9 x 4 master airscrew. That’s what I will start with. Maybe I will try an APC 9 x 4.
Dale
Absolutely DO use an APC 9-4. Sand the trailing edge enough to make sure you don't cut yourself, otherwise, straight out of the package. Use everything else absolutely stock, no modifications to anything (particularly the spraybar/venturi) and STOCK MUFFLER, and however much weight it takes to balance the airplane about 1" behind the LE. DO NOT under any circumstances replace the spraybar with an ST spraybar, or use a "chip muffler".
This combination should fly extremely well, plenty good enough to win any Advanced-class contest if you know what you are doing. The biggest potential problem is trying to control the speed, since it will want to be too fast - although it doesn't seem fast in the maneuvers.
Brett