I have a 40% sport scale homebuilt kit here. It is a low wing aircraft with side-by-side 2-place seating. It is the Piel Emeraude airplane.

http://www.fly-imaa.org/imaa/hfartic.../v9-3-19a.html

126" wingspan 35-40 pounds RTF. Recommended engine size is 3.1 - 5.2 cubic inches. (50cc - 85cc) I don't build heavy, so let's assume it weighs a maximum of 40 pounds RTF.

I want more than scale performance. I want knife edge performance. Not slow high-alpha knife edge. It's not a 3D plane. I would really like medium to high throttle knife edge performance.

Consider that I fly at 6000 feet and there is about 10% - 15% drop in engine performance here.

What engine would you put in it?

Thanks