Abstract: A machine for extracting useful work from lowspeed winds includes a sail (28) pivotally mounted to an arm (22) for pivotal motion about a first axis (32), and a base (18) to which the arm (22) is pivotally mounted for pivotal motion about a second axis (24) that is parallel to the first axis (32). Through the use of a parallelogram linkage (38, 40, 52, 54), the angle .alpha. of the sail with respect to the base is rendered independent of the angle .theta. of the arm with respect to the base. This permits the angle of attack of the sail (28) to be programmed to provide any desired motion of the arm (22) with respect to the base. In a preferred embodiment, the angle .alpha. of the sail with respect to the base is coupled to the angle .theta. of the arm with respect to the base in quadrature so that the maximum angle of attack of the sail occurs in the middle of the stroke of the arm and so that the angle of attack of the sail is reduced to zero as the arm approaches the limits of its range of motion.