GB1498222A - Vibration isolation in helicopters - Google Patents

Abstract

1498222 Vibration damping structures; linkwork TEXTRON Inc 23 May 1975 [3 June 1974] 22677/75 Headings F2S and F2K [Also in Division B7] A vibration-damping structure for interconnecting the lift unit (motor 11, rotor shaft 10, rotor blades 12, 13, Fig. 1) and the fuselage of a helicopter comprises (Fig. 4) at least one composite beam 102, 103, 104 having at opposite ends anchor points 100, 101 for fixing to the fuselage (via brackets 107, 108), the beam having rigid end members 102, 103 and a laminated central flexible element 104; and two rigid support links 109, 111 for carrying the lift unit pivotally attached to the end members 102, 103 at points 110, 112 intermediate the points 100, 101. Vertical vibrations of the rotor shaft 10 (represented by arrow 22 in Fig. 1) are transmitted through the links 109, 111 to the composite beam 102, 103, 104 resulting in oscillatory bending of the flexible section 104. No vibration is transmitted through the anchor points 100, 101 to the fuselage. The flexible section 104 consists of a stack of spring steel plates (91, 95, Fig. 3, not shown) with rubber layers (92) bonded between them. Each end of the flexible section 104 is received in a recess 105 of the rigid end member and supported between elastomeric blocks (94, 96) one sliding sliding and one bonded. The frequency of the composite beam can be adjusted by applying a load to arm 106. The lift unit may be mounted (Fig. 2, not shown) on two of the structures shown. Alternatively (Fig. 5, not shown) one composite beam may carry four support links. In the embodiments of Figs. 2 and 5 the structure incorporates torque links which transmit torques in a horizontal planes from the rotor shaft 10 to the fuselage.