Nov 4, 2014

F-35 engine fix coming

The head of the F-35 program, said by the end of December he expects to have decided on a permanent solution for a design issue that caused an F-35A engine to fail in June at Eglin Air Force Base, Florida.
The engine's manufacturer, Pratt & Whitney, has offered several potential fixes, some of which already are being tested.
The engine failure and subsequent fire were the result of micro fractures in one of the three-stage fan sections that compress air before it enters the engine. These sections are lined with a polyimide material that is designed to rub against the fan blades to reduce pressure loss.
In the case of AF-27, the third fan rubbed in excess of tolerance during maneuvers several weeks before the failure, causing the blades to heat to about 1,900 degrees -- 900 more than ever expected. This led to micro fractures in the titanium part of the rotor, which grew over the next few weeks of flying before finally failing.
The fire led officials to ground the aircraft July 3 for fleet wide engine inspections. The aircraft returned to limited flight July 14 when no systemic issues were found.
Two short mid-term fixes have already been validated.
For the first, a new engine is flown in a defined profile that subjects it to a specific set of altitudes, airspeeds, G-forces and roll rates.
The second method involves a change to the manufacturing process of the engine..
The new design already has been flight-tested on AF-2 and AF-4, which are developmental testing jets.
All 19 developmental testing aircraft will have undergone either the burn-in or pre-trenching retrofitting by the end of December.

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