View Full Version : EPR vs. N1
Crossunder
9th Jan 2007, 11:26
Done a search on the Forum, but no joy. Google not very helpful either.
Why do some jet engine manufacturers use EPR, while others use N1 for thrust setting? What are the pros and cons of the two? From what I've read so far, it seems as though EPR is a bit outdated when it comes to modern turboFANS, but still RR insists on using EPR? :confused:
Cheers,
Crossunder.
barit1
9th Jan 2007, 13:53
Crossunder - try http://www.pprune.org/forums/archive/index.php/t-10159.html - I found this through Google in the archive. It covers most of the good points. :8
One issue that seems to pop up now & then is engine deterioration. Using EPR (assuming it's properly calibrated) then EGT/TGT will gradually creep up to produce the same rated thrust after a few thousand hours.
With N1 management, two things happen as the engine deteriorates: The fan airfoils lose a bit of efficiency so they pump less airflow at the same N1, but the core runs a bit hotter to drive the fan. Thus fan thrust drops a bit, but core thrust increases a bit, and they effectively balance each other.
For a bit of education, check out the MEL for TO thrust-setting procedure if your primary thrust gage (N1 or EPR) goes dead. :cool:
Seat1APlease
9th Jan 2007, 22:35
Try googling the accident report on the 737 which crashed in the Potomac river in Washington?, having take off in icing conditions using EPR with the P7 probe covered in ice.
They thought they had enough power to get airborne but they didn't. If they had cross checked on the N1/N2 readings then things might have been different.
barit1
9th Jan 2007, 22:47
This (http://www.ntsb.gov/ntsb/brief.asp?ev_id=20020917X01907&key=1) is the NTSB report.
Except - it wasn't the Pt7 probe iced up :confused: -- it was the probe at the front end (Pt2).
JackOffallTrades
9th Jan 2007, 23:43
As a primary instrument for setting power I belive it varies according to the manufacturer. Sucks, blows, spins or whatever.... Just a good idea to understand what you're using, why and what numbers to set. My brain is too small to go any further than that.
lomapaseo
10th Jan 2007, 13:59
As a primary instrument for setting power I belive it varies according to the manufacturer. Sucks, blows, spins or whatever.... Just a good idea to understand what you're using, why and what numbers to set. My brain is too small to go any further than that.
Right-on!
a little bit like Boeing and Airbus differences.