Is this a good idea?

[NWSRG]

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??

[john_tullamarine]

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 ?

[Kaptin M]

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.

[BigHitDH]

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! :confused:

[DoctorA300]

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

[oldebloke]

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...:O

[126.9]

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..?

:}

[hector]

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!

[Tinstaafl]

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?

[126.9]

You switch off the other unit(s)?

:}

[BigHitDH]

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?

[DoctorA300]

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

[BigHitDH]

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! :ok:

[Seagul1]

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 :}

[GearDown&Locked]

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.

[Notso Fantastic]

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).

[Flight Safety]

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?

[keendog]

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.

[Cejkovice]

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

[wandrinabout]

NSWRG

What are regenerative brakes?

[Paul Wilson]

wandrinabout,
Regenerative brakes are essentially a motor run as a generator, most often used on electric cars. Pressing the brake pedal connects the circuit to a battery charger that uses the energy to recharge the on board power supply. Very usefull for an electric car, less useful for an aircraft (where do you put the energy)

[G-Foxtrot Oscar 69]

I posed a similar question to an ex-BAE engineer a few years back.

I was thinking more down the lines of using hub mounted hydraulic motors for push back and then used for extra breaking.

Apparently it came down to the extra weight and fuel required to haul them around far outweighed any real advantage.

Also as mentioned before I guess to get a global certification on such a system would cost even more again.

[NWSRG]

Folks,

Thank you all for your contributions!

So the idea that was to make me millions might need a little more tweaking!!

...but it was nice to get the old grey matter stretched a little!

[WJman]

I recently saw a TV show where NASA engineers were working on a wheel spin up device to reduce tire wear. I believe they were hoping to try an introduce it in the 7E7, then again I read in a forum here that Boeing selected electric brakes for the 7E7. Maybe they will try both as well as regenerative braking system.It could mark quite an advancement in technology.

[BigHairyBum]

I was told the best thing to avoid tyre wear on landing is a good firm touchdown........ Well thats what I usually say afterwards!!:\ :\ :\ :\

[DickBoyd]

Thanks for the link to "Tyre spin up". Several talked about tire wear, activation of spoilers, greaser landings, reaction forces on the gear, gyroscopic forces and the like. Interesting thoughts.

I was looking for comments on aquaplaning associated with a non-rotating tire.

For ABS to be useful, the tire has to rotate. A non-rotating tire at landing speeds takes considerable force to get it to begin rotating. (Moment of inertia and all.)

If the tire is not rotating, the tire can hydroplane on its melted rubber. (Reversion hydroplaning) Even on a dry pavement the melted rubber from a locked wheel reduces friction forces.

During the early part of landing, the wheels do not have full aircraft weight. Even with spoilers, there is some lift. Friction force depends on how much downward force is on the tyre. (whoops, I mean tire.)

Wet runway landings call for a "hard" landing. I guess to make sure the wheels spin.

On a wet runway when do the wheels begin to spin? At touchdown? When do spoilers deploy? Based on what sensor? Weight on wheels? Wheel spin? If the wheels don't spin due to a water layer, will the spoilers still deploy? At what tire speed do spoilers deploy? Is there an automatic go around procedure if tire spin up does not happen at touchdown or shortly after? Or an alert for manual spoilers?

If the wheel were already spinning would it more likely make runway contact rather than water contact? Would a spinning wheel be more likely to contact concrete rather than water?

What effect on friction on a wet runway would it make if the tire were brought up to 50% to 85% of landing ground speed? Would that additional rotation enhance braking by ensuring the patch area stops?

I know of at least one takeoff with locked wheels (no skis). Do any of you know of an aircraft taking off with locked wheels?

[Loose rivets]

It's all been done! Wallets molded into the sidewall inflated and as far as i can remember, worked perfectly. It was before my time, so will take time to research.

The problem was the loss of retardation. Having said this, I can't help feeling that it would save a lot of rubber if a spin-up was optional. 12,000 feet of concrete and time to have lunch between touchdown and turn off, would save a lot of bucks if there were no rotational impact, but then we would be back to a mechanical system -- with all the above disadvantages.

[oldebloke]

This has been done before_quite true at the end of the war it was felt rhat having the "big'"wheels of the bombers turning for landing would elliviate the spin up shock.....Pockets were installed to catch the airflow to spin the wheel...
Today gear wheels are smaller-no spinup shock-and the touchdown spinup is used to activate the spoilers(15mph)..
Having the wheel spin in flight would have a detrimental effect so a squat switch is also incorporated to dissallow airbourne GROUND spoiler operation until the aircraft had weight on the gear...
In the hydroplaning case,should the gear not spin up, either for failure of the system or too light a touchdown(greaser),once the weight is on the gear the spoilers are deployed manually.:ok:
The cases of B737 no spoiilers available were due to faulty squat switches,and the A320 cases were due to requiring too great a weight on the squat switch(reduced from 6ton -2.5ton):suspect:

[DickBoyd]

Oldebloke said:

In the hydroplaning case,should the gear not spin up, either for failure of the system or too light a touchdown(greaser),once the weight is on the gear the spoilers are deployed manually.
The cases of B737 no spoiilers available were due to faulty squat switches,and the A320 cases were due to requiring too great a weight on the squat switch(reduced from 6ton -2.5ton).

Thanks for the clarification. When it comes to tire friction, it seems only part of the story is told. The part that is familiar to the story teller. Most of the aviation stories about friction fail to describe the normal force.

My question of friction control is more related to automobiles. There has been more published in aviation on aquaplaning than in the automotive world. Getting an aircraft tire to spin up is still an open question to me.

Automotive and road engineers seem to be concentrating more on friction improvement when it seems to me driver (pilot)education would be cheaper and achieve better results. Better results being fewer crashes in wet weather. Especially first rain.

Granted there are some roads (and runways and taxiways) with terrible friction characteristics. What is being done to correct that?

[Willit Run]

Twas tried many years ago by one of the big tire manufacturers, and the gyroscopic forces imposed on the airframe made it rather difficult and surprising to control on short final. The idea was abandoned!