Butterflies look like no other flying animal, with unusually short, broad and large wings relative to their body size. Previous studies have suggested butterflies use several unsteady aerodynamic mechanisms to boost force production with upstroke wing clap being a prominent feature. When the wings clap together at the end of upstroke the air between the wings is pressed out, creating a jet, pushing the animal in the opposite direction. Although viewed, for the last 50 years, as a crucial mechanism in insect flight, quantitative aerodynamic measurements of the clap in freely flying animals are lacking. Using quantitative flow measurements behind freely flying butterflies during take-off and a mechanical clapper, we provide aerodynamic performance estimates for the wing clap. We show that flexible butterfly wings, forming a cupped shape during the upstroke and clap, thrust the butterfly forwards, while the downstroke is used for weight support. We further show that flexible wings dramatically increase the useful impulse (+22%) and efficiency (+28%) of the clap compared to rigid wings. Combined, our results suggest butterflies evolved a highly effective clap, which provides a mechanistic hypothesis for their unique wing morphology. Furthermore, our findings could aid the design of man-made flapping drones, boosting propulsive performance.

中文翻译：

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由于灵活的翅膀，蝴蝶使用高效的推进拍手机制飞行

蝴蝶看起来不像其他飞行动物，相对于它们的体型来说，它们的翅膀异常短、宽和大。先前的研究表明，蝴蝶使用几种不稳定的空气动力学机制来增加力的产生，其中上冲翼拍击是一个突出的特征。当翅膀在上冲程结束时拍打在一起时，翅膀之间的空气被压出，产生喷射，将动物推向相反的方向。尽管在过去的 50 年中被视为昆虫飞行的关键机制，但缺乏对自由飞行动物拍手的定量空气动力学测量。使用起飞期间自由飞翔的蝴蝶和机械拍手背后的定量流量测量，我们提供了机翼拍手的空气动力学性能估计。我们展示了灵活的蝴蝶翅膀，在上划和拍手的过程中形成杯状，向前推动蝶泳，而下划用于支撑重量。我们进一步表明，与刚性机翼相比，柔性机翼可显着增加拍手的有用脉冲 (+22%) 和效率 (+28%)。综合起来，我们的结果表明蝴蝶进化出一种高效的拍手，这为它们独特的翅膀形态提供了一个机械假设。此外，我们的发现可以帮助设计人造扑翼无人机，提高推进性能。这为它们独特的机翼形态提供了机械假设。此外，我们的发现可以帮助设计人造扑翼无人机，提高推进性能。这为它们独特的机翼形态提供了机械假设。此外，我们的发现可以帮助设计人造扑翼无人机，提高推进性能。