Reduced N1 = Full N1 x Square route of (Ambient temp / Assumed temp)
...this from Chris Brady's web page.
This formula does not take into consideration the aircraft mass and available runway - so there HAS to be something more to it. How does the FMC use the excess runway available, and actual take-off mass, to calculate the N1 for take-off?
Does it do a series of calculations or interpolations? Is it really a single formula? What have I missed?
I think I may see the misunderstanding, and this may expose a misunderstanding of my own so please feel free to correct me.
Assume you enter an assumed temp figure of 54 degrees into the FMC, the FMC thinks to itself "hmmmm, what N1 can my engines safely produce at 54 degrees" and comes up with a figure unrelated to weight, location, runway in use, wet/dry, field elevation etc. So really it can be thought of as a
power setting. Now to the runway analysis book, someone ages ago sat in a dark room and looked at the runway slope, the obstacles in the take-off path, the TODA, TORA, etc etc etc and decided on what
power setting you need for certain temperatures and weights and combinations thereof.
So the assumed temps of 30 degrees through to 60 degrees could be thought of as power setting 1 through to power setting 30. And some poor sod has worked out which power setting you need for that particular runway with that temp and at that weight (of course there are the QNH and wet runway adjustments as well).
That is how I think of it. I have to admit I have pretty much come to these conclusions on my own so if they need adjusting I am open to wise and constructive input
