Aircraft Wing Drooping Leading Edge Device

This invention relates to high lift leading edge devices for aircraft.

Leading edge devices are used to improve the low speed handling characteristics of aircraft having wings designed to operate at high subsonic and supersonic speeds, for example, by increasing the available lift of the wing during the approach and landing modes, when a high speed airfoil would be aerodynamically inefficient.

One known arrangement of high lift device is the slat, comprising spanwise sections of flap, or similar shortchord length airfoils, extendible from the leading edge of the wing when required, to modify the airflow, thus to induce flow circulation over the wing upper surface with a resultant increase in lift.

There are, however, other known means of physically modifying the basic airfoil shape such that the wing camber may be varied during flight. This must, of necessity, require a wing structure both capable of withstanding induced aerodynamic loading throughout the whole flight regime but at the same time geometrically adaptable when required in order to assume the desired camber, i.e. its structure must be substantially flexible, at least over that portion known as the leading edge.

Known arrangements of flexible leading edge involve operating linkages of significant complexity tending to limit their use in high speed wings which, ideally, should have a low thickness to chord ratio of the order of 5%. A further consequence of such complexity is in the weight and cost penalties which may be incurred. Furthermore, the flexible nature of the design demands that the wing skins, in addition to strictly conforming to the optimised aerodynamic high speed profile, be adequately flexible over at least that portion of the chord to be adapted to the required low speed profile. In known arrangements this has involved a localised moving top panel having a free trailing edge slidable over the adjacent fixed wing structure to accommodate differential movement induced by the flexure and having the correct degree of stiffness to resist lifting under aerodynamic forces. But there may be difficulties in matching this panel profile to that of the wing profile at more than one setting due to the inherent stiffness of the unconstrained trailing edge, resisting the deformation to any other desired profile. Thus there may be unacceptable aerodynamic discontinuities. Yet again, the arbitrary profiles demanded of the panel are frequently not the parabolic profiles which are assumed naturally by a plate fixed at one edge and loaded at the opposite free edge. If the demanded profile is required to meet an acceptable degree of accuracy then a means of adjustment has to be provided which may need to be considerable in extent to cope with the inherent stiffness of the panel and thus inconsistent with the available volume in thin wing sections. It is an object of the present invention to provide an improved form of leading edge which will overcome these various shortcomings.

According to the present invention, the leading edge structure and skin is of substantially constant shape and is hinged to droop into a low speed configuration, flexible skin sections being provided to extend between the constant shape upper and lower skin portions of the leading edge structure and the upper and lower skins of the main body of the wing, the upper flexible skin section being attached to link means for controlling its profile contour as the leading edge structure droops.

One arrangement according to the invention will now be described by way of example with reference to the accompanying drawings in which:

FIG. 1 shows a leading edge portion of a high speed aircraft wing.

FIG. 2 shows the same leading edge portion in its low-speed deflected configuration.

The leading edge flap device of the embodiment described is illustrated in FIG. 1 with the wing in its high speed or cruise configuration. That portion of the wing as illustrated comprises an upper wing skin 1 and a lower wing skin 2 and a spanwise extending front spar member 3 having forward facing flanges 4 and 5 and a substantially vertical web 6 extending forwardly of the spar 3 and providing a pivotal attachment 7 for a leading edge structure 9 having an outer skin 10, conforming to the wing profile, supported on a diaphragm 11 whose rearwardly extending leg 12 is hinged at said pivotal attachment 7. The diaphragm 11 is internally shaped to a substantially arcuate profile 13 and the intersection of this profile with the wing upper surface approximately defines the rearward upper boundary 14 of the skin 10 whose inner surface 10a is `scarfed` to substantially conform to the arcuate profile 13. The rearward lower boundary 15 of the skin 10 is defined by overlapping the lower wing skin 2 extending forward of the spar 3 to terminate at 16. The overlap is `scarf-jointed` to ensure minimal discontinuity of the wing profile but there are no physical attachments, thus permitting a sliding action during the camber change.

The upper wing skin 1 extending just forward of the spar flange 4 has a rebate 17 in its outer surface substantially conforming in thickness to a flexible top skin 18 to which it is bolted. This skin, which in the preferred arrangement is of standard plate, chemically etched and formed as required, extends forward in conformity with the wing profile except for its most forward portion which passes beneath the leading edge structure, conforming to the arcuate profile 13 and terminating in a reinforcing lip 19. The profile of the flap at any setting is initially designed to a parabolic form, most naturally achieved by a plate fixed at one edge and loaded at the opposite edge. The desired profile of the flexible top skin 18 is maintained by a pair of double piano hinge link assemblies 20 and 21 having riveted attachment to the top skin and bolted attachments 23 to the rearwardly extending leg 12 of the leading edge structure assembly 9, the relatively small size of the hinges ensuring that their effect is as close to the flexible top skin 18 as ideally possible.

Now referring to FIG. 2 showing the flexible leading edge in its low speed configuration, it can be seen that very little rotation of the hinge link assemblies 20 and 21 is required to deform the skin 18 to the desired profile at the full setting and at any intermediate position. As the leading edge is deployed through its operating range, rotation of the leading edge structure 9 about its pivot centre 7 causes a differential sliding action between its arcuate profile 13 and the flexible top skin 18 which together with an accompanying angular variation of the hinge link assemblies 20 and 21 deforms the skin to achieve an overall low speed upper surface profile. In any attitude aerodynamic forces will tend to draw the flexible skin 18 into close contact with the skin 10 of the leading edge structure and form a seal. Additionally, the lower rearward portion 24 of the leading edge skin 10 is similarly deflected, as shown, throughout the operating sequence thus minimising lower surface discontinuities.

Advantages of this invention principally reside in the following features:

(a) The general arrangement with the leading edge structure being of substantially fixed configuration, the elastic deformation being restricted to a small portion of the wing upper surface.

(b) The design of the flexible skin permitting the use of lightweight, uncomplicated components able to be accommodated in the thinnest airfoil sections.

(c) Simplicity of manufacture and assembly.

(d) Overall advantage of life/cost/weight effectiveness.