Gary Van de Laar, age 13, of Pocatello, Idaho, for his question:
ARE WINDMILLS STILL USED TODAY?
A windmill is a machine that uses the energy of the wind to produce power. It is a member of the class of machines known as "prime movers."
Many windmills are in use today. They are generally used to pump water, to drive electric generators for lighting and for charging storage batteries on farms. A mill used to pump water has a wheel of blades set at a common angle and mounted on a horizontal shaft. The wheel is held with its face toward the wind by a vane, or rudder.
The wind strikes the blades of the modern windmill at an angle and forces the wheel to revolve. The mill gets the full force of the wind by being mounted on a tower at least 20 feet high, above nearby buildings and other surrounding obstructions.
Many think of the picturesque beauties found in Holland when the word "windmill" is mentioned. The Dutch developed the mills in the 1400s to move water. At one time there were more than 10,000 windmills in Holland. Today, fewer than 1,000 remain.
Holland's windmills no longer pump water. That job has been turned over to more efficient engines. But the limited number of windmills that remain are regarded by many people as national monuments, and the mills are protected by law.
An early Dutch windmill stood five stories high and had five sails, each up to 100 feet long. Early sails were flat and made of sailcloth stretched over wooden frames. Later the sails were built with a twist in them, much like that of an airplane propeller.
In the modern windmill, found in many farms today, the power increases with the diameter of the wheel. But there is a practical limit in diameter over which there is little gain in power because of the increased weight. In tests, a steel wheel eight feet in diameter develops a bit over a half horsepower in a 20 mile wind. One 10 feet in diameter produces a bit over one horsepower in the same wind.
Increasing the size of the windmill's wheel in the same ratio doesn't increase the power on the same scale.
In the modern windmills that use the power of the wind to pump water, a propeller wheel turns small gears on a shaft. The small gears are made to turn larger gears, increasing the turning force. Connecting rods from the large gears move a pump rod up and down as the wind wheel revolves.
Wind electric plants also have a propeller type wheel, but use only two or three blades, rather than a dozen or more as used in water pump windmills. The two or three blades in the wind electric windmill turn at high speed.
The wheel of the wind electric plant is usually mounted on a mast held up by guy cables. The wheel is connected to an electric generator through gears. The sizes of wind electric plants range from those that produce 100 watts to those that produce 2,000 watts.