In-flight flexure and spin lock-in for antitank kinetic energy projectiles

Abstract

A time-dependent analysis, coupling the rod vibration equation and pure roll motion equation, is formulated to numerically simulate the in-flight bending behavior of antitank kinetic energy projectile rods. The projectile is modeled as undergoing continuous, simulated planar pitching motion with the aerodynamic, spin, and structural damping forces included. The main parameter affecting the projectile spin and rod deflection responses is the fin torque producing the spin. Detailed spin, deflection, maximum stress, pitching angle, and rod shape histories are obtained along the projectile trajectory. Various steady-state spin cases are studied to simulate the effect of damaged fins. The spin lock-in phenomenon at the first lateral flexing natural frequency is captured by the present model for rods with simulated damaged fins. Any deformable projectile attempting, because of damaged fins, to spin past that frequency was found to lock-in to spinning at that frequency. Both suband supercritical spin cases are computed. Predictions of the rod shape at any instant and under actual flight conditions are made.