A pigeon-inspired robot has solved the mystery of how birds fly without the vertical tail fins that human-designed airplanes rely on. Its officials say the prototype could eventually lead to passenger jets with less drag, reducing fuel consumption.
Tail fins, also known as vertical stabilizers, allow airplanes to turn from side to side and help prevent them from unintentionally changing direction. Some military aircraft, such as the Northrop B-2 Spirit, are designed without tail fins to make them less visible to radar. Instead, they use flaps that create extra drag on one side when needed, but this is an inefficient solution.
Birds do not have vertical fins and also do not appear to produce asymmetric drag on purpose. David Lentink At the University of Groningen in the Netherlands and colleagues designed the PigeonBot II (pictured below) to investigate how birds maintain themselves without stabilizers.
PigeonBot II, a robot designed to imitate the flying techniques of birds
Eric Chang
The previous model of the group, Built in 2020it flew by flapping its wings and shape-shifting like a bird, but still had a traditional airplane tail. The final design, which includes 52 real pigeon feathers, has been updated to include a bird-like tail, and test flights have been successful.
Lentink says the secret to PigeonBot II’s success lies in its programmed reflexive tail movements, designed to mimic those known in birds. If you grab a pigeon and tilt it from side to side or back and forth, its tail automatically reacts and moves in complex ways, as if stabilizing the animal in flight. This has long been thought to be the key to the birds’ stability, but now it has been demonstrated through robotic replication.
The researchers programmed a computer to control the Pigeonbot II’s nine servo motors to steer the craft using propellers on each wing, but also to automatically twist and fan the tail to create the stability that would come from a vertical fin. Lentink says these reflexive movements are so complex that a human cannot directly fly the Pigeonbot II. Instead, the operator issues high-level commands to an autopilot, telling it to turn left or right, and an on-board computer determines the appropriate control signals.
After many unsuccessful tests, when the control systems were refined, he was finally able to take off, navigate and land safely.
“Now we know the recipe for flying without a vertical tail. Vertical tails, even for a passenger plane, are just a nuisance. Weight costs, which means fuel consumption, but also drag – it’s just unnecessary drag,” says Lentink. “If you just copy our solution (for a large-scale aircraft) it will work, sure. (But) if you want to go back to something that’s a little easier to manufacture, there has to be an extra layer of research.”
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