Abstract
A training ammunition cartridge comprises a projectile and a cartridge case with a pyrotechnic propellant. The projectile has a projectile body with at least one compartment therein forming a void and containing a material that transitions from a solid to a liquid after set-back and after exiting from a barrel of a gun. The void is of such configuration as to cause the liquid material therein to induce forces and moments that, after a period of stable ballistic flight, destabilize the projectile and shorten its flight. Alternatively, the projectile void contains a solid mass that is released to shift its position after set-back and after the projectile exits from the barrel of the gun, wherein the void is of such configuration as to cause the mass, upon shifting, to induce forces and moments that, after a period of stable ballistic flight, destabilize the projectile and shorten its flight.
Claims
1. An ammunition cartridge comprising a projectile mounted on a cartridge case with a pyrotechnic propellant, the projectile having a spin-stabilized projectile body with adequate structural integrity to withstand forces of setback and spin that are applied when the projectile is fired from a gun, said projectile body having at least one compartment therein forming a void and containing a material that is a solid at ambient temperatures and that rapidly transitions from a solid phase to a liquid phase after the projectile exits from a barrel of the gun, wherein said material housed in said void transitions from the solid to the liquid phase upon reaching an elevated temperature due, at least in part, to thermal conductive heating from at least one of (1) propellant combustion and (2) external friction applied to the projectile body, whereby the liquid phase of the material progressively induces forces and moments that, after a period of initial stable ballistic flight, produces increasing yaw and flight instability, shortening the projectile's flight.
2. The ammunition cartridge defined in claim 1, wherein the material flows within the void upon transitioning from a solid to a liquid and combined forces of liquid-to-solid friction of the material and imparted resonance induce an increase in the projectile's yaw amplitude, thereby shortening the projectile's maximum range of flight.
3. The ammunition cartridge defined in claim 1, wherein said elevated temperature is above a storage and operational temperature of the ammunition cartridge.
4. The ammunition cartridge defined in claim 1, wherein said elevated temperature is at least about 160 F.
5. The ammunition cartridge defined in claim 1, wherein said projectile body is surrounded by a metal driving band which generates friction heat when the projectile transits through the barrel causing heat to flow through the projectile body to the material in the void.
6. The ammunition defined in claim 1, further comprising a metal heat sink arranged adjacent the void for absorbing heat when the propellant is ignited and the projectile is fired, causing heat to flow to the material in the void.
7. The ammunition defined in claim 1, further comprising a nose that, during high velocity flight, is heated by the friction of air traveling over an outer body of the projectile and where the heat flows to the material in the void.
8. The ammunition cartridge defined in claim 1, wherein said material housed in said void transitions from a solid to a liquid upon exiting the barrel due, in part, to high-g forces applied to the material on set-back and during its accelerated passage through the barrel, and transitions to low g-forces applied during subsequent free flight of the projectile.
9. The ammunition cartridge defined in claim 8, wherein said material is a non-Newtonian fluid.
10. The ammunition cartridge defined in claim 1, wherein said projectile body is made of a frangible material that survives set-back and flight but breaks up upon impact, thereby to preclude a ricochet.
11. The ammunition cartridge defined in claim 1, wherein the projectile material is made of a frangible material that survives set-back and flight but breaks into smaller pieces on impact.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) FIG. 1 illustrates a typical ammunition projectile trajectory having an effective range and a maximum range.
(2) FIG. 2 illustrates a Short range Training Projectile (SRTP) trajectory where forces imparted on the projectile have shortened the maximum range of this ammunition.
(3) FIG. 3 illustrates the distance where an SRTP will match the flight profile of reference ammunition which may be a ball or war-shot ammunition.
(4) FIG. 4 is a safety diagram extracted from the US Army FM 23-91, Appendix B, illustrating the methodology for calculating a Surface Danger Zone (SDZ) surrounding the impact area of a military training range.
(5) FIG. 5 shows a typical aerodynamic de-spinner projectile which is currently the prevailing approach to the design of SRTPs. FIGS. 5a and 5b, respectively, are graphs of residual velocity vs. range for such a projectile.
(6) FIG. 6 illustrates the forces induced on a projectile by a liquid housed in a void while the projectile is in free flight. The effect of liquid resonance is not depicted.
(7) FIG. 7 is an extract from AMC Pamphlet 706-165 (Distribution A for Public Release) depicting the spin decay of a 20 mm projectile with a 70% liquid fill.
(8) FIG. 8 depicts the liquid characteristics of various types of liquids when exposed to shear forces.
(9) FIG. 9 depicts a projectile traversing a barrel as a simple thermal model, where friction between the barrel and the projectile's driving band, coupled with the heat of hot propellant gases, heat the projectile. The image also depicts how the friction of high velocity air-flow over the projectiles body induces heat in the projectiles nose.
(10) FIG. 10 is a cutaway view of a projectile with a cylindrical void located along the centerline of the axis of rotation.
(11) FIG. 11 is a phantom view of a projectile with a cylindrical void geometry.
(12) FIG. 12 is a phantom view of a projectile with a spherical void geometry.
(13) FIG. 13 depicts cross-sectional views of four different projectiles with filled and partially filled voids.
(14) FIG. 14 illustrates a projectile with a symmetric fluid-filled void with a fluid in the void flowing past a sphere as the sphere moves forward, relative to the projectile body. The projectile's flight location along its trajectory is also depicted to the right of each projectile image.
(15) FIG. 15 depicts a projectile with a symmetric void and a solid spherical mass that flows forward in the cavity and moves out of alignment with the axis of rotation. The projectile's flight location along its trajectory is also depicted to the right of each projectile image.
(16) FIG. 16 shows a projectile with a non-symmetric void with a solid mass sphere off center from the axis of rotation moving forward and off center in flight. The movement accentuates yaw amplitude. The projectile's flight location along its trajectory is also depicted to the right of each projectile image.
(17) FIG. 17 shows a projectile with a symmetric cylindrical cavity and void suspended in a material that liquefies and shifts during the flight. The shift results in the projectile's center of gravity shifting. The projectile's flight location along its trajectory is also depicted to the right of each projectile image.
(18) FIG. 18 shows a projectile with a symmetric cavity and a spheroidal mass where a high density spheroid mass is suspended in a low density material that liquefies after muzzle exit, thereby shifting the center of axis, accentuating yaw amplitude and degrading the projectiles flight ballistics. The projectile's flight location along its trajectory is also depicted to the right of each projectile image.
(19) FIG. 19 is diagram showing the effect of a ricochet on a projectile with a liquid-filled void, according to the invention.
(20) FIG. 20 is a cross-sectional view of a projectile with two cavity voids containing liquids.
(21) FIG. 20A is a cross-sectional view of the projectile of FIG. 20, taken at line A-A, showing one of the voids.
(22) FIG. 20B is a cross-sectional view of the projectile of FIG. 20, taken at line B-B, showing another one of the voids.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
(23) The preferred embodiments of the present invention will now be described with reference to FIGS. 1-20 of the drawings. Identical elements in the various figures are designated with the same reference numerals.
(24) Embodiments of the present invention provide for a projectile that has an excellent ballistic match (flight path) with respect to reference ammunition for the initial stage of free flight. After a set period of transit, a liquefied material in the SRTPs void imparts forces on the projectile that rapidly degrade the SRTP's flight characteristics thus shortening the projectile's maximum range.
(25) FIG. 1 illustrates the effective range of a reference projectile and the maximum range of this projectile.
(26) FIG. 2 illustrates a location along a flight path where instability is induced, shortening the maximum range of a projectile. FIG. 3 further illustrates the resulting ballistic match distance where a SRTP matches a reference ammunition.
(27) FIG. 4 illustrates how Surface Danger Zones (SDZs) are calculated, requiring military and range owners to set aside land adjacent ranges to prevent personal injury or death. The SDZs are extended beyond the range of the ammunition to provide for an additional buffer due to ricochet danger, and metrological and geodesic factors that extend the possible flight path of ammunition in certain circumstances. A reduction in the maximum range of a projectile has a corresponding reduction in the required SDZ that must be established surrounding a range.
(28) FIG. 5 depicts a known aero ballistic de-spinning projectile, together with publically released performance data. This approach is the current prevailing technical approach to produce small caliber Short Range Training Ammunition (SRTA). This approach requires the manufacturer to carve or form a de-spin vane on the nose of the projectile. In some larger caliber weapons, where ammunition feeding mechanisms are guided by the nose of projectile, the vanes may interfere with weapon function. Moreover, there are basic aerodynamic limitations to this approach. The approach also mediately effects the flight of the projectile requiring a user to accept a loose definition of a ballistic match.
(29) FIG. 6 depicts the forces induced on a projectile with a liquid fill. According to the invention a projectile designer may adjust these forces to induce instability in the projectile and provide for a trajectory with a good ballistic match and, thereafter, with a quickly encountering instability, thus shortening the range.
(30) FIG. 7 depicts US Army test results showing spin decay rates induced on a 20 mm projectile containing a liquid cavity.
(31) FIG. 8 depicts the sheer force effect of fluids.
(32) FIG. 9 depicts a simple thermal model of the transfer of heat into a projectile. When traversing in a barrel, the projectile is heated by the hot, expanding propellant gases at the base of the projectile and is also heated by the mechanical friction of the driving band's engagement with the inner diameter of the barrel. Additionally, when a high velocity projectile exits the barrel and enters free flight the air-flow over the projectile's nose and outer surface generates friction forces that heat the projectile's nose cap. In all cases, the heat generated by friction passes through the projectile body, driving band and nose cap to the void to induce a solid-to-liquid change in the void material.
(33) FIG. 10 depicts a cylindrical cavity along the center of spin of a projectile, illustrating how the driving band is positioned to conduct the flow of heat to cause a change in the material.
(34) FIG. 11 depicts a cylindrical cavity in a projectile containing a material of the type used in the present invention.
(35) FIG. 12 depicts a spheroidal cavity containing a material of the type used in the present invention. A designer using a spheroidal cavity can utilize Greenhill's calculations to induce rapid instability where the frequency of rotation of the projectile corresponds to the natural frequency of the liquid in the void.
(36) FIG. 13 depicts partially and a fully filled voids in four different projectiles. FIG. 13 depicts a liquid-filled, symmetric void in a projectile in three stages of flight.
(37) FIGS. 14-18 depict projectiles with both symmetric and non-symmetric voids having a solid mass that is released by a phase change in the surrounding material in the void. This material fixes the position of the solid mass at set-back and at successive times during flight, illustrating the solid mass's movement from a location at the center of spin to an offset location. The movement of the mass from the centerline axial position induces increases yaw that destabilizes the projectile's flight.
(38) FIG. 19 depicts a projectile where the center of rotation of both the liquid and solid are aligned and, upon a ricochet impact, the liquid's axis of spin is no longer aligned with the solid projectile's axis of rotation. The misalignment of the rotational axis induces significant forces on the post ricochet projectile thereby shortening the ricochet danger zone.
(39) The liquid in the projectile void may include a non-Newtonian liquid, and/or a liquid characterized as a Hershel-Buckley, a Bingham and pseudo plastic liquid.
(40) FIGS. 20, 20A and 20B show a projectile in flight with two liquid filled voids. The material and void geometries induce different torques X and Y on the projectile where the twisting forces induced increase the projectile conning motion and increased yaw amplitude. Simultaneously the torque slows the projectile's rotation rate.
(41) There has thus been shown and described a novel ammunition cartridge which fulfills all the objects and advantages sought therefor. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention.
