Abstract:
An aircraft landing gear well roof including a first reinforced main structure and a second reinforced main structure spaced from each other in a transverse direction of the roof and equipped with respective mounting for articulating a structural element of the first landing gear and mounting for articulating a structural element of the second landing bear. A membrane connecting the first reinforced main structure and the second reinforced main structure is disposed between them in the transverse direction.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of and priority to French patent application No. 14 63428 filed on Dec. 30, 2014, the entire disclosure of which is incorporated by reference herein. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to aircraft, and more particularly, to the main landing gear well. It concerns more specifically the roof of this gear well, as well as the environment of that roof. 
         [0003]    The disclosure herein applies to all types of aircraft, in particular commercial aircraft. 
       BACKGROUND 
       [0004]    On existing aircraft, the main gear well roof is generally intended to provide the separation between a pressurized upper compartment, usually the cabin of the aircraft, and a lower compartment forming a gear well for accommodating two main landing gears spaced transversely from each other. 
         [0005]    This unpressurized gear well is delimited at the front by a wing box integrated into the fuselage, this box being intended for the connection of the two wings of the aircraft, on respective opposite sides thereof in the transverse direction. Moreover, the gear well roof is generally fixedly mounted on the upper skin of the wing box. Accordingly, in the event of a positive vertical maneuver of the aircraft, the tolerable deformations of the central wing box, in the transverse direction, tend to cause unintended stresses on and deformation of the gear well roof, in the same direction. To limit the negative consequences of these unintended deformations, designing a more flexible roof might be envisaged. However, this solution may prove unsuitable if the roof must absorb mechanical forces coming directly from structural elements of the landing gear, such as the strut. 
         [0006]    There is therefore a requirement to optimize the design of the environment of the roof of the main gear well, aiming in particular to solve this problematic of the compatibility of deformations between the gear well roof and the central wing box. 
       SUMMARY 
       [0007]    To address this requirement, the disclosure herein relates firstly to an aircraft landing gear well roof, the roof being intended to form a pressurization barrier between a pressurized upper compartment and a gear well for accommodating a first main landing gear and a second main landing gear, the roof comprising:
       a first reinforced main structure and a second reinforced main structure spaced from each other in a transverse direction of the roof and equipped with respective mounting for articulating a structural element of the first landing gear and mounting for articulating a structural element of the second landing bear; and   a membrane connecting the first reinforced main structure and the second reinforced main structure disposed between them in the transverse direction.       
 
         [0010]    The disclosure herein is noteworthy in that it breaks with earlier technical solutions in which the gear well roof was of relatively uniform design along its transverse direction. In fact, the disclosure herein artfully divides this roof into three distinct parts, namely the two reinforced main structures intended to form the rigid parts of the roof and an intermediate membrane, inherently more flexible, having a function similar to that of a mechanical decoupling between the two main structures. In this configuration, the intrinsic stiffness of the main structures makes it possible to absorb satisfactorily the mechanical forces introduced directly into these structures by the main landing gear. Moreover, because of the decoupling between these two main structures in the transverse direction, each of the structures is loaded only by a reduced transverse portion of the central wing box. This greatly reduces the appearance of unintended deformation of the reinforced main structures, notably in the event of a positive vertical maneuver of the aircraft. 
         [0011]    In other words, the design of the gear well roof in accordance with the disclosure herein satisfactorily addresses the problematic of compatibility of deformations between this gear well roof and the central wing box whilst being able to absorb appropriately the mechanical forces coming directly from the main landing gear. 
         [0012]    The disclosure herein has at least one of the following optional technical features, considered separately or in combination. 
         [0013]    The membrane has a rounded shape so as to define a recess in the upper surface of the roof. It may preferably have a U-shaped cross-section, perfectly optimized to absorb the pressurization forces at the same time as providing the mechanical decoupling between the two reinforced main structures in the transverse direction. 
         [0014]    The membrane has a curvature with a radius between  400  and  500  mm inclusive. 
         [0015]    The membrane has a first end and a second end fixed to the first reinforced main structure and the second reinforced main structure, respectively, a main part of the membrane being arranged between the first end and the second end. These three elements are preferably made in one piece. 
         [0016]    The first end and the second end each have a substantially vertical tangent. An angle is nevertheless possible between these tangents and the vertical direction, for example a maximum acute angle of 20°. 
         [0017]    The main part of the membrane has a substantially constant thickness, preferably of the order of 0.7 to 1.5 mm. 
         [0018]    The main part of the membrane is free of transverse stiffeners. On the other hand, longitudinal stiffeners are possible, attached to the membrane or made in one piece with the latter. 
         [0019]    The main part of the membrane has a ratio between a width in the transverse direction and a height in a vertical direction between 0.7 and 1.3 inclusive. 
         [0020]    The membrane is made of a metal or an elastomer-based material. 
         [0021]    The mounting for articulating a structural element of the first landing gear is substantially centered on the first reinforced main structure and the mounting for articulating a structural element of the second landing gear is substantially centered on the second reinforced main structure. 
         [0022]    The ratio between the transverse extent of the membrane and the transverse extent of the first and second reinforced main structures is between  0 . 1  and  0 . 2  inclusive. 
         [0023]    Each of the first and second reinforced main structures comprises a panel or a set of stiffened panels as well as at least one longitudinal beam and at least one transverse beam. 
         [0024]    In accordance with some aspects of the disclosure herein, an assembly for aircraft comprises:
       a central wing box intended for the connection of the two wings on respective opposite sides thereof in the transverse direction;   the gear well roof as described above, arranged at the rear of the central wing box and each of the first and second reinforced main structures of which is fixedly mounted on this box;   the first and second main landing gears, the structural elements of which are articulatedly mounted on the mounting equipping the first and second reinforced main structures of the roof; and   preferably, systems, such as ducts, routed longitudinally in a recess delimited by the membrane of the gear well roof.       
 
         [0029]    Each of the first and second main landing gears preferably comprises a leg articulated about an articulation axis inclined relative to the transverse direction and inclined relative to the longitudinal direction. 
         [0030]    Finally, in accordance with some aspects of the disclosure herein, an aircraft comprises such a gear well roof or such an assembly. 
         [0031]    Other advantages and features of the disclosure herein will become apparent in the following nonlimiting detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    This description will be given with reference to the appended drawings in which: 
           [0033]      FIG. 1  represents an exploded perspective view of an aircraft in accordance with the disclosure herein; 
           [0034]      FIG. 2  represents a perspective view to a larger scale of the fuselage section integrating the disclosure herein; 
           [0035]      FIG. 3  represents a side view of a part of an assembly in accordance with a preferred embodiment of the disclosure herein; 
           [0036]      FIGS. 4 and 5  show perspective views of this assembly seen from different angles; 
           [0037]      FIG. 6  is an exploded perspective view of the assembly shown in  FIGS. 4 and 5 ; 
           [0038]      FIG. 7A  represents a detailed perspective view to a larger scale of the gear well roof equipping the assembly shown in  FIGS. 4 to 6 ; 
           [0039]      FIG. 7B  represents a perspective view from below of the gear well roof shown in the preceding figure; 
           [0040]      FIG. 8  is a partial view of the gear well roof in cross-section taken along the section line VIII-VIII in  FIG. 7A ; 
           [0041]      FIG. 9  shows the gear well roof from above together with a graph showing diagrammatically the levels of deformation in the transverse direction in the event of a positive vertical maneuver of the aircraft; and 
           [0042]      FIG. 10  represents diagrammatically the deformation of the gear well roof in the event of dynamic landing. 
       
    
    
     DETAILED DESCRIPTION 
       [0043]    Referring to  FIG. 1 , there is represented an aircraft  100  of the commercial aircraft type in accordance with the disclosure herein. Throughout the following description, by convention, X corresponds to the longitudinal direction of the aircraft, Y to the direction oriented transversely relative thereto, and Z the vertical or height direction, these three directions X, Y and Z being mutually orthogonal. 
         [0044]    On the other hand, the terms “front” and “rear” are to be considered relative to a direction of forward movement of the aircraft caused by the thrust exerted by the turbojets, this direction being diagrammatically represented by the arrow  3 . 
         [0045]    The aircraft  100  includes a fuselage  102  to which two wings  104  are attached at the level of a fuselage section  102   a  specific to the disclosure herein. 
         [0046]    This fuselage section  102   a  is represented in a more detailed manner in  FIG. 2 . It comprises a fuselage exterior skin  106 , supported by substantially circular or elliptical fuselage frames  108 . Within the section  102   a  there is provided a floor  110  on top of which is a pressurized upper compartment, namely the passenger cabin  112  of the aircraft. Under the floor  110 , in front of this section  102   a , there is a first underfloor pressurized compartment  116   a  usually dedicated to technical equipment specific to the aircraft and/or freight. The underfloor compartment  116   a  is delimited at the rear by a wind centre box  2 , also arranged under the floor  100 . The central wing box  2  extends transversely the complete width of the fuselage section  102   a . It conventionally comprises an upper skin  4 , a lower skin  6 , a front skin  10 , a rear skin  8  and lateral closure panels as well as interior stiffener ribs. It is intended for the connection of the two wings  104  on respective opposite sides thereof in the direction Y. 
         [0047]    At the rear, the section  102   a  includes a gear well  12  for the accommodation of the two main landing gears (not represented in  FIG. 2 ), spaced from each other in the direction Y. The well  12 , of parallelepipedal overall shape, is delimited at the front by the rear skin  8  of the central wing box  2  integrated into the section  102   a . The fuselage is open at the bottom in order to enable raising and lowering of the landing gear, the opening being blocked by mobile doors reconstituting the fuselage in the retracted position of the gear. 
         [0048]    At the rear, the gear well  12  is delimited by an airtight end wall  16  separating this well from a second underfloor compartment  116   b  also dedicated to technical equipment and/or freight. 
         [0049]    At the top, the well  12  is delimited by a gear well roof  20  extending the complete transverse width of the fuselage section  102   a  into which it is integrated. The roof  20 , specific to the disclosure herein, is situated under the floor  110 . Moreover, it is noted that above this roof, which forms a pressurization barrier, there is provided an intermediate pressurized compartment delimited between the floor  110  and this same roof  20 . To simplify the figures, the passenger cabin and this intermediate pressurized compartment are associated with the same reference number  112 . 
         [0050]    It therefore constitutes a pressurization barrier between the pressurized passenger cabin  112  situated above this roof and the unpressurized gear well  12  accommodating the main landing gear. In this regard, in  FIG. 3 , the arrows represent the pressurization limit of the aircraft, this limit consisting of or comprising the following elements, from the front to the rear: the rear skin  10  of the central wing box  2 , its upper skin  4 , the gear well roof  20 , and the airtight end wall  16  of the gear well  12 . 
         [0051]    An assembly  40  specific to the disclosure herein will now be described with reference to  FIGS. 4 to 6 . This assembly  40 , intended to be integrated into the fuselage section  102   a , globally includes the central wing box  2 , the gear well  12  notably delimited by the roof  20  and the airtight end wall  16 , and the two main landing gears  42   a ,  42   b.    
         [0052]    One of the particular features of the disclosure herein resides in the design of the roof  20 , breaking with current technical solutions. In fact, it is divided in the direction Y into three distinct parts continuous with one another in order to fulfill the pressurization barrier function across the complete width of the fuselage. To be more precise, there are a first reinforced main structure  44   a  and a second reinforced main structure  44   b  symmetrically arranged with respect to a median plane XZ of the aircraft. The first structure  44   a  has an exterior longitudinal edge intended to be fixed directly to the fuselage, to the exterior skin and/or the frames of this fuselage. The same applies to fixing the exterior longitudinal edge of the second structure  44   b  to the fuselage on the opposite side. The interior longitudinal edges of these structures  44   a ,  44   b  are connected by a membrane  46  providing the function of mechanical decoupling between these two structures in the direction Y. 
         [0053]    In other words, the gear well roof  20  can be regarded as an assembly consisting of or comprising three parts that will be described in detail hereinafter, respectively a flexible central portion  46  connecting two more rigid lateral portions  44   a ,  44   b , the central portion notably having a lower resistance to stretching, in the direction Y, than the two lateral portions. The ratio between the two resistances can preferably be of the order of 1/1000. 
         [0054]    The assembly  40  further includes landing gear support structures. Also, a first support structure  48   a  is arranged to the rear of the gear well  12 , being fixed to the roof  20  and offset laterally outward relative thereto. It is moreover fixed to a fuselage frame  50  situated to the rear of the airtight end wall  16 , the lower end of this frame  50  being for its part fixed to a fuselage part  52  extending the complete length of the section. As can be seen better in  FIG. 6 , the part  52  reconstitutes the bottom of the fuselage under the central wing box  2  and is then extended toward the rear by a narrower portion  54  routed longitudinally via the opening of the gear well  12 . This portion  54  in the form of a beam divides the opening into two half-openings, each dedicated to the passage of one gear  42   a ,  42   b . It also enables reception of the gear well doors. 
         [0055]    The first support structure  48   a  supports the first landing gear  42   a . This has a standard design with a leg  56   a  bearing the wheels at one of its ends and being articulated at its opposite end to the first structure  48   a . The articulation axis  58   a  of the leg  56   a  is preferably inclined in the three directions X, Y and Z so that the leg can be inclined in the directions X and Y when the gear occupies its retracted position. In this regard, it is noted that  FIG. 5  represents the gear in the two positions, namely the lowered position and the raised position. In this latter position, the gears are arranged in a plane XY and their legs are inclined so as to form a V open toward the rear (only one of the two retracted gears being visible in  FIG. 5 ). 
         [0056]    Apart from the landing gear leg  56   a , the gear  42   a  includes other structural elements such as one or more lowering actuators, as well as a strut  60   a  generally made up of segments articulated to one another and the lower end of which is articulatedly mounted on the leg  56   a . For its part the opposite end of the strut  60   a  is articulatedly mounted on the lower face of the first reinforced structure  44   a  of the roof  20 , as will be described hereinafter. 
         [0057]    Moreover, it is noted that a symmetrical arrangement is provided for mounting the second main landing gear  42   b , associated with the second reinforced structure  44   b  of the roof  20 . In the figures, the elements of this arrangement bear the same reference numbers as the elements that have just been described for the arrangement associated with the first gear  42   a , the suffix “a” merely having been replaced by a suffix “b” after each reference number. 
         [0058]    Referring now to  FIGS. 7A, 7B and 8 , the gear well roof  20  will now be described in more detail. The first and second reinforced main structures  44   a ,  44   b  are symmetrical with respect to a median plane XZ. Also, only the first structure  44   a  will be described hereinafter. 
         [0059]    It includes a set of stiffened panels  60  arranged in substantially the same plane XY. These panels are stiffened by longitudinal stiffeners  62 , produced in one piece with the panels, for example, or attached thereto. 
         [0060]    The structure  44   a  also includes two longitudinal beams  64 , a first extending along the exterior edge of the set of panels and a second extending along the interior edge of that same set. 
         [0061]    The exterior longitudinal beam  64  has a length substantially equal to the total length of the roof  20  in the direction X. It is intended for the connection to the fuselage and is followed longitudinally at the front by a trunk corner  66  enabling the fixing to the rear skin of the central wing box  2 . For its part the interior longitudinal beam  64  has a substantially greater length, with a front portion projecting relative to the panels  60 , so as to be fixed to the upper skin  4  of the central wing box. 
         [0062]    A plurality of transverse beams  68  connects the two longitudinal beams  64 . There are three beams  68 , for example, each of which therefore extends the complete width of the main structure  44   a . Intermediate beams  70  interconnect the transverse beams  68 . There are two beams  70 , for example, joining at the same point  72  on the central transverse beam  68 , on respective opposite sides thereof in the direction X. 
         [0063]    The beams  70  and the beams  64 ,  68  are fixedly mounted on the upper surface of the panels  62 , in a plane XY. They may be inclined in each of the directions X and Y. 
         [0064]    On or in the vicinity of the vertical projection of the point  72  onto the lower surface of the panels  62 , mounting  74  is provided enabling the articulation of the end of the strut  60   a , as can be seen in  FIG. 7B . Also, mounting  74  is substantially centered on the main structure  44   a  and takes the form of a fitting with an orifice receiving a pivot pin of the strut  60   a , for example. 
         [0065]    The forces transmitted by the strut  60   a  in the event of dynamic landing are therefore introduced at the level of the central point  72 , and can then diffuse within the reinforced structure  44   a , being routed via the beams  70 , the beams  64 ,  68  and the stiffened panels  60 , before being introduced into the central wing box  2 . 
         [0066]    The components of each main structure  44   a ,  44   b  may be made of metal or composite materials. 
         [0067]    The two reinforced main structures  44   a ,  44   b  occupy a large portion of the width of the roof  20 . To be more precise, their respective transverse extents, referenced E 1   a  and E 1   b  in  FIG. 7A , are largely greater than the transverse extent E 2  of the membrane  46  in the direction Y. In this regard, the ratio between the cumulative extent of the structures  44   a ,  44   b  and the extent of the membrane  46  is preferably between 0.1 and 0.2 inclusive. 
         [0068]    A first function of the membrane  46  is to provide the continuity of the pressurization barrier between the two main structures  44   a ,  44   b  that have just been described. It may be made of metal but is preferably made of an elastomer-based material. 
         [0069]    As seen better in  FIG. 8 , it has a rounded shape, preferably of U-shaped cross-section, the radius of curvature R being between 400 and 500 mm inclusive. The membrane  64  also has the vertical median plane XZ as its plane of symmetry, the branches of the U-shape being on respective opposite sides of this plane. 
         [0070]    The interior of the U-shape defines a recess  76  open at the top in which are routed systems  78 , preferably pipes for the air conditioning system. The space defined by the recesses  78  is therefore cleverly exploited, enabling the longitudinal passage of systems  78  along the roof  20 . The U-shape projects generally downward in the gear well  12 , i.e. is set back downward relative to the stiffened panels  60 . This setting back is effected without hindering the wheels of the raised gear, the contour  80  of which has been partly represented in  FIG. 8  for the wheels of the raised first main landing gear. 
         [0071]    The membrane  46  has a first end  82   a  and a second end  82   b  fixed to the main structures  44   a ,  44   b , respectively, and to be more precise to the interior longitudinal beams  64  of those structures. They are fixed by rivets, bolts or similar fixing elements. Thanks to the U-shape, each of the ends  82   a ,  82   b  has a substantially vertical tangent such that the vertical air pressure resultant is advantageously zero at each of these ends. 
         [0072]    A main part  84  of the membrane  46  is arranged between the two ends  82   a ,  82   b  and forms the rounded part of the U-shape. These parts  82   a ,  82   b ,  84  are preferably made in one piece and substantially the same thickness, of the order of 0.7 to 1.5 mm. 
         [0073]    In order to provide better mechanical decoupling in the direction Y between the two main structures  44   a ,  44   b , the membrane  46  is preferably free of transverse stiffeners and, as indicated above, has a substantially constant thickness. This mechanical decoupling is advantageously facilitated by the U-shape of this membrane  46 , the main part  84  of which has a ratio between a width “I” in the direction Y and a height “H” in the direction Z between 0.7 and 1.3 inclusive. 
         [0074]    Thanks to this mechanical decoupling between the two main structures  44   a ,  44   b  in the direction Y, each of these structures is loaded only by a smaller transverse portion of the central wing box  2 . Also, in the case of a positive vertical maneuver of the aircraft leading to a large deformation of the central wing box  2  in the direction Y, the appearance of unintended deformation of the main structures  44   a ,  44   b  is limited. The stretching observed in the direction Y, with such a loading situation, has been represented on the  FIG. 9  graph. This graph shows that the considerable stretching observed on the upper skin of the central wing box  2  generates only a low level of unintended stretching on each of the two main structures  44   a ,  44   b.    
         [0075]    Moreover,  FIG. 10  shows the small deformations of the two main structures  44   a ,  44   b  in the case of dynamic landing, the intrinsic stiffness of these structures in fact making it possible to absorb appropriately the mechanical forces coming directly from the main landing gear. These forces are then transmitted to the central wing box  2 , in which they are easily absorbed and dissipated. 
         [0076]    Of course, diverse modifications may be made by the person skilled in the art to the disclosure herein that has just been described by way of nonlimiting example only. 
         [0077]    While at least one exemplary embodiment of the invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.