RELATED APPLICATION

This application claims priority from French Patent Application no. 18 74356 filed Dec. 28, 2018, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The invention relates to a leading edge slat of an aircraft wing such as a drooping leading edge slat, of which the structure of the slat is optimized.

More particularly the invention relates to a stiffening structure of such a leading edge slat.

BACKGROUND OF THE INVENTION

The wing leading edge slats are present on an aircraft on the horizontal planes, wings and horizontal planes of the fin, as well as on the vertical planes such as on the fin.

The slats present on an aircraft wing, are drooping leading edges which make it possible, through their controlled displacement, to modify the aerodynamic flow around the wing and to modify the list thereof at a given speed.

A civil transport aircraft generally comprises 3 to 5 slats distributed over the leading edges of the wings, from the root of the wing to the tip, which follow the change in the section of the wing between the two ends thereof.

A slat is thus a lifting surface of the wing which can recover, at a given spanwise position, up to 30% of the total lift of the wing section.

TheFIG. 1diagrammatically shows the section, in the plane x-z of a slat according to prior art. The axis system shown is that of the aircraft the fuselage extends parallel to the X axis and the wing substantially according to the Y axis.

Such a slat comprises an upper surface skin (110) extending from the leading edge (slat) to the trailing edge. Which is, according to certain embodiments, formed from several portions.

A spar (120) is assembled to the upper surface skin (110) to which ribs are linked.

An inner skin (130) is linked to the upper surface skin (110) by the intermediary of a stiffening system (140) such as rails, ribs, even a honeycomb structure according to the embodiment.

Several ribs distributed along the axis y, are linked to the spar and to the upper surface skin creating a box structure, on the leading edge side as well as on the trailing edge side.

The slat is linked to the wing by the intermediary of one or several interface fittings (not shown) connected by the intermediary of maneuvering arms or rails to mechanical or hydraulic actuator means in order to carry out the relative controlled displacement of the slat in relation to the wing.

The structure diagrammatically shown inFIG. 1corresponds to an example of metallic construction, but the constructions made of composite of prior art are similar.

This mechanical design has changed little.

In terms of rigidity, a slat has to be sufficiently rigid to resist the aerodynamic forces.

The aerodynamic forces that the slat is subjected to are transferred to the wing via the interface fittings and the maneuvering arms or rails which must consequently be dimensioned according to the number of fittings.

When a slat is linked to the wing by more than two interface fittings, the differences in the deformed shape between the wing and the slat produce overstressing in the interface fittings and the maneuvering elements, which is all the more so substantial when the number of interface fittings is high.

Indeed, when the connection of the slat with the wing comprises more than two fittings, which is frequent, the mounting is hyperstatic. This hyperstatism combined with the differences in deformed shapes is responsible for half of the forces to which said fittings and the slat are subjected to, with the rest coming from the aerodynamic load.

This phenomenon requires dimensioning the interface fittings and the maneuvering means in consequence which has an influence on the mass, and increases the risk of binding or jamming, which have to be taken into account in the dimensioning.

Moreover, the leading edges of the wing elements are exposed to impacts, in particular to impacts with birds.

In a conventional design such as shown inFIG. 1, the skin that forms the leading edge slat, is linked to the spar and stiffened by straight ribs (150) perpendicular to the spar. According to embodiments up to 18 ribs are thus distributed along the axis y between the spar and the skin forming the leading edge, thus forming a structure with multiple boxes.

According to an embodiment of a slat, each one of these ribs (150) weighs approximately 200 grams which is a total weight that can be attributed to this stiffening of about 3.6 kg.

In case of impact, on the slat, these straight ribs, highly rigid generate a direct transfer of the energy of the impact to the spar.

The majority component of the impact speed of an object or of a bird on the leading edge is parallel to the axis x and corresponds to the displacement speed of the aircraft.

Due to the substantial stiffness of the ribs (150) in the direction x, these ribs do not favor the distribution of the energy of the impact. The risk is damage to the spar.

In the case where the spar is damaged, the residual resistance of the structure after impact is called into question.

Multiplying the ribs, in addition to the increase in the mass, increases the rigidity of the slat and reduces its ability to follow the deformations of the wing, increasing the efforts of interface linked to the differences in the deformation between the wing and the slat.

In addition, this architectural solution of prior art is even more unfavorable with regards to the resistance in terms of the resistance to an impact in the case of a construction made from a composite material, of the type of material that has a rupture energy absorption capacity, at the same rigidity, less than that of metallic materials.

The document U.S. Pat. No. 9,708,030 describes a leading edge slat of which the structure is optimized for the resistance to impacts and which comprises teeth that aim to improve the resistance to the pulling off of the leading edge.

OBJECT AND SUMMARY OF THE INVENTION

The invention aims to overcome the disadvantages of prior art and relates for this purpose to a leading edge slat of a wing element of an aircraft, said aircraft defining a mark that comprises a main fuselage axis x and a spanwise axis y, with the wing element procuring a lift along an axis z, comprising a skin forming the leading edge slat, a spar linked to said skin and a stiffening structure linked on the leading edge side to said spar and to the skin, wherein the stiffening structure is formed from a formed sheet metal comprising a plurality of bosses distributed according to the length of the leading edge, said bosses extending between the spar and the inner face of the skin and wherein the bosses form domes that comprise a zone in contact with the skin and tangent to the latter, the hollows between the bosses being in contact with the spar and tangent to the latter. In comparison with prior art, this stiffening structure makes it possible to distribute the energy of the impact over a larger surface, which limits the risks of degradation of the spar, but also in a more substantial volume of material, making this solution compatible with a composite construction, while still retaining facility in terms of assembly.

The invention is implemented according to the embodiments and alternatives disclosed hereinafter, which are to be considered individually or according to any technically operable combination.

According to an embodiment, said slat is a moving leading edge slat. In this embodiment and in comparison with prior art, the stiffening procured by the structure object of the invention is less at an equal impact absorption capacity, thus favoring the following of the deformations of the wing and limiting the deformation incompatibility stresses.

Advantageously, the flanks of the bosses form an angle less than 90° in relation to the surface of the spar and to the surface of the skin. The inclination of the flanks of the bosses favors the absorption of the energy of the impact through the stiffening sheet metal as well as through the skin forming the leading edge slat.

According to an embodiment, the stiffening structure is formed from a composite material with continuous fibers in a thermoplastic matrix. This embodiment makes it possible to lighten the structure, by taking advantage of the best distribution of the energy of the impact to allow for a construction made of composite material.

Advantageously, the skin forming the slat and the spar are also formed from a composite material with continuous fibers and with a polymer matrix, and the stiffening structure is linked to the spar and to the skin by welding. This embodiment allows for a gain in mass and facilitates assemblies.

According to a particular embodiment, the pitch of the bosses is variable over the length of the leading edge slat.

