GB744476A - Improvements in or relating to servo operation of aircraft flying controls - Google Patents

Abstract

744,476. Fluid-pressure servomotor-control systems. BRITISH MESSIER, Ltd. Nov. 16, 1953 [Nov. 17, 1952], No. 29019/52. Class 135. In a hydraulic servomotor control system for operating aircraft control surfaces in which a by-pass connected between the two ends of a double-acting operating jack includes a valve and a pressure-operated device connected to the pressure liquid supply line for keeping the by-pass valve closed whilst supply pressure is available, but permitting it to open should supply pressure fail to allow direct manual operation of the control surface, a non-return valve is fitted in the pressure supply line enabling liquid to be maintained in the system which liquid automatically closes the by-pass valve in the event of a reversal of air load on the control surface during direct manual control to lock the jack against movement. As shown, a double-acting jack 11, having its cylinder 13 connected to the control surface, e.g. a rudder, and its piston 15 to the aircraft structure is controlled by a servo-control valve having a valve piston 20 connected through spring-pressed balls 31 and a rod 24 to the pilot's control and a ported casing 19 movable with the jack cylinder. The balls 31 are held in engagement with a groove 29 in the rod 24 by latch members 32, which engage a sleeve 39 constantly urged by a spring 40 toward the valve piston and having an arm 41 carrying a pin 42 for engagement with a non-return ball valve 45 fitted in a line 89 connected to the supply line 86. The ball 45 is engageable with a seat 47 connecting the line 89 with a line 73 leading to the left-hand end of a chamber 58 housing a differential control piston 61 operably associated with a by-pass valve 56, and a seat 46 connecting the line 73 with an exhaust line 87. The lines 86, 87 are fitted with non-return valves 84 and 50 respectively, the valve 50 being arranged to maintain a residual pressure of 50 p.s.i. in the system. The right-hand end of the chamber 58 is subjected to supply pressure through a line 70 and is connected by a line 71 to a chamber 82 of a pressure-operated valve 79 urged towards a seat 80 by a spring 81 against pressure in the chamber 82 acting on a piston 79a. By-pass lines 54, 55 connected to lines 52, 53 connecting opposite ends of the jack cylinder 13 with the servo-valve casing 19 lead to a chamber 60 of the by-pass valve 56 and are connected by lines 77, 76 respectively to an annular recess in the piston 79a and a chamber 78 of the pressureoperated valve 79. Restricted passages 83 between the annular recess and the chamber 78 during normal operation of the system permit restricted communication between the opposite ends of the jack cylinder to damp out any tendency of the rudder to flutter. The by-pass valve 56 comprises a piston 64 having valveended rods 65, 65a engageable respectively with seats 67, 66 to control communication between the by-pass lines 54, 55 and between the servovalve and the supply line 86. With pressure liquid being supplied to the system and the rudder operating under power control, the non- return valve 45 seats on the seat 46, the rod 65 engages its seat 67 to close the by-pass and the valves 84, 79 open so that movement of the rod 24 by the pilot moves the valve piston 20 relative to the casing 19 which in turn causes movement of the jack cylinder and rudder and the valve casing 20 to follow-up the movement of the valve piston. In the event of failure of the supply pressure the valves 84, 79 close automatically, any liquid in the chamber 82 returning to the supply through the lines 71, 70 and the chamber 58, the by-pass valve 56 remaining closed all the while the valve piston 20 is in its neutral position to lock the rudder, under the action of the liquid trapped in the system acting on the piston 64 and the larger left-hand face of the control piston 61. On movement of the rod 24 by the pilot the valve piston 20 moves to one end of its travel tending to move the frame on which the servo-valve and jack are mounted and the rudder directly, pressure is then generated in one or other end of the jack cylinder, which pressure acts on either the end of the rod 65 or the piston 64 to open the by-pass to allow direct manual operation of the rudder. Should the air pressure acting on the rudder suddenly reverse, as occurs at supersonic speeds, whilst the rudder is being moved by the pilot, pressure is produced in the opposite end of the jack from that in which it is being produced by the pilot. This pressure being transmitted through the servo-valve to act on the rear face of the piston 64 to close the by-pass valve and so lock the rudder. Thus the pilot can move the rudder within the limits of his strength but he cannot be reversed by reverse air pressure acting on the rudder. In the event of the valve piston 20 becoming jammed in its casing 19 any force applied to the rod 24 by the pilot urges the balls 31 out of the groove 29 to unlatch the latch members 32, the sleeve 39 is then released and the pin 42 removes the ball 45 from its seat 46 on to its seat 47 cutting off the left-hand end of the chamber 58 from supply and opening it to exhaust resulting in leftward movement of the control piston 61 and the unseating of the rod 65 to open the by-pass and the seating of the rod 65a to isolate the servo-valve from the pressure supply, leaving the pilot free to manually operate the rudder. On freeing the valve piston 20 the ball 45 may be re-seated on its seat 46 by a plunger 51 which engages the arm 41 and resets the sleeve 39 in the latch members 32 providing the valve piston 20 is first moved to its neutral position..