WingZ

Why do airliners not have wheel motors?

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It's a though that strikes me every time I see a landing... think what you could do with a wheel hub motor:

  • Before landing, spin the wheels up to touchdown speed, and see all the rubber you save compared with 0-140kt in one wheel revolution.
  • After landing, use regenerative braking and see all the brake disk material you save, while charging up a battery or ultracapacitor.
  • Taxiing in, you cut those expensive big engines and use the electric motors, drawing on all that power you stored a moment ago. 

Engines, tyres, brakes all last longer, and much less fuel.

Does the airliner industry need an Elon Musk to wake it up?? 

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59 minutes ago, WingZ said:

It's a though that strikes me every time I see a landing... think what you could do with a wheel hub motor:

  • Before landing, spin the wheels up to touchdown speed, and see all the rubber you save compared with 0-140kt in one wheel revolution.
  • After landing, use regenerative braking and see all the brake disk material you save, while charging up a battery or ultracapacitor.
  • Taxiing in, you cut those expensive big engines and use the electric motors, drawing on all that power you stored a moment ago. 

Engines, tyres, brakes all last longer, and much less fuel.

Does the airliner industry need an Elon Musk to wake it up?? 

Costs of development, production and weight.  You must also take into account every pound you bring in the air costs you fuel, not only in increased operating weight but increased burn.  That would easily offset any savings experienced on the ground.  Now the cost of maintenance.  If one of these things break doesn't sound like the plane will move. There is also costs of parts and deferrals and how it affects the operation.  This list could go on.  But the cons easily outweigh the pros.  But never hurts to be imaginative.  But two rules in life govern this idea.

1.  If it's not broken. Don't fix it.

This is a fix looking for an non-existent problem.

2. Sometimes simple is just better.

A free spinning tire on a good bearing works just fine.

Next thing you know someone thinks we should be landing on cirucular runways to avoid crosswind landings.

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Posted (edited)

They do but no one uses them. They have developed electric motors for aircraft wheels that can do what you've said and also when you land you can shut down the engines and power up the APU and run the electric motors off the APU to taxi to the gate. They developed this a long time ago but no one adopted the technology

Edited by Matthew Kane

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Posted (edited)

Yes I found a WheelTug clip after I posted... proof that any idea has already been thought of!

This one in development for at least 5 years, you have to think the marketing dept. needs a shake-up  🙂

Certainly airports have much to benefit, in terms of handling, taxiing noise (not trivial in most instances), and pollution.

Batteries are getting close to the right power density nowadays, so I'd want power on the mains too, for regen braking. You could also power up a supercapacitor just before takeoff and go electric halfway to V1!

Edited by WingZ

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9 hours ago, WingZ said:
  • After landing, use regenerative braking and see all the brake disk material you save, while charging up a battery or ultracapacitor.
  • Taxiing in, you cut those expensive big engines and use the electric motors, drawing on all that power you stored a moment ago. 

Two issues come to mind. There's a limit to how fast you can charge a battery - IIRC it's around 4C so 4 times the discharge rate. On landing you have a tremendous amount of energy that you need to dissipate in a very, very short amount of time. I don't believe you can charge a battery that quickly, and even if you do, there's a tremendous amount of heat created as a by-product (no man-made physical, chemical or electrical process is 100% efficient). I would rather have a brake fire than an internal battery fire.

Cheers!

Luke

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How much sense it makes is going to depend on the price of oil.

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Posted (edited)

Years ago when I was working at the DOT Test Track in Pueblo Colorado they were working on an energy saving subway car.  The electric motors were used for dynamic braking and the energy was stored in a battery.  That energy was used to start the car.  

Modern locomotives use dynamic braking but the energy is dissipated as heat instead of saved, at least at the time frame I'm familiar with.

At the time I was working for Air Research on a linear induction motor test vehicle so never got much of the details of the other projects.  

For aircraft, though, weight has to be a big consideration.

Noel

Edited by birdguy

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I do believe that WheelTug missed their target date though... "...coming soon to your airport in 2013!" :rolleyes:

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Interesting subject indeed!

I think it's a great idea and would be particularly cost/weight effective. Wonder what the actual issues are that it has not gained (wide) usage. Anyone have any further factual information?

Kind regards, 

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Here is another similar product using the main gear wheels:

 

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WheelTug looks like it is seriously in the works, or re-works, to be precise. A lot of airlines seem to have signed on and made public new releases.

Here is an interesting development from Stirling Dynamics becoming involved. Certification is the challenge, and of course that means testing and documentation, documentation and documentation.

https://www.stirling-dynamics.com/

Kind regards

Spirit Flyer (Stephen)

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Interesting link, thanks. It nicely shows the airport benefits. And autonomous handling would be a game changer.

Of course certification would be a major issue, especially as the OEMs are not going to release their proprietary data.

7 hours ago, Luke said:

There's a limit to how fast you can charge a battery - IIRC it's around 4C so 4 times the discharge rate. On landing you have a tremendous amount of energy that you need to dissipate in a very, very short amount of time. I don't believe you can charge a battery that quickly...

Yes you'd expect an ultracapacitor for this - they can absorb large energy spikes but have limited total storage. So probably in tandem with a battery storage solution.

There are many applications better off on electric power - the "electric jet" B787 demonstrates some of these. Like all emerging technologies, batteries will go through teething troubles. The world has been waiting for many years to get a decent battery, perhaps its time has come.

To me, it's a no-brainer, I hope they get it right.

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45 minutes ago, WingZ said:

Interesting link, thanks. It nicely shows the airport benefits. And autonomous handling would be a game changer.

To me, it's a no-brainer, I hope they get it right.

They'd better, for the consequences of not getting it right might be grim indeed. However there is every reason to adopt this direction as the obvious returns are, as you suggested, a real game changer.

Kind regards,

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