Abstract:
A countermass assembly is axially and radially restrained while within a vessel and is dispersible into its component parts upon being ejected from the vessel into an open environment. A plurality of groups arranged axially adjacent one another to form a stack. Each group is formed from a plurality of rings arranged in a nested interengagement. Each ring is an individual ring that is in a non-binding relationship with adjacent rings. The non-binding relationship allows each ring to be separable as such from its associated group when the stack is ejected from the vessel into the open environment.

Description:
This is a continuation application of co-pending application Ser. No. 09/708,252 filed Nov. 8, 2000. 
    
    
     ORIGIN OF THE INVENTION 
     The invention described herein was made in the performance of official duties by employees of the Department of the Navy and may be manufactured, used, licensed by or for the Government for any governmental purpose without payment of any royalties thereon. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to countermass assemblies, and more particularly to a countermass assembly made from a stack of nested rings. 
     BACKGROUND OF THE INVENTION 
     A variety of countermass materials and assemblies are known in the art. Materials include fluids and fluid-like substances and mixtures, powders, granular mixtures, flakes, prestressed and readily-fragmentizing glass, flying objects and exploding objects, just to name a few. Many of these materials are inappropriate for the development of a countermass designed to be launched from within a confined space. Fluid-based countermasses tend to have a low density thereby requiring a large volume to be effective. Fluids are also vulnerable to freezing and evaporating at the wide range of temperatures and storage typically required of a weapon. Mixtures of solids and fluids present settling problems in addition to the fluid related problems, as well as viscosity problems and poor dispersion characteristics. Powders tend to produce high side loads on the launch tube and do not flow out of a nozzle cleanly. Other designs have problems with stability under the high acceleration forces during ejection, resulting in breakage and buckling of the countermass. Further, many materials are not suitable for dispersion due to their inherent hazardous nature (e.g., fragmentizing glass), environmental and/or health concerns. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a countermass assembly. 
     Another object of the present invention to provide a countermass assembly that is stable prior to deployment. 
     Still another object of the present invention to provide a countermass assembly that exits a launch tube cleanly and completely. 
     Yet another object of the present invention to provide a countermass assembly that disperses safely into the environment. 
     Still another object of the present invention to provide a countermass assembly that is not toxic to personnel or the environment. 
     A further object of the present invention to provide a countermass assembly that makes efficient use of space. 
     Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings. 
     In accordance with the present invention, a countermass assembly is provided that is axially and radially restrained while within a vessel, and that is dispersible into its component parts upon being ejected from the vessel into an open (air) environment. The countermass assembly comprises a plurality of groups arranged axially adjacent one another to form a stack having a common longitudinal axis. Each group is formed from a plurality of rings arranged in a nested interengagement. Each ring is an individual ring that is in a non-binding relationship with adjacent rings. In this way, each ring is separable as such from its associated group when the stack is ejected from the vessel into the open environment. The separated rings quickly decelerate and flutter harmlessly through the air. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a stack of nested ring assemblies forming a countermass assembly according to one embodiment of the present invention; 
     FIG. 2 is a side view of a shoulder-launched projectile housing the nested ring countermass assembly in the pressure vessel of the projectile; 
     FIG. 3 is a perspective view of the countermass assembly of FIG. 1 once it has been ejected into an open environment from the aft end of the pressure vessel shown in FIG. 2; 
     FIG. 4 is a side view of one ring of the countermass assembly constructed as a roll of a strip material; 
     FIG. 5 is a perspective view of another embodiment of the present invention in which each layer of rings has a different axial length; and 
     FIG. 6 is an exploded side view of another embodiment of the present invention in which adjacent layers of nested rings are radially interlocked. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, and more particularly to FIG. 1, an embodiment of a countermass assembly according to the present invention is shown and referenced generally by numeral  10 . Countermass assembly  10  is a dispersible countermass that can be used in a variety of guns or other launch systems, the choice of which in no way limits the scope of the present invention. 
     Countermass assembly  10  is a layered stack of nested rings. More specifically, each layer of countermass assembly  10  consists of a series of individual rings  12 ,  14 ,  16  and  18  successively nested with one another. Only the top layer is visible in FIG.  1 . Although four such rings are shown in each layer of the illustrated embodiment, more or fewer individual rings can be used. The diametric thickness (i.e., D 12 , D 14 , D 16 , D 18 ) of each ring can be the same or different. At the center of each layer, a disk  20  can optionally be nested with the innermost ring  18  to completely fill the available countermass space. 
     Rings  12 ,  14 ,  16 ,  18  and disk  20  are positioned in a nested relationship as shown, and are maintained in countermass assembly  10  by means of a gun barrel or launch tube (not shown). That is, the relationship between adjacent rings and ring  18 /disk  20  is not a binding or press-fit relationship. Rather, only the gun barrel or launch tube restrains axial and radial movement of the rings and disks until assembly  10  is ejected therefrom. 
     By way of example, FIG. 2 illustrates one use of the present invention. A projectile that is to be fired from a shoulder-held launcher is shown and referenced generally by numeral  30 . The launching of projectile  30  typically occurs in a small or confined space. Thus, it is desirable to use a countermass assembly made from inert and harmless material that decelerates quickly when expelled or ejected into the surrounding open environment thereby reducing or eliminating the possibility of injury to personnel in the vicinity of the launch. In general projectile  30  includes a warhead case  31  filled with an explosive material  32 . Coupled to warhead case  31  is a pressure tube or vessel  33  housing a propelling charge  34 , a piston  35 , a nested ring countermass assembly (e.g., countermass assembly  10 ) radially restrained by pressure vessel  33 , and a retaining plug  36 . Before firing of propelling charge  34 , piston  35  and retaining plug  36  axially restrain countermass assembly  10 . 
     In operation, when propelling charge  34  is fired, warhead casing  31  and pressure vessel  33  are driven to the left while piston  35 , countermass assembly  10  and plug  36  are driven to the right. Countermass assembly  10  is only held together radially and axially by the combination of pressure vessel  33 , piston  35  and plug  36 . Therefore, when countermass assembly  10  is pushed to the right by piston  35  and ejected from the aft end of pressure vessel  33  into the surrounding open environment (e.g., air), rings  12 ,  14 ,  16 ,  18  and disks  20  disperse from their configuration as assembly  10  where the rings flutter as individual rings due to their aerodynamically unstable shape as illustrated in FIG.  3 . 
     Some or all of rings  12 ,  14 ,  16 ,  18  and disks  20  can be solid or can be made of a strip material that is wound similar to a roll of tape. For example, as illustrated in FIG. 4, one ring  12  is shown as being constructed of a strip  120 . The outboard end  120 A of strip  120  can be lightly tacked to the outermost winding of ring  12  to keep the ring configuration during assembly. When the rings (or disks  20 ) are constructed in this fashion, the strips will tend to unfurl as the rings and disks disperse. The unfurling of each ring and/or disk further slows their velocity as the unfurling strip material presents more surface area thereby increasing its aerodynamic instability. 
     Each ring and disk in countermass assembly  10  has the same axial length. However, the present invention could also be made with layers of differing axial length as illustrated by countermass assembly  100  in FIG.  5 . Specifically, a first layer of axial length L 1  consists of rings  112 ,  114 ,  116 ,  118  and disk  120 . A second layer of similar rings/disk has an axial length L 2 , and a third layer of similar rings/disk has an axial length L 3 . These lengths can be selected so that the countermass disperses in an optimal fashion for a particular application. Note that the axial lengths could also successively increase, successively decrease, or be random in length depending on the application. 
     The present invention could also be made by radially interlocking adjacent layers of nested rings as shown in the exploded view of FIG.  6 . More specifically, layers  200  and  300  are shown separated from one another along a common longitudinal axis  400 . As in the previous embodiments, each layer consists of nested rings with an optional central disk. However, the axial length of each ring/disk in a layer is varied to complement an adjacent ring/disk. For example, layer  200  has rings  212 ,  214 ,  216 ,  218  and disk  220  at its center. Layer  300  has rings  312 ,  314 ,  316 ,  318  and disk  320  at its center. The lengths of rings  212 ,  214 ,  216 ,  218  and disk  220  are l 1 , l 2 , l 3 , l 4  and l 5 , respectively. In a complementary fashion, the lengths of rings  312 ,  314 ,  316 ,  318  and disk  320  are l 5 , l 4 , l 3 , l 2  and l 1 , respectively. Thus, when layers  200  and  300  are pressed into axial engagement along axis  400 , layers  200  and  300  will be radially interlocked with one another. 
     The advantages of the present invention are numerous. The nested ring design will support a large axial load without buckling. Additionally, the circular design is optimal for supporting a tangential or hoop load when the stack is compressed axially during launch. Despite the compression-stable qualities of the stack of nested rings, they will disperse readily upon release. Additionally, the rings can be fabricated from a wide variety of materials. The strip/roll version may provide less of a threat to bystanders. In addition, the fabrication and assembly are not complicated or sensitive to minor size or material variations. 
     The countermass assembly of the present invention is easily made chemically inert and non-toxic. The design lends itself to being made form a variety of materials that are insensitive to changing and/or extreme temperatures. In addition, the use of nested rings and a central disk provides a space efficient design. 
     Although the invention has been described relative to a specific embodiment thereof, there are numerous variations and modifications that will be readily apparent to those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described.