While I seem to be on a flight to somewhere every few weeks, I have very little connection to the aircraft industry. However, I have a few questions concerning aircraft tyre operation and since I see there are some smart Freepers commenting here who do have that insight, perhaps somebody could comment on my musings…...
Here’s my question…. In flight, a tyre is at standstill and once it hits the runway, it has to hit its required rotational speed virtually instantly. If a large aircraft with 54 inch diameter tyres lands at 225 mph, this means that the tyre rotational speed goes from zero to a bit over 1,400 rpm almost instantly. That level of rotational acceleration would present a horrendous design problem for other types of ‘rotational equipment’ such as a large fan impeller but far less so for an aircraft tyre due to its lighter weight and the elasticity of the material. Regardless, at the moment of touchdown, the tyre will be grossly distorted due to the incredible acceleration and the force of the aircraft as contact is made with the tarmac. My guess is that about 99% of the amount of degradation that an aircraft tyre sees over its lifecycle happens in the first few seconds of touching the tarmac on a landing. Would that be about right? This being the case, has there ever been thought given to having the tyres already rotating to match ground speed before the plane lands? Would that not be a good thing to do? I can’t imagine that it wouldn’t be a good thing and I’m wondering why it’s not done….. i.e. cost, another maintenance item, extra weight, risk that something could fail and lock a wheel up, somebody’s assessment that tyres are already well within their limitations when accelerated from zero etc.?
The other thing I’m wondering about is this…. I haven’t really paid that much attention before but when a pilot lands, is the objective to do an initial slight ‘touch’ (a kiss between the tyres and the tarmac) to get the wheels rotating before the rest of the landing is done? It would seem that this might happen naturally anyway since there always seems to be a bit of a bounce before the wheels are in permanent contact. This would seem to me to be a good idea since putting all the weight on a tyre that’s already distorted due to the rapid acceleration would be far more likely to have a tyre blowout.
Thoughts?
That kiss is a bounce and it is almost impossible to not bounce a little. If you don’t bounce at all it is called “slick” landing which is the nirvana of landings. It happens so rarely that you remember those landing where “slicked” it.
>..has there ever been thought given to having the tyres already rotating to match ground speed before the plane lands? ... I can’t imagine that it wouldn’t be a good thing and I’m wondering why it’s not done…
Tried and discarded. Rims were designed that caused wheel rotation when lowered into the airstream. But the rotating wheels became powerful gyroscopes the pilot had to overcome during approach and landing. Became a control issue. Too dangerous!