Larry Dighera wrote:
On Tue, 09 Jan 2007 22:54:18 -0600, James Robinson
wrote in :

Considering that a C150 has a usable capacity of only 370 lb. or so
with full fuel, The electically-powered aircraft would already be
more than 200 lb. overloaded, and we haven't even considered the
pilot, passenger, or baggage. Doesn't sound too practical, does it?

Now that you put it that way, reality is beginning to dawn on me.

It's almost like all those engineers working at Cessna and Boeing and
all the rest really _do_ know what they're doing when they pick internal
combustion engines fueled by liquid hydrocarbons.

Given:

http://en.wikipedia.org/wiki/Lithium_ion_battery
Lithium ion battery
Specific energy density: 150 to 200 W?h/kg (540 to 720 kJ/kg)
Volumetric energy density: 250 to 530 W?h/L (900 to 1900 J/cm3)
Specific power density: 300 to 1500 W/kg (@ 20 seconds [2] and 285
W?h/L)

http://en.wikipedia.org/wiki/Gasoline
Gasoline
Energy content
Fuel type Megajoules/L MJ/kg BTU/US gal
Premium Gasoline 32.84 43.50 131,200

Can you quantify the prospect of replacing Avgas with LiIon batteries?

The numbers are there, you just have to deal with metric prefixes a
little bit. Li-ion at 540-720 kJ/kg is 0.540-0.720 MJ/kg. Therefore,
the energy in a kilogram of premium gasoline is equal to the energy in
(43.50/0.720) to (43.50/0.540) or about 60 to 80 kg of Li-ion batteries.

If you consider the whole system, you can get away with fewer batteries,
because electric motors in general are better at converting electrical
to mechanical energy than internal combustion engines are at converting
chemical to mechanical energy. If your engine is 30% efficient, you
only get (43.5 * 0.3) or 13.1 MJ of mechanical energy for every kilogram
of gasoline you burn. If your motor is 90% efficient, then to get that
same 13.1 MJ of mechanical energy, you need to put in about (13.1/0.9)
or 14.5 MJ of electrical energy. This would require (14.5/0.720) to
(14.5/0.540) or about 20 to 27 kg of Li-ion batteries.

Matt Roberds