Data from: Falling with style: bats perform complex aerial rotations by adjusting wing inertia

The remarkable maneuverability of flying animals results from precise movements of their highly specialized wings. Bats have evolved an impressive capacity to control their flight, in large part due to their ability to modulate wing shape, area, and angle of attack through many independently controlled joints. Bat wings, however, also contain many bones and relatively large muscles, and thus the ratio of bats’ wing mass to their body mass is larger than it is for all other extant flyers. Although the inertia in bat wings would typically be associated with decreased aerial maneuverability, we show that bat maneuvers challenge this notion. We use a model-based tracking algorithm to measure the wing and body kinematics of bats performing complex aerial rotations. Using a minimal model of a bat with only six degrees of kinematic freedom, we show that bats can perform body rolls by selectively retracting one wing during the flapping cycle. We also show that this maneuver does not rely on aerodynamic forces, and furthermore that a fruit fly, with nearly massless wings, would not exhibit this effect. Similar results are shown for a pitching maneuver. Finally, we combine high-resolution kinematics of wing and body movements during landing and falling maneuvers with a 52-degree-of-freedom dynamical model of a bat to show that modulation of wing inertia plays the dominant role in reorienting the bat during landing and falling maneuvers, with minimal contribution from aerodynamic forces. Bats can, therefore, use their wings as multifunctional organs, capable of sophisticated aerodynamic and inertial dynamics not previously observed in other flying animals. This may also have implications for the control of aerial robotic vehicles.飞行动物卓越的机动能力，源自其高度特化的翅膀所做出的精准动作。蝙蝠演化出了出色的飞行控制能力，这在很大程度上得益于它们可通过多处独立受控的关节，调节翅膀的形状、面积与攻角（angle of attack）的能力。但蝙蝠的翅膀同时包含大量骨骼与相对发达的肌肉，因此其翼身质量比（wing mass to body mass ratio）要高于所有现存其他飞行类动物。尽管蝙蝠翅膀的惯性通常会被认为会降低空中机动能力，但我们的研究表明，蝙蝠的机动动作挑战了这一固有认知。我们采用基于模型的跟踪算法，对完成复杂空中旋转动作的蝙蝠的翅膀与身体运动学（kinematics）参数进行测量。借助仅含6个运动学自由度的简化蝙蝠模型，我们证实蝙蝠可通过在扑翼周期内选择性收起单侧翅膀，完成身体滚转动作。我们还证实，该机动动作并不依赖气动力（aerodynamic forces）；此外，翅膀近乎无质量的果蝇并不会产生此类效果。针对俯仰机动动作，我们也得到了相似的研究结果。最后，我们将蝙蝠在着陆与坠落机动过程中采集的高分辨率翅膀与身体运动学数据，与包含52个自由度的蝙蝠动力学模型（dynamical model）相结合，证实了在着陆与坠落机动过程中，蝙蝠通过调节翅膀惯性来主导身体重定向，气动力仅起到极小的辅助作用。因此，蝙蝠可将翅膀作为多功能器官，实现此前其他飞行类动物未曾观测到的复杂气动力与惯性动力学（inertial dynamics）调控。该研究结果对空中机器人飞行器的控制设计也具有借鉴意义。