Intermittent turbulent gusts lift eagles
Dipendra Gupta, David Brandes, Michael J Lanzone, Tricia Miller and, Gregory P Bewley

TL;DR
This study reveals that golden eagles actively engage with strong, intermittent turbulent gusts, using nonlinear flight dynamics to harvest energy from turbulence, which has implications for understanding animal flight and aerodynamics.
Contribution
It provides the first quantitative evidence that soaring eagles exploit turbulent gusts through a ratcheting mechanism, highlighting the importance of unsteady aerodynamics in wildlife flight.
Findings
Eagles experience extreme upward accelerations during gusts, exceeding three times gravity.
Burst statistics of accelerations resemble turbulence patterns at larger scales.
A nonlinear model predicts the scale at which turbulence symmetry breaks and intermittency increases.
Abstract
Turbulence grounds aircraft and combating it in flight requires energy, yet volant wildlife fly effortlessly even on windy days. The nature of the interactions between soaring birds and transient turbulent gusts is not clear, especially when compared with our understanding of flight in larger and steadier airflows during thermal or dynamic soaring. We show that soaring golden eagles (Aquila chrysaetos) experienced short upward accelerations indicative of preferential engagement with strong and intermittent turbulent updrafts. The vertical accelerations reflect changes in lift that were as large as 25 standard deviations from the mean, or more than three times the acceleration of gravity, and so large as not to be consistent with gust mitigation or avoidance. These extreme events occurred in short bursts that mimic movement with turbulent vortices. The burst statistics and their…
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Taxonomy
TopicsAeolian processes and effects · Fluid Dynamics and Turbulent Flows · Particle Dynamics in Fluid Flows
