Patent GB-884511-A (GB)
Title: Improvements relating to hydraulic flying control systems for aircraft
Inventor: FOWLER JOHN LAWRENCE
IPC: F15B18/00
Filed: 1957-04-02
Abstract: 884,511. Fluid-pressure servomotor control systems. FAIREY CO. Ltd. April 1, 1958 [April 2, 1957; June 3, 1957], Nos. 10779/57 and 17611/57. Class 135. In an aircraft flying control system in which a fluid-pressure servomotor is provided with duplicated pressure fluid supply systems, each with its own control valve, the valve control mechanism is arranged to operate automatically in the event of failure of the main supply pressure to bring the stand-by system into operation. As shown in Fig. 2 an operating jack 11 carries main and standby control valves 20, 21 operated by a lever 26 connected to the pilot's control lever 31 through a link 35, followup lever 36 and link 28. Under normal conditions standby valve 21 is locked and provides a fixed fulcrum 25 for lever 26, but if the main pressure fails main valve 20 is locked and provides an alternative fulcrum 24. The complete valve unit shown for normal operation in Fig. 3 comprises, in addition to valves 20, 21, a changeover valve 48 and two solenoid-operated doubleended needle valves 49, 50. Each of valves 20, 21 is fitted with a locking device consisting of telescopic piston elements 100, 101 which may be expanded by pressure fluid to engage collars on the valve stem and shoulders in the valve casing. As shown, main valve 20 may be operated to place the main supply inlet 54 and exhaust 72 in communication with cylinder ports 57, 58, but lands 95, 96 on change-over valve 48 isolate standby valve 21 from the power cylinder. Also valves 49, 50 are in their extreme left- and right-hand positions respectively, so that the standby pressure supply is connected via inlet 75 and passage 80 to act on a small piston 92 at the left-hand end of valve 48, while the main pressure supply is connected via inlet 54 and passages 63, 64 to act on a large piston 90 at the right-hand end of valve 48 and also on locking elements 100, 101 whereby valve 48 is held in its extreme left-hand position and valve 21 is held locked. If the main pressure fails locking elements 100, 101 become ineffective and the standby pressure acting on piston 92 moves valve 48 to the right, a projection 98 operating a microswitch 99 to reverse the settings of valves 49, 50 so that the standby pressure fluid passes via passage 86 to effect locking of valve 20 and thus permit operation of valve 21. In an alternative arrangement, Fig. 6 (not shown), solenoid valves 49, 50 are omitted but change-over valve 48 is provided with an additional land to control admission of the standby pressure fluid to the lock of main valve 20. In a further arrangement, Fig. 5 (not shown), the main and standby valves control tandem jacks each fitted with an isolating valve similar to change-over valve 48, but only one solenoid valve is employed. An overriding manual switch and/or automatic switch operating in the event of control valve seizure may energize the solenoid valve to divert the main pressure supply from the change-over valve to simulate failure of the main system and cause the change-over to take place. Specification 606,620 is referred to.