8:50 a.m., April 16, 2009----Two University of Delaware researchers are co-authors on a paper published this week in Science that sheds new light on how animals fly. Assistant Professor Xinyan Deng and graduate student Bo Cheng, both in the Department of Mechanical Engineering, collaborated with Tyson Hedrick, a biology professor at the University of North Carolina, on the work, which has implications for both the natural and engineered worlds.

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Published by the American Association for the Advancement of Science (AAAS), Science is considered the world's leading journal of original scientific research, global news, and commentary.

For Deng, the recently published work provides the foundation for the next generation of flying robots -- tiny flapping devices with a variety of potential military and civilian applications ranging from surveillance and security to search and disaster rescue.

Since she joined the UD faculty in 2004, Deng's research has focused on biologically inspired robotic systems. Her lab, inhabited by robotic insects and boxfish robots, attracts students of all ages who are fascinated with the convergence of nature and machine.

One of the research projects from her 2006 National Science Foundation Faculty Early Career Development Award focused on development of a mathematical model for the dynamics of saccade flight in fruit flies. Saccade flight comprises a series of straight flight paths punctuated by rapid 90-degree turns. From that study, Deng found that flapping fliers benefit from substantial damping of angular velocity through a passive mechanism now known as flapping counter-torque, or FCT.

Basically, Deng explains, during initiation of turning, the fruit fly actively accelerates via asymmetric wing motion between the inside and outside wings. During deceleration, however, passive aerodynamic damping, instead of active asymmetric wing motion, accounts for most of the turn deceleration. This is because, in a flying turn, the outside wing experiences enhanced velocity during the down-stroke while the inside wing moves faster during the up-stroke. The resulting asymmetry produces the torque that slows down body rotation and straightens out the ensuing flight path.

Deng and Hedrick met at the Fourth International Symposium on Adaptive Motion of Animals and Machines (AMAM) in June 2008. Hedrick had learned of Deng's earlier work on the passive damping of the fruit fly, and he proposed a collaborative scale study. The results of the work were published in Science and quickly picked up by science Web sites around the world.

The researchers had observed that flying animals of all sizes, from tiny fruit flies to large birds, all seemed to benefit from FCT and demonstrate a similar ability to turn in flight and then straighten out to fly on a new course. Yaw turn flight data obtained from video footage of seven species -- the fruit fly, stalk-eyed fly, bluebottle fly, hawkmoth, hummingbird, fruit bat and cockatoo -- captured using high-speed video cameras was compared to the motion predicted by the mathematical model.

The researchers discovered that animals with similar morphology exhibit similar turning dynamics in terms of wingbeats regardless of their body size. They also found that the faster the wings beat, the better the animal's maneuverability and stability. These two properties are usually antagonistic in engineering systems.

So far, the researchers have looked at just one type of turn, a low-speed yaw turn, which was selected for the study because it has been widely recorded in freely flying animals. Deng is interested in extending the investigation to pitch, roll, and other mechanisms of aerodynamics.

And while she is excited at the prospect of applying the new knowledge to the further development of flapping robots, Deng is also gratified that the work has provided an answer to a longstanding scientific debate -- that is, whether the turning motion used by insects and birds is governed by inertia or frictional damping. “This work has shown that it's neither,” she says.

“Being published in Science increases the impact of our work,” she says, “and it also has confirmed for me that as engineers, we are equipped with the analytical tools to explain the physics in nature, and to do so we need to expose ourselves to the biological literature and build a broad knowledge base.”

“Conferences like the AMAM are extremely valuable for people working in interdisciplinary areas,” she adds, “because these meetings provide us with an opportunity not only to showcase our own work but also to meet potential collaborators whose expertise complements our own.”

Deng views the path between biology and engineering as a two-way corridor: “Biological systems provide the inspiration for robotic systems,” she says, “and in turn robotic systems offer a new way of investigating biological systems to gain further insight into how nature works.”

Engineers have long looked to trees and shells for inspiration on how to build stronger and lighter composite materials, to the human skeleton for effective orthotic devices, and to the sun for more efficient generation of energy.

Thanks to the work of Deng and Hedrick, engineers are one step closer to building a better flying robot.

As one news story about the research announced: “Birds do it, and now we know how.”

Article by Diane Kukich
Photo by Doug Baker