Patent GB-802536-A (GB)
Title: Improvements in and relating to aircraft control systems
IPC: G05D1/00
Filed: 1956-04-11
Abstract: 802,536. Automatic control systems for aircraft. GENERAL ELECTRIC CO. April 11, 1956 [April 11, 1955], No. 11031/56. Class 38 (4). [Also in Groups XXIX and XXXIII] An aircraft control system includes a manual controller connected to a linkage controlling the position of a control surface, a first reversible motor for positioning one portion of the linkage relative to the remaining portion to position the surface under control of an automatic controller without displacing the remaining portion or the manual controller, and a second reversible motor for positioning the whole linkage and the manual controller, wherein the second motor is energized upon predetermined relative displacement of the two portions of the linkage. The pilot's control element 24 is pivoted at 25, and connected to a rod 28 having a threaded end received in an internally threaded sleeve 29. A member 31 fast to sleeve 29 has two extensions 32, 33 gripping a spool 34 on a rod 14, so that the member 31 can rotate with respect to rod 14, but the two must move axially together. Rod 14 is connected to the valve of an hydraulic valve block 13 controlling an hydraulic jack 12 connected to move a control surface 10, whereby the surface 10 is moved in correspondence with the valve rod 14. The rod 28 and sleeve 29 constitute a turn-buckle which can be rotated by gears 30, 35 driven by an electric motor 26 energized by an amplifier 42, whereby the movement of rod 14 is determined by the positioning of the control member 24 and the output of amplifier 42. The inputs to the amplifier comprise a signal derived by the slider 54 of a potentiometer 52 controlled by a rate gyro 55, a signal derived by the slider 49 of a potentiometer 47 controlled by a position gyro 50, an answer signal derived by the slider 59 of a potentiometer 58 controlled by a gear 57 meshing with gear 30, and a rate feed-back signal generated by a tachometer generator 56 driven by the motor 26. An acceleration feedback signal or inputs from devices sensitive to airspeed, altitude or accelerations may also be provided. Short term deviations of the aircraft from a selected altitude thus energize motor 26 which is a quick response short range motor and move rod 14 to actuate the control surface to correct such deviations. When the turnbuckle has rotated a predetermined amount in either sense, a blade 65 on rod 14 contacts one or other of members 63, 64 mounted on an L-shaped member 61 supported from rod 28 by a sleeve 62. This energizes a reversible electric motor 27 in one or other sense, to position the pivot 41 of a bar 38 connected at 39 to rod 28. Centering springs 36, 37 extend from this bar to fixed structure. Thus any long term energization of motor 26 results in energization of motor 27. If the pilot is flying " hands off," motor 27 moves rod 28 the springs 36, 37 making bar 38 pivot intermediate its ends, to adjust the surface 10 until the error signals energizing motor 26 reverse in polarity. The blade 65 is then withdrawn from contact 63 or 64, and motor 27 is de-energized. If the aircraft is being flown manually, motor 27 displaces the position of zero " feel " of the control element 24. Motor 27 is a slow response, long range motor which trims the aircraft in case of e.g. shift in the aircraft centre of gravity, and relieves motor 26 of long term displacements large enough to make contacts 63, 65 or 64, 65. The slider 71 of potentiometer 72 is connected to motor 27 and provides a de-generative input to amplifier 42 to prevent instability, if an electromagnetic clutch 83 is energized. Motor 27 may also be actuated manually by closing a switch 76 mounted on the control column, to energize motor 27 over one or other of lines 81, 82 to trim the feel out.