Patent GB-971123-A (GB)
Title: Improvements in or relating to rotary wing aircraft and method for controlling same
IPC: B64C27/52
Filed: 1962-02-12
Abstract: 971,123. Rotary wing aircraft. BELL AEROSPACE CORPORATION. Feb. 12, 1962 [Feb. 13, 1961], No. 5388/62. Heading B7W. In a rigid-rotor rotary wing aircraft, the application of cyclic pitch control tilts the mast, such tilting changing the amount of cyclic pitch applied to the blades. In Fig. 2, a unit comprising the rotor shaft 5 and engine transmission 54, is attached to a frame 23, which is mounted by gimbal axes H-H and L-L on members 30, 32, and 34 of the airframe. Each blade of the rotor (not shown) on shaft 5 is attached to the shaft for blade pitch change movement only, collective and cyclic pitch changes being imposed by bodily movement and tilting of swash plate 42 in conventional manner. The lower end of transmission casing 54 is anchored to the airframe through rod 80 and damper 72, and is connected through a double-acting spring box 6 to one lever arm 101 on a torque tube 46. A further arm 44 is connected to the airframe through a trim actuator 40 (see also Fig. 3). In Fig. 3, a cyclic pitch stick 100 tilts the swash plate about a fore-and-aft axis through linkwork 102, 310, 114 and 130, and about a lateral axis through linkwork 134, 142, and 146, the latter including a bell crank lever 144, the pivotal axis D-D of which is on another bell crank lever 172 connected by rod 50 to an arm 48 on torque tube 46. Collective pitch changes are imposed by lever 154 through linkwork 160, 164, and 26, including a bell crank lever 162, the pivotal axis F-F of which is carried by two rods 176, 174, the former pivoted to the airframe and the latter to one arm of a bell crank lever connected by rod 182 to a lug 184 on the engine transmission casing 54. When the cyclic pitch stick 100 is displaced, say, forwardly, the resultant blade pitch change seeks to incline the tip path plane forwardly, and since the blades cannot flap, the mast 5 is urged to incline forwardly relative to the fuselage, the rate and extent of tilt depending on the characteristics of the spring base 6 and damper 72, Fig. 2. This results in a cyclic pitch change, since rod 146 is held relatively to the airframe by the pilot, this change washing out, wholly or to a selected degree, the pilot demanded pitch change. This is stated to remove the effects of a pilot's tending to over control due to time lag in the control effect. To trim the fuselage attitude, the pilot operates actuator 40, to move the pivot of bell crank 144 through torque tube 46, and cause a cyclic pitch change. At the same time, arm 101 of torque tube 46 (Fig. 2) moves the spring base 6 to determine a new datum attitude for the mast 5 relative to the fuselage, and with appropriate linkwork characteristics, the fuselage attitude changes, the tip path plane orientation in space remaining unchanged. The effect of mast tilt on collective pitch, due to rod 160 remaining stationary when the mast tilts, is nullified by the connection 182, 174 from the engine transmission casing 54 to the bell crank lever 162. The mast may be flexible instead of tiltable. Specification 723,452 is referred to.