Wing-wing interactions in dragonfly flight

10.2417/1200811.1269
Wing-wing interactions in
dragonfly flight
Xinyan Deng and Zheng Hu
A pair of robotic wings have been used to investigate why dragonflies
use different phase angles for different flight modes.
The dragonfly is one of the Earth’s most maneuverable insects
and oldest species. Its flight performance far exceeds other flying insects: it can hover, cruise up to 54km/h, turn 180◦ in three
wing beats, fly sideways, glide, and even fly backwards. Dragonflies intercept prey in the air with amazing speed and accuracy.
To achieve this, most change their wing motion kinematics for
different flight modes such as hovering and turning. The most
noticeable of these changes is the phase difference between foreand hind wings, defined as the phase angle by which hindwing
leads the fore. When hovering, dragonflies employ a 180◦ phase
difference (out of phase),1–3 while 54–100◦ is used for forward
flight.4, 5 When accelerating or performing aggressive maneuvers, there is no phase difference between the two wings (0◦, in
phase).1, 3, 6 Interestingly, among the various flight modes, 270◦
phase difference is rarely observed in dragonflies.
Besides having two pairs of wings for added lift force and maneuvering control, dragonflies employ an inclined stroke plane
in which the wing motion is mostly confined (see Figure 2).
Figure 1. A dragonfly in motion (viewed from right).
Figure 2. Sketches of the wing chord snapshots in hover mode (viewed
from left). Circles indicate the leading edges.
While most flying insects use a horizontal stroke plane, dragonflies’ are approximately 60◦ from the horizontal.1–3 Their wings
act as if ‘paddling’ in the air in the sense that the chord is almost horizontal during downstroke to generate the maximum
upward force and is close to being vertical during upstroke to
reduce the downward force. Therefore, their aerodynamic mechanism is ‘drag base lift generation’ as shown in computational
fluid dynamics (CFD) studies.7 CFD results also showed that
the effect of wing-wing interaction is actually detrimental to lift
force generation in dragonflies.8, 9
To simulate dragonfly motion during hovering and forward
flight (see Figure 3) we constructed a pair of dynamically-scaled
robotic wings. Briefly, we use a pair of bevel-geared robotic
wrists to generate rotational motion in co-axial roll-pitch-yaw
degrees of freedom. The stroke planes of the flappers can be
arbitrarily changed between 0–90◦ and the whole apparatus is
mounted on a linear stage driven by a stepper motor to study
forward motion. Meanwhile, a six-channel force/torque sensor
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Figure 3. Experimental setup schematics (left) and robotic wrists
(right).
Figure 4. Total lift force coefficients results from hovering (A) and forward flight (B). The straight lines in each plot stand for the total lift
force from both wings without wing-wing interaction.
was mounted at the wing base to measure instantaneous aerodynamic forces.
For those interested in the technicalities, the robotic wings are
powered by 16mm, 0.3Nm torque DC brush motors equipped
with magnetic encoders to provide kinematic feedback. These
are driven along kinematic patterns provided by a custom
MATLAB Simulink program with WinCon software that provides commands to the real-time-control and data-acquisition
board communicating with the hardware. We use proportionalintegral-derivative (PID) controllers to run the motors with precision of 0.1◦. Motion commands from the computer are amplified by analog amplifier units that directly control the input current received by the motor.
In the experiments, we employed the real dragonfly (Aeshna
juncea) kinematics from biological data2 and systematically varied kinematic parameters such as the phase differences between
the forewing and hindwings, the forward speed and the distance
between the wing bases. The effect of phase difference in hover
and forward flight is shown in Figure 4.
It is interesting to see an overall detrimental effect to lift force
generation due to wing-wing interactions. Furthermore, when
the phase difference is around 0◦ (in phase), the total lift force
tends to be higher than other cases, and it gets lower around
180◦ in hover mode and 270◦ for forward flight. Our results
proved that in-phase flight generates larger aerodynamic forces
than out-of-phase flight or single wings added together. This explains why dragonflies use in-phase flight for aggressive maneuvers such as turning or accelerating. While out-of-phase motion
is detrimental to force generation, dragonflies use it for hovering stability and vibration suppression. This makes sense, as we
have observed that out-of-phase and in-phase stroking produce
regular and irregular flight respectively.3 The results also help
explain why dragonflies never favor the 270◦ phase difference.
The study not only expands our understanding of biology, but
also gives us an indication of how to build a four-wing micro
air vehicle. Specifically, engineers will need to consider how to
coordinate the motions of the two wing pairs when the requirements are either best aerodynamic effect or best dynamical stability. In the first case energy is conserved to some extent, which
is good for long distance flight. The second case vibration—
which is detrimental to performance in tasks such as inspection
and detection—is reduced. The latter also keeps the aircraft safe
when flying in turbulence.
Eventually we would like to build a dragonfly-like aircraft.
But advanced manufacturing techniques and equipment will be
critical to make such a tiny robot possible. In addition, we will
have to find a better energy source than currently exists: a lightweight but high-power battery is required. As progress is made
in these areas, so we would hope to make progress with our
dragonfly.
Author Information
Xinyan Deng and Zheng Hu
Mechanical Engineering
University of Delaware
Newark, DE
References
1. D. E. Alexander, Unusual phase relationships between the forewings and hindwings in
flying dragonflies, J. Exp. Biol. 109, pp. 379–383, 1984.
2. R. A. Norberg, Hovering flight of the dragonfly: Aeschna juncea L., kinematics and
aerodynamics, Swimming and Flying in Nature 2, pp. 763–780, 1975.
3. G. Rüppell, Kinematic analysis of symmetrical flight manoeuvres of odonata, J Exp
Biol 144, pp. 13–42, 1989.
4. A. Azuma and T. Watanabe, Flight performance of a dragonfly, J. Exp. Biol. 137,
pp. 221–252, 1988.
5. H. Wang, L. Zeng, H. Liu, and C. Yin, Measuring wing kinematics, flight trajectory
and body attitude during forward flight and turning maneuvers in dragonflies, J. Exp.
Biol. 206, pp. 745–57, 2003.
6. A. L. Thomas, G. K. Taylor, R. B. Srygley, R. L. Nudds, and R. J. Bomphrey,
Dragonfly flight: free-flight and tethered flow visualizations reveal a diverse array of
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10.2417/1200811.1269 Page 3/3
unsteady lift-generating mechanisms, controlled primarily via angle of attack, J. Exp.
Biol. 207, pp. 4299–323, 2004.
7. Z. J. Wang, The role of drag in insect hovering, J. Exp. Biol. 207, pp. 4147–55, 2004.
8. H. Huang and M. Sun, Dragonfly forewing-hindwing interaction at various flight
speeds and wing phasing, AIAA J. 45, pp. 508–511, 2007.
9. Z. J. Wang and D. Russell, Effect of forewing and hindwing interactions on aerodynamic forces and power in hovering dragonfly flight, Phys. Rev. Lett. 99, 2007.
c 2008 Institute of Neuromorphic Engineering