Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
PW4000 Vs. GE CF6  
User currently offlineKC135Hydraulics From United States of America, joined Nov 2012, 289 posts, RR: 0
Posted (1 year 5 months 3 weeks 5 days 21 hours ago) and read 9548 times:

I noticed that the Air Force selected the PW4000 to power the KC-46 instead of a CF6, which to me seemed like the logical choice given that other aircraft in the Air Force inventory operate with this engine.

Can someone provide me with some pros and cons for each engine type? I always considered PW to be the "lesser" brand but I have no real information either way.

26 replies: All unread, showing first 25:
 
User currently offlinejetlife2 From United States of America, joined Jul 2006, 221 posts, RR: 25
Reply 1, posted (1 year 5 months 3 weeks 5 days 18 hours ago) and read 9492 times:

I will answer the question a different way. The tanker selection between Airbus and Boeing was an airplane program choice without a separate engine choice. The Boeing offering was made with the PW engine. The Airbus offering was made with the CF6(-80E if I recall). There was not a separate engine choice offered independent of the airplane. So the selection was made on the airplane/engine package as a whole, against the program criteria (capability, cost, support....etc etc exhaustively debated).

Since I work for GE I won't get into the merits of the two engines.

[Edited 2013-01-15 16:05:17]

User currently offlineMax Q From United States of America, joined May 2001, 4315 posts, RR: 19
Reply 2, posted (1 year 5 months 3 weeks 5 days 12 hours ago) and read 9378 times:

Quoting jetlife2 (Reply 1):

Since I work for GE I won't get into the merits of the two engines.

Why not ?


Many of us would be very interested and your post's are anonymous after all !



The best contribution to safety is a competent Pilot.
User currently offlineCALTECH From Poland, joined May 2007, 2164 posts, RR: 25
Reply 3, posted (1 year 5 months 3 weeks 5 days 11 hours ago) and read 9351 times:

Quoting KC135Hydraulics (Thread starter):
I noticed that the Air Force selected the PW4000 to power the KC-46 instead of a CF6, which to me seemed like the logical choice given that other aircraft in the Air Force inventory operate with this engine.

C-5M ?

http://www.lockheedmartin.com/us/aeronautics/mmro/c5m.html

"Now, with more powerful GE CF6-80C2 commercial engines (military designation F138-GE-100) engines and 70 major enhancements, the C-5M Super Galaxy "




UNITED We Stand
User currently offlineDL_Mech From United States of America, joined Feb 2000, 1924 posts, RR: 9
Reply 4, posted (1 year 5 months 3 weeks 5 days 4 hours ago) and read 9250 times:

Both are fine engines.

After a ten hour flight, bring a quart of oil to the PW (you might have to use some of it). On a GE, bring a case of oil.



This plane is built to withstand anything... except a bad pilot.
User currently offlinejetlife2 From United States of America, joined Jul 2006, 221 posts, RR: 25
Reply 5, posted (1 year 5 months 3 weeks 5 days 3 hours ago) and read 9212 times:

Quoting Max Q (Reply 2):
Quoting jetlife2 (Reply 1):

Since I work for GE I won't get into the merits of the two engines.

Why not ?


Many of us would be very interested and your post's are anonymous after all !

What I mean is I don't mind talking about GE's engines (of course as far as I can without revealing proprietary info), but it's not for me to talk about the PW product, especially as I don't work 767 so I'm not the person who should make those comparisons for GE.

By the way my posts aren't anonymous, I have my real name and position in my profile because that is GE's policy, which is fine by me.

Cheers

GHR


User currently onlinen901wa From United States of America, joined Oct 2009, 445 posts, RR: 0
Reply 6, posted (1 year 5 months 3 weeks 5 days ago) and read 9156 times:

Hi, Like DL_Mech has said, Both are Fine Engines, and from my time working on both, the CF-6 does use more Oil. Some other Observation from my time working on the CF6-80C2 and PW4000.

The Pros for the CF-6-80C2
The Engine is easier to work on then the 4000, Parts seem arranged better to get access to, and the Boro plugs are set up so when you are doing a Borescope you dont have to go from side to side ( except when borescoping the c/c then you need to go all around ), and are easy to get to, and the pulgs have a better design that last better over time. The Wiring harness are better arranged. Removing the Fan Blades is easier, and changing the balance weights are simple. The TCC ( Turbime Case Cooling ) System seems more reliable.

Some Cons for the CF-6-80C2
The Engine does not like high heat. Overtemps seem to happen more often on the CF-6-80C2 then the 4000. Its not nowhere as bad as the CF-6-80A2s and is not as common, but it does happen once in a while. The CF-6-80C2 also seem to have more N1 Fan Balance issues, that requires to change the weights around under the spinner. The CF-6-80C2 also does not like Compressor Stalls. Usally if it burps, its going to get changed. Its a shame that the Oil Tank was not set lower like the 4000 so you don't have to drag a huge ladder out to service the tank.

The Pros for the PW4000
The Engine does not seem to get bothered by high heat. The Compressor and Turbine blades in the engine seem to handle damage better. The 4000 does not have seem to have N1 Fan Balance issues and if it does, then something is going wrong. I have seen bent blades due to FOD on a 4000 with the N1 Vib not that bad. The 4000 does not seem to be affected as bad as the CF-6 in a Compressor Stall, and have boroscope one with no damage noted.

Some Cons for the PW400
The Engine is not as user friendly as the CF-6-80C2. A lot of parts seem to be burried, and not easy to get to. The Boro Plugs are not easy to remove, and the plugs get torn up easy. The Boro plug location are not as thought out as well as the CF-6. Changing Fan Blades on the 4000 can be a hard, and when you are just changing a set (2Blades) can be a task.

These are some things I have seen over the years working on them and inspecting both Engines. I tried to limit my coments to the 767 since we are talking about the KC-46, and they are my opions. I do have to say Both Companys Makes Great Engines, and enjoy working on both products over the years. The Reps I have met were helpfull and very nice people to work with. Hope some of the info has helped  


User currently offlineLAXintl From United States of America, joined May 2000, 24710 posts, RR: 46
Reply 7, posted (1 year 5 months 3 weeks 5 days ago) and read 9137 times:

I agree both PW and GE make fine equipment.

Some random comments from my flight ops experience with both.

The GE is quite reliable, but when it burps (eg compressor stall) you are likely toast. PW seems to plug along. This goes back to the JT9D vs CF6-50 days when the PW could bang but still keep going.

PW4000 started out a bit shaky reliability wise, but now is as reliable long term as the GE.

PW4000 does indeed seem to do better in warmer temps which can be beneficial and provide operators more margins. The engine was sensitive to things like sand, however later PW4000 seems to be better with revised blade coating and seals.

Fuel burn degradation on the CF6 seems to be less with age compared to the PW which spikes but then seems to stabilize. CF6 tends to inch up.

Support we found PW came in a bit cheaper as it tended to need more frequent but smaller ongoing items, while GE could would hit you with a whooper at once. Obviously airlines have all types of service agreements, so these differences can be neutralized in the grand scheme of things.



From the desert to the sea, to all of Southern California
User currently offlineferpe From France, joined Nov 2010, 2800 posts, RR: 59
Reply 8, posted (1 year 5 months 3 weeks 3 days 22 hours ago) and read 8910 times:

Quoting jetlife2 (Reply 5):
What I mean is I don't mind talking about GE's engines

I think many would appreciate a bit more substantial discussion on engines here, there has not been to much knowledgeable discussion except for our Lightsaber which I believe no longer works with turbofans. After having built an airframe drag model which makes it possible to guess on the different frames performance to some reasonable level I have now started to look into making some simple stuff for turbofan engines. The purpose is the same to be able to get us a bit closer to what really matters in these powerplants and how they differ.

What is then clear is that the little information that the OEMs gives out is very ambiguous to those that tries to understand something about these things . The data typically given is thrust, pressure ratio and bypass ratio, sometimes airflow. This seems OK but has little value if one does not state at what point of the flight envelope it is measured. It can be:

- static test bench values (dry ie running with an inlet shroud on a test site) or wet (ie in in the nacelle), the difference is typically 3% it seems.

- top of climb values, in such case with or without ram pressure in the OPR? (increases it some 50% so if this is not clear the values are worthless )

- cruise values, and in such case at what M and FL?

So we get data but if we don't know these things we discuss apples vs oranges.

Helping us interpreting such things and learn what OEMs say with these values (or not) does not give any GE program secrets away, it would however make us the interested public/professionals more enlightened and make engines discussions more interesting and common. And this is why we all hang around here isn't it  .



Non French in France
User currently offlinejetlife2 From United States of America, joined Jul 2006, 221 posts, RR: 25
Reply 9, posted (1 year 5 months 3 weeks 3 days 19 hours ago) and read 8838 times:

Quoting ferpe (Reply 8):
Helping us interpreting such things and learn what OEMs say with these values (or not) does not give any GE program secrets away, it would however make us the interested public/professionals more enlightened and make engines discussions more interesting and common. And this is why we all hang around here isn't it .

Fully agree with you and I am happy to answer any such questions! I enjoy the topic (or I wouldn't have been in aviation all these years).

Quick answer to some of your questions; Nearly all data that the OEMs quote in public is sea level static (M=0.0), uninstalled, test inlet, Std Day (15C 59F) or Cornerpoint (Commonly 30 C 86F). Sometimes you will see Cruise SFC but OEMs don't normally release that. If we do, you are entirely correct, we need to quote Alt and M and specify Std Day or other. By the way, the Type Certificate Data Sheets are a mine of public data...

Confusingly the airframers often quote "Boeing Equivalent Thrust" or "Airbus Equivalent Thrust" which is very often SL, M0.25, installed. This is more useful to them because it is closer to a net thrust at takeoff condition, but much lower than the equivalent static thrust of the same engine....

Cheers

GHR


User currently offlineferpe From France, joined Nov 2010, 2800 posts, RR: 59
Reply 10, posted (1 year 5 months 3 weeks 3 days 16 hours ago) and read 8785 times:

Quoting jetlife2 (Reply 9):
Fully agree with you and I am happy to answer any such questions!

Excellent, lets start with the 767-200 tanker engines, the one for the initial tanker deals (CF6-80C2) and the USAF one (PX4062), here the data from the

Quoting jetlife2 (Reply 9):
Type Certificate Data Sheets are a mine of public data

and another good official source, the ICAO emission databank (http://easa.europa.eu/environment/edb/aircraft-engine-emissions.php) which delivers data that the TCDS does not give(OPR, BR, Static TSFC), see below:


Engine......................Th TO....Th Cont...OPR...BR..TSFC...Max N1...........Max N2..............EGT TO...EGT Cont
PW4062 TC..............62000...50250....................................4044................10450...................654.........629
PW4X62 ICAO..........62000...................31,91 ..4.6...0,354
CF6-80C2B7F TC.....60030...56170....................................3854(117,5%)..11055(112,5%)....960 T49..925 T49
CF6-80C2B7F ICAO.60000...................31,79..5,1...0,336


As can be seen seemingly similar engines with similar data (clearly the EGTs are not measured at the same points).

Now to what extent are the FAA TCDS static data (speced as dry) comparable with the ICAO static data (not speced whether dry or wet), ie can one put the two together to get a better understanding? Further the ICAO databank also specify Climb Out (C/O) values, these should then be comparable to the Boeing Equivalent values except would they be dry or installed?



Non French in France
User currently offlinefaro From Egypt, joined Aug 2007, 1533 posts, RR: 0
Reply 11, posted (1 year 5 months 3 weeks 3 days 8 hours ago) and read 8723 times:

Quoting LAXintl (Reply 7):
The GE is quite reliable, but when it burps (eg compressor stall) you are likely toast.
Quoting n901wa (Reply 6):
The 4000 does not seem to be affected as bad as the CF-6 in a Compressor Stall, and have boroscope one with no damage noted.

I find this difference in compressor stall tolerance fascinating.

What exact design parameters make that the PW4000 is practically immune from compressor stalls vs the CF6 to which such stalls seem terminal?


Faro



The chalice not my son
User currently offlineKC135Hydraulics From United States of America, joined Nov 2012, 289 posts, RR: 0
Reply 12, posted (1 year 5 months 3 weeks 1 day 16 hours ago) and read 8425 times:

This is a great discussion! I am not a jet engine mechanic, but I have a little exposure to both PW and CFM engines.

On the F108s on the KC-135R (CFM56-2) I do notice that after an 8-10hr flight we are typically servicing 2 qts of oil on each engine, whereas on the C-17 we are servicing 1 or 0 quarts typically. Of course, apples and oranges, because the F117s we're running on the C-17s are newer and much larger, and the F108s are smaller and much older.

I did notice that the CF6 seems to have a significantly higher max continuous thrust rating than the PW4000. That seems like a pretty significant difference and I'm wondering why that is. From a performance standpoint that seems like a major selling point for an engine choice.


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 13, posted (1 year 5 months 3 weeks 12 hours ago) and read 8251 times:

Quoting faro (Reply 11):
What exact design parameters make that the PW4000 is practically immune from compressor stalls vs the CF6 to which such stalls seem terminal?

The biggest factors are the compressor map and margin (how close the engine operates to stall) and the design factors in the blades (how likely they are to be damaged during a stall).

Tom.


User currently offlineferpe From France, joined Nov 2010, 2800 posts, RR: 59
Reply 14, posted (1 year 5 months 3 weeks 10 hours ago) and read 8224 times:

Here is the typical compressor map of the engines we discuss, I have generated it by using this program:

http://www.gasturb.de/index.html

It is the PianoX of gasturbines in a way, it is made by the former head of performance simulation at MTU and he lets one use part of it for free. It is quite fun to play around with. Here the maps, low compressor or booster first (I have assumed it to have a pressure ratio together with the fan of 2):

http://i298.photobucket.com/albums/mm262/ferpe_bucket/CF6-80C2F7LCmap_zpsa5819d01.jpg

An here the high compressor map, it has then a pressure ratio of 16 to come to a joint 32 at sea level (see data above):

http://i298.photobucket.com/albums/mm262/ferpe_bucket/CF6-80C2F7HCmap_zps21642a8d.jpg

For those who need to understand more in compressor maps (I was one of them, read it many times  ): http://en.wikipedia.org/wiki/Compressor_map#Flow_axis

We have experts on the thread but I will make a first try to explain what we see. The pressure is gradually built up the faster the compressors spin. Now you don't have RPM on the x axis but rather in the diagram as curved fat lines. It is the RPM as a fraction of the sea level max RPM (I have the SL Static case as the design point). You can take it as N1 (LP spool) and N2 (HP spool), change the fraction to % and one is in familiar waters. As I have taken max power static sea level as the design point the max continuous top of climb is at some 110% N2 (LPC) and 107% N1 (HPC), this is possible as the defined engine limit is the turbine inlet temp which I have put to 1500K and as it is colder at FL310 the engine can burn more fuel before it gets to 1500K at the high turbine inlet = more mass flow and/or higher pressure = more power. Normally one would have top of climb (FL310 M0.8) as the design point but I don't have this data so I took the static sea level case as design point.

As the compressor spins faster, the working point of the compressor gets more comfortable (to the right in the diagram, analogy wing has more speed, goes further from stall), as it slows down the working point comes closer to the red top line = stall or oscillation. The way to keep the working point from getting up there is to have variable guide wanes for the early stages (changes blade alfa and flow) and stage bleeds (lowers the back-pressure on the stages). As we can see the high compressor is more critical then fan/booster (it has a PR of 16 vs 2 so no wonder), therefore you have the variable guide wanes there and multistage bleed. The booster might have a bleed port but that's it. The maps has the form of a mountain ridge, the altitude curves are the compressor efficiency levels, as you see the working line shall be close to the highest possible efficiency, especially close to the cruise point which is between 85-95% N1 I would say (we can see that the LPC is more efficient at 85-90% then above).


Now I have a question on the T49 EGT measurement point of the CF6. Here the accepted standard nomenclature for point in the Turbofan (the picture is from the Gasturb program, it shows a generic 2 axis TF. It therefore does not show the booster stages, one lumps the fan+booster PR into the inner fan PR in the program. The more elaborate and detailed 2 and 3 axis models are not free use but this model is more then enough to simulate the 2 axis TF we have on an amateur level ). Now then, T49 would mean the last point before the core nozzle, ie after the LPT (red arrow)?

http://i298.photobucket.com/albums/mm262/ferpe_bucket/Turbofanstations_zps3068c2ef.jpg

Why such a late measurement point (the real interesting temp is the high turbine inlet temp), is it because you can't make reliable sensors for hotter stations?

Edited for clarity.


[Edited 2013-01-21 00:58:52]

[Edited 2013-01-21 01:10:43]


Non French in France
User currently offlineferpe From France, joined Nov 2010, 2800 posts, RR: 59
Reply 15, posted (1 year 5 months 3 weeks 6 hours ago) and read 8165 times:

As I have given the fan (it turns out to be the outer fan and not fan+booster = inner fan map, one see that as it only goes to the fan PR of 1.7-1.8 ) and compressor then I might as well give the design point data, SL Static:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/CF6-80C2F7designpoint_zps2e8ef584.jpg


and the off design point data, first what would be the normal design point, Full continuous at Top of climb, 31000ft and M0.8 assumed for a 767, note that the full thrust is now only 16klbf instead of 60 (lower air density, even though you now compress it 36 times (see below) and you have RAM gain you still don't get as many lb mass of air into the engine as at SL ) :

http://i298.photobucket.com/albums/mm262/ferpe_bucket/CF6-80C2F7Topofclimb_zpsb9ed00be.jpg


Finally the working line at the off design Alt and M (ie how the engine works when you throttle it at 31000 feet). First a diagram where I have propulsive and thermodynamic/core efficiency vs cruise thrust (a 767 needs about 10klbf per engine at initial cruise to overcome drag, it is a busy diagram, read one curve at the time, the dots on the curve have different symbols on the top part of the Y axis as well ) :
http://i298.photobucket.com/albums/mm262/ferpe_bucket/CF6-80C2F7Workinglinedata_zps53063fca.jpg

Then the same diagram where I have changed propulsive efficiency for Bypass ratio (you can only have 4 scales on the Y axis, might be good  ) :

http://i298.photobucket.com/albums/mm262/ferpe_bucket/CF6-80C2F7WorkinglinedataBPR_zps23ae4b97.jpg

The real pros among us will see that my simulation has some (many  ) weaknesses, the ratio of speeds between core and bypass exhaust is not around 0.8 as it should be but 0.6 (bypass 20% slower then core). I have used the default demo 2 spool Turbofan as base (which is a small TF of 3300lbf SL Static thrust) and then added the CF6 parameters as best I could. Per default the program shall in novice mode (very suitable for me   ) give you reasonable values for nozzle areas core/bypass but I don't think it does they way I mishandle the program  Wow! .

One can however see that things are not to far off reality, TSFC is around 0.56 at 10klbf which is a bit to good (more like 0.58-0.60) which is most likely due to no cooling bleeds, to high efficiency for the fan/compressors and turbines. Anyway, what can be seen is how e.g BPR, PR, TSFC changes with throttle setting even at a fixed altitude and M. Also compare with the static values. Any of the normal figures we take as evidence to say A is better then B we then need to be sure we can qualify with full conditional data for an apples to apples discussion, otherwise we compare design points rather then engines   . The top of climb data is e.g. BPR 5.5, PR 36, then back off to cruise settings and you have BPR 6 and PR 25, all vs 5.1 and 32 for SL static ( all values dry = uninstalled) .

Edited for clarity

[Edited 2013-01-21 05:12:22]


Non French in France
User currently offlinejetlife2 From United States of America, joined Jul 2006, 221 posts, RR: 25
Reply 16, posted (1 year 5 months 3 weeks 3 hours ago) and read 8106 times:

We now have two threads embedded in one....

Quoting ferpe (Reply 14):
Now I have a question on the T49 EGT measurement point of the CF6.

Why such a late measurement point (the real interesting temp is the high turbine inlet temp), is it because you can't make reliable sensors for hotter stations?

Yes partially. Some engines have pyrometers as well as normal EGT probes for this reason, but they are expensive and can be unreliable. EGT is an important parameter in engine control and engine health monitoring, and it is important that the sensing circuit be reliable. Usually they are dispatch limited items depending on the redundancy of the particular engine system.

The other reason is that by measuring at the exhaust of the LPT that is the exit of all the turbomachinery. As the engine deteriorates it runs hotter for a given thrust (less efficient as it wears away from new conditions). By measuring at this station there is information about the health of the LPT. Agreed that ideally you would like T25, T3, T41, T45 and T495, and indeed many engines have most of these; which would allow you to determine the health of each module individually by the degree of variation from new. But failing that having the exit temp is very useful.


By the way it may be obvious but the reason that T49 is the last point before T5 is that it is really "4.9", T21 is "2.1", etc. On some engines EGT is actually T495 which is about as close as you can get to T5.


User currently offlineferpe From France, joined Nov 2010, 2800 posts, RR: 59
Reply 17, posted (1 year 5 months 3 weeks 1 hour ago) and read 8078 times:

Quoting jetlife2 (Reply 16):
We now have two threads embedded in one....

To some extent yes, but my questions and diagrams are about being able to show the differences between the two as asked for in the OP.

We have described the practical MR and handling differences but we have yet to see their difference in performance and thermodynamics. It was my aim to shed some light on that, to do that one needs reliable data and I think I have shown that we normally don't have that and why by using basic data from one of the engines in question (CF6-80C2B7) to show that. Unless can can correlate difference sources and then model based on that to the degree possible how shall one get a better understanding of the engines in question? To take e.g the BR values and start saying this is better than that would not be very useful at least if we don't know exactly how the data was measured.

To that end I still have this question:

- To what extent are the FAA TCDS static data (speced as dry) comparable with the ICAO static data (not speced whether dry or wet), ie can one put the two together to get a better understanding?

[Edited 2013-01-21 09:05:35]


Non French in France
User currently offlinejetlife2 From United States of America, joined Jul 2006, 221 posts, RR: 25
Reply 18, posted (1 year 5 months 3 weeks ago) and read 8042 times:

Quoting ferpe (Reply 17):
To that end I still have this question:

- To what extent are the FAA TCDS static data (speced as dry) comparable with the ICAO static data (not speced whether dry or wet), ie can one put the two together to get a better understanding?

I do not use the term "dry or wet" (except with respect to afterburning engines), but I think from your earlier posts you are referring to with or without installation drag due to the flight nacelle, is that correct?

On that assumption I will answer this way: the OEMs perform emissions certification tests on the ground static and these tests are used to comply with certification standards such as FAR34. The results from the same tests are also used to demonstrate compliance to the appropriate CAEP level - and it is this reporting that appears in the ICAO database. Therefore the test conditions are nearly always the same basis as those used to establish the data reported in the TCDS. But: the resulting data is always corrected to a reference condition such as SL Std Day/Cornerpoint as reported; The ICAO data sheet will often give the actual test condition before correction. For example I pulled the GE90-115B datasheet and it lists the date, test location, Pamb, Tamb and humdity. That particular test site is not SL it is about 800 feet AMSL.

The reference to "Takeoff, Climb, Approach" values merely means that was the power set on the test; nothing to do with flight condition. These power set values are standardized in Annex 16 Volume II - which will give you a lot of other information about how these tests are conducted and is actually pretty easy to read.

From an inlet point of view they usually will be with a test inlet, although they could have the flight nacelle/reverser installed but that is unusual; and they are always static so there is no installation drag. The customer (aircraft) bleed is usually zero as is power extracted by accessories.

Hope that clarifies.

GHR


User currently offlineferpe From France, joined Nov 2010, 2800 posts, RR: 59
Reply 19, posted (1 year 5 months 2 weeks 6 days 22 hours ago) and read 8011 times:

Quoting jetlife2 (Reply 18):
with or without installation drag due to the flight nacelle, is that correct?

Yes, but then I will use installed or not from now on. In the military we used dry or wet but this site also uses it for civil turbofans in what I though was installed or uninstalled meaning, might be wrong (it is one of the better compilations on the web, there are some values one have to doubt though e.g. TSFC for CFM56-5C):

http://www.jet-engine.net/


Quoting jetlife2 (Reply 18):
Hope that clarifies.

Thanks Gareth, this clarifies it in an excellent way!

For me this means one can concatenate the static data if one goes to the protocol to check before one relies to much on it and one has to understand the TCDS data is "corrected = derated" to comply with ISA corner conditions. For the TO etc these figures are not usable together with other figures (like the manufacturers Equivalent Thrust data) as they are apples and oranges, they do however give additional datapoints for the static test condition (more power levels like max continuous = TO ) .

[Edited 2013-01-21 11:55:14]


Non French in France
User currently offlineferpe From France, joined Nov 2010, 2800 posts, RR: 59
Reply 20, posted (1 year 5 months 2 weeks 6 days 22 hours ago) and read 7993 times:

I had another look at the site, table civil turbofans. Wet does indeed mean augmented, for the NK144 for the Tu-144 it is indeed with afterburner, for all others it must be with water injection or such (PW JT3C2, JT9D-3A...). Didn't go to these rather less interesting engines before but now it is clear.


Non French in France
User currently offlineferpe From France, joined Nov 2010, 2800 posts, RR: 59
Reply 21, posted (1 year 5 months 2 weeks 6 days 21 hours ago) and read 7964 times:

After a long (but enlightening at least for me) detour back to the PW vs GE 767 tanker engines. Unfortunately we are not quite out of the woods yet so we can compare performance data, heres why:

Given Jetlife2s info I had a look at the ICAO datasheets, they are indeed giving more info but they are not 100% consistent, here the sheet for the CF6 (the PW 4062 is the same (click on all pictures to see better) ) :
http://i298.photobucket.com/albums/mm262/ferpe_bucket/CF6-80C2F7ICAOdatasheet_zpsc3e165fc.jpg

It clearly stated F"eternity" = 267.03 kN = 62000 lbf.

I take F eternity to mean F continuous, yet both GE and PW takes that as F "5 minutes" in the TCDS. How come? Because it is called "Rated output"? In such case the rated output derated to 85% = 52700 lbf climb out power for PW4062 makes is actually above the PW 4062 continuous rating of 50250 lbf  Wow! .

[Edited 2013-01-21 13:28:40]


Non French in France
User currently offlineKC135Hydraulics From United States of America, joined Nov 2012, 289 posts, RR: 0
Reply 22, posted (1 year 5 months 2 weeks 6 days 21 hours ago) and read 7958 times:

I am still not understanding how the CF6 is able to maintain such a higher max continuous thrust rating than the PW4000. It is quite a difference!

User currently offlinejetlife2 From United States of America, joined Jul 2006, 221 posts, RR: 25
Reply 23, posted (1 year 5 months 2 weeks 6 days 20 hours ago) and read 7957 times:

Quoting ferpe (Reply 21):
I take F eternity to mean F continuous

Logical guess! But not correct. If you read the definitions of Annex 16 Vol II you will see F infinity = Rated Thrust = Takeoff Thrust.

Again it's important to repeat that the power set levels in the ICAO data are the levels specified in Annex 16, and do not relate to flight condition.

Quoting jetlife2 (Reply 18):
The reference to "Takeoff, Climb, Approach" values merely means that was the power set on the test; nothing to do with flight condition. These power set values are standardized in Annex 16 Volume II

All you know from the ICAO sheet is that at 85% of the rated Takeoff Thrust, the engine was observed to emit "X".

In real Power Management, Climb thrust varies with Alt and Mach and N1/EPR. The real Climb rating bears no connection to the ICAO test condition. Sorry.


User currently offlineferpe From France, joined Nov 2010, 2800 posts, RR: 59
Reply 24, posted (1 year 5 months 2 weeks 6 days 20 hours ago) and read 7932 times:

Quoting jetlife2 (Reply 23):
The real Climb rating bears no connection to the ICAO test condition. Sorry.

Thanks, then we know that the 85% of TO thrust gives us another fuel flow point for our off design data, we also know that GE is at Peebles Ohio ie at 800ft and PW at Middletown CT at 70ft ie SL for the ICAO data.

So our datapoints are then:

Engine................Thrust...OPR....BR...TSFC.....Max N1...Fan dia...Max N2..............EGT TO...EGT Cont
PW4062 TO.......62000...31,91 ..4.6...0,354......4044.......93''.........10450.................654.........629
....85% of TO.......52700.....................0,277
....max cont....... 50250

CF6-80C2B7.TO..60030...31,79...5,1...0,336.......3854........93''........11055..................960.........925
....85% of TO.......51030....................0,267
....max cont.........56170


Now once again the only thing sticking out is the low continuous rating of the PW4062, the slightly lower BR is at a higher TO thrust. As we have seen a higher trust of similar engine fan dia means higher core flows to spin the fan faster and this affects BR. If we'd measure them at equal TO thrust the BR would be closer and therefore also the TSFCs. At the 85% position the PW is closer therefore they could be close at cruise TSFC. Web data gives indeed both the CF680C2B and PW4060 as having TSFC of about 0.58 at some 10-12klbf at 0.8 and FL 350.

The plausible installed data can be found at PianoX which has the 767-300ER modeled with CF6-80C2B1F, it is at 0.598 at FL350 and M0.8, also reasonable as one looses some 3-4% in a nacelle.

I venture the difference in continuous rating to be differences in high turbine material and cooling technology, seems the CF6-80 can go hotter for a longer time.



Non French in France
User currently offlinejetlife2 From United States of America, joined Jul 2006, 221 posts, RR: 25
Reply 25, posted (1 year 5 months 2 weeks 6 days 19 hours ago) and read 7987 times:

That's pretty good detective work. Only a couple more caveats:

1, the Max N1 and N2 values from the TCDS are the ultimate limits and do not equate to the rated thrust (or any other) condition. The real speeds at a given condition are lower.

2. The Max Continuous power rating is somewhat of a design choice because it relates to engine-out operation. The airframer and engine OEM will decide what they need vs what they can provide. There can be cases where the "need" is low and therefore the engine OEM will demonstrate/certify only what is "Needed" vs what is "Possible". So I would be cautious about inferring too much from the value. Your conclusion could be correct but there could be other reasons at work for the difference.

If you are near Paris you should go meet some SNECMA people and you could have this conversation over a glass of wine...

Regards

GHR


User currently offlineferpe From France, joined Nov 2010, 2800 posts, RR: 59
Reply 26, posted (1 year 5 months 2 weeks 6 days 19 hours ago) and read 7969 times:

Quoting jetlife2 (Reply 25):
If you are near Paris you should go meet some SNECMA people and you could have this conversation over a glass of wine...

Thanks, I will certainly PM you next time I go to Paris    .



Non French in France
Top Of Page
Forum Index

Reply To This Topic PW4000 Vs. GE CF6
Username:
No username? Sign up now!
Password: 


Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
  • DETAILED RULES
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)


Similar topics:More similar topics...
777 Engine Differences--PW Vs GE/RR posted Sat Jun 4 2011 20:24:54 by washingtonian
CFM Vs RR Vs GE Vs PW posted Tue Mar 1 2011 07:40:39 by mir2069
Why no GE CF6-32 on 757s? posted Tue Jun 9 2009 19:28:59 by Sdq777
GE CF6 80E1 Engine Fan Specs posted Fri May 28 2004 21:31:00 by BWIA330
GE CF6 Exhaust Nozzles posted Sun Dec 16 2001 03:09:06 by TEDSKI
RB211 Vs GE posted Thu Oct 18 2001 23:27:21 by QANTAS747-438
767 & 744: GE Vs. PW posted Thu Jun 17 2010 07:08:13 by MadDogJT8D
767 RR Vs PW/GE Fuel Burn posted Fri Aug 31 2007 17:43:07 by Angelairways
GE F-110 Vs F-118 What's The Differences posted Thu Mar 23 2006 01:37:05 by 747400sp
GE 90-94B Vs RR Trent 895-17 posted Mon Jun 10 2002 01:18:01 by BOEING747400

Sponsor Message:
Printer friendly format