Nov. 19, 1998 CHAMPAIGN, Ill. -- Researchers at the University of Illinois have identified an aircraft wing that may be hazardous to your health. The wing -- similar to the kind used on some commuter aircraft -- is highly susceptible to certain icing conditions thought to be linked to some fatal accidents.
"Because of its design, this particular airfoil is very sensitive to large-droplet ice accretions," said Michael Bragg, professor of aeronautical and astronautical engineering at the U. of I. "These accretions can form when the aircraft flies through freezing rain and drizzle."
Using simulated ice accretions, Bragg and his students have examined the sensitivity of ice shape, size and location on airfoil performance. Their goal is to better understand how ice accretions affect the aerodynamics and control of small commuter aircraft.
"The current 'hub and spoke' system used by the airline industry has created the need for many more commuter flights," Bragg said. "And because commuter aircraft fly at lower altitudes -- where icing conditions are most likely to occur -- we are seeing an increased number of icing-related accidents."
While large jetliners can use hot air from the engines to prevent ice from forming on the wings, "smaller aircraft lack the power required for these systems," Bragg said. "Instead, pilots of commuter aircraft rely upon inflatable rubber boots along the wings' leading edges to 'pop' off accumulated ice."
Ice can rapidly form on wings when planes fly through clouds of supercooled water droplets, but the size of the impinging droplets makes a huge difference in their effect upon the aircraft. "The vast majority of icing encounters have occurred with droplet sizes of 2 to 50 microns," Bragg said. "These strike the wing close to the leading edge, where any ice buildup can be removed by the de-icing boots."
Larger droplets -- such as freezing rain and drizzle -- strike farther back on the wing surface, in a region currently unprotected by the boots. A ridge of ice can quickly form, which increases drag and decreases lift, with potentially deadly consequences.
"On this particular airfoil, we saw an 80 percent loss in the maximum lifting ability of the wing due to an ice accretion that was only three-quarters of an inch high," Bragg said. "This type of airfoil is very leading-edge forward-loaded; the presence of the ice shape essentially destroys the vast majority of this leading-edge lift."
To avert the threat that icing poses to aircraft built with this wing design, the de-icing boots should be extended back along the wing surface, said Bragg, who presented his preliminary findings to the Federal Aviation Administration. In addition, pilots should take other precautions -- such as increasing their air speed to enhance lift -- when icing conditions appear imminent.
"We have made significant progress in understanding the types of wing designs that are more sensitive to certain kinds of icing," Bragg said. "This information will be used by the FAA to improve the certification process, and by aircraft designers to design safer aircraft."
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