B748i or A380 order?

[SMOC]

tdracer I know you're not involved but I read a while back that Boeing was looking at changing the aft wing to body fairing which is still based on the 1960s design the forward wing to body was obviously recontoured in the 1980s with the 744.

[swh]

Why would it need a D check? It's effectively a brand new airplane - less than 100 hours.

The calender limits for A checks I believe is 2 months, 18 months for C checks, and 72 months for D checks. Checks generally have 4 triggers, hours, cycles, calender time, and ADs. Corrosion/cracks are a function of cycles and calender time, fluids/grease often need replacing on calender time/cycles, tanks need cleaning based upon calender time etc.

Note that was written just as the PIP flight test was getting started - we didn't have any data.

GE had data. The PIP engine has parts that are fairly different to the original, and those changes were not done by guessing.

We 'beat' expectations and got a full 2% (as I noted, I didn't know if that was public knowledge until I saw it in the local newspaper).

The GEnx-2B missed the target TSFC by at least 2-3% at EIS. The fan on the GEnx-2B is simply too small, they are geometrically constrained to make it larger. The 747-8 engine is not as efficient as the 77W (fan size impact).

The PIP target was for an improvement of the TSFC of 1.6% (Boeing conducts test flight of 747-8 with PIP), still not matching the original spec. Even if they managed to get 2% TSFC improvement, they are still not at the spec level.

Despite trying to make out this is super confidential information, the values are on the web if you know where to look, and how to read the data. One can easily go to EASA - Individual Engine Datasheets and pull up individual engine test results. The test results show the GEnx-2B67 is around 5% behind the TSFC of the A380 powerplants, and around 10% behind the 787 powerplants.

As a bit of a comparison (30% thrust) of of TSFC (lb/lbt/hr)
524H-T 0.3432 (744)
Trent 700 0.3162 (333)
CF6-80C2B5F 0.2966 (744ERF)
Trent 877 0.2928 (772)
CFM56-5C 0.2904 (343)
Trent 892 0.2859 (733)
GEnx-2B67 0.2751 (748)
GE90-115B 0.2587 (77W)
Trent 972 0.2551 (A380)
GP7270 0.2517 (A380)
GEnx-1B64/P1 0.2440 (787)
Trent 1000-A2 0.2361 (787)

A 2% improvement to the TSFC (0.2967) still leaves the GEnx-2B67 a long way behind the A380 and 787, and also behind the 77W.

I'm certain Boeing has a better hack on the numbers now that the certification is almost complete.

Maybe the reason behind the announcement to reduce production rates further to 18 a year ???

[swh]

The TSFCs you provide are performed at or near sea level. As such, they are not necessarily indicative of how the engines will perform at altitude where the majority of most flights will burn most of their fuel. Bigger fans will perform more favorably at lower altitudes, in similar fashion to a turboprop. However, that performance is not necessarily replicated at altitude. There are too many variables to cover here, but I think it is safe to say that you are over simplifying the issue by some margin in drawing conclusions from those numbers.

Turbofans produce most of their thrust from the fan in cruise (around 60%). One needs to get to higher mach numbers (ala Concorde) for the core to be dominant.

The powerplant tests were performed at sea level. Despite what you are trying to suggest, no marked change in the order of the results presented would be evident. All of the powerplants fly through the same atmosphere in a very narrow speed range.

The cruise TSFC will be higher (by about 0.2), however the thrust required in that phase of flight is significantly lower. Cruise thrust is in the order of 10-30% of takeoff thrust, hence the 30% rated thrust numbers were presented, (not 85% or 100%).

[cxorcist]

Swh,

The TSFCs you provide are performed at or near sea level. As such, they are not necessarily indicative of how the engines will perform at altitude where the majority of most flights will burn most of their fuel. Bigger fans will perform more favorably at lower altitudes, in similar fashion to a turboprop. However, that performance is not necessarily replicated at altitude. There are too many variables to cover here, but I think it is safe to say that you are over simplifying the issue by some margin in drawing conclusions from those numbers.

[tdracer]

swh

Your post is so far out in left field it's hard to know where to start.

D-checks for a 747 are not a 72 months, they are at 84 months. And airplanes that have been parked for a significant portion of that time routinely get that interval extended. I'm sure there are SOPs for taking an airplane out of storage (depending on how long it's been parked) which would include such things as changing fluids and some basic inspections and functional tests. But there would be absolutely no reason to do a D check on an airplane that had a few hundred cycles and a few thousand flight hours since new.

GE had data.

1.8% had been based on reviews, audits, and rig level testing of the design changes - which in turn was what Boeing was telling potential customers. FTB testing (on a single engine) prior to the start of Boeing flight testing had suggested we were going to beat that, but measuring in-flight TSFC is close to black magic so no one had much confidence until we started flying four engines and measure actual fuel mileage.

The fan on the GEnx-2B is simply too small, they are geometrically constrained to make it larger.

Bull Pure and utter Bull. The 747 'constrain' on fan diameter is at least 122 inches - as was proved by the GE FTB (which flew the GE90-115B on the inboard position). In fact, there was a study back in the late 1990s where Boeing looked at a 747 derivative with GE90s on the inboard positions and CF6 engines outboard (seriously, I was in some of the meetings) . Your so-called geometrical constraint simply doesn't exist.
The GEnx-2B was pretty much a point design for the 747. We could have simply added a bleed system to the GEnx-1B and installed it on the 747 - it would have fit (and I'm sure GE would have been happy to save a few hundred million in development costs). But it was too big to be efficient. The -1B is designed to be at least a 76k engine (planned EIS for the 787-9, maybe higher for the -10), a million pound 747 doesn't need more than 67k - which is what the -2B was designed for. Those big fans give good static sfc numbers, but they are heavy and create large amounts of drag if you're not using the thrust capability.

Cruise drag and sfc numbers are highly proprietary, in no small part because it is so hard to measure the difference. Measuring NAMS (essentially miles/gallon) is straight forward - set precise altitude and airspeed and measure fuel flow - but breaking out thrust vs.drag is very difficult (there have been some nasty battles between airframers and engine manufactures as a result).

Sea Level Static TSFC numbers can be taken with a grain of salt - as noted cruise SFC numbers are what really matter, and those can be greatly different. Based on what you published, the RB211-524T engine burns a full 15% MORE fuel than CF6-80C2 engine. Trust me, if the Rolls powered 747-400 had really burned 15% more fuel than the GE powered, Rolls and Boeing wouldn't have been able to give them away (instead of the ~200 that were produced, and that Cathay still flies). The CF6 does enjoy a small fuel burn advantage over the RB211, but it's maybe a tenth of what you're quoting.

I'm familiar with the data, and cruise TSFC numbers for the GEnx-2B are pretty much on par with the 787 -1B, and meaningfully better than the GE90-115B.

Maybe the reason behind the announcement to reduce production rates further to 18 a year ???

Been paying attention much? Airbus is expected to make a similar announcement for the A380. May have something to do with the market for big quads right now

[cxorcist]

Thank you again Tdracer! Please continue to keep an eye on this thread, your expertise is appreciated.

Within a few minutes of really looking at Swh's TSFC numbers, I knew hey were BS. All I had to do was look at his source to know he was far from accurate.

Swh,

I hope you feel like you got busted. You've been pulling crap out of your arse for years on this site. Maybe you'll do some actual research next time instead of grabbing test stand data used for emissions comparisons and pretending that translates to underwing performance.

[tdracer]

Interesting info Silberfuchs, one minor correction:

This is, of course, prior to PIP2.

The 787 -1B is 'PIP 2', GEnx-2B is just 'PIP' - although the changes are pretty much identical between the -1B 'PIP 2' and -2B 'PIP'. The 787 flight tested the GEnx-1B 'pre-PIP' but I'm pretty sure initial deliveries were 'PIP 1'.

[swh]

D-checks for a 747 are not a 72 months, they are at 84 months

The aircraft in question is a 744ERF, not a -8. Boeing say 6 years in this as well AERO - 747-8 Offers Operational Improvements and Cross-Model Commonality

The aircraft was built in 2009 and stored until recently.

1.8% had been based on reviews, audits, and rig level testing of the design changes - which in turn was what Boeing was telling potential customers. FTB testing (on a single engine) prior to the start of Boeing flight testing had suggested we were going to beat that, but measuring in-flight TSFC is close to black magic so no one had much confidence until we started flying four engines and measure actual fuel mileage.

The data I was referring was the flight tests on ZA005 and the certification of the PIP on the -1B engine.

The 747 'constrain' on fan diameter is at least 122 inches - as was proved by the GE FTB (which flew the GE90-115B on the inboard position). In fact, there was a study back in the late 1990s where Boeing looked at a 747 derivative with GE90s on the inboard positions and CF6 engines outboard (seriously, I was in some of the meetings) . Your so-called geometrical constraint simply doesn't exist.

Boeing publishes a graph of engine/ground clearance in the manuals, it clearly shows the GEnx even with this fan size posed additional constraints. I am aware of the GE90 work on the inner pod, however the clearance tends to revolve around outer pod clearance as a function of roll and pitch.

The -1B is designed to be at least a 76k engine (planned EIS for the 787-9, maybe higher for the -10), a million pound 747 doesn't need more than 67k - which is what the -2B was designed for.

Is it not true that all GE powered 787s delivered so far have either GEnx-1B64 or GEnx-1B67 powerplants ? PIP1 from what I understand was only to 70,000 lb, with a plan to get it up to 75,000 lb.

Those big fans give good static sfc numbers, but they are heavy and create large amounts of drag if you're not using the thrust capability.

The fuel saving on longer flights would be over double the additional engine weight (approx 500 kg per engine on the wings).

Measuring NAMS (essentially miles/gallon) is straight forward - set precise altitude and airspeed and measure fuel flow - but breaking out thrust vs.drag is very difficult (there have been some nasty battles between airframers and engine manufactures as a result).

Everything I have said so far on engine efficiency (TSFC) has been engine specific, I have not mentioned NAMS. One cannot state engine efficiency in terms of NAMS, one is then looking at the package and many non engine related issues come into play.

That is why I do not take a GE statement of 1-2% improvement in TSFC to mean a 1-2% drop in trip fuel, as other non engines factors come into play which are outside of GEs control. Other people it would seem do not make that distinction.

Based on what you published, the RB211-524T engine burns a full 15% MORE fuel than CF6-80C2 engine. Trust me, if the Rolls powered 747-400 had really burned 15% more fuel than the GE powered, Rolls and Boeing wouldn't have been able to give them away (instead of the ~200 that were produced, and that Cathay still flies). The CF6 does enjoy a small fuel burn advantage over the RB211, but it's maybe a tenth of what you're quoting.

The CF6 had about 5000 lb less thrust the than the 524, the engine I listed was the ERF engine which is rated for more thrust than the 524. At the same point in history, the 524 allowed for higher takeoff weights, manufacturers put into place improvements and we see many variations in thrust and TSFC. The engines have evolved since, the ERF engine produces more thrust for essentially the same fuel burn.

Airbus is expected to make a similar announcement for the A380.

I heard the next announcement was for the sale of 20 units at the DXB airshow, no engine choice yet.

I hope you feel like you got busted. You've been pulling crap out of your arse for years on this site. Maybe you'll do some actual research next time instead of grabbing test stand data used for emissions comparisons and pretending that translates to underwing performance.

You have resorted to personal attacks bully tactics, and no facts. I have NOT stated or inferred "under wing performance", I have provided my data source, anyone is free to check the numbers presented.

The GenEx engines are actually out performing the GE90 in terms of GFC/kg/nm of payload.

That is to be expected as the 77W on a ULH (e.g. HKG-JFK) will have around 40% of its TOW made up of fuel, where the -8F is around 25% (HKG-ANC). The 77W CORR LNDG will be about double the -8F.

It is not a measure of engine efficiency, it is saying it more payload efficient to have a tech stop than non-stop, which is not news.

The 787 -1B is 'PIP 2', GEnx-2B is just 'PIP' - although the changes are pretty much identical between the -1B 'PIP 2' and -2B 'PIP'. The 787 flight tested the GEnx-1B 'pre-PIP' but I'm pretty sure initial deliveries were 'PIP 1'.

Yes initially PIP1, 70,000lb max thrust. The way Deborah Case was talking the PIP1 was a change to the starter, LPT, and external aero, where PIP 2 was a HPT, and LPC/HPC change.

[tdracer]

Wait a minute swh, I went back and re-read your first post, did you really just use the SLS 30% fn number to determine "cruise" SFC? REALLY?

Sorry, but that's just too hilarious to be real! Jet engines have what is referred to as an SFC "Bucket". The engines are designed for an optimum SFC sweet spot - the low point in the SFC. Go either way in power and SFC goes UP. Since the designers are not idiots, they design the engine such that the 'bucket' corresponds with cruise power settings.

Now, try to imagine this for a minute, even though an engine at 39k cruise is producing ~10%-20% of what the engine can produce SLS (since air density is so low), it's operating at 80 or 90% of it's rated thrust - in the sweet spot of the bucket.

An engine producing 30% rated thrust at SLS is way up on the back side of the bucket and SFC is pretty poor - take that down to 10% and the engine is barely off idle and SFC is horrible. Taking those numbers as having anything to do with cruise SFC isn't apples and oranges, it's comparing apple fruit and Apple computers

By your simplistic analysis (and I'm being polite), a CF6-80C2B1 (56k) and CF6-80C2B5 (60k) engines would have different cruise fuel burn, which is funny because, aside from ratings plugs on the FADEC, they are identical engines It also explains your garbage for the RB211

If this is really your level of expertise in jet engine propulsion, I don't think I need to bother to respond to you in the future - you've clearly shown how little you really know about how jet powered aircraft work

[cxorcist]

Thanks again tdracer! I'm beginning to sound like a broken record. I hope you hang around on this thread.

Your point pins down what I tried to tell swh, but I lack the technical expertise to use the words and facts you do. On some level, what you wrote is intuitive to a thinking pilot like myself. That's how I knew swh was completely wrong to use the data he did. So I am grateful for someone on your side of the pond who actually works in the programs we like to banter about.

One of the biggest problems we have at CX is a bunch of smart guys who are bored with the job of driving airliners. Most of us just accept the job for what it is and have other parts of life define us. But there are some, usually in training or the fleet offices, who like to make stuff up and show colleagues how smart they are. Swh's display here is all too common at CX. I'd bet my firstborn he is a training check captain on the Airbus and perhaps even in the Airbus fleet office, A350XWB lanyard on proud display.

[swh]

tdracer,

No need for you now to resort to personal attacks, just stick with the facts.

Wait a minute swh, I went back and re-read your first post, did you really just use the SLS 30% fn number to determine "cruise" SFC? REALLY?

No, I did not say that, I said I presented the 30% rated thrust numbers. I further said I expect the cruise TSFC to be around 0.2 higher than the numbers presented, i.e. around 0.5.

While I fully acknowledge and agree that the test cell numbers are not the same as what will be seen installed on the airframe in cruise, the relative differences should not see any massive change.That is the point of having the tests and compiling the database. The tests are a standardized method of measuring engines against Annex 16, the actual installed thrust rating and limits are another matter.

One cannot make a statement saying the tests pose no relevance, why do the tests at all if that were the case.

Jet engines have what is referred to as an SFC "Bucket".

I did "plot" the 100%, 85%, 30%, and 7% numbers to get the polars, I had calculated the TSFC for every condition in the respective reports. I am aware of off-design conditions/considerations, hence why I have not try to deal with the installed conditions. Many factors outside of the engine manufacturers control start coming into play, for example the 747-8 has a lower initial cruise capability compared to the 788. A relatively easy way I use to get a better idea of cruise level data is by using tools like GasTurb, it does enable one to look at off-design conditions as well. I know it is not perfect as the maps are out of date compared to the latest R&D, however is it better than a wet finger into the wind.

Now, try to imagine this for a minute, even though an engine at 39k cruise is producing ~10%-20% of what the engine can produce SLS (since air density is so low), it's operating at 80 or 90% of it's rated thrust - in the sweet spot of the bucket.

This is the Mach/Altitude of relationship I would expect for any modern turbofan, taking M0.8/11km back to sea level, what percentage of max takeoff thrust do you come up with ?

aside from ratings plugs on the FADEC, they are identical engines

That is not true, the CF6-80C2 started off with mechanical control, FADEC was only introduced last 1980s/1990 (all 400 engines were FADEC). Over the years all the manufacturers make improvements. Some of the relevant GE press releases from 2002 and 2010.

GE Engine Services Launches CF6-80C2 Engine Upgrades; Upgrade Enhances Engine Performance And Time On Wing | Press Release
GE's CF6-80C2 Engines Celebrate 25 Years of Flight and Counting | Press Release

This article deals with a lot of the issues with the engine, and what was changed.

http://www.iasg.co.uk/pdfs/articles/...ne_history.pdf

It also explains your garbage for the RB211

The tests are performed to Annex 16 requirements by the manufacturers, they are what they are. They are not independently tested in a common test facility.

[cxorcist]

Nice work, Swh. You just drove off the only propulsion engineer that this thread will ever see. Your stubbornness knows no boundaries. Your data is cr@p; and your conclusions are, at this point, deliberately deceptive. If you want to continue living a lala land, knock yourself out. But I'm going to follow tdracer and ignore your posts from now on. I recommend other Ppruners do the same.

[Anotherday]

Cxorcist,

Why on earth weren't you and this forum around in 1989 when Boeing began desperately flogging the 767-400ER and airlines wouldn't touch it with a barge pole either.

[tdracer]

It's Ok cxorcist, I'm not leaving, just not bothering to respond to swh anymore.

It's obvious that he knows far more about my job than I do:
That the 747-400 MPD that I'm looking at that quotes an 8 year interval for 'D' check is wrong.
That the GEnx-2B suffers from a geometrical compromise in fan diameter - something that Boeing mysteriously neglected to tell us propulsion design leads that were working on the 747-8 years before it was launched - even before Boeing down selected between Rolls and GE (or apparently anyone else in Propulsion or at GE), that Boeing sacrificed ~10% fuel burn because we couldn't borrow anyone from the 737 group that could have shown us how to mount the engine tighter to the wing without sacrificing performance so we could get another 6" fan diameter to deal with that non-existent geometrical constraint.

Clearly, Boeing needs to hire swh into their performance group - he can look at SLS emissions data and determine TSFC at 39k/M.85 - it'll save Boeing millions in flight test costs. And he should take my job supporting in-service fleet since he obviously knows more about the CF6-80C2 engine - the one I started working on in 1985 (actually he did get one thing right - there are Hydromechanical and FADEC versions of the engine, which has absolutely nothing to do with the fact that all GE does to turn a 52k engine into a 60k engine is change the rating plug on the FADEC).
It's further obvious I can no longer read SFC numbers since what I'm seeing so totally disagrees with what he's divined from that SLS emissions data.

No, it's clear I have nothing to add to the discussion when swh is involved - he knows far more than I do about my own job.

The rest of you however will need to continue to deal with my unending vomits of irrelevant insider information .

BTW Anotherday, what the heck are you talking about?

Why on earth weren't you and this forum around in 1989 when Boeing began desperately flogging the 767-400ER

The 767-400ER wasn't even launched until 1997 (cert and delivery in 2000). Along with the 757-300, a never ending tribute to the Phil Condit school of running a proud company into the ground with no-value derivatives since actually spending money on proper airplane improvements would have hurt 'shareholder value'

[Frogman1484]

One of the biggest problems we have at CX is a bunch of smart guys who are bored with the job of driving airliners. Most of us just accept the job for what it is and have other parts of life define us. But there are some, usually in training or the fleet offices, who like to make stuff up and show colleagues how smart they are.

.

Cxorcist I think you have just described your life in here!

Why are we bothered with all of this information? We are not going to get more 747-8 or A380 or 787-9/10 etc.

We have a boat full of A350 coming ( much to Cxorcist disgust) we probably will get the new 777 in 2020 and that is it!

[cxorcist]

Froggy,

You and Swh should meet up in the Airbus fleet office. Maybe you can interweave your A350 lanyards and see what happens.

PS - Good news / Bad news today for the A359. First the good, the XWB gained one seat, from 314 to 315 seats. The bad news... The Dreambus just lost 350nm in range, from 8100nm to 7750nm. Now that's one heavy seat!!!

[Frogman1484]

cxorcist..is this what is important in your life? Frankly I would fly Boeing , Airbus in fact anything that pays my bills. Who gives a continental F... how many seats and range they have. At the end of the day you get jet lag and fly through the night on both types!!!

Get off your computer and go and play with the kids....do something that is worth while and productive...get a life beyond Pprune!


Nobody cares!!!

[cxorcist]

^^^ Says the guy who posted 24 minutes after my post.

The pot calling the kettle black? It's called an iPhone. Little time wasted.

PS - Kids are quite content at the moment. Thanks.

[Max Reheat]

Jeezus, this thread is BORING me fartless. I shall now give up following all of the nonsense and drivel!!!!

[swh]

That the 747-400 MPD that I'm looking at that quotes an 8 year interval for 'D' check is wrong.

I do not have the current 747 MPD, if they have "recently" extended the D checks to 8 years, I do apologize. I certainly was 6 years previously, and it does not change that particular 744ERF was built in 2009 and delivered in 2013. This table from Aero 20 - 747 Scheduled Maintenance Cost Reductions maybe also out of date if the MPD has been updated. Newer generation aircraft can get away without having D checks at all with phase check instead of block check maintenance schedules.

That the GEnx-2B suffers from a geometrical compromise in fan diameter - something that Boeing mysteriously neglected to tell us propulsion design leads that were working on the 747-8 years before it was launched - even before Boeing down selected between Rolls and GE (or apparently anyone else in Propulsion or at GE), that Boeing sacrificed ~10% fuel burn because we couldn't borrow anyone from the 737 group that could have shown us how to mount the engine tighter to the wing without sacrificing performance so we could get another 6" fan diameter to deal with that non-existent geometrical constraint.

I tracked down where I had read that the engine was geometrically constrained, it was published in Flight International Contenders power up for 747 fight. The article says that the 787 baseline engine could not be used and a "reduction is required after analysis revealed continuing configuration issues with the outboard engine at the 7E7 fan diameter because of interference drag and potential aeroelastic effects". The article dated October 12, 2004 says the fan size was limited to 2.56-2.64m. The GEnx-2B fan is 104.2" (2.64m), the GE press release saying it was selected was dated April 25, 2005. I was wrong in thinking it was related to ground clearance.

And he should take my job supporting in-service fleet since he obviously knows more about the CF6-80C2 engine - the one I started working on in 1985 (actually he did get one thing right - there are Hydromechanical and FADEC versions of the engine, which has absolutely nothing to do with the fact that all GE does to turn a 52k engine into a 60k engine is change the rating plug on the FADEC).

I am not sure what you are trying to get at with this comment. To put it in another context, the GEnx-2B is coming out with its second PIP, which along with PIP1 changes components within the engine without changing the rated thrust or model, it will still be a GEnx-2B. CF6-80C2 engine series over their lives have had various similar product improvements which do not change their various models, however they have changed the actual components that are installed within the engine. These product improvements reduce fuel and maintenance costs, however they do come at a cost, which some operators elect not to undertake.

he can look at SLS emissions data and determine TSFC at 39k/M.85

I did not make such a statement, and if that is your understanding of what wrote I apologize.