Abstract:
An aerodynamic fairing for a pylon of a turbojet engine, the fairing including: a frame oriented in a plane transverse to a longitudinal axis of the pylon, wherein the frame includes an upper edge, opposite side edges and a lower edge; a deck attached to the lower edge of the frame; a downstream portion of the deck includes a front edge region overlapping a rear edge portion of an upstream portion of the deck, wherein an upper surface of the front edge region is joined to the lower edge of the frame such that the front edge portion is sandwiched between the lower edge of the frame and the rear edge region of the upstream portion of the deck, and a flange extends between and attaches the upstream portion of the deck and the frame and a gap is between the lower edge of the frame and the upstream portion of the deck.

Description:
RELATED APPLICATION 
     This application claims priority to French patent application 1454379, filed May 16, 2014, the entirety of which is incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an aerodynamic fairing of the rear section of an aircraft pylon, likewise referred to as the aft pylon fairing or APF. 
     In a known manner, the aerodynamic fairing takes the shape of a box comprising two side panels assembled to each other by transverse stiffening frames spaced apart from one another along the longitudinal axis of the fairing, as well as a heat protection deck fixed on the one hand to the side panels and on the other to the frames. 
     An aft pylon fairing is exposed to high temperatures coming from the aircraft&#39;s powertrain assembly. In particular, the heat protection deck is subjected to a high-temperature primary flow from the turbojet (in the order of 600° C.), while the side panels are subjected to a secondary flow from the turbojet with a relatively low temperature (in the order of 150° C.) compared with that of the primary flow. These temperature differences generate high thermo-mechanical stresses on the box which tend to deform it. 
     French patent document FR1361556 discloses an aerodynamic fairing comprising a deck formed by consecutive portions disposed along the longitudinal axis of the fairing, each portion being directly fixed to a first frame and to a second frame directly consecutively to the first. The fact that there is a longitudinal mechanical cut-off between two consecutive deck portions means that each deck portion has its own heat expansion, something that helps to reduce the thermo-mechanical stresses acting on the box. Moreover, to prevent the high-temperature primary flow from rising and spreading in the interfaces between two consecutive deck portions, the heat protection deck is made leak-proof by thin strips fixed to the outer face of the deck portions in such a manner as to cover said interfaces and guide the primary air flow along the outer faces of the deck portions. These thin strips are effective but, on the other hand, they have to be installed on the deck portions by means of screws which complicates and slows down the fabrication of the aerodynamic fairings. 
     BRIEF SUMMARY OF THE INVENTION 
     An aerodynamic fairing for a turbojet pylon has been conceived and is disclosed herein. The faring has the shape of a box extending along a longitudinal axis and comprising at least two consecutive deck portions, an upstream portion and a downstream portion, respectively, along the longitudinal axis and each having a front end and a rear end, the fairing comprising at least one frame oriented transversely to the longitudinal axis and having a lower edge, the upstream portion having its rear end fixed to said frame and the downstream portion having its front end fixed to said frame, the upstream portion being fixed to the frame by means of a rear flange with a non-zero space situated between the lower edge of the frame and the upstream portion, the front end of the downstream portion being situated between the lower edge of the frame and the upstream portion. 
     The aerodynamic faring is advantageous in that the partial covering of a deck portion by a deck portion consecutive thereto makes it possible to prevent the primary flow with a very high temperature from rising and spreading between these two deck portions at their interface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The characteristics of the invention mentioned below, as well as others, will appear clearer on reading the following description of exemplary embodiments, said description relating to the attached drawings, in which: 
         FIG. 1  is a schematic view of an aircraft wing provided with an engine pylon and an aerodynamic fairing according to the invention; 
         FIG. 2  is a perspective schematic view of the aerodynamic fairing in  FIG. 1  according to a first embodiment of the invention; 
         FIG. 3  is a view of the fairing according to the arrow A in  FIG. 2 ; 
         FIG. 4  is a schematic perspective view of the aerodynamic fairing in  FIG. 1  according to a second embodiment of the invention; 
         FIG. 5  is a view of the fairing according to the arrow B in  FIG. 4 ; 
         FIG. 6  is a schematic perspective view of the aerodynamic fairing in  FIG. 1  according to a third embodiment of the invention; 
         FIG. 7  is a fairing view according to the arrow C in  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an engine assembly  1  fixed beneath a wing  2  of an aircraft. The engine assembly comprises a pylon  4 , as well as an engine  6  such as a turbojet attached to the wing  2  via the pylon  4 . The pylon  4  comprises in a known manner a rigid structure  8 , likewise referred to as the primary structure, allowing the turbojet  6  to be supported by known means. 
     The pylon  4  comprises secondary fairing-type structures. The secondary structures of the pylon  4  particularly include a front aerodynamic structure  24 , a rear aerodynamic structure  26  and a rear aerodynamic fairing  30  which will be referred to as the fairing in the description below. The terms “front/upstream” and “rear/downstream” should be understood in relation to a direction (along x coordinate axis in  FIG. 1 ) of movement of the aircraft developed as a result of the thrust applied by the turbojet  6 , this direction being shown schematically in all the figures by the arrow  7 . 
     As illustrated in  FIGS. 2, 4 and 6 , the fairing  30  takes the shape of a box open at the top. In other words, the fairing  30  is open to the other structures of the attaching device on which the box is intended to be mounted, namely the rear aerodynamic structure  26  and the rigid structure  8 . 
     A heat protection deck  31  forms the lower part of the box of the fairing  30 . The sides of the box of the fairing extend in a direction generally aligned with the longitudinal axis X are formed by two side panels  44 , of which one is shown in  FIGS. 2, 4 and 6 . The fairing  30  further comprises a framework formed by transverse frames allowing the side panels  44  and the deck  31  to be held together and the box to be fixed to the aforementioned structures. In the example shown in  FIGS. 2, 4 and 6 , the fairing  30  comprises five frames  32 - 1  to  31 - 5 . 
     The fairing  30  is not planar in a vertical plane XZ and substantially exhibits an arrow form (the point whereof is oriented towards the rear) in a horizontal plane XY. Moreover, the fairing  30  is closed by a frame  32 - 1  at its front end and by an inclined element in relation to the horizontal plane XY and fixed to a frame  32 - 5  at its rear end (the inclined element not being shown in the figures). On a transverse plane YZ to the box, the deck  31  has a curved form opening towards the outside (or concave) in relation to the fairing  30 . 
     The deck  31  is formed by a plurality of consecutive portions  31   a - d  according to the longitudinal direction X, each deck portion being fixed at its front end to a first frame and at its rear end to a second frame directly consecutive to the first frame. 
     At least two consecutive portions overlap/cover one another partially, in the manner of tiles, perpendicularly to a frame  32 - 3 ,  32 - 4 . In the examples illustrated in  FIGS. 2, 4 and 6 , the deck  31  comprises four deck portions  31   a  to  31   d  (from front to rear) with two deck portions  31   b ,  31   c  each partially covering the deck portion,  31   c ,  31   d , respectively, which is consecutive to them. 
     Each deck portion  31   a - d  is provided with an inner face  71  and an outer face  70  opposite the inner face  71 , the outer face  70  being intended to be shrouded in the primary flow  36 . In order to withstand the thermal stresses, a deck portion  31   a - d  is preferably realized in Inconel® or in a titanium alloy. 
     Each frame  32  occurs in the form of a structural panel extending in the transverse plane YZ to the box and having a front face, a rear face and four edges delimiting said faces. The front and rear faces, having substantially identical surfaces, are in the form of an isosceles trapezoid in the transverse plane YZ. The two lateral edges  32   b  of the frame  32  are each intended to receive a side panel  44 . The upper edge  32   a  of the frame  32 - 1  situated at the front end and of the frame  32 - 5  situated at the rear end of the fairing  30  are arranged to conform to another structure of the pylon  4  on which they are fixed, namely as in the example illustrated in  FIG. 1 , the rear aerodynamic structure  26  or the rigid structure  8 . The lower edge  32   c  of a frame has, in the transverse plane YZ, a curved shape opening towards the outside with respect to the fairing  30 . 
     An upstream deck portion  31   b ,  31   c  covering a downstream deck portion  31   c ,  31   d  at the level of a frame  32 - 3 ,  32 - 4  has its rear end fixed to said frame by means of a rear flange  50  which allows the deck portion  31   b ,  31   c  to be suspended from a frame  32 - 3 ,  32 - 4  with a non-zero space between the inner face  71  of said deck portion and the lower edge  32   c  of said frame. 
     In a first embodiment of the invention illustrated in relation to  FIGS. 2 and 3 , the second deck portion  31   b  and the third deck portion  31   c  are portions partially covering the third deck portion  31   c  and the fourth  31   d  deck portion, respectively. The second  31   b  portion and the third  31   c  portion have their rear end fixed indirectly to the third frame  32 - 3 , the fourth  32 - 4  frame, respectively, and have their front end fixed directly to the second frame  32 - 2  and the third frame  32 - 3 , respectively. 
     The second portion  31   b  and the third portion  31   c  are greater in length than the distance between the two frames  32 - 2 ,  32 - 3 ;  32 - 3 ,  32 - 4  to which they are fixed in such a manner as to cover the portions consecutive to them partially. A covering deck portion  31   b ,  31   c  preferably has a length greater by 2% to 7% than that of the distance between the frames  32 - 3 ,  32 - 3 ;  32 - 3 ,  32 - 4  to which it is fixed. 
     The other portions that are not covering have their rear and front sections fixed directly to the frames, in other words, in contact with their lower edges. Hence, as illustrated in  FIG. 2 , the first deck portion  31   a  has its front end fixed directly with the lower edge  32   c  of the first frame  32 - 1  and its rear end directly fixed with the lower edge  32   c  of the second frame  32 - 2 , whereas the fourth deck portion  31   d  has its front end directly fixed to the lower edge  32   c  of the fourth frame  32 - 4  and its rear end directly fixed to the lower edge  32   c  of the fifth frame  32 - 5 . 
     According to a longitudinal section of the fairing  30  illustrated in  FIG. 3 , a rear flange  50  allowing the rear end of a deck portion  31   b ,  31   c  to be fixed to a frame  32 - 3 ,  32 - 4  is a planar support  50   a  exhibiting a first extension  50   b  and a second extension  50   c  curved relative to the planar support  50   a . The first extension  50   b  is fixed by screwing to the front face of a frame  32 - 3 ,  32 - 4 , whereas the second extension  50   c  is fixed by screwing to the inner face  71  of a deck portion  31   b ,  31   c  to which it conforms at the level of the rear end of said portion  31   b ,  31   c . The planar support  50   a  is inclined relative to the horizontal plane XY such that the second extension  50   c  is situated according to the longitudinal axis X at a non-zero distance d from the front face of the frame  32 - 3 ,  32 - 4  on which the first extension  50   b  is fixed. 
     The length of the planar support  50   a  and its angle of inclination with respect to the horizontal plane XY are chosen such that a front edge  100  of the covered downstream portion  31   c ,  31   d  is housed between the lower edge  32   c  of the frame  32 - 3 ,  32 - 4  and the upstream covering deck portion  31   b ,  31   c.    
     The planar support  50   a  is preferably inclined in respect of the horizontal plane XY at an angle of between 15° and 70°. It will be noted that the upstream covering deck portion  31   b ,  31   c  may be in contact with or at a distance from the downstream portion  31   c ,  31   d  that it covers. 
     The invention is advantageous in that the partial covering of a deck portion  31   c ,  31   d  by a deck portion  31   b ,  31   c  makes it possible to prevent the primary flow  36  with a very high temperature from rising and spreading between these two deck portions at their interface. The heat protection deck  31  according to the invention is made leak-proof through its design. Thin sealing strips may not be required to leak-proof the deck. 
     In a second embodiment of the invention described with reference to  FIGS. 4 and 5 , a downstream deck portion  31   c ,  31   d  partially covered by an upstream deck portion  31   b ,  31   c  perpendicular to a frame  32 - 3 ,  32 - 4  has its front end indirectly fixed to said frame via a front flange  51 . The front flange  51  allows the deck portion  31   c ,  31   d  to be suspended from said frame with a non-zero space between the inner face  71  of said deck portion and the lower edge  32   c  of said frame. 
     According to a longitudinal section of the fairing  30  illustrated in  FIG. 5 , a front flange  51  has an L-shape, the base  51   a  whereof is fixed by screwing to the front section of a deck portion  31   c ,  31   d  and the long section of the L  51   b  is fixed by screwing to the rear face of a frame  32 - 3 ,  32 - 4 . The base of the L  51   a  conforms to the deck portion  31   c ,  31   d  on which it is fixed, whereas the long section of the L  51   b  itself is substantially planar. 
     The front flange  51  and the rear flange  50  fixed to a frame  32 - 3 ,  32 - 4  are preferably fixed to the latter by a plurality of screw-nut systems, each screw passing through a bore made in the front flange  51 , a bore made in the frame and a bore made in the rear flange  50 . 
     In addition to the advantages of the invention set out above, this second embodiment allows the transfer of thermo-mechanical stresses from deck portions  31   c, d  indirectly fixed to the frames  32 - 3 ,  32 - 4  towards said frames to be prevented. Hence, the framework of the box only undergoes very slight deformation by thermal expansion and the overall deformation level of the fairing  30  is therefore kept relatively low, which produces a satisfactory aerodynamic quality, contributing to the reduction in the effects of parasite drag and an improvement in the aircraft&#39;s performance/consumption ratio. 
     With reference to  FIGS. 6 and 7  and in a third embodiment of the invention, an upstream deck portion  31   b ,  31   c  covering a downstream deck portion  31   c ,  31   d  has a length substantially equal to the distance between the two frames  32 - 2 ,  32 - 3 ;  32 - 3 ,  32 - 4  to which it is fixed, whereas a covered downstream deck portion  31   c ,  31   d  is greater in length than the distance between the two frames  32 - 3 ,  32 - 4 ;  32 - 4 ,  32 - 5  to which it is fixed. The covered downstream portion  31   c ,  31   d  preferably has a length greater by 2% to 7% than the distance between the two frames  32 - 3 ,  32 - 4 ;  32 - 4 ,  32 - 5  to which it is fixed. 
     Moreover, the covered downstream deck portion  31   c ,  31   d  has at its front end a curved edge  100  twice 90° according to axes perpendicular to the longitudinal axis X and having opposite angles so as to form a housing for the free end of the adjacent covering upstream deck  31   c ,  31   d . In a sectional view according to the vertical plane XZ illustrated in  FIG. 7 , the downstream deck portion  31   c ,  31   d , except for its curved edge  100 , has an outer face  70  situated in the extension of the outer face  70  of the covering upstream deck portion  31   b ,  31   c . The curved edge  100  forms a section substantially parallel to the remainder of the covered downstream deck portion  31   c ,  31   d , but which is offset in height in respect thereof and is housed between the lower edge  32   c  of the frame  32 - 3 ,  32 - 4  and the covering upstream deck portion  31   b ,  31   c  in the space provided between the front and rear flanges  50 ,  51 . 
     The presence of the curved edge  100  optimizes the aerodynamic nature of the box, since the successive deck portions are situated in the extension of one another, thereby forming a smooth deck surface  31 . This means that the flow of the primary flow sweeping over the deck  31  is laminar. The presence of curved edges ensures tightness between two deck portions  31   b ,  31   c ;  31   c ,  31   d  which are covered and thereby make it possible to prevent the primary flow  36  with a very high temperature to rise and spread between said two deck portions. 
     In order to withstand the thermal stresses, the front and rear flanges  50 ,  51  are preferably realized in Inconel® or an equivalent titanium alloy. 
     An aerodynamic fairing ( 30 ) of a turbojet pylon has been conceived and is disclosed herein. The fairing has the shape of a box extending along a longitudinal axis (X) and comprising at least two consecutive deck portions, an upstream portion ( 31   b ) and a downstream portion ( 31   c ), respectively, along said longitudinal axis (X) and each having a front end and a rear end, the fairing ( 30 ) comprising at least one frame ( 32 - 3 ) oriented transversely to the longitudinal axis (X) and having a lower edge ( 32   c ), said upstream portion ( 31   b ) having its rear end fixed to said frame and the downstream portion ( 31   c ) having its front end fixed to said frame, said upstream portion being fixed to the frame ( 32 - 3 ) by means of a rear flange ( 50 ) with a non-zero space situated between the lower edge of the frame and the upstream portion, said front end of the downstream portion ( 31   c ) being situated between the lower edge of the frame ( 32   c ) and the upstream portion. 
     While at least one exemplary embodiment of the present 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.