Abstract:
A preform is joined to converging surfaces of a structure, such as an airfoil, to form a structural edge. The preform has a body having an acute-angle edge at one end and connecting areas extending from the opposing end for connecting the preform to converging planar elements of a wing or other similar structure. In several embodiments, the acute angle of the preform generally matches the angle relative to converging ends of the planar elements, the preform forming the outer end of smooth, continuous outer surfaces after assembly. The connecting areas may be connected to interior or exterior surfaces of the elements, depending on the orientation of the preform and elements. In another embodiment, the entire preform is placed between the outer ends of the elements for aligning and supporting the elements at the desired location and angle relative to each other.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to preforms for use in construction of vehicles and relates specifically to preforms used for forming acute structural edges.  
           [0003]    2. Description of the Related Art  
           [0004]    When constructing vehicles, it is often desirable or necessary to create edges formed using acute angles. This is especially true when constructing air vehicles, such as manned or unmanned aircraft and missiles, which may require a sharpened edge for smoothly penetrating the airflow or providing a smooth convergence of separate flows.  
           [0005]    [0005]FIG. 1 shows a prior art aircraft  11  and illustrates the numerous locations of acute structural edges. The most common use of acute edges is in leading edges  13 ,  15  and trailing edges  17 ,  19  of wings  21 ,  23 , respectively. Leading edges  13 ,  15  ensure that wings  21 ,  23  pass easily through a longitudinal airflow, whereas trailing edges  17 ,  19  allow the separated airflows on either side of wings  21 ,  23  to smoothly converge at the rear of wings  21 ,  23 . Inlet lips  25  separate onrushing air into flows entering engine nacelles  27  and flows continuing on the outer surfaces of aircraft  11 . Chines  29  are formed along longitudinal edges, providing desired aerodynamic effects and a blended shape for reducing radar cross-section.  
           [0006]    [0006]FIGS. 2 through 4 illustrate prior art methods for forming acute structural edges. Though described in terms of directions relative to their orientation in the figures in the present application, it should be noted that the edges may be located in various orientations, including orientations opposite of those shown or in inclined or vertical orientations.  
           [0007]    In FIG. 2, assembly  31  is formed by inserting a rigid edge member  33  between an upper planar element  35  and a lower planar element  37 . Edge member  33  and elements  35 ,  37  may be formed from various materials, including metals and composites. When assembled, upper surface  39  of edge member  33  registers with the outer surface of element  35  and lower surface  41  registers with lower element  37 , forming smooth, continuous outer surfaces for undisturbed airflow. A forward edge  43  has an acute included angle and is located on the forward portion of edge member  33 . Members  45  extend from a rearward portion of edge member  33  for fastening edge member  33  to elements  35 ,  37 . Members  45  are inwardly offset toward a plane (not shown) bisecting edge member  33  and parallel to forward edge  43 , forming rearward-facing shoulders  47 . The forward ends of elements  35 ,  37  abut shoulders  47 . Typical methods of fastening edge member  33  to elements  35 ,  37  include adhering members  45  to the inner surfaces of elements  35 ,  37  and mechanically fastening members  45  to elements  35 ,  37 .  
           [0008]    [0008]FIG. 3 shows assembly  49 , which is formed by assembling upper element  51  with lower element  53 , elements  51 ,  53  being formed of rigid materials, such as metals or composites. Elements  51 ,  53  terminate in forward ends  55 ,  57 , respectively, each forward end  55 ,  57  having an increased thickness and mating surface. When elements  51 ,  53  are assembled to each other, the mating surfaces are adjacent at seam  59  and forward ends  55 ,  57  are aligned to form forward edge  61 . Elements  51 ,  53  are fastened together at forward ends  55 ,  57  by fastener  63 , for example, a double-countersunk fastener, which extends through the thickness of the assembled forward ends  55 ,  57 .  
           [0009]    Like assembly  49  in FIG. 3, edge assembly  65  in FIG. 4 comprises upper element  67  and lower element  69 . Upper element  67  has a forward end  71  having an increased thickness and a downward-facing mating surface. Lower element  69  has a forward end  73  that also has an increased thickness and an upward-facing mating surface. Elements  67 ,  69  are aligned and joined to each other, the mating surfaces being adjacent at seam  75  and forward ends  71 ,  73  aligning to form forward edge  77 . Rather than being joined using fasteners, elements  67 ,  69  adhered to each other or bonded in a co-curing process.  
           [0010]    While these prior art assemblies have satisfactorily been used to form acute edge structures, improvements are needed to reduce weight and cost and increase structural integrity of edge structures. Additionally, improvements are needed to improve the ability to repair damaged edge structures and to allow for tailored material and structural properties.  
         BRIEF SUMMARY OF THE INVENTION  
         [0011]    An apparatus and method are provided for constructing acute structural edges. A preform has a body having an acute-angle edge at one end and connecting areas extending from the opposing end for bonding the preform to converging planar elements of a wing or other similar structure. In several embodiments, the acute angle of the preform generally matches the angle relative to each other of converging ends of the planar elements, the preform forming the outer end of smooth, continuous outer surfaces after assembly. The connecting areas may be connected to interior or exterior surfaces of the elements, depending on the orientation of the preform and elements. In another embodiment, the preform is placed between the outer ends of the elements for aligning and supporting the elements at the desired location and angle relative to each other.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings.  
         [0013]    [0013]FIG. 1 is a perspective view of a prior art aircraft illustrating the locations of edge structures.  
         [0014]    [0014]FIG. 2 is a schematic, cross-sectional view of a prior art edge structure.  
         [0015]    [0015]FIG. 3 is a schematic, cross-sectional view of a second type of prior art edge structure.  
         [0016]    [0016]FIG. 4 is a schematic, cross-sectional view of a third type of prior art edge structure.  
         [0017]    [0017]FIG. 5 is a schematic, cross-sectional view of an edge structure of the present invention.  
         [0018]    [0018]FIG. 6 is a schematic, cross-sectional view of a second embodiment of an edge structure of the present invention.  
         [0019]    [0019]FIG. 7 is a schematic, cross-sectional view of a third embodiment of an edge structure of the present invention.  
         [0020]    [0020]FIG. 8 is a schematic, cross-sectional view of a fourth embodiment of an edge structure of the present invention.  
         [0021]    [0021]FIG. 9 is a schematic, cross-sectional view of a fifth embodiment of an edge structure of the present invention.  
         [0022]    [0022]FIG. 10 is a schematic, cross-sectional view of the preform of FIG. 8 illustrating fibers within the preform.  
         [0023]    [0023]FIG. 11 is a schematic, cross-sectional view of the preform of FIG. 8 illustrating fibers and a core within the preform.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]    [0024]FIGS. 5 through 9 show several edge assemblies using embodiments of the preform of the present invention. The preforms are preferably woven from selected fibers in a three-dimensional weave pattern, with fibers running in lateral, longitudinal, and vertical directions. The three-dimensional weave increases the strength of the preform and allows for tailoring of characteristics of the preform through selection of fiber materials and their position within the preforms. Preforms may alternatively be formed by other methods, including braiding, knitting, and stitching, that can be used to assemble fibers in an interlocking, three-dimensional pattern with control of fiber type and orientation. After completion of the edge assembly process, the fibers of the preforms are located within a rigid matrix, such as cured resin, providing the preforms with rigidity. As in the previous sections, the various embodiments are described in terms of directions relative to their orientation in the figures, though the edges may be located in various orientations, including orientations opposite of those shown or in inclined or vertical orientations.  
         [0025]    Edge assembly  79  of FIG. 5 comprises preform  81  and upper and lower planar elements  83 ,  85  of a structure, such as an airfoil. Elements  83 ,  85  are formed from a rigid material, for example, cured composites or metal. Preform  81  is formed to have a body  87  and upper and lower extensions  89 ,  91  extending from a rear portion, or base, of body  87 . The base may be arcuate, as shown, or may be planar. Extensions  89 ,  91  have inner surfaces  93 ,  95  and outer bonding surfaces  97 ,  99 , respectively, inner surfaces  93 ,  95  terminating in tapered ends. Though not required in the most embodiments of the present invention, the use of tapered ends is preferred, as the tapered ends spread mechanical loads across a larger surface and provides better resistance to peel loads than a preform in which the longitudinal fiber layers all terminate at the same length. In some cases, however, truncated ends may be preferred, such as for repairs.  
         [0026]    Body  87  has an upper surface  101  and a lower surface  103 , or flanks, and bonding surfaces  97 ,  99  are generally parallel to surfaces  101 ,  103 . Surfaces  101 ,  103  converge to an edge  105 , or crest, at the forward end of preform  81 . Extensions are inwardly offset toward a horizontal plane (not shown) that bisects body  87 , forming shoulders  106  on a rear portion of body  87 .  
         [0027]    Preform  81  may be infused with resin prior to assembly for co-bonding to rigid planar elements  83 ,  85  (e.g., metal or cured composites) or for co-curing with uncured, composite elements  83 ,  85 . Preform  81  may alternatively be cured prior to bonding to rigid elements  83 ,  85  or may be infused with resin after assembly, for example, by a resin-transfer molding process (RTM). Preform  81  may also be attached by mechanical fasteners.  
         [0028]    In an assembly procedure of an uncured, infused, preform  81  and rigid elements  83 ,  85 , preform  81  is positioned near the outer ends of planar elements  83 ,  85 , and surfaces  101 ,  103  of preform  81  are generally aligned with the outer surfaces of elements  83 ,  85 . Surfaces  97 ,  99  are placed adjacent the inner surfaces of elements  83 ,  85 , and the outer ends of elements  83 ,  85  are placed against shoulders  106 . Preform  81  is then cured to form a rigid edge structure, bonding extensions  89 ,  91  to the inner surfaces of elements  83 ,  85 . After assembly, the outer surfaces of elements  83 ,  85  and surfaces  101 ,  103  of preform  81  form smooth, continuous surfaces.  
         [0029]    [0029]FIG. 6 shows edge assembly  107 , comprising preform  109  and upper and lower planar elements  111 ,  113 . Preform is formed to have body  115  shaped like that in the embodiment of FIG. 5, but differs from the previous embodiment in that only one extension  117  extends rearward from body  115 . Body has outer surfaces  119 ,  121 , or flanks, that converge to an edge  123 , or crest. Extension  117  has upper and lower bonding surfaces  125 ,  127  that are generally parallel to surfaces  119 ,  121  of preform  109 . Surfaces  125 ,  127  are inwardly offset, creating shoulders  129 .  
         [0030]    Assembly of preform  109  and elements  111 ,  113  is accomplished in a manner similar to that described for the previous embodiment. Preform  109  may be infused with resin and cured prior to assembly by co-bonding or mechanical fastening. Alternatively, preform  109  may be assembled uncured, or it may be infused after assembly. Bonding surfaces  125 ,  127  are bonded to the inner surfaces of elements  111 ,  113 , and body  115  is cured to form a rigid edge with surfaces  119 ,  121  parallel to the outer surface of a corresponding element  111 ,  113 .  
         [0031]    In FIG. 7, edge assembly  131  is formed of planar elements  133 ,  135  and preform  137 . Each element  133 ,  135  has a forward flange  138 ,  139  that is angled inward relative to the remainder of elements  133 ,  135 . Body  141  of preform  137  has outer surfaces  143 ,  145 , or flanks, that taper to a forward edge  147 , or crest. Extensions  149 ,  151  extend from the rear portion of body  141  and are formed to have outer bonding surfaces  153 ,  155  and tapered inner surfaces  157 ,  159 . Channels  161  are formed in the rear portion of body  141  for receiving flanges  138 ,  139 .  
         [0032]    Edge assembly  131  is assembled by inserting each flange  138 ,  139  into a channel  161  of preform  137  and placing bonding surfaces  153 ,  155  adjacent the inner surfaces of elements  133 ,  135 . The inner surfaces of channels  161  are adjacent the outer surfaces of flanges  138 ,  139 . As described above, preform  137  may be attached to elements  133 ,  135  by co-curing, co-bonding, secondary bonding, and/or mechanical fastening.  
         [0033]    [0033]FIGS. 8 and 9 show edge assemblies  163  and  165  formed using preform  167 . Referring to FIG. 8, planar elements  169 ,  171  are attached to preform  167 . Preform  167  has a body  172  having outer surfaces  173 ,  175 , or flanks, that converge to a forward edge  177 , or crest. Extensions  178 ,  179  extend rearward from the rear portion of body  172 , outer surfaces  181 ,  183  being parallel and continuous with surfaces  173 ,  175  of body  172 . Inner surfaces  185 ,  187  of extensions  178 ,  179  are tapered toward a rear edge. Elements  169 ,  171  have forward flanges  189 ,  191 , respectively, oriented to be slightly angled inward relative to the remainder of elements  169 ,  171 , matching the angle of the taper on inner surfaces  185 ,  187 .  
         [0034]    To assemble edge assembly  163 , planar elements  169 ,  171  are bonded or otherwise fastened to inner surfaces  185 ,  187 . The outer surfaces of flanges  189 ,  191  are placed adjacent inner surfaces  185 ,  187 , the angle of flanges  189 ,  191  following the taper of inner surfaces  185 ,  187 . Extensions  178 ,  179  are positioned so that their rear, terminal ends lay at the intersection of flanges  189 ,  191  and the remainder of elements  169 ,  171 , providing for a smooth, continuous transition from outer surfaces  173 ,  175  to the outer surfaces of elements  169 ,  171 .  
         [0035]    [0035]FIG. 9 shows edge assembly  165 , comprising preform  167  and planar elements  193 ,  195 . Rather than being attached to the inside of preform  167 , elements  193 ,  195  are attached to outer surfaces  173 ,  175  of body  172  and outer surfaces  181 ,  183  of extensions  178 ,  179 . Elements  193 ,  195  are positioned so that the forward portion of element  193  slightly overlaps the forward portion of element  195 , forming forward edge  197 . Preform  167  is located within a volume enclosed by elements  193 ,  195 , and in the assembly shown, no portion of preform  167  forms an outer surface of edge assembly  165  or is exposed to airflow. Rather, preform  167  provides structural support and holds elements  193 ,  195  in the desired positions.  
         [0036]    As mentioned above, preforms of the invention may be formed entirely of one of various types of fibers, or the preforms may be formed of multiple types of fibers for forming preforms having desired characteristics, such as increased mechanical stiffness, reduced electrical conductivity, reduced emissivity, and reduced reflectivity. Alternatively, the preforms may be formed of one or more types of fibers, with fibers in selected portions of the preform having coatings on the fibers or being otherwise altered to provide desired characteristics.  
         [0037]    [0037]FIG. 10 is a schematic, cross-sectional view of preform  167  showing the use of two different types of warp fibers in the weave. Fibers  198  are indicated with an “x,” and fibers  199  are indicted by a “-.” Fibers  198 , which are located in extensions  178 ,  179  and the rear and interior portion of body  172 , are preferably higher strength fibers, for example, carbon fibers. Fibers  198  are positioned in locations where stresses are higher, such as bonding areas. Fibers  199 , which may be glass fibers or similar types, are located in outer surfaces  173 ,  175 , reducing electrical conductivity in outer portions of the preform. Fibers  199  allow for tailoring of electrical conductivity, emissions of internal electromagnetic energy, and radar wave reflectivity.  
         [0038]    Referring to FIG. 11, a cross-sectional view of a preform  201  shows an insert  203 , which may be formed of foam or honeycomb and is located in the interior of preform  201 . A three-dimensional weave of fibers  198  and  199  is produced around insert  201 , which provides a rigid structural member for support during weaving. Fibers  198 ,  199  and insert  203  may be coated or otherwise modified to produce desired characteristics, such as those discussed above. Preform  201  is shown as having a shape like that of preform  167 , though an insert like insert  203  may be used to form any of the preforms within the scope of this invention.  
         [0039]    Many advantages are realized from using the present invention. Edge structures can be easily formed from preforms that allow for tailoring of the characteristics of the preform by altering the types and locations of materials in the preform. These structures are lightweight, and can be tailored for desired strength, flexibility, emissivity, and reflectivity. The preforms provide for lower cost of assembly and increased structural integrity. Reparability is enhanced, since the preforms may be installed and removed as a unit, which also decreases the man-hours required to repair a damaged edge assembly.  
         [0040]    While the invention has been shown in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention. For example, though shown as flat, the planar elements may be curved, and the preforms may be formed and cured to match the curvature of the elements. Also, preforms may be formed from a variety of composite materials, including metal- and ceramic-matrix composites or fiber-reinforced adhesives.