Electric motor for hang glider

In article ,
Morgans wrote:

| I have been trying to do some calculations of how much battery power
| would be needed to keep a hang glider flying level. With some help I
| arrived at about 1 or 2 kW (a few horse power)

That seems awfully low. Having that much power on a 6 lb R/C plane
isn't uncommon at all, and you're talking about something much larger.

| The electric RC community has nothing positive about that brand of cell.
| Lots of premature failures. Plus, the discharge rate of anything above C-15
| will kill the batteries quickly.

If he's talking about keeping it up for 30 minutes, that's only a 2C
discharge rate -- most R/C batteries can handle that with little
trouble.

A 15C dishcarge rate = only 4 minutes of power. And yes, it's hard on
the batteries.

LiPos are generally only good for about 500 charge/discharge cycles,
and that's if they're not pushed too hard -- perhaps 1/2 of their
rated dicharge rate with plenty of cooling.

| You also need to consider the charging of that many batteries. The cost
| will be a significant amount of your budget, as these batteries will catch
| fire if not charged carefully with an appropriate charger.

Also, if you have lots of LiPo cells in series, they need to be kept
balanced which gets complicated too.

Personally, if you've never done anything like this, I'd suggest
getting started with a larger electric R/C plane -- 60 sized or so,
perhaps even larger, and get used to taking care of the batteries and
motor for that.

There's a program modelers use called motocalc
(http://www.motocalc.comt) that will, given information on your plane
and it's electric power system, calculate what sort of performance you
can expect, or given certain performance requirements determine what
equipment you need to attain it. It's made for models, but I see no
reason why it wouldn't work for something ... larger, especially since
you'll probably be using gear intended for R/C use for this endeavor
anyways.

--
Doug McLaren,
The victor belongs to the spoils. --F. Scott Fitzgerald

John Moody did something similar with the Solar Riser. IIRC, it was powered by a Hughes helicopter battery and a 3 hp electric motor. He also had a panel on the top wing to charge the battery. He could get a 3-4 minute flight after leaving it in the sun for 4 hours or so, though the thing had a climb rate of approximately .00000569 fpm.

I've considered doing something similar. I know that there is at least one electric motorglider available now, from what I've heard it will climb to 8500' on a single charge. With a lithium-ion polymer battery and a brushless motor, it should be possible to rig something up for under a fortune - and the components are getting cheaper every day. Electric power has pretty much surpassed gas for small r/c planes already.