Pilot's Operating Handbook for the Piper J-3 Cub

Elevator Area (Two Sides)-10.64 Sq. Ft. Stabilizer Span (Overall)-9′ 6″ Horizontal Tail Aspect Ratio-3.57 Fin Area 4.02 Sq. Ft. Rudder Area 6.55 Sq. Ft. Rudder Height—4′ 5″ Aileron Chord-13½" Aileron Span-8′ 6″ Aileron Area (Each)—9.6 Sq. Ft. Wheel Tread-71" (Static) Tire Size 8.00 x 4 Wing Leading Edge to Axle Centerline-21" Axle Centerline to Tail Post-15'7" Tail Wheel Size-6 x 2.00 Height of Upper Surface of Wing Above Ground 6'8" level, 6' 5" 3-Point vi SERVICE MANUAL- PIPER CUB TRAINER SECTION I WING WING: The wing on the Piper Cub Trainer embodies the general type of construction used in ear- lier model Cubs with several noteworthy revisions. The wing spars are solid Sitka Spruce, rectangular in cross section with plywood plates glued to the faces of the spars at the wing strut fittings. Very little maintenance is required on the spars other than an occasional inspection of the spars at the fittings to ascertain that no looseness exists in the fitting attachments. DRAG BRACING: The drag bracing consists of tubular drag or compression struts bolted at the ends to the spars. At major overhauls of the wing panel, these compression struts should be inspected for corrosion or bowed condition. The drag wires are No. 6-40 tie rods with right hand thread at each end. These tie rods are made of high strength steel and should not be replaced with soft steel wire. It is recommended that a regular inspection of the drag wire installation be conducted to insure proper rigging and to see that the end connections are in good condition and free from corrosion. In rigging the tie rods, care should be taken in adjusting the tension to avoid marring the rod with plier or wrench marks as any scratches may induce a fatigue failure. The locknut at the end of the adjusting nipple should not be drawn up too tightly as a high stress may result. This comment also applies to rigging the tie rods. You will note that pyralin grommets have been installed on the under surface of the wing to facilitate inspection of the drag bracing. WING RIBS: The wing ribs, 12 of which are used in each panel, are constructed of aluminum alloy drawn sections riveted together with "Thompson" type rivets. The ribs are attached to the spars by means of wire brads. Past experience over a period of years indicates that the material used in the ribs is highly corrosion resistant; however, an occasional examination of the ribs to check for loose rivets or corrosion (particularly when the airplane is used in a salt air atmosphere) is advis- able. If any evidence of corrosion is noted, the advance of this may be forestalled by cleaning the surface and coating with Lionoil or any good grade of spar varnish. LEADING EDGE: The wing leading edge is covered with light gauge aluminum alloy sheet which extends back from the leading edge on upper and lower surfaces approximately halfway to the front spar. Aluminum alloy channels between the sheet metal cover and the ribs add stiffness to the surface. About the only maintenance necessary on the leading edge is an occasional examination for corrosion or looseness. Care should be taken in handling the leading edge to prevent denting the aluminum cover sheets. WING TIP BOW: The wing tip bow is a formed ash strip attached to the front and rear wing spars by steel fittings. This member is also secured to the aluminum leading edge and to the trailing edge of the wing rib nearest the tip. Rough handling of the airplane on the ground may damage the tip bow, so care should be taken when handling by means of the wing tips to apply force only at the juncture of the spars with the wing tip bow. AILERON FALSE SPAR: The aileron false spar is a formed aluminum alloy channel attached to the wing ribs by means of self-tapping sheet metal screws. Inspect the false spar to check for looseness of the attaching screws or corrosion. Be sure that all drain grom- mets in the wing trailing edge are kept open so that accumulations of moisture will drain out of the wing. AILERON HINGE BRACKETS: The aileron hinge brackets are made of tubing with sheet metal fittings for attachment to the wing spar and to the aileron false spar. These brackets must be kept securely attached to the wing structure and should be inspected occasionally for corrosion or looseness. SERVICE MANUAL-PIPER CUB TRAINER г SPAR FITTINGS: The spar butt fittings and strut fittings are made of carbon steel plates and are bolted to the spars with AN standard steel bolts. An occasional inspection to see that all nuts are drawn snug should be made. At this inspection period the bolts attaching the wings to the fuselage should be examined to see that they do not have excessive play and that all nuts are cottered. LIFT STRUTS: The lift struts are streamlined tubes attached to the wing and fuselage by means of AN standard steel bolts. In inspecting the struts, check for nicks or dents and see that the jury strut attaching clamps are in place. It is only necessary to draw jury strut clamp bolts snug, as excessive tightening may break the bolt or crush the wing strut. In handling the airplane on the ground care should be taken to prevent damage of the lift struts by pushing or lifting in the middle of the strut. Frequent inspections for corrosion of the struts should be made and if any corroded spots are found, these should be sanded down to the bare metal with fine sandpaper and metal primer should be applied. After the primer has dried, a finish coat of the desired color may be added. 2 ). SERVICE MANUAL-PIPER CUB TRAINER SECTION II RIGGING PROCEDURE RIGGING PROCEDURE: Raise the forward part of the airplane so that the wheels are just clear of the ground and support it by props under the front landing gear fittings. Raise the tail to approximate level flight position and support it there. LEVELING: Level the airplane as follows: Laterally: Using a level 30 inches long, place it across the center of the rear seat with the ends resting on the longerons. Due to the right upper longeron being ½ inch lower than the left, a ½ inch block is used under the right end of the level. Adjust the blocks under the landing gear fittings to bring the bubble to the center. Longitudinally: Place the 30-inch level along the upper left longeron in the cockpit. Raise or lower the tail to bring the bubble to the center. DIHEDRAL ANGLE: To check the dihedral angle at the front spar proceed as follows: Stretch a string along the top of the wings above the front spar, from wing tip to wing tip, and draw it tight. Check the dimension vertically from the front edge of the center section to the string. For correct dihedral this dimension should be 23 inches. On earlier models the dihedral dimension should be checked from the fuselage front spar fitting and the correct dimension should be 4½ inches. Obtain this dimension by adjusting the front struts in or out. To check for equal dihedral in each wing proceed as follows: Using the 30-inch level (without any spacer blocks) hold it spanwise against the bottom of the wing under the front spar in the space between the jury struts and lift strut attachments. Note the position of the bubble and do the same on the other wing. Re-adjust the front struts until both wings show the same amount off-level, being careful with each adjustment to set the left strut out the same number of turns as the right one is set in, and vice versa. WASH OUT: To adjust the wash out in the wings (dihedral of the rear spar) proceed as follows: Set a 3/8 inch spacer block on top of the 30-inch level at one end. Working on the rib adjacent to the outer end of the aileron, hold the level fore and aft along the bottom of the rib with the spacer block at the rear and the front end of the location of the front spar. The correct wash out will exist when the bubble is centered. Adjust the rear struts in or out to obtain this condition. TAIL ASSEMBLY: With the airplane in level position the stabilizers should be leveled at their rear spars. The hinge line should be straight from tip to tip. Plumb the fin at the rudder hinges. 3 SERVICE MANUAL-PIPER CUB TRAINER SECTION III CHASSIS CHASSIS: The main gear on the Cub Trainer consists of individually sprung wheels on which are mounted low pressure tires. TIRES: 8.00 x 4. It is important that the tires be kept fully inflated to 12 lbs. per square inch pres- sure at all times, as operation of the hydraulic brakes when the tires are soft may cause the tires to creep with consequent damage to the valve stem. It is advisable when installing a tire on a wheel to check to make certain that the beads on the tire are seated on the wheel rim. The tire should then be inflated to about 35 pounds pressure to force the tire beads out onto the taper of the rim. Air should then be let out until the correct pressure of 12 pounds per square inch is reached. This will assist materially in preventing tire "creep.” At the first sign of wear on the tire, reversing the tire on each wheel will equalize wear and give longer tire life. WHEELS: Cast aluminum wheels with Timken tapered roller bearings are lubricated at the factory and should not require additional lubrication for several hundred hours. When remov- ing wheels, dust and dirt should be kept out of the bearings. When reinstalling wheels or to remove end play in wheel on axle, do not tighten axle nut enough to cause binding of the roller bearings as this will result in excessive wear. The proper procedure in adjusting the axle nut is to tighten nut while rotating wheel until a slight drag is felt, then back nut off one castellation and cotter. WHEEL BRAKES: (OPTIONAL) A full hydraulic system of individual wheel braking is used. Heel type brake pedals are mounted one on each side. The rear seat installation is standard, front seat installation, optional. The pedals are mounted on a bearing shaft which is located under the floor and pressure on the pedal is transmitted through a push rod to a master cylinder. Each pedal is thus connected to a master cylinder for individual control of the wheels for ground maneuvering. In early airplanes of this model, the reservoir for the storage of brake fluid is located on the floor under the front seat, while later airplanes have this reservoir mounted on the engine side of the fire- wall. It is important that this reservoir be kept filled with genuine Lockheed Fluid as any air bubbles introduced into the line due to a low fluid supply will cause a loss of brake effectiveness. This fact should be kept in mind when any work is done on the brake system. An indication of air in the brake lines is found in a "fading pedal," that is, pressure applied to the pedal will cause the pedal to travel to its limit without the usual solid feeling. To remove the air or to "bleed" the system, follow this procedure: 1. Airplane on level ground with tail down. 2. Fill reservoir with brake fluid and keep filled with Lockheed Fluid during "bleeding” opera- tions. 3. Place clean vessel under the bleeder valve located at connection of brake line with wheel. 4. Press brake pedal down slowly while another person opens bleeder valve. Close bleeder valve before end of pedal travel is reached. 5. Allow brake pedal to return to "Off" position with the bleeder valve closed. 6. Try pedal for solid feeling and braking action. It may be necessary to repeat the above opera- tions, No. 4 and No. 5, several times. The fluid drained from the bleeder valve may be used again if no foreign matter such as dust or dirt is present. ( SERVICE MANUAL-PIPER CUB TRAINER It may be well to remember that air may be introduced into the lines if any fitting is disconnected. Care should be taken to prevent brake fluid from getting on brake linings during bleeding operations. Under no conditions should brake pedals be operated when wheels are removed as the brake linings may be sprung out of their housings causing damage to the linings or springs. The operating prin- ciple of these brakes depends upon the expansion of a rubber bag under the segments of brake lining. Lubricating oil will damage the system and for this reason only genuine Lockheed No. 21 Brake Fluid should be used. As this fluid will damage doped or lacquered surfaces, care should be taken to prevent spilling the liquid. A routine inspection of the brake system for leakage is advisable. LANDING GEAR FITTINGS: All hinge fittings should be lubricated regularly with engine oil and a check for wear or looseness should be made. As the hinge fittings are bushed with steel inserts, these may be replaced to remove play. Bolts should also be inspected for End play should be removed by the wear and replacement should take place at the first signs of wear. insertion of washers of correct thickness. TAIL WHEEL: (OPTIONAL) Tire size is 6 x 2.00, solid rubber. Lubricate all bearings frequently. 5 SERVICE MANUAL-PIPER CUB TRAINER SECTION IV FUSELAGE FUSELAGE FRAME: The fuselage frame is constructed of seamless steel tubing welded at the joints to form a rigid structure. A number of highly stressed members are of chrome-molybdenum steel; all other members are of 1025 steel. If it becomes necessary to replace any fuselage members, sleeve type splices should be made in accordance with practices outlined in Chapter CAAM 18 of the Civil Aeronautics Manual. Use only aircraft grade of tubing confirming to AN specifications and if the original material specifications are not known, consult the Service Department of the Piper Aircraft Corporation or use chrome- molybdenum tubing. . After replacing members, clean scale from the welded joints and apply an effective protective coating, such as zinc chromate primer, to prevent corrosion. If the fuselage has been "Metallized" for corrosion proofing, remove all of the “Metallized" coat- ing from the area which is to be welded. This is necessary as a satisfactory weld cannot be made over a surface which is covered by the "Metallizing." This cleaning is best accomplished by painting a strong solution of sodium hydroxide (caustic soda) over the area to be welded. This caustic soda is obtainable from drugstores. Apply sufficient of this solution to clean off all traces of the aluminum "Metallizing" and then rinse thoroughly with water. Accumulations of dirt in the cockpit and in the crevices between the fuselage tubes and the cloth covering should be removed occasionally as moisture will be absorbed by the dirt with the possibility of corrosion or fabric rot. A regular inspection of the lower longerons near the tailpost should be made to guard against corrosion. ENGINE MOUNT: The engine mount is similar to the fuselage in construction. An occasional check of the bolts attaching the mount to the fuselage should be made to see that these bolts and also the engine attaching bolts are snug. Do not draw these bolts too tight as a failure in one of the bolts may result. It should be remembered that terrific loads can be put on a bolt by overtightening. In handling the plane on the ground, care should be taken to prevent the application of loads at points other than fuselage clusters as bowed or kinked members may result. Wood fairing strips are used to give the fuselage its form and these may be damaged by rough handling. 9 SERVICE MANUAL-PIPER CUB TRAINER SECTION V CONTROL SURFACES AILERON: The aileron structure is of aluminum alloy with fabric covering. A channel runs the length of the aileron and serves as a main spar to which is attached the nose former ribs, nose cover sheet, trailing edge, ribs, hinges, and horn fittings. Soft aluminum rivets are used to attach the component parts to the spar. When it becomes necessary to recover the aileron, it is advis- able to check all riveted joints for looseness. The security of the hinges and control attachment should be determined. Lubricate hinges occasionally with light engine oil and check for cotter pins in hinges. VERTICAL FIN: The vertical fin has a steel tube leading edge and rear post. The ribs are of low carbon steel channel. A short stub of steel tube is welded to the lower end of the leading edge spar and fits into a tubular socket in the fuselage. An AN bolt fastens these parts to- gether. During periodic inspections these bolts should be checked for tightness and cotter pins. RUDDER: The rudder has a steel tube leading edge and trailing edge and channel steel ribs. No maintenance other than an inspection for corrosion during overhaul is necessary. Drain grommets in the rudder cover should be kept open. The hinges attaching the rudder to the tailpost and fin rear spar should be lubricated with light engine oil. Accumulations of dust and dirt on hinges should be removed. STABILIZERS: The stabilizers have a and channel steel ribs. steel frame consisting of tubular leading and trailing edges The leading edge has a tubular steel liner inside the front spar joining the two sides of the stabilizer. A stabilizer yoke is attached thereto through which an adjusting screw passes. A pulley on the lower end of the screw is turned by means of an endless cable from a crank on the left side of the cockpit. By means of this mechanism the incidence of the stabi- lizer may be adjusted over a range of several degrees. A tubular steel liner joins the two sides of the stabilizer at the trailing edge and this liner passes through a short tube installed in the fuselage. An occasional check should be made to see that the bolts attaching the leading and trailing edges to the liners are drawn snug and that cotter pins are in place. Steel tie rods brace the stabilizers to the fin and fuselage. These tie rods should not be rigged tighter than necessary as high loads may be imposed on other parts of the tail surfaces or fuselage. It should be remembered that even with the tie rods rigged "flabby," they will be tensed by a very slight deflection of the surfaces and thus will do their work as well as if they were rigged very tightly. In adjusting the tension of the tie rods, care should be taken so that marring of the rods will not re- sult. Friction tape should be wrapped around the rods near the threads. Pliers may then be used to grip the wires but be certain to grip on the tape. The nipple may then be turned with a wrench after the lock nuts have been loosened. The threads at each end of the rod must be visible through the end of the nipple. A line inspection of the tie rod end fittings should be made to check cotter pins and lock nuts. ELEVATORS: The elevator structure is very similar to the rudder. No maintenance other than in- spection for corrosion is needed. The hinges attaching the elevators to the stabilizer should be cleaned and lubricated with light engine oil at frequent intervals. A final word of caution in regard to proper care of the tail surface bracing. Do not use the tail tie rods for purposes of lifting or handling the airplane. See that this rule is adhered to strictly. 7 SERVICE MANUAL-PIPER CUB TRAINER SECTION VI CONTROL SYSTEM ELEVATORS: The fore and aft motion of the control sticks is transmitted back through the fuse- lage by means of the following linkage. The sticks are mounted on a torque tube which passes beneath the front seat above the floor board. The lower ends of the sticks are connected to a push-pull tube which passes through the torque tube and imparts action to a bellcrank located behind the rear seat. Two ½ inch 7 x 19 cables are attached to this bellcrank and are connected at the rear to the elevator horns by means of turnbuckles. The principal control system parts and brake master cylinders which are located below the floor are readily serviced and inspected by removing the inspection plates on the belly of the ship. An occasional lubrication of the elevator bellcrank located behind the rear seat will reduce con- trol system friction and prolong bearing life. AILERONS: The lateral motion of the control stick rotates the torque tube, to the rear end of which is attached an aileron control arm. Control cables are attached to this control arm and pass through composition fairleads at the edge of the floor, up the rear edge of the front lift strut to the wings. Where the cables enter the wings, as well as at turns within the wings, they pass over composition pulleys. Passing through the wing to the rear they are connected to the upper aileron horns. A balance cable connecting the lower aileron horn in each wing passes along the rear of the front spar. Lubricate all moving parts in the aileron system regularly with light engine oil to reduce friction. Inspect all cabes for wear at pulleys and fairleads. If it becomes necessary to rig the ailerons, the following method should be employed: 1. Locate control sticks at midpoint of lateral travel. 2. Line up trailing edge of aileron with the inboard wing trailing edge. 3. If the aileron is too high, open the turnbuckle on the cable attached to the upper aileron horn If the and then draw up turnbuckle on cable attached to lower aileron horn the same amount. aileron is too low, the above turnbuckle adjustments are in reverse. 4. Check to see that there is no play or looseness in the action of the ailerons when the control stick is moved. 5. Safety all turnbuckles and nuts. It may be necessary to check through the rigging several times in order to get the proper positioning of all parts. RUDDER: The rudder control system is fairly simple and very little maintenance is necessary. In- spect control cables at the fairleads under the seat, and those just ahead of the point near the tail where the cables pass through the fuselage cover. See that rudder pedal return springs are operating to hold the pedals forward. STABILIERS: The stabilizer is operated by a crank located on the left side of the cockpit. An endless, stranded cable passes around a V groove pulley attached to the crank, then back through the fuselage to another V groove pulley on the lower end of the stabilizer adjusting screw. Turning the crank forward or backward rotates the screw which in turn raises or lowers a stabilizer yoke attached to the front of the stabilizer. This alters the angle of incidence which compensates for "nose heaviness" or "nose lightness." Under no circumstances should the stranded cable from the cockpit to the rear of the fuselage be lubricated as this may cause slippage. If it becomes necessary to increase the tension in this cable, an idler pulley adjusting nut is located at the tail near the front of the stabilizer and is accessible by removal of the inspection plate on the left side of the fuselage. Do not tighten this nut excessively as binding of the driving mechanism may result. The stabilizer indicator consists of a fine wire passing back from the control crank in the cockpit, over a composition pulley in the tail of the fuselage, to the stabilizer yoke. If any adjustments are made to the stabilizer indicator system, check to assure correct functioning of the stabilizer. A return spring on the stabilizer indicator mechanism is located above the stabilizer operating crank and is accessible by removal of the indicator face plate. 8 SERVICE MANUAL-PIPER CUB TRAINER SECTION VII FUEL SYSTEM FUEL TANK: The fuel tank is located in the fuselage just behind the firewall, and has a capacity of twelve gallons (U. S.). This fuel tank is supported by flat steel straps lined with felt to prevent chafing. If it becomes necessary to remove the fuel tank, drain fuel, disconnect fuel line and shutoff valve control shaft. Remove filler cap and all lines and controls which run under the tank to the instrument panel. Then remove the diagonal fuselage tube running from the upper right longeron to the center of the fuselage cross tube at the floor behind the firewall. This is easily done by removing the bolt in each end of the tube, sliding the tube upward until it clears the lower fitting, and then sliding it downward outside the lower fitting. The tank may then be removed from the cock- pit without removing the cowling. PRIMER: A primer to assist in starting the engine is mounted on the instrument panel. A fuel line runs from a gascolator up to the primer pump and a return line runs back to the engine. Always see that the primer plunger seats firmly as irregular operation of the engine may re- sult from a leaking needle valve in the primer pump. CARBURETOR HEATER: A carburetor heater is installed on the engine and is controlled by a push-pull control on the left side of the cockpit by means of which the pilot can regulate the temperature of the air entering the carburetor. For most economical and effi- cient operation, set the heat control to provide just enough heat to result in smooth operation of the engine. Excess heat merely reduces power. It is always advisable to set heat control to "Full On" position during long glides such as an approach for a landing as this will tend to keep the engine warm and reduce the possibility of the engine failing to accelerate when the throttle is opened suddenly. Extreme care should be taken in hot weather to see that no carburetor heat is used otherwise over- heating of the engine may result. The points of the fuel system which require regular servicing are: Gascolator or fuel strainer. 1. 2. Drain in fuel tank. 3. Strainer in fuel tank. FUEL STRAINER: The gascolator is located in the engine compartment and should be inspected daily for accumulations of water or sediment. It is a good habit to remove bowl and screen from the fuel strainer at least every ten hours and clean both and flush the lines by allowing fuel to flow through with bowl removed. Always safety nut under bowl after servicing. TANK DRAIN: A drain is located at the rear of the gasoline tank and is accessible from the cock- pit. Remove the drain plug at frequent intervals to allow water and sediment to drain from the tank. TANK STRAINER: A finger strainer is located in the fuel tank outlet fitting to which the fuel line attaches. This finger strainer is intended to prevent large particles of foreign matter entering the fuel lines. The finger strainer should be removed and cleaned every 100 hours by removing the fuel line and all fittings from the bottom of the tank. 0