Behavior of a Railgun Launch Package at the Muzzle and During Sabot Discard

Abstract

Projectiles launched with ISL’s PEGASUS railgun achieve muzzle velocities well beyond 2000 m/s. The design of the corresponding 1.3-kg launch package of caliber $40\times 40$ mm2 was presented at the 18th EML-Symposium in 2016. Meanwhile, the phase after muzzle exit has been studied, and in particular, the sabot separation in the air flow has been investigated. To that end, a numerical model was used which had been previously validated by means of shock tunnel experiments. Besides the subprojectile, the launch-package essentially consists of the armature, on which the Lorentz force is acting, and further, of two sabot parts with integrated bore riders. The numerical model describes the launch-package flight in moving coordinates in the shot axis direction, i.e., the package is considered to be initially fixed in space, surrounded by a constant velocity air flow. The launch package components are able to move and to deform in the three dimensions thereafter. It is further possible to introduce lateral perturbation, e.g., linear and angular motion due to the muzzle disturbance. Although the airflow is modeled with a Eulerian code neglecting viscous effects, the computation results agree very well with the experiments. Hereby, it is demonstrated that the numerical model can effectively be used as a tool for launch package design optimization. An example is given for a fin-stabilized projectile which shall be launched with the new 6-m-long NGL60 railgun having a bore cross section of $60\times 60$ mm2.