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What Is The "N" In N1 Or N2?  
User currently offlineNorseman From United States of America, joined Feb 2001, 41 posts, RR: 0
Posted (12 years 2 months 2 weeks 21 hours ago) and read 7275 times:

I was discussing turbine engine operations with a captain today, when we both pondered what the "N" in N1 or N2 stands for. I am having a hard time finding any information on this. I know that N1 indicates low pressure compressor speed, and N2 indicates high-pressure compressor speed, but what does "N" stand for? Any insight?

9 replies: All unread, jump to last
 
User currently offlineAirplay From , joined Dec 1969, posts, RR:
Reply 1, posted (12 years 2 months 2 weeks 20 hours ago) and read 7174 times:

The International System of Units was developed in an effort to standardize measurement in scientific circles. The "SI" system really represents a modern form of the metric system.

The generally accepted SI symbol for rotational frequency is "n". Rotational frequency is normally expressed in "radians per second". "n" rotational speeds in turbine engines are predetermined maximum rotational speeds of specific shafts. Indicated rotational frequency is typcially expressed in percent of "n".

Why "n" instead of some other symbol? You could ask the same question about pi....

 Smile


User currently offlineDelta-flyer From United States of America, joined Jul 2001, 2676 posts, RR: 7
Reply 2, posted (12 years 2 months 2 weeks 20 hours ago) and read 7121 times:

N has always been used for rpm (i.e. Number of revs...) as opposed to the Greek letter omega for for angular velocity in radians per second.

Pete


User currently offlineIMissPiedmont From United States of America, joined May 2001, 6260 posts, RR: 34
Reply 3, posted (12 years 2 months 2 weeks 19 hours ago) and read 7102 times:

In other words, the N itself doesn't mean anything. It's just a letter. One of the aviation oddities as most every other letter means something starting with that letter.


Is grammar no longer taught is schools? Saying "me and her" or some such implies illiteracy.
User currently offlineNorseman From United States of America, joined Feb 2001, 41 posts, RR: 0
Reply 4, posted (12 years 2 months 2 weeks 19 hours ago) and read 7080 times:

Thanks a lot guys. The captain I was talking with said he has never gotten a good answer about "N". I even asked some guys in maintenance and their answer was "Uh, well you see...Um, It's probably..."

I knew you guys would come through!

Norseman


User currently offlineAJ From Australia, joined Nov 1999, 2381 posts, RR: 24
Reply 5, posted (12 years 2 months 2 weeks 19 hours ago) and read 7079 times:

Similar to air pressure being denoted by 'Q', as in Qnh, Qfe etc etc.
Odd.


User currently offlineBobsmuggle From Australia, joined Jul 2001, 49 posts, RR: 0
Reply 6, posted (12 years 2 months 2 weeks 10 hours ago) and read 7034 times:

QNH, QFE etc are from the old morse and alike days. QNH is short for "Question - Nil Height" which would be interpreted as "I have a question, what is the nil height"

User currently offlineAJ From Australia, joined Nov 1999, 2381 posts, RR: 24
Reply 7, posted (12 years 2 months 2 weeks 1 hour ago) and read 6985 times:

Well done Bob, I thought that info had been lost into history.
Likewise at my company runway heading is still called QDM.


User currently offlineAirplay From , joined Dec 1969, posts, RR:
Reply 8, posted (12 years 2 months 1 week 6 days 20 hours ago) and read 6956 times:

Yes....Omega is the primary SI symbol for angular velocity. "n" is an alternate.

I did a bit more research (asked some of my engine buddies) and found that the "n" I was referring to is not the same as the "N" used in N1 and N2 engine indications.

N is the symbol for "specific speed". Specific speed is defined as "the speed of an ideal pump geometrically similar to the actual pump, which when running at this speed will raise a unit of volume, in a unit of time through a unit of head".

Here are some links that explain what specific speed is:

http://www.negia.net/~nelik/ns.htm

http://www.tasonline.co.za/toolbox/pump/powns.htm

http://www.mcnallyinstitute.com/07-html/7-03.html

Again....I have no idea why they chose "N".



User currently offlineBobsmuggle From Australia, joined Jul 2001, 49 posts, RR: 0
Reply 9, posted (12 years 2 months 1 week 6 days 10 hours ago) and read 6905 times:

I have never heard QDM before... would that mean Question - Direction Magnetic???

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