Flapping wing rotorcraft benefit from the ceiling effect

Small, flapping wing robots mimic the powerful lift and flight dynamics employed by birds, bats, and bugs. More conventional craft like helicopters and prop airplanes employ rotor blades to efficiently generate lift. Flapping wing rotorcraft (FWRs) combine the benefits of both strategies using wings arranged around a central mast capable of active vertical flapping and passive rotating.

FWRs can achieve higher flight efficiency with their unique configuration but, like many small aircraft are still energy demanding. Traditional rotorcraft maximize lift by flying close to a flat surface. The so-called ceiling effect can improve energy-efficiency, but the complex dynamics introduced by the flapping wings may diminish these gains. Liu et al. numerically simulated and experimentally validated the benefits of the ceiling effect for FWRs.

“By actively flapping and passively rotating, FWRs enable the wing surface to work at an optimal angle, where all aerodynamic forces are projected vertically against gravity,” said author Zhan Tu. “This design feature distinguishes FWRs from traditional flapping wings, resulting in improved efficiency performance. In contrast to rotary wings, FWRs still inherit and benefit from the unsteady flow characteristics of their reciprocating motion, leading to higher lift coefficients.”

The team found that close to the ceiling, around 80mm away, the FWRs lift increases by 10 percent. However, at distances over 120mm, there is little difference in lift.

“There are many scenarios in urban environments where the ceiling effect can be applied, such as under bridges or overpasses to detect cracks in building structures,” Tu said. “There are also ceiling-like surfaces in the wild environment, like rocks or tree trunks.”

Future work will examine irregular, natural ceilings and wing motion parameters to optimize efficiency.

Source: “Ceiling effect of flapping wing rotorcrafts to enable energy-efficient perching,” by Fangyuan Liu, Song Li, Xin Dong, Jinwu Xiang, Daochun Li, and Zhan Tu, Physics of Fluids (2024). The article can be accessed at https://doi.org/10.1063/5.0188673 .