Patent Publication Number: US-10767494-B2

Title: CMC aerofoil

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from British Patent Application No. GB 1806774.4, filed on 25 Apr. 2018, the entire contents of which are incorporated by reference. 
     BACKGROUND 
     Technical Field 
     The present disclosure concerns a ceramic matrix composite (CMC) aerofoil. 
     Description of the Related Art 
     Ceramic matrix composites, which comprise ceramic fibres embedded in a ceramic matrix, exhibit a combination of properties that make them promising candidates for industrial applications that demand excellent thermal and mechanical properties along with low weight, such as gas turbine engine components. Existing CMCs and turbine engine components systems have various shortcomings, however, such as difficulties functioning at high temperatures without sacrificing structural stability. As CMC parts see increasing use as replacements for current metallic components in turbine engines, CMC-compatible cooling techniques are becoming increasingly important. Various cooling schemes have been attempted for CMC components, such as the placement of a series of continuous tubes into the fibrous preform of the composite during fabrication. It would be advantageous to develop a CMC component with integral cooling capabilities that can maintain a more uniform operating temperature, particularly for complex geometric parts. 
     SUMMARY 
     According to a first aspect there is provided an aerofoil comprising:
         first and second tubular CMC cores extending along a longitudinal axis of the aerofoil; and   an outer CMC layer surrounding the first and second tubular CMC cores and defining an outer shape of the aerofoil having leading and trailing edges,   wherein fibres within a wall of the second tubular CMC core extend to the trailing edge of the aerofoil.       

     Having fibres within a wall of the second tubular CMC core extending the trailing edge of the aerofoil allows air cooling channels to be positioned closer to the trailing edge of the aerofoil than would otherwise be possible, while maintaining a minimum radius of curvature for the internal tubular CMC cores. 
     The aerofoil may comprise one or more air cooling passages connecting an inner volume of the second tubular CMC core to an external surface of the aerofoil. 
     The aerofoil may comprise an inner concave external surface and an outer convex external surface, a plurality of air cooling passages connecting the inner volume of the second tubular CMC core to the inner concave external surface. 
     A plurality of air cooling passages may pass through a wall of the second tubular CMC core. 
     One or more air cooling passages may be defined by one or more gaps between adjacent facing portions of the inner surface of the second tubular CMC core. 
     The aerofoil may comprise an insert between the adjacent facing portions of the inner surface of the second tubular CMC core. A plurality of air cooling passages may be defined by passages within the insert. The insert may comprise ceramic foam, which may be open or closed celled. The insert may comprise plenums forming the plurality of air cooling passages. 
     A plurality of air cooling passages may be defined by corrugations of the inner surface of the second tubular CMC core. 
     According to a second aspect there is provided a method of forming a CMC aerofoil, comprising the steps of:
         providing first and second tubular CMC cores;   surrounding the first and second tubular CMC cores with an outer CMC layer to define an outer shape of the aerofoil having leading and trailing edges, wherein fibres within a wall of the second tubular CMC core extend to the trailing edge of the aerofoil; and   consolidating the first and second CMC cores with the outer CMC layer to form the CMC aerofoil.       

     The method may comprise the step of forming one or more air cooling passages connecting an inner volume of the second tubular CMC core to an external surface of the aerofoil. 
     The aerofoil may comprise an inner concave external surface and an outer convex external surface, the method comprising forming a plurality of air cooling passages connecting the inner volume of the second tubular CMC core to the inner concave external surface. 
     The method may comprise forming a plurality of air cooling passages passing through a wall of the second tubular CMC core. 
     The one or more air cooling passages may be defined by one or more gaps between adjacent facing portions of the inner surface of the second tubular CMC core. 
     The method may comprise providing an insert between the adjacent facing portions of the inner surface of the second tubular CMC core. 
     The method may comprise forming a plurality of air cooling passages by corrugations of the inner surface of the second tubular CMC core. 
     A plurality of air cooling passages may be defined by passages within the insert. The insert may comprise a ceramic foam, which can be open or closed celled. The insert may comprise plenums forming the plurality of air cooling passages. 
     The skilled person will appreciate that, except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied mutatis mutandis to any other aspect. Furthermore except where mutually exclusive any feature described herein may be applied to any aspect and/or combined with any other feature described herein. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Embodiments will now be described by way of example only, with reference to the Figures, in which: 
         FIG. 1  is a sectional side view of a gas turbine engine; 
         FIG. 2  is schematic sectional view of a trailing edge portion of a CMC aerofoil, in which a minimum internal radius is used; 
         FIG. 3  is a schematic sectional view of a trailing edge portion of an example CMC aerofoil in which reinforcing fibres of a tubular CMC core extend to the trailing edge of the aerofoil; 
         FIG. 4  is a schematic sectional view of an example aerofoil having two internal cores; 
         FIG. 5  is a schematic sectional view of an example aerofoil having three internal cores; 
         FIG. 6  is a perspective view of the aerofoil of  FIG. 5 ; 
         FIG. 7  is a perspective view of an example aerofoil having a cooling slot proximate its trailing edge; 
         FIGS. 8 a  and 8 b    are detailed views of the trailing edge portion of the aerofoil of  FIG. 7 ; 
         FIG. 9 a    is a sketch of a trailing edge portion of an example aerofoil, indicating a position of an insert tool; 
         FIG. 10  is a sketch of a trailing edge portion of an example aerofoil, in which a portion proximate the trailing edge is curved to aid machining; 
         FIG. 11  is a sketch of a trailing edge portion of an example aerofoil, indicating a position of an insert tool; 
         FIG. 12 a    is a sketch of a trailing edge portion of an example aerofoil, in which a portion proximate the trailing edge is curved to aid machining; 
         FIG. 12 b    is a sketch of a trailing edge portion of an example aerofoil similar to that in  FIG. 12 a   , in which an internal tool is provided within an internal core; 
         FIG. 13 a    is a sketch of the example aerofoil of  FIG. 12 a    or  12   b  after a machining operation; 
         FIG. 13 b    is a sketch of the example aerofoil of  FIG. 13 a    after a further machining operation to introduce cooling holes through the internal core and outer layer; 
         FIG. 14 a    is a sketch of a trailing edge portion of an alternative example aerofoil; 
         FIG. 14 b    is a sketch of the aerofoil of  FIG. 14 a    following a machining operation; 
         FIG. 15  is a sketch of a trailing edge portion of a further alternative example aerofoil; 
         FIG. 16  is a sectional view of a trailing edge portion of an example aerofoil having cooling channels proximate the trailing edge; 
         FIG. 17  is a sectional view of a trailing edge portion of an example aerofoil having cooling channels proximate the trailing edge formed within a ceramic foam; 
         FIG. 18  is a sectional view of a trailing edge portion of an example aerofoil having cooling channels proximate the trailing edge formed by channels provided within a ceramic foam; 
         FIG. 19  is a sectional view of a trailing edge portion of an alternative example aerofoil having cooling channels proximate the trailing edge formed by channels provided within a ceramic foam; 
         FIG. 20  is a sectional view of a trailing edge portion of an example aerofoil having cooling channels proximate the trailing edge formed by channels provided within an insert; 
         FIG. 21  is a sectional view of a trailing edge portion of an example aerofoil having cooling channels proximate the trailing edge formed by channels provided by an insert; 
         FIG. 22  is a sectional view of a trailing edge portion of an example aerofoil, in which bundles of reinforcing fibres are used to join together end portions of an internal core and an outer layer; 
         FIG. 23  is a sectional view of a trailing edge portion of an example aerofoil, in which reinforcing fibres are used to stitch together end portions of an internal core and an outer layer; 
         FIG. 24  is a sectional view of a trailing edge portion of an example aerofoil prior to a machining operation; 
         FIG. 25  is a sectional view of a trailing edge portion of the example aerofoil of  FIG. 26  following a machining operation on the trailing edge; 
         FIG. 26  is a sectional view of a trailing edge portion of the example aerofoil of  FIG. 26  following a further machining operation on the trailing edge; 
         FIG. 27  is a sketch of an example aerofoil in which cooling channels are provided proximate a trailing edge by corrugations provided in an internal core and outer layer along the trailing edge; 
         FIG. 28  is a sectional view along line AB-AB in  FIG. 29 , showing a cooling channel proximate the trailing edge; 
         FIG. 29  shows three alternative examples of trailing edge cooling channels for an aerofoil of the type shown in  FIG. 27 ; 
         FIG. 30  is an output of a computer model temperature simulation for an aerofoil having internal cores and an outer layer; 
         FIG. 31  is an output of a computer model temperature simulation for an aerofoil having internal cores and an outer layer, in which air cooling passages are provided proximate the trailing edge; and 
         FIG. 32  is a flowchart illustrating an example method of forming a CMC aerofoil. 
     
    
    
     DETAILED DESCRIPTION 
     US 2016/0101561 A1 discloses a dual-walled CMC component comprising a CMC core having a hollow shape enclosing at least one interior channel and a CMC outer layer overlying and spaced apart from the CMC core by a ceramic slurry-cast architecture positioned therebetween. The CMC core further includes a plurality of through-thickness inner cooling holes in fluid communication with the at least one interior channel. The ceramic slurry-cast architecture defines a cooling fluid path over an outer surface of the CMC core that connects the interior channel(s) to an external environment of the dual-walled CMC component. The CMC outer layer may also include a plurality of through-thickness outer cooling holes in fluid communication with the cooling fluid path, thereby extending the cooling fluid path through the CMC outer layer. 
     A particular issue with aerofoil components, for example those used for vanes or blades in high temperature portions of a gas turbine engine, relates to cooling of the trailing edge of the aerofoil. With existing designs for CMC aerofoils, the geometry requirements for internal core components may restrict the ability to incorporate cooling passages that extend close to the trailing edge of the aerofoil. The requirement for a minimum internal radius for an internal core component for the aerofoil may result in either a less sharp trailing edge, resulting in poorer aerodynamic performance (and hence reduced efficiency), or in a greater distance between the internal volume of the core closest to the trailing edge (used to carry cooling air) resulting in an increase in temperature at the trailing edge of the aerofoil. To maximise use of the material it would be beneficial to enable the temperature distribution throughout the aerofoil to be as uniform as possible 
     With reference to  FIG. 1 , a gas turbine engine is generally indicated at  10 , having a principal and rotational axis  11 . The engine  10  comprises, in axial flow series, an air intake  12 , a propulsive fan  13 , an intermediate pressure compressor  14 , a high-pressure compressor  15 , combustion equipment  16 , a high-pressure turbine  17 , an intermediate pressure turbine  18 , a low-pressure turbine  19  and an exhaust nozzle  20 . A nacelle  21  generally surrounds the engine  10  and defines both the intake  12  and the exhaust nozzle  20 . 
     The gas turbine engine  10  works in the conventional manner so that air entering the intake  12  is accelerated by the fan  13  to produce two air flows: a first air flow into the intermediate pressure compressor  14  and a second air flow which passes through a bypass duct  22  to provide propulsive thrust. The intermediate pressure compressor  14  compresses the air flow directed into it before delivering that air to the high pressure compressor  15  where further compression takes place. 
     The compressed air exhausted from the high-pressure compressor  15  is directed into the combustion equipment  16  where it is mixed with fuel and the mixture combusted. The resultant hot combustion products then expand through, and thereby drive the high, intermediate and low-pressure turbines  17 ,  18 ,  19  before being exhausted through the nozzle  20  to provide additional propulsive thrust. The high  17 , intermediate  18  and low  19  pressure turbines drive respectively the high pressure compressor  15 , intermediate pressure compressor  14  and fan  13 , each by suitable interconnecting shaft. 
     Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. By way of example such engines may have an alternative number of interconnecting shafts (e.g. two) and/or an alternative number of compressors and/or turbines. Further the engine may comprise a gearbox provided in the drive train from a turbine to a compressor and/or fan. 
       FIG. 2  shows a sectional view of a trailing edge portion of an aerofoil  200  comprising a CMC core  201  and an outer CMC layer  202 . The outer layer  202  extends beyond the inner CMC core  201  due to the need to have a minimum internal radius for the core  201 , indicated in  FIG. 2  by an outer diameter  206  of the core  201 . As the wall thickness of the core  201  increases, the distance between the trailing edge  203  of the aerofoil and the trailing edge  204  of the internal core  201  increases. This affects the ability to cool the trailing edge  203  of the aerofoil, as any cooling air will first pass along the internal volume  205  of the internal core  201  before exiting through the outer layer, possibly via holes machined through the wall of the internal core  201  and the outer layer  202 . Such holes can only extend as far as the extent of the internal core  201 , resulting in cooling air exiting the holes having to travel along the outer surface (typically along the inner face  207  of the aerofoil) before reaching the trailing edge  203 . The longer the distance this cooling air has to travel, the less cooling effect it is able to have on the trailing edge  203 , which will consequently be at a higher temperature. 
       FIG. 3  shows a sectional view of a trailing edge portion of an aerofoil  300  comprising multiple tubular internal CMC cores  301 ,  302 ,  303  and an outer CMC layer  304  surrounding the internal CMC cores  301 ,  302 ,  303 . Each of the tubular CMC cores  301 ,  302 ,  303  comprises ceramic fibres (not shown) within a ceramic matrix, with the ceramic fibres extending along the walls of the tubes  301 ,  302 ,  303 . The fibres may for example be in the form of woven fibre mats embedded within a ceramic matrix. Tubular cores  301 ,  302  are in the form of closed tubes in which the fibres extend around the tube walls, whereas tubular core  303  is an open tube, in which the ceramic fibres in the wall of the core  303  extend to the trailing edge  305  of the aerofoil  300 . This arrangement allows for cooling air within the tubular core  303  to be directed more closely to the trailing edge  305  of the aerofoil without having to reduce the minimum diameter of curvature  306  of the tubular core  303 . 
     The number of internal cores in the aerofoil may vary from a minimum of two upwards.  FIG. 4  shows an example of an aerofoil  400  with two internal cores  401 ,  402 , in which one core  402  has fibres that extend to a trailing edge  403  of the aerofoil  400 .  FIG. 5  shows an alternative example of an aerofoil  500  having three internal cores  501 ,  502 ,  503 , one of which  503  has fibres extending to a trailing edge  504  of the aerofoil  500 . In each case the aerofoil comprises first and second tubular CMC cores that extend along a longitudinal axis of the aerofoil (i.e. in a direction orthogonal to the page in  FIGS. 4 and 5 ), and an outer CMC layer surrounding the first and second tubular CMC cores, the outer CMC layer defining an outer shape of the aerofoil having leading and trailing edges, wherein fibres within a wall of the second tubular CMC core extend to the trailing edge of the aerofoil. 
       FIG. 6  shows a perspective view of an example aerofoil  600  of the type shown in  FIG. 5 , i.e. with two closed internal cores  601 ,  602 , one open internal core  603  and an outer layer  604  surrounding the internal cores  601 ,  602 ,  603 . Fibres in the open internal core  603  extend to a trailing edge  605  of the aerofoil  600 . Air cooling passages are provided by holes  606  machined along an inner concave external surface  607  of the aerofoil  600 . Cooling air can thereby pass along the bore of the internal core  603  and out of the aerofoil through the holes  606 . Due to the passage of air along the outer surface of the aerofoil when in use, the cooling air will be swept along the external surface of the aerofoil towards the trailing edge  605 . 
       FIG. 7  illustrates an alternative form of providing an air cooling passage for an aerofoil having an open internal core, with  FIGS. 8 a  and 8 b    showing detailed views (within the box  710  defined in  FIG. 7 ) of the aerofoil. The aerofoil  700  comprises two closed internal cores  701 ,  702  and one open internal core  703 . An air cooling passage is provided by a gap  704  between adjacent internal faces of the open internal core  703 . The gap  704  may extend along the entire length of the trailing edge  705  of the aerofoil. In other examples the gap  704  may be intermittent, providing a plurality of air cooling passages connecting an internal volume of the internal core  703  with an external surface of the aerofoil  700 . If the gap extends along the entire length, or along a substantial proportion thereof, it may be prone to closing up either during fabrication or use. During fabrication, an insert  901  may be provided to prevent the gap from closing up, for example as illustrated schematically in  FIG. 9 a   . The dotted lines in  FIG. 9 a    indicate material that may be machined away following consolidation of the CMC components of the aerofoil. As can be seen in this schematic drawing, an edge  902  of the internal core  903  will need to be machined away close to an adjacent face  904  of the internal core  903 . This may result in the adjacent face  904  being machined to cause fibres within the internal core being exposed parallel or at shallow angles to the surface, resulting in a large surface area exposing interfacial regions between the fibres and surrounding matrix. During use, this could result in progressive damage to the CMC core  903  due to oxidation, for example if the composite is based on silicon carbide fibres in a silicon carbide matrix. To address this issue, the shape of the internal core  903  may be adjusted in the green (i.e. unconsolidated) state, as shown schematically in  FIG. 10 . Instead of having the internal faces of the trailing edges of the internal core  903  being parallel to each other prior to consolidation, one of the edges  1001  is curved away from the other face  1002  so that, after consolidation, a machining operation can effect removal of this curved edge, resulting in the aerofoil having a trailing edge portion of the type illustrated in  FIG. 11 . In this drawing, an insert  1101 , which may be composed of a high temperature material such as graphite, is shown in place following a machining operation to remove the curved edge from the internal core and the outer layer. After removal of the insert  1101  the gap provided by the opening between adjacent faces of the internal core can serve as an air cooling passage. 
       FIGS. 12 a  and 12 b    illustrate an alternative form for the internal core  1201 , in which adjacent facing portions of the internal core are joined together, rather than having a gap between them as in the preceding examples. As with the example in  FIG. 10 , a curved portion  1202  of the internal core  1201  allows for a machining operation to be applied after consolidation to remove the curved portion  1202  without affecting the adjacent facing portion  1203  of the internal core  1201 .  FIG. 12 b    shows an insert  1204  in place within the bore of the internal core  1201  to keep the shape of the core  1201  during consolidation. 
       FIG. 13 a    shows a sketch of the aerofoil trailing edge portion of  FIGS. 12 a  and 12 b    following a machining operation, which results in a machined surface  1303  of the internal core  1301  and outer layer  1302 . A further machining process may be applied to form air cooling passages, as for example shown in  FIG. 13 b   . The air cooling passages are in the form of holes  1304  passing through the wall of the internal core  1301  and outer layer  1302 , the holes connecting an inner volume  1305  of the internal core  1301  to an external surface of the aerofoil  1300 . 
       FIGS. 14 a  and 14 b    illustrate an alternative example, in which adjacent trailing edge facing portions of the internal core  1401  are bonded together. Following consolidation, one face is machined away, resulting in a machined surface  1402  along the trailing edge of the aerofoil  1400 . 
       FIG. 15  illustrates a further alternative example, in which adjacent trailing edge facing portions of the internal core  1501  are separated by a gap  1502  proximate the trailing edge  1503  of the aerofoil  1500 . The trailing edges of the internal core  1501  and the outer layer  1504  are machined back after consolidation. 
       FIGS. 16 to 19  illustrate various options for providing air cooling channels connecting an inner volume of the internal core to an external surface of the aerofoil. In each case the air cooling channels pass between adjacent facing portions of the internal core of the aerofoil. In  FIG. 16 , a gap  1602  between adjacent facing portions of the internal core  1601  is provided, through which cooling air passes. The gap  1602  may be continuous or intermittent along the trailing edge of the aerofoil. In  FIG. 17 , a ceramic foam insert  1702  is provided between adjacent facing portions of the internal core  1701 . The ceramic foam may be open-celled, allowing cooling air to pass therethrough while maintaining a structural connection between the adjacent facing portions of the inner core  1701 . If the ceramic foam is a closed-cell foam, or if greater airflow is required, air passages  1803  may be provided within the foam insert  1802 , as shown in  FIG. 18 . An alternative form of ceramic foam insert  1902  is shown in  FIG. 19 , which fills the internal volume of the internal core  1901  and in which an air cooling passage or bore  1903  is provided along the longitudinal axis of the aerofoil, the bore  1903  connecting with a plurality of air cooling passages  1904  connecting the bore  1903  with the external surface of the aerofoil  1900 . 
       FIGS. 20 and 21  illustrate two further examples in which air cooling passages are provided between adjacent facing portions of the internal core. In these examples, an insert  2002 ,  2102  is provided between facing portions of the internal core  2001 ,  2101 . In  FIG. 20 , the insert  2002  comprises a plurality of passages  2003  connecting the internal volume of the internal core  2001  to an external surface of the aerofoil. In  FIG. 21 , the insert  2102  comprises a series of gaps or recesses  2103  that allow air to flow between the insert and the internal core  2101 . 
       FIGS. 22 and 23  illustrate two alternatives for joining the adjacent facing portions of the internal core  2201 ,  2301 , where air cooling passages pass through the wall of the internal core. In  FIG. 22 , pins  2202  are used to join together adjacent facing portions of the internal core  2201 . The pins  2202  may be formed from bundles of fibres, which may have the same composition as fibres in the internal core, and provide an increased strength bond between the adjacent facing portions to reduce the risk of delamination. The pins  2202  may be introduced prior to consolidation of the CMC components by machining holes through the internal core  2201  and outer layer  2203  and inserting a pin  2202  into each machined hole. The consolidation process then forms a bond between the pins  2202  and the surrounding material.  FIG. 23  illustrates an alternative example, in which the internal core  2301  and outer layer  2303  are stitched together using fibres  2304 , or bundles of fibres, that pass through the layers and join them together. In both of the examples in  FIGS. 22 and 23 , machined holes  2205 ,  2305  are shown, through which air cooling passes from the internal volume of the internal core to an external surface of the aerofoil. 
       FIGS. 24, 25 and 26  illustrate examples showing how machining operations following consolidation can result in different forms of trailing edge portions of the aerofoil. In the pre-machined form, shown in  FIG. 24 , the internal core  2401  and outer layer  2402  are joined together at the trailing edge  2403  of the aerofoil  2400 . Following a first machining operation, the trailing edge  2403  is machined back, with the edge of the internal core  2401  and outer layer  2402  machined back further on the inner concave surface  2405  of the aerofoil  2400  than on the outer convex surface  2406 . In this configuration, the adjacent facing portions of the internal core  2401  are joined together. Air cooling passages may then provided by machining channels through the wall of the internal core  2401  and outer layer  2402 . Machining further results in the form shown in  FIG. 26 , where a gap  2601  is formed between the adjacent facing portions of the internal core  2401 , allowing one or more air cooling channels to be formed. 
       FIG. 27  illustrates an example of an aerofoil  2700  in which gaps  2703  between adjacent facing portions of the internal core  2701  are provided by corrugations  2704  in the internal core  2701  and outer layer  2702 , the corrugations  2704  extending along the trailing edge  2705  of the aerofoil  2700 . 
       FIG. 28  is a detailed sectional view along section AB-AB shown in  FIG. 27 , and  FIG. 29  shows three different example forms the corrugations along AA-AA of  FIG. 27  may take. 
       FIG. 30  illustrates an example CMC aerofoil  3000  having a type of construction in which the internal cores  3001 ,  3002  are of closed tubular form. As discussed above, the minimum radius allowed for such cores results in any air flowing from cooling passages (not shown) connecting the internal volume  3003  of the core  3002  closest to the trailing edge  3004  of the aerofoil  3000  to the external surface of the aerofoil  3000  being too far away to provide effective cooling at the trailing edge  3004 . Computer simulations of the aerofoil  3000  show that the temperature of the aerofoil reaches a maximum at the trailing edge  3004 , which limits the maximum use temperature of the aerofoil  3000 . By comparison, as shown in  FIG. 31 , simulation of an example aerofoil  3100  having an internal core  3101  in which fibres extend to the trailing edge  3103  of the aerofoil  3100  and in which one or more air cooling passages are provided proximate the trailing edge show a more uniform temperature, demonstrating that air cooling is more effective when provided closer to the trailing edge  3103 . 
     A CMC aerofoil according to the examples illustrated above may be formed according to the process illustrated in  FIG. 32 . In a first step  3201 , first and second CMC internal cores are provided. The first and second cores may be formed for example by laying up fibres around a mandrel and impregnating the fibres with a ceramic or ceramic precursor. A silicon carbide CMC may for example be formed by laying up SiC fibres and binding the fibres together with a binder. An oxide CMC may be formed by laying up oxide fibres, for example alumina-based fibres, and impregnating the fibres with a slurry of oxide particles with a binder. Following impregnation of the fibres, the first and second tubular CMC cores are surrounded by an outer CMC layer (step  3202 ) to define an outer shape of the aerofoil having leading and trailing edges. At this stage, fibres in the wall of the second tubular CMC core extend to the trailing edge of the aerofoil. The assembled aerofoil is then subjected to a consolidation step  3203 , in which the matrix around the fibres is densified to form the final CMC aerofoil. Subsequent machining steps may be applied, for example to machine the trailing edge and/or form air cooling passages connecting an inner volume of the second tubular CMC core to an external surface of the aerofoil.