Experimental Measurements of the Wing Deformation and Force Production of Real and Bioinspired Artificial Monarch Butterfly Wings

The annual migration of monarch butterflies can span over 4000 kilometers, the longest among insects. Little is known about how the monarchs are capable of this extended flight. This study is motivated by the hypothesis that the monarchs’ flapping-wing flight is enhanced by fluid-structure interactions of their relatively large wings. However, the effects of the wing flexibility on the aerodynamic force generation of the large, slowly flapping butterfly wings are inadequately understood. The main objective of this study is to examine the aeroelastic response of a real butterfly wing at a flapping amplitude around the free flight flapping amplitude of monarchs as a function of varying flapping frequencies. In this paper, the performance of a real monarch butterfly wing was tested by measuring the wing motion and lift at a flapping amplitude of 55 deg and a comparison was made to a 20 deg amplitude motion. Both cases produced a peak lift at 10.3 Hz, approximately the flapping frequency of a real monarch butterfly. For the 55 deg case, the maximum force produced was 8.4 mN, over double that of the 20 deg case, 3.8 mN. This is sufficient to overcome a butterfly’s weight of 5 mN. For both cases, the pitch amplitude increased linearly as the frequency increased with the pitch amplitude at the peak lift being 15.4 deg and 7.5 deg for the 55 deg case and 20 deg case, respectively.