MOVABLE FLOW BODY HAVING A HYBRID LOAD INTRODUCTION RIB

A movable flow body for an aircraft including a front skin having an outer surface configured to be contacted by an ambient flow, and an inner surface opposite the outer surface, at least one load introduction rib having a skin interface side and a drive side, at least one coupling element arranged on the drive side for coupling with a drive mechanism, and at least one interface element removably attached to the front skin interface side. The at least one interface element includes a bonding surface having a shape corresponding to the shape of the inner surface of the front skin. The at least one interface element is materially bonded to the inner surface of the front skin.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of the European patent application No. 22210465.5 filed on Nov. 30, 2022, the entire disclosures of which are incorporated herein by way of reference.

FIELD OF THE INVENTION

The invention relates to a movable flow body for an aircraft, a wing for an aircraft as well as an aircraft.

BACKGROUND OF THE INVENTION

For increasing the lift coefficient of a wing of an aircraft, high-lift systems are known. These often include trailing edge flaps and movable leading-edge devices, which are selectively operable. For example, they are usually activated during takeoff and landing, i.e., moved from a retracted into an extended position.

Leading-edge devices may include leading-edge slats, which are flow bodies usually having a front skin, a back skin, and mechanical interfaces for coupling with a slat track or another drive mechanism. One or several ribs are often provided inside the flow bodies for stiffening and for carrying the skins, wherein the front skin is usually riveted to the ribs. The mechanical interfaces may include a dedicated load introduction rib that is connectable to the drive mechanism. Due to the expected loads, a load introduction rib is usually made from a metallic material, such as aluminum. Riveting a rib to a skin that is directly exposed to an ambient airflow may lead to slight imperfections on the skin that may increase the induced drag. Thus, a common joint to connect a rib to a skin of a flow body may require an elaborate reworking and coating to minimize the induced drag

Exemplarily, EP 3 712 055 A1 proposes a wing leading-edge device comprising a flow body having a front side, a back side and a plurality of ribs arranged in the flow body, wherein at least one of the ribs is a load introduction rib comprising at least one first lug for coupling with a drive mechanism. The device further comprises a second load path component having at least one second lug, wherein the second load path component is at least connected to the load introduction rib, such that a second opening of the at least one second lug is co-axial with a first opening of the at least one first lug.

SUMMARY OF THE INVENTION

It is an object of the invention to propose an alternative leading-edge device that has a reduced induced drag.

A movable flow body for an aircraft is proposed, comprising a front skin having an outer surface configured to be contacted by an ambient flow, and an inner surface opposite the outer surface, at least one load introduction rib having a skin interface side and a drive side, at least one coupling element arranged on the drive side for coupling with a drive mechanism, and at least one interface element removably attached to the front skin interface side, wherein the at least one interface element comprises a bonding surface having a shape corresponding to the shape of the inner surface of the front skin, and wherein the at least one interface element is materially bonded to the inner surface of the front skin.

The flow body may comprise an elongate shape that is intended for extending along a spanwise direction of the wing to which it is attached. The flow body further comprises a certain profile contour, which is mainly determined by the desired aerodynamic characteristics. It is preferred that the flow body is sufficiently stiff to serve for the intended purpose. It is conceivable that the flow body comprises a plurality of stiffening elements, such as ribs, spars, and stringers, which are distributed inside the flow body.

It is conceivable that the at least one load introduction rib refers to two or more load introduction ribs, if a flow body with a larger spanwise extension is considered. The load introduction rib is mechanically adapted for providing a reliable load transfer between the flow body and the drive mechanism, such as a slat track mechanism or similar. The coupling element is provided at the drive side of the load introduction rib and may include at least one of a variety of different mechanical elements that allow to couple the load introduction body with the drive mechanism. The skin interface side, however, is dedicated for the attachment of the load introduction rib to the front skin through the respective at least one interface element. The skin interface side may be arranged at a distance to the drive side, for example opposite to the drive side. The skin interface side comprises at least one interface element, which is materially bonded to the front skin.

For providing a material bonding, the at least one interface element comprises the bonding surface, which is shaped in a way that it is flushly placeable onto the inner surface of the front skin in a predetermined bonding region. Thus, if the front skin is curved, the bonding surface is curved in the same manner.

The at least one interface element may comprise a design that is compatible with the design of the load introduction rib. For example, the load introduction rib mainly comprises a flat shape with one or a plurality of cantilevers. The at least one interface element may be based on a material sheet having a sufficient material thickness and two sections that include the attachment surface and the bonding surface.

Materially bonding the bonding surface and the inner surface may be conducted by one of several possible processes that allow to provide a sufficiently sturdy connection of the interface element and the front skin. For example, the interface element and the inner surface may be bonded by gluing, welding, or co-curing. In all cases, a riveting connection between the interface element and the front skin can be eliminated, which leads to a clean outer surface of the front skin and an elimination of induced drag stemming from rivets.

The attachment of the at least one interface element and the load introduction rib may be conducted through common mechanical fasteners, such as bolts, screws, nuts, rivets and the like. Since these mechanical fasteners are arranged inside the flow body, they do not protrude into the air flow and thus do not influence the aerodynamic behavior of the flow body. Thus, the number, size and shape of fasteners does not need to be strictly limited to limit the generation of induced drag.

A core aspect lies in the separation of the at least one interface element and the load introduction rib. The material of the at least one interface element can be adapted to the material of the front skin. Preferably, the material could be selected such that a material bonding process with the front skin can be improved. The material of the at least one interface element may differ from the material of the load introduction rib. For conducting a maintenance, the at least one interface element may simply be unfastened from the load introduction rib and reattached again, after the relevant maintenance procedure is accomplished.

This design principle provides several advantages. The outer surface of the front skin is smooth and does not comprise any rivet-induced imperfections, which lead to increasing the induced drag of the flow body. Also, the attachment process between the front skin and the load introduction rib is simplified due to the elimination of several mechanical fastening steps, such as drilling and reworking rivet holes, placing a sealant, placing rivets, smoothing, and coating the rivet connections on the outer surface. Furthermore, the material of the interface element and the load introduction rib can be chosen according to mechanical requirements. The load introduction rib may comprise a sufficiently rigid material that allows a reliable load transfer as well as a mechanical rigid integration of the at least one coupling element into the load introduction rib. However, the at least one load introduction element may comprise a different material that is adapted to the front skin, for an improved bonding. The dimensional extension of the interface element may be chosen to provide a sufficient stability and limitation of local mechanical stresses. In particular, the material of the interface element may conform the material of the front skin.

In an advantageous embodiment, the at least one interface element comprises a plastic material, preferably a thermoplastic material. It is advantageous, if the front skin of the flow body is made from a fiber reinforced plastic material, such as CFRP or the like, for improving the mechanical properties and reducing the overall weight. While it would be advantageous in general to provide more components using this material, it is conceivable that a load introduction rib made from the same material may comprise a larger cross-sectional profile in comparison to a metallic load introduction rib. Also, it may be more complicated to manufacture. However, the material of the at least one interface element may be adapted to conform the material of the front skin, such as a fiber reinforced plastic material. The respective plastic material may be a thermoset plastic material or a thermoplastic material. The plastic material constitutes a matrix for reinforcement fibers embedded therein. If the front skin comprises a thermoset matrix, it may be feasible to co-cure the front skin and the at least one interface element, such that an integral part consisting of the front skin and the at least one interface element is provided. However, if the front skin comprises a thermoplastic material as a matrix, the at least one interface element may comprise the same and both components may be welded to each other. However, gluing is also conceivable. Suitable thermoplastic materials may, for example, polyetherketoneketone (PEKK), polyetheretherketone (PEEK), polyetherimide (PEI), polycarbonate (PC), polypropylene (PP) or others.

In an advantageous embodiment, the at least one load introduction rib is made from a metallic material. For example, the load introduction rib is made from an aluminum alloy, while Titanium may also be conceivable.

In an advantageous embodiment, the at least one interface element is attached to the load introduction rib through fasteners. As mentioned above, these fasteners may include bolts, screws, nuts, rivets or the like. It is advantageous if the fasteners are removable without destruction, which is the case with using screws or nuts. For preventing a vibration-induced loosening, the fasteners may be secured through suitable securing elements, e.g., a pin.

In an advantageous embodiment, the skin comprises a thermoplastic material. The thermoplastic material may, as mentioned above, include polyetherketoneketone (PEKK), polyetheretherketone (PEEK), polyetherimide (PEI), polycarbonate (PC), polypropylene (PP) or others. The at least one interface element may comprise the same type of material, such that both components can be welded to each other.

In an advantageous embodiment, the at least one interface element is welded to the skin. If both components comprise the same thermoplastic material, welding may be conducted through ultrasonic welding, laser welding, induction welding or resistance welding. However, if the front skin comprises a thermoset material and the at least one interface element comprises a thermoplastic material, welding may be provided through using a thermoplastic coupling layer that is co-cured with the front skin, to which the at least one interface element is weldable.

In an advantageous embodiment, the at least one interface element comprises an attachment surface for attachment to the rib, wherein the bonding surface and the attachment surface are arranged at an angle of 40° to 140° to each other. The bonding surface is adapted for flushly resting on the inner surface of the front skin, wherein the bonding surface may either be welded or glued or otherwise materially bonded to the inner surface. The attachment surface may include a number of through-holes for leading fasteners through, for attachment to the respective load introduction rib. The size of the bonding surface is dimensioned to achieve a sufficiently sturdy connection to the front skin. By providing both surfaces at an angle to each other, the load introduction rib may be completely flat at the interface side and the at least one interface element creates a fastening angle.

In an advantageous embodiment, the attachment surface is arranged parallel to a main extension plane of the rib. Thus, the mechanical load acting onto the attachment surface is mainly a shear load and the available surface for providing fasteners is not strictly limited.

In an advantageous embodiment, the at least one coupling element comprises at least one lug. The respective lug comprises an opening, through which a fitting in the form of a bolt, an axle or any other suitable component can be lead through. For improving the mechanical properties, the lug may comprise a bushing made from the same or another material than the respective load introduction rib. The lug constitutes a local load interface, through which mechanical loads between the drive mechanism and the load introduction rib are transferred.

In an advantageous embodiment, the flow body comprises at least two interface elements for each load introduction rib. For example, two interface elements may be attached to the same load introduction rib. The interface elements may then extend into opposite directions and create an enlarged bonding surface. Both interface elements may be attached to the same load introduction rib through the same fasteners.

The invention further relates to a wing for an aircraft, the wing having a fixed wing body and at least one flow body according to the above, wherein the at least one flow body is movably arranged on the fixed wing body.

Still further, the invention relates to an aircraft having at least one wing according to the above and/or at least one flow body according to the above.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG.1shows a movable flow body2having a front skin4, a load introduction rib6and exemplarily two interface elements8. For simplification purposes, the front skin4is only indicated by dashed lines and is otherwise substantially left out in this illustration. While it is conceivable, that the flow body2is a leading-edge slat, other types of flow bodies2are not ruled out. The load introduction rib6is exemplarily arranged parallel to a longitudinal axis (x) of an aircraft, to which it is attached. In particular, it may also be substantially parallel to a plane spanned by the longitudinal axis x and a vertical axis (2), as indicated by x and z arrows. It is further conceivable that the load introduction rib6is perpendicular to the local leading edge of the flow body2.

The front skin4is distinctly curved to provide desired aerodynamic characteristics. Thus, the load introduction rib6, which stiffens the front skin4, as well as the interface elements8have a corresponding shape to maintain the given shape of the front skin4. It is to be understood that several further ribs may be arranged inside the flow body2, wherein one or two of the ribs may be provided in the form of a load introduction rib6as shown herein. The interface elements8are exemplarily made from a material sheet, which is bent to form an elongated, curved component with an angled cross-sectional profile.

In this exemplary embodiment, the front skin4comprises a thermoplastic material, e.g., in the form of a fiber reinforced plastic material. The fibers may include carbon, glass, aramid, or other suitable fibers. As explained later on, other materials are not ruled out and the front skin4may also comprise a thermoset material or a metallic material.

The load introduction rib6comprises two coupling elements in the form of a first lug10and a second lug12. Both lugs10and12are couplable with a drive mechanism, which is not shown herein in further detail. For example, the drive mechanism may include a linkage mechanism and an actuator, which act to move the flow body2into a retracted position or one of several extended positions. The load introduction rib6may be made from an aluminum alloy and comprises usual material thicknesses and dimensions. The coupling elements10and12are arranged on a drive side14, while the interface elements8are placed at a skin interface side16, which is opposite to the drive side14.

Here, the interface elements8are attached to the load introduction rib6through a series of fasteners18, which exemplarily comprise bolts20and nuts22. The bolts20are sticked through through-holes in both interface elements8and the load introduction rib6, such that these elements are clamped together when fastening the nuts22.

The interface elements8are exemplarily made from a thermoplastic material, which conforms the thermoplastic material of the front skin4. Each of the interface elements8comprises an attachment surface24and a bonding surface26. Both surfaces24and26are arranged at an angle to each other, which in this case is about 90°. Thus, each of the interface elements8constitutes an angle to the interface side16of the load introduction rib6.

The interface elements8are shaped such that the bonding surfaces26conform the shape of the front skin4, such that the bonding surfaces26rest flushly on the inner surface of the front skin4.

InFIG.2a sectional view of the flow body4is shown, wherein the sectional plane is indicated by the letters A inFIG.1. Here, a stiffening section28of the load introduction rib6is apparent, which is provided in the form of a projecting collar. The angle between the bonding surface26and the attachment surface24is shown as a, which in this example is about 90°. Depending on the shape and position of the flow body2, other angles are conceivable. For example, the load introduction rib6may be arranged parallel to an x-z-plane of the aircraft, while the front skin4extends along a leading edge of the wing, which has a certain sweep angle. Thus, if two interface elements8are used, one of them may comprise an angle a of clearly below 90°, while the other one of them may comprise an angle a of clearly above 90°.

One of the fasteners18extending through both interface elements8and the load introduction rib6is indicated. Spacing and number of fasteners18can be selected according to the expected loads.

The bonding surfaces26of the interface elements8are bonded to an inner surface32of the front skin4. The bonding may be accomplished by welding, if both interface elements8and front skin4have compatible, weldable materials. For example, the front skin4is that made of a thermoplastic material, which may be welded to the interface elements8. However, it is also conceivable that the front skin4is made from a metallic material, which may be glued to interface elements8made from a plastic material or from a metallic material. Welding of a front skin4made from a metallic material to interface elements8made from a metallic material may be conducted as well. If the front skin4comprises a thermoset material, co-curing of the interface elements8arranged on the inner surface32or gluing both components together may be further options. In any case, the outer surface30of the front skin4remains free from any riveting connections that influence the aerodynamic behavior of the flow body4.

FIGS.3ato3ishow different examples of attaching one or two interface elements8to a load introduction rib in schematic illustrations. Further attachment options are conceivable and shall not be considered ruled out by these examples. For illustration purposes, the angled shapes of the interface elements8in the examples ofFIGS.3a,3b,3cand3eto3iare left out. However, is it to be understood that these interface elements8may include an angled shape as shown inFIG.1to provide a sufficiently large bonding surface26.

FIG.3ashows the front skin4having a single interface element8connected to the inner surface32, wherein the load introduction rib6is attached to the interface elements8through a series of fasteners18.

InFIG.3b, substantially the exemplary embodiment ofFIG.2is illustrated. Here, two interface elements8are connected to the front skin4, wherein the load introduction rib6is enclosed between the two interface elements8through fasteners18.

InFIG.3c, a single interface element8is shown arranged at the inner surface32, wherein the load introduction rip6comprises a fork34at the skin interface side16, which is attached to the interface element8through fasteners18. The interface element reaches into an intermediate space between both legs of the fork34.

InFIG.3d, a single interface element8having an Omega-shape is shown, wherein the open side of the interface element8is bonded to the inner surface32. The load introduction rib6in turn comprises a flange36, which is arranged transverse to the remaining part of the load introduction rib6and is attached to the interface element8through two series of fasteners18at both sides of the load introduction rib6.

FIG.3eshows a single interface element8with a transverse flange38, that is attached to the transverse flange36of the load introduction rib6, similar to what is shown inFIG.3d.

InFIG.3f, a slight modification ofFIG.3cis shown. Here, instead of the fork34, two lateral brackets40are attached to the load introduction rib6and the interface element8to enclose both elements.

InFIG.3g, a stepped blade is provided as an interface element8and comprises a lateral recess42to receive the load introduction rib6, wherein one of the lateral brackets40is used to clamp the load introduction rib6and the interface element8together.

FIG.3his mechanically inverted to the solution inFIG.3gand shows a single interface element8, the load introduction rib6as well as a stepped bracket44having a lateral recess42for receiving the load introduction rib6for clamping the load introduction rib6and the interface element8together.

FIG.3ishows the interface element8comprising a double-L-profile, leading to the cross-sectional profile of the interface element8having a transverse leg48. The cross-sectional profile of the load introduction rib6comprises a correspondingly transversely extending leg46, which flushly rests on the leg48of the interface element8. The load introduction rib6, the interface element8and the legs46and48are clamped together by fasteners18.

Lastly,FIG.4shows an aircraft50, having wings52with leading edges54and a fixed wing body56, at which a flow body2according to the above may be provided.

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