Originally Posted by
Thridle Op Des
Like FullWings, I flew an engine where we had an EPR of 0.982 or something equally meaningless (RR Trent 500), since then, I have always preferred N1, not as a direct measure of performance, but rather as a reliable reference I can come back to. I now operate the GP7000 engine which has a EPR variant called 'Thrust'. It's very clever (perhaps too clever), 100% 'Thrust' is exactly that, nice idea but relies on multiple sensors. For an unreliable speed reference, I am still noting the cruise N1 and pitch attitude as my reference in case the clever system becomes confused.
EPR values less than 1 are not meaningless. They mean that the thing is producing drag, not thrust. Something that you never get from N1 indication. Could be usefull in understanding what's the difference between idle thrust and dead engine. Of course you need to know EPR at the same speed on dead engine. We may check it in the SIM.