Is it a bird? Is it a plane? No, it’s PigeonBot!

Researchers in the Netherlands have developed a robot that flies like a bird, as aviation giants like Airbus look to nature to design more fuel-efficient airplanes.

Planes rely on vertical tailfins to stabilize their flight, but birds achieve stability without them. Flying without a vertical tail is far more energy-efficient, and while the aviation industry has worked to replicate this efficiency, success has so far remained elusive.

A new study may change that. David Lentink, a professor of biomimetics at the University of Groningen in the Netherlands, and his research team have developed a robot that successfully mimics bird flight.

“We wanted to understand why birds can fly stable without a vertical tail. This vertical tail is really important in aircraft, almost every design has it and removing it causes great instabilities that aerospace engineers find difficult to solve,” Lentink said.

In previous research, Lentink discovered that birds continuously adjust the shape of their wings and tails. The new study demonstrated that a robot, called PigeonBot II and equipped with real pigeon feathers, can replicate these “remarkable” movements.

‘Sophisticated fliers’

Researchers selected pigeons raised for meat as models for their robot prototype because feathers could be easily sourced for the study without impacting the wild population.

Pigeons are also “highly maneuverable and powerful flyers,” according to Lentink. This is reflected in the relatively low hunting success rate of their main predator, the peregrine falcon, which is less than 30%.

“Despite their bad name as non-interesting birds, or some people even call them flying rats, pigeons are incredibly sophisticated flyers that we can learn a lot from,” Lentink told Cybernews.

Unlike drones or aircraft, pigeons can maneuver and maintain stability even in turbulence – all without a vertical tail.

“The reflexes in birds that inspired the new control loop of our robot that enables it to fly without a vertical tail have also been studied most extensively in pigeons by neuroscientists,” Lentink said, adding that the team was able to rely on a lot of data to improve its science.

Bird-inspired planes

An algorithm controls the robot bird’s nine servo motors, which move the feathers to continuously adjust the shape of its wings and tail.

According to the University of Groningen, the algorithm mimics reflexes believed to help birds stabilize themselves – a concept proposed in 1929 by German scientist Franz Groebbels, who suggested that birds fly like “automatic airplanes.”

Researchers said they managed to confirm the concept by testing PigeonBot II in a wind tunnel and then flying it autonomously in open air. Apart from demonstrating how birds manage to fly without vertical tailfins, the study could also open a way to design more fuel-efficient airplanes.

Aerospace company Airbus has previously described biomimicry as a “fresh approach to aircraft innovation” and unveiled a concept for a “bird of prey” airplane in 2019.

This theoretical design, “inspired by the efficient mechanics of a bird,” featured wing and tail structures resembling those of an eagle or falcon, along with individually controlled feathers for active flight control.

“The European Airbus group created a concept, visualizing how such a plane should look. Our study provides the knowledge to realize their ideas,” Lentink said.

Lentink and his team’s design could also reduce a plane’s radar signature, potentially improving fighter jet operations. The scientists continue to study live birds and are developing a new robot that could outperform the latest prototype.

The study's results were published in the peer-reviewed journal Science Robotics.

It adds to a wealth of research focusing on robotic solutions inspired by living creatures, such as a robot snake designed for rescue operations by scientists at ETH Zurich or a jellyfish-like robotic gripper created by Harvard engineers.