Published: Thu, December 08, 2016
Science | By Carlton Santiago

Cameras capture breakdown of tip vortices during bird flight


Researchers at Stanford University chose to use a trained parrot wearing goggles flying through a sheet of lasers to figure out more accurately than ever before the flight dynamics of birds, providing them with inspiration and the means to develop better equations and computer models to build flying robots and drones. Lentink's lab already has some experience designing such crafts after researchers made a flapping-winged robot that can fly like an insect. Video of a be-goggled Obi showed that even a slow-flying parrotlet's wing movements are more complex than scientists had anticipated. If researchers can improve these models, not only would they better understand the nature of flight, they might improve the design of micro-drones that make use of flapping-wing technology.

The team was testing three widely-used models of animal flight, and they found that none of the models were particularly accurate. It also has implications for how flying next-generation robots and drones will be designed.

Graduate student Eric Gutierrez was responsible for making Obi's shades, which he fashioned out of 3-D printed sockets and cut down human safety lenses. They trained Obi to wear the goggles, which have some reflective markers on the side so they could monitor the bird's velocity. To protect the parrotlet, named Obi, from serious eye damage, one of the researchers used a 3D printer to build some bird-sized safety goggles.

The laser light could harm the vision of the bird if it does not protection goggles. When Obi flies through the laser sheet and the aerosol particles scientists were able to gain the clearest picture to date of the wake left by a flying bird. In previous studies of bird flight, researchers could only measure the wake a small distance behind the bird, or would have to rely on a single snapshot or time-averaged measurements.

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'We measured the three-dimensional dynamics of the tip vortex in great detail, and what we found was surprising, ' explained senior researcher Dr David Lentink. We've see this pattern in airliners but never in birds, so this suggests that some of our ideas about bird flight might lift off.

They then tested three different models, plugging in the measurements of the air patterns from Obi's flights, and comparing the models' lift estimates to their own. They confirmed their calculations by measuring the actual lift Obi produced using a custom-made sensor. The airflow around a bird's wing is a much tougher thing to observe, but being the kind of industrious researchers we're all thankful for, the engineers at Stanford came up with a plan. The differences between the three models, plus the variety of animals involved in earlier studies, including other bird species, bats and insects, makes comparison within the literature extremely challenging. The new model could help drive innovations in aerospace and robotics.

'We need new studies, new methods to really inform this design process much more reliably'.

This work is funded by the KACST Center of Excellence for Aeronautics and Astronautics at Stanford, the Office of Naval Research (ONR) Multidisciplinary University Research Initiative (MURI), a National Defense Science and Engineering Graduate Fellowship and a Stanford Graduate Fellowship. Lentink is also a member of Stanford Bio-X.

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