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

[OKIsItJustMe]

http://www.epsrc.ac.uk/newsevents/news/2012/Pages/aircraft.aspx

[font face=Times, Times New Roman, Serif][font size=5]Aircraft of the future could capture and re-use some of their own power[/font]

23 February 2012

[font size=3]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 jet engines. This would save on aviation fuel, cut emissions and reduce noise pollution at airports.

…

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.

…

"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."

…[/font][/font]

[zipplewrath]

1. Strange idea

As the article says, weight is going to be a real obstacle to implimenting this idea. Another is going to be related to not starting the main engines until you're at/near the runway. There are safety/health checks that occur after starting that could send the plane back to the gate.

It would seem if they want to pursue engineless taxiing (a laudable goal in my mind) why wouldn't they just have a "truck" tow them out to the runway, the same ones often used to park, or back them up. With a little work, they could probably be unmanned/remote pilot and run on rails or something.

'Tis sad thought to was megawatts like that just generating heat.

[Sinistrous]

2. You are correct about the weight issue.

Flying those motor-generator sets around would exact a cost in fuel consumption when in the air.

Also, don't some airports already tow aircraft to the end of the runway for takeoff?

[OKIsItJustMe]

3. From the Press Release

…

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.

…

(i.e. the researchers are aware of the weight problem.)

[zipplewrath]

6. Cuba used donkeys

There was a time, when fuel was scarce in Cuba, that they were using donkeys to pull them to the threshold.

[FogerRox]

4. Old idea, regenerative braking goes back at least

to electric golf carts in the 1960's, if not earlier.

[zipplewrath]

5. For airplanes

That's the part that's strange. Adding weight for ground operations is something they are loath to do on most aircraft. Heck, the Germans used ejectable landing gear and skids in WWII. I've been waiting for someone to dump APU's. Adding something like regenerative breaking on an airplane seems like a strange direction for aircraft design. Especially since I suspect it won't "replace" the friction brakes, but merely augment them. So you won't lose that weight, although you may get away with smaller/lighter versions.

And do ya dig the storage capacity they're talking about? Megawatts? I wanna see THAT battery.

[FogerRox]

14. Strange, yes. 1st impression is, that aint gonna fly

2nd impression a few hrs later is WTF are they talking about.

Regenerative braking is fine when you already have an battery/electric motor, like a golf cart or a Toyota Prius. Just add some wiring relays in the system, are UR all set.

An airplane doesnt use batteries & electric motor for its main form of propulsion, so they have to be added, at a major penalty.

The more I think about it -it sounds Effin stupid.

[AtheistCrusader]

24. Perhaps with a different aircraft design.

Something more like a hybrid, where the batteries and such are already present.

ARE there any hybrid commercial aircraft designs kicking around?

[FogerRox]

25. LOL, good point, but I seriously doubt.

[GliderGuider]

29. What problem are they trying to solve?

If it's noise abatement on the ground there are ways to do that.
If it's reduced fuel use on the ground there are ways to do that.
If it's fuel economy in the air, there are different ways to do that.

They haven't given a clear statement of the problem they're trying to solve. They've had a brain flash of, "Oh here's some wasted energy, what could we do with it?"

The amount of energy they're talking about reclaiming is a minuscule fraction of the energy involved in the flight itself.

As far as I can tell it's basically a classroom exercise in electrical engineering.

[zipplewrath]

32. Engine Free Taxiing

The article suggested is was part of some larger effort to reduce the energy used during taxi operations. "Engine free taxing" or some such nomenclature. But I agree, this particular study seems to be more a side exercise in "what could we do with this energy" more than any practical answer to a specific existing problem.

[Fumesucker]

30. The Swiss Gyrobus had regenerative braking in the 1940's..

http://en.wikipedia.org/wiki/Gyrobus

[Dead_Parrot]

7. If you wanted to reclaim the kinetic energy...

...it might be more practicable to use a carrier-style hook & cable arrester, hooked to to a generator. Instead of powering the aircraft's taxiing, use it to power the airport... Keep the normal brakes for when you miss.

To say this presents other problems is an understatement.

[OKIsItJustMe]

8. From the Press Release

…

"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 electricity grid."

…

[Dead_Parrot]

9. I should probably have read the article. ;)

[zipplewrath]

10. Does scream for a land based solution

They do mention in the article that other ground based ideas were considered too, so I hesitate to be too critical. And it is an interesting idea considering the amount of energy these planes have when they are landing. But one does sorta scratch the head and wonder how it could be that some land based system wouldn't make more sense.

[Lint Head]

11. Sounds like a form of perpetual motion.

[Dead_Parrot]

12. Hey, there's an idea...

line all of the aircraft up on the runway, nose to tail: When a plane lands and slams into the last one, the energy will transfer down the line to the first, which will take off...

[OKIsItJustMe]

13. Only in as much as a Prius uses a form of perpetual motion.

In both cases, they recover energy from braking to use powering a vehicle for short distances.

[GliderGuider]

15. Or they could recover energy in-flight by covering the outside of the fuselage with wind turbines...

for the thermodynamically impaired.

[AtheistCrusader]

16. Just haul them out to the tarmac with battery-powered tractors.

Problem solved, plane lighter.

Want to save fuel? Catapults, like a carrier deck. It would of course, need to be much less violent than it's military couterpart, but could also be an electrically-driven catapult.

Might save on critical engine failures on takeoff as well, given that you wouldn't have to run them up as hard, if you get the plane to minimum takeoff speed with the 'pult.

[GliderGuider]

17. They use something similar to a catapult for gliders - it's called winch launching

Most glider winches are diesel or gasoline powered, but a stationary system could use electricity. Add electric ground tugs and it could be a very interesting system.

[OKIsItJustMe]

18. These are most useful from hilltops

The glider pilot needs to quickly find a source of lift (like a ridge for example.)

Naturally, to do this sort of thing with a jetliner would require a tremendous amount of structural reinforcement, which would mean a great deal of extra weight. (Tell me again why they cannot use regenerative braking?)

[GliderGuider]

20. Regenerative braking is OK with me. And winches aren't just used from hilltops

I've done a few winch launches in Europe/UK, and they were all from flatland or in mountain valleys. The old days of bungee launches did require flinging the glider off the edge if a cliff with a giant slingshot, but that's not the practice any more.

For an airliner launch, the ground-based system would just replace some of the additional engine power needed to accelerate the plane to V2 (the speed at which the aircraft may safely take off with one engine out). Unlike a glider launch, the airliner has its engines running, so the catapult/winch wouldn't need to get the aircraft to an initial safe altitude. The additional stress on the fuselage or passengers should be minimal compared to taking off under engine power. Airliners would need to retain all their current capability for landing and taking off from uneuipped runways.

ETA: the biggest problem with winch launches like this might be turnaround time - the time to get the system ready to hook up the next victim.

[OKIsItJustMe]

26. The engine mounts are engineered to withstand the stress of takeoff

It occurred to me that you might take advantage of the engine mounts somehow, but, then, that would require two (or more) attachments, with a Y-shaped cable, increasing complexity, and the likelihood of failure.

Then I thought of the front landing gear. These are built to withstand the stress of landing, and might be engineered to take the stress of being pulled aloft as well, but, then, we’re talking about heavier landing gear (which was the supposed reason to avoid the regenerative braking scheme proposed in the OP.)

[GliderGuider]

28. Given how stringent aircraft engineering standards are

It would require a complete structural re-design. Structural retrofits of that magnitude won't pass the FAA standards.

The design itself would probably be fairly simple - it just requires an attachment point on the bottom of the aircraft, probably just in front of the main wing spar, attached directly to the spar by load-bearing members. The spar itself has plenty of excess load-bearing capacity for the job. The issues would be stability under tow (especially in cross winds) and ensuring a 100% positive release.

[AtheistCrusader]

22. Every pound means more fuel burned in flight.

That's why the airlines are jacking people around on luggage weight surcharges. Or at least part of the reason, anyway.

I'd like to see the cost/benefit tradeoff, but batteries are heavy. I can't imagine there would be a net gain on total fuel consumption, if you add some weight to the plane to taxi around on the ground, because you have to carry it with you in the air as well.

But hey, sometimes these things don't work out like we expect, so, I'd like to see the total fuel cost. Maybe on short flights this would be more workable.

[OKIsItJustMe]

19. The idea here is to recover some of the energy which is wasted, heating up the brakes

Tractors would not achieve this.

[GliderGuider]

21. Use tractors for takeoff positioning, electric winch assist for takeoff, regen for landing.

Lots of ways to improve the efficiency of operations using electricity.

[AtheistCrusader]

23. That energy might be better off wasted.

You can power the electric tugs or tractors with wind turbines, and then focus on making the planes as light as possible, win-win.

Edit: The lighter the plane, the less braking energy is needed, by the way.

[OKIsItJustMe]

27. I increasingly find myself saying

“In America, everyone is entitled to an opinion, whether it is informed or not.”

Most of the objections raised in this thread are raised in the original article (which it seems few have bothered to read.)

…

"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 electricity 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.

…

[caraher]

31. Don't forger that power and energy are different things

The 3 MW is a maximum *rate* at which the brakes convert the airliner's kinetic energy to heat, not the energy available to be converted. There's actually not a huge amount of energy to be had from landing, and it's a one-time-per-flight energy source (maybe regenerative braking *during* taxiing might be the bigger effect?).

To get a feel for why I say it's not much, the upper limit on what the brakes can extract is the kinetic energy of the plane when it touches down. For a 70 tonne A-320 at 140 knots (72 m/s) that works out to KE = 0.5 m v^2 = 0.5 (70,000 kg) (72 m/s)^2 = 180 MJ, or about 50 kWh. Another way of looking at this is that this is the energy content of about 4 kg of jet fuel. (Of course, it takes more than 4 kg of jet fuel to bring an A-320 to 140 knots, given friction, air drag and engine efficiency considerations...) But this also ignores the other mechanisms used to slow a plane (such as flaps and reverse thrust).

I wonder what fraction of a typical airliner fuel load is used in taxiing. The balance of that vs. any increased airborne fuel consumption penalties associated with lugging extra equipment will determine whether this is an energy saver. It might make airports quieter, though.