Aircraft comprising a fuselage reinforced by a ventral beam and equipped with at least one opening closed by a removable panel
The integration of a ventral beam with removable panels in the aircraft fuselage enables efficient access and removal of hydrogen tanks, addressing access challenges and simplifying maintenance by maintaining structural integrity.
Patent Information
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- AIRBUS OPERATIONS (SAS)
- Filing Date
- 2022-08-03
- Publication Date
- 2026-06-12
AI Technical Summary
Hydrogen storage tanks in aircraft fuselages are difficult to access and dismantle due to their large size and proximity to the fuselage, requiring separation of fuselage sections, which is a complex and time-consuming process given the presence of electrical and fluidic networks.
Incorporation of a ventral beam in the fuselage structure with removable panels that create large openings for tank extraction, allowing access to hydrogen storage tanks while maintaining fuselage integrity through connection systems that do not interfere with existing networks.
Facilitates easy and safe removal of hydrogen storage tanks without compromising the fuselage's structural integrity, reducing the complexity and duration of maintenance operations.
Smart Images
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Abstract
Description
Title of the invention: Aircraft comprising a fuselage reinforced by a ventral beam and provided with at least one opening closed by a removable panel
[0001] The present application relates to an aircraft comprising a fuselage reinforced by a ventral beam and provided with at least one opening closed by a removable panel.
[0002] According to one embodiment, an aircraft comprises a fuselage extending between a front tip and a rear tip, wings and a central wing box connecting the wings and the fuselage.
[0003] The fuselage has a longitudinal axis X, which extends approximately from the front tip to the rear tip, substantially horizontal when the aircraft is on the ground.
[0004] For the remainder of this description, a longitudinal direction is substantially parallel to the longitudinal axis. A transverse plane is a plane perpendicular to the longitudinal axis X. A longitudinal plane is a plane passing through the longitudinal axis X. The median longitudinal plane PLM corresponds to the plane passing through the longitudinal axis X and vertical.
[0005] The fuselage comprises a structure consisting of frames positioned in transverse planes and longitudinal reinforcements, called stringers, connecting the frames oriented approximately along the longitudinal direction. With the exception of those located at the center wing box, which have ends connected to the center wing box on either side of the median longitudinal plane PLM, all other frames extend over the entire circumference of the fuselage.
[0006] In the case of a hydrogen-powered aircraft, two hydrogen storage tanks are positioned in the fuselage on either side of the PLM median longitudinal plane, near the rearmost point of the fuselage. These hydrogen storage tanks must be thoroughly inspected periodically. Because these tanks occupy the largest possible volume within the fuselage, some parts of them are close to the fuselage and difficult to access.
[0007] If these hydrogen storage tanks need to be dismantled, it is then necessary to separate two sections of the fuselage, which proves to be a long and delicate operation given the numerous electrical and fluidic networks running along the fuselage from one section to the other.
[0008] The present invention aims to remedy all or part of the drawbacks of the prior art.
[0009] To this end, the invention relates to an aircraft comprising a fuselage and some wings, the fuselage having a median longitudinal plane, a lower generatrix, an upstream part located in front of a first transverse plane, a downstream part located behind a second transverse plane and an intermediate part located between the first and second transverse planes; the first and second planes being offset towards the rear with respect to the wings, the fuselage comprising a structure and a skin attached to the structure.
[0010] According to the invention, the fuselage structure comprises a ventral beam, positioned at the level of the lower generatrix, connecting the upstream and downstream parts of the fuselage, the fuselage comprising at least one opening, positioned near the ventral beam, extending between the first and second transverse planes and, for each opening, a removable panel configured to occupy an assembled state in which the removable panel closes the opening and a disassembled state in which the removable panel clears the opening.
[0011] The ventral beam helps to stiffen the fuselage. Thus, it is possible to create at least one large opening in the fuselage allowing the extraction of a large capacity tank, such as a hydrogen storage tank for example, and to limit the deflection of the fuselage in the median longitudinal plane between the upstream and downstream parts when the removable panel closing the opening is removed.
[0012] According to another feature, the fuselage includes first and second openings positioned on either side of the ventral beam and first and second removable panels positioned, when in the assembled state, on either side of the ventral beam.
[0013] According to another feature, the aircraft comprises at least one tank having a length and a diameter. In addition, each opening has first and second transverse edges positioned respectively at the first and second transverse planes as well as first and second longitudinal edges connecting the first and second transverse edges, the first longitudinal edge being attached to the ventral beam, the first and second longitudinal edges being spaced at a distance equal to or slightly greater than the diameter of the tank, the first and second transverse planes being spaced at a distance equal to or slightly greater than the length of the tank.
[0014] According to another feature, the intermediate section comprises main frame sections forming part of the fuselage structure and a main outer wall forming part of the fuselage skin, each main frame section having a web positioned in a transverse plane. Each removable panel comprises a secondary frame section for each main frame section of the intermediate section and a secondary outer wall, each A secondary frame section comprising a web positioned substantially in the same transverse plane as the web of the corresponding primary frame section when the removable panel is in the mounted state. In addition, the fuselage includes, for each panel, a first removable connection system linking the web of each secondary frame section of the removable panel to the ventral beam, and a second removable connection system linking the web of each secondary frame section of the removable panel to the web of the corresponding primary frame section of the intermediate section.
[0015] According to another feature, the first connection system comprises, for each section of secondary frame, at least one L-shaped angle having a first flange pressed against the ventral beam and connected to the latter and a second flange pressed against the web of the section of secondary frame and connected to the latter.
[0016] According to another feature, the second connection system comprises, for each secondary frame section, at least one splice having a first part pressed against the web of the corresponding main frame section and connected to the latter and a second part pressed against the web of the secondary frame section and connected to the latter.
[0017] According to another feature, the secondary outer wall of the removable panel includes a strip superimposed on the main outer wall and connected to the latter by removable connecting elements.
[0018] According to another feature, the ventral beam has a box-section structure.
[0019] According to another feature, the intermediate part of the fuselage includes at least one fixed outer wall connected to the ventral beam.
[0020] According to another feature, the ventral beam comprises a lower wall oriented towards the fixed outer wall and two lateral walls substantially parallel to the median longitudinal plane and connected to the lower wall, each lateral wall having an extension, projecting from the lower wall, connected to the fixed outer wall and to the secondary outer wall of a removable panel by a T-shaped angle.
[0021] Other features and advantages will become apparent from the following description of the invention, given by way of example only, with reference to the accompanying drawings, among which:
[0022] [Fig. 1] is a perspective view of an aircraft illustrating one embodiment of the invention,
[0023] [Fig.2] is a perspective view of the rear part of the aircraft visible in [Fig.1], the rear part of the fuselage being transparent,
[0024] [Fig.3] is a cross-section along plane P of [Fig.2] of the aircraft,
[0025] [Fig.4] is a perspective view of a rear part of an aircraft fuselage including removable panels in the assembled state,
[0026] [Fig.5] is a perspective view of the rear part of the fuselage visible in [Fig.4] the removable panels being in a disassembled state,
[0027] [Fig.6] is a cross-section of a lower area of an intermediate part of the fuselage illustrating one embodiment of the invention, the removable panels being in the disassembled state,
[0028] [Fig.7] is a cross-section of a lower area of an intermediate part of the fuselage illustrating one embodiment of the invention, the removable panels being in the assembled state,
[0029] [Fig.8] is a cross-section of a first connection zone between a removable panel and a ventral beam illustrating one embodiment of the invention,
[0030] [Fig.9] is a cross-section of a second connection zone between a removable panel and a fixed fuselage panel illustrating one embodiment of the invention.
[0031] According to an embodiment visible in [Fig.1], an aircraft 10 comprises a fuselage 12 extending between a front tip 12.1 and a rear tip 12.2, wings 14 extending on either side of the fuselage 12 and an empennage 16 positioned at the rear tip.
[0032] According to an embodiment shown in [Fig. 2], the fuselage 12 comprises a structure having frames 18 positioned in transverse planes and longitudinal reinforcements 20 (shown in [Fig. 9]), called stringers, connecting the frames 18 and oriented approximately along the longitudinal direction. The fuselage also includes a skin attached to the structure.
[0033] The fuselage 12 includes a lower generator G12 corresponding to the fuselage generator 12 located at the level of the median longitudinal plane PLM, the lowest in the vertical direction. When the aircraft 10 is on the ground, the lower generator G12 is oriented towards the ground.
[0034] According to one configuration, each frame 18 has a Z-shaped cross-section. The longitudinal reinforcements 20 can have a J-shaped cross-section. Of course, the invention is not limited to these cross-sections for the frames and the longitudinal reinforcements 18, 20.
[0035] According to an embodiment shown in Figures 2 and 3, the aircraft 10 comprises at least one tank 22 configured for storing hydrogen. In one arrangement, the aircraft comprises two tanks 22, 22' positioned symmetrically with respect to the median longitudinal plane PLM.
[0036] According to one configuration, each tank 22, 22' comprises a cylindrical body which has an axis parallel to the longitudinal direction as well as first and A second end wall, dome-shaped for example, closes each end of the cylindrical body. In one arrangement, the first end wall is oriented towards the forward tip 12.1 and the second end wall is oriented towards the aft tip 12.2. Each tank 22, 22' has a length (dimension taken parallel to the longitudinal direction) L22 and a diameter D22. Of course, the invention is not limited to this number of tanks and this geometry. Furthermore, the tanks 22, 22' can be configured to store other fluids. At a minimum, the aircraft 10 comprises a single tank 22.
[0037] Regardless of the configuration, the fuselage 12 comprises a first transverse plane PI, located at the first end wall of each tank 22, 22' or slightly offset towards the forward tip 12.1 relative to the latter, and a second transverse plane P2, located at the second end wall of each tank 22, 22' or slightly offset towards the aft tip 12.2 relative to the latter. The first and second transverse planes PI, P2 are spaced at a distance equal to or slightly greater than the length L22 of the tank 22 to allow for its extraction. By way of example, the first and second transverse planes PI, P2 are spaced at a distance between a first dimension equal to the length L22 of the tanks 22, 22' and a second dimension equal to the length L22 of the tanks 22, 22' plus 10%.
[0038] The first and second planes PI, P2 are offset towards the rear with respect to the wings 14.
[0039] The fuselage 12 includes an upstream part 24 located in front of the first transverse plane PI (between the first transverse plane PI and the forward tip 12.1), a downstream part 26 located behind the second transverse plane P2 (between the second transverse plane P2 and the rear tip 12.2) and an intermediate part 28 located between the first and second transverse planes PI, P2, behind the wings.
[0040] According to one feature, the fuselage structure 12 comprises a ventral beam 30, positioned symmetrically with respect to the median longitudinal plane PLM at the level of the lower generatrix G12, connecting the upstream and downstream sections 24, 26 of the fuselage 12. Thus, this ventral beam 30 has a first end 30.1 connected to the upstream section 24, more particularly to the structure of the upstream section 24, and a second end 30.2 connected to the downstream section 26, more particularly to the structure of the downstream section 26. The first end 30.1 is offset rearward with respect to the wings 14. According to one configuration, the aircraft 10 comprises a central wing box connecting the wings 14 to the fuselage 12 and a second ventral beam, different from the ventral beam 30, positioned below the central wing box and connecting the fuselage sections located at the front and rear of the central wing box.
[0041] According to an embodiment shown in [Fig. 6], the ventral beam 30 has a box-section structure. Regardless of the embodiment, the ventral beam 30 is configured, among other things, to limit the deflection of the fuselage 12 in the median longitudinal plane PLM between the upstream and downstream parts 24, 26.
[0042] According to a design visible in Figures 7 and 8, the ventral beam 30 comprises a lower wall 32 oriented towards the fuselage skin 12 and two lateral walls 34, 34' substantially parallel to each other and to the median longitudinal plane PLM. The lower wall 32 comprises two flanges 32.1, 32.1' folded at 90° against which the lateral walls 34, 34' are pressed, with connecting elements 36 (bolts or rivets, for example) ensuring the connection between the lateral walls 34, 34' and the flanges 32.1, 32.1' of the lower wall 32. Other solutions are conceivable for ensuring the connection between the lower wall 32 and the lateral walls 34, 34'.
[0043] The intermediate part 28 of the fuselage 12 includes at least one fixed outer wall 38, connected to the ventral beam 30, forming part of the skin of the fuselage 12.
[0044] In one configuration, the lower wall 32 comprises two hollow ribs 32.2, 32.2', spaced apart, parallel to each other and to the longitudinal direction, against which the fixed outer wall 38 is pressed. The latter is connected to the ribs by bonding or by fasteners such as bolts or rivets. The fixed outer wall 38 of the fuselage skin has a longitudinal reinforcement 38.1 positioned between the two hollow ribs 32.2, 32.2'. Other solutions are conceivable for ensuring the connection between the lower wall 32 and the fixed outer wall 38 forming part of the fuselage skin 12.
[0045] According to one embodiment, each side wall 34, 34' has an extension 34.1, 34.1', projecting from the lower wall 32, connected to the fixed outer wall 38 by a T-angle 39, the extension 34.1, 34.1' being connected to the leg 39.1 of the T-angle 39, the fixed outer wall 38 being connected to a first part 39.2 of the head of the T-angle 39.
[0046] In addition to the ventral beam 30, the fuselage 12 includes at least one opening 40, positioned near the ventral beam 30, extending between the first and second transverse planes PI, P2 so as to allow the extraction of at least one fuel tank 22, 22' from the fuselage, and, for each opening 40, a removable panel 42 configured to be in an assembled state in which it closes the opening 40, as illustrated in [Fig. 4], and in a disassembled state in which it uncovers the opening 40, as illustrated in [Fig. 5]. Each removable panel 42 has a perimeter substantially identical to that of the corresponding opening 40.
[0047] According to one configuration, the fuselage 12 comprises first and second openings 40, 40' positioned on either side of the ventral beam 30, attached to the ventral beam 30, identical and symmetrical with respect to the median longitudinal plane PLM. In addition, the fuselage 12 includes first and second removable panels 42, 42' positioned, when assembled, on either side of the ventral beam 30 and symmetrical with respect to the PLM median longitudinal plane. The two openings 40, 40' are located on the lower half of the fuselage 12.
[0048] According to one embodiment, each opening 40 has first and second transverse edges 40.1, 40.2 positioned respectively at the first and second transverse planes PI, P2, as well as first and second longitudinal edges 40.3, 40.4 connecting the first and second transverse edges 40.1, 40.2. The first longitudinal edge 40.3 is attached to the ventral beam 30, and the second longitudinal edge 40.4 is positioned sufficiently far from the first longitudinal edge 30.3 to allow the tank 22 to be extracted from the fuselage 12. As illustrated in [Fig. 3], in top view, the first and second longitudinal edges 40.3, 40.4 are spaced at a distance La40 equal to or slightly greater than the diameter D22 of the tank 22. For guidance, the distance La40 is between the diameter D22 and the diameter D22 increased by 10%.
[0049] Each of the first and second removable panels 42, 42' comprises first and second transverse sides 42.1, 42.2 which adjoin respectively the transverse edges 40.1, 40.2 of the corresponding opening 40 when the removable panel 42 is in the mounted state and first and second longitudinal sides 42.3, 42.4 which adjoin or slightly overlap the first and second longitudinal edges 40.3, 40.4 of the corresponding opening 40 when the removable panel 42 is in the mounted state.
[0050] Like the rest of the fuselage, the intermediate part 28 includes main frame sections 44 forming part of the fuselage structure 12 and a main outer wall 46 forming part of the fuselage skin 12.
[0051] As illustrated in [Fig. 9], each main frame section 44 comprises a web 48.1 positioned in a transverse plane and at least one flange 48.2 provided at one end of the web 48.1 onto which the main outer wall 46 is attached and fixed. In the presence of a single opening 40, each main frame section 44 has a first end 44.1 positioned at the second longitudinal edge 40.4 of the opening 40 and a second end connected to the ventral beam 30. In the presence of two openings 40, 40' positioned on either side of the ventral beam 30, each main frame section 44 has a first end 44.1 positioned at the second longitudinal edge 40.4 of the first opening 40 and a second end positioned at the second longitudinal edge of the second opening 40'.
[0052] The intermediate part 28 may also include longitudinal reinforcements.
[0053] For each opening 40, 40', the main outer wall 46 has an edge that corresponds to the second longitudinal edge 40.4 of the opening 40, 40'.
[0054] Each removable panel 42, 42' includes a secondary frame section 50 for each main frame section 44 of the intermediate part 28 as well as a secondary outer wall 52.
[0055] Like the main frame sections 44, each secondary frame section 50 comprises a web 54.1 positioned in a transverse plane and at least one flange 54.2 provided at one end of the web 54.1 on which the secondary outer wall 52 is attached and fixed. When the removable panel 42, 42 is in the mounted state, the web 54.1 of each secondary frame section 50 is positioned substantially in the same transverse plane as the web 48.1 of the corresponding main frame section 44.
[0056] Each secondary frame section 50 has a first end 50.1 positioned at the level of the first longitudinal side 42.3 of the removable panel 42, 42' and a second end 50.2 positioned at the level of the second longitudinal side 42.4 of the removable panel 42, 42'.
[0057] Each removable panel 42, 42' may also include longitudinal reinforcements.
[0058] For each opening 40, 40' and each removable panel 42, 42', the fuselage 12 includes a first removable connecting system 56 linking the web 54.1 of each secondary frame section 50 of the removable panel 42, 42' and the ventral beam 30 and a second removable connecting system 58 linking the web 54.1 of each secondary frame section 50 of the removable panel 42, 42' and the web 48.1 of the corresponding main frame section 44 of the intermediate part 28.
[0059] According to an embodiment visible in [Fig. 8], the first connection system 56 comprises, for each secondary frame section 50, at least one L-shaped angle 60 having a first flange 60.1 pressed against the ventral beam 30, more particularly against the corresponding side wall 34, 34', and connected to the latter by removable connecting elements 56.1 such as bolts or screws, for example, and a second flange 60.2 pressed against the web 54.1 of the secondary frame section 50 and connected to the latter by connecting elements 56.2. According to one configuration, the first connection system 56 comprises, for each secondary frame section 50, a single angle 60 positioned against one of the faces of the web 54.1 of the secondary frame section 50.According to another configuration, the first connection system 56 comprises, for each section of secondary frame 50, two L-shaped angles 60 positioned on either side of the web 54.1 of the section of secondary frame 50.
[0060] According to a first arrangement visible in [Fig.8], the secondary outer wall 52 the removable panel 42, 42' is pressed against a second part 39.3 of the head of the T-angle 39 and connected to the latter by removable connecting elements 56.3 such as bolts or screws for example.
[0061] According to a second arrangement, a strip of the secondary outer wall 52 is superimposed on the fixed outer wall 38 provided under the ventral beam 30 and connected to the latter by removable connecting elements such as bolts or screws for example.
[0062] According to an embodiment shown in [Fig. 9], the second connecting system 58 comprises, for each secondary frame section 50, at least one splice 62 having a first part 62.1 pressed against the web 48.1 of the corresponding main frame section 44 and connected to it by removable connecting elements 58.1, such as bolts or screws, and a second part 62.2 pressed against the web 54.1 of the secondary frame section 50 and connected to it by removable connecting elements 58.2, such as bolts or screws. In one configuration, the second connecting system 58 comprises, for each secondary frame section 50, a single splice 62, positioned against one of the faces of the web 54.1 of the secondary frame section 50.According to another configuration, the second connection system 58 comprises, for each secondary frame section 50, two splices 62 positioned on either side of the web 54.1 of the secondary frame section 50. .
[0063] According to a first arrangement, the secondary outer wall 52 of the removable panel 42, 42' and the main outer wall 46 of the intermediate part 28 of the fuselage 12 are juxtaposed and connected, along the second longitudinal side 42.4, by means of a splice or a T-angle. The secondary outer wall 52 and the main outer wall 46 are connected to the splice or the T-angle by removable connecting elements such as bolts or screws for example.
[0064] According to a second arrangement visible on [Fig.9], a strip of the secondary outer wall 52 of the removable panel 42, 42' is superimposed on the main outer wall 46, along the second longitudinal side 42.4, and connected to the latter by removable connecting elements 58.3 such as bolts or screws for example.
[0065] According to one configuration, at least one of the transverse sides 42.1, 42.2 of the removable panels 42, 42' (preferably both) is connected to the corresponding transverse edge 40.1, 40.2 of the openings 40, 40'.
[0066] The aircraft also includes networks extending between the upstream and downstream parts 24, 26, offset from the openings 40, 40'. Thus, each panel 42, 42' can be removed without impacting the networks.
[0067] According to one configuration, the intermediate part 28 of the fuselage corresponds to an unpressurized area of the fuselage 12. Consequently, the first and second systems of Connections 56, 58 are not necessarily watertight.
[0068] According to the invention, it is possible to extract the tanks 22, 22' from the fuselage 12 via the openings 40, 40', by removing the removable panels 42, 42'. Thanks to the ventral beam 30, this removal does not pose any risk to the integrity of the fuselage 12.
Claims
Demands
1. Aircraft comprising a fuselage (12) and wings (14), the fuselage (12) having a median longitudinal plane (PLM), a lower generatrix (G12), an upstream part (24) located in front of a first transverse plane (PI), a downstream part (26) located behind a second transverse plane (P2) and an intermediate part (28) located between the first and second transverse planes (PI, P2), the first and second planes (PI, P2) being offset towards the rear with respect to the wings (14), the fuselage (12) comprising a structure and a skin attached to the structure; characterized in that the structure of the fuselage (12) comprises a ventral beam (30), positioned at the level of the lower generatrix (G12), connecting the upstream and downstream parts (24, 26) of the fuselage (12);in that the fuselage (12) includes first and second openings (40, 40') positioned on either side of the ventral beam (30), extending between the first and second transverse planes (PI, P2) and first and second removable panels (42, 42'), each configured to occupy an assembled state in which the removable panel (42) closes the opening (40) and a disassembled state in which the removable panel (42) clears the opening (40), the first and second removable panels (42, 42') being positioned, when in the assembled state, on either side of the ventral beam (30);in that the aircraft comprises at least one tank (22) having a length (L22) and a diameter (D22) and in that each opening (40) has first and second transverse edges (40.1, 40.2) positioned respectively at the first and second transverse planes (PI, P2) as well as first and second longitudinal edges (40.3, 40.4) connecting the first and second transverse edges (40.1, 40.2), the first longitudinal edge (40.3) being attached to the ventral beam (30), the first and second longitudinal edges (40.3, 40.4) being spaced at a distance (La40) equal to or slightly greater than the diameter (D22) of the tank (22), the first and second transverse planes (PI, P2) being spaced at a distance equal to or slightly greater than the length (L22) of the tank (22).;
2. Aircraft according to the preceding claim, characterized in that the intermediate part (28) comprises main frame sections (44) forming part of the fuselage structure (12) as well as a main outer wall (46) forming part of the skin of the fuselage (12), each main frame section (44) having a web (48.1) positioned in a transverse plane; in that each removable panel (42, 42') comprises a secondary frame section (50) for each main frame section (44) of the intermediate part (28) as well as a secondary outer wall (52), each secondary frame section (50) having a web (54.1) positioned substantially in the same transverse plane as the web (48.1) of the corresponding main frame section (44) when the removable panel (42, 42) is in the mounted state; and in that the fuselage (12) comprises, for each panel (42, 42'), a first removable connecting system (56) linking the web (54.1) of each secondary frame section (50) of the removable panel (42, 42') and the ventral beam (30) as well as a second removable connecting system (58) linking the web (54.1) of each secondary frame section (50) of the removable panel (42, 42') and the core (48.1) of the corresponding main frame section (44) of the intermediate part (28).
3. Aircraft according to the preceding claim, characterized in that the first connection system (56) comprises, for each secondary frame section (50), at least one L-shaped angle (60) having a first wing (60.1) pressed against the ventral beam (30) and connected to the latter and a second wing (60.2) pressed against the web (54.1) of the secondary frame section (50) and connected to the latter.
4. Aircraft according to claim 2 or 3, characterized in that the second connection system (58) comprises, for each secondary frame section (50), at least one splice (62) having a first part (62.1) pressed against the web (48.1) of the corresponding main frame section (44) and connected thereto and a second part (62.2) pressed against the web (54.1) of the secondary frame section (50) and connected thereto.
5. Aircraft according to any one of the preceding claims, characterized in that the secondary outer wall (52) of the removable panel (42, 42') comprises a strip superimposed on the main outer wall (46) and connected to the latter by removable connecting elements (58.3).
6. Aircraft according to any one of the preceding claims, characterized in that the ventral beam (30) has a box-section structure.
7. Aircraft according to any one of the preceding claims, characterized in that the intermediate portion (28) of the fuselage (12) comprises at least one fixed outer wall (38) connected to the ventral beam (30).
8. Aircraft according to claims 2 and 7, characterized in that the ventral beam (30) comprises a lower wall (32) oriented towards the fixed outer wall (38) and two side walls (34, 34') substantially parallel to the median longitudinal plane (PLM) and connected to the lower wall (32), each side wall (34, 34') having an extension (34.1, 34.1'), projecting from the lower wall (32), connected to the fixed outer wall (38) and to the secondary outer wall (52) of a removable panel (42, 42') by a T-angle (39).