The internal composite design of autorotating plant wings

To facilitate their dispersion, the miniature wing elements of autorotating winged fruits (samaras) must resist considerable multidirectional flight loadings as they fall from the tree and are carried away by occasional winds. However, the structural-mechanical properties of the samara wing, which stem from its internal composite design and provide it with resistance to deformations, are as yet unexplored. Here, we used structural analyses, composite-material modeling, and finite-element simulations to investigate the structure-mechanics-function relationship in the internal composite design of the samara of the Tipuana tipu tree. We show that the planar orientation of locally parallel fiber arrays varies globally throughout the wing, yielding a thin-layer composite element in which distinct functional regions resist multi-type mechanical deformations. This wing design provides extreme resistance to deformations at non-conventional orientations that are not aligned with the geometrical axes of the wing. The composite design principles of the samara wing can be incorporated into synthetic analogs to develop advanced, bioinspired minuscule wing elements that can effectively resist multidirectional loadings. STATEMENT OF SIGNIFICANCE: The internal composite structure of autorotating plant wings (samaras) exhibits a natural design solution for paper-thin flight elements unfamiliar in conventional engineering frameworks. The orientation of the basic composite unit of the wing varies throughout the wing, thereby forming distinct functional regions with designated deformation-resistance capabilities. Adapting these design principles into simplified models promotes the engineering of ultra-small flight elements for minute aerial units.