smartt1982
Topic Author
Posts: 226
Joined: Sat Nov 24, 2007 11:17 pm

### Assumed Temp, So How Does It Really Work?

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!

tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

### RE: Assumed Temp, So How Does It Really Work?

 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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