Ministry-of-Education Key Laboratory of Fluid Mechanics, School of Aeronautic and Engineering, Beihang University, Beijing, 100191, China.
State Key Laboratory for Strength and Vibration of Mechanical Structures, School of Aerospace, Xi'an Jiaotong University, Xi'an, 710049, China.
Sci Rep. 2020 Feb 6;10(1):1975. doi: 10.1038/s41598-020-58762-5.
Previous studies on forward flight stability in insects are for low to medium flight-speeds. In the present work, we investigated the stability problem for the full range of flight speeds (0-8.6 m/s) of a drone-fly. Our results show the following: The longitudinal derivatives due to the lateral motion are approximately 3 orders of magnitude smaller than the other longitudinal derivatives. Thus, we can decouple these two motions of the insect, as commonly done for a conventional airplane. At hovering flight, the motion of the dronefly is weakly unstable owing to two unstable natural modes of motion, a longitudinal one and a lateral one. At low (1.6 m/s) and medium (3.1 m/s) flight-speeds, the unstable modes become even weaker and the flight is approximately neutral. At high flight-speeds (4.6 m/s, 6.9 m/s and 8.6 m/s), the flight becomes more and more unstable due to an unstable longitudinal mode. At the highest flight speed, 8.6 m/s, the instability is so strong that the time constant representing the growth rate of the instability (disturbance-doubling time) is only 10.1 ms, which is close to the sensory reaction time of a fly (approximately 11 ms). This indicates that strong instability may play a role in limiting the flight speed of the insect.
先前关于昆虫前飞稳定性的研究都是针对中低飞行速度的。在本工作中，我们研究了无人机全飞行速度范围（0-8.6m/s）的稳定性问题。研究结果表明：横向运动引起的纵向导数大约比其他纵向导数小 3 个数量级。因此，我们可以像通常对传统飞机那样，将昆虫的这两种运动解耦。在悬停飞行中，由于两种不稳定的运动模式（纵向和横向），无人机的运动是弱不稳定的。在低（1.6m/s）和中（3.1m/s）飞行速度下，不稳定模式变得更弱，飞行接近中性。在高飞行速度（4.6m/s、6.9m/s 和 8.6m/s）下，由于不稳定的纵向模式，飞行变得越来越不稳定。在最高飞行速度 8.6m/s 时，不稳定性非常强，代表不稳定性增长率的时间常数（干扰倍增时间）仅为 10.1ms，接近苍蝇的感觉反应时间（约 11ms）。这表明强烈的不稳定性可能在限制昆虫的飞行速度方面发挥了作用。
