A Structural Dynamic Analysis of a Manduca Sexta Forewing

Micro air vehicles (MAVs) are intended for future intelligence, surveillance, and reconnaissance use. To adequately fulfill a clandestine capacity, MAVs must operate in close proximity to their intended target without eliciting counter-observation. This objective, along with DARPA's constraint of a sub-15 centimeter span, requires future MAVs to mimic insect appearance and flight characteristics. This paper describes an experimental method for conducting a structural analysis of a Manduca Sexta (hawkmoth) forewing. Geometry is captured via computed tomography (CT), and frequency data is collected using laser vibrometry in air and vacuum. A finite element (FE) model is constructed using quadratic beams and general-purpose shell elements, and an eigenanalysis is conducted. A preliminary verification of the FE model is carried out to ensure the Manduca Sexta forewing is adequately characterized, providing a basis for future fluid-structural interaction computations. Included is a study regarding the aeroelastic effects on flapping-wing insect flight, and an analysis of the structural dynamic anomalies of conventional, flat, semi-rigid flapping wings. Experimental tests revealed the first three modes of a clamped Manduca Sexta wing in vacuum are 86 Hz, 106 Hz, and 155 Hz; tests in air reveal a frequency shift of 26.5% from vacuum, indicating a possible aeroelastic contribution to frequency response. The finite element model produced first three modes of 84.6 Hz, 106.1 Hz, and 317.7 Hz, indicating that the model is limited to the second wing mode and lower frequencies. Possible sources of error include poor geometric modeling due to low CT resolution, inadequate modeling of camber, and inaccurate estimation of material properties.