I was flying my Wasp today and chipped an APC prop tip on landing. I don't have a lot of clearance (note to self - buy those darned Krazy Legs soon!) so this isn't unusual. This necessitated a prop change so instead of the 12 X 6 I run on my Irvine .53 I thought I'd try a 13 X 6. What a difference - without touching the needles (didn't seem to need it) I noticed an immediate increase in thrust. All of a sudden I found I could do harriers consistently and was motoring around dragging my tail all over the field. I do notice acceleration isn't quite as good but it still has outstanding vertical. The revs definitely dropped (quieter!) and I noticed the motor was hotter as a result of the extra load, but this engine has the guts to handle it! Now I can see why the light 4 strokes are the hot tip on these fun fly planes. That ability to turn the bigger diameter props gives you greater thrust and better high angle of attack capability (read easier to fly). Wow - what a great afternoon flying!