Patent GB-666471-A (GB)
Title: Improvements in and relating to automatic pilots for aircraft
IPC: G05D1/08
Filed: 1946-01-31
Abstract: 666,471. Automatic control systems for aircraft. SPERRY GYROSCOPE CO., Inc. Jan. 31, 1946 [Jan. 31, 1945], No. 3145/46. Class 38 (iv). In an automatic control system for aircraft a primary control signal is produced during unbanked flight at steady speed and applied to a servomotor which controls the elevator and thereby determines the angle of incidence of the wings, the banking of the aircraft to produce a banked turn causing an interrelated variation in the primary control signal which operates the elevator to pitch the aircraft upwardly to increase the angle of incidence of the wings to an extent such that the vertical component of the lift imparted to the aircraft is maintained substantially equal to the lift previously imparted during unbanked flight. In one form of the invention the fore- and-aft axis 35, Fig. 3, of the gyro-vertical, instead of being parallel to the longitudinal axis of the aircraft is inclined upwardly towards the front so as to be parallel with the zero lift chord of the wings. Fig. 4 shows the associated control system wherein the upwardly inclined fore-and-aft axis 35 is secured to the soft iron armature 21 of a transmitter 25 of the type in which all the controlling windings are stationary, so that when the aircraft banks the rotary movement of the gimbal ring 36 with axis 35 produces a signal in the fixed coil 22 which is amplified at 24 and applied to a servomotor 15 which operates the ailerons 18, 19 in the requisite sense. Simultaneously with the banking, the shaft 34 is rotated relative to the gimbal ring 36, and a toothed sector 33 transmits rotary movement to a transmitter 32 which is similar to transmitter 25 and produces a signal which is amplified at 28 and fed to the elevator servomotor 16. Manual control of the ailerons and elevators is effected through the operation of rotary knobs 27, 81 respectively, driving the rotors of transmitters 23, 31 to introduce a corresponding signal into the associated amplifier 24 or 28. Due to the inclination at which the axis 35 of the gyro is mounted, the banking of the aircraft causes the axis 35 to move around the surface of a cone, so that the elevation of its front end above the line of relative wind is reduced, and the resultant signal passed to the elevator amplifier 28 is as though the aircraft had pitched nose down. Consequently the automatic pilot moves the elevator 29 to increase the angle of attack and hence the total lift in a direction normal to the wing span in order to maintain the vertical component of the lift at the same value as before. In a modification, Fig. 6, the true vertical lift is measured by an accelerometer 96 which may be mounted on the casing 2 of the gyro-vertical 69, the latter having an athwartship pitch-axis 79 and a roll axis 68. The voltage V1 derived from the accelerometer is proportional to the true vertical acceleration and is constant so long as the aircraft maintains its height. This voltage is applied to the primary winding 92 of a transformer 93 provided with an opposing control-winding 94 fed with a voltage V4 which is derived from a potentiometer 97 connected to a constant single-phase A.C. supply V3 and initially adjusted to represent the normal vertical lift required to support the aircraft. Any difference voltage V5 is applied through the secondary winding 98 of the transformer to a follow-up amplifier 67 and opposed in known manner by a feed-back voltage provided by a generator 77 coupled to a follow-up motor 78 which runs in one direction or the other and drives a worm gear 44 on a separate shaft provided with clutches 57, 58. With clutch 57 engaged, the motor operates to adjust the potentiometer 97 until the control voltage V4 is equal to V1. When the control is set for a banked turn the clutch 57 is opened and clutch 58 engaged, so that the resultant difference voltage causes the motor 78 to drive the rotor of a transmitter Selsyn 99 with stator windings connected to those of a pitch Selsyn 32. The rotor of the pitch Selsyn is carried on the pitch axis 79 of the gyro-vertical, so that the signal fed through an amplifier 28 to the elevator servo-motor 16 has a component due to the pitch of the aircraft about the axis 79 and the component derived from the accelerometer. Specification 666,540 is referred to.