Has altitude something to do with FLEX??

[Robini]

Hello,
I have one question to my ''project'' that i working on and would
be happy if someone could answer this question ;)
If your altitude for todays flight would be FL400 do you need more
power than if your altitude would be FL360??
I mean if you need more power at takeoff if your altitude would
be higher??

Thanks!

[TopBunk]

Robini

If I read your question correctly, you are asking if using more power at take off affects the level you can cruise at.

If that is a correct interpretation, then the answer is no.

The take off power required will be greater in any given conditions for a greater take off mass (once that take off weight exceeds the max power reduction allowed).

The take off weight will affect the maximum achievable level for the cruise.


Does that make sense?

[Robini]

Oh , sorry if i wrote a little bit strange :ok:
But i mean do you need more power at takeoff if your altitude for
todays flight would be FL400 instead of FL360??

[Cough]

Take off power has no bearing on final cruise level. Take off power is independent of climb power which can often be de-rated. Final cruise level is dictated by a combination of winds, temp at altitude, aircraft weight and perf, sector length, airspace restrictions and traffic level, turbulence reports to name but a few.

[Mad (Flt) Scientist]

If the ONLY thing that has changed between the two planned flights is the cruise altitude then the answer is "No", because if the takeoff weight is the same, then the minimum required thrust to meet the takeoff requirements is the same.

In general, however, you would usually need less fuel for a higher altitude cruise (assuming you aren't planning to cruising at an excessively high altitude on a short route); therefore if the flight were replanned to optimise the fuel load, you would expect to have a slightly lower fuel load for the higher cruise.

Since the landing conditions will be the same, less fuel required means less weight at takeoff. So the FL400 aircraft will be slightly lighter at takeoff.

That would mean that you could use slightly less thrust for the takeofff for the FFL400 mission, IF you replanned and optimised the fuel.

[Robini]

Thanks for all answers :ok:
Have a good day everyone!