ICAO's LTO power settings vs N1
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ICAO's LTO power settings vs N1
Hi,
Particularly in the emission studies I frequently encounter this power settings issue. According to the ICAO the standard power settins are:
7% idle
30% approach
85% climb
100% takeoff
Most of the researchers accept this power settings and evaluate the emissions with this settings.
What I would like to know is what is that actually? Is it something about throttle? Thrust resolver angle?
What is the relationship between the power settings and the N1 (if there is! / it should be to me).
I understand that they note the maximum takeoff power (or may be I should say thrust) as 100% and scale other power settings against to this %100 but how. For instance, I read from FDR, an average N1 is around 22-24% (standard deviation is around 2%) for CFM56-7B26 series engine, then what is the relationship between the 7% and 22% ? I dont expect a strict relationship exists, since the ICAO numbers include all of the engine or aircraft tpyes, but there must be a relationship.
Can we discuss these issues please?
Thank you.
Particularly in the emission studies I frequently encounter this power settings issue. According to the ICAO the standard power settins are:
7% idle
30% approach
85% climb
100% takeoff
Most of the researchers accept this power settings and evaluate the emissions with this settings.
What I would like to know is what is that actually? Is it something about throttle? Thrust resolver angle?
What is the relationship between the power settings and the N1 (if there is! / it should be to me).
I understand that they note the maximum takeoff power (or may be I should say thrust) as 100% and scale other power settings against to this %100 but how. For instance, I read from FDR, an average N1 is around 22-24% (standard deviation is around 2%) for CFM56-7B26 series engine, then what is the relationship between the 7% and 22% ? I dont expect a strict relationship exists, since the ICAO numbers include all of the engine or aircraft tpyes, but there must be a relationship.
Can we discuss these issues please?
Thank you.
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First of all, the relationship between thrust (Fn) and N1 is unique for each engine model, so the manufacturer should supply the curves from test cell runs with a calibrated thrust stand.
That said, the end points are pretty well defined. By spec, idle thrust will always be about 7% of takeoff, and for your example, this is 22-24% N1. Similarly for TO, 100% Fn will correspond to whatever power management calls for - for the ambient temperature specified for the test.
The 85% point is a bit trickier, although a rule of thumb I've used is the Fn/N1 local derivative in the high power region. I am used to seeing about 2.5% thrust change for each 1.0% N1. Therefore to decrease thrust 15% (i.e. from 100% to 85%) we can expect about a 6% reduction in N1.
Right now I have no way to estimate the 30% approach point, although if you plot the three points above and draw a smooth curve, you won't be far off.
Once again, these are a rule of thumb, but will give you a rough idea of what to expect from the official curves.
That said, the end points are pretty well defined. By spec, idle thrust will always be about 7% of takeoff, and for your example, this is 22-24% N1. Similarly for TO, 100% Fn will correspond to whatever power management calls for - for the ambient temperature specified for the test.
The 85% point is a bit trickier, although a rule of thumb I've used is the Fn/N1 local derivative in the high power region. I am used to seeing about 2.5% thrust change for each 1.0% N1. Therefore to decrease thrust 15% (i.e. from 100% to 85%) we can expect about a 6% reduction in N1.
Right now I have no way to estimate the 30% approach point, although if you plot the three points above and draw a smooth curve, you won't be far off.
Once again, these are a rule of thumb, but will give you a rough idea of what to expect from the official curves.
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In case I didn't make it clear, I'm sure the 7% - 30% - 85% - 100% points refer to the percentage of takeoff thrust.
I'll also state that it's a general rule (not sure if it's a spec) that thrust is directly proportional to throttle resolver angle (FADEC) or to mechanical lever angle on a hydromechanical control.
I'll also state that it's a general rule (not sure if it's a spec) that thrust is directly proportional to throttle resolver angle (FADEC) or to mechanical lever angle on a hydromechanical control.
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Thank you @barit1;
Excuse me, I have seen your reply just now.
You implied that there is 2.5% change for each 1% N1. Although you noted that this is for high power region, I extended this relationship to low power regions to find some rough results and I saw the followings;
~94% N1 for 85% thrust as you said
~58% N1 for 30% thrust
and never found a plausible N1 for 7% thrust, which is due the fact of the accuracy of the relationship in low power region. May be another relationship is existed for this regions.
Although we are talking some quadratic or cubic function between net thrust (Fn) and N1 at high power, in (C.E. Otis, Aircraft GasTurbinePowerplant) textbook, the Fg (gross thrust) is linearly related by the N1. Perhaps I get confused between Fg and Fn as expecting a lineer relationship between the N1 and thrust (Fn) as well, for no reason.
Thank you.
If you have comments please feel free.
Excuse me, I have seen your reply just now.
You implied that there is 2.5% change for each 1% N1. Although you noted that this is for high power region, I extended this relationship to low power regions to find some rough results and I saw the followings;
~94% N1 for 85% thrust as you said
~58% N1 for 30% thrust
and never found a plausible N1 for 7% thrust, which is due the fact of the accuracy of the relationship in low power region. May be another relationship is existed for this regions.
Although we are talking some quadratic or cubic function between net thrust (Fn) and N1 at high power, in (C.E. Otis, Aircraft GasTurbinePowerplant) textbook, the Fg (gross thrust) is linearly related by the N1. Perhaps I get confused between Fg and Fn as expecting a lineer relationship between the N1 and thrust (Fn) as well, for no reason.
Thank you.
If you have comments please feel free.
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I think you have the general idea - the overall curve may resemble a quadratic - but I want to emphasize that data from the calibrated test cell should be used if at all possible. (Most airline test cells will give good results - I was in the business of performing correlation tests.) 
Last edited by barit1; 25th Aug 2013 at 12:34.
