BUILDING THE BEST WINDMILL

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I. Prior Knowledge

 

Wind is created when the Sun warms the Earth.  The warming is not even, because the poles receive less heat.  Convection currents soon form trying to even out the temperature - this is the wind.  The hotter the Earth gets, the faster the convection currents trying to cool it.

 

If you are now going to try and build your own windmill consider this:-

 

Focus your attention on the ability of wind to make objects move.  Wind can do this because it has kinetic energy or energy of movement.  The faster the wind blows, the more kinetic energy it has.  This energy is transferred when wind strikes an object, causing that object to move.

 

Why not list as many things as you can that are built to catch the kinetic energy found in wind: sailboats, kites, windsocks, gliders, pinwheels, WINDMILLS.  What do you know about windmills and their capacity to catch atmospheric motion to make their blades spin.  How many different types of windmill designs are familiar to you? You may want to surf around this site and use the links to learn more about windmills.

 

II. Exploration

Windmills are designed to extract as much energy as possible from the wind. Windmills capture the energy of the wind when the wind moves the blades (or rotor) of the windmill. An effective windmill must therefore be designed to capture wind energy.

A. Suggested Materials

  • Electric fans

  • Assorted pieces of wood

  • Cloth for sails

 

III. Explanation

There are two basic classes of windmill design: horizontal axis and vertical axis. Conventional windmills, spin on a horizontal axis. The rotor, or spinning part of the windmill, is the most important part because it determines how much energy a windmill can capture and then transform into some other form of energy.

 

The rotating blades depend on either of two aerodynamic principles to derive power from the wind: drag or lift. Drag devices are simple wind machines that use flat, curved or cup-shaped blades to turn the rotor. In these, the wind merely pushes on the cup or blade, forcing the rotor to spin.

 

Lift devices, in contrast, use airfoils like those in the wing of an airplane to propel the rotor. Air flowing over the blade causes both lift and drag. As objects, like an airplane's wings, move through the air, the air pulls against them and holds them back. This is called drag. Lift is caused by wind moving at different speeds around the wing. Faster moving air has lower pressure than slowly moving air. Slower air under the wing pushes it upward as lift. The sum of these two forces on a windmill's blades generates a thrust that pulls the blade on its journey through the air, much like it pulls a sailboat through the water. This thrust is greatest when the blade is slicing through the wind. Airfoil performance is determined by the ratio of lift to drag.

 

IV. Examples From Everyday Life

A. Cup-type Anemometer: four hemispherical cups attached to radial arms which spin about a vertical shaft. These anemometers measure wind speed by their revolutions per minute. These devices work on the basis of aerodynamic drag.

Look at a picture of an anemometer.

Make Your Own Anemometer

 

When you are driving down the road and you stick your hand outside the car window, lift from the air flowing over your hand (a crude airfoil shape) lifts your hand towards the roof of the car. Drag pulls your hand towards the rear of the car. The sum of these two forces on any object generates a thrust that pulls that object through the air.

 

WINDMILL LINKS   WIND TURBINES   WINDMILL PROJECT

CONTACT:  nelson@solarnavigator.net  07905 147709 (UK)

 

This website is Copyright 1999 & 2004  NJK.   The bird logo and name Solar Navigator are trademarks. All rights reserved.  All other trademarks are hereby acknowledged.       www.maxenergy.org  is an environmental educational charity.

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