A twist of the tail in turning maneuvers of bird-inspired drones

A banked turn is a common flight maneuver observed in birds and aircraft. To initiate the turn, whereas traditional aircraft rely on the wing ailerons, most birds use a variety of asymmetric wing-morphing control techniques to roll their bodies and thus redirect the lift vector to the direction of the turn. Nevertheless, when searching for prey, soaring raptors execute steady banked turns without exhibiting observable wing movements apart from the tail twisting around the body axis. Although tail twisting can compensate for adverse yaw, functioning similarly to the vertical tail in aircraft, how raptors use only tail twisting to perform banked turns is still not well understood. Here, we developed and used a raptor-inspired feathered drone to find that the proximity of the tail to the wings causes asymmetric wing-induced flows over the twisted tail and thus lift asymmetry, resulting in both roll and yaw moments sufficient to coordinate banked turns. Moreover, twisting the tail induces a nose-up pitch moment that increases the angle of attack of the wings, thereby generating more lift to compensate for losses caused by the banking motion. Flight experiments confirm the effectiveness of tail twist to control not only low-speed steady banked turns but also high-speed sharp turns by means of coordinated tail twist and pitch with asymmetric wing shape morphing. These findings contribute to the understanding of avian flight behaviors that are difficult to study in controlled laboratory settings and provide effective control strategies for agile drones with morphing aerial surfaces.
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Reference: Hoang-Vu Phan, Dario Floreano, A twist of the tail in turning maneuvers of bird-inspired drones. Sci. Robot. 9, eado3890(2024). DOI:10.1126/scirobotics.ado3890

[@josephseale254]

I was thinking hard along those lines, sometime around 1978. I lacked the software tools to get into the details shown here, but I did do a fairly decent approximation-analysis of flapping efficiency and the induced drag generated by the flapping variation in lift. A key, both for sinusoidal time-varying symmetric lift distributions (flapping) and antisymmetric lift distributions (wing shape-shifting for roll and yaw) is an extension of the familiar analysis of the elliptic lift distribution: an ellipse is the lowest-order Lissajous figure, and the analysis extends to parametric equations where x = sin(theta) and y = cos(n*theta) or sin(n*theta) and those are your Fourier-like components of lift vs span. You get nice analytic induced wake-flow solutions for some very interesting cases. Between the math and hours of watching gulls soar over the Atlantic-wind-facing cliffs of Norway, I analyzed and just intuited much of the flight control dynamics presented here. Sadly, I never found the time and occasion (no support from an institution) to publish these results. Anyway, kudos to the people now doing this work!

[@jamesgoudy9580]

da Vinci observed and drew these behaviors, I think he would have loved to be part of this project

[@myperspective5091]

Did you experiment with tail warping? Turned the tips up and down creating a “U” shape.
I know this effect is more pronounced in the smaller birds creating a more “V” shape in the down position while in flight. This seems to be more of a thing in shore birds like Terns.

[@rignall05]

very cool, interested how you worked out the resultant attitude changes from the various control inputs available. much more complex than just aileron/elevator/rudder

[@NoobyWeeby]

finally find the perfect reference for animation!!! THANK YOU!!! I racked my brain out wondering why and how bird is turn only using tail from all the references

[@mattbrody3565]

The thing is, they kinda don't just use their tail. They use their wings more. Birds have a twisted shape to their wings which allows them to channel airflow under the wings out towards the wingtips, then redirect the flow behind them to produce little jets of air. Those jets give a little thrust, and they can tune the thrust by tuning the twist of their wings. Al Bowers did some good work on this with the Prandtl-D project for NASA. His presentations are here on YT.

[@NoobyWeeby]

@@mattbrody3565 thats sick man! thanks a lot!!

[@BobBlarneystone]

Interesting. Hmm, there's an old Popular Science or Mechanics article that describes a rubber-band powered model plane that used turkey feathers for the wings and empennage. The lift of the feathered wings was far better than conventional materials of that time.

[@marc_frank]

birds are awesome :)

[@Sherlock245]

No God is that the logic 😊

[@marc_frank]

@Sherlock245 is that a question? 😅

[@tuloxe]

Nice hope you get your drone as agile as a real bird

[@johanliebert1027]

awww I wanted it to fly by flapping its wings but it has a propeller.

[@Sherlock245]

Evolution could not have design such a specimen 😮

[@markdavis7397]

🤦‍♂

[@thomascharlton8545]

Therefore?

[@markdavis7397]

@@thomascharlton8545 A random youtube troll doesn't understand something, therefore that is positive proof that it is magic. Got it. By that measure, my college thermodynamics class was magic, lol.