Am I correct in assuming that each engine manufacturer and engine generation use different methods to determine EPR. If so this would reinforce my belief that EPR isn't a valuable tool for pilots to use. Can I reliable interpret the EPR information from the RR Trent 556 on the A346 I fly one day in the same manner as the EPR info on the A332's RR Trent 772's I fly fly the next?

I don't understand how you can say that and claim to sit in the front right hand corner.
It's another engine parameter - would you prefer just one gauge showing N1 and hide all the rest?
It's brilliant for confirming whether or not you actually do have take off thrust, and very simple for setting a good approximate approach power, even if you have an engine out as Meikleour explained in post #12.

My point is that the actual value indicated is virtually meaningless. Every other engine gauge on display give me a value which i can compare against a min and max value. I don't have a hassle with the needle indication but rather the number displayed itself. That is why I suggest the EPR value should be replaced by a corrected % to be meaningful. So for example I would like to know that at FL410 the thrust set is 77% of what that engine can produce under those conditions. A number like 1.050 means zip. Surely the technology is around to display such info?

Hi divinehover,

Your engines will be flat rated to ISA + ? (my old -22Bs were to ISA +15 degs C). So maximum thrust was always 1.526 EPR, & MCT was 1.419 up to 28 degs C at sea level (Simples?)
When it was less dense, the maximum EPRs reduced because we were now limited by another parameter usually Fan speed or TGT.

What could be simpler?

We used to Flex EPR down for reduced thrust take offs - but we knew our Max and MCT limits because we had to set them manually. You probably use FMS to control them now.

In the cruise we bugged up MCT from tables for the density altitude (in case it was needed), and expected cruise EPR using weight, density Altitude, cost index / Mach no. etc.

We had RPM limits which exceeded 100% as the engine was developed. So 77% of what? It's just a another number.
Is your TGT expressed as a % age of melting temperature?
Are your V speeds expressed as a ratio to V stall?

EPR
 

Aviatorhi says: "That's all good, but EPR measures the difference in pressures between the intake end and the core exhaust, not the fan exhaust."

Not always so, the RB211's use EPR gained from comparing the ratio between P1 (Inlet Pressure) to P Int (Integrated pressure of core exhaust and fan outlet pressure). This gives a true indication of thrust being delivered.

That would be (nearly) the boeing way on the 737. No EPR to start with, you get a big round dial with N1 and numeric EGT values. And thats it. Everything else is hidden and only pops up if something isn't right.

Oldfella... seriously!?

Was it too hard to read the rest of the post? I only say that EXACT thing in the last paragraph.

I think it's the variation in EPR ranges with environmental conditions on some engines that makes the number itself fairly useless.

RR Trent 895 max climb EPR ranges from 1.132 at a hot sea level to 1.518 at 43,000'. To fly level at 270kts, 15,000' and 160T GW you need 0.978... I can only quote these figures because I have the QRH displayed next to this posting. The numbers do not lend themselves to intuitive use, to put it mildly.

Comparing to something like the JT8 on the "classic" 737. 1.0EPR meant zero net thrust, 1.8-2.2 was full power. If you lost an engine on approach when you needed 1.3EPR on two, then 1.6 (twice the decimal part, plus one) would be a very good ballpark for the remaining motor. I can't remember now but there was another simple formula like taking 17 off the gross weight which would give you a very reasonable initial setting for a F30 3deg approach.

Point is, using N1 for a quick gross error check on takeoff, you're looking at c.85% on a full derate. Anything less than that should raise an eyebrow. Getting closer to MTOW, it's going to be into the 90's, probably 96-97% at the max.

Yes, of course you can get the books out and look up what kind of EPR to expect given various parameters but that sort of shows the lack of information from the original units used. Might as well be calibrated from blue1 to yellow15 with a limit of "sausage"... You get a power gauge on a Veyron (0-1001bhp!) and power reserve on a Rolls-Royce (100%-0), why can't we have a Thrust-o-Meter(TM) calibrated 0-100%?

In the very early days of jets, a direct force measurement (strain gage) was attempted but it was fairly useless on buried engines because it did not include inlet forces.

But podded engines are another matter - maybe Mr. A or Mr. B could give some insight whether measuring thrust mount or pylon strain is feasible.

Understand, though, that available physical thrust is a function of altitude - so tables or a corrected readout would still be necessary. :8

IEPR v's EPR
 

Aviatorhi. Apologies, did not mean to offend. I guess when the opening comment seemed incorrect I read no further.

Thrust Parameter:
 

In addition to FIS's reply:

A380 uses the THRUST parameter, here shown with eng#2 in degraded N1 mode.

Engine windmilling = 0% Thrust, TOGA = 100% Thrust (Bleeds off)

http://i474.photobucket.com/albums/r...380Display.jpg

EPR is just a calculated controlling parameter
N1 is just a calculated controlling parameter
IEPR is just a calculated controlling parameter

The engine generates thrust and needs to be protected, it needs to be kept within limitations. As mentioned before, the limitations change and the highest possible generated thrust changes as well (temperature and pressure depending).

EPR, IEPR and N1 values always need to be corrected for current atmospheric conditions, so to a pilot none of them actually make sense. One has an andvantage (don't know if it's EPR or N1, should have to go back in the books though). We might think N1 is more adapted to our pilot environment, but it isn't really. Otherwise nobody would wonder why N1 and N2 values can be greater than 100%. 100% does not mean a damn thing. I can understand a pilot says "EPR doesn't mean a thing anymore". But so does N1. Say we need full takeoff power. Today that might be 95% N1, tomorrow it can be 105%.

EPR is still perfectly usuable for fan jet engines. On low bypass ratio engines the parameter might be more understandable for us, pilots, yes. But that has never been the goal :-).

BTW, even fuel flow can be used. Never flown the 737-200 with the JT8D in real, but in the simulator IAS/2 was your fuel flow. 250kts? 1250kg/h :-).

I surmise from the above discourse that the Trent series no longer use IEPR (per RB211) which always seemed to be very well liked by pilots. Does anyone have insight re this decision?

By rudderrudderrat:
That, to me, seems like an argument for using N1.

Im hoping that post 32 is a graphical representation only.

Thats a serious margin in that sort of temperature with packs and NAI on!

Lets hope it isn't heavy or high too! lol!

Hi Beeline,
I read it differently. It looks like it's taking off using reduced thrust and is below thrust reduction altitude. The assumed temperature is 59 degs C, whilst the ambient is probably below +10 degs C and in icing.

Hi ImbracableCrunk,
If you really don't want to know your effective thrust - then stick with N1.

Cockpit Design: EPR v/s N1 indication « The Flying Engineer
"The advantage with EPR is that it is a pressure ratio, and is indicative of engine thrust. Simple physics will tell you how: Force (Thrust) = Pressure multiplied by the Area of application. According to Boeing, EPR is more directly related to, and a much better indicator of thrust than the compressor speeds (N1 and N2), and therefore is more advantageous in terms of accuracy to utilize EPR to control engine operation."

On second glance yes, Flex-temp adjustment.

Interesting concept of thrust percentage. I'm surprised they didn't integrate N1 and EPR into that parameter using both values. Or have they? Not yet been on the 380 type course.

Yes, it tells you what the thrust is more accurately but the numbers are not easily remembered and change wildly with external conditions.

You're taking off on a LR sector at near MTOW. When you line up and press TO/GA, the engines settle down at 1.213EPR. Is that good or bad? Ask the guys at Melbourne...

Hi FullWings,

I've just read that incident report at Melbourne: http://www.atsb.gov.au/media/3532364/ao2009012.pdf and couldn't find anything about the lack of awareness of EPR mentioned.

What is mentioned is the take off weight error of about 100 tons wasn't trapped with:
Flight plan Expected TOW,
INIT B flight plan expected Zero Fuel weight entry,
green dot speed difference.
Larger than expected flex temp figure.

Even if the crew didn't have a "handle" on EPR, - N1 was still displayed.

What I'm trying to say is that you get used to checking that achieved EPR = commanded EPR, not that the numbers make sense on their own. If the commanded EPR is *grossly* wrong (full derate where there should be hardly any, as above), it doesn't stand out in the same way it would with N1 as the controlling parameter. Yes, it's a good habit to look at the N1 as well as the EPR but when we're tired or in a hurry, "computer says OK" often ticks the mental boxes: all those needles lining up with the little bugs, quite compelling.

If you were in a Cessna and got 2200rpm instead of 2500rpm, you'd know there was a problem and reject the takeoff. If the gauge read 1500 one day and 3000 the next, for the same power, it wouldn't be so clear cut.