Abstract:
An example inert gas distribution arrangement includes a first fuel tank and a second fuel tank mountable to an aircraft outboard the first fuel tank. A distribution conduit is configured to communicate inert gas to the first fuel tank through a first outlet and further configured to communicate inert gas to the second fuel tank through a second outlet. Fuel in the distribution conduit is biased to flow from the second fuel tank toward the first fuel tank when the aircraft is in selected aircraft attitudes.

Description:
BACKGROUND 
       [0001]    This invention relates to limiting movement of aircraft fuel away from the aircraft&#39;s fuel zone, particularly movement of aircraft fuel through the aircraft&#39;s inert gas generation system. 
         [0002]    Inert gas distribution systems arte used to introduce inert gas to fuel tanks within an aircraft. The introduced inert gas, such as nitrogen enriched air, covers the interior of the fuel tanks and displaces a fuel-air mixture within the tanks. As the aircraft uses more fuel, more inert gas is introduced into the fuel tanks. The inert gas desirably reduces the possibility of a fuel-air mixture igniting within the fuel tanks. 
         [0003]    As known, the fuel tanks are located within a fuel zone of the aircraft. Flammable fuel is normally present within the fuel zone. The inert gas distribution system is located outside the fuel zone within a flammable leakage zone. In the flammable leakage zone, flammable fuel may be, but is not typically, present. It is often required to maintain a fuel barrier between the fuel zone and the flammable leakage zone. The onboard inert gas distribution system undesirably provides a potential pathway for fuel to leak from the fuel zone to the flammable leakage zone. 
       SUMMARY 
       [0004]    An example inert gas distribution arrangement includes a first fuel tank and a second fuel tank mountable to an aircraft outboard the first fuel tank. A distribution conduit is configured to communicate inert gas to the first fuel tank through a first outlet and further configured to communicate inert gas to the second fuel tank through a second outlet. Fuel in the distribution conduit is biased to flow from the second fuel tank toward the first fuel tank when the aircraft is in selected aircraft attitudes. 
         [0005]    An example onboard inert gas distribution system includes a distribution conduit configured to communicate inert gas from an inert gas distribution source through a fuel tank boundary to a fuel tank system within an aircraft. A flame arrestor is configured to block flame movement within the distribution conduit through the fuel tank boundary. A check valve is configured to block fuel flow from the fuel tank system through the fuel tank boundary to the inert gas distribution source. 
         [0006]    An example method of maintaining an aircraft fuel tank barrier includes biasing fuel within a distribution conduit of an on-board inert gas distribution system to flow away from a wing tank of a fuel tank system toward a fuselage tank of the fuel tank system. 
         [0007]    These and other features of the example disclosure can be best understood from the following specification and drawings, the following of which is a brief description: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  shows a front view of an example fuel tank system within an aircraft. 
           [0009]      FIG. 2  shows a schematic view of an inert gas distribution arrangement used within the  FIG. 1  aircraft. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    Referring to  FIGS. 1 and 2 , an example aircraft  10  includes a fuel tank system  14  having a fuselage tank  18  and wing tanks  22   a  and  22   b.  As can be appreciated, the fuselage tank  18  is positioned generally within a fuselage  27  of the aircraft  10  whereas the wing tanks  22   a  and  22   b  are positioned generally within the wings  26   a  and  26   b  of the aircraft  10 . 
         [0011]    The fuselage tank  18  includes an upper surface  19 , and a lower surface  20  connected by tank walls  21 . The wing tanks  22   a  and  22   b  each include upper surfaces  23   a  and  23   b,  and lower surfaces  24   a  and  24   b  connected by tank walls  25   a  and  25   b.    
         [0012]    The fuel tank system  14  also includes a pair of surge tanks  30   a  and  30   b  housed within the wings  26   a  and  26   b  laterally outside the wing tanks  26   a  and  26   b.  The surge tanks  30   a  and  30   b  are configured to collect fuel spillage from the wing tanks  26 A and  26 B. Spillage occurs during maneuvers of the aircraft  10 , for example. 
         [0013]    The periphery of the fuel tank system  14  establishes a fuel tank boundary  34 . The fuel zone of the aircraft  10  is within the fuel tank boundary  34 . As known, fuel is normally present within the area defined by the fuel tank boundary  34 . Fuel is generally undesired outside of the fuel tank boundary. 
         [0014]    An onboard inert gas distribution system  38  communicates an inert gas through the fuel tank boundary  34  to the fuel tank system  14 . In this example, the onboard inert gas distribution system  38  includes a distribution conduit  42  for communicating inert gas to the fuel tank system  14 . The example onboard inert gas distribution system  38  generates nitrogen enriched air. The onboard inert gas distribution system  38  includes a nitrogen enriched air source  46  and a pump  50  configured to move the nitrogen enriched air from the source  46  through the distribution conduit  42 . 
         [0015]    A shut off valve  54  is configured to block flow through the distribution conduit  42 . The shut-off valve  54 , in this example, blocks flow of fuel from the fuel tank system  14 , through the fuel tank boundary  34 , to the onboard inert gas distribution system  38 . The shut-off valve also blocks flow of nitrogen enriched air from the onboard inert gas distribution system  38  to the fuel tank system  14 . 
         [0016]    In this example, the shut-off valve  54  is moved to a closed position that blocks flow when the onboard inert gas distribution system  38  is not communicating the inert gas through the fuel tank boundary  34  to the fuel tank system  14 . The shut-off valve  54  is moved to an open position when the onboard inert gas distribution system  38  is communicating the inert gas through the fuel tank boundary  34  to the fuel tank system  14 . In the open position, the shut off valve  54  allows flow of nitrogen enriched air from the onboard inert gas distribution system  38  to the fuel tank system  14 . 
         [0017]    A flame arrestor  58  is positioned within the example distribution conduit  42  adjacent the fuel tank boundary  34 . The flame arrestor  58  blocks flames from propagating through the distribution conduit  42  to the fuel tank system  14 . 
         [0018]    A check valve  62  is positioned within the example distribution conduit  42 . The check valve  62  is adjacent the fuel tank boundary  34 . The check valve  62  limits fuel flow from the fuel tank system  14  to the onboard inert gas distribution system  38 . 
         [0019]    In one example, the flame arrestor  58  and the check valve  62  are integrated into a single component. 
         [0020]    In this example, the distribution conduit  42  delivers nitrogen enriched air to the fuselage tank  18  and the wing tanks  22   a  and  22   b.  Notably, the distribution conduit  42  includes a first outlet  66  that delivers the nitrogen enriched air to the fuselage tank  18 . The first outlet  66  is positioned at a vertically high position within the fuselage tank  18  near the upper surface  19 . Positioning the first outlet  66  in this area of the fuselage tank  18  helps limit fuel flow from the fuselage tank  18  into the distribution conduit  42  because gravity tends to pull the fuel away from this area of the fuselage tank  18 . In one example, the first outlet  66  is positioned at the vertically highest position within the fuselage tank  18 . A check valve  72  near the first outlet  66  also limits fuel flow from the fuselage tank  18  to the distribution conduit  42 . 
         [0021]    The distribution conduit  42  delivers nitrogen enriched air to the wing tank  22   a  through a second outlet  76 , and delivers nitrogen enriched air to the wing tank  22   b  through a third outlet  80 . As can be appreciated from the Figures, the wings  26 A and  26 B are canted relative to the fuselage  27  of the aircraft  10 . That is, laterally outer tips  28   a  and  28   b  of the wings  26   a  and  26   b  are more vertically elevated relative to ground  31  than the other areas of the wings  26   a  and  26   b.    
         [0022]    The second outlet  76  and the third outlet  80  are each positioned adjacent the outermost walls  88   a  and  88   b  of the wing tanks  22   a  and  22   b,  which are more elevated than other areas of the wing tanks  22   a  and  22   b.  Positioning the second outlet  76  and the third outlet  80  in the more elevated area near the outermost walls  88   a  and  88   b  helps limit fuel flow from the wing tanks  22   a  and  22   b  to the distribution conduit  42  because the fuel tends to move toward less elevated areas of the wing tanks  22   a  and  22   b,  which are closer to the fuselage tank  18  than the outermost walls  88   a  and  88   b.  The second outlet  76  and the third outlet  80  each include check valves  84  that limit fuel flow from the wing tanks  22   a  and  22   b  to the distribution conduit  42 . 
         [0023]    In this example, the first outlet  66  is positioned vertically below the second outlet  76  and the third outlet  80  when the aircraft  10  has a zero bank angle. Positioning the first outlet  66  of the fuselage tank  18  below the second outlet  76  and the third outlet  80  facilitates draining any fuel present in the distribution conduit  42  toward the fuselage tank  18 . That is, the portions of the distribution conduit  42  configured to communicate fuel to the wing tanks  22   a  and  22   b  are also configured to bias fuel flow within the distribution conduit  42  toward the fuselage tank  18 . 
         [0024]    The example aircraft  10  of  FIG. 1  is shown in a position having a zero bank angle. That is, the example aircraft  10  is not banked or rolled relative to the ground  31  or horizon. In this example, the aircraft  10  has a zero bank angle when the aircraft  10  is parked and during level flight operation. 
         [0025]    The example aircraft  10  rolls relative to the horizon during in-flight maneuvers. Rolling can, for example, increase the distance between the outer tip  28   a  and the ground  31  while decreasing the distance between the outer tip  28   b  and the ground  31 . In such an example, rolling would cause fuel to flow from the wing tank  22   a  to the fuselage tank  18  and from the fuselage tank  18  to the wing tank  22   b.  The check valve  84  at the third outlet  80  blocks fuel in the wing tank  22   b  from entering the distribution conduit  42 . 
         [0026]    Features of this invention include positioning fuel tank outlets for an onboard inert gas distribution system in areas of the fuel tanks that are less likely to contain fuel than other areas. Another feature of this invention includes biasing fuel in the distribution conduit to flow toward a central fuel tank. 
         [0027]    Although a preferred embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.