“…where κ(t) denotes either sweep angle or rotational angle at time t, a n and b n are the fitted coefficients (n=0, 1, 2,…, 5), and f is the flapping frequency. Details of the measurement procedure of the wing kinematics can be found in previous work (Le et al, 2013;Truong et al, 2011;Phan et al, 2015).…”
Flying insects can maintain maneuverability in the air by flapping their wings, and, to save energy, the wings should operate following optimal kinematics. However, unlike conventional rotary wings, insects operate their wings at aerodynamically uneconomical and high angles of attack (AoA). Although insects have continuously received attention from biologists and aerodynamicists, the high AoA operation in insect flight has not been clearly explained. Here, we used a theoretical blade-element model to examine the impact of wing inertia on the power requirement and flapping AoA, based on 3D free-hovering flight wing kinematics of a horned beetle, The relative simplicity of the model allowed us to search for the best AoA distributed along the wingspan, which generate the highest vertical force per unit power. We show that, although elastic elements may be involved in flight muscles to store and save energy, the insect still has to use substantial power to accelerate its wings, because inertial energy stores should be used to overcome aerodynamic drag before being stored elastically. At the same flapping speed, a wing operating at a higher AoA requires lower inertial torque, and therefore lower inertial power output, at stroke reversals than a wing operating at an aerodynamically optimal low AoA. An interactive aerodynamic-inertial effect thereby enables the wing to flap at sufficiently high AoA, which causes an aerodynamically uneconomical flight in an effort to minimize the net flight energy.
“…where κ(t) denotes either sweep angle or rotational angle at time t, a n and b n are the fitted coefficients (n=0, 1, 2,…, 5), and f is the flapping frequency. Details of the measurement procedure of the wing kinematics can be found in previous work (Le et al, 2013;Truong et al, 2011;Phan et al, 2015).…”
Flying insects can maintain maneuverability in the air by flapping their wings, and, to save energy, the wings should operate following optimal kinematics. However, unlike conventional rotary wings, insects operate their wings at aerodynamically uneconomical and high angles of attack (AoA). Although insects have continuously received attention from biologists and aerodynamicists, the high AoA operation in insect flight has not been clearly explained. Here, we used a theoretical blade-element model to examine the impact of wing inertia on the power requirement and flapping AoA, based on 3D free-hovering flight wing kinematics of a horned beetle, The relative simplicity of the model allowed us to search for the best AoA distributed along the wingspan, which generate the highest vertical force per unit power. We show that, although elastic elements may be involved in flight muscles to store and save energy, the insect still has to use substantial power to accelerate its wings, because inertial energy stores should be used to overcome aerodynamic drag before being stored elastically. At the same flapping speed, a wing operating at a higher AoA requires lower inertial torque, and therefore lower inertial power output, at stroke reversals than a wing operating at an aerodynamically optimal low AoA. An interactive aerodynamic-inertial effect thereby enables the wing to flap at sufficiently high AoA, which causes an aerodynamically uneconomical flight in an effort to minimize the net flight energy.
“…Further studies are needed to measure the flow field around the wing during four-wing flapping while modifying the handling parameters, since the leading edge vortex is an important feature of the flows created by insect wings and, thus, the forces they create [15]. In addition, recent studies have demonstrated that the wing rotation angle and/or the deflection angle at the wing root play an important role in generating the control moment in roll rotation and/or maximum translational force generation [21][22][23].…”
The aim of this study was to clarify the relationships between pitch, roll, and yaw moments during flapping and various handling parameters ((i) wingbeat amplitude, (ii) stroke plane angle, and (iii) asymmetry of the flapping duration). We investigate the effects of the combination of (i) and (ii), or the combination of (i) and (iii) for generating rotational moments. The results demonstrated that flapping amplitudes and asymmetry contributed to generating pitch and roll moments, and flapping amplitude and tilt angle affected the generation of all moments.
“…With this configuration, the flapping-wing system could produce the passive spanwise twist and chordwise camber during the flapping motion. More details can be found in Phan et al [52]. Figure 3.Wing configuration used to create wing twist and camber.…”
This study used numerical and experimental approaches to investigate the role played by the clap-and-fling mechanism in enhancing force generation in hovering insect-like two-winged flapping-wing micro air vehicle (FW-MAV). The flapping mechanism was designed to symmetrically flap wings at a high flapping amplitude of approximately 192°. The clap-and-fling mechanisms were thereby implemented at both dorsal and ventral stroke reversals. A computational fluid dynamic (CFD) model was constructed based on three-dimensional wing kinematics to estimate the force generation, which was validated by the measured forces using a 6-axis load cell. The computed forces proved that the CFD model provided reasonable estimation with differences less than 8%, when compared with the measured forces. The measurement indicated that the clap and flings at both the stroke reversals augmented the average vertical force by 16.2% when compared with the force without the clap-and-fling effect. In the CFD simulation, the clap and flings enhanced the vertical force by 11.5% and horizontal drag force by 18.4%. The observations indicated that both the fling and the clap contributed to the augmented vertical force by 62.6% and 37.4%, respectively, and to the augmented horizontal drag force by 71.7% and 28.3%, respectively. The flow structures suggested that a strong downwash was expelled from the opening gap between the trailing edges during the fling as well as the clap at each stroke reversal. In addition to the fling phases, the influx of air into the low-pressure region between the wings from the leading edges also significantly contributed to augmentation of the vertical force. The study conducted for high Reynolds numbers also confirmed that the effect of the clap and fling was insignificant when the minimum distance between the two wings exceeded 1.2c (c = wing chord). Thus, the clap and flings were successfully implemented in the FW-MAV, and there was a significant improvement in the vertical force.
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