The only reason some multi-blade
props are less efficient is that they have a klunky, un-aerodynamic shape in the
hub region, so more blades, more draggy shapes being pulled through the air!
Just because that klunky shape is rotating doesn't take away its drag! Put
a nice, streamlined, glove fairing around those blade roots, with proper
helical twist angle, and you'll have a great prop. A four-blade will you give
great takeoff and climb. How many blades on the C130J? 6! How many on the
fan of a fanjet? 18-24. Note that those fan blades maintain the correct
shape all the way to the hub, and are at the correct, very steep, helix
angle!
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