Non-Invasive Model Attitude and Deformation Measurement

The precision with which model attitude and deflection are measured in a wind tunnel is important for determining such quantities as drag coefficient, lift coefficient, moment coefficient and stability derivatives. The assumption that the wind tunnel model is a rigid body, which possesses no extra deflection under load, no flexing under dynamic loading is far from reality. Some of the techniques such as inclinometers placed on-board the model, photogrammetric techniques, X-ray imaging of the models on the film planes etc. have been used, but are found to be too slow for dynamic situations, or are incapable of measuring deflections very accurately. Thus, there is a need to devise other optics-based techniques to achieve the required measurement accuracy. The concept proposed in this document describes one such innovation in developing an optics-based system using photorefractive materials and a scanning acousto-optic system. Since optical recording normally suffers from speed limitations, electrical recording will be employed. This is feasible in photorefractive materials since under the right conditions, photo-excited carriers contribute to photo-currents that can be collected and recorded. A simple bench-top demonstration will be conducted to measure attitudes in both steady state and dynamic situations from photo-current measurement. A proof-of-concept at such tunnels as 16-T will be defined which will realistically demonstrate the concept in Phase II.