The next time you feel the breeze blowing off Lake Pend Oreille, you might think of John Hastings’ students at Sandpoint High School. They spent a month this spring considering how best to harness that energy, using tools provided by a grant from the Panhandle Alliance for Education.
The grant purchased geared stands and hubs on which Hastings’ students could mount a variety of blades to create model windmills of their own design. The blades had to be made of recycled or recyclable material. The students favored thin sheets of balsa wood, which was easy to cut with scissors and shape into different blade designs, but they also tried using old lawn signs, cardboard, and plastic bottles.
They started their investigations on the internet, looking for information about windmills already in operation. Their focus was on identifying a blade configuration that could generate maximum revolutions per minute, which maximizes electrical output.
Blade shapes ran from simple trapezoids to far more elaborate forms, including blades with carefully beveled edges to reduce drag, blades with hooked edges, and even a set of blades that rotated around a vertical hub instead of a horizontal one.
In addition to considering what was the best shape for the blades, students experimented with the angle at which the blades faced the wind and with the number of blades on a hub. Each blade configuration was mounted on a stand and subjected to wind from a fan, and the electricity it generated was measured by a voltmeter. Early findings indicated that lower angles were more effective than sharp ones, and that three blades usually generated more energy than four, with 12 volts being about the maximum generated in initial trials.
As Hastings’ students identified their most efficient combinations of material, angle, and shape, they compared notes and built on one another’s efforts in an attempt to increase their voltage. “Some students were getting pretty competitive, pushing to get another tenth of a volt, and fine sanding their blades to make them it more aerodynamic,” says Hastings.
As it turned out, he goes on, “The best configuration was a fairly traditional design.” The winning windmill, which generated 19 volts, had four elongated, oval, recycled cardboard blades. Second place, at 18 volts, went to a design with three blades cut from plastic bottles that incorporated the bend at the neck of bottle.
Hastings used the wind project with students studying science at several different levels, finding it a useful approach to the scientific method for everyone from potential poets to future engineers. Students shared their findings with others students around the state involved in KidWind, a statewide project of Boise State University to engage students in learning about wind energy.