Inertial force plays an important role in bat flight

Videos show them shifting their weight to flip upside down by pulling one wing closer to their bodies while the other is extended. They found that these flying mammals land upside down using the extra weight of their webbed wings.

But in the case of at least two bat species, wrote Dr. Swartz and a team of researchers in Monday’s paper in the journal PLOS Biology, the often-overlooked role of inertia in bat flight is a critical force.

Bats land upside down as they prefer to roost that way beneath tree limbs, on cave ceilings, and ceilings of long-abandoned houses. “They have to go from flying with their heads forward to executing an acrobatic maneuver that puts them head down and feet up”. The researchers ran the simulation again with the bats’ wing mass reduced to the proportions of a fruit fly, which have very light wings for their body mass. That simulation showed that the landing rotation was not possible in the absence of aerodynamic forces. Scientists say that the enormous wings of bats may have something to do with it. Bats have large, heavy wings compared to other insects and birds, which enable them to land in an unusual way.

Specifically, the high-speed cameras revealed bats retracted one of their wings ever so slightly when approaching the ceiling of the enclosure.

“It is a more subtle way to studying how animals and people move through the environment”, Swartz, a bat researcher at the Aeromechanics and Evolutionary Morphology Lab at Brown, told Christian Science Monitor.

The manner in which bats are able to produce the required force to exhibit the maneuvers has yet to be clearly established.

It seems the bats have turned their cumbersome wings into an advantage.

“That’s a bit of a counterintuitive conclusion”. Using this asymmetric beat, these bats also made a half turn before landing on the mesh with their feet first. “Normally you’d think that an animal would not want to have such massive wings, but here, it turns out that the mass can be used to a few benefit”.

Based on these findings, researchers are positive they will manage to revolutionize the flying technology by applying this natural movement of bats to the machines that will be developed, such as drones, which have lately become more and more popular.

“What they were doing was moving their wings in very characteristic ways in order to manipulate their center of mass and the moment of inertia”, said Kenneth Breuer, from the university’s School of Engineering. Maneuvering or directing those robotic vehicles is a challenge. The movements of the bats were tracked using three, state-of-the-art video cameras that can capture an image at 1,000 frames per second, and studied the weight distribution within the bats’ bodies and wings. Many undergraduate students collaborate with us in several areas of our research program.