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Assumed Temp, So How Does It Really Work?  
User currently offlinesmartt1982 From United Kingdom, joined Nov 2007, 225 posts, RR: 0
Posted (1 year 9 months 1 week 4 days 18 hours ago) and read 2835 times:
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Can anyone guide me to some good material written up about the principle of assumed temperature and how it works.
It is just that the material I have come across and when I was thought it has been a bit vague. I would really like to know about how exactly it works. Of course I have heard of the age old “we trick the FMC into believing it is hotter than it is”. But as was rightly pointed out by someone was “well why don’t the engines go right up to full power when we set take off power”.
Also for the airliner guys/girls out there, when you use assumed thrust, do you take your take off speeds from the assumed thrust temp or for your actual weight.
In our company we assume temp but then we always take the speeds from our ACTUAL weight not from the assumed temp we have selected!

1 replies: All unread, jump to last
 
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 1, posted (1 year 9 months 1 week 4 days 14 hours ago) and read 2794 times:

Quoting smartt1982 (Thread starter):
Of course I have heard of the age old “we trick the FMC into believing it is hotter than it is”. But as was rightly pointed out by someone was “well why don’t the engines go right up to full power when we set take off power”.

Because you're not tricking the FMC, you're tricking the engine. You're telling the FMC *and the engine* to only run up to the thrust they could achieve at the assumed temperature. Assumed temperture is just a convenient "hook" into the engine to dial the thrust back.

Quoting smartt1982 (Thread starter):
Also for the airliner guys/girls out there, when you use assumed thrust, do you take your take off speeds from the assumed thrust temp or for your actual weight.

Actual weight. Using the max ATM temperature is conservative but there's nothing wrong with it.

Tom.


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