ORIGINAL: ChuckW
ORIGINAL: WMB
Have you tried a smaler prop, say 11x5, 11x6? My ST51 loves an 11x5.
Good luck, MikeB
These are all too small for the .55-AX. OS recommends a 12x7-8 or a 13x6-7. I feel that the 13" prop is probably a bit of a stretch but likely doable. The 12x7 is near ideal. If you use an 11 inch prop on this engine it is probably best to keep the pitch fairly high (i.e. 11x8 or more). Despite the advertised "practical RPM", this engine leans toward low end "grunt" rather than a high RPM screamer. It has the torque for the 12 inch props and thrives in that RPM range.
I ordered one from OMP. The person that took my order said most of the 3-D fliers are using 11.5x4 and 12.25x3.75 APC's. The manual recommends the bigger props, but the emphasis is more on keeping prop noise down rather than performance the way I read it. When I get it, I'll do a short breakin on the bench then mount it to my 4*. I'll try the 12x7 after it gets some run in time, tht would be impressive!