Patent GB-809278-A (GB)
Title: Aircraft control system
IPC: G05D1/00
Filed: 1956-11-16
Abstract: 809,278. Automatic control systems for aircraft; phase-sensitive circuits. BENDIX AVIATION CORPORATION. Nov. 16, 1956 [Dec. 19, 1955], No. 35146/56. Class 38 (4). [Also in Groups XXIV, XXXIII, XXXIX and XL (c)] A control system for aircraft provided with an automatic pilot for operating control surfaces through servomotors and having a manual controller for operating at least one of the surfaces directly, comprises means whereby displacement of the manual controller to operate a control surface automatically disables the action of the corresponding servomotor, while leaving the other servomotors effective. In the embodiment described, the manual controller acts on the elevators and ailerons, the autopilot controlling these and the rudder. Engagement of the autopilot maintains the existing aircraft attitude, or the existing rate of turn, or reduces the pitch and roll angles to predetermined maxima, or maintains the existing altitude or level flight. Control surface servo systems.-Provision is made for control by V.O.R. or I.L.S. inputs. Fig. 1 shows the rudder signal channel and servo system. The latter comprises an amplifier 11 energizing a motor 12 which may be connected through a gear train 13 and a clutch 14 energized by a winding 108 (see Group XXIV), to the rudder (not shown). Inputs to the amplifier 11 comprise a control signal from potentiometer 171, a surface position feedback signal from potentiometer 145 energized by an inductive pick-off 17 coupled by a shaft 141 to the rudder, a motor shaft position feedback signal from potentiometer 124 energized by an inductive pick-off 15 geared to the motor shaft, a motor torque feedback signal from potentiometer 162 energized by a torque-sensitive device 18 coupled to the motor shaft, and a rate feedback signal from potentiometer 128 energized by a tachometer rate generator 16 coupled to the motor shaft. The generator 16 serves to damp the operation of motor 12 and to prevent overshoot in yaw. The amount of surface position feedback is controlled by a shaft 191 adjusting the wiper 178 of potentiometer 145 in accordance with airspeed, whereby the movement of the rudder for a given control signal is adjusted to suit the airspeed. Similar servo systems actuate servo tabs on the ailerons (not shown), Fig. 7, with primed preferences, and the elevators (not shown), Fig. 8, with double primed references. In addition, the torque feedback signal from the device 1811, Fig. 8, is coupled by a transformer 2001 to an amplifier 11<SP>111</SP> energizing a motor 12<SP>111 </SP>operating elevator trim tabs (not shown) through gearing 13<SP>111</SP> and a clutch 14<SP>111</SP> energized by a winding 108<SP>111</SP>. Magnetic phase-sensitive amplifier.-Each amplifier 11 comprises a conventional transistor preamplifier coupled to a two-stage magnetic phase-sensitive amplifier (Fig. 2). The first stage is a resetting amplifier comprising two cores 41, 42 having winding 56, 57 connected at 60 and coupled by diodes 43, 44 to the secondary winding 47 of a coupling transformer 40. An A.C. supply on leads 58 is connected between junction 60 and the centre tap 59 of winding 47. Two further windings 67, 68 are connected at 79 and are coupled through diodes 61, 62 to output leads 78, 79<SP>1</SP>, and to capacitors 72, 73 joined at 75. An A.C. supply on leads 74 is connected across junctions 75 and 79. The two A.C. supplies are connected so that diodes 43, 44 conduct on one half cycle, and diodes 61, 62 on the other. With no input signal, diodes 61, 62 conduct on one half cycle to saturate cores 41, 42. Diodes 43, 44 conduct on the other half cycle to reduce the flux in cores 41, 42 to zero. This cycle repeats, and the voltages at terminals 70, 71 are always equal. An A.C. signal developed in winding 47, however, has the effect of reducing the saturation of cores 41, 42 unequally when diodes 43, 44 conduct. This affects asymmetrically the currents passed by diodes 61, 62 during the next half cycle, whereby a resultant D.C. voltage appears on leads 78, 791. The second stage comprises a bridge having two cores 80, 81 each having three .windings. Four of these windings are connected in bridge fashion, an A.C. supply being connected across junctions 85 and 86, and an A.C. output is derived from terminals 87 and 88. The control windings 89 and 90 are earthed at a common junction and are energized from leads 78, 791. With no signal on the latter, the bridge is balanced and no signal appears on lead 91. If a D.C. current flows in leads 78, 79<SP>1</SP>, however, the impedances of the opposed pairs of windings are changed in opposite senses, and the unbalance of the bridge results in an A.C. signal on lead 91. Rudder signal chain (Fig. 1).-A lateral accelerometer 196 (which may be a damped pendulum) is coupled to the rotor 197 of an inductive pick-off 198, the stator 199 energizing a potentiometer 200, a signal from wiper 202 being fed to an integrating servo system 203 typical of several such systems used. The input signal is fed to a potentiometer 213 a tap on which is connected to an amplifier 209 controlling a constantly excited motor 210 which drives a rate generator 211 energizing potentiometer 213, and drives the rotor 218 of an inductive pick off 212 through gearing 214, a clutch 217 controlled by a winding 216, and a stop and centring device. The output signal on stator 220 energizes potentiometer 194. The portion of the output of generator 211 fed to amplifier 209 by potentiometer 213 ensures that the motor speed/energizing voltage characteristic of the motor is linear, whereby the position of the motor shaft represents the time integral of the input signal, as does the voltage on potentiometer 194, when the clutch is in. When the clutch is out, the stop and centring device 215 centres the rotor 218 with respect to stator 220, reducing the signal on the latter to zero. In addition, stops limit the displacement of rotor 218. One end of potentiometer 194 is connected to wiper 202. The wiper of potentiometer 194 thus. derives a signal representing the lateral acceleration when clutch 217 is out, and, when the clutch is in, representing the acceleration and its integral from the time of clutch engagement. This signal is fed to a potentiometer 171, and a localizer beam error signal may be added by a change-over switch 1410. Potentiometer 171 is energized by the stator 170 of an inductive pick off whose rotor 169 is coupled to a rate of yaw gyro 166, which serves to prevent oscillation and overshoot in yaw. Aileron signal chain (Fig. 7).-The roll axis of a gyro vertical 290 is coupled to the rotor 294 of an inductive pick off 288, and the angle of roll signal derived by the stator 298 is fed to a synchronizer 300 typical of several such systems used. The angle of roll signal is fed to the stator 312 of an inductive pick off 302. Any signal on the rotor 314, due to lack of correspondence between the positions of rotors 294 and 314, is fed through potentiometer 320 to an amplifier 308 controlling a motor 310, which has an A.C. supply controlled by a switch 1067. If the switch is closed, the motor drives a rate feedback generator 306, and if clutch 323 is in, the motor drives the rotor 314 through a stop and centring device 304, to align rotor 314 with stator 312, removing the energization of the motor. Thus if switch 1067 is closed and clutch 323 is in, the signal on potentiometer 320 is zero. If the switch 1067 is opened, rotor 314 is fixed, and the signal on potentiometer 320 represents the departure of the roll angle from that at the time of switch opening. If clutch 323 is put out, the centring device centres rotor 314, and the signal on potentiometer 320 represents the roll angle measured from level flight. The generator 306 serves to damp operation of the synchronizer. Potentiometer 320 is coupled through switch 416 and potentiometer 409 to potentiometer 174. A localizer beam error signal may be added by change-over switch 430. Potentiometer 174 is energized by a rate of roll gyro 167, serving to damp operation in roll and the signal on its wiper is fed to the aileron servo system which thus has inputs from potentiometers 174, 409 and 320. Potentiometer 409 is energized by a heading error signal derived from a compass 340, synchronizer 341, and integrator 342. The synchronizer 341 operates like the synchronizer 300 except that clutch 355 is kept in, whereby if switch 1075 is closed the signal on potentiometers 361 and 362 is zero. If switch 1075 is opened, the signal represents the departure of the heading from that at the time of opening. This signal is fed from potentiometer 361 to an integrator 342 similar to integrator 203. If clutch 384 is out, the rotor 392 is centred, and no signal develops on potentiometer 395. If the clutch is put in, and switch 1077 is closed, a heading error integral appears on potentiometer 395. If the switch 1077 is then opened, this signal remains stationary until clutch 385 is put out, when it drops to zero. Switch 397 connects potentiometer 395 to earth or to the heading error signal on potentiometer 362, and the resultant signal is coupled by transformer 408 to potentiometer 409. Elevator signal chain (Fig. 8).-The pitch axis of the gyro vertical 290 is coupled to the rotor 295 of an inductive pick off 289. The resulting signal on the stator 299 is applied to a synchronizer 301 similar to synchronizer 300, so that the signal on potentiometer 321 is zero, or represents the pitch error or the angle of pitch according to the positions of switch 1116 and clutch 325. This signal is fed through switch 526 and potentiometer 516 to an integrator 544 similar to integrator 342, whereby the signal on potentiometer 545 is the integrand of the input or zero, depending on the position of clutch 554. Wiper 564 thus derives a signal which is the output of potentiometer 321 with or without i