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undctiatc

N1/N2 %

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Hello all,

 

When I depart, I bring the thrust to 40% N1 stabilized then 50% and engage auto throttle.  Fully loaded on the T/O1-CLB1 profile N1 will stay at 97% or around there but N2 is 109% or greater.  Something inside tells me running that big of an engines compressor at 109% is not good.  Everything is autopilot managed on takeoff with LNAV and VNAV modes engaged.

 

No alarms go off so should I not worry about it?

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Hello all,

 

When I depart, I bring the thrust to 40% N1 stabilized then 50% and engage auto throttle.  Fully loaded on the T/O1-CLB1 profile N1 will stay at 97% or around there but N2 is 109% or greater.  Something inside tells me running that big of an engines compressor at 109% is not good.  Everything is autopilot managed on takeoff with LNAV and VNAV modes engaged.

 

No alarms go off so should I not worry about it?

Often this is correct and not an error as the N speeds can vary based on temperature. Now if your N1 was 109%, then that's a different story. Another factor might be the way the engine was originally tested, a good example is the space shuttle, where they discovered that the engines were fine up to about 104%, instead of redoing all of the tables and data and calculations to use 104 as the new "100", they simply said, its fine to go up to 104, and extrapolated the tables to match. (this is simplified version) 

 

I believe there are even some scenarios the 777 N1 can be a touch over 100%

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As the limitations chapter of your manual sais,

 

Limits are red.

Cautions are amber.

(exact number are not given)

 

As long as you dont exceed the reds.....you are good.

 

For the GE90-90B the limits are:

N1 - 109%

N2 117%

EGT redline - 1030C

EGT amber line - 1015 (max continuous thrust limit)

(I have not checked the limits on our PMDG777 engines, but I am sure Google would find something)

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