Micro Air Vehicle Systems
A Micro air vehicle (MAV or UAV) is envisaged to be a small-scale autonomous flying vehicle (say with no dimension larger than 15 cm) intended for reconnaissance over land, in buildings and tunnels, and in other confined spaces. While some progress has been made in this field, no vehicle has been able to achieve long-loiter time (over 60 minutes) or efficient hovering flight at weights less than 100 grams with a payload of about 20 grams. Several factors contributed to this poor performance including lack of understanding of aerodynamic, structural, and propulsion physics at the micro-scale. Also, none of these configurations can carry avionics packages that would permit robust out-of-sight navigation in complex urban environments. In contrast, nature has evolved thousands of miniature flying machines (insects and small birds) that perform far more difficult missions. While details underlying the operational success of biological fliers remain an ongoing research endeavor, a general picture is emerging that indicates that the overwhelming superiority of biological fliers over existing MAVs stems from two fundamental factors: ability to generate lift more efficiently than existing technologies, and ability to store and release energy efficiently.
Two efficient hovering micro air vehicle (MAV) configurations, rotary-wings and flapping-wings, can be used to generate sufficient thrust to sustain weight. The rotary-wing approach has proven successful in the high Reynolds number regime (>106), where inertial forces dominate flow characteristics. However, in the low Reynolds number regime that scales MAV flight physics, it is not clear which solution is more efficient. Hence, both hovering concepts are being examined. To develop such vehicles, challenges include: low Reynolds number flow regime (~104), low altitude environment (gust and obstacles), size and weight constraints, compact power generation and storage, micro actuators, strong aeroelastic couplings, and stringent navigational and guidance requirements. The objective of this paper is to cover the state-of-art on design concepts, aeromechanics, and multi-functional morphing wings, and identify key barriers and needs for future research.