GB1567968A

GB1567968A - Stressed skin elements such as wings or rotor blades

Info

Publication number: GB1567968A
Application number: GB52355/77A
Authority: GB
Original assignee: HUETTER U
Current assignee: HUETTER U
Priority date: 1976-12-24
Filing date: 1977-12-16
Publication date: 1980-05-21
Also published as: SE7714440L; DE2658876C3; DE2658876A1; DE2658876B2; FR2375033A1

Description

(54) STRESSED SKIN ELEMENTS SUCH AS WINGS OR ROTOR BLADES (71) I, ULRICH HijTTER of Schlierbacher Strasse 93, D-7312 Kirchheim/Teck, West Germany a Citizen of the German Federal Republic do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement The invention relates to stressed-skin elements of the kind having an outer skin (or shell) of reinforced material and a mounting rim located at or adjacent to a connection end by which the stressed-skin element is to be connected to a neighbouring part, at least some of the reinforcing material passing around the mounting rim in the form of a loop.

By stressed-skin element is meant an element in which the outer skin (or shell) is of reinforced material so as to carry a major share of any load to which it is subjected.

Such an element is normally made by a composite construction method in which the reinforced material is produced from a material, preferably a synthetic material, strengthened with fibre or strip-type reinforcement (fibre strands, woven strips or the like).

Thus, the element may be the aerofoil wing for an airplane or a rotor blade for a helicoptor rotor or fan, or the like.

The invention has particular use for the rotor blades of wind energy converts; however, its application to other stressedskin element is also possible, for example, heavily loaded rod-type building construction support elements made of plastics or concrete with high-strength fibre reinforcement, preferably using small-diameter fibres.

In the more detail "composite construction" means that the basically selfsupporting stressed-skin element is produced by the known fibre-matrix composite technique, for example, from fibrereinforced synthetic material, preferably in the form of multi-layer laminates. Materials for the fibre or strip-type reinforcement material include, for example, glass, carbon, silicon carbide or similar substances, which can be used in the form of, for example, fibre threads, strips of tissue, fabric woven at right angles or diagonally, or in the form of non-woven short-fibre matting. Polyester resin or epoxy resin are preferably used as the matrix material. The stressed-skin element may be produced in one piece, or it may also be assembled from several stressed-skin parts, in the same way, for example, as the shell of a mussel is made up of two halves.The stressed-skin element may be filled with a lightweight packing material and/or the stressed-skin element may be strengthened with ribs or other supporting elements; measures of this kind do not affect the invention, however.

For some time attempts have been made to find a connection for this type of stressedskin element which is as stable as possible and which at the same time can be produced at a resonable cost, for connecting the stressed-skin element to an adjacent part, for example attaching an aerofoil wing to the fuselage of an aeroplane, or a rotor blade to its rotor hub, or two parts of a rotor blade to each other.

A stressed-skin element made as a rotor blade is known from U.S. Patent Specification 2 182 812 which has, in the vicinity of the end by which it is to be connected, a mounting rim flange embedded in the construction material. around which some of the reinforcing material is passed in the form of a loop. The air here is to form a peg-shaped connecting end. where the peg has an annular rim on its outer circumferential surface. The peg is then clamped in pincer-fashion by a two-part component appertaining to the rotor hub. the annular rim engaging in the said part of the hub is form-locked. The cross-section of the rim flange is of rectangular, triangular or similar shape with slightly rounded corners.

This known construction method is not only very expensive, due to the construction of the hub being in several parts; in addition, it has the disadvantage that, for example, when the rotor blade is subjected to tensile or bending stress, extremely high stress peaks may occur in the fibrereinforced material, particularly in the transitional region of the rim flange, which can result in a fracture.

Another stressed-skin element is known from German Patent Specification No. 1 045 810 which has a so-called loop-connection.

In this instance a plurality of loops are formed from the reinforcing material at the connection end of the stressed-skin element, forming as a whole a flange with which the stressed-skin element can be attached to a neighbouring part. In this instance, therefore, the connection end of the stressed-skin element no longer has to be encircled and clamped by a mult-part hub. However, it has been found that in this instance also, despite careful design of the transition from the shell to the flange, high stress peaks may occur.

It is therefore an object of the invention to produce such a stressed-skin element wherein its connection to a neighbouring part can be accomplished as simply as possible, and so that at the same time high stress peaks are avoided as far as possible.

According to this invention, a stressedskin element of the kind discussed above is characterised in that the mounting rim has a substantially pear-shaped cross-section which forms a rounded head on the end nearest to the neighbouring part and which on the opposite end to the head end has a smoothly tapered tail end.

The invention is based on the realisation that to avoid the occurrence of stress peaks in the material of the shell, the reinforcement at or adjacent to the connection end of the stressed-skin element must lie as straight as possible, and must lie generally in the effective direction of the forces which occur, e.g. centrifugal force. or at any rate they must only form very large radius curves.

Therefore, in accordance with the invention. from the self-supporting part of the shell the matrix material and the reinforcing material of the stressed-skin element run without any very great change in direction along the side faces of the rim flange up to the head end. There, a relativelv small radius curve to reverse the direction of the reinforcing material by about 1800 is unavoidable. However, due to the substantially pear-shaped and therefore elongated cross-section of the rim flange, the side faces of which are very long, a large bonding connection surface is available between the material of the shell and the mounting rim.

This means that the forces which arise in the material of the shell when the stressedskin element is loaded are largely dispersed and conducted away into the mounting rim.

These means and the provision of a wellrounded shape for the head ensures that the stresses in the material of the shell remain within tolerable limits even in the vicinity of the head end of the mounting rim.

The tapering shape of the tail end of the mounting rim, i.e. tapering away to a point, is crucial for achieving a gradual (stepless) transition from the self-supporting, stressedskin element part to the region of the rim, which also prevents the occurrence of stress peaks. At all events, the entire tail end of the rim need not be made of the same material, preferably metal, as the main part of the rim. On the contrary, since a reduction in the length of the said lateral bonding connection surfaces can be made with a tail end made of synthetic material. In other words: the outer region of the tail end of the rim may be rounded off or bevelled, so that between the material of the shell and the rim a small gusset is formed which is filled in with matrix material when the rim is embedded.

The rim can have a circular shape if the stressed-skin element is to have a peg-type connecting end. However, many other shapes may also be used. Thus, it will frequently be necessary to adapt the rim flange to the aerodynamically favourable cross-section of an aerofoil wing or rotor blade.

Progressing on from this, an important concept of the invention is concerned with the problem of connecting the rim embedded in the stressed-skin element to the neighbouring part. If, as in the case of U.S.

Patent Specification 2 182 812, it is desired to clamp the connecting end of the stressedskin element according to the invention in a two-part hub. then there is a danger that very high compression stresses may occur locally in the material of the shell. Since the matrix material used for the shell is generally very brittle, compression points such as these could cause local internal stress or might be the starting point for cracks. which under certain circumstances could lead to damage to the stressed-skin element.

To eliminate this danger it is proposed that the rim which is preferably made of a metal, be connected to the neighbouring part by means of a direct connection which transmits tensile and compression forces and therefore also bending moments. This can be satisfactorily effected in that in or on the rim holes or tapped holes are provided, into which bolts are inserted or screwed.

Care has only to be taken here to ensure that the reinforcing material is passed round the holes. In a similar way, the rim can also be made with bolts moulded or welded onto it. In either case, the forces conducted from the shell via the said large-area bonding surfaces into the rim can be directly transmitted from this into the neighbouring part via the connecting element provided.

To contain the connecting elements, holes preferably in the form of tapped blind holes can be provided directly in the head end of the rim flange. However, at the head end of the rim eyes can also be provided to take the connecting elements. These eyes can continue into the rim. Preferably, however, the eyes are arranged more on the outside of the rim flange so that they are suitable for connecting elements which pass through them.

The rim can have the said substantialy per-shaped cross-section continuing along its overall length. This design is recommended for the most stable design possible for the connection end of the stressed-skin element, i.e. if both the inner and the outer surfaces of the rim are to form a bonding connection with the greatest possible surface. Conversely, when the rim should be as light in weight as possible, the connecting elements, such as bolts, for example, can project into the space inside the rim which is to be filled up with lightweight material, so that after the filling process the bolts are additionally secured. Ribs can also be provided in this case.

In order to obtain the most gradual transition with regard to the rigidity of the shell and mounting rim material. in the transition from the selfsupporting shell part to the connection end of the stressed-skin element, cut-outs may be provided in the rim in the vicinity of the tail end of the rim.

The provision of an external supporting ring can ensure that the adhesion of the reinforcing material on the rim which is very important for the success of the measures according to the invention, remains permanent even when subjected to alternating stresses. An external supporting ring of this kind is also preferably produced by the composite construction method. When the stressed-skin element has been assembled it serves at the same time to secure the connection between the parts of the shell.

An additional reinforcement of the connection end of the blade can be achieved by the provision of an inner supporting ring.

An inner supporting ring of this kind is preferably produced before the actual stressed-skin element is produced; it can be made in one or more parts; it may be produced from a metal substance or by the composite construction method.

A concave shape of the outer side surfaces of the rim is particularly advantageous when the above-mentioned external supporting ring is provided. This can be moulded into the concave region of the rim in such a way that a completely smooth curve is obtained for the outer surface of the shell. As a general rule, due to the concave shape of the external side surface of the rim, the head end of the rim is inclined slightly outwards. Conversely, if it is desired that the head end of the rim should be inclined inwards, so that the outer skin of the stressed-skin element is drawn inwards, then it is advisable to shape the rim with a concave and convex curve.

In order to ensure that the stressed-skin element is well centred, particularly if a rotatably mounted rotor blade is concerned, in the neighbouring part a complementary part conforming to the shape of the connection end of the stressed-skin element is provided through which the forcetransmitting connecting elements are appropriately passed. Good conformity for this complementary part can be obtained satisfactorily by producing the complementary part by the composite construction method as well, and by assembling all the parts, for example, a rotor blade with its hub, before the complementary part has hardened. During this assembly, if required, an exact alignment of the rotor blade can be carried out. A complementary part of this kind also has the advantage that transverse forces can be better transmitted from the stressed-skin element to the neighbouring part.

In order that the invention is readily understood a number of constructional examples of the invention are described in the following, with reference to the accompanying drawings, in which: Figure 1 shows in longitudinal section, the connection to its hub of a stressed-skin element designed as a rotor blade.

Figure 2 shows the connecting point between two parts of the rotor blade of a wind energy converter.

Figure 3 is a cross-section along the line III-III in Figure 2, on a larger scale.

Figure 4 is a detail from Figure 3, on an even larger scale.

Figure 5 is a modified connection form, different from that shown in Figure 1.

Figures 6 to 8 show different constructions of the mounting rim in the form of a flange of a stressed-skin element.

Figure 9 shows a further version of the connection between the stressed-skin element and the hub element.

Figure 9a is a section along the line a- a in Figure 9.

Figure 10 is a further example of a connection between two stressed-skin elements.

The rotor blade shown in Figure 1 comprises two shell halves 11 and 12, each with a mounting rim flange half 13 and 14 respectively. The rim flange 13, 14 shown is a rotation element with a slender, pearshaped cross-section. Further, along the cross-section, the rim flange forms a relatively thick head 15; at this point the thickness of the rim flange is at its greatest.

The head 15 is rounded, with a radius which is approximately half the thickness of the head. The thickness of the inner end 16 (or tail end) diminishes to a point. As shown, the transition from the head to the tail end is gradual and the external side surfaces 17 are concave.

The shell material 18, at its normal thickness s, extends around the rim flange 13 from the inside of the blade and then gradually diminishes along the external face of the blade, i.e. the thickness of the continuing flap 19 of stressed-skin beginning at the tail end 16 of the rim flange is reduced smoothly to zero.

An external support ring, preferably produced from the same material as the shell, is designated 20, and is wrapped round the blade after the two shell parts 11 and 12 are assembled. An inner support ring 21 can similarly be provided; this may also be produced from fibre-reinforced synthetic material or from a metal substance.

A hub in which the blade is to be rotatably mounted is indicated at 21a with dashed lines. The blade is connected to a bearing flange 23 by means of bolts 22.

Tapped holes are provided for the bolts 22 in the rim flange 13, 14. The bearing flange 23 has a complementary part 24 closely corresponding to the end of the blade.

The manner in which the shell 18, 19 is connected to the bearing flange 23, provides a connection which is tension, compression, bending and torsion resistant; it provides for form-locking supported by force-locking, as is the case with a good seaman's knot.

Figure 2 shows in detail a rotor blade of a wind energy converter which has been devided into two halves 30 and 31 because of its extreme length. Each of these blade halves 30 and 31 is assembled in turn from two shell halves, e.g. 32 and 33. The ends of the two blade halves 30 and 31 which are to be connected together both have a rim flange 34, 35 or 36, constructed according to the invention. In this case the rim flanges do not form a rotation element (as in the example shown in Figure 1), but are completely adapted to the contour of the aerofoil blade (see Figure 3).

An intermediate moulded part 40 -is clamped between the two ends of the blade.

The clamping together of the two blade halves 30 and 31 is achieved bv a plurality of double-ended studs 37 with opposite hand threads on the two shanks. Each of the two shell halves 34 and 35 is secured against the other by means of pins 38.

Each blade half 30, 31 has in turn an external supporting ring 41 or 42. due to the concave shape of the outside face of the rim flange, the external supporting rings lie completely inside the normal outer limits of the blade. Inner supporting rings are designated 43 and 44.

As can be seen clearly in Figure 4, the end faces of the two rim flange halves 34 and 35 which are facing each other must be chamfered to an acute angle. It may therefore be necessary for the shell material (e.g. 45) also to cover the end face 46 of the rim flange 34.

The layer of adhesive between the two half shells 32 and 33 is designated 47 in Figure 4.

In the constructional example according to Figure 5 of the complementary part designated 24 in Figure 1 is omitted. Instead. the bolts 52 which are used to connect the rim flange 50 to the bearing flange 51 have a collar 53 arranged as a spacer between the said parts 50 and 51. For this purpose the head of the rim flange 50 has to be made somewhat wider than in the examples described previously.

The rim flange half 55 shown in elevation in Figure 6, for the half shell of a stressedskin element, has several more or less evenly distributed cut-outs 56 in its tail end.

Several eyes are arranged at the head end, each with a tapped blind hole 58 for bolting the rim flange onto the neighbouring part.

Two holes 59 for dowels are provided for lining up one rim flange half 55 with the other rim flange half appertaining to it.

If the bolted connection between the stressed-skin element and the neighbouring part remains accessible on the face of the stressed-skin element, then, as shown in Figure 7. on the outer face of the rim flange 60 eyes 61 can be provided for bolts to be inserted (indicated at 62 with dashed lines).

Figure 8 shows an assembled rim flange in cross-sectlon. It comprises a head part 65 with tapped holes 66 through it and a wall part 68 which forms the tail end and the inner face area 67. Head and wall parts are welded together. Between each two tapped holes 66 a rib 69 can be welded on for added strength. The end of a bolt with a slot is indicated at 70 in dashed lines. Bolts of this kind can be screwed into the rim flange 65, 68 before the moulding of the shell. and then the spaces between the ribs 69 can be filled in which synthetic material, thus locking the bolts 70 at the same time. A rim flange shaped as shown in Figure 8 can also be produced by casting methods.

Figure 9 shows an example of the connection of a stressed-skin element 71 to its neighbouring part (bearing ring 72), where neither of the two ends of the clamping bolts 73 is accessible. This is also generally the case when two blade parts abut against each other at the connection, as shown in Figures 2 or 10. The two shanks of the clamping studs (or turn-buckles) 73 have oppositehand threads. The diameter of the central section of the clamping stud is slightly greater than the external diameter of the thread. An adjusting ring or sliding grooved ring 76 with hexagonal exterior is provided for drawing in the clamping stud 73, with two corresponding keys 74, so that it is rotationally fixed but axially movable. The rim flange is designated 75, a complementary part 77, and a spacer ring 78. A roller bearing for mounting the stressed-skin element 71 rotatably is indicated at 79.The sliding grooved ring 76 must be axially movable on the clamping stud 73, since it must lie firmly against both the complementary part 77 and the spacer ring 78, so that all the parts are in fixed contact with each other, and it can never be exactly determined in advance which position the sliding grooved ring 76 will assume relative to the clamping stud. In the constructional form, the sliding grooved ring 76 also acts as a spacer ring between the parts 71, 75, 77 on one hand and 72, 78 on the other hand, which are to be connected together.

In the alternative version shown in Figure 10, intermediate shaped parts 80 are provided as spacers, being adapted to the shape of the connection ends of the two stressedskin elements 81 which are to be connected to each other. The gaps which remain free initially for the clamping studs 83 are filled up with synthetic material after assembly has been completed. The difference between the construction shown in Figure 2 and that shown in Figure 10 is that the head ends of the rim flanges 84 and 85 in Figure 10 are inclined from the smooth outer contour 86 towards the inside, and that the outer side surfaces 88 or 89 of the rim flange, beginning at the head end. are first convex and then concave in shape. After this, as shown in Figure 10, there can be another slightly convex section which continues up to the tail end.Corresponding to this, the inner side surfaces which lie opposite these have, beginning at the head end, first a concave, then a convex, and if required, finally a concave shape. This means that on each rim flange 84 or 85, two inner supporting rings 91, 92 or 93, 94 respectively can be provided and, as in Figure 2, each can also have an external supporting ring 95 of 96 respectively. The latter conform to the outer profile contour.

WHAT I CLAIM IS: 1. A stressed-skin element of the kind having an outer skin (or shall) of reinforced material and a mounting rim located at or adjacent to a connection end by which the stressed-skin element is to be connected to a neighbouring part, at least some of the reinforcing material passing around the mounting rim in the form of a loop, characterised in that the mounting rim has a substantially pear-shaped cross-section which forms a rounded head on the end nearest to the neighbouring part and which on the opposite end to the head end has a smoothly tapered tail end.

2. A stressed-skin eleement according to Claim 1, characterised in that said element is connected to the neighbouring part by a connection which directly transmits tension and compression forces from the mounting rim to said neighbouring part.

3. A stressed-skin element according to Claim 1 or 2, characterised in that holes are provided directly in the head end of the mounting rim for taking connecting elements.

4. A stressed-skin element according to any one of Claims 1 to 3, characterised in that eyes are provided in the head end of the mounting rim for taking connecting elements.

5. A stressed-skin element according to Claim 4, characterised in that the eyes are attached on the outer face of the mounting rim for taking connecting elements, which latter are inserted through them.

6. A stressed-skin element according to one of Claims 1 to 5, characterised in that the mounting rim has a metal head part and a metal wall part which extends along a lateral boundary, and comprises the tail end of the mounting rim, being completed by a light weight material up to the finished form of substantially pear-shaped cross-section.

7. A stressed-skin element according to Claim 6. characterised in that the mounting rim has ribs in the areas between the holes for the connecting elements, in the vicinity of which the mounting rim displays the finished form of substantially pear-shaped cross-section.

8. A stressed-skin element according to any one of Claims 1 to 7, characterised in that the mounting rim has a plurality of spaced out cut-outs which extend in the direction of the head end.

9. A stressed-skin element according to any one of Claims 1 to 8, characterised in that the cross-section of the mounting rim is thickest in the vicinity of the head end the thickness decreasing continuously to the tail end.

10. A stressed-skin element according to anv one of Claims 1 to 9. characterised in that the ratio between the greatest thickness and the length of the cross-section of the mounting rim is around 1:1.5 to 1:8, and is preferably from 1:3 to 1:5.

11. A stressed-skin element according to any one of Claims 1 to 10. characterised

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

73 is accessible. This is also generally the case when two blade parts abut against each other at the connection, as shown in Figures 2 or 10. The two shanks of the clamping studs (or turn-buckles) 73 have oppositehand threads. The diameter of the central section of the clamping stud is slightly greater than the external diameter of the thread. An adjusting ring or sliding grooved ring 76 with hexagonal exterior is provided for drawing in the clamping stud 73, with two corresponding keys 74, so that it is rotationally fixed but axially movable. The rim flange is designated 75, a complementary part 77, and a spacer ring 78. A roller bearing for mounting the stressed-skin element 71 rotatably is indicated at 79.The sliding grooved ring 76 must be axially movable on the clamping stud 73, since it must lie firmly against both the complementary part 77 and the spacer ring 78, so that all the parts are in fixed contact with each other, and it can never be exactly determined in advance which position the sliding grooved ring 76 will assume relative to the clamping stud. In the constructional form, the sliding grooved ring 76 also acts as a spacer ring between the parts 71, 75, 77 on one hand and 72, 78 on the other hand, which are to be connected together.

In the alternative version shown in Figure 10, intermediate shaped parts 80 are provided as spacers, being adapted to the shape of the connection ends of the two stressedskin elements 81 which are to be connected to each other. The gaps which remain free initially for the clamping studs 83 are filled up with synthetic material after assembly has been completed. The difference between the construction shown in Figure 2 and that shown in Figure 10 is that the head ends of the rim flanges 84 and 85 in Figure 10 are inclined from the smooth outer contour 86 towards the inside, and that the outer side surfaces 88 or 89 of the rim flange, beginning at the head end. are first convex and then concave in shape. After this, as shown in Figure 10, there can be another slightly convex section which continues up to the tail end.Corresponding to this, the inner side surfaces which lie opposite these have, beginning at the head end, first a concave, then a convex, and if required, finally a concave shape. This means that on each rim flange 84 or 85, two inner supporting rings 91, 92 or 93, 94 respectively can be provided and, as in Figure 2, each can also have an external supporting ring 95 of 96 respectively. The latter conform to the outer profile contour.

WHAT I CLAIM IS: 1. A stressed-skin element of the kind having an outer skin (or shall) of reinforced material and a mounting rim located at or adjacent to a connection end by which the stressed-skin element is to be connected to a neighbouring part, at least some of the reinforcing material passing around the mounting rim in the form of a loop, characterised in that the mounting rim has a substantially pear-shaped cross-section which forms a rounded head on the end nearest to the neighbouring part and which on the opposite end to the head end has a smoothly tapered tail end.
2. A stressed-skin eleement according to Claim 1, characterised in that said element is connected to the neighbouring part by a connection which directly transmits tension and compression forces from the mounting rim to said neighbouring part.
3. A stressed-skin element according to Claim 1 or 2, characterised in that holes are provided directly in the head end of the mounting rim for taking connecting elements.
4. A stressed-skin element according to any one of Claims 1 to 3, characterised in that eyes are provided in the head end of the mounting rim for taking connecting elements.
5. A stressed-skin element according to Claim 4, characterised in that the eyes are attached on the outer face of the mounting rim for taking connecting elements, which latter are inserted through them.
6. A stressed-skin element according to one of Claims 1 to 5, characterised in that the mounting rim has a metal head part and a metal wall part which extends along a lateral boundary, and comprises the tail end of the mounting rim, being completed by a light weight material up to the finished form of substantially pear-shaped cross-section.
7. A stressed-skin element according to Claim 6. characterised in that the mounting rim has ribs in the areas between the holes for the connecting elements, in the vicinity of which the mounting rim displays the finished form of substantially pear-shaped cross-section.
8. A stressed-skin element according to any one of Claims 1 to 7, characterised in that the mounting rim has a plurality of spaced out cut-outs which extend in the direction of the head end.
9. A stressed-skin element according to any one of Claims 1 to 8, characterised in that the cross-section of the mounting rim is thickest in the vicinity of the head end the thickness decreasing continuously to the tail end.
10. A stressed-skin element according to anv one of Claims 1 to 9. characterised in that the ratio between the greatest thickness and the length of the cross-section of the mounting rim is around 1:1.5 to 1:8, and is preferably from 1:3 to 1:5.
11. A stressed-skin element according to any one of Claims 1 to 10. characterised

in that in the transitional region from the mounting rim to the reinforced material shell of the element a tension band is provided as an outer supporting ring, preferably made from the same material as the shell.
12. A stressed-skin element according to Claim 11, characterised in that the tension band is wound parallel to and/or inclined to a plane normal to the axis.
13. A stressed-skin element according to any one of Claims 1 to 12, characterised in that in the transitional region from the mounting rim to the reinforced material shell there is an inner supporting ring.
14. A stressed-skin element according to any one of Claims 1 to 13, characterised in that, viewed in cross-section, at least a considerable part of the outer side face of the mounting rim is concave.
15. A stressed-skin element according to any one of Claims 1 to 13, characterised in that, viewed in cross-section, the outer side face of the mounting rim beginning from the head end is first convex and then concave.
16. A stressed-skin element according to one of Claims 1 to 15, characterised in that between the connection end of the mounting rim and the neighbouring part there is a shaped part which closely conforms with the shape of the connection end.
17. A stressed-skin element according to Claim 16. characterised in that the shaped part is produced by a composite construction method as defined herein.
18. A stressed-skin element according to any one of claims 1 to 17 which is assembled from a plurality preferably two of shell parts, characterised in that the mounting rim is made of a pluralitv of parts corresponding to the number of shell parts, and that the mounting rim parts engage with each other form-locked by means of pins, projections, bolts or the like.
19. A stressed-skin element according to any one of Claims 1 to 18. characterised in that the metal mounting rim has a roughened surface to produce better adhesion between it and the reinforced material of the shell.
20. A stressed-skin element according to any one of Claims 2 to 19, characterised in that clamping studs are provided as the connecting elements between the mounting rim and the neighbouring part having opposite hand threads on their shanks, and an adjusting ring is provided on the central section of each clamping stud which is rotationally fixed but can be displaced axially.
21. A stressed-skin element constructed arranged and adapted to operate substantially in accordance with any one of the examples as hereinbefore described with reference to the accompanying drawings.