Patent GB-854732-A (GB)
Title: Aircraft automatic pilots
IPC: G05D1/08
Filed: 1957-02-15
Abstract: 854,732. Automatic control systems for aircraft. SPERRY RAND CORPORATION. Feb. 15, 1957 [March 15, 1956], No. 5237/57. Class 38 (4). In an automatic pilot a servomotor operating a control surface to control an aircraft about one of its axes is driven at a rate proportional to a signal derived from means directly responsive to angular acceleration of the aircraft about that axis. Control surface servo systems.-In Fig. 1B the difference between electric signals from damped E-type pick-offs associated with a pair of linear accelerometers 15, 16, suitably arranged in an aircraft to give a combined response to roll acceleration only, is applied to an amplifier 25 the output of which energises a servomotor 26 operating the ailerons through reduction gearing 27 and an electromagnetic clutch 28. Rate of servomotor operation is made dependent on roll acceleration by feedback from a tachometer generator 29 to the input of amplifier 25 and a relationship suited to flight conditions is ensured by controlling the generator excitation by a potentiometer 30 operated in dependence on airspeed, altitude and/or Mach number. Similar servo systems controlled by pairs of accelerometers 33, 34 and 35, 36 responsive to yaw and pitch acceleration respectively control the rudder and elevators. Clutches 28, 28<SP>1</SP> associated with the aileron and rudder drives may be disengaged by operation of a manual switch or upon incorrect operation of the automatic pilot. Synchros such as 40 which are coupled to the servomotors when they are disengaged apply follow-up signals to the inputs of the servo amplifiers to keep the servomotors positioned for re-engagement without shock. Synchros 45, 46 associated with a gyro-vertical 44 and a synchro 51 associated with a directional gyro 50 apply longer period stabilizing signals to the aileron, elevator and rudder servo systems respectively. Further long period stabilization is provided by signals, responsive to linear acceleration, derived from one of each pair of accelerometers and applied to the respective servo systems through lag networks 47, 48 and 52. Altitude reference control systems.-The gyro vertical is automatically erected by liquid level devices acting through amplifiers, Fig. 6 (not shown). This erection is automatically disabled by further liquid level devices mounted on the gyro-vertical and responsive to linear acceleration when rate of turn exceeds a predetermined value. In Fig. 5 a shaft 137 positioned by directional gyro 50 through a followup system involving synchros 139, 140 and a servomotor 142 adjusts a synchro 136 which is energized by signals from a flux valve compass 130 so that output signals representative of directional gyro error are available to correct the gyro through an amplifier 132 and torquer 138. Flux valve compass 130 is mounted on a universal support and maintained level by a pendulous mass (not shown). Gyro correction by the flux valve compass is disabled in polar regions and latitude correction (not shown) substituted. Before re-introducing magnetic correction a knob 144 adjusting the stator of synchro 140 is operated manually to produce correspondence between the compasses with the aid of an indicator 144<SP>1</SP>. A change of course signal may be produced by operation of a knob 135 movement of which is transformed into an electric signal by synchros 164, 165 associated with a differential gear 163. Pitch commands.-When it is desired to climb or dive a knob 55, Figs. 1A and 7, operating a potentiometer 56 spring biased to its central position is operated temporarily in the appropriate sense to apply a signal, modified as a reciprocal of Mach number at 58, to a motor-type integrator 61 which operates a synchro 66 so as to apply a signal to the elevator servo system. By suitably positioning a switch knob 76, Fig. 7, altitude, airspeed or Mach number may be automatically maintained constant by applying a signal from the appropriate measuring device 80, 81 or 60 to the elevator servo system through a limiter 85 and lag network 48. This signal is also applied to the elevator servo system through integrator 61 the response of which is slowed under these conditions by solenoid operation to change the ratio of gearing 65. Alternatively by suitable positioning of a switch 'knob 151 signals from a glide path radio receiver 87 may be substituted and under these conditions a signal from vertical accelerometer 35, modified in dependence on angle of bank by a potentiometer 70 is applied to integrator 61 through a switch 78 to provide damping. A servomotor 90 energized by the output of the elevator servo amplifier adjusts an elevator trim tab or horizontal stabilizer through highreduction gearing. A clutch 68 associated with the elevator drive may be disengaged by manual operation of a switch 38, Fig. 7, synchro 72 being introduced to cause follow-up of the elevator servomotor and a switch 75 being changed over so that integrator 61 follows up on the signal from the gyro-vertical. Turn and roll commands.-If switch knob 151 is moved to either of its two " bank " positions any change of course signal produced by operation of knob 135, modified in dependence on Mach number at 170, is applied through a limiter 171 to a motor-type integrator 100 which operates a synchro 106 so as to apply a signal to the aileron servo system. A switch operates to select a different limit for limiter 171 in each of the two positions of knob 151. Synchro 106 also applies a signal, modified as a reciprocal of Mach number at 128 to a motor-type integrator 101 which operates a synchro 106<SP>1</SP> so as to apply a signal to the rudder servo system. A signal which is a function of bank angle, derived from a potentiometer 188 and modified in dependence on dynamic pressure at 89, is applied through limiter 85 and lag circuit 48 to the elevator servo system to compensate for loss of lift during banking. To reduce the tendency to slow oscillation when on a Northerly heading the signal from the compass amplifier 132 is applied through an integrator 146 to the rudder servosystem. Alternatively, or in addition the gyrovertical error signal may be applied to the aileron servo system. Alternatively with switch knob 151, Fig. 7, in its " manual position, turns may be produced by operating a knob 150 in the appropriate sense to apply a signal directly to integrator 100. If the rudder and aileron servomotors are engaged when. the angle of bank exceeds a critical value, the liquid levels responsive to linear acceleration, provided to disable erection of the gyro-vertical, also cause yaw integrator 101 to continue to follow up. The signal stored by aileron integrator 100 reduces so that the aircraft automatically rolls towards level and at the critical value of bank normal conditions are restored and the aircraft follows a compass course. If switch 38, Fig. 7, is moved to its lower position only the short period stabilizers viz. the accelerometers, are effective during control of the aircraft. Radio course control.-By suitably positioning switch knob 151, Fig. 7, automatic turn signals derived from a VOR beam radio receiver 86 are applied to the aileron servo system together with signals from a range selector 176 which is set to correspond with the bearing of the beam along which it is desired to fly. Asymptotic approach to the beam is thus ensured. When an ILS approach is to be made knob 151 is positioned so that signals from a localizer radio receiver are applied to the aileron servo system. Under these conditions a unit 177 produces an additional control signal proportional to rate of change of displacement from the beam to ensure asymptotic approach. When displacement from the beam falls below a predetermined value the displacement control signal is applied to the aileron servo system through an integrator 127. Damping is introduced by applying to integrator 127 a signal, dependent on rate of movement of the aircraft relative to the beam, which is derived from yaw accelerometer 33 and the bank pick-off of the gyro-vertical. Specifications 854,733, 854,734 and 854,735 are referred to.