What does the 'N' in 'N1' and 'N2' stand for?

[SR-71A]

OK this is going to be a rather silly question, but I can't find the answer anywhere else.

I know N1 is the speed of the low pressure compressor and N2 is the high pressure compressor, but does anyone know what the 'N' in N1 and N2 stand for?

I can guess that the 'V' in the V-speeds stands for 'velocity' but I have absolutely no clue what the 'N' stands for. If anyone has any idea it would be most helpful! :)

[dixi188]

Agree. 100% of any engine parameter is only arbitary.

On our CF6-50C2 engines N1 limit is 119% and N2 limit is 109.5%.

Used to do performance checks on the Allison 501 to come up with a % of rated power. Sometimes we would get over 100% but some office type said that more than 100% was impossible, so we never wrote down anything above 100%. (mind you we often struggled to get the minimum of 93%)

Sorry if this is thread drift.

Safe flying.

[SR-71A]

Thanks for your reply!

I spoke with a friend who said he read somewhere before that the 'N' stands for 'Indicator' (as in Indicator 1 and Indicator 2), but because of the ergonomics of not using I1 and I2, they used the next letter instead, which is 'N'.

But your answer is also very plausible, and I will definitely discuss this with him over a beer!

[aerolearner]

In engineering, n is often used as the symbol for rotational speed.

BR,

aerolearner

[WindSheer]

Nacelle maybe??

[smudgethecat]

In engineering generally its common to identify any rotating shaft/ gear train etc by the prefix N

[BladePilot]

Jeez! now I'm stumped I always thought the N1 was the main road between Dublin and Belfast N = National = Irish equivalent to A road in the UK? :}

[NutLoose]

It is an abreviation of either Notational or Nominal RPM with the latter being the favourite in my Engineers eyes, Google Nominal RPM and as you see it is set RPM's the 1 and 2 just is an easy way of setting a value for independant spool rpms.

[flighttest-engineer]

Abbreviaton "N" is used for rotational shaft speeds either in RPM's or %

[727gm]

Having been an engineer, I seem to remember from school days that it was N for number of turns, as in rotational speed. As any given engines' RPM limits happen to come out to a convenient number, %RPM was introduced for ergonomic/display reasons. I guess if they'd wanted to, one could have aircraft airspeed indicators marked in % of Max Speed also.

[mach79]

"N" in mathematical terms is just a "number", so the previous poster is probably most correct.

[WindSheer]

So whilst we are on the subject, what would the average rpm be for say a cfm 56 at takeoff power e.g. 90% N1 ??

[Superpilot]

approx 16,000rpm

[Turb Coriolis]

If a fan blade goes you will wet yourself ("number 1", hence N1) and if a blade in the core goes walkabout this will cause you to "number 2" yourself (hence N2). Quite simple really.

:rolleyes:

[nicolai]

So whilst we are on the subject, what would the average rpm be for say a cfm 56 at takeoff power e.g. 90% N1 ??

approx 16,000rpm

That's N2, in case that wasn't clear. N1 is more like 5000RPM near 100% (http://www.b737.org.uk/cfm56_soi.htm)