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Adios, Queen of the Sky!

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Adios, Queen of the Sky!

Old 26th Jul 2020, 01:35
  #81 (permalink)  
 
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I thought all Qantas 747-400s had GE engines (due to commonality with their 767 fleet)?
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Old 26th Jul 2020, 03:39
  #82 (permalink)  
 
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The Longreach had RB211s probably to keep them in common with their -300 fleet rather than the 767 fleet. They did have a few GE powered -400s on a trio that were purchased from MAS. The trick was to ensure that the performance books were not mixed up. Even if they were mixed up, the F/O would pick it up and even if that happened the Captain would spot the error. Couldn't happen right?
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Old 26th Jul 2020, 04:15
  #83 (permalink)  
 
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Talking engines, what were the relative up and down sides of the pick between P&W, GE and RR on the 747? TD, I know you must be full bottle on the engineering side, if not the operators.
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Old 26th Jul 2020, 05:52
  #84 (permalink)  
 
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I could probably do an entire thread on that subject . The CF6-80C2 became the engine of choice for the 747-400 - for good reason. It had the best fuel burn (by a small margin), the best reliability, and the best FADEC. The biggest problem the CF6 had was Ice Crystal Icing issues which caused a number of shutdowns (all re-startable). Eventually the ICI issue was pretty much solved with software, but it took 20 years to get it right. GE didn't want to do a FADEC version of the CF6-80C2 - they didn't think it was cost effective (and the CF6-80C2 PMC had the best, most sophisticated hydromechanical/supervisory electric control I ever came across). But Boeing said they were not putting throttle cables on the 747-400 - if you want to be on the -400 you need FADEC. So GE developed the FADEC version - I'm not sure if it was because they developed it after the PW4000 and were able to learn from Pratt's mistakes along with a later generation of electronics - but they ended up with a much better FADEC control (including having autostart resident in the FADEC - unlike the PW4000 which required another box. There were a few issues with the CF6-80C2 FADEC that may trace back to FADEC being a bit of an afterthought - the most significant was their Permanent Magnet Alternator (PMA) - which is the primary electrical power source for the FADEC - was troublesome and sometimes ate itself (the gearbox setup could allow the PMA rotor to go into a whorl mode which would rub with the stator). However since the CF6 had aircraft backup power basic (PW4000 didn't) it never caused a shutdown.

During the 747-400 development, the popular wisdom was that the PW4000 - being a new engine - would be the dominate engine while the derivative CF6-80C2 would be a more of a niche engine. As a result, Boeing built the PW4000 nacelle in-house, while they purchased the CF6-80C2 nacelle from GE (Middle River), believing they wouldn't sell enough CF6-80C2 to justify the cost of developing the nacelle - bad move since the CF6 easily outsold the PW4000. Not surprisingly, being a completely new engine, the PW4000 had early problems. Pratt didn't think autostart would be popular and didn't design for it - then had to scramble to come up with the Supplemental Control Unit (SCU) to provide the autostart, engine monitoring, and backup power functions that GE had basic. The SCU was a kluge - it cost extra, weighed a lot, and didn't work very well. But what really ended up hurting the PW4000 was the compressor stability issues - particularly the takeoff surge. The thermal characteristics of the compressor caused it to lose surge margin something like 90 seconds after takeoff power set - at which time it could surge - right in the middle of the initial climb (often not recoverable) . Pratt put together this big song and dance for the FAA, basically claiming the probability of two engines surging on the same takeoff was less than 10-9/takeoff - so of course it then happened on an Airbus twin. Fortunately one engine recovered and they were able to limp back and land. Pratt tried a number of fixes to no avail - finally they ended up redesigning the entire compressor (based on the PW4000/112" compressor) but they didn't certify the fix until 2004 or 2005 - then it took several years to retrofit the entire worldwide fleet of PW4000/94" engines with new compressors - and it cost Pratt a fortune. The resultant engine was a major improvement - and was arguably a better engine than the CF6-80C2 - but by that time it was too little too late. Between the 767 and the 747-400, the CF6-80C2 outsold the PW4000/94" by almost two to one.

The RB211-524G/H wasn't a bad engine, although it was heavier with marginally worse fuel burn than either GE or Pratt and it only the traditional Rolls customers bought it. But it was hamstrung by some typical "what were they thinking" Rolls decisions. Probably the biggest of those was the engine control - it wasn't a FADEC, it was an "FAFC" - Full Authority Fuel Control - the inlet guide vanes and bleed valves were controlled using the same archaic pneumatic system that they'd used on the RB211 on the L1011. We were having major problems with the vane controls during the flight test program (with at least one N2 overspeed) and it continued to be a headache up to the point where I retired. There were also early issues with the "Pump and Governor" unit - the engine had a mechanical N3 overspeed governor incorporated into the Main Engine Fuel Pump - and it had been designed with ridiculously tight clearances - as a result the governor would sometimes seize which would fail the fuel pump and shutdown the engine. Ironically, about 15 years later Rolls was proposing a new fuel metering unit for the Trent 800 on the 777 - and the 777 guys pulled me into a design review due to my experience with the RB211 PAG. They were proposing using the same ridiculously tight tolerances for the new fuel metering valve that had proved so troublesome on the RB211 - and I reminded them of that. The response was along the line of 'we're smarter now, we can do this'. Sure enough, first time the did a cold fuel shock test, they new metering valve seized up and they had to open the clearances to make it work...
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Old 26th Jul 2020, 08:41
  #85 (permalink)  
 
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tdracer,

just a ppl/sep here,
but I do really enjoy your posts
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Old 26th Jul 2020, 10:29
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Seconded
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Old 26th Jul 2020, 10:36
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Actually LL it was childishly simple to avoid that mix up
First of all we used an Onboard Performance Tool, OPT, resident in our iPads to calculate all performance. We started with the a/c rego which knew the engine type without our telling it.
The biggie was that if you tried to use RR data, finding an EPR gauge would prove difficult.
Just BTW, the GE -400s we bought in were 1 from KAL and 2 from MAS. Both MAS airframes had huge problems from previous poor maintenance practices and cost a fortune to fix while the KAL had a rudder buzz felt through the pedals which took a hell of a long time to fix. It wasn't quite strong enough to give you a foot massage though.
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Old 26th Jul 2020, 23:33
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The OPT has made a huge difference. I was referring to an incident pre Ipad when the performance figures were derived from a thick paper document.
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Old 27th Jul 2020, 00:56
  #89 (permalink)  
 
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beamender99

I'm with you now. SUD/EUD was a Boeing label but LONGREACH was uniquely Qantas. I thought you were implying that Qantas had an earlier label for them.
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Old 27th Jul 2020, 01:33
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There were several internal Boeing acronyms that may not have gone over well in general use. My favorite was "Airborne Integrated Data System" - AIDS (basically an aircraft level health monitoring system) - this in the late 1980s at the same times the Acquired immunodeficiency syndrome was a big concern. As my groups focal to the (Boeing) AIDS team, I was a little reluctant to tell people outside Boeing what I was working on...
The other really good (i.e. bad) one was "Boeing Delegated Organizational Authority" - Boeing DOA. That one was so bad management promptly changed it to "Boeing Delegated Compliance Organization" - BDCO. BDCO became a sort of four letter swear word to those of us who had to regularly deal with it, but at least it wasn't embarrassing...
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Old 27th Jul 2020, 05:55
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Excellent read - well done
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Old 27th Jul 2020, 07:10
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Originally Posted by tdracer View Post
I could probably do an entire thread on that subject.
Yes, please

... PW4000 ... finally they ended up redesigning the entire compressor (based on the PW4000/112" compressor) but they didn't certify the fix until 2004 or 2005 - then it took several years to retrofit the entire worldwide fleet of PW4000/94" engines with new compressors ...
So it took 20 years or more, on the 747 fleet? Was that the reason why MTU was involved regarding compressor?

probability of two engines surging on the same takeoff was less than 10-9/takeoff - so of course it then happened on an Airbus twin.
Couldn't find that one. Any small hint?
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Old 27th Jul 2020, 07:16
  #93 (permalink)  
 
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Originally Posted by tdracer View Post
There were several internal Boeing acronyms that may not have gone over well in general use. My favorite was "Airborne Integrated Data System" - AIDS (basically an aircraft level health monitoring system) - this in the late 1980s at the same times the Acquired immunodeficiency syndrome was a big concern.
I don't think AIDS was specifically a Boeing acronym. From the 1973 report on the previous year's crash of a BEA Trident:



Though I recall that the S in this context stood for Systems in the plural, rather than the singular. The individual in question became a pioneer of QARs.

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Old 27th Jul 2020, 07:20
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tdracer, this is why I come here. Thanks for sharing such nice insights into an aircraft that I hold truely close to my heart.
Fantastic to read these insider insights to its development

Thank you
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Old 27th Jul 2020, 10:47
  #95 (permalink)  
 
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Fris
Qantas did adopt SUD and had lots of printed PR stuff, certainly in London, ready for the launch ,
I saw boxes and boxes of it awaiting destruction.
An enforced re-think seems to have produced LONGREACH which I think was brilliant.
Boeing seem to have let the SUD label die.
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Old 27th Jul 2020, 11:03
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The 747-300 was delivered to Qantas in 1984, and I recall was dubbed EUD (in lieu of SUD).
The Longreach name came with the 747-400 delivered in 1989.
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Old 27th Jul 2020, 18:46
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Originally Posted by Ray_Y View Post
Yes, please

So it took 20 years or more, on the 747 fleet? Was that the reason why MTU was involved regarding compressor?

Couldn't find that one. Any small hint?
You guys are going to make my head swell - if I was still racing I'd need to get a new helmet .
The problem with the PW4000/94" compressor was that the case didn't stay round as it got hot - which then rubbed the blade tips and increased clearances, which in turn reduced surge margin. The problem mainly affected higher time engines - or more specifically higher time compressors as the blade clearances gradually increased. Pratt tried something called "Cutback Stator" - where they changed the stators to reduce the load on the compressor stages that were prone to stall - but that just moved the problem to the front of the compressor instead of the back and in fact made the surge problem considerably worse. Somehow they got Cutback Stator certified and into service but it make the surge problem so bad it was quickly removed from service (I wasn't directly involved in Cutback Stator, but several of my friends were and they were amazed it was ever certified - they got numerous surges during the flight test program that should have alerted people to the problems).
I came back to the 747 program after Cutback Stator - after Pratt had finally admitted the problem was fundamental to the compressor design and went back to the drawing board. The result became known as "Ring Case Compressor" or RCC - by getting rid of the split case they were able to eliminate the joint structure that didn't expand at the same rate during a thermal transient (the tradeoff was that it was significantly harder to assemble). The FAA had learned from the Cutback Stator experience, and the flight test really put the engine through the ringer but RCC (which was based on the PW4000/112" compressor) worked like a charm. It eliminated the compressor stability issues, and the more stable compressor structure gave a meaningful fuel burn improvement and better performance retention (~1% fuel burn IIRC - that may not sound like much but engine designers will sell their mothers for 1% fuel burn). The RCC mod was AD'd, with a quite aggressive implementation schedule given it required the engine to be rebuilt - at every tech review we had with Pratt for the next several years, the RCC implementation status was one of the first agenda items.
I think the duel surge event was an A310, but I'm not sure (which is why I didn't specify in the original post) - maybe around year 2000? After that Pratt had to come out with a special test to measure compressor stability on higher time in-service engines. They'd run the engine at (IIRC) 1.60 EPR, hold it there for about two minutes, then a specially modified engine control would give it a big extra shot of fuel to see if it surged. If it didn't surge, then it was good for another xxx cycles - then they had to run the test again. Ideally this test was run in a test cell, but since that wasn't always practical we came up with a procedure to do it on-wing .
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Old 27th Jul 2020, 19:27
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I thought the term “SUD” was used for the few -200 conversions to stretched upper deck.
So a converted -200 was referred to as a -200SUD in stead of a -300 (which it effectively became).
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Old 27th Jul 2020, 20:21
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Originally Posted by tdracer View Post
You guys are going to make my head swell - if I was still racing I'd need to get a new helmet
Righto! Thanks

... which in turn reduced surge margin. The problem mainly affected higher time engines - or more specifically higher time compressors as the blade clearances gradually increased.
Means it wasn't a toothing problem from the start but developed later. I was wondering why such a long time end of 80s until 2005 to finally fix, and deploy over even more years on such a serious issue. Meanwhile they swapped engines with newer or overhauled ones?

My referring to MTU compressor, I found that was PW6000 for the A318, where the original design couldn't "deliver" and the MTU compressor was tried. Looks like P&W had compressor issues on more than one engine.
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Old 27th Jul 2020, 20:52
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It's rather interesting how the different manufactures seem to keep having the same issues, to the point that if I hear of a problem I can guess - with pretty good accuracy - which manufacturer is having the problem. Inclement weather - GE/CFM: Fan flutter and bearing problems - Rolls: Compressor stability and compressor case distortion - Pratt.

Yes, the takeoff surge was a wear-out problem - the reason the problem with the PW4000 went on so long is that Pratt didn't want to spend the money to fix it right. So they kept trying different inexpensive band-aids that were not effective (hence the song and dance to convince the Feds that the risk of a dual engine event was infinitesimal). It was only after the dual engine event that the FAA said "FIX IT" - yet again they tried an inexpensive band-aid with Cutback stator which failed miserably. P&W could have saved a fortune if they'd bit the bullet early on and did the proper compressor redesign fix, but the bean counters wouldn't allow it so instead of spending what it took for a proper fix early on, they ended up spending much, much more later on.
With respect to the PW6000 - according to some of the people I worked with at Pratt, the designers warned early on they were trying to do too much with the compressor but management wouldn't listen. There is design trade in compressor design - the less stages in the compressor for a given compressor pressure ratio, the smaller, lighter, and more efficient the compressor will be. However it means pushing each stage harder which means reduced stall margin. As compressors wear in service, they lose stability margin - so what might work OK when it's brand new can become a problem as it ages - so you need to design extra stability margin when it's new so it'll have a long on-wing life.
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