Drag measurements over embedded cavities inspired by the microgeometry formed by butterfly scales

The flight performance of micro air vehicles (MAVs) is greatly affected by gust loading and aircraft designers have sought out nature-inspired designs to compensate for this problem in particular. This study serves to quantify the drag on the surface of D. plexippus (Monarch butterfly) wings during the downstroke of flapping flight due to surface drag. By analyzing the scale pattern on the surface of the wing and approximating the flow conditions using solutions to the Navier-Stokes equation, the sizing requirements for testing a model of the geometry in oil are developed. Two models were constructed and the drag on their surfaces is recorded as a function of the Reynolds number based on gap height. The average partial slip velocities and corresponding drag changes are calculated and the implications of a preferential flow direction for flapping flight are discussed.