Near-Terrain Flight Operations and Performance of Unmanned Aerial Vehicles

This study aims to test and develop safe aircraft operational methods for flights in high-altitude mountainous regions. In addition to the close proximity to complex terrain and subvertical topography, flight operations in such areas are affected by poor visibility, dynamic weather conditions, and unpredictable wind conditions. This poses a risk of controlled flight into terrain (CFIT), which is the main problem tackled in this study. A series of experimental campaigns were conducted to investigate the flying environment in the mountainous regions of Nepal using an unmanned aerial vehicle (UAV). Flight path planning in the near-terrain environment was performed by cross-referencing the flight path with the digital elevation model (DEM) to ensure minimum proximity to the terrain. A numerical model of the UAV was developed with the help of the aerodynamic parameters of the aircraft deduced from the flight data of autonomous missions. The performance of the UAV was also assessed from numerical simulations and laboratory experiments. Wind and other environmental parameters and flight performance and dynamics data were collected using onboard sensors. An in situ flight path generation technique was also tested to account for the uncertainties arising from the flying environment. The experiments tested methods to perform flight performance analysis, autonomous flight planning over the DEM terrain, and flight path generation to ensure safe manual and autonomous flights that can help mitigate CFIT accidents in the mountainous flying environment.