Patent GB-760683-A (GB)
Title: Improvements relating to the control of aircraft
IPC: G05D1/08
Filed: 1952-12-17
Abstract: 760,683. Controlling aircraft. SPERRY CORPORATION. Dec. 17, 1952 [Dec. 29, 1951], No. 32002/52. Class 4. [Also in Group XXXV] A control system for an aircraft having a primary control surface, has means for producing a characteristic signal when the control surface displacement reaches a limiting angle defined by a settable quantity set in accordance with the position of means whose position depends on the position of the centre of gravity of the aircraft. As described, the control is automatic, and the said means is positioned in accordance with the output of a device computing the long term average of the displacement of the control surface, which depends on the position of the centre of gravity of the aircraft. In Fig. 1, the displacement limits of the elevator 11 are set by the displacement of a trim tab 12. A gyro vertical 14 gives a signal to the elevator pick-off stator 19 which is mixed with a climb or dive bias signal from the manually controlled potentiometer 22, and fed to the elevator servo amplifier 21. The output of this amplifier feeds the field circuit of a generator 36 driven by a separately excited motor 43, and the generator output feeds a servomotor 37 driving the elevator drum 45 and cable 46 through a magnetic clutch 8. The output from generator 36 also feeds the field of a servomotor 47 driving the trim tab drum 49 and cable 50 through reduction gearing and a magnetic clutch 9. Motor 37 has a quick response to signals from the generator 36, and the elevator is actuated to correct short term errors in trim. Motor 47 is designed to have a slow response, and the trim tab is actuated to correct long term errors of trim. The position of the trim tab is thus representative of the long term average signal from generator 36, and hence of the long term average of the force on elevator 11, and of its displacement. The output of the elevator pickoff 24 is also fed into the amplifier in opposition to the signal from pick-off 17. The magnetic clutches 8 and 9 are wired in series with a relay 29 operable by the pilot to cut the automatic pilot in or out, and with two cut out switches 32 and 33. These are operated by mechanical differentials 59 and 60. The gearing is such that drum 45 drives the differentials in the same direction, and drum 49 drives them in opposite directions. The differentials are provided with cams 66 and 69 adapted to operate the contacts of switches 32 and 33. The arrangement is such that movement of trim tab 12 in one sense rotates the differentials in opposite directions, moving the cams 66 and 69 nearer to the switch operating positions. Movement of drum 45 is thus limited before one or other contact is opened disconnecting the clutches. Movement of trim tab 12 in the other sense moves both cams away from the switch operating position, allowing greater movement of drum 45 before the clutches are disconnected. Shafts 85 and 86 driven from the differentials may drive potentiometers in a balanced bridge circuit, a balance indicator being calibrated to show the percentage of elevator movement available to the pilot compared with normal conditions of flight. In the embodiment of Fig. 4, the boss 75 is adapted to be moved up and down by slider 76 moved with the elevator by shaft 44, and to left or right by slider 77 moved with the trim tabs by shaft 48. The boss 75 operates a cut out switch in the automatic pilot on contacting the sides of cam surface 74. It will be seen that the permissible movement of slider 76, i.e. of the elevators, is dependent on the displacement of slider 77, i.e. of the trim tab.