Fake feathers could increase efficiency of airplanes

Irish Sun (ANI) Tuesday 14th April, 2009

London, April 14 : Engineers have suggested that coating the rigid wings of airplanes with artificial bristles that mimic feathers could make them more efficient.

According to a report in New Scientist, 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.

Birds use long, stiff flight feathers to help generate the lift and thrust needed to get off the ground and to stay aloft.

But, Alessandro Bottaro at the University of Genoa is more interested in how a set of smaller feathers, called coverts, keeps birds flying efficiently.

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's team 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 modeled as rigid keratin bristles 4 to 6 centimeters long and 0.5 millimeters in diameter, coating the cylinder at a density of around three fibres per square centimeter.

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 percent.

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.

Racing car drivers exploit that area of low pressure - the slipstream - to stay close to their rivals without having to combat the drag experienced by the car in front.

With the feathers, the low-pressure slipstream does not form, and the vortices affecting the cylinder are weaker.

According to Bottaro, artificial feathers could be added to aircraft or underwater vehicles to improve their efficiency, though they might need a self-cleaning system to mimic the way birds preen their feathers to ensure efficient performance.