When dogs get wet, they give their coats a good shake to get rid of the water. The same approach could work for aircraft when ice collects on their wings during cold weather.
When ice builds up while flying through cloud, rain or drizzle it alters the aircraft鈥檚 handling, making it more difficult for the pilot to control. This is because ice roughens the wing surface, increasing drag and decreasing lift. An aircraft may even lose so much height that it crashes, as happened in 1994 at Roselawn, Indiana, when 68 people died.
Large aircraft such as Boeing 747s can direct hot engine air onto their wings to keep them ice-free, but smaller planes carrying 100 people or less cannot spare the fuel. Instead, the wings have built-in electric heaters to melt the ice, or rubber strips that inflate to break it off. Both these fixes require expensive structural changes to aircraft wings, and electric heaters are inefficient and power-hungry, using around 10 kilowatts for each square metre they de-ice, which still drains fuel.
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Yueh-Jaw Lin and Suresh Venna at the University of Akron in Ohio believe fitting piezoelectric actuators to the leading edge of wings, which vibrate in response to an alternating current, could do the job more simply and efficiently. They have tested their idea by putting ice patches on sheets of composite material and aluminium leading edge wing structures like those used in aircraft.
They found that small patches of piezoelectric crystal, 3 millimetres thick, could easily shake off the ice, while using only 10 to 15 watts per square metre. The set-up works because stresses along the vibrating wing break the bond between the surface and the ice, and it simply falls off. 鈥淧lacing just three or four actuators in the right places could protect a whole wing without big modifications,鈥� says Lin.
Early next year Lin and Venna are planning to test their technique on scale models of commercial aircraft in a wind tunnel at NASA鈥檚 Glenn Research Center in Cleveland, Ohio. The tunnel uses a stream of cold air carrying water droplets to mimic cold, damp weather.
Peter Render, who investigates such systems at Loughborough University, UK, says the vibrating system will be most useful if it can prevent ice forming in the first place. 鈥淚t will be interesting to see if it can do that in the wind tunnel by stopping droplets sticking to the wing,鈥� he says.
