Donald Cooksey: NASA Wind Generation Project
(Page 7 of 9)
May/June 1976
By the Mother Earth News staff
NASA'S 100-KILOWATT WIND TURBINE GENERATOR (WTG):
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SOME TECHNICAL FACTS
This test machine consists of a rotor turbine, drive train assembly, alternator, yaw system, tower, and controls. The rotor is 125 feet in diameter, its optimum operating speed is 40 rotations per minute, and it produces 133 kilowatts of power at the hub when turned by a mass of air moving 18 miles per hour.
The windplant has no tail to "point" its blades into the wind. Instead, the yaw system allows the whole unit to pivot on top of the tower so that the rotor automatically positions itself downwind of the support. This makes it impossible for the wind to ever "push" a blade into the tower (as sometimes happens to windplants with rotors that turn upwind of their supports). And—since the tower is not subjected to the force of the wind, then blanketed by a passing blade, then left exposed again, etc., during operation—the NASA unit's tower must absorb far less dynamic interference than the structures which support most windplants.
(EDITOR'S NOTE: This "downwind operation" idea may be good and it may not. Marcellus Jacobs-who sold 50 million dollars' worth of windplants back in the '30's, '40's, and '50's and whose machines, each of which had three blades that ran upwind, are still known as absolutely the finest and most trouble-free ever built—is not impressed by the "downwind" design philosophy. "If you use only two blades and run them behind the tower," he says, "you subject those blades to extreme forces every time they rotate. First they're being pushed by the wind, then they're shielded by the support, then they're catching the force of the wind again, then they're protected by the tower, and so on. This is what caused one of the blades to sever itself from the big Grandpa's Knob plant back in 1945. You're far better off to use three blades, mount them out in front, and beef up the tower enough to hold them. I tested all those ideas 20, 30, 40 years ago and I know. ")
The 133 kilowatts of energy produced by the 125-foot rotor on the NASA windplant becomes-after the rotor's 40 rpm is stepped up to 1800 rpm by the unit's drive train-a usable 100 kw at the alternator. The rotor, yaw system, and drive train are all mounted on top of a 100-foot tall tower and the controls for the windplant are currently located on the ground in a monitoring laboratory.
THE ROTOR TURBINE
BLADES: The rotor is fitted with two all-metal blades. Each is 62.5 feet long and weighs approximately 2,000 pounds. The blades use a NACA 23000 airfoil and each one is twisted 26.5° so that its fat, slow-turning hub will bite into the air with a greater angle of attack than does its slender, fast-moving (180 mph) tip. They were fabricated by the Lockheed Corporation—for $320,000 the set!—and are designed to produce 133 kilowatts of power when rotated at 40 rpm by an 18-mph wind.
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