You can also go as small as a 10 x 8 to get more power from the engine. O.S. suggests larger propellers to cut down on noise. However, you do lose out on overall power. For 3-D operation, something like the APC 12.25X3.75 Sport Prop works out very nicely. The engine will run very well if you prop it so that you're turning in the mid-12,000's when on the ground at full throttle and leaned rich of peak RPM. This, though, will be quite a bit noisier than with the larger props turning much lower RPM!