On the aerodynamics of leading-edge high-lift devices of avian wings

Meseguer, José; Franchini, Sebastián; Pérez-Grande, Isabel; García, José Luis Sanz

doi:10.1243/095441005x9067

Cited by 36 publications

(33 citation statements)

References 10 publications

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“…Among the various characteristics of the wing that enable efficient flights, the alula, a small group of feathers that are attached to the leading edge of the wing, is known to enhance lift. In spite of its small size (corresponds to 5-10% of the wing length; Lee et al 2015), the alula has been known to increase lift in high attack angle conditions (Nachtigall & Kempf 1971;Meseguer et al 2005;Austin & Anderson 2007;Lee et al 2015) and assumed to delay the stall angle (Nachtigall & Kempf 1971;Meseguer et al 2005;Austin & Anderson 2007). Based on the stall delaying effect of the alula, it is thought that the function of the alula is comparable to that of the leading-edge slat in aeroplanes (Álvarez et al 2001;Meseguer et al 2005;Austin & Anderson 2007).…”

Section: Introductionmentioning

confidence: 99%

“…In spite of its small size (corresponds to 5-10% of the wing length; Lee et al 2015), the alula has been known to increase lift in high attack angle conditions (Nachtigall & Kempf 1971;Meseguer et al 2005;Austin & Anderson 2007;Lee et al 2015) and assumed to delay the stall angle (Nachtigall & Kempf 1971;Meseguer et al 2005;Austin & Anderson 2007). Based on the stall delaying effect of the alula, it is thought that the function of the alula is comparable to that of the leading-edge slat in aeroplanes (Álvarez et al 2001;Meseguer et al 2005;Austin & Anderson 2007). However, the stall delaying effect has not been convincingly shown across bird species (Austin & Anderson 2007;Lee et al 2015), and our previous study suggests that the function of the alula is primarily for lift enhancement due to a small streamwise vortex formed at the tip of the alula (Lee et al 2015).…”

Section: Introductionmentioning

confidence: 99%

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Characteristics of the alula in relation to wing and body size in the Laridae and Sternidae

Lee

Choi

2016

Animal Cells and Systems

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The alula is a small structure present on the leading edge of bird wings and is known to enhance lift by creating a small vortex at its tip. Alula size vary among birds, but how this variation is associated with the function of the alula remains unclear. In this study, we investigated the relationship between the size and shape of the alula and the features of the wing in the Laridae and Sternidae. Laridae birds have generally longer wings and greater loadings than Sternidae birds. The two families differed in the relationships between body size or wing length and the size or shape of the alula. In the Laridae, the aspect ratio of the alula was smaller in the species that have relatively longer wings, but the pattern was opposite in the Sternidae. The aspect ratio of the alula was greater in the species that are relatively heavier in the Sternidae but not in the Laridae. Combined, these results suggest that the species with high loading potential and long wings exhibit long alula. We hypothesize that heavier species may benefit from having longer alula if they perform flights with higher attack angles than lighter species, as longer alula would better suppress flow separation at higher attack angles. Our results suggest that the size and shape of the alula can be explained in one allometric landscape defined by wing length and loading in these two closely related families of birds with similar wing shapes. ARTICLE HISTORY

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Characteristics of the alula in relation to wing and body size in the Laridae and Sternidae

Lee

Choi

2016

Animal Cells and Systems

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“…The alula is widely recognised to operate as a high-lift device, although opinions differ as to whether it operates as a leading-edge slot/slat (e.g. Nachtigall and Kempf, 1971;Alvarez et al, 2001;Stinton, 2001;Meseguer et al, 2005) or a vortex generator (e.g. Videler et al, 2004;Videler, 2005).…”

Section: Introductionmentioning

confidence: 99%

Automatic aeroelastic devices in the wings of a steppe eagleAquila nipalensis

Carruthers

Thomas

Taylor

2007

Journal of Experimental Biology

144

143

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SUMMARY Here we analyse aeroelastic devices in the wings of a steppe eagle Aquila nipalensis during manoeuvres. Chaotic deflections of the upperwing coverts observed using video cameras carried by the bird (50 frames s–1) indicate trailing-edge separation but attached flow near the leading edge during flapping and gust response, and completely stalled flows upon landing. The underwing coverts deflect automatically along the leading edge at high angle of attack. We use high-speed digital video (500 frames s–1) to analyse these deflections in greater detail during perching sequences indoors and outdoors. Outdoor perching sequences usually follow a stereotyped three-phase sequence comprising a glide, pitch-up manoeuvre and deep stall. During deep stall, the spread-eagled bird has aerodynamics reminiscent of a cross-parachute. Deployment of the underwing coverts is closely phased with wing sweeping during the pitch-up manoeuvre,and is accompanied by alula protraction. Surprisingly, active alula protraction is preceded by passive peeling from its tip. Indoor flights follow a stereotyped flapping perching sequence, with deployment of the underwing coverts closely phased with alula protraction and the end of the downstroke. We propose that the underwing coverts operate as an automatic high-lift device, analogous to a Kruger flap. We suggest that the alula operates as a strake, promoting formation of a leading-edge vortex on the swept hand-wing when the arm-wing is completely stalled, and hypothesise that its active protraction is stimulated by its initial passive deflection. These aeroelastic devices appear to be used for flow control to enhance unsteady manoeuvres, and may also provide sensory feedback.

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“…During the last few years, authors of this paper have been involved in a cooperation programme aiming at clarifying the aerodynamic role of the wings and tails of some primitive birds [3][4][5][6]. Some of these elements still appear in extant birds, like the alula, a leadingedge high-lift device, whereas some others have been abandoned in the evolutionary process, as happened with the singular tail of Archaeopteryx, and the long fingers emerging from the leading edge of the wings of this very primitive bird (although such an element also appears in the wings of present bats).…”

Section: Introductionmentioning

confidence: 99%

Use of turbulence generators as stall-delaying devices in flight at low Reynolds numbers

Meseguer

Sanz-Andrés

Pérez-Grande

et al. 2008

Proceedings of the Institution of Mechanical Engineers, Part G:

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Wings flying at low Reynolds numbers enter a stalled flow regime by laminar boundary layer separation at the leading edge. A way to improve the flying performance of these wings at the angle of attack close to stalling is by forcing the transition of the upper-side wing boundary layer from laminar flow to turbulent flow. To force such a transition several devices can be used, the simplest one being a wire parallel to the wing leading edge. The efficiency of such a turbulence generator has been checked by testing two wing models in a low turbulence wind tunnel. One of the wings is of elliptic planform and is equipped with a leading edge wire placed along 62 per cent of the wing span. The second model simulates the wing of the very primitive bird Archaeopteryx, and it is also equipped with a wire at the leading edge which simulates one of the long fingers emerging from the leading edge of the wings of this bird. In both cases, experimental results show that these leading-edge devices are effective in delaying wing stall.

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On the aerodynamics of leading-edge high-lift devices of avian wings

Cited by 36 publications

References 10 publications

Characteristics of the alula in relation to wing and body size in the Laridae and Sternidae

Characteristics of the alula in relation to wing and body size in the Laridae and Sternidae

Automatic aeroelastic devices in the wings of a steppe eagleAquila nipalensis

Use of turbulence generators as stall-delaying devices in flight at low Reynolds numbers

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