The Shape and Performance of Hand-Carved Small Wind Turbine Blades

This paper describes measurements of the shape of a 900 mm long, hand-carved timber blade for a 500 W three-bladed horizontal axis wind turbine. Four blades were hand-carved in Nepal by reference to a master blade cut in Australia on a numerically controlled milling machine. A high definition three-dimensional scanner was used to determine the surface of one hand-carved blade as a series of profiles at 50 mm intervals along the blade's length. A surface model generated from these profiles was compared to the designed blade shape in terms of the three fundamental blade design parameters: chord, twist, and profile shape. The measured twist and chord were less that the design values, particularly in the hub region. This is consistent with the poor starting performance of the turbine when mounted with the remaining hand-carved blades. Assessment of the differences in profile shape would require a detailed computational analysis, which has not been undertaken.