GB2217820A

GB2217820A - Electrothermal cannon

Info

Publication number: GB2217820A
Application number: GB8908950A
Authority: GB
Inventors: Rheinmetall Gmbh; Tzn Forschungs-Und Entwic Gmbh; Wolfram Witt; Markus Loeffler
Original assignee: Tzn Forschung & Entwicklung; Rheinmetall GmbH
Current assignee: Tzn Forschung & Entwicklung
Priority date: 1988-04-28
Filing date: 1989-04-20
Publication date: 1989-11-01
Anticipated expiration: 2009-04-20
Also published as: GB2217820B; DE3814332A1; FR2630820B1; DE3814332C2; FR2630820A1; GB8908950D0

Description

n z 2 17 8 2 0 P1 0 1 - T ITLE 40588/wsq Apparatus for the Acceleration of

Projectiles This invention relates to an apparatus for the acceleration of projectiles which are located in a tube closed at one end using ah electrically heated plasma.

As is known from US 2899864 firing devices based on the electrothermal principle make use of the conversion of electromagnetic energy into thermal energy. In such firing devices the hot plasma required for the propulsion 6f the projectile is produced and heated by the aid of an are burning between fixed electrodes. The fixed electrodes are either located on the breech side or distributed along the tube.

Where the electrodes are situated on the breech side the gas pressure occurring on the base of the projectile first rises to a very high level, limited by the strength properties of the are combustion chamber, tube and projectire. During the acceleration of the projectile, however, this pressure very rapidly falls back again as a result of the flow processes in the tube. In this case the speed of the projectile at the end of the tube is distinctly lower than that which could have been reached with an acceleration at constant pressure.

- 2 40588/wsq If the electrodes are distributed over the length of the tube this drawback is avoided. In this case the pressure on the base of the projectile can be kept almost constant by the continuous addition of controlled electrical discharges and as a result of the consequent pressure on the said base. This system nevertheless suffers from high cost of the technical equipment involved in the multi-part tube and the supply of electrical power.

One object of this invention is to provide an apparatus which is simple to construct and which will 6nable the pressure on the base of the projectile to be kept almost constant.

According to this invention there is provided apparatus for accelerating a projectile located in a tube closed at one end using an electrically heated plasma, with two electrodes between which an arc burns which heats the plasma, the first of the two electrodes being located on the breech side, wherein the second electrode is formed by the base of the projectile.

This invention is further described and illustrated with reference to embodiments shown in the drawings by way of examples. In the drawings:

Figure 1 shows a first example of an electrothermal apparatus according to the invention, h Y 11; 40588/wsq Figure 2 shows an example according to Figure 1 at the start of the projectile acceleration, Figure 3 shows the acceleration apparatus ac7cording to Figure 1 at a later time in the projectile acceleration, Figures 4a and 4b show an example of a projectile with a wire interception, Figure 5 shows a further example of an electrothermal apparatus according to the invention, and and 7 show the apparatus of Figure 5 at two different times.

Figures 6 Referring to the drawings, Figures 1 to 3 show the operating principle of the electrothermal firing apparatus according to the invention. The firing apparatus consists of a tube 1 (of about 4m in length and with a calibre of 50mm) of a mechanically very strong material of low electrical conductivity (such as glass fibre reinforced plastic) and an electrode 2 at the breech end as well as an annular contact 3 at the muzzle end. The electrode 2 and the contact 3 are flanged to the tube 1 with screw connections 4 and face contact sealing rings 5. The tube 1 is provided with a removable and replaceable tube 6 of insulating material. The tube 1 contains a cup shaped projectile 7 of 40588/wsq electrically conductive material. The breech side of the projectile 7 is fitted with an electrically nonconductive casing 8 filled with a comparatively nonconductive liquid or pulverless material 9 with a high proportion of hydrogen (such as water, oil, lithium hydride, polyethylene powder), in order to produce a gas of low molecular weight.

The projectile 7 is connected to the electrode 2 on the breech side by a thin electrically conductive wire 10 (for example of aluminium or lithium with a diameter of 1/5 mm) passing through the material 9 of the casing 8.

The projectile 7 is connected with the contact 3 on the muzzle side by an electrically conductive wire (for example of copper with a diameter of 2. 5 mm) affixed to the base of a cup shapedrecess 12 of a projectile 7. The electrode 2 and the contact 3 are connected with the power supply system consisting of a voltage source 12 with capacitive properties, a connecting switch 13, a coil 14 and a short circuit switch 15. Under certain conditions, as later described, the short circuit switch 15 can be omitted.

Figure 2 shows the arrangement of the system at the commencement of the acceleration process. The voltage source 12 charged up to voltage U drives a high current (50 kA) through the coil 14, the contact 3, the wire 11, 5 V 40588/wsq the projectile 7, the wire 10 and the electrode 2 after the switch 13 has been closed. In this process a thin wire 10 is rapidly heated up and finally evaporates, so that an are 16 is struck between the electrode 2 and the projectile base 70, heating and evaporating the filling material 9. The resulting pressure drives the projectile 7 in the direction of the annular contact 3 on the muzzle side.

Figure 3 shows the arrangement of the system at a later moment in the acceleration process. After the current i had reached the maximum the short circuit switch 15 was closed, so that the current is now driven farther through the system through the coil 14 and the electromagnetic energy can no longer flow back into the capacitative voltage source.

The closure of the short circuit switch 15 can be dispensed with, if the withdrawal of electromagnetic energy from the current circuit through the intensively cooled are is so great that the electromagnetic energy i already consumed before it can oscillate back to the capacitative voltage source.

The are 16 burning between the base 70 of the projectile 7 and the electrode 2 on the breech side continues to heat the evaporated filling material 9, i which process the length is adapted to the accelerati - 6 40588/wsq 11 distance covered by the projectile. In addition, material is evaporated from the tube 6 of insulating material. The gas container behind the projectile 7 is thus continuously heated over the entire length and the gas pressure thus kept almost constant, as regards space and time, over the entire gas container mentioned. The wire 11 situated in front of the projectile 7 is intercepted in the cup shaped recess 17 in the projectile 7 and sheared off after the said projectile 7 emerges from the tube 1.

With suitable projectile 7 having a mass of between 200 and 300 g, speeds of between 3 and 4 km/s can be.attained at the point in which they leave the muzzle.

In order to ensure that the position or stability of the cup shaped projectile will not be effected by the shearing of the wire and the comparatively high air resistance of the said projectile after it emerges from the muzzle the projectile can in practice be accelerated, as shown in Figure 4a and 4b, by the aid of the sabot 40.

In the example shown the sabot 40 consists of two halves which open after the aerodynamically shaped projectile 41 has left the mouth, thus releasing it. During the acceleration process the wire 42 is collected in one of the two chambers 43 and 44 of the sabot 40. In order to prevent the shearing of the wire 42, if I v 1 40588/wsq necessary, the said wire 42 can be so dimensioned that it evaporates explosively shortly before emergence from the muzzle.

In order to make it unnecessary for the wire 42 to be connected by hand with the contact 3 on the muzzle side (of Figure 1) before each firing operation, the said wire 42 can also-be fired by means of a small firing device from the projectile to the electrode on the muzzle side (of the following description referring to Figure 5). In order to ensure that the wire does not have to be intercepted in every acceleration process, furthermore, it can be so designed that immediately after the commencement of the acceleration process it will evaporate and be replaced by a conductive plasma. An example of the aforementioned small firing device is illustrated in Figure 5.

This system differs from the one previously described insofar as the cup shaped recess is replaced by a small rocket 19 on the nose of projectile 18 to be accelerated. A small quantity of pulverous propellant charge is provided inside the rocket 19. The rocket 19 is fitted with a wire container 190 in which the wire 20 is provided.

To initiate the acceleration process of the projectile 7 the small rocket 19 is fired to the electrode 3 situated on the muzzle side by detonating the pulverous propellant charge by means, for instance, of an electrical detonating device (not shown in Figure 5). the speed of the rocket may be 10 m/s.

The wire 20 is drawn from the projectile 18 to the contact 3 on the mouth side (ef Figure 6 and 7). After the small rocket 19 has left the tube 1 and the wire 30 has reached and touched the contact 3 on the mouth side, the current is caused to flow. The rapidly rising current i causes rapid heating of the two wires 10 and 20 and finally their evaporation. The arcs 22 and 23 s'hown in Figure 7 are struck between the electrode 2 on the breech side and the projectile 18 and between the said projectile 18 and the contact 3 on the muzzle side. The pressure in the space between the projectile 18 and the electrode 2 on tie breech side is considerably greater than between the projectile 18 and the contact 3 on the muzzle side, since the heated gas present in the gas container in front of the projectile can escape from the tube. The projectile 18 is therefore accelerated in the direction of the muzzle of the tube.

The process of coupling the energy present in electromagnetic form into the tube 1 likewise mainly takes place in the volume of gas between the projectile 18 and the electrode 2, since in this position the arc 22 11 1 1 I 1 i i i i i 1 9..

If 9 40588/wsq is very intensively cooled by the filling material 9, so that the ohmic resistance is considerably greater than that of the arc 23 between the projectile 18 and the electrode 3 on the muzzle side.

- 40588/wsq

Claims

R% 1. Apparatus for accelerating a projectile located _in a tube closed at one end using an electrically heated plasma, with two electrodes between which an are burns which heats the plasma, the first of the two electrodes being located on the breech side, wherein the second electrode is formed by the base of the projectile.
2. Apparatus in accordance with Claim 1, wherein the projectile before the arc is struck, is connected with the breech-side electrode through an electrically conductive wire.
3. Apparatus in accordance with Claim 2, wherein the projectile, before the production of the plasma, is connected by a second electrically conductive wire with a contact located at the muzzle of the tube.
4. 'Apparatus in accordance with Claim 3, wherein the projectile has a cup shaped recess so that on the firing of the projectile the second wire will first of all be intercepted.

1 t 11 40588/wsq
5. Apparatus in accordance with Claim 2, wherein a small rocket is provided on the front part of the projectile and the electrically conductive wire is situated in a wire container and connected both with the projectile and with the rocket.
6. Apparatus in accordance with any one of Claims 1 to 5, wherein the projectile is situated on a easing of electrically non-conductive material and the easing is filled with a powder or fluid of low electrical conductivity with a high hydrogen content.
7. Apparatus in accordance with Claim 6, wherein the casing is filled with water, oil, lithium hydride or polyethylene powder.
8. Apparatus for accelerating a projectile as described herein and exemplified with reference to the drawings.

pubUaued 1989 atThe P&WntOftoe. State House, 66571 High Holborn, London WC1R 4"_. Purtherooples maybe obLtned&omThp EWOG ell, St Mary _ Or-D1r4ton, Kent BR5 3BD. Printed by Multiplex ques 1 St -POta".

techni td,, Kent, C;0jj. 1187