Abstract:
An apparatus for fixing a member to an aircraft structure including: firstly, fixing device having a shank with a head at one end, an externally machined portion of its peripheral wall at its other end, and a longitudinal interior thread at the same end as its externally machined portion, secondly, a bushing which cooperates with the machined portion of the shank so as to be fixed to the shank; and thirdly, an attachment device for attaching the member and having a threaded shank cooperating with the longitudinal interior thread.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of French Patent Application No. 0202951 filed Mar. 8, 2002, and French Patent Application No. 0206472 filed May 28, 2002. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an apparatus for fixing a member to an aircraft structure, for example a fairing, more particularly a belly fairing, or any type of conduit (for electricity, air, water, hydraulic fluid, etc.). 
   2. Description of the Related Art 
   There is a limited number of anchorage points for fixing a member to an aircraft structure because it is necessary to avoid the risk of weakening the structure. Special methods must therefore be used to drill or tapp holes in the structure. The resulting costs are relatively high and the number of fixing points is therefore intentionally limited. The same fixing point is therefore sometimes used to fix more than one member. 
   If a fixing point is used to fix more than one member, the position of the fixing point is not necessarily an ideal position for all the members. In the case of fixing an aircraft belly fairing, for example, if there is a relatively large overhang between a free edge of the fairing and its fixing point, it is possible to use the available fixing point and to fix the fairing by triangulation from that point. A first tie-rod substantially perpendicular to the fairing connects the fixing point to the fairing. The second tie-rod connects a point near the free edge of the fairing to the nearest fixing point. The second tie-rod limits the overhang but is significantly inclined in a direction normal to the fairing and is therefore unable to resist high tear-off forces. 
   It is therefore an object of the present invention to provide an apparatus that does not use the usual anchorage points on an aircraft structure. Of course, given the aeronautical application of an apparatus of this kind, the apparatus must ensure excellent fixing of members to the structure. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention proposes a system for fixing a member to an aircraft structure, the system includes: firstly, fixing devices having a shank with a head at one end, an externally machined portion of its peripheral wall at its other end, and a longitudinal interior thread at the same end as its externally machined portion, secondly, a bushing adapted to cooperate with the machined portion of the shank so as to be fixed to the shank; and thirdly, attachment devices for attaching the member and having a threaded shank cooperating with the longitudinal interior thread. 
   The member is fixed to a fixing device of the structure. A tapped hole is usually used for fitting the fixing device. Such devices are sometimes known as “pull-ins” and are used to assemble components of the aircraft structure. The invention proposes to fix a member using the tapped hole in a pull-in bolt after the latter is fitted. The fixing device is usually fitted so that the thread is at the end toward the interior of the aircraft, i.e. at the end opposite the member to be fixed. It suffices to fit the fixing device the other way around, so that the thread can be used to fix the member. 
   The machined rod can be a threaded rod, in which case the corresponding bushing is a nut. The rod can instead resemble a bolt, but with imprints in place of the thread. The bushing is then a crimping ring that is crimped to the end of the rod. 
   The attachment device includes a bore substantially perpendicular to the machined rod, for example, which allows the fixing member and the fairing to be connected with the aid of a pin, as is standard practice when fixing using a tie-rod. 
   The attachment device is fixed to the machined rod and to the thread and to guarantee that the attachment device is immobilized relative to them, it advantageously includes a lock-nut cooperating with the threaded rod of the fixing device. 
   In a preferred embodiment, the attachment device according to the invention takes the form of an eyebolt provided with a threaded rod. The attachment device then comprises only one part, which can be associated with a lock-nut. 
   In a different embodiment, the attachment device according to the invention includes a threaded shaft cooperating with the thread on the threaded rod and a yoke fixed to the shaft. This solution uses two parts (and where applicable lock-nuts). It guarantees correct mounting and orientation of the attachment device relative to the member to be fixed. The threaded shaft can be screwed all the way into the interior thread and the yoke can then be positioned relative to the axis. In this latter embodiment, the yoke is screwed to the threaded shaft, for example, and disposed between two nuts on the shaft. 
   In a different embodiment, suitable in particular for fixing conduits of all kinds (electrical, pneumatic, hydraulic, etc.), the attachment device includes a clip fixed to the machined rod by a bolt, for example. 
   The present invention also provides an aircraft whose structure includes fixing devices including: firstly, a shank having a head at one end, an externally machined portion of its peripheral wall at its other end, and a longitudinal interior thread at the same end as its externally machined portion; and secondly, a bushing adapted to cooperate with the machined portion of the shank so as to be fixed to the shank, in which aircraft the head of a fixing device is oriented toward the interior of the aircraft and the shank and its interior thread are oriented toward the exterior of the aircraft. 
   Details and advantages of the present invention will emerge more clearly from the following description, which is given with reference to the accompanying diagrammatic drawings. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a perspective bottom view of an aircraft and its belly fairing; 
       FIG. 2  is a perspective view of one example of a belly fairing; 
       FIG. 3  is an enlarged sectional view taken along the line III—III of  FIG. 1 , showing the fixing of the belly fairing close to a free edge under a wing of the aircraft; 
       FIG. 4  is an enlarged view of the detail IV in  FIG. 3 ; 
       FIG. 5  is a view corresponding to  FIG. 4  that shows an alternate embodiment; 
       FIG. 6  is an exploded perspective view of the fixing device and attachment device of  FIG. 5 ; 
       FIG. 7  shows partly in section a fixing device adapted to receive an attachment device according to the invention; and 
       FIG. 8  shows an alternate embodiment of a fixing lug according to the invention fitted to the fixing device of FIG.  7 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  is a perspective bottom view of a passenger aircraft which has a fuselage  2  and two wings  4 . The lower portion of the fuselage  2  carries a belly fairing  6  between the wings  4 .  FIG. 2  is a perspective view of one example of a belly fairing  6 . This figure shows that the belly fairing  6  has an exterior surface  8  stiffened by ribs known as frames  10  or webs  12 , according to their orientation relative to an axis  14  of the aircraft. The exterior surface  8  has openings  16  at the inboard ends of the wings  4 . 
   A first application of the present invention relates to fixing the belly fairing  6  to the structure of the fuselage  2  (see  FIGS. 3  to  6 ). It relates in particular to fixing the belly fairing  6  such that the openings  16  are configured to permit the wings  4  to pass therethrough. 
     FIG. 3  is a view in cross section taken along line III—III of FIG.  1 . This figure shows a frame  10 ′ (FIGS.  2  and  3 ). In addition to the frame  10 ′ and the exterior surface  8  of the belly fairing  6 ,  FIG. 3  also shows a section  18 , a corresponding cover section  20 , a portion  22  of the inboard end of a wing  4 , and a lower wing surface panel  24 . 
   As seen in  FIGS. 3-4 , the lower wing surface panel  24  is sandwiched between the section  18  and its cover section  20 . Likewise the portion  22  of the inboard end of the wing  4  is similarly sandwiched between [§] section  18  and cover [§] section  20 . This assembly uses fixing devices or special bolts  26  usually called “pull-in bolts”. Unlike conventional bolts, pull-in bolts are designed to work in shear.  FIG. 6  shows a pull-in bolt  26 . It conventionally has a head  28 , a shank  30  and an exterior thread  32  at the end opposite the head  28 . The thread is designed to receive a nut  34 , and usually a washer  36 . In order to resist high shear loads, the pull-in bolt is made from an alloy known for its high strength and is machined by a process that does not produce swarf. 
   As shown in  FIG. 6 , the pull-in bolt  26  also has an interior thread  38 . The interior thread  38  is concentric with the axis of the pull-in bolt  26  and is formed in its shank  30 . The interior thread  38  has a diameter significantly less than that of the exterior thread  32 . It opens onto the end face of the pull-in bolt opposite the head  28  and is usually from 10 mm to 20 mm long. 
   The pull-in bolt  26  is usually fitted so that its head  28  bears on the cover section  20  and the washer  36  and the nut  34  are on the same side as the section  18 . It is fitted by screwing a threaded rod (not shown) into the interior thread  38 . The threaded rod is then pulled toward the interior of the aircraft by a hydraulic tool, entraining the pull-in bolt  26  with it. The shank  30  of the pull-in bolt  26  is then accommodated in bores (not shown) provided for this purpose in the section  18 , the cover section  20  and the structural member to be fixed. The diameters of the bores and the shank  30  are such that the pull-in bolt  26  must be forced into place. Once the pull-in bolt  26  is in place, the threaded rod of the hydraulic tool is unscrewed from the interior thread  38  and the washer  36  and the nut  34  is fitted. The nut  34  is then tightened to a predetermined torque. 
   The present invention proposes to fit the pull-in bolt  26  “the other way around”, i.e. with the head  28  on the same side as the section  18  and the nut  34  on the same side as the cover section  20 . In this way, the interior thread  38  is on the same side as the belly fairing  6  and the interior thread  38  provides a fixing point for the fairing  6 . 
   The pull-in bolt  26  is fitted by the procedure described above, it is just that the pull-in bolt  26  is positioned differently. 
     FIG. 4  shows one example of fixing the belly fairing  6  using the interior thread  38  and an attachment device which includes a shaft  40  and a yoke  42 . 
   The shaft  40  has a central portion  44  with flats  46  and two coaxial threaded portions  48 ,  48 ′ on opposite sides of the central portion  44 . One threaded portion  48  is screwed all the way into the interior thread  38 . A lock-nut  50  is fitted and tightened to ensure that the threaded portion  48  remains screwed all the way into the interior thread  38 . 
   The yoke  42  takes the form of a stirrup member with a base  52  and two branches  54  substantially perpendicular to the base  52 , which is internally threaded so that it can be screwed onto the second threaded portion  48  of the shaft  40 , with the base  52  substantially parallel to the cover section  20 . Nuts  56  hold the yoke  42  in position relative to the shaft  40 . 
   The frame  10 ′ is equipped with a fixing member  58 . A pin  60  passing through bores (not shown) in the fixing member  58  and in the branches  54  connects the fixing member  58  to the branches  54  of the yoke  42 . 
     FIG. 5  shows a different way of fixing the belly fairing  6  using the pull-in bolt  26  and its interior thread  38 . Here the shaft  40  and the yoke  42  are replaced by an eyebolt  62 . The latter is shown to a larger scale in FIG.  6 . The eyebolt  62  has a head  64  connected to a threaded portion  66 . The head  64  is the same shape as the end of a tie-rod, and is therefore substantially cylindrical, and has a thickness that is small compared to its diameter. A hole  68  at its center is adapted to receive the pin  60  (see FIG.  5 ). The threaded portion  66  is perpendicular to the axis of the head  64  and the hole  68 . The thread on the threaded portion  66  matches the interior thread  38  of the pull-in bolt  26 . 
   The eyebolt is preferably fitted by screwing the threaded portion  66  all the way into the interior thread  38 . Ideally, in this position, the head  64  of the eyebolt is oriented correctly for the pin  60  to be inserted into the hole  68  and the corresponding hole (not shown) in the fixing member  58 . However, if its orientation is not correct, the eyebolt is unscrewed until it is in the correct position. To enable it to be retained in this position, a lock-nut  70  can be screwed onto the threaded portion  66  before it is screwed into the interior thread  38 . Once the eyebolt  62  is correctly positioned relative to the pull-in bolt  26 , the lock-nut  70  is tightened against the pull-in bolt  26  thereby immobilizing the eyebolt  62 . 
     FIG. 3  shows a first tie-rod  72  connecting the lower wing surface panel  24  to the frame  10 ′. On the lower wing surface panel  24  is a fixing member  74  of the same type as the fixing member  58  shown in  FIGS. 4 and 5 . The first tie-rod  72  has an eyelet at each end and a pin can therefore be used to fix the first tie-rod  72  to the fixing member  74 . The opposite end of the first tie-rod  72  is fixed in the same way to the fixing member  58  of the frame  10 ′. 
     FIG. 3  shows a second tie-rod  76  which connects the fixing member  74  to the frame  10 ′. Here the fixing point on the frame  10 ′ is offset toward the center of the aircraft. The belly fairing  6  is retained by triangulation with the aid of the tie-rods  72  and  76 . 
   It would equally be possible, starting with the same fixing member  74 , to perform a triangulation to retain the belly fairing  6  in the vicinity of the opening  16 . The alternative solution proposed by the invention firstly guarantees improved fixing of the belly fairing  6  to the aircraft structure. This is because an apparatus according to the invention, as described above with reference to  FIG. 4  or  FIG. 5 , is more resistant to forces tending to tear off the belly fairing  6  since the apparatus is substantially perpendicular to the fairing and therefore works essentially in traction. A tie-rod such as the second tie-rod  76  is strongly inclined in a direction normal to the exterior surface  8  of the belly fairing  6  and is therefore less effective at resisting forces tending to tear off the belly fairing  6 . 
   Using the interior thread  38  of the pull-in bolt  26  as a fixing point further reduces the overhang of the belly fairing  6  through an appropriate choice of the pull-in bolt  26 .  FIG. 3  shows that a tie-rod such as the second tie-rod  76  could not be located as close to the passage  16  for the wing  4  as the apparatus according to the invention shown in FIG.  3 . 
   Finally, an apparatus according to the present invention has the advantage of a lower unit price than prior art solutions while providing excellent fixing, as described above. No particular adaptation is required to the structure of the aircraft and fitting an apparatus according to the invention (for example a shaft and a yoke or an eyebolt) requires no more time, and possibly less time, than fitting a tie-rod. 
   An alternate apparatus according to the invention can also be used with a fixing device other than the pull-in bolt  26  and its nut  34 .  FIG. 7  shows a different fixing member that can also receive the attachment devices according to the invention described above. 
   The  FIG. 7  fixing device has a shank  130  and a bushing  134 . The shank  130  is generally cylindrical. The shank  130  has at one end a flat countersunk head  128 . The other end of the shank  130  carries peripheral imprints  132  forming a series of parallel circular grooves. Just like the shank  30  of the pull-in bolt  26 , the shank  130  has an interior thread  138  which is concentric with the axis of the shank  130  and whose diameter is significantly less than the outside diameter of the shank  130 . The interior thread  138  opens onto the end face of the shank  130  opposite the head  128  and is usually from 10 mm to 20 mm long. 
   The bushing  134  can be crimped onto the imprints  132  on the shank  130 . It has a substantially smooth interior surface which is deformed by crimping to espouse the shapes of the peripheral imprints  132 . 
   The shank  130  can be fitted into bores without using any special tool (unlike the pull-in bolt  26  described above). Once in place, the threaded end of a tool is screwed into the interior thread  138  and traction is applied to the shank  130  to apply a high pressure at the head  128 . The bushing  134  is pushed in the opposite direction and then crimped. This produces an excellent permanent assembly. Once the assembly has been completed, the tool is removed from the interior thread  138 , which remains free. 
     FIG. 8  shows an embodiment of an alternate apparatus according to the invention combined with the fixing device from FIG.  7 . This embodiment can also be used in conjunction with a pull-in bolt  26 . In  FIG. 8 , the fixing device connects a panel  78  to a structural member  80 . These two members are clamped between the bushing  134  and the head  128 . After assembling these two members, the interior thread  138  remains free. The interior thread  138  then receives a bolt  82  used to retain a fixing lug  84  which has a bearing face  86  bearing against the face of the shank  130  onto which the interior thread  138  opens. A rim  88  is provided on one side of this surface to bear against the exterior wall of the bushing  134  and thereby locate the fixing lug  84  correctly. Opposite the rim  88 , the fixing lug  84  is bent and carries a clip  90  attached by a nut and bolt  92 . The clip  90  can then receive any type of conduit (electrical, pneumatic, hydraulic, etc.). The size and type of clip are adapted to suit the type of conduit to be fixed. 
   The present invention is not limited to the embodiments described above by way of nonlimiting example. It also relates to all embodiments that may suggest themselves to the person skilled in the art that fall within the scope of the following claims.