Patent Publication Number: US-9845612-B2

Title: System and method for assembling tower sections of a wind turbine lattice tower structure

Description:
FIELD OF THE INVENTION 
     The present subject matter relates generally to assembling wind turbine towers and, more particularly, to a system and method for assembling tower components to form a lattice or “space frame” tower structure for a wind turbine. 
     BACKGROUND OF THE INVENTION 
     Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture kinetic energy of wind using known airfoil principles. The rotor blades transmit the kinetic energy in the form of rotational energy so as to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy. A power converter typically regulates the flow of electrical power between the generator and a grid. 
     Wind turbine towers typically have a tubular pole or lattice structure configuration. Conventionally, the tubular pole configuration has been much easier to assemble than the lattice structure. However, tubular poles require the use of significantly more materials than lattice tower structures, thereby making the use of such towers quite expensive. Thus, it is often desirable to utilize lattice structures for supporting a wind turbine. Unfortunately, due to the number of components included within a lattice tower structure and the numerous joints that must be formed between the adjacent tower components, the assembly of a lattice tower structure is often quite complex and time consuming. 
     Accordingly, an improved system and method for assembling wind turbine tower components for use within an open, lattice tower structure would be welcomed in the technology. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     In one aspect, the present subject matter is directed to a system for assembling a tower section of a lattice tower structure for a wind turbine, wherein the tower section includes a plurality of support legs and at least one secondary support member coupled between each adjacent pair of support legs. The system may generally include a tower assembly fixture having a plurality of radially extending fixture arms, wherein each fixture arm extends between a first end and a second end. In addition, the system may include a plurality of trolleys. Each trolley may include a base frame configured to be coupled to a respective one of the fixture arms between its first and second ends and a leg mount pivotally coupled to the base frame. The leg mount may be configured to be coupled to a bottom end of a respective one of the support legs such that, when each of the support legs is coupled to its respective leg mount, the support legs are supported above the tower assembly fixture at a substantially vertical orientation. 
     In another aspect, the present subject matter is directed to a system for assembling a lattice tower structure for a wind turbine. The system may generally include a plurality of support legs and a plurality of secondary support members configured to be assembled together to form a tower section of the lattice tower structure. The system may also include a tower assembly fixture having a plurality of radially extending fixture arms, wherein each fixture arm extends between a first end and a second end. In addition, the system may include a plurality of trolleys. Each trolley may include a base frame configured to be coupled to a respective one of the fixture arms between its first and second ends and a leg mount configured to be coupled to a bottom end of a respective one of the support legs such that, when each of the support legs is coupled to its respective leg mount, the support legs are supported above the tower assembly fixture at a substantially vertical orientation so as to allow at least one secondary support member of the plurality of secondary support members to be installed between each adjacent part of support legs. 
     In a further aspect, the present subject matter is directed to a fixture trolley for use in assembling a tower section of a lattice tower structure for a wind turbine onto a tower assembly fixture. The trolley may generally include a base frame configured to be coupled to the tower assembly fixture and a leg mount pivotally coupled to the base frame. The leg mount may be configured to be coupled to a bottom end of a support leg of the tower section such that, when the support leg is coupled to the leg mount, the support leg is supported above the tower assembly fixture at a substantially vertical orientation. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
         FIG. 1  illustrates a perspective view of one embodiment of a wind turbine in accordance with aspects of the present subject matter, particularly illustrating the wind turbine including a lattice tower structure; 
         FIG. 2  illustrates a side view of the lattice tower structure of the wind turbine shown in  FIG. 1 , particularly illustrating the cladding of the wind turbine removed from the lattice tower structure; 
         FIG. 3  illustrates a perspective view of a bottom tower section of the lattice tower structure shown in  FIG. 2  installed relative to the foundation of the wind turbine; 
         FIG. 4  illustrates a perspective view of one embodiment of a tower assembly fixture for assembling a tower section(s) of the lattice tower structure shown in  FIG. 2 , particularly illustrating various components of the fixture being exploded away; 
         FIG. 5  illustrates a perspective view of the tower assembly fixture shown in  FIG. 4  as assembled, particularly illustrating a plurality of trolleys installed onto the fixture; 
         FIG. 6  illustrates a side view of one of the fixture arms of the tower assembly fixture shown in  FIGS. 4 and 5 , particularly illustrating the various radial locations along which a trolley may be installed onto the fixture arm; 
         FIG. 7  illustrates a perspective view of one embodiment of a tower section being assembled onto the disclosed tower assembly fixture, particularly illustrating various tower components of the tower section being exploded away from the fixture; 
         FIG. 8  illustrates another perspective view of the tower section shown in  FIG. 7 , with various cross-bracing members installed between adjacent support legs of the tower section; 
         FIG. 9  illustrates a perspective view of the tower section shown in  FIG. 8  with a separate tower section assembled on top thereof so as to form a vertical tower stack on the tower assembly fixture; 
         FIG. 10  illustrates another perspective view of one embodiment of a tower section being assembled onto the disclosed tower assembly fixture, particularly illustrating various tower components of the tower section being exploded away from the fixture; 
         FIG. 11  illustrates a perspective view of the tower section shown in  FIG. 10  with a separate tower section assembled on top thereof so as to form a vertical tower stack on the tower assembly fixture; 
         FIG. 12  illustrates a further perspective view of one embodiment of a tower section being assembled onto the disclosed tower assembly fixture; 
         FIG. 13  illustrates a perspective view of one embodiment of a trolley that may be installed onto the disclosed tower assembly fixture in accordance with aspects of the present subject matter; 
         FIG. 14  illustrates a side view of the trolley shown in  FIG. 13 , particularly illustrating a leg mount of the trolley pivoted to one position relative to a base frame of the trolley; 
         FIG. 15  illustrates another side view of the trolley shown in  FIG. 13 , particularly illustrating the leg mount pivoted to a different position relative to the base frame; 
         FIG. 16  illustrates a partial perspective view of the trolley shown in  FIG. 13 , particularly illustrating a support leg coupled to a top portion of the leg mount of the trolley; 
         FIG. 17  illustrates a perspective view of one embodiment of a nesting configuration that may be utilized to assemble multiple tower sections onto the disclosed tower assembly fixture at differing radial locations on the fixture in accordance with aspects of the present subject matter; 
         FIG. 18  illustrates a perspective view of one embodiment of an upend device for upending a support leg to be installed within a tower section of the disclosed lattice tower structure in accordance with aspects of the present subject matter; 
         FIG. 19  illustrates a side view of a support leg with the upend device shown in  FIG. 18  installed relative to the bottom end of the support leg; 
         FIG. 20  illustrates another side view of the support leg and the upend device shown in  FIG. 19 , particularly illustrating the support leg being pivoted upwardly away from the ground about the upend device; 
         FIG. 21  illustrates a close-up view of the upend device shown in  FIG. 20 ; 
         FIG. 22  illustrates another perspective view of the tower section shown in  FIG. 3  with the vertical tower stack shown in  FIG. 9  being lowered downward thereon via a crane; 
         FIG. 23  illustrates a partial flow diagram of one embodiment of a method for assembling a tower section of a lattice tower structure for a wind turbine in accordance with aspects of the present subject matter; and 
         FIG. 24  illustrates a continuation of the flow diagram for the method shown in  FIG. 23 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     In general, the present subject matter is directed to an improved system and method for assembling tower sections of a lattice tower structure for a wind turbine. In several embodiments, the system may include a tower assembly fixture and a plurality of trolleys configured to be installed onto the fixture. As will be described below, the fixture may include a plurality of radially extending fixture arms, with each fixture arm being configured to have at least one trolley installed thereon. In a particular embodiment, each trolley may include a base frame configured to be coupled to its corresponding fixture arm and a leg mount configured to be coupled to a support leg of the tower section being assembled on the fixture. The various support legs of the tower section may be coupled to the leg mounts of the trolleys such that each support leg is supported above the fixture at a substantially vertical orientation so as to allow one or more secondary support members of the tower structure (e.g., circumferential spacers and/or cross-bracing members) to be installed between each pair of adjacent support legs in order to complete the assembly of the tower section. 
     As will be described below, in several embodiments, each trolley may be configured to be removably coupled to its respective fixture arm such that the trolley may be installed at a plurality of different radial locations along the fixture arm. Such adjustment of the radial position of each trolley may allow for tower sections having differing radial dimensions to be assembled on the tower assembly fixture. Moreover, in one embodiment, the leg mount of each trolley may be pivotally coupled to its corresponding base frame. Such a pivotal connection may allow the angular orientation of the leg mount to be adjusted, thereby providing a means for supporting the support legs at plurality of different substantially vertical orientations. 
     Referring now to the drawings,  FIG. 1  illustrates a perspective view of one embodiment of a wind turbine  30 . As shown, the wind turbine  30  generally includes a tower  32  extending from a tower support surface or foundation  34  (e.g., the ground, a concrete pad or any other suitable support surface). In addition, the wind turbine  30  may also include a nacelle  36  mounted on the tower  32  and a rotor  38  coupled to the nacelle  36 . The rotor  38  includes a rotatable hub  40  and at least one rotor blade  42  coupled to and extending outwardly from the hub  40 . For example, in the illustrated embodiment, the rotor  38  includes three rotor blades  42 . However, in an alternative embodiment, the rotor  38  may include more or less than three rotor blades  42 . Each rotor blade  42  may be spaced about the hub  40  to facilitate rotating the rotor  38  to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. For instance, the hub  40  may be rotatably coupled to an electric generator (not shown) positioned within the nacelle  36  to permit electrical energy to be produced. 
     In several embodiments, the tower  32  may include a plurality of structural members (e.g., vertical, horizontal and/or diagonally extending structural members) coupled to one another so as to form an open lattice tower structure  50 . Such lattice tower structures  50  are also referred to in the art as “space fame” towers. In addition, the tower  32  may also include a cladding material  52  installed onto the lattice tower structure  50  so as to completely or substantially completely cover the open structure. The cladding material  52  may generally correspond to any suitable material, including various metal materials and/or fabrics (e.g., PVC-coated fabrics and/or PTFE-coated fabrics). As is generally understood, the cladding material  52  may, in one embodiment, be formed in sheets, with each sheet being configured to be installed onto or over specific portions of the lattice structure  50 . For instance, when the cladding material  52  corresponds to a fabric, the sheet of cladding material  52  may be configured to be unrolled onto or over a portion of a specific vertical section of the lattice structure  50 . 
     Referring now to  FIG. 2 , a side view of the tower  32  shown in  FIG. 1  is illustrated in accordance with aspects of the present subject matter, particularly illustrating the lattice tower structure  50  with the cladding material  52  completely removed therefrom. As indicated above, the lattice tower structure  50  may include a plurality of structural members configured to be coupled to one another so as to form the open, “space frame” arrangement. For example, the lattice tower structure  50  may include a plurality of substantially vertically oriented support members  54  (hereinafter referred to as “support legs” or simply “legs”) coupled one on top of the other so as to form the overall vertical shape or profile of the tower structure  50 . In addition, the lattice tower structure  50  may include a plurality of secondary support members  56 ,  58  coupled between the support legs  54 , such as a plurality of horizontally oriented support members  56  (e.g., circumferential spacers and/or cladding brackets) and/or a plurality of diagonally orientated support members  58  (e.g., cross-bracing members). 
     In several embodiments, the lattice tower structure  50  may be formed by stacking a plurality of vertical tower sections one on top of the other. For instance, in the illustrated embodiment, the lattice tower structure  50  includes twelve vertical tower sections, namely a first (or top) tower section  60 , a second tower section  62 , a third tower section  64 , a fourth tower section  66 , a fifth tower section  68 , a sixth tower section  70 , a seventh tower section  72 , an eighth tower section  74 , a ninth tower section  76 , a tenth tower section  78 , an eleventh tower section  80  and a twelfth (or bottom) tower section  82 , stacked one on top of the other. Each vertical tower section may include its own set of support legs  54  and corresponding secondary support members  56 ,  58  coupled between the legs  54 , with the support legs  54  of each tower section being coupled end-to-end with the support legs  54  of adjacent tower sections. As will be described below, one or more of the tower sections may be assembled individually and/or in combination with one or more other tower sections (e.g., to form a vertical stack of tower sections) using a tower assembly fixture  102  ( FIGS. 4 and 5 ) located separate from a final tower location  44  of the wind turbine tower  32  (i.e., the location of the tower foundation  34 ). The individual tower section(s) (or the stacked tower sections) may then be moved to the final tower location  44  and stacked together to form the complete lattice tower structure  50 . 
     For instance, in a particular embodiment of the present subject matter, the tower sections (less the top and bottom tower sections  60 ,  82 ) may be assembled into separate vertical stacks, with each vertical stack including two adjacent tower sections. Specifically, as shown in  FIG. 2 , the tower sections may be assembled into five separate vertical stacks, namely a first vertical stack  84  including the tenth and eleventh tower sections  78 ,  80 , a second vertical stack  86  including the eighth and the ninth tower sections  74 ,  76 , a third vertical stack  88  including the sixth and seventh tower sections  70 ,  72 , a fourth vertical stack  90  including the fourth and fifth tower sections  66 ,  68  and a fifth vertical stack  92  including the second and third tower section  62 ,  64 . In such an embodiment, the various vertical stacks may be assembled at a separate location and subsequently stacked or installed one on top of the other above the bottom tower section  82  in a sequential manner. Thereafter, the top tower section  60  may the installed on top of the fifth vertical stack  92  (e.g., on top of the second tower section  72 ) to form the complete lattice tower structure  50 . 
     It should be appreciated that, although the lattice tower structure  50  is shown in the illustrated embodiment as including twelve tower sections, the lattice structure  50  may generally include any suitable number of tower sections. For instance, in alternative embodiments, the lattice structure  50  may include less than twelve tower sections or greater than twelve tower sections. 
     It should also be appreciated that, as described herein, the various support legs  54  included within each tower section may be configured to be assembled within the lattice tower stricture  50  so as to have a substantially vertical orientation. As used herein, the term “substantially vertical orientation” generally refers to a completely vertical orientation plus or minus an angular tolerance generally corresponding to the maximum taper angle of the lattice tower structure  50  being assembled. For instance, in one embodiment, the term “substantially vertical orientation” may correspond to a completely vertical orientation plus or minus an angular tolerance of less than about 20 degrees, such as an angular tolerance of less than about 15 degrees or less than about 10 degrees. For example, as shown in the illustrated embodiment, the support legs  54  included within the bottom, eleventh, tenth, ninth, eighth, seventh and sixth tower sections  82 ,  80 ,  78 ,  76 ,  74 ,  72 ,  70  are orientated relative to vertical at about a five degree angle so as to form the tapered lower section of the lattice tower structure  50  whereas the fifth, fourth, third and second tower sections  68 ,  66 ,  64 ,  62  include support legs  54  oriented orientated relative to vertical at about a zero degree angle so as to form the non-tapered upper section of the lattice tower structure  50 . In addition, the support legs  54  included within the top tower section  60  are orientated relative to vertical at about a five degree angle so as to form the top tapered section of the lattice tower structure  60 . In such an embodiment, each of the support legs  54  shown in  FIG. 2  may be considered to have a substantially vertical orientation as assembled within the lattice tower structure  50 . 
     Referring now to  FIG. 3 , a perspective view of the bottom tower section  82  of the lattice tower structure  50  as installed at the final tower location  44  is illustrated in accordance with aspects of the present subject matter. As shown, the bottom tower section  82  may be configured to be assembled onto and/or installed directly within the tower foundation  34 . For instance, each support leg  54  of the bottom tower section  82  may be initially sunk down into or otherwise coupled to the tower foundation  34  so as to have a substantially vertical orientation, with one or more circumferential spacers (not shown) being coupled between adjacent support legs  54  to ensure proper spacing and/or orientation of the legs  54  relative to one another. Thereafter, any other suitable secondary support members of the bottom tower section  82  may be coupled between the support legs  54 . For instance, as shown in  FIG. 3 , a plurality of cross-bracing members  58  may be coupled between adjacent support legs  54  to provide increased stiffness and structural support to the bottom tower section  82  of the lattice tower structure  50 . 
     Once the bottom tower section  82  is installed at the final tower location  44 , the remaining tower sections may then be stacked on top of the bottom tower section  82  to fully assemble the tower structure  50 . Specifically, as indicated above, the remaining tower sections may be assembled at a separate location (either individually or in combination with one or more other tower sections) and subsequently lifted into position on top of the bottom tower section  82  (e.g., via a crane). For instance, referring to the embodiment of the lattice tower structure  50  shown in  FIG. 2 , the tenth and eleventh tower sections  78 ,  80  may be assembled one on top of the other at a separate location to form the first vertical stack  84 . As will be described below with reference to  FIG. 22 , such vertical stack  84  may then be lifted via a crane  94  and placed directly on top of the bottom tower section  82  to allow the bottom tower section  82  to be coupled directly to the eleventh tower section  80 . 
     In accordance with aspects of the present subject matter, various embodiments, components and features of a system  100  (and related methods) for assembling one or more tower sections of a lattice tower structure for a wind turbine will now be described with reference to  FIGS. 4-24 . Specifically, as will be described below, the system  100  (and related methods) may allow for vertical tower sections of a lattice tower structure  50  to be assembled onto a tower assembly fixture positioned at a location separate from the final tower location  44  and subsequently stacked one on top of the other at the final tower location  44  to form the tower structure  50 . It is believed that such a system  100  (and related methods) may allow for a lattice tower structure  50  to be erected in more safe, efficient and/or effective manner than is currently provided with conventional systems (and related methods) for assembling wind turbine tower components. 
     Referring specifically to  FIGS. 4 and 5 , differing views of one embodiment a tower assembly fixture  102  that may be utilized in connection with the disclosed system  100  for assembling tower sections of a lattice tower structure  50  are illustrated in accordance with aspects of the present subject matter. Specifically,  FIG. 4  illustrates a perspective view of the fixture  102 , with various components of the fixture  102  being exploded therefrom. In addition,  FIG. 5  illustrates another perspective view of the fixture  102 , with additional system components being installed thereon. 
     As shown, the tower assembly fixture  102  may generally include a plurality of fixture arms  104  extending radially outwardly from a central framed portion  106 . In general, each fixture arm  104  may be configured to extend radially between a first end  108  terminating at the central framed portion  106  and an opposite second end  110  positioned radially outwardly from the first end  108 . In several embodiments, the first end  108  of each fixture arm  104  may be configured to be coupled to the first ends  108  of adjacent fixture arms  104  so as to define the central framed portion  106  of the fixture  102 . For example, as shown in  FIG. 4 , each fixture arm  104  may include a circumferentially extending frame member  112  (e.g., a beam) positioned at its first end  108 . By coupling the frame members  112  of adjacent fixture arms  104  end-to-end, the assembled frame members  112  may form a frame-like structure that defines the central framed portion  106  of the fixture  102 . In one embodiment, the frame members  112  may be configured to be pivotally coupled to one another (e.g., via a pinned connection) to allow the circumferential spacing between the fixture arms  104  to be adjusted when coupling the arms  104  to one another. 
     Additionally, each fixture arm  104  may include one or more support beams  114 ,  116  extending radially between its first and second ends  108 ,  110 . For instance, as shown in the illustrated embodiment, each fixture arm  104  includes a first support beam  114  and a second support beam  116  extending directly between its first and second ends  108 ,  110 , with the support beams  114 ,  116  being coupled together via one or more cross beams  118  extending circumferentially therebetween. The support beams  114 ,  116  may generally correspond to the primary structural components for the fixture  102 . For example, as will be described below, one or more fixture trolleys  120  may be mounted to and/or supported by the support beams  114 ,  116  of each fixture arm  104 . 
     As particularly shown in the illustrated embodiment, the fixture  102  includes five fixture arms  104 , one for each support leg  54  configured to form part of each pentagonal-shaped vertical tower section of the disclosed lattice tower structure  50 . However, in other embodiments, the tower assembly fixture  102  may include any other suitable number of fixture arms  104  extending radially outwardly from the central framed portion  106 , such as less than five fixture arms or greater than five fixture arms, with such number corresponding to or differing from the number of support legs  54  configured to be installed within each tower section. As such, the disclosed fixture  102  may be configured to allow tower sections having any suitable shape (e.g., triangular, square, hexagonal, etc.) to be assembled thereon. 
     In several embodiments, prior to assembling the fixture arms  104 , a plurality of base or fixture pads  122  may be placed along the ground at the anticipated locations of the fixture arms  104 . Specifically, as shown in  FIG. 4 , fixture pads  122  may be installed on the ground at spaced apart locations along the anticipated radial footprint of each fixture arm  104 . Thereafter, the fixture arms  104  may be placed on top of the pads  122  and subsequently coupled to one another. Such fixture pads  122  may generally be configured to assist in preventing shifting or disruption of the underlying ground during assembly of the tower section(s) of the lattice tower structure  50  onto the tower assembly fixture  102 , thereby maintaining a level, planar surface for the fixture  102 . 
     Additionally, as shown in  FIG. 4 , circumferential spacers  124  may also be configured to be coupled between adjacent fixture arms  104  as the fixture arms  104  are being assembled to ensure proper circumferential positioning of the arms  104  relative to one another. In several embodiments, the circumferential spacers  124  may correspond to temporary components of the fixture  102  that are configured to be removed during final assembly thereof. For instance, in one embodiment, the circumferential spacers  124  may be configured to be maintained in place while suitable tensioning rods  126  are installed between the fixture arms  104 . Specifically, as shown in  FIG. 4 , one or more tensioning rods  126  may be installed between each pair of adjacent fixture arms  104  so as to provide a permanent means for maintaining the relative positioning of the fixture arms  104 . In such an embodiment, once the tensioning rods  126  are installed, the circumferential spacers  124  may be removed from the fixture  102 . Alternatively, the circumferential spacers  124  may be maintained between the fixture arms  104  following installation of the tensioning rods  126  (or may be used as an alternative to the tensioning rods  126  for maintaining proper spacing between the arms  104 ). 
     Moreover, as shown in  FIG. 5 , the tower assembly fixture  102  may also include one or more radially extending platforms  128  configured to be installed along the side(s) of each fixture arm  104 . The platforms  128  may generally correspond to walking platforms for providing service personnel a stable walking area adjacent to each fixture arm  104 . As shown in the illustrated embodiment, one or more platforms  128  are installed along both sides of each fixture arm  104 . However, in other embodiments, a platform(s)  128  may only be installed along a single side of each fixture arm  104 . 
     Additionally, as shown in  FIG. 5 , one or more trolleys  120  may be configured to be installed onto each fixture arm  104 . As will be described below, each trolley  102  may be configured to be removably coupled to its corresponding fixture arm  104  at a plurality of different radial locations along the length of the fixture arm  104 . Such adjustable positioning of the trolleys  120  relative to the fixture arms  104  may allow the fixture  102  to be utilized when assembling tower sections having differing radial dimensions. As shown in  FIG. 5 , a single trolley  120  is installed onto each fixture arm  104 . However, as will be described below with reference to  FIG. 17 , two or more trolleys  120  may be installed onto each fixture arm  104  to allow two or more tower sections to be assembled on the fixture  102  simultaneously. 
     Referring now to  FIG. 6 , a side view of one of the fixture arms  104  described above with reference to  FIGS. 4 and 5  is illustrated in accordance with aspects of the present subject matter, particularly illustrating a trolley  120  installed on the fixture arm  104  as well as the various radial locations that the trolley  120  may be moved along the length of the fixture arm  104 . As shown, the trolley  120  may generally include a base frame  130  configured to be removably coupled to the fixture arm  104  and a leg mount  132  pivotally coupled to the base frame  130  that is configured to be secured to one of the support legs  54  included within the tower section being assembled onto the fixture  102 . 
     In general, the base frame  130  of the trolley  120  may be configured to be removably coupled to the support beam(s)  116 ,  118  of the fixture arm  104  using any suitable attachment means known in the art. For instance, as shown in the illustrated embodiment, mechanical fasteners  134  (e.g., bolts, pins and/or the like) may be utilized to couple each corner of the base frame  130  (only two corners being shown in  FIG. 6 ) to the support beams  116 ,  118  (only one of which is shown). Alternatively, any other suitable attachment means may be utilized to removably couple the base frame  130  to the support beams  116 ,  118 , such as clamps, brackets, fixture devices and/or any other suitable attachment devices. 
     As indicated above, by configuring the base frame  130  to be removably coupled to the support beams  116 ,  118 , the trolley  120  may be moved radially along the length of the fixture arm  104  to allow tower sections having differing radial dimensions to be assembled on the fixture  102 . For instance, as shown in the illustrated embodiment, the trolley  120  may be installed at seven different radial locations defined along the length of the fixture arm  104  between its first and second ends  108 ,  110 , namely a first radial location  136 , a second radial location  138 , a third radial location  140 , a fourth radial location  142 , a fifth radial location  144 , a sixth radial location  146  and a seventh radial location  148 . Thus, depending on the radial dimension of the particular tower section that is being assembled on the fixture  104 , the trolleys  120  may be positioned at the appropriate radial location on the fixture arms  104  for assembling such tower section. For example, referring to the embodiment of the lattice tower structure  50  shown in  FIG. 2 , the trolleys  120  may be positioned at the seventh radial location  148  to allow the eleventh tower section  80  to be assembled on the fixture  102 . Similarly, the trolleys  120  may be positioned at the sixth, fifth, fourth, third and second radial locations  146 ,  144 ,  142 ,  140 ,  138  to allow the tenth, ninth, eighth, seventh and sixth tower sections  78 ,  76 ,  74 ,  72 ,  70 , respectively, to be assembled on the fixture  102 . Moreover, given that the top, second, third, fourth and fifth tower sections  60 ,  62 ,  64 ,  66 ,  68  all define the same radial dimension at their bottom ends, the trolleys  120  may be positioned at the first vertical location  136  to assemble such tower sections onto the fixture  102 . 
     It should be appreciated that, in alternative embodiments, the trolleys  120  may be configured to be positioned at any other suitable number of radial locations along the length of each fixture arm  104 . Such number may, in several embodiments, generally depend on the number of tower sections desired to be assembled on the fixture  102  that have differing radial dimensions. 
     Moreover, as indicated above, the leg mount  132  for each trolley  120  may be configured to be pivotally coupled to its corresponding base frame  130 . Such a pivotal connection may allow for the angle of orientation of the leg mount  132  to be adjusted, as needed, to accommodate the differing vertical orientations of the legs  54  used across the various tower sections. For instance, in one embodiment, to assemble the top, sixth, seventh, eighth, ninth, tenth and eleventh tower sections  60 ,  70 ,  72 ,  74 ,  76 ,  78 ,  80 , the leg mount  132  may be required to be oriented at a first angle relative to vertical (e.g., about five degrees) whereas, to assemble the second, third, fourth and fifth tower sections  62 ,  64 ,  66 ,  68 , the leg mount  132  may be required to be oriented at a different, second angle relative to vertical (e.g., about zero degrees). 
     Referring now to  FIGS. 7 and 8 , perspective views showing differing stages of a vertical tower section being assembled on the disclosed fixture  102  are illustrated in accordance with aspects of the present subject matter. Specifically,  FIGS. 7 and 8  illustrate the eleventh tower section  80  being assembled onto the fixture  102 , with  FIG. 7  showing various tower components of such tower section  80  being exploded away from the fixture  102 . 
     As shown, to assemble the eleventh tower section  80 , the trolleys  120  may be initially positioned at the appropriate radial location along the fixture arms  104  so as to accommodate the specific radial dimension of the tower section  80 . For instance, each tower section may define a radial dimension  150  ( FIG. 7 ) as measured between the center of the tower section and a bottom end  96  of each support leg  54 . As shown, in the illustrated embodiment, the eleventh tower section  80  generally defines a radial dimension that requires the trolleys  120  to be positioned at the radially outermost location along the fixture arms  104  (e.g., at the seventh radial location  148 ). In addition, the angular orientation of the leg mounts  132  may be adjusted, as necessary, to ensure that each leg mount  132  is positioned at the proper orientation associated with the eleventh tower section  80  (e.g., about 5 degrees). 
     Thereafter, as shown in  FIG. 7 , the bottom end  96  of each support leg  54  of the tower section  80  may then be mounted to one of the trolleys  120 , with circumferential spacers  56  being installed between adjacent legs  54  (e.g., at the top ends  98  of the legs  54 ) to ensure proper circumferential positioning. Once all of the support legs  54  have been installed onto the fixture  102 , suitable cross-bracing members  58  may be coupled between each pair of adjacent legs  544 . For instance, as shown in  FIG. 8 , four cross-bracing members  58  (e.g., forming two “X-shapes”) may be installed between each pair of adjacent support legs  504 . Thereafter, the circumferential spacers  56  may, in one embodiment, be removed from the assembled tower section  80 . 
     Alternatively, the circumferential spacers  56  and/or the cross-bracing members  58  may be pre-installed between adjacent pairs of support legs  54 . In such an embodiment, each support leg  54  of the assembled pair of support legs  54  may then be mounted onto the trolleys  120  at the same time. 
     It should be appreciated that the various other vertical tower sections may be similarly assembled onto the fixture  102 . For example, to assemble each of the tenth, ninth, eighth, seventh and sixth tower sections  78 ,  76 ,  74 ,  72 ,  70 , the trolleys  120  may be initially moved to the appropriate radial location associated with the tower section being assembled. Thereafter, the support legs  54  for the tower section may be mounted to the trolleys  120 , with circumferential spacers  56  being installed between each pair of adjacent legs  54 . The cross-bracing members  58  may then be installed between the support legs  54  to complete the assembly. 
     It should also be appreciated that, as an alternative to assembling each tower section on the fixture  102  individually, the tower sections may be assembled one on top of the other on the fixture  102  to form a stack of two or more tower sections. Specifically, as indicated above, it may be desirable to assemble pairs of tower sections together on the fixture  102 , with the resulting vertical tower stack then being transferred over to the final tower location  44  for final assembly within the lattice tower structure  50 . For example,  FIG. 9  illustrates a perspective view of the eleventh and tenth tower sections  80 ,  78  assembled together on the fixture  102  to form the first vertical stack  84 . In such an embodiment, the eleventh tower section  80  may be initially assembled on the fixture  102  as described above with reference to  FIGS. 7 and 8 . Thereafter, the tenth tower section  78  may be assembled on top of the eleventh tower section  80  by coupling the bottom ends  96  of its support legs  54  to the top ends  98  of the support legs  54  of the eleventh tower section  80 , with suitable circumferential spacers  56  being installed between the adjacent legs  54  of the tenth tower section  78  to maintain proper positioning. The cross-bracing members  58  may then be installed, as desired, between the adjacent legs  54  of the tenth tower section  78 . 
     By assembling a vertical stack of two or more tower sections on the fixture  102 , the stack may then be transferred as a whole to the final tower location  44  of the lattice tower structure  50  for final assembly. For example,  FIG. 22  illustrates a perspective view of the vertical stack  84  shown in  FIG. 9  being lowered down onto the bottom tower section  82  of the lattice tower structure  50  shown in  FIG. 3 . Specifically, a crane  94  or other suitable lifting device may be used to lift the vertical stack  84  from the fixture  102  and transport the stack  84  to the final tower location  44 . The stack  84  may then be lowered into place to allow the adjacent tower sections to be coupled to one another. For instance in the illustrated embodiment, the bottom ends  96  of the support legs  54  of the eleventh tower section  80  may be coupled to the top ends  98  of the support legs  54  of the bottom tower section  82 . 
     It should be appreciated that, similar to the vertical stack  84  shown in  FIG. 9 , various other tower sections may be assembled together to form a vertical stack that may then be lifted up and installed at the final tower location. For instance, as indicated above with reference to  FIG. 2 , a second vertical stack  86  may be formed by stacking the eighth and ninth tower sections  74 ,  76  on the fixture  102  and a third vertical stack  88  may be formed by stacking the sixth and seventh tower sections  70 ,  72  on the fixture  102 . Similarly, a fourth vertical stack  90  may be formed by stacking the fourth and fifth tower sections  66 ,  68  on the fixture  102  while a fifth vertical stack  92  may be formed by stacking the second and third tower section  62 ,  64  on the fixture  102 . 
     It should also be appreciated that, in several embodiments, some or all of the circumferential spacers  56  utilized during the assembly process to ensure proper circumferential spacing of the legs  54  may also function as cladding brackets. In such embodiments, the cladding brackets may be maintained on the tower section(s) to allow the cladding material  52  to be coupled to the resulting lattice tower structure  50 . For instance, in one embodiment, circumferential spacers  56  doubling as cladding brackets may be installed between the adjacent legs  54  of every other tower section (e.g., the even-numbers tower sections) to allow the cladding material  52  to be coupled thereto. Thus, in the embodiment shown in  FIG. 9 , the circumferential spacers  56  shown at the top of the tenth tower section  78  may, for example, correspond to suitable cladding brackets for the latter tower structure  50 . 
     Referring now to  FIG. 10 , another perspective view showing a tower section being assembled on the disclosed tower assembly fixture  102  is illustrated in accordance with aspects of the present subject matter. Specifically,  FIG. 10  illustrates the fifth tower section  68  being assembled onto the fixture  102 , with various tower components of such tower section  68  being exploded away from the fixture  10 . 
     As shown, to assemble the fifth tower section  68 , the trolleys  120  may be initially positioned at the appropriate radial location along the fixture arms  104  so as to accommodate the specific radial dimension of the tower section  68 . For instance, as shown in  FIG. 10 , the fifth tower section  68  generally defines a radial dimension that requires the trolleys  120  to be positioned at the radially innermost location along the fixture arms  104  (e.g., at the first radial location  136 ). In addition, the angular orientation of the leg mounts  132  may be adjusted, as necessary, to ensure that each leg mount  132  is positioned at the proper orientation associated with the fifth tower section  68  (e.g., about zero degrees). 
     Thereafter, as shown in  FIG. 10 , the support legs  54  of the tower section  68  may then be mounted to each trolley  120 , with circumferential spacers  56  being installed between adjacent legs  54  to ensure proper circumferential positioning. Once all of the support legs  54  have been installed onto the fixture  102 , suitable cross-bracing members  58  may be coupled between each pair of adjacent legs  54 . For instance, as shown in  FIG. 10 , eight cross-bracing members  58  (e.g., forming four “X-shapes”) may be installed between each pair of adjacent support legs  54 . Thereafter, the circumferential spacers  56  may, in one embodiment, be removed from the assembled tower section. 
     As indicated above, in several embodiments, the fourth, third and second tower sections  66 ,  64 ,  62  may all define the same or substantially the same radial dimension as the fifth tower section  68  with respect to the position of the bottom ends  96  of each of their support legs  54  relative to the center of each tower section. As a result, such tower sections may be similarly assembled onto the fixture  102  without having to adjust the radial positioning of the trolleys  120  along the fixture arms  104 . For example, to assemble each of the fourth, third, and second tower sections  66 ,  64 ,  62 , the support legs  54  for each tower section may be mounted to the trolleys  102 , with circumferential spacers  56  being installed between each pair of adjacent legs  54 . The cross-bracing members  58  may then be installed between the support legs  54  to complete the assembly. 
     Additionally, as indicated above, the tower sections may be configured to be assembled one on top of the other on the fixture  102  to form a stack of two or more tower sections. For example,  FIG. 11  illustrates a perspective view of the fifth and fourth tower sections  68 ,  66  assembled together on the fixture to form the fourth vertical stack  90 . In such an embodiment, the fifth tower section  68  may be initially assembled on the fixture  102  in the manner described above with reference to  FIG. 10 . Thereafter, the fourth tower section  66  may be assembled on top of the fifth tower section  68  by coupling the bottom ends  96  of its support legs  54  to the top ends  98  of the support legs  54  of the fifth tower section  68 , with suitable circumferential spacers  56  being installed between the adjacent legs  54  of the fourth tower section  66  to maintain proper positioning. The cross-bracing members  58  may then be installed, as desired, between the adjacent legs  54  of the fourth tower section  66 . The resulting vertical stack  90  may then be lifted off of the fixture  102  via a crane and transported to the final tower location  44  for assembly on top of the previously installed tower section(s). For instance, referring to the embodiment shown in  FIG. 2 , the fourth vertical stack  80  formed by the fourth and fifth tower sections  66 ,  68  may be installed at the final tower location  44  by coupling the bottom ends  96  of the support legs  54  of the fifth tower section  68  to the top ends  98  of the support legs  54  of the previously installed sixth tower section  70 . 
     Referring now to  FIG. 12 , another perspective view showing a tower section assembled on the disclosed tower assembly fixture  102  is illustrated in accordance with aspects of the present subject matter. Specifically,  FIG. 12  illustrates the top tower section  60  as assembled onto the fixture  102 . 
     As shown, the top tower section  60  may be assembled onto the tower assembly fixture  102  in a manner similar to that described above with reference to  FIG. 10  for the fifth tower section  68 . Specifically, the trolleys  120  may be initially positioned at the radially innermost location along the fixture arms  104  (e.g., at the first radial location  136 ) and the angular orientation of the leg mounts  132  may be adjusted, as necessary, to ensure that each leg mount  132  is positioned at the proper orientation associated with the support legs  54  of the top tower section  60  (e.g., about five degrees). Thereafter, the support legs  54  of the tower section  60  may be mounted to each trolley  120 , with circumferential spacers  56  being installed, as necessary, between adjacent legs  54  to ensure proper circumferential positioning. Once the support legs  54  have been installed onto the fixture  102 , suitable cross-bracing members  58  may be coupled between each pair of adjacent legs  54 . For instance, as shown in  FIG. 12 , ten cross-bracing members  58  (e.g., forming five “X-shapes”) may be installed between each pair of adjacent support legs  54 . Additionally, as shown in  FIG. 12 , an uptower support assembly  152  may also be installed on top of the support legs  54  of the top tower section  60 . As is generally understood, the uptower support assembly  152  may be configured to support the various uptower components of the wind turbine  40  shown in  FIG. 1 . For instance, the nacelle  36  ( FIG. 1 ) may be mounted directly on top of the uptower support assembly  152 . 
     Referring now to  FIGS. 13-16 , several different views of one of the fixture trolleys  120  described above are illustrated in accordance with aspects of the present subject matter. Specifically,  FIG. 13  illustrates a perspective view of the trolley  120  and  FIGS. 14 and 15  illustrate side views of the trolley  120 , particularly illustrating the leg mount  132  of the trolley  120  at different angular orientations relative to its base frame  130 . Additionally,  FIG. 16  illustrates a partial perspective view of a top portion of the trolley  120  shown in  FIG. 13 , with the bottom end  96  of a support leg  54  being coupled to the leg mount  132  of the trolley  120 . 
     As particularly shown in  FIG. 13 , the base frame  130  may generally include a first sidewall  154 , a second sidewall  156  spaced apart from the first sidewall  154  and a bottom wall  158  extending between the first and second sidewalls  154 ,  156 . In several embodiments, each sidewall  154 ,  156  may include a pair of mounting brackets  160  extending outwardly therefrom for receiving suitable attachment devices for coupling the trolley  120  to its corresponding fixture arm  104 . For instance, as indicated above, mechanical fasteners  134 , such as bolts, pins and/or the like, may be utilized to couple the trolley  120  to its fixture arm  104 . In such an embodiment, a fastener  134  may be inserted through each mounting bracket  160  and coupled to one of the support beams  114 ,  116  of the adjacent fixture arm  104  (e.g., via a nut) to allow the trolley  120  to be coupled to the fixture arm  104 . 
     Additionally, as shown in  FIGS. 13-15 , the leg mount  132  may be configured to be coupled between the opposed sidewalls  154 ,  156  of the base frame  130  such that a portion of leg mount  132  extends vertically within a cavity defined between the first and second sidewalls  154 ,  156 . As indicated above, in several embodiments, the leg mount  132  may be configured to be pivotally coupled to the base frame  130 . For instance, as shown in  FIGS. 13-15 , an opening  162  may be defined in each sidewall  154 ,  156  that is configured to receive a corresponding projection  164  extending outwardly from each side of the leg mount  132 . Such a pinned or pivotal connection may provide a means for pivoting or rotating the leg mount  132  about a pivot axis  166  ( FIG. 13 ) extending through the center of the openings  162  defined in the sidewalls  154 ,  156 , thereby allowing for the angular orientation of the leg mount  132  to be adjusted relative to the base frame  130 . It should be appreciated that, in other embodiments, the pivotal connection provided between the leg mount  132  and the base frame  130  may be achieved using any other suitable means and/or configuration that allows for the angular orientation of the leg mount  132  to be adjusted relative to the base frame  130 . 
     Moreover, as shown in the illustrated embodiment, the trolley  120  may also include an angle adjustment device  168  coupled between the base frame  130  and the leg mount  132  for adjusting the angular orientation of the leg mount  130 . Specifically, as shown in  FIGS. 13-15 , the angle adjustment device  168  corresponds to a screw jack including a jack portion  170  coupled the base frame  130  and a screw portion  172  coupled to a bottom end of the leg mount  132 . In such an embodiment, by linearly actuating the screw portion  172  (e.g., by turning a wheel  174  associated with the jack portion  170 ), the angular orientation of the leg mount  132  relative to the base frame  130  may be adjusted. For instance, as shown in  FIG. 14 , by linearly actuating the screw portion  172  in a first direction (as indicated by arrow  174 ), the leg mount  132  may be rotated relative to the base frame  130  about the rotational axis in a first rotational direction (as indicated by arrow  178 ). Similarly, as shown in  FIG. 15 , by linearly actuating the screw portion  172  in a second, opposite direction (as indicated by arrow  180 ), the leg mount  132  may be rotated relative to the base frame  130  about the rotational axis in a second, opposite rotational direction (as indicated by arrow  182 ). 
     As shown in  FIGS. 14 and 15 , in one embodiment, the base frame  132  may include pivot stops  184 ,  186  positioned both forward and aft of the leg mount  132  that serve to limit the movement of the leg mount  132  relative to the base frame  130 . Specifically as shown in  FIG. 14 , the screw portion  172  may be linearly actuated in the first direction  176  until the leg mount  132  contacts a first pivot stop  184  positioned aft of the leg mount  132 . Additionally, as shown in  FIG. 15 , the screw portion  172  may be linearly actuated in the second direction  180  until the leg mount  132  contacts a second pivot stop  186  positioned forward of the leg mount  132 . As a result, the first and second pivot stops  184 ,  186  may generally define an angular range of travel  188  across which the leg  132  mount may be pivoted relative to the base frame  130 . 
     Additionally, in several embodiments, the trolley  120  may also include an angle indicator for providing an indication of the angular orientation of the leg mount  132  relative to the base frame  130 . Specifically, as shown in  FIGS. 13-15 , in one embodiment, an angle marker  190  may be coupled to one of the projections  164  extending through the openings  162  defined in the sidewalls  154 ,  156  such that the angle marker  190  is positioned along an exterior surface of the base frame  130 . Additionally, as shown in the illustrated embodiment, an angle reference guide  191  may be provided on the exterior surface of the base frame  130  adjacent to the angle marker  190 . The angle reference guide  191  may, for example, include markings, numbers and/or any other suitable feature(s) that provide an indication of the angular orientation of the leg mount  132 . As such, when the leg mount  132  is pivoted relative to the base frame  130 , the orientation of the angle marker  190  relative to the angle reference guide  191  may be referenced to allow a service worker to quickly and easily determine the current angular orientation of the leg mount  132 . 
     As indicated above, the leg mount  132  may be configured to be coupled to the bottom end  96  of one of the support legs  54  of the tower section being assembled onto the tower assembly fixture  102 . As such, the leg mount  132  may be configured to and/or may include any suitable components and/or features configured to accommodate securing the bottom end  96  of a support leg  54  thereto. For instance, as shown in  FIG. 16 , in one embodiment, each support leg  54  may correspond to a substantially “U-shaped” support beam having first and second sidewalls  192 ,  193  and an outer wall  194  extending between the sidewalls  192 ,  193 . In such an embodiment, a widthwise dimension of a top portion  195  of the leg mount  132  may be designed to be less than a corresponding width of the gap defined between the sidewalls  192 ,  193  at the bottom end  96  of the support leg  54  such that the top portion  195  of the leg mount  132  may be received within the “U-shaped” channel defined by the support leg  64 . 
     Additionally, the leg mount  132  may also include one or more mounting plates  196 ,  197 ,  198  for coupling the leg mount to the bottom end of the support leg. For instance, as shown in the illustrated embodiment, the leg mount  132  includes an outer mounting plate  196  and first and second side mounting plates  197 ,  198  extending substantially vertically from the top portion  195  of the leg mount  132 , with each mounting plate  196 ,  197 ,  198  including a plurality of mounting holes  199  ( FIG. 13 ) for receiving suitable mechanical fasteners. In such an embodiment, when the top portion  195  of the leg mount  132  is received within the “U-shaped” channel defined by the support leg  54 , the first and second mounting plates  197 ,  198  may be configured to extend adjacent to the inner surfaces of the first and second sidewalls  192 ,  193 , respectively, of the support leg  54  while the outer mounting plate  196  may be configured to extend adjacent to the inner surface of the outer wall  194 . Mechanical fasteners may then be inserted through both the mounting holes  199  defined in the mounting plates  196 ,  197 ,  198  and corresponding openings (not shown) defined in the walls of the support leg  54  to allow the leg  54  to be coupled to the leg mount  132 . 
     Referring now to  FIG. 17 , a perspective view of an embodiment in which nested tower sections have been assembled onto the disclosed tower assembly fixture  102  is illustrated in accordance with aspects of the present subject matter. As shown in  FIG. 17 , as opposed to only installing a single trolley  120  onto each fixture arm  104  of the tower assembly fixture  102 , multiple trolleys  120 A,  120 B,  120 C may be installed onto the fixture arms  104  at different radial locations along the length of each arm  104 . As a result, tower sections having differing radial dimensions may be assembled simultaneously onto the fixture  102  in a nesting configuration, thereby further increasing the efficiency at which the lattice tower structure  50  may be installed at a wind turbine location. 
     In the illustrated embodiment, three trolleys have been installed onto each fixture arm  104 , namely a first trolley  120 A, a second trolley  120 B and a third trolley  120 C, with the trolleys  120 A,  120 B,  120 C being disposed at different radial locations along the length of each fixture arm  104 . Specifically, as shown in  FIG. 17 , each first trolley  120 A is installed onto its respective fixture arm  104  at the seventh radial location  148  defined on each fixture arm  104 , which may correspond to the radial location for assembling the eleventh tower section  80  onto the tower assembly fixture  102 . Similarly, each second trolley  120 B is installed onto its respective fixture arm  104  at the fifth radial location  144 , which may correspond to the radial location for assembling the ninth tower section  76  onto the fixture  102 . Moreover, each third trolley  120 C is installed onto its respective fixture arm  104  at the third radial location  140 , which may correspond to the radial location for assembling the seventh tower section  72  onto the fixture  102 . 
     As indicated above, by installing multiple trolleys  120 A,  120 B,  120 C onto each fixture arm  104 , the tower sections may be assembled onto the tower assembly fixture  102  in a nesting configuration. For example, as shown in  FIG. 17 , the seventh tower section  72  has been assembled onto the fixture  102  using the plurality of third trolleys  120 C. Additionally, although not shown, by assembling the seventh tower section  72  onto the fixture  102 , the sixth tower section  70  may then be assembled directly on top of the seventh tower section  72  to form the third vertical stack  88 . Moreover, as shown in  FIG. 17 , the ninth tower section  76  has been assembled onto the fixture  102  using the plurality of second trolleys  120 B so as to be positioned radially outwardly from the seventh tower section  72 , with the eighth tower section  74  being stacked on top thereof to form the second vertical stack  86 . Similarly, although not shown, the eleventh tower section  80  (and, optionally, the tenth tower section  80  stacked thereon) may also be assembled onto the fixture  102  using the plurality of first trolleys  120 B so as to be positioned radially outwardly from the ninth and eighth tower sections  76 ,  76 . The nested tower sections (or nested vertical stacks) may then be removed individually from the fixture  102  for subsequent installation at the final tower location  44 . 
     Referring now to  FIG. 18 , a perspective view of one embodiment of a upend device  200  configured to facilitate upending the vertical legs  54  from a horizontal position on and/or adjacent to the ground for subsequent installation onto the tower assembly fixture  102  is illustrated in accordance with aspects of the present subject matter. As will be described below, the upend device  200  may allow a support leg  54  to be upended without damaging any components of the support leg  54 , such as any splice plates coupled to the bottom end  96  of the support leg  54 . 
     As shown, the upend device  200  may generally include a pivot tube  202  configured to provide a pivot point for rotating or pivoting a support leg  54  relative to the ground as it is being upended. Specifically, as will be described below, the pivot tube  202  may be configured to directly contact the ground so as to provide a means for allowing the bottom end  96  of each support leg  54  to be pivoted relative to the ground as the top end  96  of such support leg  54  is being lifted therefrom in order to upend the leg  54 . Additionally, as shown in  FIG. 18 , the upend device  200  may also include first and second pivot arms  204 ,  206  extending outwardly from the pivot tube  202  so as to define a channel  208  between the pivot arms  204 ,  206  for receiving the bottom end  96  of the support leg  54 . Specifically, in several embodiments, a portion of the outer wall  194  extending from the bottom end  96  of each support leg  54  may be configured to be inserted between the first and second pivot arms  204 ,  206  such that the first pivot arm  204  is received within the “U-shaped” channel defined by the support leg  54  and extends adjacent to and/or contacts the inner surface of the outer wall  194 . 
     Moreover, the second pivot arm  206  may include a raised portion  210  configured to act as a mechanical stop for the bottom end  96  of each support leg  54 . Specifically, as will be described below, when a support leg  54  is received between the first and second pivot arms  204 ,  206 , the bottom end  96  of the support leg  54  may abut against or otherwise contact the raised portion  210  of the second pivot arm  206 . In addition, the second pivot arm  206  may also include a roller  212  positioned outwardly from the raised portion  210  such that the roller  212  extends adjacent to and/or contacts the outer surface of the outer wall  194  of the support leg  54  when the bottom end  96  is engaged against the raised portion  210 . 
     Additionally, as shown in  FIG. 18 , the upend device  200  may also include a pivot stop arm  214  extending outwardly from the pivot tube  202  in a direction generally perpendicular to the first and second pivot arms  204 ,  206 . The pivot stop arm  214  may generally be configured to stop the upend device  200  and the support leg  54  from being over rotated as the support leg  54  is being pivoted relative to the ground. Specifically, the pivot stop arm  214  may be configured to contact the ground once the support leg  54  has been rotated to a substantially vertical position, thereby preventing further rotation of the support leg  54  relative to the ground. 
     One embodiment of a method for using the upend device  200  to upend a support leg  54  will now be described below with reference  FIGS. 19-21 . As shown in  FIG. 19 , the support leg  54  may be initially supported above the ground on first and second support stands  216 ,  218 . The upend device  200  may then be installed onto the bottom end  96  of the support leg  54 . For instance, as shown in  FIG. 19 , the upend device  200  may be lifted (e.g., via a crane cable  220 ) into position adjacent to the bottom end  96  of the support leg  54  and then moved lengthwise (e.g., as indicated arrow  222 ) relative to the support leg  54  such that the bottom end  96  is received between the first and second pivot arms  204 ,  206 . Specifically, as shown in  FIG. 21 , the upend device  200  may be moved relative to the support leg  54  until the bottom end  96  of the support leg  54  contacts the raised portion  210  of the second pivot arm  206 . 
     Thereafter, both the bottom end  96  of the support leg  54  and the upend device  200  may be lifted slightly (e.g., via the crane cable  220 ) to allow the support stand adjacent to the bottom end  96  (e.g., the first support stand  216 ) to be removed. The support leg  54  may then be supported relative to the ground via the upend device  200  and the remaining support stand (e.g., the second support stand  218 ) as the crane cable  220  is removed from the upend device  200  and attached to the top end  98  of the support leg  54 . The top end  98  of the support leg  54  may then be lifted slightly using the crane cable  220  to allow the remaining support stand (e.g., the second support stand  218 ) to be removed from the support leg  54 . 
     As shown in  FIG. 20 , after removal of the remaining support stand, the top end  98  of the support leg  54  may be lifted upward via the crane cable  220  as the bottom end  96  of the support leg  54  pivots relative to ground about the pivot tube  202 . The top end  98  of the support leg  54  may then continue to be lifted upward until the support leg  54  has been pivoted to a substantially vertical position and the pivot stop arm  214  is contacting the ground. The support leg  54  may then be lifted out of the upend device  200  and transported via the crane cable  220  to the location of the tower assembly fixture  102  for subsequent attachment to one of the trolleys  120 . 
     Referring now to  FIGS. 23 and 24 , a flow diagram of one embodiment of a method  300  for assembling a tower section of a lattice tower structure for a wind turbine is illustrated in accordance with aspects of the present subject matter. In general, the method  300  will be described herein with reference to the system  100  and related system components described above with reference to  FIGS. 4-22 . However, it should be appreciated by those of ordinary skill in the art that the disclosed method  300  may be implemented in accordance with any other suitable embodiment of system for assembling a tower section of a lattice tower structure. In addition, although  FIGS. 23 and 24  depict steps performed in a particular order for purposes of illustration and discussion, the methods discussed herein are not limited to any particular order or arrangement. One skilled in the art, using the disclosures provided herein, will appreciate that various steps of the methods disclosed herein can be omitted, rearranged, combined, and/or adapted in various ways without deviating from the scope of the present disclosure. 
     As shown in  FIG. 23 , at ( 302 ), the method  300  may include positioning at fixture pad(s) at each anticipated installation location of the fixture arms. Specifically, as described above with reference to  FIG. 4 , fixture pads  122  may be installed on the ground at spaced apart locations along the anticipated radial footprint of each fixture arm  104 . Thereafter, at ( 304 ), the method  300  may include positioning each fixture arm on top of the fixture pad(s) disposed at its anticipated installation location. 
     Additionally, at ( 306 ), the method  300  may include coupling each of the fixture arms together to form a tower assembly fixture. Specifically, as described above, the frame member  112  disposed at the first end  108  of each fixture arm  104  may be configured to be coupled to the frame members  112  of adjacent fixture arms  104  to assemble the arms  104  together. As such, the resulting tower assembly fixture  102  may include a central framed portion  106  and a plurality of fixture arms  104  extending radially outwardly from the central framed portion  106 . 
     Moreover, at ( 308 ), the method  300  may include coupling a circumferential spacer and/or a tensioning rod between each pair of adjacent fixture arms. For instance, as described above, in one embodiment, circumferential spacers  124  may be temporarily installed between adjacent fixture arms  104  to ensure proper circumferential positioning of the arms  104  relative to one another while suitable tensioning rods  126  are being installed between the fixture arms  104 . In such an embodiment, once the tensioning rods  126  have been installed, the circumferential spacers  124  may be removed from the fixture  102 . 
     Additionally, as shown in  FIG. 23 , at ( 310 ), the method  300  may include positioning a radially extending platform(s) along a side(s) of one or more of the fixture arms. As indicated above, such platform(s) may provide a walking surface for service personnel working on and/or around the tower assembly fixture  102 . 
     Referring particularly now to  FIG. 24 , at ( 312 ), the method  300  may include installing a trolley onto each fixture arm of the tower assembly fixture. For instance, as indicated above, the base frame  130  of each trolley  120  may be configured to be coupled to the support beam(s)  114 ,  116  forming each radially extending fixture arm  104 . 
     Additionally, when installing the trolleys  120  onto the fixture arms  102 , the radial positioning of each trolley  102  and/or the angular orientation of the leg mount  132  of each trolley  120  may be considered in light of the specific tower section being assembled onto the tower assembly fixture  102 . Specifically, at ( 314 ), the method  300  may include adjusting, as necessary, the radial position of each trolley  120  along the radial length of its respective fixture arm  104 . For instance, as indicated above, each trolley  120  may be configured to be coupled to its respective fixture arm  104  at a plurality of different radial locations so as to accommodate tower sections having differing radial dimensions. Additionally, at ( 316 ), the method  300  may include adjusting, as necessary, an angular orientation of the leg mount  132  of each trolley  120 . For example, as described above, each trolley  120  may include an angle adjustment device  168  that allows the angular orientation of the leg mount  132  to be adjusted relative to the corresponding base frame  130  of the trolley  120  so as to match the angular orientation of the leg mount  132  to the desired substantially vertical orientation for the support legs  54  of the specific tower section being assembled. 
     Moreover, at ( 318 ), the method  300  may include securing the bottom end of each support leg to one of the trolleys. For example, as indicated above, the bottom end  96  of each support leg  54  may be configured to be coupled to the leg mount  132  of one of the trolleys  120 , thereby allowing the support leg  54  to be supported above the tower assembly fixture  102  at its desired substantially vertical orientation. Thereafter, one or more secondary support members may be configured to be coupled between each pair of adjacent support legs  54 . For instance, as shown in  FIG. 24 , at ( 320 ), the method  300  may include installing a circumferential spacer(s) between each pair of adjacent support legs. Moreover, at ( 322 ), the method  300  may include installing a cross-bracing member(s) between each pair of adjacent support legs. 
     In addition to the various method elements shown in  FIGS. 23 and 24 , the disclosed method  300  may also include any other suitable method elements consistent with disclosure provided herein. For instance, upon assembling a given tower section onto the tower assembly fixture  102 , another tower section may be assembled directly on top of the previously assembled section to form a vertical tower stack. In addition, two or more trolleys  120  may be installed onto each fixture arm  104  to allow two or more nested tower sections to be assembled onto the tower assembly fixture  102 . Moreover, once a given tower section (or vertical stack) has been assembled onto the tower assembly fixture  102 , the tower section (or vertical stack) may then be removed from the fixture  102  and transported to the final tower location  44  for subsequent assembly within the lattice tower structure  50 . 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.