Flying Robots Inspired By Bats

Researchers at Virginia Tech are designing "micro air vehicles," which fly through the air on flapping wings. Their inspiration comes from nature, with the designs based on the motion of fruit bat wings.

There are over 1,000 species of bats with wings made of a thin stretchable membrane, but scientists face challenges modeling exactly how these bats use their wings to move in the air. Gathering data from live animals and then translating those data to computer analysis models is extremely complex.

The study, reported in the journal Physics of Fluids, used measurements of bat wings in real flight to create a computer representation of the "relationship between wing motion and airflow around the bat wing," according to a press release.

"Bats have different wing shapes and sizes, depending on their evolutionary function. Typically, bats are very agile and can change their flight path very quickly -- showing high maneuverability for midflight prey capture, so it's of interest to know how they do this," explained Danesh Tafti, a professor in the Department of Mechanical Engineering and director of the High Performance Computational Fluid Thermal Science and Engineering Lab at Virginia Tech.

An extended bat wing is about 17-by-9-cm and the typical bat weights roughly 30 grams, or a little over one ounce. Despite their small scale, the bats studied were able to manipulate their wing motion and timing in order to maximize forces generated by the wind. "It distorts its wing shape and size continuously during flapping," Tafti noted.

While the wings of large airplanes are static in size, the surface area of the bats' wings increased by about 30 percent on the downward stroke, in order to generate the most power, and decreased by about 30 percent on the upward stroke, in order to reduce air resistance. This allowed the bat wings to generate coefficients of force that are "about two to three times greater than a static airfoil wing used for large airplanes," said Kamal Viswanath, a study co-author.

Now that researchers have explained why the bat is such an effective flier, the next goal is to translate those adaptations to human technology. "Next, we'd like to explore deconstructing the seemingly complex motion of the bat wing into simpler motions, which is necessary to make a bat-inspired flying robot," said Viswanath.

The researchers will keep their computer model basic at first, but hope to eventually capture many of the nuanced movements done so naturally by bats in flight.

"We'd also like to explore other bat wing motions, such as a bat in level flight or a bat trying to maneuver quickly to answer questions, including: What are the differences in wing motion and how do they translate to air movement and forces that the bat generates? And finally, how can we use this knowledge to control the flight of an autonomous flying vehicle?" Tafti added.