Patent GB-801080-A (GB)
Title: Improvements in or relating to power-operated aircraft flying control systems
IPC: B64C13/24
Filed: 1955-11-09
Abstract: 801,080. Aircraft controls. HOBSON, Ltd., H. M. Nov. 6, 1956 [Nov. 9, 1955], No. 32029/55. Class 4. [Also in Group XXIX] A power-operated flying control system in an aircraft comprising a two-stage hydraulic jack actuated by an electric signalling system operable by the pilot includes a differential lever automatically movable to alternative first and second positions according to whether or not the electric signalling system is functioning the lever in its first position pivoting about a first fulcrum to impart movement to the second stage control valve under control of the movable member of the first stage jack and in its second position freed from control by the said movable member and pivotable about a second fulcrum to impart movement to the second stage control valve under control of a mechanical linkage operable by the pilot. As shown, a two-stage hydraulic jack comprises a first stage control valve 10, a first stage jack piston 11, a second stage control valve 13 and a second stage jack piston 14 connected to a control surface 7. Under electrical control on the closing of a switch, a pick-off 39 on the pilot's control member 1 coacts with a potentiometer 40 to feed signals into an amplifier 41 and thence to an electro-mechanical transducer 38 to operate the valve 10. At the same time solenoids 19 are energized to move piston valves 20 to supply pressure liquid to the upper sides of spring- loaded pistons 22 to move a back-lash lock 18 downwards to disengage links 2 and 4 in a mechanical linkage between the pilot and a floating lever 5 connected to the control surface. A solenoid 25 is also energized to move a piston valve 26 controlling a spring-loaded piston 28 which through a bell-crank lever 30 moves a differential lever 32 upwardly so that its upper end 33 coacts with a fixed fulcrum 34, a slot 37 at its lower end engaging a pin 36 carried by the rod of the jack piston 11 to move the control valve 13 on movement of the piston 11. In the event of electrical signal failure or the intentional breaking of the main control switch, the solenoids 19 and 25 are deenergized whence the springs beneath the pistons 22 move the lock 18 to interconnect the links 2 and 4, and the spring 29 acting on the piston 28 moves the bell-crank 30 to move the upper end 33 of the lever 32 out of engagement with the fulcrum 34, the lower end 47 thereof into engagement with a fixed fulcrum 47 and also free the pin 36 from the slot 37. The control surface may then be operated by the pilot through the linkage 2, 3, 4, 5, 48, 32, the control valve 13 and the piston 14. Pick-offs 49, 50 on the control surface and piston 11 respectively coact with potentiometers 51, 52 to send feed back signals to the amplifier 41 when under electrical control to return the piston 11 and control valve 13 to their neutral positions when the control surface has reached its selected position. Sign-sensing contacts 53, 53a associated with the piston 11 and over-load sensing contacts 54, 54a associated with the lock 18 operate as described in Specification 780,759.