Development and performance comparison of optimized electric fixed-wing VTOL UAV configurations

Fixed-wing VTOL UAV are unmanned aerial vehicles capable of both hover and fast forward flight. Lift during take-off and landing is generated by rotors, ducted fans or jet engines. After takeoff, they transition into forward flight mode in which a wing produces the lift. The many existing types of VTOL aircraft show the wide range of possibilities to combine vertical flight capabilities with efficient forward flight. The question arises which of these configurations is best suited for a certain mission. As a starting point for this paper, two widely used electric fixed-wing VTOL configurations are analyzed for their key design features and their consequences. Based on these findings, a self-developed configuration is presented and the underlying design considerations are explained. To allow a quantitative comparison of aircraft properties and performance among the three aircraft configurations, a design and mission analysis tool was implemented. It calculates aerodynamic aircraft performance, selects off-the-shelf powertrain and system components, dimensions the aircraft structure and evaluates the mission performance within given aircraft requirements. For each investigated configuration, the design tool is adjusted for the characteristic features. For the comparison of the configurations, a test case for a fixed-wing VTOL UAV with 5 kg take-off weight, 0.9 kg payload and hover time of 60 s is chosen. Each configuration is optimized for that mission to ensure a fair comparison. Within the optimization, aircraft geometry and, consequently, the aircraft powertrains and subsystems are changed until each configuration's cruise endurance is maximized. For the exemplary mission, the wing-borne cruise endurance differs by up to 34% among the investigated configurations. The self-developed configuration thereby yields the best endurance.