Every evening, swarms of bats leave their nests in caves and barns and descend on insects cruising through the night sky. Their effortless ability to navigate through these complex and crowded environments is the inspiration for a multidisciplinary project called AIRFOILS, which will focus on developing unmanned aircraft inspired by the flight behavior of bats, birds, and insects.
“Historically, these aircraft have not been designed to have anywhere near the kind of agility you find in the natural world,” says John Baillieul, director of the Intelligent Mechatronics Lab, and a co-principal investigator on the five-year grant from the U.S. Office of Naval Research that is supporting AIRFOILS.
Led by several BU faculty members, along with researchers from the Universities of Washington, Maryland, and North Carolina at Chapel Hill, the project is drawing together experts in biology, computer science, and robotics to find ways to bring the agility of bats’ flight to small aircraft. Such vehicles are useful in both military and civilian contexts, for disaster recovery and other missions that are difficult or dangerous for humans.
The project will involve careful biological studies of bat behavior as well as engineering studies based on that information. Thomas Kunz, a professor of biology—who is playfully referred to as “Bat Man”—will bring his considerable expertise with the animals to bear on the project. First, members of his lab are filming the behavior of bats flying at night, using thermal infrared cameras.
Next, information is extracted from the bat videos by computer science professor Margrit Betke. Tracking the flight paths of individual bats is not an easy task. Betke, seated at her computer, shows a video of bats—represented by colored dots—undulating across a black screen. The bats follow a characteristic wavelike trajectory, very different from migrating birds. This two-dimensional image, though interesting, doesn’t show how the bats move three-dimensionally through their environment. To get that kind of information, Betke’s team uses multiple cameras that have been precisely calibrated. Knowing the distance between and the angle of the two cameras, they can calculate a position for each bat.
With this information, they can begin to track individual bats to learn how they travel—their speed, the angles at which they turn, how they dodge obstacles, and their foraging strategies. Even small, simple organisms like insects are able to perform the complex tasks of flying through a crowded forest canopy or finding food in their environment. Engineered systems, on the other hand, usually require a lot of energy, weight, and computational ability to manage complexity.
The engineering side of the project is led by Baillieul and engineering faculty members Ioannis Paschalidis and Calin Belta. Baillieul says that their team will use the bats’ behavior as inspiration. During a recent visit to Texas, a group from his lab flew some prototype vehicles in the bats’ territory, and discovered that the animals routinely encounter strong wind gusts. For bats, responding to a gust is a simple matter of flattening their bodies to present less surface area to the wind; Baillieul is now looking for ways to implement that kind of capability in an aircraft. “It’s going to be interesting to see how far we can push what the animals do into the realm of engineered systems,” he says.