Aircraft typically use a vertical tail to keep the craft from rolling or yawing. Birds, on the other hand, maneuver their wings and tail feathers to counter unwanted motions. Researchers found that the list of necessary adjustments is quite small: just 4 for the tail and 2 for the wings. Implementing those 6 controllable degrees of freedom on their bird-inspired PigeonBot II allowed the biorobot to fly steadily, even in turbulent conditions, without a rudder. Adapting such flight control to the less flexible surfaces of a typical aircraft will take time and creativity, but the savings in mass and drag could be worth it. (Image credit: E. Chang/Lentink Lab; research credit: E. Chang et al.; via Physics Today)
Tag: bird flight
Hovering Hawk
Birds have a level of control in flight that would make any engineer jealous. This 2021 Audubon Photography Award winning video by Bill Bryant shows off the skills of a red-tailed hawk. On this occasion, the hawk is using strong winds coming off the Rocky Mountains to hover in place. Notice how active his wings and tail are in adjusting to the changes in the wind while his head is perfectly still. With his head still, the hawk can scan the ground for mice and other prey. It’s absolutely incredible to see how effortlessly the hawk is accounting for unsteadiness in the wind here! (Video and image credit: B. Bryant; via Audubon)
Morphing Wings Using Real Feathers
Although humanity has long been inspired by bird flight, most of our flying machines are nothing like birds. Engineers have struggled to recreate the ease with which birds are able to morph their wings’ characteristics as they change from one shape to another. Now researchers have built a biohybrid robot, PigeonBot, that uses actual pigeon feathers as part of its morphing design.
Many species of birds, including pigeons, have Velcro-like hooks in the microstructure of their feathers. These hooks help the flight feathers stick to one another and create a continuous wing surface that air cannot easily slip through, even as the wing drastically changes shape. By using actual feathers, PigeonBot shares this advantage.
PigeonBot also has a somewhat minimalist design in its articulation, using only a wrist and finger joint in each wing to control shape. The feathers are connected through an elastic ligament, which — along with their microstructure — allows them to smoothly change shape under aerodynamic loads. The end result is a remarkably capable and agile biorobot researchers can use to better understand how birds control their flight. (Image and research credit: L. Matloff et al. and E. Chang et al.; via NPR and Gizmodo)
The Best of FYFD 2019
2019 was an even busier year than last year! I spent nearly two whole months traveling for business, gave 13 invited talks and workshops, and produced three FYFD videos. I also published more than 250 blog posts and migrated all 2400+ of them to a new site. And, according to you, here are the top 10 FYFD posts of the year:
- The perfect conditions make birdsong visible
- Pigeons are impressive fliers
- The water anole’s clever method of breathing underwater
- 100 years ago, Boston was flooded with molasses
- The BZ reaction is some of nature’s most beautiful chemistry
- The labyrinthine dance of ferrofluid
- 360-degree splashes
- The extraordinary flight of dandelion seeds
- Dye shows what happens beneath a wave
- Bees do the wave to frighten off predators
Nature makes a strong showing in this year’s top posts with five biophysics topics. FYFD videos also had a good year: both my Boston Molasses Flood video and dandelion flight video made the top 10!
If you’d like to see more great posts like these, please remember that FYFD is primarily supported by readers like you. You can help support the site by becoming a patron, making a one-time donation, or buying some merch. Happy New Year!
(Image credits: birdsong – K. Swoboda; pigeon take-off – BBC Earth; water anole – L. Swierk; Boston molasses flood – Boston Public Library; BZ reaction – Beauty of Science; ferrofluid – M. Zahn and C. Lorenz; splashes – Macro Room; dandelion – N. Sharp; dyed wave – S. Morris; bees – Beekeeping International)
Underwater Snakes, Gusty Flying, and Microswimmers
If you like your fluid dynamics with a healthy dose of biology, this video’s for you! Learn about the hydrodynamics of snake strikes, how birds fly in gusty crosswinds, and the mathematical underpinnings of a microswimmer’s journey. This is the final video in our FYFD/JFM collaboration featuring research from the 2017 APS DFD meeting. If you missed any of the previous videos, you can see them all here. Which one is your favorite? Would you like to see the series continue? Let me know in the comments or on Twitter! (Image and video credit: N. Sharp and T. Crawford)
Soaring Pelicans
Earlier this summer, I looked up on a bright, sunny day and saw a quartet of black and white figures soaring overhead. Initially, I thought it might be a formation of kites or unmanned aerial vehicles (UAVs) because I saw no flapping as the group wheeled about. With the help of the Cornell Lab of Ornithology’s awesome Merlin app, I was able to identify the soarers as American white pelicans – not a species I’d expected to find flying along the Front Range of the Rocky Mountains! (Turns out, they breed on lakes around here.)
The reason I saw so little flapping is that the birds were riding thermals. As the sun heats the ground, air near the surface warms up and begins to rise due to its buoyancy. Pelicans interested in flying between breeding and foraging grounds will start testing the thermals early in the day, as soon as they begin to form. As the heating continues, the intensity of thermals strengthens and they extend higher into the atmosphere. This is where the birds can really excel at using atmospheric energy for their flight. Pelicans will circle within a thermal until they reach roughly the middle of its height. Then they will glide, gradually losing altitude until they reach another thermal where they can climb without expending their own energy. With a 2.7 meter wingspan and a relatively low drag coefficient, the pelicans can glide and soar remarkably well. Researchers have even suggested using them as a sort of biological UAV for studying atmospheric dynamics! (Image credits: D. Henise, M. Stratmoen; research credit: H. Shannon et al., pdfs – 1, 2)
Flying in Cramped Quarters
A new study has found that budgerigars (also commonly known as parakeets or budgies) fly at only two distinct speeds. The researchers flew the birds in a tapered tunnel to see how they navigated in response to widening or narrowing paths. What they found, regardless of the flight direction in the tunnel, is that the birds fly at approximately 9.5 m/s in areas wider than 2.5 times their wingspan and drop suddenly to a speed about half that when in narrower areas. The higher speed falls within the bird’s most energy-efficient range, suggesting that the birds may prefer flying at this condition. Insects like bumblebees also change speeds when entering cluttered environments, but the insects do so gradually, not suddenly like the budgerigars. The reason for this difference is not yet known, but it could relate to how the animals sense their environment or to differences in their flight efficiency when varying speed. (Image credit: J. Bendon; research credit: I. Schiffner and M. Srinivasan; submitted by Marc A.; h/t to Irmgard B.)
Hawk in Flight
For a little more than century, mankind has taken flight in fixed-wing aircraft. But other species have flown for much longer using flapping techniques, the details of which humans are still unraveling. To really appreciate flapping flight, it helps to have high-speed video, like this beautiful footage of a goshawk attacking a water balloon. The motion of the hawk’s wings is far more complex than the simple up and down flapping we imitate as children. On the downstroke, the wings and tail stretch to their fullest, providing as large an area as possible for lift. During steady flight, the bird flaps while almost horizontal for minimal drag, but as it approaches its target, it rears back, allowing the downstroke to both lift and slow the bird. In the upstroke, the bird needs to avoid generating negative lift by pushing air upward. To do this, it pulls its wings in and simultaneously rotates them back and up. Its tail feathers are also pulled in but to a lesser extent. Leaving them partially spread probably maintains some positive lift and provides stability. At the end of the upstroke, the hawk’s wings are ready to stretch again, and so the cycle continues. (Video credit: Earth Unplugged/BBC; h/t to io9)
Falcon vs. Raven
Earth Unplugged has posted some great high-speed footage of a peregrine falcon and a raven in flight. Notice how both birds draw their wings inward and back on the upstroke. By doing so, they decrease their drag and thus the energy necessary for flapping. On the downstroke, they extend their wings fully and increase their angle of attack, creating not only lift but thrust. The falcon boasts an incredibly streamlined shape, not only along its body but also along its wings. In contrast, the raven has broader wings with large primary feathers that fan out near the tips. Splaying these large feathers out decreases the strength of the bird’s wingtip vortices, thereby reducing downwash and increasing lift, much the same way winglets do on planes. That extra lift and control the big primaries provide is important for the raven’s acrobatic skill. (Video credit: Earth Unplugged; via io9)
Diving Peregrines
Few animals can compete with a peregrine falcon for pure speed. There is evidence that, when diving, the falcon can reach speeds upward of 200 mph (320 kph). That the birds can achieve this by pulling their wings back into a low-drag profile is impressive, but the control they exert to do so is even more astounding. The placement and acuity of a falcon’s eyes would require tilting its head roughly 40 degrees if diving straight down on its prey. Such asymmetry increases their drag by more than 50% and creates a torque that yaws the bird. Instead, as seen in the video above, the falcon keeps its head straight and flies in a spiral-like dive, allowing it to maintain sight contact with its target and maximizing its speed despite the extended dive. (Video credit: BBC; research credit: V. A. Tucker)
