Of course if you are happy to fly 13.5m class
you don't need a 500kg glider:
http://www.alisport.com/eu/eng/silent2electro.htm
You might consider LiPo batteries are for thrill seekers though.
Greg O.
Mike Borgelt wrote:
Unfortunately there is a "maximum weight of non lifting parts".
You may need to put the batteries in the wings. See The Binder EB29DE
at http://www.binder-flugmotorenbau.de/eb2900.html?&L=1
<http://www.binder-flugmotorenbau.de/eb2900.html?&L=1>
Not a show stopper but extra complication.
To raise a 500Kg glider through 2000 meters(launch plus retrieve)
requires 10 megajoules of energy plus what energy was required to keep
it in level flight for the time taken to get there. Say 1/3 of that.
More powerful motors are better but prop efficiency suffers as you put
more through the same diameter prop. Interesting tradeoff and design
iteration.
1 kilowatt hour = 3.6 megajoules.
Prop efficiency and motor efficiency losses will be at least 50% so
you need around 7.5 kilowatt hours of energy in the battery. You won't
want to discharge it deeply if you can help it so a little extra
helps. Say 8 kilowatt hours.
Currently the LiFePO4 batteries (currently safest Li technology) can
get around 100 watt hours per kilogram so 80 Kg of batteries. Maybe
100 Kg installed with portable charger, motor, prop and controller.
It will end up similar to flying a motorless glider with water ballast.
Not impossible. That retrieve should get you to an airfield of some
sort at least but probably not home if you like the longer cross
country flights.
Li - ion batteries may do a little better but need more protection
circuitry/physical barriers etc all of which add to weight.
Mike
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