Abstract:
According to an embodiment, an aircraft comprises a fuselage including composite skin; an enclosure located inside the fuselage; a rechargeable battery disposed inside the enclosure; and a ventilation conduit extending from the enclosure to an opening in the composite skin, the ventilation conduit including: a first portion having a first end coupled to the enclosure and a second end spaced from the composite skin, and a second portion extending between the composite skin and the second end of the first portion, the second portion comprising an electrically non-conductive material.

Description:
[0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 14/188,603, filed on Feb. 24, 2014, which in turn claims the benefit of provisional application U.S. Ser. No. 61/769,110 filed 25 Feb. 2013, both of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Lithium-ion batteries (LIBs) are desirable for mobile computing devices, certain automobiles, and certain aircraft. They have lower weight and higher energy density than rechargeable batteries such as nickel metal hydride and nickel cadmium batteries. They have no memory degradation. 
         [0003]    However, certain lithium-ion batteries have longstanding issues with failure events that result in the generation of hot gas. One solution is to vent the gas. While this solution might seem straightforward for rechargeable battery applications in a mobile device or an automobile, it is not straightforward for an aircraft having composite skin. 
       SUMMARY 
       [0004]    According to an embodiment, an aircraft comprises a fuselage including composite skin; an enclosure located inside the fuselage; a rechargeable battery disposed inside the enclosure; and a ventilation conduit extending from the enclosure to an opening in the composite skin, the ventilation conduit including: a first portion having a first end coupled to the enclosure and a second end spaced from the composite skin, and a second portion extending between the composite skin and the second end of the first portion, the second portion comprising an electrically non-conductive material. 
         [0005]    According to another embodiment, an aircraft comprises a fuselage including composite skin; an enclosure located inside the fuselage; a rechargeable battery disposed inside the enclosure; a ventilation conduit extending from the enclosure to an opening in the composite skin, the ventilation conduit including: a first portion having a first end coupled to the enclosure and a second end spaced from the composite skin, the first portion being formed of an electrically non-conductive material; a second portion extending between the composite skin and the second end of the first portion, the second portion being formed of an electrically non-conductive material; and a flange fitting attached to the second portion of the ventilation conduit, the flange fitting having a portion that extends into the opening in the composite skin; and a thermal spacer located between the flange fitting and the composite skin. 
         [0006]    According to another embodiment, an aircraft comprises a fuselage including composite skin; a fairing on an exterior surface of the composite skin; an enclosure located inside the fuselage; a rechargeable battery disposed inside the enclosure; a ventilation conduit extending from the enclosure to an opening in the composite skin, the ventilation conduit including: a first portion having a first end coupled to the enclosure and a second end spaced from the composite skin, the first portion being formed of an electrically non-conductive material; a second portion extending between the composite skin and the second end of the first portion, the second portion being formed of an electrically non-conductive material; and a flange fitting attached to the second portion of the ventilation conduit, the flange fitting having a portion that extends into the opening in the composite skin; a thermal spacer located between the flange fitting and the composite skin; a second conduit that penetrates the fairing; and a flexible hose that connects the second conduit to the second portion at the composite skin. 
         [0007]    These features and functions may be achieved independently in various embodiments or may be combined in other embodiments. Further details of the embodiments can be seen with reference to the following description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is an illustration of an aircraft including an enclosure and a ventilation conduit for the enclosure. 
           [0009]      FIG. 2A  is an illustration of a second or end portion of a ventilation conduit. 
           [0010]      FIG. 2B  is an illustration of a second or end portion of a ventilation conduit and a thermal spacer mounted to the second portion. 
           [0011]      FIG. 3  is an illustration of a ventilation conduit. 
           [0012]      FIG. 4  is an illustration of a doubler plate for a ventilation conduit. 
           [0013]      FIG. 5  is an illustration of a ventilation system for a rechargeable battery of an aircraft. 
           [0014]      FIG. 6  is an illustration of an extension of a ventilation conduit between skin and a fairing of an aircraft. 
           [0015]      FIG. 7  is an illustration of a method of mitigating consequences of a battery failure event aboard an aircraft. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Reference is made to  FIG. 1 , which illustrates an aircraft  110 . The aircraft  110  includes a fuselage, wing assemblies, and empennage (not shown). Each of these major components includes skin supported by a stiffening substructure (e.g., frames, stiffeners). At least one of the fuselage, wing assemblies and empennage includes composite skin  120 . In some embodiments, the composite skin  120  may include a fiber-reinforced material such as carbon fiber reinforced plastic (CFRP). 
         [0017]    The composite skin  120  has an exterior surface that is aerodynamically smooth. The exterior surface of the composite skin  120  may be covered with a glass epoxy surface layer and paint system. Some portions of the exterior surface of the composite skin  120  may be covered by a fairing having an exterior surface that is aerodynamically smooth. 
         [0018]    The aircraft  110  further includes a ventilation system including a ventilation conduit  130 . The conduit  130  has a second or end portion  132  that extends to an opening in the composite skin  120 . The second portion  132  of the ventilation conduit  130  is secured to the composite skin  120 . The ventilation conduit  130  may be made entirely of metal, except for the second portion  132 , which functions as an electrical insulator. Alternatively, the ventilation conduit  130  may be made entirely of a non-conductive material. 
         [0019]    For example, a first portion  134  of the ventilation conduit  130  may be made of a lightweight, corrosion-resistant metal, such as titanium or corrosion resistant steel (CRES). Alternatively, the first portion  134 , as well as the second portion  132 , may be made of an electrically non-conductive material that satisfies thermal requirements of the ventilation system. 
         [0020]    The ventilation conduit  130  overcomes a problem that is particular to the aircraft  110 . The second portion  132  provides protection against lightning strike current or other current due to electromagnetic effect (EME). Because at least the second portion  132  is non-conductive, it prevents electrical current from entering inside the aircraft  110 . 
         [0021]      FIG. 2A  illustrates an example of the second portion  132  of the ventilation conduit  130 . The second portion  132  includes a tube  210 , and a connector fitting  220  secured (e.g., bonded and riveted) to one end of the tube  210 . The connector fitting  220  has internal threads for engaging threads on the first portion  134  of the ventilation conduit  130 . 
         [0022]    The second portion  132  also includes a flange fitting  230  secured (e.g., bonded and riveted) to the other end of the tube  210 . The flange fitting  230  is configured to mount the tube  210  to the composite skin  120 . The flange fitting  230  may include a flange  232  and a tubular portion  234  that extends beyond the flange  232 . This tubular portion  234  extends into the opening in the composite skin  120 . 
         [0023]    The tube  210  is made of an electrically non-conductive material. Examples of the electrically non-conductive material include thermoplastic, and a composite with fiberglass, aramid or other nonconductive fiber. Length (L) of the tube  210  may be at least two inches to provide adequate electrical isolation against lightning strike or other electrical current. 
         [0024]    The first portion  134 , connector fitting  220 , and the flange fitting  230  may also be made of an electrically non-conductive material. 
         [0025]    Reference is now made to  FIG. 3 , which illustrates an example of a ventilation conduit  130  having a first portion  134  and an second portion  132 . The second portion  132  of the ventilation conduit  130  includes the tube  210 , the connector fitting  220 , and the flange fitting  230 . The first portion  134  of the ventilation conduit  130  is threaded onto the connector fitting  220 , and the flange fitting  230  is fastened to composite skin  120 . The tubular portion (not visible in  FIG. 3 ) of the flange fitting  230  extends through an opening in the composite skin  120 . 
         [0026]    In some embodiments, a thermal spacer  310  may be located between the flange  232  and the composite skin  120  and also in the opening of the composite skin  120  to create a thermal barrier between the second portion  132  and the composite skin  120 . The thermal spacer  310  mitigates heat transfer directly to the composite skin  120  and thereby prevents hot gases from damaging the composite skin  120  as the gases are being vented overboard the aircraft  110 . 
         [0027]    Additional reference is made to  FIG. 2B , which illustrates the thermal spacer  310  mounted to the flange fitting  230  of the second portion  132 . The thermal spacer  310  includes a first portion  312  that is configured to fit into the opening and also to surround the tubular portion  234  of the flange fitting  230 . The thermal spacer  310  includes a larger second portion  314  that is configured to sit between the flange  232  and the composite skin  120 . The thermal spacer  310  may be made of Polyether ether ketone (PEEK) thermoplastic or other thermoplastic or composite that meets the thermal requirements of the ventilation system. 
         [0028]    Additional reference is made to  FIG. 4 . In some embodiments, a doubler plate  320  may be mounted to the exterior surface of the composite skin  120 . The doubler plate  320  may be fastened to the flange fitting  230  (as shown in  FIG. 3 ). An opening in the doubler plate  320  receives the tubular portion  234  of the flange fitting  230 . The doubler plate  320  provides structural reinforcement about the opening in the composite skin  120 , and it protects the composite skin  120  against possible thermal damage from gas exiting the ventilation conduit  130 . The doubler plate  320  may be made of a material such as titanium or corrosion resistant steel. 
         [0029]    The doubler plate  320  may have a slight protrusion  330  around the opening in the skin  120  around the tubular portion  234  of the flange fitting  230  to mitigate noise. The protrusion  330  is sufficient to reduce noise of airstream passing over the opening in the composite skin  120  during flight. 
         [0030]    Returning to  FIG. 1 , the ventilation conduit  130  is not limited to any particular ventilation system aboard the aircraft  110 . In general, the ventilation system allows gas to be vented from an enclosure  140  (via the ventilation conduit  130 ) and exhausted overboard the aircraft  110 . One example of the enclosure  140  is a fuel tank. Another example of the enclosure  140  is a metal enclosure for a rechargeable battery  150 . 
         [0031]    Reference is made to  FIG. 5 , which illustrates an enclosure  510  for a rechargeable battery  550  aboard an aircraft  500 . The enclosure  510  may be located in the fuselage  502  of the aircraft  500 . 
         [0032]    If a battery failure event occurs, the battery may generate hot gas. The enclosure  510  contains the gas. 
         [0033]      FIG. 5  also illustrates a ventilation system for the enclosure  510 . The ventilation system includes a ventilation conduit  530  and a vent valve  520 . The vent valve  520  is located at an opening in a wall  512  of the enclosure  510 . The ventilation conduit  530  extends from the vent valve  520  to composite skin  504  of the fuselage  502 . The vent valve  520  is normally closed to prevent the battery environment inside the enclosure  510  from cycling with ambient airplane pressures between takeoff and cruise altitudes (e.g., sea level and 40,000 feet). Such cycling can decrease the life of the battery. 
         [0034]    A first portion  534  of the ventilation conduit  530  has a first end attached to the vent valve  520 . A second portion  532  of the ventilation conduit  530  is coupled between the first portion  534  and the composite skin  504  of the fuselage  502 . The second portion  532  of  FIG. 5  may have the same or similar construction as the second portion  132  of  FIG. 2 . 
         [0035]    If a battery failure event generates hot gas that causes pressure within the enclosure  510  to exceed a design limit, the vent valve  520  opens, and the hot gas is vented out of the enclosure  510 , through the ventilation conduit  530 , and exhausted overboard the aircraft  500 . 
         [0036]    In some embodiments, the vent valve  520  may be actively sensed and controlled (e.g., with a pressure sensor, ball valve, and actuator). In other embodiments, the vent valve  520  may be a passive valve (e.g., a spring loaded poppet valve, rupturable diaphragm). 
         [0037]    Reference is now made to  FIG. 6 , which illustrates a fairing  600  on an exterior surface of the composite skin (not shown in  FIG. 6 ). A ventilation conduit includes the second portion  132  of  FIG. 2  (not shown in  FIG. 6 ), which penetrates the composite skin. 
         [0038]      FIG. 6  also illustrates an extension  610  of the ventilation conduit between the composite skin and the fairing  600 . The extension  610  may include a second conduit  620  that penetrates the fairing  600 . The second conduit  620  may be electrically conductive or non-conductive. A flexible hose  630  connects the second conduit  620  to the second portion at the composite skin. The flexible hose  630  supports flexure of the second conduit  620 . A doubler plate  640  may be attached to the exterior surface of the fairing  600  over the second conduit  620 . 
         [0039]    Reference is now made to  FIG. 7 , which a method of using the ventilation system to mitigate the consequences of a battery failure event aboard an aircraft having a rechargeable battery within an enclosure. At block  710 , a battery failure event occurs, whereby hot gas is generated by the battery. The hot gas causes pressure in the enclosure to rise. 
         [0040]    At block  720 , the pressure causes the vent valve to open. Gas is vented out of the enclosure, through the ventilation conduit, and overboard the aircraft. The thermal spacer and the doubler plate prevent the hot gas from damaging the composite aircraft skin. As gas in the enclosure is being vented, pressure within the enclosure is reduced. 
         [0041]    If, during flight, lightning current or other current attaches to the doubler plate, the second portion of the ventilation conduit will prevent the current from entering into the aircraft.