The present invention relates to tubular projectiles used in weaponry, and more particularly to supersonic, low-drag tubular projectiles possessing solid fuel ramjet thrust augmentation.
The concept of supersonic, low-drag tubular projectiles used in weaponry is known from U.S. Pat. No. 4,301,736 to Flatau and Huerta. Well described therein are the problems to be overcome in providing on the one hand a low-drag tubular kinetic energy projectile with flight performance based upon the initial muzzle velocity, and maintaining sufficient mass on the other hand for providing adequate terminal momentum and thus destructive force upon impact. As described therein, the difficulty in providing an acceptable balance between the potentially conflicting parameters of velocity, mass, aerodynamic characteristics and payload capacity, make this a highly empirical science. The aforementioned discussion contained in the U.S. Pat. No. 4,301,736, insofar as the same bears direct relevance to the subject matter of the present invention, is incorporated herein by reference.
For over a decade, technologists have sought to successfully develop a solid fuel ramjet tubular projectile capable of sustaining the muzzle velocity in flight. The general concept of a solid fuel ramjet-type thrust augmentation arrangement in tubular projectiles is known from U.S. patent application Ser. No. 514,113, filed July 15, 1983, to Olson, Huerta and Holzman, now abandoned. This hollow projectile provides a centralized tubular design with an internal mid section constituting a combustion chamber annularly lined with solid fuel for effecting thrust augmentation. The rear portion of the projectile is provided with a thrust generating design comprising a constriction portion and a flared rear section, which operate on the hot expanding gases generated in the mid section combustion chamber in well known manner. This arrangement combines the design of a supersonic, low-drag tubular projectile with an internally arranged auto-ignited, solid fuel thrust augmentation system.
With regard to thrust augmentation such as described above, it is known that to effect auto-ignition and a sustained burn, the air flow through the combustion chamber should be subsonic. Moreover, to provide an even burn of the solid fuel and thereby optimize burn efficiency and projectile stability, the combustion chamber should be relatively narrow in cross-sectional dimension. However, a constricting combustion chamber directly opposes the ability to maintain the projectile at supersonic speed, let alone at or better than muzzle velocity. It is also true that one cannot simultaneously effectively provide both supersonic and subsonic air flow through the single-path tubular interior.
What is needed is a tubular projectile which captures the advantageous characteristics of low drag, supersonic internal flow, adequate mass and acceptable aerodynamic design on the one hand, and a self-igniting, efficient solid fuel thrust augmented projectile which can achieve a terminal velocity that equals or exceeds muzzle velocity, on the other hand, and which effectively overcomes the inherent conflicts in the above-discussed design parameters and characteristics.