Optical measurement of target displacement and velocity in bird strike simulation experiments

Thousands of bird strikes on aircraft occur annually with subsequent consequences for repair costs but also for public safety. In bird strike simulation experiments a bird or birdlike object is usually accelerated towards a target. Knowledge of the parameters of the impact, such as the velocities involved, the target displacement and the energy transferred from the projectile to the target, lead to a better understanding of the phenomenon, and eventually to better protection against damage caused by bird strikes. However, due to the extremely high velocities and energies involved in the experiments, methods for registration of the impact parameters are not obvious. Non-contact measurement techniques have a number of advantages over the more common mechanical contact methods. In this paper, a relatively simple optical technique is presented for recording the history of target displacement, from which the target velocity and energy can be readily obtained. The technique is based on the relative displacement of two moire line gratings: one grating attached to the target and the other serving as a stationary reference grating. The proposed technique has proved to be useful. Results of a representative bird strike experiment are presented.