Supplementary Material from Dynamics of hinged wings in strong upward gusts

A bird's wings are articulated to its body via highly mobile shoulder joints. The joints confer an impressive range of motion, enabling the wings to make broad, sweeping movements that can modulate quite dramatically the production of aerodynamic load. This is enormously useful in challenging flight environments, especially the gusty, turbulent layers of the lower atmosphere. In this study, we develop a dynamics model to examine how a bird-scale gliding aircraft can use wing-root hinges (analogous to avian shoulder joints) to reject the initial impact of a strong upward gust. The idea requires that the spanwise centre of pressure and the centre of percussion of the hinging wing start, and stay, in good initial alignment (the centre of percussion here is related to the idea of a ‘sweet spot’ on a bat, as in cricket or baseball). We propose a method for achieving this rejection passively, for which the essential ingredients are (i) appropriate lift and mass distributions; (ii) constant-torque hinges and (iii) a wing whose sections stall softly. When configured correctly, the gusted wings will first pivot on their hinges without disturbing the fuselage of the aircraft, affording time for other corrective actions to engage. We expect this system to enhance the control of aircraft that fly in gusty conditions.

鸟类的翅膀通过活动性极强的肩关节与躯体铰接相连。该关节具备出色的活动范围，可使翅膀完成大幅挥摆动作，从而显著调控气动载荷的产生。这在复杂飞行环境中极具实用价值，尤其是在多阵风、湍流频发的低层大气环境下。本研究构建了一套动力学模型，用以探究仿鸟类滑翔飞行器如何通过翼根铰链（wing-root hinges，类比禽鸟肩关节）抵消强上升阵风的初始冲击。该方案要求铰接式机翼的展向压力中心（spanwise centre of pressure）与打击中心（centre of percussion）在初始阶段即保持良好对齐（此处的打击中心与板球、棒球球棒上的“甜点”（sweet spot）概念相关）。我们提出了一种可被动实现该抗风效果的方法，其核心要素包括：(i) 合理的升力与质量分布；(ii) 恒扭矩铰链（constant-torque hinges）；(iii) 翼型可实现柔和失速的机翼。当参数配置合理时，受阵风影响的机翼可先通过铰链偏转，而不会干扰飞行器机身，从而为其他修正动作预留响应时间。我们预期该系统可提升飞行器在多阵风环境下的飞行控制性能。