The turbulent flows and gusts around buildings and other urban infrastructure can affect the steadiness and stability of eVTOLs and drones by generating a highly transient relative flow field, according to a paper Gusts Encountered by Flying Vehicles in Proximity to Buildings co-authered by researchers from School of Engineering, RMIT University, Melbourne, Australia, the Mechanical Engineering and Mechanics, Lehigh University, Bethlehem, USA and the Department of Aerospace Engineering, University of Maryland, College Park, USA.
“Our aim is to review existing gust models, then consider gust encounters in the vicinity of buildings as experienced by flight trajectories over the roof of a nominally cuboid building in a suburban atmospheric boundary layer,” says the abstract to the study. “Simplified models of fixed- and rotary-wing aircraft are used to illustrate the changes in lift and thrust experienced by flight around the building. The analysis showed that fixed-wing aircraft experienced a substantial increase in angle of attack over a relatively short period of time (<1 s) as they fly through the shear layer at a representative forward velocity, which can be well above typical stall angles. Due to the slow flight speeds required for landing and take-off, significant control authority of rotor systems is required to ensure safe operation due to the high disturbance effects caused by localized gusts from buildings and protruding structures. Currently there appears to be negligible certification or regulation for AAM systems to ensure safe operations when traversing building flow fields under windy conditions and it is hoped that the insights provided in this paper will assist with future certification and regulation.”
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(Image: Notional flow field about a building generated by atmospheric winds)