Background
As an emerging frontier in biomimetic intelligent microsystems, insect-scale flapping-wing micro aerial vehicles (FWMAVs) demonstrate significant application potential due to their exceptional maneuverability and stealth capabilities. The stability control of flapping-wing micro aerial vehicles (FWMAVs) has remained a critical challenge since their inception, with controllability being an essential prerequisite for practical deployment. While autonomous stable flight represents a fundamental requirement for functional utility, achieving this goal in insect-scale FWMAVs presents extraordinary technical hurdles. Like natural hovering systems (e.g., hummingbirds) and rotary-wing counterparts, FWMAVs exhibit inherent dynamic instability during operation. Without closed-loop feedback control, these vehicles typically experience rapid post-takeoff roll instability, rendering sustained hovering unachievable. Although feedback systems can theoretically stabilize flight, their implementation introduces critical tradeoffs: Additional sensors, control circuits, and computational payloads exacerbate the already stringent mass constraints (typically <1g for insect-scale systems), which further increases the difficulty of takeoff and hinders its application in practice.

Research Progress
To improve the self-stabilization performance of flapping-wing micro-aircraft, Prof. Wu Xuezhong and Xiao Dingbang's team at the National University of Defense Technology (NUDT), has proposed a cylindrical air damper with a symmetric structure. This damper generates an isotropic damping effect in the vertical direction (Fig.1A-1C)and is positioned above the FWMAV to create a Tumbler FWMAV (Fig.1D). Based on the X-type direct-drive flapping wing architecture for structural optimization, the team developed a micro-aircraft weighing 204 mg with a wingspan of 68 mm. By enhancing the lift generation mechanism, the maximum lift was increased to 7.6 mN, while maintaining the same driving conditions (Fig.1E). These advancements have laid a crucial foundation for the future integration of passive stabilization systems.

Experimental results reveal that the 241 mg Tumbler FWMAV equipped with this damper exhibits breakthrough stabilization performance: vertical stabilization duration shows 5-fold and 20-fold improvements over conventional cross-type dampers and undamped systems(Fig.1G-1H). The robot remained stable in the height direction after takeoff, with a height deviation of less than 38 mm, and the stability was maintained for over 15 seconds. Regarding horizontal offset motion and attitude angle variations, the offset distance remained within ±100 mm, and the pitch and roll angle fluctuations were less than 15°.
The cylindrical damper experiences resistance perpendicular to the surface when moving horizontally and deflecting, which can make the Tumbler FWMAV remain stable in the height direction, have certain anti-interference capabilities, and resume flight in the face of external interference, the robot regained stable hovering flight within 1.3 seconds after each disturbance.
Wind-resistance disturbance is a critical performance requirement for the development of aerial robots and poses a significant challenge for FWMAV applications. The Tumbler FWMAV that we propose demonstrates a degree of resistance to wind disturbances and can return to stable flight conditions after encountering light gusts (Fig.1I-1K). After the wind disturbance, the height fluctuated by more than 55 mm, and the attitude angle fluctuated between -40° and 20°. The robot returned to a stable hovering state within 0.7 seconds once the gust subsided. It has been verified that the Tumbler FWMAV has a good anti-disturbance self-stabilizing recovery ability under uncontrolled conditions, laying a technical foundation for the application of insect-scale aircraft.

Future Prospects
The collaborative design framework of "structural optimization-aerodynamic enhancement-passive stability control" established in this study offers a novel solution to the technical challenges between load limitations and dynamic stability in micro-aircraft. The successful realization of the Tumbler FWMAV has laid a crucial technical foundation for the practical deployment of insect-scale FWMAVs. In the future, as technology continues to evolve and optimize, this design is expected to be applied to high-precision tasks such as micro unmanned reconnaissance and search and rescue operations. This will address the operational limitations of traditional unmanned aerial vehicles in confined spaces, thereby advancing the use of micro aircraft in more complex environments.

The complete study is accessible via DOI: 10.34133/research.0787