Patent GB-641076-A (GB)
Title: Improvements in or relating to damper for rotary wing aircraft
IPC: B64C27/51
Filed: 1946-08-23
Abstract: 641,076. Helicopters. UNITED AIRCRAFT CORPORATION. Aug. 23, 1946, No. 25279. Convention date, Sept. 25, 1945. [Class 4] [Also in Group XXXII] A liquid damper for controlling drag movements of a helicopter rotor blade is provided with means for controlling the liquid flow to provide two damping rates for alternative use according to flight conditions, a fixed orifice controlling the rate of flow between the liquid chambers during hovering flight when blade movements are at a minimum and an additional passage between the chambers being provided with a relief valve arranged to open under a predetermined pressure during forward flight when high pressures are induced due to greater blade movements. As shown in Fig. 5, the damper control valve, shown in vertical section, has combined with it a liquid reservoir 104. Flow-restriction orifices 118 for damping are formed centrally of valves 116, each of which is held in the position shown by a light spring 120 so as to yield freely to pressure of liquid passing through the orifice 118 of the other valve 116. In order to byepass an orifice 118 in case of overload due to sudden spar movements, each nipple 121. receiving the pressure has a connected passage 126 leading to a passage 128 with a valve at each end capable of yielding to allow passage of liquid through the passage 128 and out into a cross-passage as shown. In another form, Fig. 7, the inner end of the pistonrod 154 is universally pivoted to the drag-link and movement of the cylinder 150 to the left from the position shown is resisted by the buffer-spring 154 to provide a bias towards the power-off range, which is removed as the cylinder moves to the right from the position shown. A clearance for the piston 152 provided at 184 allows a slow rate of leakage. Oppositely-arranged check-valves 180 are provided in piston 152. Specification 581,797 is referred to. The Specification as open to inspection under Sect. 91 comprises also a form, Figs. 4 and 5 (Cancelled), in which the blade movements are damped and controlled by a hydraulic cylinder 50, pivoted at one end to an arm 46 bolted to blade spar 32 and having the rod 54 of the piston 52 working in the cylinder 50 pivoted at its outer end on a vertical pin 56 mounted in the outer end of drag-link 34 and in line with the flapping axis of the blade. Each end of the cylinder is connected by a tube 64 to a control valve 36, shown in vertical section in Fig. 5, with inlets 88, 90 for the tubes 64 leading to a through passage 66 to allow liquid to pass from one side of the piston 52 to the other when the blade spar 32 turns on its pivot 44 and so moves the cylinder 50 relatively to the piston 52. Flow restriction orifices 76 are provided for damping in the passage 66. Byepass and check ball valves 78 with light springs 82 are provided in connection with passage 66 and liquid passing through either of restriction orifices 76 proceeds through the valve 78 at the other end of the passage 66 into the connection inlet leading to the other end of the passage 66 into the connection inlet leading to the other side of the piston; liquid may also pass through an opening 70 into a hose 42 leading to a central reservoir. This subject-matter does not appear in the Specification as accepted.