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In this thesis, the structure and aeroelastic design, analysis and optimization of conventional fixed wing is firstly addressed. Based on the study results of conventional fixed wing, the study then focuses on the more complicated aerodynamics and aeroelasticity of flapping wing Micro Air Vehicles (MAV). A Finite Element (FE) model of a composite aircraft wing is firstly used as case study for the aeroelasticity of conventional fixed wing. A MATLAB-NASTRAN interfaced optimization platform is created to explore the optimal design of the wing. Optimizations using the developed platform show that 13% of weight reduction can be achieved when the optimization objective is set to minimize wing weight; and 18.5% of flutter speed increase can be achieved when aeroelastic tailoring of composite laminate layups is carried out. The study results further showed that the most sensitive part of the wing for aeroelastic tailoring is near the engine location, which contributes to the majority of flutter speed increment for optimization. In order to facilitate the structural design of non-circular cross section fuselage of Blended-Wing-Body (BWB) aircraft, an analytical model of 2D non-circular cross section is developed, which provides efficient design and optimization of the fuselage structure without referring to FE models. A case study based on a typical BWB fuselage using the developed model shows that by optimizing the fuselage structure, significant weight saving (17%) can be achieved. In comparison with the conventional fixed wing, insect flapping wings demonstrate more complicated aerodynamic and aeroelastic phenomena. A semi-empirical quasi-steady aerodynamic model is firstly developed to model the unsteady aerodynamic force of flapping wing. Based on this model, the aerodynamic efficiency of a Flapping Wing Rotor (FWR) MAV is investigated. The results show that the optimal wing kinematics of the FWR falls into a narrow range of design parameters governed by the dimensionless Strouhal number (St). Furthermore, the results show that the passive rotational of the FWR converges to an equilibrium state of high aerodynamic efficiency, which is a desirable feature for MAV applications. Next, the aerodynamic lift coefficient and efficiency of the FWR are calculated and compared with typical insect-like flapping wings and rotary wing. The results show that the aerodynamic efficiency of FWR in typical wing kinematics is higher than insect-like flapping wings, but slightly lower than the conventional rotary wing; the FWR aerodynamic lift coefficient (CL) surpassed the other wings significantly. Based on the numerical results, the study then continued to experimental investigations of the FWR. A prototype FWR model of weight 2.6g is mounted on a load cell to measure the instantaneous lift production. The kinematics of the wing is captured using high speed camera. Aeroelastic twist of the wing is measured using the resulting wing motion. Analyses by CFD and the quasi-steady aerodynamic model is then carried out and compared with experimental results. The study revealed that passive twist of the FWR wing due to aeroelastic effects forms desirable variations of wing Angle of Attack (AoA), which improves the aerodynamic performance of FWR. The results of the thesis provide guidance for structural, aerodynamic and aeroelastic design, analysis and optimization of conventional fixed wing, as well as bio-inspired flapping wing MAVs.

For more than two decades researchers have sought to develop a micro aerial vehicle (MAV) capable of discrete remote surveillance and reconnaissance in hazardous environments where no other alternative means of observation exist. While some success has been found in multi-rotor designs such as quadcopters, these vehicles are limited in their flight duration, flight range, robustness, stealth, safety, and agility. Biology offers a source of inspiration in insect flight. Flapping-wing micro aerial vehicles (FWMAVs) have the potential to address the current shortcomings of MAVs. This dissertation approaches the development of FWMAVs by attempting to mimic two major flight components of a particular insect, the hawk moth Manduca sexta (L.). Novel methods are established to design, fabricate and assess the performance of artificial M. sexta forewings and a flapping-wing mechanism inspired by the M. sexta thorax. Results from forewing experiments indicate successful emulation of mass and forewing geometry, including camber. Flexural stiffness values are an order of magnitude greater than desired and suggest that membrane and venation structure material must change. However, lift production analysis reveals that the artificial forewings are capable of generating comparable amounts of force to naturally occurring M. sexta forewings. Kinematic simulations demonstrate advantages to using a Scotch yoke mechanism as opposed to a more traditional crank-slider mechanism to convert continuous rotary motion into oscillatory flapping-wing motion. A multibody dynamic simulation of a Scotch yoke mechanism and passively rotating forewings is developed as a tool to investigate areas of improvement for increased mechanism efficiency such as the addition of energy storing and releasing components and potential changes in mechanism geometry. Empirical performance data on various configurations of a flapping-wing system comprised of a Scotch yoke mechanism and artificial M. sexta forewings is gathered by means of a newly designed testbed capable of precisely measuring lift generation and electrical input power at sampling rates above 7 kHz. The tools and findings presented in this dissertation establish a foundation for future work in designing FWMAVs.

In the last decade, the robotics community has pushed to develop increasingly small, autonomous flapping-wing robotic vehicles for a variety of civilian and military applications. The miniaturization of these vehicles has pushed the boundaries of technology in many areas, including electronics, artificial intelligence, and mechanics; as well as our understanding of biology. In particular, at the insect scale, fabrication, actuation, and flight control of a flapping-wing robot become especially challenging. This thesis addresses these challenges in the context of the “RoboBee” project, which has the goal of creating an autonomous swarm of at-scale robotic bees. A 100mg robot with a 3cm wingspan capable of generating roll, pitch and yaw torques in the range of \(\pm 1\mu Nm\) by using a large, central power actuator to flap the wings and smaller control actuators to steer is presented. A dynamic model is used to predict torque generation capabilities, and custom instrumentation is developed to measure and characterize the vehicle’s control torques. Finally, controlled flight experiments are presented, and the vehicle is capable of maintaining a stable pitch and roll attitude during ascending vertical flight. This is the first successful controlled flight of a truly insect-scale flapping-wing robot.

Development of a new vehicle to fulfill the multi-mode locomotion reconnaissance mission proposed by the Biologically Inspired Robotics Laboratory at Case Western Reserve University is undertaken to improve the in flight handling characteristics of the current design without a loss in functionality. The vehicle is capable of both aerial and terrestrial locomotion through the incorporation of two wheel-legs at the front of a fixed wing micro air vehicle. The new vehicle weighs 7.8 ounces, less than half the weight of the previous design. The maximum dimension of the new vehicle is 25% smaller, with a wingspan of 12 inches. The reduction in weight and size allows a significant reduction in power consumption, with a corresponding increase in flight endurance. The new design has demonstrated its basic flight capabilities during a test flight sequence.

Micro Air Vehicles (MAVs) are small remotely piloted air vehicles that can be flown between or inside of buildings for military or surveillance purposes. This type of flight in the urban environment involves many aerodynamic hazards. The research in this thesis investigates how the aerodynamic interactions between a maneuvering MAV’s wingtip vortex and its distance away from a building wall could affect the MAV’s flight controls. Free flight particle image velocimetry (PIV) testing and wind tunnel testing are used to investigate the aerodynamic interactions between a MAV wingtip vortex and a wall. Elliptical instabilities and a vortex rebound off of the wall are discovered in the PIV testing while the wind tunnel results show a higher aircraft coefficient of lift near the wall. All of these results force the aircraft to experience a rolling motion while flying along a wall. It is imperative that a MAV anticipate this motion and adjust its flight controls in order to accurately fly along a wall and successfully complete its mission in an urban environment.

In this thesis, the aerodynamics of the Quad-Wing Vehicle, a Micro Air Vehicle designed to hover with four flapping wings in a dragonfly-like configuration, is investigated using Computational Fluid Dynamics (CFD), potential flows analysis, and experimental testing. The CFD analysis investigates the kinematics-parameters design space and identifies values of kinematics parameters that maximize the vertical force production in hovering mode while minimizing the aerodynamic power requirement. It also investigates other important considerations, such as the effect of scaling, multi-wing interactions, and comparison with other flapping configurations. In the potential flows analysis, an unsteady 2D panel code is developed and compared with CFD for a broad range of hovering-flight simulations. The results show that, with further development, panel codes may be useful to designers of hovering flapping MAVs because of their time-saving potential compared to CFD. The experimental testing focuses on isolating the aerodynamic forces from other measured forces on a benchtop flapping device, and the findings of the experimental study will be useful for later researchers using experimental methods to study flapping MAV aerodynamics.

Ducted fan vehicles possess a superior ability to maximize payload capacity while minimizing vehicle size. Their ability to both hover and fly at high speed is a key advantage for information-gathering missions, particularly when close proximity to a target is essential. However, the ducted fan's aerodynamic characteristics pose difficulties for stable vehicle flight and therefore require complex control algorithms. In particular, they exhibit a large nose-up pitching moment during wind gusts and when transitioning from hover to forward flight. Understanding ducted fan aerodynamic behavior and how it can be altered through flow control techniques are the two prime objectives of this work. This dissertation provides a new paradigm for modeling the ducted fan's nonlinear behavior and new methods for changing the duct aerodynamics using active flow control. Steady and piezoelectric synthetic jet blowing are employed in the flow control concepts and are compared. The new aerodynamic model captures the nonlinear characteristics of the force, moment, and power data for a ducted fan, while representing these terms in a set of simple equations. The model attains excellent agreement with current and legacy experimental data using twelve non-dimensional constants. Synthetic jet actuators (SJA) have potential for use in flow control applications in UAVs with limited size, weight, and power budgets. Piezoelectric SJAs for a ducted fan vehicle were developed through two rounds of experimental designs. The final SJA design attained peak jet velocities in the range of 225 ft/sec (69 m/s) for a 0.03â x 0.80â rectangular slot. To reduce the magnitude of the nose-up pitching moment in cross-winds, two flow control concepts were explored: flow separation control at the duct lip, and flow turning at the duct trailing edge using a CoandÄ surface. Both concepts were experimentally proven to be successful. Synthetic jets and steady jets were capable of modifying the ducted fan flow to reduce pitching moment, but some cases required high values of steady blowing to create significant responses. Triggering leading edge separation on the duct lip was one application where synthetic jets showed comparable performance to steady jets operating at a blowing coefficient an order of magnitude higher.

Presented is a high-fidelity, computational study of transitional flow over an airfoil as it is pitched up from an initial zero incidence to 40 degrees at a nominally constant pitch rate, held, and then returned in a similar manner. The Reynolds numbers were chosen to bracket the regions of laminar and transitional flows applicable to prototypical micro air vehicle conditions, 5000 < Re < 40,000. A high-order, implicit large eddy simulation technique was employed to show the degree of fidelity required to capture these highly transitional flows. Two-dimensional analyses examining the effects of Reynolds number and pitch rate were conducted and a discussion is provided. Additionally, the impact of transition and spanwise extent on the flowfield and force histories were explored through three-dimensional, spanwise periodic simulations. These simulations were shown qualitatively to compare extremely well with available experimental observations.

Weight, aerodynamic profile, and strength are considered in the design of a terrestrial drive train for a small air vehicle. Several drive trains were developed and their performance characteristics compared in order to show a progression in their designs. Each iteration contained minor improvements, approaching the goal of a durable terrestrial drive train for a small air vehicle. These drive trains were analyzed in the Case Western Reserve University low-speed wind tunnel for their influence on the performance of the aircraft. The change in lift produced by the aircraft’s airfoil ranges from -1.0% to -4.5%. The drive trains were also tested for their ability to withstand the shock and reduce the impact of landing. Spring steel wire wheel-legs are found to reduce the peak deceleration by 15.8%. The results identify one drive train that meets the performance goals and is suitable for general use in this scale application.

Research and prototyping of a fuel cell stack system for micro aerial vehicles (MAVs) was conducted by Virginia Tech in collaboration with Luna Innovations, Inc, in an effort to replace the lithium battery technology currently powering these devices. Investigation of planar proton exchange membrane (PEM) and direct methanol (DM) fuel cells has shown that these sources of power are viable alternatives to batteries for electronics, computers, and automobiles. However, recent investigation about the use of microtubular fuel cells (MTFCs) suggests that, due to their geometry and active surface areas, they may be more effective as a power source where size is an issue. This research focuses on hydrogen MTFCs and how their size and construction within a stack affects the power output supplied to a MAV, a small unmanned aircraft used by the military for reconnaissance and other purposes. In order to conduct this research effectively, a prototype of a fuel cell stack was constructed given the best cell characteristics investigated, and the overall power generation system to be implemented within the MAV was modeled using a computer simulation program. The results from computer modeling indicate that the MTFC stack system and its balance of system components can eliminate the need for any batteries in the MAV while effectively supplying the power necessary for its operation. The results from the model indicate that a hydrogen storage tank, given that it uses sodium borohydride (NaBH4), can fit inside the fuselage volume of the baseline MAV considered. Results from the computer model also indicate that between 30 and 60 MTFCs are needed to power a MAV for a mission time of one hour to ninety minutes, depending on the operating conditions. In addition, the testing conducted on the MTFCs for the stack prototype has shown power densities of 1.0, an improvement of three orders of magnitude compared to the initial MTFCs fabricated for this project. Thanks to the results of MTFC testing paired with computer modeling and prototype fabrication, a MTFC stack system may be possible for implementation within an MAV in the foreseeable future.

Micro air vehicles (MAVs) are small remote controlled aircraft used by military personnel for reconnaissance and are currently powered by batteries. The MAVs rely on the battery for propulsion, navigation, and reconnaissance equipment. The thrust of this research is to develop a fuel cell system capable of higher power densities, higher power to weight ratios, and increased overall power output than the batteries in use today. To this end, a feasibility study is first conducted to determine if fuel cells could be used to replace batteries as the MAV power source and what fuel cell configurations would show the best performance. Hydrogen, methanol, and formic acid fuel cells are considered, using a conventional flat-plate design and a novel micro-tubular design. Several micro-tubular fuel cells (MTFCs) are tested to show that these cells are a possibility for power production in MAVs. Those tested are developed and improved in collaboration between Luna Innovations, Inc. and the Center for Energy Systems Research at Virginia Tech and then manufactured by Luna Innovations, Inc. Also, an isothermal, lumped-parameter (LP) model for MTFCs is developed to predict behavior. The use of this LP model aids in understanding the dominant losses of the cell and ways of improving cell performance. Results from the feasibility study indicate that by using methanol powered MTFCs a 50% increase in overall energy output is possible, while also decreasing the mass of the power production system. Through testing and an iterative design process, an increase of three orders of magnitude of the maximum power production of the MTFCs constructed by Luna Innovations, Inc., has been realized. Results of the LP MTFC model are compared with the experimental results from the MTFC testing and tubular cells from the literature.

A transducer consisting of multiple layers of ionic polymer material is developed for applications in sensing, actuation, and control. The transducer consists of two to four individual layers each approximately 200 microns thick. The transducers are connected in parallel to minimize the electric field requirements for actuation. The tradeoff in deflection and force can be controlled by controlling the mechanical constraint at the interface. Packaging the transducer in an outer coating produces a hard constraint between layers and reduces the deflection with a force that increases linearly with the number of layers. This configuration also increases the bandwidth of the transducer. Removing the outer packaging produces an actuator that maintains the deflection of a single layer but has an increased force output. This is obtained by allowing the layers to slide relative to one another during bending. A Finite Element Analysis (FEA) method capable of modeling the structure of the multilayer transducers is developped. It is used to model the interfacial friction in multilayer transducers. Experiments on transducers with one to three layers are performed and the results are compared to Newbury's equivalent circuit model, which was modified to accommodate the multilayer polymers. The modification was performed on four different boundary conditions, two electrical the series and the parallel connection, and two mechanical the zero interfacial friction and the zero slip on the interface. Results demonstrate that the largest obstacle to obtaining good performance is water transport between the individual layers. Water crossover produces a near short circuit electrical condition and produces feedthrough between actuation layers and sensing layers. Electrical feedthrough due to water crossover eliminates the ability to produce a transducer that has combined sensing and actuation properties. Eliminating water crossover through good insulation enables the development of a small (5 mm x 30 mm) transducer that has sensing and actuation bandwidth on the order of 100 Hz. Due to the mechanical similarities of ionic transducers to biological muscles and their large flapping displacement capabilities we are studying the possibility of their use in flapping Micro Air Vehicle (MAV) application, as engines, controllers and sensors. The FEA modeling technique capable is used to design two ionic polymers actuated flapping wings.