Folks,

This is just an idea that has come to mind, and I wondered what the professionals thought! Feel free to tell me why it wouldn't be practical!

On commercial jets, each touchdown leads to smoking tires at the point of runway contact. Presumably, this is because the tires aren't rotating just as they come into contact with the tarmac.

Proposal: Each wheel to be fitted with a small hub motor. This motor would spin the wheel up to landing speed in the final approach. On landing, the wheel is spinning at the correct speed, and contact wear is reduced, thus improving tire life. Then, the motor becomes a generator, and is used for regenerative braking. So we also save on brake wear.

Modern electric motors are compact and light, and regen braking is popular in many other vehicles.

Any comments??

Outside my disciplines but some thoughts ..

(a) aircraft performance braking requirements are rather dramatic when compared to, say, motor vehicles

(b) the weight/complexity, reliability and certification considerations might just outweigh the benefits in reduced tyre wear

(c) does anyone have any data on the water film performance if one impacts a tyre at zero tangential speed delta onto a significantly wet runway ?

Also suggest you run a search in PPRuNe .. I am certain that I have seen this sort of question arise before ?

Unfortunately for aircraft tyres, their principle role in life is to act as the intermediary between the brakes and the runway surface.
With wheels already spun-up at touchdown, this would mean the brakes would then need to counter all of the work down by the small motors you propose, NWSRG, in bringing the aircraft to a stop, thereby shortening brake life.

Additionally, spun-up wheels would ADD to the landing distance required.

Just my 2 bob's worth.

It's not the landing spin-up that kills tyres, it's heat.

The tyres recieive much more wear from the sidewall deformation during taxi then they do suring the landing phase. At least that's what I'm told!

Its a weight issue pure and simple. Take a popular A/C like the B737. 4 Main wheels, Weighing approx 100 kg each, taking the weight of each MWA into account, I would guesstimate that you would need a 15hp 3 phase a/c motor, weight approx 5kg, assuming you could find one that would fit into the axle together with the wheel speed transducer for the antiskid. Airframe hardware (cables, relays, clamps, CB's etc) would come in at 10kg PER wheel. So 60kgs at 10 sectors a day of an average of 1 hour, I would put the revenue loss/weight penalty at 200000 euros a year, per aircraft. I have no Idea what the savings in tyre maintenace would be, but to be fair, lets say I doubles the life of the tyre, that would put the savings at 50000 euros a year assuming a wheel tyre replacment and overhaul/inspection costs in the range of 1000 euros and each wheel lasts approx 400 landings instead of 200. Now try to sell that one to MOL
Brgds
Doc

The scoop Idea was done during the war(WW2)to spin up the big tires to alleviate the spin up shock to the oleos.
Today too many systems ,spoilers,antiskid etc rely on the same spinup,albeit smaller wheels...

It sounds more than feasable to me. BUT, aircraft manufacturers are still working on a windscreen-wiper that does half as good a job as your motor car's does, how the heck are they gonna get this one right..?

Apparently there is a "life after avation" for large aircraft tyres when they are no longer fit for the job. My local tyre-fitter puts them on farm muck-spreaders. They are ideal on soft ground, although, as he points out, you should observe the "MAX SPEED 200MPH" limit on the sidewall!

Not only the cost of having functioning spin-up assemblies, but there's also a maintenance & serviceability cost with them. What happens if one unit fails?

You switch off the other unit(s)?

If this were to be cost-effective, rather than have some kind of motor-driven assembly, wouldn't it be much simpler to have an "impeller" attached to each wheel to take the energy from the airflow?

BigHitDH,
The impeller would increase drag on T/O. Also as someone else pointed out, wheel spinup on touchdown is used in a number of systems like automatic spoiler deployment, autobrakes etc.
Doc

rgr that: I agree I'd also like to be able to stop too!

How about four or more wheels weighing 100kgs+ spining for a speed of say 140kts and u trying to do a crosswind decrab not a nice time to find asbout gyroscopic precession

Taking aside the weight problem of the small wheel mounted electric motors, these motors could work as brake aids as well. So we would have 2 functions for the same carried weight.

So you take away the braking effect of wheel spinup to use the motors as braking aids? Imagine a 747 with 16 large electric motors (these wheels are very heavy), all of which have to function or they are all switched off. The wheel units can get extremely hot, even glowing red hot, and the motor must survive that? As well as frequent drenching? For a very questionable saving on rubber? And at a weight penalty of several hundred kilos? I think we are talking well expensive electrical units (and incredibly tough)! No way. That's why nobody has them (or will in the foreseeable future).

Could a bleed air system provide the energy to spin up wheels? Could it be simple, light weight, heat resistant, and low failure rate enough to do the job?

I came up with this bright idea on pprune a few years ago. Someone then posted that this was the single most (unsuccessfully) attempted patent application in the UK!!

Another reply said that what really kills the tyres is taxying at MGW, not the puff of smoke when landing light.

KeenDog has it right when saying that the most damaging cases for tyres is taxiing at MTOW and the during brake roll itself. Although the tyres puff smoke at touch down the impact on tyre life is minimal. Many Tyres get pulled before they achieve their life due to FOD damage on dirty runways and taxi ways.

If any motor would be put in to assist in wheel spin up then it would have to be compatible the wheel speed tachometers and Tyre pressure indicating systems TPIS that run through the axle. Also, aircraft fitted with brake cooling fans (also situated within the axle) wouldn't be able to have the device fitted.

Cejkovice

NSWRG

What are regenerative brakes?