For what it's worth, it would seem to me that as the dia.
increases so will the area within it. At some point there has to be a breakover
point where it is better to have another blade. As the dia. increases so is the
area of air being acted upon. There will be a given amount of thrust at a given
power setting so rather than increase dia. to an unreasonable size you go with
more blades which will act on a given amount of air the same as a larger dia.
prop. Now what the break over point is depends on the total load of the prop.
Everything is a contributing factor from the max HP of the engine and its
available torque to turn the prop. To the load being moved to the lift of the
wing. Everything, so its not a simple answer but it can be figured out. Just
not by me, im no math whizz however you can find the area of the prop and you
can find the amount of thrust it will produce with your engine and you can
figure your max weight. So with a little math that im not good at you can find
the max dia. prop you can swing without killing your engine. When the thrust of
a given prop dia. is no longer enough and you have HP and Torque to spare, you
can add a blade and get more thrust when you cant add to your dia. and do the
same thing. At that point the bennifit is greater than the added drag. That is
the way I see it anyway......
