Development of the high-velocity gas-dynamics gun

The subjects of this paper are the historical overview and development of the high-velocity gas-dynamics gun. These are guns that derive their energy from a reservoir of compressed gas. Other 3uns derive their energy from electricity or from high explosive. Their historical overviews and developments are covered in papers by Mr. William Weldon and Mr. Alex Wenzel.

The gas dynamics gun is viewed first from the standpoint of modern technology. An idealized configuration, the “Reference Gun”, is analysed in order to quantify the effects of gun diameter and length, projectile mass, and propellant gas pressure and composition. The analysis assumes that the propellant is an ideal gas, and formulae are derived for the base pressure and velocity of the projectile as functions of the size and loading parameters of the gun. The analysis demonstrates that the prime requirements for high velocity are a high gas pressure, a low molecular weight gas, a light projectile, and a long gun.

The history of guns is reviewed briefly from 14th century black-powder muzzle-loaders to 20th century, nitrocellulose -propellant, breech-loaded guns. The velocity limit of the modern gun is shown to be around 3 km/s, if the gun is loaded with nitrocellulose propellant and is very long (200 calibers). However, if the gun is loaded with hydrogen and the length doubled, it is shown that the velocity limit can be increased to 7 km/s, thus approaching current needs.

The problem of using hydrogen has been solved by the invention of the piston-compression light-gas gun (PCLGG). However, the limited strength of the fragile, sabot-model projectiles of experimental research has capped the maximum acceleration and has placed a demand on the gun's operating cycle to generate a constant pressure at the base of the projectile for the launching run. This second problem has been partially solved by the invention of a modification to the PCLGG known as the piston-compression, accelerated-reservoir, light-gas gun (PCARLGG). Both the PCLGG and the PCARLGG are described. The performance of the PCARLGG has been analyzed by a hydrocode developed for this purpose, and the results of the calculations are presented and compared with experiment.

The concept of a frictionless, adiabatic “Ideal Gun” is introduced in order to simplify the analysis of performance. It is shown that the performance of any ideal gun is given by a simple equation involving two dimensionless parameters that relate the projectile's velocity to its mass, its average base pressure, and the diameter and length of the gun. Based on the ideal gun equation, the maximum operating velocity of the gas-dynamics gun is estimated to be about 12 km/s.