Patent GB-734295-A (GB)
Title: Improvements in and relating to apparatus for preventing flutter of movable surfaces on aircraft
Inventor: NORTH JOHN DUDLEY
IPC: B64D45/00
Filed: 1952-11-07
Abstract: 734,295. Fluid-pressure servomotor-control systems. BOULTON PAUL AIRCRAFT, Ltd. Nov. 9, 1953 [Nov. 7, 1952], No. 28104/52. Addition to 696,028. Class 135. [Also in Group XXXIII] In apparatus according to the parent Specification for preventing flutter of a power-operated movable surface on an aircraft, the passage permitting un restricted flow of the liquid from one side of the piston to the other during power operation includes reversible return-flow preventing means adapted to be selectively conditioned, according to the direction of power operation of the movable surface, so that unrestricted flow of the liquid is permitted only in the direction corresponding to the direction of power operation, and movement of said surface by external forces in a direction counter to that of the power operation is opposed. A pump 1, driven by an electric motor 8 comprises a constant delivery pressure section 3 which supplies an accumulator 7 to maintain a basic minimum pressure in the system and a variable pressure section 2 connected by pipes 56, 57 to an operating jack 4 for a movable control surface 6. An hydraulic damper 10 is interposed between the jack 4 and the surface 6 and it is connected to the accumulator 7 through non-return valves 12, 13, opposite ends of the accumulator being connected also by a conduit 14 having a restriction 15 to provide for slow transfer of liquid and by a control valve element connected to pipes 20, 21. The control valve element comprises a pair of oppositely acting valves 24, 25 respectively biased by springs 26, 27 to close ports 33, 34, the springs exerting a loading in excess of the nominal pressure of the system. The valves 24 and 25 are respectively in communication with other ports 32, 40 and 35, 41 and further valves 42, 43 operated by solenoids 60, 61 have ports 48, 52 and 49, 53 which place the ports 40, 41 in communication with the pump section 2 or 3 depending on the positions of the valves, the solenoids being controlled by switches 58, 59 held open by liquid pressure. When the apparatus is working, the pump section 3 builds up the minimum pressure and with the solenoids de-energized the valves 24, 25 will. remain closed and communication between the ends of the cylinder 10 will be through the restriction 15 only, whereby flutter of the surface 6 is prevented. If the aircraft controls are moved to 'operate the variable pressure section 2 of the pump to move the jack 4 from, say, left to right as viewed in the drawing, pressure liquid will be supplied through valve'43 to operate valve 24 which will be moved to the left to place ports 34 and 35 in communication. This will enable liquid to transfer freely from one side to the other of cylinder 10 through pipe 21, a non- return valve 19, a pipe 17, the valve 23, an extension of pipe 17 and pipe 20. Any tendency for the surface 6 to move in a direction opposite to its powered direction of movement under aerodynamic forces would be prevented by the non-return valve 19. A similar non- return valve 18, set to. operate in the opposite direction to the valve 19, is located between the pipe 20 and port 32 of valve 24. If, as the result of failure of the system, the pressure drops suddenly, the switches 58, 59 close and energize solenoids 60, 61, to shut off the supply of liquid to the valves 24, 25 and place them in communication with the sump of the pump through pipes 54, 55 so that the valves are immediately closed by their spring loading. The surface 6 is thereby permitted to return slowly to its neutral position.