Abstract:
A turbojet vane, in particular a compressor guide vane, characterized in that the vane comprises the following elements:
       an elongate one-piece front portion ( 2 ) cut out from a pultruded section member comprising fibers bonded together by resin and forming a leading edge;   an elongate one-piece rear portion ( 3 ) cut out from a pultruded section member comprising fibers bonded together by resin and forming a trailing edge; and   a skin ( 5 ) based on resin-impregnated fibers extending between the leading edge and the trailing edge in order to form side faces of the vane and covering at least zones ( 6, 7 ) of the leading edge ( 2 ) and of the trailing edge ( 3 );   these elements being assembled together by hot compaction.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Vanes made of composite material are known that have ends carrying fastener means for fastening them to annular casings of a turbojet. 
         [0002]    Various fastener means have been proposed. For example, document US 2009/0317246 recommends ends making up a cylindrical platform forming a portion of the outer casing and carrying two fastener flanks, thereby leading to shapes that are complex to fabricate. Document 
         [0003]    US 2009/0317246 recommends joining the vanes together by means of a circular ring prior to mounting the assembly made in this way in the casing. That solution is complex to implement and requires assembly tooling. 
       OBJECT OF THE INVENTION 
       [0004]    The object of the invention is thus to propose a turbojet vane that is simple to produce and easy to mount. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    To this end, the invention provides a turbojet vane, in particular a compressor guide vane comprising the following elements:
       an elongate one-piece front portion cut from a pultruded section member comprising fibers bonded together by resin and forming a leading edge;   an elongate one-piece rear portion cut from a pultruded section member comprising fibers bonded together by resin and forming a trailing edge; and   a skin cut out from a resin-impregnated fabric fiber that extends to cover the side faces of the core, while also covering at least zones of the leading and trailing edges that are contiguous to the central portion, all of these elements being joined together by hot compaction so as to provide a particularly strong one-piece vane.       
 
         [0009]    In a particular aspect of the invention, the vane includes a core-forming central portion arranged between the leading edge and the trailing edge, and preferably, the leading edge and the trailing edge present extensions that project from the core from at least one end of the vane in order to form attachment means for attaching the vane to a casing of the turbojet. 
         [0010]    The extensions of the leading and trailing edges make it very easy to anchor the vane in an annular casing. It suffices to provide through orifices in the casing to receive these extensions which can then be fastened to complementary attachment means of the casing. 
         [0011]    In a preferred embodiment, the leading and/or the trailing edge comprises an elongate body obtained by pultrusion and impregnated with thermoplastic resin having fibers that are arranged essentially along a longitudinal axis of the leading and/or trailing edge. If the vanes are of constant section, then the leading and/or trailing edges may be cut to length from a section member bar made in the manner described. Such a technique makes it possible to obtain a leading edge and a trailing edge capable of withstanding high levels of stress. 
         [0012]    The invention also provides a turbojet specially adapted to receive such vanes, each vane being fastened to at least one casing in such a manner that the attachment means of the vane co-operate with complementary attachment means of the casing. 
         [0013]    In a preferred embodiment, the attachment means of the casing are obtained by pultrusion and impregnated with thermoplastic resin, and they are assembled to the casing by hot compaction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Other characteristics and advantages of the invention appear on reading the following description of particular embodiments of the invention with reference to the accompanying figures, in which: 
           [0015]      FIG. 1  is a plan view of a vane of the invention; 
           [0016]      FIG. 2  is a perspective view of the  FIG. 1  vane, the skin covering the core of the vane being partially cut away; 
           [0017]      FIG. 3  is a perspective view of a first technique for fastening the vane to a casing; and 
           [0018]      FIG. 4  is a perspective view of a second technique for fastening the vane to the casing. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    With reference to  FIGS. 1 and 2 , the vane  1  shown therein is a guide vane for extending behind the fan of a turbojet. In this embodiment, the vane  1  has a leading edge  2  that is in the form of a one-piece elongate structure. The vane  1  also has a trailing edge  3  that is likewise in the form of a one-piece elongate structure. 
         [0020]    The leading edge  2  and the trailing edge  3  are cut from section members obtained by pultrusion, preferably with fibers being placed obliquely (the so-called “pullbraiding” method). The section members have fibers, e.g. carbon fibers, that are arranged essentially along a longitudinal axis in order to form an elongate body. Ideally, substantially 80% of the fibers are arranged along the longitudinal axis X of the leading edge and along the longitudinal axis Y of the trailing edge, and 20% of the fibers are arranged at an angle of inclination of about 60 degrees relative to the longitudinal axis. These proportions and this arrangement for the fibers are given by way of example. The fibers are impregnated in thermoplastic resin. 
         [0021]    Between the leading edge  2  and the trailing edge  3  there extends a core  4 . A skin  5  is made up in this example of two webs  5 A and  5 B that are obtained by being cut out from a fiber fabric that has been pre-impregnated with thermoplastic resin, the webs extending on either side of the core  4  so as to cover both the core and also zones of the leading edge  2  and of the trailing edge  3  that are contiguous with the core  4 . 
         [0022]    The faces of the core  4  that are not covered by the webs  5 A and  5 B form free ends of the core  4 , and in this example they are protected and reinforced by means of a mixture  22  of short fibers and of resin inserted in a cavity defined by the webs  5 A and  5 B and the free edge of the core  4 . The leading edge  2  and the trailing edge  3  include extensions  10 ,  11 ,  12 , and  13  that extend projecting from the core  4  at each end of the vane  1 . 
         [0023]    The various components of the vane  1  are assembled together by hot compaction so as to join the components of the assembly to one another. This type of assembly imparts great strength to the vane  1  as a whole. 
         [0024]    Finally, orifices  14 ,  15 ,  16 , and  17  are formed in the extensions  10 ,  11 ,  12 , and  13  so as to transform the extensions into means for attaching the vane  1 , which means are designed to co-operate with complementary attachment means in a casing of the turbojet, as described below in detail with reference to  FIGS. 3 and 4 . 
         [0025]      FIG. 3  shows a first technique for fastening the vane  1  to an annular turbojet casing  20 . (This figure shows the outer casing of the turbojet that is made of long fibers impregnated with thermoplastic resin.) The casing  20  has orifices  26  for passing the extensions  10  and  12  of the leading edge  2  and of the trailing edge  3  through the casing  20 . The orifices  26  are shown as being of sufficient extent to allow the extensions from both the leading edge and the trailing edge to pass through the same orifice. Nevertheless, in a variant, it would be possible to make the orifices in two portions, comprising an upstream orifice and a downstream orifice respectively for passing the end of the leading edge and the end of the trailing edge. 
         [0026]    The casing  20  is fitted with means for attaching the leading edges, which means are in the form of a peripheral rail  21  extending around the casing on a face thereof that faces away from the vanes. The rail  21  defines a housing suitable for receiving the heads  24  of fastener elements  23  that are generally T-shaped or L- shaped. One of these elements is shown in the figure. 
         [0027]    The fastener element  23  has an opposite end  25  that is remote from its head  24  and that is cut so as to receive the extension  10  of the leading edge. In this example, the fastener element  23  is joined to the extension  10  by pinning. For this purpose, the end  25  includes an orifice (not shown in the drawing) that is situated in register with the orifice  14  in the extension  10  of the leading edge  2  in order to receive a fastener pin  27 . 
         [0028]    The extension  12  of the trailing edge  3  is fastened in similar manner by means of a second rail  21 ′ in which a second fastener element  23 ′ is engaged to co-operate with the extension  12  of the trailing edge  3 , the assembly being pinned together with the help of a pin  27 ′. 
         [0029]    In a preferred embodiment, the rails  21  and  21 ′ and the fastener elements  23  and  23 ′ are made by pultrusion and they are impregnated with thermoplastic resin, thus enabling the entire assembly to be joined together by a single hot compaction operation on the casing  20 . 
         [0030]    Furthermore,  FIG. 3  shows only half of the vane  1 . The terminal portions  11  and  13  that are not shown are fastened to an inner casing in a manner that is identical to that described above. Nevertheless, if the vane does not have a structural function, the vane needs to be fastened to only one of the casings. 
         [0031]      FIG. 4  shows a second technique for fastening the vane  1  to a turbojet casing  20 . In this figure the attachment means comprise an angle bar  30  arranged peripherally all around the casing. The angle bar  30  extends over a face of the casing  20  facing away from the vane  1 . The casing  20  has through orifices  26  for passing the extensions of the leading and trailing edges of the vane through the casing  20  so that they face the angle bar  30 . 
         [0032]    In preferred manner, the angle bar  30  is made by pultrusion and is impregnated with thermoplastic resin. 
         [0033]    The angle bar  30  has an L-shaped section with a first face  28  that is fastened to the casing  20  by hot compaction and a second face  29  that is fastened to the extension  10  by pinning. For this purpose, the face  29  of the angle bar  30  is pierced by an orifice that comes into register with the orifice  114  formed in the extension  10  of the leading edge. It should also be observed that the orifice  114  is formed perpendicularly relative to the orifice  14  of the above-described embodiment. It should also be observed that the extension  10  has been machined to present a flat face that comes to bear against the facing face of the flange  29 . 
         [0034]    As in the above-described example, the various elements of the casing are joined together by thermocompaction. 
         [0035]    Furthermore, the extensions  11 ,  12 , and  13  of the leading edge  2  and of the trailing edge  3  that are not shown are fastened in identical manner to respective similar angle bars. 
         [0036]    The operation of fastening the vane  1  to the angle bar  30  is repeated for all of the vanes that are to be installed. 
         [0037]    In addition to their role in fastening vanes via the extensions of their leading or trailing edges, it should be observed that the rails and the angle bars also contribute to stiffening the casing of the turbojet. 
         [0038]    Naturally, the invention is not limited to the embodiments described above and they may be subjected to variations that appear to the person skilled in the art without going beyond the ambit of the invention as defined by the claims. 
         [0039]    In particular, the materials used for making the various elements  2 ,  3 ,  4 ,  5  of the vane  1  and for making the attachment means  21 ,  23 ,  27  may equally well be composite materials or metals or a combination of both. 
         [0040]    Similarly, the reinforcements  22  that are visible in  FIG. 2  covering the free ends of the core  4  may be replaced by or associated with the skin of one or both of the webs  5 A,  5 B being folded over. Under such circumstances, the dimensions of the webs  5 A,  5 B should be adjusted to leave a flap suitable for covering the free end of the core. 
         [0041]    Similarly, the attachment means of the casing and the attachment means of the leading and trailing edges may be joined together by operations involving hot compaction, welding, adhesive, or indeed by using nut- and-bolt fasteners or any other solution that serves to hold the elements together. 
         [0042]    Finally, although  FIGS. 3 and 4  suggest identical fastener means for each of the extensions  10 ,  11 ,  12 ,  13  of the leading edge  2  and of the trailing edge  3  in two different embodiments, it is not contrary to the invention for each extension to be fastened to the casing  20  using one or the other of the fastener means in independent manner. 
         [0043]    The core may be reinforced in part or in full with short fibers. 
         [0044]    The core may be arranged to fill the volume extending between the leading edge and the trailing edge in full or only in part. The central portion may also have the shape of one or more core-forming strips. In a particular embodiment, the vane need not have a central core, the portions forming the leading and trailing edges then being contiguous. 
         [0045]    The vane may include a core of low mechanical strength or it may have no core: the mechanical connection between the leading and trailing edges is provided by the skin and/or by the reinforcements, with the core and the reinforcements preferably being made out of a single piece of plastics resin incorporating short fibers.