Duct stringer with bulkhead

Abstract

A duct stringer has duct walls providing a duct with a closed cross-section; and a bulkhead in the duct. The duct is adapted to transport fluid, and the bulkhead is adapted to block the flow of fluid along the duct. The bulkhead is adhered to the duct walls by one or more co-cured or co-bonded joints. The bulkhead includes a pair of bulkhead parts, each with a web and one or more flanges. The duct stringer is manufactured by positioning the mandrels end-to-end with the bulkhead parts back-to-back between them; wrapping or laying-up the duct walls around the bulkhead parts and the mandrels; co-curing or co-bonding the flanges of the bulkhead parts to the duct walls; and after the bulkhead has been adhered to the duct walls, removing the mandrels from opposite ends of the duct.

Claims

1. A duct stringer comprising: duct walls providing a duct with a closed cross-section, wherein the duct is adapted to transport a fluid; and a bulkhead in the duct, wherein the bulkhead is adapted to block a flow of the fluid along the duct and the bulkhead is adhered to the duct walls by one or more co-cured and/or co-bonded joints, wherein the bulkhead comprises a pair of bulkhead parts which are positioned back-to-back, each of the bulkhead parts comprises a web and a flange, and each of the flanges is adhered to the duct walls by a respective one of the co-cured and/or co-bonded joints extending around an entire periphery of the bulkhead, and wherein each of the flanges has a closed cross-section extending entirely around the bulkhead.

2. The duct stringer according to claim 1, comprising: a structural member with a hat-shaped cross-section, the structural member comprising a crown, a pair of webs and a pair of feet; and a duct member adhered to the crown and to opposed inner faces of the pair of webs, wherein the duct walls are provided by the duct member.

3. The duct stringer according to claim 1, wherein the bulkhead divides the duct into a first portion on a first side of the bulkhead and a second portion on a second side of the bulkhead; and the first portion is adapted to transport fluid via an interconnecting pipe.

4. The duct stringer according to claim 3, wherein the bulkhead is adhered to the duct walls around a full periphery of the bulkhead so that the bulkhead substantially prevents the flow of fluid between the first and second portions of the duct.

5. The duct stringer according to claim 1, wherein the duct is in fluid communication with a tank via an interconnecting pipe.

6. A structure comprising a skin; and the duct stringer according to claim 1 adhered to the skin.

7. A fuel system comprising: a first tank; a second tank; and a duct stringer including duct walls defining a duct having a closed cross-section, wherein the duct is adapted to transport a fluid; and a bulkhead in the duct, wherein the bulkhead is configured to block a flow of the fluid in the duct and the bulkhead is adhered to the duct walls by one or more co-cured and/or co-bonded joints, wherein the duct is in fluid communication with the first and second tanks, wherein the bulkhead comprises bulkhead parts positioned back-to-back to each other, each of the bulkhead parts comprises a web and a flange, and each of the flanges is adhered to the duct walls by a co-cured joint and/or co-bonded joint, and wherein the flange for each of the respective bulkhead parts extends entirely around an inner perimeter of the duct and forms a closed cross-section extending entirely around a perimeter of the web.

8. The fuel system according to claim 7, wherein the first tank is a fuel tank, and the second tank is a surge tank.

9. The fuel system according to claim 7, wherein one or both of the first and second tanks are in an aircraft wing.

10. The fuel system according to claim 7, wherein the duct is in fluid communication with the first and/or second tank via an interconnecting pipe.

11. The fuel system according to claim 7, wherein the bulkhead divides the duct into a first portion on a first side of the bulkhead which is in fluid communication with the first and second tanks; and a second portion on a second side of the bulkhead.

12. An aircraft comprising the duct stringer according to claim 1.

13. A wing comprising: a skin having an outer surface exposed to an airstream flowing over the wing and an inner surface, opposite to the outer surface; a duct stringer attached to the inner surface and including duct walls defining a duct with a closed cross-section; a bulkhead in the duct, and a co-cured and/or co-bonded joint between the bulkhead the duct walls, wherein the duct is configured to transport a gas along a portion of the duct on one side of the bulkhead, wherein the bulkhead in the duct is configured to block a flow of the gas through the duct, wherein the bulkhead comprises bulkhead parts positioned back-to-back to each other, each of the bulkhead parts comprises a web and a flange, and each of the flanges is adhered to the duct walls by a co-cured joint and/or co-bonded joint, and wherein the flange for each of the respective bulkhead parts extends entirely around an inner perimeter of the duct and forms a closed cross-section extending entirely around a perimeter of the web.

14. The wing of claim 13, wherein the skin is an upper skin and the wing further includes: a lower skin opposite the upper skin; and a first fuel tank and a second fuel tank both between the upper and lower skins, wherein the second fuel tank is separated from the first fuel tank in a spanwise direction of the wing; wherein the duct is in fluid communication with the first fuel tank and the second fuel tank.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

(2) FIG. 1 is a plan view of an aircraft;

(3) FIG. 2 is a plan view of the aircraft's fuel tank system;

(4) FIG. 3 is a tranverse cross-section across one of the duct stringers;

(5) FIGS. 4-25 show a method of manufacturing one of the duct stringers; and

(6) FIGS. 26a and 26b schematically show the formation of a co-bonded joint in the structure of FIG. 3.

DETAILED DESCRIPTION OF EMBODIMENT(S)

(7) FIG. 1 is a plan view of an aircraft 1 comprising a pair of wings 2 and a fuselage 3. FIG. 2 is a plan view of certain elements of the aircraft's fuel tank system, including a centre fuel tank 10 inside the fuselage, and wing tanks 11-13 inside the wing 2. The wing tanks comprise an inboard fuel tank 11, an outboard fuel tank 12 and a surge tank 13. The tanks 10-13 are separated by ribs 14-16.

(8) The wing tanks 11-13 are bounded fore and aft by spars 17, 18. The upper and lower boundaries of the wing tanks 11-13 are provided by upper and lower wing skins, not shown in FIG. 1. Each wing skin is stiffened by stringers running span-wise along the length of the wing. Two of the stringers attached to the upper wing skin are so-called “duct stringers” 20, 30 which are shown in FIG. 2. The other stringers attached to the upper wing skin are not shown in order to simplify the drawing.

(9) Each duct stringer 20, 30 includes a duct portion 20a, 30a outboard of an internal bulkhead 21, 31; and a structural portion 20b, 30b inboard of the internal bulkhead 21, 31.

(10) The duct portion 20a of the duct stringer 20 is in fluid communication with the outboard fuel tank 12 via an interconnecting pipe 22 and with the surge tank 13 via an outlet 23 at the end of the stringer 20. The duct portion 30a of the duct stringer 30 is in fluid communication with the inboard fuel tank 11 via an interconnecting pipe 33 and with the surge tank 13 via an outlet 34 at the end of the stringer 30. The duct portion 30a of the duct stringer 30 is also in fluid communication with the centre fuel tank 10 via an interconnecting pipe 32. Optionally, the distal end of each interconnecting pipe 22, 32, 33 is fitted with a bell mouth or float valve, not shown.

(11) During operation of the aircraft, the duct stringers 20, 30 are used to transport air in either direction between the surge tank 13 and the fuel tanks 10-13 in order to manage the air pressure within the tanks. So each duct stringer 20, 30 has two functions: stiffening the upper wing skin; and providing a duct which transports air to and from the surge tank 13.

(12) FIG. 3 is a transverse cross-sectional view of the duct stringer 20 and the upper wing skin 46 which carries it. The other duct stringer 30 has an identical construction so will not be described in detail. The duct stringer 20 comprises a structural member 25 with a hat-shaped cross-section, a duct member 26 with a closed trapezoidal cross-section; and a pair of noodles 62. The structural member 25 has a crown 40, a pair of webs 41 and a pair of feet 42. The crown 40, webs 41 and feet 42 are formed as a single laminar composite part, with plies of the composite material running from one foot 42 to the other via the webs 41 and the crown 40. The duct member 26 is adhered to the crown 40 and to the opposed inner faces of the webs 41 by respective co-cured joints. The duct member 26 and the feet 42 of the structural member are adhered to the upper wing skin 46 by co-cured joints. The duct member 26 provides duct walls which fully enclose a duct 45a,b with a closed trapezoidal cross-section which is adapted to transport air between the tanks 12, 13.

(13) The bulkhead 21 divides the duct into a first portion 45a on a first side of the bulkhead and a second portion 45b on a second side of the bulkhead as shown in FIG. 4. The first portion 45a of the duct (which runs along the duct portion 20a shown in FIG. 2) is adapted to transport air; and the second portion 45b of the duct (which runs along the structural portion 20b shown in FIG. 2) is not adapted to transport air so may optionally be blocked at its inboard end.

(14) The interconnecting pipe 22 is connected to the first portion 45a of the duct 45a by cutting a hole in the crown 40, and attaching a downpipe fitting (not shown) such as the fitting described in US2013/0316147, the disclosure of which is incorporated herein by reference.

(15) FIGS. 4-6 show the structure of the bulkhead 21. The bulkhead 21 comprises a pair of C-section bulkhead parts 21a, 21b which are positioned back-to-back to form an I-section; and a noodle 61, e.g., a fillet. Each C-section bulkhead part comprises a web 50a, b and a flange 51a,b. Each flange 51a,b is adhered to the duct member 26 by a respective co-cured or co-bonded joint.

(16) As shown in FIGS. 3 and 6, each flange 51a,b has a closed trapezeoidal cross-section and runs around the bulkhead. Each flange 51a,b is adhered to the duct member 26 around its full periphery so that the bulkhead substantially prevents the flow of fluid between the two portions of the duct.

(17) FIGS. 8-23 show a method of manufacturing the structure of FIGS. 3 and 4.

(18) A pair of mandrels 60a,b are provided. Both mandrels 60a,b are shown in FIG. 12. The mandrels are identical so only one will be described in detail with reference to FIGS. 8 to 11.

(19) The mandrel 60b may be formed of silicone rubber, and has a recess 61b at one end. The bulkhead part 21b is fitted in the recess 61b as shown in FIGS. 10 and 11. This may be achieved by laying-up the bulkhead part 21b ply-by-ply directly into the recess 61b, or by laying it up ply-by-ply on a male tool (now shown) then transferring it onto the mandrel 60b.

(20) The bulkhead part 21b at this stage is a dry-fibre preform, comprising dry carbon fibre plies and a binder. The plies are formed with darts to enable them to be laid up without wrinkling to form the corners of the flange 51b.

(21) The mandrels are then positioned end-to-end with the bulkhead between them as in FIGS. 12 and 13. Next, a noodle 61 is fitted as shown in FIGS. 14 and 15

(22) The duct member 26 is then formed by wrapping or laying-up around the bulkhead 21 and the mandrels 60a,b as shown in FIGS. 16 and 17. This may be achieved by laying-up the duct member 26 ply-by-ply directly onto the bulkhead 21 and the mandrels; 60a,b; or by laying it up as a flat or C-section charge and then wrapping the charge around the bulkhead 21 and the mandrels; 60a,b. The duct member 26 at this stage is a dry-fibre preform, comprising dry carbon fibre plies and a binder.

(23) Note that the duct member 26 is formed around the bulkhead 21 as a dry-fibre preform, rather than inserting the bulkhead 21 into a previously formed duct. This makes the structure easy to assemble.

(24) Next the assembly is placed onto the skin 46 as shown in FIGS. 18 and 19, and noodles 62 are fitted as shown in FIGS. 20 and 21. The skin 46 at this stage is a dry-fibre preform, comprising dry carbon fibre plies and a binder.

(25) Next the hat-section structural member 25 is laid-up over the assembly as in FIGS. 22 and 23. The structural member 25 at this stage is a dry-fibre preform, comprising dry carbon fibre plies and a binder.

(26) Next the assembly is covered with a vacuum bag (not shown) and the composite parts 21, 25, 26, 46, 61, 62 co-infused with epoxy resin matrix material. After infusion, the matrix material cures to form the various co-cured joints in a single curing process. After the parts are fully cured, the mandrels are removed from opposite ends of the duct as shown in FIGS. 24 and 25.

(27) In the method described above, the structure is formed by infusion of resin into dry fibre preforms, but alternatively some or all of the carbon-fibre parts 21, 25, 26, 46, 61, 62 may be laid up as “pre-preg” laminates, where each ply in the laminate is a fibre ply pre-impregnated with thermosetting epoxy resin which is cured by heating after the structure has been assembled.

(28) In the method described above, the bulkhead is a two-part bulkhead which is adhered to the duct walls by co-cured joints, but in an alternative embodiment the bulkhead may be a pre-manufactured thermoplastic single piece bulkhead which is co-bonded to the duct walls.

(29) FIGS. 26a and 26b schematically show the formation of a co-cured joint between two elements of the structure described above. In this example, the adherends are the flange 51a and the duct member 26, but the other co-cured joints are similar.

(30) The adherends are first placed together as dry-fibre preforms as in FIG. 26a, with no epoxy resin. After being co-infused with epoxy resin matrix material, the epoxy resin is cured to form the co-cured joint 70 of FIG. 26b. The adhesive at the bond line 71 is the same material as the epoxy resin matrix material in the adherends 51a, 26.

(31) 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.

(32) Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims