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This study presents the design, implementation, and assessment of a combined passive and active flow control technique with the aim of increasing the aerodynamic performance of fixed-wing Micro Air Vehicles (MAVs). Power consumption restrictions in MAVs support the choice of passive flow control solutions such as the use of a modified (tubercled) wing leading edge. This strategy successfully allows to delay and mitigate aerodynamic stall but detrimental effects are found at pre-stall operating conditions. In order to retrieve the lift-generation capabilities of the baseline wing at pre-stall, a subsidiary active flow control method making use of air blowing was designed and installed in the modified wing. Guidance to the selection of optimum settings was provided by experimental and computational analyses. The resulting hybrid flow control system demonstrated its effectiveness, thus producing generalized lift enhancements irrespectively of the attitude of the wing. [ABSTRACT FROM AUTHOR]

This paper describes the development and flight testing of a compact, re-configurable, hover-capable rotary-wing micro air vehicle that could be tube launched for increasing mission range. The vehicle design features a coaxial rotor with foldable blades, thrust-vectoring mechanism for pitch/roll control and differential rpm for yaw control. The vehicle was stabilized using a cascaded feedback controller implemented on a 1.7-gram custom-designed autopilot. Wind tunnel tests conducted using a single-degree-of-freedom stand demonstrated gust-tolerance up to 5 m/s, which was verified via flight testing. Finally, the 366-gram vehicle was launched vertically from a pneumatic cannon followed by a stable projectile phase, passive rotor unfolding, and transition to a stable hover from arbitrarily large attitude angles demonstrating the robustness of the controller. [ABSTRACT FROM AUTHOR]

Wireless ranging measurements have been proposed for enabling multiple Micro Air Vehicles (MAVs) to localize with respect to each other. However, the high-dimensional relative states are weakly observable due to the scalar distance measurement. Hence, the MAVs have degraded relative localization and control performance under unobservable conditions as can be deduced by the Lie derivatives. This paper presents a nonlinear model predictive control (NMPC) by maximizing the determinant of the observability matrix to generate optimal control inputs, which also satisfy constraints including multi-robot tasks, input limitation, and state bounds. Simulation results validate the localization and control efficacy of the proposed MPC method for range-based multi-MAV systems with weak observability, which has faster convergence time and more accurate localization compared to previously proposed random motions. A real-world experiment on two Crazyflies indicates the optimal states and control behaviours generated by the proposed NMPC. [ABSTRACT FROM AUTHOR]

The present paper aims to investigate numerically small amplitude oscillation of NACA 0012 airfoil at Re=1000. The airfoil is sinusoidally pitching around the quarter chord point with 1° pitch amplitude about a mean angle of attack. The computations are performed for mean angles of attack ranging from 0° to 60° and for pitching frequencies of 1Hz and 4 Hz. The effect of the mean angle of attack and pitching frequency on the instantaneous forces as well as the vortex structure is investigated in comparison with the non-oscillatory conditions. It was shown that airfoil oscillations at the investigated conditions change the amplitude of oscillation of the aerodynamic loads. The instantaneous drag coefficient is always positive for pitching airfoil at 1 Hz. In the meantime, there are time intervals where instantaneous drag coefficient becomes negative for pitching motion at 4Hz for mean angles of attack from 3° to 36°. [ABSTRACT FROM AUTHOR]

The work presented in this paper is part of a project called ARChEaN (Aerodynamic of Rotors in Confined ENvironment) whose objective is to study the interactions of a micro drone rotor with its surroundings in the case of flight in enclosed environments such as those encountered, for example, in archeological exploration of caves. To do so the influence of the environment (walls, ground, ceiling, etc) on the rotor's aerodynamic performance as well as on the flow field between the rotor and the surroundings is studied. This paper focuses on two different configurations, flight near the ground and flight near a corner (wall and ground), and the results are analyzed and compared to a general free flight case (i.e. far away from any obstacle). In order to carry out this analysis both numerical and experimental approaches are conducted. The objective is to validate the numerical model with the results obtained experimentally and to benefit from the advantages of both approaches in terms of flow analysis. This research work will provide knowledge on how to operate these systems as to minimize the possible negative environment disturbances, reduce power consumption and predict the micro drone's behaviour during enclosed flights. [ABSTRACT FROM AUTHOR]

This paper presents the design process and experimental results of a brand new flapping and trailing edge control mechanism for a flapping wing micro air vehicle. The flapping mechanism, whose main components are fabricated from string, is suggested and optimized further by a modified pattern search method. The trailing edge control mechanisms for pitching and rolling moments are designed to be attached onto the present flapping mechanism in a modularized fashion. Prototypes of both mechanisms are fabricated and experimentally tested in order to examine the feasibility of the designs. It is expected that the present flapping mechanism will generate enough lift for the total weight of the vehicle. The present control mechanism is found to be able to supply sufficient control moment. [ABSTRACT FROM AUTHOR]

We present a novel design of a tailless flapping wing micro air vehicle, which uses four independently driven pairs of flapping wings in order to fly and perform agile maneuvers. The wing pairs are arranged such that differential thrust generates the desired roll and pitch moments, similar to a quadrotor. Moreover, two pairs of wings are tilted clockwise and two pairs of wings anti-clockwise. This allows the micro air vehicle to generate a yaw moment. We have constructed the design and performed multiple flight tests with it, both indoors and outdoors. These tests have shown the vehicle to be capable of agile maneuvers and able to cope with wind gusts. The main advantage is that the proposed design is relatively simple to produce, and yet has the capabilities expected of tailless flapping wing micro air vehicles. [ABSTRACT FROM AUTHOR]

The stability of small unmanned air systems can be challenged by turbulence during low-altitude flight in cluttered urban environments. This paper explores the benefits of a tandem wing aircraft configuration with the implementation of a pressure-based phase-advanced turbulence sensory system on a small unmanned air system for gust mitigation. The objective was to utilise passive and active methods to minimise gust-induced perturbations. Experimentation in repeatable turbulence within a wind tunnel’s test section was conducted. The experiments focus on the roll axis, which is isolated through a specially designed roll-axis rig. The results show improvement over conventional aircraft. This work is part of a larger research project aimed at enabling safe, stable and steady small unmanned air systems flight in urban environments. [ABSTRACT FROM AUTHOR]

Automation of inspection tasks is crucial for the development of the power industry, where micro air vehicles have shown a great potential. Self-localization in this context remains a key issue and is the main subject of this work. This article presents a methodology to obtain complete three-dimensional local pose estimates in electric tower inspection tasks with micro air vehicles, using an on-board sensor set-up consisting of a two-dimensional light detection and ranging, a barometer sensor and an inertial measurement unit. First, we present a method to track the tower’s cross-sections in the laser scans and give insights on how this can be used to model electric towers. Then, we show how the popular iterative closest point algorithm, that is typically limited to indoor navigation, can be adapted to this scenario and propose two different implementations to retrieve pose information. This is complemented with attitude estimates from the inertial measurement unit measurements, based on a gain-scheduled non-linear observer formulation. An altitude observer to compensate for barometer drift is also presented. Finally, we address velocity estimation with views to feedback position control. Validations based on simulations and experimental data are presented. [ABSTRACT FROM AUTHOR]

This work investigates the design parameters and their consequences in the control of a helicopter rotor combined with a pair of fixed wings. This hybrid vehicle has a light and aerodynamically efficient rotor with a large range of pitch angles to enable both hover and forward flight. Because of the light stiff rotor and heavy wings, the hybrid vehicle exhibits couplings between the roll and pitch axes during hover flight. The rotor-wing interaction depends on a lot of parameters. In this article, we utilize a simplified theoretic model and simulations in order to gain insight in the effect of these parameters on the vehicle dynamics. Finally, a controller is designed that compensates undesired coupling between pitch and roll. [ABSTRACT FROM AUTHOR]

This paper describes the design, controls system development, and hover testing of a 60 -g meso-scale cycloidalrotor based (cyclocopter) micro air vehicle. The cycloidal rotor (cyclorotor) is a revolutionary vertical take-off and landing concept with a horizontal axis of rotation. The twin-cyclocopter utilizes two optimized cyclorotors and a horizontal tail rotor used to counteract the pitching moment generated by the cyclorotors. An innovative lightweight and high strength-to-weight ratio blade design significantly reduced cyclorotor weight and improved aerodynamic efficiency. In addition, increasing the virtual camber and incidence (by increasing chord-to-radius ratio) and using a symmetric pitching schedule with a maximum ± 45° pitching amplitude also improved rotor efficiency. Due to gyroscopic coupling and inherent instability of the cyclocopter, a closed-loop feedback control system was implemented using a custom autopilot weighing 1.5 g. The 60-g meso-scale twin-cyclocopter successfully demonstrated stable, sustained hover. [ABSTRACT FROM AUTHOR]

Recently, flapping wing micro air vehicles have received great attention with the drive to make smaller and smaller devices. This paper describes a theoretical investigation and subsequent practical implementation of a specific type of flight motor structure for this type of micro air vehicle that uses a "click' mechanism to improve mechanical efficiency. Diptera, which may use the mechanism, are the inspiration for this work. It builds on previous research into the "click" mechanism, which has been studied both from the biological and engineering points of view. It is difficult to capture the important fine details using a simple analytical model; hence, a multi-body dynamic software is used to model the device and to aid the design of a large-scale prototype. Force-deflection curves of the structure and the displacement response are obtained numerically and experimentally. The experimental and numerical results compare reasonably well, enabling the model to be used for further development and potential miniaturization of the flight motor structure. In a practical device, asymmetry occurs in the up- and down-stroke. The effects of this asymmetry are compared with previous results from analytical models. It is found that asymmetry offers a marginal improvement. [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]

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]

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]

This paper presents the design of a Micro Air Vehicle (MAV) operated by speech commands. A person from a base station can comfortably control the motion of the MAV by issuing speech commands. This system proposes to have two units, one in the base station which is the control unit and the other is a flying machine. The base station unit consists of a Digital Signal Processor (DSP) which performs a speaker dependent speech recognition algorithm for a predefined command library. The DSP generates control signals which are wirelessly transmitted to the MAV. A Field Programmable Gate Array (FPGA) is placed in the MAV for on-board operations. The FPGA receives the wirelessly transmitted control signals and alters the motion of the MAV based on the control signals received. The MAV consists of a single rotating wing with two rotors placed on either side of the fuselage, providing it with the capability of vertical take-off and landing (VTOL). [ABSTRACT FROM AUTHOR]