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Guest mikealpha

EPR scaling

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To enhance a freeware MD-11 panel with EPR gauge and correct indications for some Pratt and Whitney variants I'm getting more and more confused.The PW 4462 have am EPR scale of 0.8 (idle) to 1.6 (max). If I look with AFSD, I see with this and also some other planes a much smaller EPR scale (e.g. 1.1 to 1.35 at AGL). To make it more weird, with a constant N1 climb I see EPR values going almost down to zero at high altitudes. Which puts the Jet engines close to vacuum cleaners :)Is both that scaling and general misbehaviour buried in some air file tables, or is this a general FS bug ? How can I adjust this for a particular plane ? Can anyone shine a light on this ?Mike

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>The PW 4462 have am EPR scale of 0.8 (idle) to 1.6 (max). If I>look with AFSD, I see with this and also some other planes a>much smaller EPR scale (e.g. 1.1 to 1.35 at AGL). To make it>more weird, with a constant N1 climb I see EPR values going>almost down to zero at high altitudes. Which puts the Jet>engines close to vacuum cleaners :)>>Is both that scaling and general misbehaviour buried in some>air file tables, or is this a general FS bug ? How can I>adjust this for a particular plane ? Can anyone shine a light>on this ?>>Mike The FS EPR variable is nearly useless. To get realistic values one has to program an EPR gauge. It turned out to depend mainly on CN1 for a JT8D. A straight line based on CN1 with an offset and slope would probably be much better than the FS EPR variable. However, to get a really accurate match to an JT8D (0.01) I had to combine a third order polynmial fit with a straight line on the bottom. The idea is to match a FM table for EPR at TAT = 15 C, any variations wrt TAT are accounted from by using Corrected N1 rather than just N1. EGT is also bad, though one can at least set it in the AIR file for typical cruise conditions. I was also able to calculate a reasonable EGT, it started with the accurate EPR I calculated. There is also an 'EPR limit' in the AIR file (or, can be added from the 777 AIR file), however it can be set for only one condition; otherwise it moves way off. Ron

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Hi Ron,thanks for the info. Sounds like some work, but seeing the MS EPR readouts, that's almost as expected ;).You talked already about the subject "competent" in another thread ... ;)Mike

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