CA1197468A

CA1197468A - Large airfoil structure and method for its manufacture

Info

Publication number: CA1197468A
Application number: CA000400108A
Authority: CA
Inventors: Michael Hahn; Franz Sperber
Original assignee: Messerschmitt Bolkow Blohm AG
Current assignee: Airbus Defence and Space GmbH
Priority date: 1981-04-01
Filing date: 1982-03-31
Publication date: 1985-12-03
Also published as: ES8503080A1; DK160954B; AU551912B2; DE3113079C2; EP0061567A3; JPS57210171A; DK160954C; DK147182A; AU8199882A; DE3113079A1; US4732542A; EP0061567B1; US4643646A; GR82251B; EP0061567A2; ES510426A0; JPH0312232B2

Abstract

Abstract of the Disclosure An airfoil particularly suited for use in rotor blades of large wind-driven power plants is formed in three modular sections including a nose or leading section, a spar section and a trailing section, each separately formed and subsequently assembled. In the method of the invention the spar section is formed in two separate mold units which are configured to form part of the upper and lower aerodynamic profile of the airfoil and the two spar section units are trimmed along a junction plane and then joined together at the junction plane to form the spar section of the airfoil.

Description

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The present invention relates generally to the structure and configuration of large airfoils and to a method of making a relatively large airfoil. More particularly, the invention is directed toward the construction of large airfoils of the type which may be used as the rotor blades of large wind-driven power plants.

In development work involving the construction and development of large airfoils, it has been attempted to apply a manufacturing method utilizing foam core supported molded sections in the formation of wings, rotor blades, and the like wherein the airfoils involve large linear lengths and extension of the width thereof. Such manufacturing methods involve the utilization of molds which cannot be closed. A
particular method of the type discussed involves an operation wherein a shell of a molded section is laminated and hardened in two separate section halves of composite fiber material.
A foam core is manufactured and processed directly in each shell of the mold section and after preparation of a junction plane of the molded section halves, the halves are glued together.

Furthermore, optional procedures which may be involved in such a method include providing the mold-release section with nose reinforcements and end edge reinforcements and manufacturing the foam core to be pressure resistant and so as to be used as plate material which is glued together.
The plate material of the foam core is connected with the shell by means of foam adhesive.

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In a parallel of the application of -the -techniques dis-cussed above, a rotor blade or component, particularly a blade root, which has a large surface is formed with a shell of fiber-reinforced plastic which is supported by a foam core. Disc-shaped positive formers of the blade contour are inserted in-to the sup-port core, in accordance with this technique.
Particularly in the technique first mentioned above, known methods for the manufacture of foam core supported molded sections can no longer be used in practical applications where there are involved very large airfoils, such as the rotor blades of wind-driver power plants which may, for example, have a length of 70 meters and a section depth of about 7 meters. In a known rotor for large wind-driven power plants, the rotor is formed as a two-blade rotor having a diameter of 100.4 meters with a steel spar which is in turn encased by molded glass fiber sections which give the rotor its aerodynamic profile.
The present invention provides a large aerodynamic wing or airfoil which is relatively easy to manufac-turé and easy to handle and which will also exhibit the characeristics of rela-tively high stiffness ratios (strength) to mass.
According to the present invention there is provided alarge wind-driven power plant having a rotor blade with an air-foil structure having an upper airfoil surface and a lower air-foil surface comprising: three modular sec-tions consisting essen-tially of a leading section defining a leading edge of said air-foil, a trailing section defining a trailing edge of said airfoil, and a spar section intermediate said leading and trailing sec-tions; said modular sections being separately formed and sub-sequently asembled together to form said airfoil structure; said spar section being formed to consist essen-tially of an upper segment defining a part of said upper airfoil surface and a lower segment defining a part of said lower airfoil surface, said ~.
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parts of said upper and lower airEoil surfaces ex-tending along the section of said airfoil structure defined by said spar sec-tion; each of said upper and lower segments of said spar sec-tions being formed to comprise a plurality of laminate shells with at least one foam bar unit supporting said laminated shells; said upper and lower segments being joined together along planar sur-~faces thereof which are parallel to an imaginary plane extending between said leading and said trailing edges of said airfoil structure.
The present invention also provides a me-thod for manu-facturing an airfoil consisting essentially of a plurality of modular sections including a leading section, a trailing section and a spar section intermediate said leading and trailing sec-tions comprising the steps of manufacturing said spar section in two separate mold shells as two spar section par-ts, said spar section parts being formed to include foam bars, trimming pro-jecting portions of said foam bars along a junction plane and releasing one spar section part from its mold and joining it to the other spar section part at said junction plane.
In particular the present invention provides a method for forming an airfoil consisting essen-tially of a plurality of modular sections including a leading section, a trailing section and a spar section intermediate said leading and trailing sec-tions comprising the steps of: forming said spar section in two parts which constitute, respectively, an upper par-t and a lower part of said spar section of said airfoil; said upper part and said lower part being formed each on one side thereof to define, respectively, an upper portion and a lower portion of the aero-dynamic profile of said airfoil; joining said upper and lower parts together to i.-orm said spar section; and forming said lead-ing and trailing sections as separate modular sections of said airfoil and assemb:Ling said preformed leading, trailing and spar ections together to form said airfoil - 3a -7~6~3 SUMMARY OF THE INVENTION

Briefly, the present invention may be descrlbed as an airfoil structure particularly suited for use with rotor blades of large wind-driven power plants wherein the airfoil is formed of three modular sections which consist essentially of a nose or leading section, an intermediate spar section, and a trailing section, the modular sections being separately formed and subsequently assembled together to form the airfoil.
In the method of manufacture of the present invention, the spar section is formed in two parts in separate molds. Each of the molds forms one of the spar section parts with a portion of the upper and lower aerodynamic profile of the airfoil. In the molds, the spar section parts are trimmed along a junction plane and then the two parts are joined together at the junction plane in order to form the spar section of the airfoil.

Subsequently, the preformed leading and trailing sections of the airfoil are assembled with the spar section in order to complete the airfoil structure.

The advantages of a large airfoil in accordance with the present invention particularly involve the fact that spar flanges of the spar sections may be formed to lie at the maximum possible distance in relation to the neutral axis of the airfoil so that an optimum ratio of stiffness to mass may result.

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The spar section is formed so as to define the central portions of the upper and lower profiles of the airfoil or wing and as a result no addi-tional casings are required thereby further reducing the mass of the structure.

The nose section may be manufactured in one piece and may therefore be formed with good aerodynamic character-istics. Furthermore, the trailing sections of such an airfoil structure may be formed to be self-supporting and uniform.
The entire airfoil will have a very high ratio of stiffness to mass and the separate manufacture of the section modules simplifies transportion of the airfoil to the site at which it is to be used, since the airfoil may be transported in smaller separate modular sections which may then be assembled at the site to form the airfoil.

The trailing section may be comprised of an upper and a lower half which may be formed as lightweight laminar structures and the leading or nose shell or section and the trailing section may both be provided wi-th elastic longitudinal extensions which will enhance the assembly of the leading and trailing sections with the spar sections. The elastic extensions which may be cons-tructed as thin laminar layers will operate to compensate for minor inaccuracies during assembly of the leading and trailing sections and will there-fore facilitate assembly of the sections wi-th the central spar section.

~.a~7~8 -Screw connections may be provided in addition to glued connections in order to increase during the gluing operation the contact pressure in order to also counteract any peeling.

The spar section segments may be formed at discon-necting points with longitudinal bores and transverse bores in order to enable receipt of connecting elements. Therefore, special assembly techni~ues may be utilized.

Materials which may be particularly suitable for use with the present invention include PVC foam which is recornmended for the foam bar unit of the spar section because it dis-tinguishes itself by characteristics involving high dynamic strength. However, it does not foam freely. A unidirectional larninate of glass or carbon may be utilized for the flanse laminate and glass fiber fabrics may be utilized for the remaining larninates.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred ernbodiment of the invention.

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DESCRIPTION OF THE DRAWINGS

In the drawings:
Figure 1 is a sectional view of an airfoil structure in accordance with the present invention;
Figures 2a, 2b, and 2c show various steps in the molding oE the parts of the spar section of the airfoil, with the assembly of the parts of the spar section 'oeing shown in Figure 2c;
Figure 2d is a sectional view showing a detail of a part of the spar section shown in Figure 2c;
Figure 3 is a side view of mold apparatus for manufacturing the leading section of the airfoil;
Figure 3a is a sectional view showing a detail of the structure shown in Figure 3;
Figure 4 is a side view showing molding apparatus for manufacturing the trailing section of the airfoil;
Figure 4a is a sectional view showlng in detail the structure shown in Figure 4;
Figure 5a is a sectional view showing a division of the rotor blade of the airfoil of Figure 1 into individual segments in the longitudinal direction of the blade;
Figure 5b is a perspective view showing the spar section of the airfoil;
Figure 6 is a perspective view showing the assembled sections of the airfoil;
Figure 6a is a sectional view showing a detail of the structure of the assembled airfoili and Figure 7 is a perspective view, partially in section, showing a portion of a rotor blade in accordance with the invention.

DETAI~ED DESCRIPTION OF THE PREFERRED EMBODIMENT

The structure of the airfoil constructed in accordance with the present invention is shown in section in Figure 1. As will be noted from Figure 1, the airfoil is divided into three modular sections which cornprise a spar section 1, a nose or leading section or shell 2, and a trailing or vane section 3.
In accordance with the present inventiont each of these sections is formed asaseparate modular unit and then assembled together, in a manner to be more fully described hereinafter.
In very large wings or airfoils, also disconnecting points may be established in the longitudinal direction of the blade or airfoil (compare below Figures 5a and 5b).

Figures 2a, 2b, and 2c depict the method of manu-facture of -the spar section 1 of the airfoil depicted in Eigure 1. In Figure 2a there is shown a pair of mold tables 100a and 100b. As noted in Figure 1, the spar section 1 is divided along a longitudinally extending junction plane 8.
An upper part of the spar sec-tion 1 is located above the junction plane 8 and comprises reinforcing bar laminates 7b, flanye laminates 4b, and a thrust transmitting laminate 5b.

Located below the junction plane 8 is the lower part of the spar section 1 which similarly comprises reinforcing 7~61~3 bar laminates 7a, flange laminates 4a, and a thrust transmittiny laminate 5a.

The upper part of the spar section 1 is :Eormed in the mold table lOOb and the lower part of the spar section l is formed in the mold table lOOa. The mold table lOOb includes a mold shell lOlb which is shaped in the orm of the part of the aerodynamic profile of the upper surface of the airfoil shown in Figure 1 which is occupied by the spar section 1.
Thus, the upper part of the spar section 1 is formed in the mold lOOb with an outer shape which defines a part of the upper surface of the aerodynamic profile of the airfoil occupied by the spar section 1.

Similarly, the mold table lOOa is formed with a mold shell lOla which is shaped in the form of the part of the lower surface of the aerodynamic profile of the airfoil which is occupied by the spar section 1.

Thus, in the mold tables lOla and lOlb the lower and upper parts of the spar section 1 will be formed to define, respectively, parts of the aerodynamic profile of the airfoil so that ~hen the upper and lower parts are joined together, the spar section 1 will be formed in the shape of the aerodynamic profile of khe airEoil.

In Figure 2a, the mold table lOOb is arranged with the flange laminates 4b located on either side of the thrust transmitting laminates 5b. Similarly, the mold table lOOa is formed with flange laminates 4a on either side of the thrust transmitting laminates 5a. The flange laminates 4a and 4b are inserted in the longitudinal direction of the rotor blade and also the thrust transmitting laminates 5a and 5b are inserted in the mold shell lOla and lOlb. Particularlv, manual laminating, the "prepreg" process and the vacuum in~ection process are suitable to manufacture the laminates.

As shown in Figure 2b, two approximately cut halves of foam bar units 6a and 6b are, after hardening, glued to the associated flange laminates 4a and 4b and they are rein forced preferably at ~he si.des by means of the bar laminates 7a and 7b.

The mold shells lOOa and lOOb may be thickened at the lateral edges of the spar section 1 (compare Figures 2c and 2d) with a strip 9 in such a manner that a passage is provided for attachment on one side of the leading section 2 and for attachment on the other side of the trailing section 3.

Projecting foam bar portions are cut off along the junction plane 8 in order to compensate for manufacturing tolerances as well as mold inaccuracies in the spar sec-tion 1 as well as in the leading section 2 (compare Figure 2b).

Subsequently, one part of the spar section shown at the left in Figures 2a and 2b is released from the mold and is glued at the junction plane 8 to the counterpart of -the spar section so that the completed spar section l may be formed which, in its outer contours, will correspond directly to the profile of the airfoil. Thus, unlike prior techniclues, the wing profile in aecordanee with the present invention is struetured in a manner which does not require the utilization of additional easings.

Flgure 3 shows a mold apparatus ll for manufacture of the nose shell or leading seetion 2 of the airfoil. The seetion 2 is manufac-tured in the mold 11 or in several molds by means of a laminating proeess known in the art. Preferably, a light laminar strueture is built so that a shell results whieh will have good inherent stiffness. The edges are con-strueted as thin laminated layers 13 which, during assembly with the spar section 1, will serve as elastie extensions whieh ean compensate for minor inaccuracies.

In Figure 4 there is shown mold apparatus 15 for forming the vane section or trailing section 3 of the airfoil.
The trailing section 3 is preferably manufactured as a light laminar structure in separate molds 15 for the upper side and the lower side~ The trailing section also is provided with elastie extensions 16a and 16b at the sides thereof whieh may be eonneeted with the spar seetion l. If desired, from the point of view of the shaping of the seetion, a -thick section end edge ca~ be achieved by yluing on a foam strip 17a or 17b.

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Figures 5a and 5b show the division of the spar section 1 into modules 1-1 and 1-2 in the longitudinal direction of the rotor blade. The laminates 4a, 5a and ~b, 5b near -the disconnecting points 18 are thickened by means of additional laminates 20a ancl 20b. These thick laminates receive, in a manner known in the art, longitudinal bores 50 and transverse bores 51 to receive connecting elements 19 and 19'.

With the spar segments 1-1 and 1-2 assembled, the connecting elements 19 and 19' are inserted and prestressed.
After this assembly, the laminates 21 are applied as trans-verse force connections.

Figure 6 depicts the overall assembly of the spar section 1 together with the leading section 2 and the trailing section 3. The individual modules of the airfoil of the present invention may be separately transported and assembled on site at, for example, the location of a wind-driven power plant.

In the assembly procedure, trailing section halves 3a and 3b are glued together at an end edge thereof, i.e., at the foam str;ips 17a and 17b, and they are connected with the spar section 1 by means of glued connections 25 and screw con-nections 2~ (see E'igure 6a). Ribs 22 assist in the positioning of the elements and they are glued as reinforcements to the trailing section halves 3a and 3b and to the spar section 1.

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The leading section 2 is also glued to the spar section 1 and is attached with screwed or threaded elements similar to the screw connections 24 shown in Figure 6a. The screw connections 24 impart to the glued connections necessary contact pressure and thus will prevent peeling.

Shown in an exploded view in Figure 7 is a completed rotor blade depicted insofar as it is built in accordance with the invention, i.e., without the rotor head and without the blade tip as well as possibly a directly adjoining rotor blade section, and the blade shown in Figure 7 may be manufac-tured completely of foam. As indicated in Figure 7, the lower part of the spar section is identified with reference numeral la.

While a specific embodiment of the invention has been shown and described in detail to illustrate the applica-tion of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A large wind-driven power plant having a rotor blade with an airfoil structure having an upper airfoil surface and a lower airfoil surface comprising: three modular sections consisting essentially of a leading section defining a leading edge of said airfoil, a trailing section defining a trailing edge of said airfoil, and a spar section intermediate said lead-ing and trailing sections; said modular sections being separately formed and subsequently assembled together to form said airfoil structure; said spar section being formed to consist essentially of an upper segment defining a part of said upper airfoil surface and a lower segment defining a part of said lower airfoil surface, said parts of said upper and lower airfoil surfaces extending along the section of said airfoil structure defined by said spar section; each of said upper and lower segments of said spar sec-tions being formed to comprise a plurality of laminate shells with at least one foam bar unit supporting said laminated shells;
said upper and lower segments being joined together along planar surfaces thereof which are parallel to an imaginary plane ex-tending between said leading and said trailing edges of said air-foil structure.

2. An airfoil according to claim 1, whrein said lami-nates comprise two flange laminates with an interposed thrust transmission laminate therebetween and wherein said foam bar unit supports only said flange laminates.

3. An airfoil according to claim 1, wherein said spar section is divided into a lower and an upper segment each having one laminate shell and half of a foam bar unit and each being glued together at cut end faces of said foam bar unit half which face one another.

4. An airfoil according to claim 3, wherein said foam bar halves are glued and cut approximately with the shells.

5. An airfoil according to claim 4, wherein said foam bars are reinforced at longitudinal sides by the inclusion of bar laminates.

6. An airfoil according to claim 5, wherein said shells have at both longitudinal sides a set back step forming passages for attachment of said leading section and said trailing section with said spar section.

7. An airfoil according to claim 1, wherein said leading section is formed as a laminate.

8. An airfoil according to claim 7, wherein said laminate comprises a light laminar structure.

9. An airfoil according to claim 7 or 8, wherein said leading section terminates with elastic extensions.

10. An airfoil according to claim 1, wherein said trailing section is comprised of a lower half and an upper half.

11. An airfoil according to claim 10, wherein said trailing section halves are formed as light laminar structures.

12. An airfoil according to claim 10, wherein said trailing section halves are each formed with an elastic extension at longitudinal sides thereof adapted to be connected with said spar section.

13. An airfoil according to claim 12, wherein said trailing section halves are formed with a glued on foam strip forming a thickened trailing edge end of said trailing section.

14. An airfoil according to claim 13, wherein said trailing section halves are glued to one another at the trailing edge of said section and are connected with said spar section by means of screw connections and/or glued connections and wherein ribs are glued as positioning reinforcements in said trailing section halves and said spar section.

15. An airfoil according to claim 1, wherein said lead-ing section is connected with said spar section by means of screw connections and/or glued connections.

16. An airfoil according to claim 1, wherein said seg-ments of said spar section are thickened in the proximity of dis-connecting points thereof at their shells at least in a flange area with an additional layer.

17. An airfoil according to claim 16, wherein said spar section segment have at their disconnecting points laterally at said form bar units transverse force connection layers.

18. An airfoil according to claim 17, wherein said layers are laminates.

19. An airfoil according to claim 16, wherein said spar section segments have at their disconnecting points longi-tudinal bores and transverse bores for receiving connecting elements.

20. A method for manufacturing an airfoil consisting essentially of a plurality of modular sections including a lead-ing section, a trailing section and a spar section intermediate said leading and trailing sections comprising the steps of manu-facturing said spar section in two separate mold shells as two spar section parts, said spar section parts being formed to in-clude foam bars, trimming projecting portions of said foam bars along a junction plane and releasing one spar section part from its mold and joining it to the other spar section part at said junction plane.

21. A method according to claim 20, wherein said mold shells are thickened at longitudinal sides of said spar section with a strip in such a manner that a passage is provided for attachment to said spar section of said leading section on one longitudinal side and said trailing section on the other longi-tudinal side.

22. A method according to claim 21, wherein said lead-ing section and/or said trailing section are formed as laminar structures in one or several molds.

23. A method according to claim 22, wherein transverse force connecting layers are applied to said airfoil after assembly of said spar section parts.

24. A method for forming an airfoil consisting essen-tially of a plurality of modular sections including a leading section, a trailing section and a spar section intermediate said leading and trailing sections comprising the steps of: forming said spar section in two parts which constitute, respectively, an upper part and a lower part of said spar section of said airfoil;
said upper part and said lower part being formed each on one side thereof to define, respectively, an upper portion and a lower portion of the aerodynamic profile of said airfoil; joining said upper and lower parts together to form said spar section; and forming said leading and trailing sections as separate modular sections of said airfoil and assembling said preformed leading, trailing and spar sections together to form said airfoil.

25. A method according to claim 24, wherein said upper and lower parts are laminates prepared by a process including at least one of a manual laminating process, a "prepreg" process or a vacuum injection process.