Free-flight force measurement technique in the impulsive facility HIEST

A feasibility study of a direct acceleration measurement technique was performed in the free-piston high enthalpy shock tunnel HIEST. The technique is simple and cost effective rather than aerodynamic force balance technique. With the present technique, aerodynamic force was obtained as products of measured acceleration and mass of the model, which model was weakly suspended with thin wires. Natural vibration of the test model, which often disturbs precise measurement, can be removed through signal recovery process with a de-convolution calculation and with low-path filtering. Time response of the measurement technique guaranteed 0.1 ms with a digital low-path filter, which cut-off frequency is 10 kHz. For evaluation of the technique, wind tunnel test in HIEST was conducted to measure unsteady drag force of a 500 mm length HB-2 standard model. The comparison between the present measurement results and the measurement results in blow-down type wind tunnel showed that the difference is 5%.