GB1103901A - Helicopter rotor - Google Patents

Abstract

1,103,901. Helicopters. COPPERFIELD CORPORATION. 30 July, 1965, No. 32835/65. Headings B7G and B7W. A rigid helicopter rotor comprises blades 65 connected to a hub 56 by links 70 which are torsionally resilient. Each link is formed by three flat straps, one 73 in a vertical plane and two (71 and) 72, in the same horizontal plane. The aerodynamic axis and centre of gravity of each blade (82, Fig. 4, not shown) are ahead of the feathering axis (80) so that a downward motion of the blade produces a pitch increasing moment. The torsional stiffness of the links, which varies with speed, the mass and position of the counterweights, on arms 88, 90, fixed to the blade, which increase the pitch with increasing rotational speed, and the displacement of the centre of gravity from the feathering axis are arranged so that the blades oscillate about their feathering axis at one cycle per revolution, and the peak pitch displacement occurs 90 degrees after the application of the disturbing force. The peak force therefore occurs a further 90 degrees later because the rotors act as a gyroscope. A downward force on one side of the rotor disc therefore results in an upward force on the other side, and a cyclic pitch variation, and this may be achieved by the pilot's leaning in the required direction of tilt. The blades are attached by links 100. 101 to a swash plate 103, 105 attached to dampers 120 which prevent rapid swash plate oscillations, and acted upon by a spring 109 which resists collective pitch changes. The helicopter described has tandem rotors driven by an engine (16, Fig. 2, not shown), through a belt drive (17), shaft (18) and bevel gears (19, 20). The front of the engine may be raised to slacken the belts and disengage the engine from the rotors. The front rotor shaft (6) is tiltable laterally for yaw control by a worm-and-nut gear (Fig. 12, not shown), driven by turning handlebars (44). In a modification (Fig. 13, not shown), pitch, roll and yaw control are effected by conventional collective and cyclic control applied by control inputs to the swash plates. The blade section (Fig. 5, not shown), is designed to stall at higher incidence than conventional sections, since the helicopter described is relatively small and the blades will operate at relatively low Reynolds No. The leading edge is sharp and the maximum camber is forward of the quarter-chord point. The bottom, and rear upper surfaces are plane.