Abstract:
The present invention relates to a jet engine nacelle ( 1 ), of the type comprising an aft section forming an external structure ( 2 ) which, together with a concentric internal structure ( 4 ) comprising an internal panel ( 10 ) intended to surround a down-stream portion of the jet engine, defines an annular flow duct for a so-called secondary stream ( 3 ), characterized in that exhaust means ( 11 ) are formed in the internal panel such that any unwanted excess pressure is discharged into the annular duct.

Description:
TECHNICAL FIELD 
     The disclosure relates to a jet engine nacelle for an aircraft. 
     BACKGROUND 
     An aircraft is propelled by a number of jet engines each housed in a nacelle which also accommodates a collection of auxiliary actuating devices associated with the operation thereof and performing various functions when the jet engine is operating or stationary. These auxiliary actuating devices particularly comprise a mechanical system for actuating thrust reversers. 
     A nacelle generally has a tubular structure comprising an air inlet in front of the jet engine, a mid-section intended to surround a fan of the jet engine, and a rear section accommodating thrust reversal means and intended to surround the combustion chamber of the jet engine, and is generally terminated by an exhaust nozzle whose outlet is situated downstream of the jet engine. 
     Modern nacelles are often intended to accommodate a turbofan jet engine designed, via the blades of the rotating fan, to generate a hot air stream (also known as primary stream) from the jet engine combustion chamber. 
     A nacelle generally has an outer structure, termed Outer Fixed Structure (OFS), which, together with a concentric inner structure, termed Inner Fixed Structure (IFS), comprising an inner panel surrounding the actual structure of the jet engine to the rear of the fan, defines an annular flow duct, also termed flow path, aimed at channeling a cold air stream termed secondary steam, which flows around outside the jet engine. The primary and secondary streams are ejected from the jet engine via the rear of the nacelle. 
     Certain equipment of the jet engine conduct highly pressurized fluids. In the event of untimely breakage of this equipment, the inner panel is subjected to a high excess pressure which can lead as far as the destruction of a part of said panel and/or of the equipment housed in this environment. To avoid this destruction, it is commonly accepted to install one or more excess pressure flaps in the rear part of the inner panel of the outer structure, at the outlet of the annular duct, the gas flow rate constituting the excess pressure then being theoretically discharged directly to the outside of the nacelle. 
     Nevertheless, the gas flow rate generated by the explosion produced in the jet engine compartment can be expelled only after having travelled the whole way to the nearest excess pressure flap. Now, it has been found in practice that this distance had the effect of greatly limiting the benefit of integrating such excess pressure flaps, insofar as the structure and/or the equipment could suffer before the excess pressure is discharged. In certain cases, it has even been found that these excess pressure flaps did not play any role. 
     It is known from document U.S. Pat. No. 4,825,644 to form exhaust means in the inner panel, these exhaust means comprising at least one excess pressure flap equipped with spacing means for ensuring a minimum discharge flow rate to the outside in the event of untimely excess pressure, said spacing means being produced with the aid of at least one strut equipped with locking means designed to lock said strut in its spacing position in the event of excess pressure requiring the opening of the excess pressure flap. Consequently, the untimely excess pressure occurring in the jet engine compartment is immediately discharged inside the annular duct via the exhaust means, and cannot therefore cause the destruction of the inner panel and/or the surrounding equipment. 
     BRIEF SUMMARY 
     The disclosure aims at providing an alternative solution and to that end comprises a nacelle for a jet engine, of the type comprising a rear section made up of an outer structure which, together with a concentric inner structure comprising an inner panel intended to surround a downstream portion of the jet engine, defines an annular flow duct for a so-called secondary stream, said nacelle comprising exhaust means formed in the inner panel and comprising at least one excess pressure flap equipped with spacing means for guaranteeing a minimum discharge flow rate to the outside in the event of an untimely excess pressure, said spacing means being produced with the aid of at least one strut equipped with locking means designed to lock said strut in its spacing position in the event of excess pressure requiring the opening of the excess pressure flap, characterized in that the strut comprises a hollow casing in which a rod can slide, said casing having an end fixed in the excess pressure flap and said rod having an end fixed in the inner panel, and in that the locking means are produced with the aid, on the one hand, of a locking finger housed in the casing and having a first end mounted pivotably about an axis in the region of the end of the casing fixed in the excess pressure flap and a second end housed in a cavity formed in the rod, and, on the other hand, elastic return means designed so as to longitudinally off-center said locking finger with respect to the cavity of the rod when said rod has slid in the casing, thus preventing its rearward return. 
     Advantageously, the exhaust means are positioned at the front of the inner panel. 
     It should go without saying that another solution for overcoming the potential risk of reclosure can also exist in the integration of means for braking the reclosure movement of the excess pressure flap, such that the latter can find its point of equilibrium. 
     Thus, in a nacelle according to this disclsoure, the location of the excess pressure flap or flaps can be chosen to be as close as possible to the equipment of the jet engine which is likely to create the highest excess pressure, such that this or these excess pressure flap or flaps are capable of discharging this excess pressure without stressing the stiffness of the inner panel of the inner structure. 
     Specifically, to the disclosure seeks benefit from the very high local excess pressure in the vicinity of the point of the explosion in order to promote the immediate opening of the exhaust means, thereby finally allowing a quasi-instantaneous expulsion of the gases generated by the explosion. The risk of damaging the inner panel and/or the surrounding equipment is therefore considerably reduced. 
     The immediate advantages of such an installation are a weight and cost saving since, given that the inner panel of the inner structure is no longer stressed by any untimely excess pressure, there is no longer any need to dimension it so that it can withstand such stresses. Furthermore, aircraft manufacturers have more freedom as to the choice of the location of the excess pressure flap or flaps along the annular duct. 
     Given the position of these exhaust means, a nacelle according to an exemplary embodiment comprises detection means designed so as to make the actuation of the exhaust means visible from the outside. 
     Advantageously, the detection means comprise a control system whose activation is conditioned by the activation of the exhaust means. 
     More advantageously still, the control system is connected to at least one external mechanical display member via transmission means. 
     In an exemplary embodiment, the control system comprises a prestress trigger, connected to the transmission means, the release of which is conditioned by the actuation of the exhaust means. 
     The disclosure also relates to an aircraft comprising at least one nacelle according to an exemplary embodiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Implementation will be better understood from the detailed description which is explained below with reference to the appended drawing, in which: 
         FIG. 1  is a schematic view in longitudinal section of a nacelle according to an exemplary embodiment in the closed state; 
         FIGS. 2 and 3  are partial perspective schematic views of the inner panel of a nacelle according to an exemplary embodiment when the excess pressure flap is deployed; 
         FIG. 4  is a perspective view of the excess pressure flapin an exemplary embodiment; 
         FIG. 5  is a partial view in longitudinal section of the strut, when at rest, of the excess pressure flap represented in  FIG. 4 ; 
         FIG. 6  is a partial view in longitudinal section of the strut, when deployed, of the excess pressure flap represented in  FIG. 4 ; 
         FIG. 7  is a partial schematic view of the nacelle represented in  FIG. 2 , equipped with detection means. 
     
    
    
     DETAILED DESCRIPTION 
     A nacelle of an aircraft  1  according to an exemplary embodiment as represented in  FIG. 1 , comprises in a manner known per se an outer structure  2 , termed OFS, which defines an annular flow duct  3  with a concentric inner structure  4 , termed IFS, surrounding the structure of the jet engine (not shown) to the rear of a fan ( 5 ). 
     More precisely, this outer structure  2  is broken down into a front air inlet section  6 , a mid-section  7  intended to surround the fan  5 , and a rear section  8  generally formed by at least two half-shells. 
     The inner structure  4  comprises an inner panel  10  which surrounds a downstream portion of the jet engine. As represented in  FIGS. 2 and 3 , exhaust means  11  are provided in this inner panel  10  so that any untimely excess pressure occurring in the jet engine compartment is discharged into the annular duct  3 . 
     These exhaust means  11  are preferably positioned at the front of the inner panel  10  so as to be situated as close as possible to the sensitive regions in which excess pressure may occur due to an explosion in the jet engine compartment. These exhaust means  11  comprise at least one excess pressure flap  12  equipped with a strut  13 . The excess pressure flap  12  is attached to the inner panel  10 , and is pivotably mounted about the latter via a set of hinges  9 . 
     A nacelle according to an exemplary embodiment is represented more specifically in  FIGS. 4 to 6 . 
     The strut  13  of the excess pressure flap  12  comprises a cylindrical hollow casing  14  in which a rod  15  can slide. This casing  14  has an end  16  pivotably mounted about an axis  33  in a fastening plate  31  attached to the excess pressure flap  12 , and the rod  15 , extending the casing  14 , has an end  17  pivotably mounted in a fastening block  32  attached to the inner panel  10  of the inner structure  4 . 
     More precisely, and as represented in  FIGS. 5 and 6 , a locking finger  120  is housed in the casing  14 , and is arranged between the end  16  thereof and the rod  15 . 
     More precisely, this locking finger  120  has a first end  121  pivotably mounted about the axis  33  in the region of the end  16  of the casing  14 , and a second end  123  housed in a cavity  124  formed in the rod  15 . 
     Furthermore, elastic return means are produced in the form of at least one compression spring  122 . The latter is arranged transversely to the locking finger  120  in the region of the end  16  of the casing  14 , and has a first end  125  bearing against the inner face of the lateral surface  30  of the casing  14 , and a second end  126  housed in a transverse blind bore  127  formed in the locking finger  120 . 
     In this way, when the excess pressure flap  12  is in the closed position in the continuation of the inner panel  10  of the inner structure  4 , the casing  14 , the locking finger  120  and the rod  15  are coaxial to one another. 
     On the other hand, in the event of untimely excess pressure in the jet engine compartment which is sufficient to cause the excess pressure flap  12  to open, the rod  15  is caused to slide in the casing  14  as represented in  FIG. 11 , and the second end  123  of the locking finger  120  is extracted from the cavity  124  of the rod  15  owing to the sliding of the latter into the deployed position. The compression spring  122  can then force the first end  121  of the locking finger  120  to pivot about said axis  33 , the effect of which is to longitudinally off-center the locking finger  120  with respect to the cavity  124  of the rod  15 . Said rod will therefore be locked in the case of rearward return since the second end  123  of the locking finger  120  will no longer be positioned opposite the cavity  124  presented by the rod  15 . 
     Therefore, these locking means make it possible to lock the strut  13  in its spacing position which has been designed so as to ensure a minimum discharge flow rate to the outside in the event of untimely excess pressure. 
     It should be noted that the lateral surface  30  of the casing  14  may have an opening  128  which, during maintenance operations on the ground, makes it possible to reach the locking finger  120  and to force it to pivot about its axis  33  in order to arrange it parallel to the casing  14  and to the rod  15 , thereby finally allowing a rearward return of the latter. 
     Moreover, detection means  129  are advantageously provided to allow the operator or operators to check instantaneously from the outside whether the exhaust means  11  have been actuated or not in flight. 
     For that purpose, these detection means  129  comprise a control system whose activation is conditioned by the activation of the exhaust means  11  as represented schematically in  FIG. 7 . 
     This control system will advantageously comprise a cam whose pivoting will be controlled by the opening of the excess pressure flap  12 . This cam will preferably be connected to a prestressed trigger which is connected to transmission means  130  attached to at least one external mechanical display member  131 . 
     More precisely, the pivoting of the cam will cause the release of the prestress trigger, which as it is released will exert a pull on the transmission means advantageously produced in the form of a cable  130 , this pull causing the deployment of the mechanical member preferably produced in the form of a “pop-out” -type device  131  as represented in the deployed position in  FIG. 2 . 
     Although the disclosure has been described in connection with specific exemplary embodiments, it goes without saying that it is in no way limited thereto and that it comprises all the technical equivalents of the means described as well as the combinations thereof if they come within the scope of the disclsoure.