Marcellus Jacobs: Wind-Power Generating Inventor
(Page 9 of 12)
November/December 1973
By the Mother Earth News editors
PLOWBOY: Yes! I wanted to get to that. Tell me about the construction of your propellers. Did you make them of metal?
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JACOBS: On no. Solid metal—even aluminum—would have been too heavy. Too much centrifugal force. The more flywheel effect you get, see, the more trouble you have shifting the plant around and that means more strain on all the component parts.
We did stamp out some hollow aluminum blades once, but they weren't at all satisfactory in the north country. They had a tendency to sweat. Frost would form on their insides and throw them out of balance...and that could shake a plant completely apart.
No. Our old standby was aircraft-quality, vertical grain spruce. Sitka spruce from the West Coast. I used to go out and select the lumber personally and have carloads of it shipped back to the factory. During the war, I had a little trouble getting the quality I wanted.
PLOWBOY: And how did you turn the raw lumber into blades?
JACOBS: We rough-cut the airfoils first—from 2 X 8 planks—on a special machine. Then we put them aside in the kiln-dry rooms for several weeks to make sure they were completely set and weren't going to warp. After that we made our final cuts.
PLOWBOY: Did you hand-sand them?
JACOBS: No, we had a great big sanding machine that worked down both sides of a blade. It was set up like a planer or a duplicating lathe, you know. You clamped your raw blade into mounts on one side and then you ran a set of feeler rollers over a perfectly finished blade that was always mounted on the other side. This guided the application of power sanders to the unfinished airfoil...and you could smooth it right down to the exact contours of the master very quickly, easily and automatically this way.
PLOWBOY: How did you finish the blades?
JACOBS: With an asphalt-base, aluminum paint.
PLOWBOY: And that's all?
JACOBS: That's all they needed. Propellers we built 25 or more years ago are still going strong.
PLOWBOY: I notice that you never put a brake on your plants.
JACOBS: No, our tail vane was enough. We had it hinged so we could lock it straight behind the generator or swung away off to the side. It would remain streamlined to the wind either way, of course, so when it was in the second position it pulled the generator and propeller right around edgeways to the moving air. This took most of the wind off the blades and they'd sit up there and just idle during violent storms.
PLOWBOY: But other manufacturers could swing the tail vanes on their machines to the side too.
JACOBS: Yes, but most of them did it the wrong way. They fastened the vane straight behind the generator with springs and you had to use a line from the ground to pull it around to the side. If that line broke during a gale, there was nothing you could do about it. The windplant would run away and tear itself all to pieces...unless you had a brake that you could apply...and brakes, for some other reasons, weren't a good idea either.
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