Abstract
Flying animals such as insects display great flight performances with high stability and maneuverability even under unpredictable disturbances in natural and man-made environments. Unlike man-made mechanical systems like a drone, insects can achieve various flapping motions through their flexible musculoskeletal systems. However, it remains poorly understood whether flexibility affects flight performances or not. Here, we conducted an experimental study on the effects of the flexibility associated with the flapping mechanisms on aerodynamic performance with a flexible flapping mechanism (FFM) inspired by the flexible musculoskeletal system of insects. Based on wing kinematic and force measurements, we found an appropriate combination of the flexible components could improve the aerodynamic efficiency by increasing the wingbeat amplitude. Results of the wind tunnel experiments suggested that, through some passive adjustment of the wing kinematics in concert with the flexible mechanism, the disturbance-induced effects could be suppressed. Therefore, the flight stability under the disturbances is improved. While the FFM with the most rigid spring was least efficient in the static experiments, the model was most robust against the wind within the range of the study. Our results, particularly regarding the trade-off between the efficiency and the robustness, point out the importance of the passive response of the flapping mechanisms, which may provide a functional biomimetic design for the flapping micro air vehicles (MAVs) capable of achieving high efficiency and stability.
Highlights
Unmanned aerial vehicles (UAV), known as drones, are widely used for various missions such as filming, surveillance, and transportation (Floreano and Wood, 2015; Liu et al, 2016)
Kinematic and Force Measurements In this study, we have evaluated the flight efficiency and robustness by fixing the flexible flapping mechanism (FFM) via force balance
The aerodynamic performance of FFM with various torsion spring stiffnesses and frequencies was evaluated in terms of the wing kinematics, the lift, and the efficiency
Summary
Unmanned aerial vehicles (UAV), known as drones, are widely used for various missions such as filming, surveillance, and transportation (Floreano and Wood, 2015; Liu et al, 2016). The sophisticated aeronautical theory for the aircraft cannot be applied directly to the UAVs. The aerodynamics at the low-Reynolds number regime is fundamentally different from the large-scale aircraft. The aerodynamics at the low-Reynolds number regime is fundamentally different from the large-scale aircraft Animals such as insects and birds inhabit where drones are expected to operate. Their flight apparatus is thought to adapt to the flight in the unpredictable aerial environment through natural selection. The bio-inspired strategy, such as flapping-wings, can greatly enhance the stability and reliability of conventional UAVs. For example, computational studies suggested that the unsteady separated flows on the flappingwings can reduce the force fluctuation caused by the relatively large-scale turbulent flows (Engels et al, 2016; Ravi et al, 2016). The flapping-wings are, beneficial to enhance the stability of the UAVs
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