Patent GB-611037-A (GB)
Title: Improvements in or relating to automatic control systems
IPC: G05D1/08
Filed: 1945-03-09
Abstract: 611,037. Automatic control systems. SMITH & SONS (ENGLAND), Ltd., S., and MEREDITH, F. W. March 9, 1945, No. 6005. [Class 38 (iv)] In an automatic control system for maintaining the attitude or heading of an aircraft at a datum value by means of a servomotor responsive to deviations therefrom, means are provided for adjusting the datum by a second servomotor responsive to deviations of these conditions while the craft is under manual control. The invention is described with reference to a system for automatically flying a craft on a straight course or manually effecting changes of course and attitude in pitch. Stabilization in straight flight. A platform 11, Fig. 1, carries rate gyros 1, 5, 8 for yaw, roll and pitch respectively and a pitch pendulum 10, the controls being organized to keep the platform horizontal in space and headed in a constant direction. The elevator motor 19<SP>1</SP> is controlled through an amplifier 21 by the difference between a signal from 8 proportional to the rate of pitch and a signal from a generator 22<SP>1</SP> coupled to motor 19<SP>1</SP> proportional to the rate of movement of the elevator. A third component is provided by the pitch pendulum 10, but this is small and does not affect stabilization but determines the normal attitude of the craft. This may be modified under control of handle 51 which controls a motor to tilt platform 11. Similar control is exercised for lateral stabilization by gyro 5 and bank pendulum 7 which in normal flight is not short-circuited as shown. The rudder motor 19 is similarly under the control of a signal from rate-of-turn gyro 1 and an opposing signal from a generator 22 proportional to the rate of rudder movement. An additional signal is provided by a selsyn receiver 27 controlled by a compass 3, relay 30 being de-energized under these conditions and clamping the selsyn rotor in the position in which it was at the end of the last change of course. Course changing. To turn the craft, the pilot moves the handle 50 to operate relays 30, 31 and unbalance a self-balancing bridge, the motor of which then tilts the platform 11 to an extent corresponding to the movement of the handle. The automatic aileron control then acts to give the craft a corresponding angle of bank (pendulum 7 being shunted out at this time) and the rudder motor 19 is controlled by a signal having components proportional-respectively to the rate of turn (from gyro 1), the tangent of the angle of bank (from a potentiometer 24 controlled by the means for tilting the platform 11 and arranged to give a signal of such a value that the turn matches the bank when the craft is travelling at its cruising speed), the amount of side-slip if any (from a pendulum 25), the speed of the rudder motor (from generator 22) and the angle through which the rudder is moved. The last-mentioned signal is obtained from a selsyn 29, the rotor of which in these circumstances is clamped in the position in which it was when the change of course was initiated. Its purpose is to increase the damping of the system which is reduced by the presence of the side-slip correction During this operation, the rotor of selsyn 27 is short-circuited and allowed to follow the movement of the distant compass so that at the end of the change of course it will be clamped in a position representing the new course. Manual control. Predeterming pitch angle. During manual control, relay 66, Fig. 5, which is locked up during automatic control is released by button 69. The clutches 17 between the control surfaces and the automatic control motors are released and the motor 15 controlling the pitch angle of the platform 11 with respect to the aircraft is put under the control of the pendulum 10 so that when the automatic control takes over, the craft maintains the same attitude in pitch as when it was being controlled by the pilot. Constructional details and modifications. Fig. 3 shows an embodiment of pendulums 25 and 10, while Fig. 4 shows tangent potentiometer 24. An embodiment of the rate-of-turn device used at 1, 5 and 8 is shown in Fig. 2. Turning movement causes gyro 36 to precess against spring 41 and move arm 39 over resistor 40 so that an output voltage proportional to the rate of turn results. To ensure that selsyn 29 follows selsyn 28 when the craft is under automatic control and selsyn 27 follows selsyn 26 when changes of course are being effected, a second winding may be provided on each of the receiver rotors and energized when the other is providing the signal, as in Fig. 6 (not shown). Alternatively, a second selsyn may be associated with each receiver having its station connected to the transmitter and its rotor mechanically coupled to the first receiver, and energized in the same way as the abovementioned second winding, as in Fig. 7 (not shown). Specifications 576,248, 576,249, 576,351 and 611,005, [Group XXXVIII], are referred to.