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User currently offlineKing767 From , joined Dec 1969, posts, RR:
Posted (15 years 1 month 2 weeks 6 days 13 hours ago) and read 10773 times:

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?

6 replies: All unread, jump to last
User currently offlineTuffty From United Kingdom, joined Mar 2001, 92 posts, RR: 0
Reply 1, posted (15 years 1 month 2 weeks 6 days 13 hours ago) and read 10729 times:

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)

User currently offlineAjaaron From United Kingdom, joined Nov 2000, 123 posts, RR: 0
Reply 2, posted (15 years 1 month 2 weeks 6 days 13 hours ago) and read 10732 times:

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!

User currently offlineAmbasaid From , joined Dec 1969, posts, RR:
Reply 3, posted (15 years 1 month 2 weeks 6 days 4 hours ago) and read 10685 times:


How can the N1 exceed 100%?

User currently offlineVC-10 From United Kingdom, joined Oct 1999, 3727 posts, RR: 32
Reply 4, posted (15 years 1 month 2 weeks 6 days 4 hours ago) and read 10686 times:
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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.

User currently offlineSabenapilot From Belgium, joined Feb 2000, 2748 posts, RR: 45
Reply 5, posted (15 years 1 month 2 weeks 5 days 21 hours ago) and read 10672 times:

N3 is only used on RR engines as far as I know.

User currently offlineTuffty From United Kingdom, joined Mar 2001, 92 posts, RR: 0
Reply 6, posted (15 years 1 month 2 weeks 5 days 18 hours ago) and read 10670 times:

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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