Actuator disk model and span efficiency of flapping flight in bats based on time-resolved PIV measurements

All animals flap their wings in powered flight to provide both lift and thrust, yet few human-engineered designs do so. When combined with flexible wing surfaces, the resulting unsteady fluid flows and interactions in flapping flight can be complex to describe, understand, and model. Here, a simple modified actuator disk is used in a quasi-steady description of the net aerodynamic lift forces on several species of bat whose wakes are measured with time-resolved PIV. The model appears to capture the time-averaged and instantaneous lift forces on the wings and body, and could be used as basis for comparing flapping flight efficiency of different animal species and micro air vehicle designs.