Patent GB-926212-A (GB)
Title: Improvements in power control systems for aircraft
IPC: B64C13/00
Filed: 1959-08-31
Abstract: 926,212. Automatic aircraft control. W. W. TRIGGS (Bell Aircraft Corporation). Aug. 31, 1959, No. 29604/69. Class 38 (4). [Also in Group XXIX] A power control system, for an aircraft having a movable aerodynamic control surface 10, comprises a fluidpressure actuator 16, 18 connected to the surface and controllable manually through the pilot's stick 28, and a servomechanism controlling the actuator and comprising a housing 42 which encloses piston valve means 50, 52, the manual control means including a member 60, 62 fulcrumed on the housing, means to alternatively restrain or restore fulcruming of the member 60, 62 and means such as the tappet plungers 53, 54 on this member operatively engaging the valve means 50, 52 to control the power actuator 16, 18 when the member 60, 62 is unrestrained, an electromagnetically responsive differential pressure control valve or flapper 94 movable from a neutral position for selectively controlling fluid-pressure applications to the piston valve means 50, 52 to move it in opposite directions, and mechanical means operatively interconnecting the actuator 16 to the differential pressure control valve to restore this valve to its neutral position when the power actuator fulfils a control command. A manual input rod 22, which is linked to the fulcrumed member 60, 62 and linked through the pilot's lever 20 to the power actuator 16, is mechanically connected back through a member 130, 132 and a spring 133 to the differential pressure control valve which is acted upon mechanically through a rod 195 and an opposing spring by means responsive to the flight characteristics indicated in Fig. 1. The control valve is also responsive to electrical signals fed through an amplifier from automatic means as indicated diagrammatically in Fig. 1. In the manual mode, pressure to the flapper 94 is cut off by a solenoid operated lockout valve 104. To switch to " autopilot " mode, the solenoid valve 104 is operated by an " autopilot on " switch to supply pressure to the flapper valve and also to a pair of lockout pistons 106, 108 which move apart to immobilize the levers 60, 62; plungers 53, 54 move outwardly and the spool valves 50, 52 are under control by differential pressure in chambers 100, 102. In this mode the automatic control can, however, be overridden by the manual control. Leak ports 113, 114 across the lockout pistons 106, 108 allow them to move and actuate an override piston 115 which then releases the lockout pistons and frees the levers 60, 62. Lever 60 then actuates a limit switch 120 to disconnect the autopilot and close solenoid valve 104 thus returning the mechanism to manual mode. In a damper or stability augmentation mode an unlock solenoid valve 125 is switched to apply pressure to the outer sides of the lockout pistons 106, 108 which move inwardly and free the levers 60, 62. Pressure is still on to the flapper valve and plungers 53, 54 are urged outwardly against the levers, the spool valves 50, 52 being free for automatic actuation and also the linkage is free for manual actuation. The flapper valve 94 carries a resilient tongue engaged between the spools 50, 52 to provide a feed-back.