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Parameter maps of net aerodynamic force and net force coefficient as functions of stroke amplitude and mid-stroke angle of attack. For fixed values of wing rotation (flip duration ∆τ=0.16; flip start τ0=−0.08, flip timing τf=0), stroke amplitude was varied from 60 to 180 ° and angle of attack was varied from 0 to 90 °. In each diagram, the small open circles indicate the positions of actual measurements. Values between these measured points have been interpolated using a cubic spline. Values are encoded in pseudocolor according to the scales shown beneath each plot. This same format is used in Fig. 5, Fig. 7 and Fig. 10. (A) Net aerodynamic force, the vector sum of lift and drag, increases monotonically with increasing angle of attack and stroke amplitude. (B) Net aerodynamic force coefficient increases with angle of attack, but decreases with stroke amplitude.
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We used a dynamically scaled mechanical model of the fruit fly Drosophila melanogaster to study how changes in wing kinematics influence the production of unsteady aerodynamic forces in insect flight. We examined 191 separate sets of kinematic patterns that differed with respect to stroke amplitude, angle of attack, flip timing, flip duration and t...
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When an insect hovers, the centre of mass of its body oscillates around a point in the air and its body angle oscillates around a mean value, because of the periodically varying aerodynamic and inertial forces of the flapping wings. In the present paper, hover flight including body oscillations is simulated by coupling the equations of motion with...
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This paper focuses on an experimental investigation aimed at evaluating the aerodynamics force characteristics of three-dimensional (3D) insect-like flapping motion in the vicinity of ground. The purpose is to establish whether flapping wing insects can derive aerodynamic benefit from ground effect similar to that experienced by a fixed wing aircra...
Citations
... -steady models correlate and as = [sin(2 )](Dickinson et al. 1999;460 Sane& Dickinson 2001& Dickinson , 2002;Wang et al. 2016). Thus, is expected to be maximum461 when ≈ 45 • , which is slightly higher than that for a translated flat-plate wing(Taira & 462 Colonius 2009). ...
The power exchange between fluid and structure plays a significant role in the force production and flight efficiency of flapping wings in insects and artificial flyers. This work numerically investigates the performance of flapping wings by using a high-fidelity fluid-structure interaction solver. Simulations are conducted by varying the hinge flexibility (measured by the Cauchy number, Ch, i.e. the ratio between aerodynamic and torsional elastic forces) and the wing shape (quantified by the radius of the first moment of area, r_1. Results show that the lift production is optimal at 0.05 < Ch < 0.2 and larger r_1 where the minimum angle of attack is around 45 degree at midstroke. The power economy is maximised for wings with lower r_1 near Ch=0.2. Power analysis indicates that the optimal performance measured by the power economy is obtained for those cases where two important power synchronisations occur: anti-synchronisation of the pitching elastic power and the pitching aerodynamic and inertial powers and nearly in-phase synchronisation of the flapping aerodynamic power and the total input power of the system. While analysis of the kinematics for the different wing shapes and hinge stiffnesses reveals that the optimal performance occurs when the timing of pitch and stroke reversals are matched, thus supporting the effective transfer of input power from flapping to passive pitching and into the fluid. These results suggest that careful optimisation between wing shapes and hinge properties can allow insects and robots to exploit the passive dynamics to improve flight performance.
... The motion of insect wings is quite complicated [6] and influenced by numerous parameters, including pitch amplitude, deviation, stroke, flapping frequency, etc. [7,8]. Most theoretical and experimental studies [7,[9][10][11][12][13][14][15][16][17] have focused on rigid wings where the aeroelastic coupling of solid and fluid was ignored. ...
... The motion of insect wings is quite complicated [6] and influenced by numerous parameters, including pitch amplitude, deviation, stroke, flapping frequency, etc. [7,8]. Most theoretical and experimental studies [7,[9][10][11][12][13][14][15][16][17] have focused on rigid wings where the aeroelastic coupling of solid and fluid was ignored. The experimental study conducted by Sane and Dickinson [7] using a fruitfly-like rigid flapping wing planform at Reynolds number of about 100 revealed that lift was maximum when the pitch amplitudes and stroke were 45 z and 180 z , respectively. ...
... Most theoretical and experimental studies [7,[9][10][11][12][13][14][15][16][17] have focused on rigid wings where the aeroelastic coupling of solid and fluid was ignored. The experimental study conducted by Sane and Dickinson [7] using a fruitfly-like rigid flapping wing planform at Reynolds number of about 100 revealed that lift was maximum when the pitch amplitudes and stroke were 45 z and 180 z , respectively. Bhat et al. [18] proposed that the flapping motion profile influenced the overall change in the lift coefficient of the rigid flapping wing, while the pitching motion profile only affected the lift at stroke reversal. ...
The thorax is the central component of the insect flight drivetrain, making it essential to understand how thoracic muscles influence insect flight for flapping wing microair vehicle design. This paper presents a theoretical model that takes into account the influence of thoracic muscles on flapping wing motion with reference to real insects. The thoracic muscle effect is simulated by the chordwise torsional spring, whose stiffness is derived from a comparison test with the results of real insect experiments. The elastic deformation of the flexible flapping wing is modeled by the von Kármán nonlinear plate theory. The predictive quasi-steady aerodynamic model based on the blade element theory can estimate the aerodynamic force, and the modeling of the spanwise bending and twisting is done with quadratic polynomials. The equations of motion are solved using the Newmark-Raphson method. Results suggest that including the influence of thoracic muscles decreases cycle-averaged lift and power, but enhances the efficiency of lift production by 23%. Moreover, it also postpones pitching motion and reduces its amplitude, though the movement trends of the flapping motion remain approximately unchanged regardless of the inclusion of the thoracic muscle effect.
... Such a rotational motion of the wing with constant α andφ has also been called sweep, rotational translation or sometimes just translation in the literature [e.g., Refs. [8][9][10]. The mechanism behind the stability of the LEV has been investigated over several decades. ...
... The initial angle of attack of the wing (α 0 ) in these studies were 0 • and 20 • where the flow is nominally attached to the wing. The lift and drag on revolving wings depend highly on α [8], and at higher angles of attack a stable LEV is formed [5,7]. Accordingly, the response of revolving wings to perturbations may also be different from that of linearly translating wings. ...
Low-aspect-ratio revolving wings find applications in miniature robotic flyers and turbo-machinery. At a high angle of attack, the flow separates from a wing's leading edge, forming a leading-edge vortex. On a revolving wing, the leading-edge vortex (LEV) is stabilized by strong rotational acceleration and is known to be the primary source of high and stable aerodynamic forces acting on the wing. While previous studies have characterized the performance of revolving wings, the effects of perturbations on the flow profile and performance have not been explored. This study combined experiments and computational fluid dynamics simulations to investigate the lift, drag, and power coefficients of a wing revolving at a Reynolds number of Re=2500 and undergoing pitch perturbations. Perturbations were systematically varied to investigate the effects of the wing's initial angle, the amplitude and duration of perturbation, and the location of the pitch axis. Simulations provided insights into the flow structures around the wing and their effects on the wing-surface pressures and the aerodynamic forces. Finally, a quasisteady model was used to decompose the effects of wing rotation and pitch perturbations on the lift and drag forces. The decomposition revealed a consistent dependency of the variations in the lift on the pitch angular velocity across all perturbations, irrespective of the initial angle. The transition from the LEV-dominant to the rotation-dominant flow occurs at very low pitch rates, the values of which were found to depend on the initial angle of the revolving wing. For lower initial angles, the transition occurred at lower pitch rates. During the rotation-dominant perturbations, changes in the vortical structures around the wing were found to have a minimal effect on the lift and drag compared to the quasisteady effects. Moreover, the oscillations in the lift and drag during the perturbation could be reduced by appropriately shifting the pitch axis location. These findings highlight the dominant role of inviscid effects on the variations in loads acting on a revolving wing during pitch perturbations.
... In the past, the high vertical force generation of a flapping wing is often related to the dominant lift enhancement mechanisms such as added mass (Sane and Dickinson 2001a), delayed stall (Dickinson and Götz 1993) from the Leading Edge Vortex (LEV) and wake capture (Lua et al 2011). Added mass is the result of the sudden and accelerated motion of the wing and typically occurs at the beginning of the stroke during the accelerating phase of the stroke. ...
The rigorous numerical investigation of the class of inclined stroke plane flapping wings has brought to light the vertical force enhancement due to dipole jet interaction. In this study, the class of inclined stroke plane flapping wings with varying inter-plane distances and stroke inclinations are studied for vertical force generation. The configurations with stroke plane angles of 60° and 75° are found to produce significantly high vertical forces. Further, wake structures of the tandem flapping wing in an inclined stroke plane show various types of dipole vortex shedding and dipole jet interactions. The identified types of dipole jet interactions help in the understanding of vertical force trends of the forewing, hindwing, and hence the tandem wing configuration as a whole. It reveals the potential dipole jet interaction producing the highest vertical force in tandem wing configurations. In all, the study can classify the flows of the tandem wing configurations based on vortex shedding during hovering conditions and understand its vertical force enhancements. This not only helps in getting physical insights into the vortex dynamics of inclined stroke plane flapping wings but also in the design optimisation of the tandem wing configurations in biomimetic Micro Air vehicles (MAVs).
... For hummingbirds, upstroke produces only about half of weight support as downstroke [5][6][7] yet is still considered key to their ability to sustain hovering flight. When combined with the stroke motion, dynamic pitching of the wings helps generate unsteady lift through mechanisms such as rotational circulation, delayed stall, and accompanying leading-edge vortices to further enhance lift production for those hovering flyers [8][9][10][11][12]. ...
Previous studies suggested that wing pitching, i.e., the wing rotation around its long axis, of insects and hummingbirds is primarily driven by an inertial effect associated with stroke deceleration and acceleration of the wings and is thus passive. Here we considered the rapid escape maneuver of hummingbirds who were initially hovering but then startled by the frontal approach of a looming object. During the maneuver, the hummingbirds substantially changed their wingbeat frequency, wing trajectory, and other kinematic parameters. Using wing kinematics reconstructed from high-speed videos and computational fluid dynamics modeling, we found that although the same inertial effect drove the wing flipping at stroke reversal as in hovering, significant power input was required to pitch up the wings during downstroke to enhance aerodynamic force production; furthermore, the net power input could be positive for wing pitching in a complete wingbeat cycle. Therefore, our study suggests that an active mechanism was present during the maneuver to drive wing pitching. In addition to the powered pitching, wing deviation during upstroke required twice as much power as hovering to move the wings caudally when the birds redirected the aerodynamic force vector for escaping. These findings were consistent with our hypothesis that enhanced muscle recruitment is essential for hummingbirds' escape maneuvers.
... where T p is the propeller thrust, C D is the aerodynamic drag coefficient, α is the angle of attack, ρ is the air density, and v w is the wing velocity, which depends on the flapping frequencyq f and the geometry of the wing since the integral is computed over its area A. Coefficient C D can be determined experimentally in wind tunnel [11] measuring the wrenches for a given air speed and density, or numerically using computational fluid dynamics (CFD) models [39]. The autopilot will generate a commanded thrust (see section IV-A) to achieve constant velocity compensating several aerodynamic effects, including wind perturbations. ...
This letter is focused on the benchmark evaluation and comparison of the flapping and fixed wing flight modes on an hybrid platform developed for the realization of autonomous inspection operations outdoors. The platform combines the high range and endurance of fixed-wing UAVs (unmanned aerial vehicles), with the higher maneuverability and intrinsic safety of flapping wing in the interaction with humans during the hand launch and capture. A unified model of the hybrid platform is derived for both configurations following the Lagrange formulation to express the multi-body dynamics and aerodynamic forces of the flapping wing and the propellers. The proposed control scheme exploits the similarities of both flight modes in the tail actuation and in the generation of thrust either with the flapping wings or the propellers, in such a way that it can be implemented on conventional autopilots, facilitating in this way the adoption of this type of aerial platforms. To evaluate and compare the performance of both modes, a set of benchmark tests and metrics are defined, including the energy efficiency in forward flight, trajectory tracking, hand launch and capture, and accuracy in visual inspection. Experimental results in outdoors validate the developed prototype, identifying the fixed/flapping transitions, and evidencing the higher energy efficiency of the flapping wing mode compared to the fixed wing.
... Mechanism of insect muscles during flight.18 acceleration and thus increases aerodynamic forces8,24,25 (Figures 3(d)and (e)). ...
Wildlife always acts as an inspiration source for humans to help them study and mimic flight methods. Insects are one of the most important sources of biological systems’ inspiration to control flow and reduce aerodynamic noise. Insects are classified into different kinds, and most can fly by fluttering their wings. In general, insects’ flight muscles are divided into direct and indirect types that act synchronously and asynchronously with nerve impulses, respectively. These muscles help insects use a mixture of rotating, flapping, and pitching movements to achieve specific wing kinematics. Insects use various mechanisms for generating aerodynamic forces, including the Weis-Fogh or clap and fling mechanism, delayed stall due to unsteady motion (Wagner effect), wing rotation (Kramer effect), wake capture or wing–wake interaction, added mass, and absence of stall. On the other hand, the insect noises are divided into aerodynamic and structural. Insects’ aerodynamic noise is created by fluctuating forces, flow–solid interaction, shed vortex, and turbulence inflow. Meanwhile, insects’ structural noise is made by frictional and tymbal mechanisms. Their flow control methods are classified into two categories: wing shape and sub-structures. Wing shape features such as planform, chord length and location, twist, sweep, wingtip, and aspect ratio influence the flow around the insects. The sub-structures such as leading edge, trailing edge, swallowtail, and surface textures affect the flow too. A thorough understanding of insects’ fly, aerodynamic noise, and their control flow techniques will significantly help engineers to produce competitive products with better aerodynamic performance and aeroacoustic signature.
... The kinematics of a flapping wing is described by three motion angles (shown schematically in Fig. 1): the flapping/translation angle (φ ) along the stroke plane, the pitching angle (or feathering/rotation angle, α), and the elevation angle (θ ) of the stroke plane. This study focuses on hovering conditions and we fix the elevation angle to θ = 0 since this angle is known to be of secondary importance in force generation [32][33][34] . For hovering flight, the characteristic Reynolds number Re is defined from the average chordc, and a reference speed U r defined by the distance spanned by the radius of second moment of area R 2 = 1 S R 0 cr 2 dr over a flapping period 4,7 , where r is the local spanwise coordinate (cf. ...
Flapping Wing Micro Air Vehicles (FWMAV) are highly manoeuvrable, bio-inspired drones that can assist in surveys and rescue missions. Flapping wings generate various unsteady lift enhancement mechanisms challenging the derivation of reduced models to predict instantaneous aerodynamic performance. In this work, we propose a robust CFD data-driven, quasi-steady (QS) Reduced Order Model (ROM) to predict the lift and drag coefficients within a flapping cycle. The model is derived for a rigid ellipsoid wing with different parameterized kinematics in hovering conditions. The proposed ROM is built via a two-stage regression. The first stage, defined as `in-cycle' (IC), computes the parameters of a regression linking the aerodynamic coefficients to the instantaneous wing state. The second stage, defined as `out-of-cycle' (OOC), links the IC weights to the flapping features that define the flapping motion. The training and test dataset were generated via high-fidelity simulations using the overset method, spanning a wide range of Reynolds numbers and flapping kinematics. The two-stage regressor combines Ridge regression and Gaussian Process (GP) regression to provide estimates of the model uncertainties. The proposed ROM shows accurate aerodynamic predictions for a wide range of kinematics. The model performs best for smooth kinematics that generates a stable Leading Edge Vortex (LEV). Remarkably accurate predictions are also observed in dynamic scenarios where the LEV is partially shed, the non-circulatory forces are considerable, and the wing encounters its own wake.
... The introduction of pitching motion, whether passive rotation or active morphing, shows great potential advantages in lift and efficiency. Result of Lua et al. [22] and Sane and Dickinson [23] showed that an advance in pitching motion with a moderate angle of attack is the high-lift behavior. Recently, the impact of flapping trajectories is gradually attracting attention. ...
... However, the amplitude of elevating motion is quite smaller than that of the other two motions. Meanwhile, a small elevating motion has been proven to have minimal aerodynamic effects compared with the other two motions [23,33]. Therefore, the elevating motion has been isolated and only the sweeping and pitching motion are incorporated. ...
... Lift and power performance of two typical states are presented in Figure 18. Consistent with the previous research [23,51], aerodynamic performance, especially lift, does not vary monotonically with the pitching amplitude or phase angle. This phenomenon implies that there are some optimal values to maximize the performance. ...
The wing planform and flapping kinematics are critical for the hovering flight of flapping wing micro air vehicles (FWMAVs). The degree of influence of wing geometry and kinematic parameters on aerodynamic performance still lacks in-depth analysis. In this study, a sensitivity analysis was conducted based on the quasi-steady aerodynamic model. Each parameter was investigated independently by using the control variable method. The degree of each variable's influence on lift, power, and power loading is evaluated and compared. Furthermore, detailed exponential relationships were established between the parameters and the corresponding aerodynamic properties. It is found that, for the geometric parameters, wing area has the greatest influence on lift, and the distribution of area has the most visible effect on aerodynamic power. All geometric parameters are negatively correlated with power loading. For the kinematic parameters, flapping frequency, compared with sweeping amplitude, results in faster lift growth and slower drop in power loading, while their influence on aerodynamic power is nearly comparable. A moderate pitching amplitude with advanced rotation will maximize the lift. For the flapping trajectory, lift and power loading are primarily affected by the shape of the pitching motion rather than the sweeping motion. But the sweeping motion seems to dominate the power consumption. The research in this paper is helpful to understand the effect of each parameter and provide theoretical guidance for the development of FWMAVs.
... The authors in [2] and [3] compared flapping wing models to experimental data in hover, gliding, and flight in insects. Modeling and fluid dynamic scaling of insect flapping flight continued to be developed in [4], [5], [6], and [7], with experiments done at larger but Reynolds number similar scales. The authors in [8], [9], and [10] extensively explored the parameter space for a 2-D flapping hydrofoil. ...
... In general, the presence of crossflow shifts the coefficient of force versus pitch bias curve as hypothesized. As seen in Fig. 3, the X-direction streamwise model in (7) using the shifted pitch bias from (6) shows degrading agreement with the data at higher absolute crossflow angles, with a reduced value at the peak of the curve, and clear error at the low-bias/high crossflow extremities of the curve. The reduced peak is likely due to diminished production from the transition to drag-based paddling with the flow rather than more efficient lift-based flapping. ...
Flapping fins can enable greater maneuverability in undersea vehicles. Most work to this point has only considered inflow perpendicular to the flapping stroke plane. However, this would not be true during maneuvers or while station keeping in a current. In this article, a simple model is presented which utilizes zero-crossflow data to predict the effect of crossflow on the forces produced by a flapping fin. This model compares well to experimental data taken over an array of crossflow and bias angles. The crossflow model may be useful for flapping fin vehicle simulations, feedforward models in vehicle controllers, and the development of a flapping fin controller that can compensate for inflow angle disturbances.
