Patent Publication Number: US-11046433-B2

Title: Aerial firefighting dump gate system

Description:
REFERENCES TO RELATED APPLICATIONS 
     None. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to firefighting aircraft fire retardant dump gates. 
     Description of the Related Art 
     Firefighting aircraft, also referred to as air tankers, carry a volume of fire retardant, such as water or other chemicals, which are dumped onto designated areas for fire control operations. The fire retardant is carried in a tank or hopper within the aircraft and is released through the use of a dump gate. The release and targeting of the fire retardant is a critical operation due to the necessarily limited volume of fire retardant available on a given aircraft and the generally large areas of fire being attacked. Targeting calculations involve the air speed, altitude, wind speed, rate of climb/descent, volume of fire retardant to be dispersed, length and width of a predetermined target area, and the rate at which the fire retardant is dumped from the dump gate. As such, control of the dump gate opening and rate of flow are critical for targeting purposes. 
     U.S. Pat. No. 8,365,762, issued on Feb. 5, 2013 to Trotter, who is an inventor of the present disclosure, teaches a hydraulic control system used to operate a dump gate in a firefighting aircraft. In that design, hydraulics are advantageously employed because of their reliability, their ability to apply substantial forces to a pair of gates, and their ability to firmly and quickly control the position of the dump gates. A feedback control system was employed to provide precise position control of the gates. This system has a record of proven performance in certain models of firefighting aircraft from Air Tractors, Inc. (Olny, Tex.), including the AT-802F “Fire Boss” aircraft. 
     While hydraulics have been successfully employed for dump gate operation, hydraulics do carry certain liabilities. The hydraulic pump, actuators, reservoir, pipes and fittings are relatively heavy components, which weight must be deducted from the fire retardant payload. Hydraulics also introduce a new dynamic system in an aircraft, which also carries existing dynamic systems, such as the aircraft electric generators and storage batteries, and which might be more fully taken advantage of Hydraulics also create maintenance issues and potentials for leaking and other reliability issues. Thus, it can be appreciated that there is a need in the art for an improved dump gate and control system that addresses the problems in the prior art. 
     SUMMARY OF THE INVENTION 
     The need in the art is addressed by the systems as taught by the present invention. The present disclosure teaches a gatebox system for a hopper that contains fluid in a firefighting aircraft. The gatebox system includes a box assembly with an upper portion adapted to receive the fluid from the hopper, and a first gate opening and a second gate opening formed through a lower portion of the gatebox. A first gate is hingedly connected along an edge of the first gate opening, and a second gate is hingedly connected along an edge of the second gate opening. A drive shaft is supported within the box assembly and is rotatable in a gates-closing direction and a gates-opening direction. A first crank arm is fixed to the drive shaft and coupled to the first gate by a first connecting link, which defines an over-center geometry while the first gate is at a closed position, such that weight of the fluid on the first gate induces torque on the drive shaft in the gates-closing direction. Similarly, a second crank arm is fixed to the drive shaft and coupled to the second gate by a second connecting link, which define an over-center geometry while the second gate is at a closed position such that weight of the fluid on the second gate induces torque on the drive shaft in the gates-closing direction. And wherein, rotation of the drive shaft in the gates-opening direction is coupled to the first and second gates by the first and second crank arms and the first and second connecting links to open the first and second gates, to thereby enable control of the fluid flow from the hopper according to an angular position of the drive shaft. 
     In a specific embodiment of the foregoing gatebox system, the first and second connecting links engage the drive shaft while the first and second gates are at the closed positions to thereby prevent over-rotation of the drive shaft in the gates-closing direction. In another specific embodiment, the first crank arm and the first connecting link further comprise plural crank arms and plural connecting links disposed between the drive shaft and the first gate, and the second crank arm and the second connecting link further comprise plural crank arms and plural connecting links disposed between the drive shaft and the second gate. 
     In a specific embodiment of the foregoing gatebox system, the first and second crank arms and the first and second connecting links are configured with a geometry whereby the first gate and the second gates open out of phase with one another as the drive shaft is rotated in the gate-opening direction. 
     In a specific embodiment, the foregoing gatebox system further includes an electric motor driving a gear reduction drive coupled to rotate the drive shaft in both of the gates-opening and gates-closing directions. In a refinement to this embodiment, the gear reduction drive comprises a clutch operable to disconnect the drive shaft from the electric motor. 
     In a specific embodiment, the foregoing gatebox system further includes a servo-motor coupled to drive the drive shaft in either of the gates-opening or gates-closing directions. In a refinement to this embodiment, the gatebox system further includes a control system coupled to the servo-motor to control the angular position of the drive shaft, and thereby control of the flow of fluid through the first and second gates. 
     In a specific embodiment, the foregoing gatebox system further includes a position sensor coupled to the drive shaft that outputs a gate position signal to the control system, and a current sensor couple to the servo motor that outputs a motor current signal to the control system, and wherein the control system defines a gates-closed position of the first and second gates when the position signal indicates a closed condition and the motor current signal exceeds a predetermined current threshold. In a further refinement to this embodiment, the control system controls the flow of fluid from the first and second gates by counting the number of revolutions of the servo-motor. 
     In a specific embodiment of the foregoing gatebox system, wherein the gatebox is installed in an aircraft having plural aircraft batteries connected in parallel, the gatebox system further includes a motor power supply having a switching circuit connected to the plural aircraft batteries, which operates to switch the plural aircraft batteries into a series circuit to thereby increase the voltage available to drive the servo-motor. 
     In a specific embodiment of the foregoing gatebox system, wherein the gatebox is installed in an aircraft having an aircraft power supply providing a first voltage, the gatebox system further includes a motor power supply coupled to the servo-motor, and a battery connected in series with the aircraft power supply to thereby provide a drive voltage to the servo-motor that is greater than the first voltage. 
     In a specific embodiment, the foregoing gatebox system further includes an electric motor and a gear reduction drive coupled between the motor and the drive shaft to rotate the drive shaft in either of the gates-opening and gates-closing directions under motive force of the motor, and a clutch coupled to selectively disconnect the drive shaft from the electric motor, and a manual actuator coupled to the clutch to selectively disconnect the motor from the drive shaft, and thereby enable the first and second gates to open without use of the motor. 
     In a refinement to the foregoing embodiment, the gatebox system further includes a clutch linkage disposed between the manual actuator and the clutch, and the clutch linkage is coupled to the drive shaft through a shaft crank arm, and actuation of the manual actuator applies rotational force to the drive shaft, through the shaft crank arm, in the gates-opening direction, to thereby rotate the drive shaft past the over-center condition to enable the first and second gates to fall open under force of gravity. 
     In a further refinement to the foregoing embodiment, the clutch linkage is configured to disengage the clutch prior to applying rotational force to the drive shaft. In another refinement, the gatebox system further includes an interlock coupled between the clutch linkage and the motor, that operates to disable electric power to the motor upon actuation of the manual actuator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a functional block diagram of a fire retardant delivery system according to an illustrative embodiment of the present invention. 
         FIG. 2  is a drawing of a pilot interface according to an illustrative embodiment of the present invention. 
         FIG. 3  is a perspective view drawing of a fire retardant gatebox according to an illustrative embodiment of the present invention. 
         FIG. 4  is a section view drawing of a fire retardant gatebox according to an illustrative embodiment of the present invention. 
         FIG. 5  is a section view drawing of a fire retardant dump gates and drive linkages according to an illustrative embodiment of the present invention. 
         FIG. 6  is a section view drawing of a fire retardant dump gates and drive linkages according to an illustrative embodiment of the present invention. 
         FIG. 7  is a section view drawing of a fire retardant dump gates and drive linkages according to an illustrative embodiment of the present invention. 
         FIG. 8  is a diagram of a power supply according to an illustrative embodiment of the present invention. 
         FIG. 9  is a diagram of a power supply according to an illustrative embodiment of the present invention. 
         FIG. 10  is a perspective view drawing of an emergency dump linkage according to an illustrative embodiment of the present invention. 
         FIG. 11  is a diagram of an emergency drop linkage according to an illustrative embodiment of the present invention. 
         FIG. 12  is a diagram of an emergency drop linkage according to an illustrative embodiment of the present invention. 
         FIG. 13  is a diagram of an emergency drop linkage according to an illustrative embodiment of the present invention. 
         FIG. 14  is a diagram of an emergency drop linkage according to an illustrative embodiment of the present invention. 
         FIG. 15  is a diagram of an emergency drop linkage according to an illustrative embodiment of the present invention. 
         FIG. 16  is a diagram of an emergency drop linkage according to an illustrative embodiment of the present invention. 
         FIG. 17  is a section view drawing of a gear reduction transmission with clutch according to an illustrative embodiment of the present invention. 
         FIG. 18  is a section view drawing of a gear reduction transmission with clutch according to an illustrative embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     Illustrative embodiments and exemplary applications will now be described with reference to the accompanying drawings to disclose the advantageous teachings of the present invention. 
     While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope hereof and additional fields in which the present invention would be of significant utility. 
     In considering the detailed embodiments of the present invention, it will be observed that the present invention resides primarily in combinations of steps to accomplish various methods or components to form various compositions, apparatus and systems. Accordingly, the apparatus and system components and method steps have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the disclosures contained herein. 
     In this disclosure, relational terms such as first and second, top and bottom, upper and lower, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element. 
     In an illustrative embodiment of the present disclosure, the Air Tractor 802F fire fighting aircraft is the host for the gatebox assembly together with its related control equipment. This is also referred to as a “firegate.” Functionally speaking, the gatebox is the discharge valve system used to dispense fire retardant from the aircraft, and plays a critical role in the efficient utilization of the limited quantity of fire retardant available in any given drop flight. The Air Tractor 802F is a single engine air tanker with an 800 gallon payload that is purpose built for aerial firefighting. The aircraft drops the payload through an opening in the belly of the fuselage. This disclosure contemplates improvement to the prior art gatebox systems, which is commercially referred to as the third generation fire retardant drop system, (“GEN III FRDS”). This is an electrically driven mechanical gate system, together with an electrical system, which controls the position of the gate doors to meter the flow of fire retardant from the AT-802F fire retardant hoppers. Long term retardant and other liquid payloads may be used in the hoppers as necessary for various firefighting missions. 
     A typical fire retardant release takes a minimum of approximately one-half second, and up to a maximum of about 10 seconds depending on gate controller settings, which dynamically control the firegate opening size and duration. The controller has an interface module located in the cockpit while all other electronic equipment is mounted outside of the cockpit. Reference is directed to  FIG. 1 , for an introduction of the system components. The gatebox  64  and control system components include multiple electrical boxes to perform various functions and a mechanical gate system with moving doors coupled to an actuator. All components are protected by circuit breakers of appropriate size. The primary components include a pilot interface  52 , a gate controller  50 , a motor controller  56 , an electric motor  58 , a gatebox  64 , a transmission  62 , and an emergency dump system  68 ,  70 . In addition, there is a power supply  74  that interfaces with the aircraft power system  72 . 
     The pilot interface  52  is powered by the gate controller  50  and is the means by which various system settings are controlled. Now referring to  FIG. 2 , the pilot interface  52  consists of a display module  51  and various switches and indicators. The display module  51  is in an aluminum case with a silicone membrane type keypad. The LCD display  51  is mounted behind a sealed piece of glass. The pilot interface  52  provides messages and system status to the pilot, and accepts inputs from plural actuators  53 ,  55 ,  57 ,  73 ,  75 ,  77 ,  79 ,  81 ,  83 ,  85 , and  87  and one push button/rotary encoder. Plural indicating lamps are also provided;  59 ,  61 ,  63 ,  65 ,  67 ,  69 , and  71 . 
     The pilot interface  52  push buttons include a Mark button  53 , which is used for telemetry system only, and defines points of interest. A Distress button  55  is also used for the telemetry system only, and activates transmission of a distress signal. A Menu button  57  enters and exits controller menus operations. A Home button  77  returns the display  51  to a home screen. A MSG (Message) button  73  is also used for the telemetry system only, and receives text messages sent to the unit. A Select actuator  75  is a scroll and select device used to access menu options present on the display  51 . 
     The pilot interface  52  also comprises indicator lamps, including a time mode status lamp  59 , which is related to GPS tracking intervals. It also includes an ARMED status indicator  61 , which will be more fully discussed hereinafter. It also includes an emergency dump (E-DUMP) system status indicator lamp  69 , which will also be more fully discussed hereinafter. It also includes a satellite modem (SAT) connectivity status indicator  71 , which is related to telemetry functions. It also includes a GPS connectivity indicator  65 , which is also related to gate and telemetry functions. It also includes a distance mode (DIST) status indicator  63 , which is related to GPS tracking intervals. 
     The pilot interface  52  also includes plural toggle switches below the display area, as follows. An ARMED switch  79 , which is turned on to arm the system prior to dumping fire retardant through the gatebox. There is also a Gallons To Dump switch  81 , which enables the pilot to adjust the volume of fire retardant to be dumped. There is also a Coverage Level switch  83 , which enables the pilot to set the fire retardant cover level of each dump. There is a also a Gate Open/Close switch  85 , which enables the pilot to drive the gates open or closed, and is also used to calibrate the closed position setting. Finally, there is a FOAM switch  87 , which allows for injecting foam into the system. 
     Now referring back to  FIG. 1 , the gate controller  50  is the main control box for the system, and provides the following function. The gate controller  50  accepts inputs from the pilot interface  52 , thereby enabling the pilot to set system parameters. The gate controller  50  connects to the various feedback devices such as sensors and switches. The gate controller  50  provides the microprocessors used to control logic functions for the system. The gate controller  50  performs calculations for the requisite gate angle to meet targeted drop rates based on sensor inputs. The gate controller  50  provides feedback to the motor controller  56 . The gate controller  50  performs passive diagnostics and system self-tests. The gate controller  50  provides power and signals to the pilot interface  52 . The gate controller  50  contains an accelerometer to sense the acceleration of the aircraft. The gate controller  50  provides Automated Flight Following (AFF) and Additional Telemetry Unit (ATU) functions. The gate controller  50  records and transmits firefighting event data via cellular or satellite modems. The gate controller  50  contains a GPS module to determine location of aircraft. 
     Continuing in  FIG. 1 , the motor controller  56  processes commands from the gate controller  50  and communicates them to the electric motor  58 . The motor controller  56  also converts the 24 volt (nominal) aircraft bus power to three-phase AC power required to drive the electric motor, which is a three-phase rotating-field motor with a permanent magnet rotor. In other embodiments, a 48 volt (nominal) power supply is employed to yield higher motor torque and power ratings. The motor controller also maintains a motor shaft position and rotation count by reading a resolver  60  that rotates together with the motor  58 . In the illustrative embodiment, the motor is a Heinzmann GmbH (www.heinzmann.com) model PMS 100 series permanent magnet synchronous motor. 
     Note that the gate controller  50  further includes an internal supervisor circuit to provides redundancy by providing a discrete input signal to the motor controller  56  to open the gates if a normal drop command does not initiate gate movement within 0.8 seconds. This supervisor circuit is hardware driven and requires no software within the gate controller  50  to command the motor controller  56 . 
     The gatebox system, as generally depicted in  FIG. 1 , includes a number of system sensors that provide parametric inputs to the gate controller  50 . A hopper volume sensor (not shown) outputs a voltage proportional to the rotary position of a hopper float shaft. The gate controller  50  calculates the gallons in the hopper based on this voltage for use during drops and for display to the pilot and ground loading crew. This sensor is mounted onto the rear hopper of the aircraft. A gatebox angle sensor  66  outputs an analog voltage that is proportional to the rotary position of the gate drive shaft (discussed hereinafter). The gate controller  50  uses this signal when controlling the gatebox gate angle in normal mode only. 
     An accelerometer (not shown) is provided within the gate controller  50 , and provides the control system with a voltage proportional to the acceleration of the aircraft. This is used by the controller for flow rate and door angle calculations in normal mode only. In addition, a Hall effect sensor (not shown) is internal to the motor and outputs a signal to the motor controller  56  for position feedback control. A temperature sensor (not shown) also provides the motor controller  56  with the internal temperature of the motor, which can be used for diagnostics. Both sensor signals exit the motor  58  through a common cable for connection to the motor controller  56 . 
     Continuing in  FIG. 1 , the electric motor  58  is an AC powered servo-motor, which is used to open and close the gatebox gates. This motor  58  is controlled by the gate controller  50  through the motor controller  56  during normal system operation to precisely control the angle of the gatebox  64  gates (not shown) to achieve constant flow out of the aircraft hoppers (not shown). The motor  58  is coupled to a drive shaft (not shown) in the gatebox  64  by a splined connection to a transmission  62 , which comprises a gear reduction therein. The transmission  62  reduces the motor  58  shaft speed to achieve an appropriate output speed. The transmission  62  also multiples the motor&#39;s  58  output torque in order to provide sufficient torque to open and close the gates (not shown). Note that the motor controller  56  converts DC input power to a variable frequency and current three-phase AC power to the motor to achieve control. 
     The primary source of power in  FIG. 1  is the aircraft power bus  72 , which typically provides 24 volts DC nominal power to the gate controller  50 . In some embodiments, the motor controller  56  may be selected to operate on 24 volts. However, in other embodiments, the motor controller  56  is selected to operate on 48 volts DC (nominal). The higher voltage enables the use of motors with higher power and torque ratings. In order to provide a motor controller input voltage greater than the aircraft power bus  72  voltage, and power supply  74  is added, which provides the increased voltage. Details and options for achieving this increased voltage will be more fully discussed hereinafter. 
     In the event of a complete failure of the gatebox system of  FIG. 1 , it is necessary to provide an emergency dump system for safety reasons. This is achieved with an emergency dump actuator  68  that is coupled to the electrical system through a switch  78 , and to the transmission  62  and gatebox  64  using a mechanical linkage  70 . The transmission  62  includes a clutch (not shown) that disengages the motor  58  from the gatebox  64  upon actuation of the emergency dump  68 . Actuation also applies a rotating force on the drive shaft (not shown) in the gatebox  64  to move it past an over-center position, which enables the gates (not shown) to fall open and dump the fire retardant. The over-center mechanical arrangement will be more fully discussed hereinafter. The switch  78  disconnects the DC power supply  74  from the motor controller  56  upon actuation of the emergency dump  68  to ensure that the motor  58  cannot apply any rotational force to the system. This system and its functions will be more fully discussed hereinafter. 
     The gatebox system (or “system”) can be operated in normal mode using the control logic to open and close the gates in response to a selected Coverage Level and Gallons to Dump. Once the pilot initiates a drop by depressing the drop trigger, the controller will open the doors and adjust the door angle to maintain a constant flow rate from the hoppers. When the selected gallons to dump have been evacuated, the doors close to capture any remaining fluid in the hoppers. The control system will compensate for various dynamics during the drop event. Table  1  presents a summary of function of the system. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Parameter 
                 Device Type 
                 Action 
                 Comments 
               
               
                   
               
             
            
               
                 Dump  
                 Switch - 1NO,  
                 Opens the gates when 
                 Located on 
               
               
                 Trigger 
                 1 NC 
                 pressed, closes gates 
                 flight stick 
               
               
                   
                   
                 when released 
                   
               
               
                 ARMED  
                 Switch, 2 pos, 
                 Arms FRDS system to 
                 Status Indicator 
               
               
                 toggle 
                 locking detent 
                 enable high voltage to 
                 on Pilot 
               
               
                   
                   
                 motor, illuminate the 
                 Interface 
               
               
                   
                   
                 ARMED indicator light 
                   
               
               
                 OPEN/ 
                 Switch, 3 pos, 
                 Opens or closes door 
                 System must be 
               
               
                 CLOSE 
                 momentary, 
                 when toggled 
                 ARMED 
               
               
                 toggle 
                 center rest 
                   
                   
               
               
                 Coverage  
                 Switch, 3 pos, 
                 Increases or decreases 
                 Sets the desired 
               
               
                 Level +/− 
                 momentary, 
                 coverage level 
                 when flow rate  
               
               
                 toggle 
                 center rest 
                 toggled 
                 from the gate 
               
               
                 Gallons  
                 Switch, 3 pos, 
                 Increases or decreases 
                 Sets the desired 
               
               
                 to Dump 
                 momentary, 
                 the gallons to dump 
                 volume to drop 
               
               
                 +/− 
                 center rest 
                 when toggled 
                   
               
               
                 Foam Set/ 
                 Switch, 3 pos, 
                 Sets foam injection 
                 Controls foam 
               
               
                 Inject 
                 momentary, 
                 value or initiates foam 
                 system 
               
               
                   
                 center rest 
                 injection 
                   
               
               
                 Datawheel 
                 Push button, 
                 Rotation scrolls through 
                 Located on the 
               
               
                   
                 rotary encoder 
                 menu selections, push 
                 Pilot Interface 
               
               
                   
                   
                 selects current item 
                   
               
               
                 Mark 
                 Switch, 
                 Creates points of 
                 For telemetry 
               
               
                   
                 momentary 
                 interest 
                 system only 
               
               
                 Distress 
                 Switch, 
                 Transmits a distress 
                 For telemetry 
               
               
                   
                 momentary 
                 message 
                 system only 
               
               
                 Menu 
                 Switch, 
                 Enters/exits controller 
                   
               
               
                   
                 momentary 
                 menus 
                   
               
               
                 Home 
                 Switch, 
                 Returns display to 
                   
               
               
                   
                 momentary 
                 Home screen 
                   
               
               
                 MSG 
                 Switch, 
                 Receives text messages 
                 For telemetry 
               
               
                   
                 momentary 
                 sent to the unit 
                 system only 
               
               
                   
               
            
           
         
       
     
     During normal operation of the system, the following operating parameters exist:
         A. Circuit breakers for the system are engaged to distribute bus power from the aircraft to the gate control system   B. The system microprocessors boot up and current system parameters are displayed on the Pilot Interface   C. Coverage Level and Gallons to Dump are adjusted to the desired value by the pilot   D. The pilot toggles the ARMED switch to arm the system   E. The system is now in standby mode   F. The pilot depresses the drop trigger on the flight stick to initiate a drop
           a. The system opens the doors to maintain the desired flow rate, once the desired volume has been released the doors close automatically   
           G. Once the drop is complete, the pilot releases the drop trigger. The pilot may choose to release the trigger to close the doors prior to the release of the pre-selected volume
           a. When the doors are open in any mode, if the pilot released the drop trigger the doors will close   
           H. The system returns to standby mode and is ready for another delivery cycle       

     Reference is directed to  FIG. 3 , which is a perspective view drawing of a fire retardant gatebox  2  according to an illustrative embodiment of the present invention. The gatebox  2  is a riveted aluminum structure  4  that is mounted to the belly of the aircraft. The structure is primarily assembled from 6061-T6 aluminum sheet. The gatebox  2  attaches to the airframe (not shown) using a flange and bolt pattern  6  on the upper portion thereof. Front and rear fiberglass fairings (not shown) are attach between the gatebox  2  and belly of the airframe (not shown) to provide an aerodynamic profile. The Air Tractor AT-802F aircraft comprises forward and rear fiberglass hoppers (not shown) that have throats that exit at the belly of the aircraft to feed fire retardant into the gatebox  2 . 
     The gatebox  2  includes a first and second gate opening  7 ,  9  that each has a corresponding gate  8 ,  10  that is hinged along one edge of the gate openings. A piano style hinge is appropriate, and an O-ring seal may be disposed between the gate openings and the gates to provide a water tight seal when the gates  8 ,  10  are in a closed position to engage the gate openings  7 ,  9 . 
     A drive shaft  12  is rotatably supported within the gatebox  2  and aligned along the longitudinal axis of the aircraft in this embodiment. The drive shaft  12  is rotatable in both a gates-opening direction and a gates-closing direction, which will be more fully discussed hereinafter. Plural sets of crank arms and connecting links  14  are disposed along the length of the drive shaft  12  for opening and closing the gates  8 ,  10  by rotation of the drive shaft  12 . Each set comprises a crank  22 ,  24 , which are fixed along the length of the drive shaft  12 , and a corresponding connecting link  26 ,  28  that are disposed between a distal end of the crank arms  22 ,  24  and corresponding gate  8 ,  10 . In this embodiment, three crank arms and connecting links are provided for each gate. A minimum of one crank arm and connecting link is required for each gate. Thusly, rotation of the drive shaft  12  is converted to linear travel by the crank arm and connecting link arrangement to push the gates open in the gates-opening direction of rotation and pull the gates closed in the gates-closing direction. 
     Reference is directed to  FIG. 4 , which is a section view drawing of a fire retardant gatebox  2  according to an illustrative embodiment of the present invention.  FIG. 4  corresponds with  FIG. 3 . In  FIG. 4 , the upper mounting flange  6  is defined by the gatebox  2  aluminum sheet  4  structure, with the first gate opening  7  and the second gate opening  9  formed through a lower portion thereof. A first gate  8  is hingedly connected along an edge of the first gate opening  7 . The drive shaft  12  has a first crank arm  22  fixed thereto, which is in-turn coupled from its distal end to the first gate  8  by a first connecting link  26 , as illustrated. Similarly, the second gate  10  is hingedly connected along an edge of the second gate opening  9 , and the drive shaft  12  also has a second crank arm  24  fixed thereto, which is in-turn coupled from its distal end to the second gate  10  by a second connecting link  28 , as illustrated. As noted above, in the illustrative embodiment, there are three sets of crank arms and connecting links for each gate. Thusly, it can be appreciated that rotation of the drive shaft  12  will simultaneously open and close both gates  8 ,  10 , depending on whether it is rotated in the gates-opening or gates-closing directions. 
     Reference is directed to  FIG. 5 , which is a section view drawing of a fire retardant gatebox with drop gates and drive linkages according to an illustrative embodiment of the present invention.  FIG. 5  corresponds with  FIG. 4 . In  FIG. 5 , the gates  8 ,  10  are shown in their fully closed position. The gate openings  7 ,  9  are separated by a portion of the gatebox structure  30 , which is used to form a water tight seal while the gates  8 ,  10  are closed. O-rings or other elastomeric seals are appropriate for this application. Such seals can be applied to the gate openings  7 ,  9  or the gates  8 ,  10 , or both. The drive shaft  12  can be seen above the gates  8 ,  10 . The first gate  8  is connected to the drive shaft  12  by a first crank arm  22  and a first connecting link  26 . Note that the connecting link  26  is has an arcuate shape to facilitate clearance for the drive shaft  12 . The second gate  10  is connected to the drive shaft  12  by a second crank arm  24  and a second connecting link  28 . Note that the connecting link  28  is has an arcuate shape to facilitate clearance for the drive shaft  12 . Also note that the close clearance between the second connecting link  298  and the drive shaft  12  is such that rotation of the drive shaft  12  in the counter-clockwise direction would result in engagement between the connecting link  28  and the drive shaft, which would prevent over-rotation of the drive shaft in the gates-closing direction. This is by design. 
     Now consider the geometry of the connecting links and crank arms in  FIG. 5 , which are shown in the closed position with an over-center configuration. The second crank arm  24  has a pivot  34  at its distal end, which connects to the second connecting link  28 , which in-turn connects to a pivot  36  attached to the second gate. The centerline  38  between the crank arm pivot  34  and the gate pivot  38  lies below the centerline of the drive shaft  12 . As such, a downward load of fire retardant on the second gate will induce a rotation on the drive shaft  12  in the gates-closing direction (counter-clockwise in this view). Thusly, the drive shaft needn&#39;t hold the gate closed because the second connecting link  28  will engage the drive shaft  12  to prevent over-rotation in the gates closing direction. Other structure and stops could also be provided to prevent such over rotation. This is an important feature of the present embodiment because it provides that the motor and transmission do not have to be energized or locked to hold the gates closes. It is a passive mechanical arrangement that holds the gates closed. Of course, the first crank arm  22  and first connecting link  26  may provide the same over-center geometry. 
     Reference is directed to  FIG. 6 , which is a section view drawing of a fire retardant gatebox and drive linkages according to an illustrative embodiment of the present invention.  FIG. 6  corresponds with  FIG. 5 .  FIG. 6  illustrates two features of the present design. First, the change in linkage geometry away from the over-center condition, and second the implementation of out of phase gate linkages. In this Figure, the drive shaft  12  has been rotated  42  in the gates-opening direction. As this happens, the centerline  38  between the crank arm pivot  34  and gate pivot  36  has moved above the centerline  32  of the drive shaft  12 , and away from the over-center condition. Therefore, the weight of the fire retardant on the gates  8 ,  10  will induce rotation of the drive shaft in the gates-opening direction. This is important with respect to the emergency dump feature (described elsewhere herein) because it enables manual opening of the gates with minimal force and distance of movement. All that need occur is to disconnected the motor drive and transmission from the drive shaft  12 , and then apply just enough rotation in the gates-opening direction to move past the over-center condition. As soon as that occurs, the weight of the fire retardant will cause the gates to fall open and immediately drop the entire load of fore retardant. 
     The other feature illustrated in  FIG. 6  is the out of phase link arrangement. The rotational forces applied to the drive shaft  12  are provided by the motor and transmission (not shown) and vary along the distance of rotational travel of the drive shaft  12 . The highest forces occur as the linkages pass through the over-center position, and as the seals around the gate openings are engaged. Since there are two gates, the forces occur in two parts, and the total force is approximately twice that of a single gate operating force. By adjusting the position of the crank arms  24 ,  22 , and/or the lengths of the crank arms and connecting links  26 ,  28 , the designer can adjust these force peaks to be out of phase with one another, and therefore spread them out over the distance of rotational travel of the drive shaft  12 . This has the effect of reducing the peak torque required from the motor and transmission. In  FIG. 6 , it can bee seen that the second gate  10  has opening slightly more than the first gate  8 , and this illustrates the out of phase linkage arrangement. 
     Reference is directed to  FIG. 7 , which is a section view drawing of a fire retardant dump gates and drive linkages according to an illustrative embodiment of the present invention.  FIG. 7  corresponds with  FIGS. 5 and 6 . In  FIG. 7 , the weight of the fire retardant (not shown) has pushed the gates  8 ,  10  fully open and the fire retardant has been completely dropped by the gates. The falling action of the gates  8 ,  10  has been coupled through the connecting links  26 ,  28  and the crank arms  22 ,  24  and caused the drive shaft  12  to rotate fully  44  in the gates-open direction. The ability of the gates to fall open depends upon disconnection of the drive shaft  12  from the motor and transmission (not shown). If such a disconnect is not implemented, then the movement of the gates  8 ,  10  remains under control of the system, by the motor and transmission. 
     Reference is directed to  FIG. 8 , which is a schematic diagram of a power supply according to an illustrative embodiment of the present invention. As was discussed hereinbefore, modern aircraft commonly provide a DC power bus that provides 24-volt (nominal) power for accessories. The present disclosure contemplates the use of 24-volt motors and circuitry that can be directly coupled to such a power bus. However, the use of a higher voltage power supply offers certain advantages, particularly with respect to the available power and torque in an electric motor of a given frame size. Higher voltage also enable designers to user lighter gauge wiring for a given motor rating, since the current is halved by a doubling of the voltage.  FIG. 8  illustrates one technique for doubling the power supply voltage by rearranging the interconnection amongst plural batteries provided with the aircraft. 
       FIG. 8  illustrates an aircraft that originally provides three 24-volt batteries  80 ,  82 ,  84 , which are originally connected in parallel to drive the aircraft power bus, at terminals  88 . Under the teachings of the present disclosure, one of the batteries  84  is selected to be rewired, and interconnected with a suitable DPDT relay  86 . In its unpowered state, the relay  86  couples the selected battery  84  in parallel with the non-selected batteries  80 ,  82 . As such, the system operates as originally provided by the aircraft manufacture, in that all three batteries are in parallel and are coupled to provide 24-volts to the aircraft bus terminals  88 . The aforementioned gate controller (not shown) is coupled to drive the relay  86  into a powered state when the systems requires 48-volts for operation. This would occur at any time the gate controller operates the drive motor. When this occurs, the relay  86  contacts switch states and the selected battery  84  is temporarily wired in series with the two unselected batteries  80 ,  82 , and the 48-volts that that arrangement provides is delivered to the motor power terminal  90 . When the motor operations are complete, the relay  86  is deenergized to return to the 24-volt operating mode. 
     Reference is directed to  FIG. 9 , which is a diagram of a power supply according to an illustrative embodiment of the present invention.  FIG. 9  illustrates an alternative circuit design for providing 48-volts to the motor and motor controller (not shown) of the present disclosure&#39;s gatebox system. In this embodiment, an additional battery  94  is added to the existing aircraft power system batteries  92 . Note that only a single aircraft battery  92  is illustrated in the circuit to simplify the schematic diagram. In actuality, there would be plural batteries at the connection of battery  92 . The aircraft batteries  92  deliver 24-volts to the aircraft power bus at terminal  98 . The additional battery  94  is wired in series with the aircraft power bus to provide 48-volts to the motor power supply terminals  48 . In order to maintain a charge on the additional battery a battery charger  96  is provided, which draws power from the aircraft bus and charges the additional battery  94 . 
     During normal operation, the gatebox system of the present disclosure is operated by the gate controller utilizing an electric motor to operate the gatebox gates, and the system is designed to be reliable and trouble free. However, as in all things aviation related, redundancy and manual alternatives are needed to be certain the pilot can safely return the aircraft to ground, or avoid a dangerous aeronautical situation. To that end, the present disclosure provides an emergency drop system, which is also referred to as an emergency dump or “E-Dump” system. This system must be operable without external power of any kind, and must be operable by the pilot from the cockpit. Accordingly, the present disclosure teaches an independent, fully mechanical system configured so that the gates can be opened in the event the gatebox system is inoperative. When power is off to the gatebox system, a mechanical over-center latch arrangement is used to keep the gatebox gates closed. This latch system allows for a fire retardant load to be retained in the hoppers indefinitely without any action from the gatebox system, as was described above. 
     In order to open the gates using the emergency drop system, the pilot pushes an emergency drop handle forward in the cockpit causing a series of linkages to open the gatebox gates past the over-center latched position. The emergency drop system will function even if electrical power to the system is lost. A series of limit switches are wired into the system to cut control power to the gatebox system in the case where electrical power still exists. In one embodiment, the emergency drop handle is connected to a series of bell cranks and linkages as well as two series connected electronic limit switches. When the lever is pushed forward, the limit switches are opened. This provides a signal to the gate controller that an emergency drop has been initiated. The gate controller then inhibits any commands to the electric motor. The lever also enacts a mechanical series of linkages, which pull a release fork inside the transmission that is mounted to the front of the gatebox so as to decouple the electric motor&#39;s output shaft from the gate drive shaft. This action removes the motor from the mechanical system. Another part of the emergency drop system linkage pulls a crank arm located on the back side of the gatebox. This rotates the gatebox&#39;s drive shaft so that the gate linkages are pulled back over-center. Once pulled into the un-latched position, the gates rotate to the fully open position due to the weight of the fire retardant in the aircraft&#39;s hoppers, which instantly empties the aircraft fire retardant hoppers. 
     Reference is directed to  FIG. 10 , which is a perspective view drawing of an emergency drop system linkage according to an illustrative embodiment of the present invention. The end wall  200  of the gatebox serves as the mounting location for the mechanical components of the emergency dump system. External connections to this system include the pilot pull rod  218 , which is connected to an operating handle in the cockpit, and, the clutch rod  224 , which connects to a clutch located in the transmission (not shown) at the opposite end of the gatebox. The clutch rod  224  is illustrated in broken line because it is located behind the gatebox. The drive shaft  202  extends through the end wall  200 , and is connected to a crank arm  204  supported within a drive shaft mount  206 . Not that the drive shaft position sensor  208  is located on the mount  206 , and communicates the drive shaft position to the gate controller (not shown). A crank rod  210  is linked between the crank arm  204  and a first end of a bell crank  214 , which is rotatably supported in a suitable mount  212 . A dump link  216  is connected to the opposite end of the bell crank  214 , and is connected to the clutch rod  224  at its opposite end. The connection between the dump link  216  and the clutch rod  224  is guided and limited in range of movement by a slot  222  in the clutch rod bracket  220 . The pilot pull rod  218  is connected to the dump link  216  along its length. 
     Reference is directed to  FIGS. 11, 12, and 13 , which are operating diagrams of the emergency dump linkage system of  FIG. 10 , and according to an illustrative embodiment of the present invention. The emergency dump system functions through three states, corresponding to  FIGS. 11, 12, and 13 , respectively.  FIG. 11  shows the system in the normal state where the gates (not shown) are closed, the clutch (not shown) is engaged, and the drive shaft  202  has been rotated in the gates-closing direction such that the aforementioned over-center condition holds the gates closed. Note that in these figures, the orientation of the drive shaft  202  and crank arm  204  have been rotated ninety degrees with respect to the end wall  200  of the gatebox for visual clarity.  FIG. 12  shows the emergency dump linkage in the clutch-released state, and  FIG. 13  shows the linkage in the gates-open state. 
     In  FIG. 11 , the crank arm  204  is located to the right, which is the over-center position, whereby the gates (not shown) hold themselves closed. The bell crank  214  is also rotated to the rights, as shown, by virtue of the crank rod  210  linkage. The clutch rod  224  is forward, which is the clutch-engaged position. The pilot pull rod  218  is also in the forward position. Note that “forward” means to toward the front of the aircraft, which is up in these drawing figures. In  FIG. 12 , the pilot has pulled  226  the pilot pull rod  218  partially rearward to activate the second state of the linkage system. The pilot pull rod  218  pulls  226  the dump link  216  rearward, which pulls  228  the clutch rod  224  rearward, thereby disengaging the clutch (not shown). The movement  228  of the clutch rod  224  is limited by the slot  222  in the clutch rod bracket  220 . Once this limit of movement is reached, the dump link  216  begins rotating the bell crank  214  to the left, transitioning to the open state of  FIG. 13 . 
     In  FIG. 13 , the pilot pull rod  218  has pulled  230  fully rearward, which rotates  232  the bell crank  214  to the left. This action causes the crank rod  210  to pull  234  the crank arm  204 , thereby rotating  236  it to the left, and past the aforementioned over-center condition. The weight of the fire retardant (not shown) on the gates (not shown) promptly forces the gates open, and dumping the fire retardant from the hoppers. 
     Reference is directed to  FIGS. 14, 15, and 16 , which are emergency dump linkage diagrams according to an illustrative embodiment of the present invention. This emergency dump system functions through three states, corresponding to  FIGS. 14, 15 , and  16 , respectively.  FIG. 14  shows the system in the normal state where the gates (not shown) are closed, the clutch (not shown) is engaged, and the drive shaft  302  has been rotated in the gates-closing direction such that the aforementioned over-center condition holds the gates closed.  FIG. 15  shows the emergency dump linkage in the clutch-released state, and  FIG. 16  shows the linkage in the gates-open state. 
     The linkage arrangement in  FIGS. 14, 15, and 16  are attached to the rear bulkhead  300  of the gatebox. The drive shaft  302  is supported on a drive shaft mount  304 , and has a crank arm  306  attached to its end, which enables rotation of the drive shaft  302  by the various linkages. This embodiment comprises two levers that enable operation, and these include the crank lever  317  and the clutch lever  312 . The clutch lever  312  pivots about a clutch lever pivot  322  on a clutch lever mount  310 . The crank lever  317  pivots about a crank lever pivot  318  that is connected to the clutch lever  312 , as illustrated. A crank rod  308  is connected to a distal end of the crank arm  306  and to a crank rod pivot  320  located on the clutch lever  312 , as illustrated. Note that the crank rod pivot  320  and the clutch lever pivot  322  are aligned, one above the other, but not connected, in the aforementioned first and second states. A pilot pull rod is connected to a distal end of the crank lever  317 . A clutch rod is connected  330  to a distal end of the clutch lever  312 , and its movement is limited by a slot  326  in a clutch rod mount  324 , as illustrated. 
     In  FIG. 14 , the pilot pull rod  316  is in the forward position (toward the front of the aircraft, and up in the drawing figure). The clutch rod  328  is also in the forward position, where the clutch (not shown) is engaged. The crank arm  306  is to the right, and the drive shaft  302  is in the over-center position, holding the gates (not shown) closed as discussed hereinbefore. In  FIG. 15 , the pilot has pulled  332  the pilot pull rod  316  rearward. This action rotates  334  the crank lever  317  and the clutch lever  312  downward (counter-clockwise in the figures). Rotation of the clutch lever  312  pulls  336  the clutch rod  328  rearward, disengaging the clutch (not shown). The extent of this movement  336  is limited by the clutch slot  326  in the clutch rod mount  324 . Once the limit of the clutch slot is reached, then further rearward movement  338  ( FIG. 16 ) of the pilot pull rod  317  results in rotation  340  of the crank lever  317 . 
     In  FIG. 16 , the pilot pull rod  316  has been pulled  338  to its rearward extent, and the crank lever  317  has been rotated  340  to its full extent. This action causes the crank lever  317  to rotate about the crank lever pivot  318 , and pull the crank rod  308 , to thereby rotate the drive shaft  302  past the over-center condition. This action causes the gates (not shown) to drop open, as discussed hereinbefore. It is noteworthy to consider the utility of having the clutch lever pivot  322  and the crank arm connection point  320  aligned with one another while the crank arm  308  is full to the right. With this, pulling ( 322  in  FIG. 15 ) the pilot pull rod  316  and rotating  334  the crank lever produces no force on the crank rod  308 . This allows the full effort of the pilot&#39;s action to first disengage the clutch by rotating the clutch lever  312  first, and not beginning rotation of the crank lever  317  until the clutch rod  328  has engaged the rearward end of the slot  326 . After that occurs, then all of the pilot&#39;s pull force is directed to pulling the crank arm  306  and drive shaft  302  back over-center. 
     Reference is directed to  FIGS. 17 and 18 , which are a section view drawings of a gear reduction transmission with clutch according to an illustrative embodiment of the present invention. This device corresponds to item  16  in  FIG. 3 .  FIG. 17  illustrated the transmission with the clutch  166 ,  162  engaged, and  FIG. 17  with the clutch  166 ,  162  disengaged. The transmission comprises a housing  150 , which encloses and supports a range of shafts, gears and bearings. The servo-motor  152  is mounted to the exterior of the housing  150 , and presents a drive gear  154  within the housing  150 . A first gear reduction is achieved by meshing the drive gear  154  with a first driven gear  156 . This force is applied through shaft  157  to the next gear reduction set of gears  158  and  160 . This force is coupled, in turn, to shaft  164 . Shaft  164  is splined to a clutch cog  166 , which is shiftable to either engage the interior of clutch gear  162 , or allows clutch gear  162  to free wheel. In either case, clutch gear  162  meshes with output gear  172 , which is fixed to the output shaft  174 . The output shaft  174  is attached to the aforementioned drive shaft (not shown) in the gatebox (not shown). 
     Operation of the clutch is accomplished by sliding the clutch cog  166  along its splined connection to shaft  164  to either engage or disengage clutch gear  162 . This is accomplished by moving shift fork  168  by applying a pulling force  180  at the distal end of shift rod  176 . This is accomplished by the aforementioned clutch rod in the emergency dump system. A spring  170  is provided within the transmission housing  150  to return the clutch  162 ,  166  to the engaged condition. A weather seal boot  178  is provided about the shift rod  176 . 
     Thus, the present invention has been described herein with reference to a particular embodiment for a particular application. Those having ordinary skill in the art and access to the present teachings will recognize additional modifications, applications and embodiments within the scope thereof. 
     It is therefore intended by the appended claims to cover any and all such applications, modifications and embodiments within the scope of the present invention.