Abstract:
The subject of the invention is a translational braking device for a projectile during its trajectory comprising at least two airbrakes that are radially deployable so as to increase the projectile&#39;s aerodynamic drag. Each airbrake is a flap pivoting around a pivot integral with the projectile and parallel to its axis. The device incorporates at least one pyrotechnic piston locking at least one of the flaps in its folded position and at least two flaps are stacked one on top of the other when they are in their folded position, at least a first of the two flaps incorporates a mechanism to retain the second of the two flaps in its folded position.

Description:
BACKGROUND OF THE INVENTION 
     The technical scope of the invention is that of translational braking devices for a projectile during its trajectory. 
     Such devices are notably known in the field of artillery. 
     Patent EP138942thus describes an artillery projectile that incorporates a device to brake the nose cone whose deployment is controlled during the trajectory. 
     Such an arrangement allows firing accuracy of artillery fires to be increased whilst taking into account dispersions due to the variations in initial velocity of the projectile. Indeed, it is thus possible to lay the weapon so as to fire beyond the target aimed at, a fire control measures the real velocity of the projectile at the muzzle of the weapon and a braking command is thereafter transmitted to the projectile so as to reduce its range and thus bring it to the desired point of impact. 
     The braking device described by this patent comprises, either radially mobile fingers, or a plane frontal surface. The surface area of these braking means with respect to the section of the projectile is too small for their braking capacity to be sufficient. 
     Patent WO98/01719 describes another braking device for a projectile. This device comprises four airbrake plates stacked one on top of the other and radially mobile with respect to the projectile. 
     The braking area is thus substantially increased (it constitutes approximately double the section of the projectile) and is of a reduced bulk inside the projectile body. 
     However, this device has drawbacks. 
     The shapes of the plates are complicated to machine, they also incorporate numerous indents that reduce their mechanical strength, notably in their fully deployed position where the stresses are at their worst. 
     Moreover, the plates are unlocked by means of two gas generators that displace two retention pins, each pin immobilizing two plates. Such a structure is likely to cause dissymmetries or sticking when the plates are deploying that risk modifying the trajectory of the projectile in a non-reproducible manner. 
     SUMMARY OF THE INVENTION 
     The aim of the invention is to propose a translational braking device for a projectile that does not have such drawbacks. 
     Thus the braking device according to the invention is of a simple inexpensive design and has improved mechanical strength with respect to the previously described device. 
     It is not likely to stick, and it consequently has perfect opening symmetry of the airbrakes. 
     Thus, the subject of the invention is a translational braking device for a projectile during its trajectory comprising at least two airbrakes that are radially deployable so as to increase the projectile&#39;s aerodynamic drag, wherein each airbrake is a flap pivoting around a pivot integral with the projectile and parallel to its axis. 
     According to one characteristic of the invention, the braking device incorporates at least one pyrotechnic piston locking at least one of the flaps in its folded position. 
     According to a first embodiment of the invention, at least two flaps are stacked one on top of the other when they are in their folded position, at least a first of the two flaps incorporating means to retain the second of the two flaps in its folded position. 
     The braking device can, advantageously, incorporate at least four flaps, a first flap being locked by the pyrotechnic piston and carrying a first pin retaining a second flap in its folded position, a third flap carrying a second pin co-operating with a first retention surface integral with the second flap, a fourth flap carrying a third pin co-operating with a second retention surface integral with the third flap, a single pyrotechnic piston thereby ensuring the locking of all four flaps. 
     Each flap can have an external profile covering the arc of a circle whose diameter is substantially equal to that of an external part of the projectile and an indent intended to allow the flap to fold around an axial support integral with the projectile. 
     Each flap can, advantageously, incorporate an abutment heel intended to co-operate with a matching surface of the axial support so as to stop the opening movement of the flap. 
     The arc length of the external profile of each flap and the length of the different heels can be selected such that, in the deployed position, the free end of at least one flap presses on a neighboring flap or else on the projectile. 
     The axial supports can carry two plates, a lower plate and an upper plate, each plate supporting at least two pivots of the flaps that are thus arranged between the two plates when they are in the folded position. 
     According to a second embodiment of the invention, each flap can incorporate a toothed circular portion arranged around the pivot , such portion meshing with a central pinion coaxial to the projectile, such central pinion thereby joining together the different flaps. 
     The pyrotechnic piston can, advantageously, lock the central pinion. 
     The flaps can, in any case, be integral with a nose cone fuse of the projectile. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other advantages of the invention will become apparent from reading the following description of the different embodiments, such description being made with reference to the appended drawings, in which: 
     FIG. 1 schematically shows a projectile fitted with a braking device according to the invention, 
     FIG. 2 shows a partial longitudinal section view of a projectile fuse fitted with a braking device according to a first embodiment of the invention, 
     FIG. 3 shows this same device in the folded position and as a section along plane AA referenced in FIG. 2, 
     FIG. 4 is an analogous view to FIG. 3 but shows the device in the deployed position, 
     FIGS. 5 a  to  5   h  show the braking flaps alone, FIGS. 5 a ,  5   c ,  5   e , and  5   g  being frontal views of said flaps and FIGS. 5 b ,  5   d ,  5   f , and  5   h  being lateral views of the different flaps, each of the frontal views being associated with its lateral view for a given flap ( 5   a / 5   b ,  5   c / 5   d ,  5   e / 5   f  and  5   g / 5   h ), 
     FIGS. 6 and 7 are partial section views of two types of flap hinges, 
     FIG. 8 shows a section view in the deployed position of a device according to a first embodiment, 
     FIG. 9 shows a partial longitudinal section view of a projectile fuse fitted with a braking device according to a second embodiment of the invention, 
     FIG. 10 shows this same device in the deployed position and as a section along plane BB referenced on FIG.  9 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to FIG. 1, an artillery projectile  1  is fitted, at its rear part, with a belt  2  intended to mesh in the rifling of a weapon barrel (not shown) and to provide sealing against the propellant gases when the projectile is fired. At its front part this projectile carries a fuse  3  that is intended, in a conventional manner and according to the type of projectile in question (explosive projectile or carrier projectile), to ensure either the ignition of an explosive charge placed inside the projectile, or the priming of a gas-generating charge intended to eject a payload during the trajectory that has been placed inside the projectile (anti-tank ammunition or grenades). 
     To this end, the fuse  3  incorporates an electronic control device  4  that causes the ignition of a pyrotechnic charge  5  (that, according to the case, is a detonation relay or a gas generator). 
     In accordance with the invention, this fuse  3  also incorporates a translational braking device  6  enabling the radial deployment during the trajectory of braking flaps  7 . The deployment of the flaps  7  is controlled by the electronic control device  4  in response to a command received during the trajectory by means of a receiver  8  or else emitted by the electronic control device  4  in accordance with programming made before firing, or else modified in the first moments following firing to take into account the real initial velocity of the projectile. 
     Programming during the trajectory will be ensured by means of a receiver  8  that can use radar technology. 
     FIG. 2 shows the fuse  3  in more detail. It has an overall shape and bulk analogous to those of conventional artillery fuses. It incorporates a body  13  onto which threading  9  is made that is intended to allow it to be made integral with the projectile. The pyrotechnic charge  5  is placed in a bush integral with the body and communicates via a priming channel  10  with an electrically-operated igniting composition  11  (primer or squib), that is itself connected to the electronic control device  4 . 
     In a conventional manner neither described nor shown in detail here, the igniting component  11  is carried by a mobile flap  12  of a safety and arming device. 
     The body  13  of the fuse  3  incorporates an axial cylinder  14  that connects a lower portion of the fuse  3  incorporating the pyrotechnic charge  5  and an upper portion of the fuse  3  enclosing the electronic device  4 . A priming channel  10  passes through this cylinder. The cylinder  14  receives the braking device  6  that comprises an axial fin support  15  incorporating a tubular part  16  and two plates  17  and  18 . The tubular part  16  is mounted coaxially to the cylinder  14  and thus has an inner diameter that is equal to that of the cylinder  14 . The upper  17  and lower  18  plates are plane and perpendicular to the axis  20  of the fuse  3  and the projectile. The two plates  17  and  18  delimit a ring-shaped volume inside which flaps  7  are placed. The fin support  15  is made integral in translation and in rotation with the fuse  3  body, for example by a locking nut mounted on the cylinder  14  and not shown. 
     In accordance with this first embodiment of the invention, which is also the preferred embodiment, four flaps  7   a ,  7   b ,  7   c  and  7   d  are integral with the support  15 . 
     Each flap is hinged with respect to the support around a pivot  19  ( 19   a ,  19   b ,  19   c ,  19   d ) parallel to the axis  20  of the fuse  3  (and thus also of the projectile). 
     For reasons of clearness in the drawing, the pivots  19  are only shown schematically in FIG.  2 . The upper plate  17  carries two pivots  19   a  and  19   b  that fasten the two flaps  7   a  and  7   b . The lower plate  18  carries two pivots  19   c  and  19   d  that fasten the two pivots  7   c  and  7   d . The pivots are evenly spaced angularly around the axis  20  of the fuse  3 . 
     The different flaps are stacked on top of one another when they are in their folded position, the first flap  7   a  is in contact with the upper plate  17  and the fourth flap  7   d  is in contact with the lower plate  18 . The second flap  7   b  is placed between the first flap  7   a  and the third flap  7   c , said flap  7   c  being itself placed between the second flap  7   b  and the fourth flap  7   d . Such an arrangement of the flaps ensures their mechanical resistance to the acceleration developed when the projectile is fired. 
     FIGS. 6 and 7 show the structure of a pivot  19  in detail. FIG. 6 shows the structure of a pivot ( 19   a  or  19   d ) fastening the flaps that are directly in contact with plates  17  and  18 , that is flaps  7   a  and  7   d . Pivot  19   a  (or  19   d ) is constituted by a nut  21  having an enlarged head  21   a  housed in a counter-sink  22  arranged in the flap. A screw  23  has its head in contact with the plate  17  (or  18 ) and connects the flap and the plate. Play of around a tenth of a millimeter is provided during assembly so as to allow the flap to pivot around hinge pin  24  of pivot  19 . 
     FIG. 7 shows the structure of a pivot ( 19   b  or  19   c ) fastening the flaps that are not directly in contact with the plates  17  and  18 , that is flaps  7   b  and  7   c . 
     This pivot also incorporates a nut  21  whose enlarged head is housed in a counter-sink arranged in the flap and a screw  23  whose head is in contact with the plate  17  (or  18 ). It differs from the pivot in FIG. 6 by the presence of a brace  25  ensuring a space between the plate and the flap in question. The thickness of the brace is equal to that of the flap placed between the plate and the intermediate flap in question. 
     The flaps can be seen in greater detail in FIGS. 5 a  to  5   h . Each flap is made, for example, of steel sheeting of a thickness of 2 mm and that has a perforation  32  intended to receive the pivot  19  and in which is arranged a counter-sink  22 . The flaps can also be made of another material, for example a light alloy (aluminum-based). 
     Each flap has an external profile  26  covering the arc of a circle whose diameter is substantially equal to the external diameter of the fuse  3 . 
     Each flap also has an indent  27  intended to allow the flap to be folded around the tubular part  16  of the axial support  15 . To this end, the indent  27  incorporates a hemicylindrical portion  28  of the same diameter as that of the tubular part  16  and coaxial to its axis  20  (that is coaxial also to the axis of the fuse  3  and the projectile). The hemicylindrical portion  28  of the indent is connected on one side to a plane surface  29  that is perpendicular to the plane defined by the hinge pin  24  of the pivot  19  in question and the axis  20  of the fuse  3 , and on the other to two cylindrical surfaces  30  and  31 , the first ( 30 ) of which is coaxial to the pivot  19  and the second ( 31 ) having an axis parallel to that of the pivot and a radius equal to that of the tubular part  16 . The surface  31  constitutes an abutment heel that is intended to co-operate with the axial support  15  to stop the opening movement of the flap  7 . 
     The cylindrical surfaces  30  and  31  are arranged in the vicinity of the pivot  19  and the axis  20  of the fuse  3  is located between the hinge pin  24  of the pivot and the plane surface  29 . This results in such an arrangement that a pivotal movement of each flap around its hinge pin  24  is allowed without there being any interference between the plane surface  29  and the tubular part  16 . As a result of the shape thus adopted for the flaps, a maximal flap surface area is obtained for a minimal bulk in the folded position. 
     In addition, the different flaps have certain structural differences with respect to one another. 
     Thus, the first flap  7   a  has a hole  33  that is intended to receive the rod  35  of a pyrotechnic piston  34  (see FIG.  2 ). 
     This pyrotechnic piston is in this case a pyrotechnic retractor that comprises a gas-generating composition electrically ignited by the control device  4  and whose effect is to cause the retraction of the rod  35  from the hole  33 . Such a pyrotechnic component is well known to the expert and will therefore not be described here in any further detail. 
     The rod  35  of the retractor locks the first flap  7   a  in its folded position. 
     The first flap  7   a  also has a first pin  36  that is intended to ensure the retention of the second flap  7   b  in its folded position. To this end, it co-operates with a notch  37  made on the external circular profile  26  of the second flap  7   b.    
     The third flap  7   c  has a second pin  38  that is intended to co-operate with the plane surface  29  of the second flap  7   b  when this is in its folded position. This plane surface then constitutes a first retention surface that prevents the third flap from opening when the second flap is in the folded position. 
     Lastly, the fourth flap  7   d  has a third pin  39  that co-operates in an analogous manner with the plane surface  29  of the third flap  7   c  when this is in its folded position. This plane surface constitutes a second retention surface that prevents the fourth flap from opening when the third flap is in its folded position. 
     Thus, a single pyrotechnic piston  34  locks all the four flaps  7   a ,  7   b ,  7   c  and  7   d  and prevents them from deploying further to the centrifugal forces that are exerted on them when the projectile is fired. 
     Pins  36 ,  38  and  39  are constituted by small cylindrical rods mounted in holes made in the flaps. 
     FIG. 3 shows the four flaps in the folded locked position. 
     The section view of the fuse  3  has been carried out so as to remove the upper plate  17 . Only the first flap  7   a  is fully visible, its pivot  19   a  being to the right of the figure with the nut  21  sectioned. The second flap  7   b  is partially visible in the indent of the first flap, its pivot  19   b  is at the top of the figure with the sectioned nut  21  and the brace  25  visible. The third flap is hidden, its pivot  19   c  is at the bottom of the figure, the fourth flap is also hidden, its pivot  19   d  is at the left of the figure. 
     This figure shows how the different retention means co-operate to lock the four flaps. 
     We can thus see that, when the first flap  7   a  is immobilized by the rod  35  of the pyrotechnic piston introduced in the hole  33 , the pin  36  of the first flap is positioned in the notch  37  of the second flap  7   b , which can no longer deploy. 
     The pin  38  carried by the third flap  7   c  is in contact with the plane surface  29  of the second flap  7   b . The third flap is therefore not able to open. 
     The pin  39  carried by the fourth flap  7   d  is in contact with the plane surface  29  of the third flap  7   c . The fourth flap is therefore not able to open. 
     At a given moment during the trajectory, the electronic control device  4  will cause the rod  35  to retract from the pyrotechnic piston. The first flap  7   a  will open under the action of the centrifugal force. The pin  36  thereafter comes out of the notch  37  freeing the second flap  7   b , which can now also open. The surface  29  moves away from the pin  38 , thereby freeing the third flap  7   c , which in turn opens freeing the fourth flap  7   d.    
     Because only one locking device (the pyrotechnic piston) is employed, the four flaps open practically simultaneously. This results in a symmetry and reproducibility of the opening movement that avoids disturbances to the braking trajectory of the projectile. 
     FIG. 4 shows the flaps in their deployed position. 
     The rotation of each flap is halted by its abutment heel  31  coming into contact with the tubular part  16  of the axial support  15 . Such an arrangement enables the angle of opening of the flaps to be controlled. 
     The arc length of the external profile  26  of each flap and the length of the different abutment heels are selected such that, in the deployed position, the free end  40  of each flap (the end that is the furthest away from the pivot  19 ) presses on or lies opposite to a neighboring flap or else presses on or lies opposite to the lower plate  18  (that forms a bearing surface integral with the fuse and thus with the projectile, perpendicular to the projectile axis). 
     In this example, however, the fourth flap  7   d  presses by its free end  40  on the lower plate  18 . The third flap  7   c  presses by its end  40  on the fourth flap  7   d  and opposite plate  18  increasing the rigidity of the bearing. The first and second flaps have their free end respectively opposite the third flap and the lower plate  18 . 
     By reducing the opening amplitude of the flaps in this manner, the rigidity of the braking device in its deployed position is improved, and therefore also its mechanical bending strength. 
     The opening diameter D obtained is around 118 mm for an initial diameter of the lower plate of around 61 mm, which represents an increase in the diameter of around 90%. 
     The device according to the invention is thus seen to obtain a substantial, rigid braking surface with a reduced bulk and substantial mechanical strength. 
     Different variants are possible without departing from the scope of the invention. 
     It is thus possible to vary the number of flaps, their shape and their opening angle. 
     FIG. 8 shows a variant in which the flaps  7  are without the abutment heel. They are therefore able to deploy fully under the effect of the centrifugal force and allow a maximal opening diameter D 1  of around 140 mm to be obtained from an initial diameter of around 61 mm. 
     However, the free ends of the flaps are neither pressing on nor opposite another flap or the lower plate. This leads to bending of the flaps and less structural rigidity for the device. 
     FIGS. 9 and 10 show a second embodiment of the invention. 
     This embodiment differs from the previous ones in that all the flaps  7  are fastened onto the body  13  by screws  41  that constitute the flap pivots. Seven flaps  7  are provided and are stacked on top of one another in the folded position (FIG.  9 ). So as to allow each flap to be fastened to the body  13 , screws  41  of different lengths are provided for each flap as well as suitable braces (not shown). 
     Each flap  7  is constituted by a piece of steel sheeting that has an external profile  26  covering an arc of a circle whose diameter is substantially equal to the external diameter of the fuse. 
     Each flap  7  also has an indent  27  comprising a hemicylindrical portion  28  intended to allow the flap to fold around the axial cylinder  14  integral with the fuse body  13  and coaxial to its axis  20  (that is also coaxial to the fuse and the projectile). 
     According to this embodiment, a central cylindrical pinion  42  is mounted coaxially to the axial cylinder  14  and is free to rotate with respect to said cylinder. The teeth of the pinion are parallel to the axis  20  of the fuse and mesh with toothed circular portions  43  made on all the flaps  7  and coaxial with their pivot  41 . 
     Thus a rotation of the central pinion  42  around the axis  20  of the fuse makes all the flaps  7  either deploy or fold up (according to the selected rotational direction). 
     Such an arrangement ensures a symmetry of the opening movements of all the flaps  7 . 
     The central pinion  42  incorporates an upper flange  44  in which a hole has been made into which the rod  35  of the pyrotechnic piston  34  is housed thereby immobilizing the central pinion  42  in rotation, and thus locking all the flaps in their folded position against the effects of the centrifugal force. 
     This device operates as follows: 
     At a given moment during the trajectory, the electronic control device will ignite the pyrotechnic piston  34 . The rod  35  is extracted from its hole in the flange  44  of the pinion  42  thus unlocking it. The centrifugal force exerted on the flaps will cause them to open, such opening being symmetrical with respect to the axis  20  of the projectile because of the presence of the toothed portions  43  and central pinion  42 . The flaps continue to open until reaching the position shown in FIG. 10 in which the flaps abut against the central pinion. 
     It is possible for the opening angle of the different flaps to be controlled by acting on the length of their toothed circular portion. The opening of a flap can not continue beyond the possible relative course of this toothed portion on the central pinion. 
     Opening diameter D 2  that can be obtained with this embodiment of the invention is of around 130 mm from an initial diameter of around 61 mm. 
     The invention can naturally be applied to all types of large-caliber projectiles (over 50 mm) or medium-caliber projectiles (less than or equal to 50 mm).