Abstract:
A system and method is provided for pre-heating seals in an unpressurized gas-powered stores ejection system. The system and method allow the seals of the stores ejection system to be made pliable when operating at a low ambient temperature, and thus reliably seal during operation in Arctic cold start environments.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     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 a store is released with ejective force applied pressurized gas, such as air.  
         [0003]     2. Background Description  
         [0004]     Pneumatic stores carriage/ejector systems have been developed that utilize high-pressure (e.g., 6,000 psi) gas stored in a pressure vessel to eject stores, such as bombs, missiles, and the like. An example of such a system is disclosed in U.S. Pat. No. 5,583,312, the entirety of which is hereby incorporated by reference herein.  
         [0005]     These pneumatic stores carriage/ejector systems may use an integral valve/accumulator module to store the pressure in an accumulator affixed to a valve. Examples of such systems are disclosed, for example, in U.S. Pat. Nos. 6,347,768 and 5,857,647, the entirety of which are hereby incorporated by reference herein. Such systems operate generally as follows: when electrically triggered, a large dump valve is opened; the opening of the dump valve simultaneously provides pressure to a hook opening system and the ejector rams which force the store away.  
         [0006]     Although these systems provide a clean and effective means of ejecting stores, a deficiency exists in the technology which limits the operation use of the systems. The deficiency is that the current state-of-the-art seals do not reliably seal at extremely low temperatures, thereby limiting the deployment envelope of the systems.  
         [0007]     The aforementioned stores carriage/ejection systems provide weapons release by storing and appropriately releasing energy in the form of very high pressure (e.g., 6,000 psi) gas. The systems use seals that are typically made from resilient materials, such as rubber, or alternatively synthetic elastomer materials.  
         [0008]     In basic terms, sealing is achieved by the resilient material distorting or flowing under pressure into the gap area between mating parts, forming a seal. At extremely cold temperatures, seal materials tend to get hard and in this hardened state can not reliably distort or flow to seal gaps.  
         [0009]     When pressurized at ambient temperatures the integral valve/accumulator module system can be transitioned to extreme cold temperatures (e.g., −65° F.) without seal degradation. However, when attempting to fill these systems from empty at very low temperatures (e.g., below −30° F.) the seals are too rigid and do not reliably and repeatably seal. This cold start condition may occur, for example, when attempting to fill an empty military weapon release system in an Arctic environment.  
         [0010]     The present invention is directed to overcoming one or more of the problems or disadvantages associated with the prior art.  
       SUMMARY OF THE INVENTION  
       [0011]     This disclosure provides a means of pre-heating the seals of an unpressurized gas-powered stores ejection system to allow the seals to be more pliable at low temperature and thus reliably seal during Arctic cold start environments. According to one aspect of the invention, a stores ejection system is provided for mounting a jettisonable store on an aircraft which includes an on-board source of pressurized non-pyrotechnic gas, at least one release mechanism for releasably mounting the store, an actuation system for the release mechanism, and a heater for ensuring that seals associated with the stores ejection system remain pliable at extremely low temperatures. The heater advantageously may provide that the seals remain pliable even when the stores ejection system is unpressurized at low temperatures.  
         [0012]     The features, functions, and advantages can be achieved independently in various embodiments of the present invention or may be combined in yet other embodiments. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a schematic view of the stores ejection system of the invention;  
         [0014]      FIG. 2  is a side view of a suspension and release equipment (S &amp; RE) module to be employed in the inventive stores ejection system, illustrating the various elements and their arrangement within the system; and  
         [0015]      FIG. 3  is an enlarged partial cross-sectional view of the pneumatic actuation system employed in the S &amp; RE module shown in  FIG. 2 .  
     
    
     DETAILED DESCRIPTION  
       [0016]     This disclosure adds a heater element into an integrated accumulator valve/release piston system. In an Arctic environment, the heater element may be used to preheat an accumulator valve module prior to high pressure gas being supplied. With the mass on the materials being pre-heated, the seals remain resilient and can properly flow into a sealing position at the time the high pressure gas is added.  
         [0017]     With reference initially to  FIG. 1 , a pneumatically driven stores ejection system  10  is illustrated schematically. In the illustrated preferred embodiment, two 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  are basically identical stand-alone mechanical units, each preferably comprising a mechanism for releasably retaining and jettisoning a store, including a pair of ejector pistons  16  for thrusting the store clear of the aircraft, and an actuation system for actuating the ejector pistons, including an accumulator  22 , an accumulator pressure logic controller  24 , an enable valve  26 , an ejection dump valve  28 , an over-pressure valve  30 , and an over-pressure vent  32 . In the preferred embodiment, all of these elements are commonly housed within the housing  33  of each module  12 ,  14  ( FIG. 2 ), for compactness and modularity, but various arrangements could be employed within the scope of the invention, including arrangements wherein some or all of the elements other than the pistons  16  are housed within the aircraft remote from the housing  33 .  
         [0018]     Each dump value  28  may include one or more seals, such as O-ring seals  35   a  and  35   b  ( FIG. 3 ), that may be made from synthetic rubber.  
         [0019]     With further reference to  FIG. 1 , a manifold conduit  34  provides pressurized fluid, preferably compressed air, from a remotely located pressurization unit  36  to each of the modules  12 ,  14 . Preferably, the pressurization unit  36  incorporates ambient air filtration by means of a filter unit  38  having an ambient air inlet  40 . The air then travels via a flow passage  42  through a compressor  44 . While a four stage axial piston compressor is preferred, any known type suitable for the inventive application may be alternatively installed. The compressor is preferably driven through a shaft  46  by an electric motor  48  of known type, which in turn is controlled by a control unit  50 .  
         [0020]     A heater element  51  (that may be an electrical resistance type heater) and a thermocouple  53 , that each may be operatively connected to the pressure logic controller  24  via control lines  90  and  92 , respectively, may be embedded within each dump valve  28  for heating the O-ring seals  35   a , and  35   b , in a controlled manner, as may be required prior to pressurization. For example, each heater element  51  may be embedded within the material (e.g., steel) of the housing  33 , and the heat produced by each heater element  51  may be conducted through the material of the housing  33  to the O-ring seals  35   a  and  35   b.    
         [0021]     Alternatively or additionally, each heater element  51  and/or each thermocouple  53  may be operatively connected to the control unit  50 , as indicated by dashed control lines  94  and  96 , respectively, in  FIG. 1 . As a further alternative, the heater may be controlled using a thermocouple in the control circuitry (e.g., a thermocouple in circuitry of the pressure logic controller  24  that essentially senses ambient temperature to determine the level of heating necessary). Upon exiting the compressor  44 , the compressed air travels through a flow passage  52  into a coalescer and vent solenoid valve unit  54 , which provides a dual function of drying the air and also operating as a solenoid valve. From the coalescer and vent solenoid valve unit  54 , the dry air exits into the manifold conduit  34 , while the excess moisture is vented through a moisture vent  56 .  
         [0022]     While the pressurization unit  36  shown and described is preferred, many alternate embodiments are possible. For example, the filter unit  40  is utilized to minimize wear to the system due to impurities in the ambient air, but is not required. Furthermore, the compressor  44  could alternatively be driven hydraulically or may be driven by or comprise a portion of the main aircraft engines. Also, while air is preferred, any known clean gas could be used, and the pressurization unit  36  could actually comprise part of an onboard oxygen or 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 use of a drying unit, such as the coalescer and vent solenoid valve unit  54 , is preferred. However, the system could be operated without such a unit, albeit with increased required maintenance. Finally, while a single gas generator  36  operated to supply gas to plural S &amp; RE modules is preferred, independent generators for each S &amp; RE module could be used as well, particularly since many available gas generating systems are relatively light and miniaturized, so that undue weight and space penalties are not imposed.  
         [0023]     Now with reference to  FIGS. 2 and 3 , certain particular preferred structural details of the S &amp; RE module  12  are 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  are essentially identical, so that  FIGS. 2 and 3  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 .  
         [0024]     Structurally, the compressor feed line  58  ( FIGS. 1 and 2 ) draws pressurized air from the manifold line  34  into the accumulator  22 . Passages  60  provide fluid communication between the accumulator  22  and the pistons  16 , in order to actuate the pistons at a desired time, drawing air from a dump valve exit flow line  62  downstream of the dump valve  28 . 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 in well known fashion. The hooks  64 ,  66  may be actuated to an open position by means of a hinged hook opening linkage  68 , as is also well known in the art, which in turn is driven by a hook opening piston  70  ( FIG. 3 ). The piston  70  is reciprocatingly driven when the dump valve  28 , which is pilot pressure-actuated, is driven from the illustrated closed position to an open position, thereby permitting pressurized air from the accumulator  22  to travel through port  72  into the valve area, from whence it further flows into piston chamber  74 , thus acting to drive the piston  70  reciprocatingly downwardly 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  and into the passages  60 , thereby actuating the ejector pistons  16  to thrust the store away from the aircraft simultaneously with its release from the hooks  64 ,  66 .  
         [0025]     In operation, each S &amp; RE module  12 ,  14  is initially in an unpressurized state. Loading of a store onto an S &amp; RE module  12 ,  14  triggers a “store present” signal on a store present switch  76  provided in each module  12 ,  14 . This signal is transmitted by a control line  78  to the pressure logic controller  24 , which further transmits it through a second control line  80  to the control unit  50 . When the aircraft electrical system is powered up, the “store present” signal causes the pressure logic controller  24  to activate the heaters  51 , if necessary due to low ambient temperature, and upon heating of the O-ring seals  35   a ,  35   b ,  35   c , and  35   d  to an adequate temperature, based on readings from thermocouples  53 , as processed by the pressure logic controller  24 , to initiate the pressurization unit  36  by starting the compressor  44 , to pressurize each module  12 ,  14 . The pressure logic controller  24  maybe programmed to cycle the heaters  51  on and off, as necessary in order to ensure that the O-ring seals  35   a ,  35   b ,  35   c , and  35   d  are maintained at a temperature at which the O-ring seals  35   a ,  35   b ,  35   c , and  35   d  are pliable. Pressurized air thus flows through the manifold conduit  34  and into each of the S &amp; RE modules  12 ,  14  through feed lines  58 . When pressure in the accumulator  22  reaches a prescribed pressure, which in the preferred embodiment is approximately 6,000 psi, as detected by the pressure logic controller  24  via a third control line  82 , the enable valve  26  (which is preferably a solenoid-operated check valve) closes, isolating the S &amp; RE module  12 ,  14 . When all S &amp; RE modules reach the prescribed pressure, the remotely located pressurization system  36  is shut down. Each S &amp; RE monitor and control system  24  continuously monitors accumulator pressure and periodically activates the pressurization system  36  or vents the accumulator through the over-pressure valve  30  and over-pressure vent  32  to maintain the prescribed pressure.  
         [0026]     The aircraft stores management system (SMS)  84 , which is preferably of a type well known in the art, controls stores release. On the release command by the SMS  84 , through a fourth control line  86 , the pilot pressure-actuated high flow rate ejection dump valve  28  is actuated to an open position, permitting pressurized air from the accumulator  22  to flow through port  72  ( FIG. 3 ) 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  and  60  to pressurize and drive each of the ejector pistons  16  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  detects a “store gone” condition, which is transmitted to the control units  24 ,  50 . The controller  24  ensures that its corresponding check valve  26  remains closed, isolating the S &amp; RE system from further pressurization. At the end of the ejector piston stroke, vent ports  88  ( FIG. 3 ) are exposed, preferably discharging substantially all residual accumulator pressure and permitting the spring loaded ejector pistons to retract to their stowed position.  
         [0027]     Other aspects and features of the present invention can be obtained from a study of the drawings, the disclosure, and the appended claims.