GB2552207A

GB2552207A - Rib manufacturing

Info

Publication number: GB2552207A
Application number: GB1612221.0A
Authority: GB
Inventors: Graham Daniel
Original assignee: GKN Aerospace Services Ltd
Current assignee: GKN Aerospace Services Ltd
Priority date: 2016-07-14
Filing date: 2016-07-14
Publication date: 2018-01-17
Anticipated expiration: 2036-07-14
Also published as: GB201612221D0; GB2552207B

Abstract

A wing rib assembly comprises a central portion 14 and a plurality of feet 7 connected to its periphery. A wing cover or skin is connected to the outer surface of the feet to form the assembly. The assembly may be made by connecting the feet to the central portion first and then connecting the cover to the feet or can be made with the feet being connected to the cover first and then connecting the resulting structure to the rib central portion. The feet may take the form of a triangular shape or prism shape structures. The feet may be made by preforming a length of material, separating the length of material into a plurality of individual connection feet and connecting the connection feet to the periphery of the central portion to form a rib. The feet may include a stem 16 for attaching to the rib plate by welding such as using linear friction welding. The rib plate may be machined to reduce its width but to leave web portions 18.

Description

(54) Title of the Invention: Rib manufacturing

Abstract Title: Aircraft wing rib and cover assembly (57) Awing rib assembly comprises a central portion 14 and a plurality of feet 7 connected to its periphery. A wing cover or skin is connected to the outer surface of the feet to form the assembly. The assembly may be made by connecting the feet to the central portion first and then connecting the cover to the feet or can be made with the feet being connected to the cover first and then connecting the resulting structure to the rib central portion. The feet may take the form of a triangular shape or prism shape structures. The feet may be made by preforming a length of material, separating the length of material into a plurality of individual connection feet and connecting the connection feet to the periphery of the central portion to form a rib. The feet may include a stem 16 for attaching to the rib plate by welding such as using linear friction welding. The rib plate may be machined to reduce its width but to leave web portions 18.

10 17

10 17

FIG. 4C

10 17

10 17

10 17

10 17

Rib Manufacturing

Technical Field

The present invention is concerned with the manufacture of the structural component in aircraft wings known in the art as ribs. Although the manufacturing method is particularly suited to aircraft rib manufacture it may be employed in other related applications.

For example, the technology may be used in a variety of applications using “rib-like” reinforcing structures including architectural/civil markets.

Specific to the aerospace sector ribs can be used in wings, horizontal or vertical tail-planes (empennage), in tail-booms of helicopters, and smaller ribs in things like winglets and flaps.

An aircraft wing comprises an outer aerodynamic surface over which air is caused to flow by forward motion of the aircraft. Wings generally comprise one or more spars extending within the wing from the root, where the spar connects to the fuselage, to the wing tip.

Ribs, again within the wing, are attached at predetermined intervals along the length of the spar. The ribs generally extend in a forwards direction of flight i.e. are generally perpendicular to the spar extending in a fore and aft direction of the aircraft movement.

The shape and contour of the spar and ribs corresponds to the desired shape of the aerofoil. The outer aerodynamic surface can then be connected to the ribs and spar (by various means) to form the wing.

Ribs are conventionally machined from a billet of aluminium or other lightweight material using CNC tools so that the precise geometry of the spars can be obtained. Conventional wings made using these techniques allow a lightweight wing to be manufactured accurately for each aircraft design providing the desired strength and stiffness.

The present inventor has however devised an alternative process for optimising wing design and in particular wing rib manufacture.

Summary of the Invention

Aspects of the invention are set out in the accompanying claims.

According to a first aspect there is provided a method of manufacturing a rib, said rib comprising a central portion and a plurality of connection feet, said method comprising the steps of:

(a) pre-forming a plurality of connection feet, each foot corresponding to a predetermined cross-sectional shape;

(b) connecting said plurality of connection feet to the periphery of the central portion to form a rib; and (c) connecting a wing cover to an outer surface of the plurality of connection feet.

Thus a very unconventional manufacturing method is provided to create a rib.

The pre-forming in step (a) may be selected from an extrusion, pull-trusion, casting or additive manufacturing process. Alternatively, the pre-forming in step (a) may be to creates a length of material which is separated into a plurality of individual connection feet.

Preforming a length of material to make the individual feet allows for efficient manufacturing of long lengths of stock which can then be separated to form a plurality of individual feet. The preforming process may be any suitable process. However, extrusion is a particularly efficient process which allows for a continuous length of material to be formed having a uniform cross-section.

Using an extrusion (or similar) process allows for rib foot geometries (cross-sectional shapes) that would not be feasible with conventional rib manufacture. Thus, an optimised rib foot profile can be provided offering, amongst other benefits, increased stiffness and reduced weight compared with conventional manufacturing techniques.

Furthermore, manufacturing the rib in this way offers added advantages of improving buy-tofly ratio through manufacturing a near net shape, and also enables the use of dissimilar materials for rib feet and the main plate as discussed below. The term ‘buy-to-fly’ ratio will be understood in the art to refer to the ratio between the weight of raw material and weight of the finished component.

It also allows further optimisation of rib design since more exotic alloys can be applied to the highly loaded rib feet area without the expense of using those materials for the entire rib.

Manufacturing the rib feet as a series of (for example) extrusions allows the geometry of each foot to be optimised for the position that the foot will assume when connected to the central portion or plate of the rib. In-flight, some ribs will experience higher loads than others and the method allows each foot to be optimised for weight and strength. The feet can then be coupled to the central portion.

For example the plurality of connection feet may be positioned and connected to the periphery of the central plate at predetermined positions according to design and loading requirements.

The plurality of different connection feet may be pre-formed so as to have a plurality of crosssectional shapes for connection at predetermined positions on the periphery of the central plate. Where a number of wings are being manufactured a plurality of individual feet can be manufactured and then shared amongst the wings to be made. Each foot may be provided with a unique cross-section shape or profile for a given position around the central plate.

Being able to select material combinations in accordance with the method of the invention allows for material compatibility issues to be overcome. For example, issues with galvanic corrosion due to particular material combinations can be overcome. In one example the invention allows for a carbon fibre wing skin to be connected to an aluminium central plate using a titanium rib foot.

The preforming process may advantageously use multiple materials to further optimise the strength of the foot at the desired position thus allowing a large degree of design freedom to optimise each foot. Specifically a connection foot material may be selected according to an in-use predetermined loading at a position on the periphery of the central portion.

The method may further include the step of removing (for example by machining) the assembled rib to remove excess material at predetermined positions i.e. at locations where there are low loads.

Examples of materials which may be used include aluminium, aluminium alloys, titanium, titanium alloys or aluminium-lithium.

The connection feet may advantageously be formed by dividing or separating the length of preformed material into discrete portions - each having the same cross-section from the (for example) extrusion process. Each length can be predetermined for the required foot.

The length of preformed material may have any suitable cross-sectional shape by means of designing the die through which the material passes. Advantageously the plurality of connection feet may be pre-formed with a generally triangular cross-section and further comprise a stem portion at an apex of the generally triangular shape for connection to the periphery of the central portion. The stem may for example be of a dissimilar material to the triangle.

The triangle advantageously provides a generally flat surface opposing the stem against which the inner surface of the wing structure can be connected. The stem provides a convenient surface to connect to the central portion of plate defining the main structural body of the rib. The triangles may, for example, be in the shape of an equilateral or isosceles triangle.

The face of the triangle against which the wing structure can be assembled may be provided with a complimentary surface to a wing skin mating surface. This may for example be achieved by machining the surface so that it closely matches the wing skin. Thus a complimentary surface is provided which closely aligns with the profile of the wing surface to be attached to the plurality of feet.

The preformed feet may be any desired length. For example the lengths of the feet (measured in a fore and aft direction of flight) may be shorter at the leading a trailing edges of the wing profiled and longer in the middle. This is determined by how the length of preformed material is separated as discussed above.

Advantageously, portions of the side walls making up the triangular shape may be? machined away to expose the inner space of the preformed connection foot. This allows for excess material that is not load bearing to be removed thereby further reducing weight.

It will be recognised that the cross-sectional shape of the plurality of preformed connection feet are provided with an outer load bearing perimeter surface defining an internal space extending along the length of the connection foot.

Advantageously, because of the preforming process, for example extrusion, the inner space extending along the length of the connection foot may be provided with internal stiffening portions in the form of elongate members integral with load bearing perimeter surface.

For example, the plurality of connection feet may have a cross-section comprising a generally triangular load bearing outer surface and a centrally positioned reinforcing member, said cross-section further comprising radially extending reinforcing members extending from the centrally positioned reinforcing member to the load bearing outer surface. This crosssection, provided for in the preforming process, provides an outer surface to the rib foot and an integral internal reinforcing structure further optimising the strength of the foot.

Any suitable internal reinforcing cross-sectional shape may be used. Additionally the internal reinforcing may have different profiles for different foot location.

As discussed above any suitable pre-forming process may be used. A convenient and well understood process is the extrusion process. Other processes that can advantageously be used include casting, pull-trusion or additive manufacturing techniques (otherwise known as 3D printing or rapid prototyping) such as, for example, laser metal deposition or polymer solidification.

Each manufacturing process provides alternative advantages. For example, extrusion provides for high volume manufacturing at low cost, casting advantageously allows for complex geometries and additive manufacturing techniques allow for still more complex geometries including internal geometries.

The particular process selected largely depends on production volume and the requirement for complicated geometry and or materials selected. In some situations dissimilar materials may be used and therefore AM could be particularly advantageous.

The step of connecting the individual feet to the central portion or plate may be selected depending, for example, on the material which has been used. Advantageously linear friction welding may be used to fully optimise the strength of the connection.

Viewed from another aspect there is provided a wing spar comprising a central plate and a plurality of connection feet arranged around the perimeter of the central plate, wherein each of said plurality of connection feet is in the form of an elongate prism, said prism comprising an outer wall defining a hollow space within the elongate prism.

Viewed from yet another aspect there is provided an aircraft wing comprising at least one spar and a plurality of ribs, each rib comprising a central plate and a plurality of rib feet for connection to an outer wing surface, wherein the plurality of rib feet are in the form of preformed prisms, and wherein the rib feet are connected to the periphery of the central plate.

Viewed from yet another aspect there is provided a method of manufacturing a rib, said rib comprising a central portion and a plurality of connection feet, said method comprising the steps of:

(b) connecting said plurality of connection feet to an inner surface of a wing cover; and (c) connecting the wing cover and feet to the periphery of the central portion to form the rib.

The preforming in step (a) may be selected from an extrusion, pull-trusion, casting or additive manufacturing process. Alternatively the pre-forming in step (a) may be the creation of a length of material which is separated into a plurality of individual connection feet.

Brief Description of the Drawings

One or more embodiments of the invention will now be described, by way of example only, and with reference to the following figures in which:

Figure 1 illustrates the internal structure of a wing;

Figure 2 shows a cross-section of a rib from Figure 1;

Figure 3 shows a rib foot in cross—section through A-A’ shown in Figure 2;

Figures 4A, 4B and 4C show different rib foot cross-sections;

Figure 5 shows a conventional rib formed from a billet;

Figure 6A shows a connection foot and central plate before assembly according to the invention;

Figure 6B shows a connection foot and central plate after assembly according to the invention;

Figure 6C shows a final rib according to the invention after final machining;

Figure 7 shows an assembled rib according to the present invention when viewed from above;

Figure 8 shows an assembled rib according to the present invention when viewed from the side;

Figure 9 shows a closer view of the machined connection feet of the invention;

Figure 10 shows a still closer view of the machined feet of the invention; and

Figure 11 shows a schematic of an extrusion process.

Any reference to prior art documents in this specification is not to be considered an admission that such prior art is widely known or forms part of the common general knowledge in the field. As used in this specification, the words “comprises”, “comprising”, and similar words, are not to be interpreted in an exclusive or exhaustive sense. In other words, they are intended to mean “including, but not limited to”. The invention is further described with reference to the following examples. It will be appreciated that the invention as claimed is not intended to be limited in any way by these examples.

Detailed Description

In the figures accompanying the description there is shown a method of manufacturing a rib, said rib comprising a central portion and a plurality of connection feet, said method comprising the steps of:

a. pre-forming a plurality of connection feet, each foot corresponding to a predetermined cross-sectional shape;

b. connecting said plurality of connection feet to the periphery of the central portion to form a rib; and

c. connecting a wing cover to an outer surface of the plurality of connection feet.

Figure 1 shows the internal structure of a wing. Ribs 1 and spars 2 make up the main load bearing structure of the wing. Spars run span-wise relative to the aircraft i.e. down the length of the wing, and ribs run fore-aft between the leading edge 3 and the trailing edge 4.

Figure 2 shows a section through the wing in the plane of a rib 1. As shown, the structure of the wing is made up of ribs 1, spars 2, stringers 5 and outer skin 6. The stringers extend span-wise along the length of the wing to support the skin in a span-wise direction. The stringers 5 pass through apertures 8 machined into the rib 1.

Leading and trailing edge geometries have been excluded from figure 2 but would protrude from the spars 2 on either side. Figure 2 shows how the rib 1 creates a supporting profile for the wing covers to be fastened to. The wing covers comprise the skin 6 with pre-attached stringers 5 (also known as stiffeners), which vary in section.

The skin 6 is attached to rib feet 7 at a plurality of positions around the periphery of the rib.

Figure 3 shows a section through A-A’ shown in Figure 2 and specifically the interface of a conventional rib foot 7 and wing cover (i.e. the stringers and skin).

Conventional rib feet have a T-shape cross-section as shown in figure 3. Advantageously conventional rib feet are easy to manufacture and provide ample space 9 where fasteners, such as rivets, can be used to secure the wing covers to the ribs. It is for this, amongst other, reasons that T profiles are the conventional manner of connecting wing covers to ribs.

However, the inventors have determined that this T-shape cross-section, whilst commonly used in the industry, is quite inefficient in bending and is commonly reinforced with web features depending on the application.

The present invention will now be described with reference to figures 4A to 10.

According to the invention a manufacturing technique is provided which advantageously enables triangulated extrusions and other novel foot features to be incorporated into ribs via a suitable structural joining process such as linear friction welding or friction stir welding. Figures 4A to 4C show the evolution of a rib foot according to the present invention.

Figure 4A shows a conventional rib having a T-shaped cross-section. The upper surfaces 9 of the rib provide a convenient surface through which fasteners, such as rivets, can be located. However, bending moments during flight cause high stresses in the root of the T section i.e. the point at which the vertical and horizontal portions of the T meet. When needed this is solved by reinforcing the root.

Figure 4B shows a conceptual rib foot which has an optimal shape for load transfer. Similarly Figure 4C shows a further enhanced rib foot cross-section with internal reinforcement of the rib.

The present invention allows the complex and optimised geometries of rib feet cross-sections 4B and 4C to be commercially realised in rib manufacture. Figure 4 B shows a rib foot with an upper fastening surface 9 and two side surfaces 10a, 10b which meet at an apex 11. This shape optimises load transfer between the skin and the rib (the rib being connected to the apex 11).

Figure 4C is further enhanced and comprises a central reinforcing tube 12 and radially extending struts 13a, 13b and 13c connecting the reinforcing tube 12 to the inner surfaces of the side surfaces 10a, 10b.

The cross-sections shown in Figures 4B and 4C are formed using an extrusion (or similar process) as described further below.

Figure 5 shows a conventional rib 1 formed from a billet of aluminium. The billet is machined using CNC machine tools to form a net shape rib i.e. a shape that corresponds precisely to the design requirements for a given wing (for example a rib in the wing structure shown in figure 1 and 2).

Manufacture of a conventional rib will now be described in more detail with reference to figure 5.

The conventional rib 1 comprises a central substantially flat plate 14 and a surrounding connection blank 15 on either side of the periphery of the blank 14. Figure 5 illustrates the rib before the rib feet are machined from the connection blanks 15.

The rib feet (not yet machined in figure 5) are machined, using CNC machining, into the blanks 15. These feet comprise a T shaped profile as shown in figure 4A and recesses to receive the stringers (described above).

According to the conventional methods of making wing ribs, the necessity to machine rib feet from the solid blanks 15 means that rib billet thicknesses are much greater than would otherwise be needed for a given wing design. This increases machining time and material wastage.

According to the present invention, forming and joining the connection feet to a central plate separately opens up a range of opportunities that could be exploited to optimise the design and performance of a wing design. This includes, for example, the use of non-standard manufacturing methods for rib feet, leading to more efficient material usage.

The present invention (which avoids the machining of large billets) will now be described in further detail with reference to figures 6A to 11.

Figure 6A shows a connection foot and central plate before assembly. The method and apparatus of the invention comprises a central plate forming the main body of the rib which largely corresponds to the rib 1 shown in figure 1. The plate 14 has a peripheral edge or perimeter onto which rib feet 7 are connected.

A plurality of rib feet are positioned (as opposed to being machined in a conventional manner) around the periphery of the rib to provide a connection for the wing skin (not shown).

In figure 6A a generally triangular rib foot 7 has been pre-formed using one of a variety of techniques that allow elongate cross-sections to be formed. One such technique is an extrusion process. Extrusion will be well understood by the skilled person in the art and the extrusion process will not therefore be described in detail herein, except with reference to the discussion accompanying figure 11.

Figure 6A shows the central plate and the rib foot as they are brought together for joining, such as welding. The rib foot has a lower stem 16 and upper triangular portion 17. These two components can be extruded together or optionally separated and joined together.

The upper triangle portion 17 is in the form of a triangle with the face 9 opposing the stem and arranged to be generally flat. This is the surface onto which the wing skin can be coupled.

The extrusion defines an outer load bearing perimeter wall of portion 17 and a hollow space 18 formed during the extrusion process (using a suitably shaped die). The portion 17 may be extruded in any suitable shape and may optionally be solid in cross-section i.e. no hollow inner space.

The inner space 18 in Figure 6A shows the internal stiffening structure comprising a central circular member 12 (not shown in figure 6A) and a plurality of radially extending reinforcing members 13a, 13b and 13c. The central member 12 extends along the length of the extrusion, as do the radially extending reinforcing members 13a, 13b and 13c. The reinforcing members 13a, 13b and 13c are integral with the circular member 12 and to the inner surface of the triangle portion 17 by virtue of the extrusion (or similar) process. This enhances the rigidity and strength of the rib foot. The reinforcing portions 12, 13a, 13b and 13c can be conveniently formed simultaneously as part of the extrusion process.

It will be recognised that whilst a central tube 12 and radially extending struts 13a, 13b and 13c are shown other cross-sections providing reinforcement may equally fall within the scope of the invention.

Figure 6B shows the stem 16 and rib plate 14 after they have been coupled together. The two components may be coupled together using a variety of welding techniques, such as linear friction welding.

Solid state joining techniques such as friction stir and linear friction welding do not necessarily melt the material. A high quality joint that retains mechanical performance of the parent material can be realised. Such techniques make it possible to create parts of near net or net shape which saves cost.

In an alternative embodiment, adhesive technologies may also be used.

Figure 6C shows a cross-section of the rib incorporating a rib foot 7 wherein the rib plate 14 has been machined to reduce its width. Figure 6C is a section across the corresponding web (see figure 8) and illustrating the web portions 18. The web is created by machining process which blends the geometry of the central rib region into the added foot.

It will be appreciated that this is just one of the plurality of rib feet that are positioned and connected to the rib plate to form the complete rib which will now be further described.

Figures 7 and 8 show an assembled rib according to the present invention.

As shown a plurality of rib feet 7 have been connected to the rib plate 14. Rib feet have been connected at pre-determined positions around the periphery of the plate.

Figure 8 illustrates the curvature of the rib which is also visible in figure 1. The subtle differences between the rib feet around the periphery of the rib plate 14 can be seen in both figures 7 and 8. Specifically, each of the rib feet may be different in curvature and crosssection so that each rib foot can be optimised for the loading expected at a given position around the rib. For example rib foot 7X at the trailing edge of the rib is shorter than the rib feet 7Y,7Z towards the leading edge of the rib. Optimisation can then be provided.

Figures 9 and 10 show the rib feet in more detail. Here rib feet 7X is located at the trailing edge of the rib and has not been machined on it outer surfaces post-extrusion. Towards the leading edge a different rib foot 7Y has been machined such that outer portions of the side walls 10a and 10b have been removed to create apertures 19. This allows material to be removed to reduce weight.

It will be recognised that in manufacturing a large number of wings there will be a plurality of different rib sizes and cross-sections which are located at the same position on ribs on multiple ribs within the same wing. These can be manufactured according to the present invention in larger volumes so that the assembler of the wing has a stock of each size of rib foot needed for each position around each rib and for each wing.

The rib feet may be formed, for example, using a conventional extrusion process as illustrated in the schematic figure 11 A.

The extrusion process is just one manufacturing process that may be using according to the present invention to form lengths of rib feet stock.

Typically extrusion processes start with raw stock bar which is heated up and pushed through a die. Potentially a multi-stage process or alternatively may go straight to final form.

Feed material is fed into a feed hopper 20 or other supply line feeding an extrusion machine

21. The extrusion machine comprises a motor 22 and compression auger 23 and a heater (not shown). The material is heated and compressed by the heaters and motors and forced at high pressure through a die 24. As is well known in conventional extrusion the die has a cross-section that corresponds to the desired shape of the length of material to be made.

In this example the die has a profile corresponding to Figure 11B i.e. an outer triangular perimeter, a central circular portion and 3 radially extending struts (as per figure 4C).

As semi-molten material is forced through the die it exits the die in the desired shape in an elongate length of material. The material cools and hardens outside of the extruder. A length of rib feet stock for the given rib foot position is then formed.

The next step is to slice the rib feet stock into the desired lengths (as per 7X and 7Y in figure 8 for example.

Figure 11 C illustrates cutting points 25 of the feed stock to form the desired rib feet. The stock may be cut using a variety of techniques depending on the material forming the stock length.

Thus, according to this technique a plurality of rib feet can be pre-manufactured for coupling to the rib plate 14. Each rib foot may be pre-machined as per figure 9 and 10 before being coupled to the rib plate 14 or alternatively machined after being coupled.

The present invention advantageously allows rib feet to be manufactured in a highly efficient and flexible manner in which rib feet can be optimised for location, manufactured at low cost and then assembled onto a rib plate to form an optimised and highly efficient wing rib.

Rib feet can be manufactured in large volumes at locations that allow for low cost manufacturing. They can then be delivered for final assembly of the rib.

Although the invention has been described by way of example, it should be appreciated that variations and modifications may be made without departing from the spirit and scope of the invention as defined in the claims. Furthermore, where known equivalents exist to specific features, such equivalents are incorporated as if specifically referred in this specification

The embodiments described above involve forming the feet and then coupling them to a rib plate. Finally the skin is attached to the upper surface of the feet.

However, the inventor has established that the invention may equally be realised by forming the wing in a different order.

For example, in another embodiment individual rib feet may be attached to the wing cover (or formed onto the wing cover by an additive manufacturing technique) and the assembly then laid over and mechanically fastened to the ribs by way of, for example, laser welding. This being an alternative to the more conventional technique of attaching the rib feet to the rib and then to the wing cover. Advantageously this enables ‘one sided assembly’ of the wing box and reduced manufacturing cost.

Each individual rib foot may be attached using a solid state joining process such as linear friction welding or adhesive bonding for example. Alternatively, each foot may be formed directly onto the inner surface of the wing cover using an additive manufacturing process, in a predetermined layout.

The combined wing cover and rib feet assembly may then be attached to the rib using for example a solid state joining process. This advantageously makes it possible to assemble the wing box with access from one side rather than two.

Claims

1. A method of manufacturing a rib, said rib comprising a central portion and a plurality of connection feet, said method comprising the steps of:

2. A method as claimed in claim 1, wherein the pre-forming in step (a) is selected from an extrusion, pull-trusion, casting or additive manufacturing process.

3 A method as claimed in claim 1 wherein the pre-forming in step (a) creates a length of material which is separated into a plurality of individual connection feet.

4 A method as claimed in any preceding claim, wherein the plurality of connection feet are positioned and connected to the periphery of the central portion at predetermined positions.

5. A method as claimed in any preceding claim, wherein the connection feet are connected to the central portion by means of a solid state joining technique.

6 A method as claimed in any preceding claim, wherein a plurality of different connection feet are preformed having a plurality of cross-sectional shapes for connection at predetermined positions to the periphery of the central portion.

7 A method as claimed in any preceding claim, wherein a plurality of different connection feet are preformed from at least two different materials.

8 A method as claimed in claim 7, wherein a connection foot material is selected according to an in-use predetermined loading at a position on the periphery of the central portion.

9. A method as claimed in any preceding claim further comprising the step of machining the assembled rib to remove excess material at predetermined positions.

10. A method as claimed in any preceding claim, wherein dissimilar materials are used to manufacture the central portion and the connection feet.

11. A method as claimed in any preceding claims, wherein the connection feet are formed from a material selected from aluminium, aluminium alloys, titanium, titanium alloys or aluminium-lithium.

12. A method as claimed in any preceding claim, wherein the preformed connection feet are separated at a plurality of predetermined lengths.

13. A method as claimed in any preceding claim wherein the plurality of connection feet are pre-formed with a generally triangular cross-section and further comprise a stem portion at an apex of the generally triangular shape for connection to the periphery of the central portion.

14. A method as claimed in claim 13, wherein the plurality of connection feet are generally in the shape of an equilateral or isosceles triangle.

15. A method as claimed in claim 13 or 14, wherein a side of the generally triangular shape opposing the apex is a predetermined shape complimentary to a wing skin mating surface.

16. A method as claimed in claim 15, said method further comprising the step of removing excess material on the side opposing the apex to provide a complimentary surface which closely aligns with the profile of the wing surface to be attached to the plurality of feet.

17. A method as claimed in any preceding claim, wherein the preformed connection feet are elongate between a first end and a second end and wherein portions of the preform between the first and second end are machined away to expose the inner space of the connection foot.

18. A method as claimed in any preceding claim, wherein the cross-sectional shape of the plurality of preformed connection feet comprises an outer load bearing perimeter surface defining an internal space extending along the length of the connection foot.

19. A method as claimed in claim 18, wherein the internal space further comprises internal stiffening portions in the form of elongate members integral with load bearing perimeter surface.

20. A method as claimed in any preceding claim wherein the plurality of connection feet have a cross-section comprising a generally triangular load bearing outer surface and a centrally positioned reinforcing member, said cross-section further comprising radially extending reinforcing members extending from the centrally positioned reinforcing member to the load bearing outer surface.

21. A wing rib comprising a central plate and a plurality of connection feet arranged around the perimeter of the central plate, wherein each of said plurality of connection feet is in the form of an elongate prism, said prism comprising an outer wall defining a hollow space within the elongate prism.

22. A wing rib as claimed in claim 21, wherein the plurality of connection feet are positioned and connected to the periphery ofthe central plate at predetermined positions.

23. A wing rib as claimed in 21 or 22, wherein the plurality of different connection feet have a generally triangular cross-section and are connected to the central plate by means of a stem extending from an apex of the triangular connection feet.

24. A wing rib as claimed in any of claims 21 to 23, wherein the plurality of different connection feet are formed from at least two different materials.

25. A wing rib as claimed in claim 24, wherein a connecting foot material is selected according to an in-use predetermined loading at a position on the periphery of the central plate.

26. A wing rib as claimed in any of claims 21 to 25, wherein the central plate and the connection feet are formed of dissimilar materials.

27. A wing rib as claimed in any of claims 21 to 26, wherein the extruded connection feet are of a plurality of predetermined lengths.

28. An aircraft wing comprising at least one spar and a plurality of ribs, each rib comprising a central plate and a plurality of rib feet for connection to an outer wing, wherein the plurality of rib feet are in the form of preformed prisms, and wherein the rib feet are connected to the periphery of the central plate.

29. An aircraft wing as claimed in claim 28, wherein the extruded prisms are generally triangular in cross-section.

30. An aircraft comprising a wing as claimed in claim 29.

31. A method of manufacturing a rib, said rib comprising a central portion and a plurality of connection feet, said method comprising the steps of:

32. A method as claimed in claim 31 wherein the preforming in step (a) is selected from an extrusion, pull-trusion, casting or additive manufacturing process.

33 A method as claimed in claim 31 wherein the pre-forming in step (a) creates a length of material which is separated into a plurality of individual connection feet.

34 A method as claimed in any of claims 31 to 33, wherein the plurality of connection feet are positioned and connected to an inner surface of a wing cover at predetermined positions.

35. A method as claimed in any of claims 31 to 34 wherein the connection feet are connected to the inner surface of the wing cover by means of a solid state joining technique.

36. A method as claimed in claim 31 wherein the connection feet are formed by depositing material directly onto the inner surface of a wing cover

37. A wing spar substantially as described herein with reference to the accompanying figures.

38. A method substantially as described herein.

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Application No: GB1612221.0