"Discovering the key to birds' agility could improve drone design", Harvey et al. Nature

Originally posted on MARCH 10, 2022

Press and other articles
Quanta science podcast, November 1, 2022 - Podcast episode: Geometric Analysis Reveals How Birds Mastered Flight
Quanta magazine, August 3, 2022 - Geometric Analysis Reveals How Birds Mastered Flight
Nature Portfolio Ecology and Evolution - Behind the paper, March 10 2022: : To be (stable) or not to be
UBC Science, March 9, 2022 - Discovering the key to birds’ agility could improve drone design
University of Michigan Engineering Research News, March 9, 2022: Avian secret: The key to agile bird flight is switching quickly between stable and unstable gliding
Nature News and VIews, March 7 2022: Trade-offs between stability and manoeuvrability in bird flight

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C. Harvey, V. B. Baliga, J. C. M. Wong, D. L. Altshuler & D. J. Inman. 2022. Birds can transition between stable and unstable states via wing morphing. Nature

Abstract
Birds morph their wing shape to accomplish extraordinary manoeuvres1,2,3,4, which are governed by avian-specific equations of motion. Solving these equations requires information about a bird’s aerodynamic and inertial characteristics5. Avian flight research to date has focused on resolving aerodynamic features, whereas inertial properties including centre of gravity and moment of inertia are seldom addressed. Here we use an analytical method to determine the inertial characteristics of 22 species across the full range of elbow and wrist flexion and extension. We find that wing morphing allows birds to substantially change their roll and yaw inertia but has a minimal effect on the position of the centre of gravity. With the addition of inertial characteristics, we derived a novel metric of pitch agility and estimated the static pitch stability, revealing that the agility and static margin ranges are reduced as body mass increases. These results provide quantitative evidence that evolution selects for both stable and unstable flight, in contrast to the prevailing narrative that birds are evolving away from stability6. This comprehensive analysis of avian inertial characteristics provides the key features required to establish a theoretical model of avian manoeuvrability.