View Full Version : EPR Command Cursor B747-400 RR
I'm trying to figure out what the EPR command cursor is doing in this photo:
Photos: Boeing 747-412 Aircraft Pictures | Airliners.net (http://www.airliners.net/photo/Ansett-Australia-Airlines/Boeing-747-412/0086431/L/)
Idle is a normally a function of N3 and compressor discharge pressure.
During idle, does the command cursor just sit "idly" on top of the actual (indicated) EPR/IEPR? :)
Thanks.
Rgds.
NSEU
TopBunk
3rd Aug 2009, 08:08
nseu
It looks to me at first take as if in that photo they had had all 4 engines flame out!
The actual EPR is 0.75 which is waayyy below idle EPR of about 1.02 or so. The green line towards the top of the EPR scale is the 'reference EPR' which is also displayed in green numerically on top of the scales as 1.48.
The N1 and EGT values are however consistent with an idle descent, so I would suspect as an alternative that the EPR gauges have all failed for some reason.
Sorry that's the best I can do having been up all night looking at the bl00dy things without seeing the lower screen with the secondary engines instruments and any EICAS messages!
Nepotisim
3rd Aug 2009, 09:31
Firstly that won't be a Roller EPR figure as Pratts were fitted to the Ansett Aircraft.
Secondly, and its a guess, it will show max cruise as that is what is selected as shown above the EPR figure of 1.48. MAX CRZ.
The yellow line above that probably will be max continuous.
We will leave the correct answers to some piloty types as opposed to an engineer.:ok:
Carnage Matey!
3rd Aug 2009, 09:58
I think Nepotism has the correct answer, but I only fly RR engines.
paddy in the east
3rd Aug 2009, 10:11
The 412 was an original SQ aircraft, fitted with PW4056.
The photo is a normal descent, just like the caption says. On the PW, it's purely an EPR aircraft. No N3, just a N1 and N2.
All is well!!!!:ok:
Sorry, I should have realised that it was PW from the Ansett reference, but surely engine idle is controlled in a similar manner (with N2 and burner pressure being the controlling factors)?
It seems like the command cursor is at the bottom of the scale (why would it be anywhere else?). :confused:
Pedalz
3rd Aug 2009, 23:13
The EEC should still control through two seperate engine parameters (EPR and N3 on RR, no idea about PW) depending on normal and alternate modes. During idle, does the command cursor just sit "idly" on top of the actual (indicated) EPR/IEPR? Seeing as the aircraft is trying to get down it isn't surpriseing the EPR command cursor is resting ON the commanded EPR which would be idle for a high rate of descent. It does look strange though..
it isn't surprising the EPR command cursor is resting ON the commanded EPR
I assume you mean the actual EPR?
By the way, what is a normal EPR on a Roller in this phase of flight? Does it also dip below 1.0?
looking at the manuals, I see the EPR on the RR and PW are measured differently The Roller uses cold and hot stream pressures to calculate exit pressure ("IEPR"), the PW only hot stream.
Rgds.
NSEU