METHOD AND DESIGN FOR INCREASING THE FIRING RANGE OF ARTILLERY SHELLS

Abstract: The present invention relates to a method of increasing the range of air defence and artillery shells of the type which for reasons of firing technology have a rear surface which is at right angles to the shell axis, i.e. most conventional air defence and artillery shells. The invention also includes a design of air defence and artillery shells that corresponds with the said method. The invention is characterised by the rear surface of the shell which at the time of firing is at right angles to the shell axis being reformed to an aerodynamically more advantageous form (5, 9) when it has left the gun barrel and is on the way to the target.

Description: Method and design for increasing the firing range of artillery shells The present invention relates to a method for increasing the firing range of air-defence and artillery shells of the type which for reasons concerning firing technology have a rear surface which is at right angles to the shell axis, i.e. in principle all conventional air-defence and artillery shells. The invention also includes a design of air-defence and artillery shells that corresponds with the said method. It is well known that the rear surface that is at right angles to the axis of the shell while being desirable at firing, has an adverse affect on the shell in the case of long-range firing due to the airflow along the rear edge of the shell causing turbulence which in its turn results in low pressure and drag to the rear of the shell thus limiting the maximum range of the shell. The base-bleed technique has been much used in recent years to increase the range of air- defence and artillery shells without having to increase muzzle velocity and thereby the size of the propellant charge to a level which the gun in question would not withstand. The base-bleed technique is based on allowing gas to flow out from the rear surface of the shell preferably during the release of heat, and the flow rate of the gas in such a case shall be at a level that enables the gasflow to eliminate most of the low pressure and the drag caused. Although the base-bleed device is similar to a supplementary rocket motor with its propellant loaded interior chamber and its central flow outlet, its function is totally different from that used in shells which are fitted with supplementary rocket motors known as sustainers to increase firing range. Such rocket motors are loaded with pure rocket propellant and they provide the shell with a velocity increment, while the base-bleed device is loaded with a slow burning propellant which is intended only to eliminate drag during the portion of the shell trajectory the propellant is burning. One of the advantages of the base-bleed technique is that the base-bleed device requires considerably less space in the shell than that required by a supplementary rocket motor, but the base-bleed device does take up space in the shell which could be used for an active load. The base-bleed device furthermore represents a not inconsiderable increase in cost. The present invention now offers a simpler, cheaper and less space-consuming solution to the problem of eliminating or at least minimising the disturbing and range-reducing low pressure at the rear of air-defence and artillery shells which at the time of firing have the rear surface at right angles to the axis of the shell. In accordance with the principle of the invention, the rear surface of the shell which is at right angles to the shell axis is given a more aerodynamically advantageous form as soon as the shell leaves the barrel of the artillery gun from which it is fired. This can be achieved for example by extending the shell at the rear by a protruding conical tail section. The said tail section can thereby consist of an inflatable part initially fitted in the rear section of the shell in compressed form and secured to the shell body, and can be folded out and inflated to the desired form and hardness by the propellant gases from a small propellant charge which is ignited at the required time. Such an inflatable section part can for example be made of Kevlar and remain in a removable cover connected to the shell up to the time it is deployed. Another conceivable version of the invention is based on the rear surface of the shell itself consisting of a disposable cover which is removed from the shell as soon as the shell has left the barrel, upon which the actual shell rear section is revealed and this has an aerodynamically favourable conical form narrowing progressively to the rear. In this case also, a smaller propellant charge can be used for separating the cover in question. Both of the basic versions of the invention are now described in more detail in combination with the enclosed figures while the invention in its entirety is defined in the subsequent patent claims. The following figures are enclosed: Figure 1 A first version of a shell before firing in accordance with the invention Figure 2 the shell in accordance with Figure 1 in its trajectory towards the target Figure 3 a second version of the shell before firing in accordance with the invention and Figure 4 the shell in accordance with Figure 3 in its trajectory towards the target. The shell illustrated in Figure 1 consists of a shell body 1, fitted with a driving band 2, a fuse 3 and a removable cover 4. Inside the cover 4 there is a compressed extension part 5, shown in inflated position in Figure 2, which remains inside the cover until the shell has left the barrel from which it is fired. The extension part is made of Kevlar and it is inflated by the combustion gases from a propellant charge the position of which inside the shell is indicated by reference 6 in Figure 1. The propellant charge which also causes the removal of the cover 4, is initiated when the shell leaves the barrel of the weapon from which it is fired. The shell illustrated in Figure 3 consists of a shell body 7, a driving band 2, a fuse 3 and a removable cover 8 which differs somewhat from the cover shown in Figure 1. The cover 8 contains no components and has the sole task of providing the shell which has an aerodynamically rounded-off rear section 9 as shown in Figure 4, with a rear surface which is at right angles to the shell axis at firing. The cover 8 is ejected by a small charge built into the shell in a manner similar to that illustrated in Figure 1.

Claims: PATENT CLAIMS 1. A method to be used when firing air-defence and artillery shells (1,7) of the type which at firing have a rear surface which is at right angles to the axis of the shell and after the shell has left the gun barrel and is on the way towards the target for minimising the low pressure at the rear of the shell which adversely affects the range of the shell w h e r e i n the rear surface of the shell which after it has left the gun barrel is at right angles to the shell axis and during its flight towards the target is reformed to a configuration (5,9) which is aerodynamically more favourable compared with its original form with the right-angled rear surface. 2. A method as claimed in Claim 1 w h e r e i n the shell (1,7) when it has left the gun barrel is extended to the rear beyond its previous flat rear surface by an inflatable extension part (5) designed in accordance with the laws of aerodynamics. 3. A method as claimed in Claim 2 w h e r e i n a smaller propellant charge (6) built into the shell is initiated when the shell has left the barrel and the thereby formed propellant gases are utilised for the inflation of a extendible extension part (5) initially situated in a location (4) for this purpose in the rear of the shell which when inflated provides the rear of the shell with an aerodynamically more advantageous form. 4. A method as claimed in Claim 1 w h e r e i n limited parts of the shell (7) rear section around the base surface (8) which is at firing at right angles to the shell axis are removed when the shell has left the barrel thereby providing the shell with an aerodynamically more advantageous form. 5. A device in order in accordance with the method as claimed in Claims 1-4 at the firing of air defence and artillery shells (1,7) of the type which at firing have a rear surface which is at right angles to the shell axis, and after the shell (1,7) has left the barrel and is on its way towards the target to minimise the low pressure to the rear of the shell and thereby its adverse affect on the maximum range of the shell w h e r e i n the rear portion of the shell contains organs (5,9) which make it possible to change the form of the shell from having a rear surface which is at right angles to the shell axis to one which has a more favourable elongated pointed form during the free flight of the shell. 6. A device in accordance with that claimed in Claim 5 h e r e i n the shell (1,7) has in its rear portion a deployable and inflatable extension part (5) in a location adapted for this purpose and which in deployed condition gives the rear of the shell an elongated pointed form, and also a gas developing charge (6) which is built into the shell and which can be initiated after the shell has left the barrel and which when initiated inflates the said extension part (5). 7. A device in accordance with that claimed in Claim 6 h e r e i n the said extension part (5) is made mainly of Kevlar. 8. A device in accordance with that claimed in Claim 5 w h e r e i n the rear of the shell (7) which at the time of firing has a rear surface that is at right angles to the shell axis has parts which are so designed that they can be removed immediately after the shell has left the barrel and thereby reveal an end section (9) which narrows progressively to a point at the rear. 9. A device in accordance with that claimed in Claim 8 w h e r e i n the main part of the shell (7) is designed with a pointed form (9) narrowing to the rear and which at least up to the time of firing is surrounded by a cover (8) that provides the rear surface of the shell with its desired form at the time of firing and which can be removed when the shell has left the barrel.

Inventors: OLSSON TORBJOERN, OLSSON, TORBJOERN
Applicants: BOFORS WEAPON SYS AB, OLSSON TORBJOERN, BOFORS WEAPON SYSTEMS AB, OLSSON, TORBJOERN
Application year: 2000
Main classification: F42B10
IPC codes: F42B10