An optical angle of attack sensor

A major source of transonic and supersonic wind-tunnel test data uncertainty is due to angle of attack measurement errors caused by unknown sting and balance deflections under load. Since dynamic loads in pressurized or cryogenic wind tunnels generally exceed those in conventional low-speed atmospheric wind tunnels, the need to account for these distortions during model testing is even more acute. To meet this challenge, a novel, laser-based instrument for the in situ measurement of wind-tunnel model angle of attack has been developed which is designed to enable continuous, time-dependent measurements to be made without signal dropout. Detectors capable of 0.01° resolution over 18° range and 0.03° resolution over a 44° range with time-dependent outputs of 60 Hz have been developed. This capability is sufficient to provide accurate real-time angle of attack information for correlation with model balance measurements during transport and fighter model testing. Proof-of-concept experiments, along with the results of recent measurements conducted at the NASA Ames 9-ft×7-ft supersonic wind-tunnel, are presented. Experiments were also conducted to determine the reliable range, sensitivity, and long-term stability of the instrument