Within the context of what follows, the short-term basis involves increasing the muzzle velocity/energy of classical gun-type weapon systems as a result of increased calibres and gun-tube lengths. The medium-term basis favours utilising/introducing propellants with high chemical energy potential. The medium/ long-term basis engages the new technological approaches that offer the potential of extensive muzzle velocity/energy improvements due to the proportional use of electrical energy for projectile acceleration, and the long-term basis involves using purely electric accelerators.
Gun-type weapons using conventional propellants have reached a high-performance level as a result of combat efficiency improvements achieved, for example, with the 120mm smoothbore cannon and its ammunition. Further improvements of this weapon system are possible to a certain degree. However, they require considerable technical and financial efforts. And the great demands that will be made on a new tank armament cannot be met in this way.
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Fig 1: Operating principle of the coil gun Click picture for detailed view (61Kb) |
Preliminary technological activities for the development of a new tank gun have been completed successfully with respect to a 140mm calibre version. National and international research programmes for new propulsion technologies indicate a dramatic increase in the performance of tank guns and a new perspective to match future armour requirements. Influencing the conversion of an optimised chemical gun propulsion system by means of electrical energy and modifying its firing gas characteristics may allow full use to be made of the gun tube's characteristics. This could mean a significant increase in weapon system performance that would go far beyond the known and accepted physical boundaries of conventional propulsion.
Even today, test results obtained with purely electric propulsion indicate that there is the potential for improving further the performance of gun-type weapons in the weapon generation after next. Although electrically operated tank guns, that represent the optimum that is thought to be feasible in the field of gun-type weapons, are already in an advanced state of exploration, the problem of providing a sufficiently compact energy supply appears to be almost unsolvable. At least for the present given the effort and resources available to find a solution. However, present approaches and results indicate that a solution to this problem should not be dismissed as being unrealistic. Provided that the present levels of research and development are maintained, possible solutions may be available by 2005 with the field testing of such compact power-supply systems taking place between 2020 and 2025.
The progress made in the development of structured armours such as composite, laminar, active and reactive armours means that there is a considerably higher level of protection and an increased rate of survivability for vehicles protected with these types of armour. The forces required to penetrate these armours have been demonstrated in numerous tests.
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Fig 2: Operating principle of the rail gun Click picture for detailed view (42Kb) |
These terminal ballistic tests have shown that in the case of homogeneous targets an improved terminal effectiveness is achieved by increasing the impact velocity to the order of 2,500 metres per second.
For targets with reactive armour the tests showed that the penetration capacity is also related to the impact velocity of the penetrator. The tests indicate that the protection level of reactive armour can be reduced considerably by increasing the penetrator's impact velocity to the order of 2,500 metres per second. However, velocities of this order cannot be achieved with conventional systems.
The operating principle of the coil gun can be seen in Fig. 1. The gun comprises a number of stationary accelerator coils that are arranged in a tube and successively energised thus creating a magnetic travelling field that induces a frequency in the projectile coil. The magnetic field caused by the current and the magnetic field of the coils generates the accelerating force. The activation of individual coils must be timed to the movement of the projectile.
The operating principle of the rail gun is shown in Fig. 2. Two electrically conductive rails, arranged in parallel and connected to a power source, are located in a circular or rectangular tube and separated from each other by insulators. The projectile moves between the rails and, if so designed, acts as an electrical bridge allowing electrical current to flow from one rail to the projectile and through its base (with the armature consisting of metallic or plasma-generating material) to the other rail that acts as a return lead.
The armature made of plasma-generating material evaporates because of the high megampere currents and forms an electrically conductive plasma. The magnetic field surrounding the rails and the charge carriers flowing through the armature, generate the Lorentz force that accelerates the projectile along the rails.
The high magnetic repelling forces of the current-conducting rails must be absorbed by the external design of the accelerator tube. Therefore conductors and insulators are arranged in external tubes that are made from metal or glass fibre-reinforced material (spiral-wound tubing).
The high megampere current impulses cause rail erosion, particularly at the onset of projectile acceleration and the plasma-generating armature material at the projectile base settles on the rails and insulators in the accelerator tube and may reduce its life.
The electro-thermal gun as shown in Fig.3 consists, in its most simple design, of a conventional gun tube provided with electrical conductors used to supply power to a plasma burner installed in its breech. By applying current to the electrodes of the plasma burner an arc is generated that evaporates a certain material arranged between the electrodes heating it up to form a plasma that, in turn, generates high pressures. The medium used is a material whose gases have a lower molecular weight than conventional powder gases. This means that the gas masses to be accelerated together with the projectile can be reduced and because of this high muzzle velocities can be reached. The projectile is accelerated by the pressure of the electrically heated plasma.
In the development of electric guns the supply and especially the storage of energy will constitute the most critical technological aspect. Energy must be available in sufficient quantities when needed and the power output must be high enough without affecting other systems such as the driving or steering gears.
| STATUS AND PROGNOSIS FOR THE COMPACTING OF ENERGY SUPPLY SYSTEMS | |||
| MDS | SLS | capacitor | |
| 1995 | 80 MJ/t 2.5 MW/t | 14 MJ/t 28 GW/t | 3 MJ7/m3 * |
| feasible by the year 2000 | 150 MJ/t 5-10 MW/t | 100 MJ/t 200 GW/t** | 5 MJ/m3 (US) |
| * available in industry ** high-temperature superconducting material presently available as small samples only | |||
| MDS = magnet-dynamic store | SLS = superconducting coil | ||
Table 1 reflects the present status and makes a prognosis as to the chances of compacting energy supply systems up to the year 2000.
Electro-thermal guns represent a possible interim solution to the requirement for a medium-term increase in performance. They form part of an attempt to improve the performance of conventional guns by increasing considerably muzzle velocity/energy. By the controlled input of electro-thermally converted energy, the burning of a modified nitro-cellulose propellant charge is controlled so that during the initial phase of projectile acceleration a temperature-independent, almost constant propulsion pressure profile is achieved that is in the order of the designed gas pressure. Concurrently the thermo-dynamic characteristics of the firing gas are improved by an additive generated before or during the decomposition of the propellant in the chamber by an electrically initiated reaction.
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Fig 3: Operating principle of the electro-thermal gun Click picture for detailed view (31Kb) |
The results of preliminary tests conducted on the basis of a patent of the Federal Armed Forces Technical Center for Weapons and Ammunition indicate that it may be possible to improve considerably the characteristics of firing gases produced by conventional propellant charges. This may be achieved by adding a specific material before or during the combustion phase. The objective is to change the thermo-chemical processes so that the mean molecular weight of the firing gas is lowered, the explosion heat raised and the firing gas temperature reduced at the same time.
In many countries consideration is also given to hybrid guns because they appear to be an appropriate intermediate solution during the transition phase from conventional to electric guns. It is hoped that a hybrid gun will achieve higher muzzle velocities/energies by providing a conventional, propellant-operated gun with an additional electric acceleration component.
Hybrid guns will require less energy than electric guns. This means that the power supply and integration of the power supply system will be less problematic. Because of the utilisation of electrical and chemical energy for the propulsion of the projectile, hybrid guns require far less energy and so, in the medium term, are more likely to be realised than electric systems.
