Patent GB-608693-A (GB)
Title: Improvements in and relating to the operation of the main flying control surfaces of an aircraft
IPC: B64C13/00
Filed: 1946-02-27
Abstract: 608,693. Controlling aircraft. WATSON, C. D., and COLLAR, A. R. Feb. 27, 1946, No. 6128. [Class 4] [Also in Group XXXII] A control system for a control surface, including a pivoted tab for assisting movement thereof is provided with means for automatically substantially completely hydraulically locking the control surface in position of adjustment at the instant when aerodynamic balance is attained betweeri the surface and tab, a variable time lag being introduced between the initial operation of the pilot's control and the locking of the control surface, dependent partly on the amount and rate of movement of the pilot's actuating member. As illustrated, twin rudders 1, 2 are moved by servo tabs 3, 4, operated by links 10, 11 from the pilot's control member through rods 5, 7. The rudders are locked in their adjusted position by a piston 12d moving in a hydraulic cylinder, the liquid flow being controlled by a valve 15, shown as a separate unit from the cylinder in Fig. 1, but combined therewith in Fig. 2. The control member 5, Fig. 1, or 7, Fig. 2a, is coupled to a piston-rod 21a, the piston 21 of which moves in a cylinder 22 filled with liquid, and the ends of which carry sleeves 28, 29 enclosing compression springs 26, 27. Upon operation of the pilot's control member to move the control member 7, Fig. 2a, in the direction of the arrow A, the piston 21 and cylinder 22 move the sleeve 29 into contact with a member 32 connected to a lever 46, which opens a piston valve 44 to establish communication between conduits 12f, 12g, and thus allow movement of the piston 12d in its cylinder under the influence of the rudders 1, 2. Upon contact of the sleeve 29 with the abutment 32 the spring 27 is compressed, the amount of compression being dependent upon the amount of movement of the member 7 and also upon the rate of leakage of liquid past the piston 21, the latter of which is determined by the rate of movement of the member 7. The spring 27 expands while the rudders are moving to their adjusted position until, when aerodynamic balance is obtained between them and the tabs 3, 4 the piston 21 reaches its central position in the cylinder 22, and the sleeve 29 moves out of contact with the member 32 to close the valve 44. This prevents flow of liquid from one side to the other of the piston 12d, which is thereupon locked and holds the rudders in their adjusted position. To accommodate any errors which may arise due to the hydraulic lock becoming effective slightly before or after aerodynamic balance of the rudders is obtained, or due to change of speed or attitude of the aircraft, slow leakage of liquid may take place past the piston 12d. In addition, an adjustable valve 49 allows transfer of liquid from one side of the piston to the other when the piston valve 44 is closed. An accumulator 51 is provided to maintain the system full of liquid, the accumulator being charged by the reciprocating action of an extension 44b of the valve 44. Relief valves 66, 67 permit passage of liquid from the accumulator to the supply tank 18 in the event of excessive pressure occurring due to rise of temperature. In the case of a surface fitted with a balance tab, movement of the pilot's control member is first applied to the tab, sufficient to cause opening of the locking piston control valve 44.