GB1120193A - Vibration absorbing device - Google Patents

Abstract

1,120,193. Reducing vibrations on helicopters. BOEING CO. 12 Oct., 1965 [31 Dec., 1964 (2)], No. 43317/65. Headings B7G and B7W. [Also in Division F2] In a vibration absorbing device for a set of rotor blades of a helicopter annular housings 25, 22, rotatably mounted on a shaft 21 attached to a rotor head hub (18), Fig. 2 (not shown), and accommodated in a housing 28 secured to the fuselage of the helicopter by a member 29, pairs of cylindrical inertia members (50, 51), Fig. 6 (not shown), and (53, 54), Fig. 7 (not shown), are movably housed within the annular chambers (49), (52) respectively of the housings 22, 25 which, by means of planet and ring gearing 32, 36 and 42, 40 respectively are rotated in opposite directions at three times the speed of the rotor hub 18, i.e. the product of the speed of the hub 18 and the number of rotor blades. The annular chambers (49, 52) may be partially filled with a liquid. In a modification, Fig. 8 (not shown), a housing (56) carried by the hub (18) is rotatably mounted at (60, 61) to a stationary member (58) connected to the fuselage by a member (57) and carries a gear ring (75) which co-operates with gears (72, 83) fast on the outer ends of shafts (70, 81) which are rotatably mounted in sleeves (62, 63) in opposing sides of the member (58). The other end of the shaft (70) is splined at (78) to a housing (80) which rotates at the same speed as the shaft (70) and which has an annular chamber (103) in which at least two cylindrical members, one shown at (104), are disposed. The inner end of the shaft (81) is splined at (85) to a housing (87) which comprises a pair of sections (88, 89) connected by nuts (93) and bolts (92) and having annular chambers (99, 101) respectively, each of which receives at least two cylindrical weights such as (100), or (102). The housing (87) is rotatably mounted on bearings (94, 98) supported upon the sleeves (63, 62) and on bearings (95, 97) supported upon annular projections (96, 79) of the housing (80). Since the housings (80, 87) rotate in opposite directions the vibration damper synthesizes an elliptical locus, which is produced in the vertical-longitudinal plane at the hub (18) by the vibrations created by the rotor blades (15, 16, 17), Fig. 1 (not shown). Any of the annular chambers can be partially filled with liquid. In both of the embodiments described, the housings 22, 25 and (80, 87), instead of being driven by gearing arrangements, could be driven, e.g. synchronous motors connected to each of the housings and driven by a generator connected to the hub 18. A single housing with at least two weights movable therein in an annular chamber could be used to balance out certain periodic vibrations. In a further modification, Figs. 9-11 (not shown), arcuate members (122, 125), of the same weight, are rotatably mounted about a shaft (121) connected to a driving hub (118) and another pair of arcuate members (128, 132) of the same weight, but different from that of the members (122, 125), are rotatably mounted about the hubs (129, 133) of the members (122, 125) respectively. The members (122, 125, 128, 132) are driven at three times the speed of a drive shaft (121) by planet, sun, and ring gearing the members (122, 125) being rotated in the same direction as, and the members (128, 132) in the opposite direction to, the shaft (121). The members (122, 125, 128, 132), the shaft (121) and their gearing are enclosed within a housing (136) which is secured to the fuselage by means of a member (137). The outer ring gears (157, 169, 198, 210) of the four sets of gearings mesh respectively with servomotors (158, 170, 204, 211) which are normally not energized, however, they can be energized so that the positions of the weights (122, 125) and (128, 132) can be moved in relation to the others so that the resultant centrifugal forces of the pairs of members (122, 125) and (128, 132) can be varied and their phases can be regulated to oppose and balance out the forcing longitudinal and lateral vibratory components at the hub. In a circuit for energizing the servomotors (170, 211), the output of an accelerometer (138) mounted on top of the shaft (137) for sensing longitudinal vibrations, is connected to a band-pass filter and phase control (221) which is connected to a pair of phase detectors (222, 223), Fig. 12 (not shown), each of which receives the output of a bi-stable oscillator (224, 225) having inputs from diametrically opposed magnetic pick-offs (226, 227) and (229, 230) on arcuate members (128, 132 respectively which have magnetic inserts (228, 231). The outputs of the phase detectors 222, 223 are connected, through filters and power amplifiers (232, 233) to the servomotors (170, 211). An accelerometer 139 and a similar circuit, Fig. 13 (not shown), controls the servomotors (158, 204).