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.

45 kg of batteries alone? What would the total weight of the system
be?

I'm thinking you are going to quickly run out of wing options. I hook
in at 210 lbs. (94kg) and have flown a Wills Wing Falcon 209 & 229 (sq
ft of wing). My glide ratios from a 65 ft training hill were about 7:1
for the 209, and 8:1 for the 229. With an extra 90 lbs of motor and
batteries, you'll need a much larger wing. I havn't researched the
subject in a while, but most of the available wing designs have an
upper hook-in weight of 250 lbs (111kg). And most HG pilots fly a much
smaller wing (150-175 sq ft) since they mountain or tow launch.

Assuming you / your market will buy a wing sized to fly with power,
then a tandem training wing should work. I don't remember exactly, but
I believe I did my tandem training in a Wills Wing Condor.

Now here's another problem. Your wing will need to lift you and the
powerplant at a speed slower than you can run with the glider,
powerplant, harness, and any other gear resting on your shoulders. I
can make launch runs at about 10 mph. Any faster, and the glider will
likely pitch over and nose-plant itself. That ain't fun. Trust me, I've
done it once or twice and narrowly avoided broken bones. Otherwise,
you're talking about some sort of wheel launch.

I meant to ask you in the last post, are you currently an HG pilot? If
so, where from and what rating do you hold? If not, are there any
schools near you? Even an introductory weedend of foot-launching would
shed a lot of light on the piloting aspects of the issue.

Harry Frey
USHPGA #79944
Kicenuik Batso
Frey Stormy Petrel 2, 2a, & 3
Wills Wing Falcon 209 & 229
Wills Wing Condor
Wright 1902 glider