Abstract:
The invention relates to a launching device for a sub-caliber artillery projectile employing a base with sliding band, the base being linked to sabot sectors by means of hinges that can be detached during flight, the opening of the sabot being activated thanks to the dynamic air pressure on the flared shapes to the fore of the sectors, said hinge is flanged radially so as to prevent its becoming separated from the sabot sectors  5  outside of the flight phase.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The technical scope of the invention is that of launching devices enabling sub-caliber artillery projectiles to be fired from a gun barrel. 
     2. Description of the Related Art 
     So as to improve the range of large caliber artillery projectiles, it is possible to employ projectiles that have lift surfaces such as fins and to combine such means with the sub-calibration of the projectile so as to reduce its aerodynamic drag. 
     These solutions firstly require the use of uncoupling means between the projectile and the weapon so that the spin effect created by the gun barrel does not damage the projectile fins and secondly the use of means to compensate for the difference in caliber between the projectile and the barrel. 
     Upon exiting the barrel, these means having performed their functions, it is necessary for them to be discarded from the projectile without this hindering or perturbing the projectile&#39;s trajectory. 
     For this, it is known by document EP-0905473 to employ a sliding band around a base pushing the projectile. This base is separated from the projectile by means of a small pyrotechnic ejector. Independently from the ejection of the base, the caliber compensation means, also called sabot sectors, placed to the fore of the projectile are distanced from the projectile by the dynamic air pressure. 
     The solution using the pyrotechnic ejector is complicated since firing must be performed precisely and reliably. The impulsion of the ejector can perturb the projectile&#39;s trajectory if this impulsion is not perfectly coaxial to the trajectory. Furthermore, retaining the sabot sectors on the projectile requires machining to be performed on the projectile to be able to install pins that are sectioned upon firing. These pins need to be precisely calibrated for fracture. 
     Medium-caliber sub-caliber projectiles are known that incorporate a sabot integral with a base and which opens upon exiting the gun barrel through the effect of the centrifugal force. Such projectiles are disclosed, for example, by U.S. Pat. No. 4,419,796, DE-1262830 and U.S. Pat. No. 4,476,785. 
     These sabots are generally integral with the base and incorporate incipient fractures to facilitate the release of the projectile. Such solutions cannot be transposed to an artillery projectile whose spin is reduced by the effect of the sliding band. 
     A medium-caliber dart-type projectile is also known by patent WO93/02333 that is released by a sabot integral with a base. The solution proposed implements an embrittled hinge that fractures upon exiting the gun barrel. Such a solution is likely to perturb the trajectory of an artillery projectile. 
     Patent GB-123501 succinctly describes a sub-caliber projectile of large caliber (406 mm) wherein its sabot sectors are hinged to the base. These hinges are opened through the action of the centrifugal force. However, these hinges are not clearly defined by this patent. These hinges enable the base to be pushed rearwards out of the way of the projectile. It even seems that the sectors remain integral with the base by their hinges as suggested in  FIG. 3 . 
     This solution can not be transposed to an artillery projectile equipped with a sliding band and for which the centrifugal force is reduced and for which there is a high risk of perturbation of the projectile&#39;s flight linked to dissymmetry in opening the sabot segments. 
     SUMMARY OF THE INVENTION 
     The invention proposes to improve the release of the projectile by linking the sabot sectors to the base by a hinge having a specific geometry that does not cause interference between the sabot sectors and the base. In this way, the sectors are distanced symmetrically so as to avoid perturbing the projectile&#39;s trajectory and the base is furthermore distanced from the projectile by the pressure of the sectors on the base combined with the load created by its own aerodynamic drag. 
     In this simple manner, no parasitic stress is applied to the projectile. 
     Thus, the invention relates to a launching device for a sub-caliber artillery projectile, launching device comprising a base at its rear part that incorporates a sliding band at its periphery, base containing a rear part of the projectile and incorporating a thrust surface cooperating with a matching surface at the rear of the projectile, launching device wherein it comprises at least two cylinder sectors surrounding the projectile and intended to ensure guidance by means of exterior ring-shaped support bands, sectors in contact by at least one interior support shape with the projectile, launching device incorporating for each sector at least one hinge materializing an instantaneous axis, hinge able to be detached during flight and linking the base to the sector in question, the hinge being constituted by at least one notch on the base which cooperates with a tooth linked to the sector, the notch being delimited to the fore by a plane inclined surface and to the rear by a stop surface perpendicular to the projectile&#39;s longitudinal axis and cooperating with a matching support surface on the tooth, an edge of the tooth being in contact with the stop surface and constituting the instantaneous axis, the tooth and notch having, furthermore, a geometry such that the tooth pivots when the sector opens around the instantaneous axis without interfering with the inclined surface. 
     According to one embodiment of the invention, the notch incorporates an inclined surface forming an angle α greater than or equal to 90 degrees with a fictive plane F passing by the instantaneous axis and by a point of contact between the tooth and the inclined surface, any part of the tooth placed between the fictive plane F and the stop surface being located at a distance from the instantaneous axis that is less than the distance separating the latter axis and the point of contact between the tooth and the inclined surface. 
     According to another characteristic of the invention, the hinge may incorporate at least one means to adjust the axial pressure play between the base and the sector. 
     These means to adjust the axial pressure play may comprise at least one pressure screw at each hinge integral by an internal thread in the tooth and pressing on the inclined surface of the notch. 
     According to another characteristic of the invention, the device may incorporate at least one flange means to oppose the radial distancing between the base and the sectors when these are in contact with the projectile. 
     These flange means may thus incorporate at least one flange screw at each hinge that passes through the tooth by means of internal threading, such flange screw being oriented so as to penetrate to the rear of the launching device and into a recess made in the notch in the base, recess in contact with the flange screw so as to prevent any radial movement of the tooth with respect to the base. 
     The surfaces of the recess will be selected with dimensions such that they do not interfere with the flange screw when this rotates around the instantaneous axis in the direction of opening of the sectors. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The description given hereafter, illustrated by the appended drawings, will enable the invention to be better understood: 
         FIG. 1  shows a launching device containing a projectile, 
         FIG. 2  shows a longitudinal section view of a launching device containing a projectile, 
         FIG. 3  shows a launching device containing a projectile when the device separates from the projectile, 
         FIG. 4  shows a detailed section view of the hinging of the launching device, such longitudinal section made between the screws, 
         FIG. 5  shows a detailed section view of the means to adjust the axial play between the base and the sector, such longitudinal section made at a pressure screw, and 
         FIG. 6  shows a detailed section view of the flange means of the hinge, longitudinal section made at a flange screw. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     According to  FIG. 1  and according to one embodiment, the launching device  1  contains a projectile  2 . This device is formed of a base  3  on its rear part. The base is equipped with a sliding band  4 . The base is linked to three sectors  5  forming a sabot, only two of which can be seen in the drawing. The link is ensured by a hinge  6  between each sector  5  of the sabot and the base  3 . The external part of the sabot sectors  5  is in contact with the interior of the gun barrel thanks to bands  5   b ,  5   c  forming ring-shaped seats (bands made, for example, of a plastic material). 
     The device such as shown in this drawing is in the configuration it occupies once put in place in the gun chamber and over all its trajectory in the gun barrel. 
     According to  FIG. 2 , the fins  2   a  of the projectile  2  are contained in the base  3 . The base  3  incorporates a thrust surface  3   a  pressing on a matching rear surface of the projectile  2 . The base  3  has grooves, not shown, opening out into this thrust surface  3   a  so as to allow the fins  2   a  to pass when the base  3  separates from the projectile  2 . The sabot sectors  5  incorporate flared interior support shapes  5   a  in contact with the projectile  2  to centre it on the longitudinal axis of the launching device. 
     According to  FIG. 3 , directly upon exiting the barrel, the device  1  will open as follows. The air pressure exerted on the flared support shapes  5   a  of each sector  5  will cause a symmetrical distancing (arrows  11 ) of the sectors  5  with fracturing of the ring-shaped seats  5   b  and  5   c . These sectors  5  pressing on the base  3  by means of the hinges  6  will push the base  3  rearwards, bringing it to distance itself from the rear of the projectile  2  and thus freeing the fins  2   a . Throughout this phase, there is no radial load exerted on the projectile  2 . Following this phase, the hinges  6  (which are not integral with the base) will detach from the base  3  and each piece of the device  1  will be projected away from the trajectory of the projectile  2 . 
     According to  FIG. 4 , each hinge  6  comprises a tooth  6   a  inserted in a matching notch  3   b  made in the base  3 . The notch  3   b , of a width substantially equal to the width of the tooth  6   a , is delimited to the fore by an inclined plane surface  3   c  and to the rear by a surface  3   d , a so-called stop surface, perpendicular to the longitudinal axis of the launching device  1 . 
     The tooth  6   a  incorporates an edge  6   b  at its foot positioned to the rear of the device. This edge  6   b  in contact with the stop surface  3   d  constitutes an instantaneous axis  7  for the tooth  6   a  when the sector  5  opens. 
     According to  FIG. 5 , two pressure screws  8 , passing through the tooth  6   a  via internal threading  6   e , by tightening enable pressure to be put on the inclined surface  3   c , thereby bringing the surface  6   d , perpendicular to the longitudinal axis of the projectile  2 , into contact with the stop surface  3   d  of the base  3  to ensure the transmissions of the firing stresses from the base  3  to the sector  5 . The hinge has a surface  6   c.    
     A fictive plane F has been shown in this Figure in dotted lines passing through the instantaneous axis  7  (constituted by the edge  6   b ) and by the point of contact  8   a  between the pressure screw  8  and the inclined plane  3   c . Similarly, in the longitudinal plane of the launching device, a circle C has also been shown in this Figure centered on the instantaneous axis  7  with a radius R equal to the distance between the instantaneous axis  7  and the point of contact  8   a  between the pressure screw  8  and the inclined plane  3   c.    
     To avoid any interference between the tooth  6   a  or the pressure screws  8  and the inclined surface  3   c  of the notch  3   b  during the rotation around the instantaneous axis  7 , two conditions must be met:
         The angle α formed by the fictive plane F and the inclined plane  3   c  must not be less than 90 degrees.   The whole of that part of the tooth  6   a , including the screw  8 , placed between the fictive plane F and the support surface  6   d  must lie within the circle C.       

     In other words, any part of the tooth located behind the plane F must be at a distance that is less than R from the instantaneous axis  7 . 
     According to  FIG. 6 , a setscrew  9  (or flange screw) is inclined such that it has a penetration angle oriented towards the rear of the launching device  1 . This flange screw passes through the tooth  6  by means of an internal threading  6   g  and penetrates a cylindrical recess  10 . This flange screw  9  will ensure a flanging function by penetrating in the recess  10  until it comes into contact with the chamfer  10   d  of the recess  10  but only on that part of the chamfer  10   d  oriented the most rearwards of the launching device  1  (upper part of the recess  10  shown in  FIG. 6 ). The interference between the flange screw  9  and the chamfer  10   d  does not enable the tooth  6   a  to distance itself radially from the base  3  in direction Z. 
     The recess  10  is selected with a diameter large enough for it not to interfere with the screw  9  during the rotation of the tooth  6   a  around the instantaneous axis  7  due to the opening of sectors  5 . 
     According to another embodiment, the recess  10  may be an oblong groove.