Abstract:
The present invention relates to a nacelle ( 1 ) for a turbojet engine comprising an air intake structure ( 4 ) capable of ducting a flow of air towards a fan and a central structure ( 5 ) intended to surround the said fan and to which the air intake structure is attached, the central structure comprising a casing ( 9 ) intended to surround the fan and an external structure ( 13 ), characterized in that the air intake structure comprises, on the one hand, at least one internal panel ( 41 ) attached to the central structure via the casing and therewith forming a fixed structure and, on the other hand, at least one longitudinal external panel ( 40 ) attached removably to the fixed structure and incorporating an air intake lip ( 4   a ), the said external panel being removable between an operating position in which the external panel is aerodynamically continuous with the external structure of the central section and the air intake lip provides aerodynamic continuity with the internal panel of the air intake structure, and a maintenance position in which the external panel is separated from the external structure of the central section and the air intake lip is separated from the internal panel of the air intake structure.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The present invention relates to a nacelle for a turbojet comprising an air intake structure capable of channeling an air flow toward a fan of the turbojet and a middle structure designed to surround said fan and to which the air intake structure is attached. 
       BRIEF SUMMARY OF RELATED ART 
       [0002]    An aircraft is propelled by one or more propulsive assemblies comprising a turbojet housed in a tubular nacelle. Each propulsive assembly is attached to the aircraft by a pylon usually situated beneath a wing or on the fuselage. 
         [0003]    A nacelle usually has a structure comprising an air intake upstream of the engine, a middle section designed to surround a fan of the turbojet, a downstream section housing thrust reverser means and designed to surround the combustion chamber of the turbojet, and is usually terminated by an exhaust nozzle the outlet of which is situated downstream of the turbojet. 
         [0004]    The air intake comprises, on the one hand, an intake lip suitable for making it possible to optimally gather toward the turbojet the air necessary for supplying the fan and the compressors inside the turbojet, and, on the other hand, a downstream structure to which the lip is fitted and which is designed to properly channel the air toward the fan blades. The assembly is attached upstream of a casing of the fan belonging to the middle section of the nacelle. 
         [0005]    According to the temperature and relative humidity conditions on the ground or in flight, ice may be deposited on the profile of the lip, notably on the inner profile. This formation of ice may be dangerous for the mechanical operation of the fixed and rotating portions of the engine and cause a reduction of performance. Systems for deicing this portion of the air intake lip have therefore been produced to remedy this problem. It is possible in particular to cite documents U.S. Pat. No. 4,688,757 and EP 1 495 963 and the as yet unpublished application registered under number FR 06/02547. 
         [0006]    Currently, the maintenance operations on this equipment housed inside the air intake structure oblige the manufacturers to provide hatches for access to these various items of equipment. Despite the efforts made to optimize the positioning of the hatches and allow the easiest possible access, it is sometimes necessary to visit the internal equipment of the air intake structure with the aid of specific tools such as an endoscope, which is not entirely satisfactory with respect to the inspection of this equipment. 
         [0007]    Furthermore, if it is necessary to replace a portion of the internal equipment, it is necessary to remove the whole of the air intake structure which requires considerable toolage and involves an immobilization of the propulsive assembly and therefore usually the aircraft. 
         [0008]    It will also be noted that the operating and maintenance conditions of an air intake make it necessary to have distinct components, such as a sectorized modular lip and an outer panel that can be easily removed because of their high replacement rate due to their direct exposure to the external environment and to possible projectiles. These constraints considerably reduce the integrity of the general aerodynamic line of the air intake structure which the presence of access hatches further aggravates. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    The invention remedies the abovementioned disadvantages and for this reason consists in a nacelle for a turbojet comprising an air intake structure capable of channeling an air flow toward a fan of the turbojet and a middle structure designed to surround said fan and to which the air intake structure is attached so as to provide an aerodynamic continuity, the middle structure comprising, on the one hand, a casing designed to surround the fan and, on the other hand, an outer structure, characterized in that the air intake structure comprises, on the one hand, at least one inner panel attached to the middle structure and forming with the latter a fixed structure of the nacelle, and, on the other hand, at least one outer longitudinal panel attached in a removable manner to the fixed structure and incorporating an air intake lip, said outer panel being removable between an operating position in which the outer panel provides the aerodynamic continuity with the outer structure of the middle section and the air intake lip provides the aerodynamic continuity with the inner panel of the air intake structure, and a maintenance position in which the outer panel is separated from the outer structure of the middle section and the air intake lip is separated from the inner panel of the air intake structure. 
         [0010]    Therefore, by incorporating the air intake lip into the outer panel so as to form a single removable part, a removal and partial replacement of the air intake structure are made possible and easier. Furthermore, removal made easier in this way also makes it possible to open the air intake structure in order to gain access to internal equipment without requiring considerable and complicated maneuvers nor requiring a long immobilization time. It should also be noted that there is then no longer a connection interface between the outer panel and the air intake lip, since only one possible longitudinal interface may exist in the case of a plurality of panels. This absence of interface perpendicular to an air flow makes it possible to improve the outer aerodynamic line of the nacelle. 
         [0011]    It should also be noted that the present invention limits the size of the translatable outer panel substantially at the junction between the inner wall of the air intake and the fan casing. Therefore, the fan casing can still be fitted with its own access means. 
         [0012]    Therefore, if maintenance is necessary only on the casing of the fan or on its junction with the inner wall of the air intake, it is not necessary to needlessly remove the outer wall of the air intake. The result of this is an overall maintenance time-saving, each section retaining an option of independent access. 
         [0013]    Advantageously, the middle structure has, with the outer panel, an interface situated downstream of the air intake structure. More precisely, the nacelle has an outer panel extending slightly beyond the junction between the fan casing and the inner panel. 
         [0014]    In this manner, the impact of the aerodynamic break that said interface forms on aerodynamic performance is minimized. 
         [0015]    Preferably, the middle section comprises at least one movable cover capable of allowing external access to the nacelle. 
         [0016]    Advantageously, the lip and the outer panel of the air intake structure have an interface at which said lip and outer panel overlap partially when in the closed position. Also advantageously, the interface has an upstream point forming an abutment. Such an overlap will advantageously make it possible to fit the portion of the inner wall overlapping the lip with means for deicing the bottom zone of said lip. 
         [0017]    Advantageously, the outer panel of the air intake structure has a rear frame capable of being attached to a matching partition of the air intake structure secured to a fixed portion of the nacelle by means of the inner panel. 
         [0018]    Advantageously, the air intake structure comprises means for centering and positioning the outer panel. 
         [0019]    Preferably, the air intake structure comprises guidance means capable of allowing a substantially rectilinear movement of the outer panel toward the upstream of the nacelle so as to be able to open the outer panel. Therefore, it is easier to partially open the air intake structure and replace said structure. 
         [0020]    Advantageously, the air intake structure comprises at least one abutment means of the outer panel capable of allowing a partial opening of the latter without requiring complete removal. 
         [0021]    Preferably, the guidance means comprise at least one rail system. 
         [0022]    Advantageously, the guidance means comprise at least one rail capable of interacting with a corresponding slide or a runner. 
         [0023]    As a variant or additionally, the guidance means comprise at least one system of roller skids capable of interacting with a corresponding rail. Advantageously, the rollers are mounted on flexible axles of the “paulstra” type. Again advantageously, the rollers are mounted on at least one plate, said plate itself being attached in a flexible manner, via a swivel-joint connection or an interface of the “paulstra” type, for example. 
         [0024]    As a variant or additionally also, the guidance means comprise at least one channel-like rail capable of interacting with a corresponding slide system. 
         [0025]    Advantageously, the guidance means comprise at least one longitudinal shaft capable of sliding through a corresponding opening. Such shafts also perform a centering function. 
         [0026]    Preferably, the air intake structure comprises mechanical or manual means for moving the outer panel along the guidance means. 
         [0027]    Again preferably, the inner panel of the air intake structure comprises an acoustic shroud. 
         [0028]    Advantageously, the air intake structure comprises electric equipment for deicing the air intake structure. 
         [0029]    Advantageously, the inner panel or the outer panel is, at the junction between the air intake lip, extended by a peripheral elastic tongue capable of covering said junction when the outer panel is in the closed position. 
         [0030]    It should also be noted that the pylon by which the nacelle is attached to the aircraft extends over the downstream and middle section of the nacelle and does not usually protrude over the air intake section. Because of this, the means for guiding the movable cover cannot use the pylon as a point of attachment for the rails, and it is necessary to incorporate a distinct guidance system into the air intake. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    The application of the invention will be better understood with the aid of the detailed description that is given below with respect to the appended drawing in which: 
           [0032]      FIG. 1  is a schematic representation of a nacelle according to the invention showing an air intake structure comprising a lip incorporated into the outer panels. 
           [0033]      FIG. 2  is a schematic representation in longitudinal section of a first embodiment of the air intake structure of  FIG. 1 . 
           [0034]      FIGS. 3 to 5  are enlarged schematic representations of the zone of junction between an outer panel incorporating an air intake lip and an inner panel of the air intake structure of  FIG. 2 . 
           [0035]      FIG. 6  is a schematic representation in longitudinal section of the air intake structure of  FIG. 2  in the open position. 
           [0036]      FIGS. 7 to 9  are partial schematic representations of an air intake structure according to the invention showing a connection interface for an electric deicing installation fitted to the outer panel. 
           [0037]      FIGS. 10 and 11  are partial schematic representations of a first variant embodiment of the guidance means fitted to the air intake structure according to the invention respectively in the closed and open position. 
           [0038]      FIGS. 12 and 13  are partial schematic representations of a second variant embodiment of guidance means fitted to the air intake structure according to the invention respectively in the closed and open position, said guidance means comprising movement means. 
           [0039]      FIG. 14  is a front view in section of the guidance system shown in  FIGS. 12 and 13 . 
           [0040]      FIG. 15  is a front view in section of a variant embodiment of the guidance system making it possible to reduce the jamming effects. 
           [0041]      FIGS. 16 to 18  are enlarged partial schematic representations of various elements of the guidance system. 
           [0042]      FIG. 19  is a front view in section of a second variant embodiment of the guidance system making it possible to reduce the jamming effects. 
           [0043]      FIGS. 20 and 21  are schematic representations in longitudinal section of the guidance system of  FIG. 19 . 
           [0044]      FIGS. 22 and 23  are schematic representations in longitudinal section of an air intake according to the invention comprising pneumatic deicing means. 
           [0045]      FIGS. 24 and 25  are schematic representations of a mechanical movement system suitable for the invention. 
           [0046]      FIGS. 26 to 29  are representations of improvement that may be made to a rail/roller guidance system. 
           [0047]      FIGS. 30 and 31  are representations of an improvement designed to improve the aerodynamic continuity of the assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0048]    A nacelle  1  according to the invention as represented in  FIG. 1  is a tubular housing for a turbojet (not visible) for which it serves to channel the air flows that it generates while defining inner and outer aerodynamic lines necessary to obtain optimal performance. It also houses various components necessary to the operation of the turbojet and ancillary systems such as a thrust reverser. 
         [0049]    The nacelle  1  is designed to be attached to a fixed structure of an aircraft, such as a wing  2 , by means of a pylon  3 . 
         [0050]    More precisely, the nacelle  1  has a structure comprising a front section forming an air intake  4 , a middle section  5  surrounding a fan (not visible) of the turbojet, and a rear section  6  surrounding the turbojet and usually housing a thrust reverser system (not shown). 
         [0051]    The air intake  4  is divided into two zones, namely on the one hand an intake lip  4   a  suitable for allowing for optimally gathering to the turbojet the air necessary to supply the fan and internal compressors of the turbojet, and on the other hand a downstream structure  4   b  comprising an outer panel  40  and an inner panel  41  and to which the lip  4   a  is fitted and designed to appropriately channel the air toward the blades  8  of the fan  6 . 
         [0052]    According to the invention, the lip  4   a  is incorporated into the outer panel  40  so as to form a single removable part, the inner panel  41  being attached upstream of a casing  9  of the fan belonging to the middle section  5  of the nacelle  1  by means of attachment flanges  10 ,  11 , respectively secured to the downstream structure  4   b  and of the casing  9  and forming a junction  12 . 
         [0053]    The air intake structure  4  may be modular and comprise a plurality of outer panels  40  each defining a corresponding portion of air intake lip  4   a . In this case, the air intake structure  4  will have junction lines. However, these lines extend longitudinally relative to the nacelle  1  and they will have only a negligible impact on the aerodynamic continuity of the air intake structure  4  unlike a nacelle according to the prior art having a peripheral junction line between the outer panel  40  and the lip  4   a , said junction line being situated transversely relative to the direction of flow of the air. 
         [0054]      FIG. 1  shows the air intake structure  4  with the outer panel  40  in the partially open position. Advantageously, said outer panel can be opened only after lateral fan covers  13  fitted to the middle section are opened. 
         [0055]      FIG. 2  shows a first embodiment of an air intake structure  4  according to the invention. 
         [0056]    First of all, the inner panel  41  is made from an acoustic shroud and is connected by means of flanges  10 ,  11  to the casing  9  of the middle section  5 . This inner panel  41  therefore forms a fixed portion of the air intake structure  4  to which the outer panel  40  incorporating the air intake lip  4   a  is designed to be fitted and attached in a removable manner. 
         [0057]    To do this, each flange  10 ,  11  also supports a radial peripheral partition  14 , this partition supporting centering elements  15  and secondary centering elements  16  extending perpendicularly to said partition  14  in the upstream direction of the nacelle  1 . Preferably, three centering elements  15  and three secondary centering elements  16  will be provided uniformly distributed alternately around the air intake structure  4 . 
         [0058]    It will also be noted that the air intake structure  4  may extend axially by means of its outer panel  41  beyond a flange for attaching the inner panel  41  to the fixed structure of the nacelle  1  in order to come close to an outer structure of a thrust reverser structure belonging to the downstream section  6  of the nacelle  1  and if necessary to cover the covers  13 . A system of latches may then be provided to keep the air intake structure on the partition  14  secured to the structure of the casing  9  or to an upstream structure of the downstream structure  6 . 
         [0059]    It will also be noted that the radial peripheral partition  14  may be supported directly by the very structure of the fan casing  9  in order to provide a maximum inner covering for the air intake  4 . 
         [0060]    The outer panel  40  incorporating the air intake lip  4   a  therefore forms, according to the invention, a removable portion designed to be fitted to the fixed portion and more particularly to the peripheral partition  14 . 
         [0061]    To do this, the outer panel  40  is fitted with a peripheral front frame  17  capable of being attached against the partition  14  with the aid of fastening elements  18  such as a bolt/nut system. The front frame also has openings  19  capable of allowing the centering elements  15  and secondary centering elements  16  to pass through when the outer panel  40  is correctly positioned and in the closed position. 
         [0062]    Internal reinforcements of the existing inner and outer panels are not shown and depend on the rigidity that is sought by those skilled in the art. 
         [0063]    The centering elements  15  are terminated by a groove  20  serving as an element for the retention and support of the outer panel  40  during a removal phase allowing the front frame  17  to couple with it and not tilt. These centering elements  15  and secondary centering elements  16  also fulfill a guidance function and their length depends on the desired guidance. 
         [0064]    Sealing of the attachment between the front frame  17  of the outer panel  40  and the partition  14  may be provided with the aid of a peripheral seal. 
         [0065]    In the position thus assembled, the lip  4   a  incorporated into the outer panel  40  provides the aerodynamic continuity with the acoustic shroud  41 . Various alignment systems are shown as examples in  FIGS. 3 to 5 . 
         [0066]    The interface between the air intake lip  4   a  incorporated into the outer panel  40  and the acoustic shroud  41  of the inner panel may itself be external ( FIGS. 3 and 4 ) or internal ( FIG. 5 ) but must provide the purest possible aerodynamic continuity. Rigid centering means, such as centering pins  21  ( FIG. 5 ) capable of interacting with corresponding bores  22 , or flexible centering means, such as an elastic tongue  23  ( FIG. 4 ) provide this structural continuity. 
         [0067]    A seal  24  is placed at the interface on one or other of the inner panel  41  or outer panel  40  without distinction. 
         [0068]    Advantageously, as shown in  FIGS. 3 and 4 , the lip and the outer panel of the air intake structure have an interface at which said lip and outer panel overlap partially when in the closed position. Again advantageously, the interface has an upstream point forming an abutment. 
         [0069]    In such a case, it is also possible to have a means for deicing a bottom zone of the lip  4   a  incorporated into the portion of the inner wall  41  overlapping the lip  4   a.    
         [0070]    These systems must make it possible to provide a minimum clearance between the acoustic shroud  41  and the air intake lip  4   a  so that this junction creates the smallest possible aerodynamic turbulence. To allow a precise adjustment of this clearance and reduce it to the minimum, it is possible to provide an adjustable attachment interface between the front frame  17  and the partition  14 . 
         [0071]      FIG. 6  shows the air intake structure of  FIG. 2  in the open position. 
         [0072]    Furthermore, the outer panels  40  and inner panels may comprise electric deicing elements  26  and it will be advantageous to provide an interface for the connection of an electric supply  27  to the front frame or the partition  14 . Such a system is shown in  FIGS. 7 to 9  at different stages during the removal of the top panel  40 . 
         [0073]    When there are large air intake dimensions, for example, it is possible to carry out only a partial opening of the outer panel  40  incorporating the air intake lip  4   a . It is then useful to provide guidance and optionally actuation means. 
         [0074]    A first exemplary embodiment of an air intake structure according to the invention comprising guidance means is shown in  FIGS. 10 and 11  showing an outer panel in the closed and open position respectively. 
         [0075]    The guidance means comprise a rail  30  secured to the outer panel  40  placed at the interface with the front frame  17  and capable of interacting with a longitudinal shaft  31  supported by the partition  14  and the flange  10  of the fixed portion of the air intake structure  4 . 
         [0076]    As a structural reinforcement of the shaft  31 , a lune  32  is made in the rail to allow a reinforcement  33  of the shaft  31  on the inner panel  41 . 
         [0077]    Note the possibility of using a telescopic rail/runner system allowing a greater clearance of the outer wall  40 . 
         [0078]    A second exemplary embodiment of an air intake structure according to the invention comprising guidance means is shown in  FIGS. 12 and 13  showing an outer panel  40  in the closed and open position respectively. 
         [0079]    In this embodiment, the guidance means include actuation means. 
         [0080]    As above, the guidance means comprise a rail  35  secured to the outer panel  40  placed at the interface with the front frame  17 , and capable of interacting with a longitudinal shaft  36  supported by the partition  14  and the flange  11  of the fixed portion of the air intake structure  4 . However, this rail  35  has the particular feature of having teeth so as to be able to interact with a drive screw serving as a shaft  36 . The drive screw  36  is coupled to an electric motor or any other rotary driving means  37  and its actuation makes it possible to open and close the outer panel  40 . 
         [0081]    Clearly, these two embodiments may be combined to obtain an outer panel  40  capable of sliding either manually or mechanically as the operator wishes. 
         [0082]      FIG. 14  is a front view in section of the above embodiment. The guidance method illustrated for the embodiment comprising incorporated driving means is totally transposable with the embodiment comprising simple guidance means for manual operation. 
         [0083]    There are three rail  35 /shaft  36  guidance systems placed uniformly over the periphery of the air intake structure  4 . The systems  37  for rotating each shaft  36  are synchronized by means of a flexible drive cable  38  commonly known as a “flexshaft” capable of delivering the power of an electric motor (not visible) to all the operating systems  37 . The flexible drive cable  38  is guided around the air intake structure and reoriented in the direction of each operating system by means of passageway sheaths  39 . Clearly, it is possible not to use an electric motor but to provide manual actuation by handle, for example, or else to use more routine transmission means of the belt type or similar type. 
         [0084]      FIG. 15  shows an exemplary embodiment of the guidance means in order to reduce to the minimum any possible jamming effects that may be encountered in the case of a mechanical operation as described above. 
         [0085]    This guidance system comprises a rail  45 /slide  46  assembly placed in the upper portion of the air intake structure  4  and a detailed representation thereof is shown in  FIG. 16 . 
         [0086]    The guidance system comprises two other guidance points placed equidistant from one another around the air intake structure  4  and comprising a channel-like rail  47  in which a corresponding shaft  48  is capable of sliding. The channel-like configuration of these rails  47  makes it possible to obtain a tolerance on a possible misalignment of the air intake structure  4  when it is opened and/or closed. The shaft  48  may be a simple slide as shown in detail in  FIG. 17  or a shaft with rollers  49  as shown in  FIG. 18 , for example. 
         [0087]      FIG. 19  shows a second exemplary embodiment of the guidance means in order to further reduce the jamming effects. 
         [0088]    This guidance system comprises a first guidance point comprising a slide  50  which is placed as above in the upper portion of the air intake structure and of which a detailed representation is shown in  FIG. 19  and which comprises a skid with rollers fitted with at least two rollers  52  capable of sliding inside a corresponding rail  51 . A final abutment  54  is incorporated into the rail  51  at the end of the opening travel. 
         [0089]    It is also possible to provide the reverse arrangement, that is to say a guide rail translating inside roller plates placed on either side of the rail. This system will be described below with  FIGS. 26 to 29 . 
         [0090]    The guidance system comprises two other guidance points placed equidistant from one another around the air intake structure and comprising a shaft  55  secured to the partition  14  of the fixed portion of the air intake structure  4  and capable of sliding in an oblong opening  56  arranged in the front frame  17  of the outer panel  40 . 
         [0091]    It is also possible to add at least one handle connected to the front frame  17  and to an inner surface of the outer panel  40  half way up the air intake structure  4  on each side of the nacelle  1 . The handles are positioned at an angle dependent on the height of the nacelle  1  on the aircraft and on its accessibility for an operator on the ground. Each handle may be incorporated into a reinforcing bracket between the front frame  17  and the outer panel  40 . 
         [0092]    In addition, the outer panel  40  of the air intake structure  1  may be connected to an electric ground the invention of which is developed in document EP 0 983 939 in the name of the applicant. 
         [0093]      FIGS. 22 and 23  show the application of the invention to an air intake structure  4  comprising a pneumatic deicing system. In this case, the air intake structure  4  comprises a nozzle  60  delivering hot air from the turbojet which passes through the front frame  17  and/or the partition  14  of the fixed portion of the air intake structure  4 . The nozzle emerges in an inner sealed and peripheral compartment  61  situated at the air intake lip  4   a.    
         [0094]    This compartment  61  has an opening  62  at the lower portion of which a discharge channel  63  departs emerging at the outer panel  41  at a grating  64 . Clearly, this air discharge function may also emerge at the inner panel  40  as a variant. 
         [0095]    As mentioned above, it is possible to provide a mechanical system for driving the movable cover assisted by electric or manual actuation means. A first embodiment has been described and represented in  FIGS. 12 and 13 . Clearly other embodiments are possible as an alternative or an addition by friction (on an element underneath, for example, of the elastomer on elastomer type) or a mechanical embodiment. 
         [0096]    A second exemplary embodiment of such an operating system is shown for illustration purposes in  FIGS. 24 and 25 . 
         [0097]    In this instance, it is possible notably to envisage the installation of one or more rails  150  comprising a crenelated longitudinal surface  151  forming a rack and capable of interacting with an operating means of the gear type  152  or worm type. 
         [0098]    As shown, the crenelated surface  151  will preferably be provided on a lateral extension  153  of the rail  150 , but it could optionally be provided on a surface belonging to the rail itself. 
         [0099]    The operating means of the worm or gear type  152  can be connected to the shaft of an electric motor  154  and/or manual actuation means of the winder or handle type (not shown), preferably removable, the electric and manual operating means preferably being able to be disconnected from one another. 
         [0100]    The operating means of the gear  152  type or worm type may be mounted without distinction on the fixed structure  41 ,  9  or on the movable structure  40  depending on whether the rail  150  is itself mounted on the movable structure  40  or on the fixed structure  41 ,  9 . The positioning of the operating means depends on the necessary or desired length of movement and on the length of the rack  151  which may be provided only on a portion of the length of the rail  150 . 
         [0101]    With reference, now, to the guidance of the movable portion  40  during a translation movement, a particular embodiment consists in using rails with roller wheels or rollers as mentioned previously for  FIGS. 18 to 20 . In such a guidance method, the alignment of the movable portion  40  with the fixed portion  41  becomes critical and an incorrect alignment of the guide rail may lead to jamming. This jamming is particularly present in the case, for example, of a rail moving in translation between two roller plates placed on either side of the rail and the operations of the movable cover  40  makes it necessary to have a perfect alignment between the two elements so as to prevent these jamming effects. This consequently requires spacing tolerances in manufacture that are as small as possible, particularly in the positioning of the plates and of the rail, and in the shape of the rail itself which must have a particularly smooth surface, any surface defect, roughness or other defects being likely to lead to this jamming. 
         [0102]    An interesting improvement therefore consists in mounting the rollers on axles that are flexible and that will therefore be able to adapt to the defects of the rail, since they are unlikely to accommodate these defects by the elastic spreading of their axle. 
         [0103]    In addition to alignment in operation, this allows a simplification in the manufacture of the rails, since the tolerance of the rollers to the surface defects has been greatly increased. 
         [0104]    One exemplary embodiment is shown in  FIG. 26 . In this example, a rail  150  is mounted fixedly onto the fixed structure  41 ,  9  and guides two sets of three rollers  163  placed on either side of the rail  150  and mounted on plates  161 . 
         [0105]    Clearly, the present improvement is not limited to the plate shown in  FIG. 26  and it is possible to envisage plates with two rollers  163  or else three rollers  163 . 
         [0106]    More precisely, in order to reduce any static redundancy between the rollers  163  and the rail  150 , it is possible to envisage preferably a guidance of the rail  150  by two plates, a front plate and a rear plate, the front plate comprising two rollers while the rear plate will have three. 
         [0107]    Each roller  163  is mounted on a flexible axle  164  of the “paulstra” type. 
         [0108]    Furthermore, each plate  161  is also mounted on the movable structure  40  (if necessary on the fixed structure  41 ,  9 ) via flexible interface. 
         [0109]    As shown in  FIG. 27 , the plate  161  is mounted on the movable structure  40  via a swivel-joint interface  165 . 
         [0110]    Alternatively or in addition, and as shown in  FIG. 28 , the plate  161  is mounted on the movable structure  40  via an elastic flexible interface  166  of the “paulstra” type similar to that used for the axles  164  of the rollers  163 . 
         [0111]    Also note that the figures show the use of a polygonal rail  150 . Clearly other shapes of rail  150 , notably cylindrical, are possible. Such a shape makes it possible also to dispense with certain alignment constraints by allowing a certain rotation of the plate  161  about the rail  150 . 
         [0112]    The plates  161 ,  162  and the rollers  163  may if necessary be associated with self-centering means. 
         [0113]    Alternatively or additionally, the rollers  163  may also be mounted so as to allow a tolerance in their axial direction. 
         [0114]    To do this, and as shown in  FIG. 29 , the axles  164  of the rollers  163  are extended and fitted with elastic return means, of the spring type  170  against which the rollers  163  are mounted. 
         [0115]    Another addition relates to the aerodynamic continuity of the surfaces of the nacelle. As mentioned above when describing  FIGS. 3 and 4 , an important aspect of the design of a nacelle is the reduction of aerodynamic turbulence generated by junction faults (spreads and jumps, differences of level) between the various panels forming the nacelle. 
         [0116]    In this instance, an important point is the junction between the end of the outer panel  40  terminating the air intake lip  4   a  and the inner panel  41 . 
         [0117]    Various joining methods have already been described for  FIGS. 3 to 5 . 
         [0118]    However, these solutions only partly solve the problem since, in flight, the forces and vibrations are also partly sustained by the centering pins  21  or other attachment means and distributed over the periphery of the junction. To ensure a shearing strength at the interface of the centering pins  21 , it is necessary for this interface to be in contact. 
         [0119]    The two panels may also if necessary be operated in relative movements which disrupt the aerodynamic flow. 
         [0120]    To ensure a very high level of aerodynamic efficiency, it is necessary to provide the purest possible continuity of line (clearance and travel (alignment)). Those skilled in the art know that they cannot produce two close interfaces in contact with one another for manufacturing reasons. Since the contact at the pins is preferable for reasons of structural design, the result is that it is necessary to transfer the clearance between the two interfaces in contact with the air that is harmful to the air-capture performance and therefore to the performance of the engine. 
         [0121]    In order to further improve the aerodynamic continuity and to solve this problem, the outer panel is, at the end of the air intake lip  4   a , terminated and extended by an elastic tongue  201  forming a sort of skirt and shown in  FIG. 30 , the tongue  201  being suitable, when the outer panel  40  is in the closed position, for overlapping the end of the inner panel  41  at the end of the air intake lip  4   a.    
         [0122]    This improvement is shown in  FIGS. 30 and 31 . 
         [0123]    The elastic tongue  201  is shown on the movable portion  40  at the end of the air intake lip. It cannot usually be incorporated into the fixed portion  41  because of the direction of the air flow, otherwise there would be a risk of air spillage. 
         [0124]    The elastic tongue  201 , covering the junction between the two panels  40  and  41 , makes it possible to maintain a smooth inner surface while adapting to the relative movements and offsets between the panels  40  and  41 . 
         [0125]    The tongue  201  may be a flexible seal of the reinforced or unreinforced silicone type, or else a seal of the daisy type, for example made of metal with teflon contact. It is also possible to envisage a flexible and daisy seal. 
         [0126]    The tongue  201  may be made as shown in  FIGS. 30 and 31  with an end that is thicker than the rest of the tongue  201 , in order to be able to be placed in prestress when it is mounted on the outer wall  40  so as to ensure a permanent contact irrespective of the differences due to the manufacturing tolerances and to the aerodynamic suction effects. 
         [0127]    Consequently, this means that the shape of the end of the inner panel  41  designed to be covered by the tongue  201  is compatible with the prestress of the tongue  201 . In this instance, the end of the inner panel  41  has a slight recess corresponding to the thickness of the end of the tongue  201 . 
         [0128]    It should be noted that preferably the centering pins  21  are designed so as to have a sufficient length to be placed in contact, engaged, before being placed in contact with the tongue  201 . 
         [0129]    Although the invention has been described with reference to particular exemplary embodiments, it is evident that it is in no way limited thereto and that it comprises all the technical equivalents of the means described and their combinations if the latter enter the scope of the invention. 
         [0130]    Notably, it should be noted that the improvements presented, namely the methods of driving and guidance, the elastic tongue, are not limited to a nacelle having a particular movable cover but may be easily applied amongst others, on the one hand, to a nacelle having a movable cover also incorporating the outer wall of the middle section, and on the other hand, to other movable portions of the nacelle that are subjected to the same problems.