Single blade props are also popular on models, particularly motorized sailplanes and indoor models where every bit of efficiency is needed.
Don't have time to get into a debate on it, but all other things being equal, the less blades the more efficient. More blades come into play usually when there is a need to reduce diameter for clearance issues or to keep tip speed subsonic. Basically, there are some situations where more blades will give you a better combination of speed, economy, and/or climb, and situations where less blades will. Brian Kraut Engineering Alternatives, Inc. www.engalt.com
