Month in the Patent Office

In a helicopter rotor comprising a propulsion unit mounted at the tip of each blade, each unit including rotating masses subject to gyroscopic reaction forces tending to alter the attitude of the propulsion unit, means are provided for applying a force to the unit in opposition to the gyroscopic forces, the magnitude of the opposition force being varied in accordance with changes in the rotative speed of the rotating masses. The invention is described for a two‐bladed rotor wherein each blade 14 which is mounted for conventional pitch‐changing and flapping movements, comprises a spar 13 formed at its tip with a yoke 21 which supports a gas‐turbine engine 19. The engine carries rearwardly extending arms 32 which terminate in brackets 33 forming pivots for a control surface 31 located in the stream for propulsion gases from nozzle 26. The surface 31 has an arm 34 connected by a link 35 to a power element 36 which is controlled by an engine fuel control unit 37 adjusted by the pilot through a linkage 39 to vary the fuel supplied to the engine (and thereby the engine speed) from a fuel line 38. The rotating compressor and turbine of the engine exert gyroscopic forces which apply a positive pitching moment to the engine and this is counter‐acted by increasing the incidence of surface 31 with an increase in fuel supply where the surface, through arms 32, applies an opposing negative pitching moment to the engine. The adjustment of the surface may be made responsive directly to the speed of rotation of the engine or to twisting stresses applied to the spar 13.