Free-Flight Measurements of Static Aerodynamic Coefficients on a Complex Body

The measurement of high-quality force coefficients in the hypersonic regime within short-duration wind tunnels is challenging, particularly for complex geometries. In this study, the static free-flight force measurement technique has been applied to a finned 7 deg half-angle cone within the University of Oxford High Density Tunnel at a flight-representative Mach 7 condition. A quasi-static free-flight test is achieved by matching the locations of the center of gravity and center of pressure, reducing the static margin of the body and hence the amount of pitching motion. Static free flight becomes more difficult for complex bodies where the center of pressure is a function of angle of attack. Longitudinal static force and moment coefficients were measured at the Mach 7 condition, with the experimental data agreeing well with numerical predictions. Forces were obtained using both image tracking at 76,000 fps and the direct measurement of accelerations using an onboard inertial measurement unit. Uncertainties were at most [Formula: see text] for the lift coefficient and [Formula: see text] for the drag coefficient across all attitudes tested. The fins were also angled to allow the model to roll in free flight so that the roll coefficient could also be determined with a maximum experimental uncertainty of [Formula: see text].