On Tue, 07 Aug 2007 20:54:59 GMT, wrote in
:

In rec.aviation.piloting Larry Dighera wrote:
On Tue, 07 Aug 2007 19:14:59 GMT, wrote in
:

If you go to http://xtronics.com/reference/energy_density.htm you find
the energy densities of a lot of things.


Propane (liquid) 13,900 Wh/kg
Diesel 13,762 Wh/kg
gasoline 12,200 Wh/kg
Ethanol 7,850 Wh/kg
Methanol 6,400 Wh/kg
Secondary Lithium - ion Polymer 130 - 1200 Wh/kg
Primary Zinc-Air 300 Wh/kg
Lead Acid Battery 25 Wh/kg

So batteries have to improve by a factor of 10 to match gasoline.

When you compare the efficiency of internal combustion Otto Cycle
engines (30% - 40%) against electric motors (80% - 95%), it appears
that a factor of five might be a more realistic comparison of their
relative merits. Then there is the issue of power plant weight...

Well, you have to look at total system weight.

Agreed.

A 100 HP electric motor is not going to be particularly light

The ~100 HP Continental O-200 is about 170 lbs. If you look at the
motors offered by AstroFlight, it looks like they weigh about one
pound per horsepower, but that doesn't include the controller,
charger, etc.

and the power cables are going to weigh a whole lot more than fuel lines
for example.

True, but there are several trade offs: No oil cooler nor oil, No
gascolator nor fuel pump, etc... But the electric motor will require
a controller, a charging system, wiring, etc. It's difficult to
speculate about the weight without more specific information.

When you look at the total installed system, assuming you have batteries
5 times better than you have now, I doubt the total weight difference
will be all that much.

It's difficult to say.

Electric motors don't lose power in thin air either. With regard to
reliability, electric motors have only one moving part compared to
scores of moving parts for IC engines, their failure rate should be
substantially greater than IC engines.

AC motors have only one moving part but would require a beefy inverter
to generate (and induce more system loss) the AC.

But the controller has no moving parts either except perhaps a cooling
fan and contractor. I would guess the electrical propulsion system to
be potentially more reliable than an IC system, but there is the Sony
LI battery recall issue ...

DC motors have brushes but motor control is simpler.
If the DC motor was designed for easy inspection and replacement of
the brushes, then the failure rate should be much lower than a gas
engine.

Today, brushless DC motors, or even three-phase induction motors, are
used.

Sonex mentions a brushless DC motor:

http://www.greencarcongress.com/2007...aft-.html#more
Using a purpose-built AeroConversions brushless DC
cobalt motor, controller, and highly efficient battery ...

... the design team, in collaboration with Bob Boucher of Astro
Flight, Inc. (http://www.astroflight.com/), has designed and built
a completely new AeroConversions motor.

This motor is the most powerful, lightest-weight, and efficient
unit of this type ever produced. It is a 3 phase, 270 volt, 200
amp motor that will be over 90 percent efficient.


This works out to about 75 continuous HP by my calculations.

It will be interesting to see what the future brings.