From Studying Real Hummingbirds to Designing Hummingbird-Like Robots—A Literature Review <s> I. INTRODUCTION <s> It is the objective of this paper to review recent developments in the understanding and prediction of flapping-wing aerodynamics. To this end, several flapping-wing configurations are considered. First, the problem of single flapping wings is treated with special emphasis on the dependence of thrust, lift, and propulsive efficiency on flapping mode, amplitude, frequency, and wing shape. Second, the problem of hovering flight is studied for single flapping wings. Third, the aerodynamic phenomena and benefits produced by the flapping-wing interactions on tandem wings or biplane configurations are discussed. Such interactions occur on dragonflies or on a recently developed micro air vehicle. The currently available two- and three-dimensional inviscid and viscous flapping-wing flow solutions are presented. It is shown that the results are strongly dependent on flapping frequency, amplitude, and Reynolds number. These findings are substantiated by comparison with the available experimental data. <s> BIB001 </s> From Studying Real Hummingbirds to Designing Hummingbird-Like Robots—A Literature Review <s> I. INTRODUCTION <s> The purpose of this paper is to provide a review of recent developments in Flapping-wing Micro Air Vehicles (FMAV) in Asia in past few years. The paper discusses recent Asian research in the development of FMAV and summarizes two major strands of research divided by insect-like FMAVs and bird-like FMAVs. Also the paper summarizes the developing status of FMAV and proposes the future research focus, development trends and application prospects. <s> BIB002 </s> From Studying Real Hummingbirds to Designing Hummingbird-Like Robots—A Literature Review <s> I. INTRODUCTION <s> We are witnessing the advent of a new era of robots - drones - that can autonomously fly in natural and man-made environments. These robots, often associated with defence applications, could have a major impact on civilian tasks, including transportation, communication, agriculture, disaster mitigation and environment preservation. Autonomous flight in confined spaces presents great scientific and technical challenges owing to the energetic cost of staying airborne and to the perceptual intelligence required to negotiate complex environments. We identify scientific and technological advances that are expected to translate, within appropriate regulatory frameworks, into pervasive use of autonomous drones for civilian applications. <s> BIB003 </s> From Studying Real Hummingbirds to Designing Hummingbird-Like Robots—A Literature Review <s> I. INTRODUCTION <s> Flapping rotary wing, rotating wing, and flapping wing are feasible wing layouts applicable to micro-air-vehicles capable of hovering flight. A numerical study in this paper presents which wing layout can be more efficient in terms of aerodynamic power for the given kinematic and geometric parameters with or without the constraint of vertical force. In the cases under typical conditions, rotating wing layout is the most efficient one when a small vertical force is needed. However, if a much larger vertical force is required, flapping rotary wing is the only wing layout that fulfills the requirements of the two aspects due to its coupling effect. At relatively high Reynolds number (Re>2000), flapping amplitude (>70°), and aspect ratio (=6), comparative relationships from the cases under typical conditions among three wing layouts in terms of vertical force and aerodynamic power efficiency are kept unchanged. Nevertheless, at relatively low Re(<500)), flapping amplitude (<40°), or aspect ratio (=3), horizon... <s> BIB004 </s> From Studying Real Hummingbirds to Designing Hummingbird-Like Robots—A Literature Review <s> I. INTRODUCTION <s> In this work, a multi-objective optimization framework is developed for optimizing low Reynolds number ([Formula: see text]) hovering flight. This framework is then applied to compare the efficiency of rigid revolving and flapping wings with rectangular shape under varying [Formula: see text] and Rossby number ([Formula: see text], or aspect ratio). The proposed framework is capable of generating sets of optimal solutions and Pareto fronts for maximizing the lift coefficient and minimizing the power coefficient in dimensionless space, explicitly revealing the trade-off between lift generation and power consumption. The results indicate that revolving wings are more efficient when the required average lift coefficient [Formula: see text] is low (<1 for [Formula: see text] and <1.6 for [Formula: see text]), while flapping wings are more efficient in achieving higher [Formula: see text]. With the dimensionless power loading as the single-objective performance measure to be maximized, rotary flight is more efficient than flapping wings for [Formula: see text] regardless of the amount of energy storage assumed in the flapping wing actuation mechanism, while flapping flight is more efficient for [Formula: see text]. It is observed that wings with low [Formula: see text] perform better when higher [Formula: see text] is needed, whereas higher [Formula: see text] cases are more efficient at [Formula: see text] regions. However, for the selected geometry and [Formula: see text], the efficiency is weakly dependent on [Formula: see text] when the dimensionless power loading is maximized. <s> BIB005 </s> From Studying Real Hummingbirds to Designing Hummingbird-Like Robots—A Literature Review <s> I. INTRODUCTION <s> How does agility evolve? This question is challenging because natural movement has many degrees of freedom and can be influenced by multiple traits. We used computer vision to record thousands of translations, rotations, and turns from more than 200 hummingbirds from 25 species, revealing that distinct performance metrics are correlated and that species diverge in their maneuvering style. Our analysis demonstrates that the enhanced maneuverability of larger species is explained by their proportionately greater muscle capacity and lower wing loading. Fast acceleration maneuvers evolve by recruiting changes in muscle capacity, whereas fast rotations and sharp turns evolve by recruiting changes in wing morphology. Both species and individuals use turns that play to their strengths. These results demonstrate how both skill and biomechanical traits shape maneuvering behavior. <s> BIB006
Hummingbirds are one of the few extensively studied vertebrate species. They fly vocal agile, maneuverable and in particular hovering when feeding at flowers. There are more than 330 species in nature. The smallest one, Bee Hummingbird (Calypte Helenae, from Cuba) is only about 2 grams, whereas the largest one, Giant Hummingbird (Patag-onaGigas, from Chile), is almost 20 grams [1] . Their super agility has attracted much attention and currently inspires the development of FWMADs as they are able to perform tasks in a dangerous or inaccessible environment (Due to their small size and hovering feature, it is better than that of Unmanned Aerial Vehicle). The studies show that the aerodynamic efficiency of flapping wings at relatively low speed may be higher than that of a revolving wing at certain low Reynolds number BIB004 , BIB005 . However, some researchers keep different minds, which have no consensus. Over the The associate editor coordinating the review of this manuscript and approving it for publication was Zhonglai Wang. last decade, researchers have developed FWMADs inspired by natural flyers such as bee, beetle, dragonfly, butterfly, hummingbird etc. However, insects and hummingbirds have completely different morphology construction although they do not have a dissimilar aerodynamic mechanism. At present, some researchers analyzed and summarized the current development of FWMADs. Ward et al.  did the review study of Biomimetic Air Vehicle over the last 30 years (1984 -2014) from the view of aerodynamics, guidance and control, mechanisms, structure and materials, and system design. The flapping wing micro air vehicle (MAV) modelling was reviewed in paper  , which introduces the hover capable flapping wing flight in previous work and looks at existing modeling methods used to research the aerodynamics and overall vehicle behavior of a hypothetical MAV. Then Platzer and Jones BIB001 studied the flapping-wing aerodynamics progress and challenges. The wings of Man-made flyers inspired by the natural flyers were also studied by Rojratsirikul  . Additionally, the development of flapping wing MAV in Asia was studied by Tan et al. BIB002 . And Chen C and VOLUME 7, 2019 This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see http://creativecommons.org/licenses/by/4.0/ Zhang T Y reviewed the design and fabrication of the flapping wing MAV  . Floreano D and Wood J R also provided the future development of small autonomous drones BIB003 . Although maneuvering ability of hummingbird from view of morphology is explained BIB006 , there is no comprehensive summary on hummingbird-like robot from morphology of hummingbird to its robots. Therefore, this paper is useful and meaningful to design and develop hummingbird-like MAV. In the following subsection, the morphology of insects and flyer robotics inspired by the insects are first introduced. Then, the morphology of birds and flyers robotics inspired by the hummingbird is presented.