norseman
Posts: 41
Joined: Thu Feb 22, 2001 10:22 am

### What Is The "N" In N1 Or N2?

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?

airplay
Posts: 3369
Joined: Sat Oct 25, 2003 1:58 am

### RE: What Is The "N" In N1 Or N2?

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".

delta-flyer
Posts: 2631
Joined: Mon Jul 30, 2001 9:47 am

### RE: What Is The "N" In N1 Or N2?

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
"In God we trust, everyone else bring data"

IMissPiedmont
Posts: 6200
Joined: Wed May 23, 2001 12:58 pm

### RE: What Is The "N" In N1 Or N2?

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.
The day you stop learning is the day you should die.

norseman
Posts: 41
Joined: Thu Feb 22, 2001 10:22 am

### RE: What Is The "N" In N1 Or N2?

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

AJ
Posts: 2295
Joined: Wed Nov 03, 1999 3:54 pm

### RE: What Is The "N" In N1 Or N2?

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

Bobsmuggle
Posts: 49
Joined: Sat Jul 21, 2001 12:17 am

### RE: What Is The "N" In N1 Or N2?

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"

AJ
Posts: 2295
Joined: Wed Nov 03, 1999 3:54 pm

### RE: What Is The "N" In N1 Or N2?

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

airplay
Posts: 3369
Joined: Sat Oct 25, 2003 1:58 am

### RE: What Is The "N" In N1 Or N2?

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".

Bobsmuggle
Posts: 49
Joined: Sat Jul 21, 2001 12:17 am

### AJ

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

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