Non-wet kingfisher flying in the rain: The water-repellent mechanism of elastic feathers.

HYPOTHESIS: Flying in the rain presents a greater challenge for smaller animals such as kingfishers, compared with aircraft in the same situation. Regardless, kingfishers have developed advanced water repellency as reflected in the hydrophobicity and elasticity of their feathers. Therefore, it is possible to confirm that the elastic superhydrophobic surface can enhance the water repellency of the surface by experimental and theoretical analysis.

EXPERIMENTS: A simplified device simulating droplet impact on a kingfisher feather was configured for comparison. Moreover, the dynamic behavior of droplets (with varying Weber numbers-2 ≤ We  ≤ 42) impinging on the elastic and rigid substrate was analyzed, such as spreading, retraction, lift-off, the secondary droplet, and contact time with a high-speed camera.

FINDINGS: The elastic substrate significantly affected the retraction and lift-off of the droplet-that is, an earlier and more efficient morphological rearrangement of the droplet-reducing the contact time by up to 8.3% (17 < We  ≤ 32). The combination of elasticity and hydrophobicity is a new bioinspired strategy that provides an insight into one of the mechanisms by which birds flying in the rain cannot be bedewed while guiding the design of water-repellent surfaces.