ORIGINAL: combatpigg
The present set up here is 4.2x4......37,000rpm......140mph..... .452HP....with a gas prop
If the E props require less HP to turn for any given dimensions, then higher speeds should be pretty easy to get if the model isn't already at the wall.
So, just an interesting set of numbers to consider while bench racing......
3.8x4.75.......40,000rpm......180mph........453HP
I doubt that a 3.8'' prop would pull this plane over 90 mph in real life, but if you could build something small enough.....?
In the case of a 3.8'' prop pulling a plane to 180 mph, it would probably have to have a 12 inch span and weigh no more than 6 ozs to sustain that speed for more than 50 feet leveled out......
No idea if a 3.8" prop would pull it, but I think a 130" plane is about ideal for a 1/2A speed plane. Since it would have to turn hard fairly often, this works out to be an acceptable area to keep the wingloading down and induced drag low. The only bad thing is that a proper racing airfoil (RG14, MH-30, RK40 etc.) would mean a really thin wing so it would need bagged with glass under the skin and a proper I beam spar.
I'm actually a little leary of building little planes this fast.. It's one thing if you can make a phone call to Russia and have a molded F5D show up at your door and know that the engineering is already there and done. It's another thing for you to invest sweat and tears only to find out that you have a serious flutter problem and no throttle to shut it down. I built a JMG Penetrator/Cheap Thrills last year for the SMALL fly-in that I didn't make. It had an F5D power system in it and from 70 or 80 I couldn't give it full power for more than two or three seconds-it would flutter at about 140 and do a large dutch roll with no aileron control. Granted this is a much larger wing than we are talking about with big ailerons, but on a 1/2A that fast you might not even hear the flutter start until it was too late. [X(]
You ever experience 1/2A flutter CP?