On 5/14/2013 9:35 AM, wrote:

The FES starts instantly, has little drag when extended so needs less
power, and if powered by a fuel cell would be really light too.

If fuel cells are impractical, why not a small motor recharging the
battery? Then you could have a much smaller battery and motor. You're
low, press the switch. The battery fires up and gives you instant
power. In a few seconds the motor starts too and you use both battery
and electricity from motor and generator for a fast 2000' climb. When
the battery is out, engine-generator-motor to sustain or climb
slowly. When you shut down, the motor keeps running to recharge the
battery. If the motor didnt' start you'd have say 1000' of climb and
a few minutes of battery to sort things out for your off field
landing.

The energy density of gasoline is hard to beat.

The FES is very attractive, for sure. Windward is also working on one of
those for the SparrowHawk R. They call it "front mounted tractor", since
FES is taken.

I don't know enough about fuel cells to be sure, but I suspect one with
enough power for a good climb of 5 knots might be very expensive. Maybe
have a Li battery for the 2000' of climb, and recharge slowly from a
small fuel cell.

I've wondered if a gas-electric hybrid would be practical. A gas motor
powerful enough to supply half the energy of a 2000' climb at 500 fpm
would be about 20 hp, a fair sized motor. So again, maybe the solution
is a big enough Li battery to do the whole 2000', then use 4 hp motor to
recharge the battery over the next 30 minutes or so.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)