TM 1-410. Technical Manual, Airplane Structures 1941: Section 9 - Tires and Tubes

SECTION IX: TIRES AND TUBES

31. Tire casings.-a. Airplane tire casings are divided into four general groups, streamline, smooth contour, low pressure, and airwheel. The principal difference between these groups is in the shape of the casing in cross section as shown in figure 37.

FIGURE .37.-Casing contours.

(1) The streamline casings are of two types, pointed tread contour and rounded tread contour. Their only difference is in the shape of the tread.

(2) Smooth contour casings differ from streamline casings principally in the increased distance between the tire beads at the rim flanges.

(3) The low pressure and airwheel casings carry comparatively low air pressures relative to their large over-all tire dimensions.

b. Some tires have nonskid treads for additional braking traction and because of the difference in traction between these and tires with plain treads, casings for landing gear wheels should be used only in like pairs.

c. Casing sizes are usually designated by maximum outside diameter of casing when inflated, but in some types width of inflated casing and hub diameter are also used.

32. Inner tubes.-Inner tubes are furnished for each of the principal shapes of casings. In many sizes, tubes are obtainable in both regular and punctureproof types. Punctureproof tubes have a puncture-resisting compound bonded to the inside of the tube with the thickest portion at the tread, tapered at both edges and of sufficient width to cover tread portion of the tube.

33. Tire pressures.-a. If tire pressure is allowed to become too low the tire will completely collapse on hard impact, causing abnormal loads on the wheel. On the other hand if the pressure is carried too high the force on the rim will be abnormal which may in time cause failure of the wheel. It is therefore essential that tire pressures be kept within close limits of recommended values.

b. Most tires, except older types, have deflection markers moulded into the side walls for the purpose of determining proper inflation. When using these markers, tires should be resting on a smooth, firm surface and tires are inflated to a point where deflection markers just touch the ground as shown in figure 38. Some tires have the amount of inflation pressure moulded on the side wall. In such cases these indicated pressures are maintained, except when the tire is used as an "oversize" on certain airplanes. When tires have neither deflection markers nor pressures moulded on the side wall, the handbook of instructions for the airplane and the Air Corps Technical Order "Aircraft Tire Pressures" should be consulted for this information.

c. When operating airplanes equipped with streamline tires from frozen, rutted fields, the tire pressures may be increased 25 percent above normal to prevent tire damage. This increase in pressure can be determined by checking normal inflation with a tire gage and increasing pressure required amount. When operating from soft, sandy, or muddy fields with either streamline or standard tires, pressure may be reduced 25 percent below normal to facilitate take-offs.

34. Maintenance.-a. Landing and tail wheel tires, with a few exceptions as specified in the basic handbook of instructions for related equipment, are removed by line personnel only when there is evidence of need for further inspection or possibility of internal defects. It should be realized that considerable damage may be done to a tire and tube during removal or reinstallation if improperly done. Care must also be taken that the wheel rim is not damaged by careless use of tire-mounting tools or impact with other objects during repairs or replacements.

b. Tire casings are replaced with serviceable like casings if any of the following defects are found:

(1) Internal or side wall ruptures or breaks.

(2) Tread cuts or wear exposing fabric to moisture or dirt.

(3) Side wall blisters which cannot be repaired.

(4) Damage to beads extending through outside rubberized chafer fabric.

FIGURE 38.-Tire deflection markers.

c. Each time a. tire is removed, the wheel rim should be thoroughly cleaned and if protective coatings are worn through to the metal they will be renewed with the same material as the original. Areas worn through to the primer should be retouched.

d. Procedure for mounting casings on wheels with a drop center rim is as follows:

(1) Rub both beads of casing with soft soap. The soap can be applied either in solid form or heavy lather, as desired. This is to aid in seating beads.

(2) Mount one bead of casing on rim. When casings have red balancing dots on the side wall, they are to be so mounted that the red dot coincides with location of inner tube valve.

(3) Dust entire tube surface with tire tale, insert tube in casing, properly aline valve in valve hole and apply lock nut loosely.

(4) Add enough air to shape the tube properly, and smooth out the folds by hand. If too much air is added, difficulty will be encountered when mounting remaining bead of casing.

(5) Mount second bead of casing starting at valve and add air slowly until casing beads seat. If beads do not seat properly, deflate casing and realine them so that they will seat properly when tire is inflated.

(6) Remove valve core and fully deflate tube to relieve pressure on any folds or wrinkles and to permit tube to assume its proper contour within the casing. Be sure that both casing beads remain properly seated on rim.

(7) Replace valve core, inflate to required pressure, and tighten valve lock nut.

e. Tread cuts which do not penetrate the first layer (ply) of fabric, may be repaired by cleaning thoroughly and filling with commercial cut filler. Side wall blisters which can be cleaned with no damage to the fabric may be repaired with rubber cement. If the rubber fairing immediately above the rim flange has separated from the fabric and there is no injury to the fabric, this may also be repaired in the same manner. Inner tubes having extra thickness in the portion coming in contact with the wheel rim need not be replaced because of wrinkles, provided there is no evidence of damage due to chafing. Punctures, small cuts, or holes may be repaired by patching if it is obvious that such repairs will render the tube serviceable. For such repairs a repair kit is used and instructions on the kit container must be followed carefully. Inner tubes will be replaced if any of the following defects are found:

(1) Valve.-Physical damage or faulty attachment to the tube.

(2) Tube body.-Evidence of thin spots, chafing, or damaged areas due, to casing breaks.