Airborne four channel fiber coupled vector laser Doppler anemometer system

Using an airborne vector laser Doppler anemometer (LDA) to measure the air flow outside of the boundary layer of an airplane is a promising optical technique. Measurement of the primary flight data like true airspeed, the angle of attack, and the angle of sideslip can be directly derived from the measured wind vector. We developed an experimental system with interchangeable telescopes to study the change in the LDA sensitivity and signal rate, depending on the focusing of the measurement beam. The system has a real-time-capable field programmable gate array data acquisition system, which also can record full data dumps for off-line analysis. This paper presents the first results of an airborne measurement campaign. The true airspeed is measured with an residual error of 1% compared to the five-hole flow sensor. The angle of sideslip and the angle of attack show a standard deviation of the residual error of 0.6^∘ for the angle of sideslip and 0.2^∘ for the angle of attack.