Mid-body obturator for a gun-launched projectile

Details Mid-body obturator for a gun-launched projectile Mid-body obturator for a gun-launched projectile

1999-11-23

2001-10-02

Jordan, Charles T. (Department: 3644)

Ammunition and explosives

Projectiles

Composite

C102S526000, C102S527000

Reexamination Certificate

active

06295934

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
This invention relates generally to gun-launched projectiles and more particularly to a mid-body obturator for a gun-launched projectile.
BACKGROUND OF THE INVENTION
When launching projectiles out of large military guns or cannons, a typical loading technique is to first ram the projectile into the breach of the gun, and then to ram a propelling charge in a shell casing behind the projectile. The propelling charge is typically positioned in the breach by a shell casing rim that is similar to the rim on a bullet cartridge used with a handgun. This rim is larger than the diameter of the breach and is prevented from being inserted into the barrel of the gun.
Projectiles launched from military guns are typically rear obturated. The aft end of the projectile has a protruding ring or flange of material called an obturator or a rotating band. The obturator has a diameter smaller than the diameter of the breach, but larger than the diameter of the bore of the gun barrel. The bore is the section of the barrel that typically contains a series of rifling grooves used to impart a spin on the projectile.
During loading, the projectile is rammed into the breach in a manner similar to putting a bullet in a gun chamber. However, unlike a typical bullet, the projectile does not have a cartridge rim to stop it (only the separate propelling charge has a cartridge rim). Therefore, the aft end or rear obturator is used to stop the projectile once it has traveled an appropriate distance into the barrel. Because the rear obturator has a diameter larger than the bore diameter of the gun, the obturator is stopped during loading of the projectile in an area of the gun barrel where the inside diameter decreases from the breach diameter to the bore diameter. This area of inside diameter change is called the forcing cone. Because the obturator is located at the rear of the projectile, when the obturator stops at the forcing cone, most of the projectile is positioned in the bore of the barrel.
When the propelling charge is ignited, the rear of the projectile is forced into the bore of the gun barrel. The obturator, which has a diameter larger than the bore of the gun, is forced to extrude into the rifling grooves. This extrusion helps to prevent the charge gases created by the ignition of the propelling charge from flowing past the projectile in the rifling grooves. By preventing the charge gases from blowing by the projectile, the obturator causes the charge gases to drive the projectile out of the gun at the optimal velocity. In addition, since the rifling grooves spiral down the barrel, the grooves impart a spin to the projectile to increase flight stability. It should be noted that the term “rotating band” is often used to denote a device that provides obturation (the obstruction of gas flow) as well as imparting a rotation to the projectile. The term “obturator” typically refers to a device that only performs the obturation function. However, for the purposes of this application, the term “obturator” will be used generically to refer to both rotating bands and obturators.
Advanced projectiles (“smart” projectiles) are capable of being fired from the same guns that are used to fire the standard unguided projectiles described above. An example of an unguided projectile is a standard artillery shell, which is basically a large bullet. On the other hand, advanced projectiles have enhanced features such as electronic guidance and extended range rocket motors. For example, certain advanced projectiles are launched from a gun using a propelling charge, but then use a rocket motor and a guidance system to propel them to a selected target. These advanced projectiles must be designed to be loaded and fired in the same gun barrels that were designed to fire the standard unguided projectiles. However, advanced projectiles are often longer than standard projectiles due to their increased complexity. In addition, in order to increase the range of advanced projectiles, a relatively thin rocket motor wall is used. Because of the increased length and the thin rocket motor wall, if a standard rear obturator is used on such projectiles, the launch pressures created when the charge is ignited would buckle the aft portion of the advanced projectile.
An obturator or related device must be used in order to stop the charge gases from blowing by the projectile. This function is important in the case of advanced projectiles due to the sensitivity of the guidance electronics. Any blow-by could potentially destroy the projectile's operability. Additionally, a brake is needed to stop the projectile when it is rammed into the gun. Traditionally, both of these functions have been performed by the rear obturator or rotating band, as described above. However, since the obturator cannot be located at the rear of the projectile on an advanced projectile, the standard rear obturator/rotating band design used with unguided projectiles must be replaced by one or more components that serve the functions of sealing the rifling grooves during firing.
SUMMARY OF THE INVENTION
Accordingly, a need has arisen for an obturator for use in conjunction with an advanced gun-launched projectile that functions to seal the rifling grooves of the gun during the launching of the projectile. The present invention provides a mid-body obturator for a gun-launched projectile that addresses this need.
According to one embodiment of the present invention, an obturator is provided for a projectile launched from a gun barrel. The projectile has a mid-body annular groove that includes a shaped surface. The obturator includes an annular ring that has an inner surface that is in contact with the shaped surface of the annular groove of the projectile. The annular ring further includes an outer surface that contacts an inner surface of a bore of the gun barrel when the projectile is in the gun barrel. The radial distance between the inner surface and the outer surface of the annular ring substantially equals or exceeds the radial distance between the shaped surface of the annular groove and the inner surface of the bore of the gun barrel at at least one point when the projectile is positioned in the barrel. This feature restricts a flow of charge gases from an aft end of the projectile to a forward end of the projectile when the projectile is launched from the gun barrel.
According to another embodiment of the invention, a projectile capable of being launched from a gun barrel includes a payload segment located toward a forward end of the projectile, and a propulsion segment coupled to the payload segment and located toward an aft end of the projectile. The projectile further includes an annular groove that has a shaped surface. The annular groove is located substantially at a mid-body location of the projectile. The projectile also includes an obturator that has an annular ring. An inner surface of the annular ring is in contact with the shaped surface of the annular groove of the projectile. In addition, when the projectile is loaded in the gun barrel, an outer surface of the annular ring contacts an inner surface of a bore of the gun barrel. When the projectile is loaded, the radial distance between the inner surface and the outer surface of the annular ring substantially equals or exceeds the radial distance between the shaped surface of the annular groove and the inner surface of the bore of the gun barrel at at least one point. This configuration restricts a flow of charge gases from an aft end of the projectile to a forward end of the projectile when the projectile is launched from the gun barrel.
Embodiments of the invention provide numerous technical advantages. For example, in one embodiment of the invention, a mid-body obturator is provided that allows an advanced projectile to be launched from a gun or cannon that is normally used to fire standard unguided projectiles. Obturators incorporating teachings of the present invention operate to impede the flow of charge gases past the projectile in the gun barrel, even thou

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