Abstract: A sail-type windmill wheel is provided in which the area of the wheel facing into the wind is adjusted by an automatic variation of the blade angle of the sails. The wind wheel comprises a hub (22) with a plurality of radially extending spars (18), substantially triangular sails (10) secured along one edge to said arms, the clew of said sails secured through a sheeting cable (24) to drawbar extension springs (28), and the drawbar extension springs secured to the tip of the next adjacent arm. During high wind speeds the automatic blade angle adjustment reduces the frontal area of the wind wheel with a corresponding reduction in the force of the wind upon the wheel. During normal working wind speeds the present invention maintains the sails within an optimum blade angle range for extracting energy from the wind.