FR3033315A1 - METHOD FOR MAKING A SEALED BACKGROUND OF AIRCRAFT FUSELAGE AND FUSELAGE EQUIPPED WITH SUCH A SEALED BACKGROUND - Google Patents

Abstract

The aim of the invention is to provide a sealing base comprising a limited number of parts while achieving an optimized compromise between energy absorption and rigidity so as to withstand the violent shocks caused by the impact of foreign bodies, in particular birds. A sealed bottom (1) according to the invention comprises a stiffening panel (11) configured in a double orientation and assembled by embedding and securing to a shield of porous material (12) grooved at least partially in its thickness in a complementary configuration. The assembly thus combined is arranged between a closing wall (13) at one end (A) and a peripheral frame (15) for attaching the aircraft to the fuselage (2) at the other end (B), the wall closure member (13) being secured to the porous shield (12) and the stiffening panel (11) to the peripheral attachment frame (15) via a seal (14).

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a method for producing a waterproof bottom before an aircraft fuselage constituted. a set of parts forming a compact assembly, and an aircraft fuselage equipped with such a sealed bottom. [0002] Conventionally, a sealed bottom is disposed at the front end of the fuselage of an aircraft against the radome whose configuration and cone structure ensures, in flight, a first protection of the aircraft against frost and the impacts of foreign bodies, such as birds, as well as good penetration into the atmosphere. [0003] The radome generally receives the radar antenna of the aircraft and, in order not to disturb the signals, it is made of a material that is transparent to radar waves, for example fiberglass. The watertight funds before serve as a pressure barrier to the pressurized cabin formed in the interior space of the fuselage. They also serve as protection against foreign bodies that would cross the radome. To this end, they consist of rigid structures of metal or composite materials reinforced by beams and stiffeners to provide a high resistance to the penetration of these foreign bodies. STATE OF THE ART [0005] The front bottoms thus form assemblies comprising a large number of parts bonded together by welding, riveting, gluing or the like, which increases the weight, the thickness and the cost of such funds. In order to overcome these disadvantages, various solutions have been proposed. For example, US Pat. No. 7,766,277 discloses a deformable aircraft front wall having a dome-shaped malleable structure which can be deformed in response to a minimum impact energy by absorption of at least 50.degree. least part of that energy. This dome consists of several layers coupled together: two solid layers and a third partial layer forming an annular band on a periphery of the second layer, these three layers defining an outer perimeter. In addition, an outer rope, forming an annular layer coupled at the periphery of the first layer, extends out of the outer perimeter of the three layers to rigidly fix the dome. Such a multilayer partition, generally convex, does not resist successive violent impacts because its deformation has a low elastic limit and its rigidity is insufficient to sustainably withstand these impacts. It is also known from patent document US Pat. No. 8,033,503 a pressurization partition for an aircraft fuselage. This partition consists of a main part, flat in the unloaded state, and a support frame and coupling of the main part to the fuselage. Which main part consists of a sealing element, forming a thermoplastic membrane, between two elements composed of radial retaining ligaments in deformation of the sealing element. The substantially radial strength structure of this partition does not have sufficient overall rigidity to withstand the violent impacts of foreign bodies. Furthermore, the partition described in US patent document 20100155533 consists of a solid central element, made of a porous material made of aluminum foam, taken between a load distribution layer of fiber composite material. and an aluminum skin layer disposed on the inner side. This solution has a flexibility and an energy absorption capacity, but it does not provide sufficient rigidity to withstand the absorption of higher energy from violent impacts.

SUMMARY OF THE INVENTION The object of the invention is precisely to provide a sealing bottom comprising a limited number of parts while achieving an optimized compromise between energy absorption and rigidity so as to be able to withstand violent shocks. caused by the impact of foreign bodies, especially birds, from the atmosphere. To do this, the invention proposes to achieve a sealed bottom combining a double orientation stiffener panel and a layer of porous material. Remarkably, it has been found that such a combination has both an ability to absorb high energy impacts without breaking, thanks to the porous material absorption layer and the stiffness panel mechanical stiffness characteristics. by preserving the microstructures of the absorption layer and eliminating residual stresses in the panel. More specifically, the subject of the present invention is a method for producing a plane fuselage airtight bottom in which, in a first step, a stiffener panel configured in a double orientation is assembled by embedding and joining to a shield of porous material grooved at least partially in its thickness in a complementary configuration, then the assembly thus combined is arranged, in a second step, between a closure wall at one end of the sealed bottom and a peripheral attachment frame at fuselage of the aircraft at another end of the sealed bottom, the closure wall being secured to the porous shield and the stiffening panel to the peripheral attachment frame via a sealing junction. The porous shield integrated in the stiffening panel directly contributes to the structural rigidity of the sealed bottom. This results in a gain in mass on the entire bottom sealed. In addition, this integration and the limited number of parts minimize the bulk of the sealed bottom. According to preferred embodiments: the peripheral frame has a fuselage connecting portion of greater diameter than the other elements of the sealed bottom, namely the stiffening panel, the shield embedded in the stiffening panel and the wall closure; the fastenings between the closure wall, the porous shield and the stiffening panel are made by a technology chosen between compression and gluing, welding, crimping, brazing and co-firing; - The fastening between the peripheral frame and the stiffening panel being made by mechanical fastening, for example by bolting, riveting, screwing or equivalent; - The peripheral frame, the stiffening panel, the porous shield and the closure wall, are made of metal alloy and / or composite material. The invention also relates to a sealed bottom made according to the above process in which at least one seal is housed in compression in an annular groove to ensure the sealing junction between the peripheral frame and the stiffening panel, the front sealed bottom being dimensioned according to the front fuselage end to which it is intended to be assembled. In addition, the invention relates to an aircraft fuselage equipped with such a front sealed bottom. The front sealed bottom is advantageously coupled to the fuselage by mechanical attachment of the peripheral frame on a fuselage face of suitable configuration.

PRESENTATION OF THE FIGURES [0017] Other data and advantages of the present invention will appear on reading the description which follows, with reference to the appended figures which represent, respectively: FIG. 1, an exploded view of an example of front airtight bottom of an aircraft fuselage according to the invention; FIG. 2 is a partial cross-sectional view of the front sealing base according to FIG. 1 in assembly with the end periphery of the fuselage, and FIG. 3 is a perspective view of a front part of the fuselage after assembly with the waterproof background.

DETAILED DESCRIPTION [0018] With reference to FIG. 1, an exemplary sealed bottom front 1 according to the invention is illustrated in an exploded view. This view makes it possible to visualize the basic elements constituting the sealed bottom as they are in view of being assembled. These basic elements have a circular outer cut and comprise: a stiffening panel 11, a shield 12, a closure plate 13 at one end "A" and, via an O-ring seal 14, a peripheral frame 15 for fixing to an aircraft fuselage (not shown) at the opposite end "B". The peripheral frame 15, the stiffening panel 11 and the closing plate 13 are, in this example, made of aluminum alloy. The shield 12 is of porous material, here made from aluminum foam. More generally, the shield 12 can be made from closed or open-cell foam or metal materials, in the form of honeycombs or in the form of agglomerated beads. More specifically, the stiffening panel 11 is formed of stiffening ribs with double orientation, radial ribs 11r and concentric circular ribs 11c. An annular flange 11b surrounds the stiffening panel 11, this annular flange 11b having a substantially greater thickness, here about 50% greater, than the thickness of the ribs 11c and 11r. During assembly, the stiffening panel 11 is combined with the shield 12. To do this, this porous shield 12 has, facing the ribs 11c and 11r of the stiffening panel 11, grooves 12n configuration complementary to that of the ribs 11c and 11r. These grooves 12n are therefore adapted to receive said ribs 11c and 11r. The grooves 12n are hollowed in the thickness of the porous material of the shield 12, here in about 50% of this thickness. Thus, during assembly, the shield 12 is embedded in the stiffening panel 11, and then secured by any means of solidarization compatible compression and gluing 30 in the embodiment. The shield 12, thus integrated in the stiffener panel 11, contributes to the structural rigidity of the sealed bottom 1 while promoting, once fixed 3033315 6 in front of the fuselage, a higher energy absorption during shocks caused by the foreign bodies. It also results in a gain in mass by the use of a minimum number of parts while preserving the mechanical strength of the assembly. The assembly is continued by joining the stiffening panel 11 to the peripheral frame 15 and securing the closure plate 13 to the porous shield 12, here by gluing. Advantageously, the closure plate 13 is also riveted to the stiffening panel 11, which increases the seal and the mechanical strength of the assembly. The frame 15 is said to be peripheral in that its diameter at the end B is slightly greater than that of the other elements constituting the sealed bottom 1, in particular of the stiffening panel 11 or of the closing plate 13 which have diameters equivalent (the shield 12 having a diameter slightly smaller than the panel 11 to be embedded therein). A connecting portion 15a of the frame 15, of greater diameter, is located towards the end B for attachment to the fuselage. The partial sectional view of Figure 2 illustrates the sealed bottom before 1, once assembled and fixed on a front edge of fuselage front end 2. The compactness of said sealed bottom 1, as shown in FIG. 2, results from the integration of the shield 12 in the stiffening panel 11 and the limited number of parts. Thus, the thickness 1 e of the sealed bottom 1, excluding peripheral frame 15, varies between 60 and 80 mm depending on the embodiments, while a traditional sealed bottom has a thickness of about 200 mm. In FIG. 2, one of the screw connections 20 appears between the stiffening panel 11 and the peripheral frame 15, the other connections being distributed circularly. The seal 14, elastomeric material, is housed in a circular groove 15g formed in the peripheral frame 15. This seal 14 is thus compressed against a face 11f of the stiffening panel 11 to seal between said frame 15 and said panel 11. Alternatively, the seal 14 may be housed in a groove formed in the stiffener panel. The sealed bottom before 1 is here coupled to the fuselage 2 by peripheral smooth 22 and fastening plates 23, called "shovels", which 3033315 7 secure the connecting portion 15a of the peripheral frame 15 at the end periphery 2a fuselage 2 complementary configuration. In addition, an intercostal beam 24 is fixed to the frame 15 via a splint 25 to reinforce the rigidity of the fuselage end assembly 2 - peripheral frame 15. The composition of the sealed bottom 1 then promotes its assembly and its rapid disassembly, which makes it possible to shorten the grounding time of the aircraft to replace it, for example following an impact or during maintenance. Once the bottom sealed before 1 mounted on the front end of fuselage 2, the resulting assembly has the appearance illustrated by the perspective view of Figure 3. The fuselage front end 2 form a frustoconical fuselage portion terminating in the front sealed bottom 1 generally having a circular flat face 13f of relatively small thickness, this face being that of the closing plate 13 (see FIG. 1). In this FIG. 3, there also appears the connecting portion 15a of the peripheral frame 15 against the fuselage end 2a 2 and the annular flange 11b of the stiffening panel 11. [0032] The invention is not limited to the embodiments described and shown. It is for example possible to secure the different elements 20 of the sealed bottom by other techniques than gluing or screwing, for example by riveting, welding, crimping, brazing or co-cooking. Furthermore, the materials used may be other than aluminum alloys, in particular the porous shield may be of composite material structured in honeycomb, or made of metal balls, the closure plate may be composite or metallic material other than aluminum. In addition, the stiffening panel may be made of composite material by the stamping technology of pieces of carbon fiber coupons agglomerated with a resin. In addition, the stiffening ribs of the stiffening panel may have an "isogrid" or orthogonal conformation.

Claims (9)

REVENDICATIONS1. A method of producing an airtight bottom (1) of an aircraft fuselage (2) characterized in that, in a first step, a stiffener panel (11) configured in a double orientation is assembled by embedding and securing to a shield in porous material (12) grooved at least partially in its thickness in a complementary configuration, then the assembly thus combined is arranged, in a second step, between a closure wall (13) at one end (A) of the sealed bottom (1 ) and a peripheral frame (15) for attaching the fuselage (2) of the aircraft to another end (B) of the sealed bottom (1), the closing wall (13) being secured to the porous shield (12) and the stiffening panel (11) to the peripheral fixing frame (15) via a sealing junction (14). 2. Production method according to claim 1, wherein the peripheral frame (15) has a connecting portion (15a) to the fuselage (2) of greater diameter than the other elements of the sealed bottom (1), namely the stiffening panel ( 11), the recessed shield (12) in the stiffening panel (11) and the closing wall (13). 3. Production method according to any one of claims 1 and 2, wherein the connections between the closure wall (13), the porous shield (12) and the stiffening panel (11) are made by a technology chosen between the compression and gluing, soldering, crimping, brazing and co-firing. 4. Production method according to any one of the preceding claims, wherein the connection between the peripheral frame (15) and the stiffening panel (11) is made by mechanical fixing. 5. Production method according to any one of the preceding claims, wherein the peripheral frame (15), the stiffening panel (11) and the closure wall (13) are made of metal alloy and / or composite material. 6. A production method according to any one of the preceding claims, wherein the porous shield (12) is made from metallic or composite materials in a form selected from foam, honeycombs and balls. agglomerated. 7. Production method according to any one of the preceding claims, wherein the stiffening panel (11) comprises stiffening ribs with a double orientation in a conformation chosen between radial - concentric (11r, 11c), orthogonal and "isogrid". . 8. Watertight bottom made according to any one of the preceding claims, characterized in that at least one seal (14) is housed in compression in an annular groove (15g) to ensure the sealing junction 10 between the peripheral frame (14) and the stiffening panel (11), the front waterproof bottom (1) being dimensioned according to the dimensions of a front fuselage end (2) to which it is intended to be assembled. 9. Fuselage aircraft characterized in that it is equipped with a sealed bottom (1) front according to the preceding claim. 15