Will electric motors ever propel a 747?

Pkruse

Magneto speaks well, but his turbine course is a bit obsolete. Don't hold that against him. Billions are being spent on research and development, and we learn new things all the time. The greater the bypass ratio the better for many reasons. So we make it as big as possible within physical constraints. But we are pushing thru those constraints all the time.

MagnetoBLI

I look forward to the time aircraft eliminate the take-off from ground level and start airborne. Then HUGE bypass ratios could be possible, of course with an FOD trade-off

Pkruse

Where does the FOD come from in an airborne launch? Birds and hail? We can design for that. Not much different from a conventional propeller.

Take a look at the new PW geared turbo fan. It enables a much higher NO ratio.

MagnetoBLI

I'm mean HUGE bypass ratios that would touch the ground in conventional T&W configs; much larger than the P&W turbofan. Even distributed propulsion has limits due to wing span etc.. Design of bird damage would rise considerably though.

mfb

That would be similar to a rocket - possible, but extremely inefficient.
It is easier (requires less power) to accelerate more air with a smaller velocity difference, at least small compared to the air speed.

Pkruse

The goal at cruise for an airliner is for the fan exhaust to be one mph more than air speed. Can't really do that, but that is the theory. If the outside of the exhaust flow approaches that, it is OK for the center of the flow to be faster. They also shape the nozzle for smoother and more gradual mixing.

Ryuk1990

Don't chemical engineers typically work on batteries instead of EEs?

Pkruse

Ryuk1990: Yes and no. I have a friend who is a professor of chemistry at UCF, as is his wife. They have been working exclusively on battery development for 40 years. Certainly, these are the people who develop new technology. But to me working a real project on a real airplane, I'd expect the battery to be spec'ed out by an EE. He may very well coordinate with the professor and his wife, but as a mechanical design engineer, I would not know that.

Ryuk1990

Check this out. Elon Musk, CEO of Tesla Motors and SpaceX is planning an electrically-powered supersonic jet that also hovers!!! What the hell?

http://www.slashgear.com/elon-musk-i...-jet-04245866/

Pkruse

Ryuk1990: Two things are true in that article beyond dispute. He is not an aeronautical engineer, and this will be much more difficult than designing a space craft to dock with the ISS. Everything else he says can be debated.

But he has proven himself extremely adept at identifying excellent engineering talent, and then hiring it and retaining it. He is also very good at inspiring other people to invest lots of money in his ideas. With those skills, he can accomplish anything.

Enthalpy

An electric motor is very easy to make as good as a gas turbine. It needs no superconductors. You can take an absolutely banal squirrel-cage motor. Accept slightly higher losses than usual, for instance 5% or 10%, cool it accordingly, and then it gets as compact and light as a gas turbine.

Have a look at power plants with a gas turbine: the generator is smaller than the turbine. Sure, at a power plant, the turbine is optimized for efficiency more than mass or size, but so is the generator.

Better: electric motors improve with peripheral speed and with size. If you have an impression of big and heavy electric motors, it's because they're small at rotate at 5m/s. On a plane, they would be granted 100m/s.

This one is a steam turbine, but the general impression holds for a gas turbine:
http://de.wikipedia.org/w/index.php?...20070806180528
the generator is yellow and the turbine blue.

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A light battery is difficult to make despite so many brilliant people work hard on it. Already useable:
http://yuneeccouk.site.securepod.com/Aircraft.html
and since motors, propellers and airplanes improve with size, I suppose a commuter airliner is feasible.

But fuel cells may be ready sooner. And especially if they burn hydrogen, the mass of fuel necessary for the same trip is less than kerosene, and the volume isn't that huge, so the plane design is perfectly possible - we "only" need better fuel cells, with the propoer power and mass.

Some planes, especially drones, fly already on electric motors for tens of hours.

Ryuk1990

^Hey, which specific drones fly on electric motors?

Enthalpy

These search keywords give half a million hits:
drone "fuel cell"

http://www.tgdaily.com/sustainabilit...wers-scaneagle
http://www.msnbc.msn.com/id/45227798...litary-drones/
not necessarily the best examples. I believe to remember that at least one drone is operational, not just a prototype.

Few years ago I put some figures on an electric engine to propel a commuter, replacing the turboprop. Even without a gear, the electric motor was easy. This helped:
- Accept a good diameter (no exaggeration needed). Take many poles and a hollow rotor to save weight.
- Electronics engineers shall make the inverter with the proper frequency...
- Accept some losses, like 5% or even 10% instead of the usual <1%, since cooling is easy.
- My paper attempt was a squirrel cage. No permanent magnets needed.

I got the same mass, diameter, torque and power as a turboprop - except for the electricity source... I had put it in some forum, including the propellers distributed along the wing; was it Physforum back then?

Knowing that, I don't really understand why the recent paper design (at MIT? Read it at bbc.co.uk) wants to have superconducting alternators (at the turbine) and motors (at the distributed propellers). Copper or aluminium are good enough and available right now; an optimised design would give the proper efficiency.