Structure of the vortex wake in hovering Anna's hummingbirds (<i>Calypte anna</i>)

Wolf, Marta; Ortega-Jimenez, Victor Manuel; Dudley, Robert

doi:10.1098/rspb.2013.2391

Cited by 31 publications

(48 citation statements)

References 23 publications

(57 reference statements)

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“…Because the body does not generate any lift in hovering flight, the wake is bilateral with separate vortices from the two wings. This is also the case in hummingbirds [4,12,14], but in hummingbirds each half-stroke result in isolated vortex loops. In the pied flycatcher Ficedula hypoleuca [14], which had an inactive upstroke, the slow flight (3 m s…”

mentioning

confidence: 90%

“…In asymmetric hovering, the wake has been postulated to consist of a single vortex loop shed as the result of a powerful downstroke and in the case of an inactive upstroke no vortices are shed during the upstroke (figure 1c). Flow visualization of wakes in hummingbirds suggest the model in figure 1b as most plausible [4,12], or a more complex arrangement of bi-lateral vortices [14]. An aerodynamic analysis based on wingbeat kinematics of a hovering pied flycatcher (Ficedula hypeuca) suggested an active downstroke and an inactive upstroke [5], as expected for asymmetric hovering with an inclined stroke plane.…”

Section: Introductionmentioning

confidence: 99%

“…the downstroke ratio is 0.5 and each half-stroke generates an equal amount of lift. Superficially hummingbirds conform kinematically to symmetric hovering [1], but the downstroke generates about 66-75% of the total lift [2][3][4] due to small differences in stroke plane angle, angle of attack, camber and wing twist.…”

Section: Introductionmentioning

confidence: 99%

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The wake of hovering flight in bats

Håkansson

Hedenström

Winter

et al. 2015

J. R. Soc. Interface.

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Hovering means stationary flight at zero net forward speed, which can be achieved by animals through muscle powered flapping flight. Small bats capable of hovering typically do so with a downstroke in an inclined stroke plane, and with an aerodynamically active outer wing during the upstroke. The magnitude and time history of aerodynamic forces should be reflected by vorticity shed into the wake. We thus expect hovering bats to generate a characteristic wake, but this has until now never been studied. Here we trained nectar-feeding bats, Leptonycteris yerbabuenae, to hover at a feeder and using time-resolved stereoscopic particle image velocimetry in conjunction with high-speed kinematic analysis we show that hovering nectar-feeding bats produce a series of bilateral stacked vortex loops. Vortex visualizations suggest that the downstroke produces the majority of the weight support, but that the upstroke contributes positively to the lift production. However, the relative contributions from downstroke and upstroke could not be determined on the basis of the wake, because wake elements from down-and upstroke mix and interact. We also use a modified actuator disc model to estimate lift force, power and flap efficiency. Based on our quantitative wake-induced velocities, the model accounts for weight support well (108%). Estimates of aerodynamic efficiency suggest hovering flight is less efficient than forward flapping flight, while the overall energy conversion efficiency (mechanical power output/metabolic power) was estimated at 13%.

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confidence: 90%

Section: Introductionmentioning

confidence: 99%

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The wake of hovering flight in bats

Håkansson

Hedenström

Winter

et al. 2015

J. R. Soc. Interface.

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“…The dominating unsteady mechanism used in nature is the dynamic stall and associated LEV, which have been shown for many insects (Ellington et al, 1996;Birch and Dickinson, 2001;Sane, 2003;Johansson et al, 2013), and a few bird species (Muijres et al, 2012a, Warrick et al, 2009, Wolf et al, 2013. In this context, wind tunnel experiments of on-wing flow measurements of slow flying bats have demonstrated the presence of LEVs in the relatively small Palla's long-tongued bats ( ) the LEV contributes up to 40% of the total aerodynamic force (Table 1).…”

Section: U=4 M Smentioning

confidence: 99%

Bat flight: aerodynamics, kinematics and flight morphology

Hedenström

Johansson

2015

Journal of Experimental Biology

101

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Bats evolved the ability of powered flight more than 50 million years ago. The modern bat is an efficient flyer and recent research on bat flight has revealed many intriguing facts. By using particle image velocimetry to visualize wake vortices, both the magnitude and timehistory of aerodynamic forces can be estimated. At most speeds the downstroke generates both lift and thrust, whereas the function of the upstroke changes with forward flight speed. At hovering and slow speed bats use a leading edge vortex to enhance the lift beyond that allowed by steady aerodynamics and an inverted wing during the upstroke to further aid weight support. The bat wing and its skeleton exhibit many features and control mechanisms that are presumed to improve flight performance. Whereas bats appear aerodynamically less efficient than birds when it comes to cruising flight, they have the edge over birds when it comes to manoeuvring. There is a direct relationship between kinematics and the aerodynamic performance, but there is still a lack of knowledge about how (and if ) the bat controls the movements and shape ( planform and camber) of the wing. Considering the relatively few bat species whose aerodynamic tracks have been characterized, there is scope for new discoveries and a need to study species representing more extreme positions in the bat morphospace.

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“…Techniques that would improve confidence in the accuracy of aerodynamic estimates of power include using flow visualization (e.g. [19,62,63]) and sophisticated computational fluid dynamic (CFD) modelling [20,83].…”

Section: Scaling Of Flight Performance (A) On Being Largementioning

confidence: 99%

Evolution of avian flight: muscles and constraints on performance

Tobalske¹

2016

Phil. Trans. R. Soc. B

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One contribution of 17 to a theme issue 'Moving in a moving medium: new perspectives on flight'. Competing hypotheses about evolutionary origins of flight are the 'fundamental wing-stroke' and 'directed aerial descent' hypotheses. Support for the fundamental wing-stroke hypothesis is that extant birds use flapping of their wings to climb even before they are able to fly; there are no reported examples of incrementally increasing use of wing movements in gliding transitioning to flapping. An open question is whether locomotor styles must evolve initially for efficiency or if they might instead arrive due to efficacy. The proximal muscles of the avian wing output work and power for flight, and new research is exploring functions of the distal muscles in relation to dynamic changes in wing shape. It will be useful to test the relative contributions of the muscles of the forearm compared with inertial and aerodynamic loading of the wing upon dynamic morphing. Body size has dramatic effects upon flight performance. New research has revealed that mass-specific muscle power declines with increasing body mass among species. This explains the constraints associated with being large. Hummingbirds are the only species that can sustain hovering. Their ability to generate force, work and power appears to be limited by time for activation and deactivation within their wingbeats of high frequency. Most small birds use flap-bounding flight, and this flight style may offer an energetic advantage over continuous flapping during fast flight or during flight into a headwind. The use of flap-bounding during slow flight remains enigmatic. Flap-bounding birds do not appear to be constrained to use their primary flight muscles in a fixed manner. To improve understanding of the functional significance of flap-bounding, the energetic costs and the relative use of alternative styles by a given species in nature merit study.This article is part of the themed issue 'Moving in a moving medium: new perspectives on flight'. OverviewMuscles are obviously key to the capacity of birds for flight, and the goal of this review is to explore current hypotheses of the ways muscles permit and constrain this capacity. Insight into the phylogeny of birds is improving rapidly, and this offers great promise for improving understanding of how evolution transformed ancestral theropod forms [1] into the derived, volant bird species we observe today. Genomic study [2][3][4] and the extraordinary rate of new discovery of fossil dinosaurs [5][6][7][8][9][10] have provided rich phylogenetic hypotheses from which we can begin to test patterns of historical transformation [11]. Concurrently, modern empirical and modelling techniques in comparative biomechanics offer new ways of testing hypotheses that link form and function. These include in vivo and in situ measures of the contractile behaviour of muscle [12 -14]: high-speed, three-dimensional videography that can reveal details of wing motion [15,16]; X-ray videography of skeletal kinematics [16,17]; particle ima...

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Structure of the vortex wake in hovering Anna's hummingbirds (Calypte anna)

Cited by 31 publications

References 23 publications

The wake of hovering flight in bats

The wake of hovering flight in bats

Bat flight: aerodynamics, kinematics and flight morphology

Evolution of avian flight: muscles and constraints on performance

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