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How flight feathers stick together (1 Viewer)

Fred Ruhe

Well-known member
Netherlands
Laura Y. Matloff, Eric Chang, Teresa J. Feo, Lindsie Jeffries, Amanda K. Stowers, Cole Thomson & David Lentink, 2020

How flight feathers stick together to form a continuous morphing wing.

Science 367(6475): 293-297
DOI: 10.1126/science.aaz3358

Abstract: https://science.sciencemag.org/content/367/6475/293

Wing shapes take flight

Birds can dynamically alter the shape of their wings during flight, although how this is accomplished is poorly understood. Matloff et al. found that two mechanisms control the movement of the individual feathers. Whenever the skeleton moves, the feathers are redistributed passively through compliance of the elastic connective tissue at the feather base. To prevent the feathers from spreading too far apart, hook-shaped microstructures on adjacent feathers form a directional fastener that locks adjacent feathers. These features are found across a range of bird sizes; however, because the detachment of the hooks is noisy, they are notably absent in silent fliers, such as barn owls.

Abstract

Variable feather overlap enables birds to morph their wings, unlike aircraft. They accomplish this feat by means of elastic compliance of connective tissue, which passively redistributes the overlapping flight feathers when the skeleton moves to morph the wing planform. Distinctive microstructures form “directional Velcro,” such that when adjacent feathers slide apart during extension, thousands of lobate cilia on the underlapping feathers lock probabilistically with hooked rami of overlapping feathers to prevent gaps. These structures unlock automatically during flexion. Using a feathered morphing wings robust to turbulence. We found that the hooked microstructures fasten feathers across bird species except silent fliers, whose feathers also lack the associated Velcro-like noise. These findings could inspire innovative directional fasteners and morphing aircraft.

Free pdf: https://science.sciencemag.org/content/sci/367/6475/293.full.pdf

Enjoy,

Fred
 
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Fig. 1. Pigeon flight feathers are underactuated during wing flexion and extension. (A) Birds morph their wings during flight by flexing and extending their skeleton. (B) During morphing, as the wrist angle (qw) extends, flight feathers pivot relative to the ulna bone, measured by primary and secondary feather angles (qP and qS). (C) Linear transfer functions model the relationship between the wrist angle and feather angle. N, individuals; n, cycles each. (D) Measurements of all feather angles follow a linear relationship to wrist angle, suggesting underactuation. (E) The slopes of the linear model represent the sensitivity of the feather angles to wrist angle. (F) A linear elastic spring model corroborated from the feather transfer functions yields the normalized spring stiffness distribution of the connective tissue between the remiges. Error bars represent standard deviation.

Fred
 

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