As the wind speed increases form zero, small turbines will cut-in only when the aerodynamic torque acting on the blades exceeds the resistive torque of the generator and drive system. This Note describes the use of standard blade element theory to calculate the cut-in wind Speed, at which rotation commences, using the apparent near-universality of aerofoil lift and Drag at high incidence. The starting torque is shown to depend on the "chord-pitch" integral That, in turn, is a function only on the blade geometry.
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