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Dragonfly Flight

June 28, 2021

Childhood is difficult enough without the misinformation acquired from your child peers. One tall tale I heard as a child was the myth that dragonflies, colloquially called darners, could sew your eyes, ears, and lips shut. Thus myth was promulgated by European parents as a warning to their children that this could happen as they slept as punishment for mischief.[1] Today's parents are not that sinister. The best they can do is an elf-on-the-shelf.

Dragonfly, from archives of Pearson Scott Foresman

Dragonfly, from the archives of publisher, Pearson Scott Foresman.

(Wikimedia Commons image. Click for larger image.)


The darner dragonfly, (Kingdom, Animalia ; Phylum, Arthropoda; Class, Insecta; Order, Odonata; Suborder, Epiprocta; Family, Aeshnidae) looks like something from a nightmare. They have large compound eyes, each composed from 24,000 segments, that are reminiscent of those of the film monster, Mothra.[2] Fossils of dragonfly ancestors with wingspans of about three quarters of a meter are found from the Upper Carboniferous Period, about 325 million years ago. Dragonflies have two pairs of strong, transparent wings and an elongated body of bright iridescent or metallic colors created by structural coloration, as in the iridescent coloration of butterfly wings.

Dragonflies are of interest to developers of micro air vehicles, since they are agile fliers that are capable of sudden changes in direction; in fact, they can move in all six spatial directions, forwards, backwards, left and right, and upwards and downwards. Their wings are capable of effortless gliding, and one dragonfly mode of flight is gliding for a few seconds in between bursts of powered flight. Dragonflies have a high power/weight ratio, they can accelerate at nearly 9 G, have a maximum speed of about 30 miles per hour (50 kilometers per hour), and they cruise at about 10 miles per hour (15 kilometers per hour), moving about a hundred body-lengths per second in forward flight.

A team of researchers from the University of South Australia (Mawson Lakes, Australia), the Defence Science and Technology Group (Melbourne, Australia), and the Universiti Putra Malaysia (Kembangan, Malaysia) has just published an open access paper in the journal, Drones, on biomimetic drones inspired by dragonflies.[3-4] They discuss how flapping wing drones inspired by dragonflies are efficient in agile modes of flight, and they analyzed the fundamental principles of dragonfly flight to apply the principles of flapping wing organisms to flapping wing drones.[3] The conclude that an optimal flapping wing drone, efficient in all flight modes with high performance, would resemble a dragonfly.[3]

The research team of PhD candidates was led by Javaan Chahl, a professor of Sensor Systems at the University of South Australia. The research, which was conducted remotely during the 2020 COVID-19 lockdown, involved the students doing mathematical analysis and digitization of stereo photographs of insect wings into 3D models, as well as Rapid prototyping and testing components for flapping wing drones.[4] Their goal was to match a dragonfly's extraordinary skills in hovering, cruising, and aerobatics.[4] Chahl explains that the dragonfly is an apex insect flier,
"Dragonflies are supremely efficient in all areas of flying. They need to be. After emerging from under water until their death (up to six months), male dragonflies are involved in perpetual, dangerous combat against male rivals. mating requires an aerial pursuit of females and they are constantly avoiding predators. Their flying abilities have evolved over millions of years to ensure they survive... They can turn quickly at high speeds and take off while carrying more than three times their own body weight. They are also one of nature's most effective predators, targeting, chasing and capturing their prey with a 95 per cent success rate."[4]

Wings of different dragonflies

Two wing examples from different dragonfly families. (Javaan Chahl/University of South Australia image. Click for larger image.)


Dragonflies are notoriously difficult to capture in a pristine state; and, since museum specimens are too fragile to be removed from their cases, the research team developed an optical technique to photograph the wing geometry of 75 different dragonfly species through the glass display cases in museum collections.[4] They then modeled both the dragonfly body shape and aerodynamic properties to understand their excellent flying abilities.[3-4] Says Chahl, "Dragonfly wings are long, light and rigid with a high lift-to-drag ratio which gives them superior aerodynamic performance... Their long abdomen, which makes up about 35 per cent of their body weight, has also evolved to serve many purposes... It helps with balance, stability and maneuverability. The abdomen plays a crucial role in their flying ability."[4]

Comparison of aerodynamic lift and drag measurements of corrugated and flat wings and 3D printed drone

Left, a comparison of aerodynamic lift and drag of corrugated and flat wings versus attack angle at a Reynolds number of 22 × 103. A corrugated wing provides substantially better aerodynamic performance than a flat wing. Right, a flapping wing mechanism made using a 3D printer in a student's home laboratory. (Left image, portion of fig. 7 of ref. 3, licensed under a Creative Commons Attribution License. Right, a University of South Australia image.)


The researchers conclude that future flapping wing drones will probably resemble the insect in shape, wings and actuation.[4] They would be useful in the collection and delivery of awkward, unbalanced loads, an they can operate as agents in long surveillance missions.[4]

Dragonfly-inspired drone

A conceptual image of a 20 centimeter wingspan biomimetic dragonfly drone in flight. It was found that large, directly driven, corrugated wings are as efficient as fixed wings on drones with a much larger wingspan.

The abdomen, which contains a fuel cell energy source, also acts as a rudder and ballast.

(Fig. 15 of ref. 3, modified for clarity, licensed under a Creative Commons Attribution License.)


References:

  1. Friday 5: Scary Myths About Dragonflies, dragonflywoman web site, November 2, 2012.
  2. Mothra (1961, Ishirô Honda, Director) on the Internet Movie Database.
  3. Javaan Chahl, Nasim Chitsaz, Blake McIvor, Titilayo Ogunwa, Jia-Ming Kok, Timothy McIntyre, and Ermira Abdullah, "Biomimetic Drones Inspired by Dragonflies Will Require a Systems Based Approach and Insights from Biology, Drones, vol. 5, no. 2 (March 27, 2021), https://doi.org/10.3390/drones5020024. This is an open access publication with a PDF file here.
  4. Future drones likely to resemble 300-million-year-old flying machine, University of South Australia Press Release, April 27, 2021.

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