Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F42—AMMUNITION; BLASTING
  • F42B—EXPLOSIVE CHARGES, e.g. FOR BLASTING, FIREWORKS, AMMUNITION
  • F42B8/00—Practice or training ammunition
  • F42B8/02—Cartridges
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F42—AMMUNITION; BLASTING
  • F42B—EXPLOSIVE CHARGES, e.g. FOR BLASTING, FIREWORKS, AMMUNITION
  • F42B10/00—Means for influencing, e.g. improving, the aerodynamic properties of projectiles or missiles; Arrangements on projectiles or missiles for stabilising, steering, range-reducing, range-increasing or fall-retarding
  • F42B10/32—Range-reducing or range-increasing arrangements; Fall-retarding means
  • F42B10/48—Range-reducing, destabilising or braking arrangements, e.g. impact-braking arrangements; Fall-retarding means, e.g. balloons, rockets for braking or fall-retarding

Definitions

• Urbanization surrounding military training areas worldwide is changing the context and parameters of military training and the military utilization of land set aside for training.
• SDZs Surface Danger Zones
• SDZ Surface Danger Zone
• SRTP Short Range Training Projectiles
• SRTA Short Range Training Ammunition
• a principal objective of the present invention is to provide a training ammunition cartridge where the flight path of its projectile initially matches the flight path of a reference projectile and subsequently loses stable flight characteristics, thus shortening the maximum range of the projectile.
• the shortened maximum range can reduce the Surface Danger Zone both at the end and aside of the firing range.
• an ammunition cartridge with a projectile (a) with a void, and (b) a liquid contained in the void (which may be coupled with a solid mass that shifts) which, after barrel exit, acts on a projectile bodyand induces further, additional forces on the projectile that, after a period of stable ballistic flight, destabilize the projectile’s flight and shortens its flight.
• the projectiles according to the invention are designed to initially exhibit a very close match to
• the solid material in the void induces a combination of forces that quickly destabilize the projectiles’ flight.
• the shortening of the maximum range of the projectiles allows for a corresponding reduction in the surface danger zone surrounding a firing range. Militaries and owners of private ranges can therefore use larger caliber ammunition on ranges originally developed for small caliber ammunition.
• the void geometry of the SRTA projectile induces forces on the projectile accentuating spin decay and yaw. It is also possible to configure the geometry to shift the center of gravity of the projectile to further accentuate the projectile’s yaw amplitude and frequency, thereby further degrading the flight stability.
• the selection of the void geometry identifies what design equations to utilize in
• Liquids in a Void It is known that liquids generally exhibit nine hundred times more resistance to motion when compared to that of a gas. Liquids may also exhibit a resonance that can influence objects in flight. Prior work has shown that configurations with of a projectile’s liquid filled void often had an infinite set of initial boundary conditions and projectiles have frequently been troublesomely susceptible to picking up resonances which have imparted un-predictable forces that act on the projectile in flight. Early designers of liquid fuel rockets went to extensive efforts to understand and manage the complicated characteristics exhibited by liquid fuels in the rockets in flight.
• a projectile Like a spinning top, a projectile’s gyroscopic stability is achieved by optimizing the mass rotating around center of gravity and the axis of rotation.
• a designer can, in selecting materials and geometry, shift the solid mass in a projectile to further reduce a training projectile’s gyroscopic stability, further shortening its range.
• AMC U.S. Army Material Command
• the projectile exits the muzzle with six degrees of flight freedom acting as a solid.
• the present invention allows a designer (1) to use the Miles equation to identify a liquid-filled projectile that will initially have stable flight and where forces in the projectile subsequently destabilize the flight, or (2) to firmly establish the initial boundary conditions of barrel exit by using a material that transitions from solid to liquid after set-back.
• the change from a solid to liquid may be accomplished either by a heat-induced phase change or by the use of a Non-Newtonian liquid or dilitant.
• the liquid in the void induces forces that destabilize the projectile’s flight after an initial match period with a reference projectile.
• the material contained in the void is a solid when it transits the barrel. This solid does not retain resonance frequencies as are generally induced in liquids and which are known to be detrimental when liquid-filled ammunition exits the barrel. According to the invention, however, the material rapidly liquefies after barrel exit and, interacting with the void geometry and solid projectile body, reliably increases the yaw amplitude and frequency of the projectile.
• a selected liquid may induce desired or undesired
• a selected liquid may introduce a stabilizing damping effect.
• the present invention comprises a projectile containing a void and a select material contained in the void.
• the material is a solid or a non-Newtonian fluid at set-back that liquefies after set-back and muzzle (barrel) exit.
• the liquefied material initiates a combination of forces that induce instability in the projectile.
• Shear thickening liquids exhibit increasing viscosities with increased shear stress.
• Shear thinning liquids exhibit decreased viscosity as the shear stress is decreased. Thixotropic liquids become less viscous when shaken, agitated or otherwise stressed. Dilatant or shear thickening behavior is typically observed in fluids with a high concentration of small, solid particulate suspended within a liquid. Behaving like a true fluid under low shear stress conditions, dilatants then transition to a solid-like condition when a greater shear stress or force is applied. The greater the force (shear) applied to a dilatant material, the more
• the projectile can utilize the heat imparted to its driving band as it progresses through the barrel and/or it can harvest heat from the pyrotechnic propellant, transferring the heat to the material in the void.
• the resulting increase in temperature flows from the driving band and the propellant through the projectile body into the void.
• the heated material in the void undergoes a phase change from solid to liquid.
• the liquefied material in the void induces forces on the projectile in flight.
• high velocity projectiles may harvest heat in flight in the vicinity of the nose. It is well known that air friction encountered by high velocity projectiles in flight transfers significant heat into the projectile s nose assembly. Therefore, in certain configurations, in is advantageous to locate a void with a liquid in the void harvesting the friction heat to induce a phase change in the material housed in the void.
• the void can be filled with a non-Newtonian fluid which acts as a solid when exposed to high acceleration forces but exhibits the characteristics of a normal liquid in a reduced acceleration environment.
• the high G-forces acting on the non-Newtonian fluid cause the fluid to act as a solid mass.
• the non-Newtonian material acts as a liquid. This allows the design to establish a fixed set of barrel exit conditions that closely match those of a reference projectile and subsequently induce instability that shortens the projectiles flight path. In setting repeatable boundary
• a projectile is more susceptible to flight destabilization.
• Cavity (Void) Form and Types After selecting a void geometry, a solid-to-projectile mass ratio, and a liquid fill, the designer can use corresponding equations for stability and instability. Again, the selection of a material for post set-back liquefaction and the
• Table 1 identifies stability and instability formulas for corresponding void geometries. One may categorize voids and approaches with reference to their symmetry (or lack of symmetry) about the projectile’s axis of spin. Mathematical equations that are verified by observation correspond to each approach. Table 1 Void Geometry and Liquid Payload Induced Instability
• Cylindrical cavities are useful when producing ammunition since most projectiles have a basic cylindrical form with the cylinder capped by a conical nose. Forming processes for cup- shaped forms have long been a cost effective method of metal forming in ammunition manufacture. Therefore, it is practical to produce cylindrical voids during ammunition production.
• Stewartson s equations, published in 1959, provided mathematical solutions to induce instability when a liquid is housed in a cylindrical cavity. The set of equations allows designers to design ammunition that induces predictable instability.
• Karpov s publication of “Dynamics of Liquid Filled Shell: Resonances in Modified Cylindrical Cavities” was published in 1966 and added to this body of work.
• Spheroidal Cavities The stability and instability problem for a filled
• Non-symmetric cavities While the equations for non-symmetric cavities have less confirmatory experimentation, the basic formulas provide for a method to construct voids the induce forces to destabilize the projectile upon liquefaction of the void material. A non- symmetric cavity may be designed to quickly shift the center of gravity away from the axis of rotation.
• Laminar and Non-Laminar (turbulent flow) of Liquids The designer can modify the internal geometry and surface of the void to induce either laminar or non-laminar flow of the liquid in the void. This flow increases liquid-to-solid
• Center of Gravity Shifts It is, in certain circumstances, advantageous to select material combinations and geometry that induce center of gravity shifts after a short period of free flight. Center of gravity shifts, off-center from the axis of rotation, accentuate yaw amplitude and degrade the projectile’s flight stability.
• Figure 1 illustrates a typical ammunition projectile trajectory having an effective range and a maximum range.
• Figure 2 illustrates a Short range Training Projectile (SRTP) trajectory where forces imparted on the projectile have shortened the maximum range of this ammunition.
• Figure 3 illustrates the distance where an SRTP will match the flight profile of reference ammunition which may be a ball or war-shot ammunition.
• Figure 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.
• Figure 5 shows a typical aerodynamic de-spinner projectile which is currently the prevailing approach to the design of SRTPs.
• Figures 5a and 5b are graphs of residual velocity vs. range for such a projectile.
• Figure 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.
• Figures 7a and 7b are extracts from AMC Pamphlet 706-165 (Distribution A for Public Release) depicting the spin decay of a 20 mm projectile with a 70% liquid fill.
• Figure 8 depicts the liquid characteristics of various types of liquids when exposed to shear forces.
• Figure 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
• Figure 10 is a cutaway view of a projectile with a
• Figure 11 is a phantom view of a projectile with a
• Figure 12 is a phantom view of a projectile with a
• Figure 13 depicts cross-sectional views of four different projectiles with filled and partially filled voids.
• Figure 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.
• Figure 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.
• Figure 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.
• Figure 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.
• Figure 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.
• FIG. 19 is diagram showing the effect of a ricochet on a projectile with a liquid-filled void, according to the
• Figure 20 illustrates a projectile in flight with a two- cavity void containing liquids.
• FIG. 1 illustrates the effective range of a reference projectile and the maximum range of this projectile.
• Figure 2 illustrates a location along a flight path where instability is induced, shortening the maximum range of a projectile.
• Figure 3 further illustrates the resulting
• 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.
• SDZs are extended beyond the range of the ammunition to provide for an additional buffer due to ricochet danger, and
• a reduction in the maximum range of a projectile has a corresponding reduction in the required SDZ that must be established surrounding a range.
• Figure 5 depicts a known aero-ballistic de-spinning
• Figure 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.
• Figure 7 depicts US Army test results showing spin decay rates induced on a 20mm projectile containing a liquid cavity.
• Figure 8 depicts the sheer force effect of fluids.
• Figure 9 depicts a simple thermal model of the transfer of heat into a projectile.
• the 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
• Figure 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.
• Figure 11 depicts a cylindrical cavity in a projectile containing a material of the type used in the present invention.
• Figure 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.
• Figure 13 depicts partially and a fully filled voids in four different projectiles.
• Figure 13 depicts a liquid-filled, symmetric void in a projectile in three stages of flight.
• Figures 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
• 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.
• 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.
• Figure 20 illustrates a projectile in flight with two liquid filled voids.

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• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Fluid Mechanics (AREA)
• Aiming, Guidance, Guns With A Light Source, Armor, Camouflage, And Targets (AREA)

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• 2015
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