Abstract: A sail-type windmill providing high torque without limitations to size. Three sails are mounted to a frame for rotation about an axis generally parallel to the planes of the sails. In one version, the sails are flexible and sheets are provided for mounting the sails. Roller reefing is provided for modifying the effective area each sail member presents to the wind, including a spring biased weight associated with each sail and a line extending from the weight for effecting take-up and let-out of the sail and the sheet in response to radial movement of the weight. In another version, the sails are of metal and speed governing is provided by hydraulic cylinders operatively mounted to the sails for pivoting them about their axes of rotation, the hydraulic cylinders controlled by a aerometer mounted atop the windmill.