Windmills with increased power output due to tipvanes

Betz's formula, yielding the maximum power output of windmills is only valid under the assumption that the windmill causes a steady axial force acting on the air in a direction opposite to the undisturbed stream velocity. When radial as well as axial forces are applied to the air, this theorem is no longer valid and larger power output may be obtained. This paper deals with a type of windturbine where relatively small vanes, attached to the tips of the turbine blades, deflect the air radially outwards. It describes the lay-out of the system, its potential performance and the research concerning the feasibility of tipvanes.