Department of Aerospace Engineering, University of Michigan, Ann Arbor, United States of America.
Bioinspir Biomim. 2021 Apr 19;16(3). doi: 10.1088/1748-3190/abc86a.
Here, we reviewed published aerodynamic efficiencies of gliding birds and similar sized unmanned aerial vehicles (UAVs) motivated by a fundamental question: are gliding birds more efficient than comparable UAVs? Despite a multitude of studies that have quantified the aerodynamic efficiency of gliding birds, there is no comprehensive summary of these results. This lack of consolidated information inhibits a true comparison between birds and UAVs. Such a comparison is complicated by variable uncertainty levels between the different techniques used to predict avian efficiency. To support our comparative approach, we began by surveying theoretical and experimental estimates of avian aerodynamic efficiency and investigating the uncertainty associated with each estimation method. We found that the methodology used by a study affects the estimated efficiency and can lead to incongruent conclusions on gliding bird aerodynamic efficiency. Our survey showed that studies on live birds gliding in wind tunnels provide a reliable minimum estimate of a birds' aerodynamic efficiency while simultaneously quantifying the wing configurations used in flight. Next, we surveyed the aeronautical literature to collect the published aerodynamic efficiencies of similar-sized, non-copter UAVs. The compiled information allowed a direct comparison of UAVs and gliding birds. Contrary to our expectation, we found that there is no definitive evidence that any gliding bird species is either more or less efficient than a comparable UAV. This non-result highlights a critical need for new technology and analytical advances that can reduce the uncertainty associated with estimating a gliding bird's aerodynamic efficiency. Nevertheless, our survey indicated that species flying within subcritical Reynolds number regimes may inspire UAV designs that can extend their operational range to efficiently operate in subcritical regimes. The survey results provided here point the way forward for research into avian gliding flight and enable informed UAV designs.
在这里，我们回顾了已发表的滑翔鸟类和类似大小的无人机 (UAV) 的空气动力学效率，提出了一个基本问题：滑翔鸟类比类似的 UAV 更有效率吗？尽管有许多研究已经量化了滑翔鸟类的空气动力学效率，但这些结果并没有得到全面总结。这种缺乏综合信息的情况阻碍了鸟类和 UAV 之间的真正比较。这种比较很复杂，因为不同技术用于预测鸟类效率的不确定性水平不同。为了支持我们的比较方法，我们首先调查了鸟类空气动力学效率的理论和实验估计，并研究了与每种估计方法相关的不确定性。我们发现，研究使用的方法会影响估计的效率，并可能导致对滑翔鸟类空气动力学效率的不一致结论。我们的调查表明，在风洞中滑翔的活体鸟类的研究提供了鸟类空气动力学效率的可靠最低估计，同时量化了飞行中使用的翼型。接下来，我们调查了航空文献，以收集类似大小、非直升机 UAV 的已发表空气动力学效率。收集到的信息允许直接比较 UAV 和滑翔鸟类。与我们的预期相反，我们没有发现任何确凿的证据表明任何滑翔鸟类比类似的 UAV 更有效率或效率更低。这一非结果突出表明，需要新技术和分析进展，以减少估计滑翔鸟类空气动力学效率的不确定性。尽管如此，我们的调查表明，在亚临界雷诺数范围内飞行的物种可能会激发 UAV 设计，从而扩展其操作范围，以在亚临界范围内有效运行。这里提供的调查结果为鸟类滑翔飞行的研究指明了方向，并为明智的 UAV 设计提供了依据。
