Abstract:
An aircraft fuselage produced by assembling, at a circumferential joint, at least two sections, each section including a coating and at least one element of at least one stiffener, the aforementioned two elements having a closed cross section and being assembled by a splicing piece. The elements of the stiffener and the splicing piece are made of composite. The aforementioned splicing piece, which has two flanges, is fixed to the coatings and to the stiffener elements by working fastenings positioned only on the flanges of the aforementioned splicing piece.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the National Stage of International Application No. PCT/FR2008/051862 International Filing Date, 15 Oct. 2008, which designated the United States of America, and which International Application was published under PCT Article 21 (s) as WO Publication No. WO2009/053645 A2 and which claims priority from, and the benefit of, French Application No. 200758406 filed on 18 Oct. 2007, the disclosures of which are incorporated herein by reference in their entireties. 
     BACKGROUND 
     The aspects of the disclosed embodiments relate to the field of assembling sections of an aircraft fuselage. More particularly, the disclosed embodiments relate to the assembly of stiffeners of two sections by splices at a circumferential joint. 
     An aircraft fuselage is a structure that is usually made up of several panels assembled together. Said panels are reinforced, inside the fuselage, by reinforcing frames and stiffeners. The reinforcing frames are positioned along fuselage sections that are substantially perpendicular to a longitudinal axis of the fuselage. The stiffeners extend over the panels on the longitudinal axis. 
     When the fuselage is produced by the assembly of at least two sections, the joint between the two sections is called circumferential. At a circumferential joint, the stiffener is interrupted and takes the form of several substantially aligned stiffener elements, with one element per section. 
     However, the stresses that the stiffener has to sustain must be transmitted from one stiffener element to another despite the presence of the interruptions. 
     SUMMARY 
     To assemble two elements of a stiffener between two sections  11   a ,  11   b , as illustrated in  FIG. 1   a , it is known practice in the prior art to add a splice  3  to ends  27   a ,  27   b  of stiffener elements  2   a ,  2   b , said ends being situated at the circumferential joint  5 , in order to allow the continuity of the transmission of the stresses in the stiffener. Said splice bears on the elements  2   a ,  2   b  facing each section  11   a ,  11   b  and is assembled and fastened to the elements  2   a ,  2   b  of the stiffener by means of fasteners  7  such as rivets. 
     In the case of panels made of metal, the metal stiffeners usually have an open cross section which, because of the shape of said cross section, are called I-shaped, J-shaped or T-shaped stiffeners. For stiffeners comprising such cross sections, the splices usually used to assemble the two elements of a stiffener have a L-shaped or J-shaped cross section. 
     Nowadays, aircraft fuselages are increasingly made, for the fuselage panels, the reinforcing frames, the stiffeners and the splices, of aluminum alloy. Despite the lightness qualities of aluminum, the latter has drawbacks in terms of corrosion resistance and structural fatigue, which is particularly felt in the high-flux circumferential joints. 
     Moreover, these days, new materials, such as composite materials with a high modulus of elasticity, make it possible to envisage lighter solutions than aluminum for the production of fuselages. The panels and the stiffeners can therefore be made of a composite material such as, for example, a resin-impregnated carbon-fiber-based material. 
     For such panels, the stiffeners comprising optimal structural characteristics have a closed cross section called omega-shaped. As illustrated in  FIG. 1   b , a stiffener  2  comprises a head  21 , two webs  22 ,  23  and two flanges  24 ,  25 . The stiffener is fastened to a face of a fuselage panel by the two flanges  24 ,  25 . 
     In the case of stiffeners made of metal, of the I, J, T type, the J-shaped or L-shaped splice is fastened to each of the two elements of a stiffener by fasteners placed on the flanges and the web. In the case of stiffeners comprising a closed cross section, such as the omega-shaped stiffeners, the fasteners placed on the webs in order to assemble each stiffener element to the splice are very difficult to inspect because of the practical impossibility of gaining access to the inside of the closed cross section of the stiffener. 
     The aspects of the disclosed embodiments propose, at a circumferential joint of an aircraft fuselage, a splicing between two elements of a stiffener comprising a closed cross section which avoids the necessity of placing fasteners in the web and the head of said stiffener while ensuring the continuity of transmission of the longitudinal stresses. 
     According to the disclosed embodiments, an aircraft fuselage comprises a circumferential joint of at least two sections, each section comprising:
         a skin,   at least one element of at least one stiffener,       

     each element of a stiffener:
         being positioned substantially facing the other element at the joint,   comprising two webs,   comprising two flanges,   said two webs and two flanges determining, with the skin, a closed cross section,       

     in which fuselage the two opposing elements forming a stiffener are assembled by means of a splice, wherein the stiffener and the splice are made of composite material, and in that the splice
         comprises two webs,   comprises two flanges, said flanges each comprising a bearing surface in contact with the flanges of the elements,   is fastened to the skins and to the elements by means of working fasteners positioned only on the flanges of the splice.       

     In one embodiment, each stiffener element comprises a head between the two webs determining a stiffener cross section called omega-shaped. 
     In order to take account of the fact that all the tension-compression stresses run between the stiffener elements through the flanges of said elements, each flange of each stiffener element has an end zone comprising an increased cross section and further comprising a length greater than a distance D a , D b  of overlap of the splice. 
     Preferably, for all of the tension-compression stresses in the stiffener to be transmitted from the flanges of the elements to the flanges of the splice, each length D a , D b  of overlap is determined in order to allow working fasteners to be placed over said length of overlap. Moreover, the bearing surfaces of the flanges of the splice are in contact with the flanges of the stiffener elements over substantially all of said bearing surfaces over the lengths of overlap D a , D b . 
     In one exemplary embodiment, the bearing surfaces are substantially flat. 
     In another exemplary embodiment, said bearing surfaces are formed to be in contact with the stiffener elements and the skins while taking account of the geometry of said elements and of said skins. 
     In one embodiment, the splice comprises a head, two webs and two flanges defining an omega-shaped cross section, the internal dimensions of said cross section being determined in order to make it possible to fasten the superposed splice to the stiffener elements while ensuring that the flanges of the splice are in contact with the flanges of the stiffener elements. 
     Preferably, in order to perform a function of drainage and inspection of the fasteners placed on the ferrule, the head of the splice comprises at least one recess. 
     In another embodiment, the splice comprises two lateral portions, each comprising a web and a flange, said two lateral portions being positioned on each side of the webs of the stiffener elements and connected by a central portion positioned longitudinally on the splice between the ends of said stiffener elements and capable of holding in relative position, one relative to the other, the two lateral portions when the splice is put in place. 
     In one embodiment, in order to participate in the structural portion of the assembly, the central portion comprises a bearing surface, in line with the bearing surfaces of the flanges of the lateral portions, fastened to the skins by means of working fasteners. 
     In another embodiment, in order to prevent the webs being warped from the lateral portions, the central portion comprises at least one reinforcing rib, said rib being substantially in a cross-sectional plane of the splice and being fastened to the webs of the lateral portions. 
     In another variant embodiment, in order to improve the stability of the lateral portions, said lateral portions comprise a flanged edge at the end of the webs opposite to the flanges of the splice. 
     In another embodiment, the splice comprises two independent lateral portions, a first portion arranged on one side of the webs of the stiffener elements, a second portion on the other side of the webs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The detailed description of the disclosed embodiments is made with reference to the figures which represent: 
         FIG. 1   a , already cited, a view of a stiffener assembled by means of a splice according to the prior art, 
         FIG. 1   b , already cited, a view in perspective of a stiffener comprising an omega-shaped cross section, 
         FIG. 2 , a schematic view of a portion of an aircraft fuselage, 
         FIG. 3   a , a schematic view in perspective of an omega-shaped stiffener assembled by means of a splice according to a first embodiment of the disclosed embodiments, 
         FIG. 3   b , a view in perspective of the splice assembling two elements of an omega-shaped stiffener according to the first embodiment of the disclosed embodiments, 
         FIG. 4   a , a schematic view in perspective of an omega-shaped stiffener assembled by means of a splice according to a second embodiment of the disclosed embodiments, 
         FIGS. 4   b, c, d, e  various views of the splice according to the second embodiment illustrating variant embodiments of the splice, 
         FIG. 5 , a schematic view in perspective of an omega-shaped stiffener assembled by means of a splice according to a third embodiment of the disclosed embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     An aircraft fuselage  1 , as illustrated in  FIG. 2 , is made by assembling at least two substantially cylindrical sections  11   a ,  11   b  at circumferential joints  5 . Each section  11   a ,  11   b  comprises a skin  12   a ,  12   b  made with at least one fuselage panel. At a joint  5 , the panels are assembled together by a ferrule  4 . 
     In order to ensure that the fuselage  1  has the necessary rigidity, said fuselage comprises reinforcing frames  6  and stiffeners. The reinforcing frames  6 , the ferrule  4  and the panels are assembled at the circumferential joint. 
     At a circumferential joint  5 , the stiffeners are interrupted and appear in the form of two elements  2   a ,  2   b  per stiffener, situated facing one another when the two sections are assembled and extend, on a longitudinal axis of the fuselage, over each section  11   a ,  11   b . The elements  2   a ,  2   b  of a stiffener are fastened to a skin  12   a ,  12   b  of a section  11   a ,  11   b  of the fuselage. 
     In order to transmit the stresses from one stiffener element to another despite the presence of the interruption and thus ensure the structural continuity of the stiffener, the two elements  2   a ,  2   b  are assembled by means of a splice  3 . Said splice rests on the ends  27   a ,  27   b  of said two elements, and is fastened to the elements  2   a ,  2   b  of the stiffener by means of fasteners  7 , such as rivets. 
     A notch  37  is made in the frame  6  in order to ensure the passage of the splice  3  and allow the stresses to be transmitted from one stiffener element to another by means of said splice. 
     In the exemplary embodiments illustrated by  FIGS. 3   a  to  5 , the assembly of a stiffener, at a circumferential joint  5  between two sections  11   a ,  11   b  of an aircraft fuselage is described in the case of a closed-section stiffener comprising an omega-shaped cross section. 
     The element  2   a  of a stiffener, as illustrated in  FIG. 3   a , comprises a head  21   a , two webs  22   a ,  23   a  and two flanges  24   a ,  25   a . The two flanges are substantially coplanar. Each flange  24   a ,  25   a  is connected to a web  22   a ,  23   a  that is inclined relative to the plane of the flanges. Said webs hold the head  21   a  at a substantially constant distance from the flanges. The element  2   a  of the stiffener is fastened to the skin  12   a  of the section  11   a  by the two flanges  24   a ,  25   a . Therefore, the stiffener  2   a , assembled on the skin  12   a , advantageously forms a rigid and strong box structure. 
     In a similar manner, the element  2   b  of the stiffener comprises a head  21   b , two webs  22   b ,  23   b , and is assembled on the skin  12   b  of the section  11   b  in the same manner. 
     For the purposes of describing the exemplary embodiments, the head  21   a , respectively  21   b , has a width I a , respectively I b . The two flanges  24   a ,  25   a , respectively  24   b ,  25   b , are separated by a distance d a , respectively d b . Usually with the omega-shaped stiffeners, as shown in  FIGS. 3   a  to  5 , the distance d a , respectively d b , is greater than the width I a , respectively I b . The principles of the disclosed embodiments are however applicable in the case of stiffeners that do not satisfy this requirement of d a  being greater than or equal to I a , respectively d b  being greater than or equal to I b . 
     According to the disclosed embodiments and contrary to the prior art, the splice transmitting the stresses between the stiffener elements is entirely fastened only by the flanges so that no fastener is fastened to the webs or the head, that is to say in a location where the fastening is in a blind zone making an inspection practically impossible, for example in the case of a joint comprising a large number of fasteners. 
     In order to achieve this result while guaranteeing the structural quality of the joint, it is necessary to adapt the splice and the stiffener elements together, at least in the zones where the splice is fastened. 
     According to a first embodiment, shown by  FIG. 3   a , the splice  3 , which ensures structural continuity between the two elements  2   a ,  2   b , situated substantially facing one another, of a stiffener, has a substantially omega-shaped cross section, as for the stiffener elements  2   a ,  2   b . Said splice comprises a head  31 , two webs  32 ,  33  and two flanges  34 ,  35 , said flanges comprising a bearing surface  341 ,  351 . Said splice overlaps the ends  27   a ,  27   b  of the two elements  2   a ,  2   b  situated on each side of the joint so that the head  31  of the splice  3  overlaps the heads  21   a ,  21   b  of the ends  27   a ,  27   b  of the two stiffener elements  2   a ,  2   b , and so that the web  32 , respectively  33 , overlaps the webs  22   a ,  23   a , respectively  22   b ,  23   b , of the ends  27   a ,  27   b  of the stiffener elements  2   a ,  2   b.    
     The bearing surface  341 , respectively  351 , of the splice  3  is in contact with the flanges  24   a ,  24   b , respectively  25   a ,  25   b , of the ends  27   a ,  27   b  of the two stiffener elements  2   a ,  2   b  and on the skin  12   a , respectively  12   b , or the ferrule  4 , when said ferrule is placed on the skins  12   a ,  12   b  situated on the same side as the stiffener elements  2   a ,  2   b . The bearing surfaces  341 , respectively  351 , are fastened to the flanges  24   a ,  24   b , respectively  25   a ,  25   b , and the ferrule  4  or the skin  12   a ,  12   b  by means of fasteners  7 , such as for example rivets. 
     Preferably, the bearing surfaces  341 ,  351  of the splice  3  are formed to ensure contact in all the zones where the working fasteners must be placed while taking account of the geometry of the flanges  24   a ,  24   b ,  25   a ,  25   b  of the stiffener elements  2   a ,  2   b  and of the ferrule  4  or the skin  12   a ,  12   b.    
     In another exemplary embodiment, when the bearing surfaces  341 ,  351  of the splice  3  are substantially flat, shims are positioned so that the splice  3  is in perfect contact on said stiffener elements  2   a ,  2   b  and the ferrule  4  or the skin  12   a ,  12   b.    
     The splice  3  extends over a length of overlap D a , respectively D b , of each stiffener element  2   a , respectively  2   b , so that the number of fasteners  7  placed on said length of overlap is sufficient for all of the tension-compression stresses to be transmitted from the flanges  24   a ,  24   b , respectively  25   a ,  25   b , of the elements  2   a ,  2   b  to the flanges  34 ,  35  of the splice  3 . Because the splice  3  is fastened only to the flanges  24   a ,  24   b ,  25   a ,  25   b  of the stiffener elements  2   a ,  2   b , the length of overlap D a , D b  is greater, relative to an embodiment of a conventional splice between two sections, than the length of overlap of a splice fastened also to the web of the stiffener elements. 
     To ensure that the stresses are transmitted, the bearing surfaces  341 ,  351  of the flanges  34 ,  35  of the splice  3  must necessarily be in contact with the flanges  24   a ,  24   b ,  25   a ,  25   b  of the stiffener elements  2   a ,  2   b . For this, the internal dimensions of the cross section of the splice ( 3 ) are such that said internal dimensions are always greater than or equal to the external dimensions of a theoretical stiffener. The theoretical stiffener is characterized by an envelope of all the stiffeners, in relative position, taking account of the dimensional uncertainties and positional tolerance uncertainties, inevitable because of the manufacturing tolerances, between the two stiffener elements. 
     At the joint between the stiffener elements  2   a ,  2   b  and the splice  3 , all of the stresses are transmitted from one stiffener element to another via the flanges  24   a ,  24   b ,  25   a ,  25   b  of said elements. To take account of the increase of the stresses in said flanges, the cross section of the flanges of the stiffener elements  2   a ,  2   b  is increased, over an end zone of a length greater than the length of overlap D 8 , D b  so that the stresses remain within the structural limit of the material. Advantageously, in order therefore to ensure a progressive transmission of the stresses and to prevent an overthickness of the flange  24   a ,  24   b ,  25   a ,  25   b , at the end of the stiffener element and in the zone of fastening with the splice, each flange is widened. This widening of the flanges also makes it possible to take account of the misalignment tolerances between the two stiffener elements when the sections are assembled. 
     The flanges  34 ,  35  of the splice  3  are also given thickness and width dimensions in order, to transmit the stresses. Preferably, the width of the baseplaces  34 ,  35  is chosen so that, because of the tolerances of dimensioning and positioning of the stiffener elements  2   a ,  2   b , the flanges  34 , respectively  35 , of the splice are, over the whole of their length, always fully resting on the flanges  24   a ,  24   b , respectively  25   a ,  25   b , of said elements. 
     In order to perform a function of drainage and to allow inspection of the fasteners, in order for the two sections to be assembled together at the circumferential joint situated on the ferrule  4 , beneath the head  31  of the omega-shaped splice  3 , at least one recess  36  is made in the head  31  of said splice. 
     In a second embodiment, illustrated by  FIG. 4   a , the splice  30  used for assembling the two omega-shaped stiffener elements  2   a ,  2   b  comprises two lateral portions  10 ,  11  each comprising a substantially L-shaped cross section and a central portion  9  connecting the two lateral portions  10 ,  11  and holding together, in a predetermined position, the two lateral portions so that said two lateral portions rest only on the flanges of the stiffener elements  2   a ,  2   b.    
     The central portion  9  is wider than the distance d a  or d b  between the two flanges  24   a ,  25   a  or  24   b ,  25   b  of a stiffener element  2   a  or  2   b  in order to take account, as described in the case of the first embodiment, of the misalignment tolerances between the two stiffener elements  2   a ,  2   b  when the two sections  11   a ,  11   b  are assembled. 
     Each lateral portion  10 ,  11  comprises a web  101 ,  111  and a flange  102 ,  112  comprising a bearing surface  103 ,  113 . The two lateral portions are positioned on either side of the omega-shaped stiffener elements  2   a ,  2   b  with their webs  101 ,  111  positioned on the side of the webs  22   a ,  22   b ,  23   a ,  23   b  of the omega-shaped stiffener elements  2   a ,  2   b . The flanges  102 ,  112  of the splice  30  are fastened to the flanges  24   a ,  24   b ,  25   a ,  25   b  of the two stiffener elements  2   a ,  2   b  and the ferrule  4  or the skin  12   a ,  12   b.    
     In a manner similar to the first embodiment, the bearing surface  103 , respectively  113 , of the lateral portion  10 , respectively  11 , rests on the flanges  24   a ,  24   b , respectively  25   a ,  25   b  of the ends  27   a ,  27   b  of the two stiffener elements  2   a ,  2   b  and on the ferrule  4  or the skin  12   a , respectively  12   b . The bearing surfaces  103 ,  113  are fastened respectively to the flanges  24   a ,  24   b  and  25   a ,  25   b  and the ferrule  4  by means of fasteners  7 . 
     The lateral portions extend, on either side of the ends of the two stiffener elements, over the length of overlap D a , D b  that is sufficient to allow the working fasteners  7  to be installed and thus to ensure the transmission of the tension-compression stresses from the flanges  24   a ,  24   b ,  25   a ,  25   b  of the elements  2   a ,  2   b  to the flanges  102 ,  112  of the splice  30 . 
     The central portion  9  comprises at least one working structural zone. Said central portion is positioned between the two ends  27   a ,  27   b  of the two stiffener elements  2   a ,  2   b  when the splice is put in place. 
     In one embodiment, said structural portion of the central portion  9  comprises a bearing surface  93 , substantially in line with the bearing surfaces of the flanges, formed to rest on the skins  12   a ,  12   b , or the ferrule  4  between the ends  27   a ,  27   b  of the stiffener elements. Said central portion is therefore shorter than a distance D separating the two ends  27   a ,  27   b  of the two stiffener elements  2   a ,  2   b.    
     Advantageously, the central portion  9  is fastened, by means of fasteners  7 , such as rivets, to the ferrule  4  or the skin  12   a ,  12   b  and participates in the structural quality of the assembly. 
     In another form of producing this second embodiment, the central portion  9  also comprises at least one reinforcing rib  91 , as illustrated in  FIGS. 4   b ,  4   c ,  4   d , that is substantially perpendicular to the webs  101 ,  111  of the lateral portions  10 ,  11  and fastened to said webs of the lateral portions  10 ,  11 . The addition of a rib  91  makes it possible to better distribute the consolidation and prevent the warping of the webs  101 ,  111  of the two lateral portions  10 ,  11 . 
     In the example of  FIG. 4   b , the central portion  9  comprises a central rib  91  that is substantially perpendicular to the webs  101 ,  111  of the lateral portions  10 ,  11 . 
     In the example illustrated in  FIG. 4   c , the central portion  9  comprises two ribs  91 , substantially perpendicular to the webs  101 ,  111  of the lateral portions  10 ,  11  and said ribs are each positioned at one of the free ends  92  of said central portion. 
     In the example illustrated in  FIG. 4   d , the central portion  9  comprises only two ribs  91 , substantially perpendicular to the webs  101 ,  111  of the lateral portions  10 ,  11 . The removal of the central portion  9  saves weight. 
     In a variant of this second embodiment, illustrated in  FIG. 4   e , the lateral portions  10 ,  11  also comprise, at the end of the webs  101 ,  111  opposite to the flange  102 ,  112 , a flanged edge  104 ,  114  in the direction of the webs of the two stiffener elements, so as to enhance the stability of the splice  30 . 
     In this example, the splice comprises the two lateral portions  10 ,  11  and a central portion  9  comprising a bearing surface  93  in line with the bearing surfaces  103 ,  113  of the flanges  102 ,  112  of said two lateral portions. 
     In a third embodiment, illustrated by  FIG. 5 , the two stiffener elements  2   a ,  2   b  are assembled by a splice  300  comprising two independent lateral portions  305 , each portion comprising a cross section that is substantially Z-shaped and positioned on either side of the ends of the stiffener elements. 
     Each lateral portion  305  comprises a head  301 , a web  302  and a flange  303 , said flanges comprising a bearing surface  304 . 
     The head  301  of each lateral portion  305  is positioned on the side of the webs  22   a ,  22   b , respectively  23   a ,  23   b , of the two elements  2   a ,  2   b.    
     The bearing surface  304  of a first lateral portion  305 , respectively the second lateral portion  305 , rests on the flanges  24   a ,  24   b , respectively  25   a ,  25   b , of the ends  27   a ,  27   b  of the two stiffener elements  2   a ,  2   b  and on the ferrule  4  or the skins  12   a ,  12   b . The bearing surfaces  304  are fastened respectively to the flanges  24   a ,  24   b  and  25   a ,  25   b  and the ferrule  4  or the skins  12   a ,  12   b  by means of fasteners  7 . 
     In a manner similar to the two other embodiments, the lateral portions  305  extend, on either side of the ends of the two stiffener elements, over the length of overlap D a , D b  that is sufficient to allow the working fasteners  7  to be installed and thus ensure the transmission of the tension-compression stresses from the flanges  24   a ,  24   b ,  25   a ,  25   b  of the elements  2   a ,  2   b  to the flanges  303  of the splice  300 . 
     Advantageously, the omega-shaped stiffener and the various splices described are made wholly of composite material. The use of composite materials makes it possible to dispense with the problems of heat and corrosion encountered on metal parts. 
     The examples of stiffener splicings, at a circumferential joint, are described in the context of a closed-section stiffener comprising an omega-shaped cross section without this choice being a limitation of the disclosed embodiments. The application of the disclosed embodiments can be adapted to all the stiffeners of the fuselage and to any stiffener closed section such as for example a trapezoidal or square cross section. 
     The disclosed embodiments therefore make it possible to obtain, at a circumferential joint of an aircraft fuselage, a splice between two elements of a stiffener comprising a closed cross section, in particular an omega-shaped composite stiffener, which avoids the necessity to install fasteners in the web and the head of said stiffener while ensuring the continuity of transmission of the longitudinal stresses.