This is not from a blade guy, but...
Jacobs, of windmill fame, grandson (?) was interviewed years ago.
He was at the N or S pole, and one of the first mills was STILL spinning!
No maintainace or anything. Wow.
Anyway, he said it was decided way back that an odd number of blades was always best. I think he said why, but I do not recall.
This is what I have been doing. Beats working!
My high torque 5-blade gets noisy and stalls at low RPMs with no load.
Low RPM still being pretty fast.
A 20" box fan blade.
My 3-blade 27" ZubWoofer takes a little more to get it started but not much.
It has gotten loud, but not stalled.
No steady wind after it was finished.
It is 12" active blade, 5" hub, 25' root, 8' tip.
My 4-blade, same as above, starts just a tad easier, but takes a noticably longer gust to get to speed.
Seems to top out a little slower than the 3 blade.
Again, no steady wind after it was finished.
All that is no load.
The 3 and 4 blades go a LOT faster than the 5 blade, but they are not the same either.
The testing was in the same place in a few minutes, one at a time, in low but gusty winds.
All the same height, but the PVCs were hand held, the 20" was on a short 'tower' with a tail.
Tails work much better than a cigarrette and me guessing.
Much better! Learned that with the fan blade.
I'm leaning to the 4-blade for now.
Does OK and I have low average wind.
My cutin is kind of low,
and the alternator tops out fast, too.
A little more torque, less speed. (I can't use too much speed anyway)
Maybe I'll get a bit more amp hours?
Short gusts don't get anything but the 5-blade up to cutin anyway.
Even a strong short gust will not get the 3 and 4 blades up to cutin.
I think the 5 blade has an advantage because it is turning a bit sooner, and has overcome the KE when the main part of the gust arrives (my best guess).
But the fan blade is better balanced than the 3 and 4-blade.
Very basic I know.
I hope something helped.
G-