Sachs Gottfried, Moelyadi Mochammad Agoes
Institute of Flight Mechanics and Flight Control, Technische Universität München, Boltzmannstr. 15, 85747 Garching, Germany.
J Theor Biol. 2006 Mar 7;239(1):93-100. doi: 10.1016/j.jtbi.2005.07.016. Epub 2005 Sep 30.
The aerodynamic yawing moment characteristics of bird wings with slotted tips are dealt with. Emphasis is placed on the effect of sweep which the separated feathers constituting the wing tips show and which can reach significant values. Reference is made to basic aerodynamic characteristics of wings with sweep which yields a stabilizing yawing moment significantly larger than that of unswept wings. Then, the yawing moment characteristics are determined for a wing, the features of which are considered as representative of bird wings with sweep in their slotted tips. A sophisticated aerodynamic procedure is used for obtaining results of high precision. It is shown that the sweep in the slotted wing tips yields a stabilizing yawing moment of significant magnitude, considerably increasing with the lift coefficient. To make the significance of wing tip sweep for the ability to generate yawing moments more perspicuous, a wing modification the slotted tips of which are unswept is considered for comparison. It turns out that this wing shows yawing moments which are substantially smaller. A physical insight into the effect of slotted wing tip sweep on the aerodynamic yawing moment characteristics is provided by showing the underlying mechanism. From the results presented in this paper it follows that the sweep in slotted wing tips provides a substantial contribution to the aerodynamic yawing moment and, thus, to yaw stability. It may be concluded that this is an essential reason why there is sweep in the slotted tips of bird wings.
研究了具有开缝翼尖的鸟类翅膀的气动偏航力矩特性。重点关注构成翼尖的分离羽毛所呈现的后掠效应，该效应可达显著值。文中提及了具有后掠的翅膀的基本气动特性，其产生的稳定偏航力矩明显大于无后掠翅膀的偏航力矩。然后，确定了一种翅膀的偏航力矩特性，其特征被视为具有开缝翼尖后掠的鸟类翅膀的代表。采用了复杂的气动程序来获得高精度的结果。结果表明，开缝翼尖的后掠产生了显著大小的稳定偏航力矩，且随着升力系数大幅增加。为了使翼尖后掠对产生偏航力矩能力的重要性更加清晰，考虑了一种开缝翼尖无后掠的翅膀修改方案进行比较。结果表明，这种翅膀的偏航力矩要小得多。通过展示其潜在机制，对开缝翼尖后掠对气动偏航力矩特性的影响提供了物理见解。从本文给出的结果可以得出，开缝翼尖的后掠对气动偏航力矩有很大贡献，从而对偏航稳定性有很大贡献。可以得出结论，这是鸟类翅膀开缝翼尖存在后掠的一个重要原因。
