[QUOTE=oldbassard;11646398]I'd have to think the size of the propeller and pitch makes a difference, If you have a propeller that's 10 inches long at 5,000 rpms the two blade will have less area and time to "Bite" into the air. A blade 48 inches long will have more area and be more efficient. The blade I assume would have to be able to create a wind tunnel. So if you take a 3 bladed prop that's 10" 8 and spin it too fast, It won't have the area or time to bite into the air. Maybe a prop 10" 4 would do a better job of it[/Q