I have been taught that the EPR will definitely reduce with wear / age at a given fan speed in all engine types as will compression ratio of a piston eng for the same basic reason. When they are tested in at test cell, the boffins fudge the indication using, trimmer resisters or CDX units or programme plugs (EPR & EGT) etc.To make it appear to produce the correct EPR. There are numerous ways to fool you jet jockeys into thinking the thrust is spot on, as indicated on the dial. Even new engines are trimmed just to make all look good and even. EGT can be fudged down with resistors to prevent limiting due to inherent indicating anomalies in individual engines. EGT will appear to drift up as the temp probes age and break. N.. figures are basic RPM displayed in %.
For post #8 & #9
EPR of just <1.0 can be normal during DES at IDLE in big inlet hi bypass fans because, EPR is the ratio of the ram air press in the nose cowl to what is pumping out the back, (fan & exhaust on some) displayed as a number 1 : 1.XX (the 1 is just not displayed to simplify the display). If the engine is at idle and not using all the air forced into the nose cowl due to ram, the incoming air will compress and spill out and not pass through the engine Therefore the ratio of inlet press to outlet press is less than 1:1 ie < 1.0 EPR.
Short CCT
Last edited by Short_Circuit; 24th Oct 2007 at 22:58.
Reason: Include EPR <1.00