Research published in ICE journal hails the owl “the king of stealth”

Scientists have already shown that many owls are able to glide inches from their prey without being detected due to special feathers which absorb aerodynamic sound – the type of noise a low-flying high speed aircraft generates.

Now research published in the Institution of Civil Engineers (ICE) Journal Bioinspired, Biomimetic and Nanobiomaterials, shows owls are also capable of supressing the vibrations that occur when they flap their wings, despite repeated flapping requiring tremendous force and resulting, for most birds, in noise.

The study, led by Professor Jinkui Chu from Dalian University of Technology in China, showed this is again due to the owl’s feather structures, which during flight are able to extract the mechanical energy from the vibrations and convert it into heat – therefore enabling the owl to remain stable and quiet.

It compared the behaviour of Long Eared Owl, Golden Eagle and Pigeon primary feathers during flight, using laser displacement sensors and high speed cameras. All three birds, while differing in size, have a similar flapping flight style.

Professor Jinkui Chu, said: Many owls have a unique and fascinating ability to fly so silently that they are out of their prey’s hearing range, due to their feather structure. This behaviour has long been of interest to engineers, as we seek to apply the owl’s noise-reduction mechanisms to other purposes and situations that benefit society.

Now however, we know the owls’ silent flight ability is even more superior than we thought, you could say of all birds it is the ‘king of acoustic stealth’. It not only manages to suppress aerodynamic noise when gliding, but also mechanical noise caused by vibration during flying.

This is remarkable, considering the sudden jumping, bending and twisting the wings are subjected to when flapping and the noise that creates for other birds. In the scientific world, the process used to eliminate this mechanical noise is called ‘damping’ – which means the extraction of mechanical energy from a vibrating system usually by converting it into heat and allowing it to remain steady.

Our research showed the Long Eared Owl has superior ‘damping’ skill – meaning it can remain mind-blowingly stable and eliminate mechanical noise caused by the movement of its feathers – quite a feat of engineering.

This study will hopefully provide further insight into the owls’ silent flight mechanism and help engineers develop ideas for special materials or structures – such as on-shore wind turbines -where similar noise elimination can be applied.

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