable of 778 ft-lb of work. So, when we multiply 778 by 18,900, we find that one pound of aviation gas is capable of 14,704,200 ft-lb of work. Imagine the potential energy in the completely serviced fuel tanks of an airplane.

Kinetic Energy Kinetic energy is defined as being energy that is in motion.

An airplane rolling down the runway or a rotating flywheel on an engine are both examples of kinetic energy. Kinetic energy has the same units as potential energy, namely foot- pounds or inch-pounds. To calculate the kinetic energy for something in motion, the following formula is used: 1 2 Kinetic Energy = ⁄ 2 Mass × Velocity To use the formula, we will show the mass as weight divided by gravity and the velocity of the object will be in feet per second. This is necessary to end up with units in foot-pounds.

Figure 5-2. Hydrometer for checking battery specific gravity.

5-3 Example: An Airbus A380 weighing 600,000 lb is moving In the metric system, the force is identified in newtons (N) down the runway on its takeoff roll with a velocity of 200 fps. and the distance in meters, with the resultant units being How many foot-pounds of kinetic energy does the airplane joules. One pound of force is equal to 4.448 N and one meter possess? [Figure 5-3] is equal to 3.28 feet. One joule is equal to 0.74 ft-lb.

1 2 Kinetic Energy = ⁄ 2 Mass × Velocity Example: How much work is accomplished by jacking a 1 2 Kinetic Energy = ⁄ 2 × 600,000 ÷ 32.2 × 200 150,000-lb Airbus A-320 airplane a vertical height of 4 ft?

KE = 372,670,000 ft-lb [Figure 5-4] Force, Work, Power, & Torque Work = Force × Distance = 150,000 lb × 4 ft Force = 600,000 ft-lb Before the concept of work, power, or torque can be discussed, we need to understand what force means. According to the Example: How much work is accomplished when a tow dictionary, force is the intensity of an impetus, or the intensity tractor is hooked up to a tow bar and a Boeing 737-800 of an input. For example, if we apply a force to an object, the airplane weighing 130,000 lb is pushed 80 ft. into the hangar?

tendency will be for the object to move. Another way to look The force on the tow bar is 5,000 lb.

at it is that for work, power, or torque to exist, there must be a force that initiates the process.

Work = Force × Distance = 5,000 lb × 80 ft The unit for force in the English system of measurement = 400,000 ft-lb is pounds, and in the metric system it is newtons. One pound of force is equal to 4.448 newtons. When we In this last example, notice the force does not equal the weight calculate the thrust of a turbine engine, we use the formula of the airplane. This is because the airplane is being moved “Force = Mass × Acceleration,” and the thrust of the engine is horizontally and not lifted vertically. In almost all cases, it expressed in pounds. The GE90-115 turbofan engine (power takes less work to move something horizontally than it does plant for the Boeing 777-300), for example, has 115,000 to lift it vertically. Most people can push their car a short pounds of thrust.

distance if it runs out of gas, but they cannot get under their car and lift it off the ground.

Work The study of machines, both simple and complex, can be Friction & Work seen as a study of the energy of mechanical work. This is In calculating work done, the actual resistance overcome is true because all machines transfer input energy, or the work measured. This is not necessarily the weight of the object done on the machine, to output energy, or the work done by being moved. [Figure 5-5] A 900-lb load is being pulled a the machine.

distance of 200 ft. This does not mean that the work done (force × distance) is 180,000 ft-lb (900 lb × 200 ft). This is Work, in the mechanical sense of the term, is done when a resistance is overcome by force acting through a measurable distance. Two factors are involved: (1) force and (2) movement through a distance. As an example, suppose a small aircraft is stuck in the snow. Two men push against it for a period of time, but the aircraft does not move. According to the technical definition, no work had been done when the men were pushing against the aircraft. By definition, work is accomplished only when an object is displaced some distance against a resistive force. To calculate work, the following formula is used: Work = Force (F) × distance (d) In the English system, the force will be identified in pounds and the distance either in feet or inches, so the units will be foot-pounds or inch-pounds. Notice these are the same units that were used for potential and kinetic energy.

Figure 5-3. Kinetic energy (Airbus A380 taking off).

5-4 because the person pulling the load is not working against the total weight of the load, but rather against the rolling friction of the cart, which may be no more than 90 lb.

Friction is an important aspect of work. Without friction, it would be impossible to walk. One would have to shove oneself from place to place, and would have to bump against some obstacle to stop at a destination. Yet friction is a liability as well as an asset, and requires consideration when dealing with any moving mechanism.

In experiments relating to friction, measurement of the applied forces reveals that there are three kinds of friction.

One force is required to start a body moving, while another is required to keep the body moving at constant speed. Also, after a body is in motion, a definitely larger force is required to keep it sliding than to keep it rolling.

Thus, the three kinds of friction may be classified as: (1) starting or static friction, (2) sliding friction, and (3) rolling friction.

Static Friction Figure 5-4. Airplane on jacks.

When an attempt is made to slide a heavy object along a surface, the object must first be broken loose or started. Once employed to overcome the static friction of each wheel as in motion, it slides more easily. The “breaking loose” force well as the inertia of each car. It would be impossible for the is, of course, proportional to the weight of the body. The engine to start all of the cars at the same instant, for static force necessary to start the body moving slowly is designated friction, which is the resistance of being set in motion, would “F,” and “F'” is the normal force pressing the body against be greater than the force exerted by the engine. However, once the surface which is usually its weight. Since the nature of the cars are in motion, the static friction is greatly reduced the surfaces rubbing against each other is important, they and a smaller force is required to keep the train in motion must be considered. The nature of the surfaces is indicated than was required to start it.

by the coefficient of starting friction which is designated by the letter “k.” This coefficient can be established for various Sliding Friction materials and is often published in tabular form. Thus, when Sliding friction is the resistance to motion offered by an object the load (weight of the object) is known, starting friction can sliding over a surface. It pertains to friction produced after the be calculated by using the following formula: object has been set in motion, and is always less than starting friction. The amount of sliding resistance is dependent on the F = kF' nature of the surface of the object, the surface over which it slides, and the normal force between the object and the For example, if the coefficient of sliding friction of a surface. This resistive force may be computed by using the smooth iron block on a smooth, horizontal surface is 0.3, following formula: the force required to start a 10 lb block would be 3 lb; a 40-lb block, 12 lb.

F = mN Starting friction for objects equipped with wheels and roller In the formula above, “F” is the resistive force due to friction bearings is much smaller than that for sliding objects. For expressed in pounds; “N” is the force exerted on or by the example, a locomotive would have difficulty getting a long object perpendicular (normal) to the surface over which it train of cars in motion all at one time. Therefore, the couples slides; and “m” (mu) is the coefficient of sliding friction. On between the cars are purposely made to have a few inches of a horizontal surface, N is equal to the weight of the object in play. When starting the train, the engineer backs the engine pounds. The area of the sliding object exposed to the sliding until all the cars are pushed together. Then, with a quick surface has no effect on the results. A block of wood, for start forward the first car is set in motion. This technique is 5-5 how long it took to lift the weight, but the power required is different. If the weight is to be lifted in a shorter period Work = force x distance of time, it will take more power. The formula for power is = 90 lb x 200 ft as follows: = 18,000 ft-lb Force Gravity 90 lb Power = Force × distance ÷ time The units for power will be foot-pounds per minute, foot- 200 ft pounds per second, inch-pounds per minute or second, and possibly mile-pounds per hour. The units depend on how distance and time are measured.

Many years ago, there was a desire to compare the power Resistance of the newly evolving steam engine to that of horses.

People wanted to know how many horses the steam engine Figure 5-5. The effect of friction on work.

was equivalent to. The value we know currently as one horsepower (hp) was developed, and it is equal to 550 foot- pounds per second (ft-lb/s) because of this. It was found that example, will not slide any easier on one of the broad sides the average horse could lift a weight of 550 lb, one foot off than it will on a narrow side, assuming all sides have the the ground, in one second. The values we use today, in order same smoothness. Therefore, area does not enter into the to convert power to horsepower, are as follows: equation above.

1 hp = 550 ft-lb/s Rolling Friction 1 hp = 33,000 ft-lb/min.

Resistance to motion is greatly reduced if an object is 1 hp = 375 mile pounds per hour (mi-lb/hr.)

mounted on wheels or rollers. The force of friction for 1 hp = 746 watts (electricity conversion) objects mounted on wheels or rollers is called rolling friction.

This force may be computed by the same equation used in To convert power to horsepower, divide the power by the computing sliding friction, but the values of “m” will be appropriate conversion based on the units being used.

much smaller. For example, the value of “m” for rubber tires on concrete or macadam is about 0.02. The value of “m” for Example: What power would be needed, and also horsepower, roller bearings is very small, usually ranging from 0.001 to to raise the GE-90 turbofan engine into position to install 0.003 and is often disregarded.

it on a Boeing 777-300 airplane? The engine weighs 19,000 lb, and it must be lifted 4 ft in 2 minutes.

Example: An aircraft with a gross weight of 79,600 lb is towed over a concrete ramp. What force must be exerted Power = Force × distance ÷ time by the towing vehicle to keep the airplane rolling after once = 19,000 lb × 4 ft ÷ 2 min.

set in motion?

= 38,000 ft-lb/min.

F = mN Hp = 38,000 ft-lb/min. ÷ 33,000 ft-lb/min.

= 0.02 mu × 79,600 lb Hp = 1.15 = 1,592 lb The hoist that will be used to raise this engine into position Power will need to be powered by an electric motor because the The concept of power involves the previously discussed average person will not be able to generate 1.15 hp in their topic of work, which was a force being applied over a arms for the necessary 2 minutes.

measured distance, but adds one more consideration—time.

In other words, how long it takes to accomplish the work.

Torque If someone asked the average person if they could lift one Torque is a very interesting concept and occurrence, and it is million pounds 5 feet off the ground, the answer most definitely something that needs to be discussed in conjunction assuredly would be no. This person would probably assume with work and power. Whereas work is described as force that they are to lift it all at once. What if they are given 365 acting through a distance, torque is described as force acting days to lift it, and could lift small amounts of weight at a along a distance. Torque is something that creates twisting time? The work involved would be the same, regardless of 5-6 and tries to make something rotate. Torque = Horsepower × 5,252 ÷ rpm If we push on an object with a force of 10 lb and it moves Example: A Cessna 172R has a Lycoming IO-360 engine that 10 inches in a straight line, we have done 100 in-lb of creates 180 horsepower at 2,700 rpm. How many pound-feet work. By comparison, if we have a wrench 10 inches long of torque is the engine producing?

that is on a bolt, and we push down on it with a force of 10 lb, a torque of 100 lb-in is applied to the bolt. If the bolt Torque = 180 × 5,252 ÷ 2,700 was already tight and did not move as we pushed down on = 350 lb-ft.

the wrench, the torque of 100 lb-in would still exist. The formula for torque is: Simple Machines A machine is any device with which work may be Torque = Force × distance accomplished. For example, machines can be used for any of the following purposes, or combinations of these 5 purposes: Even though this formula looks the same as the other formula 1. Machines are used to transform energy, as in the case for calculating work, recognize that the distance value in this of a generator transforming mechanical energy into formula is not the linear distance an object moves, but rather electrical energy.

the distance along which the force is applied.

2. Machines are used to transfer energy from one place Notice that with torque nothing had to move, because the to another, as in the examples of the connecting rods, force is being applied along a distance and not through a crankshaft, and reduction gears transferring energy distance. Notice also that although the units of work and from an aircraft’s engine to its propeller.

torque appear to be the same, they are not. The units of work 3. Machines are used to multiply force; for example, a were inch-pounds and the units of torque were pound-inches, system of pulleys may be used to lift a heavy load. The and that is what differentiates the two.

pulley system enables the load to be raised by exerting a force that is smaller than the weight of the load.

Torque is very important when thinking about how engines 4. Machines can be used to multiply speed. A good work, both piston engines and gas turbine engines. Both example is the bicycle, by which speed can be gained types of engines create torque in advance of being able by exerting a greater force.

to create work or power. With a piston engine, a force in pounds pushes down on the top of the piston and tries to 5. Machines can be used to change the direction of make it move. The piston is attached to the connecting rod, a force. An example of this use is the flag hoist. A which is attached to the crankshaft at an offset. That offset downward force on one side of the rope exerts an would be like the length of the wrench discussed earlier, upward force on the other side, raising the flag toward and the force acting along that length is what creates torque.

the top of the pole.

[Figure 5-6] There are only six simple machines. They are the lever, the For the cylinder in Figure 5-6 , there is a force of 500 lb pulley, the wheel and axle, the inclined plane, the screw, pushing down on the top of the piston. The connecting rod and the gear. Physicists, however, recognize only two basic attaches to the crankshaft at an offset distance of 4 in. The principles in machines: the lever and the inclined plane.

product of the force and the offset distance is the torque, in The pulley (block and tackle), the wheel and axle, and gears this case 2,000 lb-in.

operate on the machine principle of the lever. The wedge and the screw use the principle of the inclined plane.

In a turbine engine, the turbine blades at the back of the engine extract energy from the high velocity exhaust gases. The energy An understanding of the principles of simple machines provides extracted becomes a force in pounds pushing on the turbine a necessary foundation for the study of compound machines, blades, which happen to be a certain number of inches from which are combinations of two or more simple machines.

the center of the shaft they are trying to make rotate. The number of inches from the turbine blades to the center of the Mechanical Advantage of Machines shaft would be like the length of the wrench discussed earlier.

As identified in statements 3 and 4 under simple machines, a machine can be used to multiply force or to multiply speed. It Mathematically, there is a relationship between the cannot, however, multiply force and speed at the same time.

horsepower of an engine and the torque of an engine. The In order to gain one force, it must lose the other force. To do formula that shows this relationship is as follows: otherwise would mean the machine has more power going 5-7 The concept of torque was discussed earlier in this chapter, and torque is very much involved in the operation of a lever.

When a person sits on one end of a seesaw, that person applies a downward force in pounds which acts along the distance Torque = F x d to the center of the seesaw. This combination of force and Torque = 500 x 4 distance creates torque, which tries to cause rotation.

Torque = 2,000 lb-in Torque = 166.7 lb-ft First Class Lever Force of 500 lb Piston In the first class lever, the fulcrum is located between the effort and the resistance. As mentioned earlier, the seesaw is a good example of a lever, and it happens to be a first class lever. The amount of weight and the distance from the fulcrum can be varied to suit the need. Increasing the Connecting rod distance from the applied effort to the fulcrum, compared to the distance from the fulcrum to the weight being moved, increases the advantage provided by the lever. Crowbars, shears, and pliers are common examples of this class of lever.

Crankshaft The proper balance of an airplane is also a good example, with the center of lift on the wing being the pivot point, or fulcrum, and the weight fore and aft of this point being the effort and the resistance.

When calculating how much effort is required to lift a specific weight, or how much weight can be lifted by a specific effort, 4" the following formula can be used.

Figure 5-6. Piston engine and torque.

Effort (E) × Effort Arm (L) = Resistance (R) × Resistance Arm (l) What this formula really shows is the input torque (effort × effort arm) equals the output torque (resistance × resistance out than coming in, and that is not possible.

arm). This formula and concept apply to all three classes of levers and to all simple machines in general.

In reference to machines, mechanical advantage is a comparison of the output force to the input force, or the Example: A first class lever is to be used to lift a 500-lb output distance to the input distance. If there is a mechanical weight. The distance from the weight to the fulcrum is advantage in terms of force, there will be a fractional 12 inches and from the fulcrum to the applied effort is 60 disadvantage in terms of distance. The following formulas inches. How much force is required to lift the weight?

can be used to calculate mechanical advantage.

Effort (E) × Effort Arm (L) = Resistance (R) × Resistance Arm (l) Mechanical Advantage = Force Out ÷ Force In E × 60 in = 500 lb × 12 in or E = 500 lb × 12 in ÷ 60 in Mechanical Advantage = Distance Out ÷ Distance In E = 100 lb The Lever The mechanical advantage of the lever in this example The simplest machine, and perhaps the most familiar one, is would be: the lever. A seesaw is a familiar example of a lever, with two people sitting on either end of a board and a pivoting point Mechanical Advantage = Force Out ÷ Force In in the middle. There are three basic parts in all levers. They = 500 lb ÷ 100 lb are the fulcrum “F,” a force or effort “E,” and a resistance = 5, or 5 to 1 “R.” Shown in Figure 5-7 are the pivot point “F” (fulcrum), the effort “E” which is applied at a distance “L” from the An interesting thing to note with this example lever is if the fulcrum, and a resistance “R” which acts at a distance “l” applied effort moved down 10 inches, the weight on the other from the fulcrum. Distances “L” and “l” are the lever arms.

end would only move up 2 inches. The weight being lifted would only move one-fifth as far. The reason for this is the 5-8 class levers. As shown in Figure 5-9 , the fulcrum is at one end concept of work. If it allows you to lift 5 times more weight, of the lever and the weight or resistance to be overcome is at you will only move it ⁄ 5 as far as you move the effort, because the other end, with the effort applied at some point between. a lever cannot have more work output than input.

Third class levers are easily recognized because the effort is applied between the fulcrum and the resistance. The retractable Second Class Lever main landing gear on an airplane is a good example of a third The second class lever has the fulcrum at one end and the class lever. The top of the landing gear, where it attaches to the effort is applied at the other end. The resistance is somewhere airplane, is the pivot point. The wheel and brake assembly at between these points. A wheelbarrow is a good example of the bottom of the landing gear is the resistance. The hydraulic a second class lever, with the wheel at one end being the actuator that makes the gear retract is attached somewhere in fulcrum, the handles at the opposite end being the applied the middle, and that is the applied effort.

effort, and the bucket in the middle being where the weight or resistance is placed. [Figure 5-8] The Pulley Pulleys are simple machines in the form of a wheel mounted Both first and second class levers are commonly used to help on a fixed axis and supported by a frame. The wheel, or disk, in overcoming big resistances with a relatively small effort.

is normally grooved to accommodate a rope. The wheel is The first class lever, however, is more versatile. Depending sometimes referred to as a “sheave,” or sometimes “sheaf.” on how close or how far away the weight is placed from the The frame that supports the wheel is called a block. A block and fulcrum, the first class lever can be made to gain force or tackle consists of a pair of blocks. Each block contains one or gain distance, but not both at the same time. The second class more pulleys and a rope connecting the pulley(s) of each block.

lever can only be made to gain force.

Single Fixed Pulley Example: The distance from the center of the wheel to the handles on a wheelbarrow is 60 inches. The weight in the A single fixed pulley is really a first class lever with equal arms.

In Figure 5-10 , the arm from point “R” to point “F” is equal to bucket is 18 inches from the center of the wheel. If 300 lb is placed in the bucket, how much force must be applied at the the arm from point “F” to point “E,” with both distances being equal to the radius of the pulley. When a first class lever has handles to lift the wheelbarrow?

equal arms, the mechanical advantage is 1. Thus, the force of the pull on the rope must be equal to the weight of the object Effort (E) × Effort Arm (L) = Resistance (R) × Resistance Arm (l) E × 60 inches = 300 lb × 18 in being lifted. The only advantage of a single fixed pulley is to change the direction of the force, or pull on the rope. E = 300 lb × 18 in ÷ 60 in E = 90 lb Single Movable Pulley The mechanical advantage of the lever in this example A single pulley can be used to magnify the force exerted. In would be: Figure 5-11 , the pulley is movable, and both ropes extending up from the pulley are sharing in the support of the weight.

Mechanical Advantage = Force Out ÷ Force In This single, movable pulley will act like a second class lever.

= 300 lb ÷ 90 lb The effort arm (EF) being the diameter of this pulley and the = 3.33, or 3.33 to 1 resistance arm (FR) being the radius of this pulley. This type of pulley would have a mechanical advantage of two because the Third Class Lever diameter of the pulley is double the radius of the pulley. In use, if someone pulled in 4 ft of the effort rope, the weight would There are occasions when it is desirable to speed up the movement of the resistance even though a large amount of only rise off the floor 2 ft. If the weight was 100 lb, the effort effort must be used. Levers that help accomplish this are third Effort “ E ” “ L ” Resistance “ R ” Effort “ E ” “ l ” “ L ” “ l ” Fulcrum “ F ” Fulcrum “ F ” Resistance “ R ” Figure 5-7. First class lever.

Figure 5-8. Second class lever.

5-9 is an increase in force, and ultimately torque. applied would only need to be 50 lb. With this type of pulley, the effort will always be one-half of the weight being lifted.

Bevel gears are used to change the plane of rotation, so that a shaft turning horizontally can make a vertical shaft rotate.

Block and Tackle The size of the gears and their number of teeth determine the A block and tackle is made up of multiple pulleys, some of mechanical advantage, and whether force is being increased them fixed and some movable. In Figure 5-12 , the block and or rpm is being increased. If each gear has the same number of tackle is made up of four pulleys, the top two being fixed and teeth, there would be no change in force or rpm. [Figure 5-14] the bottom two being movable. Viewing the figure from right to left, notice there are four ropes supporting the weight and The worm gear has an extremely high mechanical advantage.

a fifth rope where the effort is applied. The number of weight The input force goes into the spiral worm gear, which drives supporting ropes determines the mechanical advantage of a the spur gear. One complete revolution of the worm gear only block and tackle, so in this case the mechanical advantage makes the spur gear move an amount equal to one tooth.

is four. If the weight was 200 lb, it would require a 50 lb The mechanical advantage is equal to the number of teeth effort to lift it.

on the spur gear, which in this case there are 25. This is a force gaining machine, to the tune of 25 times more output The Gear force. [Figure 5-15] Two gears with teeth on their outer edges, as shown in Figure 5-13 , act like a first class lever when one gear drives The planetary sun gear system is typical of what would be the other. The gear with the input force is called the drive found in a propeller reduction gearbox. The power output gear, and the other is called the driven gear. The effort arm shaft of the engine would drive the sun gear in the middle, is the diameter of the driven gear, and the resistance arm is the diameter of the drive gear.

Notice that the two gears turn in opposite directions: the bottom one clockwise and the top one counterclockwise. The gear on top is 9 inches in diameter and has 45 teeth, and the gear on the bottom is 12 inches in diameter and has 60 teeth.

Imagine that the blue gear is driving the yellow one, which makes the blue the drive and the yellow the driven. The mechanical advantage in terms of force would be the effort arm divided by the resistance arm, or 9 ÷ 12, which is 0.75.

This would actually be called a fractional disadvantage, because there would be less force out than force in. The mechanical advantage in terms of distance, in rpm in this case, would be 12 ÷ 9, or 1.33.

This analysis tells us that when a large gear drives a small one, the small one turns faster and has less available force. In order to be a force gaining machine, the small gear needs to turn the large one. When the terminology reduction gearbox R E F is used, such as a propeller reduction gearbox, it means that there is more rpm going in than is coming out. The end result Effort “ E ” “ L ” “ l ” Weight Fulcrum “ F ” E ff ort “ E ” Resistance “ R ” Figure 5-9. Third class lever.

Figure 5-10. Single fixed pulley.

5-10 E ff ort Effort Support ropes E R F Weight Figure 5-12. Block and tackle.

Weight of the inclined plane are mountain highways and a loading ramp on the back of a moving truck. When weighing a small Figure 5-11. Single movable pulley.

airplane, like a Cessna 172, an inclined plane, or ramp, can be used to get the airplane on the scales by pushing it, rather than jacking it. A ramp can be seen in Figure 5-17 , where a which rotates the planetary gears and ultimately the ring gear.

Cessna 172 right main gear is sitting on an electronic scale.

In this example, the sun gear has 28 teeth, each planet gear The airplane was pushed up the ramps to get it on the scales.

has 22 teeth, and the ring gear has 82 teeth. To figure how much gear reduction is taking place, the number of teeth on With an inclined plane, the length of the incline is the effort the ring gear is divided by the number of teeth on the sun gear.

arm and the vertical height of the incline is the resistance In this case, the gear reduction is 2.93, meaning the engine has arm. If the length of the incline is five times greater than an rpm 2.93 times greater than the propeller. [Figure 5-16] the height, there will be a force advantage, or mechanical Inclined Plane advantage, of five. The Mooney M20 in Figure 5-17 weighed The inclined plane is a simple machine that facilitates the 1,600 lb on the day of the weighting. The ramp it is sitting on raising or lowering of heavy objects by application of a small is 6 inches tall, which is the resistance arm, and the length of force over a relatively long distance. Some familiar examples the ramp is 24 inches, which is the effort arm. To calculate 5-11 mechanical advantage than a coarse threaded bolt.

A chisel is a good example of a wedge. A chisel might be 8 inches long and only ⁄ 2 inch wide, with a sharp tip and tapered sides. The 8-inch length is the effort arm and the ⁄ 2 - inch width is the resistance arm. This chisel would provide a force advantage, or mechanical advantage, of 16.

Stress Whenever a machine is in operation, be it a simple machine like a lever or a screw, or a more complex machine like an aircraft piston engine or a hydraulically operated landing gear, the parts and pieces of that machine will experience something called stress. Whenever an external force is applied to an object, like a weight pushing on the end of a lever, a reaction will occur inside the object which is known as stress. Stress is typically measured in pounds per square foot or pounds per square inch (psi).

External force acting on an object causes the stress to manifest itself in one of five forms, or combination of those five. The five forms are tension, compression, torsion, bending, and shear.

Tension Tension is a force that tries to pull an object apart. In the block and tackle system discussed earlier in this chapter, the upper block that housed the two fixed pulleys was secured to an overhead beam. The movable lower block Figure 5-13. Spur gears.

the force needed to push the airplane up the ramps, use the same formula introduced earlier when levers were discussed, as follows: Effort (E) × Effort Arm (L) = Resistance (R) × Resistance Arm (l) E × 24 in = 1,600 lb × 6 in E = 1,600 l-b × 6 in ÷ 24 in E = 400 lb Bolts, screws, and wedges are also examples of devices that operate on the principle of the inclined plane. A bolt, for example, has a spiral thread that runs around its circumference. As the thread winds around the bolt’s circumference, it moves a vertical distance equal to the space between the threads. The circumference of the bolt is the effort arm and the distance between the threads is the Figure 5-14. Bevel gears. resistance arm. [Figure 5-18] Based on this analysis, a fine threaded bolt, which has more threads per inch, has a greater 5-12 Figure 5-15. Worm gear.

Figure 5-17. Ramp in use with a Mooney M20.

and its two pulleys were hanging by ropes, and the weight and makes it expand to fill the hole and securely hold the was hanging below the entire assembly. The weight being aluminum pieces together. [Figure 5-19] lifted would cause the ropes and the blocks to be under tension. The weight is literally trying to pull the rope apart, Torsion and ultimately would cause the rope to break if the weight Torsion is the stress an object experiences when it is was too great.

twisted, which is what happens when torque is applied to a shaft. Torsion is made up of two other stresses: tension and Compression compression. When a shaft is twisted, tension is experienced Compression is a force that tries to crush an object. An at a diagonal to the shaft and compression acts 90 degrees to excellent example of compression is when a sheet metal the tension. [Figure 5-20] airplane is assembled using the fastener known as a rivet. The rivet passes through a hole drilled in the pieces of aluminum, The turbine shaft on a turbofan engine, which connects to and then a rivet gun on one side and a bucking bar on the the compressor in order to drive it, is under a torsion stress.

other apply a force. This applied force tries to crush the rivet The turbine blades extract energy from the high velocity air as a force in pounds. This force in pounds acts along the length from the blades to the center of the shaft, and creates Sun gear the torque that causes rotation. [Figure 5-21] Bending An airplane in flight experiences a bending force on the wing as aerodynamic lift tries to raise the wing. This force of lift causes the skin on the top of the wing to compress and the skin on the bottom of the wing to be under tension. When the airplane is on the ground sitting on its landing gear, the force of gravity tries to bend the wing downward, subjecting the bottom of the wing to compression and the top of the wing tension. [Figure 5-22] During the testing that occurs prior to FAA certification, an airplane manufacturer intentionally bends the wing up and down to make sure it can take the stress without failing.

Shear When a shear stress is applied to an object, the force tries to cut or slice through, like a knife cutting through butter.

Ring gear Planetary gears A clevis bolt, which is often used to secure a cable to a part of the airframe, has shear stress acting on it. As shown in Figure 5-23 , a fork fitting is secured to the end of the cable, Figure 5-16. Planetary sun gear.

5-13 Force from rivet gun Distance between threads (Resistance arm) Effort arm Resistance arm Rivet head Circumference (Effort arm) Figure 5-18. A bolt and nut as an inclined plane.

and the fork attaches to an eye on the airframe with the clevis bolt. When the cable is put under tension, the fork tries to slide off the eye by cutting through the clevis bolt. This bolt would be designed to take very high shear loads.

Strain Rivet shank If the stress acting on an object is great enough, it can cause the object to change its shape or to become distorted. One characteristic of matter is that it tends to be elastic, meaning it can be forced out of shape when a force is applied and then return to its original shape when the force is removed. When Bucking bar an object becomes distorted by an applied force, the object is said to be strained.

On turbine engine test cells, the thrust of the engine is typically measured by what are called strain gages. When the force, or thrust, of the engine is pulling out against the strain gages, the amount of distortion is measured and then translated into the appropriate thrust reading.

Figure 5-19. A rivet fastener and compression.

A deflecting beam style of torque wrench uses the strain on the Uniform Motion drive end of the wrench and the resulting distortion of the beam to indicate the amount of torque on a bolt or nut. [Figure 5-24] Motion may be defined as a continuing change of position or place, or as the process in which a body undergoes Motion displacement. When an object is at different points in space at different times, that object is said to be in motion, and if The study of the relationship between the motion of bodies the distance the object moves remains the same for a given or objects and the forces acting on them is often called the period of time, the motion may be described as uniform. Thus, study of “force and motion.” In a more specific sense, the an object in uniform motion always has a constant speed.

relationship between velocity, acceleration, and distance is known as kinematics.

Speed and Velocity In everyday conversation, speed and velocity are often used as if they mean the same thing. In physics, they have definite 5-14 Wing top is Tension stress under tension Wing bottom is under compression Figure 5-22. Airplane on the ground, wing under tension and Rotation Compression compression.

an airplane and one representing the velocity of the wind, can Figure 5-20. Torsion on a rotating shaft, made up of tension and be added together in what is called vector analysis. Figure 5-25 compression.

demonstrates this, with vectors “A” and “B” representing the velocity of the airplane and the wind, and vector “C” being the and distinct meanings. Speed refers to how fast an object is resultant. With no wind, the speed and direction of the airplane moving, or how far the object will travel in a specific time. would be that shown by vector “A.” When accounting for the The speed of an object tells nothing about the direction an wind direction and speed, the airplane ends up flying at the object is moving. For example, if the information is supplied speed and direction shown by vector “C.” that an airplane leaves New York City and travels 8 hours at a speed of 150 mph, this information tells nothing about the Imagine that an airplane is flying in a circular pattern at a direction in which the airplane is moving. At the end of 8 constant speed. The airplane is constantly changing direction hours, it might be in Kansas City, or if it traveled in a circular because of the circular pattern, which means the airplane is route, it could be back in New York City.

constantly changing velocity. The reason for this is the fact that velocity includes direction.

Velocity is that quantity in physics which denotes both the speed of an object and the direction in which the object To calculate the speed of an object, the distance it travels is moves. Velocity can be defined as the rate of motion in a divided by the elapsed time. If the distance is measured in particular direction. Velocity is also described as being a miles and the time in hours, the units of speed will be miles vector quantity, a vector being a line of specific length, per hour (mph). If the distance is measured in feet and the having an arrow on one end or the other. The length of the time in seconds, the units of speed will be feet per second line indicates the number value and the arrow indicates the (fps). To convert mph to fps, divide by 1.467. Velocity is direction in which that number is acting. calculated the same way, the only difference being it must be recalculated every time the direction changes.

Two velocity vectors, such as one representing the velocity of Acceleration Acceleration is defined as the rate of change of velocity. If the velocity of an object is increased from 20 mph to 30 mph, Torque applied to shaft the object has been accelerated. If the increase in velocity is 10 mph in 5 seconds, the rate of change in velocity is 10 mph in 5 seconds, or 2 mph per second. If this were multiplied Clevis Bolt Force Shaft experiences torsion Turbine blades applied force Figure 5-23. Clevis bolt, red arrows show opposing forces trying to shear the bolt.

Figure 5-21. Turbofan engine, torque creating torsion in the shaft.

5-15 Newton’s Law of Motion First Law When a magician snatches a tablecloth from a table and leaves a full setting of dishes undisturbed, he is not displaying a mystic art; he is actually demonstrating the principle of inertia. Inertia is responsible for the discomfort felt when an airplane is brought to a sudden halt in the parking area and the passengers are thrown forward in their seats. Inertia is a property of matter. This property of matter is described by Newton’s first law of motion, which states: Objects at rest tend to remain at rest and objects in motion tend to remain in motion at the same speed and in the same direction, unless acted on by an external force.

Second Law Bodies in motion have the property called momentum. A body that has great momentum has a strong tendency to remain in motion and is therefore hard to stop. For example, a train moving at even low velocity is difficult to stop because of its large mass. Newton’s second law applies to this property.

It states: When a force acts upon a body, the momentum of that body Figure 5-24. Deflecting beam torque wrench measures strain by distortion.

is changed. The rate of change of momentum is proportional to the applied force. Based on Newton’s second law, the formula for calculating thrust is derived, which states that by 1.467, it could also be expressed as an acceleration of force equals mass times acceleration (F = MA). Earlier in this 2.93 feet per second per second (fps/s). By comparison, the chapter, it was determined that mass equals weight divided by acceleration due to gravity is 32.2 fps/s.

gravity, and acceleration equals velocity final minus velocity initial divided by time. Putting all these concepts together, To calculate acceleration, the following formula is used.

the formula for thrust is: Velocity Final (Vf) − Velocity Initial (Vi) Acceleration (A) = Weight (Velocity final − Velocity initial) Time (t) Force = Gravity (Time) Example: An Air Force F-15 fighter is cruising at 400 mph.

W (Vf − Vi) The pilot advances the throttles to full afterburner and Force = accelerates to 1,200 mph in 20 seconds. What is the average Gt acceleration in mph/s and fps/s?

Example: A turbojet engine is moving 150 lb of air per Vf − Vi second through the engine. The air enters going 100 fps and A = t leaves going 1,200 fps. How much thrust, in pounds, is the engine creating?

1200 − 400 A = W (Vf − Vi) F = mph fps A = 40 ⁄ s , or multiplying by 1.467, 58.7 ⁄ s Gt 150 (1200 − 100) In the example just shown, the acceleration was found to be F = 58.7 fps/s. Since 32.2 fps/s is equal to the acceleration due 32.2(1) to gravity, divide the F-15’s acceleration by 32.2 to find out F = 5,124 lb of thrust how many G forces the pilot is experiencing. In this case, it would be 1.82 Gs.

5-16 When an aircraft propeller pushes a stream of air backward Vector B = Wind with a force of 500 lb, the air pushes the blades forward with a force of 500 lb. This forward force causes the aircraft to move forward. A turbofan engine exerts a force on the air entering the inlet duct, causing it to accelerate out the fan duct and the tailpipe. The air accelerating to the rear is the action, and the force inside the engine that makes it happen is the reaction, also called thrust.

Circular Motion Circular motion is the motion of an object along a curved path that has a constant radius. For example, if one end of a string is tied to an object and the other end is held in the hand, the object can be swung in a circle. The object is constantly deflected from a straight (linear) path by the pull exerted on the string, as shown in Figure 5-26 . When the weight is at Vector A = Velocity of airplane point A, due to inertia it wants to keep moving in a straight line and end up at point B. It is forced to move in a circular path and end up at point C because of the force being exerted on the string.

Vector C = Movement of airplane The string exerts a centripetal force on the object, and the object exerts an equal but opposite force on the string, obeying Newton’s third law of motion. The force that is equal to centripetal force, but acting in an opposite direction, is called centrifugal force.

Centripetal force is always directly proportional to the mass of the object in circular motion. Thus, if the mass of the object in Figure 5-26 is doubled, the pull on the string must be doubled to keep the object in its circular path, provided the speed of the object remains constant.

Centripetal force is inversely proportional to the radius of the circle in which an object travels. If the string in Figure 5-25. Vector analysis for airplane velocity and wind velocity. Figure 5-26 is shortened and the speed remains constant, the pull on the string must be increased since the radius is decreased, and the string must pull the object from its linear Third Law path more rapidly. Using the same reasoning, the pull on the Newton’s third law of motion is often called the law of action string must be increased if the object is swung more rapidly and reaction. It states that for every action there is an equal in its orbit. Centripetal force is thus directly proportional and opposite reaction. This means that if a force is applied to the square of the velocity of the object. The formula for to an object, the object will supply a resistive force exactly centripetal force is: equal to and in the opposite direction of the force applied.

It is easy to see how this might apply to objects at rest. In Centripetal Force = Mass (Velocity ) ÷ Radius application, as a man stands on the floor, the floor exerts a For the formula above, mass would typically be converted force against his feet exactly equal to his weight. This law is to weight divided by gravity, velocity would be in feet per also applicable when a force is applied to an object in motion.

second, and the radius would be in feet.

Forces always occur in pairs. The term “ acting force” means Example: What would the centripetal force be if a 10-pound the force one body exerts on a second body, and reacting weight was moving in a 3-ft radius circular path at a velocity force means the force the second body exerts on the first.

of 500 fps?

5-17 Centripetal Force = Mass (Velocity ) ÷ Radius B Centripetal Force = 10 (500 ) ÷ 32.2 (3) = 25,880 lb In the condition identified in the example, the object acts like it weighs 2,588 times more than it actually does. It can also WT “ C ” be said that the object is experiencing 2,588 Gs, or force of gravity. The fan blades in a large turbofan engine, when the engine is operating at maximum rpm, are experiencing many A thousands of Gs for the same reason.

Centripetal force Heat Heat is a form of energy. It is produced only by the conversion of one of the other forms of energy. Heat may also be defined Centrifugal force as the total kinetic energy of the molecules of any substance.

Some forms of energy which can be converted into heat energy are as follows: • Mechanical Energy—this includes all methods of producing increased motion of molecules such as friction, impact of bodies, or compression of gases.

• Electrical Energy—electrical energy is converted to heat energy when an electric current flows through any form of resistance such as an electric iron, electric Figure 5-26. Circular motion.

light, or an electric blanket.

• Chemical Energy—most forms of chemical reaction regarded as a form of energy.

convert stored potential energy into heat. Some examples are the explosive effects of gunpowder, the According to this theory of heat as a form of energy, the burning of oil or wood, and the combining of oxygen molecules, atoms, and electrons in all bodies are in a continual and grease.

state of motion. In a hot body, these small particles possess relatively large amounts of kinetic energy, but in cooler • Radiant Energy—electromagnetic waves of certain bodies they have less. Because the small particles are given frequencies produce heat when they are absorbed by motion, and hence kinetic energy, work must be done to the bodies they strike such as x-rays, light rays, and slide one body over the other. Mechanical energy apparently infrared rays.

is transformed, and what we know as heat is really kinetic • Nuclear Energy—energy stored in the nucleus of energy of the small molecular subdivisions of matter.

atoms is released during the process of nuclear fission Heat Energy Units in a nuclear reactor or atomic explosion.

Two different units are used to express quantities of heat • Sun—all heat energy can be directly or indirectly energy. They are the calorie and the BTU. One calorie is equal traced to the nuclear reactions occurring in the sun.

to the amount of heat required to change the temperature of 1 gram of water 1 degree Centigrade.

When a gas is compressed, work is done and the gas becomes warm or hot. Conversely, when a gas under high pressure is This term “calorie” (spelled with a lower case c) is 1/1,000 of allowed to expand, the expanding gas becomes cool. In the the Calorie (spelled with a capital C) used in the measurement first case, work was converted into energy in the form of of the heat energy in foods. One BTU is defined as the amount heat; in the second case heat energy was expended. Since of heat required to change the temperature of 1 lb of water heat is given off or absorbed, there must be a relationship 1 degree Fahrenheit (1 °F). The calorie and the gram are between heat energy and work. Also, when two surfaces are seldom used in discussing aviation maintenance. The BTU, rubbed together, the friction develops heat. However, work however, is commonly referred to in discussions of engine was required to cause the heat, and by experimentation, it thermal efficiencies and the heat content of aviation fuel.

has been shown that the work required and the amount of heat produced by friction is proportional. Thus, heat can be 5-18 the form of friction and heat. A tremendous amount of heat A device known as the calorimeter is used to measure is given up to the atmosphere and not used inside the engine quantities of heat energy. In application, it may be used to to create power.

determine the quantity of heat energy available in 1 pound of Heat Transfer aviation gasoline. A given weight of the fuel is burned in the calorimeter, and the heat energy is absorbed by a large quantity There are three methods by which heat is transferred from one of water. From the weight of the water and the increase in its location to another or from one substance to another. These temperature, it is possible to compute the heat yield of the fuel.

three methods are conduction, convection, and radiation.

A definite relationship exists between heat and mechanical energy. This relationship has been established and verified by Conduction many experiments which show that: Heat transfer always takes place by areas of high heat energy migrating to areas of low heat energy. Heat transfer by One BTU of heat energy = 778 ft-lb of work conduction requires that there be physical contact between an object that has a large amount of heat energy and one that As discussed earlier in this chapter under the topic “ Potential has a smaller amount of heat energy.

Energy,” one pound of aviation gasoline contains 18,900 BTU of heat energy. Since each BTU is capable of 778 ft-lb of work, Everyone knows from experience that the metal handle of 1 lb of aviation gasoline is capable of 14,704,200 ft-lb of work.

a heated pan can burn the hand. A plastic or wood handle, however, remains relatively cool even though it is in direct Heat Energy and Thermal Efficiency contact with the pan. The metal transmits the heat more Thermal efficiency is the relationship between the potential easily than the wood because it is a better conductor of heat.

for power contained in a specific heat source, and how much Different materials conduct heat at different rates. Some usable power is created when that heat source is used. The metals are much better conductors of heat than others.

formula for calculating thermal efficiency is: Aluminum and copper are used in pots and pans because they conduct heat very rapidly. Woods and plastics are used Thermal Efficiency = for handles because they conduct heat very slowly.

Horsepower Produced ÷ Potential Horsepower in Fuel Figure 5-27 illustrates the different rates of conduction of For example, consider the piston engine used in a small various metals. Of those listed, silver is the best conductor general aviation airplane, which typically consumes 0.5 and lead is the poorest. As mentioned previously, copper and lb of fuel per hour for each horsepower it creates. Imagine aluminum are used in pots and pans because they are good that the engine is creating 200 hp. If we multiply 0.5 by the conductors. It is interesting to note that silver, copper, and horsepower of 200, we find the engine is consuming 100 lb of aluminum are also excellent conductors of electricity.

fuel per hour, or 1.67 lb per minute. Earlier in this chapter, one horsepower was found to be 33,000 ft-lb of work per minute.

Liquids are poorer conductors of heat than metals. Notice that the ice in the test tube shown in Figure 5-28 is not The potential horsepower in the fuel burned for this example melting rapidly even though the water at the top is boiling.

engine would be: The water conducts heat so poorly that not enough heat reaches the ice to melt it.

1.67 lb/minute × 18,900 BTU/lb × 778 ft lb/BTU Hp = 33,000 ft-lb/min Gases are even poorer conductors of heat than liquids. It is Hp = 744 possible to stand quite close to a stove without being burned because air is such a poor conductor. Since conduction is a The example engine is burning enough fuel that it has the process whereby the increase in molecular energy is passed potential to create 744 horsepower, but it is only creating 200.

along by actual contact, gases are poor conductors.

The thermal efficiency of the engine would be: At the point of application of the heat source, the molecules Thermal Efficiency = Hp Produced ÷ Hp in Fuel become violently agitated. These molecules strike adjacent = 200 ÷ 744 molecules causing them to become agitated. This process = .2688 or 26.88% continues until the heat energy is distributed evenly throughout the substance. The gases are much poorer More than 70 percent of the energy in the fuel is not being conductors of heat because molecules are farther apart in used to create usable horsepower. The wasted energy is in gases than in solids.

5-19 1.10 Materials that are poor conductors are used to prevent the 1.00 transfer of heat and are called heat insulators. A wooden 1.00 0.94 handle on a pot or a soldering iron serves as a heat insulator.

0.90 Certain materials, such as finely spun glass or asbestos, are particularly poor heat conductors. These materials are 0.80 therefore used for many types of insulation.

0.70 0.57 Convection 0.60 Convection is the process by which heat is transferred by 0.50 SILVER movement of a heated fluid (gas or liquid). For example, COPPER 0.37 0.40 an incandescent light bulb will, when heated, become increasingly hotter until the air surrounding it begins to move.

0.30 0.22 The motion of the air is upward. This upward motion of the 0.18 ALUMINUM 0.20 heated air carries the heat away from the hot light bulb by 0.08 MAGNESIUM convection. Transfer of heat by convection may be hastened 0.10 NICKEL IRON by using a ventilating fan to move the air surrounding a hot LEAD object. The rate of cooling of a hot electronics component, such as the CPU in a computer, can be increased if it is Figure 5-27. Conductivity of various metals.

provided with copper fins that conduct heat away from the hot surface. The fins provide large surfaces against which cool air can be blown. be transferred by convection because the air currents are moving toward the fire. It cannot be transferred through A convection process may take place in a liquid as well as in conduction because the conductivity of the air is very small, a gas. A good example of this is a pan of water sitting on the and the cooler currents of air moving toward the fire would stove. The bottom of the pan becomes hot because it conducts more than overcome the transfer of heat outward. Therefore, heat from the surface it is in contact with. The water on the there must be some way for heat to travel across space other bottom of the pan also heats up because of conduction. As than by conduction and convection.

the heated water starts to rise and cooler water moves in to take its place, the convection process begins. The existence of another process of heat transfer is still more evident when the heat from the sun is considered. Since When the circulation of gas or liquid is not rapid enough to conduction and convection take place only through some remove sufficient heat, fans or pumps are used to accelerate medium, such as a gas or a liquid, heat from the sun must the motion of the cooling material. In some installations, reach the earth by another method, since space is an almost pumps are used to circulate water or oil to help cool large perfect vacuum. Radiation is the name given to this third equipment. In airborne installations, electric fans and blowers method of heat transfer.

are used to aid convection.

Steam An aircraft air-cooled piston engine is a good example of convection being used to transfer heat. The engine shown in Boiling water Figure 5-29 is a Continental IO-520, with six heavily finned air-cooled cylinders. This engine does not depend on natural convection for cooling, but rather forced air convection Water coming from the propeller on the engine. The heat generated inside the engine finds its way to the cylinder cooling fins by Ice conduction, meaning transfer within the metal of the cylinder.

Once the heat gets to the fins, forced air flowing around the cylinders carries the heat away.

Metal ring to keep ice from rising Radiation Conduction and convection cannot wholly account for some of the phenomena associated with heat transfer. For example, the heat one feels when sitting in front of an open fire cannot Figure 5-28. Water as a poor conductor.

5-20 The term “radiation” refers to the continual emission of energy from the surface of all bodies. This energy is known as “radiant energy.” It is in the form of electromagnetic waves, radio waves, or x-rays, which are all alike except for a difference in wave length. These waves travel at the velocity of light and are transmitted through a vacuum more easily than through air because air absorbs some of them.

Most forms of energy can be traced back to the energy of sunlight. Sunlight is a form of radiant heat energy that travels through space to reach the earth. These electromagnetic heat waves are absorbed when they come in contact with nontransparent bodies. The result is that the motion of the molecules in the body is increased as indicated by an increase in the temperature of the body.

Figure 5-29. Aircraft piston engine cooled by convection.

The differences between conduction, convection, and radiation may now be considered. First, although conduction and Temperature convection are extremely slow, radiation takes place at the Temperature is a dominant factor affecting the physical speed of light. This fact is evident at the time of an eclipse of properties of fluids. It is of particular concern when the sun when the shutting off of the heat from the sun takes calculating changes in the state of gases.

place at the same time as the shutting off of the light. Second, radiant heat may pass through a medium without heating The three temperature scales used extensively are the it. In application, the air inside a greenhouse may be much Centigrade, the Fahrenheit, and the absolute or Kelvin scales.

warmer than the glass through which the sun’s rays pass. Third, The Centigrade scale is constructed by using the freezing and although heat transfer by conduction or convection may travel boiling points of water, under standard conditions, as fixed in roundabout routes, radiant heat always travels in a straight points of zero and 100, respectively, with 100 equal divisions line. For example, radiation can be cut off with a screen placed between. The Fahrenheit scale uses 32° as the freezing point between the source of heat and the body to be protected.

of water and 212° as the boiling point, and has 180 equal divisions between. The absolute or Kelvin scale is constructed Specific Heat with its zero point established as minus 273 °C, meaning One important way in which substances differ is in the 273° below the freezing point of water. The relationships of requirement of different quantities of heat to produce the the other fixed points of the scales are shown in Figure 5-31 .

same temperature change in a given mass of the substance.

Each substance requires a quantity of heat, called its specific When working with temperatures, always make sure which heat capacity, to increase the temperature of a unit of its system of measurement is being used and know how to mass 1 °C. The specific heat of a substance is the ratio of its convert from one to another. The conversion formulas are specific heat capacity to the specific heat capacity of water.

as follows: Specific heat is expressed as a number which, because it is a ratio, has no units and applies to both the English and the Degrees Fahrenheit = (1.8 × Degrees Celsius) + 32 metric systems.

Degrees Celsius = (Degrees Fahrenheit – 32) × ⁄ 9 Degrees Kelvin = Degrees Celsius + 273 It is fortunate that water has a high specific heat capacity.

Degrees Rankine = Degrees Fahrenheit + 460 The larger bodies of water on the earth keep the air and solid matter on or near the surface of the earth at a constant For purposes of calculations, the Rankine scale is commonly temperature. A great quantity of heat is required to change used to convert Fahrenheit to absolute. For Fahrenheit the temperature of a large lake or river. Therefore, when readings above zero, 460° is added. Thus, 72 °F equals the temperature falls below that of such bodies of water, 460° plus 72°, or 532° absolute. If the Fahrenheit reading is they give off large quantities of heat. This process keeps below zero, it is subtracted from 460°. Thus −40 °F equals the atmospheric temperature at the surface of the earth from 460° minus 40°, or 420° absolute. It should be stressed that changing rapidly.

the Rankine scale does not indicate absolute temperature readings in accordance with the Kelvin scale, but these The specific heat values of some common materials are listed conversions may be used for the calculations of changes in in Figure 5-30 .

5-21 −6 the state of gases. Expansion = (11 × 10 ) × (9 feet) × 34° Expansion = 0.003366 feet The Kelvin and Centigrade scales are used more extensively in scientific work; therefore, some technical manuals may use This amount, when added to the original length of the rod, these scales in giving directions and operating instructions. makes the rod 9.003366 ft long. Its length has only increased The Fahrenheit scale is commonly used in the United States, by ⁄ 100 of an inch.

and most people are familiar with it. Therefore, the Fahrenheit scale is used in most areas of this book. The increase in the length of the rod is relatively small, but if the rod were placed where it could not expand freely, Thermal Expansion/Contraction there would be a tremendous force exerted due to thermal Thermal expansion takes place in solids, liquids, and expansion. Thus, thermal expansion must be taken into consideration when designing airframes, power plants, or gases when they are heated. With few exceptions, solids will expand when heated and contract when cooled. The related equipment.

expansion of solids when heated is very slight in comparison Pressure to the expansion in liquids and gases because the molecules of solids are much closer together and are more strongly Pressure is the amount of force acting on a specific amount attracted to each other. The expansion of fluids is discussed of surface area. The force is typically measured in pounds in the study of Boyle’s law. Thermal expansion in solids must and the surface area in square inches, making the units of be explained in some detail because of its close relationship pressure pounds per square inch or psi. If a 100-lb weight to aircraft metals and materials. 2 was placed on top of a block with a surface area of 10 in , the average weight distribution would be 10 lb for each of It is necessary to measure experimentally the exact rate of the square inches (100 ÷ 10), or 10 psi.

expansion of each one because some substances expand more than others. The amount that a unit length of any substance When atmospheric pressure is being measured, in addition expands for a one degree rise in temperature is known as to psi, other means of pressure measurement can be used.

the coefficient of linear expansion for that substance. The These include inches or millimeters of mercury, and millibars.

coefficient of linear expansion for various materials is shown Standard day atmospheric pressure is equal to 14.7 psi, in Figure 5-32.

29.92 inches of mercury ("Hg), 760 millimeters of mercury (mm hg), or 1013.2 millibars. The relationship between these To estimate the expansion of any object, such as a steel rail, units of measure is as follows: it is necessary to know three things about it: its length, the rise in temperature to which it is subjected, and its coefficient 1 psi = 2.04 "Hg of expansion. This relationship is expressed by the equation: 1 psi = 51.7 mm Hg 1 psi = 68.9 millibars Expansion = (coefficient) × (length) × (rise in temperature) The concept behind measuring pressure in inches of mercury If a steel rod measures exactly 9 ft at 21 °C, what is its length −6.

at 55 °C? The coefficient of expansion for steel is 11 × 10 100 212 373 672 Pure water boils Material Speci fi c Heat Lead 0.031 0 32 273 492 Mercury 0.033 Pure water freezes Brass 0.094 Copper 0.095 Iron or Steel 0.113 −273 −460 0 0 Glass 0.195 Molecular motion ceases at absolute Alcohol 0.547 zero Celsius Kelvin Rankine Fahrenheit Aluminum 0.712 (centigrade) Water 1.000 Figure 5-31. Comparison of temperature scales.

Figure 5-30. Specific heat value for various substances.

5-22 involves filling a test tube with the liquid mercury and then than atmospheric if it is supercharged. The only gauge that has covering the top. The test tube is then turned upside down the flexibility to show this variety of readings is the absolute and placed in an open container of mercury, and the top is pressure gauge. Figure 5-35 shows a manifold pressure gauge, uncovered. Gravity acting on the mercury in the test tube with a readout that ranges from 10 "Hg to 35 "Hg. Remember will try to make the mercury run out. Atmospheric pressure that 29.92 "Hg is standard day atmospheric.

pushing down on the mercury in the open container tries to Differential Pressure make the mercury stay in the test tube. At some point these two forces, gravity and atmospheric pressure, will equal out and Differential pressure, or psid, is the difference between the mercury will stabilize at a certain height in the test tube. pressures being read at two different locations within a Under standard day atmospheric conditions, the air in a 1-in system. For example, in a turbine engine oil system the column extending all the way to the top of the atmosphere pressure is read as it enters the oil filter, and as it leaves the would weigh 14.7 lb. A 1 in2 column of mercury, 29.92 filter. These two readings are sent to a transmitter which inches tall, would also weigh 14.7 lb. That is why 14.7 psi powers a light located on the flight deck. Across anything is equal to 29.92 "Hg. Figure 5-33 demonstrates this point.

that poses a resistance to flow, like an oil filter, there will be a drop in pressure. If the filter starts to clog, the pressure Gauge Pressure drop will become greater, eventually causing the advisory A gauge pressure (psig) is a reading that refers to when an light on the flight deck to come on.

instrument, such as an oil pressure gauge, fuel pressure gauge, or hydraulic system pressure gauge, displays pressure which Figure 5-36 shows a differential pressure gauge for the is over and above ambient. This can be seen on the fuel pressurization system on a Boeing 737. In this case, the pressure gauge shown in Figure 5-34. When the oil, fuel, or difference in pressure is between the inside and the outside hydraulic pump is not turning, and there is no pressure being of the airplane. If the pressure difference becomes too great, created, the gauge will read zero. the structure of the airplane could become overstressed.

Absolute Pressure Gas Laws A gauge that includes atmospheric pressure in its reading The simple structure of gases makes them readily adaptable is measuring what is known as absolute pressure, or psia.

to mathematical analysis from which has evolved a detailed Absolute pressure is equal to gauge pressure plus atmospheric theory of the behavior of gases. This is called the kinetic theory pressure. If someone hooked up a psia indicating instrument of gases. The theory assumes that a body of gas is composed of to an engine’s oil system, the gauge would read atmospheric identical molecules which behave like minute elastic spheres, pressure when the engine was not running. Since this would spaced relatively far apart and continuously in motion.

not make good sense to the typical operator, psia gauges are not used in this type of application. For the manifold pressure on The degree of molecular motion is dependent upon the a piston engine, a psia gauge does make good sense. Manifold temperature of the gas. Since the molecules are continuously pressure on a piston engine can read anywhere from less than striking against each other and against the walls of the atmospheric pressure if the engine is not supercharged, to more container, an increase in temperature with the resulting increase in molecular motion causes a corresponding Coe ffi cient of Expansion Substance increase in the number of collisions between the molecules.

Per Degree Centigrade The increased number of collisions results in an increase in –6 Aluminum 25 x 10 pressure because a greater number of molecules strike against –6 Brass or Bronze 19 x 10 the walls of the container in a given unit of time.

–6 Brick 9 x 10 –6 If the container were an open vessel, the gas would expand Copper 17 x 10 and overflow from the container. However, if the container –6 Glass (Plate) 9 x 10 is sealed and possesses elasticity, such as a rubber balloon, –6 Glass (Pyrex) 3 x 10 the increased pressure causes the container to expand. For –6 Ice 51 x 10 instance, when making a long drive on a hot day, the pressure –6 Iron or Steel 11 x 10 in the tires of an automobile increases, and a tire which –6 appeared to be somewhat “soft” in cool morning temperature Lead 29 x 10 may appear normal at a higher midday temperature.

–6 Quartz 0.4 x 10 –6 Silver 19 x 10 Such phenomena as these have been explained and set forth in the form of laws pertaining to gases and tend to support Figure 5-32. Coefficient of expansion for various materials.

5-23 kept constant and the absolute pressure doubled, the volume was reduced to half the former value. As the applied absolute Vacuum pressure was decreased, the resulting volume increased.

From these observations, he concluded that for a constant temperature the product of the volume and absolute pressure of an enclosed gas remains constant. Boyle’s law is normally stated: “The volume of an enclosed dry gas varies inversely with its absolute pressure, provided the temperature remains 14.7 psi constant.” The following formula is used for Boyle’s law Atmospheric 760 mm pressure 29.92 in calculations. Remember, pressure needs to be in the absolute.

Volume 1 × Pressure 1 = Volume 2 × Pressure 2 or V P = V P 1 1 2 2 Example: 10 ft of nitrogen is under a pressure of 500 psia.

If the volume is reduced to 7 ft , what will the new pressure be? [Figure 5-37] V P = V P 1 1 2 2 10 (500) = 7 (P ) 10 (500) ÷ 7 = P Figure 5-33. Atmospheric pressure as inches of mercury.

P = 714.29 psia the kinetic theory.

The useful applications of Boyle’s law are many and varied.

Some applications more common to aviation are: (1) the Boyle’s Law carbon dioxide (CO ) bottle used to inflate life rafts and life As previously stated, compressibility is an outstanding vests; (2) the compressed oxygen and the acetylene tanks characteristic of gases. The English scientist, Robert Boyle, used in welding; (3) the compressed air brakes and shock was among the first to study this characteristic that he called absorbers; and (4) the use of oxygen tanks for high altitude the “springiness of air.” By direct measurement he discovered flying and emergency use.

that when the temperature of a combined sample of gas was 35 30 40 26 29.5 psi 80 20 Man.

Fuel Press.

Flow 90 10 Gal ("Hg) / ( Hr ) 100 0 10 4.0 psi Fuel Pressure Psi Figure 5-34. Psig read on a fuel pressure gauge.

Figure 5-35. Manifold pressure gauge indicating absolute pressure.

5-24 General Gas Law 0 S S R E P F E D I By combining Boyle’s and Charles’ laws, a single expression S ALT P 0 HORN can be derived which states all the information contained in 2 CUT-OUT 5 40 CABIN AIR both. The formula which is used to express the general gas Pressurization law is as follows: system di ff erential pressure gauge X 1000 FT Pressure 2 (Volume 2) Pressure 1 (Volume 1) = Temperature 1 Temperature 5 6 or P (V ) (T ) = P (V ) (T ) 1 1 2 2 2 1 PRESSURE DIFFERENCE .5 LIMIT: C L I UP N M I B B When using the general gas law formula, temperature and A TAKE-OFF & C 0 4 LOG 0.125 PSI pressure must be in the absolute.

1 N 0 I 0 M F R E E DN E T P .5 1 3 3 Example: 20 ft of the gas argon is compressed to 15 ft .

The gas starts out at a temperature of 60 °F and a pressure of 1,000 psig. After being compressed, its temperature is 90 °F.

Figure 5-36. Differential pressure gauge.

What would its new pressure be in psig?

Charles’ Law 60 degrees Fahrenheit = 520 degrees Rankine The French scientist, Jacques Charles, provided much of the 90 degrees Fahrenheit = 550 degrees Rankine foundation for the modern kinetic theory of gases. He found 1,000 psig + 14.7 = 1,014.7 psia that all gases expand and contract in direct proportion to the P (V ) (T ) = P (V ) (T ) 1 1 2 2 2 1 change in the absolute temperature, provided the pressure is 1,014.7 (20) (550) = P (15) (520) held constant. As a formula, this law is shown as follows: P = 1,431 psia P = 1,416.3 psig Volume 1 × Absolute Temperature 2 = Volume 2 × Absolute Temperature 1 Dalton’s Law or If a mixture of two or more gases that do not combine V T = V T 1 2 2 1 chemically is placed in a container, each gas expands throughout the total space and the absolute pressure of each Charles’ law also works if the volume is held constant, and gas is reduced to a lower value, called its partial pressure. This pressure and temperature are the variables. In this case, the formula would be as follows: Force pushing down on gas P T = P T 1 2 2 1 For this second formula, pressure and temperature must be in the absolute.

Example: A 15-ft cylinder of oxygen is at a temperature of 70 °F and a pressure of 750 psig. The cylinder is placed in the sun and the temperature of the oxygen increases to 140 °F.

What would be the new pressure in psig?

70 degrees Fahrenheit = 530 degrees Rankine 140 degrees Fahrenheit = 600 degrees Rankine 750 psig + 14.7 = 764.7 psia P T = P T 1 2 2 1 764.7 (600) = P (530) P = 764.7 (600) ÷ 530 Pressure Temperature increasing held constant P = 865.7 psia P = 851 psig Figure 5-37. Boyle’s law example.

5-25 reduction is in accordance with Boyle’s law. The pressure of The amount of buoyant force available to an object can be the mixed gases is equal to the sum of the partial pressures. calculated by using the following formula: This fact was discovered by Dalton, an English physicist, and is set forth in Dalton’s law: “A mixture of several gases Buoyant Force = Volume of Object × Density of Fluid Displaced which do not react chemically exerts a pressure equal to the If the buoyant force is more than the object weighs, the object sum of the pressures which the several gases would exert will float. If the buoyant force is less than the object weighs, separately if each were allowed to occupy the entire space the object will sink. For the object that sinks, its measurable alone at the given temperature.” weight will be less by the weight of the displaced fluid.

Fluid Mechanics Example: A 10-ft object weighing 700 lb is placed in pure water. Will the object float? If the object sinks, what is By definition, a fluid is any substance that is able to flow if it its measurable weight in the submerged condition? If the is not in some way confined or restricted. Liquids and gases object floats, how many cubic feet of its volume is below are both classified as fluids, and often act in a very similar the water line?

way. One significant difference comes into play when a force is applied to these fluids. In this case, liquids tend Buoyant Force = Volume of Object × Density of Fluid Displaced to be incompressible and gases are highly compressible.

= 10 (62.4) Many of the principles that aviation is based on, such as = 624 lb the theory of lift on a wing and the force generated by a hydraulic system, can be explained and quantified by using The object will sink because the buoyant force is less than the the laws of fluid mechanics.

object weighs. The difference between the buoyant force and the object’s weight will be its measurable weight, or 76 lb.

Buoyancy A solid body submerged in a liquid or a gas weighs less than Two good examples of buoyancy are a helium filled when weighed in free space. This is because of the upward airship and a seaplane on floats. An airship is able to float force, called buoyant force, which any fluid exerts on a body in the atmosphere and a seaplane is able to float on water.

submerged in it. An object will float if this upward force of the That means both have more buoyant force than weight.

fluid is greater than the weight of the object. Objects denser Figure 5-39 is a DeHavilland Twin Otter seaplane, with a than the fluid, even though they sink readily, appear to lose gross takeoff weight of 12,500 lb. At a minimum, the floats a part of their weight when submerged. A person can lift a on this airplane must be large enough to displace a weight larger weight under water than they can possibly lift in the air.

in water equal to the airplane’s weight. According to Title 14 of the Code of Federal Regulations (14 CFR) part 23, the The following experiment is illustrated in Figure 5-38 . The floats must be 80 percent larger than the minimum needed overflow can is filled to the spout with water. The heavy to support the airplane. For this airplane, the necessary size metal cube is first weighed in still air and weighs 10 lb. It is of the floats would be calculated as follows: then weighed while completely submerged in the water and it weighs 3 lb. The difference between the two weights is Divide the airplane weight by the density of water.

the buoyant force of the water. As the cube is lowered into 12,500 ÷ 62.4 = 200.3 ft the overflow can, the water is caught in the catch bucket.

The volume of water which overflows equals the volume Multiply this volume by 80%.

of the cube. The volume of irregular shaped objects can 200.3 × 80% = 160.2 ft also be measured by using this method. If this experiment is performed carefully, the weight of the water displaced by Add the two volumes together to get the total volume of the metal cube exactly equals the buoyant force of the water, the floats.

which the scale shows to be 7 lb.

200.3 + 160.2 = 360.5 ft Archimedes (287–212 B.C.) performed similar experiments.

By looking at the Twin Otter in Figure 5-39 , it is obvious As a result, he discovered that the buoyant force which a fluid that much of the volume of the floats is out of the water. This exerts upon a submerged body is equal to the weight of the fluid is accomplished by making sure the floats have at least 80 the body displaces. This statement is referred to as Archimedes’ percent more volume than the minimum necessary.

principle. This principle applies to all fluids, gases as well as liquids. Just as water exerts a buoyant force on submerged Some of the large Goodyear airships have a volume of objects, air exerts a buoyant force on objects submerged in it.

230,000 ft . Since the fluid they are submerged in is air, 5-26 to find the buoyant force of the airship, the volume of the Still thinking about Figure 5-41 , if the pressure was measured lb airship is multiplied by the density of air (.07651 ⁄ ft ). For this half way down, it would be half of 8.34, or 4.17 psi. In other Goodyear airship, the buoyant force is 17,597 lb. Figure 5-40 words, the pressure is adjustable by varying the height of the shows an inside view of the Goodyear airship. column. Pressure based on the column height of a fluid is known as static pressure. With liquids, such as gasoline, it The forward and aft ballonets are air chambers within the is sometimes referred to as a head of pressure. For example, airship. Through the air scoop, air can be pumped into if a carburetor needs to have 2 psi supplied to its inlet, or the ballonets or evacuated from the ballonets in order to head of pressure, this could be accomplished by having the control the weight of the airship. Controlling the weight of fuel tank positioned the appropriate number of inches higher the airship controls how much positive or negative lift it than the carburetor.

has. Although the airship is classified as a lighter-than-air aircraft, it is in fact flown in a condition slightly heavier As identified in the previous paragraph, pressure due to the than air. height of a fluid column is known as static pressure. When a fluid is in motion, and its velocity is converted to pressure, Fluid Pressure that pressure is known as ram. When ram pressure and static pressure are added together, the result is known as total The pressure exerted on the bottom of a container by a liquid is determined by the height of the liquid and not by pressure. In the inlet of a gas turbine engine, for example, total pressure is often measured to provide a signal to the the shape of the container. This can be seen in Figure 5-41 , where three different shapes and sizes of containers are full fuel metering device or to provide a signal to a gauge on the flight deck.

of colored water. Even though they are different shapes and have different volumes of liquid, each one has a height of Pascal’s Law 231 inches. Each one would exert a pressure on the bottom of 8.34 psi because of this height. The container on the left, The foundations of modern hydraulics and pneumatics were 2 3 with a surface area of 1 in , contains a volume of 231 in established in 1653 when Pascal discovered that pressure set (one gallon). One gallon of water weighs 8.34 lb, which is up in a fluid acts equally in all directions. This pressure acts why the pressure on the bottom is 8.34 psi. at right angles to containing surfaces. When the pressure in the fluid is caused solely by the fluid’s height, the pressure against the walls of the container is equal at any given level, but it is not equal if the pressure at the bottom is compared to the pressure half way down. The concept of the pressure set up in a fluid, and how it relates to the force acting on the fluid and the surface area through which it acts, is Pascal’s law.

In Figure 5-41 , if a piston is placed at the top of the cylinder and an external force pushes down on the piston, additional pressure will be created in the liquid. If the additional pressure is 100 psi, this 100 psi will act equally and undiminished from the top of the cylinder all the way to the bottom. The Catch 10 lb bucket 0.11 cu' 0.11 cu' Over fl ow can Figure 5-39. DeHavilland Twin Otter seaplane.

Figure 5-38. Example of buoyancy.

5-27 gauge at the bottom will now read 108.34 psi, and if a gauge Each container is fi lled with colored water to a height of 231 inches.

were positioned half way down the cylinder, it would read 104.17 psi, which is found by adding 100 plus half of 8.34.

Pascal’s law, when dealing with the variables of force, pressure, 2 2 2 100 in 150 in 1 in and area, is dealt with by way of the following formula.

Force = Pressure × Area In this formula, the force is in units of pounds, the pressure is in pounds per square inch (psi), and the area is in square inches. By transposing the original formula, we have two additional formulas, as follows: Pressure = Force ÷ Area and Area = Force ÷ Pressure An easy and convenient way to remember the formulas for Pascal’s law, and the relationship between the variables, is Each pressure gauge reads 8.34 psi with the triangle shown in Figure 5-42 . If the variable we want to solve for is covered up, the position of the remaining Figure 5-41. Fluid pressure based on column height.

two variables shows the proper math relationship. For example, if the “A,” or area, is covered up, what remains is cylinder, which contains a 5-in piston. The pressure of 10 psi the “F” on the top and the “P” on the bottom, meaning force created by the input piston pushes on the piston in the second divided by pressure.

cylinder, creating an output force of 50 pounds.

The simple hydraulic system in Figure 5-43 has 5 lb force 1 2 acting on a piston with a ⁄ 2 -in surface area. Based on Pascal’s Often, the purpose of a hydraulic system is to generate a law, the pressure in the system would be equal to the force large output force, with the input force being much less.

applied divided by the area of the piston, or 10 psi. As shown In Figure 5-44 , the input force is 5 lb and the output force in Figure 5-43 , the pressure of 10 psi is present everywhere is 50 lb, or 10 times greater. The relationship between in the fluid.

the output force and the input force, as discussed earlier in this chapter, is known as mechanical advantage. The The hydraulic system in Figure 5-44 is a little more complex mechanical advantage in Figure 5-44 would be 50 divided than the one in Figure 5-43 . In Figure 5-44 , the input force 1 2 by 5, or 10. The following formulas can be used to calculate of 5 lb is acting on a ⁄ 2 -in piston, creating a pressure of mechanical advantage.

10 psi. The input cylinder and piston is connected to a second Mechanical Advantage = Force Out ÷ Force In Suspension cables Neoprene cover or Nose cone support Light sign Mechanical Advantage = Distance Out ÷ Distance In Control surfaces Earlier in this chapter when simple machines, such as levers and gears were discussed, it was identified that no machine allows us to gain work. The same statement holds true for a hydraulic system, that we get no more work out of a hydraulic system than we put in. Since work is equal to force times Air valves distance, if we gain force with a hydraulic system, we must lose distance. We only get the same work out, if the system Aft balloonet Forward balloonet is 100 percent efficient.

Engines Air scoops Passenger car In order to think about the distance that the output piston will move in response to the movement of the input piston, the Figure 5-40. The Goodyear Airship and buoyancy.

5-28 volume of fluid displaced must be considered. In the study of geometry, one learns that the volume of a cylinder is equal 10 psi to the cylinder’s surface area multiplied by its height. So, 10 psi Force = 5 lb when a piston of 2 in moves down in a cylinder a distance of 3 2 10 in, it displaces a volume of fluid equal to 20 in (2 in × 10 in). The 20 in displaced by the first piston is what moves Piston area = ½ in over to the second cylinder and causes its piston to move.

In a simple two-piston hydraulic system, the relationship Pressure = force ÷ area Pressure = 5 ÷ ½ between the piston area and the distance moved is shown Pressure = 10 psi by the following formula.

Figure 5-43. Pressure created in a hydraulic system.

Input Piston Area (Distance Moved) = Output Piston Area (Distance Moved) = 60 Input Piston Area This formula shows that the volume in is equal to the volume (Distance Moved) = Output Piston Area out. This concept is shown in Figure 5-45 , where a small input (Distance Moved) piston moves a distance of 20 inches, and the larger output ⁄ 4 (30) = 15 (Distance Moved) piston only moves a distance of 1 inch.

⁄ 4 (30) ÷ 15 = Distance Moved Distance Moved = ⁄ 2 in Example: A two-piston hydraulic system, like that shown in 1 2 Figure 5-45 , has an input piston with an area of ⁄ 4 in and 2 Part of understanding Pascal’s law and hydraulics involves an output piston with an area of 15 in . An input force of utilizing formulas, and recognizing the relationship 50 lb is applied, and the input piston moves 30 inches. What between the individual variables. Before the numbers are is the pressure in the system, how much force is generated plugged into the formulas, it is often possible to analyze by the output piston, how far would the output piston move, the variables in the system and come to a realization about and what is the mechanical advantage?

what is happening. For example, look at the variables in Figure 5-45 and notice that the output piston is 20 times Pressure = Force ÷ Area 2 1 2 1 larger than the input piston, 5 in compared to ⁄ 4 in . That = 50 ÷ ⁄ 4 comparison tells us that the output force will be 20 times = 200 psi greater than the input force, and also that the output piston Force = Pressure × Area will only move ⁄ 20 as far. Without doing any formula based = 200 × 15 calculations, we can conclude that the hydraulic system in = 3,000 lb question has a mechanical advantage of 20.

Mechanical Advantage = Force Out ÷ Force In = 3,000 ÷ 50 Bernoulli’s Principle Bernoulli’s principle was originally stated to explain the action of a liquid flowing through the varying cross-sectional Force = 50 lb

10 psi Force = 5 lb 50 lb Piston area = 5 in Piston area = ½ in

A P

Force = pressure x area Force = 10 psi x5 in Force = 50 lb 10 psi Figure 5-44. Output force created in a hydraulic system.

Figure 5-42. Force, area, pressure relationship.

5-29 areas of tubes. In Figure 5-46 a tube is shown in which top surface and a relatively flat bottom surface. The curved the cross-sectional area gradually decreases to a minimum top surface acts like half of the converging shaped middle diameter in its center section. A tube constructed in this of a venturi. As the air flow over the top of the wing, the manner is called a “venturi,” or “venturi tube.” Where the air speeds up, and its static pressure decreases. The static cross-sectional area is decreasing, the passageway is referred pressure on the bottom of the wing is now greater than the to as a converging duct. As the passageway starts to spread pressure on the top, and this pressure difference creates the out, it is referred to as a diverging duct. lift on the wing. Bernoulli’s principle and the concept of lift on a wing are covered in greater depth in “Aircraft Theory As a liquid, or fluid, flows through the venturi tube, the of Flight” located in this chapter.

gauges at points “A,” “B,” and “C” are positioned to register Sound the velocity and the static pressure of the liquid. The venturi in Figure 5-46 can be used to illustrate Bernoulli’s principle, Sound has been defined as a series of disturbances in matter which states that: The static pressure of a fluid, liquid or gas, that the human ear can detect. This definition can also be decreases at points where the velocity of the fluid increases, applied to disturbances which are beyond the range of human provided no energy is added to nor taken away from the hearing. There are three elements which are necessary for the fluid. The velocity of the air is kinetic energy and the static transmission and reception of sound. These are the source, a pressure of the air is potential energy.

medium for carrying the sound, and the detector. Anything which moves back and forth, or vibrates, and disturbs the In the wide section of the venturi (points A and C of medium around it may be considered a sound source.

Figure 5-46 ), the liquid moves at low velocity, producing a high static pressure, as indicated by the pressure gauge. As the An example of the production and transmission of sound tube narrows in the center, it must contain the same volume is the ring of a bell. When the bell is struck and begins to of fluid as the two end areas. As indicated by the velocity vibrate, the particles of the medium, or the surrounding air, in gauge reading high and the pressure gauge reading low, in contact with the bell also vibrate. The vibrational disturbance this narrow section, the liquid moves at a higher velocity, is transmitted from one particle of the medium to the next, producing a lower pressure than that at points A and C. A and the vibrations travel in a “wave” through the medium good application for the use of the venturi principle is in a until they reach the ear. The eardrum, acting as detector, is float-type carburetor. As the air flows through the carburetor set in motion by the vibrating particles of air, and the brain on its way to the engine, it goes through a venturi, where the interprets the eardrum’s vibrations as the characteristic sound static pressure is reduced. The fuel in the carburetor, which is associated with a bell.

under a higher pressure, flows into the lower pressure venturi area and mixes with the air.

Wave Motion Since sound is a wave motion in matter, it can best be Bernoulli’s principle is extremely important in understanding understood by first considering water waves, like a series how some of the systems used in aviation work, including of circular waves travel away from the disturbance of an how the wing of an airplane generates lift or why the inlet object thrown into a pool. In Figure 5-47 such waves are duct of a turbine engine on a subsonic airplane is diverging seen from a top perspective, with the waves traveling in shape. The wing on a slow-moving airplane has a curved out from the center. In the cross-section perspective in Figure 5-47 , notice that the water waves are a succession Distance moved = 1 in of crests and troughs. The wavelength is the distance from the crest of one wave to the crest of the next. Water waves are known as transverse waves because the motion of the Distance moved = 20 in water molecules is up and down, or at right angles to the direction in which the waves are traveling. This can be seen Output piston by observing a cork on the water, bobbing up and down as area = Input piston area = ¼ in 2 the waves pass by.

15 in Sound travels through matter in the form of longitudinal wave Piston area (distance) = Piston area (distance) motions. These waves are called longitudinal waves because the ¼ in (20 in) = 5 in (distance) particles of the medium vibrate back and forth longitudinally 5 ÷ 5 = Distance in the direction of propagation. [Figure 5-48] When the Distance = 1 in tine of a tuning fork moves in an outward direction, the air Figure 5-45. Piston movement in a hydraulic system.

immediately in front of the tine is compressed so that its 5-30 momentary pressure is raised above that at other points in the in lead at 20 °C, despite the fact that lead is much denser surrounding medium. Because air is elastic, this disturbance than aluminum. The reason for such exceptions is found in is transmitted progressively in an outward direction from the the fact, mentioned above, that sound velocity depends on tine in the form of a compression wave. elasticity as well as density.

When the tine returns and moves in an inward direction, Using density as a rough indication of the speed of sound the air in front of the tine is rarefied so that its momentary in a given substance, it can be stated as a general rule that pressure is reduced below that at other points in the sound travels fastest in solid materials, slower in liquids, and surrounding medium. This disturbance is transmitted in the slowest in gases. The velocity of sound in air at 0 °C (32 °F) form of a rarefaction, or expansion, wave and follows the is 1,087 fps and increases by 2 fps for each Centigrade degree compression wave through the medium. The progress of of temperature rise, or 1.1 fps for each degree Fahrenheit.

any wave involves two distinct motions: (1) The wave itself Mach Number moves forward with constant speed, and (2) simultaneously, the particles of the medium that convey the wave vibrate In the study of aircraft that fly at supersonic speeds, it is harmonically. Examples of harmonic motion are the motion customary to discuss aircraft speed in relation to the velocity of a clock pendulum, the balance wheel in a watch, and the of sound, which is approximately 761 miles per hour (mph) piston in a reciprocating engine. at 59 °F. The term “Mach number” has been given to the ratio of the speed of an aircraft to the speed of sound, in Speed of Sound honor of Ernst Mach, an Austrian scientist. If the speed of In any uniform medium, under given physical conditions, sound at sea level is 761 mph, an aircraft flying at a Mach the sound travels at a definite speed. In some substances, the number of 1.2 at sea level would be traveling at a speed of velocity of sound is higher than in others. Even in the same 761 mph × 1.2 = 913 mph.

medium under different conditions of temperature, pressure, Frequency of Sound and so forth, the velocity of sound varies. Density and elasticity of a medium are the two basic physical properties The term “pitch” is used to describe the frequency of a sound.

which govern the velocity of sound. The outstanding recognizable difference between the tones produced by two different keys on a piano is a difference in In general, a difference in density between two substances pitch. The pitch of a tone is proportional to the number of is sufficient to indicate which one will be the faster compressions and rarefactions received per second, which transmission medium for sound. For example, sound travels in turn, is determined by the vibration frequency of the faster through water than it does through air at the same sounding source. A good example of frequency is the noise temperature. However, there are some surprising exceptions generated by a turbofan engine on a commercial airliner. The to this rule of thumb. An outstanding example among these exceptions involves comparison of the speed of sound in lead and aluminum at the same temperature. Sound travels at 16,700 fps in aluminum at 20 °C, and only 4,030 fps Pressure Pressure Velocity Velocity Low High Low High Low High Low High

“ A ” “ B ” “ C ”

Pressure waves Round object dropped traveling outward into the water Crest Crest Low High Low High Trough Pressure Velocity Figure 5-46. Bernoulli’s principle and a venturi.

Figure 5-47. Relationship between sound and waves in water.

5-31 high tip speeds of the fan in the front of the engine create noise, by comparison, would sound twice as loud as the a high frequency sound, and the hot exhaust creates a low jetliner’s engine. Figure 5-49 shows the sound intensity from frequency sound. a variety of different sources.

Loudness Doppler Effect When a bell rings, the sound waves spread out in all directions When sound is coming from a moving object, the object’s and the sound is heard in all directions. When a bell is struck forward motion adds to the frequency as sensed from the front lightly, the vibrations are of small amplitude and the sound and takes away from the frequency as sensed from the rear.

is weak. A stronger blow produces vibrations of greater This change in frequency is known as the Doppler Effect, and amplitude in the bell, and the sound is louder. It is evident it explains why the sound from an airplane seems different as it that the amplitude of the air vibrations is greater when the approaches compared to how it sounds as it flies overhead. As amplitude of the vibrations of the source is increased. Hence, it approaches, it becomes both louder and higher pitched. As the loudness of the sound depends on the amplitude of the it flies away, the loudness and pitch both decrease noticeably.

vibrations of the sound waves. As the distance from the If an airplane is flying at or higher than the speed of sound, source increases, the energy in each wave spreads out, and the sound energy cannot travel out ahead of the airplane, the sound becomes weaker. because the airplane catches up to it the instant it tries to leave. The sound energy being created by the airplane piles As the sound wave advances, variations in pressure occur up, and attaches itself to the structure of the airplane. As the at all points in the transmitting medium. The greater the airplane approaches, a person standing on the ground will not pressure variations, the more intense the sound wave is. be able to hear it until it gets past their position, because the The intensity is proportional to the square of the pressure sound energy is actually trailing behind the airplane. When variation regardless of the frequency. Thus, by measuring the sound of the airplane is heard, it will be in the form of pressure changes, the intensities of sounds having different what is called a sonic boom.

frequencies can be compared directly.

Resonance Measurement of Sound Intensity All types of matter, regardless of whether it is a solid, liquid, Sound intensity is measured in decibels, with a decibel or gas, have a natural frequency at which the atoms within being the ratio of one sound to another. One decibel (dB) that matter vibrate. If two pieces of matter have the same is the smallest change in sound intensity the human ear can natural frequency, and one of them starts to vibrate, it can detect. A faint whisper would have an intensity of 20 dB, and transfer its wave energy to the other one and cause it to a pneumatic drill would be 80 dB. The engine on a modern vibrate. This transfer of energy is known as resonance. Some jetliner, at takeoff thrust, would have a sound intensity of piston engine powered airplanes have an rpm range that they 90 dB when heard by someone standing 150 ft. away. A 110 dB are placarded to avoid, because spinning the prop at that rpm can cause vibration problems. The difficulty lies in the natural frequency of the metal in the prop, and the frequency Rarefaction Tuning fork of vibration that will be set up with a particular tip speed for the prop. At that particular rpm, stresses can be set up that Compression could lead to the propeller coming apart.

The Atmosphere Aviation is so dependent upon that category of fluids called gases and the effect of forces and pressures acting upon gases that a discussion of the subject of the atmosphere is important to the persons maintaining and repairing aircraft.

Amplitude Data available about the atmosphere may determine whether a flight will succeed, or whether it will even become airborne.

The various components of the air around the earth, the changes in temperatures and pressures at different levels Wave above the earth, the properties of weather encountered by length aircraft in flight, and many other detailed data are considered in the preparation of flight plans.

Figure 5-48. Sound propagation by a tuning fork.

5-32 Pascan and Torricelli have been credited with developing 600 miles and its upper boundary at 6,000 miles.

the barometer, an instrument for measuring atmospheric pressure. The results of their experiments are still used today There are also certain nonconformities at various levels.

with very little improvement in design or knowledge. They Between 12 and 30 miles, high solar ultraviolet radiation determined that air has weight which changes as altitude is reacts with oxygen molecules to produce a thin curtain of changed with respect to sea level. Today scientists are also ozone, a very poisonous gas without which life on earth could interested in how the atmosphere affects the performance of not exist. This ozone filters out a portion of the sun’s lethal the aircraft and its equipment. ultraviolet rays, allowing only enough coming through to give us sunburn, kill bacteria, and prevent rickets. At 50 to Composition of the Atmosphere 65 miles up, most of the oxygen molecules begin to break The atmosphere is a complex and ever changing mixture. Its down under solar radiation into free atoms, and to form hydroxyl ions (OH) from water vapor. Also in this region, ingredients vary from place to place and from day to day.

In addition to a number of gases, it contains quantities of all the atoms become ionized.

foreign matter such as pollen, dust, bacteria, soot, volcanic ash, spores, and dust from outer space. The composition Studies of the atmosphere have revealed that the temperature does not decrease uniformly with increasing altitude; instead it of the air remains almost constant from sea level up to its highest level, but its density diminishes rapidly with gets steadily colder up to a height of about 7 miles, where the rate of temperature change slows down abruptly and remains altitude. Six miles up, for example, it is too thin to support respiration, and 12 miles up, there is not enough oxygen almost constant at −55° Centigrade (218° Kelvin) up to about 20 miles. Then the temperature begins to rise to a peak value of to support combustion, except in some specially designed turbine engine powered airplanes. At a point several 77° Centigrade (350° Kelvin) at the 55 mile level. Thereafter it climbs steadily, reaching 2,270° Centigrade (2,543° Kelvin) at hundred miles above the earth, some gas particles spray out into space, some are dragged by gravity and fall back into a height of 250 to 400 miles. From the 50 mile level upward, a man or any other living creature, without the protective cover the ocean of air below, while others never return. Physicists disagree as to the boundaries of the outer fringes of the of the atmosphere, would be broiled on the side facing the sun and frozen on the other.

atmosphere. Some think it begins 240 miles above the earth and extends to 400 miles; others place its lower edge at The atmosphere is divided into concentric layers or levels.

Transition through these layers is gradual and without sharply defined boundaries. However, one boundary, the tropopause, Lethal level Turbojet engine at 50 ft exists between the first and second layer. The tropopause is defined as the point in the atmosphere at which the decrease 50 horsepower siren at 50 ft in temperature, with increasing altitude, abruptly ceases. The Turbojet engine at takeoff four atmosphere layers are the troposphere, stratosphere, at 150 ft ionosphere, and the exosphere. The upper portion of the Automobile horn stratosphere is often called the chemosphere or ozonosphere, Riveting machine, as heard and the exosphere is also known as the mesosphere.

by operator 120 An express train passing close by 110 The troposphere extends from the earth’s surface to about Modern turbo engine at 100 35,000 ft at middle latitudes, but varies from 28,000 ft at the takeo ff at 150 ft poles to about 54,000 ft at the equator. The troposphere is THRESHOLD OF FEELING Subway train at 20 ft (1/2 the loudness of 110 dB noise) characterized by large changes in temperature and humidity and Pneumatic drill at 50 ft by generally turbulent conditions. Nearly all cloud formations are within the troposphere. Approximately three-fourths of the Vacuum cleaner at 50 ft total weight of the atmosphere is within the troposphere. The Nearby freeway auto traffic stratosphere extends from the upper limits of the troposphere Private business office and the tropopause to an average altitude of 60 miles.

Residential area in the evening Soft whisper at 5 ft The ionosphere ranges from the 50-mile level to a level of Radio studio 300 to 600 miles. Little is known about the characteristics Faint whisper of the ionosphere, but it is thought that many electrical THRESHOLD OF AUDIBILITY phenomena occur there. Basically, this layer is characterized by the presence of ions and free electrons, and the ionization Figure 5-49. Sound intensity from different sources.

5-33 seems to increase with altitude and in successive layers. Atmospheric Density Since both temperature and pressure decrease with altitude, The exosphere, or mesosphere, is the outer layer of the it might appear that the density of the atmosphere would atmosphere. It begins at an altitude of 600 miles and extends remain fairly constant with increased altitude. This is not to the limits of the atmosphere. In this layer, the temperature true, however, because pressure drops more rapidly with is fairly constant at 2,500° Kelvin, and propagation of sound increased altitude than does the temperature. The result is is thought to be impossible due to lack of molecular substance.

that density decreases with increased altitude.

Atmospheric Pressure By use of the general gas law, studied earlier, it can be shown The human body is under pressure, since it exists at the that for a particular gas, pressure and temperature determine bottom of a sea of air. This pressure is due to the weight of the the density. Since standard pressure and temperatures have atmosphere. On a standard day at sea level, if a 1-in column been associated with each altitude, the density of the air of air extending to the top of the atmosphere was weighed, it at these standard temperatures and pressures must also be would weigh 14.7 lb. That is why standard day atmospheric considered standard. Thus, a particular atmospheric density is pressure is said to be 14.7 pounds per square inch (14.7 psi).

associated with each altitude. This gives rise to the expression “density altitude,” symbolized “Hd.” A density altitude of Since atmospheric pressure at any altitude is due to the weight 15,000 ft is the altitude at which the density is the same as of air above it, pressure decreases with increased altitude.

that considered standard for 15,000 ft. Remember, however, Obviously, the total weight of air above an area at 15,000 ft that density altitude is not necessarily true altitude. For would be less than the total weight of the air above an area example, on a day when the atmospheric pressure is higher at 10,000 ft.

than standard and the temperature is lower than standard, the density which is standard at 10,000 ft might occur at Atmospheric pressure is often measured by a mercury 12,000 ft. In this case, at an actual altitude of 12,000 ft, we barometer. A glass tube somewhat over 30 inches in length have air that has the same density as standard air at 10,000 ft.

is sealed at one end and then filled with mercury. It is then Density altitude is a calculated altitude obtained by correcting inverted and the open end placed in a dish of mercury.

pressure altitude for temperature.

Immediately, the mercury level in the inverted tube will drop a short distance, leaving a small volume of mercury vapor at Water Content of the Atmosphere nearly zero absolute pressure in the tube just above the top of In the troposphere, the air is rarely completely dry. It contains the liquid mercury column. Gravity acting on the mercury in water vapor in one of two forms: (1) fog or (2) water vapor.

the tube will try to make the mercury run out. Atmospheric Fog consists of minute droplets of water held in suspension by pressure pushing down on the mercury in the open container the air. Clouds are composed of fog. The height to which some tries to make the mercury stay in the tube. At some point these clouds extend is a good indication of the presence of water in two forces (gravity and atmospheric pressure) will equilibrate the atmosphere almost up to the stratosphere. The presence of out and the mercury will stabilize at a certain height in the water vapor in the air is quite evident in Figure 5-52 , with a tube. Under standard day atmospheric conditions, the air in a military F-18 doing a high-speed fly-by at nearly Mach 1. The 1 square inch column extending to the top of the atmosphere temperature and pressure changes that occur as the airplane would weigh 14.7 lb. A 1-in column of mercury, 29.92 inches approaches supersonic flight cause the water vapor in the air tall, would also weigh 14.7 lb. That is why 14.7 psi is equal to condense and form the vapor cloud that is visible.

to 29.92 "Hg. Figure 5-50 demonstrates this point.

As a result of evaporation, the atmosphere always contains A second means of measuring atmospheric pressure is with some moisture in the form of water vapor. The moisture in an aneroid barometer. This mechanical instrument is a much the air is called the humidity of the air. Moisture does not better choice than a mercury barometer for use on airplanes.

consist of tiny particles of liquid held in suspension in the air Aneroid barometers, or altimeters, are used to indicate as in the case of fog, but is an invisible vapor truly as gaseous altitude in flight. The calibrations are made in thousands of as the air with which it mixes. Fog and humidity both affect feet rather than in psi or inches of mercury. For example, the the performance of an aircraft. In flight, at cruising power, standard pressure at sea level is 29.92 "Hg, or 14.7 psi. At the effects are small and receive no consideration. During 10,000 feet above sea level, standard pressure is 20.58 "Hg, takeoff, however, humidity has important effects. Two things or 10.10 psi. Altimeters are calibrated so that if the pressure are done to compensate for the effects of humidity on takeoff exerted by the atmosphere is 10.10 psi, the altimeter will performance. Since humid air is less dense than dry air, the point to 10,000 ft. [Figure 5-51] allowable takeoff gross weight of an aircraft is generally reduced for operation in areas that are consistently humid.

5-34 Second, because the power output of reciprocating engines is decreased by humidity, the manifold pressure may need to be increased above that recommended for takeoff in dry air in order to obtain the same power output.

FEET I00

I Engine power output is calculated on dry air. Since water

vapor is incombustible, its pressure in the atmosphere is a total loss as far as contributing to power output. The mixture

ALT

of water vapor and air is drawn through the carburetor, and 29.8 29.9 fuel is metered into it as though it were all air. This mixture 30.0 of water vapor, air, and fuel enters the combustion chamber where it is ignited. Since the water vapor will not burn, the effective air-fuel ratio is enriched and the engine operates as though it were on an excessively rich mixture. The resulting horsepower loss under humid conditions can therefore be attributed to the loss in volumetric efficiency due to displaced air, and the incomplete combustion due to an excessively rich fuel and air mixture.

The reduction in power that can be expected from humidity Figure 5-51. An airplane’s altimeter is an aneroid barometer.

is usually given in charts in the flight manual. There are several types of charts in use. Some merely show the expected day it is difficult to cause detonation to occur. The explanation reduction in power due to humidity; others show the boost of this lies in the fact that fog consists of particles of water in manifold pressure necessary to restore full takeoff power.

that have not vaporized. When these particles enter the cylinders, they absorb a tremendous amount of heat energy The effect of fog on the performance of an engine is very in the process of vaporizing. The temperature is thus lowered, noticeable, particularly on engines with high compression and the decrease is sufficient to prevent detonation.

ratios. Normally, some detonation will occur during acceleration, due to the high BMEP, which stands for brake Fog will generally cause a decrease in horsepower output.

mean effective pressures, developed. However, on a foggy However, with a supercharged engine, it will be possible to use higher manifold pressures without danger of detonation.

Vacuum Absolute Humidity Absolute humidity is the actual amount of the water vapor in a mixture of air and water. It is expressed either in grams per cubic meter or pounds per cubic foot. The amount of water vapor that can be present in the air is dependent upon the temperature and pressure. The higher the temperatures, 14.7 psi the more water vapor the air is capable of holding, assuming Atmospheric 760 mm constant pressure. When air has all the water vapor it can pressure 29.92 in hold at the prevailing temperature and pressure, it is said to be saturated.

Relative Humidity Relative humidity is the ratio of the amount of water vapor actually present in the atmosphere to the amount that would be present if the air were saturated at the prevailing temperature and pressure. This ratio is usually multiplied by 100 and expressed as a percentage. Suppose, for example, that a weather report includes the information that the temperature is 75 °F and the relative humidity is 56 percent. This indicates Figure 5-50. Atmospheric pressure as inches of mercury.

that the air holds 56 percent of the water vapor required to 5-35 with those of similar tests. The conditions in the atmosphere vary continuously, and it is generally not possible to obtain exactly the same set of conditions on two different days or even on two successive flights. For this reason, a set group of standards must be used as a point of reference. The set of standard conditions presently used in the United States is known as the U.S. Standard Atmosphere.

The standard atmosphere approximates the average conditions existing at 40° latitude, and is determined on the basis of the following assumptions. The standard sea level conditions are: Pressure at 0 altitude (P0) = 29.92 "Hg Temperature at 0 altitude (T0) = 15 °C or 59 °F Gravity at 0 altitude (G0) = 32.174 fps/s The U.S. Standard Atmosphere is in agreement with the International Civil Aviation Organization (ICAO) Standard Atmosphere over their common altitude range. The ICAO Figure 5-52. F-18 high-speed fly-by and a vapor cloud.

Standard Atmosphere has been adopted as standard by most of the principal nations of the world.

saturate it at 75 °F. If the temperature drops and the absolute Aircraft Theory of Flight humidity remain constant, the relative humidity will increase.

This is because less water vapor is required to saturate the Before a technician can consider performing maintenance air at the lower temperature.

on an aircraft, it is necessary to understand the pieces that make up the aircraft. Names like fuselage, empennage, wing, Dew Point and so many others, come into play when describing what The dew point is the temperature to which humid air must an airplane is and how it operates. For helicopters, names be cooled at constant pressure to become saturated. If the like main rotor, anti-torque rotor, and autorotation come temperature drops below the dew point, condensation occurs.

to mind as a small portion of what needs to be understood People who wear eyeglasses have experience going from cold about rotorcraft. The study of physics, which includes basic outside air into a warm room and having moisture collect aerodynamics, is a necessary part of understanding why quickly on their glasses. This happens because the glasses aircraft operate the way they do.

were below the dew point temperature of the air in the room.

The air immediately in contact with the glasses was cooled Four Forces of Flight below its dew point temperature, and some of the water vapor During flight, there are four forces acting on an airplane.

was condensed out. This principle is applied in determining These forces are lift, weight, thrust, and drag. [Figure 5-53 ] the dew point. A vessel is cooled until water vapor begins Lift is the upward force created by the wing, weight is the to condense on its surface. The temperature at which this pull of gravity on the mass, thrust is the force created by the occurs is the dew point.

airplane’s propeller or turbine engine, and drag is the friction caused by the air flowing around the airplane.

Vapor Pressure All four of these forces are measured in pounds. Any time Vapor pressure is the portion of atmospheric pressure that the forces are not in balance, something about the airplane’s is exerted by the moisture in the air, which is expressed in condition is changing. The possibilities are as follows: tenths of an inch of mercury. The dew point for a given condition depends on the amount of water pressure present; 1. When an airplane is accelerating, it has more thrust thus, a direct relationship exists between the vapor pressure than drag.

and the dew point.

2. When an airplane is decelerating, it has less thrust than drag.

Standard Atmosphere If the performance of an aircraft is computed, either through 3. When an airplane is at a constant velocity, thrust and drag are equal.

flight tests or wind tunnel tests, some standard reference condition must be determined first in order to compare results 5-36 4. When an airplane is climbing, it has more lift than In Figure 5-56 , the air reaching the leading edge of the wing weight. separates into two separate flows. Some of the air goes over the top of the wing and some travels along the bottom. The 5. When an airplane is descending, it has more weight air going over the top, because of the curvature, has farther than lift.

to travel. With a greater distance to travel, the air going over 6. When an airplane is at a constant altitude, lift and the top must move at a greater velocity. The higher velocity weight are equal.

on the top causes the static pressure on the top to be less than it is on the bottom, and this difference in static pressures is Bernoulli’s Principle and Subsonic Flow what creates lift.

The basic concept of subsonic airflow and the resulting pressure differentials was discovered by Daniel Bernoulli, For the wing shown in Figure 5-56 , imagine it is 5 ft. wide a Swiss physicist. Bernoulli’s principle, as we refer to it 2 2 and 15 ft. long, for a surface area of 75 ft (10,800 in ). If today, states that “as the velocity of a fluid increases, the the difference in static pressure between the top and bottom static pressure of that fluid will decrease, provided there is 1 is 0.1 psi, there will be ⁄ 10 lb of lift for each square inch of no energy added or energy taken away.” A direct application 2 surface area. Since there are 10,800 in of surface area, there of Bernoulli’s principle is the study of air as it flows through would be 1,080 lb of lift (0.1 × 10,800).

either a converging or a diverging passage, and to relate the findings to some aviation concepts.

Lift and Newton’s Third Law Newton’s third law identifies that for every force there is an A converging shape is one whose cross-sectional area gets equal and opposite reacting force. In addition to Bernoulli’s progressively smaller from entry to exit. A diverging shape is principle, Newton’s third law can also be used to explain the lift just the opposite, with the cross-sectional area getting larger being created by a wing. As the air travels around a wing and from entry to exit. Figure 5-54 shows a converging shaped leaves the trailing edge, the air is forced to move in a downward duct, with the air entering on the left at subsonic velocity and direction. Since a force is required to make something change exiting on the right. Notice that the air exits at an increased direction, there must be an equal and opposite reacting force.

velocity and a decreased static pressure when looking at In this case, the reacting force is what we call lift. In order to the pressure and velocity gauges, and the indicated velocity calculate lift based on Newton’s third law, and pressure. The unit leaving must increase its velocity as it flows into a smaller space, because a unit of air must exit Newton’s second law and the formula “Force = Mass × the duct when another unit enters.

Acceleration” would be used. The mass would be the weight of air flowing over the wing every second, and In a diverging duct, just the opposite would happen. From the acceleration would be the change in velocity the wing the entry point to the exit point, the duct is spreading out and imparts to the air.

the area is getting larger. [Figure 5-55] With the increase in cross-sectional area, the velocity of the air decreases The lift on the wing as described by Bernoulli’s principle, and the static pressure increases. The total energy in the and lift on the wing as described by Newton’s third law, is air has not changed. What has been lost in velocity, which is kinetic energy, is gained in static pressure, which is potential energy.

Lift In the discussion of Bernoulli’s principle earlier in this chapter, a venturi was shown in Figure 5-46 . In Figure 5-56 , a venturi is shown again, only this time a wing is shown tucked up into the recess where the venturi’s converging shape is.

Drag There are two arrows showing airflow. The large arrow shows Thrust airflow within the venturi, and the small arrow shows airflow on the outside heading toward the leading edge of the wing.

Weight In the converging part of the venturi, velocity would increase and static pressure would decrease. The same thing would happen to the air flowing around the wing, with the velocity over the top increasing and static pressure decreasing.

Figure 5-53. Four forces acting on an airplane.

5-37 not separate or independent of each other. They are just two Pressure Velocity different ways to describe the same thing, namely the lift on a wing.

14 psi 300 mph Low High Low High Airfoils An airfoil is any device that creates a force, based on Bernoulli’s principles or Newton’s laws, when air is caused to flow over the surface of the device. An airfoil can be the wing of an airplane, the blade of a propeller, the rotor blade of Subsonic a helicopter, or the fan blade of a turbofan engine. The wing of an airplane moves through the air because the airplane Air fl ow is in motion, and generates lift by the process previously described. By comparison, a propeller blade, helicopter rotor blade, or turbofan engine fan blade rotates through the air.

These rotating blades could be referred to as rotating wings, as is common with helicopters when they are called rotary wing aircraft. The rotating wing can be viewed as a device 10 psi 400 mph Low High Low High that creates lift, or just as correctly, it can be viewed as a device that creates thrust.

Pressure Velocity In Figure 5-57 an airfoil, or wing, is shown, with some of Figure 5-55. Bernoulli’s principle and a diverging duct.

the terminology that is used to describe a wing. The terms and their meaning are as follows: is what causes the velocity of the air to increase and the static pressure to decrease. The bottom of the wing has less velocity Camber and more static pressure, which is why the wing generates lift.

The camber of a wing is the curvature which is present on top and bottom surfaces. The camber on the top is much more Chord Line pronounced, unless the wing is a symmetrical airfoil, which has The chord line is an imaginary straight line running from the the same camber top and bottom. The bottom of the wing, more wing’s leading edge to its trailing edge. The angle between often than not, is relatively flat. The increased camber on top the chord line and the longitudinal axis of the airplane is known as the angle of incidence.

Pressure Velocity Relative Wind The relative wind is a relationship between the direction of 14 psi 300 mph Low High Low High airflow and the aircraft wing. In normal flight circumstances, the relative wind is the opposite direction of the aircraft flightpath.

• If the flightpath is forward then the relative wind is backward.

• If the flightpath is forward and upward, then the relative wind is backward and downward.

Subsonic • If the flightpath is forward and downward, then the Air fl ow relative wind is backward and upward.

Therefore, the relative wind is parallel to the flightpath, and travels in the opposite direction.

10 psi 400 mph Angle of Attack Low High Low High The angle between the chord line and the relative wind is Pressure Velocity the angle of attack. As the angle of attack increases, the lift on the wing increases. If the angle of attack becomes too Figure 5-54. Bernoulli’s principle and a converging duct.

great, the airflow can separate from the wing and the lift 5-38 Chord line Leading edge Upper camber Airplane path Angle of attack Air fl ow Velocity increase Relative wind Lower camber Trailing edge Figure 5-57. Wing terminology.

Figure 5-56. Venturi with a superimposed wing.

layer becomes turbulent, drag due to skin friction is will be destroyed. When this occurs, a condition known as relatively high. As speed increases, the transition point a stall takes place.

tends to move forward. As the angle of attack increases, the transition point also tends to move forward. With higher There are a number of different shapes, known as planforms angles of attack and further thickening of the boundary layer, that a wing can have. A wing in the shape of a rectangle is the turbulence becomes so great the air breaks away from very common on small general aviation airplanes. An elliptical the surface of the wing. At this point, the lift of the wing is shape or tapered wing can also be used, but these do not have destroyed and a condition known as a stall has occurred.

as desirable a stall characteristic. For airplanes that operate at In Figure 5-58 , view A shows a normal angle of attack and high subsonic speeds, sweptback wings are common, and for the airflow staying in contact with the wing. View B shows supersonic flight, a delta shape might be used.

an extreme angle of attack and the airflow separating and becoming turbulent on the top of the wing. In view B, the The aspect ratio of a wing is the relationship between its wing is in a stall.

span, or a wingtip to wingtip measurement, and the chord of the wing. If a wing has a long span and a very narrow chord, Boundary Layer Control it is said to have a high aspect ratio. A higher aspect ratio One way of keeping the boundary layer air under control, or produces less drag for a given flight speed, and is typically lessening its negative effect, is to make the wing’s surface found on glider type aircraft.

as smooth as possible and to keep it free of dirt and debris.

As the friction between the air and the surface of the wing The angle of incidence of a wing is the angle formed by the increases, the boundary layer thickens and becomes more intersection of the wing chord line and the horizontal plane turbulent and eventually a wing stall occurs. With a smooth passing through the longitudinal axis of the aircraft. Many and clean wing surface, the onset of a stall is delayed and airplanes are designed with a greater angle of incidence at the wing can operate at a higher angle of attack. One of the the root of the wing than at the tip, and this is referred to as reasons ice forming on a wing can be such a serious problem washout. This feature causes the inboard part of the wing to is because of its effect on boundary layer air. On a high-speed stall before the outboard part, which helps maintain aileron airplane, even a few bugs splattered on the wing’s leading control during the initial stages of a wing stall.

edge can negatively affect boundary layer air.

Boundary Layer Airflow Other methods of controlling boundary layer air include wing The boundary layer is a very thin layer of air lying over the leading edge slots, air suction through small holes on the wing’s surface of the wing and, for that matter, all other surfaces of upper surface, and the use of devices called vortex generators.

the airplane. Because air has viscosity, this layer of air tends to adhere to the wing. As the wing moves forward through A wing leading edge slot is a duct that allows air to flow from the air the boundary layer at first flows smoothly over the the bottom of the wing, through the duct, to the top of the streamlined shape of the airfoil. Here the flow is called the wing. As the air flows to the top of the wing, it is directed laminar layer.

along the wing’s surface at a high velocity and helps keep the boundary layer from becoming turbulent and separating As the boundary layer approaches the center of the wing, from the wing’s surface.

it begins to lose speed due to skin friction and it becomes thicker and turbulent. Here it is called the turbulent layer. The Another way of controlling boundary layer air is to create point at which the boundary layer changes from laminar to suction on the top of the wing through a large number of turbulent is called the transition point. Where the boundary 5-39 small holes. The suction on the top of the wing draws away The center of gravity is also referred to as the center of rotation.

the slow-moving turbulent air, and helps keep the remainder of the airflow in contact with the wing. On the brightly colored airplane shown in Figure 5-60 , the three axes are shown in the colors red (vertical axis), blue Vortex generators are used on airplanes that fly at high (longitudinal axis), and orange (lateral axis). The flight subsonic speed, where the velocity of the air on the top of the control that makes the airplane move around the axis is shown wing can reach Mach 1. As the air reaches Mach 1 velocity, a in a matching color.

shock wave forms on the top of the wing, and the subsequent shock wave causes the air to separate from the wing’s upper The rudder, in red, causes the airplane to move around the surface. Vortex generators are short airfoils, arranged in pairs, vertical axis and this movement is described as being a yaw.

located on the wing’s upper surface. They are positioned such The elevator, in orange, causes the airplane to move around that they pull high-energy air down into the boundary layer the lateral axis and this movement is described as being region and prevent airflow separation. a pitch. The ailerons, in blue, cause the airplane to move around the longitudinal axis and this movement is described Wingtip Vortices as being a roll.

Wingtip vortices are caused by the air beneath the wing, Aircraft Stability which is at the higher pressure, flowing over the wingtip and up toward the top of the wing. The end result is a When an airplane is in straight-and-level flight at a constant spiral or vortex that trails behind the wingtip anytime lift velocity, all the forces acting on the airplane are in equilibrium.

is being produced. This vortex is also referred to as wake If that straight-and-level flight is disrupted by a disturbance in turbulence, and is a significant factor in determining how the air, such as wake turbulence, the airplane might pitch up closely one airplane can follow behind another on approach or down, yaw left or right, or go into a roll. If the airplane has to land. The wake turbulence of a large airplane can cause what is characterized as stability, once the disturbance goes a smaller airplane, if it is following too closely, to be away, the airplane will return to a state of equilibrium.

thrown out of control. Vortices from the wing and from the horizontal stabilizer are quite visible on the MD-11 shown Static Stability in Figure 5-59.

The initial response that an airplane displays after its equilibrium is disrupted is referred to as its static stability. If Upwash and downwash refer to the effect an airfoil has on the static stability is positive, the airplane will tend to return the free airstream. Upwash is the deflection of the oncoming to its original position after the disruptive force is removed.

airstream, causing it to flow up and over the wing. Downwash If the static stability is negative, the airplane will continue to is the downward deflection of the airstream after it has passed move away from its original position after the disruptive force over the wing and is leaving the trailing edge. This downward is removed. If an airplane with negative static stability has deflection is what creates the action and reaction described the nose pitch up because of wake turbulence, the tendency under lift and Newton’s third law.

will be for the nose to continue to pitch up even after the turbulence goes away. If an airplane tends to remain in a Axes of an Aircraft displaced position after the force is removed, but does not An airplane in flight is controlled around one or more of three continue to move toward even greater displacement, its static axes of rotation. These axes of rotation are the longitudinal, stability is described as being neutral.

lateral, and vertical. On the airplane, all three axes intersect at the center of gravity. As the airplane pivots on one of these Dynamic Stability axes, it is in essence pivoting around the center of gravity (CG).

The dynamic stability of an airplane involves the amount of time it takes for it to react to its static stability after it has been displaced from a condition of equilibrium. Dynamic stability involves the oscillations that typically occur as the airplane tries to return to its original position or attitude. Even though an airplane may have positive static stability, it may have dynamic stability which is positive, neutral, or negative.

Imagine that an airplane in straight-and-level flight is disturbed and pitches noseup. If the airplane has positive View A View B static stability, the nose will pitch back down after the disturbance is removed. If it immediately returns to straight- Figure 5-58. Wing boundary layer separation.

5-40 Longitudinal Stability Longitudinal stability for an airplane involves the tendency for the nose to pitch up or pitch down, rotating around the lateral axis, which is measured from wingtip to wingtip. If an airplane is longitudinally stable, it will return to a properly trimmed angle of attack after the force that upset its flightpath is removed.

The weight and balance of an airplane, which is based on both the design characteristics of the airplane and the way it is loaded, is a major factor in determining longitudinal stability. There is a point on the wing of an airplane, called the center of pressure or center of lift, where all the lifting Figure 5-59. Wing and horizontal stabilizer vortices on an MD-11.

forces concentrate. In flight, the airplane acts like it is being lifted from or supported by this point. This center of lift runs from wingtip to wingtip. There is also a point on the and-level flight, it is also said to have positive dynamic airplane, called the center of gravity, where the mass or stability. The airplane, however, may pass through level flight weight of the airplane is concentrated. For an airplane to have and remain pitched down, and then continue the recovery good longitudinal stability, the center of gravity is typically process by pitching back up. This pitching up and then located forward of the center of lift. This gives the airplane down is known as an oscillation. If the oscillations lessen a nosedown pitching tendency, which is balanced out by the over time, the airplane is still classified as having positive force generated at the horizontal stabilizer and elevator. The dynamic stability. If the oscillations increase over time, the center of gravity has limits within which it must fall. If it is airplane is classified as having negative dynamic stability.

too far forward, the forces at the tail might not be able to If the oscillations remain the same over time, the airplane is compensate and it may not be possible to keep the nose of classified as having neutral dynamic stability.

the airplane from pitching down.

Figure 5-61 shows the concept of dynamic stability. In view In Figure 5-62 , the center of lift, center of gravity, and center A, the displacement from equilibrium goes through three of gravity limits are shown. It can be seen that the center oscillations and then returns to equilibrium. In view B, of gravity is not only forward of the center of lift, it is also the displacement from equilibrium is increasing after two forward of the center of gravity limit. At the back of the oscillations, and will not return to equilibrium. In view C, airplane, the elevator trailing edge is deflected upward to the displacement from equilibrium is staying the same with create a downward force on the tail, to try and keep the nose each oscillation.

Longitudinal axis Lateral axis CG Vertical axis Figure 5-60. The three axes intersect at the airplane’s center of gravity. The flight control that produces motion around the indicated axis is a matching color.

5-41 of the airplane up. This airplane would be highly unstable Dutch Roll longitudinally, especially at low speed when trying to land.

The dihedral of the wing tries to roll the airplane in the opposite It is especially dangerous if the center of gravity is behind direction of how it is slipping, and the vertical fin will try to the aft limit. The airplane will now have a tendency to pitch yaw the airplane in the direction of the slip. These two events noseup, which can lead to the wing stalling and possible loss combine in a way that affects lateral and directional stability. If of control of the airplane.

the wing dihedral has the greatest effect, the airplane will have a tendency to experience a Dutch roll. A Dutch roll is a small Lateral Stability amount of oscillation around both the longitudinal and vertical Lateral stability of an airplane takes place around the axes. Although this condition is not considered dangerous, longitudinal axis, which is from the airplane’s nose to its it can produce an uncomfortable feeling for passengers.

tail. If one wing is lower than the other, good lateral stability Commercial airliners typically have yaw dampers that sense will tend to bring the wings back to a level flight attitude. a Dutch roll condition and cancel it out.

One design characteristic that tends to give an airplane good Flight Control Surfaces lateral stability is called dihedral. Dihedral is an upward wing angle, with respect to the horizontal, and it is usually The purpose of flight controls is to allow the pilot to maneuver just a few degrees. the airplane, and to control it from the time it starts the takeoff roll until it lands and safely comes to a halt. Flight controls Imagine a low wing airplane with a few degrees of dihedral are typically associated with the wing and the vertical and experiencing a disruption of its flightpath such that the left horizontal stabilizers, because these are the parts of the airplane wing drops. When the left wing drops, this will cause the that flight controls most often attach to. In flight, and to some airplane to experience a sideslip toward the low wing. The extent on the ground, flight controls provide the airplane with sideslip causes the low wing to experience a higher angle the ability to move around one or more of the three axes.

of attack, which increases its lift and raises it back to a level Flight controls function by changing the shape or aerodynamic flight attitude. The dihedral on a wing is shown in Figure 5-63. characteristics of the surface they are attached to.

Flight Controls & the Lateral Axis Directional Stability The lateral axis of an airplane is a line that runs below Movement of the airplane around its vertical axis, and the the wing, from wingtip to wingtip, passing through the airplane’s ability to not be adversely affected by a force creating airplane’s center of gravity. Movement around this axis a yaw type of motion, is called directional stability. The vertical is called pitch, and control around this axis is called fin gives the airplane this stability, causing the airplane to longitudinal control. The flight control that handles this align with the relative wind. In flight, the airplane acts like the job is the elevator attached to the horizontal stabilizer, a weather vane we use around our home to show the direction fully moving horizontal stabilizer, or on a v-tail configured the wind is blowing. The distance from the pivot point on a airplane, it is called ruddervators. An elevator on a Cessna weather vane to its tail is greater than the distance from its 182 can be seen in Figure 5-65 . In Figure 5-66 , a fully pivot point to the nose. So, when the wind blows, it creates a moving horizontal stabilizer, known as a stabilator, can greater torque force on the tail and forces it to align with the be seen on a Piper Cherokee Cruiser PA-28-140, and wind. On an airplane, the same is true. With the CG being the Figure 5-67 shows a ruddervator on a Beechcraft Bonanza.

pivot point, it is a greater distance from the CG to the vertical Depending on the airplane being discussed, movement around stabilizer than it is from the CG to the nose. [Figure 5-64] the lateral axis happens as a result of the pilot moving the Aft CG limit Forward CG limit A B C Positive static and Positive static and Positive static and positive dynamic negative dynamic neutral dynamic stability stability stability Time Time Time Center of lift Center of gravity Figure 5-61. Dynamic stability.

Figure 5-62. Longitudinal stability and balance.

5-42 control wheel or yoke, the control stick, or on some airplanes, a side stick. On the airplanes shown in Figures 5-70 and 5-71 , Pivot point (CG) a control wheel or yoke is used.

Distance to vertical stabilizer creates stability On the Cessna 182 shown in Figure 5-65 , pulling back on the control wheel causes the trailing edge of the elevator to deflect upward, causing an increased downward force that raises the nose of the airplane. Movement of the elevator causes the nose of the airplane to pitch up or pitch down by rotating around the lateral axis. The Cessna 182 control wheel can be seen in Figure 5-68.

Figure 5-64. Directional stability caused by distance to vertical stabilizer.

On the Piper Cherokee Cruiser PA-28-140 shown in Figure 5-66 , pulling back on the control wheel causes the rise up into the airstream, and the aileron on the right wing entire horizontal surface, or stabilator, to move, with the lowers down into the airstream. This increases the lift on the trailing edge deflecting upward. The anti-servo tab seen on right wing and decreases the lift on the left wing, causing the the Cherokee provides a control feel similar to what would right wing to move up and the airplane to bank to the left.

be experienced by moving an elevator. Without this tab, the stabilator might be too easy to move and a pilot could In Figure 5-69 , an aircraft can be seen doing an aileron roll.

overcontrol the airplane.

Notice that the left aileron is up and the right aileron is down, which would cause the airplane to roll around the longitudinal The ruddervators shown on the Beechcraft Bonanza in axis in a counterclockwise direction.

Figure 5-67 are also moved by the control wheel, with their trailing edges deflecting upward when the control wheel is Flight Controls and the Vertical Axis pulled back. As the name implies, these surfaces also act as the rudder for this airplane.

The vertical axis of an airplane runs from top to bottom through the middle of the airplane, passing through the center Flight Controls and the Longitudinal Axis of gravity. Movement around this axis is known as yaw, and control around this axis is called directional control. Movement The longitudinal axis of the airplane runs through the around this axis is controlled by the rudder, or in the case of middle of the airplane, from nose to tail, passing through the Beechcraft Bonanza in Figure 5-67 , by the ruddervators.

the center of gravity. Movement around this axis is known as roll, and control around this axis is called lateral control.

The feet of the pilot are on the rudder pedals, and pushing Movement around this axis is controlled by the ailerons, on the left or right rudder pedal makes the rudder move left and on jet transport airplanes, it is aided by surfaces on the or right. The trailing edge of the rudder moves to the right, wing known as spoilers.

and the nose of the airplane yaws to the right, when the right rudder pedal is pushed. The rudder pedals of a Cessna 182 The ailerons move as a result of the pilot rotating the control can be seen in Figure 5-68 .

wheel to the left or to the right, much the same as turning the steering wheel on an automobile. [Figure 5-68] When a pilot Even though the rudder of the airplane will make the nose turns the control wheel to the left, the airplane is being asked yaw to the left or the right, the rudder is not what turns the to turn or bank to the left. Turning the control wheel to the left causes the trailing edge of the aileron on the left wing to Dihedral Elevator Figure 5-63. The dihedral of a wing. Figure 5-65. Elevator on a Cessna 182 provides pitch control.

5-43 Moving horizontal stabilizer (stabilator) Rudder pedals Control wheel or yoke Figure 5-66. Moving horizontal stabilizer, known as a stabilator, on a Piper Cherokee Cruiser PA-28-140 provides pitch control.

Figure 5-68. Cessna 182 control wheel and rudder pedals.

airplane. For what is called a coordinated turn to occur, both the ailerons and rudder come into play. Let’s say we want to tabs can be installed on any of the primary flight controls.

turn the airplane to the right. We start by turning the control wheel to the right, which raises the right aileron and lowers A very common flight control to find fitted with a trim tab is the elevator. In order to be stable in flight, most airplanes the left aileron and initiates the banking turn. The increased lift on the left wing also increases the induced drag on the left have the center of gravity located forward of the center of lift on the wing. This causes a nose heavy condition, which needs wing, which tries to make the nose of the airplane yaw to the left. To counteract this, when the control wheel is moved to to be balanced out by having the elevator deflect upwards and create a downward force. To relieve the pilot of the need the right, a small amount of right rudder is used to keep the nose of the airplane from yawing to the left. Once the nose of to hold back pressure on the control wheel, a trim tab on the elevator can be adjusted to hold the elevator in a slightly the airplane is pointing in the right direction, pressure on the rudder is no longer needed. The rudder of a Piper Cherokee deflected position. An elevator trim tab for a Cessna 182 is shown in Figure 5-71.

Arrow can be seen in Figure 5-70.

Anti-servo Tab Tabs Some airplanes, like a Piper Cherokee Arrow, do not have Trim Tabs a fixed horizontal stabilizer and movable elevator. The Trim tabs are small movable surfaces that attach to the trailing Cherokee uses a moving horizontal surface known as a edge of flight controls. These tabs can be controlled from the stabilator. Because of the location of the pivot point for this flight deck, and their purpose is to create an aerodynamic movable surface, it has a tendency to be extremely sensitive force that keeps the flight control in a deflected position. Trim to pilot input. To reduce the sensitivity, a full length anti-servo tab is installed on the trailing edge of the stabilator. As the trailing edge of the stabilator moves down, the anti-servo tab moves down and creates a force trying to raise the trailing edge. With this force acting against the movement of the stabilator, it reduces the sensitivity to pilot input. The anti- servo tab on a Piper Cherokee Arrow is shown in Figure 5-70.

Balance Tab On some airplanes, the force needed to move the flight controls can be excessive. In these cases, a balance tab can be used to generate a force that assists in the movement of the flight control. Just the opposite of anti-servo tabs, balance tabs move in the opposite direction of the flight control’s trailing Ruddervators edge, providing a force that helps the flight control move.

Servo Tab On large airplanes, because the force needed to move the Figure 5-67. Ruddervators on a Beechcraft Bonanza provide pitch control.

flight controls is beyond the capability of the pilot, hydraulic actuators are used to provide the necessary force. In the event 5-44 Aileron up Rudder Aileron down Anti-servo Tab Figure 5-70. Rudder and anti-servo tab on a Piper Cherokee Arrow.

factors cause the wing to create more lift and more drag.

Figure 5-69. Aircraft performing an aileron roll.

The split flap attaches to the bottom of the wing, and deploys downward without changing the top surface of the wing. This of a hydraulic system malfunction or failure, some of these type of flap creates more drag than the plain flap because of airplanes have servo tabs on the trailing edge of the primary the increase in turbulence.

flight controls. When the control wheel is pulled back in an attempt to move the elevator, the servo tab moves and creates The slotted flap is similar to the plain flap, except when it enough aerodynamic force to move the elevator. The servo tab deploys, the leading edge drops down a small amount. By is acting like a balance tab, but rather than assisting the normal having the leading edge drop down slightly, a slot opens, force that moves the elevator, it becomes the sole force that which lets some of the high-pressure air on the bottom of the makes the elevator move. Like the balance tab, the servo tab wing flow over the top of the flap. This additional airflow moves in the opposite direction of the flight control’s trailing over the top of the flap produces additional lift.

edge. The Boeing 727 has servo tabs that back up the hydraulic system in the event of a failure. During normal flight, the servo The Fowler flap attaches to the back of the wing using a track tabs act like balance tabs. [Figure 5-72] and roller system. When it deploys, it moves aft in addition to deflecting downward. This increases the total wing area, Supplemental Lift-Modifying Devices in addition to increasing the wing camber and chord line.

If the wing of an airplane was designed to produce the This type of flap is the most effective of the four types, and maximum lift possible at low airspeed, to accommodate it is the type used on commercial airliners and business jets.

takeoffs and landings, it would not be suited for higher speed flight because of the enormous amount of drag it would Leading Edge Slots produce. To give the wing the ability to produce maximum Leading edge slots are ducts or passages in the leading edge low speed lift without being drag prohibitive, retractable high of a wing that allow high pressure air from the bottom of the lift devices, such as flaps and slats, are utilized.

wing to flow to the top of the wing. This ducted air flows over the top of the wing at a high velocity and helps keep the Flaps boundary layer air from becoming turbulent and separating The most often used lift-modifying device, for small airplanes and large, is the wing flap. Flaps can be installed on the leading edge or trailing edge, with the leading edge versions used only on larger airplanes. Flaps change the camber of the wing, and they increase both the lift and the drag for any given angle of attack. The four different types of flaps in use are called the plain, split, slotted, and Fowler. [Figure 5-73] Plain flaps attach to the trailing edge of the wing, inboard Elevator trim tab of the ailerons, and form part of the wing’s overall surface.

When deployed downward, they increase the effective Figure 5-71. Elevator trim tab on a Cessna 182.

camber of the wing and the wing’s chord line. Both of these 5-45

Next: part of the wing stalls first and the ailerons remain effective. →

Section 13

from the wing. Slots are often placed on the part of the wing ahead of the ailerons, so during a wing stall, the inboard High-Speed Aerodynamics part of the wing stalls first and the ailerons remain effective.

Compressibility Effects When air is flowing at subsonic speed, it acts like an Leading Edge Slats incompressible fluid. As discussed earlier in this chapter, Leading edge slats serve the same purpose as slots, the when air at subsonic speed flows through a diverging shaped difference being that slats are movable and can be retracted passage, the velocity decreases and the static pressure rises, when not needed. On some airplanes, leading edge slats have but the density of the air does not change. In a converging been automatic in operation, deploying in response to the shaped passage, subsonic air speeds up and its static pressure aerodynamic forces that come into play during a high angle of decreases. When supersonic air flows through a converging attack. On most of today’s commercial airliners, the leading passage, its velocity decreases and its pressure and density edge slats deploy when the trailing edge flaps are lowered.

both increase. [Figure 5-74] At supersonic flow, air acts like a compressible fluid. Because air behaves differently when The flight controls of a large commercial airliner are shown flowing at supersonic velocity, airplanes that fly supersonic in Figure 5-72 . The controls by color are as follows: must have wings with a different shape.

The Speed of Sound 1. All aerodynamic tabs are shown in green.

Sound, in reference to airplanes and their movement through 2. All leading and trailing edge high lift devices are the air, is nothing more than pressure disturbances in the shown in red (leading edge flaps and slats, trailing air. As discussed earlier in this chapter, it is like dropping a edge inboard and outboard flaps).

rock in the water and watching the waves flow out from the 3. The tail mounted primary flight controls are in orange center. As an airplane flies through the air, every point on (rudder and elevator).

the airplane that causes a disturbance creates sound energy in the form of pressure waves. These pressure waves flow 4. The wing mounted primary flight controls are in purple away from the airplane at the speed of sound, which at (inboard and outboard aileron).

standard day temperature of 59 °F, is 761 mph. The speed Stabilizer Inboard aileron tab Inboard aileron Elevator Elevator tab Upper rudder Anti-balance tabs Lower rudder Ground spoilers Inboard flap Flight spoilers Outboard flap Balance tab Outboard aileron Leading edge slats (extended) Leading edge flaps (extended) Figure 5-72. Boeing 727 flight controls.

5-46 The speed at which the shock wave forms is known as the Plain flap critical Mach number. Transonic speed is typically between Mach 0.80 and 1.20.

When an airplane is flying at supersonic speed, the entire airplane is experiencing supersonic airflow. At this speed, the shock wave which formed on top of the wing during transonic Split flap flight has moved all the way aft and has attached itself to the wing trailing edge. Supersonic speed is from Mach 1.20 to 5.0. If an airplane flies faster than Mach 5, it is said to be in hypersonic flight.

Shock Waves Slotted flap Sound coming from an airplane is the result of the air being disturbed as the airplane moves through it, and the resulting pressure waves that radiate out from the source of the disturbance. For a slow-moving airplane, the pressure waves travel out ahead of the airplane, traveling at the speed of sound. When the speed of the airplane reaches the speed Fowler flap of sound, however, the pressure waves, or sound energy, cannot get away from the airplane. At this point the sound energy starts to pile up, initially on the top of the wing, and eventually attaching itself to the wing leading and trailing edges. This piling up of sound energy is called a shock wave.

If the shock waves reach the ground, and cross the path of Figure 5-73. Four types of wing flaps.

a person, they will be heard as a sonic boom. Figure 5-76A shows a wing in slow speed flight, with many disturbances on of sound in air changes with temperature, increasing as the wing generating sound pressure waves that are radiating temperature increases. Figure 5-75 shows how the speed outward. View B is the wing of an airplane in supersonic of sound changes with altitude.

flight, with the sound pressure waves piling up toward the wing leading edge.

Subsonic, Transonic, and Supersonic Flight Normal Shock Wave When an airplane is flying at subsonic speed, all of the air flowing around the airplane is at a velocity of less than the When an airplane is in transonic flight, the shock wave that speed of sound, which is known as Mach 1. Keep in mind forms on top of the wing, and eventually on the bottom of that the air accelerates when it flows over certain parts of the wing, is called a normal shock wave. If the leading edge the airplane, like the top of the wing, so an airplane flying of the wing is blunted, instead of being rounded or sharp, a at 500 mph could have air over the top of the wing reach normal shock wave will also form in front of the wing during a speed of 600 mph. How fast an airplane can fly and still be considered in subsonic flight varies with the design of the wing, but as a Mach number, it will typically be just over Mach 0.8.

Supersonic Air fl ow When an airplane is flying at transonic speed, part of the airplane is experiencing subsonic airflow and part is experiencing supersonic airflow. Over the top of the wing, probably about halfway back, the velocity of the air will Converging Diverging reach Mach 1 and a shock wave will form. The shock wave Decreasing velocity Increasing velocity Increasing pressure Decreasing pressure forms 90 degrees to the airflow and is known as a normal Increasing density Decreasing density shock wave. Stability problems can be encountered during transonic flight, because the shock wave can cause the airflow Figure 5-74. Supersonic airflow through a venturi.

to separate from the wing. The shock wave also causes the center of lift to shift aft, causing the nose to pitch down.

5-47 supersonic flight. Normal shock waves form perpendicular to SPEED OF SOUND ALTITUDE IN FEET TEMPERATURE ( °F ) the airstream. The velocity of the air behind a normal shock (MPH) wave is subsonic, and the static pressure and density of the air 0 761 59.00 are higher. Figure 5-77 shows a normal shock wave forming 1,000 758 55.43 on the top of a wing.

2,000 756 51.87 3,000 753 48.30 Oblique Shock Wave 4,000 750 44.74 An airplane that is designed to fly supersonic will have very 5,000 748 41.17 sharp edged surfaces, in order to have the least amount of drag.

When the airplane is in supersonic flight, the sharp leading 6,000 745 37.60 edge and trailing edge of the wing will have shock waves 7,000 742 34.04 attach to them. These shock waves are known as oblique shock 8,000 740 30.47 waves. Behind an oblique shock wave the velocity of the air is 9,000 737 26.90 lower, but still supersonic, and the static pressure and density 10,000 734 23.34 are higher. Figure 5-78 shows an oblique shock wave on the leading and trailing edges of a supersonic airfoil.

15,000 721 5.51 20,000 707 −12.32 Expansion Wave 25,000 692 −30.15 Earlier in the discussion of high-speed aerodynamics, it was 30,000 678 −47.98 stated that air at supersonic speed acts like a compressible 35,000 663 −65.82 fluid. For this reason, supersonic air, when given the opportunity, wants to expand outward. When supersonic * 36,089 660 −69.70 air is flowing over the top of a wing, and the wing surface 40,000 660 −69.70 turns away from the direction of flow, the air will expand 45,000 660 −69.70 and follow the new direction. An expansion wave will occur 50,000 660 −69.70 at the point where the direction of flow changes. Behind the 55,000 660 −69.70 expansion wave the velocity increases, and the static pressure and density decrease. An expansion wave is not a shock wave.

60,000 660 −69.70 Figure 5-78 shows an expansion wave on a supersonic airfoil.

65,000 660 −69.70 70,000 660 −69.70 High-Speed Airfoils 75,000 660 −69.70 Transonic flight is the most difficult flight regime for an 80,000 660 −69.70 airplane, because part of the wing is experiencing subsonic 85,000 664 −64.80 airflow and part is experiencing supersonic airflow. For a subsonic airfoil, the aerodynamic center, or the point of 90,000 671 −56.57 support, is approximately 25 percent of the way back from 95,000 678 −48.34 the wing leading edge. In supersonic flight, the aerodynamic 100,000 684 −40.11 center moves back to 50 percent of the wing’s chord, * Altitude at which temperature stops decreasing.

causing some significant changes in the airplane’s control and stability.

Figure 5-75. Altitude and temperature versus speed of sound.

If an airplane designed to fly subsonic, perhaps at a Mach Mach 1 velocity.

number of 0.80, flies too fast and enters transonic flight, some noticeable changes will take place with respect to the airflow C. The velocity has surpassed the critical Mach number, over the wing. Figure 5-79 shows six views of a wing, with and a normal shock wave has formed on the top of the each view showing the Mach number getting higher.

wing. Some airflow separation starts to occur behind the shock wave.

The scenario for the six views is as follows: D. The velocity has continued to increase beyond the A. The Mach number is fairly low, and the entire wing critical Mach number, and the normal shock wave has is experiencing subsonic airflow.

moved far enough aft that serious airflow separation is occurring. A normal shock wave is now forming B. The velocity has reached the critical Mach number, on the bottom of the wing as well. Behind the normal where the airflow over the top of the wing is reaching 5-48 Aerodynamic Heating One of the problems with airplanes and high-speed flight is the heat that builds up on the airplane’s surface because of air friction. When the SR-71 Blackbird airplane is cruising at Mach 3.5, skin temperatures on its surface range from A 450 °F to over 1,000 °F. To withstand this high temperature, the airplane was constructed of titanium alloy, instead of the traditional aluminum alloy. The supersonic transport Concorde was originally designed to cruise at Mach 2.2, but its cruise speed was reduced to Mach 2.0 because of structural problems that started to occur because of aerodynamic heating. If airplanes capable of hypersonic flight are going to be built in the future, one of the obstacles that will have to be overcome is the stress on the airplane’s structure caused by heat.

Helicopter Aerodynamics The helicopter, as we know it today, falls under the classification known as rotorcraft. Rotorcraft is also known as rotary wing aircraft, because instead of their wing being B fixed like it is on an airplane, the wing rotates. The rotating wing of a rotorcraft can be thought of as a lift producing device, like the wing of an airplane, or as a thrust producing Figure 5-76. Sound energy in subsonic and supersonic flight.

device, like the propeller on a piston engine.

shock waves, the velocity of the air is subsonic and Helicopter Structures and Airfoils the static pressure has increased.

The main parts that make up a helicopter are the cabin, E. The velocity has increased to the point that both shock landing gear, tail boom, power plant, transmission, main waves on the wing, top and bottom, have moved to rotor, and tail rotor. [Figure 5-81] the back of the wing and attached to the trailing edge.

Some airflow separation is still occurring.

Main Rotor Systems F. The forward velocity of the airfoil is greater than Mach In the fully articulated rotor system, the blades are attached 1, and a new shock wave has formed just forward of to the hub multiple times. The blades are hinged in a way the leading edge of the wing. If the wing has a sharp that allows them to move up and down and fore and aft, and leading edge, the shock wave will attach itself to the bearings provide for motion around the pitch change axis.

sharp edge.

Rotor systems using this type of arrangement typically have three or more blades. The hinge that allows the blades to move The airfoil shown in Figure 5-79 is not properly designed to handle supersonic airflow. The bow wave in front of the wing leading edge of view F would be attached to the leading Expansion Oblique Oblique wave edge, if the wing was a double wedge or biconvex design.

shock shock These two wing designs are shown in Figure 5-80.

Air fl ow Normal shock wave Supersonic air Subsonic air Subsonic air Figure 5-78. Supersonic airfoil with oblique shock waves and Figure 5-77. Normal shock wave. expansion waves.

5-49 up and down is called the flap hinge, and movement around this Airflow over the entire hinge is called flap. The hinge that allows the blades to move wing is subsonic fore and aft is called a drag or lag hinge. Movement around this hinge is called dragging, lead/lag, or hunting. These hinges and Mach number = 0.60 their associated movement are shown in Figure 5-82 . The main rotor head of a Eurocopter model 725 is shown in Figure 5-83 , View A with the drag hinge and pitch change rods visible.

Airflow over the wing The semi-rigid rotor system is used with a two-blade main reaches Mach 0.99 rotor. The blades are rigidly attached to the hub, with the hub and blades able to teeter like a seesaw. The teetering Mach number = 0.82 action allows the blades to flap, with one blade dropping (Critical Mach number) down while the other blade rises. The blades are able to View B change pitch independently of each other. Figure 5-84 Supersonic flow shows a Bell Jet Ranger helicopter in flight. This helicopter Normal shock uses a semi-rigid rotor system, which is evident because Subsonic of the way the rotor is tilted forward when the helicopter is in forward flight.

Mach number = 0.85 With a rigid rotor system, the blades are not hinged for View C movement up and down, or flapping, or for movement fore and aft, or drag. The blades are able to move around the pitch Supersonic flow change axis, with each blade being able to independently Normal shock change its blade angle. The rigid rotor system uses blades that are very strong and yet flexible. They are flexible enough Separation to bend when they need to, without the use of hinges or a teetering rotor, to compensate for the uneven lift that occurs Normal shock in forward flight. The Eurocopter model 135 uses a rigid Mach number = 0.88 rotor system. [Figure 5-85] View D Anti-Torque Systems Supersonic flow Any time a force is applied to make an object rotate; there will be equal force acting in the opposite direction.

Normal shock If the helicopter’s main rotor system rotates clockwise when viewed from the top, the helicopter will try to rotate counterclockwise. Earlier in this chapter, it was discovered that torque is what tries to make something rotate. For this reason, a helicopter uses what is called an anti-torque system Normal to counteract the force trying to make it rotate.

shock Mach number = 0.95 One method that is used on a helicopter to counteract torque View E is to place a spinning set of blades at the end of the tail boom.

Bow These blades are called a tail rotor or anti-torque rotor, and wave their purpose is to create a force, or thrust that acts in the opposite direction of the way the helicopter is trying to rotate.

The tail rotor force, in pounds, multiplied by the distance from the tail rotor to the main rotor, in feet, creates a torque in pound-feet that counteracts the main rotor torque.

Supersonic flow Mach number = 1.05 Figure 5-86 shows a three-bladed tail rotor on an Aerospatiale View F AS-315B helicopter. This tail rotor has open tipped blades that are variable pitch, and the helicopter’s anti-torque pedals Figure 5-79. Airflow with progressively greater Mach numbers.

that are positioned like rudder pedals on an airplane, control the amount of thrust they create. Some potential problems 5-50 with this tail rotor system are as follows: Expansion • The spinning blades are deadly if someone walks Oblique Oblique wave shock shock into them.

• When the helicopter is in forward flight and a vertical fin may be in use to counteract torque, the tail rotor Air fl ow robs engine power and creates drag.

An alternative to the tail rotor seen in Figure 5-86 is a type of anti-torque rotor known as a fenestron, or “fan-in-tail” design as seen in Figure 5-87 . The rotating blades present less of a hazard to personnel on the ground and they create less drag Double wedge in flight, because they are enclosed in a shroud.

A third method of counteracting the torque of the helicopter’s Oblique Oblique main rotor is a technique called the “no tail rotor” system, shock shock or NOTAR. This system uses a high volume of air at low pressure, which comes from a fan driven by the helicopter’s engine. The fan forces air into the tail boom, where a portion of it exits out of slots on the right side of the boom and, in conjunction with the main rotor downwash, creates a Expansion wave phenomenon called the “Coanda effect.” The air coming out of the slots on the right side of the boom causes a higher Biconvex velocity, and therefore lower pressure, on that side of the boom. The higher pressure on the left side of the boom creates Figure 5-80. Double wedge and biconvex supersonic wing design. the primary force that counteracts the torque of the main rotor.

Tail rotor Tail boom Main rotor Powerplant Cabin Transmission Landing gear Figure 5-81. Main components of a helicopter.

5-51 The remainder of the air travels back to a controllable rotating nozzle in the helicopter’s tail. The air exits the nozzle at a high velocity, and creates an additional force, or thrust, that helps counteracts the torque of the main rotor. A NOTAR system is shown in Figures 5-88 and 5-89 .

For helicopters with two main rotors, such as the Chinook that has a main rotor at each end, no anti-torque rotor is needed.

For this type of helicopter, the two main rotors turn in opposite directions, and each one cancels out the torque of the other.

Drag hinge Helicopter Axes of Flight Pitch change rod Helicopters, like airplanes, have a vertical, lateral, and longitudinal axis that passes through the helicopter’s center of gravity. Helicopters yaw around the vertical axis, pitch Figure 5-83. Eurocopter 725 main rotor head.

around the lateral axis, and rotate around the longitudinal axis. Figure 5-90 shows the three axes of a helicopter and how they relate to the helicopter’s movement. All three axes will intersect at the helicopter’s center of gravity, and the Semi-rigid main rotor helicopter pivots around this point. Notice in the figure that the vertical axis passes almost through the center of the main rotor, because the helicopter’s center of gravity needs to be very close to this point.

Control Around the Vertical Axis For a single main rotor helicopter, control around the vertical axis is handled by the anti-torque rotor, or tail rotor, or from the fan’s airflow on a NOTAR type helicopter. Like in an airplane, rotation around this axis is known as yaw. The pilot controls yaw by pushing on the anti-torque pedals located on Figure 5-84. Bell Jet Ranger with semi-rigid main rotor.

the cockpit floor, in the same way the airplane pilot controls yaw by pushing on the rudder pedals. To make the nose of Lead or lag Flap hinge Drag hinge Pitch Axis of rotation Flap Figure 5-82. Fully articulated main rotor head.

5-52 When the collective pitch control lever is raised, the blade angle of all the rotor blades increases uniformly and they create the lift that allows the helicopter to take off vertically.

The grip on the end of the collective pitch control is the throttle for the engine, which is rotated to increase engine power as the lever is raised. On many helicopters, the throttle automatically rotates and increases engine power as the collective lever is raised. The collective pitch lever may have adjustable friction built into it, so the pilot does not have to hold upward pressure on it during flight.

Figure 5-85. Eurocopter Model 135 rigid rotor system.

The cyclic pitch control lever, like the yoke of an airplane, can be pulled back or pushed forward, and can be moved left and right. When the cyclic pitch lever is pushed forward, the rotor the helicopter yaw to the right, the pilot pushes on the right blades create more lift as they pass through the back half of anti-torque pedal. When viewed from the top, if the helicopter their rotation and less lift as they pass through the front half.

tries to spin in a counterclockwise direction because of the The difference in lift is caused by changing the blade angle, torque of the main rotor, the pilot will also push on the right or pitch, of the rotor blades. The pitch change rods that were anti-torque pedal to counteract the main rotor torque. By seen earlier, in Figures 5-82 and 5-83 , are controlled by the using the anti-torque pedals, the pilot can intentionally make cyclic pitch lever and they are what change the pitch of the rotor the helicopter rotate in either direction around the vertical blades. The increased lift in the back either causes the main axis. The anti-torque pedals can be seen in Figure 5-91.

rotor to tilt forward, the nose of the helicopter to tilt downward, or both. The end result is the helicopter moves in the forward Some helicopters have a vertical stabilizer, such as those direction. If the cyclic pitch lever is pulled back, the rotor blade shown in Figures 5-90 and 5-92 . In forward flight, the vertical lift will be greater in the front and the helicopter will back up.

stabilizer creates a force that helps counteract the torque of the main rotor, thereby reducing the power needed to drive If the cyclic pitch lever is moved to the left or the right, the the anti-torque system located at the end of the tail boom.

helicopter will bank left or bank right. For the helicopter to bank to the right, the main rotor blades must create more lift Control Around the Longitudinal and Lateral Axes as they pass by the left side of the helicopter. Just the opposite Movement around the longitudinal and lateral axes is handled is true if the helicopter is banking to the left. By creating by the helicopter’s main rotor. In the cockpit, there are two levers that control the main rotor, known as the collective and cyclic pitch controls. The collective pitch lever is on the side of the pilot’s seat, and the cyclic pitch lever is at the front of the seat in the middle. [Figure 5-91] Figure 5-87. Fenestron on a Eurocopter Model 135.

more lift in the back than in the front, and more lift on the Figure 5-86. Aerospatiale helicopter tail rotor.

5-53 Vertical axis Lateral axis Longitudinal axis Figure 5-88. McDonnell Douglas 520 NOTAR.

Figure 5-90. Three axes of rotation for a helicopter.

to hover is affected by many things, including whether or not it is in ground effect, the density altitude of the air, the Low pressure side available power from the engine, and how heavily loaded it is.

For a helicopter to experience ground effect, it typically needs to be no higher off the ground than one half of its main rotor system diameter. If a helicopter has a main rotor diameter of 40 ft., it will be in ground effect up to an altitude of approximately 20 ft. Being close to the ground affects the velocity of the air through the rotor blades, causing the effective angle of High pressure side attack of the blades to increase and the lift to increase. So, if Rotating nozzle Air exit slots a helicopter is in ground effect, it can hover at a higher gross weight than it can when out of ground effect. On a windy day, the positive influence of ground effect is lessened, and at a Figure 5-89. Airflow for a NOTAR.

forward speed of 5 to 10 mph the positive influence becomes less. In Figure 5-93 , an Air Force CH-53 is seen in a hover, with left than on the right, the helicopter can be in forward flight all the rotor blades flapping up as a result of creating equal lift.

and banking to the right. In Figure 5-92 , an Agusta A-109 can be seen in forward flight and banking to the right. The Forward Flight rotor blade in the rear and the one on the left are both in an In the early days of helicopter development, the ability to upward raised position, meaning they have both experienced hover was mastered before there was success in attaining the condition called flap.

forward flight. The early attempts at forward flight resulted in the helicopter rolling over when it tried to depart from the Some helicopters use a horizontal stabilizer, similar to what hover and move in any direction. The cause of the rollover is seen on an airplane, to help provide additional stability is what we now refer to as dissymmetry of lift.

around the lateral axis. A horizontal stabilizer can be seen on the Agusta A-109 in Figure 5-92 .

When a helicopter is in a hover, all the rotor blades are experiencing the same velocity of airflow and the velocity Helicopters in Flight of the airflow seen by the rotor blades changes when the Hovering helicopter starts to move. For helicopters built in the United For a helicopter, hovering means that it is in flight at a constant States, the main rotor blades turn in a counterclockwise altitude, with no forward, aft, or sideways movement. In order direction when viewed from the top. Viewed from the top, as to hover, a helicopter must be producing enough lift in its the blades move around the right side of the helicopter, they main rotor blades to equal the weight of the aircraft. The are moving toward the nose; as they move around the left side engine of the helicopter must be producing enough power of the helicopter, they are moving toward the tail. When the to drive the main rotor, and also to drive whatever type of helicopter starts moving forward, the blade on the right side anti-torque system is being used. The ability of a helicopter is moving toward the relative wind, and the blade on the left 5-54 Cyclic pitch control Collective pitch control Anti-torque pedals Anti-torque pedals Figure 5-91. Helicopter cockpit controls.

side is moving away from the relative wind. This causes the of attack and an increase in lift. The end result is the lift on blade on the right side to create more lift and the blade on the the blades is equalized, and the tendency for the helicopter left side to create less lift. Figure 5-94 shows how this occurs. to roll never materializes.

In Figure 5-94 , blade number 2 would be called the advancing The semi-rigid and fully articulated rotor systems have blade, and blade number 1 would be called the retreating blade. The advancing blade is moving toward the relative wind, and therefore experiences a greater velocity of airflow.

The increased lift created by the blade on the right side will try to roll the helicopter to the left. If this condition is allowed to exist, it will ultimately lead to the helicopter crashing.

Blade Flapping To solve the problem of dissymmetry of lift, helicopter designers came up with a hinged design that allows the rotor blade to flap up when it experiences increased lift, and to flap down when it experiences decreased lift. When a rotor blade advances toward the front of the helicopter and experiences an increased velocity of airflow, the increase in lift causes the blade to flap up. This upward motion of the blade changes the direction of the relative wind in relation to the chord line of the blade, and causes the angle of attack to decrease.

Figure 5-92. Agusta A-109 banking to the right.

The decrease in the angle of attack decreases the lift on the blade. The retreating blade experiences a reduced velocity of airflow and reduced lift, and flaps down. By flapping flapping hinges that automatically allow the blades to move down, the retreating blade ends up with an increased angle 5-55 up or down with changes in lift. The rigid type of rotor system flight. As long as the helicopter maintains forward airspeed, has blades that are flexible enough to bend up or down with while decreasing altitude and the pilot lowers the blade changes in lift. angle on the blades with the collective pitch, the rotor blades will continue to rotate. The altitude of the helicopter, which Advancing Blade and Retreating Blade Problems equals potential energy, is given up in order to have enough energy, which will then be kinetic energy, to keep the rotor The blade advancing toward the relative wind sees the airflow blades turning. As the helicopter nears the ground, the cyclic at an ever increasing velocity as a helicopter flies forward at pitch control is used to slow the forward speed and to flare higher and higher speeds. Eventually, the velocity of the air the helicopter for landing. With the airspeed bled off, and over the rotor blade will reach sonic velocity, much like the the helicopter now close to the ground, the final step is to critical Mach number for the wing of an airplane. When this use the collective pitch control to cushion the landing. The happens, a shock wave will form and the air will separate airflow through the rotor blades in normal forward flight and from the rotor blade, resulting in a high-speed stall.

in an autorotation flight condition are shown in Figure 5-95 .

In Figure 5-96 , a Bell Jet Ranger is shown approaching the As the helicopters forward speed increases, the relative wind ground in the final stage of an autorotation.

over the retreating blade decreases, resulting in a loss of lift.

Weight-Shift Control, Flexible Wing Aircraft The loss of lift causes the blade to flap down and the effective Aerodynamics angle of attack to increase. At a high enough forward speed, A weight-shift control, flexible wing type aircraft consists of the angle of attack will increase to a point that the rotor blade a fabric-covered wing, often referred to as the sail, attached to stalls. The tip of the blade stalls first, and then progresses in a tubular structure that has wheels, seats, and an engine and toward the blade root.

propeller. The wing structure is also tubular, with the fabric covering creating the airfoil shape. The shape of the wing varies When approximately 25 percent of the rotor system is stalled, among the different models of weight-shift control aircraft due to the problems with the advancing and retreating blades, being produced, but a delta shaped wing is a very popular control of the helicopter will be lost. Conditions that will design. Within the weight-shift control aircraft community, lead to the rotor blades stalling include high forward speed, these aircraft are typically referred to as trikes. [Figure 5-97] heavy gross weight, turbulent air, high-density altitude, and steep or abrupt turns.

In Figure 5-97 , the trike’s mast is attached to the wing at the hang point on the keel of the wing with a hang point bolt and Autorotation safety cable. There is also a support tube, known as a king post, The engine on a helicopter drives the main rotor system by way extending up from the top of the wing, with cables running of a clutch and a transmission. The clutch allows the engine down and secured to the tubular wing structure. The cables to be running and the rotor system not to be turning, while the helicopter is on the ground, and it also allows the rotor system to disconnect from the engine while in flight, if the engine n t i o t a o r e d a fails. Having the rotor system disconnect from the engine in l B Direction the event of an engine failure is necessary if the helicopter is of relative to be capable of a flight condition called autorotation.

wind Autorotation is a flight condition where the main rotor blades are driven by the force of the relative wind passing through the blades, rather than by the engine. This flight condition is similar to an airplane gliding if its engine fails while in Direction n of fl ight i o t a t o r d e B l a (100 mph) Blade tip speed— 400 mph experiences 300 mph air fl ow (Tip speed – airspeed) 1 Blade experiences 500 mph air fl ow (Tip speed + airspeed) 2 Blade Figure 5-94. Dissymmetry of lift for rotor blades.

Figure 5-93. Air Force CH-53 in a hover.

5-56 running down from the king post as part of the upper rigging Normal forward fl ight under power are there to support the wing when the aircraft is on the ground, and to handle negative loads when in flight. The lines that run from the king post to the trailing edge of the wing are known as reflex cables. These cables maintain the shape of the wing Direction of air fl ow when it is in a stalled state by holding the trailing edge of the wing up which helps raise the nose during recovery from the stall. If the aircraft goes into an inadvertent stall, having the trailing edge of the wing in a slightly raised position helps raise the nose of the aircraft and get it out of the dive. The passenger seat is centered under the wing’s aerodynamic center, with the weight of the pilot being forward of this point and the weight of the engine and propeller being aft.

Forward fl ight in autorotation Unlike a traditional airplane, the trike does not have a rudder, elevator, or ailerons. Instead, it has a wing that can be pivoted forward or aft, and left or right. In Figure 5-98, the pilot’s hand is on a control bar that is connected to a pivot point just forward of where the wing attaches. There are cables attached to the ends of the bar that extend up to the wing’s leading and trailing edge, and to the left and right side of the cross bar. Running from the wing leading edge to trailing edge are support pieces known as battens. The battens fit into pockets, and they give the Direction of air fl ow wing its cambered shape. The names of some of the primary parts of the trike are shown in Figure 5-98 , and these parts Figure 5-95. Rotor blade airflow during normal flight and during will be referred to when the flight characteristics of the trike autorotation.

are described in the paragraphs that follow.

In order to fly the trike, engine power is applied to get the The wings of weight-shift control aircraft are designed in a aircraft moving. As the groundspeed of the aircraft reaches a way that allows them to change their shape when subjected point where flight is possible, the pilot pushes forward on the to an external force. This is possible because the frame control bar, which causes the wing to pivot where it attaches leading edges and the sail are flexible, which is why they are to the mast and the leading edge of the wing tilts up. When sometimes referred to as flexible wing aircraft. This produces the leading edge of the wing tilts up, the angle of attack and somewhat different aerodynamic effects when compared with the lift of the wing increase. With sufficient lift, the trike rotates and starts climbing. Pulling back on the bar reduces the angle of attack, and allows the aircraft to stop climbing and to fly straight and level. Once the trike is in level flight, airspeed can be increased or decreased by adding engine power or taking away engine power by use of the throttle.

Stability in flight along the longitudinal axis, which is a nose to tail measurement, for a typical airplane, is achieved by having the horizontal stabilizer and elevator generate a force that balances out the airplane’s nose heavy tendency.

It must create stability along the longitudinal axis in a different way because the trike does not have a horizontal stabilizer or Figure 5-96. Bell Jet Ranger in final stage of autorotation.

elevator. The trike has a sweptback delta wing, with the trailing edge of the wingtips located well aft of the aircraft center of gravity. Pressure acting on the tips of the delta wing creates the force that balances out the nose heavy tendency.

5-57 a normal fixed-wing aircraft. A traditional small airplane, like the wing. If the trike is properly balanced and there is no air a Cessna 172, turns or banks by using the ailerons, effectively turbulence, the aircraft will remain stable even if the pilot’s altering the camber of the wing and thereby generating hands are removed from the bar. The same as with any airplane, differential lift. By comparison, weight shift on a trike increasing engine power will make the aircraft climb and actually causes the wing to twist, which changes the angle of decreasing power will make it descend. The throttle is typically attack on the wing and causes the differential lift to exist that controlled with a foot pedal, like a gas pedal in an automobile.

banks the trike. The cross-bar, or wing spreader, of the wing frame is allowed to float slightly with respect to the keel, and A trike lands in a manner very similar to an airplane. When it this, along with some other geometric considerations allows is time to land, the pilot reduces engine power with the foot- the sail to “billow shift.” Billow shift can be demonstrated operated throttle; causing airspeed and wing lift to decrease.

on the ground by grabbing the trailing edge of one end of As the trike descends, the rate of descent can be controlled by the wing and lifting up on it. If this was done, the fabric on pushing forward or pulling back on the bar, and varying engine the other end of the wing would become slightly flatter and power. When the trike is almost to the point of touchdown, the tighter, and the wing’s angle of attack would increase. engine power will be reduced and the angle of attack of the wing will be increased, to cushion the descent and provide a If the pilot pushes the bar to the right, the wing pivots with smooth landing. If the aircraft is trying to land in a very strong the left wingtip dropping down and the right wingtip rising crosswind, the landing may not be so smooth. When landing in up, causing the aircraft to bank to the left. This motion is a cross wind, the pilot will land in a crab to maintain direction depicted in Figure 5-99 , showing a hang glider as an example. down the runway. Touchdown is done with the back wheels The shift in weight to the left increases the wing loading on first, then letting the front wheel down.

the left, and lessens it on the right. The increased loading on the left wing increases its washout and reduces its angle of A trike getting ready to touch down can be seen in attack and lift. The increased load on the left wing causes the Figure 5-101 . The control cables coming off the control bar left wing to billow, which causes the fabric to tighten on the can be seen, and the support mast and the cables on top of right wing and the angle of attack and lift to increase. The the wing, including the luff lines, can also be seen.

change in lift is what banks the aircraft to the left. Billow on Powered Parachute Aerodynamics the left wing is depicted in Figure 5-100.

A powered parachute has a carriage very similar to the Shifting weight to the right causes the aircraft to bank right. weight-shift control aircraft. Its wing, however, has no The weight of the trike and its occupants acts like a pendulum, support structure or rigidity and only takes on the shape of an and helps keep the aircraft stable in flight. Pushing or pulling airfoil when it is inflated by the blast of air from the propeller on the bar while in flight causes the weight hanging below and the forward speed of the aircraft. In Figure 5-102 , a the wing to shift its position relative to the wing, which is powered parachute is on its approach to land with the wing why the trike is referred to as a weight-shift aircraft.

fully inflated and rising up above the aircraft. Each colored section of the inflated wing is made up of cells that are open in Once the trike is in flight and flying straight and level, the the front to allow air to ram in, and closed in the back to keep pilot only needs to keep light pressure on the bar that controls the air trapped inside. In between all the cells there are holes that allow the air to flow from one cell to the next, in order to equalize the pressure within the inflated wing. The wing is attached to the carriage of the aircraft by a large number of nylon or Kevlar lines that run from the tips of the wing all the way to the center. The weight of the aircraft acting on these lines and their individual lengths cause the inflated wing to take its shape. The lines attach to the body of the aircraft at a location very close to where the center of gravity is located, and this attachment point is adjustable to account for balance changes with occupants of varying weights.

As in weight-shift control aircraft, the powered parachute does not have the traditional flight controls of a fixed-wing airplane. When the wing of the aircraft is inflated and the aircraft starts moving forward, the wing starts generating lift.

Figure 5-97. Weight-shift control aircraft in level flight.

Once the groundspeed is sufficient for the wing’s lift greater than the weight of the aircraft, the aircraft lifts off the ground.

5-58 Wing batten Crossbar Wing attach point Wing keel Nose strut Mast Control bar with cables attached to the wing Throttle Brakes Figure 5-98. Weight-shift control aircraft getting ready for flight.

Unlike an airplane, where the pilot has a lot of control over and descending is handled with engine power. Advancing when the airplane rotates by deciding when to pull back on the the throttle makes the aircraft climb, and retarding the yoke, the powered parachute will not take off until it reaches throttle makes it descend. The inflated wing creates a lot a specific airspeed. The powered parachute will typically lift of drag in flight, so reducing the engine power creates a off the ground at a speed somewhere between 28 and 30 mph, very controllable descent of the aircraft. The throttle, for and will have airspeed in flight of approximately 30 mph. controlling engine power, is typically located on the right- hand side of the pilot. [Figure 5-103] Once the powered parachute is in flight, control over climbing Turning of the powered parachute in flight is handled by foot-operated pedals, or steering bars, located at the front of the aircraft. These bars can be seen in Figure 5-103 . Each Direction of turn Aircraft banks to the left because of increased lift on the right wing l l s t o o r t l e f a f r t c r i A Pushing the bar to t f Billow the right shifts the e l W o t weight to the left e i g d h e t t s h i f Push out Figure 5-100. Weight shift to the left causing a left-hand turn.

Figure 5-99. Direction of turn based on weight shift.

5-59 foot-operated pedal controls a set of lines, usually made from nylon that runs up to the trailing edge of each wingtip.

When the right foot pedal is pushed, the line pulls down on the tailing edge of the 8 wingtip. As the trailing edge of the right wing drop downs, drag is increased on the right side and the aircraft turns right. When pressure is taken off the foot pedal, the drag in the entire airfoil equalizes and the aircraft resumes its straight-and-level flight.

To land a powered parachute, the first action the pilot takes is to reduce engine power and allow the aircraft to descend.

With the power reduced to idle, the aircraft will descend at a rate of approximately 5 to 10 fps. As the aircraft approaches the ground, the descent rate can be lessened by increasing the engine power. Just before touchdown, the pilot pushes on Figure 5-102. Powered parachute with the wing inflated.

both foot-operated pedals to drop the trailing edges on both sides of the wing. This action increases the drag on the wing uniformly, causing the wing to pivot aft, which raises the wing leading edge and increases the angle of attack and lift.

In Figure 5-104 , the pilot is pushing on both foot pedals and the left and right wing trailing edges are deflected downward.

The aircraft has just touched down and the wing is trailing behind the aircraft, caused by the high angle of attack and the additional drag on the wing. The increase in lift reduces the descent rate to almost nothing, and provides for a gentle landing. If the pilot pushes on the foot pedals too soon, the wing may pivot too far aft before touchdown resulting in an unacceptable descent rate. In that case, it might be a relatively hard landing.

Figure 5-101. Weight-shift control aircraft landing.

5-60 Figure 5-103. Two seat powered parachute.

Figure 5-104. Powered parachute wing trailing edge.

5-61 5-62

Next: Chapter 6 →

Chapter 6

Aircraft Weight & Balance

balanced condition might not be desirable. All factors that Introduction affect aircraft safety and efficiency, in terms of its weight and The weight of an aircraft and its balance are extremely balance, are discussed in detail in this chapter.

important for operating in a safe and efficient manner. When a manufacturer designs an aircraft and the Federal Aviation Requirements for Aircraft Weighing Administration (FAA) certifies it, the specifications identify Every aircraft type certificated by the FAA receives a weight the aircraft’s maximum weight and the limits within which and balance report as part of its required aircraft records it must balance. The weight and balance system commonly before leaving the factory for delivery to its new owner.

employed among aircraft consists of three equally important The weight and balance report identifies the empty weight elements: the weighing of the aircraft, the maintaining of of the aircraft and the location at which the aircraft balances, the weight and balance records, and the proper loading of known as the center of gravity (CG). The weight and balance the aircraft.

report must include an equipment list showing weights and moment arms of all required and optional items of equipment The maximum weight of an aircraft is based on the amount included in the certificated empty weight. If the manufacturer of lift the wings or rotors can provide under the operating chooses to do so, it can weigh every aircraft it produces and conditions for which the aircraft is designed. For example, issue the weight and balance report based on that weighing.

if a small general aviation (GA) airplane required a takeoff As an alternative, the manufacturer is permitted to weigh speed of 200 miles per hour (mph) to generate enough lift an agreed upon percentage of a particular model of aircraft to support its weight, that would not be safe. Taking off and produced, perhaps 10 to 20 percent, and apply the average landing at lower airspeeds is certainly safer than doing so to all the aircraft.

at higher speeds.

After the aircraft leaves the factory and is delivered to its Aircraft balance is also a significant factor in determining owner, the requirement for placing the aircraft on scales and if the aircraft is safe to operate. An aircraft that does not reweighing it varies depending on the type of aircraft and have good balance can exhibit poor maneuverability and how it is used. For a small, GA airplane being used privately, controllability, making it difficult or impossible to fly. This such as a Cessna 172, there is no FAA requirement that it be could result in an accident, causing damage to the aircraft and periodically reweighed; but after each annual, the mechanic injury to the people on board. Safety is the primary reason must ensure that the weight and balance data in the aircraft for concern about an aircraft’s weight and balance.

records is correct. Additionally, there is an FAA requirement that the airplane always have a current and accurate weight Another important reason for concern about weight and and balance report. If the weight and balance report for an balance is the efficiency of the aircraft. Improper loading aircraft is lost, the aircraft must be weighed and a new report reduces the efficiency of an aircraft from the standpoint must be created. When an aircraft has undergone extensive of ceiling, maneuverability, rate of climb, speed, and fuel repair, major alteration, or has new equipment installed, such consumption. If an airplane is loaded in such a way that it is as a radio or a global positioning system, a new weight and extremely nose heavy, higher than normal forces are exerted balance report must be created. The equipment installer may at the tail to keep the airplane in level flight. The higher than place the airplane on scales and weigh it after the installation, normal forces at the tail create additional drag, which requires which is an acceptable way of creating the new report. If additional engine power and therefore additional fuel flow the installer knows the exact weight and location of the new to maintain airspeed.

equipment, it is also possible to create a new report by doing a series of mathematical calculations.

The most efficient condition for an aircraft is to have the point where it balances fall close to, or exactly at, the aircraft’s Over time, almost all aircraft tend to gain weight. Examples center of lift. If this were the case, little or no flight control of how this can happen include an airplane being repainted force would be needed to keep the aircraft flying straight and without the old paint being removed and the accumulation of level. In terms of stability and safety, however, this perfectly 6-1 dirt, grease, and oil in parts of the aircraft that are not easily contained in a document known as a Type Certificate Data accessible for cleaning. When new equipment is installed, Sheet (TCDS). The Aircraft Specifications typically included and its weight and location are mathematically accounted the aircraft equipment list. For aircraft with a TCDS, the for, some miscellaneous weight might be overlooked, such equipment list is a separate document.

as wire and hardware. For this reason, even if the FAA does not require it, it is a good practice to periodically place an Arm aircraft on scales and confirm its actual empty weight and The arm is the horizontal distance from the datum to any point empty weight center of gravity (EWCG).

within the aircraft. The arm’s distance is always measured in inches, and it is preceded by the algebraic sign for positive (+) Some aircraft are required to be weighed and have their or negative (−), except for a location which might be exactly CG calculated on a periodic basis, typically every 3 years. on the datum. The positive sign indicates an item is located Examples of aircraft that fall under this requirement are: aft of the datum, and the negative sign indicates an item is located forward of the datum. If the manufacturer chooses 1. Air taxi and charter twin-engine airplanes operating a datum that is at the most forward location on an aircraft, under Title 14 of the Code of Federal Regulations all the arms will be positive numbers. Location of the datum (14 CFR) part 135, section 135.185(a).

at any other point on the aircraft results in some arms being 2. Airplanes with a seating capacity of 20 or more positive numbers, or aft of the datum, and some arms being passengers or a maximum payload of 6,000 pounds negative numbers, or forward of the datum. Figure 6-1 shows or more, as identified in 14 CFR part 125, section an aircraft where the datum is the leading edge of the wing.

125.91(b).

For this aircraft, any item (fuel, seat, radio, etc.) located forward of the wing leading edge has a negative arm, and Weight & Balance Terminology any item located aft of the wing leading edge has a positive arm. If an item is located exactly at the wing leading edge, its Datum arm would be zero, and mathematically it would not matter The datum is an imaginary vertical plane from which all whether its arm was positive or negative.

horizontal measurements are taken for balance purposes, with the aircraft in level flight attitude. If the datum is viewed on a The arm of each item is usually included in parentheses drawing of an aircraft, it would appear as a vertical line that is immediately after the item’s name or weight in the Aircraft perpendicular (90 degrees) to the aircraft’s longitudinal axis.

Specifications, TCDS, or equipment list for the aircraft. For For each aircraft make and model, the location of all items example, in a TCDS, the fuel quantity might be identified is identified in reference to the datum. For example, the fuel as 98 gallons (gal) (+93.6) and the forward baggage limit in a tank might be 60 inches (60") behind the datum, and a as 100 pounds (lb) (–22.5). These numbers indicate that the radio on the flight deck might be 90" forward of the datum.

fuel is located 93.6" aft of the datum and the nose baggage is located 22.6" forward of the datum. If the arm for a piece of The datum is determined by the manufacturer; it is often the equipment is not known, its exact location must be accurately leading edge of the wing or some specific distance from an measured. When the arm for a piece of equipment is being easily identified location. Typical locations for the datum are determined, the measurement is taken from the datum to the the aircraft nose, the leading edge of the wing, the helicopter’s piece of equipment’s own CG.

mast, or a specified distance from a known point. However, most modern helicopters, like airplanes, have the datum Moment located at the nose of the aircraft or a specified distance To understand balance, it is necessary to have a working ahead of it. Figure 6-1 shows an aircraft with the leading knowledge of the principle of moments. For those unfamiliar edge of the wing being the datum. The distance from this with weight and balance terms, the word moment is the datum is measured in inches and can be either positive or product of a force or weight times a distance. The distance negative depending upon where the equipment is located in used in calculating a moment is referred to as the arm or relation to the datum.

moment arm and is usually expressed in inches. To calculate a moment, a force (or weight) and a distance must be known.

The location of the datum is identified in the Aircraft The weight is multiplied by the distance from the datum and Specifications or Type Certificate Data Sheet (TCDS).

the result is the moment, which is expressed in inch-pounds Aircraft certified prior to 1958 fell under the Civil (in-lb), a point through which the force acts. For the purpose Aeronautics Administration and had their weight and balance of illustration, compare an aircraft to a seesaw. Like the information contained in a document known as Aircraft seesaw, for an aircraft to be in balance, or equilibrium, the Specifications. Aircraft certified since 1958 fall under the FAA and have their weight and balance information 6-2 weights on either side of the fulcrum are not equal, and the Datum (leading edge of wing) distances from each weight to the fulcrum are not equal, the Positive arm product of the weights and arms (moments) are equal, and Negative arm that is what produces a balanced condition. Therefore, the lever would be balanced much like two persons sitting on a seesaw who are differing weights and located at different distances from the fulcrum.

Maximum Weight The maximum weight is the maximum authorized weight Center of gravity of the aircraft and its contents, and is indicated in the Aircraft Specifications or TCDS. For many aircraft, there Figure 6-1. Datum location and its effect on positive and negative are variations to the maximum allowable weight depending arms.

on the purpose and conditions under which the aircraft is to be flown. For example, a certain aircraft may be allowed a sum of the moments on each side of the balance point must be maximum gross weight of 2,750 lb when flown in the normal equal. Therefore, the same weight that is different distances category, but when flown in the utility category, which (in inches) from the datum have greater moments.

allows for limited aerobatics, the same aircraft’s maximum allowable gross weight might only be 2,175 lb. There are A 5 lb radio located 80" from the datum would have a moment other variations when dealing with the concept of maximum of 400 in-lb (5 lb × 80"). A 10-pound radio located 12" from weight, as follows: the datum would have a moment of 120 in-lb. Whether the • Maximum Ramp Weight—the heaviest weight to moment is preceded by a positive (+) or negative (−) sign which an aircraft can be loaded while it is sitting on the depends on its location in relation to the datum. Figure 6-2 ground. This is sometimes referred to as the maximum shows where the moment ends up being a positive number taxi weight.

because the weight and arm are both positive.

The algebraic sign of the moment, based on the datum • Maximum Takeoff Weight—the heaviest weight an location and whether weight is being installed or removed aircraft can be when it starts the takeoff roll. The [Figure 6-3] , would be as follows: difference between this weight and the maximum ramp weight would equal the weight of the fuel that • Weight being added aft of the datum produces a would be consumed prior to takeoff.

positive moment (+weight, +arm).

• Maximum Landing Weight—the heaviest weight an • Weight being added forward of the datum produces a aircraft can be when it lands. For large, wide body negative moment (+weight, −arm).

commercial airplanes, it can be 100,000 lb less than • Weight being removed aft of the datum produces a maximum takeoff weight, or even more.

negative moment (−weight, +arm).

• Maximum Zero Fuel Weight—the heaviest weight an • Weight being removed forward of the datum produces aircraft can be loaded to without having any usable a positive moment (−weight, −arm).

fuel in the fuel tanks. Any weight loaded above this value must be in the form of fuel.

When dealing with positive and negative numbers, remember that the product of like signs produces a positive answer, Datum 40 " forward and the product of unlike signs produces a negative answer.

of the firewall Radio (5 lb) Arm = 80" Center of Gravity (CG) The CG is the point at which all the weight of the aircraft is concentrated and balanced; therefore, the aircraft can be supported at that point (the CG). The magnitude of the nose-heavy and tail-heavy moments are exactly equal. It is the balance point for the aircraft and, if suspended from this point, there would be no tendency to rotate in a noseup or Center of gravity Moment = Weight (arm) nosedown attitude.

= 5 lb (80") = 400 in-lb Figure 6-4 shows a lever with the pivot point (called a Figure 6-2. Moment of a radio located aft of the datum.

fulcrum) located at the CG for the lever. Even though the 6-3 Empty Weight Force Force The empty weight of an aircraft includes all operating Distance = 70" Distance = 90" equipment that has a fixed location and is actually installed in the aircraft. It includes the weight of the airframe, powerplant, required equipment, optional or special equipment, fixed ballast, hydraulic fluid, and residual fuel and oil. Residual fuel Moment = 700 lb (90") Moment = 900 lb (70") and oil are the fluids that do not normally drain out because = 63,000 in-lb = 63,000 in-lb they are trapped in the fuel lines, oil lines, and tanks. They must Fulcrum and CG be included in the aircraft’s empty weight. For most aircraft certified after 1978, the full capacity of the engine oil system Figure 6-4. Center of gravity and a first class lever.

is also included in the empty weight. Information regarding residual fluids in aircraft systems that must be included in the empty weight, and whether or not full oil is included, will be Useful Load indicated in the Aircraft Specifications or TCDS.

To determine the useful load of an aircraft, subtract the empty weight from the maximum allowable gross weight.

Other terms that are used when describing empty weight For aircraft certificated in both normal and utility categories, include basic empty weight, licensed empty weight, and there may be two useful loads listed in the aircraft weight and standard empty weight. The term “basic empty weight” balance records. An aircraft with an empty weight of 3,100 lb applies when the full capacity of the engine oil system is may have a useful load of 850 lb, if the normal category included in the value. The term “licensed empty weight” maximum weight is listed as 3,950 lb. When the aircraft is applies when only the weight of residual oil is included in operated in the utility category, the maximum gross weight the value, so it generally involves only aircraft certified prior may be reduced to 3,700 lb, with a corresponding decrease in to 1978. Standard empty weight would be a value supplied the useful load to 600 lb. Some aircraft have the same useful by the aircraft manufacturer, and it would not include any load regardless of the category in which they are certificated.

optional equipment that might be installed in an aircraft. For most people working in the aviation maintenance field, the The useful load consists of fuel, any other fluids that are not basic empty weight of the aircraft is the most important one.

part of empty weight, passengers, baggage, pilot, copilot, and crewmembers. Whether the weight of engine oil is considered Empty Weight Center of Gravity (EWCG) part of the useful load depends on when the aircraft was The EWCG for an aircraft is the point at which it balances certificated and can be determined by looking at the Aircraft when it is in an empty weight condition. The concepts of Specifications or TCDS. The payload of an aircraft is like the empty weight and CG were discussed earlier in this chapter, useful load, except it does not include fuel.

and now they are being combined into a single concept.

A reduction in the weight of an item, where possible, may be One of the most important reasons for weighing an aircraft necessary to remain within the maximum weight allowed for is to determine its EWCG. All other weight and balance the category in which an aircraft is operating. Determining calculations, including loading the aircraft for flight, the distribution of these weights is called a weight check.

performing an equipment change calculation, and performing an adverse condition check, begin with knowing the empty Minimum Fuel weight and EWCG. This crucial information is part of what Many modern aircraft have multiple rows of seats and often is contained in the aircraft weight and balance report.

more than one baggage compartment. The weight and balance extreme conditions represent the maximum forward and rearward CG position for the aircraft. An aircraft has certain Weight Arm Moment Rotation fixed points, fore and aft, beyond which the CG should not be permitted at any time during flight. A check should be + + + Noseup made to ensure that the CG will not shift out of limits when + – – Nosedown crew, passengers, cargo, and expendable weights are added or removed. If the limits are exceeded and the aircraft is – + – Nosedown flown in this condition, it may lead to insufficient stability, – – + Noseup with resulting difficulty in controlling the aircraft. After any repair or alteration that changes the weight and balance, the Figure 6-3. Relationship between the algebraic signs of weight, Airframe and Powerplant (A&P) mechanic or repairman arms, and moments.

6-4 must ensure that no legal condition of loading can move the tare weight are wheel chocks placed on the scales and ground CG outside of its allowable limits. To determine this, the locks left in place on retractable landing gear.

mechanic will deliberately attempt to calculate the aircraft loading in such a manner as to place the CG outside the Procedures for Weighing an Aircraft limits of the aircraft. This is called an adverse-loading check.

General Concepts The most important reason for weighing an aircraft is to find For example, in a forward adverse-loaded CG check, all out its empty weight (basic empty weight) and to find out useful load in front of the forward CG limit is loaded, and where it balances in the empty weight condition. When an all useful load behind this limit is left empty. An exception aircraft is to be flown, the pilot-in-command must know what to leaving it empty is the fuel tank. If the fuel tank is located the loaded weight of the aircraft is and where its loaded CG behind the forward CG limit, it cannot be left empty because is. For the loaded weight and CG to be calculated, the pilot the aircraft cannot fly without fuel. In this case, an amount or dispatcher handling the flight must first know the empty of fuel is accounted for, which is known as minimum fuel.

weight and EWCG.

Minimum fuel is the amount needed for 30 minutes of flight at cruise power.

Earlier in this chapter it was identified that the CG for an object is the point about which the nose heavy and tail heavy For weight and balance purposes, the minimum fuel is no moments are equal. One method that could be used to find more than the quantity needed for one half hour of operation this point would involve lifting an object off the ground twice, at rated maximum continuous power. This is ⁄ 12 gallon first suspending it from a point near the front, and on the for each maximum except takeoff (METO) horsepower second lift suspending it from a point near the back. With each (hp). Because aviation gasoline (Avgas) weighs 6 pounds lift, a perpendicular line (90 degrees) would be drawn from per gallon (lb/gal), determine the number of pounds of the suspension point to the ground. The two perpendicular the minimum fuel by dividing the METO hp by 2. For lines would intersect somewhere in the object, and the point instance, an aircraft having a METO hp of 200 hp will have of intersection would be the CG. This concept is shown in a minimum fuel of 16.65 gallons or 99.99 pounds. An even Figure 6-5 , where an airplane is suspended from two different simpler way is to take the METO hp divided by 2, which is points. The perpendicular line from the first suspension point 100 pounds. Both methods in determining minimum fuel is shown in red, and the new suspension point line is shown are valued and result in essentially the same answer. In the as a blue plumb bob. Where the red and blue lines intersect latter computation, a piston engine in cruise flight burns 1 is the CG. If an airplane were suspended from two points, lb of fuel per hour for each hp, or ⁄ 2 lb for 30 minutes, hence one at the nose and one at the tail, the perpendicular drop dividing the METO by 2.

lines would intersect at the CG. Suspending an airplane from the ceiling by two hooks, however, is clearly not realistic.

For example, if a forward adverse-loaded CG check was Even if it could be done, determining where in the airplane performed on a piston engine aircraft, with the engine having the lines intersect would be difficult.

a METO hp of 200, the minimum fuel would be 100 lb (200 METO hp ÷ 2).

A more realistic way to find the CG for an object, especially an airplane, is to place it on a minimum of two scales and For turbine engine-powered aircraft, minimum fuel is not calculate the moment value for each scale reading. In based on engine hp. If an adverse-loaded CG check is being Figure 6-6, there is a plank that is 200" long, with the left performed on a turbine engine-powered aircraft, the aircraft end being the datum (zero arm), and 6 weights placed at manufacturer would need to supply information on minimum various locations along the length of the plank. The purpose fuel.

of Figure 6-6 is to show how the CG can be calculated when the arms and weights for an object are known.

Tare Weight When aircraft are placed on scales and weighed, it is To calculate the CG for the object in Figure 6-6, the moments sometimes necessary to use support equipment to aid in for all the weights need to be calculated and then summed, the weighing process. For example, to weigh a tail dragger and the weights need to be summed. In the four-column airplane, it is necessary to raise the tail to get the airplane table in Figure 6-7, the item, weight, and arm are listed in level. To level the airplane, a jack might be placed on the the first three columns, with the information coming from scale and used to raise the tail. Unfortunately, the scale is now Figure 6-6. The moment value in the fourth column is the absorbing the weight of the jack in addition to the weight of product of the weight and arm. The weight and moment the airplane. This extra weight is known as tare weight and must be subtracted from the scale reading. Other examples of 6-5 columns are summed, with the CG being equal to the total moment divided by the total weight. The arm column is not Second suspension, with blue line dropping summed. The number appearing at the bottom of that column Suspended from this point perpendicular to the first, with red line dropping is the CG. The calculation is shown in Figure 6-7.

ground perpendicular to the ground For the calculation in Figure 6-7, the total moment is 52,900 in-lb, and the total weight is 495 lb. The CG is calculated as follows: CG = Total Moment ÷ Total Weight = 52,900 in-lb ÷ 495 lb = 106.9" (106.87 rounded to tenths) Center of gravity An interesting characteristic exists for the problem in Figure 6-6 and the table showing the CG calculation. If the Figure 6-5. Center of gravity determined by two suspension points.

datum (zero arm) for the object was in the middle of the 200" long plank, with 100" of negative arm to the left and 100" of includes all the pertinent specifications for the aircraft, and positive arm to the right, the solution would show the CG to at each annual or 100-hour inspection, it is the responsibility be in the same location. The arm for the CG would not be the of the inspecting mechanic or repairman to ensure that the same number, but its physical location would be the same.

aircraft adheres to them.

Figures 6-8 and 6-9 show the new calculation.

Manufacturer-Furnished Information When an aircraft is initially certificated, its empty weight CG = Total Moment ÷ Total Weight and EWCG are determined and recorded in the weight and = 3,400 in-lb ÷ 495 lb balance record, such as the one in Figure 6-12. An equipment = 6.9" (6.87 rounded to tenths) list is furnished with the aircraft that specifies all the required equipment and all equipment approved for installation in the In Figure 6-8, the CG is 6.9" to the right of the plank’s center.

aircraft. The weight and arm of each item is included on the Even though the arm is not the same number, in Figure 6-6 the CG is also 6.9" to the right of center (CG location of 106.9 125 lb 100 lb with the center being 100). Because both problems are the 90 lb 80 lb 50 lb 50 lb same in these two figures, except for the datum location, the CG must be the same.

0" 30" 60" 95" 200" 125" 145" 170" The definition for CG states that it is the point about which CG 106.9" all the moments are equal. We can prove that the CG for the object in Figure 6-8 is correct by showing that the total Figure 6-6. Center of gravity for weights on a plank with datum moments on either side of this point are equal. Using 6.87 as at one end.

the CG location for slightly greater accuracy, instead of the rounded off 6.9 number, the moments to the left of the CG are Weight Arm Moment shown in Figure 6-10. The moments to the right of the CG, × = Item (lb) (inches) (in-lb) shown in Figure 6-8, would be as indicated in Figure 6-11.

50 +30 1,500 50 pound weight Disregarding the slightly different decimal value, the moment in both previous calculations is 10,651 in-lb. Showing that 125 +60 7,500 125 pound weight the moments are equal is a good way of proving that the CG 80 +95 7,600 80 pound weight has been properly calculated.

50 +125 6,250 50 pound weight Weight and Balance Data 90 +145 13,050 90 pound weight Before an aircraft can be properly weighed and its EWCG computed, certain information must be known. This 100 +170 17,000 100 pound weight information is furnished by the FAA to anyone for every 495 +106.9 52,900 Total certificated aircraft in the TCDS or Aircraft Specifications.

When the design of an aircraft is approved by the FAA, an Figure 6-7. Center of gravity calculation for weights on a plank Approved Type Certificate and TCDS are issued. The TCDS with datum at one end.

6-6 list, and all equipment installed when the aircraft left the Weight Arm Moment × = Item (lb) (inches) (in-lb) factory is checked. When an aircraft mechanic or repairman adds or removes any item on the equipment list, they must 50 –70 –3,500 50 pound weight change the weight and balance record to indicate the new 125 –40 –5,000 125 pound weight empty weight and EWCG, and the equipment list is revised to show what is installed.

80 –5 –400 80 pound weight 50 +25 1,250 50 pound weight Figure 6-13 is an excerpt from a comprehensive equipment 90 +45 4,050 90 pound weight list that includes all the items of equipment approved for this model of aircraft. The Pilot’s Operating Handbook (POH) or 100 +70 7,000 100 pound weight Airplane Flight Manual (AFM) for each individual aircraft 495 +6.9 3,400 Total includes an aircraft specific equipment list of the items from this master list. When any item is added to or removed Figure 6-9. Center of gravity calculation for weights on a plank from the aircraft, its weight and arm are determined in the with datum in the middle.

equipment list and used to update the weight and balance record. The POH/AFM also contains CG moment envelopes Weight Arm Moment and loading graphs.

× = Item (lb) (inches) (in-lb) 50 76.87 3,843.50 50 pound weight Figures 6-14 through 6-16 shows a TCDS for a Piper twin- engine airplane known as the Seneca (PA-34-200). The 125 46.87 5,858.75 125 pound weight main headings for the information contained in a TCDS 80 11.87 949.60 80 pound weight are included, but much of the information contained under these headings has been removed if it did not directly pertain 255 135.61 10,651.85 Total to weight and balance. Information on only one model of Figure 6-10. Moments to the left of the center of gravity.

Seneca is shown, because to show all the different models would make the document excessively long. The portion of 10. Amount of oil in empty weight the TCDS that has the most direct application to weight and balance is highlighted in yellow.

11. Amount of fuel in empty weight Some of the important weight and balance information found Weight and Balance Equipment in a TCDS is as follows: Scales 1. Engine Weighing GA aircraft, helicopters, turboprops, corporate 2. CG range jets, UAV/UAS, or transport category airliners can be accomplished in two ways: top of jack load cells and platform 3. Maximum weight scales. Equipment selection is dependent on the operator's 4. Number of seats needs and or equipment currently on hand, as well as the 5. Baggage capacity airframe manufacturer's recommendations. Top of jack load cells, as the name implies, can be used on top of the current 6. Fuel capacity wing jacks or can be used under axle for larger jets. Platforms 7. Oil capacity are very useful for small shops that do not have jacks for every type of aircraft.

8. Datum information 9. Leveling means Both types of scales feature new technologies using wireless Weight Arm Moment 125 lb Item × = 100 lb (lb) (inches) (in-lb) 90 lb 80 lb 50 lb 50 lb 50 18.13 906.50 50 pound weight 90 38.13 3,431.70 90 pound weight – 100" – 70" – 40" – 5" 100" 0" 25" 45" 70" 100 63.13 6,313.00 100 pound weight CG 6.9" 240 119.39 10,651.25 Total Figure 6-8. Center of gravity for weights on a plank with datum in the middle.

Figure 6-11. Moments to the right of the center of gravity.

6-7 Weight and Balance Data Aircraft Serial #: 18259080 FAA Registration #: N42565 Date: 04-22-2005 × = Item Weight (lb) CG Arm (in) Moment (in-lb) Standard empty weight 1,876 36.1 67,798.6 Optional equipment 1.2 13.9 16.7 Special installation 6.2 41.5 257.3 Paint – – – Unusable fuel 30.0 46.0 1,380 Basic empty weight 1,913.4 69,452.6 Figure 6-12. Typical weight and balance data for 14 CFR part 23 airplane.

operations with computer-based indication and cable-based on platform scales, the only way to level the aircraft is to wired digital indication. Mechanical or analog meter scales deflate tires and landing gear struts accordingly. This type of have mostly been replaced with the new wireless systems and scale is easy to transport and can be powered by household or digital indicators. These systems and indicators are very current or by a battery contained in the display unit.

accurate and easy to use, making the weighing job faster to accomplish and providing higher quality in readings. The display unit for the standard wired platform scales is very easy to use. [Figure 6-19] Turn on the power and the unit Platforms are available in many weight ranges and sizes. runs through the software and displays the scales in a total These systems either use ramps or the aircraft can be jacked mode. Pressing on the ZERO KEY (blue key not the number and lowered onto the platforms during regular maintenance. key) will ZERO the channels. Once completed, the unit will Platforms are easy to use and are a choice for many shops read -0- and the scale is ready to use. Select the channels by that do not have jacks for the many types of aircraft to be number and pressing the PRINT/SELECT KEY. All channels serviced. The limiting factors for platforms are the weight can be returned to TOTAL MODE by entering the number 4 range and the tire size, some aircraft have large tires and the TOTAL followed by the PRINT/SELECT KEY . If all three platform may be too small for the specific aircraft tire. It is scale switches are turned on at the same time, the total weight important to always use the right size scale and platform for of the airplane is displayed.

the aircraft type and weighing job required.

The second type of aircraft scale is a top of jack, cell-based The platform scale sits on the hangar floor in a level scale, where each jack point receives a cell-based transducer condition. Ramps and a tug are used to position the airplane on the top of the jack. It is very easy to use and level the tire on top of the platform and centered. Built into the aircraft during the weighing operation. The system is easy platform is an electronic load cell(s) that sense the weight to transport, light weight, and simple to set up. The operator being applied to it, which generates a corresponding electrical must have a jack capable of receiving and mounting the cell.

signal. Inside the load cell is an electronic strain gauge that Cells come in many weight ranges and are dependent on the measures a proportional change in electrical resistance as weight required per point to accomplish the weighing and the weight being applied to it increases. An electrical cable receiving the actual jack point type.

or wireless signal runs from the platform scale to a display unit, computer, or tablet, which interprets the resistance The top of the load cell has a concave shape that matches up change of the load cell and equates it to a specific number of with the jack pad on the aircraft, with the load cell absorbing pounds. A digital readout on the display shows the weight. In all the weight of the aircraft at each jacking point. Each load Figure 6-17, a small Piper is being weighed using wireless cell either has an electrical cable attached to it or is wireless, platform scales that incorporate electronic load cells. which connects to the display unit or computer read out that shows the weight transmitted to each load cell. An important In Figure 6-18, a Cessna 182 airplane is being weighed with advantage of weighing an aircraft this way is that it allows portable electronic platform scales. If an aircraft is weighed the technician to level the aircraft easily. When an aircraft 6-8 Comprehensive Equipment List This is a comprehensive list of all Cessna equipment that is available for the Model 182S airplane. It should not be confused with the airplane-specific equipment list. An airplane-specific list is provided with each individual airplane at delivery and is typically inserted at the rear of this Pilot’s Operating Handbook. The following comprehensive equipment list and the airplane-specific list have a similar order of listing.

The comprehensive equipment list provides the following information in column form: In the Item No column, each item is assigned a coded number. The first two digits of the code represent the assignment of item within the ATA iSpec 2200 breakdown (Chapter 11 for Placards, Chapter 21 for Air Conditioning, Chapter 77 for Engine Indicating, etc.). These assignments also correspond to the Maintenance Manual chapter breakdown for the airplane. After the first two digits (and hyphen), items receive a unique sequence number (01, 02, 03, etc...). After the sequence number (and hyphen), a suffix letter is assigned to identify equipment as a required item, a standard item or an optional item. Suffix letters are as follows: –R = required items or equipment for FAA certification –S = standard equipment items –O = optional equipment items replacing required or standard items –A = optional equipment items which are in addition to required or standard items In the Equipment List Description column, each item is assigned a descriptive name to help identify its function.

In the Ref Drawing column, a drawing number is provided which corresponds to the item.

Note If additional equipment is to be installed, it must be done in accordance with the reference drawing, service bulletin or a separate FAA approval.

In the Wt Lbs and Arm Ins columns, information is provided on the weight (in pounds) and arm (in inches) of the equipment item.

Notes Unless otherwise indicated, true values (not net change values) for the weight and arm are shown. Positive arms are distances aft of the airplane datum; negative arms are distances forward of the datum.

Asterisks (*) in the weight and arm column indicate complete assembly installations. Some major components of the assembly are listed on the lines immediately following. The sum of these major components does not necessarily equal the complete assembly installation.

Figure 6-13. Excerpt from a typical comprehensive equipment list.

A7SO 2 of 17 DEPARTMENT OF TRANSPORTATION Propeller and Propeller Limits Right Engine FEDERAL AVIATION ADMINISTRATION (continued) 1 Hartzell, Hub Model HC-C2YK-2 ( ) LE, Blade Model JC7666A-0; 1 Hartzell, Hub Model HC-C2YK-2 ( ) LEU, Blade Model JC7666A-0; A7SO 1 Hartzell, Hub Model HC-C2YK-2 ( ) LEF, Blade Model FJC7666A-0; Revision 19 1 Hartzell, Hub Model HC-C2YK-2 ( ) LEFU, Blade Model FJC7666A-0; Piper Aircraft, Inc 1 Hartzell, Hub Model HC-C2YK-2CLG (F), Blade Model (F) JC7666A PA-34-200 PA-34-200T (This model includes the Hartzell damper); or PA-34-220T 1 Hartzell, Hub Model HC-C2YK-2CLGU (F), Blade Model (F) JC7666A (This model includes the Hartzell damper).

May 2, 2013 Note: HC-( )2YK-( ) may be substituted by HC-( )2YR-( ) per Hartzell Service Advisory 61.

TYPE CERTIFICATE DATA SHEET NO. A7SO Pitch setting: High 79 ° to 81 ° , Low 13.5 ° at 30" station.

Diameter: Not over 76", not under 74".

This data sheet which is a part of type certificate No. A7SO, prescribes conditions and limitations under which the product No further reduction permitted.

for which the type certificate was issued meets the airworthiness requirements of the Federal Aviation Regulations.

Spinner: Piper P/N 96388 Spinner Assembly and P/N 96836 Cap Assembly, or Type Certificate Holder Piper Aircraft, Inc.

P/N 78359-0 Spinner Assembly and P/N 96836-2 Cap Assembly (See NOTE 4) A7SO 2926 Piper Drive Vero Beach, Florida 32960 Revision 19 Governor Assembly: 1 Hartzell hydraulic governor, Model F-6-18AL (Right); Type Certificate Holder Record The New Piper Aircraft, Inc transferred TC A7SO to Piper Aircraft, Inc on August Piper Aircraft, Inc 1 Hartzell hydraulic governor, Model F-6-18A (Left).

7, 2006 PA-34-200 Avoid continuous operation between 2200 and 2400 r.p.m. unless aircraft is I. - Model PA-34-200 (Seneca), 7 PCLM (Normal Category), Approved 7 May 1971.

PA-34-200T equipped with Hartzell propellers which incorporates Hartzell damper on both left and right engine as noted above.

Engines S/N 34-E4, 34-7250001 through 34-7250214: PA-34-220T 1 Lycoming LIO-360-C1E6 with fuel injector, Airspeed Limits V (Never exceed) 217 m.p.h. (188 knots) Lycoming P/N LW-10409 or LW-12586 (right side); and NE V (Maximum structural cruise) 190 m.p.h (165 knots) 1 Lycoming IO-360-C1E6 with fuel injector, NO May 2, 2013 V (Maneuvering, 4200 lb.) 146 m.p.h. (127 knots) Lycoming P/N LW-10409 or LW 12586 (left side). A V (Maneuvering, 4000 lb.) 146 m.p.h. (127 knots) A V (Maneuvering, 2743 lb.) 133 m.p.h (115 knots) S/N 34-7250215 through 34-7450220: A V (Flaps extended) 125 m.p.h (109 knots) 1 Lycoming LIO-360-C1E6 with fuel injector, FE V (Landing gear operating) Lycoming P/N LW-12586 (right side); and LO Extension 150 m.p.h. (130 knots) 1 Lycoming IO-360-C1E6 with fuel injector, Retract 125 m.p.h. (109 knots) Lycoming P/N LW-12586 (left side).

V (Landing gear extended) 150 m.p.h (130 knots) LE V (Minimum control speed) 80 m.p.h. ( 69 knots) Fuel 100/130 minimum grade aviation gasoline MC itations under which the product eral Aviation Regulations.

C.G. Range (Gear Extended) S/N 34-E4, 34-7250001 through 34-7250214 (See NOTE 3): Engine Limits For all operations, 2700 r.p.m. (200 hp) (+86.4) to (+94.6) at 4000 lb.

(+82.0) to (+94.6) at 3400 lb.

Propeller and Propeller Limits Left Engine (+80.7) to (+94.6) at 2780 lb.

1 Hartzell, Hub Model HC-C2YK-2 ( ) E, Blade Model C7666A-0; 1 Hartzell, Hub Model HC-C2YK-2 ( ) EU, Blade Model C7666A-0; S/N 34-7250215 through 34-7450220: 1 Hartzell, Hub Model HC-C2YK-2 ( ) EF, Blade Model FC7666A-0; (+87.9) to (+94.6) at 4200 lb.

1 Hartzell, Hub Model HC-C2YK-2 ( ) EFU, Blade Model FC7666A-0; (+82.0) to (+94.6) at 3400 lb.

1 Hartzell, Hub Model HC-C2YK-2CG (F), Blade Model (F) C7666A (+80.7) to (+94.6) at 2780 lb.

(This model includes the Hartzell damper); or Straight line variation between points given.

1 Hartzell, Hub Model HC-C2YK-2CGU (F), Blade Model (F) C7666A to Piper Aircraft, Inc on August Moment change due to gear retracting landing gear (-32 in.-lb.)

(This model includes the Hartzell damper).

Empty Weight C.G. Range None Note: HC-( )2YK-( ) may be substituted by HC-( )2YR-( ) per Hartzell Service Advisory 61.

Maximum Weight S/N 34-E4, 34-7250001 through 34-7250214: 4000 lb.- Takeoff 4000 lb. - Landing See NOTE 3.

Page No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 de); and Rev No. 18 14 12 12 12 12 15 15 18 16 15 18 18 16 18 16 18 ).

Figure 6-14. The Type Certificate Data Sheet (TCDS) shows various information about an aircraft to include weight and balance information.

Model C7666A-0; Model C7666A-0; Model FC7666A-0; 6-9 de Model FC7666A-0; e Model (F) C7666A de Model (F) C7666A 5 of 17 A7SO DEPARTMENT OF TRANSPORTATION Maximum Weight 4570 lb. - Takeoff FEDERAL AVIATION ADMINISTRATION 4342 lb. - Landing (All weight in excess of 4000 lb. must be fuel) Zero fuel weight may be increased up to a maximum of 4077.7 lb. when approved A7SO wing options are installed. Revision 19 See NOTE 11 for optional weights. Piper Aircraft, Inc PA-34-200 No. of Seats 7 (2 at +85.5, 3 at +118.1, 2 at +155.7) PA-34-200T 7 (2 at +85.5, 3 at +118.1, 2 at +157.6) PA-34-220T 6 (2 at +85.5, *2 at +119.1, 2 at +157.6) May 2, 2013 * - Optional Club Seats Maximum Baggage 200 lb. (100 lb. at +22.5, 100 lb. at +178) TYPE CERTIFICATE DATA SHEET NO. A7SO A Fuel Capacity 98 gallons (2 wing tanks) at (+93.6) (93 gallons usable) This data sheet which is a part of type certificate No. A7SO, prescribes conditions and limitations under which the product * 128 gallons (2 wing tanks) at (+93.6) (123 gallons usable) for which the type certificate was issued meets the airworthiness requirements of the Federal Aviation Regulations.

* - Optional for S/N 34-7570001, 34-7670114 through 34-8170092.

See NOTE 1 for data on system fuel.

Type Certificate Holder Piper Aircraft, Inc.

2926 Piper Drive Oil Capacity 8 qts. per engine (5 qts. per engine usable) Vero Beach, Florida 32960 See NOTE 1 for data on system oil.

Type Certificate Holder Record The New Piper Aircraft, Inc transferred TC A7SO to Piper Aircraft, Inc on August Maximum Operating Altitude 25,000 feet 7, 2006 Control Surface Movements Ailerons ( ± 2 ° ) Up 35 ° Down 20 ° I. - Model PA-34-200 (Seneca), 7 PCLM (Normal Category), Approved 7 May 1971.

Stabilator Up 12.5° ( + 0°, − 1 ° ) Down 7.5 ° ( ± 1 ° ) Rudder Left Right Engines S/N 34-E4, 34-7250001 through 34-7250214: ( ± 1 ° ) 35 ° 35 ° 1 Lycoming LIO-360-C1E6 with fuel injector, Stabilator Trim ( ± 1 ° ) Down 10.5 ° Up 6.5 ° Lycoming P/N LW-10409 or LW-12586 (right side); and Tab 1 Lycoming IO-360-C1E6 with fuel injector, (Stabilator neutral) Wing Flaps ( ± 2 ° ) Up 0 ° Down 40 ° Lycoming P/N LW-10409 or LW 12586 (left side).

Rudder Trim Tab Left Right S/N 34-7250215 through 34-7450220: ( ± 1 ° ) 25 ° 25 ° 1 Lycoming LIO-360-C1E6 with fuel injector, (Rudder neutral) Lycoming P/N LW-12586 (right side); and 1 Lycoming IO-360-C1E6 with fuel injector, Nose Wheel Lycoming P/N LW-12586 (left side).

Travel ( ± 1 ° ) Left 27 ° Right 27 ° Fuel 100/130 minimum grade aviation gasoline Manufacturer's Serial Number 34-7570001 through 34-8170092 (See NOTE 7).

Engine Limits For all operations, 2700 r.p.m. (200 hp) IIIA. - Model PA-34-220T (Seneca III), 7 PCLM (Normal Category), Approved December 17, 1980.

Propeller and Propeller Limits Left Engine Same as model PA-34-200T series except engines, windshield, instrument panel, landing gear, maximum gross weight and 1 Hartzell, Hub Model HC-C2YK-2 ( ) E, Blade Model C7666A-0; other minor changes.

1 Hartzell, Hub Model HC-C2YK-2 ( ) EU, Blade Model C7666A-0; 1 Hartzell, Hub Model HC-C2YK-2 ( ) EF, Blade Model FC7666A-0; Engines 1 Teledyne Continental TSIO-360-KB (left engine), 1 Hartzell, Hub Model HC-C2YK-2 ( ) EFU, Blade Model FC7666A-0; 1 Teledyne Continental LTSIO-360-KB (right engine).

1 Hartzell, Hub Model HC-C2YK-2CG (F), Blade Model (F) C7666A (This model includes the Hartzell damper); or Fuel 100/100LL minimum grade aviation gasoline 1 Hartzell, Hub Model HC-C2YK-2CGU (F), Blade Model (F) C7666A (This model includes the Hartzell damper).

Engine Limits Takeoff, 5 minutes, 2800 r.p.m. and 40" Hg. manifold pressure (220 hp) Max. Continuous, 2600 r.p.m. and 40" Hg. manifold pressure (200 hp) Note: HC-( )2YK-( ) may be substituted by HC-( )2YR-( ) per Hartzell Service Advisory 61.

Propeller and Propeller Limits Left Engine 1 Hartzell, Hub Model BHC-C2YF-2 ( ) UF, Blade Model FC8459-8R.

Right Engine 1 Hartzell, Hub Model BHC-C2YF-2 ( )L ( )UF, Blade Model FJC8459-8R.

Page No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Rev No. 18 14 12 12 12 12 15 15 18 16 15 18 18 16 18 16 18 A7SO 2 of 17 3 of 17 A7SO Propeller and Propeller Limits Right Engine Maximum Weight S/N 34-7250215 through 34-7450220: (continued) 1 Hartzell, Hub Model HC-C2YK-2 ( ) LE, Blade Model JC7666A-0; 4200 lb. - Takeoff 1 Hartzell, Hub Model HC-C2YK-2 ( ) LEU, Blade Model JC7666A-0; 4000 lb. - Landing 1 Hartzell, Hub Model HC-C2YK-2 ( ) LEF, Blade Model FJC7666A-0; 1 Hartzell, Hub Model HC-C2YK-2 ( ) LEFU, Blade Model FJC7666A-0; No. of Seats 7 (2 at +85.5, 3 at +118.1, 2 at +155.7) 1 Hartzell, Hub Model HC-C2YK-2CLG (F), Blade Model (F) JC7666A (This model includes the Hartzell damper); or Maximum Baggage 200 lb. (100 lb. at +22.5, 100 lb. at +178.7) 1 Hartzell, Hub Model HC-C2YK-2CLGU (F), Blade Model (F) JC7666A (This model includes the Hartzell damper).

Fuel Capacity 98 gallons (2 wing tanks) at (+93.6) (93 gallons usable) See NOTE 1 for data on system fuel.

Note: HC-( )2YK-( ) may be substituted by HC-( )2YR-( ) per Hartzell Service Advisory 61.

Oil Capacity 8 qts. per engine (6 qts. per engine usable) See NOTE 1 for data on system oil.

Pitch setting: High 79 ° to 81 ° , Low 13.5 ° at 30" station.

Diameter: Not over 76", not under 74".

Control Surface Movements Ailerons ( ± 2 ° ) Up 30 ° Down 15 ° No further reduction permitted. Stabilator Up Down 12.5° ( + 0, − 1 ° ) 7.5 ° ( ± 1 ° ) Rudder ( ± 1 ° ) Left 35 ° Right 35 ° Spinner: Piper P/N 96388 Spinner Assembly and P/N 96836 Cap Assembly, or Stabilator Trim ( ± 1 ° ) Down 10.5 ° Up 6.5 ° P/N 78359-0 Spinner Assembly and P/N 96836-2 Cap Assembly (See NOTE 4) Tab (Stabilator neutral) Governor Assembly: Wing Flaps ( ± 2 ° ) Up 0 ° Down 40 ° 1 Hartzell hydraulic governor, Model F-6-18AL (Right); Rudder Trim 1 Hartzell hydraulic governor, Model F-6-18A (Left).

Tab Left ( ± 1 ° ) 17 ° Right 22 ° (Rudder neutral) Avoid continuous operation between 2200 and 2400 r.p.m. unless aircraft is equipped with Hartzell propellers which incorporates Hartzell damper on both left Nose Wheel S/N 34-E4, 34-7250001 through 34-7350353: and right engine as noted above.

Travel ( ± 1 ° ) Left 21 ° Right 21 ° Nose Wheel S/N 34-7450001 through 34-7450220: Airspeed Limits V (Never exceed) 217 m.p.h. (188 knots) NE Travel Left Right ( ± 1 ° ) 27 ° 27 ° V (Maximum structural cruise) 190 m.p.h (165 knots) NO V (Maneuvering, 4200 lb.) 146 m.p.h. (127 knots) A Manufacturer's Serial Number 34-E4, 34-7250001 through 34-7450220 (See NOTE 7).

V (Maneuvering, 4000 lb.) 146 m.p.h. (127 knots) A V (Maneuvering, 2743 lb.) 133 m.p.h (115 knots) A II. - Model PA-34-200T (Seneca II), 7 PCLM (Normal Category), Approved July 18, 1974.

V (Flaps extended) 125 m.p.h (109 knots) FE Same as Model PA-34-200 series except engine installation, maximum gross weight, and other minor changes.

V (Landing gear operating) LO Extension 150 m.p.h. (130 knots) Engines 1 Teledyne Continental TSIO-360-E or TSIO-360-EB (left engine), Retract 125 m.p.h. (109 knots) 1 Teledyne Continental LTSIO-360-E or LTSIO-360-EB (right engine).

V (Landing gear extended) 150 m.p.h (130 knots) LE V (Minimum control speed) 80 m.p.h. ( 69 knots) MC Fuel 100/130 minimum grade aviation gasoline C.G. Range (Gear Extended) S/N 34-E4, 34-7250001 through 34-7250214 (See NOTE 3): Engine Limits For all operations, 2575 r.p.m. and 40" Hg.

(+86.4) to (+94.6) at 4000 lb.

Manifold pressure, 200 hp @ S.L. and 215 hp @ 12,000 ft.

(+82.0) to (+94.6) at 3400 lb.

(+80.7) to (+94.6) at 2780 lb.

Propeller and Propeller Limits Left engine 1 Hartzell, Hub Model BHC-C2YF-2 ( )F (See NOTE 10) S/N 34-7250215 through 34-7450220: or BHC-C2YF-2 ( )UF; Blade Model FC8459-8R or FC8459B-8R.

(+87.9) to (+94.6) at 4200 lb.

(+82.0) to (+94.6) at 3400 lb.

Right engine (+80.7) to (+94.6) at 2780 lb.

1 Hartzell, Hub Model BHC-C2YF-2 ( )L ( )F (See NOTE 10) Straight line variation between points given.

or BHC-C2YF-2 ( )L ( )UF; Blade Model FJC8459-8R or FJC8459B-8R.

Moment change due to gear retracting landing gear (-32 in.-lb.)

Pitch setting at 30" station: Empty Weight C.G. Range None Hub Serial Numbers prior to AN3943: High 79.3 ° ± 2.0 ° , Low 14.4 ° ± 0.2 ° or High 80.0 ° to 81.5 ° , Low 14.4 ° ± 0.2 ° .

Maximum Weight S/N 34-E4, 34-7250001 through 34-7250214: Hub Serial Numbers AN3943 and subsequent: 4000 lb.- Takeoff High 80.0 ° to 81.5 ° , Low 14.4 ° ± 0.2 ° .

4000 lb. - Landing See NOTE 3.

Figure 6-15. Highlights of various specifications of the aircraft found within a TCDS. Note the fuel capacity of 98 gallons and its reference to the datum (A).

6-10 15 of 17 A7SO 11 of 17 A7SO MODEL AFM/POH REPORT NO. APPROVED SERIAL EFFECTIVITY Control Surface Movements Ailerons ( ± 2 ° ) Up 35 ° Down 20 ° PA-34-220T POH VB-1110 1/8/81 34-8133001 through Stabilator Up 12.5° ( + 0°, − 1 ° ) Down 7.5 ° ( ± 1 ° ) (Seneca III) 34-8633031, and Rudder ( ± 1 ° ) Left 35 ° Right 35 ° 3433001 through 3433172 Stabilator Trim Down Up ( ± 1 ° ) 10.5 ° 6.5 ° POH VB-1150 2/20/81 34-8133001 through Tab 34-8633031, and (Stabilator neutral) 3433001 through 3433172 Wing Flaps Up 0 ° (±1°) Down 40 ° (±2°) when Piper Kit Rudder Trim 764-099V is installed Tab ( ± 1 ° ) Left 26 ° Right 26 ° POH VB-1257 10/20/89 3448001 through 3448037 (Rudder neutral) VB-1259 11/20/89 3448001 through 3448037 POH when Piper Kit Nose Wheel Left 27 ° Right 27 ° 766-203 is installed Travel 3448038 through 3448079 PA-34-220T POH VB-1556 11/5/93 (Maximum) (Seneca IV) POH VB-1558 12/6/93 3448038 through 3448079 when Piper Kit Manufacturer's Serial Number 3449001 and up.

766-283 is installed POH VB-1615 7/12/95 3447001 through 3447029 POH VB-1620 7/12/95 3447001 through 3447029 DATA PERTINENT TO ALL MODELS when Piper Kit 766-608 is installed Datum 78.4" forward of wing leading edge from the inboard edge of the inboard fuel PA-34-220T POH VB-1638 12/6/96 3449001 and up tank.

(Seneca V) POH VB-1649 1/23/97 3449001 and up when Piper Kit 766-632 (or equivalent Leveling Means Two screws left side fuselage below window.

88247-{ }) is installed VB-1930 10/25/05 3449311 and 3449323 and up POH Certification Basis Type Certificate No. A7SO issued May 7, 1971, obtained by the manufacturer when Avidyne Entegra System under the delegation option authorization.

is installed.

Date of Type Certificate application July 23, 1968.

3449311 and 3449323 and up POH VB-1955 3/20/06 when Piper kit 766-632 Model PA-34-200 (Seneca I): (or equivalent 88247-{ }) and FAR 23 as amended by Amendment 23-6 effective August 1, 1967; FAR Avidyne Entegra System is 23.959 as amended by Amendment 23-7 effective September 14, 1969; and Installed.

FAR 23.1557(c)(1) as amended by Amendment 23-18 effective May 2, 1977.

POH VB-2186 9/2/2010 3449410 and up when Garmin Compliance with FAR 23.1419 as amended by Amendment 23-14 effective G600 System is installed December 20, 1973, has been established with optional ice protection provisions.

POH VB-2193 9/10/2010 3449410 and up when Piper Kit 766-632 (or equivalent Model PA-34-200T (Seneca II): 88247-{ }) and Garmin G600 FAR 23 as amended by Amendment 23-6 effective August 1, 1967; FAR System is installed.

23.901, 23.909, 23.959, 23.1041, 23.1043, 23.1047, 23.1143, 23.1305(b)(c)(h)(p) POH VB-2230 4/30/2013 3449459, 3449467 and up and 23.1527(b) as amended by Amendment 23-7 effective September 14, 1969; when the Garmin G1000 and FAR 23.1557(c)(1) as amended by Amendment 23-18 effective May 2, 1977.

system is installed Model PA-34-220T (Seneca III and IV): NOTE 1 Current Weight and Balance Report, including list of equipment included in certificated FAR 23 as amended by Amendment 23-6 effective August 1, 1967; FAR empty weight, and loading instructions when necessary, must be provided for each aircraft at 23.207, 23.901, 23.909, 23.959, 23.1041, 23.1043, 23.1047, 23.1143, the time of original certification.

23.1305(b)(c)(h)(p) and 23.1527 as amended by Amendment 23-7 effective September 14, 1969; FAR 23.201 and 23.203 as amended by Amendment The certificated empty weight and corresponding center of gravity locations must include 23-14 effective December 20, 1973; FAR 23.1557(c)(1) as amended by undrainable system oil (not included in oil capacity) and unusable fuel as noted below: Amendment 23-18 effective May 2, 1977; FAR 23.175(a) and 23.1581(b)(2) as amended by Amendment 23-21 effective March 1, 1978; FAR 23.1545(a) as Fuel: 30.0 lb. at (+103.0) for PA-34 series, except Model PA-34-220T amended by Amendment 23-23 effective December 1, 1978; and FAR 36 (Seneca V), S/N 3449001 and up through Amendment 36-9 effective January 15, 1979.

Fuel: 36.0 lb. at (+103.0) for Model PA-34-220T (Seneca V), S/N 3449001 and up Oil: 6.2 lb. at (+ 39.6) for Model PA-34-200 Oil: 12.0 lb. at (+ 43.7) for Models PA-34-200T and PA-34-220T NOTE 2 All placards required in the approved Airplane Flight Manual or Pilot's Operating Handbook and approved Airplane Flight Manual of Pilot's Operating Handbook supplements must be Figure 6-16. Highlights of various specifications of the aircraft found within a TCDS.

Plumb Bob is weighed using load cells on jacks, leveling the aircraft is done by adjusting the height with the jacks and checking the A plumb bob is a heavy metal object, cylinder or cone shape, with a sharp point at one end and a string attached to the level at the level point. Figure 6-20 shows a Gulfstream jet on jacks with the load cells in place.

other end. If the string is attached to a given point on an aircraft, and the plumb bob can hang down so the tip just Always follow the aircraft manufacturer’s weighing and touches the ground, the point where the tip touches will be perpendicular to where the string is attached. An example leveling procedures and processes. All aircraft need to be in a flight level attitude when they are weighed unless the of the use of a plumb bob would be measuring the distance from an aircraft’s datum to the center of the main landing manufacturer’s manual specifically allows it or has a formula in the manual to use accordingly.

gear axle. If the leading edge of the wing was the datum, a plumb bob could be dropped from the leading edge and a Spirit Level Before an aircraft can be weighed and reliable readings obtained, it must be in a level flight attitude. One method that can be used to check for a level condition is to use a spirit level, sometimes thought of as a carpenter’s level, by placing it on or against a specified place on the aircraft. Spirit levels consist of a vial full of liquid, except for a small air bubble.

When the air bubble is centered between the two black lines, a level condition is indicated.

In Figure 6-21, a spirit level is being used on a Mooney M20 to check for a flight level attitude. By looking in the TCDS, it is determined that the leveling means is two screws on the left side of the airplane fuselage, in line with the trailing Figure 6-17. Weighing a Piper Archer using electronic platform scales.

edge of the wing.

6-11 a calculation, using the actual weight versus the standard weight would make a difference of 10 to 15 lb.

When an aircraft is weighed with fuel in the tanks, the weight of fuel per gallon should be checked with a hydrometer. A hydrometer consists of a weighted glass tube that is sealed with a graduated set of markings on the side of the tube.

The graduated markings and their corresponding number values represent units of pounds per gallon (lb/gal). When placed in a flask with fuel in it, the glass tube floats at a level dependent on the density of the fuel. Where the fuel intersects the markings on the side of the tube indicates the pounds per gallon.

Figure 6-18. A Cessna 182 being weighed with portable electronic platform scales.

Preparing an Aircraft for Weighing Weighing an aircraft is a very important and exacting phase chalk mark made on the hangar floor. The plumb bob could of aircraft maintenance and must be carried out with accuracy also be dropped from the center of the axle on the main and good workmanship. Thoughtful preparation saves time landing gear, and a chalk mark made on the floor. With a tape and prevents mistakes. The aircraft should be weighed inside measure, the distance between the two chalk marks could be a hangar where wind cannot blow over the surface and cause determined, and the arm for the main landing gear would be fluctuating or false scale readings. The aircraft should be known. Plumb bobs can also be used to level an aircraft, as clean inside and out, with special attention paid to the bilge described in the Helicopter Weight and Balance section of area to be sure no water or debris is trapped. The outside of this chapter. Figure 6-22 shows a plumb bob being dropped the aircraft should be as free as possible of all mud and dirt.

from the leading edge of an aircraft wing.

To begin, assemble all the necessary equipment, such as: Hydrometer 1. Scales, hoisting equipment, jacks, and leveling When an aircraft is weighed with full fuel in the tanks, the equipment.

weight of the fuel must be accounted for by mathematically subtracting it from the scale readings. To subtract it, its 2. Blocks, chocks, or sandbags for holding the airplane weight, arm, and moment must be known. Although the standard weight for aviation gasoline (Avgas) is 6.0 lb/gal and jet fuel is 6.7 lb/gal, these values are not exact for all conditions. On a hot day versus a cold day, these values can vary dramatically. On a hot summer day in the state of Florida, Avgas checked with a hydrometer typically weighs between 5.85 and 5.9 lb/gal. If 100 gallons of fuel were involved in Figure 6-19. M2000 platform scale digital indicator.

Figure 6-20. Airplane on jacks with load cells in use.

6-12 on the scales.

3. Straightedge, spirit level, plumb bobs, chalk line, and a measuring tape.

4. Applicable Aircraft Specifications and weight and balance computation forms.

Fuel System When weighing an aircraft to determine its empty weight, only the weight of residual (unusable) fuel should be included. To ensure that only residual fuel is accounted for, the aircraft should be weighed in one of the following three conditions.

1. Weigh the aircraft with absolutely no fuel in the aircraft tanks or fuel lines. If an aircraft is weighed in Figure 6-22. Plumb bob dropped from a wing leading edge.

this condition, the technician can mathematically add the proper amount of residual fuel to the aircraft and also be used to determine the weight of each gallon of account for its arm and moment. The proper amount fuel, while the Aircraft Specifications or TCDS can of fuel can be determined by looking in the aircraft’s be used to identify the fuel capacity of the aircraft. If TCDS.

an aircraft is to be weighed with load cells attached to 2. Drain fuel from the tanks in the manner specified jacks, the technician should check both the load cell by the aircraft manufacturer. If there are no specific instruction manual and aircraft maintenance manual instructions, drain the fuel until the fuel quantity to make sure it is permissible to jack the aircraft with gauges read empty and until fuel stops draining from the fuel tanks full as this may add additional stress to the tanks. The aircraft attitude may be a consideration the aircraft structure.

when draining the fuel tanks and the maintenance manual should be consulted. In this case, the unusable Never weigh an aircraft with fuel tanks partially full, because fuel will remain in the lines and system, and its it will be impossible to determine exactly how much fuel to weight and arm can be determined by reference to the account for.

aircraft’s TCDS.

Oil System 3. Weigh the aircraft with the fuel tanks completely full. If an aircraft is weighed in this condition, the The empty weight for older aircraft certificated under the technician can mathematically subtract the weight of Civil Air Regulations (CAR) part 3 does not include the usable fuel and account for its arm and moment. If engine lubricating oil. The oil must be drained before the the weight of the fuel is in question, a hydrometer can aircraft is weighed, or its weight must be subtracted from the scale readings to determine the empty weight.

To weigh an aircraft that does not include the engine lubricating oil as part of the empty weight, place it in level flight attitude, then open the drain valves and allow all the oil that is able, to drain out. Any remaining is undrainable oil and is part of the empty weight.

If it is impractical to drain the oil, the reservoir can be filled to the specified level and the weight of the oil computed at 7.5 lb/gal. Then its weight and moment are subtracted from the weight and moment of the aircraft as weighed. The amount and arm of the undrainable oil are found in NOTE 1 of the TCDS, and this must be added to the empty weight.

For aircraft certificated since 1978 under 14 CFR parts 23 Figure 6-21. Spirit level being used on a Mooney M20. and 25, full engine oil is typically included in an aircraft’s 6-13 empty weight. This can be confirmed by looking at the TCDS. its three wheels sitting on floor scales, the weight transfer If full oil is to be included, the oil level needs to be checked to each scale happens through the center of the axle for each and the oil system serviced if it is less than full. wheel. If an airplane is weighed while it is on jacks, the weight transfer happens through the center of the jack pad.

Miscellaneous Fluids For a helicopter with skids for landing gear, determining the arm for the weighing points can be difficult if the skids are The hydraulic fluid reservoir and all other reservoirs sitting directly on floor scales. The problem is that the skid containing fluids required for normal operation of the aircraft is in contact with the entire top portion of the scale, and it should be full. Fluids not considered to be part of the empty is impossible to know exactly where the center of weight weight of the aircraft are potable (drinkable) water, lavatory transfer is occurring. In such a case, place a piece of pipe precharge water, and water for injection into the engines.

between the skid and the scale, and the center of the pipe will now be the known point of weight transfer.

Flight Controls The position of such items as spoilers, slats, flaps, and The arm for each of the weighing points is the distance from helicopter rotor systems is an important factor when weighing the center of the weight transfer point to the aircraft’s datum.

an aircraft. Always refer to the manufacturer’s instructions If the arms are not known, based on previous weighing of the for the proper position of these items.

aircraft or some other source of data, they must be measured when the aircraft is weighed. This involves dropping a Other Considerations plumb bob from the center of each weighing point and from Inspect the aircraft to see that all items included in the the aircraft datum, and putting a chalk mark on the hangar certificated empty weight are installed in the proper location.

floor representing each point. The perpendicular distance Remove items that are not regularly carried in flight. Also, between the datum and each of the weighing points can then look in the baggage compartments to make sure they are be measured. In Figure 6-23, the distance from the nosewheel empty. Replace all inspection plates, oil and fuel tank caps, centerline to the datum is being measured on an airplane.

junction box covers, cowling, doors, emergency exits, and The nosewheel sitting on an electronic scale can be seen in other parts that have been removed during maintenance.

the background.

All doors, windows, and sliding canopies should be in the normal flight position. Remove excessive dirt, oil, grease, Jacking the Aircraft and moisture from the aircraft.

Aircraft are often weighed by rolling them onto ramps in which load cells are embedded. This eliminates the problems Some aircraft are not weighed with the wheels on the scales, associated with jacking the aircraft off the ground. However, but are weighed with the scales placed either at the jacking many aircraft are weighed by jacking the aircraft up and then points or at special weighing points. Regardless of what lowering them onto scales or load cells. Extra care must be provisions are made for placing the aircraft on the scales used when raising an aircraft on jacks for weighing. If the or jacks, be careful to prevent it from falling or rolling off, aircraft has spring steel landing gear and it is jacked at the thereby damaging the aircraft and equipment. When weighing wheel, the landing gear will slide inward as the weight is an aircraft with the wheels placed on the scales, release the taken off the tire. Care must be taken to prevent the jack brakes to reduce the possibility of incorrect readings caused from tipping over. For some aircraft, stress panels or plates by side loads on the scales.

must be installed before they are raised with wing jacks to distribute the weight over the jack pad. Be sure to follow All aircraft have leveling points or lugs, and care must be the recommendations of the aircraft manufacturer in detail taken to level the aircraft, especially along the longitudinal anytime an aircraft is jacked. When using two wing jacks, axis. With light, fixed-wing airplanes, the lateral level is take special care to raise them simultaneously, so the aircraft not as critical as it is with heavier airplanes. However, a does not slip off the jacks. As the jacks are raised, keep the reasonable effort should be made to level the light airplanes safety collars screwed down against the jack cylinder to along the lateral axis. Helicopters must be level longitudinally prevent the aircraft from tilting if one of the jacks should and laterally when they are weighed. Accuracy in leveling all lose hydraulic pressure.

aircraft longitudinally cannot be overemphasized.

Leveling the Aircraft Weighing Points When an aircraft is weighed, it must be in its level flight When an aircraft is being weighed, the arms must be known attitude so that all the components are at the correct distance for the points where the weight of the aircraft is being from the datum. This attitude is determined by information in transferred to the scales. If a tricycle gear small airplane has the TCDS. Some aircraft require a plumb line to be dropped 6-14 from a specified location so that the point of the weight, the The range gets smaller because of the forward limit moving bob, hangs directly above an identifiable point. Others specify back, while the aft limit stays in the same place.

that a spirit level be placed across two leveling lugs (special screws on the outside of the fuselage). Other aircraft call for a The data sheet identifies that there is a straight-line variation spirit level to be placed on the upper door sill. Lateral level is between the points given. The points being referred to are not specified for all light aircraft, but provisions are normally the forward and aft CG limits. From a weight of 2,780 lb to made on helicopters for determining both longitudinal a weight of 3,400 lb, the forward limit moves from +80.7" and lateral level. This may be done by built-in leveling to +82.0", and if plotted on a graph, that change would indicators or by a plumb bob that shows the conditions of form a straight line. From 3,400 lb to 4,000 lb, the forward both longitudinal and lateral level. The actual adjustments limit moves from +82 to +86.4", again forming a straight to level the aircraft using load cells are made with the jacks. line. Plotted on a graph, the CG limits would look like When weighing from the wheels, leveling is normally done Figure 6-25. When graphically plotted, the CG limits form by adjusting the air pressure in the nosewheel shock strut. what is known as the CG envelope.

Safety Considerations In Figure 6-25, the red line represents the forward limit up to a weight of 2,780 lb. The blue and green lines represent Special precautions must be taken when raising an aircraft on jacks. the straight-line variation that occurs for the forward limit as the weight increases up to a maximum of 4,000 lb. The 1. Stress plates must be installed under the jack pads if yellow line represents the maximum weight for the airplane, the manufacturer specifies them.

and the purple line represents the aft limit.

2. If anyone is required to be in the aircraft while it is being jacked, there must be no movement.

Empty Weight Center of Gravity (EWCG) Range 3. The jacks must be straight under the jack pads before For some aircraft, a CG range is given for the aircraft in the beginning to raise the aircraft.

empty weight condition in the TCDS. This practice is not very common with airplanes, but is often done for helicopters. This 4. All jacks must be raised simultaneously and safety range would only be listed for an airplane if the fuel tanks, devices placed against the jack cylinder to prevent the seats, and baggage compartments are so located that changes aircraft from tipping if any jack should lose pressure.

in the fuel or occupant load have a very limited effect on the Not all jacks have screw-down collars, some use drop balance of the aircraft. If the EWCG of an aircraft falls within pins or friction locks.

the EWCG limits, it is impossible to legally load the aircraft so that its loaded CG falls outside of its allowable range. If the CG Range TCDS lists an EWCG range and, after a repair or alteration The CG range for an aircraft is the limits within which the is completed, the EWCG falls within this range, then there is aircraft must balance. It is identified as a range and considered no need to compute a fore and aft check for adverse loading.

an arm extending from the forward most limit to the aft most But if the TCDS lists the EWCG range as “None” (and most limit usually expressed in inches. In the TCDS for the Piper of them do), a check must be made to determine whether it Seneca airplane, shown earlier in this chapter, the range is is possible by any combination of legal loading to cause the given in Figure 6-24.

Because the Piper Seneca is a retractable gear airplane, the specifications identify that the range applies when the landing gear is extended, and that the airplane’s total moment is decreased by 32 when the gear retracts. To know how much the CG changes when the gear is retracted, the moment of 32 in-lb would need to be divided by the loaded weight of the airplane. For example, if the airplane weighed 3,500 lb, the CG would move forward 0.009" (32 ÷ 3,500).

Based on the numbers given, up to a loaded weight of 2,780 lb, the forward CG limit is +80.7" and the aft CG limit is +94.6". As the loaded weight of the airplane increases to 3,400 lb, and eventually to the maximum of 4,000 lb, the forward CG limit moves aft. In other words, as the loaded weight of the airplane increases, the CG range gets smaller.

Figure 6-23. Measuring the nosewheel arm on an airplane.

6-15 aircraft CG to move outside of either its forward or aft limits.

CG Range: (Gear Extended) S/N 34-E4, 34-7250001 through 34-7250214 Operating CG Range (See NOTE 3) (+86.4") to (+94.6") at 4,000 lb All aircraft have CG limits identified for the operational (+82.0") to (+94.6") at 3,400 lb condition, with the aircraft loaded and ready for flight. If an (+80.7") to (+94.6") at 2,780 lb aircraft can operate in more than one category, such as normal Straight line variation between points given.

Moment change due to gear retracting and utility, more than one set of limits might be listed. As landing gear (–32 in-lb) shown earlier for the Piper Seneca airplane, the limits can change as the weight of the aircraft increases. To legally fly, Figure 6-24. Piper Seneca airplane center of gravity range.

the CG for the aircraft must fall within the CG limits.

the CG forward of the main landing gear, which must be the Standard Weights Used for Aircraft Weight and case for a tricycle gear airplane. This number is the result of Balance dividing the total moment of 66,698 in-lb by the total weight Unless the specific weight for an item is known, the standard of 1,331.5 lb.

weights used in aircraft weight and balance are as follows: • Avgas 6 lb/gal EWCG Formulas • Turbine fuel 6.7 lb/gal The EWCG can be quickly calculated by using the following formulas. There are four possible conditions and formulas • Lubricating oil 7.5 lb/gal that relate the location of the CG to the datum. Notice that • Water 8.35 lb/gal the formula for each condition first determines the moment F × L R × L • Crew and passengers 170 lb per person of the nose wheel or tail wheel and then divides it W W by the total weight of the airplane. The arm is then added to or subtracted from the distance between the main wheels Example Weighing of an Airplane and the datum (distance D).

In Figure 6-26, a tricycle gear airplane is being weighed by Formula 1 Nosewheel airplanes with datum forward of using three floor scales. The specifications on the airplane the main wheels.

and the weighing specific data are shown in Figure 6-27.

F × L By analyzing the data identified for the airplane being weighed CG = D –

( )

W in Figure 6-26, the following information is determined.

• Because the airplane was weighed with the fuel tanks Formula 2 Nosewheel airplanes with the datum aft of full, the full weight of the fuel must be subtracted and the main wheels.

the unusable fuel added back in. The weight of the fuel being subtracted is based on the pounds per gallon F × L CG = – D +

determined by the hydrometer check (5.9 lb/gal). ( )

W • Because wheel chocks are used to keep the airplane from rolling off the scales, their weight must be Formula 3 Tail wheel airplanes with the datum forward subtracted from the scale readings as tare weight.

of the main wheels.

• Because the main wheel centerline is 70" behind the R × L datum, its arm is a +70".

CG = D +

( )

W • The arm for the nosewheel is the difference between the wheelbase (100") and the distance from the datum Formula 4 Tail wheel airplanes with the datum aft of to the main wheel centerline (70"). Therefore, the arm the main wheels.

for the nosewheel is −30".

R × L CG = – D +

( )

To calculate the airplane’s empty weight and EWCG, a six- W column chart is used. Figure 6-28 shows the calculation for the airplane in Figure 6-26. Datum Forward of the Airplane–Nosewheel Landing Gear Based on the calculation shown in the chart, the CG is at The datum of the airplane in Figure 6-29 is 100" forward +50.1", which means it is 50.1" aft of the datum. This places of the leading edge of the wing root, or 128" forward of the 6-16 4,200 4,100 4,000 3,900 3,800 86.4 at 4,000 lb 3,700 3,600 3,500 Weight (lb) 3,400 82 at 3,400 lb 3,200 Forward Aft CG Limit CG Limit 3,000 2,900 2,800 80.7 at 2,780 lb 2,700 2,600 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 Center of Gravity (in) Figure 6-25. Center of gravity envelope for the Piper Seneca.

main-wheel weighing points. This is distance (D). The weight the datum of the airplane in Figure 6-30 and the main-wheel of the nosewheel (F) is 340 lb, and the distance between weighing points is 75", the weight of the nosewheel (F) is 340 main wheels and nosewheel (L) is 78". The total weight of lb, and the distance between main wheels and nosewheel (L) the airplane (W) is 2,006 lb. is 78". The total net weight of the airplane (W) is 2,006 lb.

The location of the CG may be determined by using this The location of the CG may be determined by using this formula: F × L formula: CG = – D +

( )

F × L W CG = D –

( )

W 340 × 78 = – 75 +

( )

340 × 78 2,006 = 128 –

( )

2,006 = –88.2 = 114.8 The CG location is a negative value, which means it is 88.2" The CG is 114.8" aft of the datum. This is 13.2" forward of forward of the datum. This places it 13.2" forward of the main the main-wheel weighing points, which proves the location wheels, the same location as it was when it was measured of the datum has no effect on the location of the CG so long from other datum locations.

as all measurements are made from the same location.

Location of Datum Datum Aft of the Main Wheels– Nosewheel Landing It makes no difference where the datum is located if all Gear measurements are made from the same location.

The datum of some aircraft may be located aft of the main wheels. The airplane in this example is the same one just Datum Forward of the Main Wheels–Tail Wheel discussed, but the datum is at the intersection of the trailing edge of the wing with the fuselage. The distance (D) between 6-17 Datum Right scale reading 640 lb Main wheel centerline 70" 100" Nose scale reading 225 lb Left scale reading 650 lb Chocks Nosewheel centerline Wheel base Figure 6-26. Example airplane being weighed. The datum is 70" forward of the wing root leading edge.

Landing Gear Aircraft datum: Leading edge of the wing Locating the CG of a tail wheel airplane is done in the same way as locating it for a nosewheel airplane except the Leveling means: Two screws, left side of fuselage R × L F × L below window formulas use rather than .

W W Wheelbase: 100" The distance (D) between the datum of the airplane in Fuel capacity: 30 gal aviation gasoline at +95" Figure 6-31 and the main-gear weighing points is 7.5", the weight of the tail wheel (R) is 67 lb, and the distance (L) Unusable fuel: 6 lb at +98" between the main-wheel and the tail wheel weighing points is 222". The total weight of the airplane (W) is 1,218 lb.

Oil capacity: 8 qt at –38" Determine the CG by using this formula: Note 1: Empty weight includes unusable fuel and full oil Weight Tare Net Wt. Arm Moment Item Left main scale reading: 650 lb (lb) (lb) (lb) (inches) (in-lb) 225 –2.5 222.5 –30 –6,675 Nose Right main scale reading: 640 lb 650 –5 645 +70 45,150 Left Main Nose scale reading: 225 lb 640 –5 635 +70 44,450 Right Main Tare weight: 5 lb chocks on left main 5 lb chocks on right main 1,515 –12.5 1,502.5 82,925 Subtotal 2.5 lb chock on nose –177 +95 –16,815 Fuel Total During weighing: Fuel tanks full and oil full Hydrometer check on +6 +98 588 Fuel Unuse Fuel shows 5.9 lb/gal Full Oil Figure 6-27. Specifications and weighing specific data for tricycle 1,331.5 +50.1 66,698 Total gear airplane.

Figure 6-28. Center of gravity calculation for airplane being weighed.

6-18 Datum R × L CG = D +

D = 128.0 ( )

W 114.8 100.0 13.2 50.0 67 × 222 = 7.5 +

( )

1,218 = 19.7 L = 78.0 The CG is 19.7 inches behind the datum.

Figure 6-29. The datum is 100" forward of the wing root leading Datum Aft of the Main Wheels–Tail Wheel Landing edge.

Gear The datum of the airplane in Figure 6-32 is located at the intersection of the wing root trailing edge and the fuselage.

For the example loading of the airplane, the following This places the arm of the main gear (D) at –80". The net information applies: weight of the tail wheel (R) is 67 lb, the distance between • Airplane Serial Number: 34-7250816 the main wheels and the tail wheel (L) is 222", and the total net weight (W) of the airplane is 1,218 lb.

• Airplane Empty Weight: 2,650 lb • Airplane EWCG: +86.8" Since the datum is aft of the main wheels, use the formula: For today’s flight, the following useful load items are R × L CG = – D + ( ) included: W • 1 pilot at 180 lb at an arm of +85.5" 67 × 222 • 1 passenger at 160 lb at an arm of +118.1" = – 80 +

( )

1,218 • 1 passenger at 210 lb at an arm of +118.1" = –67.8 • 1 passenger at 190 lb at an arm of +118.1" • 1 passenger at 205 lb at an arm of +155.7" The CG is 67.8" forward of the datum, or 12.2" aft of the • 50 lb of baggage at an arm of +22.5" main-gear weighing points. The CG is in the same location relative to the main wheels, regardless of where the datum • 100 lb of baggage at an arm of +178.7" is located.

• 80 gal of fuel at an arm of +93.6" Loading an Aircraft for Flight To calculate the loaded weight and CG of this airplane, a The ultimate test of whether there is a problem with an four-column chart is used in Figure 6-34.

airplane’s weight and balance is when it is loaded and ready to fly. The only real importance of an airplane’s empty weight Based on the information in the TCDS, the maximum takeoff and EWCG is how it affects the loaded weight and balance weight of this airplane is 4,200 lb and the aft-most CG limit of the airplane, since an airplane does not fly when it is empty. The pilot-in-command is responsible for the weight Datum and balance of the loaded airplane, and they make the final 153.0 decision on whether the airplane is safe to fly.

88.2 D =75.0 Example Loading of an Airplane As an example of an airplane being loaded for flight, the Piper Seneca twin will be used. The TCDS for this airplane was shown earlier in this chapter, and its CG range and CG envelope were also shown.

L = 78.0 The information from the TCDS that pertains to this example Figure 6-30. The datum is aft of the main wheels at the wing loading is shown in Figure 6-33.

trailing edge.

6-19 is +94.6". The loaded airplane in Figure 6-34 is 25 lb too Datum heavy, and the CG is 1.82" too far aft. To make the airplane safe to fly, the load needs to be reduced by 25 lb and some 19.7 D = 7.5 of the load needs to be shifted forward. For example, the baggage can be reduced by 25 lb, and a full 100 lb of it can be placed in the more forward compartment. One passenger can be moved to the forward seat next to the pilot, and the aft-most passenger can then be moved forward.

L = 222.0 With the changes made, the loaded weight is now at the 229.5 maximum allowable of 4,200 lb, and the CG has moved Figure 6-31. The datum of this tail wheel airplane is the wing root forward 4.42". [Figure 6-35] The airplane is now safe to fly.

leading edge.

Adverse-Loaded CG Checks Many modern aircraft have multiple rows of seats and often Datum more than one baggage compartment. After any repair or alteration that changes the weight and balance, the A&P 67.8 mechanic or repairman must ensure that no legal condition of loading can move the CG outside of its allowable limits. To determine this, adverse-loaded CG checks must be performed and the results noted in the weight and balance revision sheet.

During a forward adverse-loaded CG check, all useful load 142 D = –80 items in front of the forward CG limit are loaded and all useful L = 222.0 load items behind the forward CG limit are left empty. So, if there are two seats and a baggage compartment located in Figure 6-32. The datum is aft of the main wheels, at the intersection of the wing trailing edge and the fuselage.

front of the forward CG limit, two people weighing 170 lb each are seated and the maximum allowable baggage is be accounted for. Notice that the front seats show a location placed in the baggage compartment. Any seat or baggage of 82" to 88", meaning they are adjustable fore and aft. In a compartment located behind the forward CG limit is left forward check, the pilot’s seat will be shown at 82", and in empty. If the fuel is located behind the forward CG limit, the aft check it will be at 88". Additional specifications for minimum fuel will be shown in the tank. Minimum fuel is the airplane shown in Figure 6-36 are as follows: calculated by dividing the engine’s METO hp by 2.

• Airplane empty weight: 1,850 lb During an aft adverse-loaded CG check, all useful load items • EWCG: +92.45" behind the aft CG limit are loaded and all useful load items • CG limits: +89" to +99" in front of the aft CG limit are left empty. Even though the pilot’s seat will be in front of the aft CG limit, the pilot’s seat • Maximum weight: 3,200 lb cannot be left empty. If the fuel tank is located forward of • Fuel capacity: 45 gal at +95" the aft CG limit, minimum fuel will be shown.

(44 usable) 40 gal at +102" Example Forward & Aft Adverse-Loaded CG Checks (39 usable) Using the stick airplane in Figure 6-36 as an example, adverse forward and aft CG checks are calculated. Some In evaluating the two extreme condition checks, the following of the data for the airplane is shown in Figure 6-36 , such key points should be recognized. [Figure 6-37] as seat, baggage, and fuel information. The CG limits are • The total arm is the airplane CG and is found by shown, with arrows pointing in the direction where maximum dividing the total moment by the total weight.

and minimum weights are loaded. On the forward check, any useful load item located in front of 89" is loaded, and • For the forward check, the only thing loaded behind anything behind that location is left empty. On the aft check, the forward limit was minimum fuel.

maximum weight is added behind 99" and minimum weight • For the forward check, the pilot and passenger seats in front of that location. For either of the checks, if fuel is not were shown at the forward position of 82".

located in a maximum weight location, minimum fuel must 6-20 warning system, or the removal of a radio or seat, the weight S/N 34-7250215 through 34-7450220: CG Range (+87.9") to (+94.6") at 4,200 lb and balance of an aircraft changes. An alteration performed (Gear Extended) (+82.0") to (+94.6") at 3,400 lb on an aircraft, such as a cargo door being installed or a (+80.7") to (+94.6") at 2,780 lb reinforcing plate being attached to the spar of a wing, also Straight line variation between points given. changes the weight and balance of an aircraft. Any time the equipment is changed or an alteration is performed, the new −32 in-lb moment change due to gear empty weight and EWCG must be determined. This can be retracting landing gear accomplished by placing the aircraft on scales and weighing None Empty Weight it, or by mathematically calculating the new weight and CG Range balance. The mathematical calculation is acceptable if the exact weight and arm of all the changes are known.

S/N 34-7250215 through 34-7450220: Maximum 4,200 lb—Takeoff Weight 4,000 lb—Landing Example Calculation After an Equipment Change A small, twin-engine airplane has some new equipment 7 (2 at +85.5", 3 at +118.1", 2 at +155.7") No. of Seats installed and some of its existing equipment removed. The 200 lb (100 lb at +22.5, 100 lb at +178.7) Maximum details of the equipment changes are shown in Figure 6-38.

Baggage To calculate the new empty weight and EWCG, a four- 98 gal (2 wing tanks) at (+93.6") (93 gal Fuel Capacity column chart is used. [Figure 6-39] In evaluating the weight usable). See NOTE 1 for data on system fuel.

and balance calculation shown in Figure 6-39, the following Figure 6-33. Example loading information pertaining to TCDS.

key points should be recognized.

• The weight of the equipment needs to be identified • For the forward check, the CG was within limits, so with a plus or minus to signify whether it is being the airplane could be flown this way.

installed or removed.

• For the aft check, the only thing loaded in front of the • The sign of the moment (plus or minus) is determined aft limit was the pilot, at an arm of 88".

by the signs of the weight and arm.

• For the aft check, the fuel tank at 102" was filled, which • The strobe and the ADF are both being removed more than accounted for the required minimum fuel.

(negative weight), but only the strobe has a negative • For the aft check, the CG was out of limits by 0.6", moment. This is because the arm for the ADF is so the airplane should not be flown this way.

also negative, and two negatives multiplied together produce a positive result.

Equipment Change & Aircraft Alteration • The total arm is the airplane’s CG and is found by When the equipment in an aircraft is changed, such as the dividing the total moment by the total weight.

installation of a new radar system or ground proximity Moment Weight Arm Item (in-lb) (lb) (inches) Moment Weight Arm Item (in-lb) (lb) (inches) 230,020.0 Empty Weight 2,650 +86.80 230,020.0 Empty Weight 2,650 +86.80 15,390.0 Pilot 180 +85.50 15,390.0 Pilot 180 +85.50 17,955.0 Passenger 210 +85.50 18,896.0 Passenger 160 +118.10 24,801.6 Passenger 160 +155.01 24,801.0 Passenger 210 +118.10 22,439.0 Passenger 190 +118.10 22,439.0 Passenger 190 +118.10 24,210.5 Passenger 205 +118.10 31,918.5 Passenger 205 +155.70 2,250.0 Baggage 100 +22.50 1,125.0 Baggage 50 +22.50 4,467.5 Baggage 25 +178.70 17,870.0 Baggage 100 +178.70 44,928.0 Fuel 480 +93.60 44,928.0 Fuel 480 +93.60 386,461.0 Total 4,200 +92.01 407, 387.50 Total 4,225 +96.42 Figure 6-35. Center of gravity calculation for Piper Seneca with weights shifted. Figure 6-34. Center of gravity calculation for Piper Seneca.

6-21 2 at 125" 2 at 105" 2 at 82"–88" 100 lb at 140" 375 hp FUEL FUEL 95" 102" 75 lb at 60" Maximum weight Minimum weight Forward limit 89" Aft limit 99" Maximum weight Minimum weight Figure 6-36. Example airplane for extreme condition checks.

• The result of the equipment change is that the ballast in the front of the airplane. The logical choice for airplane’s weight was reduced by 22.5 lb and the CG placement of this ballast is the forward baggage compartment.

has moved forward 0.67". The CG for this airplane is 0.6" too far aft. If the forward baggage compartment is used as a temporary ballast location, Use of Ballast the ballast calculation will be as shown in Figure 6-41.

Ballast is used in an aircraft to attain the desired CG balance, Total wt. × dist. needed to shift CG when the CG is not within limits or is not at the location Ballast weight = needed desired by the operator. It is usually located as far aft or as Dist. between ballast and desired CG far forward as possible to bring the CG within limits, while using a minimum amount of weight.

Extreme Condition Forward Check Temporary Ballast Moment Weight Arm Item (in-lb) (lb) (inches) Temporary ballast, in the form of lead bars, heavy canvas bags of sand, or lead shot, is often carried in the baggage 171,032.5 Empty Weight 1,850.0 +92.45 compartments to adjust the balance for certain flight 13,940.0 Pilot 170.0 +82.00 conditions. The bags are marked “Ballast XX Pounds– 13,940.0 Passenger 170.0 +82.00 Removal Requires Weight and Balance Check.” Temporary ballast must be secured so it cannot shift its location in flight, 4,500.0 Baggage 75.0 +60.00 and the structural limits of the baggage compartment must not 17,812.5 Fuel 187.5 +95.00 be exceeded. All temporary ballast must be removed before the aircraft is weighed.

221,225.0 Total 2,452.5 +90.20 Temporary Ballast Formula Extreme Condition Aft Check The CG of a loaded airplane can be moved into its allowable Moment Weight Arm Item range by shifting passengers or cargo or by adding temporary (in-lb) (lb) (inches) ballast. To determine the amount of temporary ballast needed, 171,032.5 Empty Weight 1,850 +92.45 use this formula: 14,960.0 Pilot 170 +88.00 Total wt. × dist. needed to shift CG Ballast weight = 35,700.0 2 Passengers 340 +105.00 needed Dist. between ballast and desired CG 42,500.0 2 Passengers 340 +125.00 Figures 6-36 and 6-40 show an aft adverse-loaded CG check 14,000.0 Baggage 100 +140.00 being performed on an airplane. In this previous example, 23,868.0 Fuel 234 +102.00 the airplane’s CG was out of limits by 0.6". If there were a need or a desire to fly the airplane loaded this way, one way 302,060.5 Total 3,034 +99.60 to make it possible would be the installation of temporary Figure 6-37. Center of gravity extreme conditions check.

6-22 is being placed in the baggage compartment at 3,034 lb × (0.6") an arm of 60". The difference between the two = 39" is 39", the quantity divided by in the formula.

= 46.68 lb Viewed as a first-class lever problem, Figure 6-42 shows what this ballast calculation would look like. A ballast weight When ballast is calculated, the answer should always be of 46.68 lb on the left side of the lever multiplied by the arm rounded up to the next higher whole pound, or in this case, 47 of 39" (99 minus 60) would equal the aircraft weight of 3,034 lb of ballast would be used. To ensure the ballast calculation lb multiplied by the distance the CG is out of limits, which is correct, the weight of the ballast should be plugged back is 0.6" (99.6 minus 99).

into the four-column calculation and a new CG calculated.

Permanent Ballast The aft limit for the airplane was 99", and the new CG is at If a repair or alteration causes the aircraft CG to fall outside 98.96", which puts it within acceptable limits. The new CG of its limit, permanent ballast can be installed. Usually, did not fall exactly at 99" because the amount of needed permanent ballast is made of blocks of lead painted red and ballast was rounded up to the next whole pound. If the ballast marked “Permanent Ballast–Do Not Remove.” It should be could have been placed farther forward, such as being bolted attached to the structure so that it does not interfere with any to the engine firewall, less ballast would have been needed.

control action, and attached rigidly enough that it cannot be That is why ballast is always placed as far away from the dislodged by any flight maneuvers or rough landing. The affected limit as possible.

installation of permanent ballast results in an increase in the aircraft empty weight, and it reduces the useful load.

In evaluating the ballast calculation shown above, the following key points should be recognized.

Three things must be known to determine the amount of • The loaded weight of the aircraft, as identified in the ballast needed to bring the CG within limits: the amount formula, is what the airplane weighed when the CG the CG is out of limits, the distance between the location of was out of limits. the ballast, and the limit that is affected. If an airplane with an empty weight of 1,876 lb has been altered so its EWCG • The distance the CG is out of limits is the difference is +32.2, and CG range for weights up to 2,250 lb is +33.0 between the CG location and the CG limit, in this case to +46.0, permanent ballast must be installed to move the 99.6" minus 99".

EWCG from +32.2 to +33.0. There is a bulkhead at fuselage • The affected limit identified in the formula is the CG station 228 strong enough to support the ballast. To determine limit which has been exceeded. If the CG is too far the amount of ballast needed, use this formula: aft, it is the aft limit that has been exceeded.

Aircraft empty wt. × dist. out of limits • The aft limit for this example is 99", and the ballast Ballast weight = Dist. between ballast and desired CG Airplane empty weight: 2,350 lb 1,876 lb × 0.8" = Airplane EWCG: +24.7" Moment Weight Arm Item Airplane datum: Leading edge of the wing (in-lb) (lb) (inches) Radio installed: 5.8 lb at an arm of –28" 58,045.0 Empty Weight 2,350.0 +24.70 –162.4 Radio Install +5.8 –28.00 Global positioning system installed: 7.3 lb at an arm of –26" –189.8 GPS Install +7.3 –26.00 Emergency locater 294.0 ELT Install +2.8 +105.00 transmitter installed: 2.8 lb at an arm of +105" –105.0 Strobe Remove –1.4 +75.00 Strobe light removed: 1.4 lb at an arm of +75" 84.0 ADF Remove –3.0 –28.00 Automatic direction finder (ADF) removed: 3 lb at an arm of –28" –2,040.0 Seat Remove –34.0 +60.00 Seat removed: 34 lb at an arm of +60" 55,925.8 Total 2,327.5 24.03 Figure 6-39. Center of gravity calculation after equipment change. Figure 6-38. Twin-engine airplane equipment changes.

6-23 228 – 33 Moment Weight Arm Item (in-lb) (lb) (inches) 1,500.8 302,060.5 Loaded Weight 3,034 +99.60 = 2,820.0 Ballast 47 +60.00 = 7.7 lb 304,880.5 Total 3,081 +98.96 A block of lead weighing 7.7 pounds attached to the bulkhead Figure 6-41. Ballast calculation.

at fuselage station 228, moves the EWCG back to its proper forward limit of +33. This block should be painted red and determined, all weights are added and all moments are marked “Permanent Ballast– Do Not Remove.” added. The total weight and moment is then plotted on the CG envelope. [Figure 6-44] The total weight is plotted on the Loading Graphs & CG Envelopes vertical scale of the graph, with a horizontal line projected out The weight and balance computation system, commonly from that point. The total moment is plotted on the horizontal called the loading graph and CG envelope system, is an scale of the graph, with a vertical line projected up from that excellent and rapid method for determining the CG location point. Where the horizontal and vertical plot lines intersect for various loading arrangements. This method can be applied on the graph is the CG for the loaded aircraft. If the point to any make and model of aircraft, but is more often seen where the plot lines intersect falls inside the CG envelope, with small GA aircraft.

the aircraft CG is within limits. In Figure 6-44, there are two CG envelopes, one for the aircraft in the Normal Category Aircraft manufacturers using this method of weight and and one for the aircraft in the Utility Category.

balance computation prepare graphs like those shown in Figures 6-43 and 6-44 for each make and model aircraft The loading graph and CG envelope shown in Figures 6-43 and at the time of original certification. The graphs become 6-44 are for an airplane with the following specifications and a permanent part of the aircraft records and are typically weight and balance data.

found in the AFM/POH. These graphs, used in conjunction • Number of seats: 4 with the empty weight and EWCG data found in the weight and balance report, allow the pilot to plot the CG for the • Fuel capacity (usable): 38 gal of Avgas loaded aircraft.

• Oil capacity: 8 qt (included in empty weight) The loading graph in Figure 6-43 is used to determine the index number (moment value) of any item or weight that may • Baggage: 120 lb be involved in loading the aircraft. To use this graph, find the • Empty weight: 1,400 lb point on the vertical scale that represents the known weight.

• EWCG: 38.5" Project a horizontal line to the point where it intersects the proper diagonal weight line (i.e., pilot, copilot, baggage).

• Empty weight moment: 53,900 in-lb Where the horizontal line intersects the diagonal, project a vertical line downward to determine the loaded moment An example of loading the airplane for flight and calculating (index number) for the weight being added.

the total loaded weight and the total loaded moment is shown After the moment for each item of weight has been Ballast weight of Aircraft weight of Moment Weight Arm Item 46.68 lb at an 3,034 lb at a (in-lb) (lb) (inches) arm of 60 " CG of 99.6 " 171,032.5 Empty Weight 1,850 +92.45 14,960.0 Pilot 170 +88.00 Distance from aft limit to ballast = 39 " 35,700.0 2 Passengers 340 +105.00 0.6 " 42,500.0 2 Passengers 340 +125.00 Distance out of limits 14,000.0 Baggage 100 +140.00 In order to balance at the aft limit of 99", the moment to the left of the fulcrum must equal the moment to the right of the fulcrum. The 23,868.0 Fuel 234 +102.00 moment to the right is the weight of the airplane multiplied by 0.6".

The moment to the left is the ballast weight multiplied by 39".

302,060.5 Total 3,034 +99.60 Figure 6-42. Ballast calculation as a first class lever. Figure 6-40. Extreme condition check.

6-24 in Figures 6-45 and 6-46. The use of the loading graph to and aft of the main rotor mast or centered between the main determine the moment for each of the useful load items is rotors of a dual rotor system. Whereas airplanes have a CG shown in Figure 6-46. The color used for each useful load range only along the longitudinal axis, helicopters have both item in Figure 6-45 matches the color used for the plot on longitudinal and lateral CG ranges. Because the wings extend the loading graph. outward from the CG, airplanes tend to have a great deal of lateral stability. A helicopter, on the other hand, acts like a The total loaded weight of the airplane is 2,258 lb and the pendulum, with the weight of the helicopter hanging from total loaded moment is 99,400 in-lb. These two numbers can the main rotor shaft.

now be plotted on the CG envelope to see if the airplane is within CG limits. Figure 6-47 shows the CG envelope with Ideally, the helicopter should have such perfect balance the loaded weight and moment of the airplane plotted. The that the fuselage remains horizontal while in a hover. If CG location shown falls within the normal category envelope, the helicopter is too nose heavy or tail heavy while it is so the airplane is within CG limits for this category. hovering, the cyclic pitch control is used to keep the fuselage horizontal. If the CG location is too extreme, it may not be It is interesting to note that the lines that form the CG possible to keep the fuselage horizontal or maintain control envelope are graphic plots of the forward and aft CG limits. of the helicopter.

In Figure 6-47, the red line is a graphic plot of the forward limit, and the blue and green lines are graphic plots of the Helicopter Weighing aft limit for the two different categories. When a helicopter is being weighed, the location of both longitudinal and lateral weighing points must be known to determine its empty weight and EWCG. This is because Helicopter Weight & Balance helicopters have longitudinal and lateral CG limits. As with General Concepts the airplane, the longitudinal arms are measured from the All the terminology and concepts that apply to airplane datum, with locations behind the datum being positive arms weight and balance also apply generally to helicopter weight and locations in front of the datum being negative arms.

and balance. However, there are some specific differences Laterally, the arms are measured from the butt line, which is that need to be identified.

a line from the nose to the tail running through the middle of the helicopter. When facing forward, arms to the right of the Most helicopters have a much more restricted CG range butt line are positive; to the left they are negative.

than airplanes. In some cases, this range is less than 3". The exact location and length of the CG range is specified for Before a helicopter is weighed, it must be leveled each helicopter and usually extends a short distance fore longitudinally and laterally. This can be done with a spirit Rear Passenger Load Weight (lb) Fuel Pilot & Front Passenger Baggage 40 Oil −2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Moment Index (Moment/1,000) Figure 6-43. Aircraft loading graph.

6-25 2,400 Normal Category 2,300 2,200 2,100 2,000 1,900 1,800 Load Aircraft Weight (lb) 1,700 Utility Category 1,600 1,500 50 55 60 65 70 75 80 85 90 95 100 105 110 115 Loaded Aircraft Moment/1,000 (in-lb) Figure 6-44. CG envelope.

level, but often it is done with a plumb bob. For example, As an example of weighing a helicopter, consider the Bell the Bell JetRanger has a location inside the aft cabin where a JetRanger in Figure 6-48 , and the following specifications plumb can be attached and allowed to hang down to the cabin and weighing data shown in Figure 6-49.

floor. On the cabin floor is a plate bearing cross hairs that correspond to the horizontal and lateral axis of the helicopter. Using six-column charts for the calculations, the empty When the point of the plumb bob falls in the middle of the weight and the longitudinal and lateral CG for the helicopter cross hairs, the helicopter is level along both axes. If the tip is shown in Figure 6-50. Based on the calculations in of the plumb bob falls forward of this point, the nose of the Figure 6-50, it has been determined that the empty weight of helicopter is too low; if it falls to the left of this point, the left the helicopter is 1,985 lb, the longitudinal CG is at +108.73", side of the helicopter is too low. In other words, the tip of the and the lateral CG is at –0.31".

plumb bob always moves toward the low point.

Weight and Balance— Weight-Shift Control Aircraft and Powered Parachutes A Bell JetRanger helicopter is shown in Figure 6-48 with the leveling plate depicted on the bottom right of the figure.

The terminology, theory, and concepts of weight and balance The helicopter has three jack pads, two at the front and one that applies to airplanes also applies to weight-shift control in the back. To weigh this helicopter, three jacks would be aircraft and powered parachutes. Weight is still weight, and placed on floor scales, and the helicopter would be raised off the balance point is still the balance point. However, there are the hangar floor. To level the helicopter, the jacks would be a few differences that need to be discussed. Before reading adjusted until the plumb bob point falls exactly in the middle about the specifics of weight and balance on weight-shift of the cross hairs.

control aircraft and powered parachutes, be sure to read about their aerodynamic characteristics in Chapter 5, Physics.

Weight-shift control aircraft and powered parachutes do not Weight (lb) Item Moment (in-lb) fall under the same Code of Federal Regulations that govern certified airplanes and helicopters and, therefore, do not have 1,400 Aircraft Empty Weight 53,900 TCDS or the same type of FAA-mandated weight and balance 180 Pilot 6,000 reports. Weight and balance information and guidelines are left to the individual owners and the companies with which 140 Front Passengers 4,500 they work in acquiring this type of aircraft. Overall, the 210 Rear Passengers 15,000 industry that is supplying these aircraft is regulating itself 100 Baggage 9,200 well, and the safety record is good for those aircraft being operated by experienced pilots.

228 Fuel 10,800 2,258 Total 99,400 Figure 6-45. Aircraft load chart.

6-26 Rear Passenger Pilot & Front Passenger Fuel 160 Load Weight (lb) Baggage Oil −2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Moment Index (Moment/1,000) Figure 6-46. Example plots on a loading graph.

Weight-Shift Control Aircraft the weight of the aircraft is hanging like a pendulum under the wing. Figure 6-51 shows a two-place trike, in which the Weight-shift control aircraft, commonly known by the name mast and the nose strut come together slightly below the “trikes,” have very few options for loading, because they have wing attach point. When the trike is in flight, the weight of very few places to put useful load items. Some trikes have the aircraft is hanging from the wing attach point. The weight only one seat and a fuel tank, so the only variables for a flight of the engine and fuel is behind this point, the passenger is are amount of fuel and weight of the pilot. Some trikes have almost directly below this point, and the pilot is forward of two seats and a small storage bin in addition to the fuel tank.

this point. The balance of the aircraft is determined by how all these weights compare.

The most significant factor affecting the weight and balance of a trike is the weight of the pilot; if the aircraft has two seats, The wing attach point, with respect to the wing keel, is an the weight of the passenger must be considered. The trike adjustable location. The attach point can be loosened and acts somewhat like a single main rotor helicopter because 2,400 Normal Category 2,300 2,200 2,100 CG Location Forward Limit 2,000 1,900 1,800 Load Aircraft Weight (lb) 1,700 Aft Limit Utility Category 1,600 1,500 50 55 60 65 70 75 80 85 90 95 100 105 110 115 Loaded Aircraft Moment/1,000 (in-lb) Figure 6-47. CG envelope example plot.

6-27 moved slightly forward or slightly aft, depending on the Mean Aerodynamic Chord weight of the occupants. For example, if the aircraft is flown On small airplanes and on all helicopters, the CG location by a person that weighs more, the attach point can be moved is identified as being a specific number of inches from the a little farther aft, bringing the wing forward, to compensate datum. The CG range is identified the same way. On larger for the change in CG. Figure 6-52 shows a close-up of the airplanes, from private business jets to large jumbo jets, the wing attach point, and the small amount of forward and aft CG and its range are typically identified in relation to the movement that is available.

width of the wing.

Powered Parachutes The width of the wing on an airplane is known as the chord.

Powered parachutes have many of the same characteristics If the leading edge and trailing edge of a wing are parallel to as weight-shift aircraft when it comes to weight and balance.

each other, the chord of the wing is the same along the wing’s They have the same limited loading, with only one or two seats length. Business jets and commercial transport airplanes and a fuel tank. They also act like a pendulum, with the weight have wings that are tapered and that are swept back, so the of the aircraft hanging beneath the inflated wing (parachute).

width of their wings is different along their entire length.

The width is greatest where the wing meets the fuselage The point at which the inflated wing attaches to the structure and progressively decreases toward the tip. In relation to the of the aircraft is adjustable to compensate for pilots and aerodynamics of the wing, the average length of the chord passengers of varying weights. With a very heavy pilot, the on these tapered swept-back wings is known as the mean wing attach point would be moved forward to prevent the aerodynamic chord (MAC).

aircraft from being too nose heavy. Figure 6-53 shows the structure of a powered parachute with the adjustable wing On these larger airplanes, the CG is identified as being at a attach points.

location that is a specific percent of the mean aerodynamic chord (% MAC). For example, imagine that the MAC on Weight & Balance for Large Airplanes an airplane is 100", and the CG falls 20" behind the leading Weight and balance for large airplanes is almost identical edge of the MAC. That means it falls one-fifth of the way to what it is for small airplanes, on a much larger scale. If a back, or at 20 percent of the MAC.

technician can weigh a small airplane and calculate its empty weight and EWCG, that same technician should be able to Figure 6-54 shows a large twin-engine commercial transport do it for a large airplane. The jacks and scales are larger, and airplane. The datum is forward of the nose of the airplane, it may take more personnel to handle the equipment, but the and all the arms are being measured from that point. The CG concepts and processes are the same.

for the airplane is shown as an arm measured in inches. In the lower left corner of the figure, a cross section of the wing Built-In Electronic Weighing is shown, with the same CG information being presented.

One difference that may be found with large airplanes is the incorporation of electronic load cells in the aircraft’s landing To convert the CG location from inches to a percent of MAC, gear. With this type of system, the airplane can weigh itself as for the airplane shown in Figure 6-54, the steps are as follows: it sits on the tarmac. The load cells are built into the axles of 1. Identify the CG location, in inches from the datum.

the landing gear, or the landing gear strut, and they work in 2. Identify the leading edge of the MAC (LEMAC), in the same manner as load cells used with jacks. This system is inches from the datum.

currently in use on the Boeing 747-400, Boeing 777, Boeing 787, McDonnell Douglas MD-11, and the wide body Airbus 3. Subtract LEMAC from the CG location.

airplanes like the A-330, A-340, and A-380.

4. Divide the difference by the length of the MAC.

5. Convert the result in decimals to a percentage by The Boeing 777 utilizes two independent systems that multiplying by 100.

provide information to the airplane’s flight management As a formula, the solution to solve for the percent of MAC system (FMS). If the two systems agree on the weight and would be: CG of the airplane, the data being provided are considered accurate and the airplane can be dispatched based on that CG – LEMAC information. The flight crew has access to the information Percent of MAC = × 100 MAC on the flight deck by accessing the FMS and bringing up the weight and balance page.

The result using the numbers shown in Figure 6-52 would be: CG – LEMAC Percent of MAC = × 100 MAC 6-28 Forward ballast station +13" Aft ballast station +377" Plumb bob Aft jack point Datum +204.92" Tail Right side Leveling plate +117.7" Nose Forward jack point +55.16" +25" and −25" laterally Left side Leveling plate with crosshairs Figure 6-48. Bell JetRanger.

55.16" forward of the front jack point Datum: Left Front 650 lb centerline Scale Reading: Plumb line from ceiling left rear cabin to Leveling Means: Left Front Longitudinal arm of +55.16" index plate on floor Jack Point: Lateral arm of –25" +106" to +111.4" at 3,200 lb Longitudinal CG Right Front 625 lb +106" to +112.1" at 3,000 lb Limits: Scale Reading: +106" to +112.4" at 2,900 lb +106" to +113.4" at 2,600 lb Right Front Longitudinal arm of +55.16" +106" to +114.2" at 2,350 lb Jack Point: Lateral arm of +25" +106" to +114.2" at 2,100 lb Straight line variation between points After Scales 710 lb Reading: 2.3" left to 3.0" right at longitudinal CG Lateral CG + 106.0" Limits: Aft Jack Point: Longitudinal arm of +204.92" 3.0" left to 4.0" right at longitudinal CG Lateral arm of 0.0" +108" to +114.2" Straight line variation between points Notes: The helicopter was weighed with unusable fuel and oil. Electronic scales were used Empty weight includes unusable fuel Fuel and Oil: and zeroed with the jacks in place, so no and unusable oil tare weight needs to be accounted for.

Figure 6-49. Specifications and weighing data for Bell JetRanger.

6-29 Longitudinal CG Calculation Item Scale (lb) Tare Wt. (lb) Nt. Wt. (lb) Arm (inches) Moment (in-lb) Left Front 650 0 650 +55.16 35,854.0 Right Front 625 0 625 +55.16 34,475.0 Aft 710 0 710 +204.92 145,493.2 Total 1,985 1,985 +108.73 215,822.2 Lateral CG Calculation Item Scale (lb) Tare Wt. (lb) Nt. Wt. (lb) Arm (inches) Moment (in-lb) Left Front 650 0 650 −25 −16,250 Right Front 625 0 625 +25 +15,625 Aft 710 0 710 0 0 Total 1,985 1,985 +.31 −625 Figure 6-50. Center of gravity calculation for Bell JetRanger.

Wing attachment point adjustable for CG Wing attachment point adjustable for CG Figure 6-51. Weight and balance for a weight-shift control aircraft.

Nosewheel steering Throttle Pivot bar to control turning Figure 6-53. Powered parachute structure with wing attach points.

= 25 percent If the CG is known in percent of MAC, and there is a need to know the CG location in inches from the datum, the conversion would be done as follows: Figure 6-52. Wing attach point for a weight-shift control aircraft.

1. Convert the percent of MAC to a decimal by dividing by 100.

2. Multiply the decimal by the length of the MAC.

945 – 900 = × 100 6-30 Center of gravity 945" Trailing edge of MAC 1,080" MAC=180" Leading edge of MAC 900" Datum CG at 945" LEMAC 900" 45" Chord line MAC = 180" Figure 6-54. Center of gravity location on a large commercial transport.

3. Add this number to LEMAC. checks, how much ballast is needed, or the loaded weight and balance of the aircraft. Calculating the empty weight As a formula, the solution to convert a percent of MAC to and EWCG might involve putting the aircraft on scales and an inch value would be: weighing it, or a pencil and paper exercise after installing a new piece of equipment.

CG in inches = % MAC ÷ 100 × MAC + LEMAC The FAA requires that a current and accurate empty weight For the airplane in Figure 6-54, if the CG was at 32.5 percent and EWCG be known for an aircraft. This information must of the MAC, the solution would be: be included in the weight and balance report, which is a part of the aircraft permanent records. The weight and balance CG in inches = % MAC ÷ 100 × MAC + LEMAC report must be in the aircraft when it is being flown.

= 32.5 ÷ 100 × 180 + 900 = 958.5 There is no required format for this report, but Figure 6-55 is a good example of recording the data obtained from Weight & Balance Records weighing an aircraft. As it is currently laid out, the form would accommodate either a tricycle gear or tail dragger When a technician gets involved with the weight and balance airplane. Depending on the gear type, either the nose or the of an aircraft, it almost always involves a calculation of the tail row would be used. If an airplane is being weighed using aircraft’s empty weight and EWCG. Only on rare occasions jacks and load cells, or if a helicopter is being weighed, the are technicians involved in calculating adverse-loading CG 6-31

Aircraft Weight and Balance Report

Results of Aircraft Weighing

Make Model Serial # N# Datum Location Leveling Means Scale Arms: Nose Tail Left Main Right Main Scale Weights: Nose Tail Left Main Right Main Tare Weights: Nose Tail Left Main Right Main

Weight and Balance Calculation

Item Scale (lb) Tare Wt. (lb) Net Wt. (lb) Arm (inches) Moment (in-lb) Nose Tail Left Main Right Main Subtotal Fuel Oil Misc.

Total Aircraft Current Empty Weight: Aircraft Current Empty Weight CG: Aircraft Maximum Weight: Aircraft Useful Load: Computed By: (print name) (signature) Certificate #: (A&P, Repair Station, etc.)

Date: Figure 6-55. Aircraft weight and balance report.

6-32 item names must be changed to reflect the weight locations.

If an equipment change is being done on an aircraft, and the new weight and balance is calculated mathematically instead of weighing the aircraft, the same type of form shown in Figure 6-55 can be used. The only change would be the use of a four-column solution, instead of six columns, and there would be no tare weight or involvement with fuel and oil.

6-33

Next: Chapter 7 →

Chapter 7

Aircraft Materials, Hardware, &

Processes

Aircraft Metals Malleability Knowledge and understanding of the uses, strengths, limitations, and other characteristics of structural metals A metal that can be hammered, rolled, or pressed into various is vital to properly construct and maintain any equipment, shapes without cracking, breaking, or leaving some other especially airframes. In aircraft maintenance and repair, detrimental effect, is said to be malleable. This property is even a slight deviation from design specification, or the necessary in sheet metal that is worked into curved shapes, substitution of inferior materials, may result in the loss of such as cowlings, fairings, or wingtips. Copper is an example both lives and equipment. The use of unsuitable materials can of a malleable metal.

readily erase the finest craftsmanship. The selection of the correct material for a specific repair job demands familiarity Ductility with the most common physical properties of various metals.

Ductility is the property of a metal that permits it to be permanently drawn, bent, or twisted into various shapes Properties of Metals without breaking. This property is essential for metals used in Of primary concern in aircraft maintenance are such general making wire and tubing. Ductile metals are greatly preferred properties of metals and their alloys as hardness, malleability, for aircraft use because of their ease of forming and resistance ductility, elasticity, toughness, density, brittleness, fusibility, to failure under shock loads. For this reason, aluminum alloys conductivity contraction and expansion, and so forth. These are used for cowl rings, fuselage and wing skin, and formed terms are explained to establish a basis for further discussion or extruded parts, such as ribs, spars, and bulkheads. Chrome of structural metals.

molybdenum steel is also easily formed into desired shapes.

Ductility is similar to malleability.

Hardness Hardness refers to the ability of a material to resist abrasion, Elasticity penetration, cutting action, or permanent distortion. Hardness Elasticity is a property that enables a metal to return to may be increased by cold-working the metal and, in the case its original size and shape when the force that causes the of steel and certain aluminum alloys, by heat-treatment.

change of shape is removed. This property is extremely Structural parts are often formed from metals in their soft valuable, because it would be highly undesirable to have state and are then heat-treated to harden them so that the a part permanently distorted after an applied load was finished shape is retained. Hardness and strength are closely removed. Each metal has a point known as the elastic limit, associated properties of metals.

beyond which it cannot be loaded without causing permanent distortion. In aircraft construction, members and parts are so Strength designed that the maximum loads to which they are subjected One of the most important properties of a material is strength. do not stress them beyond their elastic limits. This desirable Strength is the ability of a material to resist deformation. property is present in spring steel.

Strength is also the ability of a material to resist stress without breaking. The type of load or stress on the material affects Toughness the strength it exhibits.

A material that possesses toughness withstands tearing or shearing and may be stretched or otherwise deformed without Density breaking. Toughness is a desirable property in aircraft metals.

Density is the weight of a unit volume of a material. In aircraft work, the specified weight of a material per cubic Brittleness inch is preferred since this figure can be used in determining Brittleness is the property of a metal that allows little bending the weight of a part before actual manufacture. Density is or deformation without shattering. A brittle metal is apt to an important consideration when choosing a material to be break or crack without change of shape. Because structural used in the design of a part to maintain the proper weight metals are often subjected to shock loads, brittleness is not a and balance of the aircraft.

7-1 very desirable property. Cast iron, cast aluminum, and very by the Society of Automotive Engineers (SAE) and the hard steel are examples of brittle metals. American Iron and Steel Institute (AISI), is used to identify the chemical compositions of the structural steels. In this system, a four-numeral series is used to designate the plain Fusibility carbon and alloy steels; five numerals are used to designate Fusibility is the ability of a metal to become liquid by certain types of alloy steels. The first two digits indicate the the application of heat. Metals are fused in welding.

type of steel, the second digit also generally (but not always) Steels fuse around 2,600 °F and aluminum alloys at gives the approximate amount of the major alloying element, approximately 1,100 °F.

and the last two (or three) digits are intended to indicate the approximate middle of the carbon range. However, a Conductivity deviation from the rule of indicating the carbon range is Conductivity is the property that enables a metal to carry heat sometimes necessary.

or electricity. The heat conductivity of a metal is especially important in welding, because it governs the amount of heat Small quantities of certain elements are present in alloy that is required for proper fusion. Conductivity of the metal, steels that are not specified as required. These elements are to a certain extent, determines the type of jig to be used to considered as incidental and may be present to the maximum control expansion and contraction. In aircraft, electrical amounts as follows: copper, 0.35 percent; nickel, 0.25 conductivity must also be considered in conjunction with percent; chromium, 0.20 percent; molybdenum, 0.06 percent.

bonding to eliminate radio interference.

The list of standard steels is altered from time to time to accommodate steels of proven merit and to provide for Thermal Expansion changes in the metallurgical and engineering requirements Thermal expansion refers to contraction and expansion that of industry. [Figure 7-1] are reactions produced in metals as the result of heating or cooling. Heat applied to a metal causes it to expand or become Metal stock is manufactured in several forms and shapes, larger. Cooling and heating affect the design of welding jigs, including sheets, bars, rods, tubing, extrusions, forgings, castings, and tolerances necessary for hot rolled material.

and castings. Sheet metal is made in a number of sizes and thicknesses. Specifications designate thicknesses in Ferrous Aircraft Metals thousandths of an inch. Bars and rods are supplied in a variety Many different metals are required in the repair of aircraft.

of shapes, such as round, square, rectangular, hexagonal, and This is a result of the varying needs with respect to strength, octagonal. Tubing can be obtained in round, oval, rectangular, weight, durability, and resistance to deterioration of specific or streamlined shapes. The size of tubing is generally structures or parts. In addition, the particular shape or form of specified by outside diameter and wall thickness.

the material plays an important role. In selecting materials for aircraft repair, these factors (plus many others) are considered The sheet metal is usually formed cold in machines, such as in relation to the mechanical and physical properties. Among presses, bending brakes, draw benches, or rolls. Forgings are the common materials used are ferrous metals. The term shaped or formed by pressing or hammering heated metal “ferrous” applies to the group of metals having iron as their in dies. Pouring molten metal into molds produces castings.

principal element.

Machining finishes the casting.

Iron Spark testing is a common means of identifying various If carbon is added to iron in percentages ranging up to ferrous metals. In this test, the piece of iron or steel is held approximately 1 percent, the product is vastly superior to iron against a revolving grinding stone, and the metal is identified alone and is classified as carbon steel. Carbon steel forms by the sparks thrown off. Each ferrous metal has its own the base of those alloy steels produced by combining carbon peculiar spark characteristics. The spark streams vary from steel with other elements known to improve the properties of a few tiny shafts to a shower of sparks several feet in length.

steel. A base metal (such as iron) to which small quantities of (Few nonferrous metals give off sparks when touched to a other metals have been added is called an alloy. The addition grinding stone. Therefore, these metals cannot be successfully of other metals changes or improves the chemical or physical identified by the spark test.)

properties of the base metal for a particular use.

Identification by spark testing is often inexact unless Steel and Steel Alloys performed by an experienced person or the test pieces differ greatly in their carbon content and alloying elements.

To facilitate the discussion of steels some familiarity with their nomenclature is desirable. A numerical index, sponsored 7-2 Wrought iron produces long shafts that are straw colored as is that cold-working may increase its strength.

they leave the stone and white at the end. Cast iron sparks are red as they leave the stone and turn to a straw color. Stainless steel may be rolled, drawn, bent, or formed to any Low carbon steels give off long, straight shafts having a few shape. Because these steels expand about 50 percent more white sprigs. As the carbon content of the steel increases, the than mild steel and conduct heat only about 40 percent as number of sprigs along each shaft increases and the stream rapidly, they are more difficult to weld. Stainless steel can be becomes whiter in color. Nickel steel causes the spark stream used for almost any part of an aircraft. Some of its common to contain small white blocks of light within the main burst. applications are the fabrication of exhaust collectors, stacks and manifolds, structural and machined parts, springs, Types, Characteristics, and Uses of Alloyed Steels castings, tie rods, and control cables.

Steel containing carbon in percentages ranging from 0.10 to The chrome-vanadium steels are made of approximately 0.30 percent is classed as low carbon steel. The equivalent 18 percent vanadium and about 1 percent chromium. When SAE numbers range from 1010 to 1030. Steels of this grade heat-treated, they have strength, toughness, and resistance to are used for making items, such as safety wire, certain nuts, wear and fatigue. A special grade of this steel in sheet form cable bushings, or threaded rod ends. This steel in sheet can be cold formed into intricate shapes. It can be folded and form is used for secondary structural parts and clamps and flattened without signs of breaking or failure. SAE 6150 is in tubular form for moderately stressed structural parts.

used for making springs; chrome-vanadium with high carbon content, SAE 6195, is used for ball and roller bearings.

Steel containing carbon in percentages ranging from 0.30 to 0.50 percent is classed as medium carbon steel. This steel Molybdenum in small percentages is used in combination is especially adaptable for machining or forging and where with chromium to form chrome-molybdenum steel, which surface hardness is desirable. Certain rod ends and light has various uses in aircraft. Molybdenum is a strong alloying forgings are made from SAE 1035 steel.

element. It raises the ultimate strength of steel without affecting ductility or workability. Molybdenum steels are Steel containing carbon in percentages ranging from 0.50 to tough and wear resistant, and they harden throughout when 1.05 percent is classed as high carbon steel. The addition of heat-treated. They are especially adaptable for welding and, other elements in varying quantities adds to the hardness of for this reason, are used principally for welded structural this steel. In the fully heat-treated condition, it is very hard, parts and assemblies. This type steel has practically replaced withstands high shear and wear, and has little deformation. It carbon steel in the fabrication of fuselage tubing, engine has limited use in aircraft. SAE 1095 in sheet form is used for mounts, landing gears, and other structural parts. For example, making flat springs and in wire form for making coil springs.

a heat-treated SAE X4130 tube is approximately four times as strong as an SAE 1025 tube of the same weight and size.

The various nickel steels are produced by combining nickel with carbon steel. Steels containing from 3 to 3.75 percent A series of chrome-molybdenum steel most used in aircraft nickels are commonly used. Nickel increases the hardness, construction is that series containing 0.25 to 0.55 percent tensile strength, and elastic limit of steel without appreciably carbon, 0.15 to 0.25 percent molybdenum, and 0.50 to 1.10 decreasing the ductility. It also intensifies the hardening effect percent chromium. These steels, when suitably heat-treated, of heat-treatment. SAE 2330 steel is used extensively for are deep hardening, easily machined, readily welded by either aircraft parts, such as bolts, terminals, keys, clevises, and pins.

gas or electric methods, and are especially adapted to high temperature service.

Chromium steel is high in hardness, strength, and corrosion- resistant properties and is particularly adaptable for heat-treated Inconel is a nickel-chromium-iron alloy closely resembling forgings, which require greater toughness and strength than stainless steel (corrosion resistant steel (CRES)) in may be obtained in plain carbon steel. It can be used for articles appearance. Aircraft exhaust systems use both alloys such as the balls and rollers of antifriction bearings. Chrome- interchangeably. Because the two alloys look very much nickel or stainless steels are the corrosion resistant metals.

alike, a distinguishing test is often necessary. One method The anticorrosive degree of this steel is determined by the of identification is to use an electrochemical technique, as surface condition of the metal, as well as by the composition, described in the following paragraph, to identify the nickel temperature, and concentration of the corrosive agent. The (Ni) content of the alloy. Inconel has nickel content greater principal alloy of stainless steel is chromium. The corrosion than 50 percent, and the electrochemical test detects nickel.

resistant steel most often used in aircraft construction is known as 18-8 steel because its content is 18 percent chromium and The tensile strength of Inconel is 100,000 pounds per square 8 percent nickel. One of the distinctive features of 18-8 steel 7-3 Series Designation Types 10xx Non-sulfurized carbon steels 11xx Resulfurized carbon steels (free machining) 12xx Rephosphorized and resulfurized carbon steels (free machining) 13xx Manganese 1.75% *23xx Nickel 3.50% *25xx Nickel 5.00% 31xx Nickel 1.25%, chromium 0.65% 33xx Nickel 3.50%, chromium 1.55% 40xx Molybdenum 0.20 or 0.25% 41xx Chromium 0.50% or 0.95%, molybdenum 0.12 or 0.20% 43xx Nickel 1.80%, chromium 0.5 or 0.80%, molybdenum 0.25% 44xx Molybdenum 0.40% 45xx Molybdenum 0.52% 46xx Nickel 1.80%, molybdenum 0.25% 47xx Nickel 1.05% chromium 0.45%, molybdenum 0.20 or 0.35% 48xx Nickel 3.50%, molybdenum 0.25% 50xx Chromium 0.25, or 0.40 or 0.50% 50xxx Carbon 1.00%, chromium 0.50% 51xx Chromium 0.80, 0.90, 0.95 or 1.00% 51xxx Carbon 1.00%, chromium 1.05% 52xxx Carbon 1.00%, chromium 1.45% 61xx Chromium 0.60, 0.80, 0.95%, vanadium 0.12%, 0.10% min., or 0.15% min.

81xx Nickel 0.30%, chromium 0.40%, molybdenum 0.12% 86xx Nickel 0.55%, chromium 0.50%, molybdenum 0.20% 87xx Nickel 0.55%, chromium 0.05%, molybdenum 0.25% 88xx Nickel 0.55%, chromium 0.05%, molybdenum 0.35% 92xx Manganese 0.85%, silicon 2.00%, chromium 0 or 0.35% 93xx Nickel 3.25%, chromium 1.20%, molybdenum 0.12% 94xx Nickel 0.45%, chromium 0.40%, molybdenum 0.12% 98xx Nickel 1.00%, chromium 0.80%, molybdenum 0.25% *Not included in the current list of standard steels Figure 7-1. SAE numerical index.

inch (psi) annealed, and 125,000 psi when hard rolled. It is Electrochemical Test highly resistant to salt water and can withstand temperatures Prepare a wiring assembly as shown in Figure 7-2 , and prepare as high as 1,600 °F. Inconel welds readily and has working the two reagents (ammonium fluoride and dimethylglyoxime qualities like those of corrosion resistant steels.

solutions) placing them in separate dedicated dropper solution 7-4 bottles. Before testing, you must thoroughly clean the metal for Aluminum is one of the most widely used metals in modern the electrolytic deposit to take place. You may use nonmetallic aircraft construction. It is vital to the aviation industry because hand scrubbing pads or 320–600 grit “crocus cloth” to remove of its high strength-to-weight ratio and its comparative ease deposits and corrosion products (thermal oxide). of fabrication. The outstanding characteristic of aluminum is its lightweight. Aluminum melts at the comparatively low Connect the alligator clip of the wiring assembly to the bare temperature of 1,250 °F. It is nonmagnetic and is an excellent metal being tested. Place one drop of a 0.05 percent reagent conductor.

grade ammonium fluoride solution in deionized water on the center of a 1 inch × 1 inch sheet of filter paper. Lay the Commercially pure aluminum has a tensile strength of about moistened filter paper over the bare metal alloy being tested. 13,000 psi, but rolling or other cold-working processes Firmly press the end of the aluminum rod over the center may approximately double its strength. By alloying with of the moist paper. Maintain connection for 10 seconds other metals, or by using heat-treating processes, the tensile while rocking the aluminum rod on the filter paper. Ensure strength may be raised to as high as 65,000 psi or to within that the light emitting diode (LED) remains lit (indicating the strength range of structural steel.

good electrical contact and current flow) during this period.

Disconnect the wiring assembly and set it aside. Remove Aluminum alloys, although strong, are easily worked because the filter paper and examine it to determine that a light spot they are malleable and ductile. They may be rolled into appears where the connection was made. sheets as thin as 0.0017 inch or drawn into wire 0.004 inch in diameter. Most aluminum alloy sheet stock used in aircraft Deposit one drop of 1.0 percent solution of reagent grade construction range from 0.016 to 0.096 inch in thickness; dimethylglyoxime in ethyl alcohol on the filter paper (same however, some of the larger aircraft use sheet stock that may side that was in contact with the test metal). A bright, be as thick as 0.356 inch.

distinctly pink spot will appear within seconds on the filter paper if the metal being tested is Inconel. A brown spot will The various types of aluminum may be divided into two appear if the test metal is stainless steel. Some stainless-steel general classes: alloys may leave a very light pink color. However, the shade • Casting alloys (those suitable for casting in sand, and depth of color will be far less than would appear for permanent mold, or die castings) Inconel. For flat surfaces, the test spot will be circular while • Wrought alloys (those which may be shaped by rolling, for curved surfaces, such as the outside of a tube or pipe, drawing, or forging).

the test spot may appear as a streak. (Refer to Figure 7-3 for sample test results.) This procedure should not be used in the Of these two, the wrought alloys are the most widely used heat-affected zone of weldments or on nickel coated surfaces.

in aircraft construction, being used for stringers, bulkheads, skin, rivets, and extruded sections.

Nonferrous Aircraft Metals The term “nonferrous” refers to all metals that have elements Aluminum casting alloys are divided into two basic groups.

other than iron as its base or principal constituent. This In one, the physical properties of the alloys are determined group includes metals, such as aluminum, titanium, copper, by the alloying elements and cannot be changed after the and magnesium, as well as alloyed metals, such as Monel metal is cast. In the other, the alloying elements make it and Babbitt.

LED 9v battery Aluminum & Aluminum Alloys − + Commercially pure aluminum is a white lustrous metal, which stands second in the scale of malleability, sixth in ductility, and ranks high in its resistance to corrosion.

Aluminum combined with various percentages of other metals forms alloys, which are used in aircraft construction.

Aluminum alloys with principal alloying ingredients are manganese, chromium, or magnesium and silicon show little attack in corrosive environments. Alloys with which substantial percentages of copper are more susceptible to corrosive action. The total percentage of alloying elements Aluminum rod stock Alligator clip is seldom more than 6 or 7 percent in the wrought alloys.

Figure 7-2. Wiring assembly schematic.

7-5 possible to heat-treat the casting to produce the desired material from which the molds are made. The advantage of physical properties. this process is that there are fewer openings (called porosity) than in sand castings. The sand and the binder, which is mixed A letter preceding the alloy number identifies the casting with the sand to hold it together, give off a certain amount of alloys. When a letter precedes a number, it indicates a slight gas, that causes porosity in a sand casting.

variation in the composition of the original alloy. This variation in composition is simply to impart some desirable Permanent mold castings are used to obtain higher quality. For example, in casting alloy 214, the addition of zinc mechanical properties, better surfaces, or more accurate to improve its pouring qualities is indicated by the letter A dimensions. There are two specific types of permanent in front of the number, thus creating the designation A214. mold castings: permanent metal mold with metal cores, and semi-permanent types containing sand cores. Because finer When castings have been heat-treated, the heat-treatment grain structure is produced in alloys subjected to the rapid and the composition of the casting is indicated by the letter cooling of metal molds, they are far superior to the sand type T, followed by an alloying number. An example of this castings. Alloys 122, A132, and 142 are commonly used in is the sand casting alloy 355, which has several different permanent mold castings, the principal uses of which are in compositions and tempers and is designated by 355-T6, internal combustion engines.

355-T51, or C355-T51.

Die-castings used in aircraft are usually aluminum or Aluminum alloy castings are produced by one of three basic magnesium alloy. If weight is of primary importance, methods: sand mold, permanent mold, or die cast. In casting magnesium alloy is used, because it is lighter than aluminum aluminum, it is important to note that in most cases different alloy. However, aluminum alloy is frequently used because types of alloys must be used for different types of castings. it is stronger than most magnesium alloys.

Sand castings and die-castings require different types of alloys than those used in permanent molds. Forcing molten metal under pressure into a metallic die and allowing it to solidify produces a die-casting; then the die is Sand and permanent mold castings are parts produced by opened and the part removed. The basic difference between pouring molten metal into a previously prepared mold, permanent mold casting and die-casting is that in the permanent allowing the metal to solidify or freeze and then removing the mold process, the metal flows into the die under gravity. In the part. If the mold is made of sand, the part is a sand casting; if die-casting operation, the metal is forced under great pressure.

it is a metallic mold (usually cast iron), the part is a permanent mold casting. Sand and permanent castings are produced by Die-castings are used where relatively large production of pouring liquid metal into the mold, the metal flowing under a given part is involved. Remember, any shape that can be the force of gravity alone. forged, can be cast.

The two principal types of sand casting alloys are 112 and Wrought aluminum and wrought aluminum alloys are divided 212. Little difference exists between the two metals in into two general classes: non-heat-treatable alloys and heat- mechanical properties, since both are adaptable to a wide treatable alloys.

range of products.

Non-heat-treatable alloys are those in which the mechanical The permanent mold process is a later development of the properties are determined by the amount of cold-work sand casting process, the major difference being in the introduced after the final annealing operation. The mechanical properties obtained by cold-working are destroyed by any subsequent heating and cannot be restored except by additional cold-working, which is not always possible. The “full hard” temper is produced by the maximum amount of cold-work that is commercially practicable. Metal in the “as fabricated” condition is produced from the ingot without any subsequent controlled amount of cold-working or thermal treatment. There is, consequently, a variable amount of strain hardening depending upon the thickness of the section.

For heat-treatable aluminum alloys, the mechanical properties Figure 7-3. Electrochemical test results of Inconel (In) and stainless are obtained by heat-treating to a suitable temperature, steel (SS) alloys.

7-6 holding at that temperature long enough to allow the alloying the group. [Figure 7-4] constituent to enter into solid solution, and then quenching to hold the constituent in solution. The metal is left in a Effect of Alloying Element supersaturated, unstable state and is then age hardened either 1000 series: 99 percent aluminum or higher, excellent by natural aging at room temperature or by artificial aging at corrosion resistance, high thermal and electrical conductivity, some elevated temperature.

low mechanical properties, excellent workability. Iron and silicon are major impurities.

Wrought Aluminum Wrought aluminum and wrought aluminum alloys are 2000 series: Copper is the principal alloying element.

designated by a four-digit index system. The system is broken Solution heat-treatment, optimum properties equal to mild into three distinct groups: 1xxx group, 2xxx through 8xxx steel, poor corrosion resistance unclad. It is usually clad group, and 9xxx group (which is currently unused). with 6000 or high purity alloy. Its best-known alloy is 2024.

The first digit of a designation identifies the alloy type. The 3000 series: Manganese is the principal alloying element second digit indicates specific alloy modifications. Should the of this group, which is generally non-heat-treatable. The second number be zero, it would indicate no special control percentage of manganese that is alloy effective is 1.5 percent.

over individual impurities. Digits 1 through 9, however, when The most popular is 3003, which is of moderate strength and assigned consecutively as needed for the second number in has good working characteristics.

this group, indicate the number of controls over individual impurities in the metal. 4000 series: Silicon is the principal alloying element of this group and lowers melting temperature. Its primary The last two digits of the 1xxx group are used to indicate use is in welding and brazing. When used in welding heat- the hundredths of 1 percent above the original 99 percent treatable alloys, this group responds to a limited amount designated by the first digit. Thus, if the last two digits were of heat-treatment.

30, the alloy would contain 99 percent plus 0.30 percent of pure aluminum, or a total of 99.30 percent pure aluminum. 5000 series: Magnesium is the principal alloying element.

Examples of alloys in this group are: It has good welding and corrosion resistant characteristics.

High temperatures (over 150 °F) or excessive cold-working • 1100—99.00 percent pure aluminum with one control increases susceptibility to corrosion.

over individual impurities.

• 1130—99.30 percent pure aluminum with one control 6000 series: Silicon and magnesium form magnesium over individual impurities.

silicide, which makes alloys heat-treatable. It is of medium strength, good forming qualities, and has corrosion • 1275—99.75 percent pure aluminum with two controls resistant characteristics.

over individual impurities.

7000 series: Zinc is the principal alloying element. The In the 2xxx through 8xxx groups, the first digit indicates the major most popular alloy of the series is 6061. When coupled with alloying element used in the formation of the alloy as follows: magnesium, it results in heat-treatable alloys of very high • 2xxx—copper strength. It usually has copper and chromium added. The • 3xxx—manganese principal alloy of this group is 7075.

• 4xxx—silicon Hardness Identification • 5xxx—magnesium Where used, the temper designation follows the alloy • 6xxx—magnesium and silicon designation and is separated from it by a dash (i.e., 7075- • 7xxx—zinc T6, 2024-T4, and so forth). The temper designation consists of a letter indicating the basic temper, which may be more • 8xxx—other elements specifically defined by the addition of one or more digits.

These designations are as follows: In the 2xxx through 8xxx alloy groups, the second digit in • F—as fabricated the alloy designation indicates alloy modifications. If the second digit is zero, it indicates the original alloy, while digits • O—annealed, recrystallized (wrought products only) 1 through 9 indicate alloy modifications. The last two of the • H—strain hardened four digits in the designation identify the different alloys in 7-7 • H1 (plus one or more digits)—strain hardened only seawater, there is no danger of a dwindling supply.

• H2 (plus one or more digits)—strain hardened and Some of today’s aircraft require more than one-half ton of this partially annealed metal for use in hundreds of vital spots. Some wing panels are • H3 (plus one or more digits)—strain hardened and fabricated entirely from magnesium alloys, weigh 18 percent stabilized less than standard aluminum panels, and have flown hundreds of satisfactory hours. Among the aircraft parts that have been The digit following the designations H1, H2, and H3 indicates made from magnesium with a substantial savings in weight the degree of strain hardening, number 8 representing the are nosewheel doors, flap cover skin, aileron cover skin, oil ultimate tensile strength equal to that achieved by a cold tanks, floorings, fuselage parts, wingtips, engine nacelles, reduction of approximately 75 percent following a full anneal, instrument panels, radio masts, hydraulic fluid tanks, oxygen 0 representing the annealed state.

bottle cases, ducts, and seats.

Magnesium & Magnesium Alloys Magnesium alloys possess good casting characteristics. Their Magnesium, the world’s lightest structural metal, is a silvery properties compare favorably with those of cast aluminum.

white material weighing only two-thirds as much as aluminum.

In forging, hydraulic presses are ordinarily used, although, Magnesium does not possess sufficient strength in its pure state under certain conditions, forging can be accomplished in for structural uses, but when alloyed with zinc, aluminum, and mechanical presses or with drop hammers.

manganese, it produces an alloy having the highest strength- to-weight ratio of any of the commonly used metals.

Magnesium alloys are subject to such treatments as annealing, quenching, solution heat-treatment, aging, and stabilizing.

Magnesium is probably more widely distributed in nature Sheet and plate magnesium are annealed at the rolling mill.

than any other metal. It can be obtained from such ores The solution heat-treatment is used to put as much of the as dolomite and magnesite, as well as from seawater, alloying ingredients as possible into solid solution, which underground brines, and waste solutions of potash. With results in high tensile strength and maximum ductility.

about 10 million pounds of magnesium in one cubic mile of Aging is applied to castings following heat-treatment where Percentage of Alloying Elements Aluminum and normal impurities constitute remainder Alloy Copper Silicon Manganese Magnesium Zinc Nickel Chromium Lead Bismuth 1100 — — — — — — — — — 3003 — — 1.2 — — — — — — 2011 5.5 — — — — — — 0.5 0.5 2014 4.4 0.8 0.8 0.4 — — — — — 2017 4.0 — 0.5 0.5 — — — — — 2117 2.5 — — 0.3 — — — — — 2018 4.0 — — 0.5 — 2.0 — — — 2024 4.5 — 0.6 1.5 — — — — — 2025 4.5 0.8 0.8 — — — — — — 4032 0.9 12.5 — 1.0 — 0.9 — — — 6151 — 1.0 — 0.6 — — 0.25 — — 5052 — — — 2.5 — — 0.25 — — 6053 — 0.7 — 1.3 — — 0.25 — — 6061 0.25 0.6 — 1.0 — — 0.25 — — 7075 1.6 — — 2.5 5.6 — 0.3 — — Figure 7-4. Nominal composition of wrought aluminum alloys.

7-8 and liners, and miscellaneous hardware for turbine engines. maximum hardness and yield strength are desired.

Titanium, in appearance, is like stainless steel. One quick method used to identify titanium is the spark test. Titanium Magnesium embodies fire hazards of an unpredictable nature.

gives off a brilliant white trace ending in a brilliant white When in large sections, its high thermal conductivity makes burst. Also, moistening the titanium and using it to draw a it difficult to ignite and prevents it from burning. It does not line on a piece of glass can accomplish identification. This burn until the melting point of 1,204 °F is reached. However, leaves a dark line similar in appearance to a pencil mark. magnesium dust and fine chips are ignited easily. Precautions must be taken to avoid this if possible. Should a fire occur, it Titanium falls between aluminum and stainless steel in terms could be extinguished with an extinguishing powder, such as of elasticity, density, and elevated temperature strength. It soapstone or graphite. Water or any standard liquid or foam has a melting point from 2,730 °F to 3,155 °F, low thermal fire extinguisher causes magnesium to burn more rapidly and conductivity, and a low coefficient of expansion. It is light, can cause explosions.

strong, and resistant to stress corrosion cracking. Titanium is approximately 60 percent heavier than aluminum and about Magnesium alloys produced in the United States contain 50 percent lighter than stainless steel. varying proportions of aluminum, manganese, and zinc. A letter of the alphabet designates these alloys, with the number Because of the high melting point of titanium, high 1 indicating high purity and maximum corrosion resistance.

temperature properties are disappointing. The ultimate yield strength of titanium drops rapidly above 800 °F. Many of the magnesium alloys manufactured in the United The absorption of oxygen and nitrogen from the air at States are produced by the Dow Chemical Company and temperatures above 1,000 °F makes the metal so brittle on have been given the trade name of Dow-metal™ alloys. To long exposure that it soon becomes worthless. However, distinguish between these alloys, each is assigned a letter.

titanium does have some merit for short time exposure up to Thus, we have Dow-metal™ J, Dow-metal™ M, and so forth.

3,000 °F where strength is not important. Aircraft firewalls demand this requirement. Another manufacturer of magnesium alloys is the American Magnesium Corporation, a subsidiary of the Aluminum Titanium is nonmagnetic and has an electrical resistance Company of America. This company uses an identification comparable to that of stainless steel. Some of the base alloys system like that used for aluminum alloys, with the exception of titanium are quite hard. Heat-treating and alloying do not that magnesium alloy numbers are preceded with the letters develop the hardness of titanium to the high levels of some AM. Thus, AM240C is a cast alloy, and AM240C4 is the of the heat-treated alloys of steel. It was only recently that same alloy in the heat-treated state. AM3S0 is an annealed a heat-treatable titanium alloy was developed. Prior to the wrought alloy, and AM3SRT is the same alloy rolled after development of this alloy, heating and rolling was the only heat-treatment.

method of forming that could be accomplished. However, it is possible to form the new alloy in the soft condition and Titanium and Titanium Alloys heat-treat it for hardness.

An English priest named Gregot discovered titanium. A crude separation of titanium ore was accomplished in 1825. In 1906, Iron, molybdenum, and chromium are used to stabilize enough pure titanium was isolated in metallic form to permit titanium and produce alloys that quench-harden and age- a study. Following this study, in 1932, an extraction process harden. The addition of these metals also adds ductility.

was developed and became the first commercial method The fatigue resistance of titanium is greater than that of for producing titanium. The United States Bureau of Mines aluminum or steel.

began making titanium sponge in 1946, and 4 years later the melting process began.

Titanium becomes softer as the degree of purity is increased.

It is not practical to distinguish between the various grades of The use of titanium is widespread. It is used in many commercially pure or unalloyed titanium by chemical analysis; commercial enterprises and is in constant demand for such therefore, the grades are determined by mechanical properties.

items as pumps, screens, and other tools and fixtures where corrosion attack is prevalent. In aircraft construction and Titanium Designations repair, titanium is used for fuselage skins, engine shrouds, The A-B-C classification of titanium alloys was established firewalls, longerons, frames, fittings, air ducts, and fasteners.

to provide a convenient and simple means of describing all titanium alloys. Titanium and titanium alloys possess three Titanium is used for making compressor disks, spacer rings, compressor blades and vanes, through bolts, turbine housings 7-9 currents on the surface of titanium and metallic couples are basic types of crystals: A (alpha), B (beta), and C (combined naturally restricted. This partly accounts for good resistance alpha and beta). Their characteristics are: to many chemicals; also, the material may be used with some • A (alpha)—all-around performance; good weld ability; dissimilar metals with no harmful galvanic effect on either.

tough and strong both cold and hot; and resistant to oxidation.

Copper and Copper Alloys • B (beta)—bendability; excellent bend ductility; strong Copper is one of the most widely distributed metals. It is both cold and hot, but vulnerable to contamination.

the only reddish-colored metal and is second only to silver • C (combined alpha and beta for compromise in electrical conductivity. Its use as a structural material is performances)—strong when cold and warm, but weak limited because of its great weight. However, some of its when hot; good bendability; moderate contamination outstanding characteristics, such as its high electrical and heat resistance; excellent forge ability.

conductivity, in many cases overbalance the weight factor.

Titanium is manufactured for commercial use in two basic Because it is very malleable and ductile, copper is ideal for compositions: commercially-pure titanium and alloyed making wire. It is corroded by salt water but is not affected titanium. A-55 is an example of commercially-pure titanium.

by fresh water. The ultimate tensile strength of copper varies It has yield strength of 55,000 to 80,000 psi and is a general- greatly. For cast copper, the tensile strength is about 25,000 purpose grade for moderate to severe forming. It is sometimes psi, and when cold rolled or cold drawn, its tensile strength used for nonstructural aircraft parts and for all types of increases to a range of 40,000 to 67,000 psi.

corrosion-resistant applications, such as tubing. Type A-70 titanium is closely related to type A-55 but has yield strength In aircraft, copper is used primarily in the electrical system of 70,000 to 95,000 psi. It is used where higher strength is for bus bars, bonding, and as lock wire.

required, and it is specified for many moderately stressed aircraft parts. For many corrosion applications, it is used Beryllium copper is one of the most successful of all interchangeably with type A-55. Both type A-55 and type the copper base alloys. It is a recently developed alloy A-70 is weldable.

containing about 97 percent copper, 2 percent beryllium, and sufficient nickel to increase the percentage of elongation.

One of the widely-used titanium base alloys is designated The most valuable feature of this metal is that the physical as C-110M. It is used for primary structural members and properties can be greatly stepped up by heat-treatment, the aircraft skin, has 110,000 psi minimum yield strength, and tensile strength rising from 70,000 psi in the annealed state contains 8 percent manganese.

to 200,000 psi in the heat-treated state. The resistance of beryllium copper to fatigue and wear makes it suitable for Type A-110AT is a titanium alloy that contains 5 percent diaphragms, precision bearings and bushings, ball cages, aluminum and 2.5 percent tin. It also has high minimum yield and spring washers.

strength at elevated temperatures with the excellent welding characteristics inherent in alpha-type titanium alloys.

Brass is a copper alloy containing zinc and small amounts of aluminum, iron, lead, manganese, magnesium, nickel, Corrosion Characteristics phosphorous, and tin. Brass with a zinc content of 30 to 35 percent is very ductile, but that containing 45 percent has The corrosion resistance of titanium deserves special relatively high strength. mention. The resistance of the metal to corrosion is caused by the formation of a protective surface film of stable oxide Muntz metal is a brass composed of 60 percent copper and 40 or chemi-absorbed oxygen. Film is often produced by the percent zinc. It has excellent corrosion-resistant qualities in presence of oxygen and oxidizing agents.

salt water. Its strength can be increased by heat-treatment. As cast, this metal has an ultimate tensile strength of 50,000 psi, Corrosion of titanium is uniform. There is little evidence of and it can be elongated 18 percent. It is used in making bolts pitting or other serious forms of localized attack. Normally, and nuts, as well as parts that come in contact with salt water.

it is not subject to stress corrosion, corrosion fatigue, Red brass, sometimes termed “bronze” because of its tin intergranular corrosion, or galvanic corrosion. Its corrosion content, is used in fuel and oil line fittings. This metal has resistance is equal or superior to 18-8 stainless steel.

good casting and finishing properties and machines freely.

Laboratory tests with acid and saline solutions show titanium Bronzes are copper alloys containing tin. The true bronzes have polarizes readily. The net effect, in general, is to decrease up to 25 percent tin, but those with less than 11 percent are current flow in galvanic and corrosion cells. Corrosion 7-10 most useful, especially for such items as tube fittings in aircraft.

Monel has been successfully used for gears and chains to Among the copper alloys are the copper aluminum alloys, operate retractable landing gears and for structural parts subject of which the aluminum bronzes rank very high in aircraft to corrosion. In aircraft, Monel is used for parts demanding usage. They would find greater usefulness in structures if both strength and high resistance to corrosion, such as exhaust it were not for their strength-to-weight ratio as compared manifolds and carburetor needle valves and sleeves.

with alloy steels. Wrought aluminum bronzes are almost as strong and ductile as medium carbon steel, and they possess K-Monel a high degree of resistance to corrosion by air, salt water, and K-Monel is a nonferrous alloy containing mainly nickel, chemicals. They are readily forged, hot or cold rolled, and copper, and aluminum. Adding a small amount of aluminum many react to heat-treatment.

to the Monel formula produces it. It is corrosion resistant and capable of being hardened by heat-treatment.

These copper base alloys contain up to 16 percent of aluminum (usually 5 to 11 percent), to which other metals, such as iron, K-Monel has been successfully used for gears and structural nickel, or manganese, may be added. Aluminum bronzes have members in aircraft, which are subjected to corrosive good tearing qualities, great strength, hardness, and resistance attacks. This alloy is nonmagnetic at all temperatures. Both to both shock and fatigue. Because of these properties, they are oxyacetylene and electric arc welding have successfully used for diaphragms, gears, and pumps. Aluminum bronzes welded K-Monel sheet.

are available in rods, bars, plates, sheets, strips, and forgings.

Nickel & Nickel Alloys Cast aluminum bronzes, using about 89 percent copper, 9 There are basically two nickel alloys used in aircraft: Monel percent aluminum, and 2 percent of other elements, have and Inconel. Monel contains about 68 percent nickel and 29 high strength combined with ductility and are resistant to percent copper, plus small amounts of iron and manganese.

corrosion, shock, and fatigue. Because of these properties, Nickel alloys can be welded or easily machined. Some of the cast aluminum bronze is used in bearings and pump parts.

nickel Monel, especially the nickel Monels containing small These alloys are useful in areas exposed to salt water and amounts of aluminum, are heat-treatable to similar tensile corrosive gases.

strengths of steel. Nickel Monel is used in gears and parts that require high strength and toughness, such as exhaust Manganese bronze is an exceptionally high strength, tough, systems that require high strength and corrosion resistance corrosion-resistant copper zinc alloy containing aluminum, at elevated temperatures.

manganese, iron, and occasionally, nickel or tin. This metal can be formed, extruded, drawn, or rolled to any desired Inconel alloys of nickel produce a high strength, high shape. In rod form, it is generally used for machined parts temperature alloy containing approximately 80 percent for aircraft landing gears and brackets.

nickel, 14 percent chromium, and small amounts of iron and other elements. The nickel Inconel alloys are frequently Silicon bronze is a more recent development composed of used in turbine engines because of their ability to maintain about 95 percent copper, 3 percent silicon, and 2 percent their strength and corrosion resistance under extremely high- manganese, zinc, iron, tin, and aluminum. Although not a temperature conditions.

bronze in the true sense because of its small tin content, silicon bronze has high strength and great corrosion resistance.

Inconel and stainless steel are similar in appearance and are frequently found in the same areas of the engine. Sometimes Monel it is important to identify the difference between the metal Monel, the leading high nickel alloy, combines the properties samples. A common test is to apply one drop of cupric of high strength and excellent corrosion resistance. This metal chloride and hydrochloric acid solution to the unknown metal consists of 68 percent nickel, 29 percent copper, 0.2 percent and allow it to remain for 2 minutes. At the end of the soak iron, 1 percent manganese, and 1.8 percent of other elements.

period, a shiny spot indicates the material is nickel Inconel, It cannot be hardened by heat-treatment.

and a copper-colored spot indicates stainless steel.

Monel, adaptable to casting and hot or cold-working, can be Substitution of Aircraft Metals successfully welded. It has working properties like those of In selecting substitute metals for the repair and maintenance steel. When forged and annealed, it has a tensile strength of of aircraft, it is very important to check the appropriate 80,000 psi. This can be increased by cold-working to 125,000 structural repair manual. Aircraft manufacturers design psi, sufficient for classification among the tough alloys.

structural members to meet a specific load requirement for an 7-11 aircraft. The methods of repairing these members, apparently affecting the interior grain structure, as well as the exterior similar in construction, vary with different aircraft. to give the best possible structure throughout.

Four requirements must be kept in mind when selecting Hammering can be used only on relatively small pieces. Since substitute metals. The first and most important of these is hammering transmits its force almost instantly, its effect is maintaining the original strength of the structure. The other limited to a small depth. Thus, it is necessary to use a very three are maintaining contour or aerodynamic smoothness; heavy hammer or to subject the part to repeated blows to maintaining original weight, if possible, or keeping added ensure complete working of the section. If the force applied weight to a minimum; and maintaining the original corrosion- is too weak to reach the center, the finished forged surface resistant properties of the metal. is concave. If the center was properly worked, the surface is convex or bulged. The advantage of hammering is that the Metalworking Processes operator has control over both the amount of pressure applied There are three methods of metalworking: hot-working, and the finishing temperature and can produce small parts of the highest grade. This type of forging is usually referred cold-working, and extruding. The method used depends on the metal involved and the part required, although in some to as smith forging. It is used extensively where only a small number of parts are needed. Considerable machining instances both hot and cold-working methods may be used to make a single part. time and material are saved when a part is smith forged to approximately the finished shape.

Hot-Working Steel is often harder than necessary and too brittle for most Almost all steel is hot-worked from the ingot into some form practical uses when put under severe internal strain. To relieve from which it is either hot or cold-worked to the finished such strain and reduce brittleness, it is tempered after being shape. When an ingot is stripped from its mold, its surface is hardened. This consists of heating the steel in a furnace to a solid, but the interior is still molten. The ingot is then placed specified temperature and then cooling it in air, oil, water, or in a soaking pit, which retards loss of heat, and the molten a special solution. Temper condition refers to the condition of interior gradually solidifies. After soaking, the temperature metal or metal alloys with respect to hardness or toughness.

is equalized throughout the ingot, then it is reduced to Rolling, hammering, or bending these alloys, or heat-treating intermediate size by rolling, making it more readily handled.

and aging them, causes them to become tougher and harder.

At times, these alloys become too hard for forming and must The rolled shape is called a bloom when its section be re-heat-treated or annealed.

dimensions are 6 inches × 6 inches or larger and square. The section is called a billet when it is square and less than 6 Metals are annealed to relieve internal stresses, soften the metal, inches × 6 inches. Rectangular sections, which have a width make it more ductile, and refine the grain structure. Annealing greater than twice their thickness, are called slabs. The slab consists of heating the metal to a prescribed temperature, is the intermediate shape from which sheets are rolled.

holding it there for a specified length of time, and then cooling the metal back to room temperature. To produce maximum Blooms, billets, or slabs are heated above the critical range softness, the metal must be cooled very slowly. Some metals and rolled into a variety of shapes of uniform cross section.

must be furnace cooled; others may be cooled in air.

Common rolled shapes are sheet, bar, channel, angle, and I-beam. As discussed later in this chapter, hot-rolled material Normalizing applies to iron base metals only. Normalizing is frequently finished by cold rolling or drawing to obtain consists of heating the part to the proper temperature, holding it accurate finish dimensions and a bright, smooth surface.

at that temperature until it is uniformly heated, and then cooling it in still air. Normalizing is used to relieve stresses in metals.

Complicated sections, which cannot be rolled, or sections of which only a small quantity is required, are usually forged.

Strength, weight, and reliability are three factors that Forging of steel is a mechanical working at temperatures determine the requirements to be met by any material used in above the critical range to shape the metal as desired. Forging airframe construction and repair. Airframes must be strong and is done either by pressing or hammering the heated steel until yet as lightweight as possible. There are very definite limits to the desired shape is obtained.

which increases in strength can be accompanied by increases in weight. An airframe so heavy that it could not support a few Pressing is used when the parts to be forged are large and hundred pounds of additional weight would be of little use.

heavy; this process also replaces hammering where high- grade steel is required. Since a press is slow acting, its force All metals, in addition to having a good strength-to- is uniformly transmitted to the center of the section, thus 7-12 weight ratio, must be thoroughly reliable, thus minimizing Another significant factor to consider in maintenance and the possibility of dangerous and unexpected failures. In repair is the ability of a material to be formed, bent, or addition to these general properties, the material selected machined to required shapes. The hardening of metals by for a definite application must possess specific qualities cold-working or forming is termed work hardening. If a piece suitable for the purpose. of metal is formed (shaped or bent) while cold, it is said to be cold-worked. Practically all the work an aviation mechanic The material must possess the strength required by the does on metal is cold-work. While this is convenient, it causes dimensions, weight, and use. The five basic stresses that the metal to become harder and more brittle.

metals may be required to withstand are tension, compression, shear, bending, and torsion. If the metal is cold-worked too much, that is, if it is bent back and forth or hammered at the same place too often, it The tensile strength of a material is its resistance to a force, will crack or break. Usually, the more malleable and ductile which tends to pull it apart. Tensile strength is measured in a metal is, the more cold-working it can stand. Any process pounds per square inch (psi) and is calculated by dividing that involves controlled heating and cooling of metals to the load in pounds required to pull the material apart by its develop certain desirable characteristics (such as hardness, cross-sectional area in square inches. softness, ductility, tensile strength, or refined grain structure) is called heat-treatment or heat-treating. With steels, the term The compression strength of a material is its resistance to “heat-treating” has a broad meaning and includes processes a crushing force, which is the opposite of tensile strength. such as annealing, normalizing, hardening, and tempering.

Compression strength is also measured in psi. When a piece of metal is cut, the material is subjected, as it comes in contact In the heat-treatment of aluminum alloys, only two processes with the cutting edge, to a force known as shear. Shear is the are included: the hardening and toughening process and the tendency on the part of parallel members to slide in opposite softening process. The hardening and toughening process directions. It is like placing a cord or thread between the is called heat-treating, and the softening process is called blades of a pair of scissors (shears). The shear strength is annealing. Aircraft metals are subjected to both shock and the shear force in psi at which a material fails. It is the load fatigue (vibrational) stresses. Fatigue occurs in materials that divided by the shear area. are exposed to frequent reversals of loading or repeatedly applied loads, if the fatigue limit is reached or exceeded.

Bending can be described as the deflection or curving of a Repeated vibration or bending ultimately causes a minute crack member due to forces acting upon it. The bending strength of to occur at the weakest point. As vibration or bending continues, material is the resistance it offers to deflecting forces. Torsion the crack lengthens until the part completely fails. This is is a twisting force. Such action would occur in a member fixed termed “shock and fatigue failure.” Resistance to this condition at one end and twisted at the other. The torsional strength of is known as shock and fatigue resistance. It is essential that material is its resistance to twisting. materials used for critical parts be resistant to these stresses.

The relationship between the strength of a material and its Heat-treatment is a series of operations involving the heating weight per cubic inch, expressed as a ratio, is known as and cooling of metals in the solid state. Its purpose is to the strength-to-weight ratio. This ratio forms the basis for change a mechanical property, or combination of mechanical comparing the desirability of various materials for use in properties, so that the metal is more useful, serviceable, and airframe construction and repair. Neither strength nor weight safe for a definite purpose. By heat-treating, a metal can be alone can be used as a means of true comparison. In some made harder, stronger, and more resistant to impact. Heat- applications, such as the skin of monocoque structures, treating can also make a metal softer and more ductile. No one thickness is more important than strength. In this instance, heat-treating operation can produce all these characteristics.

the material with the lightest weight for a given thickness In fact, some properties are often improved at the expense or gauge is best. Thickness or bulk is necessary to prevent of others. In being hardened, for example, a metal may bucking or damage caused by careless handling. become brittle.

Corrosion is the eating away or pitting of the surface or the The various heat-treating processes are similar in that they internal structure of metals. Because of the thin sections and all involve the heating and cooling of metals. They differ, the safety factors used in aircraft design and construction, however, in the temperatures to which the metal is heated, it would be dangerous to select a material possessing poor the rate at which it is cooled, and, of course, in the result.

corrosion-resistant characteristics.

The most common forms of heat-treatment for ferrous metals 7-13 are hardening, tempering, normalizing, annealing, and case Finally, there must be equipment for handling parts and hardening. Most nonferrous metals can be annealed and materials, for cleaning metals, and for straightening parts.

many of them can be hardened by heat-treatment. However, there is only one nonferrous metal, titanium, that can be case Furnaces & Salt Baths hardened, and none can be tempered or normalized.

There are many different types and sizes of furnaces used in heat-treatment. As a rule, furnaces are designed to operate in Internal Structure of Metals certain specific temperature ranges and attempted use in other ranges frequently results in work of inferior quality.

The results obtained by heat-treatment depend on the structure of the metal and on the way the structure changes In addition, using a furnace beyond its rated maximum when the metal is heated and cooled. A pure metal cannot be hardened by heat-treatment, because there is little change temperature shortens its life and may necessitate costly and time-consuming repairs.

in its structure when heated. On the other hand, most alloys respond to heat-treatment since their structures change with Fuel-fired furnaces (gas or oil) require air for proper heating and cooling.

combustion, and an air compressor or blower is therefore necessary. These furnaces are usually of the muffler type; An alloy may be in the form of a solid solution, a mechanical mixture, or a combination of a solid solution and a mechanical that is, the combustion of the fuel takes place outside of and around the chamber in which the work is placed. If an open mixture. When an alloy is in the form of a solid solution, the elements and compounds that form the alloy are absorbed, muffler is used, the furnace should be designed to prevent the direct impingement of flame on the work.

one into the other, in much the same way that salt is dissolved in a glass of water, and the constituents cannot be identified In furnaces heated by electricity, the heating elements are even under a microscope.

generally in the form of wire or ribbon. Good design requires incorporation of additional heating elements at locations When two or more elements or compounds are mixed but can be identified by microscopic examination, a mechanical where maximum heat loss may be expected. Such furnaces commonly operate at up to a maximum temperature of about mixture is formed. A mechanical mixture can be compared to the mixture of sand and gravel in concrete. The sand and gravel 2,000 °F. Furnaces operating at temperatures up to about 2,500 °F usually employ resistor bars of sintered carbides.

are both visible. Just as the sand and gravel are held together and kept in place by the matrix of cement, the other constituents of Temperature Measurement and Control an alloy are embedded in the matrix formed by the base metal.

A thermoelectric instrument, known as a pyrometer, measures An alloy in the form of a mechanical mixture at ordinary temperature in the heat-treating furnace. This instrument temperatures may change to a solid solution when heated.

measures the electrical effect of a thermocouple and, hence, When cooled back to normal temperature, the alloy may the temperature of the metal being treated. A complete return to its original structure. On the other hand, it may pyrometer consists of three parts: a thermocouple, extension remain a solid solution or form a combination of a solid leads, and meter.

solution and mechanical mixture. An alloy, which consists of a combination of solid solution and mechanical mixture Furnaces intended primarily for tempering may be heated by at normal temperatures, may change to a solid solution when gas or electricity and are frequently equipped with a fan for heated. When cooled, the alloy may remain a solid solution, circulating the hot air.

return to its original structure, or form a complex solution.

Salt baths are available for operating at either tempering or Heat-Treating Equipment hardening temperatures. Depending on the composition of the salt bath, heating can be conducted at temperatures as low as Successful heat-treating requires close control over all factors 325 °F to as high as 2,450 °F. Lead baths can be used in the affecting the heating and cooling of metals. Such control is temperature range of 650 °F to 1,700 °F. The rate of heating possible only when the proper equipment is available and in lead or salt baths is much faster in furnaces.

the equipment is selected to fit the job. Thus, the furnace must be of the proper size and type and must be controlled Heat-treating furnaces differ in size, shape, capacity, so that temperatures are kept within the limits prescribed construction, operation, and control. They may be circular for each operation. Even the atmosphere within the furnace or rectangular and may rest on pedestals or directly on the affects the condition of the part being heat-treated. Further, floor. There are also pit-type furnaces, which are below the the quenching equipment and the quenching medium must surface of the floor. When metal is to be heated in a bath of be selected to fit the metal and the heat-treating operation.

7-14 molten salt or lead, the furnace must contain a pot or crucible this transition takes time, a relatively slow rate of heating for the molten bath. must be used. Ordinarily, the cold steel is inserted when the temperature in the furnace is from 300 °F to 500 °F below The size and capacity of a heat-treating furnace depends the hardening temperature. In this way, too rapid heating on the intended use. A furnace must be capable of heating through the critical range is prevented.

rapidly and uniformly, regardless of the desired maximum temperature or the mass of the charge. An oven-type furnace If temperature-measuring equipment is not available, it should have a working space (hearth) about twice as long and becomes necessary to estimate temperatures by some other three times as wide as any part that is heated in the furnace. means. An inexpensive, yet accurate method involves the use of commercial crayons, pellets, or paints that melt at Accurate temperature measurement is essential to good heat- various temperatures within the range of 125 °F to 1,600 °F.

treating. The usual method is by means of thermocouples: the The least accurate method of temperature estimation is by most common base metal couples are copper-constantan (up observation of the color of the hot hearth of the furnace or to about 700 °F), iron-constantan (up to about 1,400 °F), and of the work. The heat colors observed are affected by many chromel-alumel (up to about 2,200 °F). The most common factors, such as the conditions of artificial or natural light, the noble metal couples (which can be used up to about 2,800 °F) character of the scale on the work, and so forth. Steel begins are platinum coupled with either the alloy 87 percent platinum to appear dull red at about 1,000 °F, and as the temperature (13 percent rhodium) or the alloy 90 percent platinum (10 increases, the color changes gradually through various shades percent rhodium). The temperatures quoted are for continuous of red to orange, to yellow, and finally to white. A rough operation. approximation of the correspondence between color and temperature is indicated in Figure 7-5 .

The life of thermocouples is affected by the maximum temperature (which may frequently exceed those given It is also possible to secure some idea of the temperature of above) and by the furnace atmosphere. Iron-constantan a piece of carbon or low alloy steel, in the low temperature is more suited for use in reducing and chromel-alumel in range used for tempering, from the color of the thin oxide film oxidizing atmospheres. Thermocouples are usually encased that forms on the cleaned surface of the steel when heated in in metallic or ceramic tubes closed at the hot end to protect this range. The approximate temperature/color relationship them from the furnace gases. A necessary attachment is is indicated on the lower portion of the scale in Figure 7-5 .

an instrument, such as a millivoltmeter or potentiometer, for measuring the electromotive force generated by the It is often necessary or desirable to protect steel or cast iron thermocouple. In the interest of accurate control, place the from surface oxidation (scaling) and loss of carbon from hot junction of the thermocouple as close to the work as the surface layers (decarburization). Commercial furnaces, possible. The use of an automatic controller is valuable in therefore, are generally equipped with some means of controlling the temperature at the desired value. atmosphere control. This usually is in the form of a burner for burning controlled amounts of gas and air and directing the Pyrometers may have meters either of the indicating type products of combustion into the furnace muffle. Water vapor, a or recording type. Indicating pyrometers give direct reading product of this combustion, is detrimental and many furnaces of the furnace temperature. The recording type produces a are equipped with a means for eliminating it. For furnaces permanent record of the temperature range throughout the not equipped with atmosphere control, a variety of external heating operation by means of an inked stylus attached to atmosphere generators are available. The gas so generated is an arm, which traces a line on a sheet of calibrated paper or piped into the furnace and one generator may supply several temperature chart. furnaces. If no method of atmosphere control is available, some degree of protection may be secured by covering the Pyrometer installations on all modern furnaces provide work with cast iron borings or chips. Since the liquid heating automatic regulation of the temperature at any desired setting. medium surrounds the work in salt or lead baths, the problem Instruments of this type are called controlling potentiometer of preventing scaling or decarburization is simplified. Vacuum pyrometers. They include a current regulator and an operating furnaces also are used for annealing steels, especially when a mechanism, such as a relay. bright non-oxidized surface is a prime consideration.

Heating Soaking The object in heating is to transform pearlite (a mixture of The temperature of the furnace must be held constant alternate strips of ferrite and iron carbide in a single grain) to during the soaking period, since it is during this period that austenite as the steel is heated through the critical range. Since rearrangement of the internal structure of the steel takes place.

7-15 Soaking temperatures for various types of steel are specified abstraction markedly. Vigorous agitation of the steel or the in ranges varying as much as 100 °F. [Figure 7-6] Small parts use of a pressure spray quench is necessary to dislodge these are soaked in the lower part of the specified range and heavy vapor films and thus permit the desired rate of cooling.

parts in the upper part of the specified range. The length of the soaking period depends upon the type of steel and the size The tendency of steel to warp and crack during the quenching of the part. Naturally, heavier parts require longer soaking to process is difficult to overcome because certain parts of ensure equal heating throughout. As a general rule, a soaking the article cool more rapidly than others. The following period of 30 minutes to 1 hour is sufficient for the average recommendations greatly reduce the warping tendency.

heat-treating operation.

1. Never throw a part into the quenching bath. By permitting it to lie on the bottom of the bath, it is apt Cooling to cool faster on the topside than on the bottom side, The rate of cooling through the critical range determines the thus causing it to warp or crack.

form that the steel retains. Various rates of cooling are used to 2. Agitate the part slightly to destroy the coating of produce the desired results. Still air is a slow cooling medium vapor that could prevent it from cooling evenly and but is much faster than furnace cooling. Liquids are the fastest rapidly. This allows the bath to dissipate its heat to the cooling media and are therefore used in hardening steels.

atmosphere.

3. Immerse irregular shaped parts so that the heavy end There are three commonly used quenching liquids: brine, enters the bath first.

water, and oil. Brine is the strongest quenching medium, water is next, and oil is the least. Generally, an oil quench Quenching Equipment is used for alloy steels and brine or water for carbon steels.

The quenching tank should be of the proper size to handle Quenching Media the material being quenched. Use circulating pumps and coolers to maintain approximately constant temperatures Quenching solutions act only through their ability to cool when doing a large amount of quenching. To avoid building the steel. They have no beneficial chemical action on up a high concentration of salt in the quenching tank, make the quenched steel and in themselves impart no unusual provisions for adding fresh water to the quench tank used properties. Most requirements for quenching media are met for molten salt baths.

satisfactorily by water or aqueous solutions of inorganic salts, such as table salt or caustic soda, or by some type of oil. The Tank location in reference to the heat-treating furnace is very rate of cooling is relatively rapid during quenching in brine, important. Situate the tank to permit rapid transfer of the part somewhat less rapid in water, and slow in oil.

from the furnace to the quenching medium. A delay of more than a few seconds, in many instances, proves detrimental to Brine usually is made of a 5 to 10 percent solution of salt the effectiveness of the heat-treatment. During transfer to the (sodium chloride) in water. In addition to its greater cooling quench tank, employ guard sheets to retard the loss of heat speed, brine has the ability to “throw” the scale from steel when heat-treating material of thin section. Provide a rinse during quenching. Their temperature considerably affects the tank to remove all salt from the material after quenching if cooling ability of both water and brine, particularly water.

the salt is not adequately removed in the quenching tank.

Both should be kept cold—well below 60 °F. If the volume of steel being quenched tends to raise the temperature of the Heat-Treatment of Ferrous Metals bath appreciably, add ice or use some means of refrigeration The first important consideration in the heat-treatment of a to cool the quenching bath.

steel part is to know its chemical composition. This, in turn, determines its upper critical point. When the upper critical There are many specially prepared quenching oils on the point is known, the next consideration is the rate of heating market; their cooling rates do not vary widely. A straight and cooling to be used. Carrying out these operations involves mineral oil with a Saybolt viscosity of about 100 at 100 °F the use of uniform heating furnaces, proper temperature is generally used. Unlike brine and water, the oils have the controls, and suitable quenching mediums.

greatest cooling velocity at a slightly elevated temperature— about 100–140 °F—because of their decreased viscosity at Behavior of Steel During Heating & Cooling these temperatures.

Changing the internal structure of a ferrous metal is When steel is quenched, the liquid in immediate contact with accomplished by heating to a temperature above its upper the hot surface vaporizes; this vapor reduces the rate of heat critical point, holding it at that temperature for a time sufficient to permit certain internal changes to occur, and then 7-16 cooling to atmospheric temperature under predetermined, Approximate Temperature Colors controlled conditions.

°Fahrenheit °Centigrade At ordinary temperatures, the carbon in steel exists in the 1,500 2,700 form of particles of iron carbide scattered throughout an iron matrix known as “ferrite.” The number, size, and distribution 2,600 of these particles determine the hardness of the steel. At 1,400 2,500 elevated temperatures, the carbon is dissolved in the iron matrix in the form of a solid solution called “austenite,” 2,400 1,300 and the carbide particles appear only after the steel has Color of Hot Body °F °C 2,300 been cooled. If the cooling is slow, the carbide particles are White 1200 2192 2,200 relatively coarse and few. In this condition, the steel is soft.

1,200 If the cooling is rapid, as by quenching in oil or water, the 2,100 carbon precipitates as a cloud of very fine carbide particles, Light Yellow 1100 2012 1,100 2,000 and the steel is hard. The fact that the carbide particles can Yellow 1050 1922 be dissolved in austenite is the basis of the heat-treatment 1,900 Light Orange 980 1796 1,000 of steel. The temperatures at which this transformation 1,800 takes place are called the critical points and vary with the Orange 930 1706 1,700 composition of the steel. The percent of carbon in the steel has Light Red 870 1598 the greatest influence on the critical points of heat-treatment.

1,600 810 Light cherry 1490 1,500 Hardening Cherry 760 1400 1,400 Pure iron, wrought iron, and extremely low carbon steels Dark Cherry 700 1292 1,300 cannot be appreciably hardened by heat-treatment, since they Blood Red 650 1202 contain no hardening element. Cast iron can be hardened, but 1,200 its heat-treatment is limited. When cast iron is cooled rapidly, Brown Red 600 1112 1,100 it forms white iron, which is hard and brittle. When cooled slowly, it forms gray iron, which is soft but brittle under impact.

1,000 In plain carbon steel, the maximum hardness depends almost entirely on the carbon content of the steel. As carbon content increases, the ability of steel to harden also increases.

°F °C Temper Colors However, this increase in the ability to harden with an 300 increase in carbon content continues only to a certain point.

Dark Blue 290 550 Purple 270 520 In practice, that point is 0.85 percent carbon content. When Yellow Brown 250 460 the carbon content is increased beyond 0.85 percent, there Straw 220 430 is no increase in wear resistance.

For most steels, the hardening treatment consists of heating the steel to a temperature just above the upper critical point, soaking or holding for the required length of time, and then cooling it rapidly by plunging the hot steel into oil, water, or brine. Although most steels must be cooled rapidly for hardening, a few may be cooled in still air. Hardening increases the hardness and strength of the steel but makes it less ductile.

Carbon steel must be cooled to below 1,000 °F in less than 1 second when hardening. Should the time required for the temperature to drop to 1,000 °F exceed 1 second, the austenite begins to transform into fine pearlite. This pearlite varies Figure 7-5. Temperature chart indicating conversion of Centigrade in hardness, but is much harder than the pearlite formed by to Fahrenheit or vice versa, color temperature scale for hardening temperature range, and tempering temperature range.

annealing and much softer than the martensite desired. After the 1,000 °F temperature is reached, the rapid cooling must 7-17 Tempering (drawing) Temperature for Temperatures Tensile Strength (psi) Steel Quenching Number Medium (n) Normalizing Annealing Hardening 100,000 125,000 150,000 180,000 200,000 Air Cool (°F) (°F) (°F) (°F) (°F) (°F) (°F) (°F) 1020 1,650–1,750 1,600–1,700 1,575–1,675 Water — — — — — 1022 (x1020) 1,650–1,750 1,600–1,700 1,575–1,675 Water — — — — — 1025 1,600–1,700 1,575–1,650 1,575–1,675 Water (a) — — — — 1035 1,575–1,650 1,575–1,625 1,525–1,600 Water 875 — — — — 1045 1,550–1,600 1,550–1,600 1,475–1,550 Oil or water 1,150 — — (n) — 1095 1,475–1,550 1,450–1,500 1,425–1,500 Oil (b) — 1,100 850 750 2330 1,475–1,525 1,425–1,475 1,450–1,500 Oil or water 1,100 950 800 — — 3135 1,600–1,650 1,500–1,550 1,475–1,525 Oil 1,250 1,050 900 750 650 3140 1,600–1,650 1,500–1,550 1,475–1,525 Oil 1,325 1,075 925 775 700 4037 1,600 1,525–1,575 1,525–1,575 Oil or water 1,225 1,100 975 — — 4130 (x4130) 1,600–1,700 1,525–1,575 1,525–1,625 Oil (c) (d) 1,050 900 700 575 4140 1,600–1,650 1,525–1,575 1,525–1,575 Oil 1,350 1,100 1,025 825 675 4150 1,550–1,600 1,475–1,525 1,550–1,550 Oil — 1,275 1,175 1,050 950 4340 (x4340) 1,550–1,625 1,525–1,575 1,475–1,550 Oil — 1,200 1,050 950 850 4640 1,675–1,700 1,525–1,575 1,500–1,550 Oil — 1,200 1,050 750 625 6135 1,600–1,700 1,550–1,600 1,575–1,625 Oil 1,300 1,075 925 800 750 6150 1,600–1,650 1,525–1,575 1,550–1,625 Oil (d)(e) 1,200 1,000 900 800 6195 1,600–1,650 1,525–1,575 1,500–1,550 Oil (f ) — — — — NE8620 — — 1,525–1,575 Oil — 1,000 — — — NE8630 1,650 1,525–1,575 1,525–1,575 Oil — 1,125 975 775 675 NE8735 1,650 1,525–1,575 1,525–1,575 Oil — 1,175 1,025 875 775 NE8740 1,625 1,500–1,550 1,500–1,550 Oil — 1,200 1,075 925 850 30905 — (g)(h) (i) — — — — — — 51210 1,525–1,575 1,525–1,575 1,775–1,825 (j) Oil 1,200 1,100 (k) 750 — 51335 — 1,525–1,575 1,775–1,850 Oil — — — — — 52100 1,625–1,700 1,400–1,450 1,525–1,550 Oil (f ) — — — — Corrosion resisting — — — — (m) — — — — (16-2)(1) Silicon chromium — — 1,700–1,725 Oil — — — — — (for springs) NOTES: (a) Draw at 1,150 °F for tensile strength of 70,000 psi. (j) Lower side of range for sheet 0.06 inch and under. Middle of range for sheet and wire 0.125 inch. Upper side of range for forgings.

(b) For spring temper draw at 800–900 °F. Rockwell hardness C-40–45.

(k) Not recommended for intermediate tensile strengths because of low (c) Bars or forgings may be quenched in water from 1,500–1,600 °F.

impact.

(d) Air cooling from the normalizing temperature produces a tensile (l) AN-QQ-S-770—It is recommended that, prior to tempering, strength of approximately 90,000 psi.

corrosion-resisting (16 Cr-2 Ni) steel be quenched in oil from a (e) For spring temper draw at 850–950 °F. Rockwell hardness C-40–45.

temperature of 1,875–1,900 °F, after a soaking period of 30 minutes at this temperature. To obtain a tensile strength at 115,000 psi, the (f ) Draw at 350–450 °F to remove quenching strains. Rockwell hardness tempering temperature should be approximately 525 °F. A holding C-60–65.

time at these temperatures of about 2 hours is recommended.

(g) Anneal at 1,600–1,700 °F to remove residual stresses due to welding or Tempering temperatures between 700 °F and 1,100 °F is not approved.

cold-work. May be applied only to steel containing titanium or (m) Draw at approximately 800 °F and cool in air for Rockwell hardness of C-50.

columbium.

(n) Water used for quenching shall be within the temperature range of (h) Anneal at 1,900–2,100 °F to produce maximum softness and corrosion 80–150 °F.

resistance. Cool in air or quench in water.

(i) Harden by cold-work only.

Figure 7-6. Heat-treatment procedures for steels.

7-18 continue if the final structure is to be all martensite. low critical point of the steel. In this respect, tempering differs from annealing, normalizing, or hardening, all of The time limit for the temperature drop to 1,000 °F increases which require temperatures above the upper critical point.

above the 1 second limit for carbon steels when alloys are When hardened steel is reheated, tempering begins at 212 °F added to steel. Therefore, a slower quenching medium and continues as the temperature increases toward the low produces hardness in alloy steels. critical point. By selecting a definite tempering temperature, the resulting hardness and strength can be predetermined.

Because of the high internal stresses in the “as quenched” Approximate temperatures for various tensile strengths are condition, steel must be tempered just before it becomes listed in Figure 7-6 . The minimum time at the tempering cold. The part should be removed from the quenching temperature should be 1 hour. If the part is over one inch in bath at a temperature of approximately 200 °F, since the thickness, increase the time by 1 hour for each additional inch temperature range from 200 °F down to room temperature of thickness. Tempered steels used in aircraft work have from is the cracking range. 125,000 to 200,000 psi ultimate tensile strength.

Hardening temperatures and quenching mediums for the Generally, the rate of cooling from the tempering temperature various types of steel are listed in Figure 7-6 . has no effect on the resulting structure; therefore, the steel is usually cooled in still air after being removed from the furnace.

Hardening Precautions A variety of different shapes and sizes of tongs for handling Annealing hot steels is necessary. It should be remembered that cooling Annealing of steel produces a fine-grained, soft, ductile metal of the area contacted by the tongs is retarded and that such without internal stresses or strains. In the annealed state, steel areas may not harden, particularly if the steel being treated is has its lowest strength. In general, annealing is the opposite very shallow hardening. Small parts may be wired together of hardening.

or quenched in baskets made of wire mesh.

Heating the metal to just above the upper critical point, Special quenching jigs and fixtures are frequently used to hold soaking at that temperature, and cooling very slowly in steels during quenching in a manner to restrain distortion.

the furnace accomplishes annealing of steel. (Refer to Figure 7-6 for recommended temperatures.) Soaking time is When selective hardening is desired, covering with alundum approximately 1 hour per inch of thickness of the material.

cement or some other insulating material may protect portions To produce maximum softness in steel, the metal must be of the steel. Selective hardening may be accomplished by cooled very slowly. Slow cooling is obtained by shutting off using water or oil jets designed to direct quenching medium the heat and allowing the furnace and metal to cool together on the areas to be hardened. This also is accomplished by to 900 °F or lower, then removing the metal from the furnace the induction and flame hardening procedures previously and cooling in still air. Another method is to bury the heated described, particularly on large production jobs.

steel in ashes, sand, or other substance that does not conduct heat readily.

Shallow hardening steels, such as plain carbon and certain varieties of alloy steels, have such a high critical cooling Normalizing rate that they must be quenched in brine or water to effect The normalizing of steel removes the internal stresses set up hardening. In general, intricately-shaped sections should not by heat-treating, welding, casting, forming, or machining.

be made of shallow hardening steels because of the tendency Stress, if not controlled, leads to failure. Because of the of these steels to warp and crack during hardening. Such better physical properties, aircraft steels are often used in the items should be made of deeper hardening steels capable of normalized state, but seldom, if ever, in the annealed state.

being hardened by quenching in oil or air.

One of the most important uses of normalizing in aircraft work Tempering is in welded parts. Welding causes strains to be set up in the Tempering reduces the brittleness imparted by hardening adjacent material. In addition, the weld itself is a cast structure and produces definite physical properties within the steel.

as opposed to the wrought structure of the rest of the material.

Tempering always follows, never precedes, the hardening These two types of structures have different grain sizes, and operation. In addition to reducing brittleness, tempering to refine the grain as well as to relieve the internal stresses, all softens the steel.

welded parts should be normalized after fabrication.

Tempering is always conducted at temperatures below the Heating the steel above the upper critical point and cooling in 7-19 still air accomplish normalizing. The more rapid quenching A third method of carburizing is that of “liquid carburizing.” obtained by air-cooling, as compared to furnace cooling, In this method, the steel is placed in a molten salt bath that results in a harder and stronger material than that obtained contains the chemicals required to produce a case comparable by annealing. Recommended normalizing temperatures for with one resulting from pack or gas carburizing.

the various types of aircraft steels are listed in Figure 7-6 .

Alloy steels with low-carbon content, as well as low-carbon Case Hardening steels, may be carburized by any of the three processes.

However, some alloys, such as nickel, tend to retard the Case hardening produces a hard, wear-resistant surface or absorption of carbon. Thus, the time required to produce case over a strong, tough core. Case hardening is ideal for a given thickness of case varies with the composition of parts that require a wear-resistant surface and, at the same the metal.

time, must be tough enough internally to withstand the applied loads. The steels best suited to case hardening are Nitriding the low carbon and low-alloy steels. If high-carbon steel is Nitriding is unlike other case hardening processes in that, case hardened, the hardness penetrates the core and causes brittleness. In case hardening, the surface of the metal is before nitriding, the part is heat-treated to produce definite physical properties. Thus, parts are hardened and tempered changed chemically by introducing a high carbide or nitride content. The core is unaffected chemically. before being nitrided. Most steels can be nitrided, but special alloys are required for best results. These special alloys When heat-treated, the surface responds to hardening while contain aluminum as one of the alloying elements and are called “nitralloys.” the core toughens. The common forms of case hardening are carburizing, cyaniding, and nitriding. Since cyaniding is In nitriding, the part is placed in a special nitriding furnace and not used in aircraft work, only carburizing and nitriding are discussed in this section. heated to a temperature of approximately 1,000 °F. With the part at this temperature, ammonia gas is circulated within the Carburizing specially constructed furnace chamber. The high temperature cracks the ammonia gas into nitrogen and hydrogen. The Carburizing is a case hardening process in which carbon is ammonia, which does not break down, is caught in a water trap added to the surface of low-carbon steel. Thus, carburized below the regions of the other two gases. The nitrogen reacts steel has a high-carbon surface and a low-carbon interior.

with the iron to form nitride. The iron nitride is dispersed in When the carburized steel is heat-treated, the case is hardened minute particles at the surface and works inward. The depth while the core remains soft and tough.

of penetration depends on the length of the treatment. Soaking periods (as long as 72 hours) are frequently required to produce A common method of carburizing is called “pack carburizing.” the desired thickness during nitriding.

When carburizing is to be done by this method, the steel parts are packed in a container with charcoal or some other Nitriding can be accomplished with a minimum of distortion, material rich in carbon. The container is then sealed with fire because of the low temperature at which parts are case clay, placed in a furnace, heated to approximately 1,700 °F, hardened and because no quenching is required after exposure and soaked at that temperature for several hours. As the to the ammonia gas.

temperature increases, carbon monoxide gas forms inside the container and, being unable to escape, combines with the Heat-Treatment of Nonferrous Metals gamma iron in the surface of the steel. The depth to which Aluminum Alloys the carbon penetrates depends on the length of the soaking period. For example, when carbon steel is soaked for 8 hours, In the wrought form, commercially-pure aluminum is known the carbon penetrates to a depth of about 0.062 inch.

as 1100. It has a high degree of resistance to corrosion and is easily formed into intricate shapes. It is relatively low In another method of carburizing, called “gas carburizing,” in strength and does not have the properties required for a material rich in carbon is introduced into the furnace structural aircraft parts. The process of alloying generally atmosphere. The carburizing atmosphere is produced by obtains high strengths. The resulting alloys are less easily using various gases or by the burning of oil, wood, or other formed and, with some exceptions, have lower resistance to materials. When the steel parts are heated in this atmosphere, corrosion than 1100 aluminum.

carbon monoxide combines with the gamma iron to produce practically the same results as those described under the pack Alloying is not the only method of increasing the strength of carburizing process. aluminum. Like other materials, aluminum becomes stronger and harder as it is rolled, formed, or otherwise cold-worked.

7-20 Since the hardness depends on the amount of cold-working any attack caused by scratching or from other abrasions.

done, 1100 and some wrought aluminum alloys are available in several strain-hardened tempers. The soft or annealed There are two types of heat-treatments applicable to condition is designated O. If the material is strain hardened, aluminum alloys: solution heat-treatment and precipitation it is said to be in the H condition. heat-treatment. Some alloys, such as 2017 and 2024, develop their full properties as a result of solution heat-treatment The most widely used alloys in aircraft construction are followed by about 4 days of aging at room temperature. Other hardened by heat-treatment rather than by cold-work. alloys, such as 2014 and 7075, require both heat-treatments.

These alloys are designated by a somewhat different set of symbols: T4 and W indicate solution heat-treated and The alloys that require precipitation heat-treatment (artificial quenched but not aged, and T6 indicates an alloy in the aging) to develop their full strength also age to a limited extent heat-treated, hardened condition. at room temperature; the rate and amount of strengthening depends upon the alloy. Some reach their maximum natural • W—solution heat-treated, unstable temper or room temperature aging strength in a few days, and are • T—treated to produce stable tempers other than F, O, designated as –T4 or –T3 temper. Others continue to age or H appreciably over a long period of time.

• T2—annealed (cast products only) Because of this natural aging, the –W designation is specified • T3—solution heat-treated and then cold-worked only when the period of aging is indicated, for example, • T4—solution heat-treated 7075–W ( ⁄ 2 hour). Thus, there is considerable difference in the mechanical and physical properties of freshly quenched • T5—artificially aged only (–W) material and material that is in the –T3 or –T4 temper.

• T6—solution heat-treated and then artificially aged The hardening of an aluminum alloy by heat-treatment • T7—solution heat-treated and then stabilized consists of four distinct steps: • T8—solution heat-treated, cold-worked, and then 1. Heating to a predetermined temperature.

artificially aged 2. Soaking at temperature for a specified length of time.

• T9—solution heat-treated, artificially aged, and then 3. Rapidly quenching to a relatively low temperature.

cold-worked 4. Aging or precipitation-hardening either spontaneously • T10—artificially aged and then cold-worked at room temperature, or because of a low temperature thermal treatment.

Additional digits may be added to T1 through T10 to indicate a variation in treatment, which significantly alters the The first three steps above are known as solution heat-treatment, characteristics of the product.

although it has become common practice to use the shorter term, “heat-treatment.” Room temperature hardening is known as Aluminum-alloy sheets are marked with the specification natural aging, while hardening done at moderate temperatures number on approximately every square foot of material. If is called artificial aging, or precipitation heat-treatment.

for any reason this identification is not on the material, it is possible to separate the heat-treatable alloys from the non- Solution Heat-Treatment heat-treatable alloys by immersing a sample of the material Temperature in a 10 percent solution of caustic soda (sodium hydroxide).

The temperatures used for solution heat-treating vary with The heat-treatable alloys turn black due to the copper content, different alloys and range from 825 °F to 980 °F. As a rule, whereas the others remain bright. In the case of clad material, they must be controlled within a very narrow range (±10 °F) the surface remains bright, but there is a dark area in the to obtain specified properties.

middle when viewed from the edge.

If the temperature is too low, maximum strength is not Alclad Aluminum obtained. When excessive temperatures are used, there is The terms “Alclad and Pureclad” are used to designate sheets danger of melting the low melting constituents of some that consist of an aluminum-alloy core coated with a layer alloys with consequent lowering of the physical properties of pure aluminum to a depth of approximately 5 ⁄ 2 percent of the alloy. Even if melting does not occur, the use of higher on each side. The pure aluminum coating affords a dual than recommended temperatures promotes discoloration and protection for the core, preventing contact with any corrosive increases quenching strains.

agents, and protecting the core electrolytically by preventing 7-21 of quench also minimizes distortion and alleviates quench Time at Temperature cracking. However, many specifications forbid the use of spray quenching for bare 2017 and 2024 sheet materials The time at temperature, referred to as soaking time, is because of the effect on their resistance to corrosion.

measured from the time the coldest metal reaches the minimum limit of the desired temperature range. The soaking time varies, Lag Between Soaking & Quenching depending upon the alloy and thickness, from 10 minutes for thin sheets to approximately 12 hours for heavy forgings. For The time interval between the removal of the material from the heavy sections, the nominal soaking time is approximately the furnace and quenching is critical for some alloys and 1 hour for each inch of cross-sectional thickness. [Figure 7-7] should be held to a minimum. The elapsed time must not exceed 10 seconds when solution heat-treating 2017 or 2024 Choose the minimum soaking time necessary to develop the sheet material. The allowable time for heavy sections may required physical properties. The effect of an abbreviated be slightly greater.

soaking time is obvious. An excessive soaking period aggravates high-temperature oxidation. With clad material, Allowing the metal to cool slightly before quenching promotes prolonged heating results in excessive diffusion of copper re-precipitation from the solid solution. The precipitation and other soluble constituents into the protective cladding occurs along grain boundaries and in certain slip planes causing and may defeat the purpose of cladding. poorer formability. In the case of 2017, 2024, and 7075 alloys, their resistance to intergranular corrosion is adversely affected.

Quenching Reheat-Treatment After the soluble constituents are in solid solution, the material is quenched to prevent or retard immediate re-precipitation.

The treatment of material, which has been previously Three distinct quenching methods are employed. The one to heat-treated, is considered a reheat-treatment. The unclad be used in any instance depends upon the part, the alloy, and heat-treatable alloys can be solution heat-treated repeatedly the properties desired. without harmful effects.

Cold Water Quenching The number of solution heat-treatments allowed for clad sheet is limited due to increased diffusion of core and Parts produced from sheet, extrusions, tubing, small forgings, cladding with each reheating. Existing specifications allow and similar type material are generally quenched in a cold one to three reheat-treatments of clad sheet depending upon water bath. The temperature of the water before quenching cladding thickness.

should not exceed 85 °F.

Straightening After Solution Heat-Treatment Using a sufficient quantity of water keeps the temperature Some warping occurs during solution heat-treatment, rise under 20 °F. Such a drastic quench ensures maximum producing kinks, buckles, waves, and twists. Straightening and resistance to corrosion. This is particularly important when flattening operations generally remove these imperfections.

working with alloys, such as 2017, 2024, and 7075. This is Where the straightening operations produce an appreciable the reason a drastic quench is preferred, even though a slower increase in the tensile and yield strengths and a slight decrease quench may produce the required mechanical properties.

in the percent of elongation, the material is designated –T3 temper. When the above values are not materially affected, Hot Water Quenching the material is designated –T4 temper.

Large forgings and heavy sections can be quenched in hot or boiling water. This type of quench minimizes distortion and Precipitation Heat-Treating alleviates cracking, which may be produced by the unequal As previously stated, the aluminum alloys are in a temperatures obtained during the quench. The use of a hot comparatively soft state immediately after quenching water quench is permitted with these parts, because the from a solution heat-treating temperature. To obtain their temperature of the quench water does not critically affect the maximum strengths, they must be either naturally aged or resistance to corrosion of the forging alloys. In addition, the precipitation-hardened.

resistance to corrosion of heavy sections is not as critical a factor as for thin sections.

During this hardening and strengthening operation, precipitation of the soluble constituents from the super- Spray Quenching saturated solid solution takes place. The strength of the High-velocity water sprays are useful for parts formed from material increases (often by a series of peaks) until a maximum clad sheet and for large sections of almost all alloys. This type is reached, as precipitation progresses. Further aging, or over- 7-22 depending upon the alloys.

Thickness (inch) Time (minutes) Many of the artificially-aged alloys reach their maximum Up to 0.032 30 natural or room temperature aging strengths after a few 0.032 to ⁄ 30 days. These can be stocked for fabrication in the –T4 or –T3 1 1 40 ⁄ to / tempers. High zinc content alloys, such as 7075, continue to 8 4 age appreciably over a long period of time. Their mechanical Over ¼ 60 property changes being sufficient to reduce their formability.

NOTE: Soaking time starts when the metal (or the molten bath) reaches a temperature within the range speci fi ed above.

The advantage of –W temper formability can be utilized; however, in the same manner as with natural-aging alloys; Figure 7-7. Typical soaking times for heat-treatment.

that is, by fabricating shortly after solution heat-treatment or retaining formability by using refrigeration.

aging, causes the strength to steadily decline until a somewhat stable condition is obtained. The submicroscopic particles that Refrigeration retards the rate of natural aging. At 32 °F, are precipitated provide the keys or locks within the grain the beginning of the aging process is delayed for several structure and between the grains to resist internal slippage and hours, while dry ice (−50 °F to −100 °F) retards aging for distortion when a load of any type is applied. In this manner, an extended period of time.

the strength and hardness of the alloy are increased.

Precipitation Practices Precipitation-hardening produces a great increase in the strength and hardness of the material with corresponding The temperatures used for precipitation-hardening depend decreases in the ductile properties. The process used to obtain upon the alloy and the properties desired, ranging from 250 °F the desired increase in strength is therefore known as aging to 375 °F. They should be controlled within a very narrow or precipitation-hardening.

range (±5 °F) to obtain best results. [Figure 7-8] The strengthening of the heat-treatable alloys by aging is The time at temperature is dependent upon the temperature not due merely to the presence of a precipitate. The strength used, the properties desired, and the alloy. It ranges from 8 is due to both the uniform distribution of a finely dispersed to 96 hours. Increasing the aging temperature decreases the submicroscopic precipitate and its effects upon the crystal soaking period necessary for proper aging. However, a closer structure of the alloy.

control of both time and temperature is necessary when using the higher temperatures.

The aging practices used depend upon many properties other than strength. As a rule, the artificially-aged alloys are After receiving the thermal precipitation treatment, the slightly over-aged to increase their resistance to corrosion.

material should be air cooled to room temperature. Water This is especially true with the artificially-aged, high-copper quenching, while not necessary, produces no ill effects.

content alloys that are susceptible to intergranular corrosion Furnace cooling tends to produce over-aging.

when inadequately aged.

Annealing of Aluminum Alloys The heat-treatable aluminum alloys are subdivided into The annealing procedure for aluminum alloys consists two classes: those that obtain their full strength at room of heating the alloys to an elevated temperature, holding temperature and those that require artificial aging.

or soaking them at this temperature for a length of time depending upon the mass of the metal, and then cooling in The alloys that obtain their full strength after 4 or 5 days still air. Annealing leaves the metal in the best condition for at room temperature are known as natural-aging alloys.

cold-working. However, when prolonged forming operations Precipitation from the supersaturated solid solution starts are involved, the metal takes on a condition known as soon after quenching, with 90 percent of the maximum “mechanical hardness” and resists further working. It may be strength generally being obtained in 24 hours. Alloys 2017 necessary to anneal a part several times during the forming and 2024 are natural-aging alloys.

process to avoid cracking. Aluminum alloys should not be used in the annealed state for parts or fittings.

The alloys that require precipitation thermal treatment to develop their full strength are artificially-aged alloys.

Clad parts should be heated as quickly and carefully as However, these alloys also age a limited amount at room possible, since long exposure to heat tends to cause some of temperature, the rate and extent of the strengthening the constituents of the core to diffuse into the cladding. This 7-23 reduces the corrosion resistance of the cladding.

Heat-Treatment of Magnesium Alloys Heat-Treatment of Aluminum Alloy Rivets Magnesium alloy castings respond readily to heat-treatment, Aluminum alloy rivets are furnished in the following and about 95 percent of the magnesium used in aircraft compositions: alloys 1100, 5056, 2117, 2017, and 2024. construction is in the cast form. The heat-treatment of magnesium alloy castings is like the heat-treatment of Alloy 1100 rivets are used in the “as fabricated” condition aluminum alloys in that there are two types of heat-treatment: for riveting aluminum alloy sheets where a low-strength rivet solution heat-treatment and precipitation (aging) heat- is suitable. Alloy 5056 rivets are used in the “as fabricated” treatment. Magnesium, however, develops a negligible condition for riveting magnesium alloy sheets. change in its properties when allowed to age naturally at room temperatures.

Alloy 2117 rivets have moderately high strength and are suitable for riveting aluminum alloy sheets. These rivets Solution Heat-Treatment receive only one heat-treatment, which is performed by the Magnesium alloy castings are solution heat-treated to manufacturer, and are anodized after being heat-treated.

improve tensile strength, ductility, and shock resistance. This They require no further heat-treatment before they are used.

heat-treatment condition is indicated by using the symbol –T4 Alloy 2117 rivets retain their characteristics indefinitely after following the alloy designation. Solution heat-treatment plus heat-treatment and can be driven anytime. Rivets made of artificial aging is designated –T6. Artificial aging is necessary this alloy are the most widely used in aircraft construction.

to develop the full properties of the metal.

Alloy 2017 and 2024 rivets are high-strength rivets suitable Solution heat-treatment temperatures for magnesium alloy for use with aluminum alloy structures. They are purchased castings range from 730 °F to 780 °F, the exact range from the manufacturer in the heat-treated condition. Since depending upon the type of alloy. The temperature range the aging characteristics of these alloys at room temperatures for each type of alloy is listed in Specification MIL-H-6857.

are such that the rivets are unfit for driving, they must be The upper limit of each range listed in the specification is reheat-treated just before they are to be used. Alloy 2017 the maximum temperature to which the alloy may be heated rivets become too hard for driving in approximately 1 hour without danger of melting the metal.

after quenching. Alloy 2024 rivets become hardened in 10 minutes after quenching. Both alloys may be reheat-treated The soaking time ranges from 10 to 18 hours, the exact time as often as required; however, they must be anodized before depending upon the type of alloy as well as the thickness of the the first reheat-treatment to prevent intergranular oxidation part. Soaking periods longer than 18 hours may be necessary of the material. If these rivets are stored in a refrigerator at a for castings over 2 inches in thickness. Never heat magnesium temperature lower than 32 °F immediately after quenching, alloys in a salt bath as this may result in an explosion.

they remain soft enough to be usable for several days.

A serious potential fire hazard exists in the heat-treatment Rivets requiring heat-treatment are heated either in tubular of magnesium alloys. If through oversight or malfunctioning containers in a salt bath or in small screen wire baskets of equipment the maximum temperatures are exceeded, the in an air furnace. The heat-treatment of alloy 2017 rivets casting may ignite and burn freely. For this reason, the furnace consists of subjecting the rivets to a temperature between used should be equipped with a safety cutoff that turns off 930 °F to 950 °F for approximately 30 minutes and the power to the heating elements and blowers if the regular immediately quenching in cold water. These rivets reach control equipment malfunctions or fails. Some magnesium maximum strength in about 9 days after being driven. Alloy alloys require a protective atmosphere of sulfur dioxide 2024 rivets should be heated to a temperature of 910 °F gas during solution heat-treatment. This aids in preventing to 930 °F and immediately quenched in cold water. These the start of a fire even if the temperature limits are slightly rivets develop greater shear strength than 2017 rivets and exceeded.

are used in locations where extra strength is required. Alloy 2024 rivets develop their maximum shear strength in 1 day Air quenching is used after solution heat-treatment of after being driven.

magnesium alloys since there appears to be no advantage in liquid cooling.

The 2017 rivet should be driven within approximately 1 hour and the 2024 rivet within 10 to 20 minutes after heat-treating Precipitation Heat-Treatment or removal from refrigeration. If not used within these times, After solution treatment, magnesium alloys may be given the rivets should be reheat-treated before being refrigerated.

an aging treatment to increase hardness and yield strength.

7-24 Solution Heat—Treatment Precipitation Heat—Treatment Alloy Temperature Temperature Temperature Temperature Quench Time of Aging (°F) Designation (°F) Designation 2017 930–950 Cold water T4 T 2117 930–950 Cold water T4 T 2024 910–930 Cold water T4 T 6053 960–980 Water T4 445–455 1–2 hours T5 or 345–355 8 hours T6 6061 960–980 Water T4 315–325 18 hours T6 or 345–355 8 hours T6 7075 870 Water 250 24 hours T6 Figure 7-8. Conditions for heat-treatment of aluminum alloys.

Generally, the aging treatments are used merely to relieve Full Annealing stress and stabilize the alloys to prevent dimensional changes The annealing of titanium and titanium alloys provides later, especially during or after machining. Both yield strength toughness, ductility at room temperature, dimensional and hardness are improved somewhat by this treatment at and structural stability at elevated temperatures, and the expense of a slight amount of ductility. The corrosion improved machinability.

resistance is also improved, making it closer to the “as cast” alloy.

The full anneal is usually called for as preparation for further working. It is performed at 1,200 to 1,650 °F. The time at Precipitation heat-treatment temperatures are considerably temperature varies from 16 minutes to several hours, depending lower than solution heat-treatment temperatures and range on the thickness of the material and the amount of cold-work from 325 °F to 500 °F. Soaking time ranges from 4 to 18 hours.

to be performed. The usual treatment for the commonly used alloys is 1,300 °F for 1 hour, followed by an air cool. A full Heat-Treatment of Titanium anneal generally results in sufficient scale formation to require Titanium is heat-treated for the following purposes: the use of caustic descaling, such as sodium hydride salt bath.

• Relief of stresses set up during cold forming or Thermal Hardening machining.

Unalloyed titanium cannot be heat-treated, but the alloys • Annealing after hot-working or cold-working, or commonly used in aircraft construction can be strengthened to provide maximum ductility for subsequent cold- by thermal treatment, usually at some sacrifice in ductility.

working.

For best results, a water quench from 1,450 °F, followed by • Thermal hardening to improve strength.

reheating to 900 °F for 8 hours is recommended.

Stress Relieving Case Hardening Stress relieving is generally used to remove stress concentrations The chemical activity of titanium and its rapid absorption of resulting from forming of titanium sheet. It is performed at oxygen, nitrogen, and carbon at relatively low temperatures temperatures ranging from 650 °F to 1,000 °F. The time at make case hardening advantageous for special applications.

temperature varies from a few minutes for a very thin sheet to Nitriding, carburizing, or carbonitriding can be used to produce an hour or more for heavier sections. A typical stress relieving a wear-resistant case of 0.0001 to 0.0002 inch in depth.

treatment is 900 °F for 30 minutes, followed by an air cool.

The discoloration or scale that forms on the surface of the Hardness Testing metal during stress relieving is easily removed by pickling Hardness testing is a method of determining the results of heat- in acid solutions. The recommended solution contains 10 to treatment, as well as the state of a metal prior to heat-treatment.

20 percent nitric acid and 1 to 3 percent hydrofluoric acid.

Since hardness values can be tied in with tensile strength values The solution should be at room temperature or slightly above.

and, in part, with wear resistance. Hardness tests are a valuable 7-25 check of heat-treat control and of material properties. For hardened steels, the diamond penetrator is used; the major load is 150 kilograms; and the hardness is read on the Practically all hardness testing equipment now uses the “C” scale. When this reading is recorded, the letter “C” must resistance to penetration as a measure of hardness. Included precede the number indicated by the pointer. The C-scale among the better-known hardness testers are the Brinell and setup is used for testing metals ranging in hardness from Rockwell, both of which are described and illustrated in this C-20 to the hardest steel (usually about C-70). If the metal is section. Also included is the Barcol tester, a popular portable- softer than C-20, the B-scale setup is used. With this setup, type hardness tester currently in use. the ⁄ 16 -inch ball is used as a penetrator; the major load is 100 kilograms; and the hardness is read on the B-scale.

Brinell Tester In addition to the C and B scales, there are other setups for The Brinell hardness tester uses a hardened spherical ball special testing. The scales, penetrators, major loads, and dial that is forced into the surface of the metal. [Figure 7-9] This numbers to be read are listed in Figure 7-11 .

ball is 10 millimeters (0.3937 inch) in diameter. A pressure of The Rockwell tester is equipped with a weight pan, and 3,000 kilograms is used for ferrous metals and 500 kilograms two weights are supplied with the machine. One weight for nonferrous metals. The pressure must be maintained at is marked in red. The other weight is marked in black.

least 10 seconds for ferrous metals and at least 30 seconds With no weight in the weight pan, the machine applies for nonferrous metals. The load is applied by hydraulic a major load of 60 kilograms. If the scale setup calls for pressure. A hand pump or an electric motor, depending on the a 100-kilogram load, the red weight is placed in the pan.

model of tester, builds up the hydraulic pressure. A pressure For a 150-kilogram load, the black weight is added to the gauge indicates the amount of pressure. There is a release red weight. The black weight is always used with the red mechanism for relieving the pressure after the test has been weight; it is never used alone.

made, and a calibrated microscope is provided for measuring the diameter of the impression in millimeters. The machine Practically all testing is done with either the B-scale setup or has various shaped anvils for supporting the specimen and the C-scale setup. For these scales, the colors may be used as an elevating screw for bringing the specimen in contact with a guide in selecting the weight (or weights) and in reading the ball penetrator. These are attachments for special tests.

the dial. For the B-scale test, use the red weight and read the red numbers. For a C-scale test, add the black weight to the To determine the Brinell hardness number for a metal, red weight and read the black numbers.

measure the diameter of the impression using the calibrated microscope furnished with the tester. Then convert the In setting up the Rockwell machine, use the diamond measurement into the Brinell hardness number on the penetrator for testing materials known to be hard. If the conversion table furnished with the tester.

hardness is unknown, try the diamond, since the steel ball may be deformed if used for testing hard materials. If the Rockwell Tester metal tests below C-22, then change to the steel ball.

The Rockwell hardness tester measures the resistance to penetration, as does the Brinell tester. [Figure 7-10] Instead Use the steel ball for all soft materials, those testing less than of measuring the diameter of the impression, the Rockwell B-100. Should an overlap occur at the top of the B-scale and tester measures the depth, and the hardness is indicated the bottom of the C-scale, use the C-scale setup.

directly on a dial attached to the machine. The dial numbers in the outer circle are black and the inner numbers are red.

Before the major load is applied, securely lock the test specimen Rockwell hardness numbers are based on the difference in place to prevent slipping and to seat the anvil and penetrator between the depth of penetration at major and minor loads.

properly. To do this, apply a load of 10 kilograms before the The greater this difference, the lower the hardness number lever is tripped. This preliminary load is called the minor load.

and the softer the material.

The minor load is 10 kilograms regardless of the scale setup.

Two types of penetrators are used with the Rockwell tester: The metal to be tested in the Rockwell tester must be ground a diamond cone and a hardened steel ball. The load, which smooth on two opposite sides and be free of scratches and forces the penetrator into the metal, is called the major load foreign matter. The surface should be perpendicular to the and is measured in kilograms. The results of each penetrator axis of penetration, and the two opposite ground surfaces and load combination are reported on separate scales should be parallel. If the specimen is tapered, the amount of designated by letters. The penetrator, the major load, and the error depends on the taper. A curved surface also causes a scale vary with the kind of metal being tested.

slight error in the hardness test. The amount of error depends 7-26 on the curvature (i.e., the smaller the radius of curvature, the The design of the Barcol tester is such that operating greater the error). To eliminate such error, a small flat should experience is not necessary. It is only necessary to exert be ground on the curved surface if possible. a light pressure against the instrument to drive the spring- loaded indenter into the material to be tested. The hardness Clad aluminum alloy sheets cannot be tested directly reading is instantly indicated on the dial.

with any accuracy with a Rockwell hardness tester. If the hardness value of the base metal is desired, the pure Several typical readings for aluminum alloys are listed in aluminum coating must be removed from the area to be Figure 7-13 . Note that the harder the material is, the higher checked prior to testing. the Barcol number. To prevent damage to the point, avoid sliding or scraping when it is in contact with the material Barcol Tester being tested. If the point should become damaged, it must be replaced with a new one. Do not attempt to grind the point.

The Barcol tester is a portable unit designed for testing aluminum alloys, copper, brass, or other relatively soft Each tester is supplied with a test disk for checking the materials. [Figure 7-12] It should not be used on aircraft condition of the point. To check the point, press the instrument steels. Approximate range of the tester is 25 to 100 Brinell.

down on the test disk. When the downward pressure brings The unit can be used in any position and in any space that the end of the lower plunger guide against the surface of the allows for the operator’s hand. It is of great value in the disk, the indicator reading should be within the range shown hardness testing of assembled or installed parts, especially on the test disk.

to check for proper heat-treatment. The hardness is indicated on a dial conveniently divided into 100 graduations.

Forging Forging is the process of forming a product by hammering or pressing. When the material is forged below the recrystallization temperature, it is called cold forged. When 1500 3500 worked above the recrystallization temperature, it is referred Pressure gauge c0 c c 90 B30 B B Hydraulic c c B ZEROMNDER 20 B actuating unit FOR RAP TESTING B B c c 0 B B c c c50 c0 10 c c B30 c c B 40 90 20 B B Hand pump 20 50 ZEROMNDER FOR RAP TESTING 80 c c B B 30 10 60 B B 0 70 40 c c 70 B c c50 60 Penetrator Penetrator Specimen Weights Elevating screw Anvil Elevating screw Hand wheel Weight pan Zero adjuster Trip lever Microscope Figure 7-9. Brinell hardness tester. Figure 7-10. Rockwell hardness tester.

7-27 Scale Major Dial Penetrator Symbol Load (kg) Color⁄Number Extruding The extrusion process involves the forcing of metal through A Diamond 60 Black an opening in a die, thus causing the metal to take the shape / " ball B 100 Red 16 of the die opening. The shape of the die will be the cross section of an angle, channel, tube, or some other shape. Some C Diamond 150 Black metals, such as lead, tin, and aluminum, may be extruded D Diamond 100 Black cold; however, most metals are heated before extrusion. The E 100 Red main advantage of the extrusion process is its flexibility.

/ " ball For example, because of its workability, aluminum can be F 60 Red / " ball economically extruded to more intricate shapes and larger G 150 Red / " ball sizes than is practical with other metals. 16 H 60 Red / " ball Extruded shapes are produced in very simple, as well as / " ball K 150 Red extremely complex, sections. In this process, a cylinder of aluminum, for instance, is heated to 750–850 °F and is then Figure 7-11. Standard Rockwell hardness scales.

forced through the opening of a die by a hydraulic ram. The opening is the shape desired for the cross section of the finished to as hot forged. Drop forging is a hammering process that extrusion. The extrusion process forms many structural parts, uses a hot ingot that is placed between a pair of formed dies in such as channels, angles, T-sections, and Z-sections.

a machine called a drop hammer and a weight of several tons is dropped on the upper die. This results in the hot metal being Aluminum is the most extruded metal used in aircraft.

forced to take the form of the dies. Because the process is Aluminum is extruded at a temperature of 700–900 °F (371–482 very rapid, the grain structure of the metal is altered, resulting °C) and requires pressure of up to 80,000 psi (552 MPa). After in a significant increase in the strength of the finished part.

extrusion, the product frequently is subjected to both thermal and mechanical processes to obtain the desired properties.

Casting Extrusion processes are limited to the more ductile materials.

Melting the metal and pouring it into a mold of the desired shape forms casting. Since plastic deformation of the metal does not occur, no alteration of the grain shape or orientation is possible. The cooling rate, the alloys of the metal, and 10 90 the thermal treatment can control the gain size of the metal.

20 80 Castings are normally lower in strength and are more brittle 30 70 than a wrought product of the same material. For intricate 40 60 shapes or items with internal passages, such as turbine blades, casting may be the most economical process. Except for engine parts, most metal components found on an aircraft are wrought instead of cast.

All metal products start in the form of casting. Wrought metals are converted from cast ingots by plastic deformation.

For high-strength aluminum alloys, an 80 to 90 percent reduction (dimensional change in thickness) of the material is required to obtain the high mechanical properties of a fully wrought structure.

Both iron and aluminum alloys are cast for aircraft uses. Cast iron contains 6 to 8 percent carbon and silicon.

Cast iron is a hard un-malleable pig iron made by casting or pouring into a mold. Cast aluminum alloy has been heated to its molten state and poured into a mold to give it the Figure 7-12. Barcol portable hardness tester.

desired shape.

7-28 Cold-Working/Hardening the desired size, it is drawn cold through a die. One end of the rod is filed or hammered to a point and slipped through Cold-working applies to mechanical working performed at the die opening. Here it is gripped by the jaws of the drawing temperatures below the critical range. It results in a strain block and pulled through the die. This series of operations is hardening of the metal. In fact, the metal often becomes so done by a mechanism known as a draw bench.

hard that it is difficult to continue the forming process without softening the metal by annealing.

To reduce the rod gradually to the desired size, it is necessary to draw the wire through successively smaller dies. Because Since the errors attending shrinkage are eliminated in cold- each of these drawings reduces the ductility of the wire, it working, a much more compact and better metal is obtained.

must be annealed from time to time before further drawings The strength and hardness, as well as the elastic limit, are can be accomplished. Although cold-working reduces the increased; but the ductility decreases. Since this makes ductility, it increases the tensile strength of the wire.

the metal more brittle, it must be heated from time to time during certain operations to remove the undesirable effects In making seamless steel aircraft tubing, the tubing is cold of the working.

drawn through a ring-shaped die with a mandrel or metal bar inside the tubing to support it while the drawing operations While there are several cold-working processes, the two with are being performed. This forces the metal to flow between which the aviation mechanic is principally concerned are cold the die and the mandrel and affords a means of controlling rolling and cold drawing. These processes give the metals the wall thickness and the inside and outside diameters.

desirable qualities that cannot be obtained by hot working.

Cold rolling usually refers to the working of metal at room Nonmetallic Aircraft Materials temperature. In this operation, the materials that have been The use of magnesium, plastic, fabric, and wood in aircraft rolled to approximate sizes are pickled to remove the scale, construction has nearly disappeared since the mid-1950s.

after which they are passed through chilled finishing rolls.

Aluminum has also greatly diminished in use, from 80 percent This gives a smooth surface and brings the pieces to accurate of airframes in 1950 to about 15 percent aluminum and dimensions. The principal forms of cold-rolled stocks are aluminum alloys today for airframe construction. Replacing sheets, bars, and rods.

those materials are nonmetallic aircraft materials, such as reinforced plastics and advanced composites.

Cold drawing is used in making seamless tubing, wire, streamlined tie rods, and other forms of stock. Wire is made Wood from hot-rolled rods of various diameters. These rods are The earliest aircraft were constructed of wood and cloth.

pickled in acid to remove scale, dipped in limewater, and Today, except for restorations and some home-built aircraft, then dried in a steam room where they remain until ready very little wood is used in aircraft construction.

for drawing. The lime coating adhering to the metal serves as a lubricant during the drawing operation.

Plastics Plastics are used in many applications throughout modern The size of the rod used for drawing depends upon the aircraft. These applications range from structural components diameter wanted in the finished wire. To reduce the rod to of thermosetting plastics reinforced with fiberglass to decorative trim of thermoplastic materials to windows.

Alloy and Temper Barcol Number Transparent Plastics 1100-O 35 Transparent plastic materials used in aircraft canopies, 3003-O 42 such as windshields, windows and other similar transparent enclosures, may be divided into two major classes or groups: 3003-H14 56 thermoplastic and thermosetting. These plastics are classified 2024-O 60 according to their reaction to heat. Thermoplastic materials 5052-O 62 soften when heated and harden when cooled. These materials can be heated until soft and then formed into the desired 5052-H34 75 shape. When cooled, they retain this shape. The same piece 6061-T 78 of plastic can be reheated and reshaped any number of times without changing the chemical composition of the materials.

2024-T 85 Figure 7-13. Typical Barcol readings for aluminum alloy. Thermosetting plastics harden upon heating, and reheating 7-29 has no softening effect. These plastics cannot be reshaped and all precautions regarding the use of flammable liquids once being fully cured by the application of heat. must be observed.

In addition to the above classes, transparent plastics are Composite Materials manufactured in two forms: monolithic (solid) and laminated. In the 1940s, the aircraft industry began to develop synthetic Laminated transparent plastics are made from transparent fibers to enhance aircraft design. Since that time, composite plastic face sheets bonded by an inner layer material, usually materials have been used more and more. When composites polyvinyl butyryl. Because of its shatter resistant qualities, are mentioned, most people think of only fiberglass, or maybe laminated plastic is superior to solid plastics and is used in graphite or aramids (Kevlar). Composites began in aviation, many pressurized aircraft.

but now are being embraced by many other industries, including auto racing, sporting goods, and boating, as well Most of the transparent sheet used in aviation is manufactured as defense industry uses.

in accordance with various military specifications. A new development in transparent plastics is stretched acrylic.

A “composite” material is defined as a mixture of different Stretched acrylic is a type of plastic, which before being materials or things. This definition is so general that it could shaped, is pulled in both directions to rearrange its molecular refer to metal alloys made from several different metals to structure. Stretched acrylic panels have a greater resistance to enhance the strength, ductility, conductivity, or whatever impact and are less subject to shatter; its chemical resistance characteristics are desired. Likewise, the composition of is greater, edging is simpler, and crazing and scratches are composite materials is a combination of reinforcement, such less detrimental.

as a fiber, whisker, or particle, surrounded and held in place by a resin forming a structure. Separately, the reinforcement and Individual sheets of plastic are covered with a heavy masking the resin are very different from their combined state. Even in paper to which a pressure sensitive adhesive has been added. their combined state, they can still be individually identified This paper helps to prevent accidental scratching during and mechanically separated. One composite, concrete, is storage and handling. Be careful to avoid scratches and composed of cement (resin) and gravel or reinforcement rods gouges which may be caused by sliding sheets against one for the reinforcement to create the concrete.

another or across rough or dirty tables.

Advantages/Disadvantages of Composites If possible, store sheets in bins that are tilted at approximately Some of the many advantages for using composite materials 10° from vertical. If they must be stored horizontally, piles are: should not be over 18 inches high, and small sheets should • High strength-to-weight ratio be stacked on the larger ones to avoid unsupported overhang.

• Fiber-to-fiber transfer of stress allowed by chemical Store in a cool, dry place away from solvent fumes, heating coils, radiators, and steam pipes. The temperature in the bonding storage room should not exceed 120 °F.

• Modulus (stiffness-to-density ratio) 3.5 to 5 times that of steel or aluminum While direct sunlight does not harm acrylic plastic, it causes • Longer life than metals drying and hardening of the masking adhesive, making removal of the paper difficult. If the paper does not roll off • Higher corrosion resistance easily, place the sheet in an oven at 250 °F for 1 minute, • Tensile strength 4 to 6 times that of steel or aluminum maximum. The heat softens the masking adhesive for easy • Greater design flexibility removal of the paper.

• Bonded construction eliminates joints and fasteners If an oven is not available, remove hardened masking paper • Easily repairable by softening the adhesive with aliphatic naphtha. Rub the masking paper with a cloth saturated with naphtha. This The disadvantages of composites include: softens the adhesive and frees the paper from the plastic.

• Inspection methods difficult to conduct, especially Sheets so treated must be washed immediately with clean delamination detection (Advancements in technology water, taking care not to scratch the surfaces.

will eventually correct this problem.)

Note: Aliphatic naphtha is not to be confused with aromatic • Lack of long-term design database, relatively new naphtha and other dry cleaning solvents, which have harmful technology methods effects on plastic. However, aliphatic naphtha is flammable • Cost 7-30 • Very expensive processing equipment A particle is a square piece of material. Glass bubbles (Q-cell) • Lack of standardized system of methodology are hollow glass spheres, and since their dimensions are equal • Great variety of materials, processes, and techniques on all axes, they are called a particle.

• General lack of repair knowledge and expertise A whisker is a piece of material that is longer than it is wide.

• Products often toxic and hazardous Whiskers are usually single crystals. They are very strong • Lack of standardized methodology for construction and used to reinforce ceramics and metals.

and repairs Fibers are single filaments that are much longer than they The increased strength and the ability to design for the are wide. Fibers can be made of almost any material and are performance needs of the product makes composites much not crystalline like whiskers. Fibers are the base for most superior to the traditional materials used in today’s aircraft.

composites. Fibers are smaller than the finest human hair As more and more composites are used, the costs, design, and are normally woven into cloth-like materials.

inspection ease, and information about strength-to-weight advantages help composites become the material of choice Laminated Structures for aircraft construction.

Composites can be made with or without an inner core of material. Laminated structure with a core center is called Composite Safety a sandwich structure. Laminate construction is strong and Composite products can be very harmful to the skin, eyes, stiff, but heavy. The sandwich laminate is equal in strength, and lungs. In the long or short term, people can become and its weight is much less; less weight is very important to sensitized to the materials with serious irritation and health aerospace products.

issues. Personal protection is often uncomfortable, hot, and difficult to wear; however, a little discomfort while working The core of a laminate can be made from nearly anything. The with the composite materials can prevent serious health issues decision is normally based on use, strength, and fabricating or even death.

methods to be used.

Respirator particle protection is very important to protecting Various types of cores for laminated structures include rigid the lungs from permanent damage from tiny glass bubbles foam, wood, metal, or the aerospace preference of honeycomb and fiber pieces. At a minimum, a dust mask approved for made from paper, Nomex®, carbon, fiberglass, or metal.

fiberglass is a necessity. The best protection is a respirator Figure 7-14 shows a typical sandwich structure. It is very with dust filters. The proper fit of a respirator or dust mask is important to follow proper techniques to construct or repair very important, because if the air around the seal is breathed, laminated structures to ensure the strength is not compromised.

the mask cannot protect the wearer’s lungs. When working Taking a high-density laminate or solid face and back plate and with resins, it is important to use vapor protection. Charcoal sandwiching a core in the middle make a sandwich assembly.

filters in a respirator remove the vapors for a period of time.

The design engineer, depending on the intended application When removing the respirator for breaks, and upon placing of the part, decides the selection of materials for the face the mask back on, if you can smell the resin vapors, replace and the back plate. It is important to follow manufacturers’ the filters immediately. Sometimes, charcoal filters last less maintenance manual specific instructions regarding testing than 4 hours. Store the respirator in a sealed bag when not in and repair procedures as they apply to a particular aircraft.

use. If working with toxic materials for an extended period, a supplied air mask and hood are recommended.

Reinforced Plastic Reinforced plastic is a thermosetting material used in the Avoid skin contact with the fibers and other particles by manufacture of radomes, antenna covers, and wingtips, and as wearing long pants and long sleeves along with gloves or insulation for various pieces of electrical equipment and fuel barrier creams. The eyes must be protected using leak-proof cells. It has excellent dielectric characteristics that make it goggles (no vent holes) when working with resins or solvents, ideal for radomes; however, its high strength-to-weight ratio, because chemical damage to the eyes is usually irreversible.

resistance to mildew, rust, and rot, and ease of fabrication make it equally suited for other parts of the aircraft.

Fiber Reinforced Materials The purpose of reinforcement in reinforced plastics is to Reinforced plastic components of aircraft are formed of either provide most of the strength. The three main forms of fiber solid laminates or sandwich-type laminates. Resins used reinforcements are particles, whiskers, and fibers.

to impregnate glass cloths are of the contact pressure type 7-31 (requiring little or no pressure during cure). These resins are properties. The most widely used are the butyls, Bunas, supplied as a liquid, which can vary in viscosity from water and neoprene.

like consistency to thick syrup. Cure or polymerization is affected by the use of a catalyst, usually benzoyl peroxide. Butyl is a hydrocarbon rubber with superior resistance to gas permeation. It is also resistant to deterioration; however, its Solid laminates are constructed of three or more layers of comparative physical properties are significantly less than resin impregnated cloths “wet laminated” together to form those of natural rubber. Butyl resists oxygen, vegetable oils, a solid sheet facing or molded shape. animal fats, alkalies, ozone, and weathering.

Sandwich-type laminates are constructed of two or more Like natural rubber, butyl swells in petroleum or coal solid sheet facings or a molded shape enclosing a fiberglass tar solvents. It has a low water absorption rate and good honeycomb or foam-type core. Honeycomb cores are made resistance to heat and low temperature. Depending on of glass cloths impregnated with polyester or a combination the grade, it is suitable for use in temperatures ranging of nylon and phenolic resins. The specific density and cell from −65 °F to 300 °F. Butyl is used with phosphate ester size of honeycomb cores varies over considerable latitude. hydraulic fluids (Skydrol™), silicone fluids, gases, ketones, Honeycomb cores are normally fabricated in blocks that are and acetones.

later cut to the desired thickness on a band saw.

Buna-S rubber resembles natural rubber both in processing and Foam-type cores are formulated from combinations of performance characteristics. Buna-S is as water resistant as alkyd resins and metatoluene di-isocyanate. Sandwich- natural rubber, but has somewhat better aging characteristics.

type fiberglass components filled with foam-type cores are It has good resistance to heat, but only in the absence of severe manufactured to exceedingly close tolerances on overall flexing. Generally, Buna-S has poor resistance to gasoline, oil, thickness of the molded facing and core material. To achieve concentrated acids, and solvents. Buna-S is normally used for this accuracy, the resin is poured into a close tolerance, tires and tubes as a substitute for natural rubber.

molded shape. The resin formulation immediately foams up to fill the void in the molded shape and forms a bond between Buna-N is outstanding in its resistance to hydrocarbons and the facing and the core. other solvents; however, it has poor resilience in solvents at low temperature. Buna-N compounds have good resistance Rubber to temperatures up to 300 °F and may be procured for low temperature applications down to −75 °F. Buna-N has fair Rubber is used to prevent the entrance of dirt, water, or air, and to prevent the loss of fluids, gases, or air. It is also used tear, sunlight, and ozone resistance. It has good abrasion resistance and good breakaway properties when used in to absorb vibration, reduce noise, and cushion impact loads.

The term “rubber” is as all-inclusive as the term “metal.” It is contact with metal. When used as a seal on a hydraulic piston, it does not stick to the cylinder wall. Buna-N is used for oil used to include not only natural rubber, but also all synthetic and silicone rubbers. and gasoline hoses, tank linings, gaskets, and seals.

Neoprene can take more punishment than natural rubber Natural Rubber and has better low-temperature characteristics. It possesses Natural rubber has better processing and physical properties exceptional resistance to ozone, sunlight, heat, and aging.

than synthetic or silicone rubber. These properties include Neoprene looks and feels like rubber. Neoprene, however, flexibility, elasticity, tensile strength, tear strength, and low is less like rubber in some of its characteristics than butyl heat buildup due to flexing (hysteresis). Natural rubber is a or Buna. The physical characteristics of neoprene, such as general-purpose product; however, its suitability for aircraft tensile strength and elongation, are not equal to natural rubber use is somewhat limited because of its inferior resistance but do have a definite similarity. Its tear resistance, as well to most influences that cause deterioration. Although it as its abrasion resistance, is slightly less than that of natural provides an excellent seal for many applications, it swells rubber. Although its distortion recovery is complete, it is not and often softens in all aircraft fuels and in many solvents as rapid as natural rubber.

(naphthas and so forth). Natural rubber deteriorates more rapidly than synthetic rubber. It is used as a sealing material Neoprene has superior resistance to oil. Although it is good for water/methanol systems.

material for use in nonaromatic gasoline systems, it has poor resistance to aromatic gasoline. Neoprene is used primarily Synthetic Rubber for weather seals, window channels, bumper pads, oil resistant Synthetic rubber is available in several types, each of which hose, and carburetor diaphragms. It is also recommended for is compounded of different materials to give the desired 7-32 Face sheet Adhesive Honeycomb Face sheet Fabricated sandwich panel Figure 7-14. Sandwich structure.

use with Freon™ and silicate ester lubricants.

There are two types of elastic shock absorbing cord. Type I Thiokol, known also as polysulfide rubber, has the highest is a straight cord, and type II is a continuous ring known as resistance to deterioration but ranks the lowest in physical a “bungee.” The advantages of the type II cord are that it is properties. Petroleum, hydrocarbons, esters, alcohols, easily and quickly replaced and does not need to be secured gasoline, or water, in general, does not seriously affect by stretching and whipping. Shock cord is available in 1 13 Thiokols. Thiokols are ranked low in such physical properties standard diameters from ⁄ 4 inch to ⁄ 16 inch.

as compression set, tensile strength, elasticity, and tear abrasion resistance. Thiokol is used for oil hoses, tank linings Three colored threads are braided into the outer cover for for aromatic aviation gasoline, gaskets, and seals. the entire length of the cord. Two of these threads are of the same color and represent the year of manufacture; the third Silicone rubbers are a group of plastic rubber materials made thread, a different color, represents the quarter of the year in from silicon, oxygen, hydrogen, and carbon. The silicones have which the cord was made. The code covers a 5-year period excellent heat stability and very low temperature flexibility. and then repeats itself. This makes it easy to figure forward They are suitable for gaskets, seals, or other applications where or backward from the years shown in Figure 7-15 .

elevated temperatures up to 600 °F are prevalent. Silicone rubbers are also resistant to temperatures down to −150 °F. Seals Throughout this temperature range, silicone rubber remains Seals are used to prevent fluid from passing a certain point, extremely flexible and useful with no hardness or gumminess.

as well as to keep air and dirt out of the system in which they Although this material has good resistance to oils, it reacts are used. The increased use of hydraulics and pneumatics in unfavorably to both aromatic and nonaromatic gasoline.

aircraft systems has created a need for packings and gaskets of varying characteristics and design to meet the many Silastic, one of the best-known silicones, is used to insulate variations of operating speeds and temperatures to which they electrical and electronic equipment. Because of its dielectric are subjected. No one style or type of seal is satisfactory for properties over a wide range of temperatures, it remains all installations. Some of the reasons for this are: flexible and free from crazing and cracking. Silastic is also • Pressure at which the system operates used for gaskets and seals in certain oil systems.

• Type fluid used in the system Shock Absorber Cord • Metal finish and the clearance between adjacent parts Shock absorber cord is made from natural rubber strands • Type motion (rotary or reciprocating), if any encased in a braided cover of woven cotton cords treated to resist oxidation and wear. Great tension and elongation are Seals are divided into three main classes: packings, gaskets, obtained by weaving the jacket upon the bundle of rubber and wipers.

strands while they are stretched about three times their original length.

7-33 Packings fluid is always coded with a green stripe, but may also have a blue, grey, red, green, or yellow dot as a part of the color code.

Packings are made of synthetic or natural rubber. They Color codes on O-rings that are compatible with hydrocarbon are generally used as “running seals,” that is, in units that fluid always contains red but never contain blue. A colored contain moving parts, such as actuating cylinders, pumps, stripe around the circumference indicates that the O-ring selector valves, and so forth. Packings are made in the form is a boss gasket seal. The color of the stripe indicates fluid of O-rings, V-rings, and U-rings, each designed for a specific compatibility: red for fuel, blue for hydraulic fluid.

purpose. [Figure 7-16] The coding on some rings is not permanent. On others O-Ring Packings it may be omitted due to manufacturing difficulties or O-ring packings are used to prevent both internal and interference with operation. Furthermore, the color-coding external leakage. This type of packing ring seals effectively system provides no means to establish the age of the O-ring in both directions and is the type most commonly used. In or its temperature limitations.

installations subject to pressures above 1,500 psi, backup rings are used with O-rings to prevent extrusion.

Because of the difficulties with color-coding, O-rings are available in individual hermetically-sealed envelopes When O-ring packing is subjected to pressure from both sides, labeled with all pertinent data. When selecting an O-ring for as in actuating cylinders, two backup rings must be used (one installation, the basic part number on the sealed envelope on either side of the O-ring). When an O-ring is subject to provides the most reliable compound identification.

pressure on only one side, a single backup ring is generally used. In this case, the backup ring is always placed on the Although an O-ring may appear perfect at first glance, slight side of the O-ring away from the pressure.

surface flaws may exist. These flaws are often capable of preventing satisfactory O-ring performance under the variable The materials from which O-rings are manufactured have been operating pressures of aircraft systems; therefore, O-rings compounded for various operating conditions, temperatures, and fluids. An O-ring designed specifically for use as a static (stationary) seal, probably will not do the job when installed Year Threads Color on a moving part, such as a hydraulic piston. Most O-rings 2000 2 Black are similar in appearance and texture, but their characteristics may differ widely. An O-ring is useless if it is not compatible 2001 2 Green with the system fluid and operating temperature.

2002 2 Red Advances in aircraft design have necessitated new O-ring 2003 2 Blue compositions to meet changed operating conditions. Hydraulic 2004 2 Yellow O-rings were originally established under AN specification numbers (6227, 6230, and 6290) for use in MIL-H-5606 fluid 2005 2 Black at temperatures ranging from −65 °F to +160 °F. When new 2006 2 Green designs raised operating temperatures to a possible 275 °F, more compounds were developed and perfected.

2007 2 Red 2008 2 Blue Recently, a compound was developed that offered improved 2009 2 Yellow low-temperature performance without sacrificing high- temperature performance, rendering the other series obsolete.

2010 2 Black This superior material was adopted in the MS28775 series.

This series is now the standard for MIL-H-5606 systems in Quarter Marking which the temperature may vary from −65 °F to +275 °F.

Quarter Threads Color Manufacturers provide color-coding on some O-rings, but this January, February, March 1 Red is not a reliable or complete means of identification. The color- April, May, June 1 Blue coding system does not identify sizes but only system fluid or vapor compatibility and, in some cases, the manufacturer.

July, August, September 1 Green Color codes on O-rings that are compatible with MIL-H-5606 October, November, December 1 Yellow fluid always contains blue but may also contain red or other colors. Packings and gaskets suitable for use with Skydrol™ Figure 7-15. Shock absorber cord color coding.

7-34 should be rejected for flaws that affect their performance. V-Ring Packings Such flaws are difficult to detect, and one aircraft manufacturer V-ring packings (AN6225) are one-way seals and are always recommends using a 4-power magnifying glass with adequate installed with the open end of the “V” facing the pressure.

lighting to inspect each ring before it is installed.

V-ring packings must have a male and female adapter to hold them in the proper position after installation. It is also By rolling the ring on an inspection cone or dowel, the necessary to torque the seal retainer to the value specified inner diameter surface can also be checked for small cracks, by the manufacturer of the component being serviced, or the particles of foreign material, or other irregularities that cause seal may not give satisfactory service. An installation using leakage or shorten the life of the O-ring. The slight stretching V-rings is shown in Figure 7-17 .

of the ring when it is rolled inside out helps to reveal some defects not otherwise visible.

U-Ring Packings U-ring packings (AN6226) and U-cup packings are used in Backup Rings brake assemblies and brake master cylinders. The U-ring and Backup rings (MS28782) made of Teflon™ do not deteriorate U-cup seal pressure in only one direction; therefore, the lip of with age, are unaffected by any system fluid or vapor, and can the packings must face toward the pressure. U-ring packings tolerate temperature extremes in excess of those encountered are primarily low-pressure packings to be used with pressures in high-pressure hydraulic systems. Their dash numbers of less than 1,000 psi.

indicate not only their size but also relate directly to the dash number of the O-ring for which they are dimensionally suited.

Gaskets They are procurable under several basic part numbers, but Gaskets are used as static (stationary) seals between two they are interchangeable; that is, any Teflon™ backup ring flat surfaces. Some of the more common gasket materials may be used to replace any other Teflon™ backup ring if it is are asbestos, copper, cork, and rubber. Asbestos sheeting of proper overall dimension to support the applicable O-ring.

is used wherever a heat-resistant gasket is needed. It is Backup rings are not color-coded or otherwise marked and used extensively for exhaust system gaskets. Most asbestos must be identified from package labels.

exhaust gaskets have a thin sheet of copper edging to prolong their life.

The inspection of backup rings should include a check to ensure that surfaces are free from irregularities, that the edges A solid copper washer is used for spark plug gaskets where it are clean cut and sharp, and that scarf cuts are parallel. When is essential to have a non-compressible, yet semisoft gasket.

checking Teflon™ spiral backup rings, make sure that the Cork gaskets can be used as an oil seal between the engine coils do not separate more than ⁄ 4 inch when unrestrained.

crankcase and accessories, and where a gasket is required that can occupy an uneven or varying space caused by a rough surface or expansion and contraction.

Rubber sheeting can be used where there is a need for a compressible gasket. It should not be used in any place where it may come in contact with gasoline or oil because the rubber deteriorates very rapidly when exposed to these U-ring O-ring substances. Gaskets are used in fluid systems around the end caps of actuating cylinders, valves, and other units. The gasket generally used for this purpose is in the shape of an O-ring, similar to O-ring packings.

Wipers Wipers are used to clean and lubricate the exposed portions V-ring U-cup of piston shafts. They prevent dirt from entering the system and help protect the piston shaft against scoring. Wipers may be either metallic or felt. They are sometimes used together, a felt wiper installed behind a metallic wiper.

Sealing Compounds Male Female Certain areas of all aircraft are sealed to withstand pressurization by air, to prevent leakage of fuel, to prevent Figure 7-16. Packing rings.

7-35 passage of fumes, or to prevent corrosion by sealing against the weather. Most sealants consist of two or more ingredients Adjustment nuts properly proportioned and compounded to obtain the best results. Some materials are ready for use as packaged, but Male V-ring adapter others require mixing before application.

One Part Sealants One part sealants are prepared by the manufacturer and are ready for application as packaged. However, the consistency of some of these compounds may be altered to satisfy a particular method of application. If thinning is desired, use the thinner recommended by the sealant manufacturer.

Female V-ring adapter V-ring packing Two Part Sealants Two part sealants are compounds requiring separate Figure 7-17. V-ring installation.

packaging to prevent cure prior to application and are identified as the base sealing compound and the accelerator.

concerning various sealants.

Any alteration of the prescribed ratios reduces the quality of the material. Combining equal portions, by weight, of base The curing rate of mixed sealants varies with changes in compound and accelerator, mixes two part sealants.

temperature and humidity. Curing of sealants is extremely slow if the temperature is below 60 °F. A temperature of 77 °F with All sealant material should be carefully weighed in accordance 50 percent relative humidity is the ideal condition for curing with the sealant manufacturer’s recommendations. Sealant most sealants.

material is usually weighed with a balance scale equipped with weights specially prepared for various quantities of Curing may be accelerated by increasing the temperature, but sealant and accelerator.

the temperature should never be allowed to exceed 120 °F at any time in the curing cycle. Heat may be applied by using Before weighing the sealant materials, thoroughly stir both infrared lamps or heated air. If heated air is used, it must be the base sealant compound and the accelerator. Do not use properly filtered to remove moisture and dirt.

accelerator, which is dried out, lumpy, or flaky. Pre-weighed sealant kits do not require weighing of the sealant and Heat should not be applied to any faying surface sealant accelerator before mixing when the entire quantity is to be installation until all work is completed. All faying surface mixed.

applications must have all attachments, permanent or temporary, completed within the application limitations of After determining the proper amount of base sealant the sealant.

compound and accelerator, add the accelerator to the base sealant compound. Immediately after adding the Sealant must be cured to a tack-free condition before applying accelerator, thoroughly mix the two parts by stirring or brush top coatings. (Tack-free consistency is the point at folding, depending on the consistency of the material.

which a sheet of cellophane pressed onto the sealant no Carefully mix the material to prevent entrapment of air in longer adheres.)

the mixture. Overly rapid or prolonged stirring builds up heat in the mixture and shortens the normal application time Aircraft Hardware (working life) of the mixed sealant.

Aircraft hardware is the term used to describe the various types of fasteners and miscellaneous small items used in To ensure a well-mixed compound, test by smearing a small the manufacture and repair of aircraft. The importance of portion on a clean, flat metal, or glass surface. If flecks or aircraft hardware is often overlooked because of its small lumps are found, continue mixing. If the flecks or lumps size; however, the safe and efficient operation of any aircraft cannot be eliminated, reject the batch.

is greatly dependent upon the correct selection and use of aircraft hardware.

The working life of mixed sealant is from ⁄ 2 hour to 4 hours (depending upon the class of sealant); therefore, apply An aircraft, even though made of the best materials and mixed sealant as soon as possible or place in refrigerated strongest parts, would be of doubtful value unless those parts storage. Figure 7-18 presents general information 7-36 were firmly held together. Several methods are used to hold between the American National series and the American metal parts together; they include riveting, bolting, brazing, Standard Unified series that should be pointed out. In the and welding. The process used must produce a union that is 1-inch diameter size, the NF thread specifies 14 threads per as strong as the parts that are joined. inch (1-14 NF), while the UNF thread specifies 12 threads per inch (1-12 UNF). Both types of threads are designated Identification by the number of times the incline (threads) rotates around a Their specification number or trade name identifies most 1-inch length of a given diameter bolt or screw. For example, 1 4 a 1/4-28 thread indicates that a ⁄ 4 -inch ( ⁄ 16 inch) diameter bolt items of aircraft hardware. Threaded fasteners and rivets are identified by AN (Air Force-Navy) numbers, NAS (National has 28 threads in 1 inch of its threaded length.

Aircraft Standard) numbers, or MS (Military Standard) numbers. Quick-release fasteners are usually identified by Class of fit also designates threads. The Class of a thread indicates the tolerance allowed in manufacturing: factory trade names and size designations.

• Class 1 is a loose fit Threaded Fasteners • Class 2 is a free fit Various types of fastening devices allow quick dismantling or replacement of aircraft parts that must be taken apart and • Class 3 is a medium fit put back together at frequent intervals. Riveting or welding • Class 4 is a close fit these parts each time they are serviced would soon weaken or ruin the joint. Furthermore, some joints require greater Aircraft bolts are almost always manufactured in the Class tensile strength and stiffness than rivets can provide. Bolts 3, medium fit.

and screws are two types of fastening devices that give the required security of attachment and rigidity. Generally, bolts A Class 4 fit requires a wrench to turn the nut onto a bolt, are used where great strength is required, and screws are used whereas a Class 1 fit can easily be turned by hand. Generally, where strength is not the deciding factor. Bolts and screws aircraft screws are manufactured with a Class 2 thread fit for are similar in many ways. They are both used for fastening ease of assembly.

or holding, and each has a head on one end and screw threads on the other. Regardless of these similarities, there are several Bolts and nuts are also produced with right-hand and left-hand distinct differences between the two types of fasteners. The threads. A right-hand thread tightens when turned clockwise; threaded end of a bolt is always blunt while that of a screw a left-hand thread tightens when turned counterclockwise.

may be either blunt or pointed.

Aircraft Bolts The threaded end of a bolt usually has a nut screwed onto it Aircraft bolts are fabricated from cadmium- or zinc-plated to complete the assembly. The threaded end of a screw may corrosion-resistant steel, un-plated corrosion-resistant steel, fit into a female receptacle, or it may fit directly into the or anodized-aluminum alloys. Most bolts used in aircraft material being secured. A bolt has a short threaded section structures are either general purpose, AN bolts, NAS and a comparatively long grip length or unthreaded portion, internal wrenching or close tolerance bolts, or MS bolts. In whereas a screw has a longer threaded section and may have certain cases, aircraft manufacturers make bolts of different no clearly defined grip length. Turning the nut on the bolt dimensions or greater strength than the standard types. Such generally tightens a bolt assembly; the head of the bolt may bolts are made for a particular application, and it is of extreme or may not be designed for turning. Turning its head always importance to use like bolts in replacement. The letter “S” tightens a screw.

stamped on the head usually identifies special bolts.

When it becomes necessary to replace aircraft fasteners, a AN bolts come in three head styles: hex head, Clevis, and duplicate of the original fastener should be used if possible.

eyebolt. [Figure 7-19] NAS bolts are available in hex head, If duplicate fasteners are not available, extreme care and internal wrenching, and countersunk head styles. MS bolts caution must be used in selecting substitutes.

come in hex head and internal wrenching styles.

Classification of Threads General Purpose Bolts Aircraft bolts, screws, and nuts are threaded in the American The hex head aircraft bolt (AN-3 through AN-20) is an National Coarse (NC) thread series, the American National all-purpose structural bolt used for general applications Fine (NF) thread series, the American Standard Unified involving tension or shear loads where a light drive fit is Coarse (UNC) thread series, or the American Standard permissible (0.006-inch clearance for a ⁄ 8 -inch hole and Unified Fine (UNF) thread series. There is one difference 7-37 Storage Storage Accelerator Mixing Ratio Application Temperature Application Sealant Base (Shelf) Life (Shelf) Life (Catalyst) by Weight Life (Work) Range and Limitations After Mixing Unmixed 12 parts of 5 days at EC-801 (black) Faying surfaces, EC-807 to 100 −20 °F after MIL-S-7502A 2–4 hours 6 months f i llet seals, and −65 °F to 200 °F EC-807 parts of flash freeze packing gaps Class B-2 EC-801 at −65 °F EC-800 (red) Use as is 8–12 hours 6–9 months Coating rivet −65 °F to 200 °F None Not applicable EC-612 P Inde fi nite Packing voids Not applicable −40 °F to 200 °F (pink) Use as is 6–9 months None non-drying up to ¼" MIL-P-20628 10 parts of 5 days at PR-1302HT PR-1302HT-A −20 °F after Sealing access 2–4 hours 6 months −65 °F to 200 °F PR-1302HT-A (red) to 100 parts flash freeze door gaskets MIL-S-8784 of PR-1302HT at −65 °F PR-727 12 parts of 5 days at Potting electrical potting PR-727A to 1½ hours −20 °F after 6 months connections and −65 °F to 200 °F PR-727A compound 100 parts of minimum flash freeze bulkhead seals MIL-S-8516B PR-727 at −65 °F Solvent Sealing hot air HT-3 release, sets ducts passing Use as is 6–9 months Not applicable −60 °F to 200 °F None (grey–green) up in 2–4 through hours bulkheads EC-776 Inde fi nite −65 °F to 200 °F (clear amber) Use as is 8–12 hours Not applicable Top coating None in airtight MIL-S-4383B containers Figure 7-18. General sealant information.

other sizes in proportion). NAS-495) are fabricated from high-strength steel and are suitable for use in both tension and shear applications. When Alloy-steel bolts smaller than No. 10-32 and aluminum- they are used in steel parts, the bolt hole must be slightly alloy bolts smaller than ⁄ 4 inch in diameter are not used in countersunk to seat the large corner radius of the shank at primary structures. Aluminum-alloy bolts and nuts are not the head. In Dural material, a special heat-treated washer used where they are repeatedly removed for purposes of must be used to provide an adequate bearing surface for the maintenance and inspection. Aluminum-alloy nuts may be head. The head of the internal wrenching bolt is recessed to used with cadmium-plated steel bolts loaded in shear on land allow the insertion of an internal wrench when installing or airplanes, but are not used on seaplanes due to the increased removing the bolt. Special high-strength nuts are used on possibility of dissimilar metal corrosion. these bolts. Replace an internal wrenching bolt with another The AN-73 drilled head bolt is like the standard hex internal wrenching bolt. Standard AN hex head bolts and bolt, but has a deeper head, which is drilled to receive washers cannot be substituted for them, as they do not have wire for safetying. The AN-3 and the AN-73 series bolts the required strength.

are interchangeable, for all practical purposes, from the standpoint of tension and shear strengths. Identification and Coding Bolts are manufactured in many shapes and varieties. A Close Tolerance Bolts clear-cut method of classification is difficult. The shape of Close tolerance bolts are machined more accurately than the the head, method of securing, material used in fabrication, general-purpose bolt. Close tolerance bolts may be hex headed or the expected usage can identify bolts.

(AN-173 through AN-186) or have a 100° countersunk head (NAS-80 through NAS-86). They are used in applications AN-type aircraft bolts can be identified by the code markings where a tight drive fit is required. (The bolt moves into position on the bolt heads. The markings generally denote the bolt only when struck with a 12- to 14-ounce hammer.) manufacturer, the material used to make the bolt, and whether the bolt is a standard AN-type or a special purpose bolt.

Internal Wrenching Bolts • AN standard steel bolts are marked with either a raised Internal wrenching bolts, (MS-20004 through MS-20024 or 7-38 dash or asterisk or a single raised dash. rivet. The Jo-bolt consists of three parts: a threaded steel-alloy bolt, a threaded steel nut, and an expandable stainless steel • AN aluminum-alloy bolts are marked with two raised sleeve. The parts are factory preassembled. As the Jo-bolt is dashes to indicate corrosion-resistant steel.

installed, the bolt is turned while the nut is held. This causes • Additional information, such as bolt diameter, bolt the sleeve to expand over the end of the nut, forming the length, and grip length, may be obtained from the bolt blind head and clamping against the work. When driving is part number.

complete, a portion of the bolt breaks off. The high shear and tensile strength of the Jo-bolt makes it suitable for use in cases For example, in the bolt part number AN3DD5A, of high stresses where some of the other blind fasteners would not be practical. Jo-bolts are often a part of the permanent • The “AN” designates that it is an Air Force-Navy structure of late model aircraft. They are used in areas that are standard bolt.

not often subjected to replacement or servicing. (Because it is • The “3” indicates the diameter in sixteenths of an inch a three-part fastener, it should not be used where any part, in ( ⁄ 16 ).

becoming loose, could be drawn into the engine air intake.)

• The “DD” indicates the material is 2024 aluminum Other advantages of using Jo-bolts are their excellent resistance alloy. to vibration, weight saving, and fast installation by one person.

• The letter “C” in place of the “DD” would indicate Presently, Jo-bolts are available in four diameters: corrosion-resistant steel, and the absence of the letters would indicate cadmium-plated steel. • 200 series, approximately ⁄ 16 inch in diameter 5 1 • The “5” indicates the length in eighths of an inch ( ⁄ 8 ). • 260 series, approximately ⁄ 4 inch in diameter • the “A” indicates that the shank is undrilled. If the • 312 series, approximately ⁄ 16 inch in diameter letter “H” preceded the “5” in addition to the “A” • 375 series, approximately ⁄ 8 inch in diameter.

following it, the head would be drilled for safetying.

Jo-bolts are available in three head styles: F (flush), P (hex Close tolerance NAS bolts are marked with either a raised head), and FA (flush millable).

or recessed triangle. The material markings for NAS bolts are the same as for AN bolts, except that they may be either Lockbolts raised or recessed. Bolts inspected magnetically (Magnaflux) Lockbolts are used to attach two materials permanently. They or by fluorescent means (Zyglo) are identified by means of are lightweight and are equal in strength to standard bolts.

colored lacquer or a head marking of a distinctive type.

Lockbolts are manufactured by several companies and conform to Military Standards, which specify the size of a lockbolt’s Special-Purpose Bolts head in relation to the shank diameter, plus the alloy used in Bolts designed for a particular application or use is classified its construction. The only drawback to lockbolt installations is as special-purpose bolts. Clevis bolts, eyebolts, Jo-bolts, and that they are not easily removable compared to nuts and bolts.

lockbolts are special-purpose bolts.

The lockbolt combines the features of a high-strength bolt and Clevis Bolts rivet, but it has advantages over both. The lockbolt is generally The head of a Clevis bolt is round and is either slotted to used in wing splice fittings, landing gear fittings, fuel cell receive a common screwdriver or recessed to receive a cross fittings, longerons, beams, skin splice plates, and other major point screwdriver. This type of bolt is used only where shear structural attachments. It is more easily and quickly installed loads occur and never in tension. It is often inserted as a than the conventional rivets or bolts and eliminates the use mechanical pin in a control system.

of lock washers, cotter pins, and special nuts. Like the rivet, the lockbolt requires a pneumatic hammer or “pull gun” for Eyebolt installation. When installed, it is rigidly and permanently The eyebolt is a special-purpose bolt used where external locked in place. Three types of lockbolts are commonly used: tension loads are to be applied. The eyebolt is designed for the pull type, the stump type, and the blind type. [Figure 7-20] the attachment of devices, such as the fork of a turnbuckle, a Clevis, or a cable shackle. The threaded end may or may Pull Type not be drilled for safetying.

Pull-type lockbolts are used mainly in aircraft primary and secondary structures. They are installed very rapidly and have Jo-Bolt approximately one-half the weight of equivalent AN steel Jo-bolt is a trade name for an internally threaded three-piece 7-39 Standard head bolt Drilled hex head bolt Countersunk head bolt Internal hex head bolt Eyebolt Clevis bolt 0 7 AIR A E S A R A N M S C S E O S O R T O A O E C I P AN standard steel bolt AN standard steel bolt AN standard steel bolt AN standard steel bolt AN standard steel bolt (corrosion resistant) AN AN SPEC 4 C Special bolt AN standard steel bolt AN standard steel bolt AN standard steel bolt AN standard steel bolt X 63-59131 S Special bolt Drilled head bolt Special bolt NAS close tolerance bolt Aluminum alloy (2024) bolt W F O Magnetically inspected Clevis bolt Reworked bolt Low strength Orange-dyed material bolt magnetically inspected Figure 7-19. Aircraft bolt identification.

bolts and nuts. A special pneumatic “pull gun” is required lockbolts. They are used primarily where clearance does to install this type of lockbolt. One person can accomplish not permit installation of the pull-type lockbolt. A standard installation since bucking is not required. pneumatic riveting hammer (with a hammer set attached for swaging the collar into the pin locking grooves) and a Stump Type bucking bar are tools necessary for the installation of stump- type lockbolts.

Stump-type lockbolts, although they do not have the extended stem with pull grooves, are companion fasteners to pull-type 7-40 Blind Type collar by splitting it axially with a sharp, cold chisel. Be careful not to break out or deform the hole. The use of a backup bar Blind-type lockbolts come as complete units or assemblies.

on the opposite side of the collar being split is recommended.

They have exceptional strength and sheet pull-together The pin may then be driven out with a drift punch.

characteristics. Blind lockbolts are used where only one side of the work is accessible and, generally, where it is difficult Aircraft Nuts to drive a conventional rivet. This type of lockbolt is installed Aircraft nuts are made in a variety of shapes and sizes. They in the same manner as the pull-type lockbolt.

are made of cadmium-plated carbon steel, stainless steel, or anodized 2024T aluminum alloy and may be obtained with Common Features either right- or left-hand threads. No identifying marking or Common features of the three types of lockbolts are the lettering appears on nuts. Only the characteristic metallic annular locking grooves on the pin and the locking collar, luster or color of the aluminum, brass, or the insert can which is swaged into the pin’s lock grooves to lock the pin identify them when the nut is of the self-locking type. They in tension. The pins of the pull- and blind-type lockbolts are can be further identified by their construction.

extended for pull installation. The extension is provided with pulling grooves and a tension breakoff groove.

Aircraft nuts can be divided into two general groups: non- self-locking and self-locking nuts. Non-self-locking nuts Composition are those that must be safetied by external locking devices, The pins of pull- and stump-type lockbolts are made of heat- such as cotter pins, safety wire, or locknuts. Self-locking nuts treated alloy steel or high-strength aluminum alloy. Companion contain the locking feature as an integral part.

collars are made of aluminum alloy or mild steel. The blind lockbolt consists of a heat-treated alloy steel pin, blind sleeve Non-Self-Locking Nuts and filler sleeve, mild steel collar, and carbon steel washer.

Most of the familiar types of nuts, including the plain nut, Substitution the castle nut, the castellated shear nut, the plain hex nut, the light hex nut, and the plain check nut are the non-self-locking Alloy-steel lockbolts may be used to replace steel high-shear type. [Figure 7-25] rivets, solid steel rivets, or AN bolts of the same diameter and head type. Aluminum-alloy lockbolts may be used to replace solid aluminum-alloy rivets of the same diameter and head type. Steel and aluminum-alloy lockbolts may also be used to replace steel and 2024T aluminum-alloy bolts, respectively, of the same diameter. Blind lockbolts may be used to replace solid aluminum-alloy rivets, stainless steel rivets, or all blind rivets of the same diameter.

Numbering System The numbering systems for the various types of lockbolts are explained by the break-outs in Figure 7-21 .

Grip Range To determine the bolt grip range required for any application, measure the thickness of the material with a hook scale inserted through the hole. Once this measurement is determined, select the correct grip range by referring to the charts provided by the rivet manufacturer. Examples of grip range charts are shown in Figures 7-22 and 7-23 .

When installed, the lockbolt collar should be swaged substantially throughout the complete length of the collar. The tolerance of the broken end of the pin relative to the top of the collar must be within the dimensions given in Figure 7-24 .

Pull type Stump type Blind type When removal of a lockbolt becomes necessary, remove the Figure 7-20. Lockbolt types.

7-41 The wing nut, AN350, is intended for use where the desired The castle nut, AN310, is used with drilled shank AN hex tightness can be obtained by hand and where the assembly head bolts, Clevis bolts, eyebolts, drilled head bolts, or studs. is frequently removed.

It is rugged and can withstand large tensional loads. Slots (called castellations) in the nut are designed to accommodate Self-Locking Nuts a cotter pin or lock wire for safety.

As their name implies, self-locking nuts need no auxiliary means of safetying but have a safetying feature included as The castellated shear nut, AN320, is designed for use with an integral part of their construction. Many types of self- devices, such as drilled Clevis bolts and threaded taper pins, locking nuts have been designed and their use has become which are normally subjected to shearing stress only. Like quite widespread. Common applications are: the castle nut, it is castellated for safetying. Note, however, • Attachment of antifriction bearings and control pulleys that the nut is not as deep or as strong as the castle nut; also, • Attachment of accessories, anchor nuts around that the castellations are not as deep as those in the castle nut.

inspection holes, and small tank installation openings The plain hex nut, AN315 and AN335 (fine and coarse • Attachment of rocker box covers and exhaust stacks thread), is of rugged construction. This makes it suitable for carrying large tensional loads. However, since it requires an Self-locking nuts are acceptable for use on certificated aircraft auxiliary locking device, such as a check nut or lock washer, subject to the restrictions of the manufacturer. Self-locking nuts its use on aircraft structures is somewhat limited.

are used on aircraft to provide tight connections that do not shake loose under severe vibration. Do not use self-locking The light hex nut, AN340 and AN345 (fine and coarse nuts at joints, which subject either the nut or bolt to rotation.

thread), is a much lighter nut than the plain hex nut and must They may be used with antifriction bearings and control be locked by an auxiliary device. It is used for miscellaneous pulleys, provided the inner race of the bearing is clamped light tension requirements.

to the supporting structure by the nut and bolt. Plates must be attached to the structure in a positive manner to eliminate The plain check nut, AN316, is employed as a locking device rotation or misalignment when tightening the bolts or screws.

for plain nuts, set screws, threaded rod ends, and other devices.

Lockbolt collar Pull-type lockbolt LC C C ALPP H T 8 8 ALPP Head type LC Lockbolt collar ACT509 = close tolerance AN-509 C-sink head C Material ALPP = pan head C = 24ST aluminum alloy (green color). Use with heat-treated alloy ALPB = brazier head lockbolts only.

ALP509 = standard AN-509 C-sink head F = 61ST aluminum alloy (plain color). Use with 75ST aluminum ALP426 = standard AN-426 C-sink head alloy lockbolts only.

H Class fi t R = mild steel (cadmium plated). Use with heat-treated alloy steel H = hole fi lling (interference fi t) lockbolts for high temperature applications only.

N = non-hole filling (clearance fi t) Diameter of a pin in 32nds of an inch C T Pin Materials E = 75S-T6 aluminum alloy Stump-type lockbolt T = heat-treated alloy steel ALSF E 8 8 Body diameter in 32nds of an inch ALSF Head type Grip length in 16ths of an inch ASCT509 = close tolerance AN-509 C-sink head ALSF = f l athead type ALS509 = standard AN-509 C-sink head Blind-type lockbolt ALS426 = standard AN-426 C-sink head BL 8 4 E Pin materials BL Blind lockbolt E = 75S-T6 aluminum alloy Diameter in 32nds of an inch T = heat-treated alloy steel Grip length in 16ths of an inch, ± ⁄ inch Body diameter in 32nds of an inch 8 Grip length in 16ths of an inch 8 Figure 7-21. Lockbolt numbering system.

7-42 The two general types of self-locking nuts currently in use ¼" Diameter / " Diameter are the all-metal type and the fiber lock type. For the sake of Grip Range Grip Range Grip Grip simplicity, only three typical kinds of self-locking nuts are Number Number Minimum Maximum Minimum Maximum considered in this handbook: the Boots self-locking and the 1 2 0.031 0.094 0.156 0.094 stainless steel self-locking nuts, representing the all-metal 3 0.094 0.156 0.219 0.156 types; and the elastic stop nut, representing the fiber insert type.

3 4 0.156 0.219 0.281 0.219 4 5 0.219 0.281 0.344 0.281 Boots Self-Locking Nut 5 6 0.281 0.344 0.406 0.344 The Boots self-locking nut is of one piece, all-metal 6 7 0.344 0.406 0.469 0.406 construction designed to hold tight despite severe vibration.

7 8 0.406 0.469 0.531 0.469 Note in Figure 7-26 that it has two sections and is essentially 8 9 0.469 0.531 0.594 0.531 two nuts in one: a locking nut and a load-carrying nut. The 9 10 0.531 0.594 0.656 0.594 two sections are connected with a spring, which is an integral 10 11 0.594 0.656 0.718 0.656 part of the nut.

11 12 0.656 0.718 0.781 0.718 12 13 0.718 0.781 0.843 0.781 The spring keeps the locking and load-carrying sections such 14 0.781 0.843 0.906 0.843 a distance apart that the two sets of threads are out of phase 14 15 0.843 0.906 0.968 0.906 or spaced so that a bolt, which has been screwed through the 15 16 0.906 0.968 1.031 0.968 load-carrying section, must push the locking section outward 16 17 0.968 1.031 1.094 1.031 against the force of the spring to engage the threads of the 17 18 1.031 1.094 1.156 1.094 locking section properly.

18 19 1.094 1.156 1.219 1.156 19 20 1.156 1.219 1.281 1.219 The spring, through the medium of the locking section, exerts 20 21 1.219 1.281 1.343 1.281 a constant locking force on the bolt in the same direction as a 21 22 1.281 1.343 1.406 1.343 force that would tighten the nut. In this nut, the load-carrying 22 23 1.344 1.406 1.469 1.406 section has the thread strength of a standard nut of comparable 23 24 1.406 1.460 1.531 1.469 1.469 1.531 Grip Range Grip Range Grip Grip 25 1.531 1.594 Number Number Minimum Maximum Minimum Maximum Figure 7-23. Blind-type lockbolt grip ranges.

1 0.031 0.094 18 1.094 1.156 size, while the locking section presses against the threads of 2 0.094 0.156 19 1.156 1.219 the bolt and locks the nut firmly in position. Only a wrench 3 0.156 0.219 20 1.219 1.281 applied to the nut loosens it. The nut can be removed and 4 0.219 0.281 21 1.281 1.344 reused without impairing its efficiency.

5 0.281 0.344 22 1.344 1.406 Boots self-locking nuts are made with three different spring 6 0.344 0.406 23 1.406 1.469 styles and in various shapes and sizes. The wing type that is 7 0.406 0.469 24 1.469 1.531 the most common ranges in size for No. 6 up to ⁄ 4 inch, the 1 1 8 0.469 0.531 25 1.531 1.594 Rol-top ranges from ⁄ 4 inch to ⁄ 6 inch, and the bellows type ranges in size from No. 8 up to ⁄ 8 inch. Wing-type nuts are 9 0.531 0.594 26 1.594 1.656 made of anodized aluminum alloy, cadmium-plated carbon 10 0.594 0.656 27 1.656 1.718 11 0.656 0.718 28 1.718 1.781 Tolerance 12 0.718 0.781 29 1.781 1.843 Pin diameter Below Above 13 0.781 0.843 30 1.843 1.906 / 0.079 to 0.032 16 14 0.843 0.906 31 1.906 1.968 0.079 to 0.050 ¼ 15 0.906 0.968 32 1.968 2.031 0.079 to 0.050 / 16 0.968 1.031 33 2.031 2.094 16 17 1.031 1.094 0.079 to 0.060 / Figure 7-22. Pull-and stump-type lockbolt grip ranges. Figure 7-24. Pin tolerance ranges.

7-43 steel, or stainless steel. The Rol-top nut is cadmium-plated damage bolt threads or plating.

steel, and the bellows type is made of aluminum alloy only.

. As shown in Figure 7-28 , the fiber locking collar is not Stainless Steel Self-Locking Nut threaded, and its inside diameter is smaller than the largest diameter of the threaded portion or the outside diameter of The stainless steel self-locking nut may be spun on and off a corresponding bolt. When the nut is screwed onto a bolt, it by hand as its locking action takes places only when the acts as an ordinary nut until the bolt reaches the fiber collar.

nut is seated against a solid surface and tightened. The nut When the bolt is screwed into the fiber collar, however, consists of two parts: a case with a beveled locking shoulder friction (or drag) causes the fiber to be pushed upward. This and key and a thread insert with a locking shoulder and creates a heavy downward pressure on the load carrying part slotted keyway. Until the nut is tightened, it spins on the and automatically throws the load carrying sides of the nut bolt easily, because the threaded insert is the proper size and bolt threads into positive contact. After the bolt has been for the bolt. However, when the nut is seated against a solid forced all the way through the fiber collar, the downward surface and tightened, the locking shoulder of the insert is pressure remains constant. This pressure locks and holds the pulled downward and wedged against the locking shoulder nut securely in place even under severe vibration.

of the case. This action compresses the threaded insert and causes it to clench the bolt tightly. The cross-sectional view Nearly all elastic stop nuts are steel or aluminum alloy.

in Figure 7-27 shows how the key of the case fits into the However, such nuts are available in practically any kind of slotted keyway of the insert so that when the case is turned, metal. Aluminum-alloy elastic stop nuts are supplied with an the threaded insert is turned with it. Note that the slot is wider anodized finish. Steel nuts are cadmium plated.

than the key. This permits the slot to be narrowed and the insert to be compressed when the nut is tightened.

Normally, elastic stop nuts can be used many times with complete safety and without detriment to their locking Elastic Stop Nut efficiency. When reusing elastic stop nuts, be sure the fiber The elastic stop nut is a standard nut with the height has not lost its locking friction or become brittle. If a nut can increased to accommodate a fiber locking collar. This be turned with the fingers, replace it.

fiber collar is very tough and durable and is unaffected by immersion in hot or cold water or ordinary solvents, such After the nut has been tightened, make sure the rounded or as ether, carbon tetrachloride, oils, and gasoline. It will not Top view Profile view Top view Profile view Top view Profile view Top view Profile view AN340 AN340 AN310 AN310 AN320 AN345 AN320 AN345 AN315 AN316 AN315 AN316 AN335 AN350 AN335 AN350 Figure 7-25. Non-self-locking nuts.

7-44 chamfered end of the bolts, studs, or screws extends at least These nuts should be used only where originally used in the the full round or chamfer through the nut. Flat end bolts, fabrication of the aircraft.

studs, or screws should extend at least ⁄ 32 inch through the nut. Bolts of ⁄ 16 -inch diameter and over with cotter pin holes Internal & External Wrenching Nuts may be used with self-locking nuts, but only if free from Two commercial types of high-strength internal or external burrs around the holes. Bolts with damaged threads and wrenching nuts are available; they are the internal and rough ends are not acceptable. Do not tap the fiber locking external wrenching elastic stop nut and the Unbrako internal insert. The self-locking action of the elastic stop nut is the and external wrenching nut. Both are of the self-locking result of having the bolt threads impress themselves into the type, are heat-treated, and can carry high-strength bolt untapped fiber.

tension loads.

Do not install elastic stop nuts in places where the temperature Identification & Coding is higher than 250 °F, because the effectiveness of the self- Part numbers designate the type of nut. The common types locking action is reduced beyond this point. Self-locking and their respective part numbers are: nuts may be used on aircraft engines and accessories when • Plain, AN315 and AN335 the engine manufacturer specifies their use.

• Castle, AN310 Self-locking nut bases are made in several forms and • Plain check, AN316 materials for riveting and welding to aircraft structure • Light hex, AN340 and AN345 or parts. [Figure 7-29] Certain applications require the installation of self-locking nuts in channels, an arrangement • Castellated shear, AN320 that permits the attachment of many nuts with only a few rivets. These channels are track-like bases with regularly The patented self-locking types are assigned part numbers spaced nuts, which are either removable or non-removable.

ranging from MS20363 through MS20367. The Boots, the The removable type carries a floating nut that can be snapped Flexloc, the fiber locknut, the elastic stop nut, and the self- in or out of the channel, thus making possible the easy locking nut belong to this group. Part number AN350 is removal of damaged nuts. Nuts, such as the clinch-type and assigned to the wing nut.

spline-type, depend on friction for their anchorage and are not acceptable for use in aircraft structures.

Letters and digits following the part number indicate such Sheet Spring Nuts Nut case Sheet spring nuts, such as speed nuts, are used with standard and sheet metal self-tapping screws in non-structural locations. They find various uses in supporting line clamps, conduit clamps, electrical equipment, access doors, and the like and are available in several types. Speed nuts are made from spring steel and are arched prior to tightening. This arched spring lock prevents the screw from working loose.

Untightened nut Locking shoulder Threaded nut core Boots aircraft nut Elastic anchor nut Keyway Tightened nut Flexloc nut Fiber locknut Elastic stop nut Figure 7-27. Stainless steel self-locking nut.

Figure 7-26. Self-locking nuts.

7-45 items as material, size, threads per inch, and whether the D = 2024-T aluminum alloy thread is right or left hand. The letter “B” following the part 5 = ⁄ 16 inch diameter number indicates the nut material to be brass, a “D” indicates R = right-hand thread (usually 24 threads per inch) 2017-T aluminum alloy, a “DD” indicates 2024-T aluminum alloy, a “C” indicates stainless steel, and a dash in place of Code Number AN320-10: a letter indicates cadmium-plated carbon steel.

AN320 = aircraft castellated shear nut, cadmium-plated carbon steel The digit (or two digits) following the dash or the material 10 = ⁄ 8 inch diameter, 18 threads per inch (this nut is usually code letter is the dash number of the nut, and it indicates the right-hand thread) size of the shank and threads per inch of the bolt on which the nut fits. The dash number corresponds to the first figure Code Number AN350B1032: appearing in the part number coding of general purpose bolts.

AN350 = aircraft wing nut A dash and the number 3, for example, indicate that the nut B = brass fits an AN3 bolt (10-32); a dash and the number 4 means it fits an AN4 bolt ( ⁄ 4 -28); a dash and the number 5, an AN5 10 = number 10 bolt bolt ( ⁄ 16 -24); and so on.

32 = threads per inch The code numbers for self-locking nuts end in three or four Aircraft Washers digit numbers. The last two digits refer to threads per inch, Aircraft washers used in airframe repair are either plain, lock, and the one or two preceding digits stand for the nut size in or special type washers.

16ths of an inch.

Plain Washers Some other common nuts and their code numbers are: Plain washers, both the AN960 and AN970, are used under Code Number AN310D5R: hex nuts. [Figure 7-30] They provide a smooth bearing AN310 = aircraft castle nut surface and act as a shim in obtaining correct grip length for a bolt and nut assembly. They are used to adjust the position of castellated nuts in respect to drilled cotter pin holes in bolts.

Use plain washers under lock washers to prevent damage to the surface material.

Aluminum and aluminum-alloy washers may be used under bolt heads or nuts on aluminum alloy or magnesium structures where corrosion caused by dissimilar metals is a factor. When used in this manner, any electric current flow is between the washer and the steel bolt. However, it is common practice Nut Fiber collar to use a cadmium-plated steel washer under a nut bearing directly against a structure as this washer resists the cutting action of a nut better than an aluminum-alloy washer.

The AN970 steel washer provides a greater bearing area than the AN960 washer and is used on wooden structures under both the head and the nut of a bolt to prevent crushing the surface.

Lock Washers Lock washers, both the AN935 and AN936, are used with machine screws or bolts where the self-locking or castellated- type nut is not appropriate. The spring action of the washer (AN935) provides enough friction to prevent loosening of the nut from vibration. [Figure 7-30] Lock washers should never be used under the following conditions: Figure 7-28. Elastic stop nut.

7-46 Boots aircraft channel assembly Elastic stopnut channel assembly Figure 7-29. Self-locking nut bases.

• With fasteners to primary or secondary structures surface or where perfect alignment with a surface is required.

These washers are used together. [Figure 7-30] • With fasteners on any part of the aircraft where failure might result in damage or danger to the aircraft or The NAS143 and MS20002 washers are used for internal personnel wrenching bolts of the NAS144 through NAS158 series.

• Where failure would permit the opening of a joint to This washer is either plain or countersunk. The countersunk the airflow washer (designated as NAS143C and MS20002C) is used to seat the bolt head shank radius, and the plain washer is • Where the screw is subject to frequent removal used under the nut.

• Where the washers are exposed to the airflow • Where the washers are subject to corrosive conditions Installation of Nuts, Washers, & Bolts Bolt & Hole Sizes • Where the washer is against soft material without a plain washer underneath to prevent gouging the surface Slight clearances in bolt holes are permissible wherever bolts are used in tension and are not subject to reversal of load. A Shake-Proof Lock Washers few of the applications in which clearance of holes may be permitted are in pulley brackets, conduit boxes, lining trim, Shake-proof lock washers are round washers designed with and miscellaneous supports and brackets.

tabs or lips that are bent upward across the sides of a hex nut or bolt to lock the nut in place. There are various methods Bolt holes are to be normal to the surface involved to provide of securing the lock washer to prevent it from turning, such full bearing surface for the bolt head and nut and must not be as an external tab bent downward 90° into a small hole in oversized or elongated. A bolt in such a hole carries none of the face of the unit or an internal tab that fits a keyed bolt.

its shear load until parts have yielded or deformed enough to allow the bearing surface of the oversized hole to contact Shake-proof lock washers can withstand higher heat than the bolt. In this respect, remember that bolts do not become other methods of safetying and can be used under high swaged to fill up the holes, as do rivets.

vibration conditions safely. They should be used only once, because the tabs tend to break when bent a second time.

In cases of oversized or elongated holes in critical members, obtain advice from the aircraft or engine manufacturer before Special Washers drilling or reaming the hole to take the next larger bolt.

The ball socket and seat washers, AC950 and AC955, are Usually such factors as edge distance, clearance, or load special washers used where a bolt is installed at an angle to a 7-47 factor must be considered. Oversized or elongated holes in Safetying of Bolts & Nuts noncritical members can usually be drilled or reamed to the It is very important that all bolts or nuts, except the self- next larger size.

locking type, be safetied after installation. This prevents them from loosening in flight due to vibration. Methods of Many bolt holes, particularly those in primary connecting safetying are discussed later in this chapter.

elements, have close tolerances. Generally, it is permissible to use the first lettered drill size larger than the normal bolt Repair of Damaged Internal Threads diameter, except where the AN hexagon bolts are used in Installation or replacement of bolts is simple when compared light-drive fit (reamed) applications and where NAS close to the installation or replacement of studs. Bolt heads and nuts tolerance bolts or AN Clevis bolts are used.

are cut in the open, whereas studs are installed into internal threads in a casting or built-up assembly. Damaged threads Light-drive fits for bolts (specified on the repair drawings as on bolts or nuts can be seen and only require replacement 0.0015 inch maximum clearance between bolt and hole) are of the defective part. If internal threads are damaged, two required in places where bolts are used in repair, or where alternatives are apparent: the part may be replaced or the they are placed in the original structure.

threads repaired or replaced. Correction of the thread problem is usually cheaper and more convenient. Two methods of The fit of holes and bolts cannot be defined in terms of shaft repairing are by replacement bushings or helicoils.

and hole diameters; it is defined in terms of the friction between bolt and hole when sliding the bolt into place. A tight drive fit, Replacement Bushings for example, is one in which a sharp blow of a 12- or 14-ounce Bushings are usually special material (steel or brass spark hammer is required to move the bolt. A bolt that requires a hard plug bushings into aluminum cylinder heads). A material blow and sounds tight is considered too tight a fit. A light-drive that resists wear is used where removal and replacement is fit is one in which a bolt moves when a hammer handle is held frequent. The external threads on the bushing are usually against its head and pressed by the weight of the body.

coarse. The bushing is installed, a thread lock compound may or may not be used, and staked to prevent loosening.

Installation Practices Many bushings have left-hand threads external and right- Examine the markings on the bolt head to determine that hand threads internal. With this installation, removal of the each bolt is of the correct material. It is extremely important to use like bolts in replacement. In every case, refer to the applicable Maintenance Instructions Manual and Illustrated Parts Breakdown.

Be sure that washers are used under both the heads of bolts and nuts unless their omission is specified. A washer guards against mechanical damage to the material being bolted and prevents corrosion of the structural members. An aluminum- alloy washer should be used under the head and nut of a steel Plain AN 960 Ball seat & socket Taper pin AN975 bolt securing aluminum alloy or magnesium alloy members.

AC9950 & AC955 Any corrosion that occurs attacks the washer rather than the Special washers members. Steel washers should be used when joining steel members with steel bolts.

Whenever possible, place the bolt with the head on top or in the forward position. This positioning tends to prevent the bolt from slipping out if the nut is accidentally lost.

Be certain that the bolt grip length is correct. Grip length is Split-Lock Internal toothlock External toothlock the length of the unthreaded portion of the bolt shank. The grip length should equal the thickness of the material being bolted together. However, bolts of slightly greater grip length may be used if washers are placed under the nut or the bolt Plain AN 935 Star lock washers head. In the case of plate nuts, add shims under the plate.

Figure 7-30. Various types of washers.

7-48 bolt or stud (right-hand threads) tends to tighten the bushing. These are not to be considered specific instructions on helicoil installation. The manufacturer’s instruction must be followed Bushings for common installations, such as spark plugs, may when making an installation.

be up to 0.040 oversize (in increments of 0.005). Original installation and overhaul shop replacements are shrunk fit: Helicoils are available for the following threads: unified a heated cylinder head and a frozen bushing. coarse, unified fine, metric, spark plug, and national taper pipe threads.

Helicoils Fastener Torque Helicoils are precision-formed screw thread coils of 18-8 Torque stainless steel wire having a diamond-shaped cross section.

[Figure 7-31] They form unified coarse or unified fine thread As the speed of an aircraft increases, each structural member classes 2-band 3B when assembled into (helicoil) threaded becomes more highly stressed. It is therefore extremely holes. The assembled insert accommodates UNJ (controlled important that each member carry no more and no less than radius root) male threaded members. Each insert has a driving the load for which it was designed. To distribute the loads tang with a notch to facilitate removal of the tang after the safely throughout a structure, it is necessary that proper insert is screwed into a helicoil tapped hole.

torque be applied to all nuts, bolts, studs, and screws.

Using the proper torque allows the structure to develop They are used as screw thread bushings. In addition to being its designed strength and greatly reduces the possibility of used to restore damaged threads, they are used in the original failure due to fatigue.

design of missiles, aircraft engines, and all types of mechanical equipment and accessories to protect and strengthen tapped Torque Wrenches threads in light materials, metals, and plastics, particularly in The three most commonly used torque wrenches are locations that require frequent assembly and disassembly and/ the flexible beam, rigid frame, and the ratchet types.

or where a screw locking action is desired.

[Figure 7-33] When using the flexible beam and the rigid frame torque wrenches, the torque value is read visually on Helicoil installation is a 5 or 6 step operation, depending a dial or scale mounted on the handle of the wrench.

upon how the last step is classed. [Figure 7-32] To use the ratchet type, unlock the grip and adjust the handle Step 1: Determine what threads are damaged.

to the desired setting on the micrometer-type scale, then Step 2: (a) New installation of helicoil—drill out relock the grip. Install the required socket or adapter to the damaged threads to minimum depth square drive of the handle. Place the wrench assembly on the specified.

nut or bolt, and pull the wrench assembly on the nut or bolt (b) Previously installed helicoil—using proper in a clockwise direction with a smooth, steady motion. (A size extracting tool, place edge of blade in fast or jerky motion results in an improperly torqued unit.)

90° from the edge of the insert. Tap with When the applied torque reaches the torque value indicated hammer to seat tool. Turn to left, applying on the handle setting, the handle automatically releases or pressure, until insert backs out. Threads are “breaks” and moves freely for a short distance. The release not damaged if insert is properly removed.

and free travel is easily felt, so there is no doubt about when the torqueing process is completed.

Step 3: Tap—use the tap of required nominal thread size.

The tapping procedure is the same as standard To assure getting the correct amount of torque on the thread tapping. Tap length must be equal to or fasteners, all torque wrenches must be tested at least once a exceed the requirement.

month or more often if necessary.

Step 4: Gauge—threads may be checked with a helicoil thread gauge.

Note: It is not advisable to use a handle length extension on Step 5: Insert assembly—using proper tool, install insert a flexible beam-type torque wrench at any time. A handle 1 1 to a depth that puts end of top coil ⁄ 4 to ⁄ 2 turn extension alone has no effect on the reading of the other types.

below the top surface of the tapped hole.

The use of a drive end extension on any type of torque wrench makes the use of the formula mandatory. When applying the Step 6: Tang breakoff—select proper breakoff tool.

formula, force must be applied to the handle of the torque Tangs should be removed from all drilled wrench at the point from which the measurements were taken.

through holes. In blind holes, the tangs may be If this is not done, the torque obtained is incorrect.

removed when necessary if enough hole-depth is provided below the tang of the installed insert.

7-49 Torque Tables Use the standard torque table as a guide in tightening nuts, studs, bolts, and screws whenever specific torque values are not called out in maintenance procedures. The following rules apply for correct use of the torque table: [Figure 7-34] 1. To obtain values in foot-pounds, divide inch-pounds by 12.

2. Do not lubricate nuts or bolts except for corrosion- resistant steel parts or where specifically instructed to do so.

3. Always tighten by rotating the nut first if possible.

When space considerations make it necessary to tighten by rotating the bolt head, approach the high side of the indicated torque range. Do not exceed the maximum allowable torque value.

Figure 7-31. Helicoil insert.

4. Maximum torque ranges should be used only when materials and surfaces being joined are of sufficient holes may not line up with the slots in the nuts for the range thickness, area, and strength to resist breaking, of recommended values. Except in cases of highly-stressed warping, or other damage.

engine parts, the nut may not be over torque. Remove 5. For corrosion-resisting steel nuts, use torque values hardware and realign the holes. The torque loads specified given for shear-type nuts.

may be used for all unlubricated cadmium-plated steel nuts of the fine or coarse thread series, which have approximately 6. The use of any type of drive end extension on a torque equal number of threads and equal face bearing areas. These wrench changes the dial reading required to obtain values do not apply where special torque requirements are the actual values indicated in the standard torque specified in the maintenance manual.

range tables. When using a drive end extension, the torque wrench reading must be computed by use of If the head end, rather than the nut, must be turned in the the proper formula, which is included in the handbook tightening operation, maximum torque values may be accompanying the torque wrench.

increased by an amount equal to shank friction, provided the latter is first measured by a torque wrench.

Cotter Pin Hole Line Up When tightening castellated nuts on bolts, the cotter pin Drill Tap Gauge Install Figure 7-32. Helicoil installation.

7-50 Aircraft Rivets Basic formula F x L = T Sheets of metal must be fastened together to form the aircraft structure, and this is usually done with solid aluminum-alloy F = Applied force rivets. A rivet is a metal pin with a formed head on one L = Lever length between centerline of drive and centerline of applied force (F must be 90° to L) end when the rivet is manufactured. The shank of the rivet T = Torque is inserted into a drilled hole, and its shank is then upset (deformed) by a hand or pneumatic tool. The second head, formed either by hand or by pneumatic equipment, is called a “shop head.” The shop head functions in the same manner 90° as a nut on a bolt. In addition to their use for joining aircraft A skin sections, rivets are also used for joining spar sections, for B holding rib sections in place, for securing fittings to various parts of the aircraft, and for fastening innumerable bracing F members and other parts together. The rivet creates a bond that is at least as strong as the material being joined.

90° Two of the major types of rivets used in aircraft are the common solid shank type, which must be driven using a bucking bar, and the special (blind) rivets, which may be installed where it is impossible to use a bucking bar.

55 0 Aircraft rivets are not hardware store rivets. Rivets purchased at a hardware store should never be used as a substitute for aircraft quality rivets. The rivets may be made from very different materials, the strength of the rivets differs greatly, L and their shear strength qualities are very different. The countersunk heads on hardware store rivets are 78°, whereas countersunk aircraft rivets have 100° angle heads for more surface contact to hold it in place.

Standards and Specifications The FAA requires that the structural strength and integrity of type-certificated aircraft conform to all T airworthiness requirements. These requirements apply to Ratchet type performance, structural strength, and integrity as well as flight characteristics. To meet these requirements, each aircraft must meet the same standards. To accomplish Flexible beam standardization, all materials and hardware must be manufactured to a standard of quality. Specifications and standards for aircraft hardware are usually identified by the organization that originated them. Some of the common standardizing organizations include: AMS Aeronautical Material Specifications AN Air Force-Navy AND Air Force-Navy Design Rigid frame AS Aeronautical Standard Te x A Formula for use with extensions Tw = B ASA American Standards Association A = Lever length of wrench B = Lever length of wrench plus extension ASTM American Society for Testing Materials Te = Required torque on bolt Tw = Torque reading on wrench dial MS Military Standard NAF Naval Aircraft Factory Figure 7-33. Common torque wrenches.

7-51 NAS National Aerospace Standard field rivet is in wide demand, because it is ready for use as received and needs no further heat-treating or annealing. It SAE Society of Automotive Engineers also has a high resistance to corrosion.

When a MS20426-AD4-6 rivet is required, the specifications The 2017-T and 2024-T rivets are used in aluminum-alloy have already been written for it in the Military Standard (MS) structures where more strength is needed than is obtainable specifications. That information is available to the aircraft with the same size 2217-T rivet. These rivets are known as manufacturers, the rivet manufacturers and the mechanic.

“ice box rivets,” are annealed and must be kept refrigerated The specifications designate the material to be used as well until they are to be driven. The 2017-T rivet should be driven as the head type, diameter, and length of the rivet. The use within approximately 1 hour and the 2024-T rivet within 10 of standardized materials in the production of aircraft makes to 20 minutes after removal from refrigeration.

each aircraft exactly the same as the previous one and makes them less expensive to build.

The 5056 rivet is used for riveting magnesium-alloy structures because of its corrosion-resistant qualities in Aircraft rivets are manufactured to much higher standards and combination with magnesium.

specifications than rivets manufactured for general use. When aircraft manufacturers started building all-metal aircraft in Mild steel rivets are used for riveting steel parts. The corrosion- the 1930s, different manufacturers had different rivet head resistant steel rivets are for riveting corrosion-resistant steels designs. Brazier heads, modified brazier heads, button heads, in firewalls, exhaust stack brackets, and similar structures.

mushroom heads, flatheads, and 78° countersunk heads were used. As aircraft standardized, four rivet head designs Monel rivets are used for riveting nickel-steel alloys. They almost completely replaced all the others. Rivets exposed can be substituted for those made of corrosion-resistant steel to the airflow over the top of the structure are usually either in some cases.

universal head MS20470 or 100° countersunk head MS20426 rivets. For rivets used in internal structures, the roundhead The use of copper rivets in aircraft repair is limited. Copper MS20430 and the flathead MS20442 are generally used.

rivets can be used only on copper alloys or nonmetallic materials, such as leather.

Solid Shank Rivets Solid shank rivets are generally used in repair work. They Metal temper is an important factor in the riveting process, are identified by the kind of material of which they are made, especially with aluminum alloy rivets. Aluminum-alloy rivets their head type, size of shank, and their temper condition.

have the same heat-treating characteristics as aluminum-alloy The designation of the solid shank rivet head type, such as stock. They can be hardened and annealed in the same manner universal head, roundhead, flathead, countersunk head, and as aluminum. The rivet must be soft, or comparatively soft, brazier head, depends on the cross-sectional shape of the before a good head can be formed. The 2017-T and 2024-T head. [Figure 7-35] The temper designation and strength rivets are annealed before being driven. They harden with age.

are indicated by special markings on the head of the rivet.

The process of heat-treating (annealing) rivets is much the The material used for most aircraft solid shank rivets is same as that for stock. Either an electric air furnace, a salt bath, aluminum alloy. The strength and temper conditions of or a hot oil bath is needed. The heat-treating range, depending aluminum-alloy rivets are identified by digits and letters on the alloy, is 625 °F to 950 °F. For convenient handling, rivets similar to those adopted for the identification of strength and are heated in a tray or a wire basket. They are quenched in cold temper conditions of aluminum and aluminum-alloy stock.

water (70 °F) immediately after heat-treating.

The 1100, 2017-T, 2024-T, 2117-T, and 5056 rivets are the five grades usually available.

The 2017-T and 2024-T rivets, which are heat-treatable rivets, begin to age harden within a few minutes after being The 1100 rivet, which is composed of 99.45 percent pure exposed to room temperature. Therefore, they must be used aluminum, is very soft. It is for riveting the softer aluminum immediately after quenching or else be placed in cold storage.

alloys, such as 1100, 3003, and 5052, which are used for nonstructural parts (all parts where strength is not a factor).

The most commonly used means for holding heat-treatable The riveting of map cases is a good example of where a rivet rivets at low temperature (below 32 °F) is to keep them in a of 1100 aluminum alloy may be used.

refrigerator. They are referred to as “icebox” rivets. Under this storage condition, they remain soft enough for driving The 2117-T rivet, known as the field rivet, is used more for up to 2 weeks. Any rivets not used within that time should than any other for riveting aluminum alloy structures. The be removed for reheat-treating.

7-52 TORQUE VALUES FOR TIGHTENING NUTS (INCH-POUNDS) On bolts, studs, On high-strength On standard bolts, studs, and and screws having a bolts, studs, and screws having a tensile strength of tensile strength screws having a 125,000 to 140,000 psi Bolt, Stud, or of 140,000 to tensile strength of Screw Size 160,000 psi 160,000 psi and over Tension-type nuts and Shear-type nuts Any nut, except shear Any nut, except shear threaded machine (AN320, AN364, or type type parts (AN-310, AN365, equivalent) or equivalent) 8–32 8–36 7–9 12–15 14–17 15–18 10–24 10–32 12–15 20–25 23–30 25–35 ¼–20 25–30 40–50 45–49 50–68 ¼–28 30–40 50–70 60–80 70–90 48-55 / – 18 80–90 85–117 90–144 60–85 100–140 120–172 140–203 / – 24 95–110 160–185 173–217 185–248 / – 1 6 ⁄ –24 95–110 160–190 175–271 190–351 140–155 235–255 245–342 255–428 / – 1 4 / –20 270–300 450–500 475–628 500–756 ½–13 240–290 400–480 440–636 480–792 ½–20 290–410 480–690 585–840 690–990 300–420 500–700 600–845 700–990 / – 1 2 480–600 800–1,000 900–1,220 1,000–1,440 / – 18 420–540 700–900 800–1,125 900–1,350 / – 1 1 660–780 1,100–1,300 1,200–1,730 1,300–2,160 / – 1 8 ¾–10 700–950 1,150–1,600 1,380–1,925 1,600–2,250 ¾–16 1,300–1,500 2,300–2,500 2,400–3,500 2,500–4,500 ⁄ –9 1,300–1,800 2,200–3,000 2,600–3,570 3,000–4,140 / – 14 1,500–1,800 2,500–3,000 2,750–4,650 3,000–6,300 8 1–8 22,00–3,000 3,700–5,000 4,350–5,920 5,000–6,840 1–14 2,200–3,300 3,700–5,500 4,600–7,250 5,500–9,000 1 ⁄ –8 3,300–4,000 5,500–6,500 6,000–8,650 6,500–10,800 1 ⁄ –12 3,000–4,200 5,000–7,000 6,000–10,250 7,000–13,500 1¼–8 4,000–5,000 6,500–8,000 7,250–11,000 8,000–14,000 1¼–12 5,400–6,600 9,000–11,000 10,000–16,750 11,000–22,500 Figure 7-34. Standard torque table (inch-pounds).

7-53 the rivets. This may be zinc chromate, metal spray, or an Icebox rivets attain about one-half their maximum strength anodized finish.

in approximately 1 hour after driving and full strength in about 4 days. When 2017-T rivets are exposed to room The protective coating on a rivet is identified by its color. A temperature for 1 hour or longer, they must be subject to rivet coated with zinc chromate is yellow, an anodized surface reheat-treatment. This also applies to 2024-T rivets exposed is pearl gray, and the metal sprayed rivet is identified by a to room temperature for a period exceeding 10 minutes. silvery gray color. If a situation arises in which a protective coating must be applied on the job, paint the rivet with zinc Once an icebox rivet has been taken from the refrigerator, it chromate before it is used and again after it is driven.

should not be mixed with the rivets still in cold storage. If more rivets are removed from the refrigerator than can be used Identification in 15 minutes, they should be placed in a separate container Markings on the heads of rivets are used to classify their and stored for reheat-treatment. Heat-treatment of rivets characteristics. These markings may be either a raised teat, may be repeated a number of times if done properly. Proper two raised teats, a dimple, a pair of raised dashes, a raised heating times and temperatures are shown in Figure 7-36 .

cross, a single triangle, or a raised dash; some other heads have no markings.

Most metals, and therefore aircraft rivet stock, are subject to corrosion. Corrosion may be the result of local climatic The different markings indicate the composition of the rivet conditions or the fabrication process used. It is reduced stock. As explained previously, the rivets have different colors to a minimum by using metals that are highly resistant to to identify the manufacturers’ protective surface coating.

corrosion and possess the correct strength-to-weight ratio.

Roundhead rivets are used in the interior of the aircraft, Ferrous metals placed in contact with moist salt air rust if not except where clearance is required for adjacent members.

properly protected. Nonferrous metals, those without an iron The roundhead rivet has a deep, rounded top surface. The base, do not rust, but a similar process known as corrosion head is large enough to strengthen the sheet around the hole takes place. The salt in moist air (found in the coastal areas) and, at the same time, resists tension.

attacks the aluminum alloys. It is a common experience to inspect the rivets of an aircraft, which has been operated near The flathead rivet, like the roundhead rivet, is used on interior salt water, and find them badly corroded.

structures. It is used where maximum strength is needed and where there is not sufficient clearance to use a roundhead If a copper rivet is inserted into an aluminum-alloy structure, rivet. It is seldom, if ever, used on external surfaces. The two dissimilar metals are brought in contact with each other.

brazier head rivet has a head of large diameter, which makes it Remember, all metals possess a small electrical potential.

particularly adaptable for riveting thin sheet stock (skin). The Dissimilar metals in contact with each other in the presence of brazier head rivet offers only slight resistance to the airflow, moisture cause an electrical current to flow between them and and because of this factor, it is frequently used for riveting skin chemical byproducts to be formed. Principally, this results on exterior surfaces, especially on aft sections of the fuselage in the deterioration of one of the metals.

and empennage. It is used for riveting thin sheets exposed to the slipstream. A modified brazier head rivet is also manufactured; Certain aluminum alloys react to each other and, therefore, it is simply a brazier head of reduced diameter.

must be thought of as dissimilar metals. The commonly used aluminum alloys may be divided into the two groups shown The universal head rivet is a combination of the roundhead, in Figure 7-37 .

flathead, and brazier head. It is used in aircraft construction and repair in both interior and exterior locations. When Members within either group A or group B can be considered replacement is necessary for protruding head rivets— as similar to each other and will not react to others within the roundhead, flathead, or brazier head—they can be replaced same group. A corroding action will take place, however, if by universal head rivets.

any metal of group A comes in contact with a metal in group B in the presence of moisture.

The countersunk head rivet is flat topped and beveled toward the shank so that it fits into a countersunk or dimpled hole Avoid the use of dissimilar metals whenever possible. Their and is flush with the material’s surface. The angle at which incompatibility is a factor that was considered when the AN the head slopes may vary from 78° to 120°. The 100° rivet Standards were adopted. To comply with AN Standards, is the most commonly used type. These rivets are used to the manufacturers must put a protective surface coating on fasten sheets over which other sheets must fit. They are also 7-54 psi 25,000 90,000 90,000 90,000 100,000 113,000 126,000 136,000 Bearing Strength psi Shear 10,000 30,000 34,000 38,000 41,000 27,000 35,000 65,000 23,000 49,000 49,000 95,000 Strength No No No No No No No No No No No No Yes Yes Use Heat Treat Before X X X X X X X Head AN470 Universal MS20470* X X X X X X X Head AN456 Brazier MS20470* X X X X X X X Head AN455 Brazier MS20470* X X X X X X X Flat Head AN442 MS20470* X X X Flat Head AN441 X X X X X Head Round AN435 MS20613* MS20613* MS20615* MS20615* MS20613* MS20615* X X X X X X X Head AN430 Round MS20470* X X X X 100° AN427 Counter- sunk Head MS20427* X X X X X X X 100° AN426 Counter- MS20426 MS20426* sunk Head X X X X X X 78° sunk Head AN425 Counter- B F C C A D D M AD DD AN Code Material Head Marking Plain Recessed Dot Raised Dot Raised Dot Raised Double Dash Raised Cross Three Raised Dashes Recessed Triangle Recessed Dash Plain Plain Plain Recessed Large and Small Dot Recessed Double Dots Rivet identification chart.

1100 Brass 2117T 2017T 2024T 5056T Monel Copper Material 7075-T73 Titanium 2017T-HD Corrosion Carbon Steel Copper Alloy) Monel (Nickel- Resistant Steel * New specifications are for design purposes.

Figure 7-35.

7-55 used on exterior surfaces of the aircraft, because they offer D—Aluminum alloy, 2017-T composition only slight resistance to the slipstream and help to minimize DD—Aluminum alloy, 2024-T composition turbulent airflow.

B—Aluminum alloy, 5056 composition The markings on the heads of rivets indicate the material C—Copper of which they are made and, therefore, their strength.

M—Monel Figure 7-37 identifies the rivet head markings and the materials indicated by them. Although there are three The absence of a letter following the AN standard number materials indicated by a plain head, it is possible to indicates a rivet manufactured from mild steel.

distinguish their difference by color. The 1100 is an aluminum color; the mild steel is a typical steel color; and The first number following the material composition letters the copper rivet is a copper color. Any head marking can expresses the diameter of the rivet shank in 32nds of an inch.

appear on any head style of the same material.

3 5 For example, 3 indicates ⁄ 32 , 5 indicates ⁄ 32 , and so forth.

[Figure 7-38] A part number identifies each type of rivet so that the user can select the correct rivet for the job. The type of rivet head The last number(s), separated by a dash from the preceding is identified by AN or MS standard numbers. The numbers number, expresses the length of the rivet shank in 16ths of an selected are in series and each series represents a particular 3 7 inch. For example, 3 indicates ⁄ 16 , 7 indicates ⁄ 16 , 11 indicates type of head.

⁄ 16 , and so forth. [Figure 7-38] The most common numbers and the types of heads they An example of identification marking of a rivet is: represent are: AN470AD3-5—complete part number AN426 or MS20426—countersunk head rivets (100°) AN—Air Force-Navy standard number AN430 or MS20430—roundhead rivets 470—universal head rivet AN441—flathead rivets AD—2117-T aluminum alloy AN456—brazier head rivets 3— ⁄ 32 in diameter AN470 or MS20470—universal head rivets 5— ⁄ 16 in length There are also letters and numbers added to a part number.

The letters designate alloy content; the numbers designate Blind Rivets rivet diameter and length. The letters in common uses for There are many places on an aircraft where access to both alloy designation are: sides of a riveted structure or structural part is impossible, or A—Aluminum alloy, 1100 or 3003 composition where limited space does not permit the use of a bucking bar.

Also, in the attachment of many non-structural parts, such as AD—Aluminum alloy, 2117-T composition aircraft interior furnishings, flooring, deicing boots, and the like, the full strength of solid shank rivets is not necessary.

Heating Time—Air Furnace For use in such places, special rivets have been designed that can be bucked from the front. Special rivets are sometimes Time at Heat-Treating Rivet Alloy Temperature Temperature lighter than solid shank rivets, yet amply strong for intended use. These rivets are produced by several manufacturers and 910 °F–930 °F 2024 1 hour 925 °F–950 °F 2017 1 hour Group A Group B Heating Time—Salt Bath 1100 2117 Time at Heat-Treating Rivet Alloy 3003 2017 Temperature Temperature 5052 2124 2024 30 minutes 910 °F–930 °F 6053 7075 2017 30 minutes 925 °F–950 °F Figure 7-37. Aluminum groupings.

Figure 7-36. Rivet heating times and temperatures.

7-56 have unique characteristics that require special installation aluminum alloy; stem 2017 aluminum alloy and sleeve 5056 tools, special installation procedures, and special removal aluminum alloy; and stem steel and sleeve steel.

procedures. That is why they are called special rivets.

Because these rivets are often inserted in locations where Self-plugging (friction lock) rivets are designed so that one head (usually the shop head) cannot be seen, they are installation requires only one person; it is not necessary also called blind rivets. to have the work accessible from both sides. The pulling strength of the rivet stem is such that a uniform job can always Mechanically-Expanded Rivets be assured. Because it is not necessary to have access to the Two classes of mechanically-expanded rivets are discussed here: opposite side of the work, self- plugging (friction lock) rivets can be used to attach assemblies to hollow tubes, corrugated • Non-structural—self-plugging (friction lock) rivets, sheet, hollow boxes, and so forth. Because a hammering force pull-thru rivets is not necessary to install the rivet, it can be used to attach assemblies to plywood or plastics.

• Mechanical lock—flush fracturing, self-plugging rivets Factors to consider in the selection of the correct rivet for Self-Plugging Rivets (Friction Lock) installation are: installation location, composition of the The self-plugging (friction lock) blind rivets are manufactured material being riveted, thickness of the material being riveted, by several companies. The same general basic information and strength desired.

about their fabrication, composition, uses, selection, installation, inspection, and removal procedures apply to If the rivet is to be installed on an aerodynamically all of them.

smooth surface, or if clearance for an assembly is needed, countersunk head rivets should be selected. In other areas Self-plugging (friction lock) rivets are fabricated in two parts: where clearance or smoothness is not a factor, the protruding a rivet head with a hollow shank or sleeve, and a stem that head type rivet may be utilized.

extends through the hollow shank. Figure 7-39 illustrates a protruding head and a countersunk head self-plugging rivet Material composition of the rivet shank depends upon the produced by one manufacturer.

type of material being riveted. Aluminum alloy 2117 shank rivets can be used on most aluminum alloys. Aluminum alloy Several events, in their proper sequence, occur when a pulling 5056 shank rivets should be used when the material being force is applied to the stem of the rivet: riveted is magnesium. Steel rivets should always be selected 1. The stem is pulled into the rivet shank.

for riveting assemblies fabricated from steel.

2. The mandrel portion of the stem forces the rivet shank to expand. The thickness of the material being riveted determines the overall length of the shank of the rivet. As a general rule, 3. When friction (or pulling action pressure) becomes the shank of the rivet should extend beyond the material great enough, it causes the stem to snap at a breakoff 3 1 thickness approximately ⁄ 64 inch to ⁄ 8 inch before the stem groove on the stem.

is pulled. [Figure 7-40] The plug portion (bottom end of the stem) is retained in the Pull-Thru Rivets shank of the rivet giving the rivet much greater shear strength Several companies manufacture the pull-thru blind rivets.

than could be obtained from a hollow rivet.

The same general basic information about their fabrication, composition, uses, selection, installation, inspection, and Self-plugging (friction lock) rivets are fabricated in two removal procedures apply to all of them.

common head styles: a protruding head like the MS20470 or universal head, and a 100° countersunk head. Other head Pull-thru rivets are fabricated in two parts: a rivet head with styles are available from some manufacturers.

a hollow shank or sleeve and a stem that extends through the hollow shank. Figure 7-41 illustrates a protruding head and The stem of the self-plugging (friction lock) rivet may have a a countersunk head pull-thru rivet.

knot or knob on the upper portion, or it may have a serrated portion. [Figure 7-39] Several events, in their proper sequence, occur when a pulling force is applied to the stem of the rivet: Self-plugging (friction lock) rivets are fabricated from several materials. Rivets are available in the following material 1. The stem is pulled through the rivet shank.

combinations: stem 2017 aluminum alloy and sleeve 2117 7-57 the head and usually does not require further stem trimming u n e r s k t a n n g u l o e when properly installed. Self-plugging (mechanical lock) C rivets display all the strength characteristics of solid shank rivets and, in most cases, can be substituted rivet for rivet.

® Bulbed CherryLOCK Rivets The large blind head of this fastener introduced the word “bulb” to blind rivet terminology. In conjunction with the Length of rivet unique residual preload developed by the high stem break load, its proven fatigue strength makes it the only blind rivet interchangeable structurally with solid rivets. [Figure 7-44] ® Wiredraw CherryLOCK Rivets Diameter of shank Diameter of shank There is a wide range of sizes, materials, and strength levels Figure 7-38. Methods of measuring rivets.

from which to select. This fastener is especially suited for sealing applications and joints requiring an excessive amount 2. The mandrel portion of the stem forces the shank to of sheet take-up. [Figure 7-45] expand forming the blind head and filling the hole.

® Huck Mechanical Locked Rivets Pull-thru rivets are fabricated in two common head styles: Self-plugging (mechanical lock) rivets are fabricated in two protruding head like the MS20470 or universal head and a sections: a head and shank (including a conical recess and 100° countersunk head. Other head styles are available from locking collar in the head) and a serrated stem that extends some manufacturers.

® through the shank. Unlike the friction lock rivet, the Huck mechanical lock rivet has a locking collar that forms a positive Pull-thru rivets are fabricated from several materials. The lock for retention of the stem in the shank of the rivet. This most commonly used are 2117-T4 aluminum alloy, 5056 collar is seated in position during the installation of the rivet.

aluminum alloy, Monel. Pull-thru rivets are designed so that installation requires only one person; it is not necessary to Material have the work accessible from both sides.

Self-plugging (mechanical lock) rivets are fabricated with Factors to consider in the selection of the correct rivet for installation are: installation location, composition of the material being riveted, thickness of the material being riveted, and strength desired.

The thickness of the material being riveted determines the overall length of the shank of the rivet. As a general rule, the shank of the rivet should extend beyond the material 3 1 thickness approximately ⁄ 64 inch to ⁄ 8 inch before the stem is pulled. [Figure 7-42] Each company that manufactures pull-thru rivets has a code number to help users obtain correct rivet for the grip range of a particular installation. In addition, MS numbers are used for identification purposes. Numbers are similar to those shown on the preceding pages.

Self-Plugging Rivets (Mechanical Lock) Self-plugging (mechanical lock) rivets are like self-plugging (friction lock) rivets, except for the way the stem is retained in the rivet sleeve. This type of rivet has a positive mechanical locking collar to resist vibrations that cause the friction lock Protruding head Countersunk head rivets to loosen and possibly fall out. [Figure 7-43] Also, the mechanical locking-type rivet stem breaks off flush with Figure 7-39. Self-plugging (friction lock) rivets.

7-58 sleeves (rivet shanks) of 2017 and 5056 aluminum alloys, Monel, or stainless steel.

The mechanical lock type of self-plugging rivet can be A used in the same applications as the friction lock type of C rivet. In addition, because of its greater stem retention B characteristic, installation in areas subject to considerable vibration is recommended.

The same general requirements must be met in the selection of the mechanical lock rivet as for the friction lock rivet. Composition of the material being joined A = Thickness of material (grip range) together determines the composition of the rivet sleeve.

3 1 B = ⁄ – ⁄ " 64 8 For example, 2017 aluminum alloy rivets for most aluminum C = Total rivet shank length alloys and 5056 aluminum rivets for magnesium.

Figure 7-40. Determining length of friction lock rivets.

Figure 7-46 depicts the sequences of a typical mechanically- locked blind rivet. The form and function may vary slightly between blind rivet styles and specifics should be obtained Rivet Identification from manufacturers.

Each company that manufactures self-plugging (friction lock) rivets has a code number to help users obtain the Head Styles correct rivet for the grip range or material thickness of a Self-plugging mechanical locked blind rivets are available particular installation. In addition, MS numbers are used for in several head styles depending on the installation identification purposes. Figures 7-51 through 7-54 contain requirements. [Figure 7-47] examples of part numbers for self-plugging (friction lock) rivets that are representative of each.

Diameters Shank diameters are measured in ⁄ 32 -inch increments and are generally identified by the first dash number: -3 indicates ⁄ 32 inch diameter, -4 indicates ⁄ 8 diameter, and so forth. Both nominal and ⁄ 64 -inch oversize diameters are available.

Grip Length Grip length refers to the maximum total sheet thickness to be riveted and is measured in ⁄ 16 of an inch. This is generally identified by the second dash number. Unless otherwise noted, most blind rivets have their grip lengths (maximum grip) marked on the rivet head and have a total grip range of ⁄ 16 inch. For example, –04 grip rivet has a grip 3 1 range of ⁄ 16 " to ⁄ 4 ". [Figure 7-48] To determine the proper grip rivet to use, measure the material thickness with a grip selection gauge (available from blind rivet manufacturers). The proper use of a grip selector gauge is shown in Figure 7-49 .

The thickness of the material being riveted determines the overall length of the shank of the rivet. As a general rule, the shank of the rivet should extend beyond the material 3 1 thickness approximately ⁄ 64 inch to ⁄ 8 inch before the stem Protruding head Countersunk head is pulled. [Figure 7-50] Figure 7-41. Pull-thru rivets.

7-59 A C B A = Thickness of material (grip range) B = 3/64 – 1/8" C = Total rivet shank length Figure 7-42. Determining length of pull-thru rivets. Before installation After installation Special Shear and Bearing Load Fasteners Figure 7-43. Self-plugging (mechanical lock) rivets.

Many special fasteners produce high strength with lightweight and can be used in place of conventional AN the shank diameter.

bolts and nuts. When AN bolts are tightened with the nut, the bolt stretches, narrowing the diameter and then the bolt is no Part numbers for pin rivets can be interpreted to give the longer tight in the hole. Special fasteners eliminate this loose diameter and grip length of the individual rivets. A typical fit, because they are held in place by a collar that is squeezed part number breakdown would be: into position. These fasteners are not under the same tensile NAS177-14-17 loads as a bolt during installation. Special fasteners are also used extensively for light sport aircraft (LSA). Always follow the aircraft manufacturer’s recommendations.

Pin Rivets Pin (Hi-Shear) rivets are classified as special rivets but are not of the blind type. Access to both sides of the material is required to install this type of rivet. Pin rivets have the same shear strength as bolts of equal diameters, are about 40 percent of the weight of a bolt, and require only about one- fifth as much time for installation as a bolt, nut, and washer combination. They are approximately three times as strong as solid shank rivets.

Pin rivets are essentially threadless bolts. The pin is headed at (Minimum grip illustrated) one end and is grooved about the circumference at the other. A metal collar is swaged onto the grooved end effecting a firm, tight fit. [Figure 7-55] Pin rivets are fabricated in a variety of materials but should be used only in shear applications.

They should never be used where the grip length is less than Figure 7-44. Bulbed CherryLOCK® rivet.

7-60 to completely fill the hole, but unlike the rivet, it fills the hole without deforming the shank. Instead, the washer head nut squeezes the metal with tremendous force against the tapered walls of the hole. This creates radial compression around the shank and vertical compression lines as the metals are squeezed together. The combination of these forces generates strength unequaled by any other fastener. [Figure 7-56] HI-LOK™ Fastening System The threaded end of the HI-LOK™ two-piece fastener contains a hexagonal shaped recess. The hex tip of an Allen wrench engages the recess to prevent rotation of the pin while the collar is being installed. The pin is designed in two basic head styles. For shear applications, the pin is made in countersunk style and in a compact protruding head style. For tension applications, the MS24694 countersunk and regular protruding head styles are available.

Figure 7-45. Wiredraw CherryLOCK® rivet.

The self-locking, threaded HI-LOK™ collar has an internal counterbore at the base to accommodate variations in material NAS = National Aircraft Standard thickness. At the opposite end of the collar is a wrenching 177 = 100° countersunk head rivet device that is torqued by the driving tool until it shears off OR 178 = flathead rivet during installation, leaving the lower portion of the collar seated with the proper torque without additional torque 14 = Nominal diameter in 32nds of an inch inspection. This shear-off point occurs when a predetermined 17 = Maximum grip length in 16ths of an inch preload or clamp-up is attained in the fastener during installation.

Taper-Lok Note: For these fasteners, “Preload” is defined as the Taper-Loks are the strongest special fasteners used in aircraft maximum tensile load experienced by a fastener in a joint construction. The Taper-Lok exerts a force on the walls of the during the fastener installation sequence. Consequently, the hole because of its tapered shape. The Taper-Lok is designed Before pulling begins 1 Stem is pulled into rivet 2 Clamp-up completed as 3 sleeve and starts to form stem continues to bulb bulbed blind head. out blind head.

Stem Locking collar Rivet head Rivet head firmly seated Clamp-up and hole Sheet gap fill action begin.

Rivet sleeve Blind side bulb head is formed below minimum Shear ring grip.

Completely installed bulbed Formation of blind head 4 6 Shear ring has moved down 5 CherryLOCK® rivet and hole fi lling are completed. stem cone until pulling head automatically stops stem Pulling head has inserted locking Shear ring now begins to break notch fl ush with top of collar, and stem has fractured flush shear from stem cone to allow rivet head.

with rivet head.

stem to pull further into rivet.

Locking collar is now ready to be inserted.

Shear ring guarantees blind side bulbed head Blind side bulbed head (Maximum grip illustrated) (In minimum grip, shear ring may not shear) Figure 7-46. CherryLOCK® rivet installation.

7-61 100° Countersunk (MS20426) Universal (MS20470) For countersunk applications For protruding head applications 100° Countersunk NAS 1097 Unisink For thin top sheet machine countersunk applications A combination of flush and protruding head for use in very thin top sheets. Eliminates need for double-dimpling. Not covered by NAS Standard.

156° Countersunk NAS 1097 A large diameter, shallow countersunk head providing wide area for honeycomb applications. Not covered by NAS Standard.

Figure 7-47. CherryLOCK® rivet heads.

term “Residual Tension” is defined as the remaining tensile threads, and a recess. The wrenching flats are used to install load experienced by a fastener in a joint after the fastener the collar. The fracture point has been designed to allow the installation sequence is complete, and after any residual wrenching flats to shear when the proper torque has been relaxation of the joint assembly. reached. The threads match the threads of the pins and have been formed into an ellipse that is distorted to provide the locking action. The recess serves as a built-in washer. This The advantages of HI-LOK™ two-piece fastener include its lightweight, high fatigue resistance, high strength, and its area contains a portion of the shank and the transition area of the fastener.

inability to be over-torqued. The pins, made from alloy steel, corrosion-resistant steel, nickel, or titanium alloy, come in many standard and oversized shank diameters. The collars are The hole shall typically be prepared so that the maximum made of aluminum alloy, corrosion-resistant steel, titanium, interference fit does not exceed 0.002-inch. This avoids or alloy steel. The collars have wrenching flats, fracture point, build up of excessive internal stresses in the work adjacent 7-62 Huck Manufacturing Company 9S P-B A 6 3 9SP-B Head Style 9SP-B = brazier or universal head Min. Max.

grip grip Grip 9SP-100 = 100º countersunk head 4 4 4 Material composition of shank A 3/16 " ¼ " A = 2017 aluminum alloy B = 5056 aluminum alloy R = mild steel Diameter Shank diameter in 32nds of an inch: 1 3 4 = ⁄ " 6 = ⁄ " Figure 7-48. Typical grip length. 8 16 5 = ⁄ " 8 = ¼" Grip range (material thickness) in 16ths of an inch 269C3 Gauge Figure 7-51. Huck Manufacturing Company codes.

2 4 6 8 Olympic Screw and Rivet Corporation Read Read RV 2 0 0 4 2 RV Manufacturer Rivet grip number to be used: −04 Olympic Screw and Rivet Corporation Rivet type 2 Figure 7-49. Grip gauge use.

2 = self plugging (friction lock) 5 = hollow pull through to the hole. The HI-LOK™ pin has a slight radius under its Material composition of shank 0 head to increase fatigue life. After drilling, deburr the edge 0 = 2017 aluminum alloy 5 = 5056 aluminum alloy of the hole to allow the head to seat fully in the hole. The 7 = mild steel HI-LOK™ is typically installed in interference fit holes for Head style 0 aluminum structure and a clearance fit for steel, titanium, 0 = universal head and composite materials.

1 = 100° countersunk Shank diameter in 32nds of an inch: 4 1 3 HI-TIGUE™ Fastening System 4 = ⁄ " 6 = ⁄ " 8 16 5 = ⁄ " 8 = ¼" The HI-TIGUE™ fastener offers all the benefits of the HI-LOK™ fastening system along with a unique radius Grip range in 16ths of an inch 2 contour on the thread lead-in, or a raised bead design that enhances the fatigue performance of the structure making it Figure 7-52. Olympic Screw and Rivet Corporation codes.

ideal for situations that require a controlled interference fit.

The HI-TIGUE™ fastener assembly consists of a pin and Townsend Company, Cherry Rivet Division CR 163 6 6 CR Cherry rivet Series number 163 Designates rivet material, type of rivet, and head style A (163 = 2117 aluminum alloy, self-plugging C (friction lock) rivet, protruding head) B Shank diameter in 32nds of an inch: 1 3 4 = ⁄ " 6 = ⁄ " 8 16 5 = ⁄ " 8 = ¼" Grip range (material thickness): Knob stem in 32nds of an inch; serrated stem in 16ths of an inch A = Thickness of material (grip range) Figure 7-53. Townsend Company, Cherry Rivet Division codes.

B = 3/64 – 1/8" C = Total rivet shank length Figure 7-50. Determining rivet length.

7-63 Military Standard Number Collar MS 20600 B 4 K 2 Military Standard MS 20600 Type of rivet and head style: 20600 = self-plugging (friction lock) protruding head Pin 20600 = self-plugging (friction lock) 100º countersunk head B Material composition of sleeve: AD = 2117 aluminum alloy B = 5056 aluminum alloy Shank diameter in 32nds of an inch: 4 1 3 4 = ⁄ " 6 = ⁄ " 8 16 8 = ⁄ " 5 = ⁄ " 4 Type of stem: K Driven collar K = knot head stem W = serrated stem Grip range (material thickness) in 16ths of an inch Figure 7-54. Military Standard Numbers.

collar. These pin rivets have a radius at the transition area.

Figure 7-55. Pin (Hi-Shear) rivet.

During installation in an interference fit hole, the radius area will “cold-work” the hole. These fastening systems can be also referred to by such terms as quick opening, quick action, easily confused, and visual reference should not be used for and stressed panel fasteners. The most desirable feature of identification. Use part numbers to identify these fasteners.

these fasteners is that they permit quick and easy removal [Figure 7-57] of access panels for inspection and servicing purposes. Turn lock fasteners are manufactured and supplied by several HI-LITE™ Fastening System manufacturers under various trade names.

The HI-LITE™ fastener is similar in design and principle to the HI-LOK™ fastener, has the controlled radius from full Dzus Fasteners diameter section to the threaded area of the HI-TIGUE™ The Dzus turn lock fastener consists of a stud, grommet, and fastener, and has a shorter transition area between the shank receptacle. Figure 7-58 illustrates an installed Dzus fastener and the first load-bearing thread. HI-LITE™ fasteners have and the various parts.

approximately one less thread. These differences reduce the weight of the HI-LITE™ fastener without lessening The grommet is made of aluminum or aluminum alloy the shear strength. HI-LITE™ fasteners are available in the material. It acts as a holding device for the stud. Grommets same materials and head configurations as the HI-LOK™ can be fabricated from 1100 aluminum tubing, if none are system, and can also be installed in high interference like the available from normal sources.

HI-TIGUE™ fastener. HI-LITE™ collars are also different and thus are not interchangeable with HI-LOK™ collars or HI-TIGUE™ collars.

Manufacturing head Lines of force Captive Fasteners Captive fasteners are used for quick removal of engine nacelles, inspection panels, and areas where fast and easy access is important. A captive fastener can turn in the body in which it is mounted, but will not drop out when it is unscrewed from the part it is holding. Some of the most commonly used are the Dzus, Camloc, and Airloc.

Radial compression Preload Turn Lock Fasteners Washer nut Turn lock fasteners are used to secure inspection plates, doors, and other removable panels on aircraft. Turn lock fasteners are Figure 7-56. Taper-Lok special fasteners 7-64 The spring is made of steel, which is cadmium plated to The hex portion breaks away once prevent corrosion. The spring supplies the force that locks the correct seating Collar or secures the stud in place when two assemblies are joined.

torque is reached The studs are fabricated from steel and are cadmium plated.

They are available in three head styles: wing, flush, and oval.

Body diameter, length, and head type may be identified or determined by the markings found on the head of the stud.

Pin [Figure 7-59] The diameter is always measured in sixteenths of an inch. Stud length is measured in hundredths of an inch and is the distance from the head of the stud to the bottom of the spring hole.

TM Figure 7-57. HI-TIGUE special fasteners.

A quarter of a turn of the stud (clockwise) locks the fastener. The fastener may be unlocked only by turning the fairings. It consists of three parts: a stud assembly, a grommet, stud counterclockwise. A Dzus key or a specially ground and a receptacle. Two types of receptacles are available: rigid screwdriver locks or unlocks the fastener.

and floating. [Figure 7-60] Camloc Fasteners The stud and grommet are installed in the removable portion; Camloc fasteners are made in a variety of styles and designs.

the receptacle is riveted to the structure of the aircraft. The Included among the most commonly used are the 2600, 2700, stud and grommet are installed in either a plain, dimpled, 40S51, and 4002 series in the regular line, and the stressed countersunk, or counter bored hole, depending upon the panel fastener in the heavy-duty line. The latter is used in location and thickness of the material involved.

stressed panels, which carry structural loads.

A quarter turn (clockwise) of the stud locks the fastener.

The Camloc fastener is used to secure aircraft cowlings and The fastener can be unlocked only by turning the stud Stud Detachable part Stud assembly Grommet Cut-away view of complete Dzus assembly Fixed part Spring and rivets Spring assembly Figure 7-58. Dzus fastener.

7-65 counterclockwise.

Airloc Fasteners The Airloc fastener consists of three parts: a stud, a cross pin, and a stud receptacle. [Figure 7-61] The studs are manufactured from steel and case hardened to prevent excessive wear. The stud hole is reamed for a press fit of the cross pin.

The total amount of material thickness to be secured with the Airloc fastener must be known before the correct length of stud can be selected for installation. The total thickness Stud assembly of material that each stud satisfactorily locks together is Grommet stamped on the head of the stud in thousandths of an inch (0.040, 0.070, 0.190, and so forth). Studs are manufactured in three head styles: flush, oval, and wing.

The cross pin is manufactured from chrome-vanadium steel and heat-treated to provide maximum strength, wear, and holding power. [Figure 7-61] It should never be used the second time; once removed from the stud, replace it with a new pin.

Receptacles for Airloc fasteners are manufactured in two types: rigid and floating. Number—No. 2, No. 5, and No.

7, classifies sizes. They are also classified by the center-to- Receptacle center distance between the rivet holes of the receptacle: No.

3 3 2 is ⁄ 4 inch; No. 5 is 1 inch; and No. 7 is 1 ⁄ 8 inch. Receptacles are fabricated from high-carbon, heat-treated steel. An upper wing assures ejection of the stud when unlocked and enables the cross pin to be held in a locked position between the upper wing, cam, stop, and wing detent, regardless of the tension to which the receptacle is subjected.

Figure 7-60. Camloc fastener.

Screws the same, and a definite grip length is provided. The AN525 Screws are the most commonly used threaded fastening washer head screw and the NAS220 through NAS227 series devices on aircraft. They differ from bolts because as they are such screws.

are generally made of lower strength materials. They can be installed with a loose-fitting thread, and the head shapes are Commonly used screws are classified in four groups: made to engage a screwdriver or wrench. Some screws have 1. Structural screws, which have the same strength as a clearly defined grip or unthreaded portion, while others are equal size bolts.

threaded along their entire length.

2. Machine screws, which include most types used for Several types of structural screws differ from the standard general repair.

structural bolts only in head style. The material in them is 3. Self-tapping screws, which are used for attaching lighter parts.

4. Drive screws, which are not actually screws but nails.

They are driven into metal parts with a mallet or DZUS F = fl ush head hammer and their heads are not slotted or recessed.

6 / = body diameter in 16ths of an inch 0.50 = length ( ⁄ of an inch) F 0.50 100 6½ Structural Screws Structural screws are made of alloy steel, are properly heat- treated, and can be used as structural bolts. These screws Figure 7-59. Dzus identification.

7-66 Roundhead screws, AN515 and AN520, have either slotted Installed fastener or recessed heads. The AN515 screw has coarse threads, and the AN520 has fine threads.

Cross pin Receptacle Countersunk machine screws are listed as AN505 and AN510 for 82° and AN507 for 100°. The AN505 and AN510 correspond to the AN515 and AN520 roundhead in material and usage.

The fillister head screw, AN500 through AN503, is a general purpose screw and is used as a cap screw in light mechanisms.

Panel Stud This could include attachments of cast aluminum parts, such as gearbox cover plates.

The AN500 and AN501 screws are available in low-carbon steel, corrosion-resistant steel, and brass. The AN500 has coarse threads, while the AN501 has fine threads. They have no clearly defined grip length.

Screws larger than No. 6 have a hole drilled through the head for safetying purposes.

The AN502 and AN503 fillister head screws are made of heat-treated alloy steel, have a small grip, and are available in Studs Stud receptacles fine and coarse threads. These screws are used as cap screws where great strength is required. The coarse threaded screws are commonly used as cap screws in tapped aluminum alloy and magnesium castings because of the softness of the metal.

Airloc cross pin Self-Tapping Screws Figure 7-61. Airloc fastener.

Machine self-tapping screws are listed as AN504 and AN506.

The AN504 screw has a roundhead, and the AN506 is 82° are found in the NAS204 through NAS235 and AN509 and countersunk. These screws are used for attaching removable AN525 series. They have a definite grip and the same shear parts, such as nameplates, to castings and parts in which the strength as a bolt of the same size. Shank tolerances are screw cuts its own threads.

similar to AN hex head bolts, and the threads are National Fine. Structural screws are available with round, brazier, AN530 and AN531 self-tapping sheet metal screws, such or countersunk heads. Either a Phillips or a Reed & Prince as the Parker-Kalon Z-type sheet metal screw, are blunt on screwdriver drives the recessed head screws.

the end. They are used in the temporary attachment of metal for riveting, and in the permanent assembly of nonstructural The AN509 (100°) flathead screw is used in countersunk assemblies. Self-tapping screws should not be used to replace holes where a flush surface is necessary.

standard screws, nuts, bolts, or rivets.

The AN525 washer head structural screw is used where raised Drive Screws heads are not objectionable. The washer head screw provides Drive screws, AN535, correspond to the Parker-Kalon a large contact area.

U-type. They are plain head self-tapping screws used as cap screws for attaching nameplates in castings and for sealing Machine Screws drain holes in corrosion proofing tubular structures. They are Machine screws are usually of the flathead (countersunk), not intended to be removed after installation.

roundhead, or washer head types. These are general purpose screws and are available in low-carbon steel, brass, corrosion- Identification & Coding for Screws resistant steel, and aluminum alloy.

The coding system used to identify screws is similar to that used for bolts. There are AN and NAS screws. NAS screws 7-67 are structural screws. Part numbers 510, 515, 550, and so inspection panels. Ganged anchor nuts allow the nuts to float on, catalog screws into classes, such as roundhead, flathead, in a channel, making alignment with the screw easy.

washer head, and so forth. Letters and digits indicate their material composition, length, and thickness. Examples of Self-locking nut plates are made under several standards AN and NAS code numbers follow. and come in several shapes and sizes. Figure 7-62 shows an MS21078 two-lug nut plate with a nonmetallic insert and an AN501B-416-7 MS21047 lightweight, all-metal, 450 °F (232 °C) nut plate.

AN = Air Force-Navy standard Nut plates can also have three riveting points if the added strength is required.

501 = fillister head, fine thread B = brass Rivnuts 416 = ⁄ 16 -inch diameter This is the trade name of a hollow, blind rivet made of 6053 7 = ⁄ 16 -inch length aluminum alloy, counter bored and threaded on the inside.

One person using a special tool, which heads the rivet on the The letter “D” in place of the “B” would indicate that the blind side of the material, can install Rivnuts. The Rivnut is material is 2017-T aluminum alloy. The letter “C” would threaded on the mandrel of the heading tool and inserted in designate corrosion resistant steel. An “A” placed before the the rivet hole. The heading tool is held at right angles to the material code letter would indicate that the head is drilled material, the handle is squeezed, and the mandrel crank is for safetying. turned clockwise after each stroke. Continue squeezing the handle and turning the mandrel crank of the heading tool until NAS144DH-22 a solid resistance is felt, which indicates that the rivet is set.

NAS = National Aircraft Standard The Rivnut is used primarily as a nut plate and in the 144 = head style; diameter and thread— ⁄ 4 -28 bolt, internal wrenching attachment of deicer boots to the leading edges of wings.

It may be used as a rivet in secondary structures or for DH = drilled head the attachment of accessories, such as brackets, fairings, 22 = screw length in 16ths of an inch—1 ⁄ 8 inches long instruments, or soundproofing materials.

The basic NAS number identifies the part. The suffix letters Rivnuts are manufactured in two head types, each with and dash numbers separate different sizes, plating material, two ends: the flathead with open or closed end and the drilling specifications, and so forth. The dash numbers and countersunk head with open or closed end. All Rivnuts, suffix letters do not have standard meanings. It is necessary except the thin head countersunk type, are available with to refer to a specific NAS page in the Standards book for or without small projections (keys) attached to the head to the legend.

keep the Rivnut from turning. Keyed Rivnuts are used as a nut plate, while those without keys are used for straight blind Riveted & Rivetless Nut Plates riveting repairs where no torque loads are imposed. A keyway When access to the back of a screw or bolt installation is cutter is needed when installing Rivnuts that have keys.

impractical, riveted or rivetless nut plates are used to secure the connection of panels. One example in aircraft this The countersunk style Rivnut is made with two different head technique is especially useful is to secure the floorboards to angles: the 100° with 0.048 and 0.063 inch head thickness and the stringers and to each other.

the 115° with 0.063 inch head thickness. Each of these head styles is made in three sizes: 6-32, 8-32, and 10-32. These Nut Plates numbers represent the machine screw size of the threads on Nuts that are made to be riveted in place in aircraft are called the inside of the Rivnut. The actual outside diameters of the 3 7 nut plates. Their purpose is to allow bolts and screws to be shanks are ⁄ 16 inch for the 6-32 size, ⁄ 32 inch for the 8-32 size, inserted without having to hold the nut. They are permanently and ⁄ 4 inch for the 10-32 size.

mounted to enable inspection panels and access doors to be easily removed and installed. When many screws are used on Open-end Rivnuts are the most widely used and are a panel, to make installation easier, normally floating anchor recommended in preference to the closed end type wherever nuts are used. The floating anchor nut fits into a small bracket, possible. However, closed-end Rivnuts must be used in which is riveted to the aircraft skin. The nut is free to move, pressurized compartments.

which makes it much easier to align it with the screw. For production ease, sometimes ganged anchor nuts are used for Rivnuts are manufactured in six grip ranges. The minimum 7-68 MS33737 Instrument nut MS21078 MS21051 MS21055 Two-lug anchor nut One-lug anchor nut Corner anchor nut To reduce magnetic influences in the flightdeck, nonmagnetic mounting nuts secure instruments in a control panel.

NAS680A MS21047 MS21059 NAS444 or A6195 Right-angle anchor nut High-temperature Two-lug floating anchor nut Anchor type tinnerman two-lug anchor nut nuts are suitable for nonstructural applications Ganged anchor nuts A1777, A1789, or A1794 U-type tinnerman nuts provide convenient anchor points for cowlings, fairings, and panels.

Figure 7-62. Various nut plates.

grip length is indicated by a plain head and the next higher KB = Closed end and key grip length by one radial dash mark on the head. Each 106 = Screw and thread size succeeding grip range is indicated by an additional radial dash mark until five marks indicate the maximum range.

Dill Lok-Skrus and Dill Lok-Rivets Dill “Lok-Skru” and “Lok-Rivet” are trade names for Notice in Figure 7-63 that some part number codes consist internally-threaded rivets. They are used for blind attachment of a “6,” an “8,” or a “10,” a “dash,” and two or three more of accessories, such as fairings, fillets, access door covers, numbers. In some, the letters “K” or “KB” replaces the door and window frames, floor panels, and the like. Lok- dash. The first number indicates the machine screw size of Skrus and Lok-Rivets are like the Rivnut in appearance the thread, and the last two or three numbers indicate the and application; however, they come in two parts and maximum grip length in thousandths of an inch. A dash require more clearance on the blind side than the Rivnut to between the figures indicates that the Rivnut has an open accommodate the barrel. [Figure 7-64] end and is keyless; a “B” in place of the dash means it has a closed end and is keyless; a “K” means it has an open end The Lok-Rivet and the Lok-Skru are alike in construction, and has a key; and a “KB” indicates that it has a closed end except the Lok-Skru is tapped internally for fastening an and a key. If the last two or three numbers are divisible by accessory by using an attaching screw, whereas the Lok-Rivet is five, the Rivnut has a flathead; if they are not divisible by not tapped and can be used only as a rivet. Since both Lok-Skrus five, the Rivnut has a countersunk head.

and Lok-Rivets are installed in the same manner, the following discussion for the Lok-Skru also applies to the Lok-Rivet.

An example of a part number code is: 10KB106 The main parts of a Lok-Skru are the barrel, the head, and an attachment screw. The barrel is made of aluminum alloy 10 = Grip length 7-69 and comes in either closed or open ends. The head is either aluminum alloy or steel, and the attachment screw is made of steel. All the steel parts are cadmium plated, and all of aluminum parts are anodized to resist corrosion. When installed, the barrel screws up over the head and grips the Flat — 0.32 Head Thickness metal on the blind side. The attaching screw is then inserted if needed. There are two head types: the flathead and the 6-45 6-75 6-100 countersunk head. The Lok-Skru is tapped for 7-32, 8-32, 8-45 8-75 8-100 10-32, or 10-24 screws, and the diameters vary from 0.230 inch for 6-32 screws, to 0.292 inch for 10-32 screws. Grip 10-45 10-75 10-100 ranges vary from 0.010 inch to 0.225 inch.

6B45 6B75 6B100 8B45 8B75 8B100 Deutsch Rivets This rivet is a high-strength blind rivet used on late model 10B45 10B75 10B100 aircraft. It has a minimum shear strength of 75,000 psi and 6K45 6K75 6K100 can be installed by one person. The Deutsch rivet consists of two parts: the stainless-steel sleeve and the hardened steel 8K45 8K75 8K100 drive pin. [Figure 7-65] The pin and sleeve are coated with 10K45 10K75 10K100 a lubricant and a corrosion inhibitor.

6KB45 6KB75 6KB100 3 1 3 The Deutsch rivet is available in diameters of ⁄ 16 , ⁄ 4 , or ⁄ 8 8KB45 8KB75 8KB100 inch. Grip lengths for this rivet range from ⁄ 16 to 1 inch.

10KB45 10KB75 10KB100 Some variation is allowed in grip length when installing the rivet. For example, a rivet with a grip length of ⁄ 16 inch can 100°— 0.48 Head Thickness be used where the total thickness of materials is between 0.198 and 0.228 inch.

6-91 6-121 6-146 8-91 8-121 8-146 When driving a Deutsch rivet, an ordinary hammer or a 10-91 10-121 10-146 pneumatic rivet gun and a flathead set are used. The rivet is seated in the previously drilled hole, and then the pin is 6B91 6B121 6B146 driven into the sleeve. The driving action causes the pin to 8B91 8B121 8B146 exert pressure against the sleeve and forces the sides of the sleeve out. This stretching forms a shop head on the end of 10B91 10B121 10B146 the rivet and provides positive fastening. The ridge on the 100°— 0.63 Head Thickness top of the rivet head locks the pin into the rivet as the last few blows are struck.

6-106 6-136 6-161 8-106 8-136 8-161 Sealing Nut Plates 10-106 10-136 10-161 When securing nut plates in pressurized aircraft and in fuel cells, a sealing nut plate is used instead of the open-ended 6B106 6B136 6B161 variety previously described. Care must be taken to use 8B106 8B136 8B161 exactly the correct length of bolt or screw. If a bolt or screw is too short, there is not enough threads to hold the device in 10B106 10B136 10B161 place. If the bolt or screw is too long, it penetrates the back 6K106 6K136 6K161 side of the nut plate and compromises the seal. Normally, a sealant is also used to ensure complete sealing of the nut plate.

8K106 8K136 8K161 Check the manufacturer’s specifications for the acceptable 10K106 10K136 10K161 sealant to be used for sealing nut plates.

6KB106 6KB136 6KB161 Hole Repair & Hole Repair Hardware 8KB106 8KB136 8KB161 Many of the blind fasteners are manufactured in oversized 10KB106 10KB136 10KB161 diameters to accommodate slightly enlarged holes resulting from drilling out the original fastener. When using rivets Figure 7-63. Rivnut data chart.

7-70 sleeves. The sleeves are manufactured in 1-inch increments.

Along their length, grooves provide a place to break or cut off excess length to match fastener grip range. The grooves also provide a place to hold adhesive or sealing agents when bonding the sleeve into the hole.

Advantages & Limitations The sleeves are used in holes that must be drilled ⁄ 64 inch oversize to clean up corrosion or other damage. The oversize hole with the sleeve installed allows the use of the original diameter fastener in the repaired hole. The sleeves can be used in areas of high galvanic corrosion where the corrosion Figure 7-64. Internally-threaded rivet (Rivnut).

must be confined to a readily replaceable part. Oversizing of holes reduces the net cross-sectional area of a part and should not be done unless absolutely required.

or even bolts, care must be taken to ensure the hole is not elongated or slanted.

Consult the manufacturer of the aircraft, aircraft engine, or aircraft component prior to repair have damaged holes with To reduce the chances of an incorrectly drilled rivet or bolt Acres sleeves.

hole, use a slightly smaller drill bit first, then enlarge to the correct diameter. The last step to prepare the hole for the Identification fastener is to deburr the hole using either a very large drill The sleeve is identified by a standard code number that bit or a special deburring tool. This practice also works well represents the type and style of sleeve, a material code, when drilling out a previously attached fastener. If the drill the fastener shank diameter, and surface finish code letter, bit does not exactly find the center of the rivet, bolt, or screw, and grip tang for the sleeve. [Figure 7-66] The basic code the hole can easily be elongated, but when using a smaller number represents the type and material of the sleeve. The drill bit, drill the head only off the fastener. Then the ring and first dash number represents the diameter of the sleeve for stem that is left can be pushed out with a pin punch of the the fastener installed, and the second dash represents the appropriate diameter. If an incorrectly drilled hole is found, grip length of the sleeve. The required length of the sleeve the options are to re-drill the hole to the next larger diameter is determined on installation and the excess is broken off the for an acceptable fastener or repair the hole using an Acres sleeve. A JK5512A-05N-10 is a 100° low profile head sleeve fastener sleeve.

of aluminum alloy. The diameter is for a ⁄ 32 -inch fastener with no surface finish and is ⁄ 8 inch in length.

Repair of Damaged Holes with Acres Fastener Sleeves Hole Preparation Acres fastener sleeves are thin-wall tubular elements with Refer to Figure 7-67 for drill number for standard or close a flared end. The sleeves are installed in holes to accept fit holes. Inspect hole after drilling to assure all corrosion is standard bolts and rivet-type fasteners. The existing fastener 1 removed before installing the sleeve. The hole must also be holes are drilled ⁄ 64 inch oversize for installation of the the correct shape and free from burrs. The countersink must be enlarged to receive the flare of the sleeve, so the sleeve is flush with the surrounding surface.

Installation After selecting the correct type and diameter sleeve, use the 6501 sleeve breakoff tool for final installation length. Refer to Figure 7-67 for the sleeve breakoff procedure. The sleeve may be installed with or without being bonded in the hole.

When bonding the sleeve in a hole, use MIL-S-8802A ⁄ 2 sealant. Reinstall original size fastener and torque as required.

Sleeve Removal Sleeves not bonded in the hole may be removed by either Figure 7-65. Deutsch rivet.

7-71 driving them out with a drift pin of the same diameter as Cable Fittings the outside diameter of the sleeve, or they may be deformed Cables may be equipped with several different types of and removed with a pointed tool. Bonded sleeves may be fittings, such as terminals, thimbles, bushings, and shackles.

removed by this method, but care should be used not to Terminal fittings are generally of the swaged type. They are damage the structure hole. If this method cannot be used, available in the threaded end, fork end, eye end, single shank drill the sleeves out with a drill 0.004 to 0.008 inch smaller ball end, and double shank ball end. The threaded end, fork than the installation drill size. The remaining portion of the end, and eye end terminals are used to connect the cable to sleeve after drilling can be removed using a pointed tool and a turnbuckle, bell crank, or other linkage in the system. The applying an adhesive solvent to the sealant.

ball end terminals are used for attaching cables to quadrants and special connections where space is limited. Figure 7-69 Control Cables & Terminals illustrates the various types of terminal fittings.

Cables are the most widely used linkage in primary flight control systems. Cable-type linkage is also used in engine The thimble, bushing, and shackle fittings may be used in place of some types of terminal fittings when facilities controls, emergency extension systems for the landing gear, and various other systems throughout the aircraft. and supplies are limited and immediate replacement of the cable is necessary.

Cable-type linkage has several advantages over the other Turnbuckles types. It is strong and lightweight, and its flexibility makes it easy to route through the aircraft. An aircraft cable has a high A turnbuckle assembly is a mechanical screw device mechanical efficiency and can be set up without backlash, consisting of two threaded terminals and a threaded barrel.

which is very important for precise control.

[Figure 7-70] Cable linkage also has some disadvantages. Tension must be Turnbuckles are fitted in the cable assembly for making adjusted frequently due to stretching and temperature changes.

minor adjustments in cable length and for adjusting cable tension. One of the terminals has right-hand threads and the Aircraft control cables are fabricated from carbon steel or other has left-hand threads. The barrel has matching right- stainless steel.

and left-hand internal threads. The end of the barrel with the left-hand threads can usually be identified by a groove or Cable Construction knurl around that end of the barrel.

The basic component of a cable is a wire. The diameter of the wire determines the total diameter of the cable. Several When installing a turnbuckle in a control system, it is necessary to screw both terminals an equal number of turns wires are preformed into a helical or spiral shape and then formed into a strand. These preformed strands are laid around into the barrel. It is also essential that all turnbuckle terminals be screwed into the barrel until not more than three threads a straight center strand to form a cable.

are exposed on either side of the turnbuckle barrel.

Cable designations are based on the number of strands and the number of wires in each strand. The most common aircraft After a turnbuckle is properly adjusted, it must be safetied.

The methods of safetying turnbuckles are discussed later in cables are the 7 × 7 and 7 × 19.

this chapter.

The 7 × 7 cable consists of seven strands of seven wires each. Six of these strands are laid around the center strand. Push-Pull Tube Linkage [Figure 7-68] This is a cable of medium flexibility and is used Push-pull tubes are used as linkage in various types of for trim tab controls, engine controls, and indicator controls.

mechanically-operated systems. This type linkage eliminates the problem of varying tension and permits the transfer of The 7 × 19 cable is made up of seven strands of 19 wires either compression or tension stress through a single tube.

each. Six of these strands are laid around the center strand.

[Figure 7-68] This cable is extra flexible and is used in A push-pull tube assembly consists of a hollow aluminum primary control systems and in other places where operation alloy or steel tube with an adjustable end fitting and a check over pulleys is frequent.

nut at either end. [Figure 7-71] The check nuts secure the end fittings after the tube assembly has been adjusted to its correct Aircraft control cables vary in diameter, ranging from ⁄ 16 to length. Push-pull tubes are generally made in short lengths ⁄ 8 inch. The diameter is measured as shown in Figure 7-68 .

to prevent vibration and bending under compression loads.

7-72

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Part Number

Sleeve Bolt Sleeve Basic Part 2 Part Number Size Length Acres Sleeve Type Number JK5511( )04( )( ) JK5512( )04( )( ) 8 ⁄ JK5516( )04( )( ) JK5517( )04( )( ) 100° JK5610 509 tension head plus fl ange JK5511( )45( )( ) JK5512 8 #6 JK5516( )45( )( ) JK5517( )45( )( ) JK5511 Protruding head (shear) JK5511( )05( )( ) JK5512( )05( )( ) 10 ⁄ JK5516( )05( )( ) JK5517( )05( )( ) 100° JK5512 Low pro fi le head JK5511( )55( )( ) JK5512( )55( )( ) JK5516( )55( )( ) 10 #8 JK5517( )55( )( ) 100° JK5610( )55( )( ) Standard pro fi le head JK5516 (509 type) JK5511( )06( )( ) JK5512( )06( )( ) JK5516( )06( )( ) 12 #10 JK5517( )06( )( ) JK5517 Protruding head (tension) JK5610( )06( )( ) JK5511( )08( )( ) JK5512( )08( )( ) 100° JK5516( )08( )( ) 16 ¼ JK5533 Oversize tension head JK5517( )08( )( ) ( ⁄ oversize bolt) 64 JK5610( )08( )( ) JK5511( )10( )( ) Part Number Breakdown JK5512( )10( )( ) 5 JK5516( )10( )( ) JK5511 A 04 N 08 L 16 ⁄ JK5517( )10( )( ) JK5511 Basic part number JK5610( )10( )( ) A Material code 04 Fastener shank diameter in 32nds JK5511( )12( )( ) JK5512( )12( )( ) N Surface fi nish 3 JK5516( )12( )( ) N = No finish 16 ⁄ JK5517( )12( )( ) C = Chemical film per MIL-C-554 JK5610( )12( )( ) 08 Length in sixteenth inch increments (Required installation length by breaking o ff at proper groove) Acres Sleeve for ⁄ Oversize Bolt L “ L ” at end of part number indicates cetyl alcohol lubricant Sleeve Bolt Sleeve 2 1 Part Number Size Length Material Material Code JK5533( )06( )( ) ⁄ 12 17 5052 Aluminum alloy ½ hard A JK5533( )08( )( ) ⁄ 16 B 21 6061 Aluminum alloy (T6 condition) JK5533( )10( )( ) ⁄ 16 A286 Stainless steel (passivate) C JK5533( )12( )( ) ⁄ 16 NOTES: Acres sleeve, JK5533 ⁄ oversize available in 1 A286 steel only Acres sleeve length in sixteenth-inch increments 2 Figure 7-66. Acres sleeve identification.

7-73 Hole Preparation for ⁄ Oversize Bolt Bolt Size Drill Number Drill Diameter 7/32 13/64 0.2187 9/32 17/64 0.2812 Existing fastener 11/32 21/64 0.3437 13/32 25/64 0.4062 Hole Preparation Acres sleeve Standard Fit Close Fit Bolt Size Structure 1/64 Oversize hole Drill Drill Drill Number Drill Number Diameter Diameter 1/8 9/64 0.1406 28 0.1405 #6 23 0.1540 24 0.1520 5/32 11/64 0.1719 18 0.1695 #8 15 0.1800 16 0.1770 #10 5 0.2055 6 0.2040 ¼ 14 0.2660 17/64 0.2656 5/16 21/64 0.3281 3/8 25/64 0.3908 Installation Procedure A. Drill out corrosion or damage to existing hole to 1/64 oversize.

B. Select proper type and length acres sleeve for existing fastener.

Acres sleeve installation C. Bond sleeve in structure hole with MIL-S-8802 class A ½ sealant.

Figure 7-67. Acres sleeve identification, installation, and breakoff procedure.

1 3 / — / diameter 7 x 19 7 strands, 19 wires to each strand Diameter 8 8 1 3 7 strands, 7 wires to each strand 32 / — / diameter 7 x 7 Diameter 16 Figure 7-68. Cable cross-sections.

7-74 of safetying equipment on an aircraft is necessary to perform Safetying Methods maintenance and inspection.

To ensure fasteners do not separate from their nuts or holding There are various methods of safetying aircraft parts. The ends, various safetying methods are used in aircraft from heavy aircraft to gliders to recreational aircraft. Safetying is most widely used methods are safety wire, cotter pins, lock washers, snap rings, and special nuts, such as self-locking the process of securing all aircraft, bolts, nuts, screws, pins, and other fasteners so that they do not work loose due to nuts, pal nuts, and jam nuts. Some of these nuts and washers have been previously described in this chapter.

Pins The three main types of pins used in aircraft structures are MS20663 Double shank ball end terminal the taper pin, flathead pin, and cotter pin. Pins are used in shear applications and for safetying. Roll pins are finding increasing uses in aircraft construction.

MS20664 Single shank ball end terminal Taper Pins Plain and threaded taper pins (AN385 and AN386) are used in joints that carry shear loads and where absence of play is essential. The plain taper pin is drilled and usually safetied with wire. The threaded taper pin is used with a taper pin washer (AN975) and shear nut (safetied with a cotter pin or AN665 Rod end terminal safety clip) or self-locking nut.

Flathead Pin Commonly called a Clevis pin, the flathead pin (MS20392) AN666 Threaded cable terminal is used with tie rod terminals and in secondary controls, which are not subject to continuous operation. The pin is customarily installed with the head up so that if the cotter pin fails or works out, the pin remains in place.

MS20667 Fork end cable terminal Cotter Pins The AN380 cadmium-plated, low-carbon steel cotter pin is used for safetying bolts, screws, nuts, other pins, and in various applications where such safetying is necessary. The AN381 corrosion-resistant steel cotter pin is used in locations where nonmagnetic material is required or in locations where AN668/MS20668 Eye end cable terminal resistance to corrosion is desired.

Figure 7-69. Types of terminal fittings.

Roll Pins The roll pin is a pressed fit pin with chamfered ends. It is Length (threads flush with ends of barrel) Pin eye Swaged terminal Barrel Figure 7-70. Typical turnbuckle assembly.

7-75 vibration. A familiarity with the various methods and means Tube, steel, or aluminum alloy Check nut Rod end, threaded Self-aligning, anti-friction rod end assembly, adjustable Clevis, rod end, adjustable Figure 7-71. Push-pull tube assembly.

1 2 3 4 5 8 7 6 Figure 7-72. Safety wiring methods.

Oil caps Drain cocks NOTE: The safety wire is shown installed for right-hand threads. The safety wire is routed in the opposite direction for left-hand threads.

Valves Figure 7-73. Safety wiring attachment for plug connectors.

7-76 AN standard fillister head screw (drilled head) AN3102 receptacle Bulkhead AN3057 adapter AN3106 plug Figure 7-74. Safety wiring attachment for plug connectors.

tubular in shape and is slotted the full length of the tube. • Example 4 illustrates the proper method of wiring The pin is inserted with hand tools and is compressed as it castellated nuts and studs. (Note that there is no loop is driven into place. Pressure exerted by the roll pin against around the nut.)

the hole-walls keeps it in place until deliberately removed • Examples 6 and 7 illustrate a single-threaded component with a drift punch or pin punch.

wired to a housing or lug.

• Example 8 illustrates several components in a closely Safety Wiring spaced closed geometrical pattern using a single wire Safety wiring is the most positive and satisfactory method of method.

safetying cap screws, studs, nuts, bolt heads, and turnbuckle barrels, which cannot be safetied by any other practical When drilled head bolts, screws, or other parts are grouped means. It is a method of wiring together two or more units together, they are more conveniently safety wired to each in such a manner that any tendency of one to loosen is other in a series rather than individually. The number of counteracted by the tightening of the wire.

nuts, bolts, or screws that may be safety wired together is dependent on the application. For instance, when safety Nuts, Bolts, & Screws wiring widely spaced bolts by the double twist method, a Nuts, bolts, and screws are safety wired by the single wire group of three should be the maximum number in a series.

or double twist method. The double twist method is the most common method of safety wiring. The single wire When safety wiring closely spaced bolts, the number that can method may be used on small screws in a closely spaced be safety wired by a 24-inch length of wire is the maximum closed geometrical pattern, on parts in electrical systems, in a series. The wire is arranged so that if the bolt or screw and in places that are extremely difficult to reach. Safety begins to loosen, the force applied to the wire is in the wiring should always be per conventional methods or as tightening direction.

required by the manufacturer, especially for Light Sport Aircraft (LSA).

Parts being safety wired should be torqued to recommend values and the holes aligned before attempting the safetying Figure 7-72 is an illustration of various methods that are operation. Never over torque or loosen a torqued nut to align commonly used in safety wiring nuts, bolts, and screws.

safety wire holes.

Careful study of Figure 7-72 shows that: • Examples 1, 2, and 5 illustrate the proper method of Oil Caps, Drain Cocks, & Valves safety wiring bolts, screws, square-head plugs, and These units are safety wired as shown in Figure 7-73 . In similar parts when wired in pairs.

the case of the oil cap, the wire is anchored to an adjacent • Example 3 illustrates several components wired in series. fillister head screw.

7-77 Straight end Hook shoulder Loop end Hook lip Hook loop Hook end Direction of pull for inspection A Clip-locking method 4 turn (min) This applies to all turnbuckle wrappings Double wrap (spiral) Double wrap Single wrap (spiral) Single wrap B Wire-wrapping method Figure 7-75. Safetying turnbuckles: (A) clip-locking method and (B) wire-wrapping method.

7-78 Cable size Diameter of Safety Wire Material Type of Wrap (inch) (inch) (Annealed Condition) Single 0.020 Stainless steel ⁄ ⁄ Single 0.040 Copper, brass 32 ⁄ Single 0.040 Stainless steel 1 1 Double 0.040 Copper, brass ⁄ Single 0.057 Copper, brass ⁄ ⁄ and greater Single 0.057 Stainless steel Galvanized or tinned steel, or soft iron wires are also acceptable.

Figure 7-76. Turnbuckle safetying guide.

the side opposite the first. Then pass the wires at the end of This system applies to any other unit that must be safety wired the turnbuckle in opposite directions through the holes in the individually. Ordinarily, anchorage lips are conveniently turnbuckle eyes or between the jaws of the turnbuckle fork, located near these individual parts. When such provision is as applicable. Bend the laid wires in place before cutting off not made, the safety wire is fastened to some adjacent part the wrapped wire. Wrap the remaining length of safety wire of the assembly. at least four turns around the shank and cut it off. Repeat the procedure at the opposite end of the turnbuckle.

Electrical Connectors When a swaged terminal is being safetied, pass the ends Under conditions of severe vibration, the coupling nut of a of both wires, if possible, through the hole provided in the connector may vibrate loose and, with sufficient vibration, terminal for this purpose and wrap both ends around the the connector may come apart. When this occurs, the circuit shank as described above.

carried by the cable opens. The proper protective measure to prevent this occurrence is by safety wiring as shown in If the hole is not large enough to allow passage of both wires, Figure 7-74 . The safety wire should be as short as practicable pass the wire through the hole, and loop it over the free end and must be installed in such a manner that the pull on the of the other wire, and then wrap both ends around the shank wire is in the direction that tightens the nut on the plug.

as described.

Turnbuckles Single Wrap Method After a turnbuckle has been properly adjusted, it must be The single wrap safetying methods described in the following safetied. There are several methods of safetying turnbuckles; paragraphs are acceptable but are not the equal of the double however, only two methods are discussed in this section.

wrap methods.

These methods are illustrated in Figure 7-75 . The clip locking method is used only on the most modern aircraft. The older Pass a single length of wire through the cable eye or fork or type aircraft still use the type turnbuckles that require the through the hole in the swaged terminal at either end of the wire wrapping method.

Double Wrap Method Of the methods using safety wire for safetying turnbuckles, the double wrap method is preferred, although the single wrap methods described are satisfactory. The method of double wrap safetying is shown in Figure 7-75 . Use two separate lengths of the proper wire as shown in Figure 7-76 .

Run one end of the wire through the hole in the barrel of the turnbuckle and bend the ends of the wire toward opposite ends Preferred Optional of the turnbuckle. Then pass the second length of the wire into the hole in the barrel and bend the ends along the barrel on Figure 7-77. Cotter pin installation.

7-79 1 1 turnbuckle assembly. Spiral each of the wire ends in opposite 1. Pigtail of ⁄ 4 to ⁄ 2 inch (three to six twists) should be directions around the first half of the turnbuckle barrel so made at the end of the wiring. This pigtail must be bent that the wires cross each other twice. Thread both wire ends back or under to prevent it from becoming a snag.

through the hole in the middle of the barrel so that the third 2. The safety wire must be new upon each application.

crossing of the wire ends is in the hole. Again, spiral the two 3. When castellated nuts are to be secured with safety wire, wire ends in opposite directions around the remaining half tighten the nut to the low side of the selected torque of the turnbuckle, crossing them twice. Then, pass one wire range, unless otherwise specified, and if necessary, end through the cable eye or fork, or through the hole in the continue tightening until a slot aligns with the hole.

swaged terminal. In the manner described above, wrap both wire ends around the shank for at least four turns each, cutting 4. All safety wires must be tight after installation, but not off the excess wire.

under such tension that normal handling or vibration breaks the wire.

An alternate to the above method is to pass one length of 5. The wire must be applied so that all pull exerted by the wire tends to tighten the nut.

6. Twists should be tight and even, and the wire between Snap ring the nuts as taut as possible without over twisting.

7. The safety wire should always be installed and twisted so that the loop around the head stays down and does not tend to come up over the bolt head, Shaft causing a slack loop.

Single-wire method Cotter Pin Safetying Cotter pin installation is shown in Figure 7-77 . Castellated Figure 7-78. External type snap ring with safety wire installation. nuts are used with bolts that have been drilled for cotter pins.

The cotter pin should fit neatly into the hole with very little side play.

wire through the center hole of the turnbuckle and bend the The following general rules apply to cotter pin safetying: wire ends toward opposite ends of the turnbuckle. Then pass 1. The prong bent over the bolt end should not extend each wire end through the cable eye or fork, or through the beyond the bolt diameter. (Cut it off if necessary.)

hole in the swaged terminal and wrap each wire end around the shank for at least four turns, cutting off the excess wire.

2. The prong bent down should not rest against the After safetying, no more than three threads of the turnbuckle surface of the washer. (Again, cut it off if necessary.)

threaded terminal should be exposed.

3. If the optional wraparound method is used, the prongs should not extend outward from the sides of the nut.

General Safety Wiring Rules 4. All prongs should be bent over a reasonable radius.

When using the safety wire method of safetying, the Sharp angled bends invite breakage. Tapping lightly following general rules should be followed: with a mallet is the best method of bending the prongs.

Snap Rings A snap ring is a ring of metal, either round or flat in cross section, which is tempered to have spring like action. This spring like action holds the snap ring firmly seated in a groove.

The external types are designed to fit in a groove around the outside of a shaft or cylinder and may be safety wired. Safety wiring of an external type snap ring is shown in Figure 7-78 .

The internal types fit in a groove inside a cylinder and are never safetied. A special type of pliers is designed to install each type of snap ring. Snap rings can be reused as long as they retain their shape and spring-like action.

7-80

Next: Chapter 8 →

Chapter 8

Cleaning & Corrosion Control

Corrosion [Figure 8-2] On the surface of aluminum alloys and Many aircraft structures are made of metal, and the most magnesium, it appears as pitting and etching and is often insidious form of damage to those structures is corrosion.

combined with a gray or white powdery deposit. On copper From the moment the metal is manufactured, it must be and copper alloys, the corrosion forms a greenish film; on protected from the deleterious effects of the environment that steel, a reddish corrosion byproduct commonly referred to surrounds it. This protection can be the introduction of certain as rust. When the gray, white, green, or reddish deposits elements into the base metal, creating a corrosion-resistant are removed, each of the surfaces may appear etched and alloy, or the addition of a surface coating of a chemical pitted, depending upon the length of exposure and severity conversion coating, metal, or paint. While in use, additional of attack. If these surface pits are not too deep, they may not moisture barriers, such as viscous lubricants and protectants, significantly alter the strength of the metal; however, the may be added to the surface.

pits may become sites for crack development, particularly if the part is highly stressed. Some types of corrosion burrow The introduction of airframes built primarily of composite between the inside of surface coatings and the metal surface, components has not eliminated the need for careful spreading until the part fails.

monitoring of aircraft with regard to corrosion. The airframe itself may not be subject to corrosion; however, the use Factors Affecting Corrosion of metal components and accessories within the airframe Many factors affect the type, speed, cause, and seriousness of means the aviation maintenance technician (AMT) must be metal corrosion. Some of these factors that influence metal on the alert for the evidence of corrosion when inspecting corrosion and the rate of corrosion are: any aircraft.

1. Type of metal This chapter provides an overview to the problems associated 2. Heat-treatment and grain direction with aircraft corrosion. For more in-depth information on 3. Presence of a dissimilar, less corrodible metal the subject, refer to the latest edition of the Federal Aviation 4. Anodic and cathodic surface areas (in galvanic Administration (FAA) Advisory Circular (AC) 43-4, Corrosion corrosion) Control for Aircraft. The AC is an extensive handbook that deals with the sources of corrosion particular to aircraft 5. Temperature structures, as well as steps the AMT can take in the course 6. Presence of electrolytes (hard water, salt water, battery of maintaining aircraft that have been attacked by corrosion.

fluids, etc.)

7. Availability of oxygen Metal corrosion is the deterioration of the metal by chemical or electrochemical attack. This type of damage can take place 8. Presence of biological organisms internally, as well as on the surface. As in the rotting of wood, 9. Mechanical stress on the corroding metal this deterioration may change the smooth surface, weaken 10. Time of exposure to a corrosive environment the interior, or damage or loosen adjacent parts.

11. Lead/graphite pencil marks on aircraft surface metals Water or water vapor containing salt combines with oxygen in the atmosphere to produce the main source of corrosion Pure Metals in aircraft. Aircraft operating in a marine environment, or Most pure metals are not suitable for aircraft construction and in areas where the atmosphere contains industrial fumes are used only in combination with other metals to form alloys.

that are corrosive, are particularly susceptible to corrosive Most alloys are made up entirely of small crystalline regions attacks. [Figure 8-1] called grains. Corrosion can occur on surfaces of those regions that are less resistant and also at boundaries between If left unchecked, corrosion can cause eventual structural regions, resulting in the formation of pits and intergranular failure. The appearance of corrosion varies with the metal.

corrosion. Metals have a wide range of corrosion resistance.

8-1 The most active metals (those that lose electrons easily), such • Soil and atmospheric dust as magnesium and aluminum, corrode easily. The most noble • Oil, grease, and engine exhaust residues metals (those that do not lose electrons easily), such as gold • Salt water and salt moisture condensation and silver, do not corrode easily.

• Spilled battery acids and caustic cleaning solutions Climate • Welding and brazing flux residues The environmental conditions that an aircraft is maintained and operated under greatly affects corrosion characteristics.

Micro-organisms In a predominately marine environment (with exposure to sea Slimes, molds, fungi and other living organisms (some water and salt air), moisture-laden air is considerably more microscopic) can grow on damp surfaces. Once they are detrimental to an aircraft than it would be if all operations established, the area tends to remain damp, increasing the were conducted in a dry climate. Temperature considerations possibility of corrosion.

are important, because the speed of electrochemical attack is increased in a hot, moist climate.

Manufacturing Processes Manufacturing processes, such as machining, forming, welding, Geographical Location or heat-treatment, can leave stresses in aircraft parts. The The flight routes and bases of operation expose some residual stress can cause cracking in a corrosive environment airplanes to more corrosive conditions than others. The when the threshold for stress corrosion is exceeded.

operational environment of an aircraft may be categorized as mild, moderate, or severe with respect to the corrosion It is important that aircraft be kept clean. How often and to severity of the operational environment. The corrosion what extent an aircraft must be cleaned depends on several severity of the operational environments in North America are factors, including geographic location, model of aircraft, and identified in Figure 8-3. Additional maps for other locations type of operation.

around the world are published in AC 43-4.

Types of Corrosion The corrosion severity of any particular area may be increased There are two general classifications of corrosion that by many factors, including airborne industrial pollutants, cover most of the specific forms: direct chemical attack and chemicals used on runways and taxiways to prevent ice electrochemical attack. In both types of corrosion, the metal formation, humidity, temperatures, prevailing winds from a is converted into a metallic compound, such as an oxide, corrosive environment, etc. Suggested intervals for cleaning, hydroxide, or sulfate. The corrosion process involves two inspection, lubrication, and preservation when located in mild simultaneous changes: the metal that is attacked or oxidized zones are every 90 days, moderate zones every 45 days, and suffers what is called anodic change, and the corrosive agent severe zones every 15 days.

is reduced and is considered as undergoing cathodic change.

Foreign Material Direct Chemical Attack Among the controllable factors that affect the onset and Direct chemical attack, or pure chemical corrosion, is an spread of corrosive attack is foreign material that adheres to attack resulting from direct exposure of a bare surface to the metal surfaces. Such foreign material includes: caustic liquid or gaseous agents. Unlike electrochemical attack where anodic and cathodic changes take place a measurable distance apart, the changes in direct chemical attack occur simultaneously at the same point. The most common agents causing direct chemical attack on aircraft are: spilled battery acid or fumes from batteries; residual flux deposits resulting from inadequately cleaned, welded, brazed, or soldered joints; and entrapped caustic cleaning solutions. [Figure 8-4] With the introduction of sealed lead-acid batteries and the use of nickel-cadmium batteries, spilled battery acid is becoming less of a problem. The use of these closed units lessens the hazards of acid spillage and battery fumes.

Figure 8-1. Seaplane operations.

Many types of fluxes used in brazing, soldering, and welding 8-2 Alloy Type of attack to which alloy is susceptible Appearance of corrosion product Highly susceptible to pitting Magnesium White, powdery, snow-like mounds and white spots on surface Low alloy steel Surface oxidation and pitting, surface, and intergranular Reddish–brown oxide (rust) (4,000–8,000 series) Aluminum Surface pitting, intergranular, exfoliation stress– White–to–grey powder corrosion and fatigue cracking, and fretting Highly corrosion resistant; extended or repeated Titanium No visible corrosion products at low temperature.

contact with chlorinated solvents may result in Colored surface oxides develop above 700 °F (370 °C) degradation of the metal’s structural properties at high temperature Uniform surface corrosion; used as sacri fi cial plating Cadmium From white powdery deposit to brown or black mottling to protect steel of the surface Crevice corrosion; some pitting in marine environments; Stainless steels Rough surface; sometimes a uniform red, brown, stain corrosion cracking; intergranular corrosion (300 series); (300–400 series) surface corrosion (400 series) Generally has good corrosion resistant qualities; Nickel–base Green powdery deposit susceptible to pitting in sea water (Inconel, Monel) Copper–base Brass, Surface and intergranular corrosion Blue or blue–green powdery deposit Bronze Chromium (Plate) Pitting (promotes rusting of steel where pits occur in No visible corrosion products; blistering of plating due to plating) rusting and lifting Will tarnish in the presence of sulfur Silver Brown–to–black fi lm Gold Highly corrosion resistant Deposits cause darkening of re fl ective surfaces Subject to whisker growth Whisker–like deposit Tin Figure 8-2. Corrosion of metals.

are corrosive, chemically attacking the metals or alloys that 3. Presence of a continuous, conductive liquid path they are used with. Therefore, it is important to remove (electrolyte) residual flux from the metal surface immediately after the 4. Electrical contact between the anode and the cathode joining operation. Flux residues are hygroscopic in nature, (usually in the form of metal to metal contact, such absorbing moisture, and unless carefully removed, tend to as rivets, bolts, and corrosion) cause severe pitting.

Elimination of any one of these conditions stops Caustic cleaning solutions in concentrated form are electrochemical corrosion.

kept tightly capped and as far from aircraft as possible.

Some cleaning solutions used in corrosion removal are, NOTE: Paint can mask the initial stages of corrosion.

in themselves, potentially corrosive agents. Therefore, Since corrosion products occupy more volume than the particular attention must be directed toward their complete original metal, painted surfaces must be inspected often for removal after use on aircraft. Where entrapment of the irregularities, such as blisters, flakes, chips, and lumps.

cleaning solution is likely to occur, use a noncorrosive cleaning agent, even though it is less efficient.

An electrochemical attack may be likened chemically to Electrochemical Attack the electrolytic reaction that takes place in electroplating, Corrosion is a natural occurrence that attacks metal by anodizing, or in a dry cell battery. The reaction in this corrosive chemical or electrochemical action, converting it back to a attack requires a medium, usually water, that is capable of metallic compound. The following four conditions must exist conducting a tiny current of electricity. When a metal comes before electrochemical corrosion can occur. [Figure 8-5] in contact with a corrosive agent and is also connected by a liquid or gaseous path that electrons flow through, corrosion 1. A metal subject to corrosion (anode) begins as the metal decays by oxidation. [Figure 8-5] During 2. A dissimilar conductive material (cathode) that has the attack, the quantity of corrosive agent is reduced and, less tendency to corrode if not renewed or removed, may completely react with the 8-3 FAIRBANKS ANCHORAGE SEATTLE MONTREAL CHICAGO DENVER NEW YORK ATLANTA LOS ANGELES DALLAS HOUSTON MIAMI HAVANA CORROSION SEVERITY ZONE MILD HAITI MODERATE PUERTO RICO MEXICO SEVERE JAMAICA ST. DOMINGO Figure 8-3. North America corrosion severity chart.

metal becoming neutralized. Different areas of the same metal surface have varying levels of electrical potential and, if connected by a conductor such as salt water, sets up a series of corrosion cells and corrosion will commence.

All metals and alloys are electrically active and have a specific electrical potential in a given chemical environment.

This potential is commonly referred to as the metal’s “nobility.” [Figure 8-6] The less noble a metal is, the more easily it can be corroded. The metals chosen for use in aircraft structures are a studied compromise with strength, weight, corrosion resistance, workability, and cost balanced against the structure’s needs.

The constituents in an alloy also have specific electrical potentials that are generally different from each other.

Exposure of the alloy surface to a conductive, corrosive medium causes the more active metal to become anodic and the less active metal to become cathodic, thereby establishing conditions for corrosion. These are called local cells. The greater the difference in electrical potential between the two metals, the greater the severity of a corrosive attack if the proper conditions are allowed to develop.

Figure 8-4. Direct chemical attack in a battery compartment.

8-4 etching, or pitting of the surface of a metal, frequently The conditions for these corrosion reactions are the presence accompanied by a powdery deposit of corrosion products.

of a conductive fluid and metals having a difference in Surface corrosion may be caused by either direct chemical or potential. If, by regular cleaning and surface refinishing, electrochemical attack. Sometimes corrosion spreads under the medium is removed and the minute electrical circuit the surface coating and cannot be recognized by either the eliminated, corrosion cannot occur. This is the basis for roughening of the surface or the powdery deposit. Instead, effective corrosion control. The electrochemical attack is closer inspection reveals the paint or plating is lifted off the responsible for most forms of corrosion on aircraft structure surface in small blisters that result from the pressure of the and component parts. underlying accumulation of corrosion products. [Figure 8-7] Forms of Corrosion Filiform Corrosion There are many forms of corrosion. The form of corrosion Filiform corrosion is a special form of oxygen concentration depends on the metal involved, its size and shape, its cell that occurs on metal surfaces having an organic specific function, atmospheric conditions, and the corrosion coating system. It is recognized by its characteristic worm- producing agents present. Those described in this section like trace of corrosion products beneath the paint film.

are the more common forms found on airframe structures.

[Figure 8-8] Polyurethane finishes are especially susceptible Surface Corrosion to filiform corrosion. Filiform occurs when the relative General surface corrosion (also referred to as uniform etch humidity of the air is between 78–90 percent, and the surface or uniform attack corrosion) is the most common form of is slightly acidic. This corrosion usually attacks steel and corrosion. Surface corrosion appears as a general roughening, aluminum surfaces. The traces never cross on steel, but they Simpli fi ed corrosion cell showing conditions that must exist for electrochemical corrosion.

Continuous liquid path (electrolyte) Current fl ow Cathodic area Anodic area Electron fl ow Electron conductor metal Elimination of corrosion by application of an organic fi lm to metal surface.

No contact between electrolyte and anode and cathode Unbroken paint fi lm Continuous liquid path (electrolyte) Cathodic area Anodic area Electron conductor metal Figure 8-5. Electrochemical attack.

8-5 cross under one another on aluminum, making the damage deeper and more severe for aluminum. If the corrosion is not Metal most removed, the area treated, and a protective finish applied, the corrosion can lead to intergranular corrosion, especially

likely to corrode

around fasteners and at seams.

(anodic)

Filiform corrosion can be removed using glass bead blasting Magnesium material with portable abrasive blasting equipment or Magnesium alloy sanding. Filiform corrosion can be prevented by storing Zinc aircraft in an environment with a relative humidity below 70 Aluminum (1100) percent, using coating systems having a low rate of diffusion Cadmium for oxygen and water vapors, and by washing the aircraft to Aluminum 2024-T4 Steel or iron remove acidic contaminants from the surface, such as those Cast iron created by pollutants in the air.

Chromium-iron (active) Pitting Corrosion Ni-Resist cast iron Pitting corrosion is one of the most destructive and intense Type 304 stainless steel (active) forms of corrosion. It can occur in any metal but is most Type 316 stainless steel (active) common on metals that form protective oxide films, such Lead-tin solder as aluminum and magnesium alloys. It is first noticeable Lead as a white or gray powdery deposit, similar to dust, which Tin blotches the surface. When the deposit is cleaned away, tiny Nickel (active) holes or pits can be seen in the surface. These small surface Inconel nickel-chromium alloy openings may penetrate deeply into structural members and (active) cause damage completely out of proportion to its surface Hastelloy alloy C (active) appearance. [Figure 8-9] Brass Copper Dissimilar Metal Corrosion Bronze Copper-nickel alloy Extensive pitting damage may result from contact between Monel nickel-copper alloy dissimilar metal parts in the presence of a conductor. While surface corrosion may or may not be taking place, a galvanic Silver solder Nickel (passive) action, not unlike electroplating, occurs at the points or areas Inconel nickel-chromium alloy of contact where the insulation between the surfaces has (passive) broken down or been omitted. This electrochemical attack can be very serious because, in many instances, the action Chromium-iron (passive) Type 304 stainless steel (passive) is taking place out of sight, and the only way to detect it Type 316 stainless steel (passive) prior to structural failure is by disassembly and inspection.

Hastelloy alloy C (passive) [Figure 8-10] Silver Titanium The contamination of a metal’s surface by mechanical means Graphite can also induce dissimilar metal corrosion. The improper use Gold of steel cleaning products, such as steel wool or a steel wire Platinum brush on aluminum or magnesium, can force small pieces of steel into the metal being cleaned, causing corrosion and ruining the adjoining surface. Carefully monitor the use of

Metal least likely

nonwoven abrasive pads, so that pads used on one type of metal are not used again on a different metal surface.

to corrode

(cathodic)

Concentration Cell Corrosion Concentration cell corrosion, (also known as crevice corrosion) is corrosion of metals in a metal-to-metal joint, Figure 8-6. The galvanic series of metals and alloys. corrosion at the edge of a joint even though the joined metals are identical, or corrosion of a spot on the metal surface covered by a foreign material. Metal ion concentration cells, 8-6 oxygen concentration cells, and active-passive cells are three general types of concentration cell corrosion.

Metal Ion Concentration Cells The solution may consist of water and ions of the metal that are in contact with water. A high concentration of metal ions normally exists under faying surfaces where the solution is stagnant and a low concentration of metal ions exist adjacent to the crevice, created by the faying surface. [Figure 8-11] An electrical potential exists between the two points: the area of the metal in contact with the low concentration of metal ions is anodic and corrodes; the area in contact with the high Figure 8-8. Filiform corrosion.

metal ion concentration is cathodic and does not show signs of corrosion.

Intergranular Corrosion Oxygen Concentration Cells This type of corrosion is an attack along the grain boundaries of The solution in contact with the metal surface normally an alloy and commonly results from a lack of uniformity in the contains dissolved oxygen. An oxygen cell can develop alloy structure. Aluminum alloys and some stainless steels are at any point where the oxygen in the air is not allowed to particularly susceptible to this form of electrochemical attack.

diffuse into the solution, thereby creating a difference in [Figure 8-14] The lack of uniformity is caused by changes oxygen concentration between two points. Typical locations that occur in the alloy during the heating and cooling process of oxygen concentration cells are under gaskets, wood, of the material’s manufacturing. Intergranular corrosion rubber, and other materials in contact with the metal surface.

may exist without visible surface evidence. High-strength Corrosion occurs at the area of low oxygen concentration aluminum alloys, such as 2014 and 7075, are more susceptible (anode). Alloys such as stainless steel are particularly to intergranular corrosion if they have been improperly heat- susceptible to this type of crevice corrosion. [Figure 8-12] treated and then exposed to a corrosive environment.

Active-Passive Cells Exfoliation Corrosion Metals that depend on a tightly adhering passive film, usually Exfoliation corrosion is an advanced form of intergranular an oxide for corrosion protection, are prone to rapid corrosive corrosion and shows itself by lifting up the surface grains attack by active-passive cells. The corrosive action usually of a metal by the force of expanding corrosion products starts as an oxygen concentration cell. The passive film is occurring at the grain boundaries just below the surface.

broken beneath the dirt particle exposing the active metal to [Figure 8-15] It is visible evidence of intergranular corrosion corrosive attack. An electrical potential will develop between and is most often seen on extruded sections where grain the large area of the passive film and the small area of the thickness is usually less than in rolled forms. This type of active metal, resulting in rapid pitting. [Figure 8-13] corrosion is difficult to detect in its initial stage. Extruded components, such as spars, can be subject to this type of corrosion. Ultrasonic and eddy current inspection methods are being used with a great deal of success.

Stress-Corrosion/Cracking This form of corrosion involves a constant or cyclic stress acting in conjunction with a damaging chemical environment.

The stress may be caused by internal or external loading.

[Figure 8-16] Internal stress may be trapped in a part of structure during manufacturing processes, such as cold- working or by unequal cooling from high temperatures.

Most manufacturers follow these processes with a stress relief operation. Even so, sometimes stress remains trapped.

The stress may be externally introduced in part structure by riveting, welding, bolting, clamping, press fit, etc. If a slight Figure 8-7. Surface corrosion.

mismatch occurs or a fastener is over-torqued, internal stress 8-7 is present. Internal stress is more important than design stress, TROUGH PITS because stress corrosion is difficult to recognize before it has overcome the design safety factor. The level of stress varies Narrow, deep from point to point within the metal. Stresses near the yield strength are generally necessary to promote stress corrosion cracking. However, failures may occur at lower stresses.

Specific environments have been identified that cause stress Wide, shallow corrosion cracking of certain alloys.

1. Salt solutions and sea water cause stress corrosion cracking of high-strength, heat-treated steel and aluminum alloys.

Elliptical 2. Methyl alcohol-hydrochloric acid solutions cause stress corrosion cracking of some titanium alloys.

3. Magnesium alloys may stress corrode in moist air.

Vertical Stress corrosion may be reduced by applying protective coatings, stress relief heat-treatments, using corrosion inhibitors, or controlling the environment. Shot peening a metal surface increases resistance to stress corrosion cracking by creating compressive stresses on the surface which should be overcome by applied tensile stress before the surface SIDEWAY PITS sees any tension load. Therefore, the threshold stress level Subsurface is increased.

Low metal ion concentration Undercutting Horizontal High metal ion concentration METAL ION CONCENTRATION CELL Figure 8-11. Metal ion concentration cell.

Figure 8-9. Types of pitting corrosion.

High oxygen concentration Low oxygen concentration OXYGEN CONCENTRATION CELL Figure 8-12. Oxygen concentration cell. Figure 8-10. Dissimilar metal corrosion.

8-8 Foreign material Passive fi lm protects creates a low oxygen exposed surface region that prevents the re-formation of passive fi lm Active metal ACTIVE – PASSIVE CELL Figure 8-13. Active-passive cell.

Figure 8-15. Exfoliation corrosion.

Fretting Corrosion environment. Metals may withstand cyclic stress for an Fretting corrosion is a particularly damaging form of infinite number of cycles so long as the stress is below corrosive attack that occurs when two mating surfaces, the endurance limit of the metal. Once the limit has been normally at rest with respect to one another, are subject to exceeded, the metal eventually cracks and fails from metal slight relative motion. It is characterized by pitting of the fatigue. However, when the part or structure undergoing surfaces and the generation of considerable quantities of cyclic stress is also exposed to a corrosive environment, the finely divided debris. Since the restricted movements of the stress level for failure may be reduced many times. Thus, two surfaces prevent the debris from escaping very easily, failure occurs at stress levels that can be dangerously low an extremely localized abrasion occurs. [Figure 8-17] depending on the number of cycles assigned to the life- The presence of water vapor greatly increases this type of limited part.

deterioration. If the contact areas are small and sharp, deep grooves resembling brinell markings or pressure indentations Fatigue corrosion failure occurs in two stages. During the may be worn in the rubbing surface. As a result, this type first stage, the combined action of corrosion and cyclic stress of corrosion on bearing surfaces has also been called false damages the metal by pitting and crack formations to such brinelling. The most common example of fretting corrosion a degree that fracture by cyclic stress occurs, even if the is the smoking rivet found on engine cowling and wing corrosive environment is completely removed. The second skins. This is one corrosion reaction that is not driven by an stage is essentially a fatigue stage where failure proceeds by electrolyte, and in fact, moisture may inhibit the reaction. A propagation of the crack (often from a corrosion pit or pits).

smoking rivet is identified by a black ring around the rivet.

It is controlled primarily by stress concentration effects and the physical properties of the metal. Fracture of a metal part Fatigue Corrosion due to fatigue corrosion generally occurs at a stress level far Fatigue corrosion involves cyclic stress and a corrosive Electrolyte enters through cracks in paint fi lm Paint fi lm Cladding Cladding Preferential corrosion along Cathode Anode grain boundaries Intergranular corrosion 7075-T6 Aluminum Steel fastener Figure 8-14. Intergranular corrosion of 7075-T6 aluminum adjacent to steel fastener.

8-9 Figure 8-16. Stress corrosion cracking.

below the fatigue limit of an uncorroded part, even though Figure 8-17. Fretting corrosion.

the amount of corrosion is relatively small.

Galvanic Corrosion extremely vulnerable. Exposure of airframe materials to salts or their solutions is extremely undesirable.

Galvanic corrosion occurs when two dissimilar metals make electrical contact in the presence of an electrolyte.

• Atmosphere—the major atmospheric corrosive agents [Figure 8-18] The rate which corrosion occurs depends on are oxygen and airborne moisture. Corrosion often the difference in the activities. The greater the difference results from the direct action of atmospheric oxygen in activity, the faster corrosion occurs. The rate of galvanic and moisture on metal, and the presence of additional corrosion also depends on the size of the parts in contact. If moisture often accelerates corrosive attack, particularly the surface area of the corroding metal is smaller than the on ferrous alloys. However, the atmosphere may surface area of the less active metal, corrosion is rapid and also contain other corrosive gases and contaminants, severe. When the corroding metal is larger than the less active particularly industrial and marine salt spray.

metal, corrosion is slow and superficial.

• Water—the corrosiveness of water depends on the type and quantity of dissolved mineral and organic Common Corrosive Agents impurities and dissolved gasses (particularly oxygen) Substances that cause corrosion of metals are called corrosive in the water. One characteristic of water that determines agents. The most common corrosive agents are acids, alkalies, its corrosiveness is the conductivity or ability to act as and salts. The atmosphere and water, the two most common an electrolyte and conduct a current. Physical factors, media for these agents, may also act as corrosive agents.

such as water temperature and velocity, also have a • Acids—moderately strong acids severely corrode direct bearing on its corrosiveness.

most of the alloys used in airframes. The most destructive are sulfuric acid (battery acid), halogen Preventive Maintenance acids (hydrochloric, hydrofluoric, and hydrobromic), Much has been done to improve the corrosion resistance nitrous oxide compounds, and organic acids found in of aircraft, such as improvements in materials, surface the wastes of humans and animals.

treatments, insulation, and modern protective finishes. All of • Alkalies—as a group, alkalies are not as corrosive these have been aimed at reducing the overall maintenance as acids. Aluminum and magnesium alloys are effort, as well as improving reliability. In spite of these exceedingly prone to corrosive attack by many improvements, corrosion and its control is a very real problem alkaline solutions unless the solutions contain a that requires continuous preventive maintenance. During any corrosion inhibitor. Substances particularly corrosive corrosion control maintenance, consult the Safety Data Sheet to aluminum are washing soda, potash (wood ashes), (SDS) for information on any chemicals used in the process.

and lime (cement dust). Ammonia, an alkali, is an exception because aluminum alloys are highly Corrosion preventive maintenance includes the following resistant to it.

specific functions: • Salts—most salt solutions are good electrolytes and 1. Adequate cleaning can promote corrosive attack. Some stainless-steel 2. Thorough periodic lubrication alloys are resistant to attack by salt solutions but 3. Detailed inspection for corrosion and failure of aluminum alloy, magnesium alloys, and other steels are 8-10 protective systems the area to be inspected. A general visual inspection of the area follows using a flashlight, inspection mirror, and a 5– 4. Prompt treatment of corrosion and touch up of l0 X magnifying glass. The general inspection is to look for damaged paint areas obvious defects and suspected areas. A detailed inspection 5. Accurate record keeping and reporting of material or of damage or suspected areas found during the general design deficiencies to the manufacturer and the FAA inspection follows.

6. Use of appropriate materials, equipment, technical Visual inspection is the most widely used technique and publications, and adequately-training personnel is an effective method for the detection and evaluation of 7. Maintenance of the basic finish systems corrosion. Visual inspection employs the eyes to look directly 8. Keeping drain holes free of obstructions at an aircraft surface or at a low angle of incidence to detect corrosion. Using the sense of touch is also an effective 9. Daily draining of fuel cell sumps inspection method for the detection of hidden, well-developed 10. Daily wipe down of exposed critical areas corrosion. Other tools used during the visual inspection are 11. Sealing of aircraft against water during foul weather mirrors, optical micrometers, and depth gauges.

and proper ventilation on warm, sunny days Sometimes the inspection areas are obscured by structural 12. Replacing deteriorated or damaged gaskets and members, equipment installations, or for some reason are sealants to avoid water intrusion and/or entrapment awkward to check visually. Adequate access for inspection 13. Maximum use of protective covers on parked aircraft must be obtained by removing access panels and adjacent equipment, cleaning the area as necessary, and removing After any period where regular corrosion preventive loose or cracked sealants and paints. Mirrors, borescopes, and maintenance is interrupted, the amount of maintenance fiber optics are useful in providing the means of observing required to repair accumulated corrosion damage and bring obscure areas.

the aircraft back up to standard is usually quite high.

In addition to visual inspection, there are several NDI Inspection methods, such as liquid penetrant, magnetic particle, eddy current, x-ray, ultrasonic, and acoustical emission, that may Inspection for corrosion is a continuing problem and must be handled daily. Overemphasizing a particular corrosion be of value in the detection of corrosion. These methods have limitations and must be performed only by qualified and problem when it is discovered and then forgetting about corrosion until the next crisis is an unsafe, costly, and certified NDI personnel. Eddy current, x-ray, and ultrasonic inspection methods require properly calibrated (each time troublesome practice. Most scheduled maintenance checklists are complete enough to cover all parts of the aircraft or used) equipment and a controlling reference standard to obtain reliable results.

engine, thus no part of the aircraft goes uninspected. Use these checklists as a general guide when an area is to be inspected In addition to routine maintenance inspections, amphibians for corrosion. Through experience, one learns that most aircraft have trouble areas where, despite routine inspection or seaplanes must be checked daily and critical areas cleaned or treated, as necessary.

and maintenance, corrosion still sets in.

Corrosion Prone Areas All corrosion inspections start with a thorough cleaning of Discussed briefly in this section are most of the corrosion problem areas common to all aircraft. These areas should be cleaned, inspected, and treated more frequently than less corrosion prone areas. This information is not necessarily complete and may be amplified and expanded to cover the special characteristics of the particular aircraft model involved by referring to the applicable maintenance manual.

Exhaust Trail Areas Both jet and reciprocating engine exhaust deposits are very corrosive and give particular trouble where gaps, seams, hinges, and fairings are located downstream from the exhaust pipes or nozzles. [Figure 8-19] Deposits may be trapped Figure 8-18. Galvanic corrosion.

8-11 and not reached by normal cleaning methods. Pay special Wheel Well and Landing Gear attention to areas around rivet heads and in skin lap joints More than any other area on the aircraft, this area probably and other crevices. Remove and inspect fairings and access receives more punishment due to mud, water, salt, gravel, plates in the exhaust areas. Do not overlook exhaust deposit and other flying debris. [Figure 8-20] Because of the many buildup in remote areas, such as the empennage surfaces.

complicated shapes, assemblies, and fittings, complete Buildup in these areas is slower and may not be noticed until area paint film coverage is difficult to attain and maintain.

corrosive damage has begun.

A partially applied preservative tends to mask corrosion rather than prevent it. Due to heat generated by braking Battery Compartments and Battery Vent Openings action, preservatives cannot be used on some main landing Despite improvements in protective paint finishes and in gear wheels.

methods of sealing and venting, battery compartments continue to be corrosion prone areas. Fumes from overheated During inspection of this area, pay particular attention to the electrolyte are difficult to contain and spread to adjacent following trouble spots: cavities, causing a rapid corrosive attack on all unprotected 1. Magnesium wheels, especially around bolt heads, lugs, metal surfaces. Battery vent openings on the aircraft skin and wheel web areas, for the presence of entrapped should be included in the battery compartment inspection and water or its effects maintenance procedure. If aircraft batteries with electrolytes, 2. Exposed rigid tubing, especially at B-nuts and ferrules, sulfuric acid, or potassium hydroxide are in use, their leakage under clamps and tubing identification tapes will cause corrosion. Regular cleaning and neutralization of acid deposits minimizes corrosion from this cause. Consult 3. Exposed position indicator switches and other the applicable maintenance manuals for the particular electrical equipment aircraft to determine the type of battery installed and the 4. Crevices between stiffeners, ribs, and lower skin recommended maintenance.

surfaces that are typical water and debris traps 5. Axle interiors Bilge Areas These are natural collection points for waste hydraulic fluids, 6. Exposed surfaces of struts, oleos, arms, links, and water, dirt, and odds and ends of debris. Residual oil quite attaching hardware (bolts, pins, etc.)

often masks small quantities of water that settle to the bottom and set up a hidden chemical cell.

Water Entrapment Areas Design specifications require that aircraft have drains installed Instead of using chemical treatments for the bilge water, in all areas where water may collect. Daily inspection of low current float manufacturers recommend the diligent point drains is a standard requirement. If this inspection is maintenance of the internal coatings applied to the float’s neglected, the drains may become ineffective because of interior during manufacture. In addition to chemical accumulated debris, grease, or sealants.

conversion coatings applied to the surface of the sheet metal and other structural components and to sealants installed in lap joints during construction, the interior compartments are painted to protect the bilge areas. When seaplane structures are repaired or restored, this level of corrosion protection must be maintained.

Lavatories, Buffets, & Galleys These areas, particularly deck areas behind lavatories, sinks, and ranges, where spilled food and waste products may collect if not kept clean, are potential trouble spots.

Even if some contaminants are not corrosive in themselves, they attract and retain moisture and, in turn, cause corrosive attack. Pay attention to bilge areas located under galleys and lavatories. Clean these areas frequently and maintain the protective sealant and paint finishes.

Figure 8-19. Exhaust nozzle area.

8-12 Engine Frontal Areas & Cooling Air Vents buckling in its early stages may be detected by sighting along spot welded seams or by using a straightedge. The only These areas are being constantly abraded with airborne dirt technique for preventing this condition is to keep potential and dust, bits of gravel from runways, and rain erosion, moisture entry points, including seams and holes created leading to removal of the protective finish. Furthermore, by broken spot welds, filled with a sealant or a suitable cores of radiator coolers, reciprocating engine cylinder preservative compound.

fins, etc., may not be painted due to the requirement for heat dissipation. Engine accessory mounting bases usually Electronic & Electrical Compartments have small area of unpainted magnesium or aluminum on Electronic and electrical compartments cooled by ram air or the machined-mounted surfaces. Inspection of these areas compressor bleed air are subjected to the same conditions must include all sections in the cooling air path, with special common to engine and accessory cooling vents and engine attention to places where salt deposits may be built up during frontal areas. While the degree of exposure is less, because marine operations. It is imperative that incipient corrosion be a lower volume of air passing through and special design inhibited and that paint touchup and hard film preservative features incorporated to prevent water formation in enclosed coatings are maintained on seaplane and amphibian engine spaces, this is still a trouble area that requires special attention.

surfaces at all times.

Circuit breakers, contact points, and switches are extremely Wing Flap & Spoiler Recesses sensitive to moisture and corrosive attack, thus inspection is Dirt and water may collect in flap and spoiler recesses required for these conditions as thoroughly as design permits.

unnoticed, because they are normally retracted. For this If design features hinder examination of these items while reason, these recesses are potential corrosion problem areas.

in the installed condition, inspection is accomplished after Inspect these areas with the spoilers and flaps in the fully component removal for other reasons.

deployed position.

Miscellaneous Trouble Areas External Skin Areas Helicopter rotor heads and gearboxes, in addition to being External aircraft surfaces are readily visible and accessible constantly exposed to the elements, contain bare steel for inspection and maintenance. Even here, certain types surfaces, many external working parts, and dissimilar metal of configurations or combinations of materials become contacts. Inspect these areas frequently for evidence of troublesome under certain operating conditions and require corrosion. The proper maintenance, lubrication, and the use special attention.

of preservative coatings can prevent corrosion in these areas.

Relatively little corrosion trouble is experienced with All control cables, whether plain carbon steel or corrosion- magnesium skins if the original surface finish and insulation resistant steel, are to be inspected to determine their condition are adequately maintained. Trimming, drilling, and riveting at each inspection period. In this process, inspect cables for destroy some of the original surface treatment and can corrosion by random cleaning of short sections with solvent never be completely restored by touchup procedures. Any soaked cloths. If external corrosion is evident, relieve tension inspection for corrosion must include all magnesium skin surfaces with special attention to edges, areas around fasteners, and cracked, chipped, or missing paint.

Piano-type hinges are prime spots for corrosion due to the dissimilar metal contact between the steel pin and aluminum hinge. They are also natural traps for dirt, salt, and moisture.

Inspection of hinges must include lubrication and actuation through several cycles to ensure complete lubricant penetration. Use water-displacing lubricants when servicing piano hinges. [Figures 8-21 and 8-22] Corrosion of metal skins joined by spot welding is the result of the entrance and entrapment of corrosive agents between the layers of metal. This type of corrosion is evidenced by corrosion products appearing at the crevices where the corrosive agents enter. More advanced corrosive attack Figure 8-20. The landing gear area should be cleaned and inspected causes skin buckling and eventual spot weld fracture. Skin more frequently than other areas.

8-13 and check the cable for internal corrosion. Replace cables that have internal corrosion. Remove light external corrosion Bare steel hinge pin Al alloy extrusions with a nonwoven abrasive pad lightly soaked in oil or, alternatively, a steel wire brush. When corrosion products have been removed, recoat the cable with preservative.

Corrosion Removal In general, any complete corrosion treatment involves cleaning and stripping of the corroded area, removing as much of the corrosion products as practicable, neutralizing any residual materials remaining in pits and crevices, restoring protective surface films, and applying temporary or permanent coatings or paint finishes.

Hidden corrosion occurs here. Joint freezes and lugs break o ff when hinge is actuated.

Repair of corrosion damage includes removal of all corrosion and corrosion products. When the corrosion damage is Figure 8-22. Hinge corrosion points.

severe and exceeds the damage limits set by the aircraft or parts manufacturer, the part must be replaced. The following cleaned of grease, oil, dirt, or preservatives. This preliminary paragraphs deal with the correction of corrosive attack on cleaning operation is also an aid in determining the extent aircraft surface and components where deterioration has not of the spread of the corrosion, since the stripping operation progressed to the point requiring rework or structural repair is held to the minimum consistent with full exposure of the of the part involved.

corrosion damage. Extensive corrosion spread on any panel is to be corrected by fully treating the entire section.

Several standard methods are available for corrosion removal. The methods normally used to remove corrosion are The selection of the type of materials to be used in cleaning mechanical and chemical. Mechanical methods include hand depends on the nature of the matter to be removed. Modern sanding using abrasive mat, abrasive paper, or metal wool, environmental standards encourage the use of water-based, and powered mechanical sanding, grinding, and buffing, non-toxic cleaning compounds whenever possible. In some using abrasive mat, grinding wheels, sanding discs, and locations, local or state laws may require the use of such abrasive rubber mats. However, the method used depends products, and prohibit the use of solvents that contain volatile upon the metal and the degree of corrosion.

organic compounds (VOCs). Where permitted, dry cleaning solvent (P-D-680) may be used for removing oil, grease, or Surface Cleaning and Paint Removal soft preservative compounds. For heavy-duty removal of The removal of corrosion includes removal of surface finishes thick or dried preservatives, other compounds of the solvent covering the attacked or suspected area. To assure maximum emulsion type are available.

efficiency of the stripping compound, the area must be The use of a general purpose, water soluble stripper can be used for most applications. There are other methods for paint removal that have minimal impact upon the aircraft structure, and are considered “environmentally friendly.” Wherever practicable, chemical paint removal from any large area is to be accomplished outside (in open air) and preferably in shaded areas. If inside removal is necessary, adequate ventilation must be assured. Synthetic rubber surfaces, including aircraft tires, fabric, and acrylics, must be thoroughly protected against possible contact with paint remover. Care must be exercised in using paint remover, especially around gas or watertight seam sealants, since the stripper tends to soften and destroy the integrity of these sealants.

Figure 8-21. Piano hinge.

8-14 Mask off any opening that would permit the stripping stress corrosion cracking. [Figure 8-23] On a non- compound to get into aircraft interiors or critical cavities. critical structure, it is not necessary to blend out pits Paint stripper is toxic and contains ingredients harmful to remaining after removal of corrosion products by both skin and eyes. Therefore, wear rubber gloves, aprons abrasive blasting, since this results in unnecessary of acid repellent material, and goggle type eyeglasses. The metal removal.

following is a general stripping procedure: Rework depressions by forming smoothly blended dish-outs, 1. Brush the entire area to be stripped with a cover of 1 1 using a ratio of 20:1, length to depth. [Figure 8-24] In areas stripper to a depth of ⁄ 32 " to ⁄ 16 ". Any paintbrush makes having closely-spaced, multiple pits, intervening material a satisfactory applicator, except that the bristles will be must be removed to minimize surface irregularity or loosened by the effect of paint remover on the binder, waviness. [Figure 8-25] Steel nut-plates and steel fasteners and the brush must not be used for other purposes after are to be removed before blending corrosion out of aluminum being exposed to paint remover.

structure. Steel or copper particles embedded in aluminum 2. Allow the stripper to remain on the surface for a can become a point of future corrosion. All corrosion products sufficient length of time to wrinkle and lift the paint.

must be removed during blending to prevent reoccurrence This may be from 10 minutes to several hours, of corrosion.

depending on temperature, humidity, and the condition of the paint coat being removed. Scrub the surface with Corrosion of Ferrous Metals a bristle brush saturated with paint remover to further One of the most familiar types of corrosion is ferrous oxide loosen finish that may still be adhering to the metal.

(rust), generally resulting from atmospheric oxidation of 3. Reapply the stripper as necessary in areas where the steel surfaces. Some metal-oxides protect the underlying paint remains tightly adhered or where the stripper has base metal, but rust is not a protective coating in any sense dried, and repeat the above process. Only nonmetallic of the word. Its presence actually promotes additional attack scrapers are to be used to assist in removing persistent by attracting moisture from the air and acting as a catalyst paint finishes. Nonwoven abrasive pads intended for for additional corrosion. If complete control of the corrosive paint stripping may also prove to be useful in removing attack is to be realized, all rust must be removed from steel the loosened paint.

surfaces.

4. Remove the loosened paint and residual stripper by washing and scrubbing the surface with water and Rust first appears on bolt heads, hold-down nuts, or other a broom, brush, or fresh nonwoven abrasive pad. If unprotected aircraft hardware. [Figure 8-26] Its presence in water spray is available, use a low to medium pressure these areas is generally not dangerous and has no immediate stream of water directly on the area being scrubbed. effect on the structural strength of any major components.

If steam-cleaning equipment is available and the area The residue from the rust may also contaminate other ferrous is sufficiently large, cleaning may be accomplished components, promoting corrosion of those parts. The rust is using this equipment together with a solution of steam- indicative of a need for maintenance and of possible corrosive cleaning compound. On small areas, any method may attack in more critical areas. It is also a factor in the general be used that assures complete rinsing of the cleaned appearance of the equipment. When paint failures occur or area. Use care to dispose of the stripped residue in mechanical damage exposes highly-stressed steel surfaces accordance with environmental laws. to the atmosphere, even the smallest amount of rusting is potentially dangerous in these areas and must be removed and controlled. Rust removal from structural components, Fairing or Blending Reworked Areas followed by an inspection and damage assessment, must be All depressions resulting from corrosion rework must be done as soon as feasible. [Figure 8-27] faired or blended with the surrounding surface. Fairing can be accomplished as follows: Mechanical Removal of Iron Rust 1. Remove rough edges and all corrosion from the The most practicable means of controlling the corrosion damaged area. All dish-outs must be elliptically of steel is the complete removal of corrosion products shaped with the major axis running spanwise on wings by mechanical means and restoring corrosion preventive and horizontal stabilizers, longitudinally on fuselages, coatings. Except on highly-stressed steel surfaces, the use and vertically on vertical stabilizers.

of abrasive papers and compounds, small power buffers and 2. In critical and highly stressed areas, all pits remaining buffing compounds, hand wire brushing, or steel wool are after the removal of corrosion products must be all acceptable cleanup procedures. However, it should be blended out to prevent stress risers that may cause recognized that in any such use of abrasives, residual rust 8-15 usually remains in the bottom of small pits and other crevices.

Pit has been cleaned up to the It is practically impossible to remove all corrosion products extent that all loose corrosion by abrasive or polishing methods alone. As a result, once a products have been removed.

part cleaned in such a manner has rusted, it usually corrodes again more easily than it did the first time.

CORROSION DAMAGE BEFORE REWORK The introduction of variations of the nonwoven abrasive pad has also increased the options available for the removal of surface rust. [Figure 8-28] Flap wheels, pads intended for use with rotary or oscillating power tools, and hand-held nonwoven abrasive pads all can be used alone or with light oils to remove corrosion from ferrous components.

LONGITUDINAL Rough edges have been Dish-out smoothed and all corrosion Chemical Removal of Rust after blending has been removed. However, As environmental concerns have been addressed in recent depression has not been shaped.

years, interest in noncaustic chemical rust removal has increased. A variety of commercial products that actively Figure 8-24. Blend of corrosion as a single depression.

remove the iron oxide without chemically etching the base metal are available and can be considered for use. If Chemical Surface Treatment of Steel at all possible, the steel part is removed from the airframe There are approved methods for converting active rust to for treatment, as it can be nearly impossible to remove all phosphates and other protective coatings. Other commercial residue. The use of any caustic rust removal product requires preparations are effective rust converters where tolerances the isolation of the part from any nonferrous metals during are not critical and where thorough rinsing and neutralizing treatment and probably inspection for proper dimensions.

of residual acid is possible. These situations are generally not applicable to assembled aircraft, and the use of chemical Location of corrosion pits Width of cleaned up area (10 times depth min) TOP VIEW TRUE PERSPECTIVE Length of cleaned up area (20 times depth min) Depth of cleaned up of corrosion CROSS SECTION ACCEPTABLE NOT ACCEPTABLE Figure 8-23. Blending or blending corrosion damage.

8-16 Corrosion of Aluminum & Aluminum Alloys Aluminum and aluminum alloys are the most widely used material for aircraft construction. Aluminum appears high TRANSVERSE in the electro-chemical series of elements and corrodes very easily. However, the formation of a tightly-adhering oxide film offers increased resistance under most corrosive 10D MIN conditions. Most metals in contact with aluminum form Corrosion damage couples that undergo galvanic corrosion attack. The alloys before removal 5D MIN of aluminum are subject to pitting, intergranular corrosion, and intergranular stress corrosion cracking. In some cases, LONGITUDINAL the corrosion products of metal in contact with aluminum are Bottom of depression after corrosion removal corrosive to aluminum. Therefore, aluminum and its alloys must be cleaned and protected.

Damage removed and surface smoothed with shallow elliptical dish-out Corrosion on aluminum surfaces is usually quite obvious, since the products of corrosion are white and generally more Figure 8-25. Blend out of multiple pits in a corroded area.

voluminous than the original base metal. Even in its early stages, aluminum corrosion is evident as general etching, inhibitors on installed steel parts is not only undesirable, but pitting, or roughness of the aluminum surfaces.

also very dangerous. The danger of entrapment of corrosive solutions and the resulting uncontrolled attack, that could NOTE: Aluminum alloys commonly form a smooth surface occur when such materials are used under field conditions, oxidation that is from 0.001" to 0.0025" thick. This is not outweigh any advantages to be gained from their use.

considered detrimental. The coating provides a hard-shell barrier to the introduction of corrosive elements. Such Removal of Corrosion from Highly Stressed Steel oxidation is not to be confused with the severe corrosion Parts discussed in this paragraph.

Any corrosion on the surface of a highly-stressed steel part is potentially dangerous, and the careful removal of corrosion General surface attack of aluminum penetrates relatively products is required. Surface scratches or change in surface slowly, but speeds up in the presence of dissolved salts.

structure from overheating can also cause sudden failure of Considerable attack can usually take place before serious these parts. Corrosion products must be removed by careful loss of structural strength develops.

processing, using mild abrasive papers, such as rouge or fine grit aluminum oxide or fine buffing compounds on cloth At least three forms of attack on aluminum alloys are buffing wheels. Nonwoven abrasive pads can also be used.

particularly serious: the penetrating pit-type corrosion It is essential that steel surfaces not be overheated during through the walls of aluminum tubing, stress-corrosion buffing. After careful removal of surface corrosion, reapply cracking of materials under sustained stress, and intergranular protective paint finishes immediately. The use of chemical corrosion, which is characteristic of certain improperly heat- corrosion removers is prohibited without engineering treated aluminum alloys.

authorization, because high-strength steel parts are subject to hydrogen embrittlement.

In general, corrosion of aluminum can be more effectively Figure 8-26. Rust. Figure 8-27. Rust on structural components.

8-17 before polishing to shorten the time and lessen the effort necessary to get a clean surface.

3. Treat any superficial corrosion present using an inhibitive wipe down material. An alternate treatment is processing with a solution of sodium dichromate and chromium trioxide. Allow these solutions to remain on the corroded area for 5 to 20 minutes, and then remove the excess by rinsing and wiping the surface dry with a clean cloth.

4. Overcoat the polished surfaces with waterproof wax.

Aluminum surfaces that are to be subsequently painted can be exposed to more severe cleaning procedures and can also be given more thorough corrective treatment prior to painting.

Figure 8-28. Nonwoven abrasive pads.

The following sequence is generally used: treated in place compared to corrosion occurring on other 1. Thoroughly clean the affected surfaces of all soil structural materials used in aircraft. Treatment includes the and grease residues prior to processing. Any general mechanical removal of as much of the corrosion products aircraft cleaning procedure may be used.

as practicable and the inhibition of residual materials by 2. If residual paint film remains, strip the area to be chemical means, followed by the restoration of permanent treated. Procedures for the use of paint removers and surface coatings.

the precautions to observe were previously mentioned in this chapter under “Surface Cleaning and Paint Treatment of Unpainted Aluminum Surfaces Removal.” Relatively pure aluminum has considerably more corrosion 3. Treat superficially corroded areas with a 10 percent resistance when compared with the stronger aluminum alloys.

solution of chromic acid and sulfuric acid. Apply the To take advantage of this characteristic, a thin coating of solution by swab or brush. Scrub the corroded area relatively pure aluminum is applied over the base aluminum with the brush while it is still damp. While chromic alloy. The protection obtained is good and the pure-aluminum acid is a good inhibitor for aluminum alloys, even clad surface, commonly called “Alclad,” can be maintained in when corrosion products have not been completely a polished condition. In cleaning such surfaces, however, care removed, it is important that the solution penetrate to must be taken to prevent staining and marring of the exposed the bottom of all pits and underneath any corrosion aluminum. More important from a protection standpoint, that may be present. Thorough brushing with a stiff avoid unnecessary mechanical removal of the protective fiber brush loosens or removes most existing corrosion Alclad layer and the exposure of the more susceptible and assures complete penetration of the inhibitor into aluminum alloy base material. A typical aluminum corrosion crevices and pits. Allow the chromic acid to remain treatment sequence follows: in place for at least 5 minutes, and then remove the 1. Remove oil and surface dirt from the aluminum excess by flushing with water or wiping with a wet surface using any suitable mild cleaner. Use caution cloth. There are several commercial chemical surface when choosing a cleaner. Many commercial consumer treatment compounds similar to the type described products are actually caustic enough to induce above that may also be used.

corrosion if trapped between aluminum lap joints.

4. Dry the treated surface and restore recommended Choose a neutral pH product.

permanent protective coatings, as required in 2. Hand polish the corroded areas with fine abrasives accordance with the aircraft manufacturer’s procedures.

or with metal polish. Metal polish intended for use Restoration of paint coatings must immediately follow on clad aluminum aircraft surfaces must not be used any surface treatment performed. In any case, make on anodized aluminum, since it is abrasive enough sure that corrosion treatment is accomplished or is to actually remove the protective anodized film. It reapplied on the same day that paint refinishing is effectively removes stains and produces a highly scheduled.

polished, lasting surface on unpainted Alclad. If a surface is particularly difficult to clean, a cleaner and brightener compound for aluminum can be used 8-18 Treatment of Anodized Surfaces surface coatings by chemical treatment, and a reapplication of protective coatings.

As previously stated, anodizing is a common surface treatment of aluminum alloys. When this coating is damaged Treatment of Wrought Magnesium Sheet & Forgings in service, it can only be partially restored by chemical Magnesium skin corrosion usually occurs around edges surface treatment. Therefore, avoid destruction of the oxide of skin panels, underneath washers, or in areas physically film in the unaffected area when performing any corrosion damaged by shearing, drilling, abrasion, or impact. If correction of anodized surfaces. Do not use steel wool or steel the skin section can be removed easily, do so to assure wire brushes. Do not use severe abrasive materials.

complete inhibition and treatment. If insulating washers are involved, loosen screws sufficiently to permit brush Nonwoven abrasive pads have generally replaced aluminum treatment of the magnesium under the insulating washer.

wool, aluminum wire brushes, or fiber bristle brushes as the Complete mechanical removal of corrosion products is to tools used for cleaning corroded anodized surfaces. Care must be practiced insofar as practicable. Limit such mechanical be exercised in any cleaning process to avoid unnecessary cleaning to the use of stiff, hog bristle brushes and similar breaking of the adjacent protective film. Take every nonmetallic cleaning tools (including nonwoven abrasive precaution to maintain as much of the protective coating as pads), particularly if treatment is to be performed under field practicable. Otherwise, treat anodized surfaces in the same conditions. Like aluminum, under no circumstances are steel manner as other aluminum finishes. Chromic acid and other or aluminum tools; steel, bronze, or aluminum wool; or other inhibitive treatments can be used to restore the oxide film.

cleaning abrasive pads used on different metal surfaces to Treatment of Intergranular Corrosion in Heat‑Treated be used in cleaning magnesium. Any entrapment of particles Aluminum Alloy Surfaces from steel wire brushes or steel tools, or contamination of treated surfaces by dirty abrasives, can cause more trouble As previously described, intergranular corrosion is an attack than the initial corrosive attack.

along grain boundaries of improperly or inadequately heat- treated alloys, resulting from precipitation of dissimilar Corroded magnesium may generally be treated as follows: constituents following heat-treatment. In its most severe form, actual lifting of metal layers (exfoliation) occurs. [Figure 8-15] 1. Clean and strip the paint from the area to be treated.

Paint stripping procedures were discussed earlier in More severe cleaning is a must when intergranular corrosion this chapter and are also addressed in FAA AC 43.13-1, is present. The mechanical removal of all corrosion products Acceptable Methods, Techniques, and Practices— and visible delaminated metal layers must be accomplished Aircraft Inspection and Repair.

to determine the extent of the destruction and to evaluate the 2. Use a stiff, hog-bristle brush or nonwoven abrasive remaining structural strength of the component. Corrosion pad to break loose and remove as much of the depth and removal limits have been established for some corrosion products as practicable. Steel wire brushes, aircraft. Any loss of structural strength must be evaluated carborundum abrasives, or steel cutting tools must not prior to repair or replacement of the part. If the manufacturer’s be used.

limits do not adequately address the damage, a designated engineering representative (DER) can be brought in to assess 3. Treat the corroded area liberally with a chromic acid the damage. solution that sulfuric acid has been added to. Work the solution into pits and crevices by brushing the Corrosion of Magnesium Alloys area while still wet with chromic acid, again using a nonmetallic brush.

Magnesium is the most chemically active of the metals used in aircraft construction and is the most difficult to protect.

4. Allow the chromic acid to remain in place for 5 to When a failure in the protective coating does occur, the 20 minutes before wiping up the excess with a clean, prompt and complete correction of the coating failure is damp cloth. Do not allow the excess solution to dry imperative if serious structural damage is to be avoided.

and remain on the surface, as paint lifting is caused Magnesium attack is probably the easiest type of corrosion by such deposits.

to detect in its early stages, since magnesium corrosion 5. As soon as the surfaces are dry, restore the original products occupy several times the volume of the original protective paint.

magnesium metal destroyed. The beginning of attack shows as a lifting of the paint film and white spots on the magnesium Treatment of Installed Magnesium Castings surface. These rapidly develop into snow-like mounds or Magnesium castings, in general, are more porous and prone even “white whiskers.” [Figure 8-29] Reprotection involves to penetrating attack than wrought magnesium skins. For the removal of corrosion products, the partial restoration of 8-19 all practical purposes, however, treatment is the same for brushes only are used and if the surface is treated following all magnesium areas. Engine cases, bellcranks, fittings, cleaning with a suitable solution of sodium dichromate. Wipe numerous covers, plates, and handles are the most common the treated surface with dry cloths to remove excess solution, magnesium castings. but do not use a water rinse.

When attack occurs on a casting, the earliest practicable Protection of Dissimilar Metal Contacts treatment is required if dangerous corrosive penetration is Certain metals are subject to corrosion when placed in contact to be avoided. In fact, engine cases submerged in saltwater with other metals. This is commonly referred to as electrolytic overnight can be completely penetrated. If it is at all or dissimilar metals corrosion. Contact of different bare practicable, separate parting surfaces to effectively treat the metals creates an electrolytic action when moisture is existing attack and prevent its further progress. The same present. If this moisture is salt water, the electrolytic action general treatment sequence in the preceding paragraph for is accelerated. The result of dissimilar metal contact is magnesium skin is to be followed.

oxidation (decomposition) of one or both metals. The chart shown in Figure 8-30 lists the metal combinations requiring If extensive removal of corrosion products from a structural a protective separator. The separating materials may be casting is involved, a decision from the manufacturer may metal primer, aluminum tape, washers, grease, or sealant, be necessary to evaluate the adequacy of structural strength depending on the metals involved.

remaining. Specific structural repair manuals usually include dimensional tolerance limits for critical structural members Contacts Not Involving Magnesium and must be referred to if any question of safety is involved.

All dissimilar joints not involving magnesium are protected by the application of a minimum of two coats of zinc Treatment of Titanium & Titanium Alloys chromate or, preferably, epoxy primer in addition to normal Attack on titanium surfaces is generally difficult to detect.

primer requirements. Primer is applied by brush or spray and Titanium is, by nature, highly corrosion resistant, but it may allowed to air dry 6 hours between coats.

show deterioration from the presence of salt deposits and metal impurities, particularly at high temperatures. Therefore, the Contacts Involving Magnesium use of steel wool, iron scrapers, or steel brushes for cleaning or To prevent corrosion between dissimilar metal joints in which for the removal of corrosion from titanium parts is prohibited.

magnesium alloy is involved, each surface is insulated as follows: If titanium surfaces require cleaning, hand polishing with aluminum polish or a mild abrasive is permissible if fiber At least two coats of zinc chromate or, preferably, epoxy primer are applied to each surface. Next, a layer of pressure sensitive vinyl tape 0.003" thick is applied smoothly and firmly enough to prevent air bubbles and wrinkles. To avoid creep back, the tape is not stretched during application.

When the thickness of the tape interferes with the assembly of parts, where relative motion exists between parts or when service temperatures above 250 °F are anticipated, the use of tape is eliminated and extra coats (minimum of three) of primer are applied.

Corrosion Limits Corrosion, however slight, is damage. Therefore, corrosion damage is classified under the four standard types, as is any other damage. These types are negligible damage, damage repairable by patching, damage repairable by insertion, and damage necessitating replacement of parts.

The term “negligible” does not imply that little or nothing is to be done. The corroded surface must be cleaned, treated, and painted as appropriate. Negligible damage, generally, is corrosion that has scarred or eaten away the surface protective Figure 8-29. Magnesium corrosion.

coats and begun to etch the metal. Corrosion damage 8-20 extending to classifications of “repairable by patching” and finish. The cleaning process may be either mechanical or “repairable by insertion” must be repaired in accordance chemical. In mechanical cleaning, the following methods are with the applicable structural repair manual. When corrosion employed: wire brush, steel wool, emery cloth, sandblasting, damage exceeds the damage limits to the extent that repair is or vapor blasting.

not possible, the component or structure must be replaced.

Chemical cleaning is preferred over mechanical since none Processes & Materials Used in Corrosion of the base metal is removed by cleaning. There are various Control chemical processes now in use, and the type used depends on the material being cleaned and the type of foreign matter Metal Finishing being removed.

Aircraft parts are almost always given some type of surface finish by the manufacturer. The main purpose is to provide Steel parts are pickled to remove scale, rust, or other foreign corrosion resistance; however, surface finishes may also be matter, particularly before plating. The pickling solution can applied to increase wear resistance or to provide a suitable be either muriatic (hydrochloric) or sulfuric acid. Cost wise, base for paint.

sulfuric acid is preferable, but muriatic acid is more effective in removing certain types of scale. The pickling solution is In most instances, the original finishes described in the kept in a stoneware tank and is usually heated by means following paragraphs cannot be restored in the field due of a steam coil. Parts not to be electroplated after pickling to unavailable equipment or other limitations. However, are immersed in a lime bath to neutralize the acid from the an understanding of the various types of metal finishes is pickling solution.

necessary if they are to be properly maintained in the field and if the partial restoration techniques used in corrosion Electrocleaning is another type of chemical cleaning used to control are to be effective.

remove grease, oil, or organic matter. In this cleaning process, the metal is suspended in a hot alkaline solution containing Surface Preparation special wetting agents, inhibitors, and materials to provide Original surface treatments for steel parts usually include the necessary electrical conductivity. An electric current is a cleaning treatment to remove all traces of dirt, oil, then passed through the solution in a manner similar to that grease, oxides, and moisture. This is necessary to provide used in electroplating.

an effective bond between the metal surface and the final Contacting Metals Aluminum alloy Calcium plate Zinc plate Carbon and alloy steels Lead Tin coating Copper and alloys Nickel and alloys Titanium and alloys Chromium plate Corrosion resisting steel Magnesium alloy Aluminum alloy Cadmium plate Zinc plate Carbon and alloy steels Lead Tin coating Copper and alloys Nickel and alloys Titanium and alloys Chromium plate Corrosion resisting steel Magnesium alloys Orange areas indicate dissimilar metal contact Figure 8-30. Dissimilar metal contacts that will result in electrolytic corrosion.

8-21 Alodizing Aluminum and magnesium parts are also cleaned by using Alodizing is a simple chemical treatment for all aluminum some of the foregoing methods. Blast cleaning, using abrasive alloys to increase their corrosion resistance and to improve media, is not applicable to thin aluminum sheets, particularly their paint bonding qualities. Because of its simplicity, it is Alclad. Steel grits are not used on aluminum or corrosion rapidly replacing anodizing in aircraft work.

resistant metals.

The process consists of precleaning with an acidic or alkaline Polishing, buffing, and coloring of metal surfaces play a very metal cleaner that is applied by either dipping or spraying.

important part in the finishing of metal surfaces. Polishing The parts are then rinsed with fresh water under pressure ® and buffing operations are sometimes used when preparing for 10 to 15 seconds. After thorough rinsing, Bonderite is a metal surface for electroplating, and all three operations applied by dipping, spraying, or brushing. A thin, hard coating are used when the metal surface requires a high luster finish.

results, ranging in color from light, bluish green with a slight iridescence on copper free alloys to an olive green on copper ® Chemical Treatments bearing alloys. The Bonderite is first rinsed with clear, cold or warm water for a period of 15 to 30 seconds. An additional Anodizing ® 10 to 15 second rinse is then given in a Deoxylyte bath.

Anodizing is the most common surface treatment of This bath is to counteract alkaline material and to make the nonclad aluminum alloy surfaces. It is typically done in ® Bonderite aluminum surface slightly acid on drying.

specialized facilities in accordance with MIL-DTL-5541F or AMS - C - 5541A. The aluminum alloy sheet or casting is the Chemical Surface Treatment and Inhibitors positive pole in an electrolytic bath in which chromic acid or As previously described, aluminum and magnesium alloys other oxidizing agent produces an aluminum oxide film on in particular are protected originally by a variety of surface the metal surface. Aluminum oxide is naturally protective.

treatments. Steels may have been treated on the surface Anodizing merely increases the thickness and density of the during manufacture. Most of these coatings can only be natural oxide film. When this coating is damaged in service, it restored by processes that are completely impractical in the can only be partially restored by chemical surface treatments.

field. However, corroded areas where such protective films Therefore, when an anodized surface is cleaned including have been destroyed require some type of treatment prior corrosion removal, the technician must avoid unnecessary to refinishing.

destruction of the oxide film. The anodized coating provides excellent resistance to corrosion. The coating is soft and The labels on the containers of surface treatment chemicals easily scratched, making it necessary to use extreme caution provide warnings if a material is toxic or flammable. However, when handling it prior to coating it with primer.

the label might not be large enough to accommodate a list of all the possible hazards that may ensue if the materials are Aluminum wool, nylon webbing impregnated with aluminum mixed with incompatible substances. The Safety Data Sheet oxide abrasive, fine grade, nonwoven abrasive pads, or fiber (SDS) should also be consulted for information. For example, bristle brushes are the approved tools for cleaning anodized some chemicals used in surface treatments react violently if surfaces. The use of steel wool, steel wire brushes, or harsh inadvertently mixed with paint thinners. Chemical surface abrasive materials on any aluminum surface is prohibited.

treatment materials must be handled with extreme care and Producing a buffed or wire brush finish by any means is also mixed exactly according to directions.

prohibited. Otherwise, anodized surfaces are treated in much the same manner as other aluminum finishes.

Chromic Acid Inhibitor A 10 percent solution by weight of chromic acid, activated In addition to its corrosion resistant qualities, the anodic by a small amount of sulfuric acid, is particularly effective in coating is also an excellent bond for paint. In most cases, parts treating exposed or corroded aluminum surfaces. It may also are primed and painted as soon as possible after anodizing.

be used to treat corroded magnesium. This treatment tends The anodic coating is a poor conductor of electricity; to restore the protective oxide coating on the metal surface.

therefore, if parts require bonding, the coating is removed Such treatment must be followed by regular paint finishes as where the bonding wire is to be attached. Alclad surfaces that soon as practicable and never later than the same day as the are to be left unpainted require no anodic treatment; however, latest chromic acid treatment. Chromium trioxide flake is a if the Alclad surface is to be painted, it is usually anodized powerful oxidizing agent and a fairly strong acid. It must be to provide a bond for the paint.

stored away from organic solvents and other combustibles.

Either thoroughly rinse or dispose of wiping cloths used in chromic acid pickup.

8-22 with mud and grease may be easily overlooked. Dirt can Sodium Dichromate Solution hide cracks in the skin. Dust and grit cause hinge fittings to A less active chemical mixture for surface treatment of wear excessively. If left on the aircraft’s outer surface, a film of dirt reduces flying speed and adds extra weight. Dirt or aluminum is a solution of sodium dichromate and chromic acid. Entrapped solutions of this mixture are less likely to trash blowing or bouncing around the inside of the aircraft is annoying and dangerous. Small pieces of dirt blown into the corrode metal surfaces than chromic acid inhibitor solutions.

Chemical Surface Treatments eyes of the pilot at a critical moment can cause an accident. A coating of dirt and grease on moving parts makes a grinding Several commercial, activated chromate acid mixtures are compound that can cause excessive wear. Salt water has a available under Specification MIL-C-5541 for field treatment serious corroding effect on exposed metal parts of the aircraft of damaged or corroded aluminum surfaces. Take precautions and must be washed off immediately.

to make sure that sponges or cloths used are thoroughly rinsed to avoid a possible fire hazard after drying.

There are many kinds of cleaning agents approved for use in cleaning aircraft. It is impractical to cover each of the various Protective Paint Finishes types of cleaning agents since their use varies under different A good, intact paint finish is the most effective barrier between conditions, such as the type of material to be removed, the metal surfaces and corrosive media. [Figure 8-31] The most aircraft finish, and whether the cleaning is internal or external.

common finishes include catalyzed polyurethane enamel, waterborne polyurethane enamel, and two-part epoxy In general, the types of cleaning agents used on aircraft are paint. As new regulations regarding the emission of volatile solvents, emulsion cleaners, soaps, and synthetic detergents.

organic compounds (VOCs) are put into effect, the use of Their use must be in accordance with the applicable waterborne paint systems have increased in popularity.

maintenance manual. The types of cleaning agents named Also, still available are nitrate and butyrate dope finishes above are also classed as light- or heavy-duty cleaners.

for fabric-covered aircraft. In addition, high visibility The soap and synthetic detergent-type cleaners are used for fluorescent materials may also be used, along with a variety light-duty cleaning, while the solvent and emulsion-type of miscellaneous combinations of special materials. There cleaners are used for heavy-duty cleaning. The light-duty may also be rain erosion resistant coatings on metal leading cleaners that are nontoxic and nonflammable must be used edges and several different baked enamel finishes on engine whenever possible. As mentioned previously, cleaners that cases and wheels.

can be effectively rinsed and neutralized must be used, or an alkaline cleaner may cause corrosion within the lap joints of Aircraft Cleaning riveted or spot-welded sheet metal components.

Cleaning an aircraft and keeping it clean are extremely important. From an AMT's viewpoint, it should be considered Exterior Cleaning a regular part of aircraft maintenance. Keeping the aircraft There are three methods of cleaning the aircraft exterior: clean can mean more accurate inspection results, and may wet wash, dry wash, and polishing. Polishing can be further even allow a flight crewmember to spot an impending broken down into hand polishing and mechanical polishing.

component failure. A cracked landing gear fitting covered Figure 8-31. Protective paint finishes are the most effective means of preventing corrosion.

8-23 The type and extent of soiling and the final desired appearance surface. The charge, as well as the dust, may be removed by determine the cleaning method to be used. patting or gently blotting with a clean, damp chamois. Do not use scouring powder or other material that can mar the plastic Wet wash removes oil, grease, carbon deposits, and most surface. Remove oil and grease by rubbing gently with a cloth soils, with the exception of corrosion and oxide films. The wet with soap and water. Do not use acetone, benzene, carbon cleaning compounds used are generally applied by spray or tetrachloride, lacquer thinners, window cleaning sprays, mop. Then high-pressure running water is used as a rinse. gasoline, fire extinguisher, or deicer fluid on plastics, because Either alkaline or emulsion cleaners can be used in the wet they soften the plastic and cause crazing. Finish cleaning the wash method. plastic by coating with a plastic polish intended for aircraft windows and windshields. These polishes can minimize Dry wash is used to remove airport film, dust, and small small surface scratches and also help keep static charges from accumulations of dirt and soil when the use of liquids is building up on the surface of the windows.

neither desirable nor practical. This method is not suitable for removing heavy deposits of carbon, grease, or oil, especially Surface oil, hydraulic fluid, grease, or fuel can be removed in the engine exhaust areas. Dry wash materials are applied from aircraft tires by washing with a mild soap solution. After with spray, mops, or cloths and removed by dry mopping or cleaning, lubricate all grease fittings, hinges, and so forth, wiping with clean, dry cloths. where removal, contamination, or dilution of the grease is suspected during washing of the aircraft.

Polishing restores the luster to painted and unpainted surfaces of the aircraft and is usually performed after the surfaces have Interior Cleaning been cleaned. Polishing is also used to remove oxidation and Keeping the interior of the aircraft clean is just as important as corrosion. Polishing materials are available in various forms maintaining a clean exterior surface. Corrosion can establish and degrees of abrasiveness. It is important that the aircraft itself on the inside structure to a greater degree, because it is manufacturer’s instructions be used in specific applications.

difficult to reach some areas for cleaning. Nuts, bolts, bits of wire, or other metal objects carelessly dropped and neglected, The washing of aircraft should be performed in the shade combined with moisture and dissimilar metal contact, can whenever possible, as cleaning compounds tend to streak cause electrolytic corrosion.

the surface if applied to hot metal or are permitted to dry on the area. Install covers over all openings where water When performing structural work inside the aircraft, clean or cleaners might enter and cause damage. Pay particular up all metal particles and other debris as soon as possible.

attention to instrument system components, such as pitot- To make cleaning easier and prevent the metal particles and static fittings and ports.

debris from getting into inaccessible areas, use a drop cloth in the work area to catch this debris. A vacuum cleaner can Various areas of aircraft, such as the sections housing radar be used to pick up dust and dirt from the interior of the flight and the area forward of the flight deck that are finished with deck and cabin.

a flat-finish paint, must not be cleaned more than necessary and never scrubbed with stiff brushes or coarse rags. A soft Aircraft interior present certain problems during cleaning sponge or cheesecloth with a minimum of manual rubbing operations due to the fact that aircraft cabin compartments is advisable. Any oil or exhaust stains on the surface must are relatively small enclosures. The possibility of restricted first be removed with a solvent, such as kerosene or other ventilation and quick buildup of flammable vapor/air petroleum-based solvent. Rinse the surfaces immediately after mixtures can occur when there is any indiscriminate use of cleaning to prevent the compound from drying on the surface.

flammable cleaning agents or solvents. Additionally, there may also exist the possibility of an ignition source from Before applying soap and water to plastic surfaces, flush the concurrent maintenance work in the form of an electrical plastic surfaces with fresh water to dissolve salt deposits and fault, friction or static spark, an open flame device, etc.

wash away dust particles. Plastic surfaces are to be washed with soap and water, preferably by hand. Wherever possible, use nonflammable agents in these operations to reduce to the minimum the fire and explosion hazards.

Rinse with fresh water and dry with a chamois, synthetic wipes designed for use on plastic windshields, or absorbent cotton.

Types of Cleaning Operations In view of the soft surface, do not rub plastic with a dry cloth The principal areas of aircraft cabins that may need periodic since this is not only likely to cause scratches, but it also builds cleaning are: up an electrostatic charge that attracts dust particles to the 1. Aircraft passenger cabin areas (seats, carpets, side 8-24 panels, headliners, overhead racks, curtains, ash trays, a nonflammable pressurizing agent, but it is best to windows, doors, decorative panels of plastic, wood, check this carefully as some may contain a flammable or similar materials) compressed gas for pressurization.

2. Aircraft flight station areas (similar materials to those 5. Abrasives—Some proprietary nonflammable mild found in passenger cabin areas plus instrument panels, abrasive materials are available for rejuvenating control pedestals, glare shields, flooring materials, painted or polished surfaces. They present no fire metallic surfaces of instruments and flight control hazard.

equipment, electrical cables and contacts, and so forth) 6. Dry cleaning agents—Perchlorethylene and 3. Lavatories and buffets (similar materials to those trichlorethylene as used at ambient temperatures are found in passenger cabin areas plus toilet facilities, examples of nonflammable dry cleaning agents. These metal fixtures and trim, trash containers, cabinets, materials do have a toxicity hazard requiring care in wash and sink basins, mirrors, ovens, and so forth) their use, and in some locations due to environmental laws, their use may be prohibited or severely restricted. In the same way, water-soluble agents can Nonflammable Aircraft Cabin Cleaning Agents & be detrimental. Fire retardant treated materials may Solvents be adversely affected by the application of these dry 1. Detergents and soaps—These have widespread cleaning agents.

application for most aircraft cleaning operations involving fabrics, headliners, rugs, windows, and Flammable & Combustible Agents similar surfaces that are not damageable by water 1. High flash point solvents—Specially refined petroleum solutions since they are colorfast and nonshrinkable.

products, first developed as “Stoddard solvent” and Care is frequently needed to prevent leaching of water- now sold under a variety of trade names by different soluble fire retardant salts that may have been used companies, have solvent properties approximating to treat such materials in order to reduce their flame gasoline, but have fire hazard properties similar to spread characteristics. Allowing water laced with fire those of kerosene as commonly used (not heated).

retardant salts to come in contact with the aluminum Most of these are stable products having a flash point framework of seats and seat rails can induce corrosion.

from 100 °F to 140 °F with a comparatively low degree Be careful to ensure only the necessary amount of of toxicity.

water is applied to the seat materials when cleaning.

2. Low flash point solvents—Class I (flash point at 2. Alkaline cleaners—Most of these agents are water- below 100 °F) flammable liquids are not to be used for soluble and thus have no fire hazard properties. They aircraft cleaning or refurbishing. Common materials can be used on fabrics, headliners, rugs, and similar falling into this “class” are acetone, aviation gasoline surfaces in the same manner as detergent and soap (AVGAS), methyl ethyl ketone, naphtha, and toluol.

solutions with only minor added limitations resulting In cases where it is absolutely necessary to use a from their inherent caustic character. This may flammable liquid, use high flash point liquids (those increase their efficiency as cleaning agents, but results having a flash point of 100 °F or more).

in somewhat greater deteriorating effects on certain fabrics and plastics.

3. Mixed liquids—Some commercial solvents are mixtures of liquids with differing rates of evaporation, 3. Acid solutions—A number of proprietary acid such as a mixture of one of the various naphthas and a solutions are available for use as cleaning agents.

chlorinated material. The different rates of evaporation They are normally mild solutions designed primarily may present problems from both the toxicity and fire to remove carbon smut or corrosive stains. As water- hazard viewpoints. Such mixtures must not be used, based solutions, they have no flash point, but may unless they are stored and handled with full knowledge require more careful and judicious use to prevent of these hazards and appropriate precautions taken.

damage to fabrics, plastics, or other surfaces and protect the skin and clothing of those using the Container Controls materials.

Flammable liquids should be handled only in approved 4. Deodorizing or disinfecting agents—A number of containers or safety cans appropriately labeled.

proprietary agents useful for aircraft cabin deodorizing or disinfecting are nonflammable. Most of these are Fire Prevention Precautions designed for spray application (aerosol type) and have During aircraft cleaning or refurbishing operations where 8-25 flammable or combustible liquids are used, the following be placed at aircraft cabin doors for immediate use if general safeguards are recommended: required.

1. Aircraft cabins are to be provided with ventilation NOTE 1: All-purpose ABC (dry chemical) type sufficient at all times to prevent the accumulation of extinguishers are not to be used in situations where flammable vapors. To accomplish this, doors to cabins aluminum corrosion is a problem, if the extinguisher shall be open to secure maximum advantage of natural is used.

ventilation. Where such natural ventilation is not NOTE 2: Portable and semi-portable fire detection and sufficient, approved mechanical ventilation equipment extinguishing equipment has been developed, tested, shall be provided and used. The accumulation of and installed to provide protection to aircraft during flammable vapors above 25 percent of the lower construction and maintenance operations. Operators flammability limit of the particular vapor being used, are urged to investigate the feasibility of utilizing measured at a point 5 feet from the location of use, such equipment during aircraft cabin cleaning and shall result in emergency revisions of operations in refurbishing operations.

progress.

3. Aircraft undergoing such cleaning or refurbishing 2. All open flame and spark producing equipment or where the work is to be done under cover must be devices that may be brought within the vapor hazard in hangars equipped with automatic fire protection area must be shut down and not operated during the equipment.

period when flammable vapors may exist.

3. Electrical equipment of a hand portable nature, used Powerplant Cleaning within an aircraft cabin, shall be of the type approved Cleaning the powerplant is an important job and must be done for use in Class I, Group D, Hazardous Locations as thoroughly. Grease and dirt accumulations on an air-cooled defined by the National Electrical Code.

engine provide an effective insulation against the cooling effect of air flowing over it. Such an accumulation can also 4. Switches to aircraft cabin lighting and to the aircraft cover up cracks or other defects.

electrical system components within the cabin area must not be worked on or switched on or off during When cleaning an engine, open or remove the cowling as cleaning operations.

much as possible. Beginning with the top, wash down the 5. Suitable warning signs must be placed in conspicuous engine and accessories with a fine spray of kerosene or locations at aircraft doors to indicate that flammable solvent. A bristle brush may be used to help clean some of liquids are being or have been used in the cleaning or the surfaces.

refurbishing operation in progress.

Fresh water, soap, and approved cleaning solvents may be used Fire Protection Recommendations for cleaning propeller and rotor blades. Except in the process During aircraft cleaning or refurbishing operations where of etching, caustic material must not be used on a propeller.

flammable liquids are used, the following general fire Scrapers, power buffers, steel brushes, or any tool or substances protection safeguards are recommended: that mar or scratch the surface must not be used on propeller 1. Aircraft undergoing such cleaning or refurbishing blades, except as recommended for etching and repair.

must preferably be located outside of the hangar Water spray, rain, or other airborne abrasive material strikes buildings when weather conditions permit. This a whirling propeller blade with such force that small pits are provides for added natural ventilation and normally formed in the blade’s leading edge. If preventive measures are assures easier access to the aircraft in the event of fire. not taken, corrosion causes these pits to rapidly grow larger.

The pits may become so large that it is necessary to file the 2. It is recommended that during such cleaning or blade’s leading edge until it is smooth.

refurbishing operations in an aircraft outside of the hangar that portable fire extinguishers be provided Steel propeller blades have more resistance to abrasion and at cabin entrances having a minimum rating of 20-B.

corrosion than aluminum alloy blades. Steel blades, if rubbed Additionally, at minimum, a booster hose line with an down with oil after each flight, retain a smooth surface for adjustable water spray nozzle capable of reaching the a long time.

cabin area for use pending the arrival of airport fire equipment must be available. As an alternate to the Examine the propellers regularly, because cracks in steel or previous recommendations, a Class A fire extinguisher aluminum alloy blades can become filled with oil that tends to having a minimum rating of 4-A plus or a Class B fire oxidize. This can readily be seen when the blade is inspected.

extinguisher having a minimum rating of 20-B must 8-26 Keeping the surface wiped with oil serves as a safety feature Dry cleaning solvent is preferable to kerosene for all cleaning by helping to make cracks more obvious. purposes, but like kerosene, it leaves a slight residue upon evaporation that may interfere with the application of some Propeller hubs must be inspected regularly for cracks and final paint films.

other defects. Unless the hubs are kept clean, defects may not be found. Clean steel hubs with soap and fresh water or with Aliphatic and Aromatic Naphtha an approved cleaning solvent. These cleaning solvents may Aliphatic naphtha is recommended for wipe down of cleaned be applied by cloths or brushes. Avoid tools and abrasives surfaces just before painting. This material can also be used that scratch or otherwise damage the plating. for cleaning acrylics and rubber. It flashes at approximately 80 °F and must be used with care. Aromatic naphtha must In special cases where a high polish is desired, the use not be confused with the aliphatic material. It is toxic, of a good grade of metal polish is recommended. Upon attacks acrylics and rubber products, and must be used with completion of the polishing, all traces of polish must be adequate controls.

removed immediately, the blades cleaned, and then coated with clean engine oil. All cleaning substances must be Safety Solvent removed immediately after completion of the cleaning of any Safety solvent, trichloroethane (methyl chloroform), is used propeller part. Soap in any form can be removed by rinsing for general cleaning and grease removal. It is nonflammable repeatedly with fresh water. After rinsing, all surfaces must under ordinary circumstances and is used as a replacement be dried and coated with clean engine oil. After cleaning the for carbon tetrachloride. The use and safety precautions powerplant, all control arms, bellcranks, and moving parts necessary when using chlorinated solvents must be observed.

must be lubricated according to instructions in the applicable Prolonged use can cause dermatitis on some persons.

maintenance manual.

Methyl Ethyl Ketone (MEK) Solvent Cleaners MEK is also available as a solvent cleaner for metal surfaces and paint stripper for small areas. This is a very active solvent In general, solvent cleaners used in aircraft cleaning must and metal cleaner with a flashpoint of about 24 °F. It is toxic have a flashpoint of not less than 105 °F, if explosion proofing when inhaled, and safety precautions must be observed during of equipment and other special precautions are to be avoided.

its use. In most instances, it has been replaced with safer to Chlorinated solvents of all types meet the nonflammable handle and more environmentally-friendly cleaning solvents.

requirements, but are toxic. Safety precautions must be observed in their use. Use of carbon tetrachloride is to be Kerosene avoided. The SDS for each solvent must be consulted for Kerosene is mixed with solvent emulsion-type cleaners for handling and safety information.

softening heavy preservative coatings. It is also used for general solvent cleaning, but its use must be followed by a AMTs must review the SDS available for any chemical, coating or rinse with some other type of protective agent.

solvent, or other materials they may come in contact with Kerosene does not evaporate as rapidly as dry cleaning during the course of their maintenance activities. In particular, solvent and generally leaves an appreciable film on cleaned solvents and cleaning liquids, even those considered surfaces that may actually be corrosive. Kerosene films may “environmentally friendly,” can have varied detrimental be removed with safety solvent, water emulsion cleaners, or effects on the skin, internal organs, and/or nervous system.

detergent mixtures.

Active solvents, such as methyl ethyl ketone (MEK) and acetone, can be harmful or fatal if swallowed, inhaled, or Cleaning Compound for Oxygen Systems absorbed through the skin in sufficient quantities.

Cleaning compounds for use in the oxygen system are anhydrous (waterless) ethyl alcohol or isopropyl (anti- Particular attention must be paid to recommended protective icing fluid) alcohol. These may be used to clean accessible measures including gloves, respirators, and face shields. A components of the oxygen system, such as crew masks and regular review of the SDS keeps the AMT updated on any lines. Fluids must not be put into tanks or regulators.

revisions that may be made by chemical manufacturers or government authorities.

Do not use any cleaning compounds that may leave an Dry Cleaning Solvent oily film when cleaning oxygen equipment. Instructions of the manufacturer of the oxygen equipment and cleaning Stoddard solvent is the most common petroleum base solvent compounds must be followed at all times.

used in aircraft cleaning. Its flashpoint is slightly above 105 °F and can be used to remove grease, oils, or light soils.

8-27 Emulsion Cleaners Mechanical Cleaning Materials Solvent and water emulsion compounds are used in general Mechanical cleaning materials must be used with care and aircraft cleaning. Solvent emulsions are particularly useful in in accordance with directions given, if damage to finishes the removal of heavy deposits, such as carbon, grease, oil, or and surfaces is to be avoided.

tar. When used in accordance with instructions, these solvent emulsions do not affect good paint coatings or organic finishes. Mild Abrasive Materials No attempt is made in this section to furnish detailed Water Emulsion Cleaner instructions for using various materials listed. Some “do’s Material available under Specification MIL-C-22543A is a and don’ts” are included as an aid in selecting materials for water emulsion cleaning compound intended for use on both specific cleaning jobs.

painted and unpainted aircraft surfaces. This material is also acceptable for cleaning fluorescent painted surfaces and is The introduction of various grades of nonwoven abrasive safe for use on acrylics. However, these properties vary with pads has given the AMT a clean, inexpensive material for the material available. A sample application must be checked the removal of corrosion products and for other light abrasive carefully before general uncontrolled use. needs. The pads can be used on most metals (although the same pad should not be used on different metals) and are Solvent Emulsion Cleaners generally the first choice when the situation arises. A very One type of solvent emulsion cleaner is nonphenolic and open form of this pad is also available for paint stripping when used in conjunction with wet strippers.

can be safely used on painted surfaces without softening the base paint. Repeated use may soften acrylic nitrocellulose Powdered pumice can be used for cleaning corroded lacquers. It is effective, however, in softening and lifting heavy preservative coatings. Persistent materials are to be aluminum surfaces. Similar mild abrasives may also be used.

given a second or third treatment as necessary.

Impregnated cotton wadding material is used for removal of exhaust gas stains and polishing corroded aluminum Another type of solvent emulsion cleaner has a phenolic base that is more effective for heavy-duty application, but it surfaces. It may also be used on other metal surfaces to produce a high reflectance.

also tends to soften paint coatings. It must be used with care around rubber, plastics, or other nonmetallic materials. Wear Aluminum metal polish is used to produce a high luster, rubber gloves and goggles for protection when working with phenolic base cleaners. long lasting polish on unpainted aluminum clad surfaces. It must not be used on anodized surfaces, because it removes Soaps & Detergent Cleaners the oxide coat.

A number of materials are available for mild cleaning use. In Three grades of aluminum wool, coarse, medium, and fine are this section, some of the more common materials are discussed.

used for general cleaning of aluminum surfaces. Impregnated nylon webbing material is preferred over aluminum wool for Cleaning Compound, Aircraft Surfaces the removal of corrosion products and stubborn paint films Specification MIL-C-5410 Type I and II materials are used and for the scuffing of existing paint finishes prior to touchup.

in general cleaning of painted and unpainted aircraft surfaces for the removal of light to medium soils, operational films, Lacquer rubbing compound material can be used to remove oils, or greases. They are safe to use on all surfaces, including engine exhaust residues and minor oxidation. Avoid heavy fabrics, leather, and transparent plastics. Nonglare (flat) rubbing over rivet heads or edges where protective coatings finishes are not to be cleaned more than necessary and must may be worn thin.

never be scrubbed with stiff brushes.

Abrasive Papers Nonionic Detergent Cleaners Abrasive papers used on aircraft surfaces must not contain These materials may be either water-soluble or oil-soluble.

sharp or needlelike abrasives that can imbed themselves in The oil-soluble detergent cleaner is effective in a 3 to 5 the base metal being cleaned or in the protective coating percent solution in dry cleaning solvent for softening and being maintained. The abrasives used must not corrode the removing heavy preservative coatings. This mixture’s material being cleaned. Aluminum oxide paper, 300 grit or performance is similar to the emulsion cleaners mentioned finer, is available in several forms and is safe to use on most previously.

surfaces. Type I, Class 2 material under Federal Specification 8-28 P-C-451 is available in 1 ⁄ 2 " and 2" widths. Avoid the use of carborundum (silicon carbide) papers, particularly on aluminum or magnesium. The grain structure of carborundum is sharp and the material is so hard that individual grains penetrate and bury themselves, even in steel surfaces. The use of emery paper or crocus cloth on aluminum or magnesium can cause serious corrosion of the metal by imbedded iron oxide.

Chemical Cleaners Chemical cleaners must be used with great care in cleaning assembled aircraft. The danger of entrapping corrosive materials in faying surfaces and crevices counteracts any advantages in their speed and effectiveness. Any materials used must be relatively neutral and easy to remove. It is emphasized that all residues must be removed. Soluble salts from chemical surface treatments, such as chromic acid or dichromate treatment, liquefy and promote blistering in the paint coatings.

Phosphoric ‑ citric Acid A phosphoric-citric acid mixture (Type I) for cleaning aluminum surfaces is available and is ready to use as packaged. Type II is a concentrate that must be diluted with mineral spirits and water. Wear rubber gloves and goggles to avoid skin contact. Any acid burns may be neutralized by copious water washing, followed by treatment with a diluted solution of baking soda (sodium bicarbonate).

Baking Soda Baking soda may be used to neutralize acid deposits in lead-acid battery compartments and to treat acid burns from chemical cleaners and inhibitors.

8-29

Next: Chapter 9 →

Chapter 9

Fluid Lines & Fittings

Introduction Aircraft fluid lines are usually made of metal tubing or higher tensile strength permits the use of tubing with thinner walls; consequently, the final installation weight is not much flexible hose. Metal tubing (also called rigid fluid lines) is used in stationary applications and where long, relatively greater than that of the thicker wall aluminum alloy tubing.

Steel lines are used where there is a risk of foreign object straight runs are possible. They are widely used in aircraft for fuel, oil, coolant, oxygen, instrument, and hydraulic lines. damage (FOD) (i.e., the landing gear and wheel well areas).

Swaged or MS flareless fittings are used with corrosion- Flexible hose is generally used with moving parts or where the hose is subject to considerable vibration. resistant tubing. Although identification markings for steel tubing differ, each usually includes the manufacturer’s name Occasionally, it may be necessary to repair or replace or trademark, the Society of Automotive Engineers (SAE) number, and the physical condition of the metal.

damaged aircraft fluid lines. Very often the repair can be made simply by replacing the tubing. However, if replacements are not available, the needed parts may have to be fabricated. Titanium 3AL–2.5V Replacement tubing should be of the same size and material Titanium 3AL–2.5V tubing and fitting is used extensively in as the original tubing. All tubing is pressure tested prior to transport category and high-performance aircraft hydraulic initial installation and is designed to withstand several times systems for pressures above 1,500 psi. Titanium is 30 percent the normal operating pressure to which it is subjected. If a stronger than steel and 50 percent lighter than steel. Cryofit tube bursts or cracks, it is generally the result of excessive fittings or swaged fittings are used with titanium tubing.

vibration, improper installation, or damage caused by Do not use titanium tubing and fittings in any oxygen collision with an object. All tubing failures should be system assembly. Titanium and titanium alloys are oxygen carefully studied and the cause of the failure determined.

reactive. If a freshly formed titanium surface is exposed in gaseous oxygen, spontaneous combustion could occur at Rigid Fluid Lines low pressures.

Tubing Materials Material Identification Copper Before making repairs to any aircraft tubing, it is important to In the early days of aviation, copper tubing was used make accurate identification of tubing materials. Aluminum extensively in aviation fluid applications. In modern aircraft, alloy, steel, or titanium tubing can be identified readily by aluminum alloy, corrosion-resistant steel, or titanium tubing sight where it is used as the basic tubing material. However, have generally replaced copper tubing.

it is difficult to determine whether a material is carbon steel or stainless steel, or whether it is 1100, 3003, 5052-O, Aluminum Alloy Tubing 6061-T6, or 2024-T3 aluminum alloy. To positively identify 1 1 Tubing made from 1100 H14 ( ⁄ 2 -hard) or 3003 H14 ( ⁄ 2 -hard) the material used in the original installation, compare is used for general purpose lines of low or negligible fluid code markings of the replacement tubing with the original pressures, such as instrument lines and ventilating conduits.

markings on the tubing being replaced.

Tubing made from 2024-T3, 5052-O, and 6061-T6 aluminum alloy materials is used in general purpose systems of low and On large aluminum alloy tubing, the alloy designation is medium pressures, such as hydraulic and pneumatic 1,000 stamped on the surface. On small aluminum tubing, the to 1,500 psi systems, and fuel and oil lines.

designation may be stamped on the surface; but more often it is shown by a color code, not more than 4" in width, painted Steel at the two ends and approximately midway between the ends Corrosion-resistant steel tubing, either annealed CRES 304, of some tubing. When the band consists of two colors, one- CRES 321, or CRES 304- ⁄ 8 -hard, is used extensively in half the width is used for each color. [Figure 9-1] high-pressure hydraulic systems (3,000 psi or more) for the operation of landing gear, flaps, brakes, and in fire zones. Its If the code markings are hard or impossible to read, it may 9-1 be necessary to test samples of the material for hardness by Too much pressure on the cutting wheel at one time could hardness testing. deform the tubing or cause excessive burring. After cutting the tubing, carefully remove any burrs from inside and outside Sizes the tube. Use a knife or the burring edge attached to the tube Metal tubing is sized by outside diameter (OD), which is cutter. The deburring operation can be accomplished by the use of a deburring tool. [Figure 9-3] This tool is capable of measured fractionally in sixteenths of an inch. For example, 6 3 8 number 6 tubing is ⁄ 16 " (or ⁄ 8 ") and number 8 tubing is ⁄ 16 " removing both the inside and outside burrs by just turning the tool end for end.

(or ⁄ 2 ") and so forth. The tube diameter is printed on all rigid tubing. In addition to other classifications or means When performing the deburring operation, use extreme care of identification, tubing is manufactured in various wall thicknesses. Thus, it is important when installing tubing to that the wall thickness of the end of the tubing is not reduced or fractured. Very slight damage of this type can lead to know not only the material and outside diameter, but also the thickness of the wall. The wall thickness is printed on fractured flares or defective flares, which do not seal properly.

Use a fine-tooth file to file the end square and smooth.

the tubing in thousandths of an inch. To determine the inside diameter (ID) of the tube, subtract twice the wall thickness If a tube cutter is not available, or if tubing of hard material from the outside diameter. For example, a number 10 piece of tubing with a wall thickness of 0.063" has an inside diameter is to be cut, use a fine-tooth hacksaw, preferably one having 32 teeth per inch. The use of a saw decreases the amount of of 0.625" – 2(0.063") = 0.499".

work hardening of the tubing during the cutting operation.

Fabrication of Metal Tube Lines After sawing, file the end of the tube square and smooth, removing all burrs.

Damaged tubing and fluid lines should be repaired with new parts whenever possible. Unfortunately, sometimes An easy way to hold small diameter tubing, when cutting it, is replacement is impractical and repair is necessary. Scratches, to place the tube in a combination flaring tool and clamp the abrasions, or minor corrosion on the outside of fluid lines tool in a vise. Make the cut about one-half inch from the flaring may be considered negligible and can be smoothed out with tool. This procedure keeps sawing vibrations to a minimum a burnishing tool or aluminum wool. Limitations on the and prevents damage to the tubing if it is accidentally hit with amount of damage that can be repaired in this manner are the hacksaw frame or file handle while cutting. Be sure all discussed in this chapter under “Rigid Tubing Inspection filings and cuttings are removed from the tube.

and Repair.” If a fluid line assembly is to be replaced, the fittings can often be salvaged; then the repair involves only Tube Bending tube forming and replacement.

The objective in tube bending is to obtain a smooth bend Tube forming consists of four processes: cutting, bending, without flattening the tube. Tubing under ⁄ 4 " in diameter flaring, and beading. If the tubing is small and made of soft usually can be bent without the use of a bending tool. For material, the assembly can be formed by hand bending during larger sizes, either portable hand benders or production installation. If the tube is ⁄ 4 " diameter or larger, hand bending benders are usually used. Figure 9-4 shows preferred methods without the aid of tools is impractical.

and standard bend radii for bending tubing by tube size.

Tube Cutting When cutting tubing, it is important to produce a square Aluminum Alloy Number Color of Band end, free of burrs. Tubing may be cut with a tube cutter or a hacksaw. The cutter can be used with any soft metal tubing, 1100 White such as copper, aluminum, or aluminum alloy. Correct use of 3003 Green the tube cutter is shown in Figure 9-2. Special chipless cutters 2014 Gray are available for cutting aluminum 6061-T6, corrosion- 2024 Red resistant steel, and titanium tubing.

5052 Purple 6053 Black A new piece of tubing should be cut approximately 10 percent 6061 Blue and Yellow longer than the tube to be replaced to provide for minor variations in bending. Place the tube in the cutting tool with 7075 Brown and Yellow the cutting wheel at the point where the cut is to be made.

Figure 9-1. Painted color codes used to identify aluminum Rotate the cutter around the tubing, applying light pressure to alloy tubing.

the cutting wheel by intermittently twisting the thumbscrew.

9-2 Using a hand bender, insert the tubing into the groove of The ordinary production tube bender accommodates tubing 1 1 the bender so that the measured end is left of the form ranging from ⁄ 4 " to 1 ⁄ 2 " outside diameter. Benders for larger block. Align the two zeros and align the mark on the tubing sizes are available, and the principle of their operation is with the L on the form handle. If the measured end is on similar to that of the hand tube bender. The radius blocks are the right side, then align the mark on the tubing with the so constructed that the radius of bend varies with the tube R on the form handle. With a steady motion, pull the form diameter. The radius of bend is usually stamped on the block.

handle until the zero mark on the form handle lines up with the desired angle of bend, as indicated on the radius Alternative Bending Methods block. [Figure 9-5] When hand or production tube benders are not available or are not suitable for a particular bending operation, a filler of Hand benders come in different sizes that correspond to the metallic composition or of dry sand may be used to facilitate tube diameter. Make sure to select the correct bender for bending. When using this method, cut the tube slightly longer the desired tube diameter. Figure 9-6 shows hand benders than required. The extra length is for inserting a plug (which available for different sizes of tubing. Typically, the tubing may be wooden) in each end. The tube can also be closed size is stamped in the bender. [Figure 9-7] by flattening the ends or by soldering metal disks in them.

Bend the tubing carefully to avoid excessive flattening, After plugging one end, fill and pack the tube with fine, dry kinking, or wrinkling. A small amount of flattening in bends is sand and plug tightly. Both plugs must be tight so they are not acceptable, but the small diameter of the flattened portion must forced out when the bend is made. After the ends are closed, not be less than 75 percent of the original outside diameter.

bend the tubing over a forming block shaped to the specified Tubing with flattened, wrinkled, or irregular bends should radius. In a modified version of the filler method, a fusible not be installed. Wrinkled bends usually result from trying to alloy is used instead of sand. In this method, the tube is filled bend thin wall tubing without using a tube bender. Excessive under hot water with a fusible alloy that melts at 160 °F. The flattening causes fatigue failure of the tube. Examples of alloy-filled tubing is then removed from the water, allowed correct and incorrect tubing bends are shown in Figure 9-8.

to cool, and bent slowly by hand around a forming block or with a tube bender. After the bend is made, the alloy is again Tube bending machines for all types of tubing are generally melted under hot water and removed from the tubing. When used in repair stations and large maintenance shops.

using either filler methods, make certain that all particles of With such equipment, proper bends can be made on large the filler are removed. Visually inspect with a borescope to diameter tubing and on tubing made from hard material. The make certain that no particles are carried into the system in production CNC™ tube bender is an example of this type of which the tubing is installed. Store the fusible alloy filler machine. [Figure 9-9] where it is free from dust or dirt. It can be re-melted and reused as often as desired. Never heat this filler in any other way than the prescribed method, as the alloy will stick to the inside of the tubing, making them both unusable.

r e t t Cut u c f Tube Flaring o e d i Two kinds of flares are generally used in aircraft tubing: the s n e p o d r a w o t e t a t o R Tube Clean cut Figure 9-3. Deburring tool.

Figure 9-2. Tube cutting.

9-3 A– Hand B–Portable hand benders C–Production bender Type Bender AB AB B B B BC B BC B BC C BC C Tube OD ¹⁄8" ³⁄16" ¹⁄4" ⁵⁄16" ³⁄8" ³⁄8" ⁷⁄16" ¹⁄2" ¹⁄2" ⁵⁄8" ⁵⁄8" ³⁄4" ³⁄4" Standard Bend ³⁄8" ⁷⁄16" ⁹⁄16" ¹¹⁄16" ¹¹⁄16" ¹⁵⁄16" 1 ³⁄8" 1 ¹⁄2" 1 ¹⁄4" 2 " 1 ¹⁄2" 2 ¹⁄2" 1 ³⁄4" Type Bender C B C C C C C C C C C C C Tube OD ⁷⁄8" 1 " 1 " 1 ¹⁄8" 1 ¹⁄4" 1 ³⁄8" 1 ³⁄8" 1 ¹⁄2" 1 ¹⁄2" 1 ³⁄4" 2 " 2 ¹⁄2" 3 " Standard Bend 2 " 3 ¹⁄2" 3 " 3 ¹⁄2" 3 ³⁄4" 5 " 6 " 5 " 6 " 7 " 8 " 10 " 12 " Figure 9-4. Standard bend radii to which bending tools form the various sizes of tubes.

single flare and the double flare. [Figure 9-10A and B] Flares are frequently subjected to extremely high pressures; therefore, the flare on the tubing must be properly shaped or the connection leaks or fails. A flare made too small produces a weak joint, which may leak or pull apart; if made too large, it interferes with the proper engagement of the screw thread on the fitting and causes leakage. A crooked flare is the result of the tubing not being cut squarely. If a flare is not made properly, flaws cannot be corrected by applying additional torque when tightening the fitting. The flare and tubing must be free from cracks, dents, nicks, scratches, or any other defects.

Figure 9-6. Hand benders.

The flaring tool used for aircraft tubing has male and female dies ground to produce a flare of 35° to 37°. Under no circumstance is it permissible to use an automotive-type flaring tool that produces a flare of 45°. [Figure 9-11] The single-flare hand flaring tool, similar to that shown in Figure 9-12, is used for flaring tubing. The tool consists of a flaring block or grip die, a yoke, and a flaring pin. The flaring block is a hinged double bar with holes corresponding to various sizes of tubing. These holes are countersunk on one end to form the outside support against which the flare is formed. The yoke is used to center the flaring pin over the end Figure 9-7. Size identification.

of the tube to be flared. Two types of flaring tools are used to make flares on tubing: the impact type and the rolling type.

Cut the tube squarely and remove all burrs. Slip the fitting Instructions for Rolling-Type Flaring Tools nut and sleeve on the tube. Loosen clamping screw used for Use these tools only to flare soft copper, aluminum, and brass locking the sliding segment in the die holder. This permits tubing. Do not use with corrosion-resistant steel or titanium. their separation. The tools are self-gauging; the proper size Figure 9-5. Tube bending.

9-4 Perfect bend Flattened bend Good Wrinkled bend Kinked bend Figure 9-9. CNC™ tube bending machine.

rapidly in cold water. Open the flaring tool by unscrewing both clamping screws. Select the hole in the flaring bar that matches the tubing diameter and place the tubing with the end you have just prepared, extending above the top of the bar by a distance equal to the thickness of the shoulder of the adapter insert. Tighten clamping screws to hold tubing Figure 9-8. Correct and incorrect tubing bends.

securely. Insert pilot of correctly sized adapter into tubing.

Slip yoke over the flaring bars and center over adapter.

flare is produced when tubing is clamped flush with the top Advance the cone downward until the shoulder of the adapter of the die block. Insert tubing between the segments of the rests on the flaring bar. This bells out the end of the tubing.

die block that correspond to the size of the tubing to be flared.

Next, back off the cone just enough to remove the adapter.

Advance the clamp screw against the end segment and tighten After removing the adapter, advance the cone directly into the firmly. Move the yoke down over the top of the die holder belled end of the tubing. This folds the tubing on itself and and twist it clockwise to lock it into position. Turn the feed forms an accurate double flare without cracking or splitting screw down firmly, and continue until a slight resistance is the tubing. To prevent thinning out of the flare wall, do not felt. This indicates an accurate flare has been completed.

overtighten. [Figure 9-13] Always read the tool manufacturer’s instructions, because there are several different types of rolling-type flaring tools Fittings that use slightly different procedures.

Rigid tubing may be joined to either an end item (such as a brake cylinder), another section of either rigid tubing, or to a Double Flaring flexible hose (such as a drain line). In the case of connection A double flare is used on soft aluminum alloy tubing ⁄ 8 " to an end item or another tube, fittings are required, which outside diameter and under. This is necessary to prevent may or may not necessitate flaring of the tube. In the case of cutting off the flare and failure of the tube assembly under attachment to a hose, it may be necessary to bead the rigid operating pressures. A double flare is smoother and more tube so that a clamp can be used to hold the hose onto the tube.

concentric than a single flare and therefore seals better. It is also more resistant to the shearing effect of torque.

Flareless Fittings Although the use of flareless tube fittings eliminates all Double Flaring Instructions tube flaring, another operation, referred to as presetting, Deburr both the inside and outside of the tubing to be flared.

is necessary prior to installation of a new flareless tube Cut off the end of the tubing if it appears damaged. Anneal assembly. Flareless tube assemblies should be preset with the brass, copper, and aluminum by heating to a dull red and cool proper size presetting tool or operation. Figure 9-14 (steps 9-5 37° A. Single-flared end Figure 9-11. Flaring tool.

3. Final tightening depends upon the tubing (step 3). For aluminum alloy tubing up to and including ⁄ 2 " outside diameter, tighten the nut from 1 to 1 ⁄ 6 turns. For steel tubing and aluminum alloy tubing over ⁄ 2 " outside 1 1 diameter, tighten from 1 ⁄ 6 to 1 ⁄ 2 turns.

After presetting the sleeve, disconnect the tubing from the fitting and check the following points: The tube should extend 3 1 ⁄ 32 " to ⁄ 8 " beyond the sleeve pilot; otherwise, blowoff may occur. The sleeve pilot should contact the tube or have a maximum clearance of 0.005" for aluminum alloy tubing or 0.015" for steel tubing. A slight collapse of the tube at the sleeve cut is permissible. No movement of the sleeve pilot, B. Double-flared end except rotation, is permissible.

Figure 9-10. Cutaway view of single-flared (A) and double- flared (B) tube ends.

1, 2, and 3) illustrates the presetting operation, which is performed as follows: 1. Cut the tube to the correct length, with the ends perfectly square. Deburr the inside and outside of the tube. Slip the nut, then the sleeve, over the tube (step 1), lubricate the threads of the fitting and nut with hydraulic fluid.

2. Place the fitting in a vise (step 2), and hold the tubing firmly and squarely on the seat in the fitting. (The tube must bottom firmly in the fitting.) Tighten the nut until the cutting edge of the sleeve grips the tube.

To determine this point, slowly turn the tube back and forth while tightening the nut. When the tube no longer turns, the nut is ready for tightening.

Figure 9-12. Hand flaring tool.

9-6 Beading lines, steel tags may be used in place of tape or decals.

[Figure 9-17B] Paint is used on lines in engine compartments Tubing may be beaded with a hand beading tool, with where there is the possibility of tapes, decals, or tags being machine beading rolls, or with grip dies. The method to be drawn into the engine induction system.

used depends on the diameter and wall thickness of the tube and the material from which it was made.

In addition to the above-mentioned markings, certain lines may be further identified regarding specific function within a The hand beading tool is used with tubing having ⁄ 4 " to system (e.g., drain, vent, pressure, or return). Lines conveying 1" outside diameter. [Figure 9-15] The bead is formed by fuel may be marked FLAM [Figure 9-17] ; lines containing using the beader frame with the proper rollers attached. The toxic materials are marked TOXIC in place of FLAM. Lines inside and outside of the tube is lubricated with light oil to containing physically dangerous materials, such as oxygen, reduce the friction between the rollers during beading. The TM nitrogen, or Freon , may be marked PHDAN.

sizes, marked in sixteenths of an inch on the rollers, are for the outside diameter of the tubing that can be beaded with Aircraft and engine manufacturers are responsible for the the rollers.

original installation of identification markers, but the aviation mechanic is responsible for the replacement when it becomes Separate rollers are required for the inside of each tubing size, necessary. Tapes and decals are generally placed on both and care must be taken to use the correct parts when beading.

ends of a line and at least once in each compartment through The hand beading tool works somewhat like the tube cutter in which lines run. In addition, identification markers are placed that the roller is screwed down intermittently while rotating immediately adjacent to each valve, regulator, filter, or other the beading tool around the tubing. In addition, a small vise accessories within a line. Where paint or tags are used, (tube holder) is furnished with the kit.

location requirements are the same as for tapes and decals.

Other methods and types of beading tools and machines are Fluid Line End Fittings available, but the hand beading tool is used most often. As a Depending on the type and use, fittings have either pipe rule, beading machines are limited to use with large diameter threads or machine threads. Pipe threads are similar to those tubing, over 1 ⁄ 16 ", unless special rollers are supplied. The used in ordinary plumbing and are tapered, both internal and grip-die method of beading is confined to small tubing.

external. External threads are referred to as male threads and internal threads are female threads.

Fluid Line Identification Fluid lines in aircraft are often identified by markers made When two fittings are joined, a male into a female, the up of color codes, words, and geometric symbols. These thread taper forms a seal. Some form of pipe thread lubricant markers identify each line’s function, content, and primary approved for particular fluid application should be used when hazard. Figure 9-16 illustrates the various color codes and joining pipe threads to prevent seizing and high-pressure symbols used to designate the type of system and its contents.

leakage. Use care when applying thread lubricant so that the lubricant does not enter and contaminate the system. Do not Fluid lines are marked, in most instances, with 1" tape or use lubricants on oxygen lines. Oxygen reacts with petroleum decals. [Figure 9-17A] On lines 4" in diameter (or larger), products and can ignite (special lubricants are available or lines in oily environment, hot lines, and on some cold oxygen systems).

Figure 9-13. Double flare tool.

9-7 STEP 1 Machine threads have no sealing capability and are similar to those used on common nuts and bolts. This type of fitting Fitting Sleeve Tube nut is used only to draw connections together or for attachment Tube Sleeve pilot through bulkheads. A flared tube connection, a crush washer, or a synthetic seal is used to make the connection fluid tight.

Machine threads have no taper and do not form a fluid-tight seal. The size of these fittings is given in dash numbers, which equal the nominal outside diameter in sixteenths of an inch.

Universal Bulkhead Fittings When a fluid line passes through a bulkhead, and it is desired Sleeve cutting edge to secure the line to the bulkhead, a bulkhead fitting should be used. The end of the fitting that passes through the bulkhead is longer than the other end(s), which allows a locknut to be installed, securing the fitting to the bulkhead.

STEP 2 Fittings attach one piece of tubing to another or to system units. There are four types: (1) bead and clamp, (2) flared fittings, (3) flareless fittings, and (4) permanent fittings (Permaswage™, Permalite™, and Cyrofit™). The amount of pressure that the system carries and the material used are usually the deciding factors in selecting a connector.

The beaded type of fitting, which requires a bead and a section of hose and hose clamps, is used only in low- or medium- pressure systems, such as vacuum and coolant systems. The flared, flareless, or permanent-type fittings may be used as connectors in all systems, regardless of the pressure.

AN Flared Fittings A flared tube fitting consists of a sleeve and a nut.

[ Figure 9-18] The nut fits over the sleeve and, when tightened, draws the sleeve and tubing flare tightly against a male fitting to form a seal. Tubing used with this type of fitting must be flared before installation. The male fitting has a cone-shaped surface with the same angle as the inside of the flare. The sleeve supports the tube so that vibration does not concentrate at the edge of the flare and distributes the shearing action over a wider area for added strength.

STEP 3 Fitting combinations composed of different alloys should 3 1 / " to / " be avoided to prevent dissimilar metal corrosion. As with 32 8 all fitting combinations, ease of assembly, alignment, and proper lubrication should be assured when tightening fittings during installation.

Standard AN fittings are identified by their black or blue color.

All AN steel fittings are colored black, all AN aluminum fittings are colored blue, and aluminum bronze fittings are Slight deformation permissible .005" maximum aluminum alloy tubing cadmium plated and natural in appearance. A sampling of AN fittings is shown in Figure 9-19. Figure 9-20 contains .015" maximum corrosion-resistant steel tubing Figure 9-14. Presetting flareless tube assembly.

9-8 Figure 9-15. To use the hand beading tool, cut with tube cutter (1), deburr (2), oil (3), and revolve tool around tube while tightening handle (4).

connection that is virtually maintenance free. Swaged additional information on sizes, torques, and bend radii. AN fittings are used to join hydraulic lines in areas where routine flared fittings are different from MS flareless fittings and disconnections are not required and are often used with they are not interchangeable. AN flared fittings are easily titanium and corrosion-resistant steel tubing. The fittings are recognized, because they have a cone at the end of the fitting installed with portable hydraulically-powered tooling, which while the MS flareless fitting has a straight end. [Figure 9-21] is compact enough to be used in tight spaces. [Figure 9-24] If the fittings need to be disconnected, cut the tubing with a MS Flareless Fittings tube cutter. Special installation tooling is available in portable MS flareless fittings are designed primarily for high-pressure kits. Always use the manufacturer’s instructions to install (3,000 psi) hydraulic systems that may be subjected to severe swaged fittings. Typical Permaswage™ fittings are shown vibration or fluctuating pressure. [Figure 9-22] Using this in Figure 9-25.

type of fitting eliminates all tube flaring, yet provides a safe and strong, dependable tube connection. The fitting consists One of the latest developments is the Permalite™ fitting.

of three parts: a body, a sleeve, and a nut. [Figure 9-23] The Permalite™ is a tube fitting that is mechanically attached to internal design of the body causes the sleeve to cut into the the tube by axial swaging. Permalite™ works by deforming outside of the tube when the body and nut are joined. The the fitting into the tube being joined by moving a ring, a counterbore shoulder within the body is designed with a component of the Permalite™ fitting, axially along the fitting reverse angle of 15° for steel connectors and 45° for aluminum length using a Permaswage™ Axial swage tool. Typical fittings. This reverse angle prevents inward collapse of the Permalite™ fittings are shown in Figure 9-26 .

tubing when tightened and provides a partial sealing force to be exerted against the periphery of the body counterbore.

Cryofit Fittings Swaged Fittings Many transport category aircraft use Cryofit fittings to join hydraulic lines in areas where routine disconnections are not A popular repair system for connecting and repairing required. Cryofit fittings are standard fittings with a cryogenic hydraulic lines on transport category aircraft is the use of sleeve. The sleeve is made of a shape memory alloy, Tinel™. Permaswage™ fittings. Swaged fittings create a permanent 9-9 FUEL X LUBRICATION PNEUMATIC HYDRAULIC X FUEL FLAM FUEL LUBRICATION X PNEUMATIC HYDRAULIC FUEL FLAM X FUEL LUBRICATION X PNEUMATIC HYDRAULIC X FUEL LUBRICATION X PNEUMATIC HYDRAULIC A FUEL X LUBRICATION X PNEUMATIC HYDRAULIC FUEL LUBRICATION X X PNEUMATIC HYDRAULIC LUBRICATION FUEL X ELECTRICAL AIR COOLANT WATER CONDUIT CONDITION COOLANT ELECTRICAL WATER FUEL CONDUIT AIR COOLANT CONDITION WATER FLAM ELECTRICAL COOLANT CONDUIT WATER AIR B COOLANT CONDITION ELECTRICAL WATER CONDUIT COOLANT AIR WATER Figure 9-17. Fluid line identification using: tape and decals (A) ELECTRICAL CONDITION CONDUIT COOLANT and metal tags (B).

FIRE BREATHING INSTRUMENT COMPRESSED Rigid Tubing Installation and Inspection OXYGEN PROTECTION GAS AIR Before installing a line assembly in an aircraft, inspect the line FIRE BREATHING INSTRUMENT COMPRESSED OXYGEN PROTECTION AIR GAS carefully. Remove dents and scratches, and be sure all nuts FIRE BREATHING INSTRUMENT COMPRESSED and sleeves are snugly mated and securely fitted by proper PROTECTION OXYGEN AIR GAS flaring of the tubing. The line assembly should be clean and FIRE BREATHING COMPRESSED INSTRUMENT PROTECTION OXYGEN AIR GAS free of all foreign matter.

FIRE BREATHING COMPRESSED INSTRUMENT PROTECTION OXYGEN AIR GAS Connection & Torque Never apply compound to the faces of the fitting or the INERTING DE-ICING VACUUM FLUID flare, as it destroys the metal-to-metal contact between the DE-ICING VACUUM INERTING fitting and flare, a contact which is necessary to produce FLUID DE-ICING VACUUM the seal. Be sure that the line assembly is properly aligned INERTING FLUID before tightening the fittings. Do not pull the installation DE-ICING VACUUM INERTING into place with torque on the nut. Correct and incorrect FLUID DE-ICING VACUUM methods of installing flared tube assemblies are illustrated in INERTING DE-ICING VACUUM FLUID Figure 9-28. Proper torque values are given in Figure 9-20 .

WARNING Remember that these torque values are for flared-type fittings SYMBOL only. Always tighten fittings to the correct torque value when installing a tube assembly. Overtightening a fitting may badly Figure 9-16. Identification of aircraft fluid lines.

The sleeve is manufactured 3 percent smaller, frozen in AN819 sleeve liquid nitrogen, and expanded to 5 percent larger than the line. During installation, the fitting is removed from the liquid nitrogen and inserted onto the tube. During a 10 to 15 second warming up period, the fitting contracts to its original size (3 percent smaller), biting down on the tube, forming a permanent seal. Cryofit fittings can only be removed by cutting the tube at the sleeve, though this leaves enough room to replace it with a swaged fitting without replacing the hydraulic line. It is frequently used with titanium tubing.

The shape memory technology is also used for end fittings, Tubing flared fittings, and flareless fittings. [Figure 9-27] AN818 nut Figure 9-18. Flared tube fitting.

9-10 AN744 to AN932 Material: Aluminum alloy........................................................................................................................................... (code D) Steel ........................................................................................................................................................... (code, absence of letter) Brass .......................................................................................................................................................... (code B) Aluminum bronze ....................................................................................................................................... (code Z–for AN819 sleeve) Size: The dash number following the AN number indicates the size of the tubing (or hose) for which the fitting is made in 16ths of an inch.

This size measures the outer diameter of tubing and the inner diameter of hose. Fittings that have pipe threads are coded by a dash number, indicating the pipe size in 8ths of an inch. The material code letter, as noted above, follows the dash number.

BOLT AN774 BOLT AN775 ELBOW AN776 ELBOW AN777 ELBOW AN778 TEE AN779 PLUG AN806 UNION AN815 NUT AN817 SLEEVE AN819 TEE AN804 PLUG AN814 NUT AN818 CAP AN820 NIPPLE AN816 ADAPTOR AN807 ELBOW AN821 ELBOW AN823 TEE AN825 CROSS AN827 UNION AN832 ELBOW AN822 TEE AN824 TEE AN826 ELBOW AN838 ELBOW AN839 ELBOW AN833 TEE AN834 ELBOW AN837 Figure 9-19. AN standard fittings.

9-11 Hose End Fittings and Minimum Bend Aluminum Steel Tubing Alloy Tubing, Hose Assemblies Radii (inches) Tubing, Bolt Outer Diameter Fitting Bolt Bolt, Fitting, MS28740 or Equivalent Fitting, or Alum. Alloy (inches) or Nut Size or Nut End Fitting Nut Torque Steel 1100-H14 Torque (in–lb) 5052-0 Minimum Maximum (in–lb) –2 20–30 1 ¹⁄8 ³⁄8 –3 ³⁄16 120 70 90–100 30–40 ²¹⁄32 ⁷⁄16 –4 250 100 135–150 40–65 ¹⁄4 ⁹⁄16 ⁷⁄8 –5 ⁵⁄16 420 210 180–200 60–85 1 ¹⁄8 ³⁄4 480 300 270–300 75–125 –6 ³⁄8 1 ⁵⁄16 ¹⁵⁄16 –8 ¹⁄2 850 500 450–500 150–250 1 ³⁄4 1 ¹⁄4 –10 ⁵⁄8 1,150 700 650–700 200–350 2 ³⁄16 1 ¹⁄2 –12 ³⁄4 900–1,000 300–500 2 ⁵⁄8 1 ³⁄4 –14 ⁷⁄8 1,000–1,100 500–600 1 1,200–1,400 500–700 –16 3 ¹⁄2 3 –20 1 ¹⁄4 1,200–1,400 600–900 4 ³⁄8 3 ³⁄4 1 ¹⁄2 –24 5 ¹⁄4 5 1,500–1,800 600–900 –28 1 ³⁄4 850–1,050 6 ¹⁄8 7 2 –32 7 8 950–1,150 Figure 9-20. Flared fitting data.

Figure 9-21. AN flared (left) and MS flareless fitting (right).

damage or completely cut off the tube flare, or it may ruin the commence at the point where the nut just begins to bottom.

sleeve or fitting nut. Failure to tighten sufficiently also may Use a wrench and turn the nut one-sixth turn (one flat on a be serious, as this condition may allow the line to blow out hex nut). Use a wrench on the connector to prevent it from of the assembly or to leak under system pressure. The use of turning while tightening the nut. After the tube assembly torque wrenches and the prescribed torque values prevents is installed, the system should be pressure tested. It is overtightening or undertightening. If a tube fitting assembly is permissible to tighten the nut an additional one-sixth turn tightened properly, it may be removed and retightened many (making a total of one-third turn), should a connection leak.

times before reflaring is necessary. If leakage still occurs after tightening the nut a total of one- third turn, remove the assembly and inspect the components for scores, cracks, presence of foreign material, or damage Flareless Tube Installation from overtightening. Several aircraft manufacturers include Tighten the nut by hand until an increase in resistance to torque values in their maintenance manuals to tighten the turning is encountered. Should it be impossible to run the nut flareless fittings.

down with the fingers, use a wrench, but be alert for the first signs of bottoming. It is important that the final tightening 9-12 SLEEVE UNION ELBOW MS20819 MS21902 MS21904 UNION ADAPTER ADAPTER ELBOW CROSS TEE MS21905 MS21903 MS21900 MS21901 MS21907 MS21906 TEE MS21909 TEE MS21910 TEE MS21911 ELBOW MS21908 SLEEVE NUT BUSHING PLUG MS21922 MS21917 MS21915 MS21913 UNION TEE ADAPTER NUT REDUCER CAP MS21924 MS21912 MS21923 MS21921 MS21916 MS21914 MS 21900 –4 D Material: aluminum alloy Size of fitting in 16ths inch – ⁄ inch Design part number: adapter, flareless tube to AN flared tube Prefix: military specification ELBOW ELBOW MS21925 MS21926 Figure 9-22. Typical MS flareless tube fittings.

9-13 Lower die/holder assembly Nut Body Sleeve Figure 9-23. Flareless fitting.

The following notes, cautions, and faults apply to the installation of rigid tubing.

Note: Overtightening a flareless tube nut drives the cutting edge of the sleeve deeply into the tube, causing the tube to be weakened to the point where normal in-flight vibration could Head assembly cause the tube to shear. After inspection (if no discrepancies are found), reassemble the connections and repeat the pressure test procedures.

Power unit Caution: Never tighten the nut beyond one-third turn (two Hydraulic Tubing flats on the hex nut); this is the maximum the fitting may be tightened without the possibility of permanently damaging Waged Fitting the sleeve and nut.

Common faults: Flare distorted into nut threads; sleeve cracked; flare cracked or split; flare out of round; inside of flare rough or scratched; and threads of nut or union dirty, damaged, or broken.

Rigid Tubing Inspection & Repair Minor dents and scratches in tubing may be repaired.

Scratches or nicks not deeper than 10 percent of the wall thickness in aluminum alloy tubing, which are not in the heel of a bend, may be repaired by burnishing with hand tools. The damage limits for hard, thin-walled corrosion- resistant steel and titanium tubing are considerably less than for aluminum tubing and might depend on the aircraft manufacturer. Consult the aircraft maintenance manual for damage limits. Replace lines with severe die marks, seams, or splits in the tube. Any crack or deformity in a flare is unacceptable and is cause for rejection. A dent of less than Disconnect 20 percent of the tube diameter is not objectionable, unless it is in the heel of a bend. To remove dents, draw a bullet of proper size through the tube by means of a length of cable, Figure 9-24. Swaged fitting tooling.

or push the bullet through a short straight tube by means of a dowel rod. In this case, a bullet is a ball bearing or slug 9-14 TM Figure 9-25. Permaswage fitting.

Figure 9-26. Permalite™ fitting.

normally made of steel or some other hard metal. In the case of soft aluminum tubing, a hard wood slug or dowel may even be used as a bullet. [Figure 9-29] A severely damaged line should be replaced. However, the line may be repaired by cutting out the damaged section and inserting a tube section of the same size and material. Flare both ends of the undamaged and replacement tube sections and make the connection by using standard unions, sleeves, and tube nuts. Aluminum 6061-T6, corrosion-resistant steel 304-1/8h and Titanium 3AL-2.5V tubing can be repaired by swaged fittings. If the damaged portion is short enough, omit the insert tube and repair by using one repair union. [Figure 9-30] When repairing a damaged line, be very careful to remove all chips and burrs. Any open line that is to be left unattended for a Figure 9-27. Cryofit fittings.

period of time should be sealed, using metal, wood, rubber, Incorrect—will damage Do not deflect into place.

flare or threads, or cause Replace tube assembly.

sleeve to crack under vibration if tightened Incorrect—may pull off or distort flare if tightened Correctly fitted and tightened .025 clearance between flare and shoulder before tightening Figure 9-28. Correct and incorrect methods of tightening flared fittings.

9-15 or plastic plugs or caps. Buna-S. Do not use for phosphate ester base hydraulic fluid (Skydrol™).

When repairing a low-pressure line using a flexible fluid connection assembly, position the hose clamps carefully Neoprene to prevent overhang of the clamp bands or chafing of the Neoprene is a synthetic rubber compound that has an tightening screws on adjacent parts. If chafing can occur, acetylene base. Its resistance to petroleum products is not the hose clamps should be repositioned on the hose.

as good as Buna-N, but it has better abrasive resistance. Do Figure 9-31 illustrates the design of a flexible fluid connection not use for phosphate ester base hydraulic fluid (Skydrol™).

assembly and gives the maximum allowable angular and dimensional offset.

Butyl Butyl is a synthetic rubber compound made from petroleum When replacing rigid tubing, ensure that the layout of the new raw materials. It is an excellent material to use with phosphate line is the same as that of the line being replaced. Remove the ester base hydraulic fluid (Skydrol™). Do not use with damaged or worn assembly, taking care not to further damage petroleum products.

or distort it, and use it as a forming template for the new part.

If the old length of tubing cannot be used as a pattern, make Flexible rubber hose consists of a seamless synthetic rubber a wire template, bending the pattern by hand as required for inner tube covered with layers of cotton braid and wire braid the new assembly. Then bend the tubing to match the wire and an outer layer of rubber-impregnated cotton braid. This pattern. Never select a path that does not require bends in type of hose is suitable for use in fuel, oil, coolant, and the tubing. A tube cannot be cut or flared accurately enough hydraulic systems. The types of hose are normally classified so that it can be installed without bending and still be free by the amount of pressure they are designed to withstand from mechanical strain. Bends are also necessary to permit under normal operating conditions: low, medium, and high.

the tubing to expand or contract under temperature changes 1 • Low pressure—below 250 psi. Fabric braid and to absorb vibration. If the tube is small (under ⁄ 4 ") and reinforcement.

can be hand formed, casual bends may be made to allow for this. If the tube must be machine formed, definite bends • Medium pressure—up to 3,000 psi. One wire braid must be made to avoid a straight assembly. Start all bends a reinforcement. Smaller sizes carry up to 3,000 psi.

reasonable distance from the fittings because the sleeves and Larger sizes carry pressure up to 1,500 psi.

nuts must be slipped back during the fabrication of flares and • High pressure—all sizes up to 3,000 psi operating during inspections. In all cases, the new tube assembly should pressures.

be so formed prior to installation that it is not necessary to pull or deflect the assembly into alignment by means of the Flexible hoses used for brake systems have sometimes a coupling nuts.

stainless steel wire braid installed over the hose to protect the hose from damage. [Figure 9-32] Flexible Hose Fluid Lines Flexible hose is used in aircraft fluid systems to connect Hose Identification moving parts with stationary parts in locations subject to Lay lines and identification markings consisting of vibration or where a great amount of flexibility is needed. It lines, letters, and numbers are printed on the hose.

can also serve as a connector in metal tubing systems.

[Figure 9-33] Most hydraulic hose is marked to identify its type, the quarter and year of manufacture, and a 5-digit Hose Materials & Construction code identifying the manufacturer. These markings are in Pure rubber is never used in the construction of flexible fluid contrasting colored letters and numerals that indicate the lines. To meet the requirements of strength, durability, and workability, among other factors, synthetics are used in place of pure rubber. Synthetic materials most commonly used in Cable Dent the manufacture of flexible hose are Buna-N, neoprene, butyl, ethylene propylene diene rubber (EPDM) and Teflon™.

While Teflon™ is in a category of its own, the others are synthetic rubber.

Bullet Buna-N Buna-N is a synthetic rubber compound that has excellent Figure 9-29. Dent removal using a bullet.

resistance to petroleum products. Do not confuse with 9-16

Next: section. If 2 cuts are required, the distance between them →

Section 19

Type of Failure Repair Method a. Make 1 or 2 cuts, as necessary, to remove damaged 1. Pin hole leak or circumferential crack in tubing.

section. If 2 cuts are required, the distance between them shall not exceed 0.30". If distance is more than 0.30", go to repair method 2.

b. Swage 1 tube-to-tube union in tube section under repair.

Not to exceed 0.30" a. Make 2 cuts to enable removal of damaged section.

2. Longitudinal crack in tubing (crack length in excess of 0.30").

b. Remove damaged section and duplicate.

c. Swage replacement section into tubing under repair using 2 New section tube-to-tube unions.

Original tubing a. Cut out defective tee or elbow.

3. Leaking tee or elbow (permanent tube connection type).

b. Duplicate tubing sections for each branch.

c. Swage splice sections to tee or elbow.

d. Connect each splice section to tubing under repair using a tube-to-tube union.

a. Cut tubing to remove defective fitting.

4. Leaking flared, flareless, or lipseal end fittings.

b. Swage appropriate end fitting to tube end.

c. Connect new end fitting to mating connection, torquing nut as required.

Figure 9-30. Permaswage™ repair.

natural lay (no twist) of the hose and are repeated at intervals limitless. Teflon™ hose is flexible and designed to meet the of not more than 9 inches along the length of the hose. Code requirements of higher operating temperatures and pressures markings assist in replacing a hose with one of the same in present aircraft systems. Generally, it may be used in the specifications or a recommended substitute. Hose suitable same manner as rubber hose. Teflon™ hose is processed and for use with phosphate ester base hydraulic fluid is marked extruded into tube shape to a desired size. It is covered with Skydrol™ use. In some instances, several types of hose stainless steel wire, which is braided over the tube for strength may be suitable for the same use. Therefore, to make the and protection. Teflon™ hose is unaffected by any known correct hose selection, always refer to the applicable aircraft fuel, petroleum, or synthetic base oils, alcohol, coolants, maintenance or parts manual. or solvents commonly used in aircraft. Teflon™ hose has the distinct advantages of a practically unlimited storage Teflon™ is the DuPont trade name for tetrafluoroethylene time, greater operating temperature range, and broad usage resin. It has a broad operating temperature range (−65 °F to (hydraulic, fuel, oil, coolant, water, alcohol, and pneumatic +450 °F). It is compatible with nearly every substance or systems). Medium-pressure Teflon™ hose assemblies are agent used. It offers little resistance to flow; sticky, viscous sometimes preformed to clear obstructions and to make materials do not adhere to it. It has less volumetric expansion connections using the shortest possible hose length. Since than rubber, and the shelf and service life is practically preforming permits tighter bends that eliminate the need for 9-17 (A) MIL-H-8794 Type Hose Clamps ¼" Min.

Two cotton braids—impregnated with synthetic compound G. ref Hose number Hose size MIL-H-8794: SIZE-6-2/90 Mfg Symbol Fitting Hose Tubing 3° Max. angular deviation Single wire braid Synthetic inner tube Quarter and year of manufacturer " Max. offset Minimum gap “G” shall be ½" or Tube OD/4 (B) MIL-H-6000 Type Hose (Views showing opposite side of hose) Figure 9-31. Flexible fluid connection assembly.

Hose size Mfg Symbol MIL-H-6000-SIZE-3-4/90 Quarter and year of manufacturer (C) MIL-H-5593 Type Hose Lay lines Hose size MIL-H-5593-6-4/90 Mfg Symbol Figure 9-32. Flexible hose with stainless braid.

Quarter and year of manufacturer special elbows, preformed hose assemblies save space and weight. Never straighten a preformed hose assembly. Use a support wire if the hose is to be removed for maintenance.

(D) MIL-H-27267 Type Hose (E) MIL-H-83797 Type Hose [Figure 9-34] Flexible Hose Inspection Check the hose and hose assemblies for deterioration at each Figure 9-33. Hose identification markings.

inspection period. Leakage, separation of the cover or braid from the inner tube, cracks, hardening, lack of flexibility, or equipped with reusable end fittings, a replacement line can be excessive “cold flow” are apparent signs of deterioration and fabricated with the use of such tooling as may be necessary to reason for replacement. The term “cold flow” describes the comply with the assembly instructions of the manufacturer.

deep, permanent impressions in the hose produced by the pressure of hose clamps or supports.

Fabrication & Replacement of Flexible Hose To make a hose assembly, select the proper size hose and When failure occurs in a flexible hose equipped with swaged end fitting. [Figure 9-35] MS-type end fittings for flexible end fittings, the entire assembly must be replaced. Obtain a hose are detachable and may be reused if determined to be new hose assembly of the correct size and length, complete serviceable. The inside diameter of the fitting is the same with factory installed end fittings. When failure occurs in hose as the inside diameter of the hose to which it is attached.

[Figure 9-36] 9-18 Support wire 1. Place hose in vise and cut 2. Locate length of hose to to desired length using be cut off and slit cover fine tooth hacksaw or cut with knife to wire braid, off wheel. taking care to not damage underlying materials. After slitting cover, twist off with pair of pliers. (See note below.)

Figure 9-34. Suggested handling of preformed hose.

3. Place hose in vise and 4. *Lubricate inside of hose Flexible Hose Testing screw socket on hose and nipple threads liberally.

counterclockwise.

All flexible hose must be proof-tested after assembly and NOTE: Hose assemblies applying pressure to the inside of the hose assembly. The fabricated per MIL-H-8790 proof-test medium may be a liquid or gas. For example, must have the exposed wire braid coated with a special hydraulic, fuel, and oil lines are generally tested using sealant.

hydraulic oil or water, whereas air or instrument lines NOTE: Step 2 applies to high- are tested with dry, oil-free air or nitrogen. When testing pressure hose only.

with a liquid, all trapped air is bled from the assembly prior to tightening the cap or plug. Hose tests, using a gas, *CAUTION: Do not use any petroleum product with hose are conducted underwater. In all cases, follow the hose designed for synthetic fluids manufacturer’s instructions for proof-test pressure and 5. Screw nipple into socket (Skydrol™ and/or HYJET using wrench on hex of fluid to be used when testing a specific hose assembly.

product). For a lubricant nipple and leave .005" to during assembly, use a [Figure 9-37] .031" clearance between vegetable soap liquid.

nipple hex and socket.

Disassemble in reverse order.

When a flexible hose has been repaired or overhauled using existing hardware and new hose material, and before the hose is installed on the aircraft, it is recommended that the hose be Figure 9-35. Assembly of MS fitting to flexible hose.

tested to at least 1.5 system pressure. A hydraulic hose burst test stand is used for testing flexible hose. [Figure 9-38] A new hose can be operationally checked after it is installed in the aircraft using system pressure.

Size Designations Hose is also designated by a dash number according to its size. The dash number is stenciled on the side of the hose and indicates the size tubing with which the hose is compatible.

It does not denote inside or outside diameter. When the dash number of the hose corresponds with the dash number of the tubing, the proper size hose is being used. [Figure 9-33] Figure 9-36. MS-type end fitting.

9-19 Single Wire Braid Fabric Covered Tube Size Hose Size Hose Size Recomm. Min. Burst Max. Proof Min. Bend OD ID OD Operating Pressure Pressure Radius MIL. Part No.

(inches) (inches) (inches) Pressure (PSI) (PSI) (PSI) (inches) MIL-H-8794-3-L ³⁄16 ¹⁄8 .45 3,000 12,000 6,000 3.00 MIL-H-8794-4-L ¹⁄4 ³⁄16 .52 3,000 12,000 6,000 3.00 MIL-H-8794-5-L ⁵⁄16 ¹⁄4 .58 3,000 10,000 5,000 3.38 MIL-H-8794-6-L ³⁄8 ⁵⁄16 .67 2,000 9,000 4,500 4.00 MIL-H-8794-8-L ¹⁄2 ¹³⁄32 .77 2,000 8,000 4,000 4.63 MIL-H-8794-10-L ⁵⁄8 ¹⁄2 .92 1,750 7,000 3,500 5.50 MIL-H-8794-12-L ³⁄4 ⁵⁄8 1.08 1,750 6,000 3,000 6.50 MIL-H-8794-16-L 1 ⁷⁄8 1.23 800 3,200 1,600 7.38 MIL-H-8794-20-L 1 ¹⁄4 1 ¹⁄8 1.50 600 2,500 1,250 9.00 MIL-H-8794-24-L 1 ¹⁄2 1 ³⁄8 1.75 500 2,000 1,000 11.00 MIL-H-8794-32-L 2 1 ¹³⁄16 2.22 350 1,400 700 13.25 MIL-H-8794-40-L 2 ¹⁄2 2 ³⁄8 2.88 200 1,000 300 24.00 MIL-H-8794-48-L 3 3 3.56 200 800 300 33.00 Construction: Seamless synthetic rubber inner tube reinforced Operating Temperatures: with one fiber braid, one braid of high tensile steel wire and Sizes 3 through 12: − 65 °F to + 250 °F covered with an oil resistant rubber impregnated fiber braid. Sizes 16 through 48: − 40 °F to + 275 °F Identification: Hose is identified by specification number, Note: Maximum temperatures and pressures should not be size number, quarter year and year, hose manufacturer’s used simultaneously.

identification.

Uses: Hose is approved for use in aircraft hydraulic, pneumatic, coolant, fuel, and oil systems.

Multiple Wire Braid Rubber Covered Tube Size Hose Size Hose Size Recomm. Min. Burst Max. Proof Min. Bend OD ID OD Operating Pressure Pressure Radius MIL. Part No.

(inches) (inches) (inches) Pressure (PSI) (PSI) (PSI) (inches) MIL-H-8788- 4-L ¹⁄4 ⁷⁄32 .63 3,000 16,000 8,000 3.00 ⁹⁄32 MIL-H-8788- 5-L ⁵⁄16 .70 3,000 14,000 7,000 3.38 ¹¹ MIL-H-8788- 6-L ³⁄8 ⁄32 .77 3,000 14,000 7,000 5.00 ⁷⁄16 MIL-H-8788- 8-L ¹⁄2 .86 3,000 14,000 7,500 5.75 ⁹⁄16 MIL-H-8788-10-L ⁵⁄8 1.03 3,000 12,000 6,000 6.50 ¹¹ MIL-H-8788-12-L ³⁄4 ⁄16 1.22 3,000 12,000 6,000 7.75 MIL-H-8788-16-L 1 ⁷⁄8 1.50 3,000 10,000 5,000 9.63 Construction: Seamless synthetic rubber inner tube reinforced Uses: High pressure hydraulic, pneumatic, coolant, fuel and oil.

with one fiber braid, two or more steel wire braids, and Operating Temperatures: − 65 °F to + 200 °F covered with synthetic rubber cover (for gas applications request perforated cover).

Identification: Hose is identified by specification number, size number, quarter year and year, hose manufacturer’s identification.

Figure 9-37. Aircraft hose specifications.

9-20 Spur Nipple Socket Reinforcement Sheath Figure 9-38. Hydraulic hose burst test stand.

Hose Fittings Flexible hose may be equipped with either swaged fittings or Figure 9-39. Reusable fittings for medium-pressure hose.

detachable fittings, or they may be used with beads and hose clamps. Hoses equipped with swaged fittings are ordered by stripe running along its length. This stripe should not spiral correct length from the manufacturer and ordinarily cannot around the hose.

be assembled by the mechanic. They are swaged and tested at the factory and are equipped with standard fittings. The Bending detachable fittings used on flexible hoses may be detached To avoid sharp bends in the hose assembly, use elbow and reused if they are not damaged; otherwise, new fittings fittings, hose with elbow-type end fittings, or the appropriate must be used. [Figure 9-39] bend radii. Bends that are too sharp reduce the bursting pressure of flexible hose considerably below its rated value.

Installation of Flexible Hose Assemblies [Figure 9-40] Slack Hose assemblies must not be installed in a manner that causes Clearance a mechanical load on the hose. When installing flexible hose, The hose assembly must clear all other lines, equipment, and provide slack or bend in the hose line from 5 to 8 percent of adjacent structure under every operating condition.

its total length to provide for changes in length that occurs when pressure is applied. Flexible hose contracts in length Flexible hose should be installed so that it is subject to a and expands in diameter when pressurized. Protect all flexible minimum of flexing during operation. Although hose must hoses from excessive temperatures, either by locating the lines be supported at least every 24 inches, closer supports are so they are not affected or by installing shrouds around them.

desirable. Flexible hose must never be stretched tightly between two fittings. If clamps do not seal at specified Flex tightening, examine hose connections and replace parts as When hose assemblies are subject to considerable vibration necessary. The above is for initial installation and should not or flexing, sufficient slack must be left between rigid fittings.

be used for loose clamps.

Install the hose so that flexure does not occur at the end fittings. The hose must remain straight for at least two hose For retightening loose hose clamps in service, proceed as diameters from the end fittings. Avoid clamp locations that follows: restrict or prevent hose flexure.

• Non-self-sealing hose—if the clamp screw cannot be tightened with the fingers, do not disturb unless Twisting leakage is evident. If leakage is present, tighten one- Hoses must be installed without twisting to avoid possible fourth turn.

rupture of the hose or loosening of the attaching nuts. Use of • Self-sealing hose—if looser than finger-tight, tighten swivel connections at one or both ends relieve twist stresses.

to finger-tight and add one-fourth turn. [Figure 9-41] Twisting of the hose can be determined from the identification 9-21 Planning Hose Line Installations Wrong Right Wrong Right 1. Provide slack or bend in the hose line to provide for changes 2. Observe linear stripe. The hose must not be twisted. High in length that will occur when pressure is applied. pressures applied to a twisted hose may cause failure or loosen the nut.

Right Wrong Wrong Right 3. Relieve sharp bends, avoid strain or hose collapse, and make cleaner installations by using Aeroquip elbows or other adapter fittings. Provide as large a bend radius as possible.

Never use less than the recommended minimum bend radius specified for the hose.

4. Provide additional bend radius when lines are subject to flexing and remember that the metal end fittings are not flexible. Place line support clamps so as not to restrict hose flexing.

Figure 9-40. Flexible hose installation.

Clamps— Initial Worm screw type radial and other Installation clamp (10 threads type (28 threads Only per inch) Hose Clamps per inch) To ensure proper sealing of hose connections and to prevent Self-sealing hose Finger-tight plus Finger-tight plus 2 breaking hose clamps or damaging the hose, follow the hose approximately 2½ complete complete turns clamp tightening instructions carefully. When available, use 15 in-lb turns the hose clamp torque-limiting wrench. These wrenches All other Finger-tight plus are available in calibrations of 15 and 25 in-lb limits. In the aircraft hose Finger-tight plus 2 1¼ complete approximately complete turns absence of torque-limiting wrenches, follow the finger-tight- turns 25 in-lb plus-turns method. Because of the variations in hose clamp design and hose structure, the values given in Figure 9-41 are Figure 9-41. Hose clamp tightening.

approximate. Therefore, use good judgment when tightening hose clamps by this method. Since hose connections are subject [Figure 9-42] The plain clamp is used to secure lines in areas to “cold flow” or a setting process, a follow-up tightening not subject to vibration.

check should be made for several days after installation.

A Teflon™-cushioned clamp is used in areas where the Support clamps are used to secure the various lines to the deteriorating effect of Skydrol™, hydraulic fluid, or fuel airframe or powerplant assemblies. Several types of support is expected. However, because it is less resilient, it does clamps are used for this purpose. The most commonly not provide as good a vibration-damping effect as other used clamps are the rubber-cushioned and plain. The cushion materials.

rubber-cushioned clamp is used to secure lines subject to vibration; the cushioning prevents chafing of the tubing.

9-22 Use bonded clamps to secure metal hydraulic, fuel, or oil lines in place. Unbonded clamps should be used only for securing wiring. Remove any paint or anodizing from the portion of the tube at the bonding clamp location. Make certain that clamps are of the correct size. Clamps or supporting clips smaller than the outside diameter of the hose may restrict the flow of fluid through the hose. All fluid lines must be secured at specified intervals. The maximum distance between supports for rigid tubing is shown in Figure 9-43.

Support tube at least / 4 " from edge of hole Grommet Figure 9-42. Rubber-cushioned clamp.

Distance Between Supports (in.)

Tube OD (in.)

Aluminum Alloy Steel ¹⁄8 9 ¹⁄2 11 ¹⁄2 ³⁄16 12 14 ¹⁄4 13 ¹⁄2 16 ⁵⁄16 15 18 ³⁄8 16 ¹⁄2 20 ¹⁄2 19 23 ⁵⁄8 22 25 ¹⁄2 ³⁄4 24 27 ¹⁄2 1 26 ¹⁄2 30 Figure 9-43. Maximum distance between supports for fluid tubing.

9-23

Next: Chapter 10 →

Chapter 10

Inspection Concepts & Techniques

Inspections are visual examinations and manual checks to determine the condition of an aircraft or component. An Aircraft operating under the flight hour system are inspected aircraft inspection can range from a casual walk around to a when a specified number of flight hours are accumulated.

detailed inspection involving complete disassembly and the Components with stated hourly operating limitations are use of complex inspection aids. normally replaced during the inspection that falls nearest the hourly limitation.

An inspection system consists of several processes, including reports made by mechanics, the pilot, or crew flying an Basic Inspection aircraft and regularly scheduled inspections of an aircraft. An Techniques/Practices inspection system is designed to maintain an aircraft in the Before starting an inspection, be certain all plates, access best possible condition. Thorough and repeated inspections doors, fairings, and cowling have been opened or removed must be considered the backbone of a good maintenance and the structure cleaned. When opening inspection plates program. Irregular and haphazard inspections invariably and cowling, and before cleaning the area, take note of any result in gradual and certain deterioration of an aircraft. The oil or other evidence of fluid leakage.

time spent repairing an abused aircraft often totals far more than any time saved in hurrying through routine inspections Preparation and maintenance.

In order to conduct a thorough inspection, a great deal of paperwork and/or reference information must be accessed It has been proven that regularly scheduled inspections and and studied before proceeding to the aircraft to conduct the preventive maintenance assure airworthiness. Operating inspection. The aircraft logbooks must be reviewed to provide failures and malfunctions of equipment are appreciably background information and a maintenance history of the reduced if excessive wear or minor defects are detected particular aircraft. The appropriate checklist or checklists and corrected early. The importance of inspections and the must be utilized to ensure that no items are forgotten or proper use of records concerning these inspections cannot overlooked during the inspection. Also, many additional be overemphasized.

publications must be available, either in hard copy or in electronic format, to assist in the inspections. These additional Airframe and engine inspections may range from preflight publications may include information provided by the aircraft inspections to detailed inspections. The time intervals for the and engine manufacturers, appliance manufacturers, parts inspection periods vary with the models of aircraft involved vendors, and the Federal Aviation Administration (FAA).

and the types of operations being conducted. The airframe and engine manufacturer’s instructions should be consulted Aircraft Logs when establishing inspection intervals.

“Aircraft logs,” as used in this handbook, is an inclusive term that applies to the aircraft logbook and all supplemental Aircraft may be inspected using a flight hours inspection records concerned with the aircraft. They may come in a system, a calendar inspection system, or a combination of variety of formats. For a small aircraft, the log may indeed both. Under the calendar inspection system, the appropriate be a small 5" × 8" logbook. For larger aircraft, the logbooks inspection is performed on the expiration of a specified are often larger and in the form of a three-ring binder. Aircraft number of calendar weeks. The calendar inspection system that have been in service for a long time are likely to have is an efficient system from a maintenance management several logbooks.

standpoint. Scheduled replacement of components with stated hourly operating limitations is normally accomplished during The aircraft logbook is the record where all data concerning the calendar inspection falling nearest the hourly limitation.

the aircraft is recorded. Information gathered in this log is In some instances, a flight hour limitation is established used to determine the aircraft condition, date of inspections, to limit the number of hours that may be flown during the time on airframe, engines, and propellers. It reflects a calendar interval.

10-1 history of all significant events occurring to the aircraft, its a. Engine section—for visual evidence of excessive components, and accessories. Additionally, it provides a place oil, fuel, hydraulic leaks, and sources of such for indicating compliance with FAA airworthiness directives leaks.

(ADs) or manufacturers’ service bulletins (SB). The more b. Studs and nuts—for proper torquing and obvious comprehensive the logbook, the easier it is to understand the defects.

aircraft’s maintenance history.

c. Internal engine—for cylinder compression and for metal particles or foreign matter on screens When the inspections are completed, appropriate entries and sump drain plugs. If cylinder compression is must be made in the aircraft logbook certifying that the weak, check for improper internal condition and aircraft is in an airworthy condition and may be returned to improper internal tolerances.

service. When making logbook entries, exercise special care to ensure that the entry can be clearly understood by anyone d. Engine mount—for cracks and looseness of having a need to read it in the future. Also, if making a mounting.

hand-written entry, use good penmanship and write legibly.

e. Flexible vibration dampeners—for condition and To some degree, the organization, comprehensiveness, and deterioration.

appearance of the aircraft logbooks have an impact on the f. Engine controls—for defects, proper travel, and value of the aircraft. High quality logbooks can mean a proper safetying.

higher value for the aircraft.

g. Lines, hoses, and clamps—for leaks, condition, Checklists and looseness.

Always use a checklist when performing an inspection.

h. Exhaust stacks—for cracks, defects, and proper The checklist may be of your own design, one provided attachment.

by the manufacturer of the equipment being inspected, or i. Accessories—for apparent defects in security of one obtained from some other source. The checklist should mounting.

include the following: j. All systems—for proper installation, general 1. Fuselage and Hull Group condition defects, and secure attachment.

a. Fabric and skin—for deterioration, distortion, k. Cowling—for cracks and defects.

other evidence of failure, and defective or insecure attachment of fittings. l. Ground run-up and functional check—check all powerplant controls and systems for correct b. Systems and components—for proper installation, response, all instruments for proper operation apparent defects, and satisfactory operation.

and indication.

c. Envelope gas bags, ballast tanks, and related 4. Landing Gear Group parts—for condition.

a. All units—for condition and security of 2. Cabin and Cockpit Group attachment.

a. General—for cleanliness and loose equipment b. Shock absorbing devices—for proper oleo fluid that needs to be secured.

level.

b. Seats and safety belts—for condition and security.

c. Linkage, trusses, and members—for undue or c. Windows and windshields—for deterioration and excessive wear, fatigue, and distortion.

breakage.

d. Retracting and locking mechanism—for proper d. Instruments—for condition, mounting, marking, operation.

and (where practicable) for proper operation.

e. Hydraulic lines—for leakage.

e. Flight and engine controls—for proper installation f. Electrical system—for chafing and proper and operation.

operation of switches.

f. Batteries—for proper installation and charge.

g. Wheels—for cracks, defects, and condition of g. All systems—for proper installation, general bearings.

condition, apparent defects, and security of h. Tires—for wear and cuts.

attachment.

i. Brakes—for proper adjustment.

3. Engine and Nacelle Group j. Floats and skis—for security of attachment and 10-2 obvious defects. b. Parachutes, life rafts, flares, and so forth— inspect in accordance with the manufacturer’s 5. Wing and Center Section recommendations.

a. All components—for condition and security.

c. Autopilot system—for general condition, security b. Fabric and skin—for deterioration, distortion, of attachment, and proper operation.

other evidence of failure, and security of attachment.

Publications c. Internal structure (spars, ribs, compression Aeronautical publications are the sources of information members)—for cracks, bends, and security.

for guiding aviation mechanics in the operation and maintenance of aircraft and related equipment. The d. Movable surfaces—for damage or obvious proper use of these publications greatly aid in the defects, unsatisfactory fabric or skin attachment, efficient operation and maintenance of all aircraft. These and proper travel.

include manufacturers’ SBs, manuals, and catalogs; FAA e. Control mechanism—for freedom of movement, regulations; ADs; advisory circulars (ACs); and aircraft, alignment, and security.

engine, and propeller specifications.

f. Control cables—for proper tension, fraying, wear, and proper routing through fairleads and pulleys.

Manufacturers’ Service Bulletins/Instructions Service bulletins or service instructions are two of several 6. Empennage Group types of publications issued by airframe, engine, and a. Fixed surfaces—for damage or obvious defects, component manufacturers. The bulletins may include: loose fasteners, and security of attachment.

purpose for issuing the publication; name of the applicable b. Movable control surfaces—for damage or airframe, engine, or component; detailed instructions for obvious defects, loose fasteners, loose fabric, or service, adjustment, modification or inspection, and source skin distortion.

of parts, if required; and estimated number of man-hours required to accomplish the job.

c. Fabric or skin—for abrasion, tears, cuts, defects, distortion, and deterioration.

Maintenance Manual 7. Propeller Group The manufacturer’s aircraft maintenance manual contains a. Propeller assembly—for cracks, nicks, bends, and complete instructions for maintenance of all systems and oil leakage. components installed in the aircraft. It contains information for the mechanic who normally works on components, b. Bolts—for proper torquing and safe tying.

assemblies, and systems while they are installed in the c. Anti-icing devices—for proper operation and aircraft, but not for the overhaul mechanic. A typical aircraft obvious defects.

maintenance manual contains: d. Control mechanisms—for proper operation, • A description of the systems (i.e., electrical, hydraulic, secure mounting, and travel.

fuel, control) 8. Communication and Navigation Group • Lubrication instructions setting forth the frequency and the lubricants and fluids that are to be used in the a. Radio and electronic equipment—for proper installation and secure mounting. various systems b. Wiring and conduits—for proper routing, secure • Pressures and electrical loads applicable to the various systems mounting, and obvious defects.

• Tolerances and adjustments necessary to proper c. Bonding and shielding—for proper installation and condition. functioning of the airplane d. Antennas—for condition, secure mounting, and • Methods of leveling, raising, and towing proper operation.

• Methods of balancing control surfaces 9. Miscellaneous • Identification of primary and secondary structures a. Emergency and first aid equipment—for general • Frequency and extent of inspections necessary to the condition and proper stowage.

proper operation of the airplane 10-3 • Special repair methods applicable to the airplane unsafe conditions and to prescribe the conditions that the product may continue to be operated. Furthermore, these • Special inspection techniques requiring x-ray, are federal aviation regulations and must be complied with ultrasonic, or magnetic particle inspection unless specific exemption is granted.

• A list of special tools There are two categories of ADs: Overhaul Manual 1. Those of an emergency nature requiring immediate The manufacturer’s overhaul manual contains brief compliance upon receipt.

descriptive information and detailed step-by-step instructions covering work normally performed on a unit that has been 2. Those of a less urgent nature requiring compliance within a relatively longer period of time.

removed from the aircraft. Simple, inexpensive items, such as switches and relays where overhaul is uneconomical, are not covered in the overhaul manual.

Also, ADs may be a one-time compliance item or a recurring item that requires future inspection on an hourly basis (accrued Structural Repair Manual flight time since last compliance) or a calendar time basis.

The structural repair manual contains the manufacturer’s information and specific instructions for repairing primary The contents of ADs include the aircraft, engine, propeller, or and secondary structures. Typical skin, frame, rib, and stringer appliance model and serial numbers affected. Also, included repairs are covered in this manual. Also, included are material are the compliance time or period, a description of the and fastener substitutions and special repair techniques.

difficulty experienced, and the necessary corrective action.

Illustrated Parts Catalog Type Certificate Data Sheets (TCDS) The illustrated parts catalog presents component breakdowns The type certificate data sheet (TCDS) describes the type of structure and equipment in disassembly sequence. Also, design and sets forth the limitations prescribed by the included are exploded views or cutaway illustrations for all applicable CFR part. It also includes any other limitations parts and equipment manufactured by the aircraft manufacturer.

and information found necessary for type certification of a particular model aircraft. [Figure 10-1] Wiring Diagram Manual The wiring diagram manual is a collection of diagrams, All TCDS are numbered in the upper right corner of each drawings, and lists that define the wiring and hook up of page. This number is the same as the type certificate number.

associated equipment installed on airplanes. The data is The name of the type certificate holder, together with all of organized in accordance with the Air Transport Association the approved models, appears immediately below the type ATA iSPec 2200 specification.

certificate number. The issue date completes this group. This information is contained within a bordered text box to set it off.

Code of Federal Regulations (CFRs) The Code of Federal Regulations (CFRs) were established The TCDS is separated into one or more sections. Each by law to provide for the safe and orderly conduct of section is identified by a Roman numeral followed by the flight operations and to prescribe airmen privileges and model designation of the aircraft that the section pertains. The limitations. A knowledge of the CFRs is necessary during the category or categories that the aircraft can be certificated in performance of maintenance, since all work done on aircraft are shown in parentheses following the model number. Also, must comply with CFR provisions. included is the approval date shown on the type certificate.

Airworthiness Directives (ADs) The data sheet contains information regarding: A primary safety function of the FAA is to require correction 1. Model designation of all engines that the aircraft of unsafe conditions found in an aircraft, aircraft engine, manufacturer obtained approval for use with this propeller, or appliance when such conditions exist and are model aircraft.

likely to exist or develop in other products of the same 2. Minimum fuel grade to be used.

design. The unsafe condition may exist because of a design defect, maintenance, or other causes. Title 14 of the CFR 3. Maximum continuous and takeoff ratings of the part 39, Airworthiness Directives, defines the authority approved engines, including manifold pressure (when and responsibility of the administrator for requiring the used), rotations per minute (rpm), and horsepower (hp).

necessary corrective action. The ADs are published to 4. Name of the manufacturer and model designation for notify aircraft owners and other interested persons of each propeller that the aircraft manufacturer obtained 10-4 approval is shown together with the propeller limits aircraft must be inspected before each flight. More detailed and any operating restrictions peculiar to the propeller inspections must be conducted by aviation maintenance or propeller engine combination. technicians (AMTs at least once each 12 calendar months, while inspection is required for others after each 100 hours 5. Airspeed limits in both miles per hour (mph) and knots.

of flight. In other instances, an aircraft may be inspected in 6. Center of gravity (CG) range for the extreme loading accordance with a system set up to provide for total inspection conditions of the aircraft is given in inches from the of the aircraft over a calendar or flight time period. These datum. The range may also be stated in percent of include phase-type inspections.

mean aerodynamic chord (%MAC) for transport category aircraft.

To determine the specific inspection requirements and rules for the performance of inspections, refer to the CFR 7. Empty weight center of gravity (EWCG) range (when that prescribes the requirements for the inspection and established) is given as fore and aft limits in inches maintenance of aircraft in various types of operations.

from the datum. If no range exists, the word “none” is shown following the heading on the data sheet.

Preflight/Postflight Inspections 8. Location of the datum.

Pilots are required to follow a checklist contained within 9. Means provided for leveling the aircraft.

the Pilot’s Operating Handbook (POH) when operating aircraft. The first section of the checklist is entitled “Preflight 10. All pertinent maximum weights.

Inspection.” The preflight inspection checklist includes 11. Number of seats and their moment arms.

a “walk-around” section listing items that the pilot is to 12. Oil and fuel capacity.

visually check for general condition as they walk around the airplane. Also, the pilot must ensure that fuel, oil, and 13. Control surface movements.

other items required for flight are at the proper levels and not 14. Required equipment.

contaminated. Additionally, it is the pilot’s responsibility to 15. Additional or special equipment found necessary for review the aircraft maintenance records, and other required certification.

paperwork to verify that the aircraft is indeed airworthy. After each flight, it is recommended that the pilot or mechanic 16. Information concerning required placards.

conduct a postflight inspection to detect any problems that might require repair or servicing before the next flight.

It is not within the scope of this handbook to list all the items that can be shown on the TCDS. Those items listed above Annual/100-Hour Inspections serve only to acquaint aviation mechanics with the type of The basic requirements for annual and 100-hour inspections are information generally included on the data sheets. TCDS discussed in 14 CFR part 91. With some exceptions, all aircraft may be many pages in length.

must have a complete inspection annually. Aircraft that are used for commercial purposes (carrying any person, other than a When conducting a required or routine inspection, it is crewmember, for hire or flight instruction for hire) and are likely necessary to ensure that the aircraft and all the major items to be used more frequently than noncommercial aircraft must on it are as defined in the TCDS. The inspector ensures that have this complete inspection every 100 hours. The scope and all installed aircraft equipment conforms to the TCDS. This detail of items to be included in annual and 100-hour inspections is called a conformity check and verifies that the aircraft is included as Appendix D to part 43. [Figure 10-2] conforms to the specifications of the aircraft as it was originally certified. Sometimes alterations are made that are A properly written checklist, such as the one shown earlier in not specified or authorized in the TCDS. When that condition this chapter, includes all the items of Appendix D. Although exists, a supplemental type certificate (STC) is issued. STCs the scope and detail of annual and 100-hour inspections are are considered a part of the permanent records of an aircraft identical, there are two significant differences. One difference and should be maintained as part of that aircraft’s logs.

involves persons authorized to conduct them. A certified airframe and powerplant (A&P) maintenance technician can Routine/Required Inspections conduct a 100-hour inspection, whereas an annual inspection For the purpose of determining their overall condition, 14 must be conducted by a certified A&P maintenance technician CFR provides for the inspection of all civil aircraft at specific with inspection authorization (IA). The other difference intervals, depending generally upon the type of operations involves authorized overflight of the maximum 100 hours that they are engaged in. The pilot-in-command (PIC) before inspection. An aircraft may be flown up to 10 hours of a civil aircraft is responsible for determining whether beyond the 100-hour limit if necessary to fly to a destination that aircraft is in a condition for safe flight. Therefore, the 10-5 DEPARTMENT OF TRANSPORTATION FEDERAL AVIATION ADMINISTRATION A27EU Revision 4 AIRBUS DEFENCE AND SPACE GMBH EADS DEUTSCHLAND GMBH DAIMLER CHRYSLER AEROSPACE AG DAIMLER-BENZ AEROSPACE AG DEUTSCHE AEROSPACE AG MESSERSCHMITT-BÖLKOW-BLOHM AG MESSERSCHMITT-BÖLKOW-BLOHM GMBH BO-209-150 FV & RV BO-209-160 FV & RV BO-209-150 FF July 9, 2015 TYPE CERTIFICATE DATA SHEET NO. A27EU This data sheet, which is a part of Type Certificate No. A27EU, prescribes conditions and limitations under which the product for which the Type Certificate was issued meets the airworthiness requirements of the Federal Aviation Regulations.

Type Certificate Holder Airbus Defence and Space GmbH Willy-Messerschmitt-Strasse 1 85521 Ottobrunn Germany Type Certificate Ownership Record Messerschmitt-Bölkow-Blohm GmbH transferred TC A27EU to Messerschmitt-Bölkow- Blohm AG on April 1, 1992 (See NOTE 4.)

Messerschmitt-Bölkow-Blohm AG transferred TC A27EU to Deutsche Aerospace AG on November 30, 1992 Deutsche Aerospace AG transferred TC A27EU to Daimler-Benz Aerospace AG on January 2, 1995 Daimler-Benz Aerospace AG transferred TC A27EU to Daimler Chrysler Aerospace AG on November 17, 1998 Daimler Chrysler Aerospace AG transferred TC A27EU to EADS Deutschland GmbH on July 10, 2000 EADS Deutschland GmbH transferred TC A27EU to Airbus Defence and Space GmbH on July 1, 2014 (See NOTE 7.)

I - Model BO-209-150 FV and RV, 2 PCLM (Normal and Utility Category), approved 9 July 1971 (FV model has fixed nose L.g.; RV model has retractable nose L.g.).

Engine Lycoming O-320-E1C or O-320-E1F Fuel 80/87 minimum grade aviation gasoline Engine limits For all operations, 2700 r.p.m. (150 hp.)

Propeller and Hartzell HC-C2YL-1B/7663A-6 propeller limits Diameter: 70 in. no further reduction permitted Pitch setting at 30 in. radius: High 27° Low 12°12' Spinner: MBB P/N 209-61056 Governor: Woodward P/N T210452 or P/N 210681 Page No. 1 2 3 4 5 6 Rev. No. 4 - - 4 2 4 Figure 10-1. Type certificate data sheet (TCDS).

10-6 2 A27EU Airspeed limits (CAS) Normal and Utility Category Never exceed 173 knots (199 m.p.h.)

Maximum structural cruising 135 knots (155 m.p.h.)

Maneuvering 117 knots (135 m.p.h.)

Flaps extended 88 knots (101 m.p.h.)

*Landing gear operation 104 knots (120 m.p.h.)

*Landing gear extended 173 knots (199 m.p.h.)

(*Applies only to the RV model).

C.G. range Normal Category (85.47) to (89.37) at 1265 lb. or less (86.92) to (89.37) at 1808 lb.

Utility Category (85.47) to (89.37) at 1265 lb. or less (86.25) to (89.37) at 1565 Maximum weight 1808 lb., for Normal Category 1565 lb., for Utility Category No. of seats 2 at (+ 90.7) Maximum baggage 110 lb. at (+114.2) Fuel capacity 39.2 gal. total (38.6 gal. usable; two 19.6 gal., wing tanks at + 90.7) Oil capacity 8 qt. (+3.94) See NOTE 1 for unusable fuel and undrainable oil data.

II - Model BO-209-160 FV and RV, 2 PCLM (Normal and Utility Category), approved 9 July 1971 (FV model has fixed nose L.g.; RV model has retractable nose L.g.).

Engine Lycoming IO-320-D1A or IO-320-D1B Fuel 100/130 minimum grade aviation gasoline Engine limits For all operations, 2700 r.p.m. (160 hp.)

Propeller and Hartzell HC-C2YL-1B/7663A-6 propeller limits Diameter: 70 in. no further reduction permitted Pitch setting at 30 in. radius: High 27° Low 14°57' Spinner: MBB P/N 209-61056 Governor: Woodward P/N T210452 or P/N 210681 Airspeed limits (CAS) Normal and Utility Category Never exceed 173 knots (199 m.p.h.)

Maximum structural cruising 135 knots (155 m.p.h.)

Maneuvering 117 knots (135 m.p.h.)

Flaps extended 88 knots (101 m.p.h.)

*Landing gear operation 104 knots (120 m.p.h.)

*Landing gear extended 173 knots (199 m.p.h.)

(*Applies only to the RV model).

C.G. range Normal Category (85.47) to (89.37) at 1265 lb. or less (86.92) to (89.37) at 1808 lb.

Utility Category (85.47) to (89.37) at 1265 lb. or less (86.25) to (89.37) at 1565 lb.

Figure 10-1. Type certificate data sheet (TCDS) (continued).

10-7 3 A27EU Maximum weight 1808 lb. for Normal Category 1565 lb. for Utility Category No. of seats 2 at (+ 90.7) Maximum baggage 110 lb. at (+ 114.2) Fuel capacity 39.2 gal. total (38.6 gal. usable; two 19.6 gal., wing tanks at + 90.7) Oil capacity 8 qt. (+3.94) See NOTE 1 for unusable fuel and undrainable oil data.

III - Model BO-209-150 FF, 2 PCLM (Normal and Utility Category), approved 9 July 1971 (fixed nose L.g.).

Engine Lycoming O-320-E2C or O-320-E2F Fuel 80/87 minimum grade aviation gasoline.

Engine limits For all operations, 2700 r.p.m. (150 hp.)

Propeller and McCauley 1C172MGM-70.5-60 or -66 propeller limits Static r.p.m. at maximum permissible throttle setting: Not over 2400, not under 2100 No additional tolerance permitted.

Diameter: Maximum 70.5 in., minimum for repairs 70 in.

No further reduction permitted Spinner: MBB P/N 209-61156 Airspeed limits (CAS) Normal and Utility Category Never exceed 173 knots (199 m.p.h.)

Maximum structural cruising 135 knots (155 m.p.h.)

Maneuvering 117 knots (135 m.p.h.)

Flaps extended 88 knots (101 m.p.h.)

C.G. range Normal Category (85.47) to (89.37) at 1265 lb. or less (86.92) to (89.37) at 1808 lb.

Utility Category (85.47) to (89.37) at 1265 lb. or less (86.25) to (89.37) at 1565 lb.

Maximum weight 1808 lb., for Normal Category 1565 lb., for Utility Category No. of seats 2 at (+ 90.7) Maximum baggage 110 lb. at (+114.2) Fuel capacity 39.2 gal. total (38.6 gal. usable; two 19.6 gal., wing tanks at + 90.7) Oil capacity 8 qt. (+3.94) See NOTE 1 for unusable fuel and undrainable oil data.

Figure 10-1. Type certificate data sheet (TCDS) (continued).

10-8 4 A27EU DATA PERTINENT TO ALL MODELS Control Surface Movements Ailerons Up 29° + 1° Down 14° + 1° Wing flaps Down 35° + 0° - 3° Stabilator Up 18° + 1° Down 9° + 1° Rudder Left 28° + 2° Right 28° + 2° Stabilator trim, distance measured between trailing edge of trim tab and trailing edge of stabilator with stabilator in the neutral position.

tab neutral: 0.32 in. Down, + 0.08 in.

nose down: 0.20 in. Up, + 0.08 in.

nose up: 0.66 in. Down, + 0.08 in.

total travel: 0.86 in. + 0.16 in.

Datum 75.51 in. forward of wing leading edge at split line of the wing/wing stub fairing.

Leveling means Two leveling points on left side of fuselage.

Serial Nos. eligible Serial Numbers 121 and subsequent.

The Federal Republic of Germany Government Certificate of Airworthiness for Export endorsed as noted below under "Import Requirements" must be submitted for each individual aircraft for which application for airworthiness certification is made.

Certification basis FAR 21.29 and FAR 23 dated 1 February 1965 as amended by Amendments 23-1 through 23-9 inclusive. Type Certificate No. A27EU, issued 9 July 1971.

Date of Application for Type Certificate: 11 May 1970.

The Luftfahrt Bundesamt originally type certificated this aircraft under its type certificate Number 680. The FAA validated this product under U.S. Type Certificate Number A27EU. Effective September 28, 2003, the European Aviation Safety Agency (EASA) began oversight of this product on behalf of Germany.

The EASA type certificate for the BO-209 models is EASA.A.357.

Import Requirements The FAA can issue a U.S. airworthiness certificate based on an NAA Export Certificate of Airworthiness (Export C of A) signed by a representative of the Luftfahrt Bundesamt on behalf of the European Community. The Export C of A should contain the following statement: ‘The aircraft covered by this certificate has been examined, tested, and found to comply with U.S. airworthiness regulations 14 CFR Part 23 approved under U.S.

Type Certificate No. A27EU and to be in a condition for safe operation.’ Service Information Each of the documents listed below must state that it is approved by the European Aviation Safety Agency (EASA) or – for approvals made before September 28, 2003 – by the Luftfahrt Bundesamt.

• Service bulletins, • Structural repair manuals, • Vendor manuals, • Aircraft flight manuals, and • Overhaul and maintenance manuals.

The FAA accepts such documents and considers them FAA-approved unless one of the following conditions exists: • The documents change the limitations, performance, or procedures of the FAA approved manuals; or •The documents make an acoustical or emissions changes to this product’s U.S. type certificate as defined in 14 CFR § 21.93.

Figure 10-1. Type certificate data sheet (TCDS) (continued).

10-9 5 A27EU Service Information, cont'd The FAA uses the post type validation procedures to approve these documents. The FAA may delegate on case-by-case to EASA to approve on behalf of the FAA for the U.S. type certificate. If this is the case it will be noted on the document.

Equipment The basic required equipment as prescribed in the applicable airworthiness regulations (see Certification Basis) must be installed in the aircraft for certification. In addition, the following items of equipment are required: 1. Stall Warning System.

2. LBA-approved Model BO-209 Approved Flight Manual, Ref. No.LF 37E-7/71 dated July 1971 or later LBA-approved revision.

3. Airplanes S/N 121 through 130 must be modified in accordance with MBB Technical Note TN 9-71 to provide an alternate static system source and an aural landing gear warning system. (These systems are incorporated in production on S/Ns 131 and subsequent).

NOTE 1. Current weight and balance report including list of equipment in certificated empty weight, and loading instructions when necessary, must be provided for each airplane at the time of original airworthiness certification. The certificated empty weight and corresponding center of gravity must include undrainable oil of 0 lbs. at +39.4 and unusable fuel of 3.6 lb. at +90.7.

NOTE 2. The following placard must be displayed in front and in clear view of the pilot: "This airplane must be operated as a Normal or Utility Category airplane in compliance with their operating limitations stated in the form of placards, markings, and manuals."

In addition, all placards required in the LBA-approved Airplane Flight Manual must be installed in the appropriate location.

NOTE 3. Information essential for proper maintenance of the airplane is contained in the Messerschmitt-Bolkow- Blohm GmbH., Model BO-209 Maintenance Manual included in MBB document Ref. LF 37E-7/71.

NOTE 4. The airplane manufacturer is: Waggon- und Maschienenbau A.G.

Donauworth, Laupheim Federal Republic of Germany (A division of Messerschmitt-Bolkow-Blohm).

NOTE 5. Installation of a Tost tow coupling (ring type), LBA approval No. 60.230.4 may be approved when installed in accordance with MBB Drwg. 209-85003 (for glider towing) or MBB Drwgs. 209-85003 and 209-8700 (for banner towing).

NOTE 6. For issuance of an airworthiness certificate in accordance with 14 CFR Part 21.182(c), the Luftfahrt Bundesamt of Germany must certify that the airplane conforms to the type design and is in a condition for safe operation. In that regard, the Luftfahrt Bundesamt of Germany will certify that the airplane complies with all applicable mandatory continuing airworthiness information (MCAI) it has issued. For issuance of an airworthiness certificate in accordance with 14 CFR Part 21.182(d) the certificating inspector, or other authorized person, must find, among other things, that the product is in a condition for safe operation. In order to make that finding, the certificating inspector or other authorized person should contact ACE-112, Federal Aviation Administration, Small Airplane Directorate, prior to issuance to determine whether showing airplane compliance with certain MCAI is necessary to support a finding that the airplane is in a condition for safe operation.

Figure 10-1. Type certificate data sheet (TCDS) (continued).

10-10 6 A27EU NOTE 7. Some of these transfers were not notified to the FAA and so in some instances the actual type certificates were not reissued.

.....END.....

Figure 10-1. Type certificate data sheet (TCDS) (continued).

10-11 where the inspection is to be conducted. inspection of systems and components. They might occur only three to six times during the service life of an aircraft.

Progressive Inspections Altimeter & Transponder Inspections Because the scope and detail of an annual inspection is very extensive and could keep an aircraft out of service Aircraft that are operated in controlled airspace under for a considerable length of time, alternative inspection instrument flight rules (IFR) must have each altimeter and programs designed to minimize down time may be utilized. static system tested in accordance with procedures described A progressive inspection program allows an aircraft to be in 14 CFR part 43, Appendix E, within the preceding 24 inspected progressively. The scope and detail of an annual calendar months. Aircraft having an air traffic control (ATC) inspection is essentially divided into segments or phases transponder must also have each transponder checked within (typically four to six). Completion of all the phases completes the preceding 24 months. All these checks must be conducted a cycle that satisfies the requirements of an annual inspection. by appropriately certified individuals.

The advantage of such a program is that any required segment Air Transport Association iSpec 2200 may be completed overnight and thus enable the aircraft to fly daily without missing any revenue earning potential.

In an effort to standardize the format in which maintenance Progressive inspection programs include routine items, such information is presented in aircraft maintenance manuals, as engine oil changes, and detailed items, such as flight Air Transport Association (now Airlines for America)issued control cable inspection. Routine items are accomplished specifications for Manufacturers’ Technical Data. The each time the aircraft comes in for a phase inspection, and original specification was called ATA Spec 100. Over the detailed items focus on detailed inspection of specific areas.

years, Spec 100 has been continuously revised and updated.

Detailed inspections are typically done once each cycle. A Eventually, ATA Spec 2100 was developed for electronic cycle must be completed within 12 months. If all required documentation. These two specifications evolved into one phases are not completed within 12 months, the remaining document called ATA iSpec 2200, developed and managed phase inspections must be conducted before the end of the by the ATA e-Business Program, a consensus-based industry th 12 month from when the first phase was completed.

standards organization administered by Airlines for America (A4A). As a result of this standardization, maintenance Each registered owner or operator of an aircraft desiring to technicians can always find information regarding a particular use a progressive inspection program must submit a written system in the same section of an aircraft maintenance request to the FAA Flight Standards District Office (FSDO) manual, regardless of manufacturer. For example, if seeking having jurisdiction over the area that the applicant is located.

information about the electrical system on any aircraft, that Section 91.409(d) of 14 CFR part 91 establishes procedures information is always found in section (chapter) 24.

to be followed for progressive inspections. [Figure 10-3] The ATA iSpec 2200 divides the aircraft into systems, such Continuous Inspections as air conditioning, that covers the basic air conditioning Continuous inspection programs are similar to progressive system (ATA 21). Numbering in each major system provides inspection programs, except that they apply to large or an arrangement for breaking the system down into several turbine-powered aircraft and are therefore more complicated.

subsystems. [Figure 10-4] Late model aircraft, both over and Like progressive inspection programs, they require approval under the 12,500-pound designation, have their parts manuals by the FAA Administrator. The approval may be sought and maintenance manuals arranged according to the ATA- based upon the type of operation and the CFR parts that coded system. The following abbreviated table of ATA System, the aircraft is operated under. The maintenance program Subsystem, and Titles is included for familiarization purposes.

for commercially operated aircraft must be detailed in the approved operations specifications (OpSpecs) of the Keep in mind that not all aircraft have all these systems commercial certificate holder.

installed. Small and simple aircraft have fewer systems than larger, more complex aircraft.

Airlines utilize a continuous maintenance program that includes both routine and detailed inspections. However, the Special Inspections detailed inspections may include different levels of detail.

During the service life of an aircraft, occasions may arise Often referred to as “checks,” the A-checks, B-checks, when something out of the ordinary care and use of an aircraft C-checks, and D-checks involve increasing levels of detail.

could possibly affect its airworthiness. When these situations A-checks are the least comprehensive and occur frequently.

are encountered, special inspection procedures, also called D-checks, on the other hand, are extremely comprehensive, conditional inspections, are followed to determine if damage involving major disassembly, removal, overhaul, and to the aircraft structure has occurred. The procedures 10-12

Next: Appendix D to Part 43—Scope and Detail of Items (as Applicable to the Particular Aircraft) To Be Included in Annual →

Section 21

Appendix D to Part 43—Scope and Detail of Items (as Applicable to the Particular Aircraft) To Be Included in Annual and 100-Hour Inspections condition, defects, and insecure attachment.

(a) Each person performing an annual or 100-hour inspection (11) Cowling—for cracks, and defects.

shall, before that inspection, remove or open all necessary inspection plates, access doors, fairing, and cowling. He shall (e) Each person performing an annual or 100-hour inspection thoroughly clean the aircraft and aircraft engine.

shall inspect (where applicable) the following components of the landing gear group: (b) Each person performing an annual or 100-hour inspection shall inspect (where applicable) the following components (1) All units—for poor condition and insecurity of attachment. of the fuselage and hull group: (1) Fabric and skin—for deterioration, distortion, other (2) Shock absorbing devices—for improper oleo fluid level.

evidence of failure, and defective or insecure attachment (3) Linkages, trusses, and members—for undue or excessive of fittings.

wear fatigue, and distortion.

(2) Systems and components—for improper installation, (4) Retracting and locking mechanism—for improper apparent defects, and unsatisfactory operation.

operation.

(3) Envelope, gas bags, ballast tanks, and related parts—for (5) Hydraulic lines—for leakage.

poor condition.

(6) Electrical system—for chafing and improper operation (c) Each person performing an annual or 100-hour inspection of switches.

shall inspect (where applicable) the following components (7) Wheels—for cracks, defects, and condition of bearings. of the cabin and cockpit group: (8) Tires—for wear and cuts. (1) Generally—for uncleanliness and loose equipment that might foul the controls.

(9) Brakes—for improper adjustment.

(2) Seats and safety belts—for poor condition and apparent (10) Floats and skis—for insecure attachment and obvious or defects.

apparent defects.

(3) Windows and windshields—for deterioration and (f) Each person performing an annual or 100-hour inspection breakage.

shall inspect (where applicable) all components of the wing and center section assembly for poor general condition, fabric (4) Instruments—for poor condition, mounting, marking, or skin deterioration, distortion, evidence of failure, and and (where practicable) improper operation.

insecurity of attachment.

(5) Flight and engine controls—for improper installation (g) Each person performing an annual or 100-hour inspection shall and improper operation.

inspect (where applicable) all components and systems that (6) Batteries—for improper installation and improper make up the complete empennage assembly for poor general charge.

condition, fabric or skin deterioration, distortion, evidence of failure, insecure attachment, improper component installation, (7) All systems—for improper installation, poor general condition, apparent and obvious defects, and insecurity and improper component operation.

of attachment.

(h) Each person performing an annual or 100-hour inspection (d) Each person performing an annual or 100-hour inspection shall inspect (where applicable) the following components of shall inspect (where applicable) components of the engine the propeller group: and nacelle group as follows: (1) Propeller assembly—for cracks, nicks, binds, and oil (1) Engine section—for visual evidence of excessive oil, leakage.

fuel, or hydraulic leaks, and sources of such leaks.

(2) Bolts—for improper torquing and lack of safetying.

(2) Studs and nuts—for improper torquing and obvious (3) Anti-icing devices—for improper operations and obvious defects.

defects.

(3) Internal engine—for cylinder compression and for (4) Control mechanisms—for improper operation, insecure metal particles or foreign matter on screens and sump mounting, and restricted travel.

drain plugs. If there is weak cylinder compression, (i) Each person performing an annual or 100-hour inspection for improper internal condition and improper internal tolerances.

shall inspect (where applicable) the following components of the radio group: (4) Engine mount—for cracks, looseness of mounting, and looseness of engine to mount.

(1) Radio and electronic equipment—for improper installation and insecure mounting.

(5) Flexible vibration dampeners—for poor condition and deterioration.

(2) Wiring and conduits—for improper routing, insecure mounting, and obvious defects.

(6) Engine controls—for defects, improper travel, and improper safetying.

(3) Bonding and shielding—for improper installation and poor condition.

(7) Lines, hoses, and clamps—for leaks, improper condition and looseness.

(4) Antenna including trailing antenna—for poor condition, insecure mounting, and improper operation.

(8) Exhaust stacks—for cracks, defects, and improper attachment.

(j) Each person performing an annual or 100-hour inspection shall inspect (where applicable) each installed miscellaneous (9) Accessories—for apparent defects in security of item that is not otherwise covered by this listing for improper mounting.

installation and improper operation.

(10) All systems—for improper installation, poor general Figure 10-2. Title 14 CFR Appendix D to Part 43—Scope and detail of items (as applicable to the particular aircraft) to be included in annual and 100-hour inspections.

10-13 § 91.409 Inspections.

(3) Enough housing and equipment for necessary (d) Progressive inspection. Each registered owner or operator of disassembly and proper inspection of the aircraft; and an aircraft desiring to use a progressive inspection program must submit a written request to the FAA Flight Standards (4) Appropriate current technical information for the district office having jurisdiction over the area in which the aircraft.

applicant is located, and shall provide— The frequency and detail of the progressive inspection shall (1) A certificated mechanic holding an inspection provide for the complete inspection of the aircraft within each authorization, a certificated airframe repair station, or 12 calendar months and be consistent with the manufacturer's the manufacturer of the aircraft to supervise or conduct recommendations, field service experience, and the kind of the progressive inspection; operation in which the aircraft is engaged. The progressive (2) A current inspection procedures manual available inspection schedule must ensure that the aircraft, at all times, and readily understandable to pilot and maintenance will be airworthy and will conform to all applicable FAA personnel containing, in detail— aircraft specifications, type certificate data sheets, airworthiness (i) An explanation of the progressive inspection, directives, and other approved data. If the progressive inspection including the continuity of inspection is discontinued, the owner or operator shall immediately notify responsibility, the making of reports, and the the local FAA Flight Standards district office, in writing, of keeping of records and technical reference the discontinuance. After the discontinuance, the first annual material; inspection under §91.409(a)(1) is due within 12 calendar months after the last complete inspection of the aircraft under the (ii) An inspection schedule, specifying the intervals progressive inspection. The 100-hour inspection under §91.409(b) in hours or days when routine and detailed is due within 100 hours after that complete inspection. A complete inspections will be performed and including inspection of the aircraft, for the purpose of determining when instructions for exceeding an inspection interval the annual and 100-hour inspections are due, requires a detailed by not more than 10 hours while en route and inspection of the aircraft and all its components in accordance with for changing an inspection interval because of the progressive inspection. A routine inspection of the aircraft and service experience; a detailed inspection of several components is not considered to (iii) Sample routine and detailed inspection forms be a complete inspection.

and instructions for their use; and (iv) Sample reports and records and instructions for their use; Figure 10-3. Title 14 CFR Section 91.409(d), Progressive Inspection.

outlined on the following pages are general in nature and are intended to acquaint the aviation mechanic with the areas Wrinkled wing skin is the most easily detected sign of to be inspected. As such, they are not all inclusive. When an excessive load having been imposed during a landing.

performing any of these special inspections, always follow Another indication easily detected is fuel leakage along the detailed procedures in the aircraft maintenance manual. riveted seams. Other possible locations of damage are spar In situations where the manual does not adequately address webs, bulkheads, nacelle skin and attachments, firewall skin, the situation, seek advice from other maintenance technicians and wing and fuselage stringers. If none of these areas show who are highly experienced with them. The following adverse effects, it is reasonable to assume that no serious paragraphs describe some typical types of special inspections. damage has occurred. If damage is detected, a more extensive inspection and alignment check may be necessary.

Hard or Overweight Landing Inspection Severe Turbulence Inspection/Over “G” The structural stress induced by a landing depends not only upon the gross weight at the time, but also upon the severity When an aircraft encounters a gust condition, the airload of impact. The hard landing inspection is for hard landings at on the wings exceeds the normal wingload supporting the or below the maximum design landing limits. An overweight aircraft weight. The gust tends to accelerate the aircraft while landing inspection must be performed when an airplane lands at its inertia acts to resist this change. If the combination of gust a weight above the maximum design landing weight. However, velocity and airspeed is too severe, the induced stress can because of the difficulty in estimating vertical velocity at the cause structural damage.

time of contact, it is hard to judge whether or not a landing has been sufficiently severe to cause structural damage. For A special inspection is performed after a flight through severe this reason, a special inspection is performed after a landing is turbulence. Emphasis is placed upon inspecting the upper and made at a weight known to exceed the design landing weight or lower wing surfaces for excessive buckles or wrinkles with after a rough landing, even though the latter may have occurred permanent set. Where wrinkles have occurred, remove a few when the aircraft did not exceed the design landing weight. rivets and examine the rivet shanks to determine if the rivets 10-14 have sheared or were highly loaded in shear. If the landing gear was lowered during a period of severe turbulence, inspect the surrounding surfaces carefully Through the inspection doors and other accessible openings, for loose rivets, cracks, or buckling. The interior of the inspect all spar webs from the fuselage to the tip. Check for wheel well may give further indications of excessive gust buckling, wrinkles, and sheared attachments. Inspect for conditions. Inspect the top and bottom fuselage skin. An buckling in the area around the nacelles and in the nacelle excessive bending moment may have left wrinkles of a skin, particularly at the wing leading edge. Check for fuel diagonal nature in these areas.

leaks. Any sizeable fuel leak is an indication that an area may have received overloads that have broken the sealant Inspect the surface of the empennage for wrinkles, buckling, and opened the seams. or sheared attachments. Also, inspect the area of attachment of the empennage to the fuselage. These inspections cover ATA iSpec 2200 Systems Sample Systems Subsystems Title Systems Subsystems Title 42 INTEGRATED MODULAR AVIONICS 21 AIR CONDITIONING STANDARD PRACTICES AND 21 -00 General STRUCTURES - GENERAL 21 -10 Compression 52 DOORS 21 -20 Distribution 53 FUSELAGE 21 -30 Pressurization Control 54 NACELLES/PYLONS 21 -40 Heating 55 STABILIZERS 21 -50 Cooling 56 WINDOWS 21 -60 Temperature Control 57 WINGS STANDARD PRACTICES - 21 -70 Moisture/Air Contaminate Control PROPELLER/ROTOR 22 AUTO FLIGHT 61 PROPELLERS/PROPULSION 23 COMMUNICATIONS 62 ROTOR(S) 24 ELECTRICAL POWER 71 POWER PLANT ENGINE TURBINE/TURBOPROP DUCTED 25 EQUIPMENT/FURNISHINGS 72 FAN/UNDUCTED FAN 26 FIRE PROTECTION 72 -20 AIR INLET SECTION 27 FLIGHT CONTROLS 73 ENGINE FUEL AND CONTROL 28 FUEL 74 IGNITION 29 HYDRAULIC POWER 75 AIR 30 ICE AND RAIN PROTECTION 76 ENGINE CONTROLS 31 INDICATING/RECORDING SYSTEMS 77 ENGINE INDICATING 32 LANDING GEAR 78 EXHAUST 33 LIGHTS 79 OIL 34 NAVIGATION 80 STARTING 35 OXYGEN 81 TURBINES 36 PNEUMATIC 82 WATER INJECTION 37 VACUUM 83 ACCESSORY GEAR-BOXES 38 WATER/WASTE This figure shows a representative number of systems/subsystems for demonstration purposes only. It is not all-encompassing and should be viewed as a learning aid to understand the numbering method of the ATA iSpec 2200 System. Consult the specific aircraft maintenance manuals or Airlines for America (A4A) for a complete description of the systems and subsystems.

Figure 10-4. ATA iSpec 2200 Systems.

10-15 the critical areas. If excessive damage is noted in any of the Flood Damage areas mentioned, the inspection must be continued until all Like aircraft damaged by fire, aircraft damaged by water damage is detected.

can range from minor to severe. This depends on the level of the flood water, whether it was fresh or salt water, and Lightning Strike the elapsed time between the flood occurrence and when Although lightning strikes to aircraft are extremely rare, repairs were initiated. Any parts that were totally submerged if a strike has occurred, the aircraft is carefully inspected are completely disassembled, thoroughly cleaned, dried, and to determine the extent of any damage that might have treated with a corrosion inhibitor. Many parts might have to be occurred. When lightning strikes an aircraft, the electrical replaced, particularly interior carpeting, seats, side panels, and current must be conducted through the structure and be instruments. Since water serves as an electrolyte that promotes allowed to discharge or dissipate at controlled locations.

corrosion, all traces of water and salt must be removed before These controlled locations are primarily the aircraft’s static the aircraft can again be considered airworthy.

discharge wicks, or on more sophisticated aircraft, null field dischargers. When surges of high-voltage electricity pass Seaplanes through good electrical conductors, such as aluminum or Because they operate in an environment that accelerates steel, damage is likely to be minimal or nonexistent. When corrosion, seaplanes must be carefully inspected for corrosion surges of high-voltage electricity pass through non-metallic and conditions that promote corrosion. Inspect bilge areas structures, such as a fiberglass radome, engine cowl or fairing, for waste hydraulic fluids, water, dirt, drill chips, and glass or plastic window, or a composite structure that does other debris. Additionally, since seaplanes often encounter not have built-in electrical bonding, burning and more serious excessive stress from the pounding of rough water at high damage to the structure could occur. Visual inspection of speeds, inspect for loose rivets and other fasteners; stretched, the structure is required. Look for evidence of degradation, bent or cracked skins; damage to the float attach fitting; and burning, or erosion of the composite resin at all affected general wear and tear on the entire structure.

structures, electrical bonding straps, static discharge wicks, and null field dischargers.

Aerial Application Aircraft Two primary factors that make inspecting these aircraft Bird Strike different from other aircraft are the corrosive nature of When the aircraft is hit by birds during flight, the external some of the chemicals used and the typical flight profile.

areas of the airplane are inspected in the general area of the Damaging effects of corrosion may be detected in a much bird strike. If the initial inspection shows structural damage, shorter period of time than normal use aircraft. Chemicals then the internal structure of the airplane must be inspected may soften the fabric or loosen the fabric tapes of fabric- as well. Also, inspect the hydraulic, pneumatic, and any other covered aircraft. Metal aircraft may need to have the paint systems in the area of the bird strike.

stripped, cleaned, and repainted and corrosion treated annually. Leading edges of wings and other areas may Fire Damage require protective coatings or tapes. Hardware may require Inspection of aircraft structures that have been subjected to fire more frequent replacement.

or intense heat can be relatively simple if visible damage is present. Visible damage requires repair or replacement. If there During peak use, these aircraft may fly up to 50 cycles is no visible damage, the structural integrity of an aircraft may (takeoffs and landings) or more in a day, most likely from still have been compromised. Since most structural metallic an unimproved or grass runway. This can greatly accelerate components of an aircraft have undergone some sort of heat- the failure of normal fatigue items. Landing gear and related treatment process during manufacture, an exposure to high items require frequent inspections. Because these aircraft heat not encountered during normal operations could severely operate almost continuously at very low altitudes, air filters degrade the design strength of the structure. The strength and tend to become obstructed more rapidly.

airworthiness of an aluminum structure that passes a visual inspection, but is still suspect, can be further determined by use Special Flight Permits of a conductivity tester. This is a device that uses eddy current For an aircraft that does not currently meet airworthiness and is discussed later in this chapter. Since strength of metals is requirements because of an overdue inspection, damage, related to hardness, possible damage to steel structures might expired replacement times for time-limited parts, or other be determined by use of a hardness tester, such as a Rockwell reasons, but is capable of safe flight, a special flight permit C hardness tester. [Figure 10-5] may be issued. Special flight permits, often referred to as ferry permits, are issued for the following purposes: 10-16 • Flying the aircraft to a base where repairs, alterations, or simple, requiring little additional expertise, while others are maintenance are to be performed or to a point of storage highly sophisticated and require that the technician be highly trained and specially certified.

• Delivering or exporting the aircraft • Production flight testing new production aircraft Training, Qualification, & Certification • Evacuating aircraft from areas of impending danger The product manufacturer or the FAA generally specifies the particular NDI method and procedure to be used in inspection.

• Conducting customer demonstration flights in new These NDI requirements are specified in the manufacturer’s production aircraft that have satisfactorily completed inspection, maintenance, or overhaul manual, FAA ADs, production flight tests supplemental structural inspection documents (SSID), or SBs.

Additional information about special flight permits may be The success of any NDI method and procedure depends found in 14 CFR part 21. Application forms for special flight upon the knowledge, skill, and experience of the NDI permits may be requested from the nearest FAA FSDO.

personnel involved. The person(s) responsible for detecting and interpreting indications, such as eddy current, x-ray, or Nondestructive Inspection/Testing ultrasonic NDI, must be qualified and certified to specific The preceding information in this chapter provided general FAA or other acceptable government or industry standards, details regarding aircraft inspection. The remainder of such as MIL-STD-410, Nondestructive Testing Personnel this chapter deals with several methods often used on Qualification and Certification or ATA iSpec 105, Guidelines specific components or areas on an aircraft when carrying for Training and Qualifying Personnel in Nondestructive out the more specific inspections. They are referred to as Testing Methods. The person must be familiar with the test nondestructive inspection (NDI) or nondestructive testing method, know the potential types of discontinuities peculiar (NDT). The objective of NDI and NDT is to determine the to the material, and be familiar with their effect on the airworthiness of a component, without damaging it, that structural integrity of the part. Additional information on NDI would render it unairworthy. Some of these methods are may be found by referring to Chapter 5 of FAA AC 43.13-1, Acceptable Methods, Techniques, and Practices—Aircraft Inspection and Repair.

Advantages & Disadvantages of NDI Methods Figure 10-6 provides a table of the advantages and disadvantages of common NDI methods. This table could be used as a guide for evaluating the most appropriate NDI method when the manufacturer or the FAA has not specified a particular NDI method to be used.

General Techniques Before conducting NDI, it is necessary to follow preparatory steps in accordance with procedures specific to that type of inspection. Generally, the parts or areas must be thoroughly cleaned. Some parts must be removed from the aircraft or engine. Others might need to have any paint or protective coating stripped. A complete knowledge of the equipment and procedures is essential and, if required, calibration and inspection of the equipment must be current.

Visual Inspection Visual inspection can be enhanced by looking at the suspect area with a bright light, a magnifying glass, and a mirror. Some defects might be so obvious that further inspection methods are not required. The lack of visible defects does not necessarily mean further inspection is unnecessary. Some defects may lie beneath the surface or may be so small that the human eye, even with the assistance of a magnifying glass, cannot detect them.

Figure 10-5. Rockwell C Hardness Tester.

10-17 or porosity. These defects may be caused by fatigue cracks, shrinkage cracks, shrinkage porosity, cold shuts, grinding and Surface Cracks heat-treat cracks, seams, forging laps, and bursts. Penetrant When searching for surface cracks with a flashlight, direct inspection also indicates a lack of bond between joined metals.

the light beam at a 5 to 45 degree angle to the inspection The main disadvantage of penetrant inspection is that the surface towards the face. [Figure 10-7] Do not direct the light defect must be open to the surface in order to let the penetrant beam at such an angle that the reflected light beam shines get into the defect. For this reason, if the part in question is directly into the eyes. Keep the eyes above the reflected light made of material that is magnetic, the use of magnetic particle beam during the inspection. Determine the extent of any inspection is generally recommended.

cracks found by directing the light beam at right angles to the crack and tracing its length. Use a 10-power magnifying Penetrant inspection uses a penetrating liquid that enters a glass to confirm the existence of a suspected crack. If this is surface opening and remains there, making it clearly visible not adequate, use other NDI techniques, such as penetrant, to the inspector. It calls for visual examination of the part magnetic particle, or eddy current to verify cracks.

after it has been processed, increasing the visibility of the defect so that it can be detected. Visibility of the penetrating Borescope material is increased by the addition of one or two types of Inspection by use of a borescope is essentially a visual dye: visible or fluorescent.

inspection. A borescope is a device that enables the inspector to see inside areas that could not otherwise be inspected The visible penetrant kit consists of dye penetrant, dye without disassembly. Borescopes are used in aircraft and remover emulsifier, and developer. The fluorescent penetrant engine maintenance programs to reduce or eliminate the inspection kit contains a black light assembly, as well as spray need for costly teardowns. Aircraft turbine engines have cans of penetrant, cleaner, and developer. The light assembly access ports that are specifically designed for borescopes.

consists of a power transformer, a flexible power cable, and Borescopes are also used extensively in a variety of aviation a hand-held lamp. Due to its size, the lamp may be used in maintenance programs to determine the airworthiness of almost any position or location.

difficult to reach components. Borescopes typically are used to inspect interiors of hydraulic cylinders and valves for The steps for performing a penetrant inspection are: pitting, scoring, porosity, and tool marks; search for cracked cylinders in aircraft reciprocating engines; inspect turbojet 1. Clean the metal surface thoroughly.

engine turbine blades and combustion cans; verify the proper 2. Apply penetrant.

placement and fit of seals, bonds, gaskets, and subassemblies 3. Remove penetrant with remover emulsifier or cleaner.

in difficult to reach areas; and assess foreign object damage (FOD) in aircraft, airframe, and powerplants. Borescopes 4. Dry the part.

may also be used to locate and retrieve foreign objects in 5. Apply the developer.

engines and airframes.

6. Inspect and interpret results.

Borescopes are available in two basic configurations. The Interpretation of Results simpler of the two is a rigid type, small diameter telescope with a tiny mirror at the end that enables the user to see around The success and reliability of a penetrant inspection depends upon the thoroughness that the part was prepared with.

corners. The other type uses fiber optics that enable greater flexibility. [Figure 10-8] Many borescopes provide images Several basic principles applying to penetrant inspection are: that can be displayed on a computer or video monitor for 1. The penetrant must enter the defect in order to form better interpretation of what is being viewed and to record an indication. It is important to allow sufficient time images for future reference. Most borescopes also include a so the penetrant can fill the defect. The defect must light to illuminate the area being viewed.

be clean and free of contaminating materials so that the penetrant is free to enter.

Liquid Penetrant Inspection 2. If all penetrant is washed out of a defect, an indication Penetrant inspection is a nondestructive test for defects open to cannot be formed. During the washing or rinsing the surface in parts made of any nonporous material. It is used operation, prior to development, it is possible that the with equal success on such metals as aluminum, magnesium, penetrant is removed from within the defect, as well brass, copper, cast iron, stainless steel, and titanium. It may as from the surface.

also be used on ceramics, plastics, molded rubber, and glass.

3. Clean cracks are usually easy to detect. Surface Penetrant inspection detects defects, such as surface cracks openings that are uncontaminated, regardless of how 10-18 Method Advantages Disadvantages • Inexpensive • Surface discontinuities only • Highly portable • Generally only large discontinuities • Immediate results • Misinterpretation of scratches Visual • Minimum training • Minimum part preparation • Portable • Locate surface defects only • Inexpensive • Rough or porous surfaces interfere with test Penetrant Dye • Sensitive to very small discontinuities • Part preparation required (removal of fi nishes and sealant, etc.)

• 30 minutes or less to accomplish • High degree of cleanliness required • Minimum skill required • Direct visual detection on results required • Can be portable • Surface must be accessible • Inexpensive • Rough surfaces interfere with test • Sensitive to small discontinuities • Part preparation required (removal of fi nishes and sealant, etc.)

Magnetic • Immediate results • Semi-directional requiring general orientation of fi eld to Particle • Moderate skill required discontinuity • Detects surface and subsurface discontinuities • Ferro-magnetic materials only • Relatively fast • Part must be demagnetized after test • Portable • Surface must be accessible to probe • Detects surface and subsurface discontinuities • Rough surfaces interfere with test • Moderate speed • Electrically conductive materials Eddy Current • Immediate results • Skill and training required • Sensitive to small discontinuities • Time consuming for large areas • Thickness sensitive • Can detect many variables • Portable • Surface must be accessible to probe • Inexpensive • Rough surfaces interfere with test • Sensitive to very small discontinuities • Highly sensitive to sound beam discontinuity orientation Ultrasonic • Immediate results • High degree of skill and experience required for exposure and • Little part preparation interpretation • Wide range of materials and thickness can be inspected • Depth of discontinuity not indicated • Safety hazard • Detects surface and internal fl aws • Very expensive (slow process) • Can inspect hidden areas X-Ray • Highly directional, sensitive to fl aw orientation • Permanent test record obtained Radiography • High degree of skill and experience required for exposure • Minimum part preparation and interpretation • Depth of discontinuity not indicated • Portable • Safety hazard • Less inexpensive than x-ray • Must conform to federal and state regulations for handling and use • Detects surface and internal fl aws • Highly directional, sensitive to fl aw orientation Isotope • Can inspect hidden areas • High degree of skill and experience required for exposure and Radiography • Permanent test record obtained interpretation • Minimum part preparation • Depth of discontinuity not indicated Figure 10-6. Advantages and disadvantages of NDI methods.

fine, are seldom difficult to detect with the penetrant appear, there are no surface defects.

inspection.

7. When conducting the fluorescent penetrant-type 4. The smaller the defect, the longer the penetrating time. inspection, the defects show up (under black light) Fine crack-like apertures require a longer penetrating as a brilliant yellow-green color and the sound areas time than defects such as pores. appear deep blue-violet.

5. When the part to be inspected is made of a material 8. It is possible to examine an indication of a defect and susceptible to magnetism, it should be inspected by a to determine its cause as well as its extent. Such an magnetic particle inspection method if the equipment appraisal can be made if something is known about is available. the manufacturing processes that the part has been subjected to.

6. Visible penetrant-type developer, when applied to the surface of a part, dries to a smooth, white coating.

The size of the indication, or accumulation of penetrant, As the developer dries, bright red indications appear shows the extent of the defect and the brilliance is a measure where there are surface defects. If no red indications of its depth. Deep cracks hold more penetrant and are 10-19 KEEP EYE ABOVE REFLECTED LIGHT BEAM Rigid Incandescent light beam Line of sight Reflected 45° Flexible light beam Fay Figure 10-8. Rigid and flexible borescopes.

Crack open to surface Eddy current is used to detect surface cracks, pits, subsurface cracks, corrosion on inner surfaces, and to determine alloy Figure 10-7. Using a flashlight to inspect for cracks.

and heat-treat condition.

broader and more brilliant. Very fine openings can hold Eddy current is used in aircraft maintenance to inspect jet engine turbine shafts and vanes, wing skins, wheels, only small amounts of penetrants and appear as fine lines.

[Figure 10-9] bolt holes, and spark plug bores for cracks, heat, or frame damage. Eddy current may also be used in repair of aluminum aircraft damaged by fire or excessive heat.

False Indications Different meter readings are seen when the same metal is With the penetrant inspection, there are no false indications in in different hardness states. Readings in the affected area the sense that they occur in the magnetic particle inspection.

are compared with identical materials in known unaffected There are, however, two conditions that may create areas for comparison. A difference in readings indicates accumulations of penetrant that are sometimes confused with a difference in the hardness state of the affected area.

true surface cracks and discontinuities.

In aircraft manufacturing plants, eddy current is used to inspect castings, stampings, machine parts, forgings, and The first condition involves indications caused by poor extrusions. Figure 10-10 shows a technician performing an washing. If all the surface penetrant is not removed in eddy current inspection on a fan blade.

the washing or rinsing operation following the penetrant dwell time, the unremoved penetrant is visible. Evidences Basic Principles of incomplete washing are usually easy to identify since When an alternating current (AC) is passed through a coil, the penetrant is in broad areas rather than in the sharp patterns found with true indications. When accumulations it develops a magnetic field around the coil, which in turn induces a voltage of opposite polarity in the coil and opposes of unwashed penetrant are found on a part, the part must be completely reprocessed. Degreasing is recommended for the flow of original current. If this coil is placed in such a way that the magnetic field passes through an electrically removal of all traces of the penetrant.

conducting specimen, eddy currents are induced into the specimen. The eddy currents create their own field that varies False indications may also be created where parts press fit to each other. If a wheel is press fit onto a shaft, penetrant the original field’s opposition to the flow of original current.

The specimen’s susceptibility to eddy currents determines shows an indication at the fit line. This is perfectly normal since the two parts are not meant to be welded together. the current flow through the coil.

Indications of this type are easy to identify since they are regular in form and shape. The magnitude and phase of this counter field is dependent primarily upon the resistance and permeability of the specimen Eddy Current Inspection under consideration and enables us to make a qualitative determination of various physical properties of the test Electromagnetic analysis is a term describing the broad material. The interaction of the eddy current field with the spectrum of electronic test methods involving the intersection original field results is a power change that can be measured of magnetic fields and circulatory currents. The most widely by utilizing electronic circuitry similar to a Wheatstone bridge.

used technique is the eddy current. Eddy currents are composed of free electrons under the influence of an induced electromagnetic field that are made to “drift” through metal.

10-20 Figure 10-9. Dye penetrant inspection.

the same material as the item is to be tested. A reference Principles of Operations standard contains known flaws or cracks and could include Eddy currents are induced in a test article when an AC is items, such as a flat surface notch, a fastener head, a fastener applied to a test coil (probe). The AC in the coil induces an hole, or a countersink hole. Figures 10-14, 10-15, and 10-16 alternating magnetic field in the article, causing eddy currents show typical surface cracks, subsurface cracks, and structural to flow in the article. [Figure 10-11] corrosion that can be detected with eddy current techniques.

Flaws in or thickness changes of the test-piece influence Ultrasonic Inspection the flow of eddy currents and change the impedance of the Ultrasonic inspection is an NDI technique that uses sound coil accordingly. [Figure 10-12] Instruments display the energy moving through the test specimen to detect flaws.

impedance changes either by impedance plane plots or by The sound energy passing through the specimen is displayed needle deflection. [Figure 10-13] on a cathode ray tube (CRT), a liquid crystal display (LCD) computer data program, or video/camera medium. Indications The specimen is either placed in or passed through the field of the front and back surface and internal/external conditions of an electromagnetic induction coil, and its effect on the appear as vertical signals on the CRT screen or nodes of data impedance of the coil or on the voltage output of one or more in the computer test program. [Figure 10-17] There are three test coils is observed. The process that involves electric fields types of display patterns: “A” scan, “B” scan, and “C” scan.

made to explore a test piece for various conditions involves Each scan provides a different picture or view of the specimen the transmission of energy through the specimen much like being tested. [Figure 10-18] the transmission of x-rays, heat, or ultrasound.

Ultrasonic detection equipment makes it possible to locate Eddy current inspection can frequently be performed without defects in all types of materials. Minute cracks, checks, and removing the surface coatings, such as primer, paint, and voids too small to be seen by x-ray can be located by ultrasonic anodized films. It can be effective in detecting surface and inspection. An ultrasonic test instrument requires access to subsurface corrosion, pots, and heat-treat condition.

only one surface of the material to be inspected and can be used with either straight line or angle beam testing techniques.

Eddy Current Instruments A wide variety of eddy current test instruments are Two basic methods are used for ultrasonic inspection. The available. The eddy current test instrument performs three first of these methods is immersion testing. In this method basic functions: generating, receiving, and displaying. The of inspection, the part under examination and the search unit generating portion of the unit provides an alternating current are completely immersed in a liquid couplant, such as water to the test coil. The receiving section processes the signal or other suitable fluids.

from the test coil to the required form and amplitude for display. Instrument outputs or displays consist of a variety The second method is called contact testing. It is readily of visual, audible, storage, or transfer techniques utilizing adapted to field use and is the method discussed in this meters, video displays, chart recorders, alarms, magnetic chapter. In this method, the part under examination and the tape, computers, and electrical or electronic relays.

search unit are coupled with a viscous material, liquid, or a paste that wets both the face of the search unit and the material A reference standard is required for the calibration of eddy under examination.

current test equipment. A reference standard is made from 10-21 Eddy current inspection on crankshaft Eddy current inspection on fan blade Figure 10-10. Eddy current inspection.

Alternating current Conductor Probe coil Primary magnetic field e e e Eddy current e Figure 10-11. Generating an eddy current.

There are three basic ultrasonic inspection methods: pulse transmission pulse, causes a spot to sweep across the screen echo, through-transmission, and resonance. Through- of the CRT or LCD. The spot sweeps from left to right across transmission and pulse echo are shown in Figure 10-19 . the face of the scope 50 to 5,000 times per second or higher if required for high-speed automated scanning. Due to the Pulse Echo speed of the cycle of transmitting and receiving, the picture on the oscilloscope appears to be stationary.

Flaws are detected by measuring the amplitude of signals reflected and the time required for these signals A few microseconds after the sweep is initiated, the rate to travel between specific surfaces and the discontinuity.

generator electrically excites the pulser, and the pulser in turn [Figure 10-20] emits an electrical pulse. The transducer converts this pulse into a short train of ultrasonic sound waves. If the interfaces The time base, triggered simultaneously with each 10-22 A B C The alternating current fl owing When the coil is placed close to an If a fl aw in the conductive material through the coil at a chosen electrically conductive material, eddy disturbs the eddy current circulation, frequency generates a current is included in the material. the magnetic coupling with the magnetic fi eld around the coil. probe is changed and a defect signal can be read by measuring the coil impedance variation.

Alternating current P Probe coil Primary magnetic field Eddy current Secondary magnetic field Conductor S Figure 10-12. Detecting an eddy current.

relationship to the front and back pulses as the flaw is in relation to the front and back surfaces of the specimen. [Figure 10-21] Pulse-echo instruments may also be used to detect flaws not directly underneath the probe by use of the angle beam testing method. Angle beam testing differs from straight beam testing only in the manner that the ultrasonic waves pass through the material being tested. As shown in Figure 10-22 , the beam is projected into the material at an acute angle to the surface by means of a crystal cut at an angle and mounted in plastic. The beam, or a portion thereof, reflects successively from the surfaces of the material or any other discontinuity, including the edge of the piece. In straight beam testing, the Figure 10-13. Impedance plane test.

horizontal distance on the screen between the initial pulse and the first back reflection represents the thickness of the of the transducer and the specimen are properly oriented, the piece; while in angle beam testing, this distance represents ultrasound is reflected back to the transducer when it reaches the width of the material between the searching unit and the the internal flaw and the opposite surface of the specimen. The opposite edge of the piece.

time interval between the transmission of the initial impulse and the reception of the signals from within the specimen are Through-Transmission measured by the timing circuits. The reflected pulse received Through-transmission inspection uses two transducers, one to by the transducer is amplified, transmitted to, and displayed generate the pulse and another placed on the opposite surface on the instrument screen. The pulse is displayed in the same 10-23 Crack Fastener removed Crack Figure 10-14. Typical surface cracks.

Fastener hole crack, fastener in place Skin Chord Skin Angle Upper member crack Second or deeper member crack Crack Skin gap Chord Skin Splice plate Figure 10-15. Typical subsurface cracks.

to receive it. A disruption in the sound path indicates a flaw and Resonance is displayed on the instrument screen. Through-transmission This system differs from the pulse method in that the is less sensitive to small defects than the pulse-echo method.

frequency of transmission may be continuously varied.

The resonance method is used principally for thickness 10-24 Skin Chord Corrosion Skin Bonded doubler Web Stringer Skin and chord web Body skin lap splice Skin and bonded doubler Figure 10-16. Typical structural corrosion.

or a resonance and is shown as a high amplitude value on the indicating screen. If the frequency is increased such that three times the wavelength equals four times the thickness, the reflected signal returns completely out of phase with the transmitted signal and cancellation occurs. Further increase of the frequency causes the wavelength to be equal to the thickness again and gives a reflected signal in phase with the transmitted signal and a resonance once more. By starting at the fundamental frequency and gradually increasing the frequency, the successive cancellations and resonances can be noted and the readings used to check the fundamental frequency reading.

[Figure 10-23] In some instruments, the oscillator circuit contains a motor- Figure 10-17. Ultrasonic inspection.

driven capacitor that changes the frequency of the oscillator.

[Figure 10-24] In other instruments, the frequency is measurements when the two sides of the material being tested changed by electronic means. The change in frequency are smooth and parallel and the backside is inaccessible. The is synchronized with the horizontal sweep of a CRT. The point where the frequency matches the resonance point of horizontal axis represents a frequency range. If the frequency the material being tested is the thickness determining factor.

range contains resonances, the circuitry is arranged to present It is necessary that the frequency of the ultrasonic waves these vertically. Calibrated transparent scales are then placed corresponding to a particular dial setting be accurately in front of the tube and the thickness can be read directly.

known. Checks are made with standard test blocks to guard The instruments normally operate between 0.25 millicycle against possible drift of frequency.

(mc) and 10 mc in four or five bands.

If the frequency of an ultrasonic wave is such that its wavelength The resonance thickness instrument can be used to test the is twice the thickness of a specimen (fundamental frequency), thickness of such metals as steel, cast iron, brass, nickel, then the reflected wave arrives back at the transducer in the copper, silver, lead, aluminum, and magnesium. In addition, same phase as the original transmission so that strengthening areas of corrosion or wear on tanks, tubing, airplane wing skins, of the signal occurs. This results from constructive interference 10-25 TEST SPECIMEN PATH OF THE PROBE (FRONT TO BACK) X X Front Back Back Front Flaw 0 1 2 3 4 Amplitude (Material Thickness) X Signal amplitude C-scan B-scan A-scan Plan view Figure 10-18. Typical structural corrosion.

and other structures or products can be located and evaluated. is positioned to provide a calibration signal representative Direct reading dial-operated units are available that measure of the expected defect. The notch size is chosen to establish thickness between 0.025 inch and 3 inches with an accuracy inspection sensitivity (response to the expected defect size).

of better than ±1 percent. Ultrasonic inspection requires a The inspection procedure gives a detailed description of the skilled operator who is familiar with the equipment being required reference standard.

used, as well as the inspection method to be used for the Couplants many different parts being tested. [Figure 10-25] Inspection with ultrasonics is limited to the part in contact Ultrasonic Instruments with the transducer. A layer of couplant is required to couple A portable, battery-powered ultrasonic instrument is used the transducer to the test piece, because ultrasonic energy for field inspection of airplane structure. The instrument does not travel through air. Some typical couplants used are generates an ultrasonic pulse, detects and amplifies the water, glycerin, motor oils, and grease.

returning echo, and displays the detected signal on a Inspection of Bonded Structures CRT or similar display. Piezoelectric transducers produce longitudinal or shear waves, the most commonly used Ultrasonic inspection is finding increasing application in waveforms for aircraft structural inspection.

aircraft bonded construction and repair. Many configurations and types of bonded structures are in use in aircraft. All of Reference Standards these variations complicate the application of ultrasonic Reference standards are used to calibrate the ultrasonic inspections. An inspection method that works well on one instrument. Reference standards serve two purposes: to part or one area of the part may not be applicable for different provide an ultrasonic response pattern that is related to the parts or areas of the same part. Some of the variables in the part being inspected and to establish the required inspection types of bonded structures are as follows: sensitivity. To obtain a representative response pattern, the • Top skin material is made from different materials and reference standard configuration is the same as that of the thickness test structure or is a configuration that provides an ultrasonic response pattern representative of the test structure. The • Different types and thickness of adhesives are used in bonded structures reference standard contains a simulated defect (notch) that 10-26 INSPECTION – NDI OVERVIEW Pulse Echo D ELAMINATION NORMAL 9 9 8 8 6 6 5 5 2 SIGNAL STRENGTH SIGNAL STRENGTH 1 1 0 0 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 DEPTH DEPTH Through-transmission Ultrasonic (TTU) WATER YOKE HANDHELD Figure 10-19. Through-transmission and pulse echo indications.

Ampli fi er RF pulser Flaw Transducer Transducer T F Rate generator Flaw B Specimen Flaw Specimen Cathode ray tube Timing circuit Figure 10-21. Pulse-echo display in relationship to flaw detection.

Cathode ray oscilloscope Figure 10-20. Block diagram of basic pulse-echo system.

10-27 Coaxial cable Quartz crystal Defect 45° Material Figure 10-22. Pulse-echo angle beam testing.

Coaxial cable • Underlying structures contain differences in core material, cell size, thickness, height, back skin material Transducer and thickness, doublers (material and thickness), incident wave Reflective wave closure member attachments, foam adhesive, steps in skins, internal ribs, and laminates (number of layers, layer thickness, and layer material) Reflective A surface Quartz crystal • The top only or top and bottom skin of a bonded structure may be accessible Wavelength T = Types of Defects F = F (Fundamental frequency) Defects can be separated into five general types to represent the various areas of bonded and laminate structures as follows: Figure 8-9. Pulse-echo 1. Type I—disbonds or voids in an outer skin-to- B adhesive interface.

It is necessary that the frequency of the ultrasonic 2. Type II—disbonds or voids at the adhesive-to-core waves corresponding to a particular dial setting be interface.

T = W F= 2F (2nd Harmonic) Material accurately known. Checks should be made with standard under test 3. Type III—voids between layers of a laminate.

test blocks to guard against possible drift of frequency.

4. Type IV—voids in foam adhesive or disbonds between If the frequency of an ultrasonic wave is such that its the adhesive and a closure member at core-to-closure A wavelength is twice the thickness of a specimen (funda- member joints.

C mental frequency), then the reflected wave will arrive 5. Type V—water in the core.

back at the transducer in the same phase as the original transmission so that strengthening of the signal will T = 1 / W F= 3F (3rd Harmonic) 2 1 Acoustic Emission Inspection occur. This results from constructive interference or a Acoustic emission is an NDI technique that involves the resonance and is shown as a high amplitude value on placing of acoustic emission sensors at various locations the indicating screen. If the frequency is increased such on an aircraft structure and then applying a load or stress.

B that three times the wavelength equals four times the The materials emit sound and stress waves that take the D thickness, the reflected signal will return completely form of ultrasonic pulses. Cracks and areas of corrosion in out of phase with the transmitted signal and cancella- the stressed airframe structure emit sound waves that are tion will occur. Further increase of the frequency causes registered by the sensors. These acoustic emission bursts T = 2W F= 4F (4th Harmonic) the wavelength to be equal to the thickness again and 1 can be used to locate flaws and to evaluate their rate of gives a reflected signal in phase with the transmitted growth as a function of applied stress. Acoustic emission signal and a resonance once more.

testing has an advantage over other NDI methods in that it Figure 10-23. Conditions of ultrasonic resonance in a metal plate.

can detect and locate all of the activated flaws in a structure By starting at the fundamental frequency and gradually in one test. Because of the complexity of aircraft structures, increasing the frequency, the successive cancellations and resonances can be noted and the readings used 10-28 to check the fundamental frequency reading. [Figure 8-10] the particles, in dry powder form, may be dusted over the H. F. Pulse surface of the part. The wet process is more commonly used oscillator amplifier in the inspection of aircraft parts.

CRT Material If a discontinuity is present, the magnetic lines of force are disturbed and opposite poles exist on either side of the discontinuity. The magnetized particles thus form a pattern in Transducer Motor the magnetic field between the opposite poles. This pattern, known as an “indication,” assumes the approximate shape of the surface projection of the discontinuity. A discontinuity Tuning capacitor Contacts may be defined as an interruption in the normal physical Horizontal time-base generator structure or configuration of a part, such as a crack, forging lap, seam, inclusion, porosity, and the like. A discontinuity may or may not affect the usefulness of a part.

Figure 10-24. Block diagram of resonance thickness measuring system.

Development of Indications When a discontinuity in a magnetized material is open to the surface and a magnetic substance (indicating medium) is available on the surface, the flux leakage at the discontinuity tends to form the indicating medium into a path of higher permeability. (Permeability is a term used to refer to the ease that a magnetic flux can be established in a given magnetic circuit.) Because of the magnetism in the part and the adherence of the magnetic particles to each other, the indication remains on the surface of the part in the form of an approximate outline of the discontinuity that is immediately below it. The same action takes place when the discontinuity is not open to the surface, but since the amount of flux leakage is less, fewer particles are held in place and a fainter and less sharply defined indication is obtained.

Figure 10-25. Ultrasonic inspection of a composite structure.

If the discontinuity is very far below the surface, there application of acoustic emission testing to aircraft has may be no flux leakage and no indication on the surface.

required a new level of sophistication in testing technique The flux leakage at a transverse discontinuity is shown and data interpretation.

in Figure 10-26 . The flux leakage at a longitudinal discontinuity is shown in Figure 10-27 .

Magnetic Particle Inspection Magnetic particle inspection is a method of detecting invisible Types of Discontinuities Disclosed cracks and other defects in ferromagnetic materials, such as The following types of discontinuities are normally detected iron and steel. It is not applicable to nonmagnetic materials.

by the magnetic particle test: cracks, laps, seams, cold shuts, In rapidly rotating, reciprocating, vibrating, and other highly- inclusions, splits, tears, pipes, and voids. All of these may stressed aircraft parts, small defects often develop to the affect the reliability of parts in service.

point that they cause complete failure of the part. Magnetic particle inspection has proven extremely reliable for the Cracks, splits, bursts, tears, seams, voids, and pipes are rapid detection of such defects located on or near the surface.

formed by an actual parting or rupture of the solid metal.

With this method of inspection, the location of the defect is Cold shuts and laps are folds that have been formed in the indicated and the approximate size and shape are outlined.

metal, interrupting its continuity.

The inspection process consists of magnetizing the part and Inclusions are foreign material formed by impurities in the then applying ferromagnetic particles to the surface area to be metal during the metal processing stages. They may consist, inspected. The ferromagnetic particles (indicating medium) for example, of bits of furnace lining picked up during the may be held in suspension in a liquid that is flushed over the melting of the basic metal or of other foreign constituents.

part; the part may be immersed in the suspension liquid; or Inclusions interrupt the continuity of the metal, because they 10-29 prevent the joining or welding of adjacent faces of the metal. the magnetic field is produced in a direction parallel to the long axis of the part. This is accomplished by placing the part Preparation of Parts for Testing in a solenoid excited by electric current. The metal part then becomes the core of an electromagnet and is magnetized by Grease, oil, and dirt must be cleaned from all parts before induction from the magnetic field created in the solenoid.

they are tested. Cleaning is very important since any grease In longitudinal magnetization of long parts, the solenoid or other foreign material present can produce nonrelevant must be moved along the part in order to magnetize it.

indications due to magnetic particles adhering to the foreign [Figure 10-30] This is necessary to ensure adequate field material as the suspension drains from the part.

strength throughout the entire length of the part.

Grease or foreign material in sufficient amount over a Solenoids produce effective magnetization for approximately discontinuity may also prevent the formation of a pattern 12 inches from each end of the coil, thus accommodating parts at the discontinuity. It is not advisable to depend upon the or sections approximately 30 inches in length. Longitudinal magnetic particle suspension to clean the part. Cleaning by magnetization equivalent to that obtained by a solenoid may suspension is not thorough and any foreign materials so be accomplished by wrapping a flexible electrical conductor removed from the part contaminates the suspension, thereby around the part. Although this method is not as convenient, reducing its effectiveness.

it has an advantage in that the coils conform more closely to the shape of the part, producing a somewhat more uniform In the dry procedure, thorough cleaning is absolutely magnetization. The flexible coil method is also useful for necessary. Grease or other foreign material holds the large or irregularly-shaped parts when standard solenoids magnetic powder, resulting in nonrelevant indications and are not available.

making it impossible to distribute the indicating medium evenly over the part’s surface. All small openings and oil Effect of Flux Density holes leading to internal passages or cavities must be plugged with paraffin or other suitable nonabrasive material. The effectiveness of the magnetic particle inspection also depends on the flux density or field strength at the surface of the Coatings of cadmium, copper, tin, and zinc do not interfere part when the indicating medium is applied. As the flux density with the satisfactory performance of magnetic particle in the part is increased, the sensitivity of the test increases, inspection, unless the coatings are unusually heavy or the because of the greater flux leakages at discontinuities and the discontinuities to be detected are unusually small. resulting improved formation of magnetic particle patterns.

Chromium and nickel plating generally do not interfere with indications of cracks open to the surface of the base metal, but prevent indications of fine discontinuities, such as inclusions.

Because it is more strongly magnetic, nickel plating is more effective than chromium plating in preventing the formation of indications.

Effect of Flux Direction To locate a defect in a part, it is essential that the magnetic lines of force pass approximately perpendicular to the defect.

Figure 10-26. Flux leakage at transverse discontinuity.

It is, therefore, necessary to induce magnetic flux in more than one direction, since defects are likely to exist at any angle to the major axis of the part. This requires two separate magnetizing operations, referred to as circular magnetization and longitudinal magnetization. The effect of flux direction is illustrated in Figure 10-28.

Circular magnetization is the induction of a magnetic field consisting of concentric circles of force about and within the part. This is achieved by passing electric current through the part, locating defects running approximately parallel to the axis of the part. Figure 10-29 illustrates circular Figure 10-27. Flux leakage at longitudinal discontinuity.

magnetization of a crankshaft. In longitudinal magnetization, 10-30 careful and intelligent interpretation and evaluation of Excessively high flux densities may form nonrelevant discontinuities revealed by this procedure are necessary.

indications, such as patterns of the grain flow in the material.

These indications interfere with the detection of patterns The residual inspection procedure involves magnetization of resulting from significant discontinuities. It is therefore the part and application of the indicating medium after the necessary to use a field strength high enough to reveal all magnetizing force has been removed. This procedure relies on possible harmful discontinuities, but not strong enough to the residual or permanent magnetism in the part and is more produce confusing nonrelevant indications. practical than the continuous procedure when magnetization is accomplished by flexible coils wrapped around the part. In general, the residual procedure is used only with steels that Magnetizing Methods have been heat-treated for stressed applications.

When a part is magnetized, the field strength in the part increases to a maximum for the particular magnetizing force Identification of Indications and remains at this maximum as long as the magnetizing force is maintained. The correct evaluation of the character of indications is extremely important but is sometimes difficult to make When the magnetizing force is removed, the field strength from observation of the indications alone. The principal decreases to a lower residual value depending on the magnetic distinguishing features of indications are shape, buildup, properties of the material and the shape of the part. These width, and sharpness of outline. These characteristics magnetic characteristics determine whether the continuous are more valuable in distinguishing between types of or residual method is used in magnetizing the part. discontinuities than in determining their severity. Careful observation of the character of the magnetic particle pattern In the continuous inspection method, the part is magnetized and the indicating medium applied while the magnetizing force is maintained. The available flux density in the part is thus at a maximum. The maximum value of flux depends directly upon the magnetizing force and the permeability of the material that the part is made of.

The continuous method may be used in practically all circular and longitudinal magnetization procedures. The continuous procedure provides greater sensitivity than the residual procedure, particularly in locating subsurface discontinuities.

The highly critical nature of aircraft parts and assemblies and the necessity for subsurface inspection in many applications have resulted in the continuous method being more widely used. Since the continuous procedure reveals more Figure 10-29. Circular magnetization of a crankshaft.

nonsignificant discontinuities than the residual procedure, Longitudinal magnetization Circular magnetization Attraction of particles at defects Attraction of particles at defects A B Figure 10-28. Effect of flux direction on strength of indication.

10-31 must always be included in the complete evaluation of the significance of an indicated discontinuity. The motor-driven movable head slides horizontally in longitudinal guides and is controlled by a switch. The spring The most readily distinguished indications are those produced allows sufficient overrun of the motor-driven head to avoid by cracks open to the surface. These discontinuities include jamming it and also provides pressure on the ends of the fatigue cracks, heat-treat cracks, shrink cracks in welds and work to ensure good electrical contact.

castings, and grinding cracks. An example of a fatigue crack is shown in Figure 10-31. A plunger-operated switch in the fixed head cuts out the forward motion circuit of the movable head motor when Magnaglo Inspection the spring has been properly compressed. In some units, Magnaglo inspection is similar to the preceding method, the movable head is hand operated, and the contact plate is sometimes arranged for operation by an air ram. Both contact but differs in that a fluorescent particle solution is used and the inspection is made under black light. plates are fitted with various fixtures for supporting the work.

[Figure 10-32] Efficiency of inspection is increased by the neon-like glow of defects allowing smaller flaw indications The magnetizing circuit is closed by depressing a pushbutton on the front of the unit. It is set to open automatically, usually to be seen. This is an excellent method for use on gears, threaded parts, and aircraft engine components. The reddish- after about one-half second. The strength of the magnetizing current may be set manually to the desired value by means brown liquid spray or bath that is used consists of Magnaglo paste mixed with a light oil at the ratio of 0.10 to 0.25 ounce of the rheostat or increased to the capacity of the unit by the rheostat short circuiting switch. The current utilized is of paste per gallon of oil. After inspection, the part must be demagnetized and rinsed with a cleaning solvent. indicated on the ammeter. Longitudinal magnetization is produced by the solenoid that moves in the same guide rail as the movable head and is connected in the electrical circuit Magnetizing Equipment by means of a switch.

Fixed (Nonportable) General Purpose Unit A fixed, general The suspension liquid is contained in a sump tank and is purpose unit provides direct current (DC) for wet, continuous, agitated and circulated by a pump. The suspension is applied or residual magnetization procedures. [Figure 10-33] to the work through a nozzle. The suspension drains from the Circular or longitudinal magnetization may be used, and work through a nonmetallic grill into a collecting pan that it may be powered with rectified AC, as well as DC. The leads back to the sump. The circulating pump is operated by contact heads provide the electrical terminals for circular a pushbutton switch.

magnetization. One head is fixed in position with its contact plate mounted on a shaft surrounded by a pressure spring Portable General Purpose Unit so that the plate may be moved longitudinally. The plate It is often necessary to perform the magnetic particle inspection is maintained in the extended position by the spring until at locations where fixed general purpose equipment is not pressure transmitted through the work from the movable available or to perform an inspection on members of aircraft head forces it back.

structures without removing them from the aircraft. It is particularly useful for inspecting landing gear and engine mounts suspected of having developed cracks in service.

Portable units supply both AC and DC magnetization.

This unit is a source of magnetizing and demagnetizing current but does not provide a means for supporting the work or applying the suspension. It operates on 200 volt, 60 cycle AC and contains a rectifier for producing DC when required.

[Figure 10-34] The magnetizing current is supplied through the flexible cables with prods or contact clamps, as shown in Figure 10-35 .

The cable terminals may be fitted with prods or with contact clamps. Circular magnetization may be developed by using either the prods or clamps.

Figure 10-30. Longitudinal magnetization of camshaft (solenoid Longitudinal magnetization is developed by wrapping the method).

10-32 cable around the part. The strength of the magnetizing current acceptable, slight burning is normally acceptable.

is controlled by an eight-point tap switch, and the duration that it is applied is regulated by an automatic cutoff similar Indicating Mediums to that used in the fixed general purpose unit.

The various types of indicating mediums available for magnetic particle inspection may be divided into two general This portable unit also serves as a demagnetizer and material types: wet and dry. The basic requirement for any supplies high amperage, low-voltage AC for this purpose.

indicating medium is that it produce acceptable indications For demagnetization, the AC is passed through the part and of discontinuities in parts.

gradually reduced by means of a current reducer.

In testing large structures with flat surfaces where current The contrast provided by a particular indicating medium on must be passed through the part, it is sometimes impossible the background or part surface is particularly important. The to use contact clamps. In such cases, contact prods are used.

colors most extensively used are black and red for the wet procedure and black, red, and gray for the dry procedure.

Prods can be used with the fixed general purpose unit, as well as the portable unit. The part or assembly being tested may For acceptable operation, the indicating medium must be be held or secured above the standard unit and the suspension of high permeability and low retentivity. High permeability hosed onto the area, while excess suspension drains into the ensures that a minimum of magnetic energy is required to tank. The dry procedure may also be used.

attract the material to flux leakage caused by discontinuities.

Low retentivity ensures that the mobility of the magnetic Prods are held firmly against the surface being tested. There particles is not hindered by the particles themselves becoming is a tendency for a high-amperage current to cause burning magnetized and attracting one another.

at contact areas, but with proper care, such burning is usually slight. For applications where prod magnetization is Demagnetizing The permanent magnetism remaining after inspection must be removed by a demagnetization operation if the part is to be returned to service. Parts of operating mechanisms must be demagnetized to prevent magnetized parts from attracting filings, grindings, or chips inadvertently left in the system or steel particles resulting from operational wear. An accumulation of such particles on a magnetized part may cause scoring of bearings or other working parts. Parts of the airframe must be demagnetized so they do not affect instruments.

Demagnetization between successive magnetizing operations Figure 10-31. Fatigue crack on the bottom end fitting of a Hydrosorb shock absorber.

Figure 10-33. Fixed general-purpose magnetizing unit.

Figure 10-32. Magnaglo inspection.

10-33 is not normally required unless experience indicates that Radiographic omission of this operation results in decreased effectiveness Because of their unique ability to penetrate material and for a particular application. Demagnetization may be disclose discontinuities, X and gamma radiations have accomplished in a number of different ways. A convenient been applied to the radiographic (x-ray) inspection of metal procedure for aircraft parts involves subjecting the part to a fabrications and nonmetallic products.

magnetizing force that is continually reversing in direction and, at the same time, gradually decreasing in strength.

The penetrating radiation is projected through the part to be As the decreasing magnetizing force is applied first in one inspected and produces an invisible or latent image in the film.

direction and then the other, the magnetization of the part When processed, the film becomes a radiograph or shadow also decreases.

picture of the object. This inspection medium and portable unit provides a fast and reliable means for checking the Standard Demagnetizing Practice integrity of airframe structures and engines. [Figure 10-36] The basic procedure for developing a reversing and gradually Radiographic Inspection decreasing magnetizing force in a part involves the use of a solenoid coil energized by AC. As the part is moved away Radiographic inspection techniques are used to locate from the alternating field of the solenoid, the magnetism in defects or flaws in airframe structures or engines with little the part gradually decreases. or no disassembly. This is in marked contrast to other types of nondestructive testing that usually require removal, A demagnetizer whose size approximates that of the work disassembly, and stripping of paint from the suspected is used. For maximum effectiveness, small parts are held as part before it can be inspected. Due to the radiation risks close to the inner wall of the coil as possible. Parts that do associated with x-ray, extensive training is required to become not readily lose their magnetism are passed slowly in and a qualified radiographer. Only qualified radiographers are out of the demagnetizer several times and, at the same time, allowed to operate the x-ray units.

tumbled or rotated in various directions. Allowing a part to remain in the demagnetizer with the current on accomplishes Three major steps in the x-ray process discussed in subsequent very little practical demagnetization. paragraphs are: exposure to radiation, including preparation; processing of film; and interpretation of the radiograph.

The effective operation in the demagnetizing procedure is that of slowly moving the part out of the coil and away from Preparation and Exposure the magnetizing field strength. As the part is withdrawn, it is The factors of radiographic exposure are so interdependent kept directly opposite the opening until it is 1 or 2 feet from that it is necessary to consider all factors for any particular the demagnetizer. The demagnetizing current is not cut off radiographic exposure. These factors include, but are not until the part is 1 or 2 feet from the opening as the part may limited to, the following: be remagnetized if current is removed too soon. Another • Material thickness and density procedure used with portable units is to pass AC through • Shape and size of the object the part being demagnetized, while gradually reducing the current to zero.

• Type of defect to be detected • Characteristics of x-ray machine used • The exposure distance • The exposure angle • Film characteristics • Types of intensifying screen, if used Knowledge of the x-ray unit’s capabilities form a background for the other exposure factors. In addition to the unit rating in kilovoltage, the size, portability, ease of manipulation, and exposure particulars of the available equipment must be thoroughly understood. Previous experience on similar objects is also very helpful in the determination of the overall exposure techniques. A log or record of previous exposures provides specific data as a guide for future radiographs. After Figure 10-34. Portable magnetic particle inspection equipment.

10-34 Prod set Contact clamp Figure 10-35. Magnetic particle inspection accessories.

exposure to x-rays, the latent image on the film is made condition or thickness variations can be immediately permanently visible by processing it successively through a determined. The following paragraphs present several factors developer chemical solution, an acid bath, and a fixing bath, that must be considered when analyzing a radiograph.

followed by a clear water wash.

There are three basic categories of flaws: voids, inclusions, and dimensional irregularities. The last category, dimensional Radiographic Interpretation irregularities, is not pertinent to these discussions, because its From the standpoint of quality assurance, radiographic prime factor is one of degree and radiography is not exact.

interpretation is the most important phase of radiography.

Voids and inclusions may appear on the radiograph in a It is during this phase that an error in judgment can variety of forms ranging from a two-dimensional plane to produce disastrous consequences. The efforts of the whole a three-dimensional sphere. A crack, tear, or cold shut most radiographic process are centered in this phase, where the nearly resembles a two-dimensional plane, whereas a cavity part or structure is either accepted or rejected. Conditions looks like a three-dimensional sphere. Other types of flaws, of unsoundness or other defects that are overlooked, not such as shrink, oxide inclusions, porosity, and so forth, fall understood, or improperly interpreted can destroy the purpose somewhere between these two extremes of form.

and efforts of radiography and can jeopardize the structural integrity of an entire aircraft. A particular danger is the false It is important to analyze the geometry of a flaw, especially for sense of security imparted by the acceptance of a part or items such as the sharpness of terminal points. For example, structure based on improper interpretation.

in a crack-like flaw, the terminal points appear much sharper in a sphere-like flaw, such as a gas cavity. Also, material As a first impression, radiographic interpretation may seem strength may be adversely affected by flaw shape. A flaw simple, but a closer analysis of the problem soon dispels this having sharp points could establish a source of localized stress impression. The subject of interpretation is so varied and concentration. Spherical flaws affect material strength to a far complex that it cannot be covered adequately in this type of lesser degree than do sharp-pointed flaws. Specifications and document. Instead, this chapter gives only a brief review of reference standards usually stipulate that sharp-pointed flaws, basic requirements for radiographic interpretation, including such as cracks, cold shuts, and so forth, are cause for rejection.

some descriptions of common defects.

Material strength is also affected by flaw size. A metallic Experience has shown that, whenever possible, it is component of a given area is designed to carry a certain load important to conduct radiographic interpretation close to plus a safety factor. Reducing this area by including a large the radiographic operation. When viewing radiographs, it flaw weakens the part and reduces the safety factor. Some is helpful to have access to the material being tested. The flaws are often permitted in components due to these safety radiograph can thus be compared directly with the material factors. In this case, the interpreter must determine the degree being tested, and indications due to such things as surface 10-35 Radiation source Specimen Void Dark Light area area Dark area Film After processing Figure 10-36. Radiograph.

of tolerance or imperfection specified by the design engineer. dislodge a few electrons, but an excess of these changes Both flaw size and flaw shape are considered carefully, since could cause irreparable harm. When a complex organism is small flaws with sharp points can be just as bad as large flaws exposed to radiation, the degree of damage, if any, depends with no sharp points. on the body cells that have been changed.

Another important consideration in flaw analysis is flaw Vital organs in the center of the body that are penetrated by location. Metallic components are subjected to numerous and radiation are likely to be harmed the most. The skin usually varied forces during their effective service life. Generally, the absorbs most of the radiation and reacts earliest to radiation.

distribution of these forces is not equal in the component or part, and certain critical areas may be rather highly stressed. If the whole body is exposed to a very large dose of radiation, The interpreter must pay special attention to these areas. death could result. In general, the type and severity of the Another aspect of flaw location is that certain types of pathological effects of radiation depend on the amount of discontinuities close to one another may potentially serve radiation received at one time and the percentage of the as a source of stress concentrations creating a situation that total body exposed. Smaller doses of radiation could cause must be closely scrutinized. blood and intestinal disorders in a short period of time.

The more delayed effects are leukemia and other cancers.

An inclusion is a type of flaw that contains entrapped Skin damage and loss of hair are also possible results of material. Such flaws may be of greater or lesser density than exposure to radiation.

the item being radiographed. The foregoing discussions on Inspection of Composites flaw shape, size, and location apply equally to inclusions and to voids. In addition, a flaw containing foreign material Composite structures are inspected for delamination could become a source of corrosion.

(separation of the various plies), debonding of the skin from the core, and evidence of moisture and corrosion. Previously Radiation Hazards discussed methods including ultrasonic, acoustic emission, Radiation from x-ray units and radioisotope sources is and radiographic inspections may be used as recommended destructive to living tissue. It is universally recognized that by the aircraft manufacturer. The simplest method used in in the use of such equipment, adequate protection must be testing composite structures is the tap test. Newer methods, provided. Personnel must keep outside the primary x-ray such as thermography, have been developed to inspect beam at all times.

composite structures.

Radiation produces change in all matter that it passes through. Tap Testing This is also true of living tissue. When radiation strikes the Tap testing, also referred to as the ring test or coin test, is molecules of the body, the effect may be no more than to widely used as a quick evaluation of any accessible surface 10-36 to detect the presence of delamination or debonding. The inspection consists of measuring or mapping of surface testing procedure consists of lightly tapping the surface with a temperatures when heat flows from, to, or through a test light weight hammer (maximum weight of 2 ounces), a coin, object. All thermographic techniques rely on differentials in or other suitable device. The acoustic response or “ring” is thermal conductivity between normal, defect-free areas and compared to that of a known good area. A “flat” or “dead” those having a defect. Normally, a heat source is used to response indicates an area of concern. Tap testing is limited elevate the temperature of the article being examined while to finding defects in relatively thin skins, less than 0.080" observing the surface heating effects. Because defect-free thick. On honeycomb structures, both sides need to be tested. areas conduct heat more efficiently than areas with defects, Tap testing on one side alone would not detect debonding on the amount of heat that is either absorbed or reflected the opposite side. [Figure 10-37] indicates the quality of the bond. The type of defects that affect the thermal properties include disbonds, cracks, impact Electrical Conductivity damage, panel thinning, and water ingress into composite Composite structures are not inherently electrically materials and honeycomb core. Thermal methods are most effective for thin laminates or for defects near the surface.

conductive. Some aircraft, because of their relatively low speed and type of use, are not affected by electrical issues.

The most widely used thermographic inspection technique Manufacturers of other aircraft, such as high-speed, high- performance jets, are required to utilize various methods of uses an infrared (IR) sensing system to measure temperature distribution. This type of inspection can provide rapid, incorporating aluminum or copper into their structures to make them conductive. The aluminum or copper (aluminum one-sided, non-contact scanning of surfaces, components, or assemblies. The heat source can be as simple as a heat is used with fiberglass and Kevlar, while copper is used with carbon fiber) is imbedded within the plies of the lay-ups either lamp, so long as the appropriate heat energy is applied to the inspection surface. The induced temperature rise is as a thin wire mesh, screen, foil, or spray. When damaged sections of the structure are repaired, care must be taken to a few degrees and dissipates quickly after the heat input is removed. The IR camera records the IR patterns. The ensure that the conductive path be restored. Not only is it necessary to include the conductive material in the repair, resulting temperature data is processed to provide more quantitative information. An operator analyzes the screen but the continuity of the electrical path from the original conductive material to the replacement conductor and back to and determines whether a defect was found. Because IR thermography is a radiometric measurement, it can be the original must be maintained. Electrical conductivity may be checked by use of an ohmmeter. Specific manufacturer’s done without physical contact. Depending on the spatial resolution of the IR camera and the size of the expected instructions must be carefully followed.

damage, each image can be of a relatively large area.

Thermography Furthermore, as composite materials do not radiate heat nearly as much as aluminum and have higher emissivity, Thermography is an NDI technique often used with thin thermography can provide better definition of damage composite structures that use radiant electromagnetic thermal with smaller heat inputs. Understanding of structural energy to detect flaws. Most common sources of heat are arrangement is imperative to ensure that substructure is not heat lamps or heater blankets. The basic principle of thermal Tap hammer 25 – 38 mm (1.00 – 1.50 in) (approximately) 38 mm Panel surface (1.50 in) (approximately) Figure 10-37. Tap testing using hammer.

10-37 mistaken for defects or damage. The weld in Figure 10-38A was made too rapidly. The long and pointed appearance of the ripples was caused by an Inspection of Welds excessive amount of heat or an oxidizing flame. If the weld were cross-sectioned, it would probably disclose gas pockets, A discussion of welds in this chapter is confined to judging porosity, and slag inclusions.

the quality of completed welds by visual means. Although the appearance of the completed weld is not a positive indication Figure 10-38B illustrates a weld that has improper penetration of quality, it provides a good clue about the care used in and cold laps caused by insufficient heat. It appears rough and making it. A properly designed joint weld is stronger than irregular, and its edges are not feathered into the base metal.

the base metal that it joins. The characteristics of a properly The puddle tends to boil during the welding operation if an welded joint are discussed in the following paragraphs.

excessive amount of acetylene is used. This often leaves slight bumps along the center and craters at the finish of the weld.

A good weld is uniform in width; the ripples are even and Cross-checks are apparent if the body of the weld is sound.

well feathered into the base metal and show no burn due to If the weld were cross-sectioned, pockets and porosity are overheating. [Figure 10-38] The weld has good penetration visible. [Figure 10-38C] and is free of gas pockets, porosity, or inclusions. The edges of the bead are not in a straight line, yet the weld is good A bad weld has irregular edges and considerable variation since penetration is excellent.

in the depth of penetration. It often has the appearance of a cold weld.

Penetration is the depth of fusion in a weld. Thorough fusion is the most important characteristic contributing to a sound weld. Penetration is affected by the thickness of the material to be joined, the size of the filler rod, and how it is added.

In a butt weld, the penetration should be 100 percent of the thickness of the base metal. On a fillet weld, the penetration requirements are 25 to 50 percent of the thickness of the base metal. The width and depth of bead for a butt weld and fillet weld are shown in Figure 10-39.

To assist further in determining the quality of a welded joint, several examples of incorrect welds are discussed in the following paragraphs.

C B A Current voltage Current Voltage Speed and speed normal slow fast low low high high Pro fi le Views Figure 10-38. Examples of poor welds: too rapidly (A), improper penetration and cold laps (B), and irregular edges and considerable variation (C).

10-38 Reinforcement ¼ to ½ T Throat 1 / to 1½ T Leg 2 to 3 T Bead width 3 to 5T T 100% Penetration 25 to 50% T Approx. ½ T A B Figure 10-39. Butt weld ( A) and fillet weld (B), showing width and depth of bead.

10-39

Next: Chapter 11 →

Chapter 11

Hand Tools & Measuring Devices

The aviation maintenance technician (AMT) spends a major wrist. Always strike the work squarely with the full face of portion of each day using a wide variety of hand tools to the hammer. When striking a metal tool with a metal hammer, accomplish maintenance tasks. This chapter contains an the use of safety glasses or goggles is strongly encouraged.

overview of some of the hand tools an AMT can expect to use. Always keep the faces of hammers and mallets smooth and free An AMT encounters many special tools as their experience from dents, chips, or gouges to prevent marring of the work.

widens. For example, large transport category aircraft have Screwdrivers different maintenance tasks from those of a light airplane, and special hand tools are often required when working on The screwdriver can be classified by its shape, type of blade, complex aircraft. and blade length. [ Figure 11-2] It is made for only one purpose, loosening or tightening screws or screw head bolts. When using This chapter outlines the basic knowledge required the common screwdriver, select the largest screwdriver whose when using the most common hand tools and measuring blade makes a good fit in the screw that needs to be turned.

instruments used in aircraft repair work. This information, however, cannot replace sound judgment on the part of the A common screwdriver must fill at least 75 percent of the individual, nor additional training as the need arises. There screw slot. If the screwdriver is the wrong size, it cuts and are many times when ingenuity and resourcefulness can burrs the screw slot, making it unusable. The damage may be supplement these basic rules. Sound knowledge is required so severe that the use of a screw extractor may be required. A of these basic rules and of the situations in which they apply.

screwdriver with the wrong size blade may slip and damage The use of tools may vary, but good practices for safety, care, adjacent parts of the structure as well.

and storage of tools remain the same.

The common screwdriver is used only where slotted head General Purpose Tools screws or fasteners are found on aircraft. An example of a fastener that requires the use of a common screwdriver is Hammers & Mallets the camlock style fastener that is used to secure the cowling Figure 11-1 shows some of the hammers that the aviation on some aircraft.

mechanic may be required to use. Metal head hammers are usually sized according to the weight of the head alone The two types of recessed head screws for common use are without the handle.

the Phillips and the Reed & Prince. Both the Phillips and Reed & Prince recessed heads are optional on several types Occasionally, it is necessary to use a soft-faced hammer, of screws. As shown in Figure 11-2 , the Reed & Prince which has a striking surface made of wood, brass, lead, recessed head forms a perfect cross. The screwdriver used rawhide, hard rubber, or plastic. These hammers are intended with this screw is pointed on the end. Since the Phillips for use in forming soft metals and striking surfaces that are screw has a slightly larger center in the cross, the Phillips easily damaged. Soft-faced hammers should not be used screwdriver is blunt on the end. The Phillips screwdriver for striking punch heads, bolts, or nails, as using one in this is not interchangeable with the Reed & Prince. The use of fashion quickly ruins this type of hammer.

the wrong type of screwdriver results in mutilation of the screwdriver and the screw head. When turning a recessed A mallet is a hammer-like tool with a head made of hickory, head screw, use only the proper recessed head screwdriver of rawhide, or rubber. It is handy for shaping thin metal parts the correct size. The most common crosspoint screwdrivers without causing creases or dents with abrupt corners. Always are the Number 1 and Number 2 Phillips. Each of these are use a wooden mallet when pounding a wood chisel or a gouge.

designed to be used for specific sized screws. A Number 1 Phillips screwdriver is used on 2, 3, and 4 screws, while a When using a hammer or mallet, choose the one best suited Number 2 Phillips is used for screw sizes 5, 6, 7, 8, and 9.

for the job. Ensure that the handle is tight. When striking a blow with the hammer, use the forearm as an extension of An offset screwdriver may be used when vertical space the handle. Swing the hammer by bending the elbow, not the 11-1 is limited. Offset screwdrivers are constructed with both ends bent 90° to the shank handle. By using alternate ends, most screws can be seated or loosened even when the swinging space is limited. Offset screwdrivers are made for both standard and recessed head screws. Ratcheting right angle screwdrivers are also available and often prove to be indispensable when working in close quarters.

Phillips Reed & Prince A screwdriver should not be used for chiseling or prying.

Do not use a screwdriver to check an electric circuit since an electric arc will burn the tip and make it ineffective. In some cases, an electric arc may fuse the blade to the unit being checked, creating a short circuit.

Phillips screwdriver When using a screwdriver on a small part, always hold the part in the vise or rest it on a workbench. Do not hold the part in the hand, as the screwdriver may slip and cause serious personal injury.

Replaceable tip screwdrivers, commonly referred to as “10 in 1” screwdrivers, allow for the quick changing of a screwdriver tip and economical replacement of the tip when it becomes worn. A wide variety of screwdriver tips, including O ff set screwdriver flat, crosspoint (Reed & Prince, Phillips), Torx (6-point star- shaped pattern), and square drive tips are available for use with the handles. [Figure 11-3] The cordless hand-held power screwdriver has replaced most automatic or spiral screwdrivers for the removal of multiple screws from an airframe. Care must be exercised when using a power screwdriver. If the slip clutch is set for too high a setting when installing a screw, the screwdriver tip will slip and rotate on top of the screw head, damaging it. The screw should be started by hand to avoid driving the screw into Flat blade screwdriver the nut or nut plate in a cross-threaded manner. To avoid damaging the slot or receptacle in the head of the screw, the Figure 11-2. Typical screwdrivers. use of cordless power drills fitted with a removable tip driver to remove or install screws is not recommended, as the drill does not have a slip-clutch installed.

Ball peen Straight peen Cross peen Tinner’s mallet Riveting hammer Figure 11-1. Hammers.

11-2 Pliers & Plier-Type Cutting Tools punch should never be struck a heavy blow with a hammer because it may bend the punch or cause excessive damage As shown in Figure 11-4 , the pliers used most frequently to the material being worked.

in aircraft repair work are the diagonal, needle-nose, and duckbill. The size of pliers indicates their overall length, Large indentations in metal, which are necessary to start a usually ranging from 5 to 12 inches.

twist drill, are made with a center punch. It should never be struck with enough force to dimple the material around the Roundnose pliers are used to crimp metal. They are not made indentation or to cause the metal to protrude through the other for heavy work because too much pressure springs the jaws, side of the sheet. A center punch has a heavier body than a which are often wrapped to prevent scarring the metal.

prick punch and is ground to a point with an angle of about 60°.

Needle-nose pliers have half round jaws of varying lengths.

The drive punch, which is often called a tapered punch, is used They are used to hold objects and make adjustments in for driving out damaged rivets, pins, and bolts that sometimes tight places.

bind in holes. The drive punch is therefore made with a flat face instead of a point. The size of the punch is determined Duckbill pliers resemble a “duck’s bill” in that the jaws are 1 1 by the width of the face, which is usually ⁄ 8 inch to ⁄ 4 inch.

thin, flat, and have the shape of a duck’s bill. They are used exclusively for twisting safety wire.

Pin punches, often called drift punches, are similar to drive punches and are used for the same purposes. The difference Diagonal pliers are usually referred to as diagonals or between the two is that the sides of a drive punch taper all “dikes.” The diagonal is a short-jawed cutter with a blade the way to the face while the pin punch has a straight shank.

set at a slight angle on each jaw. This tool can be used to Pin punches are sized by the diameter of the face, in thirty- cut wire, rivets, small screws, and cotter pins, besides being 1 3 seconds of an inch, and range from ⁄ 16 to ⁄ 8 inch in diameter.

practically indispensable in removing or installing safety wire. The duckbill pliers and the diagonal cutting pliers are In general practice, a pin or bolt that is to be driven out is used extensively in aviation for the job of safety wiring.

usually started and driven with a drive punch until the sides Two important rules for using pliers: of the punch touch the side of the hole. A pin punch is then 1. Do not make pliers work beyond their capacity. The used to drive the pin or bolt the rest of the way out of the long-nosed variety is especially delicate. It is easy to hole. Stubborn pins may be started by placing a thin piece of spring or break them or nick the edges. If this occurs, scrap copper, brass, or aluminum directly against the pin and they are practically useless.

then striking it with a hammer until the pin begins to move.

2. Do not use pliers to turn nuts. In just a few seconds, a pair of pliers can damage a nut more than years Never use a prick punch or center punch to remove objects of service.

from holes because the point of the punch spreads the object and causes it to bind even more.

Punches Punches are used to locate centers for drawing circles, to start The transfer punch is usually about 4 inches long. It has a holes for drilling, to punch holes in sheet metal, to transfer point that tapers and then turns straight for a short distance location of holes in patterns, and to remove damaged rivets, in order to fit a drill locating hole in a template. The tip has pins, or bolts.

a point similar to that of a prick punch. As its name implies, the transfer punch is used to transfer the location of holes Solid or hollow punches are the two types generally used.

through the template or pattern to the material.

Solid punches are classified according to the shape of their points. Figure 11-5 shows several types of punches.

Prick punches are used to place reference marks on metal.

This punch is often used to transfer dimensions from a paper pattern directly on the metal. To do this, first place the paper pattern directly on the metal. Then go over the outline of the pattern with the prick punch, tapping it lightly with a small hammer and making slight indentations on the metal at the Torx Flat Square drive Crosspoint tip (Phillips) major points on the drawing. These indentations can then be used as reference marks for cutting the metal. A prick Figure 11-3. Replaceable tip screwdriver.

11-3 Auto center punch Diagonal cutter Prick punch Starting punch Duckbill Pin punch Needle-nose Aligning punch Roundnose Center punch Figure 11-4. Pliers.

Drift pin Wrenches The wrenches most often used in aircraft maintenance are classified as open-end, box-end, socket, adjustable, ratcheting and special wrenches. The Allen wrench, although seldom Drive punch used, is required on one special type of recessed screw. One of the most widely used metals for making wrenches is Figure 11-5. Punches.

chrome-vanadium steel. Wrenches made of this metal are almost indestructible. Solid, nonadjustable wrenches with open parallel jaws on one or both ends are known as open-end on nut C, point A will be centered over side “Y” instead of wrenches. These wrenches may have their jaws parallel to side “X.” The centerline of the handle will now be in the the handle or at an angle up to 90°; most are set at an angle dotted line position. It is by reversing (turning the wrench of 15°. The wrenches are designed to fit a nut, bolt head, or over) the position of the wrench that a 15° arc may be made other object, which makes it possible to exert a turning action.

with the wrench handle.

Box-end wrenches are popular tools because of their Although box-end wrenches are ideal to break loose tight usefulness in close quarters. They are called box wrenches nuts or pull tight nuts tighter, time is lost turning the nut off since they box, or completely surround, the nut or bolt head.

the bolt once the nut is broken loose. Only when there is Practically all well-manufactured box-end wrenches are sufficient clearance to rotate the wrench in a complete circle made with 12 points so they can be used in places having as can this tedious process be avoided.

little as 15° swing. In Figure 11-6 , point A on the illustrated double-broached hexagon wrench is nearer the centerline of After a tight nut is broken loose, it can be completely backed the head and the wrench handle than point B and also the off or unscrewed more quickly with an open-end than with a centerline of nut C. If the wrench is inverted and installed box-end wrench. In this case, a combination wrench can be 11-4 used. A combination wrench has a box end on one end and an open-end wrench of the same size on the other.

Another option for removing a nut from a bolt is the ratcheting box-end wrench, which can be swung back and forth to remove the nut or bolt. The box-end, combination, and ratcheting wrenches are shown in Figure 11-7 .

A socket wrench is made of two parts: the socket, which is A B placed over the top of a nut or bolt head; and a handle, which X is attached to the socket. Many types of handles, extensions, Y C and attachments are available to make it possible to use socket wrenches in almost any location or position. Sockets are made with either fixed or detachable handles. Socket wrenches with fixed handles are usually furnished as an accessory to a machine. They have a four, six, or twelve-sided recess to fit a nut or bolt head that needs regular adjustment. Sockets with detachable handles usually come in sets and fit several types of handles, such as the T, ratchet, screwdriver grip, and Figure 11-6. Box-end wrench use.

speed handle. Socket wrench handles have a square lug on one end that fits into a square recess in the socket head. The torque wrench.

two parts are held together by a light, spring-loaded poppet.

Two types of sockets, a set of handles, and an extension bar The hook spanner is for a round nut with a series of notches are shown in Figure 11-8 .

cut in the outer edge. This wrench has a curved arm with a hook on the end that fits into one of the notches on the nut.

The adjustable wrench is a handy utility tool that has smooth The hook is placed in one of these notches with the handle jaws and is designed as an open-end wrench. One jaw is pointing in the direction the nut is to be turned.

fixed, but the other may be moved by a thumbscrew or spiral screwworm adjustment in the handle. The width of the jaws Some hook spanner wrenches are adjustable and fit nuts of may be varied from 0 to ⁄ 2 inch or more. The angle of the various diameters. U-shaped hook spanners have two lugs opening to the handle is 22 ⁄ 2 degrees on an adjustable wrench.

on the face of the wrench to fit notches cut in the face of the One adjustable wrench does the work of several open-end nut or screw plug. End spanners resemble a socket wrench, wrenches. Although versatile, they are not intended to replace but have a series of lugs that fit into corresponding notches the standard open-end, box-end, or socket wrenches. When in a nut or plug. Pin spanners have a pin in place of a lug, and using any adjustable wrench, always exert the pull on the the pin fits into a round hole in the edge of a nut. Face pin side of the handle attached to the fixed jaw of the wrench.

spanners are similar to the U-shaped hook spanners except To minimize the possibility or rounding off the fastener, use that they have pins instead of lugs.

care to fit the wrench to the bolt or nut to be turned.

Most headless setscrews are the hex-head Allen type and Special Wrenches must be installed and removed with an Allen wrench. Allen The category of special wrenches includes the crowfoot, wrenches are six-sided bars in the shape of an L, or they can flare nut, spanner, torque, and Allen wrenches.

be hex-shaped bars mounted in adapters for use with hand [Figure 11-9 and 11-10] 3 1 ratchets. They range in size from ⁄ 64 to ⁄ 2 inch and fit into a hexagonal recess in the setscrew.

The crowfoot wrench is normally used when accessing nuts that must be removed from studs or bolts that cannot be Torque Wrench accessed using other tools.

There are times when definite pressure must be applied to a nut or bolt as it is installed. In such cases, a torque wrench The flare nut wrench has the appearance of a box-end wrench must be used. The torque wrench is a precision tool consisting that has been cut open on one end. This opening allows the of a torque indicating handle and appropriate adapter or wrench to be used on the B-nut of a fuel, hydraulic, or oxygen attachments. It measures the amount of turning or twisting line. Since it mounts using the standard square adapter, like force applied to a nut, bolt, or screw.

the crowfoot wrench, it can be used in conjunction with a 11-5 calibrated and maintained on a preventative maintenance Open-end and calibration schedule. In order to maintain accuracy, it is crucial that a torque wrench and other measuring equipment be calibrated regularly. Some wrenches or tools Box-end may recommend six (6) month calibration intervals, while 10 mm others may schedule it at twelve (12) months.

3/8 The three most commonly used torque wrenches are the 11 mm deflecting beam, dial indicating, and micrometer setting types.

12 mm [Figure 11-10] When using the deflecting beam and the dial indicating torque wrenches, the torque is read visually on a dial or scale mounted on the handle of the wrench. The micrometer 3/8 setting torque wrench is preset to the desired torque. When 10 mm this torque is reached, the operator notices a sharp impulse or breakaway “click.” For additional information on the Ratcheting wrench installation of fasteners requiring the use of a torque wrench, refer to “Installation of Nuts, Washers, and Bolts” located in Combination wrench Chapter 7, Aircraft Materials, Processes and Hardware.

Box-end wrench Strap Wrenches The strap wrench can prove to be an invaluable tool for the Figure 11-7. Ratcheting, box-end, and combination wrenches.

AMT. By their very nature, aircraft components, such as tubing, pipes, small fittings, and round or irregularly-shaped Before each use, the torque wrench should be visually components, are built to be as light as possible while still inspected for damage. If a bent pointer, cracked or broken retaining enough strength to function properly. The misuse of glass (dial type), or signs of rough handling are found, the pliers or other gripping tools can quickly damage these parts.

wrench must be tested. Torque wrenches must be tested at If it is necessary to grip a part to hold it in place, or to rotate it periodic intervals to ensure accuracy. to facilitate removal, consider using a strap wrench that uses a plastic covered fabric strap to grip the part. [Figure 11-11] Calibrating a torque wrench is the process in which the manufacturers of the torque wrench set ensure a precise Impact Drivers torque occurs on a standard and consistent basis. Regular In certain applications, the use of an impact driver may be torque wrench calibration ensures repeatable accuracy and required. Struck with a mallet, the impact driver uses cam adherence to standards. A torque wrench is a precision action to impart a high amount of torque in a sharp impact tool and should be treated and maintained like a delicate to break loose a stubborn fastener. The drive portion of the measuring instrument. A torque wrench must be properly impact driver can accept a number of different drive bits Speed handle Ratchet handle Hinge handle Socket and universal joint combined Extension bar Socket Figure 11-8. Socket wrench set.

11-6 C F E A A = Outside diameter Crowfoot D B = Wall opening C = Center to center D = Length E = Head depth F = Total depth C A E B Flare nut Allen wrench Hook spanner Figure 11-9. Special wrenches.

Dial indicating torque wrench Micrometer “ click-type ” torque wrench Electronic torque wrench De fl ecting beam torque wrench Figure 11-10. Torque wrenches.

11-7 and sockets. The use of special bits and sockets specifically steel, cold-rolled steel, or structural steel. A blade with 18 manufactured for use with an impact driver is required. teeth per inch is preferred for solid stock aluminum, bearing [Figure 11-12] metal, tool steel, and cast iron. Use a blade with 24 teeth per inch when cutting thick-walled tubing, pipe, brass, copper, Metal Cutting Tools channel, and angle iron. Use the 32 teeth per inch blade for cutting thin-walled tubing and sheet metal. When using a Hand Snips hacksaw, observe the following procedures: There are several kinds of hand snips, each of which serves a different purpose. Straight, curved, hawksbill, and aviation 1. Select an appropriate saw blade for the job.

snips are in common use. Straight snips are used for cutting 2. Assemble the blade in the frame so that the cutting straight lines when the distance is not great enough to use a edge of the teeth points away from the handle.

squaring shear and for cutting the outside of a curve. The other 3. Adjust tension of the blade in the frame to prevent the types are used for cutting the inside of curves or radii. Snips saw from buckling and drifting.

should never be used to cut heavy sheet metal. [Figure 11-13] 4. Clamp the work in the vise in such a way that provides Aviation snips are designed especially for cutting heat-treated as much bearing surface as possible and engages the aluminum alloy and stainless steel. They are also adaptable greatest number of teeth.

for enlarging small holes. The blades have small teeth on the 5. Indicate the starting point by nicking the surface with cutting edges and are shaped for cutting very small circles and the edge of a file to break any sharp corner that might irregular outlines. The handles are the compound leverage strip the teeth. This mark also aids in starting the saw type, making it possible to cut material as thick as 0.051 at the proper place.

inch. Aviation snips are available in two types: those which 6. Hold the saw at an angle that keeps at least two teeth cut from right to left and those which cut from left to right.

in contact with the work at all times. Start the cut with a light, steady, forward stroke just outside the cutting Unlike the hacksaw, snips do not remove any material when line. At the end of the stroke, relieve the pressure and the cut is made, but minute fractures often occur along the draw the blade back. (The cut is made only on the cut. Therefore, cuts should be made about ⁄ 32 inch from the forward stroke.)

layout line and finished by hand filing down to the line.

7. After the first few strokes, make each stroke as long Hacksaws as the hacksaw frame allows. This prevents the blade The common hacksaw has a blade, a frame, and a handle.

from overheating. Apply just enough pressure on the The handle can be obtained in two styles: pistol grip and straight. [Figure 11-14] Hacksaw blades have holes in both ends; they are mounted on pins attached to the frame. When installing a blade in a hacksaw frame, mount the blade with the teeth pointing forward, away from the handle.

Blades are made of high-grade tool steel or tungsten steel and are available in sizes from 6 to 16 inches in length. The 10-inch blade is most commonly used. There are two types: Figure 11-11. Strap wrench.

the all-hard blade and the flexible blade. In flexible blades, only the teeth are hardened.

Selection of the best blade for the job involves finding the right type and pitch. An all-hard blade is best for sawing brass, tool steel, cast iron, and heavy cross-section materials.

A flexible blade is usually best for sawing hollow shapes and metals having a thin cross-section.

The pitch of a blade indicates the number of teeth per inch.

Pitches of 14, 18, 24, and 32 teeth per inch are available. A blade with 14 teeth per inch is preferred when cutting machine Figure 11-12. Impact driver.

11-8 Chisels are usually made of eight-sided tool steel bar stock, carefully hardened and tempered. Since the cutting edge is slightly convex, the center portion receives the greatest shock when cutting, and the weaker corners are protected.

The cutting angle should be 60° to 70° for general use, such as for cutting wire, strap iron, or small bars and rods. When using a chisel, hold it firmly in one hand. With the other hand, strike the chisel head squarely with a ball peen hammer.

When cutting square corners or slots, a special cold chisel called a cape chisel should be used. It is like a flat chisel except the cutting edge is very narrow. It has the same cutting angle and is held and used in the same manner as any other chisel.

Figure 11-13. Typical snips.

Rounded or semicircular grooves and corners that have fillets should be cut with a roundnose chisel. This chisel is forward stroke to cause each tooth to remove a small also used to re-center a drill that has moved away from its amount of metal. The strokes should be long and intended center.

steady with a speed not more than 40 to 50 strokes per minute.

The diamond point chisel is tapered square at the cutting end, and then ground at an angle to provide the sharp diamond 8. After completing the cut, remove chips from the blade, point. It is used for cutting B-grooves and inside sharp angles.

loosen tension on the blade, and return the hacksaw to its proper place.

Files Most files are made of high-grade tool steels that are hardened Chisels and tempered. Files are manufactured in a variety of shapes A chisel is a hard steel cutting tool that can be used for cutting and sizes. They are known either by the cross section, the and chipping any metal softer than the chisel itself. It can be general shape, or by their particular use. The cuts of files used in restricted areas and for such work as shearing rivets, must be considered when selecting them for various types or splitting seized or damaged nuts from bolts. [Figure 11-15] of work and materials.

The size of a flat cold chisel is determined by the width of Files are used to square ends, file rounded corners, remove the cutting edge. Lengths vary, but chisels are seldom under burrs and slivers from metal, straighten uneven edges, smooth 5 inches or over 8 inches long.

rough edges, and file holes and slots.

Files have three distinguishing features: 1. Their length, measured exclusive of the tang [Figure 11-16] ; 2. Their kind or name, such as a hand file shown in Figure 11-16 , that has reference to the relative coarseness of the teeth; and 3. Their cut, such as a single- or double-cut file.

Pistol grip Files are usually made in two types of cuts: single cut and double cut. The single cut file has a single row of teeth extending across the face at an angle of 65° to 85° with the length of the file. The size of the cuts depends on the coarseness of the file. The double cut file has two rows of teeth that cross each other. For general work, the angle of Straight the first row is 40° to 45°. The first row is generally referred to as “overcut,” and the second row as “upcut;” the upcut is Figure 11-14. Hacksaws.

11-9 somewhat finer than and not as deep as the overcut.

60°–70° Care and Use Files and rasps are catalogued in three ways: • Length—Measuring from the tip to the heel of the file.

Convex The tang is never included in the length.

Flat cold chisel • Shape—Refers to the physical configuration of the file (circular, rectangular, triangular, or a variation thereof).

• Cut—Refers to both the character of the teeth or the coarseness—rough, coarse, and bastard for use on heavier classes of work and second cut, smooth, and Single bevel point dead smooth for finishing work.

Most Commonly Used Files Hand Files These are parallel in width and tapered in thickness. They have one safe edge (smooth edge) that permits filing in corners and on other work where a safe edge is required.

Double bevel point Hand files are double cut and used principally for finishing flat surfaces and similar work. [Figure 11-17] Flat Files These files are slightly tapered toward the point in both width and thickness. They cut on both edges, as well as on the sides.

They are the most common files in use. Flat files are double Roundnose cut on both sides and single cut on both edges. [Figure 11-17] Mill Files These are usually tapered slightly in thickness and in width for about one-third of their length. The teeth are ordinarily single cut. These files are used for draw filing and to some Diamond point extent for filing soft metals. [Figure 11-17] Square Files These files may be tapered or blunt and are double cut. They are used principally for filing slots and key seats and for Figure 11-15. Chisels.

surface filing. [Figure 11-17] Half-Round Files Round or Rattail Files These files cut on both the flat and round sides. They may These are circular in cross section and may be either tapered be single or double cut. Their shape permits them to be used or blunt and single or double cut. They are used principally for where other files would be unsatisfactory. [Figure 11-17] filing circular openings or concave surfaces. [Figure 11-17] Lead-Float Files Triangular and Three Square Files These are especially designed for use on soft metals. They These files are triangular in cross section. Triangular files are single cut and are made in various lengths. [Figure 11-17] are single cut and are used for filing the gullet between saw teeth. Three square files, which are double cut, may be used Warding File for filing internal angles, clearing out corners, and filing taps Rectangular in section and tapers to narrow point in width.

and cutters. [Figure 11-17] This file is used for narrow space filing where other files 11-10 Tang Length Hand—taper width, parallel thickness Heel Face Edge Point Mill—taper width, parallel thickness Figure 11-16. Hand file.

cannot be used. [Figure 11-17] Pillar—taper thickness, parallel width Knife File Knife blade section. This file is used by tool and die makers on work having acute angles. [Figure 11-17] Warding—much taper width, parallel thickness Wood File Same section as flat and half-round files. This file has Square, round, and three–square—taper coarser teeth and is especially adaptable for use on wood.

[Figure 11-17] Vixen (Curved-Tooth Files) Half–round—taper Curved-tooth files are especially designed for rapid filing and smooth finish on soft metals and wood. The regular cut is adapted for tough work on cast iron, soft steel, copper, brass, aluminum, wood, slate, marble, fiber, rubber, and so forth. The Knife—taper fine cut gives excellent results on steel, cast iron, phosphor bronze, white brass, and all hard metals. The smooth cut is used where the amount of material to be removed is very slight, but where a superior finish is desired. [Figure 11-17] Vixen—parallel edges and sides The following methods are recommended for using files: Figure 11-17. Types of files. 1. Crossfiling. Before attempting to use a file, place a handle on the tang of the file. This is essential for proper guiding and safe use. In moving the file Pressure should be relieved during the backstroke.

endwise across the work (commonly known as 3. Rounding corners. The method used in filing a rounded crossfiling), grasp the handle so that its end fits into surface depends upon its width and the radius of the and against the fleshy part of the palm with the thumb rounded surface. If the surface is narrow or only a lying along the top of the handle in a lengthwise portion of a surface is to be rounded, start the forward direction. Grasp the end of the file between the thumb stroke of the file with the point of the file inclined and first two fingers. To prevent undue wear of the downward at approximately a 45° angle. Using a file, relieve the pressure during the return stroke.

rocking chair motion, finish the stroke with the heel 2. Drawfiling. A file is sometimes used by grasping it of the file near the curved surface. This method allows at each end, crosswise to the work, then moving it use of the full length of the file.

lengthwise with the work. When done properly, work 4. Removing burred or slivered edges. Practically every may be finished somewhat finer than when cross filing cutting operation on sheet metal produces burrs or with the same file. In draw filing, the teeth of the file slivers. These must be removed to avoid personal produce a shearing effect. To accomplish this shearing injury and to prevent scratching and marring of parts effect, the angle at which the file is held with respect to be assembled. Burrs and slivers prevent parts from to its line of movement varies with different files, fitting properly and should always be removed from depending on the angle at which the teeth are cut.

11-11 the work as a matter of habit. Twist Drills A twist drill is a pointed tool that is rotated to cut holes in Lathe filing requires that the file be held against the work material. It is made of a cylindrical hardened steel bar having revolving in the lathe. The file should not be held rigid or spiral flutes, or grooves, running the length of the body and stationary but should be stroked constantly with a slight a conical point with cutting edges formed by the ends of gliding or lateral motion along the work. A standard mill file the flutes.

may be used for this operation, but the long angle lathe file provides a much cleaner shearing and self-clearing action.

Twist drills are made of carbon steel or high-speed alloy steel.

Use a file with “safe” edges to protect work with shoulders Carbon steel twist drills are satisfactory for the general run from being marred.

of work and are relatively inexpensive. The more expensive high-speed twist drills are used for the tough materials, such Care of Files as stainless steels. Twist drills have from one to four spiral There are several precautions that any good craftsman takes flutes. Drills with two flutes are used for most drilling.

in caring for files. Whereas those with three or four flutes are used principally to follow smaller drills or to enlarge holes.

1. Choose the right file for the material and work to be performed.

The principal parts of a twist drill are the shank, the body, and 2. Keep all files racked and separated so they do not bear the heel. [Figure 11-19] The drill shank is the end that fits against each other.

into the chuck of a hand or power drill. The two shank shapes most commonly used in hand drills are the straight shank and 3. Keep the files in a dry place—rust corrodes the teeth the square or bit stock shank. The straight shank generally points, dulling the file.

is used in hand, breast, and portable electric or pneumatic 4. Keep files clean. Tap the end of the file against the drills. The square shank is made to fit into a carpenter’s bench after every few strokes to loosen and clear the brace. Tapered shanks generally are used in machine shop filings. Use the file card to keep files clean—a dirty drill presses. [Figure 11-20] file is a dull file. A dirty file can also contaminate different metals when the same file is used on multiple The metal column forming the core of the drill is the body.

metal surfaces.

The body clearance area lies just back of the margin. It is slightly smaller in diameter than the margin to reduce the Particles of metal collect between the teeth of a file and may friction between the drill and the sides of the hole. The angle make deep scratches in the material being filed. When these at which the drill point is ground is the lip clearance angle.

particles of metal are lodged too firmly between the teeth and On standard drills used to cut steel and cast iron, the angle cannot be removed by tapping the edge of the file, remove should be 59° from the axis of the drill. For faster drilling of them with a file card or wire brush. Draw the brush across soft materials, sharper angles are used.

the file so that the bristles pass down the gullet between the teeth. [Figure 11-18] The diameter of a twist drill may be given in one of three ways: by fractions, letters, or numbers. Fractionally, they are Drills 1 1 classified by sixteenths of an inch (from ⁄ 16 to 3 ⁄ 2 inches), by The four types of portable drills used in aviation for holding 1 1 thirty-secondths (from ⁄ 32 to 2 ⁄ 2 inches), or by sixty-fourths and turning twist drills are the hand drill, breast drill, electric 1 1 (from ⁄ 64 to 1 ⁄ 4 inches). For a more exact measurement, a power drill, and pneumatic power drill. Holes ⁄ 4 inch in letter system is used with decimal equivalents: A (0.234 inch) diameter and under can be drilled using a hand drill. This to Z (0.413 inch). The number system of classification is most drill is commonly called an “egg beater.” The breast drill is accurate: No. 80 (0.0314 inch) to No. 1 (0.228 inch). Drill designed to hold larger size twist drills than the hand drill.

sizes and their decimal equivalents are shown in Figure 11-21 .

Also, a breastplate is affixed at the upper end of the drill to permit the use of body weight to increase the cutting The twist drill should be sharpened at the first sign of power of the drill. Electric and pneumatic power drills are dullness. For most drilling, a twist drill with a cutting angle available in various shapes and sizes to satisfy almost any of 118° (59° on either side of center) is sufficient. However, requirement. Pneumatic drills are preferred for use around when drilling soft metals, a cutting angle of 90° may be flammable materials, since sparks from an electric drill are more efficient.

a fire or explosion hazard.

Typical procedures for sharpening drills are as follows: [Figure 11-22] 11-12 Lip or cutting edge ) ° – ° ( Shank e c n a r a e l c p i Figure 11-18. File card.

L 1. Adjust the grinder tool rest to a convenient height for Flute resting the back of the hand while grinding.

2. Hold the drill between the thumb and index finger of the right or left hand. Grasp the body of the drill near the shank with the other hand.

3. Place the hand on the tool rest with the centerline of Land the drill making a 59° angle with the cutting face of Body the grinding wheel. Lower the shank end of the drill slightly.

4. Slowly place the cutting edge of the drill against the grinding wheel. Gradually lower the shank of the drill Heel angle (12° – 15°) as you twist the drill in a clockwise direction. Maintain pressure against the grinding surface only until you reach the heel of the drill.

Lip angle (normally 59°) 5. Check the results of grinding with a gauge to determine whether or not the lips are the same length and at a Lip or cutting edges Heel 59° angle.

Alternatively, there are commercially available twist drill Figure 11-19. Twist drill.

grinders available, as well as attachments for bench grinders that ensure consistent, even sharpening of twist drills.

Point Margin Flute Reamers Reamers are used to smooth and enlarge holes to exact size.

Hand reamers have square end shanks so that they can be turned with a tap wrench or similar handle. The various types Straight shank of reamers are illustrated in Figure 11-23 .

A hole that is to be reamed to exact size must be drilled about 0.003 to 0.007 inch undersize. A cut that removes more than Size stamped here 0.007 inch places too much load on the reamer and should not be attempted.

Reamers are made of either carbon tool steel or high-speed Taper shank steel. The cutting blades of a high-speed steel reamer lose their original keenness sooner than those of a carbon steel reamer; however, after the first super keenness is gone, they are still serviceable. The high-speed reamer usually lasts Square shank ( used in brace ) much longer than the carbon steel type.

Figure 11-20. Drill types.

Reamer blades are hardened to the point of being brittle and 11-13 must be handled carefully to avoid chipping them. When it is tapered back for 6 to 7 threads. This tap cuts a complete reaming a hole, rotate the reamer in the cutting direction only. thread when it is cutting above the taper. It is the only tap Do not back a reamer out of a hole by rotating it opposite needed when tapping holes that extend through thin sections.

the cutting direction. Turn the reamer steadily and evenly to The plug tap supplements the taper tap for tapping holes in prevent chattering, or marking and scoring of the hole walls. thick stock.

Reamers are available in any standard size. The straight fluted The bottoming tap is not tapered. It is used to cut full threads reamer is less expensive than the spiral fluted reamer, but to the bottom of a blind hole.

the spiral type has less tendency to chatter. Both types are tapered for a short distance back of the end to aid in starting. Dies may be classified as adjustable round split die and plain Bottoming reamers have no taper and are used to complete round split die. The adjustable split die has an adjusting the reaming of blind holes. screw that can be tightened so that the die is spread slightly.

By adjusting the die, the diameter and fit of the thread can For general use, an expansion reamer is the most practical. be controlled. [Figure 11-26] This type is furnished in standard sizes from ⁄ 4 inch to 1 inch, increasing in diameter by ⁄ 32 -inch increments. Solid dies are not adjustable. Therefore, a variety of thread fits cannot be obtained with this type. There are many types Taper reamers, both hand and machine operated, are used to of wrenches for turning taps, as well as turning dies. The smooth and true taper holes and recesses. T-handle, the adjustable tap wrench, and the diestock for round split dies shown in Figure 11-27 are a few of the more common Countersink types. Information on thread sizes, fits, types, and drill speeds are shown in shown in Figure 11-28 through 11-30 .

A countersink is a tool that cuts a cone-shaped depression around the hole to allow a rivet or screw to set flush with the Layout and Measuring Tools surface of the material. Countersinks are made with various angles to correspond to the various angles of the countersunk Layout and measuring devices are precision tools. They are rivet and screw heads. The angle of the standard countersink carefully machined, accurately marked and, in many cases, shown in Figure 11-24 is 100°.

are made up of very delicate parts. When using these tools, be careful not to drop, bend, or scratch them. The finished Special stop countersinks are available. Stop countersinks product is no more accurate than the measurements or the are adjustable to any desired depth, and the cutters are layout; therefore, it is very important to understand how to interchangeable so that holes of various countersunk angles read, use, and care for these tools.

may be made. Some stop countersinks have a micrometer set arrangement (in increments of 0.001 inch) for adjusting the Rules cutting depths. [Figure 11-24] Rules are made of steel and are either rigid or flexible. The flexible steel rule bends, but it should not be bent intentionally When using a countersink, care must be taken not to remove as it may be broken rather easily. In aircraft work, the unit an excessive amount of material, since this reduces the of measure most commonly used is the inch. The inch may strength of flush joints.

be divided into smaller parts by means of either common or decimal fraction divisions.

Taps and Dies A tap is used to cut threads on the inside of a hole, while a The fractional divisions for an inch are found by dividing 1 1 die is for cutting external threads on round stock. They are the inch into equal parts: halves ( ⁄ 2 ), quarters ( ⁄ 4 ), eighths 1 1 1 made of hard tempered steel and ground to an exact size. ( ⁄ 8 ), sixteenths ( ⁄ 16 ), thirty-secondths ( ⁄ 32 ), and sixty-fourths There are four types of threads that can be cut with standard ( ⁄ 64 ). The fractions of an inch may be expressed in decimals, taps and dies: National Coarse, National Fine, National Extra called decimal equivalents of an inch. For example, ⁄ 8 Fine, and National Pipe. inch is expressed as 0.0125 (one hundred twenty-five ten- thousandths of an inch).

Hand taps are usually provided in sets of three taps for each diameter and thread series. Each set contains a taper tap, a plug tap, and a bottoming tap. The taps in a set are identical in diameter and cross section and the only difference is the amount of taper. [Figure 11-25] The taper tap is used to begin the tapping process, because 11-14 Millimeter Fractional Number Decimal Equivalent Millimeter Fractional Number Decimal Equivalent Millimeter Fractional Number Decimal Equivalent Millimeter Fractional Number Decimal Equivalent 0.1 0.0039 — 0.0410 59 2.2 0.0866 — 0.1470 26 0.15 0.0059 1.05 0.0413 2.25 0.0885 3.75 0.1476 0.2 0.0079 — 0.0420 58 — 0.0890 43 — 0.1495 25 0.25 0.0098 — 0.0430 57 2.3 0.0905 3.8 0.1496 0.3 0.0118 1.1 0.0433 2.35 0.0925 — 0.1520 24 — 0.0135 80 1.15 0.0452 — 0.0935 42 3.9 0.1535 0.35 0.0138 — 0.0465 56 2.38 0.0937 ³⁄32 — — 0.1540 23 — 0.0145 79 1.19 0.0469 ³⁄64 — 2.4 0.0945 3.97 0.1562 ⁵⁄32 — 0.39 0.0156 ¹⁄64 — 1.2 0.0472 — 0.0960 41 — 0.1570 22 0.4 0.0157 1.25 0.0492 2.45 0.0964 4.0 0.1575 — 0.0160 78 1.3 0.0512 — 0.0980 40 — 0.1590 21 0.45 0.0177 — 0.0520 55 2.5 0.0984 — 0.1610 20 — 0.0180 77 1.35 0.0531 — 0.0995 39 4.1 0.1614 0.5 0.0197 — 0.0550 54 — 0.1015 38 4.2 0.1654 — 0.0200 76 1.4 0.0551 2.6 0.1024 — 0.1660 19 — 0.0210 75 1.45 0.0570 — 0.1040 37 4.25 0.1673 0.55 0.0217 1.5 0.0591 2.7 0.1063 4.3 0.1693 — 0.0225 74 — 0.0595 53 — 0.1065 36 — 0.1695 18 0.6 0.0236 1.55 0.0610 2.75 0.1082 4.37 0.1719 ¹¹⁄64 — — 0.0240 73 1.59 0.0625 ¹⁄16 — 2.78 0.1094 ⁷⁄64 — — 0.1730 17 — 0.0250 72 1.6 0.0629 — 0.1100 35 4.4 0.1732 0.65 0.0256 — 0.0635 52 2.8 0.1102 — 0.1770 16 — 0.0260 71 1.65 0.0649 — 0.1110 34 4.5 0.1771 — 0.0280 70 1.7 0.0669 — 0.1130 33 — 0.1800 15 0.7 0.0276 — 0.0670 51 2.9 0.1141 4.6 0.1811 — 0.0292 69 1.75 0.0689 — 0.1160 32 — 0.1820 14 0.75 0.0295 — 0.7000 50 3.0 0.1181 4.7 0.1850 13 — 0.0310 68 1.8 0.0709 — 0.1200 31 4.75 0.1870 0.79 0.0312 ¹⁄32 — 1.85 0.0728 3.1 0.1220 4.76 0.1875 ³⁄16 — 0.8 0.0315 — 0.0730 49 3.18 0.1250 ¹⁄8 — 4.8 0.1890 12 — 0.0320 67 1.9 0.0748 3.2 0.1260 — 0.1910 11 — 0.0330 66 — 0.0760 48 3.25 0.1279 4.9 0.1929 0.85 0.0335 1.95 0.0767 — 0.1285 30 — 0.1935 10 — 0.0350 65 1.98 0.0781 ⁵⁄64 — 3.3 0.1299 — 0.1960 9 0.9 0.0354 — 0.0785 47 3.4 0.1338 5.0 0.1968 — 0.0360 64 2.0 0.0787 — 0.1360 29 — 0.1990 8 — 0.0370 63 2.05 0.0807 3.5 0.1378 5.1 0.2008 0.95 0.0374 — 0.0810 46 — 0.1405 28 — 0.2010 7 — 0.0380 62 — 0.0820 45 3.57 0.1406 ⁹⁄64 5.16 0.2031 ¹³⁄64 — — 0.0390 61 2.1 0.0827 3.6 0.1417 — 0.2040 6 1.0 0.0394 2.15 0.0846 — 0.1440 27 5.2 0.2047 — 0.0400 60 — 0.0860 44 3.7 0.1457 — — 0.2055 5 Figure 11-21. Drill sizes.

11-15 Millimeter Fractional Number Decimal Equivalent Millimeter Fractional Number Decimal Equivalent Millimeter Fractional Number Decimal Equivalent Millimeter Fractional Decimal Equivalent 5.25 0.2067 7.25 0.2854 9.5 0.3740 16.5 0.6496 5.3 0.2086 7.3 0.2874 9.53 0.3750 ³⁄8 — 16.67 0.6562 ²¹⁄32 — 0.2090 4 — 0.2900 L — 0.3770 V 17.0 0.6693 5.4 0.2126 7.4 0.2913 9.6 0.3780 17.06 0.6719 ⁴³⁄64 — 0.2130 — 0.2950 M 9.7 0.3819 17.46 0.6875 ¹¹⁄16 5.5 0.2165 7.5 0.2953 9.75 0.3838 17.5 0.6890 5.56 0.2187 ¹⁄32 — 7.54 0.2968 ¹⁹⁄64 — 9.8 0.3858 17.86 0.7031 ⁴⁵⁄64 5.6 0.2205 7.6 0.2992 — 0.3860 W 18.0 0.7087 — 0.2210 2 — 0.3020 N 9.9 0.3898 18.26 0.7187 ²³⁄32 5.7 0.2244 7.7 0.3031 9.92 0.3906 ²⁵⁄64 — 18.5 0.7283 5.75 0.2263 7.75 0.3051 10.0 0.3937 18.65 0.7344 ⁴⁷⁄64 — 0.2280 1 7.8 0.3071 0.3970 X 19.0 0.7480 5.8 0.2283 7.9 0.3110 — 0.4040 Y 19.05 0.7500 ³⁄4 5.9 0.2323 7.94 0.3125 ⁵⁄16 — 10.32 0.4062 ¹³⁄32 — 19.45 0.7656 ⁴⁹⁄64 — 0.2340 A 8.0 0.3150 — 0.4130 Z 19.5 0.7677 5.95 0.2344 ¹⁵⁄64 — — 0.3160 O 10.5 0.4134 19.84 0.7812 ²⁵⁄32 6.0 0.2362 8.1 0.3189 10.72 0.4219 ²⁷⁄64 20.0 0.7874 — 0.2380 B 8.2 0.3228 11.0 0.4330 20.24 0.7969 ⁵¹⁄64 6.1 0.2401 — 0.3230 P 11.11 0.4375 ⁷⁄16 20.5 0.8071 — 0.2420 C 8.25 0.3248 11.5 0.4528 20.64 0.8125 ¹³⁄16 6.2 0.2441 8.3 0.3268 11.51 0.4531 ²⁹⁄64 21.0 0.8268 6.25 0.2460 D 8.33 0.3281 ²¹⁄64 — 11.91 0.4687 ¹⁵⁄32 21.03 0.8281 ⁵³⁄64 6.3 0.2480 8.4 0.3307 12.0 0.4724 21.43 0.8437 ²⁷⁄32 6.35 0.2500 ¹⁄4 E — 0.3320 Q 12.30 0.4843 ³¹⁄64 21.5 0.8465 6.4 0.2520 8.5 0.3346 12.5 0.4921 21.83 0.8594 ⁵⁵⁄64 6.5 0.2559 8.6 0.3386 12.7 0.5000 ¹⁄2 22.0 0.8661 — 0.2570 F — 0.3390 R 13.0 0.5118 22.23 0.8750 ⁷⁄8 6.6 0.2598 8.7 0.3425 13.10 0.5156 ³³⁄64 22.5 0.8858 — 0.2610 G 8.73 0.3437 ¹¹⁄32 — 13.49 0.5312 ¹⁷⁄32 22.62 0.8906 ⁵⁷⁄64 6.7 0.2638 8.75 0.3445 13.5 0.5315 23.0 0.9055 6.75 0.2657 ¹⁷⁄64 — 8.8 0.3465 13.89 0.5469 ³⁵⁄64 23.02 0.9062 ²⁹⁄32 6.75 0.2657 — 0.3480 S 14.0 0.5512 23.42 0.9219 ⁵⁹⁄64 — 0.2660 H 8.9 0.3504 14.29 0.5625 ⁹⁄16 23.5 0.9252 6.8 0.2677 9.0 0.3543 14.5 0.5709 23.81 0.9375 ¹⁵⁄16 6.9 0.2716 — 0.3580 T 14.68 0.5781 ³⁷⁄64 24.0 0.9449 — 0.2720 I 9.1 0.3583 15.0 0.5906 24.21 0.9531 ⁶¹⁄64 7.0 0.2756 9.13 0.3594 ²³⁄64 — 15.08 0.5937 ¹⁹⁄32 24.5 0.9646 — 0.2770 J 9.2 0.3622 15.48 0.6094 ³⁹⁄32 24.61 0.9687 ³¹⁄32 7.1 0.2795 9.25 0.3641 15.5 0.6102 25.0 0.9843 — 0.2811 K 9.3 0.3661 15.88 0.6250 ⁵⁄8 25.03 0.9844 ⁶³⁄64 7.14 0.2812 ⁹⁄32 — — 0.3680 U 16.0 0.6299 25.4 1.0000 1 7.2 0.2835 9.4 0.3701 16.27 0.6406 ⁴¹⁄64 Figure 11-21. Drill sizes (continued).

11-16 Straight reamer (hand) 59° Taper reamer (hand) Spiral taper reamer (power) Straight reamer (power) Expansion reamer Adjustable reamer Figure 11-23. Reamers.

Rules are manufactured in two basic styles — those divided or marked in common fractions and those divided or marked in decimals or divisions of one one-hundredth of an inch. A rule may be used either as a measuring tool or as a straightedge.

[Figure 11-31] Combination Sets The combination set, as its name implies, is a tool that has several uses. It can be used for the same purposes as an ordinary tri-square, but it differs from the tri-square in that the head slides along the blade and can be clamped at any desired place. Combined with the square or stock head are a level and scriber. The head slides in a central groove on 12° - 15° the blade or scale, which can be used separately as a rule.

[Figure 11-32] The spirit level in the stock head makes it convenient to 59° 59° square a piece of material with a surface and at the same time tell whether one or the other is plumb or level. The head can be used alone as a simple level.

The combination of square head and blade can also be used as a marking gauge to scribe lines at a 45° angle, as a depth gauge, or as a height gauge. A convenient scriber is held frictionally in the head by a small brass bushing.

Figure 11-22. Drill sharpening procedures.

11-17 Cutter shaft Cutter 100° Pilot Body Lock nut 100° Stop Chip opening Profile view Top view Stop countersink Standard countersink Fiber collar Figure 11-24. Countersinks.

The center head is used to find the center of shafts or other marking through holes. [Figure 11-33] cylindrical work. The protractor head can be used to check angles and also may be set at any desired angle to draw lines. Before using a scriber, always inspect the points for sharpness. Be sure the straightedge is flat on the metal Scriber and in position for scribing. Tilt the scriber slightly in the The scriber is designed to serve the aviation mechanic in direction toward which it will be moved, holding it like a pencil. Keep the scriber’s point close to the guiding edge of the same way a pencil or pen serves a writer. In general, it is used to scribe or mark lines on metal surfaces. The scriber is the straightedge. The scribed line should be heavy enough to be visible, but no deeper than necessary to serve its purpose.

made of tool steel, 4 to 12 inches long, and has two needle pointed ends. One end is bent at a 90° angle for reaching and Taper Adjusting screw Adjustable round split die Plug Bottoming Plain round split die Figure 11-25. Hand taps.

Figure 11-26. Types of dies.

11-18 describing arcs and circles. Dividers should be used to transfer critical measurements because they are more accurate than a pencil compass.

Tap wrenches Calipers Calipers are used for measuring diameters and distances or Diestock for comparing distances and sizes. The three common types of calipers are inside, outside, and hermaphrodite calipers, such as gear tool calipers. [Figure 11-34] Outside calipers are used for measuring outside dimensions— for example, the diameter of a piece of round stock. Inside calipers have outward curved legs for measuring inside diameters, such as diameters of holes, the distance between two surfaces, the width of slots, and other similar jobs. A Figure 11-27. Diestock and tap wrenches.

hermaphrodite caliper is generally used as a marking gauge in layout work. It should not be used for precision measurement.

It is very important to use a scribe only where it is defining a line to be cut as scribed lines may introduce stress points Micrometer Calipers where failures can occur.

There are four types of micrometer calipers, each designed for a specific use: outside micrometer, inside micrometer, Dividers and Pencil Compasses depth micrometer, and thread micrometer.

Dividers and pencil compasses have two legs joined at the top by a pivot. They are used to scribe circles and arcs and Micrometers are available in a variety of sizes, either 0 to for transferring measurements from the rule to the work.

⁄ 2 inch, 0 to 1 inch, 1 to 2 inch, 2 to 3 inch, 3 to 4 inch, 4 to 5 inch, or 5 to 6 inch sizes. In addition to the micrometer Pencil compasses have one leg tapered to a needle point. The inscribed with the measurement markings, micrometers other leg has a pencil or pencil lead inserted. Dividers have equipped with electronic digital liquid crystal display (LCD) both legs tapered to needle points.

readouts are also in common use.

When using pencil compasses or dividers, the following The AMT uses the outside micrometer more often than any procedures are suggested: other type. It may be used to measure the outside dimensions 1. Inspect the points to make sure they are sharp.

of shafts, thickness of sheet metal stock, the diameter of drills, and for many other applications. [Figure 11-35] 2. To set the dividers or compasses, hold them with the point of one leg in the graduations on the rule. Turn the The smallest measurement that can be made with the use adjustment nut with the thumb and forefinger. Adjust of the steel rule is one sixty-fourth of an inch in common the dividers or compasses until the point of the other fractions and one one-hundredth of an inch in decimal leg rests on the graduation of the rule that gives the fractions. To measure more closely than this (in thousandths required measurement.

and ten-thousandths of an inch), a micrometer is used. If a 3. To draw an arc or circle with either the pencil dimension given in a common fraction is to be measured compasses or dividers, hold the thumb attachment on with the micrometer, the fraction must be converted to its the top with the thumb and forefinger. With pressure decimal equivalent.

exerted on both legs, swing the compass in a clockwise direction and draw the desired arc or circle.

All four types of micrometers are read in the same way. The 4. The tendency for the legs to slip is avoided by inclining method of reading an outside micrometer is discussed later the compasses or dividers in the direction in which in this chapter.

they are being rotated. In working on metals, the Micrometer Parts dividers are used only to scribe arcs or circles that are The fixed parts of a micrometer are the frame, barrel, and anvil.

later removed by cutting. All other arcs or circles are The movable parts of a micrometer are the thimble and spindle.

drawn with pencil compasses to avoid scratching the The thimble rotates the spindle, which moves in the threaded material.

portion inside the barrel. Turning the thimble provides an 5. On paper layouts, the pencil compasses are used for 11-19 National Coarse Thread Series National Fine Thread Series Medium Fit Class 3 (NC) Medium Fit Class 3 (NF) Tap Drill Tap Drill Size Diameter Size Diameter Body Preferred Nearest Body Preferred Nearest and of Body and of Body Drill Diameter Standard Drill Diameter Standard Threads for Thread Threads for Thread of Hole Drill Size of Hole Drill Size 0-80 0.060 52 0.0472 ³⁄64 " 1-64 0.073 47 0.0575 #53 1-72 0.073 47 0.0591 #53 2-56 0.086 42 0.0682 #51 2-64 0.086 42 0.0700 #50 3-48 0.099 37 0.078 ⁵⁄64 3-56 0.099 37 0.0810 #46 4-40 0.112 31 0.0866 #44 4-48 0.112 31 0.0911 #42 5-40 0.125 29 0.0995 #39 5-44 0.125 25 0.1024 #38 6-32 0.138 27 0.1063 #36 6-40 0.138 27 0.113 #33 8-32 0.164 18 0.1324 #29 8-36 0.164 18 0.136 #29 10-24 0.190 10 0.1472 #26 10-32 0.190 10 0.159 #21 12-24 0.216 2 0.1732 #17 12-28 0.216 2 0.180 #15 ¹⁄4 -20 0.250 ¹⁄4 0.1990 #8 ¹⁄4 -28 0.250 F 0.213 #3 ⁵⁄16 -18 0.3125 ⁵⁄16 0.2559 #F ⁵⁄16 -24 0.3125 ⁵⁄16 0.2703 I ³⁄8 -16 0.375 ³⁄8 0.3110 ⁵⁄16 " ³⁄8 -24 0.375 ³⁄8 0.332 Q ⁷⁄16 -14 0.4375 ⁷⁄16 0.3642 U ⁷⁄16 -20 0.4375 ⁷⁄16 0.386 W ¹⁄2 -13 0.500 ¹⁄2 0.4219 ²⁷⁄64 " ¹⁄2 -20 0.500 ¹⁄2 0.449 ⁷⁄16 " ⁹⁄16 -12 0.5625 ⁹⁄16 0.4776 ³¹⁄64 " ⁹⁄16 -18 0.5625 ⁹⁄16 0.506 ¹⁄2 " ⁵⁄8 -11 0.625 ⁵⁄8 0.5315 ¹⁷⁄64 " ⁵⁄8 -18 0.625 ⁵⁄8 0.568 ⁹⁄16 " ³⁄4 -10 0.750 ³⁄4 0.6480 ⁴¹⁄64 " ³⁄4 -16 0.750 ³⁄4 0.6688 ¹¹⁄16 " ⁷⁄8 -9 0.875 ⁷⁄8 0.7307 ⁴⁹⁄64 " ⁷⁄8 -14 0.875 ⁷⁄8 0.7822 ⁵¹⁄64 " 1-8 1.000 1.0 0.8376 ⁷⁄8 " 1-14 1.000 1.0 0.9072 ⁴⁹⁄64 " Figure 11-28. American (National) screw thread sizes.

Pitch Diameter Size and Threads Tap Drill for Pipe Threads Number Depth Nominal Pipe of of Size OD Size Minor Diameter A B L2 L1 Threads Thread Inches (inches) Drill Small End of Pipe (inches) (inches) (inches) (inches) Per Inch (inches) ¹⁄8 27 0.36351 0.37476 0.2638 0.180 0.405 0.02963 0.33388 R ¹⁄4 18 0.47739 0.48989 0.4018 0.200 0.540 0.04444 0.43294 ⁷⁄16 ³⁄8 18 0.61201 0.62701 0.4078 0.240 0.675 0.04444 0.56757 ³⁷⁄64 ¹⁄2 14 0.75843 0.77843 0.5337 0.320 0.840 0.05714 0.70129 ²³⁄32 ³⁄4 14 0.96768 0.98887 0.5457 0.339 1.050 0.5714 0.91054 ⁵⁹⁄64 1 11 ¹⁄2 1.21363 1.23863 0.6828 0.400 1.315 0.06957 1.14407 1 ⁵⁄32 1 ¹⁄4 11 ¹⁄2 1.55713 1.58338 0.7068 0.420 1.660 0.06957 1.48757 1 ¹⁄2 1 ¹⁄2 11 ¹⁄2 1.79609 1.82234 0.7235 0.420 1.900 0.06957 1.72652 1 ⁴⁷⁄64 2 11 ¹⁄2 2.26902 2.29627 0.7565 0.436 2.375 0.06957 2.19946 1 ⁷⁄32 2 ¹⁄2 8 2.71953 2.76216 1.1375 0.682 2.875 0.10000 2.61953 2 ⁵⁄8 3 8 3.34062 3.8850 1.2000 0.766 3.500 0.10000 3.24063 3 ¹⁄4 3 ¹⁄2 8 3.83750 3.88881 1.2500 0.821 4.000 0.10000 3.73750 3 ³⁄4 4 8 4.33438 4.38712 1.3000 0.844 4.500 0.10000 4.23438 4 ¹⁄4 Figure 11-29. American (National) pipe thread dimensions and tap drill sizes.

11-20 Plastic Tool or Alloy Soft Annealed Malleable Hard Cast and Hard Mild Steel Hard Steel Metals Cast Iron Iron Iron Diameter of Drill Rubber 100 FPM Steel Cast Steel 300 FPM 140 FPM 90 FPM 80 FPM 200 FPM 60 FPM 40 FPM ¹⁄16 (No. 53 – 80) 18,320 12,217 8,554 6,111 5,500 4,889 3,667 2,445 ³⁄32 (No. 42 – 52) 12,212 8,142 5,702 4,071 3,666 3,258 2,442 1,649 ¹⁄8 (No. 31– 41) 9,160 6,112 4,278 3,056 2,750 2,445 1,833 1,222 ⁵⁄32 (No. 23 – 30) 7,328 4,888 3,420 2,444 2,198 1,954 1,465 977 ³⁄16 (No. 13 – 22) 6,106 4,075 2,852 2,037 1,833 1,630 1,222 815 ⁷⁄32 (No. 1– 12) 5,234 3,490 444 1,745 1,575 1,396 1,047 698 ¹⁄4 (A – F) 4,575 3,055 2,139 1,527 1,375 1,222 917 611 ⁹⁄32 (G – K) 4,071 2,715 1,900 1,356 1,222 1,084 814 542 ⁹⁄16 (L – N) 3,660 2,445 1,711 1,222 1,100 978 7,333 489 ¹¹⁄32 (O – R) 3,330 2,220 1,554 1,110 1,000 888 666 444 ³⁄8 (S – U) 3,050 2,037 1,426 1,018 917 815 611 407 ¹³⁄32 (V – Z) 2,818 1,878 1,316 939 846 752 563 376 ⁷⁄16 2,614 1,746 1,222 873 786 698 524 349 ¹⁵⁄32 2,442 1,628 1,140 814 732 652 488 326 ¹⁄2 2,287 1,528 1,070 764 688 611 458 306 ⁹⁄16 2,035 1,357 950 678 611 543 407 271 ³⁄8 1,830 1,222 856 611 550 489 367 244 1 ¹⁄16 1,665 1,110 777 555 500 444 333 222 ³⁄4 1,525 1,018 713 509 458 407 306 204 Figure 11-30. Drill speeds.

⁷⁄16 ⁹⁄16 ⁵⁄16 ¹¹⁄16 ¹³⁄16 ³⁄16 ³⁄64 ⁵⁄64 ¹⁵⁄16 ¹⁄16 ¹⁄64 ⁷⁄64

1 2

¹⁄32 ⁶⁄32 ¹⁄8 ²⁄32 ⁵⁄32 ¹⁄4 ³⁄32 ⁴⁄32 ⁷⁄8 ³⁄4 ³⁄8 ⁵⁄8 ¹⁄2 Figure 11-31. Rules.

11-21 Scriber Protractor head Level 0 180 11 2 3 4 5 8 9 10 Stock head Center head Figure 11-32. Combination set.

Hermaphrodite calipers Figure 11-33. Scriber.

opening between the anvil and the end of the spindle where Spring inside calipers the work is measured. The size of the work is indicated by the graduations on the barrel and thimble. [Figure 11-36] Reading a Micrometer The lines on the barrel marked 1, 2, 3, 4, and so forth, indicate measurements of tenths, or 0.100 inch, 0.200 inch, 0.300 inch, 0.400 inch, respectively. [Figure 11-37] Each of the sections between the tenths divisions (between 1, Firm joint screw 2, 3, 4, and so forth) is divided into four parts of 0.025 inch adjusting inside each. One complete revolution of the thimble (from zero on calipers the thimble around to the same zero) moves it one of these divisions (0.025 inch) along the barrel.

The bevel edge of the thimble is divided into 25 equal parts.

Each of these parts represents one twenty-fifth of the distance the thimble travels along the barrel in moving from one of the 0.025 inch divisions to another. Thus, each division on the thimble represents one one-thousandth (0.001) of an inch.

These divisions are marked for convenience at every five Firm joint screw spaces by 0, 5, 10, 15, and 20. When 25 of these graduations adjusting outside have passed the horizontal line on the barrel, the spindle calipers (having made one revolution) has moved 0.025 inch.

Spring outside calipers The micrometer is read by first noting the last visible figure on the horizontal line of the barrel representing tenths of an inch. Add to this the length of barrel between the thimble and the previously noted number. (This is found by multiplying Figure 11-34. Calipers.

11-22 the number of graduations by 0.025 inch.) Add to this the number of divisions on the bevel edge of the thimble that coincides with the line of the graduation. The total of the three figures equals the measurement. [Figure 11-38] Vernier Scale Some micrometers are equipped with a vernier scale that makes it possible to directly read the fraction of a division that is indicated on the thimble scale. Typical examples of the vernier scale as it applies to the micrometer are shown in Figure 11-39 .

All three scales on a micrometer are not fully visible without turning the micrometer, but the examples shown in Figure 11-38 are drawn as though the barrel and thimble of the micrometer were laid out flat so that all three scales can be seen at the same time. The barrel scale is the lower horizontal scale, the thimble scale is vertical on the right, and the long horizontal lines (0 through 9 and 0) make up the vernier scale.

Figure 11-35. Outside micrometers. In reading a micrometer, an excellent way to remember the relative scale values is to remember that the 0.025 inch barrel scale graduations are established by the lead screw (40 any thimble graduation.

threads per inch). Next, the thimble graduations divide the 0.025 inch into 25 parts, each equal to 0.001 inch. Then, the In the first example in Figure 11-39 , the barrel reads vernier graduations divide the 0.001 inch into 10 equal parts, 0.275 inch and the thimble reads more than 0.019 inch. The each equal to 0.0001 inch. Remembering the values of the number 1 graduation on the thimble is aligned exactly with various scale graduations, the barrel scale reading is noted. the number 4 graduation on the vernier scale. Thus, the final The thimble scale reading is added to it, then the vernier reading is 0.2944 inch.

scale reading is added to get the final reading. The vernier scale line to be read is always the one aligned exactly with In the second example in Figure 11-39, the barrel reads 0.275 Thread play adjusting nut Thimble cap Anvil Spindle Fixed nut Measuring faces Barrel Thimble Ratchet stop Micrometer screw Clamp ring Frame Figure 11-36. Outside micrometer parts.

11-23 inch, and the thimble reads more than 0.020 inch and less than 0.021 inch. On the Vernier scale, the number 0 graduation coincides closest with the line on the thimble. This means that the thimble reading would be 0.020 inch. Adding this to the barrel reading of 0.275 inch gives a total measurement 0 1 of 0.2950 inch.

The third and fourth examples in Figure 11-39 are additional readings that would require use of the Vernier scale for accurate readings to ten-thousandths of an inch.

Using a Micrometer = 0.150 0.100 0.025 0.025 The micrometer must be handled carefully. If it is dropped, 0.150 in. A its accuracy may be permanently affected. Continually sliding work between the anvil and spindle may wear the surfaces. If the spindle is tightened too much, the frame may be sprung permanently and inaccurate readings will result. In any 1 0 event, follow the manufacturer’s instructions for calibration procedures and types of gauges to be used, such as gauge 0.001 blocks, gauge pins, or ring gauges.

To measure a piece of work with the micrometer, hold the frame of the micrometer in the palm of the hand with the little finger or third finger, whichever is more convenient.

0.100 0.025 0.025 = 0.151 0.001 This allows the thumb and forefinger to be free to revolve the thimble for adjustment.

0.151 in. B A variation of the micrometer is the dial indicator, which measures variations in a surface by using an accurately machined probe mechanically-linked to a circular hand whose 1 0 movement indicates thousandths of an inch or is displayed on a LCD screen. [Figure 11-40] A typical example would be using a dial indicator to measure the amount of runout, or bend, in a shaft. If a bend is suspected, the part can be rotated while resting between a 0.160 in. C pair of machined V-blocks. A dial indicator is then clamped to a machine table stand, and the probe of the indicator is positioned so it lightly contacts the surface. The outer portion Barrel Thimble 1 0 0.300 0.200 0 1 2 0.100 0.175 in. D Figure 11-38. Reading a micrometer.

Horizontal line ¹⁄10 of an inch Figure 11-37. Micrometer measurements.

11-24 of the dial is then rotated until the needle is pointed at zero.

Example 1 Example 2 The part is then rotated, and the amount of bend, or run out, 0.2944 0.2950 0 9 8 7 6 5 4 3 2 1 0 0 9 8 7 6 5 4 3 2 1 0 is displayed on the dial as the needle fluctuates. The total amount of the fluctuation is the runout.

Another common use for the dial indicator is to check for a 3 0 1 2 3 0 1 2 warp in a rotating component, such as a brake disc. In some cases, this can be done with the brake disc installed on the airplane, with the base clamped to a stationary portion of Barrel scale Vernier Scale the structure.

Example 3 Example 4 0.2153 0.1002 In either case, it is imperative that the dial indicator be 0 9 8 7 6 5 4 3 2 1 0 0 9 8 7 6 5 4 3 2 1 0 securely fastened so that movement of the indicator itself 0 10 induces no errors in measurement.

20 5 0 1 2 0 1 Slide Calipers 15 0 Often used to measure the length of an object, the slide caliper provides greater accuracy than the ruler. It can, by virtue of its specially formed jaws, measure both inside and Figure 11-39. Vernier scale readings.

outside dimensions. As the tool’s name implies, the slide caliper jaw is slid along a graduated scale, and its jaws then contact the inside or outside of the object to be measured. The measurement is then read on the scale located on the body of the caliper or on the LCD screen. [Figure 11-41] Some slide calipers also contain a depth gauge for measuring the depth of blind holes.

Figure 11-40. Dial indicator.

11-25 Vernier caliper Digital caliper Dial caliper Figure 11-41. Electronic and dial indicator slide calipers.

11-26

Next: Chapter 12 →

Chapter 12

Fundamentals of Electricity &

Electronics

Introduction Compound This chapter addresses the fundamental concepts that are A compound is a chemical combination of two or more the building blocks for advanced electrical knowledge and elements. Water is one of the most common compounds and practical troubleshooting. Some of the questions addressed is made up of two hydrogen atoms and one oxygen atom.

are: How does energy travel through a copper wire and through space? What is electric current and electromotive Molecule force? What makes a landing light turn on or a hydraulic The smallest particle of matter that can exist and still retain pump motor run? Each of these questions requires an its identity, such as water (H O), is called a molecule.

understanding of many basic principles. By adding one [Figure 12-1] Substances composed of only one type of atom basic idea on top of other basic ideas, it becomes possible are called elements. But most substances occur in nature as to answer most of the interesting and practical questions compounds, that is, combinations of two or more types of about electricity or electronics.

atoms. It would no longer retain the characteristics of water if it were compounded of one atom of hydrogen and two atoms Our understanding of electrical current must begin with the of oxygen. If a drop of water is divided and then divided again nature of matter. All matter is composed of molecules. All and again until it cannot be divided any longer, it is still water.

molecules are made up of atoms, which are themselves made up of electrons, protons, and neutrons.

Atom The atom is considered to be the most basic building block General Composition of Matter of all matter. Atoms are composed of three subatomic Matter particles: protons, neutrons, and electrons. These three Matter can be defined as anything that has mass and volume particles determine the properties of the specific atoms.

and is the substance of which physical objects are composed.

Elements are substances composed of the same atoms with Essentially, it is anything that can be touched. Matter is what specific properties. Oxygen is an example of this. The main all things are made of; whatever occupies space, has mass, property that defines each element is the number of neutrons, and is perceptible to the senses in some way. Weight is an protons, and electrons. Hydrogen and helium are examples indirect method of determining mass, but it is not the same.

of elements. Both of these elements have neutrons, protons, Weight is a measure of the pull of gravity acting on the mass and electrons but differ in the number of those items. This of an object. The more mass an object has, the more it weighs difference alone accounts for the variations in chemical and under the earth’s force of gravity. Mathematically, weight can physical properties of these two different elements. There are be stated as follows: over 100 known elements in the periodic table. [Figure 12-2] They are categorized according to their properties on that Weight = Mass × Gravity table. The kinetic theory of matter also states that the particles that make up the matter are always moving. Thermal Categories of matter are ordered by molecular activity.

expansion is considered in the kinetic theory and explains The four categories or states are: solids, liquids, gases, and why matter contracts when it is cool and expands when it is plasma. For the purposes of the aircraft technician, only hot, with the exception of water/ice.

solids, liquids, and gases are considered.

Electrons, Protons, & Neutrons Element At the center of the atom is the nucleus, which contains An element is a substance that cannot be reduced to a protons and neutrons. Protons are positively-charged simpler form by chemical means. Iron, gold, silver, copper, particles, and neutrons are neutrally-charged particles. A and oxygen are examples of elements. Beyond this point of neutron has approximately the same mass as the proton. The reduction, the element ceases to be what it is.

third particle of the atom is the electron that is a negatively- 12-1 charged particle with a very small mass compared to the maximum number of electrons that can be contained in any proton. The proton’s mass is approximately 1,837 times shell or sub-shell is the same for all atoms and is defined as greater than the electron. Due to the proton and the neutron electron capacity = 2n . In this equation, n represents the location in the central portion of the atom (nucleus) and the energy level in question. The first shell can only contain two electron’s position at the distant periphery of the atom, it electrons; the second shell can only contain eight electrons; is the electron that undergoes the change during chemical the third, 18, and so on until we reach the seventh shell for reactions. Since a proton weighs approximately 1,845 times the heaviest atoms, which have six energy levels. Because the as much as an electron, the number of protons and neutrons innermost shell is the lowest energy level, the shell begins to in its nucleus determines the overall weight of an atom. The fill up from the shell closest to the nucleus and fill outward weight of an electron is not considered in determining the as the atomic number of the element increases. However, weight of an atom. Indeed, the nature of electricity cannot be an energy level does not need to be completely filled before defined clearly because it is not certain whether the electron electrons begin to fill the next level. The Periodic Table is a negative charge with no mass (weight) or a particle of of Elements should be checked to determine an element’s matter with a negative charge. electron configuration.

Hydrogen represents the simplest form of an atom.

Valence Electrons [Figure 12-3] At the nucleus of the hydrogen atom is one Valence is the number of chemical bonds an atom can proton and at the outer shell is one orbiting electron. At a form. Valence electrons are electrons that can participate in more complex level is the oxygen atoms, which has eight chemical bonds with other atoms. The number of electrons electrons in two shells orbiting the nucleus with eight protons in the outermost shell of the atom is the determining factor and eight neutrons. [Figure 12-4] When the total positive in its valence. Therefore, the electrons contained in this shell charge of the protons in the nucleus equals the total negative are called valence electrons.

charge of the electrons in orbit around the nucleus, the atom is said to have a neutral charge.

Ions Ionization is the process by which an atom loses or gains Electron Shells & Energy Levels electrons. Dislodging an electron from an atom causes the Electrons require a certain amount of energy to stay in an atom to become positively charged. This net positively- orbit. This particular quantity is called the electron’s energy charged atom is called a positive ion or a cation. An atom level. By its motion alone, the electron possesses kinetic that has gained an extra number of electrons is negatively energy, while the electron’s position in orbit determines its charged and is called a negative ion or an anion. When atoms potential energy. The total energy of an electron is the main are neutral, the positively-charged proton and the negatively- factor that determines the radius of the electron’s orbit.

charged electron are equal.

Electrons of an atom appear only at certain definite energy levels (shells). The spacing between energy levels is such Free Electrons that when the chemical properties of the various elements are Valence electrons are found drifting midway between two cataloged, it is convenient to group several closely spaced nuclei. Some electrons are more tightly bound to the nucleus permissible energy levels together into electron shells. The of their atom than others and are positioned in a shell or sphere closer to the nucleus, while others are more loosely bound and orbit at a greater distance from the nucleus. These outermost Oxygen atom electrons are called “free” electrons because they can be easily dislodged from the positive attraction of the protons in the Nucleus Electrons nucleus. Once freed from the atom, the electron can then travel from atom to atom, becoming the flow of electrons commonly called current in a practical electrical circuit.

Electron Movement Conductors, Insulators, and Semiconductors The valence of an atom determines its ability to gain or lose an electron, which ultimately determines the chemical Hydrogen atoms and electrical properties of the atom. These properties can be categorized as being a conductor, semiconductor, or insulator, depending on the ability of the material to produce Figure 12-1. A water molecule.

free electrons. When a material has a large number of free 12-2 Figure 12-2. Periodic table of elements.

Electron 8 Protons 8 Neutrons Nucleus (1 Proton) Figure 12-3. Hydrogen atom.

electrons available, a greater current can be conducted in the material.

Conductors Figure 12-4. Oxygen atom.

Elements such as gold, copper, and silver possess many free electrons and make good conductors. The atoms in these of free electrons.

materials have a few loosely bound electrons in their outer orbits. Energy in the form of heat can cause these electrons Insulators in the outer orbit to break loose and drift throughout the material. Copper and silver have one electron in their outer Insulators are materials that do not conduct electrical current very well or not at all, such as glass, ceramic, and plastic.

orbits. At room temperature, a piece of silver wire has billions 12-3 Under normal conditions, atoms in these materials do not express electrical quantities, together with the prefixes and produce free electrons. The absence of free electrons means symbols used to represent each number.

that electrical current cannot be conducted through the material. Only when the material is in an extremely strong Static Electricity electrical field will the outer electrons be dislodged. This Electricity is often described as being either static or dynamic.

action is called breakdown and usually causes physical The difference between the two is based simply on whether damage to the insulator.

the electrons are at rest (static) or in motion (dynamic). Static electricity is a buildup of an electrical charge on the surface Semiconductors of an object. It is considered “static” due to the fact that there The material properties of semiconductors fall in between is no current flowing as in alternate current (AC) or direct conductors and insulators. In their pure state, they are not current (DC) electricity. Static electricity is usually caused good at conducting or insulating. Semiconductors can operate when non-conductive materials, such as rubber, plastic, or like a conductor or insulator depending on what external load glass, are rubbed together causing a transfer of electrons, is placed on the material. Semiconductors are used to make which results in an imbalance of charges between the two transistors and integrated circuits. Silicon and germanium materials. The fact that there is an imbalance of charges are the most widely used semiconductor materials. For a between the two materials means that the objects will exhibit more detailed explanation on this topic, refer to page 12-98 an attractive or repulsive force.

in this chapter.

Attractive and Repulsive Forces Metric Based Prefixes Used for Electrical One of the most fundamental laws of static electricity, as Calculations well as magnetics, deals with attraction and repulsion. Like charges repel each other and unlike charges attract each other.

In any system of measurements, a single set of units is usually All electrons possess a negative charge and as such repel each not sufficient for all the computations involved in electrical other. Similarly, all protons possess a positive charge and repair and maintenance. Small distances, for example, can as such repel each other. Electrons (negative) and protons usually be measured in inches, but larger distances are (positive) are opposite in their charge and attract each other.

more meaningfully expressed in feet, yards, or miles. Since electrical values often vary from numbers that are a millionth For example, if two pith balls are suspended, as shown in part of a basic unit of measurement to very large values, it is Figure 12-6 , and each ball is touched with the charged glass often necessary to use a wide range of numbers to represent rod, some of the charge from the rod is transferred to the balls.

the values of units, such as volts, amperes, or ohms. A series The balls now have similar charges and, consequently, repel of prefixes that appear with the name of the unit have been each other as shown in part B of Figure 12-6 . If a plastic rod devised for the various multiples or submultiples of the basic is rubbed with fur, it becomes negatively charged and the units. There are 12 of these prefixes, which are also known as fur is positively charged. By touching each ball with these conversion factors. Four of the most commonly used prefixes differently charged sources, the balls obtain opposite charges in electrical work are: and attract each other as shown in part C of Figure 12-6 .

Mega (M) means one million (1,000,000).

Kilo (k) means one thousand (1,000).

Although most objects become charged with static electricity by means of friction, a charged substance can also influence Milli (m) means one-thousandth (1⁄1,000).

objects near it by contact. [Figure 12-7] If a positively-charged Micro (μ) means one-millionth (1⁄1,000,000).

rod touches an uncharged metal bar, it draws electrons from the uncharged bar to the point of contact. Some electrons enter Kilo is one of the most extensively used conversion factors. It the rod, leaving the metal bar with a deficiency of electrons explains the use of prefixes with basic units of measurement.

(positively charged) and making the rod less positive than it Kilo means 1,000, and when used with volts, is expressed as was or, perhaps, even neutralizing its charge completely.

kilovolt, meaning 1,000 volts. The symbol for kilo is the letter “k.” Thus, 1,000 volts is one kilovolt or 1 kV. Conversely, A method of charging a metal bar by induction is demonstrated one volt would equal one-thousandth of a kV, or 1 ⁄1,000 kV.

in Figure 12-8 . A positively-charged rod is brought near, but This could also be written 0.001 kV.

does not touch, an uncharged metal bar. Electrons in the metal bar are attracted to the end of the bar nearest the positively- Similarly, the word “milli” means one-thousandth, and charged rod, leaving a deficiency of electrons at the opposite thus, 1 millivolt equals one-thousandth (1⁄1000) of a volt.

end of the bar. If this positively-charged end is touched by Figure 12-5 contains a complete list of the multiples used to a neutral object, electrons will flow into the metal bar and 12-4 neutralize the charge. The metal bar is left with an overall a concentrated negative charge has been placed. By using excess of electrons. an electrostatic detector, it can be shown that the charge is spread evenly over the entire surface of the disk. Since the Electrostatic Field metal disk provides uniform resistance everywhere on its A field of force exists around a charged body. This field is surface, the mutual repulsion of electrons results in an even distribution over the entire surface.

an electrostatic field (sometimes called a dielectric field) and is represented by lines extending in all directions from the Another example, shown in Figure 12-12 , is the charge on charged body and terminating where there is an equal and opposite charge. a hollow sphere. Although the sphere is made of conducting material, the charge is evenly distributed over the outside To explain the action of an electrostatic field, lines are used surface. The inner surface is completely neutral. This phenomenon is used to safeguard operating personnel of the to represent the direction and intensity of the electric field of force. As illustrated in Figure 12-9 , the intensity of the large Van de Graaff static generators used for atom smashing.

The safest area for the operators is inside the large sphere, field is indicated by the number of lines per unit area, and the direction is shown by arrowheads on the lines pointing where millions of volts are being generated.

in the direction in which a small test charge would move (or tend to move) if acted upon by the field of force. The distribution of the charge on an irregularly-shaped object differs from that on a regularly-shaped object. Figure 12-13 Either a positive or negative test charge can be used, but it shows that the charge on such objects is not evenly distributed. The greatest charge is at the points, or areas of has been arbitrarily agreed that a small positive charge is always used in determining the direction of the field. Thus, sharpest curvature, of the objects.

the direction of the field around a positive charge is always Electrostatic Discharge (ESD) Considerations away from the charge because a positive test charge would be repelled. [Figure 12-9] On the other hand, the direction of One of the most frequent causes of damage to a solid- the lines about a negative charge is toward the charge, since state component or integrated circuits is the electrostatic a positive test charge is attracted toward it. discharge (ESD) from the human body when one of these devices is handled. Careless handling of line replaceable Figure 12-10 illustrates the field around bodies having like units (LRUs), circuit cards, and discrete components can charges. Positive charges are shown, but regardless of the cause unnecessarily time consuming and expensive repairs.

type of charge, the lines of force would repel each other if the This damage can occur if a technician touches the mating charges were alike. The lines terminate on material objects pins for a card or box. Other sources for ESD can be the top and always extend from a positive charge to a negative of a toolbox that is covered with a carpet. Damage can be charge. These are imaginary lines used to show the direction avoided by discharging the static electricity from your body a real force takes. by touching the chassis of the removed box, by wearing It is important to know how a charge is distributed on an a grounding wrist strap, and exercising good professional object. Figure 12-11 shows a small metal disk on which handling of the components in the aircraft. This can include placing protective caps over open connectors and not placing an ESD-sensitive component in an environment that causes damage. Parts that are ESD sensitive are typically shipped Number Prefix Symbol in bags specially designed to protect components from electrostatic damage.

1,000,000,000,000 tera t 1,000,000,000 giga g Other precautions that should be taken with working with 1,000,000 mega M electronic components are: 1,000 kilo k 1. Always connect a ground between test equipment and 100 hecto h circuit before attempting to inject or monitor a signal.

10 deka dk 2. Ensure test voltages do not exceed maximum 0.1 deci d allowable voltage for the circuit components and 0.01 centi c transistors.

0.001 milli m 3. Ohmmeter ranges that require a current of more than 0.000001 micro μ one milliampere in the test circuit should not be used 0.000000001 nano n for testing transistors.

Figure 12-5. Prefixes and symbols for multiples of basic quantities.

0.000000000001 pico p 12-5 Electrons are attracted Charge rod by positive charge Positively-charged rod almost touching uncharged bar Pith balls When rod touches bar, electrons enter rod A Metal bar now has positive charge The rod is now less positively charged B Repulsion Figure 12-7. Charging by contact.

Electrons are attracted toward charged rod Electrons are attracted off finger and enter bar C Attraction Figure 12-6. Reaction of like and unlike charges.

4. The heat applied to a diode or transistor, when Finger is removed. Positive soldering is required, should be kept to a minimum and negative charges are by using low-wattage soldering irons and heat sinks.

mostly neutralized 5. Do not pry components of a circuit board.

6. Power must be removed from a circuit before replacing a component.

7. When using test probes on equipment and the space Rod is removed and between the test points is very close, keep the exposed excess electrons remain portion of the leads as small as possible to prevent shorting.

Magnetism Magnetism is defined as the property of an object to attract certain metallic substances. In general, these substances are Figure 12-8. Charging a bar by induction.

ferrous materials; that is, materials composed of iron or iron 12-6 Inside surface neutral Figure 12-9. Direction of electric field around positive and negative charges.

Figure 12-12. Charge on a hollow sphere.

swing freely, it aligns itself with the earth’s magnetic poles.

One end is labeled “N,” meaning the North seeking end or pole of the magnet. If the “N” end of a compass or magnet is referred to as North seeking rather than North, there is no conflict in referring to the pole it seeks, which is the North magnetic pole. The opposite end of the magnet, marked “S” is the South seeking end and points to the South magnetic pole. Since the earth is a giant magnet, its poles attract the ends of the magnet. These poles are not located at the geographic poles.

The somewhat mysterious and completely invisible force of a magnet depends on a magnetic field that surrounds the magnet. [Figure 12-15] This field always exists between Figure 12-10. Field around two positively-charged bodies.

the poles of a magnet and arranges itself to conform to the shape of any magnet.

alloys, such as soft iron, steel, and alnico. These materials, sometimes called magnetic materials, include at least three The theory that explains the action of a magnet holds that each nonferrous materials: nickel, cobalt, and gadolinium, which molecule making up the iron bar is itself a tiny magnet, with are magnetic to a limited degree. All other substances are both North and South poles as illustrated in Figure 12-16A .

considered nonmagnetic. A few of these non-magnetic These molecular magnets each possess a magnetic field, substances can be classified as diamagnetic since they are but in an unmagnetized state, the molecules are arranged at repelled by both poles of a magnet.

random throughout the iron bar. If a magnetizing force, such as stroking with a lodestone, is applied to the unmagnetized Magnetism is an invisible force, the ultimate nature of which has not been fully determined. It can best be described by the effects it produces. Examination of a simple bar magnet similar to that illustrated in Figure 12-14 discloses some basic characteristics of all magnets. If the magnet is suspended to Greatest charge Figure 12-11. Even distribution of charge on metal disk.

Figure 12-13. Charge on irregularly-shaped objects.

12-7 bar, the molecular magnets rearrange themselves in line with North Pole the magnetic field of the lodestone, with all North ends of the magnets pointing in one direction and all South ends in the opposite direction. [Figure 12-16B] In such a configuration, the magnetic fields of the magnets combine to produce the total field of the magnetized bar.

When handling a magnet, avoid applying direct heat, hammering, or dropping it. Heating or sudden shock creates misalignment of the molecules, causing the strength of a South Pole magnet to decrease. When a magnet is to be stored, devices known as “keeper bars” are installed to provide an easy path for flux lines from one pole to the other. This promotes the retention of the molecules in their North-South alignment.

The presence of the magnetic force or field around a magnet can best be demonstrated by the experiment illustrated in Figure 12-17 . A sheet of transparent material, such as glass or Lucite™, is placed over a bar magnet and iron filings are Figure 12-14. One end of magnetized strip points to the magnetic sprinkled slowly on this transparent shield. If the glass or North pole.

Lucite™ is tapped lightly, the iron filings arrange themselves in a definite pattern around the bar, forming a series of lines the two like poles are brought near each other and travel in a from the North to South end of the bar to indicate the pattern of the magnetic field. path parallel to each other. Lines moving in this manner repel each other, causing the magnets as a whole to repel each other.

As shown, the field of a magnet is made up of many individual By reversing the position of one of the magnets, the attraction forces that appear as lines in the iron filing demonstration.

Although they are not “lines” in the ordinary sense, this word of unlike poles can be demonstrated. [Figure 12-19] As the unlike poles are brought near each other, the lines of force is used to describe the individual nature of the separate forces making up the entire magnetic field. These lines of force are rearrange their paths and most of the flux leaving the North pole of one magnet enters the South pole of the other. The also referred to as magnetic flux.

tendency of lines of force to repel each other is indicated by the bulging of the flux in the air gap between the two magnets.

They are separate and individual forces, since one line will never cross another; indeed, they actually repel one another.

To further demonstrate that lines of force do not cross They remain parallel to one another and resemble stretched rubber bands, since they are held in place around the bar by one another, a bar magnet and a horseshoe magnet can be positioned to display a magnetic field similar to that of the internal magnetizing force of the magnet.

The demonstration with iron filings further shows that the magnetic field of a magnet is concentrated at the ends of Lines of force the magnet. These areas of concentrated flux are called the N North and South poles of the magnet. There is a limit to the number of lines of force that can be crowded into a magnet of N S a given size. When a magnetizing force is applied to a piece of magnetic material, a point is reached where no more lines of force can be induced or introduced. The material is then said to be saturated.

S The characteristics of the magnetic flux can be demonstrated by tracing the flux patterns of two bar magnets with like poles together. [Figure 12-18] The two like poles repel one another because the lines of force will not cross each other. As the Figure 12-15. Magnetic field around magnets. arrows on the individual lines indicate, the lines turn aside as 12-8 S S N N S N S N S N S N S N N N N S N N S S S N N N S S S S N S N S N S N S Unmagnetized Magnetized A B Figure 12-16. Arrangement of molecules in a piece of magnetic material.

of one. The nonferrous metals with a permeability greater Figure 12-20 . The magnetic fields of the two magnets do than one, such as nickel and cobalt, are called paramagnetic. not combine, but are rearranged into a distorted flux pattern.

The term ferromagnetic is applied to iron and its alloys, which have by far the greatest permeability. Any substance, The two bar magnets may be held in the hands and the North such as bismuth, having a permeability of less than one, is poles brought near each other to demonstrate the force of considered diamagnetic. repulsion between like poles. In a similar manner, the two South poles can demonstrate this force. The force of attraction Reluctance, the measure of opposition to the lines of force between unlike poles can be felt by bringing a South and a through a material, can be compared to the resistance of an North end together. [Figure 12-21] electrical circuit. The reluctance of soft iron, for instance, is much lower than that of air. Figure 12-24 demonstrates that a Figure 12-22 illustrates another characteristic of magnets.

piece of soft iron placed near the field of a magnet can distort If the bar magnet is cut or broken into pieces, each piece the lines of force, which follow the path of lowest reluctance immediately becomes a magnet itself, with a North and South through the soft iron. pole. This feature supports the theory that each molecule is a magnet, since each successive division of the magnet The magnetic circuit can be compared in many respects produces more magnets.

to an electrical circuit. The magnetomotive force, causing lines of force in the magnetic circuit, can be compared to Since the magnetic lines of force form a continuous loop, the electromotive force (emf) or electrical pressure of an they form a magnetic circuit. It is impossible to say where in electrical circuit. The magnetomotive force is measured in the magnet they originate or start. Arbitrarily, it is assumed gilberts, symbolized by the capital letter “F.” The symbol for that all lines of force leave the North pole of any magnet and the intensity of the lines of force, or flux, is the Greek letter enter at the South pole.

phi, and the unit of field intensity is the gauss. An individual line of force, called a maxwell, in an area of one square There is no known insulator for magnetic flux, or lines of centimeter produces a field intensity of one gauss. Using force, since they pass through all materials. However, they do reluctance rather than permeability, the law for magnetic pass through some materials more easily than others. Thus, circuits can be stated: a magnetomotive force of one gilbert it is possible to shield items, such as instruments, from the causes one maxwell, or line of force, to be set up in a material effects of the flux by surrounding them with a material that when the reluctance of the material is one. offers an easier path for the lines of force. Figure 12-23 shows an instrument surrounded by a path of soft iron, which offers Types of Magnets very little opposition to magnetic flux. The lines of force take the easier path, the path of greater permeability, and are Magnets are either natural or artificial. Since naturally guided away from the instrument.

occurring magnets or lodestones have no practical use, all magnets considered in this chapter are artificial or manmade.

Materials such as soft iron and other ferrous metals are Artificial magnets can be further classified as permanent said to have a high permeability, the measure of the ease magnets, which retain their magnetism long after the with which magnetic flux can penetrate a material. The magnetizing force has been removed, and temporary magnets, permeability scale is based on a perfect vacuum with a which quickly lose most of their magnetism when the external rating of one. Air and other nonmagnetic materials are so magnetizing force is removed.

close to this that they are also considered to have a rating 12-9 Tracing out a magnetic field by means of iron filings Iron filings How the iron filings arrange themselves Lucite Magnet Magnet Figure 12-17. Tracing out a magnetic field with iron filings.

Air gap Air gap S N S N N S S N Figure 12-18. Like poles repel.

Figure 12-19. Unlike poles attract.

12-10 N N S N S N S N S N S N S N S S Figure 12-22. Magnetic poles in a broken magnet.

Figure 12-20. Bypassing flux lines.

Modern permanent magnets are made of special alloys that have been found through research to create increasingly better magnets. The most common categories of magnet materials are made out of aluminum-nickel-cobalt (alnicos), strontium-iron (ferrites, also known as ceramics), neodymium-iron-boron (neo magnets), and samarium- cobalt. Alnico, an alloy of iron, aluminum, nickel and cobalt, is considered one of the very best. Others with 6 30 excellent magnetic qualities are alloys such as Remalloy™ 9 27 and Permendur™.

RADIO 12 24 COMPASS 15 21 The ability of a magnet to hold its magnetism varies greatly with the type of metal and is known as retentivity. Magnets made of soft iron are very easily magnetized but quickly lose most of their magnetism when the external magnetizing force is removed. The small amount of magnetism remaining, called residual magnetism, is of great importance in such electrical applications as generator operation.

Horseshoe magnets are commonly manufactured in two forms.

Soft iron [Figure 12-25] The most common type is made from a long bar curved into a horseshoe shape, while a variation of this Figure 12-23. Magnetic shield.

type consists of two bars connected by a third bar, or yoke.

Sometimes special applications require that the field of force Magnets can be made in many different shapes, such as balls, lie through the thickness rather than the length of a piece of cylinders, or disks. One special type of magnet is the ring metal. Such magnets are called flat magnets and are used as magnet, or Gramme ring, often used in instruments. This is pole pieces in generators and motors.

a closed loop magnet, similar to the type used in transformer cores, and is the only type that has no poles.

S N N S N S S N S N S N Repulsion Repulsion Attraction Figure 12-21. Repulsion and attraction of magnet poles.

12-11 angles to, and approximately one inch from, a current Electromagnetism carrying conductor. If no current were flowing, the North In 1820, the Danish physicist, Hans Christian Oersted, seeking end of the compass needle would point toward the discovered that the needle of a compass brought near a current earth’s magnetic pole. When current flows, the needle lines carrying conductor would be deflected. When the current flow itself up at right angles to a radius drawn from the conductor.

stopped, the compass needle returned to its original position.

Since the compass needle is a small magnet, with lines of This important discovery demonstrated a relationship between force extending from South to North inside the metal, it turns electricity and magnetism that led to the electromagnet and to until the direction of these lines agrees with the direction many of the inventions on which modern industry is based.

of the lines of force around the conductor. As the compass needle is moved around the conductor, it maintains itself in Oersted discovered that the magnetic field had no connection a position at right angles to the conductor, indicating that the with the conductor in which the electrons were flowing, magnetic field around a current carrying conductor is circular.

because the conductor was made of nonmagnetic copper. The As shown in Figure 12-28B , when the direction of current electrons moving through the wire created the magnetic field flow through the conductor is reversed, the compass needle around the conductor. Since a magnetic field accompanies a points in the opposite direction, indicating the magnetic field charged particle, the greater the current flow, the greater the has reversed its direction.

magnetic field. Figure 12-26 i llustrates the magnetic field around a current carrying wire. A series of concentric circles A method used to determine the direction of the lines of force around the conductor represent the field, which if all the lines when the direction of the current flow is known is shown in were shown would appear more as a continuous cylinder of Figure 12-29 . If the conductor is grasped in the left hand, such circles around the conductor.

with the thumb pointing in the direction of current flow, the fingers will be wrapped around the conductor in the same As long as current flows in the conductor, the lines of force direction as the lines of the magnetic field. This is called the remain around it. [Figure 12-27] If a small current flows left-hand rule.

through the conductor, there will be a line of force extending out to circle A. If the current flow is increased, the line of Although it has been stated that the lines of force have direction, force increases in size to circle B, and a further increase in this should not be construed to mean that the lines have motion current expands it to circle C. As the original line (circle) of in a circular direction around the conductor. Although the force expands from circle A to B, a new line of force appears lines of force tend to act in a clockwise or counterclockwise at circle A. As the current flow increases, the number of direction, they are not revolving around the conductor.

circles of force increases, expanding the outer circles farther from the surface of the current carrying conductor.

Since current flows from negative to positive, many illustrations indicate current direction with a dot symbol If the current flow is a steady nonvarying direct current, the on the end of the conductor when the electrons are flowing magnetic field remains stationary. When the current stops, toward and a plus sign when the current is flowing away the magnetic field collapses and the magnetism around the from the observer. [Figure 12-30] conductor disappears.

When a wire is bent into a loop and an electric current flows A compass needle is used to demonstrate the direction of through it, the left-hand rule remains valid. [Figure 12-31] the magnetic field around a current carrying conductor.

If the wire is coiled into two loops, many of the lines of force Figure 12-28A shows a compass needle positioned at right become large enough to include both loops. Lines of force N S N S S N Soft iron N S N S Figure 12-25. Two forms of horseshoe magnets.

Figure 12-24. Effect of a magnetic substance in a magnetic field.

12-12 go through the loops in the same direction, circle around the outside of the two coils, and come in at the opposite end.

[Figure 12-32] When a wire contains many such loops, it is called a coil. The lines of force form a pattern through all the loops causing Conductor a high concentration of flux lines through the center of the coil. [Figure 12-33] A B In a coil made from loops of a conductor, many of the C lines of force are dissipated between the loops of the coil.

By placing a soft iron bar inside the coil, the lines of force Magnetic lines are concentrated in the center of the coil, since soft iron has a greater permeability than air. [Figure 12-34] This combination of an iron core in a coil of wire loops, or turns, Figure 12-27. Expansion of magnetic field as current increases.

is called an electromagnet, since the poles (ends) of the coil possess the characteristics of a bar magnet.

The addition of the soft iron core does two things for the current carrying coil. First, the magnetic flux is increased.

Magnetic fields Second, the flux lines are more highly concentrated.

When direct current flows through the coil, the core becomes magnetized with the same polarity (location of North and South poles) as the coil would have without the core. If the current is reversed, the polarity is also reversed.

Conductor The polarity of the electromagnet is determined by the left-hand rule in the same manner as the polarity of the Figure 12-26. Magnetic field formed around a conductor in which coil without the core was determined. If the coil is grasped current is flowing.

in the left hand in such a manner that the fingers curve Magnetic field Checking direction of magnetic field, using N S compass and left-hand rule Compass Current carrying conductor A B Figure 12-28. Magnetic field around a current-carrying conductor.

12-13 Conventional Flow & Electron Flow Today’s technician will find that there are two competing Direction of field schools of thought and analytical practices regarding the flow of electricity. The two are called the conventional current theory and the electron theory.

Conventional Flow Direction of current Of the two, the conventional current theory was the first to be developed and, through many years of use, this method Figure 12-29. Left-hand rule.

has become ingrained in electrical publications. The theory was initially advanced by Benjamin Franklin who reasoned around the coil in the direction of electron flow (minus to that current flowed out of a positive source into a negative plus), the thumb points in the direction of the North pole.

source or an area that lacked an abundance of charge. The [Figure 12-35] notation assigned to the electric charges was positive (+) for the abundance of charge and negative (−) for a lack of The strength of the magnetic field of the electromagnet charge. It then seemed natural to visualize the flow of current can be increased by either increasing the flow of current or as being from the positive (+) to the negative (−).

the number of loops in the wire. Doubling the current flow approximately doubles the strength of the field. In a similar Electron Flow manner, doubling the number of loops approximately doubles Later discoveries were made that proved just the opposite magnetic field strength. Finally, the type of metal in the core is true. Electron flow is what actually happens when an is a factor in the field strength of the electromagnet.

abundance of electrons flow out of the negative (−) source to an area that lacks electrons or the positive (+) source. Both A soft iron bar is attracted to either pole of a permanent conventional flow and electron flow are used in industry.

magnet and, likewise, is attracted by a current carrying coil.

Many publications in current use employ both electron flow The lines of force extend through the soft iron, magnetizing and conventional flow methods. From the practical standpoint it by induction and pulling the iron bar toward the coil. If of the technician troubleshooting a system, it makes little the bar is free to move, it is drawn into the coil to a position to no difference which way current is flowing as long as it near the center where the field is strongest. [Figure 12-36] is used consistently in the analysis. The Federal Aviation Administration (FAA) officially defines current flow using Electromagnets are used in electrical instruments, motors, electron theory (negative to positive).

generators, relays, and other devices. Some electromagnetic devices operate on the principle that an iron core held away Electromotive Force (Voltage) from the center of a coil is rapidly pulled into a center position Unlike current, which is easy to visualize as a flow, voltage when the coil is energized. This principle is used in the is a variable that is determined between two points. Often, solenoid, also called solenoid switch or relay, in which the we refer to voltage as a value across two points. It is the iron core is spring-loaded off center and moves to complete electromotive force (emf) or the push or pressure felt in a a circuit when the coil is energized.

+ Dot indicates current is Cross indicates current is flowing out of the conductor flowing into the conductor Figure 12-30. Direction of current flow in a conductor.

Figure 12-31. Magnetic field around a looped conductor.

12-14 Direction of current Figure 12-32. Magnetic field around a conductor with two loops.

S N Figure 12-33. Magnetic field of a coil.

S N Figure 12-34. Electromagnet.

12-15 when a difference of pressure exists between the two tanks, water flows until the two tanks are equalized. The illustration shows the level of water in tank A to be at a higher level, reading 10 psi (higher potential energy) than the water level S N in tank B, reading 2 psi (lower potential energy). Between the two tanks, there is 8-psi potential difference. If the valve in the interconnecting line between the tanks is opened, water flows from tank A into tank B until the level of water (potential energy) of both tanks is equalized. It is important Figure 12-35. Left-hand rule applied to a coil.

to note that it was not the pressure in tank A that caused the water to flow; rather, it was the difference in pressure between conductor that ultimately moves the electrons in a flow. The tank A and tank B that caused the flow.

symbol for emf is the capital letter “E.” This comparison illustrates the principle that electrons move, Across the terminals of the typical aircraft battery, voltage when a path is available, from a point of excess electrons can be measured as the potential difference of 12 volts or (higher potential energy) to a point deficient in electrons 24 volts. That is to say that between the two terminal posts (lower potential energy). The force that causes this movement of the battery, there is an emf of 12 or 24 volts available to is the potential difference in electrical energy between the push current through a circuit. Relatively free electrons in two points. This force is called the electrical pressure or the negative terminal move toward the excessive number the potential difference or the electromotive force (electron of positive charges in the positive terminal. Recall from the moving force).

discussion on static electricity that like charges repel each other but opposite charges attract each other. The net result Current is a flow or current through a conductor. There cannot be a flow in a conductor unless there is an applied voltage from Electrons in motion make up an electric current. This electric a battery, generator, or ground power unit. The potential current is usually referred to as “current” or “current flow,” difference, or the voltage across any two points in an electrical no matter how many electrons are moving. Current is a system, can be determined by: measurement of a rate at which a charge flows through some Where region of space or a conductor. The moving charges are the free electrons found in conductors, such as copper, silver, E E = aluminum, and gold. The term “free electron” describes a Q condition in some atoms where the outer electrons are loosely E = Potential difference in volts bound to their parent atom. These loosely bound electrons E = Energy expanded or absorbed in joules (J) can be easily motivated to move in a given direction when Q = Charge measured in coulombs an external source, such as a battery, is applied to the circuit.

These electrons are attracted to the positive terminal of the Figure 12-37 illustrates the flow of electrons of electric battery, while the negative terminal is the source of the current. Two interconnected water tanks demonstrate that electrons. The greater amount of charge moving through the conductor in a given amount of time translates into a current.

Charge Current = Time or Q I = t N S N S Where: I = current in amperes (A) Q = charge in coulombs (C) T = time Figure 12-36. Solenoid with iron core.

12-16 Ohm’s Law (Resistance) The System International (SI) unit for current is the ampere The two fundamental properties of current and voltage (A), where are related by a third property known as resistance. In any C electrical circuit, when voltage is applied to it, a current 1A = 1 results. The resistance of the conductor determines the s amount of current that flows under the given voltage. In most cases, the greater the circuit resistance, the less the current.

One ampere (A) of current is equivalent to 1 coulomb (C) of charge passing through a conductor in 1 second. One If the resistance is reduced, then the current increases. This relation is linear in nature and is known as Ohm’s Law.

coulomb of charge equals 6.28 billion electrons. The symbol used to indicate current in formulas or on schematics is the By having a linearly proportional characteristic, it is meant capital letter “I.” that if one unit in the relationship increases or decreases by a certain percentage, the other variables in the relationship When current flow is one direction, it is called direct current (DC). Later in the handbook, the form of current increase or decrease by the same percentage. An example would be if the voltage across a resistor is doubled, then that periodically oscillates back and forth within the circuit is discussed. The present discussion is only concerned with the current through the resistor doubles. It should be added that this relationship is true only if the resistance in the the use of DC.

circuit remains constant. If the resistance changes, current also changes. A graph of this relationship is shown in The velocity of the charge is actually an average velocity and is called drift velocity. To understand the idea of drift Figure 12-39 , which uses a constant resistance of 20Ω. The relationship between voltage and current in this example velocity, think of a conductor in which the charge carriers are free electrons. These electrons are always in a state of shows voltage plotted horizontally along the X axis in values from 0 to 120 volts, and the corresponding values of current random motion similar to that of gas molecules. When a voltage is applied across the conductor, an emf creates an are plotted vertically in values from 0 to 6.0 amperes along the Y axis. A straight line drawn through all the points where electric field within the conductor and a current is established.

The electrons do not move in a straight direction but undergo the voltage and current lines meet represents the equation I E = ⁄ 20 and is called a linear relationship.

repeated collisions with other nearby atoms. These collisions usually knock other free electrons from their atoms, and If E = 10 V these electrons move on toward the positive end of the conductor with an average velocity called the drift velocity, 10 V Then = 0.5 A which is relatively a slow speed. To understand the nearly 20 Ω instantaneous speed of the effect of the current, it is helpful If E = 60 V to visualize a long tube filled with steel balls as shown in Figure 12-38 . It can be seen that a ball introduced in one end 60 V Then = 3 A of the tube, which represents the conductor, will immediately 20 Ω cause a ball to be emitted at the opposite end of the tube.

If E = 120 V Thus, electric current can be viewed as instantaneous, even though it is the result of a relatively slow drift of electrons.

120V Then = 6 A 20 Ω Ohm’s Law may be expressed as an equation, as follows: Equation 1 E I = R I = current in amperes (A) E = voltage (V) R = resistance (Ω) A B Where I is current in amperes, E is the potential difference measured in volts, and R is the resistance measured in ohms.

Figure 12-37. Difference of pressure.

12-17 E If any two of these circuit quantities are known, the third = ⁄ I . To find E, refer to Figure 12-40C , and cover E with the may be found by simple algebraic transposition. With this thumb. The result indicates I is to be multiplied by R, or E = equation, we can calculate current in a circuit if the voltage I × R. This chart is useful when learning to use Ohm’s Law.

and resistance are known. This same formula can be used to It should be used to supplement the beginner’s knowledge calculate voltage. By multiplying both sides of the equation of the algebraic method.

1 by R, we get an equivalent form of Ohm’s Law, which is: Resistance of a Conductor Equation 2 While wire of any size or resistance value may be used, the E = I (R) word “conductor” usually refers to materials that offer low resistance to current flow, and the word “insulator” describes Finally, if we divide equation 2 by I, we solve for resistance, materials that offer high resistance to current. There is no This relationship is true only if the resistance in the distinct dividing line between conductors and insulators; under circuit remains constant. If the resistance changes, current the proper conditions, all types of material conduct some also changes. A graph of this relationship is shown in current. Materials offering a resistance to current flow midway Figure 12-39 , which uses a constant resistance of 20Ω. The between the best conductors and the poorest conductors relationship between voltage and current in this example (insulators) are sometimes referred to as “semiconductors,” shows voltage plotted horizontally along the X axis in values and find their greatest application in the field of transistors.

from 0 to 120 volts. The corresponding values of current are plotted vertically in values from 0 to 6.0 amperes along the The best conductors are materials, chiefly metals, which Y axis. A straight line drawn through all the points where the possess a large number of free electrons; conversely, E voltage and current lines meet represents the equation I = ⁄ 20 insulators are materials having few free electrons. The best and is called a linear relationship.

conductors are silver, copper, gold, and aluminum; but some nonmetals, such as carbon and water, can be used as Equation 3 conductors. Materials such as rubber, glass, ceramics, and plastics are such poor conductors that they are usually used E R = as insulators. The current flow in some of these materials I is so low that it is usually considered zero. The unit used All three formulas presented in this section are equivalent to measure resistance is called the ohm. The symbol for the to each other and are simply different ways of expressing ohm is the Greek letter omega (Ω). In mathematical formulas, Ohm’s Law.

the capital letter “R” refers to resistance. The resistance of a conductor and the voltage applied to it determine the number The various equations, which may be derived by transposing of amperes of current flowing through the conductor. Thus, the basic law, can be easily obtained by using the triangles 1 ohm of resistance limits the current flow to 1 ampere in a in Figure 12-40 .

conductor to which a voltage of 1 volt is applied.

The triangles containing E, R, and I are divided into two Factors Affecting Resistance parts, with E above the line and I × R below it. To determine 1. The resistance of a metallic conductor is dependent on an unknown circuit quantity when the other two are known, the type of conductor material. It has been pointed out cover the unknown quantity with a thumb. The location of that certain metals are commonly used as conductors the remaining uncovered letters in the triangle indicate the because of the large number of free electrons in their mathematical operation to be performed. For example, to find outer orbits. Copper is usually considered the best I, refer to Figure 12-40A , and cover I with the thumb. The available conductor material, since a copper wire of a uncovered letters indicate that E is to be divided by R, or I = particular diameter offers a lower resistance to current E ⁄ R . To find R, refer to Figure 12-40B , and cover R with the flow than an aluminum wire of the same diameter.

thumb. The result indicates that E is to be divided by I, or R However, aluminum is much lighter than copper, and for this reason, as well as cost considerations, aluminum is often used when the weight factor is important.

2. The resistance of a metallic conductor is directly proportional to its length. The longer the length of a given size of wire, the greater the resistance.

Figure 12-41 shows two wire conductors of different lengths. If 1 volt of electrical pressure is applied across Figure 12-38. Electron movement.

12-18 Amperes (I) 6.0 5.5 To find I (amperes), E A 5.0 place thumb over I and divide E by R 4.5 as indicated.

I X R 4.0 3.5 3.0 2.5 R = 20 Ohms To find R (ohms), 2.0 B E place thumb over (Constant) R and divide as 1.5 indicated.

1.0 I X R 0.5 10 20 30 40 50 60 70 80 90 100 110 120 Volts (E) Figure 12-39. Voltage vs. current in a constant-resistance circuit.

To find E (volts), C place thumb over E E and multiply as indicated.

the two ends of the conductor that is 1 foot in length, and the resistance to the movement of free electrons I X R is assumed to be 1 ohm, the current flow is limited to 1 ampere. If the same size conductor is doubled in length, the same electrons set in motion by the 1 volt applied now find twice the resistance; consequently, Figure 12-40. Ohm’s law chart.

the current flow is reduced by one-half.

3. The resistance of a metallic conductor is inversely 0.00427 ohm. Thus, a copper wire having a resistance proportional to the cross-sectional area. This area may of 50 ohms at a temperature of 0 °C has an increase be triangular or even square, but is usually circular. in resistance of 50 × 0.00427, or 0.214 ohm, for each If the cross-sectional area of a conductor is doubled, degree rise in temperature above 0 °C. The temperature the resistance to current flow is reduced in half. This coefficient of resistance must be considered where there is true because of the increased area in which an is an appreciable change in temperature of a conductor electron can move without collision or capture by an during operation. Charts listing the temperature atom. Thus, the resistance varies inversely with the coefficient of resistance for different materials are cross-sectional area of a conductor. available. Figure 12-42 shows a table for “resistivity” of some common electric conductors.

4. The fourth major factor influencing the resistance of a conductor is temperature. Although some substances, The resistance of a material is determined by four properties: such as carbon, show a decrease in resistance as the material, length, area, and temperature. The first three ambient (surrounding) temperature increases, most properties are related by the following equation at T = 20 °C materials used as conductors increase in resistance as (room temperature): temperature increases. The resistance of a few alloys, such as constantan and Manganin™, change very little (ρ × 1) R = as the temperature changes. The amount of increase in A the resistance of a 1 ohm sample of a conductor, per Where degree rise in temperature above 0° Centigrade (C), the R = resistance in ohms assumed standard, is called the temperature coefficient ρ = resistivity of the material in circular of resistance. For each metal, this is a different value.

mil-ohms per foot For example, for copper the value is approximately 12-19 l = length of the sample in feet still being manufactured using the foot as the unit length and A = area in circular mils the mil (one thousandth of an inch) as the unit of diameter.

(ρ × l) Before using the equation R = ⁄ A to calculate the resistance Resistance and Relation to Wire Sizing of a conductor of a given American wire gauge (AWG) size, the cross-sectional area in square meters must be determined Circular Conductors (Wires/Cables) using the conversion factor 1 mil = 0.0254 mm. The most Because it is known that the resistance of a conductor is directly convenient unit of wire length is the foot. Using these proportional to its length, and if we are given the resistance of standards, the unit of size is the mil-foot. Thus, a wire has the unit length of wire, we can readily calculate the resistance unit size if it has a diameter of 1 mil and length of 1 foot.

of any length of wire of that particular material having the same diameter. Also, because it is known that the resistance of In the case of using copper conductors, we are spared the a conductor is inversely proportional to its cross-sectional area, task of tedious calculations by using a table as shown in and if we are given the resistance of a length of wire with unit Figure 12-43 . Note that cross-sectional dimensions listed on cross-sectional area, we can calculate the resistance of a similar the table are such that each decrease of one gauge number length of wire of the same material with any cross-sectional equals a 25 percent increase in the cross-sectional area.

area. Therefore, if we know the resistance of a given conductor, Because of this, a decrease of three gauge numbers represents we can calculate the resistance for any conductor of the same an increase in cross-sectional area of approximately 2:1.

material at the same temperature. From the relationship: Likewise, change of ten wire gauge numbers represents a 10:1 (ρ × 1) change in cross-sectional area—also, by doubling the cross- R = A sectional area of the conductor, the resistance is cut in half.

It can also be written: A decrease of three wire gauge numbers cuts the resistance R 1 A 1 1 of the conductor of a given length in half.

= = R 1 A 2 2 2 Rectangular Conductors (Bus Bars) If we have a conductor that is 1 meter (m) long with a cross- To compute the cross-sectional area of a conductor in square sectional area of 1 (millimeter) mm and has a resistance of 0.017 ohm, what is the resistance of 50 m of wire from the mils, the length in mils of one side is squared. In the case of a rectangular conductor, the length of one side is multiplied by same material but with a cross-sectional area of 0.25 mm ?

the length of the other. For example, a common rectangular R 1 A 1 1 1 3 bus bar (large, special conductor) is ⁄ 8 inch thick and 4 inches = = R 1 A 2 2 2 wide. The ⁄ 8 -inch thickness may be expressed as 0.375 inch. Since 1,000 mils equal 1 inch, the width in inches can 50 m 1 mm R = 0.017 Ω × × = 3.4 Ω be converted to 4,000 mils. The cross-sectional area of the 1 m 0.25 mm rectangular conductor is found by converting 0.375 to mils While the SI units are commonly used in the analysis of (375 mils × 4,000 mils = 1,500,000 square mils).

electric circuits, electrical conductors in North America are Power and Energy Power in an Electrical Circuit This section covers power in the DC circuit and energy consumption. Whether referring to mechanical or electrical systems, power is defined as the rate of energy consumption Conductor Material Resistivity (ohm meters @ 20 °C) 2 feet -8 Silver 1.64 × 10 -8 Copper 1.72 × 10 -8 Aluminum 2.83 × 10 0.5 amp ( 2 ohms) -8 Tungsten 5.50 × 10 1 foot -8 Nickel 7.80 × 10 + -8 Iron 12.0 × 10 -8 1 amp (1 ohm) Constantan 49.0 × 10 + -8 Nichrome II 110 × 10 Figure 12-41. Resistance varies with length of conductor. Figure 12-42. Resistivity table.

12-20 or conversion within that system—that is, the amount of AWG Number Diameter in mils Ohms per 1,000 ft.

energy used or converted in a given amount of time.

0000 460.0 0.04901 000 409.6 0.06180 From the scientific discipline of physics, the fundamental 00 364.8 0.07793 expression for power is: 0 324.9 0.09827 E P = 1 289.3 0.1239 t 2 257.6 0.1563 Where 3 229.4 0.1970 P = power measured in watts (W) 4 204.3 0.2485 E = energy ( E is a script E) measured in joules (J) 5 181.9 0.3133 and 6 162.0 0.3951 t = time measured in seconds (s) 8 128.5 0.6282 10 101.9 0.9989 The unit measurement for power is the watt (W), which refers to a rate of energy conversion of 1 joule (J)/second. Therefore, 12 80.81 1.588 the number of joules consumed in 1 second is equal to the 14 64.08 2.525 number of watts. A simple example is given below.

16 50.82 4.016 18 40.30 6.385 Suppose 300 joules of energy is consumed in 10 seconds.

20 31.96 10.15 What would be the power in watts?

22 25.35 16.14 energy 24 20.10 25.67 General formula P = time 26 15.94 40.81 300 J P = 28 12.64 64.9 10 s 30 10.03 103.2 P = 30 W Figure 12-43. Conversion table when using copper conductors.

The watt is named for James Watt, the inventor of the steam engine. Watt devised an experiment to measure the power of E = potential difference in volts a horse in order to find a means of measuring the mechanical E = energy expanded or absorbed in joules (J) power of his steam engine. One horsepower is required to Q = charge measured in coulombs move 33,000 pounds 1 foot in 1 minute. Since power is the rate of doing work, it is equivalent to the work divided by Current I, can also be expressed in terms of charge and time time. Stated as a formula, this is: as given by the expression: 33,000 ft-lb Charge Power = Current = 60 s Time P = 550 ft-lb/s or Electrical power can be rated in a similar manner. For Q I = T example, an electric motor rated as a 1 horsepower motor requires 746 watts of electrical energy.

Where: I = current in amperes (A) Power Formulas Used in the Study of Electricity Q = charge in coulombs (C) When current flows through a resistive circuit, energy is T = time dissipated in the form of heat. Recall that voltage can be expressed in the terms of energy and charge as given in the W Q When voltage ⁄ Q and current ⁄ t are multiplied, the charge expression: Q is divided out leaving the basic expression from physics: E E E E E = E × I = × = = power Q Q t t Where For a simple DC electrical system, power dissipation 12-21 can then be given by the equation: Power in a Series & Parallel Circuit The total power dissipated in both a series and parallel circuit General Power Formula P = I (E) is equal to the sum of the power dissipated in each resistor in the circuit. Power is simply additive and can be stated as: Where P = Power P = P + P + P + ……P T 1 2 3 N I = Current E = Volts Figure 12-44 provides a summary of all the possible transpositions of the Ohm’s Law formula and the power If a circuit has a known voltage of 24 volts and a current of formula.

2 amps, then the power in the circuit is: Energy in an Electrical Circuit P = I (E) Energy is defined as the ability to do work. Because power P = 2A (24V) is the rate of energy usage, power used over a span of time P = 48W is actually energy consumption. If power and time are multiplied together, we get energy.

Now recall Ohm’s Laws that state E = I(R). If we now substitute IR for E in the general formula, we get a formula The joule is defined as a unit of energy. There is another unit that uses only current I and resistance R to determine the of measure which is perhaps more familiar. Because power power in a circuit.

is expressed in watts and time in seconds, a unit of energy can be called a watt-second (Ws) or more recognizable from P = I (IR) the electric bill, a kilowatt-hour (kWh). Refer to Chapter 5, Physics, for further discussion on energy.

Second Form of Power Equation Sources of Electricity P = I R Electrical energy can be produced in a number of methods. The four most common are pressure, chemical, thermal, and light.

If a circuit has a known current of 2 amps and a resistance of 100 Ω, then the power in the circuit is: Pressure Source This form of electrical generation is commonly known as P = I R piezoelectric (piezo or piez taken from Greek: to press; P = (2A) 100 Ω pressure; to squeeze) is a result of the application of P = 400 W mechanical pressure on a dielectric or non-conducting crystal.

The most common piezoelectric materials used today are E Using Ohm’s Law, which can be stated as I = ⁄ R , we can again crystalline quartz and Rochelle salt. However, Rochelle salt is make a substitution such that power can be determined by being superseded by other materials, such as barium titanate.

knowing only the voltage (E) and resistance (R) of the circuit.

The application of a mechanical stress produces an electric E P = E

( )( )

polarization, which is proportional to this stress. This R polarization establishes a voltage across the crystal. If a Third Form of Power Equation circuit is connected across the crystal, a flow of current can E be observed when the crystal is loaded (pressure is applied).

P = R An opposite condition can occur, where an application of a voltage between certain faces of the crystal can produce a If a circuit has a known voltage of 24 volts and a resistance mechanical distortion. This effect is commonly referred to of 20 Ω, then the power in the circuit is: as the piezoelectric effect.

E P = R Piezoelectric materials are used extensively in transducers for converting a mechanical strain into an electrical signal.

(24 V) P = Such devices include microphones, phonograph pickups, and 20 Ω vibration-sensing elements. The opposite effect, in which a P = 28.8 W mechanical output is derived from an electrical signal input, is also widely used in headphones and loudspeakers.

12-22 light energy into electricity. Fundamentally, the device contains certain chemical elements that, when exposed to Chemical Source light energy, release electrons.

Chemical energy can be converted into electricity; the most common form of this is the battery. A primary battery Photons in sunlight are taken in by the solar panel or cell, produces electricity using two different metals in a chemical where they are absorbed by semiconducting materials, such solution like alkaline electrolyte, where a chemical reaction as silicon. Electrons in the cell are broken loose from their between the metals and the chemicals frees more electrons atoms, allowing them to flow through the material to produce in one metal than in the other. One terminal of the battery is electricity. The complementary positive charges that are also attached to one of the metals, such as zinc; the other terminal created are called holes (absence of electron) and flow in the is attached to the other metal, such as manganese oxide. The direction opposite of the electrons in a silicon solar panel.

end that frees more electrons develops a positive charge and the other end develops a negative charge. If a wire is Solar cells have many applications and have historically been attached from one end of the battery to the other, electrons used in earth orbiting satellites or space probes, handheld flow through the wire to balance the electrical charge.

calculators, and wrist watches.

Thermal Sources Schematic Representation of Electrical The most common source of thermal electricity found in the Components aviation industry comes from thermocouples. Thermocouples The schematic is the most common place where the technician are widely used as temperature sensors. They are cheap finds electronic symbols. The schematic is a diagram that and interchangeable, have standard connectors, and can depicts the interconnection and logic of an electronic or measure a wide range of temperatures. Thermocouples electrical circuit. Many symbols are employed for use in are pairs of dissimilar metal wires joined at least at one the schematic drawings, blueprints, and illustrations. This end, which generate a voltage between the two wires that section briefly outlines some of the more common symbols is proportional to the temperature at the junction. This is and explains how to interpret them.

called the Seebeck effect, in honor of Thomas Seebeck who first noticed the phenomena in 1821. It was also noticed Conductors that different metal combinations have a different voltage The schematic depiction of a conductor is simple enough.

difference. Thermocouples are used to measure cylinder head This is generally shown as a solid line. However, the line temperatures and Turbine Inlet Temperature (TIT).

types may vary depending on who drew the schematics and what exactly the line represents. While the solid line is used Light Sources to depict the wire or conductor, schematics used for aircraft A solar cell or a photovoltaic cell is a device that converts modifications can also use other line types, such as a dashed to represent “existing” wires prior to modification and solid lines for “new” wires.

There are two methods employed to show wire crossovers E E R R and wire connections. Figure 12-45 shows the two methods 2 P of drawing wires that cross: version A and version B.

I R E Figure 12-46 shows the two methods for drawing wire that connect version A and version B. If version A in IE P Figure 12-45 is used to depict crossovers, then version A for P I R wire connections in Figure 12-46 is used. The same can then be said about the use of version B methods. The technician E E R I PR encounters both in common use.

Figure 12-47 shows a few examples of the more common E P P I wire types that the technician encounters in schematics. They are the single wire, single shielded, shielded twisted pair or P IR I double, and the shielded triple. This is not an exhaustive list of wire types but a fair representation of how they are depicted.

Figure 12-47 also shows the wires having a wire number.

These are shown for the sake of illustration and vary from one Figure 12-44. Ohm’s Law formula.

12-23 installation agency to another. For further understanding of a variation between the marked value and the actual value of wire numbering system, consult the appropriate wiring guide a resistor is known as the “tolerance” of a resistor. A resistor published by the agency that drew the prints. Regardless of coded for a 5 percent tolerance is not more than 5 percent the specifics of the wire numbering system, organizations higher or lower than the value indicated by the color code.

that exercise professional wiring practices have the installed wire marked in some manner. This is an aid to the technician The resistor color code is made up of a group of colors, who has to troubleshoot or modify the system at a later date. numbers, and tolerance values. Each color is represented by a number, and in most cases, by a tolerance value. [Figure 12-49] Types of Resistors When the color code is used with the end-to-center band marking Fixed Resistor system, the resistor is normally marked with bands of color at Fixed resistors have built into the design a means of opposing one end of the resistor. The body or base color of the resistor current. [Figure 12-48] The general use of a resistor in a has nothing to do with the color code, and in no way indicates circuit is to limit the amount of current flow. There are a a resistance value. To prevent confusion, this body is never number of methods used in construction and sizing of a the same color as any of the bands indicating resistance value.

resistor that control properties, such as resistance value, the precision of the resistance value, and the ability to dissipate heat. While in some applications the purpose of the resistive element is used to generate heat, such as in propeller anti-ice boots, heat typically is the unwanted loss of energy.

Carbon Composition The carbon composed resistor is constructed from a mixture of finely grouped carbon/graphite, an insulation material A B for filler, and a substance for binding the material together.

The amount of graphite in relation to the insulation material Figure 12-45. Unconnected crossover wires. determines the ohmic or resistive value of the resistor. This mixture is compressed into a rod, which is fitted with axial leads or “pigtails.” The finished product is sealed in an insulating coating for isolation and physical protection.

There are other types of fixed resistors in common use.

Included in this group are: • Carbon film A B • Metal-oxide • Metal film Figure 12-46. Connected wires.

• Metal glaze Typical Wire No. The construction of a film resistor is accomplished by depositing a resistive material evenly on a ceramic rod. This Single SX001A22 wire resistive material can be graphite for the carbon film resistor, nickel chromium for the metal film resistor, metal and glass Shielded 12PB501-*APJ356 single wire for the metal glaze resistor, and metal and an insulating oxide for the metal-oxide resistor.

Shielded NM200A22 double wire Resistor Ratings Conductor Shielded Color Code RF300A22 triple It is very difficult to manufacture a resistor to an exact standard wire of ohmic values. Fortunately, most circuit requirements are not extremely critical. For many uses, the actual resistance in Shielding ohms can be 20 percent higher or lower than the value marked on the resistor without causing difficulty. The percentage Figure 12-47. Common wire types.

12-24 Color Band Decoding The resistance of this resistor is 86,000 ±10 percent ohms.

When the end-to-center band marking system is used, either The maximum resistance is 94,600 ohms, and the minimum resistance is 77,400 ohms.

three or four bands mark the resistor.

1. The first color band (nearest the end of the resistor) Another example is the resistance of the resistor in Figure 12-52 indicates the first digit in the numerical resistance is 960 ±5 percent ohms. The maximum resistance is 1,008 value. This band is never gold or silver in color.

ohms, and the minimum resistance is 912 ohms.

2. The second color band always indicates the second Sometimes circuit considerations dictate that the tolerance digit of ohmic value. It is never gold or silver in color.

must be smaller than 20 percent. Figure 12-53 shows [Figure 12-50] an example of a resistor with a 2 percent tolerance. The resistance value of this resistor is 2,500 ±2 percent ohms.

3. The third color band indicates the number of zeros to The maximum resistance is 2,550 ohms, and the minimum be added to the two digits derived from the first and resistance is 2,450 ohms.

second bands, except in the following two cases: (a) If the third band is gold in color, the first two Figure 12-54 contains an example of a resistor with a black digits must be multiplied by 10 percent.

third color band. The color code value of black is zero, and (b) If the third band is silver in color, the first two the third band indicates the number of zeros to be added to digits must be multiplied by 1 percent.

the first two digits.

4. If there is a fourth color band, it is used as a multiplier In this case, a zero number of zeros must be added to the first for percentage of tolerance, as indicated in the color two digits; therefore, no zeros are added. Thus, the resistance code chart in Figure 12-49 . If there is no fourth band, value is 10 ±1 percent ohms. The maximum resistance is the tolerance is understood to be 20 percent.

10.1 ohms, and the minimum resistance is 9.9 ohms. There are two exceptions to the rule stating the third color band Figure 12-50 illustrates the rules for reading the resistance indicates the number of zeros. The first of these exceptions value of a resistor marked with the end-to-center band system.

is illustrated in Figure 12-55 . When the third band is gold in This resistor is marked with three bands of color, which must color, it indicates that the first two digits must be multiplied be read from the end toward the center.

by 10 percent. The value of this resistor in this case is: There is no fourth color band; therefore, the tolerance is 10 × 0.10 ±2% = 1 = 0.02 ohms understood to be 20 percent. 20 percent of 250,000 Ω, equals 50,000 Ω.

When the third band is silver, as is the case in Figure 12-56 , the first two digits must be multiplied by 1 percent. The value Since the 20 percent tolerance is plus or minus, Maximum resistance Resistor color code = 250,000 Ω + 50,000 Ω Color Number Tolerance = 300,000 Ω Black 0 — Minimum resistance Brown 1 1% = 250,000 Ω − 50,000 Ω Red 2 2% = 200,000 Ω Orange 3 3% Yellow 4 4% The following paragraphs provide a few extra examples of Green 5 5% resistor color band decoding. Figure 12-51 contains a resistor Blue 6 6% with another set of colors. This resistor code should be read as follows: Violet 7 7% Gray 8 8% White 9 9% Gold — 5% Silver — 10% No color — 20% Figure 12-48. Fixed resistor schematic. Figure 12-49. Resistor color code.

12-25 of the resistor is 0.45 ±10 percent ohms.

Blue Orange Gray Silver Wire-Wound Wire-wound resistors typically control large amounts of current and have high power ratings. Resistors of this type are 8 6 000 10% constructed by winding a resistance wire around an insulating rod usually made of porcelain. The windings are coated with an Figure 12-51. Resistor color code example.

insulation material for physical protection and heat conduction.

Both ends of the windings are connected to terminals, which are used to connect the resistor to a circuit. [Figure 12-57] Blue Brown White Gold A wire-wound resistor with tap is a special type of fixed resistor that can be adjusted. These adjustments can be made by moving a slide bar tap or by moving the tap to a 9 6 0 5% preset incremental position. While the tap may be adjustable, the adjustments are usually set at the time of installation Figure 12-52. Resistor color code example.

to a specific value and then operated in service as a fixed resistor. Another type of wire-wound resistor is constructed of Manganin wire, used when high precision is needed.

Green Red Red Red Variable Resistors Variable resistors are constructed so that the resistive value can be changed easily. This adjustment can be manual or 2 5 00 2% automatic, and the adjustments can be made while the system that it is connected to is in operation. There are two basic Figure 12-53. Resistor with two percent tolerance.

types of manual adjustors: the rheostat and the potentiometer.

Rheostat Black Black Brown Brown A rheostat is a variable resistor used to vary the amount of current flowing in a circuit. [Figure 12-58] Figure 12-59 shows a rheostat connected in series with an ordinary 1 0 1% resistance in a series circuit. As the slider arm moves from point A to B, the amount of rheostat resistance (AB) is increased. Since the rheostat resistance and the fixed Figure 12-54. Resistor with black third color band.

resistance are in series, the total resistance in the circuit also increases, and the current in the circuit decreases. On the Black Gold (Multiplier) other hand, if the slider arm is moved toward point A, the total Brown Red resistance decreases and the current in the circuit increases.

1 0 10% 2% 2nd Band 1st Band 3rd Band Figure 12-55. Resistor with gold third band.

Green Silver (Multiplier) Red Green Yellow Yellow Silver Color Numerical Value Significance 1st band — red 2 1st digit 4 5 1% 10% 2nd band — green 5 2nd digit 3rd band — yellow 4 No. of zeroes to add Figure 12-56. Resistor with a silver third band.

Figure 12-50. End-to-center band marking.

12-26 Potentiometer The potentiometer is considered a three-terminal device.

[Figure 12-60] As illustrated, terminals 1 and 2 have the entire value of the potentiometer resistance between them.

Terminal 3 is the wiper or moving contact. Through this wiper, the resistance between terminals 1 and 3 or terminals 2 and 3 can be varied. While the rheostat is used to vary the current in a circuit, the potentiometer is used to vary the voltage in a Figure 12-57. Wire-wound resistors.

circuit. A typical use for this component can be found in the volume controls on an audio panel and input devices for flight tapered potentiometer. [Figure 12-64] Keep in mind that data recorders, among many other applications.

one-half of full potentiometer travel does not necessarily correspond to one-half the total resistance of the potentiometer.

In Figure 12-61A , a potentiometer is used to obtain a variable voltage from a fixed voltage source to apply to an electrical Thermistors load. The voltage applied to the load is the voltage between The thermistor is a type of a variable resistor that is points 2 and 3. When the slider arm is moved to point 1, the temperature sensitive. [Figure 12-65] This component entire voltage is applied to the electrical device (load); when has a negative temperature coefficient, which means that the arm is moved to point 3, the voltage applied to the load as the sensed temperature increases, the resistance of the is zero. The potentiometer makes possible the application of thermistor decreases.

any voltage between zero and full voltage to the load.

Photoconductive Cells The current flowing through the circuit of Figure 12-61 The photoconductive cell is similar to the thermistor. Like the leaves the negative terminal electron flow of the battery and thermistor, it has a negative temperature coefficient. Unlike divides one part flowing through the lower portion of the the thermistor, the resistance is controlled by light intensity.

potentiometer (points 3 to 2) and the other part through the This kind of component can be found in radio control heads load. Both parts combine at point 2 and flow through the where the intensity of the ambient light is sensed through upper portion of the potentiometer (points 2 to 1) back to the the photoconductive cell resulting in the backlighting of the positive terminal of the battery. In View B of Figure 12-61 , a control heads to adjust to the flight deck lighting conditions.

potentiometer and its schematic symbol are shown.

[Figure 12-66] In choosing a potentiometer resistance, the amount of current Circuit Protection Devices drawn by the load should be considered, as well as the current Perhaps the most serious trouble in a circuit is a direct short.

flow through the potentiometer at all settings of the slider The term “direct short” describes a situation in which some arm. The energy of the current through the potentiometer is point in the circuit, where full system voltage is present, dissipated in the form of heat.

comes in direct contact with the ground or return side of the circuit. This establishes a path for current flow that contains It is important to keep this wasted current as small as no resistance other than that present in the wires carrying the possible by making the resistance of the potentiometer as current, and these wires have very little resistance.

large as practicable. In most cases, the resistance of the potentiometer can be several times the resistance of the load.

Most wires used in aircraft electrical circuits are small Figure 12-62 shows how a potentiometer can be wired to gauge, and their current carrying capacity is quite limited.

function as a rheostat.

The size of the wires used in any given circuit is determined Linear Potentiometers In a linear potentiometer, the resistance between both terminal and the wiper varies linearly with the position of the wiper.

To illustrate, one quarter of a turn on the potentiometer results in one quarter of the total resistance. The same relationship exists when one-half or three-quarters of potentiometer movement. [Figure 12-63] Tapered Potentiometers Figure 12-58. Rheostat schematic symbol.

Resistance varies in a nonlinear manner in the case of the 12-27 A B Load Figure 12-59. Rheostat connected in series.

A Terminals Shaft Wiper Resistive strip Rotary potentiometer construction Figure 12-60. Potentiometer schematic symbol.

B by the amount of current the wires are expected to carry under normal operating conditions. Any current flow in excess of normal, such as the case of a direct short, would Figure 12-61. Potentiometer and schematic symbol.

cause a rapid generation of heat. If the excessive current flow caused by the short is left unchecked, the heat in the wire could cause a portion of the wire to melt and at the very least, open the circuit.

To protect aircraft electrical systems from damage and failure caused by excessive current, several kinds of protective devices are installed in the systems. Fuses, circuit breakers, thermal protectors, and arc fault circuit breakers are used for this purpose.

Circuit protective devices, as the name implies, all have a Figure 12-62. Potentiometer wired to function as rheostat.

common purpose—to protect the units and the wires in the circuit. Some are designed primarily to protect the wiring and to open the circuit in such a way as to stop the current 10 Ω flow when the current becomes greater than the wires can 70 Ω 30 Ω 100 Ω 100 Ω 100 Ω safely carry. Other devices are designed to protect a unit in 90 Ω 70 Ω 30 Ω the circuit by stopping the current flow to it when the unit becomes excessively warm.

A B C 25% 50% 75% Fuse Fuses are used to protect the circuit from over current Figure 12-63. Linear potentiometer schematic.

conditions. [Figure 12-67A] The fuse is installed in the circuit so that all the current in the circuit passes through it. In most fuses, the strip of metal is made of an alloy of tin and bismuth, which melts and opens the circuit when the current exceeds 12-28 the rated capacity of the fuse. For example, if a 5-amp fuse is placed into a circuit, the fuse allows currents up to 5 amps to pass. Because the fuse is intended to protect the circuit, it is quite important that its capacity match the needs of the circuit in which it is used.

When replacing a fuse, consult the applicable manufacturer’s instructions to be sure a fuse of the correct type and capacity is installed. Fuses are installed in two types of fuse holders in aircraft. “Plug-in holders” or in-line holders are used for small and low capacity fuses. “Clip” type holders are used for heavy high capacity fuses and current limiters.

Figure 12-66. Photoconductive cell schematic symbol component.

Current Limiter The current limiter is very much like the fuse. However, the There are several types of circuit breakers in general use in current limiter link is usually made of copper and will stand aircraft systems. One is a magnetic type. When excessive a considerable overload for a short period of time. Like the current flows in the circuit, it makes an electromagnet strong fuse, it opens up in an over current condition in heavy current enough to move a small armature, which trips the breaker.

circuits such as 30 amp or greater. These are used primarily Another type is the thermal overload switch or breaker.

to sectionalize an aircraft circuit or bus. Once the limiter is This consists of a bimetallic strip which, when it becomes opened, it must be replaced. The schematic symbol for the overheated from excessive current, bends away from a catch current limiter shows two triangles pointing to each other on the switch lever and permits the switch to trip open.

with a line on both sides of the triangles. [ Figure 12-67B ].

Most circuit breakers must be reset by hand. If the overload Circuit Breaker condition still exists, the circuit breaker trips again to prevent The circuit breaker is commonly used in place of a fuse and is damage to the circuit. At this point, it is usually not advisable designed to break the circuit and stop the current flow when to continue resetting the circuit breaker, but to initiate the current exceeds a predetermined value. Unlike the fuse, troubleshooting to determine the cause. Repeated resetting the circuit breaker can be reset; whereas the fuse or current of a circuit breaker can lead to circuit or component damage limiter must be replaced. [Figure 12-68] or worse, the possibility of a fire or explosion. Automatic reset type circuit breakers are not allowed in aircraft. Circuit breakers are commonly grouped on a circuit breaker panel that is accessible to the flight crew. Figure 12-69 shows a circuit breaker and a circuit breaker panel.

10 Ω 70 Ω 30 Ω 100 Ω 100 Ω 100 Ω 90 Ω Arc Fault Circuit Breaker 70 Ω 30 Ω In recent years, the arc fault circuit breaker has begun to A B C provide an additional layer of protection beyond that of the 25% 50% 75% thermal protection already provided by conventional circuit breakers. The arc fault circuit breaker monitors the circuit Figure 12-64. Tapered potentiometer.

for an electrical arcing signature, which can indicate possible wiring faults and unsafe conditions. These conditions can lead to fires or loss of power to critical systems. The arc fault circuit breaker is only beginning to make an appearance in the aircraft industry and is not widely used like the thermal type of circuit breaker.

Thermal Protectors T A thermal protector, or switch, is used to protect a motor. It is designed to open the circuit automatically whenever the temperature of the motor becomes excessively high. It has two positions—open and closed. The most common use for a thermal switch is to keep a motor from overheating. If a Figure 12-65. Schematic symbol for thermistor.

12-29 A Switches Switches control the current flow in most aircraft electrical circuits. A switch is used to start, to stop, or to change the direction of the current flow in the circuit. The switch in each circuit must be able to carry the normal current of the circuit and must be insulated heavily enough for the voltage of the circuit. Figure 12-70 shows various switches used in aircraft electrical systems.

An understanding of some basic definitions of the switch is necessary before any of the switch types are discussed. The B number of poles, throws, and positions they have designates toggle switches, as well as some other type of switches.

Pole—the switch’s movable blade or contactor. The number of poles is equal to the number of circuits, or paths for current flow, that can be completed through the switch at any one time.

Throw—indicates the number of circuits, or paths for current, Figure 12-67. Schematic symbol for fuse (A) and current limiter (B).

that it is possible to complete through the switch with each pole or contactor.

malfunction in the motor causes it to overheat, the thermal switch breaks the circuit intermittently.

Positions—indicates the number of places at which the operating device (toggle, plunger, and so forth) comes to The thermal switch contains a bimetallic disk, or strip, that rest and at the same time open or close one or more circuits.

bends and breaks the circuit when it is heated. This occurs because one of the metals expands more than the other when Toggle Switch they are subjected to the same temperature. When the strip Single-Pole, Single-Throw (SPST) or disk cools, the metals contract and the strip returns to its The single-pole, single-throw (SPST) switch allows a original position and closes the circuit.

connection between two contacts. One of two conditions exist. Either the circuit is open in one position or closed in Control Devices the other position. [Figure 12-71] Components in the electrical circuits are typically not all intended to operate continuously or automatically. Most of Single-Pole, Double-Throw (SPDT) them are meant to operate at certain times, under certain The single-pole, double-throw (SPDT) switch is shown in conditions, to perform very definite functions. There must Figure 12-72 . With this switch, contact between one contact be some means of controlling their operation. Either a can be made between one contact and the other.

switch, or a relay, or both may be included in the circuit for this purpose.

Double-Pole, Single-Throw (DPST) The double-pole, single-throw (DPST) switch connection can be made between one set of contacts and either of two other sets of contacts. [Figure 12-73] Double-Pole, Double-Throw (DPDT) The schematic symbol for the double-pole, double-throw (DPDT) switch is shown in Figure 12-74 . This type of switch makes a connection from one set of contacts to either of two other sets of contacts.

A toggle switch that is spring-loaded to the OFF position Figure 12-68. Schematic symbol for circuit breaker.

12-30 position and closing it in another, is a two-position switch. A toggle switch that comes to rest at any one of three positions is a three-position switch.

A switch that stays open, except when it is held in the closed position, is a normally open switch (usually identified as NO). One that stays closed, except when it is held in the open position is a normally closed switch (NC). Both kinds are spring loaded to their normal position and return to that position as soon as they are released.

Locking toggles require the operator to pull out on the switch toggle before moving it in to another position. Once in the new position, the switch toggle is release back into a lock, which then prevents the switch from inadvertently being moved.

Microswitches A microswitch opens or closes a circuit with a very small movement of the tripping device ( ⁄ 16 inch or less). This is what gives the switch its name, since micro means small.

Microswitches are usually pushbutton switches. They are used primarily as limit switches to provide automatic control of landing gears, actuator motors, and the like. Figure 12-75 shows a normally closed microswitch in cross-section and illustrates how these switches operate. When the operating plunger is pressed in, the spring and the movable contact are pushed, opening the contacts and the circuit. Figure 12-76 shows a pushbutton microswitch.

Rotary Selector Switches A rotary selector switch takes the place of several switches.

When the knob of the switch is rotated, the switch opens one circuit and closes another. Ignition switches and voltmeter selector switches are typical examples of this kind of switch.

[Figure 12-77] Pushbutton Switches Pushbutton switches have one stationary contact and one Figure 12-69. Circuit breaker assembly for aircraft electrical system.

and must be held in the ON position to complete the circuit is a momentary contact two-position switch. One that comes to rest at either of two positions, opening the circuit in one Figure 12-70. Various types of switches used in modern aircraft.

12-31 Figure 12-71. Single-pole, single-throw switch schematic symbol.

Figure 12-72. Single-pole, double-throw switch schematic symbol.

movable contact. The movable contact is attached to the pushbutton. The pushbutton is either an insulator itself or is insulated from the contact. This switch is spring loaded and Figure 12-74. Double-pole, double-throw switch schematic symbol.

designed for momentary contact.

switch actions are the alternate and momentary holding coil Lighted Pushbutton Switches configurations. The less known holding or latching coil switch Another more common switch found in today’s aircraft is bodies are designed to have a magnetic coil inside the switch the lighted pushbutton switch. This type of switch takes the body that is energized through two contacts in the base of the form of a ⁄ 8 -inch to 1-inch cube with incandescent or LED switch. When the coil is energized and the switch is pressed, lights to indicate the function of the switch. Switch designs the switch contacts remain latched until power is removed from come in a number of configurations; the two most common the coil. This type of design allows for some degree of remote are the alternate action and momentary action and usually control over the switch body. [Figure 12-78] have a two-pole or four-pole switch body. Other less common The display optics of the lighted pushbutton switch provide the crew with a clear message that is visible under a wide range of lighting conditions with very high luminance and wide viewing angles. While some displays are simply a transparent screen that is backlit by an incandescent light, the higher quality and more reliable switches are available in sunlight readable displays and night vision (NVIS) versions. Due to the sunlight environment of the flight deck, displays utilizing standard lighting techniques “washout” when viewed in direct sunlight.

Sunlight readable displays are designed to minimize this effect.

Lighted pushbutton switches can also be used in applications where a switch is not required and the optics are only for indications. This type of an indicator is commonly called an annunciator.

Figure 12-73. Double-pole, single-throw switch schematic symbol.

12-32 Stationary contact Operating plunger Moveable contact Grooved anchor Three-bladed spring Figure 12-75. Cross-section of a microswitch.

Dual In-Line Parallel (DIP) Switches The acronym “DIP” switch is defined as Dual In-Line Parallel switch in reference to the physical layout. DIP switches are commonly found in card cages, and line replaceable units (LRU) and are used in most cases to adjust gains, control configurations, and so forth. Each one of the switches is generally an SPST slide or rocker switch. The technician may Figure 12-77. Rotary switches.

find this switch in packages ranging in size from DIP2 through DIP32. Some of the more common sizes are DIP4 and DIP8.

relay, the electromagnet is energized due to the current. When energized, an electromagnetic field pulls the common (C) or Switch Guards arm of the relay down. When the arm or common is pulled Switch guards are covers that protect a switch from down, the circuit between the arm and the normally closed unintended operation. Prior to the operation of the switch, the (NC) contacts is opened and the circuit between the arm and the guard is usually lifted. Switch guards are commonly found normally open (NO) contacts are closed. When the energizing on systems such as fire suppression and override logics for voltage is removed, the spring returns the arm contacts back to various systems. Figure 12-79A shows a traditional switch the normally closed (NC) contacts. The relay usually has two with a guard while Figure 12-79B shows a pushbutton switch connections for the coil. The (+) side is designated as X1 and with a guard. The guard needs to be moved before the switch the ground-side of the coil is designated as X2.

can be pushed.

Series DC Circuits Relays The series circuit is the most basic electrical circuit and A relay is simply an electromechanical switch where a small provides a good introduction to basic circuit analysis. The amount of current can control a large amount of current.

series circuit represents the first building block for all of [Figure 12-80] When a voltage is applied to the coil of the the circuits to be studied and analyzed. Figure 12-81 shows this simple circuit with nothing more than a voltage source or battery, a conductor, and a resistor. This is classified as a series circuit because the components are connected end-to- end, so that the same current flows through each component equally. There is only one path for the current to take and the battery and resistor are in series with each other. Next is to make a few additions to the simple circuit in Figure 12-81 .

Figure 12-82 shows an additional resistor and a little more Figure 12-76. Pushbutton microswitch.

12-33 A Figure 12-78. Lighted pushbutton switches.

detail regarding the values. With these values, we can now begin to learn more about the nature of the circuit. In this configuration, there is a 12-volt DC source in series with two resistors, R = 10 Ω and R = 30 Ω. For resistors in a series 1 2 configuration, the total resistance of the circuit is equal to the sum of the individual resistors. The basic formula is: R = R + R + R + ………R T 1 2 3 N For Figure 12-82 , this will be: R = 10 Ω + 30 Ω T R = 40 Ω T B Now that the total resistance of the circuit is known, the current for the circuit can be determined. In a series circuit, the current cannot be different at different points within the circuit. The current through a series circuit is always the same through each element and at any point. Therefore, the current in the simple circuit can now be determined using Ohm’s Law: Figure 12-79. (A) Red guarded switch. (B) Pushbutton switch with Formula, E = I (R) a guard.

E Solve for current, I = R Formula, E = I (R) The variables, E = 12 V and R = 40 Ω T E Solve for current, I = 12 V R I = Substitute variables, 40 Ω The variables, E = 12 V and R = 80 Ω T Current in circuits, I = 0.3 A 12 V I = Substitute variables, 80 Ω Ohm’s Law describes a relationship between the variables of voltage, current, and resistance that is linear and easy to Current in circuits, I = 0.15 A illustrate with a few extra calculations. First is the act of changing the total resistance of the circuit while the other It can be seen quantitatively and intuitively that when the two remain constant. In this example, the R of the circuit T resistance of the circuit is doubled, the current is reduced by in Figure 12-82 is doubled.

half the original value.

Next, reduce the R of the circuit in Figure 12-82 to half of T The effects on the total current in the circuit are: its original value. The effects on the total current are: 12-34 voltage and voltage drop when discussing series circuits.

Multiple poles Voltage drop refers to the loss in electrical pressure or emf B3 NC caused by forcing electrons through a resistor. Because there B2 C are two resistors in the example, there are separate voltage B1 NO drops. Each drop is associated with each individual resistor.

A3 NC The amount of electrical pressure required to force a given A2 C A1 NO number of electrons through a resistance is proportional to the size of the resistor.

X1 X1 In Figure 12-83 , the values used to illustrate the idea of X2 X2 voltage drop are: Schematic Symbol for a Relay Current, I = 1 mA R = 1 kΩ Normally closed (NC) Common (C) or Arm R = 3 kΩ R = 5 kΩ Electromagnet pulls 3 Normally open (NO) contact down The voltage drop across each resistor is calculated using (+) X1 N Ohm’s Law. The drop for each resistor is the product of each Magnetic field resistance and the total current in the circuit. Keep in mind X2 (−) S that the same current flows through series resistor.

Formula: E = I (R) Relay Illustration Voltage across R : E = I (R ) 1 1 T 1 Figure 12-80. Basic relay.

E = 1 mA (1 kΩ) = 1 volt Voltage across R : E = I (R ) 2 2 T 2 E = 1 mA (3 kΩ) = 3 volt + Voltage across R : E = I (R ) 3 3 T 3 E = 1 mA (5 kΩ) = 5 volt − The source voltage can now be determined, which can then be used to confirm the calculations for each voltage drop.

Using Ohm’s Law: Formula: E = I (R) Figure 12-81. Simple DC circuit.

Source voltage = current × the total resistance E = I (R ) S T Formula, E = I (R) E Solve for current, I = R R 10Ω The variables, E = 12 V and R = 20 Ω T 12 V + I = Substitute variables, 20 Ω 12V Current in circuits, I = 0.6 A − R 30Ω Voltage Drops & Further Application of Ohm’s Law The example circuit in Figure 12-83 is used to illustrate the idea of voltage drop. It is important to differentiate between Figure 12-82. Simple DC circuit with additional resistor.

12-35 R = 1 kΩ + 3 kΩ + 5 kΩ T R I 1 mA 1 T R = 9 kΩ T 1 kΩ Now: E = I (R ) S T + R Substitute E = 1 mA (9 kΩ) 2 S 3 kΩ E = 9 volts S − R 5 kΩ Simple checks to confirm the calculation and to illustrate the concept of the voltage drop add up the individual values of the voltage drops and compare them to the results of the Figure 12-83. Example of three resistors in series.

above calculation.

E = E + E + E … +E 1 volt + 3 volts + 5 volts = 9 volts S 1 2 3 N The source voltage equals the sum of the voltage drops. The Voltage Sources in Series polarity of the voltage drop is determined by the direction A voltage source is an energy source that provides a constant of the current flow. When going around the circuit, notice voltage to a load. Two or more of these sources in series equals that the polarity of the resistor is opposite that of the source the algebraic sum of all the sources connected in series. The voltage. The positive on the resistor is facing the positive significance of pointing out the algebraic sum is to indicate that on the source, and the negative on the resistor is facing the the polarity of the sources must be considered when adding up negative on the source.

the sources. The polarity is indicated by a plus or minus sign depending on the source’s position in the circuit.

Figure 12-86 illustrates the very basic idea of Kirchhoff’s Voltage Law. There are two resistors in this example. One In Figure 12-84, all of the sources are in the same direction has a drop of 14 volts and the other has a drop of 10 volts.

in terms of their polarity. All of the voltages have the same The source voltage must equal the sum of the voltage drops sign when added up. In the case of Figure 12-84 , three cells around the circuit. By inspection, it is easy to determine the of a value of 1.5 volts are in series with the polarity in the source voltage as 24 volts.

same direction. The addition is simple enough: Figure 12-87 shows a series circuit with three voltage E = 1.5v + 1.5v + 1.5v = +4.5 volts T drops and one voltage source rated at 24 volts. Two of the voltage drops are known. However, the third is not known.

However, in Figure 12-85 , one of the three sources has been Using Kirchhoff’s Voltage Law, the third voltage drop can turned around, and the polarity opposes the other two sources.

be determined.

Again the addition is simple: With three resistors in the circuit: E = + 1.5v − 1.5v + 1.5v = +1.5 volts T E – E – E – E = 0 volts S 1 2 3 Kirchhoff’s Voltage Law Substitute the known values: A law of basic importance to the analysis of an electrical 24v – 12v – 10v − E = 0 circuit is Kirchhoff’s Voltage Law. This law simply states that the algebraic sum of all voltages around a closed path Collect known values: 2v – E = 0 or loop is zero. Another way of saying it: the sum of all the voltage drops equals the total source voltage. A simplified Solve for the unknown: E = 2 volts formula showing this law is shown below: Determine the value of E in Figure 12-88 . For this example, I = 200mA.

With three resistors in the circuit: E – E – E – E … –E = 0 volts S 1 2 3 N First, the voltage drop across each of the individual resistors must be determined.

Notice that the sign of the source is opposite that of the individual voltage drops. Therefore, the algebraic sum equals E = I (R ) 1 1 zero. Written another way: E = (200 mA) (10 Ω) 12-36 E Ohm’s Law: R = I 1.5V 1.5V 1.5V E + ' + ' + ' Specific application: R = I 68 V Substitute values: R = 200 mA Value for R : R = 340 Ω 4 4 Voltage Dividers Voltage dividers are devices that make it possible to obtain more than one voltage from a single power source. A voltage divider usually consists of a resistor, or resistors connected in Figure 12-84. Voltage sources in series add algebraically.

series, with fixed or movable contacts and two fixed terminal contacts. As current flows through the resistor, different Voltage drop across R E = 2 volts 1 1 voltages can be obtained between the contacts.

E = I (R ) 2 2 Series circuits are used for voltage dividers. The voltage divider E = (200 mA) (50 Ω) rule allows the technician to calculate the voltage across one Voltage drop across R E = 10 volts 2 2 or a combination of series resistors without having to first calculate the current in the circuit. [Figure 12-89] Because E = I (R ) 3 3 the current flows through each resistor, the voltage drops are E = (200 mA) (100 Ω) proportional to the ohmic values of the constituent resistors.

Voltage drop across R E = 20 volts 3 3 To understand how a voltage divider works, examine Figure 12-90 carefully and observe the following: Kirchhoff’s Voltage Law is now employed to determine the voltage drop across E .

Each load draws a given amount of current: I , I , I . In 1 2 3 With four resistors in the circuit E – E – E – E – E = 0 volts S 1 2 3 4 14V + − Substituting values: 100v – 2v – 10v – 20v – E = 0 + Combine: 68v – E = 0 E =24V S − Solve for unknown: E = 68v Using Ohm’s Law and substituting in E , the value for R 4 4 + − 10V can now be determined.

Figure 12-86. Kirchhoff’s Voltage Law.

E 1.5V 1.5V 1.5V 12V + − + − + − + − + + E 2 24V E S 10V − − + − E ?

Figure 12-85. Voltage sources add algebraically; one source Figure 12-87. Determine the unknown voltage drop.

reversed.

12-37 addition to the load currents, some bleeder current (I ) flows.

B R The current (I ) is drawn from the power source and is equal T 10 Ω + − to the sum of all currents.

+ The voltage at each point is measured with respect to a + R 2 common point. Note that the common point is the point at 100 V E S 50 Ω which the total current (I ) divides into separate currents (I , − T 1 − I , I ). Each part of the voltage divider has a different current 2 3 flowing in it. The current distribution is as follows: + − + − R R 3 4 100 Ω ?

Through R — bleeder current (I ) 1 B Through R — I + I 2 B 1 Figure 12-88. Determine the unknown voltage drop.

Through R — I + I , + I 3 B 1 2 The voltage across each resistor of the voltage divider is: circuit on the ground side of R .

90 volts across R When the current reaches tap B, 30 more volts have been used 60 volts across R to move the electrons through R , and in a similar manner 2 2 50 volts across R the remaining 50 volts are used for R . But the voltages 3 3 across R and R are positive voltages, since they are above 2 3 The voltage divider circuit discussed up to this point has had ground potential.

one side of the power supply (battery) at ground potential. In Figure 12-91, the common reference point (ground symbol) Figure 12-93 shows the voltage divider used previously. The has been moved to a different point on the voltage divider. voltage drops across the resistances are the same; however, The voltage drop across R is 20 volts; however, since tap A is the reference point (ground) has been changed. The voltage connected to a point in the circuit that is at the same potential between ground and tap A is now a negative 100 volts, or as the negative side of the battery, the voltage between tap the applied voltage.

A and the reference point is a negative (−) 20 volts. Since resistors R and R are connected to the positive side of the The voltage between ground and tap B is a negative 80 volts, 2 3 battery, the voltages between the reference point and tap B and the voltage between ground and tap C is a negative 50 volts.

or C are positive.

Determining the Voltage Divider Formula The following rules provide a simple method of determining Figure 12-94 shows the example network of four resistors and negative and positive voltages: (1) If current enters a a voltage source. With a few simple calculations, a formula resistance flowing away from the reference point, the voltage for determining the voltage divisions in a series circuit can drop across that resistance is positive in respect to the be determined.

reference point; (2) if current flows out of a resistance toward the reference point, the voltage drop across that resistance is The voltage drop across any particular resistor shall be called negative in respect to the reference point. It is the location E , where the subscript x is the value of a particular resistor X of the reference point that determines whether a voltage is (1, 2, 3, or 4). Using Ohm’s Law, the voltage drop across any negative or positive.

C B A Tracing the current flow provides a means for determining the voltage polarity. Figure 12-92 shows the same circuit R R 2 3 with the polarities of the voltage drops and the direction of current flow indicated.

R The current flows from the negative side of the battery to R .

Tap A is at the same potential as the negative terminal of the battery since the slight voltage drop caused by the resistance of the conductor is disregarded; however, 20 volts of the source voltage are required to force the current through R and this 20-volt drop has the polarity indicated. Stated another Figure 12-89. A voltage divider circuit.

way, there are only 80 volts of electrical pressure left in the 12-38 explanation of this formula is that the voltage drop across I T 200v any resistor or combination of resistors in a series circuit is equal to the ratio of the resistance value to the total resistance, divided by the value of the source voltage. Figure 12-95 R illustrates this with a network of three resistors and one voltage source.

150v R X E = E X S

( )

R T R R = 100 Ω + 300 Ω + 600 Ω = 1,000 Ω E T E = 10 V S 90v Voltage drop over 100 Ω resistor is: 100 Ω Load Load Load E = 100 V X

( )

R 1 1,000 Ω E = 10 V 100Ω Voltage drop over 300 Ω resistor is: I I I I I T B 1 2 3 300 Ω E = 100 V X

( )

1,000 Ω Figure 12-90. A typical voltage divider.

E = 30 V 100 Ω resistor can be determined.

Voltage drop over 600 Ω resistor is: 600 Ω Ohm’s Law: E = I (R ) E = 100 V X X X

( )

1,000 Ω E = 60 V 100Ω As seen earlier in the handbook, the current is equal to the source voltage divided by the total resistance of the series circuit.

R R R 3 2 1 C B A +50 V +30 V −20 V E S Current: I = R + − + − + − T The current equation can now be substituted into the equation for Ohm’s Law.

E S Substitute: E = R X X

( )( )

R T 100 V R X Algebraic rearrange: E = E X S

( )( )

R T This equation is the general voltage divider formula. The Figure 12-92. Current flow through a voltage divider.

C B A C B A 50 V 30 V 20 V 50 V 30 V 20 V R =100 Ω R =60 Ω R =40 Ω 3 2 1 R R R 3 2 1 100 V 100 V Figure 12-93. Voltage divider with changed ground.

Figure 12-91. Positive and negative voltage on a voltage divider.

12-39 Checking work decreases. The total resistance of a parallel combination is E = 10 V + 30 V + 60 V = 100 V always less than the value of the smallest resistor in the circuit.

T In the series circuit, the current has to pass through the resistors Parallel DC Circuits one at a time. This gave a resistance to the current equal the sum of all the resistors. In the parallel circuit, the current has several A circuit in which two of more electrical resistances or loads resistors that it can pass through, actually reducing the total are connected across the same voltage source is called a resistance of the circuit in relation to any one resistor value.

parallel circuit. The primary difference between the series circuit and the parallel circuit is that more than one path is The amount of current passing through each resistor varies provided for the current in the parallel circuit. Each of these according to its individual resistance. The total current of parallel paths is called a branch. The minimum requirements the circuit is the sum of the current in all branches. It can for a parallel circuit are the following: be determined by inspection that the total current is greater • A power source than that of any given branch. Using Ohm’s Law to calculate • Conductors the total resistance based on the applied voltage and the total current, it can be determined that the total resistance is less • A resistance or load for each current path than any branch.

• Two or more paths for current flow An example of this is if there was a circuit with a 100 Ω Figure 12-96 depicts the most basic parallel circuit. Current resistor and a 5 Ω resistor; while the exact value must be flowing out of the source divides at point A in the diagram calculated, it still can be said that the combined resistance and goes through R and R . As more branches are added to 1 2 between the two is less than the 5 Ω.

the circuit, more paths for the source current are provided.

Resistors in Parallel Voltage Drops The formula for the total parallel resistance is as follows: The first point to understand is that the voltage across any 1 1 1 1 1 branch is equal to the voltage across all of the other branches.

= + + + ...

R R R R R T 1 2 3 N Total Parallel Resistance If the reciprocal of both sides is taken, then the general The parallel circuit consists of two or more resistors connected formula for the total parallel resistance is: in such a way as to allow current flow to pass through all of the resistors at once. This eliminates the need for current to pass R = T 1 1 1 1 one resistor before passing through the next. When resistors + + + ...

R R R R 2 3 N are connected in parallel, the total resistance of the circuit Two Resistors in Parallel Typically, it is more convenient to consider only two resistors at a time because this setup occurs in common practice. Any + number of resistors in a circuit can be broken down into pairs.

Therefore, the most common method is to use the formula E R − + + R E 2 2 + 100 Ω R − 1 − E S + − + + R E 3 3 300 Ω R E 100 v S − − − + + R E 600 Ω R 4 4 − − Figure 12-94. Four resistor voltage divider. Figure 12-95. Network of three resistors and one voltage source.

12-40 for two resistors in parallel.

General formula I = I + I + I T 1 2 3 R = T 1 1 + R R 1 2 Refer to Figure 12-97 for an example. Point A and point B Combining the terms in the denominator and rewriting: represent two junctions or nodes in the circuit with three resistive branches in between. The voltage source provides R R 1 2 R = T a total current I into node A. At this point, the current must T R + R 1 2 divide, flowing out of node A into each of the branches Put in words, this states that the total resistance for two according to the resistive value of each branch. Kirchhoff’s resistors in parallel is equal to the product of both resistors Current Law states that the current going in must equal that divided by the sum of the two resistors. In the formula below, going out. Following the current through the three branches calculate the total resistance. and back into node B, the total current I entering node B T and leaving node B is the same as that which entered node R R 1 2 General formula R = A. The current then continues back to the voltage source.

T R + R 1 2 Known values R = 500 Ω Figure 12-98 shows that the individual branch currents are: R = 400 Ω I = 5 mA 500 Ω 400 Ω R = T 500 Ω + 400 Ω I = 12 mA 200,000 Ω R = T 900 Ω The total current flow into the node A equals the sum of the R = 222.22 Ω branch currents, which is: I = I + I T T 1 2 Current Source Substitute I = 5 mA + 12 mA T A current source is an energy source that provides a constant I = 17 mA T value of current to a load even when the load changes in resistive value. The general rule to remember is that the total The total current entering node B is also the same.

current produced by current sources in parallel is equal to the algebraic sum of the individual sources. Figure 12-99 illustrates how to determine an unknown current in one branch. Note that the total current into a junction of Kirchhoff’s Current Law the three branches is known. Two of the branch currents are known. By rearranging the general formula, the current in Kirchhoff’s Current Law can be stated as: the sum of the branch two can be determined.

currents into a junction or node is equal to the sum of the currents flowing out of that same junction or node. A junction General formula I = I + I + I can be defined as a point in the circuit where two or more T 1 2 3 Substitute 75 mA = 30 mA + I + 20 mA circuit paths come together. In the case of the parallel circuit, Solve I I = 75 mA – 30 mA – 20 mA it is the point in the circuit where the individual branches join.

2 2 I = 25 mA Current Dividers A It can now be easily seen that the parallel circuit is a current divider. As shown in Figure 12-96 , there is a current through each of the two resistors. Because the same voltage is applied across both resistors in parallel, the branch currents are + + + inversely proportional to the ohmic values of the resistors.

E R R S Branches with higher resistance have less current than those 1 2 − − − with lower resistance. For example, if the resistive value of R is twice as high as that of R , the current in R is half of 2 1 2 that of R . All of this can be determined with Ohm’s Law.

By Ohm’s Law, the current through any one of the branches B can be written as: Figure 12-96. Basic parallel circuit.

12-41 I = E /R X S X I T A The voltage source appears across each of the parallel resistors I I 1 3 and R represents any one the resistors. The source voltage X is equal to the total current times the total parallel resistance.

+ E = I R + + + S T T E I R R R R S T T 1 2 3 I = X Substituting I R for E R − T T S − − X − R T Rearranging I = I X T

( )

R X R I = I 2 T

( )

B R T I R T I = I 1 T

( )

And R T Figure 12-97. Kirchhoff’s Current Law.

This formula is the general current divider formula. The current through any branch equals the total parallel resistance I =17 mA T divided by the individual branch resistance, multiplied by A the total current.

I =12 mA I =5 mA 2 1 Series-Parallel DC Circuits Most of the circuits that the technician encounters will not + + + be a simple series or parallel circuit. Circuits are usually a E R R S 2 1 combination of both, known as series-parallel circuits, which − − are groups consisting of resistors in parallel and in series. An − example of this type of circuit can be seen in Figure 12-100 .

While the series-parallel circuit can initially appear to be complex, the same rules that have been used for the series and parallel circuits can be applied to these circuits.

B The voltage source provides a current out to resistor R , I =17 mA then to the group of resistors R and R and then to the next T 2 3 resistor R before returning to the voltage source. The first Figure 12-98. Individual branch currents.

step in the simplification process is to isolate the group R and R and recognize that they are a parallel network that can be reduced to an equivalent resistor. Using the formula I =75 mA T for parallel resistance, A R R 2 3 I =30 mA I =20 mA R = 1 3 23 R + R 2 3 I =? R and R can be reduced to R . Figure 12-101 now shows 2 3 23 + an equivalent circuit with three series connected resistors. The + + + total resistance of the circuit can now be simply determined E S by adding up the values of resistors R , R , and R .

1 23 4 − − − − Determining the Total Resistance A more quantitative example for determining total resistance and the current in each branch in a combination circuit is shown in the following example. [Figure 12-102] B I =75 mA T The first step is to determine the current at junction A, leading into the parallel branch. To determine the I , the total T Figure 12-99. Determining an unknown circuit in branch 2.

12-42 resistance R of the entire circuit must be known. The total T R resistance of the circuit is given as: R = R + R T 1 23 R R 2 3 Where R = Parallel network +

( )

R + R 2 3 R E S 2k Ω 3k Ω − R = Find R EQ 2k Ω + 3k Ω 6,000k Ω R = 5k Ω Solve for R EQ R = 1.2k Ω R Solve for R R = 1k Ω + 1.2k Ω Figure 12-101. Equivalent circuit with three series connected T T resistors. R = 2.2k Ω T With the total resistance R now determined, the total I can T T 1,200 Ω I = x (10.9 mA) 2,000 Ω be determined. Using Ohm’s Law: I = 6.54 mA E S I = T R T Now using Kirchhoff’s Current Law, the current in the branch 24 V Substitute values I = with R can be determined.

T 2.2k Ω I = 10.9 mA I + I = I T 2 3 T Recall that I = 10.9 mA T The current through the parallel branches of R and R can I – I = I 2 3 T 2 3 be determined using the current divider rule discussed earlier Also recall that I = 6.54 mA in this handbook.

Subtract I from I to get I 2 T 3 I = 4.36 mA Recall Parallel Branch Resistance: Alternating Current (AC) & Voltage 6,000 Ω R = 23 Alternating current (AC) has largely replaced direct current 5,000 Ω (DC) in commercial power systems for a number of reasons.

R = 1.2k Ω It can be transmitted over long distances more readily and more economically than DC, since AC voltages can be Substitute values for I : R R 1k Ω A A + + R R R E R 3 3 2 S 2 E =24 V 2k Ω 3k Ω S − − B R 4 B Figure 12-100. Series-parallel circuits. Figure 12-102. Determining total resistance.

12-43 increased or decreased by means of transformers. current is flowing. [Figure 12-104B] Because more and more units are being operated electrically In Figure 12-104C , the galvanometer indicates a current in airplanes, the power requirements are such that a number flow in the opposite direction when the magnet is pulled of advantages can be realized by using AC. Space and from the cylinder.

weight can be saved since AC devices, especially motors, are smaller and simpler than DC devices. In most AC motors, The same results may be obtained by holding the magnet no brushes are required, and commutation trouble at high stationary and moving the cylinder over the magnet, indicating altitude is eliminated. Circuit breakers operate satisfactorily that a current flows when there is relative motion between the under load at high altitudes in an AC system, whereas arcing wire coil and the magnetic field. These results obey a law first is so excessive on DC systems that circuit breakers must be stated by the German scientist, Heinrich Lenz. Lenz’s Law replaced frequently. Finally, most airplanes using a 24-volt states that the induced current caused by the relative motion DC system have special equipment that requires a certain of a conductor and a magnetic field always flows in such a amount of 400-cycle AC current. direction that its magnetic field opposes the motion.

AC and DC Compared When a conductor is moved through a magnetic field, an emf Many of the principles, characteristics, and effects of AC is induced in the conductor. [Figure 12-105] The direction (polarity) of the induced emf is determined by the magnetic are similar to those of DC. Similarly, there are a number of differences. DC flows constantly in only one direction with lines of force and the direction the conductor is moved through the magnetic field. The generator left-hand rule a constant polarity. It changes magnitude only when the circuit is opened or closed, as shown in the DC waveform (not to be confused with the left-hand rules used with a coil) can be used to determine the direction of the induced emf.

in Figure 12-103 . AC changes direction at regular intervals, increases in value at a definite rate from zero to a maximum [Figure 12-106] The left-hand rule is summed up as follows: positive strength, and decreases back to zero; then it flows in the opposite direction, similarly increasing to a maximum The first finger of the left hand is pointed in the direction of the magnetic lines of force (North to South), the thumb negative value, and again decreasing to zero. DC and AC waveforms are compared in Figure 12-103 . is pointed in the direction of movement of the conductor through the magnetic field, and the second finger points in Since AC constantly changes direction and intensity, the the direction of the induced emf.

following two effects (to be discussed later) take place in AC circuits that do not occur in DC circuits: When a loop conductor is rotated in a magnetic field, a voltage is induced in each side of the loop. [Figure 12-107] 1. Inductive reactance The two sides cut the magnetic field in opposite directions, 2. Capacitive reactance and although the current flow is continuous, it moves in opposite directions with respect to the two sides of the loop.

Generator Principles If sides A and B and the loop are rotated half a turn and the sides of the conductor have exchanged positions, the After the discovery that an electric current flowing through induced emf in each wire reverses its direction, since the wire a conductor creates a magnetic field around the conductor, formerly cutting the lines of force in an upward direction is there was considerable scientific speculation about whether now moving downward.

a magnetic field could create a current flow in a conductor.

In 1831, Faraday discovered that this could be accomplished.

The value of an induced emf depends on three factors: To show how an electric current can be created by a magnetic 1. Number of wires moving through the magnetic field field, a demonstration similar to Figure 12-104 can be used.

2. Strength of the magnetic field Several turns of a conductor are wrapped around a cylindrical 3. Speed of rotation form, and the ends of the conductor are connected together to form a complete circuit, which includes a galvanometer.

Generators of Alternating Current If a simple bar magnet is plunged into the cylinder, the Generators used to produce an alternating current are called galvanometer can be observed to deflect in one direction AC generators or alternators.

from its zero (center) position. [Figure 12-104A] The simple generator constitutes one method of generating When the magnet is at rest inside the cylinder, the an alternating voltage. [Figure 12-108] It consists of galvanometer shows a reading of zero, indicating that no 12-44 Waveform for DC Waveform for AC + 180° 270° 360° Volts 0° 90° Volts Closed Open Operation of circuit switch switch − Time Time Figure 12-103. DC and AC voltage curves.

a rotating loop, marked A and B, placed between two Motion of magnet Galvanometer magnetic poles, N and S. The ends of the loop are connected to two metal slip rings (collector rings), C and C . Current 1 2 is taken from the collector rings by brushes. If the loop is I considered as separate wires A and B, and the left-hand rule for generators is applied, then it can be observed that A as wire A moves up across the field, a voltage is induced S which causes the current to flow inward. As wire B moves down across the field, a voltage is induced which causes the I Coil current to flow outward. When the wires are formed into a N loop, the voltages induced in the two sides of the loop are combined. Therefore, for explanatory purposes, the action of either conductor, A or B, while rotating in the magnetic field is similar to the action of the loop.

Figure 12-109 illustrates the generation of AC with a simple loop conductor rotating in a magnetic field. As it is rotated S in a counterclockwise direction, varying values of voltages B Magnet at rest are induced in it.

N Position 1 The conductor A moves parallel to the lines of force. Since it cuts no lines of force, the induced voltage is zero. As the conductor advances from position 1 to position 2, the voltage induced gradually increases.

Position 2 Motion of magnet S The conductor is now moving perpendicular to the flux and cuts a maximum number of lines of force; therefore, a maximum voltage is induced. As the conductor moves beyond N I position 2, it cuts a decreasing amount of flux at each instant, and the induced voltage decreases.

C Position 3 At this point, the conductor has made one-half of a revolution I and again moves parallel to the lines of force, and no voltage is induced in the conductor. As the A conductor passes Figure 12-104. Inducing a current flow.

position 3, the direction of induced voltage now reverses since the A conductor is moving downward, cutting flux 12-45 emf

A Motion of conductor Figure 12-105. Inducing an emf in a conductor.

Figure 12-107. Voltage induced in a loop.

in the opposite direction. As the A conductor moves across the South pole, the induced voltage gradually increases in a Cycle and Frequency negative direction, until it reaches position 4.

Cycle Defined A cycle is a repetition of a pattern. Whenever a voltage Position 4 or current passes through a series of changes, returns to Like position 2, the conductor is again moving perpendicular the starting point, and then again starts the same series of to the flux and generates a maximum negative voltage. From changes, the series is called a cycle. The cycle is represented position 4 to 5, the induced voltage gradually decreases until by the symbol of a wavy line in a circle ~ . In the cycle of the voltage is zero, and the conductor and wave are ready to voltage shown in Figure 12-110 , the voltage increases from start another cycle.

zero to a maximum positive value, decreases to zero; then increases to a maximum negative value, and again decreases Position 5 to zero. At this point, it is ready to go through the same series The curve shown at position 5 is called a sine wave. It of changes. There are two alternations in a complete cycle: represents the polarity and the magnitude of the instantaneous the positive alternation and the negative. Each is half a cycle.

values of the voltages generated. The horizontal base line is divided into degrees, or time, and the vertical distance above Frequency Defined or below the base line represents the value of voltage at each The frequency is the number of cycles of AC per second (1 particular point in the rotation of the loop.

Conductor moved up Flux forward Inducted emf

S S

Inducted emf Figure 12-106. An application of the generator left-hand rule.

12-46

Brushes In current Out current A C C

Figure 12-108. Simple generator.

second). The standard unit of frequency measurement is the F = 60 cps hertz (Hz). [Figure 12-111] In a generator, the voltage and current pass through a complete cycle of values each time Period Defined a coil or conductor passes under a North and South pole of The time required for a sine wave to complete one full cycle the magnet. The number of cycles for each revolution of the is called a period. [Figure 12-110] The period of a sine coil or conductor is equal to the number of pairs of poles.

wave is inversely proportional to the frequency: the higher The frequency, then, is equal to the number of cycles in the frequency, the shorter the period. The mathematical one revolution multiplied by the number of revolutions per relationship between frequency and period is given as: second (rps).

Period is t = f Expressed in equation form: Frequency is f = t Number of poles rpm F = × 2 60 Wavelength Defined P where ⁄ 2 is the number of pairs of poles, and rpm/60 the The distance that a waveform travels during a period is number of revolutions per second. If in a 2-pole generator, commonly referred to as a wavelength and is indicated by the conductor is turning at 3,600 rpm, the revolutions per the Greek letter lambda ( l ). The measurement of wavelength second are: is taken from one point on the waveform to a corresponding point on the next waveform. [Figure 12-110] 3,600 rps = = 60 revolutions per second Phase Relationships P Since there are 2 poles, ⁄ 2 is 1, and the frequency is 60 cycles In addition to frequency and cycle characteristics, alternating per second (cps). In a 4-pole generator with an armature speed voltage and current also have a relationship called “phase.” of 1,800 rpm, substitute in the equation: In a circuit that is fed (supplied) by one alternator, there must be a certain phase relationship between voltage and rpm P F = × as follows current if the circuit is to function efficiently. In a system 2 60 fed by two or more alternators, not only must there be a 1,800 certain phase relationship between voltage and current of F = × 2 60 one alternator, but there must be a phase relationship between the individual voltages and the individual currents. Also, two F = 2 × 30 separate circuits can be compared by comparing the phase 12-47 Magnetic field N N N C2 C2 C2 C1 0° 90° 180° 270° 360° C1 0° 90° 180° 270° 360° C1 0° 90° 180° 270° 360° B A B S S S Maximum positive voltage Voltage drops to zero Zero voltage Quarter turn completed Position 2 Position 3 One half turn completed Position 1 Conductors cutting directly across the magnetic field as conductor Conductor again moving parallel to magnetic field, cutting minimum Rotating conductors moving parallel to magnetic field, cutting A passes across the North (N) magnetic pole and B passes across lines of force. minimum lines of force.

the South (S) magnetic pole.

N N C2 C2 C1 C1 0° 90° 180° 270° 360° 0° 90° 180° 270° 360° A S S Maximum negative voltage Zero voltage Position 4 Three quarters turn completed Position 5 Full turn completed Conductors again moving directly across magnetic field A passes Conductor A has made one complete cycle and is in same position across South (S) magnetic pole and B across North (N) magnetic pole. as in position A. The generator has generated one complete cycle of alternating voltage or current.

Figure 12-109. Generation of a sine wave.

characteristics of one to the phase characteristics of the other. starts to rise at the 90° position. Because voltage source one begins its rise earlier in time (90°) in relation to the second In Phase Condition voltage source, it is said to be leading the second source.

On the other hand, the second source is said to be lagging Figure 12-112A shows a voltage signal and a current signal the first source. When a waveform is said to be leading or superimposed on the same time axis. Notice that when the lagging, the difference in degrees is usually stated. If the voltage increases in the positive alternation that the current two waveforms differ by 360°, they are said to be in phase also increases. When the voltage reaches its peak value, so with each other. If there is a 180° difference between the two does the current. Both waveforms then reverse and decrease signals, then they are still out of phase even though they are back to a zero magnitude, then proceed in the same manner both reaching their minimum and maximum values at the in the negative direction as they did in the positive direction.

same time. [Figure 12-112C] When two waves, such as these in Figure 12-112A , are exactly in step with each other, they are said to be in phase. To be in A practical note of caution: When encountering an aircraft that phase, the two waveforms must go through their maximum and has two or more AC busses in use, it is possible that they may minimum points at the same time and in the same direction.

be split and not synchronized to be in phase with each other.

When two signals that are not locked in phase are mixed, much Out of Phase Condition damage can occur to aircraft systems or avionics.

When two waveforms go through their maximum and minimum points at different times, a phase difference exists Values of Alternating Current between the two. In this case, the two wave-forms are said There are three values of AC: instantaneous, peak, and to be out of phase with each other. The terms lead and lag effective root mean square (RMS).

are often used to describe the phase difference between waveforms. The waveform that reaches its maximum or Instantaneous Value minimum value first is said to lead the other waveform.

An instantaneous value of voltage or current is the induced Figure 12-112B shows this relationship. Voltage source voltage or current flowing at any instant during a cycle. The one starts to rise at the 0° position and voltage source two sine wave represents a series of these values. The instantaneous 12-48 Negative Positive alternation alternation 0° 90° 180° 270° Horizontal scale 1T 360° (Time) Positive 1T 2T 3T 4T alternation 1 second time Frequency = 2 cycles per second Negative alternation Frequency = 2 cycles per second Vertical scale (voltage) One cycle Second cycle 90° 180° One period (Repeated) (Time) 0° 360° One wavelength 270° (Distance) Cycle is de fi ned as a repetitive pattern.

1 second time Frequency = 8 cycles per second Figure 12-110. Cycle of voltage.

Figure 12-111. Frequency in cycles per second.

value of the voltage varies from zero at 0° to maximum at 90°, back to zero at 180°, to maximum in the opposite direction at 270°, and to zero again at 360°. Any point on the sine wave is considered the instantaneous value of voltage. This can be applied to either voltage or current.

Algebraically rearranging the formula and solving for Vp can Peak Value also determine the peak voltage. The resulting formula is: The peak value is the largest instantaneous value. The largest single positive value occurs when the sine wave of voltage is Vp = 1.414 × Vrms at 90°, and the largest single negative value occurs when it is at 270°. Maximum value is 1.41 times the effective value.

Thus, the 110 volt value given for AC supplied to homes These are called peak values.

is only 0.707 of the maximum voltage of this supply. The maximum voltage is approximately 155 volts (110 × 1.41 = Effective Value 155 volts maximum).

The effective value is also known as the RMS value or root mean square, which refers to the mathematical process by In the study of AC, any values given for current or voltage which the value is derived. Most AC voltmeters display the are assumed to be effective values unless otherwise specified.

effective or RMS value when used. The effective value is In practice, only the effective values of voltage and current less than the maximum value, being equal to .707 times the are used. Similarly, AC voltmeters and ammeters measure maximum value.

the effective value.

The effective value of a sine wave is actually a measure of Opposition to Current Flow of AC the heating effect of the sine wave. Figure 12-113 illustrates There are three factors that can create an opposition to the flow what happens when a resistor is connected across an AC of electrons (current) in an AC circuit. Resistance, similar voltage source. In Figure 12-113A , a certain amount of heat is to resistance of DC circuits, is measured in ohms and has a generated by the power in the resistor. Figure 12-113B shows direct influence on AC regardless of frequency. Inductive the same resistor now inserted into a DC voltage source.

reactance and capacitive reactance, on the other hand, oppose The value of the DC voltage source can now be adjusted so current flow only in AC circuits, not in DC circuits. Since that the resistor dissipates the same amount of heat as it did AC constantly changes direction and intensity, inductors and when it was in the AC circuit. The RMS or effective value capacitors may also create an opposition to current flow in of a sine wave is equal to the DC voltage that produces the AC circuits. It should also be noted that inductive reactance same amount of heat as the sinusoidal voltage.

and capacitive reactance may create a phase shift between the voltage and current in an AC circuit. Whenever analyzing The peak value of a sine wave can be converted to the an AC circuit, it is very important to consider the resistance, corresponding RMS value using the following relationship.

inductive reactance, and the capacitive reactance. All three have an effect on the current of that circuit.

Vrms = ( 0.5 ) × Vp Vrms = 0.707 × Vp 12-49 charged, and the A plate negatively charged. Current flows in Voltage the external circuit during the time the electrons are moving from B to A. The current flow in the circuit is at a maximum the instant the switch is closed, but continually decreases thereafter until it reaches zero. The current becomes zero as Current soon as the difference in voltage of A and B becomes the same 0° 90° 180° 270° 360° as the voltage of the battery. If the switch is opened as shown in Figure 12-114B , the plates remain charged. Once the capacitor is shorted, it discharges quickly as shown Figure 12-114C .

It should be clear that during the time the capacitor is being A. Voltage and current are in phase charged or discharged, there is current in the circuit, even though the circuit is broken by the gap between the capacitor Voltage source 1 (leads source 2) plates. Current is present only during the time of charge and discharge, and this period of time is usually short.

Voltage source 2 (lags source 1) The Resistor/ Capacitor (RC) Time Constant The time required for a capacitor to attain a full charge is proportional to the capacitance and the resistance of the 0° 90° 180° 270° 360° circuit. The resistance of the circuit introduces the element of time into the charging and discharging of a capacitor.

90° Difference When a capacitor charges or discharges through a resistance, a certain amount of time is required for a full charge or B. Two voltage waves, 90° out of phase discharge. The voltage across the capacitor does not change Voltage source 1 Voltage source 2 instantaneously. The rate of charging or discharging is determined by the time constant of the circuit. The time constant of a series resistor/capacitor (RC) circuit is a time interval that equals the product of the resistance in ohms and the capacitance in farad and is symbolized by the Greek letter tau ( τ ).

0° 90° 180° 270° 360° τ = RC The time in the formula is the time required to charge to 63 C. Two voltage waves, 180° out of phase percent of the voltage of the source. The time required to bring the charge to about 99 percent of the source voltage is approximately 5 τ . [Figure 12-115] Figure 12-112. In phase and out of phase conditions.

The measure of a capacitor’s ability to store charge is its Capacitance capacitance. The symbol used for capacitance is the letter C.

Another important property in AC circuits, besides resistance As can be seen from Figure 12-115, there can be no continuous and inductance, is capacitance. While inductance is represented in a circuit by a coil, capacitance is represented by movement of DC through a capacitor. A good capacitor blocks DC and passes the effects of pulsing DC or AC.

a capacitor. In its most basic form, the capacitor is constructed of two parallel plates separated by a nonconductor called Units of Capacitance a dielectric. In an electrical circuit, a capacitor serves as a reservoir or storehouse for electricity. Electrical charge, which is symbolized by the letter Q, is measured in units of coulombs. The coulomb is given by Capacitors in Direct Current the letter C, as with capacitance. Unfortunately, this can be When a capacitor is connected across a source of DC, such as a confusing. One coulomb of charge is defined as a charge having 6.28 × 10 electrons. The basic unit of capacitance storage battery in the circuit shown in Figure 12-114A , and the switch is then closed, the plate marked B becomes positively is the farad and is given by the letter f. By definition, one 12-50 The voltage rating of the capacitor is a factor in determining the actual capacitance, because capacitance decreases as the R V thickness of the dielectric increases. A high-voltage capacitor rms that has a thick dielectric must have a larger plate area in order to have the same capacitance as a similar low voltage capacitor having a thin dielectric.

A Equal heat dissipation in both circuits Factors Affecting Capacitance + 1. The capacitance of parallel plates is directly V =V proportional to their area. A larger plate area produces R rms dc a larger capacitance and a smaller area produces less − capacitance. If we double the area of the plates, there is room for twice as much charge. The charge that a B capacitor can hold at a given potential difference is doubled, and since C = Q/E, the capacitance is doubled.

Figure 12-113. Sine wave effective value.

2. The capacitance of parallel plates is inversely proportional to their spacing.

farad is one coulomb of charge stored with one volt across the 3. The dielectric material affects the capacitance of plates of the capacitor. The general formula for capacitance parallel plates. The dielectric constant of a vacuum is in terms of charge and voltage is: defined as 1, and that of air is very close to 1. These Q values are used as a reference, and all other materials Where C = E have values specified in relation to air (vacuum).

C = capacitance measured in farads The strength of some commonly used dielectric materials is E = applied voltage measured in volts listed in Figure 12-116 . The voltage rating also depends on Q = charge measured in coulombs frequency because the losses, and the resultant heating effect, increase as the frequency increases.

In practical terms, one farad is a large amount of capacitance.

Typically, in electronics, much smaller units are used. The two Types of Capacitors more common smaller units are the microfarad (μF), which is Capacitors come in all shapes and sizes and are usually -6 -12 10 farad, and the picofarad (pF), which is 10 farad.

marked with their value in farads. They may also be divided into two groups: fixed and variable. The fixed capacitors, Voltage Rating of a Capacitor which have approximately constant capacitance, may then Capacitors have their limits as to how much voltage can be be further divided according to the type of dielectric used.

applied across the plates. The aircraft technician must be Some varieties are: paper, oil, mica, electrolytic and ceramic aware of the voltage rating, which specifies the maximum capacitors. Figure 12-117 shows the schematic symbols for DC voltage that can be applied without the risk of damage a fixed and variable capacitor.

to the device. This voltage rating is typically called the breakdown voltage, the working voltage, or simply the Fixed Capacitors voltage rating. If the voltage applied across the plates is Mica Capacitors too great, the dielectric breaks down and arcing occurs The fixed mica capacitor is made of metal foil plates that are between the plates. The capacitor is then short circuited, separated by sheets of mica, which form the dielectric. The and the possible flow of DC through it can cause damage whole assembly is covered in molded plastic, which keeps out to other parts of the equipment.

moisture. Mica is an excellent dielectric and withstands higher voltages than paper without allowing arcing between the plates.

A capacitor that can be safely charged to 500 volts DC cannot Common values of mica capacitors range from approximately be safely subjected to AC or pulsating DC whose effective 50 microfarads to about 0.02 microfarads. [Figure 12-118] values are 500 volts. An alternating voltage of 500 volts (RMS) has a peak voltage of 707 volts, and a capacitor to which it is Ceramic applied should have a working voltage of at least 750 volts. The The ceramic capacitor is constructed with materials, such capacitor should be selected so that its working voltage is at as titanium acid barium for a dielectric. Internally these least 50 percent greater than the highest voltage to be applied.

12-51 Electrolytic Close Charge Two kinds of electrolytic capacitors are in use: wet electrolytic and dry electrolytic. The wet electrolytic capacitor is designed B + of two metal plates separated by an electrolyte with an ++++ electrolyte dielectric, which is basically conductive salt in −−−− A solvent. For capacitances greater than a few microfarads, the − plate areas of paper or mica capacitors must become very large; thus, electrolytic capacitors are usually used instead.

A Capacitor being charged These units provide large capacitance in small physical sizes.

Their values range from 1 to about 1,500 microfarads. Unlike Open the other types, electrolytic capacitors are generally polarized, B with the positive lead marked with a “+” and the negative + ++++ lead marked with a “−” and should only be subjected to direct −−−− voltage or pulsating direct voltage only.

A − The electrolyte in contact with the negative terminal, either in paste or liquid form, comprises the negative electrode. The B Capacitor retains charge dielectric is an exceedingly thin film of oxide deposited on Close the positive electrode of the capacitor. The positive electrode, which is an aluminum sheet, is folded to achieve maximum B + area. The capacitor is subjected to a forming process during ++ Short Removed manufacture in which current is passed through it. The flow −− of current results in the deposit of the thin coating of oxide A − on the aluminum plate.

C Capacitor discharges The close spacing of the negative and positive electrodes gives rise to the comparatively high-capacitance value, but allows greater possibility of voltage breakdown and leakage Figure 12-114. Capacitors in direct current.

of electrons from one electrode to the other.

capacitors are not constructed as a coil, so they are well The electrolyte of the dry electrolytic unit is a paste contained suited for use in high-frequency applications. They are shaped in a separator made of an absorbent material, such as gauze or like a disk, available in very small capacitance values, and paper. The separator not only holds the electrolyte in place but very small sizes. This type is fairly small, inexpensive, and also prevents it from short circuiting the plates. Dry electrolytic reliable. Both the ceramic and the electrolytic are the most capacitors are made in both cylindrical and rectangular block widely available and used capacitor.

form and may be contained either within cardboard or metal covers. Since the electrolyte cannot spill, the dry capacitor may be mounted in any convenient position. [Figure 12-119] Tantalum Voltage Similar to the electrolytic, these capacitors are constructed with a material called tantalum, which is used for the 100% 99% electrodes. They are superior to electrolytic capacitors, 98% 90% 95% 80% 86% having better temperature and frequency characteristics.

70% When tantalum powder is baked in order to solidify it, a crack 60% 63% forms inside. This crack is used to store an electrical charge.

50% 40% Like electrolytic capacitors, the tantalum capacitors are also Current 30% polarized and are indicated with the “+” and “−” symbols.

20% 10% Polyester Film 1t 2t 3t 4t 5t In this capacitor, a thin polyester film is used as a dielectric.

Charging curve for a capacitor These components are inexpensive, temperature stable, and widely used. Tolerance is approximately 5–10 percent. It Figure 12-115. Capacitance discharge curve.

12-52 can be quite large depending on capacity or rated voltage.

Oil Capacitors In radio and radar transmitters, voltages high enough to cause arcing, or breakdown, of paper dielectrics are often used.

Consequently, in these applications capacitors that use oil or oil impregnated paper for the dielectric material are preferred.

Capacitors of this type are considerably more expensive than ordinary paper capacitors, and their use is generally restricted Fixed Variable to radio and radar transmitting equipment. [Figure 12-120] Figure 12-117. Schematic symbols for a fixed and variable capacitor.

Variable Capacitors Variable capacitors are mostly used in radio tuning circuits, and they are sometimes called “tuning capacitors.” They have very combination is capable of withstanding a higher total small capacitance values, typically between 100 pF and 500 pF.

potential difference than any of the individual capacitors.

Figure 12-121 is a simple series circuit. The bottom plate Trimmers of C and the top plate of C is charged by electrostatic 1 2 The trimmer is actually an adjustable or variable capacitor, induction. The capacitors charge as current is established which uses ceramic or plastic as a dielectric. Most of them are through the circuit. Since this is a series circuit, the current color coded to easily recognize their tunable size. The ceramic must be the same at all points. Since the current is the rate type has the value printed on them. Colors are: yellow (5 pF), of flow of charge, the amount of charge (Q) stored by each blue (7 pF), white (10 pF), green (30 pF), and brown (60 pF).

capacitor is equal to the total charge.

Varactors Q = Q + Q + Q T 1 2 3 A voltage-variable capacitor or varactor is also known as a variable capacitance diode or a varicap. This device utilizes According to Kirchhoff’s Voltage Law, the sum of the the variation of the barrier width in a reversed-biased diode.

voltages across the charged capacitors must equal the total Because the barrier width of a diode acts as a non-conductor, voltage, E . This is expressed as: T a diode forms a capacitor when reversed biased. Essentially, the N-type material becomes one plate and the junctions E = E + E + E T 1 2 3 are the dielectric. If the reversed-bias voltage is increased, then the barrier width widens, effectively separating the two Equation E = Q/C can now be substituted into the voltage capacitor plates and reducing the capacitance.

equation where we now get: Q Q Q Q T 1 2 3 Capacitors in Series = + + C C C C T 1 2 3 When capacitors are placed in series, the effective plate separation is increased and the total capacitance is less Since the charge on all capacitors is equal, the Q terms can than that of the smallest capacitor. Additionally, the series be factored out, leaving us with the equation: 1 1 1 1 = + + C C C C Dielectric Strength T 1 2 3 Dielectric K (volts per .001 inch) Air 1.0 80 Paper (1) Paraffined 2.2 1,200 (2) Beeswaxed 3.1 1,800 Glass 4.2 200 Castor Oil 4.7 380 Bakelite 6.0 500 Mica 6.0 2,000 Fiber 6.5 50 Figure 12-118. Fixed capacitors.

Figure 12-116. Strength of some dielectric materials.

12-53 Consider the following example: Leaving us with the equation for capacitors in parallel: If C = 10 μF, C = 5 μF and C = 8 μF C = C + C + C 1 2 3 T 1 2 3 Consider the following example: 1 1 1 1 Then = + + 10 μF 5 μF 8 μF C T If C = 330 μF, C = 220 μF 1 2 C = = 2.35 μF T 0.425 μF Then C = 330 μF + 220 μF = 550 μF T Capacitors in Parallel Capacitors in Alternating Current When capacitors are connected in parallel, the effective plate If a source of AC is substituted for the battery, the capacitor area increases, and the total capacitance is the sum of the individual capacitances. Figure 12-122 shows a simplified acts quite differently than it does with DC. When AC is applied in the circuit, the charge on the plates constantly parallel circuit. The total charging current from the source divides at the junction of the parallel branches. There is changes. [Figure 12-123] This means that electricity must flow first from Y clockwise around to X, then from a separate charging current through each branch so that a different charge can be stored by each capacitor. Using X counterclockwise around to Y, then from Y clockwise around to X, and so on. Although no current flows through Kirchhoff’s Current Law, the sum of all of the charging currents is then equal to the total current. The sum of the the insulator between the plates of the capacitor, it constantly flows in the remainder of the circuit between X and Y. In charges (Q) on the capacitors is equal to the total charge.

The voltages (E) across all of the parallel branches are equal. a circuit where there is only capacitance, current leads the applied voltage as contrasted with a circuit in which there is With all of this in mind, a general equation for capacitors in parallel can be determined as: inductance, where the current lags the voltage.

Capacitive Reactance Xc Q = Q + Q + Q T 1 2 3 The effectiveness of a capacitor in allowing an AC flow to pass Because Q = CE: C E = C E + C E + C E depends upon the capacitance of the circuit and the applied T T 1 1 2 2 3 3 frequency. To what degree a capacitor allows an AC flow to Voltages can be factored out because: pass depends largely upon the capacitive value of the capacitor given in farads (f). The greater the capacitance of the capacitor, E = E + E + E the greater the number of electrons, measured in Coulombs, T 1 2 3 necessary to bring the capacitor to a fully charged state. Once the capacitor approaches or actually reaches a fully charged condition, the polarity of the capacitor opposes the polarity of the applied voltage, essentially acting then as an open circuit.

To further illustrate this characteristic and how it manifests itself in an AC circuit, consider the following. If a capacitor has a large capacitive value, meaning that it requires a relatively large number of electrons to bring it to a fully charged state, Figure 12-119. Electrolytic capacitors.

Figure 12-120. Oil capacitor.

12-54 then a rather high-frequency current can alternate through the is substituted in the equation and: capacitor without the capacitor ever reaching a full charge. In Xc = this case, if the frequency is high enough and the capacitance 6.28 × 60 × 0.000080 large enough that there is never enough time for the capacitor to ever reach a full charge, it is possible that the capacitor Xc = 33.2 ohms reactance may offer very little or no resistance to the current. However, the smaller the capacitance, the fewer electrons are required Once the reactance has been determined, Ohm’s Law can to bring it up to a full charge and it is more likely that the then be used in the same manner as it is used in DC circuits capacitor will build up enough of an opposing charge that it to determine the current.

can present a great deal of resistance to the current if not to the point of behaving like an open circuit. In between these two Voltage Current = , or extreme conditions lies a continuum of possibilities of current Capacitive reactance opposition depending on the combination of applied frequency E I = and the selected capacitance. Current in an AC circuit can be Xc controlled by changing the circuit capacitance in a similar manner that resistance can control the current. The actual AC Find the current flow: reactance Xc, which just like resistance, is measured in ohms E I = (Ω). Capacitive reactance Xc is determined by the following: Xc Xc = I = 2πfC 33.2 Where Xc = capacitive reactance I = 3.31 amperes f = frequency in cps C = capacity in farads Capacitive Reactances in Series and in Parallel 2π = 6.28 When capacitors are connected in series, the total reactance is equal to the sum of the individual reactances. Thus, Sample Problem: A series circuit is assumed in which the impressed voltage Xct = (Xc) + (Xc) 1 2 is 110 volts at 60 cps, and the capacitance of a condenser is 80 Mf. Find the capacitive reactance and the current flow. The total reactance of capacitors connected in parallel is found in the same way total resistance is computed in a Solution: parallel circuit: To find capacitive reactance, the equation Xc = 1/(2πfC) is used. First, the capacitance, 80 Mf, is changed to farads (Xc)t = 1 1 1 by dividing 80 by 1,000,000, since 1 million microfarads is + + (Xc) (Xc) (Xc) 1 2 3 equal to 1 farad. This quotient equals 0.000080 farad. This Phase of Current and Voltage in Reactive Circuits Unlike a purely resistive circuit, the capacitive and inductive reactance has a significant effect on the phase relationship + between the applied AC voltage and the corresponding C − + C − 2 + + + + + C C C − − − 3 1 2 − − + C − 3 Figure 12-121. Simple series circuit. Figure 12-122. Simplified parallel circuit.

12-55 current in the circuit. because the magnetic lines of force between adjacent loops are in opposition with each other. The total magnetic field for In review, when current and voltage pass through zero and the two loops is shown in Figure 12-125B . As more loops reach maximum value at the same time, the current and are added close together, the strength of the magnetic field voltage are said to be in phase. [Figure 12-124A] If the current increases. Figure 12-125C illustrates the combined effects and voltage pass through zero and reach the maximum values of many loops of a coil. The result is a strong electromagnet.

at different times, the current and voltage are said to be out of phase. In a circuit containing only inductance, the current The primary aspect of the operation of a coil is its property reaches a maximum value later than the voltage, lagging the to oppose any change in current through it. This property voltage by 90°, or one-fourth cycle. [Figure 12-124B] is called inductance. When current flows through any conductor, a magnetic field starts to expand from the center In a circuit containing only capacitance, the current reaches of the wire. As the lines of magnetic force grow outward its maximum value ahead of the voltage and the current leads through the conductor, they induce an emf in the conductor the voltage by 90°, or one-fourth cycle. [Figure 12-124C] The itself. The induced voltage is always in the direction opposite amount the current lags or leads the voltage in a circuit to the direction of the current flow. The effects of this depends on the relative amounts of resistance, inductance, countering emf are to oppose the immediate establishment and capacitance in the circuit. of the maximum current. This effect is only a temporary condition. Once the current reaches a steady value in the Inductance conductor, the lines of magnetic force no longer expand and the countering emf is no longer present.

Characteristics of Inductance Michael Faraday discovered that by moving a magnet through At the starting instant, the countering emf nearly equals the a coil of wire, a voltage was induced across the coil. If a applied voltage, resulting in a small current flow. However, complete circuit was provided, then a current was also induced.

as the lines of force move outward, the number of lines The amount of induced voltage is directly proportional to cutting the conductor per second becomes progressively the rate of change of the magnetic field with respect to the smaller, resulting in a diminished counter emf. Eventually, coil. The simplest of experiments can prove that when a bar the counter emf drops to zero and the only voltage in magnet is moved through a coil of wire, a voltage is induced the circuit is the applied voltage and the current is at its and can be measured on a voltmeter. This is commonly known maximum value.

as Faraday’s Law or the Law of Electromagnetic Induction, which states that the induced emf or electromagnetic force in The RL Time Constant a closed loop of wire is proportional to the rate of change of Because the inductors basic action is to oppose a change in the magnetic flux through a coil of wire.

its current, it then follows that the current cannot change instantaneously in the inductor. A certain time is required Conversely, current flowing through a coil of wire produces for the current to make a change from one value to another.

a magnetic field. When this wire is formed into a coil, it then The rate at which the current changes is determined by a time becomes a basic inductor. The magnetic lines of force around constant represented by the Greek letter τ . The time constant each loop or turn in the coil effectively add to the lines of for the RL circuit is: force around the adjoining loops. This forms a strong magnetic L field within and around the coil. Figure 12-125A shows a coil τ = R of wire strengthening a magnetic field. The magnetic lines Where τ = seconds of force around adjacent loops are deflected into an outer L = inductance (H) path when the loops are brought close together. This happens R = resistance (Ω) In a series RL circuit, the current increases to 63 percent of its full value in 1 time constant after the circuit is closed. This buildup is similar to the buildup of voltage in a capacitor X when charging an RC circuit. Both follow an exponential AC generator th Y curve and reach 99 percent value after the 5 time constant.

[Figure 12-126] Physical Parameters Some of the physical factors that affect inductance are: Figure 12-123. Capacitor in an AC circuit.

12-56 1. The number of turns: Doubling the number of turns emf in a coil produces a field twice as strong if the same current is used. As a general rule, the inductance varies as the square of the number of turns.

2. The cross-sectional area of the coil: The inductance of a coil increases directly as the cross-sectional area 0° 180° 360° of the core increases. Doubling the radius of a coil increases the inductance by a factor of four.

3. The length of a coil: Doubling the length of a coil, while keeping the same number of turns, halves the Current and voltage in phase A value of inductance.

emf 4. The core material around which the coil is formed: Coils are wound on either magnetic or nonmagnetic materials. Some nonmagnetic materials include air, copper, plastic, and glass. Magnetic materials include nickel, iron, steel, or cobalt, which have a permeability 0° 180° 90° 360° 270° that provides a better path for the magnetic lines of Lag force and permit a stronger magnetic field.

Self-Inductance The characteristic of self-inductance was summarized by Effect of inductance B German physicist Heinrich Lenz in 1833, and gives the direction emf of the induced emf resulting from electromagnetic induction.

This is commonly known as Lenz’s Law, which states: The emf induced in an electric circuit always acts in such a direction that the current it drives around a closed circuit produces a magnetic field, which opposes the change in magnetic flux.

0° 180° 90° 360° 270° Self-inductance is the generation of a voltage in an electric Lead circuit by a changing current in the same circuit. Even a straight piece of wire has some degree of inductance because current in a conductor produces a magnetic field.

Effect of capacitance C When the current in a conductor changes direction, there is a corresponding change in the polarity of the magnetic field Figure 12-124. Phase of current and voltage.

around the conductor. Therefore, a changing current produces a changing magnetic field around the wire. To further intensify the magnetic field, the wire can be rolled into a winding them. The number of turns in the inductor winding coil, which is called an inductor. The changing magnetic field and the core material determine the capacity of the inductor.

around the inductor induces a voltage across the coil. This Cores made of dielectric material like ceramics, wood, and induced emf is called self-inductance and tends to oppose paper provide small amounts of stored energy while cores any change in current within the circuit. This property is made of ferrite substances have a much higher degree of usually called inductance and symbolized with the letter L.

stored energy. The core material is usually the most important aspect of the inductors construction. The conductors typically Types of Inductors used in the construction of an inductor offer little resistance Inductors used in radios can range from a straight wire at UHF to the flow of current. However, with the introduction of a to large chokes and transformers used for filtering the ripple core, resistance is introduced in the circuit and the current from the output of power supplies and in audio amplifiers.

now builds up in the windings until the resistance of the core Figure 12-127 shows the schematic symbols for common is overcome. This buildup is stored as magnetic energy in inductors. Values of inductors range from nano-henries to the core. Depending on the core resistance, the buildup soon tens of henries.

reaches a point of magnetic saturation, and it can be released when necessary. The most common core materials are: air, Inductors are classified by the type of core and the method of solid ferrite, powdered ferrite, steel, toroid, and ferrite toroid.

12-57 Inductors in Parallel Opposing magnetic fields When two inductors are connected in parallel, each must have the same potential difference between the terminals.

[Figure 12-129] When inductors are connected in parallel, the total inductance is less than the smallest inductance. The general equation for n number of inductors in parallel is: Current eee eee L = T A Coils with some separation 1 1 1 1 + + + . . .

L L L L Combined magnetic fields 1 2 3 N A simple example would be: L = 10 mH, L = 5 mH, L = 2 mH 1 2 3 Current eee eee L = T 1 1 1 Coils without separation B + + 10 mH 5 mH 2 mH L = T 0.8 mH L = 1.25 mH T South North Inductive Reactance Current eee Alternating current is in a constant state of change; the effects eee of the magnetic fields are a continuously inducted voltage opposition to the current in the circuit. This opposition is called inductive reactance, symbolized by X , and is L measured in ohms just as resistance is measured. Inductance Strong magnetic field in a coil C is the property of a circuit to oppose any change in current and is measured in henries. Inductive reactance is a measure of Figure 12-125. Many loops of a coil.

how much the countering emf in the circuit opposes current Units of Inductance Current The henry is the basic unit of inductance and is symbolized with the letter H. An electric circuit has an inductance of one 100% 99% 98% 90% 95% henry when current changing at the rate of one ampere per 86% 80% second induces a voltage of one volt into the circuit. In many 70% practical applications, millihenries (mH) and microhenries 60% 63% Applied 50% voltage (μH) are more common units. The typical symbol for an 40% inductor is shown in Figure 12-127 .

30% 20% 10% Inductors in Series If we connect two inductors in series, the same current flows through both inductors and, therefore, both are subject to the same rate of change of current. [Figure 12-128] When inductors are connected in series, the total inductance L , is T the sum of the individual inductors. The general equation for 1t 2t 3t 4t 5t n number of inductors in series is: Counter emf L = L + L + L + … L T 1 2 3 N Current, counter emf, and applied voltage in an inductive circuit.

Figure 12-126. Inductor curve.

12-58 variations. the individual reactances.

The inductive reactance of a component is directly The total reactance of inductors connected in parallel is found proportional to the inductance of the component and the the same way as the total resistance in a parallel circuit.

applied frequency to the circuit. By increasing either the [Figure 12-132] Thus, the total reactance of inductances inductance or applied frequency, the inductive reactance connected in parallel, as shown, is expressed as: likewise increases and presents more opposition to current (X )T = in the circuit. This relationship is given as: L 1 1 1 + + (X ) (X ) (X ) L 1 L 2 L 3 X = 2πfL L AC Circuits Where: X = inductive reactance in ohms L f = frequency in cycles per second Ohm’s Law for AC Circuits π = 3.1416 The rules and equations for DC circuits apply to AC circuits L = inductance only when the circuits contain resistance alone, as in the case of lamps and heating elements. In order to use effective values In Figure 12-130 , an AC series circuit is shown in which the of voltage and current in AC circuits, the effect of inductance inductance is 0.146 henry and the voltage is 110 volts at a and capacitance with resistance must be considered.

frequency of 60 cps. Inductive reactance is determined by the following method.

The combined effects of resistance, inductive reactance, and capacitive reactance make up the total opposition to X = 2π × f × L L current flow in an AC circuit. This total opposition is called X = 6.28 × 60 × 0.146 L impedance and is represented by the letter Z. The unit for X = 55 ohm L the measurement of impedance is the ohm.

In any circuit where there is only resistance, the expression Series AC Circuits for the relationship of voltage and current is given by Ohm’s If an AC circuit consists of resistance only, the value of the Law: I = E/R. Similarly, when there is inductance in an AC impedance is the same as the resistance, and Ohm’s Law for circuit, the relationship between voltage and current can be an AC circuit, I = E/Z, is exactly the same as for a DC circuit.

expressed as: In Figure 12-133, a series circuit containing a lamp with 11 ohms resistance connected across a source is illustrated. To Voltage E Current = or I = find how much current flows if 110 volts DC is applied and Reactance X L how much current flows if 110 volts AC are applied, the following examples are solved: Where: X = inductive reactance of the circuit in ohms E E L I = I = (where Z = R) R Z E 110 V 110 V I = I = I = X L 11 W 11 W I = I = 10 amperes DC I = 10 amperes AC I = 2 amperes When AC circuits contain resistance and either inductance or capacitance, the impedance, Z, is not the same as the In AC series circuits, inductive reactances are added like resistances in series in a DC circuit. [Figure 12-131] Thus, the total reactance in the illustrated circuit equals the sum of L L 1 2 + − Inductor Figure 12-127. Typical symbol for an inductor.

Figure 12-128. Two inductors in series.

12-59 inductance connected in series is connected to a source of 110 volts at 60 cps. The resistive element is a lamp with 6 ohms resistance, and the inductive element is a coil with an + inductance of 0.021 henry. What is the value of the impedance and the current through the lamp and the coil?

L L 2 1 − Solution: First, the inductive reactance of the coil is computed: X = 2π × f × L Figure 12-129. Two inductors in parallel. L X = 6.28 × 60 × 0.021 L X = 8 ohms inductive reactance L resistance, R. The impedance of a circuit is the circuit’s total opposition to the flow of current. In an AC circuit, Next, the total impedance is computed: this opposition consists of resistance and reactance, either 2 2 Z = R + X inductive or capacitive or elements of both. L 2 2 Z = 6 + 8 Resistance and reactance cannot be added directly, but they Z = 36 + 64 can be considered as two forces acting at right angles to Z = 100 each other. Thus, the relation between resistance, reactance, Z = 10 ohms impedance and impedance may be illustrated by a right triangle.

[Figure 12-134] Then the current flow, E Since these quantities may be related to the sides of a right I = Z triangle, the formula for finding the impedance, or total opposition to current flow in an AC circuit, can be found I = by using the law of right triangles. This theorem, called the Pythagorean theorem, applies to any right triangle. It states I = 11 amperes current that the square of the hypotenuse is equal to the sum of the squares of the other two sides. Thus, the value of any side of a right triangle can be found if the other two sides are known. If an AC circuit contains resistance and inductance, as shown in Figure 12-135 , the relation between the sides can be stated as: 2 2 2 Z = R + X 110V AC L 60 cycles The square root of both sides of the equation gives 2 2 Z = R + X L A This formula can be used to determine the impedance when Figure 12-130. AC circuit containing inductance.

the values of inductive reactance and resistance are known. It can be modified to solve for impedance in circuits containing capacitive reactance and resistance by substituting X in the C X L1 formula in place of X . In circuits containing resistance with L both inductive and capacitive reactance, the reactances can be combined, but because their effects in the circuit are exactly opposite, they are combined by subtraction: X L2 X = X − X or X = X − X (the smaller number is L C C L always subtracted from the larger) In Figure 12-135 , a series circuit consisting of resistance and Figure 12-131. Inductances in series.

12-60 R The voltage drop across the resistance (E ) is: R E = I × R R E = 11 × 6 = 66 volts 110 V The voltage drop across the inductance (EX ) is: L EX = I × X L L EX = 11 × 8 = 88 volts L Figure 12-133. Applying DC and AC to a circuit.

The sum of the two voltages is greater than the impressed voltage. This results from the fact that the two voltages are X = 13 ohms capacitive reactance out of phase and, as such, represent the maximum voltage. C To find the impedance, If the voltage in the circuit is measured by a voltmeter, it is approximately 110 volts, the impressed voltage. This can be proved by the equation: 2 2 Z = R + X C 2 2 Z = 10 + 13 2 2 E = (E ) + (EX ) R L Z = 100 + 169 2 2 E = 66 + 88 Z = 269 E = 4,356 + 7,744 Z = 16.4 ohms capacitive reactance E = 12,100 To find the current, E = 110 volts E In Figure 12-136 , a series circuit is illustrated in which a I = Z capacitor of 200 μf is connected in series with a 10 ohm lamp. What is the value of the impedance, the current flow, I = 16.4 and the voltage drop across the lamp?

I = 6.7 amperes Solution: R The voltage drop across the lamp (E ) is: First, the capacitance is changed from microfarads to farads.

Since 1 million microfarads equal 1 farad, then: R E = 6.7 × 10 R E = 67 volts 200 μf = = 0.000200 farads 1,000,000 The voltage drop across the capacitor (EX ) is C X = C 2πfC EX = I × X C C X = C EX = 6.7 × 13 6.28 × 60 × 0.000200 farads C EX = 86.1 volts C X = C 0.07536 Impedance Z X − X L C X X Reactance L2 L1 R Resistance Figure 12-134. Impedance triangle.

Figure 12-132. Inductances in parallel.

12-61 Parallel AC Circuits The methods used in solving parallel AC circuit problems are basically the same as those used for series AC circuits.

6 Ω Out of phase voltages and currents can be added by using 110V AC 0.021 henries the law of right triangles. However, in solving circuit 60 cycles problems, the currents through the branches are added since the voltage drops across the various branches are the same and are equal to the applied voltage. In Figure 12-138 , a A parallel AC circuit containing an inductance and a resistance is shown schematically. The current flowing through the Figure 12-135. A circuit containing resistance and inductance.

inductance, I , is 0.0584 ampere, and the current flowing L through the resistance is 0.11 ampere. What is the total The sum of these two voltages does not equal the applied current in the circuit?

voltage, since the current leads the voltage. To find the applied voltage, use the following formula: Solution: 2 2 I = I + I T L R 2 2 E = (E ) + (EX ) T R C 2 2 = (0.0584) + (0.11) 2 2 E = 67 + 86.1 T = 0.0155 E = 4,489 + 7,413 T = 0.1245 ampere E = 11,902 T E = 110 volts T Since inductive reactance causes voltage to lead the current, the total current, which contains a component of inductive When the circuit contains resistance, inductance, and current, lags the applied voltage. If the current and voltages capacitance, the following equation is used to find the are plotted, the angle between the two, called the phase angle, impedance: illustrates the amount the current lags the voltage.

2 2 Z = R + (X – X ) L C In Figure 12-139 , a 112-volt generator is connected to a load consisting of a 2 μf capacitance and a 10,000-ohm resistance Example: What is the impedance of a series circuit, in parallel. What is the value of the impedance and total consisting of a capacitor with a reactance of 7 ohms, an current flow?

inductor with a reactance of 10 ohms, and a resistor with a Solution: resistance of 4 ohms? [Figure 12-137] First, find the capacitive reactance of the circuit: Solution: X = C 2πfC 2 2 Z = R + (X – X ) L C 2 2 Z = 4 + (10 – 7) Changing 2 μf to farads and entering the values into the 2 2 Z = 4 + 3 formula given: Z = 25 Z = 5 ohms Assuming that the reactance of the capacitor is 10 ohms and the reactance of the inductor is 7 ohms, then X is greater C than X . Thus, L 10 Ω 2 2 Z = R + (X – X ) L C 110 V AC 2 2 200 μf Z = 4 + (7 – 10) 60 cycles 2 2 Z = 4 + (–3) Z = 16 + 9 A Z = 25 Z = 5 ohms Figure 12-136. A circuit containing resistance and capacitance.

12-62 = 2 × 3.14 × 60 × 0.000002 4 Ω 1 10,000 = or 0.00075360 7.536 110 V AC 7 Ω = 1,327 X capacitive reactance 60 cycles C To find the impedance, the impedance formula used in a series AC circuit must be modified to fit the parallel circuit: 10 Ω RX C 2 2 Z = R + X C Figure 12-137. A circuit containing resistance, inductance, and 10,000 × 1,327 capacitance.

2 2 = (10,000) + (1,327) Since these effects are the opposite of one another, they will = 0.1315 W (approximately) cancel, leaving only the ohmic value of the resistance to oppose current flow in a circuit. If the value of resistance is To find the current through the capacitance: small or consists only of the resistance in the conductors, the E value of current flow can become very high.

I = C X C In a circuit where the inductor and capacitor are in series, I = C 1,327 and the frequency is the resonant frequency, or frequency of resonance, the circuit is said to be “in resonance” and = 0.0829 ampere is referred to as a series resonant circuit. The symbol for resonant frequency is Fn.

To find the current flowing through the resistance: E If, at the frequency of resonance, the inductive reactance is I = R R equal to the capacitive reactance, then: = 10,000 X = X , or L C = 0.011 ampere 1 2πfL = 2πfC To find the total current in the circuit: Dividing both sides by 2 fL, 2 2 2 I = I + I T R C 2 2 I = I + I Fn2 = T L R (2π) 2LC = 0.0836 ampere (approximately) Extracting the square root of both sides gives: Resonance Fn = It has been shown that both inductive reactance: 2π LC (X = 2πfL) L Where Fn is the resonant frequency in cps, C is the capacitance in farads, and L is the inductance in henries.

and capacitive reactance: With this formula, the frequency at which a capacitor and inductor is resonant can be determined.

X = C 2πfC To find the inductive reactance of a circuit use: are functions of an AC frequency. Decreasing the frequency X = 2πfL L decreases the ohmic value of the inductive reactance, but a decrease in frequency increases the capacitive reactance. At The impedance formula used in a series AC circuit must be some particular frequency, known as the resonant frequency, modified to fit a parallel circuit.

the reactive effects of a capacitor and an inductor is equal.

12-63 causes the current through the capacitor to lead the voltage by 90°, the two currents are 180° out of phase. The canceling effect of such currents would mean that no current would flow from the generator and the parallel combination of the inductor and the capacitor would appear as infinite G I 5 henries I impedance. In practice, no such circuit is possible, since some L R value of resistance is always present, and the parallel circuit, 1000 Ω sometimes called a tank circuit, acts as very high impedance.

It is also called an antiresonant circuit, since its effect in a circuit is opposite to that of a series resonant circuit, in which the impedance is very low.

Figure 12-138. AC parallel circuit containing inductance and resistance.

Power in AC Circuits In a DC circuit, power is obtained by the equation, P = EI, X L (watts equal volts × amperes). Thus, if 1 ampere of current 2 2 Z = R = X L flows in a circuit at a pressure of 200 volts, the power is 200 To find the parallel networks of inductance and capacitive watts. The product of the volts and the amperes is the true reactors, use: power in the circuit.

X + X L C True Power Defined X = X + X L C True power of any AC circuit is commonly referred to as To find the parallel networks with resistance capacitive and the working power of the circuit. True power is the power inductance, use: consumed by the resistance portion of the circuit and is measured in watts. True power is symbolized by the letter P R X X L C and is indicated by any wattmeter in the circuit. True power 2 2 2 Z = X X + (RX – RX ) L C L C is calculated by the formula: Since at the resonant frequency X cancels X , the current can L C become very large, depending on the amount of resistance. In P = I × Z such cases, the voltage drop across the inductor or capacitor Apparent Power Defined is often higher than the applied voltage.

Apparent power in an AC circuit is sometimes referred to as the reactive power of a circuit. Apparent power is the power consumed by the entire circuit, including both the resistance and the reactance. Apparent power is symbolized by the letter S and is measured in volt-amps (VA). Apparent power is a product of the effective voltage multiplied by the effective current. Apparent power is calculated by the formula: G 2 μf 110V 10,000 Ω S = I × Z Only when the AC circuit is made up of pure resistance is the apparent power equal to the true power. [Figure 12-141] When there is capacitance or inductance in the circuit, the current and voltage are not exactly in phase, and the true Figure 12-139. A parallel AC circuit containing capacitance and resistance.

power is less than the apparent power. The true power is obtained by a wattmeter reading. The ratio of the true power to the apparent power is called the power factor and is usually expressed in percent. In equation form, the relationship is: In a parallel resonant circuit, the reactances are equal and equal currents flow through the coil and the capacitor. 100 × watts (True Power) Power Factor (PF) = [Figure 12-140] volts × amperes (Apparent Power) Since the inductive reactance causes the current through the Example: A 220-volt AC motor takes 50 amperes from the coil to lag the voltage by 90°, and the capacitive reactance line, but a wattmeter in the line shows that only 9,350 watts 12-64 are taken by the motor. What are the apparent power and the five times as many turns in the primary as in the secondary.

power factor? [Figure 12-144A] The step-up transformer has a 1 to 4 turns ratio. [Figure 12-144B] Solution: The ratio of the transformer input voltage to the output Apparent power = Volts × Amperes voltage is the same as the turns ratio if the transformer is Apparent power = 220 × 50 = 11,000 watts or 100 percent efficient. Thus, when 10 volts are applied to volt-amperes.

the primary of the transformer, two volts are induced in the Watts (True Power) × 100 (PF) = secondary. [Figure 12-144A] If 10 volts are applied to the VA (Apparent Power) primary of the transformer, the output voltage across the 9,350 × 100 terminals of the secondary is 40 volts. [Figure 12-144B] (PF) = 11,000 No transformer can be constructed that is 100 percent (PF) = 85, or 85% efficient, although iron core transformers can approach this Transformers figure. This is because all the magnetic lines of force set up A transformer changes electrical energy of a given voltage in the primary do not cut across the turns of the secondary into electrical energy at a different voltage level. It consists of coil. A certain amount of the magnetic flux, called leakage two coils that are not electrically connected, but are arranged flux, leaks out of the magnetic circuit. The measure of how so that the magnetic field surrounding one coil cuts through well the flux of the primary is coupled into the secondary the other coil. When an alternating voltage is applied to is called the “coefficient of coupling.” For example, if it is (across) one coil, the varying magnetic field set up around that assumed that the primary of a transformer develops 10,000 coil creates an alternating voltage in the other coil by mutual lines of force and only 9,000 cut across the secondary, the induction. A transformer can also be used with pulsating DC, coefficient of coupling would be 0.9. Stated another way, the but a pure DC voltage cannot be used, since only a varying transformer would be 90 percent efficient.

voltage creates the varying magnetic field that is the basis of the mutual induction process.

When an AC voltage is connected across the primary terminals of a transformer, an AC flows and self induces a voltage in the A transformer consists of three basic parts. [Figure 12-142] primary coil that is opposite and nearly equal to the applied These are an iron core, which provides a circuit of low voltage. The difference between these two voltages allows reluctance for magnetic lines of force; a primary winding, just enough current in the primary to magnetize its core. This which receives the electrical energy from the source of applied is called the exciting, or magnetizing, current. The magnetic voltage; and a secondary winding, which receives electrical field caused by this exciting current cuts across the secondary energy by induction from the primary coil.

coil and induces a voltage by mutual induction.

The primary and secondary of this closed core transformer If a load is connected across the secondary coil, the load current are wound on a closed core to obtain maximum inductive flowing through the secondary coil produces a magnetic field effect between the two coils.

that tends to neutralize the magnetic field produced by the primary current. This reduces the self-induced (opposition) There are two classes of transformers: voltage transformers, voltage in the primary coil and allows more primary current used for stepping up or stepping down voltages; and current transformers used in instrument circuits. In voltage transformers, the primary coils are connected in parallel across the supply voltage. [Figure 12-143A] The primary windings of current transformers are connected in series in the primary circuit. [Figure 12-143B] Of the two types, the voltage transformer is the more common.

There are many types of voltage transformers. Most of these are either step-up or step-down transformers. The factor that determines whether a transformer is a step-up or step- down type is the “turns” ratio. The turns ratio is the ratio of the number of turns in the primary winding to the number Figure 12-140. A parallel resonant circuit.

of turns in the secondary winding. For example, the turns ratio of the step-down transformer is 5 to 1, since there are 12-65 to flow. The primary current increases as the secondary load voltage to the 110–120 volt level used in homes.

current increases, and decreases as the secondary load current Figure 12-146 shows the schematic symbol for an decreases. When the secondary load is removed, the primary iron core transformer. In this case, the secondary is current is again reduced to the small exciting current sufficient made up of three separate windings. Each winding only to magnetize the iron core of the transformer.

supplies a different circuit with a specific voltage, which saves the weight, space, and expense of three If a transformer steps up the voltage, it steps down the current separate transformers. Each secondary has a midpoint by the same ratio. This should be evident if the power formula connection called a “center tap,” which provides a is considered, for the power (I × E) of the output (secondary) selection of half the voltage across the whole winding.

electrical energy is the same as the input (primary) power The leads from the various windings are color coded minus that energy loss in the transforming process. Thus, by the manufacturer. [Figure 12-146] This is a standard if 10 volts and 4 amps (40 watts of power) are used in the color code, but other codes or numbers may be used.

primary to produce a magnetic field, there is 40 watts of 2. Audio transformers resemble power transformers. They power developed in the secondary (disregarding any loss).

have only one secondary and are designed to operate If the transformer has a step-up ratio of 4 to 1, the voltage over the range of audio frequencies (20 to 20,000 cps).

across the secondary is 40 volts and the current is 1 amp. The voltage is 4 times greater and the current is one-fourth the 3. RF transformers are designed to operate in equipment primary circuit value, but the power (I × E value) is the same.

that functions in the radio range of frequencies. The symbol for the RF transformer is the same as for an RF When the turns ratio and the input voltage are known, the choke coil. It has an air core as shown in Figure 12-147 .

output voltage can be determined as follows: 4. Autotransformers are normally used in power circuits; E N however, they may be designed for other uses. Two 2 2 = E N different symbols for autotransformers used in power 1 1 or audio circuits are shown in Figure 12-148 . If Where E is the voltage of the primary, E is the output voltage used in an RF communication or navigation circuit of the secondary, and N and N are the number of turns of 1 2 [Figure 12-148B] , it is the same, except there is no the primary and secondary, respectively.

symbol for an iron core. The autotransformer uses part of a winding as a primary; and, depending on Transposing the equation to find the output voltage gives: whether it is step up or step down, it uses all or part E N of the same winding as the secondary. For example, 1 2 E = N the autotransformer shown in Figure 12-148A could use the following possible choices for primary and The most commonly used types of voltage transformers are: secondary terminals.

1. Power transformers are used to step up or step down voltages and current in many types of power supplies.

They range in size from the small power transformer [Figure 12-145] used in a radio receiver to the large transformers used to step down high power line Primary coil Apparent power volts x amperes S Reactive power P True power Iron core Watts Secondary coil Figure 12-141. Power relations in AC circuit.

Figure 12-142. An iron-core transformer.

12-66 the primary induces a current in the secondary by magnetic induction. The sides of all current transformers are marked AC power supply AC power supply To load “H1” and “H2” on the unit base. The transformers must be installed with the “H1” side toward the generator in the circuit in order to have proper polarity. The secondary of the transformer should never be left open while the system is being operated; to do so could cause dangerously high voltages and could overheat the transformer. Therefore, the transformer output connections should always be connected with a jumper when the transformer is not being used but is left in the system.

Transformer Losses Load Meter In addition to the power loss caused by imperfect coupling, A B transformers are subject to “copper” and “iron” losses. The resistance of the conductor comprising the turns of the coil causes copper loss. The iron losses are of two types: hysteresis Figure 12-143. Voltage and current transformers.

loss and eddy current loss. Hysteresis loss is the electrical energy required to magnetize the transformer core, first in Current Transformers one direction and then in the other, in step with the applied Current transformers are used in AC power supply systems alternating voltage. Eddy current loss is caused by electric to sense generator line current and to provide a current, currents (eddy currents) induced in the transformer core by proportional to the line current, for circuit protection and the varying magnetic fields. To reduce eddy current losses, control devices.

cores are made of laminations coated with an insulation, which reduces the circulation of induced currents.

The current transformer is a ring-type transformer using a current carrying power lead as a primary (either the power Power in Transformers lead or the ground lead of the AC generator). The current in Since a transformer does not add any electricity to the circuit but merely changes or transforms the electricity that already exists in the circuit from one voltage to another, the total amount of energy in a circuit must remain the same. If it were possible to construct a perfect transformer, there would be no loss of power in it; power would be transferred undiminished from one voltage to another.

10 turns 2 turns primary secondary Since power is the product of volts times amperes, an increase in voltage by the transformer must result in a decrease in current and vice versa. There cannot be more power in the secondary side of a transformer than there is in the primary.

A The product of amperes times volts remains the same.

The transmission of power over long distances is accomplished by using transformers. At the power source, the voltage is stepped up in order to reduce the line loss during transmission.

At the point of utilization, the voltage is stepped down, since 8 turns 2 turns it is not feasible to use high voltage to operate motors, lights, primary secondary or other electrical appliances.

DC Measuring Instruments Understanding the functional design and operation of electrical measuring instruments is very important, since B they are used in repairing, maintaining, and troubleshooting electrical circuits. The best and most expensive measuring instrument is of no use unless the technician knows what is Figure 12-144. A step-down and a step-up transformer.

12-67 being measured and what each reading indicates. The purpose Red of the meter is to measure quantities existing in a circuit. For Iron core Red - Yellow this reason, when a meter is connected to a circuit, it must High-voltage not change the characteristics of that circuit.

winding Red Black Meters are either self-excited or externally excited. Those that are self-excited operate from a power source within the meter.

Yellow Primary Externally-excited meters get their power source from the Yellow - Blue 5-volt winding circuit that they are connected to. The most common analog Yellow meters in use today are the voltmeter, ammeter, and ohmmeter.

Black All of which operate on the principles of electromagnetism.

Green The fundamental principle behind the operation of the meter Green - Yellow 6-volt winding is the interaction between magnetic fields created by a current Green gathered from the circuit in some manner. This interaction is Secondary windings between the magnetic fields of a permanent magnet and the coils of a rotating magnet. The greater the current through the Figure 12-146. Schematic symbol for an iron-core power coils of the rotating magnet, the stronger the magnetic field transformer.

produced. A stronger field produces greater rotation of the coil.

While some meters can be used for both DC and AC circuit measurement, only those used as DC instruments are discussed in this section. The meters used for AC, or for both AC and DC, are discussed in the study of AC theory and circuitry.

D’Arsonval Meter Movement This basic DC type of meter movement—first employed Figure 12-147. An air-core transformer.

by the French scientist, d’Arsonval, in making electrical measurement—is a current measuring device, which is Current Sensitivity and Resistance used in the ammeter, voltmeter, and ohmmeter. The pointer The current sensitivity of a meter movement is the amount of is deflected in proportion to the amount of current through current required to drive the meter movement to a full-scale the coil. Basically, both the ammeter and the voltmeter are deflection. A simple example would be a meter movement current measuring instruments, the principal difference being that has 1 mA sensitivity. What this indicates is that meter the method in which they are connected in a circuit. While an movement requires 1 mA of current to move the needle to ohmmeter is also basically a current measuring instrument, a full-scale indication. Likewise, a half-scale deflection it differs from the ammeter and voltmeter in that it provides requires only 0.5 mA of current. Additionally, what is called its own source (self-excited) of power and contains other auxiliary circuits.

Primary Secondary 1–2 used with 1–3 “ ” 1–2 2–3 “ ” 1–3 1–2 “ ” 1–3 “ ” 2–3 2–3 “ ” 1–3 “ ” 2–3 1–2 2 Input Output A B Figure 12-148. Autotransformers. Figure 12-145. Power supply transformer.

12-68 movement resistance is the actual DC resistance of the wire Electrical Damping used to construct the meter coil.

A common method of damping by electrical means is to wind the moving coil on an aluminum frame. As the coil moves In a standard d’Arsonval meter, movement may have a in the field of the permanent magnet, eddy currents are set current sensitivity of 1 mA and a resistance of 50 Ω. If the up in the aluminum frame. The magnetic field produced by meter is going to be used to measure more than 1 mA, then the eddy currents opposes the motion of the coil. The pointer additional circuitry is required to accomplish the task. This therefore swings more slowly to its proper position and comes additional circuitry is a simple shunt resistor. The purpose to rest quickly with very little oscillation.

of the shunt resistor is to bypass current that exceeds the 1 mA limitation of the meter movement. To illustrate this, Mechanical Damping assume that the 1 mA meter in question is needed to measure Air damping is a common method of damping by mechanical 10 mA. The shunt resistor used should carry 9 mA while means. As shown in Figure 12-150 , a vane is attached to the the remaining 1 mA is allowed to pass through the meter.

shaft of the moving element and enclosed in an air chamber.

[Figure 12-149] The movement of the shaft is retarded because of the resistance that the air offers to the vane. Effective damping is To determine the proper shunt resistance for this situation: achieved if the vane nearly touches the walls of the chamber.

R = Shunt resistance SH A Basic Multirange Ammeter R = Meter resistance = 50 Ω M Building upon the basic meter previously discussed is the more complex and useful multirange meter, which is more practical.

Because the shunt resistance and the 50 Ω meter resistance are The basic idea of a multirange ammeter is to make the meter in parallel, the voltage drop across both of them is the same.

usable over a wide range of voltages. In order to accomplish this, each range must utilize a different shunt resistance. The E = E SH M example given in this handbook is that of a two-range meter.

However, once the basics of a two-range multirange ammeter Using Ohm’s Law, this relationship can be rewritten as: are understood, the concepts can easily be transferred to the design of meters with many selectable ranges.

E = I × R SH SH SH E = I × R M M M Figure 12-151 shows the schematic of an ammeter with two I × R = I × R SH SH M M selectable ranges. This example builds upon the previous 10 mA range meter by adding a 100 mA range. With the Simply solve for R SH switch selected to the 10 mA range, the meter indicates 10 mA when the needle is deflected to full-scale and likewise I × R M M R = indicates 100 mA at full-scale when selected to 100 mA. The SH I SH value of the 100 mA shunt resistor is determined the same way the 10 mA shunt resistor was determined. Recall that Substituting the values the meter movement can only carry 1 mA. This means that in a 100 mA range the remaining current of 99 mA must pass ImA × 50 Ω through the shunt resistor.

R = = 5.56 Ω SH 9 mA I × R M M R = SH Damping I SH To make meter readings quickly and accurately, it is desirable that the moving pointer overshoot its proper Substituting the values: position only a small amount and come to rest after not more ImA × 50 Ω than one or two small oscillations. The term “damping” is R = = 0.51 Ω SH 99 mA applied to methods used to bring the pointer of an electrical meter to rest after it has been set in motion. Damping may be accomplished by electrical means, by mechanical means, Precautions or by a combination of both.

The precautions to observe when using an ammeter are summarized as follows: 1. Always connect ammeter in series with the element 12-69 through which the current flow is to be measured.

The Voltmeter 2. Never connect an ammeter across a source of voltage, The voltmeter uses the same type of meter movement as such as a battery or generator. Remember that the the ammeter but employs a different circuit external to the resistance of an ammeter, particularly on the higher meter movement.

ranges, is extremely low and that any voltage, even a volt or so, can cause very high current to flow through As shown before, the voltage drop across the meter coil the meter, causing damage to it.

is a function of current and the coil resistance. In another example, 50 μA × 1,000 Ω = 50 mV. In order for the meter to 3. Use a range large enough to keep the deflection less be used to measure voltages greater than 50 mV, there must than full-scale. Before measuring a current, form be added a series resistance to drop any excess voltage greater some idea of its magnitude. Then switch to a large than that which the meter movement requires for a full-scale enough scale or start with the highest range and deflection. The case of the voltmeter, this resistance is called work down until the appropriate scale is reached. The multiplier resistance and is designated as R . [ Figure 12-152] M most accurate readings are obtained at approximately The voltmeter only has one multiplier resistor for use in one half-scale deflection. Many milliammeters have been range. In this example, the full-scale reading is 1 volt. R is M ruined by attempts to measure amperes. Therefore, determined in the following way: be sure to read the lettering either on the dial or on the switch positions and choose proper scale before The meter movement drops 50 mV at a full-scale deflection of connecting the meter in the circuit.

50 μA. The multiplying resistor R must drop the remaining M 4. Observe proper polarity in connecting the meter in the voltage of 1 V − 50 mV = 950 mV. Since R is in series with M circuit. Current must flow through the coil in a definite the movement, it also carries 50 μA at full scale.

direction in order to move the indicator needle up 950 mV scale. Current reversal because of incorrect connection RM = = 19k Ω 50 μA in the circuit results in a reversed meter deflection and frequently causes bending of the meter needle. Avoid Therefore, for 1 volt full-scale deflection, the total resistance improper meter connections by observing the polarity of the voltmeter is 20k Ω. That is, the multiplier resistance markings on the meter.

and the coil resistance.

Voltmeter Sensitivity Voltmeter sensitivity is defined in terms of resistance per Meter movement volt (Ω/V). The meter used in the previous example has a sensitivity of 20k Ω and a full-scale deflection of 1 volt.

I MM Multiple Range Voltmeters The simplified voltmeter in Figure 12-152 has only one range (1 volt), which means that it can measure voltages from 0 volts to 1 volt. In order for the meter to be more useful, I SH [+] [−] additional multiplier resistors must be used. One resistor R SH must be used for each desired range.

Meter movement For a 50 μA movement, the total resistance required is 20k 1 mA Ω for each volt of full-scale reading. In other words, the sensitivity for a 50 μA movement is always 20k Ω regardless of the selected range. The full-scale meter current is 50 μA at any range selection. To find the total meter resistance, multiply the sensitivity by the full-scale voltage for that particular range.

9 mA I SH 10 mA [+] [−] For example for a 10 volt range, R = (20k Ω/V) (10V) = 200k Ω.

T R The total resistance for the 1 volt range is 20k Ω, so R for SH M a 10 V range is 200k Ω − 20k Ω = 180k Ω. [Figure 12-153] Basic ammeter Figure 12-149. Basic meter drawing.

12-70 The Ohmmeter The meter movement used for the ammeter and the voltmeter can also be used for the ohmmeter. The function of the ohmmeter is to measure resistance. A simplified one-stage ohmmeter is illustrated in Figure 12-154 , which shows that Closed air chamber the basic ohmmeter contains a battery and a variable resistor in series with the meter movement. To measure resistance, the leads of the meter are connected across an external resistance, which is to be measured. By doing this, the ohmmeter circuit Light vane swinging in chamber with small is completed. This connection allows the internal battery clearance to produce a current through the movement coil, causing a deflection of the pointer proportional to the value of the external resistance being measured.

Zero Adjustment When the ohmmeter leads are open, the meter is at a full-scale deflection, indicating an infinite (∞) resistance or an open Figure 12-150. Air damping.

circuit. [Figure 12-155] When the leads are shorted as shown in figure “zero adjust,” the pointer is at the full right-hand Voltmeter Circuit Connections position, indicating a short circuit or zero resistance. The When voltmeters are used, they are connected in parallel purpose of the variable resistor in this figure is to adjust the with a circuit. If unsure about the voltage to be measured, current so that the pointer is at exactly zero when the leads take the first reading at the high value on the meter and then are shorted. This is used to compensate for changes in the progressively move down through the range until a suitable internal battery voltage due to aging.

read is obtained. Observe that the polarity is correct before connecting the meter to the circuit or damage occurs by Ohmmeter Scale driving the movement backwards.

Figure 12-156 shows a typical analog ohmmeter scale.

Between zero and infinity (∞), the scale is marked to indicate Influence of the Voltmeter in the Circuit various resistor values. Because the values decrease from left When a voltmeter is connected across two points in a circuit, to right, this scale is often called a back-off scale.

current is shunted. If the voltmeter has low resistance, it draws off a significant amount of current. This lowers the effective In the case of the example given, assume that a certain resistance of the circuit and change the voltage readings.

ohmmeter uses a 50 μA, 1,000 Ω meter movement and has When making a voltage measurement, use a high resistance an internal 1.5 volt battery. A current of 50 μA produces a voltmeter to prevent shunting of the circuit.

full-scale deflection when the test leads are shorted. To have 50 μA, the total ohmmeter resistance is 1.5 V/50 μA = 30k Ω.

Therefore, since the coil resistance is 1k Ω, the variable zero adjustment resistor must be set to 30k Ω – 1k Ω = 29k Ω.

1mA, 50 ohm movement Now consider that a 120k Ω resistor is connected to the ohmmeter leads. Combined with the 30k Ω internal resistance, the total R is 150k Ω. The current is 1.5 V/150k Ω = 10 μA, which is 20 percent of the full-scale current and appears on the scale shown in Figure 12-156 .

Now consider further that a 120k Ω resistor is connected to the ohmmeter leads. This results in a current of 1.5 V/75k Ω = 5.56Ω 10mA 10 μA, which is 40 percent of the full-scale current and [−] marked on the scale. Additional calculations of this type [+] 5.51Ω show that the scale is nonlinear. It is more compressed toward the left side than the right side. The center scale point 100mA corresponds to the internal meter resistance of 30k Ω. The reason is as follows: Figure 12-151. Ammeter with two ranges.

12-71 move the pointer counterclockwise and coil A, clockwise. The With 30k Ω connected to the leads, the current is 1.5 V/60k Ω coils are mounted on a light, movable frame that is pivoted in = 25 μA, which is half of the full-scale current of 50 μA. jewel bearings and free to move about axis 0. [Figure 12-158] The Multirange Ohmmeter Coil A is connected in series with R3 and the unknown resistance, R , to be measured. The series combination of A practical ohmmeter has several operational ranges. These X typically are indicated by R × 1, R × 10, R × 100, R × 1k, coil A, R3, and R is connected between the + and − brushes X of the DC generator. Coil B is connected in series with R2, R × 100k and R × 1M. These range selections are interpreted in a different manner than that of an ammeter or voltmeter. and this combination is also connected across the generator.

There are no restraining springs on the movable member of The reading on the ohmmeter scale is multiplied by the factor indicated by the range setting. For example, if the pointer is the instrument portion of the megger. When the generator is not in operation, the pointer floats freely and may come to set on the scale and the range switch is set at R × 100, the actual resistance measurement is 20 × 100 or 2k Ω. rest at any position on the scale.

If the terminals are open circuited, no current flows in coil To measure small resistance values, the technician must use A, and the current in coil B alone controls the movement of the moving element. Coil B takes a position opposite a higher ohmmeter current than is needed for measuring large resistance values. Shunt resistors are needed to provide the gap in the core (since the core cannot move and coil B can), and the pointer indicates infinity on the scale. When a multiple ranges on the ohmmeter to measure a range of resistance values from the very small to very large. For each resistance is connected between the terminals, current flows in coil A, tending to move the pointer clockwise. At the same range, a different value of shunt resistance is switched in.

The shunt resistance increases for higher ohm ranges and time, coil B tends to move the pointer counterclockwise.

Therefore, the moving element, composed of both coils and is always equal to the center scale reading on any selected range. In some meters, a higher battery voltage is used for the pointer, comes to rest at a position at which the two forces are balanced. This position depends upon the value of the the highest ohm range. [Figure 12-157] external resistance, which controls the relative magnitude of Megger (Megohmmeter) current of coil A. Because changes in voltage affect both coils A and B in the same proportion, the position of the moving The megger, or megohmmeter, is a high range ohmmeter element is independent of the voltage. If the terminals are containing a hand-operated generator. It is used to measure short circuited, the pointer rests at zero because the current insulation resistance and other high-resistance values. It is in A is relatively large. The instrument is not damaged under also used for ground, continuity, and short-circuit testing of these circumstances because the current is limited by R3.

electrical power systems. The chief advantage of the megger over an ohmmeter is its capacity to measure resistance with a There are two types of hand-driven meggers: the variable high potential, or “breakdown” voltage. This type of testing type and the constant pressure type. The speed of the variable ensures that insulation or a dielectric material will not short pressure megger is dependent on how fast the hand crank or leak under potential electrical stress.

The megger consists of two primary elements, both of which 1k ohm movement are provided with individual magnetic fields from a common permanent magnet: a hand-driven DC generator, G, which R R M2 M1 0 ∞ supplies the necessary current for making the measurement; [−] and the instrument portion, which indicates the value of the 180k Ω 19k Ω resistance being measured. The instrument portion is of the opposed coil type. Coils A and B are mounted on the movable Basic voltmeter member with a fixed angular relationship to each other and 10 V 1 V are free to turn as a unit in a magnetic field. Coil B tends to 50A, 1k ohm movement R M [+] [−] [+] Figure 12-153. Two range voltmeter.

Figure 12-152. Basic voltmeter.

12-72 Meter movement Meter movement Adjuster 0 ∞ 0 ∞ Basic voltmeter + + Internal battery − − [+] [−] Test probes [+] [−] Open Meter movement Meter movement Adjuster 0 ∞ 0 ∞ Basic voltmeter + + Internal battery Internal battery − − Current [+] [−] [+] [−] Shorted External resistor Figure 12-155. Zero adjustment.

Figure 12-154. Basic ohmmeter.

40% full-scale 45k Ω is turned. The constant pressure megger uses a centrifugal 50% full-scale 30k Ω governor, or slip clutch. The governor becomes effective only 20% full-scale 120k Ω when the megger is operated at a speed above its slip speed, at which speed its voltage remains constant.

0 Ω AC Measuring Instruments ∞ A DC meter, such as an ammeter, connected in an AC circuit indicates zero, because the meter movements used in a Full-scale d’Arsonval type movement is restricted to DC. Since the field of a permanent magnet in the d’Arsonval type meter remains constant and in the same direction at all times, the moving coil Simplified Ohmmeter Scale follows the polarity of the current. The coil attempts to move in one direction during half of the AC cycle and in the reverse Figure 12-156. Ohm scale.

direction during the other half when the current reverses.

The current reverses direction too rapidly for the coil to follow, causing the coil to assume an average position. Since 12-73 the current is equal and opposite during each half of the AC Meter movement cycle, the DC meter indicates zero, which is the average value.

Adjuster Thus, a meter with a permanent magnet cannot be used to 0 ∞ measure alternating voltage and current. For AC measurements of current and voltage, additional circuitry is required. The additional circuitry has a rectifier, which converts AC to DC.

There are two basic types of rectifiers: the half-wave rectifier and the full-wave rectifier. [Figure 12-159] R x 1 R x 10 Figure 12-159 also shows a simplified block diagram of an Range switch R x 100 AC meter. In this depiction, the full-wave rectifier precedes R x 1k the meter movement. The movement responds to the average R x 10k value of the pulsating DC. The scale can then be calibrated + to show anything the designer wants. In most cases, it is the root mean square (RMS) value or peak value.

Electrodynamometer Meter Movement The electrodynamometer can be used to measure alternating or − direct voltage and current. It operates on the same principles as the permanent magnet moving coil meter, except that the [+] [−] permanent magnet is replaced by an air core electromagnet.

The field of the electrodynamometer is developed by the same Figure 12-157. Multirange ohmmeter.

current that flows through the moving coil. [Figure 12-160] B e c a u s e t h i s m o v e m e n t c o n t a i n s n o i r o n , t h e When no current flows through the coil, the movable vane electrodynamometer can be used as a movement for both AC is positioned so that it is opposite the larger portion of the and DC instruments. AC can be measured by connecting the tapered fixed vane, and the scale reading is zero. The amount stationary and moving coils in series. Whenever the current of magnetization of the vanes depends on the strength of in the moving coil reverses, the magnetic field produced the field, which, in turn, depends on the amount of current by the stationary coil reverses. Regardless of the direction flowing through the coil.

of the current, the needle moves in a clockwise direction.

However, for either voltmeter or ammeter applications, The force of repulsion is greater opposite the larger end of the electrodynamometer is too expensive to economically the fixed vane than it is nearer the smaller end. Therefore, compete with the d’Arsonval-type movement.

the movable vane moves toward the smaller end through an angle that is proportional to the magnitude of the coil current.

Moving Iron Vane Meter The movement ceases when the force of repulsion is balanced The moving iron vane meter is another basic type of meter.

by the restraining force of the spring.

It can be used to measure either AC or DC. Unlike the d’Arsonval meter, which employs permanent magnets, it Because the repulsion is always in the same direction (toward depends on induced magnetism for its operation. It utilizes the the smaller end of the fixed vane), regardless of the direction principle of repulsion between two concentric iron vanes, one of current flow through the coil, the moving iron vane fixed and one movable, placed inside a solenoid. A pointer is instrument operates on either DC or AC circuits.

attached to the movable vane. [Figure 12-161] Mechanical damping in this type of instrument can be obtained When current flows through the coil, the two iron vanes by the use of an aluminum vane attached to the shaft so that, become magnetized with North poles at their upper ends and as the shaft moves, the vane moves in a restricted air space.

South poles at their lower ends for one direction of current through the coil. Because like poles repel, the unbalanced When the moving iron vane meter is used as an ammeter, the component of force, tangent to the movable element, causes coil is wound with relatively few turns of large wire in order it to turn against the force exerted by the springs.

to carry the rated current. When the moving iron vane meter is used as a voltmeter, the solenoid is wound with many turns of The movable vane is rectangular in shape and the fixed small wire. Portable voltmeters are made with self-contained vane is tapered. This design permits the use of a relatively series resistance for ranges up to 750 volts. Higher ranges are uniform scale.

obtained by the use of additional external multipliers.

12-74 obliquely to the shaft, and located inside the coil, are two soft iron vanes. When no current flows through the coil, a R2 M control spring holds the pointer at zero, and the iron vanes Inf. B lie in planes parallel to the plane of the coil. When current A + C R Hand X flows through the coil, the vanes tend to line up with magnetic Axis O R3 G generator lines passing through the center of the coil at right angles to − the plane of the coil. Thus, the vanes rotate against the spring Ohmmeter M action to move the pointer over the scale.

The iron vanes tend to line up with the magnetic lines regardless of the direction of current flow through the coil.

Figure 12-158. Simplified megger circuit.

Therefore, the inclined coil, iron vane meter can be used to measure either AC or DC. The aluminum disk and the drag magnets provide electromagnetic damping.

The moving iron vane instrument may be used to measure DC but has an error due to residual magnetism in the vanes.

Like the moving iron vane meter, the inclined coil type requires Reversing the meter connections and averaging the readings a relatively large amount of current for full-scale deflection and may minimize the error. When used on AC circuits, the is seldom used in high-resistance low-power circuits.

instrument has an accuracy of 0.5 percent. Because of its simplicity, relatively low cost, and the fact that no current is As in the moving iron vane instruments, the inclined coil conducted to the moving element, this type of movement is instrument is wound with few turns of relatively large wire used extensively to measure current and voltage in AC power when used as an ammeter and with many turns of small wire circuits. However, because the reluctance of the magnetic when used as a voltmeter.

circuit is high, the moving iron vane meter requires much more power to produce full-scale deflection than is required Varmeters by a d’Arsonval meter of the same range. Therefore, the Multiplying the volts by the amperes in an AC circuit gives moving iron vane meter is seldom used in high-resistance the apparent power: the combination of the true power (which low-power circuits.

does the work) and the reactive power (which does no work and is returned to the line). Reactive power is measured in Inclined Coil Iron Vane Meter units of vars (volt-amperes reactive) or kilovars (kilovolt- The principle of the moving iron vane mechanism is applied amperes reactive (kVAR). When properly connected, to the inclined coil type of meter, which can be used to wattmeters measure the reactive power. As such, they are measure both AC and DC. The inclined coil, iron vane called varmeters. [Figure 12-162] meter has a coil mounted at an angle to the shaft. Attached 0 0 Half-wave rectifier AC In Pulsing DC AC converted to pulsing DC on every positive half-cycle Full-wave rectifier AC In Pulsing DC 0 AC converted to pulsing DC on both positive and negative half-cycle Simple AC voltmeter AC In 0 Full-wave rectifier Figure 12-159. Simplified block diagram of AC meter.

12-75 almost the same (if the scale is properly calibrated) as if the Wattmeter voltage applied across the load and the current through the Electric power is measured by means of a wattmeter. Because load were multiplied together.

electric power is the product of current and voltage, a wattmeter must have two elements, one for current and the If the current in the line is reversed, the direction of current in both coils and the potential coil is reversed, the net result is other for voltage. For this reason, wattmeters are usually of the electrodynamometer type. [Figure 12-163] that the pointer continues to read up scale. Therefore, this type of wattmeter can be used to measure either AC or DC power.

The movable coil with a series resistance forms the voltage Frequency Measurement/ Oscilloscope element, and the stationary coils constitute the current element. The strength of the field around the potential coil The oscilloscope is by far one of the more useful electronic depends on the amount of current that flows through it. The measurements available. The viewing capabilities of the current, in turn, depends on the load voltage applied across oscilloscope make it possible to see and quantify various the coil and the high resistance in series with it. The strength waveform characteristics, such as phase relationships, of the field around the current coils depends on the amount of amplitudes, and durations. While oscilloscopes come in current flowing through the load. Thus, the meter deflection is a variety of configurations and presentations, the basic proportional to the product of the voltage across the potential operation is typically the same. Most oscilloscopes in general coil and the current through the current coils. The effect is bench or shop applications use a cathode-ray tube (CRT), which is the device or screen that displays the waveforms.

The CRT is a vacuum instrument that contains an electron gun, which emits a very narrow and focused beam of electrons. A phosphorescent coat applied to the back of the screen forms the screen. The beam is electronically aimed and accelerated so that the electron beam strikes the screen. When the electron beam strikes the screen, light is emitted at the point of impact.

Fixed coils Figure 12-164 shows the basic components of the CRT with a block diagram. The heated cathode emits electrons.

The magnitude of voltage on the control grid determines the actual flow of electrons and thus controls the intensity of the electron beam. The acceleration anodes increase the C A speed of the electrons, and the focusing anode narrows the beam down to a fine point. The surface of the screen is also an anode and assists in the acceleration of the electron beam.

B Pointer Movable coils Control spring Cylindrical coil A B C Shunt Moving iron segment Stationary iron segment Figure 12-160. Simplified diagram of an electrodynamometer movement.

Figure 12-161. Moving iron vane meter.

12-76 on the peak value of the voltage.

Varmeter While the beam is being swept from the left to the right by Load Current Voltage the horizontal plates, the sine wave voltage is being applied M coil coil Reactor to the vertical plates, causing the form of the input signal to be traced out on the screen.

Control Features on an Oscilloscope Figure 12-162. A varmeter connected in an AC circuit.

While there are many different styles of oscilloscopes, which range from the simple to the complex, they all have some controls in common. Apart from the screen and the ON/OFF The purpose of the vertical and horizontal deflection plates switch, some of these controls are listed as follows: is to bend the electron beam and position it to a specific • Horizontal Position—allows for the adjustment of the point of the screen. [Figure 12-165] By providing a neutral neutral horizontal position of the beam. Use this control or zero voltage to a deflection plate, the electron beam is to reposition the waveform display in order to have a unaffected. By applying a negative voltage to a plate, the better view of the wave or to take measurements.

electron beam is repelled and driven away from the plate.

• Vertical Position—moves the traced image up or down Finally, by applying a positive voltage, the electron beam is allowing better observations and measurements.

drawing to the plate. Figure 12-165 provides a few possible plate voltage combinations and the resultant beam position.

• Focus—controls the electron beam as it is aimed and converges on the screen. When the beam is in sharp Horizontal Deflection focus, it is narrowed down to a very fine point and To get a visual representation of the input signal, an internally does not have a fuzzy appearance.

generated saw-tooth voltage is generated and then applied • Intensity—essentially the brightness of the trace.

to the horizontal deflection plates. Figure 12-166 illustrates Controlling the flow of electrons onto the screen varies that the saw-tooth is a pattern of voltage applied, which the intensity. Do not keep the intensity too high for begins at a negative voltage and increases at a constant rate extended testing or when the beam is motionless and to a positive voltage. This applied varying voltage draws or forms a dot on the screen. This can damage the screen.

traces the electron beam from the far left of the screen to the • Seconds/Division—a time-based control that sets the far right side of the screen. The resulting display is a straight horizontal sweep rate. Basically, the switch is used line, if the sweep rate is fast enough. This saw-tooth applied to select the time interval that each division on the voltage is a repetitive signal so that the beam is repeatedly horizontal scale represents. These divisions can be swept across the tube. The rate at which the saw-tooth voltage seconds, milliseconds, or even microseconds. A simple goes from negative to positive is determined by the frequency.

example would be if the technician had the seconds/ This rate then establishes the sweep rate of the beam. When division control set to 10 μS. If this technician is the saw-tooth reaches the end of its sweep from left to right, viewing a waveform that has a period of 4 divisions the beam then rapidly returns to the left side and is ready to on the screen, then the period would be 40 μS. The make another sweep. During this time, the electron beam is frequency of this waveform can then be determined stopped or blanked out and does not produce any kind of a by taking the inverse of the period. In this case, ⁄ 40 μS trace. This period of time is called flyback.

equals a frequency of 25 kHz.

Vertical Deflection • Volts/Division—used to select the voltage interval If this same signal were applied to the vertical plates, it would that each division on the vertical scale represents.

also produce a vertical line by causing the beam to trace from For example, suppose each vertical division was set the down position to the up position.

to equal 10 mV. If a waveform was measured and had a peak value of 4 divisions, then the peak value Tracing a Sine Wave in voltage would be 40 mV.

Reproducing the sine wave on the oscilloscope combines • Trigger—The trigger control provides synchronization both the vertical and horizontal deflection patterns.

between the saw-tooth horizontal sweep and the applied [Figure 12-167] If the sine wave voltage signal is applied signal on the vertical plates. The benefit is that the across the vertical deflection plates, the result will be the waveform on the screen appears to be stationary and vertical beam oscillation up and down on the screen. The fixed and not drifting across the screen. A triggering amount that the beam moves above the centerline depends circuit is used to initiate the start of a sweep rather than 12-77 type equipment but are mobile and great tools for trouble shooting. [Figure 12-169] Digital Multimeter Traditionally, the meters that technicians have used have been the analog voltmeter, ammeter, and the ohmmeter. These have usually been combined into the same instrument and called a multimeter or a VOM (volt-ohm-milliammeter). This Potential approach has been both convenient and economical. Digital coil multimeters (DMM) and digital voltmeters (DVM) are more common due to their ease of use. These meters are easier to read and provide greater accuracy when compared to the older analog units with needle movement. The multimeter’s M single-coil movement requires a number of scales, which are not always easy to read accurately. In addition, the loading characteristics due to the internal resistance sometimes R Current coil Load affect the circuit and the measurements. Not only does the DVM offer greater accuracy and less ambiguity, but also higher input resistance, which has less of a loading effect and influence on a circuit.

Figure 12-163. Simplified electrodynamometer wattmeter circuit.

Basic Circuit Analysis & Troubleshooting the fixed saw-tooth sweep rate. In a typical oscilloscope, Troubleshooting is the systematic process of recognizing this triggering signal comes from the input signal the symptoms of a problem, identifying the possible cause, itself at a selected point during the signal’s cycle. The and locating the failed component or conductor in the horizontal signal goes through one sweep, retraces back circuit. To be proficient at troubleshooting, the technician to the left side and waits there until it is triggered again must understand how the circuit operates and know how to by the input signal to start another sweep.

properly use the test equipment. There are many ways in which a system can fail and to cover all of the possibilities is Flat Panel Color Displays for Oscilloscopes beyond the scope of this handbook. However, there are some While the standard CRT design of oscilloscope is still in basic concepts that enable the technician to handle many of service, the technology of display and control has evolved the common faults encountered in the aircraft.

into use of the flat panel monitors. Furthermore, the newer oscilloscopes can even be integrated with the common Before starting a discussion on basic circuits and personal computer (PC). [Figure 12-168] Some of the features troubleshooting, the following definitions are given.

of this technology include easy data capture, data transfer, • Short circuit—an unintentional low resistance path documentation, and data analysis. Hand-held oscilloscopes are between two components in a circuit or between a now available that can perform the functions of larger bench Electron gun Control grid Vertical deflection plates (V) CRT Mating Screen e e e e e e e e e e e e e e e e e e e e base connector Anode Cathode (K) & heater Accelerating anode (A3) Horizontal deflection plates (H) Preaccelerating anode (A1) Focus anode (A2) Figure 12-164. Basic components of the CRT with a block diagram.

12-78 Vertical Electrons repelled down Electrons repelled to left deflection plates (v) (−) volts (0) volts (0) volts (−) volts Horizontal deflection plates (h) Screen Beam on center Electrons attracted up Electrons attracted to right (0) volts (+) volts (0) volts (0) volts (0) volts (+) volts Figure 12-165. Possible plate voltage combinations and the resultant beam position.

component/conductor and ground. It usually creates high current flow, which burns out or causes damage to the circuit conductor or components.

• Open circuit—a circuit that is not a complete or Vertical The horizontal deflection plates (V) continuous path. An open circuit represents an beam position (0) volts will depend on infinitely large resistance. Switches are common the applied devices used to open and close a circuit. Sometimes saw-tooth voltage a circuit opens due to a component failure, such as a light bulb or a burned out resistor.

• Continuity—the state of being continuous, Horizontal deflection uninterrupted or connected together; the opposite of plates (H) a circuit that is not broken or does not have an open.

• Discontinuity—the opposite of continuity, indicating that a circuit is broken or not continuous.

Voltage Measurement Voltage is measured across a component with a voltmeter or the voltmeter position on a multimeter. Usually, there is a DC and an AC selection on the meter. Before the meter is used for measurements, make sure that the meter is selected for (+) volts the correct type of voltage. When placing the probes across a Applied (0) volts component to take a measurement, take care to ensure that the polarity is correct. [Figure 12-170] Standard practice is for the red meter lead to be installed in the positive (+) jack and (−) volts Voltage starts at a maximum negative value and increases to a the black meter lead to be installed in the negative meter jack maximum positive value, tracing (−). Then when placing the probes across or in parallel with the beam from the left to the right a component to measure the voltage, the leads should match the polarity of the component. The red lead is on the positive Figure 12-166. Saw-tooth applied voltage.

12-79 (+) volts Applied (0) volts Vertical deflection plates (v) (0) volts Input signal (–) volts Horizontal deflection plates (h) (+) volts Applied (0) volts (−) volts Figure 12-167. Sine wave voltage signal.

side of the component and the black is on the negative side, (−). The positive side of the meter is connected towards the which prevents damage to the meter or incorrect readings. positive voltage source. Ideally, the meter should not alter the current and influence the circuit and the measurements.

All meters have some resistance and will shunt some of the However, the meter does have some effect because of its current. This has the effect of changing the characteristic of internal resistance that is connected with the rest of the circuit the circuit because of this change in current. This is typically in series. The resistance is rather small and for most practical more of a concern with older analog type meters. If there purposes, this can be neglected.

are any questions about the magnitude of the voltage across Checking Resistance in a Circuit a component, then the meter should be set to measure on the highest voltage range. This prevents the meter from The ohmmeter is used to measure the resistance. In its more “pegging” and possible damage. The range should then be basic form, the ohmmeter consists of a variable resistor in selected to low values until the measured voltage is read at series with a meter movement and a voltage source. The the mid-scale deflection. Readings taken at mid-scale are meter must first be adjusted before use.

the most accurate.

Refer to Figure 12-171 for meter configurations during Current Measurement adjustments. When the meter leads are not connected (open), Current is measured with the ammeter connected in the the needle points to the full left-hand position, indicating current path by opening or breaking the circuit and inserting infinite resistance or and open circuit. With the lead placed the meter in series. [Figure 12-170] Standard practice is for together, the circuit is shorted as shown with the meter the red meter lead to be installed in the positive (+) jack and needle to the full right-hand position. When a connection the black meter lead to be installed in the negative meter jack is made, the internal battery is allowed to produce a current through the movement coil, causing a deflection of the 12-80 needle in proportion to the value of the external resistance.

In this case, the resistance is zero because the leads are shorted.

The purpose of the variable resistor in the meter is to adjust the current so that the pointer reads exactly zero when the leads are shorted. This is needed because as the battery continues to be used, the voltage changes, thus requiring an adjustment. The meter should be “zeroed” before each use.

To check the value of a resistor, the resistor must be Figure 12-168. Oscilloscope with flat panel display.

disconnected from the circuit. This prevents any possible damage to the ohmmeter, and it prevents the possibility of any inaccurate readings due to the circuit being in parallel with the resistor in question. [Figure 12-172] Continuity Checks In many cases, the ohmmeter is not used for measuring the resistance of a component but to simply check the integrity of a connection from one portion of a circuit to another. If there is a good connection, then the ohmmeter reads a near zero resistance or a short. If the circuit is open or has a very poor connection at some point like an over-crimped pin in a connector, then the ohmmeter reads infinity or some very high resistance. Keep in mind that while any measurement is being taken, contact with the circuit or probes should be avoided. Contact can introduce another parallel path and provide misleading indications.

Capacitance Measurement Figure 12-173 illustrates a basic test of a capacitor with an ohmmeter. There are usually two common modes of failure for a capacitor. One is a complete failure characterized by short circuit through the capacitor due to the dielectric breaking down or an open circuit. The more insidious failure occurs due to degradation, which is a gradual deterioration of the capacitor’s characteristics.

Figure 12-169. Handheld oscilloscope.

If a problem is suspected, remove the capacitor from the circuit and check with an ohmmeter. The first step is to short the two Inductance Measurement leads of the capacitor to ensure that it is entirely discharged.

The common mode of failure in an inductor is an open. To Next, connect the two leads as shown in Figure 12-173 across check the integrity of an inductor, it must be removed from the capacitor and observe the needle movement. At first, the the circuit and tested as an isolated component just like the needle should indicate a short circuit. Then as the capacitor capacitor. If there is an open in the inductor, a simple check begins to charge, the needle should move to the left or infinity with an ohmmeter shows it as an open circuit with infinite and eventually indicate an open circuit. The capacitor takes resistance. If in fact the inductor is in good condition, then its charge from the internal battery of the ohmmeter. The the ohmmeter indicates the resistance of the coil.

greater the capacitance, the longer it takes to charge. If the capacitor is shorted, then the needle remains at a very low or On occasions, the inductor fails due to overheating. When shorted resistance. If there is some internal deterioration of the the inductor is overheated, it is possible for the insulation dielectric, then the needle never reaches a high resistance but covering the wire in the coil to melt, causing a short. The some intermediate value, indicating a current.

effects of a shorted coil are that of reducing the number of turns. At this point, further testing of the inductor must be 12-81 done with test equipment not covered in this handbook. Tracing Opens with the Voltmeter A general procedure to follow in this case is to measure the Troubleshooting Open Faults in a Series Circuit voltage drop across each component in the circuit, keeping One of the most common modes of failure is the “open” in mind the following points. If there is an open in a series circuit. A component, such as a resistor, can overheat due circuit, then the voltage drops on sides of the component.

to the power rating being exceeded. Other more frustrating In this case, the total voltage must appear across the open problems can happen when a “cold” solder joint cracks resistor as per Kirchhoff’s Voltage Law.

leaving a wire disconnected from a relay or connector.

This type of damage can occur during routine maintenance If a voltmeter is connected across the lamp, as shown in after a technician has accessed an area for inspections.

Figure 12-175 , the voltmeter reads zero. Since no current can In many cases, there is no visual indication that a failure flow in the circuit because of the open resistor, there is no has occurred, and the soon-to-be-frustrated technician is voltage drop across the lamp indicating that the lamp is good.

unaware that there is a problem until power is reapplied to the aircraft in the final days leading up to aircraft delivery Next, the voltmeter is connected across the open resistor, as and scheduled operations.

shown in Figure 12-176 . The voltmeter has closed the circuit by shunting (paralleling) the burned out resistor, allowing The first example is a simplified diagram shown in current to flow. Current flows from the negative terminal of Figures 12-174 through 12-176 . The circuit depicted in the battery, through the switch, through the voltmeter and the Figure 12-174 is designed to cause current to flow through a lamp, back to the positive terminal of the battery. However, lamp, but because of the open resistor, the lamp will not light.

the resistance of the voltmeter is so high that only a very To locate this open, a voltmeter or an ohmmeter should be used.

small current flows in the circuit. The current is too small to light the lamp, but the voltmeter reads the battery voltage.

Tracing Opens with the Ohmmeter A simplified circuit, as shown in Figures 12-177 and 12-178, illustrates how to locate an open in a series circuit using the A V Ω ohmmeter. A general rule to keep in mind when troubleshooting with an ohmmeter is: when an ohmmeter is properly connected Ammeter symbol Voltmeter symbol Ohmmeter symbol across a circuit component and a resistance reading is obtained, the component has continuity and is not open.

Meter symbols When an ohmmeter is used, the circuit component to be tested + − A must be isolated and the power source removed from the circuit. In this case, these requirements can be met by opening the circuit switch as shown in Figure 12-177 . The ohmmeter Open the circuit + and insert ammeter in is zeroed and across all good components is zero. The voltage R series with the load 3k Ω drop across the open component equals the total voltage across − the series combination. This condition happens because the open component prevents current to pass through the series circuit. With there being no current, there can be no voltage drop across any of the good components. Because the current is + + Voltage is measured R zero, it can be determined by Ohm’s Law that E = IR = 0 volts V across a component 3k Ω − − across a component. The voltage is the same on both places across (in parallel with) the lamp. In this testing configuration, some value of resistance is read indicating that the lamp is in good condition and is not the source of the open in the circuit.

+ + Resistance is R 1 Now the technician should move to the resistor and place Ω measured across a 3k Ω − − component the ohmmeter probe across it as shown in Figure 12-178 .

When the ohmmeter is connected across the open resistor, it indicates infinite resistance, or a discontinuity. Thus, the Simplified use of meters circuit open has now been located.

Figure 12-170. Current, voltage, and resistance measurement.

12-82 Simplified ohmmeter Simplified ohmmeter 0 ∞ 0 ∞ + + − − Black lead Red lead Black lead Red lead R Open circuit Isolate from circuit connect across resistor Simplified ohmmeter + 0 ∞ R − R + − Figure 12-172. Meter adjustment.

Black lead Red lead shorts that are not immediately seen but “latent” and do not show symptoms until the aircraft is in service. Another point to keep in mind is when closing panels. Wires can become pinched between the panel and the airframe causing either a short or a latent, intermittent short. The simplified circuit, shown in Figures 12-179 through 12-182 is used to illustrate troubleshooting a short in a series circuit.

Shorted circuit In Figure 12-179 , a circuit is designed to light a lamp. A resistor is connected in the circuit to limit current flow. If the Figure 12-171. Meter configurations during adjustments.

resistor is shorted, as shown in the illustration, the current flow increases and the lamp becomes brighter. If the applied Troubleshooting Shorting Faults in a Series Circuit voltage were high enough, the lamp would burn out, but in An open fault can cause a component or system not to this case the fuse would protect the lamp by opening first.

work, which can be critical and hazardous. A shorting Usually a short circuit produces an open circuit by either fault can potentially be more of a severe nature than the blowing (opening) the fuse or burning out a circuit open type of fault. A short circuit, or “short,” causes the component. But in some circuits, there may be additional opposite effect. A short across a series circuit produces a resistors which do not allow one shorted resistor to increase greater than normal current flow. Faults of this type can the current flow enough to blow the fuse or burn out a develop slowly when a wire bundle is not properly secured component. [Figure 12-180] Thus, with one resistor shorted and is allowed to chafe against the airframe structure or out, the circuit still functions since the power dissipated by other systems, such as hydraulic lines. Shorts can also the other resistors does not exceed the rating of the fuse.

occur due to a careless technician using incorrect hardware when installing an interior. If screws that are too long are Tracing Shorts with the Ohmmeter used to install trim, it is possible to penetrate a wire bundle The shorted resistor can be located with an ohmmeter.

immediately causing numerous shorts. Worse yet, are the [Figure 12-181] First the switch is opened to isolate the 12-83 Troubleshooting Open Faults in a Parallel Circuit Simplified ohmmeter The procedures used in troubleshooting a parallel circuit are sometimes different from those used in a series circuit. Unlike a 0 ∞ series circuit, a parallel circuit has more than one path in which Needle moves current flows. A voltmeter cannot be used, since, when it is placed full-scale (short) + across an open resistor, it reads the voltage drop in a parallel branch. But an ammeter or the modified use of an ohmmeter − can be employed to detect an open branch in a parallel circuit.

Black lead Red lead If the open resistor shown in Figure 12-183 was not visually apparent, the circuit might appear to be functioning properly, because current would continue to flow in the other two branches of the circuit. To determine that the circuit is not operating properly, a determination must be made as to how the circuit should behave when working properly. First, the total Conventional current resistance, total current, and the branch currents of the circuit should be calculated as if there were no open in the circuit.

Initial charging of capacitor behaves like a shorted circuit. In this case, the total resistance can be simply determined by: Simplified ohmmeter R R = T N 0 ∞ Where R is the total circuit resistance T N is the number of resistors Needle moves full-scale (open) + R is the resistor value − Black lead Red lead Break Full charge no current + − Once charged, the capacitor behaves like an open circuit.

Figure 12-174. An open circuit.

Figure 12-173. Basic test of a capacitor with an ohmmeter.

circuit components. In Figure 12-181 , this circuit is shown with an ohmmeter connected across each of the resistors.

Only the ohmmeter connected across the shorted resistor shows a zero reading, indicating that this resistor is shorted.

Break Tracing Shorts with the Voltmeter To locate the shorted resistor while the circuit is functioning, a voltmeter can be used. Figure 12-182 illustrates that when a voltmeter is connected across any of the resistors that are not shorted, a portion of the applied voltage is indicated on V the voltmeter scale. When it is connected across the shorted resistor, the voltmeter reads zero.

Figure 12-175. Voltmeter across a lamp in an open circuit.

12-84 Break Break V Ω Figure 12-176. Voltmeter across a resistor in an open circuit.

Figure 12-178. Using an ohmmeter to locate an open in a circuit component.

30 Ω R = = 10 Ω T The total current of the circuit can now be determined initial calculation of total current being 3 amperes.

by using Ohm’s Law: Tracing an Open with an Ammeter E If the technician now places an ammeter in the circuit, the S I = T R total current would be indicated as 2 amperes as shown in T Where I is the total current T Figure 12-183 instead of the calculated 3 amperes. Since 1 E is the source voltage across the ampere of current should be flowing through each branch, S parallel branch it is obvious that one branch is open. If the ammeter is then R is the total resistance of the connected into the branches, one after another, the open T parallel branch branch is eventually located by a zero ammeter reading.

30 v I = = 3 amperes (total current) T 10 Ω Tracing an Open with an Ohmmeter A modified use of the ohmmeter can also locate this type Each branch current should be determined in a similar of open. If the ohmmeter is connected across the open manner. For the first branch, the current is: resistor, as shown in Figure 12-184 , an erroneous reading E of continuity would be obtained. Even though the circuit S I = R 1 switch is open, the open resistor is still in parallel with R Where I is the current in the first branch 1 and R , and the ohmmeter would indicate the open resistor E is the source voltage across the S had a resistance of 15 ohms, the equivalent resistance of parallel branch the parallel combination of R and R .

1 2 R is the resistance of the first branch Therefore, it is necessary to open the circuit as shown in 30 v I = = 1 ampere 30 Ω Figure 12-185 in order to check the resistance of R . In this Because the other two branches are of the same resistive way, the resistor is not shunted (paralleled) by R and R . The 1 2 value, then the current in each of those branches is 1 ampere reading on the ohmmeter now indicates infinite resistance, also. Adding up the amperes in each branch confirms the which means the open component has been isolated.

Troubleshooting Shorting Faults in Parallel Circuits As in a series circuit, a short in a parallel circuit usually causes an open circuit by blowing the fuse. But, unlike a series circuit, one shorted component in a parallel circuit Break stops current flow by causing the fuse to open. Refer to the circuit in Figure 12-186 . If resistor R is shorted, a path of almost zero resistance is offered the current, and all the circuit current flows through the branch containing the shorted resistor. Since this is practically the same as connecting a wire between the terminals of the battery, the current rises to Ω an excessive value, and the fuse opens. Since the fuse opens almost as soon as a resistor shorts out, there is no time to Figure 12-177. Using an ohmmeter to check a circuit component.

12-85 perform a current or voltage check. Thus, troubleshooting Some voltage a parallel DC circuit for a shorted component should be V accomplished with an ohmmeter. But, as in the case of checking for an open resistor in a parallel circuit, a shorted resistor can be detected with an ohmmeter only if one end of the shorted resistor is disconnected and isolated from the Zero rest of the circuit.

voltage Short V Troubleshooting Shorting Faults in Series-Parallel Circuits Logic in Tracing an Open Troubleshooting a series-parallel resistive circuit involves Figure 12-182. Voltmeter connected across resistors.

locating malfunctions similar to those found in a series or a parallel circuit. Figures 12-187 through 12-189 illustrate three points of failure in a series-parallel circuit and their generalized effects.

1. In the circuit shown in Figure 12-187 , an open has occurred in the series portion of the circuit. When the open occurs anywhere in the series portion of a series-parallel circuit, current flow in the entire circuit Figure 12-179. A shorted resistor.

stops. In this case, the circuit does not function, and the lamp, L , is not lit.

2. If the open occurs in the parallel portion of a series- parallel circuit, as shown in Figure 12-188 , part of the circuit continues to function. In this case, the lamp continues to burn, but its brightness diminishes, since the total resistance of the circuit has increased and the total current has decreased.

3. If the open occurs in the branch containing the lamp, as shown in Figure 12-189 , the circuit continues to function with increased resistance and decreased current, but the lamp does not light.

Figure 12-180. A short that does not open the circuit.

Tracing Opens with the Voltmeter 40 Ω Ω To explain how the voltmeter and ohmmeter can be used to troubleshoot series-parallel circuits, the circuit shown in Figure 12-190 has been labeled at various points. A point- R to-point description is listed below with expected results: 100 V 0 Ω 1. By connecting a voltmeter between points A and D, the battery and switch can be checked for opens.

Ω R 2. By connecting the voltmeter between points A and B, the voltage drop across R can be checked. This R R voltage drop is a portion of the applied voltage.

3 4 3. If R is open, the reading between B and D is zero.

Ω Ω 4. By connecting a voltmeter between A and E, the 50 Ω 10 Ω continuity of the conductor between the positive terminal of the battery and point E, as well as the fuse, Figure 12-181. Using an ohmmeter to locate a shorted resistor.

12-86 electrolyte is sulfuric acid (battery acid), the positive electrode is lead peroxide, and the negative electrode is lead. A typical lead-acid battery consists of six lead-acid cells in a case. Each cell produces 2 volts, so the whole Break battery produces a total of 12 volts.

R R R 1 2 3 30 V Other commonly used secondary cell chemistry types are 30 Ω 30 Ω 30 Ω nickel-cadmium (Ni-Cad), nickel-metal hydride (NiMH), lithium-ion (Li-ion), and Lithium-ion polymer (Li-ion polymer).

2a Lead-acid batteries used in aircraft are similar to automobile A batteries. The lead acid battery is made up of a series of identical cells each containing sets of positive and negative Figure 12-183. Finding an open branch in a parallel circuit.

plates. Figure 12-191 illustrates each cell contains positive plates of lead dioxide (PbO ), negative plates of spongy lead, can be checked. If the conductor or fuse is open, the and electrolyte (sulfuric acid and water). A practical cell is voltmeter reads zero.

constructed with many more plates than just two in order to get 5. If the lamp is burning, it is obvious that no open the required current output. All positive plates are connected exists in the branch containing the lamp, and the together as well as all the negatives. Because each positive voltmeter could be used to detect an open in the branch plate is always positioned between two negative plates, there containing R by removing lamp, L , from the circuit.

are always one or more negative plates than positive plates.

2 1 Troubleshooting the series portion of a series-parallel circuit Between the plates are porous separators that keep the presents no difficulties, but in the parallel portion of the positive and negative plates from touching each other and circuit, misleading readings can be obtained.

shorting out the cell. The separators have vertical ribs on the side facing the positive plate. This construction permits Batteries the electrolyte to circulate freely around the plates. In addition, it provides a path for sediment to settle to the Primary Cell bottom of the cell.

The dry cell is the most common type of primary-cell battery and is similar in its characteristics to that of an electrolytic Each cell is seated in a hard rubber casing through the top cell. This type of a battery is basically designed with a metal of which are terminal posts and a hole into which a nonspill electrode or graphite rod acting as the cathode (+) terminal, vent cap is screwed. The hole provides access for testing the immersed in an electrolytic paste. This electrode⁄electrolytic strength of the electrolyte and adding water. The vent plug build-up is then encased in a metal container, usually made permits gases to escape from the cell with a minimum of of zinc, which itself acts as the anode (−) terminal. When the leakage of electrolyte, regardless of the position the airplane battery is in a discharge condition an electrochemical reaction might assume. [Figure 12-192] In level flight, the lead weight takes place resulting in one of the metals being consumed.

Because of this consumption, the charging process is not reversible. Attempting to reverse the chemical reaction in a primary cell by way of recharging is usually dangerous and can lead to a battery explosion.

These batteries are commonly used to power items such as Break flashlights. The most common primary cells today are found R R 1 2 R in alkaline batteries, silver-oxide, and lithium batteries. The 30 Ω 30 Ω 30 Ω earlier carbon-zinc cells, with a carbon post as cathode and a zinc shell as anode were once prevalent but are not as common.

Secondary Cell A secondary cell is any kind of electrolytic cell in which the electrochemical reaction that releases energy is reversible.

The lead-acid car battery is a secondary-cell battery. The Figure 12-184. A misleading ohmmeter indication.

12-87 Open A Break R L 2 1 R R R 1 2 Break Figure 12-187. An open in the series portion of a series-parallel circuit.

B Figure 12-185. Opening a branch circuit to obtain an accurate R ohmmeter reading.

R L 2 1 Break R R R 1 2 3 30 V 30 Ω 30 Ω 30 Ω Figure 12-188. An open in the parallel portion of a series - parallel circuit.

Figure 12-186. A shorted component causes the fuse to open.

R Break permits venting of gases through a small hole. In inverted R L 2 1 flight, this hole is covered by the lead weight.

The individual cells of the battery are connected in series by means of cell straps. [Figure 12-193] The complete assembly is enclosed in an acid resisting metal container (battery box), which serves as electrical shielding and mechanical protection.

The battery box has a removable top. It also has a vent tube Figure 12-189. An open lamp in a series-parallel circuit.

nipple at each end. When the battery is installed in an airplane, a vent tube is attached to each nipple. One tube is the intake tube installation and removal of the battery. The plug consists of and is exposed to the slipstream. The other is the exhaust vent a socket and a handwheel with a course pitch thread. It can tube and is attached to the battery drain sump, which is a glass be readily connected to the receptacle by the handwheel.

jar containing a felt pad moistened with a concentrated solution Another advantage of this assembly is that the plug can be of sodium bicarbonate (baking soda). With this arrangement, installed in only one position, eliminating the possibility of the airstream is directed through the battery case where battery reversing the battery leads.

gases are picked up, neutralized in the sump, and then expelled overboard without damage to the airplane.

The voltage of lead acid cell is approximately two volts in order to attain the voltage required for the application. Each cell is To facilitate installation and removal of the battery in some then connected in series with heavy gauge metal straps to form aircraft, a quick disconnect assembly is used to connect the a battery. In a typical battery, such as that used in an aircraft for power leads to the battery. This assembly attaches the battery starting, the voltage required is 12 or 24 volts. This voltage is leads in the aircraft to a receptacle mounted on the side of the achieved by connecting six cells or twelve cells respectively battery. [Figure 12-194] The receptacle covers the battery together in series and enclosing them in one plastic box.

terminal posts and prevents accidental shorting during the 12-88 Each cell containing the plates are filled with an electrolyte the battery is expected to furnish current. Under actual service composed of sulfuric acid and distilled water with a specific conditions, the battery can be completely discharged within gravity of 1.270 at 60 °F. This solution contains positive a few minutes, or it may never be discharged if the generator hydrogen ions and negative sulfate (SO ) ions that are free to provides sufficient charge.

combine with other ions and form a new chemical compound.

When the cell is discharged, electrons leave the negative The ampere-hour capacity of a battery depends upon its total plate and flow to the positive plates where they cause the effective plate area. Connecting batteries in parallel increases lead dioxide (PbO ) to break down into negative oxygen ampere-hour capacity. Connecting batteries in series increases ions and positive lead ions. The negative oxygen ions join the total voltage but not the ampere-hour capacity.

with positive hydrogen ions from the sulfuric acid and form Life Cycle of a Battery water (H O). The negative sulfate ions join with the lead ions in both plates and form lead sulfate (PbSO ). After the Battery life cycle is defined as the number of complete charge/ discharge, the specific gravity changes to about 1.150. discharge cycles a battery can perform before its normal charge capacity falls below 80 percent of its initial rated capacity.

Battery Ratings Battery life can vary anywhere from 500 to 1,300 cycles.

The voltage of a battery is determined by the number of Various factors can cause deterioration of a battery and shorten cells connected in series to form the battery. Although the its service life. The first is over-discharging, which causes voltage of one lead-acid cell just removed from a charger is excess sulfation; second, too-rapid charging or discharging approximately 2.2 volts, a lead-acid cell is normally rated at that results in overheating of the plates and shedding of active approximately 2 volts. A battery rated at 12 volts consists of material. The accumulation of shed material, in turn, causes 6 lead-acid cells connected in series, and a battery rated at shorting of the plates and results in internal discharge. A battery 24 volts is composed of 12 cells. that remains in a low or discharged condition for a long period of time may be permanently damaged. The deterioration can The most common battery rating is the ampere-hour rating. continue to a point where cell capacity can drop to 80 percent This is a unit of measurement for battery capacity. It is after 1,000 cycles. In many cases, the cell can continue working determined by multiplying a current flow in amperes by the to nearly 2,000 cycles but with a diminished capacity of 60 time in hours that the battery is being discharged. percent of its original state.

A battery with a capacity of 1 ampere-hour should be able to continuously supply a current of 1 amp to a load for 1 1 exactly 1 hour, or 2 amps for ⁄ 2 hour, or ⁄ 3 amp for 3 hours, Cell container etc., before becoming completely discharged. Actually, the Vent cap ampere-hour output of a particular battery depends on the rate at which it is discharged. Heavy discharge current heats Terminal post the battery and decreases its efficiency and total ampere-hour output. For airplane batteries, a period of 5 hours has been Cell cover established as the discharge time in rating battery capacity.

However, this time of 5 hours is only a basis for rating and does not necessarily mean the length of time during which Plates A B C R Separators R L 2 1 Supporting ribs D E F Figure 12-190. Using the voltmeter to troubleshoot a series-parallel Figure 12-191. Lead-acid cell construction.

circuit.

12-89 Lead-Acid Battery Testing Methods Vent plug The state of charge of a storage battery depends upon the condition of its active materials, primarily the plates.

However, the state of charge of a battery is indicated by the density of the electrolyte and is checked by a hydrometer, an instrument that measures the specific gravity (weight as compared with water) of liquids.

Cells The most commonly used hydrometer consists of a small sealed glass tube weighted at its lower end so it floats upright.

[Figure 12-195] Within the narrow stem of the tube is a paper scale with a range of 1.100 to 1.300. When a hydrometer is used, a quantity of electrolyte sufficient to float the Cell strap hydrometer is drawn up into the syringe. The depth to which the hydrometer sinks into the electrolyte is determined by the density of the electrolyte, and the scale value indicated at the level of the electrolyte is its specific gravity. The more dense Figure 12-193. Connection of storage battery.

the electrolyte, the higher the hydrometer floats; therefore, the highest number on the scale (1.300) is at the lower end state of charge is considered in need of immediate recharging.

of the hydrometer scale.

When a battery is tested using a hydrometer, the temperature In a new, fully-charged aircraft storage battery, the electrolyte of the electrolyte must be taken into consideration. The is approximately 30 percent acid and 70 percent water (by specific gravity readings on the hydrometer vary from volume) and is 1.300 times as heavy as pure water. During the actual specific gravity as the temperature changes. No discharge, the solution (electrolyte) becomes less dense and correction is necessary when the temperature is between its specific gravity drops below 1.300. A specific gravity 70 °F and 90 °F, since the variation is not great enough to reading between 1.300 and 1.275 indicates a high state of consider. When temperatures are greater than 90 °F or less charge; between 1.275 and 1.240, a medium state of charge; than 70 °F, it is necessary to apply a correction factor. Some and between 1.240 and 1.200, a low state of charge. Aircraft hydrometers are equipped with a correction scale inside the batteries are generally of small capacity but are subject to tube. With other hydrometers, it is necessary to refer to a chart heavy loads. The values specified for state of charge are provided by the manufacturer. In both cases, the corrections therefore rather high. Hydrometer tests are made periodically should be added to, or subtracted from the reading shown on all storage batteries installed in aircraft. An aircraft battery on the hydrometer.

in a low state of charge may have perhaps 50 percent charge remaining, but is nevertheless considered low in the face of The specific gravity of a cell is reliable only if nothing has heavy demands that would soon exhaust it. A battery in such a Inverted position Upright position gases escape electrolyte Vent Vent Lead weight seated not sealed Lead weight seated Figure 12-194. A battery quick-disconnect assembly.

Figure 12-192. Nonspill battery vent plug.

12-90 been added to the electrolyte except occasional small amounts explosive mixture, it is important to take steps to prevent of distilled water to replace that lost as a result of normal ignition of the gas mixture. Loosen the vent caps and evaporation. Always take hydrometer readings before adding leave in place. Do not permit open flames, sparks, or other distilled water, never after. This is necessary to allow time sources of ignition in the vicinity. Before disconnecting for the water to mix thoroughly with the electrolyte and to or connecting a battery to the charge, always turn off the avoid drawing up into the hydrometer syringe a sample that power by means of a remote switch. Figure 12-197 shows does not represent the true strength of the solution. battery charging equipment.

Nickel-Cadmium Batteries Exercise extreme care when making the hydrometer test of a lead-acid cell. Handle the electrolyte carefully because Chemistry and Construction sulfuric acid burns clothing and skin. If the acid does contact Active materials in nickel-cadmium cells (Ni-Cad) are nickel the skin, wash the area thoroughly with water and then apply hydroxide (NiOOH) in the charged positive plate (Anode) bicarbonate of soda.

and sponge cadmium (Cd) in the charged negative plate (Cathode). The electrolyte is a potassium hydroxide (KOH) Lead-Acid Battery Charging Methods solution in concentration of 20–34 percent by weight pure Passing direct current through the battery in a direction KOH in distilled water.

opposite to that of the discharge current may charge a storage battery. Because of the internal resistance (IR) in the Sintered nickel-cadmium cells have relatively thin sintered battery, the voltage of the external charging source must be nickel matrices forming a plate grid structure. The grid greater than the open circuit voltage. For example, the open structure is highly porous and is impregnated with the active circuit voltage of a fully charged 12 cell, lead-acid battery is positive material (nickel-hydroxide) and the negative material approximately 26.4 volts (12 × 2.2 volts), but approximately (cadmium-hydroxide). The plates are then formed by sintering 28 volts are required to charge it. This larger voltage is needed nickel powder to fine-mesh wire screen. In other variations for charging because of the voltage drop in the battery caused of the process, the active material in the sintered matrix is by the internal resistance. Hence, the charging voltage of a converted chemically, or thermally, to an active state and lead-acid battery must equal the open circuit voltage plus the then formed. In general, there are many steps to these cycles IR drop within the battery (product of the charging current of impregnation and formation. Thin sintered plate cells are and the internal resistance).

ideally suited for very high rate charge and discharge service.

Pocket plate nickel-cadmium cells have the positive or negative Batteries are charged by either the constant voltage or active material, pressed into pockets of perforated nickel-plated constant current method. In the constant voltage method steel plates or into tubes. The active material is trapped securely [Figure 12-196A] , a motor generator set with a constant, in contact with a metal current collector so active material regulated voltage forces the current through the battery. In shedding is largely eliminated. Plate designs vary in thickness this method, the current at the start of the process is high but automatically tapers off, reaching a value of approximately 1 ampere when the battery is fully charged. The constant 1100 voltage method requires less time and supervision than does the constant current method.

1100 1200 1150 1200 1200 1300 In the constant current method [Figure 12-196B] , the current 1250 1300 remains almost constant during the entire charging process.

1100 1300 1200 This method requires a longer time to charge a battery fully and, toward the end of the process, presents the danger of overcharging, if care is not exercised.

In the aircraft, the storage battery is charged by direct current from the aircraft generator system. This method of charging is the constant voltage method, since the generator voltage Low charge Medium charge High charge is held constant by use of a voltage regulator.

When a storage battery is being charged, it generates a certain amount of hydrogen and oxygen. Since this is an Figure 12-195. Hydrometer (specific gravity readings).

12-91 depending upon cycling service requirements. The typical open around vent cap seals is potassium carbonate (K CO ).

2 3 circuit cell voltage of a nickel-cadmium battery is about 1.25 Clean up these surfaces with distilled water and dry. While volts. Figure 12-198 shows a nickel-cadmium aircraft battery. handling the caustic potassium hydroxide electrolyte, wear safety goggles to protect the eyes. The technician should also Operation of Nickel-Cadmium Cells wear plastic gloves and an apron to protect skin and clothes.

In case of spillage on hands or clothes, neutralize the alkali When a charging current is applied to a nickel-cadmium battery, the negative plates lose oxygen and begin forming immediately with vinegar or dilute boric acid solution (one pound per gallon of water); then rinse with clear water.

metallic cadmium. The active material of the positive plates, nickel-hydroxide, becomes more highly oxidized. This During overcharging conditions, explosive mixtures of process continues while the charging current is applied or until all the oxygen is removed from the negative plates and hydrogen and oxygen develop in nickel-cadmium cells.

When this occurs, the cell relief valves vent these gases only cadmium remains.

to the atmosphere, creating a potentially explosive hazard.

Additionally, room ventilation should be such as to prevent Toward the end of the charging cycle, the cells emit gas. This also occurs if the cells are overcharged. This gas is caused by a hydrogen build up in closed spaces from exceeding one percent by volume. Explosions can occur at concentrations decomposition of the water in the electrolyte into hydrogen at the negative plates and oxygen at the positive plates. The above four percent by volume in air.

voltage used during charging, as well as the temperature, Sealed Lead Acid (SLA) Batteries determines when gassing occurs. To completely charge a nickel-cadmium battery, some gassing, however slight, must In many applications, sealed lead acid (SLA) batteries take place; thus, some water is used. are gaining in use over flooded lead acid and Ni-Cad batteries. One leading characteristic of Ni-Cad batteries is The chemical action is reversed during discharge. The that they perform well in low voltage, full-discharge, high positive plates slowly give up oxygen, which is regained by cycle applications. However, they do not perform as well the negative plates. This process results in the conversion of the chemical energy into electrical energy. During discharge, the plates absorb a quantity of the electrolyte. On recharge, V Motor the level of the electrolyte rises and, at full charge, the generator electrolyte is at its highest level. Therefore, water should be added only when the battery is fully charged.

R Constant voltage The nickel-cadmium battery is usually interchangeable with charging circuit the lead-acid type. When replacing a lead-acid battery with Rheostat + a nickel-cadmium battery, the battery compartment must be clean, dry, and free of all traces of acid from the old battery.

The compartment must be washed out and neutralized with ammonia or boric acid solution, allowed to dry thoroughly, and then painted with an alkali resisting varnish.

A The pad in the battery sump jar should be saturated with a three percent (by weight) solution of boric acid and water before connecting the battery vent system.

A ON Constant current OFF charging circuit General Maintenance and Safety Precautions Refer to the battery manufacturer for detailed service instructions. Below are general recommendations for maintenance and safety precautions. For vented nickel- + cadmium cells, the general maintenance requirements are: 1. Hydrate cells to supply water lost during overcharging.

2. Maintain inter-cell connectors at proper torque values.

B 3. Keep cell tops and exposed sides clean and dry.

Figure 12-196. Battery charging methods.

Electrolyte spillage can form grounding paths. White moss 12-92 in extended standby applications, such as auxiliary or as Lithium-Ion Batteries emergency battery packs used to power inertial reference Lithium-ion batteries are the primary type of battery for units or stand-by equipment (attitude gyro).

many consumer type of equipment, such as cell phones, battery-powered tools, and computers, but now they are also It is typical during the servicing of a Ni-Cad battery to being used in commercial and military aircraft. The FAA has match as many as twenty individual cells in order to prevent certified lithium-ion batteries to be used on aircraft and one unbalance and thus cell reversal during end of discharge.

of the first aircraft to utilize the lithium-ion battery is the When a Ni-Cad does reverse, very high pressure and heat Boeing 787. The three primary functional components of a can result. The result is often pressure seal rupture, and in lithium-ion battery are the positive and negative electrodes and the worst case, a cell explosion. With SLA batteries, cell electrolyte. Generally, the negative electrode of a conventional matching is inherent in each battery. Ni-Cads also have an lithium-ion cell is made from carbon. The positive electrode is undesirable characteristic caused by constant overcharge a metal-oxide, and the electrolyte is a lithium salt in an organic and infrequent discharges, as in standby applications. It is solvent. The electrochemical roles of the electrodes reverse technically known as “voltage depression” and commonly between anode and cathode, depending on the direction of but erroneously called “memory effect.” This characteristic current flow through the cell. Lithium-ion batteries can be is only detectable when a full discharge is attempted. Thus, dangerous under some conditions and can pose a safety it is possible to believe a full charge exists, while in fact it hazard since they contain, unlike other rechargeable batteries, does not. SLA batteries do not have this characteristic voltage a flammable electrolyte and are also kept pressurized. Under depression (memory) phenomenon, and therefore do not certain conditions, they can overheat and a fire can occur.

require scheduled deep cycle maintenance as do Ni-Cads.

The Boeing 787 aircraft utilizes two large 32V 8 cell lithium- ion batteries. These batteries are much lighter and more The Ni-Cad emergency battery pack requires relatively powerful than Ni-Cad batteries used in similar-sized aircraft.

complicated test equipment due to the complex characteristics These batteries can produce 150 A for airplane power up.

of the Ni-Cad. Sealed lead acid batteries do not have these Figure 12-200 shows a B787 battery.

temperamental characteristics and therefore it is not necessary to purchase special battery maintenance equipment. Some Inverters manufacturers of SLA batteries have included in the battery An inverter is used in some aircraft systems to convert a packs a means by which the battery can be tested while still portion of the aircraft’s DC power to AC. This AC is used installed on the aircraft. Ni-Cads must have a scheduled mainly for instruments, radio, radar, lighting, and other energy test performed on the bench due to the inability to accessories. These inverters are usually built to supply measure their energy level on the aircraft, and because of current at a frequency of 400 cps, but some are designed to their notable “memory” shortcoming.

provide more than one voltage; for example, 26 volt AC in one winding and 115 volts in another.

The SLA battery can be designed to alert the technician if a battery is failing. Furthermore, it may be possible to test the There are two basic types of inverters: the rotary and the failure detection circuits by activating a Built in Test (BITE) static. Either type can be single-phase or multiphase. The button. This practice significantly reduces FAA paperwork and multiphase inverter is lighter for the same power rating than maintenance workload. Figure 12-199 shows a SLA battery.

the single-phase, but there are complications in distributing multiphase power and in keeping the loads balanced.

Figure 12-198. Nickel-Cadmium aircraft battery.

Figure 12-197. Battery charger.

12-93 The output is taken off the armature through three slip rings Rotary Inverters to provide three-phase power. The inverter would be a single- There are many sizes, types, and configurations of rotary phase inverter if it had a single armature winding and one slip ring. The frequency of this type unit is determined by inverters. Such inverters are essentially AC generators and DC motors in one housing. The generator field, or armature, the speed of the motor and the number of generator poles.

and the motor field, or armature, are mounted on a common Inductor-Type Rotary Inverter shaft that rotates within the housing. One common type of rotary inverter is the permanent magnet inverter. Inductor-type inverters use a rotor made of soft iron laminations with grooves cut laterally across the surface to provide poles Permanent Magnet Rotary Inverter that correspond to the number of stator poles. [Figure 12-203] The field coils are wound on one set of stationary poles and the A permanent magnet inverter is composed of a DC motor and a permanent magnet AC generator assembly. Each has a AC armature coils on the other set of stationary poles. When DC is applied to the field coils, a magnetic field is produced.

separate stator mounted within a common housing. The motor armature is mounted on a rotor and connected to the DC supply The rotor turns within the field coils and, as the poles on the rotor align with the stationary poles, a low reluctance path for through a commutator and brush assembly. The motor field windings are mounted on the housing and connected directly flux is established from the field pole through the rotor poles to the AC armature pole and through the housing back to the to the DC supply. A permanent magnet rotor is mounted at the opposite end of the same shaft as the motor armature, and field pole. In this circumstance, there is a large amount of magnetic flux linking the AC coils.

the stator windings are mounted on the housing, allowing AC to be taken from the inverter without the use of brushes.

When the rotor poles are between the stationary poles, there Figure 12-201 shows an internal wiring diagram for this type of rotary inverter. The generator rotor has six poles, is a high reluctance path for flux, consisting mainly of air; then, there is a small amount of magnetic flux linking the AC magnetized to provide alternate North and South poles about its circumference. coils. This increase and decrease in flux density in the stator induces an alternating current in the AC coils.

When the motor field and armature are excited, the rotor The number of poles and the speed of the motor determine begins to turn. As the rotor turns, the permanent magnet rotates within the AC stator coils, and the magnetic flux developed the frequency of this type of inverter. The DC stator field current controls the voltage. A cutaway view of an inductor- by the permanent magnets are cut by the conductors in the AC stator coils. An AC voltage is produced in the windings whose type rotary inverter is shown in Figure 12-204 .

polarity changes as each pole passes the windings.

Figure 12-205 is a simplified diagram of a typical aircraft AC power distribution system, utilizing a main and a standby This type inverter may be made multiphase by placing more AC stator coils in the housing in order to shift the phase the rotary inverter system.

proper amount in each coil.

Static Inverters As the name of the rotary inverter indicates, it has a revolving In many applications where continuous DC voltage must be armature in the AC generator section. Figure 12-202 shows converted to alternating voltage, static inverters are used in the diagram of a revolving armature, three phase inverter. place of rotary inverters or motor generator sets. The rapid progress made by the semiconductor industry is extending The DC motor in this inverter is a four pole, compound wound motor. The four field coils consist of many turns of fine wire, with a few turns of heavy wire placed on top. The fine wire is the shunt field, connected to the DC source through a filter and to ground through a centrifugal governor. The heavy wire is the series field, which is connected in series with the motor armature. The centrifugal governor controls the speed by shunting a resistor that is in series with the shunt field when the motor reaches a certain speed.

The alternator is a three-phase, four-pole, star-connected AC generator. The DC input is supplied to the generator field Figure 12-199. Sealed battery.

coils and connected to ground through a voltage regulator.

12-94 the range of applications of such equipment into voltage and considerably smaller, more compact, and much lighter in power ranges that would have been impractical a few years weight than rotary inverters. Depending on the output power ago. Some such applications are power supplies for frequency rating required, static inverters that are no larger than a typical sensitive military and commercial AC equipment, aircraft airspeed indicator can be used in aircraft systems. Some of emergency AC systems, and conversion of wide frequency the features of static inverters are: range power to precise frequency power. [Figure 12-206] 1. High efficiency 2. Low maintenance, long life The use of static inverters in small aircraft also has increased rapidly in the last few years, and the technology has advanced to 3. No warmup period required the point that static inverters are available for any requirement 4. Capable of starting under load filled by rotary inverters. For example, 250 VA emergency AC 5. Extremely quiet operation supplies operated from aircraft batteries are in production, as are 2,500 VA main AC supplies operated from a varying 6. Fast response to load changes frequency generator supply. This type of equipment has certain advantages for aircraft applications, particularly the absence Static inverters are commonly used to provide power for of moving parts and the adaptability to conduction cooling.

such frequency sensitive instruments as the attitude gyro and directional gyro. They also provide power for autosyn and Static inverters, referred to as solid-state inverters, are magnesyn indicators and transmitters, rate gyros, radar, and manufactured in a wide range of types and models that can other airborne applications. Figure 12-208 is a schematic of be classified by the shape of the AC output waveform and a typical small jet aircraft auxiliary battery system. It shows the power output capabilities. One of the most commonly the battery as input to the inverter and the output inverter used static inverters produces a regulated sine wave output. A circuits to various subsystems.

block diagram of a typical regulated sine wave static inverter is shown in Figure 12-207 . This inverter converts a low DC Semiconductors voltage into higher AC voltage. The AC output voltage is To understand why solid-state devices function as they do, held to a very small voltage tolerance, a typical variation it is necessary to examine the composition and nature of of less than 1 percent with a full input load change. Output semiconductors. The two most common materials used for taps are normally provided to permit selection of various semiconductors are germanium and silicon. The essential voltages; for example, taps may be provided for 105, 115, characteristic of these elements is that each atom has four and 125 volt AC outputs. Frequency regulation is typically valence electrons to share with adjacent atoms in forming within a range of one cycle for a 0–100 percent load change.

bonds. While both elements are used in semiconductor Variations of this type of static inverter are available, many construction, silicon is preferred in most modern applications of which provide a square wave output.

due to its ability to operate over a wider range of temperatures.

The nature of a bond between two silicon atoms is such that Since static inverters use solid-state components, they are each atom provides one electron to share with the other.

The two electrons shared are in fact shared equally between the two atoms. This form of sharing is known as a covalent bond. Such bonds are very stable and hold the two atoms together very tightly requiring much energy to break this bond. [Figure 12-209] In this case, all of the outer electrons are used to make covalent bonds with other silicon atoms.

In this condition, because all of the outer shell atoms are used, silicon takes on the characteristic of a good insulator, due to the fact that there are no open positions available for electrons to migrate through the orbits.

For the silicon crystal to conduct electricity, there must be some means available to allow some electrons to move from place to place within the crystal, regardless of the covalent bonds present between the atoms. One way to accomplish this is to introduce an impurity, such as arsenic or phosphorus, into the crystal structure, which either provides an extra electron or create a vacant position in the outer shell for electrons Figure 12-200. Boeing 787 lithium-ion battery.

12-95 Commutator Permanent magnet rotor Field coil AC coil Field coil A B AC output DC input G R A Filter B Figure 12-201. Internal wiring diagram of single-phase permanent magnet rotary inverter.

to pass though. The method used to create this condition is the surplus of electrons, the electrons are then considered the called doping. majority current carriers. This electron can easily be moved with only a small applied electrical voltage. Current flow Doping in an N-type silicon material is similar to conduction in a Doping is the process by which small amounts of additives copper wire. That is, with voltage applied across the material, electrons will move through the crystal towards the positive called impurities are added to the semiconductor material to increase their current flow by adding a few electrons or terminal just like current flows in a copper wire.

A P-type semiconductor is one that is doped with a P-type or a few holes. Once the material is doped, it then falls into one of two categories: the N-type semiconductor and the an acceptor impurity. Elements such as boron, aluminum, and gallium have only three electrons in the valence shell to share P-type semiconductor.

with the silicon atom. Those three electrons form covalent bonds with adjacent silicon atoms. However, the expected An N-type semiconductor material is one that is doped with an N-type or a donor impurity. Elements such as phosphorus, fourth bond cannot be formed and a complete connection is impossible here, leaving a “hole” in the structure of the arsenic, and antimony are added as impurities and have five outer electrons to share with other atoms. This causes the crystal. There is an empty place where an electron would naturally go, and often an electron moves into that space.

semiconductor material to have an excess electron. Due to 12-96 115 volt 3 phase 400 cycle AC output phase sequence ACB Common ground inverter A B D C 27.5 volt input Plug rear view AC Rectifier Grounded condenser + can 2 Noise slide A – Terminal B board C 1250 ohms D DC Filter Voltage regulator 500 ohms Brush connections 40 ohms DC + Slip rings DC series – shunt field field AC field – + Governor Motor Alternator Figure 12-202. Internal wiring diagram of three-phase, revolving armature.

However, the electron filling the hole left a covalent bond vacancy called a hole in the next position to the right. Once behind to fill this empty space, which leaves another hole again, this vacancy attracts the next valence electron. This behind as it moves. Another electron may then move into exchange of holes and electrons continues to progress and that particular hole, leaving another hole behind. As this can be viewed in one of two ways. The first way that this progression continues, holes appear to move as positive flow can be seen as that of electron movement. The electron charges throughout the crystal. This type of semiconductor is shown in Figure 12-210 as moving from the right to the material is designated P-type silicon material. Figure 12-210 left through a series of holes. Likewise, the second depiction shows the progression of a hole moving through a number in Figure 12-210 of the motion of the vacated hole can be of atoms. Notice that the hole illustrated at the far left of seen as migrating from the left to the right. This view is often top depiction of Figure 12-210 attracts the next valence called hole movement. The valence electron in the structure electron into the vacancy, which then produces another progresses along a path detailed by the arrows. Holes, 12-97 AC output Field Each time an electron crosses the PN junction, it creates a winding pair of ions. Figure 12-211 shows this area outlined by dashed DC lines. The circled plus signs and the circled negative signs are the positive and negative ions, respectively. These ions Flux lines are fixed in the crystal and do not move around like electrons or holes in the conduction band. Thus, the depletion zone constitutes a layer of a fixed charge. An electrostatic field, N represented by a small battery in Figure 12-211 , is established S across the junction between the oppositely charged ions.

S N The junction barrier is an electrostatic field, which has been created by the joining of a section of N-type and P-type material. Because holes and electrons must overcome this field to cross the junction, the electrostatic field is usually called a barrier. Because there is a lack or depletion of free electrons and holes in the area around the barrier, this area is called the depletion region. [Figure 12-211] As the diffusion N S of electrons and holes across the junction continue, the S strength of the electrostatic field increases until it is strong N enough to prevent electrons or holes from crossing over.

At this point, a state of equilibrium exists, and there is no further movement across the junction. The electrostatic field Magnetic flux created at the junction by the ions in the depletion zone is called a barrier.

Figure 12-203. Diagram of basic inductor-type inverter.

Forward Biased Diode Figure 12-212 illustrates a forward biased PN junction. When however, move along a path opposite that of the electrons.

an external voltage is applied to a PN junction, it is called bias. In a forward biased PN junction or diode, the negative PN Junctions & the Basic Diode voltage source is connected to the N-type material and the A single type of semiconductor material by itself is not very positive voltage source is connected to the P-type material.

useful. Useful applications are developed only when a single In this configuration, the current can easily flow. If a battery component contains both P-type and N-type materials. The is used to bias the PN junction and it is connected in such a semiconductor diode is also known as a PN junction diode.

way that the applied voltage opposes the junction field, it has This is a two-element semiconductor device that makes the effect of reducing the junction barrier and consequently use of the rectifying properties of a PN junction to convert aids in the current flow through the junction.

alternating current into direct current by permitting current flow in one direction only.

The electrons move toward the junction and the right end of the diode becomes slightly positive. This occurs because Figure 12-211 illustrates the electrical characteristics of electrons at the right end of the diode move toward the an unbiased diode, which means that no external voltage junction and leave positively charged atoms behind. The is applied. The P-side in the illustration is shown to have positively charged atoms then pull electrons into the diode many holes, while the N-side shows many electrons. The from the negative terminal of the battery.

electrons on the N-side tend to diffuse out in all directions.

When an electron enters the P region, it becomes a minority When electrons on the N-type side approach the junction, carrier. By definition, a minority carrier is an electron or hole, they recombine with holes. Basically, electrons are flowing whichever is the less dominant carrier in a semiconductor into the right end of the diode, while the bulk of the electrons device. In P-type materials, electrons are the minority carrier in the N-type material move toward the junctions. The and in N-type material, the hole is considered the minority left edge of this moving front of electrons disappears by carrier. With so many holes around the electron, the electron dropping into holes at the junction. In this way, there is a soon drops into a hole. When this occurs, the hole then continuous current of electrons from the battery moving disappears, and the conduction band electron becomes a toward the junction.

valence electron.

12-98 Housing, stator and coil assembly Armature Resistor Head assembly Fan Rotor Commutator Yoke assembly Brush assembly Resistor Condenser Brush retainer cap Figure 12-204. Cutaway view of inductor-type rotary inverter.

When the electrons hit the junction, they then become valence electrons. Once a valence electron, they can then Reverse Biased Diode move through the holes in the P-type material. When the When the battery is turned around as shown in Figure 12-213 , valence electrons move through the P-type material from then the diode is reverse biased and current does not flow. The the right to the left, a similar movement is occurring with most noticeable effect seen is the widened depletion zone.

the holes by moving from the left side of the P-type material to the right. Once the valence electron reaches the end of The applied battery voltage is in the same direction as the the diode, it then flows back into the positive terminal of depletion zone field. Because of this, holes and electrons tend the battery. to move away from the junction. Simply stated, the negative terminal attracts the holes away from the junction, and the In summary: positive terminal attracts the electrons away from the barrier.

Therefore, the result is a wider depletion zone. This action 1. Electron leaves negative terminal of the battery and increases the barrier width because there are more negative enters the right end (N-type material) of the diode.

ions on the P-side of the junction and more positive ions on 2. Electron then travels through the N-type material.

the N-side of the junction. This increase in the number of 3. The electron nears the junction and recombines and ions at the junction prevents current flow across the barrier by the majority carriers.

becomes a valence electron.

4. The electron now travels through the P-type material To summarize, the important thing to remember is that these as a valence electron.

PN junction diodes offer very little resistance to current when 5. The electron then leaves the diode and flows back to the diode is forward biased. Maximum resistance happens the positive terminal of the battery.

12-99 Main inverter AC primary bus Left generator DC bus AC bus tie breaker Main inverter power relay AC secondary bus Circuit energized by MAIN standby inverter only with AC switching inverter switch set to main relay Off Inverter switch and radar switch set to on.

Weather radar Stdby From main inverter only Secondary inverter RMI card power relay or RMI pointer 26 VAC bus Right generator Engine oil pressure ratio DC bus Oil pressure Standby inverter From standby inverter only DC power 115 VAC power 26 VAC power Figure 12-205. A typical aircraft AC power distribution system using main and standby rotary inverters.

tube rectifiers, or dry disk or solid-state rectifiers.

In aircraft with AC systems, a special DC generator is not desirable since it would be necessary for the engine accessory section to drive an additional piece of equipment. Motor generator sets, consisting of air-cooled AC motors that drive DC generators, eliminate this objection because they operate directly off the AC power system. Vacuum tube or various types of solid-state rectifiers provide a simple and efficient method of obtaining high voltage DC at low amperage.

Dry disk and solid-state rectifiers, on the other hand, are an excellent source of high amperage at low voltage.

Figure 12-206. Static inverter.

A rectifier is a device that transforms AC into DC by limiting when the diode is reversed biased. Figure 12-214 shows a or regulating the direction of current flow. The principal graph of the current characteristics of a diode that is biased types of rectifiers are dry disk and solid state. Solid-state, in both directions.

or semiconductor, rectifiers have replaced virtually all other types; and, since dry disk and motor generators are Rectifiers largely limited to older model aircraft, the major part of the Many devices in an aircraft require high amperage, low study of rectifiers is devoted to solid-state devices used for voltage DC for operation. This power may be furnished by rectification. The two methods discussed in this handbook DC engine-driven generators, motor generator sets, vacuum 12-100 Resonant filter Output keyer Buffer amplifier AC output regulator Square wave DC regulator DC input oscillator Figure 12-207. Regulated sine wave static inverter.

Gear control Flaps On Gear, flap, spoiler (MOM) switch Right fwd bus Spoiler Normally Altitude Directional Off closed relay gyro light gyro light Wheel master Battery Gyros Nose steering relay On Inverter Yaw trim Roll trim Off Auxiliary battery ADF Pilot’s audio Copilot’s map light Altitude gyro Transceiver Directional gyro Right fwd bus Transceiver light Figure 12-208. Auxiliary battery system using static inverter.

are the half-wave rectifier and the full-wave rectifier. across the load resistor with no loss in potential across the series diode.

Half-Wave Rectifier Figure 12-215B now shows the input signal being reversed.

Figure 12-215 illustrates the basic concept of a half-wave rectifier. When an AC signal is on a positive swing as shown Note that the polarities across the diode and the load resistor are also reversed. In this case, the diode is now reverse biased and in Figure 12-215A , the polarities across the diode and the load resistor are also positive. In this case, the diode is forward can be replaced with an equivalent open circuit. The current in the circuit is now 0 amperes and the voltage drop over the biased and can be replaced with a short circuit as shown in the figure. The positive portion of the input signal appears load resistor is 0 volts. The resulting waveform for a complete 12-101 N-type P-type Si A Depletion zone N-type P-type Si Si Si Si Si Si Represents electrostatic field Figure 12-211. Depletion region.

Si Si Si Full-Wave Rectifier Figure 12-216 illustrates a more common use of the diode as B a rectifier. This type of a rectifier is called a full-wave bridge rectifier. The term “full-wave” indicates that the output is a continuous sequence of pulses rather than having gaps that Figure 12-209. Valence electrons.

appear in the half-wave rectifier.

Figure 12-216C shows the initial condition, during which, a positive portion of the input signal is applied to the network.

Electron movement Note the polarities across the diodes. Diodes D2 and D4 are reverse biased and can be replaced with an open circuit.

Diodes D1 and D3 are forward biased and act as an open circuit. The current path through the diodes is clear to see, and Hole movement the resulting waveform is developed across the load resistor.

During the negative portion of the applied signal, the diodes reverse their polarity and bias states. The result is a network shown in Figure 12-216D . Current now passes through diodes Silicon atom showing one of the electrons in its D4 and D2, which are forward biased, while diodes D1 and valence shell D3 are essentially open circuits due to being reverse biased.

Silicon atom in which one electron has broken out of its valence shell and left a hole Note that during both alternations of the input waveform, the current passes through the load resistor in the same direction.

Electron moving from one silicon atom to another and leaving a hole This results in the negative swing of the waveform being flipped up to the positive side of the time line.

Figure 12-210. A hole moving through atoms.

Dry Disk Dry disk rectifiers operate on the principle that electric sinusoidal input can be seen at the far right of Figure 12-215 .

current flows through a junction of two dissimilar conducting The output waveform is a reproduction of the input waveform materials more readily in one direction than it does in the minus the negative voltage swing of the wave. For this reason, opposite direction. This is true because the resistance to this type of rectifier is called a half-wave rectifier.

current flow in one direction is low, while in the other direction it is high. Depending on the materials used, several amperes may flow in the direction of low resistance but only 12-102 Wide depletion zone Narrow depletion zone N-type P-type N-type P-type Holes Electrons + – e – + – Electron flow Figure 12-213. Reversed diode.

Figure 12-212. Forward biased PN junction.

sink. [Figure 12-218] a few milliamperes in the direction of high resistance.

Zener Diodes Three types of dry disk rectifiers may be found in aircraft: Zener diodes (sometimes called “breakdown diodes”) are the copper oxide rectifier, the selenium rectifier, and the designed so that they break down (allow current to pass) magnesium copper-sulfide rectifier. The copper oxide when the circuit potential is equal to or in excess of the rectifier consists of a copper disk upon which a layer of desired reverse bias voltage. The range of reverse bias copper oxide has been formed by heating. [Figure 12-217] breakdown-voltages commonly found can range from 2 It may also consist of a chemical copper oxide preparation volts to 200 volts depending on design. Once a specific spread evenly over the copper surface. Metal plates, usually reverse bias voltage has been reached, the diode conducts lead plates, are pressed against the two opposite faces of the and behaves like a constant voltage source. Within the disk to form a good contact. Current flow is from the copper normal operating range, the zener functions as a voltage to the copper oxide.

regulator, waveform clipper, and other related functions.

Below the desired voltage, the zener blocks the circuit like The selenium rectifier consists of an iron disk, similar to a any other diode biased in the reverse direction. Because washer, with one side coated with selenium. Its operation is the zener diode allows free flow in one direction when it similar to that of the copper oxide rectifier. Current flows is used in an AC circuit, two diodes connected in opposite from the selenium to the iron.

directions must be used. This takes care of both alternations of current. Power ratings of these devices range from about The magnesium copper sulfide rectifier is made of washer- 250 milliwatts to 50 watts.

shaped magnesium disks coated with a layer of copper sulfide. The disks are arranged similarly to the other types.

Special Purpose Diodes Current flows from the magnesium to the copper sulfide.

The unique characteristics of semiconductor material have Types of Diodes allowed for the development of many specialized types of Today, there are many varieties of diodes that can be grouped diodes. A short description of some of the more common diode into one of several basic categories.

types is given for general familiarization. [Figure 12-219] Power Rectifier Diodes Light-Emitting Diode (LED) The rectifier diode is usually used in applications that require In a forward biased diode, electrons cross the junction high current, such as power supplies. The range in which and fall into holes. As the electrons fall into the valence the diode can handle current can vary anywhere from one band, they radiate energy. In a rectifier diode, this energy ampere to hundreds of amperes. One common example is dissipated as heat. However, in the light-emitting diode of diodes is the series of diodes, part numbers 1N4001 (LED), the energy is dissipated as light. By using elements to 1N4007. The “1N” indicates that there is only one PN such as gallium, arsenic, and phosphorous, an LED can be junction, or that the device is a diode. The average current designed to radiate colors, such as red, green, yellow, blue, carrying range for these rectifier diodes is about one ampere and infrared light. LEDs that are designed for the visible light with a peak inverse voltage between 50 volts to 1,000 volts.

portion of the spectrum are useful for instruments, indicators, Larger rectifier diodes can carry currents up to 300 amperes and even cabin lighting. The advantages of the LED over the when forward biased and have a peak inverse voltage of 600 incandescent lamps are longer life, lower voltage, faster on volts. A recognizable feature of the larger rectifier diodes and off operations, and less heat.

is that they are encased in metal in order to provide a heat 12-103 in the microwatt range. The liquid crystal is encapsulated between two glass plates. When voltage is not applied to the 60 mA LCD, the display is clear. However, when a voltage is applied, 50 mA the result is a change in the orientation of the atoms of the crystals. The incident light is then reflected in a different 40 mA direction. A frosted appearance results in the regions that have voltage applied and permits distinguishing of numeric values.

30 mA Photodiode 20 mA Thermal energy produces minority carriers in a diode. The 10 mA higher the temperature, the greater the current in a reverse 120v 90v 60v 30v current diode. Light energy can also produce minority carriers. By using a small window to expose the PN junction, 1v 2v 3v 4v 5v a photodiode can be built. When light falls upon the junction 600 Aμ of a reverse-biased photodiode, electrons-hole pairs are 1200 Aμ created inside the depletion layer. The stronger the light, the greater the number of light-produced carriers, which in turn causes a greater magnitude of reverse-current. Because Junction diode characteristics of this characteristic, the photodiode can be used in light detecting circuits.

Figure 12-214. Diode biased in both directions.

Varactors The varactor is simply a variable-capacitance diode. The Liquid Crystal Displays (LCD) reverse voltage applied controls the variable-capacitance The liquid crystal display (LCD) has an advantage over the of the diode. The transitional capacitance decreases as LED in that it requires less power to operate. Where LEDs the reverse voltage is increasingly applied. In many commonly operate in the milliwatt range, the LCD operates Half-wave Rectification Input Signal Circuit Depiction Output Wave-form Across Load Resistor 120 v V+ + − + + Time R L − − 120 v V+ V– A A Forward bias (Short circuit) Time V+ V– + − − − Time R L + + V– –120 v B Reverse bias (Open circuit) B Figure 12-215. Basic concept of half-wave rectifier.

12-104 applications, the varactor has replaced the old mechanically Introduction to Transistors tuned capacitors. Varactors can be placed in parallel with The transistor is a three-terminal device primarily used an inductor and provide a resonant tank circuit for a tuning to amplify signals and control current within a circuit.

circuit. By simply varying the reverse voltage across the [Figure 12-220] The basic two-junction semiconductor must varactor, the resonant frequency of the circuit can be adjusted.

have one type of region sandwiched between two of the other type. The three regions in a transistor are the collector (C), Schottky Diodes which is moderately doped, the emitter (E), which is heavily Schottky diodes are designed to have metal, such as gold, doped, and the base (B), which is significantly less doped.

silver, or platinum, on one side of the junction and doped The alternating layers of semiconductor material type provide silicon, usually an N-type, on the other side of the junction.

the common commercial name for each type of transistor. The This type of a diode is considered a unipolar device because interface between the layers is called a junction. Selenium free electrons are the majority carrier on both sides of the and germanium diodes previously discussed are examples junction. The Schottky diode has no depletion zone or charge of junction diodes. Note that the sandwiched layer or base storage, which means that the switching time can be as high as is significantly thinner than the collector or the emitter. In 300 MHz. This characteristic exceeds that of the bipolar diode.

general, this permits a “punching through” action for the carriers passing between the collector and emitter terminals.

Diode Identification Figure 12-218 illustrates a number of methods employed Classification for identifying diodes. Typically manufacturers place some The transistors are classified as either NPN or PNP according form of an identifier on the diode to indicate which end is to the arrangement of their N and P-materials. The NPN the anode and which end is the cathode. Dots, bands, colored transistor is formed by introducing a thin region of P-material bands, the letter ‘k’ or unusual shapes indicate the cathode between two regions of N-type material. The opposite is true end of the diode.

for the PNP configuration.

The two basic types of transistors along with their circuit Output wave-form Circuit depiction Input signal Across load resistor 120 v 120 v 120 v V+ V+ D1 D2 + Time Time R L + − − D4 D3 V– V– –120 v B A Current Current D1 D2 − + + + + − + − + − − − R R + − L L − + D3 D4 Current Current D C Figure 12-216. Full-wave bridge rectifier.

12-105 PNP. On the other hand, if the arrow is pointing out, then it is an NPN type.

Lead Copper oxide Copper Transistor Theory Direction of As discussed in the section on diodes, the movement of circuit flow the electrons and holes can be considered current. Electron current moves in one direction, while hole current travels in Insulating washer the opposite direction. In transistors, both electrons and holes act as carriers of current.

A forward biased PN junction is comparable to a low- resistance circuit element, because it passes a high current for a given voltage. On the other hand, a reverse-biased PN junction is comparable to a high-resistance circuit element.

By using Ohm’s Law formula for power (P = I R) and Insulating tube assuming current is held constant through both junctions, it can be concluded that the power developed across the high resistance junction is greater than that developed across a low resistance junction. Therefore, if a crystal were to contain two PN junctions, one forward biased and the other reverse Pressure plate biased, and a low-power signal injected into the forward biased junction, a high-power signal could be produced at Figure 12-217. Copper oxide dry disk rectifier.

the reverse-biased junction.

symbols are shown in Figure 12-221 . Note that the two To use the transistor as an amplifier, some sort of external symbols are different. The horizontal line represents the base, bias voltage must modify each of the junctions. The first PN and two angular lines represent the emitter and collector. The junction (emitter-base) is biased in the forward direction.

angular line with the arrow on it is the emitter, while the line This produces a low resistance. The second junction, which without is the collector. The direction of the arrow on the is the collector-base junction, is reverse biased to produce a emitter determines whether or not the transistor is a PNP or high resistance. [Figure 12-222] an NPN type. If the arrow is pointing in, the transistor is a (+) Anode Cathode (−) Schematic symbol Approx. 0.75" Approx. 0.1" (+) Anode Cathode (−) General purpose signal diodes Approx. 1.5" Approx. 0.2" Cathode (−) (+) Anode Rectifier diodes 35 ampere silicon rectifier Figure 12-218. General purpose diodes.

12-106 With the emitter-base junction biased in the forward direction, of no use. To reduce this loss of electrons, the transistor is electrons leave the negative terminal of the battery and enter designed so that the base is very thin in relation to the emitter the N-material. These electrons pass easily through the and collector, and the base is lightly doped.

emitter, cross over the junction, and combine with the hole in the P-material in the base. For each electron that fills a Most of the electrons that move into the base fall under the hole in the P-material, another electron leaves the P-material, influence of the reverse bias of the collector. While collector- which creates a new hole and enters the positive terminal of base junction is reverse biased with respect to the majority the battery. carriers, it behaves as if it is forward biased to the electrons or minority carriers in this case. The electrons are accelerated The second PN junction, which is the base-collector junction, through the collector-base junction and into the collector. The is reverse biased. This prevents the majority carriers from collector is comprised of the N-type material; therefore, the crossing the junction, thus creating a high-resistance circuit. electrons once again become the majority carrier. Moving It is worth noting that there still is a small current passing easily through the collector, the electrons return to the through the reversed PN junction in the form of minority positive terminal of the collector supply battery Vcc, which carriers—that is, electrons in the P-material and holes in the is shown in Figure 12-223 as Ic.

N-material. The minority carriers play a significant part in the operation of the NPN transistor. Because of the way this device operates to transfer current (and its internal resistances) from the original conduction path Figure 12-223 illustrates the basic interaction of the NPN to another, its name is a combination of the words “transfer” junction. There are two batteries in the circuit used to bias the and “resistor”—transistor.

NPN transistor. Vbb is considered the base voltage supply, rated in this illustration at 1 volt, and the battery voltage PNP Transistor Operation Vcc, rated at 6 volts, is called the collector voltage supply. The PNP transistor generally works the same way as the NPN transistor. The primary difference is that the emitter, Current within the external circuit is simply the movement base, and collector materials are made of different material of free electrons originating at the negative terminal of the than the NPN. The majority and minority current carriers battery and flowing to the N-material. [Figure 12-223] are the opposite in the PNP to that of the NPN. In the case As the electrons enter the N-material, they become the of the PNP, the majority carriers are the holes instead of the majority carrier and move through the N-material to the electrons in the NPN transistor. To properly bias the PNP, the emitter-base PN junction. This emitter-base junction is polarity of the bias network must be reversed.

forward biased at about 0.65 to 0.7 volts positive with respect to the emitter and presents no resistance to the flow of Identification of Transistors electrons from the emitter into the base, which is composed of Figure 12-224 illustrates some of the more common transistor P-material. As these electrons move into the base, they drop lead identifications. The methods of identifying leads vary into available holes. For every electron that drops into a hole, due to a lack of a standard and require verification using another electron exits the base by way of the base lead and manufacturer information to properly identify. However, a becomes the base current or Ib. Of course, when one electron short description of the common methods is discussed below.

leaves the base, a new hole is formed. From the standpoint of the collector, these electrons that drop into holes are lost and Figure 12-224D shows an oval-shaped transistor. The collector lead in this case is identified by the wide space between it and the lead for the base. The final lead at the far left is the emitter. In many cases, colored dots indicate the collector lead, and short leads relative to the other leads indicate the emitter. In a conventional power diode, as seen Schottky diode LED in Figure 12-224E , the collector lead is usually a part of the mounting bases, while the emitter and collector are leads or tines protruding from the mounting surface.

Step-recovery diode Photodiode Field Effect Transistors Another transistor design that has become more important than the bipolar transistor is the field-effect transistor (FET).

Zener Varactor The primary difference between the bipolar transistor and the FET is that the bipolar transistor has two PN junctions and Figure 12-219. Schematic symbols for special purpose diodes.

12-107 PN junctions Base N P N Emitter Collector P N P Base Emitter Collector PN junctions Emitter Collector N P N Base Base Figure 12-220. Transistor.

Base P N P is a current-controlled device, while the FET has only one PN junction and is a voltage-controlled device. Within the FET family, there are two general categories of components.

Emitter Collector One category is called the junction FET (JFET), which has only one PN junction. The other category is known as the enhancement-type or metal-oxide JET (MOSFET).

Figure 12-225 shows the basic construction of the JFET and the schematic symbol. In this figure, it can be seen that the Base drain (D) and source (S) are connected to an N-type material, and the gate (G) is connected to the P-type material. With Figure 12-221. Two basic transistors with circuit symbols.

gate voltage Vgg set to 0 volts and drain voltage Vdd set to some positive voltage, a current flows between the source source (S) and the drain (D). By applying a greater voltage on and the drain, through a narrow band of N-material. If then, the gate (G), the P-channel begins to materialize and grow in Vgg is adjusted to some negative voltage, the PN junction size. Once this occurs, the source (S) to drain (D) current Id is reverse biased, and a depletion zone (no charge carriers) increases. The schematic symbol reflects this characteristic is established at the PN junction. By reducing the region of by using a broken line to indicate that the channel does not noncarriers, it has the effect of reducing the dimensions of the exist without a gate bias.

N-channel, resulting in a reduction of source to drain current.

Common Transistor Configurations Because JFETs are voltage-controlled devices, they have some A transistor may be connected in one of three different advantages over the bipolar transistor. One such advantage configurations: common-emitter (CE), common-base (CB), is that because the gate is reverse biased, the circuit that it and common-collector (CC). The term “common” is used is connected to sees the gate as a very high resistance. This to indicate which element of the transistor is common means that the JFET has less of an insertion influence in the to both the input and the output. Each configuration has circuit. The high resistance also means that less current is used.

its own characteristics, which makes each configuration suitable for particular applications. A way to determine what Like many other solid-state devices, careless handling and configuration you may find in a circuit is to first determine static electricity can damage the JFET. Technicians should which of the three transistor elements is used for the input take all precautions to prevent such damage.

signal. Then, determine the element used for the output signal. At that point, the remaining element, (base, emitter, Metal-Oxide-Semiconductor FET (MOSFET) or collector) is the common element to both the input and Figure 12-226 illustrates the general construction and the output, and thus you determine the configuration.

schematic symbol of the MOSFET transistor. The biasing arrangement for the MOSFET is essentially the same as that Common-Emitter (CE) Configuration for the JFET. The term “enhancement” comes from the idea This is the configuration most commonly used in amplifier that when there is no bias voltage applied to the gate (G), then there is no channel for current conduction between the 12-108 I and a decrease in collector voltage (E being less negative C C and going positive). The collector current, which flows through the reverse-biased junction, also flows through a high-resistance load resulting in a high level of amplification.

Because the input signal to the CE goes positive when the output goes negative, the two signals are 180° out of phase.

+ This is the only configuration that provides a phase reversal.

The CE is the most popular of the three configurations − + because it has the best combination of current and voltage − gain. Gain is a term used to indicate the magnitude of amplification. Each transistor configuration has its unique gain characteristics even though the same transistors are used.

Common-Collector (CC) Configuration This transistor configuration is usually used for impedance matching. It is also used as a current driver due to its high Figure 12-222. NPN transistor.

current gain. It is also very useful in switching circuits since it has the ability to pass signals in either direction.

circuits because they provide good gains for voltage, current, [Figure 12-227] and power. The input signal is applied to the base-emitter junction, which is forward biased (low resistance), and the In the CC circuit, the input signal is applied to the base, and the output signal is taken off the collector-emitter junction, output signal is taken from the emitter, leaving the collector as which is reverse biased (high resistance). Then the emitter the common point between the input and the output. The input is the common element to both input and output circuits.

resistance of the CC circuit is high, while the output resistance [Figure 12-227] is low. The current gain is higher than that in the CE, but it has a lower power gain than either the CE or CB configuration. Just When the transistor is connected in a CE configuration, the like the CB configuration, the output signal of the CC circuit input signal is injected between the base and emitter, which is in phase with the input signal. The CC is typically referred is a low-resistance, low-current circuit. As the input signal to as an emitter-follower because the output developed on the goes positive, it causes the base to go positive relative to emitter follows the input signal applied to the base.

the emitter. This causes a decrease in the forward bias, which in turn reduces the collector current I and increases C Common-Base (CB) Configuration the collector voltage (E being more negative). During the C The primary use of this configuration is for impedance negative portion of the input signal, the voltage on the base matching because it has low input impedance and high is driven more negative relative to the emitter. This increases output resistance. Two factors, however, limit the usefulness the forward bias and allows an increase in collector current of this circuit application. First is the low-input resistance and second is its lack of current, which is always below 1.

lc Since the CB configuration gives voltage amplification, there are some applications for this circuit, such as microphone Hole [blue] amplifiers. [Figure 12-227] Electron [green] In the CB circuit, the input signal is applied to the emitter and Collector Reverse biased junction the output signal is taken from the collector. In this case, both N the input and the output have the base as a common element.

lb P Base When an input signal is applied to the emitter, it causes the Forward biased Vcc = 6 volts junction emitter-base junction to react in the same manner as that in Emitter + N + the CE circuit. When an input adds to the bias, it increases the transistor current; conversely, when the signal opposes − Vbb = 1 volt the bias, the current in the transistor decreases.

− le The signal adds to the forward bias, since it is applied to the emitter, causing the collector current to increase. This Figure 12-223. NPN Junction. increase in I results in a greater voltage drop across the C 12-109 A B C D E Color dot E B C

Color dot B

C E B B E B C C E Figure 12-224. Common transistor lead identifications.

load resistor RL, thus lowering the collector voltage E . is usually coated with special chemical compounds. If an C The collector voltage, in becoming less negative, swings in a external field does not draw the emitted electrons away, they positive direction and is therefore in phase with the incoming form about the cathode into a negatively-charged cloud called positive signal. the space charge. The accumulation of negative electrons near the emitter repels others coming from the emitter. The Vacuum Tubes emitter, if insulated, becomes positive because of the loss of electrons. This establishes an electrostatic field between the The use of vacuum tubes in aircraft electrical and electronic cloud of negative electrons and the now positive cathode. A systems has rapidly declined due to the many advantages balance is reached when only enough electrons flow from the of using transistors. However, some systems still employ cathode to the area surrounding it to supply the loss caused vacuum tubes in special applications, and possibly some by diffusion of the space charge.

older model aircraft still in service are equipped with devices that use vacuum tubes. While these components may still be in service, their infrequent occurrence does not warrant a detailed discussion.

N-material Charge free or depletion zone Originally, vacuum tubes were developed for radio work.

I D + − They are used in radio transmitters as amplifiers for Drain (D) Source (S) controlling voltage and current, as oscillators for generating + audio and radio frequency signals, and as rectifiers for Gate (G) P-material I S + − converting AC into DC. While there are many types of V vacuum tubes for a variety of applications, the most common GG + − types fall into one of the following families: (1) diode, (2) V DD triode, (3) tetrode, and (4) pentode. Each of these vacuum tube types operates on the following fundamental principles.

JFET construction Gate (G) Gate (G) When a piece of metal is heated, the speed of the electrons in the metal is increased. If the metal is heated to a high enough temperature, the electrons are accelerated to the Drain (D) Source (S) Drain (D) Source (S) point where some of them actually leave the surface of the metal. In a vacuum tube, electrons are supplied by a piece of P-channel N-channel metal called a cathode, which is heated by an electric current.

JFET symbol Within limits, the hotter the cathode, the greater the number of electrons it gives off or emits.

Figure 12-225. JFET and the schematic symbol.

To increase the number of electrons emitted, the cathode 12-110 Filtering Characteristics of Inductors Applied voltage + The inductance provided by an inductor may be used as a Gate (G) filter, because it opposes a change in current through it by Drain (D) Source (S) storing energy in its electromagnetic field. Whenever the N N current increases, the stored energy in the electromagnetic P-material field increases. When the current through the inductor decreases, the inductor supplies the energy back into the + − circuit in order to maintain the existing flow of current.

The use of an inductor for filtering the output of a rectifier is shown in Figure 12-230. Note that in this network the MOSFET construction inductor L is in series with the load R .

1 1 The inductance L is selected to offer high impedance to the Gate (G) Gate (G) AC ripple voltage and low impedance to the DC component.

The result is a very large voltage drop across the inductor and a very small voltage drop across the load R . For the Drain (D) Source (S) Drain (D) Source (S) DC component, however, a very small voltage drop occurs across the inductor and a very large voltage drop across the N-MOSFET P-MOSFET load. The effect of an inductor on the output of a full-wave MOSFET symbol rectifier in the output waveshape is shown in Figure 12-231 .

Figure 12-226. General construction and schematic symbol of Common Filter Configurations MOSFET transistor.

Capacitors and inductors are combined in various ways to provide more satisfactory filtering than can be obtained Filtering with a single capacitor or inductor. These are referred to collectively as LC filters. Several combinations are shown One of the more common uses of the capacitor and inductor schematically in Figure 12-232 . Note that the L, or inverted that the technician may find in the field is that of the filter.

L-type, and the T-type filter sections resemble schematically Filtering Characteristics of Capacitors The nature of capacitance opposes a voltage change across its NPN PNP terminal by storing energy in its electrostatic field. Whenever Output Output the voltage tends to rise, the capacitor converts this voltage Input Input change to stored energy. When the voltage tends to fall, the capacitor converts this stored energy back to voltage. The use Common-emitter of a capacitor for filtering the output of a rectifier is illustrated in Figure 12-228 . The rectifier is shown as a block, and the capacitor C is connected in parallel with the load R .

1 1 NPN PNP Output Output The capacitor C is chosen to offer very low impedance to Input Input the AC ripple frequency and very high impedance to the DC component. The ripple voltage is therefore bypassed Common-collector to ground through the low impedance path of the capacitor, while the DC voltage is applied unchanged to the load. The NPN PNP effect of the capacitor on the output of the rectifier can be seen in the waveshapes shown in Figure 12-229 . Dotted lines show Input Input Output Output the rectifier output, while the solid lines show the effect of the capacitor. In this example, full-wave rectifier outputs are Common-base shown. The capacitor C charges when the rectifier voltage output tends to increase and discharges when the voltage Figure 12-227. Transistor configurations (common-emitter, output tends to decrease. In this manner, the voltage across common-collector, common-base).

the load R is kept fairly constant.

12-111

Next: section resembles the Greek letter pi (π) schematically. to high-frequency signals than low-frequency signals and →

Section 24

the corresponding letters of the alphabet. The pi-type filter through an inductor, then the filter presents less attenuation section resembles the Greek letter pi (π) schematically. to high-frequency signals than low-frequency signals and All the filter sections shown are similar in that the inductances is then considered a high-pass filter. Typically after an AC are in series and the capacitances are in parallel with the signal is rectified, the pulses of voltage are changed to usable load. The inductances must, therefore, offer very high form of DC by way of filtering.

impedance and the capacitors very low impedance to the ripple frequency. Since the ripple frequency is comparatively Low-Pass Filter low, the inductances are iron core coils having large values A low-pass filter is a filter that passes low frequencies well, of inductance (several henries). Because they offer such but attenuates (reduces) higher frequencies. The so-called high impedance to the ripple frequency, these coils are called cutoff frequency divides the range of frequencies that are chokes. The capacitors must also be large (several microfarads) passed and the range of frequencies that are stopped. In other to offer very little opposition to the ripple frequency. Because words, the frequency components higher than the cutoff the voltage across the capacitor is DC, electrolytic capacitors frequency are stopped by a low-pass filter. The actual amount are frequently used as filter capacitors. Always observe the of attenuation for each frequency varies by filter design.

correct polarity in connecting electrolytic capacitors.

An inductive low-pass filter inserts an inductor in series with LC filters are also classified according to the position of the load, where a capacitive low-pass filter inserts a resistor the capacitor and inductor. A capacitor input filter is one in in series and a capacitor in parallel with the load. The former which the capacitor is connected directly across the output filter design tries to block the unwanted frequency signal terminals of the rectifier. A choke input filter is one in which while the latter tries to short it out. Figure 12-234 illustrates a choke precedes the filter capacitor.

this type of circuit and the frequency/current flow response.

If it is necessary to increase the applied voltage to more than High-Pass Filter (HPF) a single rectifier can tolerate, the usual solution is to stack A high-pass filter (HPF) is a filter that passes high frequencies them. These rectifiers are similar to resistors added in series.

well, but attenuates (reduces) frequencies lower than the Each resistor drops a portion of the applied voltage rather than cutoff frequency. The actual amount of attenuation for each the total voltage. The same theory applies to rectifiers added frequency varies once again depending on filter design. In in series or stacked. Series stacking increases the voltage some cases, it is called a low-cut filter. A HPF is essentially rating. If, for example, a rectifier is destroyed with an applied the opposite of a low-pass filter.

voltage exceeding 50 volts, and it is to be used in a circuit with an applied voltage of 150 volts, stacking of diodes can It is useful as a filter to block any unwanted low frequency be employed. The result is shown in Figure 12-233 .

components of a signal while passing the desired higher frequencies. Figure 12-235 illustrates this type of circuit and Basic LC Filters the frequency/current flow response.

Analog filters are circuits that perform signal processing functions, specifically intended to remove unwanted signal Band-Pass Filter components, such as ripple, and enhance desired signals. The A band-pass filter is basically a combination of a high- simplest analog filters are based on combinations of inductors pass and a low-pass. There are some applications where and capacitors. The four basic categories of filters discussed a particular range of frequencies need to be singled out or are: low-pass, high-pass, band-pass and band-stop. All these filtered from a wider range of frequencies. Band-pass filter types are collectively known as passive filters, because they circuits are designed to accomplish this task by combining do not depend on any external power source.

the properties of low-pass and high-pass into a single filter. Figure 12-236 illustrates this type of circuit and the The operation of a filter relies on the characteristic of variable frequency/current flow response.

inductive and capacitive reactance based on the applied frequency. In review, the inductor blocks high-frequency Band-Stop Filter signals (high reactance) and conducts low-frequency In signal processing, a band-stop filter or band-rejection filter signals (low reactance), while capacitors do the reverse.

is a filter that passes most frequencies unaltered, but attenuates A filter in which the signal passes through an inductor, or those in a range to very low levels. It is the opposite of a band- in which a capacitor provides a path to earth, presents less pass filter. A notch filter is a band-stop filter with a narrow attenuation (reduction) to a low-frequency signal than to a stopband (high Q factor). Notch filters are used in live sound high-frequency signal and is considered a low-pass filter. If reproduction (public address (PA) systems) and in instrument the signal passes through a capacitor, or has a path to ground 12-112 frequency/current flow response.

Amplifier Circuits AC input An amplifier is a device that enables an input signal to control DC C R Rectifier 1 1 an output signal. The output signal has some or all of the characteristics of the input signal but generally is a greater magnitude than the input signal in terms of voltage, current, or power. Gain is the basic function of all amplifiers. Because of this gain, we can expect the output signal to be greater than Figure 12-228. A capacitor used as a filter.

the input signal. For example, if we have an input signal of 1 volt and an output signal of 10 volts, then the gain factor amplifier (especially amplifiers or preamplifiers for acoustic can be determined by: instruments, such as acoustic guitar, mandolin, bass instrument Gain = Signal out /signal in amplifier, etc.) to reduce or prevent feedback, while having Gain = 10 V/1 V = 10 little noticeable effect on the rest of the frequency spectrum.

Other names include “band limit filter,” “T-notch filter,” “band- Voltage gain is usually used to describe the operation of a elimination filter,” and “band-rejection filter.” small gain amplifier. In this type of an amplifier, the output signal voltage is larger than the input signal voltage. Power Typically, the width of the stop-band is less than 1 to 2 gain, on the other hand, is usually used to describe the decades (that is, the highest frequency attenuated is less than operation of large signal amplifiers. In the case of power gain 10 to 100 times the lowest frequency attenuated). In the audio amplifiers, the gain is not based on voltage but on watts. A band, a notch filter uses high and low frequencies that may power amplifier is an amplifier in which the output signal be only semitones apart.

power is greater than the input signal power. Most power amplifiers are used as the final stage of amplification and A band-stop filter is the general case. A notch filter is a specific drive the output device. The output device could be a flight type of band-stop filter with a very narrow range. Also called deck or cabin speaker, an indicator, or antenna. Whatever the band-elimination, band-reject, or notch filters, this kind of device, the power to make it work comes from the final stage filter passes all frequencies above and below a particular of amplification. Drivers for autopilot servos are sometimes range set by the component values. Not surprisingly, it can contained in line replaceable units (LRUs) called autopilot be made out of a low-pass and a high-pass filter, just like amplifiers. These units take the low signal commands from the band-pass design, except that this time we connect the the flight guidance system and amplify the signals to a level two filter sections in parallel with each other instead of in usable for driving the servo motors.

series. Figure 12-237 illustrates this type of circuit and the Classification The classification of a transistor amplifier circuit is determined by the percentage of the time that the current flows through the output circuit in relation to the input signal.

Voltage across C with Voltage across C with There are four classifications of operation: A, AB, B, and C.

1 1 large load circuit small load circuit Each class of operation has a certain use and characteristic.

No individual class of amplifiers is considered the best. The Figure 12-229. Half-wave and full-wave rectifier outputs using best use of an amplifier is a matter of proper selection for capacitor filter.

the particular operation desired.

L Load AC input R Rectifier Figure 12-230. An inductor used as a filter. Figure 12-231. Output of an inductor filter rectifier.

12-113 50 V C Load 150 V 150 V 50 V L-filter A 50 V Figure 12-233. Stacking diodes in a circuit.

C Load delivered to the output compared to the power supplied to the Inverted L-filter circuit. Every device in the circuit consumes power in order to operate. If the amplifier operates for 360° of input signal, B then it is using more power than if it was using only 180° of input signal. The more power consumed by the amplifier, the less there is available for the output signal. Usually the Class A amplifier is used where efficiency is of little concern and where fidelity in reproduction is desired.

Load C T-filter Class AB In the Class AB operation, the transistor current flows for more C than 50 percent but less than 100 percent of the input signal.

[Figure 12-239] Unlike the Class A amplifier, the output signal is distorted. A portion of the output circuit appears to be truncated. This is due to the lack of current through the transistor during this point of operation. When the emitter in this Load C C 1 2 case becomes positive enough, the transistor cannot conduct π-filter because the base to emitter junction is no longer forward biased. The input signal going positive beyond this point does D not produce any further output and the output remains level.

The Class AB amplifier has a better efficiency and a poorer fidelity than the Class A amplifier. These amplifiers are used Figure 12-232. LC filters.

when an exact reproduction of the input is not required but both the positive and negative portions of the input signals Class A need to be available on the output.

In the Class A operation, the current in the transistor flows for 100 percent or 360° of the input signal.

Class B [Figure 12-238] Class A operation is the least efficient class In Class B operation, the transistor current flows for only 50 of operation but provides the best fidelity. Fidelity simply percent of the input signal. [Figure 12-240] In this illustration, means that the output signal is a good reproduction of the the base-emitter bias does not allow the transistor to conduct input signal in all respects other than the amplitude, which is whenever the input signal is greater than zero. In this case, only amplified. In some cases, there may be some phase shifting the negative portion of the input signal is reproduced. Unlike between the input signal and the output signal. Typically, the rectifier, the Class B amplifier does not only reproduce half the phase difference is 180°. If the output signal is not a of the input signal, but it also amplifies it. Class B amplifiers good reproduction of the input signal, then the signal is said are twice as efficient as the Class A amplifier because the to be distorted. Distortion is any undesired change to the amplifying device only uses power for half of the input signal.

signal from the input to the output.

Class C The efficiency of an amplifier refers to the amount of power In Class C operations, transistor current flows for less than 50 percent of the input signal. [Figure 12-241] This class of 12-114 Methods of Coupling Coupling is used to transfer a signal from one stage on an amplifier to another stage. Regardless of whether an amplifier is a single stage or one in a series of stages, there must be a Load method for the signal to enter and leave the circuit. Coupling is the process of transferring the energy between circuits.

There are a number of ways for making this transfer and to Low-pass filter discuss these methods in detail goes beyond the scope of this handbook. However, four methods are listed below with a brief description of their operation.

Direct Coupling Direct coupling is the connection of the output of one stage Current directly to the input of the next stage. Direct coupling provides a good frequency response because no frequency-sensitive components, such as capacitors and inductors, are used. Yet Frequency this method is not used very often due to the complex power supply requirements and the impedance matching problems.

Frequency response RC Coupling Figure 12-234. Low-pass filter.

RC coupling is the most common method of coupling and operation is the most efficient. Because the transistor does not conduct except during a small portion of the input signal, this is the most efficient class of amplifier. The distortion of the Class C amplifier is greater (poor fidelity) than the Class A, AB, and B amplifiers because a small portion of the input Load signal is reproduced on the output. Class C amplifiers are used when the output signal is used for only small portions of time.

Band-pass filter Load Load Band-pass filter High-pass filter Current Current Frequency Frequency response Frequency Frequency response Figure 12-236. Band-pass filter.

Figure 12-235. High-pass filter.

12-115 uses a coupling capacitor and signal developing resistors. from one stage to the next. [Figure 12-244] The transformer [Figure 12-242] In this circuit, R1 acts as a load resistor action of T1 couples the signal from the first stage to the second for Q1 and develops the output signal for that stage. The stage. The primary coil of T1 acts as a load for the output of capacitor C1 blocks the DC bias signal and passes the AC the first stage while the secondary coil acts as the developing output signal. R2 then becomes the load over which the impedance for the second stage Q2. Transformer coupling is very passes AC signal is developed as an input to the base of Q2. efficient and the transformer can aid in impedance matching.

This arrangement allows for the bias voltage of each stage to be blocked, while the AC signal is passed to the next stage. Feedback Feedback occurs when a small portion of the output signal is Impedance Coupling sent back to the input signal to the amplifier. There are two types of feedback in amplifiers: Impedance coupling uses a coil as a load for the first stage but otherwise functions just as an RC coupling.

1. Positive (regenerative) [Figure 12-243] This method is similar to the RC coupling 2. Negative (degenerative) method. The difference is that R1 is replaced with inductor L1 as the output load. The amount of signal developed on the The main difference between these two signals is whether output load depends on the inductive reactance of the coil. In the feedback signal adds to the input signal or if the feedback order for the inductive reactance to be high, the inductance signal diminishes the input signal.

must be large; the frequency must be high or both. Therefore, load inductors should have relatively large amounts of When the feedback is positive, the signal being returned to inductance and are most effective at high frequencies.

the input is in phase with the input signal and thus interferes constructively. Figure 12-245 illustrates this concept applied Transformer Coupling in the amplified circuit through a block diagram. Notice Transformer coupling uses a transformer to couple the signal that the feedback signal is in phase with the input signal, which regenerates the input signal. This results in an output signal with amplitude greater than would have been without the constructive, positive feedback. This type of positive feedback is what causes an audio system to squeal.

Load Figure 12-245 also illustrates with a block diagram how negative or degenerative feedback occurs. In this case, the feedback signal is out of phase with the input signal. This causes destructive interference and degenerates the input Band-pass filter signal. The result is a lower amplitude output signal than would have occurred without the feedback.

Operational Amplifiers (OP AMP) An operational amplifier (OP AMP) is designed to be used Load with other circuit components and performs either computing functions or filtering. [Figure 12-246] Operational amplifiers are usually high-gain amplifiers with the amount of gain Band-pass filter governed by the amount of feedback.

Operational amplifiers were originally developed for analog computers and used to perform mathematical functions.

Today many devices use the operational amplifier for DC amplifiers, AC amplifiers, comparators, oscillators, and filter Current circuits. The widespread use is due to the fact that the OP AMP is a versatile device, small, and inexpensive. Built into the integrated chip, the operational amp is used as a basic Frequency building block of larger circuits.

Frequency response There are two inputs to the operational amplifier, inverting (−) and non-inverting (+), and there is one output. The polarity Figure 12-237. Band-stop filter.

12-116 + + V V CC CC − − NPN NPN Output Output Input Input − − V V EE EE Class A amplifier Class AB amplifier Figure 12-238. Simplified Class A amplifier circuit. Figure 12-239. Simplified Class AB amplifier circuit.

of a signal applied to the inverting input (−) is reversed at the output. A signal applied to the non-inverting (+) input retains its polarity on the output. To be classified as an operational + amplifier, the circuit must have certain characteristics: V CC 1. Very high gain 2. Very high input impedance − 3. Very high output impedance NPN Output This type of a circuit can be made up of discrete components, such as resistors and transistors. However, the most common form of an operational amplifier is found in the integrated circuit. This integrated circuit or chip contains the various Input stages of the operational amplifier and can be treated as if it were a single stage.

Applications − The number of applications for OP AMPs is too numerous to V EE detail in this handbook. However, the technician occasionally comes across these devices in modern aircraft and should be able to recognize their general purpose in a circuit. Some of Class B amplifier the basic applications are: 1. Go/no-go detectors Figure 12-240. Simplified Class B amplifier circuit.

2. Square wave circuits 5. Half-wave rectifier 3. Non-inverting amplifier 4. Inverting amplifier 12-117 Output Q2 C1 + V CC Q1 Input R1 R2 − Output V CC NPN RC coupled amplifier Figure 12-242. Simplified RC coupling circuit.

Input to the load is controlled by a variable inductance.

If an AC voltage is applied to the primary winding of an − iron core transformer, the iron core is magnetized and V EE demagnetized at the same frequency as that of the applied voltage. This, in turn, induces a voltage in the transformers secondary winding. The output voltage across the terminals Class C amplifier of the secondary depends on the relationship of the number of turns in the primary and the secondary of the transformer.

Figure 12-241. Simplified Class C amplifier circuit.

The iron core of the transformer has a saturation point Magnetic Amplifiers after which the application of a greater magnetic force Magnetic amplifiers do not amplify magnetism but use produces no change in the intensity of magnetization.

electromagnetism to amplify a signal. Essentially, the Hence, there is no change in transformer output, even if the magnetic amplifier is a power amplifier with a very limited input is greatly increased. The magnetic amplifier circuit frequency response. The frequency range most commonly in Figure 12-247 is used to explain how a simple magnetic associated with the magnetic amplifier is 100 Hz and less, amplifier functions.

which places it in the audio range. As a technical point, the 1. Assume that there is 1 ampere of current in coil A, magnetic amplifier is a low-frequency amplifier.

which has 10 turns of wire. If coil B has 10 turns of wire, an output of 1 ampere is obtained if coil B is Advantages of the magnetic amplifier are: properly loaded.

1. Very high efficiency, on the order of approximately 2. By applying direct current to coil C, the core of the 90 percent magnetic amplifier coil can be further magnetized.

2. High reliability Assume that coil C has the proper number of turns and, 3. Very rugged, able to withstand vibrations, moisture, upon the application of 30 milliamperes, that the core and overloads 4. No warm-up time Output Some of the disadvantages of the magnetic amplifier are: Q2 C1 1. Incapacity to handle low-voltage signals 2. Not usable in high-frequency applications Q1 Input L1 3. Time delay associated with magnetic affects V CC 4. Poor fidelity The basic operating principles of the magnetic amplifier are Impedance coupled amplifier fairly simple. Keep in mind that all amplifiers are current control devices. In this particular case, power that is delivered Figure 12-243. Simplified impedance coupling circuit.

12-118 is magnetized to the point where 1 ampere on coil A results in only 0.24 ampere output from coil B.

3. By making the DC input to coil C a continuous variable from 0 to 30 milliamperes and by maintaining an Input Output input of 1 ampere on coil A, it is possible to control the output of coil B to any point between 0.24 ampere and 1 ampere in this example.

Positive feedback The term “amplifier” is used for this arrangement because, by use of a few milliamperes, control of an output of 1 or more amperes is obtained.

Saturable-Core Reactor Input Output The same procedure can be used with the circuit shown in Figure 12-248 . A saturable-core reactor is a magnetic- core coil whose reactance is controlled by changing the permeability of the core. Varying the unidirectional flux Negative feedback controls the permeability of the core.

Figure 12-245. Feedback.

By controlling the extent of magnetization of the iron ring, it is possible to control the amount of current flowing to control such a source and use its variations to control the AC the load, since the amount of magnetization controls the output, it is necessary to include another DC winding that has impedance of the AC input winding. This type of magnetic a constant value. This winding, referred to as the reference amplifier is called a simple saturable reactor circuit.

winding, magnetizes the magnetic core in one direction.

Adding a rectifier to such a circuit would remove half the The DC control winding, acting in opposition to the reference cycle of the AC input and permit DC to flow to the load. The winding, either increases (degenerative) or decreases amount of DC flowing in the load circuit is controlled by a (regenerative) the magnetization of the core to change the DC control winding (sometimes referred to as bias). This type amount of current flowing through the load. This is essentially of magnetic amplifier is referred to as being self-saturating.

a basic preamplifier.

To use the full AC input power, a circuit such as that shown Logic Circuits in Figure 12-249 may be used. This circuit uses a full-wave Logic is considered the science of reasoning—the development bridge rectifier. The load receives a controlled DC by using of a reasonable conclusion based on known information.

the full AC input. This type of circuit is known as a self- Human reasoning tells us that certain propositions are true if saturating, full-wave magnetic amplifier.

certain conditions or premises are true. An annunciator being lit in the master warning panel is an example of a proposition, In Figure 12-250, it is assumed that the DC control winding which is either true or false. For example, predetermined and is supplied by a variable source, such as a sensing circuit. To designed conditions must be met in order for an annunciator in a master warning panel to be lit. A “LOW HYDRAULIC Output PRESS” annunciator may have a simple set of conditions that cause it to be illuminated. If the conditions are met, such as a hydraulic reservoir that is low on fluid causing the line Q2 T1 press to be low, then the logic is true and the annunciator lights. Several propositions, when combined, form a logical Q1 Input function. In the example above, the “LOW HYDRAULIC PRESS” annunciator is on if the LED is not burned out and V CC the hydraulic press is low or if the LED is not burned out and the annunciator test is being asserted.

Transformer coupled amplifier This section on logic circuits only serves as an introduction to the basic concepts. The technician encounters many Figure 12-244. Simplified transformer coupling circuit.

12-119 this handbook to cover digital logic systems due to the vast +V CC body of knowledge that it represents. However, this serves as an introduction and, in some limited cases, is useful in reading system block diagrams that use logic symbols to aid − the technician in understanding how a given circuit operates.

Inputs Output Logic Polarity + Electrical pulses can represent two logic conditions and any two differing voltages can be used for this purpose. For example, a positive voltage pulse could represent a true or 1 condition and a negative voltage pulse could then represent a −V EE false or 0 logic condition. The condition in which the voltage Power supply requirements changes to represent a true or 1 logic is known as the logic polarity. Logic circuits are usually divided into two broad classes: positive polarity and negative polarity. The voltage − levels used and a statement indicating the use of positive Inputs Output or negative logic is usually specified in the logic diagrams + provided by the original equipment manufacturers (OEMs).

Positive Input/output requirements When a signal that activates a circuit to a 1, true or high condition, has an electrical level that is relatively more positive than the other 0 or false condition, then the logic +V CC polarity is said to be positive. An example would be: Active State: 1 or True = +5 volts direct current (VDC) − 0 or False = −5 VDC Inputs Output Negative + When the signal that actives a circuit to a 1, true or high condition, has an electrical level that is relatively more negative than the other 0 or false condition, then the logic polarity is said to be negative. An example would be: −V EE Feedback Active State: 1 or True = 0 VDC 0 or False = +5 VDC Figure 12-246. Schematic symbol for the operational amplifier.

Pulse Structure situations or problems in everyday life that can be expressed Figure 12-251 illustrates the positive and negative pulse in an in some form of a logical function. Many problems and idealized form. In both forms, the pulse is composed of two situations can be condensed down to simple yes⁄no or edges—one being the leading edge and the other the trailing true⁄false statements that, if logically ordered, can filter edge. In the case of the positive pulse logic, the positive a problem down to a reasonable answer. The digital logic transition from a lower state to a higher state is the leading circuits are well suited for this task and have been employed edge and the trailing edge is the opposite. In the case of the in today’s integrated circuits found in virtually all of the negative logic pulse, the negative transition from a higher devices that we take for granted in modern aircraft. These state to a lower state is the leading edge while the rise from logical circuits are used to carry out the logical functions for the lower state back to the higher state is the trailing edge.

such things as navigation and communications. There are Figure 12-251 is considered an ideal pulse because the rise several fundamental elements that form the building blocks and fall times are instantaneous. In reality, these changes of the complex digital systems found in line replaceable take time, although in actual practice, the rise and fall can units (LRUs) and avionics card cages. The following is be assumed as instantaneous. Figure 12-252 shows the non- a very basic outline of what those elements are and what ideal pulse and its characteristics. The time required for a logic conditions they process. It is far beyond the scope of pulse to go from a low state to a high state is called the rise 12-120 state into the opposite state. In terms of a binary digit, this A B would be like converting a 1 to a 0 or a 0 to a 1. When a high voltage is applied to the inverter input, low voltage is the output. When a low voltage is applied to the input, a high voltage is on the output. This operation can be put into what is known as a logic or truth table. The standard logic symbol AC input AC output C is shown in Figure 12-253 . Figure 12-254 shows the possible logic states for this gate. This is the common symbol for an amplifier with a small circle on the output. This type of logic can also be considered a NOT gate.

The AND Gate DC The AND gate is made up of two or more inputs and a single output. The logic symbol is shown in Figure 12-255 . Inputs Figure 12-247. Magnetic amplifier circuit.

are on the left and the output is on the right in each of the depictions. Gates with two, three, and four inputs are shown; time, and the time required for the pulse to return to zero is however, any number of inputs can be used in the AND logic called the fall time. It is common practice to measure the rise as long as the number is greater than one. The operation of and fall time between 10 percent amplitude and 90 percent the AND gate is such that the output is high only when all amplitude. The reason for taking the measurements in these of the inputs are high. If any of the inputs are low, the output points is due to the non-linear shape of the pulse in the first is also low. Therefore, the basic purpose of an AND gate is 10 percent and final 90 percent of the rise and fall amplitudes.

to determine when certain conditions have been met at the The pulse width is defined as the duration of the pulse. To be same time. A high level on all inputs produces a high level more specific, it is the time between the 50 percent amplitude on the output. Figure 12-256 shows a simplified diagram of point on both the pulse rise and fall.

the AND logic with two switches and a light bulb. Notice that both switches need to be closed in order for the light bulb to Basic Logic Circuits turn on. Any other combination of switch positions is an open Boolean logic is a symbolic system used in representing the circuit and the light does not turn on. An example of AND truth value of statements. It is employed in the binary system logic could possibly be engage logic found in an autopilot. In used by digital computers primarily because the only truth this case, the autopilot would not be allowed to be engaged values (true and false) can be represented by the binary digits unless certain conditions are first met. Such conditions could 1 and 0. A circuit in computer memory can be open or closed, be: Vertical gyro is valid AND directional gyro is valid AND depending on the value assigned to it. The fundamental all autopilot control knobs are in detents AND servo circuits operations of Boolean logic, often called Boolean operators, are operational. Only when these conditions are met does the are “and,” “or,” and “not;” combinations of these make up 13 other Boolean operators. Six of these operators are discussed.

The Inverter Logic The inverter circuit performs a basic logic function called Load DC inversion. The purpose of the inverter is to convert one logic Load DC AC AC input Figure 12-248. Saturable CORE reactor circuit.

Figure 12-249. Self-saturating, full-wave magnetic amplifier.

12-121 The NOR Gate The term NOR is a combination of the NOT and OR and indicates an OR function with an inverted output. The standard logic symbol for a two-inputs NOR gate is shown DC in Figure 12-263 . Notice that an equivalent AND gate with Control Load an inverter is also shown. The logical operation of the NOR gate is such that a low output happens when any of its inputs are high. Only when all of its inputs are low is the output DC Ref high. The logic of this gate produces resultant outputs that are the opposite of the OR gate. In the NOR gate, the low output is the active output level. Figure 12-263 illustrates the logical operation of a two-input NOR gate for all of its possible combinations and the truth table.

Exclusive OR Gate AC The exclusive OR gate is a modified OR gate that produces a 1 output when only one of the inputs is a 1. The abbreviation often used is X-OR. It is different from the standard OR gate Figure 12-250. Basic preamplifier circuit.

in that when both inputs are a 1, then the output remains at a 0. The standard symbol and truth table for the X-OR gate autopilot engage. [Figure 12-257] are shown in Figure 12-264 .

The OR Gate Exclusive NOR Gate The OR gate has two or more inputs and one output and The exclusive NOR (X-NOR) gate is nothing more than an is normally represented by the standard logic symbol and X-OR gate with an inverted output. It produces a 1 output truth table. [Figure 12-258] Note that the OR gate can have when all inputs are 1s and also when all inputs are 0s. The any number of inputs as long as it is greater than one. The standard symbol is shown in Figure 12-265 .

operation of the OR gate is such that a high on any one of the inputs produces a high on the output. The only time that a The Integrated Circuit low is produced on the output is if there are no high levels on All of the logic functions so far discussed plus many other any input. Figure 12-259 is a simplified circuit that illustrates components are available in some form of an integrated the OR logic. The example used is a “DOOR UNSAFE” circuit. The digital systems found in today’s aircraft owe annunciator. Let’s say in this case that the plane has one their existence to a large extent to the design of the integrated cabin door and a baggage door. In order for the annunciator circuit (IC). In most cases, the IC has an advantage over the light on the master warning panel to extinguish, both doors use of discrete components in that they are smaller, consume must be closed and locked. If any one of the doors is not less power, are very reliable, and are inexpensive. The most secured properly, the baggage door OR the cabin door, then noticeable characteristic of the IC is its size and in comparison the “DOOR UNSAFE” annunciator illuminates. In this case, to the discrete semiconductor component, can easily be on two switches are in parallel with each other. If either one of the order of thousands of times smaller. [Figure 12-266]\ the two switches is closed, the light bulb lights up. The lamp is off only when both switches are open.

A monolithic integrated circuit is an electronic circuit that is constructed entirely on a single chip or wafer of The NAND Gate semiconductor material. All of the discrete components, The term NAND is a combination of the NOT-AND gate such as resistors, transistors, diodes, and capacitors, can and indicates an AND function with an inverted output. A be constructed on these small pieces of semiconductor standard logic symbol for a two input NAND gate is shown material and are an integral part of the chip. There are in Figure 12-260 . Notice that an equivalent AND gate with a number of levels of integration. Those levels are: an inverter is also shown. The logical operation of the NAND small-scale integration, medium-scale integration, large- gate is such that a low output occurs only if all inputs are high.

scale integration, and microprocessors. The small-scale If any of the inputs are low, the output is high. An example integration is considered the least complex design of of a two input NAND gate and its corresponding truth table the digital ICs. These ICs contain the basic components, are shown in Figure 12-261 .

such as the AND, OR, NOT, NOR and NAND gates.

[Figure 12-267] The medium-scale integration can contain 12-122 DC Generators High Theory of Operation Leading Trailing In the study of alternating current, basic generator principles edge edge were introduced to explain the generation of an AC voltage Low by a coil rotating in a magnetic field. Since this is the basis for all generator operation, it is necessary to review the Positive logic pulse principles of generation of electrical energy.

High When lines of magnetic force are cut by a conductor passing Leading Trailing through them, voltage is induced in the conductor. The edge edge strength of the induced voltage is dependent upon the speed of the conductor and the strength of the magnetic field. If Low the ends of the conductor are connected to form a complete Negative logic pulse circuit, a current is induced in the conductor. The conductor and the magnetic field make up an elementary generator.

Figure 12-251. Positive and negative pulse in an idealized form.

This simple generator is illustrated in Figure 12-269 , the same components as found in the small-scale design but together with the components of an external generator in larger numbers ranging from 12 to 100. The medium- scale designs are house circuits that are more complex, such as encoders, decoders, registers, counters, multiplexers, Input = 1 Output = 0 smaller memories, and arithmetic circuits. [Figure 12-268] (High) (Low) The large-scale integrated circuits contain even more logic gates, larger memories than the medium-scale circuits, and in some cases microprocessors.

Figure 12-253. Standard logic symbol.

Microprocessors Input Output The microprocessor is a device that can be programmed High Low to perform arithmetic and logical operations and other Low High functions in a preordered sequence. The microprocessor is usually used as the central processing unit (CPU) in today’s Figure 12-254. Possible logic states.

computer systems when it is connected to other components, such as memory chips and input/output circuits. The basic arrangement and design of the circuits residing in the microprocessor is called the architecture.

A X B A X B 90% 9 V C Pulse 50% 5 V amplitude (10 volts) A Pulse width 10% 1 V B Rise Fall X time time C Pulse characteristic from a databus D Figure 12-252. Non-ideal pulse and its characteristics.

Figure 12-255. AND gate logic symbol.

12-123 A B A f = A + B B + OR gate input/output A B f − 0 0 0 1 0 1 A B 0 1 1 1 1 1 + Truth table Figure 12-258. OR gate.

− of cutting is reduced. When the loop is vertical, no lines Figure 12-256. Simplified diagram of the AND logic.

of force are cut since the wires are momentarily traveling parallel to the magnetic lines of force, and there is no circuit which collect and use the energy produced by the induced voltage. As the rotation of the loop continues, the simple generator. The loop of wire [Figure 12-269A and B] number of lines of force cut increases until the loop has is arranged to rotate in a magnetic field. When the plane of rotated an additional 90° to a horizontal plane. As shown the loop of wire is parallel to the magnetic lines of force, in Figure 12-271 , the number of lines of force cut and the the voltage induced in the loop causes a current to flow in induced voltage once again are maximum. The direction the direction indicated by the arrows in Figure 12-269 . The of cutting, however, is in the opposite direction to that voltage induced at this position is maximum, since the wires occurring in Figures 12-269 and 12-270 , so the direction are cutting the lines of force at right angles, thus cutting (polarity) of the induced voltage is reversed. As rotation more lines of force per second than in any other position of the loop continues, the number of lines of force having relative to the magnetic field. As the loop approaches the been cut again decreases, and the induced voltage becomes vertical position shown in Figure 12-270 , the induced zero at the position shown in Figure 12-272 , since the wires voltage decreases because both sides of the loop (A and B) A and B are again parallel to the magnetic lines of force.

are approximately parallel to the lines of force and the rate If the voltage induced throughout the entire 360° of rotation Pitch servo valid +28 Roll servo valid +28 Ahrs +28 vdc Yaw damper valid +28 Trim servo valid +28 +28 vdc +28 vdc +28 vdc Attitude/heading +28 vdc Autopilot reference system Ahrs +28 vdc computer (Ahrs) +28 vdc +28 vdc (engage circuit) Attitude valid +28 +28 vdc Heading valid +28 +28 vdc When all input circuits are valid, +28 vdc Autopilot controller then the a/p can be engaged A/p controller Pitch wheel centered +28 vdc Autopilot Engage Logic Turn knob centered Figure 12-257. AND logic of system found in the aircraft wiring diagrams.

12-124 Cabin door secured 0 0 Light off 1 1 Door warn 0 1 Door unsafe Baggage door secured +28 VDC 1 1 1 0 0 1 Cabin door not secured NAND gate input/output Light on Door warn Door unsafe A B f Baggage door secured +28 VDC 0 0 1 1 0 1 0 1 1 Figure 12-259. Simplified circuit that illustrates OR logic.

1 1 0 NAND gate truth table is plotted, the curve shown in Figure 12-273 results. This voltage is called an alternating voltage because of its reversal Figure 12-261. Two input NAND gate and corresponding truth table.

from positive to negative value, first in one direction and then in the other.

DC generator (coil and commutator) are called an armature.

The generation of an emf by the loop rotating in the magnetic To use the voltage generated in the loop for producing a current field is the same for both AC and DC generators, but the action flow in an external circuit, some means must be provided to of the commutator produces a DC voltage.

connect the loop of wire in series with the external circuit.

Such an electrical connection can be effected by opening the Generation of a DC Voltage loop of wire and connecting its two ends to two metal rings, Figure 12-275 illustrates in an elementary, step-by-step called slip rings, against which two metal or carbon brushes manner, how a DC voltage is generated. This is accomplished ride. The brushes are connected to the external circuit. By by showing a single wire loop rotating through a series of replacing the slip rings of the basic AC generator with two positions within a magnetic field.

half cylinders, called a commutator, a basic DC generator is obtained. [Figure 12-274] In this illustration, the black side of Position A the coil is connected to the black segment, and the white side The loop starts in position A and is rotating clockwise.

of the coil to the white segment. The segments are insulated However, no lines of force are cut by the coil sides, from each other. The two stationary brushes are placed on which means that no emf is generated. The black brush is opposite sides of the commutator and are so mounted that each shown coming into contact with the black segment of the brush contacts each segment of the commutator as the latter commutator, and the white brush is just coming into contact revolves simultaneously with the loop. The rotating parts of a with the white segment.

A F A B f = A + B B NAND gate OR gate input/output A (1) (0) A B f F B 0 0 0 1 0 1 (0) (1) A F 0 1 1 B 1 1 1 Truth table Equivalent circuit NAND gate input/output Figure 12-262. Standard logic symbol for two inputs OR gate.

Figure 12-260. Standard logic symbol for two input NAND gate.

12-125 0 1 Position B 1 0 0 0 In position B, the flux is now being cut at a maximum rate, which means that the induced emf is maximum. At this time, 0 1 the black brush is contacting the black segment, and the 0 0 1 1 white brush is contacting the white segment. The deflection of the meter is toward the right, indicating the polarity of NOR gate input/output the output voltage.

A B f Position C 0 0 1 At position C, the loop has completed 180° of rotation. Like 0 1 0 position A, no flux lines are being cut and the output voltage 1 0 0 is zero. The important condition to observe at position C is 1 1 0 the action of the segments and brushes. The black brush at the NOR gate truth table 180° angle is contacting both black and white segments on one side of the commutator, and the white brush is contacting Figure 12-263. Logical operation of two-input NOR gate and truth both segments on the other side of the commutator. After the table.

T0 T1 T2 T3 T4 T5 T0 T1 T2 T3 T4 T4 0 1 0 0 1 A A 0 1 0 0 1 f f B A B f 0 0 0 1 1 B 0 0 0 0 1 1 1 0 1 1 1 0 X-OR gate input/output Truth table Figure 12-264. Standard symbol and truth table for X-OR gate.

T0 T1 T2 T3 T4 T0 T1 T2 T3 T4 0 1 0 1 A A 0 0 0 1 f = A + B f B A B f 0 0 1 1 B 0 0 1 0 1 0 1 0 0 1 1 1 X-NOR gate input/output Truth table Figure 12-265. Standard Symbol for X-NOR gate.

12-126 16 15 14 13 12 11 10 9 4Y 4A 4B GND 3A 3B 3Y 14 13 12 11 10 9 8 0.280" max 1 2 3 4 5 6 7 8 0.785" max 0.200" max Typical integrated logic circuit 1 2 3 4 5 6 7 Figure 12-266. Integrated circuit.

1Y 1A 1B VCC 2A 2B 2Y Quad exclusive-OR circuit loop rotates slightly past the 180° point, the black brush is contacting only the white segment, and the white brush is Input Output contacting only the black segment.

A Y B 0 0 0 Because of this switching of commutator elements, the 0 1 1 black brush is always in contact with the coil side moving 1 1 0 downward, and the white brush is always in contact with the coil side moving upward. Though the current actually reverses 1 0 1 its direction in the loop in exactly the same way as in the AC generator, commutator action causes the current to flow always Figure 12-267. Small-scale integration schematic form.

in the same direction through the external circuit or meter.

Position D 1Q 2Q 2Q Enable Gnd 3Q 3Q 4Q At position D, commutator action reverses the current in 16 15 14 13 12 11 10 9 the external circuit, and the second half cycle has the same waveform as the first half cycle. The process of commutation is sometimes called rectification, since rectification is the converting of AC voltage to DC voltage.

D Q Q D D Q Q D The Neutral Plane G G G G At the instant that each brush is contacting two segments on Q Q Q Q the commutator [ Figure 12-275A, C, and E ], a direct short circuit is produced. If an emf were generated in the loop at this time, a high current would flow in the circuit, causing an arc and thus damaging the commutator. For this reason, 1 2 3 4 5 6 7 8 the brushes must be placed in the exact position where the short occurs when the generated emf is zero. This position is 1Q 1D 2D Enable Vcc 3D 4D 4Q called the neutral plane. If the brushes are installed properly, D-register no sparking occurs between the brushes and the commutator.

Sparking is an indication of improper brush placement, which Figure 12-268. Medium-scale integration schematic form.

is the main cause of improper commutation.

is increased, the variation between maximum and minimum The voltage generated by the basic DC generator in values of voltage is reduced [Figure 12-276B] , and the output Figure 12-275 varies from zero to its maximum value twice voltage of the generator approaches a steady DC value. In for each revolution of the loop. This variation of DC voltage Figure 12-276A, the number of commutator segments is is called “ripple,” and may be reduced by using more loops, increased in direct proportion to the number of loops; that or coils, as shown in Figure 12-276A . As the number of loops 12-127 is, there are two segments for one loop, four segments for two loops, and eight segments for four loops.

The voltage induced in a single turn loop is small. Increasing the number of loops does not increase the maximum value A

N of generated voltage, but increasing the number of turns

in each loop increases this value. Within narrow limits, the output voltage of a DC generator is determined by the product of the number of turns per loop, the total flux per

B pair of poles in the machine, and the speed of rotation of the armature.

An AC generator, or alternator, and a DC generator are identical as far as the method of generating voltage in the rotating loop is concerned. However, if the current is taken from the loop by slip rings, it is an alternating current, and Figure 12-270. Inducing minimum voltage in an elementary generator.

the generator is called an AC generator, or alternator. If the current is collected by a commutator, it is direct current, and the generator is called a DC generator.

Construction Features of DC Generators Generators used on aircraft may differ somewhat in design, since various manufacturers make them. All, however, are of the same general construction and operate similarly. The major A

parts, or assemblies, of a DC generator are a field frame (or yoke), a rotating armature, and a brush assembly. The parts of a typical aircraft generator are shown in Figure 12-277 .

B Field Frame The field frame is also called the yoke, which is the foundation or frame for the generator. The frame has two functions: It completes the magnetic circuit between the poles and acts as a mechanical support for the other parts of the generator. In Figure 12-278A , the frame for a two-pole Figure 12-271. Inducing maximum voltage in the opposite direction.

generator is shown in a cross-sectional view. A four-pole generator frame is shown in Figure 12-278B .

Pole piece Armature B

B A

A Slip ring

Load Brush Figure 12-272. Inducing a minimum voltage in the opposite direction.

Figure 12-269. Inducing maximum voltage in an elementary generator.

12-128 Maximum + Voltage 360° 1 cycle 0° 90° 270° Minimum

S N

360° 180° Maximum – Voltage Figure 12-273. Output of an elementary generator.

In small generators, the frame is made of one piece of iron, but in larger generators, it is usually made up of two parts Figure 12-274. Basic DC generator.

bolted together. The frame has high magnetic properties and, together with the pole pieces, forms the major part of the exciting current, which is used to produce the magnetic field magnetic circuit. The field poles are bolted to the inside of and which flows through the field coils, is obtained from an the frame and form a core on which the field coil windings external source or from the generated DC of the machine.

are mounted. [Figure 12-278] No electrical connection exists between the windings of the field coils and the pole pieces.

The poles are usually laminated to reduce eddy current losses and serve the same purpose as the iron core of an Most field coils are connected so that the poles show electromagnet; that is, they concentrate the lines of force alternate polarity. Since there is always one North pole for produced by the field coils. The entire frame, including field each South pole, there must always be an even number of poles, is made from high-quality magnetic iron or sheet steel.

poles in any generator.

A practical DC generator uses electromagnets instead of Note that the pole pieces in Figure 12-278 project from the permanent magnets. To produce a magnetic field of the frame. Because air offers a great amount of reluctance to the necessary strength with permanent magnets would greatly magnetic field, this design reduces the length of the air gap increase the physical size of the generator.

between the poles and the rotating armature and increases the efficiency of the generator. When the pole pieces are made to The field coils are made up of many turns of insulated wire project they are called salient poles. [Figure 12-278] and are usually wound on a form that fits over the iron core of the pole to which it is securely fastened. [Figure 12-279] The A E B C D Induced EMF 1 Revolution Figure 12-275. Operation of a basic DC generator.

12-129 Armature the electrical contact between the armature coils and the external circuit. A flexible, braided copper conductor, The armature assembly of a generator consists of many commonly called a pigtail, connects each brush to the external armature coils wound on an iron core, a commutator, and circuit. The brushes, usually made of high-grade carbon and associated mechanical parts. These additional loops of wire held in place by brush holders insulated from the frame, are are actually called windings and are evenly spaced around free to slide up and down in their holders in order to follow the armature so that the distance between each winding is any irregularities in the surface of the commutator. The the same. Mounted on a shaft, it rotates through the magnetic brushes are usually adjustable so that the pressure of the field produced by the field coils. The core of the armature acts brushes on the commutator can be varied and the position as an iron conductor in the magnetic field and, for this reason, of the brushes with respect to the segments can be adjusted.

is laminated to prevent the circulation of eddy currents.

The constant making and breaking of connections to the coils Gramme-Ring Armature in which a voltage is being induced necessitates the use of There are two general kinds of armatures: the ring and the material for brushes, which has a definite contact resistance.

drum. Figure 12-280 shows a ring-type armature made up of Also, this material must be such that the friction between the an iron core, an eight-section winding, and an eight-segment commutator and the brush is low, to prevent excessive wear.

commutator. The disadvantage of this arrangement is that For these reasons, the material commonly used for brushes is the windings, located on the inner side of the iron ring, cut high-grade carbon. The carbon must be soft enough to prevent few lines of flux. As a result, they have very little voltage undue wear of the commutator and yet hard enough to provide induced in them. For this reason, the Gramme ring armature reasonable brush life. Since the contact resistance of carbon is not widely used.

is fairly high, the brush must be quite large to provide a large area of contact. The commutator surface is highly polished to Drum-Type Armature reduce friction as much as possible. Oil or grease must never A drum-type armature is shown in Figure 12-281 . The be used on a commutator, and extreme care must be used armature core is in the shape of a drum and has slots cut into when cleaning it to avoid marring or scratching the surface.

it where the armature windings are placed. The advantage is that each winding completely surrounds the core so that the entire length of the conductor cuts through the magnetic flux.

The total induced voltage in this arrangement is far greater than that of the Gramme ring-type armature.

Drum-type armatures are usually constructed in one of two methods: lap winding and the wave winding. Each

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method having its own advantage. Lap windings are used in generators that are designed for high current. The windings are connected in parallel paths and for this reason require several brushes. The wave winding is used in generators that A are designed for high voltage outputs. The two ends of each coil are connected to commutator segments separated by the A B C D E distance between poles. This results in a series arrangement of the coils and is additive of all the induced voltages.

Commutators Induced EMF Figure 12-282 shows a cross-sectional view of a typical 0 1/4 1/2 3/4 1 commutator. The commutator is located at the end of an Revolutions armature and consists of wedge shaped segments of hard drawn B copper, insulated from each other by thin sheets of mica. The segments are held in place by steel V-rings or clamping flanges fitted with bolts. Rings of mica insulate the segments from the Figure 12-276. Increasing the number of coils reduces the ripple in the voltage.

flanges. The raised portion of each segment is called a riser, and the leads from the armature coils are soldered to the risers.

When the segments have no risers, the leads are soldered to short slits in the ends of the segments.

The brushes ride on the surface of the commutator, forming 12-130 or plane of commutation. The neutral plane is the position Armature Reaction where the plane of the two opposite coils is perpendicular Current flowing through the armature sets up electromagnetic to the magnetic field in the generator. On a few generators, fields in the windings. These new fields tend to distort or the brushes can be shifted manually ahead of the normal bend the magnetic flux between the poles of the generator neutral plane to the neutral plane caused by field distortion.

from a straight-line path. Since armature current increases On nonadjustable brush generators, the manufacturer sets with load, the distortion becomes greater with an increase in the brushes for minimum sparking.

load. This distortion of the magnetic field is called armature reaction. [Figure 12-283] Compensating windings or interpoles may be used to counteract some of the effects of field distortion, since Armature windings of a generator are spaced so that, during shifting the brushes is inconvenient and unsatisfactory, rotation of the armature, there are certain positions when the especially when the speed and load of the generator are brushes contact two adjacent segments, thereby shorting the changing constantly.

armature windings to these segments. When the magnetic field is not distorted, there is usually no voltage being Compensating Windings induced in the shorted windings, and therefore no harmful The compensating windings consist of a series of coils results occur from the shorting of the windings. However, embedded in slots in the pole faces. These coils are also when the field is distorted, a voltage is induced in these connected in series with the armature. Consequently, this series shorted windings, and sparking takes place between the connection with the armature produces a magnetic field in the brushes and the commutator segments. Consequently, the compensating windings that varies directly with the armature commutator becomes pitted, the wear on the brushes becomes current. The compensating windings are wound in such a excessive, and the output of the generator is reduced. To manner that the magnetic field produced by them counteracts correct this condition, the brushes are set so that the plane of the magnetic field produced by the armature. As a result, the the coils, which are shorted by the brushes, is perpendicular neutral plane remains stationary any magnitude of armature to the distorted magnetic field, which is accomplished by current. With this design, once the brushes are set correctly, moving the brushes forward in the direction of rotation. This they do not need to be moved again. Figure 12-284A illustrates operation is called shifting the brushes to the neutral plane how the windings are set into the pole faces.

Sealed ball bearings Connector ligs Field frame Drive end frame Air scoop Brush connector bars Commutator Steel ring Drive shaft Commutator end frame Brush and holder Field winding Screw Pole shoe Field frame Armature Drive end Figure 12-277. Typical 24-volt aircraft generator.

12-131 Flux Frame N S Pole Field winding Figure 12-279. A field coil removed from a field pole.

A the generator; therefore, field distortion is reduced by the interpoles, and the efficiency, output, and service life of the Frame Flux brushes are improved.

S Types of DC Generators There are three types of DC generators: series wound, shunt N N wound, and shunt series or compound wound. The difference in type depends on the relationship of the field winding to S Pole the external circuit.

Series Wound DC Generators Field winding The field winding of a series generator is connected in series with the external circuit called the load. [Figure 12-285] The field coils are composed of a few turns of large wire; the magnetic field strength depends more on the current flow rather B than the number of turns in the coil. Series generators have very poor voltage regulation under changing load, since the greater Figure 12-278. A two-pole and a four-pole frame assembly.

the current through the field coils to the external circuit, the greater the induced emf and the greater the terminal or output voltage. Therefore, when the load is increased, the voltage Interpoles increases; likewise, when the load is decreased, the voltage An interpole is a pole placed between the main poles of a generator. An example of interpole placement is shown in Figure 12-284B . This is a simple two-pole generator with two interpoles.

An interpole has the same polarity as the next main pole in the direction of rotation. The magnetic flux produced by an interpole causes the current in the armature to change

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direction as an armature winding passes under it. This cancels the electromagnetic fields about the armature windings. The magnetic strength of the interpoles varies with the load on the generator; and since field distortion varies with the load, the magnetic field of the interpoles counteracts the effects of the field set up around the armature windings and minimizes field distortion. Thus, the interpole tends to keep the neutral plane in the same position for all loads on Figure 12-280. An eight-section, ring-type armature.

12-132 fluctuating loads. Any increase in load causes a decrease in the terminal or output voltage, and any decrease in load Commutator Slots causes an increase in terminal voltage; since the armature and the load are connected in series, all current flowing in the external circuit passes through the armature winding.

Because of the resistance in the armature winding, there is a voltage drop (IR drop = current × resistance). As the load increases, the armature current increases and the IR drop in Shaft the armature increases. The voltage delivered to the terminals Coils is the difference between the induced voltage and the voltage drop; therefore, there is a decrease in terminal voltage. This Figure 12-281. A drum-type armature.

decrease in voltage causes a decrease in field strength, because the current in the field coils decreases in proportion decreases. The output voltage of a series wound generator to the decrease in terminal voltage; with a weaker field, the may be controlled by a rheostat in parallel with the field voltage is further decreased. When the load decreases, the windings. [Figure 12-285A] Since the series wound generator output voltage increases accordingly, and a larger current has such poor regulation, it is never employed as an airplane flows in the windings. This action is cumulative, so the output generator. Generators in airplanes have field windings, which voltage continues to rise to a point called field saturation, are connected either in shunt or in compound.

after which there is no further increase in output voltage.

Shunt Wound DC Generators The terminal voltage of a shunt generator can be controlled A generator having a field winding connected in parallel by means of a rheostat inserted in series with the field with the external circuit is called a shunt generator.

windings. [Figure 12-286A] As the resistance is increased, [Figure 12-286A and B] The field coils of a shunt generator the field current is reduced; consequently, the generated contain many turns of small wire; the magnetic strength voltage is reduced also. For a given setting of the field is derived from the large number of turns rather than the rheostat, the terminal voltage at the armature brushes is current strength through the coils. If a constant voltage is approximately equal to the generated voltage minus the IR desired, the shunt wound generator is not suitable for rapidly Tightening nut Iron ring Mica V-ring Front V-ring Commutator bars Commutator bar Mica Mica insulation between bars Iron shell Back V-ring with mica inner and outer rings for insulation Slots Figure 12-282. Commutator with portion removed to show construction.

12-133 drop produced by the load current in the armature; thus, the voltage at the terminals of the generator drops as the load is If the ampere turns of the series field act in the same direction applied. Certain voltage sensitive devices are available that as those of the shunt field, the combined magnetomotive force automatically adjust the field rheostat to compensate for is equal to the sum of the series and shunt field components.

variations in load. When these devices are used, the terminal Load is added to a compound generator in the same manner voltage remains essentially constant. in which load is added to a shunt generator, by increasing Compound Wound DC Generators the number of parallel paths across the generator terminals.

Thus, the decrease in total load resistance with added load A compound wound generator combines a series winding is accompanied by an increase in armature circuit and series and a shunt winding in such a way that the characteristics field circuit current. The effect of the additive series field is of each are used to advantage. The series field coils are that of increased field flux with increased load. The extent of made of a relatively small number of turns of large copper the increased field flux depends on the degree of saturation conductor, either circular or rectangular in cross section, and of the field as determined by the shunt field current. Thus, the are connected in series with the armature circuit. These coils terminal voltage of the generator may increase or decrease with are mounted on the same poles on which the shunt field coils load, depending on the influence of the series field coils. This are mounted and, therefore, contribute a magnetomotive influence is referred to as the degree of compounding. A flat force which influences the main field flux of the generator.

compound generator is one in which the no load and full load A diagrammatic and a schematic illustration of a compound voltages have the same value; whereas an under compound wound generator is shown in Figure 12-287A and B .

generator has a full load voltage less than the no load value, and an over compound generator has a full load voltage which a n is higher than the no load value. Changes in terminal voltage o Neutral plane t i a t o R + + + + with increasing load depend upon the degree of compounding.

If the series field aids the shunt field, the generator is said

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the shunt field, the machine is said to be differentially compounded or is called a differential generator. Compound generators are usually designed to be overcompounded.

b This feature permits varied degrees of compounding by A Field excited, armature unexcited connecting a variable shunt across the series field. Such a n o i t shunt is sometimes called a diverter. Compound generators a t S o R are used where voltage regulation is of prime importance.

+ + + + Differential generators have somewhat the same characteristics + as series generators in that they are essentially constant + + current generators. However, they generate rated voltage at + no load, the voltage dropping materially as the load current + + + increases. Constant current generators are ideally suited as power sources for electric arc welders and are used almost N universally in electric arc welding.

B Armature excited, field unexcited a If the shunt field of a compound generator is connected across + + + + both the armature and the series field, it is known as a long + + shunt connection, but if the shunt field is connected across + the armature alone, it is called a short shunt connection.

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These connections produce essentially the same generator + + characteristics. A summary of the characteristics of the various + + + types of generators discussed is shown in Figure 12-288 .

+ + n o i t a t o R b Generator Ratings C Both field and armature excited A generator is rated in power output. Since a generator is designed to operate at a specified voltage, the rating usually is given as the number of amperes the generator can safely Figure 12-283. Armature reaction.

12-134 Armature windings A Compensating Compensating windings windings Field rheostat − + − + − + − + − + − + − − + + − + − + + − − + − + + −

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− + + Load Generator Compensating A B Field coils Main field windings Interpole windings To load Arm S − Main field S N windings + Figure 12-285. Diagram and schematic of a series wound generator.

N External load Interpole which they begin to produce their normal voltage. Termed windings the “coming in” speed, it is usually about 1,500 rpm.

Generator Generator Terminals On most large 24-volt generators, electrical connections Interpole B are made to terminals marked B, A, and E. The positive armature lead in the generator connects to the B terminal.

Figure 12-284. Simple two-pole generator with two interpoles.

The negative armature lead connects to the E terminal. The positive end of the shunt field winding connects to terminal A, supply at its rated voltage. Generator rating and performance and the opposite end connects to the negative terminal brush.

data are stamped on the nameplate attached to the generator.

Terminal A receives current from the negative generator brush When replacing a generator, it is important to choose one of through the shunt field winding. This current passes through the proper rating.

the voltage regulator and back to the armature through the positive brush. Load current, which leaves the armature The rotation of generators is termed either clockwise or through the negative brushes, comes out of the E lead and counterclockwise, as viewed from the driven end. Usually, passes through the load before returning to the armature the direction of rotation is stamped on the data plate. If through the positive brushes.

no direction is stamped on the plate, the rotation may be marked by an arrow on the cover plate of the brush housing.

DC Generator Maintenance It is important that a generator with the correct direction of Inspection rotation be used; otherwise, the voltage is reversed.

The following information about the inspection and maintenance of DC generator systems is general in nature The speed of an aircraft engine varies from idle rpm to takeoff because of the large number of differing aircraft generator rpm; however, during the major portion of a flight, it is at a systems. These procedures are for familiarization only.

constant cruising speed. The generator drive is usually geared Always follow the applicable manufacturer’s instructions 1 1 to revolve the generator between 1 ⁄ 8 and 1 ⁄ 2 times the engine for a given generator system.

crankshaft speed. Most aircraft generators have a speed at 12-135 of No. 000, or finer, sandpaper under the brush, rough side out. [Figure 12-289] Pull the sandpaper in the direction A of armature rotation, being careful to keep the ends of the sandpaper as close to the slip ring or commutator surface as possible in order to avoid rounding the edges of the brush.

When pulling the sandpaper back to the starting point, raise the brush so it does not ride on the sandpaper. Sand the brush only in the direction of rotation.

Field rheostat After the generator has run for a short period, brushes should be inspected to make sure that pieces of sand have not become − embedded in the brush and are collecting copper.

Load Under no circumstances should emery cloth or similar

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abrasives be used for seating brushes (or smoothing + commutators), since they contain conductive materials that cause arcing between brushes and commutator bars.

Shunt circuit Main circuit Excessive pressure causes rapid wear of brushes. Too B little pressure, however, allows “bouncing” of the brushes, resulting in burned and pitted surfaces.

Arm To load Field coils A carbon, graphite, or light metalized brush should exert a 1 1 pressure of 1 ⁄ 2 to 2 ⁄ 2 psi on the commutator. The pressure recommended by the manufacturer should be checked by the use of a spring scale graduated in ounces. Brush spring Figure 12-286. Shunt wound generator.

In general, the inspection of the generator installed in the A aircraft should include the following items: 1. Security of generator mounting 2. Condition of electrical connections 3. Dirt and oil in the generator—if oil is present, check − engine oil seal. Blow out dirt with compressed air.

4. Condition of generator brushes

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5. Generator operation + Load 6. Voltage regulator operation Condition of Generator Brushes Sparking of brushes quickly reduces the effective brush area Series field coil B in contact with the commutator bars. The degree of such Shunt sparking should be determined. Excessive wear warrants a field detailed inspection.

To load coil The following information pertains to brush seating, brush Arm pressure, high mica condition, and brush wear. Manufacturers usually recommend the following procedures to seat brushes Compound wound that do not make good contact with slip rings or commutators.

Figure 12-287. Compound wound generator.

Lift the brush sufficiently to permit the insertion of a strip 12-136 tension is usually adjusted between 32 to 36 ounces; however, armature has been turned on a lathe, carefully undercut the the tension may differ slightly for each specific generator. mica insulation to a depth equal to the width of the mica, or approximately 1.20 inch.

When a spring scale is used, the measurement of the pressure that a brush exerts on the commutator is read directly on the Each brush should be a specified length to work properly.

scale. The scale is applied at the point of contact between the If a brush is too short, the contact it makes with the spring arm and the top of the brush, with the brush installed commutator will be faulty, which can also reduce the spring in the guide. The scale is drawn up until the arm just lifts force holding the brush in place. Most manufacturers specify off the brush surface. At this instant, the force on the scale the amount of wear permissible from a new brush length.

should be read. When a brush has worn to the minimum length permissible, it must be replaced.

Flexible low resistance pigtails are provided on most heavy current carrying brushes, and their connections should be Some special generator brushes should not be replaced securely made and checked at frequent intervals. The pigtails because of a slight grooving on the face of the brush. These should never be permitted to alter or restrict the free motion grooves are normal and will appear in AC and DC generator of the brush. brushes which are installed in some models of aircraft generators. These brushes have two cores made of a harder The purpose of the pigtail is to conduct the current, rather material with a higher expansion rate than the material used than subjecting the brush spring to currents that would alter in the main body of the brush. Usually, the main body of its spring action by overheating. The pigtails also eliminate the brush face rides on the commutator. However, at certain any possible sparking to the brush guides caused by the temperatures, the cores extend and wear through any film movement of the brushes within the holder, thus minimizing on the commutator.

side wear of the brush.

DC Motors Carbon dust resulting from brush sanding should be Most devices in an airplane, from the starter [Figure 12-290] thoroughly cleaned from all parts of the generators after a to the automatic pilot, depend upon mechanical energy sanding operation. Such carbon dust has been the cause of furnished by DC motors. A DC motor is a rotating machine, several serious fires, as well as costly damage to the generator.

which transforms DC energy into mechanical energy. It consists of two principal parts—a field assembly and an Operation over extended periods of time often results in armature assembly. The armature is the rotating part in which the mica insulation between commutator bars protruding current carrying wires are acted upon by the magnetic field.

above the surface of the bars. This condition is called “high mica” and interferes with the contact of the brushes to Whenever a current carrying wire is placed in the field of a magnet, a force acts on the wire. The force is not one of attraction or repulsion; however, it is at right angles to the t i v e c o m m u l a p o u n d C u i n g wire and also at right angles to the magnetic field set up by the magnet. The action of the force upon a current carrying S h u n t c o n n 100% e c t i o n D wire placed in a magnetic field is shown in Figure 12-291 .

i f f e r e n t i a A wire is located between two permanent magnets. The lines l c o m p o of force in the magnetic field are from the North pole to the u n d i n g South pole. When no current flows, no force is exerted on the n o i wire, but when current flows through the wire, a magnetic t c e n n field is set up about it. [Figure 12-291] The direction of the o c s e i field depends on the direction of current flow. Current in one r Output voltage e S direction creates a clockwise field about the wire, and current in the other direction, a counterclockwise field.

Since the current carrying wire produces a magnetic field, Output current or load 0 100% a reaction occurs between the field about the wire and the magnetic field between the magnets. When the current flows Figure 12-288. Generator characteristics.

the commutator. Whenever this condition exists, or if the 12-137 in a direction to create a counterclockwise magnetic field counterclockwise in the other, as shown. The fields reinforce about the wire, this field and the field between the magnets each other between the wires, and the wires are forced in the add or reinforce at the bottom of the wire because the lines direction of the weaker field, away from each other. This of force are in the same direction. At the top of the wire, force is one of repulsion.

they subtract or neutralize, since the lines of force in the two fields are opposite in direction. Thus, the resulting field at the To summarize: conductors carrying current in the same bottom is strong and the one at the top is weak. Consequently, direction tend to be drawn together; conductors carrying current the wire is pushed upward. [Figure 12-291C] The wire is in opposite directions tend to be repelled from each other.

Developing Torque always pushed away from the side where the field is strongest.

If current flow through the wire were reversed in direction, If a coil in which current is flowing is placed in a magnetic the two fields would add at the top and subtract at the bottom. field, a force is produced which causes the coil to rotate. In Since a wire is always pushed away from the strong field, the coil shown in Figure 12-293 , current flows inward on the wire would be pushed down. side A and outward on side B. The magnetic field about B is clockwise and that about A, counterclockwise. As previously Force Between Parallel Conductors explained, a force develops which pushes side B downward.

Two wires carrying current in the vicinity of one another exert At the same time, the field of the magnets and the field a force on each other because of their magnetic fields. An about A, in which the current is inward, adds at the bottom end view of two conductors is shown in Figure 12-292 . In and subtracts at the top. Therefore, A moves upward. The Figure 12-292A , electron flow in both conductors is toward coil rotates until its plane is perpendicular to the magnetic the reader, and the magnetic fields are clockwise around the lines between the North and South poles of the magnet, as conductors. Between the wires, the fields cancel because the indicated in Figure 12-293 by the white coil at right angles directions of the two fields oppose each other. The wires are to the black coil.

forced in the direction of the weaker field, toward each other.

This force is one of attraction. In Figure 12-292B , the electron The tendency of a force to produce rotation is called torque.

flow in the two wires is in opposite directions. When the steering wheel of a car is turned, torque is applied.

The engine of an airplane gives torque to the propeller. Torque The magnetic fields are, therefore, clockwise in one and is developed also by the reacting magnetic fields about the current carrying coil just described. This is the torque, which turns the coil.

The right-hand motor rule can be used to determine the direction a current carrying wire moves in a magnetic field.

As illustrated in Figure 12-294 , if the index finger of the right hand is pointed in the direction of the magnetic field and the second finger in the direction of current flow, the Unseated brush thumb indicates the direction the current carrying wire moves.

The amount of torque developed in a coil depends upon several factors: the strength of the magnetic field, the number of turns in the coil, and the position of the coil in the field. Magnets are 1 1 / 32 " to / 16 " made of special steel that produces a strong field. Since there is torque acting on each turn, the greater the number of turns on the coil, the greater the torque. In a coil carrying a steady 000 sandpaper (sand side next to brush) current located in a uniform magnetic field, the torque varies at successive positions of rotation. [Figure 12-295] When the plane of the coil is parallel to the lines of force, the torque is zero. When its plane cuts the lines of force at right angles, the torque is 100 percent. At intermediate positions, the torque ranges between 0 and 100 percent.

Basic DC Motor Properly seated brush A coil of wire through which the current flows rotates when placed in a magnetic field. This is the technical basis governing Figure 12-289. Seating brushes with sandpaper.

the construction of a DC motor. [Figure 12-296] However, 12-138 if the connecting wires from the battery were permanently fastened to the terminals of the coil and there was a flow of current, the coil would rotate only until it lined itself up with the magnetic field. Then, it would stop, because the torque at that point would be 0.

A motor, of course, must continue rotating. It is therefore necessary to design a device that reverses the current in the coil just at the time the coil becomes parallel to the lines of force. This creates torque again and causes the coil to rotate.

If the current reversing device is set up to reverse the current each time the coil is about to stop, the coil can be made to Figure 12-290. DC series starter motor.

continue rotating as long as desired.

One method of doing this is to connect the circuit so that, as Position B the coil rotates, each contact slides off the terminal to which it When the coil has rotated 90° to the position shown connects and slides onto the terminal of opposite polarity. In in Figure 12-296B , segments A and B of the commutator no other words, the coil contacts switch terminals continuously longer make contact with the battery circuit and no current as the coil rotates, preserving the torque and keeping the can flow through the coil. At this position, the torque has coil rotating. In Figure 12-296 , the coil terminal segments reached a minimum value, since a minimum number of lines are labeled A and B. As the coil rotates, the segments slide of force are being cut. However, the momentum of the coil onto and past the fixed terminals or brushes. With this carries it beyond this position until the segments again make arrangement, the direction of current in the side of the coil contact with the brushes, and current again enters the coil; next to the North-seeking pole flows toward the reader, and this time, though, it enters through segment A and leaves the force acting on that side of the coil turns it downward.

through segment B. However, since the positions of segments The part of the motor that changes the current from one wire A and B have also been reversed, the effect of the current is to another is called the commutator.

as before, the torque acts in the same direction, and the coil continues its counterclockwise rotation.

Position A When the coil is positioned as shown in Figure 12-296A , Position C current flows from the negative terminal of the battery to the On passing through the position shown in Figure 12-296C , negative (−) brush, to segment B of the commutator, through the torque again reaches maximum.

the loop to segment A of the commutator, to the positive (+) brush, and then back to the positive terminal of the battery.

Position D By using the right-hand motor rule, it is seen that the coil Continued rotation carries the coil again to a position of rotates counterclockwise. The torque at this position of the minimum torque as in Figure 12-296D . At this position, the coil is maximum, since the greatest number of lines of force brushes no longer carry current, but once more the momentum is being cut by the coil.

rotates the coil to the point where current enters through A B C Wire without current located Wire with current and Resultant field and in a magnetic field accompanying field direction of force on wire Figure 12-291. Force on a current carrying wire.

12-139 segment B and leaves through A. Further rotation brings the DC Motor Construction coil to the starting point and, thus, one revolution is completed.

The major parts in a practical motor are the armature assembly, the field assembly, the brush assembly, and the The switching of the coil terminals from the positive to the end frame. [Figure 12-297] negative brushes occurs twice per revolution of the coil.

Armature Assembly The torque in a motor containing only a single coil is neither The armature assembly contains a laminated, soft-iron core, continuous nor very effective, for there are two positions coils, and a commutator, all mounted on a rotatable steel shaft.

where there is actually no torque at all. To overcome this, a Laminations made of stacks of soft iron, insulated from each practical DC motor contains a large number of coils wound on other, form the armature core. Solid iron is not used, since a the armature. These coils are so spaced that, for any position solid iron core revolving in the magnetic field would heat and of the armature, there are coils near the poles of the magnet.

use energy needlessly. The armature windings are insulated This makes the torque both continuous and strong. The copper wire, which are inserted in slots insulated with fiber commutator, likewise, contains a large number of segments paper (fish paper) to protect the windings. The ends of the instead of only two.

windings are connected to the commutator segments. Wedges or steel bands hold the windings in place to prevent them The armature in a practical motor is not placed between from flying out of the slots when the armature is rotating at the poles of a permanent magnet but between those of an high speeds. The commutator consists of a large number of electromagnet, since a much stronger magnetic field can be copper segments insulated from each other and the armature furnished. The core is usually made of a mild or annealed shaft by pieces of mica. Insulated wedge rings hold the steel, which can be magnetized strongly by induction. The segments in place.

current magnetizing the electromagnet is from the same source that supplies the current to the armature.

Magnetic field Torque Direction of current A

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B A Figure 12-293. Developing a torque.

Motion Magnetic flux + Current B Figure 12-294. Right-hand motor rule.

Figure 12-292. Fields surrounding parallel conductors.

12-140 Field Assembly A The field assembly consists of the field frame, the pole pieces, Torque and the field coils. The field frame is located along the inner wall of the motor housing. It contains laminated, soft-steel pole pieces on which the field coils are wound. A coil, consisting of several turns of insulated wire, fits over each pole piece and,

together with the pole, constitutes a field pole. Some motors have as few as two poles, others as many as eight.

Brush Brush Assembly The brush assembly consists of the brushes and their holders.

A B The brushes are usually small blocks of graphitic carbon, since this material has a long service life and also causes minimum wear to the commutator. The holders permit some play in the No torque B brushes so they can follow any irregularities in the surface of the commutator and make good contact. Springs hold the brushes firmly against the commutator. [Figure 12-298] End Frame B

The end frame is the part of the motor opposite the commutator. Usually, the end frame is designed so that it can be connected to the unit to be driven. The bearing for the drive end is also located in the end frame. Sometimes the end A frame is made a part of the unit driven by the motor. When this is done, the bearing on the drive end may be located in any one of a number of places.

Types of DC Motors C There are three basic types of DC motors: series motors, shunt Torque motors, and compound motors. They differ largely in the method in which their field and armature coils are connected.

Series DC Motor

In the series motor, the field windings, consisting of a relatively few turns of heavy wire, are connected in series with the armature winding. Both a diagrammatic and a schematic illustration of a series motor are shown in B A Figure 12-299 . The same current flowing through the field winding also flows through the armature winding. Any increase in current, therefore, strengthens the magnetism of No torque D Zero torque S 71% A

100% N

90° N 45° 0° B Figure 12-296. Basic DC motor operation.

Figure 12-295. Torque on a coil at various angles of rotation.

12-141 both the field and the armature. and load characteristics of the cumulative compound motor are somewhere between those of the series and those of the Because of the low resistance in the windings, the series shunt motor.

motor is able to draw a large current in starting. This starting current, in passing through both the field and armature Because of the series field, the cumulative compound motor windings, produces a high starting torque, which is the series has a higher starting torque than a shunt motor. Cumulative motor’s principal advantage. compound motors are used in driving machines, which are subject to sudden changes in load. They are also used where a The speed of a series motor is dependent upon the load. Any high starting torque is desired, but a series motor cannot be change in load is accompanied by a substantial change in used easily.

speed. A series motor runs at high speed when it has a light load and at low speed with a heavy load. If the load is removed In the differential compound motor, an increase in load entirely, the motor may operate at such a high speed that the creates an increase in current and a decrease in total flux in armature falls apart. If high starting torque is needed under this type of motor. These two tend to offset each other and heavy load conditions, series motors have many applications. the result is a practically constant speed. However, since an Series motors are often used in aircraft as engine starters and for increase in load tends to decrease the field strength, the speed raising and lowering landing gears, cowl flaps, and wing flaps. characteristic becomes unstable. Rarely is this type of motor used in aircraft systems.

Shunt DC Motor A graph of the variation in speed with changes of load of In the shunt motor, the field winding is connected in parallel or in shunt with the armature winding. [Figure 12-300] The the various types of DC motors is shown in Figure 12-302 .

resistance in the field winding is high. Since the field winding Counter Electromotive Force (emf) is connected directly across the power supply, the current through the field is constant. The field current does not vary The armature resistance of a small, 28-volt DC motor with motor speed, as in the series motor and, therefore, the is extremely low, about 0.1 ohm. When the armature is torque of the shunt motor varies only with the current through connected across the 28-volt source, current through the the armature. The torque developed at starting is less than armature is apparently: that developed by a series motor of equal size.

E 28 I = = = 280 amperes R 0.1 The speed of the shunt motor varies very little with changes in load. When all load is removed, it assumes a speed slightly This high value of current flow is not only impracticable but higher than the loaded speed. This motor is particularly also unreasonable, especially when the current drain, during suitable for use when constant speed is desired and when normal operation of a motor, is found to be about 4 amperes.

high starting torque is not needed.

This is because the current through a motor armature during operation is determined by more factors than ohmic resistance.

Compound DC Motor The compound motor is a combination of the series and shunt When the armature in a motor rotates in a magnetic field, a motors. There are two windings in the field: a shunt winding voltage is induced in its windings. This voltage is called the and a series winding. [Figure 12-301] The shunt winding back or counter emf and is opposite in direction to the voltage is composed of many turns of fine wire and is connected in applied to the motor from the external source.

parallel with the armature winding. The series winding consists of a few turns of large wire and is connected in series Counter emf opposes the current, which causes the armature with the armature winding. The starting torque is higher than to rotate. The current flowing through the armature, therefore, in the shunt motor but lower than in the series motor. Variation decreases as the counter emf increases. The faster the of speed with load is less than in a series wound motor but armature rotates, the greater the counter emf. For this reason, greater than in a shunt motor. The compound motor is used a motor connected to a battery may draw a fairly high current whenever the combined characteristics of the series and shunt on starting, but as the armature speed increases, the current motors are desired.

flowing through the armature decreases. At rated speed, the counter emf may be only a few volts less than the battery Like the compound generator, the compound motor has both voltage. Then, if the load on the motor is increased, the motor series and shunt field windings. The series winding may slows down, less counter emf is generated, and the current either aid the shunt wind (cumulative compound) or oppose drawn from the external source increases. In a shunt motor, the shunt winding (differential compound). The starting the counter emf affects only the current in the armature, since 12-142 End frame Commutator Field coils Bearing Armature Brush rigging Cover Figure 12-297. Cutaway view of practical DC motor.

the field is connected in parallel across the power source. As fields. Because of these characteristics, it is more difficult to the motor slows down and the counter emf decreases, more stall a series motor than a shunt motor.

current flows through the armature, but the magnetism in the field is unchanged. When the series motor slows down, the Types of Duty counter EMF decreases and more current flows through the Electric motors are called upon to operate under various field and the armature, thereby strengthening their magnetic conditions. Some motors are used for intermittent operation; Tube type brush Box type brush Figure 12-298. Commutator and brushes.

12-143 others operate continuously. Motors built for intermittent a North pole at the lower field winding and at the lower duty can be operated for short periods only and, then, must pole piece, and a South pole at the upper pole piece. When be allowed to cool before being operated again. If such a the switch is placed in the upper position, current flows motor is operated for long periods under full load, the motor through the upper field winding, the magnetism of the becomes overheated. Motors built for continuous duty may field is reversed, and the armature rotates in the opposite be operated at rated power for long periods. direction. Some split field motors are built with two separate field windings wound on alternate poles. The armature in Reversing Motor Direction such a motor, a four pole reversible motor, rotates in one By reversing the direction of current flow in either the armature direction when current flows through the windings of one set of opposite pole pieces, and in the opposite direction when or the field windings, the direction of a motor’s rotation may be reversed. This reverses the magnetism of either the armature or current flows through the other set of windings.

the magnetic field in which the armature rotates. If the wires connecting the motor to an external source are interchanged, Another method of direction reversal, called the switch method, employs a double pole, double throw switch which the direction of rotation is not reversed, since changing these wires reverses the magnetism of both field and armature and changes the direction of current flow in either the armature or the field. In the illustration of the switch method shown in leaves the torque in the same direction as before.

Figure 12-304 , current direction may be reversed through the field but not through the armature. When the switch is thrown One method for reversing direction of rotation employs two field windings wound in opposite directions on the to the “up” position, current flows through the field winding to establish a North pole at the right side of the motor and a same pole. This type of motor is called a split field motor.

[Figure 12-303] The single pole, double throw switch South pole at the left side of the motor. When the switch is thrown to the “down” position, this polarity is reversed and makes it possible to direct current through either of the two windings. When the switch is placed in the lower position, the armature rotates in the opposite direction.

current flows through the lower field winding, creating Shunt field Wire Commutator Armature Armature Commutator A Diagrammatic A Diagrammatic Shunt field B Schematic B Schematic Figure 12-299. Series motor.

Figure 12-300. Shunt motor.

12-144 Motor Speed Motor speed can be controlled by varying the current in the d i n g p o u n a l c o m i f f e r e n t i D field windings. When the amount of current flowing through 100% S h u n t c o n n e c t i o n the field windings is increased, the field strength increases, C u but the motor slows down since a greater amount of counter m u l a t i v e c o m p EMF is generated in the armature windings. When the field o u n d i n g current is decreased, the field strength decreases, and the S e motor speeds up because the counter EMF is reduced. A r i e s c o n motor in which speed can be controlled is called a variable n e c t i o n Speed of rotation speed motor. It may be either a shunt or series motor.

In the shunt motor, speed is controlled by a rheostat in series with the field windings. [Figure 12-305] The speed depends on the amount of current that flows through the rheostat to the Output power or load 0 100% field windings. To increase the motor speed, the resistance in the rheostat is increased, which decreases the field current.

Figure 12-302. Load characteristics of DC motors.

As a result, there is a decrease in the strength of the magnetic field and in the counter EMF . This momentarily increases the is bypassed and the motor speeds up. [Figure 12-306] armature current and the torque. The motor then automatically speeds up until the counter EMF increases and causes the Energy Losses in DC Motors armature current to decrease to its former value. When this Losses occur when electrical energy is converted to occurs, the motor operates at a higher fixed speed than before.

mechanical energy (in the motor), or mechanical energy is converted to electrical energy (in the generator). For To decrease the motor speed, the resistance of the rheostat the machine to be efficient, these losses must be kept to a is decreased. More current flows through the field windings minimum. Some losses are electrical; others are mechanical.

and increases the strength of the field; then, the counter EMF Electrical losses are classified as copper losses and iron increases momentarily and decreases the armature current.

losses; mechanical losses occur in overcoming the friction As a result, the torque decreases and the motor slows down of various parts of the machine.

until the counter EMF decreases to its former value; then the motor operates at a lower fixed speed than before.

Copper losses occur when electrons are forced through the copper windings of the armature and the field. These In the series motor, the rheostat speed control is connected losses are proportional to the square of the current. They are either in parallel or in series with the motor field, or in sometimes called I R losses, since they are due to the power parallel with the armature. When the rheostat is set for dissipated in the form of heat in the resistance of the field maximum resistance, the motor speed is increased in the and armature windings.

parallel armature connection by a decrease in current. When the rheostat resistance is maximum in the series connection, Iron losses are subdivided in hysteresis and eddy current motor speed is reduced by a reduction in voltage across the losses. Hysteresis losses are caused by the armature revolving motor. For above normal speed operation, the rheostat is in in an alternating magnetic field. It, therefore, becomes magnetized first in one direction and then in the other. The + residual magnetism of the iron or steel of which the armature Series is made causes these losses. Since the field magnets are field always magnetized in one direction (DC field), they have no hysteresis losses.

Shunt field Eddy current losses occur because the iron core of the M armature is a conductor revolving in a magnetic field. This sets up an EMF across portions of the core, causing currents to flow within the core. These currents heat the core and, if – they become excessive, may damage the windings. As far as the output is concerned, the power consumed by eddy currents Figure 12-301. Compound motor.

is a loss. To reduce eddy currents to a minimum, a laminated parallel with the series field. Part of the series field current 12-145 core usually is used. A laminated core is made of thin sheets that may cause shorts. Replace the motor if the of iron electrically insulated from each other. The insulation commutator is burned, badly pitted, grooved, or worn between laminations reduces eddy currents, because it is to the extent that the mica insulation is flush with the “transverse” to the direction in which these currents tend to commutator surface.

flow. However, it has no effect on the magnetic circuit. The 6. Inspect all exposed wiring for evidence of overheating.

thinner the laminations, the more effectively this method Replace the motor if the insulation on leads or reduces eddy current losses.

windings is burned, cracked, or brittle.

7. Lubricate only if called for by the manufacturer’s Inspection and Maintenance of DC Motors instructions covering the motor. Most motors used Use the following procedures to make inspection and in today’s airplanes require no lubrication between maintenance checks: overhauls.

1. Check the operation of the unit driven by the motor 8. Adjust and lubricate the gearbox, or unit which the in accordance with the instructions covering the motor drives, in accordance with the applicable specific installation.

manufacturer’s instructions covering the unit.

2. Check all wiring, connections, terminals, fuses, and switches for general condition and security.

When trouble develops in a DC motor system, check first to determine the source of the trouble. Replace the motor only 3. Keep motors clean and mounting bolts tight.

when the trouble is due to a defect in the motor itself. In most 4. Check brushes for condition, length, and spring cases, the failure of a motor to operate is caused by a defect tension. Minimum brush lengths, correct spring in the external electrical circuit or by mechanical failure in tension, and procedures for replacing brushes are the mechanism driven by the motor.

given in the applicable manufacturer’s instructions.

5. Inspect commutator for cleanness, pitting, scoring, Check the external electrical circuit for loose or dirty roughness, corrosion, or burning. Check for high mica ( IF the copper wears down below the mica, the mica insulates the brushes from the commutator.)

Clean dirty commutators with a cloth moistened with the recommended cleaning solvent. Polish rough or corroded commutators with fine sandpaper (000 or finer) and blow out with compressed air. Never use emery paper since it contains metallic particles Up B Double pole Double throw switch A Down Figure 12-304. Switch method of reversing motor direction.

Figure 12-303. Split field series motor.

12-146 connections and for improper connection of wiring. Look accordance with the applicable manufacturer’s instructions for open circuits, grounds, and shorts by following the covering the motor. If the motor still fails to operate, replace applicable manufacturer’s circuit testing procedure. If the it with a serviceable motor.

fuse is not blown, failure of the motor to operate is usually AC Motors due to an open circuit. A blown fuse usually indicates an accidental ground or short circuit. A low battery usually Because of their advantages, many types of aircraft motors causes the chattering of the relay switch, which controls the are designed to operate on alternating current. In general, motor. When the battery is low, the open circuit voltage of AC motors are less expensive than comparable DC motors.

the battery is sufficient to close the relay, but with the heavy In many instances, AC motors do not use brushes and current draw of the motor, the voltage drops below the level commutators so sparking at the brushes is avoided. AC required to hold the relay closed. When the relay opens, the motors are reliable and require little maintenance. They are voltage in the battery increases enough to close the relay also well suited for constant speed applications and certain again. This cycle repeats and causes chattering, which is very types are manufactured that have, within limits, variable harmful to the relay switch due to the heavy current causing speed characteristics. Alternating current motors are designed an arc which burns the contacts.

to operate on polyphase or single-phase lines and at several voltage ratings.

Check the unit driven by the motor for failure of the unit or drive mechanism. If the motor has failed as a result of a The speed of rotation of an AC motor depends upon the number failure in the driven unit, the fault must be corrected before of poles and the frequency of the electrical source of power: installing a new motor. If it has been determined that the fault is in the motor itself (by checking for correct voltage 120 × Frequency rpm = at the motor terminals and for failure of the driven unit), Number of poles inspect the commutator and brushes. A dirty commutator or defective or binding brushes may result in poor contact Since airplane electrical systems typically operate at 400 between brushes and commutator. Clean the commutator, cycles, an electric motor at this frequency operates at about brushes, and brush holders with a cloth moistened with the seven times the speed of a 60-cycle commercial motor with recommended cleaning solvent. If brushes are damaged or the same number of poles. Because of this high speed of worn to the specified minimum length, install new brushes in rotation, 400-cycle AC motors are suitable for operating small, high-speed rotors, through reduction gears, in lifting and moving heavy loads, such as the wing flaps, the retractable landing gear, and the starting of engines. The Frame 400-cycle induction type motor operates at speeds ranging Pole from 6,000 rpm to 24,000 rpm. Alternating current motors Shunt led are rated in horsepower output, operating voltage, full load Commutator current, speed, number of phases, and frequency. Whether the motors operate continuously or intermittently (for short intervals) is also considered in the rating.

Types of AC Motors There are two general types of AC motors used in aircraft systems: induction motors and synchronous motors. Either type may be single-phase, two-phase, or three-phase. Three-phase induction motors are used where large amounts of power are Armature required. They operate such devices as starters, flaps, landing gears, and hydraulic pumps. Single-phase induction motors are used to operate devices such as surface locks, intercooler shutters, and oil shutoff valves in which the power requirement is low. Three-phase synchronous motors operate at constant Rheostat synchronous speeds and are commonly used to operate flux gate compasses and propeller synchronizer systems. Single- phase synchronous motors are common sources of power to operate electric clocks and other small, precision equipment.

Figure 12-305. Shunt motor with variable speed control.

They require some auxiliary method to bring them up to 12-147 + + + Fast Slow Series Rheostat Fast filed Slow Rheostat Fast Slow M M M – – – Below normal speed Normal speed Above normal speed Figure 12-306. Controlling the speed of a series DC motor.

synchronous speeds; that is, to start them. Usually the starting extending from pole 1 to pole 4. Under this condition, pole winding consists of an auxiliary stator winding. 1 can be considered as a North pole and pole 4 as a South pole. At the instant of time shown as 1, the resultant magnetic Three-Phase Induction Motor field has its greatest intensity in the direction extending from The three-phase AC induction motor is also called a squirrel pole 2 to pole 5. In this case, pole 2 can be considered as a North pole and pole 5 as a South pole. Thus, between instant cage motor. Both single-phase and three-phase motors operate on the principle of a rotating magnetic field. A 0 and instant 1, the magnetic field has rotated clockwise. At instant 2, the resultant magnetic field has its greatest intensity horseshoe magnet held over a compass needle is a simple illustration of the principle of the rotating field. The needle in the direction from pole 3 to pole 6, and the resultant magnetic field has continued to rotate clockwise. At instant takes a position parallel to the magnetic flux passing between the two poles of the magnet. If the magnet is rotated, the 3, poles 4 and 1 can be considered as North and South poles, respectively, and the field has rotated still farther. At later compass needle follows. A rotating magnetic field can be produced by a two-or three-phase current flowing through instants of time, the resultant magnetic field rotates to other positions while traveling in a clockwise direction, a single two or more groups of coils wound on inwardly projecting poles of an iron frame. The coils on each group of poles revolution of the field occurring in one cycle. If the exciting voltages have a frequency of 60 cps, the magnetic field makes are wound alternately in opposite directions to produce opposite polarity, and each group is connected to a separate 60 revolutions per second, or 3,600 rpm. This speed is known as the synchronous speed of the rotating field.

phase of voltage. The operating principle depends on a revolving, or rotating, magnetic field to produce torque.

Construction of Induction Motor The key to understanding the induction motor is a thorough understanding of the rotating magnetic field. The stationary portion of an induction motor is called a stator, and the rotating member is called a rotor. Instead of salient Rotating Magnetic Field poles in the stator, as shown in Figure 12-307A , distributed The field structure shown in Figure 12-307A has poles windings are used. These windings are placed in slots around the periphery of the stator. It is usually impossible whose windings are energized by three AC voltages: a, b, and c. These voltages have equal magnitude but differ in to determine the number of poles in an induction motor by visual inspection, but the information can be obtained from phase. [Figure 12-307B] At the instant of time shown as 0, the resultant magnetic field produced by the application the nameplate of the motor. The nameplate usually gives the number of poles and the speed at which the motor is designed of the three voltages has its greatest intensity in a direction 12-148 to run. This rated, or nonsynchronous, speed is slightly less and the synchronous speed is 1,800 rpm, the difference in speed than the synchronous speed. To determine the number of is 50 rpm. The slip is then equal to 50/1,800 or 2.78 percent.

poles per phase on the motor, divide 120 times the frequency by the rated speed. Written as an equation, it is: Single-Phase Induction Motor The previous discussion has applied only to polyphase 120 × f P = motors. A single-phase motor has only one stator winding.

N This winding generates a field, which merely pulsates, instead Where: P is the number of poles per phase of rotating. When the rotor is stationary, the expanding and f is the frequency in cps collapsing stator field induces currents in the rotor. These N is the rated speed in rpm, and currents generate a rotor field opposite in polarity to that of 120 is a constant the stator. The opposition of the field exerts a turning force on the upper and lower parts of the rotor trying to turn it 180° The result is nearly equal to the number of poles per phase. from its position. Since these forces are exerted through the For example, consider a 60-cycle, three-phase motor with a center of the rotor, the turning force is equal in each direction.

rated speed of 1,750 rpm. In this case: As a result, the rotor does not turn. If the rotor starts turning, it continues to rotate in the direction in which it started, since 120 × 60 7,200 the turning force in that direction is aided by the momentum P = = = 4.1 1,750 1,750 of the rotor.

Therefore, the motor has four poles per phase. If the number Shaded Pole Induction Motor of poles per phase is given on the nameplate, the synchronous The first effort in the development of a self-starting, speed can be determined by dividing 120 times the frequency single-phase motor was the shaded pole induction motor.

by the number of poles per phase. In the example used above, [Figure 12-309] This motor has salient poles, a portion the synchronous speed is equal to 7,200/4, or 1,800 rpm.

of each pole being encircled by a heavy copper ring. The presence of the ring causes the magnetic field through the The rotor of an induction motor consists of an iron core ringed portion of the pole face to lag appreciably behind having longitudinal slots around its circumference in which that through the other part of the pole face. The net effect heavy copper or aluminum bars are embedded. These bars is the production of a slight component of rotation of the are welded to a heavy ring of high conductivity on either field, sufficient to cause the rotor to revolve. As the rotor end. The composite structure is sometimes called a squirrel accelerates, the torque increases until the rated speed is cage, and motors containing such a rotor are called squirrel obtained. Such motors have low starting torque and find cage induction motors. [Figure 12-308] their greatest application in small fan motors where the initial torque required is low.

Induction Motor Slip When the rotor of an induction motor is subjected to the In Figure 12-309 , a diagram of a pole and the rotor is revolving magnetic field produced by the stator windings, shown. The poles of the shaded pole motor resemble those a voltage is induced in the longitudinal bars. The induced of a DC motor.

voltage causes a current to flow through the bars. This current, in turn, produces its own magnetic field, which combines A low resistance, short-circuited coil or copper band is placed with the revolving field so that the rotor assumes a position in across one tip of each small pole from which the motor gets which the induced voltage is minimized. As a result, the rotor the name of shaded pole. The rotor of this motor is the squirrel revolves at very nearly the synchronous speed of the stator cage type. As the current increases in the stator winding, the field, the difference in speed being just sufficient enough to flux increases. A portion of this flux cuts the low resistance induce the proper amount of current in the rotor to overcome shading coil. This induces a current in the shading coil, and the mechanical and electrical losses in the rotor. If the rotor by Lenz’s Law, the current sets up a flux that opposes the were to turn at the same speed as the rotating field, the rotor flux inducing the current. Hence, most of the flux passes conductors would not be cut by any magnetic lines of force, through the unshaded portion of the poles. [Figure 12-310] no EMF would be induced in them, no current could flow, and there would be no torque. The rotor would then slow down.

When the current in the winding and the main flux reaches For this reason, there must always be a difference in speed a maximum, the rate of change is zero; thus, no emf is between the rotor and the rotating field. This difference in induced in the shading coil. A little later, the shading coil speed is called slip and is expressed as a percentage of the current, which causes the induced emf to lag, reaches zero, synchronous speed. For example, if the rotor turns at 1,750 rpm and there is no opposing flux. Therefore, the main field flux 12-149 Split-Phase Motor There are various types of self-starting motors, known as split-phase motors. Such motors have a starting winding displaced 90 electrical degrees from the main or running winding. In some types, the starting winding has a fairly high resistance, which causes the current in this winding 2 6 to be out of phase with the current in the running winding.

This condition produces, in effect, a rotating field and 3 5 4 the rotor revolves. A centrifugal switch disconnects the starting winding automatically after the rotor has attained approximately 25 percent of its rated speed.

Capacitor Start Motor a With the development of high-capacity electrolytic capacitors, a variation of the split-phase motor known as the b capacitor start motor, has been made. Nearly all fractional horsepower motors in use today on refrigerators and other c similar appliances are of this type. [Figure 12-311] In this adaptation, the starting winding and running winding have A the same size and resistance value. The phase shift between currents of the two windings is obtained by using capacitors 0 1 2 3 4 5 6 connected in series with the starting winding.

a b c Capacitor start motors have a starting torque comparable to their torque at rated speed and can be used in applications where the initial load is heavy. Again, a centrifugal switch is required for disconnecting the starting winding when the rotor speed is approximately 25 percent of the rated speed.

a b c 180° Although some single-phase induction motors are rated as Time high as 2 horsepower (hp), the major field of application is 1 hp, or less, at a voltage rating of 115 volts for the smaller B sizes and 110 to 220 volts for one-fourth hp and up. For even larger power ratings, polyphase motors generally are used, Figure 12-307. Rotating magnetic field developed by application since they have excellent starting torque characteristics.

of three-phase voltages.

Direction of Rotation of Induction Motors passes through the shaded portion of the field pole. The The direction of rotation of a three-phase induction motor main field flux, which is now decreasing, induces a current can be changed by simply reversing two of the leads to the in the shading coil. This current sets up a flux that opposes motor. The same effect can be obtained in a two-phase motor the decrease of the main field flux in the shaded portion of by reversing connections to one phase. In a single-phase the pole. The effect is to concentrate the lines of force in motor, reversing connections to the starting winding reverses the shaded portion of the pole face. In effect, the shading the direction of rotation.

coil retards, in time phase, the portion of the flux passing through the shaded part of the pole. This lag in time phase Most single-phase motors designed for general application of the flux in the shaded tip causes the flux to produce the have provision for readily reversing connections to the effect of sweeping across the face of the pole, from left to starting winding. Nothing can be done to a shaded pole motor right in the direction of the shaded tip. This behaves like a to reverse the direction of rotation because the direction is very weak rotating magnetic field, and sufficient torque is determined by the physical location of the copper shading produced to start a small motor. The starting torque of the ring. If, after starting, one connection to a three-phase motor shaded pole motor is exceedingly weak, and the power factor is broken, the motor continues to run but delivers only is low. Consequently, it is built in sizes suitable for driving one-third the rated power. Also, a two-phase motor runs at such devices as small fans.

one-half its rated power if one phase is disconnected. Neither 12-150 Weld at all joints Welds holding copper or aluminum bars to end ring Aluminum or Shaft copper end ring Iron core A B Aluminum or copper bars Figure 12-308. Squirrel cage rotor for an AC induction motor.

motor starts under these abnormal conditions.

Shaded poles Synchronous Motor The synchronous motor is one of the principal types of AC motors. Like the induction motor, the synchronous motor makes use of a rotating magnetic field. Unlike the induction motor, however, the torque developed does not depend on the induction of currents in the rotor. Briefly, the principle of operation of the synchronous motor is as follows: A multiphase source of AC is applied to the stator windings, and a rotating magnetic field is produced. A direct current is applied to the rotor winding, and another magnetic field is produced. The synchronous motor is so designed and constructed that these two fields react to each other in such a manner that the rotor is dragged along and rotates at the same speed as the rotating magnetic field produced by the stator windings.

Shaded poles An understanding of the operation of the synchronous motor can be obtained by considering the simple motor of Figure 12-309. Shaded pole induction motor.

Figure 12-312 . Assume that poles A and B are being rotated clockwise by some mechanical means in order to produce a rotating magnetic field. They induce poles of opposite is impractical because another motor would be required to polarity in the soft iron rotor, and forces of attraction exist perform this work. Also, such an arrangement is unnecessary between corresponding North and South poles. because a rotating magnetic field can be produced electrically by using phased AC voltages. In this respect, the synchronous Consequently, as poles A and B rotate, the rotor is dragged motor is similar to the induction motor.

along at the same speed. However, if a load is applied to the The synchronous motor consists of a stator field winding rotor shaft, the rotor axis momentarily falls behind that of the similar to that of an induction motor. The stator winding rotating field but, thereafter, continues to rotate with the field produces a rotating magnetic field. The rotor may be a at the same speed as long as the load remains constant. If the permanent magnet, as in small, single-phase synchronous load is too large, the rotor pulls out of synchronism with the motors used for clocks and other small precision equipment, rotating field and, as a result, no longer rotates with the field or it may be an electromagnet, energized from a DC source of at the same speed. Thus, the motor is said to be overloaded.

power and fed through slip rings into the rotor field coils, as in an alternator. In fact, an alternator may be operated either Such a simple motor as shown in Figure 12-312 is never used.

as an alternator or a synchronous motor.

The idea of using some mechanical means of rotating the poles 12-151 Since a synchronous motor has little starting torque, some that it has brushes and a commutator. The AC-series motor means must be provided to bring it up to synchronous speed. operates on either AC or DC circuits. Remember that the The most common method is to start the motor at no load, direction of rotation of a DC-series motor is independent allow it to reach full speed, and then energize the magnetic of the polarity of the applied voltage, provided the field field. The magnetic field of the rotor locks with the magnetic and armature connections remain unchanged. Hence, if a field of the stator and the motor operates at synchronous speed. DC-series motor is connected to an AC source, a torque is developed that tends to rotate the armature in one direction.

The magnitude of the induced poles in the rotor shown in However, a DC-series motor does not operate satisfactorily Figure 12-313 is so small that sufficient torque cannot be from an AC supply for the following reasons: developed for most practical loads. To avoid such a limitation 1. The alternating flux sets up large eddy current and on motor operation, a winding is placed on the rotor and hysteresis losses in the unlaminated portions of the energized with DC. A rheostat placed in series with the DC magnetic circuit and causes excessive heating and source provides the operator of the machine with a means reduced efficiency.

of varying the strength of the rotor poles, thus placing the 2. The self-induction of the field and armature windings motor under control for varying loads.

causes a low power factor.

The synchronous motor is not a self-starting motor. The 3. The alternating field flux establishes large currents in rotor is heavy and, from a dead stop, it is impossible to the coils, which are short circuited by the brushes; this bring the rotor into magnetic lock with the rotating magnetic action causes excessive sparking at the commutator.

field. For this reason, all synchronous motors have some kind of starting device. One type of simple starter is To design a series motor for satisfactory operation on AC, another motor, either AC or DC, which brings the rotor up the following changes are made: to approximately 90 percent of its synchronous speed. The 1. The eddy current losses are reduced by laminating the starting motor is then disconnected, and the rotor locks in field poles, frame, and armature.

step with the rotating field. Another starting method is a 2. Hysteresis losses are minimized by using high second winding of the squirrel cage type on the rotor. This permeability, transformer-type, silicon steel induction winding brings the rotor almost to synchronous laminations.

speed, and when the DC is connected to the rotor windings, the rotor pulls into step with the field. The latter method is 3. The reactance of the field windings is kept satisfactorily the more commonly used.

low by using shallow pole pieces, few turns of wire, low frequency (usually 25 cycles for large motors), AC Series Motor low flux density, and low reluctance (a short air gap).

An AC-series motor is a single-phase motor, but is not an 4. The reactance of the armature is reduced by using a induction or synchronous motor. It resembles a DC motor in compensating winding embedded in the pole pieces. If the compensating winding is connected in series with the armature, as shown in Figure 12-314 , the armature is conductively compensated.

If the compensating winding is designed as shown in Figure 12-315 , the armature is inductively compensated. If the motor is designed for operation Shaded pole on both DC and AC circuits, the compensating winding is connected in series with the armature. The axis of the compensating winding is displaced from the main field axis by an angle of 90°. This arrangement is similar to the compensating winding used in some DC motors and generators to overcome armature reaction.

Rotor The compensating winding establishes a counter magnetomotive force, neutralizing the effect of the armature magnetomotive force, preventing distortion of the main field flux, and reducing the armature reactance. The inductively compensated armature acts like the primary of a transformer, the secondary Figure 12-310. Diagram of a shaded pole motor.

12-152 Winding 1 (Starting winding) Capacitor Centrifugal switch S S N Alternator N Winding 2 (Running winding) Figure 12-311. Single-phase motor with capacitor starting winding.

of which is the shorted compensating winding. The a temperature too hot for the hand is too high for safety. Next shorted secondary receives an induced voltage by the to the temperature, the sound of a motor or generator is the action of the alternating armature flux, and the resulting best trouble indicator. When operating properly, it should hum current flowing through the turns of the compensating evenly. If it is overloaded it “grunts.” A three-phase motor winding establishes the opposing magnetomotive force, neutralizing the armature reactance.

Rotating pole 5. Sparking at the commutator is reduced by the use of structure preventive leads P , P , P , and so forth, as shown in A 1 2 3 Figure 12-316 , where a ring armature is shown for simplicity. When coils at A and B are shorted by the brushes, the induced current is limited by the relatively high resistance of the leads. Sparking at the brushes is also reduced by using armature coils having only a N single turn and multipolar fields. High torque is obtained by having a large number of armature conductors and S Rotor a large diameter armature. Thus, the commutator has a large number of very thin commutator bars and the Rotor shaft Induced poles armature voltage is limited to about 250 volts.

Rotor axis N Fractional horsepower AC series motors are called universal motors. They do not have compensating windings or preventive leads. They are used extensively to operate fans S and portable tools, such as drills, grinders, and saws.

Maintenance of AC Motors The inspection and maintenance of AC motors is very simple.

The bearings may or may not need frequent lubrication. If B they are the sealed type, lubricated at the factory, they require Rotating pole no further attention. Be sure the coils are kept dry and free structure from oil or other abuse. The temperature of a motor is usually its only limiting operating factor. A good rule of thumb is that Figure 12-312. Illustrating the operation of a synchronous motor.

12-153 with one lead disconnected refuses to turn and “growls.” A Method of Excitation knocking sound generally indicates a loose armature coil, One means of classification is by the type of excitation system a shaft out of alignment, or armature dragging because of used. In alternators used on aircraft, excitation can be affected worn bearings. In all cases, the inspection and maintenance by one of the following methods: of all AC motors should be performed in accordance with 1. A direct connected, DC generator. This system consists the applicable manufacturer’s instructions.

of a DC generator fixed on the same shaft with the AC generator. A variation of this system is a type of Alternators alternator that uses DC from the battery for excitation, Basic Alternators & Classifications after which the alternator is self-excited.

An electrical generator is a machine that converts mechanical 2. By transformation and rectification from the AC energy into electrical energy by electromagnetic induction.

system. This method depends on residual magnetism A generator that produces alternating current is referred to for initial AC voltage buildup, after which the field is as an AC generator and, through combination of the words supplied with rectified voltage from the AC generator.

“alternating” and “generator,” the word “alternator” has come 3. Integrated brushless type. This arrangement has a DC into widespread use. In some areas, the word “alternator” is generator on the same shaft with an AC generator.

applied only to small AC generators. This handbook treats The excitation circuit is completed through silicon the two terms synonymously and uses the term “alternator” rectifiers rather than a commutator and brushes. The to distinguish between AC and DC generators.

rectifiers are mounted on the generator shaft and their output is fed directly to the AC generator’s main The major difference between an alternator [Figure 12-317] rotating field.

and a DC generator is the method of connection to the external circuit. The alternator is connected to the external Number of Phases circuit by slip rings, but the DC generator is connected by Another method of classification is by the number of phases a commutator.

of output voltage. AC generators may be single-phase, two-phase, three-phase, or even six-phase and more. In the N Three-phase winding produces a rotating magnetic field S S + N – Slip rings Figure 12-313. Synchronous motor.

12-154 electrical systems of aircraft, the three-phase alternator is by far the most common.

Armature or Field Rotation Still another means of classification is by the type of stator Compensating winding and rotor used. From this standpoint, there are two types of alternators: the revolving armature-type and the revolving field-type. The revolving armature alternator is similar in construction to the DC generator in that the armature rotates through a stationary magnetic field. The revolving armature alternator is found only in alternators of low-power rating and generally is not used. In the DC generator, the EMF Main field generated in the armature windings is converted into a unidirectional voltage (DC) by means of the commutator.

In the revolving armature-type of alternator, the generated AC voltage is applied unchanged to the load by means of slip rings and brushes.

Figure 12-314. Conductively compensated armature of AC series motor.

The revolving field type of alternator has a stationary armature winding (stator) and a rotating field winding (rotor). [Figure 12-318] The advantage of having a stationary armature winding is that the armature can be connected Compensating directly to the load without having sliding contacts in the winding load circuit. A rotating armature would require slip rings and brushes to conduct the load current from the armature to the external circuit. Slip rings have a relatively short service life and arc over is a continual hazard; therefore, high voltage alternators are usually of the stationary armature, rotating field-type. The voltage and current supplied to the rotating field are relatively small, and slip rings and brushes for this circuit are adequate. The direct connection to the Main field armature circuit makes possible the use of large cross-section conductors, adequately insulated for high voltage. Since the rotating field alternator is used almost universally in aircraft systems, this type is explained in detail, as a single-phase, two-phase, and three-phase alternator.

Figure 12-315. Inductively compensated armature of AC series motor.

Single-Phase Alternator numbers of magnetic lines of force at any time.

Since the EMF induced in the armature of a generator is alternating, the same sort of winding can be used on an As a result, the voltages induced in all the windings have alternator as on a DC generator. This type of alternator is known as a single-phase alternator, but since the power the same amplitude, or value, at any given instant. The four stator windings are connected to each other so that the AC delivered by a single-phase circuit is pulsating, this type of circuit is objectionable in many applications. voltages are in phase or “series adding.” Assume that rotor pole 1, a South pole, induces a voltage in the direction A single-phase alternator has a stator made up of a number of indicated by the arrow in stator winding 1. Since rotor pole 2 is a North pole, it induces a voltage in the opposite windings in series, forming a single circuit in which an output voltage is generated. [Figure 12-319] The stator has four polar direction in stator coil 2 with respect to that in coil 1. For the two induced voltages to be in series addition, the two groups evenly spaced around the stator frame. The rotor has four poles with adjacent poles of opposite polarity. As the rotor coils are connected as shown in Figure 12-319 . Applying the same reasoning, the voltage induced in stator coil revolves, AC voltages are induced in the stator windings. Since one rotor pole is in the same position relative to a stator winding 3 (clockwise rotation of the field) is the same direction (counterclockwise) as the voltage induced in coil 1.

as any other rotor pole, all stator polar groups are cut by equal 12-155 Wye Connection (Three-Phase) A Rather than have six leads from the three-phase alternator, one of the leads from each phase may be connected to form a common junction. The stator is then called wye or star connected. The common lead may or may not be brought out P P of the alternator. If it is brought out, it is called the neutral lead.

P The simplified schematic shows a wye connected stator with P 2 the common lead not brought out. [Figure 12-321A] Each P load is connected across two phases in series. Thus, RAB is connected across phases A and B in series; RAC is connected P P across phases A and C in series; and RBC is connected across P 4 phases B and C in series. Therefore, the voltage across each P load is larger than the voltage across a single phase. The total voltage, or line voltage, across any two phases is the vector sum of the individual phase voltages. For balanced conditions, B the line voltage is 1.73 times the phase voltage. Since there is only one path for current in a line wire and the phase to which Figure 12-316. Preventive coils in AC series motor. it is connected, the line current is equal to the phase current.

Delta Connection (Three-Phase) Similarly, the direction of the voltage induced in winding A three-phase stator can also be connected so that the phases 4 is opposite to the direction of the voltage induced in coil are connected end to end. [Figure 12-321B] This arrangement 1. All four stator coil groups are connected in series so that is called a delta connection. In a delta connection, the voltages the voltages induced in each winding add to give a total are equal to the phase voltages; the line currents are equal voltage that is four times the voltage in any one winding.

to the vector sum of the phase currents; and the line current is equal to 1.73 times the phase current when the loads are Two-Phase Alternator balanced. For equal loads (equal output), the delta connection Two-phase alternators have two or more single-phase windings supplies increased line current at a value of line voltage equal spaced symmetrically around the stator. In a two-phase to phase voltage, and the wye connection supplies increased alternator, there are two single-phase windings spaced physically line voltage at a value of line current equal to phase current.

so that the AC voltage induced in one is 90° out of phase with the voltage induced in the other. The windings are electrically Alternator Rectifier Unit separate from each other. When one winding is being cut by A type of alternator used in the electrical system of many maximum flux, the other is being cut by no flux. This condition aircraft weighing less than 12,500 pounds is shown in establishes a 90° relation between the two phases.

Figure 12-322 . This type of power source is sometimes called a DC generator, since it is used in DC systems. Although its Three-Phase Alternator output is a DC voltage, it is an alternator rectifier unit. This A three-phase, or polyphase circuit, is used in most aircraft type of alternator rectifier is a self-excited unit but does not alternators, instead of a single or two-phase alternator. The contain a permanent magnet. The excitation for starting is three-phase alternator has three single-phase windings spaced so that the voltage induced in each winding is 120° out of phase with the voltages in the other two windings. A schematic diagram of a three-phase stator showing all the coils becomes complex and difficult to see what is actually happening.

A simplified schematic diagram showing each of three phases is illustrated in Figure 12-320 . The rotor is omitted for simplicity. The waveforms of voltage are shown to the right of the schematic. The three voltages are 120° apart and are similar to the voltages that would be generated by three single-phase alternators whose voltages are out of phase by angles of 120°.

The three phases are independent of each other.

Figure 12-317. Belt driven alternator for small single-engine aircraft.

12-156 obtained from the battery; immediately after starting, the unit on the main generator stator and its three-phase armature is self-exciting. Cooling air for the alternator is conducted mounted on the generator rotor shaft. Included in the exciter into the unit by a blast air tube on the air inlet cover. field are permanent magnets mounted on the main generator stator between the exciter poles.

The alternator is directly coupled to the aircraft engine by means of a flexible drive coupling. The output of the alternator The exciter field resistance is temperature compensated by a portion of the unit is three-phase alternating current, derived thermistor. This aids regulation by keeping a nearly constant from a three-phase, delta connected system incorporating a resistance at the regulator output terminals. The exciter three-phase, full-wave bridge rectifier. [Figure 12-323] This output is rectified and impressed on the main generator unit operates in a speed range from 2,100 to 9,000 rpm, with field and the pilot exciter field. The exciter stator has a a DC output voltage of 26–29 volts and 125 amperes. stabilizing field, which is used to improve stability and to prevent voltage regulator over-corrections for changes in Brushless Alternator generator output voltage.

This design is more efficient because there are no brushes to wear down or to arc at high altitudes. This generator consists of The AC generator shown in Figure 12-324 is a 6-pole, 8,000 rpm unit having a rating of 31.5 kilovoltamperes (kVA), a pilot exciter, an exciter, and the main generator system. The need for brushes is eliminated by using an integral exciter with 115⁄200 volts, 400 cps. This generator is three-phase, 4 wire, wye connected with grounded neutrals. By using an integral a rotating armature that has its AC output rectified for the main AC field, which is also of the rotating type. [Figure 12-324] AC exciter, the necessity for brushes within the generator has been eliminated. The AC output of the rotating exciter The pilot exciter is an 8-pole, 8,000 rpm, 533 cps, AC armature is fed directly into the three-phase, full-wave, rectifier bridge located inside the rotor shaft, which uses generator. The pilot exciter field is mounted on the main generator rotor shaft and is connected in series with the main high-temperature silicon rectifiers. The DC output from the rectifier bridge is fed to the main AC generator rotating field.

generator field. The pilot exciter armature is mounted on the main generator stator. The AC output of the pilot exciter is Voltage regulation is accomplished by varying the strength supplied to the voltage regulator, where it is rectified and controlled, and is then impressed on the exciter field winding of the AC exciter stationary fields. Polarity reversals of the AC generator are eliminated and radio noise is minimized to furnish excitation for the generator.

by the absence of the brushes. A noise filter mounted on the alternator further reduces any existing radio noise.

The exciter is a small AC generator with its field mounted The rotating pole structure of the generator is laminated from steel punchings, containing all six poles and a connecting hub section. This provides optimum magnetic and mechanical properties.

Armature Circuit Some alternators are cooled by circulating oil through steel tubes. The oil used for cooling is supplied from the constant speed drive assembly. Ports located in the flange connecting Rotating field the generator and drive assemblies make oil flow between the constant speed drive and the generator possible.

Slip rings S N +e N S + – Time axis 0 1 1 3 3 To exciter S –e N Figure 12-318. Alternator with stationary armature and rotating Figure 12-319. Single-phase alternator.

field.

12-157 Voltage is built up by using permanent magnet interpoles in the exciter stator. The permanent magnets assure a voltage R R A AB buildup, precluding the necessity of field flashing. The rotor A C C A of the alternator may be removed without causing loss of the B R R C AC alternator’s residual magnetism.

B R R BC B Alternator Frequency Wye connection Delta connection A B The frequency of the alternator voltage depends upon the speed of rotation of the rotor and the number of poles.

Figure 12-321. Wye and delta connected alternators.

The faster the speed, the higher the frequency; the lower the speed, the lower the frequency. The more poles on the 12 × 4,000 rotor, the higher the frequency for a given speed. When a = 400 cps rotor has rotated through an angle so that two adjacent rotor poles (a North and a South pole) have passed one winding, Starter Generator the voltage induced in that winding has varied through one Many turbine-powered aircraft use a starter generator that complete cycle. For a given frequency, the greater the number acts like a starter during the start of the engine and when the of pairs of poles, the lower the speed of rotation. A two-pole engine is online it acts like a Generator. [Figure 12-325] The alternator rotates at twice the speed of a four-pole alternator main advantage of the starter generator is saving weight by for the same frequency of generated voltage. The frequency eliminating a separate starter that is only used during the start.

of the alternator in cycles per minute (cpm) is related to the Initially used on small turboprops and light jets but large units number of poles and the speed, as expressed by the equation: are now installed on the B787 aircraft engines to power the P N PN main engines and power the electrical system.

F = × = N 60 120 Alternator Rating The maximum current that can be supplied by an alternator Where: P is the number of poles per phase f is the frequency in cps depends upon the maximum heating loss (I R power loss) that can be sustained in the armature and the maximum heating loss N is the rated speed in rpm that can be sustained in the field. The armature current of an alternator varies with the load. This action is similar to that of A For example, a 2-pole, 3,600 rpm alternator has a frequency of: 12 pole, 4,000 rpm alternator has a frequency of DC generators.

2 × 3,600 In AC generators, however, lagging power factor loads tend = 60 cps to demagnetize the field of an alternator, and terminal voltage is maintained only by increasing DC field current. For this A 4-pole, 1,800 rpm alternator has the same frequency; a reason, AC generators are usually rated according to kVA, power factor, phases, voltage, and frequency. One generator, 6-pole, 500 rpm alternator has a frequency of: for example, may be rated at 40 kVA, 208 volts, 400 cycles, 6 × 500 = 25 cps three phase, at 75 percent power factor. The kVA indicates the apparent power. This is the kVA output, or the relationship between the current and voltage at which the generator is A 12-pole, 4,000 rpm alternator has a frequency of: intended to operate. The power factor is the expression of the A +e B C A B C –e Figure 12-320. Simplified schematic of three-phase alternator with Figure 12-322. Exploded view of alternator rectifier.

output waveforms.

12-158 ratio between the apparent power (volt-amperes) and the true and an unmounted continuity light.

or effective power (watts). The number of phases is the number of independent voltages generated. Three-phase generators A portable load bank unit furnishes a load similar to that generate three voltages 120 electrical degrees apart. on the airplane for testing alternators, either while mounted in the airplane or on the shop test stand. A complete unit Alternator Maintenance consists of resistive and reactive loads controlled by selector Maintenance and inspection of alternator systems is similar switches and test meters mounted on a control panel. This load unit is compact and convenient, eliminating the difficulty to that of DC systems. Check the exciter brushes for wear and surfacing. On most large aircraft with two or four alternator of operating large loads on the airplane while testing and adjusting the alternators and control equipment.

systems, each power panel has three signal lights, one connected to each phase of the power bus, so the lamp lights Proper maintenance of an alternator requires that the unit be when the panel power is on. The individual buses throughout the airplane can be checked by operating equipment from that kept clean and that all electrical connections are tight and in good repair. If the alternator fails to build up voltage as particular bus. Consult the manufacturer’s instructions on operation of equipment for the method of testing each bus. designated by applicable manufacturer’s technical instructions, test the voltmeter first by checking the voltages of other Alternator test stands are used for testing alternators and alternators, or by checking the voltage in the suspected alternator with another voltmeter and comparing the results.

constant speed drives in a repair facility. They are capable of supplying power to constant speed drive units at input speeds If the voltmeter is satisfactory, check the wiring, the brushes, and the drive unit for faults. If this inspection fails to reveal varying from 2,400 rpm to 9,000 rpm.

the trouble, the exciter may have lost its residual magnetism.

Residual magnetism is restored to the exciter by flashing the A typical test stand motor uses 220/440 volt, 60 cycle, three-phase power. Blowers for ventilation, oil coolers, field. Follow the applicable manufacturer’s instructions when flashing the exciter field. If, after flashing the field, no voltage and necessary meters and switches are integral parts of the test stand. A load bank supplies test circuits. An AC motor is indicated, replace the alternator, since it is probably faulty.

generator set for ground testing is shown in Figure 12-326 .

Clean the alternator exterior with an approved fluid; smooth a rough or pitted exciter commutator or slip ring with 000 A typical, portable, AC electrical system test set is an analyzer, consisting of a multirange ohmmeter, a multirange sandpaper; then clean and polish with a clean, dry cloth. Check the brushes periodically for length and general condition.

combination AC DC voltmeter, an ammeter with a clip-on current transformer, a vibrating reed type frequency meter, Consult the applicable manufacturer’s instructions on the specific alternator to obtain information on the correct brushes.

E Regulation of Generator Voltage Efficient operation of electrical equipment in an airplane – depends on a constant voltage supply from the generator.

Among the factors, which determine the voltage output of a G1 L1 generator, only one, the strength of the field current, can be conveniently controlled. To illustrate this control, refer to the + diagram in Figure 12-327 , showing a simple generator with a rheostat in the field circuit. If the rheostat is set to increase the resistance in the field circuit, less current flows through CR1 CR4 the field winding and the strength of the magnetic field in C3 which the armature rotates decreases. Consequently, the CR5 CR2 voltage output of the generator decreases. If the resistance in CR3 CR6 the field circuit is decreased with the rheostat, more current flows through the field windings, the magnetic field becomes + stronger, and the generator produces a greater voltage.

B C2 Voltage Regulation with a Vibrating-Type Regulator + Refer to Figure 12-328 . With the generator running at A normal speed and switch K open, the field rheostat is adjusted so that the terminal voltage is about 60 percent of Figure 12-323. Wiring diagram of alternator-rectifier unit.

12-159 Stator Terminal block Terminal block Oil inlet cover Rotor Ball bearing Filter assembly F Exciter E E T T T 1 2 1 4 3 field S Stabilizing N Pilot exciter Radio field armature noise S filter Thermistor Rotor T T Pilot exciter Main AC field generator Exciter Main AC field armature generator stator windings 3 phase bridge rectifier Figure 12-324. A typical brushless alternator.

normal. Solenoid S is weak and contact B is held closed by the spring. When K is closed, a short circuit is placed When the terminal voltage falls below a certain critical voltage, across the field rheostat. This action causes the field current the solenoid armature contact B is closed again by the spring, to increase and the terminal voltage to rise. the field rheostat is now shorted, and the terminal voltage starts to rise. The cycle repeats with a rapid, continuous action. Thus, When the terminal voltage rises above a certain critical value, an average voltage is maintained with or without load change.

the solenoid downward pull exceeds the spring tension and contact B opens, thus reinserting the field rheostat in the field The dashpot P provides smoother operation by acting as a circuit and reducing the field current and terminal voltage. damper to prevent hunting. The capacitor C across contact B 12-160 eliminates sparking. Added load causes the field rheostat to be shorted for a longer period of time and, thus, the solenoid As the terminal voltage rises, the current flow through L1 armature vibrates more slowly. If the load is reduced and the increases and the iron core becomes more strongly magnetized.

terminal voltage rises, the armature vibrates more rapidly and At a certain speed and voltage, when the magnetic attraction the regulator holds the terminal voltage to a steady value for on the movable arm becomes strong enough to overcome the any change in load, from no load to full load, on the generator. tension of spring S1, contact points C1 are separated. The field current now flows through R1 and L2. Because resistance is Vibrating-type regulators cannot be used with generators, added to the field circuit, the field is momentarily weakened which require a high-field current, since the contacts pit or and the rise in terminal voltage is checked. Also, since the burn. Heavy-duty generator systems require a different type L2 winding is opposed to the L1 winding, the magnetic pull of regulator, such as the carbon pile voltage regulator. of L1 against S1 is partially neutralized, and spring S1 closes contact C1. Therefore, R1 and L2 are again shorted out of Three Unit Regulators the circuit, and the field current again increases; the output voltage increases, and C1 is opened because of the action of Many light aircraft employ a three unit regulator for their generator systems. [Figure 12-329] This type of regulator L1. The cycle is rapid and occurs many times per second. The terminal voltage of the generator varies slightly, but rapidly, includes a current limiter and a reverse current cut-out in addition to a voltage regulator. above and below an average value determined by the tension of spring S1, which may be adjusted.

The action of the voltage regulator unit is similar to the The purpose of the vibrator-type current limiter is to limit the vibrating-type regulator described earlier. The second of the three units is a current regulator to limit the output current output current of the generator automatically to its maximum rated value in order to protect the generator. As shown in of the generator. The third unit is a reverse current cut-out that disconnects the battery from the generator. If the battery Figure 12-330 , L3 is in series with the main line and load.

Thus, the amount of current flowing in the line determines is not disconnected, it discharges through the generator armature when the generator voltage falls below that of the when C2 is opened and R2 placed in series with the generator field. By contrast, the voltage regulator is actuated by line battery, thus driving the generator as a motor. This action is called “motoring” the generator and, unless it is prevented, voltage, whereas the current limiter is actuated by line current.

Spring S2 holds contact C2 closed until the current through it discharges the battery in a short time.

the main line and L3 exceeds a certain value, as determined by the tension of spring S2, and causes C2 to be opened.

The operation of a three unit regulator is described in the following paragraphs. [Figure 12-330] The increase in current is due to an increase in load. This action inserts R2 into the field circuit of the generator and The action of vibrating contact C1 in the voltage regulator decreases the field current and the generated voltage. When the generated voltage is decreased, the generator current is unit causes an intermittent short circuit between points R1 and L2. When the generator is not operating, spring S1 holds C1 reduced. The core of L3 is partly demagnetized and the spring closes the contact points. This causes the generator voltage closed; C2 is also closed by S2. The shunt field is connected directly across the armature. and current to rise until the current reaches a value sufficient to start the cycle again. A certain minimum value of load When the generator is started, its terminal voltage rises as current is necessary to cause the current limiter to vibrate.

the generator comes up to speed, and the armature supplies the field with current through closed contacts C2 and C1. The purpose of the reverse current cut-out relay is to automatically disconnect the battery from the generator when the generator voltage is less than the battery voltage. If this device were not used in the generator circuit, the battery would discharge through the generator. This would tend to make the generator operate as a motor, but because the generator is coupled to the engine, it could not rotate such a heavy load. Under this condition, the generator windings may be severely damaged by excessive current.

There are two windings, L4 and L5, on the soft iron core. The current winding, L4, consisting of a few turns of heavy wire, is in series with the line and carries the entire line current.

Figure 12-325. Starter generator for small business jet.

12-161 Exciter (if used) Alternator Motor Motor starting panel Alternator control panel Start-stop pushbutton V A W Voltage control VM AM Reset button 5W 5W Input terminal Output terminal Figure 12-326. AC motor generator set for ground testing.

B The voltage winding, L5, consisting of a large number of turns of fine wire, is shunted across the generator terminals.

Shunt field + When the generator is not operating, the contacts, C3 are held Rheostat open by the spring S3. As the generator voltage builds up, L5 Load magnetizes the iron core. When the current (as a result of the generated voltage) produces sufficient magnetism in the iron A – core, contact C3 is closed, as shown. The battery then receives a charging current. The coil spring, S3, is so adjusted that the Terminal connections voltage winding does not close the contact points until the voltage of the generator is in excess of the normal voltage of E the battery. The charging current passing through L4 aids the Current flow current in L5 to hold the contacts tightly closed. Unlike C1 Figure 12-327. Regulation of generator voltage by field rheostat.

and C2, contact C3 does not vibrate. When the generator slows down or, for any other cause, the generator voltage decreases to a certain value below that of the battery, the current reverses Differential Relay Switch through L4 and the ampere turns of L4 oppose those of L5.

Aircraft electrical systems normally use some type of reverse Thus, a momentary discharge current from the battery reduces current relay switch, which acts not only as a reverse current the magnetism of the core and C3 is opened, preventing the relay cut-out but also serves as a remote control switch by battery from discharging into the generator and motoring it.

which the generator can be disconnected from the electrical C3 does not close again until the generator terminal voltage system at any time. One type of reverse current relay switch exceeds that of the battery by a predetermined value.

operates on the voltage level of the generator, but the type most commonly used on large aircraft is the differential relay switch, which is controlled by the difference in voltage 12-162 C B Load K S P Figure 12-328. Vibrating-type voltage regulator.

Figure 12-329. Three unit regulator.

between the battery bus and the generator.

When the generator voltage exceeds the bus voltage by The differential type relay switch connects the generator to 0.35 volt, current flows through the differential coil, the the main bus bar in the electrical system when the generator differential relay contact closes and, thus, completes the main voltage output exceeds the bus voltage by 0.35 to 0.65 volt.

contractor coil circuit. The contacts of the main contactor It disconnects the generator when a nominal reverse current close and connect the generator to the bus.

flows from the bus to the generator. The differential relays on all the generators of a multiengine aircraft do not close when When the generator voltage drops below the bus (or battery) the electrical load is light. For example, in an aircraft having voltage, a reverse current weakens the magnetic field about a load of 50 amperes, only two or three relays may close.

the temporary magnet of the differential relay. The weakened If a heavy load is applied, the equalizing circuit lowers the field permits a spring to open the differential relay contacts, voltage of the generators already on the bus and, at the same breaking the circuit to the coil of the main contactor relay, time, raise the voltage of the remaining generators, allowing opening its contacts, and disconnecting the generator from their relays to close. If the generators have been paralleled the bus. The generator battery circuit may also be broken properly, all the relays stay closed until the generator control by opening the flight deck control switch, which opens the switch is turned off or until the engine speed falls below the contacts of the voltage relay, causing the differential relay minimum needed to maintain generator output voltage.

coil to be de-energized.

The differential generator control relay shown in Figure 12-331 Overvoltage & Field Control Relays is made up of two relays and a coil-operated contactor. One Two other items used with generator control circuits are the relay is the voltage relay and the other is the differential relay.

overvoltage control and the field control relay. As its name Both relays include permanent magnets that pivot between implies, the overvoltage control protects the system when the pole pieces of temporary magnets wound with relay coils.

Voltages of one polarity set up fields about the temporary Reverse magnets with polarities that cause the permanent magnet to Voltage Current current regulator limiter cut-out move in the direction necessary to close the relay contacts; voltages of the opposite polarity establish fields that cause Loads the relay contacts to open. The differential relay has two S3 coils wound on the same core. The coil-operated contactor, C3 called the main contactor, consists of movable contacts that A are operated by a coil with a movable iron core.

Armature L1 L4 L3 + + L2 Closing the generator switch on the control panel connects C2 L5 Shunt the generator output to the voltage relay coil. When generator Storage field – – C1 S1 S2 R1 voltage reaches 22 volts, current flows through the coil battery R2 and closes the contacts of the voltage relay. This action completes a circuit from the generator to the battery through the differential coil.

Figure 12-330. Three unit regulator for variable speed generators.

12-163 excessive voltage exists. The overvoltage relay is closed of the busses are equalized in their load sharing.

when the generator output reaches 32 volts and completes a Over-Excitation Protection circuit to the trip coil of the field control relay. The closing of the field control relay trip circuit opens the shunt field circuit When a GCU in a paralleled system fails, a situation can and completes it through a resistor, causing generator voltage occur where one of the generators becomes overexcited and to drop; also, the generator switch circuit and the equalizer tries to carry more than its share of the load, if not all of circuit (multiengine aircraft) are opened. An indicator light the loads. When this condition is sensed on the equalizing circuit is completed, warning that an overvoltage condition bus, the faulted generation control system shuts down exists. A “reset” position of the flight deck switch is used by receiving a de-excitation signal. This signal is then to complete a reset coil circuit in the field control relay, transmitted to the overvoltage circuit, and then opens the returning the relay to its normal position. field excitation output circuit.

Generator Control Units (GCU) Differential Voltage When the GCU allows the logic output to close the generator Basic Functions of a Generator Control Unit (GCU) line contactor, the generator voltage must be within a close The generator control unit (GCU) is more commonly found tolerance of the load bus. If the output is not within the on turbine power aircraft. The most basic GCU perform a specified tolerance, then the contactor is not allowed to number of functions related to the regulation, sensing, and connect the generator to the bus.

protection of the DC generation system. [Figure 12-332] Reverse Current Sensing Voltage Regulation If the generator is unable to maintain the required voltage The most basic of the GCU functions is that of voltage level, it eventually begins to draw current instead of providing regulation. Regulation of any kind requires the regulation unit it. In this case, the faulty generator is seen as a load to the to take a sample of an output and to compare that sample with other generators and will need to be removed from the a controlled reference. If the sample taken falls outside of the bus. Once the generator is off-line, it is not permitted to be limits set by the reference, then the regulation unit must provide reconnected to the bus until such time that the generator faults an adjustment to the unit generating the output so as to diminish are cleared and the generator is capable of providing a current or increase the output levels. In the case of the GCU, the output to the bus. In most cases, the differential voltage circuit and voltage from a generator is sensed by the GCU and compared the reverse current sensing circuit are one in the same.

to a reference voltage. If there is any difference between the two, the error is usually amplified and then sent back to the field Alternator Constant Speed Drive System excitation control portion of the circuit. The field excitation control then makes voltage⁄excitation adjustments in the field Alternators are not always connected directly to the airplane winding of the generator in order to bring the output voltage engine like DC generators. Since the various electrical back into required bus tolerances. devices operating on AC supplied by alternators are designed to operate at a certain voltage and at a specified frequency, Overvoltage Protection the speed of the alternators must be constant; however, the Like the voltage regulation feature of the GCU, the speed of an airplane engine varies. Therefore, the engine, overvoltage protection system compares the sampled voltage through a constant speed drive installed between the engine to reference voltage. The output of the overvoltage protection and the alternator, drives some alternators.

circuit is used to open the relay that controls the output for the field excitation. These types of faults can occur for a number A typical hydraulic-type drive is shown in Figure 12-333 .

of reasons. The most common, however, is the failure of the The following discussion of a constant speed drive system voltage regulation circuit in the GCU. is based on such a drive found on large multiengine aircraft.

The constant speed drive is a hydraulic transmission that may Parallel Generator Operations be controlled either electrically or mechanically.

The paralleling feature of the GCU allows for two or more GCU/generator systems to work in a shared effort to provide The constant speed drive assembly is designed to deliver an output of 6,000 rpm, provided the input remains between current to the aircraft electrical system. Comparing voltages between the equalizer bus and the interpole/compensator 2,800 and 9,000 rpm. If the input, which is determined by engine speed, is below 6,000 rpm, the drive increases the voltage, and amplifying the differences accomplishes the control of this system. The difference is then sent to the speed in order to furnish the desired output. This stepping up of speed is known as overdrive.

voltage regulation circuit, where adjustments are then made in the regulation output. These adjustments continue until all 12-164 Main contractor Gen. Batt.

Pivot Reverse current coil S N Voltage relay coil Pivot Voltage relay contacts S N Differential relay contacts N Permanent magnet N S Permanent magnet Differential coil Temporary magnet Temporary magnet SW Figure 12-331. Differential generator control relay.

In overdrive, an automobile engine operates at about the which it drives, as well as to the makeup and scavenger same rpm at 60 mph as it does in conventional drive at 49 gear pumps E.

mph. In aircraft, this principle is applied in the same manner.

The constant speed drive enables the alternator to produce The makeup (charge) pump delivers oil (300 psi) to the pump the same frequency at slightly above engine idle rpm as it and motor cylinder block, to the governor system, and to the would at takeoff or cruising rpm. pressurized case, whereas the scavenger pump returns the oil to the external reservoir.

With the input speed to the drive set at 6,000 rpm, the output speed is the same. This is known as straight drive and might The rotating cylinder assembly B consists of the pump and be compared to an automobile in high gear. However, when motor cylinder blocks, which are bolted to opposite sides of the input speed is greater than 6,000 rpm, it must be reduced a port plate. The two other major parts are the motor wobbler to provide an output of 6,000 rpm. This is called underdrive, A and the pump wobbler C. The governor system is the unit which is comparable to an automobile in low gear. Thus, the at the top of the left side in Figure 12-334 .

large input, caused by high engine rpm, is reduced to give the desired alternator speed. The cylinder assembly has two primary units. The block assembly of one of the units, the pump, contains 14 cylinders, As a result of this control by the constant speed drive, the each of which has a piston and pushrod. Charge pressure from frequency output of the generator varies from 420 cps at no the makeup pump is applied to each piston in order to force load to 400 cps under full load. This, in brief, is the function it outward against the pushrod. It, in turn, is pushed against of the constant speed drive assembly. Before discussing the pump wobble plate.

the various units and circuits, the overall operation of the transmission should be discussed as follows. If the plate remained as shown in Figure 12-335A , each of the 14 cylinders would have equal pressure, and all pistons would Hydraulic Transmission be in the same relative position in their respective cylinders.

But with the plate tilted, the top portion moves outward and The transmission is mounted between the generator and the the lower portion inward. [Figure 12-335B] As a result, more aircraft engine. Its name denotes that hydraulic oil is used, oil enters the interior of the upper cylinder, but oil is forced although some transmissions may use engine oil. Refer to the from the cylinder of the bottom piston.

cutaway view of such a transmission in Figure 12-334. The input shaft D is driven from the drive shaft on the accessory If the pump block were rotated while the plate remained section of the engine. The output drive F, on the opposite end stationary, the top piston would be forced inward because of of the transmission, engages the drive shaft of the generator.

the angle of the plate. This action would cause the oil confined within the cylinder to be subjected to increased pressure great The input shaft is geared to the rotating cylinder block gear, 12-165 greater pressure in the pump and motor cylinders produces the result described.

With the transmission in underdrive, the angle is arranged so there is a reduction in pumping action. The subsequent slippage between the pushrods and motor wobble plate reduces the output speed of the transmission. When the pump wobble plate is not at an angle, the pumping action is at a minimum and the transmission has what is known as hydraulic lock. For this condition, the input and output speed is about the same, and the transmission is considered to be in straight drive.

To prevent the oil temperature from becoming excessively high within the cylinder block, the makeup pressure pump forces oil through the center of this block and the pressure relief valve. From this valve, the oil flows into the bottom of the transmission case. A scavenger pump removes the oil from the transmission case and circulates it through the oil cooler and filters before returning it to the reservoir. At the start of the cycle, oil is drawn from the reservoir, passed through a filter, and forced into the cylinder block by the makeup pressure pump.

The clutch, located in the output gear and clutch assembly, is an overrunning one way, sprag-type device. Its purpose is to ratchet if the alternator becomes motorized; otherwise, Figure 12-332. Generator Control Unit (GCU).

the alternator might turn the engine. Furthermore, the clutch provides a positive connection when the transmission is driving the alternator.

enough to force it into the motor cylinder block assembly.

There is another unit of the drive that must be discussed—the Before explaining what the high-pressure oil in the motor governor system. The governor system, which consists of a unit does, it is necessary to know something about this part hydraulic cylinder with a piston, is electrically controlled. Its of the rotating cylinder block assembly. The motor block duty is to regulate oil pressure flowing to the control cylinder assembly has 16 cylinders, each with its piston and pushrod.

assembly. [Figure 12-336] These are constantly receiving charge pressure of 300 psi.

The position of the piston depends upon the point at which The center of the system’s hydraulic cylinder is slotted so the each pushrod touches the motor wobble plate. These rods arm of the pump wobble plate can be connected to the piston.

cause the wobble plate to rotate by the pressure they exert As oil pressure moves the piston, the pump wobble plate is against its sloping surface.

placed in either overspeed, underspeed, or straight drive.

The piston and pushrod of the motor are pushed outward as Figure 12-337 shows the electrical circuit used to oil is forced through the motor valve plate from the pump govern the speed of the transmission. First, the main cylinder. The pushrods are forced against the motor wobble points of the complete electrical control circuit are plate, which is free to rotate but cannot change the angle at discussed. [Figures 12-337 and 12-338] For simplification, which it is set. Since the pushrods cannot move sideways, two portions, the overspeed circuit and the load division the pressure exerted against the motor wobble plate’s sloping circuit, are considered as individual circuits.

face causes it to rotate.

Note, in Figure 12-337 , that the circuit has a valve and In the actual transmission, there is an adjustable wobble plate.

solenoid assembly (O) and a control cylinder (E), and that The control cylinder assembly determines the tilt of the pump it contains such units as the tachometer generator (D), the wobble plate. For example, it is set at an angle, which causes rectifier (C), and adjustable resistor (B), rheostat (A), and the motor cylinders to turn the motor wobble plate faster than the control coil (Q).

the motor assembly if the transmission is in overdrive. The 12-166 Figure 12-333. Constant speed drive.

procedure is reversed.

Since it is driven by a drive gear in the transmission, the tachometer (often called tach) generator, a three-phase unit, With the output speed reduction, tach generator output has a voltage proportional to the speed of the output drive. decreases; consequently, the flow of current to the solenoid The rectifier changes its voltage from AC to DC. After diminishes. Therefore, the magnetic field of the solenoid rectification, the current flows through the resistor, rheostat, becomes so weak that the spring is able to overcome it and and valve and solenoid. Each of these units is connected in reposition the valve.

series. [Figure 12-338] If a heavy load is put on the AC generator, its speed decreases.

Under normal operating conditions, the output of the tach The generator is not driven directly by the engine; the generator causes just enough current to enter the valve and hydraulic drive allows slippage. This decrease causes the solenoid coil to set up a magnetic field of sufficient strength output of the tach generator to taper off and, as a result, to balance the spring force in the valve. When the alternator weakens the magnetic field of the solenoid coil. The spring speed increases as the result of a decrease in load, the tach in the solenoid moves the valve and allows oil pressure to generator output also increases. Because of the greater output, enter the increase side of the control cylinder and the output the coil in the solenoid is sufficiently strengthened to overcome speed of the transmission is raised.

the spring force. Thus, the valve moves and, as a result, oil pressure enters the reduced speed side of the control cylinder. There are still two important circuits that must be discussed: the overspeed circuit and the load division circuit. The In turn, the pressure moves the piston, causing the angle of generator is prevented from overspeeding by a centrifugal the pump wobble plate to be reduced. The oil on the other switch (S) in Figure 12-339 and the overspeed solenoid coil side of the piston is forced back through the valve into the (R), which is located in the solenoid and valve assembly.

system return. Since the angle of the pump wobble plate is The centrifugal switch is on the transmission and is driven smaller, there is less pumping action in the transmission. The through the same gear arrangement as the tach generator.

result is decreased output speed. To complete the cycle, the 12-167 A B C F D E Figure 12-334. Cutaway of a hydraulic transmission.

The aircraft DC system furnishes the power to operate the J ). Rectifiers (K) then change the output of the transformer overspeed coil in the solenoid and coil assembly. If the secondaries from AC to DC.

output speed of the transmission reaches a speed of 7,000 to 7,500 rpm, the centrifugal switch closes the DC circuit The function of the two capacitors (L) is to smooth out the and energizes the overspeed solenoid. This component then DC pulsations.

moves the valve and engages the latch that holds the valve in the underdrive position. To release the latch, energize the The output of the current transformer (F) depends upon the underdrive release solenoid. amount of current flowing in the line of one phase. In this way, it measures the real load of the generator. The output The load division circuit’s function is to equalize the loads voltage of the current transformer is applied across resistor placed on each of the alternators, which is necessary to (H). This voltage is added vectorially to the voltage applied assure that each alternator assumes its share; otherwise, to the upper winding of transformer (J) by the output of one alternator might be overloaded while another would be transformer (F). At the same time as it adds vectorially to carrying only a small load. the upper winding of transformer (J), it subtracts vectorially from the voltage applied to the lower winding of (J).

In Figure 12-340 , one phase of the alternator provides power for the primary in transformer (G), whose secondary supplies This voltage addition and subtraction depends on the real load power to the primaries of two other transformers (J and of the generator. The amount of real load determines the phase 12-168 A B Figure 12-335. Wobble plate position.

angle and the amount of voltage impressed across resistor (H). so the load is more evenly distributed.

The greater the real load, the greater the voltage across (H), and hence, the greater the difference between the voltages applied On some drives, instead of an electrically-controlled to the two primaries of transformer (J). The unequal voltages governor, a flyweight-type governor is employed, which applied to resistor (M) by the secondaries of transformer (J) consists of a recess-type revolving valve driven by the cause a current flow through the control coil (P). output shaft of the drive, flyweights, two coil springs, and a nonrotating valve stem. Centrifugal force, acting on the The control coil is wound so that its voltage supplements governor flyweights, causes them to move outward, lifting the voltage for the control coil in the valve and solenoid the valve stem against the opposition of a coil spring.

assembly. The resulting increased voltage moves the valve and slows down the generator’s speed. Why should the speed The valve stem position controls the directing of oil to the be decreased if the load has been increased? Actually, systems two oil outlines. If the output speed tends to exceed 6,000 using only one generator would not have decreased speed, rpm, the flyweights lift the valve stem to direct more oil to but for those having two or more generators, a decrease is the side of the control piston, causing the piston to move in a necessary to equalize the loads. direction to reduce the pump wobble plate angle. If the speed drops below 6,000 rpm, oil is directed to the control piston The load division circuit is employed only when two or more so that it moves to increase the wobble plate angle.

generators supply power. In such systems, the control coils are connected in parallel. If the source voltage for one of these Overspeed protection is installed in the governor. The drive becomes higher than the others, it determines the direction of starts in the underdrive position. The governor coil springs current flow throughout the entire load division circuit. As are fully extended and the valve stem is held at the limit of explained before, the real load on the generator determines its downward travel. In this condition, pressure is directed the amount of voltage on the control coil; therefore, the to the side of the control piston giving minimum wobble generator with the highest real load has the highest voltage. plate angle. The maximum angle side of the control piston is open to the hollow stem. As the input speed increases, the As shown in Figure 12-341 , current through No. 1 control flyweights start to move outward to overcome the spring bias.

coil, where the largest load exists, aids the control coil of the This action lifts the valve stem and starts directing oil to the valve and solenoid, thereby slowing down the generator. (The maximum side of the control piston, while the minimum side source voltage of the control coils is represented by battery is opened to the hollow stem.

symbols in Figure 12-341 .) The current in the remaining control coils opposes the control coil of the valve and At about 6,000 rpm, the stem is positioned to stop drainage solenoid, in order to increase the speed of the other generators of either side, and the two pressures seek a balance point as 12-169 Figure 12-336. Control cylinder.

A B C D Latch Constant speed drive Generator R E Q P O Oil out Oil in Figure 12-337. Electrical hydraulic control circuit.

the flyweight force is balanced against the spring bias. Thus, coil spring breaks and the stem moves to the extreme position a mechanical failure in the governor causes an underdrive in that direction, output speed is reduced. If the input to the condition. The flyweight’s force is always tending to move governor fails, the spring forces the stem all the way to the the valve stem to the decrease speed position so that, if the start position to obtain minimum output speed.

12-170 A B C D Latch Constant speed drive Generator K R S J E L H Q G N K L N P J F O To load Oil out Oil in Figure 12-338. Speed control circuit.

bus voltage, while the division of load between alternators An adjustment screw on the end of the governor regulates depends upon the adjustments of their speed governors, the output speed of the constant speed drive. This adjustment which are controlled by the frequency and droop circuits increases or decreases the compression of a coil spring, discussed in the previous section on alternator constant-speed opposing the action of the flyweights. The adjustment drive systems.

screws turn in an indented collar, which provides a means of making speed adjustments in known increments. Each “click” When AC generators are operated in parallel, frequency and provides a small change in generator frequency. voltage must both be equal. Where a synchronizing force is required to equalize only the voltage between DC generators, The constant speed drive (CSD) can be an independent unit synchronizing forces are required to equalize both voltage and or mounted within the alternator housing. When the CSD and speed (frequency) between AC generators. On a comparative the alternator are contained within one unit, the assembly is basis, the synchronizing forces for AC generators are much known as an integrated drive generator (IDG). greater than for DC generators. When AC generators are of sufficient size and are operating at unequal frequencies and Voltage Regulation of Alternators terminal voltages, serious damage may result if they are suddenly connected to each other through a common bus. To The problem of voltage regulation in an AC system does not avoid this, the generators must be synchronized as closely as differ basically from that in a DC system. In each case, the possible before connecting them together.

function of the regulator system is to control voltage, maintain a balance of circulating current throughout the system, and Regulating the voltage output of a DC exciter, which eliminate sudden changes in voltage (anti-hunting) when a supplies current to the alternator rotor field, best controls load is applied to the system. However, there is one important the output voltage of an alternator. This is accomplished difference between the regulator system of DC generators by the regulation of a 28-volt system connected in the field and alternators operated in a parallel configuration. The load circuit of the exciter. A regulator controls the exciter field carried by any particular DC generator in either a two or four current and thus regulates the exciter output voltage applied generator system depends on its voltage as compared with the 12-171 cause the transistor to cut off conduction to control the alternator field strength. The regulator operating range is Latch usually adjustable through a narrow range. The thermistor provides temperature compensation for the circuitry. The transistorized voltage regulator shown in Figure 12-342 will be referred to in explaining the operation of this type S of regulator.

R The AC output of the generator is fed to the voltage regulator, where it is compared to a reference voltage, and the difference is applied to the control amplifier section of the regulator. If the output is too low, field strength of the AC exciter generator Q is increased by the circuitry in the regulator. If the output is too high, the field strength is reduced.

The power supply for the bridge circuit is CR1, which P provides full-wave rectification of the three phase output from transformer T1. The DC output voltages of CR1 are proportional to the average phase voltages. Power is supplied from the negative end of the power supply through point B, R2, point C, zener diode (CR5), point D, and to the parallel hookup of V1 and R1. Takeoff point C of the bridge is located between resistor R2 and the zener diode. In the other leg of O the reference bridge, resistors R9, R7, and the temperature Oil out compensating resistor RT1 are connected in series with V1 and R1 through points B, A, and D. The output of this leg of the bridge is at the wiper arm of R7.

Oil in As generator voltage changes occur, for example, if the voltage lowers, the voltage across R1 and V1 (once V2 starts conducting) remains constant. The total voltage change occurs across the bridge circuit. Since the voltage across the zener diode remains constant (once it starts conducting), the total voltage change occurring in that leg of the bridge is across resistor R2. In the other leg of the bridge, the voltage change across the resistors is proportional to their resistance values. Therefore, the voltage change across R2 is greater than the voltage change across R9 to wiper arm of R7. If the generator output voltage drops, point C is negative with Figure 12-339. Overspeed circuit.

respect to the wiper arm of R7. Conversely, if the generator voltage output increases, the polarity of the voltage between to the alternator field.

the two points is reversed.

Alternator Transistorized Regulators The bridge output, taken between points C and A, is Many aircraft alternator systems use a transistorized voltage connected between the emitter and the base of transistor regulator to control the alternator output. Before studying Q1. With the generator output voltage low, the voltage from this section, a review of transistor principles may be helpful.

the bridge is negative to the emitter and positive to the base.

This is a forward bias signal to the transistor, and the emitter A transistorized voltage regulator consists mainly of to collector current therefore increases. With the increase of transistors, diodes, resistors, capacitors, and, usually, a current, the voltage across emitter resistor R11 increases.

thermistor. In operation, current flows through a diode and transistor path to the generator field. When the proper This, in turn, applies a positive signal to the base of transistor voltage level is reached, the regulating components 12-172 Latch Constant speed drive Generator K R J1 E L H Q G M K L N P J2 F O To Load Oil out Oil in Figure 12-340. Droop circuit.

be excited.

Another item of interest is the line containing resistors R27, R28, and R29 in series with the normally closed contacts of the K1 relay. The operating coil of this relay is found in the lower left part of the schematic. Relay K1 is connected across the power supply (CR4) for the transistor amplifier.

When the generator is started, electrical energy is supplied 1 2 3 4 from the 28-volt DC bus to the exciter generator field to “flash the field” for initial excitation. When the field of the Figure 12-341. Relative direction of current in droop coil circuit exciter generator has been energized, the AC generator starts with unequal loads.

to produce, and as it builds up, relay K1 is energized, opening the “field flash” circuit.

Q4, increasing its emitter to collector current and increasing the voltage drop across the emitter resistor R10.

This gives a positive bias to the base of Q2, which increases its emitter to collector current and increase the voltage drop across its emitter resistor R4. This positive signal controls output transistor Q3. The positive signal on the base of Q3 increases the emitter to collector current.

The control field of the exciter generator is in the collector circuit. Increasing the output of the exciter generator increases the field strength of the AC generator, which increases the generator output.

To prevent exciting the generator when the frequency is at a low value, there is an underspeed switch located near the F+ terminal. When the generator reaches a suitable operating frequency, the switch closes and allows the generator to 12-173 R1 V1 D RT1 CR5 +28V Special bus N R7 A C R29 R9 R2 R28 CR1 R27 T2 T3 B Switch underspeed K1 F+ A+ CR4 F CR2 T1 R6 R3 R8 A A– AC gen. R Q1 Q4 Q2 Q3 exciter G K1 Gen. neg. bus T1 R11 R10 R4 CR3 Y- CR4 Figure 12-342. Transistorized voltage regulator.

12-174

Next: Chapter 13 →

Chapter 13

Mechanic Privileges & Limitations

a certificate to a person located outside of the United States Introduction is necessary for the operation and continued airworthiness Since Title 14 of the Code of Federal Regulations (14 CFR) of a U.S.-registered civil aircraft, it will issue a certificate to part 65 was covered only briefly in Chapter 2, Regulations, that person, providing they meet the necessary requirements.

Maintenance Forms, Records, and Publications, it is discussed in greater detail in this chapter. This chapter discusses the Section 65.11, Application and Issue Federal Aviation Administration (FAA) regulation governing Any person who meets the criteria for obtaining a mechanic the certification of airmen other than flight crew members.

certificate must apply by means of FAA Form 8610-2, Airman This chapter is based on the material contained in 14 CFR Certificate and/or Rating Application. If a mechanic has had part 65, which has the following subparts: a certificate suspended, they may not apply for additional • Subpart A—General ratings during the time of suspension. A revocation of a mechanic certificate prevents that person from applying for • Subpart B—Air Traffic Control Tower Operators a certificate within a period of 1 year after the revocation.

• Subpart C—Aircraft Dispatchers • Subpart D—Mechanics Section 65.12, Offenses Involving Alcohol and Drugs • Subpart E—Repairmen Any person, who has been convicted of violating federal or • Subpart F—Parachute Riggers state statutes relating to drug offenses, can be denied their application for a certificate or rating up to 1 year after the date This chapter only focuses on the certification of maintenance of conviction. The violation can be relating to any one or more technicians and, therefore, subparts B, C, E, and F are of the following actions: growing, processing, manufacturing, not addressed.

selling, disposing, possessing, transporting, or importing narcotic drugs, marijuana, depressants, or stimulants. They The FAA certificates two separate categories of maintenance may also face the suspension or revocation of any certificate technicians: mechanic and repairman. The fundamental that they currently hold.

difference between these two is that the mechanic certificate is transportable, is issued to the technician based upon Section 65.13, Temporary Certificate their training and knowledge, and is not dependent on the A qualified applicant who successfully passes all required technician’s location. Although the repairman certificate is tests with a minimum score of 70 percent may be issued a also based upon the training and knowledge of the technician, temporary certificate, which is valid for not more than 120 it is specifically issued to that technician while they are days. During this time, the FAA will review the application employed at a distinct location of a specific company. This and any supplementary documentation and will issue the certificate carries a literal address where the technician official certificate and rating.

is authorized to work using their repairman skills. When the technician is no longer employed there, the repairman Section 65.14, Security Disqualification certificate must be returned to the Flight Standards District This section was added following the terrorist attacks of Office (FSDO) that issued it.

September 11, 2001. It basically states that anyone determined by the Transportation Security Administration (TSA) to be a Mechanic Certification: Subpart A—General security threat will either have their application held if they (by 14 CFR Section) are applying for a certificate, or have the certificate that they Section 65.3, Certification of Foreign Airmen Other do hold revoked.

Than Flight Crewmembers Normally, the FAA issues these certificates only to United Section 65.15, Duration of Certificates States (U.S.) citizens or resident aliens residing in the United Mechanic’s certificates are effective until they are surrendered, States. However, if the FAA determines that the issuance of suspended, or revoked. The difference in these terms can be consider when desiring to apply for retesting: summarized in the following manner: • Wait a period of 30 days after the date of test failure • Surrendered means given up voluntarily.

and then take the test again.

• Suspended means the FAA temporarily removes the • Seek additional instruction in the subject matter certificate from the holder.

areas failed and provide a signed statement from the • Revoked means the FAA permanently removes the certificated technician providing the instruction stating certificate from the holder.

the applicant has received necessary instruction and is ready for testing.

Section 65.16, Change of Name: Replacement of Lost or Destroyed Certificate Section 65.20, Applications, Certificates, Logbooks, An application for a change of name on a certificate issued Reports, and Records: Falsification, Reproduction, under this part must be accompanied by the applicant's or Alteration current certificate and the marriage license, court order, or 14 CFR part 43, sections 43.9 and 43.11 define the other document verifying the change.

requirements for a technician to make appropriate entries in the maintenance/inspection records for the work If the technician changes their name, or is seeking a performed. This proper documentation is fundamental to replacement certificate, an application must be submitted to safe and efficient operation of the U.S. civil aircraft fleet.

the FAA at the following address: Therefore, the FAA takes strong action against those who would participate in the falsification of those records. The Federal Aviation Administration following actions are the basis for suspending or revoking Airmen Certification Branch (AFB-720) any certificate or rating held by the person who: P.O. Box 25082 • Makes fraudulent or intentionally false statement on Oklahoma City, OK 73125 an application.

It should be noted that there is a nominal charge for this service.

• Makes fraudulent or intentionally false statement in any logbook, record, or report required to show Section 65.17, Test: General Procedure compliance with any certificate requirements.

The FAA has designated certain persons to administer • Reproduces a certificate or rating for fraudulent tests associated with obtaining a mechanic certificate. The purposes.

minimum passing score for these tests is 70 percent.

• Alters any certificate or rating under this part.

Section 65.18, Written Tests: Cheating or Other Section 65.21, Change of Address Unauthorized Content If the technician changes their address, the FAA (at the If the mechanic or repairmen applicant is determined to be address shown below) must be notified in writing within 30 cheating, or otherwise involved in unauthorized conduct, they days after the change of permanent residence: are not eligible for any certificate or rating under this chapter for a period of 1 year. Furthermore, current ratings the person Federal Aviation Administration already holds may also be suspended or revoked. Examples Airmen Certification Branch (AFB-720) of unacceptable conduct for written tests are: P.O. Box 25082 • Copying or intentionally removing the test.

Oklahoma City, OK 73125 • Giving or receiving any part of a copy of the test.

Refusal to Submit to a Drug or Alcohol Test • Giving or receiving help during the test taking period.

Any technician who refuses to submit to a drug test, which • Take any part of the test on behalf of another person.

is required by 14 CFR part 120, section 120.15, is subject • Using any material or aid during the test taking period to denial by the FAA of any application for additional that is not provided by authorized test administrators.

certification or ratings, as well as suspension or revocation of any existing certificate or rating they currently hold. Part • Intentionally causing, assisting, or participating in any 120, section 120.117, Implementing a Drug Testing Program, of the previous acts.

requires a urine sample from the employee. Part 120, section 120.37, Misuse of Alcohol, requires that the employee Section 65.19, Retesting After Failure submit to a breath test. Each section contains a “Definitions” Should the mechanic or repairman fail to achieve the required section and a section titled “Employees who must be tested.” minimum passing grade, there are two options they may Persons involved with “Aircraft maintenance or preventative and testing either individually or as a combined certificate.

maintenance duties” are listed in both sections. There are various types (or rather times) when testing is required: Any person holding an aircraft (A) or aircraft engine (E) certificate prior to June 15, 1952, and which was valid on • Pre-employment that date, may exchange it for the corresponding current • Periodic certificate. If both ratings were held, the A & E certificate may be exchanged for an Airframe and Powerplant (A&P).

• Random • Post-accident Section 65.75, Knowledge Requirements • Testing based upon reasonable cause Any applicant meeting the experience requirements listed in section 65.77 must pass a written test (minimum passing • Return to duty testing score of 70% as described in section 65.17) covering the • Follow-up testing construction and maintenance of aircraft. There are three separate tests that the applicant for the A&P certificate must The numerous test methods and the harsh penalty imposed pass: General (60 questions), Airframe (100 questions), and by the FAA on those who involve themselves with these Powerplant (100 questions). Applicable portions of 14 CFR unauthorized substances or abuse the allowable use of 43 and 91 are also included in the testing. Basic principles for alcohol indicates the concern that the FAA has for the the installation and maintenance of propellers are included possible impairment of technicians. Aviation maintenance with the testing that is administered for the powerplant is a professional career choice that demands the highest rating. Successful completion of the written test is required caliber technical person to be capable of functioning at their before the candidate may apply for the oral and practical maximum potential. There is no room in this profession tests identified in section 65.79.

for a person to be involved with substance abuse. By doing so, the technician not only endangers themselves, Section 65.77, Experience Requirements but their co-workers, and ultimately the customer who is Each mechanic applicant must have a certificate of completion expecting to have an airworthy aircraft delivered following from a certificated aviation maintenance technician school a maintenance activity.

(AMTS) (14 CFR part 147) or provide documented evidence of a minimum of 18 months practical experience related Mechanic Certification: Subpart D—Mechanics to either airframe or powerplant maintenance (30 months (by 14 CFR Section) required if applying for certification for both airframe and Section 65.71, Eligibility Requirements: General powerplant).

The requirements for obtaining a mechanic certificate are: Section 65.79, Skill Requirements • Be at least 18 years of age.

Oral and practical tests to determine the applicant’s basic • Be able to read, write, speak, and understand the knowledge and skills necessary for the certificate or rating English language. ( Note: If the applicant does not sought are required to be completed after the applicant has meet this requirement and is employed outside the successfully completed the written test. The practical test United States by a U.S. carrier, the certificate will be additionally requires minor repairs and minor alterations to endorsed “valid only outside the United States.”) propellers to be demonstrated as part of the powerplant rating.

• Have passed all the required tests (written, oral, To assist the applicant, the Aviation Mechanic Practical and practical) within the preceding 24 months from Test Standards (PTS) have been published by the FAA to application.

provide standards for testing in which the applicant for the A&P certificate should be familiar. The Aviation Mechanic • Possess and demonstrate the appropriate knowledge PTS include the subject areas of knowledge and skill for and skill for the certificate rating being sought.

the issuance of an aviation mechanic certificate and/or the addition of a rating. The subject areas are the topics in which If a technician has one of the ratings and desires to add the aviation mechanic applicants must have knowledge and/or other, they must meet the requirements set forth in section demonstrate skill. The PTSs are available on the FAA website 65.77, and take the written, oral, and practical tests within at www.faa.gov.

24 months.

Section 65.73, Ratings The FAA recognizes two ratings: airframe and powerplant.

These may be attained by a person upon successful application

Next: Section 65.85, Airframe Rating: Additional Privileges →

Section 65.85, Airframe Rating: Additional Privileges

Section 65.85, Airframe Rating: Additional Privileges Section 65.80, Certificated Aviation Maintenance Technician School Students A mechanic who holds an airframe rating may approve and return to service an airframe, an appliance, or any related Whenever satisfactory evidence is shown to the FAA that a part after they have performed, supervised, or inspected student enrolled in an aviation maintenance technician school minor repairs or alterations. They may also perform the (certificated under part 147) is making satisfactory progress, maintenance actions required for a major repair or alteration, that student may take the oral and practical tests required and should initiate the appropriate form (FAA Form 337, by section 65.79, prior to completing the school’s approved Major Repair and Alteration) associated with that work.

curriculum (as required by section 65.77) and prior to taking However, the return to service action must be accomplished the written test required by section 65.75.

by a certificated A&P technician holding an Inspection Authorization (IA). (Refer to 14 CFR section 65.95.) The Section 65.81, General Privileges and Limitations airframe mechanic is also authorized to perform the 100-hour Once a technician becomes a certificated mechanic, they inspection (if required per 14 CFR part 91 section 91.409) may perform or supervise the maintenance, preventive on the airframe.

maintenance, or alterations of an aircraft or appliance (or part thereof) for which they are rated. However, they are A certificated mechanic with an airframe rating can approve not permitted to perform major repair or major alterations and return to service the airframe of an aircraft with a special to propellers nor accomplish any repair to or alteration of airworthiness certificate, in the light-sport category (refer instruments. These activities are reserved for certificated to 14 CFR part 21, section 21.190) after performing and repairmen at an authorized repair station. Also, they may inspecting a major repair or major alteration. The work must not supervise the maintenance, preventive maintenance, have been done on products that are not produced under FAA or alteration of any aircraft or appliance (or part thereof) approval (i.e., are not type certificated) and must have been for which they are rated, unless they have satisfactorily performed in accordance with instructions developed by the performed this work at an earlier date. This is where the manufacturer or person acceptable to the FAA.

benefit of keeping an on the job training (OJT) log cannot be overemphasized. Whether the technician attends a part 147 Section 65.87, Powerplant Rating: Additional maintenance training school or receives the required number Privileges of months as practical experience, they have only scratched Similarly, a mechanic holding a powerplant rating has the the surface of the tremendously complex world of aviation same limitations imposed regarding the powerplant and maintenance. The technician must either work with someone propeller as the airframe technician has on the airframe (like a shop mentor) or must perform the task satisfactorily rating. They may perform and return to service minor repairs for the FAA. The certified mechanic must have and be able to or alterations. They may also accomplish the work activities comprehend the maintenance manuals and/or instructions for required for a major repair or alteration, but the work must continued airworthiness for the task they are accomplishing.

be signed off for return to service by an IA. The privilege of performing a 100-hour inspection (if required by 14 CFR part Section 65.83, Recent Experience Requirements 91) on a powerplant or propeller is also authorized.

In addition to having the proper documentation, the mechanic is required by this regulation to have recent and relevant A certificated mechanic with a powerplant rating can work experience. Although, as it was stated earlier in this approve and return to service the powerplant or propeller chapter, the A&P certificate is valid until it is surrendered, of an aircraft with a special airworthiness certificate, in suspended, or revoked, it may not be exercised if the holder the light-sport category (refer to 14 CFR part 21, section has not been actively working as a mechanic for at least 6 of 21.190) after performing and inspecting a major repair or the preceding 24 months.

major alteration. The work must have been done on products that are not produced under FAA approval (i.e., are not type This activity can be any one or a combination of the certificated) and must have been performed in accordance following: with instructions developed by the manufacturer or person • Served as a mechanic under the certificate and rating acceptable to the FAA.

• Technically supervised other mechanics Section 65.89, Display of Certificate • Supervised (in an executive capacity) the maintenance Once a technician receives their mechanic certificate, the or alteration of an aircraft certificate must be kept in the immediate area where they normally conduct work and exercises the privileges of the certificate. When requested, the technician is required to present the certificate for inspection to the FAA, or any Section 65.93, Inspection Authorization: Renewal authorized representation from the National Transportation An IA certificate may be renewed in one of the following Safety Board (NTSB), or any federal, state, or local law ways each year the technician is seeking renewal: enforcement officer.

• The performance of at least one annual inspection for each 90 days the technician has held the IA rating.

Inspection Authorization (IA) (by 14 CFR • The performance of the inspections of at least Section) two major repairs or alterations for each 90 days Section 65.91, Inspection Authorization the technician has held the IA rating. ( Note: The An A&P mechanic who has held their certificate for at least inspections can be counted regardless of the approval 3 years, and has been active for the last 2 years, may submit or disapproval of the work.)

application using FAA Form 8610-1, Mechanic’s Application • The performance (or supervision) and approval of at for Inspection Authorization, to the FAA for consideration least one progressive inspection.

as an IA. In addition to the preceding time requirements, the IA candidate must have: • The attendance and successful completion of a refresher course (acceptable to the Administrator) that • A fixed base of operation where they can be located is at least 8 hours of instruction. This can be either a in person or by phone during a normal working week single day seminar or a combination of individual but it need not be the place where they will exercise classes acceptable to the Administrator. Some seminars their inspection authority.

are sponsored by the FAA FSDO and are free; others • Available equipment, facilities, and inspection are low cost. Private industry also frequently conducts data necessary to properly inspect the airframe, one-day sessions and usually charge for their efforts.

powerplants, propellers, or any related part or Regardless of who is conducting the seminar, it is appliance they are approving for return to service.

usually an excellent way to accomplish renewal, learn about new issues, and develop a network among peers.

The applicant who meets all the above criteria must then • Passed an oral test by an FAA inspector to determine pass a written test (or computerized version of the test) to that the applicant's knowledge of applicable regulations determine their ability to inspect the airworthiness of an and standards is current.

aircraft following either a major repair or alteration action or the performance of an annual or progressive inspection.

Because all IA certificates expire in the first quarter of each calendar year (March 31), and the regulation states that The minimum passing score for the computer test is 70 anyone holding an IA for less than 90 days need not meet percent. If the applicant fails the test, retesting cannot be the preceding renewal requirements, no renewal is required attempted until a minimum of 90 days have elapsed from the for someone who received the IA during the first quarter of failure date. Unlike the A&P test, there is no reduction in this the calendar year.

time if the applicant receives additional training.

Section 65.92, Inspection Authorization: Duration The technician with IA should note that regulations clearly state the number of annual inspections (four) and major An IA certificate expires on March 31 of each odd-numbered repair or alteration inspections (eight) are required for each year, but may only be exercised during the time the technician st 90-day period prior to March 31 . This does not mean in each holds a currently effective mechanic certificate. The IA ceases previous 90-day period the technician must have conducted to be effective if: either an annual or two major repair or alteration inspections, • The technician surrenders it, or it is suspended or st but rather their cumulative number by March 31 . Therefore, revoked.

an IA could actually go 11 months without performing any • The technician no longer has a fixed base of operations.

inspection activity relative to renewal. Then in March, they could conduct all four necessary annual inspections, or all • The technician no longer has the required facilities, eight 337-related inspections. However, the regulations do equipment, or inspection data available.

not provide for the mixing of any of these renewal activities (i.e., two annual inspections and four Major Repair and Whenever the certificate is suspended or revoked, the Alteration forms).

technician must return it to the Administrator when requested by the FAA to do so.

Another method of renewal is to meet with the FAA-assigned FSDO inspector who will determine that the applicant Although situations involving questionable ethics can exist possesses current knowledge of the applicable regulations wherever and whenever business decisions are made, the and standards. Although this is often considered the renewal scope of this discussion is limited to areas with which the method of last resort, it should not be considered a negative technician is probably associated.

experience. If the IA has been performing their activities in a professional manner throughout the year, this session A Scenario can be considered a professional follow-up or consultation.

The following incident illustrates one way that both personal Proper IA-to-FSDO inspector interaction can be enhanced ethics and technician knowledge of regulations can work with such a meeting.

together to provide them with the ability to make the right Section 65.95, Inspection Authorization: Privileges decision. Unfortunately, others in the shop did not appear as and Limitations concerned as the technician sharing the incident.

The IA may perform an annual inspection or perform or A technician working for an airline was involved in a situation supervise a progressive inspection. They may also approve that required a repair or replacement of a fuselage ice for return to service any aircraft-related part or appliance that shield. The computer inventory indicated that a replacement has undergone a major repair or alteration (except aircraft part was in stock, so the technician removed the damaged maintained in accordance with a continuous airworthiness component. It was then found that the replacement part was program operated under 14 CFR part 121).

not actually in stock. At this point, a crucial decision was to be made: Can the damaged item be reinstalled? The steps in The IA must keep their certificate available for inspection properly documenting a maintenance event are to record the by any one of the following persons: removal of the damaged part, then document the installation • Aircraft owner of an airworthy part. Once the technician has committed to • A&P technician removing the damaged part, it becomes unairworthy and cannot be reinstalled regardless of its deferability in the • FAA Administrator minimum equipment list (MEL).

• Authorized representative of the NTSB • Any federal, state, local, or law enforcement officer The actual sequence of events is as follows: • Significant impact damage to the ice shield was If the holder of an IA moves their fixed base of operation, observed and recorded.

they must notify in writing the FSDO responsible for the • The company inspector reviewed and instructed the location they are moving to before beginning to exercise the technician to replace the ice shield.

privileges of an IA. Although it is not required, good business etiquette and professional responsibility would suggest that • Availability of the replacement part was confirmed by a similar letter be written to the responsible FAA Principal computer.

Maintenance Inspector (PMI) at the FSDO in the area they • The damaged part was removed, and the technician are leaving.

prepared the surface for the replacement part.

• The new part was ordered from inventory, but the part Ethics was not in stock (inventory error).

This is a tremendously broad and diverse area of study. It is • The inspector instructed the technician to reinstall the also an area that is coming under more scrutiny by consumers, old one.

individual watchdog groups, and government review committees. Ethics, or more appropriately the lack of ethics, • The technician refused.

has caused the loss of millions of dollars through fraudulent • The inspector instructed the technician to repair it.

accounting practices, shoddy workmanship, etc. This chapter • The technician researched the structural repair examines some definitions of ethics and some examples of manual (SRM) and found that the facility did not poor business ethics in order to raise the awareness of the have the proper facility authorization to repair the technician to the importance of ethics.

damaged part.

The word “ethics” is actually a philosophical term that comes • The company inspector told the technician to apply from the Greek word “ethos,” which means character or 5-minute epoxy to the area, sand it down, and paint custom. So, it is logical that a current definition of ethics it.

is “the study of standards of conduct and moral judgment.” • The technician walked away. unscrupulous companies to get an aircraft into their shop no matter what it takes. Although the shop’s retention of clients is • The company inspector found someone else to frequently very low, there always seem to be new ones willing compromise standards. The aircraft departed on to accept a shorter-than-normal turnaround time quote. Often time—illegally and unairworthy.

these same shops underbid the job, and then continually add extra costs as the work progresses. The technician is This happens more often than one would like, is probably encouraged to avoid employment at maintenance facilities overlooked by many people, and, unfortunately, might be that do not think twice about trying to deceive the customer.

considered standard operating procedure (SOP) for some maintenance facilities. It is the responsibility of the mechanic Since companies are usually in business to make money, the to follow regulations and to question the actions of their “bottom line” mentality frequently drives management and, supervisors if the policy is circumvented to make an on-time ultimately, technician decisions. But short-term, quick-fix departure.

solutions that focus only on immediate financial success promote the idea that everything boils down to monetary This incident provides some valuable insights into how day- gain. Ethical behavior is not about monetary gain.

to-day events can lead to pressure to produce and ultimately compromise the decision-making.

In addition to monetary gain, there are other common ways 1. The incident occurred while working for a commercial that unethical behavior is rationalized: airline. The pressure for getting the aircraft in the air • Pretending that the behavior is not unethical or illegal.

is tremendous in this environment.

• Excusing the behavior by saying it is really in the 2. Inventory error added to the pressure. The damaged organization’s (or the technician’s) best interest.

part had been removed because the technician • Assuming the behavior is okay, because no one else had queried and believed a replacement part was would even be expected to find out about it.

immediately available.

• Expecting your superiors to support and protect you 3. The company inspector was either unaware of if anything should go wrong (Gellerman 1986).

regulatory requirements or simply did not care.

4. The second technician was either unaware of This latter point often leads to a significant surprise for the regulatory requirements or simply did not care.

individual technician if they compromised their standards at the encouragement of management to get the job done.

Final Observation Should there be a problem with maintenance and subsequent The underlying company culture was apparently lacking airworthiness of the aircraft, the very same managers or concern for ethical decisions and regulatory compliance.

superiors who directed that technician to shortcut proper An effective organizational culture should always encourage maintenance procedures would testify in court that they ethical behavior and discourage unethical behavior. This always encouraged their employees to work “by the book” means that not only does the upper management of an and never encouraged unauthorized shortcuts.

organization say that they conduct themselves ethically, they must do it consistently; employees, customers, vendors, Ultimately, every organization establishes a climate or and even competitors should know this company has “high culture regarding honesty, integrity, and ethical behavior.

ethical standards.” This corporate climate sets the tone for decision making at all levels and in all circumstances. This leads to the second This latter issue may sometimes have painful consequences, business example, the Aircraft Brake Scandal. Although this if the businesses are competing for a customer’s business.

incident occurred at the B.F. Goodrich Wheel and Brake The ethical company may estimate the maintenance activities Plant in Troy, Ohio, and is therefore focused on the design, to take 8 weeks and quotes that time frame to the customer.

manufacture, and test of wheels and brakes for the U.S. Air The unethical company may also know the work takes 8 Force A-7D, it is a classic case of both personal ethics and weeks, but tells the customer only 6 weeks, hoping to get “whistle blowing.” A brief review of the pertinent facts in the job. Once the plane is “captured” and maintenance has the incident follows.

begun, explanations and excuses extend the original time estimate of 6 weeks to the actual 8 weeks or longer. Although A young engineering technician is in charge of conducting the customer would be disappointed in this situation, few the required qualification testing for a newly designed customers would be able to remove an aircraft undergoing brake and rotor system awarded to the B.F. Goodrich Co.

maintenance. This “bait and switch” tactic is often used by by L.T.V. Aerospace. An aggressive time schedule and an upper management mindset of not wanting to hear bad news to help employees deal with an ethical decision: (i.e., the brakes are failing test), a senior engineer who is not 1. Recognize and clarify the dilemma.

willing to have their computations challenged, and a project 2. Get all the possible facts.

manager who states the brake will be qualified “no matter what,” ultimately lead to a congressional oversight hearing 3. List options—all of them.

in 1969. Along the way, the brake system is tested (and fails 4. Test each option by asking such questions as: 14 times), no one wants to write the required test report, low —Is it legal?

level employees seek legal advice, and the aircraft suffers serious damage during landing while conducting initial —Is it right?

flight testing due to unsatisfactory braking. (The reader is —Is it beneficial?

encouraged to look up this now famous case on the Internet 5. Make your decision.

to obtain more details.)

6. Double check your decision by asking: Some of the ethical conflicts that are evident in this situation —How would I feel if my family found out about this?

are: —How would I feel if my decision is printed in the • Young engineer (newly hired) feels intimidated by local newspaper?

senior level engineer.

7. Take action (Schermerhorn 1989).

• Early brake failure during development testing is excused away because “they are not representative Finally, the technician is encouraged to read the following code of the final design.” of ethics developed by Professional Aviation Maintenance • A company culture of intimidation and distrust.

Association (PAMA), Inc. and consider adopting it as their own.

Most of these conflicts could have easily occurred in the maintenance realm if the specifics are broadened, even a little.

“As a certified technician, my performance is a public service • Change the word “engineer” to “maintenance and, as such, I have a responsibility to the United States technician.” Government and its citizens. I must ensure that all citizens have confidence in my integrity, and that I will perform my • Instead of brake failure during development testing, work according to the highest principles of ethical conduct.

think of component test failure (with the shop norm Therefore, I swear that I shall hold in sacred trust the rights of “we don’t follow the manual on this step; we have and privileges conferred upon me as a certified technician.

developed our own (unauthorized) procedure here.”) The safety and lives of others are dependent on my skill and • The existence of a company culture of intimidation judgment; therefore, I shall never knowingly subject others and distrust transcends all lines of business.

to risks which I would not be willing to assume for myself or those who are dear to me.” For a company to nurture a healthy ethical climate and long- term success, the element of trust is fundamental both inside “As a certified technician, I am aware that it is not possible and outside the organization. This trust boosts employee to have knowledge and skill in every aspect of aviation morale and usually boosts productivity and, therefore, maintenance for every airplane, so I pledge that I will never profitability. It also aids and enhances long-term business undertake work or approve work which I believe to be beyond relationships with customers and vendors.

the limits of my knowledge. I shall not allow any superior to persuade me to approve aircraft or equipment as airworthy When differences of opinion do exist, ethical organizations when there is doubt in my mind as to the validity of my action.

pay close attention to those who are dissenting. Those Under no circumstances will I permit the offer of money or companies that are committed to promoting an ethical climate other personal favors to influence me to act contrary to my encourage rather than punish dialogue and debate about best judgment, nor to pass as airworthy aircraft or equipment policies and practices.

about which I am in doubt.” It is encouraging to note that more and more institutions of “The responsibility that I have accepted as a certified learning, whether business schools or technical colleges, are technician demands that I exercise my judgment on the adding ethics courses into their required curriculum. More airworthiness of aircraft and equipment; therefore, I pledge and more organizations are developing a corporate “code of unyielding adherence to these precepts for the advancement ethics.” Some are using the following seven-step checklist of aviation and for the dignity of my vocation.”

Next: Chapter 14 →

Chapter 14

Human Factors

Introduction Human error is the unintentional act of performing a task FAA Involvement incorrectly that can potentially degrade the system. There The FAA has had a formal involvement in this issue since are three types of human error: 1988. That was the year the first Human Factors Issues in 1. Omission: not performing an act or task.

Aviation Maintenance and Inspection National Conference was conducted, and that effort reflects a working relationship 2. Commission: accomplishing a task incorrectly.

between government research and industry activity. This 3. Extraneous: performing a task not authorized.

yearly event includes airlines, suppliers, manufacturers, schools, and government agencies. There is also an FAA website for human factors at hf.faa.gov which is a tremendous There are also four consequences of human error: resource.

1. Little or no effect.

2. Damage to equipment/hardware.

Importance of Human Factors The greatest impact in aircraft safety in the future will 3. Personal injury.

not come from improving the technology. Rather it will 4. Catastrophic.

be from educating the employee to recognize and prevent human error. A review of accident related data indicates that Why are human conditions, such as fatigue, complacency, approximately 75–80 percent of all aviation accidents are the and stress, so important in aviation maintenance? These result of human error. Of those accidents, about 12 percent conditions, along with many others, are called human are maintenance related . Although pilot/co-pilot errors tend factors. Human factors directly cause or contribute to many to have immediate and highly visible effects, maintenance aviation accidents. It is universally agreed that 80 percent errors tend to be more latent and less obvious. However, they of maintenance errors involve human factors. If they are not can be just as lethal.

detected, they can cause events, worker injuries, wasted time, and even accidents. [Figure 14-2] Definitions of Human Factors Human factors are concerned with optimizing performance Aviation safety relies heavily on maintenance. When it is … including reducing errors so that the highest level of safety not done correctly, it contributes to a significant proportion is achieved and maintained.

of aviation accidents and incidents. Some examples of —Ron LoFaro, PhD maintenance errors are parts installed incorrectly, missing FAA parts, and necessary checks not being performed. In comparison with many other threats to aviation safety, the Human factors is the study of how people interact with their mistakes of an aviation maintenance technician (AMT) can be environments.

more difficult to detect. Often, these mistakes are present but —FAA-H-8083-25, not visible and have the potential to remain latent, affecting Pilot’s Handbook of Aeronautical Knowledge the safe operation of aircraft for extended periods of time.

Human factors are those elements that affect our behavior AMTs are confronted with a set of human factors unique and performance, especially those that may cause us to make within aviation. They can be working in the evening or early errors.

morning hours, in confined spaces, on high platforms, and in a —Canadian Department of Defense (video) variety of adverse temperature/humidity conditions. The work can be physically strenuous, yet it also requires attention to Our focus is on human factors as it relates to improper actions.

detail. [Figure 14-3] Because of the nature of maintenance Note, however, that human factors exist in both proper and tasks, AMTs commonly spend more time preparing for a improper actions. [Figure 14-1] Since improper actions task than actually carrying it out. Proper documentation of usually result in human error, we should also define that term.

14-1 all maintenance work is a key element, and AMTs typically and services, and the art of ensuring successful application spend as much time updating maintenance logs as they do of human factor principles into the maintenance working performing the work. [Figure 14-4] environment.

Human factors awareness can lead to improved quality, an The spectrum of human factors that can affect aviation environment that ensures continuing worker and aircraft maintenance and work performance is broad. They safety, and a more involved and responsible work force. encompass a wide range of challenges that influence The reduction of even minor errors can provide measurable people very differently as humans do not all have the benefits including cost reductions, fewer missed deadlines, same capabilities, strengths, weaknesses, or limitations.

reduction in work related injuries, reduction of warranty Unfortunately, aviation maintenance tasks that do not take claims, and reduction in more significant events that can be into account the vast amount of human limitations can result traced back to maintenance error. Within this chapter, the in technical error and injuries. Figure 14-5 shows some of many aspects of human factors are discussed in relation to the human factors that affect AMTs. Some are more serious aviation maintenance. The most common human factors are than others but, in most cases, when you combine three or introduced along with ways to mitigate the risk to stop them four of the factors, they create a problem that contributes to from developing into a problem. Several Federal Aviation an accident or incident.

Administration (FAA) human factor resources are provided, including a direct link to aviation maintenance human factors Elements of Human Factors are at hf.faa.gov . Human factors are comprised of many disciplines.

This section discusses ten of those disciplines: Clinical What are Human Factors?

Psychology, Experimental Psychology, Anthropometrics, Computer Science, Cognitive Science, Safety Engineering, The term “human factors” has grown increasingly popular Medical Science, Organizational Psychology, Educational as the commercial aviation industry realizes that human Psychology, and Industrial Engineering. [Figure 14-6] error, rather than mechanical failure, underlies most aviation accidents and incidents. Human factors science The study and application of human factors is complex or technologies are multidisciplinary fields incorporating because there is not just one simple answer to fix or contributions from psychology, engineering, industrial change how people are affected by certain conditions or design, statistics, operations research, and anthropometry. It is situations. The overall goal of aviation maintenance human a term that covers the science of understanding the properties factors research is to identify and optimize the factors that of human capability, the application of this understanding affect human performance in maintenance and inspection.

to the design, development, and deployment of systems Human Factors Active Failure Latent Failure Assertiveness Leadership Asynchronous Communication Maintenance Resource Management Human Factors Authoritarian Leader Mental Model Communication Norms Complacency Participatory Leader HF Crew Resource Management Safety Culture Dirty Dozen* Situational Awareness applies Egalitarian Stressor to both Ergonomics Synchronous Communication Human Factors Team Proper Actions Improper Actions Inter-team Team Situational Awareness Intra-team Teamwork Instructional Systems Design * 1. Lack of Communication 2. Complacency 3. Lack of Knowledge 4. Distraction 5. Lack of Teamwork 6. Fatigue 7. Lack of Resources 8. Pressure 9. Lack of Assertiveness 10. Stress 11. Lack of Awareness 12. Norms Figure 14-1. Human factors exist in both proper and improper actions.

14-2 optimized by incorporating the many disciplines that affect Human Factors Human Factors human factors in an effort to understand how people can work Mental Mental more efficiently and maintain work performance.

State State Emotional Emotional By understanding each of the disciplines and applying them State State to different situations or human behaviors, we can correctly recognize potential human factors and address them before they develop into a problem or create a chain of problems Human Human that result in an accident or incident.

Capabilities Capabilities Clinical Psychology Physical Physical State State Clinical psychology includes the study and application of psychology for the purpose of understanding, preventing, and Human relieving psychologically-based distress or dysfunction and Limitations to promote subjective well-being and personal development.

It focuses on the mental well-being of the individual. Clinical Environmental Environmental psychology can help individuals deal with stress, coping Conditions Conditions mechanisms for adverse situations, poor self-image, and Human-Machine Human-Machine Interface Interface accepting criticism from coworkers.

Figure 14-2. Human factors and how they affect people are very Experimental Psychology important to aviation maintenance.

Experimental psychology includes the study of a variety of basic behavioral processes, often in a laboratory environment.

The focus initiates on the technician but extends to the These processes may include learning, sensation, perception, entire engineering and technical organization. Research is human performance, motivation, memory, language, Figure 14-3. Aviation maintenance technicians (AMTs) are confronted with many human factors due to their work environments.

14-3 minds as information processors. It includes research on how information is processed (in faculties such as perception, language, reasoning, and emotion), represented, and transformed in a nervous system or machine (e.g., computer).

It spans many levels of analysis from low-level learning and decision mechanisms to high-level logic and planning.

AMTs must possess a great ability to problem solve quickly and efficiently. They are constantly required to troubleshoot situations and quickly react to them. This can be a vicious cycle creating an enormous amount of stress. The discipline of cognitive science helps us understand how to better assist AMTs during situations that create high levels of stress so that their mental process does not get interrupted and affect their ability to work.

Figure 14-4. AMT documenting repair work.

Safety Engineering thinking, and communication, as well as the physiological Safety engineering ensures that a life-critical system processes underlying behaviors, such as eating, reading, and behaves as needed even when the component fails. Ideally, problem solving. In an effort to test the efficiency of work safety engineers take an early design of a system, analyze policies and procedures, experimental studies help measure it to find what faults can occur, and then propose safety performance, productivity, and deficiencies.

requirements in design specifications up front and changes to existing systems to make the system safer. Safety cannot Anthropometry be stressed enough when it comes to aviation maintenance, Anthropometry is the study of the dimensions and abilities of and everyone deserves to work in a safe environment.

the human body. This is essential to aviation maintenance due Safety engineering plays a big role in the design of aviation to the environment and spaces that AMTs have to work with.

maintenance facilities, storage containers for toxic materials, For example, a man who is 6 feet 3 inches and weighs 230 equipment used for heavy lifting, and floor designs to ensure pounds may be required to fit into a small crawl space of an no one slips, trips, or falls. In industrial work environments, aircraft to conduct a repair. Another example is the size and the guidelines of the Occupational Safety and Health weight of equipment and tools. Men and women are generally Administration (OSHA) are important.

on two different spectrums of height and weight. Although both are equally capable of completing the same task with a Medical Science high level of proficiency, someone who is smaller may be able Medicine is the science and art of healing. It encompasses to perform more efficiently with tools and equipment tailored a variety of health care practices evolved to maintain and to their size. In other words, one size does not fit all and the restore health by the prevention and treatment of illness.

term “average person” does not apply when employing such Disposition and physical well-being are very important and a diverse group of people.

directly correlated to human factors. Just like people come in many shapes and sizes, they also have very different Computer Science reactions to situations due to body physiology, physical The technical definition for computer science is the study of structures, and biomechanics.

the theoretical foundations of information and computation and of practical techniques for their implementation and Organizational Psychology application in computer systems. Yet how this relates to Organizational psychologists are concerned with relations aviation maintenance is simpler to explain. As mentioned between people and work. Their interests include earlier, AMTs spend as much time documenting repairs organizational structure and organizational change, workers’ as they do performing them. It is important that they have productivity and job satisfaction, consumer behavior, computer work stations that are comfortable and reliable.

and the selection, placement, training, and development Software programs and computer-based test equipment of personnel. Understanding organizational psychology should be easy to learn and use, and not intended only for helps aviation maintenance supervisors learn about the those with a high levels of computer literacy.

points listed below that, if exercised, can enhance the work environment and productivity.

Cognitive Science • Rewards and compensations for workers with good Cognitive science is the interdisciplinary scientific study of 14-4 Poor Lack of instructions spare parts Boring Unrealistic repetitive jobs deadlines Substance abuse Smelly fumes Poor tool control Personal life Poor training Fatigue problems Loud noises Slippery floors Poorly Snow Lack of tools designed testing and equipment for skill and knowledge Incomplete Poor or incorrect communication documentation Figure 14-5. A list of human factors that affect AMTs.

safety records. Industrial Engineering Industrial engineering is the organized approach to the study • Motivation for workers to want to do well and work of work. It is important for supervisors to set reasonable work safely.

standards that can be met and exceeded. Unrealistic work • Unifying work teams and groups so they get along standards create unnecessary stressors that cause mistakes.

and work together to get the job done right.

It is also beneficial to have an efficient facility layout so that • Treating all workers equally.

there is room to work. Clean and uncluttered environments enhance work performance. Another aspect of industrial Educational Psychology engineering that helps in the understanding of human factors is the statistical analysis of work performance. Concrete data Educational psychologists study how people learn and of work performance, whether good or bad, can show the design the methods and materials used to educate people of contributing factors that may have been present when the all ages. Everyone learns differently and at a different pace.

work was done.

Supervisors should design blocks of instruction that relate to a wide variety of learning styles.

14-5 Clinical Psychology Industrial Engineering Experimental Psychology Anthropometric Science Educational Psychology

Human Factors

Low Risk Not Complex Flight Exercise Caution Endangerment Area of Concern Organization Psychology Safety Engineering Cognitive Science Medical Science Computer Science Figure 14-6. Human factor disciplines.

are required to read back instructions or clearances given by History of Human Factors air traffic control (ATC) to ensure that the pilot receives the Around 1487, Leonardo da Vinci began research in the correct instructions and gives ATC an opportunity to correct area of anthropometrics. The Vitruvian Man, one of his if the information is wrong. Frank and Lillian Gilbreth also most famous drawings, can be described as one of the are known for their research on fatigue.

earliest sources presenting guidelines for anthropometry.

[Figure 14-7] Around the same time, he also began to Also in the early 1900s, Orville and Wilbur Wright were study the flight of birds. He grasped that humans are too the first to fly a powered aircraft and also pioneered many heavy and not strong enough to fly using wings simply human factors considerations. While others were trying attached to the arms. Therefore, he sketched a device in to develop aircraft with a high degree of aerodynamic which the aviator lies down on a plank and works two large, stability, the Wrights intentionally designed unstable aircraft membranous wings using hand levers, foot pedals, and a with cerebralized control modeled after the flight of birds.

system of pulleys. [Figure 14-8] Today, anthropometry plays Between 1901 and 1903, the brothers worked with large a considerable role in the fields of computer design, design gliders at Kill Devil Hills, near Kitty Hawk, North Carolina, for access and maintainability, simplicity of instructions, and to develop the first practical human interactive controls for ergonomic issues.

aircraft pitch, roll, and yaw. On December 17, 1903, they made four controlled powered flights over the dunes at In the early 1900s, industrial engineers Frank and Lillian Kitty Hawk with their Wright Flyer. [Figure 14-11] They Gilbreth were trying to reduce human error in medicine.

later developed practical in-flight control of engine power, [Figures 14-9 and 14-10] They developed the concept of plus an angle of attack sensor and stick pusher that reduced using call backs when communicating in the operating pilot workload. The brothers’ flight demonstrations in the room. For example, the doctor says “scalpel” and the nurse United States and Europe during 1908-1909 awakened the repeats “scalpel” and then hands it to the doctor. That is world to the new age of controlled flight. Orville was the first called the challenge-response system. Speaking out loud aviator to use a seat belt and also introduced a rudder boost/ reinforces what tool is needed and provides the doctor with an trim control that gave the pilot greater control authority. The opportunity to make corrections if it is not the necessary tool.

Wrights’ flight training school in Dayton, Ohio included a This same verbal protocol is used in aviation today. Pilots flight simulator of their own design. The Wrights patented 14-6 their practical airplane and flight control concepts, many of which are still in use today.

Prior to World War I, the only test of human to machine compatibility was that of trial and error. If the human functioned with the machine, he was accepted, if not he was rejected. There was a significant change in the concern for humans during the American Civil War. The U.S. Patent Office was concerned about whether the mass-produced uniforms and new weapons could be used effectively by the infantry men.

Evolution of Maintenance Human Factors With the onset of World War I (1914–1918), more sophisticated equipment was being developed and the inability of personnel to use such systems led to an increased interest in human capability. Up to this point, the focus of aviation psychology was on the pilot, but as time progressed, the focus shifted onto the aircraft. Of particular concern was the design of the controls and displays, the effects of altitude, and environmental factors on the pilot. The war also brought on the need for aeromedical research and the need for testing and measurement methods. By the end of World War I, two aeronautical labs were established, one at Brooks Air Force Base, Texas, and the other at Wright Field outside of Dayton, Ohio.

Figure 14-7. Vitruvian Man, one of Leonardo da Vinci’s most famous Another significant development was in the civilian sector, anthropometric drawings.

where the effects of illumination on worker productivity were examined. This led to the identification of the Hawthorne Effect, which suggested that motivational factors could significantly influence human performance.

With the onset of World War II (1939–1945), it was becoming increasingly harder to match individuals to pre-existing jobs.

Now the design of equipment had to take into account human limitations and take advantage of human capabilities. This change took time as there was a lot of research still to be done to determine the human capabilities and limitations. An example of this is the 1947 study done by Fitts and Jones on the most effective configuration of control knobs to be used in aircraft flight decks. Much of this research transitioned into other equipment with the aim of making the controls Figure 14-8. Leonardo da Vinci’s rendering of a flying device and displays easier for the operators to use.

for man.

Unfortunately, all the “lessons learned” in the WWII studies The Vietnam Conflict brought the quest for greater safety, of group dynamics, and flight crew communication were and with that, came a systematic approach for error reduction.

seemingly forgotten after the war. Post WWII aircrew studies This increased attention brought both good and bad changes.

continued to focus primarily on flight crews, especially pilot It led to the “Zero Defects” quality programs in maintenance selection, simulator training, and cockpit layout and design.

and manufacturing. Generally, this had a positive effect.

However, it also led to “crackdown programs” which were Subsequent studies of the technician focused on individual one-way communication from management (the infamous competency and included equipment design (ergonomics).

“my way or the highway” approach). This concept is more 14-7 and then become apparent later, usually at a more critical time (“Murphy’s Law”). Additional attempts to develop “foolproof” equipment designs were added to the zero-defect manufacturing goal and began to find recognition in the maintenance world as well. Subsequent efforts focused on effects of positive rather than negative motivators. The results of this effort were a reversal of the “crackdown” method, and motivation due to increased morale often improved maintenance safety performance. Studies have shown that motivation resulting from negative sources seldom achieved the same effect. This led to a “Participative Management” style recognized by some U.S. industry and a few airlines, but did not reach maintenance operations until much later.

The Airline Deregulation (1978 –1988) effort had a profound effect upon the aviation community. Prior to 1978, the airline industry was regulated by the Civil Aeronautics Act of 1938. This resulted in peaceful markets, stable routes, and consistent air fares. However, there was a downside consisting of two major problems: wasteful management practices and excessively high wages compared to other comparable skilled-labor industries. The Airline Deregulation Act brought in competitive business practices, with routes and fares controlled by their profitability. This led to a new style of airline management in which a CEO was more of a Figure 14-9. Frank Gilbreth – Industrial Engineer.

business person and less knowledgeable of aviation. Existing airlines developed new routes and added new kinds of service dictatorial than democratic, and typically had a long-term and style. Start-up airlines brought other innovative ideas.

negative effect on the company. This “crackdown” approach The numerous mergers and acquisitions added an increasing for behavior control is based upon fear and punishment, pressure to focus on the financial bottom line. Doing more which creates a problem. Errors are driven into hiding, with less became the byline. In the 1980s, maintenance departments were not immune to the pressures of mergers and staff reductions. However, fleets were extremely reliable at that time, and significant savings were aided by a reduction in number of maintenance technicians. Other new ways of conducting business included leasing of aircraft and outsourcing of maintenance. A result of deregulation was change for the maintenance programs (both personnel and departmental) and the pressure to produce and adjust.

The problem, however, was that human factors for aviation maintenance was still stuck in the 1960s model.

Figure 14-11. The Wright Brothers on December 17, 1903, flying over the dunes at Kitty Hawk with their Wright Flyer.

Figure 14-10. Lillian Gilbreth – Industrial Engineer.

14-8 physiological, psychological, and psychosocial factors.

[Figure 14-12] The programs must focus on individuals, their A detailed review of aviation literature published between physical capabilities, and the factors that affect them. They 1976 and 1987 had very little to say about maintenance. Out also should consider their mental state, cognitive capacity, of 50 published articles, only 15 even mention maintenance.

and conditions that may affect their interaction with others. In Most of these articles deal with ergonomics, one article most cases, human factors programs are designed around the examines military engine design to “solider proof” the people in the company’s existing workforce. You cannot apply maintenance duties, and one U.S. Navy article advocated identical strength, size, endurance, experience, motivation, more management control.

and certification standards equally to all employees. The company must match the physical characteristics of each As human factors awareness progressed, a “culture change” person to the tasks each performs. occurred in U.S. carriers in the 1990s. Management behavior began to change; there were practical applications The company must consider factors like each person’s size, of systems thinking; organization structure was revised; strength, age, eyesight, and more to ensure each person is and new strategy, policy, and values emerged. Virtually physically capable of performing all the tasks making up the all of these involved communication and collaboration.

job. A good human factors program considers the limitations One example is in 1991, when Continental Airlines began of humans and designs the job accordingly. An important “CRM type” training in maintenance. They saw the element when incorporating human factors into job design is importance of improving communication, teamwork, and planned rest breaks. People can suffer physical and mental participative decision making. A second example is when fatigue under many work conditions. Adequate breaks and rest United Airlines instituted a change in organization and the periods ensure the strain of the task does not overload their job of design of inspectors. They remained more accessible capabilities. Another “People” consideration, which also is during heavy maintenance and overhaul and stayed in closer related to “E” for “Environment,” is ensuring there is proper communication with mechanics during normal repairs.

lighting for the task, especially for older workers. Annual This resulted in fewer turnbacks and higher quality. A third vision testing and hearing exams are excellent proactive example is when Southwest Airlines created and sustained a interventions to ensure optimal human physical performance. strong and clear organizational structure led by the CEO. This resulted in open and positive communication between the Attention to the individual does not stop at physical abilities. maintenance and other departments. A final example is when A good human factors program must address physiological TWA instituted a new program to improve communication and psychological factors that affect performance. Companies between the maintenance trade union and maintenance should do their best to foster good physical and mental health. management. This resulted in improved quality.

Offering educational programs on health and fitness is one The Pear Model way to encourage good health. Many companies have reduced sick leave and increased productivity by making healthy There are many concepts related to the science and practice meals, snacks, and drinks available to their employees.

of human factors. However, from a practical standpoint, it is Companies also should have programs to address issues most helpful to have a unified view, or a model of the things associated with chemical dependence, including tobacco we should be concerned about when considering aviation and alcohol. Another “People” issue involves teamwork maintenance human factors. For more than a decade, the term and communication. Safe and efficient companies find ways “PEAR” has been used as a memory jogger, or mnemonic, to foster communication and cooperation among workers, to characterize human factors in aviation maintenance.

managers, and owners. For example, workers should be The PEAR mode prompts recall of the four important rewarded for finding ways to improve the system, eliminate considerations for human factors programs, which are listed waste, and help ensure continuing safety.

below.

• People who do the job.

Environment • Environment in which they work.

There are at least two environments in aviation maintenance.

There is the physical workplace on the ramp, in the hangar, • Actions they perform.

or in the shop. In addition, there is the organizational • Resources necessary to complete the job.

environment that exists within the company. A human factors program must pay attention to both environments.

People [Figure 14-13] Aviation maintenance human factors programs focus on the people who perform the work and address physical, 14-9 job. Many regulatory authorities require that the JTA serve Physical as the basis for the company’s general maintenance manual The physical environment is obvious. It includes ranges of and training plan. Many human factors challenges associated temperature, humidity, lighting, noise control, cleanliness, with use of job cards and technical documentation fall under and workplace design. Companies must acknowledge “Actions.” Clearly understandable documentation of actions these conditions and cooperate with the workforce to either ensures instructions and checklists are correct and useable.

accommodate or change the physical environment. It takes a [Figure 14-14] corporate commitment to address the physical environment.

This topic overlaps with the “Resources” component of Resources PEAR when it comes to providing portable heaters, coolers, The final PEAR letter is “R” for “Resources.” [Figure 14-15] lighting, clothing, and good workplace and task design.

It is sometimes difficult to separate resources from the other elements of PEAR. In general, the characteristics of Organizational the people, environment, and actions dictate the resources.

The second, less tangible, environment is the organizational Many resources are tangible, such as lifts, tools, test one. The important factors in an organizational environment equipment, computers, technical manuals, and so forth. Other are typically related to cooperation, communication, shared resources are less tangible. Examples include the number values, mutual respect, and the culture of the company.

and qualifications of staff to complete a job, the amount of An excellent organizational environment is promoted with time allocated, and the level of communication among the leadership, communication, and shared goals associated with crew, supervisors, vendors, and others. Resources should be safety, profitability, and other key factors. The best companies viewed (and defined) from a broad perspective. A resource guide and support their people and foster a culture of safety. A is anything a technician (or anyone else) needs to get the job safe culture is one where there is a shared value and attitude done. For example, protective clothing is a resource. A mobile toward safety. In a safe culture, each person understands phone can be a resource. Rivets can be resources. What is their individual role is contributing to overall mission safety.

important to the “Resource” element in PEAR is focusing on identifying the need for additional resources.

Actions Successful human factors programs carefully analyze all the Another major human factors tool for use in investigation of actions people must perform to complete a job efficiently maintenance problems is the Boeing developed Maintenance and safely. Job task analysis (JTA) is the standard human Error Decision Aid (MEDA). This is based on the idea that factors approach to identify the knowledge, skills, and errors result from a series of factors or incidents. The goal of attitudes necessary to perform each task in a given job.

using MEDA is to investigate errors, understand root causes, The JTA helps identify what instructions, tools, and other and prevent accidents, instead of simply placing blame on the resources are necessary. Adherence to the JTA helps ensure maintenance personnel for the errors. Traditional efforts to each worker is properly trained and each workplace has the investigate errors are often designed to identify the employee necessary equipment and other resources to perform the who made the error. In this situation, the actual factors that

PEOPLE

Physical Physiological • Physical size • Workload • Sex • Experience • Age • Knowledge • Strength • Training • Sensory limitations • Attitude • Mental or emotional state Psychological Psychosocial • Nutritional Factors • Interpersonal conflicts • Health • Lifestyle • Fatigue • Chemical dependency Figure 14-12. People who do the job.

14-10 contributed to the errors or accident remain unchanged, and or reduce the likelihood of similar errors in the future.

the mistake is likely to recur. In an effort to break this “blame 5. Feedback: the operator provides feedback to the and train” cycle, MEDA investigators learn to look for the maintenance workplace so technicians know that factors that contributed to the error, instead of the employee changes have been made to the maintenance system who made the error. The MEDA concept is based on the as a result of this MEDA process.

following three principles: • Positive employee intent (In other words, maintenance The implantation and continuous use of MEDA is a long- technicians want to do the best job possible and do term commitment and not a “quick fix.” However, airline not make intentional errors.) operators and maintenance facilities frequently decide to use the MEDA approach to investigate serious, high visibility • Contribution of multiple factors (There is often a series events which have caused significant cost to the company.

of factors that contribute to an error.)

The desire to do this is based upon the potential “payback” • Manageability of errors (Most of the factors that of such an investigation.

contribute to an error can be managed.)

This may ultimately be counterproductive because a highly When a company is willing to adopt these principles, then the visible event may not really be the best opportunity to MEDA process can be implemented to help the maintenance investigate errors. Those involved in the process may be organization achieve the dual goals of identifying those intimidated by the attention coming from upper management factors that contribute to existing errors, and avoiding future and various regulatory authorities.

errors. In creating this five-step process, Boeing initially worked with British Airways, Continental Airlines, United By using the MEDA process properly, the organization can Airlines, a maintenance worker labor union, and the FAA.

investigate the factors that contributed to an error, discover The five steps are: exactly what led to that error, and fix those factors. Successful implementation of MEDA will allow the organization to 1. Event: the maintenance organization must select avoid rework, lost revenue, and potentially dangerous which error that caused events will be investigated.

situations related to events caused by maintenance errors.

2. Decision: was the event maintenance related? If the answer is yes, then the MEDA investigation continues.

The “SHEL” model is another concept for investigating and 3. Investigation: using the MEDA results form, evaluating maintenance errors. [Figure 14-16] As with other the operator conducts an investigation to record human factors tools, its goal is to determine not only what the general information about the airplane—when the problem is, but where and why it exists. SHEL was initiated maintenance and the event occurred, what event by Professor Elwyn Edwards (Professor Emeritus, Aston initiated the investigation, the error that caused the University, Birmingham, U.K.) in 1972. It was later modified event, the factors contributing to the error, and a list slightly by the late Capt. Frank Hawkins, a Human Factors of possible presentation strategies.

consultant to KLM, in 1975. The acronym SHEL represents: 4. Prevention strategies: the operator reviews, • S oftware prioritizes, implements, and then tracks the process • H ardware improvements (prevention strategies) in order to avoid

ENVIRONMENT

Physical Organizational • Weather • Personnel • Location inside/outside • Supervision • Workspace • Labor-management relations • Shift • Pressures • Lighting • Crew structure • Sound level • Size of company • Safety • Profitability • Morale • Corporate culture Figure 14-13. Environment in which they work.

14-11

ACTIONS

• Steps to perform a task • Knowledge requirements • Sequence of activity • Skill requirements • Number of people involved • Altitude requirements • Information control requirements • Certification requirements • Inspection requirements Figure 14-14. Actions they perform.

RESOURCES

• Procedures/work cards • Ground Handling equipment • Technical manuals • Work stands and lifts • Other people • Fixtures • Test equipment • Materials • Tools • Task lighting • Computers/software • Training • Paperwork/signoffs • Quality systems Figure 14-15. Resources necessary to complete the job.

• E nvironment There are two types of failure which can occur—active • L iveware and latent. An active failure is one in which the effects are immediate. An example of this type would be an aircraft The model examines interaction with each of the four SHEL slipping off one of the lifting jacks due to improper placement components, and does not consider interactions not involving by the technician. In this example, the aircraft jack is the human factors. The term “software” is not referring to the approved item of ground support equipment, and it has been common use of the term as applied to computer programs.

properly maintained.

Instead it includes a broader view of manual layout, checklist layout, symbology, language (both technical and A latent failure occurs as a result of a decision or action nontechnical), and computer programs. Hardware includes made long before the incident or accident actually occurs.

such things as the location of components, the accessibility The consequences of such a decision may remain dormant of components and tooling. Environment takes temperature, for a long time. An example of a latent failure could also humidity, sound, light, and time of day factors into account.

involve the aircraft slipping off a joint, but in this case, it Liveware relates technician interaction with other people, could be an unapproved jack being used because funding had both on the job and off. These include managers, peers, not been approved to purchase the correct ground support family, friends, and self.

equipment (GSE).

No discussion of human factors is complete without reference The field of human factors, especially in aviation maintenance, to James Reasons’ Model of Accident Causation. This is a growing field of study. This section of this chapter has diagram, which was introduced in 1990, and revised by Dr.

presented only a small segment of the numerous observations Reason in 1993, is often referred to as the Swiss cheese model and presentations about the topic. If the technician desires to and shows how various “holes” in different systems must be learn more, numerous books exist and a review of Internet aligned in order for an error to occur. Only when the holes data will provide an abundant supply of information.

are all aligned can the incident take place.

14-12

SHEL

A good place to start researching would be the FAA’s own Software • Hardware • Environment • Liveware website at hf.faa.gov . This site, titled “ Human Factors on Aviation Maintenance and Inspection (HFAMI)” provides access to products of the Federal Aviation Administration

Flight Standards Service Human Factors in Aviation (Procedures) Maintenance and Inspection Program. Many aviation maintenance industry trade magazines include a section or at least a page devoted to human factors. “The Human Factors

Worker H E

and Ergonomics Society” is a national organization composed (Machines) (Ambient) of 22 technical groups, including one devoted to aerospace systems, which address both civilian and military issues of safety and performance.

(Personnel) Human Error Human error is defined as a human action with unintended Figure 14-16. SHEL model.

consequences. When you couple error with aviation maintenance and the negative consequences that it produces, it becomes extremely troublesome. Training, risk The “Dirty Dozen” assessments, safety inspections, etc., should not be restricted Due to a large number of maintenance-related aviation to an attempt to avoid errors but rather to make them visible accidents and incidents that occurred in the late 1980s and and identify them before they produce damaging and early 1990s, Transport Canada identified twelve human regrettable consequences. Simply put, human error is not factors that degrade people’s ability to perform effectively avoidable but it is manageable. [Figure 14-17] and safely, which could lead to maintenance errors. These twelve factors, known as the “dirty dozen,” were eventually Types of Errors adopted by the aviation industry as a straightforward means to Unintentional discuss human error in maintenance. It is important to know An unintentional error is an accidental wandering or deviation the dirty dozen, how to recognize their symptoms, and most from accuracy. This can include an error in your action importantly, know how to avoid or contain errors produced (a slip), opinion, or judgment caused by poor reasoning, by the dirty dozen. Understanding the interaction between carelessness, or insufficient knowledge (a mistake). For organizational, work group, and individual factors that may example, an AMT reads the torque values from a job card lead to errors and accidents, AMTs can learn to prevent or and unintentionally transposed the number 26 to 62. They manage them proactively in the future.

did not mean to make that error but unknowingly and unintentionally did. An example of an unintentional mistake Lack of Communication would be selecting the wrong work card to conduct a specific Lack of communication is a key human factor that can repair or task. Again, it is not an intentional mistake but a result in suboptimal, incorrect, or faulty maintenance.

mistake nonetheless.

[Figure 14-18] Communication occurs between the AMT and many people (i.e., management, pilots, parts suppliers, Intentional aircraft servicers). Each exchange holds the potential In aviation maintenance, an intentional error should really be for misunderstanding or omission. But communication considered a violation. If someone knowingly or intentionally between AMTs may be the most important of all. Lack chooses to do something wrong, it is a violation, which of communication between technicians could lead to a means that one has purposely deviated from safe practices, maintenance error and result in an aircraft accident. This procedures, standards, or regulations.

is especially true during procedures where more than one technician performs the work on the aircraft. It is critical Active & Latent that accurate, complete information be exchanged to ensure An active error is the specific individual activity that is an that all work is completed without any step being omitted.

obvious event. A latent error is the company issues that lead Knowledge and speculation about a task must be clarified and up to the event. For example, an AMT climbs up a ladder to not confused. Each step of the maintenance procedure must do a repair knowing that the ladder is broken. In this example, be performed according to approved instructions as though the active error was falling from the ladder. The latent error only a single technician did the work.

was the broken ladder that someone should have replaced.

14-13 A common scenario where communication is critical and a lack thereof can cause problems, is during shift change in an airline or fixed base operator (FBO) operation. A partially completed job is transferred from the technician finishing their workday to the technician coming on duty. Many steps in a maintenance procedure are not able to be seen or verified once completed due to the installation of components hiding the work. No steps in the procedure can be omitted and some steps still to be performed may be contingent on the work already completed. The departing technician must thoroughly explain what has occurred so that the arriving technician can correctly complete the job. A recounting of critical steps and any difficulties encountered gives insight.

A lack of communication at this juncture could result in the Figure 14-17. Safety awareness will help foresee and mitigate the risk of human error.

work being continued without certain required operations having been performed.

When a technician performs work without documentation, The approved steps of a maintenance procedure must be or documents work that was not performed, it is a sign that signed off by the technician doing the work as it is performed.

complacency may exist. Approved, written maintenance Continuing a job that has been started by someone else should procedures should be followed during all maintenance only occur after a face-to-face meeting of technicians. The inspections and repairs. Executing the proper paperwork applicable paperwork should be reviewed, the completed draws attention to a work item and reinforces its significance.

work discussed, and attention drawing to the next step.

Absence of either a written or oral turnover serves as warning To combat complacency, a technician must be trained to that an error could occur.

expect to find the fault that created the inspection item in the first place. The technician must stay mentally engaged It is vital that work not be continued on a project without in the task being performed. All inspection items must be both oral and written communication between the technician treated with equal importance, and it must never be assumed who started the job and the technician continuing it. Work that an item is acceptable when it has not been inspected.

should always be done in accordance with the approved A technician should never sign for any work that has not written procedure and all of the performed steps should been performed. Prior to the pen touching the paper for a bear the signature of the technician who accomplishes the signature, the technician should read the item before signing work. If necessary, a phone call can be made to obtain an and confirm it has been performed.

oral turnover when technicians cannot meet face-to-face at the work area. In general, the technician must see their role Lack of Knowledge as part of a greater system focused on safe aircraft operation and must communicate well with all those in that system A lack of knowledge when performing aircraft maintenance can result in a faulty repair that can have catastrophic results.

to be effective.

[Figure 14-20] Differences in technology from aircraft to Complacency aircraft and updates to technology and procedures on a single aircraft also make it challenging to obtain the knowledge Complacency is a human factor in aviation maintenance that required to perform airworthy maintenance.

typically develops over time. [Figure 14-18] As a technician gains knowledge and experience, a sense of self satisfaction All maintenance must be performed to standards specified and false confidence may occur. A repetitive task, especially in approved instructions. These instructions are based on an inspection item, may be overlooked or skipped because knowledge gained from the engineering and operation of the technician has performed the task a number of times the aircraft equipment. Technicians must be sure to use the without ever finding a fault. The false assumption might be latest applicable data and follow each step of the procedure made that inspection of the item is not important. However, as outlined. They must also be aware that differences exist in even if rare, a fault may exist. The consequences of the fault the design and maintenance procedures on different aircraft.

not being detected and corrected could cause an incident or It is important for technicians to obtain training on different accident. Routine tasks performed over and over allow time types of aircraft. When in doubt, a technician with experience for the technician’s mind to wander, which may also result in a required task not being performed.

14-14 on the aircraft should be consulted. If one is not available, or resumes, it is possible that the technician skips over a the consulted technician is not familiar with the procedure, a detail that needs attention. It is estimated that 15 percent of manufacturer’s technical representative should be contacted. maintenance related errors are caused by distractions.

It is better to delay a maintenance procedure than to do it incorrectly and cause an accident. Distractions can be mental or physical in nature. They can occur when the work is located on the aircraft or in the Distraction hangar. They can also occur in the psyche of the technician independent of the work environment. Something as simple A distraction while performing maintenance on an aircraft may disrupt the procedure. [Figure 14-21] When work as a cell phone call or a new aircraft being pushed into the THE DIRTY DOZEN Twelve human factors for aircraft maintenance proficiency Lack of Teamwork Lack of Assertiveness Lack of Communication Fatigue Stress Complacency Lack of Resources Lack of Awareness Lack of Knowledge Pressure Norms Distraction Maintainers must communicate with one another and explain what work has and has not been completed when changing shifts.

MITIGATING THE RISK Properly use logbooks and Never assume that the work Ensure that maintenance worksheets to communicate has been completed. personnel are discussing work accomplishments. exactly what has been and needs to be completed to the next shift.

Figure 14-18. Lack of communication.

14-15 hangar can disrupt the technician’s concentration on a job. [Figure 14-23] Fatigue can be mental or physical in Less visible is a difficult family or financial matter or other nature. Emotional fatigue also exists and affects mental personal issues that may occupy the technician’s thought and physical performance. A person is said to be fatigued process as work is performed. This can make performance when a reduction or impairment in any of the following of the required maintenance less effective. occurs: cognitive ability, decision-making, reaction time, coordination, speed, strength, or balance. Fatigue reduces Whatever their nature, numerous distractions can occur during alertness and often reduces a person’s ability to focus on the the course of maintaining an aircraft. The technician must task being performed.

recognize when attention to the job at hand is being diverted and assure that work continues correctly. A good practice Symptoms of fatigue can also include short-term memory is to go back three steps in the work procedure from when problems, channeled concentration on unimportant issues distraction occurred and resume the job from that point. Using while neglecting more important ones, and failure to maintain of a detailed step-by-step written procedure and signing off a situational overview. A fatigued person may be easily each step only after it is completed also helps. Incomplete distracted or may be nearly impossible to distract. They work can be marked or tagged, especially when the technician may experience abnormal mood swings. Fatigue results in is pulled from the work by a distraction, and it is unknown an increase in mistakes, poor judgment, and poor decisions when work will be resumed and by whom. Disconnect any or perhaps no decisions at all. A fatigued person may also connector and leave it plainly visible if an installation is not lower their standards.

complete. There is a tendency to think a job is finished when a component is “hooked up.” Similarly, when a step in the Tiredness is a symptom of fatigue. However, sometimes a maintenance procedure is complete, be sure to immediately fatigued person may feel wide awake and engaged in a task.

lock wire or torque the fasteners if required. This can be used The primary cause of fatigue is a lack of sleep. Good restful as an indication that all is well up to that point in the procedure. sleep, free from drugs or alcohol is a human necessity to prevent fatigue. Fatigue can also be caused by stress and Lack of Teamwork overworking. A person’s mental and physical state also naturally cycles through various levels of performance each A lack of teamwork may also contribute to errors in aircraft maintenance. [Figure 14-22] Closely related to the need for day. Variables such as body temperature, blood pressure, heart rate, blood chemistry, alertness, and attention rise and communication, teamwork is required in aviation maintenance in many instances. Sharing of knowledge between technicians, fall in a pattern daily. This is known as circadian rhythm.

[Figure 14-24] A person’s ability to work (and rest) rises and coordinating maintenance functions, turning work over from shift to shift, and working with flight personnel to troubleshoot falls during this cycle, and performance counter to circadian rhythm can be difficult. Until it becomes extreme, a person and test aircraft are all are executed better in an atmosphere of teamwork. Often associated with improved safety in the may be unaware that they are fatigued. It is easier recognized by another person or in the results of tasks being performed.

workplace, teamwork involves everyone understanding and agreeing on actions to be taken. A gear swing or other This is particularly dangerous in aviation maintenance since the lives of people depend on maintenance procedures operational check involves all the members of a team working together. Multiple technicians contribute to the effort to ensure performed at a high level of proficiency. Working alone when fatigued is particularly dangerous.

a single outcome. They communicate and look out for one another as they do the job. A consensus is formed that the The best remedy for fatigue is to get enough sleep on a item is airworthy or not airworthy.

regular basis. The technician must be aware of the amount and quality of sleep obtained. Time off is justified when The technician primarily deals with the physical aspect of the aircraft and its airworthiness. Others in the organization too little sleep has occurred and errors are probable during maintenance. Countermeasures to fatigue are often used, but perform their roles and the entire company functions as a team. Teams can win or lose depending on how well everyone their effectiveness can be short lived and many can make fatigue worse. Caffeine is a common fatigue countermeasure.

in the organization works together toward a common objective. A lack of teamwork makes all jobs more difficult Pseudoephedrine found in sinus medicine and amphetamines are also used. While they can be effective for short periods, the and, in maintenance, could result in a miscommunication that affects the airworthiness of the aircraft. underlying fatigue remains and due to this drug use, the person may have trouble getting the rest needed once off the job.

Fatigue Suggestions to help mitigate the problems caused by fatigue Fatigue is a major human factor that has contributed include looking for symptoms of fatigue in oneself and in to many maintenance errors resulting in accidents.

14-16 THE DIRTY DOZEN Twelve human factors for aircraft maintenance proficiency Lack of Teamwork Lack of Assertiveness Lack of Communication Fatigue Stress Complacency Lack of Resources Lack of Awareness Lack of Knowledge Pressure Norms Distraction People tend to become overconfident after becoming proficient in a certain task, which can mask the awareness of dangers.

MITIGATING THE RISK Always expect to find Always double check Never sign off on something something wrong. your work. that you did not fully check.

Figure 14-19. Complacency.

others. Have others check your work, even if an inspector sign fatigue that can degrade performance and also lead to errors.

off is not required. Avoid complex tasks during the bottom Shift work requires technicians to work during low cycles of your circadian rhythm. Sleep and exercise daily. Eight to of their natural circadian rhythm. It also makes sleep more nine hours of daily sleep are recommended to avoid fatigue. difficult when not on the job. Furthermore, regular night shift AMTs in airline operations are part of a system in which work makes a person’s body more sensitive to environmental most maintenance is performed at night. Fleet aircraft are disturbances. It can degrade performance, morale, and operated primarily during daytime hours to generate company safety. It can also affect one’s physical health. All of these revenue. Therefore, shift work is required to maintain the can be reflected in degraded maintenance performance—a fleet. It is already known that turning work over to other dangerous situation.

technicians during shift changes can lead to errors due to lack of communication. But shift work alone is a cause of The technician must be aware that shift work is the norm in 14-17 THE DIRTY DOZEN Twelve human factors for aircraft maintenance proficiency Lack of Teamwork Lack of Assertiveness Lack of Communication Fatigue Stress Complacency Lack of Resources Lack of Awareness Lack of Knowledge Pressure Norms Distraction In a world of ever-changing technology, maintainers must remain up to date on current equipment and how to fix it.

MITIGATING THE RISK Only fix parts that you are If you do not know how to Ensure that the maintenance trained to fix. fix something, ask for help manual you are using is up from someone who does. to date.

Figure 14-20. Lack of knowledge.

aviation. Avoidance of fatigue is part of the job. Title 14 of Lack of Resources the Code of Federal Regulations (14 CFR) part 121, section A lack of resources can interfere with a person’s ability to 377, only requires 24 hours time off during a week of work.

complete a task because of a lack of supplies and support.

Since this is obviously not enough, it is up to companies and [Figure 14-25] Low quality products also affect one’s ability technicians to regulate shift work and time off to reduce the to complete a task. Aviation maintenance demands proper potential for errors. Most importantly, each technician must tools and parts to maintain a fleet of aircraft. Any lack of monitor and control their sleep habits to avoid fatigue.

resources to safely carry out a maintenance task can cause both non-fatal and fatal accidents. For example, if an aircraft is dispatched without a functioning system that is typically nonessential for flight but suddenly becomes needed, this 14-18 THE DIRTY DOZEN Twelve human factors for aircraft maintenance proficiency Lack of Teamwork Lack of Assertiveness Lack of Communication Fatigue Stress Complacency Lack of Resources Lack of Awareness Lack of Knowledge Pressure Norms Distraction A distraction could be anything that takes your mind off the task that is being done. Any distraction while working can cause us to think we are further ahead in the process than we actually are.

MITIGATING THE RISK Once returning to the job, go Never leave tools or parts back through all of the steps lying around. Secure them Use a detailed checklist.

to ensure where you left off. before leaving the area.

Figure 14-21. Distraction.

could create a problem. or cancellations of the planned itinerary. AOG applies to any aviation materials or spare parts that are needed immediately Parts are not the only resources needed to do a job properly, for an aircraft to return to service. AOG suppliers refer but all too frequently parts become a critical issue. AMTs can qualified personnel and dispatch the parts required to repair try to be proactive by checking suspected areas or tasks that the aircraft for an immediate return to service. AOG also is may require parts at the beginning of the inspection. Aircraft used to describe critical shipments for parts or materials for on ground (AOG) is a term in aviation maintenance indicating aircraft “out of service” (OTS) at a location.

that a problem is serious enough to prevent an aircraft from flying. In these cases, there is a rush to acquire the parts to If the status of an aircraft is AOG and materials required are put the aircraft back into service and prevent further delays not on hand, parts and personnel must be driven, flown, or 14-19 THE DIRTY DOZEN Twelve human factors for aircraft maintenance proficiency Lack of Teamwork Lack of Assertiveness Lack of Communication Fatigue Stress Complacency Lack of Resources Lack of Awareness Lack of Knowledge Pressure Norms Distraction Personality differences in the workplace must be left at the door. Organizations should emphasize that a lack of teamwork can ultimately affect the safety of maintenance work.

MITIGATING THE RISK Ensure that lines of Always look out for Discuss specific duties when communication are open co-workers with safety jobs require more than one between personnel. in mind. person to eliminate any questions.

Figure 14-22. Lack of teamwork.

sailed to the location of the grounded aircraft. Usually the proper parts when they are needed. Having the correct tools problem is escalated through an internal AOG desk, then means not having to improvise. For example, an aircraft that the manufacturer’s AOG desk, and finally competitors’ had received a new interior needed to be weighed prior to AOG desks. All major air carriers have an AOG desk that is being released to fly. Two days before the planned release, the manned 24 hours a day, 7 days a week by personnel trained aircraft was weighed without the proper electronic load cells in purchasing, hazardous materials shipping, and parts placed between the aircraft jack and the aircraft. Because the manufacturing and acquisition processes. correct equipment was not used, the aircraft slipped off of one of the load cells and the jack point creased the spar. The Within an organization, making sure that personnel have the cost of improvising can be very steep. The right tools for the correct tools for the job is just as important as having the job need to be used at all times, and if they are broken, out of 14-20 THE DIRTY DOZEN Twelve human factors for aircraft maintenance proficiency Lack of Teamwork Lack of Assertiveness Lack of Communication Fatigue Stress Complacency Lack of Resources Lack of Awareness Lack of Knowledge Pressure Norms Distraction Occupations that require an individual to work long hours or stay up overnight can lead to fatigue.

Fatigue can cause a decreased attentiveness and a decreased level of consciousness, which can be very dangerous when conducting maintenance.

MITIGATING THE RISK Be aware of the symptoms Eating healthy, exercising Forfeit complex tasks if you and look for them in yourself and maintaining regular sleep know you are exhausted.

and coworkers. patterns can prevent fatigue.

Figure 14-23. Fatigue.

calibration, or missing, they need to be repaired, calibrated, or technical publications department at the appropriate or found as soon as possible. aircraft manufacturer. Most manuals are in a constant state of revision and, if organizations do not identify missing Technical documentation is another critical resource that can information in the manuals, then nothing is done to correct the lead to problems in aviation maintenance. When trying to documentation. Resources such as publications departments find out more about the task at hand or how to troubleshoot and manufacturers’ technical support are available and should and repair a system, the needed information often cannot be be used rather than ignoring the problem.

found because the manuals or diagrams are not available.

If the information is unavailable, personnel should ask Another valuable resource that the maintenance department a supervisor or speak with a technical representative should rely on is the flight crew. Organizations should 14-21 1-3 AM Peak alertness Slightly impaired Reduced alertness Dangerously drowsy 9 12 15 18 21 24 3 6 9 Alertness Level Multiple Sleep Latency Test (MSLT) Time of Day Figure 14-24. Many human variables rise and fall daily due to one’s natural circadian rhythm.

encourage open communication between flight crews and timely manner, are completed correctly with safety being the maintenance crews. The flight crew can provide valuable ultimate goal. Sacrificing quality and safety for the sake of time information when dealing with a defective part or problem. should not be tolerated or accepted. Likewise, AMTs need to Figure 14-26 shows a number of questions that flight crews can recognize on their own when time pressures are clouding their be asked to help resolve and understand maintenance issues. judgments and causing them to make unnecessary mistakes.

Self-induced pressures are those occasions where one takes When the proper resources are available for the task at hand, ownership of a situation that was not of their doing.

there is a much higher probability that maintenance will do a better, more efficient job and higher likelihood that the job In an effort to combat self-induced pressure, technicians will be done correctly the first time. Organizations must learn should ask for help if they feel overwhelmed and under a to use all of the resources that are available and, if the correct time constraint to complete a repair. Another method is to resources are not available, make the necessary arrangements have someone check the repair thoroughly to ensure that all to get them in a timely manner. The end result saves time maintenance tasks were completed correctly.

and money, and enables organizations to complete the task knowing the aircraft is airworthy. Lastly, if given a repair with a specific time limitation that you feel is unrealistic or compromises safety, bring it to Pressure the attention of the organization’s management and openly Aviation maintenance tasks require individuals to perform discuss a different course of action.

in an environment with constant pressure to do things better and faster without making mistakes and letting things Lack of Assertiveness fall through the cracks. Unfortunately, these types of job Assertiveness is the ability to express your feelings, opinions, pressures can affect the capabilities of maintenance workers beliefs, and needs in a positive, productive manner and should to get the job done right. [Figure 14-27] Airlines have not be confused with being aggressive. [Figure 14-28] It strict financial guidelines, as well as tight flight schedules, is important for AMTs to be assertive in issues relating to that pressure mechanics to identify and repair mechanical aviation repair rather than choosing not to or not being problems quickly so that the airline industry can keep allowed to voice their concerns and opinions. Not being moving. Most important, aircraft mechanics are responsible assertive could ultimately cost people their lives. The for the overall safety of everyone who uses flying as a mode following are examples of how a lack of assertiveness can of transportation.

be offset: 1. Address managers and supervisors directly by stating Organizations must be aware of the time pressures that are put the problem.

on aircraft mechanics and help them manage all of the tasks Example: “John, I have a concern with how this repair that need to be completed so that all repairs, while done in a 14-22 THE DIRTY DOZEN Twelve human factors for aircraft maintenance proficiency Lack of Teamwork Lack of Assertiveness Lack of Communication Fatigue Stress Complacency Lack of Resources Lack of Awareness Lack of Knowledge Pressure Norms Distraction When there is a lack of resources available to properly fix something, a decision should be made to cease maintenance until the proper parts are available.

MITIGATING THE RISK Maintain a sufficient supply Preserve all equipment Never replace a part with one of parts and order any through proper maintenance. that is not compatible for the anticipated parts before they sake of getting the job done.

are required.

Figure 14-25. Lack of resources.

is being rushed.” Example: “John, what do you think?” 2. Explain what the consequences will be.

When being assertive with co-workers or management, Example: “If we continue, the result will be that the deal with one issue at a time rather than trying to tackle a part will break sooner rather than later.” number of problems at once. It is also important to have documentation and facts to back up your argument, which can 3. Propose possible solutions to the problem.

give people a visual account of what you are trying to explain.

Example: “We could try doing things another way or A lack of assertiveness in failing to speak up when things you may want to try this way.” do not seem right has resulted in many fatal accidents. This 4. Always solicit feedback and include other opinions.

can easily be changed by promoting good communication 14-23 between co-workers and having an open relationship with When and where did the event occur?

supervisors and management. Maintenance managers must be familiar with the behavior styles of the people they supervise Were there any indications prior to failure?

and learn to utilize their talents, experience, and wisdom.

As the employees become aware of behavior styles and Did the system surge or flicker?

understand their own behavior, they see how they unwittingly contribute to some of their own problems and how they can How often does the system cycle? make adjustments. Assertive behavior may not be a skill that comes naturally to every individual, but it is a critical skill What was the range of transmission or reception? to achieve effectiveness. AMTs should give supervisors and management the kind of feedback required to ensure that they What was the time of retractions or extensions? will be able to assist mechanics in doing their job.

Stress Were there noises in the aircraft or headsets?

Aviation maintenance is a stressful task due to many factors.

Were there vibrations or stiffness of system controls? [Figure 14-29] Aircraft must be functional and flying in order for airlines to make money, which means that maintenance must be done within a short timeframe to avoid flight delays Was irregular trim required?

and cancellations. Fast-paced technology that is always changing can add stress to technicians. This demands that Was there ease or lack of control?

AMTs stay trained on the latest equipment. Other stressors include working in dark, tight spaces, lack of resources to Were smoke or fumes present?

get the repair done correctly, and long hours. The ultimate stress of aviation maintenance is knowing that the work they Was there a loss of amperage and/or voltage?

do, if not done correctly, could result in tragedy.

Figure 14-26. Questions that technicians can ask flight crews in an Everyone handles stress differently and particular situations effort to resolve and understand maintenance issues.

can bring about different degrees of difficulty for different people. For example, working under a strict timeline can be difficult to perform tasks, as technicians are often a stressor for one person and normal for another. The causes contorted into unusual positions for a long period of stress are referred to as “stressors” and are categorized as of time.

physical, psychological, or physiological. Following is a list of each and how they may affect maintenance.

Psychological Stressors Psychological stressors relate to emotional factors, such Physical Stressors as a death or illness in the family; business worries; poor Physical stressors add to a person’s workload and make their interpersonal relationships with family, co-workers, or work environment uncomfortable.

supervisors; and financial worries.

• Temperature—high temperatures in the hangar • Work-related stressors—over anxiousness can hinder increase perspiration and heart rate causing the body performance and speed while conducting maintenance to overheat. Low temperatures can cause the body to if there is any apprehension about how to do a repair feel cold, weak, and drowsy.

or concerns about getting it done on time.

• Noise—hangars that have high noise levels (due to • Financial problems—impending bankruptcy, aircraft taking off and landing close by) can make recession, loans, and mortgages are a few examples it difficult for maintenance personnel to focus of financial problems that can create stressors.

and concentrate.

• Marital problems—divorce and strained relationships • Lighting—poor lighting within a work space makes can interfere with one’s ability to perform their job it difficult to read technical data and manuals.

correctly.

Likewise, working inside an aircraft with poor lighting increases the propensity to miss something or to repair • Interpersonal problems—problems with superiors something incorrectly.

and colleagues due to miscommunication or perceived competition and backstabbing can cause • Confined spaces—small work spaces make it very a hostile work environment.

14-24 THE DIRTY DOZEN Twelve human factors for aircraft maintenance proficiency Lack of Teamwork Lack of Assertiveness Lack of Communication Fatigue Stress Complacency Lack of Resources Lack of Awareness Lack of Knowledge Pressure Norms Distraction Pressure to get things repaired is always present in aviation. Maintainers must not let the pressures of time constraints get in the way with safely finishing a repair.

MITIGATING THE RISK Ensure that the pressure is Ask for extra help if time is Communicate if you think not self-induced. an issue. you will need more time to complete a repair rather than rush through it.

Figure 14-27. Pressure.

lacking the proper nutrition, can result in low energy and induce symptoms like headaches and shaking.

Physiological Stressors Physiological stressors include fatigue, poor physical • Lack of sleep—a fatigued AMT is unable to perform condition, hunger, and disease.

to standard for long periods of time and can become sloppy with repairs and make significant mistakes.

• Poor physical condition—trying to work when ill or not feeling well can force the body to use more • Conflicting shift schedules—the effect of changing energy fighting the illness, leaving less energy to sleep patterns on the body’s circadian cycle can lead perform vital tasks.

to a degradation of performance.

• Proper meals—not eating enough, or eating foods 14-25 THE DIRTY DOZEN Twelve human factors for aircraft maintenance proficiency Lack of Teamwork Lack of Assertiveness Lack of Communication Fatigue Stress Complacency Lack of Resources Lack of Awareness Lack of Knowledge Pressure Norms Distraction Lack of assertiveness in failing to alert others when something does not seem right can result in many fatal accidents. Do not let something that you know is wrong continue by ignoring it.

MITIGATING THE RISK Provide clear feedback when Allow co-workers to give Never compromise your a risk or danger is perceived. their opinions and always standards.

accept corrective criticisms.

Figure 14-28. Lack of assertiveness.

People cope with stress in many different ways. Specialists Norms say that the first step is to identify stressors and the Norms is short for “normal,” or the way things are normally symptoms that occur after exposure to those stressors. Other done. [Figure 14-31] They are unwritten rules that are recommendations involve development or maintenance of a followed or tolerated by most organizations. Negative healthy lifestyle with adequate rest and exercise, a healthy norms can detract from the established safety standard and diet, limited consumption of alcoholic drinks, and avoidance cause an accident to occur. Norms are usually developed of tobacco products.

to solve problems that have ambiguous solutions. When faced with an ambiguous situation, an individual may use Lack of Awareness another’s behavior as a frame of reference around which to Lack of awareness is defined as a failure to recognize all the form their own reactions. As this process continues, group consequences of an action or lack of foresight. [Figure 14-30] norms develop and stabilize. Newcomers to the situation are In aviation maintenance, it is not unusual to perform the same then accepted into the group based on adherence to norms.

maintenance tasks repeatedly. After completing the same Very rarely do newcomers initiate change in a group with task multiple times, it is easy for technicians to become less established norms.

vigilant and develop a lack of awareness of what they are doing and what is around them. Each time a task is completed Some norms are unsafe in that they are non-productive or it must be treated as if it were the first time.

detract from the productivity of the group. Taking shortcuts in 14-26 aircraft maintenance, working from memory, or not following group’s perception of the newcomer’s credibility.

procedures are examples of unsafe norms. Newcomers are better able to identify these unsafe norms than long-standing Norms have been identified as one of the dirty dozen in members of the group. On the other hand, the newcomer’s aviation maintenance and a great deal of anecdotal evidence credibility depends on their assimilation into the group. The points to the use of unsafe norms on the line. The effect of newcomer’s assimilation, however, depends on adherence unsafe norms may range from the relatively benign, such as to the group norms. Everyone should be aware of the determining accepted meeting times, to the inherently unsafe, perceptiveness of newcomers in identifying unhealthy norms such as signing off on incomplete maintenance tasks. Any and develop a positive attitude toward the possibility that behavior commonly accepted by the group, whether as a norms may need to be changed. Finally, as newcomers become standard operating procedure (SOP) or not, can be a norm.

assimilated into the group structure, they build credibility with Supervisors need to ensure that everyone adheres to the same others. Once this has been done, a relative newcomer may standards and that unsafe norms are not tolerated. AMTs begin to institute change within the group. Unfortunately, should pride themselves on following procedure, rather than such actions are often difficult to do and rely heavily on the unsafe norms that may have been adopted as regular practice.

THE DIRTY DOZEN Twelve human factors for aircraft maintenance proficiency Lack of Teamwork Lack of Assertiveness Lack of Communication Fatigue Stress Complacency Lack of Resources Lack of Awareness Lack of Knowledge Pressure Norms Distraction Stress is the subconscious response to the demands placed on a person.

MITIGATING THE RISK Take time off or a short Healthy eating, exercise, and Discuss with a co-worker and break if you are feeling a sufficient amount of rest ask them to monitor your stressed. can reduce stress levels. work.

Figure 14-29. Stress.

14-27 THE DIRTY DOZEN Twelve human factors for aircraft maintenance proficiency Lack of Teamwork Lack of Assertiveness Lack of Communication Fatigue Stress Complacency Lack of Resources Lack of Awareness Lack of Knowledge Pressure Norms Distraction After completing the same tasks multiple times, maintainers can develop a lack of awareness for what is around them. They tend to lack common sense and vigilance because they have completed the same task so many times.

MITIGATING THE RISK Check to see if what you are Even if you are highly working on conflicts with an proficient in a task, always Always ask co-workers to existing modification or have someone check check your work.

repair. your work.

Figure 14-30. Lack of awareness.

4. Forgotten tools and parts.

Example of Common Maintenance Errors In an effort to identify the most frequently occurring 5. Failure to lubricate. [Figure 14-33] maintenance discrepancies, the United Kingdom Civil 6. Failure to secure access panels, fairings, or cowlings.

Aviation Authority (CAA) conducted in-depth studies of 7. Fuel or oil caps and fuel panels not secured.

maintenance sites on aviation maintenance operations. The following list is what they found to be the most common 8. Failure to remove lock pins. [Figure 14-34] occurring maintenance errors.

All of the maintenance discrepancies listed above can be 1. Incorrect installation of components.

avoided if the proper procedures are followed on the job 2. Fitting of wrong parts.

card that is being used. [Figure 14-35] Regardless of how 3. Electrical wiring discrepancies to include crossing many times the task has been completed, each time you connections. [Figure 14-32] 14-28 THE DIRTY DOZEN Twelve human factors for aircraft maintenance proficiency Lack of Teamwork Lack of Assertiveness Lack of Communication Fatigue Stress Complacency Lack of Resources Lack of Awareness Lack of Knowledge Pressure Norms Distraction Norms is short for “ normal, ” or the way things are normally done. They are unwritten rules that are followed or tolerated by most of the organization. Negative norms can detract from the established safety standard and cause an accident to occur.

MITIGATING THE RISK Ensure that everyone follows The easiest way of Be aware that just because it the same standard. accomplishing something seems normal does not make may not be the standard. it correct.

Figure 14-31. Norms.

pick up a job card, treat it like it is the first time you have broken at the maintenance level, the likelihood of the accident ever completed the task, and complete it with diligence and occurring can be drastically decreased. Figure 14-37 is a list complete accuracy. of maintenance-related incidents/accidents and their causes.

It is easy to see how many of the “Dirty Dozen” contributed Historically, twenty percent of all accidents are caused by to the causes or were considered contributing factors.

a machine failure, and eighty percent by human factors.

[Figure 14-36] Originally focusing on the pilot community, Where to Get Information human factors awareness has now spread into the training Following is a list of websites and references that are good sphere of maintenance technicians. An in-depth review of sources of information on human factors.

an aviation incident reveals time and again that a series of human errors (known also as a chain of events) was allowed to build until the accident occurred. If the chain of events is 14-29 Incident On March 20, 2001, a Lufthansa Airbus A320 almost crashed shortly after takeoff because of reversed wiring in the captain's sidestick flight control. Quick action by the co-pilot, whose sidestick was not faulty, prevented a crash.

Cause The investigation has focused on maintenance on the captain's controls carried out by Lufthansa Technik just before the flight. During the previous flight, a problem with one of the two elevator/aileron computers (ELAC) had Lock pin occurred. An electrical pin in the connector was found to be damaged and was replaced. It has been confirmed that two pairs of pins inside the connector had accidentally been crossed during the repair. This changed the polarity in the sidestick and the respective control channels “bypassing” the control unit, which might have sensed the error and would have triggered a warning. Clues might have been seen on the electronic centralized aircraft monitor (ECAM) screen during the flight control checks, but often pilots only check for a deflection indication, not the direction. Before the aircraft left the hangar, a flight control check was performed by the mechanic, but only using the first officer’s sidestick.

Figure 14-34. Lock pins located on the landing gear of an aircraft.

Figure 14-32. A description of a Lufthansa Airbus A320 that almost crashed due to reversed wiring of the flight controls.

MAINTENANCE JOB CARD WORKNO A26 JOB 1 OF 1 97471 4A Accident D-4 SSFOR - PORTABLE INTERFACE UNIT UZ0030 1 OF 2 -400 AD-NOTE Alaska Airlines Flight 261, a McDonnell Douglas MD-83 FRAWB41 263 FZE 1 0.00 0.00 18.11.02 PAC aircraft, experienced a fatal accident on January 31, 2000, 1 ZONE 221-222 in the Pacific Ocean. The two pilots, three cabin crewmembers, and 83 passengers on board were killed and SOLID STATE FLIGHT DATA RECORDER (IF APPLICABLE) the aircraft was destroyed.

MS 31-31-00-007-002-500 (AMM 31-31-01) F1 SSFDR DATA COPY Cause NOTE: THIS IS A DUPLICATE INSPECTION!

The subsequent investigation by the National PERFORMANCE AND INSPECTION MUST BE DONE BY TWO PERSONS.

Transportation Safety Board (NTSB) determined that PERFORMANCE = B1 inadequate maintenance led to excessive wear and INSPECTION = B1 catastrophic failure of a critical flight control system during flight. The probable cause was stated to be “a loss of Make a copy of the FDR data with the portable interface (PI) unit A General airplane pitch control resulting from the in-flight failure of (1) This taskwork the hand-hold portable interface (PI) unit to make a the horizontal stabilizer trim system jackscrew assembly’s copy of the data from the flight data recorder (FDR) when the FDR acme nut threads. The thread failure was caused by is in the airplane excessive wear resulting from Alaska Airlines’ insufficient (a) The PI puts the data on a removable PC card (PCMCIA).

(b) The data on the PC card can then be analyzed by the applicable lubrication of the jackscrew assembly.” airline personnel.

Figure 14-33. A description of Alaska Airlines Flight 261 that Figure 14-35. A sample picture of a maintenance job card that crashed due to insufficient lubrication of the jackscrew assembly.

explains the steps of each maintenance task.

Federal Aviation Administration (FAA) There are a number of human factors resources within the FAA’s Maintenance Fatigue Section FAA. The most direct link for aviation maintenance human The FAA has sponsored a multi-disciplinary subject matter factors is the FAA Human Factors website at hf.faa.gov . It expert work group involving industry, labor, research, offers document access and services, including most of the and government to investigate the issues associated with FAA maintenance human factors documents dating back to maintenance fatigue, and the practical science-based methods the 1988 start of FAA’s maintenance human factors research that can be used to manage fatigue risk. For more information, and development program. New documents include videos, visit the website at www.mxfatigue.com .

PowerPoint presentations, and other media.

14-30 Accidents in Aviation S E S U A C N A M U H Accidents T E C H N I C A L C A U S E S 1903 Present Time Figure 14-36. Statistical illustration showing that 80 percent of all aviation accidents are caused by human factors.

FAA Safety Team International Ergonomics Association (IEA) The FAA Safety Team has a dedicated website that provides The International Ergonomics Association (IEA) is a up-to-date information safety concerns, upcoming seminars, federation of over 40 ergonomics and human factors societies featured courses and resources. For more information, visit located all over the world. All members of the HFES are the website at www.faasafety.gov . automatically also members of the IEA. The main contact point within the IEA is through the office of their Secretary Other Resources General. For more information, visit their website at iea.cc .

System Safety Services The mission of System Safety Services is to assist clients in developing the best possible safety system to meet their needs. They have an experienced and professional team of individuals with years of experience in aviation and human factors. The website provides a lot of information on human factors including articles, upcoming events, presentations, safety videos, training aids and workshops. For more information, visit their website at www.system-safety.com .

Human Factors & Ergonomics Society (HFES) The Human Factors and Ergonomics Society (HFES) is the only organization in the United States dedicated specifically to the human factors profession. The HFES was formed in 1957 and typically maintains about 5,000 members. For more information, visit their website at www.hfes.org .

14-31 INCIDENT August 26, 1993, an Excalibur Airways Airbus 320 took off from London-Gatwick Airport (LGW) and exhibited an undemanded roll to the right on takeoff, a condition which persisted until the aircraft landed back at LGW 37 minutes later. Control of the aircraft required significant left sidestick at all times and the flight control system was degraded by the loss of spoiler control.

CAUSE Technicians familiar with Boeing 757 flap change procedures lacked the knowledge required to correctly lock out the spoilers on the Airbus during the flap change work that was done the day before the flight. Turnover to technicians on the next shift compounded the problem. No mention of incorrect spoiler lockout procedure was given since it was assumed that the 320 was like the 757. The flap change was operationally checked, but the spoiler remained locked out incorrectly and was not detected by the flight crew during standard functional checks. The lack of knowledge on Airbus procedures was considered a primary cause of this incident.

INCIDENT April 26, 2001, an Emery Worldwide Airlines DC-8-71F left main landing gear would not extend for landing.

CAUSE Probable cause was failure of maintenance to install the correct hydraulic landing gear extension component and the failure of inspection to comply with post-maintenance test procedures. No injuries.

ACCIDENT On May 25, 2002, China Airlines Flight 611 Boeing 747 broke into pieces in mid-air and crashed, killing all 225 people on board.

CAUSE The accident was the result of metal fatigue caused by inadequate maintenance after a previous incident.

ACCIDENT On August 26, 2003, a Colgan Air Beech 1900D crashed just after takeoff from Hyannis, Massachusetts. Both pilots were killed.

CAUSE The improper replacement of the forward elevator trim cable and subsequent inadequate functional check of the maintenance performed resulted in a reversal of the elevator trim system and a loss of control in flight. Factors were the flight crew’s failure to follow the checklist procedures and the aircraft manufacturer’s erroneous depiction of the elevator trim drum in the maintenance manual.

ACCIDENT On September 28, 2007, American Airlines Flight 1400 DC-9 experienced an in-flight engine fire during departure climb from Lambert St. Louis International Airport (STL). During the return to STL, the nose landing gear failed to extend, and the flight crew executed a go-around, during which the crew extended the nose gear using the emergency procedure. The flight crew conducted an emergency landing, and the 2 flight crewmembers, 3 flight attendants, and 138 passengers deplaned on the runway. No occupant injuries were reported, but the airplane sustained substantial damage from the fire.

CAUSE American Airlines’ maintenance personnel’s use of an inappropriate manual engine-start procedure, which led to the uncom- manded opening of the left engine air turbine starter valve, and a subsequent left engine fire.

Figure 14-37. A list of maintenance-related incidents/accidents and their causes.

14-32

Glossary

Algebra. The branch of mathematics that uses letters or A symbols to represent numbers in formulas and equations.

Absolute humidity. The actual amount of the water vapor in a mixture of air and water.

Allowance. The difference of the upper and lower variation of a part.

Absolute pressure. Equal to gauge pressure plus atmospheric pressure. Also known as psia.

Alodizing. A simple chemical treatment for all aluminum alloys to increase their corrosion resistance and to improve Absolute temperature. Temperature measured relative to their paint bonding qualities.

absolute zero. Absolute temperature scales include Kelvin and Rankine.

Alteration. A change or modification to an aircraft from its previous state Acceleration due to gravity. The acceleration of an object caused by gravity. On earth, it is measured as 32.2 feet per Alternating current. An electric current that reverses second per second (32.2 fps/s).

direction in a circuit at regular intervals.

Addition. The process in which the value of one number is Ammeter. An instrument for measuring electric current in added to the value of another.

amperes.

Advisory Circulars (AC). Issued to inform the aviation Ampere. A unit of measure of the rate of electron flow or public in a systematic way of nonregulatory material. An current in an electrical conductor. One ampere of current AC is issued to provide guidance and information in a represents one coulomb of electrical charge (6.24 × 1018 designated subject area or to show a method acceptable to charge carriers) moving past a specific point in one second.

the Administrator for complying with a related 14 CFR part.

Annealing. The process of heating a metal to a prescribed Aircraft Specifications. FAA recordkeeping documents temperature, holding it there for a specified length of time, issued for both type-certificated and non-typecertificated and then cooling the metal back to room temperature.

products which have been found eligible for U.S. airworthiness certification.

Annual inspection. An inspection required by the FAA once every 12 calendar months if other suitable inspections Airfoil. Any device that creates a force, or lift, based on do not occur within that timeframe. An A&P technician with Bernoulli’s principles or Newton’s laws, when air is caused inspection authorization must perform this inspection.

to flow over the surface of the device.

Anodizing. The most common surface treatment of nonclad Airworthiness certificate. A document required to be aluminum alloy surfaces. The aluminum alloy sheet or casting onboard an aircraft that indicates the aircraft conforms to is the positive pole in an electrolytic bath in which chromic type design and is in condition for safe operation.

acid or other oxidizing agent produces an aluminum oxide film on the metal surface. Aluminum oxide is naturally Airworthiness directive (AD). Issued by the FAA in protective, and anodizing merely increases the thickness and response to deficiencies and/or unsafe conditions found density of the natural oxide film.

in aircraft, engines, propellers, or other aircraft parts.

Compliance with an AD is mandatory.

Apparent power. That power apparently available for use in an AC circuit containing a reactive component. It is the Alclad aluminum. Used to designate sheets that consist of product of effective voltage times the effective current, an aluminum alloy core coated with a layer of pure aluminum expressed in volt-amperes.

to a depth of approximately 5 ⁄ 2 percent on each side.

Archimedes’ principle. The buoyant force that a fluid exerts G-1 upon a submerged body is equal to the weight of the fluid Boyle’s law. States that the volume of an enclosed dry gas the body displaces. varies inversely with its absolute pressure, provided the temperature remains constant.

Area. A measurement of the amount of surface inside a two- dimensional object. Break lines. Line on a drawing indicating that a portion of the object is not shown on the drawing.

Arm. The horizontal distance that a part of the aircraft or a piece of equipment is located from the datum. British thermal unit (Btu). The amount of heat required to change the temperature of 1 pound of water by 1 degree Armature. The rotating part of an electric generator or motor. Fahrenheit.

Aspect ratio. The relationship of the length (wingtip to Buoyancy. The upward force that any fluid exerts on a body wingtip), or span, of an airfoil to its width, or chord. submerged in it.

Assembly drawing. A description of an object made up of Buttock line (BL). The longitudinal axis of the aircraft that two or more parts. serves as the reference location for positions to the left and right of center. The positions are usually dimensioned in Atom. The smallest particle composed of a nucleus that inches.

contains protons, neutrons, and electrons, which revolve around the nucleus. C Calorie. The amount of heat required to change the B temperature of 1 gram of water by 1 degree Centigrade.

Ballast. A weight installed or carried in an aircraft to move the center of gravity to a location within its allowable limits. Camber. The curvature of a wing as viewed by cross section.

A wing has upper camber on its top surface and lower camber Base. In mathematics, used to refer to a particular mathematical on its bottom surface. The upper camber is more pronounced; object that is used as a building block. A base-a system is the lower camber is comparatively flat. This causes the one that uses a as a new unit from which point counting starts velocity of the airflow immediately above the wing to be again. (See decimal system.) In the mathematical expression much higher than that below the wing.

n a , read as “a to the nth power,” a is the base.

Capacitance (C). The property of an electric conductor that Basic empty weight. Standard empty weight plus optional characterizes its ability to store an electric charge.

equipment.

Capacitive reactance (X ). The measure of a capacitor’s c Bernoulli’s principle. Equivalent to the principle of opposition to alternating current.

conservation of energy, this principle states that the static pressure of a fluid (liquid or gas) decreases at points where Capacitor. An electrical component that stores an electric the velocity of the fluid increases, provided no energy is charge.

added to or taken away from the fluid.

Case hardening. A process in which the surface of a metal is Binary number system. The binary number system is a changed chemically by introducing a high carbide or nitride number system that has only two digits, 0 (zero) and 1. content. Case hardening produces a hard, wear-resistant Binary numbers are made from a series of zeros and ones. An surface, or case, over a strong, tough core.

example of an 8-bit binary number is 11010010. The prefix “bi” in the word binary is a Latin root for the word “two.” Center of gravity (CG). The point about which the nose-heavy and tail-heavy moments are exactly equal in Block diagrams. Used to show a simplified relationship of magnitude.

a more complex system of components.

Center of gravity range. The center of gravity range for an Borescope. A device that enables the inspector to see aircraft is the limits within which the aircraft must balance.

inside areas that could not otherwise be inspected without It is identified as a forward-most limit (arm) and an aft-most disassembly. limit (arm).

G-2 Centrifugal force. The apparent force occurring in Convection. The process by which heat is transferred by curvilinear motion acting to deflect objects outward from the movement of a heated fluid (gas or liquid).

axis of rotation. For instance, when pulling out of a dive, it is the force pushing the pilot down in their seat. Corrosion. The deterioration of metal by chemical or electrochemical attack.

Centripetal force. The force in curvilinear motion acting toward the axis of rotation. For instance, when pulling out Cosine (cos). A trigonometric function comparing two sides of a dive, it is the force that the seat exerts on the pilot to of a right triangle as follows: offset the centrifugal force.

adjacent side Cos = hypotenuse Charles’ Law. States that all gases expand and contract in direct proportion to the change in the absolute temperature, Coulomb. A measure of electrical output. One coulomb is provided the pressure is held constant. 6.24 × 1018 electrons.

Chemical energy. Energy released from chemical reactions. Countersink. A tool that cuts a cone-shaped depression around a hole in order to allow a rivet or screw to set flush Circular magnetization. The induction of a magnetic field with the surface of the material.

consisting of concentric circles of force about and within a part, which is achieved by passing electric current through Current. The flow of electrical charge.

the part.

D Circumference (of a circle). The linear measurement of the Dalton’s Law. States that a mixture of several gases which distance around a circle. The circumference is calculated by do not react chemically exerts a pressure equal to the sum of multiplying the diameter of the circle by 3.1416.

the pressures which the several gases would exert separately if each were allowed to occupy the entire space alone at the Code of Federal Regulations (CFR). Established by law to given temperature.

provide for the safe and orderly conduct of flight operations and to prescribe airmen privileges and limitations.

Datum. An imaginary vertical plane or line from which all measurements of arm are taken. The datum is established Compression ratio. The ratio of the volume of a cylinder by the manufacturer. Once the datum has been selected, all with the piston at the bottom of its stroke to the volume of moment arms and the location of CG range are measured the cylinder with the piston at the top of its stroke.

from this point.

Computer aided design (CAD). Using a computer in the Debonding. Separation of the bond between the skin design of a product.

laminates and the core of a composite structure.

Computer aided design drafting (CADD). Using a Decibels. The unit for measuring sound intensity. One computer in the design and drafting process.

decibel is the smallest change in sound intensity the human ear can detect.

Computer aided engineering (CAE). Using a computer in the engineering of a product.

Decimal system. The number system, also called the base-ten system, based on the number 10. Consisting of ten symbols, Computer aided manufacturing (CAM). Using a computer or digits (0, 1, 2, 3, 4, 5, 6, 7, 8, 9), the main principle is that in the manufacturing of a product.

10 is considered as a new unit from which point counting starts again.

Computer graphics. Drawing with the use of a computer.

Degradation. The alteration of material properties (e.g., Conduction. The transfer of heat which requires physical strength, modulus, coefficient of expansion) which may result contact between an object that has a large amount of heat from deviations in manufacturing or from repeated loading energy and one that has a smaller amount of heat energy.

and/or environmental exposure.

Conductor. A material that will carry electric current.

Delamination. Separation of the bond between the individual plies of a laminated composite structure.

G-3 Dividend. In a division problem, the number to be divided Denominator. The lower part of a fraction (represented by by the divisor. In 6 ÷ 2 = 3, the dividend is 6.

N the letter D in ⁄ D ), the quantity by which the numerator is divided. Division. The process of finding how many times one number (the divisor) is contained in another number (the dividend).

Density. The weight of a substance per unit volume.

Divisor. In a division problem, the number by which dividend Detail drawing. A description of a single part, given in is to be divided. In 6 ÷ 2 = 3, the divisor is 2.

such a manner as to describe bylines, notes, and symbols the specifications for size, shape, material, and methods of Doping. The process by which small amounts of additives manufacture to be used in making the part. called impurities are added to the semiconductor material to increase their current flow by adding a few electrons or Detailed inspection. A thorough examination of an item a few holes.

including disassembly. The overhaul of a component is considered to be a detailed inspection. Dynamic stability. The property of an aircraft that causes it, when disturbed from straight-and level flight, to develop Detonation. Uncontrolled burning of fuel in the cylinder of forces or moments that restore the original condition of a reciprocating engine. Detonation causes explosive burning straight and level.

of the fuel which creates an increased cylinder pressure, excessive cylinder head temperature, and decreased engine E performance.

Eddy current inspection. An inspection method where eddy currents are induced into the material to be tested. In aircraft Dew point. The temperature to which humid air must be manufacturing plants, eddy current is used to inspect castings, cooled at constant pressure to become saturated.

stampings, machine parts, forgings, and extrusions.

Dial indicator. Measures variations in a surface by using an Electrical energy. Electrical energy is converted to heat accurately machined probe mechanically linked to a circular energy when an electric current flows through any form hand whose movement indicates thousandths of an inch, or of resistance such as an electric iron, electric light, or an is displayed on a liquid crystal display (LCD) screen.

electric blanket.

Diameter (circle). The length of a line passing directly Electromotive force (EMF). The pressure or force that through the center of a circle. Twice the radius of the circle.

causes electrons to flow in an electrical circuit.

Die. Used for cutting external threads on round stock.

Electrostatic field. A field of force that exists around a charged body.

Difference. The answer to a subtraction problem.

Empennage. The section of the airplane that consists of the Direct current (DC). Electricity that flows in one direction vertical stabilizer, the horizontal stabilizer, and the associated at all times.

control surfaces.

Directional stability. Stability about the vertical axis of an Empty-weight center of gravity range. The distance aircraft, whereby an aircraft tends to return, on its own, to between the allowable forward and aft empty-weight CG flight aligned with the relative wind when disturbed from limits.

the equilibrium state.

Empty-weight center of gravity. The center of gravity of Discontinuity. An interruption in the normal physical an aircraft when it contains only the items specified in the structure or configuration of a part, such as a crack, forging aircraft empty weight.

lap, seam, inclusion, porosity, and the like. A discontinuity may or may not affect the usefulness of a part.

Empty weight. See standard empty weight.

Dissimilar metal corrosion. Caused by contact between Energy. The capacity of a physical system to perform work.

dissimilar metal parts in the presence of a conductor.

There are two types of energy, kinetic and potential.

G-4 Exploded view drawing. A pictorial drawing of two or more H parts that fit together as an assembly. The view shows the Heat. The total kinetic energy of the molecules of any individual parts and their relative position to the other parts substance.

before they are assembled.

Henry. The basic unit of inductance, symbolized with the Exponent (power). A shorthand method of indicating how letter H. An electric circuit has an inductance of one henry many times a number, called the base, is multiplied by itself.

when current changing at the rate of one ampere per second For example, in the number 43, the 3 is the power or exponent induces a voltage of one volt into the circuit.

and 4 is the base. That is, 43 is equal to 4 × 4 × 4 = 64.

Hermaphrodite caliper. Generally used as a marking Extension lines. Used to extend the line showing the side gauge in layout work. It should not be used for precision or edge of a figure for the purpose of placing a dimension measurement.

to that side or edge.

Hidden lines. Indicates invisible edges or contours.

F FAA Form 337. This form must be completed when a major Horsepower. A measure of power equal to 550 foot-pounds repair or alteration is accomplished.

per second or 33,000 foot-pounds per minute and 746 Watts.

Ferrous metals. Metals having iron as their principal Hot start. Occurs when the engine starts, but the exhaust constituent.

gas temperature exceeds specified limits. This is usually caused by an excessively rich air-fuel mixture entering the Force. The intensity of an impetus, or the intensity of an combustion chamber.

input.

Humidity. The amount of water vapor in the air.

Foreign object damage (FOD). Any damage caused by any loose object to aircraft, personnel, or equipment. These Hung start. Occurs when the engine starts normally, but the loose objects can be anything from broken runway concrete rpm. remains at some low value rather than increasing to the to shop towels and safety wire.

normal starting rpm. This is often the result of insufficient power to the starter, or the starter cutting off before the engine N Fraction. A number written in the form ⁄ D in which N is starts self-accelerating.

the numerator and D is the denominator. For example, ⁄ 16 is a fraction.

Hydrometer. An instrument for determining the specific gravity of liquids.

Frequency. The number of cycles (on/off) completed per unit of time. Usually expressed in Hertz.

Hypotenuse. The side of a right triangle that is opposite the right angle. The hypotenuse is the longest side of a right Fretting corrosion. Occurs when two mating surfaces, triangle.

normally at rest with respect to one another, are subject to slight relative motion.

I Improper fraction. A fraction with the numerator equal to Friction. The opposition to movement between objects.

or greater than the denominator.

Fuel grade. The rating system used for aviation gasoline.

Inside calipers. Calipers with outward curved legs for It rates fuel according to its antidetonation characteristics.

measuring inside diameters, such as diameters of holes.

Fuse. A protective device containing a special wire that melts Installation drawing. A drawing that includes all necessary when current exceeds the rated value for a definite period.

information for a part or an assembly in the final installed position in the aircraft.

Fuselage stations (FS). Reference locations, usually given in inches, used to determine forward and aft positions on an Intergranular corrosion. An attack along the grain aircraft. FS − 0 is the datum.

boundaries of an alloy that commonly results from a lack of uniformity in the alloy structure.

G-5 Longitudinal magnetization. The magnetic field is produced Inductance. The ability of a coil or conductor to oppose a in a direction parallel to the long axis of the part. This is change in current flow. accomplished by placing the part in a solenoid excited by electric current.

Inductive reactance. The opposition to the flow of current which inductances put in a circuit. Longitudinal stability. The tendency for an aircraft nose to pitch up or pitch down, rotating around the lateral axis Inductor. A coil of wire that produces inductance in an (wingtip to wingtip).

electrical circuit.

M Insulator. A material that does not conduct electrical current Magnetic particle inspection. A method of detecting very well or not at all. Examples are glass, ceramic, and invisible cracks and other defects in ferromagnetic materials plastic.

such as iron and steel. The inspection process consists of magnetizing the part and then applying ferromagnetic Ion. An atom or group of atoms in which the number of particles to the surface area to be inspected.

electrons is different from the number of protons. It is a positive ion if the number of electrons is less than the number Maintenance. This includes inspection, overhaul, repair, of protons, and a negative ion if the number of electrons is preservation, and the replacement of parts, but excludes greater than the number of protons.

preventive maintenance.

Isometric drawings. A drawing that uses a combination of Major alteration. An alteration not listed in the aircraft, the views of an orthographic projection and tilts the object aircraft engine, or propeller specifications: (1) that might forward so that portions of all three views can be seen in appreciably affect weight, balance, structural strength, one view.

performance, powerplant operation, flight characteristics, or other qualities affecting airworthiness; or (2) that is not J done according to accepted practices or cannot be done by Joule. The amount of work done by a force of one newton elementary operations.

when it acts through a distance of one meter.

Major repairs. A repair that (1) if improperly done, might K appreciably affect weight, balance, structural strength, performance, powerplant operation, flight characteristics, Kinetic energy. Energy due to motion, defined as one half or other qualities affecting airworthiness, or (2) is not mass times velocity squared.

done according to accepted practices, or cannot be done by elementary operations.

Kirchhoff’s Law (voltage). A basic law of electrical currents stating that the algebraic sum of the applied voltage and the Malfunction or Defect Report. A report (FAA Form 8010- voltage drop around any closed circuit is zero.

4) providing the FAA and industry with a very essential service record of mechanical difficulties encountered in L aircraft operations. Such reports contribute to the correction Lateral stability. The stability about the longitudinal axis of of conditions or situations which otherwise will continue an aircraft; the rolling stability, or the ability of an airplane to prove costly and/or adversely affect the airworthiness to return to level flight due to a disturbance that causes one of aircraft.

of the wings to drop.

Manufacturer’s maintenance manual. A manual Lever. The simplest machine. There are three basic parts provided by an aircraft manufacturer that outlines the in all levers: the fulcrum “F,” a force or effort “E,” and a methods, techniques, and practices prescribed for each resistance “R.” person performing maintenance, alteration, or preventive maintenance on an aircraft, engine, propeller, or appliance.

Load cell. A component in an electronic weighing system that is placed between the jack and the jack pad on the aircraft.

Mass. A measure of the quantity of matter in an object.

The load cell contains strain gauges whose resistance changes with the weight on the cell.

Matter. Any substance that has mass and takes up space.

G-6 Maximum landing weight. The heaviest weight an aircraft dependable tube connection. The fitting consists of three can have when it lands. For large wide body commercial parts: a body, a sleeve, and a nut.

airplanes, it can be 100,000 pounds less than maximum takeoff weight, or even more. Multiplication. The process of repeated addition.

Maximum ramp weight. The heaviest weight to which N an aircraft can be loaded while it is sitting on the ground, Negative number. A number that is less than zero.

sometimes referred to as the maximum taxi weight.

Nomogram. A graph that usually consists of three sets of Maximum takeoff weight. The heaviest weight an aircraft data. Knowledge of any two sets of data enables the reader can have when it starts the takeoff roll. The difference to determine the third set.

between this weight and the maximum ramp weight would equal the weight of the fuel that would be consumed prior Normalizing. The process of heating the part to the proper to takeoff.

temperature, holding it at that temperature until it is uniformly heated, and then cooling it in still air.

Maximum weight. The maximum authorized weight of the aircraft and its contents, and is indicated in the Aircraft Nuclear energy. Energy stored in the nucleus of atoms is Specifications or Type Certificate Data Sheet.

released during the process of nuclear fission in a nuclear reactor or atomic explosion.

Maximum zero fuel weight. The heaviest weight an aircraft can be loaded to without having any usable fuel in the fuel Numerator. The upper part of a fraction (represented by tanks. Any weight loaded above this value must be in the N the letter N in ⁄ D ).

form of fuel.

O Mean aerodynamic chord (MAC). The average distance Oblique view. A view that is similar to an isometric view from the leading edge to the trailing edge of the wing.

except with two of the three drawing axes always at right angles to each other.

Mechanical advantage. A ratio of the resistance force to the effort force.

Ohm’s Law. Explains the relationship between voltage, current, and resistance in an electrical circuit, and states that Mechanical energy. This includes all methods of producing current flow in an electrical circuit is directly proportional to increased motion of molecules such as friction, impact of the amount of voltage applied to the circuit.

bodies, or compression of gases.

Ohmmeter. A current measuring instrument that provides METO horsepower. The maximum power allowed to its own source (self-excited) of power.

be continuously produced by an engine. Takeoff power is usually limited to a given amount of time, such as 1 minute Ohm. The standard unit used to measure resistance.

or 5 minutes.

One-hundred-hour inspection. A complete inspection Mixed number. A combination of a whole number and a that is required for all aircraft operated for hire every 100 fraction. For example, 5 ⁄ 8 is a mixed number.

hours. An annual inspection must be conducted by an A&P mechanic with Inspection Authorization.

Molecule. The smallest particle of an element or compound that retains the chemical properties of the element or Operating center of gravity range. The center of gravity compound.

for an aircraft loaded and ready for flight.

Moment. In determining weight and balance, the moment is Orthographic projection. A method of showing all six the product of a weight multiplied by its arm.

possible views of an object: front, top, bottom, rear, right side, and left side.

MS flareless fittings. Designed primarily for highpressure (3,000 psi) hydraulic systems that may be subjected to severe Outside calipers. Used for measuring outside dimensions, vibration or fluctuating pressure. Using this type of fitting such as the diameter of a piece of round stock.

eliminates all tube flaring, yet provides a safe and strong, G-7 P Plumb bob. A heavy metal object, cylinder- or coneshaped, Parallel circuit. A circuit in which two or more electrical with a sharp point at one end that is suspended by a string resistances or loads are connected across the same voltage to produce a vertical reference line useful in aircraft source.

measurements.

Pascal’s Law. The law that states that pressure applied Positive number. A number that is greater than zero.

anywhere to a body of fluid causes a force to be transmitted equally in all directions; the force acts at right angles to any Potential difference. A difference in electrical pressure.

surface in contact with the fluid.

Potential energy. Energy that is stored.

Percentage. Used to express a number as a fraction of 100.

Using the percentage sign, %, 90 percent is expressed as 90%.

Potentiometer. A variable tapped resistor that can be used as a voltage divider.

Permeability. Used to refer to the ease with which a magnetic flux can be established in a given magnetic circuit.

Power (exponent). A shorthand method of indicating how many times a number, called the base, is multiplied by itself.

Perspective view. A drawing that shows a three-dimensional For example, in the number 43, 3 is the power, or exponent, object (portraying height, width, and depth) as it appears to an and 4 is the base. That is, 43 is equal to 4 × 4 × 4 = 64.

observer. It most closely resembles the way an object would look in a photograph.

Power. Power is the time rate at which work is done or energy is transferred.

Phantom line. Composed of one long and two short evenly spaced dashes, indicates an alternate position of parts of the Powers of ten. Also called scientific notation. It is a shorthand object or the relative position of a missing part.

method of depicting very large or very small numbers.

Pictorial drawing. A drawing that is similar to a photograph.

Pressure. The amount of force acting on a specific amount It shows an object as it appears to the eye, but it is not of surface area, typically measured in pounds per square satisfactory for showing complex forms and shapes.

inch or psi.

Pitch (aircraft maneuver). Rotation of an aircraft about Preventive maintenance. Simple or minor preservation its lateral axis.

operations and the replacement of small standard parts not involving complex assembly operations.

Pitch (rivet layout dimension). The distance between the centers of adjacent rivets installed in the same row.

Product. The result of multiplication.

Pitch (thread dimension). The linear distance, measured Progressive inspection. Breaking down the large task of parallel to the length of a threaded fastener, between conducting a major inspection into smaller tasks which can corresponding points on two adjacent threads.

be accomplished periodically without taking the aircraft out of service for an extended period of time.

Pitch angle (helicopter rotor blade). The angle between the chord line of a rotor blade and the reference plane of the Proportion. A proportion is a statement of equality between main rotor hub, or the plane of rotation of the rotor.

two or more ratios. The example of A is to B as C is to D can be represented A:B = C:D or A/B = C/D.

Pitch angle (propeller specification). The angle between the chord line of a propeller blade and the plane of rotation.

Pythagorean Theorem. An equation used to find the length of a third side of any right triangle when the lengths of two sides Pitch axis (aircraft axis). The lateral axis of an aircraft that 2 2 2 are known. The Pythagorean Theorem states that a + b = c .

extends from wing tip to wing tip and passes through the The square of the hypotenuse (side opposite the right angle) is center of gravity. This is the axis about which the aircraft equal to the sum of the squares of the other two sides (a and b).

pitches.

Q Pitch distribution (propeller specification). The gradual Quenching. The rapid cooling of metal in the heat-treatment twist in the propeller blade from shank to tip.

G-8 process. Rheostat. A variable resistor used to vary the amount of current flowing in a circuit.

Quotient. The result of dividing two numbers.

Root. A number that when multiplied by itself a specified Radiant energy. Electromagnetic waves of certain number of times will produce a given number. The two most frequencies produce heat when they are absorbed by the commonly used roots are the square root and the cube root.

bodies they strike such as x-rays, light rays, and infrared rays.

Routine inspection. A visual examination or check of an R item in which no disassembly is required.

Radiation. The continuous emission of energy from the S surface of all bodies.

Schematic diagram. A diagram that locates components Radical sign. The symbol √, used to indicate the root of a with respect to each other within a system.

number.

Scientific notation. Used as a type of shorthand to express Radiographic inspection. Inspection using radiography to very large or very small numbers. For example, to express locate defects or flaws in airframe structures or engines with 1,250,000,000,000 in scientific notation is 1.25 × 1012.

little or no disassembly.

Sea level pressure. The atmospheric pressure at sea level.

Radius (circle). Equal to one-half the diameter of a circle. Average sea level pressure is 29.92 inches of mercury, or 1013.25 millibars.

Ratio. The comparison of two numbers or quantities.

Sectional view. A view obtained by cutting away part of an Reamers. Tools made of either carbon tool steel or high- object to show the shape and construction at the cutting plane.

speed steel that are used to smooth and enlarge holes to exact size. Semiconductor. Any device based on either preferred conduction through a solid in one direction, as in rectifiers, Rectifier. A device for converting alternating current to or on a variation in conduction characteristics through a direct current. partially conductive material, as in a transistor.

Relative humidity. The ratio of the amount of water vapor Series circuit. The most basic electrical circuit in which actually present in the atmosphere to the amount that there is only one possible path for current to flow. Current would be present if the air were saturated at the prevailing must pass through the circuit components, the battery and temperature and pressure. the resistor, one after the other, or “in series.” Remainder. The leftover number in the process of division. Series-parallel DC circuits. A grouping of parallel resistors connected in series with other resistors.

Repair. The restoration of an aircraft component to its previous state. Signed numbers. A signed number can be either a positive or negative number. A positive number is a number that is Repair station. A maintenance facility certificated under 14 greater than zero. A negative number is a number that is CFR part 145 to perform maintenance functions. less than zero.

Resistance. The opposition a device or material offers to Sine. A trigonometric function comparing two sides of a the flow or current. right triangle as follows: opposite side Sine = Resonance. The increase in amplitude of vibrations of hypotenuse an electric or mechanical system exposed to a periodic force whose frequency is equal or very close to the natural Sine wave. A continuous waveform with a constant frequency of the system. frequency and amplitude.

Retentivity. The ability of a material to hold its magnetism Sketch. A simple rough drawing that is made rapidly and after the magnetizing field has been removed. without much detail.

G-9 Slide caliper. Often used to measure the length of an object. Stress. The internal resistance of an object to external It provides greater accuracy than a ruler. forces attempting to strain or deform that object. Measured in pounds per square foot or pounds per square inch (psi).

Solenoid. A loop of wire, often wrapped around a metal core, which produces a magnetic field when an electrical current Subtraction. The process where the value of one number is is passed through it. taken from the value of another.

Specific gravity. The ratio of the mass of a solid or liquid Sum. The resulting answer in the addition process.

to the mass of an equal volume of water.

Supplemental Type Certificates (STC). A document Specific heat. The quantity of heat necessary to increase the issued by the FAA approving a product (aircraft, engine, or temperature of a unit of the mass of a substance 1 °C. The propeller) modification.

specific heat of a substance is the ratio of its specific heat capacity to the specific heat capacity of water. Surface corrosion. Caused by either direct chemical or electrochemical attack, it appears as a general roughening, Speed of sound. The speed of sound at sea level under etching, or pitting of the surface of a metal, frequently standard temperature and pressure conditions is 1,108 feet accompanied by a powdery deposit of corrosion products.

per second or 658 knots.

Swaged Fittings. These fittings create a permanent Spirit level. A leveling instrument placed on or against a connection that is virtually maintenance free. Swaged specified place on the aircraft. Spirit levels have vials that fittings are used to join hydraulic lines in areas where routine are full of liquid, except for a small air bubble. When the disconnections are not required and are often used with air bubble is centered between the two black lines, a level titanium and corrosion resistant steel tubing.

condition is indicated.

T Square root. A non-negative number that must be multiplied Tangent (tan). A trigonometric function comparing two by itself to equal a given number.

sides of a right triangle as follows: opposite side Standard empty weight. The weight of the airframe, Tan = adjacent side engines, all permanently installed equipment, and unusable fuel. Depending upon the part of the Federal regulations under Tap. Instrument used to cut threads on the inside of a hole.

which the aircraft was certificated, either the undrainable oil or full reservoir of oil is included.

Tare weight. The weight of any chocks or devices used to hold an aircraft on scales when it is weighed. The tare Standard weights. Values used in weight and balance weight must be subtracted from the scale reading to get the calculations if specific weight for an item is unknown. The net weight of the aircraft.

following are examples: Tempering. Process that reduces the brittleness imparted by • Aviation gasoline 6 pounds per gallon hardening and produces definite physical properties within • Crew and passengers 170 pounds per person the steel. Tempering always follows, never precedes, the • Lubricating oil 7.5 pounds per gallon hardening operation.

• Turbine fuel 6.7 pounds per gallon Thermal expansion. The increase in size of a material as • Water 8.35 pounds per gallon temperature increases.

Static stability. The initial response that an airplane displays Tolerance. The sum of the plus and minus allowance figures.

after its equilibrium is disrupted.

Torque. The tendency of a force to cause or change rotational Strain. A deformity or change in an object due to stress.

motion of a body.

Stress corrosion. Occurs as the result of the combined effect Transformer. A device that changes electrical energy of a of sustained tensile stresses and a corrosive environment.

given voltage into electrical energy at a different voltage level.

G-10 It consists of two coils that are not electrically connected, Volume. The amount of space within a three-dimensional but arranged so that the magnetic field surrounding one coil solid.

cuts through the other coil.

W Transistor. A three-terminal device primarily used to Waterline (WL). A horizontal reference plane used to locate amplify signals and control current within a circuit.

vertical positions on an aircraft. Positions are usually given in inches above or below the waterline.

Trapezoid. A four-sided figure with one pair of parallel sides.

Watt. A unit of power equal to one joule per second.

True power. The power dissipated in the resistance of a circuit, or the power actually used in the circuit.

Weighing points. Locations on an aircraft that the manufacturer designates for the placement of scales when Triangle. A three-sided figure in which the sum of the three weighing aircraft.

angles equal 180°.

Weight. A measure of the pull of gravity acting on the mass Trigonometry. The study of the relationships between the of an object.

angles and sides of a triangle.

Whole numbers. The numbers: 0, 1, 2, 3, 4, 5, and so on.

Type Certificate Data Sheet (TCDS). The FAA issues a type certificate when a new aircraft, engine, propeller, etc., Wiring diagrams. A diagram that shows the electrical wiring is found to meet safety standards set forth by the FAA. The and circuitry, coded for identification, of all the electrical TCDS lists the specifications, conditions and limitations appliances and devices used on aircraft.

under which airworthiness requirements were met for the specified product, such as engine make and model, fuel type, Work. The amount of energy transferred by a force.

engine limits, airspeed limits, maximum weight, minimum crew, etc.

Z Zero fuel weight. The weight of an aircraft without fuel.

U Ultrasonic inspection. Uses high frequency sound energy to Zone numbers. On drawings, these are similar to the conduct examinations and make measurements. Ultrasonic numbers and letters printed on the borders of a map, used inspection can be used for flaw detection/evaluation, for locating a particular point in the drawing.

dimensional measurements, and material characterization.

Useful load. Fuel, any other fluids that are not part of empty weight, passengers, baggage, pilot, copilot, and crewmembers. It is determined by subtracting the empty weight from the maximum allowable gross weight.

V Vapor pressure. The portion of atmospheric pressure that is exerted by the moisture in the air (expressed in tenths of an inch of mercury).

Volt. The basic unit of electrical potential or electromotive force. A potential of one volt appears across a resistance of one ohm when a current of one ampere flows through that resistance.

Voltmeter. A current-measuring instrument, designed to indicate voltage by measuring the current flow through a resistance of known value.

G-11

Index

Allowances and Tolerances ........................................... 4-9 Symbols Alloying ......................................................................... 7-7 100-Hour Inspections ................................................... 10-5 Alodizing ...................................................................... 8-22 Alternating Current (AC) ........................................... 12-43 A Alternators ................................................... 12-154 , 12-171 Abrasive Papers ........................................................... 8-28 Alternator Transistorized Regulators ....................... 12-172 Acceleration ................................................................. 5-15 Altimeter .................................................................... 10-12 AC Circuits ................................................................ 12-59 Aluminum ...................................................................... 7-5 AC Motors ............................................................... 12-147 Aluminum Alloy Rivets ............................................... 7-24 Direction of Rotation of Induction ....................... 12-150 Aluminum Alloys ........................................ 7-5 , 7-20 , 7-23 Induction Motor Slip ............................................ 12-149 Aluminum Alloy Tubing ................................................ 9-1 Rotating Magnetic Field ....................................... 12-148 American Iron and Steel Institute (AISI) ....................... 7-2 Shaded Pole Induction .......................................... 12-149 American National Fine (NF) ...................................... 7-37 Single-Phase Induction ......................................... 12-149 American National Standards Institute (ANSI) ............. 4-7 Split-Phase ............................................................ 12-150 Amplifier Circuits .................................................... 12-113 Synchronous ......................................................... 12-151 Classification ........................................................ 12-113 Three-Phase Induction .......................................... 12-148 Class A .............................................................. 12-114 Acoustic Emission ..................................................... 10-28 Class AB ........................................................... 12-114 AC Series ................................................................. 12-152 Class B .............................................................. 12-114 Acting force ................................................................. 5-17 Class C .............................................................. 12-114 Advancing Blade .......................................................... 5-56 AN Flared Fittings ......................................................... 9-8 Adverse-Loaded CG Checks ........................................ 6-20 Angle of Attack ............................................................ 5-38 Advisory Circulars (ACs) ............................................ 2-10 Annealing ..................................................................... 7-23 Aerodynamic Heating .................................................. 5-49 Anodizing ..................................................................... 8-22 Aeronautical Information Manual (AIM) .................... 1-20 Anti-Torque Systems ................................................... 5-50 After Solution ............................................................... 7-22 Apparent Power ......................................................... 12-64 Aircraft Certification Service (AIR) .............................. 2-2 Approved Airplane Inspection Program (AAIP) ......... 2-12 Aircraft Drawings .......................................................... 4-1 Arc Fault Circuit Breaker ........................................... 12-29 Aircraft Listings ........................................................... 2-27 Arm ................................................................................ 6-2 Aircraft Logs ................................................................ 10-1 Armatur .................................................................... 12-155 Aircraft Maintenance Manual (AMM) ..... 2-33 , 2-44 , 4-11 Armature ..................................................... 12-130 , 12-131 Aircraft Maintenance Technicians (AMTs) ................... 1-1 Drum-Type ....................................................... 12-130 Aircraft on ground (AOG) ......................................... 14-19 Gramme-Ring ................................................... 12-130 Aircraft Registration .................................................... 2-37 Atom ............................................................................ 12-1 Aircraft Theory of Flight ............................................. 5-36 Attraction ....................................................................... 5-1 Aircraft Weighing .......................................................... 6-1 Autorotation ................................................................. 5-56 Airfoils ......................................................................... 5-38 Auxiliary Power Units (APUs) ............................. 1-4 , 1-16 Airplane Flight Manual (AFM) ............................ 2-33 , 6-7 Aviation gasoline (AVGAS) ........................................ 1-25 Air traffic control (ATC) ............................................. 2-22 Aviation Gasoline (AVGAS) ....................................... 1-25 Air Transport Association (ATA) ................................ 10-4 Aviation Safety Inspector (ASI) .................................... 2-4 Air Transport Association (ATA) 100 ......................... 2-30 Axes of an Aircraft ....................................................... 5-40 Airworthiness Directives (AD) .................................... 2-26 B Airworthiness Directives (ADs) .................................. 10-4 Airworthiness Limitations ........................................... 2-33 Baking Soda ................................................................. 8-29 Alclad Aluminum ......................................................... 7-21 Ballast .......................................................................... 6-22 Aliphatic and Aromatic Naphtha ................................. 8-27 Barcol Tester ................................................................ 7-27 Allowances ..................................................................... 4-9 I-1 Basic Inspection ........................................................... 10-1 CG Envelopes .............................................................. 6-24 Preparation ................................................................ 10-1 CG Range ..................................................................... 6-15 Techniques/Practices ................................................ 10-1 Charles’ Law ................................................................ 5-25 Batteries ..................................................................... 12-87 Checklists ..................................................................... 10-2 Lead-Acid ............................................................... 12-91 Chemical Cleaners ....................................................... 8-29 Primary Cell ........................................................... 12-87 Chemical Energy .......................................................... 5-18 Secondary Cell ....................................................... 12-87 Chisels .......................................................................... 11-9 Bearing Load Fasteners ................................................ 7-60 Chord Line ................................................................... 5-38 Bending ........................................................................ 9-21 Circuit Breaker ........................................................... 12-29 Bernoulli’s Principle .......................................... 5-29 , 5-37 Circuit Protection Devices ......................................... 12-27 Bilateral Aviation Safety Agreement (BASA) ............ 2-18 Circular Conductors ................................................... 12-20 Bilge Areas ................................................................... 8-12 Circular Motion ............................................................ 5-17 Bill of Material ............................................................... 4-7 Civil Air Regulations (CAR) ....................................... 2-23 Binary Number System ................................................ 3-27 Civil Aviation Authority (CAA) ....................... 2-23 , 14-28 Blade Flapping ............................................................. 5-55 Cleaning .............................................................. 8-23 , 8-24 Bolts ................................................................... 7-37 , 7-47 Exterior ..................................................................... 8-23 Close Tolerance .................................................... 7-38 Interior ...................................................................... 8-24 General Purpose .................................................... 7-37 Container Controls ................................................ 8-25 Identification and Coding ..................................... 7-38 Fire Prevention Precautions .................................. 8-25 Internal Wrenching ............................................... 7-38 Fire Protection Recommendations ........................ 8-26 Special-Purpose .................................................... 7-39 Flammable and Combustible Agents .................... 8-25 Bonded ....................................................................... 10-26 Nonflammable Aircraft Cabin Cleaning Agents and Solvents ................................................................. 8-25 Borescope ................................................................... 10-18 Types of Cleaning Operations .............................. 8-24 Boundary Layer Airflow .............................................. 5-39 Code of Federal Regulations (CFRs) ........................... 10-4 Boyle’s Law ....................................................... 5-22 , 5-24 Commutators ............................................................ 12-130 Brinell Tester ............................................................... 7-26 Compensating Windings .......................................... 12-131 British Thermal Unit (BTU) .......................................... 5-3 Component Maintenance Manual (CMM) ................... 2-33 Brushless Alternator ................................................. 12-157 Composite Materials .................................................... 7-30 Buna-N ......................................................................... 9-16 Compressibility Effects ................................................ 5-46 Buoyancy ..................................................................... 5-26 Computer Graphics ........................................................ 4-1 Butyl ............................................................................. 9-16 Computer Aided Design (CAD) ................................. 4-1 C Computer Aided Design Drafting (CADD) ............... 4-1 Computer Aided Engineering (CAE) ......................... 4-1 Calipers ...................................................................... 11-19 Computer Aided Manufacturing (CAM) .................... 4-1 Camber ......................................................................... 5-38 Computing Area of Two-Dimensional Solids ............. 3-18 Capacitance ................................................................ 12-50 Computing Surface Area of Three-Dimensional Solids 3-23 Alternating Current ................................................. 12-54 Computing Volume of Three-Dimensional Solids ...... 3-20 Capacitive Reactance Xc ........................................ 12-54 Conduction ................................................................... 5-19 Direct Current ......................................................... 12-50 Conductors ..................................................... 12-18 , 12-23 Parallel .................................................................... 12-54 Contamination Control ................................................. 1-25 Reactances in Series and in Parallel ....................... 12-55 Convection ................................................................... 5-20 Series ...................................................................... 12-53 Conventional Flow ..................................................... 12-14 Capacitor .................................................................... 12-50 Cooling Air Vents ........................................................ 8-13 Capacitor Start Motor .............................................. 12-150 Copper .................................................................. 7-10 , 9-1 Capstan servo ................................................................. 4-2 Copper Alloys .............................................................. 7-10 Carbon dioxide (CO ) extinguishers .............................. 1-5 Corrosion ........................................................................ 8-1 Casting ......................................................................... 7-28 Forms .......................................................................... 8-5 Center of gravity (CG) .................................. 2-5 , 5-40 , 6-3 Concentration Cell .................................................. 8-6 Centigrade scale ........................................................... 5-21 Active-Passive ..................................................... 8-7 Centripetal force ........................................................... 5-17 Metal Ion Concentration ...................................... 8-7 Cessna 172 ................................................................... 5-11 I-2 Oxygen Concentration ......................................... 8-7 Designated Airworthiness Representatives (DAR) ..... 2-14 Dissimilar Metal ..................................................... 8-6 Designated Engineering Representatives (DER) ......... 2-13 Exfoliation .............................................................. 8-7 Designated Manufacturing Inspection Representatives (DMIR) ........................................................................ 2-14 Fatigue .................................................................... 8-9 Dies ............................................................................ 11-14 Filiform ................................................................... 8-5 Differential Relay Switch ........................................ 12-162 Fretting .................................................................... 8-9 Digital Images .............................................................. 4-23 Galvanic ................................................................ 8-10 Digital Multimeter ..................................................... 12-78 Intergranular ........................................................... 8-7 Dihedral ........................................................................ 5-42 Pitting ...................................................................... 8-6 Doping ........................................................................ 12-96 Stress-Corrosion/Cracking ...................................... 8-7 Doppler Effect .............................................................. 5-32 Surface .................................................................... 8-5 Double Flaring ............................................................... 9-5 Types .......................................................................... 8-2 Beading ....................................................................... 9-7 Direct Chemical Attack .......................................... 8-2 Double Flaring Instructions ........................................ 9-5 Electrochemical Attack ........................................... 8-3 Fittings ........................................................................ 9-5 Corrosion Control ................................................. 8-1 , 8-21 Flareless Fittings ........................................................ 9-5 Corrosion Limits .......................................................... 8-20 Drain Cocks ................................................................. 7-77 Corrosion Prone Areas ................................................. 8-11 Drills .......................................................................... 11-12 Corrosion Removal ...................................................... 8-14 Dual In-Line Parallel (DIP) Switches ........................ 12-33 Counter Electromotive Force (emf) ......................... 12-142 Countersink ................................................................ 11-14 E Couplants ................................................................... 10-26 Coupling ................................................................... 12-115 Eddy Current .............................................................. 10-20 Direct .................................................................... 12-115 Electrical Conductivity .............................................. 10-37 Impedance ............................................................ 12-116 Electrical Energy .......................................................... 5-18 RC ......................................................................... 12-115 Electrical Safety ............................................................. 1-1 Transformer .......................................................... 12-116 Fire Safety .................................................................. 1-1 Cube Roots ................................................................... 3-13 Physiological Safety ................................................... 1-1 Current ....................................................................... 12-16 Electrochemical Test ...................................................... 7-4 Current Dividers ......................................................... 12-41 Electrodynamometer Meter Movement ..................... 12-74 Current Limiter .......................................................... 12-29 Electrolytic ................................................................. 12-52 Current Transformers ................................................. 12-67 Electromagnetism ...................................................... 12-12 Electromotive Force (Voltage) .................................. 12-14 D Electron ........................................................................ 12-2 Conductors ............................................................ 12-3 Dalton’s Law ................................................................ 5-25 Conductors, Insulators, and Semiconductors ........ 12-2 Datum ................................................................... 6-2 , 6-17 Insulators ............................................................... 12-3 DC Generator .............................................. 12-123 , 12-135 Semiconductors ..................................................... 12-4 Compound Wound ............................................... 12-134 Electron Flow ............................................................. 12-14 Series Wound ....................................................... 12-132 Electronic Numerical Integrator and Calculator .......... 3-27 Shunt Wound ........................................................ 12-133 Electronic Weighing .................................................... 6-28 DC Motor ...................................... 12-137 , 12-138 , 12-140 Electron Shells ............................................................. 12-2 Armature ............................................................... 12-140 Electrons, Protons, and Neutrons ................................. 12-1 Brush .................................................................... 12-141 Electrostatic Field ........................................................ 12-5 End Frame ............................................................ 12-141 Element ........................................................................ 12-1 Field ...................................................................... 12-141 Elements of Human Factors ......................................... 14-2 DC Voltage .............................................................. 12-125 Anthropometry ......................................................... 14-4 decibel (dB) .................................................................. 5-32 Clinical Psychology .................................................. 14-3 Defueling ...................................................................... 1-28 Cognitive Science ..................................................... 14-4 Delta Connection (Three Phase) .............................. 12-156 Computer Science ..................................................... 14-4 Density ........................................................................... 5-2 Educational Psychology ........................................... 14-5 Department of Defense (DoD) ..................................... 2-41 Experimental Psychology ......................................... 14-3 Department of Transportation ........................................ 2-1 I-3 Industrial Engineering .............................................. 14-5 Mill ......................................................................... 11-10 Medical Science ....................................................... 14-4 Round or Rattail ..................................................... 11-10 Organizational Psychology ....................................... 14-4 Square ..................................................................... 11-10 Safety Engineering ................................................... 14-4 Triangular and Three Square .................................. 11-10 Empty Weight ................................................................ 6-4 Vixen (Curved-Tooth Files) ................................... 11-11 Empty Weight Center of Gravity (EWCG) ........... 6-2 , 6-4 Warding .................................................................. 11-10 Empty Weight Center of Gravity (EWCG) Range ...... 6-15 Wood ...................................................................... 11-11 Emulsion Cleaners ....................................................... 8-28 Filtering .................................................................... 12-111 Solvent Emulsion ..................................................... 8-28 Fire Extinguishers ................................................... 1-7 , 1-8 Water Emulsion ........................................................ 8-28 Fire Protection ................................................................ 1-5 Energy ................................................................. 5-2 , 12-20 Using Fire Extinguishers ............................................ 1-8 Engine Frontal .............................................................. 8-13 Fire Safety ...................................................................... 1-5 Environmental Protection Agency (EPA) ...................... 1-6 Fittings ........................................................................... 9-1 Ethics ............................................................................ 13-6 Fixed base operator (FBO) ......................................... 14-14 Exosphere ..................................................................... 5-33 Fixed Resistor ............................................................ 12-24 Extinguishers .................................................................. 1-5 Flex .............................................................................. 9-21 Bromochlorodifluoromethane (Halon 1211) .............. 1-6 Flexible Hose ...................................................... 9-16 , 9-18 Bromotrifluoromethane (Halon 1301) ........................ 1-6 Flexible Wing Aircraft ................................................. 5-56 Carbon dioxide (CO ) ................................................. 1-5 Flight Controls ............................................................. 6-14 Chlorobromomethane (Halon 1011) .......................... 1-6 Flight Management System (FMS) .............................. 6-28 Dibromodifluoromethane (Halon 1202) ..................... 1-6 Flight Standards District Office (FSDO) ............ 2-2 , 10-12 Halogenated hydrocarbon ........................................... 1-6 Flight Standards Service (AFS) ..................................... 2-2 Methyl bromide (Halon 1001) .................................... 1-6 Float-type carburetor .................................................... 5-30 Extruding ...................................................................... 7-28 Fluid Lines .................................................. 9-7 , 9-16 , 9-17 Fluid Pressure ............................................................... 5-27 F Fluids ............................................................................ 6-14 Flux Density ............................................................... 10-30 FAA .............................................................................. 2-30 Force .............................................................................. 5-4 FAA Involvement ........................................................ 14-1 Foreign Object Damage (FOD) ............................. 1-4 , 9-1 Fasteners Forging ......................................................................... 7-27 Airloc ........................................................................ 7-66 Form 337, Major Repair and Alteration ...................... 2-38 Camloc ..................................................................... 7-65 Forms ........................................................................... 2-33 Captive ..................................................................... 7-64 Forward Biased Diode ............................................... 12-98 Hi-Tigue ................................................................... 7-61 Forward Flight ............................................................. 5-54 Taper-Lok ................................................................. 7-61 four forces of flight .............................................. 5-4 , 5-36 Turn Lock ................................................................. 7-64 Power .......................................................................... 5-6 Federal Aviation Administration (FAA) ........... 1-20 , 14-30 Torque ........................................................................ 5-6 FAA Safety Team ................................................... 14-31 Work ........................................................................... 5-4 FAA’s Maintenance Fatigue Section ..................... 14-30 Rolling .................................................................... 5-6 Federal Communications Commission (FCC) ............. 2-38 Sliding ..................................................................... 5-5 Ferrous ........................................................................... 7-2 Static ....................................................................... 5-5 Ferrous Metals ............................................................. 7-16 Fractional Powers ......................................................... 3-13 Fiber Reinforce ............................................................ 7-31 Fractions ......................................................................... 3-2 Field Effect Transistors ............................................ 12-107 Free Electrons .............................................................. 12-2 Field Frame .............................................................. 12-128 Freon .............................................................................. 1-6 Field Rotation ........................................................... 12-155 Frequency ................................................................. 12-158 Files .............................................................................. 11-9 Frequency Measurement ............................................ 12-76 Flat .......................................................................... 11-10 Frequency of Sound ..................................................... 5-31 Half-Round ............................................................. 11-10 Fueling Hazards ........................................................... 1-26 Hand ....................................................................... 11-10 Fueling Procedures ....................................................... 1-26 Knife ....................................................................... 11-11 Fuel System .................................................................. 6-13 Lead-Float .............................................................. 11-10 I-4 Fundamentals of Electricity and Electronics ............... 12-1 Hole Repair .................................................................. 7-70 Fuse ............................................................................ 12-28 Push-Pull Tube Linkage ....................................... 7-72 Fuselage stations (FS) .................................................... 4-9 Repair of Damaged Holes with Acres Fastener Sleeves .................................................................. 7-71 G Hole Repair Hardware ................................................. 7-70 Horizontal Deflection ................................................. 12-77 Gaskets ......................................................................... 7-35 Hose Clamps ................................................................ 9-22 Gas Laws ...................................................................... 5-23 Hose Fittings ................................................................ 9-21 Gauge pressure (psig) .................................................. 5-23 Human Error .............................................................. 14-13 Gear .............................................................................. 5-10 Human Factors ............................................ 14-1 , 14-2 , 14-6 General Gas Law .......................................................... 5-25 Human Factors and Ergonomics Society (HFES) ..... 14-31 Generator Brushes .................................................... 12-136 Human Factors on Aviation Maintenance and Inspection Generator Control Units (GCU) ............................... 12-164 (HFAMI) .................................................................... 14-13 Generator Terminals ................................................ 12-135 Hydraulic Ground Power Units ................................... 1-22 Gravity ........................................................................... 5-2 Hydraulic lock .............................................................. 1-12 Ground Air Heating ..................................................... 1-24 Hydraulic Transmission ........................................... 12-165 Ground Movement of Aircraft ..................................... 1-11 Hydrochloric acid vapor ................................................ 1-6 ground power unit (GPU) ............................................ 1-21 Hydrometer .................................................................. 6-12 Ground Support Air Units ............................................ 1-23 Ground Support Equipment (GSE) ............................ 14-12 I H Illustrated Parts Catalogues (IPC) ................................ 4-11 Impact Drivers ............................................................. 11-6 Hacksaws ..................................................................... 11-8 Impenetrability ............................................................... 5-1 Halogenated hydrocarbon extinguishers ........................ 1-6 Inclined Coil Iron Vane Meter ................................... 12-75 Hammers ...................................................................... 11-1 Inclined Plane ............................................................... 5-11 Hand Tool .................................................................... 11-1 Inductance .................................................................. 12-56 Hardening ..................................................................... 7-29 Inductor-Type Rotary Inverter ................................... 12-94 Hardness Testing .......................................................... 7-25 Inspection ..................................................................... 8-11 Hearing Protection ......................................................... 1-4 Inspection authorization (IA) ....................................... 2-16 Heat .............................................................................. 5-18 Inspection Authorization (IA) (by 14 CFR Section) .... 13-5 Heat Transfer ............................................................... 5-19 Section 65.91, Inspection Authorization .................. 13-5 Heat Treatment .................................................... 7-16 , 7-24 Section 65.92, Inspection Authorization: Duration .. 13-5 Annealing ................................................................. 7-19 Section 65.93, Inspection Authorization: Renewal .. 13-5 Case Hardening ........................................................ 7-20 Section 65.95, Inspection Authorization: Privileges and Carburizing ........................................................... 7-20 Limitations ............................................................... 13-6 Nitriding ................................................................ 7-20 Inspection of Composites ........................................... 10-36 Hardening ................................................................. 7-17 Inspection of Welds ................................................... 10-38 Hardening Precautions ............................................. 7-19 Instructions for Continued Airworthiness (ICA) ........... 2-4 Normalizing .............................................................. 7-19 Instrument Flight Rules (IFR) ...................................... 2-22 Heat Treatment of Magnesium Alloys ......................... 7-24 Integrated Circuit ..................................................... 12-122 Heat Treatment of Nonferrous Metals ......................... 7-20 International Ergonomics Association (IEA) ............. 14-31 Heat Treatment of Titanium ......................................... 7-25 International Organization for Standardization (ISO) ... 4-7 Full Annealing .......................................................... 7-25 Interpoles .................................................................. 12-132 Stress Relieving ........................................................ 7-25 Inter-turbine temperature (ITT) ................................... 1-14 Thermal Hardening ................................................... 7-25 Inverters ..................................................................... 12-93 Helicoils ....................................................................... 7-49 Involving Magnesium .................................................. 8-20 Helicopters ................................................................... 1-10 Ionosphere .................................................................... 5-33 Helicopter Structures ................................................... 5-49 Ions ............................................................................... 12-2 Helicopter Weighing .................................................... 6-25 Iron Vane Meter ......................................................... 12-74 Helicopter Weight and Balance ................................... 6-25 ISO 9001 ...................................................................... 2-41 High-Speed Aerodynamics .......................................... 5-46 High-Speed Airfoils ..................................................... 5-48 I-5 Logic Polarity ....................................................... 12-120 J NAND Gate .......................................................... 12-122 Jacking ......................................................................... 6-14 NOR Gate ............................................................. 12-122 JET A ........................................................................... 1-25 OR Gate ................................................................ 12-122 JET A-1 ........................................................................ 1-25 Longitudinal ................................................................. 5-53 JET B ........................................................................... 1-25 Longitudinal Axis ........................................................ 5-43 Job task analysis (JTA) .............................................. 14-10 Loudness ...................................................................... 5-32 K M Kelvin scales ................................................................ 5-21 Mach Number .............................................................. 5-31 Kerosene ...................................................................... 8-27 Magnesium ..................................................................... 7-8 Kinetic Energy ............................................................... 5-3 Magnesium Alloys ......................................................... 7-8 Kinetic theory ............................................................... 5-23 Magnetic Amplifiers ................................................ 12-118 Kirchhoff’s Current Law ............................................ 12-41 Magnetic Particle ....................................................... 10-29 Kirchhoff’s Voltage Law ........................................... 12-36 Magnetism .................................................................... 12-6 K-Monel ....................................................................... 7-11 Magnets ........................................................................ 12-9 Main Rotor Systems ..................................................... 5-49 L Maintenance Error Decision Aid (MEDA) ................ 14-10 Laminated Structures ................................................... 7-31 Maintenance Instruction Manuals (MIM) .................... 4-11 Landing Gear ...................................................... 6-17 , 8-12 Maintenance Manual .................................................... 10-3 Land Planes .................................................................... 1-8 Main Wheels ................................................................ 6-17 Lateral .......................................................................... 5-53 Mallets .......................................................................... 11-1 Lateral Axis .................................................................. 5-42 Manifold pressure gauge .............................................. 5-23 Law of Conservation ...................................................... 5-1 Manufacturers’ Service Bulletin .................................. 10-3 Law of Exponents ........................................................ 3-12 Mass and Weight ............................................................ 5-1 LC Filters ................................................................. 12-112 Material Safety Data Sheet (MSDS) .............................. 1-2 Band-Pass ......................................................... 12-112 Matter ................................................................... 5-1 , 12-1 Band-Stop ......................................................... 12-112 Maximum except takeoff (METO) ................................ 6-5 High-Pass (HPF) ............................................... 12-112 Maximum Weight .......................................................... 6-3 Low-Pass ........................................................... 12-112 Mean Aerodynamic Chord ........................................... 6-28 Leading edge of the MAC (LEMAC) .......................... 6-28 Mean aerodynamic chord (MAC) ................................ 6-28 Least common denominator (LCD) ............................... 3-2 Mechanical Energy ...................................................... 5-18 Leveling ....................................................................... 6-14 Mechanic Certification: Subpart A - General (by 14 CFR Lever .............................................................................. 5-8 Section) ........................................................................ 13-1 First Class Lever ..................................................... 5-8 Refusal to Submit to a Drug or Alcohol Test ........... 13-2 Second Class Lever ................................................. 5-9 Section 65.3, Certification of Foreign Airmen Other Third Class Lever ................................................... 5-9 Than Flight Crewmembers ....................................... 13-1 Lighted Pushbutton Switches ..................................... 12-32 Section 65.11, Application and Issue ....................... 13-1 Light Emitting Diode (LED) .......................................... 7-5 Section 65.12, Offenses Involving Alcohol and Light-Emitting Diode (LED) ................................... 12-103 Drugs ........................................................................ 13-1 Light Sport Aircraft (LSA) ......................... 2-16 , 2-40 , 7-77 Section 65.13, Temporary Certificate ...................... 13-1 Liquid Crystal Displays (LCD) ................................ 12-104 Section 65.14, Security Disqualification .................. 13-1 Liquid Penetrant ......................................................... 10-18 Section 65.15, Duration of Certificates .................... 13-1 Lithium Ion Batteries ................................................. 12-93 Section 65.16, Change of Name: Replacement of Lost or Destroyed Certificate ................................................ 13-2 Loading Graphs ............................................................ 6-24 Section 65.17, Test: General Procedure ................... 13-2 Logic Circuits ........................................................... 12-119 Section 65.18, Written Tests: Cheating or Other .............................................................................. 12-121 Unauthorized Content ............................................... 13-2 AND Gate ............................................................. 12-121 Section 65.19, Retesting After Failure ..................... 13-2 Exclusive NOR Gate ............................................ 12-122 Section 65.20, Applications, Certificates, Logbooks, Exclusive OR Gate ............................................... 12-122 Reports, and Records: Falsification, Reproduction, or Inverter Logic ....................................................... 12-121 Alteration .................................................................. 13-2 I-6

Next: Section 65.71, Eligibility Requirements: General .... 13-3 →

Section 28

Section 65.21, Change of Address ........................... 13-2 Neoprene ...................................................................... 9-16 Mechanic Certification: Subpart D - Mechanics (by 14 Newton’s Law of Motion ............................................. 5-16 CFR Section) ................................................................ 13-3 First ........................................................................... 5-16 Section 65.71, Eligibility Requirements: General .... 13-3 Second ...................................................................... 5-16 Section 65.73, Ratings .............................................. 13-3 Third ............................................................... 5-17 , 5-37 Section 65.75, Knowledge Requirements ................ 13-3 Nickel-Cadmium Batteries ......................................... 12-91 Section 65.77, Experience Requirements ................. 13-3 Nomograms .................................................................. 4-23 Section 65.79, Skill Requirements ........................... 13-3 Nosewheel .................................................................... 6-17 Section 65.80, Certificated Aviation Maintenance Notice of Proposed Rulemaking (NPRM) ................... 2-26 Technician School Students ..................................... 13-4 Nuclear Energy ............................................................ 5-18 Section 65.81, General Privileges and Limitations .. 13-4 Nut Plates ..................................................................... 7-68 Section 65.83, Recent Experience Requirements ..... 13-4 Nuts .................................................................... 7-41 , 7-47 Section 65.85, Airframe Rating: Additional Identification and Coding ..................................... 7-45 Privileges .................................................................. 13-4 Internal and External Wrenching .......................... 7-45 Section 65.87, Powerplant Rating: Additional Non-Self-Locking ................................................. 7-41 Privileges .................................................................. 13-4 Self-Locking ......................................................... 7-42 Section 65.89, Display of Certificate ....................... 13-4 Sheet Spring .......................................................... 7-45 Megger (Megohmmeter) ............................................ 12-72 O Mercury barometer ....................................................... 5-34 Metal-Oxide-Semiconductor FET (MOSFET) ........ 12-108 Occupational Safety and Health Administration (OSHA) ..

Metal Tube Lines ........................................................... 9-2 ...................................................................................... 14-4 Methyl Ethyl Ketone (MEK) ....................................... 8-27 Ohmmeter .................................................................. 12-71 Metric System .............................................................. 3-26 Ohm’s Law ..................................................... 12-17 , 12-59 Microfiche .................................................................... 4-23 Oil Capacitors ............................................................ 12-53 Microfilm ..................................................................... 4-23 Oil Caps ....................................................................... 7-77 Micrometer Calipers .................................................. 11-19 Oil System .................................................................... 6-13 Micro-organisms ............................................................ 8-2 Original equipment manufacturer (OEM) ................... 2-30 Microprocessors ....................................................... 12-123 Orthographic .................................................................. 4-9 Microswitches ............................................................ 12-31 Oscilloscope ............................................................... 12-76 Mild Abrasive Materials .............................................. 8-28 Over-Excitation Protection ...................................... 12-164 Minimum Fuel ............................................................... 6-4 Over “G” .................................................................... 10-14 Molecule ...................................................................... 12-1 Overhaul Manual ......................................................... 10-4 Moment .......................................................................... 6-2 Overvoltage Protection ............................................ 12-164 Mooney M20 ................................................................ 5-11 Oxygen Hazards ........................................................... 1-25 Motion .......................................................................... 5-14 Oxygen Servicing Equipment ...................................... 1-24 MS Flareless Fittings ..................................................... 9-9 P Cryofit ........................................................................ 9-9 Swaged ....................................................................... 9-9 Parallel ....................................................................... 12-62 MS (Military Standard) numbers ................................. 7-37 Parallel Conductors .................................................. 12-138 Multirange Ohmmeter ................................................ 12-72 Parallel DC Circuits ................................................... 12-40 Parallel Generator Operations .................................. 12-164 N Part Manufacture Approval (PMA) ............................... 2-4 NAS (National Aircraft Standard) numbers ................ 7-37 Pascal’s Law ................................................................ 5-27 National Aeronautics and Space Administration (NASA) .

Percentage .................................................................... 3-10 ........................................................................................ 2-1 Permanent Ballast ........................................................ 6-23 National Coarse (NC) .................................................. 7-37 Permanent Magnet Rotary Inverter ............................ 12-94 National Fire Protection Association (NFPA) ............... 1-5 Phantom Lines ............................................................. 4-17 National Transportation Safety Board (NTSB) ........... 13-5 phosgene gas .................................................................. 1-6 Nautical miles (NM) .................................................... 2-11 Phosphoric-citric Acid ................................................. 8-29 NDI Methods ............................................................. 10-17 Photoconductive Cells ............................................... 12-27 Negative Powers .......................................................... 3-12 Physical Parameters ................................................... 12-56 I-7 Pins ............................................................................... 7-75 Rectangular Conductors ............................................. 12-20 Cotter ................................................................. 7-75 Rectifiers .................................................................. 12-100 Flathead ............................................................. 7-75 Diode ....................................................... 12-103 , 12-105 Roll .................................................................... 7-75 Light-Emitting Diode (LED) ............................ 12-103 Tape ................................................................... 7-75 Liquid Crystal Displays (LCD) ........................ 12-104 Plastics ......................................................................... 7-29 Photodiode ........................................................ 12-104 Pliers ............................................................................ 11-3 Power Rectifier Diodes ..................................... 12-103 Plumb Bob ................................................................... 6-11 Schottky Diodes ................................................ 12-105 PN Junctions .............................................................. 12-98 Varactors ........................................................... 12-104 PNP Transistor ......................................................... 12-107 Zener Diodes ..................................................... 12-103 Polyester Film ............................................................ 12-52 Full-Wave Rectifier .............................................. 12-102 Porosity .......................................................................... 5-1 Half-Wave Rectifier ............................................. 12-101 Potential Energy ................................................... 5-2 , 5-19 Rectifier Unit ........................................................... 12-156 Power .................................................................. 5-4 , 12-20 Reheat Treatment ......................................................... 7-22 Power and Energy ...................................................... 12-20 Reinforced Plastic ........................................................ 7-31 Powered Parachute ........................... 1-11 , 5-58 , 6-26 , 6-28 Relative Wind .............................................................. 5-38 Power of Zero .............................................................. 3-12 Relays ......................................................................... 12-33 Power Rectifier Diodes ............................................ 12-103 Resistance .................................................................. 12-18 Powers .......................................................................... 3-11 Resistance of a Conductor ......................................... 12-18 Powers of Ten .............................................................. 3-12 Resistance and Relation to Wire Sizing ................. 12-20 Precipitation Practices .................................................. 7-23 Resistors ......................................................... 12-24 , 12-50 Preflight ........................................................................ 10-5 Variable Resistors ................................................... 12-26 Pressure ........................................................................ 5-22 Potentiometer ...................................................... 12-27 Absolute ................................................................... 5-23 Rheostat .............................................................. 12-26 Differential ............................................................... 5-23 Wire-Wound ........................................................... 12-26 Gauge ........................................................................ 5-23 Resistors in Parallel .................................................... 12-40 Preventive Maintenance ............................................... 8-10 Resonance ......................................................... 5-32 , 12-63 Proportion ...................................................................... 3-8 Retreating Blade ........................................................... 5-56 Pulley ............................................................................. 5-9 Reverse Current Sensing .......................................... 12-164 Block and Tackle .................................................. 5-10 Rigid Fluid Lines ........................................................... 9-1 Single Fixed Pulley ................................................. 5-9 Riveted and Rivetless Nut Plates ................................. 7-68 Single Movable Pulley ............................................ 5-9 Deutsch ................................................................. 7-70 Pulse Structure ......................................................... 12-120 Dill Lok-Skrus and Dill Lok-Rivets ..................... 7-69 Punches ........................................................................ 11-3 Rivets .................................................................. 7-51 , 7-57 Pure Metals .................................................................... 8-1 Blind ..................................................................... 7-56 Push-Pull Tube Linkage ............................................... 7-72 Dzus ...................................................................... 7-64 Pythagorean Theorem .................................................. 3-25 Friction Lock ........................................................ 7-57 Mechanical Lock .................................................. 7-58 Q Bulbed CherryLOCK Rivets ............................. 7-58 Huck Mechanical Locked Rivets ....................... 7-58 Quenching .................................................................... 7-22 Wiredraw CherryLOCK Rivets ......................... 7-58 R Pin ......................................................................... 7-60 Pull-Thru ............................................................... 7-57 Radiant Energy ............................................................. 5-18 Solid Shank ........................................................... 7-52 Radiation ...................................................................... 5-20 Standards and Specifications ................................ 7-51 Radiation Hazards ...................................................... 10-36 Rockwell Tester ........................................................... 7-26 Radiographic .............................................................. 10-34 Rolling-Type Flaring ..................................................... 9-4 Radiographic Interpretation ....................................... 10-35 Roots ............................................................................ 3-12 Radio Station License .................................................. 2-38 Rotary Inverters ......................................................... 12-94 Ratio ............................................................................... 3-7 Rotary Selector Switches ........................................... 12-31 Reamers ...................................................................... 11-13 Rubber .......................................................................... 7-32 Reciprocating Engines ................................................. 1-11 I-8 Ruddervators ................................................................ 5-42 Society for Testing and Materials (ASTM). ................ 2-41 Rules .......................................................................... 11-14 Society of Automotive Engineers (SAE) .............. 2-41 , 7-2 soda-acid ........................................................................ 1-5 S Sodium Dichromate Solution ....................................... 8-23 Solution Heat Treatment .............................................. 7-21 Safety Around Hazardous Materials .............................. 1-2 Solvent Cleaners .......................................................... 8-27 Acid ............................................................................ 1-2 Sound ................................................................. 5-30 , 5-46 ALK ............................................................................ 1-2 Sound Intensity ............................................................ 5-32 CARC ......................................................................... 1-2 Sources of Electricity ................................................. 12-22 RAD ........................................................................... 1-2 Chemical ................................................................. 12-23 Safety Data Sheets (SDSs) ............................................. 1-2 Light ....................................................................... 12-23 Saturable-Core Reactor ............................................ 12-119 Pressure .................................................................. 12-22 Scales ............................................................................. 6-7 Thermal .................................................................. 12-23 Screwdrivers ................................................................ 11-1 Special Airworthiness Information Bulletin (SAIB) ... 2-27 Screws .......................................................................... 7-66 Special Federal Aviation Regulations (SFAR) .............. 2-1 Identification and Coding ..................................... 7-67 Special Flight Permits ................................................ 10-16 Machine ................................................................ 7-67 Special Inspections ..................................................... 10-12 Structural ............................................................... 7-66 Special Wrenches ......................................................... 11-5 Scriber ........................................................................ 11-18 Specific Gravity ............................................................. 5-2 Sealed Lead Acid (SLA) Batteries ............................. 12-92 Specific Heat ................................................................ 5-21 Seals ............................................................................. 7-33 Speed ............................................................................ 5-14 Packings ................................................................... 7-34 Speed of Sound ............................................................ 5-31 O-Ring .................................................................. 7-34 Spirit Level ................................................................... 6-11 V-Ring .................................................................. 7-35 Split-Phase Motor .................................................... 12-150 Sealing Compounds .................................................. 7-35 Spoiler Recesses ........................................................... 8-13 One Part ................................................................ 7-36 Square Roots ................................................................ 3-12 Two Part ................................................................ 7-36 Stability ........................................................................ 5-40 Wipers ...................................................................... 7-35 Directional ............................................................ 5-42 Seaplanes ............................................................. 1-8 , 10-16 Dutch Roll ............................................................. 5-42 Self-Inductance .......................................................... 12-57 Dynamic ................................................................ 5-40 Semiconductors .......................................................... 12-95 Lateral ................................................................... 5-42 Reverse Biased Diode ............................................ 12-99 Longitudinal .......................................................... 5-41 Series .......................................................................... 12-59 Static ..................................................................... 5-40 Series Circuit ................................................... 12-82 , 12-83 Static Electricity ........................................................... 12-4 Series DC Circuits ...................................................... 12-33 Static Inverters ........................................................... 12-94 Series-Parallel Circuits ............................................... 12-86 Steel ................................................................................ 9-1 Series-Parallel DC Circuits ........................................ 12-42 Stitch Lines .................................................................. 4-18 Service Bulletins (SB) .................................................. 2-33 Strap Wrenches ............................................................ 11-6 Servicing Aircraft ......................................................... 1-20 Stratosphere .................................................................. 5-33 Ground Support Equipment ..................................... 1-21 Stress ............................................................................ 5-12 Electric Ground Power Units ................................ 1-21 Bending .................................................................... 5-13 Shock Absorber Cord ................................................... 7-33 Compression ............................................................. 5-13 Shock Waves ................................................................ 5-47 Shear ......................................................................... 5-13 Expansion .......................................................... 5-48 Strain ........................................................................ 5-14 Normal Shock .................................................... 5-47 Tension ..................................................................... 5-12 Oblique Shock ................................................... 5-48 Torsion ..................................................................... 5-13 Shop Safety .................................................................... 1-1 Structural Repair Manual .......................... 2-33 , 4-11 , 10-4 Sine Wave .................................................................. 12-77 Subsonic ....................................................................... 5-47 Single-Phase Alternator ........................................... 12-155 Subsonic Flow .............................................................. 5-37 Ski Planes ....................................................................... 1-9 Sun ............................................................................... 5-18 Slack ............................................................................. 9-21 Supersonic .................................................................... 5-47 Slide Calipers ............................................................. 11-25 I-9 Supplemental Lift-Modifying Devices ........................ 5-45 Thermistors ................................................................ 12-27 Flaps .................................................................. 5-45 Thermography ............................................................ 10-37 Slats ................................................................... 5-46 Three-Phase Alternator ............................................ 12-156 Slots ................................................................... 5-45 Three-Phase Induction Motor .................................. 12-148 Supplemental Type Certificates (STC) ................. 2-4 , 2-27 Three Unit Regulators .............................................. 12-161 Suspected Unapproved Parts (SUP) ............................. 2-24 Tie-Down Procedures .................................................... 1-8 Switches ..................................................................... 12-30 Time Constant ............................................................ 12-50 Synthetic Rubber .......................................................... 7-32 Titanium ................................................................ 7-9 , 8-20 System Safety Services .............................................. 14-31 Titanium Alloys .................................................... 7-9 , 8-20 Title 14 of the Code of Federal Regulations (14 CFR) .. 2-1 T Part 1 Definitions and Abbreviations ......................... 2-3 Part 3 General Requirements ...................................... 2-1 Tabs .............................................................................. 5-44 Part 21 Certification Procedures for Products and Anti-servo ................................................................. 5-44 Parts ............................................................................ 2-3 Balance ..................................................................... 5-44 Part 23 Airworthiness Standards: Normal, Utility, Servo ......................................................................... 5-44 Acrobatic, and Commuter Category Airplanes .......... 2-4 Trim .......................................................................... 5-44 Part 25 Airworthiness Standards: Transport Category Tantalum .................................................................... 12-52 Airplanes .................................................................... 2-5 Tap ................................................................. 10-36 , 11-14 Part 27 Airworthiness Standards: Normal Category Taps and Dies ............................................................. 11-14 Rotorcraft .................................................................... 2-5 Tare Weight ................................................................... 6-5 Part 29 Airworthiness Standards: Transport Category Taxiing ......................................................................... 1-19 Rotorcraft .................................................................... 2-5 Taxi Signals ................................................................. 1-20 Part 33 Airworthiness Standards: Aircraft Engines ... 2-8 Technical Standard Order (TSO) ................................... 2-4 Part 35 Airworthiness Standards: Propellers .............. 2-8 Temperature ................................................................. 5-21 Part 39 Airworthiness Directives ............................... 2-8 Temporary Ballast ........................................................ 6-22 part 43 Maintenance, Preventive Maintenance, The Atmosphere ........................................................... 5-32 Rebuilding, and Alterations ........................................ 2-2 Density ..................................................................... 5-34 Part 45 Identification and Registration Marking ........ 2-8 Pressure .................................................................... 5-34 Part 47 Aircraft Registration .................................... 2-10 The “Dirty Dozen” ..................................................... 14-13 Part 65 Certification: Airmen Other Than Flight Complacency .......................................................... 14-14 Crewmembers ........................................................... 2-10 Distraction .............................................................. 14-15 part 91 General Operating and Flight Rules ............... 2-2 Fatigue .................................................................... 14-16 Part 119 Certification: Air Carriers and Commercial Lack of Assertiveness ............................................. 14-22 Operators .................................................................. 2-10 Lack of Awareness ................................................. 14-26 Part 121 Operating Requirements: Domestic, Flag, and Lack of Communication ......................................... 14-13 Supplemental Operations ......................................... 2-11 Lack of Knowledge ................................................ 14-14 Part 125 Certification and Operations: Airplanes Having Lack of Resources .................................................. 14-18 a Seating Capacity of 20 or More Passengers or a Lack of Teamwork ................................................. 14-16 Maximum Payload Capacity of 6,000 Pounds or More; and Rules Governing Persons on Board Such Norms ..................................................................... 14-26 Aircraft ..................................................................... 2-12 Pressure .................................................................. 14-22 Part 135 Operating Requirements: Commuter and On- Stress ...................................................................... 14-24 Demand Operations and Rules Governing Persons on Physical ............................................................... 14-24 Board Such Aircraft .................................................. 2-12 Physiological ....................................................... 14-25 Part 145 Repair Stations ........................................... 2-13 Psychological ...................................................... 14-24 Part 147 Aviation Maintenance Technician Schools 2-13 The Neutral Plane .................................................... 12-127 Part 183 Representatives of the Administrator ......... 2-13 The Pear Model ............................................................ 14-9 Toggle Switch ............................................................ 12-30 The Pilot in command (PIC) ........................................ 10-5 Double-Pole, Double-Throw (DPDT) .................... 12-30 The RL Time Constant ............................................... 12-56 Double-Pole, Single-Throw (DPST) ...................... 12-30 Thermal Efficiency ...................................................... 5-19 Single-Pole, Double-Throw (SPDT) ...................... 12-30 Thermal Expansion ...................................................... 5-22 Single-Pole, Single-Throw (SPST) ........................ 12-30 Thermal Protectors ..................................................... 12-29 I-10 Tolerances ...................................................................... 4-9 Varactors .................................................................... 12-53 Torque ...................................................... 5-4 , 7-49 , 12-138 Varmeters ................................................................... 12-75 Cotter Pin Hole Line Up ....................................... 7-50 Velocity ........................................................................ 5-14 Torque ................................................................... 7-49 Vernier Scale .............................................................. 11-23 Torque Tables ....................................................... 7-50 Vertical Axis ...................................................... 5-43 , 5-52 Torque Wrenches .................................................. 7-49 Vertical Deflection ..................................................... 12-77 Torque Wrench ............................................................ 11-5 Vibrating-Type Regulator ........................................ 12-159 Total Parallel Resistance ............................................ 12-40 Voltage ..................................................................... 12-164 Towing ......................................................................... 1-17 Voltage Dividers ........................................................ 12-37 Transformer Losses .................................................... 12-67 Voltage Regulation .................................... 12-164 , 12-171 Transformers .............................................................. 12-65 Voltmeter ................................................................... 12-70 Transistors ................................................................ 12-105 W Transonic ...................................................................... 5-47 Transparent Plastics ..................................................... 7-29 Washers .............................................................. 7-46 , 7-47 Transportation Security Administration (TSA) ........... 13-1 Bolt and Hole Sizes .............................................. 7-47 Trigonometric Functions .............................................. 3-24 Installation Practices ............................................. 7-48 Trimmers .................................................................... 12-53 Lock ...................................................................... 7-46 Troposphere ................................................................. 5-33 Plain ...................................................................... 7-46 True Power ................................................................. 12-64 Repair of Damaged Internal Threads .................... 7-48 Turbofan ....................................................................... 1-15 Special Washers .................................................... 7-47 Turbofan Engines ......................................................... 1-15 Waterline (WL) .............................................................. 4-9 Turboprop .................................................................... 1-14 Wattmeter ................................................................... 12-76 Turboprop Engines ....................................................... 1-14 Wave Motion ............................................................... 5-30 Turnbuckles Weighing an Aircraft ..................................................... 6-5 Double Wrap ......................................................... 7-79 Weighing Points ........................................................... 6-14 Single Wrap .......................................................... 7-79 Weight and Balance ........................................ 6-1 , 6-6 , 6-7 Twist Drills ................................................................ 11-12 Weight-Shift Control ................................ 1-11 , 5-56 , 6-27 Twisting ....................................................................... 9-21 Whole Numbers ............................................................. 3-1 Two-Phase Alternator .............................................. 12-156 Wing Flap ..................................................................... 8-13 Two Resistors in Parallel ........................................... 12-40 Wingtip Vortices .......................................................... 5-40 Type Certificate Data Sheets (TCDS) ......... 2-30 , 6-2 , 10-4 Wiring ................................................................ 7-77 , 7-80 Type certificates (TCs) .................................................. 2-3 Cotter Pin Safetying .............................................. 7-80 Snap Rings ............................................................ 7-80 U Turnbuckles .......................................................... 7-79 Ultrasonic ................................................................... 10-21 Wiring Diagram Manual .............................................. 10-4 Pulse Echo .............................................................. 10-22 Work .............................................................................. 5-4 Resonance ............................................................... 10-24 Wrenches ...................................................................... 11-4 Underwriters Laboratory (UL) ....................................... 1-6 Wrought Aluminum ....................................................... 7-7 Unified Coarse (UNC) ................................................. 7-37 Wye Connection (Three-Phase) ............................... 12-156 Unified Fine (UNF) ...................................................... 7-37 Z Uniform Motion ........................................................... 5-14 Universal Bulkhead Fittings .......................................... 9-8 Zener Diodes ............................................................ 12-103 Universal Numbering System ........................................ 4-3 Zone Numbers ................................................................ 4-8 U.S. Department of Labor Occupational Safety and Health Administration (OSHA) ................................................. 1-2 Useful Load .................................................................... 6-4 V Vacuum Tubes ......................................................... 12-110 Valence Electrons ........................................................ 12-2 Valves .......................................................................... 7-77 I-11

Overview

Key points

Section 1

Table of Contents

Section 2

Section 3

Chapter 1

Safety, Ground Operations, &

Servicing

Chapter 2

Records, & Publications

Section 6

Aircraft

Original Airworthiness

Recurrent Airworthiness

Flight Standards

B. Methods of balancing flight controls SAMPLE

Section 7

Advisory

Circular

Section 8

Subpart A—General

SPECIAL AIRWORTHINESS

INFORMATION BULLETIN

SAMPLE

Supplemental Type Certificate

Number SA7855SW

SAMPLE

SAMPLE

New Aircraft (Face Side)

STANDARD AIRWORTHINESS CERTIFICATE

N12345 Boeing 787 43219

Transport

None

E.R. White E.R. White

SAMPLE

STANDARD AIRWORTHINESS CERTIFICATE

N54321 Jackson 47G - 4 3191HG

Normal

None

9 Feb 2015 SW - XX form?

E.J. Smith E.J. Smith

Figure 4-1. Sample FAA Form 8130-7, Special Airworthiness Certificate

Front

SPECIAL AIRWORTHINESS CERTIFICATE

Back

SAMPLE

SAMPLE

SAMPLE

Chapter 3

Mathematics in Aviation

Maintenance

Chapter 4

Aircraft Drawings

Chapter 5

Physics for Aviation

Section 13

Chapter 6

Aircraft Weight & Balance

Aircraft Weight and Balance Report

Results of Aircraft Weighing

Weight and Balance Calculation

Chapter 7

Aircraft Materials, Hardware, &

Processes

Part Number

Chapter 8

Cleaning & Corrosion Control

Metal least likely

Chapter 9

Fluid Lines & Fittings

Section 19

Chapter 10

Inspection Concepts & Techniques

Section 21

Chapter 11

Hand Tools & Measuring Devices

Chapter 12

Fundamentals of Electricity &

Electronics