Only one propeller blade on this airplane.

[1600vw]

http://www.youtube.com/watch?v=fqiBb98o1D8

[FlyingRon]

The Sensenich shop up in Lancaster has a single bladed wood prop on the wall along with some pictures of the cub it was flown on.

[crusty old aviator]

One is the most efficient number of blades to have on a prop, but dynamically balancing a one-bladed prop can be tricky, which is why they went with two blades, way back when, and the idea stuck.