Aircraft wing box

An aircraft wing box is disclosed having a fuel tank with a fuel-tight boundary, upper and lower covers, forward and aft spars, and a partition including an inboard portion, an outboard portion, and a third portion between the inboard and outboard portions. Each cover is attached to each spar, the inboard portion of the partition is joined to each cover and joined to one of the spars, the outboard portion of the partition is joined to each cover and joined to one of the spars, each cover is joined to the partition. The inboard part, outboard part and third part of the partition are integrally formed as a single-piece; and the single-piece provides part of the fuel-tight boundary of the fuel tank.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to United Kingdom Patent Application GB 2004722.1, filed Mar. 31, 2020, the entire contents of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to an aircraft wing box having a fuel-tight boundary, and a method of manufacturing the wing box.

BACKGROUND OF THE INVENTION

Boundaries between sections of a fuel tank system in an aircraft wing require fuel-tight sealing. Each seal formed between adjacent parts of the fuel boundary needs to be carefully manufactured to form the fuel-tight boundary, and subsequently each seal needs to be regularly inspected and maintained to ensure that the seal remains fuel-tight. This requires a significant amount of time and effort.

SUMMARY OF THE INVENTION

A first aspect of the invention provides an aircraft wing box comprising: a fuel tank with a fuel-tight boundary; upper and lower covers; forward and aft spars; and a partition which provides part of the fuel-tight boundary of the fuel tank, the partition comprising an inboard portion, an outboard portion, and an intermediate portion between the inboard and outboard portions, wherein: each cover is attached to each spar; the inboard portion of the partition is joined to each cover and joined to one of the spars; the outboard portion of the partition is joined to each cover and joined to one of the spars; each cover is joined to the partition; and the inboard, outboard and intermediate portions of the partition are integrally formed as a single-piece.

A second aspect of the invention provides an aircraft wing box, comprising: a root and a tip, the wing box extending from the tip to the root in a spanwise direction, a forward spar and a aft spar spaced apart in a chordwise direction, and an upper cover and a lower cover each extending between the front and aft spars, a fuel-tight partition comprising a first portion extending in a substantially chordwise direction, a second portion extending in a substantially chordwise direction, and a third portion between the first and second chordwise portions and extending in a substantially spanwise direction, wherein the first, second and third portions are integral with each other.

A further aspect of the invention provides a method of manufacturing the wing box of the first or second aspect, the method comprising machining, casting, pressing, co-curing or moulding material to form the partition as a single piece; and installing the partition the partition in the wing box.

By way of non-limiting example, the partition may be machined or cast from a single piece of metal material, or moulded as a single piece by hot isostatic pressing. Alternatively the partition may be formed from a single fibre preform which is infused with a matrix material.

The following comments apply to each aspect of the invention, where applicable.

Forming the portions of the partition integrally with each other provides two advantages. Firstly, it makes the wing box quicker and easier to assemble since the partition can be installed into the wing box as a single modular unit. Secondly, it makes the partition less prone to fuel leakage since it is not necessary to seal the junctions where the portions of the partition meet.

Typically the wing box has a root and a tip, and the inboard/first portion of the partition is closer to the root of the wing box than the outboard/second portion.

The forward spar may form a front boundary of the wing box, or it may be a centre spar of the wing box.

The aft spar may form a rear boundary of the wing box, or it may be a centre spar of the wing box.

A part of the fuel-tight boundary may be formed by one of the spars.

The covers and one or both of the spars may provide part of the fuel-tight boundary of the fuel tank.

In some embodiments the inboard/first portion is joined to one of the spars and the outboard/second portion is joined to the other one of the spars. In a preferred embodiment the inboard/first portion is joined to the aft spar and the outboard/second portion is joined to the forward spar.

Alternatively the inboard/first portion and the outboard/second portion may be joined to the same one of the spars. In a preferred embodiment the inboard/first portion and the outboard/second portion are both joined to the forward spar. In this case the second/intermediate portion may have a curved concave forward surface facing the forward spar and a curved convex aft surface facing away from the forward spar.

At least one of the covers may be integrally formed as a single piece with at least one of the spars.

The intermediate/third portion of the partition may comprise a diaphragm with a planar diaphragm web.

The fuel-tight boundary may be a boundary between two adjacent fuel bays arranged to hold fuel, for instance an inboard fuel bay and an outboard fuel bay.

Alternatively the fuel-tight boundary may be a boundary between a fuel bay arranged to hold fuel and a dry bay arranged to be free of fuel.

The partition may comprise at least one foot or flange attached to the upper cover and at least one foot or flange attached to the lower cover, wherein each foot or flange is integrally formed with the rest of the partition as a single-piece.

The inboard portion may have a post or flange attached to one of the forward spar and aft spar, the outboard portion may have a post or flange attached to one of the forward spar and aft spar, and each post or flange may be integrally formed with the rest of the partition as a single-piece.

DETAILED DESCRIPTION OF EMBODIMENT(S)

FIG.1shows an aircraft1with port and starboard fixed wings2,3, and a fuselage4with a nose5and a tail6. The aircraft1is a typical jet passenger transonic transport aircraft but the invention is applicable to a wide variety of fixed wing aircraft types, including commercial, military, passenger, cargo, jet, propeller, general aviation, etc. with any number of engines9attached to the wings or fuselage.

Each wing2,3has a cantilevered structure with a length extending in a span-wise direction from a wing root7to a wing tip8, the wing root7being joined to the fuselage4. The wings2,3are similar in construction so only the port wing2will be described in detail with reference to the following Figures.

In the following description, the terms “front” or “forward” refer to components towards a leading edge11of the wing, and the terms “rear” or “aft” refer to components towards a trailing edge12of the wing. The position of features may be construed relative to other features, for example a forward component may be disposed on a forward side of another component, but towards the rear of the vehicle. Similarly, the terms “upper” and “lower” refer to the position of features relative to other features and in accordance with a normal orientation of the aircraft1. Similarly, the terms “inboard” and “outboard” refer to the relative positions of features in the spanwise direction of the wing box. That is, an inboard component is closer to the root of the wing box than an outboard component, and an outboard component is closer to the tip of the wing box than an inboard component.

FIG.2shows a schematic view of a wing box10of the port wing2of the aircraft1. The wing box10is a support structure arranged to support a significant proportion of the loads on the wing2. The wing box10has a forward spar13which forms the front boundary of the wing box, an aft spar14which forms the rear boundary of the wing box, an upper cover15, and a lower cover16.

Each of the elements13-16of the wing box extends substantially the entire length of the wing2from a root7aof the wing box10(which typically coincides with the root7of the wing2) to a tip8aof the wing box10(which may coincide with the tip8of the wing2, or the tip8of the wing may be a wingtip device such as a winglet). The upper cover15and lower cover16have outer aerodynamic surfaces. The wing2also includes a leading edge structure (not shown) and a trailing edge structure (not shown) that are aerodynamically shaped to combine with the wing box10to form an aerofoil shaped body.

The covers15,16may be reinforced with stringers. Stringers are typically spanwise extending reinforcing members attached to the inside of the covers15,16.

As shown inFIG.3, the wing box10also includes a plurality of chordwise ribs extending between the spars13,14and between the covers15,16. The ribs are spaced along the spanwise direction of the wing2, with each rib defining a rib plane. The rib plane of each rib extends substantially parallel to each adjacent rib plane, although it will be understood that the orientation of adjacent ribs with respect to each other may vary. The ribs are arranged as part of an aircraft fuel system, such that some of the ribs are baffle ribs18,71,72designed to allow at least some free-flow of fuel across the rib plane (indicated by a dotted line), and some ribs18i,18jare fully sealed to form a fuel-tight boundary substantially preventing fuel freely flowing across the rib plane (indicated by a solid line).

The number of baffle ribs18may vary from what is shown inFIG.3, which is schematic only.

FIG.4shows a plan view of the wing box10in which only the sealed ribs18i,18jand other sealed parts18b,18d,18e,18h,30a,31aforming a fuel-tight boundary are shown.

The wing box10contains an inner tank20, an outer tank21, and a vent tank22, shown inFIG.4. The inner wing tank20is adjacent the root7aof the wing box10, the outer wing tank21is generally outboard of the inner wing tank20, and the vent tank22is located outboard of the outer wing tank21and towards the tip8aof the wing box10. Each of these tanks20,21,22forms part of an aircraft fuel system that supplies fuel to the engines9.

Each of the fuel tanks20,21,22is bounded by a fuel-tight boundary. Some portions of the fuel-tight boundary are external parts of the wing box (for example covers and spars) and other are internal (for instance ribs etc). The internal portions of the fuel-tight boundary are referred to below as partitions, since they provide a partition between internal spaces within the wing box.

The upper and lower portions of the fuel-tight boundary of each fuel tank are provided by the covers15,16; and the forward and rear portions of the boundary of each fuel tank are provided by the spars13,14.

The partition between the outer tank21and the vent tank22is formed by an outboard rib18ithat prevents fuel freely flowing between the two respective tanks21,22. The partition31between the inner tank20and the outer tank21is formed by a rearward portion18eof a first (inboard) rib; a forward portion18hof a second (outboard) rib; and a diaphragm31aextending between the first and second ribs.

The partition31between the inner and outer fuel tanks20,21is therefore Z-shaped, having a first portion18e(inboard portion) extending in a substantially chordwise direction, a second portion18h(outboard portion) extending in a substantially chordwise direction, and an intermediate third portion (diaphragm31b) between the first and second chordwise portions18e,18hextending in a substantially spanwise direction.

The wingbox10also includes a dry-bay23adjacent to the engine9. The engine's centre-line is indicated by a dashed line9a. The boundary between the inner fuel tank20and the dry-bay23is a fuel-tight partition30ensuring that fuel from the inner tank20is prevented from leaking into the dry-bay23. The partition30is formed by an inboard portion (partition wall18b); an outboard portion (partition wall18d); and an intermediate portion (rear wall30a) between the inboard and outboard walls18b,18d.

As noted above,FIG.3is schematic only and the size of the dry-bay23may be smaller than shown.

The design of this fuel tank lay-out, including the position of the dry-bay23, is partly driven by certification requirements relating to unconstrained engine rotor failure, and so is at least partially dependent on the position of the wing-mounted engine. Fuel tank layouts may also necessitate consideration of, e.g., individual fuel tank volumes, weight distribution across the wings2,3, and fuel system routing (e.g. fuel lines), among a number of other factors. In this particular case, this has resulted in complex shaped fuel tank boundaries that are assembled from many different parts. Each connection between components at the fuel-tight boundary of a partition creates an additional interface that needs to be sealed.

FIGS.5and6shows the dry-bay partition30in detail. The partition30has a generally ‘U’ shaped profile, with the rear wall30ahaving a curved surface that continuously curves between the planar inboard and outboard portions18b,18d.

The rear wall30ahas a curved concave forward surface facing the forward spar and a curved convex aft surface facing away from the forward spar. The curved concave forward surface is labelled35inFIG.3. The curved convex aft surface is the surface visible inFIGS.5and6. The rear wall30ahas a manhole, closed by a manhole cover32.

The curved profile of the rear wall30aimproves structural efficiency, reducing stress concentrations that would otherwise build up at sharp edges/corners, and helping to resist the loads generated by fuel slosh and pulse loads—particularly pulse loads during a rapid deceleration of the aircraft which may cause fuel to rush towards the forward spar13.

As shown most clearly inFIG.6, the partition30has an upper U-shaped flange151which is joined to the upper cover15by a sealed joint; and a lower U-shaped flange152which is joined to the lower cover16by a sealed joint.

The partition30also has an inboard flange143which is joined to the forward spar13by a sealed joint; and a similar outboard flange (not visible) which is joined to the forward spar13by a sealed joint.

All parts18b,30a,18d,151,152,143of the partition30shown inFIG.5(apart from the manhole cover32) are integrally formed as a single-piece. For example, the partition30may be machined from a block of aluminium, cast as a single-piece, or moulded as a single piece by hot isostatic pressing (HIP). The HIP process may subject metal powder to both elevated temperature and isostatic gas pressure in a high pressure containment vessel.

Forming the partition30from a single-piece of material reduces the number of sealed joints required, which makes assembly of the wing box quicker and easier. In the example ofFIG.6only six sealed joints are required for the entire boundary of the dry bay: two joints between the partition30and the covers15,16; two joints between the partition30and the forward spar13; and two joints between the forward spar13and the covers15,16.

The number of sealed joints can be further reduced to five by integrally forming the forward spar13and one of the covers15,16as a single piece, as described for example in US 2019/0329860.FIG.7shows a wing box with such an arrangement. In this case the forward spar113and upper cover115are integrally formed to form a spar-cover such that the composite laminate material of the spar extends continuously into the cover through a fold region117between the spar and the cover. There is no need to seal the fold region117to prevent fuel leakage.

Whilst the partition30may have at least some vertical load carrying capacity (e.g. aerodynamic loads transmitted from the upper and lower covers), the majority of the loads in this particular example are taken by adjacent baffle ribs18inboard and outboard of the partition30, each of which connects to the upper and lower covers by respective upper and lower rib feet25,26as shown inFIG.6

In an alternative example shown inFIG.8, the dry bay partition may be formed integrally as a single modular unit230which includes baffle ribs218a,218cwhich are joined to the aft spar14so that the unit230has a generally ‘H’ shaped profile.

The unit230has an H-shaped upper flange251which is joined to the upper cover15by a sealed joint; and an H-shaped lower flange252which is joined to the lower cover16by a sealed joint.

The baffle ribs218a,218ceach include a number of holes19that allow fuel to freely flow between the fuel bays either side of the rib plane. The baffle ribs218a,218cmay also have flanges (not shown) which are joined to the aft spar14.

All parts of the unit230shown inFIG.8(apart from the manhole cover) are integrally formed as a single-piece. For example, the unit230may be machined from a block of aluminium, cast as a single-piece, or moulded as a single piece by hot isostatic pressing (HIP).

Unlike the partition30, the unit230may be engineered to withstand vertical loads transferred from the upper and lower covers.

FIGS.9and10show the Z-shaped partition31between the inner and outer fuel tanks21,22.

The partition30has an inboard portion18e, an outboard portion18hand a diaphragm31a.

The partition30has a Z-shaped upper flange351which is joined to the upper cover15by a sealed joint; and a Z-shaped lower flange (not visible in the views ofFIGS.9and10) which is joined to the lower cover16by a sealed joint.

The partition30also has a pair of rib posts363which are attached to the inner edges of the baffle half-ribs71,72as shown inFIG.10. The outer edges of the baffle half-ribs71,72are attached to the forward and aft spars respectively by rib posts73. This joint does not need to be sealed.

The inboard portion18ehas a planar web which extends in a substantially chordwise direction and is joined to the aft spar14by a fuel tight joint with a rib post343. The outboard portion18hhas a planar web which extends in a substantially chordwise direction and is joined to the forward spar13by a fuel tight joint with a rib post similar to the rib post343.

The diaphragm31ahas a planar web which extends in a substantially spanwise direction.

All parts18e,31a,18h,351,363of the partition31shown inFIG.9are integrally formed as a single-piece. For example, the partition31may be machined from a block of aluminium, cast as a single-piece, or moulded as a single piece by hot isostatic pressing (HIP).

In this particular example the half-ribs71,72and rib posts73are separately formed from the partition31and attached to the partition by fasteners, co-curing or co-bonding. In an alternative example, the half-ribs71,72and rib posts73may be formed integrally with the partition31as a single-piece.

FIG.11shows an H-shaped modular unit431which may be installed in a wing box10aas an alternative to the partition31as shown inFIG.12.

The unit431includes a Z-shaped partition with an inboard portion418e, an outboard portion418hand a diaphragm431a.

The unit431has an H-shaped upper flange451which is joined to the upper cover15by a sealed joint; and an H-shaped lower flange452which is joined to the lower cover16by a sealed joint. Note that the spanwise part of the H-shaped flange452is hidden from view by the diaphragm431a.

The unit431also has a pair of rib posts463which are attached to the inner edges of the baffle half-ribs71,72.

The inboard portion418eof the fuel partition has a planar web which extends in a substantially chordwise direction and is joined to the aft spar14by a fuel tight joint with a rib post (not shown). An inboard baffle rib portion418fextends in a substantially chordwise direction and is joined to the forward spar13by an unsealed joint with a rib post (not shown).

The outboard portion418hof the fuel partition has a planar web which extends in a substantially chordwise direction and is joined to the forward spar13by a fuel tight joint with a rib post (not shown). An outboard baffle rib portion418gextends in a substantially chordwise direction and is joined to the aft spar14by an unsealed joint with a rib post (not shown).

The diaphragm431ahas a planar web which extends in a substantially spanwise direction.

All parts418e,431a,418h,451,452,463,418f,418gof the unit431shown inFIG.11are integrally formed as a single-piece. For example, the unit431may be machined from a block of aluminium, cast as a single-piece, or moulded as a single piece by hot isostatic pressing (HIP).

In this particular example the half-ribs71,72and rib posts73are separately formed from the unit431and attached to the partition by fasteners, co-curing or co-bonding. In an alternative example, the half-ribs71,72and rib posts may be formed integrally with the unit431as a single-piece.

The rib portions418f,418geach include a number of holes19that allow fuel to flow through the rib plane.

The unit431, including the rib portions418f,418g, is configured to withstand the vertical loads transferred from the upper and lower covers.

FIG.13shows a fifth example of a partition531for forming the fuel-tight boundary between fuel tanks (for example the inner and outer fuel tanks20,21shown inFIGS.3and4). Like reference numerals are used to denote like parts with the partitions31, and similar reference numerals but numbered in the500series are used to denote similar parts.

The partition531has an inboard portion518e, an outboard portion518hand a diaphragm531a.

The partition531has upper flanges551a,551b,551cwhich are joined to the upper cover15by respective sealed joints; and lower flanges552a,552b,552cwhich are joined to the lower cover16by respective sealed joints.

The partition531also has a pair of rib posts563. Each rib post563comprises a foot563ajoined to the diaphragm531a, and a flange563bwhich is attached to an inner edges of one of the baffle half-ribs71,72.

The inboard portion518ehas a planar web which extends in a substantially chordwise direction and is joined to the aft spar14by a fuel tight joint. The outboard portion518hhas a planar web which extends in a substantially chordwise direction and is joined to the forward spar13by a fuel tight joint.

The diaphragm531ahas a planar web which extends in a substantially spanwise direction. The partition531has a generally Z-shaped profile.

The inboard portion518e, outboard portion518hand diaphragm531aare integrally formed as a single-piece from carbon fibre reinforced polymer (CFRP) laminate material.

The CFRP laminate material extends continuously from the inboard portion518eto the diaphragm531avia a curved fold region564, and also extends continuously from the diaphragm531ato the outboard portion518hvia a curved fold region565. There is no need to seal the fold region564,565to prevent fuel leakage.

Preferably the material comprises laminate plies and/or fibres (such as carbon fibres) which extend continuously from the inboard portion518eto the diaphragm531avia the curved fold region564.

Preferably the CFRP laminate material comprises laminate plies and/or fibres (such as carbon fibres) which extend continuously from the diaphragm531ato the outboard portion518hvia the curved fold region565.

Optionally the CFRP laminate material comprises laminate plies and/or fibres (such as carbon fibres) which extend continuously from the inboard portion518eto the outboard portion518hvia both curved fold regions564,565.

The CFRP laminate material may also extend continuously from the planar webs into the flanges551a,551b,551c,552a,552b,552cvia respective fold regions.

The foot563aof the rib post563may be formed from CFRP laminate material, and joined to the diaphragm531aby a co-cured joint. Alternatively the foot563amay be attached to the diaphragm531aby fasteners.

The partition531may be formed from other types of composite material, including glass fibre reinforced polymer (GFRP).

The partition531may be formed by any suitable method, for example hand lay-up of composite plies onto a lay-up table which are then co-cured on the lay-up table under a vacuum bag and/or in an autoclave, automatic fibre placement of pre-impregnated fibre tows or courses onto a mandrel which are co-cured on the mandrel after placement, or resin transfer moulding (RTM) in which resin is injected into a dry fibre preform in a closed mould.

If the RTM process is used, then most or all of the portions of the partition531may be made from a single fibre preform. For example the inboard portion518e, outboard portion518hand diaphragm531amay be integrally formed from a single fibre preform. The directions of the fibres may vary—being different in the diaphragm531athan in the inboard and outboard portions for example.

It will be clear to the skilled person that many of the features described in relation to each example can be appropriately combined with the features of other examples.

FIGS.5,6and8show a fuel-tight boundary formed between a fuel bay and a dry-bay, whilstFIGS.9-13show a fuel-tight boundary between adjacent fuel bays. It will be clear to the skilled person that each of the examples may be used to form the fuel-tight boundary between adjacent fuel bays or between a fuel bay and a dry-bay.

All of the partitions ofFIGS.5,6, and8-13may be installed in a wing box with separate spars and covers (like the wing box10ofFIG.2), or installed in a wing box with an integrated spar-cover (like the wing box ofFIG.7). In the wing box10each cover15,16is attached to a flange of each spar13,14by fasteners, and the cover/spar joint is sealed to make it fuel-tight (for instance by applying a fillet of sealant material). In a wing box with an integrated spar-cover each cover15,16may be integrally formed with a respective one of the covers.

The inboard portion18b,18e,418e,518eof each partition is joined to each cover15,16and joined to one of the spars13,14. Each joint may be sealed to make it fuel-tight (for instance by applying a fillet of sealant material and/or by affixing a seal plate to cover the joint).

The outboard portion18d,18h,418e,518eof each partition is joined to each cover15,16and joined to the forward spar13. Each joint may be sealed to make it fuel-tight (for instance by applying a fillet of sealant material and/or by affixing a seal plate to cover the joint).

Each cover15,16is joined to the partition via a flange or flanges151,251,351,451,551a-c,552a-c. Each joint may be sealed to make it fuel-tight (for instance by applying a fillet of sealant material and/or by affixing a seal plate to cover the joint).

The partition531ofFIG.13has upper flanges551a,551b,551cwhich are joined to the upper cover15by respective sealed joints; and lower flanges552a,552b,552cwhich are joined to the lower cover16by respective sealed joints. In an alternative embodiment, the partition531may not have the upper flanges551a,551b,551cand the diaphragm531amay instead be attached to the upper cover by stringers or rib feet which are carried by the upper cover.

The first/inboard, second/outboard and third/intermediate portions of the partition are integrally formed as a single-piece (for instance by machining, casting, pressing or resin-transfer moulding). This enables the partition to be manufactured and installed as a single modular unit, and reduces the number of joints which need to be sealed by applying sealant material.

It will be clear that many of the features described in relation to each example may be varied within the normal activity of the skilled person.

It will be clear that any of the attachment portions (e.g. feet, posts or flanges) of the partitions of any of the previous examples may be formed integrally with or separately from the partition. For example, the feet, posts or flanges may be integrally formed with the inboard, outboard and intermediate portions. In alternative examples, the feet, posts or flanges may be separately formed and subsequently attached to the partition.

Where the word or appears this is to be construed to mean ‘and/or’ such that items referred to are not necessarily mutually exclusive and may be used in any appropriate combination.