In an effort to help "fact" rule over "opinion" here on the kr net, I've been looking for a simple explanation on propeller efficiency and I think I found it at the following web page.
http://www.djaerotech.com/dj_askjd/dj_questions/fourblade.html It is a fairly simple read and I've included some of it below. Make sure you read the entire article and not just the part that supports your opinion. Two blades Vs. multi-blades? Each is better some of the time. Larry Flesner ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ In the real world things aren't quite so perfect. The power from the motor is spread over the disk by the propeller blades, but for a finite number of blades they can't get it spread perfectly even across the entire surface. With only two blades the power gets concentrated in two radial stripes, with a relatively thin layer of peanut bu... oops, I mean power, spread over the rest of the disk. Whenever you concentrate a lot of power into a relatively concentrated space, the induced losses get worse. By adding blades we can spread the power more evenly over the disk, and improve on those induced losses. So let's all use 10,000 bladed props, right? Well, not quite. Two things get in the way. If you increase the number of blades, those blades need to be narrower. For a given amount of power you need roughly the same total blade area to absorb it in a given diameter, so that area divided among more blades means the blades get skinnier. One side effect is that with their chord now reduced, their Reynolds numbers get lower, and you all probably know what happens to the efficiency of airfoils when their Reynolds numbers (a.k.a. "Scale effect"; chord times speed times air density divided by air viscosity) get smaller. An even bigger effect in most cases (at least for full-scale props) is that their profile losses get worse. We're moving a greater number of objects through the air, so we create a bigger stir and lose a greater amount of energy doing so. More blades means lower induced losses, but higher profile losses. High power/low speed situations like takeoff and climb are dominated by induced losses, so more blades tend to help there. Cruise and other high speed flight conditions have higher mass flow through the prop (because of the higher speed), so they tend to be more sensitive to profile losses. Just as with an aircraft, where the highest L/D will occur when induced drag is exactly equal to parasite drag, for a propeller the optimum number of blades in any given flight condition will be where the induced losses are equal to the profile losses.
