To better understand dragonflies’ remarkable flapping wing aerodynamic performance, we measured the kinematic parameters of the wings in two different flight modes (Normal Flight Mode (NFM) and Escape Flight Mode (EFM)). When the specimens switched from normal to escape mode the flapping frequency was invariant, but the stroke plane of the wings was more horizontally inclined. The flapping of both wings was adjusted to be more ventral with a change of the pitching angle that resulted in a larger angle of attack during downstroke and smaller during upstroke to affect the flow directions and the added mass effect. Noticeably, the phasing between the fore and hind pair of wings varies between two flight modes, which affects the wing-wing interaction as well as body oscillations. It is found that the momentum stream in the wake of EFM is qualitatively different from that in NFM. The change of the stroke plane angle and the varied pitching angle of the wings diverts the momentum downwards, while the smaller flapping amplitude and less phase difference between the wings compresses the momentum stream. It seems that in order to achieve greater flight maneuverability a flight vehicle needs to actively control positional angle as well as the pitching angle of the flapping wings.

为了更好地理解蜻蜓出色的扑翼动力特性，我们在两种不同的飞行模式（正常飞行模式（NFM）和逃生飞行模式（EFM））下测量了机翼的运动学参数。当标本从正常模式切换到逃逸模式时，拍打频率不变，但机翼的行程平面更呈水平倾斜。调节两个翼的拍打角度，以增加俯仰角度，从而在下冲程产生较大的迎角，在上冲程产生较小的迎角，从而影响流向和增加质量效应。值得注意的是，前翼和后翼之间的相位在两种飞行模式之间变化，这会影响机翼-机翼的相互作用以及机体的振动。结果发现，EFM之后的动量流与NFM中的动量流在质上是不同的。冲程平面角的变化和机翼变化的俯仰角使动量向下转移，而较小的拍打幅度和机翼之间的相位差较小则压缩了动量流。为了获得更大的飞行机动性，飞行器似乎需要主动控制位置角以及拍打机翼的俯仰角。