EPR vs N1
Joined: Mar 2002
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From: Seat 1A
iEPR = Thrust
N1 = half the information needed to work out thrust.
N1 = half the information needed to work out thrust.
iEPR. Is that Apple pressure ratio?
Joined: Jul 2013
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From: Everett, WA
It used to be, EPR was more representative of thrust than N1. That was somewhat offset by EPR being more susceptible to error than N1.
With FADEC engine control, EPR became less susceptible to error - the FADEC could compare inlet pressure to aircraft total pressure, and model outlet pressure based on other engine parameters to compare to measured exit pressure. EPR also had other advantages relative to N1 - thrust at N1 is more dependent on ambient conditions (temp and humidity) than EPR. Meanwhile N1 powersetting had to account for the ambient uncertainties.
Short story, N1 had to "give away" thrust to insure takeoff thrust was available.
As newer engines go to ever high bypass ratios (already approaching 10 to 1), combined with the inherent difficulties in measuring EPR, I expect N1 to become the predominant power setting parameter in the future.
With FADEC engine control, EPR became less susceptible to error - the FADEC could compare inlet pressure to aircraft total pressure, and model outlet pressure based on other engine parameters to compare to measured exit pressure. EPR also had other advantages relative to N1 - thrust at N1 is more dependent on ambient conditions (temp and humidity) than EPR. Meanwhile N1 powersetting had to account for the ambient uncertainties.
Short story, N1 had to "give away" thrust to insure takeoff thrust was available.
As newer engines go to ever high bypass ratios (already approaching 10 to 1), combined with the inherent difficulties in measuring EPR, I expect N1 to become the predominant power setting parameter in the future.
Joined: Jun 2009
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From: somewhere
THRUST
Rumour I heard was that future RR engines will be controlled to N1 rather
than EPR.
than EPR.
0% THRUST equals windmilling thrust.
100% THRUST equals TOGA bleed off.
% THRUST is based upon N1,
N1 is the parameter for the thrustsetting in degraded mode.
Last edited by A33Zab; 31st August 2013 at 07:15. Reason: Added image.
Thread Starter
Joined: Dec 2002
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From: Stabchester
Maybe slight threat creep here, main point was problems of EPR as a thrust setting parameter in the CRZ, what can we do to get rid of the phasing I see on a regular basis with out of sync n1 spools , you only need about .3% to be significant in reducing pax comfort levels and that cycling harmonic beat, anyone work At RR to comment on this hugely frustrating problem ?
Joined: Sep 1998
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From: wherever
N1 produces most of the thrust. If it's spinning at the correct speed, you'll have your thrust, regardless of pressure ratios, ice, whatever. EPR, on the other hand...
iEPR. Is that Apple pressure ratio?
iEPR. Is that Apple pressure ratio?
"Most of the thrust" How much?
"correct speed" What is the correct speed?
If I set 95% N1 on my engine I only know the rotor is turning at 95%. Without knowledge of air density this information is meaningless.
Aviator Extraordinaire
Joined: May 2000
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From: Oklahoma City, Oklahoma USA
Solely relying on EPR, without the crosscheck of N1 can be a fatal trap. Several T/o accidents can be contributed to the inadvertent miss setting of power at T/O., by using EPR alone.
This is what I learned from the Air Florida accident at KDCA.
Joined: Mar 2007
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From: Another Planet.
WOT'S IT SAYING NOW?
If I recall correctly from Hans Kunicke's book about the jet engine, the statement that EPR is ok for turbojet engines, but DIFFICULT TO MEASURE ACCURATELY in hi-bypass fan engines sez it all!
Had to fly EPRs on classic 74s some years ago and was sooooooh happy to move onto a 'frame with N1s.
Using the TLAR principle, a strange looking N1 will stick out like the dog's
s, but 1 point something or other never did it for me.
Maybe Hans would comment if he's still around and aware of this thread?
Which reminds me, I must call a millibar by it's proper name, a hectopascal, so's I can sound like I come from the far west and make words have more syllabubs and sound important...............................
Had to fly EPRs on classic 74s some years ago and was sooooooh happy to move onto a 'frame with N1s.
Using the TLAR principle, a strange looking N1 will stick out like the dog's
s, but 1 point something or other never did it for me.Maybe Hans would comment if he's still around and aware of this thread?
Which reminds me, I must call a millibar by it's proper name, a hectopascal, so's I can sound like I come from the far west and make words have more syllabubs and sound important...............................
Joined: Dec 2005
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From: U.K.
I agree with FULLWINGS's post 100% ..
Nobody has given a definitive advantage to EPR on here, and I do not know of one ... only massive disadvantages. So why use it as the primary thrust reference ? It is not only the increased complexity of the measurement, but also the fact that it requires and independent system to keep it anti-iced ... another potential source of failure.
I have flown with engines from all Western manufacturers, and they all make good products. I cannot see what disadvantage GE is at because it uses N1 .. it is simpler, more reliable and prevents beating. What is there not to like ?
Nobody has given a definitive advantage to EPR on here, and I do not know of one ... only massive disadvantages. So why use it as the primary thrust reference ? It is not only the increased complexity of the measurement, but also the fact that it requires and independent system to keep it anti-iced ... another potential source of failure.
I have flown with engines from all Western manufacturers, and they all make good products. I cannot see what disadvantage GE is at because it uses N1 .. it is simpler, more reliable and prevents beating. What is there not to like ?
Joined: Jul 2009
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From: Not far from a big Lake
Does anyone look at fuel flow to figure out thrust any more?
The old F-4 did most of its cruise around 3000 lb/hr per side.
Of course it was a straight turbojet with a variable nozzle which opened to limit EGT.
If the Air Florida mentioned previously had cross checked their EPR with fuel flow, they would have seen the problem straight away.
The old F-4 did most of its cruise around 3000 lb/hr per side.
Of course it was a straight turbojet with a variable nozzle which opened to limit EGT.
If the Air Florida mentioned previously had cross checked their EPR with fuel flow, they would have seen the problem straight away.
Joined: Jun 2001
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From: Great Southern Land
If the Air Florida mentioned previously had cross checked their EPR with fuel flow, they would have seen the problem straight away.
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From: dubai
Machinbird
Good point.
I know some, that ensured the total FF for all engine operating cruise, was maintained during engine out work. It was a quick reference power setting, should other parameters, not be at hand.
Good point.
I know some, that ensured the total FF for all engine operating cruise, was maintained during engine out work. It was a quick reference power setting, should other parameters, not be at hand.
Last edited by doubleu-anker; 2nd September 2013 at 04:55.
