Recently, a novel concept of flapping Micro-Air-Vehicles (FMAVs) with four wings has been proposed, which potentially utilizes the clap-and-fling effect for lift enhancement and agile maneuvers through an adjustment of wing kinematics. However, the application of the clap-and-fling effect in the four-winged FMAVs is underexplored and the dynamic stability is still unclear. In this paper, aerodynamics and flight dynamic stability of the four-winged FMAVs are studied experimentally and numerically. Results show that the clap-and-fling effect is observed when the flapping frequency is above 18 Hz. Due to the clap-and-fling effect, the lift generation and aerodynamic efficiency are both improved, which is mainly attributed to the fling phase. Further studies show that the clap-and-fling effect becomes weaker as the wing root spacing increases and is almost absent at a wing root spacing of 1.73 chord length. In addition, a wing with an aspect ratio of 3 can increase both lift generation and efficiency due to the clap-and-fling effect. Finally, according to the dynamic stability analysis of the four-winged FMAV, the divergence speed of the lateral oscillation mode is about 4 times faster than that of the longitudinal oscillation mode. Our results can provide guidance on the design and control of four-winged FMAVs.

中文翻译：

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带有四个拍打翼的微型飞机在悬停飞行中的空气动力学和动力稳定性

近来，已经提出了一种具有四个机翼的扑翼微型飞行器（FMAV）的新颖概念，其潜在地利用拍打和甩打效果来通过调整机翼运动学来增强升力和敏捷机动。然而，拍击和逃跑效应在四翼FMAV中的应用尚未得到充分研究，动态稳定性仍不清楚。在本文中，对四翼FMAV的空气动力学和飞行动力学稳定性进行了实验和数值研究。结果表明，当拍击频率高于18 Hz时，可以观察到拍手和拍手的效果。由于拍手和甩子的作用，升力的产生和空气动力效率都得到了改善，这主要归因于甩子阶段。进一步的研究表明，随着翼根间距的增加，拍手和甩拳的效果变得更弱，而翼根间距为1.73弦长时几乎没有。另外，由于拍手和甩子的作用，长宽比为3的机翼可以提高升力的产生和效率。最后，根据四翼FMAV的动态稳定性分析，横向振荡模式的发散速度大约是纵向振荡模式的发散速度的4倍。我们的结果可以为四翼FMAV的设计和控制提供指导。横向振荡模式的发散速度大约是纵向振荡模式的发散速度的4倍。我们的结果可以为四翼FMAV的设计和控制提供指导。横向振荡模式的发散速度大约是纵向振荡模式的发散速度的4倍。我们的结果可以为四翼FMAV的设计和控制提供指导。