Patent Publication Number: US-2022234715-A1

Title: Joint for Connecting a Center Wing Box and Bulkhead in an Aircraft

Description:
RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional App. No. 63/142,117, filed 27 Jan. 2021, the disclosure of which is incorporated by reference herein in its entirety. 
    
    
     TECHNOLOGICAL FIELD 
     The present disclosure relates generally to the field of aircraft and, particularly, to a connection between sections of an aircraft. 
     BACKGROUND 
     Aircraft can include a center wing box that is positioned between and connected to the wings. The center wing box experiences stresses such as tension, compression, shear and torsion due to aerodynamic forces from the wings while in flight, and due to the weight of the wings themselves and from the fuel contained within the wings when the aircraft is on the ground. In addition, the center wing box transmits forces from the wings to the fuselage. 
     Aircraft can be manufactured in a modular fashion. Different sections of the aircraft can be manufactured separately and then brought together and assembled. For example, a wing assembly can be manufactured separately from a fuselage. During the assembly process, a mostly complete fuselage is lowered onto a complete wing and then connected together. This can enable high production rates and save factory space and assembly costs. This modular approach requires a secure connection that adequately connects the center wing box to the fuselage. 
     SUMMARY 
     One aspect is directed to a joint for connecting a center wing box to a bulkhead of an aircraft with the bulkhead comprising a web and a deck. The joint comprising a flex angle member comprising a first section shaped to abut against and be connected to one of the center wing box and the bulkhead, a second section shaped to abut against and be connected to a first side of the deck of the bulkhead, and an intermediate rounded corner positioned between the first and second sections. First support members are attached to the center wing box at first pins. Second support members are attached to the web of the bulkhead at second pins. One of the first and second support members supports the second section of the flex angle member. The first support members are positioned on a first side of the deck of the bulkhead and the second support members are positioned on an opposing second side of the deck. 
     In another aspect, the first support members support the second section of the flex angle member and the first pins are coincident with a center of a radius of the intermediate rounded corner of the flex angle member. 
     In another aspect, the second support members support the second section of the flex angle member and the second pins are positioned at a point incident with a center of a radius of the rounded corner that is positioned at an intersection of the web and the deck of the bulkhead. 
     In another aspect, support fittings are attached to the center wing box with the first support members mounted to the support fittings with the first pins; and stiffeners are mounted on the web of the bulkhead with the second support members mounted to the stiffeners with the second pins. 
     In another aspect, the first and second support members comprise a lug with opposing clevis and the support fittings and stiffeners are positioned between the clevis. 
     In another aspect, the flex angle member is constructed from one of fiber reinforced composite and metallic material. 
     In another aspect, corner fittings are laterally offset from the flex angle member and comprise first and second sections aligned at an angle to fit at an intersection of the center wing box and the bulkhead with the corner fittings comprising a different construction than the flex angle member and are less flexible than the flex angle member. 
     In another aspect, the flex angle member is a first flex angle member and abuts against and is connected to the center wing box and further comprising a second flex angle member that abuts against and is connected to the web of the bulkhead and the deck. 
     In another aspect, the first and second support members are aligned in pairs with the first and second support members of each of the pairs overlapping on opposing sides of horizontal deck. 
     One aspect is directed to an aircraft comprising: a fuselage; a wing assembly comprising a center wing box positioned in the fuselage and wings that extend outward from opposing sides of the fuselage; a bulkhead positioned in the fuselage and comprising a web and a deck; and a joint that connects the center wing box to the bulkhead. The joint comprises: a flex angle member comprising a first section that is connected to one of the center wing box and the bulkhead, a second section that extends across the deck of the bulkhead, and an intermediate corner positioned between the first and second sections; first support members spaced apart across a width of the fuselage on a first side of the deck; and second support members spaced apart across a width of the fuselage on an opposing second side of the deck and with one of the first and second support members contacting against the second section of the flex angle member. 
     In another aspect, the first support members support the second section and the first support members are attached to the center wing box with pins that are located at a center of a radius of the corner. 
     In another aspect, the second support members support the second section and are attached to the web with pins that are located at a center of a radius of the corner. 
     In another aspect, the first and second support members are aligned in pairs along the width of the fuselage, with the first and second support members of each of the pairs overlapping on opposing sides of the deck. 
     In another aspect, the flex angle member is a first flex angle member that is attached to the center wing box and further comprising a second flex angle member with a first section that is attached to the web, a second section that is positioned across the deck, and a rounded intermediate corner. 
     In another aspect, the flex angle member is located along a central section of the fuselage and further comprising angled corner fittings laterally offset from and on opposing sides of the flex angle member with the angled corner fittings having an angled shape to contact against the center wing box and the deck of the bulkhead and comprising a different construction than the flex angle member and are less flexible than the flex angle member. 
     In another aspect, the flex angle member is a first flex angle member that is connected to the center wing box and further comprising one or more additional flex angle members with the additional flex angle members comprising a first section that is connected to the center wing box, a second section that extends outward from the center wing box and extends across the deck of the bulkhead, and an intermediate corner. 
     One aspect is directed to a method of connecting a center wing box to a bulkhead of an aircraft. The method comprises: positioning an intermediate rounded corner of a flex angle member at an intersection of the center wing box and the bulkhead; connecting a first section of the flex angle member to the center wing box; connecting a second section of the flex angle member to the bulkhead; connecting first support members to the center wing box and contacting a first side of the second section of the flex angle member; and connecting second support members to the bulkhead and overlapping with the first and second support members on opposing sides of the bulkhead. 
     In another aspect, the method comprises connecting the first support members to the center wing box with first pins that are located at a center of a radius of the rounded corner. 
     In another aspect, the flex angle member is a first flex angle member and further comprising: connecting a first section of a second flex angle member to a first section of the bulkhead; connecting a second section of the second flex angle member to a second section of the bulkhead; positioning a rounded corner of the second flex angle member that is positioned between the first and second sections at an intersection of the first and second sections of the bulkhead; and connecting the second support members to the bulkhead within pins that are coincident with a radius of the rounded corner. 
     In another aspect, the method comprises attaching a first corner fitting to the center wing box on a first lateral side of the flex angle member and attaching a second corner fitting to the center wing box on a second lateral side of the flex angle member with the first and second corner fittings abutting against the flex angle member. 
     The features, functions and advantages that have been discussed can be achieved independently in various aspects or may be combined in yet other aspects, further details of which can be seen with reference to the following description and the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is perspective view of an aircraft. 
         FIG. 2  is a side schematic view of a fuselage of an aircraft. 
         FIG. 3  is partial perspective view of a center wing box attached at a joint to a bulkhead within a fuselage of an aircraft. 
         FIG. 4  is a partial perspective view of a joint connecting a center wing box and a bulkhead. 
         FIG. 4A  is a side view of a joint connecting a center wing box and a bulkhead. 
         FIG. 5  is a schematic side view of a forward flex angle member. 
         FIG. 6  is a partial perspective view of a joint connecting a center wing box and a bulkhead. 
         FIG. 7  is a perspective schematic view of a rear flex angle member. 
         FIG. 7A  is a schematic side view of a forward flex angle member. 
         FIG. 8  is a partial perspective view of a joint connecting a center wing box and a bulkhead. 
         FIG. 9  is a schematic view of a connection of a support member and a stiffener or support fitting. 
         FIG. 10  is a flowchart diagram of a method of connecting a center wing box to a bulkhead of an aircraft. 
     
    
    
     DETAILED DESCRIPTION 
     As seen in  FIG. 1 , an aircraft  100  includes a fuselage  101  with a nose  109  and a tail  108 . A wing assembly  102  includes a center wing box  20  positioned between and supporting opposing wings  103 . Engines  105  are attached to the wings  103  to power the aircraft during flight. The center wing box  20  is positioned in the fuselage  101  and operatively joins the wing assembly  102  with the fuselage  101 . 
       FIG. 2  illustrates a side schematic view of the fuselage  101  with the wings  103  removed for clarity. The fuselage  101  includes an elongated shape with a length L that extends between the tail  108  and nose  109 . In one example as illustrated in  FIG. 2 , the fuselage  101  is divided into an upper section  110  and a lower section  111 . The upper section  110  includes a cabin area  106  with a floor  104 . The upper section  110  includes various components to provide for transporting passengers, such as but not limited to seats, overhead storage, restrooms, and various other amenities. 
     The lower section  111  is positioned below the floor  104  of the upper section  110 . The lower section  111  includes a forward cargo deck  112  for holding cargo on either the right or left side of the fuselage  101 . The center wing box  20  is located aft of the forward cargo deck  112 . The center wing box  20  is connected to a bulkhead  30  at a joint  40  that is positioned aft of the forward cargo deck  112 . A main landing gear wheel well  113  is positioned immediately aft of the center wing box  20 . A lower aft hold  114  that includes an aft cargo hold or deck is positioned aft of the main landing gear wheel well  113 . 
     The aircraft design with the bulkhead  30  offset from the center wing box  20  facilitates the assembly process when the aircraft  100  is manufactured in separate assemblies. This offset positioning facilitates rapid wing to body join when a mostly complete fuselage  101  is lowered onto a fully complete wing assembly  102 . This supports a higher rate of production than would be available in other designs. In the illustrated embodiment, the aircraft  100  is a commercial aircraft with the upper section  110  configured for passengers and flight crew and the lower section  111  configured for cargo storage and aircraft equipment. The joint  40  that connects the center wing box  20  and bulkhead  30  is also applicable in various other aircraft, including but not limited to various commercial and non-commercial aircraft. These aircraft  100  can include the same or different configurations for storing cargo and/or passengers. 
       FIG. 3  illustrates a forward section of the center wing box  20 . The outer skin of the fuselage  101  is removed for clarity. The center wing box  20  includes spars, including a front spar  21 , that extend across the width W of the fuselage  101 . Overwing beam  23  are spaced apart across the width W and are aligned substantially perpendicular to the front spar  21 . The center wing box  20  also includes an upper skin and lower skin (not illustrated). Stringers (not illustrated) can be attached to the skins to provide for additional mechanical support. 
     The bulkhead  30  is positioned across the width W of the fuselage  101 . In one example as illustrated in  FIG. 3 , the bulkhead  30  is positioned at a bottom  115  of the fuselage  101 . Other examples can include the bulkhead  30  having different heights relative to the bottom  115  of the fuselage  101 . The center wing box  20  can also include various sizes and be positioned at various locations within the fuselage  101 . In one example, both the center wing box  20  and the bulkhead  30  are contained within the lower section  111  of the fuselage  101 . As illustrated in the example of  FIG. 3 , the bulkhead  30  has a limited height with a top  116  of the bulkhead  30  positioned below a top of the center wing box  20 . This aligns the top  116  of the bulkhead  30  along the front spar  21 . 
     The bulkhead  30  includes panels  32  with a curved shape that conform to the substantially rounded sectional shape of the fuselage  101 . A horizontal deck  31  forms a chord that extends across the width W and is attached to the opposing sides of the panels  32 . The bulkhead  30  also includes a vertical wall that includes a web  33  that extends between the horizontal deck  31  and the lower panels  32 . In one example, the panel  32  is aligned substantially vertically within the fuselage  101 . Horizontal stiffeners  34  are attached to and provide additional strength to the panel  32 . 
     As illustrated in  FIGS. 4, 4A, and 5 , a forward flex angle member  85  is positioned at the bulkhead  30 . The forward flex angle member  85  includes a first section  87 , second section  86 , and an intermediate rounded corner  38 . The corner  38  includes a rounded shape with a radius R 1 . In one example as illustrated in  FIG. 5 , the forward flex angle member  85  is a separate from the bulkhead  30  and includes the first section  87  being substantially planar to be positioned over the horizontal deck  31 , a second section  86  that is substantially planar to be positioned over the web  33 , and the rounded corner  38 . The forward flex angle member  85  can be a single piece, or formed by two or more pieces that are integrally attached together. In other examples, one or both of the first and second sections  87 ,  86  are formed by sections of the bulkhead  30 , including but not limited to the first section formed by the horizontal deck  31  and the second section formed by the web  33 . 
     The corner  38  of the forward flex angle member  85  includes a radius R 1  that extends from a center point C. The rounded corner  38  positions the first and second sections  87 ,  86  at an angle ß which can range between about 85° and about 95°. In one example, the angle ß is 90°. 
     The bulkhead  30  further includes vertical stiffeners  36  that are attached to and provide support to the web  33 . The stiffeners  36  are attached to the web  33  in various manners, including but not limited to mechanical fasteners, adhesives, and combinations thereof. The vertical stiffeners  36  can be constructed of various materials, including but not limited to aluminum and titanium. 
     Support members  60  are attached to bulkhead  30  and provide support to the horizontal deck  31 . Each of the support members  60  is attached to a vertical stiffener  36  at a pin  62 . The pin  62  is coincident with the center point C of the radius R 1  of the rounded corner  38 . The support member  60  further includes a contact edge  61  that contacts against and supports and underside of the horizontal deck  31 . In one example, the contact edge  61  is flat. In other examples, the contact edge  61  includes different shapes. 
     In one example as illustrated in  FIG. 9 , the support member  60  is formed as a lug  79  with a pair of spaced apart clevis  77 ,  78  sized to receive an end of the vertical stiffener  36 . The pin extends through each clevis  77 ,  78  and the vertical stiffener  36 . In another example, the support member  60  includes a single section that abuts against and is connected to one side of the vertical stiffener  36 . As illustrated in  FIG. 6 , the vertical stiffeners  36  and support members  60  extend across the width of the bulkhead  30 . In one example as illustrated in  FIG. 6 , the spacing is equal across the width of the bulkhead  30 . 
     A second flex angle member  50  is attached to and extends outward from the front spar  21 .  FIGS. 7 and 7A  schematically illustrate the flex angle member  50  that includes a first section  51 , a second section  52 , and an intermediate rounded corner  53 . Both the first and second sections  51 ,  52  are substantially flat with the rounded corner  53  having a radius R 2 . The first and second sections  51 ,  52  are aligned at angle α that can be within a range of between about 85°-95°. The flex angle member  50  includes a length L 1  measured between opposing ends  54 ,  55 . In one example as illustrated in  FIG. 3 , the length L 1  is sized to extend across the width W of the lower section of the fuselage  101 . In one example as illustrated in  FIG. 4A , the aft flex angle member  50  is a separate from the center wing box  20 . The aft flex angle member  50  includes the first section  51  being positioned against the center wing box  20 , the second section  52  is positioned over the horizontal deck  31 , and the rounded corner  53  is positioned at the intersection of the front spar  21  of the center wing box  20  and the horizontal deck  31 . The forward flex angle member  85  can be a single piece, or formed by two or more pieces that are integrally attached together. In other examples, one or both of the first and second sections  51 ,  52  are formed by these components, including but not limited to the first section  51  formed by the front spar  21  and the second section  52  formed by the horizontal deck  31 . 
     In one example, the flex angle member  50  includes the first and second sections and corner  53  constructed from a single piece. In other examples, the flex angle member  50  is constructed from two or more different pieces that are connected together. 
     In one example, one or both of the flex angle members  50 ,  85  is constructed of a fiber reinforced composite or metallic material, such as a carbon fiber reinforced polymer (CFRP) material. Fiber reinforced composite materials additionally or alternatively may be described as, or referred to as, fiber reinforced polymers, or plastics. As used herein, a fiber reinforced composite material should be understood to include at least an epoxy or other polymer or binding material together with fibers, such as (but not limited to) carbon fibers, boron fibers, para-aramid (e.g., Kevlar®) fibers, and/or other fibers. In other examples, the flex angle member  50  is constructed from a metal and/or metal alloy. 
     The use of carbon fiber materials for one or both of the flex angle members  50 ,  85  provides for lower corrosion and fatigue cracking when compared to metallic materials. In one example, the aircraft design includes a fuselage  101  that is wide to accommodate a large cabin area  106  in the upper section  110 . In one example, the cabin area  106  has a width to accommodate twin aisles and three sets of seats in each row. The wider fuselage cross section results in significantly higher relative lateral displacements of the wings  103  versus the fuselage  101  which challenges designs that include a metallic flex angle member  50  due to the high level of strain introduced to the flex angle member. The carbon fiber materials are also able to be exposed to moisture that can accumulate in this area of the aircraft  100  and lead to corrosion in other materials. Further, carbon fiber is better able to handle the significant cyclic loading that occurs during operation of the aircraft  100 . Carbon fiber is less likely to have fatigue cracking. Further, the location of the joint  40  makes it difficult to access after the aircraft  100  is assembled thus design concerns that minimize issues are appreciated. 
       FIG. 8  illustrates flex angle members  50  mounted at the joint  40 . For each flex angle member  50 , the first section  51  is positioned against and attached to the front spar  21 . The second section  52  is positioned on and overlaps with the horizontal deck  31  of the bulkhead  30 . The first and second sections  51 ,  52  are attached by one or more mechanical fasteners and adhesives. In one example, the second section  52  overlaps with the first section  87  of the forward flex angle member  85 . 
     Support fittings  56  extend over and are secured with adhesives and/or mechanical fasteners to the first section  51  of the flex angle member  50  and the front spar  21 . In one example, the support fittings  56  have a T shape with a top member that contacts against the front spar  21  and first section  51 , and an outwardly-extending brace. Support members  70  are attached to the support fittings  56 . 
     Support members  70  are positioned on and attached to the second section  52  of the flex angle member  50 . The support members  70  include a contact edge  71  that contacts the second section  52  and the horizontal deck  31  or first section  87 . The attachment can be formed by one or more mechanical fasteners and adhesives. The support members  70  have a length to extend outward beyond the second section  52  and onto the horizontal deck  31 . In one example as illustrated in  FIG. 9 , the support members  70  include a lug  79  with clevis  77 ,  78  that are spaced-apart clevis  78  and receive the support fitting  56 . As illustrated in  FIG. 7A , the pin  72  is coincident with a center C of the radius R 2  of the rounded corner  53  of the flex angle member  50 . 
     The location of the pin  72  at the corner  53  minimizes the bending of the flex angle member  50 . This lowers the interlaminar stresses and laminate bending strain in the radius R 2  to an acceptable level for the carbon fiber construction. 
     Stiffeners  80  are attached to the horizontal deck  31  and/or first section  87  of the flex angle member  85 . The stiffeners  80  are aligned substantially perpendicular to the support members  70 . The stiffeners  80  provide support to prevent buckling of the horizontal deck  31 . One or more additional stiffeners  80  are attached to the underside of the horizontal deck  31  (see  FIG. 4A ). 
     As illustrated in  FIGS. 4 and 4A , the support members  60 ,  70  are aligned in pairs across the length of the flex angle members  50 ,  85 . Each pair includes a support member  70  on a first side of the horizontal deck  31  of the bulkhead  30  and a support member  60  on an opposing second side of the horizontal deck  31 . The pairs can be spaced at various intervals across the flex angle members  50 ,  85 . The lengths of the support members  60 ,  70  further provide for them to overlap one another. That is, the distal section of each support member  60 ,  70  overlap on opposing sides of the horizontal deck  31  of the bulkhead  30 . This provides additional support to the bulkhead  30 . 
     The joint  40  formed by the flex angle member  50  and support members  60 ,  70  is configured to both provide a pressure seal that seals the pressure difference between the center wing box  20  and the forward cargo deck  112 . In one example, the center wing box  20  is in communication with the landing gear wheel well  113  and experiences a first pressure level, and the forward cargo deck  112  has a different second pressure level. In one example, the forward cargo deck  112  is pressurized during flight. The joint  40  is further configured to provide a shear continuous load path to accommodate movement of the center wing box  20  relative to the bulkhead  30  and/or fuselage  101 . Further, the joint  40  allows for the wing assembly  102  to flex with respect to the fuselage  101 . The flexible nature of the joint  40  is lighter than an otherwise rigid structure that would resist the movement and would add weight to the aircraft  100 . 
     In one example, the flex angle member  50  is a single piece that extends across the width. In other examples, the flex angle member  50  is constructed from two or more separate pieces that each extend across a limited section of the width. When combined together, the separate pieces extend across the entire width to form the joint  40 . 
     In one example, the joint  40  includes both an aft flex angle member  50  and a forward flex angle member  85 . In another example, the joint includes just a single flex angle member (i.e., either just the aft flex angle member  50  or the forward flex angle member  85 ). 
     As illustrated in  FIG. 3 , the flex angle member  50  is positioned at a central section of the fuselage  101 . In one example, the flex angle member  50  is centered along the width W. Corner fittings  90  are positioned on the lateral sides of the flex angle member  50 . The corner fittings  90  provide further support to the flex angle member  50 . The corner fittings  90  provide a substantial shear connection between the center wing box  20  and the horizontal deck  31 . 
     As best illustrated in  FIG. 8 , the corner fittings  90  include an angled shape with a first section  91  that contacts against the front spar  21  and a second section  92  that contacts against the panels  32  of the bulkhead  30 . A corner  93  is positioned between the first and second sections  91 ,  92  and seats in the intersection of the front spar  21  and panels  32 . The corner fittings  90  include an angle shape with the first and second sections  91 ,  92  aligned at an angle within a range of about 85°-95°. The corner fittings  90  include a different construction than the flex angle member  50  and are less flexible than the flex angle member  50 . In one example, the corner fittings  90  are constructed from titanium or aluminum. The corner fittings  90  are attached to the other structures through one or more of mechanical fasteners and adhesives. 
     One or more support members  70  are connected to the front spar  21  and are positioned on the corner fittings  90 . The support members  70  are connected with pins  72  to the support fittings  56  and have a length to extend over and be connected to each of the second section  92  and the horizontal deck  31 . Likewise, one or more support members  60  are connected with pins  62  to the web  33  of the bulkhead  30 . The support members  60  extend outward from the web  33  on a second side of the horizontal deck  31 . In one example, the support members  60 ,  70  aligned with the corner fittings  90  are aligned in pairs. 
     In one example, corning fittings  90  are further positioned against the bulkhead  30  to support the flex angle member  85 . 
       FIG. 10  illustrates a method of connecting a center wing box  20  to a bulkhead  30  of an aircraft  100 . The method includes positioning a rounded intermediate corner  53  of a flex angle member  50  at an intersection of the center wing box  20  and the bulkhead (block  160 ). The method includes connecting a first section  51  of the flex angle member  50  to the center wing box  20  (block  161 ) and connecting a second section  52  of the flex angle member  50  to the bulkhead  30  (block  162 ). First support members  70  are connected to the center wing box  20  (block  163 ). The first support members  70  support a first side of the second section  52  of the flex angle member  50 . Second support members  60  are connected to the bulkhead  30  (block  164 ). The second support members  60  support the opposing second sides of the second section  52 . 
     The designs disclosed above with the joint  40  connecting the center wing box  20  to the low bulkhead  30  allows a rapid wing to body join where a mostly complete fuselage  101  is lowered onto a fully complete wing assembly  102 . This enables higher production rates and saves factory space and assembly costs. This design also decouples the wing and fuselage loading, allow them to deform independently at the front spar  21 . Further, the design provides for a cost and weight improvement as it eliminates structure which forces the wing and fuselage to move in tandem which is expensive and may have maintenance issues. 
     The device  10  can be used on a variety of aircraft  100 . Aircraft  100  include but are not limited to manned aircraft, unmanned aircraft, manned spacecraft, unmanned spacecraft, manned rotorcraft, unmanned rotorcraft, satellites, rockets, missiles, and combinations thereof. 
     By the term “substantially” with reference to amounts or measurement values, it is meant that the recited characteristic, parameter, or value need not be achieved exactly. Rather, deviations or variations, including, for example, tolerances, measurement error, measurement accuracy limitations, and other factors known to those skilled in the art, may occur in amounts that do not preclude the effect that the characteristic was intended to provide. 
     The present invention may be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the invention. The present embodiments are to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.