Methods Used to Evaluate the Hawkmoth (Manduca Sexta) as a Flapping-Wing Micro Air Vehicle

Examining a biological flapping-flight mechanism as a mechanical system provides valuable insight related to the development and construction of Flapping-Wing Micro Air Vehicles (FWMAVs). Insects provide excellent candidates for this reverse-engineering, and one species in particular, the hawkmoth Manduca sexta, stands out as an exceptional model. Engineers with FWMAV aspirations can benefit greatly from knowledge of M.sexta\u27s advanced yet deceptively simple flight mechanism. Avenues for investigating this mechanism include finite element modeling, nanoindentation for material properties, and mechanical power output calculations or measurement. This paper presents these concepts and reviews existing literature to provide a platform for ongoing FWMAV research and design

Micro-Scale Flapping Wings for the Advancement of Flying MEMS

This research effort presents conceptual micro scale air vehicles whose total dimensions are less than one millimeter. The initial effort was to advance the understanding of micro aerial vehicles at sub-millimeter dimensions by fabricating and testing micro scale flapping wings. Fabrication was accomplished using a surface micromachining process called PolyMUMPs™. Both rigid mechanical structures and biomimetic devices were designed and fabricated as part of this effort. The rigid mechanical structures focused on out of plane deflections with solid connections and assembling a multiple hinge wing structure through the aid of residual stress. These devices were actuated by double hot arm thermal actuators. The biomimetic structures derived from three different insect wings to include; the dragonfly, house fly, and butterfly were selected based off of an attribute that each insect possesses in nature. The dragonfly was chosen for its high maneuverability and hovering capabilities. The house fly wing was chosen because of its durability and the butterfly wing was chosen because of its flexibility. The fabricated wings utilize a thermal bimorph structure consisting of polysilicon and gold which allows device actuation through joule heating. The released micro wings had an initial upward deflection due to residual stress between the gold and polysilicon material layers. Joule heating, from an applied bias, forces the wing to deflect downward due to the coefficient of thermal expansion mismatch between the material layers. Each fabricated bio-wing structure was tested for deflection range as well as operating frequency. From the experimental testing of the micro scale flapping bio-wings, aerodynamic values were calculated to include; aspect ratio, reduced frequency in a hover, Reynolds number of a hovering device, drag force, and gravitational force. The research verified insect based wings on the micro scale are capable of producing the desired flapping motion

Laser Dot Projection Photogrammetry and Force Balance Measurement Techniques for Flapping Wing Micro Air Vehicles

The purpose of this research was to develop testing methods capable of analyzing the performance of a miniature flapping-wing mechanism that can later be adapted to a flapping wing micro air vehicle (MAV). A previously designed and built flapping only mechanism was used for testing, while a previously designed flapping and pitch mechanism was fabricated utilizing an Objet Eden 500V 3-dimensional printer and its operation demonstrated. The flapping mechanism was mounted on a six component force balance. Force and moment data were collected for a variety of wing sets at different flapping frequencies. The testing was conducted using wings composed of aluminum tubing and/or stainless steel wire for frame material, and thin latex as membrane material. The normal and axial force averages were taken with the force balance and compared. The axial force measurement was verified using an air bearing table and a load cell as a secondary means of measurement. Time accurate force data was also taken. A non-intrusive photogrammetry method using laser dot projection was developed allowing for the shape of the wing during flapping to be measured. The result was that approximately 98 data points representing wing shape and orientation were collected at 1000 Hz. Comparisons were made between laser dot projection photogrammetry and a more a traditional method using potentially intrusive marked targets for photogrammetry, with good correspondence. Differences in force data were then analyzed with the insight gained regarding wing shape. This research demonstrates the capability to study the forces and moments involved in flapping flight as well as shape changing of wings during flapping flight

Finite Element Analysis of a Highly Flexible Flapping Wing

Small unmanned aerial systems are being designed to emulate the flapping kinematics of insects and birds which show superior control in slow speed regimes compared to fixed wing or rotorcraft aircraft. The flight of flapping wing vehicles is characterized by aeroelastic effects. Most research has been dedicated towards understanding the aerodynamic side of the aeroelastic response with minimal effort spent towards validating the structural response. A finite element model of a wing from a commercial flapping wing vehicle was created to validate the structural response. Vacuum testing allowed the isolation of the inertial response for a direct comparison to the finite element model. Wing tip displacement amplitude was matched to within 8%. The membrane kinematics of the finite element model were similar to the vacuum test article but overall membrane deflections predicted by the finite element solver were less than observed deflections seen in the vacuum. This research shows that significant focus must be placed on validating the structural side of a flexible structure in order to correctly model the complete aeroelastic response

Reynolds Number Effects on Thrust Coefficients and PIV for Flapping Wing Micro Air Vehicles

For the last several years the Air Force Institute of Technology (AFIT) has conducted research in aerodynamics for flapping wing micro air vehicles (MAVs). The focus of this research was to augment this effort by measuring thrust, velocity, and torque in tanks of water and glycerin using a scale and a reaction torque cell. The results for different flapping mechanisms are compared to a rotating propeller with the goal of elucidating the design trade space between rotorcraft and flapping wings at Reynolds numbers less than 100,000. In addition, flow visualization and quantitative velocity data were captured in the wake of the flapping wing. One flapping-wing mechanism was designed to incorporate a coupled 4-bar planar and 4-bar spatial linkage system to prescribe motion which included both flapping and rotation. Thrust and velocity data were found to follow the general trends for a flapping wing with passive rotation. The passive rotation angle setting was found to alter thrust and velocity patterns

The Evaluation of a Biologically Inspired Engineered MAV Wing compared to the Manduca Sexta Wing under Simulated Flapping Conditions

In recent years, researchers have expressed a vested interest in the concepts surrounding flapping wing micro air vehicles (FWMAVs) that are capable of both range and complex maneuvering. Most research in this arena has found itself concentrated on topics such as flapping dynamics and the associated fluid-structure interactions inherent in the motion; however there still remain a myriad of questions concerning the structural qualities intrinsic to the wings themselves. Using nature as the template for design, FWMAV wings were constructed using carbon fiber and Kapton and tested under simplified flapping conditions by analyzing ‘frozen’ digital images of the deformed wing by methods of photogrammetry. This flapping motion was achieved via the design and construction of a flapper that emulates several of the kinematic features that can be seen in naturally occurring flyers. The response to this motion was then compared to the inspiring specimen\u27s wings, the North American Hawkmoth (Manduca Sexta), under the same flapping conditions in order to identify some of the key features that nature has deemed necessary for successful flight. Results showed that though the engineered wing emulated several of the structural characteristics of the biological wing; it still required some design modifications to compare more closely to the biological wing in the flapping motion. Additionally, this research also speaks to the effects of air on the biological wing

Investigation of Aerodynamics of Flapping Wings for Miro Air Vehicle Applications

A coupled CFD-CSD solver was used to simulate the aerodynamics of a flexible flapping wing. The CFD solver is a compressible RANS (Reynolds Averaged Navier Stokes) solver. Multibody dynamics solver `MBDyn', was used as the structural solver to take into account non linear shell straining, making it possible to analyze low aspect ratio wings with large deformations. Validation of the two codes was carried out independently. The solvers were then coupled using python and validated against prior experiments and analysis on spanwise and chordwise flexible wings. As realistic MAV wings are extremely flexible and lightweight, under the effect of high inertial and aerodynamic forces, they undergo large non linear deformations over a flap cycle. However, there is a dearth of experimental data on well characterized flapping wings (with known structural and mass properties) at MAV-scale Reynolds numbers. Systematic experiments were carried out on rigid and flexible flapping wings in an open jet wind tunnel and forces were measured using a test bed. Pure flapping of rigid wings did not generate sufficient propulsive force and may not be a viable configuration. Passive pitching of rigid wing generated both, target vertical and propulsive forces. Dynamic wing twist was then incorporated using flexible wings. A flexible wing was fabricated using a combination of unidirectional carbon fiber strips (chordwise ribs), carbon rod (leading edge spar) and mylar film (membrane). Structural model of the wing (combination of beam and shell elements) was developed and then coupled to the CFD model. CFD-CSD analysis of flexible wing was carried out and good correlation was obtained for all the configurations. This comprehensive experimental data set can also be used to validate other aeroelastic analyses of the future. Further, the analysis was used to gain more insights into flow physics. It was observed that as a result of flexibility, by taking advantage of unsteady flow features, a lighter, simpler mechanism could be used to produce larger forces than a rigid wing. The validated, comprehensive analysis developed in this work may serve as a design tool for deciding configurations and wing kinematics of next generation MAVs

Investigation into Reynolds Number Effects on a Biomimetic Flapping Wing

This research investigated the behavior of a Manduca sexta inspired biomimetic wing as a function of Reynolds number by measuring the aerodynamic forces produced by varying the characteristic wing length and testing at air densities from atmospheric to near vacuum. A six degree of freedom balance was used to measure forces and moments, while high speed cameras were used to measure wing stroke angle. An in-house created graphical user interface was used to vary the voltage of the drive signal sent to the piezoelectric actuator which determined the wing stroke angle. The Air Force Institute of Technology baseline 50 mm wing was compared to wings manufactured with 55, 60, 65, and 70 mm spans, while maintaining a constant aspect ratio. Tests were conducted in a vacuum chamber at air densities between 0.5% and 100% of atmospheric pressure. Increasing the wingspan increased the wing’s weight, which reduced the first natural frequency; and did not result in an increase in vertical force over the baseline 50 mm wing. However, if the decrease in natural frequency corresponding to the increased wing span was counteracted by increasing the thickness of the joint material in the linkage mechanism, vertical force production increased over the baseline wing planform. Of the wings built with the more robust flapping mechanism, the 55 mm wing span produced 95% more vertical force at a 26% higher flapping frequency, while the 70 mm wing span produced 165% more vertical force at a 10% lower frequency than the Air Force Institute of Technology baseline wing. Negligible forces and moments were measured at vacuum, where the wing exhibited predominantly inertial motion, revealing flight forces measured in atmosphere are almost wholly limited to interaction with the surrounding air. Lastly, there was a rough correlation between Reynolds number and vertical force, indicating Reynolds number is a useful modelling parameter to predict lift and corresponding aerodynamic coefficients for a specific wing design

Design and Control of Flapping Wing Micro Air Vehicles

Flapping wing Micro Air Vehicles (MAVs) continues to be a growing field, with ongoing research into unsteady, low Re aerodynamics, micro-fabrication, and fluid-structure interaction. However, research into flapping wing control of such MAVs continues to lag. Existing research uniformly consists of proposed control laws that are validated by computer simulations of quasi-steady blade-element formulae. Such simulations use numerous assumptions and cannot be trusted to fully describe the flow physics. Instead, such control laws must be validated on hardware. Here, a novel control technique is proposed called Bi-harmonic Amplitude and Bias Modulation (BABM) which can generate forces and moments in 5 vehicle degrees of freedom with only two actuators. Several MAV prototypes were designed and manufactured with independently controllable wings capable of prescribing arbitrary wing trajectories. The forces and moments generated by a MAV utilizing the BABM control technique were measured on a 6-component balance. These experiments verified that a prototype can generate uncoupled forces and moments for motion in five degrees of freedom when using the BABM control technique, and that these forces can be approximated by quasi-steady blade-element formulae. Finally, the prototype performed preliminary controlled flight in constrained motion experiments, further demonstrating the feasibility of BABM