I use a 10x7 on a OS46FX on a SIG Kougar and it flies it just peachy. Every airplane uses a different prop. Fast planes like a Kougar like a high pitch short prop. Big floaters use a large diameter low pitch prop. High pitch gives speed, low pitch pulling power. Of course I'm using a second rate engine so that may be why. I'm going to throw it away and get a Magnum or one of those other Chinese things. At least they will fit the same mount as they are pirated copies of a poorly made engine. Cylinders flake off all of them you know.