Abstract:
A paintball comprising a thin-walled capsule filled with paint, wherein the surface of the capsule is formed as a polyhedron, for example, a dodecahedron. The angled surface faces of the polyhedron cause turbulent air flow over a greater percentage of the paintball surface than in a prior art smooth, spherical paintball. The air flow thus remains “attached” over more of the paintball surface, thereby reducing form drag of the paintball. An added benefit of a paintball formed in accordance with the invention is that the structure includes a plurality of intrafacial edges which are currently believed to be preferred lines of impact breakage of the paintball.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/580,608, filed Jun. 17, 2004 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates to aerodynamic spheroids; more particularly, to paintballs for use in hunting sport games; and most particularly, to an improved paintball having a polyhedral outer surface for reduced drag and greater range.  
       BACKGROUND OF THE INVENTION  
       [0003]     So-called “paintballs” are an integral element of a well-known mock hunting sport wherein players attempt to deliver paintballs into rupturing contact with other players. See, for example, U.S. Pat. Nos. 5,001,880; 5,018,450; 5,393,054; 5,353,712; 5,448,951; 5,640,945; 5,762,058; 5,823,173; 5,936,190; 6,082,439; 6,145,441; 6,230,630; 6,375,981; 6,530,962; 6,574,945; and 6,615,739, the relevant disclosures of which are hereby incorporated by reference.  
         [0004]     The sport or recreational activity known as “War Games” is currently one of the fastest growing sports in North America. Typically, players are arranged into two or more teams and shoot paintballs at members of the opposing teams in a hide-and-seek setting. When a paintball strikes a player of an opposing team, the paintball ruptures and releases the fill material or “paint” onto that player. Any player who has been struck by a paintball is marked and thus disqualified from continuing in the game.  
         [0005]     A paintball comprises a generally spherical capsule having a typical thickness of about 0.010 inch and enclosing a charge of a colored liquid, referred to generally as “paint.” The paint, while typically liquid in most paintballs today, may be in any phase. The current invention is not limited to liquid fill materials, or to single-phase fill materials. Typically, the capsule is formed of gelatin and the paint is a dyed aqueous sugar solution that may include additives such as starch and polyethylene glycol to improve breakage resistance in handling and firing.  
         [0006]     In the sport, a paintball typically is fired from a hand-held gun employing a compressed-gas charge which can accelerate the paintball without causing it to rupture within the gun. In organized paintball activities, the discharge velocity of a paintball is limited to 300 feet per second; at higher paintball velocities, human injury can result. Thus, a typical paintball gun can discharge a paintball at about 298 feet per second.  
         [0007]     The limit on initial muzzle velocity creates a resulting limit in range of fire of a regulation paintball from a regulation gun.  
         [0008]     The flight of a paintball is typically ballistic, following paraboloid path dictated by gravitational acceleration in the vertical direction and muzzle velocity in the horizontal direction. The path is not ideally parabolic, however, because a projectile is subject to both frictional drag forces and form drag forces in the horizontal direction, causing a progressive reduction in velocity during the flight. The practical result is that the range of a paintball is significantly less than theoretical, typically only about one-tenth the ideal range in the absence of drag. A greater range from the same initial velocity is highly desirable.  
         [0009]     What is needed in the art is a means for increasing the range of a paintball within the initial velocity limitations of the sport.  
         [0010]     It is a principal object of the present invention to provide an improved paintball that can travel farther than prior art paintballs.  
       SUMMARY OF THE INVENTION  
       [0011]     Briefly described, a paintball in accordance with the invention comprises a thin-walled capsule filled with paint, wherein the surface of the capsule is formed as a polyhedron, for example, a dodecahedron. The angled surface faces of the polyhedron cause turbulent air flow over a greater percentage of the paintball surface than in a prior art smooth, spherical paintball. The air flow thus remains “attached” over more of the paintball surface, thereby reducing form drag of the paintball.  
         [0012]     An added benefit of a paintball formed in accordance with the invention is that the structure includes a plurality of interfacial edges which are currently believed to be preferred lines of impact breakage of the paintball. The manufacturing processes used to create the paintball also may be used to induce false mold markings along the interfacial edges, such that the parting line from the manufacturing process does not introduce asymmetry into the paintball shape. Further, the edges may be preferentially raised, or indented, to control the impact breakage characteristics and the deformable body characteristics of the ball during firing and flight. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:  
         [0014]      FIG. 1  is an isometric view of a paintball in accordance with the invention having an outer surface in the form of a regular dodecahedron;  
         [0015]      FIG. 2  is a wire-frame perspective view of a paintball similar to the one shown in  FIG. 1  illustrating a concave face, a convex face, and a septa positioned within the paintball chamber forming first and second sub-chambers;  
         [0016]      FIG. 3  is a wire-frame perspective view of a paintball having a buckyball shape;  
         [0017]      FIG. 4  is a wire-frame perspective view of a paintball having a triacontahedron shape;  
         [0018]      FIG. 5  is a wire-frame perspective view of a paintball having a pentagonal dodecahedron shape;  
         [0019]      FIG. 6  is a wire-frame perspective view of a paintball having a icosahedron shape;  
         [0020]      FIG. 7  is a wire-frame perspective view of a paintball having a hexakisoctahedron shape;  
         [0021]      FIG. 8  is a wire-frame perspective view of a paintball having a triakisoctahedron shape;  
         [0022]      FIG. 9  is a wire-frame perspective view of a paintball having a icositetrahedron shape;  
         [0023]      FIG. 10  is a wire-frame perspective view of a paintball having a octahedron shape;  
         [0024]      FIG. 11  is a wire-frame perspective view of a paintball having a cube shape;  
         [0025]      FIG. 12  is a wire-frame perspective view of a paintball having a hexakistetrahedron shape;  
         [0026]      FIG. 13  is a wire-frame perspective view of a paintball having a tetrahedron shape;  
         [0027]      FIG. 14  is a wire-frame perspective view of a paintball having a deltoid dodecahedron shape;  
         [0028]      FIG. 15  is a wire-frame perspective view of a paintball having a diakisdodecahedron shape;  
         [0029]      FIG. 16  is a wire-frame perspective view of a paintball having a pentagonal icositetrahedron shape;  
         [0030]      FIG. 17  is a wire-frame perspective view of a paintball having a tetrahedral pentagonal dodecahedron shape;  
         [0031]      FIG. 18  is a wire-frame perspective view of a paintball having a deltoid dodecahedron shape;  
         [0032]      FIG. 19  is a wire-frame perspective view of a paintball having a trigonal dipyramid shape;  
         [0033]      FIG. 20  is a wire-frame perspective view of a paintball having a tetragonal dipyramid shape;  
         [0034]      FIG. 21  is a wire-frame perspective view of a paintball having a rhombohedron shape; and  
         [0035]      FIG. 22  is a graphical representation of drag coefficients (CD) for three-dimensional ellipsoidal bodies of revolution as a function of aspect ratio. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0036]     Referring to  FIGS. 1 and 2 , paintball  10  in accordance with the invention includes a semi-rigid capsule shell  12  defining a closed chamber  13  for enclosing a liquid charge of paint (not visible in  FIGS. 1 and 2 ). Shell  12  is formed in a generally spheroid shape defining a closed polyhedron on at least the outer surface of shell  12 , the polyhedron comprising faces  14  intersecting at interfacial edges  16 . Faces  14  may be planar, convex outwards  14   a,  or concave outwards  14   b,  or combinations thereof. While one of the faces  14  of paintball  10  in  FIG. 2  is shown as convex outward  14   a,  and one of faces  14  is shown as concave outward  14   b,  it will be understood that more than one of faces  14  may be either convex outward  14   a  or concave outward  14   b.  This includes an embodiment where all of faces  14  on paintball  10  are either convex outward  14   a  or concave outward  14   b.  Moreover, faces  14  may be identical or non-identical.  
         [0037]     A currently-preferred polyhedron is a regular dodecahedron, as shown in  FIGS. 1 and 2 , although other closed polyhedra are fully comprehended by the invention. For instance, as best seen in  FIGS. 3-21 , the invention all includes, but is not limited to, polyhedra such as a buckyball  10   a , triacontahedron  10   b,  pentagonal dodecahedron  10   c,  icosahedron  10   d,  hexakisoctahedron  10   e,  triakisoctahedron  10   f,  icositetrahedron  10   g,  octahedron  10   h,  cube  10   i,  hexakistetrahedron  10   j,  tetrahedron  10   k,  deltoid dodecahedron  10   l,  diakisdodecahedron  10   m,  pentagonal icositetrahedron  10   n,  tetrahedral pentagonal dodecahedron  10   c,  deltoid dodecahedron  10   p,  trigonal dipyramid  10   q,  tetragonal dipyramid  10   r,  and rhombohedron  10   s,  respectively.  
         [0038]     As best seen in  FIGS. 1 and 2 , interfacial edges  16  are currently believed to be preferred lines of impact breakage of the paintball. The manufacturing processes used to create paintball  10  also may be used to induce false mold markings  18  along one or more of interfacial edges  16 , such that the parting line from the manufacturing process does not introduce asymmetry into the paintball shape. It will be understood that false mold markings  18  may extend generally around the circumference of paintball  10  along one or more of interfacial edges  16 . Further, interfacial edges  16  may be preferentially raised, or indented, to control the impact breakage characteristics and the deformable body characteristics of paintball  10  during firing and flight.  
         [0039]     Paintball  10  may include a plurality of similar or dissimilar liquid or other material charges within the closed chamber of shell  12  which may be separated internally by one or more septa  20  that divide the chamber into at least first and second sub-chambers  13   a,    13   b  as best seen in  FIG. 2 . The one or more septa  20  are intended to rupture at impact, along with shell  12 , thereby mixing the liquid charges. The internal septa  20  can also cause the liquid charges to rotate with the shell, preventing paintball rotation from being viscously damped out, as disclosed in U.S. Pat. No. 5,640,945.  
         [0040]     The purpose of providing shell  12  as a closed polyhedron is to reduce form drag, thereby promoting longer flight of a paintball so equipped. The benefits of reduced drag are well known for spherical and ellipsoidal bodies, and are equally applicable to polyhedral bodies, for the same reasons. A currently-preferred polyhedral shaped shell can reduce form drag on a paintball by between 25% and 50% as compared to an unfeatured, spherical paintball of otherwise identical weight, size, and composition.  
                                     TABLE 1                       Aspect Ratio   Laminar Flow   Turbulent Flow                                1:1   0.47   0.27       2:1   0.27   0.06       4:1   0.2   0.06       8:1   0.25   0.13                 Drag coefficients for three-dimensional ellipsoidal bodies of revolution. Source: Mechanics of Fluids, By Irving H. Shames, 2 nd  edition, © 1982, Table 10.3, Page 409, McGraw Hill, ISBN 0-07-056385-3.  FIG. 22  is a graphical representation of the data presented in Table 1.             
 
         [0041]     With reference to  FIG. 22 , for a sphere, with an aspect ratio of 1:1, the drag coefficient is dramatically reduced by causing a transition from laminar to turbulent flow. In addition, whether the flow is turbulent or laminar, slightly increasing the aspect ratio of the projectile, such that it is somewhat elongated in the direction of motion, causes a reduction in total drag on the body. This is due to the fact that the streamlined flow on the trailing edge of the body results in better pressure recovery. However, if the aspect ratio is increased too far, then the overall drag begins to increase again, and skin friction affects overtake the importance of the pressure recovery. The important thing to note from the figure below is that the total drag coefficient, CD, on the projectile decreases nearly linearly with increasing aspect ratio, as the projectile becomes less spherical in shape.  
         [0042]     The results illustrated in Table 1 and  FIG. 22  are demonstrated in Table 2 set forth below, which shows the positive influence that deforming the shape of the projectile body can have upon the drag coefficient. For a spherical shape having an aspect ratio of 1:1, which is the shape used by virtually all paintballs today, the drag coefficient, CD, is 0.47. If transition to turbulence can be induced, then the drag coefficient can be reduced dramatically to approximately 0.27. Such a reduction will result in extended range of the projectile flight. Note that whether the flow regime is laminar or turbulent, a reduction in the drag coefficient, C D , can be achieved by increasing the aspect ratio of the projectile. For example, in laminar flow conditions, elongating the projectile to an aspect ratio of 1.1:1 reduces the drag coefficient by approximately 5%. As the deformation becomes more pronounced, for example with an aspect ratio of 1.25:1 under laminar flow conditions, the drag coefficient CD can be reduced by approximately 11%. Even better reductions in drag coefficient are achieved for a given deformation when the flow is in the turbulent range. Thus, a paintball that can cause the boundary layer flow to transition from laminar flow to turbulent flow will have a decreased drag coefficient, C D , and a corresponding increase in range for a given muzzle velocity. Additionally, a projectile which is deformed into an oblong shape will have a lower drag coefficient, C D , and a corresponding increase in range for a given muzzle velocity than a projectile which is generally spherical in shape.  
                                         TABLE 2                           Estimated drag coefficients for three-dimensional       ellipsoidal bodies of revolution of various aspect ratios, obtained by       linear interpolation of the data presented in Table 1.                            Approximate %   Approximate %       Ellipsoidal   Aspect   Approximate   Approximate   Reduction in   Reduction in       Shape   Ratio   Laminar C D     Turbulent C D     Laminar C D     Turbulent C D                                                                           1:1   0.47   0.27   Not Applicable   Not Applicable                                             1.11:1   0.45   0.25    5%    9%                                             1.25:1   0.42   0.22   11%   19%                                             1.43:1   0.38   0.18   18%   33%                                             1.67:1   0.34   0.13   29%   52%                                             2:1   0.27   0.06   43%   78%                  
 
         [0043]     It is desirable to have a paintball projectile that is generally spheroidal in shape during the process of storage, transportation, and loading from the paintball feeder into the breech of a paintball gun. The generally spheroid shape has numerous materials handling advantages, including the primary advantages of being able to load the projectile into the gun without need to orient the projectile in a particular fashion, and for compatibility with the large installed user-base of paintball guns which have the ability to manipulate and fire only those projectiles that are generally spheroid. At the same time, a paintball which can be initially fired in a generally spheroid shape, and can be caused to deform into an elongated aspect ratio as illustrated in Table 2 during the process of firing the paintball from the gun or during its flight from the muzzle to the target, can exhibit reduced total drag coefficient, C D , and hence improved range. The present invention meets these needs.  
         [0044]     While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.