Abstract:
A stores ejection system for retaining stores on the underside of an aircraft and forcibly jettisoning the stores away from the aircraft is disclosed. The ejection system includes a plurality of ejector mechanisms for releasably holding and jettisoning the stores away from the aircraft, a plurality of storage devices for storing pressurized gas to actuate the ejector mechanisms, and a central control system for maintaining the pressure of the gas, and actuating the release of the gas. The central control system monitors the pressure of the storage devices and heats only those storage devices that have a pressure below the operating pressure.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to store carriers for mounting a releasable store on an aircraft and, more particularly, to a stores ejection system from which stores are released with ejective force applied at forward and aft locations by thrusters which are actuated by cold, clean pressurized gas, such as air. 
     The store referred to herein may be used to contain munitions, such as bombs, or contain other material to be dropped from an aircraft. Military aircraft used to dispense bombs, rockets, and other stores in flight usually include racks located beneath the wings and fuselage designed to release the stores upon command. Typical racks are shown in U.S. Pat. Nos. 4,043,525; 4,347,777; 5,583,312; 5,907,118; and 6,035,759 each by the same inventor and assignee as in the present application and incorporated herein by reference. 
     At the time of target acquisition, a release mechanism is activated which results in mechanical release and subsequent forcible ejection of that weapon away from the aircraft. State of the art bomb ejector racks utilize pyrotechnic cartridges that on ignition, generate high pressure gas for actuating the mechanical release mechanism, as well as for providing high pressure to ejection rams which forcibly eject the store from the aircraft. This method was originated at Douglas Aircraft Company, formerly an operating division of McDonnell Douglas Corporation, in 1944, and is currently a widely used method on all weapon release devices. 
     While such pyrotechnic cartridges provide a weight efficient means of storing and releasing energy as a power source, they also have certain undesirable characteristics. For example, a great deal of cleaning and maintenance is required after firing a pyrotechnic device, at the cost of a great deal of labor and downtime for the aircraft. When fired, the chemical burning of the explosive charge within the pyrotechnic cartridge results in a large amount of residue being deposited within the system. This residue also contains moisture and corrosives. After burning, the moisture in the system tends to further gather debris, form ice, and otherwise clog the internal and external workings of the bomb rack mechanism. Thus, if not properly disassembled and cleaned after a scheduled number of firings, the stores rack will quickly become corroded and unreliable, and will require replacement. 
     Other problems associated with the use of pyrotechnic cartridges in bomb ejector systems include the necessity for use of hazardous cleaning solvents, which pose their own unique stowage, use, handling, and disposal considerations. Additionally, ground crew post-flight action is required to remove and dispose of the spent cartridges. Removal of live cartridges is required prior to off-loading unreleased stores, further increasing crew workload and turnaround time. Furthermore, prior to cartridge installation, the ground crew must utilize special equipment to conduct stray voltage checks, in order to assure that an inadvertent firing will not occur. Logistically, adequate supplies of cartridges must be maintained to support bomb rack operation, which imposes additional unique shipping, storage, and handling requirements because of their explosive nature. Cartridges have a limited shelf life as well, before becoming unreliable, so date monitoring and inventory control is necessary. Finally, parts life of the stores rack is limited because of the effects of pyrotechnic gas erosion, resulting in significant logistic and cost burdens. 
     Stores ejection systems are known in the prior art which avoid the use of pyrotechnic cartridges. For example, U.S. Pat. No. 4,204,456 to Ward discloses a pneumatic bomb ejector, which uses a suitable pressurized gas, such as air or nitrogen, as a stored energy source for actuating the ejector. However, the system is disclosed as being utilizable only with a particular type of customized mechanism which does not employ ejector rams to forcibly eject the store. This means that it may only be used for applications wherein it is not necessary to ensure that the store clears the aircraft slipstream by forcibly ejecting it away from the aircraft. Furthermore, the Ward system is not adaptable to the standardized ejection systems in use in almost all existing military aircraft, limiting its practical applicability. Another problem with the Ward system is that the gas is pre-charged prior to operation. However, as the aircraft climbs to altitude, and the ambient temperature drops, the pressure level drops as well. As the pressure level varies, so does the performance output. Without an onboard pressure maintenance system, the stores ejector may not operate reliably. 
     Another prior art approach is disclosed in U.S. Pat. No. 4,905,568 to Hetzer et al. This patent discloses an ejector mechanism which, like that of Holt, utilizes high pressure gas, preferably nitrogen, as an energy source, with hydraulics as the energy transfer medium. Hetzer does attempt to compensate for pressure variations in the stored accumulator gas by employing heating coils to alter temperature of the gas as altitude changes. However, no central control system is disclosed to independently monitor and control the pressure of multiple accumulators. 
     Still another prior art approach is disclosed in U.S. Pat. No. 5,583,312 to Jakubowski, Jr. where a renewable energy source is provided to power an ejector mechansim. The renewable energy source comprises and on-board compressor that is used to pressurize one or more accumulators. As pressure varies in an accumulator, gas is released through a vent valve to reduce the pressure, and gas pressure is increased by actuating an on-board compressor. Some problems with an on-board compressor can comprise the compressor adding undesirable weight, occupying undesirable space, requiring large amounts of aircraft electrical power, requiring additional aircraft wiring, generating significant heat which must be managed, high cost and long charge times, particularly where the compressor fills multiple racks. 
     As can be seen, there is a need for an improved apparatus and method that monitors and maintains the pressure of gas contained in multiple accumulators for use by a stores ejection system. 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention, a stores ejection system for retaining a plurality of stores on an aircraft and forcibly jettisoning the stores away from the aircraft, the ejection system may comprise a plurality of ejector mechanisms, each ejector mechanism for releasably holding and releasing a store away from the aircraft; a plurality of storage devices, each storage device for storing pressurized gas at an operating pressure selected for actuating an ejector mechanism to release a store and forcibly jettison the store; a plurality of dump valves, each dump valve movable between a closed position in which a storage device is isolated from an ejector mechanism, and an open position in which pressurized gas is free to flow from the storage device to the ejector mechanism for pneumatic actuation of the ejector mechanism to release and jettison the store; a plurality of heaters, each heater operable to heat the pressurized gas within a storage device to increase the pressure of the gas contained within to an operating pressure; and a thermal central control unit for detecting the pressure within each of the plurality of storage devices, activating a heater to heat an individual storage device that is below the operating pressure, and deactivating the heater when the individual storage device reaches the operating pressure. 
     In another aspect of the invention, a control system for monitoring and maintaining the pressure in accumulators used to provide energy to operate a stores ejection system on an aircraft may comprise, at least one sensor for providing data indicating the pressure within an accumulator; at least one heater adapted to heat the accumulators; and a central processing unit in communication with said sensor and said heater, for receiving said data, determining whether the pressure within an individual accumulator is below operating pressure, activating a heater until the pressure within said individual accumulator reaches a predetermined level and receiving a signal from a management unit to actuate said stores ejection system. 
     In another aspect of the invention, a stores ejection system, for holding a store on the underside of an aircraft and forcibly releasing the store away from the aircraft, comprises a plurality of ejector mechanisms, each ejector mechanism for releasably holding and releasing the store away from the aircraft; a plurality of storage devices, each storage device for storing pressurized gas at an operating pressure selected for actuating an ejector mechanism to release the store, each storage device being free of connection to any pressure source on board the aircraft; a plurality of dump valves, each dump valve movable between a closed position in which a storage device is isolated from an ejector mechanism, and an open position in which the pressurized gas stored within the storage device is free to flow from the storage device to an ejector mechanism for pneumatic actuation of an ejector mechanism to release the store; a fill valve for initial charging of said plurality of storage devices, the fill valve being constructed and arranged to permit filling of each storage device only while the aircraft is in a landed condition; a plurality of heaters, each heater operable to heat the pressurized gas within a storage device to increase the pressure of the gas contained within to the operating pressure; and a thermal central control unit for detecting the pressure within each of said plurality of storage devices, activating a heater to heat an individual storage device that is below said operating pressure and deactivating said heater when said individual storage device reaches the operating pressure. 
     A method of holding and releasing a store from an aircraft while in flight, the aircraft having a stores ejection system comprising a plurality of ejector mechanisms and a plurality of storage devices, the method comprising the steps of connecting the plurality of storage devices with a pressure source located external to the aircraft and filling the plurality of storage devices prior to take-off with a gas until the pressure within each filled storage device reaches an operating pressure selected for actuating an ejector mechanism to release a store and forcibly jettison the store away from the aircraft, monitoring the pressure of the gas contained within each of the plurality of storage devices; detecting a pressure drop in at least one of the plurality of storage devices; and heating the gas in each storage device having a pressure below operating pressure to increase the pressure of the gas contained within to the operating pressure. 
    
    
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram illustrating the stores ejection system with a heating coil according to an embodiment of the present invention; 
     FIG. 2 is a schematic diagram illustrating the stores ejection system with a heating blanket according to an embodiment of the present invention; 
     FIG. 3 is diagram illustrating an enlarged, partial cutaway view of the pneumatic actuation system according to an embodiment of the present invention; 
     FIG. 4 is a diagram illustrating an enlarged, partial cutaway view of the accumulator according to an embodiment of the present invention; 
     FIG. 5 is a schematic diagram illustrating a charge cart according to an embodiment of the present invention; and 
     FIG. 6 is a diagram illustrating a bottle cart according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
     Improved apparatuses and methods are provided by the present invention that achieves a proper operating pressure in a plurality of gas storage devices, such as gas accumulators. In doing so, the gas accumulators provide sufficient energy to operate ejector mechanisms that hold and release stores. The present invention can be adapted to various pneumatic ejector mechanisms. The accumulator and ejector mechanisms are commonly used to eject stores carried on an aircraft. The stores may include munitions such as bombs. Unlike prior art stores ejection systems, the present invention has a small weight and space requirement, while also providing a central control unit that monitors and maintains multiple accumulators at a proper operating pressure using heaters, such as, heating coils and/or heating blankets. While each accumulator is commonly used to power ejector mechanisms on an aircraft, the improved apparatuses and methods may also be used in other pneumatically operated mechanisms, such as a munitions loading device on a tank. 
     Referring now to FIGS. 1 and 2, two embodiments of a pneumatically driven stores ejection system  10  are illustrated schematically. In each illustrated embodiment, two suspension and release equipment (S &amp; RE) modules  12  and  14  are included in the system  10 , though in actuality any number of such modules may be employed, depending upon the configuration of the aircraft and weapons system with which the system  10  is to be used. The S &amp; RE modules  12 ,  14  may be identical stand-alone mechanical units, each preferably comprising a mechanism for releasably holding and releasing a store, a pair of ejector pistons  16  for thrusting the store clear of the aircraft, and an actuation system for actuating the ejector pistons. Each actuation system may include a storage device for pressurized gas, such as an accumulator  22 ,  23 , an accumulator pressure sensor  24 ,  96 , a check valve  26 ,  98 , an ejection dump valve  28 ,  100  an over-pressure valve  30 ,  102  and an over-pressure vent  32 ,  104 . 
     A single ground fill port  34  provides pressurized fluid, preferably compressed air, from a remotely located pressurization unit, such as a charge cart  36  to each of the modules  12 ,  14 . Preferably, the fill port  34  incorporates a filter unit  38  having a hose attach fitting  39  for coupling to the charge cart  36 . 
     Referring to FIG. 5, the charge cart  36  may comprise a compressor  44 . In one embodiment of the invention, a four-stage axial piston compressor may be used, although any known type of compressor is suitable for the inventive application and may be alternatively installed. The compressor  44  is preferably driven through a shaft  46  by an electric motor  48  of known type, which in turn is controlled by a cart control unit  42 . Upon exiting the compressor  44 , the compressed air may travel through a flow passage  52  into a coalescer and vent solenoid valve unit  54 , which may provide a dual function of drying the air and also operating as a solenoid valve. From the coalescer unit  54 , the dry air exits into the manifold conduit  58 , while the excess moisture is vented through a moisture vent  56 . 
     Referring to FIG. 6, in another embodiment, the ground charge cart  36  may comprise an already fielded bottle cart that holds several large bottles of compressed gas, typically nitrogen. The large bottles supply a reservoir of high-pressure gas. The large bottles may come in 3000 psi and 6000 psi ratings. A bottle cart may comprise a pressure intensifier device that allows a consistent supply of gas at 3000 psi or 6000 psi. 
     In one embodiment, the charge cart  36  shown and described may be used, although many alternate embodiments are possible. For example, the compressor  44  could alternatively be hydraulically driven. Also, while air is used, any known clean gas could be used, and the charge cart  36  could actually comprise a nitrogen generating system. Dry air is desirable in order to minimize system corrosion and because water freezes at high altitude ambient temperatures, resulting in further corrosive conditions within the system. Thus, the a drying unit, such as the coalescer unit  54 , may be used. However, the charge cart  36  could be operated without such a unit, albeit with increased required maintenance. Finally, while a single compressor located on a single charge cart  36  operates to supply gas to a multitude of S &amp; RE modules, independent compressors for each S &amp; RE module may be used. 
     Referring to FIG. 1, when the aircraft electrical system is powered up, a “store present” check is run by control unit  50 . A store present switch  76 ,  112  may be coupled to each module  12 ,  14 . When a store is present, a signal may be transmitted through a control line  90 ,  106  from the store present switch  76 ,  112  to the central control unit  50 . 
     If an accumulator  22 ,  23  is in an unpressurized state, the charge cart  36  may be actuated to pressurize the accumulator  22 ,  23 . The pressure in each accumulator  22 ,  23  is monitored by a pressure gauge located on the charge cart  36 . The pressure gauge may not require electrical power, and in one embodiment, the accumulators  22  and  23  may be pressurized to approximately 6000 psi. When all S &amp; RE modules  12 ,  14  reach the prescribed pressure, the charge cart  36  is shut down and the manifold conduit  58  is detached from the hose attach fitting  39 . The check valve  26 ,  98  may be a spring-loaded valve that closes when the manifold conduit  58  is detached. In one embodiment, the spring-loaded valve requires no electrical power to function. The accumulators  22 ,  23  may be pressurized by the charge cart  36  with the aircraft power off. When the aircraft is powered, the control unit  50  runs the store present check. If a store is empty, the control unit  50  opens an over-pressure valve  30 ,  102  to release the gas contained within an associated accumulator  22 ,  23  through an over-pressure vent  32 ,  104 . The over pressure vent  32 ,  104  may also be opened and closed manually by ground personnel using a manual setting handle (MSH). 
     In order to maintain the pressure of the gas within each accumulator  22 ,  23  at the correct operating pressure, the central control unit  50  may provide thermal control to heat the pressurized gas within each accumulator  22 ,  23  upon sensing a drop in pressure to increase the pressure of the gas to the operating pressure. The central control unit  50  detects variances in the pressure of the gas in each accumulator  22 ,  23  through pressure sensors  24  and  96 . A temperature sensor may be provided instead of, or in addition to, the pressure sensor  24 ,  96  to detect a drop in temperature of the gas in an accumulator  22 ,  23 , where the drop in temperature is indicative of a drop in pressure below the operating pressure. When a temperature sensor is used, the control unit  50  may obtain the mass value of the air contained in an accumulator  22 ,  23 . One method of calculating the mass value is to obtain a pressure reading from the charge cart  36  when the charge cart  36  fills the accumulator  22 ,  23 . Using the pressure reading, volume of the accumulator, and the temperature of the gas, the control unit  50  may calculate the mass value. The control unit  50  may use the mass value to calibrate temperature readings in the accumulators  22 ,  23  to correspond to a pressure value. 
     Referring to FIGS. 1 and 2, when a pressure sensor  24 ,  96  detects a drop in pressure in an accumulator  22 ,  23 , a signal may be sent to the central control unit  50  along a control line  78 ,  80  indicating the pressure drop. The central control unit  50  may then direct a heater  18 ,  92 ,  20 ,  94 , to heat the gas in the accumulator  22 ,  23  suffering the pressure loss, thereby increasing the pressure of the gas within that accumulator  22 ,  23  up to the correct operating pressure. 
     The heater element, as shown in FIG. 1, may be a resistance heater  18 ,  92  in the form of a coil inserted into the accumulator  22 ,  23 , or as shown in FIG. 2, the heater may be a thermal blanket  20 ,  94  wrapped around the outside of an accumulator  22 ,  23 . An accumulator  22 ,  23  may also be wrapped in insulation to reduce the loss of heat. The stores ejection system  10  may include a safety device (not shown) operable to disable the heater  18 ,  92 ,  20 ,  94  if the pressure within the accumulator  22 ,  23  drops to approximately atmospheric pressure due to a catastrophic leak in the accumulator  22 ,  23 . In another embodiment, the safety device is integrated with the control unit  50 . The control unit  50  monitors the pressure in the accumulators  22 ,  23  and has a control logic routine that prevents the heater  18 ,  92 ,  20 ,  94  for an accumulator  22 ,  23  from activating when the accumulator  22 ,  23  is at atmospheric pressure. The stores ejection system  10  may include associated plumbing to prevent overheating of an accumulator  22 ,  23 . It is to be understood that heating devices other than those disclosed or shown herein may also be used. 
     Each accumulator  22 ,  23  may be coupled to the aircraft in a different location, and thus each accumulator  22 ,  23  may experience different thermal loads, resulting from, for example, aerodynamic heating and/or engine heat. The central control unit  50  may monitor each accumulator  22 ,  23  individually, and heat each accumulator  22 ,  23  separately so that each remains at the proper operating pressure. Thus, all the accumulators  22 ,  23  do not need to be heated simultaneously. The central control unit  50  may also open the over-pressure valve  30 , through control line HH to vent gas from an accumulator  22 ,  23  so as to reduce the pressure within. Gas is typically vented from an accumulator  22 ,  23  seconds or less before a store is released. 
     Now with reference to FIGS. 1-4, one structural detail of an S &amp; RE module  12 , for one embodiment, is illustrated. It should, of course, be noted that the structure of each of the S &amp; RE modules forming a part of the system  10  may be essentially identical, so that FIGS. 3 and 4 could just as well illustrate the S &amp; RE module  14 , or any other S &amp; RE module forming a part of the system  10 . It should further be noted that this design minimizes the changes necessary to adapt the invention to commercially available S &amp; RE systems. Thus, with the exception of the accumulators  22 ,  23  and related structure, including the dump valve  28 ,  100 , the illustrated stores ejection system is conventional. 
     Referring to FIGS. 3 and 4, passages  60  and  114  provide fluid communication between the accumulator  2223  and the pistons  16  and  110  through dump valve exit flow lines  62  that lie downstream of dump valves  28  and  100 . Inside hooks  64  and outside hooks  66  of a type well known in the art are preferably employed to releasably secure the store to the S &amp; RE module  12 ,  14 . The hooks  64 ,  66  may be actuated to an open position by means of a hinged hook opening linkage  68 , which in turn is driven by a hook opening piston  70 . The hook opening piston  70  is reciprocatingly driven when a dump valve  28 ,  100 , is opened, thereby permitting pressurized air from an accumulator  22 ,  23  to travel through port  72  into the valve area, where it further flows into piston chamber  74 , acting to drive the piston  70  reciprocatingly downward to actuate the hook opening linkage  68 . At the same time, pressurized air is also permitted by the open valve  28  to flow through the dump valve exit flow line  62 ,  120  and into the passages  60 ,  114  and  116 ,  118 , thereby actuating the ejector pistons  16  to thrust the store away from the aircraft simultaneously while being released from the hooks  64 ,  66 . Another S &amp; RE module is disclosed in, but not limited to, U.S. Pat. No. 6,035,759 to Jakubowski Jr. et al, and is herein incorporated by reference. 
     Referring also to FIGS. 1 and 2, aircraft stores management system (SMS)  84  controls the release of the stores through the central control unit  50 . On a release command by the SMS  84 , through a control line  108 ,  86 , an ejection dump valve  28 ,  100  is actuated to an open position, permitting pressurized air from an accumulator  22  to flow through port  72 , into the valve area, then into the piston chamber  74 , where it simultaneously drives the piston  70  downwardly to release the hooks  64 ,  66  while also flowing through passages  62 ,  120  and  60 ,  114 ,  116 ,  118  to pressurize and drive each of the ejector pistons  16 ,  110  to their extended positions, thus fully releasing and thrusting the store clear of the aircraft. As the hooks  64 ,  66  open, the store present switch  76 ,  112  detects a “store gone” condition, which is transmitted to the central control unit  50  along control line  90 . At the end of an ejector piston  16 ,  110  stroke, vent ports  88  are exposed, preferably discharging substantially all residual accumulator pressure and permitting the spring-loaded ejector pistons  16 ,  110  to retract to their stowed position. Alternatively, it may sometimes be desirable to hold some of the residual accumulator  22  pressure to reduce the charge time and power consumption necessary to recharge the system for the next firing. If the aircraft returns with the store on board, the vent valve  30  can be actuated to dump accumulator  22 ,  23  pressure to prevent unintended release. 
     Pneumatic S &amp; RE systems  12 ,  14  may operate with filtered, dry air, thus eliminating the build-up of residue and corrosive materials produced when using pyrotechnics. Cleaning requirements after firing are eliminated and corrosion control maintenance activities are limited to environmental conditions. Electrical stray voltage checks requiring specialized ground test equipment are eliminated and crew workload and turnaround time is reduced. 
     It should be understood, of course, that the foregoing relates to some embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.