Like flying snakes floating through the air.
Flying snakes can glide up to 24 meters without getting out of control as they wave their bodies in flight as if they were floating in the air. This appears to be a more specialized strategy to stabilize their flight than an evolutionary remnant of general snake behavior, according to a new paper in Nature Physics. The work could eventually lead to a new, improved control template for dynamic flight robots.
Virginia Tech co-author Jake Socha has been studying these fascinating creatures for about 20 years. The special gliding ability of these snakes – there are five known species, including Chrysopelea pelias and Chrysopelea paradisi – was first discovered by a British scientist at the end of the 19th century who one day observed a gliding flight through his tea garden in Southeast Asia. However, scientists had paid little attention to determining the exact physics and biomechanics until Socha published a paper in 2002 that outlined its preliminary findings on basic aerodynamics.
Socha found that the snake pressed its comb scales against the tree trunk and used the rough surface to maneuver up to a branch. Then it dangles its body at the end of the branch and contracts like a feather to throw itself in the air. The initial angle of inclination when hanging the snake determines the trajectory. To ensure maximum gliding distance, the snake sucks its stomach and smoothes its body. She curves inward like a frisbee to create buoyancy and waves her body in an S-shaped motion that serves to increase the air pressure beneath it.
Enlarge /. A flying snake starts from a branch and glides to the ground.
YouTube / nature
Three years later, Socha reported on the most important variables: the glide angle and horizontal speed as well as the body mass of a snake, the body length and the amplitude and frequency of its body waves when gliding. In particular, he found that size (body size and length) plays a role – the smaller the snake, the further it can slide horizontally. While the ripple frequency was not particularly important for predicting flight behavior, the amplitude of the ripple played a key role in stabilizing the snake while gliding.
By 2010, Socha's laboratory had test snakes leaping from artificial branches attached to a high tower in the laboratory, and held the movement as they slid to the ground with four cameras. This enabled him to create 3D models of the body positions during the flight and to analyze the forces acting on the bodies and the basic sliding dynamics. He found that the snakes could slide up to 24 meters from the start branch.
The next step was to take a 3D printed model of a flying snake in flattened glide mode and examine the patterns of fluid flow by submerging the model in a tank of running water. Among other things, he worked with the aeronautical engineer at George Washington University, Lorena Barba, to carry out computer simulations of the airflow patterns of the 3D model. They found that sucking seems to play an important role: when the snake flattens its body, it makes itself more aerodynamic. Air vortices form above it, which "suck up" like a low-pressure area in the eye of a tornado – an effect that is particularly well suited to the snake's angle of attack (usually between 20 and 40 degrees).
And that brings us to Socha's recent research on flying snakes, which uses motion detection to examine the exact kinematics of air ripple and its effects on gliding performance in more detail. He and his co-authors were particularly interested in determining whether the wavy behavior was a specific flight control strategy for the animals or just a "behavioral remnant of the snake movement" because, as the authors note, "all snakes are capable of lateral waviness". an evolutionary old motor pattern created by waves of muscle contraction spreading throughout the body. "
Enlarge /. We welcome our snake robot overlords.
YouTube / nature
For these experiments, Socha et al. used live flying snakes (in this case Chrysopelea paradisi) and placed reflective infrared markers along the back of the body. They recorded these marker positions as snakes glided through a large hall at Virginia Tech's Moss Arts Center. The trials were conducted in a four-story black box theater called Cube, which was modified to keep snakes safe.
Socha's team hung black plastic sheets on the sides and the back wall and pulled curtains over the sidewalk railing. They also covered the floor with soft foam pads so that the snakes were not injured when they landed. They placed an artificial tree, covered with false leaves and tendrils, in the middle of the gliding arena, with a branch of a real oak serving as a suitable starter. Then they let the snakes jump and slide to their heart's content for nine days, and used a 23-camera motion detection system to record the infrared markings.
Based on this data, the team developed an "anatomically accurate" mathematical 3D model of the snake flight and carried out simulations of gliders with and without ripple, which took inertia and aerodynamic effects into account. They found that while simulated gliders could reach a certain distance without ripple, such gliders ultimately failed due to the destabilizing effects of pitching and rolling. In contrast, simulated gliders with waves stabilized the rotational movement and allowed much longer gliding. "This work shows that air waves in snakes have a different function than known applications of wave formation in other animals," the authors concluded.
There are reservations, of course. "The interpretation of why animals have developed certain shapes and behaviors, particularly in terms of stability, must be treated with caution," wrote Jim Underwood of the University of London in an accompanying paper. "Just showing that a particular snake-gliding strategy is unstable is not enough to show that it cannot be a good one: if you freeze an owl in a perfectly lifelike gliding pose, the bird still can't be thrown around to achieve a stable glide. "
However, the work should prove useful for the improved design of robots inspired by the movements of flying snakes. "The newly discovered kinematic components of air ripple … form the theoretical basis for the design of a bio-inspired flying snake robot that glides with air ripple as a control template," the authors wrote, adding that this "should significantly simplify the control of a flying snake-like robot . "
Bonus: The same theoretical model is used in further research by Socha et al. Benefit from flying snakes.
DOI: Nature Physics, 2020.10.1038 / s41567-020-0935-4 (About DOIs).
Listing image from YouTube / Nature Video