Patent GB-129861-A (GB)
Title: Improvements in and relating to the Control of Aircraft.
Inventor: MARSHALL ROBERT
IPC: B64C13/24
Filed: 1918-09-09
Abstract: 129,861. Marshall, R. Sept. 9, 1918. Steering and balancing.-The rudders, elevators, &c. of aircraft are operated by means of a fluid-pressure servo-motor which actuates the controls through a link and sliding-block device the throw of which is varied by the control lever simultaneously with the actuation of the valves of the servo-motor, and through a lost-motion device which allows the servo-motor to be returned to its normal position without returning the controls. Hydraulic or screw-and-nut locking-gear is provided for retaining the controls in position, and the screw gear may be used to actuate the controls directly if the servo-motor should fail. The servo-motor comprises diaphragm chambers 3, 4, Figs. 1 and 3, having the diaphragms connected by a rod 5 engaging a crank 8 mounted on a shaft 9 which carries a pair of links 10 in which slide blocks 12 connected bv rods 15 to levers 13 on a shaft 17. One link 10 actuates the elevators and the other the rudders, the corresponding levers 13 each having claw-clutch engagement with a pair of levers 23 connected to the respective control wires &c. 24, the clutches allowing sufficient lost motion for the return of the servomotor to normal position. The blocks 12 are adjusted in the links 10 by means of connexions- 31, 30, 28, 27 to a corresponding pair of control levers 25. which simultaneously actuate the operating-valve 34 of the servo-motor by means of arms 38. These arms are formed with fingers 50, Figs. 4 and 6, which engage opposite sides of a stud 51 pivoted at 52 to a slide 45 and normally pressed by a spring 54 into the position shown, with a lug 53 resting on the slide 45. This slide is connected to the pistons 41, 42 of the valve 34 which operates in a casing 40 connected at 35 to a fluid-pressure reservoir 1, at 37 to a relay valve 36, and at 48 to atmosphere. The relay valve 36, Fig. 7, is operated by differential pistons working in a casing connected at 68 to the valve 34, at 66 to the reservoir, at 63 to the diaphragm chamber 4, and at 64 to a manuallycontrolled release valve 55, Fig. 3. The diaphragm 3 is always exposed to reservoir pressure through a pipe 6, Fig. 3. When the control lever 25 for the elevator or rudder is operated, the valve 34, Fig. 4, is moved by the engagement of one of the fingers 50 with the stud 51, thereby opening the relay valve to exhaust at 48, whereupon the relay valve 36, Fig. 7, moves to the left and connects the diaphragm casing 4 to exhaust through the release valve 55 when this is opened by the pilot. The servo-motor then operates the links 10, the block 12 of one of which has been adjusted by the operation of the control lever 25. Attached to the links 10 is a sliding bar 56, Figs. 4 and 6, carrying tappets 57, one of which is brought by the movement of the link into contact with the stud 51, thereby restoring the slide 45 and valve 34 ready for another operation. When the control lever 25 is returned to normal position, the finger 50 displaces the stud 51 about its pivot without moving the slide 45. An hydraulic locking-gear is provided for each control and comprises cylinders 81, 82, Fig. 10, connected by a passage 83 with valve 84, Fig. 9, and provided with pistons the rod of which is connected to a lever 78 loose on the pivot 26 of the control levers 25. The lever 78 has clawdutch engagement with loose levers 76, 77 which are connected by rods or wires to the corresponding pair of the levers 23, Fig. 1, so as to move in unison therewith. The valve S4 is normally held open by a spring, allowing the pistons to move as the controls are operated by the servomotor. The piston-rod carries a projection 104 which thus follows the movement of the control lever 25 and, by engagement with a cam 106 thereon, effects the closure of the valve 84 through a shaft 100 and gearing 101, 102, 94, 95, 96. When the control lever 25 is returned, the cam 106 tilts so as to clear the pin 104, allowing the valve 84 to be re-opened by its spring. In an alternative hydraulic gear, the pistons are stationary and the cylinders move, the by-pass valve being operated by engagement with a cam moving with the control lever. In the screw locking- gear, the lever 78 is connected to a nut 145, Fig. 20, engaging a screw 144 geared to a hand-wheel 147, the arrangement being such that the servomotor is unable to operate except as the screw is rotated by means of the hand-wheel. The deflexion of the rudder &c. corresponding to a given rotation of the hand-wheel may be indicated on a scale. An auxiliary diaphragm chamber connected directly to the reservoir may be provided to ensure the return of the servo-motor to its normal position. In modifications, there may be two operating-valves 34, one for the elevators and one for the rudder; a third operating-valve working through a second relay valve may actuate the ailerons; or there may be a separate servo-motor to each control. Vacuum may be used instead of pressure. According to one of the Provisional Specifications, the servo-motor may comprise two single-acting cylinders of different diameters.