Flycatchers boost lift by Leading Edge Vortex

In a new study, published online today (14 March 2012) in Biology Letters, our lab shows that the high-lift mechanism Leading Edge Vortex (LEV) appear to be common to most animal flyers, as it appears in slow flying pied flycatchers. These birds hover and fly slowly when foraging on aerial insects, and they have a powerful downstroke when the LEV boost the lift by 100%. This is much stronger than found in for example hummingbirds, but that could be explained by the fact that the flycatcher has a feathered (inactive) upstroke. As flycatchers catch insects they need to be equally good at maneuvering in the air, and the LEV helps them to achieve the required turn radii. This mechanism was thought to be restricted to insects, as it was key to explaining why e.g. a bumblebee can fly, and subsequently our group has found this in slowly flying bats. Now, we extend the set of animas using LEV in slow flight to include also normal hoverers (i.e. animals having an inclined stroke plane and inactive back-/upstroke) in this spectacular study.

New paper about aerodynamics in slow-flying flycatcher

Just of the press from the Journal of the Royal Society Interface is a paper about pied flycatcher aerodynamics, by aouthors Florian Muijres, Melissa Bowlin, Christoffer Johansson and Anders Hedenström. Stereo flow-visualization was used to study the wake vortices shed off the wings of flycatchers as they flew slowly in the wind tunnel. The results sow that the aerodynamic force is mainly from the downstroke, resulting in a closed vortex loop. The results also show that the tail is involved in deflecting the downwash, resulting in an aerodynamic efficiency comparable to that of cruising flight. During the upstroke the wings generate no significant forces, but the body-tail configuration does to some degree, and so the upstroke phase of slow flight is not completely uninteresting from an aerodynamics viewpoint.