I'm just new here myself,but I'm flying a big stik .60 with a .90 engine on it and it flys awesome. I'm only running a 13x6 prop. I would believe a 13x6 prop on a .40 size plane even with a .55 engine seems very large. It would definely make sense as most of you guys are saying that slamming the throttle wide open at such a low speed could be a cause for a big problem. That big of a prop on such a small plane....I could see the motor spinning the plane before the prop,but wouldnt the plane tend to turn to the left instead of right?