Dufo
Topic Author
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N1 & N2 Over 100% In Cruise?

Mon Jul 24, 2000 2:44 am

I have a question regarding a picture found on address http://www.airliners.net/open.file?id=70059

Is it normal that N1 and N2 values are above 100%?

Regards,
Jernej
I seriously think I just creamed my pants without any influence from any outside variables.
 
JETPILOT
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RE: N1 & N2 Over 100% In Cruise?

Mon Jul 24, 2000 6:39 am

It is not uncomon for N1, and N2 limits to be above 100%.

So normal can fall anywhere below the limits.
 
Dufo
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RE: N1 & N2 Over 100% In Cruise?

Mon Jul 24, 2000 8:12 am

Tnx for this info, Jetpilot!
And I have another question related to this. What is the limiting factor on high altitude flights (let's say on a B777)? EGT, N1 or N2?

Regards,
Jernej
I seriously think I just creamed my pants without any influence from any outside variables.
 
DeltaAir
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RE: N1 & N2 Over 100% In Cruise?

Mon Jul 24, 2000 12:25 pm

I believe this can vary between airline due to the fact that the engine software can be altered, but it isn't a good idea to go over 105% due to the fact that you are red lining.
 
AAR90
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RE: N1 & N2 Over 100% In Cruise?

Mon Jul 24, 2000 2:26 pm

Not normal "in cruise", but quite normal during takeoff. Especially with older engines that have received multiple upgrades. i.e. the RB211 engines on AA's 757s have redlines at 110.0% (N1), 101.3% (N2) and 100.2% (N3); the CF6's on AA's 767s go up to 117.5% (N1) and 112.5% (N2).
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smartt1982
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RE: N1 & N2 Over 100% In Cruise?

Tue Apr 24, 2012 1:10 pm

What is the reason you can get over 100% then?, is 100% not the max?
 
113312
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RE: N1 & N2 Over 100% In Cruise?

Tue Apr 24, 2012 2:04 pm

It is not unusual that early designs of a particular powerplant establish a nominal 100% value. Later versions of the same engine, utilizing improved components, can be rated at higher power output with a higher RPM. Without changing the indicating system, the result is a power setting above 100%.

The limiting factor can be any of the N1, N2 or EGT. Which limit is reached first depends upon environmental factors. On most modern engines, the N1 limit is usually reached first.
 
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Starlionblue
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RE: N1 & N2 Over 100% In Cruise?

Tue Apr 24, 2012 2:37 pm

Quoting smartt1982 (Reply 5):
What is the reason you can get over 100% then?, is 100% not the max?

You'd think so, but that would be too simple.  

Typically the reason is that the engine was rated at X power during the design process, but at entry into service or later it has been rated higher. So if X is 100%, it can now go higher.

For example the Space Shuttle Main engines would go to 104.5% in regular service, and could go up to 111% in emergencies.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
N243NW
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RE: N1 & N2 Over 100% In Cruise?

Wed Apr 25, 2012 3:07 am

Quoting AAR90 (Reply 4):
the CF6's on AA's 767s go up to 117.5% (N1) and 112.5% (N2)

That's pretty incredible - I jumpseated on a 767 test flight a while back, and we were empty and at 105% N1 all the way up to FL410. That thing climbed like a bat out of hell.
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