Flow fields in complex terrain and their challenges to micro-flight

Major challenges to low speed micro flight are the transient and time-averaged velocities arising from the Atmospheric Boundary Layer (ABL), particularly turbulence a few metres above the ground. In this paper, existing data from meteorologists and wind engineers are reviewed and measurements dedicated to understanding the spatial and temporal velocity fields that MAVs experience are briefly described. Spectra obtained for a range of terrains, flight and wind speeds followed the expected 5/3rds Kolmogorov law. Transient flow pitch angles were investigated (obtained from four small laterally displaced probes), in order to understand the possible roll and pitch inputs to MAVs. For some data sets very considerable differences in pitch angles were observed between the four probes. It was noted that the variation with lateral separation decreased relatively slowly with reducing separation. This effect is thought to explain the increasing piloting difficulties experienced in maintaining good roll control for decreasing scales of craft.