morrisond
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777X Vs 787-11/12

Wed Sep 21, 2011 12:33 am

With all the proposed changes Boeing is contemplating with the 777X - New Wing box/wing, new engines, 787 like systems/avionics, why not just use that new wing box/ wing with the 787 Barrel/cockpit/tail, which should be a bunch lighter than the 777?

You do give up width as max you are 9w vs. 10W, however you may be able to go a little longer than 77W (you only need 9-12' extra length to pick up 36-45 seats, as you would need new gear anyways for the higher weight, and you could design it to give you enough clearance. You may be able to sling 95K GTF's under the wing and outdue the 350 which is 9w (although with a little more room) as well.

The often speculated 787-11 and -12. There would be lots of room in the belly for cargo. The 777-200 is almost identical in size and takeoff weight to the 789, and that design (777) grew to be almost 50% heavier, with extended wings and gear. How heavy would the 787-11/12 have to be to better the 777X in size and capability? Would you end up with a better aircraft? Would the extra length allow another Cargo container in the belly?

Seems like a lot better plan than investing Billions into upgradeing a 20 year old barrel design, that is very space inefficient.

Put the 787 wing on the photocopier and hit 'enlarge', no systems to redo (vs the changes you would have to make to 777X), other than new nose gear(extra length), no new interior to redesign, no new production chain to figure out, etc...

A reasonable idea?
 
tdscanuck
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RE: 777X Vs 787-11/12

Wed Sep 21, 2011 2:48 am

Quoting morrisond (Thread starter):
With all the proposed changes Boeing is contemplating with the 777X - New Wing box/wing, new engines, 787 like systems/avionics, why not just use that new wing box/ wing with the 787 Barrel/cockpit/tail, which should be a bunch lighter than the 777?

At that point, it's a new airplane from a certification point of view and you might as well just go cleansheet, which is exactly what the 777X is trying to avoid.

Quoting morrisond (Thread starter):
How heavy would the 787-11/12 have to be to better the 777X in size and capability?

Heavier, since you're trying to get the same capacity with a skinnier fuselage.

Quoting morrisond (Thread starter):
Would you end up with a better aircraft?

No.

Quoting morrisond (Thread starter):
Would the extra length allow another Cargo container in the belly?

Yes.

Quoting morrisond (Thread starter):
Seems like a lot better plan than investing Billions into upgradeing a 20 year old barrel design, that is very space inefficient.

The "inefficiency" of the 777 barrel is grossly overplayed...if it was an inefficient cross section they wouldn't have picked it in the first place. Note that the A350 has basically the same cross section. The 777 is probably one of the best fuselages ever built from a structural standpoint.

Quoting morrisond (Thread starter):
Put the 787 wing on the photocopier and hit 'enlarge', no systems to redo (vs the changes you would have to make to 777X),

This is basically what they're talking about doing already with the 777X.

Tom.
 
morrisond
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RE: 777X Vs 787-11/12

Wed Sep 21, 2011 12:55 pm

Quoting tdscanuck (Reply 1):
Heavier, since you're trying to get the same capacity with a skinnier fuselage.

So a 787-11/12 that is 9-12' longer than a 777x would be heavier? At worst I think it would be a wash, the cockpit, barrel and tail sections must be lighter. Plus significantly less investment than redoing all the 777 systems.

Quoting tdscanuck (Reply 1):
Quoting morrisond (Thread starter):
With all the proposed changes Boeing is contemplating with the 777X - New Wing box/wing, new engines, 787 like systems/avionics, why not just use that new wing box/ wing with the 787 Barrel/cockpit/tail, which should be a bunch lighter than the 777?

At that point, it's a new airplane from a certification point of view and you might as well just go cleansheet, which is exactly what the 777X is trying to avoid.

I agree and that's the point I'm trying to make, it seems silly to make all those changes to the 777 without going cleansheet, it would be a lot cheaper and much more timely to design a new bigger wing for the 787 and stretch it.

In order for a 777x to be more efficient than a 787-11/12 you would have to basically re-engineer the whole plane (777), why bother when they have a brand new Widebody Cross Section that is state of the art.

Can you fit bigger containers in the 777 Belly vs the 787 or are they the same? Can you do an more efficient arrangement in the higher fare paying sections of the 777 that you can't do with the 787 cross section?

Can you build the 777 at a lower cost than the 787? Once the 787 is up to speed, I think the answer is no and by 2020 composite materials should have advanced so that the 787 barrel can be made lighter and less expensively.
 
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seabosdca
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RE: 777X Vs 787-11/12

Wed Sep 21, 2011 1:07 pm

Quoting morrisond (Reply 2):
Can you do an more efficient arrangement in the higher fare paying sections of the 777 that you can't do with the 787 cross section?

Yes. The 777 can do 6-abreast in "staggered" business configurations (like LX's) and 7-abreast in conventional ones.

Quoting morrisond (Reply 2):
So a 787-11/12 that is 9-12' longer than a 777x would be heavier?

Compare the A340-300 to the A340-600 to get your answer. The reinforcements to allow the fuselage to be stretched that far are a big part of why the 346 was so heavy. If it had somehow been as light as the 77W, the 346 would have probably been better than the 77W.
 
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SEPilot
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RE: 777X Vs 787-11/12

Wed Sep 21, 2011 1:27 pm

Quoting seabosdca (Reply 3):
If it had somehow been as light as the 77W, the 346 would have probably been better than the 77W.

I doubt that; two large engines are almost always more efficient than four smaller ones powering the same aircraft, even taking into account the extra spare thrust that a twin requires to account for engine out operations. Jet engines gain efficiency with size, as the surface area to volume ratio goes down, which leads to lower thermal losses (to put it in the simplest terms that are readily understandable.) There are many other factors, but they almost all favor the large engine over the small one. I believe the drag of two large nacelles is also less than four small ones as well.
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jacobin777
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RE: 777X Vs 787-11/12

Wed Sep 21, 2011 2:23 pm

Quoting seabosdca (Reply 3):
Quoting morrisond (Reply 2):
Can you do an more efficient arrangement in the higher fare paying sections of the 777 that you can't do with the 787 cross section?

Yes. The 777 can do 6-abreast in "staggered" business configurations (like LX's) and 7-abreast in conventional ones.

Even 8-across is possible - such as BA's Club World.
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morrisond
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RE: 777X Vs 787-11/12

Wed Sep 21, 2011 2:34 pm

Quoting seabosdca (Reply 3):
Can you do an more efficient arrangement in the higher fare paying sections of the 777 that you can't do with the 787 cross section?

Yes. The 777 can do 6-abreast in "staggered" business configurations (like LX's) and 7-abreast in conventional ones.

So a 787 can only do 5 and 6? I can see the Value of 6 over 5, but 7 across seems like something that wouldn't be pursued by a lot of carriers?

Quoting morrisond (Reply 2):
So a 787-11/12 that is 9-12' longer than a 777x would be heavier?

Compare the A340-300 to the A340-600 to get your answer. The reinforcements to allow the fuselage to be stretched that far are a big part of why the 346 was so heavy. If it had somehow been as light as the 77W, the 346 would have probably been better than the 77W.

Think of it this way, to make a 787-12 carry the same passenger load as a 777x it would only have to be 9-12' longer, as you are designing a new Center wing box anyways in both cases, and as the 787 can be made all composite I would assume it would be lighter, and as your 787 nose and tail are lighter no need to reinforce as much.

A 250' long 787 shouldn't be heavier than a 240' 777.
 
frmrCapCadet
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RE: 777X Vs 787-11/12

Wed Sep 21, 2011 3:53 pm

I think someone made the point a few years ago that a plastic plane can be stretched without as much weight increasa as an aluminum one. Not an engineer so don't know if it is true, but seemed persuasive at the time.
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RE: 777X Vs 787-11/12

Wed Sep 21, 2011 4:32 pm

Quoting frmrCapCadet (Reply 7):
I think someone made the point a few years ago that a plastic plane can be stretched without as much weight increasa as an aluminum one. Not an engineer so don't know if it is true, but seemed persuasive at the time.

This should be the case, as the strength to weight ratio is better with CFRP. But you still have practical limits, and the stiffness to strength ratio on CFRP is less than Al. This is why CFRP wings flex so much more than Al wings; you will have the same effect with the fuselage. If you stretch it too much you may have enough strength, but the fuselage flexes too much. That might just pose a lot more problems (as when the fuselage flexes you change control surface effect; when the tail goes down it will push the plane into a dive, and when it goes up you will go into a climb. This can be compensated with FBW, but it still could get interesting.)
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
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seabosdca
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RE: 777X Vs 787-11/12

Wed Sep 21, 2011 4:35 pm

Quoting SEPilot (Reply 4):
I doubt that; two large engines are almost always more efficient than four smaller ones powering the same aircraft

I'm hypothesizing based on the actual performance of the aircraft. The A340NG, lightened, would have dramatically better payload range than the 77W, and I think operating cost would not have been far off. The Trent 500 was really very good, and four of them very well might outperform two GE90-115Bs on an airframe of equivalent weight.

It was really the extraordinarily heavy empty weight that did all the damage, not the four engines.

[Edited 2011-09-21 09:36:43]
 
flyingcello
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RE: 777X Vs 787-11/12

Wed Sep 21, 2011 5:21 pm

Hi guys,

Long time observer here, but signed up officially this week...

The 787 was planned as a -8 and -9...maybe someone at Boeing had an idea back then of a -10, but the design sweet spot was somewhere around the -8 / -9. A -10 is now looking viable, but to me a -11 (never mind a -12) is a step too far. Longitudinal strength becomes compromised (adding weight), as does control authority.

Also, consider that 787 was Y2...with a clear direction for Y1 to replace 737 and Y3 to replace 777 / 747. If 787-11 was to happen, Boeing lose any motivation to do Y3 for a generation. While that might be financially attractive, it will sacrifice sales in the longer term.

A 777X (with Al-Li fuselage?) complete with CFRP wing would bring most of the potential Y3 benefit to the table quickly...and still leave the sector intact for a true Y3 (Y3NG?) later...maybe a BWB...

In any engineering exercise, you compromise a design once you take it too far from the original...a 787-11 would be the equivalent of a 767-500 or an A330-400...just asking too much from the original design. The A340-600 is being quoted here as the example, and if nothing else, it does look just too darn long!

787-8, 787-9, 787-10, 777-8, 777-9...that is a formidible line-up...

[Edited 2011-09-21 10:41:38]
 
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SEPilot
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RE: 777X Vs 787-11/12

Wed Sep 21, 2011 6:56 pm

Quoting seabosdca (Reply 9):

It was really the extraordinarily heavy empty weight that did all the damage, not the four engines.

I still don't buy that. The fuel burn difference is on the order of 10%; I don't think the empty weight difference contributes that much. The 777 has from the outset had better fuel burn than the comparable A340 model from what I understand; and the A343 did not suffer from excess empty weight like the A346 did. Certainly the A330 (which I understand is pretty much structurally identical to the A342/343) is very efficient structurally.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
morrisond
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RE: 777X Vs 787-11/12

Wed Sep 21, 2011 7:13 pm

Quoting FlyingCello (Reply 10):
In any engineering exercise, you compromise a design once you take it too far from the original...a 787-11 would be the equivalent of a 767-500 or an A330-400...just asking too much from the original design. The A340-600 is being quoted here as the example, and if nothing else, it does look just too darn long!

If you have to design a whole new center section anyways, just the center section would need to be stronger than 788 or 789, you don't have to redesign your existing sections.

the 787-11/12 would use a center section with the wing root say 5' wider (and 10m total additional width on the wing) than the small wing with an additional 10' added to the front and back of the section for an extra 25' in length over 787-10. Basically you take the 787-10 Forward and rear sections and graft them to them to your new center section, to get a 250-260' 787-12.

Then take 787-8 or 9 sections to get a 220-230' 787-11 with more range like the 777-200LR.

It would be a stretch too far if you tried to use the existing wing box and center section, however that could never take enough wing to lift the required weight anyways.

Quoting FlyingCello (Reply 10):
A 777X (with Al-Li fuselage?) complete with CFRP wing would bring most of the potential Y3 benefit to the table quickly...and still leave the sector intact for a true Y3 (Y3NG?) later...maybe a BWB...

I agree on Y3, it should be a BWB or something other than Tube and Wing, no point in investing even more money in round tubes(777) when you can get the capacity you need with a 787 stretch, and 777 will never get you into A380 territory.
 
LAXDESI
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RE: 777X Vs 787-11/12

Wed Sep 21, 2011 7:28 pm

My model suggests, for equivalent technology and cabin comfort, an operating efficiency dividing line of around 370-380 seats(3 class) between 9-abreast and 10-abreast platform.

One can argue that the proposed 777-9X is not of comparable technology and cabin comfort as A350-10, but is close enough. Boeing is on the right track with 388 seater 777-9X to compete against 350 seater A350-10. My model suggests that both will attract customers, with cabin layout being a critical factor in the decision making process. Link to a thread where I compare the proposed 777-9X to A350-1000.
A350-10 Versus B777-9X Economic Analysis (by LAXDESI Sep 20 2011 in Tech Ops)


A350-11(or 787-12) with 380 seats should be more efficient than 777-9X on GSM(gallon seat mile) basis. However, for Boeing the development cost will be significantly higher to build a 787-11/12 versus 777-8/9X.
 
morrisond
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RE: 777X Vs 787-11/12

Wed Sep 21, 2011 7:59 pm

Quoting LAXDESI (Reply 13):
A350-11(or 787-12) with 380 seats should be more efficient than 777-9X on GSM(gallon seat mile) basis. However, for Boeing the development cost will be significantly higher to build a 787-11/12 versus 777-8/9X.

Why would it be though? You don't really have to change any systems or build processes with 787-11/12. To really make the 777x competitive you would need to build a new CFRP wingbox /wing, change the internal ribs to extra width, new interior and 787 the systems (more electric, avionics) which should cost a lot more than just building a new center section for the 787. Both would need new engines so that's a wash, but the lower thrust range the 787-11/12 may need (assuming it has lower weight) is one where more competition exists so power should be cheaper.

Basically your building a complete new plane with 777x, and may have to be certified as such as all your keeping is the external shape - you might as well start from scratch. The 787-11/12 may just be viewed as a derivative and just require a wing bending test and reduced flight test program.

I would have to guess that a 787-11/12 could be done a lot quicker than 777x as well as the changes are not nearly as large, when the team is done with 787-10 just move right on to 11 and 12, they would be very familiar with the design so no relearning necessary.

787-9 2013
787-10 2015
787-11/12 2016-17 vs 2018-2020 for 777x
 
PITingres
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RE: 777X Vs 787-11/12

Wed Sep 21, 2011 8:12 pm

Quoting morrisond (Reply 14):
To really make the 777x competitive you would need to build a new CFRP wingbox /wing, change the internal ribs to extra width, new interior and 787 the systems (more electric, avionics) ...

All of which are arguable, and the publicly available hints appear to dispute your view on that. Various posters have suggested that at least some of the current 777 structures are overbuilt, presumably in such a way that it's not just a matter of shaving off a millimeter here and a centimeter there (else it would have been done by now). In particular there have been repeated suggestions that several tonnes of weight could be removed from the existing structure given sufficient effort. There's no consensus that a 777X needs all-electric architecture, or CRFP this-or-that. As for the interior, some airlines already fly 10x on the 777, and every cm that can be carved out by thinning / reshaping / redistributing is just a plus.

On the other hand, a 787-more-than-10 would need (at the very least) significant undercarriage work, which implies changes to the landing gear retract outlines in the fuselage, which sounds like a seriously Big Deal. It's not just a matter of making bigger holes!

You seem to be asserting that a useful 777-X would be in essence an all-new airframe, and Boeing (who ought to know) seems to disagree.
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morrisond
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RE: 777X Vs 787-11/12

Wed Sep 21, 2011 8:29 pm

Quoting PITingres (Reply 15):
All of which are arguable, and the publicly available hints appear to dispute your view on that. Various posters have suggested that at least some of the current 777 structures are overbuilt, presumably in such a way that it's not just a matter of shaving off a millimeter here and a centimeter there (else it would have been done by now). In particular there have been repeated suggestions that several tonnes of weight could be removed from the existing structure given sufficient effort. There's no consensus that a 777X needs all-electric architecture, or CRFP this-or-that. As for the interior, some airlines already fly 10x on the 777, and every cm that can be carved out by thinning / reshaping / redistributing is just a plus.

On the other hand, a 787-more-than-10 would need (at the very least) significant undercarriage work, which implies changes to the landing gear retract outlines in the fuselage, which sounds like a seriously Big Deal. It's not just a matter of making bigger holes!

You seem to be asserting that a useful 777-X would be in essence an all-new airframe, and Boeing (who ought to know) seems to disagree.

I don't disagree with the view that they don't need to do a whole new wingbox/wing, I'm more responding to the views on this forum and in various articles that in order for it to be anywhere competitive with the A350-1000 they have to use CFRP. My point being that to do it in CFRP you would be better off to build an XL wing/undercarriage for the 787 instead as you wouldn't have to do much systems work, and your expense would be less.

If they can stick with the basic 777 Wingbox/wing (albeit using the the excess strength to make it longer) that could be cheaper, but it wouldn't be any lighter and I don't think they will be able to make the wing big enough to get by with 15% less power without changing the wingbox.
 
LAXDESI
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RE: 777X Vs 787-11/12

Wed Sep 21, 2011 8:45 pm

Quoting morrisond (Reply 14):
However, for Boeing the development cost will be significantly higher to build a 787-11/12 versus 777-8/9X.

Why would it be though?

You do raise an interesting question and back it up with many good points. My estimate on development cost is based on what I have read on A.net. I look forward to some informed comments on this issue.

It seems to me that the current 777-9X(388 seats) specs. allow for the possibility of 777-10X(418 seats with 8,000nm range) at a later date with more powerful engines.

787-11/12 with a cabin width of 18ft. at 9-abreast in Y should be equally comfortable as 10-abreast Y 777-8/9X with 19.5 ft cabin width.
 
JoeCanuck
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RE: 777X Vs 787-11/12

Wed Sep 21, 2011 9:06 pm

Quoting morrisond (Reply 16):
If they can stick with the basic 777 Wingbox/wing (albeit using the the excess strength to make it longer) that could be cheaper, but it wouldn't be any lighter and I don't think they will be able to make the wing big enough to get by with 15% less power without changing the wingbox.

You bring up a few good points...what if not just the fuselage but the wings as well were built from lighter aluminum alloys...instead of going with a composite wing...same wing, lighter material.

On the other hand, what if a larger 787 wing was the basis of the new 777 wing? So the basic box crossing two platforms.

I'm sure it's possible...but practical...?

What the heck...these are just ideas...and crazy is at least interesting.
What the...?
 
PITingres
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RE: 777X Vs 787-11/12

Wed Sep 21, 2011 9:25 pm

Quoting morrisond (Reply 16):
I'm more responding to the views on this forum and in various articles that in order for it to be anywhere competitive with the A350-1000 they have to use CFRP. My point being that to do it in CFRP you would be better off to build an XL wing/undercarriage for the 787 instead as you wouldn't have to do much systems work ...

Ah. That's fair enough. I don't pretend to know enough about wing or wingbox structure (period, never mind CFRP vs metal) to talk sense about it except what I've read here. I don't know if your statement re a CFRP wing is correct or not, but I'm willing to at least consider it.

The most plausible posts I've read re upgrading the 777 seem to imply that the wing and wingbox materials would remain the same (or at least similar), but the structure details would be smacked around enough to save significant weight. Without being able to point to blueprints and talk alternatives, I guess that's the best we can do here.
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morrisond
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RE: 777X Vs 787-11/12

Wed Sep 21, 2011 10:34 pm

Here is John O's article mentioning the CFRP wing, http://www.flightglobal.com/blogs/fl...oeings-777-upgrades-come-into.html however he doesn't talk about a new Wing Box, if you don't have to change that then maybe it makes sense to keep the 777, however if you want to stretch it, you may have to lengthen the gear to get enough rotation angle, which means new wingbox. However the higher lift wing may mean that you can get away with less rotation angle and more length but it would be hard to envision lower thrust as well.

By going 787-11/12 you also get the benefits of the 787 design, bigger windows, more cabin humidity, higher cabin altitude. I know which Tube I would rather fly in....
 
BMI727
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RE: 777X Vs 787-11/12

Thu Sep 22, 2011 12:30 am

Quoting morrisond (Reply 2):
So a 787-11/12 that is 9-12' longer than a 777x would be heavier?

In absolute terms, maybe not. But from a structural efficiency standpoint, almost certainly.

Quoting FlyingCello (Reply 10):
The 787 was planned as a -8 and -9...maybe someone at Boeing had an idea back then of a -10, but the design sweet spot was somewhere around the -8 / -9. A -10 is now looking viable, but to me a -11 (never mind a -12) is a step too far. Longitudinal strength becomes compromised (adding weight), as does control authority.

Boeing backed themselves into a corner. The smaller wing will do just fine on the -9, but when they scrapped the larger wing the chance for a really competitive 787-10 went out the window. If they had to do it all again, I think Boeing would've made the 787-9 longer to almost where the -10X would be now.

But that's water under the bridge. Going forward, I think the best option is to scrap the 787-10X and replace it with a longer 787-10 with a new wing, wingbox, and possibly landing gear. It would have to be about a 30-35 foot stretch, putting it right about where the 777-300ER with 9 across is now but lighter and with not quite as much range. Hopefully that could get in the air late this decade, so not long after the A350-1000.

In the meantime, sell as many 777s as possible and then launch the Y3 covering the capacity from the 77W and up for EIS in mid-2020s.

Quoting FlyingCello (Reply 10):
787-8, 787-9, 787-10, 777-8, 777-9...that is a formidible line-up...

Considering what the 787-10, and 777NG would be and when they would enter service, I would have to disagree.
Why do Aerospace Engineering students have to turn things in on time?
 
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Stitch
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RE: 777X Vs 787-11/12

Thu Sep 22, 2011 1:01 am

Quoting BMI727 (Reply 21):
Boeing backed themselves into a corner. The smaller wing will do just fine on the -9, but when they scrapped the larger wing the chance for a really competitive 787-10 went out the window. If they had to do it all again, I think Boeing would've made the 787-9 longer to almost where the -10X would be now.

I don't see what would keep Boeing from returning to the 64m (or even going to 65m) with the 787-10X. That extra span was in the wing-tip extensions, anyway, as I recall.
 
JoeCanuck
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RE: 777X Vs 787-11/12

Thu Sep 22, 2011 1:54 am

I think the -10 basic stretch is a done deal. While no stretch is a piece of cake, this one is as close to one as you can get. Even a 6000nm range lets the plane reach, for example, all of China, Europe and most of S. America from Vancouver, all of Asia, Africa and Europe from DXB, all of Asia and Europe and most of Africa and the US and Canada from Beijing.

That's a lot of places from a lot of other places...for very little extra investment.

They would be nuts not to do it.

There's also nothing stopping Boeing from using the -10 LGW fuse as the basis of a HGW -10, -11 or whatever with a new wing, engines and gear...should they choose to go that way.
What the...?
 
tdscanuck
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RE: 777X Vs 787-11/12

Thu Sep 22, 2011 2:00 am

Quoting morrisond (Reply 2):
Can you fit bigger containers in the 777 Belly vs the 787 or are they the same?

Same size containers. Bigger pallets though...

Quoting morrisond (Reply 2):
Can you do an more efficient arrangement in the higher fare paying sections of the 777 that you can't do with the 787 cross section?

Yes.

Quoting morrisond (Reply 2):
Can you build the 777 at a lower cost than the 787?

Almost certainly yes, given how mature the 777 production system is.

Quoting morrisond (Reply 2):
Quoting tdscanuck (Reply 1):
Heavier, since you're trying to get the same capacity with a skinnier fuselage.

So a 787-11/12 that is 9-12' longer than a 777x would be heavier?

I would expect so. The issue is stiffness...as you get longer, you need to maintain stiffness. The 787 cross section is at a huge disadvantage, even at equal length, due to smaller diameter. If it's longer that problem gets worse. I suspect it would overshadow the weight savings due to material.

Quoting morrisond (Reply 2):
I agree and that's the point I'm trying to make, it seems silly to make all those changes to the 777 without going cleansheet, it would be a lot cheaper and much more timely to design a new bigger wing for the 787 and stretch it.

Either way, they're doing a new wing. So it's a new wing plus a major systems/fuselage redesign if you use the 787 as a base, or just a new wing if you use the 777 as the base. The latter is cheaper and easier.

Quoting morrisond (Reply 2):
In order for a 777x to be more efficient than a 787-11/12 you would have to basically re-engineer the whole plane (777), why bother when they have a brand new Widebody Cross Section that is state of the art.

The 787 wasn't designed to be stretched that far...it's very unlikely that it could be competitive with a 777X. The 787 cross-section isn't viable at the 777-300 capacity point (otherwise the 777 would have used that cross section in the first place).

Quoting morrisond (Reply 14):
You don't really have to change any systems or build processes with 787-11/12.

You can probably use the same build process, but it's unlikely that the 787-8/9 systems have so much extra capacity that they can stretch to -11/12 without changes.

Tom.
 
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RE: 777X Vs 787-11/12

Fri Sep 23, 2011 2:24 pm

Quoting tdscanuck (Reply 24):
I would expect so. The issue is stiffness...as you get longer, you need to maintain stiffness. The 787 cross section is at a huge disadvantage, even at equal length, due to smaller diameter. If it's longer that problem gets worse. I suspect it would overshadow the weight savings due to material.

The Barrel Diameters really aren't that different. The 777 Diameter is 244" while the 787 is 235" H by 227" W. Only a 9" difference in height (the one that is more relavant to the strength discussion), and you are using composites which should easily be able to overcome that difference.

The 787 interior is 15" thinner inside, meaning it is more comfortable at 9W than Current 777 at 10W.

Quoting tdscanuck (Reply 24):
Either way, they're doing a new wing. So it's a new wing plus a major systems/fuselage redesign if you use the 787 as a base, or just a new wing if you use the 777 as the base. The latter is cheaper and easier.

Yes either one your doing a new wing and if that includes having to do a new Wing Box, you have to redesign the whole center section anyways, and can you build in the strength you need on the 787 XL Center section you need in combination with the front and rear sections that you have already designed for the 787-10 to get the necessary strength.

You basically build your center 787 XL section 25' longer than the existing one with sufficient strength to get the length you need. No need to redesign the front and tail sections.

You may have to upsize a few things on 787 systems but they should not be that different than what is envisioned for 787-10, vs to gain efficiency on 777 you would have to do major changes on systems and start from scratch on a lot.
 
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RE: 777X Vs 787-11/12

Fri Sep 23, 2011 3:04 pm

Quoting morrisond (Reply 25):
The Barrel Diameters really aren't that different. The 777 Diameter is 244" while the 787 is 235" H by 227" W. Only a 9" difference in height (the one that is more relavant to the strength discussion), and you are using composites which should easily be able to overcome that difference.

The stiffness works as the fourth power of the diameter; this means that a relatively small increase in diameter has a huge increase in stiffness. Also, the stiffness to strength ratio for CFRP is lower than for aluminum, which means with the same strength you will get more deflection with CFRP as opposed to aluminum (hence the much greater wing flex with CFRP wings). Fuselage flex with an airliner is much more important than wing flex, and hence with the CFRP fuselage (especially with the smaller diameter) and a very long fuselage you may have to add structure to get the necessary stiffness beyond what is required for structural strength. Hence you may lose the weight savings of CFRP. Overall, you are probably better off with the larger diameter Al fuselage rather than trying to extend a smaller diameter CFRP fuselage to get the same capacity. There comes a point (as the A346 proved) where a extending a given fuselage diameter is a case of diminishing returns, and that will be true no matter what the material; however with different materials that point will be different. Unfortunately, I believe the point for Al is farther out than for CFRP.
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RE: 777X Vs 787-11/12

Fri Sep 23, 2011 3:06 pm

Quoting morrisond (Reply 25):
can you build in the strength you need on the 787 XL Center section you need in combination with the front and rear sections that you have already designed for the 787-10 to get the necessary strength.

Sure, you can design any level of strength in you want... but you'll likely add too much weight. That's the lesson the A340-600 teaches us.
 
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RE: 777X Vs 787-11/12

Fri Sep 23, 2011 3:30 pm

Quoting SEPilot (Reply 26):
Also, the stiffness to strength ratio for CFRP is lower than for aluminum, which means with the same strength you will get more deflection with CFRP as opposed to aluminum...(with)...a very long fuselage you may have to add structure to get the necessary stiffness beyond what is required for structural strength.

Interesting. Many have offered the opinion that monolithic CFRP barrel construction would allow Boeing to stretch the 787 fuselage without anywhere near the weight penalty Airbus took to stretch the A340 fuselage to create the A340-500 and A340-600.

[Edited 2011-09-23 08:31:10]
 
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RE: 777X Vs 787-11/12

Fri Sep 23, 2011 3:56 pm

Quoting Stitch (Reply 28):
Interesting. Many have offered the opinion that monolithic CFRP barrel construction would allow Boeing to stretch the 787 fuselage without anywhere near the weight penalty Airbus took to stretch the A340 fuselage to create the A340-500 and A340-600.

I do not have experience with designing in CFRP; however, I do understand the factors involved. My initial thought was that this would be the case; however, when I started thinking about the specifics, I realized that I was probably wrong. Flexibility is the issue; it doesn't hurt wings, but it does hurt fuselages. Flexibility and strength are two very different characteristics, and if you need maximum stiffness (low flexibility) CFRP is not your friend. However, the fatigue resistance of CFRP is very important for fuselages especially, as is corrosion resistance. So the moral seems to be that CFRP is a wonderful material for building aircraft but you cannot stretch the fuselage too far (and not as far as you can with Al.)
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
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RE: 777X Vs 787-11/12

Fri Sep 23, 2011 5:18 pm

What about doing CFRP panels instead of barrels? How does that compare to an Al fuse?
 
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RE: 777X Vs 787-11/12

Fri Sep 23, 2011 6:39 pm

Quoting morrisond (Thread starter):
Seems like a lot better plan than investing Billions into upgradeing a 20 year old barrel design, that is very space inefficient.

It is not particularly inefficient it is just not wide enough for a decent 10 abreast. A 9 abreast 787 is more comfortable than a 10 abreast 777 but less than a 9 abreast 777. One of the problem with widebody design is that there is a width that is initially envisioned, then the airlines try to squeeze as many seats as possible. The original intent for the 787 was to give one of the most passenger requested features, individual armrests at 8 abreast. That went out the window quickly and few will be delivered a 8 abreast in regular Y.

Quoting morrisond (Reply 6):
Think of it this way, to make a 787-12 carry the same passenger load as a 777x it would only have to be 9-12' longer, as you are designing a new Center wing box anyways in both cases, and as the 787 can be made all composite I would assume it would be lighter, and as your 787 nose and tail are lighter no need to reinforce as much.

A 250' long 787 shouldn't be heavier than a 240' 777.

There is another problem with exceeding 240 feet. Airports are designed to allow aircraft that can fit within a 75m by 75m box or less. 250' is 76.2 meters. A 250' long 787 would be extremely impractical.
 
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RE: 777X Vs 787-11/12

Fri Sep 23, 2011 7:05 pm

Quoting AADC10 (Reply 31):
There is another problem with exceeding 240 feet. Airports are designed to allow aircraft that can fit within a 75m by 75m box or less.

I believe 80m x 80m is the standard. The A380-800 was designed to this.
 
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RE: 777X Vs 787-11/12

Fri Sep 23, 2011 7:53 pm

Quoting Stitch (Reply 32):
I believe 80m x 80m is the standard. The A380-800 was designed to this.

Correct, that is why the wing span is 79.8 meter where Airbus actually wanted about 83-84 meters. But 80 m x 80 m is only for ICAO Category F airplanes. Smaller airplanes might be designed to fit with a 75 m x 75 m box? And maybe some airports were designed with these measurements in mind?
 
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RE: 777X Vs 787-11/12

Fri Sep 23, 2011 7:59 pm

Quoting YTZ (Reply 30):
What about doing CFRP panels instead of barrels? How does that compare to an Al fuse?

If you are talking about my post, it makes no difference. It is a factor of the material itself, not the construction.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
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RE: 777X Vs 787-11/12

Fri Sep 23, 2011 8:00 pm

Quoting EPA001 (Reply 33):
But 80 m x 80 m is only for ICAO Category F airplanes. Smaller airplanes might be designed to fit with a 75 m x 75 m box?


The next step down, Code E, is 52m to less than 64m. And as FAA Categories map directly to their equivalent ICAO Codes, FAA Category V is also 52m to less than 65m.
 
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RE: 777X Vs 787-11/12

Fri Sep 23, 2011 8:05 pm

Quoting Stitch (Reply 35):
The next step down, Code E, is 52m to less than 64m. And as FAA Categories map directly to their equivalent ICAO Codes, FAA Category V is also 52m to less than 65m.

OK, thanks for the information. I could not find the right measurements that quickly with google.
 
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RE: 777X Vs 787-11/12

Fri Sep 23, 2011 8:07 pm

Quoting SEPilot (Reply 26):

The stiffness works as the fourth power of the diameter; this means that a relatively small increase in diameter has a huge increase in stiffness. Also, the stiffness to strength ratio for CFRP is lower than for aluminum, which means with the same strength you will get more deflection with CFRP as opposed to aluminum (hence the much greater wing flex with CFRP wings).

As morrisond points out, the entire fuselage doesn't have to be strengthened, only the stretched section, since the current fuselage sections are already designed to support themselves. This should remain true regardless of what they are attached to and as long as the plane is stretched from the middle, leaving the current front and rear sections intact.
What the...?
 
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RE: 777X Vs 787-11/12

Fri Sep 23, 2011 9:03 pm

Quoting EPA001 (Reply 33):
Correct, that is why the wing span is 79.8 meter where Airbus actually wanted about 83-84 meters. But 80 m x 80 m is only for ICAO Category F airplanes.

If you think it's hard now to get airports to spend money on improvements to support the A380... Imagine if they went forward with a 83-84m wing?
harder than woodpecker lips...
 
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RE: 777X Vs 787-11/12

Fri Sep 23, 2011 9:10 pm

Quoting mffoda (Reply 38):
If you think it's hard now to get airports to spend money on improvements to support the A380... Imagine if they went forward with a 83-84m wing?

It might not be much of an issue, to be honest.
 
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RE: 777X Vs 787-11/12

Fri Sep 23, 2011 9:26 pm

Quoting Stitch (Reply 39):
It might not be much of an issue, to be honest.

I don't know the answer? But how many airports can currently handle the A380? I remember that one the selling points on the 747-8 was airport compatibility... And, it would certainly not be benefit to airports to support an even larger 83-84m wing? Just thinking out loud??
harder than woodpecker lips...
 
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RE: 777X Vs 787-11/12

Fri Sep 23, 2011 9:31 pm

Quoting mffoda (Reply 40):
But how many airports can currently handle the A380?

Out of this thread, just opened today: Article "Where The Airbus A380 Will Fly Next" (by KU747 Sep 23 2011 in Civil Aviation)

Quoting astuteman (Reply 3):
So as of last month, the A380 was cleared for service into 130 of the world's major airports.

So with 130 airports A380 ready, and more to come, the handling of an A380 will not be a big issue imho.
 
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RE: 777X Vs 787-11/12

Fri Sep 23, 2011 10:11 pm

Quoting EPA001 (Reply 41):
So with 130 airports A380 ready, and more to come, the handling of an A380 will not be a big issue imho.

You still haven't answered my question!

Quoting mffoda (Reply 38):
Quoting EPA001 (Reply 33):
Correct, that is why the wing span is 79.8 meter where Airbus actually wanted about 83-84 meters. But 80 m x 80 m is only for ICAO Category F airplanes.

If you think it's hard now to get airports to spend money on improvements to support the A380... Imagine if they went forward with a 83-84m wing?

This (above) was the first post regarding this question... (Imagine if they went forward with a 83-84m wing?) Is it your perception that it would have easier to get to 130 airports with an 83-84m wing?

What I was saying, is that the 80 X 80m box is pretty much the max as far as all but a few airports are concerned... Although, Groom Lake can handle some more VLA capacity.  
harder than woodpecker lips...
 
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RE: 777X Vs 787-11/12

Fri Sep 23, 2011 10:22 pm

Quoting mffoda (Reply 42):
You still haven't answered my question!

I have answered a specific question you asked. What more do you want?  

Your other question was in my opinion already answered by Stitch, and since I agree with his answer, I did not react to you anymore.

Quoting mffoda (Reply 42):
Is it your perception that it would have easier to get to 130 airports with an 83-84m wing?

Like Stitch said, if you have to make accommodations for 80 m x 80 m, the difference is not that big to make accommodations for 84 m x 84 m. Maybe at some airports it would be (a bit) more problematic (read: it would be more costly), but overall I do not think that many airports made big changes to be A380 ready. Mostly small changes were sufficient for airports to be A380 ready.

Of course there is a difference in being able to handle an A380, or a couple of A380's, or having a whole fleet of them like EK, SQ, etc, etc, which will mostly fly from and to your home airport..
 
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RE: 777X Vs 787-11/12

Sat Sep 24, 2011 12:42 am

Quoting morrisond (Reply 25):
You basically build your center 787 XL section 25' longer than the existing one with sufficient strength to get the length you need. No need to redesign the front and tail sections.
Quoting JoeCanuck (Reply 37):
As morrisond points out, the entire fuselage doesn't have to be strengthened, only the stretched section, since the current fuselage sections are already designed to support themselves.

You do need to redesign the front and rear sections. The front takes the nose gear load...bending moment goes up with the stretch (longer arm and more weight). The tail takes the empennage loads...if you're careful you can keep the tail volume the same and not change it but that's not guaranteed (typically you're going to lose on either the horizontal or the vertical, but maybe not both).

Quoting Stitch (Reply 28):
Many have offered the opinion that monolithic CFRP barrel construction would allow Boeing to stretch the 787 fuselage without anywhere near the weight penalty Airbus took to stretch the A340 fuselage to create the A340-500 and A340-600.

I've heard that many times, and I have no idea why it keeps getting said. CFRP is a wonderful manterial but it doesn't change fundamental statics...if you make it longer, you need more structure. More structure is always heavier.

Quoting YTZ (Reply 30):
What about doing CFRP panels instead of barrels? How does that compare to an Al fuse?

Better than Al (for same size), worse than barrels (for same size).

Tom.
 
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RE: 777X Vs 787-11/12

Sat Sep 24, 2011 1:36 pm

Quoting JoeCanuck (Reply 37):
As morrisond points out, the entire fuselage doesn't have to be strengthened, only the stretched section, since the current fuselage sections are already designed to support themselves. This should remain true regardless of what they are attached to and as long as the plane is stretched from the middle, leaving the current front and rear sections intact.

It's not that simple, as tdscanuck said. Even if the end structures remain the same, the center and intermediate sections have to be beefed up. Ultimately the fuselage must be analyzed as a unit, and there are definite limits as to how much flex can be tolerated. The ideal is that the structural elements taper from thickest in the center to thinnest at the ends, but with real world construction techniques (especially if you are stretching an existing design) this is not always feasible.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler

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