Projectile propulsion through a porous supersonic nozzle with application to airguns

Abstract

The purpose of this study is to show theoretically and ics. experimentally that a porous barrel can allow pneumatic airgun projectiles to reach velocities in excess of Mach 1 of the gas behind the projectile. Thermodynamic steady flow relations indicate that pneumatic virgins using a non-porous, constant area barrel are limited to exit velocities of Mach l of the gas immediately behind the projectile, no matter how , high the reservoir gas pressure is. Various virgins, such as the Crosman 760 and DIANA RWS 34, are analyzed to examine the commercially available airgun technologies, and to determine the advantages that may be achieved using a porous barrel. A water analogy experiment shows that a porous barrel can serve as a supersonic nozzle. Busemann flow equations also account for gas velocity increasing with gas outgun from a channel if the velocity before the outgun is greater than or equal to Mach 1 .