Body Accelerations During the Wingbeat in Six Bat Species: The Function of the Upstroke in Thrust Generation

ABSTRACT The kinematics and aerodynamics of Rhinolophus ferrumequinum, R. hipposideros, Myotis nattereri, M. mystacinus, Plecotus auritus and Eptesicus serotinus in horizontal flight at various flight speeds are described. Three kinematic patterns can be recognized. At low speeds M. nattereri, M. mystacinus and P. auritus use a ‘tip-reversal’ upstroke in which thrust is generated during the backward ‘flick’ of the chiropatagium. R. hipposideros also uses this kinematic pattern, but does not appear to generate thrust during the upstroke. Both R. ferrumequinum flying at 3·12ms−1 and E. serotinus flying at 3·44ms−1 accelerate during the ‘vertical’ upstroke (in which the wings move perpendicularly to the flight path), indicating that their wings are active. When flying at 4·16 m s−1, E. serotinus also uses a’vertical’upstroke, but in this case it decelerates, which suggests that thrust is not being generated. At minimum power speed (4·8ms−1), R.ferrumequinum uses a ‘reduced-span’ upstroke, thrust is not generated during the upstroke and the animal decelerates.