Aircraft of the future could capture and re-use some of their own

February 23, 2012

Tomorrow's aircraft could contribute to their power needs by harnessing energy from the wheel rotation of their landing gear to generate electricity.

They could use this to power their taxiing to and from airport buildings, reducing the need to use their . This would save on , cut and reduce at .

The feasibility of this has been confirmed by a team of engineers from the University of Lincoln with funding from the Engineering and Physical Sciences Research Council (EPSRC). This forms part of the Research Councils UK Energy Programme.

The energy produced by a plane's during landing – currently wasted as heat produced by friction in the aircraft's disc brakes - would be captured and converted into electricity by motor-generators built into the landing gear. The electricity would then be stored and supplied to the in-hub motors in the wheels of the plane when it needed to taxi.

'Engine-less taxiing' could therefore become a reality. ACARE (the Advisory Council for Aeronautics Research in Europe) has made engine-less taxiing one of the key objectives beyond 2020 for the European aviation industry.

"Taxiing is a highly fuel-inefficient part of any trip by plane with emissions and noise pollution caused by jet engines being a huge issue for airports all over the world," says Professor Paul Stewart, who led the research.

"If the next generation of aircraft that emerges over the next 15 to 20 years could incorporate this kind of technology, it would deliver enormous benefits, especially for people living near airports. Currently, commercial aircraft spend a lot of time on the ground with their noisy jet engines running. In the future this technology could significantly reduce the need to do that."

The University of Lincoln's research formed part of a project that aimed to assess the basic feasibility of as many ways of capturing energy from a landing aircraft as possible.

"When an Airbus 320 lands, for example, a combination of its weight and speed gives it around three megawatts peak available power," Professor Stewart explains. "We explored a wide variety of ways of harnessing that energy, such as generating electricity from the interaction between copper coils embedded in the runway and magnets attached to the underside of the aircraft, and then feeding the power produced into the local grid."

Unfortunately, most of the ideas weren't technically feasible or simply wouldn't be cost-effective. But the study showed that capturing energy direct from a plane's landing gear and recycling it for the aircraft's own use really could work, particularly if integrated with new technologies emerging from current research related to the more-electric or all-electric aircraft.

A number of technical challenges would need to be overcome. For example, weight would be a key issue, so a way of minimising the amount of conductors and electronic power converters used in an on-board energy recovery system would need to be identified.

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3.3 / 5 (6) Feb 23, 2012
the engines have to keep the airplane moving so the tires roll to generate electricity. This silly scheme would only give "free" electricity if the generator was used instead of the brakes. Then the cost and additional weight of the generator(s) and battery(s)/super-capacitor(s) to store the energy for use when it is needed would likely make this highly cost ineffective. Another naive idea from university types w/ no practical, real world experience. Let's see which aircraft manufacturer scrambles to get the rights to this.
not rated yet Feb 23, 2012
Looks good to me. Capturing the energy in supercaps and using in-wheel motors is good. What I don't understand is that there are no generators on board in the first place.
5 / 5 (1) Feb 23, 2012
Why can't the airplane have a wheeled battery-powered taxi-tow vehicle to move it around after it lands? They already exist!
4 / 5 (2) Feb 24, 2012
@deatopmg: It's not an issue with "university types"--many groundbreaking studies with no real applications are published every week, but they possibly pave the way for future research that may, in turn, produce something useful.

The issue here is the research is not at all groundbreaking, and quite mind-numbingly redundant and completely unnecessary. A high school student could plug in the speed and mass of a plane into E = 1/2 * mv^2 and find the heat-energy expended by the plane while braking.

Another clue that points to the incompetence of the researchers (or authors) is their line about the plane's peak power output being 3 megawatts; this is an absolutely useless metric. Why not mention total energy generated during braking, instead of the "peak power output" value that's only attained for fractions of a second as the wheels reach their maximum speed (right after spinning up once they touch down). Absolutely no useful information is present here.
3 / 5 (1) Feb 24, 2012
What I don't understand is that there are no generators on board in the first place.

There are. They are auxiliary power systems (APUs) that are used for startup and can be used to supply electricity in the event of engine failure. But they run on the normal fuel so there's not much advantage of using those to drive electric motors in the wheels as opposed to just using the engines for thrust.

Why can't the airplane have a wheeled battery-powered taxi-tow vehicle to move it around after it lands? They already exist!

But not at every airport.

In effect it really depends on whether the end-to-end (taxi-takeoff-flight-land-taxi) use-case is more energy efficient if you include the additional weight of a battery system and the electric motors. Given that planes often wait around with their engines idling (which uses fuel and produces exhausts) it might be worth it economically and/or ecologically.
3 / 5 (2) Feb 24, 2012
Two major problems here:

1. What would they use to safely store that energy?

2. What will this system weigh?

If it is too bulky or heavy it will cost more to lug it through the sky from airport to airport than it saves. And that is before anyone has considered where to put the energy that is gathered.

Another thing: the vast majority of the stopping power of an aircraft does not come from wheel brakes. It is aerodynamic. Thrust Reversers shorten landing distances by another 10 to 15 percent. The brakes don't even become useful until most of the aircraft weight is on the wheels.

So, how much energy could we be talking about and how much extra runway would we need to recover it? This smells to me like yet another Rube Golderbergian scheme...
1 / 5 (1) Feb 24, 2012
This is just another green wet dream. Perhaps the government could mandate it's use and we all could sing Kumbaya my Lord as we land.

Oh wait, this is a government mandate and it will not qualify for funding if God is mentioned.
not rated yet Feb 24, 2012
To me the more widespread use of ground based tractors used to move aircraft at ground would be much more efficient. Then if those are not available, use current system of taxing by main engines.
not rated yet Feb 25, 2012
Why don't the wheels have blades or paddles to let them auto-rotate in the slipstream as the plane come in to land? This could generate electricity and reduce the need to kill speed uselessly through use of flaps. Further this would reduce tyre wear as the wheels would be up to speed before the plane touches down.
not rated yet Feb 25, 2012
@PPihkala: One very big reason to start the engines after pulling away from the gate is to provide the interior of the aircraft with power for the HVAC. Another major reason is so that the rest of the aircraft flight controls and equipment can be properly tested before takeoff.

In other words, there is a need to burn a significant amount of fuel anyhow, adding taxi power to the list isn't going to change that equation too much.
not rated yet Feb 26, 2012
I am so underwhelmed by this amazing advance in thinking that I am abou...zzzzzzzzzz..........zzzZZzzZzzZZzzzz............zzz

*wakes up briefly*

....t ready to make some roller skates for my cat that do the same thing, so whe.....zzzzzzzzzz...ZZzzzzZzzzZzzzzZZ
1 / 5 (1) Feb 26, 2012
@jerkinwithmirkin: You display your own complete incompetence with such rants.
Peak power output is extremely important in designing an energy capture system, it dictates the peak rate at which it must be able to capture and store energy, affecting for example current carrying caparity of conductors, peak charge rate of capacitors or batteries etc.
These affect cooling requirements, conductor CSA etc which in turn have a big impact on weight and size.
All your use of E = 1/2 MV^2 tells you is the energy to be dissipated.

Anybody who has followed the development of KERS in F1 will be all too familiar with these implications, scaling that up to a jumbo will be a very difficult task.

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