I like that question because I have been wondering the same thing for many years. I always have assumed that the basic reason is that the overhead is in cost, mechanical and maintenance complications, and simple brute weight, would be far too high for the reduction in tyre wear to justify.

However it does seem to me that we should be able to design tyres so contoured that when they are lowered into the slipstream they rotate. Apart from slowing the flight of the plane slightly (which usually would be beneficial I reckon), this should bring them far closer to matching ground speed at the point of touching down.

Of course the match would not be perfect, but even if the average tyre speed could be brought to half the ground speed, that should greatly reduce the amount of rubber lost on landing, spread the area over which the abrasion damage is worst, reduce the frequency of tyre changing, and reduce the shock of landing and the associated stress on the landing gear.

This always seems so obvious to me, safe and cheap into the bargain; could someone please explain what is so stupid about it?

I remember someone inventing exactly this a few years back. Blowouts are not infrequent, so the "pre-landing-wheel-up-to-speed-device" was supposed to be quite a money saver. I'll try to find something on the web.

Well, there are loads of links and quite a few patents applied for. I quite like the idea that the wheels will act as gyros and destabilise the aircraft. I don't have time to read all these at the moment, but here's a selection:

http://www.freepatentsonline.com/7594626.html

http://cr4.globalspec.com/thread/17808/Pre-Spin-Airplane-Wheels

http://uk.answers.yahoo.com/question/index?qid=20090501080607AAfumUB

http://www.faqs.org/patents/app/20090182462

Nice one Pete!

The magnetic patent sounds lousy to me, but the other one seems reasonable in principle. However the blog and Q&A both have interesting discussions. That should teach me (yet again, again!) to look things up more assiduously. I had thought up my turbine approach years ago, in sublime faith in my own originality, only to find that English Electric had beaten me to it by half a lifetime!

One thing I am sceptical about is the idea of the hazards of gyroscopic effects. Such effects certainly are real, but they should not be relevant to a landing plane surely? In landing the wheels would not be affected by pitch, and a landing plane should not be doing much rolling or yawing. Is there any special precaution against gyroscopic effects in takeoff, does anyone know? Such as braking before retracting the wheels?

In WWI several British fighters at least had engines that rotated, creating enormous gyroscopic forces, most famously the Camel. Novice Pilots were strictly warned against flying any way but up on take-off, until they were more than 500 feet up. In his book "The Way Of a Transgressor" Negley Farson describes how he nearly dies as a result of neglecting that advice. Conversely, the Camel could actually use the forces to achieve murderously rapid dogfight manoeuvres.

I reject the idea that landing with stationary wheels does the tyres no significant harm. I am sure that we all have seen actual flashes of fire from airliner tyres on landing, and how often do we not see puffs of smoke? That is a terribly dramatic way to do no harm to a tyre!

I wonder whether anyone has been thinking of designing aircraft tyres with deliberately consumable treads, possibly even detachable. Let down the tyres, slip on the treads, reinflate, and Bob's your uncle for the next few landings! Frankly, I suspect that some such scheme might be worth doing for cars as well.

I was very interested in the items concerning anti-skid braking on aircraft. I had no idea that anything of the type was used.

I remember a fairly recent newspaper story (last 2 years) along the usual lines: the idea works, has been patented, and will be in use within six months. Maybe it was just a puff for investment purposes. However, the idea was to mould vanes into the tyre (presumably the side wall) to have the airflow spin them up during the approach descent.

After my father stopped being a motor engineer for health reasons, he joined Vickers Aircraft at Brooklands in Weybridge. (In the days before proper computers, his job was to calculate airframe stresses under a range of loadings and aerodynamic conditions - with a slide rule!) He told me in the early 60's that anybody who could solve this tyre problem would be a millionaire, so Vickers/BAC were looking at this seriously, half a century ago.

I'm pretty unconvinced by the gyro effect. The wheels are huge, so at a landing speed of 125mph they have quite a low angular velocity (granted, a large mass, but moment of inertia is linear with mass but squared on the angular momentum). My Volvo Turbo does 125mph too (and a bit over), and the wheels are about a quarter the diameter so the AV is about times 4 and the MI about times 16. If the gyro effect was important, it would surely affect car steering too. The plane effect is not related to steering the wheels - the main gear is fixed in relation to the whole aircraft.

I'm not sure the rotary engine effect was gyroscopic. I think it was more inertial due to the high engine mass, being as the cylinders and heads and valvegear were all going round with the propeller (to say nothing of the air resistance of the engine itself). As you opened the throttle, the engine accelerated, and the reactive torque on the fixed crankshaft drove the airframe in the opposite direction. At low speeds, the pilot did not have enough control surface to correct the attitude. I don't think the problem was lack of ability to change direction of the plane in steady flight, which is what a plain gyro would do.

Incidentally. this torque problem used to affect seaplanes too. At take-off, the propeller torque would submerge one float much more than the other, with more water drag, so the plane would taxi in an arc until the airspeed got high enough for the air rudder to be effective. Schneider trophy planes would start take-off downwind, and make a completely involuntary 180 degree turn before they reached take-off speed.

Anyway, the engines on a 747 weigh seven tons each, and most of the insides go round at 30,000 revs per minute. That gyro effect would be huge compared to the slow wheels. And all the engines rotate the same direction - they don't try to pair them to compensate, which argues it's not too important.

The issue with a mechanical wheel rotator system is mainly that a 747 has 20 wheels, so that's a lot of motors and control mechanism to add to the aircraft weight (the whole time it flies), and a lot of reliability issues. And if one whole side of your wheel rotator system fails and the other works, you have a real yaw problem when you touch down.

I'm also wondering if the wheel impact spin-up is actually useful. If you put energy into pre-rotating the wheels, then the brakes would have to dispose of that extra energy as well as the momentum of the aircraft. And the instant braking effect of the skid is exactly at the right moment, and direction, to take a few knots off the airspeed and tug the nose down a little, which reduces the rebound on touchdown nicely.

An aircraft tyre takes an outrageous smack on each landing. Up to 450 tons spread over the main 16 wheels, so about 30 tons static weight. In a rough landing, maybe dropping on one side first, I would expect 100 tons momentarily on each tyre. So, if a tyre only lasts 40 landings because of the tread loss due to skids, I would be fairly happy because I would expect hidden structural damage to be progressing along nicely too by then.