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Aircraft Thrust Settings And N1 N2  
User currently offlineN808NW From United States of America, joined Aug 2004, 374 posts, RR: 4
Posted (8 years 1 month 3 weeks 4 days 18 hours ago) and read 32767 times:

I'm trying to make my aircraft on F/S perform as realistically as possible(edditing cfg files). I've never fully understood what N1 and N2 are on engine instruments and how they relate to thrust and the position of the throttle. such as 100% N1 or N2 isn't full throttle.
-what take off settings are used on a 100/70/50/20% (differnt settings for each load?) full (fuel and pax) 744 or 772? and for other aircraft?
-what setting are used at cruse, and once again how dose N1 N2 compare to the throttle location?


-Jason  swirl 


All flights have great IFE...get yourself a window seat, thats something no PTV can beat! flew 808 Pacific an Atlanic
15 replies: All unread, jump to last
 
User currently offlineN8076U From United States of America, joined Jun 2006, 425 posts, RR: 9
Reply 1, posted (8 years 1 month 3 weeks 4 days 17 hours ago) and read 32767 times:

I can't answer all of your questions, but I can answer a couple. Keep in mind these are somewhat generic answers, and there is always an exception to the rule (RR with 3 spools, etc).

N1 is the low-pressure spool. In other words, the "first stage" or "large fan" at the front of the engine, and the forward set of core compressor blades spin with this. The rearmost turbine blades also spin with this N1 spool.

N2 is the high-pressure spool. The rest of the core compressor blades not spun by the N1 spool are connected to the N2 spool. The forward-most turbine blades closest to the combustion process also are connected to the n2 spool.

One other thing must be taken into account if the engine is a Pratt and Whitney. EPR (engine pressure ratio) is used to set thrust on these engines, where RR, GE and the CFM engines use N1 to set takeoff power. With respect to the 747/777 with P&W engines, EPR and N2 are on the primary display with EGT and fuel flow, and N1 is on the secondary display with oil temp, oil pressure, etc.

At takeoff power, the % for N1 and N2 is usually "in the neighborhood of" 100%, give or take 10% or so, some specific engines may be a little higher or lower. Each aircraft/engine combination will have exact numbers specified in the flight manual. So if you want more than an approxamation, you need to be more specific as to exactly which engine on which model aircraft.

Chris



Don't blame me, I don't work here...
User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 2, posted (8 years 1 month 3 weeks 4 days 17 hours ago) and read 32767 times:

Not ALL Rolls Royce turbine engines use only N1 to set thrust.
The RR RB211 series, for example use EPR.

That said, the RR Conway series used N1, no EPR gauges fitted, at least on the old Conway powered B707's.


User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2548 posts, RR: 24
Reply 3, posted (8 years 1 month 3 weeks 4 days 10 hours ago) and read 32767 times:

Strictly speaking, N1 is the rotational speed of the LP spool, not the spool itself. Similarly for N2 and the HP spool.

On a big fan engine, typical idle values might be 25% N1 and 60% N2. Full power 100%-110% N1 and 95%-100% N2. N1 rpm tends to be fairly linear with throttle position between idle and maximum.

Takeoff N1 can indeed be reduced at lower weights, or on long runways.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlineN8076U From United States of America, joined Jun 2006, 425 posts, RR: 9
Reply 4, posted (8 years 1 month 3 weeks 4 days 10 hours ago) and read 32767 times:

Quoting 411A (Reply 2):
Not ALL Rolls Royce turbine engines use only N1 to set thrust.

That's why I added an anti-flame disclaimer,  Wink

Quoting N8076U (Reply 1):
Keep in mind these are somewhat generic answers, and there is always an exception to the rule

But thanks for that info, as I didn't realize that about the RB211s.

Chris



Don't blame me, I don't work here...
User currently offlineN8076U From United States of America, joined Jun 2006, 425 posts, RR: 9
Reply 5, posted (8 years 1 month 3 weeks 4 days 8 hours ago) and read 32767 times:

Quoting Jetlagged (Reply 3):
N1 is the rotational speed of the LP spool, not the spool itself

Yes, you're right. The low-pressure (LP) and high-pressure (HP) spool are often referred to as the N1/N2 spool, but I agree that technically, it is incorrect to call them that. I didn't even realize I did that  Wink

Chris



Don't blame me, I don't work here...
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 6, posted (8 years 1 month 3 weeks 4 days 6 hours ago) and read 32767 times:

As for thrust setting, it depends. A turbine has a maximum RPM above which the loads will be above what it is designed for. At this setting, it will provide a certain amount of thrust in one set of conditions, where temperature and altitude are the largest contributors. For your purposes, set the maximum RPM and take whatever performance that will give you.

In real life, many aircraft also have limits on turbine temperatures. In other words, you may not be able to use full RPM as that may mean overtemp at the turbines in certain conditions, and/or if the engine is worn.

To save wear on the engines, pilots may use less than the full thrust available for takeoff if the aircraft is light and/or there is a long runway available. Common terms for this procedure is using flex thrust or derated thrust.

Rgds,
/Fred



I thought I was doing good trying to avoid those airport hotels... and look at me now.
User currently offlineZSOFN From United Kingdom, joined Jun 2005, 1413 posts, RR: 6
Reply 7, posted (8 years 1 month 3 weeks 4 days 4 hours ago) and read 32767 times:

Out of interest, say using a common aircraft/engine combo such as a 737NG (CFM56-7Bs), what sort of engine settings are used for climbout? I've never been able to get an answer on this one before.

Say at a higher weight and therefore assuming no derate, 100% N1 is used for takeoff, but once configured for climb with gear up and flaps retracted, what sort of limits are placed on the engines during the climb phase?


User currently offlineChksix From Sweden, joined Sep 2005, 345 posts, RR: 4
Reply 8, posted (8 years 1 month 3 weeks 4 days 4 hours ago) and read 32767 times:

The N1 CLB tables depend on temp and altitude. I'd be happy if I could attach a picture to the post since the tables can't be found on the internet...


The conveyor belt plane will fly
User currently offlineZSOFN From United Kingdom, joined Jun 2005, 1413 posts, RR: 6
Reply 9, posted (8 years 1 month 3 weeks 4 days 3 hours ago) and read 32767 times:

It would be great if you could - you can attach a picture by first uploading it to somewhere like imageshack and then inserting the URL of the picture between image tags like so: [ img ]picture url[ / img ]

I've put spaces in there so that you can see what to do; do as above but remove all the spaces, and it should work fine. Would love to see the tables if possible!

Cheers

Tom


User currently offlineSeanp11 From United States of America, joined Jan 2006, 290 posts, RR: 0
Reply 10, posted (8 years 1 month 3 weeks 3 days 20 hours ago) and read 32767 times:

Quoting ZSOFN (Reply 7):
Out of interest, say using a common aircraft/engine combo such as a 737NG (CFM56-7Bs), what sort of engine settings are used for climbout? I've never been able to get an answer on this one before.

It really depends on the variant. A 737-800 can get up to 100% N1 at low enough temperatures and high enough altitudes, and can be as low as 81% N1 at low temperatures and low altitude.


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17030 posts, RR: 67
Reply 11, posted (8 years 1 month 3 weeks 3 days 20 hours ago) and read 32767 times:

Just to give you an illustration of the whole low pressure spool/high pressure spool thing. A picture says a thousand words. This shows how the spools are co-axial. Low pressure is red. High pressure is green.

http://science.howstuffworks.com/turbine6.htm



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineColAvionLover From Panama, joined Dec 2008, 108 posts, RR: 0
Reply 12, posted (3 years 6 months 2 weeks 1 day 20 hours ago) and read 32481 times:
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Quoting Chksix (Reply 8):

The N1 CLB tables depend on temp and altitude. I'd be happy if I could attach a picture to the post since the tables can't be found on the Internet...

I think on PMDG's Files, there's such table. I remember using those tables for my simulated flights. Generally the V1 VR V2 table.



JDM's
User currently offlineWestJetForLife From Canada, joined Jun 2005, 814 posts, RR: 1
Reply 13, posted (3 years 6 months 2 weeks 1 day 1 hour ago) and read 32334 times:

Quoting N808NW (Thread starter):
-what take off settings are used on a 100/70/50/20% (differnt settings for each load?) full (fuel and pax) 744 or 772? and for other aircraft?
-what setting are used at cruse, and once again how dose N1 N2 compare to the throttle location?

DISCLAIMER: Forgive me, professional pilots and AMEs, if I get some of this wrong. I've had very little training in turbine engine theory.

Answer #1: as many posters have said above, it varies on the weight of the aircraft, length of runway, temperature outside and other factors. Usually, the pilots use a thrust settings table in either the POH or QRH (I'm not sure which one, though) to determine the takeoff thrust for that leg's flight. Most of the times, to save engine wear and fuel, a de-rated (Boeing) or FLEX (Airbus) thrust setting is used if there is a long enough runway or the payload is lighter and does not facilitate a full-throttle takeoff.

During pre-flight, the pilots will cross-check the N1 thrust settings in the manual with the PERF INIT page on the FMC, and can select various thrust settings on the FMC.

Example: I'm using the PMDG 737NG manual for a reference; I don't have an actual 737NG manual with me, so this is the closest bet.

Boeing 737-700
Departure airport: CYYC (Calgary International Airport) runway 34
Altitude (MSL/Mean Sea Level): 3,557 feet.
Temperature: 20°C/68°F

Using the PMDG table, with the selected temperature and altitude parameters, a thrust setting of approximately 96.1% N1 (fan spool) would be used. That's at 24KN full-thrust takeoff power if the aircraft is fully loaded. De-rated thrust could be anywhere between 5-10% lower than max thrust (86.5-91.3%), the former being if the aircraft is extremely light and there is a long enough runway.

Answer #2: Cruise settings are generally varied for weight, speed, altitude and different types of flight. From what I have heard, or I've noticed during a sim ride or two, the cruise N1 at altitude generally appears to be anywhere between 86-90% N1 to maintain cruise speed. Thankfully, with the introduction of FADEC and other marvelous technological advances, the autothrottle sets the thrust levers to a certain position that correlates with the N1 demands of cruise flight.

Once again, if someone who is type-rated in the 737 or knows more than I do about this wishes to correct some of my mistakes, please do so.

Nik



I need a drink.
User currently offlinePihero From France, joined Jan 2005, 4410 posts, RR: 76
Reply 14, posted (3 years 6 months 2 weeks 2 hours ago) and read 32186 times:
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@WestJetForLife
Performance computations do take into account all the parameters of a runway, not only in terms of altitude, length, temperature and wind, but also obstacles, routingt on the SID...etc... actual values from a thorough study of that runway environment.

Secondly, taking off at MTOW doesn't mean that we cannot derate / flex...(whatever you call the reduced takeoff thrust ), to the contrary,; so much in fact that one could spend years on the line without ever seeing a full thrust takeoff.

Finally, on modern airplanes, there's one parameter from which all others derive and that's the chosen *Cost Index*, and AFAIK, there's no graph on engine data for that. One could find tables for a given Mach or a given schedule -long range for instance - but that's it.



Contrail designer
User currently offlineWestJetForLife From Canada, joined Jun 2005, 814 posts, RR: 1
Reply 15, posted (3 years 6 months 1 week 6 days 21 hours ago) and read 32114 times:

Quoting Pihero (Reply 14):

How could I forget cost index and other stuff like that? You can obviously tell I just know the bare-bones of turbine operations. :P

Thanks for the assist!  

Nik



I need a drink.
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