Abstract:
A modified projectile round which is configured to function with a propellant cartridge such as described in U.S. Pat. No. 7,004,074. The projectile assembly uses a High-Low gas pressure cartridge to launch the projectile. When the high pressure cartridge is ignited, hot propellant gases rupture a burst cup and shoot propellant gases toward the aft end of the projectile. The hot propellant gases impinge against a delay carrier located in the aft end of the projectile. The contents of the delay carrier are thereby ignited. The delay carrier includes one or more delay columns ultimately terminating in an igniter charge. The delay columns burn as the projectile is in flight. A specified amount of time later, the igniter charge ignites an ignitable payload—such as a marker flare candle.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the field of gas-propelled projectiles. More specifically, the invention comprises a marker flare projectile having an improved delay column ignition system 
     2. Description of the Related Art 
     Although the present invention can be configured to operate from a variety of different launchers, it was primarily developed to be fired from launchers adapted to fire 40 mm grenades (such as the U.S. Army&#39;s M433). The invention incorporates elements from a prior design reduced to practice by the same inventor. The prior design is disclosed and claimed in U.S. Pat. No. 7,004,074 to Van Stratum (2006), which is hereby expressly incorporated by reference. 
     Gas-propelled projectiles typically use solid propellant encapsulated in a cartridge case. A projectile is seated in the open mouth of the cartridge case. Ignition of the propellant is provided by percussive or electrical means. The burning propellant generates pressurized gas which forces the projectile out of the mouth of the case and then typically through a barrel bore. 
     This type of system is typically used to launch 40 mm grenades. The same approach can be used to launch other types of projectiles, however. An example of such a projectile is a marker flare. A marker flare projectile has a mass which is similar to that of a grenade round. Thus, the propulsion system developed for use with grenade rounds can be used to launch a marker flare. The incorporated U.S. Pat. No. 7,004,074 illustrates and describes an effective approach to the problem of launching large masses at low velocities. The &#39;074 invention uses a high-pressure cartridge embedded within a low-pressure larger cartridge. A burst cup metering system is used to meter propellant gases from the high pressure cartridge into the low pressure cartridge, thereby accelerating the projectile in a smooth and controlled fashion. This approach helps to reduce the peak recoil loads experienced by a user. The high pressure found within the high pressure cartridge also ensures the reliable ignition and combustion of the propellant it contains. 
     The burst cup approach results in hot metered gases exiting the high pressure case in the direction of the mouth of the low pressure case. The present invention makes use of this phenomenon. In addition to propelling the marker flare down the bore of the firing weapon, the hot gases exiting the high pressure case are used to ignite a delay column in the aft end of the marker flare round. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a modified marker flare round which is configured to function with a propellant cartridge such as described in U.S. Pat. No. 7,004,074.  FIGS. 2 and 3  illustrate the invention&#39;s most significant features.  FIG. 2  shows a projectile assembly using a High-Low gas pressure cartridge to launch a marker flare round. High pressure chamber  31  is formed within high pressure cartridge  42  (The high pressure chamber is normally filled with solid propellant, which is not shown in the view). Low pressure chamber  30  is formed within low pressure cartridge  38 . Burst cup  46  closes the open mouth of the high pressure cartridge. 
     When the high pressure cartridge is ignited, the solid propellant burns and hot propellant gases rupture the burst cup. The gases then shoot out through charge vent hole  52  (toward the mouth of low pressure cartridge  38 ). These propellant gases expel marker flare round  124  from the mouth of the low pressure cartridge and accelerate it down the bore of the weapon. 
     The hot propellant gases also impinge against the exposed aft end of delay carrier  96 . The contents of the delay carrier are thereby ignited. The delay carrier includes one or more delay columns ultimately terminating in a flare igniter charge. The delay columns burn as the marker flare round is in flight. A specified amount of time later, the flare igniter charge ignites the flare itself (generally after the marker flare round has struck the earth and buried its nose cone in the ground). The flare&#39;s aft closure is detached from the balance of the round and the flare then burns brightly. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view, showing a projectile assembly. 
         FIG. 2  is a perspective view with a cutaway, showing internal details of the marker flare round cartridge. 
         FIG. 3  is a sectioned detail view, showing the composition of the delay carrier. 
         FIG. 4  is a sectional view, showing the ignition of the propellant and the ignition of the delay carrier. 
         FIG. 5  is a sectioned elevation view, showing the marker flare round after it has impacted the earth. 
         FIG. 6  is a sectioned elevation view, showing the ignition of the flare candle. 
         FIG. 7  is a sectioned detail view, showing the joint between the nose cap, tube, and flare sleeve. 
         FIG. 8  is a sectioned elevation view, showing the burning of the flare candle and the expulsion of the flare sleeve and aft closure. 
     
    
    
     REFERENCE NUMERALS IN THE DRAWINGS 
     
       
         
               
               
               
               
             
           
               
                   
               
             
             
               
                 11 
                 projectile assembly 
                 12 
                 low pressure case 
               
               
                 14 
                 projectile 
                 16 
                 rifling ring 
               
               
                 18 
                 nose cup 
                 30 
                 low pressure chamber 
               
               
                 31 
                 high pressure chamber 
                 34 
                 percussion primer 
               
               
                 36 
                 propellant 
                 38 
                 low pressure cartridge 
               
               
                 42 
                 high pressure cartridge 
                 46 
                 burst cup 
               
               
                 52 
                 charge vent hole 
                 84 
                 cushion 
               
               
                 86 
                 tube 
                 88 
                 candle 
               
               
                 90 
                 flare sleeve 
                 92 
                 potting 
               
               
                 94 
                 aft closure 
                 96 
                 delay carrier 
               
               
                 98 
                 igniter charge 
                 100 
                 delay column 
               
               
                 102 
                 flare igniter charge 
                 104 
                 input opening 
               
               
                 106 
                 output opening 
                 110 
                 propellant gases 
               
               
                 112 
                 clevis 
                 114 
                 descending flange 
               
               
                 116 
                 tang 
                 118 
                 channel 
               
               
                 120 
                 sealant 
                 122 
                 ground 
               
               
                   
               
             
          
         
       
     
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows the major components of a 40 mm projectile round. Projectile  14  is mated with low pressure case  12  to form projectile assembly  11 . Those skilled in the art will know that projectile  14  can assume many forms, including a fragmentation grenade, a smoke round, a flare round, etc. It generally includes a rifling ring  16  sized to engage the rifling on the bore of the grenade launching weapon. Nose cone  18  provides an aerodynamically efficient shape. 
       FIG. 2  shows projectile assembly  11  sectioned in half to show internal details of the present invention (a marker flare round). The present invention is a cartridge designed to propel a marker flare candle a considerable distance downrange from the firing weapon (typically 400 m to 800 m). The projectile is designed to embed the flare candle into the ground when it strikes, leaving the candle&#39;s burning end pointing upward. The flare candle remains in that position as it burns, thereby illuminating a targeted area. 
     Cylindrical candle  88  is made of suitable flare material. It is housed within hollow cylindrical tube  86 . Nose cap  18  covers the forward end of the candle. The nose cap is hollow, leaving a space between the nose cap and the forward end of the candle. This space is preferably filled by cushion  84 , which is made of a low density foam. 
     The aft end of the candle is covered by aft closure  94 . Aft closure  94  is connected to flare sleeve  90  by conventional means, such as a threaded engagement. Flare sleeve  90  is a hollow cylinder which slides over tube  86 . The forward extreme of the flare sleeve engages with the aft extreme of nose cap  18  in a sliding fit (which will be explained in more detail subsequently). 
     The assembly of aft closure  94 , candle  88 , tube  86 , flare sleeve  90 , nose cap  18 , and cushion  84  together makes up marker flare round  124 . This assembly is expelled from the weapon upon firing, travels downrange, and strikes the target area. Thus, it must be able to withstand the substantial acceleration of the firing cycle as well as the impact with the target. It is therefore important to eliminate any open space within the projectile in order to prevent unwanted deformations. As an example, potting  92  is used to fill a gap existing between aft closure  94  and candle  88 . The potting can be any suitable compound which transitions from a liquid to a solid in order to fill the volume. 
     The reader will note additional significant features of the marker flare round in  FIG. 2 . Aft closure  94  includes delay carrier  96  located in its center. The delay carrier is positioned directly over high pressure cartridge  42 , which is located in the closed base of low pressure cartridge  38 . High pressure cartridge  42  (which is described in detail in the incorporated U.S. Pat. No. 7,004,074) has a closed aft end, an open forward end, and a continuous side wall. It contains propellant  36  (The propellant is not shown in the view, but occupies the hollow interior of the high pressure cartridge). The open forward end of the high pressure cartridge is closed by a burstable cover. Upon ignition of percussion primer  34 , the propellant within the high pressure cartridge ignites. The hot propellant gases then burst the burstable cover and vent through charge vent hole  52 . Thus, a metering system is created in which the hot propellant gases are metered from high pressure chamber  31  into low pressure chamber  30 . The gases expel marker flare round  124  from low pressure cartridge  38  and accelerate it down the bore of the firing weapon. 
     A variety of burstable covers can be used in high pressure cartridge  42 , including a simple “wad” crimped into the cartridge&#39;s open mouth. However, a hollow hemispherical burst cup  40  is preferably used. This is retained within the high pressure cartridge by a suitable mechanical interference. The burst cup is preferably embossed with rupture lines so that it will burst in a predictable fashion. 
     Delay carrier  96  is aligned with high pressure cartridge  42  so that the propellant gases exiting the high pressure cartridge will strike the aft end of the delay carrier.  FIG. 3  shows a sectioned detail view of the delay carrier. The potting surrounding the delay carrier and the flare candle itself have been removed so that the delay column may be fully visualized. Delay carrier  96  holds the components in position. The aft end of the delay carrier opens into input opening  104 . The forward end opens into output opening  106 . An internal passage connects the input opening to the output opening. 
     Igniter charge  98  is located within the internal passage proximate input opening  104 . When the high pressure cartridge ignites, the hot propellant gases ignite igniter charge  98 , which in turn ignites the adjacent delay column  100 . Delay column  100  is a specialized type of combustible which takes a fixed amount of time to burn from one end to the other. Two or more such delay columns can be stacked within the passage inside the delay carrier in order to establish a set delay. When the last delay column burns through, it ignites flare igniter charge  102 . The flare igniter charge is located proximate a surface of the flare candle, so its ignition actually starts the burning of the flare candle. 
     It is important that the delay carrier be firmly retained in the aft closure, so that it is not dislodged during the firing cycle. While many methods of securing the delay carrier can be used, one good approach is to peen or otherwise deform a portion of the aft closure into the delay carrier. This plastic deformation will create an interference fit which then securely retains the delay carrier in the aft closure.  FIG. 3  depicts such a deformation in the region where the delay carrier meets the aft closure. 
     The operation of the marker flare round will now be described, beginning with  FIG. 4 .  FIG. 4  shows the round just after high pressure cartridge  42  has detonated and separated the marker flare round from the low pressure cartridge. Propellant gases  110  impinge upon the aft portion of the delay column, thereby setting off igniter charge  98 , which in turn starts the first delay column burning. The projectile passes through the bore of the firing weapon and begins its free flight. Within the delay carrier, the delay columns continue to burn. 
     It may take many seconds for the projectile to reach the target area and impact the ground. For most applications, it is desirable to light the flare after impact. As an example, two ten-second delay columns can be used to provide a twenty second delay between the ignition of the high pressure cartridge and the ignition of the flare. During this delay, the projectile flies through the air and strikes the ground in the target area. 
       FIG. 5  shows marker flare round  124  after it has struck ground  122  and embedded its forward portion. Nose cap  18  and cushion  84  absorb the impact forces so that the balance of the projectile remains intact. At this point (depending on the delay configuration selected) the second delay column  100  is still burning toward flare igniter charge  102 . 
     In  FIG. 6 , flare igniter charge  102  has ignited and thereby ignited candle  88 . Candle  88  then starts producing a large quantity of hot gas, which builds pressure between the aft end of the candle and the aft closure. In order for the candle to burn freely and illuminate the target area, it is at this point desirable to remove the aft closure. Turning briefly back to  FIG. 2 , the reader will recall that aft closure  94  and flare sleeve  90  are connected together, with the flare sleeve slidably fitting over tube  86 . The forward portion of flare sleeve  90  is also slidably engaged with the aft portion of nose cap  18 . 
       FIG. 7  shows the slidable engagement between the forward portion of the flare sleeve and the aft portion of the nose cap in greater detail. The nose cap includes descending flange  114 , which in combination with tube  86  creates clevis  112 . The forward portion of flare sleeve  90  creates tang  116  which fits snugly into clevis  112 . Tang  116  includes a channel  118  extending all the way around the circular cross section of the flare sleeve. Sealant  120  fills this channel. After the flare sleeve is advanced into engagement with the nose cap, sealant  120  is applied. This creates a suitable engagement between the nose cap and the flare sleeve, which prevents the two components from separating prematurely. 
     Returning now to  FIG. 6 , the reader will recall that the flare candle has started burning and is producing pressurized gas, which tends to force the aft closure away from the flare candle. The aft closure is retained on the flare candle by the tang and clevis engagement between the nose cap and the flare sleeve. Shortly after the candle starts burning, the tang is forced out of the clevis and the flare sleeve and aft closure are propelled free of the candle (as a unit, since they are connected). 
       FIG. 8  shows this action. Flare sleeve  90 , with the aft closure still attached, has been propelled free of tube  86 . The candle&#39;s burning gases will propel it a short distance away. At this point the flare candle is free to burn. It will emit a bright light until the candle is exhausted. 
     Looking back at  FIG. 2 , the reader will note that that flare sleeve  90  is slidably connected to tube  86  rather than directly to candle  88 . The tube is a container which holds the candle in a conformed shape and serves to mechanically reinforce the candle material. The tube may therefore be viewed as part of the flare candle itself. Thus, the slidable attachment between the flare sleeve and the tube may be viewed as a slidable attachment between the flare sleeve and the flare candle itself. 
     Those skilled in the art will realize that the components thus described can be used to create a delayed ignition of many types of ignitable payloads in a projectile round. A marker flare candle is a common example of such an ignitable payload. However, the system described could be used to ignite an explosive payload as well. The explosive payload could be ignited while airborne (using a short delay in the delay carrier) or after it has landed in the target area (using a long delay in the delay carrier). The system could also be used to ignite a smoke-generating payload. 
     Although the preceding description contains significant detail, it should not be construed as limiting the scope of the invention but rather as providing illustrations of the preferred embodiment of the invention. Thus, the scope of the invention should be fixed by the following claims, rather than by the examples given.