We don't have a recommended propeller size for that engine. Usually, O.S. would recommend using a cut-down 12 or 13-inch propeller for breaking. Basically, you should use a propeller that will allow the engine to turn about 15,000-16,000 RPM when it's on the ground. Don't expect to get much in the way of low-speed operation. The engine was designed to run in a ducted-fan system, and would not deliver a low idle RPM in an airplane.