cle containing enough hydraulic fluid to cover the end of the hose. The air-laden fluid is then forced from the system by operating the brake. If the brake system is a part of the main hydraulic system, a portable hydraulic test stand may be used to supply the pressure. If the system is an independent master cylinder system, the master cylinder will supply the necessary pressure. In either case, each time the brake pedal is released the bleeder valve must either be closed or the bleeder hose pinched off;
otherwise, more air will be drawn back into the system. Bleeding should continue until no more air bubbles come through the bleeder hose into the container.
Pressure Method of Bleeding Brakes In the pressure method, the air is expelled through the brake system reservoir or other spe.
cially provided location. Some aircraft have a bleeder valve located in the upper brake line. In using this method of bleeding, pressure is applied using a bleed tank (figure 942). A bleed tank is a portable tank containing hydraulic fuid under pressure. The bleeder tank is equipped with an air valve, air gage, and a connector hose. The connector hose attaches to the bleeder valve on the brake assembly and is provided with a shutoff valve.
Wheel brake ing the entire operation. A low fluid supply will allow air to be drawn into the system.
(3) Bleeding should continue until no more air bubbles are expelled from the system, and a firm brake pedal is obtained.
(4) After the bleeding operation is completed, check the reservoir fluid level. With brake pressure on, check the entire system for leaks.
Brakes which have become overheated from excessive braking are dangerous and should be treated accordingly. Excessive brake heating weakens the tire and wheel structure and increases tire pressure.
AIRCRAFT LANDING WHEELS Aircraft wheels provide the mounting for tires which absorb shock on landing, support the aircraft on the ground and assist in ground control during taxi, takeoff and landing. Wheels are usually made from either aluminum or magnesium. Either of these materials provides a strong, light weight wheel requiring very little maintenance.
1. Split wheel-the most popular type. (Figures 9-43 and 9-44 Heavy aircraft wheel, Figures 9-45 and 9-46 Light aircraft wheel.)
2. Removable flange type Figure 9-47.
3. Drop center fixed flange type Figure 9-48.
The split wheel is used on most aircraft today.
Illustrations of wheels used on light civilian type and heavy transport type aircraft are shown to illustrate the similarities and differences.
Split Wheels hate abso trated in figure 9-43 is used on the Boeing B-727 transport aircraft.
FIGURE 9-42. Preasure method of bleeding brakes, Perform this method of bleeding strictly in accordance with the specific manufacturer's instructions for the aircraft concerned.
Although the bleeding of individual systems presents individual problems, observe the following precautions in all bleeding operations:
(1) Be certain that the bleeding equipment to be used is absolutely clean and is filled with the proper type of hydraulic fluid.
(2) Maintain an adequate supply of huid dur- Description-The numbers in parenthesis refer to figures 9-43 and 9-44.
A. The main landing gear wheel is a tubeless, split-type assembly made of forged aluminum.
B. The inner and outer wheel half assemblies are fastened together by 18 equally spaced tie bolts (11), secured with nuts (9). A tubeless tire valve assembly installed in the web of the inner wheel half (48), with the valve stem (7) protruding through a vent hole in the outer wheel half (30), is used to inflate the tubeless tire used with 373
43 11 12 34 35 36 38 48 5 14 13 30 23 24 25 22 21 FIcURE 9-43. Split wheel-heavy aircraft.
Index No. Description WHEEL, LANDING GEAR, 49 x 17, TUBELESS, MAIN CO tO M CONE BEARING RING, RETAINING IDENTIFICATION PLATE INSTRUCTION PLATE
SEAL PLATE, IDENTIFICATION
CONE, BEARING INSERT, HELI-COIL
VALVE ASSY, TUBELESS TIRE CUP, BEARING
CAP, VALVE WHEEL HALF, OUTER
VALVE, INSIDE WHEEL HALF, ASSY, INNER
STEM, VALVE NUT GROMMET, RUBBER (TIRE AND RIM ASSOC.) WEICHT, WHEEL BALANCE, 1/4 oz.
NUT 33 BOLT, MACHINE WASHER BOLT 34 35 NUT WASHER, FLAT WASHER 36 IDENTIFICATION PLATE
PACKING, PREFORMED INSTRUCTION PLATE PACKING, PREFORMED 38 BOLT, MACHINE PLUG, MACHINE THD, THERMAL PRESSURE 39 NUT RELIEF, ASSY OF 40 WASHER, FLAT 16 PACKING, PREFORMED 41 BOLT, MACHINE WHEEL HALF ASSY, OUTER 42 BRACKET NUT 43 SHIELD, HEAT WEIGHT, WHEEL BALANCE, 1/4 oz. 44 SCREW BOLT, MACHINE 45 INSERT
WASHER INSERT, HELI-COI
NUT CUP, BEARINC WASHER, FLAT 48 WHEEL HALF, INNER
BOLT, MACHINE
WASHER, FLAT FICURE 9-44. Parts list-split wheel, heavy aircraft.
this wheel. Leakage of air from the tubeless tire through the wheel half mating surfaces is prevented by a rubber packing
(14) mounted on the register surface of the inner wheel half. Another packing
(13) mounted on the inner register surface of the inner wheel half seals the hub area of the wheel against dirt and moisture.
C. A retaining ring (2) installed in the hub of the inner wheel half holds the seal (3) 374 and bearing cone (4) in place when wheel is removed from axle. The seal retains the bearing lubricant and keeps out dirt and moisture. Tapered roller bearings (1, 4, 29, 47) in the wheel half hubs support the wheel on the axle.
D. Inserts (45) installed over bosses in the inner wheel half (48) engage the drive slots in the brake disks, rotating the disks as the wheel turns. A heat shield (43), mounted underneath and between the in-
22 11 10 10 9 FIcURE 9-45. Split wheel--light aircraft.
Index No. Description Fixed Flange Wheels WHEEL ASSEMBLY (With Valve Assy) SEAL ASSY 9-48) are special use wheels such as military, for Drop center fixed fange aircraft wheels (figure CONE, Bearing high pressure tires. Some may be found installed VALVE ASSY, Tubeless tire on older type aircraft.
CODE, Valve NUT CAP, Valve give added support to the rim at the outboard Outboard radial ribs are provided generally to SPACER bead seat. The principal difference between wheels 7 GROMMET used for streamline tires and those used for smooth & STEM, Valve contour tires is that the latter are wider between 10 NUT WASHER the flanges.
11 BOLT 12 PACKING 13 WHEEL-HALF ASSY, Outer 14 PLATE, Identification 15 PLATE, Instruction 16 CUP, Bearing Grease WHEEL-HALF ASSY, Inner retainer - 17 WIRE, Lock 18 SCREW Axle- 19 20 INSERT, Heli-coil KEY, Torque Bearing nut 21 PLATE, Identification 22 PLATE, Instruction 23 24 WHEEL-HALF, Inner CUP, Bearing Fairing, disc FIcURE 9-46. Parts list-split wheel, light aircraft.
A brake-drum liner may be held in place by means of steel bolts projecting through the casting with lock nuts on the inner side. These can be tightened easily through spokes in the wheel.
The bearing races are usually shrink-fitted into the hub of the wheel casting and provide the surfaces on which the bearings ride. The bearings are the tapered roller type. Each bearing is made up of a cone and rollers. Bearings should be cleaned and repacked with grease periodically in accordance with applicable manufacturer's instructions.
Brake drum liner FicURE 9-48. Fixed fange, drop center wheel.
Wheel Bearings The bearings of an airplane wheel are of the tapered roller type and consist of a bearing cone, rollers with a retaining cage, and a bearing cup, or outer race. Each wheel has the bearing cup, or race, pressed into place and is often supplied with a hub cap to keep dirt out of the outside bearing.
Removable flange - Removable Snap ring Lockring flange Wheel casting retainer Grease 00(3) Fairing disc Fairing - retaining screw A. Drop center. B. Flat base.
FIGURE 9-47. Removable flange wheels.
Suitable retainers are supplied inboard of the inner bearing to prevent grease from reaching the brake Felt seals are provided to prevent dirt from fouling multiple-disk brakes. Seals are also supplied on amphibian airplanes to keep out water.
Beads Made of steel wires embedded in rubber and wrapped in fabric, the beads anchor the carcass plies and provide firm mounting surfaces on the wheel.
AIRCRAFT TIRES Aircraft tires, tubeless or tube type, provide a cushion of air that helps absorb the shocks and roughness of landings and takeoffs: they support the weight of the aircraft while on the ground and provide the necessary traction for braking and stopping aircraft on landing. Thus, aircraft tires must be carefully maintained to meet the rigorous demands of their basic job... to accept a variety of static and dynamic stresses dependably--in a wide range of operating conditions.
Aircraft Tire Construction Dissect an aircraft tire and you'll find that it's one of the strongest and toughest pneumatic tires made. It must withstand high. speeds and very heavy static and dynamic loads. For example, the main gear tires of a four-engine jet transport are required to withstand landing speeds up to 250 mph, as well as static and dynamic loads as high as 22 and 33 tons respectively. Typical construction is shown in figure 9-19.
Flippers These layers of fabric and rubber insulate the carcass from the bead wires and improve the durability of the tire.
Layers of fabric and rubber that protect the carcass from damage during mounting and demounting. They insulate the carcass from brake heat and provide a good seal against movement during dynamic operations.
Bead Toe The inner bead edge closest to the tire center line.
Bead Heel The outer bead edge which fits against the wheel flange.
Innerliner Made of rubber compound for toughness and durability, the tread is patterned in accordance with aircraft operational requirements. The circumferential ribbed pattern is widely used today because it provides good traction under widely varying runway conditions.
On tubeless tires, this inner layer of less permeable rubber acts as a built-in tube, it prevents air from seeping through casing plies. For tube type tires, a thinner rubber liner is used to prevent tube chafing against the inside ply.
Tread Reinforcing Ply Tread Reinforcement Rubber compound cushion between tread and One or more layers of reinforced nylon cord casing plies, provides toughness and durability.
fabric strengthens the tread for high speed opera- It adds protection against cutting and bruising tion. Used mainly for high speed tires. throughout the life of the tread.
Breakers Not always used, these extra layers of reinforcing nylon cord fabric are placed under the tread rubber to protect casing plies and strengthen tread area. They are considered an integral part of the carcass construction.
Casing Plies/Cord Body Diagonal layers of rubber-coated nylon cord fabric (running at opposite angles to one another) provide the strength of a tire. Completely encompassing the tire body, the carcass plies are folded around the wire beads and back against the tire sidewalls (the "ply turnups").
Sidewall Sidewalls are primarily covers over the sides of the cord body to protect the cords from injury and exposure. Little strength is imparted to the cord body by the sidewalls. A special sidewall construction, the "chine tire," is a nose wheel tire designed with built-in deflector to divert runway water to the side, thus reducing water spray in the area of rear mounted jet engines.
Apex Strip The apex strip is additional rubber formed around the bead to give a conture for anchoring the ply turnups.
Tread • Breakers Tread Reinforcing ply Inner liner Sidewall Plies Chafers Cord body Bead heel Ply turnups
• Bead toes Flippers Wire beads Apex strip FIGURE 9-49. Aircraft tire construction.
Aircraft Tire Care Tires are as vital to the operation of aircraft as they are to the operation of an automobile. During ground operation tires can be considered as ground control surfaces. The same rules of safe driving and careful inspection apply on the runway as on the highway.
They include control of speed, braking, and cornering, and inspection for proper inflation, cuts, bruises, and signs of tread wear. Contrary to what most people think-including many beginning pilots- the toughest demand on aircraft tires is rapid heat buildup during lengthy ground operations, not the impact of hard landings.
Aircraft tires are designed to flex more than automotive tires-over twice as much. This flexing causes internal stress and friction as tires roll on the runway. High temperatures are generated, damaging the body of the tire.
The best safeguards against heat buildup in aircraft tires are short ground rolls, slow taxi speeds.
minimum braking. and proper tire inflation.
Excessive braking increases tread abrasion. Likewise, fast cornering accelerates tread wear. Proper inflation assures the correct amount of flexing and keeps heat buildup to a minimum, increasing tire life and preventing excessive tread wear.
Infiation pressure should always be maintained as specified in the aircraft maintenance manual or according to information available from a tire dealer.
Even though using a tire gage is the only accurate way to spot-check inflation, a quick visual inspection of the tread can reveal if air pressure has been consistently high or low. Excessive wear in the shoulder area of the tire is an indication of under inflation. Excessive wear in the center of the tire suggests over inflation.
Tires should also be carefully inspected for cuts or bruises. The best way to avoid aircraft tire cuts and bruises is to slow down when unsure of runway or taxiing surface conditions.
Since airplane tires have to grip the runway in the same way car tires grip the road, tread depth is also important. Tread grooves must be deep enough to permit water to pass under the tires, minimizing the danger of skidding or hydroplaning on wet runways. Tire treads should be inspected visually or with an approved depth gage according to manufacturers' specifications.
Another inspection goal is detection and removal of any traves of gasoline or oil on the tires.
Such mineral fluids damage rubber, reducing tire lite. Likewise, tires should be inspected for ozone or weather checking. Electricity changes oxygen in the air to ozone, which also prematurely ages rubber.
MATCHING DUAL, TIRES Matching tires on dual wheels, or dual wheels on a O. D. Range of Tires Maximum Tolerance multi-wheel gear configuration, is necessary so that each Permissable tire will have the same contact area with the ground and thereby carry an equal share of the load. tires having inflated diameters within the tolerances Up to 24" 25" to 32" 5/18" 1/4" listed below should be paired together on dual wheels. 33" to 40" 3/8" Tires should not be measured until they have been 49" to 55" 41" to 48" 7/16" 1/2" mounted and kept fully inflated for at least 12 hours, 56" to 65" • 9/16" at normal room temperatures. 86" and up 5/8" FIcURE 9-50. Matching tires on dual wheel installations.
Aircraft tires should be stored in a cool dry place away from electric motors. The manufacturers specifications should be followed at all times when performing tire maintenance.
Tires on dual wheel aircraft will have a longer operational life if matched as suggested in figure
9-50.
AIRCRAFT TIRE MAINTENANCE All aircraft tire manufacturers publish maintenance manuals and instruction manuals.
The following discussion on aircraft tires is excerpted from the B.F. Goodrich publication Care and Maintenance of Aircraft Tires, Fourth Edition, and is published with their permission.
Proper Inflation For Satisfactory Service Proper inflation is undoubtedly the most neces- • в просо sary maintenance function for safe, long service from aircraft tires.
Tire pressures should be checked with an accurate gage at least once a week or oftener, and it is recommended that they be checked before each flight. Otherwise, if a slow leak should develop, it could cause severe loss of air within two or three days, with resulting damage to the tire and tube.
Air pressures should only be checked when tires are cool. Wait at least two hours after a flight before checking pressures (three hours in hot weather).
For New Mountings A newly mounted tire and/or tube should be checked at least daily for several days, after which the regular inflation control schedule may be followed. This is necessary because air is usually trapped between the tire and tube at the time of mounting, giving a false pressure reading. As this trapped air seeps out under the beads of the tire and around the valve hole in the wheel, the tire may become severely under inflated within a day or two.
Allow For Nylon Stretch All aircraft tires are now made with nylon cord, and the initial 21-hour stretch of a newly mounted nylon tire may result in a 5 percent to 10 percent drop in air pressure. Thus, such a tire should not be placed in service until it has been left to stand at least 12 hours after being mounted and inflated to regular operating pressure. The air pressure should then be adjusted to compensate for the decrease in pressure caused by the stretching of the cord body.
Tubeless Air Diffusion Loss Maximum allowable diffusion is 5 percent for any 24-hour period. However, no accurate tests can be made until after the tire has been mounted and inflated for at least 12 hours, and air added to compensate for pressure drop due to normal nylon cord body expansion, and any changes in tire temperature. A pressure drop of over 10 percent during this initial period should be suffcient reason to not place the tire and wheel assembly into service.
For Duals: Equalize Pressures Differences of air pressure in tires mounted as duals, whether main or nose, should be cause for concern, as it ordinarily means that one tire is carrying more of the load than the other. If there is a difference of more than 5 lbs., it should be noted in the log. The log-book should then be referred to on each subsequent inflation check Impending tire or tube failure can often be detected by this method. Should a pressure difference be found, check the valve core by spreading a little water over the end of the valve. If no bubble appears, it can be assumed that the valve core is holding pressure satisfactorily.
Sources of Pressure Data Inflation of nose wheel tires should follow the recommendations of the aircraft manufacturers, because they take into consideration both the extra 379
load transferred to the nose wheel by the braking effect and by the static load. Air pressure in the nose wheel tire, based on the static load only, would result in under inflation for the load carried when the brakes are applied. Tail wheel tires, however, should be inflated in accordance with the axle static load.
When tires are inflated under load, the recommended pressure should be increased by 4 percent.
The reason is that the deflected portion of the tire causes the volume of the air chamber to be reduced, and increases the inflation pressure reading, which must then be offset in accordance with the above Effects of Under Inflation Under inflation results in harmful and potentially dangerous effects. Aircraft tires which are under inflated are much more likely to creep or slip on the wheels on landing or when brakes are applied.
Tube valves can shear off, and the complete tire, tube and wheel assembly can be destroyed under such conditions. Too-low pressures can also cause rapid or uneven wear at or near the edge of the Under inflation provides more opportunity for the sidewalls or the shoulders of the tire to be crushed landing no veron by the wheel's rim flanges on landing or upon striking the edge of a runway while maneuvering the aircraft. Tires may flex over the wheel flange.
with greater possibility of damage to the bead and lower sidewall areas. A bruise break or rupture of the tire's cord body can result.
Severe under inflation may result in cords being loosened and the tire destroyed because of extreme heat and strain produced by the excessive flexing action. This same condition could cause inner tube chafing and a resultant blowout.
Observe Load Recommendations Since the beginning of air transportation, aircraft tires have been doing their required job with increasing efficiency and safety. But there is a limit to the load that any aircraft tire can safely and efficiently carry.
Loading aircraft tires above the limit can result in these undesirable effects:
1. Undue strain is put on the cord body and beads of the tire, reducing the factor of safety and reducing service life.
2. There is greater chance of bruising upon striking an obstruction or upon landing (bruise breaks, impact breaks and flex breaks in the sidewall or shoulder).
3. Possibility of damaging wheels. Under the severe strain of an extra load, a wheel may fail before the tire does.
Note: While additional air pressure (inflation) to offset increased loads can reduce excessive tire deflection, it puts an added strain on the cord body, and increases its susceptibility to cutting, bruises and impact breaks.
Nylon Flat-Spotting Nylon aircraft tires will develop temporary fat spots under static load. The degree of this flatspotting will vary according to the drop in the internal pressure in the tire and the amount of weight being sustained by the tire. Naturally, flatspotting can be more severe during cold weather and is more difficult to work out of a tire at lower temperatures.
Under normal conditions, a flat spot will disappear by the end of the taxi run. If it doesn't, the tire can generally be reshaped by overinflating it 25 percent or 50 percent and moving the aircratt until the low spot is on the upper side. This pres-
PREVENTIVE MAINTENANCE SUMMARY
• Check tire pressures with an accurate gage at least once a week, and before each flight.
should be at ambient temperature.
• Check newly mounted tires or tubes daily for several days.
• Newly mounted tires should not be placed in service until cord body stretch has been compensated with re-inflation.
• Check for abnormal diffusion loss.
• Follow inflation recommendations carefully - guard against underinflation.
• Observe load recommendations.
• Move aircraft regularly or block up when out of service for long periods.
FIcURE 9-51. Preventive maintenance summary.
sure should be left in the tire for one hour. It may even be necessary to taxi or tow the aircraft until the reshaping is accomplished. Needless to say, any flat spot can cause severe vibration and other unpleasant sensations to both pilot and passengers.
Aircraft that is to remain idle for a period longer than three days should either be moved every 48 hours or blocked up so that no weight is on the tires. Aircraft in storage (out of service for more than 14 days) should be blocked up so that there is no weight on the tires.
Figure 9-51 gives a brief, summary checklist of tire preventive maintenance.
Tires with cuts or other injuries which expose or penetrate the cord body, should be removed and repaired, recapped or scrapped. Where a cut does not expose the carcass cord body, taking the tire out of service is not required.
Remove any tires that show signs of a bulge in the tread or sidewall. This may be the result of an injury to the cord body, or may indicate tread or ply separation. Always mark such a bulged area with tire crayon before deflating the tire;
otherwise, it may be very difficult, if not impossible, to locate the area after the tire is deflated.
Sidewall Injuries
TIRE INSPECTION--MOUNTED ON WHEEL Leaks Or Damage At Valve To check valves for leaks, put a small amount of water on the end of the valve stem and watch for air bubbles. If bubbles appear, replace the valve core and repeat this check.
Always inspect the valve to be sure the threads are not damaged; otherwise, the valve core and valve cap will not fit properly.
damaged, the valve can usually be rethreaded, inside or outside, by use of a valve repair tool, without demounting the tire from the wheel.
Make certain that every valve has a valve cap on it-screwed on firmly with the fingers. The cap prevents dirt, oil and moisture from getting inside the valve and damaging the core. It also seals in air and serves as protection in case a leak develops in the valve core.
Check the valve to be sure it is not rubbing against the wheel. If it is bent, cracked, or severely worn, demount the tire and replace the tube or valve at once.
Treaa Injuries Carefully inspect the tread area for cuts or other Be sure to remove any glass, stones, metal or other foreign objects that might be embedded in the tread or that have penetrated the Use a blunt awl for this purpose, although a medium size screwdriver can be used if a blunt awl is not available. When probing an injury for foreign material, be careful not to enlarge the injury or drive the point of the awl or screwdriver into the cord body beyond the depth of the injury.
When prying out foreign material that might be embedded, the other hand should be held over the injury in such a way that the object will not fly out and strike the person conducting the inspection Inspect both sidewalls for evidence of weather or ozone checking and cracking, radial cracks, cuts.
snags, gouges, etc. If cords are exposed or damaged. the tires should be removed from service.
When To Remove For Recapping Check tires for possible need of recapping. They should be taken out of service when:
(a) They have one or more flat spots. Generally.
a single flat spot or skid burn does not expose the carcass cord body and the tire may remain in service, unless severe unbalance is reported by the aircraft crew.
(b) They show 80 percent or more tread wear.
(c) There are numerous cuts that would require repair. In other words, if the cost of repairing the cuts would amount to 50 percent or more of the recapping cost. it would be considered more economical to have the tire recapped.
Uneven Wear Check tires for evidence of wheel misalignment.
Tires showing such wear should be demounted.
turned around and remounted, in order to even up the wear. Also, check for spotty, uneven wear due to faulty brakes so mechanical corrections can Wheel Damage Inspect the entire wheel for damage. Wheels which are cracked or injured should be taken out of service and laid aside for further checking. repair or replacement.
When inspecting a mounted tire on the wheel of a plane, always be sure that nothing is caught between the landing gear and the tire, and that no parts of the landing gear are rubbing against the tire.
At this time, also check the nacelle into which the tire fits, when the landing gear is retracted Clearances are sometimes close and any foreign 381
A. A valve cap for every valve. B. Depth gage shows wear. C. Mark and remove foreign objects.
FIGURI: 9-52. Basic tire maintenance material or loose or broken parts in the nacelle can cause severe damage to the tire and even cause it to fail upon landing.
Figure 9-52 shows checks to be accomplished while tire is mounted.
TIRE INSPECTION-TIRE DEMOUNTED Periodic Demounting A definite schedule can be set up to provide for regular inspections of tires and tubes, after a certain number of hours or landings, and that each individual tire and tube be removed from the wheel for that inspection. However, if an airplane has made an emergency or particularly rough landing, the tire and tube should be demounted and inspected as soon as possible to determine whether any hidden damage exists. The wheel should also be examined at the same time.
Probe Injuries Probe all cuts, punctures and other tread injuries with a blunt awl and remove any foreign material. When prying out the foreign material imbedded in the tread, the hand should be held over the injury in such a position that the object will not fly out and strike the person conducting the inspection in the face.
Squeezing the sidewalls together will also assist, as this will open up the cuts and injuries.
and depth of cuts and injuries can then be determined by probing with the awl. Do not push the awl point into the cord body beyond the depth of the injury.
Repairable Injuries Injuries into, or through, the carcass cord body, measuring no more than ¼" on the outside and ⅛" on the inside, would be considered punctures and are easily repaired without the need for fabric reinforcement inside the tire. Tires qualified to speeds over 160 mph can be repaired if they meet the following qualifications: injuries through the tread must not penetrate more than 40 percent of the actual body plies; they should measure no more than 1½" long and ¼" wide before tread is removed; and after the tread has been removed, injuries should not be over 1" long and ⅛" wide on the surface.
Tires qualified to speeds of less than 160 mph can be repaired if the injury penetrates through more than 40 percent of the actual plies, and is no larger than 1" in length. Naturally, there must be a limit as to the number of such injuries that there can be in the tire. The decision to recondition or not recondition such a tire should be left up to the tire manufacturer.
Sidewall Conditions Inspect both sidewalls for evidence of weather or ozone checking and cracking, radial cracks, cuts or snags.
(a) Scrap any tires with radial cracks extending to the cords.
(b) Scrap any tires with weather-checking, ozone-checking, or cracking, which extends to the cords. Weather-checking is a normal condition affecting all tires and, until cords are exposed, will in no way affect the serv.
iceability or safety of the tire.
(c) Tires with cuts or snags in the sidewall area which have damaged the outer ply should be scrapped.
Bead Damage Check the entire bead and the area just above the heel of the bead on the outside of the tire for 382
A. Probe with blunt awl, shield work. B. Are sidewall cords exposed? C. Finishing & trip damage, repairable.
FIGURE 9-53. Basic tire maintenance chafing from the wheel flange or damage from tire tools. Any blistering or separation of the chafer strips from the first ply beneath requires repairing or repiacement of the chafer strip. If cords in the first ply under the chafer strip are damaged, the tire should be scrapped.
If protruding bead wire, bead wire separation, or a badly kinked bead is found, the tire should be scrapped.
Loose or blistered finishing strips can generally be replaced during the retreading process, but tires should not be continued in service in that condition.
Figure 9-53 shows checks to be made with tire demounted.
Bulges--Broken Cords Check any tires which were marked for bulges when the tire was mounted and inflated. If no break is found on the inside of the tire, probe with an awl to determine whether separation exists. If separation is found, the tire should be discarded, unless there is only a small localized separation between the tread or sidewall rubber and the cord body. In this case, spot repair or retreading may be satisfactory.
Any tire found with loose, frayed or broken cords inside should be scrapped.
IMPORTANT: Do not use an awl or any pointed tool on the inside of a tubeless tire for probing or inspection purposes.
Tubeless Tires--Bead Area A tubeless tire fits tighter on the wheel than a tube type tire, in order to properly retain air pressure. Therefore, the face of the bead (the flat surface between the toe and heel of the bead) must not be demaged as this may cause the tire to leak.
The primary sealing surface of the tubeless tire is this area, so examine it carefully for evidence of damage by tire tools, slippage while in service, or damage that would permit air to escape from inside the tire. Bare cords on the face of the bead normally will cause no trouble, and such a tire should be fit for continued service either as is, or after retreading.
Liner Blisters Tubeless tires with liner blisters or liner separation areas, larger than 4" x 8", should be scrapped.
Generally, small blisters (not over two inches in diameter) will cause no trouble and do not need to be repaired. However, do not pierce the blisters or cut them, as this will destroy the airretaining ability of the tire.
Thermal Fuze Some aircraft wheels have fusible plugs that are designed to melt at specific elevated temperatures and relieve air pressure to prevent the tire's blowing out or breaking of the wheel. Should air be lost due to the melting of one of these plugs, it is recommended that the tire involved be scrapped.
However, an effort should be made to determine whether the plug melted at a much lower temperature than it should have, or whether air could have been lost around the plug because of improper installation.
If a tire has been subjected to a temperature high enough to melt one of these fuze plugs, it should be carefully inspected for evidence of reversion of the rubber coating in the rim contact area.
Figure 9-54 shows typical marking for bulged area, rubber reversion around rim, and outer sidewall damage.
A. Mark bulged areas. B. Outer sidewall ply damaged, C. Reversion of rubber from high scrap tire. wheel heat.
FIGURE 9-54. Basic tire maintenance
TUBE INSPECTION Proper Size In tube type tires, failure of an inner tube can easily cause irreparable damage to the tire in which it is mounted, as well as to the wheel and the aircraft itself. It is very important that tubes be of the proper size and equipped with the correct When inspecting tubes do not inflate with more air than that which is required to simply round out the inner circumference of the tube.
much air places a strain on splices and areas around valve stems. In addition, excessive air will damage fabric base tubes by causing the fabric base to pull away from the outside of the tube.
Inspect the tube carefully for leaks while under pressure, preferably by inflating and submerging in water. If the tube is too large to be submerged in an available water tank, spread water over the surface as you inspect the tube, and look for bubbles.
Valve Stems Examine the tube carefully around the valve stem for leaks, signs of valve pad separation, and bent or damaged valve stems.
Wrinkles Tubes with severe wrinkles should be removea from service and scrapped. These wrinkles are evidence of improper fitting of the tube within the tire, and wherever a wrinkle occurs, chafing takes place. A blowout could result.
Chafing Inspect tubes for evidence of chafing by the toes of the tire beads. If considerable evidence of this chafing is present, remove the tube from service and scrap.
Thinning Where the heat is greatest, the tube has a tendency to be stretched over the rounded edge of the bead seat of the wheel. This is one of the reasons why, when mounting, tubes should always be inflated until the tire beads are in position, and then completely deflated and reinflated to the final pressure. The stretch on the tube is then equalized throughout its inner and outer periphery.
Also check tubes for possible thinning out due to brake drum heat in the area where they contact the wheel and bead toes.
In figure 9-55 it can be seen that the "set" or shape of the tube can assist in determining when it should be removed from service because of thinning in the bead area. In addition, feeling the tube with the fingers in that area will tell, after a little practice, when the life has gone out of the tube and it should be scrapped.
On wheels with only one brake drum this heatset condition will normally show up on only one side of the tube. In those cases where the brake drum is a considerable distance from the rim, it is unlikely that this condition will ever be experienced 384