Mr Cox

I have been using the MAS 5.5x4.5 and 5.5x4 on an AP wasp. The 5.5x4.5 was a little to high load for the engine, at least in my plane (old school pylon style with a thick wing) and using 10% Nitro. The 5.5x4 was a better match and that's what I've been using mainly.

For comparison the load of the MAS 5.5x4.5 is slightly higher than for a cox gray 5.5x4.

Here are some rpm numbers I get on my JB welded CS on 10% Nitro (no thrust data though):

APC 5.7x3 18200 rpm (nice scream to it)
Graupner 6x3 17400 rpm (good match, nice idle at 3000 rpm)
Cox (gray) 6x3 16000-16400 rpm (unstable, seemed like a too high load)
Cox (gray) 5.5x4 16400-16600 rpm (unstable, seemed like a too high load)
MAS 5.5x4.5 16000-16200 (unstable, seemed like a too high load)

(This should/could fly something, I just don't know what yet...)