Abstract:
A shroud panel ( 60 ) is attached to a wing skin overhang ( 28 ) by a series of pivoting butt straps ( 86 ) to permit relative strains to occur.

Description:
This application claims priority to UK Patent Application No. 1120996.2 filed 7 Dec. 2011, the entire content of which is hereby incorporated by reference. 
     BACKGROUND OF INVENTION 
     The present invention is concerned with apparatus for attachment of panels to aircraft aerodynamic structures. More specifically, the present invention is concerned with an apparatus for attaching shroud panels to the trailing edge of aircraft wing covers. 
     Known aircraft aerodynamic structures such as wings and stabilisers comprise a rear spar, abutted on its top and bottom surfaces by upper and lower skins or covers. In order to provide a smooth aerodynamic surface rearward of the spar, wings and stabilisers are provided with shroud panels, which extend rearward of the spar and act as a continuation of the skins. 
     A problem in the attachment of such shroud panels at the trailing edge of wings and stabilisers is that strains experienced in flight differ between the wing or stabiliser and the shroud panel. Such strain differentials can cause excessive stresses to develop, requiring frequent service checks and component replacement and/or repair. 
     As a result, existing attachment schemes between the shroud panels and the aerodynamic structure are quite bulky in order to handle the stresses imparted thereon. This increases the weight and cost of the aircraft. 
     SUMMARY OF INVENTION 
     It is an aim of the present invention to overcome, or at least mitigate this problem. 
     According to a first aspect of the present invention there is provided an aircraft fixed aerodynamic structure assembly comprising:
         a fixed aerodynamic structure component,   a shroud panel,   in which the shroud panel is attached to the fixed aerodynamic structure component by a plurality of attachment members, each attachment member being connected to at least one of the shroud panel and the fixed aerodynamic structure component by an articulated joint.       

     According to a second aspect of the present invention there is provided an aircraft shroud assembly comprising:
         a shroud panel,   a plurality of attachment members extending from an edge of the shroud panel in use, each attachment member being connected to the shroud panel via an articulated joint.       

     By “aircraft fixed aerodynamic structure” we mean a structure of the aircraft attached to the fuselage which controls or influences flight, such as an aircraft wing, vertical stabiliser or horizontal stabiliser. 
     Preferably, the attachment members pivot at one or both ends, and are provided as pivoting butt straps. 
     Advantageously, the provision of such pivoting butt straps allows relative movement between adjacent locations on the shroud panel and wing or stabiliser. Therefore the stresses produced in both parts by any strain differential resulting from thermal or force effects are reduced. 
     Preferably the attachment members are pivotably connected to both the shroud panel and aerodynamic structure component. 
     Preferably at least one of the butt straps has a range of motion limited by an abutment with the shroud panel or the wing trailing edge component. This may be defined by a shoulder formed in the butt strap, which may also act to keep the outer wing surface flush. 
     Preferably h the shroud panel and the wing trailing edge component are also attached by a non-pivotable butt strap, being rotationally fixed to the shroud panel and trailing edge component. This takes any side load, whilst allowing relative expansion/contraction. 
     Preferably the non-pivotable butt strap is located in substantially the spanwise centre of the shroud panel. A plurality of pivotable putt straps may be provided on either spanwise side of the non-pivotable butt strap. 
     Preferably a spoiler rib extending from the trailing edge of the wing, which spoiler rib is connected to the shroud panel at a trailing edge thereof. 
     Preferably the spoiler rib and shroud panel are connected by a strut, which strut extends in a vertical spanwise plane in use. 
    
    
     
       SUMMARY OF DRAWINGS 
       An apparatus in accordance with the present invention will now be described with reference to the accompanying drawings in which: 
         FIG. 1  is a side view of a wing trailing edge comprising an apparatus according to the present invention, 
         FIG. 1 a    is a detail view of region A of the apparatus of  FIG. 1 , 
         FIG. 2  is a top view of the trailing edge comprising the apparatus of  FIG. 1 , and, 
         FIG. 3  is a rear view of a part of the apparatus of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Directional terms such as “forward” and “rearward” denote the direction applicable when the wing is in flight. 
     A wing trailing edge assembly  10  comprises a rear spar  12  which runs in a spanwise direction along the wing. The rear spar comprises a vertical plate  14  and two forwardly depending flanges  16 ,  18  at the top and bottom thereof. The flanges  16 ,  18  are tapered slightly to diverge in a forward direction. The rear spar  12  therefore defines a forward facing concavity. 
     A stiffener  20  is provided against the forward facing side of the spar  12 . The stiffener  20  comprises a main plate  22  extending vertically and in a chordwise direction. A peripheral flange  24  runs around the edge of the main plate  22  giving it a cup-like shape. The plate  22  tapers outwardly in a forward direction and is nested within the concavity formed by the spar  12 . 
     At the top surface of the spar  12 , an upper wing skin  26  is provided which has a small overhang  28  over the rear of the spar  12 . The overhang defines a number of bores  30  equally spaced in a spanwise direction (see  FIG. 2 ). 
     A lower wing skin  27  extends over the lower part of the rib  12  in a similar manner, having an overhang  29 . 
     A first spoiler rib  32  extends from the rear of the spar  12 . The rib  32  defines a lug  34  at a first end which is connected to a dogleg portion  36  and then to a main beam  38 . At the end of the main beam opposite the lug  34  an attachment portion  40  is defined whereby the rib  32  is bolted to the spar  12  and stiffener  20 . A spoiler (not shown) is pivotably attached to the lug  34 . 
     The rib  32  is generally constructed as a chordwise vertical plate  42  having a peripheral flange  44  extending in a spanwise direction for structural rigidity. 
     Turning to  FIG. 2 , it can be seen that as well as the first spoiler rib  32 , a second spolier rib  46  is also provided. The second spoiler rib  46  is a mirror image of the first rib  32  and the plates  42  are offset by a distance d. The flanges  44  extend in opposite directions. 
     Turning to  FIG. 3 , a rib attachment plate  47  is provided extending between the ribs  32 ,  46 . The rib attachment plate  47  has a vertical spanwise plate  48  having two side flanges  50 ,  52  which are bolted to the ribs  32 ,  46  respectively. 
     The plate  48  extends to a double pivot mount  54  defining a first bore  56  and a second bore  58 . 
     Turning back to  FIG. 1 , an upper shroud panel  60 , and lower shroud panel  62  are provided. Both shroud panels are attached to, and extend from the skin overhangs  28 ,  29  respectively. 
     The lower shroud panel comprises a plate like extension  64  of the wing skin  27  having stiffening ribs  66  defined thereon. Proximate the end opposite the wing skin overhang  29 , the panel defines an attachment lug  68  defining a bore  70 . 
     The upper shroud panel  60  also comprises a plate like extension  72  of the upper wing skin  26  having a number of stiffening ribs  74  defined thereon. At a first end of the panel  60 , a row of bores  76  are defined, equally spaced in a spanwise direction. The locations of the bores  76  match those of the bores  30  on the upper wing skin overhang  28 . 
     The upper shroud panel  60  further defines a first strut attachment bracket  78  proximate the trailing edge thereof. The bracket comprises a plate  80  attached to the shroud panel  60 , and a downwardly depending vertical spanwise flange  82  defining a bore  84  (see  FIG. 3 ). 
     In order to attach the upper shroud panel  60  to the upper wing skin overhang  28 , a plurality of pivoting butt straps  86  are provided. Each butt strap  86  is obround in plan (as shown in  FIG. 2 ) and comprises a first attachment region  88  connected to a second attachment region  92  via a shoulder or step  90 . The attachment regions  88 ,  92  define respective bores  94 ,  96 . 
     Turning to  FIG. 1 a   , in an installed position, the first region  88  of each strap  86  is positioned such that the bore  94  aligns with one of the bores  30  on the wing skin overhang  28 . A first fastener  98  is inserted in order to form a pivoting joint between the strap  86  and the overhang  28 . 
     The second region  90  of each strap  86  is positioned such that the bore  96  aligns with one of the bores  76  on the shroud panel  60 . A second fastener  100  is inserted in order to form a pivoting joint between the strap  86  and the shroud panel  60 . The step in the straps  86  produced by the shoulder  90  accounts for the difference in thickness between the thick wing skin and the thinner shroud panel. By providing a step, the outer surfaces can be made flush. 
     As shown in  FIG. 2 , a plurality of straps  86  are used to attach the shroud panel  60  to the overhang  28 . 
     In addition, a central butt strap  102  is provided which is similar to the pivoting butt straps  86 , but comprises a row of three bores on each side. The central butt strap is positioned at the spanwise centre of the shroud panel  60  with pivoting straps  86  either side. 
     A lower strut  104  joins the attachment lug  68  of the lower shroud panel  62 , via a pinned connection in the bore  70  to the main beam  38  of the rib  32 , where it also pinned. The lower strut  104  extends in a fore-aft direction in a vertical chordwise plane. 
     An upper strut  106  is pin joined to the upper shroud panel  60  at the bore  84  and extends to the bore  56  of the double pivot mount  54 . It will be noted that the strut  106  extends in a vertical spanwise plane as shown in  FIG. 3 . 
     In use, each of the pivoting butt straps  86  can pivot about either attachment in order to allow relative deformation (under thermal or mechanical stresses) between the skin overhang  28  and the shroud panel  60 . The degree of permitted relative deformation is determined in part by the geometry of the shoulder  90 . The central strap  102  ensures that spanwise load can be taken by the structure without significant relative movement between the panels. 
     For example, should a change in temperature cause the shroud panel to expand in a spanwise direction by a degree greater than the skin overhang, this will be permitted by outward pivoting of the shroud side of the pivotable butt straps away from the central butt strap. 
     The assembly as described above provides a stable structure for the reaction of the various forces experienced in flight. The ribs are arranged to support the shroud panels vertically (via the upper struts) whilst the panels support the ribs in a spanwise (lateral) sense though the struts. This functionality arises because the struts are angled in the vertical spanwise plane and in compression have both a vertical and horizontal (spanwise) load carry capacity. 
     Variations of the above embodiment fall within the scope of the present invention. For example, the pivoting but straps may be connected to any other suitable component, not just the wing skin overhang. 
     It will also be noted that the butt straps are simple components which are inexpensive and easily replaced, as well as providing multiple redundancy. 
     The rib may be any other kind of rib, not just a spoiler rib.