Pratt & Whitney is still evaluating several potential long-term solutions to correct a problem that led to a fire last summer on one of its engines that power the F-35 Joint Strike Fighter, the chief of the company’s F135 engine program said on April 2.
The source of the engine fire aboard the Air Force F-35A flight last summer was excessive flexing that caused the engine to overheat and develop microcracks as it rubbed against a polyimide material that creates a seal between the fan blades and the stator. The rubbing, called a rub-in or burn-in, is a normal way during flight operations to create a seal that prevents air that is compressed as it makes it way through the engine from blowing black and decreasing engine performance.
One of the potential fixes under consideration is a pre-trenching that is part of the manufacturing process and is being incorporated into new engines, which is the near-term solution arrived at last year following the fire, Mark Buongiorno, vice president of the F135 program for Pratt & Whitney, told sister publication Defense Daily during the company’s annual media day. The pre-trenching basically refers to cutting a channel into the seal material where the fan blade nears the stator as part of the manufacturing process.
“So what we’ve said is there is really an insignificant reduction in performance in the engine given the pre-trench we have today but what we’d like to do is evaluate opportunities to make that return to that other configuration” that involves a burn-in, Buongiorno said.
For the potential burn-in solutions, the company is looking at different seal materials and other configurations as a potential “to get that matched set for anything that cuts itself in during the operation,” Buongiorno said. The value of the burn-in is “you eliminate the tolerances on the rotating hardware and on the static hardware so it’s a perfectly matched set,” he said.
“Whereas when you pre-trench you have to accommodate for a certain level of tolerances,” Buongiorno said. “So that’s why engine manufacturers use a certain kind of rub in.”
Pratt & Whitney will meet with the F-35 Joint Program Office this summer to discuss the way forward with the F135 fix, Buongiorno said. He added that he doesn’t know when a decision will be made on the final fix.
The F-35 fire incident forced a temporary grounding of the aircraft fleet. However, the program schedule remains intact with the Marine Corps slated to achieve initial operating capability this summer with their F-35Bs and the Air Force next year.
Pratt & Whitney is a division of United Technologies Corp. [UTX].