Turbine blade with adjustable tips

Abstract

Embodiments of the invention relate to blades for turbines, such as wind turbines, comprising a structural frame with a sail mounted thereon. In certain embodiments, a portion of the frame contributes to the buoyancy of the blade. In further embodiments, the frame comprises strengthening cords. In further embodiments, the frame comprises a reinforced tip. In further embodiments, the blade has a tip arranged to articulate relative to a body portion to alter the aerodynamic profile of the blade as the blade rotates to thereby assist up-strokes of the blade.

The invention claimed is: 
     
       1. A method of operating a blade arrangement including a plurality of blades for a turbine, the blades each having a structural frame and a sail mounted on the structural frame, the structural frame including a body portion, a tip and a hinge connecting the tip to the body portion, the method comprising:
 rotating the tip relative to the body portion at the hinge to vary the aerodynamic properties of the blade, the hinge defining a hinge axis in a plane of the blade and inclined with respect to a longitudinal axis of the blade, wherein the blades are arranged to rotate about an axis, wherein rotating the tip relative to the body portion at the hinge includes rotating a cord element that acts to support the sail of the blade; 
 providing an actuator for moving the tip relative to the body portion, wherein the actuator comprises a motor and pulley system, configured to control the tension of corresponding cords, by which the motor and pulley system cause the tip to articulate relative to the body portion; 
 providing a sensor for determining a rotational position of a selected one of said blades relative to the axis; and 
 rotating the tip of the selected blade relative to the body portion of the selected blade in dependence on the position of the selected blade about the axis.