Birds are turning what we know about lift and drag on its head, with new research showing they use drag to take off and lift to land.
So much for the conventional wisdom that states drag slows us down and lift sends us off, defying gravity.
Researchers at Standford University measured five parrotlets flying around in an instrumented flight chamber and found the birds used their body weight to help them takeoff and used lift to slow down. The research was published in Nature Communications.
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Parrotlets measured in a special flight chamber
In order to come to their conclusions, Chin and David Lentink, assistant professor of mechanical engineering at Stanford, had to measure both the horizontal and vertical forces as they were happening. To do that they placed sensor panels around the chamber covering the birds' flight paths. Each panel had three sensors. Sensors were also affixed to two perches which were used for takeoff and landing.
They also added windows to the flight chamber so they could film wing movements. The researchers relied on five high-speed cameras that could shoot 1,000 frames per second, Stanford University explained in a news release. Chin and Lentink combined the measured motion from the images with the measurements from the sensors to determine the lift and drag during takeoff and landing.
“Something like this has never existed before,” said Lentink in the news release. “The measuring technology itself is an engineering achievement.”
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It may seem impossible to get birds to fly the way the researchers needed them to, but using parrotlets made it easier. They are easily trained and were more than happy to take the 80-centimeter flight from one perch to the other all in the name of a millet seed.
The researchers found the birds tilted their wings at an incline when taking off so that to orient the lift forward to accelerate and the drag upward so that half their body weight could be supported. “Many other flapping animals probably make similar use of lift and drag during takeoff and landing,” said Chin.
While these findings do challenge conventional wisdom, Lentink said its too soon to rebuild our view on airborne technologies. He does say we should revisit how bird flight and aerodynamics are taught. “None of the aerospace literature came up with using drag to support weight,” said Lentink. “That standard drawing has to be revised.”