Hovering is a key behaviour 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 aerodynamic quasi-steady performance of wings from 13 species of hummingbirds from Colombia and California to determine how wing morphology mediates hovering performance. We attained lift and drag over a range of angles of attack for Reynolds numbers below 20 000. 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 accurate drag and lift measurements combined allow us to compare aerodynamic lift and power factor. The power factor captures the efficacy of hummingbird wings to lift a unit weight with a minimum of aerodynamic power. To quantify the effect of wing morphology on the airflow we performed particle image velocimetry and visualized the leading edge vortex (LEV) for the upstroke and downstroke configuration of the wing. Even though wing camber is inverted for the upstroke, the structure of the leading edge vortex is still remarkably similar. The power factor on the other hand is much lower during the upstroke. Our findings suggest that precise drag measurements are important to evaluate the hover efficacy of spinning and flapping wings that generate leading edge vortices.
|Title of host publication||Proceeding of the Annual Main Meeting of the Society for Experimental Biology, 01-04 July 2011, Glasgow, Scotland|
|Publication status||Published - 2011|
|Event||Society for Experimental Biology (SEB) annual meeting 2001, Glasgow, Scotland - |
Duration: 1 Jul 2011 → 4 Jul 2011
|Conference||Society for Experimental Biology (SEB) annual meeting 2001, Glasgow, Scotland|
|Period||1/07/11 → 4/07/11|