Abstract:
A wind turbine blade comprising a fairing with a rigid structural component ( 12 ) which forms the majority of the aerodynamic profile and a non-actively controllable elastically deformable trailing edge component ( 14 ) mounted on the structural component to complete the aerodynamic profile. The trailing edge component ( 14 ) is formed from a material having an elastic modulus in the range of 0.5 to 2.5 GPa such it will elastically buckle when loading on the trailing edge component exceeds a predetermined threshold. The structural component ( 12 ) comprises a unidirectional reinforcing layer adjacent to the trailing edge component with at least one layer of unidirectional fibres ( 26 ) extending in a substantially spanwise direction.

Description:
INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS 
       [0001]    This application is a continuation of Patent Cooperation Treaty International Patent Application PCT/GB2013/052376, filed Sep. 11, 2013, and entitled “WIND TURBINE BLADE,” which is incorporated by reference herein in its entirety, and which claims priority to United Kingdom Patent Application GB1217212.8, filed on Sep. 26, 2012. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    The present invention relates to wind turbine blades. 
         [0004]    2. Description of the Related Art 
         [0005]    Wind turbines typically include one or more blades to capture the kinetic energy of the wind. During use, the blades are subject to various aerodynamic and inertial loads which typically occur in the edgewise direction and in the flapwise direction. Edgewise loads are those parallel to the chord of the blade, while flapwise loads are perpendicular to the edgewise direction. The direction of these loads can be seen in  FIG. 1 , in which “x” denotes the direction of edgewise loads and “y” denotes the direction of flapwise loads. 
         [0006]    In order to increase the proportion of available wind energy captured by a particular wind turbine, it is known to increase the length of the blades to increase the swept area of the turbine. However, as each blade rotates, inertial and aerodynamic forces along the blade result in an edgewise loading. As the blade passes the tower until it reaches the azimuth, the trailing edge of the blade is compressed due to gravitational loading. Furthermore, in some cases where the rotor is accelerating, such as start up and grid loss, the trailing edges of the blades have additional compressive loading. This may cause buckling of the trailing edge, as shown in  FIG. 2 . 
         [0007]    To prevent buckling of the trailing edge, it is known to add reinforcing material to the blade in order to increase its rigidity. For example, in large blades it is known to increase the thickness of the undercamber in order to increase the rigidity of the blade in the region of the trailing edge, as shown in  FIG. 3 . 
         [0008]    However, this increases the thickness of the trailing edge, resulting in greater levels of noise, poor aerodynamic performance and parasitic mass. Further, this effect is exacerbated in longer blades (&gt;45 m) since the linear velocity of a wind turbine blade is proportional to the rotor diameter and higher speeds create more noise. 
         [0009]    It is also known to apply an adhesive reinforcing tape to the outer surface of the fairing in the region of the trailing edge, particularly in the case of blades having aerodynamic fairings made of fibre reinforced plastic. Since the rigidity of the blade is lowest at the trailing edge tip and the compressive loading is greatest at this point, the reinforcing tape is typically placed as close as possible to the tip of the trailing edge. However, this also results in an increase in the thickness of the trailing edge, resulting in greater levels of noise. 
         [0010]    US Patent Application Publication No. 2010/0047070 discloses a blade with a sacrificial plastic element fixed into the trailing edge to prevent the otherwise periodical alternating vortex shedding from the trailing edge. Although this document expresses a preference for the plastic element to have a sharp edge, it does not specify any particular requirement for the shape of the plastic element. Some examples have a flexible strip on the top and bottom surfaces of the plastic element to act as lightning protection 
       SUMMARY 
       [0011]    According to a first aspect of the present invention, there is provided a wind turbine blade comprising a fairing having an aerodynamic profile, the fairing comprising a rigid structural component which forms the majority of the aerodynamic profile, and a non-actively controllable elastically deformable trailing edge component mounted on the structural component to complete the aerodynamic profile, wherein the trailing edge component is formed from a material having an elastic modulus in the range of 0.5 to 2.5 GPa such that it will elastically buckle when loading on the trailing edge component exceeds a predetermined threshold, wherein the structural component comprises a unidirectional reinforcing layer adjacent to the trailing edge component, the unidirectional reinforcing layer comprising at least one layer of reinforcing fibres extending in a substantially spanwise direction. 
         [0012]    With this arrangement, the opposing requirements of noise reduction and structural rigidity are decoupled. Specifically, the unidirectional reinforcing layer increases the rigidity of the trailing edge of the blade, particularly in its ability to resist compression caused by edgewise loading while the trailing edge component reduces the level of noise. Thus, the presence of the elastically deformable trailing edge component allows the structural component to retain a greater thickness so that there is sufficient room for it to be reinforced with the uni-directional reinforcing layer. This increases the resistance of the blade to permanent buckling without any corresponding increase in the noise levels generated. When the blade is subjected to extreme loading conditions in which the threshold is exceeded, the trailing edge can flex and buckle before recovering its original shape when the loading conditions return to normal and the loading on the trailing edge component falls below the threshold. Thus, aerodynamic performance can be maintained below the loading threshold, for example during normal operating conditions, without experiencing buckling damage of the blade during extreme conditions and without the need for sacrificial components. 
         [0013]    “Extreme” operating conditions are considered to be those which result in the maximum anticipated compressive loading of the trailing edge, e.g. during a grid loss, or in winds with a recurrence period of 50 to 100 years. 
         [0014]    In addition, if the trailing edge is damaged either during transport, installation, or in use, the structure of the blade is not compromised and the trailing edge component can simply be replaced. 
         [0015]    The requirement for uni-directional fibers extending in a substantially spanwise direction means that at least some of the fibres can deviate from an exactly spanwise direction. The overriding requirement is that the uni-directional fibers resist compression caused by edgewise loading to a significant extend and the term should be understood in this context. 
         [0016]    The invention bears a superficial relationship to blades such as those disclosed in US Patent Application Publication No. 2009/0290982. These have a trailing edge component which can be actively driven to alter the profile of the blade. The present invention is conceptually different in that the trailing edge component is non-actively controllable and is deflected only as a result of forces induced by the effects of the blade travelling through the air during extreme loading cases. In effect it is a passive component, while those of US 2009/0290982 are active and require the provision of a controller and drive mechanism. 
         [0017]    The invention also bears a superficial relationship to US Patent Application Publication No. 2012/0141274. This discloses a wind turbine blade including a main foil section and a trailing edge section which may be separately formed from and coupled to the main foil section to define the trailing edge section of the blade. The trailing edge section is pivotal relative to the main foil and is biased to a low wind speed position in order to better capture wind energy at lower wind speeds. As the wind speed and loading on the blade increases from zero, the trailing edge section pivots towards an optimum wind speed position in which the trailing edge axis is in line with that of the main foil section. Thus, in contrast to the present invention, the trailing edge component deforms or pivots when loading is under a certain threshold, rather than when the threshold is exceeded. In fact, US 2012/0141274 describes the use of a stop mechanism to prevent the trailing edge from pivoting beyond the optimal wind speed position when the optimal wind speed threshold is exceeded. 
         [0018]    The invention also bears a superficial relationship to Japanese Patent Publication No. 2000/120524, which discloses a wind turbine blade with a separate trailing edge component. By forming the trailing edge as a separate component, the trailing edge thickness can be reduced relative to that typically obtainable with large blades. This inhibits the generation of Karman vortices and reduces the noise produced by the blade. However, there is no reinforcement in the region of the trailing edge. In addition, the trailing edge component is divided into a number of discrete longitudinal sections to avoid buckling. 
         [0019]    The unidirectional reinforcing layer may be present only in the region of the trailing edge of the fairing. In a preferred embodiment, the structural component further comprises an additional unidirectional reinforcing layer adjacent to its leading edge, the additional unidirectional reinforcing layer comprising at least one layer of unidirectional fibres extending in a substantially spanwise direction. 
         [0020]    With this arrangement, the edgewise rigidity of the fairing in the region of the leading edge is increased and this has been found to further reduce buckling of the trailing edge. 
         [0021]    The structural component may be formed from any suitable material. Also, the reinforcing layers may be adhered to the outer surface of the structural component. In a preferred embodiment, the structural component is formed from a fibre reinforced plastic and the unidirectional reinforcing layer and/or the additional unidirectional reinforcing layer is co-cured with the fibre reinforced plastic such that it is an integral part of the structural component. This allows more control over the rigidity characteristics of the blade and prevents damage to or removal of the reinforcing layer as may be the case with reinforcing tapes. 
         [0022]    The unidirectional reinforcing layer and/or the additional unidirectional reinforcing layer may comprise a single layer of reinforcing fibre and/or may be uniformly thick. In a preferred embodiment, the unidirectional reinforcing layer and/or the additional unidirectional reinforcing layer comprises a concentrated region of at least two, preferably at least five, more preferably 8 to 10, layers of unidirectional fibres extending in a substantially spanwise direction. This ensures that the fairing is made more rigid in areas where buckling can be a problem, without unnecessarily increasing the thickness and weight of the fairing in other less critical areas. 
         [0023]    All of the reinforcing layer could be in the concentrated region and/or be of constant thickness. Alternatively, the reinforcing layer could be formed of the concentrated region and a thinner region. 
         [0024]    The concentrated region may be formed entirely of unidirectional fibres extending in a substantially spanwise direction. Alternatively, the concentrated region comprises at least five layers of unidirectional fibres extending in a substantially spanwise direction and at least one layer of multiaxial fibres, for example biaxial fibres at ±45° to the direction of the unidirectional fibres. A layer of multiaxial fibres acts to increase the resistance of the reinforcing layer to transverse cracking and can assist the manufacture of the fairing by improving the air flow through the mould to allow air to be more easily drawn out of the mould under a vacuum. 
         [0025]    The ratio of unidirectional to multiaxial fibres in the unidirectional reinforcing layer may be less than 5:1. In a preferred embodiment, the ratio of the layers of unidirectional to multiaxial fibres is at least 5:1. 
         [0026]    The concentrated region may extend along substantially the entire span of the fairing. Preferably, it extends along less than half of the span of the fairing, more preferably along approximately ⅓ to ¼ the span. 
         [0027]    The concentrated region may be positioned anywhere along the blade. In a preferred embodiment, the concentrated region is in a central region of the blade. 
         [0028]    The reinforcing layer may be absent from the root and/or tip ends of the blade, or be one layer thick in these regions. Preferably, the unidirectional reinforcing layer and/or the additional unidirectional reinforcing layer comprises at least two layers of unidirectional fibres, extending in a substantially spanwise direction, in the vicinity of the root end of the blade. This increases the rigidity of the blade in the region of the root end, where loading can be high, particularly with very large blades. 
         [0029]    The chordwise dimension of the trailing edge component may be constant along the span of the fairing. In a preferred embodiment, the chordwise dimension of the trailing edge component increases, preferably gradually, in the spanwise direction towards the blade tip. With this arrangement, the trailing edge component forms an increasing proportion of the aerodynamic profile in the tipwise direction. This allows the unidirectional reinforcing layer adjacent to the trailing edge component to be made thicker to further strengthen the structural component in areas where the moment of inertia of the fairing is lower but the compressive forces are high. 
         [0030]    The trailing edge component may be present along the entire length of the blade. Alternatively, the trailing edge component may be absent in certain areas of the blade and the structural component tapered towards its trailing edge in these areas, In a preferred embodiment, the structural component has a blunt trailing edge, or “flat back” in the vicinity of the blade root and the trailing edge component is absent at this point. 
         [0031]    The reinforcing layers may extend in the spanwise direction beyond or as far as the trailing edge component. Preferably, the trailing edge component extends in a spanwise direction beyond the spanwise extent of the unidirectional reinforcing layer and/or the additional unidirectional reinforcing layer. The trailing edge component may extend beyond the reinforcing layers towards the blade root. Preferably, the trailing edge component extends in a spanwise direction beyond the spanwise extent of the unidirectional reinforcing layer and/or the additional unidirectional reinforcing layer towards the blade tip. 
         [0032]    Preferably, the trailing edge component is formed from a material which is able to sustain elastically a strain of greater than 2%. 
         [0033]    The trailing edge component may be made from any suitable material. Preferably, it is made from a material selected from a group including, but not limited to, rubber, silicon, acetal, ABS, nylon, acrylic, PBT, PET, polypropylene, PU, TPO, and polyethylene. 
         [0034]    The trailing edge tip of the trailing edge component, i.e. the rearmost edge of the trailing edge component, may be of any suitable thickness. Preferably, the trailing edge component has a trailing edge tip thickness of less than 5 mm. This reduces the level of noise generated at the trailing edge of the blade. 
         [0035]    Preferably, the chordwise dimension of the trailing edge component at its widest point represents less than 25% of the chord length of the aerodynamic profile. 
         [0036]    In a preferred embodiment, the chordwise dimension of the trailing edge component is at its widest point inward of the blade tip and decreases from its widest point towards the blade tip. 
         [0037]    The trailing edge component may extend in a spanwise direction all the way to the blade tip such that the trailing edge of the aerodynamic profile of the fairing is defined by the trailing edge component at that point. Preferably, the trailing edge of the aerodynamic profile at the blade tip is formed by the structural component, whereas the trailing edge component is absent at this point. With this arrangement, the trailing edge component is present only in the regions of the trailing edge which are susceptible to buckling. 
         [0038]    Preferably, the trailing edge component comprises a unitary piece extending across at least 1 metre of the span of the fairing, preferably the unitary piece extends across 10 metres of the span of the fairing, more preferably the unitary piece extends across 20 metres of the span of the fairing. 
         [0039]    The structural component may have an open-ended cross-section. In a preferred example, the structural component has a closed cross-section. The trailing edge end of the closed cross-section, i.e. the rearmost end of the structural component, may be defined by a structural wall on which the trailing edge component is mounted. 
         [0040]    The trailing edge component may be pivotally mounted on the structural component. Preferably, the trailing edge component is non-pivotally mounted on the structural component. 
         [0041]    The trailing edge component may be mounted on the structural component using a groove and boltrope arrangement and/or a locking clip. 
         [0042]    There may be a step or gap between the structural component and the trailing edge component. In a preferred example, the aerodynamic profile formed by the structural component and the trailing edge component is continuous. In other words, there is no step between the structural component and the trailing edge component. The transition between the outer surfaces of the structural component and the trailing edge is smooth. This encourages laminar flow over the surface of the fairing to reduce drag and noise. 
         [0043]    According to a second aspect of the present invention, there is provided a method of preventing buckling of the trailing edge of a wind turbine blade having an fairing with an aerodynamic profile, the method comprising the steps of providing a rigid structural component to form the majority of the aerodynamic profile, mounting a non-actively controllable elastically deformable trailing edge component on the structural component to complete the aerodynamic profile, wherein the trailing edge component is formed from a material having an elastic modulus in the range of 0.5 to 2.5 GPa and wherein the structural component comprises a unidirectional reinforcing layer adjacent to the trailing edge component, the unidirectional reinforcing layer comprising at least one layer of unidirectional fibres extending in a substantially spanwise direction, and allowing the trailing edge component to buckle when loading on the trailing edge component exceeds a predetermined threshold. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0044]    An example of the present invention will now be described with reference to the following drawings in which: 
           [0045]      FIG. 1  is a schematic section view of a wind turbine blade, which shows the edgewise and flapwise load directions and is included for background interest only; 
           [0046]      FIG. 2  is a schematic isometric section view of a wind turbine blade, which is included for background interest only and which shows buckling of the trailing edge; 
           [0047]      FIG. 3  is a schematic section view of a wind turbine blade, which is included for background interest only and which shows a standard undercamber profile along with a thicker undercamber profile used to increase the rigidity of the trailing edge of a conventional blade; 
           [0048]      FIG. 4  is a schematic section view of a wind turbine blade in accordance with the present invention, showing the structural component and the trailing edge component as separate; 
           [0049]      FIG. 5  is a schematic section view of the wind turbine blade of  FIG. 4 , showing the structural component and the trailing edge component as connected; 
           [0050]      FIG. 6  is a schematic top view of a wind turbine blade in accordance with the present invention; 
           [0051]      FIG. 7  is a schematic section view of the trailing edge of the wind turbine blade of  FIG. 6  taken through line VII-VII; 
           [0052]      FIG. 8  is a schematic section view of the trailing edge of the wind turbine blade of  FIG. 6  taken through line VIII-VIII; 
           [0053]      FIG. 9  is a schematic section view of the trailing edge of the wind turbine blade of  FIG. 6  taken through line IX-IX; 
           [0054]      FIG. 10  is a schematic section view of the trailing edge of the wind turbine blade of  FIG. 6  taken through line X-X; 
           [0055]      FIG. 11  is a graph showing the relationship between bending moment, chord size and optimal trailing edge component size along the blade span; and 
           [0056]      FIGS. 12 to 16  are enlarged views of the trailing edge of a wind turbine blade in accordance with the present invention, the trailing edge component and the structural component being connected by first to fifth alternative connection means, respectively. 
       
    
    
     DETAILED DESCRIPTION 
       [0057]    As shown in  FIG. 4  and  FIG. 5 , the wind turbine blade  10  comprises a structural component  12  and a separate trailing edge component  14 . The trailing edge component  14  is mounted on to the structural component  12  to form the aerodynamic profile of the blade  10 , as shown in  FIG. 5 . As with conventional blades, the aerodynamic profile of blade  10  has a leading edge  16  and a trailing edge  18 , as shown in  FIG. 4 . 
         [0058]    The structural component  12  defines the leading edge  16  and the majority of the outer surface of the aerodynamic profile of the blade  10 . As can be seen in  FIG. 4  and  FIG. 5  the aft-most part of the structural component  12  does not define the trailing edge  18  in this region. Instead, the structural component  12  has an attachment surface  20  to which the trailing edge component  14  is connected as described below, and the trailing edge component  14  defines the trailing edge  18 . Consequently, the aft part of the structural component  12  can be made thicker to satisfy the edgewise strength, stiffness and local buckling requirements of the blade  10  in these regions without compromising the aerodynamic performance of the blade  10  as the trailing edge  18  is defined by the non-structural trailing edge  14  which can be very thin. 
         [0059]    The structural component  12  comprises a load bearing spar  22  which extends along the length of the blade  10 , as is well known in the art. An aerodynamic fairing  24  is mounted on the spar to form the outer surface of the structural component  12 . The structural component can essentially be constructed in a similar manner to that described in our earlier application, International Patent Application Publication no. WO 2009/034291. 
         [0060]    The trailing edge component  14  is non-rotatably attached to the attachment surface  20  of the structural component  12 . The trailing edge component is also passive. By “passive” it is meant that there is no active drive mechanism to change the shape or orientation of the trailing edge component  14 . Any changes to the shape or orientation of the trailing edge component  14  are brought about purely by the forces induced by the effects of the blade travelling through the air during use. 
         [0061]    The trailing edge component  14  is shaped such that it extends from the structural component  12  in a continuous manner. In other words, the aerodynamic profile of the blade  10  defines a smooth curve having substantially no step between the outer surfaces of the structural component  12  and the trailing edge component  14 . Depending on the position along the length of the blade  10 , the trailing edge component  14  can represent between 0% and 25% of the chord of the blade  10 . 
         [0062]    As a very thin trailing edge, i.e. one with a thickness of less than 10 mm, will tend to buckle under loads which put the trailing edge in compression, the trailing edge component  14  is made from a material that is able to sustain large deformations elastically, where “large” is considered as a strain level of 2% or more. The typical strain in this part of the blade could be determined by well known Finite Element Modelling techniques for example. Suitable materials include rubber or any other polymer. Further, the material should be sufficiently stiff that deformation of the trailing edge component  14  during normal operation is negligible, i.e. less than 5 mm. This ensures that the aerodynamic properties of the blade  10  during normal use remain unchanged. 
         [0063]    As the top and bottom surfaces of the trailing edge component  14  are connected, curved plates, the trailing edge component  14  exhibits stable post-buckling behaviour. Thus, the transverse deflections caused by buckling will stabilise quickly. In other words, the trailing edge component  14  remains temporarily buckled at a more or less constant deflection, i.e. there is no continual ripple. 
         [0064]    The trailing edge component  14  can be made by casting, injection moulding, extrusion, or any other appropriate method. 
         [0065]    In normal use, the blade  10  functions as a conventional wind turbine blade. However, in extreme operating conditions, the elastic nature of the trailing edge component  14  allows it to buckle temporarily when edgewise loads exceed a predetermined threshold, the threshold being defined as the point at which the loads exceed normal operating conditions. When the loading returns to that of normal operating conditions, i.e. when edgewise loading falls below the threshold, the trailing edge component  14  will recover its shape. Depending on the rheological characteristics of the material employed, the shape recovery may or may not be instantaneous. 
         [0066]    As shown in  FIG. 6  to  FIG. 10 , a reinforcing layer  26  is added to the aft part of the structural component  12  in the region of the root of the fairing where the chord is at its widest and midway between the root and the tip of the fairing  24  to increase its strength and stiffness. An additional reinforcing layer  28  is added to the leading edge part of the structural component  12  approximately midway between the root end  30  and the tip end  32  of the fairing  24 . 
         [0067]    Both the reinforcing layer  26  and the additional reinforcing layer  28  comprise layers of unidirectional reinforcing fibres ( 34 :  FIGS. 7 and 9 ) extending approximately parallel with the outer surface of the structural component  12  to increase the resistance of the structural component  12  to edgewise bending, thus reducing deflection and buckling of the trailing edge. Layers  26  and  28  are placed on top of and co-cured with the fibre reinforced plastic from which the structural component  12  is made such that they form an integral part of the structural component  12 . Additional layers of reinforcing fibre can be added as required, i.e. in regions with an increased risk of buckling. The reinforcing layer  26  is one or two layers thick in the region of the root end  30  of the fairing  24  and the reinforcing layers  26  and  28  midway along the blade are 8 to 10 layers thick, for a 50 metre blade, or up to 60 layers thick for an 85 metre blade. The thicker, or “concentrated” regions, of the reinforcing layer  26  and additional reinforcing layer  28  extend along approximately one quarter to one third of the length of the blade  10  and are located approximately centrally along the blade  10 . Other non-uni-directional fibers may also be included. For example, one or more layers of bi-axial fibers (±45°) may be included to increase resistance to transverse cracking. 
         [0068]    The trailing edge component  14  does not extend from the structural component  12  along the entire length of the blade  10 . Instead, the blade  10  has a flat back, formed by the aft end of the structural component  12 , in the region of the root end  30  of the blade  10 , as shown in  FIG. 7 . The chordwise dimension of the trailing edge component  14  gradually increases in the spanwise direction towards the tip  32  of the fairing  24  from zero at around ⅕ of the blade length to its full extent for around ⅕ of the blade length before tapering back to zero at around 3/4 of the blade length and beyond the spanwise extent of reinforcement layers  26  and  28 , as shown in  FIGS. 8 to 10 . For example, as measured from the root end  30  of the fairing  24  towards the tip, a 50 metre blade may have a trailing edge component  14  which is absent from the root end  30  of the fairing  24  to around 12 metres of the span, increases from zero to its full extent along the next 4 to 5 metres, remains at its full extent for approximately 10 to 13 metres, before tapering back to zero at around 35 metres. 
         [0069]      FIG. 11  shows the variations of bending moment (top graph), chord size (second graph) and requirement for uni-directional material (third graph) along the length of the blade (depicted at the bottom of  FIG. 11 ). 
         [0070]    Although the tangential velocity of the blade  10  is greatest at the blade tip  32 , it is not necessary for the trailing edge component  14  to extend all the way to the tip  32 . This is because the compressive forces which cause buckling (shown as the bending movement in  FIG. 11 ) decrease from the root end  30  towards the blade tip  32 , such that they are at their lowest at the blade tip  32 . Consequently, the structural component  12  does not require reinforcement in the region of the blade tip  32  and can be made sufficiently thin to reduce noise levels without the need for a separate trailing edge component  14 . 
         [0071]    Conversely, although the compressive forces which cause buckling increase towards the root end  30 , a separate trailing edge component is not required in this region as the chord is wider and hence the moment of inertia of the blade  10  is higher. However, despite the increase in the moment of inertia, the loads experienced at the widest point of the blade can increase by an even greater amount, particularly for very large blades. Therefore, a small amount of reinforcement can be beneficial in this region. 
         [0072]    As a result of these effects, the need for increased reinforcement by the reinforcing layer  26  is greatest towards the centre of the blade and tapers off towards the root and tip. 
         [0073]    Since the trailing edge  18  of the blade  10  is defined by the trailing edge component  14  in the noise and buckling-critical regions, rather than by the structural component  12 , an increase in the thickness of the structural component  12  in the regions of reinforcement layers  26  and  28  will not result in a substantial increase in the noise levels generated by the blade or a decrease in its aerodynamic performance. Suitable strengthening material includes fibre reinforced plastics such as e-glass, s-glass, r-glass, carbon fibre, etc, combined with epoxy, polyester, vinylester, or polyurethane resins. 
         [0074]    The trailing edge component  14  can be connected to the structural component  12  by any suitable means. Example means of connection can be seen in  FIG. 12  to  FIG. 16 . 
         [0075]      FIG. 12  and  FIG. 13  show the trailing edge component  14  connected to the structural part  12  using a boltrope  36  ( FIG. 12 ) or a pair of boltropes  36  ( FIG. 13 ) held in a groove or grooves  38  set in the attachment surface  20  of the structural component  12 . 
         [0076]      FIG. 14  shows the trailing edge component  14  connected to the structural part  12  using two locking clips  40 . Although two clips  40  are shown, in practice, any suitable number of locking clips  40  may be used. 
         [0077]      FIG. 15  shows the trailing edge component  14  connected to the structural part  12  using a fastener  42 . The fastener  42  is set in a recess  44  in the trailing edge component  14  and the recess  44  is filled by a filler  46  to smooth the outer surface of the trailing edge component  14 . 
         [0078]      FIG. 16  shows the trailing edge component  14  connected to the structural part  12  using adhesive  48 . To strengthen the joint, the attachment surface  20  has an extension  50  which fits in a corresponding groove  52  in the trailing edge component  14 . 
         [0079]    Although the trailing edge component  14  is described as extending along only part of the length of the blade  10  and increasing gradually in size before tapering off, it may extend along the entire blade  10 , or any part thereof and/or have a constant chordwise dimension. For example, the trailing edge component could be fixed only to the outer 75% of the blade, where the compressive strains in the trailing edge and/or noise generation are most significant, or to the mid-section of the blade where buckling is more likely to occur.