Aerodynamic mechanism of wing-tip partial clap-and-fling in a four-wing flapping-wing micro air vehicle under hovering condition

Efficient lift generation under limited geometric scale and flapping frequency remains a central challenge for hovering flapping-wing micro air vehicles (FWMAVs). Although the clap-and-fling mechanism is known to enhance lift, its full-span implementation in existing two-wing and four-wing configurations often induces strong drag impulses and high energy consumption, while experimental investigations of localized clap-and-fling interactions in realistic three-dimensional four-wing systems remain scarce. In this study, a wing-tip partial clap-and-fling mechanism is experimentally and numerically investigated using a four-wing hovering FWMAV with an adjustable fore–hind wing phase difference. A single-motor-driven four-wing platform with a spatial five-link transmission is developed to realize controllable phase coordination between the fore and hind wings. Force measurements, smoke-flow visualization, and three-dimensional computational fluid dynamics simulations are performed to compare a wing-tip partial clap-and-fling condition (φ = 180°) with a non-interacting baseline (φ = 0°) at Re ≈ 2 × 104. The results show that the localized wing-tip interaction increases the mean lift by 14.3% in experiments and 17.9% in simulations, while inducing only a moderate drag increase. Flow-field analysis reveals that the lift enhancement is primarily driven by a sustained leading-edge vortex system formed through localized gap-jet-induced vortex interaction and delayed trailing-edge vortex shedding, which prolongs the low-pressure region over the wing surface. By confining wing–wing interaction to the outer-span region, the wing-tip partial clap-and-fling mechanism provides an efficient and controllable lift-augmentation pathway, offering new aerodynamic insights for phase-coordinated design of low-Reynolds-number multi-wing FWMAVs.