A Pratt and Whitney F135 engine undergoes altitude testing at the Arnold Engineering Development Center. (Air Force)
WASHINGTON — Part of Pratt & Whitney’s F135 engine, which powers the F-35 Joint Strike Fighter program, was damaged during a ground test in December and will need a redesign, according to the head of the F-35 program.
“You may or may not know that we managed to do some pretty good damage to an engine down in Florida,” US Air Force Lt. Gen. Christopher Bogdan said at this week’s Aviation Week conference outside Washington, D.C. He said the damage came during “accelerated mission testing” where engines are worn out on the ground in order to identify future problems.
The part in question is the first stage Integrally Bladed Rotor (IBR). Sometimes referred to as a “blisk,” the IBR is a one-piece combination of blade and disks — hence the “blisk” terminology. The IBR “blew” during a ground station test, Bogdan said. The engine where this particular crack occurred had undergone 2,200 hours of testing, the equivalent of nine years of service, according to company figures.
While Pratt has launched an investigation into the incident, the engine manufacturer is confident the problem will be relatively minor.
The company had already begun a redesign for the IBR as part of a movement to reduce overall engine costs, according to both Bogdan and Pratt spokesman Matthew Bates. The new design replaces the current hollow blade design with solid blades, which allow the company to use simpler, and hence cheaper, manufacturing techniques.
That redesign will add roughly six pounds to the engine; although the engine in question was a STOVL F-35B model, the IBR redesign will impact the engines for all three JSF variants. While weight is closely monitored on the F-35, Bogdan did not seem concerned about the extra weight.
“We conduct Accelerated Mission Testing on our ground test engines specifically to discover any issues early and prior to occurrences in flight,” Bates wrote in a statement. “Our investigation is ongoing, but we have determined this incident does not pose a flight safety risk and will have no near term impact to the operational fleet.”
“We expect that within this year that fix will be done, we’ll put it back on an engine and do the [qualification] testing some more,” Bogdan said. “We will cut that into production sometime in the next year.”
“The retrofit not all that significant. You just take the module out and put the new blisk in,” Bogdan said. “We would have liked it to happened at the one in a half or two time life but it happened just near the end of the first life, so we need to make sure we fix it so the engine goes full life.”
“Now we’re talking about whose going to pay for this and what the contract language needs to state going forward in the future, for any future concurrency,” Bogdan added.
Bogdan also touched on previously reported cracks to the bulkhead of an F-35B ground testing model, noting that finding cracks is part of the purpose of running those tests and promising that more cracks will be found during future life-cycle test.
“We planned for it, we budgeted for it, [and] we have the timespan to fix them, but it’s going to happen,” he said of future cracks.■