Abstract
Only seldom are square/rectangular shapes found in nature. One notable exception is the bird feather rachis, which raises the question: why is the proximal base round but the distal end square? Herein, it is uncovered that, given the same area, square cross sections show higher bending rigidity and are superior in maintaining the original shape, whereas circular sections ovalize upon flexing. This circular‐to‐square shape change increases the ability of the flight feathers to resist flexure while minimizes the weight along the shaft length. The walls are themselves a heterogeneous composite with the fiber arrangements adjusted to the local stress requirements: the dorsal and ventral regions are composed of longitudinal and circumferential fibers, while lateral walls consist of crossed fibers. This natural avian design is ready to be reproduced, and it is anticipated that the knowledge gained from this work will inspire new materials and structures for, e.g., manned/unmanned aerial vehicles.
Highlights
Exception is the bird feather rachis, which raises the question: why is the proximal base round but the distal end square? it is uncovered that, given the same area, square cross sections show higher bending rigidity and are superior in maintaining the original shape, whereas circular sections ovalize upon
This circular-to-square shape change increases the ability of the flight feather shaft is filled with air at the calamus feathers to resist flexure while minimizes the weight along the shaft length
The and foam at the walls are themselves a heterogeneous composite with the fiber arrangements adjusted to the local stress requirements: the dorsal and ventral regions are composed of longitudinal and circumferential fibers, while lateral walls consist of crossed fibers
Summary
The larger the cross-sectional shape change, the greater the decrease in I, and the less the ability to resist further flexural force This indicates that the changing cross-sectional shape to square, which provides higher flexural rigidity, can partially counterbalance the large reduction in I caused by the tapering of the shaft toward the distal free end to reduce profile drag,[4,24] save energy, and decrease the weight.
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