EPR vs N1
 

hi.. just wondering what the answers would be to the EPR vs N1 questions.
i don't really use EPR.

how is it better than N1 if it is?

thanks

:)

Silberfuchs;

Very helpful post. Wondering if you could clarify one point here:

When you say that EPR is not a linear indication of thrust; if a new engine is producing 60,600 # of thrust with an EPR of say, 1.9, if that engine is showing 1.9 EPR 5 years later is it still producing 60,600 # of thrust, or do we need to compare it to N1 to find the answer? Is this the reason that we need to "know the RPM of the fan" (to quote an earlier posting in this thread)?

Thanks

Is the A330 tail fuel system the same as the 340?
Is fuel transfer done from center back to tail as well?

Well I guess I didn't do too badly. I got the call yesterday to go to HK for the second interview. Not until April though!!! And do they have to call so late? I was fast asleep. LOL ;)

Medflyer

Just to add to the always knowledgable silberfuchs. It is my understanding that EPR is more or less a direct indication of thrust whereas N1 is only the rotational speed of one component of the engine. However when setting EPR it is good to have an N1 indication to ensure EPR is being set within the defined rotational limits of the low pressure compressor N1. This can be highlighted by looking at the Air Florida crash into the Patomac River. The Capt used reverse to power back from the gate, in doing so ingesting snow into the engine freezing the EPR probes. On the take-off roll EPR was set however as noted by the co-pilot N1 was indicating low. He chose to ignore the indication with disasterous results.

Correct me if I am wrong, but I didn't think N1 was linear either ?
IE most of the thrust variation comes in the 75-100% N1 range

External differences
 

Hey, this may seem to general, but I dont see alot of 777 and 747's up in the great white area I am flying, Can anyone tell me an easy way to tell a 777 200 vs 300 , (emergency exits ...) and a 747 100 vs 200....

Cheers

Snowbirdbrad

Snowbirdbrad, the 777-300 is longer than the -200. As for the 747 Classic, the -100 has only 3 cabin windows on the upper deck , whereas the -200 has more(can't remember the exact number of the top of my head). Also, if the engine is anything other than a JT9D, it's probably not a -100.

With respect to the A330 CWT, I believe the -200 has one as it's the long range version. CX only operate -300 though.

Cheers

Remember that a jet engine produces thrust by accelerating a relatively small (compared to a propeller) mass of air by a relatively large amount. EPR is trying to quantify this by representing on instruments the ratio of tailpipe pressure to inlet pressure.

I think when Silberfuchs says EPR is not a linear indication of thrust, he means that 2.0 epr is not twice as much as 1.0 epr. It is actually alot more. I would say it is almost a logarithmic scale.