How Can Owls Fly Silently?

While it adds to the owl's mystique, silent flight serves a very practical purpose. It helps this nocturnal creature sneak up on its prey. But how do owls fly silently in the first place?

The design of owls' wings allows them to fly in almost absolute silence. Different parts of their wings and the characteristics of their feathers contribute to their silent flight. Owls have broad wings with large surface areas that help them to float through the air without flapping too much. Less flapping makes less noise.

The main reason owls can fly silently is the uniquely designed leading edges of their primary feathers. When most birds fly, turbulence — created when air gushes over the surface of their wings — causes noise. Owls' wings, however, are unique because they reduce noise caused by turbulence.

An owl's primary feathers are serrated like a comb. This design breaks down turbulence into smaller currents called micro-turbulences. Then the edge of the feather muffles the sound of air flowing over the wing and shifts the angle at which air flows. These soft feathers allow air to pass through which eliminates sound. Some people suspect that, as the owls flies, these feathers may also shift sound energy created by the owl's wing to a higher frequency that prey can't hear.

Owls' secondary feathers are made up of soft fringes that reduce turbulence behind their wings. The trailing feathers on the back end of the wing are tattered, and the rest of the wing and the legs are covered in downy feathers. As the owl flies, the trailing fringe and tattered feathers break sound waves over the wings as air flows over them. The down feathers absorb any remaining noise created in flight. The down absorbs frequencies above 2,000 hertz — the measure of frequency — which eliminates all sounds that owls' potential prey can hear [source: Roach].

So, the secret's in the wings. But does this noise-reducing design have a place in your next airplane flight?

Engineers constantly search for ways to improve aircraft technology, and nature inspires the greatest innovations. They look to the design of owls' wings to reduce the noise created by aircraft while keeping takeoff energy efficient.

Geoffrey Lilley, a professor emeritus of aeronautics and astronautics at the University of Southampton in England, studies owl flight and the ways it can help aeronautics. Lilley works in conjunction with the Quiet Aircraft Technology project within the Vehicle Systems Program located at NASA's Langley Research Center in Hampton, Va. He and his colleagues are forging the path of owl-influenced aircraft design.

So how can engineers modify an enormous aircraft to mirror the anatomy of the owl? Researchers propose the possibility of creating retractable fringe to mirror owls' trailing feather. For the owl, this fringe reduces turbulence and noise. Some researchers think that applying a velvety coating — similar to that of an owl — on landing gear will absorb noise just as it does for the owl [source: Roach].

Could owls' feathers change your next flight? Airports like Chicago O'Hare and Heathrow have strict noise restrictions on aircrafts take-off. If engineers find a way to reduce noise, more flights can take off every day, and revenue can increase. For an industry struggling with fuel costs and other problems, the wise old owl may provide some solutions.