Patent GB-578698-A (GB)
Title: Improvements in or relating to means for actuating the control surfaces of aircraft
IPC: B64C13/00
Filed: 1944-01-11
Abstract: 578,698. Fluid-pressure. servomotors; valves. FAIREY AVIATION CO., Ltd., LISLE, W. G., and CHURN, C. R. Jan. 11, 1944, No. 535. [Class 135] In a fluid-pressure servomotor arrangement for operating the control surfaces of aircraft, both parts of the fluid-pressure jack or the like are movable and the pilot's control column d, Fig. 1, is connected through lost-motion means h, j to one of these parts and to the control surface c and is also connected through a movement reducing system of levers of which the control column forms a part, to the other part of the jack so that normally the movement of the control column acts on the control valve of the jack to bring about movement of the control surface and at the same time imparts a slight movement to the other part of the jack whilst in the event of a failure of fluid-pressure the control column, it takes up the lost motion and acts directly on the control surface. As shown in Fig. 1, the control column d has a fixed pivot e at one end and is connected intermediately by a pin-and-slot connection h, j to the cylinder a of the jack and to a rod k connected to the control surface by a crank arm m: Near the pivot e the column d is also connected by a link o to a lever p having a fixed pivot q and pivoted intermediately at s to the rod t of the jack piston b, the movement of which due to the arrangement of the levers p and d is small compared to the movement of the lever d. The lever d is also connected to a control valve g having a fluid-pressure supply line u and a return line v. On operation of the lever d, the valve g opens to admit fluid-pressure to one side or other of the piston b so that the jack cylinder a is moved in the same sense to operate the control surface c. The cylinder continues to move until it has caught up the valve when the fluid-pressure is cut off. Meanwhile the fluid-pressure on the piston b reacts through the linkage p, o on the control lever d so that the pilot always has a sense of " feel " of the control though the major part of the effort is supplied by the jack. In the event of the pressure failing, the lever d takes up the lost motion at h, j and to facilitate this the ends of the jack are connected through a byepass valve x operated manually or on a substantial fall in pressure in the supply u. In order to maintain the lever d in a set position, a further jack y, z is disposed tandem-wise of the first, its cylinder z being connected to a fixed point 11 and its piston' z being fixed to the piston-rod t. The ends of the cylinder y may be connected to one another by conduits 12, 13 or to the corresponding ends of the cylinder -c by conduits 12, 14 or isolated from one another and from the ends of the cylinder a. A valve construction for doing this is shown in Fig. 2 and comprises four linearly arranged spring-closed valves 20, 21, 22, 23 in chambers 16, 17, 18, 19. The valves are opened in pairs 21, 22, and 20, 23 by the respective inclined surfaces 30, 31 and 29, 32 on a slidable plunger 28 operated by a lever 36 so that when the inner pair 21, 22 are opened the ends of the cylinder y are connected by conduits 12 and ports 33, 34, 35 and the piston z is free to move whilst when the outer pair 20, 23 are opened, the ends of the cylinder a connect respectively with the ends of the cylinder y through passages 14, 33, 12 and 14, 34, 12 and hence the reaction hitherto taken by the control column d is taken by the cylinder y.