As silent as a flying owl
If you watch an owl flapping or gliding, it’s like viewing film footage with the sound on ‘mute’—they are so silent. That’s because their wings have velvety surfaces, comb-like serrations (see photo) at the leading edge, and trailing-edge fringes which dramatically suppress the sound of air rushing over the wings. Therefore the owl’s prey (mice and voles) can be taken by surprise.
Also, with wing noise suppressed to a level below the owl’s own hearing range, they can better hear (and thus locate) prey while flying—crucial for hunting at night.
These features have caught the attention of researchers in the dramatically-expanding field of biomimetics or bio-inspiration, whereby engineers copy biological design. Owl wings have already inspired quieter fan blades in computers. More recently researchers using wind tunnel facilities have explored these noise suppression characteristics in more detail, especially the leading-edge serrations. Each is “the tip of a single barb, having a very complicated 3D shape”, and its size and orientation differ according to its position.
The owl wing design also efficiently resolves the trade-off between effective sound suppression and aerodynamic force production. In striving to understand how, the researchers see an ultimate goal of mimicking those design aspects across many man-made technologies. For example, so the blades of multi-rotor drones can ‘chop’ the air more quietly, without unduly sacrificing lift; similarly in other aircraft, wind turbines, and fluid machinery in general.
There’s some way yet to go, though, before the sound-suppressing design features of owl wings are fully understood, and man’s mimicry of them in aviation technology comes to fruition. Which raises the question: how did owls come to have such enviable design characteristics in the first place? Design implies, well, that they were designed, which of course, implies a Designer. However, don’t be surprised in this age of widespread evolutionary belief if you don’t hear that proclaimed from the rooftops. When it comes to crediting the Creator, many today would rather that be kept as silent as an owl in flight (see Romans 1:18).
References and notes
- I.e. so it is silent at frequencies above 2 kHz. (Mice and voles hear most acutely at 2–20 kHz, while the owl’s hearing range is 3–6 kHz.) Lilley, G.M., A study of the silent flight of the owl, 4th AIAA/CEAS Aeroacoustics Conference 2340:1–6, 1998 | doi:10.2514/6.1998-2340. Return to text.
- Dawson, E., PC Authority, October 2006, p. 15, also: A quiet fan of the Designer’s, Creation 29(1):11, December 2006; creation.com/fan. Return to text.
- Rao, C. et al., Owl-inspired leading-edge serrations play a crucial role in aerodynamic force production and sound suppression, Bioinspiration & Biomimetics 12(4):6008, 4 July 2017. Return to text.