image: A black-footed albatross soars over the Pacific Ocean. Engineers are working to mimic the amazing ability of albatrosses to harness the wind for the next generation of autonomous drones.
Credit: Michael Miller
How does one of the biggest birds in the world spend so much time in the air?
Albatrosses have 11-foot wingspans that carry them across oceans. But it’s how they use these wings that makes them world-class flyers, according to a University of Cincinnati aerospace engineering professor.
UC Assistant Professor Sameh Eisa and his research partners hope to harness their amazing abilities for the next generation of drones.
He received a $700,000 grant from the Defense Advanced Research Projects Agency, part of the U.S. Department of Defense, to develop innovations in unmanned aerial vehicles using animal-inspired engineering called biomimicry.
The project is based on his recent breakthroughs in developing model-free, real-time flight controls to harness the natural abilities of the albatross.
Albatrosses use a principle called dynamic soaring to master the wind for both distance and time in the air. Eisa and his team developed a first-of-its-kind approach to dynamic soaring they call “a natural extremum-seeking system” after the way the birds (and their drone-mimic) identify the minimum and maximum pitch, yaw and roll and air speeds needed for optimal efficiency.
The birds tack into the wind like a sailboat to gain lift and altitude, finding faster air currents as they climb. When they eventually lose the forward momentum needed to stay in the air, they turn, harnessing the kinetic energy of gravity and wind that propels them forward. At the bottom of this glide path, sometimes mere inches off the water, they turn back into the wind and do it again — all without wasting a single wingbeat.
“They use it skillfully,” Eisa said. “GPS trackers show these birds can fly hundreds of miles a week. By the time they die, they’ve flown 20 times the distance between the Earth and the moon.”
But Eisa said there’s more to the bird’s energy-efficient flight than its enormous wings.
“Albatrosses literally have a nose for wind,” Eisa said.
The birds are able to gauge wind speed and direction through their sensitive nostrils, allowing them to make fine flight adjustments to maximize each leg of upward and downward flight path.
Eisa’s analyses show that energy from the wind balances the energy traditionally lost in flight. Meanwhile, the total energy of each dynamic soaring cycle is near constant. An applied mathematician, Eisa put the birds’ abilities to the test in simulations and found that computers could do no better at charting the optimal course in real time.
“They are solving an optimization problem that is unbelievably complicated,” Eisa said.
For a drone to fly like an albatross and achieve autonomous soaring, it will have to measure both changing wind speeds and direction to calculate the best angle of attack and rolling action to adjust flight controls in real time, he said.
“If we can get closer to how the albatross does it, we can be more efficient,” he said.
Eisa and his students are collaborating with researchers in industry, weather experts and the Massachusetts Institute of Technology on the project called Albatross.
Traditionally, wind is the enemy of drones, Eisa said. But their project is trying to turn this obstacle into an advantage.
Using Eisa’s recent characterization for dynamic soaring as a natural extremum-seeking system, new flight control designs will be developed to mimic dynamic soaring in real time. Researchers will test, validate and implement these designs and methods in experiments by UC’s DARPA industrial team members to demonstrate how much energy dynamic soaring saves compared to normal flight.
That’s one reason biomimicry has been such an important tool for aerospace engineers, he said.
“Nature has been optimizing flight for millions of years of evolution,” Eisa said. “So to take this gift from nature and make it available to humanity is engineering at its best.”