Marcellus Jacobs: Wind-Power Generating Inventor
(Page 3 of 12)
November/December 1973
By the Mother Earth News editors
PLOWBOY: Did it work?
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JACOBS: Oh yes, after a fashion. But there were several things wrong with the setup. It wasn't efficient, you know...there was no real gain. One of those big water-pumping windmill wheels is designed to catch all the wind in its diameter right at the start. Otherwise it'll never go. It'll just sit there. Unless the pump has lost its prime, that wheel has to lift water right from the instant it begins turning. It needs a lot of starting torque...and that's why it has so many large blades.
Once the wheel gets up some speed, however, about 80% of those blades get in each other's way. They begin fighting each other. In fact, a water-pumping windmill needs all the power it generates just to run itself in an 18 or 20 mph wind. You can pull the pump rod loose and the wheel won't run away. It can't. The force of the wind during a storm may blow the wheel into the tower and push the tower over...but the fan won't over-rev and tear itself apart.
The wheel we finally came up with for a windplant, now, is altogether different. There's no load on it at the beginning, you see...just the very slight drag of two ball bearings. The three little blades sticking out of the wheel's hub are all you need to start the thing turning in a two mph breeze. And those narrow blades are also all you need to catch every bit of air that moves through the wheel's diameter when the wind blows 20 mph. They'll do it better than all those sails on a water-pumping windmill's fan too. A three-bladed windplant propeller may develop between six and eight horsepower in an 18 mph wind, while an ordinary windmill wheel of the same diameter sitting right beside it won't produce much over two.
PLOWBOY: How long did you experiment with the old water-pumping windmill fans before you gave up on them?
JACOBS: Well, we messed around for three years or so. We even made a governor that turned every one of the blades—to feather them—on such a wheel...but there were just too many other factors working against the design. To put it very simply: If you can catch all the wind that moves through a certain diameter with three blades, there's no need to have fifty of them hanging out there. The extras just get in the way.
PLOWBOY: But why three? Why not two blades? Or four?
JACOBS: We tried them. We tried those other numbers. See, I learned to fly in 1926 or '27 and that gave me the idea that an airplane-type propeller was what we wanted. Most of those props, of course, had only two blades so that's what we used.
PLOWBOY: You took one right off an airplane?
JACOBS: No. They didn't have the right pitch. But we made some windplant propellers that were quite similar to the ones used on aircraft. We didn't stay with them long, though. I discovered—very early in the game—that a two-bladed propeller has vibration problems that a prop with three blades doesn't have.
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