Patent GB-502473-A (GB)
Title: Improvements in or relating to automatic pilots for aircraft
IPC: G05D1/08
Filed: 1937-06-15
Abstract: 502,473. Fluid-pressure servomotor-control systems. SPERRY GYROSCOPE CO., Inc. June 15, 1937, No. 16615. Convention date, June 19, 1936. [Class 135] An automatic pilot for aircraft comprises an attitude control unit such as the gyroscope 2, a control device 10, 13 positioned adjacent the attitude control unit and actuated by the relative turning of the unit and the aircraft, a relay 21 adjacent the control device and operated thereby to control a remote rudder-actuating servomotor 23 and fluid-pressure operated follow-up means 32 adjacent the relay constructed to move proportionately to the servomotor without being mechanically connected thereto whereby to impart a follow-up movement to the control device. The arrangement shown in Figs. 1, 2 is designed to maintain the craft in level flight regardless of changes in its weight or centre of gravity: A gyro-vertical or artificial horizon 2 is mounted in a casing 1 from which air is continuously evacuated by a pump 16, and is pivoted in a gimbal ring 4 itself pivoted on trunnions 5 in a frame 6. Movements of the gyroscope about an axis normal to that of the trunnions 5 are transmitted by a roller 9 to a bail 7 which rotates a shutter 10 which in its neutral position half laps ports 12, 12<1> in a pivoted member 13 connected by pipes 20, 20<1> to a casing containing a diaphragm 19 and having air apertures 17. The differential control of the ports 12, 121 by the gyroscope therefore causes the diaphragm to be deflected. The diaphragm is connected to a hydraulic relay valve 21 which has three collars 74, 73, 741 which, when moved from the neutral position shown in Fig. 2, permit oil or like pressure liquid to flow from a pump 28 via a pipe 29 and one or other of pipes 24, 24<1> to the servomotor 23. The piston 27 of the latter is connected by cables 26 to the elevator 25. The fluid displaced by the piston 27 passes back through the valve 21 and one of the passages 33, 331 to the cylinder 32 of the follow-up device. The latter is unitary with the valve 21 and its cylinder has the same capacity as the servomotor 23 and contains a piston 36 connected by a rod 38 to a worm 40 which acts rackwise on a segmental gear 46 fixed to the member 13 which it rotates. The ends of the cylinder 32 are connected by a byepass conduit 44 controlled by a needle valve 45, Fig. 1, or a ported screw' plug 45, Fig. 2. The effect of this is that the ports 12, 12<1> are not returned quite to their original positions relative to the shutter and the elevator is left slightly depressed so as to check any tendency of the craft to climb without repeated operations of the servomotor. Any tendency of the craft to descend is similarly checked. The piston 36 and the relay valve member 21 are each provided with centralizing springs 42, 43 respectively. The relay valve shown in Fig. 2 differs from the diagrammatic form in Fig. 1, in that it has two additional collars 80, 801 and an axial bore 85 whereby fluid passing these collars passes to a drain pipe 31. The exhaust passages 82, 82<1> are connected by a duct 83 to a pipe 30. The desired inclination of the craft may be set by pressing and then turning a knob 55 having its shaft capable of pin-and-slot engagement with a shaft 48 splined inside the worm 40. The same action disengages a spring-pressed clutch disc 50 from a gear 52 connected to an altituderesponsive device. Thus the gear 52 meshes with a gear 58 connected to a Bourdon tube 60, the other end of which is fixed but in fluid connection by a pipe 61 with the casing 62 of a diaphragm exposed to atmospheric pressure or with the intake manifold of the engine. The worm 40 also meshes with a gear 66 having its hub connected by a flexible band 65 with the hub of an inclination indicating' cylinder 63 visible through a window 64 in the front of the housing. The band 65 is .tensioned by a spring 68. The ailerons are controlled in the same way by a shutter 101 moving relatively to ports in a rotatable member 15 in response to transverse inclinations of the craft relative to the gyroscope. The shutter 10<1> is secured to the gimbal ring 4. Similar indicating and adjusting means for the aileron control are mounted in the front of the housing 1 on its opposite side. A byepass valve 71 is opened when it is desired to effect manual control. The rudder may be controlled by a similar servomotor arrangement with a hydraulic follow-up connection, the shutter in this case being controlled by a directional gyroscope.