Musk's next?: electric jets

[Dr Mordrid]

Elon Musk just did a short interview with TIME Magazine, and it has an item which could be his next venture:

a supersonic electric aircraft

Seems the start is more limited by the number of hours in his day.

Link is a 2008 NASA funded IEEE paper on electric ducted fan jets and an image showing the difference between one and a conventional turbofan engine. Basically, it replaces the turbojet with a superconducting electric motor while keeping the high-bypass fan that provides much of a turbofans thrust. Not that Musk would necessarily copy this for a supersonic aircraft, but it shows where the general thinking is heading.

http://ewh.ieee.org/...ongoC_2AP01.pdf

Manuscript received August 26, 2008.

This research supported by the NASA Fundamental Aeronautics Program
and the Department of Defense Research and Engineering (DDR&E) division
under the URETI on Aeropropulsion and Power. Support also received from
Florida State University’s Center for Advanced Power Systems (CAPS)

[Jammrock]

While this would be really cool to have, I foresee two problems.

1. We still don't have an easy, cheap way to build high temperature superconductivity. At least that I am aware of...
2. The ability to store the amount of electrical energy needed to power such a vehicle, and do it without using a lot of weight, is still science fiction. Maybe a super capacitor advance could do it?

[Dr Mordrid]

High-temperature superconducting motors & equipment are already a fact. Sumitomo Electric put one in a Toyota Crown back in 2008.

Generation is partly covered in the PDF in the form of a compact superconducting generator developed by the USAF, and a HTS motor, but a recent advance in solid oxide fuel cells at the U of Maryland is also promising because they allow the use of conventional hydrocarbon fuels without the high operating temps of previous versions.

http://www.scientificamerican.com/article.cfm?id=next-generation-flex-fuel-cells-ready

http://www.technologyreview.com/energy/39203/?p1=A1

[Umfriend]

"High temprature' being around -200 Celsius?

[Dr Mordrid]

It'a a bit higher now, copper oxide HTC's are at -140 °C.

These newer materials are good enough that near here Detroit Edison is testing a superconducting transmission cable that has integrated cooling channels, insulation etc. One small cable replaced 3 conventional ones.

As for the coolant; small cryocoolers sre pretty common these days and about the size of a portable fridge and about 80-100kg. Scale up as required.

[VJ]

I don't know how cryocoolers work, but most cooling systems have problem operating in low temperatures. Also, the cooling system will have to be up to aviation specs regarding reliability and failback meaures. Still, technology is evolving, so it doesn't hurt to start designing concepts that take its existence into account.

But energy storage will still be a problem...

[MultimediaMan]

While I think it is a noble endeavour, I don't think that this one will pan out anytime soon.

Most people don't realize how optimized the turbofan powerplant is. A good deal of the turbofan's engineering goes into the the turboshaft within. Turboshaft engines can only made into certain shapes dictated by the shaft powerplant dimensions. So this isn't just a matter of slapping in an electric motor. You are better to start with a very clean sheet of paper.

Consider: Induction electric motors can be had in a number of shapes; each form factor has advantages and disadvantages of some kind. Actually, this is were I'd bet the breakthrough innovations happen first.

But it doesn't really address the 800lb. Gorilla: what will power these beasts? Fuel cells? Capacitors? Batteries? Possibly.... they might even make it to the runway. But into the air... that is where things get complex. There is a reason jet aircraft are jet aircraft: nothing comes close to their perceived speed vs. cost efficiency. I have no doubt some areas of aviation, particularly light aviation, have the potential to go electric and do it practically.

But heavy commercial aviation is another matter. Power generation, storage and delivery mechanisms will have to be vastly improved to make them commercially viable. We will need to see seagoing systems before attempting airborne systems of such scale.

[Dr Mordrid]

We'll see. Through Tesla he has contacts with A123 which was begat via MIT, and anyone who can go from Tom Muerller's garage to an orbital spacecraft and medium lift launcher in just 8 years has to be taken seriously. He has hundreds of topflight aerospace engineers at his disposal just through SpaceX.

[Umfriend]

I know nothing of these things but I would wager that the energy density of fossil fuels is way way higher than that of any depository of electric energy (and I'll include fuel cells with that one). Moreover, the depositories itself are, I speculate, quite a bit heavier. Indeed, a fuel tank is simply emptied wheras batteries retain their full weight. My quess is we're still talking about this 20 years from now.

[Dr Mordrid]

Nothing so far says it has to use batteries as a primary power source. Many electric jet concepts are more like a hybrid car; using the battery for buffering/emergency/high load power and a hydrocarbon fueled superconducting mini-generator (1 meter) like the USAF has designed or a solid oxide fuel cell (again: hydrocarbon capable) for main power.

[VJ]

I have no doubt some areas of aviation, particularly light aviation, have the potential to go electric and do it practically.

Some companies are working on electric aircraft in general aviation:
Yuneec
elektra-flyer
Lisa Aviation
Equator Aircraft

However, either they are closer to sail planes than to airplanes, they fall in the ultralight category, or they have very limited range. Combine the limited range with long charge times, and it sort of negates some of the benefits of flying...

[Evildead666]

I suppose all-electric powerplants are a logical step.

Some day, in the near to far future, nearly everything will run off electricity, no matter how that electricity is generated.
Fuel Cell, Nuclear Fusion, Fusion in a bottle, whatever.

Its good that companies and people are thinking of these engines and products, that may have just a blank box with "Electrical Power Supply" written on it for now.
But when we DO get that breakthrough that allows us to have a 1m^3 power source that doesn't need refuelling for days/weeks, we will have the tech to put it to good use.