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N1 and N2 - What are They?

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What does N1 and N2 mean? I think they refer to the % capacity of the engine blades (inner and outer), but I'm not sure - can anyone clarify? Thanks!Jason

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Every modern turbofan consists of semi-independent two major parts - compressor (that sucks air in) and turbine in the rear. Turbine generates actual power. These 2 units have their own free-spinning shafts. N1 is the % of max revolutions for the compressor and N2 is the equivalent for the turbine.Michael J.

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>Every modern turbofan consists of semi-independent two major >parts - compressor (that sucks air in) and turbine in the >rear. Turbine generates actual power. These 2 units have >their own free-spinning shafts. N1 is the % of max >revolutions for the compressor and N2 is the equivalent for >the turbine. >>Michael J. Close. N1 is the speed of the low speed compressor, N2 is the speed of the high speed compressor. The low speed fan is the farthest forward (closest to the inlet)and is connected to the low speed turbine. The N2 (high speed) compressor is connected to the high speed turbine. That pair is located closest to the combustor section.Of course that is in a twin spool motor. There are 3 spool motors out there.

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So what exactly is EPR (Engine Pressure Ratio) then - is it like the ratio of N1 to N2?

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Nop!N1 is the speed of fan+booster+low pressure turbine.N2 is the speed of high pressure compressor+high pressure turbine.N1 is 4 to 5000 rpm, N2 is 9 to 12,000 rpm as far as I recall.EPR is the pressure ratio (pressure out / pressure in) delivered by the high pressure compressor (HPC). A good HPC delivers a high EPR, with a good surge margin at all speed.For Pratt&Withney engines, the engine is driven by EPR, meaning that the thrust is set by setting an EPR.For GE or CFMI engines, the engine is driven by N1, meaning that the thrust is set by setting a N1 level. I don't know about Rolls Royce engines.From a pilote stand point, it does not really make any difference. It is just a different philosophy from different engine makers.Bien amicalementMichelKSEA

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Guest Martin

RR engines use EPR as primary thrust reference. They (at least the heavy commercial engines) also have N3, i.e. a third spool (or "rotor"). In those engines N2 becomes "intermediate pressure (compressor and turbine)" and N3 "high pressure".MartinIt's a lot like life and that's what's appealing

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Guest ilh

In PIC's aircraft.cfg, I see N2 rated to 29,200rpm.Lee Hetherington (KBOS)

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Lee,I will check for the exact values in the right documentation (Boeing or GE) but it appears the N2 is much lower than 29,000rpm.At take-off power, for the GE90-94B engine (the one for the 777-200ER) 100%N1 is 2,500rpm and 100%N2 is 10,400rpm.For the CF6-80C2B6F (for the 767-300ER) those values are respectively 3,600rpm and 10,700rpm.Again, I will have to check those values unless somebody-else can do it before I can.Anyway, as we use percentages instead of rpm's, those differences in rpm's are maybe not that important for our business !!Bien amicalementMichelKSEA

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I'm consistently impressed with the level of knowledge that gets exhibited in this forum. I am interested in the backgrounds of various people who post certain topics - in this case with the engines. Would anyone who has posted a response to this topic mind telling us if they work with jet engines on a daily basis? Again, an enormous amount of knowledge here and I am impressed.Jason (not involved with jet engines at all) - thanks

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Jason,I was first to post a reply here but I was slightly off. I simply forgot this stuff.As to my sources ?. There is a good book "The turbine pilot's flight manual" which has relevant data. You can buy this book through Amazon. But if you download Dreamfleet's manual for their 737 (manual is free) you will get even more detailed information. It applies to 737 but all jet engines are similar in their main design principles.Michael J.

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Would anyone who has posted a >response to this topic mind telling us if they work with jet >engines on a daily basis? Yep, 40 hours a week.

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Guest Ian_Riddell

>In PIC's aircraft.cfg, I see N2 rated to 29,200rpm.Ah, hah! So it's true... There was a supersonic version of the 767 being developed at the PIC "skunkworks" (grin).BTW, the real engine would fall to bits at half this speed ;-)Chrs.I.P.S. RR's use IEPR (Integrated EPR), which measures the pressure going into the engine (just in front of the big fan) and the total pressure coming out of the engines (i.e. core and LP compressor), giving a more reliable indication of thrust than standard EPR.P.P.S. Here's a diagram of the N1 and N2 rotors on a P&W:http://www.ozemail.com.au/~iriddell/767/P&WEngine.JPGThe N1 rotor shaft runs up the middle of the N2 rotor shaft.I've been told that 100% N1, 2, 3, etc was originally the advised maximum for original versions/prototypes of a particular engine.... i.e. before long series of modifications were carried out to the engine to improve its reliability. This is why rpms greater than 100% are often seen in normal ops.P.P...etc...S. Er... Who changes the tires in PlaneMech's airline? (40 hours a week on engines.... crikey!) :-)

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>>P.P...etc...S. Er... Who changes the tires in PlaneMech's >airline? (40 hours a week on engines.... crikey!) :-) You got me....I also do airframe work. The only engine stuff today was wandering over out of boredom to watch a guy look for an oil leak.But,I did go with him to go do power runs...so that might qualify for engine work.Plus I drove one from the hangar to the terminal and I had to start the engines, so....Really though, the hub I work at has gone type specific so all the planes have AE3007/s on them. Rolls/Royce seems to have gotten the bugs out of them for now, so the engine type work is kinda spotty.

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Guest B1900 Mech

I do it all! One day I might break down a main tire, The next, trouble shoot a radar problem. It's the %$#@@&** paperwork that kills me!!! More than a doctor!

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