If you've heard a whole
lot about the F-35 engine fires but are a little unclear on what
happened, the head of the program did a pretty good job of explaining
the cause and the planned fixes.
Air Force Lt. Gen.
Christopher Bogdan, who heads the F-35 program, said the engine failure
and subsequent fire that halted testing of the F-35 were the result of
micro fractures in one of the three-stage fan sections that compress air
before it enters the engine, reported the Pentagon's news agency
Friday. These sections are lined with a polyimide material designed to
rub against fan blades to reduce pressure loss.
The investigation into
the F-35 engine fire that temporarily caused the fleet of fighter planes
to be grounded this summer found the third fan rubbed well above
tolerance during maneuvers several weeks before the failure, causing the
blades to heat to about 1,900 degrees — 900 more than ever expected,
Bogdan said. This led to tiny fractures in the titanium part of the
rotor, which grew over the next few weeks of flying before finally
failing.
The result? The rotor separated from the airplane. And as pieces of the engine flew out through the fuel tank, the fire ignited.
The F-35 is made by Lockheed's Fort Worth-based Lockheed Martin Aeronautics unit at the company's massive facility there.
Engine manufacturer Pratt
& Whitney came up with two short-term fixes that will keep the
planes in the sky until a permanent solution comes. For the first, a new
engine is worked to "burn in" the rubbing in a controlled environment.
That process has already been used on four test airplanes.
The second fix involves a
change to the manufacturing process of the engine, eliminating the
rubbing on the polyimide lining completely by "pre-trenching" the
lining. That worked great, Bogdan said, but the process of replacing the
engine takes about a week. That makes the alternative burn-in approach
essential for getting planes in the air in the meantime.
Long term, Pratt &
Whitney is mulling a few options in addition to the pre-trenching
approach, from changing the polyimide material to one that can handle
more heat, to treating the tips of the titanium fan blades to withstand
more heat, to some combination of the options.
Bogdan estimated it won't
be until near the end of 2015 before engines are coming off the
production line with the chosen solution. Once that happens, he added,
any engines that are not in airplanes yet will be retrofitted.
Bethesda-based Lockheed
Martin Corp. hasn't been hurt too much by the testing delays. Bruce
Tanner noted during a media call to discuss third quarter earnings that
despite being grounded for a month and a half, the F-35 was still close
to meeting its delivery goals.
As for Pratt and Whitney,
sure, the company will have to swallow the costs for the fixes. But as
Reuters reported last week, it also announced it had won a contract to
build an eighth batch of 48 engines for the F-35, bringing the total
value of the deal to $1.05 billion.
- Source: http://www.bizjournals.com
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