I have read where people have used airplane motors in helis, but i think the problem they've had is over heating (that's why a heli motor has bigger fins on the head). You could try and find a head with big fins (if they even make such a thing for your 40), or you can just put it in and see what happens (it mite over heat, and it mite not). what are you putting it in? You can buy heli motors pretty cheap now a days.