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121 ON THE AERODYNAMICS OF WINDMILL BLADES Martin C Jischke University of Oklahoma Norman Oklahoma The optimum twist of a windmill blade is examined on the basis of elementary blade element theory For a given wind speed and blade angular velocity it is shown that the maximum power efficiency is achieved when the blade is twisted according to a program that depends upon the variation of the sectional lift and drag coefficients with angle of attack Results for a typical airfoil cross section show that the optimum angle of attack decreases from the maximum lift coefficient angle of attack at the blade root to greater than eighty percent of this value at the blade tip INTRODUCTION The energy crisis in the United States has caused a considerable growth of interest in alternative sources of energy in the past few years Among the several energy sources being explored wind energy a form of solar energy shows much promise in selected areas of the United States where the average wind speeds are high These areas include the Aleutian Islands the Columbia River Basin the Atlantic Coast of the New England states the southeast boundary of Texas and the Great Plains area which includes most of Oklahoma Estimates of the potential contribution of wind power to the energy needs of the nation vary from as low as five percent to as much as one hundred percent While the latter figure is suspect it is clear that in the high wind speed regions of the country wind power can if properly developed become a significant energy source Initial estimates suggest that electrical power can be developed from the wind at a cost of approximately 400 per installed kilowatt as compared with 250 to 400 per installed kilowatt for fossil fuels While energy storage remains problematic for wind power it would seem that the environmental benignity and low operating costs of wind power coupled with the growing costs of fossil fuels will make wind power increasingly attractive in the future The utilization of






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