Air intake structure for aircraft engine

In an air intake structure (14) of an aircraft engine pod, the link or connection between the air intake lip (15), the front reinforcing frame (16) and the acoustic panel (17) is implemented in such a way that the lip (15) can be dismantled without breaking the link between the frame (16) and the panel (17). Moreover, the internal, rear part (15a) of the lip (15) normally covers the front part (17a) of the panel (17), as well as the members (22, 24) ensuring the link between the latter and the frame (16).

DESCRIPTION
 1. TECHNICAL FIELD
 The invention relates to an air intake structure usable on any type of
 aircraft engine or turbo-jet having an air intake.
 In such a structure, the invention more specifically applies to the link
 between an air intake lip, a front reinforcing frame and an acoustic panel
 placed immediately behind the lip in the extension thereof.
 By convention, the terms "front" and "rear" are used throughout the text
 using as the reference the front and rear of the engine.
 Comparably, the terms "internal" and "external" are used throughout the
 text using for the reference the complete engine.
 Conversely and still in accordance with convention, in the absence of a
 precision to the contrary, the terms "interior" and "exterior" are used to
 designated the position or orientation of parts with respect to the air
 intake structure considered in isolation.
 2. PRIOR ART
 As is very diagrammatically shown in perspective of FIG. 1, an aircraft
 engine comprises a central part 1 housing the actual engine and an annular
 part 2, called a pod, coaxially surrounding the central part of the engine
 and defining therewith an annular or fan duct 3. A fan, driven by the
 central part 1 of the engine, is placed at the inlet of the fan duct 3.
 The front part of the pod 2 constitutes an air intake structure 4, whose
 function is in particular to ensure the aerodynamic flow of air on the one
 hand towards the fan duct 3 and on the other around the pod
 As shown in section and on a larger scale in FIG. 2, which illustrates a
 first known method for implementing the air intake structure 4, such a
 structure conventionally comprises on the side of the fan duct 3, an air
 intake lip 5, a front reinforcing frame 6 and an acoustic panel 7.
 In cross-section, the air intake lip 5 is in the form of a rearwardly open
 U. It forms the external envelope of the front part of the air intake
 structure. It ensures the splitting of the air between the portion
 penetrating the fan duct and the portion flowing around the pod.
 The front reinforcing frame 6 is placed in the interior and to the rear of
 the air intake lip 5. It ensures the mechanical strength of the front part
 of the pod and aids in maintaining shape and dimensioning. To this end,
 the front reinforcing frame 6 is fixed to the interior of the air intake
 lip 5, on the side of the fan duct and the outside of the engine, e.g. by
 means of rivets (illustrated by mixed lines 8).
 The acoustic panel 7 forms the external envelope of the pod, to the rear of
 the air intake lip 5 and on the side of the fan duct 3. Said panel has a
 structure able to attenuate the noise produced by the central part of the
 engine and in particular the fan. In practice, this structure is normally
 of the composite, sandwich type, i.e. the panel 7 integrates a honeycomb
 core. In the known assembly method illustrated in FIG. 2, the front part
 7a of the acoustic panel 7, which as no honeycomb core, is externally
 covered by the rear part 5a of the air intake lip 5 and fixed thereto by
 rivets (illustrated by mixed lines 9).
 In view of its front position, the air intake lip 5 is exposed to damage
 and deterioration, which can in particular be due to erosion as a result
 of the air flow entering the engine, rain, hail, particles present in the
 atmosphere, etc. It can also be a question of accidental damage due to
 flight impacts (birds) or ground impacts, during the taxying phase
 (throwing up of pebbles) or during handling.
 In order to ensure maintenance, it is clear that the air intake lip 5 of an
 aircraft engine must be frequently dismantled. In order to facilitate
 interventions, it is desirable for such a dismantling to be performable
 easily and rapidly. Therefore maximum importance is attached to the method
 used for assembling the air intake lip, the front reinforcing frame and
 the acoustic panel.
 In the known assembly method illustrated by FIG. 2, the air intake lip 5 is
 fixed on the one hand to the front reinforcing frame 6 and on the other to
 the acoustic panel 7, without there being any link between frame and
 panel. Thus, on dismantling the air intake lip 5 by removing the rivets 8
 and 9, there is no longer any connection between the front reinforcing
 frame 6 and the acoustic panel 7. Thus, the assembly loses all its
 rigidity, its dimensional references, etc.
 To obviate this disadvantage, specific equipment and tools have been
 designed in order to restore from the outset a certain rigidity to the
 pod. However, the putting into place of such equipment, which surround the
 external structure of the air intake, causes heavy handling, which is very
 disadvantageous for the maintenance personnel. This also involves the
 equipment being present at the repair locations, which is also very
 disadvantageous.
 FIG. 3 shows in section another known method for assembling the air intake
 lip 5, the front reinforcing frame 6 and the acoustic panel 7. In this
 case, the rear part 5a of the air intake lip 5 and the front part 7a of
 the acoustic panel 7 are placed end to end in an extension of one another.
 Each of these two parts is then fixed by rivets (respectively illustrated
 by mixed lines 8 and 9) on a rear part 6a of the front reinforcing frame
 6, placed in the interior of parts 5a and 7a of lip 5 and panel 7.
 When this method is used, the dismantling of the air intake lip 5 takes
 place by removing the rivets 8 and does not eliminate the link provided by
 the rivets 9 between the acoustic panel 7 and the front frame 6.
 However, this method has the disadvantage of leaving uncovered the front
 end and leading edge of the acoustic panel 7 in the fan duct 3. This front
 end of the panel 7, as well as its leading edge, are consequently exposed
 to phenomena such as erosion, delamination, water introduction, etc. In
 view of the fact that the acoustic panel 7 is normally made from a
 composite material, this leads to a difficultly acceptable speeding up of
 damage to said panel.
 DESCRIPTION OF THE INVENTION
 The invention specifically relates to an air intake structure in which the
 link between the air intake lip, the front reinforcing frame and the
 acoustic panel is such that the disadvantages of the prior art methods are
 eliminated. In particular, the dismantling of the lip does not eliminate
 the link between the frame and the panel and the front end and leading
 edge of said panel are not exposed to the air flow in the fan duct.
 According to the invention, this result is obtained by means of an air
 intake structure for an aircraft engine comprising:
 an air intake lip with a rearwardly open U-shaped cross-section and having
 an internal, rear part,
 a front reinforcing frame installed in the air intake lip,
 an acoustic panel having a front part fixed to the front reinforcing frame
 by first fixing means in order to form a rigid assembly and
 second fixing means, independent of the first fixing means, for fixing the
 internal, rear part of the air intake lip to said rigid assembly,
 characterized in that the internal, rear part of the air intake lip covers
 the front part of the acoustic panel and the first fixing means.
 In a first embodiment of the invention, the front part of the acoustic
 panel is placed in the extension of an internal, rear part of the
 reinforcing frame and the internal, rear part of the air intake lip is
 fixed on the one hand to the rear, internal part of the reinforcing frame
 and on the other hand to the front part of the acoustic panel by second
 fixing means.
 In this case, the first fixing means advantageously comprise a plurality of
 linking or joining parts, which are circumferentially distributed about a
 longitudinal axis of the engine and overlap the rear, internal part of the
 front reinforcing frame and the front part of the acoustic panel within
 the structure. The first fixing means also comprise fixing members, such
 as rivets, linking the linking parts on the hand to the rear, internal
 part of the front reinforcing frame and on the other hand to the front
 part of the acoustic panel.
 In order to compensate a possible thickness difference, shims, which are
 also traversed by the fixing members, can be placed between the linking
 parts and the rear, internal part of the front reinforcing frame.
 Advantageously, the second fixing means then comprise other fixing members,
 linking the rear, internal part of the air intake lip on the one hand to
 the rear, internal part of the front reinforcing frame and on the other to
 the front part of the acoustic panel, at locations offset with respect to
 the linking parts.
 According to a second embodiment of the invention, the front part of the
 acoustic panel is offset towards the interior of the structure, with
 respect to the rear, internal part of the front reinforcing frame. The
 first fixing means, such as rivets, then comprise at least one linking
 part, as well as fixing members linking said part on the one hand to the
 rear, internal part of the front reinforcing frame and on the other to the
 front part of the acoustic panel within the structure.
 In this second embodiment of the invention, the front part of the acoustic
 panel can be substantially parallel to the rear, internal part of the
 front reinforcing frame. The first fixing means then comprise two linking
 parts in the form of rectangular, circular extrusions, whereof two
 contiguous flanges, oriented substantially radially with respect to the
 longitudinal axis of the engine, are fixed to one another and whereof the
 other flanges are respectively fixed to the rear, internal part of the
 front reinforcing frame and to the front part of the acoustic panel by the
 aforementioned fixing means.
 The contiguous flanges of the two linking parts can both be oriented
 towards the interior of the structure. As a variant, they can also be
 oriented towards the interior of the structure for the part fixed to the
 rear, internal part of the front reinforcing frame and towards the
 exterior of the structure for the part fixed to the front part of the
 acoustic panel.
 In the second embodiment of the invention, the front part of the acoustic
 panel can also be obliquely oriented so as to terminate in the vicinity of
 the trailing edge of the front reinforcing frame. The first fixing means
 then comprise a single linking part in the form of an open, circular
 extrusion, fixed on the one hand to the rear, internal part of the front
 reinforcing frame and on the other to the front part of the acoustic panel
 by linking means.
 In the second embodiment of the invention, the second fixing means
 advantageously comprise other fixing members such as rivets linking the
 rear, internal part of the air intake lip to the rear, internal part of
 the front reinforcing frame, whilst traversing the linking part.

DETAILED DESCRIPTION OF SEVERAL PREFERRED EMBODIMENTS OF THE INVENTION
 FIGS. 4 and 5 illustrate a first embodiment of an air intake structure 14
 for an aircraft engine in accordance with the present invention. In
 conventional manner, said structure 14 comprises an air intake lip 15, a
 front reinforcing frame 16 and an acoustic panel 17.
 The air intake lip 15 has a U-shaped cross-section which is open towards
 the rear and forms the external envelope of the front part of the engine
 pod.
 The front reinforcing frame 16 is installed in the interior and to the rear
 of the lip 15 and also roughly has a rearwardly open, U-shaped
 cross-section. It serves to ensure the rigidity and shape and dimensional
 maintenance of the front part of the pod.
 Finally, the acoustic panel 17 forms the external envelope of the pod, on
 the side of the engine fan duct 13, to the rear of the air intake lip 15.
 It is made from a composite, sandwich material including a honeycomb core
 and internal and external skins. In the front part 17a of the panel 17,
 which does not have a honeycomb core, said skins are connected to one
 another.
 On the external periphery of the pod, an external, rear part 16b of the
 front reinforcing frame 16 is fixed to the interior of a front part 20b of
 an external envelope 20, e.g. by means of rivets symbolized by the mixed
 lines 21. A rear, external part 15b of the air intake lip 15 is fixed to
 the rear, external part 16b, in the extension of part 20b, e.g. by means
 of rivets symbolized by the mixed lines 28.
 On the internal periphery of the pod, around the fan duct 13, an internal,
 rear part 16a of the front reinforcing frame 16 is fixed to the front part
 17a of the acoustic panel 17 by first fixing means 19, which can assume
 different forms, as will be shown hereinafter. Moreover, the rear,
 internal part 15a of the lip 15 is fixed at least to the rear, internal
 part 16a of frame 16 by second fixing means 18, independent of the first
 fixing means 19, and which will be described hereinafter. Moreover and in
 accordance with the invention, the rear, internal part 15a of the air
 intake lip 15 covers both the rear part 16a of the frame 16, the front
 part 17a of the panel 17 and the first fixing means 19. Due to this
 arrangement and as is shown in mixed line form in FIG. 4, the removal of
 the second fixing means 18 and rivets 28 makes it possible to dismantle
 the air intake lip 15 without eliminating the link between the frame 16
 and the panel 17, ensured by the first fixing means 19. Thus, the frame 16
 and panel 17 form an assembly which remains rigid following the
 dismantling of the second fixing means 18. Moreover, the arrangement is
 such that the front part 17a of the acoustic panel 17 is completely
 covered by the rear part 15a of the air intake lip 15. This prevents any
 accelerated damage risk for the acoustic panel 17.
 In the first embodiment illustrated in FIGS. 4 and 5, the front part 17a of
 the acoustic panel 17 is placed in the extension of the rear, internal
 part 16a of the front reinforcing frame 16.
 In this case, the first fixing means 19 comprise a plurality of linking
 parts 22, as well as fixing members, such as rivets 24, linking the parts
 22 on the one hand to the rear, internal part 16a of the frame 16 and on
 the other to the front part 17a of the panel 17.
 As is more specifically illustrated by FIG. 5, the parts 22 are
 approximately H-shaped parts, which are regularly distributed over the
 entire circumference of the structure around the longitudinal axis of the
 engine. More specifically, the parts 22 overlap the parts 16a and 17a
 towards the interior of the air intake structure, so that the central
 branch of the H is positioned along the junction line between these two
 parts. Each part 22 is then fixed by two rivets 24 to the rear, internal
 part 16a of the frame 16 and by two other rivets 24 to the front part 17a
 of the acoustic panel 17.
 To take account of the fact that the front part 17a of the acoustic panel
 17 is generally thicker than the rear, internal part 16a of the front
 reinforcing panel 16, preferably a shim 26 (FIG. 4) is placed between part
 16a and each of the parts 22.
 As is more particularly illustrated in FIG. 4, the rivets 24 traverse the
 parts 22, as well as part 16a or part 17a. More specifically, the rivets
 24 have milled heads, housed in hollowed out portions machined in parts
 16a and 17a towards the exterior of the structure. This arrangement makes
 it possible to completely house the rivet heads in recesses. In other
 words, the rivet heads are flush with the surfaces of parts 16a and 17a
 turned towards the exterior of the structure.
 Moreover, the rear, internal part 15a of lip 15 covers parts 16a and 17a,
 as well as the heads of rivets 24. The second fixing means by which said
 part 15a is fixed to parts 16a and 17a are then constituted by fixing
 members such as rivets 18 (illustrated by mixed lines in FIG. 4). Certain
 of these rivets 18 fix the lip 15 to the frame 16 whilst traversing parts
 15a and 16a thereof at locations offset with respect to the parts 22 and
 as is more particularly illustrated in FIG. 5. Other rivets 18 traverse
 part 15a of lip 15, as well as part 17a of panel 17 at locations which are
 also offset with respect to parts 22.
 It is therefore possible to dismantle the air intake lip 15 by removing the
 rivets 18 and 28 without there being any risk of eliminating the link
 ensured between the frame 16 and acoustic panel 17 by the second fixing
 means 19. Thus, the rivets 24 are masked by the lip 15. Therefore the
 maintenance personnel cannot inadvertently pierce them when the air intake
 lip is removed.
 With reference to FIGS. 6A, 6B and 6C a description will now be given of
 three variants of a second embodiment of the invention.
 This second embodiment of the invention essentially differs from the first
 by the fact that instead of being placed in the extension of the rear,
 internal part 16a of the frame 16, the front part 17a of the acoustic
 panel 17 is displaced towards the interior of the structure with respect
 to said part 16a.
 More specifically, in the variants of FIGS. 6A and 6B, the front part 17a
 of the acoustic panel 17 is oriented substantially parallel to the rear,
 internal part 16a of the front reinforcing frame 16. Under these
 conditions, the first fixing means 19 linking the frame 16 to the panel 17
 comprise two linking parts 30 and 32, both having the shape of a
 rectangular, circular extrusion.
 In these two variants, a first cylindrical flange of the linking part 30 is
 fixed to the interior of the rear, internal part 16a of the frame 16 by
 fixing members such as rivets 34 and a first cylindrical flange of the
 linking part 32 is fixed to the interior of the front part 17a of the
 panel 17 by fixing members such as rivets (illustrated by the mixed lines
 36).
 In the variant of FIG. 6A, the second flanges of linking parts 30, 32 both
 extend radially towards the interior of the structure and are fixed to one
 another by fixing members such as rivets (illustrated by mixed lines 38).
 In the variant of FIG. 6B, the second flange of the linking part 30 extends
 radially towards the interior of the structure and the second flange of
 the linking part 32 extends radially towards the exterior of the
 structure. These two flanges are also fixed to one another by fixing
 members such as rivets (illustrated by the mixed lines 38).
 In the variant illustrated in FIG. 6C, the front part 17a of the acoustic
 panel 17 is oriented obliquely, so that its leading edge terminates in the
 vicinity of the internal, trailing edge of the rear part 16a of frame 16.
 Under these conditions, the first fixing means 19 linking the frame 16 to
 the panel 17 comprise a single linking part 30 in the form of an open,
 circular extrusion. A first cylindrical flange of said linking part is
 fixed in the interior of the rear, internal part 16a of frame 16 by fixing
 members such as rivets 34 and the second flange of the linking part 30 is
 fixed in the interior of the front part 17a of panel 17 by fixing members
 such as rivets (illustrated by mixed lines 36).
 In the three variants of the second embodiment of the invention described
 hereinbefore with reference to FIGS. 6A to 6C, the second fixing means 18
 comprise fixing members such as rivets, which traverse the parts 15a and
 16a. As a function of the particular case, these rivets 18 can also
 traverse the corresponding flange of part 30 or can be placed level with
 not shown windows provided for this purpose in said flange.
 The heads of the rivets 34 are also housed in hollows machined in the
 internal face of part 16a, so as to be flush with said face, as in the
 previously described first embodiment.
 The rear, internal part 15a of the air intake lip 15 is also extended
 towards the rear, so as to ensure the continuity with the surface of the
 acoustical panel 17 turned towards the fan duct, whilst integrally
 covering the front part 17a of panel 17, as well as the first fixing means
 19.
 As in the first embodiment of the invention, this arrangement makes it
 possible to reserve the integrity of the link between frame 16 and panel
 17 when lip 15 is dismantled, whilst ensuring the protection of the front
 part 17a of panel 17 when the lip 15 is in place. This arrangement also
 avoids any risk of an accidental dismantling of the link between frame 16
 and panel 17 during the removal of lip 15, because the first fixing means
 19 connecting the frame and panel are entirely covered by the rear,
 internal part 15a of lip 15.
 Obviously, the invention is not limited to the embodiments described in
 exemplified manner hereinbefore. Thus, the forms and shapes given to the
 front reinforcing frame 16, to the front part 17a of acoustic panel 17 and
 to the parts for linking these two structural elements can undergo various
 modifications without passing outside the scope of the invention. In
 addition, the parts 22 can be fixed to the frame 16 at a location
 displaced towards the front and towards the interior of the air intake
 structure. Moreover, instead of being used in one piece, the air intake
 lip can comprise a rear, internal part divided up into two sections
 respectively surrounding the rear, internal part of frame 16 and the front
 part of panel 17 and fixed thereto.