Meeting Abstract

105.2  Wednesday, Jan. 7  Where’s the LEV? Aerodynamics of the hummingbird wing during hovering TOBALSKE, B.W.*; WARRICK, D.R.; University of Montana, Missoula bret.tobalske@mso.umt.edu

Leading-edge vortices (LEVs) are considered essential features of wing aerodynamics during hovering in insects and have recently been reported to enhance lift production in a slow-flying bat (Glossophaga soricina). To test for similar patterns in hummingbirds, birds that are uniquely adept at hovering, we used digital particle image velocimetry (DPIV) and measured near-field flow (< 5 mm from wing surface) about the wings of hovering rufous hummingbirds (Selasphorus rufus, 3.3 g, n = 5). We also measured a series of model wings and dried hummingbird wings spun as propellers. We mounted the propellers on a force plate to compare direct measures of lift (L) and drag (D) with estimates made using DPIV. In live birds, we found no evidence of sustained, attached LEVs during up or downstroke although a transient LEV was produced during the rapid change in angle of attack at the end of downstroke. In the propeller models, coefficients of L and D were < 2.5 and maximum L:D ratios were < 3.7. These L:D ratios were comparable with previously reported measurements for models of similarly-sized hawkmoth (Manduca sexta) wings but 4x < maximum L:D ratio previously reported for a dried, spinning hummingbird wing. We observed reasonable congruence between transducer measurements and circulation-based estimates of lift. The major conclusion from our research, novel in a comparative context, is that LEVs do not dominate the flow about hummingbird wings during hovering. NSF IOB-0615648.