hiMy question is what is preceisely is the EPR reading? as far as i know, it is an acronym for engine pressure ratio. how does the EPR relate to N1 and N2 (and N3 for RR) readings?and while i am at it, what are the main differences in the three variants?appologies if this has already been explained. sometimes, i find the search function on AVSIM to be a bit unwieldy.thanksTomsax

As far as I understand the EPR is the measurement of air pressure going into the compressor vs the air pressure exhausted through the turbine. The N1, N2 and N3 are % of the rotation of the N1, N2 or N3 spool. There is no direct link (I think) between them as the air pressures at the compressor is the ambient air pressure, and will therefore differ.

>hi>My question is what is preceisely is the EPR reading? as far>as i know, it is an acronym for engine pressure ratio. how>does the EPR relate to N1 and N2 (and N3 for RR) readings?>>and while i am at it, what are the main differences in the>three variants?>>appologies if this has already been explained. sometimes, i>find the search function on AVSIM to be a bit unwieldy.>>thanks>TomsaxHi,The search engine of this forum and of other forums can be quite useless sometimes...There's a topic that refers the EPR and there's a link into the NASA website which has a brief theoretical explanation. As for wikipedia, I haven't found any references.Topic: http://forums.avsim.net/dcboard.php?az=sho...ing_type=searchLink:http://www.grc.nasa.gov/WWW/K-12/airplane/epr.htmlI'm sure a google search on the subject won't let you down.I'm not an aerodinamic or thermodinamic especialist, but I figure that if the spool rotating speeds can be used as a measure of output thrust, AND if EPR can also be used for the same purpose, then there must be some kind of relationship between EPR and spool rotating speeds... Maybe it's too far-fetched or just plain wrong, but it seems logical to me... May the real specialists enlighten us all :-)Cheers,Pedro Venda.

thanks gents for the information. i appreicate it! love this forum. people are so willing to help out.Tomasx

You mean i'm not a specialist :-( LOL

"As far as I understand the EPR is the measurement of air pressure going into the compressor vs the air pressure exhausted through the turbine. The N1, N2 and N3 are % of the rotation of the N1, N2 or N3 spool. There is no direct link (I think) between them as the air pressures at the compressor is the ambient air pressure, and will therefore differ."On the Roller, integrated EPR is used. This is the relationship between the air pressure going in the engine intake versus the air pressure coming out of the turbine and the coldstream duct. The exhaust pressure values have to be processed to make them meaningful, but they are a good representation of thrust.Similarly, N1's are also a good representation of actual thrust after a bit of data processing (Most of the thrust comes from the N1 fan at the front).Cheers.Q>

Thanks for the extra info :-)I hope some of this comes up in my airframes and systems exam tomorrow LOL

> There is no direct link (I>think) between them as the air pressures at the compressor is>the ambient air pressure, and will therefore differ.>>Alister, are you sure about this? I have only scraped the surface of how turbofans work but it is my impression that the pressure is greatly augmented after air is admitted to the several compressors since their job is to compress air!Best Regards,Victor Limahttp://www.precisionmanuals.com/images/forum/800driver.jpg

Everything you'd ever want to know about engines:http://en.wikipedia.org/wiki/Jet_engine