Timing is everything. Bad timing is breaking your engine on the very day your customer tries for a third time to cancel your rival and a new report rubbishes the benefits of competing engines. But that’s what happened to Pratt & Whitney on February 4, when a turbine blade on an F135 Joint Strike Fighter engine broke during “proof testing”. That was the day the Pentagon told Congress it still intends to cancel the General Electric/Rolls-Royce F136 alternative engine.
The blade problem is not news. That’s why the engine was being proof tested, to see if it was susceptible to a unique blade vibration that causes high-cycle fatigue. This follows a blade failure on a test stand in August last year. What is news is that this latest incident will delay the first flight of Lockheed Martin’s F-35 STOVL JSF, which was scheduled for mid-year.
The two blades that have failed so far were in STOVL F135s – Pratt thinks the problem is tied to the heavier load on the third turbine stage in the STOVL engine, because the low-pressure turbine has to work harder to power the shaft-driven lift fan. The latest engine to fail was to power the first F-35B – aircraft BF-1 – now Pratt will have to proof-test a replacement engine, which will delay the start of STOVL ground testing by a month – maybe more, they don’t know yet.