Patent GB-791623-A (GB)
Title: Improvements in or relating to power-operated aircraft controls
Inventor: ELMER ARTHUR ERNEST HENRY
IPC: B64C13/24
Filed: 1954-12-16
Abstract: 791,623. Fluid-pressure servomotor-control systems. BRITISH MESSIER, Ltd. Nov. 30, 1955 [Dec. 16, 1954], No. 36519/54. Class 135. [Also in Group XXXVIII] A fully powered aircraft control system comprises a pilot's control element coupled to a first reversible servomotor and a first signal position transmitter, a flight controller (e.g. a control surface) coupled to a second reversible servomotor and a second signal position transmitter, means for energizing the first servomotor proportionately to the difference between the two signals, and means for energizing the second servomotor proportionately to the difference between the second signal and a control signal. The control signal may be the first signal or a signal from an autopilot. As illustrated, the pilot's control stick 1 is connected by a rod 2 to the pick-off 4 of a potentiometer 5, and to the piston of an hydraulic jack 3 comprising chambers 20, 21 fed with fluid under pressure from conduit 12 through restrictions 22, 23, and exhausting through orifices 24, 25 to a return conduit 14. A flap 27 obturates the orifices differentially under the control of a winding 28 energized by electric circuits R<SP>1</SP> N<SP>1</SP> and Ll N<SP>1</SP>, where N<SP>1</SP> is a neutral line. In similar fashion circuits R<SP>11</SP> N<SP>11</SP> and L<SP>11</SP> N<SP>11</SP> control a flap 67 differentially obturating exhaust orifices 65, 66 connected to chambers 42, 43 in a block 31 supplied with fluid under pressure from a conduit 13 through restrictions 50, 51. The chambers 42, 43 are at the ends of a valve member 32, having lands 33, 34, 35, 36, forming annular chambers 37, 38, 39, 40, 41. The chamber 39 is connected to the pressure conduit 13 and the chambers 38, 40 to the exhaust conduit 15. The lands 34, 35 co-operate with ports 52, 53 which are connected to chambers 37 and 41, and to an hydraulic jack 8 connected to a control surface 6 and the wiper 9 of a potentiometer 10. The wiper 9 is connected to the lines L" and R<SP>1</SP>, and the wiper 4 to the lines L<SP>1</SP> and R<SP>11</SP>. When the stick and surface 6 are in their neutral positions, the lines L<SP>1</SP>, R<SP>1</SP> and L", R<SP>11</SP> are equally energized, the flaps 27 and 67 are centred, the valve member 32 is centred, and the hydraulic pressures in chambers 20 and 21 of jack 3 are equal, as are those in the chambers 54 and 55 of jack 8. If the control stick is displaced, say, to the right, the current in line L<SP>1</SP> increases, the flap 27 moves to the right, and the pressure in chamber 21 rises that in chamber 20 falling, producing a centring force on the stick. Similarly, the current in line R<SP>11</SP> increases, the flap 67 moving to the right, whereby the pressure in chamber 43 rises and that in chamber 42 falls. The valve 32 moves to the left, opening port 52 to the pressure chamber 39, and port 53 to the exhaust chamber 40. The chambers 37 and 41 are thus connected to pressure and exhaust, balancing the pressures on the control valve, and the piston of jack 8 moves to the right, deflecting the surface. In addition, the signal derived by the pick-off 9 increases, lessening the unbalance between the currents in lines L<SP>11</SP> and R<SP>11</SP>. The surface continues to deflect until the reaction on the surface equals the force applied by the jack 8, i.e. is proportional to the current difference between lines L<SP>11</SP> and R<SP>11</SP>. This is also the current difference between lines L<SP>1</SP> and R<SP>1</SP>, whereby the centering force applied by the jack 3 is proportional to the load on the surface 6. A two-way switch in the line R<SP>11</SP> may connect this line to a wiper 79 controlled by an autopilot 77, whereby the surface 6 is controlled by the autopilot instead of the stick 1. The pilot retains the feel on his stick, or if flying " hands off," the stick is moved in correspondence with the surface. Specification 712,329 is referred to.