Patent GB-542944-A (GB)
Title: Improvements in or relating to actuating mechanism for aircraft controls
IPC: B64C13/00
Filed: 1940-08-02
Abstract: 542,944. Controlling aircraft. DE HAVILLAND AIRCRAFT CO., Ltd., BISHOP, R. E., and TAMBLIN, W. A. Aug. 2, 1940, No. 12537. [Class 4] A control surface fitted with a servo-tab is controlled by means including a doubleacting, initially stressed, yielding connector so that the surface and tab move together in either direction until a predetermined resistance is encountered, whereupon the tab moves to a position in which the air pressure upon it assists the movement of the control surface. Means for giving the tab an initial setting may be provided. In one form, Fig. 1, a telescopic member 16, 17 has the part 17 connected to an arm 28 fixed to the rudder spindle 29, and a collar on the part 16 is connected by a link 34 to one arm of a bell crank lever 37 pivoted on the spindle 29. A pin 38 carried by the other arm supports a twoarmed lever 39, one end of 'which is connected by a link 41 to a horn 143 on the tab. The other end of the lever 39 is connected by a rod 44 to a screwed socket 42 on the fuselage, the socket being rotable by a sprocket and chain for adjusting the initial position of the tab. The part 16 has a central fixed washer 20 through which passes a rod 21 having discs 22, 24, 25 fixed to it, the disc 22 engaging inturned edges 23 on the part 17. Initially stressed springs 18, 19 are interposed between the washer 20 and the disc 24 and between the end of the member 17 and the disc 25 which normally rests against the washer 20. The levers 28, 37 consequently move together until the resistance encountered is sufficient to compress one or other of the springs 18, 19, the parts then taking up the position shown in chain lines. The maximum relative displacement is determined by stops on the rod 21. Twin rudders actuated through two such telescopic devices are described. Fig. 3 shows an aileron pivoted at 66 and moved by an arm 64 connected by a link 63 to a lever 53 pivoted on the spindle 52 of a pulley 50 movable by the pilot. The servo-tab is connected by a link 60 to an arm 59, pivoted at 66 and connected by a link 58 to the pulley, the arms 59, 64 normally occupying parallel positions. The lever 53 has a roller 54 engaged on opposite sides by spring pressed plungers 55 in cylinders 57 on the pulley. Alternatively the aileron may be controlled from the pulley by a telescopic member similar to that shown in Fig. 1, the plunger being connected to the aileron and the collar being connected to an arm similar to the arm 59, Fig. 3. Fig. 5 shows an alternative control for a single rudder in which a rocking lever 80, connected to the rudder bar, is coupled by a telescopic member 15 to an arm 28 fixed to a pin 82 on the rudder, and by a rod 81 to a lever 90 pivoted about the rudder spindle 29. The servo-tab is connected by a link 85 to a two-armed lever 84, 86 pivoted on the pin 82, and arm 86 being connected by a link 87 to a two-armed lever 88 pivoted to the lever 90 at 89. The other end of the lever 88, which is normally coincident with the axis of the spindle 29 is connected to a screwed shaft 91 which screws into a threaded sleeve rotatable by the pilot for adjusting the initial setting of the tab.