Flapping Mechanism Research Articles

Twist-Coupled Flapping Mechanism for Bird-Type Flapping-Wing Air Vehicles

Abstract In flapping-wing air vehicles, the flapping mechanism is directly related to the movement of the wing making it one of the major factors in determining aerodynamic performance. In this study, a method to increase aerodynamic performance using the flapping mechanism is discussed. This paper presents a twist-coupled mechanism that can increase thrust by combining twisting motion with flapping motion. The proposed mechanism generates twisting motion by the 4-bar planar link mechanism and flapping motion by the 4-bar spatial link mechanism. The mechanism can be driven by only one actuator by connecting two crankshafts with a pair of gears and rotating them at once. Here, we define the design parameters and constraints and search for the optimal design parameters to maximize aerodynamic force. Optimization is carried out by a genetic algorithm, a global optimization algorithm, combining kinematic and aerodynamic analyses. We then search for the design parameters that maximize thrust. Based on our optimization results, the proposed mechanism has the figure-of-eight wingtip trajectory motion like the flying animals. The aerodynamic efficiency of the proposed mechanism was validated by an aerodynamic measurement test comparing a reference mechanism that can only generate flapping motion without twisting motion. For comparative validation, prototypes of the proposed mechanism and the reference mechanism were designed and fabricated. Thrust and lift were measured by the wind tunnel test. From the wind tunnel test, it is confirmed that the proposed mechanism can generate aerodynamic loads more efficiently than the reference mechanism.

Parameter sensitivity analysis under failure condition of lifting device mechanism

The sensitivity of each influencing parameter in the selected range of the complex multi-hinge space flap mechanism under typical fault conditions is studied, and the influence degree of each parameter and its dispersion on the driving torque of the mechanism is determined. Firstly, the rigid-flexible coupling dynamic model of the mechanism is established considering the flap deformation, and then the influence of four parameters that may cause mechanism failures, such as hinge friction, aerodynamic load, driving speed and assembly error, on the driving torque of the mechanism is explored. Then, the drive torque of the mechanism under each parameter value is given, finally, the sensitivity of each selected parameter is obtained by the direct de rivation method. The results show that the parameters are positively correlated with the driving torque, the aerodynamic load coefficient and hinge friction parameters are the most sensitive to the driving performance of the mechanism, while the driving speed is the smallest. After the aerodynamic load increased by 30%, the maximum driving torque of the inner mechanism increased by 28.8%; when the hinge friction parameter was in the range of 0~0.05, the maximum torque of the inner and outer mechanisms increased by 8.6% and 8.4% respectively. In engineering applications, the lubrication of each spherical hinge should be increased, the driving speed should be reduced, and the manufacturing and assembly accuracy should be improved.To a certain extent, it can prevent failures and improve the reliability of the flap mechanism.

Design and Optimization of a Hinged Mechanism Guiding Flap to Three Positions

The design of high-lift devices for commercial aircraft is a multidisciplinary problem. One of the difficulties is that the mechanism is difficult to accurately guide the flap to the aerodynamic design position. Therefore, the traditional high-lift device often adopts a complex mechanism, which brings the disadvantages of high structure weight and low reliability. The hinge flap composed of pure rods improves these disadvantages with a small loss of aerodynamic performance. In this paper, a new type of hinge flap mechanism that can meet the needs of three-position design is studied. First, the calculation method of the mechanism parameters and the kinematics simulation are introduced. The guiding position of the mechanism is basically consistent with the aerodynamic design position, and the maximum error is less than 0.1 mm. Then, the mechanism parameters are optimized, including two aspects. The fairing size and the tangential load of the mechanism are optimized for the support part, and the inboard and outboard rotary actuators are optimized to maintain a linear relationship as much as possible with a maximum deviation of no more than 0.058 deg. Finally, the aerodynamic performance of the takeoff and landing configurations guided by the mechanism is evaluated.

Aerodynamic Evaluation of Flapping Wings with Leading-Edge Twisting

The purpose of the current study is to emphasize the characteristics and phenomena of leading-edge twisting in flapping wing vehicles. A fused deposition modeling (FDM) 3D printing method is applied to develop the flapping mechanisms with bevel gears to achieve the leading-edge twisting. Three flapping mechanisms were developed, including simple flapping only (type-A1: normal servo mechanism), flapping with continuous leading-edge twisting (type-B: servo-bevel gear mechanism), and flapping with restricted leading-edge twisting via mechanical stoppers (type-B1: servo-bevel gear mechanism with adjustable mechanical stoppers). Utilizing a low-speed wind tunnel, the aerodynamic performances of these mechanisms are examined by extracting their lift and net thrust forces. The wind tunnel testing data showed that the flapping with restricted leading-edge twisting via mechanical stoppers (type-B1) showed better performance than the simple flapping (type-A1) by 32.9%, and also better performance than the flapping with continuous leading-edge twisting (type-B) by 64%. Next, MATLAB software was used to create the 3D wing surfaces from the instantaneous stereophotography Kwon3D trajectories to fully sketch the leading-edge twisting features. The 2D airfoil cut sections at the mean aerodynamic chord at different stroke moments depict the instantaneous angles of attack to justify the aforementioned wind tunnel testing data and it was verified using a theoretical trajectory model. This comprehensive study using the 3D-printed mechanisms is well suited for the quantitative evaluation of the lift contribution from leading-edge twisting.

In-line swimming dynamics revealed by fish interacting with a robotic mechanism.

Schooling in fish is linked to a number of factors such as increased foraging success, predator avoidance, and social interactions. In addition, a prevailing hypothesis is that swimming in groups provides energetic benefits through hydrodynamic interactions. Thrust wakes are frequently occurring flow structures in fish schools as they are shed behind swimming fish. Despite increased flow speeds in these wakes, recent modeling work has suggested that swimming directly in-line behind an individual may lead to increased efficiency. However, only limited data are available on live fish interacting with thrust wakes. Here we designed a controlled experiment in which brook trout, Salvelinus fontinalis, interact with thrust wakes generated by a robotic mechanism that produces a fish-like wake. We show that trout swim in thrust wakes, reduce their tail-beat frequencies, and synchronize with the robotic flapping mechanism. Our flow and pressure field analysis revealed that the trout are interacting with oncoming vortices and that they exhibit reduced pressure drag at the head compared to swimming in isolation. Together, these experiments suggest that trout swim energetically more efficiently in thrust wakes and support the hypothesis that swimming in the wake of one another is an advantageous strategy to save energy in a school.

Performance of Semi-Active Flapping Hydrofoil with Arc Trajectory

The semi-active flapping foil driven by the swing arm is a simple structure to realize the propulsion of the flapping foil. The motion trajectory of this semi-active flapping foil mechanism is a circular arc, and its hydrodynamic characteristics are not clear. This paper systematically investigates the working characteristics and hydrodynamic performance of this semi-active flapping foil with a circular arc track. Compared with the traditional flapping foil structure, the special design parameters of the semi-active flapping foil driven by the swing arm mainly include the length of the swing arm and the stiffness of the torsion spring. In this paper, the three-dimensional fluid-structure coupling method is used by solving the fluid dynamics equation and the structural dynamics equation, and the working characteristics of the structure with different motion and geometric parameters are analyzed. From the results, increasing the swing arm length is beneficial to improving the peak efficiency of the flapping foil, and also to improving the thrust coefficient corresponding to the peak efficiency point. Under a certain swing arm length, reducing the spring stiffness is also conducive to improving the peak efficiency of the propulsion system, but it is adverse to the thrust coefficient. Further analysis shows that the maximum angle of attack is the key factor affecting the efficiency of this flapping foil propulsion. For the flapping foil described in this paper, its peak efficiency is usually concentrated near αmax=0.2 rad. However, for the thrust coefficient of this kind of flapping foil propulsion, the influencing factors are relatively complex, including swinging arm, the spring stiffness, and the advance coefficient. The maximum angle of attack remains the key factor affecting the peak thrust in the range of advance coefficient far from the starting state.

Development of a flapping mechanism inspired by the flexible wing-base structure of insects for wing motion control

Development of a flapping mechanism inspired by the flexible wing-base structure of insects for wing motion control

How dependent basic events with interval‐valued probabilities affect fault tree analysis

AbstractThis paper studies the effect of the dependence state between basic events (BEs) on fault tree analysis (FTA) when the probabilities of events are characterized by interval values. The well‐known Frèchent bounds are extended for modeling six different types of dependence states between BEs. Three indices, called average dependence effect (ADE), location effect (LE) and size effect (SE), are defined for evaluating the effect of the dependence states between BEs on the probability of top event (TE) and identifying influential and non‐influential dependence states. Then, the proposed method is applied to fault tree (FT) examples, thereby explaining the dependence problem in FTA. To further verify the practicability of the method, FTA of the unilateral asymmetric movement failure of an aircraft flap mechanism is performed. The results show that: (i) the opposite and negative dependence contribute to the reliability of a parallel system while the perfect and positive dependence reduce it, (ii) the perfect and positive dependence contribute to the reliability of a series system while the opposite and negative dependence reduce it, and (iii) parallel systems are more reliable than series systems regardless of the dependence between BEs.

An application of dependent Kriging combined with spherical decomposition sampling for the system reliability analysis of flap mechanism

An application of dependent Kriging combined with spherical decomposition sampling for the system reliability analysis of flap mechanism

Analytical Study on Lift Performance of a Bat-Inspired Foldable Flapping Wing: Effect of Wing Arrangement

In this work, we use a three-dimensional computational fluid dynamics (CFD) simulation to comprehend how the two wing arrangement variables, i.e., inner/outer wing proportion and mid-stroke dihedral, affect the lift characteristic of a bat-inspired span foldable flapping wing. The employed flapping mechanism is based on previous work. In this study, the structure parameters of the flapping mechanism remain unchanged across all simulations. Based on the CFD results, the tendency and work point regarding maximum lift generation can be found by changing both of the variables. As a result, when modifying the inner/outer wing proportion without changing the total wing shape and area, the maximum time-averaged lift appears in the case of the inner wing occupying half of the semi-span. In addition, when changing the dihedral, the maximum time-averaged lift was obtained when the inner wing dihedral was equal to zero. To discuss the lift variation of the foldable flapping wing, pressure distribution and vorticity of the flow field at certain time points were provided corresponding to the instantaneous lift curves. The conclusions of this research are able to help understand the wing arrangement of birds and bats issued from natural selection, and also support the future design of flapping wing micro-aerial-vehicles.

Aerodynamic Performance of a Flyable Flapping Wing Rotor With Passive Pitching Angle Variation

This article is based on an experimental study on the aerodynamic performance of a flapping wing rotor (FWR) and enhancement by passive pitching angle variation (PPAV) associated with powered flapping motion. The PPAV (in this article, 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> –50 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> ) is realized by a specially designed sleeve-pin unit as part of a U-shape flapping mechanism. Through experiment and analysis, it is found that the average lift produced by an FWR of PPAV is >100% higher than the baseline model, the same FWR of a constant pitching angle 30 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> under the same input power. It is also noted that the lift–voltage relationship for the FWR of PPAV is almost linear and the aerodynamic efficiency is also over 100% higher than the baseline FWR when the input voltage is under 6 V. The aerodynamic lift or efficiency of the FWR of PPAV can be also increased significantly by reducing the weight of the wings. An FWR model is fabricated and achieved vertical take-off and free flight powered by 9 V input voltage. The mechanism of PPAV function provides a feasible solution for aerodynamic improvement of a bioinspired FWR and potential application to micro air vehicles.

Functional characteristics of the rigid elytra in a bamboo weevil beetle Cyrtotrachelus buqueti.

The bamboo weevil beetle, Cyrtotrachelus buqueti, has evolved a particular flight pattern. When crawling, the beetle folds the flexible hind wings and stuffs under the rigid elytra. During flight, the hind wings are deployed through a series of deployment joints that are passively driven by flapping forces. When the hind wings are fully expanded, the unfolding joint realises self‐locking. At this time, the hind wings act as a folded wing membrane and flap simultaneously with the elytra to generate aerodynamics. The functional characteristics of the elytra of the bamboo weevil beetle were investigated, including microscopic morphology, kinematic properties and aerodynamic forces of the elytra. In particular, the flapping kinematics of the elytra were measured using high‐speed cameras and reconstructed using a modified direct linear transformation algorithm. Although the elytra are passively flapped by the flapping of the hind wings, the analysis shows that its flapping wing trajectory is a double figure‐eight pattern with flapping amplitude and angle of attack. The results show that the passive flapping of elytra produces aerodynamic forces that cannot be ignored. The kinematics of the elytra suggest that this beetle may use well‐known flapping mechanisms such as a delayed stall and clap and fling.

Nanogenerators integrated self-powered multi-functional wings for biomimetic micro flying robots

Under rigorous weight and power constraints, improving the energy systems and the onboard sensing approaches for flapping-wing micro air vehicles (FWMAVs) are monumental challenges. Mechanical energy transformation and integrated self-powered sensing hold great promising features to improve the flying performance of FWMAVs. Herein, we introduce novel triboelectric nanogenerators (TENGs) integrated multi-functional wings to address these challenges. Synthetically, The TENGs integrated wings can realize the mechanical energy transformation, the motion monitoring of flapping wings, and the pneumatic functions for FWMAVs. Firstly, a lightweight and ultra-thin sandwich structure integration technique with silk-fibroin film as the coated friction layer is realized for the TENGs integrated wings. Secondly, the wind tunnel test verifies the feasibility of the mechanical transformation and reveals the effects of the operating conditions of the FWMAVs on the triboelectric energy performance. The triboelectric energy performance of the TENGs integrated wings, whose entire thickness and the weight increases are less than 20 µm and 0.2 g respectively is verified to achieve 468.7 V voltage, 100.6 μA current, and 379.8 μW power. Likewise, as an attractive potential application, it is demonstrated to provide an accurate self-powered measurement of the flapping mechanism frequency based on the triboelectric principle. The aerodynamic measurements verify that the TENGs integrated wings maintain the pneumatic functions, which guarantee flight stability, and they positively enhance 29.89% of the onboard load of the FWMAV.

One-sized bilobed flap does not fit all standing cones: a mathematical analysis of the standing cone in bilobed flap dynamics.

The bilobed flap (BLF) is a workhorse for nasal repair. Alterations to the length and orientation of the BLF's standing cutaneous deformity (SCD) have been suggested as a means of preventing Z-plasty-induced flap lengthening and consequent ipsilateral alar depression. To investigate the effect of design variations of the SCD on bilobed flap mechanics. Geometric analysis of the BLF was performed using commercially available graphing software. BLFs were designed with a SCD equal to one radius (rBLF) and one diameter (dBLF) of the primary defect as well as with a more superiorly-oriented one diameter SCD (soBLF). Lengths from the pivot point to the distal edges of the primary defect and primary lobe were measured and compared. Elongation or a more superior orientation of the SCD without changes to the rest of the flap design forms a primary lobe along a shorter arc resulting in insufficient flap length to resurface the primary defect. The insufficient length requires secondary motion to complete the repair and possible unintended alar displacement. Modification of the size and orientation of the SCD alters the location of the pivot point, which is a key determinant of BLF mechanics. Therefore, changes to the SCD require alterations to the remainder of the flap design to ensure aesthetic and functional success.

Bioinspired light-driven photonic crystal actuator with MXene-hydrogel muscle

The butterfly Apatura ilia’s wings change colors during flapping, which plays a major role in conveying information and avoiding predators. Inspired by the muscle-driven flapping mechanism, here, we fabricate a highly efficient photothermally responsive MXene-hydrogel muscle and achieve a dynamic structural color imaging system based on the MXene-hydrogel muscle manipulated photonic crystal actuator arrays. Our optimized MXene-hydrogel-muscle artificial muscle has a stable and quick photothermal response owing to the high photothermal transformation efficiency of MXene (∼100%). Consequently, our photonic crystal (PhC) actuator exhibits robust structural stability and fatigue resistance (more than 500 cycles), and its response time is ∼5 s. The PhC actuator can give real-time visual feedback in response to heating and near-infrared irradiation. They offer exciting possibilities for applications in sensors, displays, camouflage coatings, cryptography, and many other fields. Our experiments and theoretical analysis reveal the quantitative structure-activity relationship of the responsive PhC actuator.

Dynamic simulation of complex multi-hinge space flap mechanism

Dynamics simulation of large civil aircraft complex multi-hinge space flap mechanism was studied, and a set of dynamics simulation modeling method of complex multi-hinge space flap mechanism based on Motionview was proposed. Firstly, a moving digital prototype of the complex multi-hinge space mechanism was constructed. The multi-point constraint RBE3 element was used to associate the intersection points of the rigid multi-hinge mechanism to the body of the flap surface considering flexibility, and the rigid-flexible coupling dynamic model of the flap mechanism was formed. The dynamics simulation of the mechanism was carried out under the aerodynamic load conditions of cruise, take-off and landing, the driving torque and hinge point load dynamics indexes of the complex multi-hinge space flap mechanism were obtained. The simulation results show that the driving arm of the inner mechanism bears most of the lateral load from the flap wing surface, the radial direction of the joints bearing at each hinge bears the aerodynamic pulling force from the flap wing surface. And the inner mechanism of the flap is the main bearing part, the load capacity of the inner rocker arm is almost four times that of the outer rocker arm. The dynamic simulation research can provide a certain reference for the design and improvement of the complex multi-hinge space flap mechanism.

Dynamic simulation of flap mechanism considering assembly error

The existence of assembly error will have an impact on the kinematic accuracy and dynamic performance of mechanical system, which can not be ignored. Therefore, a dynamic simulation method of flap mechanism considering assembly error is established. Firstly, the motion digital prototype of flap mechanism and the rigid flexible coupling dynamic model considering the deformation of flap wing surface are established, and then when the error direction is fixed, by setting the deviation values of the two driving shafts, the influence on the driving torque of the flap mechanism and the load of key components under the working conditions of 2mm, 4mm and 6mm is explored. Then, through the eight error directions defined by the deviation function, the influence of the direction error of the drive shaft assembly on the driving torque of the flap mechanism is obtained when the error size is 6mm fixed. The results show that when the assembly deviation of the two driving shafts is in the three working conditions with the selected size, the flap trajectory basically coincides, and the driving torque of the inner mechanism increases by 10.19% when the error is 6 mm; When the size of the assembly error remains fixed, the change of the error direction will increase the driving torque of the flap mechanism. The dynamic simulation study can provide some theoretical guidance for the manufacturing and assembly of this type of high-lift device.

Mechanism Design and Motion Analysis of a Flapping-Wing Air Vehicle

Micro flapping-wing air vehicles (FWAV) are highly appreciated by scientists and scholars around the world due to their small size, high flexibility, and better manoeuvrability. There are huge potential applications of flapping-wing robots in rescue, survey, and search, as they can enter more dangerous and narrow spaces to accomplish tasks that were previously impossible for people. In this paper, we first analyze the flapping motion of birds by reviewing a large amount of information and literature and identifying the sources of lift and thrust during flight. Then, the double crank and double rocker mechanisms are optimized as the flapping mechanism. Proper flapping-wing size is further determined by analyzing the relative position between the driving mechanism and the flapping mechanism. Moreover, a pitch mechanism consisting of ball hinges is designed to realize the wing’s pitching motion for additional thrust. The fuselage and landing gear of the flapping-wing robot are designed for low air resistance and lightweight, and the tail mechanism are designed to have both roll and pitch freedoms, offering excellent manoeuvrability during flight. Simulation results show positive lift force is generated based on the novel pitching design for the small wing. The research in this paper is an important resource for novice researchers to design and study the advanced and complex problems of flapping-wing air vehicles.

Experimental surrogate-based design optimization of wing geometry and structure for flapping wing micro air vehicles

We present the experimental design optimization of a flapping wing and the development of a non-circular gear based flapping mechanism to enhance the propulsive efficiency of a flapping wing micro air vehicle (FWMAV). The proposed flapping mechanism consists of a very simple structure, which excludes any linkages but utilizes non-circular gears to achieve a desired flapping amplitude and angular velocity. An optimal wing was obtained via a surrogate-based global optimization reflecting the noise generated from the experiments. Compared to the baseline wing, the optimal wing was improved more than three times in terms of propulsive efficiency. The analysis showed that one of wing geometric parameters, the non-dimensional radius of second moment of area rˆ2, plays an essential role in designing an optimal wing. To achieve high efficiency, rˆ2 should decrease as the wing area increases. Simultaneously, rˆ2 determined other optimal values of geometry parameters such as aspect ratio and camber angle. Furthermore, rˆ2 was also closely related to an optimal vein position which not only generated a moderate wing angle of attack but also reduced the adverse effect of angle of attack fluctuation. Through the optimal wing and the proposed flapping mechanism, we could be able to achieve better efficiency and robust manufacturing compared with the previously reported tailless-FWMAVs.

Mechanism and Kinematics for Flapping Wing Micro Air Vehicles Maneuvering Based on Bilateral Wings

With the development and application of a bionic flapping micro aircraft vehicle (FMAV), further requirements for its high maneuvering flight characteristics have been put forward. A controlling tail cannot meet the requirements of the maneuvering flight of insect-sized FMAVs, and it has become necessary to find new mechanisms for high maneuvering flight. In this study, two flapping mechanisms with movable hinges based on a double crank rocker mechanism (DCRM) and a single crank slider mechanism (SCSM) are proposed. The instantaneous flapping angles, their extremum and means, and the flapping amplitudes of the two mechanisms are studied for various hinge offsets. A comparison between these two mechanisms indicates that the mechanism based on SCSM is more appropriate in providing adjustable flapping amplitudes for lateral wings. Finally, a dragonfly-like prototype assembled using a carbon fiber plate with adjustable wings is designed and manufactured based on the SCSM. Flight tests are conducted to show that the rack and pinion mechanism can accomplish the movement of hinges neatly, and the proposed flapping mechanism makes left turns and right turns effectively while continuing to fly forward. The prototype is good in terms of crashworthiness and the replacement of components, and it offers an easy and reliable technique for the maneuvering flight of FMAVs.