Patent GB-845678-A (GB)
Title: Control apparatus for aircraft
IPC: G05D1/00
Filed: 1957-11-01
Abstract: 845,678. Automatic control systems for aircraft. SPERRY RAND CORPORATION. Nov. 1, 1957 [Nov. 21, 1956], No. 34242/57. Class 38 (4). In an aircraft autopilot signals produced by two separate instruments responsive to motion of the aircraft about one of its axes control a servo-operated control surface and a characteristic signal is produced if the difference between functions of the two signals exceeds a predetermined value. As shown, signals produced by a gyro vertical 44, corresponding to pitch deviations of an aircraft, control a servo-system 12 correcting pitch by adjusting elevators 69. Signals from a manual controller 39, a radio receiver 86, an altimeter 80, a Mach meter 60, or an airspeed meter 81 may also be introduced by closing the appropriate switch associated with a computer 61 so that pitch attitude may either be selected manually, or automatically varied to cause the aircraft to follow a radio glide path or to maintain constant altitude or speed. Servo-system 12 is also controlled by a follow-up signal, dependent on rate of servomotor operation, developed by tachometer generator 13, and a further follow-up signal, dependent on acceleration of the aircraft about its pitch axis, developed by accelerometers 35, 36. A rate of pitch signal is derived from and added to the latter signal by an integrating circuit 48. To provide a continuous check on the operation of the auto-pilot, the combined signals from the gyro vertical and computer 61 are applied through a phase-sensitive demodulator 15, differentiating network 18, 19, magnetic modulator 24, transistor amplifier 26, and rectifier 28 to one winding 29 of a differential relay 30 which compares them with signals from accelerometers 35, 36 applied through a phase-sensitive demodulator 70, filter network 73, magnetic modulator 63, transistor amplifier 76, and rectifier 79 to the other differential relay winding 78. A comparison is thus made between desired and actual rates of pitch and differences above a predetermined value cause operation of relay 30 to disengage a clutch 68 and render servo-system 12 ineffective to adjust the elevators. To prevent such disconnection during manually controlled manoeuvres a switch 91 associated with manual controller 39 short-circuits the contacts of relay 30. To provide a further continuous check on operation of the auto-pilot, the combined signals from the gyro-vertical, computer 61 and the accelerometers are applied through a phase-sensitive demodulator 50 and a filter network 53 to one winding 64 of modulator 63 which compares them with signals from generator 13 applied through phase-sensitive demodulator 70 and filter network 73 to another winding 65 of modulator 63. A comparison is thus also made between desired and actual rates of servosystem operation and differences above a predetermined value also cause operation of relay 30 to disengage clutch 68. Compensation for variations of airspeed or Mach number is provided in the system by resistors automatically adjusted in accordance with those quantities. Arrangements for causing operation of relay 30 in the event of a power supply failure are referred to.