Abstract:
An anti-armor projectile has a tail fin boom having an inner hollow area. A warhead made of high density materials is disposed in the hollow area to serve as a kinetic-energy penetrator that is released upon impact to increase the lethality of the anti-armor projectile.

Description:
GOVERNMENT INTEREST 
   The invention described herein may be manufactured and used by or for the Government of the United States of America for government purposes without the payment of any royalties therefor. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to an armor-penetrating tandem-projectile. 
   2. Description of the Related Art 
   Certain types of chemical energy (CE) warheads are formed by cone-shaped metallic liners which are later transformed into a metallic liquid jet by an explosive shaping charge carried on board the projectile. The CE warhead must be activated very near the target (about 1–2 meters) so that the formed metallic jet does not break up. Also, a spacer/spike in front of the liner provides a very short time delay needed to form the jet, when an impact fuse is mounted on the tip of that spacer spike. Alternatively, a proximity fuse may be used instead of the impact fuse if the intended target is moving (as in helicopters) or is relatively distant (4,000–5,000 meters) and a direct impact is less likely to happen. This last scenario is the actual incentive for the concept of multipurpose (MP) projectiles. 
   Anti-armor kinetic energy (KE) projectiles are long rods launched at high speed, causing damage due to their kinetic energy (mass and speed). Therefore, they are usually made of high density materials to increase the mass for a given volume. 
   U.S. Pat. No. 6,109,185 includes several tandem warhead configurations including KE-CE, CE-KE, KE-KE, or CE-CE arrangements. U.S. Pat. No. 4,102,271 discloses a KE-CE combination. U.S. Pat. No. 5,191,169 shows multiple EFP (explosively formed projectile) configurations. U.S. Pat. No. 5,744,746 shows a CE-CE tandem configuration. U.S. Pat. No. 4,497,253 shows a KE-KE configuration. 
     FIG. 1  illustrates a conventional multipurpose (MP) projectile  10 , with its typical main components. Projectile  10  includes a metallic conical liner  12  which transforms into a liquid metallic jet after detonation. A conical nose windshield  14  reduces the drag and also provides a stand-off distance between the point of impact and the conical liner  12 . A tail fin boom  16  is used to mount a stabilizing fin set piece  18 . The tail fin boom  16  is usually screwed to the main body through threads  20  and to the fin set piece  18  through another set of threads  22 . 
     FIG. 2  shows a conventional chemical energy (CE) projectile  30  also known as a HEAT (High Explosive Anti-Tank) projectile. It also has a metallic conical liner  32  and a front stand-off spacer  34 , usually referred to as “the spike.” The solid tail fin boom  36  is also used to mount the stabilizing fin set piece  38 . The tail fin boom  36  is attached to the main body of the projectile through threads  40 , and a fin set piece  38  is attached to the tail fin boom  36  through another set of threads  42 . In both  FIGS. 1 and 2 , the boom is usually solid (no internal holes or cavities) and only serves to carry the stabilizing fins. 
     FIG. 3  illustrates details of tail fin boom  50  of the MP projectile of  FIG. 1 , showing the threads  52  needed to connect to the main body of the projectile, as well as threads  54  needed to attach the tail set fins  56 , which are part of the fin piece  57 , to the tail fin boom. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a tandem warhead, in which the tail fin boom is provided with an added warhead. The forward-momentum energy released through impact is used as a mechanism for the added warhead release. The present invention includes a restraining mechanism to restrain the added warhead from spin slipping with respect to the spinning carrier projectile and to restrain the added warhead from backward movement at launch (set back), by resting the rod rear-end on an impact load-carrying end-piece. The restraining mechanism alters upon impact of the projectile to enable forward release of the added warhead through the destruction of the threads on a front screwing nut. 
   More particularly, the present invention increases the lethality of MP and CE warhead projectiles, by utilizing and converting the tail fin boom into a tube carrying an added high-density KE penetrator rod warhead. The penetrator rod is positioned to impact the target after the detonation of the front main CE or MP warhead. The release mechanism for the added KE penetrator rod is the forward momentum energy released by the stoppage of the main carrier projectile upon impact with the target. Upon impact, the added penetrator slips forward, following into the hole created by the MP/CE liquid metal jet, imparting more kinetic energy and causing deeper penetration damage to the target. 
   The present invention can be applied to both categories of projectiles (MP projectiles and fin-stabilized CE projectiles) and can be applied as well to the existing stock of both 120 mm and 105 mm CE and MP munitions. To retrofit the existing stock, the tail boom must be modified, and the fin unit, usually screwed onto the tail fin boom, must be modified to account for the heavier weight of the added KE warhead. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of a conventional multipurpose projectile configuration. 
       FIG. 2  is a cross-sectional view of a conventional chemical energy warhead projectile. 
       FIG. 3  is a cross-sectional view of a conventional tail fin boom of a multipurpose anti-armor projectile. 
       FIG. 4  is a cross-sectional view of an added KE penetrator rod warhead in a modified tail fin boom according to the present invention. 
       FIG. 5  shows details of the added KE penetrator rod warhead shown in  FIG. 4 . 
       FIG. 6  is a cross-sectional view of detail area (A) of  FIG. 4 , showing the front support design for the added KE penetrator rod warhead. 
       FIG. 7  is a cross-sectional view of the front screwing nut  70  of  FIG. 6 . 
       FIG. 8  is a cross-sectional view of an adapter piece  68 , of  FIG. 6 . 
       FIG. 9  is a cross-sectional view of detail area (B) of  FIG. 4 , showing the rear support design for the added KE penetrator rod warhead. 
       FIG. 10  is a cross-sectional view of the release of the added KE penetrator rod warhead and the carrier projectile upon impact with a target. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 4  shows an anti-armor projectile according to the present invention. The projectile includes a tail fin boom  50 , front threads  52 , rear threads  54 , fins  56 , and a fin set piece  57 . The tail fin boom has a fin-end (first end), and a main body end (second end). An added kinetic energy rod warhead  58  is housed in a long central hole provided in the tail fin boom itself. This added rod warhead is shown in  FIG. 5 . The rod warhead  58  may be of circular cross section as given by section E—E, among other possible shapes. The rod warhead is usually made of high-density material (e.g., tungsten or depleted uranium). The embodiment of  FIG. 5  shows the rod with stepped-down ends  60 ,  62 ,  64 , and  66 . Reduced size ends are needed to arrange for the support, resting, and attachment of the added warhead to the main carrier body of the projectile. The front-step  60  and rear-step  62  are non-circular as shown by sections C—C and G—G of  FIG. 5 . The steps  64  and  66  are depicted as being of circular cross section by sections D—D and F—F of  FIG. 5 ; however, they can also be of any other cross sectional shape. 
   The present invention provides novel features to enable the functioning of the added warhead. First, the added warhead should not spin relative to the spinning carrier projectile. Such relative spin may cause in-flight dynamic instability for the carrier projectile or cause inaccuracy in target hitting. Second, the added warhead should be supported at its rear end (toward the fins) such that the support part can withstand the inertia force due to the large launch acceleration (set-back force). Third, the added warhead must be restrained from relative axial movement (relative to the main carrier projectile); however, it also must be able to be released freely forward, when the carrier projectile movement is suddenly halted at impact with a target. The present invention provides for these three considerations to be satisfied in the warhead and the carrier projectile. These features are described next for the preferred embodiment. 
     FIG. 6  depicts the front end  60  of the rod which enables a resting function and the forward release arrangement. The front end  60  is of non-circular cross section, a square section in this embodiment, for example. This square end  60  rests inside a matching shaped hole of a small sleeve piece  68 . This sleeve piece  68  is connected to the carrier projectile through a screwing nut  70  which is screwed to the inner body of the carrying projectile  72  through restraining threads  74 . The screwing nut  70  may have a hexagonal head to allow for the assembly and tightening of the warhead assembly to allow substantially no relative motion between the main carrier projectile and the newly added warhead rod. The threads on the screwing nut  70  (i.e., the restraining threads  74 ) are precalculated to fail (by being sheared off) by the forward momentum force of the rod warhead  58  at the moment of impact with the target. Details of both the tightening nut  70  and the adjacent small sleeve piece  68  are shown in  FIGS. 7 and 8  respectively. 
   The rod rear end  62  is also of non-circular cross section (square in the present embodiment of  FIG. 5 ) to be matched in a corresponding non-circular recess in the fin set piece  57 , as shown in  FIG. 9 . The end of the rear non-circular end  62  must rest on a surface  78  of the fin set piece  57 , to withstand the rod acceleration inertia force load generated at launch. 
     FIG. 10  shows the operation of the added rod warhead. When a MP projectile, using either an impact fuse or a proximity fuse, impacts a target surface  80 , the rear part of the projectile represented by the tail fin boom  50  proceeds forward toward the target surface  80 . The inertia force of the rod warhead  58  will push forward the short sleeve piece  68  which will in turn push forward the tightening nut  70 . The threads on the tightening nut  70  will shear off from the tail fin boom  50  and both pieces will move forward, followed by the rod warhead  58  which has lost its restraining obstacles. The rod warhead  58  will move forward inside the just created hole  84  created by the main CE warhead (for the impact-fuse scenario), or hit the solid surface  80  causing a new hole and added damage (in the proximity-fuse scenario), where the debris  82  is shown. In either case, more damage is done to the target  80  than if the boom had no added rod warhead  58 . 
   The above-described embodiments illustrate various non-limiting arrangements of the present invention. The scope of the present invention is limited only by the breadth of the attached claims. Every aspect of the design or fitting of parts, threads, and the like can be easily changed in location, size, or type, without departing from the basic teachings of this invention. Varying rod warhead size, length, mass, shape, or other parameters to obtain enhanced lethality performance over the given configuration is within the scope of this invention. Changes by those skilled in the art to rearrange or improve this design in terms of easier manufacturability, cost, material choice, or lethality performance fall within the scope of the present invention.