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 | Effect of flyer plate velocity and rate of crater expansion
Author : Yadav, H. S.
Source : Defence Science Journal ; Vol:52(4) ; 2002 ; pp 429-438
Subject : 623.4 Armaments and Ballistics;623 Military Science and Engineering
Keywords : Explosive reactive armour ;Shaped charge jet ;Warheads ;Precision shaped charge warhead ;Target penetration ;Flyer plate velocity ;Crater
Abstract : "The reduction in the penetration power of the jet due to its interaction with an obliquely moving plate of explosive reactive armour (ERA) sandwich has been studied. It has been assumed that the length of the jet, which gets disturbed due to its interaction with the edge of the hole made by the impact of the tip of the jet when the plate was stationary, does not contribute to penetration in the target. The jet length, which comes out of the hole undisturbed, penetrates the target. This length of the jet has been calculated considering the variation in plate velocity and rate of expansion of the crater in the plate with time. The time taken by the jet to shift its position from the centre to the wall of the hole has been determined for different velocities of the sandwich plate and varying expansion rates of the hole produced by the jet in the plate, corresponding to a constant velocity of the jet. This analysis has been used to obtain the length of undisturbed jet coming out of the hole and its penetration in the target. The present study establishes the effect of the plate velocity and rate of crater expansion on the performance of the ERA. It has been found that both these parameters affect the performance of the ERA, and the metal plates of lower density and higher strength make the ERA more effective. " |
| | Plastic Guidance Fins for Long Rod Projectiles
Author : Bundy, Mark L.
Source : Defence Science Journal ; Vol:47(4) ; 1997 ; pp 473-485
Subject : 533.6 Aerodynamics;623.4.021 Targets;623.4 Armaments and Ballistics
Keywords : Solid propellant ;Projectiles;Target penetration;Aerodynamic drag;Kinetic energy (KE) penetrators
Abstract : Projectile tail fins on long rod kinetic energy (KE) penetrators serve the same purpose as fletchings (feathers) on an arrow, namely, they help align the projectile axis with its velocity vector. This reduces the projectile's yaw and hence reduces its aerodynamic drag. In addition, a low yaw angle at target impact helps to maximise the projectile's target penetration. It is typical for projectiles to exit the gun muzzle and enter free flight at some ndn-zero yaw angle. Aerodynamic forces acting on yawed tail fins create a stabilising torque about the projectile's centre of gravity (CG). This torque can be increased by making the fin material lighter. Most conventional long rod penetrators fired from high performance guns have tail fins made from aluminium. However, aluminium can undergo catastrophic oxidation (rapid burning) in-bore. Coating aluminium with Al/sub 2/O/sub 3/ {hardcoat) prevents ignition of the substrate, provided solid propellant grain impacts do not chip the brittle hardcoat off the surface. Plastic is lighter than aluminium and less exothermic when oxidized. Therefore, other factors aside, it is conceivable that plastic fins could increase projectile stability while incurring less thermal erosion than aluminium. However, thermal loads are not the only concern when considering plastic as an alternative tail fin material. The mechanical strength of plastic is also a critical factor. This paper discusses some of the successes and failures of plastic fins, at least relatively thin fins, for use as KE stabilisers. |
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