Abstract: A cross flow turbine having one or more aerofoil blades rotatably mounted about a central axis and connected to said axis at or near each end of the one or more blades. The blades have a degree of torsional flexibility that make them twistable about the longitudinal blade axis to reduce the aerodynamic efficiency of the blades to control the rotational speed of the turbine. The twist of the blades can be actively controlled by means of a spring, other mechanical actuator or motor.

Abstract: A windmill includes a hub assembly (13) connected to a shaft (3) and having a plurality of blades (6) extending therefrom. Each blade comprises an inner section (6a) hingeably connected to a hub member (14) along a first axis (8) and an outer section (6b) hingeably connected to the inner portion along a second hinge axis (7) extending from a point on the trailing edge (11) of the blade adjacent the first hinge axis to a point on the leading edge (12) remote from the first hinge axis. The blades are resiliently biased towards a rest position wherein the inner section of each blade lies in a plane at an angle to the plane of rotation of the blades and the outer sections extend outwardly in a plane at an angle to the plane of the inner section and at a pitch angle to the plane of rotation.