Davide,


OS list the prop sizes for most of their engines, aiming to achieve the lowest possible noise level.

These sizes would usually not necessarily achieve the best performance.


In the USA, for high speed planes, most people would use a buzzy 10x6, or 10x7 prop.

My own experience tells me that for aerobatic flight, an 11x6, or 11.5x5 are much better and get a good percentage of the engine's power into use.


The 12x7 size that the instructions state would have the engine spinning at just over 9,000 RPM and making some 60% of its real power potential. You might get a reasonable pull, but not very much speed.