Max T/O Thrust Bleeds OFF / ON and N1

[Breakthesilence]

Hi guys,

I was going deeper in my full-of-bugs mind reasoning about the Maximum T/O thrust with Bleeds ON and OFF (or Packs ON / OFF, depends on the aircraft model and procedures; for simplicity, I will mean also Packs ON / OFF in the following)

Let's say, you have an Engine rated 22K.
Given 15°C OAT and Sea Level, your maximum T/O thrust should match this rating.
As you get additional thrust configuring with Bleeds OFF, it should be correct to think that 22K are reached in this configuration, so with Bleeds ON you are producing less than 22K.

Why can't we increase the Bleeds ON N1, to reach 22K?

It is supposed to have more thrust with Bleeds OFF, and that is actually, but the engine is able to run faster (There's no "N1 Limit with Bleeds ON") so what's the matter?

Is it a problem of engine construction and parameters which forbid us to run it faster than a specific N1 or to produce the Max Rating with Bleeds ON?

[tdracer]

What typically is done is, the max rating is bleeds off. The max N1/EPR rating has a 'debit' for bleeds on. This is done to protect margins (EGT, turbine inlet temp, etc.).

The thrust and N1/EPR is not significantly affected by the bleed, but the max rating is. You could still potentially obtain the same thrust by setting the no-bleed N1/EPR with bleeds on (assuming the FADEC lets you) but you would be technically overboosting the engine and have the potential for a limit exceedance.

[Breakthesilence]

Thank you :ok:

In simple terms, it is not designed to run faster than the N1 setting provided in certain atmospheric conditions with Bleeds On.

[FE Hoppy]

It may well be the compressor casing which is limiting max rated thrust. As the bleed is normally taken from the latter compressor stages the pressure required to ensure enough air entering the combuster may well be beyond the capability of the compressor casing.