Abstract:
The present disclosure relates to an aircraft turbojet engine nacelle, the nacelle including a rear section without a lower bifurcation, the rear section including a thrust reversal system, the thrust reversal system including a mobile cowl. The nacelle includes a guide system that translates as one with the mobile cowl, the guide system collaborating with at least one slide that is fixed in relation to the nacelle, the guide system and the slide being arranged near the position referred to as the 6 o&#39;clock position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of International Application No. PCT/FR2016/050119, filed on Jan. 21, 2016, which claims priority to and the benefit of FR 15/50489 filed on Jan. 21, 2015. The disclosures of the above applications are incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates to a turbojet engine nacelle, a propulsion unit equipped with such a nacelle, as well as an aircraft provided with such a propulsion unit. 
       BACKGROUND 
       [0003]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0004]    An aircraft is propelled by several turbojet engines each housed in a nacelle, each nacelle further accommodating a set of auxiliary actuating devices relating to its operation and ensuring various functions when the turbojet engine is in operation or shut down. 
         [0005]    The modern nacelles are intended to accommodate a bypass turbojet engine capable of generating, via the blades of the rotating fan, a hot gas flow (also called primary flow) and a cold air flow (also called secondary flow) which circulates outside of the turbojet engine through an annular passage, also called flow path, formed between two concentric walls of the nacelle. The primary and secondary flows are ejected from the turbojet engine by the backside of the nacelle. 
         [0006]    A turbojet engine nacelle generally has a tubular structure including:
       a front section, or air inlet, located in front of the turbojet engine;   a mid-section, intended to surround the fan of the turbojet engine;   a rear section, intended to surround the combustion chamber of the turbojet engine and generally including thrust reverser means;   an ejection nozzle, whose outlet is located downstream of the turbojet engine.       
 
         [0011]    The rear section generally has an outer structure, which defines, with a concentric inner structure, called “Inner Fixed Structure” (IFS), the annular flow path used to channel the cold air flow. 
         [0012]    The thrust reverser means allow, during the landing of an aircraft, improving the braking capability of said aircraft by redirecting forwards a major fraction of the thrust generated by the turbojet engine. In this phase, the thrust reverser generally obstructs the flow path of the cold flow and directs said cold flow forwardly of the nacelle, thereby generating a counter-thrust which is added to the braking of the aircraft wheels. The means implemented to carry out this reorientation of the cold flow vary according to the thrust reverser type. A common configuration is that of the thrust reversers called “cascade thrust reversers”. In this type of thrust reverser, the outer cowl of the rear section is sliding. The rearward translation of this sliding cowl allows uncovering thrust reverser cascades putting in communication the cold flow path and the outside of the nacelle. The translation of the sliding cowl further allows deploying blocking flaps in the cold flow path. Thus, by the combined action of the blocking flaps and the thrust reverser cascades, the cold flow is redirected forwardly of the nacelle. 
         [0013]    As mentioned above, the thrust reverser means are housed in the rear section of a nacelle. Three types of structural configuration for the rear section are mainly known, namely the structures respectively called “C-duct” “D-duct” and “O-duct” structures. 
         [0014]    In a D-duct structure nacelle, the inner and outer structures of the rear section of the nacelle are secured to each other, via two connecting islets called bifurcations. The bifurcations are disposed respectively according to the positions called “twelve o&#39;clock” position (upper bifurcation) and “six o&#39;clock” position (lower bifurcation). It should be recalled that the “twelve o&#39;clock” and “six o&#39;clock” positions are conventionally defined by analogy with a watch dial, the nacelle being in the operation position, that is to say under the wing. The “twelve o&#39;clock” position is accordingly located at the attachment mast of the nacelle, while the “six o&#39;clock” position corresponds to the diametrically opposite position. In the case of a D-duct structure nacelle, the sliding cowl is mounted in translation on the outer structure of the rear section. The sliding cowl is generally constituted of two half parts. 
         [0015]    In an O-duct or C-duct structure nacelle, the rear section is configured such that a lower bifurcation is not necessary. This represents a great gain in efficiency for the propulsion unit since the cold flow path is no longer obstructed in its lower part as is the case for the D-duct structures. Furthermore, the O-duct or C-duct structures also allow significant gains in terms of mass. 
         [0016]    In an O-duct or C-duct structure, the sliding cowl, or movable cowl, is generally mounted on slides disposed on either side of the suspension pylon (or mast) of the propulsion unit. These slides may be disposed directly on the pylon, or on an intermediate member secured to the pylon when the propulsion unit is mounted. The cowl is guided and supported only at these slides, therefore only in the vicinity of the “twelve o&#39;clock” position. 
         [0017]    Moreover, in an O-duct structure, the sliding cowl forms a one-piece structure. In order to meet various constraints such as avoiding the re-ingestion of air by the motor, avoiding directing a fraction of the thrust towards the fuselage of the aircraft, etc., the profile of the cascades ensuring the redirection of the cold flow, is generally not uniform along the circumference of the cascade assembly. It follows therefrom that the lateral efforts associated with the thrust reversal undergone by the cascades are not uniformly distributed. The sum of these lateral efforts is non-zero, which generates a lateral force applied on the cascade assembly and therefore on the propulsion unit. This lateral force generates a pendulum movement of the propulsion unit. 
         [0018]    This non-uniform distribution also generates a non-uniform deformation of the thrust reverser, which become oval during the thrust reversal phases. 
       SUMMARY 
       [0019]    The present disclosure provides an aircraft turbojet engine nacelle, the nacelle including a rear section without a lower bifurcation, the rear section including a thrust reverser system, the thrust reverser system including a movable cowl, the nacelle being characterized in that it includes a guide system secured in translation to the movable cowl, said guide system cooperating with at least one crosshead fixed relative to the nacelle, the guide system and the crosshead being disposed in the vicinity of the position called “6 o&#39;clock” position. 
         [0020]    Thus, by providing a guide system cooperating with a fixed crosshead, lateral strain absorbing at the lower part of the nacelle is provided, in the “six o&#39;clock” position. The parasitic distortions and movements generated in the “O-duct” or “C-duct” type nacelles of the state of the art are accordingly limited, and may even be totally suppressed. Furthermore, the guide system in accordance with the present disclosure simply integrates into the nacelle because the guide system is advantageously inserted instead of a solid cascade, the one normally positioned at six o&#39;clock. Moreover, a short type guiding will be advantageously made, thus allowing correctly absorbing the lateral forces while limiting the risk of hypostatism in the guiding of the movable cowl. 
         [0021]    In one form, the crosshead cooperates with the guide system via at least one bearing member, such as a pad, the crosshead being shaped so that the spacing, along the translation direction of the guide system, between the farthest bearing points of the crosshead is less than one-fifth (⅕ th ) of the guide length provided by the guide system. 
         [0022]    In another form, the crosshead is secured to a peripheral frame intended to be fastened to the fan casing of a turbojet engine. 
         [0023]    In in yet another form, the crosshead is fastened directly to the fan casing. 
         [0024]    In one form, the guide system includes a guide rail. 
         [0025]    In another form, the guide rail has two lateral slides. 
         [0026]    In another form, the crosshead includes at least two guide pads each cooperating with one of the two slides of the guide rail. 
         [0027]    In one variation, the thrust reverser system includes thrust reverser cascades, such as sliding thrust reverser cascades. 
         [0028]    In another variation, the thrust reverser system includes sliding thrust reverser cascades, one front end of the guide system being secured to a peripheral frame secured to the thrust reverser cascades. 
         [0029]    In one form, the guide system is disposed between two thrust reverser cascades. 
         [0030]    In another form, the guide system is disposed at the location normally occupied by a cascade called solid cascade. 
         [0031]    In yet another form, the guide system is secured to the front peripheral frame. 
         [0032]    In other forms, one rear end of the guide system is secured to a peripheral frame of the movable cowl. 
         [0033]    In still another form, the guide system is extended by a beam secured to the movable cowl. 
         [0034]    The present disclosure also concerns an aircraft propulsion unit, including a bypass turbojet engine, the propulsion unit including a nacelle as defined above. 
         [0035]    Further, the present disclosure relates to an aircraft including at least one propulsion unit as defined herein, the propulsion unit being supported by a pylon, the pylon including guide rails of the movable cowl of the nacelle. 
         [0036]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0037]    In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which: 
           [0038]      FIG. 1 a    is a perspective view of a nacelle in “direct jet” configuration in accordance with the teachings of the present disclosure; 
           [0039]      FIG. 1 b    is a perspective view of a nacelle in a “reverse jet” configuration in accordance with the teachings of the present disclosure; 
           [0040]      FIG. 2 a    is a perspective view of a rear section of a nacelle having a thrust reverser system in a retracted position in accordance with the teachings of the present disclosure; 
           [0041]      FIG. 2 b    is a perspective view of a rear section of a nacelle having a thrust reverser system in a deployed position in accordance with the teachings of the present disclosure; 
           [0042]      FIG. 3 a    is an enlarged perspective view of the rear section of the nacelle of  FIG. 2 a    in accordance with the teachings of the present disclosure; 
           [0043]      FIG. 3 b    is an enlarged perspective view of the rear section of the nacelle of  FIG. 2 b    in accordance with the teachings of the present disclosure; 
           [0044]      FIG. 3 c    is a, enlarged perspective view corresponding to  FIG. 3 a   , without a crosshead and a peripheral frame to which the crosshead is secured in accordance with the teachings of the present disclosure; 
           [0045]      FIG. 4 a    is a perspective view of a guide system and a crosshead in a position corresponding to a thrust reverser system in a retracted position in accordance with the teachings of the present disclosure; 
           [0046]      FIG. 4 b    is a perspective view of a guide system and a crosshead in a position corresponding to a thrust reverser system in a deployed position in accordance with the teachings of the present disclosure; 
           [0047]      FIGS. 5 a  and 5 b    are partial perspective views of a nacelle rear section having an enlarged guide rail in accordance with the teachings of the present disclosure; and 
           [0048]      FIG. 6  is a partial side view of a nacelle rear section showing a guide system and a crosshead in accordance with the teachings of the present disclosure. 
       
    
    
       [0049]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
       DETAILED DESCRIPTION 
       [0050]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
         [0051]      FIGS. 1 a  and 1 b    show a view of a nacelle  1  in accordance with the present disclosure. Said nacelle includes an air inlet  2 , a mid-section  3 , as well as a rear section  4 . In  FIG. 1   a,  the nacelle  1  is represented alone, while in  FIG. 1 b   , the nacelle  1  may be seen mounted on a pylon  5  (also known under the name of “engine mast”). Moreover,  FIG. 1 a    shows the nacelle in the “direct jet” configuration, that is to say with the thrust reverser system in the retracted position, while  FIG. 1 b    shows the nacelle in the “reverse jet” configuration, that is to say with the thrust reverser system in the deployed position. Thus, it is visible in  FIG. 1 b    that a movable cowl  20  of the rear section  4  is in the backward position, exposing a thrust reverser cascade assembly  22 . In the example, the movement of the movable cowl  20  is supported and guided by rails  50  disposed on either side of the pylon  5 . 
         [0052]    In the example, the structure of the nacelle is of the “O-duct” type and therefore includes no bifurcation in the lower part of the cold flow path. It should be noted that the present disclosure is also applicable to a nacelle with a C-duct structure. 
         [0053]      FIGS. 2 a  and 2 b    represent one part of the rear section of the nacelle of  FIGS. 1 a    and  1   b,  showing the members of the thrust reverser system respectively in the retracted position and in the deployed position. 
         [0054]    The thrust reverser system comprises a movable cowl  20 , in one piece, which forms the outer surface of the rear section of the nacelle. The movable cowl  20  is slidably mounted, in the example via rails  50 , secured to the pylon  5  supporting the propulsion unit (namely, the assembly formed by a turbojet engine and the associated nacelle). The thrust reverser system further comprises thrust reverser cascades  22 , in the example sliding cascades, and blocking flaps  24  movable in rotation. The thrust reverser system includes actuators (not shown), in particular electromechanical actuators, allowing sliding the movable cowl between the retracted position ( FIG. 2 a   ) and the deployed position ( FIG. 2 b   ) thereof, and conversely. 
         [0055]    When the thrust reverser system is retracted ( FIG. 2 a   ):
       the movable cowl  20  is in the retracted position, corresponding to a forward position in which it provides the aerodynamic continuity with the mid-section of the nacelle;   the blocking flaps  24  are in the retracted position, a position in which they are aligned with the inner surface of the movable cowl  20 ;   the thrust reverser cascades  22  are in the retracted (or forward) position, a position in which they are disposed around the fan casing of the turbojet engine.       
 
         [0059]    When the thrust reverser system is deployed ( FIG. 2 b   ):
       the movable cowl is in the deployed position, corresponding to a backward position, in which it uncovers the thrust reverser cascades  22  which are in the backward position thereof;   the blocking flaps  24  are in the deployed position, a position in which they obstruct at least partially the cold flow path;   the thrust reverser cascades  22  are in the deployed (or backward) position, a position in which they are disposed backwards of the fan casing of the turbojet engine, and in which they redirect the cold flow outwardly of the nacelle.       
 
         [0063]    It should be noted that since the thrust reverser cascades  22  are in the example sliding cascades, said sliding cascades being linked in translation to the movable cowl  20 , and the relative position of the thrust reverser cascades  22  relative to the movable cowl  20  may not vary during the deployment or the retraction of the thrust reverser system. 
         [0064]    The thrust reverser cascades  22  are secured to a front peripheral frame  26 . Several housings  28  are provided for the actuators of the thrust reverser system. These housings  28 , four housings in the example of  FIGS. 2 a  and 2 b   , are disposed between some of the thrust reverser cascades  22 . 
         [0065]    In the “six o&#39;clock” position (or in the vicinity of this position), at the location normally occupied by a cascade called solid cascade, such a solid cascade being provided to limit a redirection of the cold flow downwards, a guide system  30  is disposed. Thus, the guide system  30  is advantageously disposed between two thrust reverser cascades  22 , backwards of the front peripheral frame  26  of the cascades  22 . 
         [0066]    According to the present disclosure, the guide system  30  is fixed relative to the movable cowl  20  (and therefore, in the example, relative to the thrust reverser cascades  22 ), being in the example secured to the front peripheral frame  26 . The guide system  30  cooperates with a crosshead  32 , movable relative to the movable cowl  20  and to the thrust reverser cascades, and therefore relative to the guide system  30 . The crosshead  32  is however fixed relative to the non-movable members of the nacelle and of the propulsion unit. In the example, the crosshead  32  is secured to a peripheral frame  34 , which is in the example a part secured to the fan casing, known under the name of intermediate casing shroud. Alternatively, the crosshead  32  may be fastened directly to the fan casing. Thus, as visible in  FIGS. 2 a  and 2 b   , the relative position of the crosshead  32  and of the guide system  30  is related to the position of the movable cowl  20  and therefore of the thrust reverser cascades  22 . This relative position has two extremes, corresponding to the retracted and deployed positions of the thrust reverser system. These two extreme positions are more visible in  FIGS. 3 a    (retracted thrust reverser) and  3   b  (deployed thrust reverser). 
         [0067]      FIGS. 4 a  and 4 b    are isolated views of the guide system  30  and of the crosshead  32 . The guide system  30  includes a body  300  which has a front part  302 , provided to be fastened to the front peripheral frame  26 , for example by splicing, and a rear part  304 , provided to be fastened to the movable cowl  20 , for example by riveting and/or splicing. In the example, the guide system  30  is secured to a peripheral frame  202  (visible in  FIG. 3 c   ) of the movable cowl  20 . The guide system  30  includes a protruding portion, a guide rail  306 . In the example, the guide rail  306  includes two lateral slides  308 ,  310 . In the example of  FIGS. 4 a  and 4 b   , the guide system  30  constitutes a one-piece part. However, it might be desired to make this member in two or more parts, for example the body  300  and the guide rail  306 , for example in order to allow fastening the rail  306  to the body  300  in an adjustable manner (for example in height). Furthermore, these two members might be made of different materials, for example a composite material for the body  300  and a metal material for the rail  306 . 
         [0068]    The crosshead  32  includes guide pads  320  (visible in  FIG. 5 b   ) cooperating with each of the lateral slides  308 ,  310 . In the example, the crosshead  32  includes four guide pads, disposed on either side of the rail  306 , facing each other in pairs. The guide pads are constituted or coated with a material facilitating the sliding, such as for example Teflon. The guide pads  320  may be mounted in rotation on the crosshead  32 , or form sliding pads. 
         [0069]      FIG. 5 a    shows an enlarged guide rail  306 , thereby increasing the rigidity of the guide system. 
         [0070]      FIG. 6  shows the guide system and the crosshead  32  seen from the side. In the example, the guiding length R provided by the rail  306  is of 500 mm, while the longitudinal spacing L between the bearing points of the guide pads is of  80  mm. In order to provide a satisfactory lateral strain absorbing while reducing the risk of hyperstatism, it is advantageous to carry out a short guiding. To this end, the ratio between the longitudinal spacing L between the bearing points of the pads and the guide length R is lower than 0.2. 
         [0071]    In a variant not represented, the guide rail might have, at its rear part, an extension extending in the form of a beam secured to the movable cowl  20 . Thus, via this extension, the guide system will be fixedly fastened to the movable cover  20  and will participate in the rigidity of said movable cover. 
         [0072]    Although the present disclosure has been described relating to a various forms, it is obvious that it is in no way limited thereto and that it comprises all the technical equivalents of the described means as well as the combinations thereof. 
         [0073]    The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.