Electromagentic projectile launcher

Details Electromagentic projectile launcher Electromagentic projectile launcher

1989-05-31

1990-06-19

Bentley, Stephen C.

Ordnance

Accelerating

124 3, F41B 600

Patent

active

049342436

DESCRIPTION:

BRIEF SUMMARY
The invention relates to an electromagnetic projectile launcher.
Electromagnetic projectile launchers (usually referred to as "railguns") utilise high direct current (DC) to launch projectiles. The basic construction of a railgun (see FIG. 1) comprises a power supply circuit having two generally parallel rails bridged by a projectile armature. In operation the rails are short-circuited until the current level required for launch is achieved whereupon the current is allowed to flow through the projectile armature. The projectile armature is accelerated to launch speed owing to the inter-action of the current in the projectile armature with the magnetic field induced between the rails.
The typical requirements for the switch short circuiting the rails during the current build up are: very low resistance (usually less than 10.mu..OMEGA.); high current bearing capability (usually of the order of 1 MA for periods of 200 ms); capacity for repeated operation; and capacity for current transfer without damage to itself.
In several practical embodiments of such a short-circuiting switch, the switch itself is a subsidiary railgun and is usually referred to as a "railswitch". The railswitch has its own set of rails and has an armature which is tethered during the current build up. Once released, the switch armature is driven, similarly to the projectile armature, to a final position, in which position the current has been switched to flow through the projectile armature.
In one form of railswitch, the switch armature (see FIG. 2, for example) commutates the current across a gap in one of the rails and, in its final, arrested position, remains as a resistive element in the circuit thereby affecting the performance of the railgun.
Other forms of railswitches have been proposed in which the switch armature is eliminated from the circuit in the arrested position thereof. However, in those proposals the projectile armature is itself in the circuit, and thus subject to ohmic heating and electro-motive forces, during the current build up.
All of these forms of railswitch suffer from arcing at the trailing edge of the switch armature causing damage to the switch armature and the rails therefor. This problem arises because a reactance voltage, driven by the elemental inductance of the circuit, is generated during commutation of the current. Although solutions have been proposed to this problem (for example see U.S. Pat. No. 4369692), none have been entirely successful.
It is an object of the present invention to provide an electromagnetic projectile launcher in which at least some of the aforementioned disadvantages are reduced or obviated.
According to the invention, an electromagnetic projectile launcher comprises an electrical power source for supplying direct current, a pair of substantially parallel rails, a first armature and a second, projectile armature. The armatures are located between the rails for movement relative thereto. Each rail has first and second conductive zones which overlap one another in the longitudinal direction of the rails. The first zone of each rail is electrically connected to the source. The first armature is, in a start position, in electrical contact with the first zones and is propellable by electromagnetic forces along the rails thereby to disengage from the first zones. The second armature is propellable by the first armature into electrical contact with the second zones thereby to be propellable by electromagnetic forces along the rails independently of the first armature. The overlap of the first and the second zones extend in the longitudinal direction such that the second armature at least partially contacts said second zones before the first armature completely disengages from said first zones. The edges of the first zones from which the first armature disengages are tapered in a sense to cause current in the first armature to concentrate in the first armature as close to the second armature as possible.
Preferably, the first armature is releasably restrainable in said start position.


REFERENCES:
patent: H000357 (1987-11-01), Howland et al.
patent: 4369692 (1983-01-01), Kemeny

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