Calibration Technique for Recovery of Short Duration Aerodynamic Force

Force measurement is one of the key issues for design of high speed vehicle configurations. They are routinely tested in impulse facilities where the test duration is in the order of few milliseconds. Since, the experiments are performed in short test times, it is expected that the model never achieves the steady state. So, the measurement diagnostics must account this fact while inferring the forces from the measured parameters. One of the methods is the determination of characteristics system response function by including the dynamics of the system. The aim of this work is to develop a calibration experimental setup and measure axial force on generic aerodynamic body configurations during a short time (~0.6？ms). A generic aerodynamic model attached to a “stress bar” is suspended freely and an impulse load is applied at the tip of the model. An accelerometer fitted with the model records the signal corresponding to the motion of the model. Then, the system characteristics function (impulse response function) is obtained from input force history and output accelerometer signal and further used to predict any unknown forces of similar nature. The recovered forces are compared well with the applied ones with a reasonable accuracy of %. 1. Introduction There has been an increase in the demand for dynamic calibration of force measuring devices in many industrial applications, automobiles, and aircrafts [1–3]. With respect to high speed and hypersonic flow environment, the force measurement on aerodynamic models is challenging due to the need for fast response devices and dynamics involved in the integrated model-balance system [4]. Most of these measurements are performed in short duration impulse facilities where the typical time scale of measurement is in the order of few milliseconds or less. The traditional technique is to obtain velocity data from laser-Doppler interferometry from which acceleration data can be derived [5]. The other method is to obtain the acceleration history from the model directly and to subsequently determine the forces with the knowledge of mass. In this way, the cause of the motion can be predicted from model accelerations by determining the forces during steady-state measurements [6–8]. Each of these techniques has relative merits/demerits and is best suited when the size of model is small. But, when the size and weight of the model increase, it is almost impossible to obtain steady-state signal during short time-scale measurement. So, the system dynamics must be included in the measured signals for predicting the unknown