Meeting Abstract

97.2  Saturday, Jan. 7  The silent flight of owls BACHMANN, Thomas; Technische Universität Darmstadt, Germany bachmann@sla.tu-darmstadt.de

Barn owls are nocturnal birds of prey that detect prey mainly by using acoustic information. To improve the localization of prey owls evolved a slow and silent flight. Here, anatomical adaptations of barn owl wings to low speed and silent flight are presented. Three-dimensional surface scans and reconstructions of internal structures such as bones, skin and feather rachises were used to analyze aerodynamically relevant parameters. Fixed barn owl wings and artificially manufactured airfoil models were investigated in wind tunnel experiments to visualize the flow around the wing. Barn owl wings are huge in relation to their body mass leading to a low wing-loading. This enables the owl to fly slowly and increases the maneuverability. The skeleton elements of the wing appear elongated and narrow with little space for muscles. This observation suggests a rather steady flight with little movements within the wing. Since movements within the wing causes the feathers to rub against each other, wing movement produces sound emission. Barn owls reduced this noise during flight by a low wing-beat frequency. Additionally, a velvet-like surface structure of the barn owl feathers decreases friction noise and stabilize the air flow around the wing. A serrated leading-edge enriches the boundary layer of the wing energetically by which the flow stays laminar. Fringes along the trailing edge of the wing allow a smooth transition of the different air flows of the upper and lower side. The interaction of these anatomical specializations and the specific flight behavior of owls result in a silent flight.