Transient resonance of rolling finned projectiles

Abstract

Finned projectiles that are intentionally spun are known to become locked in at a resonance condition where the roil rate matches the pitch/yaw frequency. This phenomenon, called roll lock-in, results in an amplification of the trim angle, which can lead to yaw instability. A less severe phenomenon is that of transient resonance where the roll rate locks in at resonance briefly before continuing to build up to the design value. However, the trim amplification during the brief period of resonance may be sufficient to destabilize the projectile. In this paper, the problem of transient resonance for finned projectiles with a centre-of-mass asymmetry is studied. Numerical simulations are used to illustrate transient normal and reverse resonance. No yaw amplification is seen in both cases; rather the absolute value of the complex angle of attack shows a drop during passage through resonance. It is suggested that this is a general feature of the yaw response of finned projectiles undergoing transient resonance.