L. Christoffer Johansson, Lasse Jakobsen & Anders HedenstrÃm (2018)
Flight in Ground Effect Dramatically Reduces Aerodynamic Costs in Bats.
Current Biology (advance online publication)
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Highlights
Aerodynamic power is 29% lower when bats fly close to rather than far from ground
Measured savings are twice the savings expected from models
Wing motion is varied with distance to ground, which may modulate ground effect
The results challenge our understanding of how animals use ground effect
Summary
Most flying animals, from insects to seabirds perform flights close to ground or water when taking off or landing drinking, and feeding or when traveling near water surfaces When flying close to a surface within approximately one wingspan, the surface acts as an aerodynamic mirror, interrupting the downwash , resulting in increased pressure underneath the wing and suppression of wingtip vortex development This aerodynamic interaction lowers the energy added to the air by the animal, reducing the cost of flying. Modeling suggests that flapping wings in ground effect can affect the expected power savings compared to gliding flight, either positively or negatively, depending on the wing motion Although aerodynamic theory predicts substantial power reductions when animals fly in ground effect , quantitative measurements of savings are lacking. Here, we show, through wake-based power measurements, that Daubentonâs bats utilize % less aerodynamic power when flying in compared to out of ground effect, which is twice the predicted savings. Contrary to theoretical predictions we find no variation in savings with distance above ground when in ground effect. Given alterations in kinematics with ground proximity, we hypothesize that modulation of wing kinematics raises the achievable benefit from ground effect relative to current model predictions. The savings from ground effect are comparable to formation flight but are not limited to large bird species. Instead, ground effect is experienced by most flying animals and may have facilitated the evolution of powered animal flight.
Non-dino....