Theory of transonic gas guns

Abstract

A review is given of analytica1 methods for predicting the muzzle velocity of compression gas guns. Steady adiabatic expansion theory, quasi-steady theory and unsteady theory are all examined, with emphasis placed on simplified analytical methods applicable to subsonic and transonic muzzle velocities. New formulae are obtained and compared with numerical results from a full theoretical treatment of the gas flow. The comparisons show that the new analytic results are remarkably effective and can therefore be used for gun, design. The effects of atmospheric counter pressure are treated separately and a new method of correcting the predicted velocity is given. An analysis of data from actual subsonic guns highlights the importance of muzzle pressure reflections in reducing the retarding pressure at low subsonic speeds. The observed muzzle velocities are about 10% below the muzzle velocities predicted by theory. Finally, nitrogen, helium and hydrogen are compared as potential driver gases for transonic guns.