STRUCTURAL CONNECTING ROD FOR AIRCRAFT, COMPRISING A CONNECTING ROD BODY WITH A SANDWICH STRUCTURE

Abstract

To facilitate manufacturing and improve the performance of a structural connecting rod (20) for an aircraft, this connecting rod comprises a connecting rod body (26) and two end portions (28) arranged on either side of the connecting rod body along a longitudinal central axis of the connecting rod (24). Each end portion (28) includes at least one mounting lug (30) projecting from the connecting rod body (26) along the longitudinal central axis (24). According to the invention, the connecting rod body (24) has a sandwich structure comprising two opposing outer skins (34) between which is sandwiched a honeycomb inner core (38). At least one of the two outer skins (34) includes a skin extension (44) to form part of said at least one mounting lug (30) of at least one of the two end portions (28). Figure 5

Description

Title of the invention: STRUCTURAL CONNECTING ROD FOR AIRCRAFT, COMPRISING A CONNECTING ROD BODY WITH STRUCTURE SANDWICH Technical field

[0001] The invention relates to the field of structural connecting rods for aircraft. Such connecting rods are generally installed in the aircraft so as to transmit significant forces between the parts which they connect.

[0002] These structural connecting rods can, for example, be installed within the central wing box, or within a landing gear.

[0003] The invention relates more preferably, but not exclusively, to commercial aircraft. STATE OF PRIOR ART

[0004] The implementation of structural connecting rods is widespread within aircraft.

[0005] Several types of connecting rods exist, including metal connecting rods which have the advantage of being easy to manufacture. However, their high mass is a real disadvantage.

[0006] There are also connecting rods made of composite material, the mass of which is significantly reduced compared to that of metal connecting rods. However, the junction between the connecting rod body and the end portions often proves complicated to produce, especially when these end portions each include one or two mounting lugs. Statement of the invention

[0007] To address the drawback mentioned above, the invention firstly relates to a structural connecting rod for an aircraft, the connecting rod comprising a connecting rod body and two end portions arranged on either side of the connecting rod body along a longitudinal central axis of the connecting rod, each end portion comprising at least one mounting lug projecting from the connecting rod body along the longitudinal central axis.

[0008] According to the invention, the connecting rod body has a sandwich structure comprising two opposite outer skins between which an inner cellular core is sandwiched, and at least one of the two outer skins comprises a skin extension to form a part of said at least one mounting lug, of at least one of the two end portions of the connecting rod.

[0009] The invention thus differs from the prior art by providing a sandwich structure, the outer skin(s) of which are extended to form part of one or more mounting lugs. This design makes it possible to obtain a mass lightened, while providing excellent mechanical properties, in particular in bending in a given direction, as well as in traction and compression. The transfer of forces between the connecting rod body and the end portions of the connecting rod is facilitated by the skin extension(s), which form an integral part of one or more mounting lugs. Finally, the design specific to the present invention allows simple, rapid and inexpensive manufacturing, in particular by producing a sandwich panel which can then be cut to obtain several connecting rods according to the invention.

[0010] The invention preferably provides at least one of the following optional features, taken alone or in combination.

[0011] Preferably, at least one of the two outer skins comprises two skin extensions to form a part of said at least one mounting lug of each of the two end portions of the connecting rod.

[0012] Preferably, the inner cellular core is made: - closed or open pore foam, or - honeycomb, or - using tubular elements secured to each other by being stacked in a stacking direction parallel to the longitudinal central axis, each tubular element having a hollow centered on a tubular element axis orthogonal to the longitudinal central axis of the connecting rod.

[0013] Preferably, the two opposing outer skins are each made using a composite material, preferably a carbon fiber reinforced polymer (CFRP) material.

[0014] Preferably, the structural connecting rod comprises, associated with at least one of the mounting lugs, a transition piece comprising: - a first part sandwiched between one of the two outer skins and one end of the inner core in the direction of the longitudinal central axis, the first part of the transition piece having an increasing thickness as it extends in the direction of the associated ear; - a second part extending the first part, and integral with the extension of skin forming an integral part of said associated ear.

[0015] Preferably, the first part of the transition piece has a first chamfer, pressed against a second chamfer made on the end of the internal core.

[0016] Preferably, the second part of the transition piece has a constant or substantially constant thickness.

[0017] Preferably, at least one of the end portions of the connecting rod comprises two facing mounting lugs, each of the two lugs having: - an external skin formed by the extension of skin; - a central body formed by the second part of the transition piece; and - an internal skin formed by a closing piece with a generally U-shaped section, the two branches of the U respectively forming the internal skin of each of the two facing ears, and the branch of the U being pressed against the end of the internal cellular core of the connecting rod body, between the two ears.

[0018] Preferably, the structural connecting rod comprises two lateral webs respectively covering two sides of the internal cellular core.

[0019] The invention also relates to a method of manufacturing a plurality of structural connecting rods like that described above, the method comprising the following steps: - production of a sandwich panel comprising two skins enclosing an inner honeycomb body; and - cutting the panel along parallel cutting lines, so as to obtain said plurality of structural rods.

[0020] Preferably, the cuts are implemented simultaneously.

[0021] Preferably, the sandwich panel is produced by hot press or autoclave.

[0022] Finally, the invention also relates to an aircraft comprising at least one such connecting rod. structural.

[0023] Other advantages and characteristics of the invention will appear in the detailed non-limiting description below. Brief description of the drawings

[0024] This description will be made with regard to the attached drawings among which;

[0025] [fig. 1] represents a schematic front view of an aircraft;

[0026] [fig.2] represents a perspective view of one of the landing gears fitted the aircraft of [fig.l];

[0027] [fig.3] represents a front view of a central wing box equipping the aircraft of [fig.l];

[0028] [fig.4] represents a perspective view of a structural connecting rod equipping the aircraft of [fig.l], the connecting rod being in the form of a first preferred embodiment of the invention;

[0029] [fig.5] represents a partial perspective view of the connecting rod shown in the figure previous, cut by the median longitudinal plane P of [fig.4];

[0030] [fig.6] represents an enlarged plan view of one end of the connecting rod shown in the [fig-5] ;

[0031] [fig.7] represents an exploded perspective view of the connecting rod shown in figures 4 at 6;

[0032] [fig.8] is a perspective view diagrammatically showing a step in the production of a sandwich panel, for the manufacture of several structural connecting rods;

[0033] [fig.9] is a perspective view diagrammatically showing a later step for the production sandwich panel;

[0034] [fig.10] is a perspective view schematizing a further stage for the production of the sandwich panel;

[0035] [fig.l 1] is a plan view diagrammatically showing a cooking step of the sandwich panel;

[0036] [fig. 12] is a plan view schematically illustrating an alternative embodiment for the cooking the sandwich panel;

[0037] [fig. 13] is a perspective view diagrammatically showing a step of cutting out the sandwich panel;

[0038] [fig. 14] is a perspective view diagrammatically showing a step of cutting the sandwich panel, so as to obtain the structural connecting rods;

[0039] [fig. 15] is a perspective view diagrammatically showing a step of fixing the lateral sails to the structural connecting rods;

[0040] [fig. 16] is a perspective view diagrammatically showing a stage of finishing the end portions of one of the structural connecting rods;

[0041] [fig.17] is a perspective view of a structural connecting rod similar to that of [fig.4], and presented according to an alternative embodiment;

[0042] [fig. 18] represents a perspective view of another structural connecting rod in the form of a second preferred embodiment of the invention;

[0043] [fig. 19] represents an enlarged partial plan view of one end of the connecting rod shown in [fig. 18];

[0044] [fig.20] represents an exploded perspective view of the connecting rod shown in the figures 18 and 19;

[0045] [fig.21] is a perspective view diagrammatically showing a stage in the manufacture of the core internal alveolar part of the connecting rod shown in Figures 18 to 20; and

[0046] [fig.22] is a perspective view diagrammatically showing a stage of cutting a panel sandwich obtained with the core shown in [fig.21], so as to obtain the structural connecting rods. DETAILED DISCLOSURE OF PREFERRED EMBODIMENTS

[0047] With reference to [fig. 1], there is shown an aircraft 100 of the commercial airplane type, comprising two wings 2 fixed to a fuselage 3 and each carrying a turbomachine 1, such as a turbojet.

[0048] The two wings 2 are fixed to each other by a central wing box 4, an example of which is shown in [fig.3]. This central wing box 4 is conventionally produced using an upper wall 6, a lower wall 8, side walls 10, and structural connecting rods 12 connecting the two walls 6, 8, 10.

[0049] The aircraft 100 is also equipped with several landing gears 14, including one example is shown in [fig.2]. It classically comprises several articulated structural connecting rods 16.

[0050] The invention relates to structural connecting rods intended to equip the aircraft, such as the connecting rods described above, forming an integral part of the central wing box 4, or of the landing gear 14. Nevertheless, other applications can be envisaged for the structural connecting rod according to the invention, which can be integrated into any aircraft cell, without departing from the scope of this invention.

[0051] Referring now to Figures 4 to 6, there is shown a structural connecting rod 20 according to a first preferred embodiment of the invention.

[0052] The structural connecting rod 20 extends along a longitudinal central axis 24, parallel to a longitudinal direction 22 of this same connecting rod. Overall, the connecting rod 20 comprises a connecting rod body 26 extending over a very large part of the length of the connecting rod, of which it constitutes the central portion in relation to the direction 22. On either side of the connecting rod body 26, along the axis 24, two end portions 28 are provided. These end portions 28 are of identical or different designs, but in all cases they allow the connecting rod to be fixed to the two aircraft elements to be connected. In the first preferred embodiment which is envisaged, the two end portions 28 are of identical designs, being arranged symmetrically with respect to a median transverse plane of the connecting rod. Consequently, only one of the two end portions 28 will be described below.

[0053] The end portion 28 comprises at least one mounting lug 30, arranged projecting from the connecting rod body 26 along the axis 24. Preferably, there are two mounting lugs 30 which equip the end portion 28, to form a fixing yoke while being parallel or substantially parallel to each other.

[0054] Each mounting ear 30 is pierced with an orifice 32 to receive a fixing member (not shown), such as a hinge pin intended to pass through the yoke.

[0055] One of the particularities of the invention lies in the design of the connecting rod 20, the connecting rod body 26 of which has a sandwich structure. More precisely, the connecting rod body 26 is made of two opposite outer skins 34, between which is sandwiched an inner cellular core 38, here a foam. The foam can be closed-pore or open-pore, while having a high rigidity. It can for example be a metal foam, but any so-called rigid foam is suitable. Generally speaking, it can be a dense foam (density between 30 and 300 kg / m3), rigid, having a high compressive strength, compatible with transformation temperatures and having a capacity for bonding to composite materials.

[0056] At each of the two ends of the foam core 38, opposite in the direction 22, a chamfer 40 is provided on each of two upper and lower faces. The two opposite chamfers 40 lead to a reduction in the thickness of the foam core 38, according to the stacking direction 42 of the elements of the sandwich structure. The stacking direction 42 is orthogonal to the longitudinal direction 22 of the connecting rod.

[0057] Each of the two outer skins 34 has, respectively at its two opposite ends along the direction 22, two skin extensions 44 intended to form a part of one of the two mounting ears 30 of each of the two end portions 28.

[0058] Furthermore, for each lug 30, a transition piece 46 is provided, one part of which is located in the connecting rod body 26, and the other part of which is integrated into the relevant lug 30. More precisely, the transition piece 46 firstly comprises a first part 46a sandwiched between one of the two outer skins 34 and one of the ends of the inner core 38. This first part 46a, of generally triangular shape, thus has an increasing thickness as it extends in the direction of its associated lug 30. This increasing thickness is materialized by the presence of a chamfer 48, called the first chamfer, which is pressed against the chamfer 40 of the core 38, called the second chamfer. The cooperation of these two chamfers 40, 48 allows the connecting rod body 26 to have a constant overall thickness, up to the terminal part of its two opposite longitudinal ends.

[0059] The transition piece 46 also comprises a second part 46b extending the first part 46a, being integral with the latter. The second part 46b has a constant or substantially constant thickness, being parallelepipedal.

[0060] With this design, each of the two ears 30 of the yoke is formed by stacking, in the direction 42, an external skin formed by the skin extension 44, a central body formed by the second part 46b of the transition piece, and an internal skin. These three stacked elements are integral with each other.

[0061] As regards the two internal skins of the two ears 30 forming the yoke, these are formed by a closing piece 54 of generally U-shaped section, as is best seen in [fig.6]. The two branches 56 of the U in fact form respectively the internal skin of each of the two facing ears 30. In addition, the base of the U 58 is pressed against the end of the internal core 38 of reduced thickness by the chamfers 40, being located between the base of the two ears 30.

[0062] Finally, to form the connecting rod laterally and isolate the internal core 38 from the exterior, two lateral webs 60 are provided covering the two opposite sides of the core 38. Each lateral web 60 has two opposite edges in the direction 42, these edges being pressed respectively against the two external skins 34, for better confinement of the core 38.

[0063] With the exception of the internal core 38, all of the constituent elements of the connecting rod which have been described above are preferably made using a material composite, and more preferably in a carbon fiber reinforced polymer material, also called CFRP, or CRFP (from the English Carbon Fiber Reinforced Polymer). Other composite materials can nevertheless be used, without departing from the scope of the invention.

[0064] A method of manufacturing a plurality of structural connecting rods 20, such as that which has just been described above, will now be described.

[0065] First of all, the assembly of different elements is carried out to produce a sandwich panel. During this assembly, which will be described with reference to Figures 8 to 10, the elements adhere to each other by the nature of their material, or by the interposition of adhesive layers.

[0066] First of all, with reference to [fig.8], the U-shaped closing pieces 54 are assembled at the ends of an inner alveolar body in the form of a foam plate 38', already chamfered. Then, with reference to [fig.9], the transition pieces 46 are put in place, followed by the outer skins 34 as can be seen in [fig-10].

[0067] The panel 62 thus obtained is then subjected to a cooking step, by polymerization. This cooking step is carried out in a conventional manner, for example by hot pressing the panel 62 as shown diagrammatically in [fig. 11], or under autoclave 64 as can be seen in [fig. 12].

[0068] When the polymerization is complete, the obtained hardened panel 62 is trimmed along its periphery, according to a trimming line 66 shown in [fig. 13]. The objective of this trimming is to obtain a panel with protruding edges.

[0069] Then, the panel 62 undergoes several cuts, along cutting lines 68 parallel to each other, and parallel to the longitudinal direction 22 of the connecting rods 20 obtained following these cuts. [fig. 14] schematically represents these cuts, which can be carried out successively, or simultaneously for a gain in productivity.

[0070] The same panel 62 can give rise to a large number of structural connecting rods 20, depending on the initial dimension of the panel and the dimension of the desired connecting rods.

[0071] Once the connecting rods 20 have been obtained, the lateral webs 60 are placed, for example by gluing onto the outer skins 34, so as to close a watertight envelope in which the inner cellular core 38 is located. This step is shown diagrammatically in [fig-15].

[0072] Finally, the manufacturing process of the connecting rods 20 is completed by the optional machining of the mounting lugs 30, and the drilling of their orifices 32. The machining consists of rounding the lugs 30 on each of the two end portions 28, as can be seen in [fig. 16].

[0073] Referring now to [fig. 17], an alternative embodiment is shown, in which the inner cellular core 38 is replaced by a honeycomb bar. The cells of the honeycomb bar are oriented parallel to the direction 42 of stacking of the elements of the sandwich structure.

[0074] The other elements of the connecting rod 20 are similar to those presented in the description of the first preferred embodiment, just as the manufacturing method remains identical or similar.

[0075] Referring now to Figures 18 to 20, a connecting rod 20 according to a second preferred embodiment of the invention will be described. The connecting rod 20 has many features in common with the connecting rod described previously, within the framework of the first preferred embodiment. Thus, in the figures, the elements which bear the same numerical references correspond to identical or similar elements.

[0076] In the second preferred embodiment, it is essentially the nature of the internal cellular core 38 which differs, just as the lateral webs 60 can possibly be eliminated.

[0077] The inner cellular core 38 is here produced using tubular elements 70, 70' secured to each other by being stacked in a stacking direction 72, corresponding to the longitudinal direction 22 of the connecting rod 20 and parallel to the axis 24. Each tubular element 70, 70' has a hollow 74 centered on a tubular element axis 76, orthogonal to the axis 24 of the connecting rod. The hollows 74, also called cells, thus remain open laterally on both sides of the connecting rod 20, on the side of the ends of the tubular elements. They are for example provided in a number between five and thirty, and preferably greater than ten.

[0078] With the exception of the two tubular elements 70' located respectively at the two opposite longitudinal ends of the core 38, these tubular elements 70 are preferably of square or rectangular section. For the two end tubular elements 70', the section is of trapezoidal shape, so that each of them defines the two second chamfers 40 intended to cooperate with the transition pieces 46.

[0079] For the manufacture of the connecting rods 20, it is also planned here to manufacture a sandwich panel, the production of the inner cellular body 38' of which is shown diagrammatically in [fig.21]. It consists of arranging several tubes 78 adjacently, according to the stacking direction 72 orthogonal to the axis of these tubes 78.

[0080] Once the central plate 38' has been assembled in this way, the operations of assembling the other components and the step of baking the panel are then carried out in a manner identical or similar to that set out in the description of the first preferred embodiment.

[0081] The cuts are then made along cutting lines 68 parallel to the stacking direction 72, and therefore orthogonal to the tubular element axes 76, as shown diagrammatically in [fig.22].

[0082] Thanks to the extensions of the skins 44, the invention allows better transmission of forces from the connecting rod body 26 to the mounting lugs 30. This transmission of forces is further improved by the presence of the transition pieces 46, ensuring the junction between the connecting rod body 26 and the end portions 28.

[0083] Even with a reduced mass, the structural connecting rod 20 according to the invention provides excellent mechanical properties, in particular in traction and compression, but also in bending in a direction orthogonal to the longitudinal direction 22 of this connecting rod.

[0084] Finally, the design of the structural connecting rod 20 allows simple, rapid and inexpensive manufacturing, in particular by producing a large surface area sandwich panel, which can then be cut to obtain several identical connecting rods.

[0085] Of course, various modifications may be made by those skilled in the art to the invention which has just been described solely by way of non-limiting examples, and within the limits of the scope of the appended claims.

Claims

Claims

1. Method for manufacturing a plurality of structural connecting rods (20), each connecting rod comprising a connecting rod body (26) as well as two end portions (28) arranged on either side of the connecting rod body along a longitudinal central axis of the connecting rod (24), each end portion (28) comprising at least one mounting lug (30) projecting from the connecting rod body (26) along the longitudinal axis (24), characterized in that it comprises the following steps: - producing a sandwich panel (62) comprising two skins (34) enclosing a honeycomb inner body (38'), at least one of the two outer skins (34) comprising a skin extension (44) to form a part of said at least one mounting lug (30), of at least one of the two end portions of the connecting rod (28); and - cutting the panel (62) along parallel cutting lines (68), so as to obtain said plurality of structural connecting rods (20).

2. Method according to claim 1, characterized in that two lateral sails (60) are placed respectively covering two sides of the internal cellular core (38).

3. Method according to one of claims 1 or 2, characterized in that the cutouts (68) are implemented simultaneously.

4. Method according to any one of claims 1 to 3, characterized in that at least one of the two outer skins (34) comprises two skin extensions (44) to form a part of said at least one mounting lug (30) of each of the two end portions (28) of the connecting rod.

5. Method according to any one of claims 1 to 4, characterized in that U-shaped closing pieces (54) are assembled at the ends of the inner alveolar body (38').

6. Method according to any one of claims 1 to 5, characterized in that transition pieces (46) are put in place, the transition pieces comprising: - a first part (46a) sandwiched between one of the two outer skins (34) and one end of the inner core (38) in the direction of the longitudinal central axis (24), the first part (46a) of the transition piece (46) having an increasing thickness as it extends in the direction of the associated ear (30), the first part having a first chamfer (48) pressed against a second chamfer (40) made on the end of the internal core (38); - a second part (46b) extending the first part (46a), and integral with the skin extension (44) forming an integral part of said associated ear (30).

7. Method according to one of claims 1 to 6, characterized in that the inner cellular core (38) is made: - of closed or open pore foam, or - of honeycomb, or - using tubular elements (70, 70') secured to each other by being stacked in a stacking direction (72) parallel to the longitudinal central axis (24), each tubular element (70, 70') having a hollow (74) centered on a tubular element axis (76) orthogonal to the longitudinal central axis (24) of the connecting rod.

8. Method according to claims 5 and 6, characterized in that at least one of the end portions (28) of the connecting rod comprises two mounting lugs (30) facing each other, each of the two lugs having: - an external skin formed by the skin extension (44); - a central body formed by the second part (46a) of the transition piece (46); and - an internal skin (56) formed by the closing piece (56) of generally U-shaped section, the two branches of the U respectively forming the internal skin (56) of each of the two facing lugs (30), and the branch of the U (56) being pressed against the end of the internal cellular core (38) of the connecting rod body (26), between the two lugs (30).

9. Method according to any one of the preceding claims, characterized in that the sandwich panel (62) is produced by hot press or autoclave (64).

10. Aircraft (100) comprising at least one structural connecting rod (20) produced according to the method according to any one of claims 1 to 9.

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