Patent Publication Number: US-10773787-B2

Title: Wing-to-fuselage joints and aircraft including the same

Description:
FIELD 
     The present disclosure relates to wing-to-fuselage joints and aircraft including the same. 
     BACKGROUND 
     Traditional aircraft manufacturing methods and designs are limited by engineering constraints, such as limitations imposed by the widespread use of metals such as aluminum in the airframe structure. For example, the physical properties of aluminum generally require that complex structures be assembled from a plurality of distinct aluminum components that are bolted or otherwise coupled to one another. As a more specific example, the formability of components such as aluminum plates, sheets, and extrusions may require that a traditional wing-to-fuselage joint in a commercial aircraft be a complex structure formed from a plurality of distinct components coupled together. Such a complex design may require using rivets, fasteners, and fittings that concentrate and resolve loads within localized areas. By contrast, modern aircraft manufacturing may employ the use of composite materials that may be formed into continuous, unitary structures with complex contours and highly tailored structural properties. However, such composite materials may present engineering and manufacturing difficulties when incorporated into traditional airframe designs optimized for aluminum construction. 
     SUMMARY 
     Wing-to-fuselage joints and aircraft including the same are disclosed herein. An aircraft includes a fuselage with an outer fuselage skin that at least partially defines an outer surface of the fuselage and a wing assembly operably coupled to the fuselage via a wing-to-fuselage joint. The wing assembly includes a left wing region, a right wing region, and a center wing region between the left wing region and the right wing region. The left wing region includes a lower left-wing-region skin that at least partially defines a lower left-wing-region airfoil surface and an upper left-wing-region skin that at least partially defines an upper left-wing-region airfoil surface. The right wing region includes a lower right-wing-region skin that at least partially defines a lower right-wing-region airfoil surface and an upper right-wing-region skin that at least partially defines an upper right-wing-region airfoil surface. The center wing region includes a lower center-wing-region skin. 
     In some examples, the wing-to-fuselage joint includes a single skin segment that at least partially defines both the outer fuselage skin and the lower center-wing-region skin. 
     In some examples, the wing assembly includes a single skin segment that at least partially defines each of the upper center-wing-region skin and at least one of the upper left-wing-region skin and the upper right-wing-region skin. 
     In some examples, the aircraft further includes a wheel well within the fuselage rearward of the center wing region and comprising a wheel-well pressure deck constructed at least partially of an upper wheel-well skin, the center wing region further includes an upper center-wing-region skin, and a single skin segment at least partially defines both the upper wheel-well skin and the upper center-wing-region skin. 
     In some examples, the center wing region further includes an upper center-wing-region skin, the wing assembly further includes a forward-most center wing spar and an aft-most center wing spar within the center wing region, and a maximum vertical distance between the lower center-wing-region skin and the upper center-wing-region skin is at least 35% of a maximum longitudinal distance between the forward-most center wing spar and the aft-most center wing spar. 
     In some examples, the wing assembly further includes a single forward-most wing spar that spans the left wing region, the center wing region, and the right wing region. 
     In some examples, the wing assembly further includes a single left forward-most wing spar that spans the left wing region and a left half of the center wing region and a single right forward-most wing spar that spans the right wing region and a right half of the center wing region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an example aircraft. 
         FIG. 2  is a schematic cross-sectional fragmentary rear elevation view depicting aircraft including wing-to-fuselage joints according to the present disclosure. 
         FIG. 3  is a schematic fragmentary bottom plan view depicting aircraft including wing-to-fuselage joints according to the present disclosure. 
         FIG. 4  is a schematic fragmentary side elevation view depicting aircraft including wing-to-fuselage joints according to the present disclosure. 
         FIG. 5  is a schematic fragmentary cutaway top plan view depicting aircraft including wing-to-fuselage joints according to the present disclosure. 
         FIG. 6  is a fragmentary cutaway bottom perspective view depicting an aircraft including wing-to-fuselage joints according to the present disclosure and that includes a single forward-most wing spar. 
         FIG. 7  is a fragmentary cutaway top perspective view of the aircraft of  FIG. 6 . 
         FIG. 8  is a fragmentary cutaway top perspective view depicting an aircraft including wing-to-fuselage joints according to the present disclosure and that includes a single left forward-most wing spar and a single right forward-most wing spar. 
         FIG. 9  is a flowchart schematically representing aircraft production and service methodology. 
         FIG. 10  is a block diagram schematically representing an aircraft. 
     
    
    
     DESCRIPTION 
     Wing-to-fuselage joints and aircraft including the same are disclosed herein. Generally, in the figures, elements that are likely to be included in a given example are illustrated in solid lines, while elements that are optional to a given example are illustrated in dash-dot lines. However, elements that are illustrated in solid lines are not essential to all examples of the present disclosure, and an element shown in solid lines may be omitted from a particular example without departing from the scope of the present disclosure. 
       FIG. 1  is an illustration of an example aircraft  10  that includes a wing-to-fuselage joint  102  according to the present disclosure. Aircraft  10  generally may be utilized to transport persons and/or cargo, and may be a commercial aircraft or a military aircraft. As illustrated in  FIG. 1 , aircraft  10  generally includes a fuselage  20  and a wing assembly  100  operatively coupled to fuselage  20 . In some aircraft  10 , fuselage  20  may be generally cylindrical. Fuselage  20  and/or wing assembly  100  define one or more wheel wells  180  operatively coupled to and/or configured to receive a corresponding landing gear structure  30 . Wing assembly  100  is coupled to fuselage  20  via wing-to-fuselage joint  102 , which may be covered by a wing root fairing  40  to optimize aerodynamic properties of aircraft  10 . Such a configuration may be contrasted with an aircraft design such as may be associated with fighter jet aircraft, in which a wing assembly and a fuselage are not well defined and/or distinct components of the aircraft. 
     While  FIG. 1  illustrates aircraft  10  as a fixed-wing aircraft, this is not required, and it is additionally within the scope of the present disclosure that wing-to-fuselage joint  102  may be utilized with any aircraft  10  that includes a fixed airfoil surface coupled to fuselage  20 . As examples, aircraft  10  may include and/or be a vertical take-off and landing (VTOL) aircraft, a gyrodyne, a gyroplane, and/or a tilt-rotor aircraft. In such examples, wing assembly  100  may refer to any appropriate lift surface and/or airfoil surface that is statically coupled to fuselage  20 . 
       FIGS. 2-5  are schematic views of illustrative, non-exclusive examples of components and portions of wing-to-fuselage joints  102 . Wing-to-fuselage joint  102  may be optimized for aircraft manufacturing methods and designs that employ composite materials that may be formed into complex contours and shapes. For example, wing-to-fuselage joint  102  generally may be configured such that an outer surface of wing assembly  100  is blended into and/or coextensive with an outer surface of fuselage  20 , such as may be impractical to achieve using traditional metallic construction materials such as aluminum. Such a design may serve to distribute a stress and/or a bending load imparted on fuselage  20  by wing assembly  100  (or vice versa) across a larger surface area, thereby minimizing fatigue of the constituent materials and strengthening wing-to-fuselage joint  102 . 
       FIG. 2  is a schematic cross-sectional fragmentary rear view of aircraft  10 . As schematically illustrated in  FIG. 2 , fuselage  20  of aircraft  10  includes an outer surface  22  and an outer fuselage skin  24  that at least partially defines outer surface  22 , and wing assembly  100  is operably coupled to fuselage  20  at wing-to-fuselage joint  102 . As used herein, wing-to-fuselage joint  102  is intended to refer to any appropriate portion(s), component(s), and/or an entirety of a coupling and/or interface between wing assembly  100  and fuselage  20 . Wing assembly  100  includes a left wing region  110  that extends from a left-hand side of fuselage  20 , a right wing region  130  that extends from a right-hand side of fuselage  20 , and a center wing region  150  that extends between left wing region  110  and right wing region  130  within fuselage  20 . As illustrated in dashed lines in  FIG. 2 , center wing region  150  may refer to a portion of wing assembly  100  that is generally enclosed by fuselage  20  and/or that is within a region that is positioned directly between a forward portion and a rearward portion of fuselage  20 . However, this is not required, and it is within the scope of the present disclosure that center wing region  150  may include and/or be any appropriate portion of wing assembly  100  positioned between left wing region  110  and right wing region  130 . 
     As used herein, positional terms such as “left,” “left-hand,” “right,” “right-hand,” “top,” “upper,” “bottom,” “lower,” “above,” “below,” “forward,” “aft,” “rearward,” and the like are considered from the perspective of aircraft  10  positioned upright and in level flight such that fuselage  20  is generally parallel to a ground surface and such that aircraft  10  moves in a forward direction. As used herein, directional terms such as “longitudinal,” “lateral,” and the like are considered with respect to a long axis of fuselage  20 . For example, a direction parallel to the long axis of fuselage  20  may be described as a longitudinal direction, whereas a direction perpendicular to the long axis of fuselage  20  may be described as a lateral direction. As used herein, the term “coextensive,” as used to describe adjacent components and/or regions, is intended to refer to components and/or regions that are smoothly connected to each other without abrupt and/or sharp edges, corners, discontinuities, ledges, etc. 
     As schematically illustrated in  FIG. 2 , left wing region  110  includes a lower left-wing-region skin  114  that at least partially defines a lower left-wing-region airfoil surface  112  and an upper left-wing-region skin  118  that at least partially defines an upper left-wing-region airfoil surface  116 . Similarly, right wing region  130  includes a lower right-wing-region skin  134  that at least partially defines a lower right-wing-region airfoil surface  132  and an upper right-wing-region skin  138  that at least partially defines an upper right-wing-region airfoil surface  136 . Center wing region  150  includes a lower center-wing-region skin  152  and also may include an upper center-wing-region skin  154 . 
     As discussed, wing-to-fuselage joints  102  according to the present disclosure may be particularly well suited for aircraft manufacturing techniques and designs that employ composite construction materials. For example, outer fuselage skin  24 , lower left-wing-region skin  114 , upper left-wing-region skin  118 , lower right-wing-region skin  134 , upper right-wing-region skin  138 , lower center-wing-region skin  152 , and/or upper center-wing-region skin  154  may be constructed of a composite material, such as a fiber reinforced composite material. 
       FIG. 3  is a schematic fragmentary bottom view of wing-to-fuselage joint  102 , and  FIG. 4  is a schematic fragmentary side view of wing-to-fuselage joint  102 . As schematically illustrated in  FIG. 3 , wing assembly  100  may include a forward-most center wing spar  156  positioned at or near a forward-most edge of center wing region  150  and an aft-most center wing spar  158  positioned at or near a rear-most edge of center wing region  150 . As further schematically illustrated in  FIG. 3 , aircraft  10  may include wheel well  180  defined within fuselage  20  aft of center wing region  150 . As schematically illustrated in  FIGS. 3-4 , wheel well  180  may include a wheel-well pressure deck  182  (illustrated in  FIG. 4 ) that defines a top surface of wheel well  180  and a rear wheel-well bulkhead  186  that defines an aft surface of wheel well  180 . Rear wheel-well bulkhead  186  may be described as extending downward from a rearward edge of wheel-well pressure deck  182 . Wheel-well pressure deck  182  may be at least partially defined by an upper wheel-well skin  184  (illustrated in  FIG. 4 ), and rear wheel-well bulkhead  186  may be at least partially defined by a wheel-well-bulkhead skin  188 . It is additionally within the scope of the present disclosure that wheel well  180  be positioned forward of center wing region  150 . 
     As further schematically illustrated in  FIG. 4 , center wing region  150  may be characterized by a maximum vertical distance  155  between lower center-wing-region skin  152  and upper center-wing-region skin  154 . As examples, maximum vertical distance  155  may be at least 25%, at least 30%, at least 35%, and/or at least 40% of a maximum longitudinal distance  159  (illustrated in  FIG. 3 ) between forward-most center wing spar  156  and aft-most center wing spar  158 . Such a configuration may yield a center wing region  150  that is deeper than that of a traditional aircraft design, which may increase a total fuel capacity of aircraft  10  and/or may more effectively distribute a bending load and/or stress through center wing region  150 . As further schematically illustrated in  FIG. 3 , aircraft  10  may include a keel beam  170  extending from at least partially within center wing region  150  rearward across wheel well  180 , and optionally further extending forward of center wing region  150 . Keel beam  170  may be configured to enhance a longitudinal rigidity of fuselage  20 . 
     As schematically illustrated in  FIG. 3 , and as described herein, wing-to-fuselage joint  102  may include at least one single skin segment  200  that spans two or more of fuselage  20 , left wing region  110 , right wing region  130 , center wing region  150 , and wheel well  180 . As used herein, the term “single skin segment” is intended to refer to a skin (i.e., sheet-like) component that during the manufacturing process takes the form of a unitary component, a continuous component, and/or a component that is not held together by mechanical fasteners. Hence, all regions of a surface of a single skin segment  200  may be described as being coextensive with one another. For example, when wing-to-fuselage joints  102  employ composite construction materials, a single skin segment  200  may consist of a single lay-up of multiple plies of composite material. However, upon final assembly and curing of a wing-to-fuselage joint  102 , the discrete nature of the single skin segment  200  may no longer be apparent, in so far as adjacent skin segments may effectively become coextensive with the single skin segment. 
     As schematically illustrated in  FIG. 3 , wing-to-fuselage joint  102  may include a single skin segment  210  that at least partially defines each of outer fuselage skin  24  and lower center-wing-region skin  152 . Single skin segment  210  may be described as blending center wing region  150  into fuselage  20  in a longitudinal direction, such as to reduce a localized stress at an interface between center wing region  150  and fuselage  20 . Additionally or alternatively, single skin segment  210  may at least partially define each of lower center-wing-region skin  152  and keel beam  170 . As examples, single skin segment  210  may be coextensive with an exterior surface of keel beam  170 , may form a portion of keel beam  170 , and/or may be integrally formed with at least a portion of keel beam  170 . 
     As illustrated in  FIG. 3 , single skin segment  210  may be described as having a first lateral width  212  at a first transition  201  between center wing region  150  and fuselage  20  forward of center wing region  150  and/or as having a second lateral width  214  at a second transition  202  between center wing region  150  and fuselage  20  rearward of center wing region  150 . First lateral width  212  and/or second lateral width  214  may be any appropriate widths for distributing a bending load and/or stress across first transition  201  and/or second transition  202 . As examples, each of first lateral width  212  and second lateral width  214  may be at least 20%, at least 25%, at least 30%, and/or at least 35% of maximum longitudinal distance  159  between forward-most center wing spar  156  and aft-most center wing spar  158 . 
     Additionally or alternatively, single skin segment  210  may be described as extending from center wing region  150  by a distance sufficient to reduce a bending load and/or stress at an interface between center wing region  150  and fuselage  20 . For example, single skin segment  210  may extend forward of center wing region  150  by a distance that is at least 25%, at least 50%, and/or at least 75% of maximum longitudinal distance  159  between forward-most center wing spar  156  and aft-most center wing spar  158 . Similarly, single skin segment  210  may extend rearward of center wing region  150  by a distance that is at least 25%, at least 50%, and/or at least 75% of maximum longitudinal distance  159  between forward-most center wing spar  156  and aft-most center wing spar  158 . 
     Wing-to-fuselage joint  102  and/or a single skin segment  200  also may be described as forming a smooth transition between wing assembly  100  and fuselage  20 . Stated differently, wing-to-fuselage joint  102  and/or a single skin segment  200  (such as single skin segment  210 ) may be configured to blend an outer surface of wing assembly  100  into outer surface  22  of fuselage  20  without forming sharp corners, edges, and/or other regions susceptible to a concentration of a bending load and/or stress. As an example, wing-to-fuselage joint  102  may be configured such that, at any longitudinal cross-section at first transition  201  and/or at second transition  202 , a change in a radius of curvature between outer fuselage skin  24  and lower center-wing-region skin  152  is less than 5%, less than 2%, and/or zero. 
     Wing-to-fuselage joint  102  and/or single skin segment  210  additionally or alternatively may be described as being configured such that lower center-wing-region skin  152  is at least partially coextensive with outer fuselage skin  24 . For example, first lateral width  212  at first transition  201  between center wing region  150  and fuselage  20  forward of center wing region  150  may correspond to an extent to which lower center-wing-region skin  152  is coextensive with outer fuselage skin  24  forward of center wing region  150 . As more specific examples, lower center-wing-region skin  152  may be coextensive with outer fuselage skin  24  forward of center wing region  150  across a distance that is at least 20%, at least 25%, at least 30%, and/or at least 35% of maximum longitudinal distance  159  between forward-most center wing spar  156  and aft-most center wing spar  158 . 
     Similarly, wing-to-fuselage joint  102  and/or single skin segment  210  may be described as being configured such that lower center-wing-region skin  152  is at least partially coextensive with outer fuselage skin  24  rearward of center wing region  150 . For example, second lateral width  214  at second transition  202  between center wing region  150  and fuselage  20  rearward of center wing region  150  may correspond to an extent to which lower center-wing-region skin  152  is coextensive with outer fuselage skin  24  rearward of center wing region  150 . As more specific examples, lower center-wing-region skin  152  may be coextensive with outer fuselage skin  24  rearward of center wing region  150  across a distance that is at least 20%, at least 25%, at least 30%, and/or at least 35% of maximum longitudinal distance  159  between forward-most center wing spar  156  and aft-most center wing spar  158 . 
     As further schematically illustrated in  FIG. 3 , wing-to-fuselage joint  102  may include a single skin segment  220  that at least partially defines each of lower left-wing-region skin  114  and lower center-wing-region skin  152  and/or a single skin segment  230  that at least partially defines each of lower right-wing-region skin  134  and lower center-wing-region skin  152 . Single skin segment  220  and/or single skin segment  230  may be described as being configured such that lower left-wing-region skin  114  and/or lower right-wing-region skin  134  are coextensive with lower center-wing-region skin  152 . Additionally or alternatively, single skin segment  220  and/or single skin segment  230  may be described as being configured such that wing-to-fuselage joint  102  forms a smooth transition between wing assembly  100  and fuselage  20 . As an example, single skin segment  220  and/or single skin segment  230  may be configured such that, at any lateral cross-section along a left transition between lower left-wing-region skin  114  and lower center-wing-region skin  152  and at any lateral cross-section along a right transition between lower right-wing-region skin  134  and lower center-wing-region skin  152 , a change in the radius of curvature is less than 5%, less than 2%, and/or zero. 
     Single skin segment  210 , single skin segment  220 , and single skin segment  230  may refer to distinct single skin segments  200  and/or may be spaced apart following assembly of wing-to-fuselage joint  102 . Additionally or alternatively, two or more of single skin segment  210 , single skin segment  220 , and single skin segment  230  may refer to and/or be the same single skin segment  200 . As an example, in an example of wing-to-fuselage joint  102  that includes single skin segment  210 , single skin segment  220 , and single skin segment  230 , wing-to-fuselage joint  102  equivalently may be described as including a single skin segment  200  that at least partially defines each of outer fuselage skin  24 , lower center-wing-region skin  152 , lower left-wing-region skin  114 , and lower right-wing-region skin  134 . 
       FIG. 5  is a schematic fragmentary top view of wing-to-fuselage joint  102 .  FIG. 5  further schematically illustrates wheel well  180  positioned rearward of center wing region  150 . As schematically illustrated in  FIG. 5 , wing-to-fuselage joint  102  may include a single skin segment  240  that at least partially defines each of upper left-wing-region skin  118  and upper center-wing-region skin  154  and/or a single skin segment  250  that at least partially defines each of upper right-wing-region skin  138  and upper center-wing-region skin  154 . Single skin segment  240  and/or single skin segment  250  may be configured such that upper left-wing-region skin  118 , upper right-wing-region skin  138 , and upper center-wing-region skin  154  are coextensive with each other. In such an example, single skin segment  240  and single skin segment  250  may be the same single skin segment  200 . 
     As further schematically illustrated in  FIG. 5 , wing-to-fuselage joint  102  also may include a single skin segment  260  that at least partially defines each of upper wheel-well skin  184  and upper center-wing-region skin  154 . In such an example, upper wheel-well skin  184  may be described as being coextensive with upper center-wing-region skin  154 . Additionally or alternatively, wing-to-fuselage joint  102  may be characterized by a third transition  203  between upper wheel-well skin  184  and upper center-wing-region skin  154 . As an example, third transition  203  may be planar, at least substantially planar, concave downward, and/or otherwise lack a region that is concave upward and/or that forms a local minimum of height within third transition  203 . Such a design may restrict fluids and/or foreign objects from collecting at a lowest point or region at a transition region between upper wheel-well skin  184  and upper center-wing-region skin  154 . As another example, wing-to-fuselage joint  102  may be configured such that, at any longitudinal cross-section along third transition  203  between upper wheel-well skin  184  and upper center-wing-region skin  154 , a change in radius of curvature is less than 5%, less than 2%, and/or zero. 
     As further schematically illustrated in  FIG. 5 , wing-to-fuselage joint  102  further may include a single skin segment  270  that at least partially defines each of upper center-wing-region skin  154 , upper wheel-well skin  184 , and wheel-well-bulkhead skin  188 . In such an example, single skin segment  270  may be considered to be the same as and/or an extension of single skin segment  260 , and/or upper center-wing-region skin  154  may be described as being coextensive with upper wheel-well skin  184  and/or wheel-well-bulkhead skin  188 . Single skin segment  270  additionally or alternatively may be described as partially defining and/or extending across each of upper wheel-well skin  184  and wheel-well-bulkhead skin  188 , such that single skin segment  270  forms a smooth transition between wheel-well pressure deck  182  and rear wheel-well bulkhead  186 . 
     Single skin segment  240 , single skin segment  250 , single skin segment  260 , and single skin segment  270  may refer to distinct single skin segments  200  and/or may be spaced apart following assembly of wing-to-fuselage joint  102 . Additionally or alternatively, two or more of single skin segment  240 , single skin segment  250 , single skin segment  260 , and single skin segment  270  may refer to and/or be the same single skin segment  200 . As an example, in an example of wing-to-fuselage joint  102  that includes single skin segment  240  and single skin segment  250 , wing-to-fuselage joint  102  equivalently may be descried as including a single skin segment  200  that at least partially defines each of upper left-wing-region skin  118 , upper center-wing-region skin  154 , and upper right-wing-region skin  138 . 
     With continued reference to  FIG. 5 , forward-most center wing spar  156  may be a single unitary component, or may refer to each of a plurality of distinct components. As an example, and as schematically illustrated in  FIG. 5 , wing assembly  100  may include a single forward-most wing spar  160  that spans left wing region  110 , center wing region  150 , and right wing region  130 . More specifically, single forward-most wing spar  160  may be a continuous structure, may be a unitary structure, and/or may lack mechanical fasteners to form a full length of the single forward-most wing spar  160 . Stated differently, in such an example, the portions of single forward-most wing spar  160  respectively located within left wing region  110 , center wing region  150 , and right wing region  130  may be described as being coextensive, or at least partially coextensive, with one another. In such an example, forward-most center wing spar  156  may correspond to a portion of single forward-most wing spar  160  that is positioned within center wing region  150 . Such a configuration may serve to more effectively distribute a bending load and/or stress at wing-to-fuselage joint  102  relative to a traditional wing assembly configuration in which a left wing box and a right wing box each includes a distinct forward-most wing spar section that are coupled to a central wing box by mechanical fasteners. 
     As another example, and as schematically illustrated in  FIG. 5 , wing assembly  100  may include a single left forward-most wing spar  162  that spans left wing region  110  and a left half of center wing region  150  and a single right forward-most wing spar  164  that spans right wing region  130  and a right half of center wing region  150 . In such an example, the portions of single left forward-most wing spar  162  respectively located within left wing region  110  and center wing region  150  may be described as being coextensive, or at least partially coextensive, with each other. Similarly, the portions of single right forward-most wing spar  164  respectively located within center wing region  150  and right wing region  130  may be described as being coextensive, or at least partially coextensive, with each other. In such an example, forward-most center wing spar  156  may refer to the portions of single left forward-most wing spar  162  and single right forward-most wing spar  164  that are positioned within center wing region  150 . Such configurations may serve to more effectively distribute a bending load and/or stress at wing-to-fuselage joint  102  relative to a traditional wing assembly configuration in which a left wing box and a right wing box each includes a distinct forward-most wing spar section that is coupled to a central wing box by mechanical fasteners. Such configurations also may offer manufacturing benefits over examples of aircraft  10  that include a single forward-most wing spar  160 . For example, manufacturing an aircraft  10  that includes a single forward-most wing spar  160  may necessitate utilizing a manufacturing apparatus such as an autoclave configured to enclose an entirety of the single forward-most wing spar  160 , whereas manufacturing an aircraft  10  that includes a single left forward-most wing spar  162  and a single right forward-most wing spar  164  may be accomplished by utilizing a significantly smaller manufacturing apparatus. 
     Turning now to  FIGS. 6-8 , illustrative non-exclusive examples of aircraft  10  including wing-to-fuselage joints  102  are illustrated. Where appropriate, the reference numerals from the schematic illustrations of  FIGS. 2-5  are used to designate corresponding parts of  FIGS. 6-8 ; however, the examples of  FIGS. 6-8  are non-exclusive and do not limit aircraft  10  and/or wing-to-fuselage joints  102  to the illustrated examples of  FIGS. 6-8 . That is, aircraft  10  and/or wing-to-fuselage joints  102  are not limited to the specific examples of  FIGS. 6-8 , and aircraft  10  may incorporate any number of the various aspects, configurations, characteristics, properties, etc. of wing-to-fuselage joints  102  that are illustrated in and discussed with reference to the schematic representations of  FIGS. 2-5  and/or the examples of  FIGS. 6-8 , as well as variations thereof, without requiring the inclusion of all such aspects, configurations, characteristics, properties, etc. For the purpose of brevity, each previously discussed component, part, portion, aspect, region, etc. or variants thereof may not be discussed, illustrated, and/or labeled again with respect to  FIGS. 6-8 ; however, it is within the scope of the present disclosure that the previously discussed features, variants, etc. may be utilized with the examples of  FIGS. 6-8 . 
       FIGS. 6-7  illustrate an example of aircraft  10  that includes single forward-most wing spar  160  that spans left wing region  110 , right wing region  130  (illustrated in  FIG. 6 ), and center wing region  150 . In the example of  FIGS. 6-7 , and as illustrated in  FIG. 6 , wing-to-fuselage joint  102  includes a single skin segment  200  such that lower center-wing-region skin  152  is coextensive with outer fuselage skin  24  forward of center wing region  150  and rearward of center wing region  150 , with lower left-wing-region skin  114 , and with lower right-wing-region skin  134 . As best illustrated in  FIG. 7 , the example additionally includes a single skin segment  200  such that upper center-wing-region skin  154  is coextensive with upper left-wing-region skin  118 , with upper right-wing-region skin  138  (not visible in  FIG. 7 ), with upper wheel-well skin  184 , and with wheel-well-bulkhead skin  188 . More specifically, upper center-wing-region skin  154  is coextensive with upper wheel-well skin  184  such that third transition  203  is substantially planar, and upper wheel-well skin  184  is coextensive with wheel-well-bulkhead skin  188  such that a transition between wheel-well pressure deck  182  and rear wheel-well bulkhead  186  is smoothly curved. 
       FIG. 8  illustrates an example of aircraft  10  that includes single left forward-most wing spar  162  that spans left wing region  110  and the left half of center wing region  150  and single right forward-most wing spar  164  that spans right wing region  130  and the right half of center wing region  150 . Similar to the example of  FIGS. 6-7 , and as illustrated in  FIG. 8 , the example of  FIG. 8  includes wing-to-fuselage joint  102  with a single skin segment  200  such that upper center-wing-region skin  154  is coextensive with upper left-wing-region skin  118 , with upper right-wing-region skin  138 , with upper wheel-well skin  184 , and with wheel-well-bulkhead skin  188 . More specifically, upper center-wing-region skin  154  is coextensive with upper wheel-well skin  184  such that third transition  203  is substantially planar, and upper wheel-well skin  184  is coextensive with wheel-well-bulkhead skin  188  such that a transition between wheel-well pressure deck  182  and rear wheel-well bulkhead  186  is smoothly curved. As further illustrated in  FIG. 8 , the example aircraft  10  includes keel beam  170  that extends across wheel well  180  through center wing region  150  and forward of center wing region  150 . 
     Turning now to  FIGS. 9-10 , examples of the present disclosure may be described in the context of an aircraft manufacturing and service method  500  as shown in  FIG. 9  and an aircraft  10  as shown in  FIG. 10 . During pre-production, exemplary method  500  may include specification and design  504  of the aircraft  10  and material procurement  506 . During production, component and subassembly manufacturing  508  and system integration  510  of the aircraft  10  takes place. Thereafter, the aircraft  10  may go through certification and delivery  512  in order to be placed in service  514 . While in service, the aircraft  10  is scheduled for routine maintenance and service  516  (which may also include modification, reconfiguration, refurbishment, and so on). 
     Each of the processes of method  500  may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of venders, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on. 
     As shown in  FIG. 10 , the aircraft  10  produced by exemplary method  500  may include an airframe  518  with a plurality of systems  520  and an interior  522 . Examples of high-level systems  520  include one or more of a propulsion system  524 , an electrical system  526 , a hydraulic system  528 , and an environmental system  530 . Any number of other systems also may be included. Although an aerospace example is shown, the principles of the subject matter disclosed herein may be applied to other industries, such as the automotive industry. 
     Apparatus and methods disclosed herein may be employed during any one or more of the stages of the production and service method  500 . For example, components or subassemblies corresponding to production process  508  may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft  10  is in service. Also, one or more apparatus examples, method examples, or a combination thereof may be utilized during the production stages  508  and  510 , for example, by substantially expediting assembly of or reducing the cost of an aircraft  10 . Similarly, one or more of apparatus examples, method examples, or a combination thereof may be utilized while the aircraft  10  is in service, for example and without limitation, to maintenance and service  516 . 
     Illustrative, non-exclusive examples of inventive subject matter according to the present disclosure are described in the following enumerated paragraphs: 
     A. An aircraft, comprising: 
     a fuselage, wherein the fuselage comprises an outer fuselage skin that at least partially defines an outer surface of the fuselage; and 
     a wing assembly operably coupled to the fuselage via a wing-to-fuselage joint, wherein the wing assembly comprises:
         a left wing region comprising a lower left-wing-region skin that at least partially defines a lower left-wing-region airfoil surface and an upper left-wing-region skin that at least partially defines an upper left-wing-region airfoil surface;   a right wing region comprising a lower right-wing-region skin that at least partially defines a lower right-wing-region airfoil surface and an upper right-wing-region skin that at least partially defines an upper right-wing-region airfoil surface; and   a center wing region between the left wing region and the right wing region and comprising a lower center-wing-region skin.       

     A1. The aircraft of paragraph A, wherein the wing-to-fuselage joint includes a (first) single skin segment that at least partially defines both the outer fuselage skin and the lower center-wing-region skin. 
     A1.1. The aircraft of paragraph A1, 
     wherein the wing assembly further comprises a forward-most center wing spar and an aft-most center wing spar within the center wing region; and 
     wherein the (first) single skin segment has a (first) lateral width at a (first) transition between the center wing region and the fuselage forward of the center wing region that is at least 20%, at least 25%, at least 30%, and/or at least 35% of a maximum longitudinal distance between the forward-most center wing spar and the aft-most center wing spar. 
     A1.1.1. The aircraft of paragraph A1.1, wherein at any longitudinal cross-section at the (first) transition, a change in radius of curvature between the outer fuselage skin and the lower center-wing-region skin is less than 5%, less than 2%, and/or zero. 
     A1.2. The aircraft of any of paragraphs A1-A1.1.1, 
     wherein the wing assembly further comprises a/the forward-most center wing spar and an/the aft-most center wing spar within the center wing region; and 
     wherein the (first) single skin segment extends forward of the center wing region by a distance that is at least 25%, at least 50%, and/or at least 75% of a/the maximum longitudinal distance between the forward-most center wing spar and the aft-most center wing spar. 
     A1.3. The aircraft of any of paragraphs A1-A1.2, 
     wherein the wing assembly further comprises a/the forward-most center wing spar and an/the aft-most center wing spar within the center wing region; and 
     wherein the (first) single skin segment has a (second) lateral width at a (second) transition between the center wing region and the fuselage rearward of the center wing region that is at least 20%, at least 25%, at least 30%, and/or at least 35% of a/the maximum longitudinal distance between the forward-most center wing spar and the aft-most center wing spar. 
     A1.3.1. The aircraft of paragraph A1.3, wherein at any longitudinal cross-section at the (second) transition, a change in radius of curvature between the outer fuselage skin and the lower center-wing-region skin is less than 5%, less than 2%, and/or zero. 
     A1.4. The aircraft of any of paragraphs A1-A1.3.1, 
     wherein the wing assembly further comprises a/the forward-most center wing spar and an/the aft-most center wing spar within the center wing region; and 
     wherein the (first) single skin segment extends rearward of the center wing region by a distance that is at least 25%, at least 50%, and/or at least 75% of a/the maximum longitudinal distance between the forward-most center wing spar and the aft-most center wing spar. 
     A2. The aircraft of any of paragraphs A-A1.4, wherein the lower center-wing-region skin is at least partially coextensive with the outer fuselage skin. 
     A2.1. The aircraft of paragraph A2, 
     wherein the wing assembly further comprises a/the forward-most center wing spar and an/the aft-most center wing spar within the center wing region; 
     wherein the lower center-wing-region skin is coextensive with the outer fuselage skin forward of the center wing region for a/the (first) lateral width that is at least 20%, at least 25%, at least 30%, and/or at least 35% of a/the maximum longitudinal distance between the forward-most center wing spar and the aft-most center wing spar. 
     A2.1.1. The aircraft of paragraph A2.1, wherein at any longitudinal cross-section at a/the (first) transition between the center wing region and the fuselage forward of the center wing region, a change in radius of curvature between the outer fuselage skin and the lower center-wing-region skin is less than 5%, less than 2%, and/or zero. 
     A2.2. The aircraft of any of paragraphs A2-A2.1.1, 
     wherein the wing assembly further comprises a/the forward-most center wing spar and an/the aft-most center wing spar within the center wing region; 
     wherein the lower center-wing-region skin is coextensive with the outer fuselage skin rearward of the center wing region for a/the (first) lateral width that is at least 20%, at least 25%, at least 30%, and/or at least 35% of a/the maximum longitudinal distance between the forward-most center wing spar and the aft-most center wing spar. 
     A2.2.1. The aircraft of paragraph A2.2, wherein at any longitudinal cross-section at a/the (second) transition between the center wing region and the fuselage rearward of the center wing region, a change in radius of curvature between the outer fuselage skin and the lower center-wing-region skin is less than 5%, less than 2%, and/or zero. 
     A3. The aircraft of any of paragraphs A-A2.2.1, 
     wherein the wing-to-fuselage joint includes a (second or the first) single skin segment that at least partially defines both the lower left-wing-region skin and the lower center-wing-region skin; and 
     wherein the wing-to-fuselage joint further includes a (third or the first or the second) single skin segment that at least partially defines both the lower right-wing-region skin and the lower center-wing-region skin. 
     A4. The aircraft of any of paragraphs A-A3, wherein the lower left-wing-region skin and the lower right-wing-region skin are coextensive with the lower center-wing-region skin. 
     A5. The aircraft of any of paragraphs A-A4, wherein at any lateral cross-section along a left transition between the lower left-wing-region skin and the lower center-wing-region skin and at any lateral cross-section along a right transition between the lower right-wing-region skin and the lower center-wing-region skin, a change in radius of curvature is less than 5%, less than 2%, and/or zero. 
     A6. The aircraft of any of paragraphs A-A5, 
     wherein the center wing region further comprises an upper center-wing-region skin; 
     wherein the wing-to-fuselage joint includes a (fourth) single skin segment that at least partially defines both the upper left-wing-region skin and the upper center-wing-region skin; and 
     wherein the wing-to-fuselage joint further includes a (fifth or the fourth) single skin segment that at least partially defines both the upper right-wing-region skin and the upper center-wing-region skin. 
     A7. The aircraft of any of paragraphs A-A6, 
     wherein the center wing region further comprises an/the upper center-wing-region skin; and 
     wherein the upper left-wing-region skin, the upper right-wing-region skin, and the upper center-wing-region skin are coextensive with each other. 
     A8. The aircraft of any of paragraphs A-A7, further comprising: 
     a wheel well within the fuselage rearward of the center wing region and comprising a wheel-well pressure deck constructed at least partially of an upper wheel-well skin; 
     wherein the center wing region further comprises an/the upper center-wing-region skin; and 
     wherein the wing-to-fuselage joint includes a (sixth or the fourth or the fifth) single skin segment that at least partially defines both the upper wheel-well skin and the upper center-wing-region skin. 
     A8.1. The aircraft of paragraph A8, 
     wherein the wheel well further comprises a rear wheel-well bulkhead extending downward from a rearward edge of the wheel-well pressure deck and constructed at least partially of a wheel-well-bulkhead skin; and 
     wherein the wing-to-fuselage joint further includes a (seventh or the sixth or the fifth or the fourth) single skin segment that at least partially defines both the upper wheel-well skin and the wheel-well-bulkhead skin. 
     A9. The aircraft of any of paragraphs A-A8, further comprising: 
     a/the wheel well within the fuselage rearward of the center wing region and comprising a/the wheel-well pressure deck constructed at least partially of an/the upper wheel-well skin; 
     wherein the center wing region further comprises an/the upper center-wing-region skin; and 
     wherein the upper wheel-well skin is coextensive with the upper center-wing-region skin. 
     A9.1. The aircraft of paragraph A9, 
     wherein the wheel well further comprises a/the rear wheel-well bulkhead extending downward from a/the rearward edge of the wheel-well pressure deck and constructed at least partially of a/the wheel-well-bulkhead skin; and 
     wherein the upper center-wing-region skin is coextensive with the wheel-well-bulkhead skin. 
     A10. The aircraft of any of paragraphs A8-A9.1, wherein at any longitudinal cross-section along a (third) transition between the upper wheel-well skin and the upper center-wing-region skin, a change in radius of curvature is less than 5%, less than 2%, and/or zero. 
     A11. The aircraft of any of paragraphs A8-A10, wherein a/the (third) transition between the upper wheel-well skin and the upper center-wing-region skin is planar or concave downward. 
     A12. The aircraft of any of paragraphs A8-A11, wherein across a full span of the upper wheel-well skin and the upper center-wing-region skin, no region is concave upward. 
     A13. The aircraft of any of paragraphs A-A12, 
     wherein the wing assembly further comprises a/the forward-most center wing spar and an/the aft-most center wing spar within the center wing region; 
     wherein the center wing region further comprises an/the upper center-wing-region skin; and 
     wherein a maximum vertical distance between the lower center-wing-region skin and the upper center-wing-region skin is at least 25%, at least 30%, at least 35%, and/or at least 40% of a maximum longitudinal distance between the forward-most center wing spar and the aft-most center wing spar. 
     A14. The aircraft of any of paragraphs A-A13, wherein the wing assembly further comprises a single forward-most wing spar that spans the left wing region, the center wing region, and the right wing region. 
     A15. The aircraft of any of paragraphs A-A13, wherein the wing assembly further comprises: 
     a single left forward-most wing spar that spans the left wing region and a left half of the center wing region; and 
     a single right forward-most wing spar that spans the right wing region and a right half of the center wing region. 
     A16. The aircraft of any of paragraphs A-A15, further comprising: 
     a/the wheel well defined within the fuselage aft of the center wing region; 
     wherein the wing assembly further comprises a keel beam extending from at least partially within the center wing region rearward across the wheel well. 
     A16.1. The aircraft of paragraph A16, wherein the keel beam further extends forward of the center wing region. 
     A16.2 The aircraft of paragraph A16 when depending from paragraph A1, wherein the single skin segment at least partially defines both of the lower center-wing-region skin and the keel beam. 
     A17. The aircraft of any of paragraphs A-A16.2, wherein the outer fuselage skin, the lower left-wing-region skin, the upper left-wing-region skin, the lower right-wing-region skin, the upper right-wing-region skin, the lower center-wing-region skin, and a/the upper center-wing-region skin are constructed of a fiber reinforced composite material. 
     A18. The use of the aircraft of any of paragraphs A-A17 to transport at least one of people and cargo. 
     As used herein, the terms “adapted” and “configured” mean that the element, component, or other subject matter is designed and/or intended to perform a given function. Thus, the use of the terms “adapted” and “configured” should not be construed to mean that a given element, component, or other subject matter is simply “capable of” performing a given function but that the element, component, and/or other subject matter is specifically selected, created, implemented, utilized, programmed, and/or designed for the purpose of performing the function. It is also within the scope of the present disclosure that elements, components, and/or other recited subject matter that is recited as being adapted to perform a particular function may additionally or alternatively be described as being configured to perform that function, and vice versa. Similarly, subject matter that is recited as being configured to perform a particular function may additionally or alternatively be described as being operative to perform that function. 
     As used herein, the term “and/or” placed between a first entity and a second entity means one of (1) the first entity, (2) the second entity, and (3) the first entity and the second entity. Multiple entries listed with “and/or” should be construed in the same manner, i.e., “one or more” of the entities so conjoined. Other entities optionally may be present other than the entities specifically identified by the “and/or” clause, whether related or unrelated to those entities specifically identified. Thus, as a non-limiting example, a reference to “A and/or B,” when used in conjunction with open-ended language such as “comprising,” may refer, in one example, to A only (optionally including entities other than B); in another example, to B only (optionally including entities other than A); in yet another example, to both A and B (optionally including other entities). These entities may refer to elements, actions, structures, steps, operations, values, and the like. 
     The various disclosed elements of apparatuses and steps of methods disclosed herein are not required to all apparatuses and methods according to the present disclosure, and the present disclosure includes all novel and non-obvious combinations and subcombinations of the various elements and steps disclosed herein. Moreover, one or more of the various elements and steps disclosed herein may define independent inventive subject matter that is separate and apart from the whole of a disclosed apparatus or method. Accordingly, such inventive subject matter is not required to be associated with the specific apparatuses and methods that are expressly disclosed herein, and such inventive subject matter may find utility in apparatuses and/or methods that are not expressly disclosed herein.