David,
Thanks to all for their insight on this plane. Your thoughts on the 55 AX powered, lighter version mirror mine. Almost everyone commenting here and on thread on RC Groups have changed the fuel tank to a 12-16 oz to acommodate the 61-65 engines and most mention putting at least 2 oz of lead in the tail. It seems like there is about a pound difference in weight. The 55 AX is rated at 1.68 bhp and the 65 AX is rated at 1.73 bhp. This makes the 55 AX about 97% of the 65's bhp, with these numbers based on OS specs. Recommended prop size is about 1" less on the 55, which is an advantage in ground clearance. Loss would be in torque, which might be apparent in vertical. I'm not sure if I will try SPA competition or use this as a sweet sport plane, but I think I will build with the 55 AX as light as possible. I think it will be easier to "up-size" the engine later rather than go smaller. The physical size of the 55 AX is dramatically smaller than the 61 SF or the 75 AX.
I will continue to follow here and RCG and much appreciate all of the help on this thread. That's what makes this such a great activity.
Jim
Last edited by JimDFlyer; 02-20-2014 at 09:24 AM.
Reason: typo