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