Patent Publication Number: US-2022212773-A1

Title: Aircraft keel beam assembly

Description:
RELATED APPLICATIONS 
     This non-provisional patent application claims priority to U.S. Provisional Patent Application No. 63/134,587 filed on Jan. 6, 2021, which is incorporated by reference as if fully provided herein. 
    
    
     FIELD 
     This disclosure relates to the field of aircraft and, in particular, to a keel beam assembly of an aircraft. 
     BACKGROUND 
     Large aircraft typically have a large cutout at the bottom side of the fuselage to accommodate the wing structure and main landing gear bay. To provide structural support for this cutout, the aircraft may include a keel beam disposed underneath the center wing box extending longitudinally, or forward and aft, through the cutout. In addition to transferring fuselage forces in the longitudinal direction, the keel beam may also provide structure that protects the aircraft in the event of a wheels-up emergency landing. However, the load path that a typical keel beam provides may involve complicated structure that interferes with installation of environmental control systems (e.g., aircraft ducts). Additionally, the structural support of the keel beam may cause undesirable force coupling between the fuselage and wings. 
     SUMMARY 
     Embodiments described herein provide a keel beam assembly for an aircraft. The keel beam assembly includes a cutback configuration at its forward end. This provides a technical benefit in providing flexibility in the keel beam assembly that enables increased independent movement as between the wings and fuselage pressure barrier of the aircraft, and the shape of the cutout reduces an undesirable stress concentration. Additionally, the cutback configuration creates an increased open area for improved assembly of the keel beam to the aircraft and improved installation of aircraft systems, such as environmental control systems. Furthermore, despite the increased open area, the cutback configuration provides sufficient vertical support for a wheels-up emergency landing. 
     One embodiment is a keel beam assembly of an aircraft. The keel beam assembly includes a keel attach chord to connect to a wing center section of the aircraft, the keel attach chord extending in a longitudinal direction between a rear spar and front spar of the aircraft. The keel beam assembly also includes a lower chord disposed underneath the keel attach chord and extending in the longitudinal direction between an aft wheel well bulkhead and a forward bulkhead of the aircraft. The keel beam assembly further includes a forward web to couple the keel attach chord and the lower chord, the forward web including a front edge extending in a diagonal direction from the keel attach chord that is downward and aft toward the lower chord to create an open area forward from the front edge. 
     Another embodiment is an aircraft including a fuselage, a wing center section, and a fuselage cutout to house the wing center section. The fuselage cutout defined by a forward bulkhead and an aft bulkhead of the fuselage. The aircraft also includes a keel beam assembly extending through the fuselage cutout from the aft bulkhead to the forward bulkhead, the keel beam assembly includes a forward web at a forward end of the keel beam assembly, the forward web including a front edge extending in a diagonal direction that is downward and aft toward to create an open area forward from the front edge and aft of the forward bulkhead of the fuselage. 
     Yet another embodiment is a keel beam assembly of an aircraft. The keel beam assembly includes a pair of keel attach chords to connect to a wing center section of the aircraft, and a pair of lower chords disposed underneath the pair of keel attach chords to span a fuselage cutout of the aircraft from an aft bulkhead to a forward bulkhead. The keel beam assembly also includes a pair of forward webs to form sidewalls connecting the pair of keel attach chords to the pair of lower chords, wherein the forward webs include a cutback frontside that extends in a diagonal direction from the pair of keel attach chords that is downward and aft toward the pair of lower chords to create an open area between the forward bulkhead and the keel beam assembly. 
     The features, functions, and advantages that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Some embodiments are now described, by way of example only, and with reference to the accompanying drawings. The same reference number represents the same element or the same type of element on all drawings. 
         FIG. 1  is a side view of an aircraft in an illustrative embodiment. 
         FIG. 2  is a side view of the keel beam assembly in an illustrative embodiment. 
         FIG. 3  is a front perspective view of the keel beam assembly in an illustrative embodiment. 
         FIG. 4  is a side view of a front portion of the keel beam assembly in an illustrative embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The figures and the following description illustrate specific example embodiments. It will be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles described herein and are included within the contemplated scope of the claims that follow this description. Furthermore, any examples described herein are intended to aid in understanding the principles of the disclosure are to be construed as being without limitation. As a result, this disclosure is not limited to the specific embodiments or examples described below, but by the claims and their equivalents. 
       FIG. 1  is a side view of an aircraft  100  in an illustrative embodiment. The aircraft includes a fuselage  102  with a fuselage cutout  104  along its bottom side to accommodate a wing center section  110  and a main gear wheel well  120 . The wing center section  110  includes structure coupling the wings (not shown) and fuselage  102  of the aircraft  100 . The main gear wheel well  120  is configured to store the main landing gear of the aircraft  100  during flight. The fuselage cutout  104  is an open area in the fuselage  102  defined by a forward bulkhead  106  and aft bulkhead  108 . That is, the forward bulkhead  106  may comprise a vertical barrier (sometimes referred to as a fuselage pressure barrier) to a forward fuselage section and the aft bulkhead  108  may comprise a vertical barrier to an aft fuselage section. 
     The aircraft  100  includes a keel beam assembly  150  for structural support of the fuselage cutout  104 . The keel beam assembly  150  extends in a longitudinal direction, or forward and aft, between the forward bulkhead  106  and the aft bulkhead  108  and is configured to absorb compressive loads of the fuselage  102 . In addition to transferring loads forward and aft through the fuselage cutout  104 , the keel beam assembly  150  transfers load between the wings and fuselage  102  and also protects the fuselage  102  in case of a wheels-up emergency landing of the aircraft  100 . However, the load path that a typical keel beam provides may involve complicated structure that interferes with installation of environmental control systems (e.g., aircraft ducts). Additionally, the structural support provided by a typical keel beam may cause undesirable force coupling between the fuselage  102  and wings of the aircraft  100 . 
     The keel beam assembly  150  is therefore enhanced with a cutback configuration that provides increased space for assembling the keel beam assembly  150  to the fuselage  102  and installing aircraft systems, such as environmental control systems. The keel beam assembly  150  configuration advantageously simplifies integration with the forward bulkhead  106  and reduces keel web stress concentration. Moreover, the keel beam assembly  150  provides sufficient load path from the ground to the forward bulkhead  106  in case of a wheels-up emergency landing while realizing cost and weight savings. Additional details and technical benefits of the keel beam assembly  150  are discussed below. 
       FIG. 2  is a side view of the keel beam assembly  150  in an illustrative embodiment. As shown in  FIG. 2 , a forward portion of the keel beam assembly  150  is disposed underneath the wing center section  110  and an aft portion of the keel beam assembly bridges the main gear wheel well  120  aft of the wing center section  110 . The keel beam assembly  150  includes a keel attach chord  210  to support and/or connect to the wing center section  110 . The keel beam assembly  150  also includes a lower chord  220  disposed underneath the keel attach chord  210 . The keel attach chord  210  and lower chord  220  generally comprise beam support structures for the fuselage cutout  104 . 
     In one embodiment, and as shown in  FIG. 2 , the forward bulkhead  106  and a horizontal pressure panel  244  of the fuselage  102  comprises a front spar offset pressure barrier. In this configuration, the front spar  204  and forward bulkhead  208  are offset, with the front spar  204  disposed aft of the forward bulkhead  208 . In such embodiments, the keel attach chord  210  extends in a longitudinal direction between a rear spar  202  and front spar  204  of the aircraft  100 , and the lower chord  220  extends in the longitudinal direction between an aft wheel well bulkhead  206  and a forward bulkhead  208  of the aircraft  100 , as shown in  FIG. 2 . The lower chord  220  is attached to the forward bulkhead  208  via a forward keel splice  228 , and attached to the aft wheel well bulkhead  206  via an aft keel splice  226 . The aft keel splice  226  may also attach the keel attach chord  210  to the aft wheel well bulkhead  206 . However, it will be appreciated that the keel beam assembly  150  may attach with fuselage  102  in alternative configurations including non-offset versions of the forward bulkhead  106 . 
     The keel beam assembly  150  further includes a forward web  230  to couple the keel attach chord  210  and the lower chord  220 . The forward web  230  includes a front edge  232  extending in a diagonal direction from the keel attach chord  210  that is downward and aft toward the lower chord  220  to create an open area  250  forward from the front edge  232 . The forward web  230  thus includes a cutback configuration which increases the size of the open area  250  as compared to vertical structure in this region that may otherwise occupy this area. The keel beam assembly  150  thus includes a front end or front portion that provides a cutout for improved ergonomic access for installing the keel beam assembly  150  and various aircraft systems (e.g., environment control systems, wires for thermal sensor, duct burst sensors, etc.). Additionally, the cutback configuration of the forward web  230  provides a technical benefit in providing flexibility in the keel beam assembly  150  that enables increased independent movement as between the wings and fuselage  102  of the aircraft  100  and the shape of the cutout reduces an undesirable stress concentration. 
     The open area  250  extends in a transverse direction, or an inboard/outboard direction, across the fuselage  102  and is sized to accommodate environmental control systems for the aircraft  100 . Generally, the open area  250  is disposed aft of the forward bulkhead  208  and forward from the front edge  232  of the forward web  230 . The open area  250  may also be generally disposed underneath the front spar  204  and above the lower chord  220 . In one embodiment, the open area  250  is enclosed or defined by the front edge  232  of the forward web  230 , the lower chord  220 , the forward bulkhead  208 , and/or the supporting structure of the front spar  204 . In one embodiment, the open area  250  is created by removing the lightly loaded portion of the forward web  230 . 
     An aft portion of the keel beam assembly  150  may include a keel box  278  disposed over the lower chord  220  and extending between the aft wheel well bulkhead  206  and the rear spar  202 . A forward portion of the keel beam assembly  150  may include, in addition to the forward web  230 , one or more mid webs  261  and one or more aft webs  262  which are disposed aft of the forward web  230 . Vertical support structures  271 - 273  coupling between the lower chord  220  and keel attach chord  210  may be provided along the forward portion to support underneath the wing center section  110 . For instance, a first vertical support structure  271  and a second vertical support structure  272  may support directly underneath respective spanwise beams (not shown) of the wing center section  110 . The vertical support structures  271 - 273  may frame the under-wing web panels  230  and  261 - 262  for stability. In one embodiment, the forward web  230  may include a wall structure in a vertical plane with sides defined by a boundary of the first vertical support structure  271 , lower chord  220 , front edge  232 , and keel attach chord  210 . In some embodiments, a rear portion of the front edge  232  extends vertically downward to create a trapezoid-shaped corner of the cutout. 
       FIG. 3  is a front perspective view of the keel beam assembly  150  in an illustrative embodiment.  FIG. 3  generally shows that the keel beam assembly  150  is symmetrical with pairs of structural components that mirror each other about a center line, forming mirrored left and right sides with respect to the transverse direction. As such, the keel beam assembly may include a pair of keel attach chords  210 , a pair of lower chords  220 , and a pair of forward webs  230 . The pair of forward webs  230  form sidewalls which respectively connect one of the pair of keel attach chords  210  to a corresponding one of the pair of lower chords  220 . The forward webs  230  include a cutback frontside, or front edge  232 , that extends in a diagonal direction from the pair of keel attach chords  210  that is downward and aft toward the pair of lower chords  220 . This creates the open area  250  between the forward bulkhead  106  (not shown in  FIG. 3 ) and the keel beam assembly  150 , as earlier described. 
     As further shown in  FIG. 3 , keel beam assembly  150  includes a diagonal stiffener  310  disposed along the front edge  232  of each forward web  230 . The diagonal stiffener  310  is configured to provide a vertical load path for the keel beam assembly  150 . That is, the diagonal stiffener  310  strengthens the structural support for vertical forces acting on the keel beam assembly  150 . The diagonal stiffener  310  may thus help the keel beam assembly  150  provide sufficient vertical support for a wheels-up emergency landing while also providing an increased size of the open area  250 . The pair of diagonal stiffeners  310  are coupled with each other with one or more transverse stiffeners  312  and/or one or more transverse webs  314 - 318  extending inboard/outboard and configured to strengthen the cutback frontend of the keel beam assembly  150 . The transverse webs may include a lower transverse web  314 , a transverse closing web  316 , and an upper transverse web  318 . 
     The pair of lower chords  220  may be coupled with each other with a lower truss shear web  322  and an upper truss shear web  324  and/or a lattice fitting  326 . This structure extends inboard/outboard to strengthen the front-end portion of the lower chords  220  that is underneath the open area  250  to prevent buckling of the unsupported cutout length due to the cutback configuration. In some embodiments, webs of the keel beam assembly  150 , including the forward webs  230 , transverse webs  314 - 318 , and shear webs  322 - 324  include a sheet-like metal structure such as aluminum to provide wall structure between beams of the keel beam assembly  150 . Webs of the keel beam assembly  150  may be integrally machined with diagonal stiffeners  310  and/or stiffeners/ribs for increased strength of the keel beam assembly  150  and support of the wing center section  110 . 
     The keel beam assembly  150  also includes a pair of closeout end fittings  330  to couple the pair of diagonal stiffeners  310  with the pair of keel attach chords  210 . In some embodiments, the corner at which the forward web  230  joins the keel attach chord  210  is disposed directly underneath the front spar  204 .  FIG. 3  also shows that the keel attach chord  210  may support underneath and/or attach with a lower skin panel  340  of the wing center section  110 . Additionally, the keel beam assembly  150  may include one or more vertical stiffeners disposed at an inboard side of the forward web  230  that extends in a vertical direction and across the diagonal stiffener  310  to connect the lower chord  220  and the keel attach chord  210 . The vertical stiffeners  410  may provide structural support and stability for the wing stringers and stability for the keel beam webs. 
       FIG. 4  is a side view of a front portion of the keel beam assembly  150  in an illustrative embodiment. The wing center section  110  may include a gusset  420  to support the vertical load path for the diagonal stiffener  310 . The gusset  420  may help prevent a radius of the front spar  204  from opening in failsafe cases such as rotorburst. In one embodiment, a front edge  232  (or diagonal stiffener  310 —not shown) of the forward web  230  extends from its front end disposed underneath the gusset  420  (e.g., with respect to forward/aft direction) to its back end attached with the lower chord  220 . The front edge  232  and/or diagonal stiffener  310  may thus integrate with a front spar offset pressure barrier configuration and support the front spar  204  in offset alignment with the forward bulkhead  208 . Additional structure for the front spar offset pressure barrier may include one or more vertical bulkhead stiffeners  432  and one or more horizontal pressure panels  244 . 
     The front edge  232  of the forward web  230  extends in the diagonal direction (e.g., downward back toward a tail of the aircraft  100 ) at angle  450 . The angle  450  may be defined as between the lower chord  220  and the front edge  232  of the forward web  230 . In one embodiment, the angle  450  is in a range from thirty degrees to fifty degrees. In one particular embodiment, the angle  450  is approximately thirty-seven degrees. However, it will be appreciated that technical benefits of the keel beam assembly  150  described herein may be realized with alternative cutback angles. 
     Although specific embodiments were described herein, the scope is not limited to those specific embodiments. Rather, the scope is defined by the following claims and any equivalents thereof.