Unstable Wing Design Is Essential

“How do birds fly?” is a very old question that remains basically unanswered. We aren’t talking about simple fixed-wing flight, which uses the old physics model that a rapidly moving fluid exerts minimum pressure at a right angle to the direction of motion. We use that model for airplanes, but birds have another feature called unstable wing design. The unanswered question about bird flight is how they can be so agile. Drones have a problem with this issue because, with their fixed-wing structure, they can’t make quick direction changes.

Christina Harvey of the University of California, Davis, and Daniel Inman of the University of Michigan have examined the flight dynamics of 22 bird species. They concluded that unstable wing design is the key to what birds can do. For example, seagulls can change the shape of their wings by adjusting their wrist and elbow joints. Changing their wing shape allows them to handle wind gusts easily. Aerospace engineers have not been able to duplicate that part of flight dynamics, but most bird species manage it quite well.

Drones working in an urban environment must handle sudden wind gusts and rapid direction changes, but with a fixed-wing design, that is almost impossible. The study’s authors point out that future business-level drones or personal aircraft must be able to implement unstable wing design. However, engineers have yet to find a way to do that. Researchers funded by the National Science Foundation (NSF) and the National Academy of Science (NAS) are working to understand how the complex design of bird wings allows unstable flight.

It is fascinating that the earliest birds of flight seen in the fossil record had a wing design that allowed unstable flight. We even find fossil birds that resemble our modern hummingbirds, which have very unstable wing design. We continue to see examples of intelligence in the design of living things. Much of what you and I enjoy, from velcro to rockets and modern aircraft, had their start when thinking people saw the design God built into life and copied it to benefit all of us.

— John N. Clayton © 2022

References: The U.S. National Science Foundation (NSF) and the National Academy of Sciences (NAS), in their December 2022 reports,