Box rib

Abstract

A rib can be manufactured comprising two opposing outer skins and a plurality of internal reinforcement members connecting the skins together.

Claims

1. A rib for an aircraft wing, said rib comprising: a pair of opposing outer rib skins, each outer rib skin extending from an upper edge connectable to an upper outer wing skin of the aircraft wing to a lower edge connectable to a lower outer wing skin of the aircraft wing, one of the outer rib skins spaced apart in a span-wise axis of the wing from the other of the outer rib skins in use so as to define an internal space there-between that separates the outer rib skins in the span-wise axis such that the outer rib skins are nonoverlapping along the span-wise axis; and a plurality of internal reinforcement members extending across the space and connecting the pair of opposing outer rib skins; wherein at least one of the reinforcement members has a stepped or tapered cross-section such that a portion of the reinforcement member between the opposing outer rib skins has a smaller cross-section than portions adjacent to the opposing outer rib skins.

2. The rib of claim 1, wherein the internal reinforcement members are extrusions.

3. The rib of claim 1, wherein the opposing outer rib skins are substantially parallel.

4. The rib of claim 1, wherein upper and lower surfaces of the outer rib skins are configured to follow a predetermined contour corresponding to a wing aerofoil shape.

5. The rib of claim 4, wherein each of the reinforcement members extends along the lengths of the outer rib skins from the upper to the lower surfaces.

6. The rib of claim 1, wherein the reinforcement members are all substantially parallel.

7. The rib of claim 1, wherein at least two of the reinforcement members are arranged at varying angles with respect to each other.

8. The rib of claim 4, wherein at least one of the reinforcement members extends part-way along the length of at least one of the outer rib skins measured from an upper or lower surface.

9. The rib of claim 1, wherein spaces between adjacent reinforcement members are arranged to receive stringers to extend span wise along the length of the wing.

10. The rib of claim 1, wherein a portion of a reinforcement member adjacent to an upper or lower surface of the rib and proximate to an inner surface of one of the outer rib skins includes a hole arranged to receive a fastening.

11. The rib of claim 10, wherein the hole is a tapped hole arranged to receive a threaded fastening.

12. The rib of claim 1, wherein a leading edge or trailing edge end of the rib is arranged to be coupled to a spar of the wing.

13. The rib of claim 12, wherein leading or trailing edges of the rib are provided with a plurality of holes to receive a fastener to attach the spar to the rib.

14. The rib of claim 1, wherein the reinforcement members are connected to the outer rib skins by one of friction stir welding, linear friction welding, or rotary friction welding.

15. The rib of claim 1, wherein the reinforcement members and outer rib skins are formed of a same material.

16. The rib of claim 1, wherein the opposing outer rib skins are formed of a first material and wherein one or more of the reinforcement members are formed of a second material.

17. The rib of claim 1, wherein the outer rib skins in use extend from the upper outer wing skin of the aircraft wing to the lower outer wing skin of the aircraft wing.

18. A method of manufacturing a rib for an aircraft wing, wherein the rib comprises a pair of opposing outer rib skins, each outer skin extending from an upper edge connectable to an upper outer wing skin of the aircraft wing to a lower edge connectable to a lower outer wing skin of the aircraft wing, one of the outer rib skins spaced apart in a span-wise axis of the wing from the other of the outer rib skins in use so as to define an internal space there-between that separates the outer rib skins in the span-wise axis such that the outer rib skins are nonoverlapping along the span-wise axis, said rib further comprising a plurality of internal reinforcement members extending across the space and connecting the pair of opposing outer rib skins: said method comprising the steps of: (A) welding a first skin to a first side of the reinforcement members; and (B) welding the opposing side of each reinforcement member to the second skin; wherein at least one of the reinforcement members has a stepped or tapered cross-section such that a portion of the reinforcement member between the opposing outer rib skins has a smaller cross-section than portions adjacent to the opposing outer rib skins.

19. A method of manufacturing a rib for an aircraft wing, wherein the rib comprises a pair of opposing outer rib skins, each outer rib skin extending from an upper edge connectable to an upper outer wing skin of the aircraft wing to a lower edge connectable to a lower outer wing skin of the aircraft wing, one of the outer rib skins spaced apart in a span-wise axis of the wing from the other of the outer rib skins in use so as to define an internal space there-between that separates the outer rib skins in the span-wise axis such that the outer rib skins are nonoverlapping along the span-wise axis, said method comprising the steps of: (A) extruding a plurality of rib sub-sections, each rib sub-section comprising two opposing outer rib skin portions, one of the outer rib skin portions of each rib sub-section spaced apart in a span-wise axis of the wing from the other of the outer rib skins portions of that rib sub-section in use so as to define an internal space there-between that separates the outer rib skin skin portions along the span-wise axis such that the outer rib skin skin portions are nonoverlapping along the span-wise axis, and a plurality of reinforcement portions extending across the space and connecting the two opposing outer rib skin portions; and (B) connecting the plurality of the rib sub-sections together to form the rib; wherein at least one of the reinforcement portions has a stepped or tapered cross-section such that a portion of the reinforcement portion between the opposing outer rib skins has a smaller cross-section than portions adjacent to the opposing outer rib skins.

20. The method of claim 19, wherein the outer rib skin portions are provided with a matching portion arranged in use to abut with a corresponding matching portion of an adjacent rib sub-section.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 1 illustrates the internal structure of a wing;

(3) FIG. 2 shows a cross-section of a rib from FIG. 1;

(4) FIG. 3 shows a rib foot in cross-section through A-A′ shown in FIG. 2;

(5) FIGS. 4(a) to 4(c) show existing approaches to rib foot design and FIG. 4 (d) shows a rib described herein;

(6) FIG. 5 shows a top down view of the present rib arrangement;

(7) FIG. 6 shows a cross-section through A-A′ in FIG. 5;

(8) FIG. 7 shows a spar and rib connection;

(9) FIG. 8 shows a cross-section through FIG. 7, corresponding to FIG. 5;

(10) FIG. 9 shows a top down view of rib/skin coupling points;

(11) FIG. 10 is a cross-section through a rib having non-uniform and optimised reinforcements; and

(12) FIG. 11 shows an extruded and modular rib construction.

(13) 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. It will also be recognised that the invention covers not only individual embodiments but also combination of the embodiments described herein.

DETAILED DESCRIPTION

(14) FIG. 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.

(15) FIG. 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.

(16) Leading and trailing edge geometries are shown in dotted lines in FIG. 2 and extend from the spars 2 on either side. FIG. 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 stringers extend along the length of the wing from the fuselage to the wing tip.

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

(18) FIG. 3 shows a section through A-A′ shown in FIG. 2 and specifically the interface of a conventional rib foot 7 and wing cover (i.e. the stringers and skin). As shown the rib 1 has a ‘T shaped’ upper section which can be conveniently connected to the wing surface 6 by means of rivets 9 or the like. Thus, the wing outer surface can be secured to the rib.

(19) FIG. 4 illustrates different configurations of rib feet.

(20) FIG. 4(a) shows a conventional T-section rib foot which provides a simple means to connect the rib to the skin.

(21) FIG. 4 (b) shows a T-Section rib with stiffening webs (shown in dotted lines) that offer more efficient performance in terms of rigidity. However, the improvement in rigidity comes at a price since these ribs can be more expensive to manufacture in terms of additional material requirements and machining time.

(22) FIG. 4 (c) shows an extruded or additive manufactured rib foot with internal reinforcements within a triangular body. This advantageously offers improved performance without excessive material requirements although the manufacturing process is more complex than the basic rib foot shown in FIG. 4(a).

(23) FIG. 4(d) shows an unconventional and alternative rib approach which dispenses with the conventional rib foot connection. Specifically, an entirely different concept is used for the rib construction using a pair of load bearing face skins, reinforced with members located between the load bearing skins. In effect a ‘sandwich’ type structure is used.

(24) Conventional ribs, such as that shown in FIG. 4(a), are based on the concept of a single plate that is reinforced with stiffening webs and has plurality of ‘feet’ for attachment to the wing skins. These structures can then be optimised to meet the specific load bearing requirements of the wing.

(25) The present disclosure uses a completely different structure which will now be described with reference to FIGS. 4 (d) to 11.

(26) FIG. 4 (d) shows the configuration of rib comprising a central reinforcement 10 and two opposing load bearing skins 11a, 11b.

(27) FIG. 5 shows one example rib structure described herein in a top down view of the arrangement shown in FIG. 4(d). FIG. 5 shows the reinforcement 10 and the two opposing load bearing skins 11a, 11b.

(28) The reinforcements 10 are coupled to each load bearing skin 11a, 11b at interfaces 12. The reinforcements and skins may be coupled together using conventional techniques. However, advantageously the reinforcements may be connected by a friction stir welding process to create a single component rib incorporating the two skins and intermediate reinforcements.

(29) FIG. 6 shows a cross-section through A-A′ from FIG. 5. As shown the reinforcements 10 extend from the upper surface 13 of the rib 1 to the lower surface 14. The outer wing skin surface 6 can then be coupled to the upper and lower surfaces 13, 14.

(30) FIGS. 5 and 6 illustrate the unconventional ‘box’ structure of the rib described herein. The ‘box’ is formed by the outer surfaces 11a, 11b. The intermediate reinforcements 10 extending between the surfaces provide the structure with rigidity. Advantageously the alternative design allows for increased flexibility in rib design and allows for optimisation of strength and minimisation of material usage. It also conveniently allows the rib to be manufactured easily using techniques such as friction stir welding.

(31) FIG. 7 illustrates how the rib can be coupled to the spars (shown in FIG. 1). The rib may be conveniently coupled directly to the spar 2 at coupling points 15. These couplings may also be in the form of friction stir welds.

(32) FIG. 8 is a corresponding cross-section to that shown in FIG. 5 but illustrating the connection 16 between the rib 1 and spar 2.

(33) As described above the connection 15 between the rib and spar may be made in a number of suitable ways. Similarly, the outer side surfaces 11a, 11b can also be coupled to the reinforcements 10 using conventional couplings (such as rivets) or my means of friction stir welding or the like.

(34) Referring to FIG. 9, holes 17 may be tapped into the reinforcement outer side surface or a point at which the two meet (as shown in FIG. 9). The tapped holes 17 (i.e., holes with threads cut into them to receive a fastening such as a bolt or screw) allows the outer wing surface 6 to be coupled to the rib without the need for nuts or the like on the inside of the wing. This may dramatically reduce the assembly time for the wing since access inside the wing body to attach nuts or the like is no longer required.

(35) Similarly, the spar and rib may also be connected in a similar way using holes 18 on the outer edge of the rib assembly. These holes 18 may be conventional holes to receive a nut and bolt or may also be tapped to receive a threaded fastener.

(36) FIG. 10 shows another cross-section through a rib described herein. As shown the reinforcements 10 are not linear between the upper and lower surfaces but instead have been optimised for strength and rigidity. As shown some reinforcements are straight whilst some are arranged at angles, are serpentine and even vary in width, i.e., they may be selectively tapered or change in width/thickness depending on loading requirements.

(37) The rib as described herein provides an extremely versatile design which can be fully optimised to accommodate the expected loads. For example, the distribution and size of the reinforcements may be matched closely to stress models of the wing to optimise the wing's strength whilst minimising the material used. This advantageously not only simplifies the manufacturing of the rib but it also minimises the material and thus the weight. Since each wing will contain a plurality of ribs, even a modest material saving can make significant difference to the overall weight of the wing. The reinforcing structure could be optimised with a wide range of example geometries.

(38) For metallic reinforcements, it may be possible to bend extrusions, pre-join metal reinforcement details, cast optimised internal structure for joining, additively manufacture internal structure, add access/system hole reinforcing rings and so forth. The arrangement provides a range of manufacturing processes to be used.

(39) The couplings described here may, as described above, be conventional couplings or welds. Welding may include conventional welding or friction stir welding. Further alternatives may include linear friction welding or rotary friction welding of blocks could also be used to create cover interface ‘land’ on one face sheet before adding the next. A friction stir weld (or similar operation) could conveniently be used on the skin 11a, 11b surface to weld the reinforcements to the skins from the outside of the box structure. This further facilitates efficient manufacture.

(40) Still further, the rib may be formed of a composite material, such as a carbon fibre reinforced plastic (thermoset or thermoplastic). For thermoset composite processing, it would be possible to pre-fabricate the internal structure and co-cure or secondary bond it. Alternatively, the whole composite structure could be delivered in a one-shot cure process. Where cost and production rate are significant considerations, infusion and out of autoclave curing could also be used. To allow a composite component to be suitably connected to an adjacent part of the wing, inserts could be integrated at the interface points to receive a coupling such as a nut and bolt or rivet.

(41) For thermoplastic composite processing (for example a material comprising a carbon fibre and plastic/resin mix), a central reinforcing structure could be molded and then thermoplastic welded to the face sheets, for example.

(42) A further alternative may be to use ‘hybrid box ribs’ comprising composite and metallic materials where appropriate to do so. For example, a rib comprising composite skins with an optimised titanium reinforcing structure may be used. This could be low cost extrusion or a high performance additively manufactured or cast structure. This could be secondary bonded, co-cured, or in the case of thermoplastic a hybrid joining method that combining chemical bonding with mechanical interlocking which may be achieved by the re-melting potential of the material.

(43) It will be recognised that any suitable combination of material may be used according to a rib arrangement and manufacturing method described herein. For example, aluminium and aluminium alloys may be used which can be conveniently welded and are also light. Similarly, more exotic materials may be used either alone or in combination such as titanium and titanium alloys. A broad range of combinations of materials can be used for the sub-components of the rib. This could be a combination of metallic, composite and plastic (thermoplastic and thermoset) materials. In effect a multi-material rib may be realised in an unconventional configuration and unconventional manufacturing method.

(44) FIG. 11 shows a further arrangement of a box rib described herein.

(45) The outer surfaces 11a, 11b and reinforcement could be fabricated using extrusions. Here two adjacent extrusions 19, 20 may be first extruded to a predetermined shape (cross-section) and then welded or otherwise bonded together. For example, the two adjacent extrusions could be friction stir welded together to create a net shape. Advantageously, the rib may then be formed without using separate skins 11a, 11b described above. This negates the need for separate skins and moves the rib to skin interface holes 17 away from the friction stir welded joint 21. This may then provide an advantage in terms of mechanical performance.

(46) An alternative rib construction approach as described herein provides a range of technical advantages including, but not limited to: 1. Improved buy to fly ratios on metallic ribs. 2. Low cost net shape manufacture for metallic ribs. For example, aluminium friction stir welding is fast, high performance, tailorable and in this case it would be very simple since the joining is all in one plane (flat). 3. Disruptively low finishing costs compared to current ribs, for example, if friction stir welding is used to join extrusions, finishing would be significantly reduced to some edge profiling and cut-outs. All of the historic roughing and deep pocket machining would be gone, removing huge costs from the process. Furthermore, non-recurring costs associated with needing multiple fixtures for different machining stages on different ribs would be gone, since every single rib is flat on each side and as such can be vacuumed (for example) onto a flat bed. 4. Enhanced design freedom, new optimisation opportunities, especially for composite ribs where historic attempts at ‘black metal’ designs have not been successful. This approach could enable new architectures. 5. Enabler for low cost wing-box assembly, the new style of rib could contain threaded holes for assembly, to avoid use of nuts and sealing of nuts in wing box assembly. Furthermore, the new style of rib could afford new design freedoms for alternative cover-rib and spar-rib interface designs that give improved performance or reduced assembly hours. 6. Applicable to a range of materials, aluminium alloys, titanium alloys, magnesium alloys, thermosets, thermoplastics 7. Qualification of a metallic option based on friction stir welding.

(47) As described above the box rib structure may be conveniently formed by welding (for example friction stir welding) a pair of skins 11a, 11b to a plurality of reinforcements 10. The welds may for example be continuous along the length of the reinforcements or may be intermittent as required according to the loading on the reinforcement and rib.

(48) The box rib structure may also be formed using an additive manufacture process. Additive manufacture allows 3 dimensional shapes to be formed by adding material, usually layer by layer, to generate the desired structure. Additive manufacturing techniques allow intricate and complex shapes, including internal geometries, to be created in metallic form using powder metals (in one example process).

(49) In each of the embodiments described herein an additive manufacturing process many conveniently be used. For example, a powder bed fusion process may be used to build the opposing skins and reinforcement portions in a layer-by-layer approach. Advantageously such a process allows the internal geometries (e.g. thicknesses, densities, distributions and shapes/contours) to be fully optimised. This may for example be in response to a determination of desired strength through finite element analysis or other modelling. Thus, the rib can be fully optimised and complex internal shapes such as those illustrated in FIG. 10 may be realised.