Bird Wearing Tiny Aviator Goggles Flies Through Lasers for Science

Obi the parrotlet readies for takeoff. Wearing his mini protective goggles, he waits patiently for a signal: a decisive finger point to a target perch. The finger moves in a flash and so does Obi, right to the directed spot where he is rewarded with a seed.

Such is a typical day for the good-natured bird, who is helping researchers to design the next generation of animal-inspired aircraft.

The goggles are needed for eye protection because Obi has been flying through a sheet of laser light in a specially designed wind tunnel where the air is infused with tiny particles that are primed to scatter and track vortices produced by his wingtip flaps. A somewhat similar phenomenon happens when an airplane takes off and produces contrails.

Stanford mechanical engineer David Lentink likened the particle "fog" to dry ice used at a concert.

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"The airflow patterns generated by the bird's wings are traced by the fog, which is visible and recorded in the laser sheet," Lentink told Seeker. "In this way, we were able to measure the flow velocity in the wake of the bird."

Lentink's graduate student Eric Gutierrez made Obi's aviator goggles using lenses from laser safety goggles, 3D-printed sockets and veterinary tape. Out of all the birds recruited for the study, Obi was most comfortable wearing the goggles. The parrotlet also liked the seed rewards so much that he would "fly for food," even though he received other treats before each flight.

Obi's efforts, outlined in the journal Bioinspiration and Biomimetics, shows three widely accepted models used to interpret the airflow generated by flying animals are inaccurate.

"Based on the current literature and textbooks, I expected these vortices to be very smooth, like donut-shaped vortices blown by someone smoking a cigar," said. "The classic picture is that flying animals create lots of beautiful, well-organized vortex loops that peacefully flow downstream. Seeing them break up violently within 2–3 wingbeats was entirely unexpected."

Lentink, lead author Gutierrez and their team are the first to document this dramatic breakdown that birds like Obi create when they flap their wings to achieve lift for flight. The researchers attribute their success to a super-fast laser and to the high-speed cameras that recorded airflow at 1,000 frames per second.

The scientists are particularly interested in the dynamics of the bird's wingtip vortices, since these are key to lift. The tornado-shaped air results from the difference between higher air pressure over the wing and lower pressure below.

Since the accepted models explaining these vortices proved to be wrong, Gutierrez and his colleagues hope to contribute to a new model that could be used to predict the lift generated by flying animals. Bio-inspired robots are a specialty of Lentink and his students, who developed the first flapping robot that can take off and land vertically like an insect, as well as a swift-like robot with wings that deform as it swoops and glides.

Lentink pointed out that flying animals are more efficient and maneuverable than even the slickest and most modern human-designed aircraft. The bar-tailed godwit, for example, weighs mere ounces, yet can fly nonstop from Alaska to New Zealand with ease.

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"Birds can take off like a helicopter and fly fast and far like an airplane," Lentink said.

He continued that "birds are great at flying in turbulent flow... found around trees and buildings, where aerial robots stall and crash. Bats and insects are also very accomplished flyers in their own right, so understanding how animals fly is a huge inspiration for inventing better flying robots."

Geoff Spedding of the USC's Department of Aerospace and Mechanical Engineering also gains inspiration from flying animals, and has studied bats and other critter flyers.

Spedding told Seeker that he's "delighted that more sophisticated measurements are being applied to animal flight," thanks to the studies on Obi and other animals in Lentink's lab.

"It is interesting to note that the key technology here is in the bird-safety-goggles," Spedding added. "These are ultimately what allow the motions close to the bird to be recorded. As a community, we always search for improved and more realistic descriptions of nature, and ways in which real-life can be simplified into a useful and practical model. This work will be relevant and helpful in this respect."

Gutierrez and co-authors Dan Quinn and Diana Chin said the little goggles could be useful for other scientists doing research where bird eyes would need to be protected. So the authors also published 3D drawings of their goggle design.

Photo: Obi the parrotlet wearing protective goggles. Credit: Eric Gutierrez, Lentink Lab at Stanford University