# Patent

## Title
Composite aerofoil

## Abstract

A composite blade (26) comprises a three-dimensional arrangement of reinforcing fibers (58) and a matrix material (60) infiltrated around the three-dimensional arrangement of woven reinforcing fibers (60). The three-dimensional arrangement of woven reinforcing fibers (58) defines a plurality of cavities (56) within the aerofoil (28). The composite blade (26) comprises an aerofoil portion (38) and a root portion (36). The aerofoil portion (38) comprises a leading edge (44), a trailing edge (46), a concave pressure surface wall (50), a convex suction surface wall (52) and a tip (48). The aerofoil portion (36) comprises a plurality of webs (54) extending between, and being secured to, the concave pressure surface wall (50) and the convex suction surface wall (52) to produce a Warren girder structure. The three-dimensional arrangement of woven reinforcing fibers (58) are arranged to produce the concave pressure surface wall (50), the convex suction surface wall (52) and the plurality of webs (54). The matrix material (60) is an organic resin and the reinforcing fibers (58) comprise carbon fibers.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a divisional of U.S. application Ser. No. 11/262,781, filed 1 Nov. 2005 now U.S. Pat. No. 8,038,408, which claims foreign priority to United Kingdom patent App'n Ser. No. GB 0424481.0, filed 5 Nov. 2004.


BACKGROUND OF THE INVENTION
The present invention relates to a composite aerofoil, in particular to a composite fan blade, for a gas turbine engine.
Conventionally compressor blades, or fan blades, comprise forged, or machined, solid metal.
One problem with conventional solid low-pressure compressor blades, or fan blades, is that they are relatively heavy in weight due to their size. The gas turbine engines to which these fan blades are secured require that the rotor disc is made sufficiently strong to carry the operational loads of the fan blades and this entails strengthening the rotor disc and as such means increasing the mass and weight of the rotor disc. In addition the gas turbine engines to which these fan blades are secured require that the fan casing containment system is sufficiently strong to contain a fan blade should it become detached due to bird ingestion and as such means increasing the mass and weight of the fan casing. Thus these features add to the weight of the gas turbine engine.
In order to reduce the weight of large compressor blades, e.g. low-pressure compressor blades or fan blades, it is known for the fan blade to comprise a number of metal workpieces, which are diffusion bonded together with an intervening honeycomb structure to produce a hollow fan blade. This reduces the weight of the fan blade and enables corresponding reductions in the weight in the rotor disc and fan casing containment system.
In order to reduce the weight of large compressor blades, e.g. low-pressure compressor blades or fan blades, it is known for the fan blade to comprise a number of metal workpieces, which are diffusion bonded together and superplastically formed to produce a hollow fan blade. This reduces the weight of the fan blade and enables corresponding reductions in the weight in the rotor disc and fan casing containment system.
Also in order to reduce the weight of small and large compressor blades, e.g. low-pressure compressor blades or fan blades, it is known for the fan blade to comprise a composite material, for example fibre, or cloth, reinforced resin. It is also known for the composite material fan blade to comprise metal parts. This also reduces the weight of the fan blade and enables corresponding reductions in weight in the rotor disc and fan casing containment system.
However, a low-pressure compressor blade, or fan blade, comprising composite material has substantially the same weight as a hollow low-pressure compressor blade, or hollow fan blade, comprising a number of metal workpieces, which are diffusion bonded together and superplastically formed.
SUMMARY OF THE INVENTION
Accordingly one aspect of the present invention seeks to provide a novel composite compressor blade.
Accordingly one aspect of the present invention provides a composite aerofoil comprising a three-dimensional arrangement of reinforcing fibres and a matrix material infiltrated around the three-dimensional arrangement of woven reinforcing fibres, and wherein the three-dimensional arrangement of woven reinforcing fibres defining at least one cavity within the aerofoil.
Additionally in accordance with an aspect of the present invention there is provided a composite aerofoil comprising a leading edge, a trailing edge, a concave pressure surface wall, a converse suction surface wall and a tip, the composite aerofoil comprising a three-dimensional arrangement of woven reinforcing fibres and a matrix material infiltrated around the three-dimensional arrangement of woven reinforcing fibres, the three-dimensional arrangement of woven reinforcing fibres defining a plurality of cavities, the plurality of cavities being spaced apart between the leading edge and the trailing edge. The composite aerofoil comprising at least one web extending between, and being secured to, the concave pressure surface wall and the convex suction surface wall to produce a Warren girder structure, the three-dimensional arrangement of woven reinforcing fibres being arranged to produce the concave pressure surface wall, the convex suction surface wall and at least one web to produce the Warren girder structure.
Possibly the three-dimensional arrangement of woven reinforcing fibres defines a plurality of cavities.
Possibly the aerofoil is secured to a root.
The root may comprise a three-dimensional arrangement of woven reinforcing fibres and a matrix infiltrated around the three-dimensional arrangement of woven reinforcing fibres. The three-dimensional arrangement of woven reinforcing fibres in the aerofoil extend into and form the three-dimensional arrangement of woven reinforcing fibres in the root.
The root may comprise a metal member.
Possibly the aerofoil comprises a leading edge, a trailing edge, a concave pressure surface wall, a convex suction surface wall and a tip.
Possibly the at least one cavity is arranged within the aerofoil.
Possibly the plurality of cavities is spaced apart between the leading edge and the trailing edge.
Possibly the aerofoil comprises a plurality of webs extending between, and being secured to, the concave pressure surface wall and the convex suction surface wall to produce a Warren girder structure.
Possibly the webs extending longitudinally of the aerofoil from adjacent the root to adjacent the tip.
Possibly the three-dimensional arrangement of woven reinforcing fibres are arranged to produce the concave pressure surface wall, the convex suction surface wall and the plurality of webs to produce the Warren girder structure.
Possibly the matrix material is a resin. Preferably the matrix material is an organic resin. Possibly the reinforcing fibres comprise carbon fibres. Alternatively the matrix material may be a metal or alloy. Alternatively the reinforcing fibres may be silicon carbide, silicon nitride or boron.
Possibly the at least one cavity is hollow. Alternatively the at least one cavity is filled with a low-density material. The low-density material may be a foamed adhesive.
Possibly the at least one cavity may be defined by a hollow member arranged within the aerofoil. The hollow member may be rigid or resilient. The hollow member may be filled with a foamed adhesive.
Possibly the aerofoil is a fan blade, a fan outlet guide vane, a compressor blade, a compressor vane, a propeller blade, a helicopter blade, a ship propeller blade or a wind turbine blade.
One aspect of the present invention also provides a novel method of manufacturing a composite aerofoil.
Accordingly one aspect of the present invention provides a method of manufacturing a composite aerofoil comprising weaving a three-dimensional arrangement of reinforcing fibres, the three-dimensional arrangement of woven reinforcing fibres defining at least one cavity within the aerofoil, infiltrating a matrix material around the three-dimensional arrangement of woven reinforcing fibres.
Further, in accordance with an aspect of the present invention there is provided a composite aerofoil comprising a leading edge, a trailing edge, a concave pressure surface wall, a converse suction surface wall and a tip, the composite aerofoil comprising a three-dimensional arrangement of woven reinforcing fibres and a matrix material infiltrated around the three-dimensional arrangement of woven reinforcing fibres, the three-dimensional arrangement of woven reinforcing fibres defining a plurality of cavities, the plurality of cavities being spaced apart between the leading edge and the trailing edge, the composite aerofoil comprising at least one web extending between, and being secured to, the concave pressure surface wall and the convex suction surface wall to produce a Warren girder structure, the three-dimensional arrangement of woven reinforcing fibres being arranged to produce the concave pressure surface wall, the convex suction surface wall and at least one web to produce the Warren girder structure and infiltrating a matrix material around the three-dimensional arrangement of woven reinforcing fibres.
The method may comprise placing the woven three-dimensional arrangement of reinforcing fibres in a mould, inserting at least one mandrel into the at least one cavity within the aerofoil and infiltrating the matrix material around the three-dimensional arrangement of woven reinforcing fibres, within the mould and around the at least one mandrel.
The method may comprises placing at least one rigid hollow member within the woven three-dimensional arrangement of reinforcing fibres while the woven three-dimensional arrangement of reinforcing fibres is on a loom, placing the woven three-dimensional arrangement of reinforcing fibres and the at least one rigid hollow member in a mould and infiltrating the matrix material around the three-dimensional arrangement of woven reinforcing fibres, within the mould and around the at least one rigid hollow member.
The method may comprises placing at least one flexible hollow member within the woven three-dimensional arrangement of reinforcing fibres while the woven three-dimensional arrangement of reinforcing fibres is on a loom, the flexible hollow member containing a thermally expandable material, placing the woven three-dimensional arrangement of reinforcing fibres and the at least one flexible hollow member in a mould and infiltrating the matrix material around the three-dimensional arrangement of woven reinforcing fibres, within the mould and around the at least one flexible hollow member.
The method may comprise weaving at least one tape of thermally expandable material into the three-dimensional arrangement of woven reinforcing fibres.
Possibly the matrix material is a resin. Preferably the matrix material is an organic resin. Preferably the reinforcing fibres comprise carbon fibres.
Possibly the method comprises heating and pressurising the matrix material to consolidate and cure the composite material.
The thermally expandable material comprises adhesive foam.
Possibly the aerofoil is a fan blade, a fan outlet guide vane, a compressor blade, a compressor vane, a propeller blade, a helicopter blade, a ship propeller blade or a wind turbine blade.



BRIEF DESCRIPTION OF THE DRAWINGS
An aspect of the present invention will be more fully described by way of example with reference to the accompanying drawings in which:
FIG. 1 is partially cut away view of a gas turbine engine having a fan blade according to aspects of the present invention.
FIG. 2 shows an enlarged partially cut away perspective view of a fan blade according to aspects of the present invention.
FIG. 3 is a further enlarged cross-sectional view through the fan blade along the line A-A shown in FIG. 2.
FIG. 4 is a sectional view of a portion of a preform of three-dimensional arrangement of woven reinforcing fibres used in the fan blade prior to infiltration of a matrix material.
FIG. 5 is an alternative further enlarged cross-sectional view through the fan blade along the line A-A in FIG. 2.
FIG. 6 is another further enlarged cross-sectional view through the fan blade along the line A-A in FIG. 2.
FIG. 7 is a view of a preform of a three-dimensional arrangement of woven reinforcing fibres and mould used in a first method of manufacturing a fan blade according to aspects of the present invention.
FIG. 8 is a view of a preform of a three-dimensional arrangement of woven reinforcing fibres and mould used in a second method of manufacturing a fan blade according to aspects of the present invention.
FIG. 9 is an alternative sectional view of a portion of a preform of three-dimensional arrangement of woven reinforcing fibres used in the fan blade prior to infiltration of a matrix material.
FIG. 10 shows an alternative enlarged partially cut away perspective view of a fan blade according to aspects of the present invention.



DETAILED DESCRIPTION OF THE INVENTION
A turbofan gas turbine engine 10, as shown in FIG. 1, comprises in flow series an inlet 12, a fan section 14, a compressor section 16, a combustion section 18, a turbine section 20 and an exhaust 22. The fan section 14 comprises a fan rotor 24 carrying a plurality of circumferentially spaced radially outwardly extending fan blades 26. The fan blades 26 are arranged in a bypass duct 28 defined by a fan casing 30, which surrounds the fan rotor 24 and fan blades 26. The fan casing 30 is secured to a core engine casing 32 by a plurality of circumferentially spaced radially extending fan outlet guide vanes 34. The fan rotor 24 and fan blades 26 are arranged to be driven by a turbine (not shown) in the turbine section 20 via a shaft (not shown). The compressor section 16 comprises one or more compressors (not shown) arranged to be driven by one or more turbines (not shown) in the turbine section 20 via respective shafts (not shown).
A fan blade 26 according to aspects of the present invention is shown more clearly in FIGS. 2 and 3. The fan blade 26 comprises a root portion 36 and an aerofoil portion 38. The root portion 36 is arranged to locate in a slot 40 in the rim 42 of the fan rotor 24, as shown in FIG. 1, and for example the root portion 36 may be dovetail shape, or firtree shape, in cross-section and hence the corresponding slot 40 in the rim 42 of the fan rotor 24 is the same shape. The aerofoil portion 38 has a leading edge 44, a trailing edge 46 and a tip 48 remote from the root portion 36 and the fan rotor 24. A concave pressure surface wall 50 extends from the leading edge 44 to the trailing edge 46 and a convex suction surface wall 52 extends from the leading edge 44 to the trailing edge 46.
The aerofoil portion 38 of the fan blade 26 is hollow and comprises a plurality of webs 54, which extend between, and are secured to, the concave pressure surface wall 50 and the convex suction surface wall 52 in order to define a plurality of cavities 56. The plurality of cavities 56 and the plurality of webs 54 are spaced apart between the leading edge 44 and the trailing edge 46. The webs 54 extend longitudinally of the aerofoil portion from adjacent the root portion 36 to adjacent the tip 48. The arrangement of the concave pressure surface wall 50, the convex suction surface wall 52 and webs 54 form a Warren girder structure.
The fan blade 26 comprises a three-dimensional arrangement of woven reinforcing fibres 58 and a matrix material 60 infiltrated around the three-dimensional arrangement of woven reinforcing fibres 58. The three-dimensional arrangement of woven reinforcing fibres 58 and matrix material 60 define the cavities 56 within the fan blade 26. In particular the three-dimensional arrangement of woven reinforcing fibres 58 and the matrix material 60 form the concave pressure surface wall 50, the convex suction surface wall 52 and the webs 54. Thus the reinforcing fibres 58 are arranged within the concave pressure surface wall 50, the convex suction surface wall 52 and the webs 54. A first set of the reinforcing fibres 58A extend generally longitudinally of the fan blade 26 from the root portion 36 to the tip 48, a second set of the reinforcing fibres 58B extend generally chordally of the fan blade 26 from the leading edge 44 to the trailing edge 46 and a third set of the reinforcing fibres 58C which have portions which extend generally chordally of the fan blade 26 and which have portions which extend transversely to the first and second sets of reinforcing fibres 58A and 58B. The third set of reinforcing fibres 58C cross and interlock with the first and second set of reinforcing fibres 58A and 58B to bind the three-dimensional arrangement of reinforcing fibres 58 together. FIG. 4 shows one three-dimensional arrangement of woven reinforcing fibres in a preform prior to infiltration with a matrix material. This arrangement is known as orthogonal interlock because the reinforcing fibres 58C are perpendicular to the reinforcing fibres 58A and 58B. However, the reinforcing fibres 58C are really only a special case of the reinforcing fibres 58B.
The three-dimensional arrangement of woven reinforcing fibres 58 are arranged to produce the concave pressure surface wall 50, the convex suction surface wall 52 and the plurality of webs 54 to produce the Warren girder structure.
The matrix material 60 may be a resin, for example the matrix material 60 is an organic resin and the reinforcing fibres 58 may comprise carbon fibres, glass fibres, Kevlar (RTM) fibres or other suitable fibres. The matrix material 60 may be a metal, or alloy, and the reinforcing fibres 58 may be silicon carbide, silicon nitride or boron.
In an alternative embodiment, as shown in FIG. 5, at least one, preferably a respective hollow member 80, is arranged within the aerofoil portion 38 which defines each of the cavities 56. The hollow member 80 is rigid.
In a further embodiment, as shown in FIG. 6, at least one, preferably each, of the cavities 56 is defined by a respective hollow member 90 arranged within the aerofoil portion 38. The hollow member 90 is flexible. The at least one cavity 56 is filled with a low-density material 94. The low-density material may be a foamed adhesive.
In a first method of manufacturing the fan blade 26, as shown in FIG. 7, a preform 62 comprising the three-dimensional arrangement of woven reinforcing fibres 58 is placed in a mould 64 defining the external shape of the fan blade 26. The mould 64 comprises two mould halves 66 and 68 and the mould 64 also comprises a plurality of mandrels 72, which extend into the mould 64 from an end 74 of the mould 70 corresponding to the tip 48, or root portion 36, of the fan blade 26. The mandrels 72 also extend into the cavities defined within the preform 62 of the three-dimensional arrangement of reinforcing fibres 58. The mandrels 72 have a constant, or tapering, cross-section to allow subsequent removal of the mandrels 72. A resin is injected into the mould 64 and the resin infiltrates around the three-dimensional arrangement of woven reinforcing fibres 58 and fills the volume around the reinforcing fibres 58 and between the mould 64 and the mandrels 72. The mould 64 is heated and pressurised in an autoclave to cure the resin to form the matrix material 60 around the three-dimensional arrangement of woven reinforcing fibres 58. The mould 64 defines the exterior shapes of the concave pressure surface wall 50 and the convex suction surface wall 52 of the fan blade 26 and the mandrels 72 define the shapes of the cavities 56. The completed fan blade 26 is removed from the mould 64 and the mandrels 72 are removed from the fan blade 26. The ends of the cavities 56 are then closed.
In a second method of manufacturing the fan blade 26, as shown in FIG. 8, while a preform 62 of the three-dimensional arrangement of woven reinforcing fibres 58 is on the loom, a number of rigid hollow members 80 are positioned within the cavities in the preform comprising the three-dimensional arrangement of woven reinforcing fibres 58 and the weave may be closed around the rigid hollow members 80. The preform comprising the three-dimensional arrangement of woven reinforcing fibres 58 is placed in a mould 82 defining the external shape of the fan blade 26. The mould 82 comprises mould halves 84 and 86. A resin is injected into the mould 82 and the resin infiltrates around the three-dimensional arrangement of woven reinforcing fibres 58 and fills the volume around the reinforcing fibres 58 and between the mould 82 and the rigid hollow members 80. The mould 82 is heated and pressurised in an autoclave to cure the resin to form the matrix material 60 around the three-dimensional arrangement of woven reinforcing fibres 58. The mould 82 defines the exterior shapes of the concave pressure surface wall 50 and the convex suction surface wall 52 of the fan blade 26 and the rigid hollow members 80 define the shapes of the cavities 56. The completed fan blade 26 is removed from the mould 82 and the rigid hollow members 80 are retained in the fan blade 26.
The rigid hollow members 80 must be capable of withstanding the temperatures and pressures applied in the autoclave. The rigid hollow members 80 may have varying cross-section areas and hence enable much greater variation in the shapes of the cavities 54 in the fan blade 26. The preform has enough elasticity to allow the rigid hollow members 80 to be inserted. The rigid hollow members 90 are sealed.
The main advantage of this method is that the three-dimensional arrangement of woven reinforcing fibres 58 and the matrix material 60 completely enclose rigid hollow members 80 and there is no need to close apertures in the finished fan blade 26.
In a third method of manufacturing the fan blade 26, as shown in FIG. 8, while a preform of the three-dimensional arrangement of woven reinforcing fibres 58 is on the loom, a number of flexible hollow members 90 are positioned within the cavities in the preform comprising the three-dimensional arrangement of woven reinforcing fibres 58 and the weave is closed around the flexible hollow members 90. Each of the flexible hollow members 90 is provided with a predetermined, measured, quantity/volume of foaming material e.g. a foaming adhesive, for example Hysol BMI, trade name, compatible foaming adhesive. The preform comprising the three-dimensional arrangement of woven reinforcing fibres 58 is placed in a mould 82 defining the external shape of the fan blade 26. A resin is injected into the mould 82 and the resin infiltrates around the three-dimensional arrangement of woven reinforcing fibres 58 and fills the volume around the reinforcing fibres 58 and between the mould 82 and the flexible hollow members 90. The mould 82 is heated and pressurised in an autoclave to cure the resin to form the matrix material 60 around the three-dimensional arrangement of woven reinforcing fibres 58. During the curing process the adhesive foams by a given factor of its initial volume and provides an internal hydrostatic pressure to help consolidate the interior of the fan blade 26. The mould 82 defines the exterior shapes of the concave pressure surface wall 50 and the convex suction surface wall 52 of the fan blade 26 and the flexible hollow members 90 define the shapes of the cavities 56. The completed fan blade 26 is removed from the mould 82 and the flexible hollow members 90 are retained in the fan blade 26 together with the adhesive foam 94.
The advantage of this method is that the flexible hollow member 90 it is easier to insert into the preform and it may be treated in the loom as a warp. The flexible hollow members 90 may have varying cross-sectional areas and hence enable much greater variation in the shapes of the cavities 54 in the fan blade 26. The flexible hollow members 90 are sealed.
The main advantage of this method is that the three-dimensional arrangement of woven reinforcing fibres 58 and the matrix material 60 completely enclose flexible hollow members 90 and there is no need to close apertures in the finished fan blade 26. Another advantage is that the cavities 56 may be provided in a lattice pattern, instead of running longitudinally of the fan blade 26.
In a fourth method of manufacturing the fan blade 26 while a preform of the three-dimensional arrangement of woven reinforcing fibres 58 is produced on the loom, one or more tapes of foaming material are woven into the preform as a warp, or weft, element and the tapes of foaming material are positioned in the preform comprising the three-dimensional arrangement of woven reinforcing fibres 58 where cavities are required. The tapes of foaming material e.g. foaming adhesive may comprise for example Hysol BMI, trade name, compatible foaming adhesive. The preform comprising the three-dimensional arrangement of woven reinforcing fibres 58 is placed in a mould 82 defining the external shape of the fan blade 26. A resin is injected into the mould 82 and the resin infiltrates around the three-dimensional arrangement of woven reinforcing fibres 58 and fills the volume around the reinforcing fibres 58 and within the mould 82. The mould 82 is heated and pressurised in an autoclave to cure the resin to form the matrix material 60 around the three-dimensional arrangement of woven reinforcing fibres 58. During the curing process the adhesive foams on the tapes of foaming material by a given factor of it's initial volume and provides an internal hydrostatic pressure to help consolidate the interior of the fan blade 26 and to define the cavities 56. The mould 82 defines the exterior shapes of the concave pressure surface wall 50 and the convex suction surface wall 52 of the fan blade 26 and the foamed tape of foaming material define the shapes of the cavities 56. The completed fan blade 26 is removed from the mould 82 and the foamed tape of foaming material is retained in the fan blade 26.
Any three-dimensional weave of the tape of foaming material within the three-dimensional arrangement of woven reinforcing fibres is possible, as long as there is sufficient allowance for expansion of the foaming material during curing of the resin.
The advantage of this method is that it is not necessary to provide rigid or flexible hollow members within the preform to define the cavities.
FIG. 9 shows an alternative three-dimensional arrangement of woven reinforcing fibres in a preform prior to infiltration with a matrix material. This arrangement is known as angle interlock because the reinforcing fibres 58C are angled to the reinforcing fibres 58A and 58B. However, the reinforcing fibres 58C are really only a special case of the reinforcing fibres 58B. This arrangement of reinforcing fibres may give a better resistance to bird, or other large object, impact.
In the examples described previously the root portion 36 of the fan blade 26 also comprises a three-dimensional arrangement of woven reinforcing fibres and a matrix infiltrated around the three-dimensional arrangement of woven reinforcing fibres. The three-dimensional arrangement of woven reinforcing fibres in the aerofoil portion 38 extend into and form the three-dimensional arrangement of woven reinforcing fibres in the root portion 36.
An alternative fan blade 126 according to aspects of the present invention is shown more clearly in FIGS. 10. The fan blade 126 comprises a root portion 136 and an aerofoil portion 138. The root portion 136 is arranged to locate in a slot 40 in the rim 42 of the fan rotor 24, and for example the root portion 136 may be dovetail shape, or firtree shape, in cross-section and hence the corresponding slot 40 in the rim 42 of the fan rotor 24 is the same shape. The aerofoil portion 138 has a leading edge 144, a trailing edge 146 and a tip 148 remote from the root portion 136 and the fan rotor 24. A concave pressure surface wall 150 extends from the leading edge 144 to the trailing edge 146 and a convex suction surface wall 152 extends from the leading edge 144 to the trailing edge 146.
The aerofoil portion 138 of the fan blade 126 is hollow and comprises a plurality of webs 154, which extend between, and are secured to, the concave pressure surface wall 150 and the convex suction surface wall 152 in order to define a plurality of cavities 156. The plurality of cavities 156 and the plurality of webs 154 are spaced apart between the leading edge 144 and the trailing edge 146. The webs 154 extend longitudinally of the aerofoil portion from adjacent the root portion 136 to adjacent the tip 148. The arrangement of the concave pressure surface wall 150, the convex suction surface wall 152 and webs 154 form a Warren girder structure.
The fan blade 126 comprises a three-dimensional arrangement of woven reinforcing fibres 158 and a matrix material 160 infiltrated around the three-dimensional arrangement of woven reinforcing fibres 158. The three-dimensional arrangement of woven reinforcing fibres 158 and matrix material 160 define the cavities 156 within the fan blade 126. In particular the three-dimensional arrangement of woven reinforcing fibres 158 and the matrix material 160 form the concave pressure surface wall 150, the convex suction surface wall 152 and the webs 154. Thus the reinforcing fibres 158 are arranged within the concave pressure surface wall 150, the convex suction surface wall 152 and the webs 154.
The fan blade 126 differs in that the root portion 136 comprises metal, for example a titanium alloy, which has cavities 162, which interconnect with the cavities 156 in the aerofoil portion 138. The hollow rigid members 80 are secured to the root portion 136. The hollow rigid members 80 are inserted in the preform of the three-dimensional arrangement of woven reinforcing fibres 158 and they will not come out after the matrix material 160 is infiltrated around the reinforcing fibres 158. The hollow rigid members 80 may comprise a metal, for example a titanium alloy.
The fan blade 126 may be manufactured in a similar manner to those described above for the fan blade 26. However, in the first method the mandrels may be hollow rigid members, which are retained in the aerofoil portion 138 in order to secure the root portion 136. The hollow members may be provided with features, e.g. teeth, ridges or ribs extending transversely, chordally, of the aerofoil, to provide interlocking with the matrix material 160 or they may be tapered to increase in cross-section towards the tip of the aerofoil portion.
It may be necessary to provide some metal members into, or onto, the aerofoil portion of the fan blade for strengthening purposes. For example it may be necessary to provide a metal member around the leading edge, and possibly the trailing edge, of the aerofoil portion to reduce erosion of the leading edge of the fan blade.
One possible advantage of the present invention is that there is a reduction in weight of the fan blade compared to a fan blade comprising a number of metal workpieces diffusion bonded and superplastically formed and also relative to a fan blade comprising a composite material.
Another possible advantage of the present invention is that there is flexibility for positioning of the cavities within the fan blade so that the stiffness of the fan blade and hence the vibrational frequencies and modeshapes may be manipulated and/or controlled.
Although aspects of the present invention have been described with reference to a fan blade, a low-pressure compressor blade, the present invention is also applicable to other compressor blades. Aspects of the present invention are also applicable to fan outlet guide vanes or to compressor vanes. Aspects of the present invention are also applicable to integrally bladed rotors. Additionally aspects of the present invention are also applicable to propeller blades, helicopter blades, ship propeller blades or wind turbine blades. Thus generally aspects of the present invention are applicable to aerofoils or hydrofoils.
Aspects of the present invention are applicable to smaller compressor blades or compressor vanes simply by reducing the thread size. Typically in carbon fibre weaves 12k tows are used, e.g. 12 thousand carbon fibres in the thread cross-section. The carbon fibre threads may have threads comprising 3k tows or less.

## Claims

1. A composite aerofoil comprising:
a leading edge;
a trailing edge;
a concave pressure surface wall;
a convex suction surface wall;
a tip;
a three-dimensional arrangement of woven reinforcing fibers;
a matrix material infiltrated around the three-dimensional arrangement of woven reinforcing fibers, the three-dimensional arrangement of woven reinforcing fibers defining a plurality of cavities, the plurality of cavities being spaced apart between the leading edge and the trailing edge; and
at least one web extending between, and being secured to, the concave pressure surface wall and the convex suction surface wall to produce a Warren girder structure, the three-dimensional arrangement of woven reinforcing fibers being arranged to produce the concave pressure surface wall, the convex suction surface wall and at least one web to produce the Warren girder structure.

2. A composite aerofoil as claimed in claim 1 wherein the composite aerofoil is secured to a root.

3. A composite aerofoil as claimed in claim 2 wherein the root comprises a three-dimensional arrangement of woven reinforcing fibers and a matrix infiltrated around the three-dimensional arrangement of woven reinforcing fibers.

4. A composite aerofoil as claimed in claim 2 wherein the root comprises a metal member.

5. A composite aerofoil as claimed in claim 2 wherein the webs extending longitudinally of the aerofoil from adjacent the root portion to adjacent the tip.

6. A composite aerofoil as claimed in claim 3 wherein the three-dimensional arrangement of woven reinforcing fibers in the aerofoil extend into and form the three-dimensional arrangement of woven reinforcing fibers in the root.

7. A composite aerofoil as claimed in claim 1 wherein the matrix material is a resin.

8. A composite aerofoil as claimed in claim 7 wherein the matrix material is an organic resin.

9. A composite aerofoil as claimed in claim 7 wherein the reinforcing fibers comprise carbon fibers.

10. A composite aerofoil as claimed in claim 1 wherein the matrix material is a metal or alloy.

11. A composite aerofoil as claimed in claim 10 wherein the reinforcing fibers are silicon carbide, silicon nitride or boron.

12. A composite aerofoil as claimed in claim 1 wherein the at least one cavity is hollow.

13. A composite aerofoil as claimed in claim 12 wherein the at least one cavity is defined by a hollow member arranged within the aerofoil.

14. A composite aerofoil as claimed in claim 13 wherein the hollow member is selected from the group comprising a hollow member and a resilient hollow member.

15. A composite aerofoil as claimed in claim 14 wherein the hollow member is filled with a foamed adhesive.

16. A composite aerofoil as claimed in claim 1 wherein the at least one cavity is filled with a low-density material.

17. A composite aerofoil as claimed in claim 16 wherein the low-density material is a foamed adhesive.

18. A composite aerofoil as claimed in claim 1 wherein the aerofoil is selected from the group comprising a fan blade, a fan outlet guide vane, a compressor blade, a compressor vane, a propeller blade, a helicopter blade, a ship propeller blade and a wind turbine blade.