Windmills

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Introduction 

   Windmills have been used for thousands of years for providing power to do useful work.  Wind is considered a renewable energy source. Renewable energy is one of the keys to sustainable development. In this project, students will assemble a windmill using their own design for construction of the driving blades. When the blades turn they will cause an attached axle to rotate which will be used to do work. The work done will take the form of lifting a small weight attached to a string attached to the windmill axle. For extra credit (not required) students can use their windmills to generate electricity by using them to turn the shaft of a small hobby motor backwards causing it to act as a generator and light an LED attached to the motor terminals. Wind for operating the windmill will be provided at school by real wind on windy days or by a box fan on non-windy days. 


Objective 

   The objective is to design a functional windmill (stand, support and blades attached to an axle at the center) that will achieve the best performance in lifting weights or generating current. 

   Students will optimize their designs in a test phase, during which they are allowed to change the size, number, shape, curvature, pitch and stiffness of the blades as well as direction of rotation and angle of wind. Students are advised to keep notes of the changes they make in their windmills so that they can remember which configurations provide the best performance.

   Performance will ultimately be assessed at school by calculating the micro-horsepower developed by the student windmills with teacher assistance. Check out the following website for detailed information on windmill construction: http://www.creative-science.org.uk/8blade.html

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Project Description 

   Students should research windmills, blade shapes, the effect of blade pitch on performance, and the effect of the angle of the wind on the blades. Blades may be wood, plastic, aluminum, 8 ply cardboard or other materials. Stiffening materials and glue to apply them can also be used. When the blades are completed and attached to the windmill, the students should test the windmill outside on a windy day or by using a box fan inside. The test consists of lifting a weight suspended from the axle of the windmill by a string. As the axle turns it will wind up the string and lift the weight.  

   At school weights will be lifted a certain fixed distance of  1 meter, which is the standard 0.75 meter student desktop plus the 25 cm distance from the table top to the center of the windmill axle hub. We will measure the time it takes to lift the weight the fixed distance. The weight, time, and distance will then be used in a formula to calculate horsepower developed by the windmill.


Extra credit assignment

   Wind generated electricity can be achieved simply by attaching the axle of student windmill’s to the shaft of a small hobby motor. Driving the shaft backwards induces a small voltage across it’s terminals which can be used to light an LED. After students succeed with the weight lifting part of the project they may want to experiment with this concept for extra credit. A suitable motor is sold by Radio Shack for $2.95 LED’s are about a dollar. The current generated may be very small and so the light emitted will appear as a faint spark. Therefore try and set up your fan and windmill-generator in a dark closet. If you see no light try switching the terminals of the LED. Extra credit work is not required to attain an A grade. Good Luck! 

 

Grading Rubric

In order to obtain a grade of ‘A’ :

   •  The windmill is functional. It does work by lifting a weight by a string attached to the axle.

  •  The windmill is carefully designed. 

   •  The report contains an accurate diagram drawn to scale with a ruler or computer draw program and clearly labeled (one page).

     The student demonstrates skill in scientific writing by providing an account of the steps involved in construction which provides specific detail but is small in size (one page).

     A journal is included. Key decisions and discoveries are discussed including what problems where encountered and how they were solved in designing and building. 

     An inventory is included that lists and costs all components used. Total cost is calculated.

   •  The weight of the windmill is given in metric units. 

   •  A self-assessment is included which summarizes what was learned, honestly discusses the deficiencies and strengths of the project and grades the assignment.

   •  Resource and bibliography. People, books, websites etc are acknowledged.

© Sean Wilmot 2012