Background of the invention

[0001] The invention relates to a rotor blade for a turbine in a wind power plant. The rotor blade comprises an elongated frame consisting of at least two interconnected frame halves. The halves are made from a composite material, comprising a reinforcement material and matrix plastic. The rotor blade is also provided with an aerodynamic leading edge and an aerodynamic trailing edge. Further, it has a tip and, at an opposite end thereto, a connecting part by which it is attached to a wind turbine.

[0002] The invention further relates to a method for making a rotor blade for a turbine in a wind power plant.

[0003] The field of the invention is described in more detail in the preambles of the independent claims of the application.

[0004] Kinetic energy contained in wind can be converted to electric power in a wind power plant. The wind power plant is equipped with a wind turbine whose rotor blades are subject to the wind, making the turbine rotate. The most common wind power plant constructions include horizontal-shaft wind power plants wherein a wind turbine rotates on a vertical plane. Typically, such a turbine employs three rotor blades. The capacities and size of wind power plants are constantly on the increase. Consequently, the rotor blades for turbines also become larger and larger. Such large rotor blades are made from reinforced plastic so as to make their rigidity/weight ratio good. Today, rotor blades are made from two halves that are glued together during assembly. The rotor blade halves are manufactured by laminating a glass-fibre reinforced ma- terial against a mould, whereafter a polymer matrix is added. After hardening, an inner layer is fastened to an inner surface of the rotor blade halves to add to the thickness of the structure and reduce the risk of buckling. Typically, the inner surface of a half is provided with a foamy core material, which is rather a slow procedure. Further, the inside of the rotor blades is usually provided with web plates to connect the inner surfaces of the rotor blade halves. These web plates are difficult to fasten. Known rotor blades have been found to suffer from drawbacks relating e.g. to their strength, structural complexity, and difficult assembly. Brief description of the invention

[0005] An object of the present invention is to provide a novel and improved rotor blade for a turbine in a wind power plant and a method for making the same.

[0006] A rotor blade according to the invention is characterized in that the cross-section of the frame is a box-type structure comprising longitudinal surface plates that form part of an aerodynamic outer surface of the rotor blade, as well as web plates that connect the surface plates to one another; longitudinal seams between the frame parts reside in the web plates; the frame parts are provided with transverse projections at the longitudinal seams; and the projections are provided with seam surfaces attached against one another.

[0007] A method according to the invention is characterized by providing the interconnectable frame parts with transverse projections and providing these with seam surfaces; fastening the frame parts to one another by arranging the seam surfaces of the projections against one another; arranging longitudinal seams between the frame parts in to the web plates of the frame; and extending longitudinal surface plates of the box-type frame to an outer surface of the rotor blade and utilizing them as part of the aerodynamic surface of the rotor blade.

[0008] The idea is that the cross-section of the frame of the rotor blade is a box-type structure. The frame provides the rotor blade with a strength-theoretically advantageous box structure, a so-called torsion box, dimensioned to receive torsional loads, deflection, and fatigue loads the rotor blade is subject to. Fastened to the frame are provided leading and trailing edge components that have been manufactured in separate phases. The box- type frame is provided with surface plates and web plates that connect opposite surface plates to one another. The surface plates extend all the way to an outer surface of the rotor blade, thus forming part of the aerodynamic surface of the rotor blade. The web plates are covered by the leading and trailing edge components. Further, the frame is made of two or more frame parts, each having projections which are transverse in relation to the frame and which are provided with seam surfaces for interconnecting the frame parts. Longitudinal seams between the frame parts reside in the web plates of the frame.

[0009] An advantage is that a rotor blade made of a plurality of sep- arate components is easier to manufacture and assemble than the known structures. Further, when the rotor blade is made of a plurality of different rotor blade components, the structure and material of each component may be designed according to the criticalness of a particular component and the loads it will be subject to. When the longitudinal seam surfaces between the frame parts are arranged in projections located transversely in relation to the web plates, it is possible to ensure that the frame parts are fastened reliably to one another. The projections may be dimensioned large enough to enable them to be provided with a wide seam surface to ensure good fastening. The projections may be shaped so as to enable seam surfaces to be readily pressed therefrom against one another by a pressing device during assembly. In addi- tion, a seam and oppositely arranged projections may provide the web plates with good reinforcement against buckling. One or more longitudinal seams between the frame parts divide the web plate into two or more smaller plate fields, in which case buckling sensitivity decreases as a plate field size decreases. In such a case, the web plates do not have to be reinforced with sep- arate stiffening pieces. The dimensions and number of seams and projections may intentionally be overdimensioned so as to achieve necessary additional stiffening against buckling. Thus, this structure enables the strength properties of a rotor blade to be improved and also at the same time the manufacture thereof to be alleviated.

[0010] The idea of an embodiment is that the transverse projections provided for the seams are directed away from the frame.

[0011] The idea of an embodiment is that the leading edge component and the frame define a leading edge space therebetween and, correspondingly, the trailing edge component and the frame define a trailing edge space therebetween. The longitudinal seams between the frame parts are located in the leading edge space and in the trailing edge space. In a complete rotor blade, the longitudinal seams thus reside inside the construction, out of sight. In such a case, the projections and the seam surfaces therein may be dimensioned large enough since they have no influence on the aerodynamic properties of the rotor blade. In addition, the seam surfaces may be shaped taking the manufacturing and strength technology related issues into account when in the complete rotor blade the seam resides inside the structure.

[0012] The idea of an embodiment is that the cross-section of the frame is substantially rectangular in shape. However, with respect to strength properties, its corners are rounded. In addition, the outer surface of the frame is provided with connecting recesses into which the connecting surfaces of the leading and trailing edge components are attached e.g. with an adhesive. Owing to the cross-section whose shape resembles a rectangle, the frame forms an extremely stiff but yet lightweight torsion box.

[0013] The idea of an embodiment is that the frame comprises two frame halves whose cross-section has substantially the shape of the letter U.

[0014] The idea of an embodiment is that the interconnected frame halves are symmetrical in shape, in which case the frame may be manufactured by connecting two similar frame halves to one another. This makes the manufacture simpler and reduces manufacturing costs. Frame halves may be manufactured by using one and the same mould.

[0015] The idea of an embodiment is that web pieces are arranged between the frame halves. In such a case, each web plate of the frame comprises two or more longitudinal seams. The seams divide each web of the frame into three or more smaller plate fields whose strength against buckling is better. Further, projections are provided at each longitudinal seam to further support the web plates e.g. against buckling.

[0016] The idea of an embodiment is that the frame, the leading edge space and the trailing edge space are hollow structures. The frame needs no transverse supporting plates to support the inner surfaces against one another but the construction of the frame per se is sufficiently rigid. Further, when the box-type frame receives a vast majority of the forces and loads the rotor blade is subject to, the leading and trailing edge components may be hollow plate structures. This embodiment enables the structure of the rotor blade to be made lightweight.

[0017] The idea of an embodiment is that the inner surface of one or more frame parts is provided with at least one longitudinal stiffener shaped therein to form a projection-like section in the inner surface. During manufacture, the longitudinal stiffener is integrated into the frame part, and it is made of the same reinforced plastic as the frame part.

[0018] The idea of an embodiment is that at least one of the components of the rotor blade is provided with at least one electric heating element. Prior to assembly, heating cables or corresponding heating elements may be fastened to the inner surface of the rotor blade component e.g. by appropriate fastening members or with an adhesive. It is also possible to arrange the heating element as an insert in to a reinforcement preform prior to feeding the matrix plastic, in which case the heating element is integrated as part of the rotor blade component. When the rotor blade is made of a plurality of components that are separately manufactured, it is easy to arrange an electric heating element in the rotor blade construction and this may be carried out in many different ways. Preferably at least the leading edge component is provided with a heating element. This embodiment enables freezing of the rotor blade to be avoided in cold conditions and thus the service life and efficiency of a wind power plant to be improved.

[0019] The idea of an embodiment is that at least one of the components of the rotor blade is provided with at least one lightning protection el- ement. The lightning protection element, such as an electrically conductive network, cable or a corresponding component, may be fastened to the inner surface of a blade component or, alternatively, it may be integrated during manufacture as a non-detachable part of the component. It may also be possible to use an electrically conductive reinforcement material as the reinforce- ment or part of the reinforcement. This embodiment enables the lightning protection element to be easily arranged in the structure of the rotor blade and this may be implemented in many different ways.

[0020] The idea of an embodiment is that the outer surface and the inner surface of the frame are made of the same plastic material. In such a case, the inner surface of the frame part is not treated with any additional material but the inner surface of the composite frame part consists of a matrix plastic and a reinforcement. Of course, it is possible that the reinforcements of the inner and outer surfaces of the frame part differ from one another, but even then no additional material is added to the inner surface in a separate phase.

[0021] The idea of an embodiment is that the rotor blade is at least

30 metres in length. The rotor blade may be 30 to 50 metres in length. Owing to the solution disclosed in this patent application, the rotor blade may be even longer, i.e. more than 50 metres in length.

[0022] The idea of an embodiment is that the frame parts are rein- forced with carbon fibre. The frame part may be reinforced with carbon fibre only, which gives an extremely good stiffness/weight ratio. In some cases, it is possible to use carbon fibre as the main reinforcement, in which case some other reinforcement is used in smaller amounts and in selected locations of the structure.

[0023] The idea of an embodiment is that a module principle is applied to the construction of the rotor blade. In such a case, different leading edge components and, correspondingly, different trailing edge components that may have mutually different shapes and dimensions may be fastened to a basic frame. This enables rotor blades having different profiles to be manufactured easily. It is relatively simple to vary the leading and trailing edge compo- nents since they are not subject to heavy loads that could restrict the design of these components. No changes are necessary to the frame structure of the rotor blade even if the properties and outer appearance of the rotor blade are varied by means of the edge modules.

[0024] The idea of an embodiment is that in its longitudinal direction the rotor blade comprises a plurality of successive rotor blade components. Two, three or even more frame parts, leading edge components and trailing edge components may be arranged in succession. For connecting, ends of the components to be interconnected in succession may be provided with connecting portions. This embodiment alleviates the manufacture of particularly long rotor blades. The manufacture and handling of the rotor blade components necessitate less space and the manufacturing equipment may be shorter. Only assembly requires a full rotor blade length.

[0025] The idea of an embodiment is that the leading edge component has a plate structure and its layer thickness may be uniform. Such a plate piece is simple and quick to manufacture. The leading edge is mainly subjected to aerodynamic pressure load only, in which case it may have a simple and lightweight structure. It is possible to use e.g. glass fibre or carbon fibre as a reinforcement in the leading edge component.

[0026] The idea of an embodiment is that the trailing edge compo- nent has a sandwich structure and its layer thickness may be uniform. Such a plate piece is simple and quick to manufacture. The trailing edge is mainly subjected to aerodynamic pressure load only, in which case it may have a simple and lightweight structure. Further, since the loads directed to the trailing edge component are relatively small, fibre glass may be used as a reinforcement. Consequently, the manufacturing cost of the trailing edge component may be small.

[0027] The idea of an embodiment is that the tip of the rotor blade is provided with a tip component having a curved or sloping aerodynamic surface with respect to the surface of the rotor blade. The tip component enables the aerodynamic efficiency of the rotor blade to be improved. This enables the capacity of a wind turbine to be increased with no need to increase the length of the rotor blades. The tip components may have different profiles, in which case the rotor blades of each turbine may be provided with appropriate tip components, taking wind conditions into account, for instance.

[0028] The idea of an embodiment is that a technique called vacu- um injection is employed in the manufacture of a frame part, wherein the frame parts are formed in a female mould by means of a vacuum bag. In such a case, a reinforcement preform is arranged against a mould surface, whereafter so-called bagging is performed wherein the mould is enveloped completely or partly by the vacuum bag. The bag thus serves as one mould half. Next, a vacuum is sucked into the bag, i.e. air is removed from the mould, the reinforcement preform, and the bag. After this or simultaneously with suction, a matrix plastic is fed to a space between the vacuum bag and the mould surface to fill the reinforcement preform and to give the frame part a shape corresponding with that of the mould surface. After the frame part has hardened, it may be removed from the mould and finished for assembly. When necessary, the seam surfaces in the frame part may be machined so as to achieve a straight, smooth and good connecting surface for interconnecting.

[0029] The idea of an embodiment is that one or more adhesives are used for interconnecting the rotor blade components.

[0030] The idea of an embodiment is that mechanical connecting members are used for interconnecting the rotor blade components. Suitable mechanical connecting members include bolts, screws, rivets or the like.

[0031] The idea of an embodiment is that a method called RTM (Resin Transfer Moulding) is used in the manufacture of the frame part, where- in the frame parts are formed in a mould in which a reinforcement preform is arranged and into which the matrix plastic is fed. The mould contains a female mould and a male mould provided with an openable and closable mould space therebetween. After the reinforcement preform has been arranged in the mould space, the mould is closed and a vacuum is created in the mould space. Next, the matrix plastic is fed into the mould space to fill the reinforcement preform and give the frame part a shape corresponding with that of the mould space. Once the frame part has hardened, the mould can be opened and the frame part may be forwarded to finishing stages. When the manufacture takes place between stiff mould surfaces, a piece to be manufactured is provided with ex- tremely good dimensional accuracy and surface quality. Consequently, the seam surfaces in the frame parts do not have to be finished by machining, which makes the manufacture quicker.

[0032] The idea of an embodiment is that the frame part is formed in a mould comprising at least a female mould, and the frame part is kept in the female mould until assembly of the frame. This enables two female moulds to be arranged against one another during assembly, in which case the seam surfaces of the frame parts in the female moulds become adjusted against one another. The seam surfaces are provided with an adhesive, and the frame parts are pressed against one another by means of the female moulds. Owing to this embodiment, no separate assembly support is necessary but the frame part is moved and handled by means of the female mould.

Brief description of the figures

[0033] Some embodiments of the invention will be explained in greater detail in the attached drawings, in which

Figure 1 schematically shows a wind power plant wherein a rotor blade construction to be disclosed may be used,

Figure 2 schematically shows a frame half of which a frame of a rotor blade may be formed,

Figure 3 schematically shows a frame part of a rotor blade wherein frame halves are mounted on top of one another, producing a box-type structure,

Figure 4 schematically shows a frame of a rotor blade after a leading edge component has been fastened thereto,

Figure 5 schematically shows the rotor blade disclosed in Figure 4 after a trailing edge component has also been fastened thereto,

Figure 6 schematically shows an alternative rotor blade whose tip is provided with a tip component,

Figure 7 schematically shows an arrangement for manufacturing a composite frame half in an open mould,

Figure 8 schematically shows an arrangement for manufacturing a frame half in a closable mould,

Figure 9 schematically shows connecting the frame halves and using female moulds as a manufacturing support,

Figure 10 schematically shows a structure of a cross-section of a frame of a rotor blade and connecting the frame halves,

Figure 11 schematically shows a rotor blade in cross-section, Figure 12 is a diagram showing phases and matters related to the manufacture of a rotor blade, and

Figure 13 schematically shows yet another alternative structure of a frame of a rotor blade.

[0034] For the sake of clarity, the figures show some embodiments of the invention in a simplified manner. In the figures, like reference numerals identify like elements.

Detailed description of some embodiments of the invention

[0035] Figure 1 shows a wind power plant comprising a shaft 1 hav- ing a base 2 in a lower part thereof and an engine room 3 as well as a wind turbine 4 in an upper part thereof. The engine room 3 is provided with necessary power transfer members, such as gears, for transferring rotational motion of the wind turbine 4 to an electric generator wherein kinetic energy is converted into electric energy. The engine room 3 is further provided with necessary control means and apparatus for controlling electric equipment and the wind turbine 4 as well as for turning the engine room 3 according to wind direction.

[0036] The wind power plant shown in Figure 1 is a horizontal-shaft apparatus, in which case its wind turbine 4 rotates in a vertical plane. Typically, a turbine with three rotor blades 5a, 5b, and 5c is employed in such a horizon- tal-shaft wind power plant. The power of existing wind power plants is 1 to 5 MW, so their wind turbines are also very large. The rotor blades 5 are usually more than 30 metres in length. In order for the weight of a rotor blade 5 to remain reasonable, the rotor blade 5 is made of a composite material, i.e. it comprises one or more reinforcements and one or more matrix plastics. In ad- dition to its own mass, the rotor blade 5 is also subject to wind-related deflection, torsional, and shear forces. When the rotor blade 5 is provided with a box- type frame disclosed in this patent application, the loads the rotor blade 5 is subject to are well in control.

[0037] Each rotor blade 5 is fastened to a rotor 6 of the turbine 4. An innermost end of the rotor blade is provided with a connecting part 7 by which it is fastened to the rotor 6. At an opposite end, i.e. an outermost end, resides a tip 8 of the rotor blade 5. Further, a longitudinal edge of the rotor blade 5 is provided with a leading edge 9 while an opposite longitudinal edge is provided with a trailing edge 10. The leading edge 9 meets an air flow before the trailing edge 10, at which the air flow leaves the rotor blade 5. [0038] For the sake of clarity, Figure 1 designates the turning of the engine room 3 by arrow A, rotation of the turbine 4 by arrow B, turning of the rotor blade 5 around its longitudinal axis by arrow C and, further, the length of the rotor blade 5 by arrow L.

[0039] Figure 2 shows a frame half 11a which is an elongated groove-like piece made of a composite material. The cross-section of the frame half 11a has substantially the shape of the letter U. The frame half 11a tapers towards the tip of the rotor blade. The innermost end may be provided with a different cross-section for the connecting part. Further, the frame half 11a comprises seam surfaces 12 which may extend in a uniform manner from the inner end of the frame half 11 a to the outer end thereof.

[0040] In Figure 3, a second frame half 11b is arranged on top of the first frame half 11a. The frame halves 11a and 11b may be symmetrical with respect to one another and they may also be made of exactly the same material. Alternatively, frame halves different from one another may be used. The seam surfaces 12 of the frame halves 11a, 11b may be attached to one another by an adhesive. An assembled frame 13 has a box-type cross-section having longitudinal surface plates 14a, 14b and web plates 15a, 15b. Longitudinal seams 16 are thus formed in the web plates 15a, 15b of the frame 13. In a complete rotor blade, the web plates 15a, 15b and the seams 16 reside inside the structure, out of sight, as will be shown by the figures to be discussed below.

[0041] In Figure 4, an elongated leading edge component 17 constituting the leading edge 9 of the rotor blade 5 is fastened to the frame 13. The leading edge component 17 may be rather a simple piece whose cross-section has substantially the shape of the letter U. The design and construction of the leading edge component 17 are mainly dictated by aerodynamic facts. The dimensions of the leading edge component 17 decrease towards the tip 8 of the rotor blade, in a manner similar to those of the frame 13. The frame 13 may be provided with recesses or corresponding fastening surfaces provided in advance against which the fastening surfaces of the leading edge component 17 may be arranged and attached e.g. with an adhesive. The leading edge component 17 covers the web plate 15b of the frame 13 and the seam 16 located therein. The leading edge 9 of the rotor blade 5 is provided with a leading edge space 18, which may be a hollow empty space. [0042] In Figure 5, yet another rotor blade component is fastened to the frame 13, namely an elongated trailing edge component 19 constituting the trailing edge 10 of the rotor blade 5. Since the trailing edge component is not subjected to any significant loads, it may be shaped quite freely, taking aero- dynamic facts into account. The trailing edge component 19 may be rather a simple sandwich structure with curved side surfaces and a strongly wedge-like shape. The frame 13 may be provided with recesses or corresponding fastening surfaces to which the fastening surfaces of the trailing edge component 19 may be attached e.g. with an adhesive. The trailing edge component 19 covers the web plate 15a of the frame 13 and the seam 16 located therein. The trailing edge 10 of the rotor blade 5 is provided with a trailing edge space 20, which may be a hollow empty space. Thus, the cross-section of the rotor blade 5 may comprise three longitudinal chambers, namely an inner space 21 of the frame 13, the leading edge space 18 as well as the trailing edge space 20, each of which extends uniformly from the connecting part 7 of the rotor blade all the way to the tip 8 thereof. The structure is rigid with no need to arrange any internal support elements in these spaces to support the inner surfaces defining the spaces. It is to be noted that, although not shown in the figure, the tip 8 is closed by an appropriate tip part. As can be seen, the surface plates 14a, 14b of the frame 13 form a part of the outer surface of the rotor blade 5.

[0043] Figure 6 shows an embodiment of the rotor blade 5, wherein the tip 8 of the rotor blade is provided with a tip component 22 constituting curved surfaces whose purpose is to improve the aerodynamic properties of the rotor blade. Alternatively, the tip component 22 comprises sloping surfaces. The different tip components 22 are similar in that they are arranged at the tip of the rotor blade to form an aerodynamic surface whose direction differs from that of a longitudinal axis P of the rotor blade. Further, the rotor blade 5 may be formed in the longitudinal direction such that a plurality of similar rotor blade components are connected in succession. In such a case, the frame may be formed by arranging frame halves in succession, the leading edge may be formed by connecting a plurality of leading edge components in succession and, further, the trailing edge may be formed by connecting a plurality of trailing edge components in succession. This is illustrated in transverse lines T in the figure. In practice, however, it may be advantageous to form the load- bearing box-type frame 13 from frame halves corresponding with the total length of the rotor blade 5 and use longitudinal connections between the leading and trailing edge components only.

[0044] Figures 4 to 6 show the structure of the leading edge component 17 and the trailing edge component in a simplified manner. The end facing the connecting part 7 is, of course, closed. Further, the components 17 and 19 may extend to the connecting part 7 and connect therewith in a streamlined manner.

[0045] Figure 7 shows an arrangement for manufacturing frame halves. The technique in question is so-called vacuum injection wherein only one mould half is used. Reinforcements 23 for a frame half are placed against the mould surface of a female mould 24. Alternatively, a prefabricated reinforcement preform may be used which is arranged correspondingly in the female mould 24. When the reinforcements 23 and possible inserts and other elements to be integrated into the structure have been arranged in place, so- called bagging is carried out wherein the mould 24 is enveloped by a vacuum bag 25. Of course, it is possible that not the entire mould 24 is fitted into the vacuum bag 25, but the bag 25 may cover an open part of the mould only and it may elsewhere be sealed to the mould. The important point is that the bag 25 forms one mould surface after a vacuum is sucked into the bag 25 by a pump 26. The ambient air pressure then presses the bag 25' tightly against the reinforcements 23. At the same time, matrix plastic is fed into the bag 25 from a feeding point 27, whereby the matrix plastic penetrates between the female mould 24 and the bag 25, wetting and filling the reinforcements. This method is quite quick and the mould costs are moderate. The seam surface 12 being formed may have to be finished prior to assembly e.g. by machining.

[0046] Figure 8 shows an alternative manner of manufacturing a frame half. This method utilizes a two-part mould 28 comprising a female mould 28a and a male mould 28b that can be moved with respect to one another in direction V in order to open and close a mould space 29. The rein- forcements 23 are arranged in the mould space 29, whereafter the mould space 29 is closed. Air is removed by suction from the mould space 29 along a line S, and matrix plastic is fed into this space from a feed channel R to fill the mould space 29. This method and applications thereof enable dimensionally accurate composite pieces having a good surface quality to be manufactured quickly. Consequently, the seam surfaces 12 of the manufactured frame half may be so straight and uniform that they do not necessarily have to be finished at all for gluing.

[0047] The manufacturing techniques shown in Figures 7 and 8 may also be used for the manufacture of other rotor blade components disclosed in the present invention.

[0048] Figure 9 shows a solution for interconnecting the frame halves 11a, 11b. After being manufactured, the frame halves may be kept in the female moulds 28a as long as until assembly, making them easy to move and handle. Further, no separate manufacturing support is necessary for as- sembly gluing but the female mould 28a serves as one. During assembly, an adhesive 30 is applied to the seam surfaces 12, whereafter the female moulds 28a are pressed against one another, in which case the seam 16 is subject to a pressing force V.

[0049] Figure 10 shows an embodiment of the cross-section of the frame 13. The frame parts 11a and 11b may comprise projections 31 extending by a transverse distance X outwards from the outer surface of the web plates 15a, 15b. Since in a complete rotor blade the seams 16 remain in the leading and trailing edge spaces, the projections 31 may be dimensioned quite freely, taking the strength and manufacture related facts concerning the seam 16 into account. Such projections 31 are easy to be provided with sufficiently large seam surfaces 12 e.g. for gluing. As can be seen from the right-hand seam 16 of the figure, the projections 31 alleviate the pressing of the seam 16 during assembly. Further, the projections 31 and the seams 16 may serve as elements stiffening the web plates 15a, 15b, in which case buckling, i.e. deflec- tion 32 of the surface indicated in the figure, may be avoided. Further, the inner surfaces of the frame 13 may be provided with longitudinal stiffeners 33 to stiffen the surface plates 14a, 14b, and possibly also web plates 15a, 15b. The longitudinal stiffener 33 may be integrated into the surface defining the inside of the frame, and it may form a projection in the inner surface. The longitudinal stiffeners 33 comprise a reinforcement and a matrix plastic, and they may be made simultaneously in connection with the manufacture of the frame half 11a, 11b. The frame 13 may also have recesses or corresponding fastening points 34 to which the fastening points of the leading and trailing edge components may be fastened.

[0050] Figure 11 shows the cross-section of the rotor blade 5 after assembly. The leading edge component 17 may be provided with an electric heating element 35 which may comprise a plurality of heating cables, the electric current running therein heating the leading edge component 17 and preventing ice formation. The rotor blade components 11a, 11b, 17, 19, 22 may also be provided with a lightning protection element 36 which may be e.g. an electrically conductive network, cable or the like. The elements 35 and 36 may be fastened to the rotor blade components 11a, 11b, 17, 19, 22 in connection with the manufacture thereof, in which case they are so-called inserts, or they may be fastened after manufacture to the inner surface of the rotor blade components by using an adhesive or suitable mechanical fasteners.

[0051] Figure 12 is a diagram showing phases related to the manufacture of a rotor blade for a wind rotor. The purpose of the figure is to clarify matters and features discussed above in this patent application. The figure needs not be explained in any further detail.

[0052] It is also possible that contrary to what has been disclosed above, the cross-section of the frame 13 is provided with more than two frame halves or frame components that together constitute a box-type structure.

[0053] Figure 13 shows an embodiment wherein web pieces 11c and 11d are arranged between the frame halves 11a, 11b. This embodiment is relevant particularly when a rotor blade is especially large and the height of the frame 13 is great. Buckling may be avoided when the plate field of the web plates 15a, 15b is divided into several smaller parts - in this case, into three plate fields. The frame halves 11a, 11b and the web pieces 11c, 11d, i.e. the frame parts, are at the longitudinal seams 16 provided with transverse projections 31. When necessary, two or more web pieces 11c, 11d may be arranged on top of one another in the height direction of the frame. The web pieces may be manufactured by the same technique as the frame halves.

[0054] As distinct from the figures set forth above, it is possible to direct the projections 31 towards the inside of the frame or, further, it is possible to alternatively extend at least part of the transverse projection 31 towards the inside of the frame and part thereof away from the frame.

[0055] In some cases, features disclosed in this application may be used as such, irrespective of other features. On the other hand, when necessary, the features disclosed in this application may be combined in order to provide various combinations. [0056] The drawings and the related description are only intended the idea of the invention. The details of the invention may vary with¬e of the claims.