Patent Publication Number: US-3880083-A

Title: Bimetallic mass stabilized flechette

Description:
United States Patent Wasserman et a1.  
 [- 1 Apr. 29, 1975 1 BIMETALLIC MASS STABILIZED FLECHETTE [75] Inventors: Saul Wasserman, Rockaway, NJ;  
 Robert S. Salzman, Manhattan. N.Y.; Walter C. OKeefe, Landing. NJ.  
 [73] Assignee: The United States of America as represented by the Secretary of the Army, Washington, DC.  
 [22] Filed: May 19, 1967 [21] Appl. No.: 642,648  
 [52] US. Cl l02/92.4; l02/D1G. 7 [51] Int. Cl. F42b 11/02 [58] Field of Search 102/38, 41, 92.3, 92.4, l02/D1G. 7  
 [56] References Cited UNITED STATES PATENTS 34.285 l/l862 Mcfford 102/92.4  
 1.178.516 4/1916 Hardcastle IOZ/DIG. 7 2.433.334 12/1947 Birkeland 2,482,132 9/1949 Studler et a1. 102/92.3 X 3.344.711 10/1967 Mawhinn ey et a1. l02/D1G. 7  
 Primary Examiner-Robert F. Stahl Attorney, Agent, or Firm-Nathan Edelberg; Robert P. Gibson; Vincent W. Cleary 9 Claims, 6 Drawing Figures BIMETALLIC MASS STABILIZED FLECHETTE The invention relates to a mass stabilized flechette and more particularly to a bimetallic mass stabilized flechette.  
  Prior art flechette designs were either fin stabilized or aft flare stabilized. Both the fins and the aft flare, each located at the rear of their respective flechettes, have an aerodynamic force acting on them which must compensate for the force acting on the nose of the flechette. When the resultant action point for these forces is located behind the center of gravity, the flechette has aerodynamic static stability.  
  Conventional fin stabilized flechettes have been launched by explosive means, but the ejective forces and therefore the launch velocities, had to be held low to prevent damage to the fins. The novel mass stabilized flechette, to be described below, since it has no fins, can withstand higher explosive forces without sustaining damage and therefore can be launched at higher velocities than the fin stabilized flechette. Conventional aft flare stabilized flechettes can be explosively launched without sustaining damage, but, due to the high drag of the flare, have a quicker velocity decay than the novel mass stabilized flechettes. The velocity decay is a function of the ballistic coefficient of the flechette.  
 I weight Ballistic coefficient The larger the ballistic coefficient, the smaller the velocity decay will be over the same increment of time. Therefore, given a fixed weight and diameter, the only way to improve the ballistic coefficient is to design the flechette shape to have the lowest drag coefficient possible within the limits of the design criteria, hence, the invention.  
  Denser packing of a multiplicity of flechettes is possible due to the aerodynamic exterior shape of the inventive flechette. The body portion of the flechette can be cylindrical or can be made hexagonal in shape to further increase the packing density without changine its superior aerodynamic characteristics. On fin and aft flare stabilized conventional flechettes, the presence of fins and body flares prevents dense packing.  
  This invention is superior to existing flechette designs by possessing the following characteristics:  
  1. Ability to withstand without damage the forces of explosive ejection necessary for launching at the velocity required for lethality;  
  2. Superior flight and terminal ballistics producing zero yaw and low coefficient of drag;  
 3. Capability of high density packing;  
  4. Increased penetrability due to a nose of uranium alloy 111 /2 which has yield strengths in the range of 100,000-300,000 PSI and hardness on the Rockwell C scale between 39 and 55.  
  If flechettes of various weights are considered, velocity is not the only parameter which determines lethality. However, if the flechette weight is held fixed, velocity is the major factor since lethality is a function of the kinetic energy.  
 KE /2 (Mass)(velocity) Therefore, the higher the velocity the greater the kinetic energy. The greater the KB, the more capability the flechette has to penetrate and kill a target.  
  Yawing motion, as above mentioned, is the angular motion of the flechette about its own center of gravity in reference to the flight path traced by the center of gravity. Yaw angle is defined as the angle between the longitudinal axis of the flechette and the tangent line to the trajectory. Drag is defined as the retarding force exerted on the flechette by the air flow. The lowest drag force occurs when the orientation of the flechette with respect to the air flow is at 0 angle of attack. This is due to the fact that the smallest cross sectional area is presented to the air flow when the flechette is in this orientation. Therefore, it is desirable to have the flechette remain at a 0 angle of attack in order to keep the velocity drag decay to a minimum.  
  It is therefore an object of the present invention to provide a mass stabilized flechette which eliminates the undesirable feature of the above mentioned factors.  
  Another object is the provision of a mass stabilized flechette which can fly at a zero angle of attack and have a low draw coefficient.  
  Still another object is to provide a mass stabilized flechette having superior penetration capability upon impact.  
  A further object is the provision of a mass stabilized flechette which can be densely packed with other similar flechettes.  
  The above objects as well as others together with the benefits and advantages of the invention will be apparent upon reference to the detailed description set forth below, particularly when taken in conjunction with the drawing annexed hereto in which:  
 FIG. 1 shows the cone portion of the flechette.  
  FIG. 2 shows the cone portion as attached to the body portion of the flechette.  
  FIG. 3 illustrates an embodiment of the present invention.  
 FIG. 4 is a diagrammatic showing of the invention.  
  FIG. 5 is a cross sectional view of the body portion of the flechette showing the body portion to be circular.  
  FIG. 6 is a cross sectional view of the body portion of an embodiment of the flechette showing the body portion to be hexagonal.  
  The cone portion 12 is made of an uranium alloy and the body portion 14 is made of either high strength aluminum or beryllium. Body portion 14 which may be circular or hexagonal in cross section, FIGS. 5 and 6 respectively, has a constant length of 2.77 calibers, which in conjunction with cone 12 gives the most rearward aerodynamic center of pressure. The amount of stability a mass stabilized flechette has is determined by how far the aerodynamic center of pressure is behind the center of gravity. The larger the separation, the more stable the flechette. Therefore, the most desirable center of pressure is the most rearward aerodynamic center of pressure that can be obtained. The dimensions of cone 12 have been selected to obtain the desired flechette weight. A diameter has been chosen such that cone l2 possesses about 86% of the total weight of flechette 10.  
  Assembly of the flechette 10 is accomplished by the mating of body portion member 16 and the hollow cone receptacle 18 and the bonding thereof with epoxy (Epon VIII). A 89.7 grain uranium-aluminum or an- 85.4 grain uranium-beryllium flechette design is shown in FIGS. 1 and 2, but scaling down will produce stable flechettes in weights as low as grains.  
  Uranium alloy 1 I 1 /2 was selected as the material for cone 12 due to the fact that it was developed expressly for projectiles. Its composition consists of 1% Molybdenum, 1% Zirconium, 1% Columbium, 0.5% Titanium and 96.5% Uranium (depleted).  
  Uranium alloy 111 /2 has superior penetrating capabilities and also the high density necessary to maintain the center of gravity of the flechette forward of the aerodynamic center of pressure.  
  The beryllium or aluminum employed in the body portion 14 has the high strength and rigidity necessary to withstand the shock of explosive ejection. The aerodynamic stability of the flechette also requires the low density of beryllium or aluminum.  
  An alternate design, as seen in FIG. 3, could possess a slightly blunted nose 20 of cone 22. The cone 22 is attached to body portion 24 of flechette 26 in a manner similar to FIGS. 1 and 2. This design would provide still greater penetration.  
  The scientific principal involved in the aerodynamic mass stabilization of this invention, as seen in FIG. 4, requires the proper location of the aerodynamic center of pressure, CP, with respect to the center of gravity, CG, of the flechette. The location of the CG forward of the CP is the requirement necessary for stability. FIG. 4 shows the angle of attack AA, the relative direction of the wind RW, the normal force NF, the axial force AF, and the resultant force RF. It can readily be seen that the normal force NF times the distance between the center of gravity CG and the center of pressure CP equals the restoring moment of the flechette.  
  As would be applicable for explosive warhead ejection, these flechettes would be packed in a dense matrix of woods metal, which is a low melting alloy (15811 composed of approximately:  
 Bismuth 507: Lead 257: Cadmium 13% Tin 1271 launched by high explosives and buffered with a 2 inch layer of styrofoam. The buffering and matrix materials are designed to transform and attenuate peak shock waves. This attenuation provides a more efficient energy transfer from explosive to flechettes because it reduces the effects of explosive shock by leveling out the energy pulse providing for a smooth transfer of energy. This is similar to a spring acting to reduce the effect of shock loads. A wave shaping device, which causes the shock wave to take the form of a plane which is ori- YY normal to their longitudinal axis, may be employed to ented such that it imparts its energy to the flechettes further the proper transfer of explosive energies. After explosive impact, the matrix material breaks loose of the flechettes, thus allowing them to fly independently to the target.  
  Obviously many modifications and variations of the present invention are possible 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 otherwise than as specifically described.  
 We claim:  
  1. A mass stabilized flechette for employment in warheads and explosive launch ejection systems comprisa forward solid cone-shaped portion comprised of a base and nose portion,  
 said base portion defining a hollow receptacle,  
 a rearward solid body portion having a forward and rearward end,  
 said forward end having an integral member which is axially aligned with and adapted to be inserted and secured in said hollow receptacle,  
 said cone-shaped portion comprising about 86% of the total weight of the flechette,  
 said body portion being 2.77 calibers in length which in conjunction with said cone-shaped portion results in a rearward aerodynamic center of pressure.  
  2. A flechette of the type described in claim 1 wherein said cone-shaped portion is made of a high density material to provide the center of gravity forward of the aerodynamic center of pressure.  
  3. A flechette of the type described in claim 2 wherein said cone portion is made of an uranium alloy.  
  4. A flechette of the type described in claim I wherein said body portion is made of a low density high strength material to provide aerodynamic stability and to be able to withstand the shock of explosive ejection.  
  5. A flechette of the type described in claim 4 wherein said body portion is made of a material selected from the group consisting of aluminum and beryllium.  
  6. A flechette of the type described in claim 1 wherein the cross sectional shape of the body portion is hexagonal.  
  7. A flechette of the type described in claim 1 wherein said cone has a blunted nose.  
  8. A flechette of the type described in claim 1 wherein said cone portion and body portion are bonded together in axial alignment with an epoxy.  
  9. A flechette of the type described in claim 1 wherein the cross sectional shape of the body portion is circular.