Lifer, as I found, there is very little air passing through the swept area. This creates a low pressure area and that is what influences the tail rising UP hill as it furls. Gravity would keep the tail on a level plain.
We had a Chevy Luv pickup we ran around with. The hood was hinged above the radiator, near the front bumper. The latch was broken in a previous crash, so, we never bothered to fix it.
When a Large box truck or semi passed us, going in the opposite direction, that hood would lift, sometimes 8 " or more from the truck creating the low pressure area as it went by.
I'm no scientist, physicist, weathercist or anything. I just know what I experience and try to reason out why.
From Boating experience in my entire life, Volvo make a dual prop system on their outdrives. One set of blades was COUNTER rotating from the direction of the other. This is pulling water INTO the second and counter rotation creates more force from changing the rotation of the water.
Mr Jacobs reasoned that too many blades caused TORQUE for slow pumping of water, but not sufficient RPM's to run a generator.
My thinking about that ring at the blade tips, if all that air is passing ALONG the blades, where does it go when it strikes that ring ? It HAS to become turbulent, ??
Two props fixed with no yaw, would probably work, fastened apart and had the same pitch to catch the wind from different directions, but, I would rather let the mill yaw and accept the wind at a direct path not at an angle if it can't yaw ?