Abstract:
A fuel jettison system which provides pilot-initiated automatic operation to jettison fuel down to a 60 minute useable fuel remaining level while the manual operation, requiring the pilot to hold down the jettison panel switch, jettisons fuel down to a 20-minute useable fuel remaining level. The pilot can interrupt jettisoning at any time. This termination sequence operates in either automatic or manual mode. The port and starboard main fuel tanks jettison fuel independently through independent shutoff valves and associated circuit logic to thereby maintain aircraft balance.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to an aircraft fuel jettison system, and more particularly to an aircraft fuel jettison system which independently jettisons fuel from a multiple of fuel tanks to maintain equal aircraft balance. 
         [0002]    Aircraft often include provisions for the jettison of fuel to selectively reduce the overall weight of the aircraft. This may be necessitated in response to particular conditions. 
         [0003]    Fuel is conventionally jettisoned by a fuel jettison system with auxiliary jettison pumps and associated piping to pump fuel from the aircraft fuel tanks to an overboard location. Such a system utilizes auxiliary pumps within each fuel tank which are not used for any other purpose and which comprise a significant load factor and installation expense. 
         [0004]    Conventional fuel jettison systems generally rely upon existing fuel tank quantity meters to determine the quantity of fuel which has been jettisoned. This may complicate aircraft control under certain circumstances as conventional fuel jettison systems typically just jettison to a predefined useable fuel remaining level irrespective of fuel location and aircraft fuel balance. 
         [0005]    Accordingly, it is desirable to provide a fuel jettison system which provides independent jettisoning to a multiple of useable fuel remaining levels from a multiple of fuel tanks to maintain equal balance. 
       SUMMARY OF THE INVENTION 
       [0006]    The fuel jettison system according to the present invention generally includes an overboard fuel jettison conduit, a fuel pump, a fuel jettison conduit, a shutoff valve, and a dip conduit. The overboard fuel jettison conduit communicates jettisoned fuel from the fuel pump to an overboard location typically from an aft section of one of the sponsons. 
         [0007]    The shutoff valve is located in each fuel jettison conduit within the aircraft cabin sidewall. The shutoff valve is in communication with a fuel management control system for selective operation thereby. The shutoff valve is powered open by an actuator such as a solenoid valve and is closed in response to a mechanical bias. A manual actuator such as a lever accessible from within the aircraft cabin may also be utilized to overcome the bias and open the shutoff valve. Since the shutoff valves are located in the cabin sidewalls, they are accessible to crew should a malfunction occur. 
         [0008]    The shutoff valve includes an inward venting feature which permits the fuel jettison conduit to be vented such that the fuel pump may be operated to completely purge fuel from the fuel jettison conduit at the completion of a fuel jettison event to assure that all fuel downstream of the shutoff valve is purged from the fuel jettison system. The inward venting feature also facilitates ground support fuel pump checkout without having to actually jettison fuel which is advantageous in a shipboard environment. 
         [0009]    In operation, the fuel jettison system provides pilot-initiated automatic operation to jettison fuel down to, for example, a sixty (60) minute useable fuel remaining level. The fuel management control system communicates with fuel level probes of an FQGS to independently operate the shutoff valve such that aircraft balance is maintained. That is, the fuel jettison control system includes control algorithms which will independently operate each shutoff valve such that when each fuel tank separately reaches the sixty (60) minute useable fuel remaining level, the fuel management control system separately shuts the shutoff valve then purges that fuel jettison conduit. Pilot-initiated automatic operation is initiated by actuation of a fuel jettison switch. 
         [0010]    The fuel jettison system requires pilot-initiated manual operation to jettison further fuel down to a minimum, for example, twenty (20) minute useable fuel remaining level. This operation is achieved by holding the fuel jettison switch throughout the jettisoning operation to the minimum twenty (20) minute useable fuel remaining level. Since the bellmouth opening of the dip conduit is located at the minimum twenty (20) minute useable fuel remaining level, under no situation will the fuel jettison system jettison a quantity of fuel greater than this minimum twenty (20) minute useable fuel remaining level. 
         [0011]    The present invention therefore provides a fuel jettison system which provides independent jettisoning to a multiple of useable fuel remaining levels from a multiple of fuel tanks to maintain equal balance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows: 
           [0013]      FIG. 1  is a general perspective view an exemplary rotary wing aircraft embodiment for use with the present invention; 
           [0014]      FIG. 2  is a general top phantom view an exemplary rotary wing aircraft illustrating the fuel jettison system of the present invention; and 
           [0015]      FIG. 3  is schematic block diagram representation of the fuel jettison system according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]      FIG. 1  schematically illustrates a rotary-wing aircraft  10  having a main rotor system  12 . The aircraft  10  includes an airframe  14  having an extending tail  16  which mounts a tail rotor system  18 , such as an anti-torque system. The main rotor assembly  12  is driven about an axis of rotation R through a main gearbox (illustrated schematically at  20 ) by one or more engines  22 . The main rotor system  12  includes a multiple of rotor blades  24  mounted to a rotor hub  26 . Although a particular helicopter configuration is illustrated and described in the disclosed embodiment, other configurations and/or machines, such as high speed compound rotary wing aircraft with supplemental translational thrust systems, dual contra-rotating, coaxial rotor system aircraft, turbo-props, tilt-rotors and tilt-wing aircraft, will also benefit from the present invention. 
         [0017]    The aircraft  10  includes a fuel system  28 . The fuel system  28  generally includes a fuel management control system  30 , a port main fuel tank  32  and a starboard main fuel tank  34  which communicate fuel to the engines  22 . As generally understood, each fuel tank  32 ,  34  may generally contain a pressure refuel/defuel valve, fuel quantity and low-level sensors, high-level shutoff valves, low-level shutoff valves, check valve sump drains, as well as other fuel communication components (illustrated somewhat schematically at F in  FIG. 2 ) which need not be further described herein as such components are directed to communication of fuel to the engines  22 . 
         [0018]    The port main fuel tank  32  and the starboard main fuel tank  34  are preferably located in sponsons  36 ,  38  mounted to a port and starboard side of the airframe  14 . Both main fuel tanks are crashworthy, self-sealing and interchangeable. It should be understood that other fuel tank arrangements will benefit from the present invention, however, the illustrated arrangement is typical of a rotary wing aircraft. 
         [0019]    The fuel system  28  further includes a fuel jettison system  40  ( FIG. 2 ) to selectively jettison fuel from the main fuel tanks  32 ,  34  to a safe overboard location in response to the fuel management control system  30 . It should be understood that the fuel jettison system  40  is preferably independent of a fuel communication path from the main fuel tanks  32 ,  34  to the engines  22  to minimize unintentional fuel loss. Although only the fuel jettison system  40  from the single port main fuel tank  32  will be described in detail herein, each fuel tank within the fuel system  28  will include similar components. 
         [0020]    Referring to  FIG. 3 , the fuel jettison system  40  generally includes an overboard fuel jettison conduit  42 , a fuel pump  44 , a fuel jettison conduit  46 , a shutoff valve  48 , a flex joint  50 , a self sealing break away valve  52 , a check valve  54  and a dip conduit  56 . 
         [0021]    The overboard fuel jettison conduit  42  communicates jettisoned fuel from the fuel pump  44  to an overboard  58  location typically from an aft section of one of the sponsons  36 ,  38 , here illustrated as the starboard sponson  38  ( FIG. 2 ). The overboard fuel jettison conduit  42  penetrates a tub outer mold line  60  (illustrated schematically) of the airframe  14 . The overboard fuel jettison conduit  42  includes a pressure sensor  62  which communicates with the fuel management control system  30  for confirmation of fuel pump  44  “on” operation. A condensation drain  64  may also be located within the overboard fuel jettison conduit  42  outboard of the tub outer mold line  60 . 
         [0022]    The fuel pump  44  is preferably a 600 lb/min minimum pump 3-phase, 400 hz 5-hr run dry capability pump in communication with the fuel management control system  30 . The fuel pump  44  is in communication with the overboard fuel jettison conduit  42  and the fuel jettison conduit  46 . The fuel jettison conduit  46  communicates with an input to the fuel pump  44  at a fitting  66  such as the illustrated “Y” fitting which provides communication with each main fuel tanks  32 ,  34  through each of the respective fuel jettison conduits  46 . It should be understood that any number of fuel jettison conduits  46 —one for each fuel tank—communicate with the fuel pump  44 . The fuel pump  44  is preferably located below an aircraft cabin floor  68  generally along an aircraft centerline BL 0.0 such that the fuel jettison path from each main fuel tanks  32 ,  34  is generally of the same length. 
         [0023]    Each fuel jettison conduit  46  communicates between the fuel pump  44  and the respective fuel tank  32 . The fuel jettison conduit  46  may pass through the aircraft cabin floor  68  and an aircraft cabin sidewall  70 . The flex joint  50  is thereby located intermediate a cabin to sponson interface  72  adjacent the cabin sidewall  70  such that relevant movement of the sponsons  36 ,  38  relative the airframe  14  is accommodated thereby. The self sealing break away valve  52  is preferably located in the fuel jettison conduit  46  intermediate a frangible plane  74  which forms a portion of the cabin sidewall  70  such that the fuel jettison conduit  46  becomes sealed should the sponsons  36 ,  38  break away from the airframe  14 . 
         [0024]    The shutoff valve  48  is preferably positioned within the aircraft cabin sidewall  70  and is in communication with the fuel management control system  30  for selective operation thereby. The shutoff valve  48  is powered open by an actuator  76  such as a solenoid and is closed in response to a mechanical spring bias. Should power be lost, the shutoff valve  48  is biased toward the closed position. That is, the shutoff valve  48  is biased to a closed position and requires power application such as application of 28V DC current controlled by the fuel management control system  30  to open. Notably, electrically powered components need not be located within the fuel tank with the fuel jettison system  40 . 
         [0025]    A manual actuator  78  such as a lever accessible from within the aircraft cabin may also be operated to manually open the shutoff valve  48 . Since the shutoff valves  48  are located in the cabin sidewalls  70 , they are accessible to crew should such a need arise. 
         [0026]    The shutoff valve  48  also preferably includes an inward venting feature which vents the fuel jettison conduit  46  to operate the fuel pump  44  after the shutoff valve  48  has closed to purge fuel from the fuel jettison conduit  46  at the completion of a fuel jettison event. This assures that all fuel downstream of the shutoff valve  48  is purged from the fuel jettison system  40 . The inward venting feature also facilitates ground support fuel pump checkout without having to actually jettison fuel. This may be advantageous in a shipboard environment. 
         [0027]    The fuel jettison conduit  46  communicates with the dip conduit  56  located within the fuel tank  32 . The dip conduit  56  includes a bellmouth opening  57  thereto at a minimum useable fuel remaining level which is preferably a twenty (20) minute useable fuel remaining level. The fuel jettison conduit  46  penetrates the fuel tank  32  at a relatively low waterline so as to minimize priming times (and total fuel jettison times). Preferably, the dip conduit  56  penetrates into the fuel tank  32  at a level greater than the minimum useable fuel remaining level, for example, a sixty (60) minute useable fuel remaining level. It should be understood, however, that any useable fuel remaining levels may be utilized with the present invention and that the 20 minute and 60 minute time is for example only. The check valve  54  located within the dip conduit  56  assures that fuel will not be inadvertently jettisoned while the fuel pump  44  is in an “off” position. 
         [0028]    The fuel management control system  30  typically includes a processing module, such as a microprocessor and a memory device in communication therewith. The fuel management control system  30  stores data and control algorithms in the memory device or other suitable memory location. The control algorithms are the scheme by which the shut off valve  48  operational decisions are made. The fuel management control system  30  preferably utilizes the existing aircraft fuel quantity gauging system (FQGS)  80  ( FIG. 1 ). 
         [0029]    In operation, the fuel jettison system  40  provides pilot-initiated automatic operation to jettison fuel down to the sixty (60) minute useable fuel remaining level. The fuel management control system  30  communicates with fuel level probes of the existing FQGS  80  to independently operate the shutoff valve  48  such that aircraft balance is maintained. That is, the fuel jettison system  40  includes control algorithms which will independently operate each shutoff valve  48  such that when each fuel tank  32 ,  34  reaches the sixty (60) minute useable fuel remaining level, the fuel management control system  30  shuts the shutoff valve  48  then purges that fuel jettison conduit  46 . Preferably, the pilot-initiated automatic operation is initiated by actuation of a fuel jettison switch  82  ( FIG. 1 ). 
         [0030]    The fuel jettison system  40  requires pilot-initiated manual operation to jettison further fuel down to the minimum twenty (20) minute useable fuel remaining level. Preferably, this operation is achieved by holding the fuel jettison switch  82  throughout the jettisoning operation from the sixty (60) minute useable fuel remaining level to the minimum twenty (20) minute useable fuel remaining level. Since the bellmouth opening  57  of the dip conduit is located at the minimum twenty (20) minute useable fuel remaining level, under no situation will the fuel jettison system  40  jettison a quantity of fuel greater than this minimum twenty (20) minute useable fuel remaining level. 
         [0031]    As a fail-safe feature, the fuel pump  44  is commanded closed after a time period such as 11 seconds after the FQGS  80  has detected the total fuel remaining quantity equivalent to 60 minute useable fuel remaining level in automatic operation and equivalent to 20 minute useable fuel remaining level in manual operation. That is, the shutoff valve  48  may be closed but the fuel pump may continue to operate until the time limit elapses. 
         [0032]    It should be understood that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to the normal operational attitude of the vehicle and should not be considered otherwise limiting. 
         [0033]    It should be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit from the instant invention. 
         [0034]    Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present invention. 
         [0035]    The foregoing description is exemplary rather than defined by the limitations within. Many modifications and variations of the present invention are possible in light of the above teachings. The preferred embodiments of this invention have been disclosed, however, one of ordinary skill in the art would recognize that certain modifications would come within the scope of this invention. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.