De-icing planes in the air

Photo courtesy of Virginia Tech

De-icing a plane at the airport prior to takeoff is familiar to winter travelers, but planes also experience plummeting temperatures and rapid ice formation in flight. Once ice forms on the wings, it can inhibit a pilot’s ability to safely operate the aircraft by disrupting airflow over lifting surfaces. Researchers believe equipping planes to remove ice while flying at altitudes from 35,000ft to 42,000ft would provide a better way to maintain safety.

Jonathan Boreyko, associate professor in Virginia Tech’s Department of Mechanical Engineering, is leading a team working with Collins Aerospace to use ice to control ice formation on airplane wings.

In a study published in Physical Review Letters, Boreyko’s team leveraged Cassie’s Law, which shows air can be trapped under water drops if the drops are suspended atop a structure that’s bumpy and water-repellent. With a structure that could trap air underwater, the researchers seek to make ice form in a layer with less surface adhesion.

Making a surface water-repellent typically requires a chemical coating that must be periodically replenished, and the bumpy surface also wears. The team took an approach that doesn’t require fragile chemical coatings or ultra-fine bumps, opting for a simple, durable structure of millimeter-sized aluminum pillars.

Pedestals 1mm tall by 0.5mm wide were machined into a pattern, set 1mm apart. As the temperature dropped, frost preferentially grew on the pillar tops, producing elevated frost tips. As more water was added, it was absorbed into the porous frost layer. When water drops subsequently impacted the surface, they were caught on the frost pedestals.

Lead author Hyunggon Park says the freezing drops created tiny ice bridges that sealed air gaps in valleys between the frost-tipped pillars.

“The water drops were being caught by the frost tips and building ice bridges to trap air pockets underneath,” Park notes. In time, a continuous and air-trapping ice canopy formed over the frost-tipped pillars.

Other de-icing methods may still allow a sheet of ice to adhere more directly to a large surface, but these trapped air gaps suspend the sheet, lowering the adhesion ice has to the surface.

“By using larger pillars in place of nanostructures, and frost tips in place of a hydrophobic coating, we found we can get the same benefit of trapping air underneath the forming ice while avoiding the durability concerns,” Boreyko says. “This should make our approach practical for enhancing de-icing on aircraft or heat exchangers.”

With a weaker bond, it’s possible to use the air pockets to then push ice away. This will be the next step in the researchers’ process, as Boreyko’s team continues to develop their method.

Virginia Tech College of Engineering Dept. of Mechanical Engineering