LIGHTNING STRIKE PROTECTION MATERIAL

Abstract

A lightning strike protection material for an aircraft includes an electrically-conductive grid with grid-forming members and nodes where grid-forming members overlap or intersect. A plurality of the grid-forming members and/or nodes include an outward-facing surface, and at least a portion of the outward-facing surface is concave.

Claims

1. A lightning strike protection material for an aircraft, comprising an electrically-conductive grid comprising a multiplicity of grid-forming members and a multiplicity of nodes where grid-forming members overlap or intersect, wherein a plurality of the grid-forming members and/or nodes comprise an outward-facing surface, and wherein at least a portion of the outward-facing surface is concave.

2. The lightning strike protection material according to claim 1, wherein the grid is flexible.

3. The lightning strike protection material according to claim 1, wherein the grid-forming members are elongate, and have a mean aspect ratio of at least 3:1 and no more than 20:1, and the grid optionally comprises an expanded mesh.

4. The lightning strike protection material according to claim 1, wherein the grid-forming members are elongate, and have a mean aspect ratio of at least 50:1 and no more than 30,000:1, and the grid-forming members optionally comprise interwoven wires.

5. The lightning strike protection material according to claim 1, wherein the mean thickness of the grid-forming members is at least 0.02 mm and is no more than 0.30 mm.

6. The lightning strike protection material according to claim 1, wherein the grid comprises openings having a four-sided shape.

7. The lightning strike protection material according to claim 1, wherein a distance between centers of adjacent nodes in the mesh is at least 1.0 mm, and is no more than 10.0 mm.

8. The lightning strike protection material according to claim 1, having a mass per unit area of at least 20 g/m.sup.2 and no more than 400 g/m.sup.2.

9. The lightning strike protection material according to claim 1, having an open area of the grid of at least 30% and no more than 95%.

10. The lightning strike protection material according to claim 1, wherein at least 10% of the grid-forming members and/or nodes (as calculated by number) comprise at least a portion of an outward-facing surface that is concave.

11. The lightning strike protection material according to claim 1, wherein substantially none of the grid forming members or none of the nodes comprises at least a portion of an outward facing surface that is concave.

12. The lightning strike protection material according to claim 1, wherein at least 80% of the concave outer surfaces, as calculated by surface area, face substantially in one direction.

13. The lightning strike protection material according to claim 1, wherein the grid comprises a sheet having two faces, and at least 80% of the concave outer surfaces face at least partially away from one face of the sheet.

14. The lightning strike protection material according to claim 1, wherein the grid comprises a sheet having two faces, and at least 80% of the concave outer surfaces are on one face of the sheet.

15. The lightning strike protection material according to claim 1, wherein at least one concave surface is elongate and has a same cross-sectional shape along its length, which cross-sectional shape is concave.

16. The lightning strike protection material according to claim 1, wherein at least one concave surface has a shape consistent with a volume of revolution, and/or has a conical shape, a bell-shape, a frusto-conical shape or a horn shape.

17. The lightning strike protection material according to claim 1, comprising an indicator to indicate which of two faces of the lightning strike protection material comprises concave surfaces.

18. A laminate for an aircraft structure, the laminate comprising a lightning strike protection material according to claim 1, a composite material and optionally at least one layer of paint overlying the lightning strike protection material.

19. An aircraft structure comprising a laminate according to claim 18, the aircraft structure optionally comprising a fuselage or part thereof, a wing or part thereof, a tail or part thereof, a flight control surface, a flap, an elevator, an aileron or a rudder, or part thereof, a radome or part thereof, or an engine cowling or part thereof.

20. A method of forming a lightning strike protection material, the method comprising: providing a sheet of blank material; and forming a grid in accordance with the lightning strike protection material according to claim 1.

21. A method of forming a lightning strike protection material according to claim 1, the method comprising: providing a multiplicity of grid-forming members, a plurality of the grid-forming members each comprising a concave surface; and forming a grid from the plurality of grid-forming members.

22. A method of forming a laminate according to claim 18, the method comprising: contacting un-cured composite material with the lightning strike protection material; and curing the composite material.

23. A method of forming an aircraft structure according to claim 19, the method comprising: contacting un-cured composite material with the lightning strike protection material, in a mold or former shaped to provide an aircraft structure or part thereof; and curing the composite material.

24. A lightning strike protection material comprising an electrically-conductive sheet in a form of a lattice, the sheet having a first face and a second face, the lattice comprising multiple lattice members and multiple nodes, the nodes being located at the meeting point of lattice members, a plurality of the lattice members comprising a concave surface that faces away from the first face.

25. An aircraft comprising a lightning strike protection material according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Embodiments of the disclosure herein will now be described by way of example only with reference to the accompanying schematic drawings of which:

[0063] FIG. 1A shows a plan view of an example of a lightning strike protection material according to a first embodiment of the disclosure herein;

[0064] FIG. 1B shows a perspective view of a portion of the lightning strike protection material of FIG. 1A;

[0065] FIG. 2A shows a plan view of a further example of a lightning strike protection material according to another embodiment of the disclosure herein;

[0066] FIG. 2B shows a schematic side-on view of a portion of the lightning strike protection material shown in FIG. 2A;

[0067] FIG. 3 shows cross-sectional views of examples of wires for use in a lightning strike protection material according to an embodiment of the disclosure herein;

[0068] FIG. 4 shows a schematic cross-sectional view of an example of a laminate according to an embodiment of the disclosure herein;

[0069] FIG. 5 shows a schematic perspective view of an example of a portion of aircraft fuselage according to an embodiment of the disclosure herein;

[0070] FIG. 6 shows a schematic of an example of a method of making a lightning strike protection material according to an embodiment of the disclosure herein;

[0071] FIG. 7 shows a schematic of an example of a further method of making a lightning strike protection material according to a further embodiment of the disclosure herein;

[0072] FIG. 8 shows a schematic of an example of a method of making a laminate according to an embodiment of the disclosure herein;

[0073] FIG. 9 shows a schematic of an example of a method of making an aircraft component according to an embodiment of the disclosure herein; and

[0074] FIG. 10 shows a schematic perspective view of an example of an aircraft according to an embodiment of the disclosure herein.

DETAILED DESCRIPTION

[0075] An example of a lightning strike protection material according to a first embodiment of the disclosure herein will now be described by way of example only with reference to FIGS. 1A and 1B. The lightning strike protection material is denoted generally by reference numeral 1 and comprises a grid 2 comprising a multiplicity of grid-forming members, a few of which are labelled 3A, 3B, 3C. The grid 2 comprises a multiplicity of nodes, a few of which are labelled 4A, 4B. The nodes 4A, 4B are at the intersection point of grid-forming members. For example, node 4A is at the intersection point of grid-forming members 3A, 3B, 3D, 3E. The grid 2 comprises a plurality of diamond-shaped openings between the grid-forming members. Two of the openings 8A, 8B are labelled. The grid-forming members are provided with an upper surface which is concave. Several of those upper surfaces 5A, 5B are labelled in FIG. 1B. A concave v-shaped notch is formed along the length of each grid-forming member.

[0076] The grid 2 is formed from 0.05 mm thick copper foil. The length of each grid-forming member is about 1.4 mm. The thickness 6 of the grid is about 0.15 mm. The width 7 of each grid-forming member is about 0.1 mm. The grid has an open area of about 80% i.e. the area of the openings is about 80% of the total area of the grid (the sum of the area of the openings and the area of the grid-forming members and nodes). The lightning strike protection material 1 has an area weight of about 75 g/m.sup.2.

[0077] A method of making the lightning strike protection material of FIGS. 1A and 1B will now be described with reference to FIG. 6. The method is denoted generally by reference numeral 400, and comprises providing 401 a sheet of blank material, in this case a sheet of 0.05 mm thick copper foil. The method comprises forming 402 the grid 2 from the copper foil by stamping the copper foil. The stamping process cuts the copper foil in the appropriate places so that the cut foil can be pulled to form the grid. The stamping process also forms the concave surfaces on the upper surface 5A, 5B of the grid-forming members.

[0078] Alternatively, forming 402 a grid may comprise forming 403 a grid substantially without the concave surfaces, and then forming 404 the concave surfaces in the grid.

[0079] The lightning strike protection material 1 may be incorporated into a laminate material to protect underlying composite material from the effects of a lightning strike. In this connection, FIG. 4 shows a schematic cross-sectional view through an example of a laminate in accordance with an embodiment of the disclosure herein. The laminate is denoted generally by reference numeral 200 and comprises lightning strike protection material 1 in contact with an underlying composite material 201. The underlying composite material 201 comprises a plurality of layers of electrically non-conductive composite. Such composite material comprises a fiber component dispersed in a binding matrix. A layer of paint 202 covers the lightning strike protection material 1. The paint is approximately 0.2 mm thick and is of the type that is usually applied to the surface of a commercial passenger aircraft. Referring to FIGS. 1A and 1B, lightning strike protection material 1 is in the form of a sheet and has a first face 10 and a second face 11. Lightning strike protection material 1 is arranged so that the first face 10 and upper concave surfaces 5A, 5B face outwards towards the paint 202. The thicknesses of the lightning strike protection material 1 and paint 202 have been exaggerated in FIG. 4 for clarity.

[0080] In the event of a lightning strike, the lightning strike protection material in the vicinity of the lightning strike will typically evaporate, with the resultant gases rupturing the paint. Furthermore, and without wishing to be bound by theory, the concave shape provides a greater surface area from which the metal grid of the lightning strike protection material evaporates in the event of a lightning strike.

[0081] The sacrificial destruction of a portion of lightning strike protection material is a high-energy event in so far as there is sufficient energy to locally destroy the lightning strike protection material. Without wishing to be bound by theory, it is anticipated that providing the lightning strike protection material with a concave surface will focus the vaporization of the lightning strike protection material in a similar manner to the focusing of an explosion by a concave surface using the Munroe effect. By focusing the vaporization, the overlying paint may be ruptured more easily than when using a conventionally-shaped lightning strike protection material.

[0082] A method of making the laminate of FIG. 4 will now be described with reference to FIG. 8. The method is denoted generally by reference numeral 600 and comprises contacting 601 un-cured composite material with lightning strike protection material 1 and curing 602 the composite material. This is typically achieved by providing a mold that is to shape the composite material. The lightning strike protection material 1 is placed into the bottom of the mold, with the first face 10 and the concave surfaces 5A, 5B facing the mold surface. Un-cured composite material is then introduced into the mold, and pressure and heat are applied to the composite material in the mold to cure the composite material. The cured composite material, along with the lightning strike protection material 1 are removed from the mold. A layer of paint is then applied 603 to the lightning strike protection material.

[0083] The method described above in relation to FIGS. 4 and 8 may be used to make an aircraft structure or part thereof, as will now be described with reference to FIG. 9. The method is denoted generally by reference numeral 700 and comprises contacting 701 un-cured composite material with lightning strike protection material 1, and curing 702 the composite material. This is typically achieved by providing a mold that is to shape the composite material into the desired shape of the aircraft structure or part thereof. The lightning strike protection material 1 is placed into the bottom of the mold, with the first face 10 and the concave surfaces 5A, 5B facing the mold surface. Un-cured composite material is then introduced into the mold, and pressure and heat are applied to the composite material in the mold to cure the composite material. The cured composite material, along with the lightning strike protection material 1 are removed from the mold. A layer of paint is then applied 703 to the lightning strike protection material. FIG. 5 shows a schematic perspective view of part of an aircraft fuselage 301 comprising laminate 200 and made using the method as described above in relation to FIG. 9. FIG. 10 shows an aircraft 1000 comprising the part of an aircraft fuselage 301.

[0084] A further example of a lightning strike protection material according an embodiment of the disclosure herein will now be described with reference to FIGS. 2A and 2B. The lightning strike protection material is denoted generally by reference numeral 101 and comprises a grid 102. The grid 102 comprises a multiplicity of grid-forming members, some of which are labelled 103A, 103B, 103C, 103D, 103E. In this case, the grid-forming members comprise bronze wires that are interwoven to form a grid structure. The grid comprises a multiplicity of nodes 104A, 104B that are formed where the wires overlap. For example, node 104A is formed where wires 103A and 103B overlap, and node 104B is formed where wires 103A and 103C overlap. Each of the wires 103A, 103B, 103C, 103D, 103E is generally oval in cross-section, with a concave v-shaped surface 105B, 105C, 105D, 105E facing outwards from a first face 110 of the grid 102 (the grid having a first face 110 and a second face 111). The concave v-shaped surface may be formed by drawing the wire to have such a shape. The grid 102 comprises square openings, only some of which 108A, 108B are labelled.

[0085] Each wire has a diameter of about 0.08 mm, and the mesh size is about a 1.0 mm square. The open area is about 85%, with an area weight of about 80 g/m.sup.2.

[0086] A method of making the lightning strike protection material 101 will now be described with reference to FIG. 7. The method of forming a lightning strike protection material is denoted generally by reference numeral 500. The method 500 comprises providing 501 a multiplicity of grid-forming members, a plurality of the grid-forming members each comprising a concave surface, and forming 502 a grid from the plurality of grid-forming members. In this case, the grid-forming members are brass wires of about 0.08 mm diameter that have been drawn to provide a concave surface such as that shown in FIG. 2B. The wires are woven into a grid, the wires being arranged such that all of the concave surfaces face in substantially the same direction.

[0087] The lightning strike protection material 101 may be used in substantially the same way as lightning strike protection material 1 described above.

[0088] FIG. 3 shows a cross-sectional view through three wires that may be used in lightning strike protection materials. Wire A is a prior art wire that is generally oval in cross-section. Wire B is crescent-shaped in cross-section, and wire C is Pacman-shaped in cross-section.

[0089] While the disclosure herein has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the disclosure herein lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[0090] The examples above describe how lightning strike protection material may be used on aircraft. Those skilled in the art will realise that the lightning strike protection material in accordance with the disclosure herein may be used with structures other than aircraft, such as wind turbines.

[0091] The examples above describe grid-forming members that are concave in cross-section along the length of the grid-forming member. Those skilled in the art will realise that other arrangements may be possible. For example, the concave surface may be in the shape of a surface of revolution, such as conical surface, a frusto-conical surface or a horn-shaped surface, such as a surface in the shape of Gabriel's Horn. A plurality of such surfaces of revolution may be provided along a grid-forming member, for example. The concave surface may be in the form of an indentation, for example, which may have any suitable shape.

[0092] The examples above describe grids in which all grid-forming members are provided with concave surfaces. This need not be the case, of course.

[0093] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the disclosure herein, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the disclosure herein that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, while of possible benefit in some embodiments of the disclosure herein, may not be desirable, and may therefore be absent, in other embodiments.

[0094] While at least one example embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the example embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a”, “an” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.