I saw a thread on that a little while back and as I recall, the guy with a US 41 was getting scale-like flight on his but not much more than that. I am planning on putting a 3.2 (52cc) Fox on mine. But then, I have a tendency to do more vertical stuff than scale stuff so I don't mind having the extra power. Besides, one can always back off the throttle to fly scale but if the airplane is underpowered, it will never have the extra umph to save it if you need it.