Ordnance – Barrels – Recoil absorbers and climb arrestors
Reexamination Certificate
2001-07-05
2002-12-24
Carone, Michael J. (Department: 3641)
Ordnance
Barrels
Recoil absorbers and climb arrestors
C089S014200
Reexamination Certificate
active
06497170
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a muzzle brake vibration absorber for use on a gun barrel. More particularly the muzzle brake vibration absorber is used to store potential energy during gun firing and re-introduce the energy, in part, to the gun barrel out of phase relative to the gun barrel motion. This results in the firing deviation of the gun barrel being mitigated. Most particularly, the muzzle brake vibration absorber also may function as, or in combination with, a muzzle brake or fuze setting device for the gun system.
By improving the accuracy of the gun system, the gun system provides a greater operational efficiency through greater accuracy. This decreases the logistical burden to resupply ammunition to operational combat units.
2. Brief Description of the Related Art
Numerous attempts have been made to improve the accuracy of gun weapon systems, particularly those guns systems that are subject to vibrational disturbance during firing. With gun systems becoming increasingly accurate, the affect of vibrational disturbances on gun accuracy has become more pronounced. Additionally, the use of longer and more slender gun barrels, such as that on the XM291 tank gun system, for providing higher projectile exit velocities increases the occurrence of flexural vibrations within the gun systems.
Several methods have been used to improve the accuracy of gun weapon systems.
One method includes the extension of the gun mount/cradle of the gun systems. One means of reducing the receptance of a gun barrel to flexural vibrations is to decrease the effective cantilevered length of the gun system. This may be achieved by increasing the length of the supporting structure that holds the gun barrel which effectively increases the ratio of stiffness to inertia of the system. The square of the ratio of stiffness to inertia is indicative of the resistance of a gun barrel to low frequency vibrations.
A variation on the extended mount approach has been to utilize a traditional mount to support the gun barrel, and to incorporate damping pads through a mount extension that couples the barrel to the cradle with low stiffness and high damping. The result is that the mount extension need not be as solid, since increased stiffness is not the primary objective of the approach. An example of this approach is the British 30 mm, L21A1, system commonly called the RARDEN. (see Geeter et al., “Low Dispersion Automatic Cannon System (LODACS) Final Report (U),” ARDEC Technical Report ARSCD-TR-8201 1, Picatinny Arsenal, New Jersey, August 1982).
Although the extension of the gun mount/cradle may succeed in reducing vibrations, it can present a negative impact of increasing the imbalance of several gun weapon systems, since the center of gravity of typical gun systems is forward of the trunnion bearings. This imbalance necessitates the application of control torques, equal and opposite to the weight of the gun weapon system, multiplied by the horizontal offset of the center of gravity from the pivot point. These requirements places a heavy burden on the pointing system.
Further, for many gun systems extension of the gun mount/cradle becomes ungainly as the ratio of in-mount barrel length to overall barrel length increases. Packaging such support structures in a fielded weapon system becomes difficult.
Another approach has been the incorporation of thicker gun barrels. Gun barrels may be constructed with thicker walls. Since the stiffness is a function of the outer radius to the fourth power, and the inertia is a function of the outer radius to the second power, significant increase to the ratio of stiffness to inertia of the system can be made.
Thicker gun barrels increase the ratio of stiffness to inertia, but require a significant ratio between the inner radius (the radius of the bore) and the outer radius. If the wall thickness, that is the difference between the inner and outer radii, is reasonably small relative to either radius, a thin walled approximation would have the inertia and stiffness increase proportionally to each other, thus no net gain. For example, a Taylor series expansion of the ratio of stiffness to inertia as a function of outer diameter is dominated by the linear term for barrels whose wall thickness is a fraction of the bore radius. The second term exists, but it doesn't dominate until the wall thickness becomes impractical.
A related problem with this approach is that increased weight of the barrel is a direct consequence. This exacerbates both the extension of the center of gravity of the gun further out from the trunnions, and increases overall weapon weight which is supposed to be minimized.
A composite barrel construction is another approach. Gun barrels may be constructed of materials with a higher stiffness to inertia ratio, such as carbon fiber reinforced epoxy, or composite over-wraps of traditional gun steel barrels. The goal is to increase the net ratio of stiffness to inertia of the system, and this can be achieved. This is discussed in Hasenbein, et al., “Metal Matrix Composite-Jacketed Cannon Tube Program,” ARDEC-Benét Technical Report ARCCB-TR-9 1027, Watervliet Arsenal, NY, August 1991.
Composite barrel construction is a viable means to enhance the structural stability of gun weapon systems. It is, however, challenged by the need to protect the barrel from the hot and erosive action of the propellant gases. This typically results in a composite over-wrap incarnation over a thin-walled steel barrel. The remaining challenge is to maintain the bond between the base material and the composite over-wrap during both manufacture, especially the autofrettage process, and the firing loads which create concurrent radial dilation of the barrel and axial recoil loads. This firing dynamic challenge is exacerbated by the pressure discontinuity that travels behind the obturation of the projectile with a speed that may resonant a traveling flexural wave of the bore surface. Other challenges include impaired heat transfer across the insulting composite and increase recoil velocity of the cannon during operation.
Fluted gun barrels also have been used. Gun barrels may be constructed with flutes that look like fins emanating from the center of the gun. In analogy with design of an I-Beam the general design concept is to get the steel at a greater radius for an increased stiffness; without increasing the inertia in proportion. An example of this approach is the British 30-mm, L21A1 system commonly called the RARDEN. (See Geeter, et al., “Low Dispersion Automatic Cannon System (LODACS) Final Report (U),” ARDEC Technical Report ARSCD-TR-;82011, August 1982). However, fluted gun barrels are expensive to manufacture, increase system weight, and compromise a desirable static stress distribution that is manufactured into most large caliber gun barrels using a process called autofrettage.
The application of active controls and feed-forward cancellation has been used. If the input excitation can be anticipated, a control signal can be applied through an actuation system to preempt the disturbance energy. An example for a tank gun system while traversing rough terrain would be the use of a sensor to detect vertical acceleration of the tank hull, and apply immediate counteraction force through the elevation actuator system. In many tank guns the center of gravity extends forward of the trunnion bearings. This is a result of the limited working volume within the armor protected turret. Thus, a vertical heave upwards applies a torque to the gun system that may be cancelled by an applied downward force at the elevation coupling, behind the trunnions. For current systems, feed-forward cancellation treats the gun barrel as a rigid body, and ignores flexural modes, and in particular the first flexural mode.
The concept behind active feed-back vibration cancellation is to sense the vibrations of the structure under control, both amplitude and phase, and to apply control forces to the structure to cancel the detected vibrations. This requires bot
Carone Michael J.
Chambers Troy
Moran John F.
Sachs Michael C.
The United States of America as represented by the Secretary of
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