Morphing Wing Research Articles

Morphing flap driven by link with antagonistic shape memory alloy wires

Abstract This paper describes a study of a morphing flap using antagonistically arranged shape memory alloy (SMA) wires as actuators. The main focus of this study is to examine how existing aircraft structures and mechanisms can be modified to make the morphing airfoil more practical. The first step is to consider the drawbacks of existing morphing airfoils and then examine the advantages of the morphing airfoil proposed in this study. Then, a morphing airfoil is proposed to realize four significant technical issues: weight reduction, compatibility with existing structures, securing internal space, and seamless skin made with shape memory polymer (SMP) films. First, elemental experiments were conducted to examine the feasibility of the mechanical design, and the feasibility of the design of a large-morphing airfoil operating test model was confirmed. Next, aerodynamic and structural-mechanical analyses are conducted while designing the experimental operating model to verify whether it could operate up to the target flap angle under simulated flight conditions. After completing the experimental model, actuation tests are conducted as a morphing wing and confirm whether the wing could operate at the target flap angle in a realistic environment. As a result, the two-way morphing flap angle was experimentally observed. It is noted that only aerodynamic force was not considered in the experiment, which is further investigated in wind tunnel tests in future study. In addition, control rate of the proposed system seems improved than conventional model because of the reduction of the wire length of the actuation system. Thus, the results obtained in this study suggested the proposed link-driven SMA wire mechanism can be applied to make the morphing airfoil more practical.

Design and dynamic analysis of a spanwise morphing wing for Mars exploration

The application of spanwise morphing wings makes it possible to transport and launch large-size Mars exploration UAVs. This article proposes a modular variable spanwise morphing wing for high-aspect-ratio aircrafts, and analyses the characteristics of the morphing wing by theoretical analysis, numerical simulation and experimental verification. The novel spanwise morphing wing is based on the Sarrus-inspired deployable structure, which can increase the wing's lift by changing the spanwise length. The pre-strain torsion springs are assembled to provide the initial driving moment of the morphing mechanism. A regular triangle cross section is selected by evaluating the bending and torsional stiffness, and deployable triangular prism mechanisms are identified. Through releasing the pre-strain torsion springs to achieve expansion and implant Sarrus linkages along the straight motion paths. A lockable structure is designed, and the main factors affecting the self-locking property are analysed. A rigid origami skin is proposed, which maintains the airfoil's continuous smoothness after spanwise morphing. The kinematics of the spanwise morphing wing unit is developed using the Lagrange equation, and the theoretical models of morphing wings with different numbers of units are obtained. The unit numbers influence fully expanded time, and the time decreases gradually along the wingtip's direction. Finally, a one-way fluid-structure interaction analysis is performed to investigate the spanwise morphing mechanism and origami skin response under aerodynamic loads. Results show that the skeleton mechanism's maximum stress is below the material's yield strength, and the origami skin's maximum out-of-plane deformation is less than 0.5% of the wing chord, which provides a necessary theoretical basis for applying the spanwise morphing wing.

Fixed-time attitude control for hypersonic morphing vehicles: A dynamic memory event-triggering approach

This paper focuses on achieving fast attitude tracking and resource preservation for hypersonic morphing vehicles (HMVs) in continuous morphing stages. Firstly, the most remarkable feature of an HMV are the morphing wings, leading to dramatic aerodynamic property changes. As a result, fast tracking and excellent adaptation to various morphing statuses are necessary to guarantee the success of flight missions. Thus, this work employs the fixed-time stability theory to establish a high-performance controller, including variable exponent coefficients. Compared to the traditional constant exponent coefficient-based methods, some singularity problems are avoided, and the global fixed-time stability is ensured. Then, in order to implement the control input in a low-resource occupation, the dynamic event-triggering mechanism is presented to provide a flexible updating policy. The proposed event-triggering technology has a more concise and efficient structure than the traditional methods. In this case, the controller and the dynamic variable of the event-triggering method simultaneously adopt the exponent coefficients. Finally, the closed-loop stability is proven via the Lyapunov thesis, and simulation results show the effectiveness and the advantage of the proposed control strategy.

CGull: A Non-Flapping Bioinspired Composite Morphing Drone.

Despite the tremendous advances in aircraft design that led to successful powered flights of aircraft as heavy as the Antonov An-225 Mriya, which weighs 640 tons, or as fast as the NASA-X-43A, which reached a record of Mach 9.6, many characteristics of bird flight have yet to be utilized in aircraft designs. These characteristics enable various species of birds to fly efficiently in gusty environments and rapidly change their momentum in flight without having modern thrust vector control (TVC) systems. Vultures and seagulls, as examples of expert gliding birds, can fly for hours, covering more than 100 miles, without a single flap of their wings. Inspired by the Great Black-Backed Gull (GBBG), this paper presents "CGull", a non-flapping unmanned aerial vehicle (UAV) with wing and tail morphing capabilities. A coupled two degree-of-freedom (DOF) morphing mechanism is used in CGull's wings to sweep the middle wing forward and the outer feathered wing backward, replicating the GBBG's wing deformation. A modular two DOF mechanism enables CGull to pitch and tilt its tail. A computational model was first developed in MachUpX to study the effects of wing and tail morphing on the generated forces and moments. Following the biological construction of birds' feathers and bones, CGull's structure is mainly constructed from carbon-fiber composite shells. The successful flight test of the proof-of-concept physical model proved the effectiveness of the proposed morphing mechanisms in controlling the UAV's path.

Development and investigation for rigid-flexible coupling dynamic performances of the morphing wing with clearance joints

Morphing wings have enjoyed much research interest due to their advantages in improving aircraft adaptability to various service environments. A single drive and continuous variable bending morphing mechanism with multiple configurations is proposed. The morphing wing designed based on this mechanism can have the advantages of lightweight, multiple configurations and smooth morphing shapes. Transient aerodynamic loads will destroy the dynamic performance of the wing during the multi-mode morphing process. Therefore, it is crucial to analyze the vibration characteristics for the reliability of the morphing wing. However, it is difficult to obtain its dynamic model and solution because of the complex configuration and the multi-mode morphing. In this paper, a mathematical model for the multi-mode morphing of the morphing mechanism based on lockable joints is described using the constraint equation firstly. Then, a rigid-flexible coupling dynamic model of the morphing wing with clearance joints is established. Finally, the influence of the infective joint and the flexible link on the vibration properties of the morphing wing is analyzed in detail. Moreover, differences in the dynamic parameters between rapid and regular actuation are discussed. The results obtained in this paper have an important engineering value for the design and manufacture of the morphing wing.

Inverse design of bistable composite laminates with switching tunneling method for global optimization

Bistability enables adaptive designs with tunable deflections for applications including morphing wings, robotic grippers, and consumer products. Composite laminates may be designed to exhibit bistability due to pre-strains that develop during the processing of the polymer matrix, enabling fast reconfiguration between two stable shapes. Unfortunately, designing bistable laminates is challenging because of their highly nonlinear behavior. Here, we propose the Switching Tunneling Method to address this challenge by alternating between gradient-based local minimization and tunneling search phases, with the enhancement of objective expression switching to improve numerical conditioning. Results demonstrate high effectiveness compared to existing optimizers; the Switching Tunneling Method achieves a 99% success rate in finding all energy minima across general composite layups. Additionally, our method facilitates the inverse design of variable pre-strain fields, enabling bioinspired, positive Gaussian curvatures, which are not possible with conventional pre-strain laminates. Validations through both finite element analysis and 3D printed samples confirm the optimal designs.

Influence of bioinspired morphing on the flow field characteristics of UAV wings at low Reynolds number

The aerodynamic performance of unmanned aerial vehicles (UAV) can be improved by optimizing the surface flow characteristics over a wide range of angle of attack (AoA) through novel mechanisms. Recently, the bioinspired camber morphing concept has received greater attention because of the proven ability of nature species towards the retention of aerodynamic performance under different environmental conditions. In particular, birds like Eagles ( Accipitriformes) increase their wing camber in the course of flight to achieve maximum climbing altitude with good manoeuvring capability. The biomimetic designs such as the corrugated bone structure of Eel fish ( Anguilliformes) helps to achieve the wing camber morphing with optimal aerodynamic load distributions. The present work is focused on the bioinspired variable camber morphing (VCM) strategy to enhance the flow control behaviour and aerodynamic forces for a specific UAV wing configuration at various AoA. Here, NACA 4412 airfoil is used as a baseline wing configuration and the camber morphing mechanisms which are derived through Eel fish and Eagle are analysed. The model with Eagle wing morphing (EWM) mechanism is considered as a primary case of VCM and Eel fish’s corrugated structure is taken as a secondary case of VCM model. The coefficient of lift ( C L ), coefficient of drag ( C D), coefficient of pressure ( C p) and endurance factor are estimated for both morphed and baseline wing configurations through high fidelity numerical simulations. Interestingly, it is observed that the EWM wing configuration has excellent surface flow control characteristics than the CSM wing configuration and the results are presented with a detailed discussion.

Steady as they hover: kinematics of kestrel wing and tail morphing during hovering flights.

Wind-hovering birds exhibit remarkable steadiness in flight, achieved through the morphing of their wings and tail. We analysed the kinematics of two nankeen kestrels (Falco cenchroides) engaged in steady wind-hovering flights in a smooth flow wind tunnel. Motion-tracking cameras were used to capture the movements of the birds as they maintained their position. The motion of the birds' head and body, and the morphing motions of their wings and tail were tracked and analysed using correlation methods. The results revealed that wing sweep, representing the flexion/extension movement of the wing, played a significant role in wing motion. Additionally, correlations between different independent degrees of freedom (DoF), including wing and tail coupling, were observed. These kinematic couplings indicate balancing of forces and moments necessary for steady wind hovering. Variation in flight behaviour between the two birds highlighted the redundancy of DoF and the versatility of wing morphing in achieving control. This study provides insights into fixed-wing craft flight control from the avian world and may inspire novel flight control strategies for future fixed-wing aircraft.

ECR Spotlight – Mario Martinez Groves-Raines

ECR Spotlight is a series of interviews with early-career authors from a selection of papers published in Journal of Experimental Biology and aims to promote not only the diversity of early-career researchers (ECRs) working in experimental biology but also the huge variety of animals and physiological systems that are essential for the ‘comparative’ approach. Mario Martinez Groves-Raines is an author on ‘ Steady as they hover: kinematics of kestrel wing and tail morphing during hovering flights’, published in JEB. Mario is a PhD Student in the lab of Dr Shane Windsor (University of Bristol, UK), Dr Abdulghani Mohamed (RMIT, Australia) and Professor Simon Watkins (RMIT, Australia), investigating the flight of birds from an aerodynamics and flight control perspective, learning and inspiring new flight techniques for human-made aircraft.

Time-Varying Aeroelastic Modeling and Analysis for a Morphing Wing

The paper presents a novel time-varying aeroelastic modeling approach for the morphing wing with the process of camber changing. The time-varying modeling methodology includes structural dynamics modeling, unsteady aerodynamic modeling, and interpolation for fluid–structure coupling. Firstly, the morphing wing is modularized and divided into fixed and variable parts by the floating frame of reference formulation. It is combined with the Craig–Bampton method to reduce order and eliminate nonindependent degrees of freedom. Then, the unsteady vortex-lattice method is used to calculate the transient, unsteady aerodynamic force for time evolution. Furthermore, the above time-varying structural dynamics modeling and a fluid–structure coupling interpolation are integrated to construct overall aeroelastic modeling, obtaining a set of differential-algebraic equations. Finally, these equations are numerically solved by the generalized-α method. The proposed approach provides an innovative idea to deal with the incredible complexity of the aeroelastic effect as structural characteristics change over time. It can efficiently and accurately analyze the morphing wing’s transient response or flutter property. To verify and utilize the time-varying aeroelastic modeling approach, numerical calculations and comparative studies were carried out regarding the time-varying characteristics of the structural modes, aerodynamic calculations, and flutter prediction of the morphing wing.

The Coupled Wing Morphing of Ornithopters Improves Attitude Control and Agile Flight

The Coupled Wing Morphing of Ornithopters Improves Attitude Control and Agile Flight

Innovative Skin Structures: Synthesis, Void Analysis, and Hysteresis Modeling of Zero Poisson’s Ratio Skin for Span Morphing Wing

This paper explores the use of carbon fiber-reinforced elastomeric skins for advancing flexible morphing wing technologies, highlighting exceptional 1D morphing capabilities. The study focuses on synthesizing a specially engineered elastomer-based skin with a zero Poisson’s ratio, achieved through precise formulation and fabrication onto unidirectional carbon fiber. Poisson’s ratio of the 1D skin is confirmed to be zero via image analysis. Micro-CT tomography evaluates carbon fiber quality and voids under varied prestretch conditions, revealing proportional increases in void sizes. X-ray tomography also provides insights into void distribution and morphology during pre- and post-cyclic stretching. The innovative approach enables seamless 1D morphing, achieving an impressive 200% stretch with a slight increase in actuation force and hysteresis loss percentage. Inspired by continuum mechanics, the proposed “Exp-ln-ln” framework accurately models the loading–unloading stretching of the skin. An extensive parametric investigation assesses key parameters, advancing fiber-reinforced elastomeric materials for aerospace morphing skins.

Enhancing Longitudinal Flight Performance of Drones through the Coupling of Wings Morphing and Deflection of Aerodynamic Surfaces

In nature, gliding birds frequently execute intricate flight maneuvers such as aerial somersaults, perched landings, and swift descents, enabling them to navigate obstacles or hunt prey. It is evident that birds rely on different wing–tail configurations to accomplish a wide range of aerial maneuvers. For traditional fixed‐wing unmanned aerial vehicles (UAVs), pitch control primarily comes from the tail's elevators, while adjusting flight lift and drag involves deploying wing flaps. Although these designs ensure reliable flight, they compromise the drones’ maneuverability to maintain longitudinal stability. Therefore, the study introduces a biomimetic morphing wing UAV, and presents a pitch control strategy that simultaneously engages morphing wings, ailerons, and tail elevators. The pull‐up maneuver tests indicate that the proposed control method results in a pitch rate that is approximately 2.5 times greater than when using only the elevator control. A closed‐loop control system for the drone is also established. The closed‐loop flight experiment, which tracks a 45° pitch angle, demonstrates the effectiveness of the proposed coupled control method in adjusting the flight attitude. In addition, during cruising, the UAV employs three configurations, straight wing, forward‐swept wing, and back‐swept wing, to cater to different mission objectives and augment its flight capabilities.

Design and rigid-flexible dynamic analysis of a morphing wing eight-bar mechanism

Design and rigid-flexible dynamic analysis of a morphing wing eight-bar mechanism

Effect of wing morphing on stability and energy harvesting in albatross dynamic soaring

Dynamic soaring, which harvests energy from the wind, can enhance Unmanned Aerial Vehicles’ (UAVs’) range and endurance. However, energy harvesting efficiency issues hinder UAV applications, which can be addressed by wing morphing. Therefore, this study investigates the influence of albatross wing morphing during dynamic soaring. By constructing a parametric model, the shape of the albatross wing can be modeled and achieve morphing based on joints. From the video data, this paper summarizes the typical wing morphing patterns of the albatross and notices that changes primarily occur during the leeward descent phase. This paper first analyzes the aerodynamic performance of different wing morphing patterns and finds that the drag coefficient can be reduced by 7.75% with a suitable morphing pattern. This paper also explores the drag coefficient reduction mechanism and finds that downwash airflow decreases by 30.32% after wingtip anhedral. Interestingly, the lift-to-drag ratio shows minimal variation under different morphing patterns, within 2%. From the stability perspective, this study finds that the neutral point position changes after morphing. The maximum longitudinal static margin change is 4.9%, enhancing longitudinal stability by increasing the restorative moment arm. The lateral neutral point is 4.87% closer to the center of gravity, decreasing the roll and yaw moments. It can be observed that wingtip anhedral significantly increases the stability of the albatross. Moreover, a flight simulation is carried out to study the morphing influence on trajectory and energy harvesting. The results show that maximum energy gained is improved by 47.99%, and endurance is increased by 13.05%. The results also indicate that the effects of wing morphing are global rather than limited to the phase of morphing occurrence. Finally, based on the results, this paper proposes wing morphing regularity about the wingtip for UAVs. Wingtip bends downward can significantly increase the UAVs’ stability and reduce drag, but the overall trajectory needs to be reconsidered after introducing wing morphing.

Design and research of a new multi-loop closed-chain morphing wing mechanism

Innovative design and investigation into multi-configurable morphing wing mechanism (MWM) have been focused on meeting the evolving needs of morphing aircraft with extensive spatial and velocity domains. In this paper, a design methodology for multi-loop closed-chain mechanism (MLCCM) involved the substitution of Bennett mechanism links with sub-mechanisms, and an innovative design of 4-RSPCR MLCCM is proposed based on the method, incorporating equivalent spherical mechanism and group theory. Subsequently, a multi-module morphing wing mechanical network consisting of the 4-RSPCR MLCCM is proposed, and the degrees of freedom (DOF) for the multi-module MWM is analyzed using graph theory. In addition, kinematic models for single module mechanism are established, and research on kinematic modeling methods for multi-module mechanisms is conducted. Finally, a prototype of a six-module MWM is constructed, and deformation experiments is conducted. The results show that the proposed innovative mechanisms and the novel multi-module morphing wing mechanical network facilitate the serialized design for various wing planar shapes. Furthermore, these mechanisms enable multi-configurational deformations, including bi-directional bending and variable span. These findings lay the groundwork for fundamental research and engineering applications of morphing wings in morphing aircraft.

Bi-direction and flexible multi-mode morphing wing based on antagonistic SMA wire actuators

This work evaluates the viability of a cutting-edge flexible wing prototype actuated by Shape Memory Alloy (SMA) wire actuators. Such flexible wings have garnered significant interest for their potential to enhance aerodynamic efficiency by mitigating noise and delaying flow separation. SMA actuators are particularly advantageous due to their superior power-to-weight ratio and adaptive response, making them increasingly favored in morphing aircraft applications. Our methodology begins with a detailed delineation of the fishbone camber morphing wing rib structure, followed by the construction of a multi-mode morphing wing segment through 3D-printed rib assembly. Comprehensive testing of the SMA wire actuators’ actuation capacity and efficiency was conducted to establish their operational parameters. Subsequent experimental analyses focused on the bi-directional and reciprocating morphing performance of the fishbone wing rib, which incorporates SMA wires on the upper and lower sides. These experiments confirmed the segment’s multi-mode morphing abilities. Aerodynamic assessments have demonstrated that our design substantially improves the Lift-to-Drag ratio (L/D) when compared to conventional rigid wings. Finally, two phases of flight tests demonstrated the feasibility of SMA as an aircraft actuator and the validity of flexible wing structures to adjust the aircraft attitude, respectively.

A Soft Robotic Morphing Wing for Unmanned Underwater Vehicles

A Soft Robotic Morphing Wing for Unmanned Underwater Vehicles

Active compound shape/vibration control of piezo-actuated variable camber wing section via hybrid feedback/feedforward control scheme

The new concept of compliant morphing wings with piezoelectric conformal actuators has presented its unique advantages compared with rigid morphing wings, but it has also brought a new challenge to design and control. In this study, a compound shape/vibration control strategy for one kind of piezocomposite actuated wing with variable camber is proposed with the purpose to realize a fast, smooth shape morphing process, while overcoming epiphytic vibration problems due to the necessary structural flexibility. A piezo-actuated variable trailing edge wing section was designed by using a compliant corrugated structure installed with actuators made of Macro Fiber Composite (MFC). A compound shape/vibration control system was designed in terms of active disturbance rejection control (ADRC) strategy combined with a feedforward compensator for the MFC actuators to eliminate the nonlinear hysteretic/creep issues. An experimental device was established for verification. The experimental results show that rapid, accurate shape morphing can be achieved with the proposed hybrid feedforward/feedback control scheme while suppressing structural vibration. The compound control of low-frequency shape control and high-frequency vibration suppression can be synergistically realized, and the deformation and stability while controlling such compliant morphing wings can be properly balanced. The proposed compound control strategy is a feasible way to realize favorable dynamic control performance of compliant morphing wings in the future.

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.