EPR gage

[mixomax]

Why do you set " power" on 744's (RB 211 524-H) based on EPR and not on N1 or N3 like on the 757's.
Would it be because , looking at the ratio of total inlet to pressure
oulet,gives a more precise number?Yet, you still monitor the other gages to sense possible disagrement , should one of the pressure sensor becomes clogged.
Talking about clogged sensor,if Pt 1 (inlet sensor) is blocked,the EPR number is going to be higher than normal,what about if the Pt 7 (the outlet one) is experiencing blockage,what would be the reading?
Anyone for a simple formula????

Thank you very much un advance

[avioniker]

It's much more common for the Pt7 lines to develop leaks.
In that case the system detects lower pressure at the outlet so the pressure ratio will be reported accordingly. Usually it will go low. Just as though the tube or pickup were blocked.
When there's an EPR problem on an overnight there's a lot of seniority checking going on for low readings. It tends to be dirty and on hush-kitted JT-8's it can quickly develop into a real expedition with all the disassembly needed to work on the probes.
Ah, life in a tool box...:ugh:

[QAVION]

"Why do you set " power" on 744's (RB 211 524-H) based on EPR and not on N1 or N3 like on the 757's."

Isn't this because GE owns the copyright on N1's as primary engine indication? (Or is that another Urban Legend?)
:confused:

In other words, RR and P&W didn't have a choice (unless they wanted to pay royalties to GE).

Regards.
Q.

Inlet pressure is "P2" on the 744RR. You can see the P2T2 sensor just in front of the fan at the 12 o'clock position.
Exhaust pressure (Pint) is a combination of P5 (core) and P1.3 (fan) exhaust.

[HotDog]

Very much doubt that QAVION, I used to operate the Convair 880 which had GE CJ805 engines and our primary thrust indication was EPR.

[Daysleeper]

We do set thrust by EPR on RB211-535c powered 757's:ok:

[HotDog]

The Pratt & Whitney JT9D, which is a high bypass engine, uses EPR (PT7/PT2) as the primary engine thrust parameter.

[QAVION]

"Very much doubt that QAVION, I used to operate the Convair 880 which had GE CJ805 engines and our primary thrust indication was EPR."

Then it must be a classic case of garbage in, garbage out, Hot Dog.... :} That's what I've been told by a number of different sources. I even heard a rumour that the copyright was about to expire... so expect a flood of new aircraft with N1 primary engine indicators ;)

Cheers.
Q.

P.S. BTW, do they still fly Convairs... or were they too uneconomical because of the royalties they had to pay? :p

(Just joshing.... I want to keep this urban myth running as long as I can)

[HotDog]

No, unfortunately not. They were a fantastic aircraft, built like a brick sh!thouse! You could extend the main gear for speedbrake at 319KTS with a VLO of 374KTS. Very advanced electrics, Freon packs for airconditioning but they only carried about 110 pax in all EY config and the engines were very inefficient.

[B73567AMT]

The RB211 uses IEPR (integrated EPR) which is a ratio of all three 'airflows' in the engine. There are sensors for the inlet, bypass and core the outputs of which are integrated to give an accurate EPR reading.


Which RB211s are you referring to??
The -535s that I work on only take readings from fan inlet and LP fan exhaust.

[QAVION]

Which RB211s are you referring to??

In my case, the ones fitted to our 747's (Classic RB211-524D4's and 747-400 RB211-524G2-T, etc) have integrated EPR.

So you don't have some kind of multiple connector which combines these exhaust pressures?

Regards.
Q.

[B73567AMT]

It takes P1 from the P1 probe mounted approx 12 o'clock in the fan inlet, and there are 4 Pf rakes measuring fan exit pressure.

These are the only parameters going to the transmitter.

[Wino]

EPR is a linear indication of thrust.
RPM is not.

.1 epr anywhere on the guage is the same amount of the thrust (devide rated thrust into MAX Epr and you get a good idea)

N1 however as a measure of thrust is very poor. It moves all over the place depending on temperature and rotational speed. To go from 40 percent N1 to 50 Percent N1 may be an increase of a 1000 lbs of thrust. but go from 97 to 98 might be 10,000 lbs of thrust depending on the engine and application.

Furthermore, if you have an engine that is flat rated in thrust below and certain temperature (Virtually all of them are) the RPM that correspondes to that rated thrust will decrease with temperature. So you can overpressure the crap out of the engine and its mounts while still well below the rotational limits of the engine. The same EPR however will equal the same thrust regardless of temperature.


HOWEVER, this whole arguement falls apart once you leave sea level..

Cheers
WIno