Abstract:
A method is provided for providing, e.g. manufacturing, a thrust reverser inner fixed structure. The method includes (a) providing an acoustic inner barrel that includes a first honeycomb core and an annular inner skin radially inward of the first honeycomb core; (b) providing a bifurcation panel that includes a second honeycomb core; and (c) arranging a corner fitting between and attaching the corner fitting to the acoustic inner barrel and the bifurcation panel.

Description:
[0001]    This application claims priority to U.S. Patent Appln. No. 61/803,048 filed Mar. 18, 2013. 
     
    
     FIELD OF TECHNOLOGY 
       [0002]    The invention relates to the field of protective systems for aircraft propulsion system components and in particular, to a liquid interface diffusion (LID) bonded titanium inner fixed structure (IFS) with bonded-in corner fitting for an aircraft engine nacelle system. 
       RELATED ART 
       [0003]    A nacelle system is the aerodynamic structure that surrounds an aircraft engine. It includes parts commonly referred to as engine cowling, but the nacelle system typically includes other components as well including the inlet cowl, fan cowl, thrust reverser, core cowl and nozzle. 
         [0004]      FIG. 1  illustrates an assembled, complete aircraft propulsion assembly  100 , and  FIG. 2  shows an exploded view of the aircraft propulsion assembly  100  of  FIG. 1 . Referring to  FIGS. 1 and 2 , components of the aircraft propulsion system include an engine assembly  102  at the tail end of which are an exhaust cone  104  and an exhaust nozzle  106 . The forward end of the engine assembly  102  includes a nacelle inlet  110  having a nacelle inlet lip  112 . Aft of the nacelle inlet  110  is a fan cowl  120  comprising fan cowl halves  122 ,  124 . A thrust reverser  130  comprising thrust reverser halves  132 ,  134  is aft of the fan cowl  120 . A pylon/strut assembly  140  connects the aforementioned component to a wing of an aircraft. The thrust reverser  130  includes an outer fixed structure, a translating sleeve, and an inner fixed structure as shown in  FIG. 3 . 
         [0005]      FIG. 3  shows thrust reverser half  330  which exposes a one half section  332  of an inner fixed structure (IFS) formed in two “clam-shell” halves, only one clam-shell half being shown. It is understood that the unseen second section is essentially a mirror image of the section  332 . The IFS section has a forward end  334  with an exterior surface  335  that faces in the direction of the engine and fan cowl, and an aft end  336  with an exterior surface (not shown) that faces in the direction of the exhaust nozzle. The IFS halves  332  are connected together by latches  338  at the bottom and hinged to the pylon  140  ( FIG. 2 ) at the top. Bumpers  340  provide a structural bridge between the gaps that separates the two IFS halves  332 . The structural bridge provides a hoop load path to resist the crushing pressure of the fan air stream upon the barrel sections and bifurcations. 
         [0006]    The inner fixed structure illustrated in  FIG. 3  encases portions of the engine assembly located between the engine fan case and the nozzle. The inner fixed structure is configured to create an aerodynamically smooth path for air, and a fire and heat boundary by enclosing portions of the engine assembly. 
         [0007]    The inner fixed structure section  332  is a one-piece honeycomb sandwich comprising an inner skin, an outer skin and a cellular core between the inner and outer skins, all bonded together. Referring to  FIG. 4 , the honeycomb sandwich is typically an acoustic structure with an imperforate annular inner skin  402 , a perforated annular outer skin  404 , and a cellular core  406  suitable for use in acoustic applications. The inner skin  402  may be &amp;Lined from a metallic or a graphite composite material (e.g., carbon fiber); the outer skin may also be formed from a metallic or graphite composite material; and the cellular core  406  may be formed from a graphite composite material. 
         [0008]    Referring again to  FIG. 3 , the inner fixed structure section  332  has an upper bifurcation wall portion  342 , a lower bifurcation wall portion  344  and inner acoustic barrel portion  346  formed between the two wall portions  342 ,  344 . The honeycomb sandwich is acoustic wherever possible to control noise, but is interrupted by a number of structures and formations such as cooling holes  348 , the bumpers  340 , the latches  338 , mounting members and the like. 
         [0009]    Aft of its forward end where it interfaces with the fan section, the diameter of the inner acoustic barrel portion  346  increases to form an enlarged barrel portion  350  of suitable size and shape to enclose the rear engine mounts and the turbine section of the engine. The inner acoustic barrel portion  346  then decreases in diameter to wrap around the forward portion of the exhaust nozzle  106  ( FIG. 2 ). 
         [0010]    Acoustic treatment of an inner fixed structure is always at a premium because of the large number of openings and attachments. 
         [0011]    One potential opportunity for increasing acoustic treatment [area] is at the corner joints between the barrel  346  and the bifurcations  342 ,  344 . This is generally achieved by using a high density core to form the corner piece. However, the high density core cannot be formed to a tight radius, nor is it suitable for acoustic treatment (the cells are too close together). Consequently, a lot of potential acoustic area is lost, as shown in  FIG. 5 . 
         [0012]    In conventional inner fixed structures with graphite-epoxy (GR-EP) skins, a high density core is placed in the corner with doubler plies added to both skins in this zone to assure structural integrity in this highly loaded area. The core density and the doubler plies render this construction not suitable for acoustic treatment. In addition, the graphite-epoxy high density core must be thermally protected against high engine core temperatures and thus IFSs require insulation blankets. 
         [0013]    There is a need for an inner fixed structure which increases the acoustic treatment for noise suppression in corners/joints of the inner fixed structure between the barrel and the bifurcations. 
       SUMMARY OF THE INVENTION 
       [0014]    According to an aspect of the invention, a thrust reverser inner fixed structure comprises an acoustic inner barrel, a first bifurcation panel that includes a bifurcation panel honeycomb core disposed between panel inner and outer skins, and a corner fitting, wherein the corner fitting is liquid interface diffusion (LID) bonded to the acoustic inner barrel and the first bifurcation panel. 
         [0015]    According to another aspect of the invention, a thrust reverser inner fixed structure comprises an acoustic inner barrel that comprises a barrel honeycomb core having an annular interior skin radially inward of the first honeycomb core, a first bifurcation panel, and a corner fitting, wherein the corner fitting is LID bonded to the acoustic inner barrel and the first bifurcation panel. 
         [0016]    According to another aspect of the invention, a thrust reverser inner fixed structure comprises an acoustic inner barrel that includes a barrel honeycomb core having an annular interior skin radially inward of the first honeycomb core, a first bifurcation panel that includes a bifurcation panel honeycomb core disposed between panel inner and outer skins, and a corner fitting, wherein the corner fitting is LID bonded to the acoustic inner barrel and the first bifurcation panel. 
         [0017]    According to another aspect of the invention, a method is provided for providing a thrust reverser inner fixed structure. The method includes (a) providing an acoustic inner barrel that includes a first honeycomb core and an annular inner skin radially inward of the first honeycomb core; (b) providing a bifurcation panel that includes a second honeycomb core; and (c) arranging a corner fitting between and attaching the corner fitting to the acoustic inner barrel and the bifurcation panel. 
         [0018]    According to a further aspect of the invention, another method is provided for providing a thrust reverser inner fixed structure. The method includes (a) forming an acoustic inner barrel that includes a first honeycomb core; (b) forming a bifurcation panel that includes a second honeycomb core; (c) forming a corner fitting independent of the acoustic inner barrel and the bifurcation panel; and (d) connecting the acoustic inner barrel to the bifurcation panel with the corner fitting. 
         [0019]    In any of the above embodiments, the corner fitting may be titanium. The barrel honeycomb core may also or alternatively include a titanium annular inner skin and/or a titanium honeycomb acoustic core. The bifurcation panel may also or alternatively include a titanium skin and/or a titanium honeycomb acoustic core. 
         [0020]    In any of the above embodiments, the titanium honeycomb core may be formed, for example, by super plastic formation (SPF) processing or 360° SPF processing. 
         [0021]    In any of the above embodiments, the corner fitting may include a first set of flanges that form a first channel, and/or a second set of flanges that form a second channel. An end surface/face skin of the bifurcation panel may be LID bonded or otherwise attached to the first set of flanges, and the end surface/face skin of the barrel may be LID bonded or otherwise attached to the second set of flanges. 
         [0022]    In any of the above embodiments, the corner fitting may be attached to the acoustic inner barrel and/or the bifurcation panel by liquid interface diffusion (LID) bonding. The corner fitting may also or alternatively be attached to the acoustic inner barrel and/or the bifurcation panel by an adhesive. The corner fitting may also or alternatively be attached to the acoustic inner barrel and/or the bifurcation panel by one or more mechanical fasteners. 
         [0023]    In any of the above embodiments, a portion of the corner fitting may be inserted into a channel in the acoustic inner barrel. A portion of the corner fitting may also or alternatively be inserted into a channel in the bifurcation panel. A portion of the acoustic inner barrel may also or alternatively be inserted into a channel in the corner fitting. A portion of the bifurcation panel may also or alternatively be inserted into a channel in the corner fitting. 
         [0024]    In any of the above embodiments, the corner fitting may be formed discretely from the acoustic inner barrel and/or the bifurcation panel. 
         [0025]    In any of the above embodiments, the corner fitting may be formed by one or more of the following processes: casting and/or machining. 
         [0026]    The foregoing features and the operation of the invention will become more apparent in light of the following description and the accompanying drawings. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0027]      FIG. 1  illustrates an assembled, complete aircraft propulsion assembly; 
           [0028]      FIG. 2  shows an exploded view of the aircraft propulsion assembly; 
           [0029]      FIG. 3  shows a thrust reverser half which exposes a one half section of an inner fixed structure (IFS) formed in two “clam-shell” halves; 
           [0030]      FIG. 4  illustrates a honeycomb sandwich comprising an inner skin, an outer skin and a cellular core between the inner and outer skin panels; 
           [0031]      FIG. 5  is a more detailed illustration of a prior art non-acoustic corner between the inner acoustic barrel and the bifurcation panel; 
           [0032]      FIG. 6  illustrates a thrust reverser inner fixed structure component comprising an acoustic inner barrel that comprises a honeycomb core, a first bifurcation panel that includes a honeycomb core, and a corner fitting, wherein the corner fitting is LID bonded to the acoustic inner barrel and the first bifurcation panel; 
           [0033]      FIG. 7  is a pictorial illustration of an embodiment of the corner fitting; 
           [0034]      FIG. 8  is an isometric view of the embodiment of the corner fitting, along with a cross sectional illustration of the embodiment of the corner fitting; 
           [0035]      FIG. 9  is a side sectional illustration of the corner fitting overlaid on a curved portion of an acoustic sandwich panel; 
           [0036]      FIG. 10  is a side sectional illustration of a corner fitting connecting an acoustic inner barrel with a bifurcation panel; 
           [0037]      FIG. 11  is a side sectional illustration of another corner fitting connecting an acoustic inner barrel with a bifurcation panel; 
           [0038]      FIG. 12  is a side sectional illustration of another corner fitting connecting an acoustic inner barrel with a bifurcation panel; 
           [0039]      FIG. 13  is a pictorial illustration of the barrel with the honeycomb core exposed (i.e., the annular inner skin removed), and the corner fitting; and 
           [0040]      FIG. 14  is a pictorial illustration of the barrel with annular inner skin of the acoustic inner barrel covering the honeycomb core, and the barrel joined to the corner fitting. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0041]      FIG. 6  illustrates a thrust reverser inner fixed structure component  600  comprising an acoustic inner barrel  602  that includes a barrel honeycomb core  604 , a first bifurcation panel  606  that includes a bifurcation panel honeycomb core  608 , and a corner fitting  610 . This corner fitting  610  is attached to the barrel  602  and/or the first bifurcation panel  606 . The corner fitting  610 , for example, may be liquid interface diffusion (LID) bonded and/or otherwise attached to the barrel  602  and the first bifurcation panel  606 . LID bonding combines the attributes of brazing and diffusion bonding to attain near-base metal properties in a bonded sandwich panel. The result is a lightweight component that can stand up to harsh exhaust environments. 
         [0042]    The barrel honeycomb core  604 , the bifurcation panel honeycomb core  608  or both the barrel honeycomb core  604  and the bifurcation panel honeycomb core  608  may each be discretely formed from titanium. For example, the barrel  602  may include one or more titanium skins and a titanium honeycomb acoustic core (or equivalent material) between the skins, so as not to require thermal insulation to protect the structure. It is contemplated that the bifurcation panel  606  may be of a similar construction or of dissimilar materials (such as GR-EP) and/or constructions, if they are suitably isolated or insulated from engine core heat. 
         [0043]      FIG. 7  is a pictorial illustration of the corner fitting  610 . The corner fitting  610  is preferably a titanium component that may, for example, be a machined casting or machined. The corner fitting  610  includes a web  612  and a plurality of flanges  613 - 616  that form first and second channels  618 ,  620 .  FIG. 8  is an isometric view of the embodiment of the corner fitting  610 , along with a cross sectional illustration of the embodiment of the corner fitting  610 . 
         [0044]      FIG. 9  is a side sectional illustration of the corner fitting  610  overlaid on a curved portion  900  of an acoustic sandwich panel  902 . Since the corner fitting  610  may be cast and/or machined as described above, an inner radius R 1  of the corner fitting  610  may be (e.g., about six times) smaller than an inner radius R 2  of the curved portion  900 , which is intended to represent a minimum radius the panel  902  may be bent without crushing and/or otherwise losing structural integrity of its honeycomb core. It is worth noting that a curved portion of an acoustic sandwich panel such as the portion  900  is typically ineffective for noise attenuation. However, the relatively small radius R 1  of the corner fitting  610  enables the acoustic inner barrel  602  and/or the bifurcation panel  606  (see  FIG. 6 ) to be enlarged, which may increase their effective area for noise attenuation. 
         [0045]    Referring to  FIG. 10 , the bifurcation panel  606  is mated and attached to the corner fitting  610 . An end portion  622  of the core  608  of  FIG. 10 , for example, is inserted into the channel  618 . First and/or second skins  624  and  626  of the bifurcation panel  606  are respectively LID bonded to the flanges  613  and  614 . The first and/or the second skins  624  and  626  may also or alternatively be bonded to the flanges  613  and  614  using one or more techniques other than LID bonding such as, for example, welding, brazing and/or adhering with an adhesive (e.g., epoxy). In addition, the first and/or the second skins  624  and  626  may also or alternatively be mechanically attached to the flanges  613  and  614  using one or more rivets, screws, bolts or any other type of mechanical fasteners. 
         [0046]    The acoustic inner barrel  602  is also mated and attached to the corner fitting  610 . An end portion  628  of the core  604  of  FIG. 10 , for example, is inserted into the channel  620 . First and/or second skins  630  and  632  of the barrel  602  are respectively LID bonded to the flanges  615  and  616 . The first and/or the second skins  630  and  632  may also or alternatively be bonded to the flanges  615  and  616  using one or more techniques other than LID bonding such as, for example, welding, brazing and/or adhering with an adhesive (e.g., epoxy). In addition, the first and/or the second skins  630  and  632  may also or alternatively be mechanically attached to the flanges  615  and  616  using one or more rivets, screws, bolts or any other type of mechanical fasteners. 
         [0047]    With the interface described above and illustrated in  FIG. 10 , a portion  634  of a surface of the corner fitting  610  between the skins  624  and  632  is left exposed. A portion  636  of an opposite surface of the corner fitting  610  between the skins  626  and  630  is also left exposed. However, in other embodiments such as that illustrated in  FIG. 11 , the acoustic inner barrel  602  and bifurcation panel  606  may share one or more skins  638  and  640 . Each of these shared skins  638  and  640  respectively overlaps and is attached to the corner fitting  610 . In this manner, the corner fitting  610  provides a structural core at the corner joint between the barrel  602  and the panel  606 . 
         [0048]      FIG. 12  illustrates an alternate embodiment corner fitting  610 ′ for connecting the acoustic inner barrel  602  to the bifurcation panel  606 . In contrast to the corner fitting  610  of  FIG. 10 , the corner fitting  610 ′ is configured having a plurality of recesses  642 - 645  rather than the flanges  613 - 616 . End portions  646  and  648  of the corner fitting  610 ′, which form the recesses  642 - 645 , respectively extend into channels  650  and  652  of the barrel  602  and the panel  606 . The skins  624 ,  626  and  630 ,  632 , which may form the channels  650  and  652 , respectively overlap the end portions  646  and  648  and are seated within the recesses  642 - 645 . One or more of the skins  624 ,  626 ,  630  and  632  are respectively attached (e.g., LID bonded) to the end portions  646  and  648  and/or a central portion  654  of the corner fitting  610 ′. 
         [0049]      FIG. 13  is a pictorial illustration of the honeycomb core  604  of the acoustic inner barrel  602 , and the corner fitting  610 . The honeycomb core may be formed from titanium. 
         [0050]      FIG. 14  is a pictorial illustration of annular inner skin  612  of the acoustic inner barrel covering the honeycomb core  604 , and the barrel joined to the corner fitting  610 . 
         [0051]    One titanium manufacturing option is the use of 360° SPF process, which enables the forming of axis symmetric-skins These may then be LID bonded into core cowl structures. Cowls would subsequently be trimmed into two or three high temperature sections to contain engine core heat. A primary advantage will be that this allows the now thermally isolated bifurcation structures to be manufactured of lighter/cheaper materials. 
         [0052]    A thrust reverser inner fixed structure component according to aspect of the present invention provides a blanket-less IFS structure that can withstand elevated engine core temperatures without the need for an insulating blanket. 
         [0053]    Although titanium is a preferred metal for the corner fitting, the first honeycomb core and the annular skins of the acoustic inner barrel, as well as the honeycomb core of the bifurcation panel and its annular skins, it is contemplated that one or more of these elements may be formed from metals such as, for example, aluminum or inconel. If aluminum is used, then an insulting blanket may be provided to protect against elevated engine core temperatures. It is also contemplated that one or more of the skins and/or other elements may be formed from a composite material such as carbon fiber. For example, the barrel  602  and the corner fitting  610  may be formed from metal and LID bonded together, whereas one or more of the bifurcation panel skins may be formed from a composite and adhered and/or mechanically attached to the corner fitting  610 , or vice versa. 
         [0054]    While various embodiments of the present invention have been disclosed, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible within the scope of the invention. For example, the corner fitting and the acoustic inner barrel may interface in the manner shown in  FIG. 10  whereas the corner fitting and the bifurcation panel may interface in the manner shown in  FIG. 12 , or vice versa. In another example, one or more of the skins may be attached to the corner fitting in a different manner than one or more of the skins. Accordingly, the present invention is not to be restricted except in light of the associated claims and their equivalents.