Equipped with a tiny pair of goggles, Obi the parrotlet is braving haze and lasers to help researchers learn what happens when a bird flaps its wings.
Researchers have long known how planes fly and use wind tunnels to continually test and update new designs. But this doesn't work to study the flapping of bird wings, and most suggestions of how this works are theoretical. But researchers at Stanford University recently figured out a way to put those theories to the test, reports Liat Clark for Wired. The study was published in the journal Bioinspiration & Biomimetics.
Lead author Eric Gutierrez trained Obi to fly through a cloud of micron-sized aerosol particles illuminated by a sheet of lasers. This allowed the researchers to visualize the air currents created by Obi’s wings.
“When the bird flaps its wings it moves these particles,” Chin tells Clark. “In this plane, we can visualize how tiny particles are moving and then calculate the velocity field. Based on those velocity fields we should be able to theoretically calculate the lift force the bird is generating in flight.”
But there was one complication. Flying through lasers is not easy on the eyes, so Gutierrez and mechanical engineer David Lentink designed a pair of special goggles for Obi. They cut protective plastic from a pair of human safety goggles and fitted it into 3D printed sockets secured by veterinary tape. The goggles also had reflective markers on the sides to help calculate the parrotlet’s velocity, according to the press release.
Previous models assumed that birds and flying animals worked on principles similar to, though not exactly like, airplane wings. With aircraft, air flows over and under the wing creating lift, and producing a spinning mass of air in its wake called vortices, which break up hundreds of meters behind it. Researchers believed vortices produced by birds behaved in a similar way. Obi’s flight showed that isn’t the case.
Instead, according to Clark, the vortices produced by the bird break up within two to three wing beats, and much closer to the bird and much more violently. They compared their measurements to the three prevailing models of how much lift birds produce with each wing beat. What they found is that none of the models accurately predicted the lift generated by the bird.
“If you look at the classic picture of animal flight we always think of these animals generating nice smooth vortices, but they actually turn out to be much more complex,” Lentick says in a video explaining the research. “It’s a starting point for us to now really figure out how these animals fly.”
That’s also important for the advancement of flying drones and robots, which will move much more like birds than fixed-wing aircraft. “Many people look at the results in the animal flight literature for understanding how robotic wings could be designed better,” Lentink says in the press release. “Now, we’ve shown that the equations that people have used are not as reliable as the community hoped they were. We need new studies, new methods to really inform this design process much more reliably.”