Thu Apr 12, 2001 9:25 am

I am sorry if this has been discussed before (I tried the search function, but I did not get what I was looking for). I think I might have an understanding of what they are, but I am probably wrong. Could someone please explain what they indicate?
Thanks, Tom

P.S. Seems the Airport code search is down for the moment, but could someone please tell me which airport is XNA?
Posts: 91
Joined: Tue Mar 13, 2001 8:03 pm

RE: N1,N2,N3

Thu Apr 12, 2001 9:33 am

they relate to the speed at which sections of the engine are rotating. N1 is your fan speed, N2 is your LP speed and N3 is your HP speed. they are normally given as a percentage though. They may differ from engine to engine though which part they relate to (the ones that i gave you were for an RB211)
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Joined: Thu Nov 02, 2000 9:31 am

RE: N1,N2,N3

Thu Apr 12, 2001 9:39 am

This indicates the %age of the maximum RPM of various turbines on the jet engine as follows:

N1 is the speed of the big fan at the front of the engine which can be seen from outside.

N1 can sometimes exceed 100% on take off. Pilots will sometimes use this as a direct indication of power, so for example typically will use 55-60% N1 on approach, although they do not actively watch this to set power while on approach - when u fly the plane u adjust power automatically to suit the flight profile.

N2 is the turbine inside the engine and N3 is a turbine further in the core of the engine.

When the engine is started N2 starts to turn which drives N1 and one can see the % increases on the EICAS screens in the cockpit.

hope that gives u food for thought!

RE: N1,N2,N3

Thu Apr 12, 2001 5:46 pm


How can the N1 exceed 100%?
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RE: N1,N2,N3

Thu Apr 12, 2001 5:56 pm

100% is a nominal figure

N1 is the Fan Spool [Rotor] (compressor AND turbine)

N2 is the Intermediate Spool (or HP Spool if a twin spool engine)

N3 is the HP Spool.
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RE: N1,N2,N3

Fri Apr 13, 2001 1:39 am

N3 is only used on RR engines as far as I know.
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Joined: Tue Mar 13, 2001 8:03 pm

RE: N1,N2,N3

Fri Apr 13, 2001 3:56 am

Yeah thats right because no one else makes a triple spool engine as such, most others run the fan as part of the lp spool. if you do an air start you would look at your N1 on non RR engines to ensure that the engine has begun to turn. on RR engines though you'd look for your N2 to build Big grin

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