Yeaton Isaac J, Socha John J, Ross Shane D
Department of Mechanical Engineering Virginia Tech Blacksburg, VA United States of America.
Bioinspir Biomim. 2017 Mar 17;12(2):026013. doi: 10.1088/1748-3190/aa60e2.
Gliding flight-moving horizontally downward through the air without power-has evolved in a broad diversity of taxa and serves numerous ecologically relevant functions such as predator escape, expanding foraging locations, and finding mates, and has been suggested as an evolutionary pathway to powered flight. Historically, gliding has been conceptualized using the idealized conditions of equilibrium, in which the net aerodynamic force on the glider balances its weight. While this assumption is appealing for its simplicity, recent studies of glide trajectories have shown that equilibrium gliding is not the norm for most species. Furthermore, equilibrium theory neglects the aerodynamic differences between species, as well as how a glider can modify its glide path using control. To investigate non-equilibrium glide behavior, we developed a reduced-order model of gliding that accounts for self-similarity in the equations of motion, such that the lift and drag characteristics alone determine the glide trajectory. From analysis of velocity polar diagrams of horizontal and vertical velocity from several gliding species, we find that pitch angle, the angle between the horizontal and chord line, is a control parameter that can be exploited to modulate glide angle and glide speed. Varying pitch results in changing locations of equilibrium glide configurations in the velocity polar diagram that govern passive glide dynamics. Such analyses provide a new mechanism of interspecies comparison and tools to understand experimentally-measured kinematics data and theory. In addition, this analysis suggests that the lift and drag characteristics of aerial and aquatic autonomous gliders can be engineered to passively alter glide trajectories with minimal control effort.
滑翔飞行——在没有动力的情况下在空中水平向下移动——已经在种类繁多的分类群中进化出来，并具有许多与生态相关的功能，如躲避捕食者、扩大觅食地点和寻找配偶，并且被认为是通向动力飞行的一条进化途径。从历史上看，滑翔一直是在理想化的平衡条件下被概念化的，在这种条件下，作用在滑翔器上的净空气动力与其重量平衡。虽然这个假设因其简单性而颇具吸引力，但最近对滑翔轨迹的研究表明，平衡滑翔对大多数物种来说并非常态。此外，平衡理论忽略了物种之间的空气动力学差异，以及滑翔器如何通过控制来改变其滑翔路径。为了研究非平衡滑翔行为，我们开发了一个滑翔的降阶模型，该模型考虑了运动方程中的自相似性，这样仅升力和阻力特性就决定了滑翔轨迹。通过对几种滑翔物种的水平和垂直速度的速度极坐标图的分析，我们发现俯仰角，即水平与弦线之间的夹角，是一个可以用来调节滑翔角和滑翔速度的控制参数。改变俯仰会导致速度极坐标图中平衡滑翔构型的位置发生变化，这些构型决定了被动滑翔动力学。这样的分析提供了一种新的种间比较机制和工具，以理解实验测量的运动学数据和理论。此外，这种分析表明，可以设计空中和水上自主滑翔器的升力和阻力特性，以用最小的控制努力被动地改变滑翔轨迹。
