744 EPR...

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i was just looking at some flight deck screenshots (Real) and above the N1 readings on the INBRD CRT was a space for EPR readings... What does EPR stand for, and what is it related to?

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EPR Stands for Engine Pressure Ratio.This indicates the differences in pressure in front of the engine, and behind the engine. Using this info, you can calculate how much forward thrust the engine produces.Michael Henke

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EPR Stands for Engine Pressure Ratio.This indicates the differences in pressure in front of the engine, and behind the engine. Using this info, you can calculate how much forward thrust the engine produces.Michael Henke

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ah thanks - and why was it only displaying on several of the photos i viewed? does it only show at a certain period of flight or something?

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Depends what engines the aircraft is equiped with...Aircraft equiped with Rolls Royce engines use EPR as the primary indication for the engines.

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ah don't worry, found a website which details it - so basically it is there to determine engine thrust..

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What's the website?Ken.

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More importantly, will PMDG model this on their 747?Jeff

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>>More importantly, will PMDG model this on their 747?I asked this a while back, the response was yes, yipee!

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EPR is Engine pressure ratio, its basically a measure of the pressure across the engine basically from the compressor to the end nozzle taking into account the losses through the inlet. Heres a basic formula of how to work out the EPR.EPR= compressor pressure ratio x burner pressure ratio x turbine pressure ratio x nozzle pressure ratioOf course you need to know all of the other values, but this is usually computed by the aircraft and isn't normally found on conventional smaller aircraft which usually just show the RPM or N1/N2 readings on larger jets.Also EPR from my experience on the Airbus fleets is usually only found on certain engine types/manufacturers, particuarly the A320 variants of CFM and IAE.http://www.grc.nasa.gov/WWW/K-12/airplane/Images/epr.gifRegardsG-MIDY/Lawrence :-scatterAMD 3000+ | 6800GT | 1GB GeiL |

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well, yes thats the site i looked at... now i understand how its calculated, but how do i read it instead of N1 (which is a percentage)Are certain values (like 1.00) idle? Or would 2.00 be MAX? Also, am i right in assuming this would only appear on the RR variant?

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>well, yes thats the site i looked at... now i understand how>its calculated, but how do i read it instead of N1 (which is a>percentage)>>Are certain values (like 1.00) idle? Or would 2.00 be MAX? >No, not really. An EPR of 1.00 would indicate a stopped engine. Normal idle values would be 1.05 to 1.10 depending on the engine. Takeoff EPR varies with temp and pressure alt. and does not corelate directly with N1. EPR indicates pressure ratio only and therefore does not have certain 'fixed' values to indicate takeoff or max power. These values are calculated based on temp and pressure altitude and will vary for any given thrust should the temp/press. change.>Also, am i right in assuming this would only appear on the RR>variant?Both the RB211 and PW4000 use EPR. The CF6-80 uses N1Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.precisionmanuals.com/images/forum/ng_driver.jpg

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so the pilots of a 744 would have to find out temp and pressure before a flight, then be able to factor these in to the EPR values? or, would the FMC provide this info....if so, how do temp, pressure and other misc values affect the EPR...? i.e. higher temp makes the EPR higher...

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As has been said, EPR is a ratio - it tells how many times the pressure of the air being exhausted is higher than the pressure of the air going into the engine. An EPR of 1.0 would indicate an engine that is not producing thrust - not necassarily a stopped engine. The advantage of EPR over N1/N2 is the fact that it is a more direct way of measuring thrust. EPR is also dependant on airspeed - while an engine at idle thrust may have have an EPR of 1.03 when the aircraft is stationary, you may get an EPR of 0.78 when going 320 knots at the same N1/N2! Basically that would mean the engine is "braking" the aircraft. No, not breaking ;-)Adrian

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I'm not sure if this is true, if the OAT (Outside Air Temparature) is higher, the overall EPR is lower, because the air pressure drops if the air temparature rises, so the overall EPR should be lower than normal. This is why airplanes usually fly during nighttime in hot countries. I've visited Turkey 4 times now, and 4 times I departed back to Holland during nighttime.Like I said in the beginning, I'm not sure if this is true, hope somebody else can confirm this answer.Michael Henke

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>I'm not sure if this is true, if the OAT (Outside Air>Temparature) is higher, the overall EPR is lower>Like I said in the beginning, I'm not sure if this is true,>hope somebody else can confirm this answer.>Sure: higher temp (and consequently higher pressure) = lower epr.That's also why higher alituted = less power.But also less resistance = less power needed.So even if climbing you indeed have less power available it does not negatively affect the flight as the airplane is encountering less resistance.But now that i think of it...don't know for sure, but by diminishing the air pressure, the intake pressure is lower and so is lower the outlet pressure...So maybe the coefficient remains costant?Don't know for sure...

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>so the pilots of a 744 would have to find out temp and>pressure before a flight, then be able to factor these in to>the EPR values? or, would the FMC provide this info....>>if so, how do temp, pressure and other misc values affect the>EPR...? i.e. higher temp makes the EPR higher...

EPR isn't necessary, you don't even really need to know the basic concepts just the figures ie a certain EPR on takeoff will be reached to consider it safe, just like N1. EG 1.36 should be attained with a certain power setting as a N1 of 96% would with regard to atmospheric pressure and temperature including altitude.

G-MIDY/Lawrence :-scatterAMD 3000+ | 6800GT | 1GB GeiL |

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i guess the big question now is did PMDG model EPR on the respective engine variants...

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To all you EPR fans:don't put your hopes that high - EPR simulation is extremely complicated. While you can actually simulate N1/N2 behaviour on a computer, EPR is not that easy. Either you take a mathematical model or you take empirical data - either way, I doubt it would work fully realistic. Even PS1.3 "cheated". FS does have an internal EPR variable (so I've heard) but its "Microsoft EPR" - meaning it has nothing to do with reality :-)

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Slightly off topic......anyone know of a graph that shows this - Higher altitude = Less powerLess resistance = Less power needed.I guess the lines would cross over at some point and that would be the most efficient altitude to fly at. I was always told it was about 36000 feet but the FMC tells a different story sometimes.Cheers for helpG

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i think it depends on weight.... thus the reason for the 'step climb' function on the 744...

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>would be the most efficient altitude to fly at. I was always>told it was about 36000 feet but the FMC tells a different>story sometimes.As the other poster said, it also (and mainly) depends on weight.A transoceanic flight starts very low and ends up very high because of fuel consumption.So basically the optimum level depends on many conditions not just thrust and air density.

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