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Background:
Background:
A unique feature of phylum Odonta is the direct flight mechanism; each wing operates independently with flight musculature attached directly to the wing bases, enabling powerful, controlled, unrivaled flight. This mechanism gives dragonflies the capability for fast forward flight, hovering, and backward flight.
Recent Study:
Recent Study:
A dragonfly’s hindwing has the greatest effect on its aerodynamics, motivating scientists to analyze the flapping motion of the hindwing. A kinematic analysis of species Sympetrum flaveolum revealed key insights about dragonfly wing motion.
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The scientists began by recording tethered dragonfly flight using high-speed videography at 6000 fps. The wing position was traced using the nodus, the pterostigma and a trailing edge point of the wing as markers (see Figure 1). They were able to capture one complete flapping cycle with around 150 frames. Due to the high frame rate, the changes in the wing position from one frame to another were minimal, so that the error of reconstructing the wing positions was less than 1 degree.
Figure 1. The image of the dragonfly hindwing with critical tracking points O, N, P and T, where O is at the wing root, N is at the nodus, P is at the middle of the pterostigma and T is at the intersection of the anterior median vein and the trailing edge of the hindwing (Chen et. al, 2013).
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Figure 2. (a) Simple figure-eight (S8) flapping trajectory. (b) Double figure- eight (D8) flapping trajectory (Chen et. al, 2013).
The flapping pattern of the dragonfly hindwing at the nodus and the pterostigma was shown to be either a simple figure-eight (S8) or a double figure-eight (D8) (Fig. 2) (Chen et. al, 2013). The characteristic feature differentiating the two different trajectories is the cross-over of the flapping path at stroke reversals. There is only one cross-over for the simple figure-eight trajectory, while there are two cross-overs for the double figure-eight trajectory.
The scientists found no fixed rules for the switching between different flapping patterns; however, one possible interpretation is that the dragonfly uses different flapping patterns to achieve different aerodynamic effects. This still needs to be explored.
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Future Applications:
Future Applications:
The kinematic model for each flapping pattern (S8 and D8) can be used in computational simulations of dragonfly flight. These simulations can help to develop robotic micro-air-vehicles (MAV’s) with flight capabilities like dragonflies. MAV’s offer a wide range of applications such as military scouting and search and rescue. Thus, detailed studies of dragonfly wing kinematics are critical and necessary in understanding the advanced aerodynamics of dragonfly flight.
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It was recorded that both the ONP wing angle and OP wing distance vary with each flapping cycle, implying that the leading wing edge is not one ridged piece (Chen et. al, 2013). The scientists believe the wing consists of two pieces hinged at the nodus (N) with a 40 degree freedom of rotation. As shown in Figure 3, the leading edge of the hindwing bends most forward and starts rotating at the start of pronation; the pleated wing surface is stretched and flattened most at this point. The scientists believe bending the leading edge forward and flattening the wing makes wing rotation easier during pronation.
Fig. 3. Changes of angle ONP (black line) and distance OP (grey line) with respect to three flapping cycles (Chen et. al, 2013).
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References:
Chen, Y.H., Stoke, M., Zhao, Y., Huang, W.M. (2013). Dragonfly (Sympetrum flaveolum) flight: Kinematic measurement and modelling. Journal of Fluids and Structures, 40,
115-126.
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