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)

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.

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!

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.

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

Tire Spin up. Can it reduce aquaplaning?
 

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?

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.

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:

Spin up to prevent aquaplane
 

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?

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!