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Engineers confirm feasibility of aircraft regenerative braking from landing gear

A team of engineers from the University of Lincoln, with funding from the UK’s Engineering and Physical Sciences Research Council (EPSRC), has confirmed the feasibility of aircraft regenerate braking from the landing gear to provide power for taxiing to and from airport buildings, reducing the need to use jet engines.

The energy produced by a plane’s braking system 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.

Theoretically, an energy recovery system integrated into a plane’s landing gear might be able to provide all the power needed for taxiing from a runway back to the airport terminal. If at any time a limited amount of power was available, the plane could supplement this with its conventional engines. A plane would also need to run its jet engines prior to take-off, so an energy recovery system would probably only be used to meet a proportion of the plane’s energy needs during taxiing from the terminal to the runway.

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. 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 electricity grid.

—Professor Paul Stewart, research leader

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 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 minimizing the number of conductors and electronic power converters used in an on-board energy recovery system would need to be identified.

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.

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.

—Professor Stewart

The project was carried out under the auspices of the EPSRC-funded Airport Energy Technologies Network (AETN) established in 2008 to undertake low-carbon research in the field of aviation, and was undertaken in collaboration with researchers at the University of Loughborough. The 12-month ”Feasibility Study of Energy Recovery from Landing Aircraft” received total EPSRC funding of £161,000 (US$256,000).

The initial projects associated with the EPSRC-funded Airport Energy Technologies Network (AETN) were the outputs of a Sandpit event in November 2009. Sandpits are intensive discussion forums where free thinking is encouraged in order to delve deep into specific issues and identify innovative solutions.

Comments

Engineer-Poet

I'm not sure the analysts looked at the whole picture.  An airplane using magnets to interact with coils in the runway could not only be braked for energy recovery, it could be guided to avoid sliding off the runway in icy conditions and accelerated for quicker and quieter takeoffs.

Also, the power quoted in the article is too low. An A320-200 touching down at 110 kts and totally empty at 42,600 kg braking at 1/4 g would generate 6 megawatts.

Arne

The kinetic energy in that emtpy A320-200 is less than 20 kWh.

You would need a ~20 kWh battery, capable of taking in 6 MW, that is 300C. Are there lithium batteries that can handle that kind of power?

A 20 kWh battery with state of the art technology weighs about 100 kg.

Suppose this 20 kWh replaces jet fuel at a conversion efficiency of 10%. This means you would save ~200 kWh worth of jet fuel which weighs less than 20 kg.

In short, adding 100 kg of battery to save 20 kg of fuel doesn't seem a viable proposition to me.

mahonj

It is a combination of MASS and speed, not weight and speed.

Who would land an empty A320 ?
You would expect it to contain passengers, luggage and fuel reserves.
It might also contain fuel for the next leg (to decrease turnaround time).

However, Anne is right, the energy saved is marginal.

The problem here is to add efficiency without too much complexity and weight.

Coils in the runway are a bad idea in terms of the amount of work needed to implement it.

Better to store the energy in supercaps/LiIons in the plane, but this might be expensive and heavy.

Lots of people ae working on this - here is an example with Lufthansa and Airbus.

http://www.lufthansa-technik.com/applications/portal/lhtportal/lhtportal.portal?requestednode=395&_pageLabel=Template7_8&_nfpb=true&webcacheURL=TV_I/Media-Relations-new/Press-Releases/E_Taxi_Demonstration_EN.xml

http://www.theskywardblog.com/2012/02/electric-aircraft-taxiing-great-fuel-savings-opportunity-unnecessary-complexity/

The main thing is not to use the turbofans for taxiing - electric motors would be much better, especially for short haul aircraft.

I suppose what will swing it is the increased cost of oil, especially if it looks like staying high. While oil was cheap, al this was just "research project stuff", but once the aviation fuel gets really expensive, people will take it seriously.

Herm

I think landing arrestor cables made out of rubber is a more practical idea.. once the bungee cords are stretched you can use them to launch the next plane.. if the wind direction flips.

mahonj

Quick - patent that.
I'll go in 50%

ejj

The taxibot people aren't going to be happy with this research & some of the discussion going on here.

http://www.youtube.com/watch?v=6HxrUm9s8NI

SJC

I see it as less wear on brakes and tires rather than fuel and energy savings. If the energy captured can help them taxi to the gate and save fuel,then all the better.

Engineer-Poet

Wheeltug PLC is now using the Chorus motor previously written up here.  It doesn't store energy, but it lets the aircraft taxi on power from the APU and leave the main engines off until just before takeoff.

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