Super agile drone? Give it feathers

A bird-inspired drone points to a lesson well-known to technologists: Nature knows best.
Written by Greg Nichols, Contributing Writer

Time and again, biological-inspired design proves the secret to unlocking the potential of manmade creations. That fact is reinforced in a next-gen drone inspired by the wing and tail shape of birds of prey, as well as flight behavior.

The resulting drone, modeled after the northern goshawk, flies with heretofore unseen agility for a drone thanks to careful coordination of its flight surfaces. It was developed by scientists of the Laboratory of Intelligent Systems of EPFL led by Dario Floreano.

"Goshawks move their wings and tails in tandem to carry out the desired motion, whether it is rapid changes of direction when hunting in forests, fast flight when chasing prey in the open terrain, or when efficiently gliding to save energy," says Enrico Ajanic, the first author and PhD student in Floreano's lab. Floreano adds: "our design extracts principles of avian agile flight to create a drone that can approximate the flight performance of raptors, but also tests the biological hypothesis that a morphing tail plays an important role in achieving faster turns, decelerations, and even slow flight."

The bird-inspired design is a further evolution of a drone the team created in 2016, this one adding the extensible tail and wings. Floreano has also done work on other bio-inspired drones, including a tug drone inspired by wasps, which we covered in 2018.

"It was fairly complicated to design and build these mechanisms, but we were able to improve the wing so that it behaves more like that of a goshawk," says Ajanic. "Now that the drone includes a feathered tail that morphs in synergy with the wing, it delivers unparalleled agility." 

Much like an airplane can extend its flaps, birds change the shape of their wings and tail to increase or reduce air resistance and change lift coefficients. The bird-inspired drone is capable of flying much slower than traditional fixed wing drones, but it can also optimize its wing shape to fly much faster. 

Interestingly, the use of a propeller instead of a bird's flapping motion actually makes the drone more efficient as a flying unit than a bird, whose wings have to pull double duty. The result is a drone that's much faster than most fixed-wing drones but provides agility that puts it in the class of quadcopters, which are incredibly nimble but not nearly as fast as fixed-wing aircraft. Quadcopters also suffer from reduced flight time due to energy consumption. 

"The drone we just developed is somewhere in the middle. It can fly for a long time yet is almost as agile as quadrotors," says Floreano. This combination of features is especially useful for flying in forests or in cities between buildings, as it can be necessary during rescue operation. The project is part of the Rescue Robotics Grand Challenge of NCCR Robotics.

One drawback of the new drone is that it takes an incredible amount of skill to operate successfully. As any novice fixed-wing drone operator can testify, it's hard work keeping a conventional fixed-wing aircraft in flight, particularly if conditions are optimal. This drone adds several layers of complexity that make manual flight impractical for most pilots.

However, the additional of AI and semi-autonomy to the flight controls should drastically lower the bar, making future drones that use this design practical for a wide range of pilots. Possible uses include search and rescue, rogue drone pursuit, and law enforcement, to name a few. The team's research appears in Science Robotics.

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