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N1 & N2 Over 100% In Cruise?  
User currently offlineDufo From Slovenia, joined May 1999, 803 posts, RR: 4
Posted (14 years 3 months 1 week 4 days 15 hours ago) and read 4978 times:

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.
8 replies: All unread, jump to last
 
User currently offlineJetpilot From United States of America, joined May 1999, 3130 posts, RR: 29
Reply 1, posted (14 years 3 months 1 week 4 days 11 hours ago) and read 4816 times:

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

So normal can fall anywhere below the limits.


User currently offlineDufo From Slovenia, joined May 1999, 803 posts, RR: 4
Reply 2, posted (14 years 3 months 1 week 4 days 10 hours ago) and read 4802 times:

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.
User currently offlineDeltaAir From United States of America, joined May 1999, 1094 posts, RR: 0
Reply 3, posted (14 years 3 months 1 week 4 days 6 hours ago) and read 4783 times:

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.

User currently onlineAAR90 From United States of America, joined Jan 2000, 3476 posts, RR: 46
Reply 4, posted (14 years 3 months 1 week 4 days 4 hours ago) and read 4774 times:

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).



*NO CARRIER* -- A Naval Aviator's worst nightmare!
User currently offlinesmartt1982 From United Kingdom, joined Nov 2007, 225 posts, RR: 0
Reply 5, posted (2 years 6 months 1 week 2 days 5 hours ago) and read 3039 times:

What is the reason you can get over 100% then?, is 100% not the max?

User currently offline113312 From United States of America, joined Apr 2005, 574 posts, RR: 1
Reply 6, posted (2 years 6 months 1 week 2 days 4 hours ago) and read 2991 times:

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.


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17071 posts, RR: 66
Reply 7, posted (2 years 6 months 1 week 2 days 3 hours ago) and read 2961 times:

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."
User currently offlineN243NW From United States of America, joined Jul 2003, 1638 posts, RR: 20
Reply 8, posted (2 years 6 months 1 week 1 day 15 hours ago) and read 2681 times:

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.



B-52s don't take off. They scare the ground away.
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