Measurement of vehicle stability coefficients in hypersonic wind tunnels

This study considers the measurement of aerodynamic stability derivatives on scaled free-flight models subjected to hypersonic flows. Models of a conceptual vehicle design are tested in order to make predictions about their full scale dynamic behavior. These models are designed to meet the scaling laws described in the literature regarding free flight testing in compressible flows. Commercial CAD packages and 3D printing are used for design and fabrication of the models. Aerodynamic forces on these models are measured using a combination of on-board instrumentation (accelerometers/gyroscopes) and analysis of high-speed video footage. A light-weight instrumentation system is utilized to measure angular movements (pitch, roll and yaw) and accelerations and transmit the sensor data by a Bluetooth transceiver to a computer for post processing. High-speed cameras were used to track model motion and to visualize the flow field with schlieren techniques. Models are tested in the University of Southern Queensland’s medium-duration hypersonic wind tunnel (TUSQ). TUSQ allows for a period of approximately 200 ms of steady Mach 5.85 flow. Sensor data and results from image processing were in good agreement, with percentage error remaining below 15.9% throughout, giving validation for the technique. Sensor data is transformed from the local coordinate frame on-board the model to the global frame relative to the flow direction. Aerodynamic coefficients were determined from this data over a range of angles of attack. It is clear from the data that useful insights can be made about the stability characteristics of the model and that results could be utilized as a validation case for later numerical studies. Runs with large movements were chosen for preliminary analysis due to the data having a large signal to noise ratio. Coefficients are found to follow the trends expected in the case of lift and pitching moment, showing the model to be statically stable. Due to the sensitivity of drag to other rotations apart from pitch, a trend was challenging to quantify. This study shows that it is indeed possible to get useful dynamic data from free flight testing.