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601,014. Helicopters. ATREX MANUFAC TURING CO., Inc. July 7, 1944, No. 13018. Convention date, May 3, 1943. [Class4] In a helicopterrotor in which the bladesare moumted for pitch-change and free flapping movement on a blade-carrying member universally connected to a rotatable support, the rotor is stabilized against tilting, e.g. while hovering, by control means connected between the blades and the support which vary the angle of the blades when there is an angular displacement between the axes of rotation of the support and member so as to increase the lift of the depressed blade and decrease the lift of the elevated blade. As shown, Figs. 3 and 4, applied to a helicopter having two pairs of counter-rotating blades, the drive to the lower rotor comprises a sleeve 23, hub 31 and yoke 32, the latter being pivoted by pins 44, 45 to a gimbal ring 46 pivoted by pins 47, 48 to a housing 49 carrying a collar 51 in which the blades are mounted for pitch-change movement. The blade mounting includes a flexible joint 62 to permit the blade to flap within desired limits. The blades are connected by tubes 65, 66, having bifurcated lower ends, slidable shafts 67, 68 and universal joints 70, 72 to studs 69, 71 which are threaded in arcuate flanges formed on the gimbal ring 66, and are adjustable axially by means of lock nuts. Tilting of the rotor about the axis of pins 47, 48 thus effects a differential adjustment of the pitch angle of the blades, the amplitude of which depends on the adjustment of the studs 69, 71. Tilting about the axis of pins 44, 45 has no effect on the blades. The upper rotor is mounted on a bell housing 78 driven by a shaft 24 through an arm 98 pivoted by pins 94, 95 to a gimbal ring 91 pivoted by pins 87, 88 to a skirt 83 secured to the housing. The blades are connected by gearing 130, 128 and 131, 129 to the bifurcated upper ends of tubes 146, 147 which enclose shafts 114, 115 connected by universal joints 116, 117 to studs 110, 111 threaded in an annular neck 109 of the gimbal rings 91, the studs being adjustable axially by means of lock nuts. A ball-race 107 is provided between the two rotor assemblies, and a spring 134 prevents angular displacement when idling. A plurality of circumferentially spaced holes are provided in the flange and neck of gimbal rings 46 and 91 respectively so that by choosing the appropriate pair of holes for studs 69, 71 and 110, 111, and adjusting the positions of the collar 51 on the housing 49 and the housing 78 on the skirt 83, the angular setting of the rotors relative to their gimbal rings may be varied as required. The rotors are driven through gearing and an over-running clutch.
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