Patent GB-931661-A (GB)
Title: Aircraft flight control system
IPC: B64D45/00
Filed: 1961-06-13
Abstract: 931,661. Automatic control of aircraft. SPERRY RAND CORPORATION. June 13, 1961 [June 23, 1960], No. 21288/61. Class 38 (4), In an aircraft autopilot means producing an output on approach to a stall condition causes an airspeed error signal, which has previously been maintained at a null despite variations of airspeed, to be effective to control the pitch channel of the autopilot to move the aircraft away from a stall condition. Automatic pitch attitude control.-As shown, signals dependent on the pitch attitude of an aircraft are applied from a gyro vertical 46 through a variable inductive device 53 and amplifier 51 to control a follow-up servomotor 20 adjusting one end of a differential linkage 14. Signals from a tachometer generator 52 driven by servomotor 20, applied to the input of amplifier 51 both directly and through an integrating circuit, provide rate and position feedback respectively. Linkage 14 adjusts at a point 13 a control valve of a fixed-piston type hydraulic servomotor 10 so that the elevators 11 are positioned to maintain the desired pitch attitude automatically. Damping.-Signals dependent on angular acceleration about the pitch axis, derived from an accelerometer 62 and integrated at 64, energize through a line 17 a torque-motor operated valve controlling an auxiliary hydraulic servomotor which adjusts a point 16 of linkage 14 to provide damping. Signals dependent on the position of the auxiliary servomotor are produced by a potentiometer 18 and fed back. Servo-assisted manual control.-A pivoted manual elevator controller 27 is mechanically coupled through a link 28 with linkage 14 and signals dependent on the force exerted are derived from a pick-off 29 and applied through a non-linear attenuator 33 to control an integrating servomotor 42 adjusting the rotor of a variable inductive device 53 so that adjustment of the elevators is assisted by servomotor 20. The manual effort required, or " feel," is increased with airspeed by causing the latter to adjust attenuator 33 automatically. " Feel " is further modified in dependence on angle of bank by applying signals from the bank pick-off of gyro 46 through a cosine resolver to energize the generator field windings of integrator 42. Vertical acceleration limiting.-Signals from a vertical accelerometer 66 are applied to a gate 40 so that if the acceleration is outside predetermined limits in each sense a further signal is applied through a line 41 to control integrator 42, and hence the elevators, in a sense to reduce vertical acceleration and increase " feel." Signals resulting from excessive acceleration and from manual control are caused to modify the damping by applying them to a summator 59. Airspeed control.-The output of a variable inductive device 78, supplied with signals dependent on airspeed from a meter 71, is normally maintained zero by a follow-up servomotor 79 controlled by the output and adjusting the rotor of inductive device 78. If, however, signals from an angle of attack meter 90 exceed a predetermined limit set by a gate 91 indicating approach to a stall condition, a relay 94 operates to permit only signals from gate 91 to control servomotor 79. Decrease in airspeed or increase in angle of attack then produces an output from inductive device 78 which is applied through a line 75 to the elevator control system to cause the aircraft to keep away from the stall condition. Under these conditions a relay 102 is also operated by the angle of attack signals to prevent pick-off 29 and vertical accelerometer 66 from controlling the elevators. Specifications 612,810, 673,534, 820,887 and 931,662 are referred to.