Patent GB-626287-A (GB)
Title: Improvements in automatic control means for aircraft
IPC: G05D1/04
Filed: 1943-07-28
Abstract: 626,287. Automatic control systems for aircraft. SPERRY GYROSCOPE CO., Inc. July 28, 1943, No. 12296. Convention date, July 28, 1942. [Class 38 (iv)] In an automatic pilot for aircraft a control signal is developed in the direction control arrangements during a turn and applied to alter the bank angle maintained by the automatic pilot as set on or in connection with an altitude reference. An azimuth gyroscope 1 controls the rudder 3 by an A.C. signal derived from an inductive pick-off 4 and passed through an amplifier 5 to energize a torque motor 6. A continuous turn may be imposed by a knob 15 which is adapted to determine the speed at which a member 9 of a Selsyn element 8 in the control chain is turned; as shown, a ball 14 coupling a constant speed disc 11 to a cylinder 13 is radially adjusted by the knob 15. A change of course may be obtained by turning the member 8<SP>1</SP> of the Selsyn element 8 by means of the knob 10. The ailerons 18, 19 are controlled by a gyro-vertical 2 operating an inductive pick-off 25 giving a reversible-phase A.C. signal which is passed through an amplifier 24 to energize a torque motor 61. To obtain banking upon initiation of a continuous turn the knob 15 operates also a similar transmitter 20, the output of which is in series opposition with the signal from the roll pickoff. To ensure that the bank is correct for the rate of turn the voltage appearing across the rudder torque motor 61 is applied through a delaying circuit 26 in series with the output of the bank transmitter 20 ; the delay action avoids transient effects when entering the turn, or during gusts of wind. The elevator 29 is controlled from a pick-off, similar to pick-off 25, preferably placed within the gimbal ring of the gyrovertical 2 ; the pick-off output is passed through an amplifier 28 to a torque motor and co-operates with a signal which may be applied by a manual pitch control knob 81. The torque motors are all arranged to control hydraulic servomotors as described in Specification 612,804. An automatic climb and glide control 36, as described in Specification 626,285, may also operate through the amplifier on the elevator 29. The amplifiers 5, 24, 28 are arranged as shown in Fig. 2. The signals from elements 9, 25 and 30 are applied through a transformer 41 to the grids of a double phase-sensitive detector-and-rectifier tube 42 which is energized from an A.C. source 54 through cathode bias resistors and stabilized by a back-coupling transformer 43 ; screen grids are excited from an A.C. source 54<SP>1</SP>. These sources are set in phase coincidence or opposition with the grid or signal voltages so that unidirectional opposed voltages appear on resistances 46, 46<SP>1</SP>, the resultant of which varies in magnitude and polarity with the strength and phase of the input signal. Two rate-taking circuits 45, 89 and 47, 91 are cascaded with each of these resistances and a byepass resistance 50 is provided so that D.C. voltages are applied to the grids of an amplifier tube 53 containing the first and second time derivatives of the signal, whereby hunting of the controls is prevented. A transformer 48 is interposed in this grid circuit so that signal voltages representing the sum of the signals from elements 20, 25, 26, or from elements 30, 31 may be introduced without the time derivatives (see also Specification 626,364, which is referred to) ; these voltages are also subject to control by a voltage limiter 40 (back-to-back copper oxide rectifiers), and a current-limiting resistor 401, preventing excessive action of the servo systems and unsafe conditions arising. The voltage limiter also prevents saturation of the valve 53 by the gyro output alone such as would annul the anti-hunting provision. A transformer 52 also permits any other control factor to operate the servo systems, e.g. the altitude control 36. The tube 53 controls a power amplifier 60 which furnishes current for the torque motor coils 61 and at terminals F, G, a voltage for the bank correction circuit. The bank correction circuit, Fig. 3, comprises resistances and condensers arranged so that the input voltage produces a proportionate time-delayed voltage across resistances 70, which is applied to the grids of a stabilized amplifier tube 72 in the output circuit of which is a transformer 73, which furnishes a phasereversible A.C. output voltage at terminals D, E, and comprises a voltage limiting circuit 110. Since any persisting rudder control signal will produce a voltage for adjusting the ailerons, the invention will tend to correct lateral lack of trim in straight flight.