Vergleichende Untersuchungen zur flugbiologischen Funktion des Daumenfittichs (Alula spuria) bei V�geln

Nachtigall, Werner; Kempf, B.

doi:10.1007/bf00298144

Cited by 59 publications

(30 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…High-lift devices have no advantages at low angles of attack, at which they simply add to the total drag on the aerofoil, and an automatic mechanism of this sort would ensure that the alula was only deployed when it was needed. Independent of whether passive deflection of the alula actually stimulates its active protraction, our observation that passive deflection precedes active protraction helps clarify earlier controversy, based on data from wind tunnel experiments with isolated wings, over whether the alula deploys passively or actively (Graham, 1930;Brown, 1963;Nachtigall and Kempf, 1971;Alvarez et al, 2001).…”

Section: What Sensory Information Might the Covert Feathers And Alulasupporting

confidence: 65%

“…According to this hypothesis, which differs from the classical functional description of the alula as a leading-edge slot or slat (e.g. Nachtigall and Kempf, 1971), the alula would therefore be acting much like a strake on a delta-winged aircraft, serving to promote and stabilise the formation of a leading-edge vortex over the portion of wing behind it (see also Videler, 2005).…”

Section: Wing Morphing During Gliding Perching Manoeuvresmentioning

confidence: 99%

“…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%

“…Videler et al, 2004;Videler, 2005). Because the alula feathers are muscularised at the base, the alula is usually assumed to operate as an active control device, although its potential for passive deflection has been noted on several occasions on the basis of wind tunnel studies on the wings of freshly killed birds (Graham, 1930;Brown, 1963;Nachtigall and Kempf, 1971). There appears to be no published detailed analysis of the kinematics of deployment of the alula in flying birds; we therefore use our observations of the aeroelastic deformation of the alula to clarify this aspect of its function.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Automatic aeroelastic devices in the wings of a steppe eagleAquila nipalensis

Carruthers

Thomas

Taylor

2007

Journal of Experimental Biology

138

143

View full text Add to dashboard Cite

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.

show abstract

Section: What Sensory Information Might the Covert Feathers And Alulasupporting

confidence: 65%

Section: Wing Morphing During Gliding Perching Manoeuvresmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Automatic aeroelastic devices in the wings of a steppe eagleAquila nipalensis

Carruthers

Thomas

Taylor

2007

Journal of Experimental Biology

138

143

View full text Add to dashboard Cite

show abstract

“…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%

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

Lee

Choi

2016

Animal Cells and Systems

View full text Add to dashboard Cite

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

show abstract