Dumb EPR question

[Fatboyslim]

Does EPR increase or decrease on T/O and why??

[CCA]

Decrease due to Ram Rise, therefore thrust should be set by 80KTS so your not chasing the ram rise loss.

[jtr]

Ram temp will result in a decrease in thrust as V increases, but doesn`t ram pressure increase more than counter this?

On the Rolls, I thought the figure increases on the roll (will take more notice in future)

Certainly the EPR value on a go-around is higher than a take off for the same conditions, and I thought the reason was ram rise only, as that is really the only difference b/t the two scenarios isn`t it?

[quid]

I agreee with CCA. Standard day setting for my a/c are 1.85 for t/o and 1.81 for go-around. Takeoff EPR must be set by 80 kts, any faster than that the EPR reading will start to fall off and you may overboost. Depending on the actual conditions, the 1.85 set on t/o may fall back to 1.78-1.80 shortly after gear is retracted.

[jtr]

Are both charts the same? All the ones I can remember looking at have T/O figures drawn up for packs off, and G/A for packs on. After applying the corrections, and assuming you are operating at above ISA conditions (to eliminate any throw on from a derate) the figures I have come up with G/A EPR higher. This is on an A330 so is there any possibility that FADEC makes the numbers do different things?
(Sorry to original poster, not trying to hi-jack the post, but am quite curious now)

[Cough]

737-200

T/O Epr - Typical 2.10
G/A EPR - Typical 2.08

EPR = Pressure at back / Pressure at Front

On T/O - Pressure at back is constant (give or take), pressure at front increases (ram effect) hence EPR decreases.

[scroggs]

For the RR-powered 747-200, ISA conditions at msl, t/o EPR = 1.69, g/a EPR = 1.64. T/o EPR is packs off, G/A packs on but the difference is more to do with the increased IAS in the G/A case.

[expedite_climb]

Good old 'EPR' button on the MCP.... works a treat ...!!!!!!!