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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 5 months 2 weeks 6 days 5 hours ago) and read 7748 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 5 months 2 weeks 6 days 5 hours ago) and read 7647 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 5 months 2 weeks 6 days 4 hours ago) and read 7594 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, 6278 posts, RR: 34
Reply 3, posted (12 years 5 months 2 weeks 6 days 4 hours ago) and read 7575 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.


Quit calling an airport ramp "Tarmac" and a taxiway "runway".
User currently offlineNorseman From United States of America, joined Feb 2001, 41 posts, RR: 0
Reply 4, posted (12 years 5 months 2 weeks 6 days 3 hours ago) and read 7553 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, 2386 posts, RR: 24
Reply 5, posted (12 years 5 months 2 weeks 6 days 3 hours ago) and read 7552 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 5 months 2 weeks 5 days 18 hours ago) and read 7507 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, 2386 posts, RR: 24
Reply 7, posted (12 years 5 months 2 weeks 5 days 10 hours ago) and read 7458 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 5 months 2 weeks 5 days 5 hours ago) and read 7429 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 5 months 2 weeks 4 days 18 hours ago) and read 7378 times:

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

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