If the aircraft stands in one place under a heavy static load for several days, local stretching may cause an out-of-round condition with a resultant thumping during takeoff and landing.

On dual-wheel installations, tires should be matched according to the dimensions indicated in table 11-1. Tires vary somewhat in size between manufacturers and can vary a great deal after being used. When two tires are not matched, the larger one supports most or all of the load. Since one tire is not designed to carry this increase in load, a failure may result.

Learning Objective: Identify the procedures for the selection, storage, and inspection of aircraft tire tubes.

The purpose of the inner tube is to hold the air in the tire. Tubes are identified by the type and size of the tire in which they are to be used.

Tubes are designated for the tires in which they are to be used. For example, a type I tube is designed for use in a type I tire. The size of the tube is the size of the tire in which it is designed to fit. Inner tubes required to operate at 100 psi or higher inflation pressures are usually reinforced with a ply of nylon cord fabric around the inside circumference. The reinforcement extends a minimum of one-half inch beyond that portion of the tube that contacts the rim.

Table 11-1.Tolerances for Diameters of Paired Tires in Dual Installations

Type III and type VII inner tubes have radial vent ridges molded on the surface, as shown in figure 11-29. These vent ridges relieve air trapped between the casings and the inner tube during inflation. Inner tube valves are designed to fit specific wheel rims. However, special valve-bending configurations or extensions to provide access to the valve stem when you are servicing the tire may be required.

Tubes should be stored under the same conditions as new tires. New tubes should be stored in their original containers. Used tubes should be partially inflated (to avoid creasing), dusted with talc (to prevent sticking), and stored in the same manner as tires. Each tube should be plainly marked to identify contents, size, type, cure date, and stock number. Under no circumstances should inner tubes be hung over nails or hooks.

Inner tubes should be inspected and classified as serviceable or nonserviceable. Usually, leaks due to punctures, breaks in the tire, and cuts can be detected by the eye. Small leaks may require a soapy water check. Complete submersion in water is the best way to locate small leaks. If the tube is too large to be submerged, spread soapy water over the entire surface and examine carefully for air bubbles. The valve stem and valve base should be swished around to break any temporary seals. The tube should be checked for bent or broken valve stems and stems with damaged threads.

Figure 11-29.Inner tube vent ridges.