Thanks for your post
HazelNuts39
If I set a certain N1 setting for take off and do not move the thrust levers as I climb, what will the N1 display show (assuming no autothrottle etc.)?
That depends on the display. In most cases it will show actual N1 increasing as the engine spools up, settling at the N1 that you have set (assuming that your engine is N1-controlled).
I understand what you are saying, and I realize it is correct, however it is not really the answer I am looking for. I think you might have misunderstood my post just a little. The thing is that I am trying to understand the basics of how engine thrust and fan speed is affected by increased density altitude in a pure aerodynamic sense, disregarding any autothrottle or FADEC systems or specific technicalities.
I know some things can't be oversimplified, but yet..
Also I might have worded myself poorly. When I said "set a certain N1 setting" I didn't mean set the N1 as a permanent setting or in a computer or whatever, I meant move the throttle levers so that we have a specific N1 power setting at sea level on take off (again disregarding any FMS etc to control performance on T/O or climb or whatever)
Let me try again to make myself more clear:
We are on the runway and move the thrust levers 3/4 forward. We take off and climb and do not move the thrust levers from their position. Will the N1 that we had on the take-off roll at sea level increase or decrease?
As I said in my previous post, if I understand correctly the N1 percentage displayed will decrease, correct? So for a given throttle lever setting RPM will decrease with altitude, which means that we need to move the throttle levers forward to keep the same N1 setting as we climb.
If we again disregard any FMS or FADEC etc., this will mean that as we climb, engine performance will deteriorate due to higher density altitude / lower density? Does this not always apply? (you wrote see previous posts, but I couldn't really find an answer to this, probably because some of the replies given might have been a little too complicated for me to understand, so if you care to point me in the right direction on this I would appreciate it)
P.S. Density depends on pressure and temperature. It is usual to separate these parameters, since they have distinctly different effects on engine performance, as explained in earlier posts.
This to me is very interesting. When you say this, are you referring to the issue where some engines are EGT limited, and with a lower temperature can increase power output? In that case I understand what you are saying, but just to confirm, is it not still correct to say that as long as density altitude increases, if all other factors stay constant, engine performance will decrease?
Thanks