Abstract:
An airburst hand grenade constructed so as to jump 1–2 m above the ground before detonating. The hand grenade includes a detonator, a warhead, and support legs for raising the hand grenade from a horizontal position to an upright position once it has landed after being thrown. The detonator includes a delay unit, an upper charge which releases the support legs, a jump charge which propels the warhead into the air, and an explosive cartridge which initiates a main charge. Because the grenade detonates above ground, the fragments are spread essentially horizontally and at an angle to the ground and consequently attack the target from above, which results in a much larger target surface and the capability of spreading fragments behind a shelter.

Description:
This is a nationalization of PCT/SE02/01861 filed Oct. 11, 2002 and published in English. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a hand grenade with an airburst. 
   2. Description of the Related Art 
   Existing constructions of fragmentation hand grenades all have one basic shortcoming; the active fragments are very unlikely to find the target owing to the fact that detonation takes place with the hand grenade lying on the ground, whereby the effect does not occur. 
   Fragmentation hand grenades have a casing which strives to spread fragments uniformly in all directions, see for instance U.S. Pat. No. 4,781,117 A. This means that the major part of the fragments is directed into the ground or into the air when detonating. Only the few fragments that start from a horizontal ring round a lying hand grenade constitute a potential danger to a lying target. An irregularity or depression in the ground which is as high as the height of a lying hand grenade constitutes a direct obstacle to a hit. A minimum irregularity in the ground affords the target natural protection also at a distance of less than 1 m. It is also highly probable that such obstacles exist in each throw. 
   A solution to this problem is demonstrated in U.S. Pat. No. 5,866,841 A where a hand grenade has a plurality of legs which are unfolded and raise the hand grenade to a vertical position after it has come to rest on the ground. This means that no fragments will be directed into the ground where their effect is wasted. However, there remains the problem with irregularities that still constitute an obstacle to a hit. Besides, in combat using hand grenades a target will only by mistake be located in a position other than lying and thus is not exposed to the fragments. This means that the excellent penetration values of a modern hand grenade do not matter since the fragments will not reach the target. 
   SUMMARY OF THE INVENTION 
   The invention solves the above problem by a hand grenade being caused to jump  1 – 2  m above the ground before detonating. Thus the fragments will attack the target from above, which results in a target surface that is many times larger and makes it possible to give off fragments behind a shelter. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in more detail with reference to the following Figures: 
       FIG. 1  shows the use of a hand grenade according to the invention, and 
       FIG. 2  is an exploded view of a hand grenade according to the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
   A hand grenade according to the present invention is handled largely as an ordinary hand grenade. Once the hand grenade is thrown, a pyrotechnic delay unit ( 3 ) starts in the hand grenade detonator ( 2 ). As the hand grenade lands in the target area and is lying still on the ground, the delay unit ( 3 ) releases a pyrotechnic charge ( 4 ) in the upper part of the hand grenade detonator which shoots away a locking cover ( 8 ) from the upper side of the hand grenade. When the locking cover ( 8 ) has been removed, a number of support legs/spring legs ( 9 ), such as five or six legs, are released, which are articulated to a spring leg mounting ( 10 ) in the bottom of the hand grenade. The support legs ( 9 ) unfold at 90 degrees in all directions and raise the hand grenade from a lying horizontal position to a standing vertical position, with the mechanism ( 1 ) facing upwards and the spring leg mounting ( 10 ) in the bottom surrounded by the support legs ( 9 ) which form a star-shaped support against the ground. A lump assembly including a guide tube ( 7 ) is fastened centrally in the spring leg mounting ( 10 ) by a thread and moves loosely in a tubular duct ( 19 ) through the grenade body. The guide tube ( 7 ) extends through the entire grenade body and terminates in contact with the hand grenade detonator ( 2 ) in the upper part of the grenade. The delay unit ( 3 ) initiates a pyrotechnic jump charge ( 5 ) in the bottom of the hand grenade detonator. The gas pressure from the charge ( 5 ) acts on the guide tube end surface ( 18 ). The guide tube ( 7 ), which is in contact with the ground by the intermediary of a base plate ( 16 ), will be pressed against the ground whereas the hand grenade will be pressed upwards. When the hand grenade has reached a height of 1–2 m, the delay unit ( 3 ) releases an explosive cartridge ( 6 ) in the lowermost part of the detonator. The explosive cartridge ( 6 ) ignites the main charge ( 13 ) of the hand grenade which detonates. If an airburst is not desired, the guide tube ( 7 ) can be unscrewed from the spring leg mounting ( 10 ) in one motion and removed from the hand grenade, thereby preventing jumping. The detonation then occurs lying on the ground. 
     FIG. 2  is an exploded view of a preferred embodiment of a hand grenade according to the invention. The hand grenade has a mechanism ( 1 ) which can be a prior-art standard mechanism with striking pin, mainspring, handle and safety catch. The lower part of the mechanism housing is provided with a fixedly joined circular sheet ( 15 ) whose diameter is slightly larger than the mechanism housing. The sheet ( 15 ) serves as a seal against and holder of the locking cover ( 8 ) on the upper side of the hand grenade. The mechanism ( 1 ) has an internal thread for the hand grenade detonator ( 2 ). 
   The locking cover ( 8 ), is a cylindrical cover, which fits tightly over the upper part of the grenade body. Its edges ( 17 ) extend somewhat down along the sides of the grenade body and lock the spring legs ( 9 ) against the sides of the grenade body. 
   Centrally there is circular hole whose diameter is slightly smaller than the sheet ( 15 ) of the mechanism housing, which sheet can thus hold the locking cover ( 8 ) in place, squeezed between the mechanism sheet ( 15 ) and the grenade body. Here are also moisture-proof seals arranged. When the upper pyrotechnic charge ( 4 ) of the hand grenade detonator is initiated, a gas pressure is generated, which acts against the underside of the locking cover with such a force that the locking cover ( 8 ) is deformed and urged past the mechanism ( 1 ). When the locking cover ( 8 ) has been removed, the spring legs ( 9 ) are released. 
   The hand grenade detonator ( 2 ) consists of a continuous tube with a cylindrical waist with an increased diameter. In the upper part of the tube there is a detonating composition ( 11 ) which is initiated by the striking pin of the mechanism. From the detonating composition ( 11 ) extends, axially through the tube, a duct containing a delay unit ( 3 ) which in the lower part may pass into another unit of a pressed type with improved time performance. The delay unit is in this example a pyrotechnic unit but may just as well be electric. An explosive cartridge ( 6 ) is arranged in the lower part of the tube. The waist surrounding the tube has an upper and a lower space which are separated from each other by intermediate material. The circumferential surface of the waist is provided with a thread connecting to the upper part of the grenade body. The upper space will thus be located on the outside of the grenade body and the lower space in the interior of the grenade body immediately above the inserted guide tube ( 7 ). Both spaces are axial recesses in the material of the waist, which annularly surround the tube. The spaces communicate with the delay unit ( 3 ) of the tube through one or more radial apertures ( 20 ). The spaces are filled with a pyrotechnic unit ( 4 ,  5 ) whose function in the upper case is to remove the locking cover ( 8 ) and, in the lower, to generate gas pressure to cause jumping upwards. The charges ( 4 ,  5 ) are environmentally protected by varnish, lids or the like. The upper part of the tube is provided with a thread to which the hand grenade mechanism ( 1 ) connects. Between 2 and 2.5 s after the delay unit ( 3 ) of the tube has been initiated, the first pyrotechnic charge ( 4 ) will fire away the locking cover ( 8 ), the removal of which releases the spring legs ( 9 ) which in turn raise the hand grenade to an upright position. After further 0.5 to 1 s, the inner charge ( 5 ), the jump charge, is initiated and throws the hand grenade upwards between 1 and 2 m. Finally, when an optimal height has been reached, the delay charge ( 3 ) triggers the explosive cartridge ( 6 ) and the hand grenade bursts. The times mentioned above are approximations and calibrates to achieve an optimal effect. 
   The guide tube ( 7 ) moves freely but in a moisture-proof manner in a duct ( 19 ) in the core line of the grenade body. Its upper end connects to the hand grenade detonator ( 2 ) and the jump charge ( 5 ) thereof. There it also encloses the explosive cartridge ( 6 ) which in its entirety extends into the tube ( 7 ). The guide tube ( 7 ) thus constitutes an interruption in the ignition chain, I.e. before a jump has occurred or the guide tube ( 7 ) has been removed, initiation of the main charge ( 13 ) cannot take place. This is an important improvement of safety compared with prior-art constructions where the explosive cartridge is stored separately and fastened in the hand grenade when required. The lower part of the guide tube is fastened in the centre of the spring leg mounting ( 10 ) by a continuous thread. 
   The guide tube ( 7 ) is held vertically upright by the unfolded spring legs ( 9 ) and thus also the hand grenade body. When the jump charge ( 5 ) is initiated, the gas pressure will act on the end surface ( 18 ) of the tube and a force will arise between the guide tube ( 7 ) and the grenade body. The relatively great length of the guide tube will guide the grenade body to maintain its orientation also during the jump phase. Here also a minor rotation may be introduced if required for stability, for instance by grooving. A fixedly connected base plate ( 16 ) is arranged under the thread of the guide tube. Thus the base plate ( 16 ) is positioned under the spring leg mounting ( 16 ) and constitutes the lower boundary of the hand grenade and its contact surface on the ground. The base plate ( 16 ) is given a suitable design to increase friction against the ground if rotation is necessary. The base plate ( 16 ) has a somewhat larger diameter than the spring leg mounting ( 10 ) with the spring legs ( 9 ) folded back and its edge is grooved so as to provide a good grip for the thrower&#39;s fingers. The thrower can thus easily unscrew and remove the guide tube ( 7 ) and thus also the base plate ( 16 ) immediately prior to throwing if a ground detonation is desired. Alternatively the guide tube ( 7 ) and the base plate ( 16 ) with thread can be separate parts which only move in each other. Then the jump function would not occur if the base plate ( 16 ) was removed and thus the mounting of the guide tube was removed. The guide tube ( 7 ) would remain in the grenade body and consequently still constitute an interruption in the ignition chain until the guide tube ( 7 ) is fired away by the pyrotechnic charge ( 5 ). 
   In the preferred embodiment, six support legs/spring legs ( 9 ) are uniformly distributed round the grenade body. They are locked in the upper part of the edge ( 17 ) of the locking cover and are articulated to the spring leg mounting ( 10 ) where also the spring function is to be found. Under the edge ( 17 ) of the locking cover, the upper part of the spring legs ( 9 ) hooks into a shoulder or a notch in the grenade body which locks the spring legs, and thus also the spring leg mounting to the grenade body in a fixed position. The locking ceases by the locking cover ( 8 ) being removed. Then the spring legs ( 9 ) unfold at 90 degrees from the core line of the grenade body and raise the lying hand grenade. The spring legs ( 9 ) are either separate components which jointly cover the circumferential surface of the entire grenade body and are therefore formed to good gripping surfaces for the thrower&#39;s hand, or somewhat lowered into grooves in the circumferential surface and may then consist of merely the springs themselves. 
   The spring leg mounting ( 10 ) is a sheet which is separate from the grenade body and which in its periphery constitutes the point of articulation for the spring legs ( 9 ) and the abutment for the prestressed springs. The abutment for the springs may also consist of the guide tube base plate ( 16 ) which directly engages the underside of the mounting. Consequently the base plate ( 16 ) of the guide tube will obtain automatic friction locking while at the same time the spring force in the raising function does not occur when a ground detonation is selected, which may be desirable. The guide tube ( 7 ) is positioned in the centre of the spring leg mounting ( 10 ) in a threaded through hole. 
   The warhead ( 14 ) of the grenade body consists of a shell of preformed fragments ( 12 ) cast into a plastic matrix. In the grenade body, a suitable explosive is cast to a main charge ( 13 ). Centrally in the core line of the grenade body there is a continuous plastic lined duct ( 19 ). The threaded joint for the hand grenade detonator ( 2 ) is arranged at the upper end of the duct. There are also surface ducts arranged for distribution of the gas pressure from the upper pyrotechnic charge ( 4 ) to the inner surface of the locking cover. At the lower end there is a moisture-proof seal against the guide tube ( 7 ) which runs in the duct. The guide tube ( 7 ) guides the grenade so that the mechanism ( 1 ) is oriented upwards at the moment of detonation. Thus the entire underside and also the sides of the grenade may be given such a softly rounded conical shape that the major part of the total number of fragments of the hand grenade are directed downwards to the circle on the ground where the effect is to be expected. A minor part of the fragments from the top surface of the grenade body are allowed to be spread upwards so that a certain degree of coverage in that direction is obtained if a ground detonation has been selected. The shape and material of the fragments are selected so that an effect on predetermined targets is obtained within the desired effective radius and then ceases as soon as possible in order to minimise the risks to the thrower. Preforming of the fragments provides this possibility of guiding. The explosive in the main charge ( 13 ), and optionally a primary charge, and also the point of initiation are selected to achieve the above. The conical shape of the grenade body results in sufficient space for the spring leg mechanism in the bottom of the grenade. The spring legs ( 9 ) will also guide the contact surface of the hand grenade with the thrower&#39;s hand so that he does not have to handle a cone but a well-shaped surface. 
   The locking cover charge and the jump charge of the hand grenade detonator need not be symmetrical as in the drawing. The locking cover charge ( 4 ) can be shallower and have an increased diameter. The jump charge ( 5 ) should be narrower, as close as possible to the diameter of the guide tube ( 7 ). The spring legs ( 9 ) may consist of the springs themselves, without separate leg parts, which extend in grooves in the plastic casing of the hand grenade which is then adjusted for a good grip. The guide tube ( 7 ) can be made in two parts, tube and base plate ( 16 ) with thread. A cylinder having the inner diameter of the tube protrudes from the thread into the open lower part of the tube. The tube is kept in place in the duct ( 19 ) by an O-ring when the base plate ( 16 ) has been removed. 
   Airburst solves the problem with poor target access. If the hand grenade is made to detonate at a height of between 1 and 2 m, about half of the fragments will hit the ground within the circle where the speed of the fragments is still such that an effect may arise. Targets located within the circle will, independently of posture, expose a considerably larger surface to fragments and thus receive a many times greater amount of fragments. The angle (ν) of the fragments will be from above or obliquely from above, which fully eliminates small topographical formations as shelter. Also destroyed walls, furniture, large logs, stones and pits in the ground will be wholly or partly eliminated as shelter depending on the angle (ν) of the fragments. The obstructing effect of snow disappears even if the hand grenade can jump out of the snow. 
   According to the invention, the path of the hand grenade is controlled in the jump and, thus, without tumbling. As a result, the warhead ( 14 ) can be designed so that the fragments ( 12 ) are collected and directed towards the area where the greatest effect can be achieved, instead of being spread spherically in all directions, which increases the probability of hitting the target If a traditional ground detonation is desired, a change is made by unscrewing the guide tube ( 7 ) from the hand grenade in one motion. A hand grenade according to the invention gives a considerable improvement over prior art which spreads fragments in all directions and in which the major part of the fragments will be lost. 
   The invention being thus described, it will be apparent that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be recognized by one skilled in the art are intended to be included within the scope of the following claims.