From Studying Real Hummingbirds to Designing Hummingbird-Like Robots—A Literature Review <s> B. MORPHOLOGY INTRODUCTION OF BIRD AND FLYER ROBOTICS INSPIRED BY THE BIRDS <s> To investigate how birds that differ in morphology change their wing and body movements while flying at a range of speeds, we analyzed high-speed (60 Hz) video tapes of black-billed magpies (Pica pica) flying at speeds of 4-14 m s-1 and pigeons (Columba livia) flying at 6-20 m s-1 in a wind-tunnel. Pigeons had higher wing loading and higher-aspect-ratio wings compared with magpies. Both species alternated phases of steady-speed flight with phases of acceleration and deceleration, particularly at intermediate flight speeds. The birds modulated their wingbeat kinematics among these phases and frequently exhibited non-flapping phases while decelerating. Such modulation in kinematics during forward flight is typical of magpies but not of pigeons in the wild. The behavior of the pigeons may have been a response to the reduced power costs for flight in the closed wind-tunnel relative to those for free flight at similar speeds. During steady-speed flight, wingbeat frequency did not change appreciably with increasing flight speed. Body angle relative to the horizontal, the stroke-plane angles of the wingtip and wrist relative to the horizontal and the angle describing tail spread at mid-downstroke all decreased with increasing flight speed, thereby illustrating a shift in the dominant function of wing flapping from weight support at slow speeds to positive thrust at fast speeds. Using wingbeat kinematics to infer lift production, it appeared that magpies used a vortex-ring gait during steady-speed flight at all speeds whereas pigeons used a vortex-ring gait at 6 and 8 m s-1, a transitional vortex-ring gait at 10 m s-1, and a continuous-vortex gait at faster speeds. Both species used a vortex-ring gait for acceleration and a continuous-vortex gait or a non-flapping phase for deceleration during flight at intermediate wind-tunnel speeds. Pigeons progressively flexed their wings during glides as flight speed increased but never performed bounds. Wingspan during glides in magpies did not vary with flight speed, but the percentage of bounds among non-flapping intervals increased with speed from 10 to 14 m s-1. The use of non-flapping wing postures seemed to be related to the gaits used during flapping and to the aspect ratio of the wings. We develop an 'adverse-scaling' hypothesis in which it is proposed that the ability to reduce metabolic and mechanical power output using flap-bounding flight at fast flight speeds is scaled negatively with body mass. This represents an alternative to the 'fixed-gear' hypothesis previously suggested by other authors to explain the use of intermittent flight in birds. Future comparative studies in the field would be worthwhile, especially if instantaneous flight speeds and within-wingbeat kinematics were documented; new studies in the laboratory should involve simultaneous recording of wing kinematics and aerodynamic forces on the wing. <s> BIB001 </s> From Studying Real Hummingbirds to Designing Hummingbird-Like Robots—A Literature Review <s> B. MORPHOLOGY INTRODUCTION OF BIRD AND FLYER ROBOTICS INSPIRED BY THE BIRDS <s> Aerodynamic theory predicts that the power required for an animal to fly over a range of speeds is represented by a ‘U’-shaped curve, with the greatest power required at the slowest and fastest speeds, and minimum power at an intermediate speed1,2,3,4,5,6. Tests of these predictions, based on oxygen consumption measurements of metabolic power in birds7,8,9,10,11,12 and insects13, support a different interpretation, generating either flat or ‘J’-shaped power profiles, implying little additional demand between hovering and intermediate flight speeds14. However, respirometric techniques represent only an indirect assessment of the mechanical power requirements of flight and no previous avian study has investigated an animal's full range of attainable level flight speeds. Here we present data from in vivo bone-strain measurements of pectoralis muscle force coupled with wing kinematics in black-billed magpies (Pica pica ), which we use to calculate mechanical power directly. As these birds flew over their full range of speeds, we offer a complete profile of mechanical power output during level flapping flight for this species. Values of mechanical power output are statistically indistinguishable (that is, the power curve is flat) over most forward-flight speeds but are significantly higher during hovering and flight at very low speeds. <s> BIB002 </s> From Studying Real Hummingbirds to Designing Hummingbird-Like Robots—A Literature Review <s> B. MORPHOLOGY INTRODUCTION OF BIRD AND FLYER ROBOTICS INSPIRED BY THE BIRDS <s> By combining appearance and behavior in animals with physical laws, we can get an understanding of the adaptation and evolution of various structures and forms. Comparisons can be made between animal bodies and various technical constructions. Technical science and theory during the latest decades have resulted in considerable insight into biological adaptations, but studies on structures, forms, organs, systems, and processes in the living world, used in the right way, have also aided the engineer in finding wider and better solutions to various problems, among them in the design of micro-air vehicles (MAVs). In this review, I discuss the basis for flight and give some examples of where flight engineering and nature have evolved similar solutions. In most cases technology has produced more advanced structures, but sometimes animals are superior. I include how different animals have solved the problem of producing lift, how animal wings meet the requirements of strength and rigidity, how wing forms are adapted to various flight modes, and how flight kinematics are related to flight behavior and speed. The dynamics of vorticity is summarized. There are a variety of methods for the determination of flight power; it has been estimated adequately by lifting-line theory, by physiological measurements, and from mass loss and food intake. In recent years alternative methods have been used, in which the mechanical power for flight is estimated from flight muscle force used during the downstroke. Refinements of these methods may create new ways of estimating flight power more accurately. MAVs operate at the same Reynolds numbers as large insects and small birds and bats. Therefore, studies on animal flight are valuable for MAV design, which is discussed here. J. Morphol. 252:52–81, 2002. © 2002 Wiley-Liss, Inc. <s> BIB003 </s> From Studying Real Hummingbirds to Designing Hummingbird-Like Robots—A Literature Review <s> B. MORPHOLOGY INTRODUCTION OF BIRD AND FLYER ROBOTICS INSPIRED BY THE BIRDS <s> Staying aloft when hovering and flying slowly is demanding. According to quasi-steady-state aerodynamic theory, slow-flying vertebrates should not be able to generate enough lift to remain aloft. Therefore, unsteady aerodynamic mechanisms to enhance lift production have been proposed. Using digital particle image velocimetry, we showed that a small nectar-feeding bat is able to increase lift by as much as 40% using attached leading-edge vortices (LEVs) during slow forward flight, resulting in a maximum lift coefficient of 4.8. The airflow passing over the LEV reattaches behind the LEV smoothly to the wing, despite the exceptionally large local angles of attack and wing camber. Our results show that the use of unsteady aerodynamic mechanisms in flapping flight is not limited to insects but is also used by larger and heavier animals. <s> BIB004 </s> From Studying Real Hummingbirds to Designing Hummingbird-Like Robots—A Literature Review <s> B. MORPHOLOGY INTRODUCTION OF BIRD AND FLYER ROBOTICS INSPIRED BY THE BIRDS <s> Hummingbirds are very distinctive in their form and behavior, the evolution of which is tightly connected to the evolution of their primary source of energy - floral nectar. About forty million years ago, the practical use of this dense fuel, available only in widely-dispersed, insect-sized aliquots - it was originally intended for insect pollinators - presented a severe test to the avian bauplan. This selective pressure forced broad changes in form and function, affecting anatomical structures ranging from the feeding apparatus to the locomotor system. We describe here how these pressures shaped a bird that flies like a bird into one that flies like a fly. <s> BIB005 </s> From Studying Real Hummingbirds to Designing Hummingbird-Like Robots—A Literature Review <s> B. MORPHOLOGY INTRODUCTION OF BIRD AND FLYER ROBOTICS INSPIRED BY THE BIRDS <s> Micro Air Vehicles (MAVs) with flapping wings try to mimic their biological counterparts, insects and hummingbirds, as they can combine high agility manoeuvres with precision hovering flight. Near-hovering flapping flight is naturally unstable and needs to be stabilized actively. We present a novel mechanism for pitch moment generation in a robotic hummingbird that uses wing twist modulation via flexible wing root bars. A custom build force balance, sensitive enough to measure the cycle averaged pitch moment as well as lift force, is also presented. The introduced prototype mechanism generates pitch moment of up to ± 0.5 mNm. Finally we integrate a Shape Memory Alloy (SMA) wire to actuate the wing root bar ends. We present achievable displacement versus bandwidth as well as generated pitch moment. <s> BIB006 </s> From Studying Real Hummingbirds to Designing Hummingbird-Like Robots—A Literature Review <s> B. MORPHOLOGY INTRODUCTION OF BIRD AND FLYER ROBOTICS INSPIRED BY THE BIRDS <s> Flying animals with flapping wings may best exemplify the astonishing ability of natural selection on design optimization by excelling both stability and maneuverability at insect/hummingbird scale. Flapping Wing Micro Air Vehicle (FWMAV) holds great promise in bridging the performance gap between engineering system and their natural counterparts. Designing and constructing such a system is a challenging problem under stringent size, weight and power (SWaP) constraints. In this work, we presented a systematic approach for design optimization and integration for a hummingbird inspired FWMAV. Our formulation covers aspects of actuation, dynamics, flight stability and control, which was validated by experimental data for both rigid and flexible wings, ranging from low to high wing loading. The optimization yields prototypes with onboard sensors, electronics, and computation units. The prototype flaps at 30Hz to 40Hz, with 7.5 to 12 grams of system weight and 12 to 20 grams of maximum lift. Liftoff was demonstrated with added payloads. Flapping wing platforms with different requirements and scales can now be designed and optimized with minor modifications of proposed formulation. <s> BIB007
In terms of birds, they have endoskeletons. The muscles attached to bones along the wing are applied for flight and maneuvering. Therefore, birds and flying insects have distinct flight mode. The birds with larger wings and weight spend the most time in forwarding flight with a low flapping frequency such as gliding, soaring. By contrast, hummingbirds can perform hovering flight with a high flapping frequency similar to the flight patterns of insect, thanks to the special morphological construction of hummingbird. For instance, the hummingbird's forearm bone and the upper arm are significantly shorter than that of a pigeon BIB005 . Although the birds' flight modes are different, the wing motion of all birds composes of upstroke and downstroke. The birds, excluding hummingbirds, flap their wings to balance the weight, and the circulations of strokes posed to generate the lift during the downstroke, whereas the drag is produced during the upstroke. Hummingbirds, however, generate aerodynamic lift in both upstroke and downstroke. Hovering flight can be mostly discovered in flying insects and hummingbirds. Certain bats BIB004 and birds BIB001 are also able to fly in hovering, but they only use it in transitions (taking-off, landing and perching) since hovering requires more than twice the energy necessary for cruising BIB002 and more anaerobic metabolism. In nature, there are two categories of hovering. Certain birds generate the most of lift during the downstroke when fully extending wings, and reduce drag by flexing their wings in the upstroke. Such kind of hovering is called asymmetric hovering BIB003 or avian stroke  , shown in Fig. 2 (a) . However, for the hummingbirds and insect, their wings remain fully extended throughout the wingbeat except for rotating and twisting at the end of each half stroke, which is called symmetric hovering or insect stroke, seen in Fig. 2 (b) . In symmetric hovering condition, the body axis is inclined at a desirable angle and the wing presents an eight-like pattern in a vertical plane when hovering and an oval pattern is employed in most situations in forward and backward flight [37] ,  , shown in Fig. 2 (c) . Due to the flight behaviors of hummingbirds, certain hummingbird-like FWMADs such as Nanohummingbird  , Micro-hummingbird  , BIB007 and Gianthummingbird  , BIB006 were developed. However, there are still great challenges when designing FWMADs such as weight distribution of different components, energy-costing, wing design and tail's function. Therefore, the study of hummingbirds' morphologies is quite necessary and useful. This will not only help to understand the muscle kinematics in flight, skeleton structure and their aerodynamic mechanism, but also benefit from inspired FWMADs' development. In this paper, a review of the morphology of the hummingbird in hovering flight is studied including muscle, construction of skeleton, aerodynamic in hovering, wing performance and tail performance. The comparison of motor mass and muscles mass of hummingbird are studied. The weight distributions of main components of FWMADs are also given. The designed wing inspired by the hummingbirds is presented based on scaling law. The wing efficiency is verified by a flight test. To explore the function of the tail, the inspired tail is introduced simply.