Space shuttle's rudder could cut aircraft noise

Airliners could be made quieter as they come in to land if designers took a crinkly leaf out of the space shuttle's book, Airbus suggests.

In a US patent filed last week, Airbus notes that the space shuttle's rudder – the hinged steering surface on the rear of the tail fin – splits to present two large surfaces to the airstream, helping to brake the craft as it glides back to Earth

Airbus engineer Klaus Bender in Hamburg, Germany, says such a "spreading rudder" could slow airliners down too, reducing the need to deploy the noisy, flat air brakes on top of the wing, which howl like the reed in a clarinet.

Airbus is not cheekily trying to patent the space shuttle's rudder. Its claimed innovation is a way to make the spread rudder work without making more of a racket than the air brakes.

Serrated edge
The idea is to carve serrations into the rudder's trailing edge to help break up the noise-producing vortex that would otherwise be generated there.

As well as increasing braking drag in a novel, low-noise way, the idea avoids the loos of lift that occurs when ordinary air brakes are deployed. With more lift from the wings, less engine power is needed as the aircraft approaches the runway, further reducing the noise.

But does the physics hold up? "It seems plausible," says Trevor Cox, an acoustics engineer at the University of Salford in the UK. When a serrated edge moves through a fluid it produces eddy currents which are more disorganised than those produced by a straight edge. That reduces the pressure difference, "and that in turn creates less noise", Cox says.

The concept of serrated edges is also being studied for wind turbine blades, in the hope that they will produce less noise to annoy nearby residents, Cox says