Main structure of an aircraft fuselage comprising frames attached directly to a skin and associated method

Abstract

A main structure (S) of an aircraft fuselage comprising at least one panel (1), a plurality of stiffeners (2), extending parallel to a longitudinal axis (X) and comprising two flanges (21) fixed directly to the panel (1), and a plurality of frames (3), each frame (3) extending substantially transversely to the longitudinal axis (X) and comprising a base (31), the base (31) comprising alternating feet (33) fixed directly to the panel (1) and arches (34) bypassing the body (22) of the stiffeners (2); at least one first stiffener (2) of the plurality of stiffeners (2) comprises at least one notch (23), formed at least partly in a flange (21), defining a first junction zone, a foot (33) of a frame (3) being fixed directly to the panel (1) at least partly along the first junction zone. Abstract figure: Figure 4

Description

Title of the invention: Main structure of an aircraft fuselage comprising frames fixed directly to a skin and associated method Technical field

[0001] The present invention relates to the field of aeronautical structures and more particularly to the main structure of an aircraft fuselage. The invention relates in particular to the assembly of the elements of a main structure of an aircraft fuselage.

[0002] As is known, a main structure of an aircraft fuselage extends longitudinally along an axis and comprises a panel, also known as a "skin", which forms the outer envelope of the fuselage. In order to absorb the various forces which pass through an aircraft during use, it is necessary for the mechanical strength of the main structure to be high. As such, it also comprises a plurality of stiffeners, called "stringers", which extend along the length of the fuselage, and a plurality of frames which define the profile of the aircraft fuselage (generally round or ovoid) and which extend transversely to the stiffeners.

[0003] More specifically, with reference to [Fig. 1], there is shown an example of a main structure SAA of an aircraft fuselage of the prior art which extends longitudinally along an axis X and comprises a panel 101, a plurality of frames 102 and a plurality of stiffeners 103 orthogonal to the frames 102. Each stiffener 103 has in this example a T shape and as such comprises a body 132 and two flanges 131 intended to be fixed to the panel 101. Each frame 102 comprises a body known under the designation "core" 122 and a base 121, intended to be fixed to the panel 101 in a manner orthogonal to the stiffeners 103.

[0004] Similarly, [Fig. 2] shows a main SAA structure in which each stiffener 103 has an omega shape which makes it possible to further stiffen the structure of the aircraft. On such a structure, each frame 102 is fixed to the panel 101 by means of supports 125 connected to the web 122 which form the base 121. Such frame / stiffener (smooth) structures are known to those skilled in the art and form the main SAA structure of the fuselage.

[0005] With reference to [Fig.l], to allow the assembly of the main structure SAA, the base 121 of each frame 102 comprises, along the length of the frame 102, an alternation of feet 123 and arches 124 to bypass the bodies 132 of the stiffeners 103. In other words, each foot 123 allows the frame 102 to be fixed between two adjacent stiffeners 103. Each arch 124 allows the frame 102 to bypass a stiffener 103.

[0006] In practice, each sole 131 of the stiffeners 103 must be fixed to a continuous part of the panel 101 in order to ensure stable fixing. Similarly, the base 121 of the frames 102 must be fixed to a continuous surface.

[0007] Furthermore, for the main structure SAA to be sufficiently rigid, it is necessary that the fixing surface between each foot 121 of the frames 102 and the panel 101 be sufficiently large. In practice, the space available between two adjacent stiffener soles 131 of stiffeners 103 is too small to allow robust fixing. Also, it has been proposed in the prior art to fix the base 121 of the frames 102 directly onto the soles 131 of the stiffeners 103. In other words, the feet 123 of the frames 103, the sole 131 of the stiffeners 103 and the panel 101 are superimposed as illustrated in [Fig.l].

[0008] In practice, to fix the base 121 of the frames 102 on a continuous surface, it is necessary to significantly increase the surface area of ​​the soles 131 of the stiffeners 103, which increases the mass of the main structure SAA. This presents a significant drawback in the aeronautical field which aims to limit greenhouse gas emissions. As illustrated in [Fig.l], it is necessary to machine notches 133 in the soles 131 of the stiffeners 103 between the fixing locations of the frames 102 to limit the mass. Machining all of the stiffeners 103 is not desirable because it increases the manufacturing time while increasing the risk of defects as well as the quantity of rejected material.

[0009] Furthermore, due to manufacturing tolerances, the soles 131 of two adjacent stiffeners 103 may have slightly different thicknesses, which may lead to docking defects of the base 121 of the frames 102 and may therefore weaken the structure of the aircraft. Also, it may be necessary to adjust the thickness of the soles 131 of the stiffeners 103 (commonly referred to as “shimming”), which is time-consuming and increases manufacturing and assembly times and costs. In addition, adjusting the thickness of the soles 131 increases the mass of the aircraft.

[0010] Furthermore, on a main metal structure, the frames 102 and the stiffeners 103 are generally fixed to the panel by rivets. However, there is a desire to manufacture the structure of aircraft in a thermoplastic or thermosetting composite material, so as to limit the mass of the aircraft. A limited mass makes it possible to limit fuel consumption and therefore greenhouse gas emissions. All the parts of the main structure are then assembled with or without fixing (for example by welding, co-firing, assembly by fixing, etc.).

[0011] The assembly described above, carried out by welding, has a major drawback because it results in the formation of a weld (frame / stiffener connection) on an already welded surface (stiffener / panel connection). The formation of two overlapping welds is not desirable because it can alter the mechanical resistance of the structure.

[0012] An immediate solution would be to increase the spacing between the stiffeners, but this would affect the mechanical strength of the main structure. Another solution would be to increase the width of the frame feet in order to increase the mechanical strength, but this would significantly increase the mass and size of the frames and therefore of the aircraft.

[0013] The invention thus aims to eliminate at least some of these drawbacks by proposing a reliable main structure for an aircraft fuselage, which allows robust fixing of both the stiffeners and the frames on the panel while avoiding fragile areas. PRESENTATION OF THE INVENTION

[0014] The invention relates to a main structure of an aircraft fuselage extending along a longitudinal axis, the main structure comprising: • at least one panel, • a plurality of stiffeners extending parallel to the longitudinal axis, each stiffener comprising two longitudinal flanges extending on either side of a longitudinal body, each flange being fixed directly to the panel, and • a plurality of frames, each frame extending substantially transversely to the longitudinal axis, each frame comprising a core connected to a base, the base comprising an alternation of feet fixed directly to the panel and arches bypassing the body of the stiffeners.

[0015] The main structure is remarkable in that at least one first stiffener of the plurality of stiffeners comprises at least one notch, formed at least in part in a sole, defining a first junction zone, a foot of a frame being fixed directly to the panel at least in part along the first junction zone.

[0016] Thanks to the main structure according to the invention, the stiffener as well as the frame are fixed directly to the panel, which allows a robust fixing and therefore an optimal mechanical strength of the main structure. The addition of material on the soles to form a support for the base of the frame is limited, unlike the prior art, which allows a significant weight saving, making it possible to limit fuel consumption. This also makes it possible to limit losses and the quantity of material discarded during the manufacture of the stiffeners, which advantageously limits costs and production times.

[0017] The main structure according to the invention also makes it possible to limit stacking of the panel, soles and a foot, which limits the risk of fragile areas forming, such as the risk of welding on a surface already containing a weld bead. Such a main structure can advantageously be made with thermoplastic materials.

[0018] The formation of a notch in the sole makes it possible to form a larger contact surface between the foot of the frame and the panel. The frame is thus fixed to the panel over a continuous surface large enough to allow optimal mechanical resistance of the main structure.

[0019] Preferably, each stiffener has, in a cross-sectional plane to the longitudinal axis, an omega shape, in which the body comprises a head and two lateral flanks connecting the head respectively to each flange. Such an omega shape gives the stiffener significant rigidity, while limiting its mass.

[0020] Preferably, the main structure comprises a second stiffener, adjacent to the first stiffener and comprising at least one notch, formed at least in part in a sole, defining a second junction zone, a foot of a frame being fixed directly to the panel at least in part along the second junction zone. The foot is thus inserted between the first stiffener and the second stiffener and can be connected to the panel both on the first junction zone and on the second junction zone. This allows a larger surface area for direct fixing between the frame foot and the panel, which makes it possible to limit the mass of the main structure while ensuring reliable and robust fixing of the frame to the panel.

[0021] According to a preferred aspect of the invention, the foot of the frame is fixed entirely and directly to the panel, allowing a reliable and robust fixing. The frame is thus fixed on a continuous surface, without it being necessary to add material on the soles to form a continuous support for the base of the frame, allowing a significant weight saving, which is particularly advantageous in the aeronautical field which aims to limit fuel consumption and therefore greenhouse gas emissions. Direct fixing on the panel also makes it possible to avoid the need to level two adjacent parts to form a flat surface, which simplifies production and limits manufacturing times and costs. By "continuous surface", it is meant that the surface for fixing the frame to the panel has no difference in level or no difference in docking.

[0022] Preferably, the frame is made of composite material. This makes it lighter while remaining robust. More preferably, the frame is made of thermoplastic material. This allows for long-lasting thermoplastic connections to be made without overlapping welds.

[0023] Preferably, each stiffener is in one piece, which makes it possible to avoid connecting portions which could be weakened. Each stiffener is also more easy to install, which limits manufacturing times. In addition, this allows for a stiffener with a continuous body and a discontinuous sole. In other words, the sole includes notches to allow the feet to pass through while forming a sturdy, single-piece stiffener.

[0024] Preferably, each frame is a single piece, which makes it possible to avoid connections that could weaken the assembly. Each frame is thus fixed along its entire length to the panel while forming a bridge (commonly referred to as a “mouse hole”) above the stiffeners and while being formed from a single piece, which ensures a frame with significant mechanical strength. In addition, such a single-piece frame is simple and practical to install.

[0025] Preferably, the first stiffener comprises at least one notch on each flange, the two notches being positioned at the same longitudinal position. In other words, the stiffener comprises two notches positioned opposite each other. The feet of the same frame can thus be fixed in a similar manner on either side of the body of the stiffener directly on the panel. This makes it possible to guarantee a robust fixing of the entire frame on the panel.

[0026] In a preferred embodiment, at least the first stiffener comprises a plurality of notches spaced along the length of the stiffener, so as to define a plurality of joining zones for fixing the set of frames directly to the panel. Thus, the set of frames of the main structure can be fixed directly to the panel. This makes it possible to guarantee a robust fixing of the set of frames on the panel while ensuring significant rigidity of the main structure. Preferably, the notches of the plurality of notches are spaced from each other proportionally to the pitch of the frames of the plurality of frames.

[0027] In a first embodiment, the flange of the first stiffener having a nominal width along an axis transverse to the longitudinal axis, the notch has a width less than 50% of the nominal width of the flange, preferably between 20% and 40% of the nominal width of the flange. In other words, in this first embodiment, the notch extends transversely substantially over a third of the width of the flange from the free end. This makes it possible to form a junction zone sufficient to allow the frames to be fixed directly to the panel while ensuring continuity in the passage of the forces which pass through the flanges of the stiffener. The stress concentrations are thus limited in the flanges of the stiffener.

[0028] In a second embodiment, the flange of the first stiffener having a nominal width along an axis transverse to the longitudinal axis, the notch has a width greater than 50% of the nominal width of the flange, preferably between 60% and 80% of the nominal width of the flange. In other words, in this second embodiment, the notch extends transversely substantially over two-thirds of the width of the flange from the free end. This makes it possible to form a large junction zone to allow the frames to be fixed effectively directly to the panel while ensuring continuity in the passage of forces which pass through the flanges of the stiffener. Stress concentrations are thus limited in the flanges of the stiffener.

[0029] In a third embodiment, the notch extends at least partly into the body of the stiffener. In other words, in this third embodiment, the notch extends transversely substantially over the entire nominal width of the flange defined along an axis transverse to the longitudinal axis. This makes it possible to form an optimal junction zone for fixing the stiffener directly to the panel effectively, even when the frames are close to each other.

[0030] In a preferred embodiment, the junction zone has a trapezoidal shape. This makes it possible to define a sufficiently large fixing surface to fix the foot of the frame while limiting the mechanically weakened areas in the sole and ensuring that sufficient rigidity is maintained. A trapezoidal shape also makes it easier to dock the foot in the first junction zone, by limiting the risks of damage to the stiffener.

[0031] Preferably, the junction zone has a minimum length defined along the longitudinal axis, the foot of the frame having a width substantially equal to the minimum length. This ensures that the foot of the frame is fixed over the entire contact surface available on the panel. This also optimizes the fixing surface of the stiffeners and frames for optimal fixing and therefore optimal mechanical strength of the main structure.

[0032] Preferably, the width of the frame foot is between 90% of the minimum length of the junction zone and 100% of the minimum length of the junction zone. Such a dimension makes it possible to ensure limited play between the stiffener and the frame foot in the junction zone, which makes it possible to maximize the surface area for fixing the frame foot to the panel, while taking into account the manufacturing tolerances of the parts for assembly.

[0033] In one embodiment, the body comprising a head and two lateral flanks connecting the head respectively to each flange, each flange having in a section plane transverse to the longitudinal axis a flange thickness, the head having a head thickness, at least a portion of the head having a head thickness greater than the flange thickness. A thickened head makes it possible to increase the inertia of the stiffener, which makes it possible, even in the event of the formation of a notch, to maintain a high level of rigidity of the stiffener.

[0034] In a first embodiment, the head has a uniformly thick greater than the thickness of the soles, which allows for a simpler and faster manufacturing process.

[0035] In a second embodiment, the head has a thickness locally greater than the thickness of the soles. In other words, the head has an excess thickness only on a part of the head, which makes it possible to form a stiffener whose stiffness is increased while limiting its mass and its size.

[0036] In a third embodiment, the head and the sides have a thickness uniformly greater than the thickness of the soles, which makes it possible to reinforce the stiffener around the notch to ensure optimal mechanical strength.

[0037] In a preferred embodiment, each stiffener flange and each frame foot is fixed to the panel by thermoplastic welding, which allows a reliable and rapid process.

[0038] The invention also relates to an aircraft comprising a fuselage comprising a main structure as described above.

[0039] Finally, the invention relates to a method for manufacturing a main structure of an aircraft fuselage, the soles of at least the first stiffener being fixed directly to the panel, a notch being formed at least in part in a sole of the first stiffener, the notch defining a first junction zone, the method comprises a step consisting of: fixing the foot of the frame directly to the panel according to the first junction zone defined by the notch. PRESENTATION OF FIGURES

[0040] The invention will be better understood on reading the description which follows, given by way of example, and referring to the following figures, given by way of non-limiting examples, in which identical references are given to similar objects.

[0041] [Fig.l] is a schematic representation of a main structure of an aircraft fuselage according to a first example of the prior art.

[0042] [Fig. 2] is a schematic representation of a main structure of an aircraft fuselage according to a second example of the prior art.

[0043] [Fig. 3] is a schematic representation of a main structure of an aircraft fuselage according to one embodiment of the invention.

[0044] [Fig.4] is a close-up view of a main structure of an aircraft fuselage according to an alternative embodiment of the invention.

[0045] [Fig.5] is a schematic representation of a stiffener of the main structure of [Fig.4].

[0046] [Fig.6] is a schematic representation of a cross-sectional view of the stiffener of [Fig.5] according to a first embodiment.

[0047] [Fig.7] is a schematic representation of a cross-sectional view of the stiffener of [Fig.5] according to a second embodiment.

[0048] [Fig.8] is a schematic representation of a cross-sectional view of the stiffener of [Fig.5] according to a third embodiment.

[0049] [Fig.9] is a schematic representation of a cross-sectional view of the stiffener of [Fig.5] according to a fourth embodiment.

[0050] [Fig. 10] is a top view of the stiffener of the main structure of [Fig. 3] showing attachment areas.

[0051] [Fig. 11] is a top view of the main structure of [Fig.3].

[0052] [Fig. 12] is a schematic representation of an alternative embodiment of the main structure of [Fig.3].

[0053] [Fig. 13] is a schematic representation of a main structure of an aircraft fuselage according to a third embodiment of the invention.

[0054] It should be noted that the figures set out the invention in detail to implement the invention, said figures can of course be used to better define the invention where appropriate. DETAILED DESCRIPTION OF THE INVENTION

[0055] [Fig. 3] shows a main structure S of an aircraft fuselage according to one embodiment of the invention. In this example, the aircraft extends along a longitudinal axis X. The main structure S comprises a panel 1, also known as a “skin”, which forms the outer envelope of the fuselage. It goes without saying that the main structure S could comprise more than one panel 1 fixed to each other, for example by welding. In order to stiffen the panel 1 and to absorb the forces which pass through the aircraft during use, the main structure S also comprises a plurality of stiffeners 2, also known to those skilled in the art as “smooth”, and a plurality of frames 3. Each stiffener 2 extends longitudinally along an axis parallel to the axis X of the aircraft and each frame 3 extends transversely relative to the stiffeners 2.

[0056] In this example, for the sake of simplicity and clarity, the panel 1 is represented in a plane (X, Y), that is to say flat, it goes without saying that the panel 1 is generally defined according to a curved surface which follows the profile of the fuselage of the aircraft. Also, in this example, the main structure S is defined in an orthogonal reference frame (X, Y, Z), in which the plane (X, Y) corresponds to a horizontal plane, Y defining a transverse axis, and the axis Z defines an axis orthogonal to the plane (X, Y), in other words a vertical axis Z, as represented in [Fig.3].

[0057] In this example, the panel 1 is made of a composite material, preferably a thermoplastic or thermosetting material in order to form a main structure S that is both lightweight and robust. A panel 1 is described as “made of a composite material”, however, as is known, such a panel 1 made of composite material may include, for example, inserts made of a different material. It goes without saying that the panel 1 could alternatively be made of a metallic material.

[0058] With reference to Figures 4 and 5, as described previously, each stiffener 2 extends longitudinally along an axis parallel to the longitudinal axis X and is fixed directly to the panel 1. Each stiffener 2 is preferably in one piece, which makes it possible to limit the joints and therefore the fragile areas. By the term "in one piece" is meant that each stiffener 2 is formed in one piece in a single piece.

[0059] Preferably, each stiffener 2 comprises a composite material. More preferably, each stiffener 2 is made of a thermoplastic or thermosetting material making it possible to form a main structure S that is both light and robust. In this example, each stiffener 2 is fixed to the panel 1 by thermoplastic welding. It goes without saying that the stiffeners 2 could alternatively be fixed to the panel 1 in a different manner, for example by co-firing, co-consolidation, by means of fasteners or by any other known means of thermoplastic assembly. Similarly, the stiffeners 2 could alternatively be made of a metallic material.

[0060] Each stiffener 2 comprises a longitudinal body 22 and two longitudinal flanges 21 extending on either side of the body 22, each flange 21 being fixed directly to the panel 1.

[0061] More specifically, in this example, as shown in Figures 4 and 5, each stiffener 2 has in a transverse section plane (Y, Z) to the longitudinal axis X an omega shape Q, which allows significant rigidity. As such, the body 22 substantially defines a bridge and comprises a head 24 and two lateral flanks 25 connecting the head 24 respectively to each flange 21. In other words, along the transverse axis Y, the stiffener 2 successively comprises a first flange 21, a first lateral flank 25, the head 24, a second lateral flank 25 and a second flange 21. Each stiffener 2 is thus symmetrical along an axis parallel to the longitudinal axis X.

[0062] Preferably, each sole 21 has a nominal width L21, defined along the transverse axis Y, between 15x103 and 60x103 m. Such a nominal width L21 allows an optimal surface area to ensure robust fixing of the stiffener 2 on the panel 1, without oversizing the main structure S, which could penalize its mass.

[0063] With reference to [Fig. 3], as described previously, each frame 3 extends transversely to the plurality of stiffeners 2, so as to form a grid on the panel 1 whose mechanical resistance is high.

[0064] In this example, each frame 3 comprises a core 32 connected to a base 31 fixed to the panel 1. The core 32 of the frame 3 extends orthogonally to the panel 1. In this example, the base 31 comprises an alternation of feet 33 fixed directly to the panel 1 and arches 34, known to those skilled in the art under the designation “mouse hole”, which go around the body 22 of each stiffener 2. Each frame 3 is preferably in one piece, making it possible to limit the joints and therefore the fragile areas.

[0065] Preferably, each frame 3 is made of a composite material. More preferably, each frame 3 is made of a thermoplastic or thermosetting material making it possible to form a main structure S that is both light and robust. The frames 3 could alternatively be made of a different material, for example a metallic material.

[0066] According to one aspect of the invention, to allow the fixing of frames 3 directly on the panel 1, at least one stiffener 2 comprises a notch 23, formed at least in part in the sole 21, as shown in [Fig. 5]. The notch 23 defines a junction zone ZJ adapted to receive one of the feet 33 of the plurality of frames 3.

[0067] More specifically, with reference to [Fig. 10], a first stiffener 2A comprises a notch 23A, formed partly in one of the flanges 21A. The notch 23A defines a first junction zone ZJ-A for fixing one of the feet 33 of one of the frames 3, as shown in [Fig. 1 1]. Preferably, the first stiffener 2A comprises two notches 23A, each formed respectively in the flanges 21A. As shown in FIGS. 10 and 11, the two notches 23A are formed at the same longitudinal position on the two flanges 21A of the first stiffener 2A, that is to say along the longitudinal axis X, opposite each other relative to the body 22A. This advantageously makes it possible to fix two consecutive feet 33 of a frame 3. The notches 23A are preferably symmetrical.

[0068] In practice, the first stiffener 2A preferably comprises a plurality of pairs of notches 23A distributed along the length of the stiffener 2, as shown in [Fig. 11], so as to define a plurality of first junction zones ZJ-A for a plurality of feet 33 of the plurality of frames 3. In other words, each sole 21 is discontinuous along the longitudinal axis X.

[0069] Preferably, still with reference to Figures 10 and 11, a second stiffener 2B, adjacent to the first stiffener 2A, comprises a notch 23B, formed partly in one of the flanges 21B. The notch 23B defines a second junction zone ZJ-B for fixing the foot 33 of the frame 3. The first stiffener 2A and the second stiffener 2B are preferably identical, also all of the characteristics of the first stiffener 2A apply to the second stiffener 2B, the same applies to the notches 23.

[0070] In other words, the notch 23A of the first stiffener 2A and the notch 23B of the second stiffener 2B are positioned opposite each other, at the same longitudinal position, on the two adjacent stiffeners 2A, 2B so as to allow the passage of one of the feet 33 of one of the frames 3 and allow the latter to be fixed directly to the panel 1 between the two stiffeners 2A, 2B. For this, the first junction zone ZJ-A and the second junction zone ZJ-B positioned opposite each other define an intermediate junction zone ZJ-i between the flanges 21A, 21B of the two adjacent stiffeners 2A, 2B, shown in [Fig. 11]. The first junction zone ZJ-A, the intermediate junction zone ZJ-i and the second junction zone ZJ-B define an overall junction zone ZG on the panel 1 for the foot 33 of the frame 3.

[0071] In this example, each pair of adjacent stiffeners 2 comprises a plurality of notches 23 and defines between the two facing flanges 21A, 21B a plurality of overall junction zones ZG to allow the fixing of all the feet 33 of all the frames 3 directly on the panel 1.

[0072] Thus, thanks to the notches 23, both the set of stiffeners 2 and the set of frames 3 are fixed directly to the panel 1, which makes it possible to overcome the drawbacks of the prior art by allowing fixing on a continuous surface, and therefore a robust fixing, while limiting the mass of the main structure S. The fuel consumption of the aircraft is thus advantageously limited, which is particularly advantageous in the aeronautical field. A direct fixing of each frame 3 on the panel 1 also makes it possible to avoid the risk of carrying out welding on a weakened surface already comprising a weld. By direct fixing, it is meant that the frame 3 is not secured directly to the stiffener 2.

[0073] With reference to [Fig. 10], the first junction zone ZJ-A and the second junction zone ZJ-B have, in the horizontal plane (X, Y), a trapezoidal shape. Such a shape makes it possible to define a fixing surface on the panel 1 large enough to fix the foot 33 of the frame 3 while limiting the mechanically weakened zones in the sole 21 and ensuring that sufficient rigidity is maintained. In this example, each junction zone ZJ has a minimum length LZJ, defined along the longitudinal axis X, between 15x103 and 60xl0 3 m. Such a length LZJ makes it possible to fix the foot 33 on a surface sufficient to allow robust fixing and increase the mechanical strength of the main structure S. The minimum length LZJ is defined as a function of the width L33 of the foot 33 of the frame 3, as shown in [Fig.l 1].Preferably, the width L33 is substantially equal to the minimum length LZJ, preferably, the width L33 of the foot 33 of the frame 3 is between 90% and 100% of the minimum length LZJ of the junction zone ZJ (0.90*LZJ <L33<LZJ). Cela permet d’optimiser la surface de fixation du pied 33 du . frame 3 on panel 1 while taking into account the manufacturing tolerances of the different parts for their assembly.

[0074] Preferably, all the notches 23 are identical (apart from the manufacturing clearances) to define substantially identical junction zones ZJ-A, ZJ-B to allow the fixing of feet 33 of frames 3 of the same dimensions. Thus, the frames 3 and the stiffeners 2 can have standard profiles, which makes it possible to limit manufacturing times while improving stock management.

[0075] To define a junction zone ZJ large enough to allow optimal fixing of the foot 33 of the frame 3, with reference to figures 5 and 10 to 13, the notch 23 has a width L23, defined along the transverse axis Y.

[0076] In a first embodiment, shown in Figures 10 to 12, the width L23 of the notch 23 is less than 50% of the nominal width L21 of the sole 21. Preferably, the width L23 of the notch 23 is between 20% and 40% of the nominal width L21 of the sole 21. In other words, the notch 23 extends substantially transversely over a third of the nominal width L21 of the sole 21, from the free end of the sole 21. The junction zone ZJ formed by the notch 23 thus allows the fixing of a foot 33 while ensuring continuity of forces in the sole 21, which limits the appearance of stress concentration in the latter.

[0077] In a second embodiment, shown in [Fig. 13], the width L23 of the notch 23 is greater than 50% of the nominal width L21 of the sole 21. Preferably, the width L23 of the notch 23 is between 60% and 80% of the nominal width L21 of the sole 21. In other words, the notch 23 extends substantially transversely over two-thirds of the nominal width L21 of the sole 21, from the free end of the sole 21. The junction zone ZJ formed by the notch 23 thus allows the fixing of a foot 33 whose dimensions are sufficiently large while ensuring continuity of forces in the sole 21, which limits the appearance of stress concentration in the latter. This is particularly advantageous for positioning a foot 33 of frame 3 between two stiffeners 2 which are close to each other.

[0078] In a third embodiment, shown in Figures 4 and 5, the notch 23 also extends partly into the body 22 of the stiffener 2. In other words, the notch 23 extends transversely over the entire nominal width L21 of the sole 21. Preferably, the notch 23 extends into the lateral flanks 25. This makes it possible to form a junction zone ZJ whose dimensions are optimal for fixing the foot 33 of the frame 3. This is particularly advantageous for positioning a foot 33 of the frame 3 between two stiffeners 2 which are very close to each other.

[0079] In practice, the width L23 of the notch 23 is configured to define a clearance J transverse (i.e. along the transverse axis Y), shown in [Fig. 11], limited between the flange 21 of the stiffener 2 and the foot 33 of the frame 3. Preferably, the clearance J is between 1x103 and 5x103 m. Such a clearance J allows the sole 21 to maintain a sufficiently high rigidity, while ensuring that the foot 33 of the frame 3 is fixed over its entire available contact surface on the panel 1. In other words, a limited clearance J makes it possible to optimize the fixing surface of both the stiffener 2 and the frame 3 for optimal fixing and therefore optimal mechanical strength of the main structure S. The presence of a clearance J also makes it possible to ensure the fixing of the sole 21 of the stiffener 2 and the foot 33 of the frame 3 directly on the panel 1 despite the manufacturing tolerances, without the sole 21 and the foot 33 risking interference.

[0080] In one embodiment, the flanges 21 and the body 24 of each stiffener 2 have a uniform thickness Ep2, as shown in [Fig.6]. This allows simple and rapid manufacture of the stiffeners 2 from a uniform plate. In this example, the thickness Ep2 of the stiffener 2 is between 0.8 xlO3 and 5x103 m.

[0081] Alternatively, with reference to Figures 7 and 8, the head 24 of each stiffener 2 is thickened. For this purpose, the head 24 has a head thickness Ep24 greater than the flange thickness Ep21 so as to reinforce the stiffener 2 and increase the stiffness of the main structure S. In this example, the head thickness Ep24 is between 0.9x103 and 10x103 m. The head thickness Ep24 may be regular over the entire width (defined along the transverse axis Y) of the head 24 (as shown in [Fig.7]) or non-uniform (as shown in [Fig.8]).

[0082] In an alternative embodiment, with reference to [Fig.9], the head 24 and the flanks 25 of each stiffener 2 are thickened. For this purpose, the flanks 25 have a flank thickness Ep25 substantially equal to the head thickness Ep24, the flank thickness Ep25 and the head thickness Ep24 being greater than the flange thickness Ep21. This makes it possible to reinforce the stiffener 2 around the notch 23. In this example, the head thickness Ep24 and the flank thickness Ep 25 are between 0.9x103 and 10x103 m. It goes without saying that the head thickness Ep24 and the flank thickness Ep25 could be different while being greater than the flange thickness Ep21. Similarly, it goes without saying that only the flanks 25 could be thickened.

[0083] Preferably, when the head 24 and / or the flanks 25 have a thickness greater than the sole thickness Ep 21, the head 24 and / or the flanks 25 have, along the longitudinal axis X, a thickness Ep24, Ep25 which is heterogeneous and locally thickened substantially opposite each notch 23.

[0084] More precisely, as shown in Figures 4 and 5, the head 24 has, along the length of the stiffener 2, a portion 26 which has a head thickness Ep24 greater than the rest of the head 24. This makes it possible to increase the stiffness of the stiffener. 2 locally while limiting its mass. In practice, in this example, the head 24 comprises several portions 26 which have a head thickness Ep24 greater than the sole thickness 21, each portion 26 being positioned longitudinally at the level of a notch 23. In other words, the material shrinkage due to the formation of the notch 23 is advantageously compensated by the increase in the head thickness Ep24, which makes it possible to ensure significant rigidity even with the notch 23. The example of [Fig.4] only has a locally thickened head 24, identical characteristics apply for sides 25 also thickened, as shown in [Fig.3].

[0085] It goes without saying that the head 24 (and / or the sides 25) could alternatively have a thickness Ep24 (Ep25) greater than the thickness of the flange 21 uniformly over the entire length of the stiffener 2, along the longitudinal axis X.

[0086] A thickened head 24 is particularly advantageous when the notch 23 is deep as illustrated in Figures 3 and 4.

[0087] Also thickened flanks 25 make it possible to significantly limit the influence of the notch 25.

[0088] It goes without saying that the main structure S can comprise both a plurality of stiffeners 2 having a uniform thickness Ep2 over the entirety of the flanges 21 and the body 22 and a plurality of stiffeners 2 having a thickened head 24 and / or sides 25.

[0089] A method of manufacturing a main structure S as described above will now be described, with reference to [Fig. 11]. In this example, the panel 1, each stiffener 2 and each frame 3 is made of a thermoplastic material. The fixing of the different parts together is carried out, in this example, by thermoplastic welding. The fixing of the stiffeners 2 could alternatively be carried out by co-consolidation or by any known method of assembling thermoplastic parts. Similarly, each frame 3 could alternatively be fixed to the panel 1 in a different way, for example by co-consolidation, by means of fixing or by any known method of assembling thermoplastic parts.

[0090] In this example, all the stiffeners 2 are identical and a plurality of notches 23 has been made in each. More precisely, in this example, each stiffener 2 comprises a plurality of pairs of notches 23 formed along the stiffener 2, facing each other in the flanges 21.

[0091] The method comprises a first step E1 of positioning, in this example, a first stiffener 2A along the longitudinal axis X of the aircraft and of fixing the first stiffener 2A to the panel 1. In this example, the first stiffener 2A is fixed to the panel 1 by thermoplastic welding of its flanges 21 A. The fixing of the first stiffener 2A makes it possible to position a first notch 23A on the panel 1, the first notch 23A defining a first junction zone ZJ-A.

[0092] In a second step E2, an operator positions a second stiffener 2B along the longitudinal axis X of the aircraft and fixes the second stiffener 2B to the panel 1, in this example by thermoplastic welding. The second stiffener 2B is positioned adjacent to the first stiffener 2A so as to place a second notch 23B opposite the first notch 23A of the first stiffener 2A. The second notch 23B defines a second junction zone ZJ-B, the first junction zone ZJ-A and the second junction zone ZJ-B being positioned between the bodies 22 of the first stiffener 2A and the second stiffener 2B, as shown in [Fig.l 1]. The first junction zone ZJ-A and the second junction zone ZJ-B define between them an intermediate junction zone ZJ-i.

[0093] All stiffeners 2 are fixed in a similar manner to panel 1.

[0094] Alternatively, it goes without saying that all of the stiffeners 2 could be fixed at the same time to the panel 1.

[0095] Each pair of adjacent stiffeners 2A, 2B makes it possible to position opposite each other a first notch 23A and a second notch 23B and therefore a first junction zone ZJ-A and a second junction zone ZJ-B.

[0096] In a third step E3, the operator positions one of the frames 3 transversely to the plurality of stiffeners 2. The frame 3 is positioned so that each foot 33 is positioned between two notches 23A, 23B facing each other. In other words, each foot 33 of the frame 3 is placed in contact with the panel 1 both in the first junction zone ZJ-A, the intermediate junction zone ZJ-i and the second junction zone ZJ-B.

[0097] The method then comprises a step E4 of fixing the foot 33 of the frame 3 directly to the panel 1. In this example, the foot 33 is fixed by thermoplastic welding. It goes without saying that the foot 33 could be fixed to the panel 1 by any means of assembling thermoplastic parts.

[0098] All frames 3 are fixed in a similar manner to panel 1. Each foot 33 of each frame 3 is positioned between two adjacent stiffeners 2A, 2B and is connected directly to panel 1 in a first junction zone ZJ-A and a second junction zone ZJ-B.

[0099] Thanks to the notches 23, each frame 3 is fixed directly to the panel 1, which makes it possible to avoid the superposition of the panel 1, the sole 21 and the foot 33, as was the case in the prior art. The fixing of the main structure S is thus more secure and more robust and makes it possible to avoid the formation of fragile zones. The main structure S according to the invention also makes it possible to limit the mass of the aircraft while ensuring significant mechanical strength and stiffness.

Claims

Claims

1. Main structure (S) of an aircraft fuselage extending along a longitudinal axis (X), the main structure (S) comprising: • at least one panel (1), • a plurality of stiffeners (2) extending parallel to the longitudinal axis (X), each stiffener (2) comprising two longitudinal flanges (21) extending on either side of a longitudinal body (22), each flange (21) being fixed directly to the panel (1), and • a plurality of frames (3), each frame (3) extending substantially transversely to the longitudinal axis (X), each frame (3) comprising a web (32) connected to a base (31), the base (31) comprising an alternation of feet (33) fixed directly to the panel (1) and arches (34) going around the body (22) of the stiffeners (2), • main structure (2) characterized in that at least one panel (1) comprises a plurality of stiffeners (2) extending parallel to the longitudinal axis (X), each stiffener (2) comprising two longitudinal flanges (21) extending on either side of a longitudinal body (22), each flange (21) being fixed directly to the panel (1), and • a plurality of frames (3), each frame (3) extending substantially transversely to the longitudinal axis (X), each frame (3) comprising a web (32) connected to a base (31), the base (31) comprising an alternation of feet (33) fixed directly to the panel (1) and arches (34) going around the body (22) of the stiffeners (2), at least one first stiffener (2A) of the plurality of stiffeners (2) comprises at least one notch (23A),formed at least in part in a sole (21), defining a first junction zone (ZJ-A), a foot (33) of a frame (3) being fixed directly to the panel (1) at least in part along the first junction zone (ZJ-A).,

2. Main structure (S) according to claim 1, comprising a second stiffener (2B), adjacent to the first stiffener (2A) and comprising at least one notch (23B), formed at least in part in a sole (21), defining a second junction zone (ZJ-B), a foot (33) of a frame (3) being fixed directly to the panel (1) at least in part along the second junction zone (ZJ-B).

3. Main structure (S) according to one of claims 1 to 2, in which the foot (33) of the frame (3) is fixed entirely and directly to the panel (1).

4. Main structure (S) according to one of claims 1 to 3, in which the frame (3) is made of composite material.

5. Main structure (S) according to one of claims 1 to 4, in which the first stiffener (2A) comprises at least one notch (23) on each sole (21), the two notches (23) being positioned at the same longitudinal position.

6. Main structure (S) according to one of claims 1 to 5, in which the flange (21) of the first stiffener (2A) having a nominal width (L21) along an axis (Y) transverse to the longitudinal axis (X), the notch (23) has a width (L23) less than 50% of the nominal width (L21) of the flange (21), preferably between 20% and 40% of the nominal width (L21) of the flange (21).

7. Main structure (S) according to one of claims 1 to 5, in which the sole (21) of the first stiffener (2A) having a nominal width (L21) along an axis (Y) transverse to the longitudinal axis (X), the notch (23) has a width (L23) greater than 50% of the nominal width (L21) of the sole (21), preferably between 60% and 80% of the nominal width (L21) of the sole (21).

8. Main structure (S) according to one of claims 1 to 5, in which the notch (23) extends at least partly into the body (22) of the stiffener (2).

9. Main structure (S) according to one of claims 1 to 8, in which the junction zone (ZJ) has a trapezoidal shape.

10. Main structure (S) according to one of claims 1 to 9, in which the junction zone (ZJ) has a minimum length (LZJ) defined along the longitudinal axis (X), the foot (33) of the frame (3) having a width (L33) substantially equal to the minimum length (LZJ).

11. Main structure (S) according to one of claims 1 to 10, in which the body (22) comprising a head (24) and two lateral flanks (25) connecting the head (24) respectively to each sole (21), each sole (21) having in a section plane (Y, Z) transverse to the longitudinal axis (X) a sole thickness (Ep21), the head (24) having a head thickness (Ep24), at least one portion (26) of the head (24) has a head thickness (Ep24) greater than the sole thickness (Ep21).

12. Aircraft comprising a fuselage comprising a main structure (S) according to one of claims 1 to 11.

13. Method for manufacturing a main structure (S) of an aircraft fuselage according to one of claims 1 to 11, the soles (21) of at least the first stiffener (2) being fixed directly to the panel (1), a notch (23A) being formed at least in part in a sole (21) of the first stiffener (2), the notch (23A) defining a first junction zone (ZJ-A), the method comprises a step consisting of: • fix the foot (33) of the frame (3) directly to the panel (1) according to the first junction zone (ZJ-A) defined by the notch (23).

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