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Instantaneous force and structural deformation experiments were performed on a flexible, structurally characterized, low-aspect-ratio representative flapping wing. A six-component force balance was...

A computational study is conducted on thin flat plates to simulate flows of Reynolds numbers at 104 to provide understanding and guidance for micro air vehicles and other low-Reynolds-number airfoi...

The paper discusses the development of a nonlinear aeroelastic coupled trim model of a twin cyclocopter in forward flight. The twin cyclocopter consists of two cycloidal rotors as main thrusters an...

A large variety of gusts that develop in the atmospheric boundary layer affect aerial vehicles. This study, performed in water tow tanks, compares the response of a flat plate wing to transverse ve...

In this paper, aiming to drive the unmanned aerial vehicle (UAV) to the optimal position of the vertical plane in the close formation flight, a control method that is based on extended state observ...

Investigated and revealed are new insights into the individual, decoupled effects of induced camber and spanwise bending on the lift, drag, and endurance for an optimum flexibility membrane-and-fra...

An enhanced nonlinear aeroelastic-coupled-flight dynamics framework that enables the investigation of propeller aerodynamics and inertial effects on the response of a very flexible aircraft is pres...

At low Reynolds numbers, revolving wings become less efficient in generating lift for hovering flight due to the increasing adverse viscous effects. Flying insects use reciprocating revolving wings...

Experimental and computational study of flapping-wing insect at low Reynolds number is conducted in this work. The paper is broadly divided into two sections: experiments and computational fluid dy...

Demand is growing for unmanned air vehicles (UAVs) with greater autonomy, including the ability to navigate without GPS information, such as indoors. In this work, a novel visual odometry algorithm...

The solution to the simultaneous stabilization problem of a finite set of MIMO unstable plants considered in this Note is based on the frequency-shaped central plant and its sufficiency condition for simultaneous stabilization. The novel method proposed in this Note to acquire the frequency-shaped central plant from a finite set of MIMO unstable plants used v-gap metric between the plants, the frequency-shaping of the plants that used the pre- and post-compensators, and the robust stabilization theory. An optimization problem is formulated to obtain the pre- and post-compensators that reduce the minimum among the maximum v-gap metrics of all the frequency-shaped plants as well as induce required frequency characteristics on all the plants in the set without instigating pole-zero cancellation with any plants in the set. A novel iterative algorithm is developed to solve this optimization problem to attain the compensators. The plant with a maximum v-gap metric that is the minimum among the maximum v-gap metrics of all the frequency-shaped plants is identified as the frequency-shaped central plant. Also, the sufficiency condition of the frequency-shaped central plant is the most suitable sufficiency condition for the simultaneous stabilization. The capability of the iterative algorithm presented in this Note is demonstrated by a realistic design example. For that, the simultaneous stabilization of the finite set of MIMO unstable plants of the NAV is accomplished. The limitation of the method presented in this Note is that it is only applicable to the plants that have similar frequency characteristics. The present work is supported by National Programme for Micro Air Vehicle program. The authors thank Aeronautics Research and Development Board, New Delhi, for partial funding.

Because of the highly integrated nature of their dynamics, flapping-wing micro air vehicles exhibit significant coupling, including interactions between aeroelastic wing behavior, actuator dynamics...

The objective of this paper is to understand roles of abdominal motion in the pitch stability of flapping flights of butterflies numerically, and a two-dimensional butterfly model has thoracic pitc...

The performance and effectiveness of serpentine dielectric barrier discharge plasma actuators as hingeless high-lift devices on a three-dimensional airplane model were investigated. Attempts were m...

The current work is concerned with longitudinal trajectory tracking control and simulation of a flapping-wing micro air vehicle. For the purpose of accurate simulation studies, a nonlinear and time...

A computational study has been conducted on various airfoils to simulate flows at Reynolds numbers (Re) primarily between 104 and 105 to provide understanding and guidance for MAV and other low-Rey...

The increasing usage of low-Reynolds-number (10,000–100,000 tip Reynolds number) scale quadrotors for civilian and military applications provides the impetus for the development of reliable design ...

Flapping rotary wing is a novel aerodynamic configuration proposed in recent years for micro air vehicles. To understand the aerodynamic characteristics of this wing layout, a computational fluid d...

An optical tracking facility was used to record the free flight of the Monarch butterfly for a large number of sequential flaps. The system automatically tracked reflective markers, which were modi...

The main objective of this paper is to provide a rigorous coupling between body flight dynamics and flow dynamics (unsteady aerodynamics) in hovering of insects and flapping-wing micro air vehicles...

Flapping-wing micro air vehicles are not confined to undergoing the normal-hovering motion implemented by flying insects. In this study, the water-treading motion, which originates from aquatic pro...

A computationally tractable nonlinear aeroelastic model of a bioinspired flapping-wing micro air vehicle, which includes motor dynamics and is suitable for control evaluation, is developed in this ...

An approach to modeling longitudinal airplane aerodynamics during unsteady maneuvers was developed for a micro air vehicle at angles of attack well past stall under unsteady conditions, including dynamic stall as might be experienced in perching maneuvers. To gather unsteady micro air vehicle flight data, an offboard motion tracking system was used to capture free-flight trajectories of a micro air vehicle with a weight of 14.44 g (0.0594 oz) and a wingspan of 37.47 cm (14.75 in.), operating at a nominal Reynolds number of 25,000. The measured trajectories included nominal gliding flight as well as mild-to-aggressive stalls. For the most aggressive stall case, the maximum lift coefficient reached a value near 2.5. The new model derived from the test data relied on a so-called separation parameter that modeled the aerodynamic lag during rapid changes in the angle of attack, and it thereby captured the effects of dynamic stall seen in the lift, drag, and moment coefficient data. Results from the model were ...

Flapping rotary wing, rotating wing, and flapping wing are feasible wing layouts applicable to micro-air-vehicles capable of hovering flight. A numerical study in this paper presents which wing layout can be more efficient in terms of aerodynamic power for the given kinematic and geometric parameters with or without the constraint of vertical force. In the cases under typical conditions, rotating wing layout is the most efficient one when a small vertical force is needed. However, if a much larger vertical force is required, flapping rotary wing is the only wing layout that fulfills the requirements of the two aspects due to its coupling effect. At relatively high Reynolds number (Re>2000), flapping amplitude (>70°), and aspect ratio (=6), comparative relationships from the cases under typical conditions among three wing layouts in terms of vertical force and aerodynamic power efficiency are kept unchanged. Nevertheless, at relatively low Re(

The vortical flow structures generated by the flapping wings of the DelFly II micro air vehicle in hovering flight configuration are investigated using particle image velocimetry. Synchronous force measurements are carried out to establish the relation between the unsteady forces and force generation mechanisms: particularly, the leading-edge vortex and the clap-and-peel motion. The formation of conical leading-edge vortices on both wings is revealed, which occurs rapidly at the start of the outstroke as a result of the wing–wing interaction. The leading-edge vortices of the outstroke interact with those of the instroke, which are shed and, by mutual induction, advect upstream as a vortex pair at the end of previous instroke. The leading-edge vortex pairs induce a strong inflow into the region formed between the upper and lower wings during the peeling phase, resulting in the formation of a low-pressure region. This, together with the leading-edge vortices and a momentum increase formed by the clap, accou...

The main focus of this research is the generation of a computational aeroelastic model for a macrofiber composite actuated micro air vehicle. Two M8528-P1 actuators were used to deform the surface of a forward-swept thin, compliant composite wing. The general approach, which included MATLAB, ABAQUS, and Athena Vortex Lattice, is described. The planform design and initial flight testing are discussed. The computational model was validated first with static tests, and then quasi-static wind-tunnel tests were used to validate the aeroelastic model. Digital image correlation was used to compare the expected and measured displacements of the wing. Flight loads were also compared for various angles of attack. The results indicated good agreement for angles of attack well within the standard flight envelope, despite small discrepancies in geometry.

Three-dimensional unsteady flow fields of a flapping, low-aspect-ratio wing have been investigated by means of highly resolved tomographic particle image velocimetry (Tomo-PIV) measurements and computational fluid dynamics (CFD). Furthermore, force measurements have been carried out. Tomo-PIV was applied to the flow above a flat plate wing during the downstroke. High spatial resolution and large volume thickness could be achieved by using sensitive sCMOS cameras and a traversing setup. The CFD calculations covered the complete period of motion. The analysis of the vortex-dominated flow fields provides a deeper understanding of vortex interaction and three-dimensionality of low Reynolds number (Re=18,000 and Re=36,000) flows. Two different Strouhal numbers (St=0.06 and St=0.13) are considered and their effects on the development of a leading edge and tip vortex are discussed. The PIV results show instantaneous flow fields after a leading edge separation that are dominated by small-scale turbulent vortex st...

Using a quasi-steady, blade-element analysis, we investigated the role of asymmetrical flapping mechanisms in hovering flight, for insect inspired micro air vehicles. The current analysis was applied to a 30 cm half-span wing, beating not more than 6 Hz. An implementation of asymmetrical flapping exhibited significantly greater lift generation, which can be attributed to the increase in angular velocity squared form for lift that occurs with increasing asymmetry. Significant improvements in the lift-to-power ratio were observed, for a house-fly-like mode of flapping, when the wing-beat frequency was below the natural frequency. At a frequency ratio of 0.3, a 75% increase in performance was observed with the use of asymmetrical flapping. At flapping frequencies above the natural frequency, however, asymmetry was found to be detrimental to performance, due to an increase in inertial forces. In a low inertia, an inclined stroke plane system, characteristic of dragonflies, we see that, in its most efficient flapping condition, asymmetrical flapping is detrimental to performance. However, in compliant systems in which elastic forces are significant, we see that asymmetry can improve the aerodynamic efficiency of the wing-actuation system Refereed/Peer-reviewed

Micro air vehicles promise to play an important part in public, private, and military arenas in the coming years. Small, lightweight, agile, and inexpensive, these flying machines are of interest in domestic search-and-rescue operations, law enforcement, reconnaissance, mapping, and urban combat operations. Nature demonstrates that flapping wings are an extremely effective solution to the problem of hovering flight with good agility in close quarters. However, the highly unsteady, largely separated character of the flow complicates aerodynamic analysis of these vehicles, and these challenges are magnified in a design setting when the sensitivities to many geometric and kinematic parameters must be assessed. In this paper, computational fluid dynamics simulation is applied as a means to evaluate kinematic parameters of flapping wings for a four-wing, dragonfly-like micro air vehicle. It is shown that high-frequency, moderate-amplitude flapping is preferred for wings flapping in a vertical stroke plane, and...

Incremental nonlinear dynamic inversion is a sensor-based control approach that promises to provide high-performance nonlinear control without requiring a detailed model of the controlled vehicle. In the context of attitude control of micro air vehicles, incremental nonlinear dynamic inversion only uses a control effectiveness model and uses estimates of the angular accelerations to replace the rest of the model. This paper provides solutions for two major challenges of incremental nonlinear dynamic inversion control: how to deal with measurement and actuator delays, and how to deal with a changing control effectiveness. The main contributions of this article are 1) a proposed method to correctly take into account the delays occurring when deriving angular accelerations from angular rate measurements; 2) the introduction of adaptive incremental nonlinear dynamic inversion, which can estimate the control effectiveness online, eliminating the need for manual parameter estimation or tuning; and 3) the incorporation of the momentum of the propellers in the controller. This controller is suitable for vehicles that experience a different control effectiveness across their flight envelope. Furthermore, this approach requires only very coarse knowledge of model parameters in advance. Real-world experiments show the high performance, disturbance rejection, and adaptiveness properties.

This study explores the aerodynamic characteristics of a flapping-wing micro aerial vehicle (MAV) in hovering configuration by means of force and flowfield measurements. The effects of flapping frequency and wing geometry on force generation were examined using a miniature six-component force sensor. Additional high-speed imaging allowed identification of the notable different deformation characteristics of the flexible wings under vacuum condition in comparison to their behavior in air, illustrating the relevance of aeroelastic effects. Flow visualization around the flapping wing by means of planar particle image velocimetry (PIV) measurements revealed the formation, development, and shedding of the vortical structures by the wings during flapping motion, with particular emphasis on the clap-and-fling phase. Further stereoscopic PIV measurements performed in the wake showed a momentum surplus wake induced by the clap-and-fling, indicative of thrust generation. The vortical structures in the wake formed d...

In this paper, a novel method for aerodynamic model identification of a micro-air vehicle is proposed. The principal contribution is a technique of wind estimation that provides information about the existing wind during flight when no air-data sensors are available. The estimation technique employs multi-objective optimization algorithms that utilize identification errors to propose the wind-speed components that best fit the dynamic behavior observed. Once the wind speed is estimated, the flight experimentation data are corrected and utilized to perform an identification of the aircraft model parameters. A multi-objective optimization algorithm is also used, but with the objective of estimating the aerodynamic stability and control derivatives. Employing data from different flights offers the possibility of obtaining sets of models that form the Pareto fronts. Deciding which model best adjusts to the experiments performed (compromise model) will be the ultimate task of the control engineer., The authors would like to thank the Spanish Ministry of Innovation and Science for providing funding through grant BES-2012-056210 and projects TIN-2011-28082 and ENE-25900. We also want to acknowledge the Generalitat Valenciana for financing this work through project PROMETEO/2012/028.

Recent interest in high-angle-of-attack flight, aerobatic maneuvering, vertical/short takeoff and landing, etc., of small unmanned aerial vehicles necessitates more detailed modeling of the complex aerodynamics associated with these flight regimes. This includes modeling the effect of the propeller slipstream, also called prop wash, which is the main source of airflow that helps maintain lift and control during near-zero forward-speed flight like that encountered during vertical/short takeoff and landing, as well as during high-angle-of-attack flight/aerobatic maneuvering like hovering. Propeller slipstream models based on conventional theories, such as the momentum theory, have been used extensively in the literature to predict the induced air velocity within the slipstream. However, because these conventional theories consider only acceleration of air within the slipstream and not diffusion, their applicability in regions far downstream of the propeller where diffusion is dominant, is questionable. This...

The aerodynamic performance of flapping micro air vehicles in hover conditions is dependent on many parameters, including the wing design. With the goal of optimizing the wing for hover performance, the initial focus was to reduce the uncertainty in the thrust measurements. This is because lower uncertainty in this metric enables better resolution in comparing the performance of different designs. Aerodynamic performance variability was deemed to be the fault of an imprecise manufacturing technique. Therefore, adjustments were made to the fabrication process until a permissible level of uncertainty was attained for optimization; the goal was less than 5%. This paper chronicles the progression of the wing fabrication process and details how the uncertainty was evaluated. Four fabrication methods and two different wing designs are included in this study: a carbon fiber hand layup technique, carbon fiber cured in a machined mold, and two variations of a machined plastic skeleton reinforced with a carbon fibe...

The nexus of advanced manufacturing methods, computer-aided design tools, and modern structural-analysis software has enabled the design and fabrication of structurally complex wing structures with unique features. This is particularly true for small unmanned aircraft, in which discrete structural hinges can easily be integrated into the overall vehicle design. This paper examines the use of discrete structural hinges for tailoring the low-frequency flight dynamics of the vehicle. For sufficiently soft discrete structural hinges, substantial coupling between flexible and rigid modes occurs, leading to the potential to modify the flight dynamic behavior through structural flexibility. Using a multibody flight dynamics simulation tool with a nonlinear lifting-line aerodynamic representation, different structural-hinge elastic properties, orientation, and location on the aircraft are examined. The results for a small unmanned aircraft indicate that flexibility mostly affects the longitudinal modes and associ...

Typical missions of micro aerial vehicles include remote sensing tasks in confined spaces, which limit wingspans and restrict maneuvering. Under these conditions, loiter may be limited by reduced endurance brought about by the increased power needs that may accompany wingspan and turning radius restrictions. A theoretical study was therefore performed with the primary purpose to explore aircraft configurations that are more suitable for such constrained flight domains. The theoretical performance model used for this investigation is based on a higher-order potential flow method that uses a table–lookup routine for profile drag prediction and section-lift adjustments for stall prediction. The model considers the increased lift needs during banked flight. Based on this flight performance model, parametric sweeps and multi-parameter gradient-based optimizations were applied to explore those micro aerial vehicle configurations that have minimum power requirements. Typical midspan chord Reynolds numbers ranged...

This paper describes a technique, called quarter-cycle constant period frequency modulation, to control the motion of wings on a flapping wing micro-air vehicle. This technique allows control over the wingbeat period and three additional points (the two zero crossings and the reversal of wing direction) within a single wingbeat cycle, allowing modulation of the wing’s velocity to provide direct control over six degrees of freedom of overall vehicle motion. Using a blade element based aerodynamic model, both instantaneous and cycle-averaged forces and moments are analytically computed for a specific type of wingbeat motion that enables nearly decoupled, multi-degrees of freedom control of an aircraft. Wing motion is controlled using oscillators whose frequencies and three additional parameters change once per wingbeat cycle. A control oriented dynamic model of the vehicle is derived, which is based on a cycle-averaged representation of the forces and moments, and control derivatives are calculated. A cycle...

Micro-air-vehicle wing designs often incorporate flexible structures that mimic the skeletal and membrane attributes found in natural flyers. Accurate performance predictions for these wing types require coupling of aerodynamic and structural simulations. Such fluid–structure interaction simulations are often performed using high-fidelity, numerically expensive techniques such as computational fluid dynamics coupled to nonlinear structural finite element analysis. Although the computational cost of conducting many conceptual design trade studies with these methods is prohibitive, simplified approaches may lack sufficient fidelity to provide conceptual design insights. This paper summarizes the development, comparison, and application of an efficient fluid–structure interaction method to simulate flexible-wing performance for rapid conceptual design of micro air vehicles. An advanced potential flow model computes aerodynamic performance, whereas a corotational frame and shell finite element structural mode...

Fixed-wing micro aerial vehicles experience attitude control difficulties as they operate in highly turbulent environments. Previous research has identified pressure-based control as a potential approach for augmenting the performance of, or replacing, autopilots reliant on inertial sensors. However, implementation requires an in-depth understanding of the correlation that exists between oncoming gusts and wing surface-pressure variations. This paper investigates the variation of correlation along a representative micro aerial vehicle wing chord and wingspan between upstream flow pitch angle variation and wing surface-pressure variation. Atmospheric turbulence was replicated within the controlled environment of a wind tunnel using planar grids that generated a turbulence intensity of 12.6%. Despite the unsteady nature of the pressure field, it was discovered that high correlation is evident in the vicinity of the leading edge. Thus, a few optimally placed sensors can be used for a pressure-based attitude ...