On fixed-wing micro-air vehicles with hovering capabilities

The present paper investigates the possibility to improve the aerodynamic performance of a fixed-wing micro air vehicle (MAV) concept so as to simultaneously allow high cruise speed for covertness and hovering flight for stable image transmission. Two fixed-wing MAV configurations were tested and compared: a tilt-wing concept powered by two non-coaxial counter-rotating propellers and a tilt-body concept based on a coaxial rotor. The different configurations were separately analyzed based on wind tunnel experiments. The tilt-wing concept, although superior to the tilt-rotor concept, does not provide a significant benefit over an equivalent tilt-body MAV configuration. Finally, two tilt-body coaxial prototypes were designed and successfully flight tested to demonstrate the capability of fixed-wing MAV configurations to lift off, sustain hover flight and perform transition between forward and hover flight. Special attention was paid to the coaxial tail-sitter concept for which the propellers slipstream guarantees aerodynamic efficiency over the whole flight envelope. Side-by-side comparison of a mini- and a micro-sized coaxial tail-sitter model was carried out and discussed.