Patent GB-676398-A (GB)
Title: Helicopter
IPC: B64C27/04
Filed: 1950-09-14
Abstract: 676,398. Multi-rotor helicopters. KAMAN AIRCRAFT CORPORATION. Sept. 14, 1950 [Sept. 14, 1949; Nov. 12, 1949], No. 22627/50. Class 4. In a helicopter comprising two lifting rotors of which the collective blade pitches are varied differentially for yaw control purposes, the control transmission is so arranged that under conditions of auto-rotation the differential collective pitch adjustment is automatically reversed as compared with that obtained under normal power-on conditions. The invention is described as applied to a machine with two intermeshing rotors carried by inclined hollow drive shafts 18, 20, Fig. 8, coupled to the engine by bevel gearing 64, 62, 66, 76, the pitch adjustment of the blades 26 being effected by flaps 30, Fig. 3, carried near the tips and which twist the blades, as described in U.S.A. Specification 2,455,866. Rotor construction.-Each flap 30 is pivotally mounted on an outrigger 106 and is operated by a linkage 142, 132, 120 and a bell crank 116 connected to a rod 112 or 114 passing through the hollow drive shaft. The lower ends of the rods are connected to a gimbal system 160 operated by the cyclic and collective pitch control mechanism. A second gimbal system 211, Fig. 10, is connected to rods 206, 208 for controlling the second rotor. The blade 26 may oscillate about a drag pivot 86 between stops formed by shoulders 87, 88, such movements causing automatic adjustment of the flap 30, whereby the blade pitch is adjusted in accordance with the power input. Pitch control mechanism.-Control in azimuth is effected by a hand lever 34, fore-and-aft movement of which is transmitted to a push-pull rod 266 connected to rods 272, 274 operating the gimbals 160, 211 through rods 176, 222, transverse movement of the lever being communicated to the gimbals through linkages 282, 290, 170, 166 and 284, 291 and 220. Springs 294, 296,297 oil the rods 266, 290, 291 bias the control lever to the neutral position. Simultaneous collective pitch control is effected by a second hand lever 33. movement of which is transmitted by members 250. 252 to rods 158, 218 connected to pivoted arms 150, 209 carrying the gimbals 160. 211. which are thus raised or lowered bodily. Yaw control (power-on conditions).-Movement of the steering pedals 35, 36 results in three simultaneous adjustments as follows: (a) the interconnected cross bars 306, 312 are rotated to move links 316, 318 connected to the push-pull rods 250, 252 in opposite directions, whereby the rods 158, 218 and gimbals 160, 211 are also moved in opposite directions to impose differential collective pitch variations to the rotors and thus unbalance their reaction torques ; (b) a link 334 and transverse rod 340 rotate a cross bar 342 to move the fore-and-aft cyclic pitch control rods 272, 274 in opposite directions and thus impose a supplementary differential tilting of the rotor lift vectors; (c) a rudder 38, Fig. 1 (not shown), is operated by cables 40, 41. Yaw control (auto-rotative conditions).- When the lever 33 is moved to adjust the blade pitch to the value to ensure auto-rotation an arm 402 operates a reversing mechanism 358, Figs, 18-22 (not shown), by means of which the directions of movement of the rods 250, 252 are reversed upon movement of the pedals 35, 36, thereby reversing control adjustment (a), but having no effect upon (b) and (c). By this means adequate yaw control is assured under power-off conditions.