FR2650884A1 - CHARGE FOR ELECTROTHERMIC LAUNCHER - Google Patents

Abstract

This load 2 comprises at least one insulating element 4 which can be decomposed by pyrolysis and, in this element, an electrical resistance 22, one end of which is intended to be brought to a high voltage relative to its other end in order to heat the resistance and to cause thus a pyrolysis of the element, which transforms the latter into a gaseous medium capable of propelling a projectile 14 out of the launcher. The resistor forms a winding in the insulating element, the two ends of this winding are distant from each other and the winding is very weakly inductive and distributed substantially homogeneously in the element. Application to the acceleration of projectiles up to very high speeds.

Description

CHARGE FOR ELECTROTHERMIC LAUNCHER

DESCRIPTION

  The present invention relates to a charge for electrothermal launcher. It applies to the acceleration of projectiles up to very high speeds. An electrothermal launcher belongs to the category of launchers that use electrical energy to propel projectiles. Three types of electric launchers are known: - the launcher with rails, - the induction launcher, and - the electrothermal launcher to which

reports the present invention.

  In an electrothermal launcher, a suitable medium is formed and heated by means of electrical energy which is generally provided by a bank of

  capacitors, in order to propel a projectile.

  The category of electrothermal launchers is divided into two main classes, namely slow-blow electrothermal launchers and

  fast discharge electrothermal launchers.

  In a slow-blow electrothermal launcher, the capacitor bank supplies its energy to the propulsion medium for the duration of the trip.

  projectile inside the launcher.

  Slow-discharge launchers have been developed mainly by the American company J.C.DEVICES and the following documents relate to them: (1) article by R. L. BURTON et al. entitled "EMET Technology for rail launchers", reports of "3rd Symposium on electromagnetic launch technology",

  April 21-24, 1986, Austin Texas USA.

  (2) article entitled "Plasma -pulse-

  accelerator ", by Jurgen G.H. SALGE et al., Fur Hochspannungstechnik Institute, Technische Universitit Braunschweig R.F.A. and Wolfram WITT, Rheinmetal

GmbH, D sseldorf R.F.A.

  In a discharge electrothermal launcher

  fast, the energy of the capacitor bank is transferred to a load for a very short time, so that the projectile does not have time to move during this time of energy transfer. The fast-loading launchers are mentioned in the following document: (3) communication by M. GUILLEMOT, A. NICOLAS and M. ROCHE, entitled "Projectile Launching by an electrothermal gun" and presented at the 4th Symposium on Electromagnetic Launch Technology, Austin ,

U.S.A., 19-21 April 1988.

  The present invention relates to a charge for electrothermal launcher, which is suitable for fast discharge electrothermal launchers and therefore

  more particularly usable with these.

  To do this, it is necessary to design a load which allows a fast discharge of the bank of capacitors as well as a very strong heating of the medium

  thruster by means of a high voltage.

  The present invention aims to solve this problem. Specifically, it relates to a load for electrothermal launcher, this load comprising at least one electrically insulating element, decomposable by pyrolysis and, in this element, an electrical resistor whose end is intended to be raised to a high electrical voltage by ratio at its other end in order to heat the resistance and thereby cause pyrolysis of the element, which

Z650884

  converts the latter into a gaseous medium able to propel a projectile out of the launcher, characterized in that the electrical resistance forms a coil in the insulating element, in that the. two ends of this winding are distant from each other, and in that the winding is very weakly inductive and distributed in a substantially homogeneous manner in the element. By "very weakly inductive winding" is meant a winding whose inductance does not exceed about 20 nH, this inductance for example being of

the order of some nanohenrys.

  - The use of a very low inductive winding allows the fast discharge of the capacitor bank and this, even if the winding electrical resistance has, which is preferable, a

  large length, for example of the order of 1 meter.

  The distance from each other of the two ends of the winding helps to avoid breakdowns between the different parts or turns of this winding, this being important to allow the use of a high supply voltage of the resistor, this voltage (of the order of 30 kV for example) to achieve a very high power heating of the

resistance.

  According to a particular embodiment of the filler object of the invention, it further comprises: - an electrically insulating sheath provided with a housing in which is placed each element, - an electrically conductive envelope which contains the sheath, and an electrode which is electrically isolated from the envelope and which is intended to carry one end of the winding at the high voltage, the other end of the winding being brought to a reference potential. The object of the invention may comprise a plurality of elements in the housing of the electrically insulating sheath. According to a preferred embodiment of the filler object of the invention, each element comprises at least one sheet made of an electrically insulating material, decomposable by pyrolysis, the resistance corresponding to this element is on this sheet and has substantially the shape a line in crenets lengthened according to their height, a line whose two ends respectively correspond to the two ends of the winding relative to the element and are respectively placed in two opposite edges of the sheet, and this sheet is rolled on itself by such that the two opposite edges are respectively at the two ends of the roll thus obtained. The resulting winding is regular and the dispersion of this winding (and thus the resistance) in the electrically insulating element is substantially

  homogeneous throughout the volume of this element.

  The element may comprise a plurality of such sheets which are stacked so that the electrical resistances respectively corresponding to said sheets are electrically isolated from each other, and which are rolled together on

  themselves to form a single roll.

  Each element can be made of an electrically insulating plastic material, decomposable by

pyrolysis and highly hydrogenated.

  Finally, each electrical resistance can be

  made of a metallic material or carbon.

  The present invention will be better understood at 2LO8s40

  The following description, examples of

  EXECUTION given purely by way of indication and in a purely limiting manner, with reference to the attached drawings in which: FIG. 1 is a diagrammatic view of a particular embodiment of the feedstock of the present invention, in place in an electrothermal Launcher at rapid discharge, - Figure 2 schematically illustrates a sheet that includes this load, - Figure 3 shows this sheet rolled on itself, Figure 4 is a schematic and partial sectional view of the load shown in Figure 1, and FIG. 5 is a diagrammatic and partial sectional view of another load according to the invention. In Figure 1, there is shown schematically a particular embodiment of the object of the invention. In this particular embodiment, the load 2 comprises an element 4 which comprises a rolled sheet along the X axis of the load and which will be described later. This element 4 is in a housing 5 in the form of a cylinder of revolution X axis, which is provided with an electrically insulating sheath 6, for example made of a plastic material such as polyethylene. The insulating sheath 6 is itself housed in an envelope

  metal 8 eg Brass.

  The cylindrical housing 5 in which is the element 4 in the form of a roll is closed on one side of this roll, by a metal washer 10 for example brass. This cylindrical housing is closed, on the opposite side, by a thin metal foil 12, for example made of brass, which is in contact with its

2650-884

  periphery, with the metal casing 8. The projectile 14, intended to be launched by means of the electrothermal launcher 36 in which the load 2 is placed, is, before its launch, against the thin sheet 12. The base of the projectile can be The projectile may also be in contact with the metal casing 8. This projectile 14 may be electrically insulating or conductive. Alternatively, there is no thin sheet 12 and the projectile 14 is electrically conductive, for example metallic, closes said opposite side of the housing 5 and can still be in contact with

the metal casing 8.

  An electrode 16, for example made of brass, which extends along the X axis and which is sheathed by a coaxial insulator 18, for example made of polyethylene, passes through the wall of the metal casing 8, which is opposite the washer. , In a way that

  the electrode 16 is in contact with this washer 10.

  Insulator 18 electrically isolates

  the electrode 16 of the metal casing 8.

  Element 4 comprises a sheet 20 of rectangular shape (FIG. 2), made of an electrically insulating plastic material which can be decomposed by pyrolysis. On one side of this sheet is an electrical resistor 22 having substantially the shape of a crenellated line whose base is close to an edge 24 of the sheet 20 and which are elongated according to their height, the summit of the crenellations being close opposite edge 26

of sheet 20.

  The ends 23 and 25 of the resistor 22 are wider than the rest of the latter and are respectively at the two corners of the sheet

  which correspond to the edges 24 of this sheet.

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  In Figure 3, we see that the sheet 20 is rolled on itself to obtain a roller whose axis is parallel to the edge 24 of the sheet. The roll thus obtained is, as already indicated, placed in the housing 5 provided in the sheath 6. The length of this housing is such that the ends of the resistor 22 are then respectively in contact with the washer 10 and the thin sheet 12 or, when there is no thin sheet 12, with the washer 10 and the projectile 14 (electrically

-conductor in this case). -

  To do this, it is preferable that the ends 23 and 25 of the resistor are respectively on the other two edges 27 and 28 of the sheet. However, if the ends of the resistor are not exactly on the edges 27 and 28 but are very close to them, the load works all the same, because of breakdowns occurring between the washer 10 and the corresponding end of the resistor and between the thin sheet 12 '(or the projectile 14 if there is no thin sheet 12) and the other end of the resistor when the electrode 16 is brought to a high voltage with respect to the metal shell 8

  (and to projectile 14 if it is conductive).

  The element 4 in the form of a roll is seen in

  cut in Figure 4 in its housing 5.

  The resistor 22 may be formed by depositing a metal or carbon on the sheet 20. The latter may be made of a material selected from the group consisting of: mylar (registered trademark), kapton (trademark), polyethylene or

polyvinyl chloride.

  The sheet 20 provided with its resistance 22 can also be obtained from a sheet which is made of one of the preceding materials and covered with a metal layer which is engraved so as to

  obtain the resistance 22 in the form of crenellations.

  As a purely indicative and in no way limiting, the sheet 20 has a thickness of the order of 1 mm and is formed on this sheet a dozen crenellations. The dimensions of the sheet depend on

  inner diameter of the launcher tube with which La-

  load comprising this sheet is intended to be used. For example, for a launcher whose tube has an inner diameter of 9mm, one can use a rectangular sheet of 20cm long and 5cm wide. It will be noted that the crenellated form of the resistor 22 gives it a very low inductance and also makes it possible to distribute the potentials regularly and thus to obtain the best insulation.

electric possible.

  It will also be noted that the structure of the element 4 shown in FIG. 3 allows the thermal "contact" between the electrically insulating sheet and the resistance to be well controlled and reproducible. It can be seen in FIG. 3 that, if necessary, one or more additional sheets 30, 32 may be used. Each additional sheet is made of the same material as the sheet 20 and has a crenellated resistor such as sheet 20. These sheets 20, 30, 32 are stacked and rolled together to obtain a single roll, each resistor having an end located at one end of this roll and another end located in the other

end of the roll.

  Alternatively, if necessary, instead of one or more additional sheets provided with resistors, one or more sheets identical to the sheet 20 but not provided with resistors may be used, all these sheets being superposed and

rolled together.

  FIG. 5 is a diagrammatic and partly sectional view of a load according to the invention, in which not only a single element 4 but a plurality of roll-shaped elements 4, which are parallel to each other, are used. others and placed in the housing 5 of the sheath, parallel to the axis X, the corresponding resistors

  these rollers being then mounted in parallel.

  In a variant not shown, the load may comprise not a single element 4 but a plurality of elements 4 in the form of rollers, arranged one after the other along the X axis in the housing of the sheath 6. Good Of course, these rollers are then arranged relative to each other so that the electrical resistances corresponding to these rollers are mounted in series between the washer 10 and the feuillince 12 (or -the projectile 14 if there is

no de-leaf 12).

  The charge which is the subject of the present invention can be used on all electrothermal launchers

fast discharge.

  FIG. 1 diagrammatically shows a launcher of this type which bears the reference 36. The latter is in the form of a tube and its front end is of course open, while its rear end is closed by a closing cap. 38 which is screwed there after introducing the load 2 in a chamber 37a provided for this purpose in the launcher, at the rear of it. When the projectile is secured to the load 2, it is set up in the launcher at the same time as this load and when it is not secured, it can be put in place in the launcher by the back of this one, before the charge of course, or from the front

(open) of the tube 37 of the launcher 36.

  The closure lid 38 is bored at its center to leave enough space for an electrode 40 called "electrical contact". This electrical contact 40 passes through the closing cap 38 from one end to the other and is separated by a seal

electrically insulating 39.

  An end 39a of the contact 40 opens into

room 37a.

  The other end 39b 'of the contact 40 is electrically isolated from the outer surface of the launcher and electrically connected to a terminal of a power supply 42 via a

gas quick switch 44.

  This power supply 42 comprises a bank of capacitors, able to store in form

  electrical energy of the order of 8 kJ.

  When the lid is screwed into the rear part of the launcher 36, the end 39b of the contact

  electrical 40 is pressed against the electrode 16.

  The terminal of the power supply 42 which is electrically connected via the switch 44 to the contact 40 is intended to be brought to a high voltage, of the order of 30 kV for example, with respect to ground. The other terminal of the power supply 42 is grounded. The lid 38 and the rest of the launcher are metallic and are also grounded. As a result, the metal shell 8, which, like the projectile, is in contact with the launcher, is also grounded and the same applies to the projectile when the latter is

driver.

  1 1 Aihsi, when the switch 44 is closed, one end of the resistor 22 is very quickly brought to the high voltage relative to its other end and the capacitor bank discharges very quickly through this resistance. The latter is then heated to very high temperature, for example of the order of 10,000 to 30,000OC. The highly hydrogenated plastic material which constitutes the sheet is thus very quickly decomposed by pyrolysis and is transformed into a gas (and even, if the temperature is sufficient, into a plasma) whose relaxation is used

to launch the projectile 14.

  The insulating qualities of the highly hydrogenated plastic material are put to good use in the load to achieve the necessary electrical insulation between the different parts of the resistor which is, so to speak, intimately mixed with the plastic material. This electrical insulation is maintained despite the very high temperature reached by the resistance due to the high speed of heating (a few microseconds). But, quickly, the temperature is homogenized in the load, the resistance is mixed with the insulating plastic material and the whole becomes gaseous and forms the propellant medium. This is essentially composed of hydrogen and carbon, hence a low mass gas

  atomic constituting an excellent propellant medium.

  It is specified that the thin sheet 12 has a sufficiently small thickness, for example of the order of 0.5 m, so that almost all of the energy resulting from the expansion of the propellant medium serves the purpose.

propulsion of the projectile 14. -

  In an alternative embodiment, the washer is removed and the corresponding side of the housing 5

  is closed by the electrode 16 and the insulator-18.

  The electrode 16 is then in contact with the end of the resistor, which is located on said side, or is very close to this end so that a breakdown occurs between them when the electrode is brought to the high voltage. In this variant, preferably, the electrode has transverse dimensions substantially

  equal to the diameter of the housing 5, or the sheet 20 is.

  wound so that the ends 23 and 25 of the resistor 22 are substantially on the X axis (whereas in the case of FIG.

  23 and 25 are at the periphery of the roll obtained).

  The pressures and temperatures achieved with a fast discharge electrothermal starter are much higher than those obtained with conventional powder charges. This results in the possibility of obtaining at the same time a better yield (ratio of the kinetic energy of the projectile to the energy used to propel it, that is to say the energy stored in the bench capacitors, in the case of the electrothermal launcher shown in Figure 1) and higher speeds, o o the interest of the fast discharge electrothermal launcher, particularly vis-à-vis a launcher to

classic powder.

  The charge described with reference to Figures 1 to 5 is particularly well suited to such a fast discharge electrothermal launcher and has a good performance.

Claims (7)

  1; Charge for electrothermal starter, said charge (2) comprising at least one electrically insulating element (4), decomposable by pyrolysis and, in this element, an electrical resistance (22), one end of which is intended to be raised to a high electrical voltage by ratio at its other end to heat the resistance and thereby cause pyrolysis of the element (4), which transforms the latter into a gaseous medium capable of propelling a projectile (14) out of the launcher, characterized in that the electrical resistance (22) forms a winding in the insulating element (4), in that the two ends of this winding are distant from each other, and in that the winding is very weakly inductive and distributed sensibly homogeneous in the element (4).   2. Charge according to claim 1, characterized in that it further comprises: - an electrically insulating sheath (6), provided with a housing (5) in which is placed-each element (4), - an envelope electrically conductor (8) which contains the sheath (6), and - an electrode (16) which is electrically isolated from the casing (8) and which is intended to carry one end of the winding at the high voltage, the other end of the casing (8). winding being brought to a reference potential. - 3. Load according to claim 2, characterized in that it comprises a plurality of elements (4) in the housing (5) of your sheath electrically insulating (6).   4. Load according to any one of   Claims 1 to 3, characterized in that each   element (4) comprises at least one sheet (20) made of an electrically insulating material, decomposable by pyrolysis, in that the resistance (22) corresponding to this element is on this sheet and has substantially the shape of a line in crenets lengthened according to their height, line whose two ends respectively correspond to the two ends of the coil relative to the element and are respectively placed in two opposite edges (27, 28) of the sheet   (20), and in that this sheet is rolled on it   even in such a way that the two opposite edges (27, 28) are respectively at both ends of the roll thus obtained.   5. Charge according to claim 4, characterized in that the element (4) comprises a plurality of sheets (20, 30, 32) which are stacked so that the electrical resistances (22) respectively corresponding to said sheets are electrically insulated. each other, and which are rolled together on themselves to form a single roll. 6. Charge according to any of the   Claims I to 5, characterized in that * each   element (4) is made of an electrically insulating plastic material, decomposable by pyrolysis and highly hydrogenated.   7. Load according to any of the   Claims I to 6, characterized in that each   electrical resistance (22) is made of a material metallic or carbon.