Performance analysis of hovering UAVs for wind monitoring applications

Abstract

The aim of this research was to analyse the performance of hovering multirotor Unmanned Aerial Vehicles (UAVs) for wind monitoring applications, whilst operating in the inherently highly stochastic nature of open field atmospheric conditions. The two custom built UAVs, a quadcopter and a hexacopter used for the purposes of this research, were each equipped with sensor suites specifically developed for this study. The sensor suites measured and recorded UAV platform and flight parametric data, as well as environmental data, including wind speed and direction by means of an onboard ultrasonic wind sensor. Experimental data were collected during open field hovering flights in different ambient conditions at wind speeds of up to 12 m/s. Data collection flights were conducted at different altitudes above ground and in close proximity to a Light Detection and Ranging (LiDAR) wind measurement unit. A wind data comparison between the UAV-based measurements and the ground-based LiDAR unit wind measurements indicated that there is a strong correlation in measurements of both wind speed and wind direction across all the altitudes at which UAV operations were conducted. The study also focused on the effect of increasing wind speed on the power consumption of hovering UAVs, which in turn effects the flight endurance of the systems under study. The impact of the wind conditions, and to a lesser extent the atmospheric air density at the time of UAV operations, were analysed. It was found that, for both tested UAVs, the power demand to maintain stable hovering flight decreased for higher wind speeds due to a higher air mass flow rate passing through the UAV rotors as a result of the higher incident wind speeds. For the hexacopter UAV, following a drop in power demand as the wind speed increased, the power demand stabilized at its minimum value at an incident wind speed of 8.0 m/s, beyond which power demand started to increase with an increase in wind speed. When operating in undisturbed hovering conditions, UAV power demand was observed to increase with a decrease in atmospheric air density, yet the overall effect of air density on the power demand of both test UAVs was found to be marginal.