Design of a Freely Rotating Wind Tunnel Test Bench for Measurements of Dynamic Coefficients

The needs to improve performances of artillery projectiles require accurate aerodynamic investigation methods. The aerodynamic design of a projectile usually starts from numerical analyses, mostly including semiempirical methods and/or Computational Fluid Dynamics (CFD), up to experimental techniques composed of wind-tunnel measurements or free-flight validations. In the frame, the present paper proposes a dedicated measurement methodology able to simultaneously determine the stability derivative C m$\alpha$ and the pitch damping coefficient sum Cmq + Cm$\alpha$ in a wind tunnel by means of a single and almost non-intrusive metrological setup called MiRo. This method is based on the stereovision principle and a three-axis freely-rotating mechanical test bench. In order to assess the reliability, repeatability and accuracy of this technique, the MiRo wind tunnel measurements are compared to other sources like aerodynamic balance measurements, alternative wind tunnel measurements, Ludwieg tube measurements, free-flight measurements and CFD simulations