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Biomimetic Drones Inspired by Dragonflies Will Require a Systems drones Article Biomimetic Drones Inspired by Dragonflies Will Require a Systems Based Approach and Insights from Biology Javaan Chahl 1,2,* , Nasim Chitsaz 1 , Blake McIvor 1 , Titilayo Ogunwa 1 , Jia-Ming Kok 3 , Timothy McIntyre 1 and Ermira Abdullah 4 1 UniSA STEM, University of South Australia, Mawson Lakes, SA 5095, Australia; [email protected] (N.C.); [email protected] (B.M.); [email protected] (T.O.); [email protected] (T.M.) 2 Joint and Operations Analysis Division, Defence Science and Technology Group, Melbourne, VIC 3207, Australia 3 Aerospace Division, Defence Science and Technology Group, Melbourne, VIC 3207, Australia; [email protected] 4 Department of Aerospace Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 Seri Kembangan, Malaysia; [email protected] * Correspondence: [email protected] Abstract: Many drone platforms have matured to become nearly optimal flying machines with only modest improvements in efficiency possible. “Chimera” craft combine fixed wing and rotary wing characteristics while being substantially less efficient than both. The increasing presence of chimeras suggests that their mix of vertical takeoff, hover, and more efficient cruise is invaluable to many end users. We discuss the opportunity for flapping wing drones inspired by large insects to perform these mixed missions. Dragonflies particularly are capable of efficiency in all modes of flight. We will explore the fundamental principles of dragonfly flight to allow for a comparison Citation: Chahl, J.; Chitsaz, N.; between proposed flapping wing technological solutions and a flapping wing organism. We chart one McIvor, B.; Ogunwa, T.; Kok, J.-M.; McIntyre, T.; Abdullah, E. Biomimetic approach to achieving the next step in drone technology through systems theory and an appreciation Drones Inspired by Dragonflies will of how biomimetics can be applied. New findings in dynamics of flapping, practical actuation Require a Systems Based Approach technology, wing design, and flight control are presented and connected. We show that a theoretical and Insights from Biology. Drones understanding of flight systems and an appreciation of the detail of biological implementations may 2021, 5, 24. https://doi.org/10.3390/ be key to achieving an outcome that matches the performance of natural systems. We assert that an drones5020024 optimal flapping wing drone, capable of efficiency in all modes of flight with high performance upon demand, might look somewhat like an abstract dragonfly. Academic Editor: David R. Green Keywords: drone; dragonfly; insect; biomimetic; biological inspiration; aerodynamics; design Received: 1 March 2021 Accepted: 21 March 2021 Published: 27 March 2021 1. Introduction Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in From emergence until death, the flight performance of the dragonfly is tested. Typi- published maps and institutional affil- cally, males establish and fight to maintain a territory with favourable oviposition sites after iations. a short period of orientation following emergence. This involves perpetual, dangerous, aerial combat against male rivals, with only the best aviators achieving the territory needed to breed. Mating requires an aerial pursuit of females that innately stresses the flight perfor- mance of males. Upon successfully overcoming the female’s defences against weak fliers, successful mating often requires the males to carry the female’s inert mass. Throughout Copyright: © 2020 by the authors. Licensee MDPI, Basel, Switzerland. all of this aerial combat, aerial predators are a constant threat, requiring defensive air This article is an open access article combat maneuvers at regular intervals. Most combat is over a water surface, under which distributed under the terms and predators lurk and from which a dragonfly is unlikely to extract itself. Finally, feeding is conditions of the Creative Commons an effort in pursuit and counter-evasion against prey animals, the evolution of which is Attribution (CC BY) license (https:// also locked in a deadly loop with the dragonfly’s evolving flight performance. It is a life of creativecommons.org/licenses/by/ aerial combat, pursued for 300 million years, by the oldest extant form of flying insect, the 4.0/). archetypal member of Palaeoptera [1,2]. Drones 2021, 5, 24. https://doi.org/10.3390/drones5020024 https://www.mdpi.com/journal/drones Drones 2021, 5, 24 2 of 24 It can be argued that dragonflies have made the least accommodation for other practi- calities of existence of any flying insect. Long, unencapsulated, permanently horizontal wings sprout from a heavily muscled thorax, while their large, high-resolution eyes float on a delicate retractable gimbal neck to stabilise sensory input, all optimised for flight and combat. Dragonflies are so highly adapted to flight that their limbs are more suited to aerial grappling than walking; a grounded dragonfly serves no evolutionary purpose and the bloodless wings of adult insects do not heal. Evolution has committed the dragonfly to its aerial life. The single-role lifestyle of adult Odonata is the motivation for our attempt here to understand their critical system level characteristics, so that we can chart a course to a high performance flapping wing drone. Dragonflies have been shown in quantitative studies to demonstrate superior flight performance compared to most other insects. Scale must be considered in this assessment, as the Odonata order contains relatively large species, particularly in terms of wingspan. The nature of aerodynamics ensures that larger species with longer wings have a physics advantage in some aspects of flight. Dragonfly mastery of the air has been shown in a number of studies based on high speed video analysis of normal flight, aerial combat, and predation. High-performance turning flight has been shown, with loads in turns exceeding 40 m/s2 [3] and an ability to takeoff while carrying more than three times their own body weight [4]. Dragonflies have been shown to pursue prey animals using the chasing strategies found in missiles [5] and to have exceptionally high success rates in capturing aerial prey [6,7]. They have been found to exhibit advanced guidance laws that camouflage their apparent motion with respect to their opponent [8,9] using means that have not been convincingly identified. It has been demonstrated that they have a surprisingly efficient glide performance comparable to that of model aircraft with substantially higher Reynolds numbers (Re). Observed lift-to-drag ratios range from 3.5 to over 10 [10–12]. Some species of dragonfly have been observed to migrate across hundreds of kilometres [13], a difficult, energetic achievement for such a small organism. Energy scavenging by dragonflies has also been observed: they soar on thermal updrafts and on rising air currents caused by slopes [14]. The evolutionary argument and the measured realities of dragonfly mastery of flight align, indicating that they may be the apex insect flyer. The challenge is to understand the ingredients of this design so that technological systems might be able to achieve some of the same characteristics. 1.1. Biomimetics and Bioinspiration Biomimetics is a broad approach, without a standard methodology. The range of techniques is a spectrum from “inspiration” to “mimicry”. The two extremes on this spectrum have limitations. Inspiration might entail simply looking at the outside of a biological system such as a dragonfly, which might help the engineer to decide what application to create: for example, an insect-styled drone. This allows the imagination to be channeled and certainly is a valid engineering approach, complete with expectations and requirements. However, the solution is the result of engineering and does not create a particular head start for the engineer. Inspiration might even create undue constraints, since the operating principles applied might be quite different than in the organism. Mimicry creates problems of technological incompatibility between the solutions grown by biology and the highly refined mechanisms in common engineering use. Essentially the components required to make a copy often do not exist. For example, conventional technologies for motion are rotational, yet the known rotating motor in nature is a flagellum with parts on a molecular scale [15], while large motive systems are based on muscle. Artificial muscles, on the other hand, remain elusive. The problems of copying solutions becomes even deeper when organs and cellular mechanisms start to be considered, showing clear limitations to the mimicry approach. Srinivasan has advocated an approach that accepts the differences in component technology but ensures that the principles of operation are preserved [16]. In many cases, it is inviolable system characteristics that allow the organism to operate, not details of Drones 2021, 5, 24 3 of 24 implementation. We will assert that this is the case with dragonflies, despite all appearances. This approach requires an understanding of both the class of technological system being created and of the biological system being mimicked. This argument is supported by the failures of early ornithopters. Despite detailed bird anatomy and observations, there was, at first, no understanding of aircraft. Subsequent work identified the role of mass, balance, and wings, allowing a progression from Cayley [17], to Lilienthal [18], and culminating with the Wright Brothers [19]. In the case of flight, it seems that the
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