Abstract:
A bleeding mechanism for use in the propulsion system of a recoilless, insensitive munition utilizing a utilizing a fluidic countermass. The present bleeding mechanism utilizes a firing pin or a similar puncture or tear device. A heat sensitive material blocks the movement of the firing pin. A mechanical locking mechanism locks the firing pin in position until it is unlocked by the melting of the heat sensitive material. When the insensitive munition is exposed to heat, the reaction of the heat sensitive material within the bleeding mechanism allows the firing pin to be released and to rupture a cartridge seal. The cartridge may be filled with a compressed compound, which releases gas under pressure to the countermass container, causing a countermass cover to rupture, thereby emptying the countermass fluid.

Description:
FEDERAL INTEREST STATEMENT 
     The inventions described herein may be manufactured, used and licensed by the United States Government for United States Government purposes without payment of any royalties thereon or therefore. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates in general to the field of weaponry. In particular, the present invention relates to a bleeding mechanism for use in the propulsion system of a recoilless, insensitive munition utilizing a fluidic countermass. 
     BACKGROUND OF THE INVENTION 
     The U.S. Department of Defense is currently moving toward the long-term goal of insensitive munition-compliant inventory. The acquisition treatment of insensitive munitions was the subject of a Jan. 26, 1999, memorandum from the Under Secretary of Defense for Acquisition, Technology and Logistics. The overall intent of the memorandum was to focus scarce resources on forward fit incorporation of insensitive munition-compliant technology. 
     Insensitive munition is expected to save lives and materials. As defined in STANAG 4439, insensitive munitions mean: “Munitions which reliably fulfill their performance, readiness and operational requirements on demand, but which minimize the probability of inadvertent initiation and severity of subsequent collateral damage to weapon platforms, logistics systems and personnel when subjected to unplanned stimuli.” 
     “Unplanned stimuli” include thermal and mechanical impact threats of Fast Cook-Off (FCO), Slow Cook-Off (SCO), Bullet Impact (BI), Fragment Impact (FI), Sympathetic Detonation (SD), Shaped Charge Jet (SCJ), and Spall impact (SI) as presented in MIL-STD-2105B. 
     The memorandum adds: “All munitions and weapons shall be designed to conform with insensitive munitions (unplanned stimuli) criteria and to use materials consistent with safety and interoperability requirements. Requirements shall be determined during the requirements validation process and shall be kept current throughout the acquisition cycle for all acquisition programs. Interoperability, to include insensitive munitions policies, shall be certified per CJCSI 3170.01 A.” “The ultimate objective is to design and field munitions which have no adverse reaction to unplanned stimuli, analogous to Hazard Division 1.6 (TB 700-2/NAVSEAINST 8020.8B/T.O. 11A-1-47/DLAR 8220.1, “Department of Defense Ammunition and Explosives Hazard Classification Procedures”).” 
     While prior efforts to develop an insensitive munition (IM) propulsion system for a recoilless weapon utilizing a countermass presented certain advantages, they still suffered from numerous shortcomings, amongst which are the following:
         a. Recoilless weapons often utilize filament wound barrels in order to maximize strength and minimize weight. Because cutting holes in these barrels would compromise their integrity, the common practice of venting the propulsion system will not be feasible.   b. The utilization of heat sensitive materials to allow the countermass to drain will be difficult because the countermass behaves as a heat sink, preventing the heat sensitive materials from heating durng a cook off.   c. Other features located within the barrel relied on heat to activate, but the percussion cap located on the surface of the barrel is exposed to the heat much earlier than the in-barrel features.   d. Some of these features utilized eutectic alloys to solder mechanical components. While eutectic alloys have an excellent temperature response, the processes to solder these components lack an industrial base for full rate production. Additionally, the eutectic alloy is costly.       

     According to United States Code, Title 10, Chapter 141, Section 2389—Ensuring safety regarding Insensitive Munitions (IM)—the Secretary of Defense shall ensure, to the extent practicable, that munitions under development of procurement are safe throughout development and fielding when subject to unplanned stimuli. 
     Two tests are used to simulate munitions exposed to a fire: Slow Cook Off (SCO) and Fast Cook Off (FCC). In SCO, munitions in packaged configuration are heated at a rate of 6° C./hour until it reacts. In FCC, munitions are engulfed in a flame of at least 1700° C. until it reacts. It is desirable for the reaction to be limited to no more than burning (Type 5 reaction). A detonation is not acceptable (Type 1 reaction). 
     Recoilless weapons operate by using expanding propellant gases to propel a projectile forward and a mass backwards in order to minimize recoil. Some recoilless weapons utilize a fluid as a countermass, which is propelled backwards in order to minimize the hazard of the back blast to allow for firing from enclosure. 
     When tested for IM, the propulsion systems of the recoilless weapons sometimes ignite, launching the projectile, which fails IM requirements with a Type 4 deflagration. The warhead may become armed and detonate, which fails IM with a Type 1 detonation. It has been found that the removal of the countermass will often prevent the projectile from leaving the barrel and arming. 
     It would therefore be desirable to provide a bleeding mechanism for use in the propulsion system of a recoilless, insensitive munition (IM) utilizing a utilizing a fluidic countermass that addresses the foregoing problems associated with convention IM systems. The bleeding mechanism would be activated by excess heat, and as a result, it would cause the countermass container to rupture. Once ruptured, the countermass fluid will drain out. Without a countermass, the propulsion system will no longer function. The need for such a bleeding mechanism has heretofore remained unsatisfied. 
     SUMMARY OF THE INVENTION 
     The present invention satisfies this need and describes a novel bleeding mechanism for use in the propulsion system of a recoilless, insensitive munition (IM) utilizing a utilizing a fluidic countermass. 
     According to a preferred embodiment, the present bleeding mechanism utilizes a firing pin or a similar device which is held in place by any one or more of:
         a. A heat sensitive material that bonds to a firing pin.   b. A heat sensitive material that blocks the movement of the firing pin.   c. A mechanical device that locks the firing pin in position until a heat sensitive material unlocks the device.       

     The insensitive munition generally includes a tubular barrel within which a projectile (or warhead) is housed. A propulsion system and a liquid filled countermass container are also housed within the barrel, behind the projectile. 
     The present bleeding mechanism can either form part of the insensitive munition, or it can be externally and separately connected to the insensitive munition. In either design, the bleeding mechanism is connected to an inlet of the countermass container. 
     When the insensitive munition is exposed to an unplanned stimulus, such as heat, the reaction of a heat sensitive material within the bleeding mechanism allows a firing pin to be released and to rupture a cartridge seal. The cartridge may be filled with a compressed gas or a compound that releases gas when exposed to heat. The released gas may be any suitable gas such as carbon dioxide, nitrogen, and helium. The compound may be a material that outgases when heated, such as sodium bicarbonate, potassium carbonate, and potassium bicarbonate, or an energetic material that combusts to generate gas. 
     The compressed gas from the cartridge will flow into the countermass container and may:
         a. Rupture the container, allowing or forcing the fluid out of the countermass container.   b. Force the fluid within the countermass container to travel to either:
           i. the propulsion system in order to achieve a Type 6, no reaction; or   ii. the warhead to assist in an IM feature used to improve the warhead IM performance.   
               

     With the fluid removed from the countermass container, if the propulsion system activates, the projectile will remain within the insensitive munition. 
     If the bleeding mechanism is located outside the barrel it will be readily exposed to the heat of a cook off. The filament wound barrel of the weapon is a good insulator and restricts the flow of heat to the heat sensitive device. The positioning of the device outside the weapon allows it to react to the thermal stimuli in a timely manner. 
     More specifically, the present bleeding mechanism utilizes a heat sensitive material that may include any one or more of the following designs:
         a. Low melting temperature materials including but not limited to alloys, ionomer plastics, waxes, or salts.   b. Low boiling temperature materials in an ampoule.   c. Shape memory materials that deform, unlocking the locking mechanism.   d. Reactive materials initiated by heat.   e. Commercially available indium, bismuth, lead, and tin-based alloys.   f. Commercially available plastics, such as polyethylene and ionomers.   g. Waxes.   h. Soluble salts used inside ballistic material to provide cooling during a cook off. Reference is made to the following web site: http://www.rockyresearch.com/news/RR_News_Archives_022411. pdf   i. Alcohol filled ampoules used in automatic fire sprinkler heads.   j. Shape Memory alloys and shape memory composites.   k. Slow burning propellant (base bleed material), slow burning pyrotechnics.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features of the present invention and the manner of attaining them, will become apparent, and the invention itself will be best understood, by reference to the following description and the accompanying drawings: 
         FIG. 1  is a representation of a conventional recoilless, insensitive munition; 
         FIG. 2  is a representation of an insensitive munition that is provided with a bleeding mechanism according to a preferred embodiment of the present invention; 
         FIG. 3  is comprised of  FIGS. 3A and 3B , wherein  FIG. 3A  is an enlarged representation of the bleeding mechanism of  FIG. 2 , shown in a deactivated state, and  FIG. 3B  is a greatly enlarged view of a bleeding controller that forms part of the bleeding mechanism of  FIG. 3A ; 
         FIG. 4  is an enlarged representation of the bleeding mechanism of  FIGS. 2 and 3 , shown in an activated state; 
         FIGS. 5, 6, 7  are representations of a first embodiment of a countermass container forming part of the insensitive munition of  FIG. 2 , illustrating progressive stages before and after the bleeding mechanism of  FIG. 4  is activated; 
         FIGS. 8, 9, 10  are representations of a second embodiment of the countermass container of the insensitive munition of  FIG. 2 , illustrating progressive states before and after the bleeding mechanism of  FIG. 4  is activated; 
         FIG. 11  is a representation of another embodiment of the bleeding mechanism of  FIG. 2 , shown in a deactivated state; 
         FIG. 12  is a representation of the bleeding mechanism of  FIG. 11 , shown in an activated state; 
         FIG. 13  is a representation of yet another embodiment of the bleeding mechanism of  FIG. 2 , shown in a deactivated state; and 
         FIG. 14  is a representation of the bleeding mechanism of  FIG. 13 , shown in an activated state. 
     
    
    
     Similar numerals refer to similar elements in the drawings. It should be understood that the sizes of the different components in the figures are not necessarily in exact proportion or to scale, and are shown for visual clarity and for the purpose of explanation. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  is a representation of a conventional recoilless, insensitive munition  10  having a tubular barrel or launch tube  15 . A warhead or projectile  20  is placed within the launch tube  15 . A propulsion system  25  and a liquid filled countermass container  30  are also housed within the launch tube  15 , behind the projectile  20 . 
     Since the insensitive munition  10  often utilizes a filament wound barrel  15  in order to maximize strength and minimize weight, cutting holes in the barrel  15  to allow the countermass  35 , within the countermass container  30 , will compromise the integrity of the insensitive munition  10 , and is therefore neither feasible nor recommended. 
     Wherefore, the present invention generally describes a novel bleeding mechanism  100  for use as an external auxiliary to an insensitive munition  200 , for example as part of a storage unit or container  217 , as illustrated in  FIG. 2 . Since the bleeding mechanism  100  is located externally relative to the barrel  215 , it is not shielded from the heat of the cook off. 
     Alternatively, the bleeding mechanism  100  can form an integral part of the insensitive munition  200 , and could be secured externally, to a barrel  215 , or it could be placed internally relative to the barrel  215  of the insensitive munition  200 . 
     The recoilless insensitive munition  200  further includes a projectile  220 , a propulsion system  225  that contains a propellant  226 , and a countermass container  230  that contains a fluidic countermass  235 . 
     The countermass container  230  is generally cylindrically shaped and is open at one end thereof. When the countermass container  230  is filled with the fluidic countermass  235 , its open end is sealed with an elastic countermass cover  236 . The countermass cover  236  is secured to the barrel  215  by means of a countermass cover retention feature  238  that is either known or available, and thus it will not be described in detail. 
     The countermass cover  236  is preferably made of elastomeric material, such as Polyethylene, in order to allow for expansion under pressure. The fluidic countermass  235  is preferably a saline solution, but could be any other suitable solution, including but not limited to Iron oxide solution, plastic confetti. 
     The countermass container  230  also includes a compressed gas inlet  240  that is connected to an inlet tube  250 , for allowing the compressed air to enter, through the inlet  240  to the countermass container  230 , via the inlet tube  250 , as it will be explained later in greater detail. The inlet tube  250  forms part of the bleeding mechanism  100 . 
       FIGS. 3A and 3B  illustrate the bleeding mechanism  100  of  FIG. 2 , shown in a deactivated state. The bleeding mechanism  100  generally includes a source of pressurized fluid, such as a cylinder or a canister  300  of pressurized carbon dioxide, CO 2 . The cylinder  300  includes a neck  302  that is hermetically sealed with a seal  305 . In this state, the seal  305  is still unruptured and maintains pressure within the cylinder  300 . 
     The bleeding mechanism  100  further includes a bleeding controller  310  that controls the flow of the gas to the countermass container  230 , as illustrated in  FIGS. 2, 5, 6, and 7 . The bleeding controller  310  generally includes a generally cylindrically shaped bleeding chamber  320  that retains the neck  302  of the cylinder  300  at one of its ends. The bleeding chamber  310  further retains the tube  250 , and provides a path for the gas that escapes from the cylinder  300 . 
     The opposite end of the bleeding controller  310  houses a slidable firing pin assembly  340 . The firing pin assembly  340  includes a firing pin  346  that protrudes axially, in the direction of the seal  305 , within the bleeding chamber  310 . The firing pin assembly  340  further includes a support body  348  that supports the firing pin  346 , and that is capable of sliding axially toward the seal  305 , as it will be explained in connection with  FIG. 4 . 
     Under normal conditions, that is in the absence of an unplanned stimulus, the support body  348  compresses a spring  344  against a base  342 . This compression state is maintained by means of a locking mechanism  333 , as long as the thermal and other conditions remain within predefined normal parameters. 
     According to this preferred embodiment, the locking mechanism  333  includes a The locking feature such as a ball, and a heat sensitive alloy  370 . In this compression state, the heat sensitive alloy  370  is placed within a crevice, indentation, or deformation  375  within the inner surface of the bleeding chamber  320 . The locking ball  360  is placed against the alloy  370  and retains it in place. 
     The heat sensitive material  370  can be a low melting point eutectic solder, such as an Indium/tin alloy. Since a small amount of the eutectic solder (or alloy) is needed, the cost of the locking mechanism  333  will not be significantly affected. The eutectic alloy  370  has an ideal thermal response to heat, melting completely at a precise temperature. The present invention utilizes the eutectic alloy  370  as a secondary feature in the locking mechanism  333 , allowing the higher mechanical properties of the steel ball  360  to hold back the firing pin  346 . 
     The locking ball  360  is preferably spherically shaped. The locking ball  360  can be made of any suitable material, including but not limited to stainless steel. The crevice  375  is shaped and dimensioned so that in the compressed state, as it accommodates the unmelted alloy  370 , a portion  365  of the locking ball  360  protrudes outwardly from the crevice  375 , so as to engage an edge  350  of the support body  348 . As a result, the locking mechanism  333  retains the firing pin assembly  340  in a locked position, with the spring  344  compressed against the base  342 . 
     Referring now to  FIG. 4 , it illustrates the bleeding mechanism  100  in an activated state. If and when the environmental conditions change, that is when the insensitive munition  200  is exposed to an unplanned stimulus, for example, if the thermal conditions surrounding the insensitive  200  change, such as when the heat sensitive alloy  370  is exposed to elevated temperatures, for example, approximately 250° F., then the heat sensitive alloy  370  melts, causing the locking ball  360  to recede within the crevice  375 . The recession of the locking ball  360  unlocks the locking mechanism  333  by releasing the edge  350  of the support body  348  from the wedging of the ball  360 , and causes the spring  344  to expand, forcing the support body  348  and the firing pin  346  forward toward the seal  305 , rupturing it. 
     As the seal  305  is ruptured, the pressurized gas within the cylinder  300  expands and escapes, through the ruptured seal  305 , the bleeding chamber  320 , and the tube  250 , to the countermass container  230 . 
       FIGS. 5, 6, and 7  the progressive stages of the countermass container  230  before and after the bleeding mechanism  100  has been activated. 
       FIG. 5  illustrates the countermass container  230  when the bleeding mechanism  100  has not been activated ( FIGS. 2, 3A, 3B ). In this particular preferred embodiment, the countermass container  230  is provided with one or more openers  500 ,  505 , that are retained by the countermass cover retention feature  238 . Each of the openers  500 ,  505  has a sharp edge  510  that is positioned in close proximity to the countermass cover  236 , along the periphery of the countermass container  230 . 
     When the bleeding mechanism  100  is not been activated, the countermass cover  236  is in a “deflated” or undeployed state, and the sharp edge  510  of the openers  500 ,  505 , remains at a safe distance from the countermass cover  236  so as not to puncture it. 
       FIGS. 6 and 7  illustrate the countermass container  230  when the bleeding mechanism  100  has been activated ( FIG. 4 ). As the gas from the cylinder  300  is injected into the countermass container  230  under pressure, it causes the countermass cover  236  to be deployed and to be ruptured by the openers  500 ,  505 , at one or a plurality of ruptures or tears  520 ,  525 , respectively. 
     As more clearly illustrated in  FIG. 7 , input air  700 , at atmospheric pressure enters the countermass container  236  through the rupture  520 , and further forces the fluid countermass  235  to drain through the rupture  525 , until the countermass container  230  is emptied of its fluid content  235 . Consequently, the propulsion system  226  will be disabled. 
       FIGS. 8, 9, and 10  illustrate another embodiment of the countermass container of the insensitive munition of  FIG. 2 , showing progressive states after the bleeding mechanism  100  of  FIG. 4  has been activated. The countermass container  830  of  FIGS. 8, 9, and 10  is similar in design, construction, and operation to the countermass container  230  of  FIGS. 5, 6, and 7 , with the exception that the countermass container  830  does not include the opener  500 ,  505  of  FIGS. 5, 6, and 7 . 
     Rather, the countermass cover  836  of the countermass container  830  is made of a readily rupturable material, such as for example, polyethylene, that ruptures when the countermass cover  836  is deployed under pressure from the injected gas, as explained earlier. 
       FIG. 11  illustrates another bleeding mechanism  1100 , shown in a deactivated state. The bleeding mechanism  1100  includes a bleeding controller  1110  that controls the flow of the gas to the countermass container  230 . The bleeding controller  1110  generally includes a generally cylindrically shaped bleeding chamber  1120  and a sliding assembly  1130 . 
     The sliding assembly  1130  retains the neck  302  of the cylinder  300  in a slidable relationship relative to the housing  1112 . The bleeding chamber  310  provides a path for the gas that escapes from the cylinder  300 . 
     In this embodiment, the firing pin  346  is secured to a fixed structure  1111 , and the pressurized gas cylinder  300  is retained in a spring loaded position, against a housing  1112 . 
     To this end, the body of the cylinder  3300  is surrounded by a spring  1144  that is compressed against the bottom side  1114 . This compressed position is maintained by means of a locking mechanism  1133  that is similar in function to that of the locking mechanism  333 . 
     The locking mechanism  1133  includes a sliding assembly  1130  that surrounds, and that is tightly secured to the neck  302  of the cylinder  300 . The sliding assembly  1130  includes an indentation within which the heat sensitive alloy  370  is housed. The locking ball  360  is inserted within the indentation, atop the heat sensitive alloy  370 , such that a portion of the locking ball  360  protrudes from the indentation. 
     The protruding portion of the locking ball  360  engages a sleeve  1150  that is affixed to the housing  1112 . As a result, the engagement of the sleeve  1150  and the locking ball  360  retains the spring in a compressed position, holding the cylinder  300  at a distance from the firing pin  346 . 
       FIG. 12  is a representation of the bleeding mechanism  1100  of  FIG. 11 , shown in an activated state. As explained earlier, when the insensitive munition  200  is exposed to excessive heat, the heat sensitive alloy  370  melts, causing the locking ball  360  to be depressed within the indentation of the sliding assembly  1130 . 
     In turn, the sleeve  1150  disengages from the locking bail  360 , which allows the sliding assembly  1130 , along with the cylinder  300  to be propelled forward toward the firing pin  346 . As a result, the firing pin  346  punctures the seal  305  of the cylinder  300 , resulting in the escape of the gas from within the cylinder  300  to the countermass container  230 , through the tube  250 , as described earlier. 
       FIGS. 13, 14  illustrate another bleeding mechanism  1300  that is similar in design, construction, and operation to the bleeding mechanism  1100  of  FIGS. 11, 12 , with the single exception that it uses a different type of spring. The bleeding mechanism  1300  uses a Bellville type spring  1344  that engages the bottom  1360  of the cylinder  300 . The stacked Bellville (disc) spring  1344  provides high force in a compact form. 
     It should be understood that other modifications might be made to the present bleeding mechanism  100  without departing from the spirit and scope of the invention. For example, the present invention may be applied to single use recoilless rifles utilizing a liquid countermass, and for the IAM (Individual Assault Munition). 
     Furthermore, all examples and conditional language recited herein are principally intended expressly to be only for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor(s) to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. 
     Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both chemical and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of composition.