The influence of internal moving parts on the ballistic flight path of a projectile

In the case of the ballistic flight path of an artillery shell whose internal component is only partially restrained with respect to the geometric axes, the internal component's dynamic behavior creates gyrodynamic torques which affect the shell's instantaneous heading angle and spin rate. In the present investigation of such nonrigid shells' trajectories, a model is proposed which encompasses a shell case whose internal body is capable of both independent rotation and translation. An examination of the resulting equation of motion shows that the shell's heading angle resembles a linear damped harmonic oscillator driven by a forcing function that is created exclusively by the internal component. Not all internal motion, however, leads to destabilization; stability instead depends on: (1) the ratio of moments of inertia of the internal element; (2) applied aerodynamic moments; and (3) the combined component/body transfer function.