Month in the Patent Office

A mass balance for an aircraft control surface pivotally connected to an element of an aircraft comprises an arm integral with said surface extending into said element and arranged to remain within said element, and a balancing lever pivoted on said arm so as to have two portions of unequal length, the longer being directed forwards and carrying a mass balance, and the shorter being directed rearwards and connected to means for varying the position of said lever in response to variation in the position of the control surface, so that to each position of the surface there corresponds a position of the lever which is always within the said element. In the embodiment of FIGS. 1, 2 and 3, the control surface 1 has a spar 10 secured to a part 37, FIG. 3, rotatably mounted in the airframe structure 39a, and has two forwardly extending portions 4, 4a, FIG. 1, accommodating pivots 5 of a lever 6 having at one end a balance weight 7, and at its other end a ball joint 9 working in a slot 62 in a member 60 slidable laterally on rods 61a, 61b by a link 13 attached to a casing 16 containing a ball race 17 secured to rod 18, FIG. 3. Secured to a bearing ring 36 is a toothed segment 20a engaging a pinion 22 integral with a toothed wheel 24 and mounted on a shaft 23 journalled in the airframe, so that rotation of the bearing ring 36 involves rotation of wheel 24. This wheel engages a member 26 toothed at 25 and having an internal thread engaging a thread 27 cut on shaft 18, which also has an extension 28 slotted and keyed at 29 to prevent rotation, so that rotation of wheel 24 shifts rod 18 longitudinally. A pin (not shown) is normally spring‐urged into bores 41, 42 in ring 36 and part of the airframe 39a respectively, so that ring 36 and the segment 20a remain fixed relative to the wing as the surface rotates, that is fixed relative to pinion 22, and the rod 18 is not actuated. As a result, the balancing lever 6 moves as though it were integral with the control surface. When, however, the surface has rotated through an angle a, FIG. 2, one of other of pins 48a or 486, FIG. 1, operate on a cam surface to withdraw the pin from bore 42, so that ring 36 can rotate relatively to the wing. At the same time, a finger 35 contacts one or other of two abutments on ring 36, so as to rotate the ring with the surface. This rotates pinion 22 and wheel 24, and rod 18 is moved axially. As a result, rod 52 is raised against spring 59, to depress a plunger 56 and lock segment 20a and ring 36 to the surface. The movement of rod 18 slides the member 60, which modifies the pivotal relationship of lever 6 to the surface, so that as in FIG. 2, the counterbalance 7 remains within the wing contour as the surface is progressively deflected. Axial movement of rod 18 pivots rod 6 relatively to the surface through a bell crank device instead of member 60.