Yaw Card Perturbation of Projectile Dynamics

Projectile flight through a yaw card range is investigated with particular attention given to the apparent change in the flight coefficients. Encounters of the projectile with the yaw cards are treated as impulses, resulting in calculated abrupt changes in the yaw modal arms' phases and amplitudes. Further approximations are made to describe small perturbing encounters and to obtain an expression for the apparent or range value for the overturning moment coefficient. For 7.62-mm ammunition, apparent flight coefficients are calculated point by point for various yaw card spacings and compared with simple approximating expressions. Resonance conditions are also investigated, whereby the yawing motion of a spin-stabilized projectile can be amplified. These resonance conditions force the amplitude ratio for the fast and slow modal arms toward unity and the encountering phase angle of the projectile toward a value that maximizes the amplification for each encounter.