NASA recently tested non-stick coatings on Boeing’s ecoDemonstrator 757 that could eventually help aircraft become more fuel efficient by reducing insect residue that creates a surprising amount of drag.
NASA and Boeing engineers spent about two weeks in Shreveport, LA, testing non-stick wing coatings designed to shed insect residue and help reduce fuel consumption. Researchers with the Environmentally Responsible Aviation (ERA) Project assessed how well five different coatings worked to prevent insect remains from sticking to the leading edge of the airplane’s right wing.
Because most insects fly relatively close to the ground, NASA explained, the 757 made 15 flights from the Shreveport Regional Airport that each included several takeoffs and landings. Shreveport was chosen in part because of its significant bug population, and the crews worked around storms and winds to ensure the bugs would be present.
“One of the five coating/surface combinations showed especially promising results," said Fay Collier, ERA Project Manager. “There still is a lot of research to be done, but early data indicated one coating had about a 40% reduction in bug counts and residue compared to a control surface mounted next to it.”
Bug residue causing drag has long been a challenge for the aviation community, according to Mia Siochi, Senior Materials Scientist at NASA’s Langley Research Center in Hampton, VA.
“Laminar aircraft wings are designed to be aerodynamically efficient,” she said. “If you have bugs accumulating, it causes the airflow to trip from smooth or laminar to turbulent, causing additional drag. An aircraft that’s designed to have laminar wings flying long distance can save 5-6% in fuel usage. Surprisingly, all you need are little bugs that trip the flow and you lose part of this benefit.”
Prior to development and testing of the non-stick coatings, the researchers studied bug chemistry and what happens when an insect hits a surface at a high velocity.
“We learned when a bug hits and its body ruptures the blood starts undergoing some chemical changes to make it stickier,” said Siochi. “That’s basically the survival mechanism for the bug.”
Materials scientists then turned to nature—lotus leaves, in particular—to create the right combination of chemicals and surface roughness in the test coatings, Siochi added.
“When you look at a lotus leaf under the microscope, the reason water doesn’t stick to it is because it has these rough features that are pointy,” she explained. “When liquid sits on the microscopically-rough leaf surface, the surface tension keeps it from spreading out, so it rolls off. We’re trying to use that principle in combination with chemistry to prevent bugs from sticking.”
The best-performing coating is an epoxy with fillers—this is all Siochi, through the Langley communications team, could share about its make-up. “Our materials scientists can’t say more until the patent process is complete,” the spokesperson relayed.
Engineers at Langley developed and tested more than 200 coating formulations in a small wind tunnel, then took a number of those to flight on the wing of a NASA jet. They selected the best candidate non-stick coatings to fly on the ecoDemonstrator, while a team comprised of experts from NASA, Boeing, the U.S. Department of Transportation, and University of California-Davis identified the best location for testing.
Where does the project go from here? “We are talking with possible industries about commercialization,” according to the spokesperson. “Any product applications would be up to industry and aircraft manufacturers.”