Abstract:
A drain for expelling fluids from an interior of an aircraft to an exterior of the aircraft, the drain including a drain tube disposed at the interior of the aircraft having a first end disposed in fluid communication with an aircraft equipment to be drained and an opposite second end, wherein the drain tube terminates at the second end at a location within the interior of the aircraft, a seal which extends between the second end of the drain tube and an outer skin of the aircraft, delimiting a drainage cavity, and a drainage pathway extending from the cavity through the outer skin to the exterior of the aircraft.

Description:
CROSS REFERENCE TO RELATED APPLICATION AND CLAIM OF PRIORITY 
       [0001]    The present application claims priority to U.S. provisional patent application No. 61/773,298 filed on Mar. 6, 2013, the entire contents of which are hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to a system for draining fluids from an aircraft and, more particularly, to a system for expelling leaked or otherwise unwanted fluid from aircraft components to an exterior of the aircraft where the system includes protection against lightning direct strike and attachment. 
       RELATED ART 
       [0003]    Certain aircraft systems and components include drain systems which collect and expel  10  fluids which may leak from the systems or components or which otherwise accumulate in a cavity within the aircraft. The fluids may be flammable liquids such as fuel or oil or non-flammable fluids such as water. The drainage system directs such fluids to the exterior of the aircraft where the fluid is released into the atmosphere. 
         [0004]    Traditional drain systems typically consist of one or more drain tubes connected at one end with the aircraft system or component that is susceptible to leakage, a body which extends between the first end and an outer skin of the aircraft, and a second opposite end which extends through the outer skin and protrudes slightly from the aircraft.  FIG. 1 , for example, shows a schematic cross-section view of a portion of a conventional drainage system including a plurality of drain tubes  10 ,  12 ,  14 , and  16  each having first ends (not shown) disposed in fluid communication with an aircraft system or component. The drain tubes  10 ,  12 ,  14 , and  16  further include respective second ends  18 ,  20 ,  22 , and  24  which each extend through an outer skin  26  of the aircraft to an exterior where the drain tubes  10 ,  12 ,  14 , and  16  terminate. The seconds ends  18 ,  20 ,  22 , and  24  of the drain tubes  10 ,  12 ,  14 , and  16  typically extend about 0.65 inches or more beyond the aircraft outer skin  26 . The drainage system of  FIG. 1  is for an auxiliary power unit (APU) disposed in a tail cone of the aircraft. The drain tubes  10 ,  12 ,  14 , and  16  are respectively connected to the following APU components: an inlet plenum drain; a fuel control drain; a bearing seal witness drain; and a turbine plenum drain. In use, any excess fluids which leak or are otherwise discharged from these various APU components are driven by gravity through the drain tubes  10 ,  12 ,  14 , and  16  to the second ends thereof  18 ,  20 ,  22 , and  24  where the fluids pass through the outer skin  26  are expelled into the atmosphere. 
         [0005]    As mentioned, each of the drain tubes  10 ,  12 ,  14 , and  16  extend from the outer aircraft skin  26  about 0.65 inches or more. That is, the drain tubes protrude into the atmosphere surrounding the aircraft. Additionally, the drain tubes, or at least the second protruding ends thereof, may be composed of a conductive material. As such, the protruding drain tubes may be susceptible to lightning strike and attachment. This is particularly the case with regard to the APU drain tubes illustrated in  FIG. 1  which are traditionally disposed on the lower angled surface of the aircraft composite tail cone at the APU access door skin. This is considered to be “zone 2A—swept stroke” and thus lightning effects must be considered. 
         [0006]    Accordingly, there is a need for an aircraft drainage system which allows for expulsion of leaked or discharged fluids while at the same time minimizing lightning damage potential. 
       BRIEF SUMMARY 
       [0007]    The disclosure provides a drain for expelling fluids from an interior of an aircraft to an exterior of the aircraft, the drain including a drain tube disposed at the interior of the aircraft having a first end disposed in fluid communication with an aircraft equipment to be drained and an opposite second end, wherein the drain tube terminates at the second end at a location within the interior of the aircraft, a seal which extends between the second end of the drain tube and an outer skin of the aircraft, delimiting a drainage cavity, and a drainage pathway extending from the cavity through the outer skin to the exterior of the aircraft. 
         [0008]    The disclosure further provides a drainage system for an aircraft auxiliary power unit disposed in a tail cone of the aircraft, the drainage system including a drain tube having a first end disposed in fluid communication with the APU and configured to receive excess fluid from the APU, the drain tube further including an opposite second end, wherein the drain tube terminates at the second end at a location within the tail cone above a lower angled outer skin of the tail cone, a seal which surrounds and seals the second end of the drain tube, wherein the seal extends downwardly to the angled outer skin of the tail cone and seals thereagainst, delimiting a hermetically sealed drainage cavity, a perforation extending through the angled outer skin to an exterior of the aircraft, and a flange disposed on the outer skin at the exterior of the aircraft and extending over the perforation, the flange being configured to direct drained fluid at the exterior of the aircraft and to cover the perforation at the exterior of the aircraft to prevent lightning from entering the cavity, wherein the perforation is disposed in the angled outer skin at a relative low point of the cavity to facilitate gravity fed drainage of the fluid therethrough. 
         [0009]    The above described and other features are exemplified by the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a schematic cross-sectional view of a conventional aircraft drain arrangement; 
           [0011]      FIG. 2  is a side view of an aircraft; 
           [0012]      FIG. 3  is a partial cross section view of a tail cone of the aircraft of  FIG. 2 ; 
           [0013]      FIG. 4  is perspective view of an access door of the tail cone of  FIG. 3 ; 
           [0014]      FIG. 5  is a perspective view of a drainage system according to one exemplary embodiment; 
           [0015]      FIG. 6  is another perspective view thereof; 
           [0016]      FIG. 7  is another perspective view thereof; 
           [0017]      FIGS. 8-10  are various cross-sectional views thereof; and 
           [0018]      FIG. 11  is a schematic cross sectional view of the drainage system of  FIG. 6 . 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      FIG. 2  shows an exemplary aircraft  50  having a tail cone  52 . An auxiliary power unit (APU) is disposed within the tail cone  52 .  FIG. 3  shows an enlarged cross-sectional partial view of the tail cone  52 . The tail cone  52  includes an outer skin  54  which extends over the internal aircraft structure which houses the APU  58 . An APU access door  60  is disposed on a lower side  62  of the tail cone  52 . The access door  60  is movable between a closed position (as shown) in which the APU  58  and an interior of the tail cone  52  are inaccessible, and an open position (not shown) in which the door  60  is positioned away from the tail cone such that the APU and tail cone interior may be accessed. The door  60  is typically hinged such that it pivots between the open and closed positions. The lower side  62  of the tail cone  52  is angled with a low point disposed toward the aircraft&#39;s front such that the lower side  62  angles upwardly in the aft direction. Thus, the outer skin of the tail cone  52 , including the APU access door  60 , correspondingly angles upwardly in the aft direction such that a low point is located toward the aircraft front. 
         [0020]      FIG. 4  shows the APU access door  60  as including an outer skin  64  having an inner side  66  and an outer side  68 . The inner side  66  of the skin  64  is disposed within the tail cone interior; the outer side  68  is on the exterior of the aircraft and is exposed to the atmosphere. A honeycomb structure  70  is disposed on the inner side  66  of the skin  64  and lends strength and reinforcement to the door  60 . The honeycomb structure  70  extends over much of the door  60  but includes a cut away portion  72  which exposes a portion of the inner skin  66 . 
         [0021]    A drainage system  100  is shown adjacent to the inner skin  66  of the door  60  at the cutaway portion  72  of the honeycomb structure  70 . The drainage system  100  includes a seal  102  and one or more drain tubes  104 . As will be discussed in detail, the seal  102  is affixed at one side to the internal structure of the aircraft and while an opposite side of the seal  102  engages the inner side  66  of the outer skin  64  of the door  60  when the door is in the closed configuration.  FIG. 4  shows the seal  102  engaging the door  60  in the closed position. The drain tubes  104  terminate within the seal  102 , as will be discussed herein in further detail, and extend in an opposite direction away from the seal  102 . 
         [0022]      FIG. 5  shows an enlarged view of the drainage system  100 . In this illustrative embodiment, four drain tubes  104  extend into the seal  102 . However, the drainage system  100  may include more or less drain tubes  104  depending upon a specific application and requirements of the system  100 . 
         [0023]      FIGS. 6-7  is an enlarged view of the drainage system  100  and a partial view of the door  60 . As shown, the system  100  further includes a bracket  106  and a flange  108 . The flange  108  receives and supports the drain tubes  104  in a generally vertical orientation. The flange  108  is mounted upon the bracket  106  which is connected to an interior structure of the aircraft. In the illustrated example, the bracket  106  is connected to the APU  58 . The bracket  106  includes a mounting surface  110  upon which an upper side  112  of the seal  102  is fixedly mounted. As referenced above, a lower side  114  of the seal  104  is in contact with and engages the inner side  66  of the outer skin  64  of the door  60 . When the door  60  is moved into the opened position, the lower side  114  of the seal  102  disengages from the door  60  thus allowing the door  60  to move to a location remote from the seal  102  and the drain tubes  104 . When the door  60  is moved back into the closed position, the inner side  66  of the door  60  is brought proximate to the seal  102  such that the lower side  114  of the seal  102  contacts and, as discussed further herein, sealingly engages with the door  60 . 
         [0024]      FIGS. 8 and 9  are cross-sectional views of the arrangement of  FIGS. 6 and 7  taken along the axes Y-Y and X-X, respectively. As shown, the seal  102  delimits a cavity  120  at an interior of the seal  102 . The cavity  120  extends through the seal  102  and is bounded at an upper region by the flange  108  and the drain tubes  104 , and is further bounded at a lower region by the inner side  66  of the skin  64  of the APU access door  60 . This holds when the door  60  is in the closed position, as illustrated. When the door  60  is moved to the open position, the lower side  114  of the seal disengages from the inner side  66  of the door  60  such that the door  60  is free to travel to a position away from the bracket  106 , drain tubes  104 , and seal  102 . In this open position, the cavity  120  is open and exposed to the environment. As discussed above, when the door  60  is brought into the closed position, the seal  102  sealingly engages against the inner side  66  of the skin  64  of the door. In this closed position, the seal cavity  120  is hermetically sealed with respect to the remainder of the interior of the tail cone. 
         [0025]    The drain tubes  104  extend through the flange  108  and through the bracket  106  into the cavity  120 . The drain tubes terminate in the upper region of the cavity  120  proximate to the upper side  112  of the seal  102 . 
         [0026]    At the lower region of the cavity  120 , the lower portion  114  of the seal is engaged against the outer skin  64  of the door  60 . As such, a portion  65  of the inner side  66  of the door skin  64  is disposed within the cavity  120 . A perforation  122  is formed in this portion  65  of the outer skin  64  of the door  60 . The perforation  122  extends from the cavity  120 , through the outer skin  64  of the door  60 , to an exterior of the aircraft. In the exemplary illustrated embodiment, the perforation  122  is a hole having a circular shape. However, the perforation  122  may assume any desired shape suitable for a particular application of the drainage system  100 . For example, the perforation may curvilinear shaped, rectilinear shaped, or a combination shape having both curvilinear and rectilinear features. In the illustrated embodiment, the system  100  includes a single perforation  122 . In an alternate embodiment, the drainage system may include more than one perforation. Such multiple perforations can be similarly or differently shaped and they can be disposed proximate or distal to one another. 
         [0027]    Where the cavity  120  includes a low point, the perforation(s) are preferably positioned proximate to such low point. For example, where the aircraft outer skin  64  is angled relative to a vertical axis of the aircraft and the drainage system is disposed at such angled outer skin  64 , a low point is created within the cavity. In such situation, the seal  102  is affixed perpendicularly to the angled outer skin  64 , as shown in the drawings, thus the cavity itself will be angled and will likely include an area which is lower on the vertical axis than other areas within the cavity. The perforation is preferably disposed within this low area to facilitate gravity induced drainage of any fluids within the cavity  120 . 
         [0028]    A scupper flange  124  is disposed at the exterior of the aircraft on the outer side  68  of the skin  64  of the door  60  proximate to the perforation  122 . The scupper flange  124  extends over the perforation  122  and serves to direct expelled fluid in a predetermined direction at the exterior of the aircraft. Also, the scupper flange  124  serves to cover the perforation  122  and protect the cavity  120  and the remainder of the drainage system  100  from lightning which may occur at the exterior of the aircraft. That is, the scupper flange, preferably made of carbon fiber or a similar material, blocks the perforation  122  and the cavity  120  and thus prevents a lightning strike from entering. 
         [0029]      FIG. 10  shows another cross-sectional view of the seal  102  and drain tubes  104  in isolation. The exemplary contour and shape of the seal  102  and of the corresponding cavity  120  are illustrated. 
         [0030]    As mentioned, the drain tubes  104  of the drainage system  100  terminate at one end in the cavity  120 . The drain tubes  104  extend away from the seal  102  within the aircraft interior and terminate at opposite second ends at an aircraft system or component that is susceptible to fluid leakage or accumulation which requires periodic drainage. In the illustrated example, the drain tubes  104  extend to and are in fluid communication with various components of the APU  58 . For example, the drain tubes may extend to one or more of the APU inlet plenum drain, the fuel control drain, the bearing seal witness drain, and the turbine plenum drain. When fluid enters the drain tubes  104 , it is fed by gravity to the terminal ends of the drain tubes  104  disposed within the cavity  120  within the seal  102 . The fluid descends from the terminal ends of the drain tubes  104 , and flows downward through the cavity  120  to the area  65  of the inner side  66  of the outer skin  66  of the door  60 . As discussed, the perforation  122  is formed at a low point of this area  65 . Therefore, the leaked fluid is drawn by gravity into the perforation  122 , through the outer skin  64  of the door  60 , and into and through the scupper flange  124  from where it is expelled into the atmosphere. Of course, this scenario is with the door in the closed position. With the door in the open position, assuming the aircraft is grounded, liquid descending from the drain tubes  104  would simply fall from the tail cone to the ground. 
         [0031]    In the illustrated embodiment, the seal  102  has an oval cross-section and thus the delimited cavity  120  possesses a correspondingly ovoid shape. This is merely exemplary, however. The seal  102  can assume any cross-sectional shape suitable for receiving the drain tubes  104 , for extending to and engaging with the door  60 , and for surrounding the perforation  122 . 
         [0032]    The seal  102 , in the instant embodiment, is formed of a flexible material and is configured to absorb movement of the bracket  106  and APU  58  relative to the aircraft outer skin  64  and, vice versa, movement of the outer skin  64  relative to the interior components of the drainage system  100 .  FIG. 11  is a schematic cross-section of the drainage system  100  in which the lower side  114  of the seal  102  is compressed against the door  60 . This compression may be a result of the relative motion described above. 
         [0033]    Additionally and/or alternatively, the seal  102  may further be formed of a fire resistant material. 
         [0034]    As discussed herein, the seal  102  is affixed at the upper side  112  to the mounting surface  110  of the bracket  106 . The seal  102  extends from the bracket  106  toward the APU access door  60  and includes the freely extending lower end  114  which, in the closed position, contacts and seals against the inner side  66  of the door skin  64 . In this configuration, the seal is not affixed to the door  60 , but instead the lower side  114  of the seal  102  sealingly engages the seal surface inner side  66  to hermetically seal the cavity  120  when the door  60  is closed. When the door is moved into the opened position, the engagement of the seal  102  and the door  60  is broken and the cavity  120  is exposed. 
         [0035]    In alternate embodiment, the lower side  114  of the seal  102  is affixed to the inner side  66  of the outer skin  64  of the door  60 . In this configuration, the upper side  112  of the seal  102  extends freely towards the bracket  106  which, in this embodiment, includes a sealing surface  110 . In the closed position, the upper side  112  of the seal  102  contacts and sealingly engages the sealing surface  110  of the bracket to thus form and hermetically seal the cavity  120 . When the door is moved to the open position, the upper side  112  of the seal  102  disengages the bracket  106  and, because the seal  102  is affixed to the door  60 , the seal travels with the door  60  as it moves away from the bracket  106  and drain tubes  104  into the open position. 
         [0036]    The drainage system  100  creates a drainage pathway  150  as illustrated in  FIG. 8 . The pathway  150  extends from the drain tubes  104 , into and through the cavity  120 , into the perforation  122  and through the outer skin  64  of the aircraft, and finally into the scupper flange  124  from which the fluid is expelled into the atmosphere. The fluid is driven along the pathway by gravity and perhaps by a pressure differential created between the stationary air within the cavity and the moving air at the exterior of the aircraft passing around the scupper flange  124 . The drainage pathway  150  is suited for fluid movement only in the direction described, fluid may not move in the opposite direction of the described fluid pathway  150 . 
         [0037]    As described, the fluid pathway  150  is suitable for fluid flow but is not a suitable pathway for lightning or movement of lightning energy. The scoop flange  124  inhibits entry of lightning into the cavity  120 . Moreover, the described pathway  150  does not provide any direct pathway for lightning to travel into the aircraft. That is, the seal is an elastic, fire-resistant, non-conductive material which does not offer a pathway for lightning. Furthermore, metallic conductive items such as the bracket  106  and drain tubes  104  are disposed at a distance from the outer skin  64  of the aircraft and from the perforation  122  formed therein. Thus, even if lightning somehow penetrated the cavity  122  or attached to a fluid droplet in scupper flange  124 , further movement of the lightning within the aircraft would be inhibited. 
         [0038]    The illustrated embodiment of the aircraft drainage system  100  is described as being disposed at the tail cone of the aircraft to provide drainage to the APU  58 . This is merely exemplary. The system  100  may be utilized at a variety of locations across the aircraft. More specifically, the drainage system  100  may be used at any location on the aircraft where drainage of flammable or non-flammable fluids is desired, and particularly in areas susceptible to lightning exposure. 
         [0039]    As used herein the terms “comprising” (also “comprises,” etc.), “having,” and “including” is inclusive (open-ended) and does not exclude additional, unrecited elements or method steps. The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. The term “or” means “and/or.” Reference throughout the specification to “one embodiment”, “another embodiment”, “an embodiment”, and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various embodiments. 
         [0040]    While the invention has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.