Influence of Yaw Cards on the Yaw Growth of Spin-Stabilized Projectiles

Abstract

A simple extension of the standard linear theory, describing the free-flight motion of a projectile, now includes the influences due to the projectile impacting yaw cards. The card impacts are modeled as ideal delta function impulses that are shown to alter the usual yawing motion of a spin-stabilized projectile passing through a yaw card range. Card-induced changes in the complex-valued yaw modes are expressed as difference equations. Known analytic solutions to these difference equations show how card impacts influence a projectile's yawing motion by relating simple expressions of the card spacing to a parameter describing the material density of the yaw cards. These solutions also reveal that both bounded and unbounded yaw mode magnitudes can be induced by yaw card impacts. Furthermore, the model shows that moments caused by repeated projectile and card interactions should not always be treated as negligible. Examples of these results for a typical small arms projectile (7.62 mm) launched from an unworn gun tube are presented.