>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...

>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 |

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

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 :-)

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

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

>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.