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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.NOMENCLATURE ω i = i th natural frequency INTRODUCTIONOver the course of last two decades, the demand for unmanned intelligence, surveillance and reconnaissance (ISR) assets has grown at an extraordinary pace. Physical separation of an aircraft and its human operator has provided unprecedented loiter times, range, low-cost compared to equivalent manned systems, and pilot safety. To supplement future ISR capabilities, many have proposed "micro" air vehicles (MAVs) that would revolutionize the field of remote sensing with their low cost, extreme maneuverability, and inconspicuous operation [11]. If successfully manufactured, the MAV of the future will be capable of a multitude of close-quarters reconnaissance tasks, ranging from battlefield operations to safety inspections of civilian structures. Table 1 outlines the Defense Advanced Research Projects Agency's (DARPA) vision for the MAV [11].

To properly model the structural dynamics of the forewing of the Manduca sexta species, it is critical that the material and structural properties of the biological specimen be understood. This paper presents the results of a morphological study that has been conducted to identify the material and structural properties of a sample of male and female Manduca sexta specimens. The average mass, area, shape, size and camber of the wing were evaluated using novel measurement techniques. Further emphasis is placed on studying the critical substructures of the wing: venation and membrane. The venation cross section is measured using detailed pathological techniques over the entire venation of the wing. The elastic modulus of the leading edge veins is experimentally determined using advanced non-contact structural dynamic techniques. The membrane elastic modulus is randomly sampled over the entire wing to determine global material properties for the membrane using nanoindentation. The data gathered from this morphological study form the basis for the replication of future finite element structural models and engineered biomimetic wings for use with flapping wing micro air vehicles.

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Historically, the approach in material selection was to find the proper material that serves a specific application. Recently, a new approach is implemented such that materials are being architected and topologically tailored to deliver a specific functionality. Periodic cellular materials are increasingly gaining interest due to their tunable structure-related properties. However, the concept of structure–property relationship is not fully employed due to limitations in manufacturing capabilities. Nowadays, additive manufacturing (AM) techniques are facilitating the fabrication of complex structures with high control over the topology. In this work, the mechanical properties of additively manufactured periodic metallic cellular materials are investigated. The presented cellular materials comprise a shell-like topology based on the mathematically known triply periodic minimal surfaces (TPMS). Maraging steel samples with different topologies and relative densities have been fabricated using the powder bed fusion selective laser sintering (SLS) technique, and three-dimensional printing quality was assessed by means of electron microscopy. Samples were tested in compression and the compressive mechanical properties have been deduced. Effects of changing layer thickness and postprocessing such as heat treatment are discussed. Results showed that the diamond TPMS lattice has shown superior mechanical properties among the examined topologies.

An investigation was conducted assessing the feasibility of reproducing the biological flapping motion of the wings of the hawkmoth, Manduca sexta (M.sexta) by artificially stimulating the flight muscles for Micro Air Vehicle research. Electromyographical signals were collected using bipolar intramuscular fine wire electrodes inserted into the primary flight muscles, the dorsal longitudinal and dorsal ventral muscles, of the adult M.sexta. These signals were recorded and associated with wing movement using high speed video. The signals were reapplied into the corresponding muscle groups with the intention of reproducing similar flapping motion. A series of impulse signals were also directed into the primary flight muscles as a means of observing muscle response through measured forewing angles. This study pioneered electromyographic research on M.sexta at the Air Force Institute of Technology with tests conducted with fine wire electrodes. Through this process, the research showed the deformational structural changes that take place when a wing is removed from an insect and proved that muscular stimulation is a viable method for generating wing movement. This study also assisted in developing an understanding related to the role that a thorax-like fuselage could play in future micro aircraft designs. This study has shown that partial neuromuscular control of the primary flight muscles of M.sexta is possible with electrical stimulants which could be used to directly control insect flight.

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