Leading Edge Vortices In Bats

Leading-edge vortex on a bat's wing

Using Digital Particle Image Velocimetry, scientists are able to show the velocity of the airflow surrounding the wing of the bat. This demonstrates the leading edge vortices that occur on the surface of a bat wing.

Bats are different than insects and birds in the way that they fly. They are different because instead of rigid wings like insects, or stiff wings like birds, they have a very flexible wing due to a membrane that covers over two-dozen independent joins. Because of this membrane the bats are able to have more maneuverability and fly using less energy. But even with this advantage flying at slow speeds and hovering is very difficult. Insects use several different techniques to hover and to do this they mostly use leading edge vortices. But for the longest time, these leading edge vortices were thought only to apply to insects. In recent years, however, studies have shown that the reason bats can hover and fly so slowly is due to these leading edge vortices.

What are leading edge vortices? And how do they form? These two questions go hand in hand. When a bat completes its down stroke, the sharp leading edge cuts through the air that flows over the length of the wing, then comes back and “reattaches” itself to the wing.  It forms a vortex, where instead of the air just flowing over the wing it comes back, creating a circulating movement of air over the wing. This generates lift, and then on the upstroke a lot of this lift is conserved because the upstroke sheds the vortex, and since the bat brings its wings close to its body, does not generate a lot of drag. This makes the down stroke more efficient because less of the aerodynamic forces generated are lost. These vortices generate a significant part the lift needed to sustain the flight of the bat when it is hovering and or flying at slow speeds.

These vortices, in slow and hovering flight, account for a good portion of the aerodynamic forces to sustain the flight of a bat. Some scientists have even shown that up to forty percent of the lift in slow and or hovering flight is generated by these leading edge vortices. If that amount of force can be generated from these vortices hopefully scientists can work with engineers to use this information and apply it to new technologies. Especially when it comes to the maneuverability and the hovering capabilities found in animals that have these leading edge vortices. Some are trying to build micro air vehicles with these capabilities, but maybe one day we will all by hovering and flying with the help of these leading edge vortices.


One Comment

Lorena Barba posted on December 12, 2011 at 10:45 pm

Leading-edge vortices are fascinating, the most important discovery about insect flight, I think. Now they have been seen in swifts and bats!
I wonder what other creatures use them … flying snakes? Hmm, interesting thought.
But don’t think humans we’ll be using them any time soon; we’re just too big.