Patent GB-872215-A (GB)
Title: Improvements in or relating to aircraft flying controls
Inventor: ELMER ARTHUR ERNEST HENRY
IPC: B64C13/00
Filed: 1956-08-14
Abstract: 872,215. Fluid-pressure servomotor-control systems. BRITISH MESSIER Ltd. Aug. 14, 1957 [Aug. 14, 1956], No. 24864/56. Class 135. [Also in Group XXXIII] A servo-operated aircraft flying control system comprises a first linkwork directly connecting the manual control member to the control surface, and a second linkwork, one member of which is arranged for angular movement about a pivotal mounting, this linkwork directly connecting the manual control member to the servo-control, and means responsive to the power supply for locking the member of the second linkwork against angular movement when the power supply fails. General arrangement.-In the system shown the servomotor consists of a fixed piston 29 and moving cylinder 28 in a casing 22 furnished with inlet and exhaust passages 53, 54, and also coupled to a link 36 by which the control surface is operated. The servomotor control valve 26 is actuated by a differential link 23 which may be operated by the pilot's input member 11 through a lever 13 and members 16, 18, or by an automatic pilot 67 through a torque motor 68, output lever 69 and link 71. The casing 22 also houses a cylinder by-pass valve 75, a pair of valves 62, 63 under the control of a selector 61, which may be of the type described in Specification 767,823 and a spring- loaded latching piston 40 which automatically governs the operation of link 23 according to the mode of operation of the system. Direct manual operation.-In this condition with no pressure liquid supply to inlet 53 bypass valve 75 is open, and piston 40 is moved to the right by its loading spring 41 to rotate a bell-crank lever 44 anti-clockwise, and lift a link 50 to engage a notch 49a in a pivoted latch 49 with a pin 19 on link 23. The latter is thus locked and a direct mechanical connection established from the pilot's input member 11, through members 13, 16, 18 to casing 22, by the reciprocation of which movement can be imparted to the control surface operating link 36. Hydraulic power operation.-Selector 61 is operated to open valve 62 and close valve 63, and pressure liquid admitted to inlet 53, to close cylinder by-pass valve 75 and move piston 40 to the left against spring 41. Bell-crank lever 44 is thus rotated clockwise to disengage notch 49a from pin 19, thus releasing link 23 which may pivot about a pin 47 at its upper end to operate the servomotor control valve 26 in response to movements of the pilot's input 11 through members 13, 16, 18. In the event of power failure spring 41 operates piston 40 and bell-crank 44 to engage notch 49a with pin 19 and thus re-establish the direct manual connection. Automatic operation..-Selector 61 is operated to close valve 62 and open valve 63, thus exhausting liquid supplied to piston 40, so that spring 41 rotates bell-crank 44 anticlockwise to engage notch 49a and pin 19. Under these conditions pin 47 at the upper end of link 23 is able to move in the horizontal portion of an inverted T-slot 46 in bell-crank 44 in response to movement of members 69, 71, arising from signals from the automatic pilot 67, and thus operate valve 26 through link 23 which pivots about pin 19. A feedback signal to the automatic pilot is derived from a potentiometer 72. Should the electric power supply fail, valve 62 is opened and valve 63 closed, so that pressure liquid is supplied to piston 40, rotating bell-crank 44 to engage pin 47 in the end of the limb portion of slot 46, and disengage notch 49a from pin 19, thus permitting hydraulic power operation. The pilot may exercise over-riding control by applying sufficient force to the control column to disengage lever 23 from latch 49, the sides of the notch 49a being suitably sloped for this purpose.