Patent Abstract:
A fitting is provided to fix a vertical tail stabilizer of an aircraft to a composite skin and a composite frame of the aircraft in an area of a rear fuselage thereof. The fitting includes a first composite piece having lugs to attach to the vertical tail stabilizer and having vertical walls to fix the fitting to the composite frame of the rear fuselage. The fitting further includes at least one pair of additional composite pieces, each having a horizontal wall to fix the fitting to the composite skin of the rear fuselage. A second pair of additional composite pieces may be provided to further secure the fitting to the skin of the aircraft.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. §119(e) of Spanish Patent Application No. ES 200901039, filed Apr. 21, 2009, which application is incorporated herein by reference in its entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to fittings for attaching the vertical tail stabilizer of an aircraft and more particularly to fittings manufactured in composite. 
     BACKGROUND OF THE INVENTION 
     Despite the trend in recent years to implement the use of composites, such as the CFRP (Carbon Fiber Reinforced Plastic), in the largest possible number of components of an aircraft due to the weight savings that this material entails with respect to aluminum (the preferred metallic material used in aircraft), most aircraft manufacturers are hesitant to use carbon fiber to manufacture fittings, because their complexity makes them rather expensive to manufacture. 
     This is especially applicable to the fittings used for attaching vertical tail stabilizers which continue to be made with metallic materials. 
     The use of metal fittings as elements for attaching components made with composite materials in fuselage areas of the aircraft also made with composite materials brings forth several problems, such as their greater weight, and particularly those problems relating to the reduction of the effective skin area and to the assembly difficulties. 
     It is possible to manufacture fittings with composites having a shape similar to that of metallic fittings but, besides the cost resulting from the complex shape, they present, among others, the drawback that it is very difficult to achieve with this shape an optimized laminate structure able to perform the required load distribution. 
     The present invention aims to solve these drawbacks. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide fittings integrally manufactured with composite material for attaching the vertical tail stabilizer in the rear area of a structured aircraft fuselage based on a skin manufactured with composite material as a unitary piece, and on frames also manufactured with composite material. 
     It is another object of the present invention to provide fittings for fixing the vertical tail stabilizer in the rear area of an aircraft fuselage which can be easily assembled. 
     In a first step, these and other objects are achieved with a fitting comprising:
         A first piece manufactured with composite material comprising lugs for fixing the vertical tail stabilizer and vertical walls for fixing the fitting to the fuselage frames.   At least one pair of additional pieces manufactured with composite material comprising horizontal walls for fixing the fitting to the fuselage skin.       

     In a first kind of fitting, these pair of additional pieces have an angular shape and are designed so that their horizontal walls are fixed to the skin by their inner face, and so that their vertical walls are fixed to the first piece. A suitable fitting for fixing the vertical tail stabilizer with a vertical load is thus achieved. 
     In another kind of fitting, the fitting also comprises a second pair of additional pieces, also manufactured with a composite material, with an angular shape, designed so that their horizontal walls are fixed to the skin by their upper face, being their vertical walls fixed to the lugs of the first piece. A suitable fitting for fixing the vertical tail stabilizer with an inclined load is thus achieved. 
     In a second step, these and other objects are achieved by providing assembly processes for these fittings. 
     In a preferred embodiment, the assembly of the fitting intended for fixing the vertical tail stabilizer with a vertical load comprises the following steps:
         Assembling the first piece on the inner part of the skin, having previously incorporated the bushings in the boreholes of the lugs.   Assembling the pair of additional pieces fixing the horizontal walls to the skin by means of a mechanical attachment and fixing the vertical walls to the first piece by means of a mechanical attachment or a chemical attachment.       

     A very simple assembly process requiring no additional tasks in the final assembly line is thus achieved. 
     In another preferred embodiment, the assembly of the fitting intended for fixing the vertical tail stabilizer with an inclined load comprises the following steps:
         Assembling the first piece on the inner part of the skin.   Assembling the first pair of additional pieces fixing the horizontal walls to the skin by means of a mechanical attachment and fixing the vertical walls to the first piece by means of a mechanical attachment or a chemical attachment.   Assembling the second pair of additional pieces fixing the horizontal walls to the skin by means of a mechanical attachment and fixing the vertical walls to the lugs by means of a chemical attachment or by means of installing the bushings which must be incorporated in the boreholes of both elements.       

     A simple assembly process for this type of fitting is thus achieved. 
     Other features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments of its object in relation to the attached drawings. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a fitting for fixing a vertical tail stabilizer fixed on an aircraft rear fuselage, according to the known art. 
         FIG. 2  is a perspective view of the fitting of  FIG. 1 . 
         FIGS. 3   a  and  3   b  are, respectively, cross sections of  FIG. 1  according to axes A-A and B-B. 
         FIGS. 4   a  and  4   b  are perspective views of a fitting for fixing a vertical tail stabilizer with a vertical load according to the present invention. 
         FIG. 5  is a cross-section view of the fitting of  FIGS. 4   a  and  4   b.    
         FIGS. 6   a  and  6   b  are perspective views of a fitting for fixing a vertical tail stabilizer with an inclined load according to the present invention. 
         FIG. 7  is a cross-section view of the fitting of  FIGS. 6   a  and  6   b.    
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In order to better understand the invention, we will first describe a fitting for fixing a vertical tail stabilizer known in the art in relation to  FIGS. 1-3 . 
     It relates to a fitting  11  of a piece comprising lugs  15 ,  15 ′ to receive the load element of the vertical stabilizer, a pair of horizontal walls  21 ,  21 ′ which are fixed to the skin  5  and a pair of vertical walls  27 ,  27 ′ (continuous or segmented in two parts as shown in  FIG. 2 , depending on the location of the fitting) which are fixed to the frames  7  of the fuselage.  FIGS. 3   a  and  3   b  show the corresponding attachments in detail. 
     As a person skilled in the art will understand, the terms “horizontal” and “vertical” must not be interpreted in a strict geometric sense, but rather as terms to merely identify the mentioned components of the fitting. In addition, the shape of the central body  13  of the fitting  11  can differ from some fittings to others depending on their location. 
     As previously indicated, the basic problems brought forth with metallic fittings having the shape of fitting  11 , apart from their weight, are determined by their assembly conditions. Since it is a unitary machined piece, the adjustment for the assembly must be done in contact with the skin  5  and the boreholes  19 ,  19 ′ of the lugs  15 ,  15 ′ must be re-worked in situ in order to assure that their axis is located in the correct position, which requires an in situ installation of the bushings that must be assembled therein in order to adjust to the attachment bolt for fixing the element of the vertical tail stabilizer with the lugs  15 ,  15 ′ between which it is introduced. 
     These same types of problems will occur in the case of a fitting of composite material having a similar shape and, in addition, the problem relating to the difficulty of optimizing its laminates, since the conditioning factors of the load distribution would require high thickness in some components, particularly in the lugs  15 ,  15 ′, as suggested in the graphic depiction of  FIG. 2 . 
     In relation to the state of the art, the basic idea of the present invention is to configure the fitting in two or more parts which facilitate both the optimization of the laminates of its different components, together with its assembly. 
     In a preferred embodiment of the invention for fittings for fixing vertical tail stabilizers with a vertical load, the fitting  41 , illustrated in  FIGS. 4-5 , comprises three pieces, all of which are manufactured in a composite material:
         A first piece  43  comprises lugs  45 ,  45 ′ for fixing the vertical tail stabilizer and vertical walls  47 ,  47 ′ for the fixing to the fuselage frames. The unitary-piece configuration of this piece  43  facilitates its assembly.   A pair of pieces  49 ,  49 ′ (colored in black in  FIG. 4   a ) having an angular shape, and having horizontal walls  51 ,  51 ′ for fixing the fitting  41  to the skin  5  of the fuselage, also having vertical walls  53 ,  53 ′ intended to be fixed to the central body  44  of the first piece  43 .       

     Piece  43  is fixed on the inner part of the skin  5  of the fuselage (requiring a smaller cavity), having a configuration allowing it to be easily placed in its correct position whereby the boreholes  48 ,  48 ′ of the lugs  45 ,  45 ′ can incorporate the aforementioned bushings  50 ,  50 ′, preventing having to assembly them in situ. 
     Next, the pieces  49 ,  49 ′ are fixed to the central body  44  of the piece  43  in the final assembly line, whereby their correct positioning is assured, preferably by mechanical means and particularly by means of rivets, although in the case of the vertical walls  53 ,  53 ′ they can also be attached by chemical means and particularly by means of adhesives. The possible gap between the horizontal walls  51 ,  51 ′ and the skin  5  of the fuselage can be covered with a suitable filling layer. 
     This partition of the fitting  41  into pieces  43 ,  49 ,  49 ′ allows optimizing its corresponding laminates depending on the loads each of them has to support. Piece  43  needs a high percentage of plies in the same direction as the leading load whereas pieces  49 ,  49 ′ need a stacking that is more oriented towards passing the shear loads to the skin  5  of the fuselage. 
     In another preferred embodiment for fittings for fixing vertical tail stabilizers with an inclined load, the fitting  71 , illustrated in  FIGS. 6-7 , comprises five pieces, all of which are manufactured with composite material:
         A first piece  73  comprises the lugs  75 ,  75 ′ for fixing the vertical tail stabilizer and vertical walls  77 ,  77 ′ for the attachment to the fuselage frames.   A pair of pieces  79 ,  79 ′ (colored in black in  FIG. 6   a ) having an angular shape, having horizontal walls  81 ,  81 ′ for fixing the fitting to the skin of the fuselage, being their vertical walls  83 ,  83 ′ intended for being attached to the central body  74  of the first piece  73 .   A second pair of additional pieces  90 ,  90 ′ (colored in black in  FIG. 6   a ) having an angular shape, designed so that in the operation for fixing the fitting, their horizontal walls  91 ,  91 ′ are fixed to the skin by their upper face, being their vertical walls  93 ,  93 ′ fixed to the lugs  75 ,  75 ′ of the first piece  73 .       

     The first piece  73  of the fitting  71  is fixed on the inner part of the skin  5  of the fuselage like in the previous case and, in a similar way, can be easily placed in its correct position whereby the boreholes  78 ,  78 ′ of the lugs  75 ,  75 ′ are located in their final position, without the need of being reworked. 
     The pieces  79 ,  79 ′ are fixed, like in the previous case, to the central body  74  of the piece  73  in the final assembly line, whereby their correct positioning is assured, preferably by mechanical means and particularly by means of rivets, although in the case of the vertical walls  83 ,  83 ′ they can also be attached by chemical means and particularly by means of adhesives. The possible gap between the horizontal walls  81 ,  81 ′ and the skin  5  of the fuselage can be covered with a suitable filling layer. 
     For their part, pieces  90 ,  90 ′ are fixed on the outer part of the skin  5  in the final assembly line, whereby their correct positioning is assured. Their vertical walls  93 ,  93 ′ are fixed to the lugs  75 ,  75 ′ by means of adhesives or simply by means of the bushings  80 ,  80 ′ which are introduced in the boreholes  78 ,  78 ′ of both pieces, being their horizontal walls  91 ,  91 ′ fixed to the skin  5  by means of rivets. The possible gap between the horizontal walls  91 ,  91 ′ and the skin  5  of the fuselage can be covered with a suitable filling layer. 
     This partition of the fitting  71  into pieces  73 ,  79 ,  79 ′,  90 ,  90 ′ allows optimizing its corresponding laminates depending on the loads each of them has to support. 
     The complementary function provided by the vertical walls  93 ,  93 ′ of pieces  90 ,  90 ′ for the lugs  75 ,  75  for withstanding the inclined load of the stabilizer can be observed in this sense. In fact, and as it is shown in  FIGS. 6   a  and  6   b , the surface of these vertical walls  93 ,  93 ′ is larger than that of the lugs  75 ,  75 ′. 
     It must be taken into account to that respect that when the load acting on the fitting  71  does not vertically comes into contact with the lugs  75 ,  75 ′, the direction of the load does not coincide with the direction of 0° of its laminates, which is the main one, which would force, when using the conventional configuration, to a very high thickness of the lugs  75 ,  75 ′, causing the length of the bushings  80 ,  80 ′ to possibly be greater than the distance between said lugs  75 ,  75 ′. 
     The modifications comprised within the scope defined by the following claims can be introduced in the embodiments described above.

Technology Classification (CPC): 8