N1 vs. N2?

[magyar]

so N1 is the tinyer blades rotating inside the cowling and N2 is the rotational speed of the propeller? Tell me if i'm right about this

[pika]

N1 is the fan section and N2 is inside the engine core.

[TopperHarley]

N1 and N2 are used for jet aircraft. Ive never heard anyone refer to N1 or N2 on prop a/c.

The "N1 stage" (or N1 shaft) generally refers to the front fan and low pressure compressor and associated turbine. N1 is the rotational speed (as a percentage of max RPM) of the fan and low-pressure compressor.

N2 is the speed of the high pressure compressor and associated turbine.

On most a/c, the N1 and N2 shafts are independent. Some a/c like the 747-400 with RR engines have an N3 shaft, where N3 is the high pressure compressor and turbine, and N2 is now the intermediate compressor and turbine.

[Hedley]

There is very little that is new under the sun:

http://www.pprune.org/flight-testing/211113-n1-n2.html

[iflyforpie]

There is an N number (not to be confused with American reges) for each rotating assembly (or spool) in a turbine engine.

If you are a tiny little air molecule going into an engine the stages are numbered in the order you first encounter them. On most turbofans, N1 is the fan and low pressure compressor. N2 is the high pressure compressor. They are all attached to their respective turbines by concentric shafts so the order reverses as the air molecule hits the turbines ie: first is the N2 turbine, then the N1.

On some RR engines, they have three spools: N1 is the fan and its shaft and turbine. N2 is the low pressure compressor, and N3 is the high pressure compressor.


On free-turbine turboprop/turbo shaft engines, the rotating assemblies are labeled (sometimes, not always) Ng for the gas producer shaft and Np for the power turbine and gear box. I can't remember how it goes with multi-spool free turbines like the PW100s. Generally there isn't a separate instrument for Ng on turboprops since the prop RPM is proportional.

[magyar]

I am specifiaclly refering to the king air200, on start up i hear them call N1 increasing...and they look at the turbine RPM guage as reference. I thought than that N2 is the prop rpm, the spinning of the propeller but i guess i may have mixed up two things there.
So there is an N1 on the king air but is there an N2?

[iflyforpie]

I've never heard of N1 and N2 in regards to a King Air (mind you, I've never flown one, only fixed them, and it was a while ago). There are two tachs for each engine. First is the gas producer which gives the core RPM in percent. This is what is turned by the starter-generator and this is what you look at for when to turn on fuel and turn off the starter.

The second one is a dual-needle tach that gives the power turbine RPM in percent on a large needle and prop RPM in RPM on a smaller needle. You want to make sure the power turbine and prop are free and turning before adding fuel to the engine, but on a turbo prop, this is easily done by simply looking out the window. On turbofans you need to see movement on the N1 (fan) tach before adding fuel because they are impossible to see from the cockpit.

What these are specifically called with regards to a King Air I am not sure. Each aircraft manufacturer makes up it's own mind with regards to terminology. If I had to guess I would say N1 is the gas producer and N2 is the power turbine/prop.

[navajo]

Hi,

N1 is the gas generator RPM, and, if I well understand how it works, is the same rotation speed of the compressor shaft of the PT6 and you read it in percent of RPM, and N2 is the rotation speed of the prop in RPM. This is written in the King Air 200 POH. So be careful of the information you got on this forum.

[Ref Plus 10]

N1 is as stated, Gas Generator speed, given most commonly as a percentage of a maximum RPM, sometimes called NG. Propeller RPM is Np, not N2...however, you can call it whatever you like when you're the only one around.

[navajo]

Sorry Ref, I guess it's depend of the version of the POH you are using! The important thing is to understand how it's works!

[iflyforpie]

I don't think anybody is going to be firing up a King Air without an approved course. Even the numbers are different when you talk to different people.

[ditar]

I've only flown turboprops with PT6's, but in each one Ng/N1 is the gas generator RPM and Np/N2 is the prop RPM.

[looproll]

Hi,

N1 is the gas generator RPM, and, if I well understand how it works, is the same rotation speed of the compressor shaft of the PT6 and you read it in percent of RPM, and N2 is the rotation speed of the prop in RPM. This is written in the King Air 200 POH. So be careful of the information you got on this forum.

this is correct in reference to King Air's
Np=N2

[A Regulator]

Here are a couple of links for you to check out regarding the fundamentals of Aircraft Gas Turbine Engines.

http://www.waybuilder.net/sweethaven/Av ... ?iNum=0216


http://www.waybuilder.net/sweethaven/Av ... ?iNum=0216

[FE_PLT]

I fly and fix the Bell 412CF which uses the PT6T-3D. N1 (38100 rpm @ 100%) also known as Ng is your gas generator composed of 3 stages of axial compressor, 1 stage of centrifugal compressor (1:7 ratio) which is hooked up to a single stage turbine. N1 will drive your starter-generator, tach-generator, fuel cluster and oil pumps. Close by downstream in the airflow is the "free turbine" called N2 of Nf (33000 rpm @ 100%). Then on to the combined gearbox, sprag clutch and so on. Through all kind of reduction gears it then goes to the rotor @ 324 rpm. In the case of the PT6 engine as opposed to a turbofan engine, the N2 output is not connected to any compressor. It's simply an impeller being driven by gases. Turbofans are similar but internally different.

If you look how the engine is installed, N1 in the case of this helicopter is located in the front of the powerplant whereas in the case of the King Air N2 is to turn the prop. Like someone mentioned it is relative to the airflow only.

Also just to add more on the N's. "N" simply refers to a rotational speed. Just like Q for torque, T for temp or P for pressure. To all of them you can add numbers for describing specific systems or letters for abbreviation like Qm= mast torque , Qe= engine torque , Nr = Rotor RPM. Also Hd= density altitude, Hp=pressure altitude but that's totally unrelated to engines.

[ptc]

im flying a B1900 down in NZ and they use N1 for gas gen RPM and N2 for prop RPM