Patent GB-873644-A (GB)
Title: Improvements in or relating to operating systems for the flying controls of aircraft
Inventor: HARRISS JOHN HENRY
IPC: B64C13/24
Filed: 1958-10-16
Abstract: 873,644. Fluid-pressure servomotor-control systems. AUTOMOTIVE PRODUCTS CO. Ltd. Oct. 15, 1959 [Oct. 16, 1958], No. 33070/58. Class 135. [Also in Group XXXIII] In a power-assisted flying control system for an aircraft each flying control surface, i.e. aileron, elevator, rudder, or any surface combining the functions of at least two of these surfaces, is divided into at least two parts, one part of each surface being operated through a servo-device drawing power from one source and the other part or parts of each surface being operated through a servo-device or devices drawing power from another or from each of several further sources respectively. In an embodiment each aileron, elevator and rudder is divided into two parts and each part has its own servomotor consisting of a fixed piston 35 and a movable cylinder 34 connected at 38 with the part 10a of the surface. A control valve 44 is connected through a link 56, lever 57 and link 58 with a lever 63 which is mechanically coupled to the pilot's control. The servomotor of one part of each control surface is connected at 54, 55 with the supply and exhaust conduits of one hydraulic system whilst the servomotor of the other part of each surface is connected to a second hydraulic system. A third hydraulic system is connected to a valve 81 of each servomotor for centring the corresponding part of the control surface in the event of failure of its hydraulic system. A chamber 34b is permanently connected to the hydraulic supply conduit 54 through a valve 78, the control valve 44 and a conduit 53 whilst a chamber 34a may be connected through a conduit 52 with either the supply or exhaust conduit depending upon the direction of movement of the control valve. The pressure in the supply conduit 54 normally has access through a conduit 88, valves 85 interconnected by a conduit 91 and a conduit 94 with a valve 99 which is thereby held against a loading spring 102 in such a position as to admit pressure fluid to the valve 78 to hold the latter in the position shown. Should the supply pressure fail the valve 99 is depressed by its spring to exhaust the pressure acting on the valve 78 so that the pressure in the third system is able to move the valves 78, 81 to the right to connect both ends of the servomotor to exhaust, the chamber 34a being connected to exhaust through a non-return valve 40 and the chamber 34b, and to connect the spaces on the outer sides of a pair of pistons 72, 73 to the third pressure system so that the cylinder 34 is centralized relative to the piston 35. At the same time pressure acting on a piston 59 is released allowing that piston to descend to withdraw a projection 66 from a notch 65 in the lever 63 whereby the lever is disconnected from the link 58. Should, during normal operation, the control valve 44 or the servomotor 34, 35 become jammed, a block 83 to which the lever 57 is pivoted becomes displaced so that one of the valves 85 interrupts communication between, the supply conduit 54 and the valve 99 to cause the valves 78, 81 and the piston 59 to operate as in the case of hydraulic failure. In a modification, the centring pistons 72, 73 are mounted in a cylinder that is separate from the servomotor, and a valve is interposed between the valves 99, 78 whereby the pilot can disable the servomotor at will.