Flapping Wing Micro Air Vehicle Research Articles

NGHIÊN CỨU ẢNH HƯỞNG CỦA YẾU TỐ BIẾN DẠNG ĐẾN CÁC ĐẶC TÍNH KHÍ ĐỘNG CỦA CÁNH VẪY KIỂU CÔN TRÙNG Ở CHẾ ĐỘ BAY TREO

Insect-mimicking flapping-wing micro air vehicles (FWMAVs) are currently of great research interest due to their many practical applications. Most of the studies have focused on the rigid wing, which is much simpler. However, the wings of these FWMAVs, as well as those of insects in nature, are light and flexible structures, thus the deformation is unavoidable. In this study, a spring-body system is used to model the insect-like wing structure, combined with an aerodynamic program based on the UVLM model. The co-simulation framework is validated with published experimental data. Results show that using the flexible wing significantly increases the lift force as well as improves energy efficiency.

Improved Model for Flexible Flapping Wings: Considering Spanwise Twisting and Bending

Insect wings and biomimetic wings in flapping-wing micro air vehicles (FWMAVs) are flexible and subject to passive deformations, including spanwise twisting and bending. This raises a typical bilateral fluid–structure interaction (FSI) issue, which is conventionally solved based on combined computational fluid dynamics (CFD) and computational solid dynamics (CSD) methods. To reduce the computational cost of this FSI issue while maintaining a reasonable accuracy, a theoretical model with improved adaptability is proposed here. The improvement results from the consideration of spanwise bending: the distribution of which is formulated by a quadratic polynomial. The aerodynamic force is approximated by a predictive quasi-steady aerodynamic model based on the blade element theory. The FSI iteration at a time step is converged within 0.5 s in our model, whereas a traditional CFD–CSD solution takes about 30 s. Compared to our previous model, the current model can better match the experimental measurements of insect wings. Further analysis reveals that considering spanwise bending affects the stiffness design of flexible flapping wings quantitatively. To maintain a high lift efficiency, the structural stiffness of the wing should be appropriately decreased. Our model provides a refined tool for the wing design in FWMAVs and can promote the development of FWMAVs.

Micro-structures, nanomechanical properties and flight performance of three beetles with different folding ratios.

When beetles are not in flight, their hind wings are folded and hidden under the elytra to reduce their size. This provided inspiration for the design of flapping-wing micro aerial vehicles (FWMAVs). In this paper, microstructures and nanomechanical properties of three beetle species with different wing folding ratios living in different environments were investigated. Factors affecting their flight performance, that is, wind speed, folding ratio, aspect ratio, and flapping frequency, were examined using a wind tunnel. It was found that the wing folding ratio correlated with the lift force of the beetles. Wind speed, folding ratio, aspect ratio, and flapping frequency had a combined effect on the flight performance of the beetles. The results will be helpful to design new deployable FWMAVs.

More Detailed Disturbance Measurement and Active Disturbance Rejection Altitude Control for a Flapping Wing Robot Under Internal and External Disturbances

With the goal of designing a biologically inspired robot that can hold a stable hover under internal and external disturbances. We designed a tailless Flapping-wing Micro Aerial Vehicle (FMAV) with onboard 3D velocity perception. In this way, the wind disturbance caused by the relative motion of the FMAV can be quantified in real time based on the established altitudinal dynamics model. For the rest of the total disturbance, an active disturbance rejection controller is proposed to estimate and suppress those disturbances. In comparison with the traditional PID controller, this proposed approach has been validated. The results show that, in the hovering flight with the internal unmodeled dynamics, the root-mean-square of height controlled is only 2.53 cm. Even with the different weights of loads mounting on the FMAV, the ascending trajectory of flights remains impressively consistent. In the forward flight with the external disturbance, the root-mean-square error of height controlled is 2.78 cm. When the FMAV flies over a ladder introducing an abrupt external disturbance, the maximum overshoot is only half of that controlled by the PID controller. To our best knowledge, this is the first demonstration of FMAVs with the capability of sensing motion-generated wind disturbance onboard and handling the internal and external disturbances in hover flight.

Design and Testing of a Bioinspired Lightweight Perching Mechanism for Flapping-Wing MAVs Using Soft Grippers

Flapping-wing MAVs are starting to emulate the advanced flight maneuverability of insects and birds, however they struggle to achieve a similar aptitude for taking off and landing in challenging cluttered environments. The ability to perch on objects such as branches or metal struts would result in a wide range of potential landing sites, both indoors and outdoors, and would increase the achievable mission duration, thus allowing a more versatile usage of MAVs. While perching is particularly challenging with flapping-wing MAVs, these vehicles are highly promising for complex missions in confined spaces. In this letter a systematic bioinspiration approach was adopted to design a new lightweight perching solution suitable for bird-size flapping-wing MAVs. The proposed concept combines a four-bar linkage mechanism with an active-passive actuation method to achieve a large gripping power at low energy consumption. Additionally it relies on compliant soft grippers inspired by the Fin Ray effect, which lead to a high adaptability to different perching surface textures and shapes. A prototype of the proposed concept was manufactured and tested experimentally in gripping tests and rail-guided perching tests. With a total mass of 45 g the concept is suited for bird-size MAVs in the weight range of 150–300 g. Flight tests on a surrogate (multirotor) platform demonstrate the approach functions successfully in realistic free-flight conditions.

Design and Fabrication of a Flapping-Wing Robot Based on Slider-Crank Mechanism


 Tailless Flapping-Wing Micro Air Vehicles (FW-MAVs) have gained more attention recently because they utilize energy more efficiently compared to fixed-wing aircraft and rotorcrafts. FW-MAVs could be used commercially to explore confined spaces with insufficient air or serve as surveillance robots. However, due to their use of unsteady aerodynamics and small size, the research and design process is very complicated. In this paper, I propose a flight mechanism for a light-weighted, two-winged, hummingbird-inspired flapping-wing robot. Five versions of the robot were built; each version improved upon the issues of the previous one. Calculations were performed to optimize the stroke amplitude and the transmission ratio of the gears. Four groups of control experiments were conducted to investigate the relationship between different factors (voltage, motor type, wing area, and the number of veins) and the robot’s lift, which was monitored by a pressure sensor. I analyzed the results from the experiments and built a final version of the robot based on a slider-crank mechanism. The main structure of the final version is made of three 3mm carbon fiber boards, and the wings are made of 0.025mm PET (polyethylene terephthalate) material, reinforced by three carbon fiber rods: two 0.5mm ones across the membrane and a 1mm one at the leading edge. The robot weighs 16.3g and can produce enough lift to overcome its gravity under 9V with an off-board power source by exhibiting an upward trend during a tethered flight test.

Position Controller for a Flapping-Wing Drone Using UWB

This paper proposes an integral approach for accurate ultra-wideband indoor position control of flapping-wing micro-air vehicles. Three aspects are considered to achieve a reliable and accurate position controller. The first aspect is a velocity/attitude flapping-wing model for drag compensation. The model is compared with real flight data and shown to be applicable for more than one type of flapping-wing drone. The second improvement regards a voltage-dependent thrust control. Lastly, a characterisation of ground effects in flapping-wing flight is obtained from hovering experiments. The proposed controller improves position control by a factor [Formula: see text], reaching a mean absolute error of 10[Formula: see text]cm for the position in [Formula: see text] and [Formula: see text], and 4.9[Formula: see text]cm for the position in [Formula: see text].

Effect of Wing Membrane Material on the Aerodynamic Performance of Flexible Flapping Wing

Flexible deformation of the insect wing has been proven to be beneficial to lift generation and power consumption. There is great potential for shared research between natural insects and bio-inspired Flapping wing Micro Aerial Vehicles (FWMAVs) for performance enhancement. However, the aerodynamic characteristics and deformation process of the flexible flapping wing, especially influenced by wing membrane material, are still lacking in-depth understanding. In this study, the flexible flapping wings with different membrane materials have been experimentally investigated. Power input and lift force were measured to evaluate the influence of membrane material. The rotation angles at different wing sections were extracted to analyze the deformation process. It was found that wings with higher elastic modulus membrane could generate more lift but at the cost of more power. A lower elastic modulus means the wing is more flexible and shows an advantage in power loading. Twisting deformation is more obvious for the wing with higher flexibility. Additionally, flexibility is also beneficial to attenuate the rotation angle fluctuation, which in turn enhances the aerodynamic efficiency. The research in this paper is helpful to further understand the aerodynamic characteristics of flexible flapping wing and to design bio-inspired FWMAVs with higher performance.

Should friction losses be included in an electromechanical model of a bioinspired flapping-wing micro aerial vehicle to estimate the flight energetic requirements?

The paper aims to examine the effects of mechanical losses on the performance of a bioinspired flapping-wing micro aerial vehicle (FWMAV) and ways to mitigate them by introducing a novel electromechanical model. The mathematical model captures the effect of a DC gear motor, slider-crank, flapping-wings aerodynamics, and frictional losses. The aerodynamic loads are obtained using a quasi-steady flow model. The parameters of the flight mechanism are estimated using published experimental data which are also used to validate the mathematical model. Incorporating the flapping mechanism friction losses into the mathematical model enables capturing the physics of the problem with higher accuracy, which is not possible with simpler models. It also makes it possible to estimate the aerodynamic energetic requirements. Moreover, the model enabled evaluations of the effects of adding bioinspired elastic elements on the efficiency of the system. Although it is established through experimental studies that the addition of a bioinspired elastic element can improve system efficiency and increase lift generation, the existing mathematical models fail to model and predict such effects. It has been demonstrated that the addition of an elastic element can reduce friction losses in the system by decreasing the internal forces. Optimised parameters for a FWMAV incorporating elastic elements are also obtained.

Optimal Processing Parameters of Transmission Parts of a Flapping-Wing Micro-Aerial Vehicle Using Precision Injection Molding.

In this study, we designed and fabricated transmission parts for a flapping-wing micro-aerial vehicle (FW-MAV), which was fabricated by precision injection molding, and analyzed its warpage phenomena. First, a numerical simulation (Moldflow) was used to analyze the runner balance and temperature, pressure, and stress distributions of the base, gears, and linkage of the transmission structures in an FW-MAV. These data were then applied to fabricate a steel mold for an FW-MAV. Various process parameters (i.e., injection temperature, mold temperature, injection pressure, and packing time) for manufacturing transmission parts for the FW-MAV by precision injection molding were compared. The Taguchi method was employed to determine causes of warpage in the transmission parts. The experimental results revealed that the causes of warpage in the transmission parts were, in order of importance, the mold temperature, injection pressure, packing time, and injection temperature. After the transmission parts were assembled on the FW-MAV, experiments revealed that the MAV could achieve a flight time of 180 s. Mass production of the FW-MAV by precision injection molding could potentially produce substantial savings in time, manpower, and cost.

Modeling and Control of Flapping-Wing Micro-Aerial Vehicles With Harmonic Sinusoids

Flapping-wing micro-aerial vehicles (FWMAVs) provide unique control challenges both in control authority and in the complexity of modeling flapping-wing aeromechanics. We provide a control-critical, closed-form model for FWMAV flight, particularly tailored to augmenting yaw torque authority of the vehicle (a common challenge for FWMAVs). The model provides invertible nonlinear closed-form expressions for thrust and moments in terms of trigonometric polynomial input voltages and the wingstroke shape, and respects asymmetries inherent to the vehicle. We apply the model to characterize the Harvard RoboBee, providing an optimization-based system identification process. Using the inverted mapping between wingstroke shape and control axes, we achieve lateral and heading control of the vehicle. Our model and asymmetric system identification, in collaboration with the chosen control scheme, allow full control authority of the position and the heading of the vehicle.

Development of an Insect-like Flapping-Wing Micro Air Vehicle with Parallel Control Mechanism

Most traditional flapping-wing micro air vehicles (FMAVs) adopt a serial control mechanism, which means that one drive corresponds to one degree of freedom. However, the serial mechanism often struggles to meet FMAV requirements in terms of stiffness, size, and reliability. In order to realize a compact reliable control mechanism, we developed a two-wing insect-like FMAV with a parallel control mechanism. The prototype possesses an optimized string-based flapping wing mechanism, a 2RSS/U parallel control mechanism, and an onboard power supply and controller. The pulley’s profile of the string-based mechanism was refined to reduce the deformation and impact of the string. The parameters of the parallel mechanism were designed to enable the stroke plane to rotate a large angle to produce control torque. The prototype had a flapping frequency of 25 Hz, a full wingspan of 21 cm, and a total weight of 28 g. A PID controller with a decoupler based on the kinetics solution of parallel mechanism was designed to control the FMAV. A force and torque (F/T) experiment was carried out to obtain the lift and control torque of the prototype. The measured data showed that the flapping wing mechanism provided sufficient lift and the control mechanism generated a toque caused by the stroke plane rotation and trailing edge movement and were linear to the control input. A flight test was carried out to verify the flight stability of the prototype. The result shows that the attitude angle only fluctuates within a small range, which proved that the control mechanism and control strategy were successful.

Horizontal take-off of an insect-like FMAV based on stroke plane modulation

PurposeVertical take-off is commonly adopted in most insect-mimicking flapping-wing micro air vehicles (FMAV) while insects also adopt horizontal take-off from the ground. The purpose of this paper is to study how insects adjust their attitude in such a short time during horizontal take-off by means of designing and testing an FMAV based on stroke plane modulation.Design/methodology/approachAn FMAV prototype based on stroke plane rotating modulation is built to test the flight performance during horizontal take-off. Dynamic gain and decoupling mixer is added to compensate for the nonlinearity during the rotation angle of the stroke plane getting too large at the beginning of take-off. Force/torque test based on a six-axis sensor validates the change of aerodynamic force and torque at different rotation angles. High-speed camera and motion capture system test the flight performance of horizontal take-off.FindingsStroke plane modulation can provide a great initial pitch toque for FMAV to realize horizontal take-off. But the large range of rotation angles causes nonlinearity and coupling of roll and yaw. A dynamic gain and a mixer are added in the controller, and the FMAV successfully achieves horizontally taking off in less than 1 s.Originality/valueThe research in this paper shows stroke plane modulation is suitable for insect’s horizontal take-off

An efficient, modular controller for flapping flight composing model-based and model-free components

We present a controller that combines model-based methods with model-free data-driven methods hierarchically, utilizing the predictive power of template models with the strengths of model-free methods to account for model error, such as due to manufacturing variability in the RoboBee, a 100 mg flapping-wing micro aerial vehicle (FWMAV). Using a large suite of numerical trials, we show that the model-predictive high-level component of the proposed controller is more performant, easier to tune, and able to stabilize more dynamic tasks than a baseline reactive controller, while the data-driven inverse dynamics controller is able to better compensate for biases arising from manufacturing variability. At the same time, the formulated controller is very computationally efficient, with the MPC implemented at 5 KHz on a Simulink embedded target, via which we empirically demonstrate controlled hovering on a RoboBee.

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.

Longitudinal Mode System Identification of an Insect-like Tailless Flapping-Wing Micro Air Vehicle Using Onboard Sensors

In this paper, model parameter identification results are presented for a longitudinal mode dynamic model of an insect-like tailless flapping-wing micro air vehicle (FWMAV) using angle and angular rate data from onboard sensors only. A gray box model approach with indirect method was utilized with adaptive Gauss–Newton, Levenberg–Marquardt, and gradient search identification methods. Regular and low-frequency reference commands were mainly used for identification since they gave higher fit percentages than irregular and high-frequency reference commands. Dynamic parameters obtained using three identification methods with two different datasets were similar to each other, indicating that the obtained dynamic model was sufficiently reliable. Most of the identified dynamic model parameters had similar values to the computationally obtained ones, except stability derivatives for pitching moment with forward velocity and pitching rate variations. Differences were mainly due to certain neglected body, nonlinear dynamics, and the shift of the center of gravity. Fit percentage of the identified dynamic model (~49%) was more than two-fold higher than that of the computationally obtained one (~22%). Frequency domain analysis showed that the identified model was much different from that of the computationally obtained one in the frequency range of 0.3 rad/s to 5 rad/s, which affected transient responses. Both dynamic models showed that the phase margin was very low, and that it should be increased by a feedback controller to have a robustly stable system. The stable dominant pole of the identified model had a higher magnitude which resulted in faster responses. The identified dynamic model exhibited much closer responses to experimental flight data in pitching motion than the computationally obtained dynamic model, demonstrating that the identified dynamic model could be used for the design of more effective pitch angle-stabilizing controllers.

The Optimisation of Aerodynamic Performance Enhancement of a Flapping Wing using Response Surface Methodology

Flapping-Wing Micro Air Vehicles (FW-MAVs) are small hand-held flying vehicles that can manoeuvre in constrained space owing to their lightweight, low aspect ratio and can fly in a low Reynolds number environment. Among all wing types, flapping wings have the most potential in fulfilling this flight requirement since it offers good agility in confined spaces. However, the design problem for the flapping wings lies in lift generation and figuring out the main factors that play the biggest role in generating lift. In the present work, the effects of design parameters such as camber, velocity and frequency of the flapping wing have been investigated using the response surface methodology (RSM). The standard quadratic model of RSM called Central Composite Design (CCD) was utilized to identify and optimize the flapping wing. The experimental results were found to be in good agreement with the predicted outcomes. Out of 20 experimental trials determined by CCD, the optimum camber, velocity, and frequency were found to be 15%, 4.29 m/s and 9 Hz respectively. The experimental results in this study are reasonable and accurate and can be used for describing the aerodynamic parameters. This study also established the usefulness of RSM in optimizing the aerodynamic properties for flapping wing mechanism.

Fluid–structure interaction analysis of flexible flapping wing in the Martian environment

Flapping-wing micro air vehicle (FWMAV) is an attractive idea for Mars exploration because of its high capability in a thin atmosphere. The biggest challenge for its development is an appropriate understanding of a flapping flight with flexible wings, which is significantly complicated because flexible flapping wings can undergo large-scale deformations due to the effects of wing inertia and the aerodynamic forces exerted by the surrounding atmosphere. Fluid–structure interaction (FSI) analysis is a powerful tool for accurate investigations, but it usually has a very high computational cost, making it challenging to perform necessary parametric studies for practical designing. An efficient FSI analysis method is required. On Mars, whose atmospheric density is around 1% that of Earth, aerodynamic forces have a relatively small influence on wing deformation and may even be negligible in some cases. We thus investigate the relative contributions of the inertial force of a flapping wing and the aerodynamic forces exerted by the surrounding Martian atmosphere using a two-way coupled FSI simulation, and identify the conditions under which the aerodynamic forces are negligible. Then, we develop a computationally efficient one-way coupled FSI analysis system based on the interface-capturing method to design a flexible flapping wing for Mars exploration. Under the obtained conditions, we perform parametric studies on hovering flight with flexible flapping wings in the Martian environment with multiple aerodynamic parameters, various kinematic parameters, and material properties of the wing. We conclude that an FWMAV with a payload of around 5 g can fly for more than 1 min for the maximum density of the Martian atmosphere.

Effect of spanwise groove on the dynamic stall characteristics of an airfoil

Numerical simulations are conducted to investigate the effect of triangular groove on the dynamic stall characteristics of a NACA 0012 airfoil at a Reynolds number of 135,000. The right-angled triangular grooves are placed at either 10%, 25%, or 50% chord locations on the suction and have depths of 0.025c and 0.05c, measured normal to the surface of the airfoil. The solutions that are second order accurate in time and space are obtained using pressure-based finite volume solver and the 4-equation transition SST turbulence model viz. γ- Re θt is used to predict transition and viscous stresses accurately. The airfoil is in harmonic pitch motion about its quarter-chord with a maximum circular frequency of 18.67 rad/s. The results suggest that the presence of a groove, except for the deeper grove at 0.5c, quickens the dynamic stall, but with smaller rise in C l,max and a less severe fall in lift at the stall. The mean C l value during the downstroke is improved by up to 8% for the deeper groove at 0.25c, reducing the hysteresis in lift significantly. The grooves at 0.1c, 0.25c, and 0.5c also reduce the drag by 4%, 7%, and 9% during a complete cycle, with subsequent improvements of 54%, 69%, and 63% in the l/d ratio. The current finding can be thus used to enhance the performance of flapping wing MAVs, helicopter rotors, and wind turbine blades as these applications encounter the dynamic stall phenomena frequently.

Analysis of nonlinear aerodynamic performance and passive deformation of a flexible flapping wing in hover flight

The flexibility of insect wings and model wings in flapping-wing micro air vehicles (FWMAVs) is crucial to guarantee an economic flight. Since the wing deformation is bilaterally coupled with the aerodynamic force, conventional simulations on this fluid–structure interaction (FSI) problem mostly build up their models using computational fluid dynamics (CFD) and computational solid dynamics (CSD) methods, which requires high computational costs. Alternatively, an analytical model is proposed here for a quick estimate of the aerodynamic performance and passive deformation on flexible flapping wings. The deformation is simplified into a rigid-body rotation at the wing root, a spanwise twist, and a shortening along the span. The aerodynamic force is approximated by a predictive quasi-steady model and the spanwise twist is modeled using a quadratic polynomial. Results show that the introduction of wing flexibility can attenuate the lift generation due to the negative rotational lift and adverse translation–rotation coupling effect after each stroke reversal. The wing with moderate stiffness is recommended to achieve a high lift. An increase of aspect ratio and root cutoff can also enhance the dimensional lift generation, while the most economic wing design has an aspect ratio around 5 and no root cut-off. More importantly, the increase of flapping frequency can only result in a lift enhancement within certain limits. However, the power consumption keeps increasing as the frequency goes up, indicating a significant breakdown of performance. Our findings can uncover the role of wing flexibility in both insects and FWMAVs and therefore contribute to the design of FWMAVs.