Abstract:
The present disclosure is directed to propellant gas initiation of a non-pyrotechnic projectile tracer. In some embodiments, cartridge-propellant gasses act upon a piston to break a frangible chemiluminescent liquid chemical ampoule to initiate a luminous reaction independently of and prior to any projectile motion. The piston may be a distinct piston, a separate component functioning as a piston, or the overall tracer container acting in the manner of a piston. Embodiments of the disclosure are applicable to direct-fire ammunition ranging from small arms through large caliber main battle tank ammunition.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of U.S. Provisional Patent Application No. 61/474,582, filed Apr. 12, 2011 and titled PROPELLANT GAS OPERATION/INITIATION OF A NON-PYROTECHNIC PROJECTILE TRACER, which is incorporated in its entirety herein by reference thereto. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention is related to projectile tracer assemblies, and more particularly to non-pyrotechnic projectile tracer assemblies and related methods. 
       BACKGROUND 
       [0003]    Base-mounted tracers for gun-launched projectiles have traditionally been characterized by the use of pyrotechnic compounds that are ignited/initiated by the act of firing the projectile. The hot propellant gases come into contact with and ignite the tracer&#39;s pyrotechnic compounds. Upon the projectile&#39;s exit from the launching gun and for a portion of or all of the projectile&#39;s flight, the tracer marks the projectile&#39;s trajectory by virtue of the combusting pyrotechnic tracer compound. 
         [0004]    Because tracers are pyrotechnic in nature, they present a potential fire hazard during employment, particularly on firing ranges during training operations. This issue is addressed by the use of non-pyrotechnic tracer elements such as liquid bi-chemical chemiluminescent elements (U.S. Pat. No. 6,990,905). Typically, chemiluminescent systems consist of two liquid chemicals that when brought together in intimate contact experience a reaction, the products of which are visible light and infrared energy. Initially, the two chemicals are kept separate by the use of special/frangible containers (transparent or equipped with a transparent section) positioned coaxially one inside the other. Upon activation, one or both of these special/frangible containers is ruptured, thus allowing the two liquid chemicals to come into contact with each other and start the reaction. The rupturing of the container(s) is accomplished by subjecting the projectile to stimulation at the desired time of tracer activation, typically launch and/or target impact. Launch stimuli may be predicated upon acceleration (setback) of the projectile, spin-up of spin-stabilized projectiles in guns that are rifled, and deceleration (set forward) of the projectile as it emerges from the gun&#39;s barrel (ending acceleration) and encounters open air. These stimuli act upon designed mechanisms, such as inertia masses (US Patent Application Publication No. 2010/0175577), to rupture the container(s). 
       SUMMARY 
       [0005]    The present invention overcomes drawbacks experienced in the prior art and provides other benefits. Embodiments of the invention provide a non-pyrotechnic projectile tracer, such as an ammunition round with chemiluminescent tracer portion configured for propellant gas operation or initiation of the non-pyrotechnic tracer material upon firing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a cross-sectional side view of a projectile having a tracer configured in accordance with embodiments of the disclosure. 
           [0007]      FIG. 2  is a cross-sectional side view of a projectile having a tracer with a piston-activator configured in accordance with embodiments of the disclosure. 
           [0008]      FIG. 3  is a cross-sectional side view of a small-caliber projectile having a tracer configured in accordance with embodiments of the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]      FIG. 1  is a cross-sectional side view of a projectile  100  having a tracer  110  configured in accordance with embodiments of the disclosure. The tracer  110  includes an outer cylindrical ampoule  112  positioned within a tracer cavity  114 . In one embodiment, the outer ampoule  112  is non-frangible when the projectile is fired from a gun or other launching mechanism. The illustrated outer ampoule  112  has an open internally-threaded end  116  and an opposite closed end  118  with a pronounced protrusion  120 . The outer ampoule  112  is positioned on an aft end  122  of the projectile  100  such that the protrusion  120  on the outer ampoule  112  is bearing against a blind end  124  of the projectile tracer cavity  114 . The tracer  110  includes an externally threaded stepped closure  126  equipped with a central window  128  constructed of a rugged, high temperature resistant material, such as sapphire. The window  128  can be substantially transparent to visible and/or infrared radiation. The stepped closure  126  can have threads to match the outer ampoule  112 . The tracer  110  further includes an inner frangible cylindrical ampoule  130  positioned longitudinally within the outer ampoule  112 , the inner ampoule  130  having a first end  132  bearing against the outer ampoule protrusion  120  and a second end  134  opposite the first end  132  and proximate to the central window  128 . The outer ampoule  112  can contain a first chemiluminescent component and the inner ampoule  130  can contain a second chemiluminescent component. 
         [0010]    The tracer  110  can further include an externally threaded capture ring  136  (threaded to match the designated projectile interface) whose central hole can permit a smooth sliding fit with the stepped closure  126 . The capture ring  136  can include an internal sliding seal that bears upon the smaller diameter section of the stepped closure  126 . The entire outer ampoule  112  is sized to be a sliding fit in the projectile&#39;s tracer cavity  114 . The tracer  110  is secured in the projectile  100  by the capture ring  136  external threads mating up with the projectile tracer cavity  114  internal threads. When assembled, the outer ampoule  112  is captured in the projectile tracer cavity  114  by the capture ring  136  with the outer ampoule protrusion  120  bearing against the blind closed end  124  of the projectile tracer cavity  114  and the transparent window  128  exposed and flush with the aft end of the capture ring  136 . In some embodiments, the projectile  100  comprises a medium (i.e., 20-75 mm) or large caliber (75 mm and larger) direct fire ammunition. 
         [0011]    The tracer  110  activation sequence is as follows: upon firing, the cartridge primer ignites the main propelling charge which generates the propelling gasses. As the cartridge internal pressure rapidly increases, the cartridge internal pressure bears against all exposed surfaces (the cartridge case internal surfaces and the projectile  100  base) including the smaller diameter section of the stepped tracer closure  126  with the tracer transparent window  128 . The propelling gas pressure force generated on the stepped tracer closure column  126  loads the tracer outer ampoule  112 , which in turn passes the column load against the closed end protrusion  120  that in turn bears against the blind end  124  of the projectile tracer cavity  114 . At a predetermined pressure value, the protrusion  120  is loaded to the point where it collapses, crushing the frangible inner ampoule  130 . This action frees the two liquid chemiluminescent chemicals to come into contact and react in a luminescent reaction, while maintaining a liquid-tight integrity. The radiation released from this reaction (visible and/or infrared) escapes from the outer ampoule  112  through the transparent window  128  facing aft towards the gunner. The forward sliding motion of the outer ampoule  112  is arrested when the outer ampoule  112  is crushed to the point where the two liquid chemicals are hydraulically compressed, halting the forward motion of the outer ampoule  112 . In some embodiments, a physical/mechanical motion limiting/stop feature (not illustrated) can also be utilized. The tracer  110  is accordingly activated independent of the motion of the projectile  100 , (including projectile acceleration/setback, spin-up, and deceleration/set-forward/impact). 
         [0012]      FIG. 2  is a cross-sectional side view of a projectile  200  having a tracer  210  with a piston-activator  240  configured in accordance with embodiments of the disclosure. The projectile  200  includes several features generally similar to those described with reference to  FIG. 1 , including an inner ampoule  230  positioned within an outer ampoule  212  within a projectile tracer cavity  214 . The inner ampoule  230  is positioned against an outer ampoule protrusion  220  as described above with reference to  FIG. 1 . In this embodiment, the tracer  210  is shielded from the propellant gasses by a stepped piston  240 , the smaller diameter of which bears against an aft surface  242  of the outer ampoule  212 , leaving the larger diameter&#39;s aft end  244  to be acted upon by the propellant gasses. The whole piston  240  is supported by the projectile&#39;s aft end or drag cone/fin  252 . A plurality of small equalizing ports/holes  246  is positioned in a tapered forward-facing end  248  of a projectile drag cone/fin  252  that communicates with the stepped diameter of the piston  240 . The piston  240  is held in position by a plurality of shear pins  250  arranged radially around the periphery of the piston&#39;s larger diameter and anchored in the projectile aft end or drag cone/fin  252 . The sheer pins  250  are configured to securely maintain the piston&#39;s position and prevent activation of the tracer  210  prior to firing of the projectile, such as during rough handling and/or transport. The shear pins  250 , however, are configured so they will shear and release the piston upon application of very high loads applied on the piston by the pressurized gas generated upon firing of the projectile. 
         [0013]    The piston  240  is positioned in the projectile&#39;s aft end or drag cone/fin  252  such that the force of the propellant gasses can push the piston  240  forward a calculated distance after first shearing the shear pins  250 . In some operational settings, the propellant gasses provide approximately 82,000 pounds psi of force at launch. The moving piston  240  transmits this force to the tracer ampoule  212  causing it to move forward as well. This forward motion crushes the outer ampoule protrusion  220  and initiates the tracer action in a manner similar to the embodiment described above with reference to  FIG. 1 . Upon shot exit from the gun barrel and after the projectile  200  transitions the muzzle shock bottle phenomenon, the forward motion of the projectile  200  causes a near vacuum/low-pressure area to be established at the projectile&#39;s aft end or drag cone/fin  252  as well as air to be forced into the forward facing equalizing ports  246 . This near vacuum/low pressure acting upon the aft face of the large diameter section of the piston  240 , coupled with air pressure on the forward surface of the stepped section of the piston  240  from the air entering the forward facing equalizing ports  246 , results in a force to effect the separation of the piston  240  from the projectile  200 . This separation unmasks the functioning tracer  210 . 
         [0014]      FIG. 3  is a cross-sectional side view of a small-caliber projectile  300  having a tracer  310  configured in accordance with embodiments of the disclosure. The projectile  300  includes several features generally similar to those described above with reference to  FIGS. 1 and 2 . In this embodiment, the projectile  300  has a tubular aft end  344  in which is positioned a metallic cylindrical liner  360 . In some embodiments, the liner  360  can be steel or an alloy of steel. The liner  360  serves as a re-enforcing element to maintain projectile integrity upon the spin-stabilized projectile&#39;s  300  exit from the barrel as centrifugal forces act upon the chemiluminescent payload to burst the projectile  300 . A frangible inner ampoule  330  containing one of the chemiluminescent components is positioned within the liner  360 . The frangible ampoule  330  has a smaller diameter than the inside diameter of the metallic liner  360  and its forward end  362  is nested into a centrally-located depression  364 . In some embodiments, the inner ampoule  330  is long enough so that when seated into the projectile  300 , an aft end  366  projects slightly from an aft end  368  of the metallic liner  360 ; i.e., the inner ampoule  330  is slightly longer than the metallic liner  360 . An annular space  370  between the frangible ampoule  330  and the inside diameter of the metallic liner  360  is nearly filled with the second chemiluminescent component leaving a small air space. A transparent lens  328  manufactured from a tough heat and shock resistant transparent material (such as, for example, artificial sapphire as commonly used with scratch-proof watch crystals), is treated with a sealant on its periphery then positioned in the base of the projectile  300 , in effect sealing the aft open end  344  of the projectile  300 . The lens  328  is held in this position by the sealant as well as a cannelure/crimp groove  372  impressed on the projectile&#39;s outer surface  374 . The cannelure  372  is configured to maintain the lens&#39;  328  position and prevent activation of the tracer  310  during handling and transport. Lastly, the lens  328  is secured by rolling the aft open end  344  of the projectile copper jacket  374  over the aft outer edge of the lens  328 . In some embodiments, the projectile  300  is a small-caliber ammunition, such as 5.56 mm×45 (.22-caliber), 7.62 mm×51 (.30-caliber), 12.7 mm×99 (.50 caliber Browning Machine Gun), and up to 20 mm caliber. 
         [0015]    The tracer  310  functions at firing by the lens  328  being moved forward by the propelling gas pressure acting upon it. During this slight forward motion, independent of the projectile  300 , the lens  328  first overcomes the cannelure  372  then fractures the internal frangible ampoule  330 , allowing the chemiluminescent components to mix and fluoresce. In some embodiments, the lens  328  can make contact with the aft end  368  of the metallic liner  360  shortly before the lens  328  comes into light contact with the aft end  366  of the frangible ampoule  330 . The small air space in the annular chemiluminescent component  370  enables the slight forward motion of the lens  328  without the hydraulic resistance should the chemiluminescent components become solidly compressed. The lens&#39;  328  forward motion is halted by the lens  328  outer periphery encountering the annular aft end  368  of the metallic liner  360 . The radiation liberated by the chemiluminescent payload escapes rearward from the projectile  300  through the transparent lens  328  to be seen by the weapon&#39;s gunner/spotter. 
         [0016]    From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the scope of the invention. Accordingly, the invention is not limited except as by the appended claims.