Patent GB-831683-A (GB)
Title: Improvements in control-conditioning devices, especially for the controls of aircraft and flight trainers
Inventor: ORAM JOHN ANDERSON
IPC: B64C13/24
Filed: 1955-04-28
Abstract: 831,683. Fluid-pressure servomotor-control systems. AIR TRAINERS LINK Ltd., [formerly AIR TRAINERS Ltd.]. April 19, 1956 [April 28, 1955], No. 12298/55. Class 135. [Also in Group XXXIII] In a control conditioning device comprising a spring 18, Fig. 1, the stiffness of which can be varied under load, connected at one end to a support 12 through a position controlled ram 10 having a valve 16 connected to the other end of the spring 18 via a linkage 30, 28, 22 of adjustable ratio, movement of the latter end of the spring 18 under the influence of an applied load results in the anchored end of the spring being moved to an extent determined by the adjustment of the linkage. Upon movement of a control column or rudder bar, not shown, which is connected to the lever 20, the operator meets the resistance of the hydraulic ram 10, connected to a lever 14 that is fixed to the torsion bar spring 18 attached to the lever 20, the latter being joined to the lever 22 by a cylinder 24. The spring 18 and cylinder 24 permit a small relative displacement between the levers 20, 22 and lever 14, but since lever 22 is coupled to the valve 16 by lever 28 and rod 30, the valve body being fixed to the ram 10, the latter changes in length and the valve body " follows up " the valve movement, subsequent movement of the lever 30 being effected by the ram. The lower end of lever 28 is slotted at 32 and co-operates with a pivot 34 in a rack 36 meshing with a gear on the shaft of an electric motor 38; a sector 40 carries the motor 38 and rack 36 and is pivoted on a shaft 42, the sector 40 having teeth engaging a gear driven by another electric motor 44. Adjustment of the position of the pivot 34 in the slot 32 either manually or by the motor 38 alters the stiffness of the control by varying the deflection of the spring 18 for a given ram movement; the slot 32 may extend up to or beyond the point of attachment of the rod 30, and when the pivot coincides with the rod 30 ram movement is impossible. The datum to which a free control returns can be varied by energizing the motor 44 to rotate the sector 40, the control always returning to the same position irrespective of the pivot position. In a modification, the lever 28, Fig. 2, is centred between springs 46, 48 slidable on a rod 50 connected to the lever 22, Fig. 1, the position of lever 28, Fig. 2, being determined by a link 54 which can be moved when a roller 56 presses the latter into contact with a friction roller 58 of an automatic pilot servomotor 60; one or other of the springs 46, 48 is deflected in the event of the control position demanded by the servomotor 60 differing from the zero load position of the control, so that on release of the link 54 the lever 28 and hence the control are suddenly returned to the control position to simulate the violent jump of the control which occurs upon disengagement of the automatic control when one control surface is out of trim. The deflections of springs 46, 48 may operate a trim indicator, not shown. Where the apparatus is used in an actual aircraft the control surface is operated from the end of the ram that is connected to the lever 14. The stiffness of the system may be adjusted in accordance with airspeed.