The Stanford researchers' PigeonBot provides insight into the mechanics of bird wings

Katie Ramirez
January 18, 2020

And they found that the structures were present in most species of birds other than owls, which allowed them to fly more silently. It turns out that the way birds fly is not very well understood, since the relationship between the dynamic shape of the wing and the positions of the individual feathers is very complex.

Just like Velcro used in fasternings, it is even possible to hear the distinctive "ripping" sound as feathers are pulled apart again and folded back in the bird's body, scientists discovered.

Lentick led a team to try to pinpoint some of the unique ways that bird wings work. Passenger planes, of course, do not need to dive or roll on short notice, but drones and other small craft can find the ability extremely useful. In Science Robotics, Eric Chang et al. measured the kinematics of wing flexion and extension in cadavers of common pigeons. For their study, they invented a robot called PigeonBot that has a pair of "biohybrid morphing wings". The findings could also advance scientists' understanding of feather evolution, he said.

Lentink says that several doctoral students realized that simply by moving the birds' "wrist" and "finger", the feathers would fall into place.

The first PhD student, Amanda Stowers, analyzed the skeletal movement and determined that we only needed to emulate the movement of the wrist and fingers on our robot to activate the 20 primary and 20 secondary flight feathers. "And that's really cool". Roboticists have tried to replicate feathery fliers for nearly two decades, but these efforts have been hindered by use of rigid feather-like panels and a lack of understanding of the skeletal and muscular mechanics behind birds' highly morphable wings.

"Whenever the skeleton moves, the feathers are redistributed passively through compliance of the elastic connective tissue at the feather base".

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The researchers used a wind tunnel to see how the feather-and-rubber band design worked under turbulent conditions.

"Since the Wright brothers, aerospace engineers have tried to create wings that can change shape, or morph, as well as birds can morph their wings", said Lentink. "It requires an enormous force to separate them". Separating the locked feathers makes an audible sound for most birds.

The new robot is described Thursday in Science Robotics.

It's worth noting that the PigeonBot doesn't incorporate something you might associate with birds' wings - flapping.

The researchers say the findings could inspire new kinds of morphing aircraft.

He sees it as a sign that drone designs of the future may move away from fixed-wing or rotary-wing technologies. The alignment of these feathers is what determines the shape of the wing.

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