Department of Aerospace Engineering, University of Bristol, Queen's Building, University Walk, Bristol BS8 1TR, UK.
Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK.
J Exp Biol. 2019 May 8;222(Pt 9):jeb185488. doi: 10.1242/jeb.185488.
Birds primarily create and control the forces necessary for flight through changing the shape and orientation of their wings and tail. Their wing geometry is characterised by complex variation in parameters such as camber, twist, sweep and dihedral. To characterise this complexity, a multi-view stereo-photogrammetry setup was developed for accurately measuring surface geometry in high resolution during free flight. The natural patterning of the birds was used as the basis for phase correlation-based image matching, allowing indoor or outdoor use while being non-intrusive for the birds. The accuracy of the method was quantified and shown to be sufficient for characterising the geometric parameters of interest, but with a reduction in accuracy close to the wing edge and in some localised regions. To demonstrate the method's utility, surface reconstructions are presented for a barn owl () and peregrine falcon () during three instants of gliding flight per bird. The barn owl flew with a consistent geometry, with positive wing camber and longitudinal anhedral. Based on flight dynamics theory, this suggests it was longitudinally statically unstable during these flights. The peregrine falcon flew with a consistent glide angle, but at a range of air speeds with varying geometry. Unlike the barn owl, its glide configuration did not provide a clear indication of longitudinal static stability/instability. Aspects of the geometries adopted by both birds appeared to be related to control corrections and this method would be well suited for future investigations in this area, as well as for other quantitative studies into avian flight dynamics.
鸟类主要通过改变翅膀和尾巴的形状和方向来产生和控制飞行所需的力。它们的机翼几何形状具有复杂的变化参数，如弯度、扭转、倾斜和后掠角。为了描述这种复杂性，开发了一种多视角立体摄影测量设置，以便在自由飞行中以高分辨率准确测量表面几何形状。鸟类的自然图案被用作基于相位相关的图像匹配的基础，允许在室内或室外使用，同时对鸟类没有干扰。该方法的准确性进行了量化，并证明足以描述感兴趣的几何参数，但在靠近机翼边缘和某些局部区域的准确性降低。为了展示该方法的实用性，针对一只仓鸮（）和一只游隼（）在每只鸟三次滑翔飞行中，展示了表面重建。仓鸮以一致的几何形状飞行，具有正弯度和纵向下反角。根据飞行动力学理论，这表明它在这些飞行中纵向静态不稳定。游隼以一致的滑翔角度飞行，但在不同的空气速度范围内具有不同的几何形状。与仓鸮不同，它的滑翔配置并没有清楚地表明纵向静态稳定性/不稳定性。这两种鸟类采用的几何形状的某些方面似乎与控制校正有关，这种方法非常适合该领域的未来研究，以及对鸟类飞行动力学的其他定量研究。
