Lentink D, Müller U K, Stamhuis E J, de Kat R, van Gestel W, Veldhuis L L M, Henningsson P, Hedenström A, Videler J J, van Leeuwen J L
Experimental Zoology Group, Wageningen University, 6709 PG Wageningen, The Netherlands.
Nature. 2007 Apr 26;446(7139):1082-5. doi: 10.1038/nature05733.
Gliding birds continually change the shape and size of their wings, presumably to exploit the profound effect of wing morphology on aerodynamic performance. That birds should adjust wing sweep to suit glide speed has been predicted qualitatively by analytical glide models, which extrapolated the wing's performance envelope from aerodynamic theory. Here we describe the aerodynamic and structural performance of actual swift wings, as measured in a wind tunnel, and on this basis build a semi-empirical glide model. By measuring inside and outside swifts' behavioural envelope, we show that choosing the most suitable sweep can halve sink speed or triple turning rate. Extended wings are superior for slow glides and turns; swept wings are superior for fast glides and turns. This superiority is due to better aerodynamic performance-with the exception of fast turns. Swept wings are less effective at generating lift while turning at high speeds, but can bear the extreme loads. Finally, our glide model predicts that cost-effective gliding occurs at speeds of 8-10 m s(-1), whereas agility-related figures of merit peak at 15-25 m s(-1). In fact, swifts spend the night ('roost') in flight at 8-10 m s(-1) (ref. 11), thus our model can explain this choice for a resting behaviour. Morphing not only adjusts birds' wing performance to the task at hand, but could also control the flight of future aircraft.
滑翔鸟类会不断改变翅膀的形状和大小，大概是为了利用翅膀形态对空气动力学性能的深远影响。通过解析滑翔模型从空气动力学理论推断出翅膀的性能范围，已定性预测鸟类应调整翼展以适应滑翔速度。在此，我们描述了在风洞中测量的实际雨燕翅膀的空气动力学和结构性能，并在此基础上构建了一个半经验滑翔模型。通过测量雨燕行为范围的内外情况，我们发现选择最合适的翼展可以使下沉速度减半或使转弯速率提高两倍。展开的翅膀在慢速滑翔和转弯时更具优势；后掠翼在快速滑翔和转弯时更具优势。这种优势源于更好的空气动力学性能——高速转弯除外。后掠翼在高速转弯时产生升力的效果较差，但能承受极端载荷。最后，我们的滑翔模型预测，在8-10米/秒的速度下会出现高效滑翔，而与敏捷性相关的品质因数在15-25米/秒时达到峰值。事实上，雨燕在夜间（“栖息”）以8-10米/秒的速度飞行（参考文献11），因此我们的模型可以解释这种休息行为的选择。形态变化不仅能使鸟类的翅膀性能适应手头的任务，还可能控制未来飞机的飞行。
