Pratt & Whitney is rolling out software and hardware fixes this summer that will reduce PW1100G start-up delays to between 90s and 100s, down from about 3min, the company tells Flightglobal. The modifications come after some customers expressed dissatisfaction with a thermal issue that can cause the geared-turbofan engines to have much longer start-up delays than the industry standard of less than 1min. The PW1100G’s start delay can be 3min, or 6min for a dual-engine start, P&W says. By comparison, CFM International has said its Leap-1A needs around 50s to cool before starting-up...
After the engines are shut down, rising heat causes a “temperature differential” between the top and bottom of the engine, which can cause a “slight bowing of the rotor” as the engine’s metal expands at different rates, he says. The degree of bowing depends on factors including ambient air temperature and is only the “thickness of a hair”, Bromberg says. Still, if the engine is started when the bowing is at its worst, a “harmonic vibration” can develop, he says.
”The engine will bounce a little… to the point where it can eat into the seals that are surrounding the blades,” according to Bromberg. A software fix already incorporated into the engines measures how long the engine has cooled, and, if needed, causes the engine to initially spin slowly during a start, allowing the “temperature to even our across the motor”, says Bromberg. Hence the 3min start.
P&W is further addressing the problem by applying a coating to some engine blades and strengthening the engine's third and fourth shaft bearings to prevent the harmonic vibration, Bromberg says. "Then ultimately we are going to put coating on some of the blades that will improve the sealing function in the compressor," Bromberg says.
...Qatar chief executive Akbar al Baker had even threatened to cancel PW1100G orders in favour of Leap-1A powerplants, though earlier this month Al Baker expressed confidence P&W has addressed his concerns. Bromberg says the geared turbofans have a 99% dispatch reliability rate and are meeting thrust, fuel burn and noise expectations.
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