I went through ALOT of props before I found the one I really liked.

Here's the props I tried and what I thought of them


GWS 8.4 - Not enough prop. It flew slow and smooth, but lacked the punch I needed for 3D maneuvers.
APC 8.6 - Nice prop, but WAY too punchy. Couldnt get a smooth throttle response from it. I kept having to jockey the throttle around to maintain the correct thrust. It seemed like it wanted to jerk the plane around instead of flying it smoothly.

GWS 9.4 - Much better, but seemed to cavitate a little due to the flexabilty of the blades when I really popped the throttle to it which gave this aweful fluttering buzz noise.

APC 9.4 - PERFECTION AT LAST. Smooth throttle response, hovers just a tad below 1/2 throttle, and has instant punch-out when I hit the throttle. The stiffness of the prop means no cavitation when you punch it. Im sticking with this one on the F3A, as its the best one Ive found. It seems to pull the plane much easier and more smoothly.

They say max prop for the BP21 should be a 8.4 but I honestly think that's really conservative. It flys much better on a 9.4
Ive been using the 9.4 for a while now with no adverse affects. I havent checked to see how many amps its drawing, but the current equipment Im using is handling it fine. No overheating or anything. Im using the E-flite 20amp ESC and of course the Thunderpower lipo above.