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follow-up thread -> Bleed air load (incl. Anti-Ice) and effect on engine parameters


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Firstly, I apologize for re-opening this topic, but the initial thread got closed with my claim dismissed without leaving me the opportunity to clarify so, here we are.

Initial post:


What I would like to add following Nico's feedback:

1/ Regarding initial post

My report concerns in-flight/hi power settings behavior (climb/cruise), I agree that on ground the impact is visible.
See below screeshots, notice how the N1/N2/EGT... remain identical.




2/ Regarding N1 effect on ground:

- I need to check more papers on the CF6 version - but on the PW, you have a modulating idle concept where the idle setting increases to match the bleed pressure demand. Bleed pressure demand increases with air conditioning load, and anti-ice systems. See FCOM Chap. 1.17.20

- In case the N1 remains the same, you should still see a change in EGT, FF and N2 (because you are taking power from the engine).


3/ Regarding in-flight effects

- FCOM Chap. 1.13.30 mentions (on PW at least) a decrease of Thrust Limit relative to bleed load. 

- For the same reasons stated above and in original thread, increasing bleed load (by the use of anti-ice, or running both packs from the same engine etc) should have a visible impact on EGT/N2/FF/N1. You are taking power from the engine, the power you take is power that won't be used to spin the turbines. Your efficiency decreases, at a given fuel flow, you will have a lower N1 and higher EGT. And a lower N1 will reduce your thrust (and therefore impact climb rate).

Note: Only FCOM references are posted in order not to post copyrighted material publicly, more details can be provided by PM.

Hopefully it is clearer this time.


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