Modeling of the 35-mm Rarefaction Wave Gun

Report No. ARL-TR-3792
Authors: Terence P. Coffee
Date/Pages: May 2006; 46 pages
Abstract: The rarefaction wave gun (RAVEN) is designed to reduce the recoil momentum of a gun while having a minimal effect on the projectile velocity. The recoil reduction is achieved by venting gas out the breech through an expansion nozzle. This is similar to a recoilless rifle. The difference is that the venting is delayed until the projectile is some distance down tube. The opening of the breech creates a rarefaction wave that travels down the bore of the gun. If the timing is done correctly, the rarefaction wave will not reach the projectile until at or after muzzle exit. Hence, the projectile does not know the breech has opened, and the venting has no effect on the muzzle velocity. As a proof of principal, a 35-mm RAVEN gun was designed, built, and fired. The breech is a moving piston. When the piston has moved a specified distance, it will open a vent into an expanding nozzle. There is a small reduction in the muzzle velocity due to the motion of the breech. That is, the chamber becomes larger than for a fixed breech gun. If the timing is correct, there is no additional reduction in the muzzle velocity due to the venting. In this report, a one-dimensional model of the RAVEN is presented. The model covers the interior ballistics, the motion of the projectile and the breech, the opening of the vent, the flow through the nozzle, and the blow down of the gun. The model is validated against the 35-mm RAVEN data.
Distribution: Approved for public release
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Last Update / Reviewed: May 1, 2006