Department of Integrative Biology, University of California, Berkeley, Berkeley, CA 94720, USA
College of Astronautics, Nanjing University of Aeronautics & Astronautics, 29 Yudao St., 210016 Nanjing, China.
J Exp Biol. 2019 Feb 4;222(Pt 3):jeb176263. doi: 10.1242/jeb.176263.
Flying organisms frequently confront the challenge of maintaining stability when moving within highly dynamic airflows near the Earth's surface. Either aerodynamic or inertial forces generated by appendages and other structures, such as the tail, may be used to offset aerial perturbations, but these responses have not been well characterized. To better understand how hummingbirds modify wing and tail motions in response to individual gusts, we filmed Anna's hummingbirds as they negotiated an upward jet of fast-moving air. Birds exhibited large variation in wing elevation, tail pitch and tail fan angles among transits as they repeatedly negotiated the same gust, and often exhibited a dramatic decrease in body angle (29±6 deg) post-transit. After extracting three-dimensional kinematic features, we identified a spectrum of control strategies for gust transit, with one extreme involving continuous flapping, no tail fanning and little disruption to body posture (23±3 deg downward pitch), and the other extreme characterized by dorsal wing pausing, tail fanning and greater downward body pitch (38±4 deg). The use of a deflectable tail on a glider model transiting the same gust resulted in enhanced stability and can easily be implemented in the design of aerial robots.
飞行生物在靠近地球表面的高度动态气流中移动时，经常面临保持稳定的挑战。无论是由附肢和其他结构（如尾巴）产生的空气动力或惯性力，都可以用来抵消空气动力的干扰，但这些反应尚未得到很好的描述。为了更好地理解蜂鸟如何针对单个阵风来调整翅膀和尾巴的运动，我们拍摄了安娜蜂鸟在快速移动的空气射流中向上飞行的过程。鸟类在多次通过同一阵风时，在翅膀抬高、尾巴俯仰和尾巴扇形角度方面表现出很大的变化，并且经常在过境后表现出明显的身体角度减小（29±6 度）。在提取三维运动学特征后，我们确定了一系列控制策略来应对阵风过境，一种极端情况是连续拍打翅膀，不扇动尾巴，身体姿势几乎没有受到干扰（向下俯仰 23±3 度），另一种极端情况是翅膀向上俯仰暂停，尾巴扇动，身体向下俯仰角度更大（38±4 度）。在同一阵风下通过的滑翔机模型使用可偏转的尾巴可以提高稳定性，并且可以很容易地应用于空中机器人的设计中。
