For the past 25 years, Professor of Engineering and Biology Sharon Swartz and Professor of Engineering Kenneth Breuer ’82 P’14 P’16 have been fascinated by animal flight. The two professors have collaborated on research involving the flight of bats using Brown’s Animal Flight and Aeromechanics Wind Tunnel, a testing facility that allows researchers to study wild-caught birds and bats.
The “three-dimensional pattern of (wing) movement” has been a key point of study in understanding how bats are able to fly, Swartz said. But to understand this movement, Swartz and Breuer needed an advanced way to investigate the animals.
After Swartz and Breuer received a grant from the National Science Foundation in 2017, Breuer and a colleague at the Massachusetts Institute of Technology designed an updated wind tunnel that was ultimately installed two years later. The tunnel is housed in the Prince Engineering Laboratory in Barus and Holley.
In his research, Breuer has used various methods to understand bat flight, ranging from studying bats in the field to using robots that “mimic aspects of flapping flight” in a wind tunnel, he said. In 2017, Breuer even helped design a bat-inspired robot for search and rescue missions, The Herald previously reported.
The wind tunnel is a “fantastic resource” for this research, Breuer said. According to Swartz, it can “act like a treadmill for a flying animal,” allowing researchers to record dozens to hundreds of wing beats.
“If you don’t have a wind tunnel, the animal flies at exactly the speed that it wants to fly,” Swartz said. By contrast, “in a wind tunnel, the animal will fly at the speed that you ask it to fly, because the wind speed is where you set it.”
When handling live animals, the researchers use the utmost care.
“We have to follow very, very strict guidelines,” Breuer said, noting that researchers must ensure that the animals “are not in any pain or duress during the tests.”
When it comes to understanding animal flight, using robots is often simpler than live bats. PhD student Ronan Gissler GS has been studying “stability and flapping flight” and conducting research in the Swartz and Breuer labs using these robots, he told The Herald.
These robots are “not quite as complex” as real animals and can’t move their wings in as many ways, Gissler said. This increased simplicity allows him to “systematically vary the parameters of the robot” to obtain clearer results, he explained.
PhD student Ronan Gissler GS, pictured top right, has been studying “stability and flapping flight” and conducting research in the Swartz and Breuer labs using these robots, he told The Herald.
In their work together, Swartz and Breuer advanced their understanding of the role of membranes in bats’ wings. These membranes are analogous to muscles in the face, according to Breuer. The experiment included using botox to inhibit the use of those muscles in order to better understand their function.
“Eventually we were able to show that those muscles in the skin of the wing actually turn on and off with every wing beat,” Swartz said. “We think that they changed the stiffness of the skin, and that would lead to an influence on wing shape.”
Following this experiment, Swartz has continued to research bats, but now spends more time in the field and lab instead of the wind tunnel. She is currently focused on understanding the purpose of sensing hairs on a bat’s body. These hairs keep track of how the muscle moves — stretching and contracting — and communicates that information to the spinal cord, according to Swartz.
“How do (bats) perceive the environment? How does the bat know whether the muscle is relaxed or contracted?” Swartz asked.
“I think the little hairs help the bat do that,” she added.
Breuer will continue to use the wind tunnel in his research, but is shifting his focus to the study of bird flight. In this research, he is using both live birds and robots — like in his work with bats — to focus on the energetic flow between birds in group flight.
“We measure how much energy it takes for them to fly and what kinds of interactions they have when they fly together,” Breuer explained.
In fact, Breuer and Gissler have already made some discoveries.
“We proved that birds are actually consuming less energy, (and) metabolic cost is going down by being in that group,” Gissler said.
But due to recent changes in government regulations and research funding, both Swartz and Breuer are still uncertain what grants they will receive. The two rely on these grants to continue their studies with live animals.
“It’s a mess,” Swartz said.
Despite the funding uncertainty, Breuer still finds that “watching the animals fly is always a joy.”
“These are amazing creatures,” Breuer said. “They’re amazing machines, so it’s just beautiful to watch … You just develop an appreciation for watching nature and the beauty of evolution.”
