Abstract:
An integrated pylon structure for a propulsion system is suitable for one end to be connected to an aircraft wing and the other end to be connected to an aircraft engine. The pylon structure includes a pylon box section ( 110 ) formed from an upper and a lower bean, a frame ( 100 ) and a side wall panel. The pylon structure has a thrust reverser hood connection structure, provided on the side wall and connected with a nacelle thrust reverser hood having a front fixed hood ( 301 ) and a rear movable hood ( 302 ). A guide rail allows the rear movable hood to slide and open relative to the pylon box section. The engine thrust reverser hood is directly connected to the side wall of the pylon box section and a guide rail on the side wall guides the opening of the thrust reverser hood.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to the technical field of structural design, general design, aerodynamic design and strength design of civil aircrafts, and more specifically to a structural connection form of a pylon with an airfoil and an engine. 
     BACKGROUND OF THE INVENTION 
     A pylon is a connection interface of an aero-engine and an airfoil and mainly functions to mount the engine, transfer engine load, provide a pathway for systems such as a wiring system, environment control system, electrical system and hydraulic system between the engine and the airfoil, and ensure a smooth aerodynamic shape. The design of the pylon structure should take into account various factors such as noise, weight, fuel consumption rate, aerodynamics, system deployment, and engine installation and maintenance. 
     As shown in  FIG. 1 , a pylon  10 ′ in a conventional configuration is usually designed as a rigid box-shaped structure consisting of an upper beam, a lower beam, a frame having a plurality of vertical stations, and a sidewall which are connected to one another, and assembled with the engine via a front installation joint  20 ′ and a rear installation joint  30 ′. The total load of the engine is transferred via the front installation joint and the rear installation joint, and torque is usually transmitted by virtue of the rear installation joint  30 ′. 
     The pylon in the conventional configuration transmits torque via the rear installation joint  30 ′. To have an enough long arm of force to transmit torque, the rear installation joint  30 ′ must have a larger width, which causes the shape of a rear edge of the pylon wider, affecting aerodynamic performance of the aircraft. Besides, the front installation joint  20 ′ is an individual component independent from the pylon but connected to the pylon, and the whole engine installation structure is heavy. 
     The conventional pylon is hingedly connected to a nacelle. As shown in  FIG. 2 , a pylon sidewall  11 ′ is provided with thrust reverser cowl hinges  12 ′ and fan cowl hinges  13 ′, wherein the thrust reverser cowl hinges  12 ′ are connected with a thrust reverser cowl body (not shown) via a guide rail beam (not shown), and the guide rail beam is provided with a guide rail for guiding the thrust reverser cowl body. 
     A conventional aircraft engine duct auxiliary structure for rectifying external ducted airflow is located between a nacelle external duct and a nacelle core cowl body and is connected together with the nacelle core cowl body, and is opened along with the core cowl body upon servicing. It can be seen that the conventional engine duct auxiliary structure is a design integral with the nacelle and turns out to be a component of the nacelle. 
     SUMMARY OF THE INVENTION 
     A first object of the present invention is to provide a novel connection form of connecting a pylon to an airfoil and an engine, which can meet structural needs of small space and achieve weight reduction when an LEAP-X model engine is used. 
     A second object of the present invention is to provide a novel connection form of connecting a pylon to an airfoil and an engine, which omits rearward torque transmission and performs forward torque transmission, thereby reducing an engine duct space occupied by the pylon, reasonably solving issue about load transmission of the engine, and thereby achieving reduction of fuel consumption rate, reduction of aerodynamic loss and noise reduction. 
     A third object of the present invention is to provide a novel connection form of connecting a pylon to an airfoil and an engine, which solves issue about movement of a rear cowl of a core cowl of an engine nacelle. 
     According to one aspect of the present invention, there is provided a pylon structure of an integrated propulsion system, which is adapted to be connected to an aircraft airfoil at one end and connected to an aero-engine at the other end, the pylon structure comprising a pylon box segment consisting of an upper beam, a lower beam, a frame and a sidewall panel, wherein the pylon structure further comprises:
         a thrust reverser cowl connection structure disposed on a left wall and a right wall and connected to a nacelle thrust reverser cowl comprising a front fixed cowl and a rear moveable cowl, the thrust reverser cowl connection structure comprising at least one guide rail for guiding the rear moveable cowl to enable the rear moveable cowl to slideably open relative to the pylon box segment.       

     In this aspect of the present invention, the engine thrust reverser cowl is directly connected to a sidewall of the pylon box segment, and the thrust reverser cowl is guided to open via the guide rail on the sidewall, thus a guide rail beam is canceled to thereby not only save space and meet the installation requirement of the LEAP-X model engine, but also reduce the weight of the whole propulsion system. 
     Preferably, the thrust reverser cowl connection structure comprises an upper guide rail and a lower guide rail for guiding the rear movable cowl, and an intermediate guide rail for guiding a nacelle grid. 
     Further preferably, the rear movable cowl is provided with a structure slideably engaged with the upper guide rail and the lower guide rail. 
     In an embodiment, the pylon structure further comprises a front installation joint which is disposed on a front wall of the front end frame of the frame and connected to a fan casing of the aero-engine. 
     Integrated design of the front installation joint and the pylon may not only save space but also facilitate reduction of the weight of the whole propulsion system. 
     Preferably, the front installation joint comprises:
         a first lug and a second lug respectively protruding outward from two opposite sides of the front end frame;   a first link and a second link respectively connected to the first lug and the second lug at one end, and respectively adapted to be connected to the aero-engine at the other end;   wherein the first link and the first lug are pivotally connected at a first connection point, and the second link and the second lug are connected respectively at a second connection point and a third connection point.       

     In this aspect of the present invention, the integrated design of the front installation joint and the frame of the pylon can transmit vertical and lateral load as well as torque, overcomes the drawback of the current front installation joint about failure to transmit torque, releases the torque-transmitting function of the rear installation joint so as to reduce the width of the rear installation joint so that the rear installation joint occupies less engine duct space, which facilitates reduction of fuel consumption rate, facilitates retraction of a rear edge of the pylon and achieves reduction of aerodynamic loss. Meanwhile, the integrated design of the front installation joint and the frame of the pylon may effectively reduce the weight of the structure and lower a height of an undercarriage. 
     Preferably, connecting bolts running through the first link and the second link respectively at the first connection point, the second connection point and the third connection point are transition-fitted with bushings disposed at these connection points and formed in mounting holes of the first lug and the second lug. 
     Further preferably, the first link is further connected to the first lug at a fourth connection point, and the fourth connection point and the second connection point are arranged opposite to each other and respectively located inside, the first connection point and the third connection point, wherein a connecting bolt running through the first link at the fourth connection point is clearance-fitted with the bushing disposed in the mounting hole of the first lug at the fourth connection point. 
     The fourth connection point is arranged such that when the front installation joint is connected to the engine via the first link and the second link, the first link is a standby design for possible damages and security purpose. 
     Again further preferably, the connecting bolt at the fourth connection point is clearance-fitted with the bushing with a first clearance, and the first clearance is set in a way that when any one of the first connection point, the second connection point and the third connection point fails, the connecting bolt at the fourth connection point partially contacts with the bushing. 
     When any one of the first connection point, the second connection point and the third connection point fails, for example, when the second connection point fails, due to the load of the engine, a front end frame of the pylon slightly rotates about the third connection point, and the first clearance at the fourth connection point partially disappears, i.e., the fourth connection point participates in receiving a force. 
     Preferably, the front installation joint of the present invention further comprises a third lug protruding outward from a front wall of the front end frame and a third link having one end connected to the third lug at a fifth connection point and the other end adapted to be connected to the engine, and a connecting bolt running through the third link at the fifth connection point is clearance-fitted with a busing disposed in a mounting hole of the third lug at the fifth connection point. 
     The fifth connection point is arranged such that when the front installation joint is connected to the engine via the first, second and third links, the third link is a standby design for possible damages and security purpose. 
     Further preferably the connecting bolt at the fifth connection point is clearance-fitted with the bushing with a second clearance, and the second clearance is greater than the first clearance and set in a way that when the first link or the second link completely fails, the connecting bolt at the fifth connection point partially contacts with the bushing. 
     When the whole first link or the whole second link completely fails, the second clearance at the fifth connection point partially disappears due to the load of the engine, and the third link participates in receiving a force. 
     In another embodiment of the present invention, there is included an engine duct auxiliary structure with one end connected to the pylon box segment and the other end adapted to be connected to a nacelle core cowl comprising a core front cowl and a core rear cowl, the engine duct auxiliary structure comprising a front frame hinged with the core front cowl and a rear frame connected with the core rear cowl, the rear frame comprising at least one guide rail for guiding the core rear cowl to enable the core rear cowl to slideably open relative to the pylon box segment. 
     The integrated design of the engine duct auxiliary structure and pylon box segment may, on the one hand, meet the need of engine-nacelle-pylon box segment integrated design, and on the other hand, provide a narrower structural shape of the engine duct auxiliary structure to substantially increase the area of an engine external duct flow passageway, reduce the engine fuel consumption rate, improve aircraft economics and present a higher market competitiveness. 
     Preferably, the front frame comprises a front beam, a rear beam, an intermediate cross beam and an intermediate slant beam, wherein one end of the front beam is connected to the pylon box segment, and the other end is connected to the core front cowl; wherein the rear beam is located downstream of the front beam, and one end thereof is connected to the pylon box segment and the other end thereof is connected to the core front cowl; wherein both ends of the intermediate cross beam are respectively connected to the front beam and the rear beam; wherein one end of the intermediate slant beam is connected to the intermediate cross beam, and the other end is inclined towards the rear beam and connected to the pylon box segment; wherein the rear frame extends rearward from the rear beam and its upper end is connected to the pylon box segment. 
     Further preferably, the rear beam of the front frame is connected to the pylon box segment via a pivoting seat, and the other end of the intermediate slant beam is also connected to the pivoting seat. 
     Further preferably, the intermediate cross beam is pivoted with a plurality of hinges, and the other end of the plurality of hinges is connected to the core front cowl so that the core front cowl rotatably opens relative to the pylon box segment. 
     Advantageous effects of the present invention are as follow: the engine thrust reverser cowl is directly connected to the sidewall of the pylon box segment, and the thrust reverser cowl is guided to open via the guide rail on the sidewall, thus a guide rail beam is canceled to thereby not only save space and meet the installation requirement of the LEAP-X model engine, but also reduce the weight of the whole propulsion system. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Other features and advantages of the present invention can be made more apparent by the following preferred embodiments described in detail with reference to figures, wherein identical reference numbers denote identical or like parts, wherein 
         FIG. 1  is a schematic view of an aircraft pylon in a conventional configuration; 
         FIG. 2  is a schematic view of a conventional nacelle connector; 
         FIG. 3  illustrates an overall schematic view of a pylon structure of an integrated propulsion system according to a preferred embodiment of the present invention; 
         FIG. 4 a    illustrates an in-use state of an LEAP-X model engine mounted to a pylon structure of an integrated propulsion system according to a preferred embodiment of the present invention, wherein a thrust reverser structure of the LEAP-X model engine is in a normal deployed position; 
         FIG. 4 b    is a view similar to  FIG. 4 a   , but the thrust reverser structure of the LEAP-X model engine is in a maintenance deployment position, and a grid is removed to clearly show the nacelle; 
         FIG. 5  illustrates an in-use state in which a front installation joint of  FIG. 3  is connected to a fan casing of the engine; 
         FIG. 6 a    illustrates a schematic view of the front installation joint of the pylon structure of the integrated propulsion system according to a preferred embodiment of the present invention, wherein a fastener for fixing a boomerang link; 
         FIG. 6 b    is a view similar to  FIG. 6 a   , wherein the installation joint is assembled with a fastener; 
         FIG. 7  is a schematic view showing reception of force of the front installation joint of  FIG. 6 a    in a normal state; 
         FIG. 8  is a schematic view showing reception of force of the front installation joint of  FIG. 6 a    in a state that a second connection point fails; 
         FIG. 9  is a schematic view showing reception of force of the front installation joint of  FIG. 6 a   , in a state that a second boomerang link fails; 
         FIG. 10  illustrates space of the engine duct occupied by a pylon box segment of the pylon structure of the integrated propulsion system according to a preferred embodiment of the present invention; 
         FIG. 11  illustrates a mounting position of a fan air valve in the pylon structure of the integrated propulsion system according to a preferred embodiment of the present invention; 
         FIG. 12 a    illustrates a schematic view in which the pylon structure of the integrated propulsion system according to a preferred embodiment of the present invention is connected with the LEAP-X engine nacelle, wherein a nacelle core cowl is in a normal use state, and a thrust reverser cowl connection structure is removed from a pylon side panel for the sake of clarity; 
         FIG. 12 b    is similar to  FIG. 12 a   , but the nacelle core cowl is in a maintenance use position; and 
         FIG. 13  illustrates main structures of the engine duct auxiliary structure of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Embodiments are described in detail below with reference to figures which constitute part of the description. The figures exemplarily exhibit specific embodiments, and the present invention is implemented in these embodiments. The shown embodiments are not intended to exhaust all embodiments according to the present invention. It may be appreciated that other embodiments may be used, and structural or logical changes can be made without departing from the scope of the present invention. Regarding figures, terms indicative of directions such as “outward” and “downward” are used with reference to orientations of the described figures. If the orientations of the figures change, these terms also change accordingly. Since assemblies of the embodiments of the present invention can be implemented in many orientations, these direction terms are used for illustration purpose not for limitation purpose. Hence, the following specific embodiments are not intended to limit the present invention, and the scope of the present invention is defined by the appended claims. 
     The internationally advanced LEAP-X engine employs a novel O-DUCT thrust reverser structure, and a thrust reverser body composite material structure cowl body employs integral forming technology. Main advantages are simple maintenance, light weight and easy reduction of noise levels. The fuel consumption of the LEAP-X engine decreases by 116% as compared with that of CFM56 engine of current B737 and A320, and the noise of the LEAP-X engine decreases by over 10 decibels as compared with the internationally most rigorous fourth-level requirement. It is estimated that the propeller integration technology (namely IPS technology) of the present invention achieves 1.5% fuel consumption reduction and 2-decibel noise reduction. 
     Structurally, the engine is connected to the pylon box segment structure via front and rear installation joints, and an engine core cowl IFS structure is connected to the pylon box segment via a BIFI structure. Additionally, an O-shaped thrust reverser is connected with a sidewall guide rail structure of the pylon box segment, and the whole engine, nacelle and pylon structure wholly bears a force and performs a function of the propulsion system. Therefore, this technology is called propeller integration technology (namely, IPS technology). 
     Since the integration technology is a brand-nevi technology, and meanwhile the engine, the thrust reverser structure and pylon structure all are distinct from the conventional form, and the IPS pylon needs to be substantially improved to achieve the design targets such as weight reduction, noise reduction, SFC reduction and aerodynamic loss reduction. 
     The following problems need to be solved from perspective of pylon structure:
         (1) Reducing the space of engine duct occupied by the pylon;   (2) Reasonably solving transfer issue of the engine load;   (3) Solving problems related to engine nacelle;   (4) Solving the problem about arrangement of systems in the pylon.       

       FIG. 3  illustrates an overall schematic view of a pylon structure of an integrated propulsion system according to a preferred embodiment of the present invention. The pylon structure is adapted to be connected to an aircraft airfoil at one end and connected to an aero-engine at the other end, and the pylon structure comprises a pylon box segment  110  consisting of an upper beam, a lower beam, a frame  100  and a sidewall panel  102 ; wherein the pylon structure further comprises a thrust reverser cowl connection structure, a front installation joint  130  and an engine duct auxiliary structure  150 . 
     Again as shown in  FIG. 3 , the thrust reverser connection structure is disposed on the sidewall panel  102  of the pylon box segment  110  and connected with a nacelle thrust reverser cowl comprising a front fixed cowl  301 , and a rear movable cowl  302 . The thrust reverser connection structure comprises three guide rails: an upper guide rail  121 , an intermediate guide rail  122  and a lower guide rail  123 . The upper guide rail  121  and the lower guide rail  123  are used to guide the rear moveable cowl  302  to allow the rear movable cowl to open relative to the pylon box segment; and the intermediate guide rail  122  is used to guide a nacelle grid  303 . The rear movable cowl  302  is provided with a structure such as a slider that is slideably engaged with the upper guide rail  121  and the lower guide rail  123 . Certainly, if the upper guide rail  121  and lower guide rail  123  are configured as a slider, it is also feasible to provide corresponding guide rails on the rear moveable cowl  302 . 
     In the present embodiment, hinges are omitted from the IPS pylon so that the guide rails are directly connected with the pylon. This facilitates reduction of nacelle weight, meanwhile increases nacelle sound absorption area and facilities noise reduction. 
     Regarding the structural form of the pylon sidewall, panel and guide rails, as compared with the conventional aircraft structure design, the connection form for connecting the pylon with the thrust reverser is changed from a hinge-hinge beam structure to a guide rail-slider structure. This new connection form is advantageous mainly in reducing the weight of the connection structure, increasing an area of sound-absorbing cells of the nacelle and facilitating noise reduction. 
     The guide rail and the sidewall panel  102  of the pylon are manufactured separately, and the connection manner still employs fastener connection. The fastener connection is described as follows: a fastener is directly mounted on the sidewall panel in two forms: one is that the sidewall panel and the guide rail share the fastener, and the other is that the sidewall panel does not share the fastener with the guide rail. First, positions of the sidewall panel not sharing the fastener are mounted first. These positions generally conflict with the positions of the guide rail, so countersunk screws need to be used upon installation. Then the guide rail is mounted on the sidewall panel. At this time, the fastener shared by the sidewall panel and the guide rail is mounted. This form is advantageous in simplifying part processing, not affecting the arrangement of the fastener due to the position of the guide rail, facilitating the mounting of the fastener on the sidewall panel and ensuring the force transmission of the pylon box segment. 
       FIG. 4 a    illustrates an in-use state of an LEAP-X model engine mounted to a pylon structure of the integrated propulsion system according to a preferred embodiment of the present invention, wherein a thrust reverser structure of the LEAP-X model engine is in a normal deployed position; and  FIG. 4 b    is a view similar to  FIG. 4 a   , but the thrust reverser structure of the LEAP-X model engine is in a maintenance deployment position, and a nacelle grid  303  is removed to clearly show the nacelle. Upon maintenance, the rear movable cowl  302  moves backwards away from the front fixed cowl  301  along the upper guide rail  121  and the lower guide rail  123 . It should be appreciated that although there are two guide rails here to guide the rear movable cowl  302 , it is feasible to set only one guide rail or a plurality of guide rails according to needs. 
     A main function of the installation joints of the present invention is to connect the engine and transfer the load of the engine to the pylon structure. A conventional engine installation manner is that the engine is connected with the pylon via the front and rear installation joints, and the torque of the engine is transferred to the aircraft pylon via the rear installation joint, while the present invention, by using integrated design of the front installation joint and the pylon frame, can transfer vertical and lateral load, as well as transfer the torque. The present invention may be used to equip the engine on any type of aircraft. 
     In the present embodiment, as shown in  FIG. 5 , the front installation joint  130  is disposed on a front wall of the front end frame  100  and connected to a first connector  201 , a second connector  203  and a third connector  205  on a fan casing  200  of the aero-engine. 
     Introduction is presented for a specific design of the front installation joint  130  in the present embodiment. As shown in  FIG. 6 a   , the front installation joint  130  is adapted to be integrally formed with the front end frame  100  of the aircraft pylon and comprises a first lug  10 , a second lug  20 , a third lug  30 , a first link  70 , a second link  80 , and a third link  90 . The first lug  10  and the second lug  20  respectively protrude outward from both sides of the front end frame  100 ; and the first link  70 , the second link  80  and the third link  90  are respectively connected to the first lug  10 , the second lug  20  and the third lug  30  at one end, and respectively adapted to be connected to the aero-engine at the other end. In the present embodiment, the first link and the second link are preferably boomerang links and the third link is preferably a straight link, but these links may be links in any other shapes. 
     As shown in  FIG. 6 b   , the first link  70  and the first lug  10  are connected respectively at a first connection point  1  and a fourth connection point  4 , the second link  80  and the second lug  20  are connected respectively at a second connection point  2  and a third connection point  3 , and the third link  90  and the third lug  30  are connected at a fifth connection point  5 . In the present embodiment, the first lug, the second lug and the third lug are preferably a double-lug with a mounting hole which is provided on each lug of the double-lug at the respective connection points. A bushing  50  is mounted in each mounting hole, and a bolt hole is formed on each link at each connection point. One connecting bolt  40  is mounted on a corresponding link respectively at the first through fifth connection points  1 ,  2 ,  3 ,  4 ,  5  and runs through the bushing  50  in the mounting hole on the corresponding lugs through these connection points. 
     Again as shown in  FIG. 5 , the front installation joint of the present embodiment is connected to the first connector  201 , the second connector  203  and the third connector  205  on the engine fan casing  200  via the two boomerang links and one straight link, and the whole front installation joint and the engine have totally three connection point. The fourth connection point  4  on the first link  70  and the third link  90  are standby designs for possible damages and security purpose. That is to say, in normal working conditions, as shown in  FIG. 7  and with reference to  FIG. 6 a   , the three connection points, the first connection point  1 , the second connection point  2  and the third connection point  3 , jointly bear a vertical load (Z direction) and a course torque (X direction) transferred from the engine, and the first connection point  1  and the third connection point  3  bears a lateral load (Y direction). When any one of the first connection point  1 , the second connection point  2  and the third connection point  3  fails, the fourth connection point  4  participates in bearing the vertical load (Z direction) and lateral load (V direction). For example, when the second connection point  2  fails, the first connection point  1 , the fourth connection point  4  and the third connection point  3  jointly bear the vertical load (Z direction), lateral load (Y direction) and course torque (X direction) transferred from the engine. When the whole first link  70  or the Whole second link  80  fails, i.e., both of its connection points fail, for example, when the second link  80  completely fails, the third link  90  will participate in receiving a force, and the first connection point  1 , the fourth connection point  4  and the fifth connection point  5  jointly bear the vertical load (Z direction), the lateral load (V direction) and engine torque transferred from the engine. 
     Again as shown in  FIG. 7 , in the connection points where the first link  70  and the second link  80  are respectively connected to the first lug  10  and the third lug  30 , the connecting bolt is transition-fitted with the bushing at the first connection point  1 , the second connection point  2  and the third connection point  3  so that under normal working conditions, the three connection points bear all loads and torques. 
     To allow the first link  70  and the third link  90  to be standby designs for possible damages and security purpose, and the first link  70  to be a preferable standby design for possible damages and security purpose, i.e., preferably act before the third link  90  acts, the connecting bolt  40  is clearance-fitted with the bushing at the fourth connection point  4 , and the connecting bolt  40  is also clearance-fitted with the bushing at the fifth connection point  5 , but the clearance at the fifth connection point  5  is slightly greater than the clearance at the fourth connection point  4 . Therefore, as shown in  FIG. 8 , when any one of the connection points  1 ,  2  and  3  fails, for example, when the second connection point  2  fails, due to the load of the engine, the front end frame  100  of the pylon slightly rotates with connecting bolt  40  at the third connection point  3  as a rotation shaft so that the connecting bolt  40  at the fourth connection point  4  partially contacts with the bushing, i.e., the clearance between the connecting bolt  20  and the bushing partially disappears at the fourth connection point  4 , and the fourth connection point  4  begins to participate in receiving the force, and the connection points  1 ,  4  and  3  bear the vertical load, lateral load and the course torque. When the whole first link  70  or the whole second link  80  completely fails, for example, when the second link  80  completely fails, as shown in  FIG. 8 , due to the load of the engine, the third link  90  is pulled downward so that the connecting bolt  20  at the fifth connection point  5  partially contacts with the bushing, i.e., this partial clearance disappear, such that the third link  90  participates in receiving the force, and the connection points  1 ,  4  and  5  bear the vertical load, lateral load and the course torque. 
     In the embodiment as shown in  FIG. 5  through  FIG. 9 , the first connection point  1 , the fourth connection point  4 , the second connection point  2  and the third connection point  3  are preferably arranged in a straight line so that reverse vectors in the straight line direction offset each other. Furthermore, preferably the fourth connection point  4  and the second connection point  2  are arranged opposite to each other and respectively located inside the first connection point  1  and the third connection point  3 . Besides, although in the present embodiment, the fifth connection point  5  is vertically (namely Z direction) located above other connection points  1 ,  2 ,  3  and  4  and located at an intermediate position of other connection points in a lateral direction (namely, Z direction). It should be appreciated that the fifth connection point  5  may be vertically located below other positions such as connection points  1 ,  2 ,  3  and  4  so long as the third link  9  does not receive the force after the front installation joint is connected to the engine. 
     As compared with the prior art, the front installation joint in the above embodiment has the following advantages:
         1) the front installation joint of the engine is integral with the pylon frame, omitting a mounting bracket, namely, omitting a docking form, so that the installation joint is directly connected to the engine fan casing via a link, thereby reducing the weight of a mounting portion of the engine;   2) the installation joint not only bears the load in the vertical direction and horizontal direction, but also bears the engine torque, thereby releasing a torque-bearing function of the rear installation joint;   3) since the front installation joint  130  bears the torque, the width of the shape of the rear installation joint is reduced, and an engine external duct space  304  occupied by the pylon is reduced as shown in  FIG. 10 , which facilitates reduction of fuel consumption rate, facilitates retraction of a rear edge  140  of the pylon and achieves reduction of aerodynamic loss; and   4) the design of the first link and the third link enables the whole front installation joint to have a function of standby design for possible damages and security purpose.       

     As shown in  FIG. 11 , since a duct separation surface is apparently narrower than a conventional pylon, a fan air valve (namely, FAV)  401  is arranged in the engine duct auxiliary structure (namely, BIFI)  150  not in the pylon box segment  110 . Meanwhile, since the BIFI is an auxiliary structure, a skin may be made as a detachable skin. As such, it is feasible to take out the FAV without removing the pre-cooler  402 , thereby improving FAV maintenance performance and reducing the maintenance cost. 
     As shown in  FIG. 12 a    and  FIG. 12 b   , a nacelle core cowl of a nacelle  500  of the LEAP-X engine comprises a core front cowl  501  and a core rear cowl  502 , wherein the core rear cowl  502  needs to be opened by sliding rearward. To meet the need of the core rear cowl  502 , in the present embodiment, BIFI structure no longer serves as part of the nacelle thrust reverser structure as in the conventional BIFI structure, it is integrally arranged with the pylon box segment  110 , i.e. it is suspended below the pylon box segment  110  and provides a guide rail  151  to guide the core rear cowl to slideably open thereon. The BIFI is located between an inner surface of the rear moveable cowl  302  of the nacelle thrust reverser structure and the core rear cowl  502  of the nacelle core cowl, and its surface serves as an airflow separation surface of the engine external duct, so it needs to be designed narrower. 
     As shown in  FIG. 13  and with reference to  FIG. 12 a   , there is an engine duct auxiliary structure  150  for connecting the nacelle  500  with the pylon box segment  110 , comprising: a front frame  152  comprising a front beam  153  (usually called front end wall), a rear beam  154 , an intermediate cross beam  155  and an intermediate slant beam  156 ; wherein one end of the front beam  153  is connected to the pylon box segment  110 , and the other end is connected to a core front cowl  501  of the nacelle  500 . The rear beam  154  is arranged in the rear of the front beam  153 , and one end thereof is connected to the pylon box segment  110  and the other end thereof is connected to the core front cowl  501  of the nacelle  500 . Both ends of the intermediate cross beam  155  are respectively connected to the front beam  153  and the rear beam  154 . One end of two intermediate slant beams  156  is connected to the intermediate cross beam  155 , and the other end is inclined towards the rear beam  154  and connected to the pylon box segment  110 . A rear frame  157  extends rearward from the rear beam  154  and its upper end is connected to the pylon box segment  110 , and the rear frame  157  is provided with at least one guide rail  151  for guiding the core rear cowl  502  of the nacelle  500 . Those skilled in the art may understand that the number of the guide rail  151  is preferably two. 
     Specifically, the rear beam  154  of the front frame  152  is connected to the pylon box segment  110  via a pivoting seat  158 , and the other end of the intermediate slant beam  156  is also connected to the pivoting seat  158 . 
     The intermediate cross beam  155  is pivoted to the core front cowl  501  of the nacelle  500  via a plurality of hinges (which are not shown, and may be provided at a connection position  159  as shown). 
     Both sides of the front beam  153  of the engine duct auxiliary structure  150  are connected to the pylon box segment  110  to transfer the course load and the vertical load, and a connecting portion (e.g., a single lug) extending out of the pylon box segment  110  keeps a gap on both sides upon being connected thereto so that it does not transfer lateral load; and an intermediate shear pin leaves a gap in the front and in the rear to allow it to only transfer the lateral load. 
     The core front cowl  501  of the nacelle  500  may be connected to the engine duct auxiliary structure  150  via a hinge, which ensures rotatable opening of the core front cowl  501 . The guide rail  151  is used to connect a connection interface of the core rear cowl  502  of the nacelle  500 , which ensures slideable opening of the core rear cowl. Use of the guide rail  151  may ensure that the core rear cowl  502  may be opened rearward, and an O-shaped thrust reverser of the pylon box segment  110  can also be achieved, which facilitates implementation of the pylon box segment  110 . The engine duct auxiliary structure  150  is narrower, which is directly conducive to the saving of the fuel, since the engine duct auxiliary structure  150  is a structure in the engine external duct. 
     In the structure shown in  FIG. 13 , the front frame  152  of the engine duct auxiliary structure  150  is connected to a main structure of the pylon box segment  110  in a lug-connector connection manner, and the rear frame  157  is connected to the main structure of the pylon box segment  110  in a surface connection manner. However, it may be appreciated that the engine duct auxiliary structure  150  is connected to the main structure of the pylon box segment  110  in a detachable connection manner, e.g., a hinge or a hinged support. The hinged supports of the pylon box segment  110  and the rear frame  157  are pivoted together via two ends of a pivoting rod, and meanwhile, hinges of the pylon box segment  110  and the rear frame  157  may also be pivoted to each other via a pin-shaped fastener. As such, both the front frame  152  and the rear frame  157  are both upwardly pivoted to the pylon box segment  110 , and the front frame  152  is connected to the core rear cowl  501 . That is to say, joints at respective locations are not fixed connections and all are detachable, thereby achieving excellent maintainability. 
     The engine duct auxiliary structure  150  is apparently narrower than the conventional pylon, which allows the LEAP-X engine duct to have better aerodynamic properties and reduces engine fuel consumption (about 0.75% as estimated). It is a part of the pylon structure, and the BIFI structure is not a main force-bearing structure but a second-level structure relative to the pylon box segment  110 . 
     The technical contents and technical features of specific embodiments of the present invention are already revealed as above. However, it should be appreciated that as guided by the creation idea of the present invention, those skilled in the art can make various modifications and improvements to the above-disclosed various features and combinations of features not explicitly shown here, but these variations and/or combinations all fall within the protection scope of the present invention. The above depictions of embodiments are only exemplary not restrictive. 
     
       
         
               
             
               
               
             
           
               
                   
               
               
                 Reference signs: 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                  10′ pylon 
                  11′ pylon sidewall 
               
               
                  12′ thrust reverser cowl hinge 
                  13′ fan cowl hinge 
               
               
                  20′ front installation joint 
                  30′ rear installation joint 
               
               
                  1 first connection point 
                  2 second connection point 
               
               
                  3 third connection point 
                  4 fourth connection point 
               
               
                  5 fifth connection point 
               
               
                  10 first lug 
                  20 second lug 
               
               
                  30 third lug 
                  40 connecting bolt 
               
               
                  50 bushing 
               
               
                  70 first link 
                  80 second link 
               
               
                  90 third link 
               
               
                 110 pylon box segment 
               
               
                 100 front end frame 
                 102 side panel 
               
               
                 121 upper guide rail 
                 122 intermediate guide rail 
               
               
                 123 lower guide rail 
                 130 front installation joint 
               
               
                 140 pylon rear edge 
                 150 engine duct auxiliary structure 
               
               
                 151 guide rail 
                 152 front frame 
               
               
                 153 front beam 
                 154 rear beam 
               
               
                 155 intermediate cross beam 
                 156 intermediate slant beam 
               
               
                 157 rear frame 
                 158 pivoting seat 
               
               
                 159 connection position 
               
               
                 200 engine fan casing 
               
               
                 201 first connector 
                 203 second connector 
               
               
                 205 third connector 
               
               
                 301 front fixed cowl 
                 302 rear moveable cowl 
               
               
                 303 nacelle grid 
                 304 engine external duct space 
               
               
                 401 fan air valve 
                 402 precooler 
               
               
                 500 nacelle 
               
               
                 501 core front cowl 
                 502 core rear cowl