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
A. Natural contour. B. Taking a "set". C. Thinned out at edges.
FIGURE 9-55. Inner tube inspection.
Fabric Base Tubes In cases where brake drum heat is a recognizable factor, careful checking of the tube, as well as the tire beads, should be made to prevent a failure which might be disastrous. In such instances, fabric base tubes should always be used.
These have a layer of nylon cord directly imbedded in the inner circumference of the tubes to protect them from thinning out under brake drum heat. Additional protection is also provided against chafing action of the tire bead toes and from damage during mounting and demounting.
MOUNTING AND DEMOUNTING The object of these instructions is to show how to do the job as easily, and safely as possible, using proper tools, without damaging tires, tubes or wheels.
Almost every experienced aircraft tire service man has developed methods which are more or less his own, and undoubtedly some of these methods are as practical as the suggestions given here.
These instructions are intended to be simple, so that they can be carried out with tools which are commonly available, in contrast to the specialized equipment that is usually available only at larger airports or military installations.
Inspection, Tube Installation Before mounting any tire, examine the wheel carefully to make sure there are no cracked or injured parts. Naturally, the tire and tube should be carefully inspected, as described in the pages dealing with tire and tube inspection. A quick check should always be made to be certain that no foreign material is inside the tire or clinging to the inner tube.
Dust the inside of the tire and the inner tube outer surface with tire talc or soapstone before the tube is installed in the tire. This will prevent its sticking to the inside of the tire or to the tire beads.
Dusting also helps the tube assume its normal shape inside the tire during inflation, and lessens the chances of wrinkling or thinning out.
It is good practice to always mount the tube in the tire with the valve projecting on the serial side of the tire.
Lubrication Tubeless tires fit tighter on the wheel than the tube type. It is therefore desirable to lubricate the toes of the beads with an approved 10 percent vegetable oil soap solution, or plain water. This will facilitate mounting and accomplish proper seating of the tire beads against the wheel flanges so there will be no air loss. Care must be used, however, to make certain that none of the solution gets on the area of the bead making contact with the wheel flange.
On tube type tires, lubrication of tire beads may or may not be necessary, depending upon the type of wheel being used. An approved mounting solution, such as the 10 percent vegetable oil soap solution, or water mentioned above, can be used on the bead toes, and even on the rim side of the inner tube, to facilitate mounting.
Balance Balance in an aircraft wheel assembly is very important. From a wear standpoint, when the wheels are in landing position a heavy spot in a wheel assembly will have a tendency to remain at the bottom and thus will always strike the ground or runway first. This results in severe wear at one area of the tire tread and can necessitate early replacement. In addition, unbalanced tires can cause severe vibration which may affect the operation of the aircraft. In fact, pilots have reported that sometimes instruments could not be read because of such vibration.
A. Valve projecting on serial side of tire. B. Tube balance mark aligned with tire balance mark.
FICURE 9-56. Basic tire and tube assembly.
Balance marks appear on certain aircraft tubes to indicate the heavy portion of the tube. These marks are approximately ½" wide by 2" long.
When the tube is inserted in the tire, the balance mark on the tube should be located at the balance mark on the tire (figure 9-56). If the tube has no balance mark, place the valve at the balance mark on the tire.
When mounting tubeless aircraft tires, the red dot balance mark on the tire must always be placed at the valve that is mounted in the wheel.
Inflation Safety After the tire and tube are mounted on the wheel the assembly should be placed in a safety cage for inflation. The cage should be placed against an outside wall, constructed so as to withstand, if necessary, the effects of an explosion of either the tire, tube or wheel (figure 9-57).
The air line from the compressor or other air source should be run to a point at least 20 to 30 ft.
away from the safety cage and a valve and pres sure gage installed at that point. The line should A. Clip-on chuck permits inflation at B. Recommended for all aircraft tire shops.
safe distance from tire safety cage.
FICURE 9-57. Inflation precautions.
then be continued and fastened to the safety cage with a rubber hose extending from that connection.
A clip-on chuck is then fitted on the end of the hose for actual inflation purposes. This arrangement makes it unnecessary to reach into the cage to check air pressures or to be anywhere near the safety cage while the tire is being infiated.
Seating Tube Type Tires To seat the tire beads properly on the wheel, first inflate the tire to the pressure recommended for that particular size and for the aircraft on which it is to be mounted. Then the tire should be completely deflated and finally reinflated to the correct pressure (do not fasten valve to rim until this has been done). Use the valve extension for inflation purposes, it necessary.
This procedure accomplishes the following: it helps to remove any wrinkles in the tube and to prevent pinching the tube under the toe of the bead; it eliminates the possibility of one section of the tube stretching more than the rest and thinning out in that area; and it assists in the removal of air that might be trapped between the inner tube and the tire.
NOTE: With tubeless tires, it is not necessary to go through this inflation-deflation-reinflation procedure.
Let Stand-Then Recheck It is recommended that a newly-mounted assembly be stored away from work areas for at least 12 hours and preferably for 24 hours. This is for the purpose of determining if there is any structural weakness in either the tire, tube or wheel. This also permits rechecking of the tire, after the 12- or 24-hour period, to determine any drop in pressure and to judge whether this drop in pressure is in accordance with normal tire growth.
By such a test, when the assembly is mounted on the aircraft, it can be done with the assurance that each part of the assembly is satisfactory for service.
Demounting Safety Always be sure to deflate tires completely before demounting. There have been many serious accidents caused by failure to follow this important step. For even a better practice, it is recommended that tires be deflated before wheels are removed from the aircraft.
NOTE: Use caution when unscrewing valve cores, as the air pressure within the tube or tire can cause a valve core to be ejected like a bullet.
Handle Beads and Wheels With Care With any type of wheel, the tire beads must be loosened from the wheel flange and bead seat before any further steps are taken in demounting.
Be very careful not to injure the beads of the tire or the relatively soft metal of the wheel. Even with approved tools, extreme care must be taken.
A. Tubeless Split Wheels In the tubeless design, the tire and wheel are used to retain air pressure. Inflation is accomplished through a tubeless tire inflation valve installed in the wheel. The wheel valve hole, in which the tubeless tire inflation valve is mounted;
is sealed against loss of air by a packing ring or by an "O" ring. (See figure 9-58.)
Split wheels are sealed against loss of air by an "O" ring mounted in a groove in the mating surface of one of the wheel halves.
Demountable flange wheels are similarly sealed against loss of air by an "O" ring installed in a groove on the wheel base under the area covered by the demountable flange.
The air pressure contained in the tubeless tire seals the tire bead against the wheel bead seat to prevent loss of air.
Wheels used with disc brakes have thermal fuze (relief) plugs installed in the rotor drive area of the wheel as a protective measure against the tire blowouts due to excessive heat. The plugs have a fusible metal core that melts at a predetermined temperature to relieve the high pressure build-up.
Mounting Check tubeless tire inflation valve and thermal relief plugs for proper installation, and absence of damage. Refer to wheel manufacturer's manual for installation procedure.
Inspect "O" ring used to seal wheel for damage and replace if necessary.
Lubricate "O" ring (as specified by the wheel manufacturer) and install in wheel groove. Make sure the "O" ring is free of kinks or twists and is seated properly.
Mounting a demountable flange on a wheel base.
be careful not to dislocate or damage the "O" ring previously installed in the wheel base.
Mount tubeless tires in the same manner as tube type tires. Make sure that the wheel bead seats are clean and dry to insure proper sealing of the tubeless tire bead.
Assemble wheel halves of split type wheels with the light sides (impression stamped "L" on the 387
A. "O"-ring seal is vital - handle and install carefully. B. Inspect valve seals for signs of damage or deterioration.
FICURE 9-58. Split wheel seal inspection.
flanges) 180° apart from each other to insure minimum out-of-balance condition.
Be sure that nuts, washers, and bolts used to assemble split type wheels are in proper order and that the bearing surfaces of these parts are properly lubricated. Tighten to recommended torque values. See wheel manufacturer's manual for recommended procedures.
Demounting The procedure for demounting tubeless tires is generally the same as for tires with tubes. However, care must be taken to avoid damaging: (1) the wheel's "O" ring groove and mating register surfaces; (2) the flange area that seats the tire bead; and (3) the tubeless tire inflation valve hole sealing area. These areas of the wheel are critical and if damaged will result in failure of the wheel and tire unit to maintain required air pressure.
B. Tube Type Tires Mounting With the tube entirely deflated, insert it in the tire (folding makes this easier, particularly in small diameter tires), and inflate until the tube is just rounded out. The valve core should be in the valve during this operation.
Apply with brush or swab a 10 percent solution of vegetable oil soap to the rim of the tube extend ing well up into the tire. Use care not to lubricate any part of the bead which comes in contact with the rim flange.
Insert the valve hole section of the wheel into the tire and push the valve through the valve hole in the wheel.
Insert the other side of the wheel while holding the valve. in position. Be careful during this op eration not to pinch the tube between the wheel sections.
Inflate, deflate and reinflate to the recommended pressure.
Install the locking nut or nuts and tighten securely. Put on valve cap and tighten with fingers.
Demounting Remove valve core and fully deflate.
Do not use a pry bar, tire irons or any other sharp tool to loosen tire bead as the wheel may be damaged. Break bead before loosening tie bolts to prevent damage to register surfaces.
Use a bead breaker only to loosen tire bead from both wheel half flanges by applying pressure around the entire circumference of each sidewall.
Remove the tie bolts and the bolt nuts from the wheel and pull out both parts of the wheel from the tire.
C. Removable Side Flange Drop Center Wheels Mounting Fully deflate tube and line up tube balance mark with tire balance mark. Start tire over flange on an angle, being careful not to damage valve.
Be sure to remove valve extensions or valve fishing tools before wheel is installed.
Demounting Be sure to deflate fully.
Make full use of the wheel in pulling bead over flange on removable side.
Work wheel up and down to ease it out of tire.
For one-man demounting, tire can be leaned against a wall or bench, valve side out.
D. Smooth Contour Tail Wheel Tires Note: Smooth contour tires are usually harder to handle because of stiffer beads, small clearances and small diameters.
Mounting Inflate tube sufficiently to round out and be sure tube is worked in all around to avoid pinching.
Work bead opposite valve over edge of wheel first. Deflate tube.
Keep second bead on edge of wheel to allow for inserting valve in valve hole.
Inflate, deflate, reinfiate.
Demounting Be sure to use tools with good leverage.
Be careful not to damage soft metal of rim flange.
Keep tube inflated after lock ring is removed.
Work tube out carefully, using water as a lubricant before completing demounting.
F. Flat Base Wheels Removable Flange Locking Ring Mounting Examine wheel and flanges carefully for burrs or gouges.
Line up tube and tire balance marks.
Dust tube with talc.
Lean tire against bench or wall--flange outward.
Pry flange loose evenly to prevent binding.
Demounting Loosen bead carefully.
Use lead hammer or rubber mallet to loosen side ring.
Pry up side ring carefully and evenly.
Place wheel and tire on a wooden block about 14" high and large enough to fit over the wheel hub, so that wheel can be removed easily.
CAUSES OF AIR PRESSURE LOSS
IN TUBELESS AIRCRAFT TIRES There can be numerous causes for loss of air pressure within an aircraft wheel and tire assembly, therefore, it is economical and wise to follow a systematic check list. Without such a procedure, trial and error substitution of parts can needlessly increase tire maintenance costs.
For example, complaints of air loss in tubeless aircraft tire assemblies, while more common during cold weather, have no seasonal limitations. Factors which may seem distantly related to the problemchanges in tire maintenance personnel, inaccurate gages, air temperature fluctuations-are often the underlying causes of unsatisfactory tire service, further emphasizing the need for simple check procedures.
For guidance in setting up uniform inspection methods, there are general areas of the tire and wheel assembly which can be involved in air pressure loss. (See figure 9-59.)
E. One Piece Drop Center Wheels Mounting Insert wheel in tire, reversing the customary procedure. (Valve hole side goes in first.)
Pry bead over flange with small bites-use a fairly thin tool.
When first bead is on wheel, insert tube. Be sure no part of tube is caught under bead.
Inflate, deflate, reinflate.
Demounting After loosening bead, lay tire flat with wooden block, 3 to 4 inches high under sidewall. Work bead off in small bites. FIcURE. 9-59. Air loss in split wheels.
Damaged Beads-Check for exposure of the carcass cord body in bead toe area or under face of the bead.
Improperly Seated Beads-Condition can be caused by: (a) insufficient air pressure; (b) beads not lubricated; (c) kinked or distorted beads.
Cut or Puncture--Check for cut or puncture entirely through the carcass cord body and liner.
Air Temperature Was tire inflated in heated room and then stored outside? Air pressure will drop approximately 1 psi for every 4° drop in temperature. Tires should be checked and pressure adjusted for specific requirements when tires have reached the outside ambient temperature.
Venting of Tubeless Tires Tubeless aircraft tires are vented in the sidewall area to permit any air that has diffused through the liner and cord body to escape, thus preventing pressure build up within the carcass cord body and possible tread or ply separation. Rate of diffusion will vary by manufacturer and the maximum permissible is no more than 5 percent in any 24-hour period.
Vent holes penetrate the sidewall rubber to, or into, the carcass cord body and may vary in size, depth and angle. Therefore, the amount of air diffused through these holes will vary. Thus, when water or a soapy solution is brushed over the outside of an inflated tubeless tire, air bubbles form.
Some vent holes may emit a continuous stream of bubbles, where others may produce intermittent bubbles. This is normal and does not mean that there is anything wrong with the tire. In fact, as long as a tubeless tire is in an inflated condition, air will be coming out of these vent holes. Where the rate of loss exceeds 5 percent 24 hours, recheck for possible injuries. Vent holes may be covered or closed by spilled solvent or by the tire paint.
They may also be covered during the retreading process, Check for evidence that tubeless tires have been revented after being retreaded.
Initial Stretch Period All aircraft tires are of nylon construction and a certain amount of stretch occurs after the tire has been inflated. This, in itself, will reduce air pressure within the tire. It is absolutely necessary that the tire be inflated to its regular air pressure and let stand at least 12 hours in order to permit this expansion of the cord body. This may result in as much as 10 percent drop in air pressure.
Compensate by reinflating the tire to original pressure. Only after this initial stretch period can it be determined if there is any true air loss within the tire.
THE WHEEL Any of the following wheel conditions can contribute to air loss in the bead area of the tire:
Cracks Or Scratches In The Bead Ledge Or Flange Area Cracks can usually be traced to fatigue failure while scratches and gouges are the result of handling damage or the improper use of tire irons.
Exceptionally Smooth Enamel Surface On Bead Seat Ledges Corrosion Or Wear in Bead Ledge Area Usually occurs at the toe area of the tire bead.
Poor Seating In Bead Area May be caused by accumulation of rubber from the tire or dirt.
Knurls Wheels converted from tube-type use should have knurls removed.
Porous Wheel Assemblies Can be protected either by proper paint procedure and/or an impregnation process.
Holes for attachment of components of wheel assembly. In case of through bolts used to attach such items as drive lugs for brake assembly, etc., the mounting screws or bolts must be properly sealed. The recommendations of the wheel manufacturer should be followed.
Cracks in the wheel well area, in most cases, cannot be repaired.
Sealing Surfaces Look for damage or improper machining of sealing surfaces. Care should be taken to see that there is no handling damage. Any irregularities should be corrected before remounting wheel and tire. (See figure 9-60.)
Foreign material or paint can impair the sealing surface. Thus, all foreign material should be cleaned from the sealing surface before assembly of the wheel. A light, even coat of primer is per.
missible. However, surface must be free of runs or dirt inclusions.
FIGURE 9-60. Wheel inspection.
Improper Installation of "O" Rings Twisting or failure to provide lubricant when specified, may cause loss of air. The wrong size or type of "O" ring, or an "O" ring of the wrong compound for special low temperature service, may also cause leakage.
Inspect used "O" rings carefully. Be sure they are not thinned out, deformed, chipped, damaged or otherwise deteriorated.
Wheel Tie Bolts Proper torque and torquing procedure, as specified by the wheel manufacturer, should be followed to assure adequate compression of sealing "O" ring under all temperature conditions. Low torques, low temperatures, and shrinkage of the wheel halves may cause a significant lessening of compression on the "O" ring seal.
Tubeless Wheel Valve Holes Tubeless wheel valve holes and surrounding area must be free of scratches, gouges and foreign material.
The proper rubber grommet or "O" ring must be used as specified by the wheel manufacturer.
Seals other than those specified may not function properly under the compression loads and low temperatures required for good sealing. Tightening of tubeless valve should follow specific instructions of wheel manufacturer.
Valve core should be checked and replaced when found leaking.
Valve caps should be used and tightened finger tight.
Thermal Fuze Installation A faulty thermal fuze may cause leakage and require replacement. Usually this is the result of a poor bond between thermal melting material and bolt body.
Sealing surface for thermal fuze gasket must be clean and free from scratches and dirt. In some cases, surface can be repaired in accordance with manufacturer's instruction.
Be sure that sealing gasket is the one specified by the wheel manufacturer, sized and compounded for its specific job. Gasket should be free of dis tortion, cuts, etc.
To guard against air pressure losses before as sembly the best insurance is a careful and complete inspection. After assembly, if air loss occurs, the use of a soap solution (or, if possible, complete immersion of wheel-tire assembly) may pinpoint the exact source of leakage.
GOOD PRESSURE GAGE PRACTICE Quite often it is found that the differences in reported air pressures are entirely due to the difference in accuracy in different gages, rather than in any change in air pressure.
It is not unusual to find an inaccurate tire gage in constant use with a tag that states that the gage reads a certain number of pounds too high, or too low. Unfortunately, this error will change as ditferent pressures are checked. A tire gage reading 10 Ibs. high at 80 Ibs. pressure may very well read 25 Ibs. too high at 150 Ibs. pressure. Therefore, incorrect tire gages should either be repaired or replaced. They should not be continued in service.
Cold temperatures may also affect tire gages and cause pressure readings lower than they actually are. Occasionally, too, a gage has been mistakenly treated with oil or some other lubricant in expectation of making it work better.
will actually cause incorrect readings and probably render the gage unfit for further service.
It is good practice to have gages recalibrated periodically and to use the same gage for performing an inflation cycle-for the original 12- or 24- hour stretch period. Dial type gages, of good quality, are highly recommended for all tire maintenance installations-regardless of size!
Storing Aircraft Tires and Tubes The ideal location for tire and tube storage is a coo., dry and reasonably dark location, free from air currents and dirt. While low temperatures (not below 32° F.) are not objectionable, high room temperatures (80° F.) are detrimental and should be avoided.
Avoid Moisture, Ozone Wet or moist conditions have a rotting effect and may be even more damaging when the moisture contains foreign elements that are further detrimental to rubber and cord fabric. Strong air currents should be avoided, since they increase the supply of oxygen and quite often carry ozone, both of which cause rapid aging of rubber. Also, particular care should be taken to store tires away from electric motors, battery chargers, electric welding equipment, electric generators and similar equipment as they all create ozone.
Fuel and Solvent Hazards Care should be taken that tires do not come in contact with oil, gasoline, jet fuel, hydraulic fluids, or any type of rubber solvent, since all of these are natural enemies of rubber and cause it to disintegrate rapidly. Be especially careful not to stand or lay tires on floors that are covered with oil or grease. When working on engines or landing gear, tires should be covered so that oil does not drip Store In Dark The storage room should be dark, or at least free from direct sunlight. Windows should either be given a coat of blue paint or covered with black plastic. Either of these will provide some diffused lighting during the daytime. Black plastic is preferred as it will lower the temperature in the room during the warm months and permit tires to be stored closer to the windows.
Tire Racks Preferred Whenever possible, tires should be stored in regular tire racks which hold them up vertically.
The surface of the tire rack against which the weight of the tire rests should be flat and, if pos- Without With Tube Size Tube Inserted 26x6 5 33" 5 36" 44" 5 47" 3 4 sible, 3 to 4 inches wide in order that no permanent distortion to the tire is caused. If tires are piled on top of one another, they should not be stacked too high, as this will cause distortion of the tire and might result in trouble when the tires are put into service. This is particularly true of tubeless tires, as those on the bottom of the stack may have the beads pressed so closely together that a bead seating tool will have to be used to force the tire beads onto the wheel far enough to retain air pressure for inflation (figure 9-61).
Safe Tube Storage Tubes should always be stored in their original cartons, so that they are protected from light and air currents. They should never be stored in bins or on shelves without being wrapped, preferably in several layers of heavy paper.
Tubes can also be stored by inflating slightly and inserting them in the same size of tire. This of course, should only be done as a more or less temporary measure. However, before using such an assembly, the tube should be removed from the tire and the inside of the tire carefully examined, since quite often foreign material will get between the two and if not removed, could cause irreparable damage to both tire and tube.
Under no circumstances should tubes be hung over nails or pegs, or over any other object that might form a crease in the tube. Such a crease will eventually produce a crack in the rubber.
REPAIRING Many aircraft tires and tubes which become injured in service can be successfully repaired. Likewise, aircraft tires which have become worn out in service, or flat spotted and removed prematurely, Without With Tube Size Tube Inserted 56" SC and larger
12.50-16 4
15.00-16 3
17.00-16 3
15.50-20 3
17.00-20 3 4 smaller sizes of tubess tires may be stacked five high. This would include sizes througi 39 × 13. Larger sizes of tubless tires should not be stacked more than four nigh FIcURE 9-61. Permissible tire stacking.