Abstract:
A practice ammunition projectile has a projectile head with one or more sheets of plastic material, each having a plurality of frangible “bubble shaped” compartments containing liquid chemical components for optical and/or Infrared marking of a target upon impact. The sheets are preferably flexible sheets in the nature of a “bubble wrap” of the type used as padding for packaging. These so-called “matrix packages” are installed adjacent the inner surface of the shell forming the projectile head and provide stability when the compartments break up upon setback when the projectile is fired from a weapon.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Provisional Patent Application No. 61/803,827, filed Mar. 21, 2013. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to the field of training ammunition and, more specifically, to a non-pyrotechnic training ammunition cartridge having a projectile that can mark its point of impact both by day and by night. 
     Military gunners often fire their weapons at long range in military training areas that include grass, vegetation and low lying trees. Hence, while there is some value in firing projectiles that directly mark a target on impact, the morphology and terrain on a military range frequently preclude gunners from having direct views of the actual impact points. 
     Good military training devices should simulate the effects of live fire high-explosive detonations. In combat such detonations generate visual and near infra-red light and heat, forming a multi-spectral signature. High explosive detonations also produce smoke plumes. The light and heat resulting from high-explosive detonations can be detected by an array of fire control devices used by the military. The smoke plumes are also visible to the naked eye. 
     The target locating devices used in the military have visual cameras and cameras that operate in the near and/or far IR spectrum. Accordingly it is desired that practice ammunition simulate the effects seen in combat and that practice ammunition generate multi-spectral marking signatures, upon impact, that can be viewed by these cameras. 
     Currently, military forces use a wide array of technologies to detect and identify targets and adjust fire. Traditionally, they have used pyrotechnic devices in training ammunition allowing gunners to trace their fire and mark their targets. These pyrotechnic devices produce smoke and heat plumes from combustion of pyrotechnic compounds. Unfortunately, these pyrotechnic devices frequently generate dangerous unexploded ordnance (UXO) and pyrotechnic compounds frequently have chemicals that contaminate ground water. Ground water contamination and UXO are expensive to remediate. Additionally, pyrotechnic devices can also start range fires, leading to destruction of ecosystems and soil erosion. 
     To prevent the generation of UXO and range fires during training, inert practice ammunition cartridges have been developed which do not employ energetic pyrotechnics to trace the flight and mark the impact of the projectile. For example, low density, dry fine powders have been used to create a plume for visibly marking the target upon impact. This marking agent has been used, for example, in the US Army&#39;s M781 40 mm low velocity cartridge. 
     Chemi-luminescent technology, such as that taught in the U.S. Pat. No. 6,619,211, has also been used to mark both the trace and point of impact by night. Two liquid chemical components are placed in separate frangible compartments or ampoules that break open on setback when the projectile is fired from a weapon. This allows the components to mix and luminesce, thereby providing a visible trace during flight if the projectile ogive is transparent or translucent, and marking the point of impact when the projectile strikes the target. As disclosed in this patent, the frangible ampoules are located near center of a projectile&#39;s axis of rotation and, when the liquids are released from their compartments, they tend to destabilize the projectile as it spins, resulting in projectile yaw. 
     The U.S. Pat. No. 8,438,978 discloses a multi-spectral marking projectile having chemical components that are caused to mix upon setback, due to the initial acceleration and the centrifugal forces, and thereby produce an exothermic reaction which emits heat during the flight of the projectile. This serves to warm the chemi-luminescent materials during flight and provides an Infrared marking signature when the projectile strikes the target. 
     The U.S. Pat. No. 7,055,438 also discloses a flameless tracer/marker utilizing heat marking chemicals in addition to chemo-luminescent materials. 
     The subject matter of the various patents noted above is incorporated herein by reference. 
     SUMMARY OF THE INVENTION 
     The principal objective of the present invention is to provide a non-pyrotechnic ammunition projectile that provides a visual effect upon impact that closely stimulates the effects of live fire detonations: marking signatures that may be seen by day and detected by military night vision and thermal sensors by night. 
     A further objective of the present invention is to provide a training projectile of the type described above having a configuration that can be manufactured at a reasonable cost. 
     A still further objective of the present invention is to provide a training projectile of this type which carries reactive liquid components, such as chemi-luminescent or exothermic materials, yet is configured to remain stable in flight and does not suffer from instability generally resulting from on-board liquids. 
     A still further objective of the present invention is to provide a training projectile of this type which carries a fine dry powder as marking agent in the projectile head which bursts open upon impact and creates a powder plume for visibly marking the target. 
     These objects, as well as other objects which will become apparent from the discussion that follows, are achieved according to the present invention, by providing the projectile with one or more sheets of material, each having a plurality of frangible “bubble shaped” compartments containing liquid chemical components for optical and/or Infrared marking. The sheets are preferably flexible or conformal sheets of plastic material in the nature of a “bubble wrap” of the type used as padding for packaging. These so-called “matrix packages” are installed in a compartment formed by the head of the projectile body adjacent the inner surface of the compartment wall. The “bubbles” formed in the sheets which contain the chemical components are designed to break upon impact, releasing the components and allowing them to mix and chemically react. The components may of the type that create chemi-luminescence to create light, or they may be of the type that mixes create heat. Multiple components may be provided to create both light and heat. 
     Advantageously, two or more separate sheets are arranged in an adjacent concentric configuration leaving an open space in the center of the projectile head. This space may be either left empty or, in a preferred embodiment of the invention, filled with a fine dry powder marking agent that is released and forms a plume when the projectile head breaks open upon impact. 
     For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a spin stabilized 40 mm projectile of the type to which the present invention relates. 
         FIGS. 2A ,  2 B and  2 C are representative diagrams, not to scale, showing the method of making a flexible and frangible bubble wrap sheet according to the invention, with bubbles filled with a liquid. 
         FIG. 3  is a cutaway view of the head of the projectile of  FIG. 1 , showing the compartment wall with indentations designed to accommodate bubbles of a bubble wrap sheet. 
         FIG. 4  is a view of the projectile head shown in  FIG. 3  with the frangible bubble wrap sheets according to the invention, which contain liquid chemical materials, arranged adjacent the compartment wall. 
         FIG. 5  is an composite view of the projectile heads shown in  FIGS. 3 and 4  with two “bubble wrap” sheets containing a reactive liquid chemi-luminescent in each and a fine dry powder contained in a compartment inside the bubble wrap sheets. 
         FIG. 6  is perspective view of the projectile of  FIG. 1  showing the spin moments and forces that would occur without use of the bubble wrap sheets according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention will now be described with reference to  FIGS. 1-6  of the drawings. Identical elements in the various figures are designated with the same reference numerals. 
     The present invention concerns a projectile with a frangible head that can be configured in multiple calibers (with differing trajectories, spin rates, etc.). Upon impact, the ogive (head) breaks open and releases both day and night marking agents. 
     While most of projectiles in use today behave as rigid bodies while in flight, more and more projectiles are designed to carry a liquid or non-rigid payload. Some examples of such are (1) artillery rounds that generate smoke and comprise a spin stabilized shell with a canister filled with white phosphorous; (2) marking projectiles with liquid chemical components that mix upon impact to generate specific signatures in a broad range of radiation bands; (3) leas-than-lethal projectiles having a liquid with aggressive chemicals or marking paint; and (4) projectiles that carry medical supplies (e.g., intravenous fluid bags). 
     There can be a significant difference in flight behavior between liquid-filled and solid-filled projectiles. The difference is due to motion of the liquid inside the spinning projectile during flight. This motion causes forces to act on the projectile body that disrupt the spin and can prematurely terminate the flight by instability. Characteristics of this instability are sharp increases in the angle of attack (AOA) accompanied by large changes in spin rate. When launched, the motion of the projectile causes the fluid to spin up in a time-dependent manner, although it may subsequently achieve steady state. 
     According to the invention, the liquid chemical components in the projectile are contained in a matrix of frangible “bubbles” or ampoules formed in a sheet of material, layered adjacent to the inner surface of the projectile body. This “matrix packaging” configuration minimizes the problematic movement of unstable moments, inertia, friction and resonances generated by a liquid, all of which can disturb the flight characteristics of the projectile. 
     The bubbles or ampoules in the bubble wrap sheet according to the invention are designed break upon impact when the projectile strikes the ground or a target, allowing the constituent chemical materials to mix and react together. 
     Upon impact, the head of the projectile (ogive) breaks apart generally releasing the reacting chemicals into the atmosphere, forming a visual and IR signature visible at night or through near IR night vision devices. 
     Maintaining the liquid chemical materials close to the inner surface of the outer wall of the ogive provides for good ballistic stability of the projectile because its center of gravity does not shift during flight. This configuration is not able to change the spin rate, since the liquid will neither rotate nor oscillate in inertial waves, hence having no chance to influence the so-called “spin decay”, typical of a liquid payload with free liquid in a full container. 
     It should be noted that the “bubble wrap” packing must be carefully designed to avoid “eigenvalue” resonance. Also both sheet layers must be properly contained so that they cannot move or be deformed during setback and in flight. 
     Having these issues in mind, it may be seen that packing the liquid materials in “bubble wrap” layers improves the flight behavior of marking projectiles. This applies also to other types of non-rigid payload projectiles such as non-lethal projectiles that carry liquid components. 
       FIG. 1  shows a 40 mm projectile  10  of the type to which the present invention relates. The various dimensions of the projectile are indicated, relative to the number of calibers. The projectile has an ogive  12  that carries one or more marking agents, including liquid chemical materials which react when missed. These liquids are contained and constrained in a matrix package of bubble wrap sheets, as will be explained below, which maintains the stability of the projectile in flight. 
     The bubble wrap sheet according to the invention is illustrated in  FIGS. 2A ,  2 B and  2 C.  FIG. 2A  shows a plastic sheet  14  containing depressions or “bubbles”  16  filled with a liquid  18 . Once filled, a cover sheet  20  is applied and heat-sealed to the sheet  14  to form a composite sheet  22 . This composite sheet is shown in perspective in  FIG. 2C . 
       FIG. 3  shows the interior of the head (ogive)  12  of the projectile  10  without the “bubble wrap” sheets according to the invention that contain the reactive liquid chemical materials. The wall of the ogive  12  is formed of a plastic or composite material or of a thin-walled metal. The inner surface of the wall is provided with small indentations to receive the bubbles of the bubble wrap sheets  22 . 
     The wall of the ogive  12  is designed to break up upon impact and release its contents. Internal to the ogive  12  is a space filled by a shaped container  26  surrounded by two “bubble wrap” sheets  28  and  30  having frangible bubbles filled with various liquid chemical materials, as is shown in  FIGS. 4 and 5 . If the ogive is relatively long, the liquid mass contained in the bubbles is preferentially located near the front of the projectile. 
     As noted above, the bubbles are designed to break open upon impact with the target, releasing the materials and allowing them to mix end react chemically together. If the materials are chemi-luminescent components they will luminesce; if they are exothermic components they will create heat. Both types of components may be provided either in separate compartments or in a common compartment in the projectile. 
     The container  26  in the center of the ogive  12  advantageously contains a dyed fine dry powder that is released upon impact for visual (day) marking. 
     As is illustrated in  FIG. 6 , a projectile  10  containing a liquid is subject to a number of liquid-induced forces  32 ,  34  and  36  which can make it unstable in flight. The use of the bubble wrap package according to the invention, located adjacent the outer wall of the projectile, minimizes (1) the coefficient induced side force, (2) the moment force, and (3) the destabilizing resonances when liquids are contained in the bubbles. This design minimizes spin decay and optimizes gyroscopic stability of a projectile containing the reactive liquid chemical mix that functions on impact. 
     There has thus been shown and described a novel training ammunition cartridge with reactive liquid materials for marking a point of impact which achieves all of the objects and advantages sought therefor. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, which is to be limited only by the claims which follow.