A bearing in the shaft-driven lift fan of the short take-off and vertical landing (STOVL) propulsion system for Lockheed Martin's X-35 Joint Strike Fighter concept demonstrator has failed during engine ground testing at Pratt & Whitney.
The bearing failed after 67h of testing, equivalent to about 18 months of service life or about 800 hover events, says Lockheed Martin. The failure was not unexpected, the company maintains, as tell-tale metallic contamination had been detected in the lift fan lubrication system during oil tests conducted after each propulsion system run.
The failure was "not catastrophic", Lockheed Martin says, and was contained within the bearing housing. Another Rolls-Royce Allison-supplied lift fan is to be fitted to the engine. Ground testing is set to resume in April.
Lockheed Martin does not yet know what impact the delay will have on flight testing of the STOVL X-35, set to begin in the third quarter. The biggest impact will be on the development of software for the integrated flight and propulsion control system, which requires data from the engine ground tests.
The lift fan had already accumulated twice the running time of any previous unit, says Lockheed Martin, adding it has been "pleased with the durability of the fan".
Source: Flight International
