RE: WHats the best prop for a OS.40MAXFP Engine?
Hi partner. The FP is a great sport engine, but not a very fast motor (also is a plain bearing one). To obtain the maximum power from it try a scimitar prop design like APC or similar props ballanced carefully. Try one that give you some 13.000/13.500 rpm in the air because this engine dont have the power curve in the high rpm. For speed purpose i would try from 9X6 to 9X8, testing each in the model. For normal sport i would try a 10X6 or 11X5 for trainer duties, the same for scale models. This engine haves great torque at lower rpm and will serve you better as a sport engine. You could also try hotter fuels with more nitro in search for more speed, and in general OS engines run fine with nitrated fuels up to 20%, as we see in our flying field.. (reduce compression ratio if you note detonation or plug blowing, also reduce the prop load in this case)
enclosed a pic from my 40 FP
have a nice day