AC 43.13-1А Page 141 1972 Chapter 8. AIRCRAFT EQUIPMENT Section 1. LANDING GEAR EQUIPMENT
326. GENERAL. Many factors affect the scope and frequency of landing gear aystem inspection and maintenance. The possibility of system malfunction increases with severe operating conditions, such as pilot training and agricultural operations. Cracks are the foremost area of concern, followed closely by worn, sheared, bent, or broken bolts, and elongated boltholes, Although these defects occur during normal aircraft usage, adverse operating conditions accelerate the problem.
Improper adjustment or lubrication can also cause malfunctioning, especially in landing gear retraction mechanisms. Excessive lubrication or the wrong type of lubricant can often be as bad or worse than none at all. With regard to lubrication, closely follow the manufacturer's service and maintenance instructions.
residue around bolts, rivets, and pins is a good indication of looseness or wear, Thoroughly clean and re-inspect the landing gear to determine the extent of any damage or wear. Some components may require removal and complete disassembly for detailed inspection. Others may require a specific check using an inspection process such as dye penetrant, magnetic particle, radiographic, ultrasonic, or eddy current (see Chapter 7). The frequency, degree of thoroughness, and selection of inspection methods are dependent upon the age, use, and general condition of the aircraft.
Inspect the aircraft structure surrounding any visible damage to insure that no secondary damage remains undetected. Forces can be transmitted along the affected member to remote areas where subsequent normal loads can cause failure at a later date.
CAUTION Inspect grease fittings after applying high pressure lubricant to determine that the spring-loaded ball has reseated, Failure of the ball to reseat is an indication of an internal fallure of the fitting which can result in serious damage to the part
327. INSPECTION. Inspect the aircraft landing gear and all associated hardware closely for cracks, cleanliness, lubrication, leaks, deformation, excessive wear, and security of attachments. Before removing any accumulated dirt, cloaely observe the area being inspected while the wingtips are gently rocked up and down.
Excessive motion between normally close fitting components may indicate wear, cracks, or improper adjustment. If a crack exists, it will generally be indicated by dirt or metallic part!- cles which tend to outline the fault. Seepage of rust inhibiting ofa, used to coat internal surfaces of steel tuber, also assists in the early detection of cracks. in addition, a sooty, olly
a. Types of Malfunctions.
(1) Cracks. Príme locations for cracks on any landing gear are bolts, boltholes, pins, rivets, and welds. The following are typical locations where cracks may develop:
(a) Bolts. Most suaceptible areas are at the radius between the head and the shank, and in the location where the threads join the shank, as shown in figure 8.1.
(b) Boltholes and Pinholes, Cracks primarily occur at the edge of boltholes or pinholes on FIOURE 8.1.Typical bolt cracks.
Chap 8 Par 326
the surface and down inside the bore. (See figures 8.2 and 8.3.)
(c) Riveted Joints or Seams, The usual types of failure in this area are deformation of the rivet heads and skin cracks originating at the rivet holes.
(d) Rod Ends. Cracks and subsequent failures usually begin at the thread end near the bearing and adjacent to or under the jam nut.
(See figure 8.1.)
TYPICAL LANDING GEAR FITTING - CRACKS FIGURE 8.2.-Typical cracks near boltholes.
FIGURE 8.8.- Typical bolthole cracks.
FIGURE 8.4.- Typical rod-end cracks.
Par 327 AC 43.13-1A 1972
(e) Welds. Cracks develop primarily along the edge of the weld adjacent to the base metal and along the centerline of the bead.
(2) Elongated holes are especially prevalent in taper-pin holes and boltholes or at the riveted joints of torque tubes and push-pull rods.
(See figure 8.5.)
FIGURE 8.5.-Typical torque tube bolthole elongation.
(3) Deformation is common in rods and tubes and usually is noticable as stretched, bulged, or bent sections. As deformations of this type are difficult to see, the hands should be passed along the tube to feel for evidence of this discrepancy. Deformation of sheet metal web sections, at landing-gear component attachment points, usually can be seen when the area is highlighted with oblique lighting.
b. Landing Gear Components. The following items are usceptible to service difficulties and should be given attention.
(1) Shock Absorbers. Inspect the entire shock-strut for evidence of leaks, cracks, and possible bottoming of the piston, as this condition causes overloading of landing gear components and contributes to fatigue cracks. Check all bolts, boltholes, pins, and bushings for condition, lubrication and proper torque values.
Grease fitting holes (pressure type) are especially vulnerable to cracks and cross-threading damage. Check all safety wire and other locking devices, especially at the main packing gland nuts.
When assembling shock-struts, use the correct type and number of "O"-rings, chevron seals, and backup rings. Use only the correct filler valve core assembly, and follow the manufacturer's instructions when servicing with fluid and air. Either too much or too little air or oil will affect aircraft handling characteristics during taxi, takeoff, and landing, and can cause structural overloads.
Shock cords and rubber discs deteriorate with age and exposure. When this type of shock absorber is used, inspect for general con- Chap 8
AC 43.13-1A 1972 dition, i.e., cleanliness, stretching, fraying, and broken strands. These components must be kept free of petroleum products as they accelerate deterioration of the rubber.
(2) Nose Gear Assembly. Attention should be given to the steering mechanism and should include items such as: torque-links (scissors), torque-tubes, control rods and rod-end bearings, shimmy dampers, cables, and turning stops. In addition, check all nose landing gear components, including mud scrapers and slush deflectors, for damage from natural elements.
(a) Towing of some aircraft with the rudder locks installed may cause damage to the nose steering linkage and rudder control sygtem. Exceeding the steering or towing stops should be followed by a close inspection of the entire nose steering assembly. A broken steering stop will allow turning beyond the design limit, transmitting excessive loads to structures and to the rudder control system. It is recommended that the nose steering arc limits be indicated on the steering collar or fuselage.
(b) Inspect ahimmy dampers for leakage around the piston ahaft and at fluid line connections, and for abnormal wear or looseness around the pivot points. Also check for proper rigging, "bottoming" of the piston in the cylinder, and the condition of the external stops on the steering collar.
(3) Tailwheels. Disassembly, cleaning, and rerigging of tailwheels are periodically necessary. Inspect for loose or broken bolts, broken springs, lack of lubrication, and general condition. Check steerable tailwheels for proper steering action, steering-horn wear, clearances, and for security and condition of steering springs and cables.
(4) Gear Doors. Inspect gear doors frequently for cracks, deformation, proper rigging, and general condition. Gear door hinges are especially susceptible to progressive cracking, which can ultimately result in complete failure, allowing the door to move and cause possible jamming of the gear. This condition could also result in the loss of the door in flight. In addition, check for proper safetying of the hinge pins and for distorted, sheared, loose, or cracked hinge rivets. Inspect the Chap 8 Page 143 wheelwells for improper location or routing of components and related tubing or wiring which could interfere with the travel of the gear door actuating mechanisms.
(5) Floats. In order to maintain floats in an airworthy condition, frequent inspections should be made because of the rapidity with which corrosion takes place on aluminum alloy metal parts, particularly when the aircraft is operated in salt water. Examine metal floats and all metal parts on wooden or fiberglas floats for corrosion and take corrective action in accordance with the procedures described in Chapter 6. Repair damage to metal floats in the general manner outlined in Chapter 2 pertaining to aluminum and aluminum alloy structures. In the case of wooden floats, make repairs in accordance with general procedure outlined in Chapter 1. Repair fiberglass floats in accordance with the manufacturer's instructions or other acceptable practices.
(6) Skis and Ski Installation. It is advisable to examine aki installations frequently to keep them maintained in airworthy condition. If shock cord is used to keep the ski runner in proper trim, periodically examine to assure that the cord has enough elasticity to keep the runner in its required attitude and the cord is not becoming loose or badly frayed. Replace old or weak shock cords. When other means of restraint are provided, examine for excessive wear and binding, and replace or repair when of cable attachment, both on the ski and the air- such conditions are found. Examine the points SESTE plane structure, for bent lugs due to excessive loads having been imposed while taxiing over rugged terrain or by trying to break loose frozen skis. If skis which permit attachment to the wheels and tires are used, maintain proper tire pressure as underinfiated tires may push off the wheels if appreciable side loads are developed in landing or taxiing.
(a) Repair of Ski Runners. Fractured wooden ski runners usually require replacement. If a split at the rear end of the runner does not exceed 10 percent of the ski length, it may be repaired by attaching one or more wooden crosspieces across the top of the runner using glue and bolts. Bent or torn metal Par 327
runners may be straightened if minor bending has taken place and minor tears may be repaired in accordance with procedures recommended in Chapter 2 relative to repair of metal structures.
(b) Ski Pedestals.
1. Tubular pedestals. Damaged pedestals made of steel tubing may be repaired by using standard tube splices as shown in Chapter 2, figures 2.5 and 2.15.
2. Cast pedestals. Consult an FAA representative on the repair of cast pedestals.
3. Sheet metal pedestals. Repair damaged pedestals made of aluminum alloy sheet in the general manner outlined in Chapter 2.
(7) Wheels. Inspect wheels at periodic intervals for cracks, corrosion, dents, distortion, and faulty bearings in accordance with the manufacturer's service information. In splittype wheels, recondition boltholes which have become elongated due to some play in the through-bolt, by the use of inserts or other suitable means. Pay particular attention to the condition of the through-bolts and nuts. Carefully inspect wheels used with tubeless tires for damage to the wheel flange and for proper sealing of the valve. The sealing ring used between the wheel halves should be free of damage and deformation. In bolting wheel halves together, tighten the nuts to the proper torque value.
Periodically accomplish an inspection to assure the nuts are tight and there is no movement between the two halves of the wheel. Any movement between the wheel halves normally causes elongation of the boltholes. If the wear is too great to be corrected, as stated above, it may necessitate scrapping of the wheel. Maintain grease retaining felts in the wheel assembly in a soft, absorbent condition. If any have become hardened, wash them with a petroleum-base cleaning agent; if this fails to soften them, they should be replaced.
(a) Corrosion of Wheels. Thoroughly clean wheels if corroded and then examine for soundness. Smooth and repaint bare corroded spots with a protective coating such as zinc chromate primer and aluminum lacquer, or some other equally effective coating to prevent further corrosion. Replace wheels having se- Par 327 AC 43.13-1A 1972 vere corrosion which might affect their strength.
(b) Dented or Distorted Wheels. Replace wheels which wobble excessively due to deformation resulting from a severe side-load impact.
In questionable cases, consult the local representative of the FAA concerning the airworthiness of the wheels. Dents of a minor nature do not affect the serviceability of a wheel.
(c) Wheel Bearings. Periodically inspect wheel bearings for condition. Replace damaged or excessively worn parts. Pack bearings with a high-melting-point grease prior to their installation. Avoid preloading the wheel bearing when installing on aircraft by tightening the axle nut just enough to prevent wheel drag or sideplay.
(8) Brakes. Maintain the clearance between the moving and stationary parts of a brake in accordance with the manufacturer's instructions. Disassemble and inspect the brake periodically and examine the parts for wear, cracks, warpage, corrosion, elongated holes, etc. If any of these or other faults are indicated, repair, recondition, or replace the affected parts in accordance with the manufacturer's recommendations. Surface cracks on the friction surfaces of the brake drums occur frequently due to high surface temperatures These surface cracks may be disregarded as seriously affecting the airworthiness until they become cracks of approximately 1 inch in length.
(a) Hydraulic Brakes. For proper maintenance, periodically inspect the entire hydraulic system from the reservoir to the brakes, Maintain the fluid at the recommended level with proper brake fluid. When air is present in the brake system, bleed in accordance with the manufacturer's instructions. Replace flexible hydraulic hose which has deteriorated due to long periods of service and replace hydraulic piston seals when there is evidence of leakage.
Service antiskid units according to the manufacturer's instructions.
(b) Mechanical Brakes. Keep the working parts of mechanically operated brakes free from dirt and foreign matter so the brakes can work freely at all times. Slack in the linkage system must be kept to a minimum.
Chap 8
AC 43.13-1A 1972
(9) Micro-Switches. Inspect micro-switches for security of attachment, cleanliness, general condition, and proper operation. Check associated wiring for chafing, proper routing, and to determine that protective covers are installed on wiring terminals, if required. Check the condition of the rubber dust boots which protect the micro-switch plungers from dirt and corrosion.
328. CLEANING AND LUBRICATING. It is recommended that only easily removable neutral solutions be used when cleaning landing gear components. Any advantage, such as speed or effectiveness, gained by using cleaners containing corrosive materials, can be quickly counteracted if these materials become trapped in close-fitting surfaces and crevices. Wear points, such as landing gear up-and-down latches, jack-screws, door hinges, pulleys, cables, bellcranks, and all pressure-type grease fittings should be relubricated after every cleaning operation. To obtain proper lubrication of the main support bushings, it may be necessary to jack the aircraft.
NoTE: Anytime the aircraft is on jacks, check the landing gear main support bushings for wear. Consult the aircraft manufacturer's overhaul manual for specific wear tolerances.
During winter operation, excess grease may congeal and cause increased loads on gear retraction system electric motors and hydraulic pumps. This condition can lead to component malfunctions; therefore, it is recommended lubrication.
329. EMERGENCY SYSTEMS. Exercise emergency landing gear systems periodically to insure proper operation and to prevent inactivity, dirt, and corrosion from rendering the system inoperative when needed. Most emergency systema employ either mechanical, pressure-bottle or free-fall extension capabilities. Check for proper safetying of triggering mechanisms, and for the presence of required placards and Chap & Page 145 necessary accessories such as cranks, levers, handles, etc.
330. SPECIAL INSPECTIONS. Any time an aircraft has experienced a hard or overweight landing, it is recommended that a special structural inspection, which includes the landing gear, be performed. Typical areas which require special attention are landing gear support trusses for cracked welds, sheared bolts and rivets, and buckled structures; wheels and tires for cracks and cuts; and upper and lower wing surfaces for wrinkles, deformation, and loose or sheared rivets. If any damage is found, a detailed inspection is recommended.
331. RETRACTION TESTS. Periodically, perform a complete operational check of the landing gear retraction system. Inspect the normal extension and retraction system, the emergency extension system, and the indicating and emergency warning system. Determine that the actuating cylinders, linkage, slide tubes, sprocketa, chain or drive gears, gear doors, and the up-and-down locks are in good condition and properly adjusted and lubricated. In addition an electrical continuity check of micro-switches and associated wiring is recommended. Only qualified personnel should attempt adjustments to the gear position and warning system microswitches and then only by closely following the manufacturer's recommendations.
332. TIRES. It is essential that tires be inspected frequently for cuts, worn spots, buiges on the sidewalls, foreign bodies in the treads, and tread condition. Defective tires may be repaired or retreaded in accordance with the following paragraphs. The term, "retread," for the purpose of this advisory circular, refers to the several means of restoring a used tire, whether by applying a new tread alone or tread and sidewall material in varying amounts. It refers as well to the process of extending new sidewall material to cover the bead area of the tire. Aircraft tires are identified by type and rating (figure 8.6).
Par 327
rage 146 AC 43.13-1A 1972 MF G under (b) Bead injuries that exceed the limits Type FAR 87.167 Design and rating outlined in paragraph (1) (a) or affect the seal (TSO C62) of the bead on tubeless-type tires.
No_. Smooth contour.! (c) Evidence of separation between plies No. - High pressure.! or around bead wire.
Yes_ Low pressure.? (d) Injuries requiring reinforcement.
V_ VI_ IV No. No_ No_. N/A. Low profile! Extra low presaure.! lined under paragraph (1) (b) and all injuries This includes injuries larger than those out- VII. Yes_. Extra high pressure "low speed".? requiring sectional repair.
VII Yes_ Extra high pressure "high (e) Kinked or broken beads.
speed." • (f) Weathering or radial cracks extendvI. VIII. Yes_ Yes_ Extra high pressure Extra bigh pressure-low pro- file "low speed." › -Low pro- ing into the cord body. (g) Evidence of blisters or heat damage.
file high speed." (h) Cracked, deteriorated, or damaged inner liners of tubeless tires.
I Inactive for new dealgn.
• Low speed for ground speeds below 160 m.p.h
• High speed for ground speeds above 160 m.p.b.
FIGURE 8.6.-Aircraft tire types and ratings.
Tires rated for groundspeeds in excess of 160
m.p.h. have the type and rating embossed on the sidewall.
a. Repair and Retreading of Low-Speed Tires.
The following procedures are applicable to other than Type VII and Type VIII high-speed aircraft tires.
(1) Tires having injuries of the following types may be repaired:
(a) Bead injuries where only the chafe resistant material is damaged or loose, or where minor injuries do not penetrate into more than 25 percent of the tire plies, up to a maximum of three damaged plies.
(b) Injuries in tread or sidewalls may be repaired by the spot repair method. This includes cuts in the tread area that are smaller than 1/2 inch in length and do not penetrate more than the following number of plies into the cord body.
Ply rating: out depth Макітит Less than 8 None.
8 through 16 2 plies.
More than 16 - - 4 plies.
(2) Nonrepairable Tires. If any of the following conditions exist, repair of the tire is not recommended:
(a) Evidence of flex breaks.
(3) Spot Repairs. Use repair methoda conforming to the best aviation industry practices.
Skive injuries require spot repairs at an approximate 45° angle to remove damaged rubber and cords.
Buff away exposed cord (refer to paragraph
(1) (b) for cord damage limits) leaving only the ends at the skive line and the rubber between the cord plies exposed. Clean the area thoroughly before applying the vulcanizing cement. As soon as the cement is completely dry, cover the skived area of the carcass with repair cushion gum. Fill the cavity in the carcass with repair cushion gum and roll to remove air. The tread cavity can then be filled with tread repair gum well-rolled, to provide a solid repair.
(4) Bead or Chafe Repairs. Use repair methods conforming to the best aviation industry practices. Trim the frayed fabric ends. Turn back the loose area, buff and clean the surface, and immediately cement. Secure the fabric back in position. Vulcanize repairs larger than 2 inches.
(5) Retreadable Tires. Tires which are sound or which can be repaired as listed above may be retreaded as set forth in Specification MIL-R-7726.
(6) Marking of Retreaded Tires, Permanently mark each retreaded tire. Whenever it is necessary to replace the area containing the original marking, such markings must be replaced. In addition, each retreaded tire will:
(a) Display the letter "R" followed by a Par 332 Chap 8
AC 43.13-1A 1972 number "1", "2", etc., to signify the sequential number of retreads applied thereon.
(b) Display the speed category increase if the tire is qualified for the increased speed in accordance with the requirements specified in FAR 87.167 (Technical Standard Order TSO-
(c) Display the month and year of retread application.
(d) Display the name of the person retreading the tire.
(7) Balance. Each repaired or retreaded tire should not exceed the static unbalance limits as forth in Technical Standard Order TSO-C62.
(8) Tire Installation. Install the tire on the wheel in such a manner that the tire-bead chafing area will not be torn or the tube pinched during the mounting process. When mounting tubeless tires, use procedures that assure a positive seal between the tire-bead and the wheel-rim area.
(9) Clearance. For retractable landing gears, maintain sufficient clearance between the tire and the surrounding structure during the retraction process. Carefully check clearances following installation of wheel assemblies equipped with retreaded tires because of the growth factor which may have increased the tire diameter and cross section.
b. Refreading Types VIl and VIll High-Speed Tires. The following paragraphs describe ways of substantiating the acceptability of methods, techniques, and practices to be used in retreading of high-speed tires. Other methods may be
(1) Number of Retreads. The wide variation in tire operating environments which may affect total carcass life and serviceability makes it inadvisable to prescribe arbitrarily the maximum number of times a high-speed tire should be retreaded. This aspect, therefore, is controlled by thorough inspection of the carcass before retreading.
(2) Condition of Tire to be Retreaded. Retread only those tire carcasses found serviceable by thorough inspection. During inspection, use equipment, techniques, and procedures which Chap 6 Page 147 are recommended by the tire manufacturer or that are equivalent to those in general use by FAA certificated repair agencies rated for retreading of high-speed aircraft tires. Determine the acceptability of damaged tires for retreading in accordance with established industry practices.
(3) Retreading Criteria,
(a) Processes, Methods, Techniques, Pracfices, and Equipment. The suitability of specific retread manufacturer's injury limitations, retreading processes, and equipment used is determined either by satisfactory service experience or substantiating tests.
(b) Materials. The acceptability of materials used in a retreading process may be determined by following the tire manufacturer's recommendations, or the materials may be sub- • stantiated by analysis and tests, such as dynamometer testing, or through satisfactory service experience.
(c) Unbalance. The moment of static unbalance in ounce-inches shall be no greater than the following moment values:
1. Tire diameters up to and including 28 inches: Moment = 01D' + 38D.
2. Tire diameters greater than 28 inches: Moment = 034D' - .804D.
D = Tire diameter (actual).
(d) Balance Marker. To indicate the lightweight point of the tire, remove old balance marker, and durably affix a new relocated balance marker, consisting of a single red dot of appropriate size to the sidewall of the tire immediately above the bead.
(e) Burst Pressure. Retreaded tires shall be capable of withstanding without failure, a burst pressure of at least 8 times the rated inflation pressure.
(f) Temperature. The airworthiness of retreaded tires shall not be adversely affected as a result of their being subjected to extreme ambient temperatures expected to be encountered during normal airplane operation.
(g) Tread Design. Substantiate decreases or increases in the number of tread ribs and grooves and changes in skid depth by dynamometer tests that are applicable to the tire groundspeed range.
Par 332
(h) Underskld Thickness. The thickness of the rubber between the carcass and the bottom of the tread pattern (underskid) is not normally less than 80% of the mold skid depth.
Requalify by dynamometer test, tire underskid/ tread thickness which is greater than that previously qualified.
(I) Venting. Substantiate changes in venting pattern by dynamometer test.
(4) Marking and Identification. Do not obliterate the original manufacturer's marking and identifying data, unless it is necessary for proper retreading or repair. Permanently emboss the tire sidewall with retread information. If necessary, replace original identifying markings and include the following retread identification:
(a) Name of identifying letters of the retreading company.
(b) The letter "R" followed by a numeral "1", "2", etc., to signify frst, second, etc., time the tire has been retreaded.
(c) Plant location of the retread manufacturer.
(d) Month and year of retread in numerical figures.
(•) If the dynamometer retread qualification speed is less than the previous (original) tire qualification speed, remove the previous speed marking and indicate the new (lower) rated speed. Identify tires that have been retreaded for use only on aircraft of a specific make/model and type design.
(5) Quality Control. The retreader's quality control system will be expected to maintain a satisfactory level of workmanship throughout the retreaded process including assurance that each retreaded tire is vented to prevent tread breakdown or separation.
(6) Records of Work Performed. Include at least the following information in the retreader's work record for each tire processed:
(a) Tire size.
(b) Ply rating.
(c) Speed rating.
(d) Serial number.
(•) Retread number.
(f) Type of tread applied.
(g) Month and year applied.
Par 332 AC 43.13-1A 1972
(7) Dynamometer tests. An acceptable means of determining that the methods, techniques, and practices utilized in the retread process will produce a tire that meets the requirements of FAR 48.18 is by subjecting a representative tire to the following dynamometer tests:
(a) General, Load-speed-time data compiled by the airplane manufacturer is the basis for establishing representative dynamometer tests. To determine tire performance, simulate the most critical combination of takeoff weight, speed, and airplane center-of-gravity position. Also, consider increased speeds resulting from elevated airport operations and high ambient temperatures.
(b) Selection of Tires for Qualification Testing. Retread only tires that are worn at least 80% from actual aircraft useage or which have undergone simulated equivalent operation during dynamometer testing. The sample retreaded tire must be properly identified and bear the qualifying retreaders markings.
(c) Test Inflation Pressure. Inflate the sample tire to the pressure necessary to obtain the same defection on the flywheel (under the rated static load) as the flat-plate deflection the tire would have at its rated static load and inflation.
(d) Test Speeds. The applicable dynamometer test speeds corresponding to the maximum operational groundspeeds are as follows:
lium operation prold speed of alreract Dynamometer test speed (m.p.h.)
Over Not over 160 180 180 180 200 200 200 225 226 225 250 250
(e) Test Landing Interval. Schedule minimum time between landings to assure carcass peak temperatures of not less than 160° F. or contained air peak temperatures of not less than 140° F. for each run. Measure the carcass temperatures within 1 inch of the rim flange and also in the shoulder or crown area. Record any unavoidable deviations in the substantiating test data.
(8) Dynamometer Test Procedures. The highspeed retreaded tire shall withstand 100 dynamometer landings and at least three taxi-test Chap •
AC 43.13-1A CHG 1 1975 cycles. The dynamometer landings will consist of 50 Test A, load-speed-time cycles and 50 Test B, energy cycles.
(a) Test A, Load-speed-time.
I. Speed cycle. Land the tire against a dynamometer flywheel rotating at n peripheral speed of S, m.p.h. Immediately thereafter, decrease the flywheel speed at an average deceleration rate of D ft./sec./sec. until a value of S, is attained. No specific rate of deceleration is required after the flywheel's peripheral speed reaches a value of S2. Decrease the speed of the flywheel in the above manner until a roll distance of RD feet has been covered, at which time the tire is unlanded.
2. Load cycle. After landing, increase the load from zero to L, pounds within T, seconds. Linearly increase the load with time to a value of Is pounds within T, seconds after landing, or at the moment of unlanding, whichever occurs first. If it is necessary to continue the roll after Ta seconds to complete the required roll distance (RD), maintain the load at L pounds.
3. Symbol definitions. Determine the numerical values, which are used for the following symbols, from the applicable airplane load-speed-time data:
S, = Initial dynamometer test speed.
S=Speed at which the average deceleration between S, and S, does not exceed the specified values.
D=Constant rate of deceleration between S, and S, speeds.
RD = Roll distance in feet.
I, = Initial tire load.
L=Maximum rated static load of the tire.
T, =Time for applying L, load. A T, tolerance of +1 second is acceptable.
S1-VS -2D (RD) T¿= D T, is the elapsed time for applying the Ly load A T, tolerance of +10% is acceptable.
When T, is calculated by the aforementioned formulu, S, may be ignored and D is assumed constant throughout roll distance (RD).
Chap 8 Page 149
4. Test load adjustment. If the test load curve results in loads at a given speed being less than those dictated by the applicable aircraft data, eliminate the condition by making adjustments in Ta, L, and/or T1
(b) Test B, Energy.
1. Kinetic energy. Calculate and adjust the kinetic energy of the flywheel for the rated maximum static load of the tire. In the event that the correct number of flywheel plates cannot be used to obtain the calculated kinetic energy value or proper flywheel width, select a greater number of plates and adjust the dynamometer speed to achieve the required kinetic energy.
2. Kinetic energy computation. Compute kinetic energy as follows:
KE=CWV:
Where KE = Kinetic energy, ft.-lb.
C=0.011 W=tire load, pounds V = 120 m.p.h.
3. Speed cycle. Land the test tire at 90 m.p.h. and unland at 0 m.p.h. Decrease the landing speed as necessary to assure that 56% of the calculated kinetic energy is absorbed by the tire.
4. Load cycle. Upon landing, and during the entire roll test, force the tire agninst the flywheel at its rated static load.
(c) Taxi Test.
1. Test parameters. Conduct a minimum of three dynamometer taxi tests under the following conditions:
Speed = 35 m.p.h.
Tire Load = Maximum static rating Roll Distance =35,000 feet.
2. Tire temperature. Heat the test tire to a temperature of not less than 120° F. at the start of each of the three taxi test cycles. Rolling the tire on the dynamometer is acceptable in obtaining this minimum tire temperature.
Make no adjustments in the tire inflation pressure to compensate for increases due to temperature rise.
(9) Alternate Dynamometer Tests.
(a) Variable Loading. An alternate dynamometer test which more realistically simulates Par 332
Page 150 AC 43.13--1A CHG 1 1975 actual airplane performance on the runway may be used in lien of the deceleration load-speedtime schedule, An acceleration lead-sperd-time tube is not pinched. A pinched tube will chafe against the walls of the carcass and a thin spot will result in the rubber. In time, the tube wall schedule, wherein the dynamometer flywheel is will leak at this point. The pinching generally accelerated to the applicable conditions, is accept- is due to the sticking of the tube to the cauass wall during the first inflation and the failure
(b) Alternate Procedure for Reinforced-tread of the carcass to properly seat against the flange.
Tires. Qualification of a high-speed tire with (d) The tube is then confined to a smaller a given ply rating and reinforced tread will an space and wrinkling (pinching) of the tube retomatically qualify a lesser ply rating reinforced sults. Complete deflation followed by inflation tread tire of the same size and skid depth, pro- allows the tube to properly accommodate itself to the careass which should now seat it-elf tightly
1. The test conditions S, RD, S., Th against the flanges.
and T, are no less severe than those which are *333. TIRE SLIPPAGE. To reduce the possibility applicable to the lesser ply rating tire. of tire and tube failure due to slippage, and to
2. The ratio of the test loads, I, to In provide a means of detecting tire slippage, tires is not less than that applicable to the lesser ply should be marked and indexed with the wheel rating tire. Make any necessary adjustment in rim. Marking should be accomplished by paintthis ratio by increasing In. ing a mark 1 inch in width and 2 inches in length
(10) Optional Dynamometer Equipment. Dynamic tests may be conducted on any dynanometer test equipment which will provide the load, speed, time, and roll distance parameters of the tire.
c. Tubes. Punctured tubes may be repaired by the use of cemented or vulcanized patches.
(1) The procedure for making such repairs is substantially identical to that used in connection with repair of automobile tires:
(a) Keep the size of the patch to a minimum and avoid use of an excessive number of patches, particularly in one area, as the weight of the material may contribute to excessive wheel vibration due to the tube being out-of-balance.
(b) The use of vulcanized patches is recommended because they are considered more re liable.
(c) Reinstalled tires should be inflated, deacross the tire sidewall and wheel ri. The paint used should be of a permanent type and contrasting color, such as white, red, or orange.
Preflight inspection should include a check of slippage marks for alignment. If the slippage mark is not in alignment, the aircraft should not be operated until a detailed inspection is made, the reason deterined, and if necessary the condition corrected.
334. TIRE MAINTENANCE. A progiam of tire maintenance can minimize tire failures and increase tire service life. Overinflation wears the center of the tread excessively, and reduces a tire's resistance to bruising, strains the fires beads, reduces traction and skid resistance. Underinflation increases deflection and may cause breakdown of the tire sidewalls. The manufacturer's recommendations should be followed to obtain maximum tire service life.
flated, and again inflated to insure that the inner- 345.-349. RESERVED. * Por 332 Chap 8
AC 43.13-1A Page 151 1972 Section 2. LIFE PRESERVERS AND LIFERAFTS
344. GENERAL. Inflatable life preservers and liferafts are subject to general deterioration due to aging. Experience has indicated that such equipment may be in need of replacement at the end of 5 years due to porosity of the rubber-coated material. Wear of such equipment is accelerated when stowed on board aircraft because of vibration which causes chaffing of the rubberized fabric. This ultimately results in localized leakage. Leakage is also likely to occur where the fabric is folded because sharp corners are formed. When these corners are in contact with the carrying cases, or with adjacent parts of the rubberized fabric, they tend to wear through due to vibration.
345. INSPECTION PROCEDURE FOR LIFE PRE- SERVERS. Life preservers should be inspected at 8-month intervals for cuts, tears, or other damage to the rubberized material. Check the mouth valves and tubing for leakage, corrosion, and deterioration. Remove the carbon dioxide cylinder and check the discharge mechanism by operating the lever to ascertain that the pin operates freely. Check the gaskets and valve cores of the cylinder container and the pull cord for deterioration. If no defects are found, inflate the preserver with air to a 2- pound pressure and allow to stand for 12 hours. If the preserver still has adequate rigidity at the end of that time, deflate and fit with CO, cylinders having weights not less than that indicated on them by the manufacturer.
All cylinders made in accordance with joint Army/Navy Specification MIL-C-00601D are so stamped and have a minimum permissible weight stamped on them. The use of such CO, cylinders is recommended. These cylinders have the 5/82-inch end disc sealed by an electric welding process, which is intended to provide a superior seal compared to the older type, which have a similar disc surrounded by a thin rubber seal. Inasmuch as the rubber is subject to deterioration, its ability to maintain pressure will possibly be affected. Leaky electrically welded seals will probably be discovered upon final inspection at the manufacturer's plant. If such a cylinder is up to weight at the end of 3 months in all probability it will remain so until used; whereas, the old type with the rubber seal is apt to lose its pressure with age. Having fitted the preserver with an adequately charged cylinder, mark the preserver to indicate the date of inspection and pack into its container, It is recommended that the aforementioned procedure be repeated every 12- month period, utilizing the CO, cartridge for inflation. Carbon dioxide permeates the rubberized fabric at a faster rate than air and will indicate if the porosity of the material is exces-
346. REPAIR OF LIFE PRESERVERS. Leaks may be disclosed by immersion in soapy water. Repair leaks by the use of patches in accordance with the recommendations of the manufacturer.
Clean corroded metal parts and replace missing or weakened lanyards. Life preserves which do not retain sufficient rigidity after the 12-hour period, because of general deterioration and porosity of the fabric, are beyond economical repair and should be replaced.
347. INSPECTION PROCEDURE FOR LIFERAFTS.
Liferafts should be inspected at 8-month intervals for cuts, tears, or other damage to the rubberized material. If the raft is found to be in good condition, remove the CO, bottle(s) and inflate the raft with air to a pressure of 2 pounds. The air should be introduced at the fitting normally connected to the CO, bottle(s).
After at least 1 hour to allow for the air within the raft to adjust itself to the ambient temperature, check pressure and adjust, if necessary, to 2 pounds and allow the raft to stand for 24 hours. If, after 24 hours, the pressure is Chap 8 Par 344
Pago 152 less than 1 pound, examine the raft for leakage by using soapy water. In order to eliminate pressure variations due to temperature differences at the time the initial and final reading are taken, test the raft in a room where the temperature is fairly constant. If the pressure drop is satisfactory, the raft should be considered as being in an airworthy condition and returned to service after being fitted with correctly charged CO, bottles as determined by weighing them. Rafts more than 5 years old are likely to be unairworthy due to deterioration. It is suggested that the rafts be marked to indicate the date of inspection and that soapstone be used when folding them preparatory to insertion into the carrying case. Take care to see that all of the raft's required equipment is on board and properly stowed. If the raft lanyard, used to prevent the raft from floating away from the airplane, is in need of replacement, use a lanyard not less than 20 feet long and having a breaking strength of about 75 pounds. It is recommended that the aforementioned procedure be repeated every 18-month period utilizing the CO, bottle(s) for inflation. If a single bottle is used for inflating Par 347 AC 43.13-1A 1972 both compartments, it should be noted whether the inflation is proceeding equally to both compartments. Occasionally the formation of carbon-dioxide snow" may occur in one passage of the distribution manifold and divert a larger volume of gas to one compartment, which may burst if the mattress valve is not open to relieve the pressure. If the pressure is satisfactory, return the raft to service in accordance with the procedure outlined.
348. REPAIR OF LIFERAFTS. When leaks due to tears, abrasion, or punctures are found, make repairs in accordance with the recommendations of the manufacturer. Recement partially torn away supporting patches on the tube to restore the raft to its airworthy condition. Replace mildewed or weak lanyards, particularly those by which the CO, bottle is operated. This applies also to the line used to attach the raft to the airplane. Check all metal parts for corrosion, and clean or repair if found to be defective. If leaky mattress valves have been found, they must be replaced.
349.-359. RESERVED.
Chap 8