On Fixed-Wing Micro-Air Vehicles with Hovering Capabilities

Abstract

Abstract : Fixed-wing micro air vehicles (MAV) are very attractive for outdoor surveillance missions since they generally offer better payload and endurance capabilities than rotorcraft or flapping-wing vehicles of equal size. They are generally less challenging to control than helicopter in outdoor environment. However, high wing loading associated with stringent dimension constraints requires high cruise speeds for fixed-wing MAVs and it has been difficult so far to achieve good performances at low-speed flight using fixed-wing configurations. The present paper investigates the possibility to improve the aerodynamic performance of classical fixed-wing MAV concepts so that high cruise speed is maintained for covertness and stable hover flight is achieved to allow building intrusion and indoor surveillance. Monoplane wing plan forms are compared with biplane concepts using low-speed wind tunnel measurements and numerical calculations including viscous effects. Wind-tunnel measurements including the influence of counter-rotating propellers indicate that a biplane-twin propeller MAV configuration can drastically increase low-speed and high-speed aerodynamic performances over the classical monoplane fixed-wing concept. Control in hover flight can highly benefit from the effect of counter-rotating propellers as demonstrated by flight tests. After describing the flight dynamics model including the prop wash effect over control surfaces, a control strategy is presented to achieve autonomous transition between forward flight and hover flight. Both hardware and software architectures necessary to perform real flight are presented.