Patent Publication Number: US-2016244142-A1

Title: Flat kinked rear pressure bulkhead

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of the European patent application No. 15382071.1 filed on Feb. 23, 2015, the entire disclosures of which are incorporated herein by way of reference. 
     FIELD OF THE INVENTION 
     This invention relates to the rear pressure bulkhead of commercial aircraft. 
     BACKGROUND OF THE INVENTION 
     As shown in  FIGS. 1 and 2  the rear pressure bulkhead  11  of a commercial aircraft is the structural component that separates a pressurized cabin  13  from an unpressurized rear section  15  and is therefore subjected to important loads. 
     Curved and flat rear pressure bulkheads  11 , see, respectively,  FIGS. 1 and 2 —made of metallic and/or composite materials are known in the art. 
     U.S. Pat. No. 5,062,589 describes a rear pressure bulkhead of curved geometry made up with a monolithic composite panel of particular thickness and made of a fiber-mesh, a woven or a fleece-like reinforcement of a particular radius of curvature and preferably made of Kevlar; a possibly thicker edged portion of, preferably, carbon fiber-reinforced material, which possibly matches any taper of the fuselage, and a transition from the calotte shaped part to the edge having a radius of curvature smaller than the particular radius of the calotte shaped partition. 
     EP 2 098 448 A1 describes a rear pressure bulkhead of curved geometry made of a composite material, comprising three layers: an outer layer and an inner layer symmetrical with one another, which are made of a fiber laminate, and the intermediate layer or core made of a lightweight material. With such a sandwich-type shape, the resulting bulkhead is able to withstand the bending loads coming from the strain and pressurization of the fuselage without having to increase its stiffness by means of using some type of stiffener. The bulkhead comprises a ring that is attached to the ends of the sandwich shape. This ring is split into several parts to facilitate the assembly of the bulkhead made of composite material to the fuselage skin. 
     While the primary objective of the rear pressure bulkhead is to resist the differential pressures between the pressurized cabin and the unpressurized rear section also play a role in separating the space allocated to both compartments and in that sense both the curved and the flat bulkhead prevents optimal use of space in both compartments. 
     SUMMARY OF THE INVENTION 
     The invention provides an aircraft fuselage with a rear pressure bulkhead separating a pressurized cabin and an unpressurized rear end section that comprises flat portions forming one or more kinks between them, one of said kinks being contiguous to the rear border of the floor of the pressurized cabin. A flat kinked rear pressure bulkhead contributes to a space optimization of the aircraft due to an increase of the size of the unpressurized rear end section that allows additional space for location of systems that are not allowed in a pressurized area, is easier to manufacture and assemble than a curved rear pressure bulkhead and has a better bending inertia than a flat rear pressure bulkhead. 
     In an embodiment, the rear pressure bulkhead comprises upper and lower flat portions forming a kink contiguous to the rear border of the floor of the pressurized cabin. Preferably, the upper flat portion is perpendicular to the longitudinal axis of the fuselage and the lower flat portion forms an angle α with the floor of the pressurized cabin comprised between 30-60°. 
     In an embodiment, the rear pressure bulkhead comprises upper, middle and lower flat portions forming a first kink between the upper and middle flat portions and a second kink between the middle and lower flat portions contiguous to the rear border of the floor of the pressurized cabin. The middle flat portion is disposed in the same plane as the floor of the pressurized cabin so that also serves as a floor of the upper part of the pressurized cabin. Preferably the upper flat portion is perpendicular to the longitudinal axis of the fuselage and the lower flat portion forms an angle β with the floor comprised between 30-60°. 
     The rear pressure bulkhead can be made with a metallic or composite material. 
     In an embodiment with composite material, the rear pressure bulkhead comprises sandwich-type panels in the flat portions and monolithic panels in the kinks and the ends. 
     In another embodiment with composite material, the rear pressure bulkhead is a monolithic panel with stiffening elements in its flat portions. 
     Other characteristics and advantages of the present invention will be clear from the following detailed description of embodiments illustrative of its object in relation to the attached figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 and 2  are schematic side views of the rear part of aircraft fuselages with, respectively, flat and curved rear pressure bulkheads. 
         FIGS. 3 a  and 3 b    are schematic side views illustrating aircraft fuselages with, respectively, a flat rear pressure bulkhead known in the art and a flat kinked rear pressure bulkhead according to the invention. 
         FIGS. 4 and 5  are schematic side views illustrating two embodiments of aircraft fuselages with a flat kinked rear pressure bulkhead. 
         FIG. 6  is a detailed view of the area of  FIG. 5  framed by a circle. 
         FIG. 7  is a schematic side view illustrating an embodiment of a flat kinked rear pressure bulkhead made with sandwich-type composite panels in the flat portions and monolithic panels in kinks and ends. 
         FIG. 8  is a schematic side view illustrating an embodiment of a flat kinked rear pressure bulkhead made with a monolithic panel with stiffening elements in its flat portions. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In accordance with one embodiment of the present invention,  FIG. 1  illustrates a dispenser, generally indicated at  2  and having a tip structure  4 , for mixing at least two separate streams of components into a combined fluid stream, such as a sealant, or tissue sealant or other combined fluid stream. Although the dispensers, systems and methods are generally illustrated and described in the context of a tissue sealant dispenser, it is understood that the present invention is not limited to such a dispenser or to the mixing of tissue sealant components, and that the present invention has applications in a variety of settings where mixing of component fluid streams is desired 
     As shown in  FIG. 1 , dispenser  2  includes at least two fluid component sources, illustrated in the form of hollow cylinders or barrels  6  and  8 , although other source containers from which fluid components are provided may be used. In the embodiment of  FIG. 1 , each barrel  6 ,  8  has a generally cylindrical interior or bore in which one of the fluid components such as fibrinogen or thrombin for forming fibrin tissue sealant is stored. The distal end  7 ,  9 , respectively, of each barrel has an outlet port  11 ,  13 , respectively, for communicating with the dispensing tip structure, generally at  4 . 
     As noted in the Background in reference to  FIGS. 1 and 2 , a rear pressure bulkhead  11 , flat or curved, is used to separate a pressurized cabin  13  from an unpressurized rear section  15  in aircraft fuselages  10  known in the art having a curved shape with a vertical symmetry plane and a central longitudinal axis. 
     The technical evolution of the rear pressure bulkhead  11  of aircraft fuselages has been oriented by two basic objectives: structural efficiency to support differential pressures at both sides and ease of manufacture. In that sense the basic alternatives considered have been a flat or curved geometry on the one hand and the use of metallic or composite material on the other hand. In general terms it can be said that from a structural point of view the curved bulkheads are more efficient than the flat ones but more difficult to manufacture. 
     Flat or curved pressure bulkheads (especially the curved) have the drawback that the space in the unpressurized rear section  15  delimited by them does not allow optimum use of the same to shelter systems housed therein which involves its oversizing and thus an increase in weight and drag. 
     The rear pressure bulkhead  12  proposed by the present invention is a bulkhead formed by flat portions with one or more kinks between them allowing on the one hand to be more effective structurally than a flat bulkhead  11  and, on the other hand, allocating to the unpressurized rear section  15  areas formerly allocated to the pressurized cabin  13  improving the overall distribution of spaces of the aircraft fuselage and thereby reducing the size of the unpressurized rear section  15  and, consequently, the aircraft weight. 
     This flexibility allows additional space in the unpressurized rear section  15  for location of systems that are not allowed in a pressurized area due to safety reasons. It also allows the use of non-critical systems housed in the unpressurized rear section  15  as additional shielding for blade impacts on aircraft with engines mounted on the rear fuselage. 
     Comparing  FIGS. 3 a  and 3 b   , the greatest structural efficiency of a flat kinked rear pressure bulkhead  12  with respect to a typical prior art flat rear pressure bulkhead  11  with stiffening elements  16  in the side facing the unpressurized rear section  15  to support the differential pressure P can be appreciated. The flat kinked rear pressure bulkhead  12  has greater inertia than the flat rear pressure bulkhead  11  as their corners are separated from the neutral fiber  18  which makes unnecessary the stiffening elements  16 . 
       FIG. 4  shows an embodiment of a rear pressure bulkhead  12  with two flat portions  31 ,  35  with a kink  41  between them adjacent to the end of the floor  17  of the pressurized cabin  13  which separates the upper and lower compartments  21 ,  23  intended for, typically, passengers and cargo, respectively. This arrangement allows allocating to the unpressurized rear section  15  the space  45  that would have belonged to the lower compartment  23  of the pressurized cabin  13  if the rear pressure bulkhead  12  did not have the kink  41 . Preferably the angle α between the flat portion  35  and the floor  17  shall be comprised between 30-60°. 
       FIG. 5  shows an embodiment of a rear pressure bulkhead  12  with three flat portions  31 ,  33 ,  35  with a first kink  41  between the flat portions  31  and  33  and a second kink  43  between the flat portions  33 ,  35  adjacent to the rear border  19  of the floor  17  of the pressurized cabin  13 . This arrangement allows allocating to the unpressurized rear section  15  the space  47  that would have belonged to the lower compartment  23  of the pressurized cabin  13  if the rear pressure bulkhead  12  did not have the kinks  41  and  43 . It should be noted that in this embodiment the portion  33  of the rear pressure bulkhead  12  is disposed at the same level as the floor  17  so it can be considered as a continuation of the same and bear the same function of supporting passenger seats. However, the rear pressure bulkhead  12  and the floor  17  of the pressurized cabin  13  are not connected together (they are subject to very different loads) but arranged such that a functional continuity between them is maintained even in case of displacements between the rear border  19  of the floor  17  and the second kink  43 . In this regard,  FIG. 6  shows schematically a rolling device  71  provided in the lower flat portion  35  of the rear pressure bulkhead  12  to facilitate such a functional continuity. Preferably the angle β between the flat portion  35  and the floor  17  shall be comprised between 30-60°. 
     The rear pressure bulkhead  12  can be manufactured with metallic or composite materials. 
     In the last case, it can be a monolithic or sandwich structure although the preferred option is a mixed structure combining sandwich type panels in the flat portions and monolithic panels on the kinks and ends, such as those shown in  FIG. 7  that correspond to the rear pressure bulkhead shown in  FIG. 5 : the rear pressure bulkhead  12  is formed by sandwich type panels  51 ,  53 .  55  in the flat portions  31 ,  33 ,  35 , by the monolithic panels  57 ,  59  in the kinks  41 ,  43  and by the monolithic panels  61 ,  63  in the ends, properly shaped to be joined to the skin of the aircraft fuselage  10 . The more stressed areas (edges, kinks) are therefore built with a monolithic structure (more weight but less thickness required) while the interior areas are built with a sandwich structure (less weight but more thickness required). Due to this fact, a compromise solution is achieved, reducing thickness without much weight increase. 
     The rear pressure bulkhead  12  can also be, as shown in  FIG. 8 , a monolithic panel  73  with stiffening elements  75  in its flat portions (for a rear pressure bulkhead with two flat portions as that shown in  FIG. 4 ). 
     Although the present invention has been described in connection with various embodiments, it will be appreciated from the specification that various combinations of elements, variations or improvements therein may be made, and are within the scope of the invention as defined by the appended claims. 
     While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.