On Tuesday, May 14, 2013 7:17:35 PM UTC-4, Eric Greenwell wrote:
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)

So, have I done my H.S. physics correctly: a 360kg glider needs about 1hp to
sustain it, given that its normal sink rate is about 1m/s? At that rate your
4hp motor would work really well with enough battery capacity for a 2000' climbout.

Matt