The Role of Coupled Wing-Body Dynamics on Power Consumption in Butterflies

The annual migration of Monarch butterflies spans over 4000 km. However, the aerodynamic efficiency behind their long-range flight is inadequately understood. To investigate the power consumption associated with the flight of Monarch butterflies, 69 flight segments from 9 butterfly specimens are analyzed. In particular, the coupled wing-body motion and the role of body undulation are analytically modeled and compared to the experimental measurements. The butterfly body is considered as a single mass system and the aerodynamic lift is calculated with a quasi-steady formulation. The two-way coupled dynamic model yields the body undulation amplitude and phase offset which agree well with the experimental measurements. A statistically significant decrease in the mean power coefficient is observed for the coupled wing-body system compared to the decoupled system, which suggests that body undulation reduces power consumption. The estimated energy savings from the coupled wing-body motion could extend the migration flight time by an average of 1.5 hours. This resultant reduction in power predicted with the coupled wing-body model suggests the potential benefits of bioinspired development of long-range micro robotic flyers.