Electric motor questions

Props designed for electric motors are typically more lightly built, because there's no pulsation of power like in an IC engine, so the blades flex less and are subject to less fatigue (each revolution of an IC engine, the prop blades absorb the power stroke, then give a good bit back to power the next compression - They basically accelerate and decelerate every revolution) . This allows them to be built slightly more aerodynamically efficiently than can IC engine props. An electric prop on an IC engine, however, will quickly fail and throw a blade. Their lighter weight also lends less flywheel to the engine.

You absolutely CAN use IC props on electric motors. In my experience, electric props often use just as large (or larger) a shaft hole than to IC engine props. Smaller electric props especially, because they're held on by a collet rather than a simple screw.

I've seen electric motors for different 1/2a scale electric planes that turned anywhere from under 10Krpm to one turning a 4x4 prop at a good bit over 40,000. Its props looked very much like IC props, but were still more lightly built. Slower, larger props are more efficient, so non-speed focused RC planes do tend to turn lower RPM's.

J