Hello,
This motor on APC 9x4.5, with 3S LiPo delivers 1184 grams ( 41.76 oz) of static thrust @21.4 Amps., delivering 237.6 Watts ( please refer to the data available on
www.cobramotorsusa.com).

I would like to build a mini-stunt monoplane for this motor and wonder how to size it.

People fly 1/2 A C/L models (~35" wing span, 20% wing thickness, 230 sq.in area, 21" profile fuselage, no flaps ) using 0.049-0.061 engines.

My initial calculations show that Cobra C2808-22, in the configuration shown above, is equivalent to 0.12 glow engine and is, therefore, two times more powerful than 0.061 glow engine.

I wonder if a model having 40" wing span having 300 sq.in area and 26" fuselage length will fly ok using my Cobra?

Taking only the static thrust ( 1184 grams) as the main factor, it seems it will fly very well.

The entire electric installation (motor, ESC, governor, prop and 3S 1800 20C battery) is ca. 400 grams (14 oz ) and I can build the complete, finished structure weighting 350 grams (12.3 oz.)

Himax published data show that, for example, HC3510 Outrunner is more or less equivalent to 0.15 glow, has 250W max power and can fly the models weighting 24-32 oz in 3D R/C flight. The parasitic drag of lines will consume about 1/6 of the available power in C/L flight but I believe my 750 grams (26-27 oz) RFT mini-stunt should fly ok. on, say, 45-50' long and thin ( 0.010") lines.

I would be grateful for your comments, suggestions and friendly critique.
Thank you,
Matt



 

This 3S 2100 battery weights 5.3oz. http://www.atlantahobby.com/Store/pc/3-Cell-2100mAh-3S-11-1V-ProLite-+-Power-25C-LiPo-1205p19261.htm
That should help with your equation. I think your plan might be worth a try.
If the motor turns out to be too small, just put on/in something with a bit more poop.

Good luck,
Chris