New wake study of a bat from Brown university

In a new study, published on-line in the Journal of the Royal Society Interface, the Brown University group report on wake measurements from the Brazilian free-tailed bat (Tadarida brasiliensis), using the PIV technique in a wind tunnel (Hubel et al.). This species differs in morphology and ecology from previously studied bat species, having higher aspect ratio wings and mainly flying in he open airspace when feeding on insects. So, does that make it's wake and aerodynamic properties different from other bats? The answer is "no"! Even if the authors argue that the Brazilian free-tailed bat has a wake very similar to that of the swift (Apus apus), it shows all of the characteristic wake features previously observed in bats. These include wing-root vortices and revers-vortices shed at the end of the upstroke. According to the authors when comparing the new data with previously studied bats: "the structure of their wakes is remarkably similar". Hence, it seems as if the notion of a typical "bat wake" receives support from this new study. Further studies will hopefully answer what features of the bat design make bat wakes different from those of birds.

New paper about bat aerodynamics from Animal Flight Lab

A new paper, entitled Comparative aerodynamic performance of flapping flight in two bat species using time-resolved wake visualization from the lab was published today in the Journal of the Royal Society Interface, in which Florian Muijres and co-workers compare two species of bat with regard to their aerodynamic performance. Florian has developed very detailed methods for analyzing the wake properties, as recorded by time-resolved stereo PIV in the Lund University wind tunnel. The two species being compared, Glossophaga soricina and Leptopnycteris yerbabuenae, differ with a factor of 2 in mass and in some ecological respects. The Leptonycteris is a migrant while the Glossophaga is a resident, while they are both fruigivores that eat/drink nectar from plants using hovering flight. A measure of flight economics, the maximum lift to drag, was similar between the species, but it occurred at a higher speed in the larger species. This could reflect different performance optima between the two species associated with requirements for slow flight in Glossophaga and cruising/migratory flight in Leptonycteris. The wake geometry showed the typical bat features in both species, including reversed vortex loops at the transition between up-/downstroke and vortices shed from the wing roots.