Patent GB-897580-A (GB)
Title: Improvements in or relating to automatic trimming systems for the control surfaces of dirigible moving craft
Inventor: STONE COLWYN FRANCIS
IPC: B64C13/00
Filed: 1959-11-04
Abstract: 897,580. Controlling aircraft. SMITH & SONS (ENGLAND) Ltd., S. Sept. 29, 1960 [Nov. 4, 1959], No. 37407/59. Class 4. [Also in Group XXXV]. In an automatic trimming system for a control surface of a dirigible craft, there is provided in the craft control means for controlling the operation of an actuator for positioning said surface, said control means including an input member for said actuator, a control run forming a mechnical linkage between said input member and a manual control member and being arranged to position the input member in response to movements of the control member, an artificial feel device arranged to apply a resilient load acting against movement of the control run in either direction from a datum position and an automatic control system having an output motor coupled directly to the control run and capable of operation automatically to position the control surface in response to manoeuvre demand signals generated within the system and the trimming system comprising load relieving means actuable to relieve load on the output motor of the automatic control system by adjusting said datum position of the control run, a trimming motor for driving the load relieving means, means coupling the trimming motor to the automatic control system for energization in dependence upon the load on the output motor, and means responsive to adjustment of said datum position by more than a predetermined amount to inhibit action of the trimming motor in the sense to increase the said adjustment whilst permitting action of the trimming motor in the sense to decrease the said adjustment. An aircraft elevator 1 is positioned by a hydraulic actuator 2 in accordance with movement of input member 3 connected by control run 4 to control column 5 or auto-pilot servo-motor 7. The motor 7 is energised by amplifier 8 which receives one input as a demanded rate of elevator movement generated at 9 and another input as a feed-back signal from generator 10. Control run 4 is attached to the output member 11 of a screw jack 12, the body of which is connected to a member 13 positioned with reference to aircraft structure by feel springs 14 and connected by a link 15 to a piston in an air chamber 16, the pressure in which is controlled by a conventional pilot installation, to provide feel to column 5. Jack 12 may be operated to trim elevator 1 and thus relieve column 5 or servo 7 of continuously-imposed loads. Operation is by means of an electric motor 24, rigidly located with reference to the body of jack 12 as by a platform 30 attached to the jack body. Motor 24 is energized from amplifier 8 through an electric network 31, the connection being such that an output from amplifier 8 which is symptomatic of a load on motor 7 produces operation of motor 24 in a sense as to relieve this load. Thus motor 24 effects automatic trim of the elevator when the auto-pilot is operating, the characteristics of the network 31, the motor 24 and the coupling between the motor 24 and control run 4 being such that only long term loads on the motor 7 are relieved. However, run-away operation of motor 24 could result in the application of dangerous undesired elevator movement, and to prevent this motor 24 is connected to a spring loaded slipping clutch 32 which has a slipping torque greater than the maximum steady torque which can be generated by the motor. The driven member of the clutch carries a ratchet wheel 33 engageable by a double pawl 17 pivotally mounted on platform 30, but normally held in a mid non-engaging position by centering springs 18. The tail of the pawl is extended beyond platform 30 for engagement, upon lateral movement of the platform upon operation of jack 12, with either of a pair of spring loaded buffers 19, the springs being provided to permit maximum movement of the control run under normal manual or automatic operation. If, for example, motor 24 runs away in a sense such as to retract jack 12 this will tend to move control run 4 to the left as viewed in the drawing, such movement being resisted by motor 7 with the result that the part of the control run to the left of motor 7, including platform 30, will be moved to the right against the resistance of feel mechanism 13-16 until pawl 17 engages the right hand buffer 19 and is rocked thereby to engage ratchet wheel 33 and restrain the associated element of the slipping clutch which causes motor 24 to be retarded. Alternative apparatus for operating pawl 17 comprises a spring-loaded switch operated by member 13 in either direction about a mean position to energize solenoids associated with pawl 17.