The presence of the FW induces an additional inflow into the LEV which is favourable in this case. Body motion during backward flight. (Online version in colour.). Time history of forces (Fv, vertical force; FH, horizontal force; W, weight = 1.275 mN) and muscle-mass-specific power consumption. )Download figureOpen in new tabDownload powerPoint, Figure 1. The λ2-criterion is based on the observation that a pressure minimum as a detection criterion is insufficient for locating vortex cores. Dragonfly, any of a group of roughly 3,000 species of aerial predatory insects most commonly found near freshwater throughout most of the world. Taking into account the body motion, we found that αgeom was significantly reduced. I love dragonflies and after loosing my father I was at a friends place a couple hours after I was told he had passed… I had a huge dragonfly hanging around where i was sitting that morning, a few months latter in the early hours (1.30am) at a new years party i had another appear and … (g) Stroke plane reorientation (blue shading) due to change in body angle from forward to backward flight. Dragonfly wings are highly corrugated, which increases the stiffness and strength of the wing significantly, and results in a lightweight structure with good aerodynamic performance. A.T.B.-O. We define the parasite drag (pressure drag + viscous drag on the body) coefficient as , where is the mean horizontal force and the average translation velocity of the body and Sfrontal the frontal area presented to the flow. In these flight modes, the DS is conventionally regarded as vertical force producing and the US, thrust (horizontal force) producing [11,31,50]. Likewise, Mukundarajan et al. In this study, we use a mechanical model ‘hovering’ dragonfly to revisit the efficiency implications of phase on hovering with flapping, tandem wings. Der Platz ist typbedingt knapper als auf einem gleichlangen Mono. This βb is slightly less than the stroke plane angle measured in forward flight (relative to the longitudinal axis), which is about 50–60° [37,49]. In figure 7, we present the evolution of the wake structures during the second stroke based on the HW timing. Willmott et al. Hence, the LEV circulation should be much smaller than that measured in the DS. During the DS, horizontal forces for the FW are attenuated by 5.5%. The phasing of the FW and HW may help reduce oscillations in the body posture during flight [31]. WWI. Bomphrey et al. In the present work, our goal is to investigate the kinematics and aerodynamics of a dragonfly in backward flight. Also, the backward velocity of the body in the upright position enhances the wings' net velocity in the US. Current literature, summarized in table 6, indicates that, during forward flight, the DS generates 80% of the total force created by cicadas [39], 80% for dragonflies [49], 75–84% for damselflies [6] and 80% of body weight in hawkmoths [66]. The body kinematics are documented in figure 3. Table 2.Forces from three different grids set-up. )Download figureOpen in new tabDownload powerPoint, Figure 12. The reconstruction process captured both the kinematics and deformations. (d) Montage of 3D model of dragonfly used in CFD simulation. )Download figureOpen in new tabDownload powerPoint, Figure 3. represents the time half stroke averaged values. The veins and membranes have a complex design within the wing that give rise to whole-wing characteristics which result in dragonflies being supremely versatile, maneuverable fliers. Previous insect flight studies have measured the AoA at locations between the leading edge and quarter-chord or near the rotation axis of the wing [19,41]. III. The average Euler angles are shown. These changes influence both (i) the production and (ii) orientation and reorientation of aerodynamic forces, consequently determining the type of free flight manoeuvre that is performed. I went out to go see them and when I looked up there were six large mature dragonflies flying over the house right where yogi my dog was lying at that time. A–D represent snapshots where the flow field is evaluated in figure 10. Abstract. Hence, unsteady straining and viscous effect need to be eliminated to identify a vortex core properly. We came back out a little later and a black and white dragonfly showed up and was flying around us. Examples of such manoeuvres include well-studied modes like hovering, forward and turning flight [1–6], which have improved our understanding of flight mechanics and for engineers especially, fostered the design of micro-aerial vehicles (MAVs) [7–9]. We used an in-house immersed boundary method flow solver for simulating incompressible flows in this study. The HW led the FW typical of dragonfly flight [49,50]. We report the AoAs at four spanwise locations approximately 0.25, 0.5, 0.75 and 0.9R, where R is the distance from the wing root to tip (figure 4). (Online version in colour.). There was a preparatory stage (t = −20 ms to 0 s). In figure 10, the vortical structures are projected on a 2D slice cut at mid-span, similar to figure 9a. Unlike most other insects, such as flies, wasps, and cicadas, that have either reduced hindwings or functionally combined forewings and hindwings as a single pair, dragonflies have maintained two pairs of wings throughout their evolution [1]. In addition to body motion, we observed some tail movement typical of dragonfly flight. This mechanism can be generalized to nearly all flapping insects, ... Desiccation is mechanically disastrous to dragonfly wings as well as to other flying insects. The loop creates a downward jet which boosts vertical force production. Lehmann [58] reported that an HW leading by 90° could achieve the same mean lift as an isolated wing due to wake capture. The mechanical properties of dragonfly wings need to be understood in order to perform simulated models. (Online version in colour.). ), Figure 11. As the wings separate from each other during the excursion, the initial increase in HW LEV circulation is maintained in addition to the new vorticity influx formed as the LEV grows during translation (figure 10b–d). animation is a simulation of a wing flapping mechanism. (Online version in colour. ϕ, θ and ψ are the flap, deviation and pitch angles. The blood circulation is essential for the maintenance of reasonable water content in wings. There was around 10 flying around that we could find. If the address matches an existing account you will receive an email with instructions to reset your password. We also tracked the velocity of the leading edge at the spanwise locations where we calculated the angles of attack (see electronic supplementary material). Force vectors in mid-sagittal plane. Our study shows that dragonflies can use backward flight as an alternative to forward flight voluntarily. This figure shows the mechanism of vorticity transfer from the fore to HW during backward flight. The reason for LEV absence during the US was attributed to very low angles of attack as the wing slices through the air, hence, no flow separation. ϕ, θ and ψ are the flap, deviation and pitch angles. Figure 5. The angle between the force vector and longitudinal axis is obtained from the dot product of the force vector and a unit vector parallel to the longitudinal axis. The body of a dragonfly looks like a helical structure wrapped with metal. Also, both the FW and HW have LEVs on them. Dragonfly species are characterized by long bodies with two narrow pairs of intricately veined, membranous wings that, … All authors contributed to the final paper. Wing kinematics and twist. Red and green force vectors represent and , respectively. The wings flapped at high angles of attack while deforming considerably. Mechanism of WWI. This time instant (t = 0 s) is the start of the flight. Table 1.Morphological parameters for the dragonfly in this study. Two-dimensional (2D) cross-sections show that the angle between the chord line of the least deformed wing (dashed line) and deformed wing (solid line with red tip) is the twist angle. Considering that mature males exhibit territorial behavior under the scorching sun and the reduced pigments show antioxidant abilities (Futahashi et al. For force production, a strong LEV was present on both wing pairs. (Online version in colour. In the US, the LEV formed covers the entirety of the wing surface (figures 7e,f and 8b,d). [1] also arrived at a similar conclusion with smoke visualizations on dragonflies in tethered and free forward light. Grey shading indicates the FW DS. )Download figureOpen in new tabDownload powerPoint, Figure 6. )Download figureOpen in new tabDownload powerPointFigure 11. At the onset of flight, the dragonfly rested on a platform posing at an initial body angle of approximately 87°. Using this strategy, body rotation is used to redirect the flight forces, especially if the forces are directionally constrained within the animal's body frame [33,36]. The morphological parameters of the selected dragonfly are shown in table 1, and the flight video can be found in the electronic supplementary material. A.T.B.-O. We captured dragonflies (Erythemis simplicicollis) from the wild and transported them to the laboratory for motion capture. The upright body posture was used to reorient the stroke plane and the flight force in the global frame; a mechanism known as ‘force vectoring’ which was previously observed in manoeuvres of other flying animals. Most of the tilt is accomplished through fuselage rotation because the tilt of the tip-path is limited by the range of motion of the swash plates. The US is often ‘aerodynamically inactive’ as a result [20]. Concurrently, another vortex forms on the upper surface of the wing during reversal because of the rapid increase in AoA during wing rotation (figure 7d). A least-squares reference plane (LSRP) is generated based on the nodes on the reconstructed wing surface to quantify wing twist (see [40]). Solid and dashed arrows show resultant force and its components, respectively. More precisely, we aim to identify the role that force vectoring plays in the execution of a backward flight manoeuvre. However, obvious body translation did not occur until the successive DS during which the wing generated enough propulsive force. Similarly, a tilt of the stroke plane has been reported to precede changes in the flight direction of insects [32]. χ is the body angle. produce larger forces during the DS due to the higher relative wing velocity and the AoA in comparison to the US [31,32]. We compared three simulation cases: (i) with all four wings (ALL; shown in figures 8 and 9), (ii) the FW only (FO), and (iii) HW only (HO), to elucidate WWI during flight (table 4). Insects first flew in the Carboniferous, some 350 million years ago. (Online version in colour. Ueff is the vector sum of the wing (Uflap) and body (Ub) velocity. All the DS-to-US LEV circulation ratios are less than unity (table 3). Force asymmetry: DS versus US. The peak vertical and horizontal forces during the flight are about 9 and 5.5 times the body weight, respectively. Experimental details. In addition to redirecting the force, we found that the force magnitude is significantly increased in the US (when compared with forward flight). During this time he worked on developing a flying robot that employed the principles of the dragonfly's mechanisms of flight. The bottom row (d–f) represents snapshots during HW US at t/T = 0.52, 0.70 and 0.87, respectively. Wing kinematics and twist. Grey shading denotes the DS phase. Since the flight forces are a strong function of wing kinematics, generated flight forces vary drastically during flight because the kinematics of the upstroke (US) and downstroke (DS) can be utterly different [3,20,31]. They can hover, cruise up to 54km/h, turn 180° in three wing beats, fly sideways, glide, and even fly backwards (Alexander, 1984; Appleton, 1974; Whitehouse, 1941). L, body length; R, wing length from root to tip, , mean chord length. Flow features at maximum force production during second stroke for each wing pair. Force generation and muscle-specific power consumption. represents the maximum circulation per half stroke. Unter Deck zeigt sich der neueste Dragonfly angnehem hell und zeitgemäß. We selected one flight sequence and reconstructed the video in Autodesk Maya (Autodesk Inc.). Dragonfly is one of the most maneuverable insects and one of the oldest flying species on earth. This table reports the contribution of each half stroke to the total aerodynamic force during a flapping cycle in different flight modes of insects. Our χ corroborated previous observation in dragonfly backward flight (100°) [11]. Both wing pairs swept through a stroke plane (βb) that maintained an orientation of 35 ± 4° measured relative to the straight line that connects the head to the tail in the absence of body deformation (body longitudinal axis, figure 3e). The mass and length measurement uncertainties are ±1 mg and ±1 mm, respectively. Comparing the CD measured from our simulation (Reynolds number based on body length, Reb ∼ 3860) with results for forward flight of dragonflies of similar Reb approximately 2460–7790 in the literature, the results were comparable indicating that an upright body posture did not substantially influence body drag production. The average muscle-mass-specific power consumed by the dragonfly was 146 W kg−1 (FW: 54 W kg−1; HW: 92 W kg−1). I. Gliding flight and steady-state aerodynamic forces, Three-dimensional flow and lift characteristics of a hovering ruby-throated hummingbird, Lift production in the hovering hummingbird,, doi:10.1146/annurev.fluid.36.050802.121940, The reverse flight of a monarch butterfly (Danaus plexippus) is characterized by a weight-supporting upstroke and postural changes. Alterations in kinematics and aerodynamic features which are different from hovering and forward flight characterize backward flight of dragonflies. The wings of dragonflies are mainly composed of veins and membranes, a typical nanocomposite material. This was in the same range (76–156 and 160 W kg−1) measured by Wakeling & Ellington [52] and Azuma et al. The geometric (dashed lines) and effective angles of attack (solid lines) and twist angles at four spanwise location are reported. In this study, we investigated the backward free flight of a dragonfly, accelerating in a flight path inclined to the horizontal. A vorticity threshold was set to capture the vortex. The effective AoA (αeff) here is the angle between the chord and the vector sum of the body and wing velocity measured at the leading edge. Previous studies have indicated that the FW experience in-wash due to the HW and the HW are affected by the downwash from the FW with benefits being dependent on the phase difference between wing pairs [31,54–57]. The research objectives are then presented along with the research contributions. The dragonfly's fore and hindwings typically counterstroke, or beat out of phase. (c) LEV circulation during the second and third stroke. The forces and muscle-mass-specific power consumption are displayed in figure 5. Structural Analysis of a Dragonfly Wing S.R. Kinematics definitions. For most of the stroke (figure 7), the LEV grows in size and strength while being stably attached. Compared to hovering [61], βh in backward flight was about 15° less. Velocities, accelerations and kinematics of flapping flight, Surface tension dominates insect flight on fluid interfaces, Computational investigation of cicada aerodynamics in forward flight, 3D reconstruction and analysis of wing deformation in free-flying dragonflies, Scaling law and enhancement of lift generation of an insect-size hovering flexible wing, State-space representation of the unsteady aerodynamics of flapping flight, Vortex dynamics and new lift enhancement mechanism of wing–body interaction in insect forward flight, A versatile sharp interface immersed boundary method for incompressible flows with complex boundaries, Wing kinematics measurement and aerodynamics of a dragonfly in turning flight, Three-dimensional flow structures and evolution of the leading-edge vortices on a flapping wing, Study of lift enhancing mechanisms via comparison of two distinct flapping patterns in the dragonfly, Dragonfly flight. The average Euler angles are shown. Their flight performance far exceeds other insects. Although the magnitude of both US and DS forces change from cycle to cycle, and were produced in a somewhat uniform direction with respect to the longitudinal axis of the body. (Online version in colour.). (c) Snapshots of the dragonfly in backward flight. Patterns of blood circulation in the veins of a dragonfly forewing. (Online version in colour.). (Online version in colour.). This video is unavailable. The mechanism of WWI was also illustrated (figures 10 and 11). These backward sequences included turning and straight backward flight, very short backward flight after take-off and backward flight of individuals with impaired wings. Here, we demonstrate with a mechanical model dragonfly that, despite presenting no advantage in terms of lift, flying with two pairs of wings can be highly effective at improving aerodynamic efficiency. Validations of the flow solver are in the works of Wan et al. The flight forces were computed by the integration of the wing surface pressure and shear stress. Gilles Martin, a nature photographer, has done a two-year study examining dragonflies, and he also concluded that these creatures have an extremely complex flight mechanism. Computational set-up. An LEV forms as the wings translate during the DS. Relative to the large number of works on its flight aerodynamics, few researchers have focused on the insect wing structure and its mechanical properties. High-resolution uniform grids surround the insect in a volume of with a spacing of about with stretching grids extending from the fine region to the outer boundaries. (Online version in colour. Currently, the variation of forces on a half-stroke basis and the roles of the US and DS in force generation during backward flight are less understood. The tail motion trailed the body's by about half a wingbeat, although the profile of the time histories was similar. In turning, the dragonfly has high maneuverability due to the four wings' ability to flap independently. 2. Subscripts 1, 2 denote vortices created by flapping strokes 1 and 2. Nevertheless, in the global frame, the stroke plane in backward flight is almost perpendicular to that in forward flight due to the change in the body angle in backward flight (figure 3g). Corresponding to these large forces was the presence of a strong leading edge vortex (LEV) at the onset of US which remained attached up until wing reversal. Although just qualitatively characterized in the literature, it has been documented that insects use backward flight for predator evasion, prey capture, flight initiation, station keeping and load lifting [10–15]. Enter your email address below and we will send you your username, If the address matches an existing account you will receive an email with instructions to retrieve your username. (a) FW DS t/T = 0.35, (b) FW US t/T = 0.82, (c) HW DS t/T = 0.25, (d) HW US t/T = 0.70. (c,d) Measured flight forces. Figure 10. 2–40°) [31,37,49]. (Online version in colour. Furthermore, we will identify other aerodynamic mechanisms related to backward flight, if any, and quantify their contributions with regard to this unique flight mode. The problems in dragonfly mechanism are identified and explained. Because force production is proportional to wing velocity squared, insects adjust wing speed by altering the stroke amplitude and/or frequency [5,11,17]. ), it is known that a wing with an LEV imparts greater momentum to the fluid, leading to the production of larger forces than under steady-state conditions [26–29]. (Online version in colour. Here, we compare our findings; kinematics, aerodynamics and flow features, with hovering and forward flights which have been documented in the literature.