Talons and Turbulence Auburn University Raptor Center
Supports Engineering Aviation Research

A CONCERTED EFFORT IN SUPPORT OF AVIATION RESEARCH

Vrishank Raghav was enjoying his first experience at Jordan-Hare Stadium on a fall afternoon in 2018 when Nova — also known as War Eagle VII — took his traditional pregame flight to the delight of more than 80,000 fans.

Raghav, who had just joined the Department of Aerospace Engineering as an associate professor, was intrigued by Nova’s performance and how controlled it seemed while soaring through the air. After the game, he researched where Nova spent time when not rallying the Auburn Tigers to victory and learned of the Auburn University Raptor Center.

The Auburn University Raptor Center, a division of the College of Veterinary Medicine, is a rehabilitation and education facility providing critical education and conservation efforts for raptors.

Raghav and the Raptor Center soon formed a partnership. In 2018, he received funds from Auburn University’s Intramural Grants Program (IGP) to study a red-tailed hawk named Petey. The goal was to learn how birds can quickly adapt to adverse aerodynamic environments due to changing weather conditions — where traditional aircraft and unmanned aerial vehicles seem to struggle. 

“You look around on a bad weather day, and most flights are grounded, and there are delays all around the country,” Raghav said. “But birds are still flying, and it appears that the bad weather doesn’t affect them. The big question for us researchers and engineers is how they have adapted to achieve smooth flight in adverse conditions.”   

Calvin Johnson, Dean of the College of Veterinary Medicine, agreed that studying the unique adaptations that raptors make to changing air conditions could be quite interesting.

 “We’ve noticed that raptors are instinctively able to respond to turbulence and variable wind currents that would normally ground most manmade aircraft. This is another example of the value of studying nature to provide clues for enhanced engineering.“

Raghav and his team set up a row of upward-facing fans to generate wind gusts for Petey to fly through to track how he adjusts his flight pattern to compensate for the perturbation. However, before clearing Petey for takeoff, he sent a flapping-wing drone through the upward-facing fans, which crashed as soon as it encountered them.

Petey sailed through the wind gusts without seemingly any movement at all. Or did he?

Raghav set up four high-speed cameras near the flight zone, tracking multiple points on Petey’s body for each test flight. When looking at it with the naked eye, it appears that the perturbations didn’t impact the bird, but when the cameras were slowed down, Raghav learned that Petey was performing several adjustments. One hypothesis is that Petey reduces his wing pitch angle to reduce the force the gust will induce on it. 

“It’s all instinctive for the bird,” Raghav said.   

A mathematical model was created based on Petey’s flights and information tracked from the cameras to learn when the wind speed (or low-gust ratio) is lower than Petey’s flight speed — the model can determine his flight path. However, the model fails to accurately predict the flight path when the wind speed or disturbance exceeds the bird’s flight speed.

“This leads us to believe the bird is doing something beyond just pitching its wings down to mitigate the effects of the adverse environment,” Raghav said. “There’s still plenty to learn, but we have taken the first step.”

Raghav’s research was cited on Physics World’s website, which is one of the most recognized physics websites worldwide. This work was also recently accepted for publication in the peer-reviewed journal, Bioinspiration & Biomimetics. 

Another challenge Raghav’s team faced was not related to math or science. It was based on Petey’s mood.   

Johnson said the bird’s adaptations to unpredictable situations is a complex process. 

First, the bird’s health takes precedence. The college’s veterinarian participates in the process, and Raptor Center trainers help make the course, and the project, more conducive to success.   

“Our veterinarians carefully evaluate the research space and advise on ways to optimize it to make the bird feel secure. Also, the veterinarian will evaluate the testing process for noises or distracting movements that could impact the bird’s response,” Johnson said.

Raghav did all he could to ensure successful flights each day, including having proper protocols covered by the Institutional Animal Care and Use Committee (IACUC) at Auburn University and the U.S. Fish and Wildlife Service. Yet, if Petey didn’t want to fly, there was nothing to be done.

Trainers would use food as motivation for Petey to fly approximately six times each day. Sometimes, even with food, Petey decided he didn’t want to move.

“We had about six good runs each day because after you are done with feeding, the day is over because he’s not going to take off,” Raghav said. “As expected, he didn’t fly to our will. It depended entirely on the day and other factors inherent to the bird.”

Raghav said the Raptor Center was a significant partner in getting the first steps of this research off the ground. 

“The collaboration with the Raptor Center was great,” he said. “We all accommodated each other’s schedules, but when everyone was together, everything went well — as long as Petey was happy to fly.” 

Johnson said the research collaboration between the Raptor Center and the College of Engineering was very compatible with the Center’s mission.