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Title:
THRUST REVERSER INNER FIXED STRUCTURE
Document Type and Number:
WIPO Patent Application WO/2019/155015
Kind Code:
A1
Abstract:
A thrust reverser inner fixed structure comprising: a barrel portion; a discrete bifurcation; and a joint joining the discrete bifurcation to the barrel portion.

Inventors:
LUCAS, Scott (Bancroft Road, Burnley Lancashire BB10 2TQ, BB10 2TQ, GB)
MITCHELL, Michael (Bancroft Road, Burnley Lancashire BB10 2TQ, BB10 2TQ, GB)
HILL, Graeme (Bancroft Road, Burnley Lancashire BB10 2TQ, BB10 2TQ, GB)
FURMSTON, Simon (Bancroft Road, Burnley Lancashire BB10 2TQ, BB10 2TQ, GB)
Application Number:
EP2019/053192
Publication Date:
August 15, 2019
Filing Date:
February 08, 2019
Export Citation:
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Assignee:
SAFRAN NACELLES LIMITED (Bancroft Road, Burnley Lancashire BB10 2TQ, BB10 2TQ, GB)
International Classes:
F02K1/64; F02K1/72
Foreign References:
US5101621A1992-04-07
US20170284216A12017-10-05
US9834313B22017-12-05
US5083426A1992-01-28
EP2781728A22014-09-24
US20150098810A12015-04-09
US9168716B22015-10-27
US20170363042A12017-12-21
US4283028A1981-08-11
Attorney, Agent or Firm:
BARKER BRETTELL LLP (100 Hagley Road, Edgbaston, Birmingham West Midlands B16 8QQ, B16 8QQ, GB)
Download PDF:
Claims:
CLAIMS

1. A thrust reverser inner fixed structure comprising:

a barrel portion;

a discrete bifurcation; and

a joint joining the discrete bifurcation to the barrel portion,

wherein the discrete bifurcation comprises an acoustic treatment.

2. A thrust reverser inner fixed structure according to claim 1 , wherein the barrel portion has a length and is curved in a lateral direction such that the curvature in a given lateral direction has a consistent (non-zero) sign at all points along the length of the barrel portion.

3. A thrust reverser inner fixed structure according to claim 1 or claim 2, wherein the discrete bifurcation comprises one or more bodies.

4. A thrust reverser inner fixed structure according to claim 1 , claim 2 or claim 3, wherein the discrete bifurcation has a first longitudinal edge and a second longitudinal edge.

5. A thrust reverser inner fixed structure according to claim 4, wherein the discrete bifurcation includes at least one bend such that the first longitudinal edge and the second longitudinal edge are located in differently oriented planes.

6. A thrust reverser inner fixed structure according to any one of claims 1 to 5, wherein the discrete bifurcation comprises a beam or track for connecting to another component or structure.

7. A thrust reverser inner fixed structure according to claim 6, wherein the beam or track is integral to the discrete bifurcation.

8. A thrust reverser inner fixed structure according to any one of the preceding claims, wherein the acoustic treatment comprises a plurality of recesses or cells formed in the discrete bifurcation.

9. A thrust reverser inner fixed structure according to any one of the preceding claims, wherein the acoustic treatment is formed by an additive manufacturing process such as three-dimensional printing.

10. A thrust reverser inner fixed structure according to any one of the preceding claims, wherein the acoustic treatment includes perforations.

1 1. A thrust reverser inner fixed structure according to any one of the preceding claims, wherein the acoustic treatment includes a honeycomb material.

12. A thrust reverser inner fixed structure according to any one of the preceding claims, wherein the acoustic treatment includes a fabricated lattice structure.

13. A thrust reverser inner fixed structure according to any one of the preceding claims, wherein the acoustic treatment includes a sound absorbing foam material.

14. A thrust reverser inner fixed structure according to claim 8 or any one of claims 9 to 13 when dependent on claim 8, wherein the acoustic treatment comprises a skin.

15. A thrust reverser inner fixed structure according to claim 14, wherein the skin is perforated at least in part.

16. A thrust reverser inner fixed structure according to claim 14 or claim 15, wherein the skin at least partially covers the recesses or cells.

17. A thrust reverser inner fixed structure according to any one of the preceding claims, wherein the discrete bifurcation comprises one or more integral bumper fitting pads, bumper mounts or bumpers.

18. A thrust reverser inner fixed structure according to any one of the preceding claims, wherein the discrete bifurcation comprises a seal retaining feature.

19. A thrust reverser inner fixed structure according to claim 18, wherein the seal retaining feature is integral to the discrete bifurcation.

20. A thrust reverser inner fixed structure according to claim 18 or claim 19, wherein the seal retaining feature extends across the discrete bifurcation in a longitudinal direction.

21. A thrust reverser inner fixed structure according to claim 18, claim 19 or claim 20, wherein the seal retaining feature follows a path having no more than 10 bends, e.g. a straight path. 22. A thrust reverser inner fixed structure according to any one of claims 18 to 21 , wherein a sealing element is retained by the seal retaining feature.

23. A thrust reverser inner fixed structure according to any one of the preceding claims, wherein the joint comprises one or more, e.g. a plurality of, mechanical fasteners.

24. A thrust reverser inner fixed structure according to any one of the preceding claims, wherein the discrete bifurcation and/or the barrel portion comprise a connecting flange.

25. A thrust reverser inner fixed structure according to any one of the preceding claims, wherein the discrete bifurcation or the barrel portion comprises a groove for receiving an edge of the other of the discrete bifurcation or the barrel portion. 26. A thrust reverser inner fixed structure according to any one of the preceding claims comprising more than one discrete bifurcation.

27. A thrust reverser inner fixed structure according to claim 26, wherein the barrel portion is disposed between a first discrete bifurcation and a second discrete bifurcation, a first joint joining the first discrete bifurcation to the barrel portion and a second joint joining the second discrete bifurcation to the barrel portion.

28. A thrust reverser inner fixed structure according to any one of the preceding claims, wherein the thrust reverser inner fixed structure comprises a first half and a second half, each of the first half and the second half comprising: a barrel portion; a discrete bifurcation; and a joint joining the discrete bifurcation to the barrel portion.

29. A thrust reverser inner fixed structure according to any one of the preceding claims comprising a fire retardant structure arranged at least partially within the barrel portion(s).

30. A discrete bifurcation for a thrust reverser inner fixed structure, the discrete bifurcation being adapted to be joined to a barrel portion, wherein the discrete bifurcation comprises an acoustic treatment.

31. A discrete bifurcation according to claim 30 comprising one or more bodies.

32. A discrete bifurcation according to claim 31 , wherein one or more of the bodies is/are machined or manufactured by an additive manufacturing process such as three-dimensional printing or comprise, or consist essentially of, a plastic moulding or is/are manufactured at least in part by resin transfer moulding.

33. A discrete bifurcation according to claim 30, claim 31 or claim 32 having a first longitudinal edge and a second longitudinal edge and at least one bend such that the first longitudinal edge and the second longitudinal edge are located in differently oriented planes.

34. A discrete bifurcation according to any one of claims 30 to 33, wherein the discrete bifurcation comprises a beam or track for connecting to another component or structure.

35. A discrete bifurcation according to claim 34, wherein the beam or track is integral to the discrete bifurcation.

36. A discrete bifurcation according to any one of claims 30 to 35, wherein the acoustic treatment comprises a plurality of recesses or cells formed in the discrete bifurcation.

37. A discrete bifurcation according to any one of claims 30 to 36, wherein the acoustic treatment is formed by an additive manufacturing process such as three- dimensional printing.

38. A discrete bifurcation according to any one of claims 30 to 37, wherein the acoustic treatment includes perforations.

39. A discrete bifurcation according any one of claims 30 to 38, wherein the acoustic treatment includes a honeycomb material.

40. A discrete bifurcation according to any one of claims 30 to 39, wherein the acoustic treatment includes a fabricated lattice structure.

41. A discrete bifurcation according to any one of claims 30 to 40, wherein the acoustic treatment includes a sound absorbing foam material.

42. A discrete bifurcation according to claim 36 or any one of claims 37 to 41 when dependent on claim 36, wherein the acoustic treatment comprises a skin,

43. A discrete bifurcation according to claim 42, wherein the skin is perforated at least in part.

44. A discrete bifurcation according to claim 42 or claim 43, wherein the skin at least partially covers the recesses or cells.

45. A discrete bifurcation according to any one of claims 30 to 44 comprising one or more integral bumper fitting pads, bumper mounts or bumpers.

46. A discrete bifurcation according to any one of claims 30 to 45 comprising a seal retaining feature.

47. A discrete bifurcation according to claim 46, wherein the seal retaining feature is integral to the discrete bifurcation.

48. A discrete bifurcation according to claim 46 or claim 47, wherein the seal retaining feature extends across the discrete bifurcation in a longitudinal direction.

49. A discrete bifurcation according to claim 46, claim 47 or claim 48, wherein the seal retaining feature follows a path having no more than 10 bends, e.g. a straight path.

50. A discrete bifurcation according to any one of claims 30 to 49 comprising a connecting flange.

51. A discrete bifurcation according to any one of claims 30 to 50 comprising a groove for receiving an edge of a barrel portion.

52. A nacelle comprising a thrust reverser inner fixed structure according to any one of claims 1 to 29 or a bifurcation according to any one of claims 30 to 51.

53. An aircraft engine comprising a thrust reverser inner fixed structure according to any one of claims 1 to 29, a bifurcation according to any one of claims 30 to 51 or a nacelle according to claim 52.

54. An aircraft comprising a thrust reverser inner fixed structure according to any one of claims 1 to 29, a bifurcation according to any one of claims 30 to 51 , a nacelle according to claim 52 or an aircraft engine according to claim 53. 55. A method of manufacture of a thrust reverser inner fixed structure, comprising: providing a barrel portion;

providing a discrete bifurcation, wherein the discrete bifurcation comprises an acoustic treatment; and

joining the discrete bifurcation to the barrel portion.

Description:
THRUST REVERSER INNER FIXED STRUCTURE

The present disclosure concerns an inner fixed structure (IFS) of a thrust reverser. The disclosure also concerns a bifurcation for an inner fixed structure (IFS) of a thrust reverser.

The inner fixed structure (IFS) of a thrust reverser may sometimes be known as a core cowl, an inner barrel or an inner bottle. It is known for an inner fixed structure of a thrust reverser to comprise two halves, each half comprising a composite body comprising a barrel portion and two bifurcations. The barrel portion is located between the bifurcations. One of the bifurcations (sometimes known as the 12 o’clock or 12H bifurcation) typically has mounted thereon a beam or track for connecting the bifurcation to another component such as a pylon extending from a wing of an aircraft. The bifurcation also has mounted thereon a plurality of bumpers. The bumpers on one bifurcation contact the bumpers on the other bifurcation when the inner fixed structure is fitted on an aircraft. Alternatively, the bumpers may contact the pylon when the inner fixed structure is fitted to an aircraft. The beam or track and/or the bumpers are mounted on the bifurcation using suitable mechanical fasteners and/or joining techniques.

The position of the beam or track and/or the bumpers is determined to a significant extent by the shape and dimensions of the composite body. However, the composite body is a relatively inaccurate component and it is vital for the beam or track and/or the bumpers to be accurately positioned. Thus, mounting the beam or track and/or the bumpers is a complicated procedure, which typically involves the use of liquid shims or solid shims.

A first aspect provides a thrust reverser inner fixed structure comprising:

a barrel portion;

a discrete bifurcation; and

a joint joining the discrete bifurcation to the barrel portion.

The barrel portion may be curved in a lateral direction. The barrel portion may have a length and may be curved in the lateral direction such that the curvature in a given lateral direction has a consistent (non-zero) sign at all points along the length of the barrel portion. By a consistent sign is meant that the sign of the curvature in the given lateral direction is only ever negative or positive.

The barrel portion may comprise, or consist essentially of, a composite material.

The discrete bifurcation may comprise one or more bodies. One or more of the bodies may be machined.

The discrete bifurcation, or the body or bodies therein, may comprise, or consist of any suitable material or combination of materials including one or more of a metallic material, a composite material, carbon fibre, a polymeric material, e.g. polyether ether ketone or similar.

One or more airwashed surfaces of the discrete bifurcation may be coated, typically to improve smoothness and aerodynamic properties. For instance, one or more airwashed surfaces of the discrete bifurcation may be coated with graphene, to provide a smoother surface or surface with improved aerodynamic properties.

The discrete bifurcation may be manufactured by any suitable process. The discrete bifurcation may be manufactured by an additive manufacturing process, e.g. three- dimensional printing. The discrete bifurcation may comprise a plastic moulding. The discrete bifurcation may be manufactured at least in part by resin transfer moulding.

The discrete bifurcation may have a first longitudinal edge and a second longitudinal edge. An inner surface (or surfaces) and an outer surface (or surfaces) may extend between the first longitudinal edge and the second longitudinal edge. The discrete bifurcation may include at least one bend such that the first longitudinal edge and the second longitudinal edge are located in differently oriented planes.

The discrete bifurcation may comprise a beam or track for connecting to another component or structure. The beam or track may be integral to the discrete bifurcation.

The discrete bifurcation may be perforated at least in part. The discrete bifurcation may comprise an acoustic treatment. The acoustic treatment may comprise, or consist essentially of, a plurality of recesses or cells formed, e.g. machined, in the discrete bifurcation. The acoustic treatment may be formed by an additive manufacturing process such as three-dimensional printing. The acoustic treatment may include one or more of: perforations; honeycomb material; a fabricated lattice structure; and/or a sound absorbing foam material. The acoustic treatment may comprise a skin, which may be perforated at least in part. The skin may cover at least partially the recesses or cells, e.g. machined cells; honeycomb material; fabricated lattice structure(s); and/or sound absorbing foam material. The skin may be continuous or discontinuous, e.g. may comprise a plurality of skin elements. The skin may comprise, or consist essentially of, a composite material or a metallic material, a polymeric material, e.g. poly ether ether ketone or similar. For instance, a composite skin may be bonded or fastened by any suitable technique to the discrete bifurcation. A metallic skin may be bonded, brazed, fastened or welded, e.g. friction stir welded, to the discrete bifurcation. A metallic skin may for example comprise, or consist essentially of, one or more of stainless steel, an aluminium alloy, an aluminium- lithium alloy, titanium or a titanium alloy. The inner surface(s) of the discrete bifurcation may comprise one or more recesses or cells, which may be machined recesses or cells.

The discrete bifurcation may comprise one or more bumpers. The bumpers may each comprise a bumper mount. The discrete bifurcation may comprise one or more bumper fitting pads. The bumper(s), bumper mount(s) or bumper fitting pad(s) may be integral to or separate from the discrete bifurcation.

The discrete bifurcation may comprise a seal retaining feature. The seal retaining feature may be integral to or separate from the discrete bifurcation. The seal retaining feature may extend across the discrete bifurcation in a longitudinal direction. The seal retaining feature may follow a relatively simple path such as a path with relatively few bends, e.g. no more than 10 bends or no more than 5 bends. The path followed by the seal retaining feature may be curved at least in part, e.g. the path may have one or more curved portions. The path followed by the seal retaining feature may be straight. A sealing element may be retained by the seal retaining feature. The joint may comprise one or more, e.g. a plurality of, mechanical fasteners.

The discrete bifurcation and/or the barrel portion may comprise a connecting flange.

The discrete bifurcation or the barrel portion may comprise a groove for receiving an edge of the other of the discrete bifurcation or the barrel portion.

The thrust reverser inner fixed structure may comprise more than one discrete bifurcation. The barrel portion may be disposed between a first discrete bifurcation and a second discrete bifurcation, a first joint joining the first discrete bifurcation to the barrel portion and a second joint joining the second discrete bifurcation to the barrel portion. The thrust reverser inner fixed structure may comprise a first half and a second half, each of the first half and the second half comprising a barrel portion; a discrete bifurcation; and a joint joining the discrete bifurcation to the barrel portion.

The inner fixed structure may comprise a fire retardant treatment, e.g. a structure such as a fire blanket. The fire retardant treatment may be applied to at least a portion of the barrel portion(s). For instance, the fire blanket may be arranged at least partially within the barrel portion(s). The fire retardant treatment may be applied to at least a portion of one or more of the discrete bifurcation(s). For instance, the fire blanket may cover at least a portion of one or more of the discrete bifurcation(s).

A second aspect provides a discrete bifurcation for a thrust reverser inner fixed structure, the discrete bifurcation being adapted to be joined to a barrel portion.

The discrete bifurcation may comprise one or more bodies. One or more of the bodies may be machined. One or more of the bodies may be manufactured by an additive manufacturing process such as three-dimensional printing.

The discrete bifurcation, or the body or bodies therein, may comprise, or consist of any suitable material or combination of materials including one or more of a metallic material, a composite material, carbon fibre, a polymeric material, e.g. polyether ether ketone or similar.

One or more airwashed surfaces of the discrete bifurcation may be coated, typically to improve smoothness and aerodynamic properties. For instance, one or more airwashed surfaces of the discrete bifurcation may be coated with graphene, to provide a smoother surface or surface with improved aerodynamic properties.

The discrete bifurcation may be manufactured by any suitable process. The discrete bifurcation may be manufactured by an additive manufacturing process, e.g. three- dimensional printing. The discrete bifurcation may comprise a plastic moulding.

The discrete bifurcation may have a first longitudinal edge and a second longitudinal edge. An inner surface (or surfaces) and an outer surface (or surfaces) may extend between the first longitudinal edge and the second longitudinal edge. The discrete bifurcation may include at least one bend such that the first longitudinal edge and the second longitudinal edge are located in differently oriented planes.

The discrete bifurcation may comprise a beam or track for connecting to another component or structure. The beam or track may be integral to or separate from the discrete bifurcation.

The discrete bifurcation may be perforated at least in part.

The discrete bifurcation may comprise an acoustic treatment. The acoustic treatment may comprise, or consist essentially of, a plurality of recesses or cells formed, e.g. machine, in the discrete bifurcation. The acoustic treatment may be formed by an additive manufacturing process such as three-dimensional printing. The acoustic treatment may include one or more of: perforations; honeycomb material; a fabricated lattice structure; and/or a sound absorbing foam material. The acoustic treatment may comprise a skin, which may be perforated at least in part. The skin may cover at least partially the recesses or cells, e.g. machined cells; perforations; honeycomb material; fabricated lattice structure(s); and/or sound absorbing foam material. The skin may be continuous or discontinuous, e.g. may comprise a plurality of skin elements. The skin may comprise, or consist essentially of, a composite material, a metallic material or a polymeric material, e.g. poly ether ether ketone or similar. For instance, a composite skin may be bonded by any suitable technique to the discrete bifurcation. A metallic skin may be bonded, brazed, fastened or welded, e.g. friction stir welded, to the discrete bifurcation. A metallic skin may for example comprise, or consist essentially of, stainless steel, an aluminium alloy, an aluminium- lithium alloy, titanium or a titanium alloy.

The inner surface(s) of the discrete bifurcation may comprise one or more recesses or cells, which may be machined recesses or cells.

The discrete bifurcation may comprise one or more bumpers. The bumpers may each comprise a bumper mount. The discrete bifurcation may comprise one or more bumper fitting pads. The bumper(s), bumper mount(s) or bumper fitting pad(s) may be integral to or separate from the discrete bifurcation.

The discrete bifurcation may comprise a seal retaining feature. The seal retaining feature may be integral to or separate from the discrete bifurcation. The seal retaining feature may extend across the discrete bifurcation in a longitudinal direction. The seal retaining feature may follow a relatively simple path such as a path with relatively few bends, e.g. no more than 10 bends or no more than 5 bends. The path followed by the seal retaining feature may be curved at least in part, e.g. the path may have one or more curved portions. The path followed by the seal retaining feature may be straight. A sealing element may be retained by the seal retaining feature.

The discrete bifurcation may comprise a connecting flange.

The discrete bifurcation may comprise a groove for receiving an edge of a barrel portion.

A third aspect provides a nacelle comprising a thrust reverser inner fixed structure according to the first aspect or a bifurcation according to the second aspect.

A fourth aspect provides an aircraft engine comprising a thrust reverser inner fixed structure according to the first aspect, a bifurcation according to the second aspect or a nacelle according to the third aspect. A fifth aspect provides an aircraft comprising a thrust reverser inner fixed structure according to the first aspect, a bifurcation according to the second aspect, a nacelle according to the third aspect or an aircraft engine according to the fourth aspect.

A sixth aspect provides a method of manufacture of a thrust reverser inner fixed structure, comprising:

providing a barrel portion;

providing a discrete bifurcation; and

joining the discrete bifurcation to the barrel portion.

Joining the discrete bifurcation to the barrel portion may include using one or more, e.g. a plurality of, mechanical fasteners. Example embodiments will now be described with reference to the accompanying drawings, in which:

Figure 1 shows an example of a half of an inner fixed structure of a thrust reverser; Figure 2 shows a portion of another example of a half of an inner fixed structure of a thrust reverser;

Figure 3 shows in schematic cross-section a portion of an example of an inner fixed structure of a thrust reverser attached to a wing of an aircraft;

Figure 4 shows a portion of another example of a half of an inner fixed structure of a thrust reverser;

Figure 5 shows in schematic cross-section a portion of another example of an inner fixed structure of a thrust reverser attached to a wing of an aircraft;

Figure 6 shows in schematic cross-section a portion of another example of a half of an inner fixed structure of a thrust reverser;

Figure 7 shows in schematic cross-section an example of an inner fixed structure of a thrust reverser attached to a wing of an aircraft;

Figure 8 shows in schematic cross-section an example of an inner fixed structure of a thrust reverser attached to a wing of an aircraft; and

Figure 9 shows an example of an aircraft. Figure 1 shows generally an example of a half 1 of an inner fixed structure of a thrust reverser.

The half 1 comprises a body 5. The body 5 comprises a barrel portion 3 disposed between a first bifurcation 2 and a second bifurcation 4. The first bifurcation 2 and the second bifurcation 4 extend radially outwards from opposite longitudinal sides of the barrel portion 3. The first bifurcation 2 and the second bifurcation 4 are of the same length as the barrel portion 3. The first bifurcation 2 and the second bifurcation 4 may not be the same length as the barrel portion 3. Each of the first bifurcation 2 and the second bifurcation 4 may be shorter or longer than the barrel portion 3.

It is known for the body 5 comprising the barrel portion 3, the first bifurcation 2 and the second bifurcation 4 to be formed as a single piece. Typically, the single piece may comprise a composite material, e.g. comprising a sandwich panel. The single piece is curved in a lateral direction such that at the curvature in the lateral direction includes portions with both a positive and a negative sign of curvature. Such a single piece can be relatively difficult to manufacture from a composite material such as a sandwich panel.

The inner fixed structure of a thrust reverser may comprise two halves, such as the half 1 , one half facing the other, in what is known as a d-duct arrangement.

For example, the first bifurcation 2 of each half may have a beam or track (not shown) fixed thereto, the beam or track being adapted to be connected to another component or structure, e.g. a translating cowl, a translating aircraft structure, a pylon extending from a wing of an aircraft. The beam or track may extend in a longitudinal direction at least partially across the first bifurcation 2. The beam or track may be fixed to the first bifurcation 2 at a location distal from the barrel portion 3. The first bifurcation 2 of each half may also have one or more bumpers (not shown) mounted thereon. Typically, the or each bumper may be mounted on the first bifurcation 2 at a location closer to the barrel portion 3 than the beam of track. The first bifurcation 2 of each half may be connected, typically hingedly connected, via the beam or track to a pylon extending from a wing, the pylon being disposed between the two first bifurcations. The bumpers mounted on each first bifurcation 2 may then contact the pylon or each other. The second bifurcation 4 of each half may have mounted thereon a beam or track with a latch component such that the two second bifurcations can be latched together to securely close the inner fixed structure of the thrust reverser and the thrust reverser as a whole. The second bifurcation 4 of each half may have one or more bumpers (not shown) mounted thereon. Typically, the or each bumper may be mounted on the second bifurcation 4 at a location closer to the barrel portion 3 than the beam or track. When the inner fixed structure of the thrust reverser is closed, the bumpers mounted on each second bifurcation 4 may then contact each other.

A bifurcation, e.g. the first bifurcation 2, adapted to be connected via a beam or track to the pylon may be known as a 12 o’clock or 12H bifurcation. A bifurcation, e.g. the second bifurcation 4, located on the opposite side of the barrel portion from the 12H bifurcation may be known as a 6 o’clock or 6H bifurcation.

In a d-duct arrangement, an inner fixed structure of a thrust reverser is made up of a pair of halves, each half having a 12H bifurcation, a 6H bifurcation and a barrel portion between the 12H bifurcation and the 6H bifurcation. In an o-duct arrangement, an inner fixed structure of a thrust reverser comprises a pair of opposing 12H bifurcations adapted to be connected via a beam or track to either side of a pylon extending from a wing and a barrel portion extending between the two 12H bifurcations. In an o-duct arrangement, the inner fixed structure does not contain any 6H bifurcations. In an o-duct arrangement the barrel portion may be a single piece or may comprise a plurality of pieces.

In a c-duct arrangement, an inner fixed structure of a thrust reverser may comprise an outer casing and an inner casing. The outer casing comprises a pair of halves, each half having a 12H bifurcation, a 6H bifurcation and a barrel portion between the 12H bifurcation and the 6H birfurcation. The inner casing is disposed within the outer casing. The inner casing may comprise a pair of halves, each half having a 12H bifurcation, a 6H bifurcation and a barrel portion between the 12H bifurcation and the 6H bifurcation. In an alternative c-duct arrangement, the inner casing comprises a pair of opposing 12H bifurcations adapted to be connected via a beam or track to either side of a pylon extending from a wing and a barrel portion extending between the two 12H bifurcations. In the alternative c-duct arrangement, the inner fixed structure does not contain any 6H bifurcations. In the alternative c-duct arrangement the barrel portion may be a single piece or may comprise a plurality of pieces.

The inner fixed structure of a thrust reverser is typically configured such that, when the inner fixed structure is fitted to a pylon, the inner fixed structure is longitudinally and circumferentially sealed in an air-tight manner. The sealed volume within the inner fixed structure constitutes a fire zone. The fire zone is intended to contain any fire resulting from a malfunctioning of an aircraft engine housed within a nacelle comprising the inner fixed structure of the thrust reverser. Typically, the fire zone is lined with a fireproof structure, typically in the form of a fire blanket, which may comprise titanium or stainless steel and insulating materials. A fireproof coating may be applied to at least a portion of the inner fixed structure in the fire zone.

Figure 2 shows a partially cut-away view of a portion of an example of a half 20 of an inner fixed structure of a thrust reverser.

The half 20 comprises a barrel portion 21. The barrel portion 21 is curved in a lateral direction through around 160° of arc and has a first longitudinal edge 32 and a second longitudinal edge 33. In embodiments, the barrel portion 21 may be curved in the lateral direction through a lesser or greater degree of arc. The barrel portion 21 may have a uniform or non-uniform radius of curvature.

A first discrete bifurcation 22 is joined to the first longitudinal edge 32 of the barrel portion 21 . A second discrete bifurcation 23 is joined to the second longitudinal edge 33 of the barrel portion 21. The first discrete bifurcation 22 may constitute a 12H bifurcation and the second discrete bifurcation 23 may constitute a 6H bifurcation or vice versa.

The first discrete bifurcation 22 is shown in detail in Figure 2. The first discrete bifurcation 22 comprises a body 34, which may be a machined body. The body 34 has a first longitudinal edge 35 and a second longitudinal edge 36. An inner surface (or surfaces) 37 and an outer surface (or surfaces) 38 extend between the first longitudinal edge 35 and the second longitudinal edge 36. The body 34 includes a bend 39 such that the first longitudinal edge 35 and the second longitudinal edge 36 are located in differently oriented planes. The bend 39 is closer to the first longitudinal edge 35 than the second longitudinal edge 36.

Along the first longitudinal edge 35, the body 34 of the first discrete bifurcation 22 comprises a groove 24 adapted to receive the first longitudinal edge 32 of the barrel portion 21. The first longitudinal edge 32 of the barrel portion 21 is secured in the groove 24 using any suitable joining or bonding technique, thereby joining the barrel portion 21 to the first discrete bifurcation 22.

Close to the second longitudinal edge 36, and running parallel thereto, the body 34 of the first discrete bifurcation 22 comprises a beam or track 26 adapted to connect the first discrete bifurcation 22 to another component or structure, e.g. a pylon extending from a wing of an aircraft. The beam or track 26 is integral to the body 34 of the first discrete bifurcation 22.

The inner surface 37 of the first discrete bifurcation 22 comprises an array of rectangular recesses 27. Each recess 27 has a base 40, which is perforated (e.g. sometimes known as acoustic drilling) to aid noise cancellation/reduction. A piece of honeycomb material 28 is present in each recess 27. The pieces of honeycomb material 28 may be made from any suitable material. The pieces of honeycomb material 28 may be held in the recesses 27 by any suitable joining or bonding technique. The recesses 27 may not be rectangular. The recesses 27 may be of any shape or shapes. The recesses 27 may be of a shape or shapes that tessellate across at least a portion of the inner surface 37.

A skin 29 covers the pieces of honeycomb material 28 in the recesses 27. The skin 29 may be made from any suitable material. The skin 29 may be bonded or joined to the body 34 by any suitable joining or bonding technique. The skin 29 may be continuous across the extent of the recesses 27. Alternatively, the skin 29 may be discontinuous. For instance, the skin 29 may comprise a plurality of skin elements, each skin element covering one or some of the recesses 27.

In embodiments, the outer surface 38 of the first discrete bifurcation 22 may comprise an array of recesses. Each recess may be covered with a skin, which is perforated (e.g. sometimes known as acoustic drilling) to aid noise cancellation/reduction. A piece of honeycomb material may be present in each recess. In such an embodiment, the skin (or skin elements) would be on the outer surface of the discrete bifurcation rather than the inner surface. Such a configuration may be beneficial, since, for example, it may be easier to perforate the skin than the body of the discrete bifurcation to aid noise cancellation/reduction. Further, the body of the discrete bifurcation may be stronger, since it is not perforated. Consequently, the body of the discrete bifurcation may not need to be as large, e.g. thick, to provide adequate mechanical strength. As a result, less material may be used, potentially reducing weight and cost. Reducing weight may help to increase fuel efficiency. Another benefit of this configuration is that it may be easier and/or cheaper to provide an aerodynamic form for the outer surface with the skin than through machining and/or finishing the body of the discrete bifurcation.

In embodiments, the array of recesses may be provided (i.e. defined at least in part) by a separate component that can be attached to the body of the discrete bifurcation. For instance, the separate component may be received at least partially in a larger recess on a surface of the discrete bifurcation.

In embodiments, the first discrete bifurcation may comprise a different acoustic treatment. For instance, it will be appreciated that honeycomb material is an example of a noise attenuating material. Any suitable noise attenuating material may be used instead of or as well as honeycomb material. In embodiments, no noise attenuating material may be present in the recesses. The recesses may be of a size that makes them noise attenuating without the presence of a noise attenuating material therein.

In the vicinity of the bend 39, the body 34 further comprises a pair of bumper fitting pads 30 at four longitudinally-spaced locations on the inner surface 37. The bumper fitting pads 30 are integral to the body 34 of the first bifurcation 22. Each pair of bumper fitting pads 30 is adapted to receive a bumper 31 thereon. The bumpers 31 may be fixed to the pads 30, e.g. using bolts, typically without the use of liquid or solid shimming. The body 34 may comprise any suitable number and arrangement of bumper fitting pads 30. In embodiments, the bumper fitting pads may be separate from, and fixed to, the body of the first bifurcation. In embodiments, the bumper fitting pads and bumpers may be integral with each other. In embodiments, the bumper fitting pads and bumpers may be integral to the body of the first bifurcation. In embodiments, the body of the first bifurcation may comprise more than one bend. The body may comprise any number of bends such that the first longitudinal edge and the second longitudinal edge are located in differently oriented planes.

The outer surface 38 of the first discrete bifurcation 22 constitutes an airwashed surface. Accordingly, the outer surface 38 may have an aerodynamic form. Typically, the inner surface 37 of the first discrete bifurcation 22 may not constitute an airwashed surface. Thus, there may be a lesser requirement, or no need, for the inner surface 37 to have an aerodynamic form.

The second discrete bifurcation 23 may have some or all of the above-described features of the first discrete bifurcation 22. Only a small portion of the second discrete bifurcation 23 can be seen in Figure 2.

The second discrete bifurcation 23 includes a body 41 , which may be a machined body. The body 41 has a first longitudinal edge 42 and a second longitudinal edge (not shown). An inner surface (or surfaces) 44 and an outer surface (or surfaces) 45 extend between the first longitudinal edge 42 and the second longitudinal edge. The body 41 includes a bend 43 such that the first longitudinal edge 42 and the second longitudinal edge are located in differently oriented planes. The bend 43 is closer to the first longitudinal edge 42 than the second longitudinal edge.

Along the first longitudinal edge 42, the body 41 of the first discrete bifurcation 23 comprises a groove 25 adapted to receive the second longitudinal edge 33 of the barrel portion 21.

The second discrete bifurcation 23 may have none, some or all of the above-described further features of the first discrete bifurcation 22.

By providing a discrete bifurcation with a machined body, part accuracy may be improved. Consequently, bumpers and/or beams or tracks may be located more accurately without recourse to relatively complicated techniques such as liquid or solid shimming. Further, by providing a discrete bifurcation with an integrated beam or track and/or with an integrated bumper fitting pad or bumper fitting, fewer mechanical fasteners and/or smaller joining areas may be required. Thus, more of the discrete bifurcation may be acoustically treated (e.g. acoustically drilled), thereby reducing noise during operation. For instance, it may be possible to acoustically drill closer to the edges of the bifurcation.

In embodiments, the barrel portion may have a non-uniform width. The first longitudinal edge may not be straight. The second longitudinal edge may not be straight.

In embodiments, one or more bumpers may be integral to the body of the first discrete bifurcation. The body may comprise any suitable number and arrangement of bumpers.

Figure 4 shows a partially cut-away view of a portion of an example of a half 400 of an inner fixed structure of a thrust reverser.

The half 400 comprises a barrel portion 401. The barrel portion 401 is curved in a lateral direction through around 160° of arc and has a first longitudinal edge 403 and a second longitudinal edge (not shown). The barrel portion 401 may be curved in the lateral direction through a lesser or greater degree of arc. The barrel portion 401 comprises a connecting flange 407. The connecting flange 407 extends along the length of the barrel portion 401. The connecting flange 407 extends a circumferential distance around the barrel portion 401 and terminates at the first longitudinal edge 403.

A first discrete bifurcation 402 is joined to the connecting flange 407 of the barrel portion 401. A second discrete bifurcation (not shown) may be joined to the second longitudinal edge of the barrel portion 401. The first discrete bifurcation 402 may constitute a 12H bifurcation.

The first discrete bifurcation 402 is shown in detail in Figure 4. The first discrete bifurcation 402 comprises a body 404, which may be a machined body. The body 404 has a first longitudinal edge 406 and a second longitudinal edge 405. An inner surface (or surfaces) 41 1 and an outer surface (or surfaces) 410 extend between the first longitudinal edge 406 and the second longitudinal edge 405. The body 404 includes a bend 408 such that the first longitudinal edge 406 and the second longitudinal edge 405 are located in differently oriented planes. The bend 408 is closer to the first longitudinal edge 406 than the second longitudinal edge 405. The bend 408 is a right- angled corner. In embodiments, the bend may not be a right-angled corner. The bend may be more or less sharp than a right angle. The bend may be curved at least in part. The bend may pass through more or fewer than 90°. The body may comprise more than one bend.

The body 404 comprises a first body portion 41 8, which extends from the second longitudinal edge 405 to the bend 408. The first body portion 418 extends radially relative to the barrel portion 401 . The body 404 comprises a second body portion 419 which extends from the first longitudinal edge 406 to the bend 408. The second body potion 419 extends circumferentially relative to the barrel portion 401.

The second body portion 419 includes a connecting flange 417. The connecting flange 417 extends along the length of the first discrete bifurcation 402. The connecting flange 417 terminates at the first longitudinal edge 406 of the first discrete bifurcation 402.

The connecting flange 417 of the first discrete bifurcation 402 and the connecting flange 407 of the barrel portion 401 are disposed such that they overlap each other. A plurality of mechanical fasteners 420 joins the connecting flange 417 of the first discrete bifurcation 402 to the connecting flange 407 of the barrel portion 401. Thus, the barrel portion 401 is joined to the first discrete bifurcation 402. The connecting flange 417 of the first discrete bifurcation 402 may be disposed inside the connecting flange 407 of the barrel portion 401 (as shown in Figure 4) or vice versa.

Close to the second longitudinal edge 405, and running parallel thereto, the body 404 of the first discrete bifurcation 402 comprises a beam or track 409 adapted to connect the first discrete bifurcation 402 to another component or structure, e.g. a pylon extending from a wing of an aircraft. The beam or track 409 is integral to the body 404 of the first discrete bifurcation 402. The inner surface 41 1 of the first body portion 418 of the first discrete bifurcation 402 comprises an array of rectangular recesses 412. Each recess 412 has a base 416, which is perforated (e.g. sometimes known as acoustic drilling) to aid noise cancellation/reduction. A piece of honeycomb material may be present in each recess 412. The pieces of honeycomb material, if present, may be made from any suitable material. The pieces of honeycomb material, if present, may be held in the recesses 412 by any suitable joining or bonding technique. The recesses 412 may be of any shape or shapes. The recesses 412 may be of a shape or shapes that tessellate across at least a portion of the inner surface 41 1.

A skin 414 covers the recesses 412. The skin 414 may be made from any suitable material. The skin 414 may be bonded or joined to the body 404 by any suitable joining or bonding technique. The skin 414 may be continuous across the extent of the recesses 412. Alternatively, the skin 414 may be discontinuous. For instance, the skin 414 may comprise a plurality of skin elements, each skin element covering one or some of the recesses 412.

In embodiments, the outer surface 410 of the first discrete bifurcation 402 may comprise an array of recesses. Each recess may be covered with a skin, which is perforated (e.g. sometimes known as acoustic drilling) to aid noise cancellation/reduction. A piece of honeycomb material may be present in each recess. In such an embodiment, the skin (or skin elements) would be on the outer surface of the discrete bifurcation rather than the inner surface. Such a configuration may be beneficial, since, for example, it may be easier to perforate the skin than the body of the discrete bifurcation to aid noise cancellation/reduction. Further, the body of the discrete bifurcation may be stronger, since it is not perforated. Consequently, the body of the discrete bifurcation may not need to be as large, e.g. thick, to provide adequate mechanical strength. As a result, less material may be used, potentially reducing weight and cost. Reducing weight may help to increase fuel efficiency. Another benefit of this configuration is that it may be easier and/or cheaper to provide an aerodynamic form for the outer surface with the skin than through machining and/or finishing the body of the discrete bifurcation.

In embodiments, the array of recesses may be provided (i.e. defined at least in part) by a separate component that can be attached to the body of the discrete bifurcation. For instance, the separate component may be received at least partially in a larger recess on a surface of the discrete bifurcation.

In embodiments, the first discrete bifurcation may comprise a different acoustic treatment. For instance, it will be appreciated that honeycomb material is an example of a noise attenuating material. Any suitable noise attenuating material may be used instead of or as well as honeycomb material. In embodiments, no noise attenuating material may be present in the recesses. The recesses may be of a size that makes them noise attenuating without the presence of a noise attenuating material therein.

A seal retaining feature 413 for a sealing element extends longitudinally across the inner surface 41 1 The seal retaining feature 413 is disposed in the first body portion 418 between the recesses 412 and the bend 408. The seal retaining feature 413 is integral to the body 404 of the first discrete bifurcation 402. The seal retaining feature 413 is straight. Alternatively, the seal retaining feature 413 may include one or more bends and may follow a non-straight path across the inner surface 41 1.

Two bumpers 415 protrude from the inner surface 41 1 of the first body portion 41 8. The bumpers 415 are at longitudinally-spaced locations on the inner surface 41 1.

The bumpers 415 are integral to the body 404 of the first bifurcation 402. The body 404 may comprise any suitable number and arrangement of bumpers 415. The bumpers 415 are located on the opposite side of the seal retaining feature 413 from the bend 408.

In embodiments, one or more of the bumpers 415 may be separate from (i.e. not integral to) the body 404 of the first bifurcation 402. In embodiments, one or more of the bumpers 415 may be located on the same side of the seal retaining feature 413 from the bend 408.

The seal retaining feature may be disposed inboard or outboard of the bumpers. Alternatively, the seal retaining feature may be inboard of one of more of the bumpers and outboard of one or more of the bumpers. The body of the first bifurcation may comprise more than one bend. The body may comprise any number of bends such that the first longitudinal edge and the second longitudinal edge are located in differently oriented planes.

The outer surface 410 of the first discrete bifurcation 402 constitutes an airwashed surface. Accordingly, the outer surface 410 may have an aerodynamic form. The inner surface 41 1 of the first discrete bifurcation 402 may not constitute an airwashed surface. Thus, there may be a lesser requirement, or no need, for the inner surface 41 10 to have an aerodynamic form.

The second discrete bifurcation, if present, may have some or all of the above- described features of the first discrete bifurcation 402.

Figure 5 shows in schematic cross-section a portion of an example of an inner fixed structure 500 of a thrust reverser attached to a wing 501 of an aircraft. A pylon 502 extends downwards from an underside of the wing 501. The inner fixed structure 500 is attached to the pylon 502.

The inner fixed structure 500 comprises a first half 504 and a second half 504 '.

The first half 504 comprises a barrel portion 503. The barrel portion 503 is curved in a lateral direction and has a first longitudinal edge 509 and a second longitudinal edge (not shown). The barrel portion 503 comprises a connecting flange 507. The connecting flange 507 extends along the length of the barrel portion 503. The connecting flange 507 extends a circumferential distance around the barrel portion 503 and terminates at the first longitudinal edge 509.

A first discrete bifurcation 505 is joined to the connecting flange 507 of the barrel portion 503. A second discrete bifurcation (not shown) is joined to the second longitudinal edge of the barrel portion 503, e.g. via another connecting flange. The first discrete bifurcation 505 constitutes a 12H bifurcation. The second discrete bifurcation constitutes a 6H bifurcation.

The first discrete bifurcation 505 comprises a body 514, which may be a machined body. The body 514 has a first longitudinal edge 506 and a second longitudinal edge 516. An inner surface (or surfaces) 519 and an outer surface (or surfaces) 518 extend between the first longitudinal edge 506 and the second longitudinal edge 516. The body 514 includes a bend 520 such that the first longitudinal edge 506 and the second longitudinal edge 516 are located in differently oriented planes. The bend 520 is a right-angled corner. In embodiments, the bend may not be a right-angled corner. The bend may be more or less sharp than a right angle. The bend may be curved at least in part. The bend may pass through more or fewer than 90°. The body may comprise more than one bend.

The body 514 comprises a first body portion 517, which extends from the second longitudinal edge 516 to the bend 520. The first body portion 517 extends radially relative to the barrel portion 503. The body 514 comprises a second body portion 515 which extends from the first longitudinal edge 506 to the bend 520. The second body portion 515 extends circumferentially relative to the barrel portion 503.

The second body portion 515 includes a connecting flange 508. The connecting flange 508 extends along the length of the first discrete bifurcation 505. The connecting flange 508 terminates at the first longitudinal edge 506 of the first discrete bifurcation 505.

The connecting flange 508 of the first discrete bifurcation 505 and the connecting flange 507 of the barrel portion 503 are disposed such that they overlap each other. A plurality of mechanical fasteners (not shown) joins the connecting flange 508 of the first discrete bifurcation 505 to the connecting flange 507 of the barrel portion 503. Thus, the barrel portion 503 is joined to the first discrete bifurcation 505. The connecting flange 508 of the first discrete bifurcation 505 may be disposed inside the connecting flange 507 of the barrel portion 503 or vice versa.

Close to the second longitudinal edge 516, and running parallel thereto, the body 514 of the first discrete bifurcation 505 comprises a beam or track (not shown) adapted to connect the first discrete bifurcation 505 to the pylon 502 extending from the wing 501 of the aircraft. The beam or track is integral to the body 514 of the first discrete bifurcation 505. The inner surface 519 of the first body portion 515 of the first discrete bifurcation 505 comprises an array of recesses 512. Each recess 512 is perforated (e.g. sometimes known as acoustic drilling) to aid noise cancellation/reduction. A piece of honeycomb material may be present in each recess 512. The pieces of honeycomb material, if present, may be made from any suitable material. The pieces of honeycomb material, if present, may be held in the recesses 512 by any suitable joining or bonding technique. The recesses 512 may be of any shape or shapes. The recesses 512 may be of a shape or shapes that tessellate across at least a portion of the inner surface 519.

A skin 513 covers the recesses 512. The skin 513 may be made from any suitable material. The skin 513 may be bonded or joined to the body 514 by any suitable joining or bonding technique. The skin 513 is continuous across the extent of the recesses 512. Alternatively, the skin 513 may be discontinuous. For instance, the skin 513 may comprise a plurality of skin elements, each skin element covering one or some of the recesses 512.

In embodiments, the array of recesses may be provided (i.e. defined at least in part) by a separate component that can be attached to the body of the discrete bifurcation. For instance, the separate component may be received at least partially in a larger recess on a surface of the discrete bifurcation.

In embodiments, the first discrete bifurcation may comprise a different acoustic treatment. For instance, it will be appreciated that honeycomb material is an example of a noise attenuating material. Any suitable noise attenuating material may be used instead of or as well as honeycomb material. In embodiments, no noise attenuating material may be present in the recesses. The recesses may be of a size that makes them noise attenuating without the presence of a noise attenuating material therein.

A seal retaining feature 521 for a sealing element 522 extends longitudinally across the inner surface 519 The seal retaining feature 521 is integral to the body 514 of the first discrete bifurcation 505. The sealing element 522 is retained in the seal retaining feature 521. The seal retaining feature 521 may be straight. Alternatively, the seal retaining feature 521 may include one or more bends and may follow a non-straight path across the inner surface 519. At least one bumper mount 510 protrudes from the inner surface 519 of the first body portion 517. Each bumper mount 510 has a bumper pad 51 1 mounted thereon. The bumper pad 51 1 abuts the pylon 502.

The bumper mount(s) 510 is/are integral to the body 514 of the first bifurcation 504. The body 514 may comprise any suitable number and arrangement of bumper mounts 510.

The bumper mount(s) 510 is/are located inwardly of the recesses 512. The seal retaining feature 521 is located inwardly of the bumper mount(s) 510.

The seal retaining feature may be located inwardly or outwardly (i.e. disposed inboard or outboard) of the bumper mount(s). Alternatively, the seal retaining feature may be inboard of one of more of the bumper mounts and outboard of one or more of the bumper mounts.

The body of the first bifurcation may comprise more than one bend. The body may comprise any number of bends such that the first longitudinal edge and the second longitudinal edge are located in differently oriented planes.

The outer surface 518 of the first discrete bifurcation 505 constitutes an airwashed surface. Accordingly, the outer surface 518 may have an aerodynamic form. The inner surface 519 of the first discrete bifurcation 505 may not constitute an airwashed surface. Thus, there may be a lesser requirement, or no need, for the inner surface 519 to have an aerodynamic form.

The second discrete bifurcation may have some or all of the above-described features of the first discrete bifurcation 505.

The second half 504' comprises a barrel portion 503 '. The barrel portion 503 ' is curved in a lateral direction and has a first longitudinal edge 509' and a second longitudinal edge (not shown). The barrel portion 503 ' comprises a connecting flange 507'. The connecting flange 507' extends along the length of the barrel portion 503 '. The connecting flange 507' extends a circumferential distance around the barrel portion 503 ' and terminates at the first longitudinal edge 509'. The first discrete bifurcation 505 ' comprises a body 514', which may be a machined body. The body 514' has a first longitudinal edge 506' and a second longitudinal edge 516'. An inner surface (or surfaces) 519' and an outer surface (or surfaces) 51 8' extend between the first longitudinal edge 506' and the second longitudinal edge 516'. The body 514' includes a bend 520' such that the first longitudinal edge 506' and the second longitudinal edge 516' are located in differently oriented planes. The bend 520' is a right-angled corner. In embodiments, the bend may not be a right-angled corner. The bend may be more or less sharp than a right angle. The bend may be curved at least in part. The bend may pass through more or fewer than 90°. The body may comprise more than one bend.

The body 514' comprises a first body portion 517', which extends from the second longitudinal edge 516' to the bend 520'. The first body portion 517' extends radially relative to the barrel portion 503 '. The body 514' comprises a second body portion

515' which extends from the first longitudinal edge 506' to the bend 520'. The second body portion 515 ' extends circumferentially relative to the barrel portion 503 '.

The second body portion 515 ' includes a connecting flange 508 '. The connecting flange 508 ' extends along the length of the first discrete bifurcation 505 '. The connecting flange 508 ' terminates at the first longitudinal edge 506' of the first discrete bifurcation 505'.

The connecting flange 508 ' of the first discrete bifurcation 505 ' and the connecting flange 507' of the barrel portion 503 ' are disposed such that they overlap each other. A plurality of mechanical fasteners (not shown) joins the connecting flange 508 ' of the first discrete bifurcation 505 ' to the connecting flange 507' of the barrel portion 503 '. Thus, the barrel portion 503 ' is joined to the first discrete bifurcation 505'. The connecting flange 508 ' of the first discrete bifurcation 505 ' may be disposed inside the connecting flange 507' of the barrel portion 503 ' or vice versa.

Close to the second longitudinal edge 516', and running parallel thereto, the body 514 ' of the first discrete bifurcation 505 ' comprises a beam or track (not shown) adapted to connect the first discrete bifurcation 505 ' to the pylon 502 extending from the wing 501 of the aircraft. The beam or track is integral to the body 514' of the first discrete bifurcation 505 '.

The inner surface 519' of the first body portion 515' of the first discrete bifurcation 505' comprises an array of recesses 512'. Each recess 512' is perforated (e.g. sometimes known as acoustic drilling) to aid noise cancellation/reduction. A piece of honeycomb material may be present in each recess 512'. The pieces of honeycomb material, if present, may be made from any suitable material. The pieces of honeycomb material, if present, may be held in the recesses 512' by any suitable joining or bonding technique. The recesses 512' may be of any shape or shapes. The recesses 512' may be of a shape or shapes that tessellate across at least a portion of the inner surface 519'.

A skin 513 ' covers the recesses 512'. The skin 513 ' may be made from any suitable material. The skin 513 ' may be bonded or joined to the body 514' by any suitable joining or bonding technique. The skin 513 ' is continuous across the extent of the recesses 512'. Alternatively, the skin 513 ' may be discontinuous. For instance, the skin 513 ' may comprise a plurality of skin elements, each skin element covering one or some of the recesses 512'.

In embodiments, the array of recesses may be provided (i.e. defined at least in part) by a separate component that can be attached to the body of the discrete bifurcation. For instance, the separate component may be received at least partially in a larger recess on a surface of the discrete bifurcation.

In embodiments, the first discrete bifurcation may comprise a different acoustic treatment. For instance, it will be appreciated that honeycomb material is an example of a noise attenuating material. Any suitable noise attenuating material may be used instead of or as well as honeycomb material. In embodiments, no noise attenuating material may be present in the recesses. The recesses may be of a size that makes them noise attenuating without the presence of a noise attenuating material therein.

At least one bumper mount 510' protrudes from the inner surface 519' of the first body portion 517'. Each bumper mount 510' has a bumper pad 51 1 ' mounted thereon. The bumper pad 51 1 ' abuts the pylon 502. In embodiments, the bumper pads 51 1 of the first discrete bifurcation 505 of the first half 504 may abut the bumper pads 51 1 ' of the first discrete bifurcation 505 ' of the second half 504'.

The bumper mount(s) 510' is/are integral to the body 514' of the first bifurcation 504'. The body 514' may comprise any suitable number and arrangement of bumper mounts 510'.

The bumper mount(s) 510' is/are located inwardly of the recesses 512'.

The sealing element 522 retained in the seal retaining feature 521 abuts the inner surface 519' of the first discrete bifurcation 505' of the second half 504'. Accordingly, a longitudinal air-tight seal is provided between the first discrete bifurcation 505 of the first half 504 and the first discrete bifurcation 505 ' of the second half 504'. In embodiments, a sealing element and a seal retaining feature may be disposed, additionally or alternatively, in the first discrete bifurcation 505 '. In embodiments, both the first discrete bifurcation 505 of the first half 504 and the first discrete bifurcation 505' of the second half 504' may be provided with a seal retaining feature and a sealing element, in which case the sealing elements may seal against the pylon or against each other.

The body of the first bifurcation may comprise more than one bend. The body may comprise any number of bends such that the first longitudinal edge and the second longitudinal edge are located in differently oriented planes.

The outer surface 518' of the first discrete bifurcation 505 ' constitutes an airwashed surface. Accordingly, the outer surface 518 ' may have an aerodynamic form. The inner surface 519' of the first discrete bifurcation 505 ' may not constitute an airwashed surface. Thus, there may be a lesser requirement, or no need, for the inner surface 519' to have an aerodynamic form.

The second discrete bifurcation may have some or all of the above-described features of the first discrete bifurcation 505 '. In an embodiment, the two first discrete bifurcations 505, 505 ' may be joined to the same barrel portion. Accordingly, the inner fixed structure may have an o-duct arrangement.

Figure 3 shows in schematic cross-section a portion of an example of an inner fixed structure 300 of a thrust reverser attached to a wing 301 of an aircraft. A pylon 302 extends downwards from an underside of the wing 301. The inner fixed structure 300 is attached to the pylon 302.

The inner fixed structure 300 comprises a first half 304 and a second half 304'.

The first half 304 comprises a barrel portion 303. The barrel portion 303 is curved in a lateral direction and has a first longitudinal edge 309 and a second longitudinal edge (not shown). The barrel portion 303 comprises a connecting flange 307. The connecting flange 307 extends along the length of the barrel portion 303. The connecting flange 307 extends a circumferential distance around the barrel portion 303 and terminates at the first longitudinal edge 309.

A first discrete bifurcation 305 is joined to the connecting flange 307 of the barrel portion 303. A second discrete bifurcation (not shown) is joined to the second longitudinal edge of the barrel portion 303, e.g. via another connecting flange. The first discrete bifurcation 305 constitutes a 12H bifurcation. The second discrete bifurcation constitutes a 6H bifurcation.

The first discrete bifurcation 305 comprises a body 314, which may be a machined body. The body 314 has a first longitudinal edge 306 and a second longitudinal edge 316. An inner surface (or surfaces) 319 and an outer surface (or surfaces) 318 extend between the first longitudinal edge 306 and the second longitudinal edge 316. The body 314 includes a bend 320 such that the first longitudinal edge 306 and the second longitudinal edge 316 are located in differently oriented planes. The bend 320 is a right-angled corner. In embodiments, the bend may not be a right-angled corner. The bend may be more or less sharp than a right angle. The bend may be curved at least in part. The bend may pass through more or fewer than 90°. The body may comprise more than one bend. The body 314 comprises a first body portion 3 17, which extends from the second longitudinal edge 316 to the bend 320. The first body portion 317 extends radially relative to the barrel portion 303. The body 314 comprises a second body portion 315 which extends from the first longitudinal edge 306 to the bend 320. The second body portion 315 extends circumferentially relative to the barrel portion 303.

The second body portion 315 includes a connecting flange 308. The connecting flange 308 extends along the length of the first discrete bifurcation 305. The connecting flange 308 terminates at the first longitudinal edge 306 of the first discrete bifurcation 305.

The connecting flange 308 of the first discrete bifurcation 305 and the connecting flange 307 of the barrel portion 303 are disposed such that they overlap each other. A plurality of mechanical fasteners (not shown) joins the connecting flange 308 of the first discrete bifurcation 305 to the connecting flange 307 of the barrel portion 303. Thus, the barrel portion 303 is joined to the first discrete bifurcation 305. The connecting flange 308 of the first discrete bifurcation 305 may be disposed inside the connecting flange 307 of the barrel portion 303 or vice versa.

Close to the second longitudinal edge 316, and running parallel thereto, the body 314 of the first discrete bifurcation 305 comprises a beam or track (not shown) adapted to connect the first discrete bifurcation 305 to the pylon 302 extending from the wing 301 of the aircraft. The beam or track is integral to the body 314 of the first discrete bifurcation 305.

The outer surface 318 of the first body portion 315 of the first discrete bifurcation 305 comprises an array of recesses 312. A piece of honeycomb material may be present in each recess 312. The pieces of honeycomb material, if present, may be made from any suitable material. The pieces of honeycomb material, if present, may be held in the recesses 312 by any suitable joining or bonding technique. The recesses 312 may be of any shape or shapes. The recesses 312 may be of a shape or shapes that tessellate across at least a portion of the outer surface 318.

A skin 313 covers the recesses 312. The skin 313 is perforated to aid noise cancellation/reduction. The skin 313 may be made from any suitable material. The skin 313 may be bonded or joined to the body 314 by any suitable joining or bonding technique. The skin 313 is continuous across the extent of the recesses 312. Alternatively, the skin 313 may be discontinuous. For instance, the skin 313 may comprise a plurality of skin elements, each skin element covering one or some of the recesses 312.

In embodiments, the array of recesses may be provided (i.e. defined at least in part) by a separate component that can be attached to the body of the discrete bifurcation. For instance, the separate component may be received at least partially in a larger recess on a surface of the discrete bifurcation.

In embodiments, the first discrete bifurcation may comprise a different acoustic treatment. For instance, it will be appreciated that honeycomb material is an example of a noise attenuating material. Any suitable noise attenuating material may be used instead of or as well as honeycomb material. In embodiments, no noise attenuating material may be present in the recesses. The recesses may be of a size that makes them noise attenuating without the presence of a noise attenuating material therein.

A seal retaining feature 321 for a sealing element 322 extends longitudinally across the inner surface 319. The seal retaining feature 321 is integral to the body 314 of the first discrete bifurcation 305. In other embodiments, the seal retaining feature may be a separate component, which may be bonded or fastened by any suitable method to the body. The sealing element 322 is retained in the seal retaining feature 321. The seal retaining feature 321 may be straight. Alternatively, the seal retaining feature 321 may include one or more bends and may follow a non-straight path across the inner surface 319.

At least one bumper mount 310 protrudes from the inner surface 319 of the first body portion 317. Each bumper mount 310 has a bumper pad 31 1 mounted thereon. The bumper pad 31 1 abuts the pylon 302. In embodiments, a given bumper pad may abut an opposing bumper pad on an opposing bifurcation.

The bumper mount(s) 310 is/are integral to the body 314 of the first bifurcation 304. The body 314 may comprise any suitable number and arrangement of bumper mounts 310. The bumper mount(s) may be separate components, which may be bonded or fastened by any suitable method to the body.

The bumper mount(s) 310 is/are located inwardly of the recesses 312. The seal retaining feature 321 is located inwardly of the bumper mount(s) 310.

The seal retaining feature may be located inwardly or outwardly (i.e. disposed inboard or outboard) of the bumper mount(s). Alternatively, the seal retaining feature may be inboard of one of more of the bumper mounts and outboard of one or more of the bumper mounts.

The body of the first bifurcation may comprise more than one bend. The body may comprise any number of bends such that the first longitudinal edge and the second longitudinal edge are located in differently oriented planes.

The outer surface 318 of the first discrete bifurcation 305 constitutes an airwashed surface. Accordingly, the outer surface 318 may have an aerodynamic form. The inner surface 319 of the first discrete bifurcation 305 may not constitute an airwashed surface. Thus, there may be a lesser requirement, or no need, for the inner surface 319 to have an aerodynamic form.

The second discrete bifurcation may have some or all of the above-described features of the first discrete bifurcation 305.

The second half 304' comprises a barrel portion 303 '. The barrel portion 303 ' is curved in a lateral direction and has a first longitudinal edge 309' and a second longitudinal edge (not shown). The barrel portion 303 ' comprises a connecting flange 307'. The connecting flange 307' extends along the length of the barrel portion 303 '. The connecting flange 307' extends a circumferential distance around the barrel portion 303 ' and terminates at the first longitudinal edge 309'.

The first discrete bifurcation 305 ' comprises a body 314', which may be a machined body. The body 314' has a first longitudinal edge 306' and a second longitudinal edge 316'. An inner surface (or surfaces) 319' and an outer surface (or surfaces) 318 ' extend between the first longitudinal edge 306' and the second longitudinal edge 316'. The body 314' includes a bend 320' such that the first longitudinal edge 306' and the second longitudinal edge 316' are located in differently oriented planes. The bend 320' is a right-angled corner. In embodiments, the bend may not be a right-angled corner. The bend may be more or less sharp than a right angle. The bend may be curved at least in part. The bend may pass through more or fewer than 90°. The body may comprise more than one bend.

The body 314' comprises a first body portion 3 17', which extends from the second longitudinal edge 316' to the bend 320'. The first body portion 317' extends radially relative to the barrel portion 303 '. The body 3 14' comprises a second body portion 315' which extends from the first longitudinal edge 306' to the bend 320'. The second body portion 315 ' extends circumferentially relative to the barrel portion 303 '.

The second body portion 315 ' includes a connecting flange 308 '. The connecting flange 308 ' extends along the length of the first discrete bifurcation 305 '. The connecting flange 308 ' terminates at the first longitudinal edge 306' of the first discrete bifurcation 305'.

The connecting flange 308 ' of the first discrete bifurcation 305 ' and the connecting flange 307' of the barrel portion 303 ' are disposed such that they overlap each other. A plurality of mechanical fasteners (not shown) joins the connecting flange 308 ' of the first discrete bifurcation 305 ' to the connecting flange 307' of the barrel portion 303 '. Thus, the barrel portion 303 ' is joined to the first discrete bifurcation 305'. The connecting flange 308 ' of the first discrete bifurcation 305 ' may be disposed inside the connecting flange 307' of the barrel portion 303 ' or vice versa.

Close to the second longitudinal edge 316', and running parallel thereto, the body 314 ' of the first discrete bifurcation 305 ' comprises a beam or track (not shown) adapted to connect the first discrete bifurcation 305 ' to the pylon 302 extending from the wing 301 of the aircraft. The beam or track is integral to the body 314' of the first discrete bifurcation 305 '.

The outer surface 318' of the first body portion 315' of the first discrete bifurcation 305' comprises an array of recesses 312'. A piece of honeycomb material may be present in each recess 312'. The pieces of honeycomb material, if present, may be made from any suitable material. The pieces of honeycomb material, if present, may be held in the recesses 312' by any suitable joining or bonding technique. The recesses 312' may be of any shape or shapes. The recesses 312' may be of a shape or shapes that tessellate across at least a portion of the outer surface 318'.

A skin 313 ' covers the recesses 312'. The skin 313 ' is perforated to aid noise cancellation/reduction. The skin 313 ' may be made from any suitable material. The skin 313 ' may be bonded or joined to the body 314' by any suitable joining or bonding technique. The skin 313 ' is continuous across the extent of the recesses 312'. Alternatively, the skin 313 ' may be discontinuous. For instance, the skin 313 ' may comprise a plurality of skin elements, each skin element covering one or some of the recesses 312'.

In embodiments, the array of recesses may be provided (i.e. defined at least in part) by a separate component that can be attached to the body of the discrete bifurcation. For instance, the separate component may be received at least partially in a larger recess on a surface of the discrete bifurcation.

In embodiments, the first discrete bifurcation may comprise a different acoustic treatment. For instance, it will be appreciated that honeycomb material is an example of a noise attenuating material. Any suitable noise attenuating material may be used instead of or as well as honeycomb material. In embodiments, no noise attenuating material may be present in the recesses. The recesses may be of a size that makes them noise attenuating without the presence of a noise attenuating material therein.

At least one bumper mount 310' protrudes from the inner surface 319' of the first body portion 317'. Each bumper mount 310' has a bumper pad 31 1 ' mounted thereon. The bumper pad 31 1 ' abuts the pylon 302. In embodiments, the bumper pads 31 1 of the first discrete bifurcation 305 of the first half 304 may abut the bumper pads 31 1 ' of the first discrete bifurcation 305 ' of the second half 304'.

The bumper mount(s) 310' is/are integral to the body 314' of the first bifurcation 304'. The body 314' may comprise any suitable number and arrangement of bumper mounts The bumper mount(s) 310' is/are located inwardly of the recesses 312'.

The sealing element 322 retained in the seal retaining feature 321 abuts the inner surface 319' of the first discrete bifurcation 305 ' of the second half 304'. Accordingly, a longitudinal air-tight seal is provided between the first discrete bifurcation 305 of the first half 304 and the first discrete bifurcation 305 ' of the second half 304'. In embodiments, a sealing element and a seal retaining feature may be disposed, additionally or alternatively, in the first discrete bifurcation 305 '. In embodiments, both the first discrete bifurcation 305 of the first half 304 and the first discrete bifurcation 305' of the second half 304' may be provided with a seal retaining feature and a sealing element, in which case the sealing elements may seal against the pylon or against each other.

The body of the first bifurcation may comprise more than one bend. The body may comprise any number of bends such that the first longitudinal edge and the second longitudinal edge are located in differently oriented planes.

The outer surface 318' of the first discrete bifurcation 305 ' constitutes an airwashed surface. Accordingly, the outer surface 318 ' may have an aerodynamic form. The inner surface 319' of the first discrete bifurcation 305 ' may not constitute an airwashed surface. Thus, there may be a lesser requirement, or no need, for the inner surface 319' to have an aerodynamic form.

The second discrete bifurcation may have some or all of the above-described features of the first discrete bifurcation 305 '.

In an embodiment, the two first discrete bifurcations 305, 305 ' may be joined to the same barrel portion. Accordingly, the inner fixed structure may have an o-duct arrangement.

Figure 6 shows in schematic cross-section a portion of another example of a half 600 of an inner fixed structure of a thrust reverser.

The half 600 comprises a barrel portion 601. The barrel portion 601 is curved in a lateral direction, e.g. through around 180° of arc, and has a first longitudinal edge 603 and a second longitudinal edge (not shown). In embodiments, the barrel portion 601 may be curved in the lateral direction through a lesser or greater degree of arc. The barrel portion 601 comprises a connecting flange 602. The connecting flange 602 extends along the length of the barrel portion 601. The connecting flange 602 extends a circumferential distance around the barrel portion 601 and terminates at the first longitudinal edge 603.

A first discrete bifurcation 620, which may constitute a 12H bifurcation, comprises a first body 617, a second body 616 and a sandwich panel 613.

The first body 617 may be a machined body. The first body 617 has a first longitudinal edge 606 and a second longitudinal edge 621. An inner surface (or surfaces) 619 and an outer surface (or surfaces) 618 extend between the first longitudinal edge 606 and the second longitudinal edge 621. The first body 617 includes a bend 622 such that the first longitudinal edge 606 and the second longitudinal edge 619 are located in differently oriented planes. The bend 622 is a right-angled corner. In embodiments, the bend may not be a right-angled corner. The bend may be more or less sharp than a right angle. The bend may be curved at least in part. The bend may pass through more or fewer than 90°. The body may comprise more than one bend.

On one side of the bend 622, the first body 617 extends radially relative to the barrel portion 601 , while on the other side of the bend the first body 617 extends circumferentially relative to the barrel portion 601.

The first body 617 includes a first connecting flange 605. The first connecting flange 605 extends along the length of the first body 617. The first connecting flange 605 terminates at the first longitudinal edge 606 of the first body 617.

The first connecting flange 605 of the first body 617 and the connecting flange 602 of the barrel portion 601 are disposed such that they overlap each other. A plurality of mechanical fasteners (not shown) joins the first connecting flange 605 of the first body 617 to the connecting flange 602 of the barrel portion 601. Thus, the barrel portion 601 is joined to the first discrete bifurcation 620. The first connecting flange 605 of the first body 617 may be disposed inside the connecting flange 602 of the barrel portion 601 or vice versa.

A seal retaining feature 607 for a sealing element 608 extends longitudinally across the inner surface 619 of the first body 617. The seal retaining feature 607 is integral to the first body 617. The sealing element 608 is retained in the seal retaining feature 607. The seal retaining feature 607 may be straight. Alternatively, the seal retaining feature 607 may include one or more bends and may follow a non-straight path across the inner surface 619 of the first body 617.

At least one bumper mount 609 protrudes from the inner surface 619 of the first body 617. Each bumper mount 609 has a bumper pad 610 mounted thereon. The bumper pad 610 is configured to abut a pylon extending from a wing of an aircraft.

The bumper mount(s) 609 is/are integral to the first body 617. The first body 617 may comprise any suitable number and arrangement of bumper mounts 609.

The seal retaining feature 607 is located inwardly of the bumper mount(s) 610. The seal retaining feature may be located inwardly or outwardly (i.e. disposed inboard or outboard) of the bumper mount(s). Alternatively, the seal retaining feature may be inboard of one of more of the bumper mounts and outboard of one or more of the bumper mounts.

The first body may comprise more than one bend. The body may comprise any number of bends such that the first longitudinal edge and the second longitudinal edge are located in differently oriented planes.

The first body 617 includes a second connecting flange 61 1. The second connecting flange 61 1 extends along the length of the first body 617. The second connecting flange 61 1 terminates at the second longitudinal edge 621 of the first body 617.

The first discrete bifurcation 620 comprises a second body 616. The second body 616 may be a machined body. The second body may comprise a beam or track (not shown) adapted to connect the first discrete bifurcation 620 to a pylon extending from a wing of an aircraft. The beam or track may be integral to the second body 616. The beam or track extends in a longitudinal direction at least partially across the second body 616. The second body 616 includes a first connecting flange 615.

The sandwich panel 613 comprises a central portion 623, which is disposed between a first connecting flange 612 and a second connecting flange 614. The sandwich panel may comprise, or consist essentially of, any suitable materials such as polyether ether ketone (PEEK) or carbon fibre composite (CFC).

The second connecting flange 61 1 of the first body 617 and the first connecting flange 612 of the sandwich panel 613 are disposed such that they overlap each other. A plurality of mechanical fasteners (not shown) joins the second connecting flange 61 1 of the first body 617 to the first connecting flange 612 of the sandwich panel 613. The second connecting flange 61 1 of the first body 617 may be disposed inside the first connecting flange 612 of the sandwich panel 613 or vice versa.

The first connecting flange 615 of the second body 616 and the second connecting flange 614 of the sandwich panel 613 are disposed such that they overlap each other. A plurality of mechanical fasteners (not shown) joins the first connecting flange 615 of the second body 616 and the second connecting flange 614 of the sandwich panel 613. The first connecting flange 615 of the first body 616 may be disposed inside the second connecting flange 614 of the sandwich panel 613 or vice versa.

Figure 7 shows in schematic cross-section an example of an inner fixed structure 712 of a thrust reverser attached to a wing 700 of an aircraft. A pylon 701 extends downwards from an underside of the wing 700. The inner fixed structure 712 is attached to the pylon 701. The inner fixed structure 712 has a d-duct arrangement.

The inner fixed structure 712 includes a first half 713 and a second half 714.

The first half 713 comprises a barrel portion 703. The barrel portion 703 is disposed between a first discrete bifurcation 702 and a second discrete bifurcation 704. A first joint 708 joins the first discrete bifurcation 702 to the barrel portion 703. A second joint 709 joins the second discrete bifurcation 704 to the barrel portion 703. The first discrete bifurcation 702 constitutes a 12H bifurcation and is hingedly connected to the pylon 701. The second discrete bifurcation 704 constitutes a 6H bifurcation. The second half 714 comprises a barrel portion 706. The barrel portion 706 is disposed between a first discrete bifurcation 705 and a second discrete bifurcation 707. A first joint 710 joins the first discrete bifurcation 705 to the barrel portion 706. A second joint 71 1 joins the second discrete bifurcation 707 to the barrel portion 706. The first discrete bifurcation 705 constitutes a 12H bifurcation and is hingedly connected to the pylon 701. The second discrete bifurcation 707 constitutes a 6H bifurcation. The second discrete bifurcation 704 of the first half 713 and the second discrete bifurcation 707 of the second half 714 may be releasably secured together by a latch. When the two second discrete bifurcations 704, 707 are secured together, the inner fixed structure 712 surrounds an internal volume 715. The internal volume 715 is longitudinally sealed in an air-tight manner. The internal volume 715 is also circumferentially sealed in an air-tight manner by neighbouring components (not shown) forward and aft of the inner fixed structure 707. One or more sealing elements are disposed between the two first discrete bifurcations 702, 705. One or more sealing elements are disposed between the two second discrete bifurcations 704, 707. The sealing elements define the extent of a fire zone, which includes the internal volume 715. The fire zone 715 could contain a fire blanket (not shown) around its perimeter.

Figure 8 shows in schematic cross-section an example of an inner fixed structure 807 of a thrust reverser attached to a wing 800 of an aircraft. A pylon 801 extends downwards from an underside of the wing 800. The inner fixed structure 807 is attached to the pylon 801. The inner fixed structure 807 has a o-duct arrangement.

The inner fixed structure 807 includes a barrel portion 806 disposed between a first discrete bifurcation 802 and a second discrete bifurcation 805. A first joint 803 joins the first discrete bifurcation 802 to the barrel portion 806. A second joint 804 joins the second discrete bifurcation 805 to the barrel portion 806. The first discrete bifurcation 802 constitutes a 12H bifurcation and is hingedly connected to the pylon 801. The second discrete bifurcation 805 constitutes a 12H bifurcation and is hingedly connected to the pylon 801. The first discrete bifurcation 802 and the second discrete bifurcation 805 are connected to opposite sides of the pylon 801.

When attached to the pylon 801 , the inner fixed structure 807 surrounds an internal volume 808. The internal volume 808 is longitudinally sealed in an air-tight manner. The internal volume 808 is also circumferentially sealed in an air-tight manner by neighbouring components (not shown) forward and aft of the inner fixed structure 807. One or more sealing elements are disposed between the first discrete bifurcation 802 and the second discrete bifurcation 805. The one or more sealing elements define the extent of a fire zone, which includes the internal volume 808. The fire zone 808 could contain a fire blanket (not shown) around its perimeter.

In embodiments, the inner fixed structure may be longitudinally sealed in an airtight manner by a sealing element (or sealing elements) disposed relatively close to the circumference of the region defined in part by the barrel portion(s). Accordingly, the inner fixed structure may have a relatively small fire zone. Consequently, a smaller fireproof structure, e.g. a fire blanket, may be required, thereby reducing cost and/or weight and/or complexity.

Figure 9 shows an aircraft 900. The aircraft 900 comprises a fuselage 901 , a first wing 902 and a second wing 903, the first wing 902 and the second wing 903 extending from opposite sides of the fuselage 901.

A first nacelle 904 is connected via a pylon to an underside of the first wing 902. A second nacelle 905 is connected via a pylon to an underside of the second wing 903. The first nacelle 904 and the second nacelle 905 each house an engine. One or both of the first nacelle 904 and the second nacelle 905 include an inner fixed structure as described herein.

In embodiments, the discrete bifurcation(s) may comprise a non-radiused bend between a portion extending circumferentially relative to the barrel portion and a portion extending radially relative to the barrel portion. The non-radiused (i.e. non- rounded) bend may comprise one or more sharp corners such as a. right-angle. Such embodiments of the inner fixed structure may comprise a relatively small fire zone, since the longitudinal air-tight seal may be provided relatively closer to the circumference of the region defined in part by the barrel portion(s). Consequently, a smaller fireproof structure, e.g. a fire blanket, may be required, thereby reducing cost and/or weight and/or complexity.

By providing an inner fixed structure comprising a barrel portion, a discrete bifurcation and a joint joining the discrete bifurcation to the barrel portion, a number of problems may be alleviated.

For instance, when manufacturing a single body (e.g. a sandwich panel) comprising the barrel portion and the bifurcation(s), it can be difficult to reliably manufacture the required radius-ed corner between the barrel portion and the birfurcation.

Another consequence is that manufacture of the barrel portion(s) may be simplified, since the barrel portion(s) may be curved in a lateral direction in only one sense or direction (i. e. with a consistent positive or negative sign). For instance, barrel portions may be formed from complete barrels or cylinders. Such complete barrels or cylinders could conveniently be formed using any suitable process for instance filament winding, e.g. using an automated fibre placement (AFP) robot or similar process. For instance, a complete barrel or cylinder could be cut into sections to provide two or three barrel portions for an inner fixed structure for a thrust reverser.

It may be possible to optimise the shape of the discrete bifurcations for improved aerodynamic performance. Such optimisation would be more difficult, if not impossible, in the case of an inner fixed structure comprising one or two single bodies (e.g. a sandwich panel) comprising the barrel portion(s) and the bifurcation(s).

Integrating one or more of the beams or tracks, bumper fitting pads, bumper mounts, bumpers and/or seal retaining features into the discrete bifurcation(s) may reduce the number of mechanical fasteners that are required.

By providing a discrete bifurcation, e.g. with a machined body, part accuracy may be improved. Consequently, bumpers and/or beams or tracks may be located more accurately without recourse to relatively complicated techniques such as liquid or solid shimming. Further, by providing a discrete bifurcation with an integrated beam or track and/or with an integrated bumper fitting pad or bumper fitting or bumper, fewer mechanical fasteners and/or smaller joining areas may be required. Thus, more of the discrete bifurcation may be acoustically treated (e.g. acoustically drilled), thereby reducing noise during operation. For instance, it may be possible to acoustically drill closer to the edges of the bifurcation.

A simplified, e.g. straight, seal path may be provided. The seal path may include no more than 10 bends or no more than five bends.

Maintenance and repair of the inner fixed structure may also be facilitated, since it may be possible to undo the joint, e.g. by removing mechanical fasteners, between the barrel portion and the discrete bifurcation. Thus, for example, the barrel portion could be replaced relatively easily.

In embodiments, the discrete bifurcation(s) may be stiffer than the barrel portion(s). For instance, the discrete bifurcation(s) may comprise a metal body, e.g. a machined metal body and the barrel portion(s) may be made from a composite material. A consequence of the discrete bifurcation(s), in particular the 12H bifurcations, being stiffer than the barrel portion(s) is that the inner fixed structure may be more stable, exhibiting less of a pendulum effect during aircraft operation.

Further, the use of acoustic treatments other than honeycomb material may be facilitated, since the honeycomb material may not need to serve an additional purpose of increasing the stiffness of the bifurcation. Accordingly, the acoustic performance of the inner fixed structure may be further improved. Suitable additional or alternative acoustic treatments may include fabricated lattice structures and/or a sound absorbing foam material. The fabricated lattice structures and/or the sound absorbing material may be retained at least partially within one or more recesses in the discrete bifurcation. The fabricated lattice structure may have a 50mm by 50mm grid pattern. The fabricated lattice structure may have at least a l Omm by l Omm grid pattern, up to or at least a 75mm by 75mm grid pattern and/or up to a 200mm by 200mm grid pattern. The fabricated lattice structure may have up to or at least a 50mm by 50mm grid pattern. The fabricated lattice structure need not have a regular grid pattern. The fabricated lattice structure need not have a square grid pattern. The lattice structure may comprise cells with a longest dimension of at least 10 mm, up to or at least 50mm, up to or at least 75mm and/or up to 200mm.

Larger cells may be cheaper and/or easier to manufacture. However, larger cells may not provide as good acoustic performance as smaller cells.

In embodiments, a suitable lattice structure for noise attenuation may be provided, e.g. moulded into, a skin for covering at least a portion of a surface, e.g. an outer surface or an inner surface, of a discrete bifurcation.

It will be understood that the invention is not limited to the embodiments above- described and various modifications and improvements can be made without departing from the concepts herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.