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The dragonfly wing is passively deformed under flapping and has the strength to withstand high flapping frequency simultaneously. These characteristics of deformation and vibration of the wing are important for flapping flight. However, the effect of these characteristics on flapping flight has not been well understood. The purpose of this study is to investigate deformation and vibration characteristics of the dragonfly wing, and then to develop an artificial wing suitable for flapping flight on the basis of the dragonfly wing. In this study, natural frequency and deformation of the dragonfly wing are measured, and the artificial wing is fabricated on the basis of the results. From the measured results, the dragonfly wing has the high natural frequency of about 120 Hz, and thereby, it does not resonate with flapping. Although base-side of the wing is hardly deformed, the tip-side of the wing is greatly deformed because of the torsional deformation from the nodus of dragonfly wing. On the basis of characteristics of the dragonfly wing, the deformable artificial wing that can deform in the same manner of dragonfly wings was fabricated. Then, aerodynamic force and power consumption under flapping when using the deformable artificial wing was measured. As a result, the power efficiency of aerodynamic force using the deformable artificial wing is five times greater than the power efficiency using a non-deformable wing.

Insect- and bird-size drones--micro air vehicles (MAV) that can performautonomous flight in natural and man-made environments are now an active and well-integrated research area. MAVs normally operate at a low speed in a Reynolds number regime of 104-105 or lower, in which most flying animals of insects, birds and bats fly, and encounter unconventional challenges in generating sufficient aerodynamic forces to stay airborne and in controlling flight autonomy to achieve complex manoeuvres. Flying insects that power and control flight by flapping wings are capable of sophisticated aerodynamic force production and precise, agilemanoeuvring, through an integrated system consisting of wings to generate aerodynamic force, muscles to move the wings and a control systemtomodulate power output fromthemuscles. In this article, we give a selective review on the state of the art of biomechanics in bioinspired flight systems in terms of flapping and flexible wing aerodynamics, flight dynamics and stability, passive and activemechanisms in stabilization and control, as well as flapping flight in unsteady environments. We further highlight recent advances in biomimetics of flapping-wing MAVs with a specific focus on insect-inspired wing design and fabrication, as well as sensing systems. [ABSTRACT FROM AUTHOR]

Vortex formation has numerous influences on the aerodynamic characteristics of fixed-wing micro air vehicle wings. Despite the mature understanding of vortices on fixed-wing and flapping micro air vehicle wings, the behavior of vortices over the morphing micro air vehicle wing has not been fully explored. Thus, the current work is conducted to investigate the influence of vortex structure over a series of twist-morphing micro air vehicle wings. Twist morphing micro air vehicle and baseline wings are simulated through fluid-structure interaction analysis. The validation results for each wing exhibited good correlation in the overall lift coefficient distribution trend. The vortex formation results show that vortex formations are significantly altered throughout angle of attack changes. For a given angle of attack cases below the stall angle, each morphing wing exhibited higher intensities of tip vortex structure formations and leading edge vortex-tip vortex interactions compared to the baseline wings. Stronger leading edge vortex-tip vortex interactions improved the low-pressure region over the morphing wing surface and further induce better lift performance. In fact, the morphing wing with higher morphing force induces better lift performance. [ABSTRACT FROM AUTHOR]

The Aerodynamic Characterization Facility is a unique facility located at the University of Florida's Research and Engineering Education Facility designed with the intent to study complex low Reynolds number, unsteady aerodynamic phenomena. This facility includes an open jet, open return wind tunnel specifically designed to operate in the low Reynolds number regime where current research efforts are being tasked for Micro Air Vehicle flight platforms. Specifically, the wind tunnel operates with freestream velocities ranging from nominally 0 to 22 m/s with 0.1 m/s resolution provided by a variable frequency drive utilized to control the tunnel. The test section entrance is 1.07m² with a length of 4.6 m. Flow uniformity investigations at free stream velocities of 2 and 4 m/s demonstrate a uniform flow core throughout the test section of at least 50% of the 1.14 m² contraction exit. Hot wire anemometry investigations present turbulence intensities less than 0.22% for free stream velocities greater than 1 m/s. The facility is also equipped with a dynamic motion rig and active turbulence generator. The dynamic motion rig is utilized to investigate unsteady aerodynamics over dynamic kinematic motions similar to what one might find in small birds and insects. The active turbulence generator provides a means to introduce atmospheric-like turbulence into the wind tunnel to understand the coupling between turbulence and unsteady flow phenomena associated with bird and insect flight. [ABSTRACT FROM AUTHOR]

In this article, a computational fluid dynamics -based computational method is developed to simulate the virtual flight of a flying wing micro air vehicle. The virtual flight simulation model is composed of unsteady Reynolds averaged Navier-Stokes equations, motion equations, and flight control equations. The flow solver is established based on low Mach number preconditioning method, momentum source method, implicit dual time-stepping algorithm, and lower upper symmetric Gauss–Seidel iteration scheme on hybrid dynamic meshes. S-A turbulence model is also introduced to close the Reynolds averaged Navier-Stokes equations. Fourth-order Adams prediction-correction method is adopted to couple computational fluid dynamics and rigid body dynamics. The multidisciplinary computational method is validated as a reliable tool for virtual flight simulation through simulating wing-rock motion of a delta wing. Finally, the developed method is used to simulate the virtual flight of the micro air vehicle. The effectiveness of the computational method is proved in the virtual flight simulation. [ABSTRACT FROM AUTHOR]

This study investigates the longitudinal motion control of unmanned aerial vehicles through a simulation in MATLAB. The linear model of an unmanned aerial vehicle is applied to controllers to explicate the longitudinal motion of the unmanned aerial vehicle. The ideal performance for an unmanned aerial vehicle is to achieve the desired response instantly with 100% precision. However, currently available controllers need further improvements. Thus, a proportional-derivative linear quadratic regulator controller is developed and compared with a proportional-integral-derivative controller, a linear quadratic regulator controller, and a proportional linear quadratic regulator controller. The proportional-derivative linear quadratic regulator controller enhances the response of the system by reducing settling time by more than 95% compared with other available controllers. Additionally, the proportional-derivative linear quadratic regulator improves the root mean square error by almost 50% compared with the proportional linear quadratic regulator controller and improves rise time by almost 96% with reasonable overshoot. [ABSTRACT FROM AUTHOR]

The aerodynamic characteristics around a micro air vehicle wing with an inverse-Zimmerman configuration are numerically investigated by an in-house programmed solver particularly dedicated for aircrafts operating in low Reynolds number regime. The complex three-dimensional aerodynamic performance was investigated in terms of force generation and flow structures visualization. Results show that the flow around the low aspect ratio MAV wing is characterized by complex three-dimensional separation-dominated flow. The flow fields exhibit separation, reattachment, secondary separation, secondary reattachment, and strong interaction between the separated boundary layer and wingtip vortices. In addition, the effect of tip-attached vertical stabilizers on flow structure and aerodynamic forces is addressed in this paper. The stabilizers significantly influence both the flow structure and aerodynamic forces via reducing the strength of wingtip vortices and shedding and interacting of wingtip vortices. Eventually, the unsteadiness of the aerodynamics revealed that higher angle of attack will result in stronger unsteady phenomena as demonstrated by the oscillating forces. [ABSTRACT FROM AUTHOR]

Piezoelectrically actuated flapping-wing micro air vehicle (MAV) is an emerging technology. This paper discusses limitations of presently used voltage drivers for the piezoelectric actuators used in such applications and suggests an active filter-based unipolar high-voltage driver. A Chebyshev polynomial has been used to extract a unipolar sinusoidal high voltage signal from a unipolar square wave signal for driving the piezoelectric actuators at low frequency in flapping-wing MAV applications. The filter is based on Sallen-Key topology and is suitable for connecting a piezo-bimorph in series or parallel electrical connection. We have considered an application-specific piezoelectric bimorph actuator of 40 Hz flapping frequency and 32 nF capacitance in each piezoelectric layer to design a driver. The driver circuit in verified by simulation results of OrCAD® software. The driver circuit can control the frequency of the sinusoidal driving voltage, which causes wing-flapping, by radio control communication. [ABSTRACT FROM AUTHOR]

This research compared a tractor and a pusher configuration for a tilt-body vertical take-off and landing micro air vehicle using an experiment in a subsonic wind tunnel. All tests were conducted in the range 6-10 m/s and 6000-8000 RPM of the freestream and the propeller rotation, respectively. The wing model was a rectangular platform with an NACA 0012 airfoil and AR=1. The incidence angles varied within the range 0°-90° to cover flight configuration from cruise to hover and vice versa. Basically, the downstream of the propeller is stronger than the upstream. Thus the wing submerses in the propeller's downstream, which is the tractor configuration, and has an advantage over the other configuration by increasing the freestream velocity and decreasing the angle of attack. The results of the experiment found that the wing aerodynamics of the tractor were improved by the prop-wash effect with increases of about 1-1.13 times in the wing lift curve slope and about 0.9-1.12 times in the factor K of the drag polar curve. However, in the case of the pusher, the change was not significant. The stall angle, the maximum lift coefficient, and the drag coefficient at zero angle of the wing all increased in both the tractor and the pusher configurations due to the prop-wash effect. Moreover, after experiencing the prop-wash effect, the aerodynamic center of the tractor wing was almost at the same point. [ABSTRACT FROM AUTHOR]

Evolutionary Robotics allows robots with limited sensors and processing to tackle complex tasks by means of sensory-motor coordination. In this article we show the first application of the Behavior Tree framework on a real robotic platform using the evolutionary robotics methodology. This framework is used to improve the intelligibility of the emergent robotic behavior over that of the traditional neural network formulation. As a result, the behavior is easier to comprehend and manually adapt when crossing the reality gap from simulation to reality. This functionality is shown by performing real-world flight tests with the 20-g DelFly Explorer flapping wing micro air vehicle equipped with a 4-g onboard stereo vision system. The experiments show that the DelFly can fully autonomously search for and fly through a window with only its onboard sensors and processing. The success rate of the optimized behavior in simulation is 88%, and the corresponding real-world performance is 54% after user adaptation. Although this leaves room for improvement, it is higher than the 46% success rate from a tuned user-defined controller. [ABSTRACT FROM AUTHOR]

Micro Air Vehicles (MAVs) driven by electric propellers are of interest for military and civilian applications. The rotational speed control of such electric propellers is an important factor for improving the flight performance of the vehicles, such as their positioning accuracy and stability. Therefore, this paper presents a nonlinear adaptive control scheme for the electric propulsion system of a certain MAV, which can not only speed up the convergence rates of adjustable parameters, but can also ensure the overall stability of the adjustable parameters. The significant improvement of the dynamic tracking accuracy of the rotational speed can be easily achieved through the combination of the proposed control algorithm and linear control methods. The experimental test results have also demonstrated the positive effect of the nonlinear adaptive control scheme on the flight performance of the MAV. [ABSTRACT FROM AUTHOR]

By the simulation of the unique spin flying style of maple seed, a new type of micro air vehicle in imitation of maple seed is designed. Referenced to the appearance and weight distribution of maple seed, the general layout design for the micro air vehicle is completed, then the flight status at different rotating speed is analyzed by using the dynamic mesh unsteady flow method. The flight control scheme for this kind of aircraft is designed by magnetic field azimuth calibration according to its unique flying style. Finally, a prototype is produced for flight tests. Results show that the micro air vehicle in imitation of maple seed has good aerodynamic efficiency and the control scheme is effective and reliable, thus increasing the controllability and practicability of this kind of aircraft. [ABSTRACT FROM AUTHOR]

We report on an actuator based on dielectric elastomers that is capable of antagonistic actuation and passive folding. This actuator enables foldability in robots with simple structures. Unlike other antagonistic dielectric elastomer devices, our concept uses elastic hinges to allow the folding of the structure, which also provides an additional design parameter. To validate the actuator concept through a specific application test, a foldable elevon actuator with outline size of 70 mm \bm \times 130 mm is developed with angular displacement range and torque specifications matched to a 400-mm wingspan micro-air vehicle (MAV) of mass 130 g. A closed-form analytical model of the actuator is constructed, which was used to guide the actuator design. The actuator consists of 125-\mum-thick silicone membranes as the dielectric elastomers, 0.2-mm-thick fiberglass plate as the frame structure, and 50- \mum-thick polyimide as the elastic hinge. We measured voltage-controllable angular displacement up to \pm 26^\circ and torque of 2720 mN \cdot mm at 5 kV, with good agreement between the model and the measured data. Two elevon actuators are integrated into the MAV, which was successfully flown, with the foldable actuators providing stable and well-controlled flight. The controllability was quantitatively evaluated by calculating the correlation between the control signal and the MAV motion, with a correlation in roll axis of over 0.7 measured during the flights, illustrating the high performance of this foldable actuator. [ABSTRACT FROM PUBLISHER]

Biomimetic air vehicles (BAV) are a class of unmanned aircraft that mimic the flapping wing kinematics of flying organisms (e.g. birds, bats, and insects). Research into BAV has rapidly expanded over the last 30 years. In this paper, we present a comprehensive bibliometric review of engineering and biology journal articles that were published on this subject between 1984 and 2014. These articles are organized into five topical categories: aerodynamics, guidance and control, mechanisms, structures and materials, and system design. All of the articles are compartmented into one of these categories based on their primary focus. Several aspects of these articles are examined: publication year, number of citations, journal, authoring organization and country, non-academic funding sources, and the flying organism focused upon for bio-mimicry. This review provides useful information on the state of the art of BAV research and insight on potential future directions. Our intention is that this will serve as a resource for those already engaged in BAV research and enable insight that promotes further research interest. [ABSTRACT FROM AUTHOR]

A multiple component structure consisting of two Euler-Bernoulli beams connected to a rigid mass is used to model the heave dynamics of a wing micro air vehicle. In the time domain, the attainment of aC0-semigroup in the context of sesquilinear forms is demonstrated. In addition, the closed loop system is demonstrated to generate an exponentially stableC0-semigroup. In the frequency domain, the infinite dimensional transfer function is determined and used to examine several properties of the system. Finally, an optimal control is used to morph the wings to a desired shape, and simulation results are demonstrated. [ABSTRACT FROM AUTHOR]

Wing rock phenomenon has been studied extensively on slender delta wings but a little is understood about wing rock occurring on rectangular wing planforms, which is the focus of this paper. Specifically, a systematic procedure is discussed for experimental studies of single degree-of-freedom wing rock on rectangular wings. The characterization of limit cycle oscillations in terms of amplitude and frequency is based on the free-to-roll tests in wind tunnel. Rectangular wings with aspect ratio from 2 to 4.5 (with increment of 0.25) are studied at low Reynolds numbers (less than 0.1 million) and low Strouhal numbers ( 10 − 2 ) that are typical for the flight of micro air vehicles in urban environment. The changing trend in oscillation amplitude and frequency of the resulting sustained limit cycle oscillations is analyzed. The results indicate that wing rock occurs in post-stall regime (14–16° of angle of attack) and its amplitude tends to increase from aspect ratio 2 to 3.25 and decrease thereafter. The wing-rock frequency shows a decrease from aspect ratio of 2 to 3.75 and increase thereafter. [ABSTRACT FROM AUTHOR]

This study attempts to present a new and comprehensive cycle for the design of fixed wing micro air vehicles. The idea is to propose a complete cycle containing all micro air vehicles design subjects such as aerodynamics, stability, structure, and navigation. The main aim of the cycle is to decrease the designing time for an optimum design. In this method, the sizing process is started simultaneously, which involves the following cases: specification of mission and aviation plan; determination of planform and aspect ratio; constraint analysis; estimation of plane weight. Completion of these four phases results in the specification of the geometry and dimensions of the wing in an optimum manner. After determination of the planform geometry, selection of the airfoil is carried out by complying with the defined criteria. After this stage, the wing of micro air vehicle is designed completely and analysis is carried out to determine the aerodynamics coefficients. Next step is designing the fuselage for the airplane. Then micro air vehicle and aerodynamic center of wing are calculated and stability equations for micro air vehicle are simulated. The results of these processes are determination of surfaces, dimensions and airfoils of the tails and center of gravity of the plane. After calculation of the control surfaces, the designed micro air vehicle is analyzed in XFLR5 software. Next step is selection of electric equipment such as motor, batteries, servo, etc. The final step of design is the optimization of the micro air vehicle for increasing its performance and endurance. After the design, steps of manufacturing will be started. [ABSTRACT FROM PUBLISHER]

In this paper, a new computational method is developed based on computational fluid dynamics (CFD) coupled with rigid body dynamics (RBD) and flight control law in an in-house programmed source code. The CFD solver is established based on momentum source method, preconditioning method, lower–upper symmetric Gauss–Seidel iteration method, and moving overset grid method. Two-equation shear–stress transportk− ω turbulence model is employed to close the governing equations. Third-order Adams prediction-correction method is used to couple CFD and RBD in the inner iteration. The wing-rock motion of the delta wing is simulated to validate the capability of the computational method for virtual flight simulation. Finally, the developed computational method is employed to simulate the longitudinal virtual flight of a dual rotor micro air vehicle (MAV). Results show that the computational method can simulate the virtual flight of the dual rotor MAV. [ABSTRACT FROM PUBLISHER]

Purpose -- The purpose of this paper is to describe the research performed on flexible-wing micro air vehicle (MAV). Typical attributes associated with the aerodynamics of MAVs are low Reynolds number, low altitude flying environments and low aspect ratio platforms. These attributes give birth to several challenges such as poor aerodynamic performance, nonlinear lift patterns and reduced gust tolerance. Flexible-wing MAV is renowned for improved aerodynamic characteristics such as smooth flight in gusty conditions than its rigid-wing counterpart. Design/methodology/approach -- The wind-tunnel experiments are carried out for various configurations to determine the ways of further enhancing lift. The baseline geometric description for all MAVs includes 15-cm box dimension and an aspect ratio of 1. The experimental results of the baseline configuration are compared with other experimental results available in literature. After due validation, the effects of following parameters are quantized and compared with the rigid-wing counterpart: underlying skeleton; wing membrane extension; wing membrane relaxation; and wing membrane material (latex, silk, poly-vinyl chloride plastic sheet and nylon). Findings -- It is found that the skeleton layout significantly governs the lift characteristics. The effect of membrane extension and relaxation proved to be of little advantage. Latex sheets are found to be the best choice for membrane material. The aerodynamic assessment at low Reynolds number has demonstrated significant improvement of lift characteristics for flexible wings over rigid-wing counterparts. Research limitations/implications -- The results presented in this paper are based on wind-tunnel experimentation. Further experimentation through flight test may be needed to reveal the true aerodynamic performance under unsteady maneuvers. Practical implications -- The material properties vary significantly during fabrication. A technique to standardize the properties of flexible membranes is a missing link in literature and warrants further investigation. Originality/value -- This concept of flexible wing has shown high potential. The primary objective of this paper is to experimentally investigate ways of further enhancing the lift of flexible-wing MAVs by controlling flexibility passively. While various researchers have spent many years on developing the optimum wing frame for the flexible wing, research on different wing materials has been limited. This is the first paper of its kind covering all aspects of wing-frame design, material, effects of extension and relaxation on wing membrane. [ABSTRACT FROM AUTHOR]

The unsteady aerodynamic thrust and aeroelastic response of a two-dimensional membrane airfoil under prescribed harmonic motion are investigated computationally with a high-order Navier–Stokes solver coupled to a nonlinear membrane structural model. The effects of membrane prestress and elasticity are examined parametrically for selected plunge and pitch–plunge motions at a chord-based Reynolds number of 2500. The importance of inertial membrane loads resulting from the prescribed flapping is also assessed for pure plunging motions. This study compares the period-averaged aerodynamic loads of flexible versus rigid membrane airfoils and highlights the vortex structures and salient fluid–membrane interactions that enable more efficient flapping thrust production in low Reynolds number flows. [ABSTRACT FROM AUTHOR]