Abstract:
A system for fixing a member to an aircraft structure includes, firstly, fixing members comprising 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 bush which cooperates with the machined portion of the shank so as to be fixed to the shank, and, thirdly, an attachment for attaching the member and having a threaded shank cooperating with the longitudinal interior thread. Applications include fixing a belly fairing to an aircraft.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a device 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.).  
           [0003]    2. Description of the Prior Art  
           [0004]    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 holes and tapped 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.  
           [0005]    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, 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 the fairing to the nearest fixing point. The second tie-rod limits the overhang but is significantly inclined to the normal to the fairing and is therefore unable to resist high tear-off forces.  
           [0006]    It is therefore an object of the present invention to provide a new fixing device that does not use the usual anchorage points on an aircraft structure. Of course, given the aeronautical application of a device of this kind, the device must ensure excellent fixing of members to the structure.  
         SUMMARY OF THE INVENTION  
         [0007]    To this end, the present invention proposes a system for fixing a member to an aircraft structure, the system including, firstly, fixing members comprising 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 bush adapted to cooperate with the machined portion of the shank so as to be fixed to the shank, and, thirdly, attachment means for attaching the member and having a threaded shank cooperating with the longitudinal interior thread.  
           [0008]    Thus the member is fixed to a fixing member of the structure. The tapped hole used for fixing the member is usually used only for fitting the fixing member. 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, after the latter is fitted. The fixing device is usually fitted so that the thread is at the end towards 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.  
           [0009]    The machined rod can be a threaded rod, in which case the corresponding bush is a nut. The rod can instead resemble a bolt, but with imprints in place of the thread. The bush is then a crimping ring that is crimped to the end of the rod.  
           [0010]    The attachment means include a bore substantially perpendicular to the machined rod, for example, which allows the fixing device and the fairing to be connected with the aid of a pin, as is standard practice when fixing using a tie-rod.  
           [0011]    The fixing device is fixed to the machined rod and to the thread and to guarantee that the fixing device is immobilized relative to them, it advantageously includes a lock-nut cooperating with the threaded rod of the attachment means.  
           [0012]    In a preferred embodiment, the attachment means of the fixing device according to the invention take the form of an eyebolt provided with a threaded rod. The fixing device then comprises only one part, which can be associated with a lock-nut.  
           [0013]    In a different embodiment, the attachment means of the fixing device according to the invention include 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 means 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.  
           [0014]    In a different embodiment, suitable in particular for fixing conduits of all kinds (electrical, pneumatic, hydraulic, etc.), the attachment means include a clip fixed to the machined rod by a bolt, for example.  
           [0015]    The present invention also provides an aircraft whose structure includes fixing members 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 bush adapted to cooperate with said machined portion of said shank so as to be fixed to said shank, in which aircraft said head of a fixing member is oriented toward the interior of said aircraft and said shank and its interior thread are oriented toward the exterior of said aircraft.  
           [0016]    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 DRAWINGS  
       [0017]    [0017]FIG. 1 is a perspective bottom view of an aircraft and its belly fairing.  
         [0018]    [0018]FIG. 2 is a perspective view of one example of a belly fairing.  
         [0019]    [0019]FIG. 3 is a partial view to a larger scale and in section taken along the line III-III in FIG. 1, showing the fixing of the belly fairing close to a free edge under a wing of the aircraft.  
         [0020]    [0020]FIG. 4 is a view to an enlarged scale of the detail IV from FIG. 3.  
         [0021]    [0021]FIG. 5 is a view corresponding to FIG. 4 for a different embodiment.  
         [0022]    [0022]FIG. 6 is an exploded perspective view of the fixing device from FIG. 5.  
         [0023]    [0023]FIG. 7 shows partly in section a fixing member adapted to receive a fixing device according to the invention.  
         [0024]    [0024]FIG. 8 shows a different embodiment of a fixing device according to the invention fitted to the fixing member from FIG. 7. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    [0025]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 the axis  14  of the aircraft. The exterior surface  8  has openings  16  at the inboard ends of the wings  4 .  
         [0026]    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  adjoining openings  16  for the wings  4  to pass through.  
         [0027]    [0027]FIG. 3 is a view in cross section relative to the axis  14  of the aircraft. 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 .  
         [0028]    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 . This assembly uses special bolts  26  usually called “pull-in bolts”. Unlike conventional bolts, pull-ins are designed to work in shear. FIG. 6 shows a pull-in. 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 is made from an alloy known for its high strength and is machined by a process that does not produce swarf.  
         [0029]    As shown in FIG. 6, the bolt  26  also has an interior thread  38 . The interior thread  38  is concentric with the axis of the 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 bolt opposite the head  28  and is usually from 10 mm to 20 mm long.  
         [0030]    The 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 towards the interior of the aircraft by means of a hydraulic tool, entraining the bolt  26  with it. The shank  30  of the bolt  26  is then accommodated in bores 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 bolt  26  must be forced into place. Once the 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  are fitted. The nut  34  is then tightened to a predetermined torque.  
         [0031]    The present invention proposes to fit the 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 .  
         [0032]    The bolt  26  is fitted by the procedure described above, it is just that the bolt  26  is positioned differently.  
         [0033]    [0033]FIG. 4 shows one example of fixing the exterior fairing  6  using the interior thread  38  and a fixing device which includes a shaft  40  and a yoke  42 .  
         [0034]    The shaft  40  has a central portion  44  with flats  46  and two coaxial threaded portions  48  on respective 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 remains screwed all the way into the interior thread  38 .  
         [0035]    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 .  
         [0036]    The frame  10 ′ is equipped with a fixing member  58 . A pin  60  passing through bores in the fixing member  58  and in the branches  54  connects the fixing member  58  to the branches  54  of the yoke  42 .  
         [0037]    [0037]FIG. 5 shows a different way of fixing the belly fairing  6  using the 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. It has a head  64  to which is connected a threaded portion  66 . The head  64  is the same shape as the end of a tie-rod, and is therefore a substantially circular cylinder, 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  naturally matches the interior thread  38  of the bolt  26 .  
         [0038]    The eyebolt is fitted by screwing the threaded portion  66  all the way into the interior thread  38 , for example. 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 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 is correctly positioned relative to the bolt  26 , the lock-nut  70  is tightened against the bolt  26 , thereby immobilizing the eyebolt  62 .  
         [0039]    A fixing device such as that described above with reference to FIG. 4 or FIG. 5 is used in conjunction with a conventional fixing device. FIG. 3 shows two such devices. It 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 tie-rod  72  to the fixing member  74 . The tie-rod  72  is fixed in the same way to the fixing member  58  of the frame  10 ′.  
         [0040]    [0040]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 .  
         [0041]    It would equally well 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 a fixing device 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 fixing device 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 to the normal to the exterior surface  8  of the fairing  6  and is therefore less effective at resisting forces tending to tear off the fairing  6 .  
         [0042]    Using the interior thread  38  of the bolt  26  as a fixing point further reduces the overhang of the belly fairing  6 , through an appropriate choice of the 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 fixing device according to the invention shown in FIG. 3.  
         [0043]    Finally, a fixing device according to the present invention has the advantage of a lower unit price than prior art solutions whilst providing excellent fixing, as described above. No particular adaptation is required to the structure of the aircraft and fitting a fixing device 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.  
         [0044]    A fixing device according to the invention can also be used with a fixing member other than the bolt  26  and its nut  34 . FIG. 7 shows a different fixing member that can also receive the fixing devices according to the invention described above.  
         [0045]    The FIG. 7 fixing member has a shank  130  and a bush  134 . The shank  130  is a circular cylindrical shank. It 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 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.  
         [0046]    The bush  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 imprints  132 .  
         [0047]    The shank  130  can be fitted into bores without using any special tool (unlike the 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 bush  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.  
         [0048]    [0048]FIG. 8 shows one embodiment of a fixing device according to the invention combined with the fixing member from FIG. 7. This embodiment can also be used in conjunction with a bolt  26 . In FIG. 8, the fixing member connects a panel  78  to a structural member  80 . These two members are clamped between the bush  134  and the head  128 . After assembling these two members, the interior thread  138  remains free. It 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 bush  134  and thereby locate the fixing lug correctly. Opposite the rim  88 , the fixing lug is bent and carries a clip  90  attached by means of a nut and bolt  92 . The clip 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.  
         [0049]    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.