Wing Folding Research Articles

Aerodynamic effects on an emulated hovering passerine with different wing-folding amplitudes

Bird flight involves complicated wing kinematics, especially during hovering flight. The detailed aerodynamic effects of wings with higher degrees of freedom (DOFs) remain to be further investigated. Therefore, we designed a novel multiarticulate flapping-wing robot with five DOFs on each wing. Using this robot we aimed to investigate the more complicated wing kinematics of birds, which are usually difficult to test and analyze. In this study the robot was programmed to mimic the previously observed hovering motion of passerines, and force measurements and particle image velocimetry experiments. We experimented with two different wing-folding amplitudes: one with a larger folding amplitude, similar to that of real passerines, and one with only half the amplitude. The robot kinematics were verified utilizing direct linear transformation, which confirmed that the wing trajectories had an acceptable correlation with the desired motion. According to the lift force measurements, four phases of the wingbeat cycle were characterized and elaborated through camera images and flow visualization. We found that the reduction in folding amplitude caused a higher negative force during upstrokes and also induced a greater positive force at the initial downstroke through ‘wake capture’. This could increase the vertical oscillation while hovering despite a minor increase in average force production. This phenomenon was not observed during forward flight in previous studies. Our results provide a critical understanding of the effect of wing folding which is required for designing the wing kinematics of future advanced flapping-wing micro aerial vehicles.

Parameterized Fictitious Mode of Morphing Wing with Bilinear Hinge Stiffness

As a typical morphing wing, a folding wing with structural nonlinearities may encounter complex nonlinear aeroelastic effects during the in-flight morphing process. This paper presents a novel parameterized modeling methodology for efficient modal and nonlinear aeroelastic analysis of a folding wing with bilinear hinge stiffness and the variation of the folding angle. The most attractive feature of the present modeling methodology is that the nonlinear structural dynamics of the folding wing at different folding angles can be efficiently represented via a parameterized fictitious mode. To demonstrate the accuracy of the present method in representing the nonlinear dynamics of the morphing wing, a folding wing with bilinear stiffness in both fuselage–inboard and inboard–outboard hinges was selected as a numerical example. The nonlinear dynamic model of the selected example can be divided into nine subsystems according to different combinations of fuselage–inboard and inboard–outboard hinge stiffness. This paper focuses on the efficient investigation of structural modes, flutter stability, and nonlinear aeroelastic behaviors of the folding wing at the complete morphing parameter space. Besides, the numerical results computed via the present parameterized fictitious mode method were also compared with the direct commercial software. The comparison shows that the nonlinear dynamics of the morphing wing with bilinear hinge stiffness can be investigated efficiently via the present parameterized modeling method.

Reliability Evaluation for Cable-Spring Folding Wing Considering Synchronization of Deployable Mechanism

The cable-spring folding wing is a novel type of rigid-flexible coupling structure for missiles, which is composed of several sets of deployable mechanisms, with each composed of a wheel-rope transmission system and a parallel spring driving mechanism. The movement of the cable is initiated by the driving force produced by parallel springs, which directly changes the magnitude and the distribution of the driving force. Therefore, the cable-spring folding wing system has the typical characteristics of strong nonlinearity and motion coupling. In addition, each deployable mechanism shares an identical structure, but the distribution of motion parameters is discrepant due to external loads. Asynchronous movement of the cable-spring folding wing will occur and become a significant issue, which is detrimental to the working performance and could even lead to failure. Focusing on these problems, the multi-body dynamics theoretical model and simulation model of deployable mechanism are established, the kinematic and dynamic characteristics of critical components are studied, and the key factors affecting the deployment performance are investigated. A new reliability method with an angular precision control for deployable mechanism is proposed based on the theoretical model. The effectiveness of the proposed model and method is verified by comparing it with the Monte Carlo method. On this basis, the reliability evaluation for cable-spring folding wing, comprehensively considering deployment performance and synchronization, is carried out.

Design of Bionic Foldable Wing Mimicking the Hind Wings of theC. BuquetiBamboo Weevil

AbstractThe bamboo weevil, Cyrtotrachelus buqueti, has excellent flight ability and strong environmental adaptability. When it flies, its fore wings and hind wings are unfolded, whereas when it crawls, its fore wings are closed, and its flexible hind wings are regularly folded under the fore wings. In this paper, the hind wing folding/unfolding pattern of C. buqueti is analyzed and a new bionic foldable wing with rigid–flexible coupling consisting of a link mechanism and a wing membrane is constructed. The movement of the link at the wing base mimics the contraction of a muscle in the thorax that triggers scissor-like motion and the deployment of the veins. Elastic hinges are used to mimic the rotational motion of the wing base and the vein joints. The static/dynamic characteristics of bionic foldable wings are further analyzed, and the LS-DYNA software is used to investigate rigid–flexible coupling dynamics. The elastic deformation of the wing membrane, kinematic characteristics of the linkage mechanism, and modes of the whole system are calculated. Static analysis of the structure reveals that the foldable wing has excellent stiffness characteristics and load-bearing capacity. The bionic foldable wing is constructed using three-dimensional (3D) printing technology, and its folding and unfolding performance is tested. Evaluation of its performance shows that the bionic wing has a large fold ratio and can achieve stable folding and unfolding motions. A slightly tighter assembly between the pin and the hinge hole ensures that the wing does not fold back during flapping.

Multi-body dynamics modeling and transient characteristics analysis for a folding wing

The investigation of modeling the time evolution of a folding wing during the morphing process and the dynamic characteristics analysis is carried out. The governing equations with uniform form are developed from the integration of floating frame method in multi-body dynamics and component mode synthesis in structural dynamics. The time-dependent aerodynamic force is taken into the governing equations. The equation achieves the time-dependent coupling between structure and aerodynamics and avoids the data transmission and low efficiency, which holds true for the multi-segmented folding wing. The relative parameters in constraint equations are easily modified to be applied to both slow and fast-varying processes for a folding wing. Also, the influence of the velocity and attack angle on transient responses can be investigated. Transient response analysis shows that slower morphing means more stable transient responses. The flexibility of the folding wing has the significant influence on transient responses. To some extent, the aerodynamic force can be beneficial to the morphing process.

Dynamics and reliability analysis of the deployment process of spring folding wing

A “X” type spring folding wing is taken as the research object in this paper, and schematic diagrams of unfolding and locking process are drawn according to its structure and working principle. The theoretical model of kinematics and dynamics which considering the gravity moment is established by simplifying the geometric model of deployment mechanism of the folding wing, so the curve of deployment angle and angular velocity of the outer wing during the deployment process can be obtained. The pulley diameter, preload force and stiffness of the spring-actuated are taken as random variables, and the deployment time and angular velocity are regarded as evaluation indicators. The Monte Carlo method is used to analyse the reliability of deployment process of the folding wing, and the reliability of the deployment process is obtained. The results show that the reliability of the deployment process of the spring folding wing is high.

Fast structural dynamic modeling and analysis for horizontally folding wing

To investigate the structural dynamic characteristics of a folding wing effectively, a fast structural dynamic modeling approach is proposed. Firstly, the interface compatible relationship of the traditional fixed interface component modal synthesis method is modified, and the internal force of the interface is completely expressed in the structural dynamic equation, so that the influence of the connection stiffness on the wing structure dynamics can be considered. Then, on the basis of the fixed interface component modal synthesis method, the main mode of fixed-loaded interface is introduced to establish the mixed-loaded interface component modal synthesis method, which makes it feasible to accurately reflect the influence of elasticity and inertia of fuselage and outer wing on inner wing. The structural dynamics modeling method based on two different kinds of component modal synthesis method analyzed and deduced in detail. The application of component modal synthesis method in the fast structural dynamics modeling of folding wing is achieved. The whole program is compiled in MATLAB. At the same time, the dynamic characteristics of the folding wing with different folding angles, different connections and different connection positions is investigated. The results of the method proposed in this paper are compared with the results of the repeated finite model established in MSC.NASTRAN to verify the effectiveness from the aspects of natural frequency and vibration mode.

Simulation Analysis of the Aerodynamic Performance of a Bionic Aircraft with Foldable Beetle Wings in Gliding Flight.

Beetles have excellent flight performance. Based on the four-plate mechanism theory, a novel bionic flapping aircraft with foldable beetle wings was designed. It can perform flapping, gliding, wing folding, and abduction/adduction movements with a self-locking function. In order to study the flight characteristics of beetles and improve their gliding performance, this paper used a two-way Fluid-Structure Interaction (FSI) numerical simulation method to focus on the gliding performance of the bionic flapping aircraft. The effects of elastic model, rigid and flexible wing, angle of attack, and velocity on the aerodynamic characteristics of the aircraft in gliding flight are analyzed. It was found that the elastic modulus of the flexible hinges has little effect on the aerodynamic performance of the aircraft. Both the rigid and the flexible wings have a maximum lift-to-drag ratio when the attack angle is 10°. The lift increased with the increase of the gliding speed, and it was found that the lift cannot support the gliding movement at low speeds. In order to achieve gliding, considering the weight and flight performance, the weight of the microair vehicle is controlled at about 3 g, and the gliding speed is guaranteed to be greater than 6.5 m/s. The results of this study are of great significance for the design of bionic flapping aircrafts.

DYNAMIC MODELING AND STABILITY CONTROL OF FOLDING WING AIRCRAFT

During the deformation process, the dynamic modeling of the folding-wing aircraft presents the characteristics of multi-rigid、multi-degree of freedom and strong nonlinearity. At the same time, parameters such as aerodynamics/torque, pressure center, centroid and moment of inertia will also change greatly, which will seriously affect Flight stability. Therefore, this paper will mainly study the multi-rigid dynamics modeling and deformation stability control of the folding wing aircraft. The multi-rigid dynamic model of the folding wing aircraft is established based on the Kane method with the additional force and moment expressions. The functional relationship between the aerodynamic parameters and the folding angle is fitted through aerodynamic calculations. and the longitudinal dynamic characteristics of the aircraft at different folding angular speeds are analyzed. It is shown that the speed, height and pitch angle of the folding wing aircraft will change during the deformation process by analyzing the longitudinal dynamic characteristics, and the aircraft cannot maintain stable flight. A stability control method is proposed for the deformation process of the folding-wing aircraft based on the active disturbance rejection control theory. The nonlinear terms, coupling terms and parameter time-varying terms are regarded as the total internal and external disturbances in the longitudinal nonlinear dynamic model of the folding-wing aircraft, using the extended state observer to estimate and compensate the total disturbance in real time. The PD controller is proposed for compensated systems to realize decoupling control of speed channel and height channel. The stability of the system is proved by Lyapunov stability theory, and mathematical simulation is used to verified the stability of the folding wing aircraft. The simulation results show that the stability controller based on the active disturbance rejection control theory can solve the problems of strong nonlinearity and time-varying parameters caused by aircraft deformation, and ensure the high-precision and stable control of the aircraft.

Calculation of Hinge Moments for a Folding Wing Aircraft Based on High-Order Panel Method

Calculating hinge moments during the morphing process is a critical aspect in the folding wing design. The deficiencies of the traditional flat-plate aerodynamic model in the calculation are expounded in this work, and a flight simulation platform based on a high-order panel method is established. On the basis of the platform, a typical flight-folding process of the aircraft is simulated, and the results of different aerodynamic models are compared. Results show that airfoil thickness has a great influence on the aerodynamic loading distribution of wing surfaces and thus affects the hinge moments during the folding process. The flat-plate method, which ignores the influence of the airfoil thickness, shows a great simulation error in hinge moment, whereas the high-order panel method can effectively describe the thickness effect and obtain reliable simulation results.

Miniaturization re-establishes symmetry in the wing folding patterns of featherwing beetles

Most microinsects have feather-like bristled wings, a state known as ptiloptery, but featherwing beetles (family Ptiliidae) are unique among winged microinsects in their ability to fold such wings. An asymmetrical wing folding pattern, found also in the phylogenetically related rove beetles (Staphylinidae), was ancestral for Ptiliidae. Using scanning electron, confocal laser scanning, and optical microscopy, high-speed video recording, and 3D reconstruction, we analyze in detail the symmetrical wing folding pattern and the mechanism of the folding and unfolding of the wings in Acrotrichis sericans (Coleoptera: Ptiliidae) and show how some of the smaller featherwing beetles have reverted to strict symmetry in their wing folding. The wings are folded in three phases by bending along four lines (with the help of wing folding patches on the abdominal tergites) and locked under the closed elytra; they unfold passively in two phases, apparently with the help of the elasticity provided by resilin unevenly distributed in the wing and of convexities forming in the cross-sections of the unfolding wing, making it stiffer. The minimum duration of folding is 3.5 s; unfolding is much more rapid (minimum duration lowest recorded in beetles, 0.038 s). The folding ratio of A. sericans is 3.31 (without setae), which is greater than in any beetle in which it has been measured. The symmetrical wing folding pattern found in A. sericans and in all of the smallest ptiliids, in which ptiloptery is especially pronounced, is the only known example of symmetry re-established during miniaturization. This direction of evolution is remarkable because miniaturization is known to result in various asymmetries, while in this case miniaturization was accompanied by reversal to symmetry, probably associated with the evolution of ptiloptery. Our results on the pattern and mechanisms of wing folding and unfolding can be used in robotics for developing miniature biomimetic robots: the mechanisms of wing folding and unfolding in Ptiliidae present a challenge to engineers who currently work at designing ever smaller flying robots and may eventually produce miniature robots with foldable wings.

Parametric active aeroelastic control of a morphing wing using the receptance method

This study proposes the parametric active aeroelastic control of a folding wing, which is a promising concept of morphing wings, by integrating the parameterized aeroservoelastic model and the receptance-based control strategy. It starts with establishing the parameterized aeroservoelastic model of the folding wing with respect to its folding angle and air speed. The transfer functions between the embedded sensors and the actuators of the folding wing are then efficiently obtained using the parameterized aeroservoelastic model. Finally, control gains for varying folding angle and air speed of the wing are synthesized using the receptance method. The results of numerical analyses show that smooth evolutions of the control gains can be obtained over a wide range of folding angles and air speeds, although the dynamic behavior of the folding wing is sensitive to these parameters. In addition, the active aeroelastic control can effectively suppress aeroelastic vibrations and expand flutter boundaries of the folding wing. The benefit of the parametric active aeroelastic control for the folding wing, i.e., smoothly switching among the control laws without exciting undesirable vibrations is highlighted.

Simulation analysis the aerodynamic characteristics of variable sweep wing missile

When the sweep of the variable sweep folding wing missile changes, the lift-drag ratio is improved so that the missile is able to adapt to subsonic flight, transonic flight and supersonic flight. This paper designs different 3D models of variable sweep wing missile aerodynamic shape and completes the aerodynamic characteristics analysis of the missile by CFD according to the Basic Aerodynamics, Missile General Design Principle, Flight Dynamics of Missile. The simulation analysis of the missile in different flight conditions with different sweeps is carried out, and the wing sweeps applicable to different flight conditions are summarized.

Resonance-Driven Passive Folding/Unfolding Flapping Wing Actuator

The wings of flapping-wing micro aerial vehicles (MAVs) face the risk of breakage. To solve this issue, we propose the use of a biomimetic foldable wing. In this study, a resonant-driven piezoelectric flapping-wing actuator with a passive folding/unfolding mechanism was designed and fabricated, in which the folding/unfolding motion is passively realized by the centrifugal and lift forces due to the stroke motion of the wings. Although the passive folding/unfolding is a known concept, its feasibility and characteristics in combination with a resonant system have not yet been reported. Because the resonant actuation is necessary for extremely small, insect-scale MAVs, research is required to realize such MAVs with a foldable-wing mechanism. Therefore, we first examine and report the performance of the resonant-driven passive folding/unfolding mechanism. We also present a simplified theoretical model demonstrating an interaction between the resonant actuation system and folding/unfolding mechanism. We successfully demonstrate the folding/unfolding motion by the fabricated actuator. In addition, the theoretical model showed good agreement with the experiment.

Aerodynamical Optimization of Adaptable Span Wing of Telescopic Spar and Foldable Wing Tip using Computational Fluid Dynamics

The project aims to analyze aerodynamic coefficients of adaptable span wing, which increases the lift of the aircraft at various flight conditions by increasing the span of the wing and also decreases its span to adapt Group V airport gate, which is restricted to a maximum 65 m wingspan of aircraft. Present days there is no adaptable wing that changes its shape or its span. All the commercial airplane wings are only fixed wings. To increase more lift at the time of takeoff or landing, the pilot has to stay with the ailerons and flaps. But at the time of the cruise, flaps give more induced drag. Adaptable span wing paves a way to have a lift at any time with less induced drag. Airports are 6 types based on the maximum span of their gates. To increase the lift, it is easy to increase the span of a wing and to keep it fixed, but if the span is more than 65 m, it falls under the category of Group VI airports. These Group VI airports are less available, and Group V airports are mostly available worldwide. This project aims to increase the span beyond 65 m and also to accommodate in Group V airports. Methods of Telescopic spar expansion and foldable wingtip are used. For this work Boeing 777-300 ER Wing with its airfoil is taken as a reference. One side of the wing is taken for analysis, and the models have made in CATIA V5 of various length from its original half span 29.3m to 34.3m by increasing one by one metre. Also, with foldable wingtip span is increased at its unfolded state with 2m. Each and every model is analyzed with a variable angle of attack, and lift curves were obtained. These curves help us to determine the optimized span of the adaptable wing.

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.

Design, Fabrication, and Analysis of Flapping and Folding Wing Mechanism for a Robotic Bird

Emulating periodic main wing movement of a bird for generating lift and thrust remains a significant challenge in developing a robotic bird. The sequences of main wing motion are comprised of flapping, folding, bending, and twisting. In this paper, we concentrate on the flapping and folding motion, and design two wing mechanisms based on a 4-bar linkage structure: one is only for Flapping Motion (FM) and the other is for simultaneous Flapping and Folding Motion (FFM) during a wing stroke. We derive relationships between length and angle of links to analyze kinematic characteristics of the mechanisms and conduct an optimization to select the length parameters of links that allow maximization of the flapping angle. We run a simulation to confirm the performance of the optimized parameters by examining physical properties, and fabricate two wing mechanisms accordingly. In particular, the folding motion is achieved without using an additional actuator. Force measurements to investigate a lift profile of each mechanism and their quantitative comparison of the performance of both types confirm the benefits of the folding motion in the perspectives of wing frequency and lift. We expect that our kinematic formulation, design procedures, and comparative measurement results can help develop a wing mechanism to create a truly biomimetic robotic bird.

Evaluation of DNA degradation and establishment of a degradation analysis model for Lepidoptera specimens.

Millions of museum specimens are integral to biodiversity studies; however, DNA degradation may limit the ability to obtain DNA sequences. In this study, a degradation analysis model for Lepidoptera specimens was established. Based on this model, we revealed the characteristics of DNA fragment distribution caused by external DNA damage factors during specimen preservation. We found that the degree of DNA degradation increased over time; DNA degradation of spread and dried adult specimens was significantly higher than that in the folded and formalin-fixed larval specimens. However, the effects of folding wings on DNA degradation and the effects of the preservation method/stage (formalin-fixed larval vs air-dried adult specimens) were different for different species.

气动载荷对折叠翼展开性能影响研究

气动载荷对折叠翼展开性能影响研究

Reliability Analysis of Folding Wing Deployable Mechanism Considering Common Cause Failure

Reliability Analysis of Folding Wing Deployable Mechanism Considering Common Cause Failure