There is a growing desire to operate Uncrewed Air Vehicles (UAVs) in urban environments for parcel delivery, and passenger-carrying air taxis for Advanced Air Mobility (AAM). The turbulent flows and gusts around buildings and other urban infrastructure can affect the steadiness and stability of such air vehicles by generating a highly transient relative flow field. 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. 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.

This paper examines the possibility of using a Multi-Rotor Unmanned Aircraft System (MUAS) for atmospheric flow measurements around a tall building. This novel sensing approach is proposed, whereby we attempt to determine the oncoming flow velocity magnitude and direction from measurements of the power required by each of the MUAS rotors. Extensive wind-tunnel testing was completed to determine the power required by the fore and aft rotor-pairs at varying flow velocities and directions. The results show that it is possible to map between rotor power consumption and the oncoming flow vectors, however, a unique and accurate mapping is only possible over a very small region of the measurement space. Thus, it is concluded that the practical use of this sensing method is limited. Examination of power consumption curves also revealed that the conditions under which a Vortex Ring State (VRS) develops for small MUAS. The characteristics of VRS development are similar to those of full-size helicopters, indicating that the VRS is Reynolds number independent. The reduction in power consumption due to the presence of updraft flows of various magnitudes was also quantified, indicating that significant endurance improvements of MUAS are possible and can be achieved when operating windward of large buildings.

Fixed-wing micro aerial vehicles experience attitude control difficulties as they operate in highly turbulent environments. Previous research has identified pressure-based control as a potential approach for augmenting the performance of, or replacing, autopilots reliant on inertial sensors. However, implementation requires an in-depth understanding of the correlation that exists between oncoming gusts and wing surface-pressure variations. This paper investigates the variation of correlation along a representative micro aerial vehicle wing chord and wingspan between upstream flow pitch angle variation and wing surface-pressure variation. Atmospheric turbulence was replicated within the controlled environment of a wind tunnel using planar grids that generated a turbulence intensity of 12.6%. Despite the unsteady nature of the pressure field, it was discovered that high correlation is evident in the vicinity of the leading edge. Thus, a few optimally placed sensors can be used for a pressure-based attitude control system for micro aerial vehicles.