Page 73 explains how to find the horsepower required for a different number of blades if it is known for a certain number of blades. It gives a couple of formulas for you to figure out the new diameter and is based of your changing the blade area by a constant.


The page appears to be within a paper on boat "screw propellers" and it's highly doubtful that constants would be identical for both air and water. Has there ever been a boat that ran just one bladed props? There certainly haven't been any production aircraft during the golden age of props. There was certainly good reason for fuel efficiency in the 60s.

Efficiency really is only one very insignificant detail within the definition "better".

"2 is more efficient than 3" is most certainly nowhere close to "2 is better in every way than 3" and never will be "2 is always better than 3".
Yet modelers seem to have decided that 2 is always better in every way. Fortunately, the difference in efficiency is not significant, otherwise all the IMAC, pattern, and scale planes would be struggling to fly with their 3 bladers.