February 18, 2014
Building Better Aircraft Based On Bat Wing Motions
[ Watch the Video: Bats Inspire Next-Gen Aircraft ]
Lee Rannals for redOrbit.com - Your Universe OnlineResearchers are studying how bats flap their wings in hopes it will help in designing small flying vehicles in the future.
The team studied how bats use their wings to manipulate the air around them and wrote about their findings in a paper published in the journal Physics of Fluids. Over 1,000 bat species have hand membrane wings in which their fingers are “webbed” and are connected by a flexible membrane.
Virginia Tech researchers used experimental measurements of the movements of the bats’ wings in real flight, then analyzed them to see the direct relationship between wing motion and airflow around the bat wing.
"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," Danesh Tafti, the William S. Cross professor in the Department of Mechanical Engineering and director of the High Performance Computational Fluid Thermal Science and Engineering Lab at Virginia Tech, said in a statement.
Researchers found that bat wings manipulated the wing motion with correct timing to maximize the forces generated by the wing. Tafti said the bat distorts its wing shape and size continuously during flapping.
A bat can increase the area of the wing by about 30 percent to help maximize favorable forces during the downward movement of the wing. It is also able to decrease the area by a similar amount on the way up to help minimize unfavorable forces.
The forces manipulated by the bat are about two to three times greater than a static airfoil wing used for large airplanes, according to Kamal Viswanath, a co-author who was a graduate research assistant working with Tafti when the work was performed and is now a research engineer at the US Naval Research Lab's Laboratories for Computational Physics and Fluid Dynamics.
"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," Viswanath said in a statement.
In future studies, the researchers want to be able to keep the wing motion as simple as possible, but with the same force production as that of a real bat. This study, along with future studies, will help researchers design better micro air vehicles.
"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 said.
Image 2 (Below): This is the time history of coherent vortex formation around the bat wing. Bottom plot shows lift and thrust coefficient variation for a flapping cycle over normalized time. Credit: D. Tafti/VT