Aerodynamic Characteristics and Static-Restoring Tendencies of a Hopea hainanensis-Inspired Double-Winged Samara at Different Attitudes

Low-Reynolds-number micro aerial vehicles and lightweight deployment systems require aerodynamic configurations that provide vertical support and favorable passive responses to attitude disturbances. Winged seeds delay descent through autorotation, wing curvature, and mass distribution, offering a natural model for such designs. A three-dimensional model of a Hopea hainanensis-inspired double-winged samara was developed, and steady multiple-reference-frame (MRF) simulations were performed at seven rotating attitudes (−45, −22.5, −10, 0, 10, 22.5, and 45 degrees) and a nonrotating 90-degree reference. Aerodynamic forces, moments, surface pressure distributions, and streamline structures were compared. Negative deflections maintained relatively high vertical support, whereas the vertical force decreased progressively with positive deflection. The −45-degree attitude combined strong vertical support, limited lateral offset, and a restoring moment increment, producing the highest equal-weight score among the rotating cases. The pitching moment response varied nonlinearly with disturbance amplitude, and the static-restoring tendency became more evident over moderate and large deflections. Surface pressure distributions, streamline structures, and the equivalent aerodynamic line of action showed that redistribution of wing loading and migration of the effective moment arm jointly governed the force and moment variations. These results characterize the quasi-steady aerodynamic response under prescribed rotation and provide guidance for the passive aerodynamic design of low-Reynolds-number aerial vehicles and lightweight deployment systems.