68S54 - Century II, IIB & III Service Manual

LIST OF ILLUSTRATIONS FIGURE TITLE 1-1 THE CENTURY FAMILY OF AUTOPILOTS 1-2 CENTURY Il AND IIB CONSOLE/AMPLIFIER. . . . . . . . . . . . .. 1-3 DIRECTIONALGYRO(52D54). . . . . . . . . . .. e e e e e e e 14 AIRCRAFT TRIM EFFECTS.. . . e e e e e e e e e ey . 1-5 CENTURY |l SYSTEM CONFIGURATIONS ..... e e e e e 1-6 BLOCK DIAGRAM- CENTURY Il CONSOLE/AMPLIFIER 1-7 CENTURY HICONSOLE. . . . . . . . . . . . .. . 1-8 CENTURY Il SYSTEM CONFIGURATIONS. . . . . . e e e e e s 19 BLOCK DIAGRAM - CENTURY 111 1D395 AMPLIFIER. . . . . . . . .. 1-10 RADIO COUPLER. . . . . . . e e e e e e e 111 BLOCK DIAGRAM- RADIO COUPLER 1C388 - . e e e e e e e 1-12 BLOCK DIAGRAM- GLIDE SLOPE. COUPLER 1C493. 113 WIND EFFECTSONAPPROACH. . . . . . . .. e e e e e e e 114 STABILIZER/TRACKER SYSTEM. . . e e e e e e e e e e 1-15 BLOCK DIAGRAM- STABILIZER/TRACKER.. . e e e e e e e 1-16 BLOCK DIAGRAM- AUTOMATIC TRIM SYSTEM. 1-17 TYPICAL TRIM SENSORS. . . . ‘o 1-18 TYPICAL TRIM SERVO AND AMPLIFIERS. 1-19 TRIM TAB OPERATION. . . e e . 1-20 ~ TRIM SENSOR IN “UP ELEVATOR” CONDITION.. . . . . . e e e e 1-21 TRIM SENSOR IN “DOWN ELEVATOR”CONDITION. . . . . . . . . . . 3-1 66D141 TEST SET.. . . 3-2 QUICK CHECKS CENTURY n TROUBLESHOOTING LOGIC CHART . . 3-3 CENTURY Ii INTERCONNECT WIRINGDIAGRAM. . . . . . . . . .. 35 CENTURYIITESTSET-UP.. . . . . . . . . . ¢ . v v v o v v v v 3-6 .QUICK CHECKS CENTURY n TROUBLESHOOTING LOGIC CHART .« o 3-7 CENTURY lI INTERCONNECT WIRINGDIAGRAM. . . . . . .. . .. 4-1A CENTURY Ii1 SCHEMATIC. . . s e e s e e s e e s 4-1B CENTURY II PRINTED CIRCUIT BOARD e e e e e e 4-1C CENTURY IIB SCHEMATIC. . . . . . . . . .. 4-1D CENTURY IIB PRINTED CIRCUIT BOARD 4-2 CENTURY Il TEST SET-UP. . . 4-3 CENTURY Il & IIB CONSOLE ADJUSTMENTS. 44 CENTURY Il CONSOLE SCHEMATIC.. . . . . . ... . . . . .+ .« .. 4-4A 1D395 AMPLIFIER SCHEMATIC. . . s e ek e e e e 4-4B 1D395 AMPLIFIER PRINTED CIRCUIT BOARD.. e e e e e e 4-5A 1C515 AMPLIFIER SCHEMATIC.. . . . . . e e e e e e e e e 4-5B 1C515 AMPLIFIER PRINTED CIRCUIT BOARD. . . . . C e e e e e e . 4-6A 1C515 -1 & -2 AMPLIFIER SCHEMATIC. . . . . . . . . . e e e 4-6B 1C515-1 & -2 AMPLIFIER PRINTED CIRCUITBOARD. . . . . . . .. 4-7 CENTURY Ill AMPLIFIER TEST SET-UP. . . . . e e e e e e e 4-8 SELECTOR RESISTOR CHART. . . . e e e e e e e e e e 4-9A ROLL SIGNAL FILTER 1B440 SCHEMATIC. . . 4-9B ROLL SIGNAL FILTER PRINTED CIRCUIT BOARD.. 4-10A PITCH SIGNAL FILTER SCHEMATIC. . . 4-10B PITCH SIGNAL FILTER PRINTED CIRCUIT BOARD. . 4-11A 1C388 RADIO COUPLER SCHEMATIC- S/N 6.000 & ABOVE. . . . . . . . 4-12A 1C388 RADIO COUPLER SCHEMATIC- S/N 1.480 to 6,000. . 413A 1C388 RADIO COUPLER SCHEMATIC- S/N UP TO 1,480.. 4-11B 1C388 RADIO COUPLER PRINTED CIRCUIT BOARD S/N 6 000 & ABOVE.. 4-12B 1C388 RADIO COUPLER PRINTED CIRCUIT BOARD S/N 1,480 TO 6,000. 4-13B 1C388 RADIO COUPLER PRINTED CIRCUIT BOARD S/N UP TO 1 480414 1C388C RADIO COUPLER SCHEMATIC S/N 6,000 & ABOVE. .. 4-15 1C388C RADIO COUPLER SCHEMATIC S/N 1,480 TO 6,000.. Issued: Jan. 1973. FIGURE 4-16 417 4-18 4-19A 4-19B 4-20A 4-20B 4-20C 4-21A 421B 4-22A 4228 4-23A 4-23B 4-24A 4-24B 425 427 4-28 5-1 5-2 5-3 6-1 6-2 6-3 TABLES 41 42 Page iv. TITLE PAGE CENTURY Il RADIO COUPLER TESTSET-UP. . . . . . . . . . . . . . . 4-44A CENTURY III RADIO COUPLER TEST SET-UP. . . . . . . .. 4-44B "GLIDE SLOPE COUPLER TEST SET-UP. . . . . . T e e e .4-50 GLIDE SLOPE COUPLER SCHEMATIC. . . . . . . . . . . .4-51 GLIDE SLOPE COUPLER PRINTED CIRCUIT BOARD. . . . . 4-52 TRIM AMPLIFIER 79C54 SCHEMATIC. . . . . . . . . . . .4-55 TRIM AMPLIFIER 79C54 PRINTED CIRCUIT BOARD. . . . . . . . . .. 4-56 TRIM AMPLIFIER 79C54-3 SCHEMATIC.. . 4-57 TRIM AMPLIFIER 79C53 SCHEMATIC. . . . . .4-58 TRIM AMPLIFIER 79C53 PRINTED CIRCUIT BOARD. . . . . . 4-59 TRIM AMPLIFIER 1C646 SCHEMATIC. . . . . . . . o e e e e 4-60 TRIM AMPLIFIER 1C646 PRINTED CIRCUIT BOARD. . . . . . 4-61 TRIM AMPLIFIER 1C671 SCHEMATIC. . . . . . . . . . . . .4-62 TRIM AMPLIFIER 1C671 PRINTED CIRCUIT BOARD. . . . . 4-63 TRIM AMPLIFIER 1B369 & 1B389 SCHEMATIC.. . . . . . . . . . . . . 4-64 TRIM AMPLIFIER 1B369 & 1B389 PRINTED CIRCUIT BOARD. .4-65 SYNCHRONOUS FILTER.. . . . . .4-66 ONE HALF CYCLE CONDITION.. C e e e e e e e s .4-68 PHASEDETECTOR. . . . . . . « " & v v v o o e e 0 0w e w a0 0 4-68 CENTURY 111 30D207 CABLE HARNESS. . . . . . . . . . .5-1 CENTURY 11 30B198 CABLE HARNESS. . e e e e e e e . 5-2 GLIDE SLOPE COUPLER 30C291 CABLE HARNESS.. . . . . . . 53 CENTURY (IB CONSOLE/AMPLIFIER. . . . . . . . . . . .6-3 CENTURY 11l CONSOLE (1C404) s e e e a e e e e e . .6-13 66D94 TEST BOX. .. C h e e e e s e e e e e e e e e e 6-15 LIST OF TABLES . TITLE PAGE TRIM AMPLIFIER PARTS LIST CHART . . < 3-19 TRIM AMPLIFIER TEST PROCEDURES AND CENTERING ADJUSTMENTS. . . .3-22 Issued: Jan. 1973 11 1R TRIM — ( Century 111 CENTURY FIGURE 1-1 THE CENTURY FAMILY OF AUTOPILOTS 1.1 1.11 SECTION | SYSTEM THEORY CENTURY Il: BASIC OPERATION Operator’s Manual Extracts - The Century 11 Autopilot is an extremely simple, all electronic, two- axis autopilot system. It is called a two-axis system because it controls both Heading and Roll. Before discussing “How It Works", sections of the Operator’s Manual are extracted below to ac- quaint you with “How To Work It". Roll (Aileron) Engagement - The Century Il incorporates a fail-safe electrical engage and disengage mechanism in the roll servo which is operated by an ON-OFF switch in the console (Fig. 1-2). When this switch only is engaged, the autopilot is responsive to only the roll axis outputs of the attitude gyro and the commands of the console roll/turn control. Rall Command Knob - The roll command knob ~an be used to maneuver the aircraft through the roll axis without the D.G. Hdg. command. When the Heading mode switch is engaged the roll knob is removed from the autopilot and is ineffective. However: it should be left in the centered position, for convenience, in case the roll switch is engaged. Heading Mode - The heading mode switch is located to the right of the engage switch on the Cen-tury console. It is the function of this Push On-Push Off Switch to remove the roll.command knob from the autopilot circuit and add the D.G. heading command and the optional coupler functions to the basic roll attitude control. Prior to engagement of the heading mode, the D.G. course selector and coupler modes should be preset. CENTURY Il CONSOLE/AMPLIFIER Y > ey CENTURY HB CENTURY 11B CONSOLE/AMPLIFIER FIGURE 1-2 Issued: Jan. 1973 Page 1-1 Course Selector D.G. - The course selector D.G. (Fig. 1-3) replaces the standard directional gyro and provides a fully visible course indicator around the normal D.G. opening. The D.G. dial is marked in 5° intervals and numbered each 30° around its azimuth. A center indice is provided at the top to align selected heading. Additional indices are located each 45° to facilitate rapid heading selection without mental arithmetic. Any heading may be selected, either before or after engagement and turns up to 180° may be programmed directly, either right or left. If the course indicator is rotated beyond 180° from the D.G. dial heading, the course selector will command a revérsal on bank to reach the resultant selected heading in the shortest direction. The D.G. dial is normally set to the magnetic compass with the caging knob on the left in the usual fashion while the course selector indicator is rotated by the Hdg. Knob on the right. Direc- tion of rotation of both the knob and indicator commands the same direction of turn. CAGING KNOB COURSE SELECTOR DIRECTIONAL GYRO (52D54) FIGURE 1-3 Aircraft Trim Effects - An important axiom to remember is that if the airplane is properly “trimmed’’, an Edo Avionics autopilot in heading mode will never fly the airplane with a wing down. This statement can be changed slightly to apply to an airplane without an autopilot; In order to fly a ““trimmed”’ airplane on a constant heading, the wings must be held level. Consider the effect of rudder trim in Figure 1-4. Viewing the airplane from the rear, note that with left rudder applied the right wing must be lowered to offset the rudder effect and keep the heading constant, i. e., the left turn effect of the rudder is canceled by the right turn effect of the bank. Since the autopilot is slaved to a heading this is exactly what it will do in order to maintain that heading when the rudder is out trim. Thus when operating on autopilot heading mode with a wing down, rudder trim in the direction toward the low wing is required. Page 1-2 Issued: Jan. 1973 1.1.2 Issued: System Configuration - As can be seen from the Operator’s Manual, the Century Il is an easy system to operate. The most complicated Century 11 consists of only six parts (seven, consider- ing the interconnecting electrical cable harness) as illustrated in Fig. 1-5. They are as follows: 1. Console-Amplifier - The Console-Amplifier is the focal point of the Century Il autopilot. It is both the command console through which the pilot operates the autopilot, and the computer which provides the necessary mixing of signals and voltage amplification tc drive the autopilot servos. The Console-Amplifier provides reference excitation voltages to the Directional Gyro and Artificial Horizon which in turn supply the Console-Amplifier with the needed roll reference and directional command signal to fly the aircraft. 2. Artificial Horizon - The Artificial Horizon provides the roll reference signal for the system. It receives excitation from the console-amplifier and converts it to an attitude reference signal to tell the autopilot the roll attitude of the aircraft. Loss of this roll attitude signal will cause the autopilot to fly with its “‘eyes closed’’ and therefore it may fly at any bank angle—even upside down. 3. Directional Gyro - The Directional Gyro (D.G.) supplies ‘‘compass” information to the Cen- tury Il. It also receives and controls the frequency of the reference excitation signal used by the system. The pilot, by selecting a heading on the D.G. (aligning ““Heading bug‘’), directs the auto- pilot to fly that heading. 4. Roll Servo - The Roll Servo receives power from the console amplifier and applies force to the aircraft controls. A solenoid controls engagement to the controls and a force limiting clutch is provided to limit the maximum force the servo can apply. The setting of the clutch is deter- mined during F.A.A. certification and its maximum setting as contained in the servo data should never be exceeded. 5. Roll Signal Filter - The Roll Signal Filter is a “Rate’ circuit that plugs in line with the Artifi- cial Horizon. Its purpose is to tell the console-amplifier “how fast”’ the aircraft is rolling in one direction or the other. The Roll Signal Filter is not used in all types of aircraft. Its need is deter- mined during the F.A.A. certification. In general, incorrect operation of the Roll Signal Filter will cause “‘overshooting of bank angles or control wheel nervousness’. 6. Radio Coupler - The Radio Coupler is an option with all Century |l systems except those with PN101’s, KP1-650, etc. The Radio Coupler plugs in line with the D.G. and provides radio coup- ling for navigation and approaches. When a PN101 or KPI-550 is used with the Century I, a special radio coupler, 1C388-C (Collins), must be used to provide correct matching of the heading datum synchro to the autopilot. LEFT RUDDER~__ RIGHT BANK REAR VIEW AIRCRAFT TRIM EFFECTS FIGURE 14 Jan. 1973 Page 1-3 J Dp °oarv sy 4 CONSOLE/AMPLIFIER ROLL SERVO Two axis autopilot with optional radio coupler Weight: Including gyros, 9 pounds Power: 24 Volt - 1.5 Amp 12 Volt-2 Amp Optional Radio Coupler weight, ¥ pound CENTURY |l SYSTEM CONFIGURATIONS FIGURE 1-5 1.1.3 Basic Signal Flow - In the block diagram (Fig. 1-6) aircraft A+ power is supplied to the console ‘ amplifier where it is controlled by the ON-OFF switch on the console. After the switch, A+ goes three ways: 1. To the servo engage solenoid. 2. To the servo amplifier circuit. 3. To the voltage regulator and then to the 5KHz oscillator, The Oscillator supplies the 5 KHz regulated excitation in a 27 + 1 volt peak to peak square wave to: 1. Internal circuits of the console-ampilifier. 2. The D.G. and Radio Coupler if installed. 3. The Artificial Horizon. The excitation is used in the console-amplifier to: 1. Generate the Roll Command Signal. 2. Control timing circuits (synchronous filters) {Phase detectors). 3. Supply regulated power.for amplifier. The D.G. uses the excitation to generate a ‘‘Heading Error Signal” that tells the autopilot how far the heading bug is from the “Lubber Line” on the gyro and which way it needs to turn to get the bug back under the “Lubber Line”. The Radio Coupler uses the excitation for power and timing circuits. : . ' Page 14 ' lIssued:. Jan. 1973 -1 4dNnvld d31d1TdWVY/3TOSNOD 11 AHNINID - WVHDVYIA D018 OAHIS 110Y dN-MO17109 $2INOHLI3T3 1Nd1IN0 DANIS ¥3aLd SNONOYHINAS HIAIHG CEIFIRE < Ov Que HOL03130 ISVHd Jv 0314N00 HINHOISNVHL ANIOd SHOLO313Q ISVHA ANV N SH31714 SNONOUHONAS $.o- OL NOILYLIIX3 110H .m ZHA S YOo1vITIISO 440/NO NOILY LIDX3 770 HILIWIT ONY Y3474 SNONOUHINAS HILIMS ONIQY3IH dIRHTINY v St NOILV1IOX3 IN3NISOray BONDI ONIMILNID TIOH AGNVINNOD TT0M Page 1-5 Jan. 1973 Issued ~ e The Artificial Horizon uses the excitation to generate an Attitude Reference Signal that tells the autopilot the attitude of the aircraft. If a roll signal filter is installed, it uses excitation for power. As you can see, the excitation signal is very important and anything that disturbs the excitation signal will affect the autopilot though sometimes, the effect is very subtle. Signal Processing - The most important signal in the autopilot is the Attitude Reference Signal from the Artificial Horizon. Its signal is fed directly to the summing point in the console- amplifier which represents aircraft positior. (or position plus rate if a roll signal filter is used). With only this signal, the aircraft can fly straight and level if all adjustments are correct. To cause turns, the signal from the Roll Command knob is also supplied to the summing point at which time the aircraft will bank until the horizon signal cancels the command signal. It will stay banked until a different command is injected by the pilot. The D.G. Signal will also cause a bank in the ;ame manner as the roll command knob, but as the aircraft nears the selected course, the command decreases until the aircraft rolls out on the select- ed heading. Bank limiting is provided by limiting the maximum amplitude of the command and D.G. signal. The Horizon Signal is not limited in any way. After signals are mixed at the summing point, they are amplified by the second AC amplifier, processed by the second synchronous filter and amplified by the third AC amplifier. They are then transformer coupled to the phase detector, changed to DC, amplified by the driver and the servo output, and sent to the servo motor to move the aircraft controls. Some of the voltage to servo motor is tapped off and sent to the “Electronic Fullow-Up Circuit’’, which is an elec- tronic model of the servo motor. The output of this circuit is used to control the servo amplifier and prevent oscillation. While this has been a rather brief explanation, a more detailed explanation of the theory >f oper- ation of individual circuits may be found in the repair and overhaul section under the specific component containing the circuit. This explanation has been provided to assist troubleshooters in understanding the role that each part plays in the system. For it is only through understanding that-the system can be efficiently serviced, adjusted and fatilty components located. The Century 11B system is identical with the Century Il and the console-amplifiers are inter- changeable except for the retaining clip. The Century 11B offers the following additional features: 1. Easier Operation. . : 2. improved switches and heavy-duty internal components. 3. Adjustable roll threshold for “’Fine Tuning’’ the electronic follow-up. - 4, Smoother roll action. _Page 1-6 Issued: Jan. 1973 - 1.2 1.21 CENTURY IlI: BASIC OPERATION Operator’s Manual Extracts - The Century IlI is a light weight (approximately 18 pounds), all electronic, three axis autopilot system. It is called a three axis system because it controls head- ing, roll and pitch. Note that the standard Century lll, although referred to as a three axis sys- tem, contains only two controls servos. Before discussing the general theory of operation of the Century 111, it is necessary to know how the system operates; therefore, the following extracts from the Century Il Pilot’s Operating Manual are provided. If you happen to have a copy of the Pilot’s Operating Manual handy and are not familiar with the Century 11, it would be helpful for you to read the entire manual. Command Console - The Century 1l console {Fig. 1-7) is designed to provide convenient finger- tip command of all basic autopilot functions. Magnetic engage and mode switches are designed with logical interlocking features for operational ease and simplicity. The lucite face panel incor- porates optically engineered night lighting with provisions for dimming control through the stan- dard aircraft instrument rheostat. Roll (Aileron) Engagement - The Century 111 is.separated into two distinct systems, the Roll/ Heading and Pitch Altitude. Each is engaged separately by means of a fail-safe electric servo engage mechanism. The Roll engage acts as an autopilot master switch as well as the roll engage switch. In this capa- city the roll must be engaged for all other engage and mode switches to become operative. With this roll switch only engaged, the autopilot is responsive only to the roll axis of the attitude gyro and the commands of the console roll/turn control. 1S CENTURY I[1l CONSOLE FIGURE 1-7 Issued: Jan. 1973 Page 1-7 Page 1-8 Roll Command Knob - The roll command knob controls the roll axis of the aircraft when roll mode switch is engaged. It is useful in manuevering and will permit steeper bank angles (up to 30°) than those resulting from D.G. heading commands. When the heading mode switch is en- gaged, the roll knob is removed from the autopilot circuit and is ineffective. However it should be left in the centered position for convenience. NOTE: Do not use roll mode during approach configuration on twin engine aircraft as engine failure will result in excessive heading deviation. Heading Mode - The heading mode switch is lovated directly adjacent and to the right of the roll engage switch. It is the function of the heading mode switch to remove the roll command knob from the autopilot circuit and add the D.G. heading command and coupler functions to the basic roll attitude control. This switch is interlocked with tI:e roll engage so that the roll function will be engaged simultaneously with the heading mode switch. Prior to engagement of the heading mode, the D.G. course selector and coupler modes should be set. (See sections on coupler opera- tion when optional coupler is installed). Course Selector D.G. - The course selector D.G. dial is marked in 59 intervals and numbered each 300 around its azimuth. A center indice is provided at the top to align selected heading. Addi- tional indices are located each 45° to facilitate rapid heading selection without mental arithmetic. Any heading may be selected, either before or after engagement, and turns up to 180° may be programmed directly, either right or left. If the course indicator is rotated beyond 180° from the D.G. card heading, the course selector will command a reversal in bank to reach the resultant selected heading in the shortest direction. The D.G. dial is normally set to the magnetic compass with the caging knob on the left in the usual fashion, while the course selector indicator is rotated by the heading knob on the right. Direction of rotation of both the knob and indicator commands the same direction of turn. Trim Indicator and Pitch Command Wheel - Prior to engagement of the pitch axis, it is desirable "to adjust the autopilot pitch to match the attitude being flown. In this way the pilot can transi- tion from hand flight to autopilot smoothly during the climbout or other pitch maneuvering. The pitch servo effort meter (labeled “Trim"’) to the left of the pitch control wheel receives the same error signal as the servo amplifier. Therefore, the effort meter indicates the difference be- tween the autopilot pitch command setting and the attitude of the aircraft. Thus, if it is pointing upward prior to pitch mode engagement, it indicates that the aircraft can be expected to increase pitch upon engagement. Conversely a down needle indicates a decrease pitch attitude upon engagement. For a smooth transition, the needie should be centered manually by the pitch command knob before the pitch mode is engaged. After engagement, the needle will stay centered because the servo continously commands or flies the aircraft to null or zero out the error signal. The pitch command wheel is in the autopilot circuit when the pitch mode switch only is engaged. It is removed from the circuit and becomes ineffective upon engagement of the altitude hold. During altitude hold operation it may be set to level or preprogrammed to produce a climb or descent upon altitude hold disengagement. Pitch {Elevator) Engagement - The pitch mode switch engages the autopilot pitch servo and makes the autopilot responsive to the pitch attitude of the artificial horizon and commands of the pitch command wheel. Pitch attitudes may be directed by rotating the command in the appropriate direction. The computor system in combination with optional automatic trim will maintain this constant attitude through power changes and during gear and flap position transitions. On air- craft not equipped with the Edo-Aire Mitchell automatic trim, it will be necessary to disengage the pitch and manually trim the airplane during attitude, airspeed, or gear flap transitions. (See section on automatic trim). Issued: Jan. 1973 1.2.2 Altitude Hold - The altitude hold is a ‘“‘command’’ type which requires no pitch command adjust- ment prior to engagement. Engagement of the altitude mode switch will remove the pitch com- mand wheel from the circuit and initiate a smooth transition to the pressure altitude at which it was engaged. Barometric sensors provide precise altitude holding with nominal climb and dive limitations for operation in turbulence. Automatic Trim Cperations - The Edo Avionics automatic trim provides full time automatic trim with the autopilot on. The system is F.A.A. approved for full time use from take off to touchdown. When the autopilot pitch is engaged, the trim system goes on full time and will correct aircraft trim to the attitude and airspeed changes that are called for by the autopilot pitch command, power changes, etc. When the autopilot is off, the trim button on the control wheel is depressed by the. ;pilot any time he wishes to relieve control forces. This will be particulary helpful during approaches when speed is being reduced and additional trim changes are required by the lowering of flaps and gear. The pilot can override the trim system at any time by manual operation of the aircraft trim con- trol. In addition, the circuit breaker switch labeled “Trim” on the instrument panel may be pulled to disconnect the electric trim system from the aircraft electrical system. System Configuration - The basic Century 11l consists of seven components, not counting the cable harness. With all of its options, the total system is made up of twelve components. These components are illustrated in Fig. 1-8 and are as follows: 1. Console - The console is the link between the pilot and the electronic “brain of the auto- pilot. Through the console system A+ is controlled and all of the basic autopilot functions are commanded to the computer/amplifier. The console also contains the limit and centering potentiometers used during initial flight adjustments. These adjustments are located under the face plate. 2. Amplifier - The amplifier contains the computer logic circuits and amplifiers that provide the command signals to the roll and pitch servos. Also, all reference signals such as those from the D.G. and artificial horizon and all command signals from the console are mixed and processed within the amplifier. 3. Artificial Horizon - The artificial horizon provides roll and pitch references for the system. It receives excitation from the amplifier and converts it to attitude reference signals which tell the autopilot the roll and pitch attitude of the aircraft. As with the Century 11 system, loss of the attitude signals would cause the aircraft to fly at any bank angle or at any pitch attitude. With- out attitude reference, the autopilot is “blind’’ and therefore could not tell the difference between right side up or upside-down. 4. Directional Gyro - The Directional Gyro (D.G.) provides a “sense of direction” for the auto- pilot. The pilot, by selecting a heading on the D.G., directs the autopilot to fly that heading. This is accomplished through the excitation signal which the D.G. converts to a heading signal and applies to the amplifier. One other function of the D.G. in the Century Il system is control- ling the system excitation frequency. The D.G. contains the tuned circuits for the excitation os- cillator contained within the amplifier. 5. Ailtitude Hold Sensor - The Altitude Hold Sensor supplies the Century 11l with an altitude reference signal. The sensor will lock on to the indicated altitude when the altitude mode but- ton on the console is pressed. As long as the aircraft remains at that altitude, the sensor will sup- ply a nulled or zero signal to the amplifier. Any deviation in altitude causes a signal change which is applied to the amplifier and processed to correct the altitude deviation. Issued: Jan. 1973 ' Page 19 6. Roll Servo - The Roll Servo provides the force to control the aircraft ailerons. It receives its power from the amplifier. A solenoid controls engagement of the servo to the controls and a force limiting clutch is provided to limit the maximum force applied by the servo. The setting of the clutch is determined during F.A.A, certification and its maximum setting as contained in the servo data should never be exceeded. 7. Pitch Servo - The Pitch Servo is identical to the roll servo except it controls the elevator or stabulator of the aircraft. It also receives its power from the amplifier. 8. Radio Coupler - The Radio Coupler is an optional unit which provides radio coupling for navigation and approaches when plugged in line with the system’s D. G. Three types of radio couplers are used with the system, depending on the aircraft’s radio and navigation display system. The 1C388 coupler is used with all systems using a standard Omni/Localizer Converter and Edo Avionics 52D54 Directional Gyro as course and heading inputs. The 1C388-C coupler is required when the Century 111 is coupler to navigation systems such as the PN 101, KP1-550, etc., and the 1C388-2 Radio Coupler is used with Edo Avionics NSD-360 Navigation Situation Display. 9. Glide Slope Coupler - The glide slope coupler is an automatic analog computer that directs the autopilot to intercept and track the approach glide path. This unit, together with the Radio Coupler, provides a complete and automatic ILS intercept capability for the Century 1l auto- pilot. 10. Automatic Pitch Trim System - This system consists of a trim amplifier, servo and sensor which provides automatic trim corrections. A detailed discussion on its operation is provided in paragraph 1.6 of this section. 11. Stabilizer and Omni Tracker Back-Up System -(Optional) - The stabilizer back-up system is a yaw and roll axis stabilizer which is capable of performing short term heading as well as omni navigation course functions. Refer to paragraph 1.5 of this section for a complete description of this system. GLIDE SLOPE COUPLER & STAB BACKUP SYSTEM /[ / ] / ‘ ¥ YV ALTITUDE HOLD ROLL PITCH SERVO AMPLIFIER SERVO "TRIM SERYVO {Automatic Pitch Trim Optional) / / Z CONSOLE Full three axis autopilot with optional radio coupler and automatic trim system,back-up system and glide slope coupler NOTE: Stabilizer back-up systems were discontinued after 1969. Weight: Including gyros, 19 pounds Power 24 Volt - 1.9 .Amp 12 Vot -3 Amp CENTURY Il SYSTEM CONFIGURATIONS FIGURE 1-8 Page 1-10 Issued: Jan. 1973 1.2.3 In the block diagram, (Fig. 1-9) it can be seen that the Century 11l is an expanded Century Il system. The Century lll uses the same basic circuit as the Century !l in the roll section and dup- licates it to form the pitch section. Aircraft power is applied to the system through the console. The “ROLL’* mode switch on the console serves two functions: When engaged it applies A+ to the system and also places the auto- pilot under control of the Roll Command Knob. With A+ applied to the system, the 5 KHz oscillator within the amplifier is activated and supplies the system with a 5 KHz square wave excitation signal. This signal is virtually the “backbone” of the Century 11l autopilot. As can be seen in Fig. 1-9, the excitation signal is routed to the D.G. (which is a part of the oscillator since it contains the tuned circuit for the oscillator), the artificial horizon, the console and the various synchronous filters and phase detectors within the amplifier. The D.G. uses the excitation to generate a “‘Heading Error Signal” or D.G. signal that tells the autopilot how far and in which direction the “heading bug” is from the gyro “‘Lubber Line*. This signal is applied to the first AC amplifier in the roll section of the amplifier. It is switched in or out by a transistor switching circuit controlled by the 1uii command signal. Whenever the roll command signal is present (i.e. when the console is in “ROLL‘ only mode) the switch is open and therefore the D.G. signal will not be passed into the amplifier. By pressing the Heading (HDG) mode on the console, the roll command signal is removed {within the console) and the D.G. “ signal is allowed to pass into the ampl:fier. The Artificial Horizon uses the excitation signal to generate the roll and pitch reference signals for the amplifier. These signals tell the autopilot what attitude the aircraft is in. The console uses the excitation to generate the roll and pitch command signals. It also uses excit- ation to generate the roll and pitch limit and threshold signals. These signals are controlled by six screw-driven potentiometers located in the lower right corner of the console, under the face plate. Pitch excitation is also applied to the altitude sensor to generate the altitude hold signal. This signal is active whenever the ALT mode switch is pressed on the console. The altitude hold signal replaces the pitch command signal and therefore places the pitch section of the amplifier under guidance of the altitude hold signals. In this configuration, the autopilot will cause the aircraft to maintain whatever altitude was present at the time the ALT mode switch was pressed. The excitation signals are also used by the roll and pitch signal filters and by the optional radio coupler. From this brief explanation, the important role the excitation signal plays in the system should be apparent. Further understanding of the 5 KHz excitation signal and its function will be relat- ed in the simplified theory of operation that follows. A more detailed explanation is provided in Section 1V. Signal Processing - The roll and pitch reference signals originating from the artificial horizon pro- vide the autopilot with aircraft attitude information. In fact, they tell the autopilot what the aircraft is doing. These attitude signals are fed to summing points within the amplifier (See Fig. 1-9). When the 1D395 amplifier is used, the attitude signals may be first passed through a roll or pitch signal filter. These filters are actually rate circuits that tell the amplifier “how fast’’ an attitude change is occurring; therefore, they provide rate information to the autopilot. Note that a roll and pitch filter will never be used together with a 1D395 amplifier. (Design of the signal filters is such that only one may be plugged in line at a time.) (In the 1D515 and 1D515-1 ampli- fiers, both the roll and pitch sianal filters are built-in. Issued: Jan. 1973 Page 1-11 d3141TdINY S6EAL 111 AHNLNID - WvHOVIA 00149 6L 3HNOId _ 10dLN0 0OAH IS diAlbg LNd1NQ OAY3S HIAIHG —— e — e - — - — - - - - - — = dN'‘MOT104 3I0SNOD WOud JINCHLIATI NINLSNFAY LIWET HOLMd R N an Mmoa JVYNOILS HIAH1dWY + D1 +v Y ANV HILINIT ANV HaLTHd SNONOBHONA! 181 H31 N4 1INIOd €o123130 9IS 0T0H 3aNLNLTY DIS ANVAWOD HOLId Y3141 TdWY IV 1SL Y31 1dWvY H31AITdNY Jv Jue IV ONZ 370SNOD Jv a374N0I HIWHO4SNYHL ONYWWOD 1708 TYNIIS JINIHIATH HOLM = ¥ i ] t L (Q37IVISNI 41} HALIS TYNDIS 770U HO HOLId AYNIIS 30N3Y3434W 1104 JTOSNOD WOu4 ININLISNrAY LiWiD 110 ] | } J YILNDD _l 1HO 1431 dM*M01104 JINOHLII3 -—— ¥3L4 el | AS OGNV H3LTH SNONQUHIN SNONONHONAS 151 _ OHAD HiG IHL NIHLIM OINIVANDD S HOLVT11ISO ZHX § JH1 HOL TOHINOD — AININDIYS 1INDHID n_wz:hm._.wuh HO123130 3SVHI 110H U3 TdWY HIAEITdNY 1417dWY 3V QuE v aNZ ¥3 Jv 18L OAH3S 1704 ANIOd ! IV a31dN0I DNIAWNS HIAWHOASNVEL | — *943 M ‘SHOLDILI0 ISVHA 'SHIL NI SNONOBHINAS :S1INJHID _ IVYNUILNI O1 NOILVLIOX3 ZH% § YOLY1UIS0 OAu3S HOLd fillll' FTOSNOD NOILV11IXT HOLId ONV NOZIHOH VIO LHY o1 NOILY1OX3 110 Jan. 1973 Issued Paage 1-12 1.3 1.3.1 1.3.2 With just the roll and pitch referenoe signals, the autopilot, if correctly adjusted, will keep the air- craft straight and fevel. To command a turn or climb, the rolli command and pitch command knobs on the console may be used. When the rolt knob is rotated, a roll command signal is applied to the summing point in the amplifier at which time the aircraft will bank until the roll reference signal from the hori- zon cancels the command signal. It will stay in a bank until a different command is injected (i. e. return of the roll command knob to center position). The pitch command knob and pitch reference signal produces the same effect, but of course, controls the pitch section of the ampli- fier. Depending on the mode of operation, roll and pitch command signals originate from the roll command, D. G. signal, pitch command and altitude hold signal. Regardless of which is present, the result to the summing point is essentially the same. For example, in the HDG mode, a D. G. signal will be generated when the heading bug on the D. G. is not aligned with the lubber line. In this case, the aircraft will bank in a direction that will correct the “’error””. In doing so, the D. G. signal will greadully decrease the bank and the autopilot will roll out the aircraft on the proper heading. Bank limiting of the aircraft is provided by limiting the maximum amplitude of the coramand signal. The bank and pitch limiting of command signals are provided for in this manner before they reach the summing point. The reference signals, however, are not limited in anyway. After the command and reference signals are mixed at the summing point, they are amplified by the second AC amplifier, processed by the second synchronous filter and amplified by the third AC amplifier. The synchronous filters throughout the amplifier serve to shape the command sig- nals into.a more perfect square wave and filter out other signal components, such as nocise. After the third amplifier stage, the processed command (command + reference signal) signal is trans- former coupled, to the phase detector, changed to DC, amplified by the driver and servo output, and sent to the servo motor to move the controls. A portion of the servo output signal is fed back to the electronic follow-up circuit. The output of th|s circuit is used to control the servo amplifier and prevent oscillation. A complete and detailed theory of operation on the Century 1l is presented in Section iV of this manual. The primary objective in this presentation has been to familiarize you with a general knowledge of the parts which make up a Century HI and how they are interconnected to form the autopilot system. RADIO COUPLER One of the optional comoonents which may be inws connected with the Century 11 is the radio coupler (Fig. 1-10). This aevice permits guidance of the autopilot with a radio signai. Basic Operation - The radio coupler is installed in line with the directional gyro and receives its power and excitation from the amplifier. In principle, the radio coupler provides a heading sig- nal which corresponds to the direction of the course to be flown. This heading signal is coupled to a radio deviation signal in such a manner that any radio deviation will cause a proportional heading deviation. Signal Processing - In Fig. 1-11, the radio voupler is broken down into block diagram form to show how the radio and heading (D.G.) signals are mixed. Issued: Jan. 1973 ' Page 1-13 Figure 1-10 Radio Coupler The radio signal (standard ARINC 150 mv) is applied to a chopper where it is transformed into AC and amplified. It is then coupled, through an isolation transformer, and changed back into DC by the phase detector. The DC signal is then passed on to the radio limiter circuit. Here the signal is limited to a value corresponding to 100% or full scale deviation of the omni/loc indica- tor. This function is part of the intercept capability of the radio coupler. However, before more is said about it, we will first track the D.G. signal’s path. The D.G. signal is transformer coupled (for isolation purposes) in the radio coupler and changed into a DC voltage by the phase detector. From the phase detector the signal is applied to two diodes and two potentiometers in parallel. This provides the necessary circuitry for establishing a crosswind capability (Ref. Fig. 1-11). The cireuit is adjusted in such a manner that any D.G. signal which corresponds to 15° (approximately) of heading deviation or greater is passed. Assume that the aircraft is flying on a heading of 90° and the pilot wishes to track a radial on a course of 130°, He would set his omni course selector to 1302 and set the D.G. course indicator to match. This will generate a signal from the D.G. which will be passed through one of the diodes since the deviation at this point is 40°. This D.G. signal is mixed with the limited radio deviation signal at the summing point. Remember, the radio signal is limited to a value of 100% even though the actual deviation at this point is considerably greater. As the aircraft turns in re- sponse to the heading and radio command, the D.G. will be nulled by the limited radio signal (the radio signal is opposite in polarity to the D.G. signal). At this point the aircraft will be on a heading that will intercept the radial at a 45° angle. Since the limited radio signal corresponds to 100% of deviation, the autopilot always “‘thinks’’ it is just 100% off the selected radial. There- fore, it will always seek to intercept the radial at the same angle regardiess of the actual deviation beyond 100%. When the aircraft approaches the active region of the radial {within 100% deviation) the radio signal will begin to decrease. This change causes the intercept angle to decrease. As the aircraft heading reaches 15° of the radial heading, the D. G. signal is blocked by the crosswind circuit. At this point the system is responding primarily to the radio deviation signal. 1f the D. G. signal was not blocked, the system would not have a crosswing capability. In this situation, the D. G. and radio signal would null at one specific point or heading—the actual aircr9ft heading. If a crosswind were present, the D. G. signal would prevent the aircraft from establishing any crab to compenstae for the corsswind; therefore, the radio course would have to be offset to compensate for the crosswind. By blocking the D. G. signal at 150 deviation, the radio deviation, signal is permitted to crab the aircraft an amount proportional to the crosswind {up to 159) in order to keep the aircraft on course. Short term variations in heading such as produced by turbulent air, are passed to the summing point through a high pass filter. Also a very small amount of steady state D.G. signal by-passes the filter to provide dampening. Issued: Jan. 1973 88€01 H31dNOJ OIAVvH - WvHOHVIA v._oO|_m_ LL-L 3HNOIS r-—- - - """-""-"""—-"=-—"—"="—=-"—"""—"—"—"—"——=-- 1 NOILY108t Giva un » ANOD wioisoave | JOT-HOA YAH1TWY TH1 NIHLIM WO A311ddNS 34Y 540103130 I5VHd GNY SHIJJOHD 3H1 JAIYQ 0L NOLLYLIOXT ONY xwfi LINJHID GNIMSSOMD Ld3DHILNI LHOIY o oL ANIOd 1d30HIALNI L4371 NO1LYT081 pessss=sr=m=="""7 - I ' 1 ' ! & ¥ol1d3i30 “ aq ISYHd aw t ' | | < U3l ALIYYT) HOJ NMOHS LON SNOILINNY oiavy ONIHOLIMS 31VY OIQVY ONY $TV13Q HILIMS 300W 310N I | | | | | _ _ | _ _ | | | _ | | | _ | “ v @ 00H - HA1417dWY 0L _ . . . ||— Page 1-15 Issued: Jan. 1973 14 1.4.1 1.4.2 Page 1-16 GLIDESLOPE COUPLER (OPTIONAL)} The glideslope coupler is an automatic analog computer that directs the autopilot to intercept and track the approach glide path. This unit together with the Radio Coupler, provides a com- plete and automatic ILS intercept capability for the Century |1l autopilot. Basic Operation - In order for the glideslope coupler to operate, three conditions must be met. First, the Radio Coupler must be set in the LOC NORM mode. Second, the console must be set in the ALT mode. Third, the glideslope deviation indicator must be deflected upward for a period of twenty seconds. This provides assurance that the glide path will be intercepted from below in the normal manner. With these three conditions met, the glideslope coupler will arm automatically after the twenty second period. The arming function assures that approaches to the glideslope will occur in a safe manner. For example, the LOC NORM. condition prevents inadvertent coupling when flying reverse course or tracking outbound on the front course. The ALT mode condition prevents coupling from a high rate of descent and the glideslope deviation indicator condition, requiring an up deflection for twenty seconds, prevents coupling from above which could result in a very uncomfortable, if not dangerous, pitch down condition. Signal Processmg Before the glideslope coupler can receive power, the LOC NORM mode must be switched in on the Radio Coupler This provides the circuit ground for the glideslope coupler’ electronics. After the ground is established, the glideslope coupler receives a 150 mv meter signal from the aircraft’s glideslope receiver. This signal is chopped, amplified and transformer coupled to a phase detector as shown in Fig.1-32. From the phase detector, the glideslope signal is applied to the arm and engage logi¢ switching circuits. The arm switching ‘circuit requires a glideslope deviatien signal which is equivalent to approxi- mately sixty percent full scale up needle deflection and a +DC altitude engage signal to activate. The sixty percent glideslope deviation signal must be present for at least twenty seconds before arming will take place. With arming, the arm switching circuit will allow the engage switching circuit to turn on as the glideslope deviation signal reaches zero deviation. At this point, the engage switching circuit acti- vates relay K1, Before continuing with the function of relay K1, we will back-track and follow the path of the glideslope signal beyond the point of the arm and engage logic switching circuits. The glideslope signal at this point is split into two. paths. One leads to a high gain integrator circuit and the other (steady state path) leads to a chopper. During intercept, the steady state path, through the rate circuit, is the primary controlling signai. This signal is chopped and mixed with the pitch reference signal from the horizon at T2. At this point of intercept, when K1 activates, the shunt which had been across T2, and thus preventing mixing of the glideslope signal with the pitch reference signal, is removed. Therefore, the pitch reference signal, now being applied to the amplifier will be a composite of the glideslope signal and the pitch reference signal. Effectively, the autopilot will now be commanded by a varying horiz un pitch reference signal. When glideslope intercept takes place (an instant before center needle), a preset down command is also mixed with the glideslope/pitch reference signal. The command signal provides an auto- matic 3 degree pitch down command to the autopilot which, along with the rate circuit, helps prevent overshoot and places the aircraft on the proper glide angle. (Al glideslopes are adjusted for a no wind 3° up angle of pitch from the ground.) Issued: Jan. 1973 £6¥0L H3I1dNOD IdO1S IAITD - WYHOVIA MD019 ¢l-1 34NOId Fo==== Y3417V 0L NOWWOD HOLId 1no {2V) TYNOIS d70H 3aN1ILTY - dNV'Y HOLVIIANI 340718 30170 3IDVONI 30NLILTY | 1no Oll_la_ |! t 1 1 ! 1 I 1 ) 1 f ) ! 1 ! | ! I 1 | I ! 1 1 1 | } 1 ) I I | | I ) 1 r ' ! 1 ' H314174WY OL 143 L1V 1GIXIN Iuv SIVNOIS 44 IMNIYIATY ML aNv 34078 30179 JTONY HOLW 178vISNraY OHLVLIOXS | SN GR | H3IOHD 4100410 ONIHILIMS L SU34dOHD ONY ¥0103130 I5VHd SJINOYLI33 NOILYINDIY 3JOVLI0A NOILYLIDX 3 HO1VINO3IY ¥iwnos OIS NOLLYIAIG 34078 3019 HOLVHOZINI NIVD KON Linown b vy 40193130 ISVHd Ll 1l o SANNON™. LINJH12 ¥4I 1INOS HILIIVINY av [ ] ALb o0 (33 INY! NOLLYLIOXE WL J0A BTV (¥3WNo olave) TVIWHON ¥3ZITVD01 (Qiavul TYNDIS 34075 3619 INCZINOH) TYNDIS o AONIYISIY HOLM Page 1-17 Issued: Jan. 1973 Page 1-18 The integrator circuit mentioned earlier allows the autopilot to fly the aircraft centered on the glideslope regardless of the head or tail wind conditions. Basically, this circuit is a high gain amplifier which provides additional voltage to the glideslope signal. The circuit also has a 200 MFD capacitor feedback which effectively keeps the output of the integrator from acting on short term deviations off center needle. Therefore the integrator will only provide an output when there is a constant deviation. Consider the following example: Assume that an autopilot without an integrator has intercepted the glideslope and is coupled. A strong headwind is present and the autopilot, due to the headwind, cannot maintain center needle. Instead, some point slightly below center is achieved. To understand this, refer to Fig. 1-13. In this illustration the path of the aircraft at a fixed 3° angle of descent is shown in a strong headwind condition as compared to a zero wind condition. (Remember that the aircraft is set to approximately 3° pitch down automatically upon glide- slope intercept. To the autopilot, this represents the correct attitude on the glideslope). It can be seen that with a strong headwind the aircraft would reach the ground at a much shorter dis- tance than under zero wind conditions. Thus it would undershoot the approach. The electronics of the autopilot together with the glideslope signal, of course, would not allow undershoot to this degree. However, since the preset 3° pitch down command represents the correct attitude, this signal would continously oppose the glideslope signal which is telling the autopilot that it is below center glideslope. The result is an electronic averaging. This average command would place the aircraft slightly below center needle. Therefore, the aircraft would track the glideslope parallel but slightly below center. CONDITIONS: J IDENTICAL AIRCRAFT 1. INTERCEPY GLIDE SLOPE AT SAME POINT AND PITCH DOWN 3° 2. ESTABLISH 500 FEET PER MINUTE OESCENT 3. 120 MPH INDICATED AIRSPEED AIRCRAFT “A” HAS A 20 MPH TAILWIND AIRCRAFT “8" NO WIND - AIRCRAFT "C” HAS A 20 MPH HEADWIND G EXAGGERATED FOR CLARITY 1 3MINUTES 3MINUTES 3MINUTES TMILES B MILES SMILES WIND EFFECTS ON APPROACH FIGURE 1-13 Issued: Jan. 1973 The integrator prevents off center tracking by sensing any constant deviation of the glide slope signal. It allows approximately 10 to 15 seconds to pass before acting upon the signal. In this way short term deviations caused by rough air will not cause an output from the integrator. With long term deviation, however, the integrator provide an additional signal which is mixed with the glide slope signal. The resultant signal corrects the deviation ‘and aliows tracking of the glide slope without needle off-set. In Fig. 1-12, a push button switch is shown across the integrator circuit. This button is located on one end of the glideslope coupler and is used during flight adjustment. It effectively shorts the. integrator while adjusting the pitch or glideslope angle. Also note that the integrator is shorted prior to intercept of the glideslope. This is accomplished through a set of contacts on relay K1 (not shown in Fig. 1-12). This assures that the integrator will not provide a false out- put at the point of intercept. 15 STABILIZER SYSTEM AND OMNI TRACKER 1.5.1 Description - The stabilizer system is a yaw and roll axis stabilizer which is capable of performing short term heading hold as well as omni navigation course functions. It may also be used as a- stabilizer back-up option, providing a “standby‘’ system to maintain the yaw and roll modes of flight with the Edo-Aire Mitchell Century |l and llI autopilots. Its principal components are a rate gyro and servo amplifier combined, a small panel mounted on- off switch, a panel mounted azimuth trim switch, a control wheel mounted azimuth disconnect switch and an aileron servo assembly. See Fig. 1-14. 15.2 Basic Operation - The rate gyro used in the stabilizer has only one gyro wheel. It is inclined at a 450 angle (with reference to the fore and aft center line of the fuselage) which permits sensing in both the yaw and roll axis. The rotating gyro wheel is retained by a moveable gimbal which is centered by a pair of calibrated springs. A metal vane attached to the moveable #nbal changes the flux gap of an electrical pickoff to provide gyro error signals, which are sent to the servo am- plifier. The electronic gyro-amp accepts the error signals from the rate gyro and through the process of mixing and comparing like and unlike voltages determines the DC polarity and how much of the corrective signal shall be fed to the aileron servo motor. See Fig. 1-15. The servo motor is a geared, DC, electrically reversible motor, which is engaged or disengaged to a cable capstan by a solenoid operated idler gear. The cable capstan has a short length or aircraft control cable {(commonly called a bridle), wrapped around it, usually one or more turns, with the ends mechanically fastened to the aircraft control cables. Therefore, the rotational torque generated at the capstan is transmitted to the aircraft control cables. The omni tracker is an option which can be plugged into the stabilizer system which permits radio navigation course functions. The same signal that is generated by the omni converter to move the course needle is used by the electronic radio tracker. The processed omni signal is summed with the rate gyro signal in the servo amplifier to drive the aileron servo motor. This maintains the aircraft on an omni radial. See Fig. 1-14. When used as a stabilizer back-up option, a small relay chiangeover box is added to the installa- tion. This relay box is usually remotely located and contains the relay which automatically engages the stabilizer system when the autopilot system is in the “OFF"* position and the back- up system switch is in the ““ON"’ position. When installed as an autopilot back-up system, the stabilizer uses the same roll (aileron) servo as installed with the autopilot and requires no additional servo. Issued: Jan. 1973 ' . Page 1-19 TO WHEEL SWITCH TRIM ON/OFF KNOB SWITCH \ TRACKER STABILIZER 0] STABILIZER/TRACKER SYSTEM FIGURE 1-14 STABILIZER AILERON DETECTOR RATE NETWORK TRACKER BLOCK DIAGRAM - STABILIZER/TRACKER FIGURE 1-15 Page 1-20 Issued: Jan. 1973 1.6 1.6.1 1.6.2 AUTOMATIC TRIM SYSTEM Description - The automatic trim system provides an automatic means of positioning the pitch control trim system to relieve the pilot or autopilot of pitch change pressures. When an aircraft is placed in a climb or descent configuration, or a power change is initiated, (and on some aircraft as fuel is consumed), an attitude change occurs. This causes a deflection of the control surfaces into the moving slipstream, which creates a force that is fed back through the contro! column to the pilot. To relieve this control pressure, the pilot activates a trim sensor switch mounted on the control wheel which enables the automatic trim system to operate, there- by reducing the fatigue of the pilot. When the Century 11l autopilot is “ON" (pitch mode), the automatic pitch-trim system is in constant operation and no special manipulation is required by the pilot. This provides another added bonus! When the autopilot is switched “OFF* it always hands the aircraft back to the pilot in a ““Trimmed’’ condition. Basic Theory of Operation - The automatic pitch trim system consists of three basic units, a trim sensor, a pitch trim servo amplifier, and a pilot’s wheel mounted control switch. See Fig. 1-16. The trim sensor is an assembly consisting of a fixed mounting plate with two adjustable contacts and a sliding or rotating bar with a common contact, which is attached to pulleys that ride on the “UP*” and “DOWN?" elevator cables. Cable tension operates the moveable portion of the trim sensor which initiates appropriate trim action. See Fig. 1-17.. Since both types of sensor assem- blies work by the same principle, only the sliding bar type, (the most common) will be used for the example. The pitch trim servo and amplifier are normally installed on the same mounting bracket. See Fig. 1-18. The pitch trim servo is a geared, DC, electrically reversible motor. The servo capstan has a short length of aircraft control cable (bridle) wrapped around it with the ends mechanically fastened to the trim control cables. Therefore, the rotational torque generated at the servo cap- stan is transmitted to the trim cables. The pitch trim amplifier supplies the operating power for the servo. It is a dual sided amplifier, one side of which runs the servo motor in a clockwise direction; the opposite side runs the servo motor in a counterclockwise direction. The contacts on the trim sensor merely determine which side of the dual amp will operate, and for how long, theréby causing the servo motor to run in the desired CW or CCW direction and for the proper amount of time. The pilot’s wheel mounted switch is usually installed in the left side of the control wheel and can be operated with the left thumb. The pilot uses this switch to trim out the control forces when the autopilot is not engaged. Since the trim sensor works on the principle of ‘“Tension’’ on the control cables, an under- standing of how that. tension is applied to and removed from the controls is necessary. The ~ pilot or autopilot, applies it by moving the control yoke fore or aft. This displaces the elevator . or pitch control into the moving slipstream. This is perfectly normal and is the pilot’s way of controlling or making the aircraft do what he wants. There are two control cables connected between the control yoke to the elevator or pitch con- trol. Both cables will be pulled respectively for “UP" or “DOWN" deflection of the elevator or pitch control. Obviously, you can not push on a flexible cable and get any work out of the other end. Issued: Jan. 1973 Page 1-21 TRIM TAB TRIM AMPLIFIER - TRIM SENSOR —_ - STABILIZER .’ ELEVATOR CONTROL WHEEL SWITCH A+ FROM AIRCRAFT 8USS A+ FROM | AUTOPILOT BLOCK DIAGRAM - AUTOMATIC TRIM SYSTEM FIGURE 1-16 When the pilot pulls the control yoke aft, the control cable is pulled that will deflect the trailing edge of the elevator "UPWARD” into the slipstream. The slipstream immediately tries to return the deflected control surface to a neutral or “Streamlined’’ position, which it will do unless the pilot holds aft pressure (pulls) on the control column with an equal force that will maintain the control surface in its deflected condition. It is this pulling on the control cable which places it under tension. The opposite (down) control cable will not have tension on it, at this time, as it is not performing any work. In fact, under the above conditions, it could be removed however, when the situation is reversed, it will be needed for the downward pull. On long cross country flights, the continuous effort of constant pressure on the control column is very tiring for the pilot. To minimize the fatigue problem and to aid in aircraft control, trim tabs are used. They are a small auxiliary control or portion of a primary control which is hinged and built into or mounted on the primary control. In this case, it will be used for pitch trim. It is the trim tabs that remove the ““tension” from the aircraft control cables. The trim tabs work by the very same principle as the elevators. They are deflected into the slipstream by the pilot. However, they are not a free floating type of control. Once they are positioned by the pilot or the pitch trim servo, they will remain in that position until moved again by the pilot or auto- matic trim. They are not connected to the control yoke, but are usually operated by a small hand wheel or crank and aircraft cables (trim cables). They cannot streamline themselves and . must be manually operated both ways. Page 1-22 Issued: Jan. 1973 COMMON UP o - CONTACT "UP/ ELEVATOR CABLE CONTACT ""DOWN"* ELEVATOR CABLE (A) IIUPII ELEVATOR CABLE DOWN CONTACT / —— Ve~ N TZZ 772 e e T ey I 77770 ";/7"" KL= ~\ (( ® }, COMMON \\ :’ / “DOWN" - ELEVATOR CABLE ' CONTACT (B) TYPICAL TRIM SENSORS FIGURE 1-17 Issued: Jan. 19_773 Page 1-23 Page 1-24 TYPICAL TRIM SERVO AND AMPLIFIER FIGURE 1-18 Once the pilot deflects a trim tab, the slipstream immediately tries to streamline or neutralize it. Not being free to rotate about its hinge or pivot point, it must move in an up or down direction striving to streamline itself. As it is mechanically attached to the trailing edge of the elevator, it is carried “UP’ or “DOWN" by the trim tab’s action. As the trim tab is deflected more and more into the slipstream, the greater the “UP** or “DOWN" travel of the elevator. Just as an elevator or pitch control flies an aircraft up or down, a trim tab flies an elevator up or down. See Fig. 1-19. Therefore, a properly adjusted trim tab can ““fly* the elevator into the desired defiected position and maintain it there. As the trim tab has now assumed the entire workload, it has removed the tension from the “‘pulled”’ elevator control cable and control yoke. Now that the principle of applying and removing tension to a control cable has been reviewed, it can be applied to the trim sensor. With the elevator surface in a neutral or streamlined position, both elevator control cables will have equal tension. In this position, the comman contact and sliding bar assembly of the trim sensor will be in the ““Neutral’’ position and no trim signal will be generated. See Fgg.1-17(b)' When the elevator is deflected upward, the moving slipstream tries to force it back into the neu- tral position. This force creates a greater tension on the ““UP‘ elevator cable which causes the sliding bar and its contact to slide upward, making contact with the fixed up command contact. See Fig. 1-20. ' This energizes one side of the servo-amp causing it to energize the servo, which begins to move the trim tab in the proper direction. The servo will continue to run until the trim tab is deflected sufficiently to relieve the tension on the up control cable. At this time the sliding bar and its contact will move back to its center or neutral position. This breaks the circuit to the servo-amp which also stops the servo and trim tab. Issued: Jan. 1973 SLIPSTREAM SLIPSTREAM - G~up ELEVATOR ELEVATOR STABILIZER NEUTRAL STABILIZER ELEVATOR % Ooown ELEVATOR TRIM TAB OPERATION FIGURE 1-19 When the elevator is deflected downward, the same sequence of events occur. However, the down command and common contacts now energize the opposite side of the servo-amp and the servo runs in the opposite direction. See Fig. 1-21. Remember! When the autopilot is engaged, the automatic trim system is fully automatic and working 100% of the time. When the autopilot is off, the automatic trim system will not work until the pilot depresses his control wheel mounted trim.switch. The pilot manually positions the contro! yoke to his desired position, then depresses his trim switch which now supplies the power for the automatic trim system. Once the power has been supplied, the system works exactly as before. When the con- - trol forces have been neutralized, the pilot merely releases ‘his trim switch. He can trim the air- craft as often as desired by pressing and releasing his trim switch. Issued: Jan. 1973 Page 1-25 IIUPII ELEVATOR CABLE IR e )] - & -zg": z,,f_zz-«‘iazzzzzz N ELEVATOR CABLE FORCES BAR AGAINST UP CONTACT ol & TRIM SENSOR IN ““UP ELEVATOR" CONDITION FIGURE 1-20 op @] CABLE TENSIONELEVATOR CABLE FORCES BAR AGAINST DOWN CONTACT 77N ) e > 3 .2 MFEZZZZ AT L7 R (e - /{r W W2 N2V “DOWN" ELEVATOR CABLE gl ® TRIM SENSOR IN “DOWN ELEVATOR” CONDITION FIGURE 1-21 Page 1-26 ‘ Issued: Jan. 1973 SECTION Ii AUTOPILOT INSTALLATION DATA The following section contains a parts description, nomenclature and location for each supplemental type certificate (STC) held by Edo Avionics for the Century Il and Il autopilots. This section is arranged alphabetically according to airframe man- facture and then numerical within a specific manufacture according to aircraft model. An index of manufacturers is provided on the following page. In addition to the above mentioned information, the data sheets also contain servicing data which include servo clutch settings, trim sensor joint settings and bridie cable part numbers, At the top of each data page the aircraft manufacturers name, the system (Century 1l or Century 111}, the autopilot kit (AK) and STC numbers and the model(s) covered by the STC are listed. To the left of this page is an outline drawing of the listed aircraft. The circled numbers show location of the various autopilot components and correspond to the numbers in parenthesis under the LOCATION column on the data page. - MOONEY — — — — INDEX AERO COMMANDER- — — AEROSTAR— — — — AMERICAN AVIATION — — BEECHCRAFT- — — — BELLANCA— — — — BRITTEN—-NORMAN- — — CESSNA- — — — — DEHAVILLAND — — — HELIO- — — — — PIPER—m — — — — WREN— — — — — Issued: Jan. 1973 2.1 AERO COMMANDER 100/180 2-2 Issued: Jan. 1973 AERO COMMANDER 'CENTURY II AK293 STC SA1080SW AERO COMMANDER 100/180 | . - PART DESCRIPTIO LOCATION NOMENCLATURE CONSOLE-AMPLIFIER 1C385 ARTIFICIAL HORIZON 52D66 DIRECTIONAL GYRO 52D54 ROLL SERVO 1C363-293R MAIN CABLE HARNESS 30C198 RADIO COUPLER (OPT.) 1C388 . ‘ (1) Instrument panel (1) Instrument Panel (1) Instrument panel - (3) Under floor, pilot’s side, first bay aft of wing strut attach point. (1) Instrument panel SERVICING DATA - Roll Servo Clutch Setting (lbs): 35+ 5 Pitch Servo Clutch Setting (lbs): itch Trim Servo Clutch Setting (Ibs): - #'rim Sensor Point Gap (in.): Roll - 30B221 Bridile Cable(s): Limitations Placard Part Number: 13A344-293 AERO COMMANDER 500A, 5008, 500U, AND 500S 24 Issued: Jan. 1973 AERO COMMANDER CENTURY Il AK221 , . 'STC SAG80SW AERO COMMANDER 500A, 5008, 500U, AND 5008 PART DESCRIPTIONAND NOMENCLATURE LOCATION ROLL SIGNAL FILTER 1B440 _ CONSOLE 1C404 ARTIFICIAL HORIZON 52D67 DIRECTIONAL GYRO 652D54 ROLL SERVO 1C465-1-221R PITCH SERVO 1C470-1-221P ALTITUDE HOLD 1C4071 MAIN CABLE HARNESS 30D207-6 RADIO COUPLER 1C388 TRIM SERVO 1C469-1221 TRIM SENSOR 1C365-221 TRIM SWITCH 4045 AMPLIFIER 1C515-1 OR 1C395 NOTE: AK353 SA1394SW with " (6) On forward cabin bulkhead above air duct, right side (middle} (1) Under instrument panel near artificial horfzon {1) Lower portion of pedéstal " (1) Instrument panel (1) Instrument panel (3) Under inspection plate in center floprboard (4) Under center floorboard, just aft of roll servo (1)_ Instrument panel (7) Just forward of Station 252.0 in aft fuselége at top (é) Mounted at bulkhead station 198 at bottom of aft fuselage,.center Left side of pilot’s control wheel - {2) Under floorboard between roli and piich servos Command/Electric Trim SERVICING DATA Roll Servo Clutch Setting {lbs): 35+ 5 Pitch Servo Clutch Setting (lbs): 20+ 2 Pitch Trim Servo Clutch Setting (lbs): 20 + 2 “rim Sensor Point Gap (in.): .010 + .002 dridle Cable(s): Roll - 30B262. Pitch - 30B263 Limitations Placard Part Number: See AFM Supplement ~ AERO COMMANDER CENTURY Ili AK270 N STC SA929SW AERO COMMANDER 680FL 1 ' ION _ PART DE%%RIPT 0 LOCATION NOMENCLATURE CONSOLE - 1C404 (1)}Lower portion of pedestal . ARTIFICIAL HORIZON 52D67 DIRECTIONAL GYRO 52D54 - ' BOLL SERVO 1C465-1-270R PITCH SERVO 1C470-1-270P ALTITUDE HOLD 1C407 MAIN CABLE HARNESS 30D207-7 RADIO COUPLER 1C388 TRIM SERVO 1C469-1-270 TRIM SENSOR 1C365-270 TRIM SWITCH 40545 AMPLIFIER 1C515 ' (1) Instrument panel - {1} Instrument panel {3) Under floor befween pilot’s seats {4) Under floor just aft of Station 178.812. Remove center floor panel in baggage compart. (6) On forward cabin bulkhead on top of air duct, on right side of A/C C/L (1) Instrument panel " {7) Aft of fuselage on A/C C/L, just forward of Station 328.0 at top of fuselage - - (8) At bulkhead Station 254.0 at bottom of buselage on A/C C/L Left side of pilot’s control wheel {2) Forward of Station 5.50, lower section right side in radar compartment SERVICING DATA Roll Servo Clutch Setting (lbs): 35+ 5 Pitch Servo Clutch Setting (lbs): 20+ 2 . _ Pitch Trim Servo Clutch Setting (lbs): " Trim Sensor Point Gap (in.): .010 + .002 Jridle Cable(s): Roll - 30B262 Pitch - 30B263 Limitations Placard Part Number: See AFM Supplement 20+3