The wake of hovering flight in bats

Area of Science:

• Aerodynamics
• Biomechanics
• Animal Flight

Background:

• Hovering is stationary flight achieved through flapping.
• Bats use specific wing movements for hovering, but their wake has not been studied.

Purpose of the Study:

• To investigate the wake generated by hovering nectar-feeding bats.
• To analyze the aerodynamic forces and efficiency of bat hovering flight.

Main Methods:

• Trained Leptonycteris yerbabuenae bats to hover.
• Used time-resolved stereoscopic particle image velocimetry and high-speed kinematic analysis.
• Employed a modified actuator disc model to estimate forces and efficiency.

Main Results:

• Hovering bats produce a characteristic wake of bilateral stacked vortex loops.
• The downstroke generates most weight support, with the upstroke contributing to lift.
• Aerodynamic efficiency of hovering is lower than forward flapping flight.
• Overall energy conversion efficiency was estimated at 13%.

Conclusions:

• The study characterizes the wake of hovering bats for the first time.
• While both strokes contribute to lift, their precise contributions are difficult to disentangle from the wake.
• Hovering flight in bats is less aerodynamically efficient than forward flight.