Projectile modification method

A method of modifying a projectile includes removing material from an aft end of the projectile, and coupling a device to the aft end. The method may be used to convert a spin-stabilized projectile into a fin stabilized projectile, by modifying the aft end of a spin-stabilized projectile to accept a fin kit. The modifying may involve removing material with lathe, and may include forming external threads on the aft end that may engage corresponding internal threads on the device, to effect the coupling of the device to the aft end. The modification method allows versatility in employing projectiles, including existing stocks of projectiles. In particular the method allows spin-stabilized projectiles to be converted to more accurate fin-stabilized projectiles.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The invention is in the field of gun-fired projectiles.

2. Description of the Related Art

Projectiles, such as artillery projectiles, have long been used in warfare. There is a general desirability for improving all aspects of such projectiles, including accuracy.

SUMMARY OF THE INVENTION

According to an aspect of the invention, an existing projectile is modified by removing material, and a device is installed on the modified aft end.

According to another aspect of the invention, an existing projectile is modified by forming threads on its aft end, and a device that engages the threads is installed on the modified aft end.

According to yet another aspect of the invention, a tail fin kit to be installed on an existing projectile includes a base, and fins coupled to the base. The fins may have a curved shape, and may initially be in a recess in the base.

According to a further aspect of the invention, a method of modifying a projectile includes the steps of: removing material from an aft end of the projectile; and coupling a device to the aft end of the projectile.

According to a still further aspect of the invention, a projectile includes: a projectile body; and a tail fin kit coupled to an aft end of the projectile body. The tail fin kit includes a base and fins hingedly coupled to the base.

According to another aspect of the invention, a tail fin kit for retrofit on a projectile includes: a hollow base with internal threads for coupling with external threads of the projectile; and fins hingedly coupled around a perimeter of the base.

DETAILED DESCRIPTION

A method of modifying a projectile includes removing material from an aft end of the projectile, and coupling a device to the aft end. The method may be used to convert a spin-stabilized projectile into a fin stabilized projectile, by modifying the aft end of a spin-stabilized projectile to accept a fin kit. The modifying may involve removing material with lathe, and may include forming external threads on the aft end that may engage corresponding internal threads on the device, to effect the coupling of the device to the aft end. The modification method allows versatility in employing projectiles, including existing stocks of projectiles. In particular the method allows spin-stabilized projectiles to be converted to more accurate fin-stabilized projectiles.

FIG. 1shows a projectile10in its unmodified form. The term “projectile,” as used herein, is defined as an object that is intended to be shot from a gun (launcher with a barrel having a muzzle)), and that is capable of withstanding the accelerations (forces) involved in such gun launching. The projectile10has a projectile body12, with a fuze14installed in a front or forward end16of the body12. The fuze14is installed in the field, into a suitable opening in the front end16of the projectile body12. A closure plug may be placed in the opening for the fuze14during shipment of the projectile10, prior to the installation of the fuze14.

FIG. 2shows the projectile as part of a cartridge20. The cartridge includes a casing22that couples to an aft end24of the projectile body12. The casing22encloses a propellant28and a primer30. The primer30may be used to initiate combustion of the propellant28, providing the force to drive the projectile10out of the cartridge casing22, and out of a gun or other launcher (not shown) that the cartridge20is fired out of. An igniter34is located in an aft opening36of the projectile body12. The igniter34is used to initiate the rocket propellant38that is located in the projectile body12. The rocket motor igniter34is optionally employed so that the trajectory of the projectile10may be extended at the user's discretion. The illustrated embodiment is a rocket-assisted projectile. However, it will be appreciated that the modification method described herein is not limited to employment with rocket-assisted projectiles, and may be employed on a variety of types of conventional projectiles, including but not limited to high explosive projectiles, projectiles with base burners, cargo projectiles, etc.

The cartridge20may include a rifling band40that provides a pressure seal that prevents flow of high-pressure gases around the aft end24of the projectile body12. This keeps the high-pressure gases behind the projectile10, to drive the projectile10, rather than dissipating the pressure by allowing some of the high-pressure gas to “leak” around the projectile body12. The rifling band40or other structure on the projectile10may be configured to engage rifling in the gun or other launcher, to spin the projectile10during launch.

FIG. 2also shows the forward opening44that receives the fuze14. The fuze14may any of a variety of different types of fuzes, with different characteristics, the forward part of the projectile10may also include a payload, such as a warhead46, for example including a high explosive48.

FIGS. 3 and 4illustrate the material removal from the projectile aft body24in order to modify the projectile body12to receive a device, such as a tail fin kit, as described further below. The material may be removed, as shown at50, to create radial space around the outside of the projectile body12for the device. The rifling band40is also removed. In addition the removal of material includes producing external threads54on part of the aft body24. The external threads54may be configured to engage internal threads on the device that is later coupled onto the modified projectile aft end.

The removing of the material50may be accomplished by use of a lathe (not shown). The projectile body12may be secured to the lathe using openings in projectile body12that are along a longitudinal axis60of the body12. In particular, the front end16may be secured by insertion of an inert loading plug56in the forward opening44, and by use of a chuck or other holder the body of the projectile10. The inert loading plug56prevents the fuze14(FIG. 1) from introducing additional hazards into the projectile modification process. The aft end24may be secured by placement of a plug or other locator into the aft opening36(after removal of the igniter34), to produce a pilot surface for the lathe.

It will be appreciated that any of a variety of suitable lathes may be used in modifying the aft end24. Lathes have the advantage of easily making axisymmetric surfaces, and features such as the external threads54. A robotic lathe may be particularly effective in making accurate and repeatable modifications of projectile aft ends, and would be advantageous in modifying existing projectiles, which may be filled with explosive or other energetic materials. However it will be appreciated that alternatively or in addition other sorts of tools may be used in removing the material50, and/or in otherwise modifying the projectile aft end24.

The removal of the material50may be accomplished on existing projectiles. In particular the machining may be performed on live projectiles, projectiles having a warhead, rocket motor or other energetic materials.

The removing of the material50may create any of a variety of suitable shapes for receiving a device on the aft end24of the projectile12. One suitable shape is illustrated inFIGS. 3 and 4, with the modified aft end shape having a cylindrical device-receiving surface64, with the external threads54cut into the aft end of the surface64. Forward of the device-receiving surface64is a curved recess66for receiving a slipping obturator, as described further below.

The removal of the material50creates the modified aft end24′ shown inFIG. 5.FIG. 5also illustrates one example of a device that may be coupled onto the modified aft end24′, a tail kit70. The tail kit70includes a base72, and a number of fins76hingedly coupled to the base72. The illustrated embodiment shows the tail kit70as having six fins76, but it will be appreciated that a greater or lesser number of fins could be employed.

FIG. 6shows the fins76in a stowed or folded state or condition, with the fins76located within a recess78around the perimeter of the base72. The fins76may have curved shapes that aid in keeping them within the recess78when the fins76are in the stowed condition. Alternatively it will be appreciated that the fins76may be planar, or have other suitable shapes or configurations.

FIG. 7shows the fins76in a deployed state or condition. In the deployed state the fins76are in the airstream surrounding the projectile10. The deployed fins76provide stability to the flight of the projectile10.

FIG. 8illustrates a deployment mechanism80used in extending the fins76from their initial stowed state. With reference in addition toFIG. 9, which shows the modified projectile10as part of a modified cartridge20′, the fins76pivot around pins82, driven by spring forces from springs84. The springs84are wrapped around the pins82, between a pair of fin protrusions86and88that also encircle the pin82. In the stowed condition the springs84are preloaded with both compression and torsion forces.

A slipping obturator94of the modified projectile10may be used to keep the fins76in the stowed condition while the projectile10is in a barrel of a gun or other launcher. Alternative design features can be employed to restrain the tail fins76prior to firing the projectile10. For instance, a separate retaining band can be provided to restrain the tail fins76during storage, handling and loading. This retaining band would be fabricated from some suitable frangible material which would disintegrate during the gun firing event, leaving the tail fins free to deploy at muzzle exit. The barrel keeps the obturator94in place prior to and during the launch process. As the projectile10exits the muzzle of the gun or other launcher, the obturator94(no longer restrained by the barrel) falls away, and no longer keeps the fins76in place. The obturator94may be fabricated from a polymer material, and may be overcome by the forces experienced at muzzle exit and are discarded from the projectile10. The fins76rotate outward into the air stream under torsion forces from the preloaded springs84. When the fins76deploy far enough, they align with fin lock notches98in the base72. The compression force from the springs84drives the fins76in a direction along the longitudinal axes of the pins82, into the fin lock notches98. This fixes the fins76in the deployed condition, preventing the fins76from pivoting in either direction.

The slipping obturator94may be an obturator made of nylon (or another suitable material), so as to allow the modified projectile to be launched from a barrel having rifling or other spin-producing features, without achieving the full spin rate intended by such features. For example a spin-stabilized projectile may come out of a cannon (or other launcher) at an intended spin rate of 250-300 Hz. It may be desirable for the fin-stabilized modified projectile to have a much slower spin rate. The slipping obturator94acts as a clutch, engaging the rifling, but allow some slippage between the obturator94and the projectile body12. This may allow the modified projectile10to emerge from the launcher at a small fraction of the full spin rate, for example at a spin rate of 20-30 Hz.

The modified cartridge20′ shown inFIG. 9shows the projectile10as having a fuze114coupled to the projectile body12. The fuze114may have different characteristics than the conventional fuze14shown inFIG. 1. It will be appreciated that the fuzes14and114are examples of a wide variety of possible fuze configurations usable as part of the projectile10.

The various parts of projectile may be made from any of a variety of suitable material. It will be appreciated that 105 mm artillery shells or 155 mm artillery shells, to give two examples of projectiles, are made of well-known materials. The various parts of the tail fin kit70may be made of suitable materials. For instance the base72, the fins76, and the pins82may be made of aluminum or steel.

Although the modification method is described above in terms of putting a tail fin kit70on the aft end24of the projectile body12, it will be appreciated that alternatively other devices may be placed on the modified aft end24. Examples of other suitable devices include an additional rocket motor, a larger warhead, or an aft guidance kit. The modifications for utilizing these additional devices may be the same as those described above, or may involve removing material to achieve a different configuration.

The projectile10in the illustrated embodiment is only one of a wide variety of projectiles that may be modified according to the method described above. It will be appreciated that projectiles with various characteristics, such as various types of warheads or other payloads, various sizes, or the presence or absence of propulsion systems, may be modified as described above to receive a device such as a tail fin kit.

The modification method described above may have the benefit of allowing spin-stabilized projectiles to be converted into fin-stabilized projectiles. Fin-stabilized projectiles may be more accurate that spin-stabilized projectiles. Relying on fin stabilization may allow for additional control methods to be used to further increase accuracy of projectiles. The methods allow conversion of existing projectile stocks, and utilization of existing rifle-barreled launchers. It will be appreciated that the ability to convert extensive projectile stocks to improve accuracy provides a considerable benefit.