Experimental wires repair themselves
As part of its initiative to combat the problems associated with aging aircraft, the FAA has funded a suite of projects at the University of Dayton Research Institute (UDRI) that includes self-healing wires, smart clamps and radio wire fault detectors. The goal of the project is to eliminate the time-consuming task of tracing wire faults.
UDRI research chemist Robert Kauffman is developing wires that can repair themselves after they are damaged. He has developed a non-toxic, water-based solution called Patch–for power-activated technology for coating and healing–which the editors of R&D Magazine recently honored as one of this year’s most technologically significant new products, and has already received a commercial licensee. The inexpensive solution contains a polymer–similar to white craft glue–that could be embedded in wiring insulation. When the wire suffers a fault, its arcing electricity acts as a catalyst to trigger a chemical reaction. The polymer then reacts with ambient moisture to form a chemically bonded skin over the breached area. “If it’s simply hairline cracks in the insulation, this healing takes about a couple of seconds; if you have a scrape where you’ve removed, say, a couple of millimeters of the insulation, that might take 20 to 30 seconds,” said Kauffman.
Michael Walz, electrical systems program manager at the FAA’s William J. Hughes Technical Center in Atlantic City, N.J., is enthusiastic about the results. “The nice part about this is that as it starts to repair, it starts to increase resistance, and as it increases resistance it gets rid of a lot of the fault current, actually reducing the severity of the issue.”
The researchers are investigating ways to incorporate the polymer into new wires. “According to the wiring people we talked to, it should be pretty simple to do. You simply pass the wire through the water solution and then place it in a drying tower,” Kauffman said. He added that this would not be a significant departure from the current process, under which some adhesive is applied to the copper to make the insulation stick to it. Kauffman’s polymer solution, which has adhesive properties, would merely be used as a substitute. Kauffman was able to convince the U.S. Navy to produce an initial 2,000-yard run of the wire as part of a wire manufacturing trial the service was conducting. Several hundred feet were sent to the FAA for testing. “If it actually becomes a wire, it will become a wire standard,” said Walz. “Aircraft designers can look at it and see if they want to use it.”
Another application of the patented process would be spraying the solution directly into a compartment where there is a known or suspected fault. “Since most wiring is inaccessible… what we want to do is come up with a repair solution that is totally non-toxic and can just be misted into a compartment, so that the reaction occurs wherever it finds exposed wiring or cracked insulation,” said Kauffman.
Researchers have not yet determined how long the repair would last, said Walz. “We’ll give it the full rigors of a normal wire. If it can pass everything a normal wire does, if it can chemically bond and it’s just as good as the wire insulation and we can prove it with data, then it would be a permanent fix.”
Immediately after the R&D list was unveiled, the University announced it had commercially licensed the self-healing wire technology to Ohio-based Pinnacle Systems, which is preparing for sample production. According to Joseph D’Angelo, Pinnacle’s chief technology officer, preliminary conversations have already been held with a commercial aircraft builder, but the new technology will require qualification and testing, which could be more than a year away.
“We’re looking in the next year-and-a-half to have something that customers can touch and feel and see how this meets their needs,” D’Angelo told AIN, adding that the establishment of actual production could take up to two years. “That’s the worst case, assuming qualification is a bear. A lot of it is dictated by the industry.” The company hopes to be able to produce the self-healing wire at a cost to consumers not much greater than that of regular wire.
More Tools in the Fault Fight
URDI is also investigating new technologies aimed at preventing damage to wires and cable bundles due to clamp failure. “Once a clamp breaks, the wires start to sway and hit structures, and that’s when you can get a lot of damage,” said Kauffman. “Not only does structure such as the edge of a rib damage the insulation, but it also provides a ground for the electricity to arc to.” One solution the Dayton team has come up with involves adding to the bundle a piezo electric wire that can sense vibration. If the vibration pattern becomes abnormal, it could be a signal that the bundle is no longer properly secured.
A second project for which the university is seeking a patent involves embedding in the clamps themselves sensors that would send out a signal if they were damaged or otherwise incorrectly attached, along with their location. “The basic idea is that someone can just walk along an airplane, take a reading and quickly find out if any clamps have broken,” said Kauffman, who is looking to apply a newly awarded $100,000 FAA grant toward developing a prototype.
Another possible time-saving technology was discovered by accident while Kauffman served as one of the researchers investigating the 1996 explosion of TWA Flight 800. During his experiments searching for a spark that could have ignited the empty fuel tank on the aircraft, Kauffman found that certain metals carrying electricity in the presence of water undergo an electrolytic reaction. “You could see the water start to bubble and at the same time the AM radio I was listening to [started to buzz with] static,” he said. “The moment the reaction stopped, the radio would come back.” During that process, Kauffman discovered, radio frequencies were being emitted. His goal now is to create a handheld radio fault-detection device that would allow maintenance technicians to target damaged wires quickly.
The researchers hope to earn enough funding for them to produce working test samples of all these systems. “You don’t know where this stuff is going to lead you, especially in the early stages,” said Walz. “Repair techniques we’re looking at can help maintenance [people] quickly, and that’s where I really hope some of this shakes out in the near term.”