It is an aerial manoeuvre far beyond the capabilities of the most sophisticated modern aircraft: landing upside down on a ceiling. But it is routine business for bats, and now scientists have learned precisely how they do it.
Researchers using high-speed cameras to observe bats in a special flight enclosure said these flying mammals exploit the extra mass of their wings, which are heavy for their body size compared to those of birds and insects, in order to perform the upside-down landing.
They land that way in order to roost, as bats do, upside down on cave ceilings or under tree limbs.
Brown University scientists observed two species: Seba's short-tailed bat and the lesser dog-faced fruit bat.
They tracked their motions using three synchronised high-speed video cameras taking images at 1000 frames per second, and studied weight distribution in the bats' body and wings.
They found that by flapping wings while folding one of them a bit towards their body, a bat can shift its centre of mass to perform a midair flip in order to alight on a ceiling.
"Flying animals all manoeuvre constantly as they negotiate a three-dimensional environment," Brown biology and engineering professor Sharon Swartz said.
"Bats employ this specific manoeuvre every time they land, because for a bat, landing requires reorienting from head forward, back up, belly down, to head down, toes up."
When approaching their touchdown spot, bats are not flying quickly, making it difficult to muster the aerodynamic forces generated by pushing against the air that could help position them for an upside-down landing.
But their heavy wings enable them instead to generate inertial forces to reorient in midair.
"This is similar to the way in which divers twist and turn during a high dive," said Kenny Breuer, a Brown professor of engineering, ecology and evolutionary biology.
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