Meeting Abstract
Soaring birds including hawks and vultures exhibit emarginated primary feathers that collectively create a slotted wing-tip. Research has indicated these wing-tip slots reduce induced drag, resulting in a more efficient wing (i.e. better lift:drag ratio). These feathers routinely deform due to aerodynamic and inertial loading during flapping and gliding flight. Here we provide evidence that spanwise bending and twisting in these feathers results in greater roll stability and stall minimization. We measured primary feathers from 8 species and quantified force production and deformation at varying attack angles through a range of velocities. Markedly-emarginated primary feathers bend and twist more than less-emarginated feathers. Bending reorients forces medially, thereby contributing to roll stability for the animal. Twisting into incurrent flow decreases local attack angles and reorients force vertically. These findings reveal that emarginated primary feather slots are likely of greatest benefit during accelerative behaviors where attack angles are often high and variable, including take-off, landing, maneuvering or flying in turbulent conditions. NSF DGE−0809127, DGE−1313190 and IOS IOS-0923606.
