Aerodynamic characterization of a non-lethal finned projectile at low subsonic velocity

To characterize the trajectory of a low subsonic fin-stabilized projectile with at a low angle of attack, the use of a Point-Mass Model (PMM), taking into account only gravity and a constant zero-yaw drag coefficient, seems justified for short-range applications and/or with limited computing resources. This approach does not take into account the attitude of the projectile in flight and when it hits the target, neglecting any possible instability in flight. The use of non-lethal or less lethal projectiles where serious injuries must absolutely be avoided requires however that the impact conditions are perfectly controlled. This paper starts from a 12-gauge finned-geometry to numerically and experimentally predict static aerodynamic coefficients at different angles of attack (drag, lift and pitching moment) at very low velocities, up to 0.1 Mach. Validation of these two forces and moment is essential to begin the full characterization of the projectile’s flight behaviour. The added value of a 3-DOF model over a PMM was then analyzed and seems negligible in height and range as long as the launch conditions are not completely disrupted. The slightest destabilization makes the PMM inappropriate and knowledge of the pitch damping coefficient becomes necessary to optimize stabilization following minor disturbances, even at those low velocities.