As I look out of my office window and watch the heart-stopping acrobatics of feeding swifts, it's not difficult to see why so many aircraft designers find inspiration in nature - from birds to bats to insects. Now it's the turn of the swift. Hoping to demonstrate the endurance and performance benefits of a combined flapping and gliding approach to Micro Air Vehicle (MAV) design, researchers have developed an experimental flyer capable of combining both unsteady and steady aerodynamics.

MAVs are unmanned aerial vehicles generally designed for remote observation of hazardous environments or aerial photography. For the most part they're either fixed wing or rotary aircraft, but occasionally you might come across a flapper. Fixed wing craft have the advantage of high endurance but generally suffer from relatively low maneuverability and rotary systems are more stable craft and much more maneuverable, but time aloft suffers as a result. A combination of flying modes would appear to offer the best of both worlds.

Researchers from the Bionik-Innovations-Centrum (B-I-C) at the University of Applied Science in Bremen and the Ocean Ecosystems Department at the University of Groningen in the Netherlands have developed a flapping wing ornithopter MAV to look into the feasibility of implementing different modes of flight and aerodynamic mechanisms to improve overall efficiency.

The combination of flight modes has been made possible by using a rigid wing design and applying some engineering know-how based on the kinematics of the wings of swifts and swiftlets.

The model was mounted to a two-axes force balance and its combination flight modes observed in wind tunnel tests. In glide mode the MAV achieved a lift-to-drag ratio of 8:6 and managed to maintain a large effective angle of attack during flapping flight, leading to the development of lift-enhancing leading edge vortices. A blade-element analysis showed twice the predicted force for slow speed flapping.

The study concludes that combining flight modes can enhance energy efficiency and has the potential to offer mission versatility, although the experimental models developed for this project are not yet ready to be used for mission flights.

The paper entitled Using bird flight modes to enhance overall flapping wing micro air vehicle performance by William Thielicke, Eize J. Stamhuis and Antonia B. Kesel was presented to the 2011 Meeting of the Society of Experimental Biology at the Scottish Exhibition and Conference Centre in Glasgow recently.

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