Hover Mode Research Articles

A Novel Tailsitter UAV with Configurable Wings

In this study, we propose a novel tailsitter unmanned aerial vehicle with configurable wings using a parallel link mechanism. It has two flight modes: a hover mode and a forward flight mode by pitching, similar to conventional tailsitters. In addition, it can deform its airframe in each flight mode. In the hover mode, it can tilt the frame in the pitch direction while hovering. In the forward flight mode, it can change the configuration of the wings during forward flight. In experiments, we show that it can transition from the hover mode to the forward flight mode with three wing configurations: non-staggered wings (biplane) and positively and negatively staggered wings (tandem wing plane), using an attitude controller for conventional quadrotors.

Design and Development of an Air–Land Amphibious Inspection Drone for Fusion Reactor

This paper proposes a design method for a miniature air–land amphibious inspection drone (AAID) to be used in the latest compact fusion reactor discharge gap observation mission. Utilizing the amphibious function, the AAID realizes the function of crawling transportation in the narrow maintenance channel and flying observation inside the fusion reactor. To realize miniaturization, the mobile platform adopts the bionic cockroach wheel-legged system to improve the obstacle-crossing ability. The flight platform adopts an integrated rotor structure with frame and control to reduce the overall weight of the AAID. Based on the AAID dynamic model and the optimal control method, the control strategies under flight mode, hover mode and fly–crawl transition are designed, respectively. Finally, the prototype of the AAID is established, and the crawling, hovering, and fly–crawling transition control experiments are carried out, respectively. The test results show that the maximum crawling inclination of the AAID is more than 20°. The roll angle, pitch angle, and yaw angle deviation of the AAID during hovering are all less than 2°. The landing success rate of the AAID during the fly–crawl transition phase also exceeded 77%, proving the effectiveness of the structural design and dynamic control strategy.

Experimental assessment of blowing effect on vehicle performance and aero-acoustics in small-rotor/wing interaction

The tiltrotor design for urban air mobility (UAM) combines vertical take-off and landing (VTOL) capability with fixed-wing efficiency. However, it confronts challenges posed by downward force due to rotor wake effect. Previous research has employed active flow control, such as blowing air, primarily during forward flight using a single air outlet slot. However, the implications for rotor performance and aero-acoustic characteristics have remained unexplored. The experimental approach in this study involves controlled blowing air with moderate momentum in hover mode, concentrating on rotor performance, download force, noise signature, and the influence of port patterns. It is found that the radial port pattern emerges as pivotal for mitigating downward force and augmenting rotor efficiency. The efficacy of noise reduction hinges on both receiver orientation and port pattern selection. This investigation significantly contributes to understanding the role of blowing effect in optimizing tiltrotor designs, particularly in the context of rotor wake-wing interaction.

A comparative study of three modes for realizing transmedia standing-and-hovering behavior in robotic dolphins

Three different hovering modes, namely, the caudal fin, pectoral fins, and multi fins, were utilized to achieve the standing-and-hovering behavior in robotic dolphins. A three-dimensional dolphin model, consisting of body, caudal fin, and symmetric pectoral fins, was used as the virtual swimmer to implement three hovering modes. A novel paddling motion was proposed, and a symmetric shape was designed of the pectoral fins. The hovering mechanisms of different modes were revealed, and the mapping relationships between different motion and performance parameters such as hovering height, efficiency, stability, and rapidity were established. The respective advantages of the three hovering modes were compared. The results showed that the caudal fin mode had the best hovering stability, while the pectoral fins mode had the best hovering rapidity. Moreover, it is worth noting that the multi fins mode had both the good hovering stability and rapidity. Therefore, the optimal hovering mode and motion parameters can be selected based on different expected objectives to achieve the best results. This study provides a new approach to break through the spatial barriers to movement of underwater robots and provides a solid hydrodynamic theoretical basis for the development of cross-medium robots with multiple hovering modes.

Minimization of Aerial Cost and Mission Completion Time in Multi-UAV-Enabled IoT Networks

The application of unmanned aerial vehicles (UAVs) in IoT networks, especially data collection, has received extensive attention. Due to the urgency of the mission and limitation of the network cost, the mission completion time and number of UAVs are research hotspots. Most studies mainly focus on the trajectory optimization of the UAV to shorten the mission completion time. However, under different data collection modes, flying mode (FM) and hovering mode (HM), the collection time will also greatly affect the mission completion time. This paper studies the data collection from ground IoT devices (GIDs) in Multi-UAV enabled IoT networks. The problem of data collection is formulated to minimize the aerial cost and maximum mission completion time of UAVs by optimizing mission allocation, UAV trajectory, and UAVs’ flying speeds. In view of the complexity and non-convexity of the formulated problem, we propose a heuristic-based approximation algorithm to optimize the mission allocation of UAVs. Then, we specifically optimize the trajectory of the UAV for GIDs to minimize the flight time and collection time. Since the UAV’s flying speed affects the mission completion time, the successive convex approximation (SCA) technique is adopted to optimize it. Simulation results show that our scheme achieves the performance of near-optimal solution.

Experimental Investigation for a Small Helicopter in Hovering and Forward Flight Regimes

In this effort, experiments are conducted for a small-scale remotely controlled (RC) helicopter in both hovering and forward flight modes. An open wind tunnel type is used as a source of forward airflow for the helicopter model with flow speed (v∞) ranges from 3 to 12 m/s. A test rig was designed and manufactured to provide safe and reliable averaged thrust measurement in hovering and forward flight regimes. The helicopter is controlled via an adhoc-designed graphical user interface program using a microcontroller along with sensors to measure the blade collective pitch (θ0), rotational speed (Ω), and shaft angle of attack (αs). The averaged thrust for the helicopter is measured and compared with blade element theory and an unsteady model based on strip theory. Measurements are conducted for six rotational speeds and five collective pitch angles in hovering mode. Additionally, forward flight measurements were conducted for five rotational speeds, five collective pitch angles, two forward airflow speeds, and two shaft angles of attack. Uncertainty analysis is performed to certify a statement of the obtained results by combining both bias uncertainty from measuring instrument specifications and precision uncertainty through experimental repeatability. Results can be used for preliminary sizing of rotors for such small helicopters in both flight modes.

Underactuated hovering control of the minitype autonomous underwater helicopter

This work presents the development of the MAUH, a new type of minitype autonomous underwater helicopter capable of autonomous hovering using only four vertical thrusters. A nonlinear dynamic model of the MAUH was derived based on this underactuated hovering mode. The outer loop controller adopts integral sliding mode control (ISMC) to compute the intermediate command signal needed for the inner loop controller, while the inner loop controller, based on non-singular terminal sliding mode control (NTSMC), is utilized to track orientation error. Finally, simulations and experimental results demonstrate the effectiveness of the proposed underactuated hovering mode and control methods.

Mode Adaptive Secure UAV Relay Transmissions

Unmanned aerial vehicles (UAV) can enhance wireless transmission security by improving the secrecy rate through relaying the legitimate transmission and injecting artificial noise to the eavesdroppers. However, due to the inherent mechanical energy consumption and the long-range signal propagation pathloss, the traditional cruising and hovering UAV relay modes are deficient in energy utilization and secrecy rate, respectively. Modeling of the secrecy energy efficiency with respect to UAV mode adaptation is limited in the literature and deserves further investigation. Therefore, in this paper, we propose a secrecy rate-energy efficient UAV relay mode adaptation scheme for secure wireless communications scenarios where the eavesdropping locations are known, i.e., the eavesdropper is a hijacked internal legitimate node. In this secure system, the UAV cooperatively assists the legitimate transmissions and injects artificial interference to the eavesdropper. We investigate optimum UAV placement and relay period planning for the hovering and the cruising relay modes, respectively. By modeling the UAV modes transfer and maximizing the secrecy energy efficiency, the optimum mode adaptation ratios are obtained under both the secrecy rate-prioritized and the energy-saving criteria. In addition, the proposed UAV relay mode adaptation mechanism is further studied for each UAV task division, to adapt to the dynamic channel variations and enhance the security. Our theoretical analysis shows that the mode adaptation ratio is determined by the secrecy rate-energy gain between the cruising and the hovering modes, and by the energy consumption threshold of the UAV relays. Our numerical results demonstrate that the proposed scheme achieves higher secrecy energy efficiency than the traditional schemes.

Safe Reinforcement Learning for Transition Control of Ducted-Fan UAVs

Ducted-fan tail-sitter unmanned aerial vehicles (UAVs) provide versatility and unique benefits, attracting significant attention in various applications. This study focuses on developing a safe reinforcement learning method for back-transition control between level flight mode and hover mode for ducted-fan tail-sitter UAVs. Our method enables transition control with a minimal altitude change and transition time while adhering to the velocity constraint. We employ the Trust Region Policy Optimization, Proximal Policy Optimization with Lagrangian, and Constrained Policy Optimization (CPO) algorithms for controller training, showcasing the superiority of the CPO algorithm and the necessity of the velocity constraint. The transition trajectory achieved using the CPO algorithm closely resembles the optimal trajectory obtained via the well-known GPOPS-II software with the SNOPT solver. Meanwhile, the CPO algorithm also exhibits strong robustness under unknown perturbations of UAV model parameters and wind disturbance.

UAV Swarm for Connectivity Enhancement of Multiple Isolated Sensor Networks for Internet of Things Application

The Internet of Things (IoT) can be supported by multiple isolated sensor networks (MISN) when the connectivity of IoT is constrained by obstacles. Mobile nodes have been used as relays to connect partitioned networks. However, mobile nodes have the problem of not being able to move or moving slowly when encountering obstacles. In order to tackle this issue, three types of Unmanned Aerial Vehicle (UAV) swarm modes are proposed, and UAV swarm assisted connectivity enhancement algorithms (UsCE) are designed. A UAV swarm with high degree of freedom and flexibility provides a new way in IoT for solving the above connectivity problem. Our target is to find an optimal solution that minimizes the number of UAVs in the swarm and maximizes the connection time of MISN. We divide the working modes of a UAV swarm into hovering and flying. Firstly, the ground sink nodes are classified by a MISN's sink node classification algorithm to generate hovering points for the UAV swarm. Secondly, the results are optimized and adjusted by a minimum UAV swarm hovering connection algorithm to obtain an optimal solution under the hovering mode. Finally, we achieve an optimal connectivity when the UAV swarm works in flying mode through the UAV swarm flight connectivity algorithm and compare it with two previously proposed algorithms. Simulation results show that the complexity of the algorithms is low, the connection time of MISN increases significantly, and the number of UAVs is small. An optimal UAV swarm assisted connectivity enhancement scheme for MISN of different scales is derived.

МЕТОД ПІДТВЕРДЖЕННЯ РЕСУРСНИХ ХАРАКТЕРИСТИК МЕТАЛЕВОЇ ЛОПАТІ НЕСУЧОГО ГВИНТА ВЕРТОЛЬОТА ЗА РЕЗУЛЬТАТАМИ ВИПРОБУВАНЬ

The helicopter main rotor blade is the basic product that determines the reliability and service life of the helicopter as a whole. The problem of predicting and ensuring the specified blade life is an urgent problem considered at the stage of its design. The analysis of the design, structural materials and design and technological solutions of the main rotor blade (RB) of the Mi-8 helicopter has been carried out. A brief description of the main rotor blade of the Mi-8 helicopter is presented. The analysis was carried out and a standard flight cycle (SFC) of the helicopter was developed. The type of bench equipment for carrying out bench fatigue tests of the blade has been selected and justified. The loads on the main rotor blade for the SFC are determined. To determine the fatigue life of a blade, it is necessary to know the characteristics of the stress-strain state. The calculation of the stress-strain state (SSS) of a blade by the finite element method (FEM) using the ANSYS system is presented. The characteristics of the stress-strain state of the spar of the regular and irregular parts of the rotor blade of a helicopter are determined using the ANSYS system. The use of numerical methods for calculating the characteristics of the stress-strain state can significantly reduce the time and cost of designing a blade. The paper presents the results of calculating the regular part of the main rotor blade of the Mi-8 helicopter in the hover mode in the case of its loading with aerodynamic and inertial load from rotation, as well as the force from its own weight. With the help of the ANSYS system, a finite element model of the regular part of the blade was developed, consisting of a set of beam elements of variable section, a calculation was carried out taking into account the geometric nonlinearity of the structure's behavior, and an analysis of the results obtained was carried out. To describe the response of materials to an external action, a model of an elastically deformable isotropic body was used with the assignment of the corresponding elastic constants of the material. The analysis of the calculation results includes the determination of reactions at the attachment points, the values of the maximum displacements of structural elements and stresses in dangerous sections. Dangerous sections are determined and the values of the longitudinal force and bending moment in these sections are calculated. The assessment of the static strength of the blade by the safety factor was carried out. When evaluating the static strength, the equivalent stresses according to Mises were considered as the maximum design stresses. To assess the fatigue strength, we analyzed the distribution of the main tensile stresses in the power elements over typical stress concentrators. The maximum level of the main tensile stresses in the dangerous section indicates that the blade material operates in the zone of high-cycle fatigue. A technique for calibrating strain gauge channels has been developed. The calculation of the characteristics of the rotor blade of a helicopter is based on the requirements set forth in the technical literature, regulatory documents. When performing work, the requirements of the Aviation Rules, Part 29 (AP - 29) were taken into account. These studies were the basis for the development of a method for confirming the resource characteristics of a helicopter main rotor blade based on the results of flight and bench tests.

An Unmanned Helicopter Energy Consumption Analysis

The number of operations incorporating E-VTOL aircrafts is increasing each year, and the optimization of the energy consumption of such vehicles is a major problem. In this paper, a small-scale ARCHER helicopter’s energy consumption is analyzed, wherein different flight conditions, main rotor revolutions, and flight control system settings are considered. The helicopter dynamic model was developed in the FLIGHTLAB environment and was then validated based on flight test data. The model used for the calculation of energy consumption was developed using the electric and dynamic characteristics of the main rotor, electric motor, and transmission system. The main part of this work concerns the analysis of electric energy consumption during the vehicle’s flight via the use of an automatic flight control system (AFCS) that ensures repeatable flight conditions. The AFCS was designed such that it includes both path and attitude control to provide hover and cruise control modes. The helicopter’s energy consumption was analyzed during different phases of flight, when executing maneuvers, and using different main rotor angular velocities to perform - a given task. The results show that the level of energy consumption significantly depends on the helicopter’s main rotor revolutions, flight speed, and the maneuvers performed. The proposed methodology can be used in prospective energy-efficient mission planning and UAV helicopter design.

CFD-based pesticide selection for a nozzle used in a six-rotor UAV in hover mode for tea spraying.

A key challenge for unmanned aerial vehicle (UAV) spraying sometimes used in tea plantations is the downwash flow structure there stronger than in crops. In addition, the UAV spray is affected by the relationship between the nozzle design and the pesticide. However, there is little current research on this aspect. As a preliminary step this study focuses on the most appropriate pesticide for a designated nozzle in a six-rotor UAV according to the nozzle-pesticide relationship using a three-dimensional computational fluid dynamics model. This model considers the downwash flow structure effect and nozzle spray performance in hover. Nozzle FVP110-02, widely used in six-rotor UAVs, is used as a representative nozzle and bifenthrin and tea saponin water, commonly used in tea plantations, are used as the pesticides. The downwash flow structure of the six-rotor UAV in hover was conveniently controlled by the flight height and rotational speed, thereby causing the turbulence to be more stable. For nozzle FVP110-02, bifenthrin was more appropriate than tea saponin water at the same concentration, whilst bifenthrin and tea saponin water at a concentration of 1:1000 showed the best performance under identical working conditions. The numerical model developed here was shown to be effective for investigating the relationship between nozzle and pesticide. Our findings will help to not only improve UAV spraying for tea cultivation but also provide guidelines for pesticide selection in crops. Further work will address the comparison of the rigorous qualification of the numerical simulations with the measurements by the field test. © 2023 Society of Chemical Industry.

Modelling of Flow Characteristics of Main Rotor with Elliptical Root Section in Hover Mode

The modelling of a helicopter main rotor flow field in hover regime is being considered. The aerodynamic and aeroacoustics characteristics of two rotor models with different blade root geometries are compared. The first rotor has the shape of NACA0012 air foil in the root section of the blades. The second rotor model has an elliptic air foil in the root of the rotor blade. The amplitude and temporal characteristics of the aeroacoustics emission in near-field are investigated using Computational Fluid Dynamics (CFD).

Automatic bridge crack detection using Unmanned aerial vehicle and Faster R-CNN

In order to improve the efficiency and accuracy of bridge crack detection, this paper introduces Deep Learning for bridge crack detection with Unmanned Aerial Vehicles (UAVs). In this study, a method for deciding the distance range for stable imaging was used, and we have done a set of verification experiments on three types of UAVs. Then a Two-RTSs system for UAV hovering accuracy was proposed, and the displacement and attitude angle changes of UAV were acquired. The results indicated that DJI M210-RTK could acquire high-quality images at longer distances and had better stability in hover mode. So, we decided to use the DJI M210-RTK for bridge crack recognition. Finally, the Faster Region Convolutional Neural Network (Fatesr R-CNN) algorithm based on VGG16 transfer learning is used for the apparent detection of a bridge located in Hunan Province. Our method can achieve precision, recall and F1-score of 92.03 %, 96.26 %, and 94.10 %, respectively. The outcome of this study shows that automatic bridge crack detection using UAVs and Faster R-CNN can be more efficient while maintaining high accuracy.

To tread or not to tread: comparison between water treading and conventional flapping wing kinematics

Hovering insects are limited by their physiology and need to rotate their wings at the end of each back-and-forth motion to keep the wing’s leading edge ahead of its trailing edge. The wing rotation at the end of each half-stroke pushes the leading edge vortex away from the wing which leads to a loss in the lift. Unlike biological fliers, human-engineered flapping wing micro air vehicles have different design limitations. They can be designed to avoid the end of stroke wing rotation and use so-called water-treading flapping kinematics. Flapping wings using conventional flapping kinematics have a designated leading and trailing edge. In the water-treading mode, the role of the leading and trailing edges are continuously alternated throughout the stroke. Here, we compare velocity field and force measurements for a rectangular flapping wing conducting normal hovering and water-treading kinematics to study the difference in fluid dynamic performance between the two types of flapping kinematics. We show that for similar power consumption, the water-treading mode produces more lift than the conventional hovering mode and is 50% more efficient for symmetric pitching kinematics. In the water-treading mode, the leading edge vortex from the previous stroke is not pushed away but is captured and keeps the newly formed leading edge vortex closer to the wing, leading to a more rapid increase of the lift coefficient which is sustained for longer. This makes the water-treading mode a promising alternative for human-engineered flapping wing vehicles.

Rotor performance enhancement by alternating current dielectric barrier discharge plasma actuation

An experimental system was established to explore the plasma flow control effect for helicopter rotors in hover mode. With the plasma actuator applied at the leading edge of the rotor blades, alternating current dielectric barrier discharge (AC-DBD) plasma actuation was generated by a sinusoidal AC high-voltage generator. By direct force measurement, the influence of actuation parameters on the aerodynamic performance of the rotor was investigated at a tip Reynolds number of 1.7 × 105. AC-DBD actuation can delay the blade stall to more than 3° with a 20% increase of about in the thrust coefficient at the post-stall pitch. At a constant motor power driving the rotor, AC-DBD actuation could reduce the rotor’s torque at the stalled pitch and increase the rotational speed of the rotor. Also, AC-DBD actuation could maintain a relatively high hover efficiency of the rotor at large collective pitches. In a wide range of actuation parameters, AC-DBD plasma actuation could improve the rotor’s aerodynamic performance at large blade pitches. High-speed photography of the tuft motion on the blade’s upper surface showed that AC-DBD plasma actuation could promote the reattachment of the blade’s separation flow.

A novel [formula omitted] adaptive-hybrid control with guaranteed stability for a class of uncertain nonlinear systems: A case study on SA330 Puma

The helicopter is a highly unstable nonlinear non-minimum phase multiple-input multiple-output (MIMO) system with strong coupling between degrees of freedom. Therefore, its modeling will cause many problems such as control complexity. In addition, hover and forward flight modes are one of the most widely used helicopter flight modes used in many operations. To achieve and stay in these situations, you need very precise settings and timely manual control of the bird. This paper seeks to provide an L1 adaptive-hybrid control method to solve helicopter control problems in the Koppler system. In this regard, three channels in the coupler system are considered for the design of this controller. The proposed controller also proves the stability of the system during switching between channels. The helicopter that is modeled in this research and its data is used to implement and simulate the Coupler system control is the SA330 Puma helicopter, which is a medium-sized twin-engine support helicopter, in the category of 6 tons, built by Eurocopter France (ECF), and is in service several domestic operators and the armed forces, including the British Air Force. This device is a completely unstable dynamic system. In addition to the inherent instability of this bird, by adding an external load hanging to this system, the challenge of controlling this system is doubled hence, it is necessary to maintain its stability by using a suitable control system. In the meantime, the modeling of the hanging load should be done in three dimensions and two planes, and like most of the work done, only the movement of the plane should not be considered. For this purpose, an L1 adaptive-hybrid control method is proposed and fully developed in the paper, then it is properly designed for the Coupler system, which contains three channels: Pitch, Roll, and Collective, taking into account the load hanging on the helicopter. Finally, by simulating the results, it can be seen that the main goals, even in the presence of various disturbances, have the desired, efficient, and very good performance.

Numerical investigation of helicopter hover state of flight enhancement by applying active flow control over helicopter special tip airfoil

In conventional helicopter there are many operation limits and constraints, one of them is the maximum take-off weight and ability of main rotor to produce thrust during the hover mode of flight. In this study a numerical investigation is performed to show the effect of active flow control technique over the helicopter tip blade in hover mode to enhance the main rotor ability to produce lift by improving total performance of used airfoil. Active flow control applied to upper airfoil surface of blade tip close to the leading edge to control the boundary layer by adding momentum using small oscillating jet. The advantage of this technique comes from the small energy required to enrich the boundary layer which we use very small jet for excitation. Model is formed in 2D and is numerically investigated for airfoil used in main rotor blade tip with known geometry and performance parameter for clean rotor given by NASA test stand. Results shows very good impact on the hover mode in 2D model which gives enhancement in the overall performance represented by lift to drag ratio in the used tip airfoil in different case study used depending on the study plan that considered various excitation parameter. More than 60% increase in total performance represented by lift to drag ratio is obtained using suitable parameter and excitation point.

Three-dimensional sweeping motion effects on hovering dragonflies

This paper describes numerical simulations of the typical hovering mode of dragonfly wings with different sweeping motions. The simulation process involves solving the three-dimensional unsteady Navier–Stokes equations and exploring the effects of the sweeping motion on aerodynamic performance. Various parameters related to the three-dimensional sweeping motion are studied, including the sweeping amplitude, phase difference between flapping and sweeping motions, asymmetry of sweeping amplitudes of the forewing and hindwing, and frequency of sweeping motion. The results show that as the sweeping amplitude of the forewing and hindwing increases from 0 to 35°, the time-averaged lift and the lift efficiency increase by ∼4 times and ∼3.6 times respectively, while the power consumption first decreases and then increases. Moreover, increasing the sweeping amplitude delays the shedding of the trailing edge vortex. A phase difference of ∼60° between flapping and sweeping maximizes efficiency and the change in phase difference can lead to vertical forces in opposite directions on the forewing and hindwing. Accordingly, the flow field interference between the two wings will be more serious. Greater symmetry between the sweeping amplitudes of the two wings leads to better lift performance. There is an optimal sweeping frequency which is also the same as the flapping motion, representing an elliptical trajectory that can make lift ∼0.75 times higher. The optimal combination of various sweeping motion parameters may contribute to better aerodynamic performance in the hovering state. This research provides theoretical guidance for the design of dragonfly-like aircraft with multiple degrees of freedom.