Patent GB-660551-A (GB)
Title: Improvements in or relating to aircraft flight control systems
IPC: G05D1/06
Filed: 1942-02-05
Abstract: 660,551. Electric control systems. SPERRY CORPORATION. Feb. 5, 1942. [Feb. 10, 1941] No. 1555/42. Class 40 (i). [Also in Group XXXV] In an automatic control system for aircraft the immediate heading of the craft in azimuth is continuously controlled, at least in part. by means responsive to a total control voltage or current derived from the sum of two voltages or currents, one of which increases or decreases as a function of the departure of the aircraft from a predetermined flight path, the other being derived from the rate of change of the said voltage and current ; the immediate heading in elevation is controlled by similar means. The total control voltage may include a component voltage dependent on the acceleration of departure of the aircraft from a predetermined path. The direction of the aircraft in azimuth is controlled by radio signals received by an antenna 6 and doubly modulated in known manner, the control being effected by a two-phase motor 8 one field of which is energised in the appropriate direction by current proportional in magnitude to signals fed through a range receiver 5 and heading control amplifier 27, the rudder being operated through a directional gyro 22 with a heading control 21 geared to the rotor of the motor 8. A follow-up signal is provided by a potentiometer 28 which has a contact arm geared to the motor 8 and feeds back into the heading control amplifier 27 a voltage proportional to the heading correction and bucking the signal from the range receiver 5. Motor 8 operates to change the heading of the aircraft until the bucking signal becomes equal to the positional signal. Simultaneously with the operation of the rudder and in order to avoid skidding, the aircraft is banked in proportion to the rate of turn effected by the rudder, by a bank control motor 32 connected through gearing 33 to the bank control 23 of the gyro pilot. The motor 32 is similar to the turn control motor 8 and is energised in one field by signals received through a bank control amplifier 35 from a rate-of-turn measuring device 34 responsive to the speed of the rudder motor 8. A follow-up signal proportional to the angle of bank is also applied to the bank control amplifier by a potentiometer 36 driven by the motor 32, this followup signal being arranged to buck the rate of turn signal received from the device 34. In addition, a rate of bank measuring device 37 is provided for measuring the speed of the bank control motor 32 and feeds back into the amplifier 35 a rate of bank signal which exercises a positive braking action as the resultant signal received by amplifier 35 from the rate of turn device 34 and follow-up potentiometer 36 approaches zero. Automatic control of the aircraft in a vertical plane is effected by a motor 40 geared to the elevator control 25 of the automatic pilot and controlled by a signal received through an amplifier 39 and glide path receiver 38 from an antenna 38a. A correction proportional to the deparature in altitude is provided by a follow-up potentiometer 42, and overrunning of the motor 40 and consequent hunting'is, obviated by feeding back to the amplifier 39 a braking signal derived from a speed-measuring device 43. Heading-control amplifier. The range receiver 5, Fig. 4 separates the two modulating frequencies received by antenna 6, and the output signals are amplified by tuned amplifiers 46, 47 coupled to a rectifier network 50 by transformers 48, 49. The derived D.C. signal, which is proportional to the relative strengths of the modulation frequencies and varies in sign in dependence on that which predominates, is fed through a low pass filter 181 and operates the vertical needle of the cross pointer instrument 7 in known manner. The D.C. output signal from terminals 51 is fed to terminals 52 of the turn control amplifier shown in Fig. 3. Fig. 4 shows also a power supply for the turn control motor, comprising a D.C. energized vibrator 53 which supplies A.C. at terminals 56 (connected to terminals 61 of Fig. 3) and, by means of a rectifier and filter circuit provides D.C. at terminals 59, 60, the latter being connected to terminal 62 of Fig. 3, One D.C. signal input terminal 52, Fig. 3 is connected over line 65 to the vibrator 72 of a vibrator modulator, the other terminal 52 being connected through a centre tapped resistor 31 and potentiometer 28 to a lead 66 connected to the centre tapped primary of a transformer 75 connected across the vibrator contacts. The D.C. signal is thereby converted to A..C. and applied through a conventional amplifying circuit, comprising valves 81, 83, 84 to a pair of triodes, 86, 87 connected in push-pull. The latter are connected through a transformer with a split primary 88 to a network which includes one field winding 92 of the motor 8. This field 92 lags or leads the other field 93 by 90 degrees according to the direction of the D.C. signal fed to terminals 52, thereby rotating the motor armature in the direction to restore the aircraft to the required heading. A corresponding movement is given simultaneously through a clutch 175 to the contact arm of potentiometer 28, which is connected to a battery 29 and provides a follow-up voltage between conductors 64, 66. Manual control of the aircraft is obtained by closing a switch 63 to short circuit the automatic input signal, and rotating a knob 177 geared to the potentiometer arm, thereby providing the correcting signal for the control circuit. A heading correction proportional to the acceleration of departure from course is provided by a circuit responsive to the rate of change of the positional signal, and comprising an adjustable inductance 96, Fig. 4, shunting the receiver output, and a resistor 97 and condenser 98 in parallel with one another and in series with the receiver output. When the D.C. error signal increases from a steady condition the temporary increase in reactance results in a proportionately increased voltage at terminals 51. Further, the condenser 98 byepasses the rising current from resistor 97 and additionally increases the output at terminals 51. There is thus superimposed on the receiver output a signal component proportional to the first and second derivatives of change. The converse takes place in response to movement of the aircraft towards course. The elements 96 to 98 are contained in the device 44 illustrated diagrammatically in Fig. 2. Banking control. The rate-of-turn measuring device 34, Fig. 1, which is associated with the banking control comprises an inductanceresistance bridge with two pairs of arms formed by field winding 92, Fig. 3, of the heading- control motor 8, resistance 102, inductance 99 and resistance 100 in series, and a resistance 101. An unbalance voltage proportional to the motor speed is opposed by the output of a follow-up potentiometer 36 geared to the banking motor 32 and the resultant signal applied over conductor 103 to the input transformer 113 of an amplifying circuit feeding the field winding 110 of the banking motor. The braking circuit for this motor, embodying a resistance-inductance bridge formed by field winding 110, inductance 111 and resistance 113 in series and resistances 112, 114 respectively, forms the subject-matter of Specification 660,575, [Group XXXV]. The resistanceinductance bridge associated with the field winding of the heading-control motor 8 may be adapted as a motor-speed measuring- device, as described in Specification 660,576. Elevator control. The operating circuits for the elevator control motor 40 are similar to those of the heading control motor, with the exception that they include a resistanceinductance bridge to provide a braking-signal as in the banking control. The glide path transmitter defines a path of constant intensity along which the aircraft is guided. A directional correction proportional to the rate of change of departure in a vertical direction from course may be derived from a bridge circuit embodied in a device 45 connected in the output circuit of the glide path receiver 38 and comprising a pair of oppositely arranged resistance arms 166, 167, Fig. 6, and mutually coupled indutances 168, 169. U.S.A. Specification 1,992,970 is referred to.