Patent GB-803572-A (GB)
Title: Control systems for aircraft
Inventor: SEDGFIELD HUGH BROUGHAM
IPC: B64C13/24
Filed: 1954-03-17
Abstract: 803,572. Automatic control systems for aircraft. SPERRY GYROSCOPE CO., Ltd. Feb. 22, 1955 [March 17, 1954], No. 7783/54. Class 38 (4). [Also in Groups XXIX and XXXIII] In an aircraft control system an hydraulic servomotor operating a control surface is controllable either electrically or mechanically in dependence on relative displacement between a manual controller and the control surface. Electric manual operation.-In Fig. 1 manual control of aircraft elevators 202 is rendered effective by operation of a push-button Y to energize a self-holding relay D, contacts d 2  of which close to energize a solenoid-operated valve 229<SP>1</SP> to the position shown so that an hydraulic changeover valve 223 moves to the left-hand position as shown to couple a control valve 209 to an hydraulic servomotor 210 controlling the elevators. Under these conditions any difference between the outputs of potentiometers 206, 207 associated with a manual control column 201 and the elevators respectively, is derived by an electrical differential 245 and applied through an amplifier 248 to control electric actuator 208 of control valve 209 so that servomotor 210 is operated to maintain positional correspondence between the elevators and the control column. " Feel " is imparted to the manual control by a spring-restrained piston 2161 the neutral position of which can be adjusted by push-buttons U and V controlling a reversible motor 216<SP>11</SP> to effect trim. The stiffness of the restraining springs and hence the amount of feel may be automatically adjusted in dependence on airspeed by a motor 293, controlled by an airspeed detector 291, angularly adjusting a support 257<SP>1</SP> about a pivot 257<SP>11</SP>. A push-button M may be operated to energize a relay A and thereby introduce into the input of amplifier 248 the output of a detector 212 responsive to short term oscillations of the aircraft to stabilize the manual control. Potentiometers 206, 207 may be replaced by variable inductive devices. A valve 271 operates on failure of a normal source of fluid pressure P1 for the control system to change over to an auxiliary source P2. Automatic operation.-When automatic control of the elevators is desired a push-button N is operated to energize a relay B, contacts of which connect to the input of amplifier 248 the outputs of short-term detector 212, a long-term detector 213 and feedback potentiometer 207. The vertical course and/or attitude of the aircraft is thus maintained automatically, potentiometer 206 being disconnected from amplifier 248. The error voltage derived from potentiometers 206, 207, however, is then effective to control reversible motor 216<SP>11</SP> through an amplifier 269 so that control column 201 follows movements of the elevators in readiness for reversion to manual control. Non-electric manual operation.-More direct manual control of the elevators is obtainable by operation of a push-button X to interrupt the self-holding circuit of relay D whereupon valve 2291 moves to its other position to change over valve 223 so that a control valve 211 is coupled to servomotor 210. Under these conditions the elevators may be controlled by control column 201 acting on valve 211 through mechanical link 282, follow-up from the elevators being provided by a mechanical link 281 associated with a mechanical differential 284. To avoid a jolt on change-over to this form of control, valve 223 is slowed down towards the end of its movement by the action of a restriction 231<SP>11</SP>. With this form of control the end of a lever 256 is secured by an electromagnetically-operated lock 258 which under the other forms of control is withdrawn as shown to permit a predetermined amount of lost motion to avoid conflict between the controls and to allow for expansion. The system changes over automatically from automatic to non-electric manual control by interruption of the holding circuit of relay D if (a) a spring 265 associated with mechanical link 282 is stressed sufficiently to open contacts h; (b) the output of amplifier 248 exceeds a predetermined value so that a relay C is operated to open contacts c 1 ; (c) the positional error signal exceeds a predetermined value so that a relay E is operated to open contacts e 1  (the operating point of relay E may be made variable with airspeed); (d) there is excessive movement of valve 209 opening contacts k; or (e) a relay (not shown) operates to open contacts on failure of the supply to potentiometers 206, 207. An alternative arrangement utilizing different forms of hydraulic components and mechanical linkage is described in the Provisional Specification. Specifications 803,576 and 803,577 are referred to.