Device for fixing a member to an aircraft structure

[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.

[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.

[0017] FIG. 1 is a perspective bottom view of an aircraft and its belly fairing.

[0018] FIG. 2 is a perspective view of one example of a belly fairing.

[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] FIG. 4 is a view to an enlarged scale of the detail IV from FIG. 3.

[0021] FIG. 5 is a view corresponding to FIG. 4 for a different embodiment.

[0022] FIG. 6 is an exploded perspective view of the fixing device from FIG. 5.

[0023] FIG. 7 shows partly in section a fixing member adapted to receive a fixing device according to the invention.

[0024] FIG. 8 shows a different embodiment of a fixing device according to the invention fitted to the fixing member from FIG. 7.

[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] 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] 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] 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] 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] 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.