Flying lizards are truly gliders, but that doesn’t mean they’re unsophisticated. Newly reported observations of the species in the wild show that flying lizards don’t simply hold their forelimbs out a la Superman. Instead, they reach back with their forelimbs, pressing their arms into the underside of the thin patagium that serves as their flight surface while rotating their hands to grasp the upper side of the patagium. This forms a composite wing with a thicker leading edge and seems to be how the lizards control their glide. Close observation of their flight shows that, while holding their patagium, the lizards actively arch their backs to camber their composite wing. This can increase their maximum lift coefficient, allowing them to glide longer distances. (Image and research credit: J. Dehling, source)
Tag: flight
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)
Visualizing F-18 Flow
Flow visualization techniques are helpful outside of wind and water tunnels, too. The photo above comes from the F-18 High Alpha Research Vehicle (HARV) program in which techniques like smoke and dye visualization were used in-flight to visualize airflow around an F-18 at large angles of attack. During flight a glycol-based liquid dye was released from tiny holes along the plane’s forebody, creating the pattern seen here later on the ground. This particular test corresponded to about 26 degrees angle of attack. (Photo credit: NASA Dryden)
The Silence of Owls
Owls are nearly silent hunters, able to swoop down on their prey without the rush of air over their wings giving away their approach, thanks to several key features of their feathers. The trailing edge of their feathers–or any lifting body, like an airplane wing–are a particular source of acoustic noise due to the interaction of turbulence near the surface with the edge. Since owls are especially good at eliminating self-produced noise in a frequency range that overlaps human hearing, investigators want to learn what works for owls and apply to it aircraft. A recent theoretical analysis uses a simplified model of the feather as a porous, elastic plate. The researchers found that the combination of porosity with the elasticity of the trailing edge significantly reduced noise relative to a rigid edge. (Photo credit: N. Jewell; research credit: J. Jaworski and N. Peake)
Wind Tunneling Testing for BASE Jumpers
While we usually think of wind tunnel testing airplane models, the truth is that wind tunnels today test a much wider array of subjects. From oil rigs and skyscrapers to athletes and police sirens, if you can imagine it, it’s probably been stuck in a wind tunnel. This video shows some wind tunnel testing of a tracking suit used for BASE jumping. The primary focus seems to be on lift and drag at angle of attack–which can be used to determine glide ratios for the pilot–but there is also some study of localized turbulence generation, as evidenced by the use of smoke generators and the streamers attached to the suit’s arms and legs. (submitted by Jason C)
Dove in Flight
This spectacular high-speed video shows a dove in flight. Note how its wings flex through its stroke and the way the wings rotate over the course of the downstroke and reversal. There is incredible beauty and complexity in this motion. The change in wing shape and angle of attack is what allows the bird to maximize the lift it generates. Note also how the outer feathers flare during the downstroke. This promotes turbulence in the air moving near the wing, which prevents separated flow that would cause the dove to stall. (See also: how owls stay silent. Video credit: W. Hoebink and X. van der Sar, Vliegkunstenaars project)
Pterosaur Aerodynamics
The pterosaur was an enormous prehistoric reptile that flew with wings of living membrane stretched over a single long bone, unlike any of today’s flying creatures. New research using carbon fiber wing analogues and wind tunnel testing suggests that the pterosaur would have been a slow, soaring flyer well adapted to using thermals for lift. Once on a thermal, the pterosaur could coast, perhaps for hours at a time, with little to no flapping necessary. See the research paper or the Scientific American article for more. #
Flying Snake Video
A follow-up on the flying snakes. This video shows researchers filming the actual snakes gliding and performing maneuvers. See also the Scientific American article on their work. #
Bell’s Powered Kite
Inventor Alexander Graham Bell is best known for the telephone but also made many contributions to early aeronautics. This man-carrying kite, the Cygnet III, was a powered kite with a “wing” made of 3,393 tetrahedral cells; it managed enough lift to fly on March 1, 1912. National Geographic is featuring photos from the early days of flight courtesy of the Smithsonian National Air and Space Museum. They’re well worth checking out. #
The Silence of Owls
Owls are among the most silent hunters in nature, thanks to their feathers. The leading edge of the wing, shown in the bottom part of the photo, has a serrated comb-like edge, which breaks flow over the wing into small vortices, which are quieter than larger ones. The fringe-like trailing edge breaks the flow up further and helps absorb the sound produced by the turbulence. The fluffy feathers along the owl’s body can also help muffle noise. Researchers are investigating ways to use these techniques to quiet aircraft. # (via jshoer)
