Patent GB-729721-A (GB)
Title: Improvements in monitoring systems for automatic pilots
IPC: G05D1/00
Filed: 1953-10-28
Abstract: 729,721. Automatic steering control systems. BENDIX AVIATION CORPORATION. Oct. 28, 1953 [Nov. 21, 1952], No. 29812/53. Class 38 (4). In a system for checking the operation of an automatic pilot, signals from means, separate and independent from the automatic pilot and responsive to the position of a control surface and an attitude of the craft, are combined with signals setting the attitude datum so that a resultant signal above a predetermined magnitude is produced upon faulty operation of the automatic pilot. In Fig. 3 combined valve and magnetic amplifiers 7<SP>1</SP>, 711, 7<SP>111</SP> of an autopilot, not fully shown, respectively control reversible two-phase electric servomotors 8<SP>1</SP>, 8<SP>11</SP>, 8<SP>111</SP> operating the elevators, ailerons and rudder through electromagnetically engaged clutches 12. Elevator amplifier 7<SP>1</SP> has an input (not shown) which is the algebraic sum of A.C. signals from the following sources (also not shown): (a) a variable inductive device constituting the pitch pick-off of a gyro-vertical producing a pitch deviation signal; (b) a variable inductive device associated with servomotor 8<SP>1</SP> producing a positional follow up signal; (c) a tachometer alternator associated with servomotor 8<SP>1</SP> producing a rate follow-up signal; (d) a variable inductive device associated with an aneroid bellows producing an altitude deviation signal; (e) a radio receiver producing a signal dependent on deviation from a glide path; (f) a variable inductive device associated with a knob for manual control of the aircraft pitch attitude. In a similar manner aileron amplifier 7<SP>11</SP> has an input (also not shown) which is the algebraic sum of A.C. signals derived from the bank pick-off of the gyro-vertical, a flight path radio receiver, a manually operated variable inductive device and position and rate follow-up generators associated with servomotor 811. Finally, rudder amplifier 7<SP>111</SP> has an input (not shown) which is the sum of A.C. signals derived from the pick-off of a rate of turn gyro, a manually operated variable inductive device and position and rate follow-up generators associated with servomotor 8<SP>111</SP>. To continuously check the operation of the aileron control, a signal from the bank pick-off 409 of a monitor gyrovertical 411 is opposed to a signal from a variable inductive device 417 associated with the ailerons and any difference, representing faulty operation, is applied through valve amplifiers 433, 450 so that if the error exceeds a predetermined value, determined by the bias on a valve 481, for a time dependent on the setting of a delay unit 472, relays 490 and 901 are operated to disengage the autopilot by deenergizing clutches 12. Indication of disengagement is given by lamp 997 and bell 998. To prevent disconnection of the autopilot when the above-mentioned difference signal is not zero, due to operation of the manual control knob or the flight path radio receiver, signals from the latter sources are combined and applied to the monitor circuit at 400. In a similar manner, operation of the pitch control is checked by a monitor circuit in which a signal from pitch pick-off 521 of monitor gyro vertical 411 is opposed to that from a variable inductive device 500 associated with the elevators the difference being applied to amplifiers 633, 650 and delay nuit 672 to operate a relay 492 and disengage the autopilot if the discrepancy is excessive and sustained. To prevent disconnection of the autopilot due to operation of the manual control knob or the glide path radio receiver, signals from these sources are injected into the elevator monitor circuit at 547,548. A pick-off 509 associated with aneroid 513 also compensates for altitude changes in the elevator monitor circuit. When the autopilot is disengaged either deliberately by manual operation of a switch 350 or by the monitor through relay 490 or 492, a relay 903 operates to connect the output of amplifier 650 to control a servomotor 840 which adjusts an inductive device 532 to maintain a zero signal in the elevator monitor circuit in readiness for re-engagement of the autopilot. Direct manual operation of the control surfaces is possible even when the autopilot is in operation but the effect on the monitor circuits results in disconnection of the autopilot. Specifications 662,831, 662,832, 662,853, 671,912 and 675,751 are referred to.