The windmill I'm looking at has a two-bladed turbine with a flap-construction instead of the more rigid three-bladed turbines. The vendor claims that this construction is self-adjusting, reliable, requires little maintenance, etc. Books and articles I have read so far about windmills recommend the three-bladed turbines as the best solution. Of all the commercial windmills I have seen, less than 1% have been two-bladed.
Offered by Jan.
Three blades may have a little more stability, the trade-off is a little less power from the extra weight (inertia), but not real significant that you would really need to worry about it. As far as life expectancy, the 3 blade may be more stable, but as long as the 2 blade is balanced, you should be OK. Are the 2 and 3 blades interchangeable?
Offered by Steve.
What about potential life span for a two-bladed construction vs. a three-bladed? The Home Power magazine said in an article about windmills in #65 that:
It should be noted that several of the manufacturers offer two blade and three blade versions of the same model. Because they're more efficient, two bladed systems put out more power at any given wind speed than the three blade versions. In my opinion, the added efficiency that a two blade version has over the three blade version is not worth the resultant shorter life span of the two blade model.
Offered by Jan.
I remember an interview in Mother Earth News years ago with Marcellus Jacobs the founder of Jacobs Windgenerator Co. He resumed building generators after something like a 15 year shutdown, but I don't know where he went from there, he was 80+ years old at the time 70's or 80's. He invented the 3 blade propeller with adjustable pitch angle. He donated the patent to the government during WWII so they could use it on fighter planes because during high speed turns a single prop would tend to tear the engine loose from the mounts (the same thing can happen on the windgenerator and during much testing he settled on the 3 blade prop).
He also said "If you want power, nail a flat thin board to a broom stick", simple and cheap as well as effective, but not slick and efficient. Triangle shaped sails on broom sticks or heavy dowel rods would also work, you stretch them taut and the wind blows them into the shape necessary. Refer to the sail windmills seen in Greece along the coast. You could salvage an old pair of bluejeans for sail material or some similar fabric, you know. Any of these methods of prop or sail building would work well on our little model or a scaled up version, I think.
Offered by Jay.