A bee and a jumbo jet: common sense would tell you that the tiny insect couldn't possibly cause any troubles for the massive airplane, right?
Actually, no. Bees can cause trouble. So can mosquitoes. Even lowly gnats.
When flying insects get in the way of an airplane's wing during takeoff or landing, it's not just the bugs that suffer. Those little blasts of bug guts disrupt the laminar — or smooth — flow of air over the airplane's wings, creating more drag on the airplane and contributing to increased fuel consumption.
That's why a group of researchers at NASA's Langley Research Center — the "bug team" — recently ran several flight tests of coatings that may one day reduce the amount of bug contamination on the wings of commercial aircraft. Over the course of a few days, the bug team put the coatings through a series of real-deal takeoffs and landings on NASA Langley's HU-25C Falcon aircraft.
"The reason we do these tests at low altitudes or do a lot of takeoffs and landings is because bug accumulation occurs at anywhere from the ground to less than 1,000 feet," said Mia Siochi, a materials researcher at NASA Langley.
Bug accumulation not only costs the airlines more money because of increased fuel burn, but it can also lead to increased pollution as that fuel is burned. Both issues are important to a team that's doing this work as part of NASA's Environmentally Responsible Aviation (ERA) project.
For each flight test, researchers attached surfaces covered with engineered coatings and then an uncoated "control" surface to each wing of the HU-25C. In all, researchers tested eight coatings.
"We fly [test] controls and assume that if the other surfaces were not coated they would get the same density of bug strikes," Siochi said.
In other words, if the engineered coatings came back with fewer bug splats on them than the control surfaces, they're working. And Siochi and her team did, in fact, find that the coated surfaces had fewer and smaller splats.
That's right, size was important, too. One of the notable differences in the characteristics of insect residues between coated and uncoated surfaces is the smaller area of the residue. In some cases, residue heights were also reduced. The combination of lower residue height and smaller splat area can help reduce disruption in laminar flow. Smaller splats also increase the probability that the contaminants will come off during flight and keep the wing surface clean.
Even if this round of flight tests bolsters the case for the use of NASA Langley's bug coatings, it will probably be quite some time before they end up on commercial airliners. In addition to reducing the number and size of bug residues, the coatings have to be durable enough to withstand a lot of time in operation — years even. So some of the more promising surfaces are undergoing environmental durability testing in conditions that mimic rain, humidity and ultraviolet radiation.
There's also cost to consider. Siochi says the savings in fuel have to be enough to make up for the cost of applying the coatings.
"So we have to get through that hurdle of practical application of these materials," Siochi said.
In the meantime, NASA's dealing with lots of bug guts. That may seem like a gross job to some, but Siochi's fellow researcher John Gardner doesn't mind at all. He rode along on the flight tests to keep an eye on the coatings and watch for any anomalies. Finding bugs to fly through in the hot, humid Virginia weather was easy, Gardner said — fun, too.
"I've done other research projects," Gardner said, "and this is definitely the most fun I've had."