GB2105445A

GB2105445A - Ammunition unit

Info

Publication number: GB2105445A
Application number: GB08225595A
Authority: GB
Inventors: Kjell Mattsson; Christer Lagerstam; Kurt Pettersson; Torsten Wik
Original assignee: Bofors AB
Current assignee: Saab Bofors AB
Priority date: 1981-09-09
Filing date: 1982-09-08
Publication date: 1983-03-23
Also published as: DK153251C; FR2512540A1; NO823045L; SE8105347L; SE444983B; NO151640C; NO151640B; CH658717A5; DK391882A; DE3233044A1; DK153251B; FR2512540B1; GB2105445B

Abstract

There is provided an ammunition unit, preferably for training purposes, intended to be fired from a gun barrel at supersonic speed. The ammunition unit comprises an intermediate body part (1) to which is connected a substantially cylindrical spike (2) as well as a finned tail section (3). The length (L1) and design of the spike and the design and connection of the tail section to the intermediate part are such that the ammunition unit, up to a predetermined firing distance, has substantially the same ballistic properties as the equivalent normal live ammunition but which has a significantly reduced maximal firing range as compared with such normal live ammunition. This is because a dead air stream zone is obtained around the spike at supersonic speeds, but at sub-sonic speeds the air stream follows the spike surface and results in a substantial braking force. The length L1 of the spike is 1.6-2.0 the diameter D of the body a truncated conical part 1a of the body has a length of 1-3% of the total length of the unit and a conical angle between 10 DEG and 20 DEG .

Description

SPECIFICATION Ammunition unit The present invention provides a supersonic ammunition unit, particularly suitable for practice or training purposes, comprising a cylindrichl intermediate body part to which at the forward end is connected a substantially cylindrical nose section in the form of a spike having a diameter which is much less than the diameter of the intermediate body part, while a tail section is connected to the rearward end of the intermediate body part.

In order to reduce firing costs, normal live ammunition is commonly replaced by training or practice ammunition during military training sessions. It is then important that the ballistic properties of the training ammunition substantially correspond to those of the live ammunition it replaces.

In order to meet this requirement it has previously been suggested that, for instance, the maximal firing range of a training ammunition unit must correspond to the maximal firing range of the particular live ammunition unit it is replacing.

This then means that comparatively large areas must be closed off in order to allow military training sessions.

The object of the present invention is to provide an ammunition unit which, because of its advantageous ballistic characteristics, can be used in substantially smaller proving grounds than previously, The invention is based on the knowledge that a spike has favourable ballistic properties.

According to the present invention, an ammunition unit is provided with a substantially cylindrical nose section in the form of a spike having such a length and configuration, and a tail section having such a configuration and connection to the intermediate body part, that the ammunition unit up to a predetermined firing distance has substantially the same ballistic properties as the live ammunition it replaces, but which has a significantly reduced maximal firing range as compared with normal live ammunition, for instance in preferred instances half the maximal firing range of normal live ammunition.

An important feature of the new training ammunition unit is the length of the substantially cylindrical spike compared with the outer caliber of the intermediate body part. According to one preferred embodiment of the invention, said length amounts to 1.6-2.0 of the diameter of the intermediate body part, more preferably 1.65-1.85 thereof, and specifically about 1.7 of the diameter of the intermediate body part.

By using in accordance with the invention a spike nose, a so-called dead air stream zone is obtained around the spike at supersonic speeds which means that the braking effect of the front end of the body portion of the unit is eliminated.

At subsonic speeds, however, the air stream follows the spike surface and said front end, which results in substantiai braking force being imparted on the ammunition unit.

This means that the ammunition unit has a substantially undisturbed ballistic trajectory at supersonic speeds, but as soon as the speed of the ammunition unit has been reduced to subsonic levels, then a substantial braking force is imparted on the ammunition unit. In consequence of this enhanced braking force, a substantially reduced maximal firing range is obtained. Further, the spike makes the ammunition unit more stable at supersonic speeds as well as at subsonic speeds and even at the supersonic speeds as well as at subsonic speeds and even at the supersonic passage. By using the proposed spike nose, the distance between the so-called Tp and Tc points (see below) can be considerably increased by a value up to one caliber.

In a preferred embodiment of the invention, the tail section is comparatively long, it that its length exceeds the lengths of the intermediate body part and nose spike, and is provided with fins extending longitudinally with full caliber along the main part of the tail section length. Such specific design of the tail section also contributes to the stability of the ammunition unit.

The present invention makes it possible to manufacture the ammunition unit efficiently and economically by means of cold pressing. The use of cold pressing techniques results in an ammunition unit of good mechanical strength whereby, for instance, heat treating of the projectile body becomes unnecessary. This is an advantage because the risk of skewed fins due to heat treating is eliminated. Cold pressing also enables the ammunition unit to be pressed in one working operation into a substantially finished product. Only minor lathe turning work and application of the driving band and a guide band, if any, will normally be necessary after the pressing. It will thus be appreciated that the design of the ammunition unit, and the fact that it can be manufactured by cold pressing techniques result in savings with respect to material, energy and costs.

In the following, a preferred embodiment of the invention will be described more in detail with reference to the accompanying drawings, in which: Figure 1 shows a training projectile, in perspective from behind; Figure 2 shows the projectile of Figure 1 in a perspective view from the front end; Figure 3 shows in a side view the projectile according to Figures 1 and 2; Figure 4a shows in a side view schematically the air stream conditions at supersonic speeds for the training projectile according to Figures 1 to 3; Figure 4b shows in a side view schematically the air stream conditions at subsonic speeds for the training projectile according to Figures 1 to 3; Figure 5a is a ballistic diagram for a predetermined firing distance for a training projectile according to the invention as well as for a corresponding normal live projectile;; Figure 5b is a ballistic diagram for the maximal firing ranges for a training projectile according to the invention as well as for a corresponding normal live projectile; Figure 6a shows in a side view a cylindrical workpiece used as a starting material when manufacturing the new projectile by means of cold pressing, and Figure 6b shows in a side view schematically the moment in the manufacturing process when the training projectile has obtained its final shape in a schematically illustrated pressing tool.

Figures 1 to 3 show a training projectile comprising a substantially cylindrical intermediate body part 1 to which is connected a spike nose 2 and a tail section 3. Such a spike 2 is, in principle, previously known. The spike nose is substantially cylindrical with a diameter d (Figure 3) which is much less than the outer diameter D of the body part 1, and in a specific example the spike diameterdis about 1/3 of the intermediate body part diameter D. The tail section is provided with a number of fins 3a, for instance six fins.

The cylindrical spike 2 has a length L, which in this preferred case is about 1.7 of the diameter D of the intermediate body part. This length L, can vary however, depending on the caliber, ammunition type etc, but normally is preferably between 1.6 and 2.0 of said diameter D, more preferably between 1.65 and 1.85 thereof.

In the illustrated embodiment, the length L2 of the tail section exceeds the lengths L1 and L3 of the spike 2 and the intermediate body part 1, respectively. The fins extend longitudinally with full caliber along the main part of the tail section.

At their point of connection with the intermediate body part, however, the fins are bevelled to a subcaliber dimension with the outer fin edge surfaces 3a' tapered forwardly to the intermediate body part. The trailing end portion of the intermediate body part 1 is formed as a truncated cone 1 a with a conical angle a which preferably is between 100 and 200, more preferably about 150. The conical surface is tapered rearwardly to conform with the leading end of the fins.

Preferably the length of the conical portion is 1 to 3%, more preferably 2%, of the total length of the projectile. The object of the conical portion is to direct the longitudinal air stream which is passing along the outer surface of the intermediate body part down into the space between the fins 3a to improve the stability of the projectile.

The length L3 of the intermediate body part 1 is in this case less than both the spike and the tail section lengths. The intermediate body part is provided with a front annular groove and a back annular groove to receive a front guide band 4 and a driving band 5. The guide band as well as the driving band may be made of plastics materials such as acetal or any other corresponding material.

In Figure 3 the centre of gravity of the ammunition unit is indicated by Tp and the centre of pressure indicated by Tc and the distance between Tp and Tc, which is important for the stability properties of the projectile, is indicated by A.

The Figures 4a and 4b illustrate the air stream conditions at supersonic and subsonic projectile speeds, respectively. In Figure 4a the air compression shock wave is indicated by 6 and a dead air zone in form of a rotation symmetrical zone around the spike of the projectile by 7. This dead air zone is limited by the outer side surface of the spike, a radical front surface 1b on the intermediate body part and a straight, conical imaginary outer surface 8 extending from the forward end surface of the spike to the periphery of the radial front surface 1 b. An undisturbed air stream is obtained in the direction indicated by the arrow 9 along the straight conical outer surface 8 so that there is no braking effect imparted on the projectile from the radial front surface.

This means that the projectile at supersonic speeds assumes a ballistic trajectory similar to that for a projectile having an ogival nose, a conical nose or a corresponding nose shape. The spike nose moves Tp and Tc rearwardly on the longitudinal axis of the projectile and increases the distance A, thereby helping to ensure a desired high stability for the projectile. It is understood that the projectile is stable not only at supersonic speeds but also at the supersonic passage and at subsonic speeds.

Figure 4b illustrates the air stream conditions at subsonic speeds. The air stream 10 then follows the outer spike side surface and the radial front surface 1 b on the intermediate body part.

This means that the radical front surface has a braking effect on the projectile speed which reduces the maximal firing range considerably, for instance we have obtained a reduction to half the distance of a corresponding normal live projectile.

Figures 5a and Sb illustrate the ballistic properties of the training projectile compared with a corresponding normal live projectile. By way of example, the comparison is made for a Bofors 9 cm model 77 live projectile, having a weight of approximately 3.7 kg. The training projectile has also a caliber of 9 cm and a weight of approximately 3 kg. The y-axis indicates the height of the trajectory in metres and the x-axis the firing distance also in metres. The maximal predetermined firing distance for the ammunition in question is 800 metres.

The trajectory a relates to the live projectile and the trajectory b to the training projectile fired from a gun with a muzzle velocity Vo=670m/s and Vo=7 1 5m/s, respectively. It is evident that the ballistic properties are substantially the same for the two projectiles up to a predetermined firing distance which means that realistic training sessions can be held with the gun service.

Diagram Sb illustrates the ballistic trajectories for maximal firing range in which the y-axis represents the height and the x-axis the horizontal range in meters. The trajectory a' for the live ammunition projectile is more than double (6,000 m) the maximal firing range for the training projectile. This is so because of the considerable braking of the training projectile flight at subsonic speeds, It is to be noted that the projectile is stable for all speeds, for instance between 0 and 3 times the sonic speed. This means that the training ammunication rounds can be easily traced and found.

The described training projectile is preferably made by a cold pressing method. In such a method a workpiece is disposed in a cold pressing tool and the projectile is made in the tool in one step only, so that the spike nose and the fins are formed at the same time. The projectile is finished by a minor full caliber lathe turning operation.

Figure 6a shows a workpiece 11 which is used as the starting material, for instance for a 9 cm training projectile. The workpiece comprises a cylindrical body with a diameter of 92 mm and a length of 200 mm. The pressing tool halves are indicated by 12,12'. The pressing is carried out in one step only and Figure 6b illustrates the finished product in the tool in which the parting plane has been indicated by De and the molding space by F.

When the projectile body has been pressed and removed from the tool it is machined in a lathe into its final design and dimensions, according for instance to the embodiment illustrated in Figure 3. The length of the complete projectile is in this case approximately 465 mm.

Cold pressing methods are previously known per se and will not be described more in detail in this connection.

Although the present invention has been particularly described in relation to practice ammunition, the teachings hereof can also be applied to normal live ammunition.

An important advantage of the ammunition units of this invention is that they lend themselves to large scale production.

Claims

1. A supersonic ammunition unit comprising a generally cylindrical intermediate body part (1) to which is connected a substantially cylindrical nose section in the form of a spike (2) having a diameter (d) which is substantially less than the diameter (D) of the intermediate body part, and a tail section (3), wherein the length (L,) and configuration of the spike and the configuration and connection of the tail section to the intermediate body part are such that the ammunition unit, up to a predetermined firing distance has substantially the same ballistic properties as equivalent normal live ammunition but which has a significantly reduced maximal firing range as compared with such normal live ammunition.

2. Ammunition unit according to Claim 1, wherein the spike (2) has a length (L,) which is 1.6-2.0 of the diameter (D) of the intermediate body part (1).

3. Ammunition unit according to Claim 1, wherein the spike (2) has a length (L,), which is 1.65-1.85 of the diameter (D) of the intermediate body part (1).

4. Ammunition unit according to Claim 3, wherein the spike (2) has a length (L,) which is approximately 1.7 of the diameter (D) of the intermediate body part (1).

5. Ammunition unit according to any of the preceding claims, wherein the tail section (3) has a length (L2) which exceeds the lengths of the intermediate body part and the spike, and is provided with fins (3a) extending longitudinally with full caliber along the major part of the tail section length (L2).

6. Ammunition unit according to Claim 5, wherein the intermediate body part (1) at its rearward end comprises a conical portion (1a) formed as a truncated cone, said conical portion having an axial extension of 13%, preferably 2 26, of the total length (L+L2+La) of the ammunition unit, and wherein the forward ends of the fins (3a) are bevelled to a subcaliber dimension with the outer fine edge surfaces (3a') tapered forwardly to conform to the narrowest part of said conical portion (1 a).

7. Ammunition unit according to any of the preceding claims, wherein said intermediate body part (1) is provided with a guide band (4) of the plastics material and a driving band (5), also of a plastics material.

8. A practice ammunition unit according to any of the preceding claims.

9. A supersonic ammunition unit having ballistic characteristics substantially as shown by curves b and b' of Figures 5a and Sb respectively, as compared with the ballistic characteristics of the equivalent normal live ammunition represented by curves a and a' of said Figures.

1 0. A supersonic ammunition unit substantially as hereinbefore described with reference to Figures 14b of the accompanying drawings.