Air Liner Tire Wear

I think the lubricants they use on the aircraft are more tolerant to the cold (and heat for that matter).

I agree with Sledriver as all aircraft on longhaul flights often fly so high that it can get to -60°C up there, and I do believe that the wheel wells are not specially insulated or heated.......its normal business so to say. Perhaps someone in the aircraft industry can assist more accurately.

I also suspect that a cold tire, having less grip because it is cold, will also wear less under the same conditions as a warmer one......thats what happens with car tires.

Which is why a winter tire is softer, so that it generates more heat easily in use to improve the grip in cold conditions....by raising the temperature of the rubber as it flexes.

A tyre warms up pretty quickly when forced, suddenly, to accelerate to landing speed while many tons of aircraft settle upon it; the evidence that heat is released is the smoke that comes from it at the instant of landing. It's a severe duty for any tyre to withstand, which is why aircraft have so many of them.

1. Yes, they use special lubricants to withstand cold temperatures. But they are not probably gonna be at high altitude temperature, because the landing gears are down in the initial approach, to make sure they work and help speeding down, so they will be at approximately the temperature of the air in the approach line. Lots of forced convection... Mainly, the grease in the landing gear struts must not freeze to allow deployment.

2. And the tires and filled with high pressure nitrogen to minimize temperature effects.

3. Off course they'd slip in ice runways. Also in heavy rain. Thanks there's ABS, automatic braking with controlled intensity, and engine reverse to help stopping.

Sometimes they dont stop anyway... but they are only statistics...

I thought that the tyres on jet aircraft were spun up before landing, so the lubricant would already have been primed - come-on you airplane specialists, help us out with some facts.

No, they're not. Except for some unvoluntary movement caused by air impact.

The system is as simple as it can be. A retractable shock strut, axles, wheels and brakes with ABS. Nothing more than this.

Most turbofan aircraft typically operate at 35,000-40,000 ft in the stratosphere where the average (standard) temperature is -69 F. The wheel wells are not heated nor pressurized; therefore, the landing gear becomes thoroughly cold soaked during extended flights (as occasional wheel-well stowaways have discovered). During the descent to landing, some warming occurs. When the gear are extended into the slipstream for landing, they are rapidly "warmed" by convection towards the ambient temperature, but the wheel, hubs and bearings can still be very cold at landing. The tires, bearings and lubricants must be certified to function at extreme temperatures, and the aircraft wheel-bearing grease does not solidify or become sufficiently viscous to seriously affect rotating performance. As a side note, the certification process requires cold-weather testing of the aircraft and its systems. I had the opportunity to participate in this once, and we took our aircraft to Churchill, Canada for about two weeks in the winter where the temperature averaged -35 to -40F. Wheel rotation (or lockup) was never a problem. Starting the turbines is tough, and anything that accumulates moisture is solidly frozen. Doors, APU's, brakes, switches, ECU's, generators all have to work properly. The components are designed to withstand such temperatures, and sometimes they don't work as advertised which requires a "fix" or replacement before certification is granted.

Every so often, an aircraft tire manufacturer produces a tread design such that the slipstream will "pre-spin" the wheel to reduce touchdown wear, but these never were cost-effective to my knowledge. There have also been a few aircraft with electric motors to pre-spin the main landing wheels, but the additional weight and problems with the motors and mechanism outweighed the benefits. The bottom line is the tires (and the landing gear itself) take a severe "beating" on touchdown. They're designed that way.

Great response You get an A and move to front of the class..

1-What determines the life span of the tire and are they recapped?

2-If some one could save 30-50 % tire wear on each landing, would it be of value?

No fun if the wheel comes off before you get there!

1- The life span is determined by visual inspection. When worn, replace.

After wheel disassembly the tire is more detailed inspected to check wear level in its reinforcements. If acceptable, yes, they are recapped, as many times as possible.

2- Yes, would be. But an airplane landing is not a process so well controlled as you might think. When the tires are damaged by the track, that's not because the pilot was angry (well, sometimes its true, but...), but because there was windy, cloudy, rainy, wind-shear, end of runway (hit brakessssssssss), failure in the ABS module, some other airplane part in the way, etc. I used to work for a large carrier that had a record of tire recapping, an average of 10 times each tire. This was due to a special training with the pilots to land sssssmmmmoooooooottttthhhllllyyyyy. The problem with this procedure is that can only be done with good time and visibility. When airplane is shaking, put your tires on the ground, and apply load as soon as possible to make brakes work and avoid running out to the grass.

Anything that ADDS weight to the tire and wheel assembly will be rejected. Simple economics strongly favor light weight.

Pilots Need Your Help: For the sake of argument lets say we can provide a very inexpensive way to pre spin airliner wheels for touch down. Is there a Gyro effect that would make control of the air craft harder and under what conditions. Or would the reverse be come the effect of the spinning wheels?

Dellori3

Yes, there will be this gyro effect. It could make the aircraft harder to control, depending on the number of wheels and dimensions of the aircraft.

The most important question here is not the price of the device, but teh extra equipment to be loaded aboard, and, of course, the fact that there's one more thing to cause troubles during operation.

For an example, there are options to install fans in the aircraft wheel hubs to help brakes efficiency. It seems important, inexpensive and simple, doesn't it? Just one electric motor and a fan. Well, most of aircraft just does not have it installed, for the reasons stated above.

I think the added weight would be in the 5 lb range for two wheels , the nose gear for example.

Thanks for the reply on the Gyro effect . Need to talk to the pilots and see if they can handle it, if given exact details.

Thanks

dellori3

5 lb plus the associated inertia related to the aircraft (i.e., 5 lb times the square of the distance from the device CG to the aircraft CG). This is a data normally supplied together with the weight of the device to be added.

Negligible gyroscopic effects. Keep in mind, airplanes already have some significant rotating mass(es); i.e., the engine(s).

Incidently, airplanes experience exactly the opposite of what you suggest on takeoff. The rotating wheels are stopped manually, automatically or by friction when they are retracted.

Yes, this is to avoid gyro effect but, most important, to avoid any tire piece or any junk attached to the tire to loose and hit any system in the landing gear wheel well.