Epr<> Drag ??

[BESTGLIDESPEED]

Just wondering the other day during a descent,...

Why would the EPR indication during an idle descent is during most of the time, lower than 1.0 ?

Isn´t this a sign of incoming Pt greater than outcoming Pt ? ( whatever the stages ). That is... more presure incoming than outcoming ? thus , our engine "blocking " instead of at least letting flow-by the airmass ?


Even more worrying...

This happens during most of the CRUISE phase too !!!



What piece of info am I missing here ?



( can´t sleep... )


Thx.

[Chris Scott]

Which engine are you talking about, I wonder. It's a new one on me.
Maybe the forward of the 2 pressures on your engine is taken after the fan? Has the Tech manual got an engine cutaway, or specific definition of EPR?

Otherwise, you might be needing a hot toddy...

[Mad (Flt) Scientist]

I'm pretty sure idle EPR on a BR700 is below 1.0. 0.9-something, if I recall correctly.

Might be related to whether its "IEPR"; again, I hazily recall that some types use just the core or bypass EPRs, while some use an averaged value of some kind. if the engine is at low power, such that the thrust is disproportiantely from core over fan, maybe a fan-biased EPR will read below 1.0 even when there's a small amount of net thrust?