viable power

[philc]

Thanks to some discussion here, I decided to bite the bullet and put together a power system for a CL plane. The big cost was a charger, but I needed one anyway, since I wanted to put a motor in a sailplane anyway.

I'm using 8 Sanyo CP1700 cells, a timer-type speed control, and either a Graupner Speed 500 with 2.5 reduction, or a Kyosho Endoplasma with 2 reduction. The Speed 500 will turn a 9/6 prop about 7500 rpm for 2.5-3 min. The Endo will turn an 8/6 about 10,500 for 2 min.

The following calculator comes fairly close if you half the battery capacity and double the cell resistance.
http://custompaintjob.com/ezcalc/dma.asp

I figure I can build a 10-11 ounce plane(~450 squares) so the final result will be about 30-32 ounces and have enough power for some decent aerobatics for close to 2 min. I was surprised how well the rpm held up. Both setups held the rpm within a couple hundred for about 80% of the run time.

Once I get my feet wet, I will try upping the current. The Endo is supposed to be able to take 40 amps or so and 30,000 rpm. That will bring the power up to 240 watts or so, which should give pretty lively performance, at least for a minute or so!

[robertc]

Sounds Good. I made a 10 cell one work as a first try to prove to those friends of mine who actually fly control line it would work and built an S400 to prove to myself it too could be done. Neither of mine were optimised and the 10 cell was a large bodied r/c model grabbed for the experiment. Your 8 cell with motor running geared and efficiently should perform better than my 10 cell model that used a direct drive (heavy) speed 700. Let us know how it turns out. My thoughts on this game lead me to believe you need to prop more for speed than thrust ( ie in r/c terms more toward the general sport flyer than prop hanging) and design for thin wings with large area to keep wing loading down and drag down.
However this is from only a few experiments so far and I may be wrong.
regards
Bob