Meeting Abstract

P2.138  Jan. 5  Batty is only skin deep SWARTZ, S*; BISHOP, K; TIAN, X; SONG, A; ISRAELI, E; GALVAO, R; BISHOP, K; BREUER, K; Brown University, Providence, RI; Brown University, Providence, RI; Brown University, Providence, RI; Brown University, Providence, RI; Brown University, Providence, RI; Brown University, Providence, RI; Brown University, Providence, RI; Brown University, Providence, RI sharon_swartz@brown.edu

Bats wings generate aerodynamic forces through the use of forelimbs that possess not only highly specialized gross morphology but also distinctive material characteristics. We demonstrate that the skin of the arm portion of the wing membrane (plagiopatagium) undergoes substantial stretching and recoil in every wingbeat in small flying foxes (Cynopterus brachyotis). The deformation is greater in the spanwise than chordwise directions; this parallels the lower spanwise vs. chordwise stiffness, which is, in turn, dictated by the anisotropy of the wing collagen/elastin network of the wing. Wing membrane skin in the distal portions of the wing also deforms during the flight stroke, but to a lower degree than in the plagiopatagium. Building from studies of membranous wing models in a wind tunnel, we hypothesize that the regular, patterned deformation of the wing membrane skin contributes to the maintenance of attached flows at high angles of attack, allowing bat wings to generate significantly more lift than would be possible with a more rigid wing. We show that these material affects can be more significant than wing shape in determining aerodynamic performance of the bat wing, and propose that some inferences concerning bat flight mechanics and energetics based on wing shape, particularly aspect ratio, alone may require additional testing.