Abstract: The present invention relates to a device for converting fluid flow kinetic energy into rotational kinetic energy comprising a body mounted for vertical rotation about a longitudinal axis thereof, a plurality of horizontally spaced vertically extending vanes pivotably mounted on said body and rotatable between an open position in which the vane extends outwardly from the body and a closed position in which the vane lies with one surface thereof adjacent the surface of the body, and the plurality of feather members spacedly mounted longitudinally of each frame and extending outwardly and transversely of the surface opposite to said one surface of said vane, said feathers being dimensioned to abut said body when said vane is in said open position to provide stop means for each vane, the center gravity of each vane being located at the position in the feather members such that on the rotational speed of the body reaching a preselected maximum all the vanes assume a position between the open and closed position w