Both biological and artificial fliers must contend with aerial perturbations that are ubiquitous in the outdoor environment. Flapping fliers are generally least stable but also most maneuverable around the roll axis, yet our knowledge of roll control in biological fliers remains limited. Hummingbirds are suitable models for linking aerodynamic perturbations to flight control strategies, as these small, powerful fliers are capable of remaining airborne even in adverse wind conditions. We challenged hummingbirds to fly within a steady, longitudinally (streamwise) oriented vortex that imposed a continuous roll perturbation, measured wing kinematics and neuromotor activation of the flight muscles with synchronized high-speed video and electromyography and used computational fluid dynamics (CFD) to estimate the aerodynamic forces generated by observed wing motions. Hummingbirds responded to the perturbation with bilateral differences in activation of the main flight muscles while maintaining symmetry in most major aspects of wing motion, including stroke amplitude, stroke plane angle, and flapping frequency. Hummingbirds did display consistent bilateral differences in subtler wing kinematic traits, including wing rotation and elevation. CFD modeling revealed that asymmetric wing rotation was critical for attenuating the effects of the perturbation. The birds also augmented flight stabilization by adjusting body and tail posture to expose greater surface area to upwash than to the undesirable downwash. Our results provide insight into the remarkable capacity of hummingbirds to maintain flight control, as well as bio-inspiration for simple yet effective control strategies that could allow robotic fliers to contend with unfamiliar and challenging real-world aerial conditions.

中文翻译：

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飞行肌肉补充和机翼旋转的调制使蜂鸟能够减轻空中侧倾扰动。

生物飞行物和人工飞行物都必须与室外环境中普遍存在的空中干扰作斗争。襟翼飞行器通常最不稳定，但围绕侧倾轴​​的操纵性最高，但是我们对生物飞行器的侧倾控制的了解仍然有限。蜂鸟是将空气动力学扰动与飞行控制策略联系起来的合适模型，因为这些小而强大的飞行器即使在不利的风力条件下也能够保留在空中。我们向蜂鸟发出挑战，要求它们在一个稳定的纵向（沿流向）涡流中飞行，该涡流会产生连续的侧倾扰动，通过同步的高速视频和肌电图测量机翼运动学和飞行肌肉的神经运动激活，并使用计算流体力学（CFD）来估计由观察到的机翼运动产生的空气动力。蜂鸟对扰动做出反应时，主要飞行肌肉的激活出现了双边差异，同时在机翼运动的大多数主要方面（包括冲程幅度，冲程平面角度和拍打频率）保持对称。蜂鸟确实在微妙的机翼运动学特征（包括机翼旋转和仰角）方面显示出一致的双边差异。CFD模型表明，不对称的机翼旋转对于减弱扰动的影响至关重要。禽类还可以通过调节身体和尾巴的姿势来增强飞行稳定性，以使较大的表面积暴露于上冲而不是不期望的下冲。我们的结果提供了蜂鸟保持飞行控制的非凡能力的洞察力，以及简单有效的控制策略的生物灵感，这些策略可使机器人飞行器应对陌生而富挑战性的现实空中条件。