This book is about flapping wing aerodynamics. It presents various aspects of the aerodynamics of natural flyers, such as birds, bats, and insects, and of human – engineered micro air vehicles (MAVs) for both rigid and flexible wing structures. This edition focuses on the many recent developments since the publication of our earlier book titled Aerodynamics of Low Reynolds Number Flyers. We have substan­tially expanded Chapter 1 to offer a general and comprehensive introduction to low Reynolds number flight vehicles for both biological flyers and human-made MAVs. In particular, we summarize the scaling laws to relate the aerodynamics and various flight characteristics to a flyer’s size, weight, and speed on the basis of simple geo­metric and dynamics analyses. In Chapter 2, closely following the previous edition, we discuss the aerodynamics of fixed rigid wings. It considers both two – and three­dimensional airfoils with typically low aspect ratio wings. Both Chapters 3 and 4 have been significantly expanded and updated. Chapter 3 examines the interplay between flapping kinematics and key dimensionless parameters such as the Reynolds num­ber, Strouhal number, and reduced frequency for rigid wings. The various unsteady lift enhancement mechanisms are addressed, including leading-edge vortex, rapid pitch-up and rotational circulation, wake capture, tip vortices, and clap-and-fling. It also discusses both detailed time-dependent and simplified quasi-steady analyses along with experimental observations. Efforts have been made to contrast fixed and flapping wing aerodynamics in the context of geometry and tip, as well as of stall margins. Chapter 3 presents individual and varied objectives in regard to maximizing lift, mitigating drag, and minimizing power associated with flapping wings.

Chapter 4 addresses the role of structural flexibility of low Reynolds number wing aerodynamics. Due to the interplay between structural and fluid dynamics, additional dimensionless parameters appear, resulting in multiple time and length scales. For fixed wings, structural flexibility can further enhance stall margin and flight stability; for flapping wings, passive control can complement and possibly replace active pitching to make the flight more robust and more power efficient. Chapter 4 also discusses the airfoil shape, the time-dependent fluid and structural dynamics, and the spanwise versus chordwise flexibility of a wing. The scaling laws linking lift and power with fluid and structural parameters are of fundamental interest and offer insight into low Reynolds number flight sciences while providing guidelines for

vehicle development. Finally, recent advances and future perspectives are summa­rized and presented in Chapter 5.

As in the previous edition, we have benefited from collaborations and interac­tions with many colleagues. In addition to those colleagues named in the previous edition, we would like to acknowledge the generous intellectual and financial sup­port provided by the U. S. Air Force Research Laboratory, in particular the Flight Vehicle Directorate (now Aerospace Systems Directorate) and the Office of Scien­tific Research.

We feel sure that significant advancements in both scientific and engineering endeavors of flapping wing aerodynamics will continue to be achieved, and we enthusiastically await these new breakthroughs and developments.

Wei Shyy, Hikaru Aono, Chang-kwon Kang, and Hao Liu

This is an ideal book for graduate students and researchers interested in the aerodynamics, structural dynamics, and flight dynamics of small birds, bats, and insects, as well as of micro air vehicles (MAVs), which present some of the richest problems intersecting science and engineer­ing. The agility and spectacular flight performance of natural flyers – made possible by their flexible, deformable wing structures as well as outstanding wing, tail, and body coordination – are particularly sig­nificant. To design and build MAVs with performance comparable to natural flyers, it is essential to understand natural flyers’ combined flex­ible structural dynamics and aerodynamics. The primary focus of this book is to address recent developments in flapping wing aerodynam­ics. This book extends the work presented in Aerodynamics of Low Reynolds Number Flyers (Shyy et al. 2008).

Dr. Wei Shyy is the Provost of the Hong Kong University of Science and Technology and former Clarence L. “Kelly” Johnson Collegiate Professor and Department Chair of Aerospace Engineering at the Uni­versity of Michigan. Shyy is the author or co-author of four books and numerous journal and conference articles dealing with a broad range of topics related to aerial and space flight vehicles. He is Editor of the Cambridge Aerospace Series with Vigor Yang (Georgia Tech) and Co­Editor-in-Chief of the nine-volume Encyclopedia of Aerospace Engi­neering (2010). He received the 2003 AIAA Pendray Aerospace Lit­erature Award and the ASME 2005 Heat Transfer Memorial Award. He has led multi-university centers under the sponsorship of NASA, the U. S. Air Force Research Laboratory, and industry. His professional views have been quoted in various news media, including the New York Times and USA Today.

Dr. Hikaru Aono is a Research Scientist at the Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency. He has made contributions to biological aerodynamics and related fluid – structure interaction issues.

Dr. Chang-kwon Kang is a Postdoctoral Research Fellow at the Univer­sity of Michigan. His expertise includes analytical and computational modeling of the performance of flapping wings for micro air vehicles, aeroelastic dynamics of flapping wings, and other complex systems.

Dr. Hao Liu is a Professor of Biomechanical Engineering at Chiba University in Japan. He is well known for his contributions to biologi­cal, flapping-flight research, including numerous publications on insect aerodynamics simulations and physical realization of MAVs.