Recent research as uncovered many ne facts about the wake flows, and inferred magnitude and time-history of aerodynamic forces, the presence of unsteady aerodynamic high-lift mechanisms in bats (leading edge vortex), and efficiency of flight in birds such as passerines and swifts. Research in the wind tunnel forms a basis to build new aerodynamic theories about animal flight, which are then used for theoretical modelling and generating predictions about flight performance in the wild.
Bats in motion
Our first study on bats focused on the wake properties of a small nectar eating bat (Glossophaga soricina) This is a well studied species which have been held and bred in captivity for decades and therefore ideal for aerodynamic studies. It also proved very convenient as a wind tunnel animal because these bats will feed honey water from a thin tube suspended in the test section, and hence we could count on repeatable flight behaviour as the bats would return to the feeder to feed.
Wake models of cruising flight
A comparison between suggested wake models of birds (A) and of bats (B) in cruising flight Bat wakes appeared somewhat different from those of birds, which was explained by the ‘hovering’ upstroke and different wing design from birds. The bat wake also exhibits other novel features, such that each wing generates its own isolated vortex loop, while in birds there seem to be one vortex loop shed from the whole animal.
Air flow visualisation
At slow speeds the bats generate more lift than a conventional wing due to the development of a leading edge vortex (LEV). This is the same mechanism that allows most insects to fly, and so our observations extend the use of LEV into the domain of vertebrates. In Glossophaga soricina the LEV contribution of lift was approximately 40 %.