The soaring potential of a micro air vehicle in an urban environment

Achieving useful endurance with Micro Air Vehicles (MAVs) using on-board electric powerplants remains challenging. This paper experimentally examined the feasibility of using orographic 'slope' lift in an urban built environment to increase the endurance of MAV platforms. The glide polar of a soaring MAV was measured in a wind-tunnel and validated through flight-testing, then compared with the velocity field immediately upwind of a representative urban building. The velocity field was mapped using a 1:100 scale model of the building in a wind-tunnel with a scaled atmospheric boundary layer. The vertical velocity component was found to be in the order of 15% to 50% of the mean wind velocity at building height. These results were compared with data measured on the full-size building and found to agree well. As the sink rate of the MAV was less than the available vertical velocity component for a wide flight speed range, it was concluded that it is possible to 'soar' immediately upwind of urban buildings to increase endurance. However, considerable control challenges are thought to exist since the full-scale data demonstrated that the flow exhibited high turbulence intensities.