Abstract:
According to a preferred embodiment, a multi-piece fastener with self-indexing nut is disclosed. The multi-piece fastener is designed for use in low clearance areas such as aircraft wing side-of-body joint locations. The multi-piece fastener comprises a stud comprising an elongated part extending between a first end face and a second end face, a threaded head fastener, a threaded tail fastener, and a wrenching feature. A self-indexing feature is provided on the stud and head fastener which allows automatic orientation of the head fastener with respect to the stud.

Description:
RELATED APPLICATION 
     This application is a continuation-in-part of, and claims priority from, pending prior application Ser. No. 11/162,260 filed Sep. 2, 2005, and is incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to a method and apparatus for improving installation of joint elements in limited clearance situations, and more particularly to a method and apparatus utilizing a multi-piece fastener to secure joint elements. 
     BACKGROUND 
     Aerospace and military applications often provide unique challenges to design and manufacturing. Often manufacturing requires the assembly of multiple elements within regions providing limited clearance and reduced accessibility. Traditional attachment methodologies and fasteners may be difficult to position within such regions. In addition, assembly of such structures commonly requires precise tensioning of such fasteners to minimize stresses and insure proper functioning. The use of traditional fasteners, such as commonly used bolt assemblies, can result in difficult installation, ergonomic issues, inconsistent torque application, and sub-optimum joint fatigue performance. 
     One such assembly that suffers from the aforementioned concerns is the wing side-of-body joint assembly used in aerospace applications. The wing side-of-body joint is configured around chordwise stiffeners, typically referred to as chords, used to transmit wing skin and stringer loads into the body and wing center structure. Presently, the fasteners used in this application are high strength protruding head bolts and nuts. The limited clearance present in the chord elements, however, dictates undesirable constraints on how the bolts may be orientated and their installation sequence. Often, limited clearance may make traditional bolt assemblies virtually impossible to utilize or re-torque after installation. 
     It is also highly desirable to torque bolts from the nut side. Such nut-side torque application is known to deliver consistent optimum joint fatigue performance. Torque application from the head side often results in the bolt turning inside the hole, which can score the bolt and/or fastener and result in galling and improper bolt tensioning. Therefore, it is highly desirable for the fastener assemblies utilized in the wing side-of-body joint assembly to be torqued from the nut side. The limited clearance imposed by the chord elements, however, makes such nut-side torque application unfeasible in certain locations. 
     What is needed is a method and fastener assembly that is suited for assembly within reduced clearance regions of the joint assembly. Additionally, it would be highly desirable to have a method and fastener assembly that would allow for nut-side only torque application even within such reduced clearance regions. 
     Further difficulties arise where a fastener assembly requires a precisely tightened nut (threaded head fastener). In wing-side of body joints with low clearance regions, nuts may require tightening to a precise orientation. With prior solutions, this had been done as follows: One end of a bolt is inserted into a low clearance region, and a nut is inserted into the low clearance region. The nut is tightened to some arbitrary degree onto the bolt and then examined to see whether the orientation meets what is required. If the nut is not in the proper orientation, then the nut must be adjusted again. This process must be repeated until proper orientation is achieved. As the nut is located in a low clearance region, examination of the nut is difficult or impossible while it is being tightened. This tightening and re-tightening process requires much trial and error which is time-consuming and difficult. Therefore there exists a need for a fastener which can quickly, easily, and accurately be tightened to a specific orientation. 
     SUMMARY 
     In accordance with the present invention an aerospace wing side body joint assembly is provided comprising at least one chord element, having an internal reduced clearance region, and at least one skin element. At least one cylindrical bolt assembly passes through the chord element and the skin element and secures them together. The cylindrical bolt assembly is comprised of a cylindrical stud having a threaded tail section and is used a threaded head section protruding into the internal reduced clearance region. A threaded head fastener inserted into the internal reduced clearance region engages the threaded head section. A nut element (threaded tail fastener) engages the threaded tail section and is used to introduce a torque without rotating the cylindrical stud. 
     Further in accordance with the present invention, a spring loaded stop projection (pawl) on the stud and stop indentations on the threaded head fastener are provided to allow the threaded head fastener to automatically stop at a desired orientation. Upon insertion of the bolt into the head fastener, the projection on the bolt is depressed such that the head fastener can rotate over the projection and be fastened onto the stud. As the head fastener is being tightened onto the stud, the stop projection continues to be depressed until it pops up into an indentation in the threaded head fastener. At this point, the head fastener is immobile relative to the stud, ensuring that further rotation is no longer possible and that the head fastener is in proper orientation with respect to the stud. This system may be referred to as a self-indexing nut system. 
     Other objects and features of the present invention will become apparent when viewed in light of the detailed description and preferred embodiment when taken in conjunction with the attached drawings and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of an aircraft in accordance with the present invention; 
         FIG. 2  is a detailed illustration of a wing side-of-body joint assembly for use in the aircraft illustrated in  FIG. 1 . 
         FIG. 3  is a detailed illustration of a portion of the wing side-of-body joint assembly illustrated in  FIG. 2 . 
         FIGS. 4A-C  are detailed illustrations of an assembly of the wing side-of-body joint assembly illustrated in  FIG. 2 . 
         FIG. 5A-C  are detailed illustrations of an alternate assembly of the wing side-of-body joint assembly illustrated in  FIG. 2 . 
         FIG. 6  is a detailed illustration of a cylindrical stud for use in the wing side-of-body joint assembly illustrated in  FIG. 2 . 
         FIG. 7  is a detailed illustration of an alternate cylindrical stud for use in the wing side-of-body joint assembly illustrated in  FIG. 2 . 
         FIG. 8  is a detailed illustration of an alternate cylindrical stud for use in the wing side-of-body joint assembly illustrated in  FIG. 2 . 
         FIG. 9  depicts an embodiment of a fastening device, including a threaded head fastener with stop indentations and a stud with stop projections. 
         FIG. 10  depicts an alternate embodiment of the fastening device shown in  FIG. 9 , wherein the threaded head fastener is fastened onto the stud. 
         FIG. 11  depicts an alternate embodiment of the device depicted n  FIG. 9  as utilized in a low-clearance region of a wing-side of body joint. 
         FIG. 12  depicts alternate embodiments of stop projections and stop indentations of the fastening device depicted in  FIG. 9 . 
         FIG. 13  depicts an embodiment of a fastening device, including a threaded head fastener with stop indentations and a stud with ball-bearing shaped stop projections. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to  FIG. 1 , which is an illustration of an aircraft  10  in accordance with the present invention. The aircraft  10  is comprised of a plurality of joint assemblies wherein traditional fastening and assembly techniques may unfeasible or cost prohibitive. One such joint assembly is referred to as the wing side-of-body joint assembly  12 , see  FIG. 2 . The wing side-of-body joint assembly  12  is located where the wing  14  joints the aircraft body side  16 . This joint assembly  12  is very important as it is used to join a variety of structures together to form a reliable joint that is preferably highly resistant to joint fatigue. 
     As illustrated in  FIG. 2 , the joint assembly  12  is used to join a variety of different structures. Aluminum or titanium chords  18 , also referred to as a first joint element, are utilized to join primary structures such as aluminum or carbon fiber-reinforced composite skin elements  20 , also referred to as a second joint element, stringers  22 , stringer fittings  24 , and body frames  26 . In addition, the chords  18  are utilized to affix additional stiffeners such as body web stiffeners  28  and spice plates  30 . Thus the joint assembly  12  joins a wide plurality of structures and must do so reliably and efficiently. 
     One embodiment of a wing side-of-body joint is described in further detail below. 
     A body frame section  26  is a part of the aircraft body side  16  and is found at the point on the aircraft body to which the wing  14  connects. It is fastened to the upper supporting chord element  200 , described below. 
     The main components of one embodiment of a wing side of body joint include an upper supporting chord element  200  and a lower supporting chord element  228 , an upper wing section  212  and a lower wing section  238 , and an upper interior section  220  and a lower interior section  246 . 
     The upper and lower supporting chord elements  200  and  228  have a cross-section resembling a crossed capital T, and comprise a middle chord layer  204  and  230  and a top or bottom chord layer  202  and  232  which are substantially parallel to each other, and are connected by a central wall chord layer  206  and  234 , which runs perpendicular to both top or bottom  202  and  232  and middle chord layer  204  and  230 . A portion of the wall chord layer  206  and  234 , the extension  210  and  236 , extends from the middle chord layer  204  and  230  and is used to connect the upper and lower supporting chord elements  200  and  228 . 
     The upper wing section  212  comprises an upper skin layer  214  and a lower skin layer  216 , and a stringer element  218  therebetween. The upper skin layer  214  and lower skin layer  216  are fastened to the top chord layer  202  and middle chord layer  204  of the upper supporting chord element  200 , respectively, each being fastened with fasteners  34 . The lower skin layer  216  of the upper wing section  212  is overlaid upon the middle chord layer  204  and the stringer  218 , and is fastened to both of those parts. Overlaid upon and connecting to the lower skin layer  216  may be a stringer fitting  24 . 
     The upper interior section  220  comprises an upper skin layer  222  and lower skin layer  224 , and a stringer  226  therebetween. The upper and lower skin layers  222  and  224  are fastened to the top and middle chord layers  202  and  204  of the upper supporting chord element, respectively, each being fastened with fasteners  34 . The lower skin layer  224  of the upper interior section  220  is overlaid upon the middle chord layer  204  and the stringer  226 , and is fastened to both of those parts. Overlaid upon and connecting to the lower skin layer  224  may be a stringer fitting  24 . 
     The lower wing section  238  comprises an upper skin layer  240 , a lower skin layer  242 , and a stringer element  244  therebetween. The upper skin layer  240  is fastened to the middle chord layer  230  of the lower supporting chord element  228  with fasteners  34  and the lower skin layer  242  is connected to the lower chord layer  232  of the lower supporting chord element  228  with fasteners  34 . A portion of the stringer  244  is also overlaid upon and connected to the middle chord layer  230  of the lower supporting chord element  228 . 
     The lower inner section  246  comprises an upper skin layer  248 , a lower skin layer  250 , and a stringer  252  therebetween. The upper skin layer  248  is fastened to the middle chord layer  230  of the lower supporting chord element  228  with fasteners  34  and the lower skin layer  250  is connected to the lower chord layer  232  of the lower supporting chord element  228  with fasteners  34 . A portion of the stringer  252  is also adjacent to and connected to the middle chord layer  230  of the lower supporting chord element  228 . 
     A spice plate  30  is adjacent to and fastened with fasteners  34  to the lower skin layers  242  and  250  of the lower wing section  238  and lower inner section  246 . The spice plate  30  serves to fasten the skin elements  242  and  250  together. 
     The extensions  210  and  236  of the upper and lower supporting chord elements  200  and  228  are each connected to a body web stiffener  28 , thereby connecting the upper and lower portions together. 
     An issue often arises with wing side-of-body joint assemblies  12  when joint elements such as the chord elements  18  are configured to produce internal reduced clearance regions  32 . As can be visually seen in  FIG. 2 , when such chord elements  18  have such reduced clearance regions  32  in addition to being fastened on multiple sides, the ability to position traditional headed bolts into the reduced clearance region  32  may be difficult or impossible. In addition, the ability to nut-side tighten to prevent bolt rotation may be increasingly difficult with existing designs. The present invention, however, utilizes a special cylindrical bolt assembly  34  to allow simplified joint assembly and reliable nut side torque application. 
     A simplified detail of the joint assembly  12  is illustrated in FIGS.  3  and  4 A-C. The present cylindrical bolt assemblies  34  are comprised of a cylindrical stud  36  having a threaded head section  38  and a threaded tail section (nut)  40 . The threaded head section  38  allows the cylindrical stud  36  to be pushed from outside the reduced clearance region  32  through both the chord  18  and skin  20 . This way, only a threaded head fastener  42 , and possibly head washers  44 , need be navigated into the reduced clearance region  32  rather than an entire bolt assembly. This drastically reduces assembly difficulties. In addition, the present invention contemplates the use of a cap nut  46  as the threaded head fastener  42 . The cap nut  46  may be tightened down against the cylindrical stud  36  until the end of the stud  36  on the threaded head section  38  contacts the bottom of the cap nut  46 , thus limiting further rotation of the nut  46  and forming a rigid fastener head  48 . A crimp or non-metallic insert in the cap nut  46  ensures that the nut  46  remains firmly locked in place after the fastener installation is complete. In this fashion, all the benefits of a traditional solid head bolt are achieved without the assembly difficulties. A nut element  50 , in combination with tail washers  52 , may be torqued onto the cylindrical stud  36  without rotation of the stud by restraining rotation of the cap nut  46  with a conventional wrench. 
     Although the formation of a rigid fastener head  48 , as described above, will preclude stud rotation during installation of the nut element  50 , the present invention further contemplates the use of a wrenching features  54  formed on the threaded tail section  40 . The wrenching feature  54  is intended to encompass a wide variety of features capable of restraining rotation of the cylindrical stud  36  without requiring access to the threaded head fastener  42 . These include, but are not limited to, prismatic extensions  56  as shown in  FIG. 6 , hexagonal recesses  58  as shown in  FIG. 7 , and spline recesses  59  as shown in  FIG. 8 . The wrenching features are restrained with a corresponding wrench or key to secure the cylindrical stud  36  while torque is applied purely to the nut element  50 . 
     In addition, the wrenching feature  54  allows for the use of an open head nut  60  as the threaded head fastener  42 , as shown in  FIGS. 5A-5C . The open head nut  60  is threaded onto the threaded head section  38  until the desired threat protrusion level is achieved. Thread protrusion is the length of thread from the threaded head section  38  projecting past the nut  60  as it is installed, and is commonly used as a means to ensure proper engagement of typical bolt and nut elements. During this operation, rotation of the stud  36  is prevented by reacting the nut  60  locking torque at the wrenching feature  54 . Installation of the nut element  50  is then accomplished by applying a torque to the nut element  50  and using the wrenching feature  54  to keep the stud  36  from rotating. This allows for a standard nut to be utilized as the threaded head fastener  42  which may reduce cost and simplify disassembly should it be desirable. A threaded head fastener with stop features (indentation)  110  may also be used to provide automatic orientation of the head fastener  110  with respect to the stud  36  and  120 . Finally, as an added feature to reduce weight or further conserve space, the wrenching feature  54  may be frangible as shown in  FIG. 4C . This means that after its use to restrain the cylindrical stud  36  while torque is applied to the nut element  50 , the wrenching feature  54  may be broken off to reduce weight or improve accessibility to other joint regions. 
     A mechanism to automatically orient the threaded head fastener with respect to the stud is provided in  FIGS. 9-12 . Referring now to  FIG. 9 , a cylindrical bolt assembly with a threaded head fastener with stop indentations  110  and stud  120  exhibiting the stop projections  112  are shown. The nut has two stop indentations  112  into which two stop projections  122  fit, to lock the threaded head fastener in the proper orientation with respect to the bolt. The threaded head fastener also comprises a base  114 , into which the second end  124  of the stud  120  fits. 
     Referring now to  FIG. 10 , an assembled stud and threaded head fastener  110  is shown. To assemble the threaded head fastener and stud into this configuration, the second end  124  of the stud  120  is inserted into the base  114  of the threaded head fastener  110 . The stop projections  122  may be either in a depressed or raised position. In the depressed position, the stop projections  122  are substantially within the stud  120 , thereby allowing for the head fastener to rotate and fasten onto the stud. The stop projections  122  are also sloped such that upon insertion of the stud  120  into the head fastener  110 , the stop projections  122  are pushed into the depressed position, allowing the head fastener  110  to pass over the stop projections  122  so that the head fastener  110  may be fastened onto the stud  120 . Rotational fastening continues until the stop projections q 22  re-emerge into the stop indentations  112  on the head fastener  110 . The stop projections  122  may be spring loaded so that they are biased towards the raised position. This allows the stop projections  122  to spring out of the stud once they are aligned with the stop indentations  112  of the head fastener  110 , thereby locking the stud  110  into a fixed position relative to the head fastener  120 . In  FIG. 13 , a ball-bearing shaped projection  123  is shown and serves the same function as stop projection  122 . The ball-bearing shaped projection  123  may be depressed into the stud  120  and may retain the head fastener  110  in a fastened position. 
     Referring now to  FIGS. 11A-11C , a wing-side of body joint utilizing the fastener with self-indexing nut system is shown, as well as a method of assembling a fastener with self-indexing nut system. 
     The fastener with self-indexing nut system comprises a stud  120  with a threaded head fastener  110  and a threaded tail fastener  50  or nut. The stud  120  comprises a first end  126  and a second end  124 , and a stud  120  extending therebetween. Spaced apart from the first end is a first threaded section  128  which runs to an unthreaded middle section  130 . Spaced apart from the second end  124  is a second threaded section  132  which runs to the unthreaded middle section  130 . 
     A wing-side of body joint comprises a chord element  18  and skin element  20  which define a reduced clearance region  32 . A stud  120  with stop projections  122  fits through the chord  18  and skin  20  into the reduced clearance region  32 . The second threaded section  132  is fastened to a threaded head fastener  110 . A threaded tail fastener or nut  50  is attached to the first threaded section. A wrenching feature  54  is found adjacent to the first end  126  of the stud  120 . 
     For assembly, the threaded head fastener  110  is placed within the low-clearance region  32 , over the hole through which the stud  120  is to be inserted. The stud  120  is then inserted and the head fastener  110  is rotated until the stop projections  122  emerge through the stop indentations  112 . At this point, a threaded tail fastener is fastened to the non-blind end and the wrenching feature may be broken off. During installation of the threaded tail fastener, the wrenching feature is held to prevent turning of the stud within the hole, thereby preventing scoring of the stud hole. 
     Referring now to  FIG. 12 , alternate stop indentations and stop projections are shown. Note that the stop projections may be found towards the end of the head fastener or spaced apart from the head fastener and that stop indentations and stop projections may be of any shape, including but not limited to circular, rectangular, square, triangular, hexagonal, star shaped, or any other appropriate shape. 
     While the invention has been described in connection with one or more embodiments, it is to be understood that the specific mechanisms and techniques which have been described are merely illustrative of the principles of the invention, numerous modifications may be made to the methods and apparatus described without departing from the spirit and scope of the invention as defined by the appended claims.