Why do CF6 engines have no EPR indications?
N1 as a primary parameter is a patended system by General Electric (GE). From the Aerowinx Forum, messsage by Mariano Anchorena: …I have also done some research about it a couple of years ago. I can try to briefly explain why N1 is used for thrust setting in GE engines. Please, keep in mind I am not an engineer, and some innaccurate or wrong information may be present. EPR was first used as a reference thrust setting parameter because thrust, itself, is a function of area and pressure. On older pure compressor (no bypass flow) engines, measuring EPR was easy because only one probe was needed on the only exhaust (core flow). This becomes more complicated in high by-pass ratio engines, where the nessecity for two probes (core and by-pass) arises, which, in turn, causes the need to come up with some way to mix the measurements of both probes, and figure out a way of blending both readings in such a way as to come up with an accurate and realistic EPR indication. But, this is not the end
