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Airplanes in Motion, on the Ground
Jamais Cascio, 3 Aug 05

chorusmotor.gifAs I mentioned, I'm on a scenario project that has entailed a bit of travel. Upon my arrival at the airport yesterday evening, I couldn't help but be reminded of what can only be an incredibly inefficient use of the airplane's jet engines as a way of traveling around the tarmac. Effectively, it's a temporary transformation of a jetliner into a sluggish, ungainly, and utterly wasteful sort of bus. Not all airports rely on jets to move under their own power, though; in many, diesel "tow tugs" pull the jets to and fro. While undoubtedly more efficient than relying on the jet's own engines, these are still noisy, fuel-guzzling ways of moving around the runway.

But Boeing, working with a technology group called Chorus Motors, has come up with an ingenious solution -- an onboard electric motor attached to the nose wheel of the plane. In tests on a 767 under conditions equivalent to real-world use, the electric motor performed very well, showing that replacing tugs and jets with electric motors could have real benefits:

“We believe onboard electric motors have a great many advantages,” added Bob Carman, Chorus Motors’ WheelTug™ program manager. “They could reduce the need for ground tugs and their associated costs, allow faster flight turnarounds and increased fuel efficiency per trip, and reduce airplane noise and emissions at airports, to name just a few advantages.”

Such a replacement only became possible recently.

Advances in electric motor technology -- "power density," as [technology director at Boeing's R&D group "Phantom Works" Jim] Renton called it -- have made such a system feasible, he said. Essentially, electric motor researchers have found a way to package significantly more power into a smaller and lighter motor.

[...] Researchers at Phantom Works believe that the system can be built to be "weight neutral," meaning that as much weight could be removed from the plane as the system would add. For example, less fuel would be needed, and that would produce a significant weight savings.

WorldChanging's Jeremy Faludi works with Chorus Motors, and suggested we might be interested in this story. He was right; this is one of those developments that has both evolutionary results and revolutionary potential. Not only would this reduce fuel use and corresponding emissions, it's also indicative of the power of new generation electric motors. Imagine a plug-in hybrid with a motor like this -- we might well be on the verge of the first hybrid-electric NASCAR champion.

If Jeremy has the time, I would encourage him to fill in details and his own observations about the project in the comments.

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Essentially, this means that the aircraft can taxi on the power of its APU, with all main engines shut off.  It can also back itself away from a gate.

I've long wondered why nobody did this.  Guess it was just waiting for power/weight to get high enough.

Posted by: Engineer-Poet on 3 Aug 05

Yes, Engineer-Poet, it runs the plane from the APU ("Auxiliary Power Unit", for those not in the biz) with jet-engines off. And more importantly, as you said, the planes can drive backwards as well as forwards.

Jamais, slight correction to the post: currently all planes have to be pushed backwards by the tow-tug vehicles; their jets can only push them forwards.

And to elaborate, waiting for tugs to come and hook up wastes time; it's possible that if all planes had motorized wheels, airports might get one extra flight per day per gate. (This alone would make the invention financially desireable, even ignoring the other benefits.) The invention's main environmental benefits are that it:
- saves fuel
- reduces air pollution
- reduces noise pollution
- reduces engine wear (there're always little bits of debris on runways that get sucked into the engines.)

And EP, you're right that this would've been done long ago, except that no one else has been able to get the power density that Chorus motors get. At some point we'll have photos up on the website so you can see how small they are.

Posted by: Jer on 4 Aug 05

But presumably wouldn't an extra flight per gate per day result in more pollution being emitted than was originally saved by installing these devices?

This isn't intended to be a nitpicking point, I do understand that more efficient use of existing resources and infrastructure will be part of the solution, but there is a danger that increases in fuel efficiency of any kind just cause us to do more with what we have available i.e. "Great, hybrids. Now we can drive twice as far." or "Wow, with these savings in heating bills, we can afford to attend that trade conference in South Africa." New Scientist just published a very interesting editorial on just this subject, basically arguing that energy saving in itself will not help, if we do not address the question of what is done with the resources that are saved. Still, we have to start somewhere. Does anyone have any thoughts on how we can ensure that great advances in technology like the one posted above result in actual cuts in net emissions, not just greater resource efficiency, and hence more damaging activities? Seems to me that this is where regulatory measures and mandatory limits to emissions come in.

Posted by: Sami Grover on 4 Aug 05

Like every other engineer sitting around hot and bothered in a grounded jet, I have wondered the same thing, why not just put some power to those wheels and drive off? Of course the answer is that the motors were too heavy until now.

But I also bet that a lot of those same folks had a further thought- why not make a network of vacuum filled tubes in which maglevs could skoot from hither to yon in a blink, using almost no fuel relative to these whales pushing a lot of high Mach air out of the way?

This is an old, old idea, even older than I am: I think Goddard started it, and there is much good thinking about it on the web, but as with the wheel motors, the technology just wasn't there until now. But now is now.

Posted by: wimbi on 4 Aug 05

Actually, I wondered why air motors (running off APU bleed air) wouldn't have sufficed.

I read the Chorus spec sheet (they're HQ'ed in Gibraltar, a domain I'd never seen before).  What they have is a very clever method for doing what every BSEE knows is possible:  adjusting the number of poles in the motor stator to suit the torque/speed demands of the moment.

Genius consists of looking at what everyone has looked at before, and seeing what no one has seen before.  My hat's off to them.

Posted by: Engineer-Poet on 4 Aug 05

The other thing I like about Chorus Motors is their parent company, Borealis. They are also developing special Peltier type devices that convert heat energy into direct electricity at 70-80% Carnot efficiencies using quantum electron thermotunnelling on chips. Any heat source can be used to generate electricity, not to mention secondary heat recovery. And recently, they have come up with Photon Chips™, converting sunlight directly into electricty. These guys are phenomenal!

Posted by: Xavier on 4 Aug 05

To me, this is sort of a finger in the dike solution. It's a good idea that should be implemented, but it won't resolve the longer term problem that current planes won't be affordable to fly if the price of fuel goes up a lot more. We're gonna need to switch to those blimp-like things that a previous post mentioned.

Although only briefly mentioned in the post, this motor is probably more significant for other applications (transportation and otherwise) where it could make a substantial impact on fuel consumption. I'd like to see a post on the recent innovations in electric motors. I've seen many individual articles but no aggrigation.

Posted by: Erik Ehlert on 4 Aug 05

Actault fuel is not the most important cost of a flight and people were flying back decades ago when flights cost far more inflation ajusted. Just will mean fewer people will fly.. wich is prolly a damn good thing

Posted by: wintermane on 4 Aug 05



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