Abstract:
A floor to fuselage attachment structure incorporates a truss having an upper angled attachment engaging the floor proximate an edge and extending at an angle upward from the floor edge to attach to the fuselage. Additionally, the truss includes a lower angled attachment engaging the floor proximate the edge and extending at an angle downward to attach to the fuselage. The upper and lower angled attachments support the floor with the edge spaced from the fuselage and further have a plurality of apertures for providing airflow between a first volume above the floor and a second volume below the floor.

Description:
BACKGROUND 
   1. Field of the Invention 
   This invention relates generally to the field of structural architecture for aircraft, and more particularly, to an attachment structure to support a floor substructure to a fuselage with venting for pressure equalization. 
   2. Description of the Related Art 
   Attachment of a honeycomb floor structure to a honeycomb aircraft fuselage requires distribution of the loads through the honeycomb structure to avoid load concentrations and the ability to provide adequate equalization venting between the passenger compartment and the cargo bay in the event of rapid decompression in either of the compartments. Extension inboard is constrained by passenger cabin interior fascia, window seat and passenger foot rest area; therefore this structure must occupy a minimal amount of space for design efficiency. 
   In current aircraft applications the floor is tied directly to the fuselage wall using a traditional “pi” type fitting. This structural architecture places too high a tear off load on the bond between the pi fitting and the honeycomb fuselage wall. 
   Typical aircraft utilize independent features or structures for addressing the decompression venting and the load distribution between the floor and fuselage wall. It is therefore desirable to provide unique structural designs that incorporate load distribution between the floor and the fuselage wall in a minimal amount of space and yet provide for decompression venting. 
   SUMMARY 
   In exemplary embodiments the floor to fuselage attachment structure incorporates a truss having an upper angled attachment engaging the floor proximate an edge and extending at an angle upward from the floor edge to attach to the fuselage. Additionally, the truss includes a lower angled attachment engaging the floor proximate the edge and extending at an angle downward to attach to the fuselage. The upper and lower angled attachments support the floor with the edge spaced from the fuselage and further have a plurality of apertures for providing airflow between a first volume above the floor and a second volume below the floor. 
   In various embodiments, the angled attachments in the truss each employ a web containing the plurality of apertures with a connection feature extending from a first edge of the web and engaging a top surface of the floor proximate the edge and a second connection feature extending from a second edge of the web and engaging an inner surface of the fuselage. The connection feature connecting to the fuselage is typically a flange attached to the web at a predetermined angle for engaging the fuselage inner surface. The connection feature engaging the floor for various embodiments is a horizontal plate extending from the web of the upper and lower angled attachment or a channel engaging both webs. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
       FIG. 1  is an isometric view of a fuselage section incorporating one embodiment of the present invention; 
       FIG. 2  is a partial pictorial view of the embodiment of  FIG. 1  demonstrating venting capability; 
       FIG. 3  is a detail section view of the first embodiment; 
       FIG. 4  is an isometric exploded, view of the first embodiment elements shown in  FIG. 3 ; 
       FIG. 5  is a partial pictorial view of a second embodiment incorporating the invention; 
       FIG. 6  is a detail section view of the second embodiment; 
       FIG. 7  is a detail section view of a third embodiment; 
       FIG. 8  is an exploded isometric view of the elements of the third embodiment of  FIG. 7 ; 
       FIG. 9  is a detail section view of a fourth embodiment; 
       FIG. 10  is a detail section view of a fifth embodiment; 
       FIG. 11  is a section view of an exemplary pi fitting; 
       FIG. 12  is a partial pictorial view of a sixth embodiment with alternative vent shape; 
       FIG. 13  is a detail section view of the elements of the sixth embodiment; 
       FIG. 14  is a detail view of the vent apertures; and 
       FIG. 15  is a detail section of one support element. 
   

   DETAILED DESCRIPTION 
   As shown for a first embodiment in  FIG. 1 , a truss having upper and lower angled attachments  10  and  12  is employed to split and distribute the load path from a honeycomb floor  14  into a honeycomb fuselage  16  while providing the largest gap between floor and fuselage structure in a minimum amount of space. As seen in  FIG. 2 , the angled attachments have integral vent holes  18  that can equal the area of the gap between floor and fuselage to allow equalization of pressure in the passenger and cargo compartments, as represented by flow arrows  20   a - 20   d , if decompression occurred in either of the compartments. The angled attachments are suitably sized to allow some flexure between floor and fuselage wall. The fuselage wail bulges under cabin pressure and needs the floor to help retain its shape. This attachment arrangement while described for the embodiments herein with honeycomb floor to honeycomb fuselage joints is applicable to either metallic or composite floor to fuselage joints as well as. 
   This floor to fuselage wall attachment consists of multiple components that transfer load between floor and fuselage wall. The actual number and arrangement of attachment components can vary according to the floor configuration with a general structural configuration providing two angled webs going from the floor to the fuselage wall using various end arrangements to attach to the floor and fuselage wall. The optimum angle at which the upper and lower attachment angles run from floor to wall is determined by strength requirements through the joint and hole area required for venting from one compartment to the other. 
   In both the upper and lower angled webs, there are features for attachment to the fuselage wall and the floor. As shown in  FIG. 3  for the first embodiment, a first feature on the upper element is an attachment flange  22  that attaches the angled web  24  to the fuselage wall using a 2-part epoxy or alternatively incorporating fasteners. The second feature is an angled fitting  26  that incorporates a horizontal plate  28  which attaches to the floor and a butt plate  30 . The angled webs can run the entire length of a fuselage barrel section or segmented for manufacturing, strength or compartment configuration reasons. Similarly for the lower attachment element with web  32  a nesting angled fitting  34  has a horizontal plate  36  which attaches to the bottom of the floor and a butt plate  38  which extends between the floor edge  40  and the butt plate on the upper angled fitting. Attachment flange  42  connects the lower web to the fuselage wall as described for the upper attachment flange. An exploded view of the elements of this embodiment is shown in  FIG. 4 . 
   Variations of this attachment in alternative embodiments, described in greater detail subsequently include incorporating one or both of the angles into the face sheets of the composite honeycomb floor; providing separate upper and lower metal or composite angles with flanges to support and/or position floor in the fuselage barrel; and including separate metallic or composite webs which use pi (π) shaped edge components or angles to bond or fasten to floor and/or fuselage wall. 
   An important feature of each of these arrangements is a hole pattern in the web that allows a non point load distribution between floor and fuselage wall as well as adequate air passage between compartments for equalizing air pressure on structural components in the advent of rapid decompression in one of the compartments. The size, shape and number of holes are determined by strength and venting requirements of the specific aircraft. 
     FIGS. 5 and 6  show a second embodiment of the novel structure with upper element  10  having an extended horizontal floor attachment plate  44  and lower element  12  having an angle support  46  with a horizontal engagement flange  48  connected to the horizontal floor attachment plate. Angled crook  50  provided as a portion of the support engages the web of the upper element for additional rigidity. The composite floor box  14  is connected to the attachment plate at an edge member  52  which also engages a vertical support  54  which carries a portion of the vertical loading on the floor while the horizontal floor attachment plate reacts tension forces from the fuselage during pressurization as previously described. The upper surface  56  of the floor box merges into a continuous horizontal surface with the attachment plate. 
     FIGS. 7 and 8  show a third embodiment employing horizontal engagement flanges  58 ,  60  on both the upper and lower element to connect to the floor box  14 . For the embodiment as shown, the upper engagement flange is received in a recess  62  in the floor box to provide a flat floor surface. 
     FIG. 9  discloses a fourth embodiment incorporating features from the first and third embodiments with the lower end of the upper element and the upper end of the lower element terminating in a channel  64  providing horizontal upper and lower attachment flanges  66 ,  68  with a vertical buttressing plate  70  to receive the floor box end. Attachment of webs  24 ,  32  to the connection elements is altered in various embodiments with a single integrated piece shown for the embodiment of  FIGS. 7 and 8 . An alternative embodiment is shown in  FIG. 10  with modified Pi fittings  72  employed to attach the web to the channel and upper and lower attachment flanges. The angle of the legs for the pi fittings accommodates the appropriate geometry for the elements as a whole while allowing very simple web structure. An un-angled (perpendicular) pi fitting is shown in  FIG. 11  as a reference. 
   As previously described, the hole pattern for the web in the upper and lower elements allows communication between the cargo hold and passenger compartment. In  FIGS. 12-15  an embodiment is shown with an exemplary elliptical hole  74  employed in the pattern, in the example embodiment for an aircraft application having a 2.5″ thick honeycomb composite floor and a 1.0″ thick honeycomb composite fuselage wall with a nominal radios of 80.0 inches, the upper and lower elements have a length  76  of approximately 10″ formed from 0.050″ thick 6Al 4V Titanium with bend radius on the formed elements of 0.25″. A die forming process provides a flange  78  perpendicularly extending from the web a distance  80  of approximately 0.35″ for greater rigidity. The upper and lower fuselage attachment flanges have a width  82  of approximately 3″ and are welded to the web with, full penetration welds  84  at a preselected angle for flush engagement with the fuselage inner surface. The horizontal engagement flanges have a length  86  of 1.5″ and are bonded to the floor. The elliptical holes in the pattern each, have a major axis  88  of 8.0″ with a minor axis  90  of 6.5″ with a separation of holes  92  of 1.5″ and separation  94  of 1.0″ from each edge of the web. 
   Having now described the invention in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present invention as defined in the following claims.