thedrifter
08-11-04, 09:55 AM
LOTS AND LOTS OF GUNS: Future Tank Gun Systems
http://www.*************/pics/SoldierTech_TankGun1.jpg
Man portable and vehicle-launched ATGMs (Anti Tank Guided Missiles) may be the most prolific anti-tank weapon on the modern armored battlefield, but the kinetic energy (KE) penetrator remains the benchmark by which armor protection is evaluated. Unjammable, unaffected by explosive reactive armor, relatively inexpensive and brutally efficient, the KE penetrator drives armor development. But in the race to keep up with the Joneses, how do you build a better penetrator? In short, is there a future for a bigger, better gun in our tank forces? Some modern technologies may provide the answer.
Showcasing the Sabot
Since KE rounds are completely dependent on mass and velocity to penetrate armor, you can increase armor penetration in essentially two ways: make the penetrator heavier, or make them faster. Up through World War Two, making penetrators larger and increasing velocity were pretty much one and the same, since AT projectiles up to that point were "full sized" -- what left the tube was what hit the target. However, as armor thickness increased, AT ammunition research revealed that smaller "subcaliber" projectiles or penetrators achieved higher velocities, with more kinetic energy, than the larger, "full size" projectiles fired out of the same cannon. Not only were the smaller projectiles more aerodynamically efficient (with less surface area and atmospheric drag), but because their contact "footprint" on the target surface area was smaller, their energy was concentrated on a smaller portion of the target when they hit, for better penetration. Thus was born the SABOT round.
For the last 50 years the sub-caliber "Sabot" KE penetrator, made from a variety of metals, from steel to tungsten to depleted uranium, has been the standard design for KE ammunition, and given its advantages (low surface area, high energy transfer) this is unlikely to change in the foreseeable future. However, with tanks now sporting guns in the 120-125mm range, what options are left in improving KE penetrator performance? One obvious disadvantage to simply making a larger tank gun is that bigger is, well bigger. As the size of cannon projectiles has gone up, the number of rounds an individual tank can carry has gone down; a WWII 75mm Sherman tank could carry over 90 main gun rounds, while the 105mm M1 could carry 55, and the 120mm M1A1 can carry only 40. Clearly there comes a point of diminishing returns on tank gun development. Cannon diameter and projectile sizes can only get so large before the size of the projectile limits the amount of ammunition carried, making vehicle combat ineffective. So while the simple answer may be to go with a bigger gun, because it has the very real advantage of being available now, this may not be the best answer.
Electromagnetic Ecstasy
One option is to abandon the "expanding gas" (i.e. solid or liquid propellant based) principle altogether, and develop electromagnetic (EM) guns. EM guns have the advantage of being able to fire significantly smaller projectiles (several grams as opposed to several kilograms) at much higher velocities for correspondingly greater kinetic energy. In addition, because of the smaller projectile size, more projectiles could be carried in a given space than in the case of current propellant based ammunition, and because the ammunition is completely inert, and has no propellant charge, it is safer to handle and store.
EM guns come in two varieties, continual (or linear) accelerators called rail guns, and pulse accelerators, called coil guns. Essentially two electrically charged rails, rail guns use the repulsive effect of the two magnetic fields created by the charged rails to continuously accelerate a conductive billet (called an armature) down the barrel. Because the rail gun is accelerating the armature, a non-metallic (plastic or ceramic) projectile can be used as the actual penetrator. Coil guns, as the name implies, are made up of a series of individual EM coils wrapped around a non-conductive barrel. The coil gun accelerates the projectile, which in this case must be made of a ferromagnetic (affected by magnetic fields) but non-magnatizable metal, by energizing the coils individually to attract the projectile to the center of each coil. As the projectile is pulled into the center of each coi,l the electrical current is cut and the next coil in the sequence is energized, accelerating the projectile down the barrel. Both types of EM cannon offer significant improvements in KE over current expanding gas weapons but, the technologies needed to move these weapons from the laboratory onto the battlefield may not become available for a while.
Propellant Power
Another option is to utilize electricity to improve the effectiveness of existing solid propellants. One of the limiting factors in expanding gas propellants is the rate at which they are ignited, and the speed at which the ignited propellant releases energy. In a conventional tank round the propellant is ignited at the rear of the projectile (where the primer is) and burns forward. As the propellant burns, energy is released, which drives the projectile forward. Unfortunately, chamber pressure is still building as the projectile leaves the barrel, which means that a large amount of usable energy is wasted.
http://www.*************/pics/SoldierTech_TankGun4.jpg
Schematic of a coil gun (graphic from global-defence.com).
The possible solution? The Electro-Thermal Chemical (ETC) process, where electricity is used increase not only the propagation rate of propellant combustion, but increase the total amount of energy released by the propellant. Unlike the stand-alone EM technology, ETC is a process that can be integrated into existing weapon systems. What's more, ETC is completely scalable. You can apply a relatively low amount of electrical energy (less than 100 kilojoules) to speed up conventional propellant ignition (which would cause an earlier peak in chamber pressure, allowing more expanding gas energy to be used to accelerate the projectile). Or at the other end of the spectrum, you can apply very large amounts of energy (5 mega joules) for tailor-made propellants, converting them to a high energy plasma rather than burning in the conventional sense -- this results in even higher chamber pressures than through electrically charged conventional propellants.
Though not as technically complex as EM technology, ETC has a number of challenges to overcome. Since it is a dual propellant technology reduction in component size, in both the conventional propellant and the electrical charging components, will need to be developed. In addition, simply developing a small enough electrical power source to provide the high-energy pulses necessary that will fit in tactical vehicles is still several years away. As such, it is not anticipated that this technology will be ready for evaluation in 2007 at the earliest.
Finally, there is the bigger is better option; build a bigger conventional cannon. Several countries, the United States and Germany among them, are looking into developing 140mm conventional cannons. Conventional munition development has the advantage of building off of well-established and currently available technology. In addition, in computer modeling studies, a 140mm cannon will deliver as much kinetic energy as would a EM cannon, but available half a century sooner.
Conventional gun technology has gone about as far as it can go (in terms of cannon size). As such, if making the bullets larger is impractical, then a means must be developed to make projectiles faster (in a sense boosting the v over the m in the kinetic energy equation Ek=˝(mv2)). To this end, research will probably focus on making more efficient and more powerful propellants. In the short term this means developing ETC technology.
continued........
http://www.*************/pics/SoldierTech_TankGun1.jpg
Man portable and vehicle-launched ATGMs (Anti Tank Guided Missiles) may be the most prolific anti-tank weapon on the modern armored battlefield, but the kinetic energy (KE) penetrator remains the benchmark by which armor protection is evaluated. Unjammable, unaffected by explosive reactive armor, relatively inexpensive and brutally efficient, the KE penetrator drives armor development. But in the race to keep up with the Joneses, how do you build a better penetrator? In short, is there a future for a bigger, better gun in our tank forces? Some modern technologies may provide the answer.
Showcasing the Sabot
Since KE rounds are completely dependent on mass and velocity to penetrate armor, you can increase armor penetration in essentially two ways: make the penetrator heavier, or make them faster. Up through World War Two, making penetrators larger and increasing velocity were pretty much one and the same, since AT projectiles up to that point were "full sized" -- what left the tube was what hit the target. However, as armor thickness increased, AT ammunition research revealed that smaller "subcaliber" projectiles or penetrators achieved higher velocities, with more kinetic energy, than the larger, "full size" projectiles fired out of the same cannon. Not only were the smaller projectiles more aerodynamically efficient (with less surface area and atmospheric drag), but because their contact "footprint" on the target surface area was smaller, their energy was concentrated on a smaller portion of the target when they hit, for better penetration. Thus was born the SABOT round.
For the last 50 years the sub-caliber "Sabot" KE penetrator, made from a variety of metals, from steel to tungsten to depleted uranium, has been the standard design for KE ammunition, and given its advantages (low surface area, high energy transfer) this is unlikely to change in the foreseeable future. However, with tanks now sporting guns in the 120-125mm range, what options are left in improving KE penetrator performance? One obvious disadvantage to simply making a larger tank gun is that bigger is, well bigger. As the size of cannon projectiles has gone up, the number of rounds an individual tank can carry has gone down; a WWII 75mm Sherman tank could carry over 90 main gun rounds, while the 105mm M1 could carry 55, and the 120mm M1A1 can carry only 40. Clearly there comes a point of diminishing returns on tank gun development. Cannon diameter and projectile sizes can only get so large before the size of the projectile limits the amount of ammunition carried, making vehicle combat ineffective. So while the simple answer may be to go with a bigger gun, because it has the very real advantage of being available now, this may not be the best answer.
Electromagnetic Ecstasy
One option is to abandon the "expanding gas" (i.e. solid or liquid propellant based) principle altogether, and develop electromagnetic (EM) guns. EM guns have the advantage of being able to fire significantly smaller projectiles (several grams as opposed to several kilograms) at much higher velocities for correspondingly greater kinetic energy. In addition, because of the smaller projectile size, more projectiles could be carried in a given space than in the case of current propellant based ammunition, and because the ammunition is completely inert, and has no propellant charge, it is safer to handle and store.
EM guns come in two varieties, continual (or linear) accelerators called rail guns, and pulse accelerators, called coil guns. Essentially two electrically charged rails, rail guns use the repulsive effect of the two magnetic fields created by the charged rails to continuously accelerate a conductive billet (called an armature) down the barrel. Because the rail gun is accelerating the armature, a non-metallic (plastic or ceramic) projectile can be used as the actual penetrator. Coil guns, as the name implies, are made up of a series of individual EM coils wrapped around a non-conductive barrel. The coil gun accelerates the projectile, which in this case must be made of a ferromagnetic (affected by magnetic fields) but non-magnatizable metal, by energizing the coils individually to attract the projectile to the center of each coil. As the projectile is pulled into the center of each coi,l the electrical current is cut and the next coil in the sequence is energized, accelerating the projectile down the barrel. Both types of EM cannon offer significant improvements in KE over current expanding gas weapons but, the technologies needed to move these weapons from the laboratory onto the battlefield may not become available for a while.
Propellant Power
Another option is to utilize electricity to improve the effectiveness of existing solid propellants. One of the limiting factors in expanding gas propellants is the rate at which they are ignited, and the speed at which the ignited propellant releases energy. In a conventional tank round the propellant is ignited at the rear of the projectile (where the primer is) and burns forward. As the propellant burns, energy is released, which drives the projectile forward. Unfortunately, chamber pressure is still building as the projectile leaves the barrel, which means that a large amount of usable energy is wasted.
http://www.*************/pics/SoldierTech_TankGun4.jpg
Schematic of a coil gun (graphic from global-defence.com).
The possible solution? The Electro-Thermal Chemical (ETC) process, where electricity is used increase not only the propagation rate of propellant combustion, but increase the total amount of energy released by the propellant. Unlike the stand-alone EM technology, ETC is a process that can be integrated into existing weapon systems. What's more, ETC is completely scalable. You can apply a relatively low amount of electrical energy (less than 100 kilojoules) to speed up conventional propellant ignition (which would cause an earlier peak in chamber pressure, allowing more expanding gas energy to be used to accelerate the projectile). Or at the other end of the spectrum, you can apply very large amounts of energy (5 mega joules) for tailor-made propellants, converting them to a high energy plasma rather than burning in the conventional sense -- this results in even higher chamber pressures than through electrically charged conventional propellants.
Though not as technically complex as EM technology, ETC has a number of challenges to overcome. Since it is a dual propellant technology reduction in component size, in both the conventional propellant and the electrical charging components, will need to be developed. In addition, simply developing a small enough electrical power source to provide the high-energy pulses necessary that will fit in tactical vehicles is still several years away. As such, it is not anticipated that this technology will be ready for evaluation in 2007 at the earliest.
Finally, there is the bigger is better option; build a bigger conventional cannon. Several countries, the United States and Germany among them, are looking into developing 140mm conventional cannons. Conventional munition development has the advantage of building off of well-established and currently available technology. In addition, in computer modeling studies, a 140mm cannon will deliver as much kinetic energy as would a EM cannon, but available half a century sooner.
Conventional gun technology has gone about as far as it can go (in terms of cannon size). As such, if making the bullets larger is impractical, then a means must be developed to make projectiles faster (in a sense boosting the v over the m in the kinetic energy equation Ek=˝(mv2)). To this end, research will probably focus on making more efficient and more powerful propellants. In the short term this means developing ETC technology.
continued........