Aeroballistics of Yawing-Spinning Target Practice Projectiles: Gyroscopic and Dynamic Instabilities

Despite extensive studies, mechanisms governing the aeroballistics of yawing and spinning projectiles are still difficult to understand. This is especially true for target practice projectiles settled with additional roll damping devices. Almost no publication is dedicated to the aeroballistics of this kind of projectile. Aeroballistic investigations are based on Computational Fluid Dynamics (CFD) computations, six-Degree-of-Freedom (6-DoF) flight dynamic computations, and free flight tests. The first part of the paper is devoted to aerodynamic comparisons between classical and target practice projectiles. For classical projectiles, it is well-known that, for small angles of attack, the spin induces a weak asymmetry of the boundary-layer profiles. For target practice projectiles, the roll damping devices, settled as longitudinal grooves, can generate important modifications of the flow. As expected, the grooves significantly increase the roll damping moment but also act on the boundary-layer asymmetry, strongly increasing the Magnus moment. The second part of the paper is dedicated to the flight dynamic behavior. According to the grooves' design, dynamic and gyroscopic instabilities can appear on the trajectory. Finally, free flight test results highlight the large range reduction obtained with the target practice projectile. The agreement between CFD simulations, flight dynamic computations, and free flight tests is satisfactory.