Abstract: An overspeed spoiler for vertical axis wind turbines of the type having straight or curved airfoil blades attached to a vertical shaft formed by a relatively thin flat blade shaped spoiler element hinge mounted on the trailing edge, leading edge, or at a central position of a portion of the airfoil section with the element having two portions one of which is held flush or against a surface by spring means with a surface of the blade towards the turbine rotor axis and the other lies substantially parallel to the chordline of the airfoil, the weight and configuration of the element being such that a predetermined turbine rotor speed the element rotates against the spring force because of centrifugal action and takes up a position generally transverse to the air flow direction such as to cause much increased drag and control overspeeding of the rotor.