| 1. |
- Bowlin, Melissa, et al.
(author)
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Aerodynamic costs of flying with holey wings
- 2009
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In: Comparative Biochemistry and Physiology. Part A: Molecular & Integrative Physiology. - : Elsevier BV. - 1095-6433. ; 153A:2, suppl. 1, s. 122-122
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Conference paper (peer-reviewed)
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| 2. |
- Johansson, Christoffer, et al.
(author)
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The near and far wake of Pallas' long tongued bat (Glossophaga soricina).
- 2008
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In: Journal of Experimental Biology. - : The Company of Biologists. - 1477-9145 .- 0022-0949. ; 211:Pt 18, s. 2909-2918
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Journal article (peer-reviewed)abstract
- The wake structures of a bat in flight have a number of characteristics not associated with any of the bird species studied to this point. Unique features include discrete vortex rings generating negative lift at the end of the upstroke at medium and high speeds, each wing generating its own vortex loop, and a systematic variation in the circulation of the start and stop vortices along the wingspan, with increasing strength towards the wing tips. Here we analyse in further detail some previously published data from quantitative measurements of the wake behind a small bat species flying at speeds ranging from 1.5 to 7 m s(-1) in a wind tunnel. The data are extended to include both near- and far-wake measurements. The near-/far-wake comparisons show that although the measured peak vorticity of the start and stop vortices decreases with increasing downstream distance from the wing, the total circulation remains approximately constant. As the wake evolves, the diffuse stop vortex shed at the inner wing forms a more concentrated vortex in the far wake. Taken together, the results show that studying the far wake, which has been the standard procedure, nevertheless risks missing details of the wake. Although study of the far wake alone can lead to the misinterpretation of the wake topology, the net, overall circulation of the main wake vortices can be preserved so that approximate momentum balance calculations are not unreasonable within the inevitably large experimental uncertainties.
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| 3. |
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| 4. |
- Wolf, Marta, et al.
(author)
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Kinematics of flight and the relationship to the vortex wake of a Pallas' long tongued bat (Glossophaga soricina).
- 2010
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In: Journal of Experimental Biology. - : The Company of Biologists. - 1477-9145 .- 0022-0949. ; 213:12, s. 2142-2153
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Journal article (peer-reviewed)abstract
- To obtain a full understanding of the aerodynamics of animal flight, the movement of the wings, the kinematics, needs to be connected to the wake left behind the animal. Here the detailed 3D wingbeat kinematics of bats, Glossophaga soricina, flying in a wind tunnel over a range of flight speeds (1-7 m s(-1)) was determined from high-speed video. The results were compared with the wake geometry and quantitative wake measurements obtained simultaneously to the kinematics. The wingbeat kinematics varied gradually with flight speed and reflected the changes observed in the wake of the bats. In particular, several of the kinematic parameters reflected the differences in the function of the upstroke at low and high flight speeds. At lower flight speeds the bats use a pitch-up rotation to produce a backward flick which creates thrust and some weight support. At higher speeds this mechanism disappears and the upstroke generates weight support but no thrust. This is reflected by the changes in e.g. angle of attack, span ratio, camber and downstroke ratio. We also determined how different parameters vary throughout a wingbeat over the flight speeds studied. Both the camber and the angle of attack varied over the wingbeat differently at different speeds, suggesting active control of these parameters to adjust to the changing aerodynamic conditions. This study of the kinematics strongly indicates that the flight of bats is governed by an unsteady high-lift mechanism at low flight speeds and points to differences between birds and bats.
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