Originally Posted by
Hilife
How would lowering the collective (that is, reducing power) help to cool the engine? I understand that it is less fuel, but less fuel means a lower Ng, so less air coming in since the compressor is now giving a decrease in air pressure.
So in a sense isn't fuel flow proportional to Ng which means a nearly equal TOT would occur?
You kind of answered your own question in your first paragraph.
Lowering the collective reduces the load on the PT/N2/NR, which, without a corresponding reduction in fuel flow (Wf, governed by the FCU), would result in a PT/N2/NR increase. As such the FCU automatically reduces Wf, which results in a corresponding reduction of Ng/P3 & ITT.
So in a sense isn't fuel flow proportional to Ng. Yes and no. As a result of a number of factors, the correlation between Wf and Ng is not always a linear function.
I believe your last sentence is what stumps me. How could fuel flow and Ng not be linear assumed they are controlled by the FCU. If i could grasp how they are different, I believe that would help to answer the root of my question. I appreciate your reply!