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
the tops of buildings and towers. On western farms and railroad stations,
the pumping windmill was 20-50 feet high with a 6-16 foot wheel diameter”
(45)]. With 10-mph wind speed, a 6 foot-diameter wheel, a 2-foot diameter
pump cylinder, a windmill-pump could lift 52 gallons per hour to a
height of 38 feet. A 12-foot in diameter wheel could lift 80 gallons per
hour to a height of 120 feet. (Naar, p. 46).
The growth of wind-electricity in America was greatly stunned in 1937 with
the Rural Electrification Act, which made low-cost electricity more
available. However, in the 1970’s, due to oil shortages, earlier
prototypes of high-speed horizontal-axis windm ills were developed.
High-speed horizontal-axis types are used for many purposes, come in many
sizes. These include the typical windmills on a California windmill farm
and other windmill farms, and any other wind turbines in which the shaft
turned by th e aerofoils is horizontal. High-speed horizontal types may
have 1, 2, 3, 4, or many aerofoils. Low-speed types such as European ones
have much larger aerofoils in relation to their height above the ground.
Low speed types such as American Midwest ones are usually a pinwheel, with
many small blades encircled with an outer frame like a wheel.
Vertical-axis windmills were first developed in the Persians in
1500 BCE to mill corn. Sails were mounted on a boom, which was attached
to a shaft that turned vertically. By 500 BCE, the technology had spread
to Northern Africa and Spain. Low-speed ve rtical-axis windmills are
popular in Finland. They are about 150 years old. They consist of a
55-gallon oil drum split in half. They are used to pump water and aerate
land. They are inefficient. High-speed vertical-axis windmills include
the Darrieus
models. These have long, thin, curved outer blades, which rotate at 3 to
4 times the wind speed. They have a low starting torque and a high
tip-speed ratio. They are inexpensive and are used for electricity
generation and irrigation. There are three types, the delta, chi, and
gamma models. All models are built on a tripod. The advantages to a
Darrieus-windmill are that it can deliver mechanical power at ground
level. The generator, gearbox, and turbine components are on the ground,
instead of at t he top of a tower as in horizontal-axis windmills. They
cost much less to construct, because there is less material, and the pitch
of the blades does not have to be adjusted. Another type of HSVAW’s are
the Madaras and Flettner types, revolving cylinder s which sit on a
tracked carriage. “The motion of a spinning cylinder causes the carriage
to move over a circular track and the carriage wheels to drive an electric
generator” (Justus). The Savonius model, which originated in Finland in
the 1920’s, is a n S-shaped blade, which rotates and turns a vertical
shaft. Today, these types of windmills are very popular with scientists
and their technology is being developed.
Windmills Today Many windmills are used today: some estimates say 150,000
(Cheremisinoff 31), in the Midwest. They are used to heat water,
refrigerate storage buildings or rooms, refrigerate produce, dry crops,
irrigate crops, heat buildings, and charge batteries for tr actors on
farms (33). Ever since the energy shortages of the 70’s, the growing
concern of pollution due to the burning of fossil fuels and the depletion
of natural resources, windmills have been greatly studied and developed.
Today, Sandia National Laboratories, Alcoa, GE, Boe ing, Grumman, UTC,
Westinghouse, and other scientists are researching and developing
Darrieuses and new types of windmills. Today, windmills are used to
operate sawmills and oil mills in Europe. They are used in mining to
extract minerals, to pump water , to generate electricity, and to charge
batteries. “Windmills have been used on buoys moored far out in the
ocean, the power being used for the collection and transmission of
oceanographic and weather data. They also work in deserted places as an
aid t o radio and telephone communications and they are used to work
navigation lights on isolated hazards” (Calvert 77).
My Windmill
I built a windmill of my own. The goal of the windmill was to get
as much electrical energy as possible. This immediately ruled out any
new-wave type windmill. Instead, I went to Home Depot and got a returned
ceiling fan. I took off the white box wit h the motor and switches and
left the spinning black box on. I mounted the blades on the black box. I
put this on a post and a support. Then I got a Maxon DC motor and, after
fashioning a clamp-like device to hold the motor on to the support, I put
a r ubber tire on the spinning shaft of the motor and adjusted it so that
this rubber tire would be rotated by the spinning black box upon which the
blades spun. Next, I attached two large wires to the motor. I then made
a circuit. This circuit was a littl e difficult to make. It had a place
for the wires from the motor, ran through resistors and a variable
resistor, and then an Ammeter and then the place where I was to plug in
the light. In parallel was a place for a battery and/or a voltmeter.
After a few minor adjustments, I was ready to test my product. At first,
when the circuit was completed, the current flow was very low. There were
a number of adjustments I had to make in order to make the windmill work
better. First, I moved the fan that was blowing air on the blades,
farther away. I added a seco nd fan and adjusted the angle of these two
so that they were blowing at the center of the windmill. I turned the
windmill around so that it faced away from the fans. I loosened the
screws that held the blades on. I inserted a piece of cardboard 1/3″ th
ick into this space. This was to adjust the pitch angle of the blades so
that they would “cut through” the air better. The adjustments I made were
excellent. They worked. When I connected everything, I began to notice
an immediate change in the Ammete r. I was seeing as much as 20 milliamps
and 6.1Volts. Before, there were 5 milliamps and 3.5 Volts. I began to
experiment more with the angles of the fans, distances, and stuff like
that. For my light source, I used a green light. It had an internal
resistance of 450 ohms. This bulb was 1/2 W. It lit up easily and was
bright. The Future
The Future will likely bring bigger and better things for the wind
turbine. Many new wind turbine models are being built. The wind turbine
holds much promise for energy production in the years to come.
BY DAN TORTORA
Bibliography Calvert, N. G. Windpower Principles: Their application on
the small scale. London: Charles Griffin and Co., Ltd., 1979.
Cheremisinoff, Nicholas P. Fundamentals of Wind Energy. Ann Arbor: Ann Arbor Science Publishers, Inc. 1978.
Gipe, Paul. Wind Energy Comes of Age. New York: John Wiley and Sons, Inc. 1995.
Hau, E., J. Langenbrinck, and W. Palz. Large Wind Turbines. Berlin: Springer-Verlag, 1993.
Hills, Richard L. Power From the Wind: A History of Windmill Technology. London: Cambridge University Press, 1994.
Justus, C. G. Winds and Wind System Performance. Philadelphia: The Franklin Institute Press, 1978.
Naar, Jon. The New Wind Power. New York: Penguin Books, 1982.
Taylor, R. H. Alternative Energy Sources for the Centralized Generation of Electricity. Bristol, England: Adam Hilger, Ltd. 1983.
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