39.2 Saturday, Jan. 5 Small aspect ratio differences impact hover efficacy among 12 hummingbird species KRUYT, J.W.*; QUICAZAN-RUBIO, E.M.; VAN HEIJST, G.J.F.; ALTSHULER, D.L.; LENTINK, D.; Stanford University; Wageningen University; University of California, Riverside; Technical University of Eindhoven; University of British Columbia; Stanford University; Wageningen University email@example.com
Hovering is a key behavior of hummingbirds that allows them to time-effectively extract nectar from flowers and catch arthropod prey, which is critical to their high-energy lifestyle. The aerodynamic power demands are high during hovering but how these demands compare among different species is not fully understood. Here we compare the quasi-steady aerodynamic performance of wings from 12 species of hummingbirds to determine how wing morphology mediates hovering performance. We attained lift and drag over a range of angles of attack for Reynolds numbers representative for every species. Whereas other spinner experiments recorded negative drag at low angles of attack, our spinner measured drag accurately across the full range of wing angles. The force measurements allow us to compare hover efficacy among different wings through the power factor, which captures the efficacy of hummingbird wings to lift a unit weight with a minimum of aerodynamic power. We found a strong effect of aspect ratio on quasi-steady aerodynamic performance at angles of attack that are relevant to hovering flight in hummingbirds. To quantify the effect of wing morphology on the airflow we performed particle image velocimetry and visualized the leading edge vortex (LEV) for the up and down stroke configuration of the wing. Our findings show that small differences in aspect ratio affect the hover efficacy of spinning hummingbird wings while having only small effect on quasi-steady flow structure. This result shows the value of precise drag force measurements on wings that produce leading edge vortices.