97.4 Saturday, Jan. 7 A Novel Unsteady Aerodynamic Mechanism in Avian Flight CRANDELL, KE*; TOBALSKE, BW; University of Montana, Missoula; University of Montana, Missoula email@example.com
The overarching significance of Reynolds number (Re), along with differences in body size, musculoskeletal morphologies, and wing kinematics, all lend support to the hypothesis that unsteady aerodynamics are only prevalent in insect flight. Consistent with this, it is generally assumed that quasi-steady aerodynamics are adequate for understanding flight in birds and bats. Unsteady mechanisms in insects, at Re<7,000, include leading edge vortices (LEV’s), rotational circulation, wake recapture, and “clap and fling.” Recently, LEV’s and rotational circulation have been observed on hummingbirds and small bats, but these animals are at the same Re as large insects. We undertook this study to test for unsteady effects in larger birds. Here, we present results from particle image velocimetry (PIV) and kinematic analyses of diamond doves (Geopelia cuneata, n = 5) during take-off. The birds used an unsteady mechanism previously unrecognized in vertebrates: the clap and peel. We estimate net thrust production from the ‘clap’ phase, wing-wing contact, to be 8% of body weight. Circulation grows continuously as the wings come apart during the “peel” phase, kinematically distinct from a “fling.” This initiates lift production earlier during wing translation and, thereby, directly overcomes the Wagner effect. This may contribute up to 24% body weight support during slow flight. This extends our understanding of the relevance of unsteady aerodynamics to vertebrate flight. NSF IOS-0923606 and IOS-0919799.