Abstract:
A lightning protection system, method and aircraft are provided for reducing the flammability of jet fuel spilled during an in-flight refueling operation between a supplying aircraft and a receiving aircraft. An inert gas is injected adjacent to a refueling interface in order to displace oxygen in the fuel-air mixture and thereby reduce the ability of the fuel vapor to ignite upon occurrence of an ignition source such as lightning. The refueling system may comprise a boom or a hose and drogue type device.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to in-flight refueling and associated systems and methods for providing a safe means for transferring fuel from one aircraft to another while flying in adverse weather conditions.  
       BACKGROUND OF THE INVENTION  
       [0002]     In-flight refueling (or air-to-air refueling) is an operation where fuel is transferred from one aircraft to another aircraft during flight. The purpose of this operation is to extend the flight of an aircraft and thus increase its operational effectiveness. In most military cases, aircraft require many refueling events to extend the distance it can cover to complete its mission. Due to current safety requirements, an aircraft&#39;s flight distance may be unnecessarily extended to circumvent adverse weather where lightning may be encountered. While aircraft are designed to withstand an in-flight lightning strike, there is a concern that a lightning strike during in-flight refueling may ignite the fuel that is spilled during the refueling process and result in fire or explosion in one or both of the aircraft performing the refueling maneuver. Therefore, in-flight refueling is typically performed many miles from weather conditions where lightning may occur to minimize the potential for a lightning strike. As a result, more fuel is used to extend the aircraft&#39;s flight distance in order to avoid these weather conditions and, therefore, more refueling operations may be required. Thus, there is a need to protect an aircraft from igniting fuel spilled during in-flight refueling operation as a result of lightning strike.  
         [0003]     Two methods of refueling aircraft in flight are typically practiced. One method is to use a rigid boom attached to the refueling aircraft with a connector and nozzle at its distal end to connect the refueling aircraft to the receiving aircraft. A second method is to use a flexible hose trailed behind the refueling aircraft that is attached to a drogue disposed at the end to connect the refueling aircraft to the receiving aircraft. In both methods, the fuel is transported from a tank in the refueling aircraft through a duct, across a connector and nozzle and then through a receiving duct in the receiving aircraft and finally into the receiving aircraft&#39;s fuel tanks. Typically, both systems incorporate a valve mechanism in the connector, close to the junction between the two aircraft such that if an emergency disconnect is performed, the valve will close and stop fuel flow to minimize loss of fuel into the surrounding air-stream. Jet fuel is flammable when the correct proportions of fuel vapor and oxygen are present. The oxygen content required to ignite and sustain combustion of fuel may change with air pressure or temperature changes; however, it is well known that jet fuel will only ignite when the proper fuel oxygen ratio is present in the fuel-air mixture.  
         [0004]     Therefore, there exists a need for a device to reduce the flammability of the spilled jet fuel and air mixture during an in-flight refueling operation to eliminate the potential of ignition in the event of a lightning strike.  
       SUMMARY OF THE INVENTION  
       [0005]     Aspects of the invention are directed generally to fuel shielding nozzles for refueling aircraft and associated systems and methods. An airborne refueling system in accordance with one embodiment of the present invention includes a fuel delivery device having a deployable portion configured to be deployed from an aircraft during in-flight refueling. The deployable portion may include at least a portion of a fuel line, an inert gas line and a conductor with a connector for temporary attachment to a receiving aircraft.  
         [0006]     In further embodiments, the system may further include an aircraft, with the fuel delivery device being carried by the aircraft and an inert gas injecting system being located with the fuel delivery device. The injecting system may, in some embodiments, be a passive system where high pressure inert gas is passed from the refueling aircraft via a refueling device to at least one location on a surface of at least one of the conductor and connector. In further embodiments the injecting system may be an active system where inert gas is generated within the refueling aircraft and then actively transported from the refueling aircraft via a refueling device to at least one location on a surface of at least one of the conductor and connector.  
         [0007]     In further embodiments the system may include a fire suppression system being carried by the refueling aircraft. The fire suppression system may be, in some embodiments, a high pressure storage system containing an inert gas that is non-reactive to fuel and that is distributed to the conductor via a duct in the fuel delivery device. In further embodiments, the fire suppression system may be a generation system where inert gas is controllably produced and distributed to the conductor via a duct in the fuel delivery device.  
         [0008]     A method for refueling an aircraft in accordance with another aspect of the invention may include deploying from a refueling aircraft a portion of a refueling system that includes a fuel line, a fire suppression system, and a conductor with a connector. The method may further include injecting the inert fluid adjacent to the interface of the connector and the receiving aircraft.  
         [0009]     In further embodiments the method may further include generating an inert fluid within the tanker aircraft and injecting the inert fluid adjacent to the interface of the connector and the receiving aircraft. Other aspects and features of the present invention, as defined solely by the claims, will be come apparent to those of ordinary skill in the art upon review of the following non-limited detailed description of the invention in conjunction with the accompanying figures. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIGS. 1   a  and  1   b  show a refueling aircraft refueling a receiver aircraft in accordance with preferred embodiments of the present invention.  
         [0011]      FIG. 2   a  shows a perspective view of a boom type conductor in accordance with a first preferred embodiment of the invention.  
         [0012]      FIG. 2   b  shows a cross-sectional schematic view of a boom type conductor in accordance with another embodiment of the invention.  
         [0013]      FIG. 3  shows a cross-sectional schematic view of a hose and drogue type conductor in accordance with a second preferred embodiment of the invention.  
         [0014]      FIG. 4  shows a flowchart for a preferred method for shielding fuel from ignition during a refueling operation. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]     The present invention is directed to a system, method, and aircraft for reducing the risk associated with the flammability of fuel spilled during an in-flight refueling operation. Specific details of various embodiments of the invention are set forth in the following description and in the Figures to provide a thorough understanding of the invention. Well known structures, systems and methods often associated with in-flight refueling have not been shown or described in detail to avoid unnecessarily obscuring the description of the various embodiments of the invention. One skilled in the art will understand that the invention may have other embodiments and this description should not be construed as limited to the embodiments set forth herein.  
         [0016]     In preferred embodiments of the invention,  FIGS. 1   a  and  1   b  generally depict a refueling aircraft  10  adapted to provide fuel to a receiving aircraft  20  during a typical in-flight refueling operation. During in-flight refueling, the refueling aircraft  10  holds a steady flight position while a receiving aircraft  20  maneuvers into a refueling position, typically behind and below the refueling aircraft. When in position the refueling aircraft will deploy a fuel delivering device  30 , 30 ′ towards the receiving aircraft. Coupled to the distal end of the fuel delivering device  30 , 30 ′ is a conductor  40 , 40 ′ adapted to connect to a receiver  50 , 50 ′ on the receiving aircraft  20 . The receiving aircraft  20  may then temporarily couple the conductor  40 , 40 ′ to the receiver  50 , 50 ′.  
         [0017]     In a preferred embodiment of  FIG. 1   a , the fuel delivering device  30  consists of a rigid, telescoping boom attached to the refueling aircraft  10 . The boom preferably contains a fuel duct to passably flow fuel and a duct to passably flow an inert gas. The fuel duct and the inert gas duct are coupled to a conductor  40  adapted to connect to a receiver  50  on the receiving aircraft  20 .  
         [0018]     In an alternative preferred embodiment of  FIG. 1   b , the fuel delivering device  30 ′ consists of a flexible hose depending from the refueling aircraft  10 . The hose preferably contains a fuel duct to passably flow fuel and an inert gas duct to passably flow an inert gas. The fuel duct and the inert gas duct are also coupled to a conductor  40 ′ that is adapted to couple to a receiver  50 ′ on the receiving aircraft  20 .  
         [0019]     Generally, fuel is transferred from fuel tanks within the refueling aircraft through the refueling device  30  and into the receiving aircraft  20 . During the fuel transfer, an inert fluid is passed from an inert gas system  60  in the refueling aircraft  10 , through the fuel delivering device  30  and is injected from the conductor  40  into the external airstream adjacent to the conductor  40  and receiver  50 . Alternatively, the inert fluid may be injected into the internal fuel stream being transferred from the refueling aircraft  10  to the receiving aircraft  20 . Preferably, the refueling device  30 , 30 ′ provides both the fuel and the inert gas ducts or lines within a common housing such as a flexible hose or rigid tube, although in alternative embodiments the lines may be provided in separate housings.  
         [0020]     In a further aspect of the present embodiment the inert gas system  60  may be a high pressure storage vessel containing an inert gas such as nitrogen. The system may contain a means  65 , such as one or more valves, for controlling the flow of the inert gas from the storage vessel to the conductor  40 . In another embodiment the inert gas system  60 ′ may be an inert gas generating device, such as a Air Products membrane separator to separate nitrogen from ambient air for example, that can be controllably operated to generate an inert gas. These systems are in use in many commercial and military aircraft. The system may further include valves or other means  65 ′ for controlling the flow of the inert gas from the on-board inert gas generating device to the conductor  40 .  
         [0021]      FIGS. 2   a  and  2   b  generally illustrate preferred embodiments of a device for injecting a fluid adjacent to a conductor  40  and a connector  70  that are attached to a boom-type of fuel delivering device  30 . The fuel delivering device  30  may include a fuel duct  75  for passing a fluid such as jet fuel and a second duct  80  for passing an inert gas, as represented by the arrows in  FIG. 2   b . The conductor may also contain a plenum  87  for distributing inert gas from the second duct  80  to injecting ducts  85 ,  95 . The conductor  40  may include a number of ducts  85  that connect the internal inert gas duct to an outer surface of the conductor  40  and are adapted to inject inert gas into the adjacent air stream. The conductor may also include a number of ducts  95  that connect the fuel duct  75  to an inner surface of the conductor  40  and are adapted to inject inert gas directly into the fuel duct.  
         [0022]      FIG. 3  generally illustrates a preferred embodiment of a device for injecting a fluid adjacent to a conductor  40 ′ and a connector  70 ′ that are attached to a hose and drogue type of fuel delivering device  30 ′. The fuel delivering device  30 ′ may include a fuel duct  75 ′ for passing a fluid such as jet fuel and a second duct  80 ′ for passing an inert gas (represented by the arrows in  FIG. 3 ). The conductor may also contain a plenum  87 ′ for connecting the second duct  80 ′ to a number of injecting ducts  95 ′ and distributing an inert gas to the injecting ducts adapted to inject inert gas into the fuel duct of the conductor  40 ′.  
         [0023]     In another embodiment of the present invention,  FIG. 4  is a block diagram illustrating a preferred method for a fire suppression system for reducing the flammability of fuel spilled during an in-flight refueling operation. The method may include aligning a refueling aircraft and a second aircraft to be refueled  110  in close proximity so a physical connection can be established. The method further includes deploying a device adapted to flow at least one fluid from the refueling aircraft to a conductor located on the distal end of the refueling device  120 , the deployment occurring prior to or at about the same time as the aircraft alignment. The conductor can then be detachably coupled to a receiving location on the second aircraft  130 . Fuel is transferred from the refueling aircraft to the second aircraft through the refueling device  140 . Concurrently, during at least a portion of the refueling time, an inert gas is transferred from the refueling aircraft to the conductor  150  where it is then injected from the conductor into at least one of the adjacent, external airstream and into the internal fuel duct to reduce the fuel-oxygen ratio and thus reduce the flammability of the fuel. Upon completion of the refueling operation, fuel and inert gas transfer is stopped, and the refueling device is decoupled from the receiving aircraft  160 . The receiving aircraft is safely maneuvered away from the refueling aircraft and may resume its normal flight operations.  
         [0024]     A lightning protection system, method and aircraft for reducing the flammability of jet fuel during an in-flight refueling operation have been disclosed. The scope of the invention is not limited by the specific embodiments disclosed herein, and one skilled in the art will understand there are other modifications and embodiments of the invention not described, but are in the scope of the claims that follow.