Cubitt's Patent Sails

3D Model

Diagrammatic model by Cliff Featherston.

The sails of a windmill need to rotate at a constant pace, requiring the angle of the shutter blades that catch the wind to be constantly adjusted to suit the wind speed. In 1807, Sir William Cubitt invented a mechanism that allowed the shutters to be adjusted while the sails were still rotating. In this model, the windshaft has been cut away to show how a rod passing through its centre transfers the movement of the adjustment mechanism, at the rear of the cap, to the shutter control linkage mounted on the sails.