I here of many people claiming a large performance decrease using a multiblade prop due to decreased efficiencies. I thought the efficiency differance was very small. Any way to calculate this? Any sites that show test results between 2 and 3 or 4 blade props? Not talking just RPM and thrust differance but an evaluation of efficiency also.

Sport Pilot,

I can't point you to the data you want offhand, but I will make an observation. When you go to a 3 or 4 bladed prop from a 2 bladed one, a lot of things change. If you don't change the pitch and/or diameter, you will greatly increase load on the engine, and probably take it out of its ideal RPM range. If you reduce the diameter, you will definitely reduce efficiency. And, yes, all things being equal, more blades is less efficient. My suspicion is that people who see large performance reductions are not making the other adjustments to match the prop to the engine and plane, and that is a more visible problem than the efficiency. Just a guess.

banktoturn

Try http://www.djaerotech.com/dj_askjd/d...fourblade.html

There are a couple of other related Q&As on that site including an interesting one about single-blade props so it's worth trying a search in "Ask J & D".

Steve