An optical angle of attack sensor

A major source of transonic and supersonic wind-tunnel test data uncertainty are 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. A novel laser-based instrument for the in-situ measurement of wind-tunnel-model angle of attack that enables continuous, time-dependent measurements to be made without signal dropout is described. 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. The results show that 0.01° sensitivity can be achieved and that optical and detector packaging requirements are less stringent than those for current tilt-sensor or accelerometer model installations