Feather coating to reduce drag

Coating the rigid wings of airplanes with artificial bristles that mimic feathers could make them more efficient, according to engineers. An Italian team has demonstrated how feather-like structures help reduce drag on a cylinder and says they could have the same effect on underwater and aerial vehicles.

Although they may not look like they can have much of an effect, during gliding some covert feathers stick up at right angles to the wing's surface and vibrate in the airflow. To test whether this has any effect on flight performance Bottaro and Julien Favier, also at Genoa, added synthetic coverts to a computer model of a 20-centimetre-diameter cylinder and put it in a virtual wind tunnel.

Their synthetic feathers are modelled as rigid keratin bristles 4 to 6 centimetres long and 0.5 millimetres in diameter, coating the cylinder at a density of around three fibres per square centimetre. The cylinder was orientated with its long axis perpendicular to the air flow, placing the synthetic feathers parallel to the wind.

As the wind speed increased the bristles started to vibrate in a similar way to real covert feathers, reducing the drag on the cylinder by 15%.
The researchers say that's because the fibres help to cushion the effects of the air flow on the cylinder itself. Normally the air flows rapidly across the cylinder and creates an area of low pressure behind it. This encourages the formation of strong vortices, creating turbulence and increasing the drag on the cylinder.

Source: newscientist.comAdded: 20 May 2009