A barely visible fog hangs in the air in a California laboratory, illuminated by a laser. And through it flies a parrot, outfitted with a pair of tiny, red-tinted goggles to protect its eyes.
As the bird flaps its way through the water particles, its wings generate disruptive waves, tracing patterns that help scientists understand how animals fly.
In a new study, a team of scientists measured and analyzed the particle trails that were produced by the goggle-wearing parrot’s test flights, and showed that previous computer models of wing movement aren’t as accurate as they once thought. This new perspective on flight dynamics could inform future wing designs in autonomous flying robots, according to the study authors.
When animals fly, they create an invisible “footprint” in the air, similar to the wake that a swimmer leaves behind in water. Computer models can interpret these air disturbances to calculate the forces that are required to keep a flyer aloft and propel it forward.
A team of scientists had recently developed a new system that tracked the airflow generated by flight at an unprecedented level of detail. They wanted to compare their improved observations to several commonly used computer models that use wake measurements to estimate flying animals’ lift, to see if their predictions would be on track.
Flight of the parrotlet
For the study, the researchers enlisted the help of a Pacific parrotlet — a type of small parrot — named Obi. Obi was trained to fly between two perches that are positioned about 3 feet (1 meter) apart, through a very fine mist of water droplets, which are illuminated by a laser sheet. The water particles that seeded the air were exceptionally small, “only 1 micron in diameter,” said study author David Lentink, an assistant professor of mechanical engineering at Stanford University in California. (In comparison, the average strand of human hair is about 100 microns thick.)
Obi’s eyes were protected from the laser’s light with custom goggles: a 3D-printed frame that is fitted with lenses cut from human safety glasses — the same type of glasses worn by Lentink and his team.
When the laser flashed on and off — at a rate of 1,000 times per second — the water droplets scattered the laser’s light, and high-speed cameras shooting 1,000 frames per second captured the trails of disturbed particles as Obi fluttered from perch to perch.