Re: Delta Ratio

From:         ehahn@mallard.mitre.org (Ed Hahn)
Organization: The MITRE Corporation, McLean, Va.
Date:         18 Sep 96 13:52:15 
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"m" == MikeM727  <mikem727@aol.com> 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 | ehahn@mitre.org | (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.