FR2810106A1 - PROCESS FOR OBTAINING A CONSTANT LOW CONSTANT GAP BETWEEN AT LEAST TWO SUCCESSIVE PROJECTILE ELEMENTS, IDENTICAL FROM A BALLISTIC POINT OF VIEW AND PROJECTILE DESIGNED FOR THE APPLICATION OF THIS PROCESS - Google Patents

Abstract

On a tandem projectile comprising a first element, followed by at least another element, all the parts are designed so that the ballistic coefficients of these different elements are identical, so that, over a portion of the trajectory as large as possible , a gap is established which remains constant between these elements and their points of impact on the objective coincide. By applying negative or positive accelerations to the various elements of the projectile for short periods of time and over time so that they are driven at the same speed, a train of elements is produced which practically follow each other on the same trajectory and which are separated from each other by a gap which remains constant.

Description

The subject of the invention is a method for obtaining a small difference

  remaining constant between two successive projectile elements of

  preferably on the same trajectory, identical from the point of view of

  tick and pulled simultaneously from the same tube.

  The invention also relates to a projectile designed for the application of this method comprising: - a first projectile element, - at least a second projectile element preferably placed behind the first, - a device ensuring the separation between the first element and the following element (s) to bring them, at the time of the shooting or by the

  following a predetermined deviation.

  Tandem projectiles, i.e. projectiles with a first element followed by one or more other elements, are used against

special shields.

  On structured shields, shields with protective ceramic layers or similar shields, the first element of the projectile digs a crater. and, at the point of impact, the special protective devices, such as for example the ceramic layers, intended to deflect the first element of the projectile, are destroyed. The second element penetrates into the crater dug by the first and is able to puncture the shield itself, since the special protection device, mentioned above, has previously

been destroyed.

  In the event that the shielding comprises several layers each presenting special protection devices, these may be destroyed by the successive impacts of more than two elements constituting the projectile, it being understood that the last of these elements will ultimately ensure the

  perforation of the shielding which is no longer protected.

  The use of these projectiles, called tandem projectiles, is parti-

  especially important for attacking active or reactive armor, these protection devices being deactivated by the impact of the first element and the second element can then perforate the armor itself. The first and second elements or both, resp. more than two elements following the first must be separated on their trajectory by a perfectly defined distance, because if this difference is too small the protection device triggered by the first element, for example in the case of reactive armor, risk of further disrupt the action of the second element and if the difference is too large, the impact of the second element, in the case of a moving objective, will no longer coincide with that of the first element; furthermore, it should be taken into account that the reactive protective devices can possibly be designed to reactivate in a relatively short time interval after

The impact of a first element.

  In order to have the desired distance between the first and the second element for any range, a tandem projectile of the type mentioned (DE-A-34 18 444) comprises, between the first and the second element, a device for separation can be activated by means of a proximity rocket at a distance such that the two successive elements arrive on the objective

with the optimal gap.

  However, the proximity rocket poses a problem for this type of projectile.

  In a simple version, the proximity rocket will be relatively insensitive and prone to disturbances; thus, for example, it may react when passing over any obstacle on the ground located far from the objective and will then trigger the separation device prematurely. A proximity rocket with higher reaction accuracy will be

  necessarily more complex, which will result in a number of information

  suitable for the manufacturing price and the reliability of the

operation of the projectile.

  In addition, a proximity rocket may, depending on its design, possibly-

  be triggered prematurely by enemy countermeasures (for example by a cloud of metallic particles sent towards

of the attacking tandem projectile).

  Furthermore, such a proximity rocket must be able to function perfectly, even after long-term storage in

  bad weather conditions.

  In order to eliminate these problems, it was proposed at the time (request

  German Patent No. P 35 34 101.7-15) to replace the proximity rocket

  ted by an aerodynamically different design of the first and second elements so that the second element having undergone a strong

  deceleration from the first element following the action of the device

  tif of separation, catches up with the effect of its aerodynamic behavior and thus the difference between the two elements remains, over a relatively large distance, between limits which seem admissible for the type of job described above . In addition, provision may be made for the separation device to be activated only after a certain delay after

  the start of the blow, for example by a delay rocket like those used

  placed in anti-aircraft munitions, which enabled the use of this type of projectile on large as well as on short ranges, without having the disadvantages described above which are inherent in proximity rockets and which essentially concern the risk of disturbance of

its operation.

  But another serious drawback appeared for this type of projectiles: indeed. due to the different aerodynamic properties of the two elements, their points of impact, at the end of equivalent paths, will necessarily be different; even if, at the end of a relatively long journey that the two elements cross separately, their difference in time is still still between the admissible limits, the expected effect will not always be obtained because the impact of the second element

4 2810106

  will not coincide with that of the first and the action of the second element

  will therefore not benefit from the preparatory effect achieved by the former.

  Starting from this situation, the invention therefore aims to propose a method or a projectile capable of implementing this method which consists, without using a proximity rocket, of placing, over a long portion of their trajectory, the two elements at a constant or almost constant distance while ensuring, to a large extent, the concordance of their

impact points.

  This object is achieved in accordance with the invention, by the fact that each of these projectile elements successively undergoes a

  speed variation such that once the desired distance is reached, the two elements

  the same speed and their distance is kept constant.

  This process consists in firing simultaneously, from the same gun,

  according to the invention, all of the elements, at least two, identical

  ballistic ticks loaded one behind the other in the same ammunition. After the start of the stroke, the different elements are subjected, with small time shifts, to an acceleration (positive or negative) such that at the end of the acceleration phase all the elements have the same speed, I order in which the different elements are accelerated or decelerated to be

  defined so as to avoid any risk of collision between these elements.

  "Ballistically identical" means that the different elements

  are designed to follow each other on the same trajectory, taking into account possible aerodynamic interactions, such as for example disturbances by eddies which detach, the effects of dead water zones, etc. For one of the elements , the speed variation induced by the device can be zero if the other element or elements are first accelerated then braked or vice versa first braked then accelerated. What matters is that at a given moment the different elements are animated at the same speed once they have placed themselves on the trajectory at the distance beforehand

defined from each other.

  All projectile elements (except one, if applicable) are accelerated or decelerated for a short period of time so that, ultimately, they are driven at the same speed, but

  are placed at a defined distance from each other on the path

  roof. Furthermore, the different elements being strictly identical from a ballistic point of view, they do not only move to the same

  speed but also follow practically the same trajectory.

  This process could also be implemented by means of interior ballistics; however, in accordance with the invention, no attempt was made to

  solution at the level of the barrel but only at the level of the projectile.

  Thus, the projectile for the application of the method according to the invention is characterized by the fact - that the first projectile element and the following element (s) have ballistic coefficients (i.e. the magnitude which determines the deceleration and which results from a relation between the mass of the projectile, its section and the coefficient of drag) identical - and that the separation device is designed so that it ensures either in the first place the deceleration of the second element or of one of the following elements and then brings the first element or one of the preceding elements at the same speed, that is to say the acceleration of the first element or of one of the elements which precedes the last at a higher speed to then also accelerate the second element or each of the following elements at the same speed so that ultimately the first and second elements or the first and the following elements move hundred at the same speed and be separated from each other from the

previously defined distance.

  The two elements (or all of the elements) have the same ballistic coefficient which determines their trajectory, and which is a quantity into which the drag, the section and the mass of the projectile enter. Insofar as it is technically possible to design elements which are not absolutely identical but which, despite the difference in some of their characteristics, nevertheless have an equivalent ballistic coefficient and therefore follow exactly the same trajectory, such a solution can be adopted for the realization

  of the invention and is therefore included in its object.

  The separation device is designed either to first accelerate the first element and then bring the next element at the same speed, or to first brake the second element and then bring the element

previous at the same speed.

  For this purpose, the separation device can for example be constituted

  by a propellant charge placed in each of the projectile elements.

  These charges are then initiated with a certain time lag, for example by means of pyrotechnic devices, themselves initiated at the start of the blow and which ensure the triggering with the slight delay desired of the various elements, starting with the first so that at the end of the acceleration phase all the elements have the same speed, possibly higher than their initial speed, and that they are separated from the previously defined distance and that these differences

be maintained.

  According to another preferred version of the invention, the separation device can be designed in the form of a series of aerodynamic brakes,

  one per projectile element, which are activated in due time and then deactivated

  vés. These aerodynamic brakes can for example be constituted by strips which are put in place on the periphery of the element when it is a question of ensuring their braking and which, once the braking action

  completed, can be ejected by pyrotechnic effect or dropped.

  The various aerodynamic brakes can be installed with a certain time lag, for example by means of a delay rocket. We can then, as on an anti-aircraft munition, determine in advance the moment from which the different elements

  should fly at the desired distance to be fully effective.

  Preferably, the aerodynamic brake of the second or last element is activated as soon as it leaves the tube because, due to the concordance of the points of impact and the constant distance which, according to the invention, must separate the elements on their trajectory, it is important that these deviations are made over the entire trajectory to ensure that the projectile according to the invention is fully effective over the whole

of its trajectory.

  Thus, it may for example be advantageous to briefly brake the second element of a tandem projectile, as soon as it leaves the mouth, by the launching shoe which releases the first element without braking it; after this braking of the second element, a propellant, ignited by with a slight delay by the combustion gases, will accelerate again to

  that it reaches the same speed as the first element.

  In order to bring the elements of a projectile of the latter type in particular as close as possible to an intervention distance, it will preferably be ensured that the second or the last of the following elements is

  braked not only as soon as possible, but also relatively-

  ment strong so that it reaches its desired final speed and ultimately its predetermined deviation from the element in front of it, after a journey as short as possible. Preferably the first or the corresponding previous element will be braked in the same way and

  so intense; but it is also possible to apply to the elec-

  braking action earlier and less intensely

  se. Preferably the aerodynamic brakes provided on the different elements

  of the projectiles will be of identical design.

  The projectile, according to the invention, can be a projectile stabilized by rotation, but it will preferably be a projectile stabilized by empennage and, moreover, preferably, a sub-calibrated projectile, in which case the aerodynamic brakes or at least one of them act in interaction with the elements of the launching shoe and can be ejected or separated by pyrotechnic means at the same time as these elements. The projectile, according to the invention, is preferably designed as

  kinetic penetrating projectile but may also include a formed charge.

  In addition, it is possible to design a mixed projectile, comprising a kinetic piercing part and a shaped charge, provided that

  these two parts have the same ballistic coefficient mentioned above.

  On the whole it is always necessary, as we have already mentioned above, to take into account the reciprocal influence which the different elements of the projectile exert on each other; so for example it is possible

  that the additional propellant of a previous element of the projectile does not

  re not only the acceleration of this element, but at the same time the braking of the next element; moreover, once the various elements of a projectile are brought to the desired distance, the head wave of the preceding element can generate a certain area of dead water which, around the element which follows at a distance a few meters only, can produce a flow different from that existing around

  of the previous element and in particular around the first element.

  The attached diagrams illustrate in more detail, by way of example, the object of the invention; these figures show: Fig. 1: the speed of two elements of a tandem projectile in accordance with the invention, as a function of the flight time of each of these elements, and FIG. 2 a diagram, similar to that of FIG. 1, but with different values and in addition the indication of the distance separating the elements of the projectile. The diagrams represented in the figures each relate to a

  tandem projectile comprising a first and a second element.

  The drag of the second element (index 2) is only increased during the time interval t2, at t2, (that is to say during the duration dt2) and its speed therefore passes by braking v2. = v2 (t2,) to v2. = v2 (t,). We thus realize

  a gap between the first and the second element.

  At time t1, which is generally offset by dt with respect to t2e, the drag of the first element (index 1) is then increased until time t1. (duration dt1) in the same way as previously that of the second element, so that the speed in flight Vla

  is brought back for life. This value is not identical to v2.

  but the relation v1 (t ,.) = v2 (t ,.) must be verified.

  Except during the time interval between t2z. and t1., (inter-

  valley which corresponds to dt + d ,.), the two elements of the projectile

  then have the same speed over the entire trajectory.

  Taking into account the characteristics of the projectile and the additional resistance coefficients, the different time intervals must be chosen respecting the following principles: a) The interval d, 2 is defined so that between the first and the second element s' establish a gap roughly corresponding to the gap

  optimal, but preferably a little lower than this value.

  b) The interval d, 1 must be defined so that the speed of the first element is reduced to the speed of the second element, measured

at time t ,.

  c) The time interval dt between the instants of activation of the two aerodynamic brakes, must be defined so that due to the speed difference between the first and the second element, it is established in l 'time interval between t, and tl., a difference corresponding to that required for an effective action against the objective (for example with active shielding). When we interpret the path a (fig. 2) as an integral in time of the speed, it follows from the figures that the surface delimited by the speed curves is

  equal to the difference obtained which must correspond to the optimal difference sought.

  We can thus reveal the correlations between the actions of

  braking which results in variations in drag and inter-

time valles.

  Figure 2 shows that the braking rate (slope of curves v1 and v2) is not necessarily the same for the first and for the second element, as is the case in the diagram in Figure 1. Anyway , the speed variations undergone by the first and the second element in the time interval between ta, and t1. don't matter. The value of the acceleration (negative) can be different for the first and for the second element; what matters is that after time t1. the speed of these two elements is the same and that

  only one curve appears on the speed diagram.

  In the lower part of Figure 2 there is shown the difference a between the first and the second element as a function of time; this difference appears in the upper part in the form of a hatched surface, included between the curves which represents the evolution of the speed of the

first and second element.

  As we can see, a0 is the difference between the first and the second element until time t2 ,, i.e. roughly between the exit of the projectile from the mouth until the start of the separation between the two elements. This difference a0 can vary from zero to a few centimeters. The difference a then increases during the speed variation experienced by the first and the second element, until, at time t1, the speed of the two elements is the same; the difference then reaches its optimal theoretical value ah, which is maintained on the

  rest of the trajectory until impact on the objective.

  At time t, the difference between the two elements reaches a value

  minimum a, i, and the projectile is then at the minimum distance

  the efficiency, which means that the tandem projectile has traversed the

  path on which it is ineffective or not yet fully effective.

  In order that this minimum efficiency distance is as reduced as possible, it will be ensured that the instant t2 is as close as possible to the instant t0 of the start of the stroke and that, moreover, the slope of the curve of v2 between t2, and t2, and that of the curve of v, between t1 ,, and t1. are as stiff as possible, so that the instant t1, can coincide with the instant

t2, or even be earlier.

l

Claims (8)

  1. Method for obtaining a small gap remaining constant between at least two projectile elements preferably succeeding one another on the same trajectory, identical from a ballistic point of view and fired simultaneously from the same tube, characterized by fact that each of these projectile elements successively undergoes a speed variation such that once the desired distance is reached, the two elements have the same speed and their distance is kept constant.   2. Projectile for the application of the method according to claim 1, - a first projectile element, - at least a second projectile element preferably placed behind the first.   - a device ensuring the separation between the first element and the following element (s) to bring them, at the time of firing or thereafter, to a predetermined gap, characterized in that - the first element projectile and the following element (s) have ballistic coefficients (i.e. the quantity which determines the deceleration and which results from a relation between the mass of the projectile, its section and the coefficient of trail) identical - and that the separation device is designed so that it ensures first of all the deceleration of the second element or of one of the following elements and then brings the first element or one of the preceding elements at the same speed, either the acceleration of the first element or of one of the elements preceding the last one at a higher speed to then also accelerate the second element or each of the following elements at the same speed of s orte that in the end, the first and the second elements or the first and the following elements move at the same speed and are separated from each other by the previously defined distance. 3. Projectile according to claim 2, characterized in that the separation device consists of a number of aerodynamic brakes, preferably of identical design, each of these   brakes fitted to a projectile element.   4. Projectile according to claim 3, characterized in that each of the aerodynamic brakes can be triggered by a system   timed, preferably consisting of a pyrotechnic device.   5. Projectile according to one of claims 3 or 4, characterized by   the fact that the aerodynamic brake of each element of the projectile   may, after its braking action, detach from it and / or become ineffective.   6. Projectile according to one of claims 3 to 5, characterized by   the fact that the aerodynamic brake of the second or last of the projectile elements can be activated when the projectile leaves the mouth from the barrel.   7. Projectile according to claim 2. characterized in that   the separation device consists of a number of propellants   identical additional sources, adjusted so that at the end of the phase   of combustion of this set of propellants, each element of the projecti- the presents the same speed.   8. Projectile according to claim 2, characterized in that either the first element, or each of the preceding elements or the second element, or each of the following elements is equipped with a braking device and an additional propellant for first ensure its acceleration or deceleration and then bring it, by deceleration, to the speed of the next projectile element, or   by acceleration to the speed of the previous projectile element.