Morphing Aircraft Research Articles

Research on morphing aircraft maneuver control based on active disturbance rejection control

Aiming at the problems of model uncertainties caused by morphing aircraft during morphing process and disturbance encountered when maneuvering, a morphing aircraft maneuver control method based on active disturbance rejection control (ADRC) is proposed to eliminate the influences of model uncertainty and external disturbance and improve the rapidity and accuracy of maneuver control. Firstly, a nonlinear model for morphing aircraft is established and the impact mechanism of morphing process is analyzed. Then, the ADRC technique is used to design the angular rate robust control law and the control performance of ADRC law is analyzed under the influence of disturbance. Finally, the immelmann turn maneuver is selected to verify the performance of the designed control law with aerodynamic parameters perturbation combined with the morphing process. The simulation results show that the method possesses good decoupling effect and strong disturbance rejection ability. Moreover, the aircraft's maneuverability and the control margin of control surface can be effectively improved through morphing

Numerical Simulation of Folding Tail Aeroelasticity Based on the CFD/CSD Coupling Method

This paper presents a CFD/CSD coupling method for aeroelastic simulation of folding tail morphing aircraft. The unsteady aerodynamic analysis is based on an in-house computational fluid dynamics (CFD) solver for the Euler equations, and emphasis is made on developing an efficient dynamic mesh method for the tail’s hybrid fold motion/elastic vibration deformation. The structural dynamic analysis is based on the computational structural dynamics (CSD) technique for solving the structural equation of motion in modal space. The aeroelastic coupling was achieved through successive iterations of CFD and CSD computations in the time domain. An adaptive multi-functional morphing aircraft allowing tail fold motion was selected to be studied. By using the developed method, aeroelastic simulation and mechanism analysis for fixed configurations at different folding angles and for variable configurations during the folding process were performed. The influence of folding rate on tail aeroelasticity and its influence mechanism were also analyzed.

Neural network-based adaptive optimal tracking control for hypersonic morphing aircraft with appointed-time prescribed performance

In this paper, an adaptive optimal attitude tracking controller for hypersonic morphing aircraft with appointed-time prescribed performance is presented. A proper error transformation methodology is developed to ensure the performance constraints are met without knowing initial tracking conditions. Subsequently, an adaptive composite control scheme is devised for the transformed system, comprising a feedforward neuro-backstepping controller and a feedback optimal controller. The former is employed to convert the optimal tracking problem into an equivalent optimal regulation problem, while the latter is constructed using adaptive dynamic programming (ADP) with a single critic network to achieve optimality. A novel weight-tuning law for the critic network is introduced, incorporating a stability indicator and the concurrent learning technique. This approach relaxes the underlying restrictive conditions in ADP, improving the robustness and availability of the system. The stability of the closed-loop system is analyzed using the Lyapunov direct method. Finally, the effectiveness and improved performance of the proposed control scheme are validated through numerical simulations.

Current Status and Development Trends of Morphing Wing of Aircraft

Abstract:: Aircraft morphing wings, also known as adaptive wings or shape-variable wings, represent a revolutionary development in the field of aerospace engineering. Inspired by the adaptability observed in birds and insects during flight, researchers have been exploring potential applications of morphing wing technology to enhance the performance and efficiency of aircraft. This innovative technology holds the promise of improving aerodynamic efficiency, reducing fuel consumption, and enhancing overall flight maneuverability. This manuscript aims to explore and analyze the potential applications and effects of morphing wing technology for aircraft. Furthermore, this paper aims to gain an in-depth understanding of the principles and implications of morphing wing technology for aircraft and to assess its potential advantages in terms of flight performance, handling characteristics, and energy efficiency. Based on different driving mechanisms, patents related to aircraft morphing wings were systematically categorized and summarized, highlighting the most typical intra-wing and extra-wing deformations. Through an examination of patents related to aircraft morphing wings, various morphing wing technologies' unique characteristics were summarized. A comparative analysis of different deformation methods revealed their respective strengths and limitations. The paper concludes with a summary of current technical challenges facing morphing wing technology and a forward-looking exploration of its future trends and directions. Categorizing aircraft morphing wings into intra-wing and extra-wing deformations based on the method of deformation, this paper elaborates on the operational principles, advantages, and limitations of these two categories. Compared to traditional fixed wings, morphing wings exhibit superior flight performance, and it is anticipated that more patents will be developed in the future.

Unsteady aerodynamic characteristics of a morphing tail configuration

Morphing aircraft is an important trend in the future development of next-generation aircraft. This paper focuses on aircraft with a small aspect ratio flying wing configuration that includes morphing tails. The unsteady aerodynamic characteristics of the morphing tail configuration are numerically simulated using the unstructured overset grid technique and the dual-time method, focusing on the effects of the tail deflection angle over time, Mach number, and side slip angle on the unsteady aerodynamic characteristics of the entire aircraft and tails. The second derivative of the tail deflection angle with time should be continuous, and the maximum angular velocity and maximum angular acceleration should be minimized. The hysteresis loop area is closely related to the Mach number. The sideslip angle aggravates the nonlinearity of the unsteady aerodynamic characteristics of the entire aircraft. The unsteady aerodynamic characteristics during tail morphing are affected by static (wing downwash effect and projected area effect) and dynamic (flow field hysteresis effect, additional motion effect, and wall implication effect) characteristics. The enclosed research provides a reference for the aerodynamic and control system designs of morphing tail configurations.

Autonomous Shape Decision Making of Morphing Aircraft with Improved Reinforcement Learning

The autonomous shape decision-making problem of a morphing aircraft (MA) with a variable wingspan and sweep angle is studied in this paper. Considering the continuity of state space and action space, a more practical autonomous decision-making algorithm framework of MA is designed based on the deep deterministic policy gradient (DDPG) algorithm. Furthermore, the DDPG with a task classifier (DDPGwTC) algorithm is proposed in combination with the long short-term memory (LSTM) network to improve the convergence speed of the algorithm. The simulation results show that the shape decision-making algorithm based on the DDPGwTC enables MA to adopt the optimal morphing strategy in different task environments with higher autonomy and environmental adaptability, which verifies the effectiveness of the proposed algorithm.

Gliding Analysis of Segmented Flapping Wing

A variety of aircraft morphing technologies have been investigated and represented by various researchers in the public domain. The morphing wing concepts involved the modification of aircraft wings during the in-flight course. Most of the technologies/concepts were based on biomimicry, where wing aerodynamic performance improved due to the change in wing shape. Here we describe a novel concept where in the flow parameters of airfoils arranged in configurations are investigated. The flow parameters are investigated using the numerical simulation tool ANSYS. A 2d flow simulation is performed using a Fluent solver to evaluate the flow configuration of the airfoils arranged in different configurations. The first configuration of airfoils is named a base, wherein the airfoils are arranged at zero angles of attack. The other two configurations are arranged by increasing the angular position of airfoils i.e., 15, 30, and 45 degrees. All these configurations are aerodynamically investigated at different sub-sonic speeds.

Neural network based adaptive nonsingular practical predefined-time fault-tolerant control for hypersonic morphing aircraft

This paper develops a novel Neural Network (NN)-based adaptive nonsingular practical predefined-time controller for the hypersonic morphing aircraft subject to actuator faults. Firstly, a novel Lyapunov criterion of practical predefined-time stability is established. Following the proposed criterion, a tangent function based nonsingular predefined-time sliding manifold and the control strategy are developed. Secondly, the radial basis function NN with a low-complexity adaptation mechanism is incorporated into the controller to tackle the actuator faults and uncertainties. Thirdly, rigorous theoretical proof reveals that the attitude tracking errors can converge to a small region around the origin within a predefined time, while all signals in the closed-loop system remain bounded. Finally, numerical simulation results are presented to verify the effectiveness and improved performance of the proposed control scheme.

Research on the Performance of Slender Aircraft with Flare-Stabilized-Skirt

In this paper, a morphing aircraft with a deployable flared skirt is proposed, and the influence of the flare skirt on the static stability of hypersonic aircraft is studied. The theoretical model of static stability of slender aircraft is established, and the position of the center of pressure can be used as a theoretical basis to measure static stability. Three-dimensional compressible Reynolds-averaged Navier–Stokes (RANS) solver and an SST k-ω turbulence model are used to analyze the aerodynamic characteristics of the aircraft and the influence effect of the flared skirt on the pressure distribution of the body, and the influence trend on the position of the pressure center is verified. At the same time, the reliability of the code and grid is verified by a classic example, and the results are in good agreement with the experimental data in the current literature. Finally, the static stability of an aircraft with flared skirts with different deployment angles is quantitatively measured by defining the stability derivative at the common point. The results show that the static stability of the aircraft with the same forebody is improved by more than 100% under different flight Mach numbers when the flared skirt deployment angle is 30° compared to 0°.

L1 Adaptive Control Based on Dynamic Inversion for Morphing Aircraft

Morphing aircraft are able to keep optimal performance in diverse flight conditions. However, the change in geometry always leads to challenges in the design of flight controllers. In this paper, a new method for designing a flight controller for variable-sweep morphing aircraft is presented—dynamic inversion combined with L1 adaptive control. Firstly, the dynamics of the vehicle is analyzed and a six degrees of freedom (6DOF) nonlinear dynamics model based on multibody dynamics theory is established. Secondly, nonlinear dynamic inversion (NDI) and incremental nonlinear dynamic inversion (INDI) are then employed to realize decoupling control. Thirdly, linear quadratic regulator (LQR) technique and L1 adaptive control are adopted to design the adaptive controller in order to improve robustness to uncertainties and ensure the control accuracy. Finally, extensive simulation experiments are performed, wherein the demonstrated results indicate that the proposed method overcomes the drawbacks of conventional methods and realizes an improvement in control performance.

Control Design and Flight Test of Aerodynamics-Driven Monoplane–Biplane Morphing Aircraft

Increasing the aspect ratio of the wing of an aircraft reduces drag and increases its range and endurance. However, a large wingspan complicates takeoff and landing. Therefore, an aerodynamics-driven monoplane–biplane morphing (MBM) aircraft was proposed, which cruises as a high-aspect-ratio monoplane and takes off and lands as a biplane, switching between two patterns during flight. This concept of MBM was validated in our previous work via wind tunnel experiments. We further develop it beyond this phase and introduce its applications under real flight conditions here. We constructed a test plane with a wingspan of 6 m and conducted a series of flight experiments on it. To examine its performance and facilitate its initial flight test, we built aerodynamic and dynamic models of the aircraft to analyze its morphing behavior through simulations. The corresponding controller algorithm and hardware system were also developed. The successful implementation of these systems enables bidirectional morphing during flight from a large-span monoplane to a half-span biplane. The test results, comprising data and photographs, validated the success of these trials. The concept of MBM, the corresponding models, and the control algorithm for morphing were thus verified.

Optimization design of a novel zero Poisson’s ratio honeycomb structure for in-plane mechanical performance

The excellent deformation performance of structure is the material basis of intelligent morphing aircraft. In this study, a zero Poisson’s ratio honeycomb structure consisting of sinusoidal corrugated walls is applied to morphing aircraft. The in-plane mechanical properties of the structure are deduced theoretically based on the assumption of small strain. According to the application requirements of tensile deformation and shear deformation, an optimization model is established with geometric parameters as optimization variables, and its mechanical properties are optimized by interior point method. The results show that the equivalent mechanical properties of the new zero-Poisson ratio honeycomb structure are greatly improved. The research provides important reference for the innovative design and optimization of honeycomb structures.

Rapid Parametric CAx Tools for Modelling Morphing Wings of Micro Air Vehicles (MAVs)

This paper shows a series of tools that help in the research of morphing micro air vehicles (MAVs). These tools are aimed at generating parametric CAD models of wings in a few seconds that can be used in aerodynamic studies, either via CFD directly using the model obtained or via wind tunnel through rapid prototyping with 3D printers. It also facilitates the analysis of morphing wings by allowing for the continuous parametric deformation of the airfoils and the wing geometry. In addition, one of the tools greatly simplifies the purely experimental design of this type of vehicle, allowing the transfer of experimental measurements to the computer, generating virtual models with the same deformation as the physical model. This software has two fundamental parts. The first one is the parameterization of the airfoils, for which the CST (Class-Shape Transformation) method will be used. CST coefficients can be modified according to the actuator variable that changes the wing geometry. The second part is the generation of a three-dimensional parametric model of the wing. We used OpenCASCADE technology in its Python version called PythonOCC, which enables the generation of geometries with good surface quality for typical and non-standard wing shapes. Finally, the use of this software for the study of a morphing aircraft will be shown, as well as improvements that could be incorporated in the future to increase its capabilities for the design and analysis of MAVs.

Analysis of the Short-Term Dynamics of Morphing Aircraft Caused by Shape Change Based on the Open-Loop Response and the Reachable Set Theory

This work investigates the short-term dynamics caused by shape changes of morphing aircraft. We select a symmetric variable sweep morphing aircraft as the object of study and establish a six-degree-of-freedom multi-loop cascade model, and the coupling between derivative terms is eliminated by matrix transformation. Considering that the change in aerodynamic shape significantly affects the aerodynamic forces of the aircraft in a short period of time, and the variation in mass distribution generates additional aerodynamic forces and moments, we analyze the effects of these factors on the dynamic characteristics of the aircraft based on the open-loop response starting from the steady-state flight conditions. In addition, we analyze the improvement in maneuvering performance brought by morphing as an additional control input. We apply reachable set theory to multi-loop equations of motion and use the size of the reachable set to measure the maneuverability of aircraft. The results confirm that morphing can effectively improve the maneuverability of the aircraft.

Bio-inspired design and performance evaluation of a novel morphing nose cone for aerospace vehicles

An effective way to improve the flight capability and environmental adaptability of aerospace vehicles is to design a morphing aircraft structure, which can actively change their aerodynamic shape. During different physiological activities, the abdomens of bees are regularly deformed to improve the efficiency of movement. This was used as an inspiration for the design of a nose cone for aerospace vehicles. Based on the deformation mechanism of the bee abdomen, a bionic design of a variable configuration morphing nose cone (MNC) mechanism with high sensitivity is proposed, which can realize real-time reverse self-locking of the mechanism via auxiliary branch chains. Theoretical models for the kinematics and dynamics of the MNC mechanism under two configurations are derived, verifying that the proposed mechanism has good kinematic and dynamic characteristics. The theoretical models are validated through simulation studies. In addition, static finite element simulations are performed to verify that the auxiliary locking branch chain can significantly improve the bearing capacity of the proposed mechanism. Moreover, the force and thermal parameters of different configurations of the MNC under corresponding typical working conditions are analyzed, enabling the improvement of the aerospace vehicle aerodynamic characteristics by the morphing of its nose cone. Finally, based on the analytic hierarchy process, different drag and heat flux reduction schemes are comprehensively evaluated.

Analysis and design of control systems via parameter‐based approach

Analysis and design of control systems via parameter‐based approach

Application of electrolaminates for the development of biomimetic morphing unmanned aerial vehicles

Morphing aircraft offer the promise of performance that can be optimized for a range of flight profiles. But such capability places challenging demands on the morphing system that cannot easily be met with conventional actuators or smart materials. Electrolaminates use electrostatic forces controlled by the application of a voltage (typically high-voltage but extremely low-current) to controllably bond or unbond layers of a laminated composite structure together. Such on-demand bonding can be used to effectively change the stiffness of the structure or control elongation or twist of the structure. This technology has multiple benefits compared to other smart material or conventional actuator-driven approaches; it is thin and light, has very low energy requirements, and offers rapid response capabilities controlled by simple electronics. These capabilities can enable bio-inspired morphing with large numbers of degrees of freedom and high spatial resolution. We designed, fabricated, and tested a fully functional morphing-wing unmanned aerial vehicle (UAV) with telescoping wings and a splaying, bird-like tail enabled by electrolaminates. Key features of the current UAV configuration include: a variable wingspan of 1.2–2.4 m with a corresponding change in the wing area of nearly a factor of four; no vertical tail; and a horizontal tail area variable by a factor of three. The ability to asymmetrically control the tail area allows for independent pitch and body circulation control. The tail area is changed by a separate electrolaminate clamping mechanism. The variable-area tail uses ‘feathers’ that can be overlapped or splayed as needed. The practical shape-changing is enabled by electrolaminate materials that can rapidly lock the orientation of the feathers. The electrolaminate clutches support more than 5 nm of torque and are sufficient to resist expected flight loads. We also designed, fabricated, and tested other morphing-wing designs enabled by electrolaminate technology to create a wing with smoothly sliding skin that is capable of changing chord and camber with a single linear actuator. Our results suggest that electrolaminates can practically enable bio-inspired, small (Group 1 and 2) morphing UAVs.

A Nonlinear Programming-Based Morphing Strategy for a Variable-Sweep Morphing Aircraft Aiming at Optimizing the Cruising Efficiency

This work develops a morphing decision strategy to optimize the cruising efficiency for a variable-sweep morphing aircraft, and a simple and practical guidance and control system is given as well. They can work in tandem to accomplish a cruise mission effectively. To make the morphing decision accurately, we take into account the equilibrium equations of forces; the variations in airspeed, altitude, and mass and the optimal configurations for different cruise conditions are solved based on the nonlinear programming method with the objective of minimum engine thrust. Considering that a large amount of computational resources are required to solve the nonlinear programming problems, we establish an offline database of the optimal configurations and design a database-based online morphing decision process. In addition, the proposed morphing decision strategy includes an anti-disturbance mechanism, which ensures that the optimal configuration can be given accurately without chattering under fluctuating airspeed measurements. Comparative results from the simulations finally validate the effectiveness of the proposed strategy.

Application Status and Future Prospect of Aircraft Morphing Wing

Application Status and Future Prospect of Aircraft Morphing Wing

Adaptive fault-tolerant controller for morphing aircraft based on the L2 gain and a neural network

This paper presents an adaptive neural network fault-tolerant controller approach for the parameters of morphing aircraft that change violently during changing sweep angle processes and with morphing mechanisms that are prone to failure. We establish a nonlinear dynamic model of a morphing aircraft and analyze the variation laws of the aircraft parameters at different sweep angles. Considering the dynamic changes of the aircraft in morphing and morphing mechanism failure, by using recursive damped least squares (RDLS) to estimate the aircraft system model and offset the adverse effects of parameter mutation on the system, a radial basis function neural network (RBFNN) is used to further compensate for unmodeled parts such as actuator delay. The L2 gain is used to design a robust controller to constrain the errors generated by the RDLS and RBFNN in the learning process. The closed-loop stability is guaranteed by Lyapunov stability theory and the technique of compact set. Lastly, the comparison results of simulation indicate that this method satisfies the design criteria in the morphing process and fault situations, confirming the robustness of the controller.