A supporting surface I for aircraft is provided with a control surface II adjustable on the surface I and an auxiliary surface III adjustable on the lower side of the surface II and adapted to participate in the adjustment of the surface II and also throughout at least part of its movement to be adjusted independently of the surface II; the surface II is adjustable so that it is given a motion compounded of a rotation and a fore‐and‐aft displacement. In one form, an auxiliary surface III is nested normally on a control surface II and is connected thereto by links 2, 3 and a tension spring. The surfaces II, III are simultaneously operated from a crank 4 through a link 6 and the surface III is adjustable independently of the surface II from a crank 7 through a link 9. In a modification, the surface II is connected by links to out‐riggers on the wing I so that the surfaces II, III are adjustable together and are moved rearwardly and downwardly. In a further modification, the abutting surfaces of the wing 1 and the surface II are so shaped as to leave a slot when the surface II is moved. The surface III may be arranged so that when in its extreme adjusted position it closes the slot formed at its leading edge during its initial movement. In another form, the surfaces II, III are operated by means concentric with the axis of articulation of the control surface II and in a modification the surface III is operable by cam means and only after a predetermined adjustment of the surface II. In a further form, the surfaces II, III are housed normally in a recess 23 at the rear of a wing. The surface III is again connected to the surface II on outriggers connected thereto by links 3, 2. The surfaces are adjustable as one by a rack 19 and a pinion 22. After the surfaces have been fully adjusted towards the rear, the surface III is independently adjustable through a rack and pinion. The leading edge of the surface III is shaped so that on adjustment of the surface III a slot between the surface II and the wing is uncovered. In a modification, the link 2 is replaced by a pin‐and‐slot and the rack for adjusting the surface III only engages with its pinion when the rack 19 has been disengaged, due to rearward adjustment of the surfaces. In a further modification, the surface III is adjusted by an endless band connected to the pin moving in the slot. In a further modification, the surface II comprises two portions separated by a slot and the surfaces II, III are nested normally in the underside of a wing. In a still further modification, the recess 23 is closed when the surfaces have been adjusted rearwardly by a surface IV and a slot forming slat 47 is adjusted concurrently with the surface III, this is effected by a rope 50 carrying a pin 56 which engages in a slot 55 in discs 57 connected to the slat 47 by a link 59 when the surface III is in position prior to adjustment, In a still further form, the surface II is connected to outriggers 63 by links 66, 64 and 69, 67 connected and operated from a link 71 as shown. The surface III is adjusted by rotation of the pivot axis 76 or through links from a rod rotatable in the surface II. In a still further form, the adjusting mechanism is carried by the leading edge of the surface II.
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