GB2234335A - Systems for firing propellant charges - Google Patents

Abstract

The problem of vent hole sealing in breechloading guns is overcome by arranging to fire the charge by a system in which the gun obturator bolt 17 is modified to enable it to act as electric, magnetic or, especially, electromagnetic field producing means operatively connected to a source external of the gun breech 10, whereby energy sufficient to cause the charge 11 to fire is induced into an electrical ignition circuit within the charge 11 itself. For electromagnetic fields the central portion of the bolt consists of a dielectric tube with a conductive core 52. For electric fields the bolt is separated from the breech block 12 by an insulating sleeve. For magnetic fields the bolt is non-magnetic but contains a magnetisable insert and is disposed in a coil. <IMAGE>

Description

SYSTEMS FOR FIRING PROPELLANT CHARGES This invention concerns systems for firing propellant charges, and relates in particular to such systems of the type used to fire a propellant charge in a gun.

For convenience, a gun may be defined as a device having a relatively long tubular barrel closed at one end and open at the other (the muzzle) and so designed that, if a charge of a propellant substance is placed in the barrel at the closed end, and a projectile is placed next to it on its muzzle side, then when the charge is ignited the expanding gases resultinq from the ensuing bumina of the charge will accelerate the projectile along and out of the barrel.

In the early days of guns - both of the large artillery pieces referred to as cannon and of their smaller relations the hand weapons - it was common to insert the charge (usually loose gun powder) into the barrel from the muzzle end (hence these guns were known as "muzzleloaders"), to tamp it firmly into place, to insert the projectile (a ball-shaped object of stone, iron or lead) into the barrel in the same way (holding it in place with a wad of paper or rag), and then to ignite the gunpowder charge through a very small hole (the touch or vent hole) drilled into the barrel at the closed end.For various reasons (one of which was that part of the resultant gases tended to escape through the vent hole, "burning" it bigger and bigger each time) the whole system was most unsatisfactory, and over the centuries gave way to the use of guns in which the charge and projectile were combined into a cartridge (usually with percussion cap ignition), and the cartridge was inserted into the gun at the blosed"end through a port (the breech aerture) 'thich could be opened to allow the cartridge to be inserted and then sealed tightly shut (by the breech block) to prevent any leakage of the aases therethrough (hence such guns were known as "breech-loaders").

In certain cases, however, it was found desirable not to combine the charge and the projectile into the single cartridge form, but instead to keep the two separate - and indeed this has almost always been so for the larger calibre guns, and has especially been the case for naval guns (when, almost from the beginning, the powder charge was contained in pre-prepared correctlysized canvas bags7 This system of using separate charges and projectiles is now finding further popularity with land-based guns - those of the type currently used in tanks, for example.The prime reason is the very simple one that there is little point in using a large and expensive charge, resulting in unnecessary wastage of materials and considerable barrel wear, if the target is only a hundred yards away - and if the charge can be loaded separately of the projectile then an appropriate charge can always be picked for the particular target to be destroyed (just as it is quite usual to select an appropriate projectile), At present, then, modern guns are still breech-loaded, but the charge for each projectile is separate therefrom, and accordingly is loaded into the breech separately.The charge is ignited in a manner in essence identical to the vent-hole system employed when guns were in their infancy: the main charge, once again typically contained in a canvas bag, is ignited by burning gases injected through a "vent" hole at or near the end of the breech; a primary ignition cartridge device similar in appearance to a blank rifle cartridae is the source of the burning gases, and this device is fitted into, and retained in the outer end of, the hole throuah which the aases pass; ignition of the cartridge can be by either electrical or percussion means, needing as appropriate either electrical contacts or a mechanical firing mechanism; and naturally, such a firing system also needs means to remove the spent cartridge after firing and to insert a new cartridge before each next firing.

This whole approach to the matter suffers from one severe disadvantage: apart from the obvious complexity of the required cartridge handling and firing mechanisms, and the need to carry an adequate supply of cartridges, a vent hole sealing problem exists, just as it did in the early days of the cannon. Now, while, when the primacy igniting cartridge is fired,pressure from the burning gases seals the open end of the cartridge against the sides of the vent hole in which it is situated, unfortunately, as the hole is necessarily quite long and the burning gases travel dozen it, and into the breech, relatively slowly, a considerable delay occurs before the main charge in the breech ignites, and there is a further delay before the back pressure wave from the main charge reaches the cartridge.This time difference between when sealing of the vent hole by the cartridge occurs and when the main charge pressure wave returns can be long enough to allow the open end of the cartridge to'Yelax and the seal to break, and if this happens then hot gases from the main charge can escape up the vent hole past the cartridge. A small escape of gases might in itself not matter, but the temperature of the gases is so high that damage to the "sealing" metal surfaces can take place, which naturally leads to further increases in gas escapes during subsequent firings. In the limit, the damage can be so extensive that ultimately either the used cartridge cannot be removed, or a new cartridge cannot be inserted.

The present invention seeks to deal with the problem of the vent hole by doing away with it entirely, and by arranging to fire the charge by a system in which sufficient electrical energy essentially from a source external of the gun is induced, coupled by means of an electric, magnetic or electromagnetic field, into an electrical ignition circuit within the charge itself.

In one aspect, therefore, this invention provides a method of firing a gun propellant charge of the type which contains within itself an electrical ignition circuit, fn which method sufficient electrical energy to operate the ignition circuit is induced thereinto, from an energy source distant from the charge, by way of a coupling field (between the source and the ignition circuit) which is electric, magnetic or electromagnetic in character.

It is the prime purpose of the method of this invention to facilitate the firing of the main propellant charge in a gun - specifically a gun of relatively large calibre, such as would generally be referred to as an artillery piece - and thus it is very much preferred that the charge be, in operation, within the breech of a gun, while the energy source, while possibly mounted thereon, and while very probably (as discussed below) having a field radiating element (a field producinq means) within the breech, is essentially external of the breech of the gun. The follodng discussion is therefore mainly concerned with such a situation.

Propellant charges of the type containing within themselves electrical ignition circuits are not per se new.

In the past, however, such charges have always been fired by the direct connection of their ignition circuits to a source of electrical energy. Thus, it is well known to arrange for an ignition "filament" buried in the charge to have its terminal ends protruding therefrom, so that they may be electrically-connected, by such physical means as a pair of wires, to a battery or dynamo/magneto generator. Indeed, devices of this general nature are presently used to ianite the electrically-fired cartridges the use of which is referred to above0 However, for at least two very good reasons a physical contact - an actual electricallyconductive pathway - between the mergy source and the ignition filament terminals is extremely difficult when the charge in question is that employed as the main propellant charge positioned in the breech of a gun.

Firstly, because the main charge is (as explained above) not of any single standard size its position in the breech volume is always somewhat random - which makes rather difficult the sure provision of physical contact to two terminals on it. Secondly, because - as can be imagined - the chemical and physical environments within the breech as the main charge burns are somewhat hostile, it is not easy to ensure that the contacts in the breech itself remain clean and in a state to provide good electrical connections with the charge terminals (assuming that physical contact has been made).Thus, for these - and other - reasons it has so far proven impossible to provide a satisfactory electrical ignition system for a gun propellant charge by simply connecting the energy source to the ignition circuit' The present invention, therefore, relies not upon physical/electrical contact, but relies instead upon the coupling/induction effect of electric, magnetic or electromagnetic fields, It is not, of course, suggested that the coupling of two circuits by field induction is in itself new, but it is stated that it is new and inventive when applied in the defined manner, as is now described in more detail The ignition circuitry The charge ignition circuit is basically conventional, and thus in essence consists of an electrically-heatable filament possible associated with a temperature sensitive firing capo However, whether the coupling field be electric, magnetic or electromagnetic it is considered unlikely that under practical conditions (iOeO in the gun turret of a tank) sufficient electrical energy could reliably be induced into the ignition circuit without some intermediate energy storage and trigger means. It is preferred, therefore, that the ignition circuit be connected to an electrical energy storage device - a capacitor - together with associated circuitry > such as a DIAC device designed to allow the storage device to charge up slowly (as the ignition circuit receives field-coupled energy) and then to discharge suddenly through the filament.

Moreover, while the wiring of the ignition circuit will itself undoubtedly act as a receiving aerial/ inductive loop for the coupling field, nevertheless its unaided capabilities in this area are likely to be poor.

Preferably, therefore, the circuit is associated with additional field coupling means enabling it to couple more.

efficiently with, and accordingly receive more energy from, the induced field If the field is an electric field then the additional coupling means acts as one half (or plate) of a capacitor, and so may be a metal foil sheet suitably orientated and positioned within the charge (say, at the base thereof) and connected into the circuit.

Alternatively, if the induction field is a magnetic field then the coupling means acts as a "magnetic" coil, and may indeed be such a coil wrapped around and/or suitably orientated dnd positioned on the charge (again, say, at the base thereof) and also connected into the circuit0 Finally, if the induction field is an electromagnetic field then the coupling means acts as a "radio" receiving aerial, and may be a plate-like foil or a series of wire loops suitably orientated and positioned on the charge (yet again, say, at the base thereof) and connected into the circuit0 The energy source and field producing means Just as the ignition circuit itself is in essence conventional, so is the energy source.Thus, whichever type of induction field is used so is employed any convenient energy source: in each case suitable electrically-powered (oscillator) circuitry drives means for producing the desired electric, magnetic or electromagnetic field - and in line with the comments given above for the ignition system the final element of such circuitry, which element is the field producing means, will in effect be merely a capacitor plate, an electromagnetic coil or a "radio" transmitting antenna respectively.

Nevertheless, because of the nature of the environment in which these field producing means have to operate their particular physical form needs some explanation.

Firstly, however, it is necessary to consider the general construction of the breech of a gun - which may be done with reference to Figure 1 of the accompanying drawings, which Figure shows in simplified diagrammatic (and slightly "exploded") form an axial cross-section of the relevant parts of that portion of the back end of a gun referred to generally as the breech.

The breech of a gun consists essentially of four main elements. These are: that part (10) of the gun barrel distant from the muzzle and specially adapted to retain the projectile (not shown) and propellant charge (11), which part is itself often referred to generally as "the breech", and which has an axial opening, or port (at the muzzle-opposed end thereof) referred to as the breech aperture; a substantial, massive closure member (12) for the breech aperture, which closure member is referred to as the breech block, and which is intended to be removably lockable in position so that it can be removed to allow insertion into the breech 10 of the projectile and charge 11 and then locked into place (by means not shown) to close > or block - the breech aperture; the obturator ring (13) which, apart from internal and external steel corner rings (14, 15 and 16), is made of a relatively elastically-deformable electrically-insulating material, and the purpose of which is to be flattened and "expanded" by the pressure wave generated as the propellant charge 11 burns so as tightly to seal any small gaps which may exist between the "sealing" faces of the breech aperture and the breech block 12; and the obturator bolt (17), a "mushroom headed" bolt disposed axially of the breech block 12 with its head on the inside thereof (so that the obturator ring 13 is sandwiched between the head and the block) and its shank located within an axial passage in the block 12, the purpose of this bolt 17 being simply to absorb and spread the forces generated by the burning charge 11 so as evenly to squash the obturator ring 13.

Finally, it should be noted that the gun barrel (including the breech and the breech block) is necessarily made from gun steel, which is a particular steel alloy that is both magnetic and electrically conductive. The obturator bolt is also usually made from gun steel, though this is perhaps more a matter of convention or convenience than of necessity.

Returning, now, to the problem of the nature of the energy source's field-producing elements, which elements must be located so that the field they produce is capable of coupling with the charge ignition circuitry, it is clear that in each case the element itself must be within the breech, for otherwise the nature of the material (gun steel.) from which the breech is made will block the produced field. Moreover, in order to avoid drilling access holes through the breech metal (it is the whole purpose of the invention to remove one such access holes), the element must almost inevitably be a part of the breech which is already present.Finally, because the only breech component which makes contact with the outside world yet at the same time need not be - or need not wholly be - of an electrically-conductive or magnetic character is the obturator bolt, it is clear that this bolt, appropriately modified, is suitable for use as that element which the energy source is connected to so as to produce the desired coupling induction field The invention proposes the induction of energy from the energy source into the charge ignition circuitry via one of three coupling fields, and in order of increasing present preference these are magnetic, electric, and electromagnetic. In each case the appropriate design of the obturator bolt/ring combination is different, and in each case there are advantages and disadvantages.The three cases may be summarised as follows: Magnetic Induction As is well known, electrical energy may be transferred between two coils of conductive material if they are coupled by an alternating magnetic field. Thus, if an alternating current is passed around one coil, to generate in the vicinity thereof an alternating magnetic field, then a second coil placed within that field will have induced in it a corresponding alternating current.

In this form of the invention, the obturator bolt is made of a non-magnetic (or relatively non-magnetic) steel - for example, an austenitic stainless steel - with a magnetic steel (gun steel) core in the shank supplied with an appropriate winding to convert the bolt into an electromagnet which is magnetically "spaced" from the breech block so as to allow the generated magnetic field to extend through the formed non-magnetic "window" into the interior of the breech.

This magnetic coupling method should -not be susceptible to fouling, but since the majority of the surrounding structure is of a conducting magnetic material high losses occur due to hysteresis and eddy currents, requiring corresponding high input energy Moreover, while accurate positioning of the charge is not essential, the required input energy does increase with greater separation of the energy source magnetic field launch section (the obturator bolt head) and the charge-carried pick-up coil.

Although in any event energy transfer from source to ignition circuitry is somewhat low when using magnetic induction methods, it can be maximised by suitable tuning of the coils and selection of the appropriate field frequency However, the optimum combination of these factors, and the limits imposed on them, depend laraely upon the actual physical situation of each gun type, and it is not intended here to provide any specific data relevant thereto.

Electric Induction As is also well known, electrical energy can be transferred between two conductors by a coupling alternating electrostatic field. Thus, if an alternating voltage is applied across two plate-like conductors placed adjacent but out of contact with each other, there is formed a circuit around which flows a current proportional to the voltage across the plates.

In this form of the invention a high-frequency alternating field is employed, and while the obturator bolt may be used as it is as the first plate-like conductor, electrically connected to the energy source, it must of course be insulated from the gun steel breech surroundings. This is easily effected by minor modifications to the obturator ring (to provide an annular insulating element electrically separating the bolt's head edges from the breech) and to the obturator bolt shank (to provide it with an insulating sleeve electrically separating the shank from the breech block).

This form of coupling (the capacitive coupling of high frequencies to a pick-up surface on the propellant charge) is undoubtedly more satisfactory than the magnetic coupling method. While the system can suffer from contamination of insulators, fouling of the obturator bolt surface (the energy launch section) is of little consequence.

Moreover, accurate location of the charge is not important, even though variation in position will cause significant changes in the coupling capacitance, which will determine the maximum energy available for coupling (that is, for a particular energy needed to ignite the charge, that energy must be transferrable even when the charge is in such a position as to give minimum coupling).

To obtain maximum coupling by the electric field the capacitance between the input and output electrodes should be as large as possible; this means using the largest possible electrodes. As stated above, the receiving electrode can be a foil or metallised disc (at the end of the charge) whose diameter is close to the breech diameter; the obturator bolthead is also almost equal in diameter to the breech, and therefore is effectively the best transmitting electrode.

It will be appreciated that significant separation distances can be achieved with electric field coupling using a combination of power and frequency. However, the optimum combination of these factors, and the limits imposed on them, depend largely upon actual physical situation of each gun type, and it is not intended here to provide any specific data relevant thereto.

Electromagnetic induction Again, it is well known that electrical energy can be transferred between two systems by a coupling electromagnetic field - that is, by the radiation of electromagnetic energy.

The energy may be chosen from the full spectrum of electromagnetic radiation, and thus it may be energy with a frequency corresponding to that of gamma rays and hard X-raps, to that of light waves (Including ultra-violet, visible and infra-red), or to that of radio waves (from microwaves to very long waves). Radiation of the chosen wavelength and frequency is launched from a transmitting antenna and picked up by a suitably tuned corresponding receiving antenna, and at the moment considerable activity is taking place in the field of beamed power transmission by this method, the interest being chiefly shown in the use of microwave radiation (that is, radiation that may very roughly be placed in the frequency range of a few gigahertz to a few tens of gigahertz).

In this form of the invention electromagnetic energy, conveniently in the low gigahertz microwave frequency range, is injected into the breech which is then used as a waveguide to direct most if not all of the energy to the receiving antenna (aerial) forming part of the ignition circuitry in the charge, and the obturator bolt is used as the radiating element (the transmitting antenna). As with the magnetic induction method, the obturator bolt needs to be especially constructed to serve as the desired antenna; one typical example of such a special construction is that wherein the bolt is modified so as to have a conductive core sector extending axially from one end to the other and insulated from the material of the surrounding portion.

A major advantage of this electromagnetic induction method, using a modified obturator bolt as the transmitting antenna, is that once launched into the barrel (conveniently in a circular waveguide mode) little or no attentuation of the energy occurs regardless of the separation distance to the receiving antenna in the charge.

Moreover, nearly all the energy launched is actually collected by the charge (which does not have to survive, and can take the form of an elaborate foil structure, so collecting nearly all the launched energy regardless of charge position). As the collecting parts are so efficient the transmitting antenna (the bolt head) can be relatively inefficient, allowing scope for a design which will operate in the harsh breech environment.

Naturally, the radiation frequency should be chosen to fit the physical circumstances. By way purely of example, for a breech tube of 140 mm diameter about 1.3 gigahertz is a reasonable sustainable minimum frequency, although higher frequencies are possible, and could offer advantages.

The charge firing system of the invention employs a coupling field wherchy energy from a source quite serrate frOR.

the charge is induced into the charge's ignition circuitry so as to fire the charge. The coupling field is either electric, magnetic or electromagnetic, and the separation between the source field producing means and the charge circuit's field pick-up means consistent with using a source of reasonably low energy to ensure charge ignition varies, as explained, dependent upon the type of field.

Indeed, the main reason why a source generating electromagnetic radiation is preferred is that, because the breech walls can act as a waveguide, the separation becomes almost irrelevant. The nature of the source's field producing means is dictated essentially by the fact that the field must be enabled to penetrate into the breech space yet there must be no "additional" holes or other weak points in the breech metal. Thus, as already explained, the field producing means must be the obturator bolt (which of necessity penetrates the breech block metal), suitably modified as required by the particular coupling field chosen (and in another aspect the invention provides a gun obturator bolt which has been modified to allow it to be used as the coupling field producing means in the charge firing system of the invention).As explained above, the preferred coupling field is electromagnetic, and in such a case the obturator bolt is conveniently so modified as to have a conductive core section extending axially from one end to the other and insulated from the surrounding bolt materials -The position of the source itself is effectively irrelevant (other than that it can hardly be within the breech, and that it should be relativly convenient to connect to the obturator bolt),but most preferably it is, as stated, external of the gun (possibly detachably mounted on the outside of the breech), and constitutes an appropriate circuit, capable with its field producing means of forming the chosen field, suitably connected up to a primary source of electrical energy such as a battery or generator.

The amount of energy induced into the charge's ignition circuitry is sufficient to operate the circuit that is to say, there is no energy source in the charge circuitry itself, and the whole of the energy for firing the charge is, according to the invention, induced into the circuitry via the coupling field more or less at the moment of firing the gun.It had been thought possible that the ignition circuit could be pre-energised (by an internal battery, say), the induced energy then acting merely as a triggering signal, but this was discounted on the grounds of the fairly obvious dangers associated therewith, not the least of which would be accidental premature firing of the charge It is true that such dangers could be minimized by requiring the ignition circuitry to operate only upon the reception of an energy signal coded in some fashion (and indeed such a coding system can in fact be used with the invention, and might be useful in ensuring that only the correct charges, or set of charges, could be used with the correct gun), but even so it is felt that the dangers of the charge being, as it were, permanently primed outway any advantages (as regards, say, the need for a mere trigger signal to be at a much lower energy level) There are other aspects two the problem of safety, and a few of these are now briefly discussed. The problem stems again from the fact that the ignition circuitry will always actually be within the charge of all the systems described.

The first line of protection is the inherent coupling requirements; a significant quantity of energy is needed (assuming that, as discussed above, the whole of the energy is to be induced). As the gun's energy source circuit will have a particular frequency the charge circuitry can be "tuned" to accept only that frequency.

The result is that the charge can only be ignited by a high energy field of the correct frequency.

If a second line of protection is required, at least three methods are possible: a first is to keep a vital element of the charge ignition circuit separate for installation before loading; a second is to include a "safety pin" (which could be a strip of foil shortening out the ignition circuit) for removal before loading; and a third solution is that mentioned above - to use a more complex circuit in the charge, and to employ a coded signal to ignite the charge (one system of achieving this is to use the majority of the time the coupling is active to charge a storage capacitor in the charge circuit, and then, when the correct time has elapsed, a coded signal using the coupling field initiates the discharge of the capacitor if the correct code is used).

The invention extends, of course, to a gun suitable for use in the charge firing system of the invention and having an obturator bolt so modified as to allow it thus to be used.

Various embodiments of the invention are now described, though only by way of illustration, with reference to the accompanying drawings in which: Figure 2 shows diagrammatically a typical capacitordriven ignition circuit suitable for use in a charge fired by the system of the invention; Figure 3 shows diagrammatically a gun breech similar to that of Figure I (referred to hereinbefore), but modified to use magnetically coupled energy induction to fire the charge, Figure 4 is like Figure 3 but uses electricallycoupled energy induction; and Figure 5 is like Figures 3 and 4 but uses electromagnetically-coupled energy induction.

Where possible, like parts have been given the same reference numerals (as in Figure 1).

Figure 1 has already been described hereinbefore, and needs no further discussion, save to point out that the systems of Figures 3, 4 and 5 are in essence no more than modifications of the Figure 1 system.

The circuit of Figure 2 is a very simple conventional capacitor-charged ignition circuit. Briefly, it comprises a capacitor (20) in series with a DIAC trigger device (21) and an ignition element (22), and fed with electrical energy from an aerial (23) via a diode rectifier (24). Energy picked up by the aerial 23 is rectified and fed to the capacitor 20; when the charge stored causes the voltaae across the capacitor to rise to the DIAC 21 trigger level the DIAC's resistance drops suddenly from a high to a low value, - the capacitor is thus short-circuited through the ignition element, and the latter fuses (to ignite the propellant charge).

The system of Figure 3 employs magnetic field coupling, and is presently the least preferred of the three systems of the invention. In brief, the obturator bolt 17 is made for the most part of relatively non-magnetic austenitic stainless steel, but has axially disposed within it an insert (30) of magnetisable gun steel.

Around the obturator bolt shank 18 is disposed an electrical winding (31) (with appropriate connections to the outside), and by passing an alternating current around this winding 31 the combination of winding and gun steel insert 30 is converted into an electromagnet generating an alternating magnetic field filling the space (in a manner not shown) between the head of the obturator bolt 17 and the rearmost charge 11. At the back of this charge, wound (in this case) around its peripheral surface near its back face), is a pick-up winding (32) (which may be "tuned"), and the electrical energy induced therein by the magnetic field is fed to the charge ignition circuit (not shown) buried within the charge 11.

while unforeseen factors may alter the power output or the efficiency with which the power is transferred, experiments show that it appears unlikely that a sufficient rate of energy transfer output can be obtained by magnetic coupling for separations of greater than about 1 inch.

Figure 4 shows the system using electric field coupling.

In this case the modifications to the basic equipment are relatively slight; it is necessary merely electrically to insulate the obturator bolt, and this can be done simply by supplying an insulating sleeve (40) around the shank 18 to separate the bolt from the breech block 12 and the inner corner ring 16, and by making the outer front corner ring 15 of an insulating material so as to separate the bolt head from the breech 10. The charge 11 need only contain a (foil) capacitor plate (41) suitably connected to the ignition circuit (again, not shown).

When the mechanical arrangement of Figure 4 is analysed electrically the significant capacitance is that between the bolt 17 and the pick-up plate 41. This is the coupling capacity, and it varies inversely with separation distance.

The rate of energy transfer for this electric field coupling system is about an order of magnitude greater than that for the magnetic system.

The electromagnetic field coupling system of the invention is shown in Figure 5. This time modifications needed to the obturator bolt are more significant: the central portion of the bolt has been replaced by a dielectric tube (heavy lines 50) widening out at the bolt end into a cone shape (the heavy hatched area 51), the tube/cone combination having a central core (52) of conductive materials conveniently gun steel.

An antenna of this kind presents a low impedance to the generator, and matching sections are needed. Once matched, however, nearly all the power is launched into the breech tube, to be picked up by the antenna (53) at the base of the charge 11. While fouling of the bolt head reduces the launching efficiency, reception of a few watts in a frequency band around 1 to 3 gigahertz presents little difficulty.

Unlike both other systems, the electromagnetic coupling system provides an excellent rate of energy transfer practically regardless of the separation of the charge from the bolt.

Test Results The three methods have been subjected to a number of test situations, and the results (with respect to the four main factors "charge position latitude", "power transfer efficiency", "power limit" and "ease of mechanical implementation") are given qualitatively in the Table below.

TABLE

Factor Magnetic Electric Electro magnetic Latitude of position of charge Low Medium Very High Power transfer efficiency Low Low High Power limit Low Medium/ High High Ease of mechanical implementation Medium Low Medium The factor of charge position latitude is probably the most significant factor of any reliable system, the electromagnetic method being easily the best in this respect. It is necessary to consider the power transfer efficiency and power limit together (to some extent); as a given power is needed at the ignition circuit the combination will determine if ignition is possible. In this case, the electromagnetic system performs well, and while the electric field is moderately good, the magnetic coupling yields a rather poor capability. Ease of mechanical implementation is included as a rough guide only (electric field utilisation is somewhat more difficult than the others due to the necessity of insulating the bolt, and of the replacement of the steel edges of the obturator pad with insulating material).

Claims (13)

CLAIMS:

1. A method of firing a gun propellant charge of the type which contains within itself an electrical ignition circuit, in which method sufficient electrical energy to operate the ignition circuit is induced thereinto, from an energy source distant from the charge, by way of a coupling field Cbetween the source and the ignition circuit) which is electric, magnetic or electromagnetic in character

2. A method as claimed in claim 1, in which the charge is, in operation, within the breech of a gun, while the energy source, while associated with a field producing means within the breech, is essentially external of the breech of the gun.

3. A method as claimed in either of the preceding claims, in which the charge ignition circuit is an electricallyheatable filament connected to a capacitor together with associated circuitry causing the capacitor to charge up slowly (as the ignition circuit receives field-coupled energy) and then to discharge suddenly through the filament.

4. A method as claimed in any of the preceding claims, in which the charge ignition circuit is associated with additional field coupling means enabling it to couple more efficiently with, and accordingly receive more energy from, the induced field.

5. A method as claimed in claim 4, in which the induction field is an electromagnetic field, and the coupling means acts as a "radio" receiving aerial, and is a plate-like foil or a series of wire loops suitably orientated and positioned on the charge and connected into the circuit.

6 A method as claimed in any of the preceding claims, in which the energy source employs suitable electricallypowered (oscillator) circuitry driving means for producing the desired electric, magnetic or electromagnetic field the final element of such circuitry, which element is the field producing means, being in effect merely a capacitor plate, an electromagnetic coil or a "radio" transmitting antenna respectively0

7. A method as claimed in claim 7, in which the field producing means is the gun obturator bolt appropriately modified for use as that element to which the energy source is connected so as to produce the desired coupling induction field.

8. A method as claimed in claim 7, in which the coupling field is electromagnetic in nature, and the obturator bolt is so modified as to have a conductive core section extending axially from one end to the other and insulated from the material of the surroundinq portion.

9 A method as claimed in either of claims 7 and 8, in which electromagnetic energy in the low gigahertz microwave frequency range is injected into the gun breech, using the obturator bolt as the radiating element, the breech then being used as a wave guide to direct the energy to a receiving antenna forming part of the ignition circuitry in the charge,

10 A method as claimed in any of the preceding claims and substantially as described hereinbefore.

11 A gun obturator bolt which has been modified to allow it to be used as the coupling field producing means in the charge firing system as defined in any of the preceding claims.

12. A gun suitable for use in the charge firing system as defined in any of claims 1 to 8, and having an obturator bolt as defined in any of claims 9 to 11.

12 A gun obturator bolt as claimed in claim 11, which bolt is so modified as to have a conductive core section extending axially from one end to the other and insulated from the surrounding bolt material0 130 A gun obturator bolt as claimed in either of claims 11 and 12 and substantially as described hereinbefore.

14. A gun suitable for use in the charge firing system as defined in any of claims 1 to 10,. and having an obturator bolt as defined in any of claims 11 to

13.

Amendments to the claims have been filed as follows CLAIMS: 1. A method of firing a gun propellant charge which contains within itself a wholely separate closed electrical ignition circuit, in which method sufficient electrical energy to operate the ignition circuit is induced thereinto, from an energy source distant from the charge, by way of an electromagnetic coupling field, the gun obturator bolt, suitably modified, being employed as the radiating element for the field.

2. A method as claimed in claim 1, in which the charge ignition circuit is an electrically-heatable filament connected to a capacitor together with associated circuitry causing the capacitor to charge up slowly (as the ignition circuit receives field-coupled energy) and then to discharge suddenly through the filament.

3 A method as claimed in either of the preceding claims, in which the charge ignition circuit is associated with additional field coupling means enabling it to couple more efficiently with, and accordingly receive more energy from, the induced field.

4. A method as claimed in claim 3, in which the coupling means acts as a "radio" receiving aerial, and is a platelike foil or a series of wire loops suitably orientated and positioned on the charge and connected into the circuit.

5. A method as claimed in any of the preceding claims, in which the energy source employs suitable electricallypowered (oscillator) circuitry driving means for producing the desired electromagnetic field, the final element of such circuitry, which element is the field producing means, being a "radio" transmitting antenna constituted by the gun obturator bolt.

6. A method as claimed in;any of the preceding claims, in which the obturator bolt is so modified as to have a conductive core section extending axially from one end to the other and insulated from the material of the surrounding portion.

7. A method as claimed in any of the preceding claims, in which electromagnetic energy in the low gigahertz microwave frequency range is injected into the gun breech, employing the obturator bolt as the radiating element, the breech then being used as a waveguide to direct the energy to a receiving antenna forming part of the ignition circuitry in the charge0 8. A method as claimed in any of the preceding claims, and substantially as described hereinbefore.

9. A gun obturator bolt which has been modified to allow it to be used as the coupling electromagnetic field producing means in the charge firing system as defined in any of the preceding claims0 10. A gun obturator bolt as claimed in claim 9, which bolt is so modified as to have a conductive core section extending axially from one end to the other and insulated from the surrounding bolt material.

11. A gun obturator bolt as claimed in either of claims 9 and 10 and substantially as described hereinbefore.