Hi Ed,I want to mention that my SK50 and a friend s (new) one absolutely wants more prop than 12x6 :Some RPM checks(with a borrowed Tach) showed more than 12000 RPM s on mine(no nitro) and about 12900-13000+ for him with some nitro.(mine was 11x7 APC his was 12x6 other than APC-forgot the brand)