Patent GB-716427-A (GB)
Title: Improvements in or relating to hydraulic pistons for aircraft control systems
Inventor: WATSON CYRIL DANIEL
IPC: B64C1/00
Filed: 1951-04-18
Abstract: 716,427. Controlling aircraft. NATIONAL RESEARCH DEVELOPMENT CORPORATION. April 18, 1952 [April 18, 1951], No. 9099/51. Class 4 In an hydraulic control system for aircraft wherein means are provided whereby in the event of the aircraft being subjected to acceleration in excess of a predetermined magnitude the pilot's control column is shifted automatically towards a position which results in relief of the resultant stresses, and a motor driven pump delivers liquid from a reservoir to the interior of a jack cylinder of which latter the piston is operably connected with the pilot's control column and also via a spring supported acceleration responsive moving-mass type, restrictor valve, to the reservoir, the restrictor valve being such that in straight and level flight the restriction to liquid flow therethrough is small, the jack piston comprises a main piston slidable in the jack cylinder and a subsidiary piston for connection to the pilot's control column and which normally moves as one with the main piston but which is slidable in the main piston against spring influence to free the pilot's control column in the event of seizure of the main piston. A cylinder 23 contains a main piston 11 which carries a subsidiary piston 13, the piston rod of which is connected to the pilot's control column. The crown of the piston 11 is formed with two pressure relief valves 19, 20 operating in opposite directions and the piston 13 is centred within the piston 11 by two springs 14. 15 and a slidable spring loaded piston member 17 is located within the piston 13. A stem-like member 26 is biased to the position shown by the spring 14 and a manually operated plunger 38 is provided. The piston assembly is incorporated in a system (not shown) in which a pump delivers liquid from a reservoir to the interior of the cylinder 23 and, via an acceleration responsive restrictor valve, back to the reservoir, the restrictor valve being such that in straight and level flight the restriction to flow therethrough is small. The space 16 within the piston 11 is full of pressure liquid from the pump and normally the non-return valves remain closed and the pistons 11 and 13 move in unison but if acceleration forces, as in pulling out of a dive, close the restrictor valve to cause a build up of pressure in the cylinder 23. the pistons 11 and 13 and, thus the pilot's control column, will be moved in a sense to reduce the acceleration. If the piston 11 becomes seized in the cylinder 23 the excessive pressure therein opens the valve 19 and acts directly on the piston 13 to move the control column in the appropriate direction, whereafter the piston 13 uncovers ports 24, 25 and places the interior space 16 in communication with the reservoir through further ports 33, 34. Should the piston 11 be seized at the outer limit of its travel in the cylinder 23, return movement of the control column will cause the piston 13 and the valve member 17 to move as one until the valve member bears on the end of the stem-like member 26 whereafter movement of the piston 13 relative to the stationary member 17 uncovers ports 27 and 28 and places the space 16 in communication with the reservoir through ports 29, 30; 27, 28; 31, 32 and 33, 34. The valve member 17 is located in the space 37 of the piston 13 by friction spring means 35, 36, and the pilotoperated push rod 38 enables the member 17 to be returned to its normal position when the piston 11 is freed.