Rotary-wing Micro Research Articles

Design, development, and flight testing of a tube-launched coaxial-rotor based micro air vehicle

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.

Design and control of the first foldable single-actuator rotary wing micro aerial vehicle

The monocopter is a type of micro aerial vehicle largely inspired from the flight of botanical samaras (Acer palmatum). A large section of its fuselage forms the single wing where all its useful aerodynamic forces are generated, making it achieve a highly efficient mode of flight. However, compared to a multi-rotor of similar weight, monocopters can be large and cumbersome for transport, mainly due to their large and rigid wing structure. In this work, a monocopter with a foldable, semi-rigid wing is proposed and its resulting flight performance is studied. The wing is non-rigid when not in flight and relies on centrifugal forces to become straightened during flight. The wing construction uses a special technique for its lightweight and semi-rigid design, and together with a purpose-designed autopilot board, the entire craft can be folded into a compact pocketable form factor, decreasing its footprint by 69%. Furthermore, the proposed craft accomplishes a controllable flight in 5 degrees of freedom by using only one thrust unit. It achieves altitude control by regulating the force generated from the thrust unit throughout multiple rotations. Lateral control is achieved by pulsing the thrust unit at specific instances during each cycle of rotation. A closed-loop feedback control is achieved using a motion-captured camera system, where a hybrid proportional stabilizer controller and proportional-integral position controller are applied. Waypoint tracking, trajectory tracking and flight time tests were performed and analyzed. Overall, the vehicle weighs 69 g, achieves a maximum lateral speed of about 2.37 m s−1, an average power draw of 9.78 W and a flight time of 16 min with its semi-rigid wing.

Aerodynamic analysis of hummingbird-like hovering flight

Flapping wing micro aerial vehicles are studied as the substitute for fixed and rotary wing micro aerial vehicles because of the advantages such as agility, maneuverability, and employability in confined environments. Hummingbird’s sustainable hovering capability inspires many researchers to develop micro aerial vehicles with similar dynamics. In this research, a wing of a ruby-throated hummingbird is modeled as an insect wing using membrane and stiffeners. The effect of flexibility on the aerodynamic performance of a wing in hovering flight has been studied numerically by using a fluid–structure interaction scheme at a Reynolds number of 3000. Different wings have been developed by using different positions and thicknesses of the stiffeners. The chordwise and spanwise flexural stiffnesses of all the wings modeled in this work are comparable to insects of similar span and chord length. When the position of the stiffener is varied, the best-performing wing has an average lift coefficient of 0.51. Subsequently, the average lift coefficient is increased to 0.56 when the appropriate thickness of the stiffeners is chosen. The best flexible wing outperforms its rigid counterpart and produces lift and power economy comparable to a real hummingbird’s wing. That is, the average lift coefficient and power economy of 0.56 and 0.88 for the best flexible wing as compared to 0.61 and 1.07 for the hummingbird’s wing. It can be concluded that a simple manufacturable flexible wing design based on appropriate positioning and thickness of stiffeners can serve as a potential candidate for bio-inspired flapping-wing micro aerial vehicles.

Recent progress in flapping wings for micro aerial vehicle applications

Micro aerial vehicles using flapping wings are under investigation, as an alternative to fixed-wing and rotary-wing micro aerial vehicles. Such flapping-wing vehicles promise key potential advantages of high thrust, agility, and maneuverability, and have a wide range of applications. These applications include both military and commercial domains such as communication relay, search and rescue, visual reconnaissance, and field search. With the advancement in the computational sciences, developments in flapping-wing micro aerial vehicles have progressed exponentially. Such developments require a careful aerodynamic and aeroelastic design of the flapping wing. Therefore, aerodynamic tools are required to study such designs and configurations. In this paper, the role of several parameters is investigated, including the types of flapping wings, the effect of the kinematics and wing geometry (shape, configuration, and structural flexibility) on performance variables such as lift, drag, thrust, and efficiency in various modes of flight. Kinematic variables have a significant effect on the performance of the flapping wing. For instance, a high flap amplitude and pitch rotation, which supports the generation of the strong leading-edge vortex, generates higher thrust. Likewise, wing shape, configuration, and structural flexibility are shown to have a large impact on the performance of the flapping wing. The wing with optimum flexibility maximizes thrust where highly flexible wings lead to performance degradation due to change in the effective angle of attack. This study shows that the development of the flexible flapping wing with performance capabilities similar to those of natural fliers has not yet been achieved. Finally, opportunities for additional research in this field are recommended.

PAC: A novel self-adaptive neuro-fuzzy controller for micro aerial vehicles

There exists an increasing demand for a flexible and computationally efficient controller for micro aerial vehicles (MAVs) due to a high degree of environmental perturbations. In this work, an evolving neuro-fuzzy controller, namely Parsimonious Controller (PAC) is proposed. It features fewer network parameters than conventional approaches due to the absence of rule premise parameters. PAC is built upon a recently developed evolving neuro-fuzzy system known as parsimonious learning machine (PALM) and adopts new rule growing and pruning modules derived from the approximation of bias and variance. These rule adaptation methods have no reliance on user-defined thresholds, thereby increasing the PAC’s autonomy for real-time deployment. PAC adapts the consequent parameters with the sliding mode control (SMC) theory in the single-pass fashion. The boundedness and convergence of the closed-loop control system’s tracking error and the controller’s consequent parameters are confirmed by utilizing the LaSalle–Yoshizawa theorem. Lastly, the controller’s efficacy is evaluated by observing various trajectory tracking performance from a bio-inspired flapping wing micro aerial vehicle (BI-FWMAV) and a rotary wing micro aerial vehicle called hexacopter. Furthermore, it is compared to three distinctive controllers. Our PAC outperforms the linear PID controller and feed-forward neural network (FFNN) based nonlinear adaptive controller. Compared to its predecessor, G-controller, the tracking accuracy is comparable, but the PAC incurs significantly fewer parameters to attain similar or better performance than the G-controller.

Numerical and experimental investigation of an airfoil design for a Martian micro rotorcraft

The present paper aims at investigating the impact of an airfoil design on the propulsion system for a Martian rotary wing micro air vehicle. The main challenge for flying on Mars is the atmosphere’s density and speed of sound that are significantly lower than on Earth. It leads to compressible ultra-low Reynolds number ([Formula: see text]) flows for a coaxial rotorcraft with a 30 cm diameter . Since those flows are unknown in the biosphere, numerical tools have not been validated yet. Therefore, the test section from a known depressurized experiment is simulated in 3D for solver assessment. XFoil, a program for the analysis of subsonic airfoil, is also evaluated in the Martian flow conditions for evaluating its ability to be used in an optimization process. Based on the XFoil’s performance evaluations, both the camber line and thickness distribution are optimized in 2D incompressible and compressible flows. Optimal shape is a highly cambered airfoil shifting the boundary layer separation downstream. For optimization assessment, airfoils from each optimization step are numerically evaluated with the validated solver showing that small variations in the airfoil design has little impact on the 2D aerodynamic performance. A compressible optimal airfoil is also proven to be more aerodynamically effective than the experimentally effective airfoils from literature. Finally, the impact of airfoil shapes on the 3D rotor performance is evaluated with a depressurized experimental campaign recreating the Martian atmosphere in terms of kinematic viscosity. The impact of gas composition is also assessed in subsonic flows.

Unsteady aerodynamics of a pitching-flapping-perturbed revolving wing at low Reynolds number

Due to adverse viscous effects, revolving wings suffer universally from low efficiency at low Reynolds number (Re). By reciprocating wing revolving motion, natural flyers flying at low Re successfully exploit unsteady effects to augment force production and efficiency. Here we investigate the aerodynamics of an alternative, i.e., a revolving wing with concomitant unsteady pitching and vertical flapping perturbations (a pitching-flapping-perturbed revolving wing). The current work builds upon a previous study on flapping-perturbed revolving wings (FP-RWs) and focuses on combined effects of pitching-flapping perturbation on force generation and vortex behaviors. The results show that, compared with a FR-RW, pitching motion further (1) reduces the external driving torque for rotating at 0° angle of attack (α0) and (2) enhances lift and leads to a self-rotating equilibrium at α0 = 20°. The power loading of a revolving wing at α0 = 20° can be improved using pitching-flapping perturbations with large pitching amplitude but small Strouhal number. Additionally, an advanced pitching improves the reduction of external driving torque, whereas a delayed pitching weakens both the lift enhancement and the reduction of external driving torque. Further analysis shows that pitching effects can be mainly decomposed into the Leading-Edge-Vortex (LEV)-mediated pressure component and geometric projection component, together they determine the force performance. LEV circulation is found to be determined by the instantaneous effective angle of attack but could be affected asymmetrically between upstroke and downstroke depending on the nominal angle of attack. Pitching-flapping perturbation thus can potentially inspire novel mechanisms to improve the aerodynamic performance of rotary wing micro air vehicles.

Linear vs Nonlinear MPC for Trajectory Tracking Applied to Rotary Wing Micro Aerial Vehicles

Precise trajectory tracking is a crucial property for Micro Air Vehicles (MAVs) to operate in cluttered environment or under disturbances. In this paper we present a detailed comparison between two state-of-the-art model-based control techniques for MAV trajectory tracking. A classical Linear Model Predictive Controller (LMPC) is presented and compared against a more advanced Nonlinear Model Predictive Controller (NMPC) that considers the full system model. In a careful analysis we show the advantages and disadvantages of the two implementations in terms of speed and tracking performance. This is achieved by evaluating hovering performance, step response, and aggressive trajectory tracking under nominal conditions and under external wind disturbances.

A bibliometric review of progress in micro air vehicle research

Micro air vehicle research has exponentially expanded since the first articles began to be published in the late 1990s. This article presents a comprehensive bibliometric review of journal articles published on micro air vehicle research from 1998 until 2015. The articles are classified into three types of micro air vehicle: fixed-wing, rotary-wing, and flapping-wing (biomimetic). These types are based upon their primary means of generating lift and propulsive thrust. The specific type of research in these articles is also examined, divided into subcategories of: aerodynamics; guidance, navigation, and control; propulsion; structures and materials; and system design. Numerous bibliometric indicators are presented and analyzed to understand how micro air vehicle research is expanding, which authoring organizations are leading the research, which external sponsoring organizations are providing funding, and the challenges that remain for future researchers. The analysis shows that the majority of the research articles are being written by organizations from the US, China, UK, France, and South Korea. Although biomimetic micro air vehicles are currently the most popular type of micro air vehicle, in recent years the growing popularity of rotary-wing micro air vehicles (especially as a guidance, navigation, and control test platform) has caused it to rival biomimetic micro air vehicles in popularity.

Indoor/Outdoor Scan-Matching Based Mapping Technique with a Helicopter MAV in GPS-Denied Environment

This work focuses on autonomous operation of rotary-wing Micro Aerial Vehicles (MAVs) in previously unexplored, GPS-denied environments. This type of operation requires the MAV to simultaneously estimate a map of its surroundings and its own position within that map. This work presents a refined algorithm for performing Simultaneous Localization and Mapping (SLAM) which does not rely on revisiting previously mapped areas. The algorithm is first benchmarked against previously published algorithms. Different scenarios, both indoors and outdoors, are then presented, showing the high amount of detail captured by the proposed method. Scenarios were mapped using three different platform types, including a conventional main-tail rotor helicopter, showing that the algorithm is platform-independent and does not require the rotorcraft's dynamic model, which can be complex. Experimental validation of the SLAM method shows an accuracy of approximately 0.1% of the traveled course length. The algorithm is capable of operating in real time on small form factor computers.

Development of a Coaxial MAV with Real-Time Obstacle Avoidance Capability

This paper discusses the development, implementation and deployment of a computationally light, yet robust real-time collision avoidance system on a hover capable coaxial rotary wing Micro Air Vehicle (MAV). The real-time capability of the algorithm is demonstrated by performing all computations required for processing the depth camera image onboard at 13 Hz using a single core of a 1.6 GHz quad core processor based single-board computer. The primary sensor used is Microsoft Kinect which has an operating range of 0.5 – 3.5 m. The algorithm uses template matching feature of an open source library OpenCV to find a window through which a vehicle of specified dimensions and known speed can pass safely. The actuator control and active yaw stabilization is done using Navstik which is a Micro Navigation & Control hardware. Two test vehicles are built and equipped with this framework for proof of concept.

Four-Rotor Autonomous Vehicle

Four rotary-wing micro air vehicles use four motors as the power unit, by adjusting the motor speed control flight of underactuated systems [. In order to achieve four-rotor autonomous vehicle autonomous flight control, preliminary design of flight control system, and use F5F100LEA single-chip as computer control unit, Proposed the flight system hardware design. Vehicle has the advantages of light weight, small size, low power consumption. After several laboratory tests, the design and reliable performance, to meet the aircraft take off, hover, landing flight mode control requirements.

HIGH-RESOLUTION MULTISENSOR INFRASTRUCTURE INSPECTION WITH UNMANNED AIRCRAFT SYSTEMS

Abstract. This paper reports on the investigations made at Fraunhofer Institute for Non-Destructive Testing (IZFP) where different rotary wing micro UAS have been used to scan infrastructures including bridges and monuments at high resolutions for remote damage assessment and monitoring purposes. The aerial pictures taken at high speed and frequency have then been stitched together to obtain full 2D and 3D building reconstructions at a resolution allowing damages and cracking to be observed still in the millimeter range. With these ultra hi-res building reconstruction models a specific data base could be created for each object in order to provide extensive information for long term evaluation and life cycle management. The UAS also have been equipped with sensors for damage size estimation, which combined with an image processing software developed to allow automatic cracking pattern recognition could be used for further analysis.

Experimental Performance Evaluation of Coaxial Rotors for a Micro Aerial Vehicle

Because of their potential for application in both civil and military sectors as well as the challenge in designing a tiny flying vehicle, micro aerial vehicles have attracted enormous attention. Several configurations of micro aerial vehicles are under development, namely fixed wing, rotary wing, and flapping wing. Under rotary-wing micro aerial vehicles, coaxial contrarotating configurations with a stabilizer bar seem to provide excellent stability behavior in pitch and roll degrees of freedom. This paper presents the results of an experimental study performed on a coaxial-contrarotor helicopter model to evaluate the performance of the rotor system using different rotor blades. The thrust and power of the rotors in independent and coaxial configurations were observed. The percentage thrust loss in the coaxial configuration was seen to be dependent on the ratio of the upper- and lower-rotor revolutions per minute as well as the spacing between the rotors. A theoretical analysis using a nonuniform inflow model was developed, which corroborated very well with the experimental data. Using low-Reynolds-number drag coefficients for the airfoil, the estimated power consumption of the rotors was found to match very well with the experimental data. A closed-form solution using a uniform inflow model to estimate the thrust performance of a coaxial rotor is proposed, which also matches with the experimental observations.

Design and Analysis of a Gyroscopically Controlled Micro Air Vehicle

Micro air vehicles have emerged as a popular option for diverse robotic and teleoperated applications in both open terrain and urban environments because of their inherent stealth and portability. To perform many of the tasks envisioned for micro air vehicles, agility is essential. To date, research efforts to improve agility have focused primarily on constructing complex controllers to enable existing vertical-take-off- and-landing vehicles, such as remote-controlled helicopters and quadrotors, to perform aerobatic maneuvers autonomously. In this work, we adopt a system-level perspective and analyze a new design for a rotary-wing micro air vehicle that utilizes gyroscopic dynamics for attitude control. Unlike traditional vehicles where attitude control moments are generated by aerodynamic control surfaces, the proposed vehicle will leverage the existing angular momentum of its counter rotating components. This paradigm has the potential to yield significant increases in agility when compared to state-of-the-art micro vertical take-off and landing vehicles. The proposed design reduces mechanical complexity by precluding the use of complex mechanisms, such as the swashplate. The capacity to rapidly generate large gyroscopic control moments, coupled with the precision gained from eliminating the need for complex and restrictive aerodynamic models, improves both agility and adaptability. We present the development of a gyroscopically controlled micro air vehicle including comprehensive models of the dynamics and the aerodynamics with an emphasis on the design and analysis of such systems. A dynamics simulator that incorporates these models and mechanical hardware solutions to challenges that arose during prototyping will also be presented.

Use of calculus of variations to determine the shape of hovering rotors of minimum power and its application to micro air vehicles

In this paper, calculus of variations and combined blade element and momentum theory (BEMT) are used to demonstrate that, in hover, when neither root nor tip losses are considered; the rotor, which minimizes the total power (MPR), generates an induced velocity that varies linearly along the blade span. The angle of attack of every blade element is constant and equal to its optimum value. The traditional ideal twist (ITR) and optimum (OR) rotors are revisited in the context of this variational framework. Two more optimum rotors are obtained considering root and tip losses, the ORL, and the MPRL. A comparison between these five rotors is presented and discussed. The MPR and MPRL present a remarkable saving of power for low values of both thrust coefficient and maximum aerodynamic efficiency. The result obtained can be exploited to improve the aerodynamic behaviour of rotary wing micro air vehicles (MAV). A comparison with experimental results obtained from the literature is presented.

System Identification of a Rotary-Wing Micro Air Vehicle

System Identification of a Rotary-Wing Micro Air Vehicle

Non-Line-of-Sight Indoor Localization of Micro Air Vehicles Using First-Arrival Sound

This paper presents a technique and its system that localizes a rotary-wing Micro Air Vehicle (MAV) in indoor environments even under Non-Line-of-Sight (NLoS) conditions. The technique is based on the system with the MAV having a wireless microphone and a ground station having multiple microphones. The technique identifies the location of the MAV in two-dimensional space by measuring the Time-of-Arrival (ToA) of acoustic signals caused by the rotation of blades at the MAV. The technique then applies an iterative algorithm that corrects the NLoS errors and computes the true ToA based on maps of known indoor environments in a computationally inexpensive manner. To suppress noise in the received signals and thus improve the robustness of ToA estimation, the generalized cross-correlation with phase transform and a bandpass filter is derived and applied. The performance of the proposed technique was examined experimentally by its comparison with three existing ToA-based localization techniques. Experimental results show the superiority of the proposed technique, demonstrating its potential for aiding indoor MAVs in autonomous navigation.

Design Optimization of Rotary-Wing Micro Air Vehicles

In this paper, a new design methodology is introduced to automate the configuration layout design and geometric sizing of rotary-wing micro air vehicles (MAV). The objective of this design-optimization problem is to organize a given set of components and payloads such that the resulting flight vehicle has the most compact overall size and still fulfils the given physical and control constraints. Genetic algorithm (GA) is chosen as the optimization engine because of its proven robust performance. A detailed discussion is presented to explain how the rotary-wing MAV design problem can be formulated as a GA optimization problem. From the case study performed, it is demonstrated that the proposed methodology is able to achieve the design goal.

Design, Fabrication, and Performance Test of a Rotary-Wing Micro Aerial Vehicle

Design, Fabrication, and Performance Test of a Rotary-Wing Micro Aerial Vehicle