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danieln

FLEX/assumed temps.

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Hi guys, Just wondering, how does one calculate the most appropriate assumed outside temperature for derated takeoffs? I can see there are Assumed temp limit charts and N1% difference charts for various derates available in the ops manual, but how do we actually go about calculating the more optimum assumed temperature for a takeoff? The tutorial flight provides a very elementary explanation to flex temps but it doesn't talk about deriving specific numbers. For example when 40C is used for OAT 15C Never really cared about it before the NGX came out, but since service based maintenance failures occur I guess the stress on the engines is simulated to some extent? (or not?)

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One word: http://www.topcatsim.com/ If you want to play with it though, take a good size runway and aim for something like 92%N1, then see what suits you best D-TO1 or D-TO2 or a mix of assumed temp and D-TO. Topcat has me often take off with flaps 1 and then assumed temp of about 45-50 degrees. It extends the life time of engines a lot! So better use up more asphalt than engine! Hope it helps happy.png

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The easiest way is a payware option: TOPCAT takeoff and performance tool.It will figure the best derate (either assumed temp, or derated, or both!) option for you based on your aircraft weight, airport runway criteria, and weather. Very painless, no looking up info on charts, and it's very accurate because it's based on the real world NG data.

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One word: http://www.topcatsim.com/ If you want to play with it though, take a good size runway and aim for something like 92%N1, then see what suits you best D-TO1 or D-TO2 or a mix of assumed temp and D-TO. Topcat has me often take off with flaps 1 and then assumed temp of about 45-50 degrees. It extends the life time of engines a lot! So better use up more asphalt than engine! Hope it helps happy.png
Thanks for that, I'll definitely be checking that out! With the PMDG failure simulation, are engines constantly used without adequate derating more likely to fail quicker than those which are, or - are serviced based failures purely based on hours of use and completely disregard engine stressing?

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I believe it's one of the things it monitors. It says in the manual that this function will take note of how the aircraft is used IE hard landing etc. So I would think they programmed it to notice wear and tear of the engine.

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