Electric motor for hang glider

nestofdragons wrote:
I do not want to spool the fun here, but ... whichs formulas did you
use to get those figures?

They were from he
http://www.ornithopter.org/forum/sho...98&postcount=3 .
Even though the question asked on that page was regarding flapped
flight the answer was given in general terms of energy needed. It
ignored the 80% engine efficiency and the propeller efficiency which I
thought was also 80%.

I used some basic formulas and totally get
other figures. OK, I assume a bad efficienty of the prop and took it
for safety at 50%. I get for 10,5 glide ratio, 1300 N total weight, 16
m2 surface, climb rate of 2m/s --- needed power of about 10 kW!

Those are the approximate figures that were used for the calculations.
I should have doubled (approximately) the final result to allow for
engine & propeller. So I would guesstimate 3 kW for level flight. For
climbing at 2 m/s I think the power needed would need to be doubled
again to 6 or 7 kW.

So perhaps a more accurate cost calculation would be:

7000 W needed

= 45 kg of batteries at 150 kWh per kg

= 0.75 kg for each 1 minute of flight

= $250 for each minute of flight, at about a kilo per minute

$2500 for ten minutes seems a bit steep so I can understand why
manufacturers might not be making these yet. The gasoline engines for
hang gliders (including harness) are around $5000 total. A harness by
iteself is $500 - $1000. An Electric engine + prop is around $500 -
$1000.