Spin-Yaw Lock-In of a Rotationally Symmetric Missile

Abstract

Spin―yaw lock-in has usually been associated with small aerodynamic asymmetries that produce a trim angle that rotates with the missile. Recent trajectory calculations using wind-tunnel measurements ofthe aerodynamic moment acting on a rotationally symmetric missile predicted spin―yaw lock-in. Thus, an asymmetry-induced trim moment is not necessary for lock-in. For a side moment that varies with the roll angle between the angle-of-attack plane and a fixed plane on the missile, this paper shows that lock-in of the coning motion and the rolling motion can occur. The conditions on the aerodynamic moments for occurrence of lock-in are derived and appropriate stability criteria are obtained. A simple case of a hypersonic finned missile is considered and the existence of lock-in is demonstrated.