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.

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 – keep 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.

Drag race

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.

A coating of "feathers" on this cylinder in an airflow reduces the turbulence behind it (shown in orange and blue), curring aerodynamic drag by about 15%. The solid line in the graph shows the drag on the coated cylinder, the dashed line that of one with a smooth surface (Image: Alessandro Bottaro)

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