744 EPR...

[Guest alexhn]

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?

[Guest Flightfreak]

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

[Guest Flightfreak]

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

[Guest alexhn]

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?

[Guest Babubhai]

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

[Guest alexhn]

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

[kmanning 12]

What's the website?Ken.

[AWACS 12]

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

[Guest ahmedem]

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

[G MIDY 101]

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 |

[Guest alexhn]

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?

[CF104 0]

>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

[Guest alexhn]

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...

[Guest yawdamper]

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

[Guest Flightfreak]

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