Hardware-in-loop adaptive neural control for a tiltable V-tail morphing aircraft

This paper proposes an adaptive neural control(ANC)method for the coupled nonlinear model of a novel type of embedded surface morphing aircraft which has a tiltable V-tail.A nonlinear model with sixdegrees-of-freedom is established.The first-order sliding mode differentiator(FSMD)is applied to the control scheme to avoid the problem of“differential explosion”.Radial basis function neural networks are introduced to estimate the uncertainty and external disturbance of the model,and an ANC controller is proposed based on this design idea.The stability of the proposed ANC controller is proved using Lyapunov theory,and the tracking error of the closed-loop system is semi-globally uniformly bounded.The effectiveness and robustness of the proposed method are verified by numerical simulations and hardware-in-the-loop(HIL)simulations.

Novel robust control framework for morphing aircraft

This paper develops a robust control methodology for a class of morphing aircraft,which is called innovative control effector（ICE） aircraft.For the ICE morphing aircraft,the distributed arrays of hundreds of shape-change devices are employed to stabilize and maneuver the air vehicle.Because the morphing aircraft have the inherent uncertainty and varying dynamics due to the alteration of their configuration,a desired control performance can not be satisfied with a fixed feedback controller.Therefore,a novel control framework including an adaptive flight control law and an adaptive allocation algorithm is proposed.Firstly,a state feedback adaptive control law is designed to guarantee closed-loop stability and state tracking in the presence of uncertain dynamics caused by the wing shape change due to different flight missions.In the control allocation,many distributed arrays are managed in an optimal way to improve the robustness of the system.The scheme is used to an uncertain morphing aircraft model,and the simulation results demonstrate their performance.

A review of control strategies used for morphing aircraft applications

This paper reviews the various control algorithms and strategies used for fixed-wing morphing aircraft applications. It is evident from the literature that the development of control algorithms for morphing aircraft technologies focused on three main areas. The first area is related to precise control of the shape of morphing concepts for various flight conditions. The second area is mainly related to the flight dynamics, stability, and control aspects of morphing aircraft. The third area deals mainly with aeroelastic control using morphing concepts either for load alleviation purposes and/or to control the instability boundaries. The design of controllers for morphing aircraft/wings is very challenging due to the large changes that can occur in the structural, aerodynamic, and inertial characteristics. In addition, the type of actuation system and actuation rate/speed can have a significant effect on the design of such controllers. The aerospace community is in strong need of such a critical review especially as morphing aircraft technologies move from fundamental research at a low Technology Readiness Level(TRL) to real-life applications. This critical review aims to identify research gaps and propose future directions. In this paper, research activities/papers are categorized according to the control strategy used. This ranges from simple Proportional Integral Derivative(PID) controllers at one end to complex robust adaptive controllers and deep learning algorithms at the other end. This includes analytical, computational, and experimental studies. In addition, the various dynamic models used and their fidelities are highlighted and discussed.

A novel adaptive coordinated tracking control scheme for a morphing aircraft with telescopic wings

Inspired by flight biology,morphing flight technology has great potential to improve the adaptability and maneuverability of aircraft.This paper is devoted to the flight control problem of morphing aircraft,and aimed at safe and fuel-saving flight through morphing actively.Specifically,the longitudinal dynamics of a morphing aircraft with telescopic wings is modelled as a strict-feedback nonlinear system.Through fitting the expression of aerodynamic parameters by the mor-phing ratio,the model uncertainties induced by morphing errors are embedded in the dynamics.To meet the safety and fuel-saving requirements,an Adaptive Coordinated Tracking Control Scheme(ACTCS)is then proposed,which consists of a morphing control module and a tracking control module.For the morphing control module,an on-line morphing decision model is given in an optimization process with respect to the morphing ratio,and a second-order tracking filter is introduced to smooth the decision output and ensure the physical realizability.For the tracking control module,the novel adaptive controllers for the velocity and altitude subsystems are proposed based on the dynamic surface control method,in which adaptive mechanisms are designed to com-pensate for the model uncertainties.Finally,the proposed ACTCS is simulated in nine different cases of the test flight mission,to verify its effectiveness,robustness and fuel-saving effect.

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.

Design and applications of morphing aircraft and their structures

Morphing aircraft can adaptively regulate their aerodynamic layout to meet the demands of varying flight conditions,improve their aerodynamic efficiency,and reduce their energy consumption.The design and fabrication of high-performance,lightweight,and intelligent morphing structures have become a hot topic in advanced aircraft design.This paper discusses morphing aircraft development history,structural characteristics,existing applications,and future prospects.First,some conventional mechanical morphing aircraft are examined with focus on their morphing modes,mechanisms,advantages,and disadvantages.Second,the novel applications of several technologies for morphing unmanned aerial vehicles,including additive manufacturing for fabricating complex morphing structures,lattice technology for reducing structural weight,and multi-mode morphing combined with flexible skins and foldable structures,are summarized and categorized.Moreover,in consideration of the further development of active morphing aircraft,the paper reviews morphing structures driven by smart material actuators,such as shape memory alloy and macro-fiber composites,and analyzes their advantages and limitations.Third,the paper discusses multiple challenges,including flexible structures,flexible skins,and control systems,in the design of future morphing aircraft.Lastly,the development and application of morphing structures in the aerospace field are discussed to provide a reference for future research and engineering applications.

Design,modeling,and control of morphing aircraft:A review

A morphing aircraft can adapt its configuration to suit different types of tasks,which is also an important requirement of Unmanned Aerial Vehicles(UAV).The successful development of an unmanned morphing aircraft involves three steps that determine its ability and intelligent:configuration design,dynamic modeling and flight control.This study conducts a comprehensive survey of morphing aircraft.First,the methods to design the configuration of a morphing aircraft are presented and analyzed.Then,the nonlinear dynamic characteristics and aerodynamic interference caused by a morphing wing are described.Subsequently,the dynamic modeling and flight control methods for solving the flight control problems are summarized with respect to these features.Finally,the general as well as special challenges ahead of the development of intelligent morphing aircraft are discussed.The findings can provide a theoretical and technical reference for designing future morphing aircraft or morphing-wing UAVs.

A systematic method of smooth switching LPV controllers design for a morphing aircraft

This paper is concerned with a systematic method of smooth switching linear parameter- varying （LPV） controllers design for a morphing aircraft with a variable wing sweep angle. The morphing aircraft is modeled as an LPV system, whose scheduling parameter is the variation rate of the wing sweep angle. By dividing the scheduling parameter set into subsets with overlaps, output feedback controllers which consider smooth switching are designed and the controllers in over- lapped subsets are interpolated from two adjacent subsets. A switching law without constraint on the average dwell time is obtained which makes the conclusion less conservative. Furthermore, a systematic algorithm is developed to improve the efficiency of the controllers design process. The parameter set is divided into the fewest subsets on the premise that the closed-loop system has a desired performance. Simulation results demonstrate the effectiveness of this approach.

Flexible smart sensing skin for“Fly-by-Feel”morphing aircraft

Flexible smart sensing skin is a key enabling technology for the future"Fly-by-Feel"control of morphing aircraft.It represents the next-generation skin of aircraft that can exhibit a more powerful sensing function than a conventional one and could be mounted on arbitrary curvilinear surfaces,especially for advanced autonomic,morphing aircraft.Recent significant technical advances in flexible electronics have overcome many historic drawbacks of conventional smart skin,e.g.,only a limited number of discrete block sensors can be integrated due to the inevitable structural damage and heavy guidelines.Herein,we review the key developments in flexible sensors technology and highlight both the state-of-the-art devices and the potential applications for the measurement of aircraft.We begin with the importance of flexible smart skin for morphing aircraft and then expand to the latest progress in various types of flexible sensors.Then we highlight flexible sensors as smart skin to measure aerodynamic parameters and monitor the structural health,and further to achieve the Fly-by-Feel control.Finally,the challenges and opportunities on flexible smart sensing skin are discussed,from the functional design to practical applications.

Gain self-scheduled H_∞ control for morphing aircraft in the wing transition process based on an LPV model

This article investigates gain self-scheduled H 1 robust control system design for a tailless fold- ing-wing morphing aircraft in the wing shape varying process. During the wing morphing phase, the aircraft＇s dynamic response will be governed by time-varying aerodynamic forces and moments. Nonlinear dynamic equations of the morphing aircraft are linearized by using Jacobian linearization approach, and a linear parameter varying （LPV） model of the morphing aircraft in wing folding is obtained. A multi-loop controller for the morphing aircraft is formulated to guarantee stability for the wing shape transition process. The proposed controller uses a set of inner-loop gains to provide stability using classical techniques, whereas a gain self-scheduled H 1 outer-loop controller is devised to guarantee a specific level of robust stability and performance for the time-varying dynamics. The closed-loop simulations show that speed and altitude vary slightly during the whole wing folding process, and they converge rapidly after the process ends. This proves that the gain self-scheduled H 1 robust controller can guarantee a satisfactory dynamic performance for the morphing aircraft during the whole wing shape transition process. Finally, the flight control system＇s robustness for the wing folding process is verified according to uncertainties of the aerodynamic parameters in the nonlinear model.

Non-fragile switched H_∞ control for morphing aircraft with asynchronous switching

This paper deals with the problem of non-fragile linear parameter-varying（LPV） H_∞ control for morphing aircraft with asynchronous switching.The switched LPV model of morphing aircraft is established by Jacobian linearization approach according to the nonlinear model.The data missing is taken into account in the link from sensors to controllers and the link from controllers to actuators,which satisfies Bernoulli distribution.The non-fragile switched LPV controllers are constructed with consideration of the uncertainties of controllers and asynchronous switching phenomenon.The parameter-dependent Lyapunov functional method and mode-dependent average dwell time（MDADT） method are combined to guarantee the stability and prescribed performance of the system.The sufficient conditions on the solvability of the problem are derived in the form of linear matrix inequalities（LMI）.In order to achieve higher efficiency of the designing process,an algorithm is applied to divide the whole set into subsets automatically.Simulation results are provided to verify the effectiveness and superiority of the method in the paper.

Recent Progress on Aeroelasticity of High-Performance Morphing UAVs

The high-performance morphing aircraft has become a research focus all over the world.The morphing aircraft,unlike regular unmanned aerial vehicles(UAVs),has more complicated aerodynamic characteristics,making itmore difficultto conduct its design,model analysis,and experimentation.This paper reviews the recent process and the current status of aeroelastic issues,numerical simulations,and wind tunnel test of morphing aircrafts.The evaluation of aerodynamic characteristics,mechanism,and relevant unsteady dynamic aerodynamicmodeling throughout the morphing process are the primary technological bottlenecks formorphing aircrafts.The unstable aerodynamic forces have a significant impact on the aircraft handling characteristics,control law design,and flight safety.In the past,the structural analysis of morphing aircrafts,flight dynamics modeling,computational mesh morphing technology,and aerodynamic calculation were performed in promoting the development of next generation UAVs,with nonlinear dynamic challenges includingtransonic aeroelastic problems and high angle of attack aeroelastic problems.At present,many facets of these difficulties,together with the accompanying numerical simulation studies,remain under-explored.In addition,wind tunnel experiments face significant challenges in the dynamic morphing process.Finally,dynamic unsteady aerodynamic characteristics in the continuous morphing process still need to be verified by more related experiments.

Transient aeroelastic responses and flutter analysis of a variable-span wing during the morphing process

To investigate the transient aeroelastic responses and flutter characteristics of a variablespan wing during the morphing process,a novel frst-order state-space aeroelastic model is proposed.The time-varying structural model of the morphing wing is established based on the Euler-Bernoulli beam theory with time-dependent boundary conditions.A nondimensionalization method is used to translate the time-dependent boundary conditions to be time-independent.The time-domain aerodynamic forces are calculated by the reduced-order unsteady vortex lattice method.The morphing parameters,i.e.,wing span length and morphing speed,are of particular interest for understanding the fundamental aeroelastic behavior of variable-span wings.A test case is proposed and numerical results indicate that the flutter characteristics are sensitive to both of the two morphing parameters.It could be noticed that the aeroelastic characteristics during the wing extracting process are more serious than those during the extending process at the same morphing speed by transient aeroelastic response analysis.In addition,a faster morphing process can get better aeroelastic performance while the mechanism comlexity will arise.

Correction method of airfoil thickness effect in hinge moment calculation of a folding wing

The influences of airfoil thickness on the aerodynamic loading distribution and the hinge moments of folding wing aircraft are presented in this work.The traditional panel method shows deficiencies in the calculation of folding wing's hinge moments.Thus, a thickness correction strategy for the aerodynamic model with CFD results is proposed, and an aeroelastic flight simulation platform is constructed based on the secondary development of ADAMS.Based on the platform,the developed aerodynamic model is verified, then the flight-folding process of the folding wing aircraft is simulated, and the influences of airfoil thickness on the results are investigated.Results show that the developed aerodynamic model can effectively describe the thickness effect of the folding wing.Airfoil thickness, which cannot be considered by the panel method, has a great influence on the hinge moments during the folding process, and the thickness correction has great significance in the calculation of folding wing's hinge moments.

Deployment of SMP Miura-ori sheet and its application:Aerodynamic drag and RCS reduction

Origami,such as Miura-ori,is the art of folding two-dimensional materials into complex,elaborate,and multifunctional three-dimensional objects.In this paper,SMP MO sheet are prepared,and the accuracy of deployable process is verified by experiments.The folding and deployable process of SMP MO sheet is divided into 4 stages,and each stage is described in detail.The stiffness of smart deployable stage is characterized by an exponential decline at the beginning and a gradual decrease to 0,and this is similar to the theoretical shear equivalent modulus in the Y direction.The effects of various parameters on strain and stress are also explored.The purpose of studying these mechanical characteristics is to provide driving force reference in application;In terms of application,the flow field and electromagnetic characteristics of MO sheet in different directions are studied.The aerodynamic drag and RCS reduction of MO unit cell and graded MO sheet during the deployable process are evaluated.When the dihedral fold angle is about 45°,the RCS reduction and drag reduction characteristics of MO sheet are relatively optimal,which is most beneficial to morphing aircraft.