DESIGN AND ANALYSIS OF WINDMILL BLADES FOR DOMESTIC APPLICATIONS

The optimum twist of a windmill blade is examined on the basis of elementary bladeelement 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. The materials used were stainless steel, e-glass epoxy and gray cast iron and results were tabulated.