A Synopsis of Yaw-Induction Techniques Used During Projectile Free-Flight Aerodynamics Experiments

Projectile free-flight motion measurement from yaw cards, spark ranges, and instrumented projectiles and accompanying analyses have become integral components of weapon system development. The projectiles aerodynamics can be extracted from these free-flight motion data by fitting to the 6-degree-of-freedom equations of motion. Because many of these aerodynamic coefficients vary as a function of angle of attack, generating a sufficiently large angle of attack andor a variety of angles of attack is necessary for complete aerodynamic characterization. Achieving this often requires special attention. Over the years, numerous yaw-induction techniques have been developed to deliberately increase the angular disturbances experienced by the projectile during launch. Yaw-induction during free-flight experiments is often necessary for two main reasons 1 to produce angular motion large enough to diminish the effect of measurement and modeling errors, thereby increasing the accuracy of the fitted data, and 2 to produce a set of shots at varying yaw levels to characterize the nonlinear behavior of aerodynamic coefficients with respect to yaw. This report describes a variety of techniques that have been used to induce free-flight projectile angle of attack during the launch phase, and provides insight pertaining to their implementation and success based upon some quantitative results.