Abstract:
The invention relates to a nacelle for an aircraft engine that comprises a front cowling ( 13 ) and a rear cowling ( 1   a ), the rear cowling ( 1   a ) being mounted so as to slide between an upstream position defining a reduced nozzle ( 9 ) section and a downstream position defining an enlarged nozzle ( 9 ) section. The nacelle includes an intermediate member ( 25 ) arranged edge-to-edge with said front cowling ( 13 ), said member defining a housing ( 27 ) for receiving the upstream edge ( 11 ) of said rear cowling ( 1   a ) when the latter is in the upstream position.

Description:
TECHNICAL FIELD 
     The present invention relates to a nacelle for aircraft engine with a nozzle of variable cross section. 
     BACKGROUND 
     Patent application FR06/05512, filed by the applicant company on 21 Jun. 2006, discloses a nacelle for an aircraft engine comprising a cascade-type thrust reverser defining a nozzle of variable cross section. 
     A nacelle such as this is depicted schematically in the attached  FIGS. 1 to 3 . 
     It notably comprises a thrust reverser  1  delimiting a cold air flow path  3  with an inner structure  5  surrounding an aircraft engine (not depicted). The direction in which the air flows through this flow path is indicated by the arrow F 1 . 
     More specifically, the thrust reverser  1  comprises an outer wall  1   a , able to move axially under the action of a first series of actuators  7 , and an inner wall  1   b  able to move under the action of a second series of actuators (which are not depicted). 
     By operating only the first series of actuators  7  it is possible to modify the cross section of the rear part  9  of the outer wall  1   a  of the thrust reverser, which will then define a cold air ejection nozzle of variable cross section. 
       FIG. 1  depicts the outer wall  1   a  in the minimum cross section nozzle configuration, in which configuration the upstream zone  11  (in relation to the direction F 1 ) of the outer wall  1   a  of the thrust reverser  1  slides between a cowl  13  surrounding the fan casing  21  and an annular wall  17  attached to the front frame  19  of the thrust reverser, itself attached to the fan casing  21  of the engine (it being recalled here that the front frame  19  supports cascades of vanes  23  allowing the thrust reversal function to be implemented). 
       FIG. 2  indicates (arrow F 2 ) the sliding movement with which the cowl  13  may be endowed for operations of maintenance on the casing  21 . 
       FIG. 3  indicates (arrow F 3 ) the sliding movement with which both the outer wall  1   a  and the inner wall  1   b  may be endowed in the thrust reversal configuration, causing cold air to circulate from the flow path  3  to the outside through the thrust reversal cascades of vanes  23  (arrow F 4 ). 
     One of the problems associated with the nacelle that has the aforementioned architecture relates to the interface between the outer wall  1   a  of the thrust reverser  1  and the cowl  13 . 
     Specifically, for aerodynamic performance reasons, it is essential for the step  25  formed by the cowl  13  in relation to the outer wall  1   a  to be as shallow as possible. 
     It is therefore necessary that, in this zone of mutual overlap, on the one hand the thickness of the cowl  13  and on the other hand the clearance between this cowl and the outer wall  1   a  be minimized. 
     The requirement of minimal thickness for the cowl  13  prevents the provision of reinforcements (ribs or the like) for this cowl in said zone of overlap. 
     What this means is that this cowl  13  is liable to experience deformation in this zone, which deformation may lead to a jamming of the relative movement of the outer wall  1   a  in relation to the cowl  13 , given the small clearances there are between these two members. 
     BRIEF SUMMARY 
     The disclosure seeks to eliminate this risk of jamming. 
     This is achieved with a nacelle for an airplane engine, of the type comprising a front cowl and a rear cowl, this rear cowl being mounted such that it can slide between an upstream position defining a small cross section of nozzle and a downstream position defining an enlarged cross section of nozzle, notable in that it comprises an intermediate member positioned edge to edge with said front cowl, this member defining a housing able to accommodate the upstream edge of said rear cowl when this cowl is in its upstream position. 
     The presence of this intermediate member makes it possible to create aerodynamic continuity between the front cowl and the rear cowl without these two components interacting with one another directly: in that way it becomes possible to get around the problems of deformation and small clearances likely to lead to these components jamming on each other. 
     According to other optional features of the nacelle according to the invention:
         said intermediate member comprises a region for accommodating said front cowl, this region being positioned upstream of said housing: this accommodating region allows the front cowl to be centered in relation to the intermediate member;   said front cowl has reinforcements situated just upstream of said region: these reinforcing members allow the front cowl to be stiffened particularly near its downstream edge;   said front cowl comprises reinforcements situated in line with said region, said region being offset radially inward by a distance that corresponds substantially to the combined radial thickness of said front cowl and of said reinforcements: this arrangement allows the reinforcing members to be located in close proximity to the downstream edge of the front cowl;   said housing comprises a radially inner edge defining a slope for the upstream edge of said rear cowl: this slope allows the downstream cowl to be centered in relation to the housing of the intermediate member;   said housing has a radially outer edge defining a slope for the upstream edge of said rear cowl: this particular arrangement allows the reinforcements to be positioned on the interior face of the rear cowl, near the upstream edge of this cowl;   this nacelle comprises a seal adjacent to said slope: such a seal seals the connection between the intermediate member and the rear cowl;   said rear cowl comprises, on its interior face, reinforcements positioned near its upstream edge: the presence of these reinforcements stiffens the upstream part of the rear cowl;   the line where said front cowl meets said intermediate member is contained in a plane not perpendicular to the axis of said nacelle: such a meeting line, allowed by the presence of the intermediate member, notably provides better access to certain fixed members of the nacelle when the front cowl is in the maintenance position, slid forward;   said intermediate member comprises a leg supporting actuating means, notably means of actuating said rear cowl: this arrangement allows particularly simple placement of the actuating means (actuators for example);   said intermediate member can be attached to the fan casing of said engine;   said intermediate member comprises two halves that can be mounted in an articulated manner on a support pylon for said engine;   said intermediate member forms part of a cowl of the fan of said engine;   this nacelle comprises a cascade-type thrust reverser with cascades of vanes the exterior part of which forms said rear cowl;   said thrust reverser comprises, in addition to said exterior part, an interior part able to move independently of said exterior part: this particular embodiment corresponds to the one set out in the preamble of this description;   said intermediate member forms an integral part of the fixed structure of said thrust reverser: this intermediate member may in particular be attached to the front frame of the thrust reverser;   said front cowl incorporates the air intake lip of this nacelle;   said front cowl can be mounted such that it can slide on said engine.       

    
    
     
       Other features and advantages of the present invention will become apparent in the light of the description which will follow, and from studying the attached figures in which: 
         FIGS. 1 to 3 , mentioned in the preamble of this description, show, in axial section, a thrust reverser of a nacelle of the prior art; 
         FIG. 4  depicts, in axial section, an intermediate member according to the invention mounted on the front frame of a thrust reverser; 
         FIGS. 5 to 7 , which are similar to  FIGS. 1 to 3 , show a thrust reverser equipped with the intermediate member of  FIG. 4 , in three different configurations of the outer wall of this thrust reverser; 
         FIGS. 8 and 9  depict two possible alternative forms of the front cowl collaborating with the intermediate member according to the invention; 
         FIG. 10  depicts an alternative form of the intermediate member according to the invention designed to accommodate members for actuating the outer wall of the thrust reverser; 
         FIG. 11  depicts a thrust reverser comprising the intermediate member of  FIG. 10 ; 
         FIGS. 12 to 15  depict the dynamics of the opening, during maintenance operations, of an intermediate member according to another alternative form of the invention; 
         FIG. 16  depicts a thrust reverser equipped with yet another alternative form of intermediate member according to the invention; and 
         FIGS. 17 and 18  depict, in side view, a nacelle equipped with the intermediate member of  FIG. 16 , the front cowl of this nacelle being mounted such that it can slide in relation to the fan casing, and incorporating the air intake lip. In these  FIGS. 17 and 18 , this front cowl is in the operating position and maintenance position, respectively. 
     
    
    
     DETAILED DESCRIPTION 
     Across all the figures, identical references denote members or sets of members that are identical or analogous. 
     Referring now to  FIGS. 4 to 7 , it may be seen that an intermediate member  25  is attached to the front frame  19  of the thrust reverser  1 , this intermediate member defining a housing  27  able to accommodate the upstream edge  11  of the outer wall  1   a  of the thrust reverser  1 . 
     This thrust reverser may possibly be of the same type as the one in  FIGS. 1 to 3 , that is to say one with a variable cross section nozzle. 
     The intermediate member  25  extends over at least part of the circumference of the front frame  19 , so that the housing  27  is of annular shape. 
     This intermediate member is connected to the front frame  19  by a leg  29 , which itself also is of substantially annular shape. 
     Downstream of the housing  27  (downstream being determined in relation to the direction in which the air flows along the flow path  3 , as indicated by the arrow F 1  in  FIGS. 1 and 2 ) there is preferably a slope  31  making it easier to center and to fit the upstream edge  11  of the outer wall  1   a  inside the housing  27 . 
     There is preferably also a seal  33 , positioned just upstream of the slope  31 , to allow a sealed connection between the outer wall  1   a  and the intermediate member  25 . 
     Upstream of the housing  27  there is a centering member  35  that allows a front cowl of the nacelle  13  to be correctly centered and positioned. 
     This centering member  35  may itself have a slope  37  to make this centering easier. 
     The front cowl  13  frees access to the fan casing  21  during maintenance operations, by sliding in relation to this casing. 
       FIGS. 5 to 7  show three different positions of the outer wall  1   a  of the thrust reverser  1 , these corresponding to various nozzle cross sections desired for various phases of flight of an aircraft. 
     In the particular example depicted, the inner wall  1   b  of the thrust reverser is kept in an upstream position, that is to say covers the cascades of vanes  23  of the reverser, so that the thrust reverser function is not active. 
     However, it must of course be appreciated that when the thrust reverser function is desired, the outer cowl  1   a  and the inner cowl  1   b  slide downstream of their positions depicted in  FIG. 7 , thus uncovering the cascades of vanes  23  and allowing the flow of air flowing through the member  3  to be reversed. 
       FIG. 8  reveals the fact that circumferential reinforcements  39  can be provided under the inner face of the cowl  13 , these reinforcements being separated axially from the downstream edge of the cowl  13  or by a distance d 1  corresponding substantially to the axial length of the centering member  35 . 
     If it is desired to improve the rigidity of the downstream end of the cowl  13 , then the reinforcements  39  can be positioned as indicated in  FIG. 9 , that is to say directly adjacent to the downstream edge of this cowl, in which case it is necessary to ensure that the centering member  35  is offset radially in relation to the outer face  41  of the intermediate member  25  by a distance of d 2  substantially equal to the combined radial thickness of the cowl  13  and of the reinforcements  39 . 
     In the alternative form depicted in  FIG. 10 , it may be seen that holes  43  may be provided in the leg  29  of the intermediate member  25 , these holes being able to accommodate actuators  7  for actuating the outer wall  1   a  of the thrust reverser  1  (see  FIG. 11  in particular). 
     It can also be seen from  FIGS. 9 and 11  that provision may be made for a slope  45  to be positioned on the edge  47  situated radially on the outside of the housing  27 . 
     As can be seen in  FIG. 11 , such an arrangement of the slope  45  means that reinforcements  49  can be provided that are located under the upstream edge  11  of the outer wall  1   a  of the thrust reverser  1 . 
       FIGS. 12 to 15  show the dynamics of opening of a nacelle equipped with an alternative form of intermediate member  25  according to the invention, in which alternative form this intermediate member may be formed of two halves each mounted such that it can pivot on a nacelle support pylon (not depicted), about axes substantially parallel to the axis of this nacelle. 
     In this case, the leg  29  of the intermediate member  25  is not definitively mounted on the front frame  19  of the thrust reverser: each leg  19  of the associated half intermediate member  25  may be separated from the front frame  19  at the time of maintenance operations. 
     Starting out from a normal operating configuration depicted in  FIG. 12 , in which the cowl  13  sits edge to edge with the intermediate member  25 , and the upstream edge  11  of the outer wall  1   a  penetrates the housing  27  of the intermediate member  25 , the first thing to do is to slide the front cowl  13  toward the upstream end of the nacelle, as can be seen in  FIG. 13 . 
     The outer  1   a  and inner  1   b  walls of the thrust reverser are then slid in the downstream direction of the nacelle, notably by means of the actuators  7 , as has been depicted in  FIG. 14 . 
     That then leads to a situation in which the intermediate member  25  no longer collaborates either with the front cowl  13  or with the outer wall  1   a  of the thrust reverser. 
     Starting from this situation, each half intermediate member  25  is pivoted about the pylon (not depicted) that supports the nacelle (opening of the “gull-wing” door type). 
     In  FIGS. 16 to 18  it can be seen that, by suitably varying the thickness e separating the upstream edge  51  from the front  53  of the housing  27  of the intermediate member  25  it is possible to obtain a line  55  where the front cowl  13  meets the outer wall  1   a  of the thrust reverser that is inclined at some arbitrary angle α with respect to the axis A of a nacelle  57 . 
     In particular, and as can be seen in  FIGS. 17 and 18 , provision may be made for the lower part  59  of the meeting line  55  to be positioned further toward the upstream end of the nacelle than the upper part  61  of this meeting line. 
     Thanks to this special arrangement, and when the front cowl of the nacelle  13  is mounted such that it can slide in relation to the fan casing  21  for maintenance operations (see  FIG. 18 ), easier access can be had to members  63  (pumps, electronic housing, etc.,) attached to the lower half of the fan casing  21  and near the upstream edge  65  of this fan casing. 
     It will have been appreciated from the foregoing description that the intermediate member  25  constitutes a fixed component that collaborates independently with, on the one hand, the front cowl  13  and, on the other hand, the outer wall  1   a  of the thrust reverser. 
     Thanks to this intermediate member  25 , the issues involved become simple matters of the dynamics of the moving component/fixed component, and the risks of jamming inherent to the systems of the prior art are obviated. 
     Indeed, all that is required is, on the one hand, for the front cowl  13  and, on the other hand, for the outer wall  1   a , to be dimensioned with tolerances suited to obtaining perfectly dependable dynamics in relation to the intermediate member  25 . 
     Of course, the present invention is not in any way restricted to the embodiments described and depicted, which have been provided simply by way of examples. 
     In particular, it will be appreciated that the present invention can also be applied to nacelles of the so-called “plain” types, that is to say to nacelles that have no thrust reverser means. 
     In such instances, the outer wall described above in fact forms the simple rear cowl of a rear part of the nacelle of variable nozzle cross section, rather than the outer wall of a thrust reverser. 
     Thus also, it may be possible to have the intermediate member  25  form an integral part of a cowl covering the casing  21 , it being possible for this cowl to be opened slidably like the cowl  13  described above, or alternatively in the “gull-wing” manner, for example about the pylon that supports the nacelle.