Development of a flying wind measurement system for collective operation

Abstract

Using a multirotor aircraft for wind measurements results in a novel add-on to conventional measurement technologies because outdoor measurements at several arbitrary locations in three-dimensional space at high temporal and spatial resolution have not been possible before. If such a swarm measurement is to be realized with a group of conventional multirotor aircraft, a number of potential problems exist. To cope with these problems, the present work has been divided into two parts. On the one hand, the underlying effects have been investigated by analytical calculations, simulations and experiments to gain a deeper understanding and derive guidelines and procedures regarding flying wind measurements, as well as multirotor design in general. On the other hand a purpose designed aircraft has been developed most suited for the measurement task. Together with a probe manufacturer a custom flow measurement probe was developed. This design combines the robustness of a Prandtl tube with the high temporal resolution and directional sensitivity of a triple hot wire probe. The data acquisition system for the probe was also customized and connected to the autopilot in order to make live-readings and automatic alignments of the aircraft with the wind direction possible. Finally, to address the problem of vibrations a modal analysis and frequency tuning of the measurement boom has been conducted. The flight and measurement performance of the first prototype aircraft could be demonstrated with great success. To characterize the lower end of the measurable wind speed range free flights in a gust wind tunnel have been undertaken, while the "real life" measurement performance was shown in a field test next to a met mast at wind speeds up to 13 m/s.