Aircraft Tire Composition (Dunlop)
The only items between the the aircraft structure and the earth are its tires. These take the full load especially during landing and must provide for a comfortable ride during taxi to the hanger. Aircraft tires must be checked during preflight for the proper pressure and other irregularities and by maintaining them the pilot or aircraft owner can increase their service life and reduce operating cost.
As can be seen from the image above and below the tread is the part that comes into contact with the run/taxiway. Under normal conditions you may expect this part to wear if the tires are kept under proper inflation as specified by the aircraft manufacturer.
Proper inflation is important as this will keep the tire from a premature end due to excessive wear or even a blown tire during landing. In this article we show you some tips to keep your tires in the best condition possible.
The tread is made of a thick rubber to provide the correct level of traction so that it does not wear away too quickly, giving the tire its full life span. The tread contains grooves to get rid of any rain during landings on wet surfaces.
With normal landing techniques tires should last you for years. Flight schools may expect a shorter life span due to higher student pilot induced stresses on the landing gear.
The sidewall is the part that contains the air pressure and deforms during rough landings. It is made from rubber reinforced with fabric and or steel cords.
Within the tire you will find layers of cords and these layers (or plies) are layed out in different orientations (longitudinal/ diagonal) to provide flexibility and stiffness for the rubber, see image to the right.
With proper installation on the wheel and correct tire pressure we make sure that the load is evenly distributed, this reduces the rolling resistance (and of course the take off distance) and ensures maximum life from the tires.
This causes more heat to be generated in the rubber as the tire deforms when rolling. As a result it will reduce the life span due to the breakdown of the rubber components. Take off distance will also increase as the possibility for the tire to come off the wheel during a not so perfectly executed crosswind landing.
Take off distance will increase and you may not be able to clear obstacles beyond the end of the runway, which is an important factor here! Ironically, landing distances will reduce with under inflated tires and increase with proper inflated tires, think about rolling resistance!
As we all know, air gets thicker when cold. For tires this means that every 5° F temperature change the pressure in the tire will also change about 1 %. So a lower OAT will result in lower tire pressures too. Make sure to check these when colder weather approaches.
Check the pressure when the wheels, with inflated tires, are installed on the aircraft. There is about 4 % difference (increase of pressure) when the tires are loaded with the full aircraft weight.
Check the pressures regularly (monthly) and during preflight. Expect to bring them up to the correct pressure about once every couple of weeks. If you let the aircraft sit too long with under inflated tires it will become difficult to tow around and the tires will develop flat spots, which you will notice during taxi.
The pilot operating handbook or the aircraft flight manual will state the correct numbers depending on the aircraft model and actual load. Make sure that you verify your pressure gauge with a good one from the maintenance shop, some cheap ones are not to be trusted at all.
Most common in cars but not so much in general aviation aircraft. When replacing the inner tubes make sure to use talcum powder as it makes the tube slides in easily with out any folds that might rupture someday. Also do inspect the wheel on the inside for any burrs as they will cause a flat tube eventually.
Ultraviolet rays from the sun will result in damage to the rubber, especially so when aircraft are sitting outside their whole lives and as a result you will need to replace them sooner.
As you can see tire maintenance is important for safety reasons and top performance of the aircraft. Check them during preflight and keep the pressure to the correct value and they will last you for a very long time to come.