The barn owl wing: an inspiration for silent flight in the aviation industry?

Abstract

Barn owls are specialists in prey detection using acoustic information. The flight apparatus of this bird of prey is most efficiently adapted to the hunting behavior by reducing flight noise. An understanding of the underlying mechanisms owls make use of could help minimize the noise disturbances in airport or wind power plant neighborhood. Here, we characterize wings of barn owls in terms of an airfoil as a role model for studying silent flight. This characterization includes surface and edge specialization (serrations, fringes) evolved by the owl. Furthermore, we point towards possible adaptations of either noise suppression or air flow control that might be an inspiration for the construction of modern aircraft. Three-dimensional imaging techniques such as surface digitizing, computed tomography and confocal laser scanning microscopy were used to investigate the wings and feathers in high spatial resolution. We show that wings of barn owls are huge in relation to their body mass resulting in a very low wing loading which in turn enables a slow flight and an increased maneuverability. Profiles of the wing are highly cambered and anteriorly thickened, especially at the proximal wing, leading to high lift production during flight. However, wind tunnel experiments showed that the air flow tends to separate at such wing configurations, especially at low-speed flight. Barn owls compensated this problem by evolving surface and edge modifications that stabilize the air flow. A quantitative three-dimensionally characterization of some of these structures is presented.

Flexural stiffness of feather shafts: geometry rules over material properties

“…Interestingly, the calami of pigeons were relatively longer than the calami of barn owls. Both species of birds are of a comparable body mass; however, the wings of barn owls are much larger, which results in a very low wing loading of 33.0Nm -2 (Bachmann et al, 2011). The low wing loading enables the owl to fly slowly without beating its wings at high frequencies.…”

“…because of smaller and narrower feathers (Bachmann et al, 2007). As pigeons have the same body mass as barn owls, their wing loading is much higher (96.8Nm -2 ) (Bachmann et al, 2011). Therefore, pigeons have to beat their wings at high frequencies to become airborne (Berg and Biewener, 2006;Berg and Rayner, 1995;Tobalske and Dial, 1996), which in turn results in high forces acting on the feathers.…”

“…Barn owls fly slowly over vegetation while searching for prey (Mebs and Scherzinger, 2000;Taylor, 1994). The slow flight is enabled by a large wing area that is due to large feathers (Bachmann et al, 2007), which in turn results in low wing loading (Bachmann et al, 2011;Johnson, 1997). Consequently, mechanical loadings in the dorso-ventral as well as in the lateral direction are low.…”

Owl Inspired Silent Flight

“…Anatomically and geometrically, the wing can be divided into a proximal and a distal part. 24 The proximal part is highly cambered and has a thickened leading edge.…”

Features of owl wings that promote silent flight

“…A major disadvantage of low flight velocities is the increased influence of induced drag, which negatively affects the flight performance. The general shape of owl wings is suited to reducing this influence, either by an overall elliptical shape, which is especially prominent for barn owls [37,38], or by the expression of slotted wings due to feather emarginations [39,40] that can be found for many species within the Strigidae family.…”