There is an electric motorglider that has been in series production
for over a year now, with others entering the market this year. 57 HP
motor running at 190 - 288V and pulling up to 160A. The Li-ion
battery pack delivers 10,000 feet of climb before depletion. In the
absence of soaring conditions, this translates to roughly 100 miles of
range. Certainly these are not figures that meet airplane
requirements, but they do very nicely for a motorglider, and I think
they go along way toward proving the feasibility of electric powered
aircraft for certain applications.

http://lange-flugzeugbau.com/htm/eng...tares_20E.html



On Apr 16, 5:07 am, Dylan Smith wrote:
On 2008-04-15, Larry Dighera wrote:

Another limitation is that for something the size of a C-172, your
battery has to deliver around 120 kW to get off the ground and
climb to altitude.

I don't see that fact as being too limiting. Why do you feel that's
an issue?

120kW, or about 160 horsepower, at any sane voltage is going to be a
tremendous amount of current. If your supply voltage to the motor was
600 volts, you'd need to deliver 200 amps. This requires a serious piece
of cable to do efficiently (i.e. without getting insanely hot). It also
needs batteries or a power source with a very low resistance to not also
get very hot. With typical high current motive applications like trains
or cars you can just add more metal to the conductors to the motors. You
have a weight issue with aircraft, though, with both the control
circuitry and the high voltage, high current wiring.

Of course gasoline also requires tanks, but they are often just sealed
parts of the wing structure, so their weight isn't really significant.
I don't know the strength of carbon-fiber or Kevlar composite, but
pressure cylinders constructed of them are about 60% lighter than
comparable Al cylinders

It's not just the tanks - you also have to make an idiot proof fuelling
system that can be operated by the typical 17 year old line boy, but is
capable of handling *five tonnes* per square inch of pressure.

To put that into perspective, that's like two SUVs sitting on each
square inch of pipe, connector and tank. Without even considering the
energy content of the actual fuel, the potential energy of even an
inert gas at those sorts of pressure would result in very bad stuff
happening if someone got careless with the fuelling equipment.

While the engineering challenges can be solved, it's never going to be
anything remotely resembling low cost due to the enormous pressures
involved, and the safety issues with handling anything at those enormous
pressures.

--
From the sunny Isle of Man.
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