Question about GE CF6 and rated thrust
 

At what N1 setting does one achieve a rated thrust level at sea level?

My main example would be CF6-50C2B (53,200lbs). Does the engine achieve this thrust at 100% N1, or does it achieve this power at the maximum N1 setting, between 117 and 118.5%?

If it achieves 53k thrust at 100% N1, how much more thrust is it producing at maximum power?


Thanks guy.


As an aside, does anyone have any detailed charts or any sort of information they could send me regarding the CF6-50C2 as it pertains to DC-10s? I'm working on a flight dynamics engine for a flight simulator program and I want to ensure I'm being as accurate as I can be given the constraints of the simulator software.

Depends on the temperature/pressure of the day. Any N1-managed engine will have a power management curve in which you enter with ambient conditions and look up the proper N1 for that day. (different temp or pressure => different air density!)

The N1 curve will have two separate regimes:

1) In the flat-rated regime, N1 increases with TAT and altitude, to maintain the constant flat-rated thrust (53K in this case). In this regime, rated TO thrust does not change; the changes in air density with temp & pressure are accounted for by adjusting N1.

2) Above the flat-rating break TAT, N1 decreases with TAT to protect the hot section.

PS - don't let "100% N1" confuse you. It's a purely arbitrary number - equivalent to 3500 rpm IIRC. This value means nothing except to the mechanical guys.

The chart for Take-Off Thrust looks like this.

Enter with OAT and PA. Then correct for bleed configuration.
http://i104.photobucket.com/albums/m...006/FM0517.jpg
If you need to convert N1 to RPM use this chart.
http://i104.photobucket.com/albums/m...MEA_000038.jpg

Rated thrust is Max Takeoff Thrust at ISA. (sealevel, 15 C etc)

So, looking at Clarence Oveur's diagram,
the CF6 50C2 engine will output;

52.500 lbf at N1= 111,8 at 15C and sealevel

Cheers,

M

PS: Using X-Plane?

Not quite.
Besides just stating the obvious - I am sure everybody can use the chart - note that there is a difference between installed thrust and ideal thrust.

Why the hostile tone?
You did not answer DAL2728's question.

He asked at what N1 the PUBLISHED thrust is.
(the one given in the FAA certificate and other publications)
There is only ONE EXACT answer to that question = 111,8 N1

M

That is just not correct. It is not possible to give an exact answer until the variables have been defined.

May I suggest that you read the post by barit1, as I get the impression that there are a few things here, that you don't quite understand.

Clarence,

All variables are defined. I suggest you think again.
Here is DAL's question;

My main example would be CF6-50C2B (53,200lbs).
Does the engine achieve this thrust at 100% N1, or does
it achieve this power at the maximum N1 setting, between 117 and 118.5%?

The thrust (53,200 lbs) is the PUBLISHED thrust by the FAA.
Now the FAA publishes their thrust as MAX TO THRUST at ISA
(Standard Athmosphere which is Sealevel, 15 deg C, 1013,25 mb)
If you look that up in your diagram you get about 111,8 N1 - PERIOD!

barit1 gives an excellent explenation, but it's not answering the
question above.

There is probably other scenarios where you will get exactly 53,200 lbs of thrust, but thats not the point here.

M

I see you still don't understand.

At sea level, using a -50C2, you will have rated thrust, 51,800 lbs, with an N1 ranging from anywhere between 100.6 to 114.6. That is the closest to an exact answer there is, until all variables have been defined.

You came up with an answer. Not the answer, but a answer. I don't see why that is so difficult to understand?

ISA is setting up the conditions vs temp and airpressure. Sealevel sets altitude variable. I don't see where Morten is wrong.

The question was At what N1 setting does one achieve a rated thrust level at sea level?

The answer is anywhere between 100.6 and 114.6. There is not one exact answer as XPMorten claims. He took it upon himself to define the temperature, to come up with an answer. It is one answer out of many.

There is a certain envelope in which rated thrust can be achieved. As long as you stay within this envelope rated thrust is available. This envelope is defined by Temperature and Pressure Altitude. If the thrust is constant, N1 must be variable. Therefore, as only PA was defined, N1 can only be expressed as being somewhere between the MIN and MAX range as depicted on published charts.

It really is basic stuff.

Thanks everyone for your help on this. The way I had stuff set up, I was achieving the rated thrust right near the top-end of the N1 scale. I will be shifting that all over a bit.

I'm working in a DC-10-30ER for FS2004 and FSX at the moment. Everyone's welcome to take a look at our progress at this site:


Your comments there are most welcome if you know a little something about DC-10s!

http://www.xsimulate.co.uk/forum/

If you need more engine data or explanations send me an email.

I will definitely do that. Thanks again!

I'm still not convinced. Rating an engine must mean running it under set conditions (ISA) and measuring the output, then making placards stating that this engine is rated 53,200lbs.

Can't anyone else chime in?

How do you go about running the mill at exactly ISA? Totally impractical in the real world!

For performance acceptance testing, airlines have test cells from SL (AMS or FCO for example) to over 5000 ft (Joburg), and Montreal gets real cold much of the year, and Abu Dhabi real hot. So a method is required to correct the data from whatever non-standard conditions exist to ISA SL. Clarence has posted such a chart above. (Actually, in the test cell a humidity correction is applied too, a refinement which is omitted for the on-wing case)

So - run the engine per the chart, with appropriate temp & alt. corrections, and it will produce rated thrust.

What about hot day performance?

Note that at SL 30C, zero bleed, the N1 reaches a peak of 114.6%, and this is the hottest TAT at which full rated thrust can be produced. Above this temp, N1 must be rolled back, which of course means less thrust is available. The corresponding aircraft performance is also reduced.

If you're looking at an EPR-rated engine, you'll also see reduced EPR (& thrust) under these conditions.

It's all done to reduce hot section wear & tear; you just can't carry as much load under this circumstance.

Assuming you're running with your packs on, do you need to add an additional .6% N1 to get the same power level, or do you simply lose .6% N1 and an appropriate amount of thrust as a result?

We all agree, I have just given an explenation to
where the published number 53,200 lbf comes from and how
it is meassured.
Having a standandard day is the only meaningful way
of comparing engine performance, thats why the FAA has these standards.

Like I said, the engine will offcourse hit 53,200 lbf (and higher!!) at other temp/alt/N1 scenarios, but that wasn't the point. You have no way of
knowing one single other datapoint in that diagram that gives
exactly 53,200 lbf unless you get your hands on some thrust/N1 diagrams.

M

Not true. And it is, in any case, of no relevance here.

That is exactly the point. But one that seem unexplicably hard for you to understand.

Of course you do. That is the purpose of the chart.

I will agree with on one thing. Barit1 does give an excellent explanation. It's just a shame you don't seem to understand any of it.:ugh: