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Due to imperfect water entry, a high speed supercavitating projectile, while moving in the forward direction, rotates inside the cavity. This rotation leads to a series of impacts between the projectile tail and the cavity wall. The impacts affect the trajectory as well as the stability of motion of the projectile. The present paper discusses the in-flight dynamics of such a projectile. Equations of motion of the projectile are developed for two distinct phases of motion – Phase I: the projectile moves in the cavity without interaction with the cavity wall, and Phase II: the tail impacts on the cavity wall. The equations are found to be coupled and nonlinear. A simple model based on the concepts of flow planes is used to determine the forces acting on the projectile during impact. The effect of the mass distribution on the projectile dynamics is also studied. The results show that despite the impacts with the cavity wall, the projectile nearly …