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ABSTRACT: Flight feathers of birds interact with the flow field during flight. They bend and twist under aerodynamic loads. Two parameters are mainly responsible for flexibility in feathers: the elastic modulus (Young's modulus, E) of the material (keratin) and the geometry of the rachises, more precisely the second moment of area (I). Two independent methods were employed to determine Young's modulus of feather rachis keratin. Moreover, the second moment of area and the bending stiffness of feather shafts from fifth primaries of barn owls (Tyto alba) and pigeons (Columba livia) were calculated. These species of birds are of comparable body mass but differ in wing size and flight style. Whether their feather material (keratin) underwent an adaptation in stiffness was previously unknown. This study shows that no significant variation in Young's modulus between the two species exists. However, differences in Young's modulus between proximal and distal feather regions were found in both species. Cross-sections of pigeon rachises were particularly well developed and rich in structural elements, exemplified by dorsal ridges and a well-pronounced transversal septum. In contrast, cross-sections of barn owl rachises were less profiled but had a higher second moment of area. Consequently, the calculated bending stiffness (EI) was higher in barn owls as well. The results show that flexural stiffness is predominantly influenced by the geometry of the feathers rather than by local material properties.
Journal of Experimental Biology 02/2012; 215(Pt 3):405-15. · 3.00 Impact Factor
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ABSTRACT: Owls are known for their silent flight. Even though there is some information available on the mechanisms that lead to a reduction of noise emission, neither the morphological basis, nor the biological mechanisms of the owl's silent flight are known. Therefore, we have initiated a systematic analysis of wing morphology in both a specialist, the barn owl, and a generalist, the pigeon. This report presents a comparison between the feathers of the barn owl and the pigeon and emphasise the specific characteristics of the owl's feathers on macroscopic and microscopic level. An understanding of the features and mechanisms underlying this silent flight might eventually be employed for aerodynamic purposes and lead to a new wing design in modern aircrafts.
A variety of different feathers (six remiges and six coverts), taken from several specimen in either species, were investigated. Quantitative analysis of digital images and scanning electron microscopy were used for a morphometric characterisation. Although both species have comparable body weights, barn owl feathers were in general larger than pigeon feathers. For both species, the depth and the area of the outer vanes of the remiges were typically smaller than those of the inner vanes. This difference was more pronounced in the barn owl than in the pigeon. Owl feathers also had lesser radiates, longer pennula, and were more translucent than pigeon feathers. The two species achieved smooth edges and regular surfaces of the vanes by different construction principles: while the angles of attachment to the rachis and the length of the barbs was nearly constant for the barn owl, these parameters varied in the pigeon. We also present a quantitative description of several characteristic features of barn owl feathers, e.g., the serrations at the leading edge of the wing, the fringes at the edges of each feather, and the velvet-like dorsal surface.
The quantitative description of the feathers and the specific structures of owl feathers can be used as a model for the construction of a biomimetic airplane wing or, in general, as a source for noise-reducing applications on any surfaces subjected to flow fields.
Frontiers in Zoology 02/2007; 4:23. · 4.46 Impact Factor
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ABSTRACT: Barn owls have undergone many adaptations to optimize flight behaviour for catching small rodents in environments where visibility is impaired. These birds have, for example, developed structures that reduce noise production during flight and they have adapted wing form to slow flight. For such reasons, the wing of the barn owl serves – in a biomimetic sense - as a role model for the construction of airplane wings. The biological part of such a project is to exactly measure wing form. Measuring under life conditions has turned out to be a difficult problem, because wing form in bird flight is not constant. The DLR Göttingen and the RWTH Aachen have developed two different systems which allow high precision measurements of the owl wings during free flight. Both systems rely on multiple cameras that record the barn owl during flight. The first system uses a fine random pattern of light points which is projected onto the wing surfaces. Each surface is being recorded by two synchronised high speed cameras. By correlating the dot patterns recorded by the two cameras a 3D model can be generated. The second approach uses a number of laser sheets, to create cross sections of the wing. Line lasers are affixed to a frame so that unbroken laser lines are projected onto the wing surface perpendicular to the flight path. The shape of the laser lines on the wing surface is recorded with single-lense reflex cameras, and three-dimensional shape of the upper and lower side of the wing is reconstructed. The weaknesses and the strengths of both approaches will be discussed and compared.
Flow Sensing in Air and Water;
