the apc 14X4w is the prop that i use. it provides a lot of thrust, so much so that the plane won't sit still on the ground even at idle. there isn't much room between the bottom of the prop arc and the ground, but the landing gear is pretty stiff so as long as your runway is flat there's nothing to worry about. i have an os 70 surpass II on my plane, but the 14X4w should work well for the 61fx too.