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markadeane

Thoughts on the 737NG / CFM spool down time

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Hi all,Firstly, I purchased 737NG yesterday and I'm a convert. I spent a week or so trying to decide on the best payware small-to-medium airliner and the quality of this product completely validates my choice! If there's anyone reading this who is in the same position, trust me, this package is the one you want. Look no further.I have one question though, I am aware that the engines on the 300/400 models takes somewhere in the region of 3 minutes to spool down from idle to completely stoppped. The PMDG model comes to a stop rather more abruptly. Is that an accurate reflection of the CFM engine behaviour on the 600/700 or is it something that wasn't / couldn't be modelled accurately?Just curious, and seriously, 10 out of 10 guys, this package is fantastic!

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I am sure that the engines actually take longer to spool down than has been modelled. And I would guess the lack of modelling is due to extreme difficulty to reproduce that effect as I have never seen it exhibited in ANY flight model much less one of this high caliber.Roger CurtissCleveland, OH

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The 3 minutes you mention is the time in the manual stated to allow the engines to idle prior to shut down ie leave them running to allow temperatures to stabilise in all parts of the engine prior to shutting the engine down. THis apparently is to avoid a situation known as thermal shock and also turbine seal rub (all terribly techie- all we need to know is that if we have a sensible taxi speed we can close the power levers coast onto stand, do the vital actions and we should roughly have let 3 minutes pass then pull the start levers!)The engines actually spool to a stop pretty quickly but this is dependant on wind as they can easily be blown round bu tthe wind as they are very free to turn. Hope that helpsKris

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Fair comment Kris,I live in Wellington, New Zealand. Wellington has a reputation as one of the windiest places in the country and admittedly that could have a *very* big influence on the spool-down time!

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MarkWe work on the premise that when N1 goes below 10% it is safe for people to approach ie this is when we turn off the Anti-collision lights. In some windy airports you may find the N1 stage (fan at the front) never actually comes to a complete halt. Kris

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