An optical technique for measuring of ventilation rates in models.

Describes adaptation of photo-electrical optical technique to measure ventilation rates in wind tunnel models. Illustrates probe photographically and diagrammatically. It comprises essentially a light-emitting diode and a hybrid photodiode-amplifier detector. Compares technique with conventional tracer gas technique using helium and a katharometer and finds good agreement. Considers optical probe has considerable potential for measurements in small and multi-celled models where conventional techniques are not feasible.