Why are electric props different, and why are they for electric only?

One of the reasons that comes to mind is that the thicker, heavier props used for nitro or gas engines produce a flywheel effect that tends to keep the engines running at idle especially in the four stroke engines that only fire on every other revolution. That is not necessary on electric motors. But they are YOUR props. They can be interchanged if you want to.

The electric motors run much smoother than the glow/gas so the prop doesn't have to withstand the ignition impulses. It is highly not recommended to put an electric prop on a glow/gas engine.

Don't wooden props have a top speed that's too slow for many electric motors as well?

The thicker props made for glow and gas engines are built to withstand the pressure pulses of those engines. Since electric motors are so much smoother, the props can be built much thinner. That makes them require significantly less torque to push through the air, reducing your amp draw. If you were to put an electric only prop on a glow or gas engine, it would probably break after a while. If you put a glow/gas prop onto an electric motor, the amp draw would increase to the point of possibly burning up the motor or ESC and performance and flight time would suffer. Wet power uses thick props because it must; electric uses thin props because it can.

Just curious, does anyone make thin 'wooden' props for electrics (bamboo would work, I would think)? These would be great for early scale electrics, like WW-1 planes.

Look in Towers magazine, there are wood props for electric only.

Thx.