Abstract:
A method for forming a trailing edge wedge for a wing wherein the size and configuration of a trailing edge wedge at various points along the span of the trailing edge wedge are adjusted and analyzed in an iterative manner to form an improved trailing edge wedge. An improved wing assembly is also provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    Other features of the present invention are discussed and claimed in commonly assigned copending U.S. application Ser. No. ______ entitled Spanwise Tailoring of Divergent Trailing Edge Wings. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The invention relates to the field of transonic wings for aircraft and more particularly to a trailing edge device that increases the coefficient of lift, decreases the coefficient of drag with the combined effect of reducing fuel consumption.  
         BACKGROUND OF THE INVENTION  
         [0003]    The aerodynamic drag of modern transonic wings consists of three components: lift-induced drag, profile drag and compressibility drag. Profile drag includes skin friction related drag and base drag due to trailing-edge bluntness. At relatively slower speeds (Mach numbers below the design condition), the wing drag consists of the lift-induced drag and profile drag. As the speed is increased, shock waves appear on the wing surface. These shock waves cause increased drag and are the major portion of the drag that was referred to above as compressibility drag. Compressibility drag increases dramatically with increasing speed and strongly limits the efficiency of a wing in terms of its lift-to-drag ratio. For example, modern air transport wing designs are developed to delay the onset of this drag rise until a point that is above a cruise design speed condition. The aerodynamics engineer utilizes both wing sweep and airfoil section characteristics as the primary variables in achieving a design that sufficiently delays the onset of compressibility drag while also attaining high lift and low drag.  
           [0004]    Another consideration for the aerodynamics engineer related to the design of an efficient aircraft is trim drag. Trim drag is the drag associated with balancing the lifting forces with the center of gravity of the flight vehicle. Wings in general have a nose-down pitching moment caused by the distribution of lift, both chordwise and spanwise, over typical operating conditions.  
           [0005]    One approach for obtaining a wing with an improved airfoil design is set forth in U.S. Pat. No. 4,542,868 to Boyd entitled “Trailing Edge Device For An Airfoil”, which is incorporated by reference as if fully set forth herein. The methodology set forth in the &#39;868 patent utilizes a small, generally triangular wedge-like member for attachment to or near the trailing edge of an airfoil, which improves the coefficient of lift and reduces the coefficient of drag providing an overall increase in fuel economy at cruise conditions. While applying the result to the entire span of the wing (i.e., the distance between the centerline of the fuselage of the aircraft and the distal end of the wing) can yield some improvement in the efficiency of wings, further improvements are nonetheless possible.  
           [0006]    In this regard, we have noted that the application of a wedge shaped member having a substantially constant cross-section to the trailing edge of an airfoil may unnecessarily increase the base drag and the pitching moment of the wing. Accordingly, there remains a need in the art for an improved application of the &#39;868 patent across the wing trailing edge.  
         SUMMARY OF THE INVENTION  
         [0007]    In one preferred form, the present invention provides a method for forming an improved trailing edge wedge for a wing. The method includes the steps of: a) providing a baseline trailing edge wedge; b) coupling the baseline trailing edge wedge to the wing to form a baseline assembly; c) segregating the baseline assembly into a plurality of airfoil segments, each of the airfoil segments being defined by a set of characteristics including a trailing edge bluntness, a trailing edge included angle and a trailing edge wedge height; and d) tailoring a spanwise variation of the baseline trailing edge wedge in terms of a trailing edge bluntness, a trailing edge included angle and a trailing edge wedge height at each of the airfoil segments to form the improved wing assembly. Between step (c) and step (d), the methodology may further include the step of assessing an aerodynamic benefit to determine a plurality of most favorable airfoil segment configurations.  
           [0008]    In another preferred form, the present invention provides a wing assembly having an airfoil structure and a trailing edge wedge. The airfoil structure includes an inboard wing portion, which is configured to abut a fuselage, and a mid-span wing portion, which is coupled to a distal end of the inboard wing portion, and a trailing edge that extends the length of inboard wing and mid-span wing portions. The trailing edge wedge is coupled to the wing structure proximate the trailing edge. The trailing edge wedge extending throughout the entirety of the mid-span wing portion and no more than partially through the inboard wing portion. Preferably, the outboard wing portion is configured such that at least a portion of the outboard wing includes a trailing edge wedge but to a lesser degree than the mid-span wing.  
           [0009]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings, wherein:  
         [0011]    [0011]FIG. 1 is a top plan view of a wing that is being modified in accordance with the teachings of the present invention;  
         [0012]    [0012]FIG. 2 is an airfoil sectional view taken along the line  2 - 2  of FIG. 1;  
         [0013]    [0013]FIG. 3 is a top plan view of a wing constructed in accordance with the teachings of the present invention;  
         [0014]    [0014]FIG. 4 is an airfoil sectional view taken along the line  4 - 4  of FIG. 3;  
         [0015]    [0015]FIG. 5 is an airfoil sectional view taken along the line  5 - 5  of FIG. 3;  
         [0016]    [0016]FIG. 6 is a bottom plan view illustrating a wing assembly that is being modified in accordance with the teachings of the present invention;  
         [0017]    [0017]FIG. 7 is an airfoil sectional view taken along the line  7 - 7  of FIG. 6; and  
         [0018]    [0018]FIG. 8 is a perspective view illustrating a wing assembly having a tailored divergent trailing edge constructed in accordance with the teaching of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    With reference to FIGS. 1 and 2 of the drawings, the basic approach to designing a wing with a trailing edge wedge in accordance with the teachings of the present invention is to start with a baseline wing  10 . In the particular example provided, the baseline wing  10  has a conventional trailing edge  14 . Those skilled in the art will appreciate, however, that the baseline wing  10  may be otherwise configured. For example, the baseline wing  10  may include a baseline trailing edge wedge  100  (FIG. 6) that extends, for example, over the entire span of the baseline wing  10 .  
         [0020]    The baseline wing  10  is divided into a plurality of airfoil segments  18  that are taken through the baseline wing  10  in a direction that is parallel to the direction of air flow across the baseline wing  10  (i.e., the airfoil segments  18  are taken in a direction that is generally perpendicular to the longitudinal axis  20  of the baseline wing  10 ). As those skilled in the art will appreciate, each airfoil segment  18  can be defined by a set of parameters that includes trailing edge bluntness  22  and trailing edge included angle  24 .  
         [0021]    The airfoil segments  18  need not be equally spaced apart across the span of the baseline wing  10 , but should be positioned so as to permit various critical areas of the baseline wing  10  to be thoroughly analyzed. For example, a typical transonic wing will have the highest per area loading in a midspan region and as such, at least one airfoil segment  18 , and preferably several airfoil segments  18 , should be positioned in the areas of transition into and out of the midspan region. Analysis with modern computers and analytic tools such as a Navier-Stokes CFD calculation permit the baseline wing  10  to be segregated into a plurality of very closely spaced airfoil segments  18 , which permits the aerodynamic engineer to evaluate the entire baseline wing  10  in terms of wave drag, profile drag, induced drag and trim drag, the resultant of which is typically expressed as ML/D. Other characteristics could also or alternatively be assessed, including wing bending moments and/or buffet boundary.  
         [0022]    With the baseline wing  10  segmented into the plurality of airfoil segments  18 , modifications are next made to various parameters of the set of parameters for each airfoil segment  18 , such as to the trailing edge bluntness  22  or the trailing edge included angle  24 . Thereafter, the modified airfoil segment  18   a  is preferably analyzed to assess the aerodynamic benefit of the modifications. As noted above, the analysis may be performed analytically, or may be performed empirically as in a wind tunnel, a water tunnel or in actual flight. The steps of modifying the airfoil segment  18  and analyzing the modified airfoil segment  18   a  are repeated using different parameters until a most favorable airfoil segment configuration has been identified for each of the locations of the airfoil segments  18 . Thereafter, the most favorable airfoil segment configurations are amalgamated to obtain an improved wing. It should be noted that modifications to any one airfoil segment  18  will likely effect the performance of adjacent airfoil segments  18  and as such, the optimization of any particular airfoil segment  18  cannot be performed on an independent basis.  
         [0023]    The rationale for tailoring the spanwise variation of the airfoil segments is to more fully utilize concepts, such as a diverging trailing edge or a trailing edge wedge, in the areas where they provide a benefit and to omit them from areas where they provide little or no benefit. Design of a wing with this methodology provides an airfoil that is relatively more efficient.  
       EXAMPLE I  
     Spanwise Tailoring of a Divergent Trailing Edge to a Transonic Wing  
       [0024]    A systematic study of variations in the spanwise trailing edge bluntness  22  and the trailing edge included angle  24  was conducted to maximize the aerodynamic properties of the baseline wing  10  of FIGS. 1 and 2, and more specifically to improve transonic wave drag and maximize both range and fuel burn. Both the baseline wing  10  and the improved wing  30  (FIG. 3) can be generally described as including a high pressure surface  32 , a low pressure surface  34  that is disposed opposite the high pressure surface  32 , a leading edge  36  that connects the high pressure and low pressure surfaces  32  and  34  on a forward side, and a trailing edge base  38  that connects the high pressure and low pressure surfaces  32  and  34  on a rearward side that is opposite the leading edge  36 . A chord  40  couples the leading edge  36  and the trailing edge base  38 .  
         [0025]    The improved wing  30  is illustrated to be segregated into three distinct zones: an inboard wing portion  44 , a mid-span wing portion  46  and an outboard wing portion  48 . The inboard wing portion  44  is configured to be coupled to an inboard side of a fuselage  50  and has a length of about 30% of the span of the improved wing  30 . The inboard wing portion  44  is configured with a proximal end  52 , which abuts the fuselage  50 , and a distal end  54 , which abuts the mid-span wing portion  46 . As illustrated in FIG. 4, the proximal end  52  is configured such that the trailing edge base  38  has relatively small amount of trailing edge bluntness  22  (e.g., about 0.1% of the magnitude of the chord  40 ).  
         [0026]    As illustrated in FIG. 5, the distal end  54  of the inboard wing portion  44  is configured such that the trailing edge base  38  has a relatively larger amount of trailing edge bluntness  22  (e.g., about 0.5% of the chord  40 ) and high pressure and low pressure surfaces  32  and  34  that are defined by diverging slopes in an area adjacent the blunt trailing edge base  38 , which is illustrated to be generally perpendicular to the chord  40 . In the particular embodiment illustrated, the diverging slopes of the high pressure and low pressure surfaces  32  and  34  define an included trailing edge angle  24  of about −15° and the high pressure surface  32  of the inboard wing portion  44  includes a region of high local concentrated concave curvature  66  immediately prior to the trailing edge base  38 . The transition between the proximal and distal ends  52  and  54  proceeds in a tailored manner, which may or may not be uniform, but could also include discontinuous variations, too. Preferably, the trailing edge base  38  has a height that varies between about 0.1% of the chord  40  to about 1.0% of the chord  40  between the proximal and distal ends  52  and  54  of the inboard wing portion  44 . Also preferably, the region of high local concave curvature  66  occurs within about the last 5% of the chord  40 .  
         [0027]    Returning to FIG. 3, the mid-span wing portion  46  is coupled to the distal end  54  of the inboard wing portion  44  and extends to a point that is located at about 80% of the span of the improved wing  30 . In the particular embodiment provided, the configuration of the trailing edge base  38  and the high pressure surface (not specifically shown) of the mid-span wing portion  46  are uniform over the length of the mid-span wing portion  46  and are substantially identical to the configuration of distal end  54  of the inboard wing portion  44 .  
         [0028]    The outboard wing portion  48  is coupled at a proximal end  70  to the distal end  72  of the mid-span wing portion  46 . The configuration of the trailing edge base  38  and the high pressure surface (not specifically shown) at the proximal end  70  of the outboard wing portion  48  are configured substantially identically to the configuration of the trailing edge base  38  and the high pressure surface (not specifically shown) at the distal end  72  of the mid-span wing portion  46 . Both the trailing edge bluntness and the included trailing edge angle reduce at a uniform rate to about −10° and about 0.3% of the chord  40 , respectively, at the tip  76  of the improved wing  30 .  
       EXAMPLE II  
     Spanwise Tailoring of a Trailing Edge Wedge to a Wing  
       [0029]    With reference to FIGS. 6 and 7, a systematic study of variations in the spanwise configuration of a baseline trailing edge wedge  100  was conducted to maximize the aerodynamic properties of a conventional wing  102 , and more specifically to improve transonic wave drag and maximize both range and fuel burn. The wing  102  can be generally described as including a high pressure surface  132 , a low pressure surface  134  that is disposed opposite the high pressure surface  132 , a leading edge  136  that connects the high pressure and low pressure surfaces  132  and  134  on a forward side, and a trailing edge  114  that is connected to the high pressure and low pressure surfaces  132  and  134  on a rearward side that is opposite the leading edge  136 . A chord  140  couples the leading edge  136  and the trailing edge  114 . The wing  102  is illustrated to be segregated into three distinct zones: an inboard wing portion  144 , a mid-span wing portion  146  and an outboard wing portion  148 . The inboard wing portion  144  is configured to be coupled to an inboard side of a fuselage  150  and has a length of about 30% of the span of the wing  102 . The inboard wing portion  144  is configured with a proximal end  152 , which abuts the fuselage  50 , and a distal end  154 , which abuts a proximal end  156  of the mid-span wing portion  146 . The mid-span wing portion  146  has a length of about 50% of the span of the wing  102  and is coupled at its distal end  158  to the proximal end  160  of the outboard wing portion  148 .  
         [0030]    The baseline trailing edge wedge  100  is installed at the trailing edge  114  of the wing  102  and is located forwardly of the trailing edge  114  by a distance  160  of 0.0% of the chord  140  to less than about 4.0% of the chord  140 . The baseline trailing edge wedge  100  has a height  162  of about 0.4% of the chord  140  to about 0.8% of the chord  140  and a wedge angle of about 10° to about 45°. The wing  102  with the baseline trailing edge wedge  100  were segregated into a plurality of airfoil segments  118  that were optimized using the iterative process described above to develop an improved trailing edge wedge  170 , which is illustrated in FIG. 8.  
         [0031]    In the particular example provided, the improved trailing edge wedge  170  extends over only the mid-span wing portion  146  and the outboard wing portion  148 . The portion of the improved trailing edge wedge  170  that is coupled to the mid-span wing portion  146  has a trailing edge base  138  with a trailing edge bluntness of about 0.5% of the chord  140 , which is maintained over the length of the outboard wing portion  148 . The size of the improved trailing edge wedge  170 , however, decreases slightly toward the tip  176  of the outboard wing portion  148 . As those skilled in the art will appreciate, further variations in the trailing edge bluntness and the size (e.g., height  162  and wedge angle) of the baseline trailing edge wedge  100  may also be studied to maximize the aerodynamic benefit.  
         [0032]    While the invention has been described in the specification and illustrated in the drawings with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined in the claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the invention will include any embodiments falling within the foregoing description and the appended claims.