From: email@example.com (Ed Hahn) Organization: The MITRE Corporation, McLean, Va. Date: 18 Sep 96 13:52:15 References: 1 2 Followups: 1
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"m" == MikeM727 <firstname.lastname@example.org> writes: m> In article <airliners.1996.1875@ohare.Chicago.COM>, m> GWilson404@aol.com writes: >> Delta is sometimes used to mean the ratio of either ambient or >> engine m> face >> total pressure to sea level static standard pressure, 1013.25mb or >> 14.69psia. At constant temperature the thrust of a jet engine is >> directly proportional to this value , which therefore has to be >> taken into account in field performance calculations. m> This sounds to me more like a description of EPR, Engine Pressure m> Ratio. I've never heard EPR referred to as "Delta". Of course the m> term "delta" can be used to mean any differential. I think GWilson is trying to say that the Delta ratio is the ratio of ambient pressure at a particular altitude to sea level pressure, independent of vehicle speed. Thus, Delta can be tabulated on standard atmosphere tables. Jet engine performance is a function of Delta. EPR, on the other hand, is exhaust total pressure over inlet total pressure for a specific engine at an instantaneous point in time, something quite different. ed -------- Ed Hahn | email@example.com | (703) 883-5988 -------- The above comment reflects the opinions of the author, and does not constitute endorsement or implied warranty by the MITRE Corporation. Really, I wouldn't kid you about a thing like this.