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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? |
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 |
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 |
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 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.
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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.
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I will definitely do that. Thanks again!
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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?
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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 |
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. 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: |
Never mind :rolleyes:
M |
Did a bit of digging:
http://www.airweb.faa.gov.... http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgFAR.nsf...... http://www.airweb.faa.gov/Regulatory_and_Guidance_Library...... Quoted from that document: PART 1--DEFINITIONS AND ABBREVIATIONS (a) Part 1 Sec. 1.1 is amended as follows: Sec. 1.1 [Amended] 1. The following new definitions are added: "Rated takeoff power," with respect to reciprocating, turbopropeller, and turboshaft engine type certification, means the approved brake horsepower that is developed statically under standard sea level conditions, within the engine operating limitations established under Part 33, and limited in use to periods of not over 5 minutes for takeoff operation. "Rated takeoff thrust," with respect to turbojet engine type certification, means the approved jet thrust that is developed statically under standard sea level conditions, within the engine operating limitations established under Part 33, and limited in use to periods of not over 5 minutes for takeoff operation. 2. The definitions of "maximum continuous power" and "maximum continuous thrust" are amended to read as follows: "Rated maximum continuous power," with respect to reciprocating, turbopropeller, and turboshaft engines, means the approved brake horsepower that is developed statically or in flight, in standard atmosphere at a specified altitude, within the engine operating limitations established under Part 33, and approved for unrestricted periods of use. "Rated maximum continuous thrust," with respect to turbojet engines, means the approved jet thrust that is developed statically or in flight, in standard atmosphere at a specified altitude, within the engine operating limitations established under Part 33, and approved for unrestricted periods of use. http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgFAR.nsf... Interesting requirement of Standard atmosphere there.... :} |
Give it up Clarence.
These flightsim enthusiasts obviously know it all, and have nothing left to learn. It's the curse of the internet. Access to everything but understanding. |
It would be interesting to get "schooled" on the subject instead of being told to "get lost, you don't get it anyway".
I wan't to know why the FAA documents can't be trusted... |
Originally Posted by Techman
(Post 2849507)
Give it up Clarence.
These flightsim enthusiasts obviously know it all, and have nothing left to learn. It's the curse of the internet. Access to everything but understanding. behind screen-names, raising themself above everyone else. Fortunately, the other 99% of pilots around here are true gentlemen :ok: M |
It would seem to me that barit1 and Clarence Oveur have provided all the information you need to understand that rated thrust is not confined to ISA conditions.
If you are not prepared to listen to knowledgeable professionals then what is the point? I am terribly sorry XPMorten, but the best efforts of barit and CO seems to have been wasted on you. Are you here to learn from professionals who do this for a living, or are you here to tell them how it works? |
Please don't lump me into the category of a "flightsim enthusiast who knows it all" because I started this thread wanting to learn and I am still learning.
This thread was civil but some people took it a little personal so if we can keep it confined to the topic at hand I think we can all continue learning. :-) My next question is, can max continuous thrust (I've seen it quoted as 46000lbs or so) be maintained all the way to to cruise? At what altitude does the engine start losing the ability to create 46000lbs? I know the thinning air planes a big role in the engine's reduction of power. |
Techman:
I understand that. It's the primary qualification run to achieve the FAA acceptance which is interesting to me. The manufacturer states that we have a 50000 lbs engine here. How does he prove that? He sets it up in a rig and lets it run through the FAA approved qualification (rating) process. If the mfg of the engine could choose test conditions himself he would set it up in a more favourable condition. That's my understanding of why set (ISA) conditions are needed to validate test results. Can't compare apples and oranges... |
Originally Posted by Techman
(Post 2849562)
I am terribly sorry XPMorten, but the best efforts of barit and CO seems to have been wasted on you.
Are you here to learn from professionals who do this for a living, or are you here to tell them how it works? I happen to have a degree in combustion engineering which gives me the right to an opinion. signing off this thread. M |
Given that the fan airflow creates most of the thrust in a high-bypass machine like CF6, the rated thrust is a matter of pushing a specified airflow (about 1400 lbs/sec) through a geometrically-specified fan nozzle annulus.
To pump this much airflow on a standard day, it takes about 3800 rpm. If a hotter day (lower air density), more rpm is needed, and if a colder day, less rpm to achieve rated thrust. Similarly with altitude. In the engine development testing, enough data are acquired over a range of temperatures & pressure altitudes that the shape (slope, etc.) of the power management curves is well verified. The net result is that the left-hand side of the chart essentially contains lines of constant fan airflow, and thus constant thrust. :cool: |
XPMorten,
What does it matter? You seem not wanting to listen anyway. (BTW. What PM? Please do tell) chksix, Where do you find a test cell that is at ISA conditions? barit1 has explained it well. |
If the testcell isn't at ISA then conversion tables are used to translate the current performance to ISA conditions.... is that correct?
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The "IF" is superfluous - I was in the business 33 years and NOT ONCE encountered SL ISA:
15.0 C 14.696 PSIA (1013.25 Mb, if you prefer) ZERO humidity :8 |
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