title: Leading edge vortices in lesser long-nosed bats occurring at slow but not fast flight speeds.
abstract: Slow and hovering animal flight creates high demands on the lift production of animal wings. Steady state aerodynamics is unable to explain the forces required and the most commonly used mechanism to enhance the lift production is a leading edge vortex (LEV). Although LEVs increase the lift, they come at the cost of high drag. Here we determine the flow above the wing of lesser long-nosed bats at slow and cruising speed using particle image velocimetry (PIV). We find that a prominent LEV is present during the downstroke at slow speed, but not at cruising speed. Comparison with previously published LEV data from a robotic flapper inspired by lesser long-nosed bats suggests that bats should be able to generate LEVs at cruising speeds, but that they avoid doing so, probably to increase flight efficiency. In addition, at slow flight speeds we find LEVs of opposite spin at the inner and outer wing during the upstroke, potentially providing a control challenge to the animal. We also note that the LEV stays attached to the wing throughout the downstoke and does not show the complex structures found in insects. This suggests that bats are able to control the development of the LEV and potential control mechanisms are discussed.
authors.affiliation: Department of Biology, Lund University, Ecology Building, SE-223 62 Lund University, Sweden. Department of Biology, Box 351800, 24 Kincaid Hall, University of Washington, Seattle, WA 98195-1800, USA.
authors.forename: Florian T
authors.initials: FT
authors.lastname: Muijres
authors.forename: L
authors.initials: L
authors.lastname: Christoffer Johansson
authors.forename: York
authors.initials: Y
authors.lastname: Winter
authors.forename: Anders
authors.initials: A
authors.lastname: Hedenström
mesh_terms: D000401:Aircraft / Q000295:instrumentation*; D000818:Animals; D032701:Biomimetics / Q000295:instrumentation*; D002685:Chiroptera / Q000502:physiology*; D003198:Computer Simulation; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D025461:Feedback, Physiological / Q000502:physiology; D005426:Flight, Animal / Q000502:physiology*; D008954:Models, Biological; D017711:Nonlinear Dynamics; D005082:Physical Exertion / Q000502:physiology; D012212:Rheology / Q000379:methods; D012371:Robotics / Q000295:instrumentation*; D014921:Wings, Animal / Q000502:physiology*