Kinetic energy penetrator
From Free net encyclopedia
Image:Obus 501556 fh000022.jpg Image:KineticEnergyProjectile.GIF A kinetic energy penetrator is a type of ammunition which, like a bullet, does not contain explosives, but uses kinetic energy to penetrate the target. The most common modern type of kinetic energy penetrator is known as armour-piercing fin-stabilized discarding sabot (APFSDS), a type of long-rod penetrator (LRP). The term is used for more powerful projectiles than ordinary bullets which have increased armour penetration capabilities due to:
- being fired with a very high muzzle velocity
- concentrating the force on a small impact area without having too small a mass
To produce very high speeds the ammunition is normally composed of a narrow penetrator surrounded by a sabot which expands the diameter to the full barrel width of the firing gun. This allows the pressure of the propellant gases to act on the full-size base and produce rapid acceleration of the round, which is lighter than a full metal round of the same diameter would be. Once the round leaves the barrel the sabot falls off, leaving the penetrator travelling at high speed and with a smaller cross-sectional area, which reduces aerodynamic drag during the flight to the target (see external ballistics and terminal ballistics). This technique was first used in anti-tank guns during World War 2; Germany developed sabots under the name "Treibspiegel" ("Propulsion mirror").
KE-penetrators for modern tanks are commonly just 2-3 centimeters in diameter, and 50-60 centimeters long; as more modern penetrators are developed, their length tends to increase and the diameter to decrease. To maximize the amount of kinetic energy released on the target, the penetrator must be made of a dense material, such as tungsten or depleted uranium (DU). The hardness of the penetrator is of lesser importance. In fact, DU is not particularly hard. An advantage of DU is that it is pyrophoric: the fragments of the penetrator ignite on contact with air. Additionally, DU penetrators exhibit significant adiabatic shear band formation. During impact, fractures along these bands cause the tip of the penetrator to continuously shed material. This erosion maintains the tip's conical shape. Other materials such as unjacketed tungsten tend to deform into a less effective rounded profile.
Few countries use DU ammunition because of its cost and environmental effects. Battle sites where DU rounds have been used typically have residual uranium dust in and around battle-damaged vehicles. This dust is mildly radioactive and highly toxic, thus the lingering effects of it can create public health problems. It is disputed whether dust from spent DU rounds is linked to cancer and other illnesses.
Because a long, thin rod is aerodynamically unstable and tends to tumble in flight, two different approaches have been used to stabilise them. The oldest is rifling, which spins the round. For projectiles that are spherical or oblong, rifling works well. However, once the projectile's length is more than 6 or 7 times its diameter, rifling is less effective so an alternative approach is to add fins like those of an arrow to the base and fire the round from a smooth-bore gun. This is the approach commonly used in recent Russian, German and US guns. Rifling decreases the penetration capability of projectiles with high length-to-diameter ratios, so to make APFSDS work with a rifled barrel a bearing sleeve system is needed on the projectile to prevent excessive spin of the penetrator.
Typical velocities of APFSDS rounds vary between maufactors and muzzle length/types. As a typical example, the american General Dynamics KEW-A1 has a muzzle velocity of 1740 m/s. APFSDS rounds generally operate in the vicinity of 1400 to 1850 m/s. The sabots also travel at a huge velocity and upon separation may continue for many hundreds of metres at speeds lethal to light vehicles and troops before being slowed by the increased drag they experience.
It is generally accepted that KE-penetrators are the most effective ammunition for penetrating armour. Two other common types of shell are HEAT and HESH. They are widely deployed but not generally against armour (for example, HESH ammunition is more effective at destroying buildings and light-skinned vehicles).
The counterpart of APFSDS in rifle ammunition is the saboted flechette. A rifle firing flechettes, the Special Purpose Individual Weapon, was under development for the US Army, but the project was abandoned.