622,105. Aircraft control systems. BRITISH THOMSON-HOUSTON CO., Ltd. Jan. 4, 1946, No. 398. Convention date, Jan. 6, 1945. [Class 4] [Also in Group XXXV] An aircraft rudder is controlled by a composite signal from the rudder and elevator control-signal generators, the proportion of the components of the signal depending on the angle of bank so that when the bank is vertical the rudder is controlled solely by the elevator signal. Corresponding arrangements may be made to control the elevator which, when the bank is vertical, is controlled solely by the rudder signal. The invention is applicable to a system of servo operation under manual control, but is described in connection with an automatic pilot. Operation of automatic pilot to maintain straight and level flight. Any deviation in roll is corrected by a differential transformer 53 with a movable primary actuated by a gyro 14. The output of this transformer acts through a discriminating rectifier on valve-controlling solenoids to operate a fluid-pressure servomotor driving the ailerons in the appropriate direction, movement of the ailerons being accompanied by movement of the primary of a second signal producer 56 similar to 53 and acting in opposition to it. Similar arrangements are made to preserve a predetermined pitch angle which is variable by a knob 83 which adjusts a bias voltage in the circuit of the pitch signal generator 54 and the opposing generator 57 controlled by the elevator position. In these conditions the apparatus 61 which also is included in the circuit is without effect. The rudder is similarly controlled from a gyro compass 13, apparatus 60 which is included in the signal circuit being without effect at this stage. Operation of automatic pilot during a banked turn. The turn is initiated by a control knob which causes the operation of a course-changing motor 74 in the appropriate direction at a selected speed, injects a voltage of the appropriate phase and amplitude into the rollstabilizing circuit to induce a desired angle of bank and moves the primary windings of mixing-transformers 60, 61. The primary of transformer 60 is fed from the rudder control generator and receives a signal which depends on the speed of the course-changing motor. It has two secondaries. One, connected in the elevator control circuit, passes on a signal proportional to the sine of the angle of the primary with the normal position and the other, connected in the rudder control circuit, passes on a signal proportional to the cosine of that angle. In consequence, the whole of the rudder signal goes to the rudder in normal flight and to the elevator when the bank is vertical. The mixing transformer 61 is of similar construction, but has its priming connected to the pitch signal generator and gives the whole of its output to the elevator control circuit in level flight and to the rudder when the bank is vertical. The mixing transformers may be operated from the gyro vertical in accordance with the actual angle of bank instead of manually in accordance with the desired angle and may have laws other than those in the arrangement described.