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Pre-spinning Wheels Prior To Touch-down

Fri Jan 26, 2001 3:15 am

Anyone knows why the wheels of an aircraft's landing gear are not given an amount of pre-spin to limit wear and tear of the tyres at touch-down?
I think this could easily be achieved by making use of the airflow and some form of blades mounted on the wheels.
Or am I being naive now?

Ben.
 
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RE: Pre-spinning Wheels Prior To Touch-down

Fri Jan 26, 2001 3:23 am

I have actually considered this many times. No internal mechanism could get the wheels spinning fast enough without being completely inefficient in terms of space, weight, or fuel, and while I suppose some sort of forward-facing fan setup could get them turning, it's easier just to replace the tires from time to time.
 
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RE: Pre-spinning Wheels Prior To Touch-down

Fri Jan 26, 2001 3:37 am

Yes, I concurr with the above. I too have thought about that but came to the same realization: It would be too complex and heavy...those disadvantages overcoming R&Ring a tire every hundred landings or so. Another disadvantage I thought of ( a theory of mine ) is that all those spinning wheels may set up some kind of gyroscopic procession which could adversely effect the handling of the aircaft when you least need problems...approach and landing.
 
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Bruce
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RE: Pre-spinning Wheels Prior To Touch-down

Fri Jan 26, 2001 3:38 am

Don't they spin at least a little from the air rushing around them while in air - before touchdown?

Seems to me that at 180 knots a wheel would spin some.
Bruce Leibowitz - Jackson, MS (KJAN) - Canon 50D/100-400L IS lens
 
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RE: Pre-spinning Wheels Prior To Touch-down

Fri Jan 26, 2001 3:48 am

Don't see how. Air rushing over a uniformly curved surface would seem to want keep the wheel from spinning...it certainly wouldn't try to spin the tire. I once thought of employing vanes on the outer surface of the wheel to let the slipstream turbine drive the wheel--I could just see what happens after a few hunderd hours in service. The vanes would be vulnerable and get broken off/damaged, adversely affecting wheel balancing and we'd probably get an E.A. to remove them before long. Another million dollar theory from a mechanic who thinks he's an engineer Smile
 
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RE: Pre-spinning Wheels Prior To Touch-down

Fri Jan 26, 2001 3:56 am

Most large aircraft have spin-up systems which apply small amount of brake pressure when aircraft leaves the ground via the skid sensors. This is counter the gyroscopic princibles of the spinning wheels. The force would be great at low handling speeds. this is why they are not turned for landing Smile
 
exPratt
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RE: Pre-spinning Wheels Prior To Touch-down

Fri Jan 26, 2001 3:58 am

Spinning up of the wheels before landing was tried many years ago. The gyroscopic effects of those large rotating masses apparently caused the airplanes to make some strange gyrations on touchdown causing the plan to be abandoned.
 
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RE: Pre-spinning Wheels Prior To Touch-down

Fri Jan 26, 2001 4:12 am

Maybe put some kind of internal motor, a small one??
I had similiar thoughts a few weeks ago.

Greg
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RE: Pre-spinning Wheels Prior To Touch-down

Fri Jan 26, 2001 4:13 am

Thank you for your replies !
The gyroscopic effect seems like a very plausible explanation to me.
So much for my great idea...
 
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RE: Pre-spinning Wheels Prior To Touch-down

Fri Jan 26, 2001 4:14 am

I am just a pilot but have some insight possibly into why they dont do this.

Large aircraft have a system on the aircraft for anti-skid and also part of that is wheel not turning light. If that pre-spin system was there in icing conditions or turbulence it may only spin one wheel or any combination. Setting off the anti-skid system prior to touchdown. This could make the landing tricky at times. The weight and cost of fins or other systems to do this pre-spin might also be heavy or expensive.

Another problem is that the spoiler panels that come out after landing are tied into Main-wheel spinup. I don't know if that would be a huge problem but I think it would be interesting applying fixes to that system too.

I think my main point is that it is just a lot easier to change the tires. Plus a fresh piece of rubber is always nice to have. We dont want them to last too long and I think that the complexity of the pre-spinning wheel will be too much for very little gain. One other point is it would take a little longer to stop the Aircraft due to the initial overcoming of static-friction.

I hope this helps. Again I am not an engineer.

Gary


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