ATMOSPHERIC WINDS: IMPLICATIONS FOR MICRO AIR VEHICLES

摘要

A major challenge to low speed micro flight is the transient and time-averaged velocities arising from the Atmospheric Boundary Layer (ABL), particularly turbulence a few metres above the ground. In this paper, prior work on the temporal and spatial characteristics of the ABL close to the ground, and the relative turbulence as perceived by a moving craft, is considered. New measurements are described that document the time-averaged and transient velocities at a height of 4m above the ground. These were made using a bank of four multi-hole probes laterally separated by 150 mms on a mast above a test car, in order to understand more about the wind environment of MAVs. Roads through category 2 terrains were traversed at various speeds (including with the vehicle stationary and in the influence of a large building), under atmospheric winds of 45 m/s. Relative turbulence intensities of about 4% to 30% were measured - the highest intensities occurring with the vehicle stationary. Flow pitch angles were investigated and it was found that the variation with lateral separation did not reduce significantly as the separation reduced. Since this implies that the roll inputs arising from vertical fluctuations would increase with reducing span, it is postulated that flapping wing propulsion and control be considered for very small aircraft. Further processing of the existing data and further testing with reducing probe separation is planned, including investigating correlations of vertical velocity fluctuations with closer lateral probe separations.