Flight Stability Research Articles

Numerical Investigation of an Unmanned Aerial Vehicle Launch from Military Transport Aircrafts

Launching a fixed-wing unmanned aerial vehicle (UAV) out of the cargo hold of a flying transport aircraft (TA) is numerically investigated. A numerical tool chain is established to capture the dynamic motion of the UAV during launch, in which the DLR-TAU Code flow solver is coupled with a flight mechanics tool. A parameter study investigates how the UAV launch speed, position, and orientation relative to the loading platform of two different TAs affect its trajectory and aerodynamic behaviors. Furthermore, the influence of the angle of attack of the TA on the UAV trajectory and pitch angle is analyzed. This information will help design a launch mechanism that ensures a safe separation and aerodynamically stable flight after launch.

Learning‐based collision avoidance and robust H∞ optimal formation control for uncertain quadrotor UAV systems

AbstractThis paper investigates the robust optimal formation control for the position subsystem of quadrotor unmanned aerial vehicles (UAVs) subject to external disturbances and collision constraints. To prevent collision with both members of the formation and external obstacles, a collision avoidance potential function is constructed using relative position and velocity information. The basic bounded control input can ensure the stable flight and collision avoidance of a quadrotor UAV system. Based on the approximate dynamic programming (ADP) framework and two‐player zero‐sum differential game theory, the optimal controller is designed to further enhance the control performance of the system. The optimal value function is approximated by a single layer neural network, which avoids solving complex nonlinear Hamilton‐JacobiIsaac (HJI) equation. The stability of the closed loop system is proved. The effectiveness of the robust optimal formation controller based on learning is validated through MATLAB simulation in two distinct scenarios.

Develop and Design Small Scale UAV

Nowadays, many people want to buy a small-scale unmanned aerial vehicle (UAV) either for recreational purposes, photography and video editing or for air surveillance. The main issue with conventional small-scale UAVs is that they require experience to operate them. Besides that, the control system also plays important role for its flight stability and endurance for small-scale UAV. The weight of the load and travelling speed also being issued for small-scale UAV. As a result, three objectives were formulated based on the problem statement which are to fabricate the appropriate size of a small-scale UAV in term of its mass and frame size; to design the control system and increase the stability of the small-scale UAV; and to test the flight endurance of the small-scale UAV. This research is conducted through the following methodology, which is designing the quadcopter body mainframe, constructing the circuit diagram, developing the RC transmitter and receiver for Arduino and testing the UAV functionality and flight test. Softwares that were involved in this project are Solidworks, Arduino compiler, Proteus, Processing and Matlab. The equipments that are used are Arduino UNO, MPU-6050 sensor, Li-Po 11.1V battery, Electronic Speed Controller (ESC), brushless DC motor, 2.4 GHZ RC transmitter and 6-channel receiver. The limitation also being found from those experiments. Finally, the results and discussion will show and explain about the early sketch for quadcopter body mainframe including dimension for each part and stress-strain diagram using Solidworks. It also includes the simulation and hardware connection for brushless DC motor and MPU-6050 sensor using Proteus, Arduino compiler, Processing and Matlab software.

QUAV attitude control based on linear active disturbance rejection control

Unmanned Aerial Vehicle (UAV) are currently gaining popularity. This paper proposes a method to apply Linear Active Disturbance Rejection Control (LADRC) to Quadrotor Unmanned Aerial Vehicle (QUAV) controller to optimize the traditional PID controller. Firstly, the application and shortcomings of traditional PID control in UAV are introduced, and the LADRC method is proposed. Then linear simplification and Parameter Setting of ADRC are carried out. In the Simulink environment, according to the mathematical model of the QUAV, a QUAV dynamics simulation platform is established. Finally, according to different control channels, different control algorithms are designed, and tracking models are introduced in various attitudes to simulate and verify the control effect of LADRC. The results show that the LADRC controller is effective, the LADRC can be effectively combined with the traditional PID control. The application in the QUAV can realize more precise QUAV speed tracking control and the stable flight of the QUAV. Compared with the traditional PID controller, under the experimental conditions of this paper, the LADRC controller has more precise control accuracy and more efficient control efficiency. Finally, this paper summarizes the design of LADRC and makes a brief outlook on the development of UAVs.

Full envelope nonlinear flight controller design for a novel electric VTOL (eVTOL) air taxi

AbstractOn-demand urban air transportation gains popularity in recent years with the introduction of the electric VTOL (eVTOL) aircraft concept. There is an emerging interest in short/medium range eVTOL air taxi considering the critical advantages of electric propulsion (i.e. low noise and carbon emission). Using several electric propulsion systems (distributed electric propulsion (DEP)) has further advantages such as improved redundancy. However, flight controller design becomes more challenging due to highly over-actuated and coupled dynamics. This study defines and resolves flight control problems of a novel DEP eVTOL air taxi. The aircraft has a fixed-wing surface to have aerodynamically efficient cruise flight, and uses only tilting electric propulsion units to achieve full envelope flight control via pure thrust vector control. The aircraft does not have conventional control surfaces such as aileron, rudder or elevator. Using pure thrust vector control has some design benefits, but the control problem becomes more challenging due to the over-actuated and highly coupled dynamics (especially in transition flight). A preliminary flight dynamics model is obtained considering the dominant effects at hover and high-speed forward flight. Hover and forward flight models are blended to simulate the transition dynamics. Two central challenges regarding the flight control are significant nonlinearities in aircraft dynamics during the transition and proper allocation of the thrust vector control specifically in limited control authority (actuator saturation). The former challenge is resolved via designing a sensor-based incremental nonlinear dynamic inversion (INDI) controller to have a single/unified controller covering the wide flight envelope. For the latter one, an optimisation-based control allocation (CA) approach is integrated into the INDI controller. CA requires special attention due to the pure thrust vector control’s highly coupled dynamics. The controller shows satisfactory performance and disturbance rejection characteristics. Moreover, the CA plays a vital role in guaranteeing stable flight in case of severe actuator saturation.

Solar-Powered Drone for Extended Flight Time

Drones can now fly for longer periods and have a smaller carbon footprint. These drones have solar cells that use sunlight's energy to power the drone and other components on board. Agriculture, disaster relief, and environmental protection can all benefit from the development of solar-powered drones. The present research aims to increase battery life so that flights can last longer. It gives a general overview of the drone's parts and solar cells, outlining potential applications. Incorrect weight distribution can cause instability and make it difficult to achieve lift, rendering the drone incapable of flight and confined to ground-based operations The drone being discussed has a well-balanced weight distribution, which restricts its functionality and prevents it from flying correctly. Proper weight distribution has been achieved in the drone under consideration in this study, leading to stable flight and improved endurance.

Grasping extreme aerodynamics on a low-dimensional manifold

Modern air vehicles perform a wide range of operations, including transportation, defense, surveillance, and rescue. These aircraft can fly in calm conditions but avoid operations in gusty environments, encountered in urban canyons, over mountainous terrains, and in ship wakes. With extreme weather becoming ever more frequent due to global warming, it is anticipated that aircraft, especially those that are smaller in size, will encounter sizeable atmospheric disturbances and still be expected to achieve stable flight. However, there exists virtually no theoretical fluid-dynamic foundation to describe the influence of extreme vortical gusts on wings. To compound this difficulty, there is a large parameter space for gust-wing interactions. While such interactions are seemingly complex and different for each combination of gust parameters, we show that the fundamental physics behind extreme aerodynamics is far simpler and lower-rank than traditionally expected. We reveal that the nonlinear vortical flow field over time and parameter space can be compressed to only three variables with a lift-augmented autoencoder while holding the essence of the original high-dimensional physics. Extreme aerodynamic flows can be compressed through machine learning into a low-dimensional manifold, which can enable real-time sparse reconstruction, dynamical modeling, and control of extremely unsteady gusty flows. The present findings offer support for the stable flight of next-generation small air vehicles in atmosphere conditions traditionally considered unflyable.

Dynamic Flight Stability of a Hovering Flapping-Rotary-Wing Vehicle

The aerodynamic performance and mechanisms of the compound layout of flapping-rotary-wing (FRW) vehicles have been studied extensively in the literature, but open-loop stability has rarely been involved. To bridge this gap, a hovering stability analysis of a 30 g FRW prototype has been conducted. Averaged-model assumptions and small-disturbance linearization method were used to formulate the model, in which the stability derivatives were calculated using numerical simulation. The modal characteristics and physical causes were studied with the techniques of eigenvalue and eigenvector analysis and compared with those of a helicopter. The results show that the FRW has two unstable modes: an unstable oscillatory mode and a slow divergence mode. The former mode features a horizontally circling trace of the center of gravity, coupled with a periodic oscillation of pitch and roll angles, which is dominated by a coupling roll (or pitch) moment produced by a forward (or sideward) speed perturbance. The latter mode features a decreased (or increased) wing rotation speed accompanied by an increasing downward (or upward) motion speed of the body owing to a strong dependence between the aerodynamics and the passive rotation of the wing. Longitudinal–lateral coupling and rotational–vertical coupling mark the distinction in modal characteristics between the FRW and the helicopter. The model and results of this study may offer a reference for the stability analysis and control design for FRW vehicles.

Modeling and Simulation Analysis of Bionic Flapping-Wing Flight Attitude Control Based on L1 Adaptive

Flapping-wing flight control is a multi-input and multi-output nonlinear system with uncertainties, which is affected by modeling errors, parameter variations, external disturbances, and unmodeled dynamics. Parameter uncertainty has a great impact on the stability control of flapping-wing flight, and gain adjustment is a common means to deal with parameter uncertainty, but it is complex and time-consuming. Based on the mechanism of flapping-wing flight, a nonlinear dynamic model for flapping-wing dynamic flight is established by analyzing the forces, moments, and attitude changes of the fuselage and wing in detail. Based on the constructed dynamic model, a fast robust adaptive flapping-wing flight control method is proposed. The state predictor is designed to estimate and monitor the uncertain parameters in the flapping-wing attitude control model, and the adaptive law adjusts the parameter estimation to ensure that the output error between the state predictor and the controlled object is stable in the Lyapunov sense, and finally the adaptive control law is obtained. At the same time, the Monte Carlo-support vector machine method is used to optimize the boundary of the control parameters in the flight control to obtain the control parameters that can meet the control expectations, and the obtained parameters are classified and judged according to the stable level flight conditions. Based on the adjusted parameters and the predetermined control signal, the control amount is adjusted according to the control law. When the adaptive gain is large enough, the simulation results show that the system has good transient response characteristics.

Self-Tuning PID Controller for Quadcopter using Fuzzy Logic

Tracking has become a necessary feature of a drone. This is due to the demand for drones, especially quadcopters, to be used for activities such as surveillance, monitoring, and filming. It is crucial to ensure the quadcopters perform the tracking with stable flight. Despite the advantages of having VTOL ability and great maneuverability, quadcopters require an effective controller to overcome their under-actuation and instability behavior. Even though a PID controller is commonly used and promising with its simple mechanism, it requires very proper tuning to ensure the stability of the system is not affected. In this paper, a simple Fuzzy algorithm is proposed to be incorporated into a PID controller to form a self-tuning Fuzzy PID controller. The Fuzzy logic controller works as the self-adjuster to the PID parameters. A mathematical model of the DJI Tello quadcopter is derived with position and attitude control loops that are designed to track a variety of trajectories with stable flight. The proposed method uses a simple architecture where the ranges of PID parameters are used as scaling factors for Fuzzy controller outputs. The results of the simulations show the tracking error performance metrics, which are IAE, ISE, and RMSE, are smaller compared to the values of the PID controller. Beyond its impact on quadcopter control, the proposed self-tuning approach holds promise for broader applications in nonlinear systems.

CONTROL SYSTEMS OF PRIMARY AND ALTERNATIVE POWER SUPPLY SOURCES OF UNMANNED AERIAL VEHICLES

The article is devoted to the development of technical possibilities for organizing the energy supply of UAVs. Through the Controlled blocks of the optical system, an issue aimed at identifying and solving possible problems that will occur in the process of power supply of drones due to alternative energy sources and ground-related power sources distributed in different areas was developed. Considering the possibilities of power supply distribution and attenuation in the areas where power sources are located, the possibilities of application of UAVs for control of the research object at a stable flight height have been studied and solved. A study of the limiting conditions and threshold values required for the power of signals received from a food source is presented. Keywords: UAV, Optical system, alternative energy transfer, atmosphere, sources of nutrition.

Transition to turbulence in the wake of dandelion-like spoke disk

In order to solve the inevitable instability problem of dandelion-like unpowered aircraft, transient simulations are carried out for the transition to turbulence of the wake from stable to unstable stage under different Reynolds numbers, and the vortex mode characteristics presented by the vortex structure as the Reynolds number increases are identified. Furthermore, by monitoring the velocity and lift and drag coefficients at different positions in dandelion flow field, the spectral characteristics of flow velocity and aerodynamic coefficients in the turbulent phase triggered by extreme aerodynamic environment are revealed. Compared with solid disk, it is found that the bandgap structure is more conducive to expanding the stable flight threshold of the dandelion-like aircraft, that is, the canopy configuration has weakening effect on airflow fluctuations. In addition, an evaluation method for unsteady boundary Reynolds number and load capacity of a dandelion-like aircraft is presented. The proposed method aims to plan a reasonable number of filaments (or porosity) for further designing dandelion-like aircraft with flight stability and high load capacity under aerodynamic conditions at different Reynolds numbers.

Simultaneous arm morphing quadcopter and autonomous flight system design

Purpose The purpose of this paper is to obtain values that stabilize the lateral and longitudinal flight of the quadrotor for which the morphing amount and the best Proportional-Integral-Derivative (PID) coefficients are determined by using the simultaneous perturbation stochastic approximation (SPSA) optimization algorithm. Design/methodology/approach Quadrotor consists of body and arms; there are propellers at the ends of the arms to take off and rotors that rotate them. By reducing the angle between mechanism 1 and the rotors with the horizontal plane, the angle between mechanism 2 and the arms, the rotors rise and different configurations are obtained. Conventional multi-rotor aircraft has a fixed fuselage and does not need a tail rotor to change course as helicopters do. The translational and rotational movements are provided by the rotation of the rotors of the aircraft at different speeds by creating moments about the geometric center in 6-degree-of-freedom (DOF) space. These commands sent from the ground are provided by the flight control board in the aircraft. The longitudinal and lateral flight stability and properties of different configurations evaluated by dynamic analysis and simulations in 6 DOF spaces are investigated. An algorithm and PID controller are being developed using SPSA to achieve in-flight position and attitude control of an active deformable aircraft. The results are compared with the results of the literature review and the results of the previous article. Findings With SPSA, the best PID coefficients were obtained in case of morphing. Research limitations/implications The effects of quadrotor arm height and hub angle changes affect flight stability. With the SPSA optimization method presented in this study, the attitude is quickly stabilized. Practical implications With the optimization method, the most suitable PID coefficients and angle values for the lateral and longitudinal flight stability of the quadrotor are obtained. Social implications The transition rate and PID coefficients are determined by using the optimization method, which is advantageous in terms of cost and practicality. Originality/value With the proposed method, the aircraft can change shape to adapt to different environments, and the parameters required for more stable flight for each situation will be calculated, and this will be obtained more quickly and safely with the SPSA optimization method.

Vortices and Forces in Biological Flight: Insects, Birds, and Bats

Insects, birds, and bats that power and control flight by flapping their wings perform excellent flight stability and maneuverability by rapidly and continuously varying their wing motions. This article provides an overview of the state of the art of vortex-dominated, unsteady flapping aerodynamics from the viewpoint of diversity and uniformity associated with dominant vortices, particularly of the relevant physical aspects of the flight of insects and vertebrates in the low- and intermediate-Reynolds-number ( Re) regime of 100 to 106. After briefly describing wing morphology and kinematics, we discuss the main vortices generated by flapping wings and the aerodynamic forces associated with these structures, focusing on leading-edge vortices (LEVs), wake vortices, and vortices generated by wing motions over a broad Re range. The LEVs are intensified by dynamic wing morphing in bird and bat flight, producing a significantly elevated vortex lift. The complex wake vortices are the footprints of lift generation; thus, the time-averaged vortex lift can be estimated from wake velocity data. Computational fluid dynamics modeling, quasi-steady models, and vortex lift models are useful tools to elucidate the intrinsic relationships between the lift and the dominant vortices in the near- and far-fields in flapping flight.

Effect of Bending Deformation on the Lateral Force of Spinning Projectiles with Large Aspect Ratio

The bending deformation can affect the lateral force of spinning projectiles with large aspect ratios, thus interfering with their flight stability. Based on the established spin–deformation coupling motion model, the unsteady Reynolds averaged Navier–Stokes (URANS) equations are solved to simulate the flow over a large−aspect−ratio projectile undergoing spin and spin−deformation coupling motion by using the dual−time stepping method and dynamic mesh technique, obtaining the lateral force. Furtherly, the flow mechanism is analyzed for the changed lateral force induced by the bending deformation. The results indicate that the variation of transient lateral force for the head of a projectile is consistent with that of the deformation−induced additional sideslip angle; affected by the deformation−induced compression wave and expansion wave, the time−averaged lateral force for the middle of a projectile will be increased at small angles of attack, but changed little at large angles of attack; at small angles of attack, the change trend of transient lateral force for the tail of a projectile is similar to that of additional angle of attack caused by the deformation; at large angles of attack, the characteristic of phase lag is presented between the transient lateral force for the tail of a projectile and the additional sideslip angle.

Research on Variable-Swept Hybrid Aerial Underwater Vehicle Plunge-Diving Control Based on Adaptive Dynamic Surface Control

The variation in aerodynamic parameters during the process of a variable sweepback hybrid aerial underwater vehicle (HAUV) affects flight stability. During the air–water trans-media locomotion, there are medium mutations and solid–liquid gas coupling phenomena, resulting in the complex dynamic process of HAUV. To ensure stable control during the trans-media process of a variable sweepback vehicle, this study proposes a neural-network-based adaptive dynamic surface control method for aircraft flight-path angle. This method aims to establish an effective control model for the entire process of air to media transition, in response to the characteristics of uncertainty and external disturbances in the process of variable backsweeping in the air and media transition. By utilizing the multibody dynamics method, the dynamic equations for variable-swept vehicles are established and transformed into a rigorous feedback system with model uncertainty. The adaptive dynamic surface method in this paper introduces a first-order filter, which overcomes the “differential explosion” problem in traditional backstepping control design through differential filtering; the unknown parameters present in the model are estimated online through adaptive laws, and the uncertain parts of the system are overcome through nonlinear damping items. By analyzing Lyapunov stability, the semi-global stability of the required closed-loop system can be obtained, and adjusting the controller parameters can make the tracking error infinitely small. Numerical simulations are conducted to illustrate the tracking control of flight-path angles for different plunge-diving angle rates and strategy of ingress. The results show that HAUV with variable-swept configuration with different strategy has a great effect on the stability of plunge-diving locomotion; the designed controller can effectively track the target trajectory and has a certain degree of robustness and adaptability.

Numerical Analysis of Bioinspired Tails in a Fixed-Wing Micro Air Vehicle

Bird tails play a key role in aerodynamics and flight stability. They produce extra lift for takeoff and landing maneuvers, enhance wing functions and maintain stability during flight (keeping the bird from yawing, rolling and pitching, or otherwise losing control). This paper investigates the use of bioinspired horizontal stabilizers for Micro Air Vehicles (MAVs) involving a Zimmerman wing-body geometry. A selection of five tail shapes of the main types existing in nature is presented, and a parametric analysis is conducted looking into the influence of the most relevant tail geometric parameters to increase the longitudinal static stability of the vehicle. Based on the parametric study, a smaller subset of candidate tail designs are shortlisted to perform a detailed aerodynamic analysis. Then, steady RANS CFD simulations are conducted for a higher-fidelity study of these candidate tail designs to obtain an optimum of each tail type. The criterion for selection of the optimum tail configuration is the maximum aerodynamic efficiency, CLCD , as well as a high longitudinal static stability. The squared-fan tail provides the highest aerodynamic efficiency while maintaining a high longitudinal stability of the vehicle. In conclusion, this paper provides an innovative study of improving longitudinal stability and aerodynamics through the implementation of bioinspired horizontal stabilizers in vehicles with these characteristics.

Development of Unmanned Aerial Vehicle for Detecting the Forest Fires

In recent years, forest fires can be brought under control in line with the information obtained from Unmanned Aerial Vehicles (UAVs), which play an important role in determining the progression of fires, detecting heat points and determining intervention locations. In this study, if the UAV detects the fire by autonomously positioning in the area where the fire is located, the point where the fire reaches the most intense temperature is determined with the help of the thermal camera, and it is ensured that the fireball is dropped to the target with a 100% success rate. The requirements of the UAV, which will be produced in order to realize this task, such as fast, load-carrying and stable flight are also taken into consideration. In addition to being economical and long-lasting of the materials inside, it will be able to fly efficiently in most weather conditions (foggy, dark, etc.). In the construction of the UAV, a domestic Electronic Speed Controller (ESC) with a unique design is produced to meet the sufficient current. With this acquisition, ESC, which will meet the requirements by sending sufficient current to more than one Brushless DC (BLDC) motor, has been tested on our Radio Controlled (RC) aircraft and included in the project.

Trajectory Tracking of a Quadcopter UAV using PID Controller

UAVs or Drones are aircraft with no onboard pilot to control the flight. They are introduced in a few categories such as single-rotor, multi-rotors, fixed-wing, and hybrid VTOL. As for multirotor drones, quadcopters are the most well-known either commercially or in the research field. Due to its advantages, a quadcopter has been chosen to perform various tasks across various fields such as entertainment, military, meteorological reconnaissance, civil and emergency responses. As the demand for quadcopters has diverged, the required features of quadcopters have also diverged. One of the current features required by quadcopters is the ability to track trajectories. However, due to its nature of non-linearity, under-actuated and unstable, controlling quadcopter for an accurate and stable performance is quite a challenge. Despite the various proposed methods throughout the past decades, PID controller is still used as either the main controller or the base controller in most cases of industrial control, including quadcopter, mainly due to its simplicity and robustness. However, to design a proper PID controller for quadcopter system is a challenge as it defies the control inputs of four with its six degree-of-freedom form, in which six inputs are required to be controlled to ensure a stable and accurate flight. This paper derived a mathematically model of a quadcopter with Newton-Euler’s equation. Some assumptions on the body and structure of the quadcopter are taken into account to make the modelling possible. Then, a manually tuned PID controller is designed to achieve the objective of controlling the operation and stability of the quadcopter during its flight. The designed controller is tested with five different trajectories which are circular, square, lemniscate, zigzag, and spiral. The results show the proposed controller successfully tracks the desired trajectories, which prove PID controller can be used to control a quadcopter.

Aerial Torsional Work Utilizing a Multirotor UAV with Add-on Thrust Vectoring Device

Aerial manipulation aims to combine the versatility and the agility of aerial platforms with the manipulation capabilities of robotic arms. Their fast deployment allows for their implementation in maintenance tasks and support during disaster situations. However, the under-actuated nature of multirotor UAVs limits the magnitude and direction of the forces an aerial vehicle can safely exert during manipulation tasks. In this paper, the problems associated with UAVs and torsional tasks constraints regarding valve turning are addressed. An add-on thrust vectoring device which enhances manipulation options available to a conventional multirotor UAV is developed and described. The proposed system allows for a partial decoupling of the attitude and velocity vector of a multirotor. This permits stable translational flight and higher torque capabilities for torsional tasks. The separation of attitude and the velocity vector that allows for the design of a passive mechanism for valve operation is presented in this paper as well. The experimental results illustrate the forces and torques that can be generated in the evaluated operation modes.