ORIGINAL: jaka
...The Byron fan could of course the be used but as this is a pusher fan, all air is going forward so the engine gets no cooling air if you use it as it is....
Brian, I admit that I did not think of this, when I suggested to do the break-in with the fan...
In this case, Jan is absolutely right and a rigid wooden prop is the only type that would not fail at these RPM levels.
However, a 10x8 (Zinger or TF) prop will absorb 5.28 HP at 22,000 RPM, which is beyond the capability of this engine. The 11x7 would be even worse (6.77 HP).
A 9x8 could be fine, at 3.47 HP and is even less likely to fail.