Patent Publication Number: US-2012036798-A1

Title: Tower for a Wind Power Installation

Description:
The invention relates to a method for constructing a tower for a wind power installation and to a tower for a wind power installation. 
     A wind power installation is an apparatus for generating electric energy. The wind power installation is provided with a foundation, a tower which is constructed on the foundation and a nacelle which is arranged on the tower. The drive unit connected to rotor blades is situated on the nacelle for generating energy. 
     The structure of the tower is oriented to the static load generated by the nacelle on the tower and the dynamic loads generated by the rotation of the rotary blades of the rotor and by the movement possibility of the nacelle in dependence on the direction of the wind. Known towers are produced from steel rings or concrete elements. The bases of the known towers, in this case, are either polygons or ring-shaped circle segments. 
     Polygonal towers, which are produced from individual concrete segments, are known from WO 2003/069099 A. In addition, constructing such polygonal towers from timber is known (DE 10 2007 006 652 A1). 
     Looked at from an economic point of view, it is desirable to construct the height of the towers in an economically maximized manner as the return of a wind power installation depends on the hub height of the rotor and the return increases as the height increases. At the same time the demands on the statics of the tower and the material of the tower created by the greater height of the tower increase. The wall thicknesses increase and this means that the costs of constructing the tower increase. 
     Apart from the operating stresses which act on the tower, climatic stresses also act on the tower. In the case of steel towers, this climatic stress is counteracted by applying a coat of paint onto the tower. Where reinforced concrete is used, the steel framework absorbs the tensile stresses of the tower. The concrete covering absorbs the pressure loads and at the same time serves to protect the steel structure against environmental influences in the form of moisture and chemical reactions caused by the surrounding atmosphere. The thickness of the concrete has to ensure that the steel framework is protected from these loads. In the case of timber structures, corresponding meteorological stresses are counteracted by coats of paint. At the same time, it is only possible to use timber materials that are authorized for exterior use for the construction of timber towers. 
     Consequently, it is the object of the invention to provide a method for constructing a tower for a wind power installation and to provide a tower for a wind power installation, where it is possible to increase the height of the structure and at the same time to save on material and/or to reduce production costs. 
     With regard to said method, the object as claimed in the invention is achieved in that a coating is applied at least partially onto the exterior surface of the tower, and the coating is applied such that the coating absorbs tensile stresses which act on the exterior surface of the tower, and that the coating seals the exterior surface of the tower against environmental influences, in particular humidity, which act on the surface from the outside. 
     With reference to steel towers, a coating of this type makes it possible to reduce the amount of steel necessary with regard to tensile stresses as the coating absorbs tensile stresses, and at the same time to save on the painting of the steel elements. With regard to concrete towers, it is possible to reduce the concrete covering over the steel framework such that there is a reduction in costs. With regard to timber towers, the coating makes it possible to use timber materials and their connection means that are only authorized for interior use. 
     A further teaching of the invention provides that the coating is applied over the entire surface in the coated section of the tower and covers the coated section. In this case it is advantageous for the coating to be a laminate, a foil, a woven fabric, a textile or a plate. In a particularly preferred manner, it is a foil, a plate, a woven fabric and/or textile produced from plastics material, wherein, in a particularly preferred manner, polypropylene, polyurethane, polyvinyl chloride, polyester, polycarbonate or polythene are used as the materials. Such materials are capable of absorbing tensile stresses and at the same time provide a closure and consequently a seal against the environmental influences which act on the surface of the tower. At the same time, such materials have a lower weight per surface area than, for example, coats of paint on the surface of the tower such that this weight is able to be reduced in the structure with regard to the static pressure load, as a result of which the tower structure is able to be designed overall in a more slender manner. At the same time, the costs of said materials are lower than, for example, coats of paint. 
     A further teaching of the invention provides that the coating is applied at various points during the constructing of the tower. The coating is applied once the tower has been constructed as the first variant. This can be effected from the top or bottom. As an alternative, the coating can be applied in sections during the construction of the tower or can be applied onto the individual components even before the tower is constructed. If the coating is applied before the tower is constructed, it has proved advantageous for the coating to be applied on site at the place of construction. This reduces the costs of the coating and at the same time it can be ensured that the coating is not damaged when the individual elements are being transported. The individual sections of the coating are subsequently connected together, wherein, in a particularly preferred manner, the connecting is effected by bonding or welding the joints. 
     A further teaching of the invention provides that the coating is applied directly onto the components of the tower. In a preferred manner, the applying is effected over the entire area by means of bonding. As an alternative to this, bonding can also be effected in sections to a surface of a component. The bonding ensures that the static load is absorbed by the coating. 
     A further teaching of the invention provides that the tower is constructed at least in part from steel, concrete, in particular reinforced concrete, and/or timber. In a preferred manner, the timber is laminated plywood and/or wood composite materials. 
     A further teaching of the invention provides that, where timber is used as tower material, the vapor permeability of the coating is less than that of the timber itself. In this way the diffusion is reversed, i.e. the vapor permeability of the tower is not increased towards the outside, but towards the inside. 
     A further teaching of the invention provides that heat is generated in the interior of the tower, wherein, in a preferred manner, in the case of wind power installations this is the power electronics of the wind power installation. The generation of heat causes the moisture located in the interior of the tower to be removed upwards and the moisture emerging from the timber to be moved towards the interior of the tower and then also removed upwards. If the coating is damaged, removal of the moisture inwards is ensured. Through the particles and minerals located in the moisture, the damage to the coating is gradually closed and at the same time it is additionally ensured that the moisture escapes towards the inside. 
     A further teaching of the invention provides that the support structure of the tower is constructed from materials which are not suitable for exterior use. In this case these are materials which have only been authorized for interior use in the construction of buildings. The applying of the coating makes it possible to use these types of materials and also connection means for the support structure of a tower for a wind power installation because the coating ensures the state of interior use for the materials. 
     A further teaching of the invention provides that the tower is assembled on site from individual components. 
     The components assembled on site are plane elements. Assembling the tower in this manner from individual plane elements ensures that the transport cost of the individual towers is reduced in a considerable manner. 
     A further teaching of the invention provides that the components of the tower are mounted in a helix. In this case, it is preferred that the helix is a simple helix or a multiple helix. 
     A further teaching of the invention provides that the upper joints of the individual components of a helix have either a continuous line or a graduation. 
     A further teaching of the invention provides that in the joints the components have slots which are arranged transversely to the direction of the joint. Connection means are inserted into said slots, said connection means, in a preferred manner, being metal plates, in a particularly preferred manner in this case, perforated plates. A further teaching of the invention provides that said connection means are inserted into the slots or openings and are bonded. In addition, the joint openings can be masked for example with a tape or Plexiglas. In a preferred manner, the insertion of the adhesive is effected by means of injecting the spaces between component and connection element. As an alternative to this, wood parts or wood dowels can be used when the components are timber elements. These connection means, on the one hand, are cost-efficient elements which certainly provide the necessary strengths with regard to shear or shear loads between the individual components. 
     With regard to the tower, the object as claimed in the invention is achieved in that the tower for a wind power installation is provided with a coating on the surface of the exterior of the tower, said coating absorbing at least part of the tensile stresses acting on the surface and sealing the surface of the exterior of the tower against the environmental influences, in particular moisture, which act on the surface from the outside. With reference to steel towers, a coating of this type makes it possible to reduce the amount of steel necessary with regard to tensile stresses as the coating absorbs tensile stresses, and at the same time to save on the painting of the steel elements. With regard to concrete towers, it is possible to reduce the concrete covering over the steel framework such that there is a reduction in costs. With regard to timber towers, the coating makes it possible to use timber materials and their connection means that are only authorized for interior use. 
     An advantageous teaching of the invention provides that the coating is applied onto the surface of the exterior of the tower at least partially over the entire area. The coating is a laminate, a foil, a woven fabric, and/or a textile or a plate. In a preferred manner, these are produced from plastics material, wherein, in a particularly preferred manner, this is a plastics material produced from polypropylene, polythene and/or polyurethane. Such materials are capable of absorbing tensile stresses and at the same time provide a closure and consequently a seal against the environmental influences which act on the surface of the tower. At the same time, such materials have a lower weight per surface area than, for example, coats of paint on the surface of the tower such that this weight is able to be reduced in the structure with regard to the static pressure load, as a result of which the tower structure is also able to be designed overall in a more slender manner. At the same time, the costs of said materials are lower than, for example, coats of paint. 
     A further teaching of the invention provides that the coating is bonded at least partially on the surface of the tower. In a preferred manner, the coating consists of individual sections which are connected together, wherein the connecting is effected in a preferred manner by means of bonding or welding. The bonding ensures that the static load is absorbed by the coating. 
     A further teaching of the invention provides that the tower is constructed at least partially from steel, concrete, in particular reinforced concrete, and/or timber. The timber is preferably laminated plywood and/or wood composite materials. 
     A further teaching of the invention provides that the vapor permeability of the coating is less than that of the timber. In this way the diffusion is reversed, i.e. 
     the vapor permeability of the tower is not increased towards the outside, but towards the inside. In addition, in a preferred manner, a heat generator is arranged in the interior of the tower, wherein, in a preferred manner, this is the power electronics of a wind power installation. The generation of heat causes the moisture located in the interior of the tower to be removed upwards and the moisture emerging from the timber to be moved towards the interior of the tower and then also removed upwards. If the coating is damaged, removal of the moisture inwards is ensured. Through the particles and minerals located in the moisture, the damage to the coating is gradually closed and at the same time it is additionally ensured that the moisture escapes towards the inside. 
     A further teaching of the invention provides that the support structure of the tower is constructed at least partially from materials which are not suitable for exterior use. In this case these are materials which have been authorized simply for interior use in the construction of buildings. The applying of the coating makes it possible to use these types of materials and also connection means for the support structure of a tower for a wind power installation because the coating ensures the state of interior use for the materials. 
     According to a further teaching of the invention, the tower is assembled on site from individual components. The individual components are preferably plane elements. Assembling the tower in this manner from individual plane elements ensures that the transport cost of the individual towers is reduced in a considerable manner. 
     A further teaching of the invention provides that the components are assembled to form a helix, wherein, in a preferred manner, this is a simple helix or a multiple helix. In a preferred manner, the upper joint sides of the individual components have a continuous line or a graduation. 
     A further teaching of the invention provides that in the joints the components have slots which are arranged transversely to the direction of the joint and/or longitudinally to the direction of the joint. Connection means, which, in a preferred manner, are metal plates, in a particularly preferred manner, perforated plates, which, in a preferred manner, are bonded, are inserted in a preferred manner into the slots. In addition, the joint openings can be masked for example with a tape or Plexiglas. In a preferred manner, the insertion of the adhesive is effected by means of injecting the spaces between component and connection element. As an alternative to this, wood parts or wood dowels can be used when the components are timber elements. These connection means, on the one hand, are cost-efficient elements which certainly provide the necessary strengths with regard to shear or shear loads between the individual components. 
    
    
     
       The invention is explained below by way of preferred exemplary embodiments in conjunction with a drawing, in which, in detail: 
         FIG. 1 : shows a three-dimensional view of a wind power installation with a tower as claimed in the invention, 
         FIG. 2 : shows a three-dimensional view of the tower as claimed in the invention, 
         FIG. 3 : shows the sides of the tower as claimed in the invention arranged next to each other, 
         FIG. 4 : shows an alternative embodiment of the tower as claimed in the invention, 
         FIG. 5 : shows an alternative embodiment of the tower as claimed in the invention, 
         FIG. 6 : shows an alternative embodiment of a tower as claimed in the invention, 
         FIG. 7 : shows an inside view of the wall elements in  FIG. 6 , 
         FIG. 8 : shows a three-dimensional view of a base element of a further alternative embodiment of the tower, 
         FIG. 9 : shows a three-dimensional view of the constructing of a tower in  FIG. 8 , 
         FIG. 10 : shows a three-dimensional representation of a connection means as claimed in the invention, 
         FIG. 11 : shows a view of a detail in  FIG. 10 , 
         FIG. 12 : shows a finished mounted view of  FIG. 10 , 
         FIG. 13 : shows an alternative connection possibility, 
         FIG. 14 : shows a sectioned view of a detail in  FIG. 13 , 
         FIG. 15 : shows an alternative connection possibility, 
         FIG. 16 : shows an alternative connection possibility, 
         FIG. 17 : shows a top view of  FIG. 16 , 
         FIG. 18 : shows a method for applying a coating, 
         FIG. 19 : shows a side view of a coated tower wall, 
         FIG. 20 : shows a side view of a wall structure as claimed in the invention, 
         FIG. 21 : shows a side view of an adapter for fastening a nacelle to a tower as claimed in the invention, 
         FIG. 22 : shows a top view of the underside of the connector, 
         FIG. 23 : shows a first embodiment of an adapter as claimed in the invention and 
         FIG. 24 : shows a second embodiment of an adapter as claimed in the invention. 
     
    
    
       FIG. 1  shows a wind power installation  30 , which consists of a tower  31  which stands on a foundation  32 , and a nacelle  33  which is connected to the tower  31  by means of an adapter  35 . A rotor  34 , which has rotor blades  36 , which are connected to the nacelle  33  in a hub  37 , is provided on the nacelle  33 , which is horizontally rotatable. 
     Different embodiments of the tower  31  are represented below. 
     As shown in  FIG. 2 , the tower  31  has an exterior side  38 . The tower  31  is realized as a polygon. In the present case this is a hexagon, other polygons, such as a tetragon, pentagon, octagon, decagon or dodecagon or larger are equally easily possible. The same also applies to a circular cross section. The tower  31  in  FIG. 2  has six tower sides  39  which, over their whole surface, can be realized in a conical manner. The tower sides  39  are formed from individual wall elements  40  which, where applicable, have a shortened wall element  41  on the bottom side and  42  on the top side. In the embodiment in  FIG. 2 , the wall elements  40  are realized as a tapered trapeze, wherein the individual wall elements can be assembled together from different part elements. The embodiment in  FIG. 2  has a helical structure. This can be seen in  FIG. 3  where the six sides are shown next to each other. In this case, the individual wall elements  39 , from side to side, are arranged offset in relation to each other always upwards by a sixth of the wall height, wherein, in this case, the dimensions of the individual wall elements  40  have been taken into consideration corresponding to the tapering of the individual tower sides  39 . The six wall elements, in this case, form a helix section  43 . This design ensures that the seventh-following wall element is arranged directly on top of the first wall element and these two wall elements stand one on top of the other on the side of the joint. In the case of other polygons, the offset is 1/n* height of the wall element  40 , wherein n is the number of polygon corners. These specifications also apply to the embodiments of the tower design in  FIG. 4  and  FIG. 5 . 
     According to the embodiment in  FIG. 4 , the tower  31  also has a simple helix design. The towers shown once again have six sides and each side has a bottom and a top closure element, where applicable in the form of a shortened wall element  41 ,  42 . The individual wall elements in between are tapered, wherein the bottom and top joint side are realized parallel to each other, but inclined upwards at an angle a in relation to the foundation side. The angle a, however, is selected in an advantageous manner such that it corresponds to 360° through the number of sides, so that once again where there are N sides, the N+1 wall element can once again be arranged on the first wall element of a helix section  43 . The bottom and top sides of the joints of the wall element  40 , in this case, form a continuous line  56 . 
     The embodiment in  FIG. 5  also represents a simple helix arrangement, wherein the embodiment in  FIG. 5  differs to the embodiment in  FIG. 4  in that the top and bottom sides of the wall elements  40  have three sections, which, in this case, are a first rising section  57 , a horizontal section  58  connecting thereto and a second rising section  59 . Overall this means that once again a continuous line  56  is formed, the ascent of which alters, however, with reference to the individual wall elements. 
       FIG. 6  shows a further embodiment of a tower  31  as claimed in the invention. The design of said tower comprises a multiple helix. The tower is constructed in the form of a base element  53  which stands on a foundation  32 . Tower elements  54  are placed onto the base element  53 . The tower is terminated by a closure element  55 , on top of which the nacelle  33  or the adapter  35  is then arranged. The base element  53  has a plurality of shortened wall elements  41 . The number of shortened wall elements  41  in the base element  53  represents the number of helix strands screw-connected together. If six shortened wall elements  41  are arranged in the base element  43 , this means that six helix turns have been rotated into each other. 
     In the representation in  FIG. 6  and  FIG. 7 , the wall elements  40  are designed as two triangles which are arranged offset by an angle to each other along a line  46 . The line  46 , in this case, is realized as exterior edge  46 . The two triangles form part surfaces  44  and  45 , as can be seen in  FIG. 7 . The base element  53  is shown in  FIG. 8 . In the current embodiment in  FIG. 8 , twelve shortened wall elements  41  are provided in the base element  53  such that, in total, twelve helix strands are rotated with each other. In the embodiment in  FIG. 8  and  FIG. 9 , however, the wall element is realized as circle segment  50 . The placing one on top of the other and the connecting of the individual tower elements  54  to each other or to the base element  53  is effected in an identical manner, however, irrespective of whether the wall elements are realized as a curved element or as a circle segment element. The individual tower elements  54  are either placed onto the tower element  54  or base element  53  lying below, pre-assembled with an intermediate plane  52  as shown in  FIG. 9 , or are mounted individually. 
     One type of connection connecting the individual wall elements  40  one to another, in this case, is shown in  FIG. 7 . The two joint surfaces  47  contacting each other in the mounted state are connected by way of a connection means, in the case of timber elements for example adhesive. In the case of steel elements, the joints can be welded. In addition, the joint surfaces can be provided with recesses  48  which are not provided over the entire width of the joint surface  47 , but terminate before perforating the outside wall surface  38 .  FIG. 7  shows the interior surface  51  of the tower wall such that the recesses  48  are visible. Connection means  49  are inserted into the recesses  48  and are subsequently connected to the wall elements  40 . The connection means  49  can be dowels or metal plates or sheets. Connecting is effected, for example, with adhesive which is injected into the recesses  48 . In addition, the outside surfaces of the recess can then be masked, for example, with adhesive tape or the like. However, the connection possibilities shown in  FIG. 7 , such as bonding the joints and providing recesses and inserting connection means, are not restricted in this case to the multiple helix embodiment. Such embodiments can also be used with the simple helix forms, such as shown in  FIGS. 2 to 5 . 
     More possibilities for connecting the wall elements to each other are shown below in  FIGS. 10 to 17 . 
     The connection of the wall elements  40  to each other can be effected in different ways. In this case, recesses  48  are provided in each case, connection means  49  being inserted into said recesses. Said connection means are then connected to the wall elements, for example by bonding or the like, in order to create a holding operative connection. Said operative connection can then absorb shear movements and the like or the stresses resulting therefrom. A further variant is shown in  FIG. 10 , in this case triangular or wedge-shaped recesses  48  are provided in the wall elements  40 . Adhesive can be applied to the joint surfaces  47  of the wall elements  40 . The same applies to the faces  64  of the recesses  48 . The connection means  49  is provided as a rhombic cuboid in the form of a dowel  61 . If timber is used as the material for the wall elements  40 , the dowels  61  are also wooden dowels. Said dowels  61  can either be inserted into the recesses  48  once the wall elements  40  have been positioned onto the joint surfaces  47 , or the dowels  61  are inserted into the recess  48  of the already mounted wall element  40  and the wall element lying above is placed onto the dowels by way of the recesses provided there and then arranged together on the joint surface  47  and locked by means of bonding or similar connection methods. The bonding is shown in  FIG. 11  as adhesive  60 . A more extensive representation of the wooden dowel  61  is shown in  FIG. 12 . 
       FIGS. 13 and 14  show the form of connection of the sheet elements marked out already for  FIG. 7  in slots. In the embodiment in  FIG. 13 , recesses  48  are provided in the wall elements  40  in the form of slots, said slots being admitted into the joint surface  47 , however not in a completely continuous manner from the interior surface  51  as far as the exterior surface  38  but leaving a residual wall element  65 . Perforated plates  62  are inserted into the slots  48 . Adhesive is once again applied onto the joint surfaces  47  and the next wall element  40  is placed with its recess  48  onto the perforated plates  62  on the wall. As an alternative to this, once again the wall elements can also be placed one on top of another and the perforated plates are inserted into the recesses  48  that are then present and, as shown in  FIG. 14 , are bonded with adhesive  60 . The end face of the perforated plates can then be covered in its turn by an adhesive tape or another suitable covering means. This also serves, among other things, as protection against corrosion. 
     A further embodiment of the connection possibility is shown in  FIG. 15 . In this case, the joint surfaces are provided along the face with recesses  48  in the form of grooves  63  parallel to the exterior surface  38  or interior surface  51  of the wall element  40 . Tongues as connection means  49  are inserted into said grooves  63 . The fastening of the tongues  63  in the grooves  64  is effected by means of adhesive  60 . The grooves  64  of the wall element  40  which is then to be arranged thereon are placed onto the tongues  63 . A further embodiment in this connection is shown in  FIGS. 16 and 17 . Recesses  48  in the form of a slot extending parallel to the exterior surface  38  or interior surface  51  of the wall element  40  are also provided here in the joint surfaces  47  of the wall elements  40 . Elongated plates  66  as connection means  49  are inserted into the slots  48  and are also bonded to each other. A top view of the joint surfaces  47  of the wall elements  40  with inserted plates  66  is shown in  FIG. 17 . 
       FIG. 18  shows the applying of a coating  69  onto a wall element  40 . A bonding device  67  is provided for this purpose, said bonding device spraying the adhesive  60  onto the tower exterior surface  38  of the wall element  40 . The coating  69 , which is provided as roll  68 , is applied directly after the spraying. The coating  69  is rolled onto the surface moistened with adhesive by the roll  68  and consequently applied onto the surface of the wall element  40 . The applying can be effected onto the individual sides  39  of the tower once the tower  31  has been constructed. As an alternative to this, each individual wall element can be directly coated before construction of an individual wall element, or the coatings are effected once the individual wall element has been attached to the tower such that the coating of the wall elements is effected in an individual manner in the mounted state. Once the coating  39  has been applied, the joints of the coating (not shown) are connected together such that the tower is covered in a continuous, entire manner by the coating  69 . The finished coated state is shown in  FIG. 19 . 
       FIG. 20  then shows the operating state of the wind power installation  30  and the vapor pressure gradient prevailing here, shown in the form of the moisture movement  71  and the removal of the moisture by means of heat dissipation  72 . The vapor permeability of the coating  69  is less than that of the material of the wall element  40 . This is especially necessary where timber is used because it ensures that moisture possibly passing through the coating  69  is removed from the transition region between coating and timber and also from the timber construction as such. The heat dissipation  72  influences the climatic conditions within the tower such that there is a water vapor gradient from outside to inside. The moisture that collects on the surface of the interior surface  51  of the tower  31  and has passed through the wall element  40  is entrained by the rising heat and is removed out of the tower  31  by said heat. The water vapor generated in this case rises and escapes from the tower. As an alternative to this or in addition to it, suction of the water vapor can also be provided. Consequently, a temperature gradient prevails in such a manner that the exterior temperature is lower than the temperature in the interior of the tower  31 . 
     As the connections for nacelles  33  with reference to the towers  31  are realized substantially in the shape of a segment of a circle, an adapter  35  as claimed in the invention is proposed, said adapter making possible a transition between the polygonal tower  31  and the circle segment-shaped connection of the nacelle  33 . For this purpose there is provided a side wall  76 , at the bottom end of which is provided a flange  73  which has bores  74 . The flange  73  is provided centrally with an opening  75 . The flange  73  is used for the purpose of being positioned on the polygonal joint surface  47  of the top-most section of the tower  31  and being connected to the tower by means of the bores  74 . Connection regions  74  for the nacelle  33  are provided on the upper section of the side wall  46 . Where applicable, it is possible for a reinforced section  78  to be provided on the side wall  76  in order to obtain better load-bearing capacity of the side wall  76 . 
     LIST OF REFERENCES 
     
         
           30  Wind power installation 
           31  Tower 
           32  Foundation 
           33  Nacelle 
           34  Rotor 
           35  Adapter 
           36  Rotor blade 
           37  Hub 
           38  Tower exterior surface 
           39  Tower side 
           40  Wall element 
           41  Shortened wall element 
           42  Shortened wall element 
           43  Helix section 
           44  Part surface 
           45  Part surface 
           46  Edge 
           47  Joint surface 
           48  Recess 
           49  Connection means 
           50  Segment 
           51  Tower interior surface 
           52  Intermediate plane 
           53  Base element 
           54  Tower element 
           55  Closure element 
           56  Continuous line 
           57  Rising section 
           58  Horizontal section 
           59  Rising section 
           60  Adhesive 
           61  Dowel 
           62  Perforated plate 
           63  Groove 
           64  Tongue 
           65  Residual region 
           66  Plate 
           67  Bonding device 
           68  Roll 
           69  Coating 
           70  Heat dissipation 
           71  Moisture movement 
           72  Heat dissipation 
           73  Flange 
           74  Bore 
           75  Opening 
           76  Side wall 
           77  Nacelle connection 
           78  Reinforced section