Method of manufacturing a wind turbine blade

Abstract

A method and mould system for manufacturing at least a root section of a wind turbine blade is described. The method and system utilise a mould inlay which is arranged on top of a mould surface of a mould part so as to change the radius of curvature of the mould part and thereby also the diameter of a root section manufactured via the mould part and mould inlay. Further, blades manufactured via the method and mould system are described.

Claims

1. A method of manufacturing at least a root section (30) of a wind turbine blade (10, 110, 310), the root section (30) comprising a composite structure with a fibre-reinforced polymer material including a polymer matrix and fibre-reinforcement material, the method comprises the steps of: a) providing at least a first mould part (40, 140) for manufacturing at least a first root section part (31) of said root section, the first mould part (40, 140) having a longitudinal direction and comprising a first mould surface (42, 142), the first mould surface (42, 142) defining at least a part of an outer surface of said first root section part (31) manufactured in the first mould part (42, 142), the first mould surface (42, 142) having an end part (44, 144) with a first radius of curvature (R.sub.1); b) providing a mould inlay (50, 150, 250) having an outer surface (52, 152, 252) and an inner surface (54, 154, 254) on top of the first mould surface (42, 142) with the outer surface (52, 152, 252) facing the first mould surface (42, 142) such that the mould inlay (50, 150, 250) extends at least from the end part (44, 144) along a longitudinal section of the first mould surface (42, 142), the mould inlay (50, 150, 250) having an outer surface (52, 152, 154) which at least at the end part (44, 144) has a radius of curvature corresponding to the first radius of curvature (R.sub.1) and the inner surface (54, 154, 254) has a second radius of curvature (R.sub.2) being smaller than the first radius of curvature (R.sub.1), and wherein the mould inlays comprise a proximal end and a distal end, the mould inlays being arranged so that the proximal end is arranged nearest the end part and the distal end is arranged farthest from the end part, and wherein the distal end of the mould inlay is tapered, the second radius of curvature (R.sub.2) corresponding to the distal end, and wherein the mould inlay (50, 150, 250) is curved; c) providing fibre-reinforcement material (60, 62; 160, 162; 360, 362) and fastening means (64, 164, 264, 364) for fastening a connection part of the root section (30) to a hub of a wind turbine (2) on top of the mould inlay (50, 150, 250) and the first moulding surface (40, 140), and optionally also sandwich core material, wherein the connection part of the root section (30) has a cylindrical contour along an entirety thereof, the connection part of the root section (30) having a radius of curvature equal to the second radius of curvature (R.sub.2); d) providing resin to the fibre-reinforcement material (60, 62; 160, 162; 360, 362); and e) curing the resin in order to form the composite structure.

2. The method according to claim 1, wherein step c) further comprises the steps of: c1) providing a number of outer fibre reinforcement layers to form an outer skin; c2) providing a number of fastening members on top of the outer reinforcement layers and optionally a number of intermediate inserts; and c3) providing a number of inner fibre reinforcement layers to form an inner skin.

3. The method according to claim 1, wherein the mould inlay has a length of 50-200 centimetres.

4. The method according to claim 3, wherein the mould inlay has a length of 60-175 centimetres.

5. The method according to claim 4, wherein the mould inlay has a length of 70-150 centimetres.

6. The method according to claim 1, wherein the tapered distal end has a length of 20-40 centimetres.

7. A first turbine blade manufactured according to the method of claim 1, a second wind turbine blade being manufactured according to the following steps: f) providing at least said first mould part (40, 140); g)providing fibre-reinforcement material (60, 62; 160, 162; 360, 362) and fastening means (64, 164, 264, 364) for fastening the root section (30) to the hub of the wind turbine (2) on top of the first moulding surface (40, 140) only, and optionally also sandwich core material; h) providing resin to the fibre-reinforcement material (60, 62; 160, 162; 360, 362); and i) curing the resin in order to form the composite structure.

8. A mould part and mould inlay combination, comprising: a mould part (40, 140) for manufacturing at least a root section part, the mould part (40, 140) having a longitudinal direction and comprising a first mould surface (42, 142), the first mould surface (42, 142) defining at least a part of an outer surface of said root section part, the mould part (40, 140) comprising an end part (44, 144) with a mould surface (42, 142) having a first radius of curvature (R.sub.1, R.sub.1′); and a mould inlay (50, 150, 250, 350) comprising an outer surface (52, 152, 252, 352) and an inner surface (54, 154, 254, 354), the mould inlay (50, 150, 250, 350) being adapted for being arranged on top of the mould surface (42, 142) at the end part (44, 144) of the mould part (40, 140) so as to change a radius of curvature of the mould surface (42, 142), the outer surface (52, 152, 252, 352) having a radius of curvature corresponding to the first radius of curvature (R.sub.1, R.sub.1′) and the inner surface (54, 154, 254, 354) having a second radius of curvature (R.sub.2, R.sub.2′) being smaller than the first radius of curvature (R.sub.I, R.sub.i′), and wherein the mould inlays comprise a proximal end and a distal end, the mould inlays being adapted for being arranged so that the proximal end is arranged nearest the end part and the distal end is arranged farthest from the end part, and wherein the distal end of the mould inlay is tapered, the second radius of curvature (R.sub.2, R.sub.2′) corresponding to the distal end, and wherein the mould inlay (50, 150, 250) is curved.

9. The mould part and mould inlay combination according to claim 8, wherein the mould inlay is substantially semi-circular.

10. The mould part and mould inlay combination according to claim 8, wherein the mould inlay is made of a foamed polymer or a fibre-reinforced polymer.

11. A method of manufacturing at least a root section (30) of a wind turbine blade (10, 110, 310), the root section (30) comprising a composite structure with a fibre-reinforced polymer material including a polymer matrix and fibre-reinforcement material, the method comprises the steps of: a) providing at least a first mould part (40, 140) for manufacturing at least a first root section part (31) of said root section, the first mould part (40, 140) having a longitudinal direction and comprising a first mould surface (42, 142), the first mould surface (42, 142) defining at least a part of an outer surface of said first root section part (31) manufactured in the first mould part (42, 142), the first mould surface (42, 142) having an end part (44, 144) with a first radius of curvature (R.sub.1); b) providing a mould inlay (50, 150, 250) having an outer surface (52, 152, 252) and an inner surface (54, 154, 254) on top of the first mould surface (42, 142) with the outer surface (52, 152, 252) facing the first mould surface (42, 142) such that the mould inlay (50, 150, 250) extends at least from the end part (44, 144) along a longitudinal section of the first mould surface (42, 142), the mould inlay (50, 150, 250) having an outer surface (52, 152, 154) which at least at the end part (44, 144) has a radius of curvature corresponding to the first radius of curvature (R.sub.1) and the inner surface (54, 154, 254) has a second radius of curvature (R.sub.2) being smaller than the first radius of curvature (R.sub.1), and wherein the mould inlays comprise a proximal end and a distal end, the mould inlays being arranged so that the proximal end is arranged nearest the end part and the distal end is arranged farthest from the end part, and wherein the distal end of the mould inlay is tapered, the second radius of curvature (R.sub.2) corresponding to the distal end, and wherein the mould inlay (50, 150, 250) is curved; c) providing fibre-reinforcement material (60, 62; 160, 162; 360, 362) and fastening means (64, 164, 264, 364) for fastening the root section (30) to a hub of a wind turbine (2) on top of the mould inlay (50, 150, 250) and the first moulding surface (40, 140), and optionally also sandwich core material, wherein the fastening means (64, 164, 264, 364) has a cylindrical contour corresponding to a cylindrical contour of the root section (30); d) providing resin to the fibre-reinforcement material (60, 62; 160, 162; 360, 362); and e) curing the resin in order to form the composite structure, wherein the distal end of the mould inlay is tapered such that an inner surface of the distal end has a constant radius of curvature equal to the second radius of curvature (R.sub.2) and an outer surface of the distal end varies in radius of curvature from a radius of curvature equal to the first radius of curvature (R.sub.1) and towards the second radius of curvature (R.sub.2).

12. A method of manufacturing at least a root section (30) of a wind turbine blade (10, 110, 310), the root section (30) comprising a composite structure with a fibre-reinforced polymer material including a polymer matrix and fibre-reinforcement material, the method comprises the steps of: a) providing at least a first mould part (40, 140) for manufacturing at least a first root section part (31) of said root section, the first mould part (40, 140) having a longitudinal direction and comprising a first mould surface (42, 142), the first mould surface (42, 142) defining at least a part of an outer surface of said first root section part (31) manufactured in the first mould part (42, 142), the first mould surface (42, 142) having an end part (44, 144) with a first radius of curvature (R1); b) providing a mould inlay (50, 150, 250) having an outer surface (52, 152, 252) and an inner surface (54, 154, 254) on top of the first mould surface (42, 142) with the outer surface (52, 152, 252) facing the first mould surface (42, 142) such that the mould inlay (50, 150, 250) extends at least from the end part (44, 144) along a longitudinal section of the first mould surface (42, 142), the mould inlay (50, 150, 250) having an outer surface (52, 152, 154) which at least at the end part (44, 144) has a radius of curvature corresponding to the first radius of curvature (R.sub.1) and the inner surface (54, 154, 254) has a second radius of curvature (R.sub.2) being smaller than the first radius of curvature (R.sub.1), and wherein the mould inlays comprise a proximal end and a distal end, the mould inlays being arranged so that the proximal end is arranged nearest the end part and the distal end is arranged farthest from the end part, and wherein the distal end of the mould inlay is tapered, the second radius of curvature (R.sub.2) corresponding to the distal end, and wherein the mould inlay (50, 150, 250) is curved; c) providing fibre-reinforcement material (60, 62; 160, 162; 360, 362) and fastening means (64, 164, 264, 364) for fastening the root section (30) to a hub of a wind turbine (2) on top of the mould inlay (50, 150, 250) and the first moulding surface (40, 140), and optionally also sandwich core material, wherein the fastening means (64, 164, 264, 364) has a cylindrical contour corresponding to a cylindrical contour of the root section (30); d) providing resin to the fibre-reinforcement material (60, 62; 160, 162; 360, 362); and e) curing the resin in order to form the composite structure, wherein the distal end of the mould inlay is tapered such that an outer surface of the distal end has a constant radius of curvature equal to the first radius of curvature (R.sub.1) and an inner surface of the distal end varies in radius of curvature from a radius of curvature equal to the second radius of curvature (R.sub.2) and towards the first radius of curvature (R.sub.1).

13. A method of manufacturing at least a root section (30) of a wind turbine blade (10, 110, 310), the root section (30) comprising a composite structure with a fibre-reinforced polymer material including a polymer matrix and fibre-reinforcement material, the method comprises the steps of: a) providing at least a first mould part (40, 140) for manufacturing at least a first root section part (31) of said root section, the first mould part (40, 140) having a longitudinal direction and comprising a first mould surface (42, 142), the first mould surface (42, 142) defining at least a part of an outer surface of said first root section part (31) manufactured in the first mould part (42, 142), the first mould surface (42, 142) having an end part (44, 144) with a first radius of curvature (R.sub.1); b) providing a mould inlay (50, 150, 250) having an outer surface (52, 152, 252) and an inner surface (54, 154, 254) on top of the first mould surface (42, 142) with the outer surface (52, 152, 252) facing the first mould surface (42, 142) such that the mould inlay (50, 150, 250) extends at least from the end part (44, 144) along a longitudinal section of the first mould surface (42, 142), the mould inlay (50, 150, 250) having an outer surface (52, 152, 154) which at least at the end part (44, 144) has a radius of curvature corresponding to the first radius of curvature (R.sub.I) and the inner surface (54, 154, 254) has a second radius of curvature (R.sub.2) being smaller than the first radius of curvature (R.sub.1), and wherein the mould inlays comprise a proximal end and a distal end, the mould inlays being arranged so that the proximal end is arranged nearest the end part and the distal end is arranged farthest from the end part, and wherein the distal end of the mould inlay is tapered, the second radius of curvature (R.sub.2) corresponding to the distal end; c) providing fibre-reinforcement material (60, 62; 160, 162; 360, 362) and fastening means (64, 164, 264, 364) for fastening the root section (30) to a hub of a wind turbine (2) on top of the mould inlay (50, 150, 250) and the first moulding surface (40, 140), and optionally also sandwich core material, wherein the fastening means (64, 164, 264, 364) has a cylindrical contour corresponding to a cylindrical contour of the root section (30); d) providing resin to the fibre-reinforcement material (60, 62; 160, 162; 360, 362); and e) curing the resin in order to form the composite structure, wherein the mould inlay has a semi-circular contour.

Description

(1) The invention is explained in detail below with reference to an embodiment shown in the drawings, in which

(2) FIG. 1 shows a wind turbine,

(3) FIG. 2 shows a schematic view of a wind turbine blade,

(4) FIG. 3 shows a perspective view of a mould part for use in the invention,

(5) FIG. 4 shows a perspective view of a mould part according to the invention,

(6) FIG. 5 shows a side view of a lay-up in a mould part according to the invention with a first embodiment of a mould inlay arranged on the mould surface of the mould part,

(7) FIG. 6 shows a side view of a lay-up in a mould part according to the invention with a second embodiment of a mould inlay arranged on the mould surface of the mould part,

(8) FIG. 7 shows a side view of a lay-up in a mould part according to the invention without a mould inlay arranged on the mould surface of the mould part,

(9) FIG. 8 shows a side view of a lay-up in a mould part known per se with a mould inlay arranged on the mould surface of the mould part,

(10) FIG. 9 shows a top view of a root section manufactured according to the lay-up of FIG. 5,

(11) FIG. 10 shows a top view of a root section manufactured according to the lay-up of FIG. 6 or 7,

(12) FIG. 11 shows a top view of a root section manufactured according to the lay-up of FIG. 8, and

(13) FIG. 12 shows an end view of a root section part manufactured according to the invention.

(14) FIG. 1 illustrates a conventional modern upwind wind turbine 2 according to the socalled “Danish concept” with a tower 4, a nacelle 6 and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub 8 and three blades 10 extending radially from the hub 8, each having a blade root 16 nearest the hub and a blade tip 14 farthest from the hub 8.

(15) FIG. 2 shows a schematic view of a first embodiment of a wind turbine blade 10. The wind turbine blade 10 has the shape of a conventional wind turbine blade and comprises a root section 30 closest to the hub, a profiled or an airfoil section 34 farthest away from the hub and a transition section 32 between the root section 30 and the airfoil section 34. The blade 10 comprises a leading edge 18 facing the direction of rotation of the blade 10, when the blade is mounted on the hub, and a trailing edge 20 facing the opposite direction of the leading edge 18.

(16) The airfoil section 34 (also called the profiled section) has an ideal or almost ideal blade shape with respect to generating lift, whereas the root section 30 due to structural considerations has a substantially circular or elliptical cross-section, which for instance makes it easier and safer to mount the blade 10 to the hub. The diameter (or the chord) of the root section 30 may be constant along the entire root area 30. The transition section 32 has a transitional profile gradually changing from the circular or elliptical shape of the root section 30 to the airfoil profile of the airfoil section 34. The chord length of the transition section 32 typically increases with increasing distance r from the hub. The airfoil section 34 has an airfoil profile with a chord extending between the leading edge 18 and the trailing edge 20 of the blade 10. The width of the chord decreases with increasing distance r from the hub.

(17) A shoulder 40 of the blade 10 is defined as the position, where the blade 10 has its largest chord length. The shoulder 40 is typically provided at the boundary between the transition section 32 and the airfoil section 34.

(18) It should be noted that the chords of different sections of the blade normally do not lie in a common plane, since the blade may be twisted and/or curved (i.e. pre-bent), thus providing the chord plane with a correspondingly twisted and/or curved course, this being most often the case in order to compensate for the local velocity of the blade being dependent on the radius from the hub.

(19) The blade 10 comprises a shell structure that defines the aerodynamic structure of the blade 10. The aerodynamic shell may be integrally formed, but often the pressure side and the suction side of the aerodynamic shells are manufactured separately and then later adhered to each other along the leading edge and trailing edge of the shell parts. Accordingly, the root section 30 may also be manufactured by first manufacturing a first root section part 31 and a second root section part. The root section or root section part may be manufactured separately, but typically the root section or root section part will be manufactured integrally with the rest of the blade shell or blade shell part.

(20) FIG. 3 shows a perspective view of the first mould part 40 for manufacturing at least a first root section part 31 according to the invention. The first mould part 40 is designed as a conventional mould part known per se and comprises a mould surface 42, which defines the outer surface of the root section part 31. The mould surface 42 (and thereby also the outer surface of the root section part 31) has a first radius of curvature R.sub.1 at an end part 44 of the first mould part 40. The first mould part 40 is rigid, and the root section part is manufactured by use of a vacuum assisted resin transfer moulding (VARTM) process by arranging fibre material and fastening elements in a mould cavity formed between the rigid first mould part 40 and a flexible vacuum bag (not shown), which is sealed against the first rigid mould part, after which a resin is drawn into the mould cavity. Finally, the resin is cured in order to form a composite structure comprising the first root section part 31.

(21) FIG. 4 shows a perspective view of a first mould part 140 according to the invention for manufacturing at least a root section part according to the invention. The first mould part 140 comprises a first mould surface 142, which defines the outer surface of the root section part. The first mould part 140 comprises a recess 143 formed in the first mould surface 142 at an end part 144 of the first mould surface 142. The mould surface 142 is formed so that it has a first radius of curvature R.sub.1′ at a part proximal to the end part 144 of the first mould surface 142. The mould surface 142 has a second radius of curvature R.sub.2′ at a distal part for manufacturing a distal part of the root section part, the second radius of curvature R.sub.2′ being smaller than the first radius of curvature R.sub.1′. The recess 143 comprises a tapering part distal to the end part 144 of the first mould surface, where the radius of curvature gradually changes from the first radius of curvature R.sub.1′ to the second radius of curvature R.sub.2′. The first mould part 140 is rigid, and the root section part is manufactured by use of a vacuum assisted resin transfer moulding (VARTM) process by arranging fibre material and fastening elements, such as bushings, and possibly core material and inserts in a mould cavity formed between the rigid first mould part 140 and a flexible vacuum bag (not shown), which is sealed against the first rigid mould part, after which a resin is drawn into the mould cavity. Finally, the resin is cured in order to form a composite structure comprising the first root section part. If the fibre material is arranged directly on the forming surface, the blade root section manufactured via the first mould part 140 will have a proximal part that has a larger diameter than a distal part of the root section.

(22) FIG. 5 shows a side view of a lay-up in the mould part 140 according to the invention with a first embodiment of a mould inlay 50 arranged on the mould surface 142 of the mould part 140. It is seen that the mould inlay 50 is arranged in the recess 143 of the mould surface 142. The mould inlay has an outer surface 52 facing the mould surface 142 of the mould part 140 and an inner surface 54 facing away from the mould surface 142 of the mould part 140. In the shown embodiment, the outer surface 52 of the mould inlay 50 has a radius of curvature R.sub.1 that corresponds to that of the radius of curvature in the recess 143 of the mould surface 142. The inner surface 54 of the mould inlay 50 has a second radius of curvature R.sub.2 that corresponds to the radius of curvature R.sub.2′ at the distal part for manufacturing the root section part. The mould inlay 50 comprises a tapered wedge part 58 at a distal part of the mould inlay 50 and which follows the tapering part of the recess 143 of the mould surface 142. Accordingly, the radius of curvature with the mould inlay 50 arranged on top of the mould surface 142 is substantially constant along the entire part for manufacturing the root section part. The mould inlay 50 may for instance be semi-circular so as to follow the entire mould surface. However, it is also possible to use a plurality of single mould inlays.

(23) An outer fibre skin 60 comprising a number of fibre layers is arranged on top of the mould inlay 50 and the mould surface 142. Fastening members 64 in form of bushings for fastening the blade to the hub of a wind turbine as well as possible intermediate inserts 66 are arranged on top of the outer fibre skin 60. Further a wedge 65 may be arranged in longitudinal extension of the fastening member. Alternatively, the wedge may be integrally formed with the fastening member. Finally, an inner fibre skin 62 comprising a number of fibre layers is arranged on top of the bushings 64 and the possible intermediate inserts 66.

(24) After the lay-up has been arranged on top of the mould inlay 50 and the mould surface 142, a flexible vacuum bag (not shown) is sealed against the mould part 142, after which a resin is drawn into the mould cavity formed between the mould part 142 and the vacuum bag. Finally, the resin is cured in order to form a composite structure comprising the first root section part.

(25) FIG. 6 shows a side view of a lay-up in a mould part 140 according to the invention with a second embodiment of a mould inlay 150 arranged on the mould surface of the mould part, and wherein like parts are marked with like numerals of the embodiment shown in FIG. 5. Therefore, only the differences between the two embodiments are described. This embodiment differs from the embodiment shown in FIG. 5 in that the mould inlay 150 is thinner and has a larger second radius of curvature so that the mould inlay 150 does not fill out the entire recess 143 of the mould surface 142. Accordingly, a root section part manufactured via the mould part and mould inlay combination will have a proximal root section part that has a larger diameter than the distal root section part. However, the root end part and accordingly also the diameter of the circle along which the fastening members are disposed are changed compared to a root section part manufactured via a lay-up arranged directly on the mould surface 142.

(26) FIG. 7 shows a side view of a lay-up in the mould part 140 according to the invention without a mould inlay arranged on the mould surface 142 of the mould part 140, and wherein like parts are marked with like numerals of the embodiment shown in FIG. 5. This embodiment differs from FIG. 5 in that the outer fibre skin 260, the fastening member 264, and the inner fibre skin 262 are arranged directly on top of the mould surface 142.

(27) FIG. 8 shows a side view of a lay-up in the mould part known per se 40 with a mould inlay 350 arranged on the mould surface 42 of the mould part 40. The mould part 40 and the mould inlay 350 together form a mould part and mould inlay combination according to the invention. The mould inlay 350 is arranged so that an outer surface 352 of the mould inlay 350 faces the mould surface 42 of the mould part 30, and an inner surface 354 of the mould inlay 350 faces away from the mould surface 42 of the mould part 42. The outer surface 352 of the mould inlay 350 has a radius of curvature R.sub.1 that corresponds to that of the radius of curvature of the mould surface 142. The inner surface 54 of the mould inlay 50 has a second radius of curvature R.sub.2 which is smaller than the first radius of curvature R.sub.1. As with the other embodiments, the mould inlay 350 comprises a tapered wedge part at a distal end of the mould inlay 350.

(28) An outer fibre skin 360 comprising a number of fibre layers is arranged on top of the mould inlay 350 and the mould surface 42. Fastening members 364 in form of bushings for fastening the blade to the hub of a wind turbine as well as possible intermediate inserts are arranged on top of the outer fibre skin 360. Finally, an inner fibre skin 364 comprising a number of fibre layers is arranged on top of the bushings 364 and the possible intermediate inserts.

(29) After the lay-up has been arranged on top of the mould inlay 350 and the mould surface 42, a flexible vacuum bag (not shown) is sealed against the mould part 42, after which a resin is drawn into the mould cavity formed between the mould part 42 and the vacuum bag. Finally, the resin is cured in order to form a composite structure comprising the first root section part.

(30) A blade root section manufactured by use of the mould part and mould inlay combination shown in FIG. 8 comprises a proximal root section part having a diameter which is larger than the diameter of the distal root section part.

(31) The mould inlays and recesses as shown in FIGS. 5-8 advantageously have a length of 50-200 centimetres, or 60-175 centimetres, or 70-150 centimetres. In one preferred embodiment, the mould inlays have a length of approximately 100-110 centimetres.

(32) FIG. 9 shows a top view of a blade 10 having a root section manufactured according to the lay-up of FIG. 5. It is seen that such a blade has a conventional shape and corresponds to a blade that would have been manufactured with a mould part without a recess in the mould surface, e.g. via the mould part shown in FIG. 3.

(33) FIG. 10 shows a top view of a root section manufactured according to the lay-up of FIG. 6 or 7. In such an embodiment, the blade comprises a root section having a proximal part with a first diameter D.sub.1 and a distal part having a second diameter D.sub.2, wherein the first diameter D.sub.1 is larger than the second diameter D.sub.2.

(34) FIG. 11 shows a top view of a root section manufactured according to the lay-up of FIG. 8. In such an embodiment, the blade comprises a root section having a proximal part with a first diameter D.sub.1 and a distal part having a second diameter D.sub.2, wherein the first diameter D.sub.1 is smaller than the second diameter D.sub.2.

(35) Accordingly, the invention also provides a series of wind turbine blades according to FIGS. 9-11 having identical outboard parts but with different diameters at a part proximal to the root end. The proximal part preferably extends along less than 5% of the total blade length. In other words, at least 95% of the blade length of the blades in the series is identical.

(36) While blades as shown in FIGS. 10 and 11 may look aesthetically displeasing, the transition in root diameter will not necessarily be seen, when the blade is installed on a wind turbine, since the inner part of the blade may be located within the outer hull of the hub or spinner of the wind turbine.

(37) FIG. 12 shows an end view of a root section part manufactured according to the invention. It is seen that the root section part comprises a plurality of fastening members 64 and a plurality of intermediate inserts 66 sandwiched between an outer fibre skin 60 and an inner fibre skin 62. The fastening members 64 are preferably bushings and are accessible from a root end of the blade so that the blade may be mounted to the hub of a wind turbine, e.g. by use of stay bolts.

(38) The intermediate inserts 66 may be made of a fibre-reinforced composite, e.g. in form of a fibre pultrusion. The wedge 65 arranged in longitudinal extension of the bushings 64 may be made of wood or a foamed polymer.

LIST OF REFERENCE NUMERALS

(39) 2 wind turbine

(40) 4 tower

(41) 6 nacelle

(42) 8 hub

(43) 10, 110, 310 blade

(44) 14 blade tip

(45) 16 blade root

(46) 18 leading edge

(47) 20 trailing edge

(48) 22 pitch axis

(49) 30 root section

(50) 32 transition section

(51) 34 airfoil section

(52) 40, 140 first mould part

(53) 42, 142 first mould surface

(54) 143 recess

(55) 44, 144 end part

(56) 50, 150, 250 mould inlay

(57) 52, 152, 252 outer surface of mould inlay

(58) 54, 154, 254 inner surface of mould inlay

(59) 56, 156, 256 proximal end of mould inlay

(60) 58, 158, 258 distal end of mould inlay

(61) 60, 160, 260, 360 outer fibre skin

(62) 62, 162, 262, 362 inner fibre skin

(63) 64, 164, 264, 364 fastening member/bushing

(64) 65, 165, 265, 365 wedge

(65) 66 intermediate insert

(66) r local radius, radial distance from blade root

(67) L blade length

(68) L.sub.i length of mould insert

(69) R.sub.1 first radius of curvature

(70) R.sub.2 second radius of curvature