Реферат: Wind Power Essay Research Paper The wind

already been fixed. There is also a .009

probability of a bird or insect being struck by the blades. Windmill

makers must use artificial sound or florescent paint or scents to scare

away flying creatures.

Brakes

Mechanical brakes are used to hold windmills at rest when they are

not needed, are not functioning, or are under repair. Greek windmills

used sticks or logs jammed into the ground to keep the windmill stopped,

but modern brakes are more sophisticated. Many windmills today use

airbrakes like those used in planes. Other windmills have rope brakes.

Ropes connected to the aerofoils are simply pulled and tethered to a post

to keep the aerofoils from turning. The torque on a rope brake can be

calculated b y the equation (M-m)(R2 + r)g.

The Types of Windmills

There are a number of types of windmills. They are divided into

Horizontal-Axis and Vertical-Axis types. Low speed horizontal-axis

windmills are used for water pumping and air compressing. American

windmills (of the Midwest) are an example. Earlier wi ndmills such as the

ones in England and Holland build a couple hundred years ago are another

example. The horizontal-axis was invented in Egypt and Greece in 300 BCE.

“It had 8 to 10 wooden beams rigged with sails, and a rotor which turned

perpendicular

to the wind direction” (Naar 5). This specific type of windmill became

popular in Portugal and Greece. In the 1200’s, the crusaders built and

developed the post-mill, which where used to mill grain. It was first used

to produce electricity in Denmark i n the late 1800’s and spread soon

after to the U.S. In America, windmills made the great plains. They were

used to pump water and irrigate crops. During World War I, farmers rigged

windmills to generate 1 kW of DC current. They mounted their devices o n