Torsional Impulse in Gun Launched Projectiles

An investigation of torsional impulse due to "free run" is described. "Free run" is characterized by positive forward motion of a projectile before reaching the origin of gun-tube rifling. This factor permits the projectile to reach an appreciable forward velocity before rotation begins. The instrumentation package for a hard wired experiment is shown and the experimental results are reviewed. The purpose of this investigation is to characterize the in-bore environment when a projectile is subjected to free run in the gun tube. The effect of this condition is important in projectiles which may be adversely affected by these dynamic load conditions. Two types of projectiles were analyzed. The investigation included analytical modeling which used the Super Sceptre computer program and experimental testing which used modified standard projectiles, respectively. The experiments were conducted with the use of a wire-in-bore technique. This procedure provides hard wire communication between the instruments on board the projectile and the recorder in the ground station. This paper is concerned primarily with the discussion of the experimental technique and the results of the tests. Accurate data retrieval during such testing is necessarily difficult since the instrumentation is subjected to the high setback forces along the axis of the projectile, that is, forward accelerations of many, many times gravity, and the extreme lateral forces due to balloting, etc., while at the same time sensing the angular motion about the projectile axis. Therefore, the recorded signals might well contain much extraneous information.