Patent GB-735505-A (GB)
Title: Dual source aircraft attitude control system
Inventor: FEENEY THOMAS AQUINAS
IPC: B64C13/00
Filed: 1950-12-19
Abstract: 735,505. Fluid-pressure servomotor-control systems. NORTHROP AIRCRAFT, Inc. Dec. 19, 1950, No. 30955/50. Class 135. [Also in Group XXXIII] A control system for an aircraft comprising two sources of power for moving a control surface in accordance with signals initiated by the aircraft pilot (human or automatic), movement of the surface under one source being taken up'by the other source upon cessation of the application of power by the first source. The pilot's signals applied by a control column 7, Fig. 1, are carried by cables 3 to two hydraulic power units 8, 9, operating an eleven 4 of an all-wing aircraft, the unit 8 also incorporating an electric power unit 11. The hydraulic units are of the kind described in Specification 701,504, and each comprises a moving cylinder 28, Fig. 2, controlled by a piston valve 26 and having a piston rod 31 pivoted to the wing and an end 29 connected to turn the elevon about its axis 16. The valve is moved by a rod 25 attached to an arm 24 extending from a rod 19 rotated by the cables 3, and movement of the elevon causes the valve housing 27, attached to the cylinder 28, to follow-up the valve until a neutral position is reached. Elevon movement is transmitted by quadrants 58, 59 and cable 50 via' pulleys 59a, 52, 51 to a cam 46, Fig. 3, movable relatively to a quadrant 40 carrying switches 41a, 41b. The pressure in the hydraulic supply line 34 is limited by a regulatng valve 38 to permit the cylinder and piston to stall if the eleven is submitted to excessive air loads. The electric power unit comprises a reversible motor 75, Fig. 4, having a brake 77 and driving the elevon through a torque limiting device 76, high-speed reduction gear 74, a clutch 72, a low-speed reduction gear 71, a pulley 61, cable 62 and quadrants 63, 64. The pilot signals are applied to the rod 19 which causes rotation of the quadrant 40 and closure of the corresponding switch 41a, 41b by engagement of the appropriate roller 43 on the cam 46, to cause the motor 75 to rotate in the appropriate direction. Movement of the elevon causes rotation of the cam 46 to followup the quadrant to open the closed switch when the pilot's signal ceases. The source 121 of electrical energy may be connected to the switches 41a, 41b by a switch 122 or a pushbutton 126, both under the pilot's control, or by a switch P which closes if the hydraulic pressure in line 34 falls below a predetermined value. Closure of any of these switches closes valves L in the line 34 to permit the hydraulic motors to " free wheel," and engages the clutch 72 which is open during hydraulic operation. The torque limiting device 76 comprises an epicyclic gear engaging a rack 87 movable against springs by excessive air loads on the elevon to throw one or other switch 104, 107 according to the up or down position of the elevon to switch off the motor and apply the brake 77 and also to light a warning lamp 124a or 124b. Movement of the rack under dangerously high loads also closes a switch 111 to open the clutch to permit the elevon to free wheel slightly to reduce the loads. When the load has been reduced, the switches open to restore the pilot's control. Should the power source 121 fail, while the elevon is being operated electrically, valves L and clutch 72 automatically open to place the surface under hydraulic power. Specification 735,502 also is referred to.