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dalecary
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RE: PIA Claims B777-200LR Not Upto Specifications...

Thu May 25, 2006 9:36 pm

Quoting Zeus419 (Reply 197):
>> A32X/330/350/345/380 <<

. . . No. that's not ridiculous for a nation with so many people (over 1 billion total, including 350million middle-class inhabitants . . . and rising . . . and one of the worlds fastest growing economies (7-10%) per annum . . . and one of the world's biggest exporters of labor/manpower . . .

Oh yes it is. And you as an aviation journalist should know better about the inefficiencies of too many types in a fleet. Apart from the A32Xs, they are only ordering small numbers of 330/340/350/380. Completely stupid fleet planning.
Although the 350 order might be in question along with all the other 350 orders.
 
widebodyphotog
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RE: PIA Claims B777-200LR Not Upto Specifications...

Thu May 25, 2006 9:57 pm

Zeus419

Again your continued belligerence only further proves your ignorance of airline operations and the capability of the aircraft you are discussing...

According to Airbus ACAP for A340-500/600 There are two different spec A340-500HGW and two RCT options on each of those models. The models without lower capacity RCT have lower OEW and higher structural payload capability, and the models with higher capacity RCT have higher OEW and lower structural payload capacity. The specific info I gave was for A340-500 WV0XX which is the past standard spec A340-500. And the payload/range point at which extra fuel for additional range begins to displace payload is "range with maximum payload"...The latest spec, according to Airbus ACAP, I will detail here:

A340-500HGW Version Specifications

So which spec are you referring to? Which spec with what options does Kingfisher have on order? I'll bet a dollar to everyone on A.net that you do not know and be supremely confident I'll win that bet...With that said there is no way you are positive of the capability of any airline specific A340-500, or any other airliner for that matter...

Quoting Zeus419 (Reply 194):
Antares, you’ve hit an important nail on the head: A twin engined aircraft cannot fly over mountains that high — due to engine-out / descent considerations. (e.g. over the Himalayas). It has to fly a big circle around them, or go a completely different route. However, a quad can hop straight over a 31,000ft mountain range no probs.

Completely untrue and you've given no specifics to support your claim relative to aircraft operations. Flying through the Afghan corridor as Antares referenced 777-200LR is well within EOC for any 777-700LR takeoff weight and the airplane can have initial cruise of at or above FL320 at TOW >735Klb. A takeoff weight which PK has not yet approached in their 777-200LR ops so far, which means that FL340 or higher is available directly, depending on RVSM restrictions if any. At the highest available MTOW 777-200LR is limited to FL300 for the initial step cruise...

As I've detailed in this thread several times the TOW capability of 777-200LR is far in excess of what will be required of the airplane even for the most extreme of ranges and payloads operators will use. PIA is not using the airplane at even close to its full capability and is not taxing the airplane at all. From what I can surmise it looks as though someone has done a static operational analysis based on MTOW use and divulged the factors and performance figures based on that. MTOW use is not realistic operational analysis point at all in the case of 777-200LR as in most cases MTOW will not be approached, even with maximum fuel load and nominal payloads for ultra long range.

Relative to A340-500, including the HGW versions, you simply sacrifice too much weight of aircraft and fuel for gains in the marginal areas of operation that only occur 1-5% of the time. Even in those cases there is no real sacrifice to operating the 772LR as initial altitudes, climb rates, and ceilings are well within parameters for safe egress from basically any location that would warrant ULH operation.

Just as an aside, as I was reviewing the A340-500HGW spec I have to remark on how freakishly heavy the airplane is. The highest fuel capacity versions have structural weights that are up to 8t heavier than even a 777-300ER and 31t heavier than 777-200LR, which is equivalent to the entire design passenger load of A340-500!!! I have to put this out as a rhetorical question what in the world do you get for that extra 31t of dead weight?



-widebodyphotog
 
Zeus419
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RE: PIA Claims B777-200LR Not Upto Specifications...

Thu May 25, 2006 10:02 pm

>> Oh yes it is. And you as an aviation journalist should know better about the inefficiencies of too many types in a fleet. Apart from the A32Xs, they are only ordering small numbers of 330/340/350/380. Completely stupid fleet planning.<<

My day-job notwithstanding, I do know of the efficiencies of the common Airbus cockpit; common fly-by-wire architecture; common handling characteristics; common inventory management & supply chain; common maintenance practices etc. etc. I'm sure Dr Vijay Mallya knows that too.

As for the A345s, Mallya says in his own words: "For the first time, we will be able to offer direct non-stop services between India and the USA."

Sounds like quite an important fleet planning decision to me.

As for the A330s, well, there's no more efficient aircraft flying today for intra-regional travel -- crucial for a country situated where India is. And as for the A380s, I predict these will serve Kingfisher well at international hubs where -- as a small carrier (presently) -- they'll be able to maximise the number of passenger customers they can fly into limited slots.
 
OldAeroGuy
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RE: PIA Claims B777-200LR Not Upto Specifications...

Thu May 25, 2006 10:15 pm

Quoting Zeus419 (Reply 194):
Antares, you’ve hit an important nail on the head: A twin engined aircraft cannot fly over mountains that high — due to engine-out / descent considerations. (e.g. over the Himalayas). It has to fly a big circle around them, or go a completely different route. However, a quad can hop straight over a 31,000ft mountain range no probs

It doesn't matter if you are a Twin or a Quad, you still have to plan for a depressurization and a descent to FL100 so the passengers can breath.

The operational advantages of a Quad in high terrain have been much overstated by one of the two OEM's making long range Quads.

Quoting Zeus419 (Reply 194):
Hmm . . . now maybe Widebody & OlderAero should go and ask Kingfisher themselves (right next door to PIA ) why they just placed orders & options for 10 A345-HGWs . .

If someone has good rational explanation of Kingfisher's fleet planning, I'd like to hear it. I'm not counting the obvious explanation that they want to collect 5 examples of every twin aisle Airbus airplane.

Zeus419,

I appreciate your changing of my user name from OldAeroGuy to OlderAeroGuy.

Of course I'm assuming this is your short hand for Older(and Wiser)AeroGuy. It's a good abbreviation since the full name would be too clumsy.

You do ask a lot of questions and I realise this is a requirement of your profession. People on this forum have been good about answering them. However, you have at least a couple of open questions that have been asked of you with no response.

Please provide answers to these questions asked of you:

What routes flown by current A345, A345HGW, or 772LR customers require longer flight distances for Twin operations due to ETOPS rules?

What revenue/operating cost advantages does the A345HGW have over the 772LR?

On an open forum like this one, we need to have some give and take. You can't expect to always be the inquisitor. Sometimes you need to be the responder.
 
widebodyphotog
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RE: PIA Claims B777-200LR Not Upto Specifications...

Thu May 25, 2006 11:24 pm

Quoting Zeus419 (Reply 202):
My day-job notwithstanding, I do know of the efficiencies of the common Airbus cockpit; common fly-by-wire architecture; common handling characteristics; common inventory management & supply chain; common maintenance practices etc. etc. I'm sure Dr Vijay Mallya knows that too.

Sorry to say but again you are just blowing smoke...The fleet commonality benefits claimed by Airbus are wildly overstated as it pertains to fleet operations. Pilot training notwithstanding there are vast differences in supply chain management through the Airbus line. Even for example, between A340-200/-300 and A340-500/-600 80% of the suppliers and inventory are different. In addition to the incredible fuel burn disparities vs their Boeing counterparts, the total benefits of Airbus cockpit/fleet commonality do not outweigh the increased total cost of operation. Just ask SQ for the real scoop on that...SQ could have very easily procured some A340-600's to compliment their -500 fleet but they went the 777-300ER way without much convincing from Boeing...AC is replacing their A340-500's...EK, no more A345's for them, or -600's for that matter, they bought 10 772LR and a boat load of 773ER. CX is in for more than a dozen 777-300ER, and are an A340-600 operator...there will be more Airbus operators flipping this summer, you can take that to the bank...The trend is all in one direction.



-widebodyphotog
 
Zeus419
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RE: PIA Claims B777-200LR Not Upto Specifications...

Thu May 25, 2006 11:25 pm

Widebody:-

>> According to Airbus ACAP for A340-500/600 There are two different spec A340-500HGW and two RCT options on each of those models. . . . . The specific info I gave was for A340-500 WV0XX which is the past standard spec A340-500. <<

So why on earth do that? Since we were discussing A345s with newer the 380t MTOW.

In any case, the data sheet you linked to (and I assume that it is correct) simply reconfirms what I was saying all along, because REGARDLESS of which RCT is used on the 380t aircraft, the "range with maximum payload" is given as 7,400nm in both cases!

And even with the larger RCT, the max payload is still as I described as being "just under" 60,000kg. In fact, the figures for the smaller RCT actually go to almost 136,000lb (62,000kg) of payload. That’s actually a higher max structural payload than the data I had available to me.

I also see that range with max fuel+payload using the bigger ‘RCT7’ is increased to 9,200nm. I assume they’re using a payload figure of 59,150lb (26,830kg) at this extended range.

>> So which spec are you referring to? <<
Red herring. See above.

By the way, I'm not denying that the B777-300ER is a killer plane. But I've not been debating that. But since you mention it, IMHO indeed it deserves the orders it has got. It is equally apparent, however, that the B777-200LR only survives because it's thrown-in with its larger sibling during the bulk-buy sales campaigns.

I maintain that if/when the "new" A350 puts the brakes on B777-300ER sales, the B777-200LR (which is hanging on to the 300ER's coat-tails) will do likewise.

And as for 9,000nm+ ULR ops in general, I don't think we're ever going to see spectacular sales from that market segment -- for the simple reason that most people can't endure 18+ hours sitting in a plane.

[Edited 2006-05-25 16:59:18]
 
OldAeroGuy
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RE: PIA Claims B777-200LR Not Upto Specifications...

Fri May 26, 2006 12:05 am

Zeus419,

Still no answers to the two questions I asked you?

And if you think the 772LR rides on the coat tails of the 773ER, what does that say about the future of the A345HGW given the history of the A346HGW?

OldAeroGuy
 
widebodyphotog
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RE: PIA Claims B777-200LR Not Upto Specifications.

Fri May 26, 2006 1:46 am

Quoting OldAeroGuy (Reply 203):
It doesn't matter if you are a Twin or a Quad, you still have to plan for a depressurization and a descent to FL100 so the passengers can breath.

While it does not necessarily negate the need to plan for depressurization, the 777-200LR APU is operable at all altitudes, this as you know, is a requirement of ETOPS, while the A340 APU operation is limited to FL100 before it can be restarted...The 777-200LR APU by itself can maintain 10,000ft cabin at all operable altitudes IIRC.

Quoting Zeus419 (Reply 205):
By the way, I'm not denying that the B777-300ER is a killer plane. But I've not been debating that. But since you mention it, IMHO indeed it deserves the orders it has got. It is equally apparent, however, that the B777-200LR only survives because it's thrown-in with its larger sibling during the bulk-buy sales campaigns.

What you've said relative to the 200LR is rediculous on the face of it as, with the exception of SQ and now IT, all A340-500 operators are now or have been A340-600 operators...The combined orders for 777-300ER/200LR have been done with near parity model to model unless you are calling orders for five or six -300ER along with two or three -200LR "bulk buys". The greatest disparity in a combined order is the EK order for 40 -300ER and 18 -200LR/F. If you think those -200LR aircraft were "thrown in" you were terribly misinformed...

Quoting Zeus419 (Reply 205):
And as for 9,000nm+ ULR ops in general, I don't think we're ever going to see spectacular sales from that market segment -- for the simple reason that most people can't endure 18+ hours sitting in a plane.

Currently there are at least three carriers operating 18h+ flights already. I don't see them pulling those flights as of yet, however they are looking for ways to abate the cost of fuel that is pushing CASM way up on those operations...I don't know how you would define "spectacular" but the 777-200LR has the flexibility to be used on the same routes that the -200ER is used on with the added benefits of higher payload capability, and improved field performance, without increasing costs relative to revenue generating potential. Can you say the same A340-500 to A340-300? That in itself seems to be a driving issue for operators who are currently pretty thin on payload over the 6,500-7,500nm segments. The -200LR is the cure for that without increasing seat capacity or incurring significant operational costs...

We will see how the orders fall out, but I don't see carriers that are concerned with fuel/operating costs running towards the higher gross weight A340's at this moment.



-widebodyphotog
 
brendows
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RE: PIA Claims B777-200LR Not Upto Specifications.

Fri May 26, 2006 2:03 am

Quoting Widebodyphotog (Reply 207):
What you've said relative to the 200LR is rediculous on the face of it as, with the exception of SQ and now IT, all A340-500 operators are now or have been A340-600 operators

Just a little addition, AC doesn't operate the A346 (although they have(/had) it on order.)  Smile
 
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lightsaber
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RE: PIA Claims B777-200LR Not Upto Specifications...

Fri May 26, 2006 3:35 am

Quoting Widebodyphotog (Reply 207):
while the A340 APU operation is limited to FL100 before it can be restarted...

Really? I didn't know this... Do you have a link? Not that I doubt your information... Just every APU design I've seen required a designed light point of > 35,000ft. Or... are you stating that the APU doesn't have the capability to pressurize the cockpit? That I could believe? Or... did they just not bother to certify the APU > 10k?

Sorry to nitpick, but its pretty hard to design an APU that won't light at 25,000 ft. Yes, for 35,000ft its a challenge...

Or... did Airbus go for a pure "ram start/electrical start" APU? Without the triple explosive start charges, the APU wouldn't be certified to start at altitude...  scratchchin  Not having the charges certainly would save MX costs... I'm not sure about insurance. Anyone?

I'm just curious.

Also, since there is no structural reason PIA couldn't upgrade the engines via chipping to GE90-115s, if they really have an issue with climb, why haven't they upgraded? Its one stupid ROM chip per engine... that *all* of the difference. Its a 15 minute upgrade (once the licensing fees to Beoing and GE were paid and the FAA certs mailed to PIA).

Lightsaber
 
OldAeroGuy
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RE: PIA Claims B777-200LR Not Upto Specifications...

Fri May 26, 2006 3:52 am

Quoting Antares (Reply 195):
I just don't know, but I'm interested in finding out if this is what the PIA kerfuffle is really about.

I think it has more to do with pilot labor issues and/or management control of the airline than airplane performance.
 
OldAeroGuy
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RE: PIA Claims B777-200LR Not Upto Specifications...

Fri May 26, 2006 4:10 am

Quoting Lightsaber (Reply 209):
Also, since there is no structural reason PIA couldn't upgrade the engines via chipping to GE90-115s, if they really have an issue with climb, why haven't they upgraded? Its one stupid ROM chip per engine... that *all* of the difference. Its a 15 minute upgrade (once the licensing fees to Beoing and GE were paid and the FAA certs mailed to PIA).

While there is a difference in MTO between the two ratings, I think that MCLB, MCT and MCRU are identical.
 
widebodyphotog
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RE: PIA Claims B777-200LR Not Upto Specifications.

Fri May 26, 2006 4:21 am

Quoting Lightsaber (Reply 209):
Sorry to nitpick, but its pretty hard to design an APU that won't light at 25,000 ft. Yes, for 35,000ft its a challenge...

Don't mind your "nitpick" it tends to keep me on my toes...I'll revise and clarify that according to FAA certification rules governing ETOPS the APU has to demonstrate 95% start reliability for 45,000ft or the maximum operating altitude, whichever is lower, for certification...For Non-ETOPS the reliability figure escapes me but "sufficient" operability has to be maintained up to FL100...Certification above that is not required for non ETOPS but will probably be a requirement of LROPS...

Quoting Lightsaber (Reply 209):
Or... did Airbus go for a pure "ram start/electrical start" APU? Without the triple explosive start charges, the APU wouldn't be certified to start at altitude... Not having the charges certainly would save MX costs... I'm not sure about insurance. Anyone?

Gonna have to check the guy next door and his reference material on the A340-500 handling for that one...

Quoting Lightsaber (Reply 209):
Also, since there is no structural reason PIA couldn't upgrade the engines via chipping to GE90-115s, if they really have an issue with climb, why haven't they upgraded? Its one stupid ROM chip per engine... that *all* of the difference. Its a 15 minute upgrade (once the licensing fees to Beoing and GE were paid and the FAA certs mailed to PIA).

Yes, you are right and at least one 777-200LR customer has ordered their ships with GE90-115B spec engines...Most engine selections have not been made yet.



-widebodyphotog
 
antares
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RE: PIA Claims B777-200LR Not Upto Specifications...

Fri May 26, 2006 7:46 am

Well guys you've scared the whatsit out of me by revealing that the jets that fly the Afghan corridor and by inference other high altitude zones are designed to regain crucial functions at 10,000 feet in the event of a range of engine and cabin pressure mishaps.

There is no 10,000 feet option (of any appropriate size) all the way from the Aghan corridor and across northern Pakistan, the India border Himalaya zones and even into a substantial part of the eastern Himalayas.

If I'd been reading this gripping thread while flying over one of those areas I'd be ordering a stuff drink NOW.

I've been told that the sustainable single engine altitude of a large heavy long distance twin departing Delhi or Kathmandu or Lhasa is only 19,000 feet if the crisis came shortly after takeoff. Apparently any big twin too. Anyone really know for sure?

Since that is about as high as the valley floors in the adjacent ranges a very prompt and accurate return to point of departure would have to take place.

Antares

PS Meanwhile, let's wait and see if there is a further report about PIA's issues, since this really doesn't seem to have anything to do with the actual jet.
 
OldAeroGuy
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RE: PIA Claims B777-200LR Not Upto Specifications...

Fri May 26, 2006 8:38 am

Quoting Antares (Reply 213):
Well guys you've scared the whatsit out of me by revealing that the jets that fly the Afghan corridor and by inference other high altitude zones are designed to regain crucial functions at 10,000 feet in the event of a range of engine and cabin pressure mishaps.

There is no 10,000 feet option (of any appropriate size) all the way from the Aghan corridor and across northern Pakistan, the India border Himalaya zones and even into a substantial part of the eastern Himalayas.

Don't be too scared. An airplane transiting the Himalayas needs to have an enhanced supply of O2 onboard. If you have a rapid decompression, you need to descend to an appropriate terrain clearance altitude usually FL250 or less and clear the high terrain before descending to FL100 where everyone can take off their masks.

This will require more O2 than if you could descend immediately to F100. That's one reason why airplanes that spend their lives not flying over high terrain often have 12 minute chemical O2 systems onboard. Twelve minutes will suffice for rapid descent from FL430 to FL100.

Over high terrain routes, gaseous passenger O2 systems come into play. By carrying gasous O2 (at the cost of extra weight) you can interrupt your rapid descent to FL250 and cruise there for terrain clearance reasons. You don't want to be higher than FL250 in most cases because your passengers may start to suffer symptoms of the bends and some may have trouble absorbing the O2 available because they aren't pressure breathing the O2 the airplane is supplying.

This rapid descent to FL250 or less is one of the reasons Quads don't have a huge advantage over Twins in high terrain.

Decompressions and engine failures in cruise occur at about the same frequency. If an engine fails on a Quad, it will be able to maintain a higher cruise altitude than a Twin with an engine failure. But even if a engine failure occurs on a Twin, it doesn't descend to its engine out altitude immediately. Instead, it drifts down at a much slower rate than the profile it would follow if it had had a rapid decompression. Under most cirumstances, a Twin's engine out altitiude is as high or higher than its terrain clearance decompression altitude.

Since Twins and Quads both have to plan for decompression as well as enroute engine failures, they usually can fly the same routes.

There are some circumstances where Twins will need to follow alternate routings if high terrain is encounted soon after takeoff, but these are fairly rare. Usually the airplane prime routing and decompression routing will also suffice for engine out routing as well.

Twin routing over high terrain isn't as big an issue as some Quad OME's would lead you to believe.
 
antares
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RE: PIA Claims B777-200LR Not Upto Specifications...

Fri May 26, 2006 9:23 am

OldAeroGuy,

Thanks indeed for the detailed explanation.

Years ago I asked one of the Qantas captains who lived near me at the time why Qantas didn't use the corridor from Bangkok to London via Yunnan and Tibet and central Asia when they were using it the other way.

He said they just couldn't get a fully laden jumbo past 29,000 feet departing Bangkok by the time they reached what WW11 crews called 'the hump' when they were flying missions across the eastern end of Himalayas.

At that point even the loss of one of four engines had highly undesirable consequences for safe flight above complex and high terrain. He went into a rather disconcerting explanation that if you did end up in a high altitude valley even at 23-24 thousand feet there wasn't the right airspeed or turning space available to get out of trouble in down drafts or confronted by a dead end.

He also captivated the dinner party by recreating what he believed happened to the Thai A310 that botched a go around at Kathmandu and flew at full speed into a high altitude cliff face.

This wasn't an issue if arriving from central Asia over Tibet, but the jets were configured with additional oxygen packs. He also said that part of the forgotten history of Qantas ops was the original reason for those packs which had been fitted to some/all (?) jumbos lay in early concerns over a cabin pressure crisis mid Pacific when a cyclonic storm was raising high winds closer to sea level. The view was that a jet flying at a low altitude through severe storm systems was not a good idea if hours short of Nadi or other safe haven.

I have no reason to query his account. He had a long career with Qantas and was very highly regarded.

Antares
 
Zeus419
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RE: PIA Claims B777-200LR Not Upto Specifications...

Fri May 26, 2006 8:13 pm

Antares, the OldGuy is very good at spinning side-issues so as to try and mask uncomfortable ones. But I suppose he's only doing his job!  

In fact, I'd hire him myself if I wanted a spinmeister to eclipse all others, as he does such an excellent job, and is so nice about it, unlike some others here.

Anyway, the long and short of it is that "Twins cannot fly over the Himalayas".

I have that on good authority.

(Of course, the OlderGuy and his chums will try to redefine and re-spin what is meant by the term "flying over the Himalayas", to a point where it suits the 'Party Line'.)

I also have it on good authority that the A340-500/-600 specifically has "No significant loss of altitude" with an engine out over the Himalayas — regardless of the red-herring issues which the eminent OlderGuy raises.

Another fact which I have on good authority is that the A340 can fly a direct 'great circle' route which is 500nm shorter, and around an hour quicker from Bangkok (BKK) to London (LHR) than a twin-engined jetliner. The optimum route involves flying right over the Himalayas, and then over Russia, whereas the twin has to divert to the west, over Pakistan, and then over Iran(!!), and thence to the south of the Caspian sea, and subsequently weave a jagged route through the likes of Iraq, Syria, and then Turkey, over the Black Sea, before finally reaching friendly shores. (well, to be fair, I suppose Turkey, and maybe Pakistan are "friendly", but I don’t know about the others).

Of course the twin doesn't have to do this if it opts to take an even more circuitous route further south to avoid the aforementioned geographical hotspots. Alternatively, it could go due north out from BKK towards China, before finally heading west.

Little wonder then, that Thai Airways chose the quad A345 over the B777.

[Edited 2006-05-26 13:22:25]
 
antares
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RE: PIA Claims B777-200LR Not Upto Specifications...

Fri May 26, 2006 8:41 pm

Zeus419,

I had heard the big twins do not fly the corridor that Qantas had pioneered over Tibet, although they do of course use Lhasa Airport, which is somewhat lower than Lhasa itself and a heck of a drive from memory as well.

However perhaps someone in the forum has a clearer memory of this, but I think the first and last quad jet to ever fly directly across either the Karakorums or Himalayas was a Super DC8 service to Bangkok operated by SAS in the late 60s. But not for long, as the lee side turbulence experienced even at quite a high cruising altitude was a safety of flight issue.

I do not know of anyone currently goes straight out of say Delhi headed for a trans polar route to the US. They stay well clear of it. Nor do I believe anyone has a scheduled flight that does the most direct possible line from a major US city into Delhi across that massive chain of peaks.

There may be geopolitical reasons for this as well as operational ones.

But I thank you for raising such issues. This has been an intriguing thread, even though much of the technicalities are way beyond my knowledge or comprehension.

What drew me to it was a fascination with the fact that there are two parts of the planet where civil aviation is especially hard pushed by nature, the other being Antarctica.

Over the rest of the world there is no reason why you can't just climb to cruise altitude and get on with business. But not around K2 or Everest, or Dome C or the South Pole.

Antares
 
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zeke
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RE: PIA Claims B777-200LR Not Upto Specifications...

Fri May 26, 2006 9:38 pm

Quoting Zeus419 (Reply 216):
I also have it on good authority that the A340-500/-600 specifically has "No significant loss of altitude" with an engine out over the Himalayas --- regardless of the red-herring issues which the eminent OlderGuy raises.

For ISA +10 conditions, one engine inoperative.

777-200/TRENT877 will 28000 ft at 150t,
777-200ER/TRENT892 will do 29000 at 151t
777-300/TRENT892 will do 26000 at 172t

A340-600, at 380t 26000 ft, 300t, 34000, 200t 41000.

Quoting Antares (Reply 217):
However perhaps someone in the forum has a clearer memory of this, but I think the first and last quad jet to ever fly directly across either the Karakorums or Himalayas was a Super DC8 service to Bangkok operated by SAS in the late 60s. But not for long, as the lee side turbulence experienced even at quite a high cruising altitude was a safety of flight issue.

From memory new routes from China to India are being opened up, or have opened up over that area.
 
widebodyphotog
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RE: PIA Claims B777-200LR Not Upto Specifications...

Fri May 26, 2006 9:52 pm

Quoting Zeus419 (Reply 216):
Anyway, the long and short of it is that "Twins cannot fly over the Himalayas".

In the immortal words of Ronald Reagan: "There you go again"...

AF, VN fly twins over the Himalayas everyday. The 777's are actually scheduled in faster than the A340's through certain routes up there because certain carriers do not use additional oxygen packs on the ships they run so they have to fly routes that allow lower ceiling...The extra oxygen is standard kit for AF ETOPS, can't confirm that for VN though. The fact is that looking at current tracks NO ONE flies directly over the highest peaks of the Himalayas, they either fly to the South or North depending on their level of equipment. Not doing that regardless of how many engines you have would be patently reckless, weather, turbulence, lots of yucky stuff...

There are many twins flying shorter range flights over the high mountains around there everyday as well. The biggest limiting factor is not so much EOC but if there is enough oxygen on board to mitigate against rapid descent in the case of rapid depressurization or an IFSD circumstance.

Quoting Zeus419 (Reply 216):
Little wonder then, that Thai Airways chose the quad A345 over the B777.

TG's A340 selection had more to do with the price of the airplane and their, no offense, inability to maintain ETOPS maintenance standards, than the capability of the 777. Also the -200LR was not available when they placed their order IIRC.



-widebodyphotog
 
Zeus419
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RE: PIA Claims B777-200LR Not Upto Specifications...

Fri May 26, 2006 9:53 pm

Zeke, I quoted an official example of the A346HGW (or A345) flying the BKK-LHR route. Airbus confirms that it can fly a great-circle route directly to LHR. That's a 500nm shorter route than the twin can do.

Airbus have twins too. They should know.

[Edited 2006-05-26 14:56:46]
 
OldAeroGuy
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RE: PIA Claims B777-200LR Not Upto Specifications...

Fri May 26, 2006 10:50 pm

Quoting Zeus419 (Reply 216):
Antares, the OldGuy is very good at spinning side-issues so as to try and mask uncomfortable ones. But I suppose he's only doing his job!

In fact, I'd hire him myself if I wanted a spinmeister to eclipse all others, as he does such an excellent job, and is so nice about it, unlike some others here.

Anyway, the long and short of it is that "Twins cannot fly over the Himalayas".

Well, I'm amazed. When I provide a reasonable technical analysis of a situation, you dismiss it as spin. Please explain how I'm masking an "uncomfortable" issue. Remember, Antares asked a question about decompression, O2 and escape routes. My reply was direct to that point.

It's a sad situation when reasoned discussion is dismissed as "spin" and a slogan such as "Twins cannot fly over the Himalayas" is accepted as truth.

In the meantime, you still haven't provided any information on your earlier statements that I asked you to support.

In addition to the earlier questions I asked you, I'll now add a third:

Please provide data to support your statement that "Twins cannot fly over the Himalayas". Air France flies CDG-BKK. The great circle for this route goes over Nepal and Northern India. This is essentially the same route that Thai would fly from BKK to LHR. Air France has A343's, 772ER's and 773ER's.

Show us that either:

AF uses A343's exclusively on this route so thay can fly great circle

or

AF 777's on this city-pair fly a route that is significantly longer than great circle to avoid the high terrain.

When it comes to spin in this thread, you appear to be the only object that is rotating.

[Edited 2006-05-26 16:09:01]
 
Zeus419
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RE: PIA Claims B777-200LR Not Upto Specifications...

Fri May 26, 2006 11:43 pm

OK, Olderchap:-

You wrote:-

>> Air France flies CDG-BKK. The great circle for this route goes over Nepal and Northern India. This is essentially the same route that Thai would fly from BKK to LHR. Air France has A343's, 772ER's and 773ER's.<<

I don’t know the specifics of Air France, but I do know that VN flies B777s SGN-CDG on a route which avoids the Himalayas. i.e., it passes well south of the Karakoram Range in Pakistan, south of the Indian Himalayas. In short, there is nothing of any significant elevation on that route. It's therefore longer than the great circle route, and means going over Afghanistan.
 
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RE: PIA Claims B777-200LR Not Upto Specifications.

Fri May 26, 2006 11:53 pm

Quoting Zeus419 (Reply 222):
I don�t know the specifics of Air France, but I do know that VN flies B777s SGN-CDG on a route which avoids the Himalayas. i.e., it passes well south of the Karakoram Range in Pakistan, south of the Indian Himalayas. In short, there is nothing of any significant elevation on that route. It's therefore longer than the great circle route, and means going over Afghanistan.

And VN's 777-200ER trip time is 45 min faster by schedule than AF's A340-300...

Quoting Zeus419 (Reply 220):
Airbus confirms that it can fly a great-circle route directly to LHR. That's a 500nm shorter route than the twin can do.

And who says the GC route is always the fastest route? That all depends on wind, weather, season, RVSM restrictions, AND the capability of the aircraft.




-widebodyphotog

[Edited 2006-05-26 16:55:36]
 
Zeus419
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RE: PIA Claims B777-200LR Not Upto Specifications...

Fri May 26, 2006 11:58 pm

Widebody:-

Assuming your flight-time number is correct (and I don't know that it is) -- do you know what route AF takes? They might not be taking the CG route for other reasons. And we all know know the A343 has a slower cruise than B777.

Anyway, all of this is another red herring. The fact is that evidently the Himalayas, Tibet Plateau etc IS a problem for the B777.

b.t.w. Airbus is now offering on-board oxygen generators to obviate any 20min shortfall in the cabin for quads.

[Edited 2006-05-26 17:16:06]
 
jacobin777
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RE: PIA Claims B777-200LR Not Upto Specifications.

Sat May 27, 2006 12:18 am

Quoting Zeus419 (Reply 222):

I don't know the specifics of Air France, but I do know that VN flies B777s SGN-CDG on a route which avoids the Himalayas. i.e., it passes well south of the Karakoram Range in Pakistan, south of the Indian Himalayas. In short, there is nothing of any significant elevation on that route. It's therefore longer than the great circle route, and means going over Afghanistan.

1)what does flying over Afghanistan have to do with anything? Many carriers fly over Afghanistan without a problem
2)As Widebody states, there are many other variables which dictate what particular route a plane takes
3) even at face value, taking a quick look at the chart below, the route south of the Himalayas/K2 region is barely even 1% of the other route(in terms of distance)....still more efficient to fy a twin versus a quad..

(the red point on the Pakistan/Indian border is LHE-a majour hub for PK)

 
Zeus419
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RE: PIA Claims B777-200LR Not Upto Specifications...

Sat May 27, 2006 12:44 am

SO -- back to my original point: Still no evidence that 777s fly over the Himalayas, despite exclamations to the contrary.
 
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RE: PIA Claims B777-200LR Not Upto Specifications...

Sat May 27, 2006 1:03 am

Quoting Zeus419 (Reply 226):
SO -- back to my original point: Still no evidence that 777s fly over the Himalayas, despite exclamations to the contrary.

1)Even if the 777's don't fly over the Himalayas, does it really make a difference for air carriers?

2)You refuse to answer anyone's questions when they can't be answered, or to which there isn't any answers...
 
OldAeroGuy
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RE: PIA Claims B777-200LR Not Upto Specifications...

Sat May 27, 2006 1:05 am

Quoting Zeus419 (Reply 222):
don’t know the specifics of Air France, but I do know that VN flies B777s SGN-CDG on a route which avoids the Himalayas. i.e., it passes well south of the Karakoram Range in Pakistan, south of the Indian Himalayas. In short, there is nothing of any significant elevation on that route. It's therefore longer than the great circle route, and means going over Afghanistan.

OK Zeus419, let's take this as an example.

I don't know how the VN 777's are equipped with regard to O2, but they may have a 12 min. chemical system not suitable of operation in high terrain which may explain the routing. A Quad with a similar system would find itself flying the same routing.

Now let's look at the distance penalty. The SGN-CDG is 5462nm. The routing you're describing is about 5520 depending on airways. So the difference is about 60nm. Where does the 500nm you claim as being the difference between Twin and Quad operations from BKK-LHR come from?

And Widebodyphotog is correct about the great circle not always being the most efficient routing due to enroute winds.

Quoting Zeus419 (Reply 224):
Anyway, all of this is another red herring. The fact is that evidently the Himalayas, Tibet Plateau etc IS a problem for the B777.

No, the only red herring is your insisting that the Himalaya Plateau represents a significant operational penalty for Twins but not Quads.

And to return to an earlier reply of yours:

Quoting Zeus419 (Reply 216):
Antares, the OldGuy is very good at spinning side-issues so as to try and mask uncomfortable ones. But I suppose he's only doing his job!

No one is paying me to respond to A.net threads. I do so because I dislike seeing issues being mis-stated or mis-represented.
 
Zeus419
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RE: PIA Claims B777-200LR Not Upto Specifications...

Sat May 27, 2006 1:29 am

>> I don't know how the VN 777's are equipped with regard to O2, but they may have a 12 min. chemical system not suitable of operation in high terrain which may explain the routing. A Quad with a similar system would find itself flying the same routing. <<

It doesn’t matter how the B777 (or A330) is equipped for O2, you’ll still never fly them directly over that region. Anyone can see that would be madness to fly over the Tibet Plateau etc. . . . on one engine.

But a quad with one engine out? It will just carry on, and pax will hardly realise.

>> Where does the 500nm you claim as being the difference between Twin and Quad operations from BKK-LHR come from?<<

You must be getting a short memory, because I explained that route that in quite some detail earlier.
But indeed, since then I’ve found a shorter one — as in the VN example.

>> And Widebodyphotog is correct about the great circle not always being the most efficient routing due to enroute winds.<<

That’s another red herring. Especially as the reverse could equally apply. — i.e. you might get a shorter routing AND better winds (or no winds). So, really that point you raise is irrelevant.

>> No, the only red herring is your insisting that the Himalaya Plateau represents a significant operational penalty for Twins but not Quads.<<

Oh I see, now you are resorting to twisting the whole thing around.

And to Jacobin:-
You wrote: >>You refuse to answer anyone's questions when they can't be answered, or to which there isn't any answers.<<

Well then, a question without an answer, by definition, is a stupid question in the first place.
 
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RE: PIA Claims B777-200LR Not Upto Specifications.

Sat May 27, 2006 1:41 am

Quoting Zeke (Reply 218):

For ISA +10 conditions, one engine inoperative.

First, nice data. But to nitpick, the trent, as a triple spool, will have different performance variation with temperature than a double spool. Not much... but it could be a 2,000 ft difference which might matter in this situation.

2nd the Himalayas are the *one* point on earth where ISA +10 at cruise isn't a conservative assumption. Why? The mountains will deflect storm winds upward and thus you can have stratospheric conditions that are way off ICAO conditions. Why do I know this? Easy, for *some* engines, the turbine case cooling must be reduced over the Himalayas as the non-homogenous engine inlet temperatures can cause *brutal* case rubbings during flight.

Sidenote: Turbine Case cooling is always reduced during climb as the moment induced upon the engines turing turn over combined with throttle changes also can create tip/case intereference issue.

Quoting Antares (Reply 193):
Can the 777-200LR (or the A345) actually reach an appropriate altitude if fully loaded when flying from Karachi along the tightly defined approaches to the Afghan corridor under the most adverse hot weather conditions?

Interesting question needs to be edited a little to take into acount the unique high altitude temperature variations. Alas, I do not know the impact this has on the GE-90's engine out cruise characteristics.

FYI, I find it odd for me to post so much in favor of the triple spool in this thread. Personally, I think the GTF makes for better economics. (A twin spool GTF.) But we happen to be talking about a very rare scenario where the thermodynamic differences between the double and triple spools actually comes into play in a way other than engine weight or TSFC. Interesting...

Lightsaber

Note: turbine case cooling is that series of pipes on the outside of the engine. Usually, its a few big pipes feeding a couple of round rings that impinge low pressure compressor air onto the ouside of the turbine casing to control the tip clearence gap. (Its done via optical sensors measuring the 1st stage turbines tip clearence and actively controlling the external cooling flow rate.)
 
OldAeroGuy
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RE: PIA Claims B777-200LR Not Upto Specifications...

Sat May 27, 2006 1:43 am

Quoting Zeus419 (Reply 229):
>> Where does the 500nm you claim as being the difference between Twin and Quad operations from BKK-LHR come from?<<

You must be getting a short memory, because I explained that route that in quite some detail earlier.
But indeed, since then I’ve found a shorter one — as in the VN example.

Yes, but I don't see the necessity for the Twin routing you are suggesting for BKK-LHR and the range difference you are quoting is erroneous.

Quoting Zeus419 (Reply 229):
>> No, the only red herring is your insisting that the Himalaya Plateau represents a significant operational penalty for Twins but not Quads.<<

But a quad with one engine out? It will just carry on, and pax will hardly realise.

Oh I see, now you are resorting to twisting the whole thing around.


But if the Quad or Twin is depressurized, all the passengers will realize that.

I only want to have an honest statement of the operational constraints when flying in this area. Engine failures are one constraint but depressurization profiles are another. You want to focus on one but not the other. That is intellectually dishonest.

[Edited 2006-05-26 18:48:16]

[Edited 2006-05-26 18:49:39]

[Edited 2006-05-26 18:50:54]

[Edited 2006-05-26 19:09:06]
 
jacobin777
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RE: PIA Claims B777-200LR Not Upto Specifications.

Sat May 27, 2006 2:35 am

Quoting Zeus419 (Reply 229):
Well then, a question without an answer, by definition, is a stupid question in the first place.

1)as my microbiolgy professor used to say.."there is no such thing as a stupid question"
2)I should have stated to which you don't have an anwer to.....

Quoting Zeus419 (Reply 229):

It doesn’t matter how the B777 (or A330) is equipped for O2, you’ll still never fly them directly over that region. Anyone can see that would be madness to fly over the Tibet Plateau etc. . . . on one engine.



Quoting Zeus419 (Reply 229):

But a quad with one engine out? It will just carry on, and pax will hardly realise.



Quoting Zeus419 (Reply 229):

That’s another red herring. Especially as the reverse could equally apply. — i.e. you might get a shorter routing AND better winds (or no winds). So, really that point you raise is irrelevant.

if your point holds true, then why aren't we seeing carriers such as AF fly their A343's? And out of the thousands of daily flights, how many satisfy this condition you seem to be harping ad nauseam about?

The cost benefits of flying a twin greatly outweigh this minour inconveniences of one particular trip...

Quoting Lightsaber (Reply 230):
First, nice data. But to nitpick, the trent, as a triple spool, will have different performance variation with temperature than a double spool. Not much... but it could be a 2,000 ft difference which might matter in this situation.

2nd the Himalayas are the *one* point on earth where ISA +10 at cruise isn't a conservative assumption. Why? The mountains will deflect storm winds upward and thus you can have stratospheric conditions that are way off ICAO conditions. Why do I know this? Easy, for *some* engines, the turbine case cooling must be reduced over the Himalayas as the non-homogenous engine inlet temperatures can cause *brutal* case rubbings during flight.

Sidenote: Turbine Case cooling is always reduced during climb as the moment induced upon the engines turing turn over combined with throttle changes also can create tip/case intereference issue.



Quoting Lightsaber (Reply 230):
Interesting question needs to be edited a little to take into acount the unique high altitude temperature variations. Alas, I do not know the impact this has on the GE-90's engine out cruise characteristics.

FYI, I find it odd for me to post so much in favor of the triple spool in this thread. Personally, I think the GTF makes for better economics. (A twin spool GTF.) But we happen to be talking about a very rare scenario where the thermodynamic differences between the double and triple spools actually comes into play in a way other than engine weight or TSFC. Interesting...

Lightsaber

Note: turbine case cooling is that series of pipes on the outside of the engine. Usually, its a few big pipes feeding a couple of round rings that impinge low pressure compressor air onto the ouside of the turbine casing to control the tip clearence gap. (Its done via optical sensors measuring the 1st stage turbines tip clearence and actively controlling the external cooling flow rate.)

I think I need to get a PhD.. spin 
 
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RE: PIA Claims B777-200LR Not Upto Specifications...

Sat May 27, 2006 3:00 am

Quoting Lightsaber (Reply 230):
FYI, I find it odd for me to post so much in favor of the triple spool in this thread. Personally, I think the GTF makes for better economics. (A twin spool GTF.) But we happen to be talking about a very rare scenario where the thermodynamic differences between the double and triple spools actually comes into play in a way other than engine weight or TSFC. Interesting..

You Know Lightsaber through the 787 program I have really come to appreciate the three spool engine more and more, and have come to the conclusion that the logical path for increased turbofan efficiency must be the GTF...However reluctantly, the thought of mega SHP gearboxes still makes me a bit nervous, but as the demand for higher BPR with lower thrust lapse for climb continues the GTF seems like the only way through...

Quoting OldAeroGuy (Reply 228):
Now let's look at the distance penalty. The SGN-CDG is 5462nm. The routing you're describing is about 5520 depending on airways. So the difference is about 60nm. Where does the 500nm you claim as being the difference between Twin and Quad operations from BKK-LHR come from?

I'll add to this by saying for a lot of routes, especially Eastbound Polar routes the deviation from the GC can be 300-400nm without losing time vs the shorter path simply because the winds are that strong...As far as routings in this part of the world it looks like 100-200nm N of GC is well within time savings for seasonal conditions.

Quoting Zeus419 (Reply 226):
SO -- back to my original point: Still no evidence that 777s fly over the Himalayas, despite exclamations to the contrary.

I have to give it to you, you are the master of the non sequitur. As has been detailed here in any situation the benefits of flying strict GC routes are basically non-existent. Unless you have "free flight" navigation capabilities and routes have no winds or weather strict GC routes are not practical. Commercial airplane routes are by airways that are dependant on ground based navigational way points for the most part. Weather, wind, and MEL are a constant and have greater influence on route selection than EOC in all but the most extreme cases. Not a single commercial airliner flies over the highest mountain peaks of the Himalayas in routine operation as weather makes this a very dangerous proposition. I don't think anyone has claimed that ETOPS twins can fly "directly" over the high Himalayas, but the fact is that they don't need to for efficient routing and it is not practical for any aircraft to do so because of the influences that have been detailed.

However it's funny you mentioned the BKK-LHR though. By schedules BR67, a 777-300ER, takes only 5-15 mins longer than QF1, BA010, TG910, or TG916 which are all 747-400's...I guess BR's new 77W's get to go supersonic on that 500nm deviation around the mountains...



-widebodyphotog
 
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RE: PIA Claims B777-200LR Not Upto Specifications...

Sat May 27, 2006 3:08 am

Quoting Widebodyphotog (Reply 233):
However it's funny you mentioned the BKK-LHR though. By schedules BR67, a 777-300ER, takes only 5-15 mins longer than QF1, BA010, TG910, or TG916 which are all 747-400's...I guess BR's new 77W's get to go supersonic on that 500nm deviation around the mountains...

And this time difference is easily explained as the 744 cruises at 0.85M and the 773ER cruises at 0.84M.
 
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RE: PIA Claims B777-200LR Not Upto Specifications.

Sat May 27, 2006 4:26 am

Quoting Jacobin777 (Reply 232):

I think I need to get a PhD..

Oops, if you have any questions, feel free to ask. I manage people at every education you can imagine from mad scientists to those who coud not care less about any theory. So sometimes I realize I have to step back and re-explain as these groups demand different levels of detail.

It comes down to the fact that high inlet temperatures (at altitude) and/or climbing, the triple spool has nice thermodynamic cycle advantages in its favor.  spin 

Quoting Widebodyphotog (Reply 233):
You Know Lightsaber through the 787 program I have really come to appreciate the three spool engine more and more, and have come to the conclusion that the logical path for increased turbofan efficiency must be the GTF...However reluctantly, the thought of mega SHP gearboxes still makes me a bit nervous, but as the demand for higher BPR with lower thrust lapse for climb continues the GTF seems like the only way through...

The GTF will eventually find a home. The economics are just too good.
1. You get the triple spools RPM on the LPC and its turbine. Yes, you add the gearbox, but I've seen the work done to get the failure predictions down. It impressed me.
2. I too wonder at why more 787 customers haven't picked the triple spool. RR has a great reputation right now. Yes, GE does too... I wonder how much GE's ability to diversify risk and offer financing is impacting sales? I can only speculate.

At worst, a GTF offers an 8% TSFC advantage over a double spool and 5 to 6% over a triple spool. Also, you get most of the triple spools weight reduction (at > 60k thrust) due to component efficiency gains. I also like the fact that a GTF fan is pretty cheap to make. The gears+bearings+fanblades is actually cheaper than the latest generation curved fan blade technology. As long as the fan is < 100" in diameter. Its very proprietary where each manufacturer's ability to make a low cost fan blade ends. But I can vouch that all three engine makers can make a GTF 100" fan cheaply. I can also vouch that the GE-90's fan is still the achilies heal in that engines manufacturing costs. The quantity of 777 fan blades by each manufacturer hasn't been great enough for any of them to acheive the knowledge point breakthrough to make a low cost 110"+ fan, curved or straight bladed.

The neat thing about the GTF is that it brings its efficiencies to any thrust range. Ok, maybe not down to a business jet's thrust, but I've worked on 15k concepts all the way to 125k. The 787 would have been a perfect launch platform. But that didn't happen... so now my hope is the ~33k range for the A320NG/B737RS. However, the 8133 concept that I worked on is obsolete in the world of $70/bbl+ oil. The one I worked on lacked two critical bits of technology that would (combined) reduce fuel burn 5% but at $30/bbl oil weren't worth the weight on the 1 hour mission. I think IAE/Pratt will still optimize for the 1 hour mission but $70/bbl oil will make it so that a few changes that improve climb efficiency are either break even or better. Just my  twocents 

Lightsaber
 
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RE: PIA Claims B777-200LR Not Upto Specifications...

Sat May 27, 2006 5:28 am

Quoting Lightsaber (Reply 235):
The neat thing about the GTF is that it brings its efficiencies to any thrust range. Ok, maybe not down to a business jet's thrust, but I've worked on 15k concepts all the way to 125k. The 787 would have been a perfect launch platform. But that didn't happen...

Yes, the first part is the whole key to the future for the GTF. Thrust per unit fan area decreases by some amount with higher BPR despite increased spool efficiency, but as the size and BPR of the engine increases the thrust capability can still increase significantly. From this I think that the first application of the GTF will be in the high thrust segment for future large aircraft such as Boeing Y3. GTF's of 120-140,000lbt, fan diameters of 140-150 inches with BPR 12-13, are not inconceivable in such an application...But does that then mean 150,000shp gearboxes?!

I think, especially now that the thrust range has been expanded, that the 787 was quite a bit under the size where the GTF would come into it's own at the moment, but the interesting thing is that it's almost there because of the application integrated CFRP fuselage construction that dramatically reduces the specific weight of the airframe. I believe that a GTF in the 55-75Klbt power capability would have been physically too large to mate up with the 787 airframe. However scaling the GTF up into the 100Klb+ range could realize the perfect marriage of efficient power plant and airframe. The high thrust application GTF with the low specific weight airframe achieved by CFRP construction. Hopefully that marriage will come to be.



-widebodyphotog
 
PVD757
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RE: PIA Claims B777-200LR Not Upto Specifications...

Sat May 27, 2006 5:49 am

Quoting Lightsaber (Reply 235):
Oops, if you have any questions, feel free to ask. I manage people at every education you can imagine from mad scientists to those who coud not care less about any theory. So sometimes I realize I have to step back and re-explain as these groups demand different levels of detail.

It comes down to the fact that high inlet temperatures (at altitude) and/or climbing, the triple spool has nice thermodynamic cycle advantages in its favor.

Count me in to this category. My sorry little business degree is being overpowered right now in regards to this engineering discussion, but I'm fascinated nonetheless. I just don't know some of the acronyms that everyone is spitting out. I get the winds and temps and how they affect performance. I even have a basic concept of the engine and the components and how they interact, I just can't get the rest of the GTF, TSFC, and the difference between the double and the triple spool other than I look at it as some sort of overdrive in the gearbox that allows more efficiency at higher rates?

Sorry, not trying to be stupid.
 
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RE: PIA Claims B777-200LR Not Upto Specifications...

Sat May 27, 2006 6:02 am

Quoting Widebodyphotog (Reply 236):
I think that the first application of the GTF will be in the high thrust segment for future large aircraft such as Boeing Y3. GTF's of 120-140,000lbt, fan diameters of 140-150 inches with BPR 12-13, are not inconceivable in such an application...But does that then mean 150,000shp gearboxes?!

Very unlikely to see a GTF in this segment first IMO. How about heat dissipation of the gearbox? And how about durability? Has anybody tinkered with gearboxes beyond 50,000hp yet?

Quoting Lightsaber (Reply 235):
The neat thing about the GTF is that it brings its efficiencies to any thrust range.

What about the ALF502? That's a GTF, isn't it? Were the reliability problems with that engine related to the gearbox?
 
jacobin777
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RE: PIA Claims B777-200LR Not Upto Specifications...

Sat May 27, 2006 6:41 am

Quoting Lightsaber (Reply 235):

It comes down to the fact that high inlet temperatures (at altitude) and/or climbing, the triple spool has nice thermodynamic cycle advantages in its favor

ahh..that makes sense.... checkmark ..i'm making my way through engine dynamics 101... Smile

Quoting Lightsaber (Reply 235):
GTF



Quoting Lightsaber (Reply 235):
LPC

if you can define those two, it shall help through the conversations...

merci in advance.. Smile

Quoting PVD757 (Reply 237):
Sorry, not trying to be stupid.

you're not, probably 2/3 of the people here (including me) have no clue.... Wink
 
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lightsaber
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RE: PIA Claims B777-200LR Not Upto Specifications.

Sat May 27, 2006 7:22 am

Quoting Widebodyphotog (Reply 236):
But does that then mean 150,000shp gearboxes?!

It would. Thus why I think a lower thrust engine will get the GTF first. Imagine the 737 with an engine that gets 15% lower TSFC... quite a different market, eh?
8% lower TSFC from the Geared Turbo Fan.  Smile
3% lower from contra rotation
2% to 3% lower by adding a 2nd High turbine stage (worth it at $70/bbl, not at $30 bbl)
2% due a bunch of incrimental improvements.

Quoting PVD757 (Reply 237):
Count me in to this category. My sorry little business degree is being overpowered right now in regards to this engineering discussion, but I'm fascinated nonetheless. I just don't know some of the acronyms that everyone is spitting out. I get the winds and temps and how they affect performance. I even have a basic concept of the engine and the components and how they interact, I just can't get the rest of the GTF, TSFC, and the difference between the double and the triple spool other than I look at it as some sort of overdrive in the gearbox that allows more efficiency at higher rates?

I'll do a quick summary.

A geared turbo fan has a fixed gearbox between the turbine that powers the fan and the fan? Now, that same turbine powers the first half of the compressor (called the low compressor). All airfoils operate at their peak efficiency at the same mach number. Rather than explain the speed of sound, think of it as RPM times diameter with a temperature correction. ok?

Now the fan is a really big diameter, so it needs to spin at a low RPM. Overspeeding the fan quickly has huge noise and fuel efficiency penalties. But... fans are usually run 7% to 10% overspeed! About 1400 RPM when you might really want 1300 RPM for the fan.

The fan must be powered by the relatively small diameter turbine (low turbine). That turbine is powered by hot gases coming out the high turbine.
So hot gases mean the turbine needs a higher RPM to be efficient. The smaller diameter and hot gasses mean that the optimum RPM for the turbine is about 4,500 RPM.
The low compressor is most efficient in the 3,500 to 4,000 RPM range.

Ok, so you have one part that is most efficient at 4,500 RPM powering a part that would do best at 1,300 RPM. Simple solution, put in a gear box! Now, since the low compressor is happiest at 4,000 RPM (or less), that's the speed you run the low turbine. Because the fan is slowed down, you gain about 3% improvement in fuel efficiency. Because the turbine is sped up, you gain about 5% in fuel efficiency. We engineers say TSFC rather than fuel efficiency as its a number we can put into our equations.  spin 

Now TSFC is "Thrust Specific Fuel Consumption."
It the amount of fuel burned per hour (in lbm) divided by the engines thrust (at that setting). Values are dropping (better fuel efficiency) toward a TSFC of 0.510 for cruise. The harder you run a jet engine, the more thrust you get for each pound of fuel (about 7.8 lbm per gallon) so engine makers prefer to quote takeoff TSFC, but for long haul planes cruise is what we discuss. Climb is important too... but one actually looks at dozens of design points... so on a.net we usually just talk cruise to simplify things.  spin 

A link on TSFC:
http://www.grc.nasa.gov/WWW/K-12/airplane/sfc.html

Now, if you haven't realized, there is concern over the gearbox durability and reliability. Thus, Rolls Royce has chose another alternative. Their fan is powered by its own turbine, but the fan still runs at the inefficient 1,300 ish RPM.

But, their fix is instead of running the low compressor and its turbine at a very inefficient 1,300 RPM, they put those two on their own shaft and bearings at about 4,000 RPM. This improves fuel efficiency by about 2% (or lowers TSFC by 2%, a good thing).

What it also does is reduce engine weight! By about a ton per engine! Why? Engines are made from lots of nickel and titanium (some other stuff too). Nickel is rather heavy. Well, a more efficient compressor means that less compressor is needed as well as less turbine. This makes the engine shorter. That shorter engine, called a "triple spool" has quite a bit fewer parts in it. Really, the only downside is the extra set of bearings added which can be a bear to service. We call this new shaft the "intermediate spool" even though it has the low compressor on it. RR calls the "low compressor" the "intermediate compressor" so have fun calling it what you want.  Smile

Why aren't triple spools the only engines offered? There very heavy for *small* engines. But at 60,000 lbf and above ... they're very light. Thus why the only narrow body with a triple spool is the 757. All the other triple spool engines go on widebodies.

Also, GE and RR have been able to make their double spools as efficient or even more efficient than RR's triple spools by spending money on optimizing the other parts of an engine. On a Boeing 777, if you're flying > 4,000nm get the GE-90. For flights less than 4,000nm get the Trent triple spool. I'm ex-Pratt, but since Pratt blew the Pw4098's fuel efficiency... they're out of the game effectively.  cry  And the pw4168 is the most efficient engine on the Airbus A330... but one needs 72k of thrust for the latest A330's and its a bit of a story why the Pratt's are stuck at 68k thrust...  cry  (68k is 68,000 lbf of thrust)

Since engines have to be started, takeoff, climb, cruise, land, be restarted in flight (rare, but important), produce minimum emissions, burn minimum fuel, weigh as little as possible, survive for thousands of takeoffs and hours of operation, not spit out fireballs (awwww...) etc. they are very complicated. Some added cooling to increase cruise fuel efficiency must be turned down or off for large changes in engine thrust. I alluded to that earlier. Some engines are more sensitive to wear and tear, etc.

Please take all RPM's as approximate. I was too lazy to look up exact numbers.

My background: I designed gas turbine engines for almost 5 years at Pratt. I also have some experience at Solar gas turbines. My current job is propulsion related, but my employer strickly forbids me from discussing my job in online forums. What I can say is I'm much more involved on the fuel aircraft system side than before, so I'm getting a different perspective.  spin 

This thread has been discussing a situation where the better climb durability and increased climb thrust of a triple spool compared to a double spool has been important. Also, all airplanes must fly safely such that if they suddenly lose an engine's thrust everyone is ok.  Smile That means you do not fly a 777 or any other two engine plane directly over K2 or everest (unless they're "light") but you're allowed to fly a four engine plane. It happens that the A340 does very well in an engine out situation. Your seeing a bit of argument over how much of a diversion is required by the 777 due to those tall mountains... And some argument on the weights PIA is flying their 777's at and if they're light enough or not to safely fly near K2/Everest. But I know the kind of work Oldaeroguy and Widebodyphotog do, so I'm going to believe them.

Unfortunately, you will find a lot of A vs. B on these forums. I will vouch that neither OldAeroguy nor Widebodyphotog take sides; they both will present their data and tell you the conclusions they make. Most of the time we're making assumptions off incomplete data... so expect some small errors. But this is discussion. I'm certainly not in the market for a 777 or an A340.  duck 

I hope this helps,
Lightsaber
 
jacobin777
Posts: 12262
Joined: Sat Sep 11, 2004 6:29 pm

RE: PIA Claims B777-200LR Not Upto Specifications.

Sat May 27, 2006 7:31 am

Great....time to get another PhD .... spin 

at least I have flight to London to read it on.. biggrin 


thanks much kindly for the information....... Smile
 
Lumberton
Posts: 4176
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RE: PIA Claims B777-200LR Not Upto Specifications.

Sat May 27, 2006 7:40 am

I'd add you to my RU list,but you're already there.  Wink Much obliged for the layman's explanation.

Quoting Lightsaber (Reply 240):
Now, if you haven't realized, there is concern over the gearbox durability and reliability.
***
What it also does is reduce engine weight! By about a ton per engine!

But doesn't the gear box itself add weight? Are you saying that the weight savings elsewhere compensate for the gearbox weight?

IIRC you posted elsewhere that many crashes win WWII were from gearbox failures? How will the OEM's sell gearbox reliability?
 
widebodyphotog
Posts: 885
Joined: Wed Jun 30, 1999 9:23 am

RE: PIA Claims B777-200LR Not Upto Specifications...

Sat May 27, 2006 9:34 am

Quoting Rheinbote (Reply 238):
Very unlikely to see a GTF in this segment first IMO. How about heat dissipation of the gearbox? And how about durability? Has anybody tinkered with gearboxes beyond 50,000hp yet?

Hey, where there is a will there is a way. The pressure on fuel prices is huge and the incentives are very high for reducing fuel burn for commercial airliners. There is no real techincal reason why we could not have very high HP gearboxes now. Basically it's a problem of acceptance in a very conservative industry....

Quoting Rheinbote (Reply 238):
What about the ALF502? That's a GTF, isn't it? Were the reliability problems with that engine related to the gearbox?

That design has nothing to do with the concept and scale of powerplants OEM's like PW has experimented with. Like comparing apples and cockroaches...

Quoting Lightsaber (Reply 240):
Why aren't triple spools the only engines offered? There very heavy for *small* engines. But at 60,000 lbf and above ... they're very light. Thus why the only narrow body with a triple spool is the 757. All the other triple spool engines go on widebodies.

Dammit 'Saber you really nailed there! Indeed the three spools have come into their own in the high thrust application. In the interim, between now and the advent of the GTF for commercial airliners, I think we will see them basically taking a greater slice of the pie...

Quoting Lightsaber (Reply 240):
Unfortunately, you will find a lot of A vs. B on these forums. I will vouch that neither OldAeroguy nor Widebodyphotog take sides; they both will present their data and tell you the conclusions they make. Most of the time we're making assumptions off incomplete data... so expect some small errors. But this is discussion. I'm certainly not in the market for a 777 or an A340.

Thanks, and I'll say this for myself though, I have some fundamental conceptual disagreements with what Airbus does, and I have a few with Boeing as well. In terms of aeronautical engineering and aircraft operations I'm basically a purist and have to share my points of view from that perspective. But it's intellectually honest I believe. For a living I have to give operators realistic evaluations of what they or doing or what they will do in the future based on the figures and factors that are real. I don't claim to have all the answers but if I disagree with you it is for substantive reasons and not because of some blind loyalism...

Regards,



widebodyphotog
 
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lightsaber
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RE: PIA Claims B777-200LR Not Upto Specifications...

Sat May 27, 2006 10:21 am

Oh, I missed a few definitions:

Oh, if it helps, engines work by "Squeeze-bang-blow" You squeeze the air, "bang" fuel (add heat energy) and then "blow" the air/fuel through the turbine to extract work (more work out due to volumetric expansion)

Engine terms:
GTF=geared turbo fan
LPC=Low pressure compressor
LPT=Low pressure turbine, usually drives the LPC and fan
HPC=High pressure compressor
HPT=High pressure turbine (only drives the HPC, on the GeNx also a generator)
IPC=Intermediate Pressure compressor. An RR term for the LPC on its own turbine
IPT=In a Triple spool, the turbine that drives the LPC (aka IPC).
RPM=Revolutions per minute (in my posts, there are other uses for this)
Cassing=the pressure vessal that holds the engine together.

Quoting Lumberton (Reply 242):
But doesn't the gear box itself add weight? Are you saying that the weight savings elsewhere compensate for the gearbox weight?

IIRC you posted elsewhere that many crashes win WWII were from gearbox failures? How will the OEM's sell gearbox reliability?

The gearbox more than compensates. By having a slow turning (or more precisely, low mach #) LPC, extra stages must be added to it and the LPT (since it too is turning too slowly for the optimal blade shapes). This stretches out the engine. The pressure vessal (aka casing) of the engine must be made from Inconel 715 (ok, in low pressure designs Inconel 625 is possible, but 715 casts easier in spin casting). That's a really heavy nickel alloy. The longer the engine, the thicker the nickel must be to keep the engine "stiff" (adding weight) *and* the longer the casing must be (adding weight). The gearbox adds a few hundred pounds yet in total on a 60k engine would weigh in like a triple spool. (or net 2,000 lbm weight savings).


You recall correctly on the WWII engines. About half of the engine failures were due to gearbox failures. Why?

1. No temperature sensors. We now have cheap reliable temperature sensors.

2. No synthetic oil. This makes a huge difference!

3. New gear tooth designs (this really helps)

4. Testing, testing, and more testing.

To my knowlege, only Pratt has taken the time to characterize high horsepower gearboxes into the detail required to predict (via oil pressure and temperature) a gearbox failure 100+ cycles before the failure.

Quoting Widebodyphotog (Reply 243):
There is no real techincal reason why we could not have very high HP gearboxes now. Basically it's a problem of acceptance in a very conservative industry....

 checkmark 

Quoting Widebodyphotog (Reply 243):
That design has nothing to do with the concept and scale of powerplants OEM's like PW has experimented with. Like comparing apples and cockroaches...

Its more like comparing a Lexus to an old Ford Pinto. They're both cars, but I tell you which one I'd want to drive...

Quoting Widebodyphotog (Reply 243):
Dammit 'Saber you really nailed there! Indeed the three spools have come into their own in the high thrust application. In the interim, between now and the advent of the GTF for commercial airliners, I think we will see them basically taking a greater slice of the pie...

Thanks for the compliment. I agree. It seems that RR has done a lot to minimize bearing size. Yes, some of this comes from their purchase of Allison. Great pre-diffuser tech from their too... That's translates to free compressor efficiency improvements.  spin  But this will allow RR to size the triple spool much smaller. But where is the market?

You see, IAE is gearing up to launch a GTF for their next engine. (Finally, the "superfan!"). Due to contracts, that locks both RR and Pratt into IAE for the A320NG and 737RS. Thus, that keeps the triple spool out of the < 35k market for a generation. I do belive Boeing will allow IAE to offer an engine on the 737RS. Why? Its either that or Airbus will be the only one with a GTF and you know GE will get its engine on the Airbus too... Lets put it this way, a GTF offers the same drop in fuel burn as composites and bleedless combined! I expect a solution like the 787 where IAE and CFM (or will it be GE solo sans SNECMA) share a nacelle. With bleedless designs, that's quite possible.

Of course I start opening up a whole new can of worms. But just my  twocents  As an engine guy, I think bleedless systems are a waste. But now that I do a more systems approach... I know bleedless is the future.  Wink

What else is out there? The A350 is determined to use 787 derived engines (locking out a GTF)... This leaves Boeings "Y" designs (737RS, 773NG) and whatever Airbus does. Personally, I would love to see an E-jet size plane with a GTF. The drop in fuel burn is amazing... I did a like work on a concept Pw800 that was really neat... and amazingly cheap to build. But Bombardier said no and that's the last I heard of it...  Sad

Everyone, have a great weekend!
Lightsaber
 
Rheinbote
Posts: 1103
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RE: PIA Claims B777-200LR Not Upto Specifications...

Sat May 27, 2006 5:31 pm

Quoting Widebodyphotog (Reply 243):
Quoting Rheinbote (Reply 238):
Very unlikely to see a GTF in this segment first IMO. How about heat dissipation of the gearbox? And how about durability? Has anybody tinkered with gearboxes beyond 50,000hp yet?

Hey, where there is a will there is a way.

Okay, so why don't we go for warp-drives straight away?  Wink

Just kidding. It seems to me that Lightsaber has more background in this area than me, so maybe you believe him when he gives a hint where to expect GTF applications first.

A 150,000hp gearbox is deemed technically unfeasible within the timeframe that has to be considered for Y3.
 
Rheinbote
Posts: 1103
Joined: Sun May 21, 2006 9:30 pm

RE: PIA Claims B777-200LR Not Upto Specifications...

Sat May 27, 2006 7:59 pm

Quoting Lightsaber (Reply 244):
I expect a solution like the 787 where IAE and CFM (or will it be GE solo sans SNECMA) share a nacelle. With bleedless designs, that's quite possible.

Are you sure they share the nacelle structure and aero shape? They share the larger portion of the pylon (sans the lower rear quarter where some ancillary equipment is located) for interchangeability. But the nacelles are engine-specific AFAIK.
 
OldAeroGuy
Posts: 3928
Joined: Sun Dec 05, 2004 6:50 am

RE: PIA Claims B777-200LR Not Upto Specifications...

Sat May 27, 2006 9:55 pm

Quoting Widebodyphotog (Reply 243):
Thanks, and I'll say this for myself though, I have some fundamental conceptual disagreements with what Airbus does, and I have a few with Boeing as well. In terms of aeronautical engineering and aircraft operations I'm basically a purist and have to share my points of view from that perspective. But it's intellectually honest I believe. For a living I have to give operators realistic evaluations of what they or doing or what they will do in the future based on the figures and factors that are real. I don't claim to have all the answers but if I disagree with you it is for substantive reasons and not because of some blind loyalism...

Second your thoughts, especially the thanks to Lightsaber, WBP. My customers don't pay me to repeat marketing slogans. And follow-on business requires that any data I provide be backed by a sound engineering analysis. I may not have all the technical data in hand since proprietary rights do apply, but I can't afford to make a statement that will mis-lead my customers.
 
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zeke
Posts: 16735
Joined: Thu Dec 14, 2006 1:42 pm

RE: PIA Claims B777-200LR Not Upto Specifications...

Sat May 27, 2006 11:22 pm

Quoting OldAeroGuy (Reply 247):
Second your thoughts, especially the thanks to Lightsaber, WBP. My customers don't pay me to repeat marketing slogans. And follow-on business requires that any data I provide be backed by a sound engineering analysis. I may not have all the technical data in hand since proprietary rights do apply, but I can't afford to make a statement that will mis-lead my customers.

I know you have side stepped a line of debate that was previously raised by Zeus419.

Can a 777 of any model maintain an altitude with a normal commercial payload, and fitout from a major SE asian port, maintain sufficient altitude, or with drift down safely to permit direct tracking (along designated established airways) over the Himalayas ?

I disagree with your cruise speeds for the 777 and 747 previously mentioned, I agree these maybe reached during the sector, they are however overstated for the initial cruise segment, and maybe for say the first 1/3 of a flight while fuel is burned off to reach a more optimum altitude.

I know of no operator that flight plans at variable cost index (which is what your inferring by constant mach).
 
astuteman
Posts: 7508
Joined: Mon Jan 24, 2005 7:50 pm

RE: PIA Claims B777-200LR Not Upto Specifications...

Sun May 28, 2006 12:27 am

I'd stopped reading this thread when the "tennis" got going - there's a lesson there....

Quoting Lightsaber (Reply 235):



Quoting Lightsaber (Reply 240):

Fabulous stuff. I could read posts like that all day, no problem  thumbsup .
Got any more?  pray   Smile

Quoting Lumberton (Reply 242):
I'd add you to my RU list,but you're already there.

Ditto  Smile

Quoting Lightsaber (Reply 240):
I will vouch that neither OldAeroguy nor Widebodyphotog take sides; they both will present their data and tell you the conclusions they make. Most of the time we're making assumptions off incomplete data... so expect some small errors. But this is discussion

FWIW I'd second that, also  checkmark 

Regards

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