747400sp
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What if Boeing Was To Make A Super Twin?

Mon Jul 04, 2011 6:20 pm

I was wondering, what if Boeing built a bigger sister to the 777 like the 747 was to the 707?
 
CHRISBA777ER
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What if Boeing Was To Make A Super Twin?

Mon Jul 04, 2011 6:28 pm

You mean an A388/A389 size twin?

Engine capacity I'd guess - nobody out there has a 180-200klbs thrust engine and the GE90 family (or anything else for that matter) can scale up that high. We're talking a totally new turbofan family. Massively expensive to develop - the likes of GE and RR will not want to go there as they have too much on with their respective 787 and A350 family engines, not to mention the LeapX and GTF technologies etc.

Wont happen for a long time - if ever.
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wn700driver
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What if Boeing Was To Make A Super Twin?

Tue Jul 05, 2011 12:30 am

Quoting CHRISBA777ER (Reply 1):
thrust engine and the GE90 family (or anything else for that matter) can scale up that high.

No, I don't think any existing engine can scale up that high.

But I think it would be foolish to rule out the possibility. Both B & A have their hands full now with everything from 350s, 787s, NEOs, & 737/97s. Even Airbus has hinted that the NEO may only be a stop gap for something totally new in the early 2020s. We'll see...
However, if Embraer & Bombardier begin to erode B&A's duopoly (and hopefully they'll do some good amount of damage there this decade) in the lower 150-210 seat market, we're sure to see some re-prioritization. If A continues to stumble along, for example, with just enough 380 sales to keep the line semi-viable then B could decide that a 560-720 pax twin would be worth pursuing. I'll defer to the experts here, but I think we'd need something in the neighborhood of about 160 - 190k out of those powerplants. I'll go even further out on a limb and say that they'd have to be aft & center mounted, likely meaning a T-tail config. Anything with 190k power will have very serious asymmetrical thrust issues in an engine-out event.
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Starlionblue
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What if Boeing Was To Make A Super Twin?

Tue Jul 05, 2011 2:29 am

Quoting wn700driver (Reply 2):
I'll defer to the experts here, but I think we'd need something in the neighborhood of about 160 - 190k out of those powerplants. I'll go even further out on a limb and say that they'd have to be aft & center mounted, likely meaning a T-tail config. Anything with 190k power will have very serious asymmetrical thrust issues in an engine-out event.

Most likely such large engines will be wing mounted. The thrust asymmetry issue can be resolved with a long fuselage (more swingarm) and a larger tail. On the other hand, putting such engines on the tail creates enormous structural issues. You also have problems with control line redundancy in case of an uncontained failure and problematic fuel line design. Not to mention weight distribution and maintenance issues.
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wn700driver
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What if Boeing Was To Make A Super Twin?

Tue Jul 05, 2011 7:19 am

Quoting Starlionblue (Reply 3):
Not to mention weight distribution and maintenance issues.

I think the cg issues can be taken care of by moving the wings further aft, and are there any mx issues other than accesability?

Quoting Starlionblue (Reply 3):
You also have problems with control line redundancy in case of an uncontained failure and problematic fuel line design.

Yeah that could be problematic...

Quoting Starlionblue (Reply 3):
(more swingarm) and a larger tail.

Is a larger tail any lighter than addt'l structure weight aft? Also, with a clean wing design, you may only need a smaller wing area, somewhere again that weight could be saved. Also, part of my thinking on the issue that I forgot to mention in my last post was about FOD ingestion... I'm wondering at what point (thrust wise) that starts to become issue-matic and it actually would be desirable to mount the engines higher.

Anyway, that said, it could still be more desirable to go wing mounted. But I just think it will be thought about both ways...
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Starlionblue
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What if Boeing Was To Make A Super Twin?

Tue Jul 05, 2011 10:12 am

FOD ingestion shouldn't be a problem unless you mount the engines further out like on the 380. That wouldn't happen on a twin.

Quoting wn700driver (Reply 4):
... are there any mx issues other than accesability?

I don't think so but it's a doozy. Apart from the height off the ground, stuff gets mushed into a smaller space and the engines are not as easy to get on and off as wing mounted.

Quoting wn700driver (Reply 4):


Quoting Starlionblue (Reply 3):
(more swingarm) and a larger tail.

Is a larger tail any lighter than addt'l structure weight aft?

You'd have to ask an expert but I think it would be much lighter. Also the wing needs to be stronger (= heavier) without the engines hanging off it.

Quoting wn700driver (Reply 4):
I think the cg issues can be taken care of by moving the wings further aft

Yes.
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redflyer
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RE: What If Boeing Was To Make A Super Twin?

Wed Jul 06, 2011 10:44 pm

Quoting CHRISBA777ER (Reply 1):
Massively expensive to develop - the likes of GE and RR will not want to go there as they have too much on with their respective 787 and A350 family engines, not to mention the LeapX and GTF technologies etc.

I agree that it would be massively expensive to develop, but I think they wouldn't go there because the market for such a bird (VLA) would be somewhat limited, at least for the foreseeable future.
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DocLightning
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RE: What If Boeing Was To Make A Super Twin?

Wed Jul 06, 2011 11:41 pm

One of the issues is that an engine will need to be constructed so that it can be loaded into a cargo plane and flown to an AOG situation.

To make an engine with significantly more thrust than the GE-90-115B will probably require a larger fan, with a larger fan case, with a larger outer diameter, which can't be loaded into a 747F.

There are ways around this, but l doubt that airlines want to pay for an An-225 every time an entine needs to be ferried somewhere.
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n901wa
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RE: What If Boeing Was To Make A Super Twin?

Wed Jul 06, 2011 11:47 pm

I think if they were to go that route, I think it would end up in the Blended Wing Design. But who knows what Boeing got hid away  
 
redflyer
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RE: What If Boeing Was To Make A Super Twin?

Thu Jul 07, 2011 2:13 am

Quoting DocLightning (Reply 7):
One of the issues is that an engine will need to be constructed so that it can be loaded into a cargo plane and flown to an AOG situation.

To make an engine with significantly more thrust than the GE-90-115B will probably require a larger fan, with a larger fan case, with a larger outer diameter, which can't be loaded into a 747F.

If they could sling the engine under the wing to power the plane, they could probably also put a hard point under the same wing to carry a spare engine to the AOG situation. 747's have (or at least had in the case of the classics) the ability to do just that, and I believe other aircraft had or have that capability as well.

But just to play my own devil's advocate, I wonder if a spare engine of such an enormous size (assuming the theoretical engine we're talking about here would be proportionately larger as well compared to current technology) wouldn't create so much drag that slinging it under the wing for a ferry flight would render that option not viable.
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qfa787380
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RE: What If Boeing Was To Make A Super Twin?

Thu Jul 07, 2011 2:17 am

Boeing has been talking about developing a 777NG with a shrink and a stretch of the 77W(I would guess 3-4 rows each way). Add new engines a composite wing and possible composite fuselage and I think that's the direction they'll take with an EIS in the early 2020s. Boeing see the VLA market as a niche and I don't think they will concern themselves with a 748 replacement in the form of a twin.
 
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RE: What If Boeing Was To Make A Super Twin?

Thu Jul 07, 2011 3:10 am

Quoting DocLightning (Reply 7):
To make an engine with significantly more thrust than the GE-90-115B will probably require a larger fan, with a larger fan case, with a larger outer diameter, which can't be loaded into a 747F.

On the crazy-talk side of the idea spectrum, I wonder if there might be some way to drive two fans by one core?
 
C46
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RE: What If Boeing Was To Make A Super Twin?

Thu Jul 07, 2011 3:32 am

Quoting redflyer (Reply 6):
I agree that it would be massively expensive to develop, but I think they wouldn't go there because the market for such a bird (VLA) would be somewhat limited, at least for the foreseeable future.

Agreed and since the A380 has that market for the next 30+ years (basing that on what the 747 did) I agree with others that said it'd be just too expensive to develop an engine to drive a similar sized twin.

Quoting pzlpw5 (Reply 11):
On the crazy-talk side of the idea spectrum, I wonder if there might be some way to drive two fans by one core?

Are you thinking of one core driving two side-by-side fans by some geared mechanism? Or two fans in a row? The TF-39 had a 1 1/2 fan stage design so I'm sure it possible but not sure how efficent that design would be. And with a side-by-side design I'm sure it'd be a significant challenge to figure out how to develop enough energy in the core to drive the fans. Who knows what we'll see in 20 years though  
 
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akiss20
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RE: What If Boeing Was To Make A Super Twin?

Thu Jul 07, 2011 11:44 am

Quoting pzlpw5 (Reply 11):
Quoting DocLightning (Reply 7):
To make an engine with significantly more thrust than the GE-90-115B will probably require a larger fan, with a larger fan case, with a larger outer diameter, which can't be loaded into a 747F.

On the crazy-talk side of the idea spectrum, I wonder if there might be some way to drive two fans by one core?

Are you talking about a multi-stage fan? If so, sure, almost every military turbofan out there is a multistage fan, but that doesn't solve the problem. Multi-stage fans will give you a higher thrust to weight ratio and will increase thrust if you can get enough energy out of the core, but it isn't nearly as efficient as increasing fan diameter. To be at all feasible, you would have to almost double the air mass flow going through the bypass. In commercial turbofans, about 70-80% of the thrust is produced by the bypass (especially on these larger, high BPR engines like the GE90 or the PW4000). The problem with increasing fan diameter from the GE90 is that your tip speeds are starting to get ridiculous so you will get larger shocks on more of the blade which equals inefficiences. You also need to start stiffining the blades substantially for aeromechanical reasons. All of this would be a substantial hit to efficiency.

If you are talking about two fans, side by side, on one core then you are essentially creating a turbo prop as the core would have to run a shaft which could be split by a differential to run each fan. It would be ridiculously difficult and I am guessing a basic back-of-the-envelope analysis would decree it far too costly and heavy.
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RE: What If Boeing Was To Make A Super Twin?

Thu Jul 07, 2011 3:13 pm

Quoting wn700driver (Reply 4):
Quoting Starlionblue (Reply 3):
(more swingarm) and a larger tail.

Is a larger tail any lighter than addt'l structure weight aft?

Yes a large tail is heavy but the benefit of having an increased tail arm is that you can stuff it with PAX.

Think of all the planes that have increased thrust, and been turned into pencils with no larger tail surfaces.

Fred
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astuteman
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RE: What If Boeing Was To Make A Super Twin?

Thu Jul 07, 2011 6:35 pm

Quoting QFA787380 (Reply 10):
Boeing see the VLA market as a niche and I don't think they will concern themselves with a 748 replacement in the form of a twin.

But they'll build a 773ER stretch ....

Quoting wn700driver (Reply 2):
B could decide that a 560-720 pax twin would be worth pursuing. I'll defer to the experts here, but I think we'd need something in the neighborhood of about 160 - 190k out of those powerplants

mmm
14 replies and nobody's mentioned the Ecoliner concept....   

http://www.youtube.com/watch?v=CVWQ5h5UOfk

Rgds
 
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Stitch
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RE: What If Boeing Was To Make A Super Twin?

Thu Jul 07, 2011 9:34 pm

Quoting astuteman (Reply 15):
14 replies and nobody's mentioned the Ecoliner concept...

It was one of the first things that crossed my mind, but with CFRP not looking to be significantly lighter than Al, I expect the Ecoliner will require more than 250,000 pounds of thrust. And I am absolutely am convinced we shall not see a "thrusting APU".
 
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DocLightning
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RE: What If Boeing Was To Make A Super Twin?

Fri Jul 08, 2011 5:50 am

Quoting AKiss20 (Reply 13):

If you are talking about two fans, side by side, on one core then you are essentially creating a turbo prop as the core would have to run a shaft which could be split by a differential to run each fan. It would be ridiculously difficult and I am guessing a basic back-of-the-envelope analysis would decree it far too costly and heavy.

Worse than two engines?

Tough, yes, but worse than two engines? I wonder...
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akiss20
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RE: What If Boeing Was To Make A Super Twin?

Fri Jul 08, 2011 11:53 am

Quoting DocLightning (Reply 17):
Quoting AKiss20 (Reply 13):

If you are talking about two fans, side by side, on one core then you are essentially creating a turbo prop as the core would have to run a shaft which could be split by a differential to run each fan. It would be ridiculously difficult and I am guessing a basic back-of-the-envelope analysis would decree it far too costly and heavy.

Worse than two engines?

Tough, yes, but worse than two engines? I wonder...

It would involve a complete redesign of our fundamental idea of how a turbofan were to work. The GE90, still a standard turbofan, was a complete redesign of the core and booster and cost $2 billion to develop. Granted they now have a monopoly in 777 engines (although Rolls is trying to potentially break in with their new Trent) but still, 2 billion for a redesign that follows standard turbofan form. I am guessing the development costs of this kind of engine would be on the order of 8-9 billion and it might not even be possible. The amount of energy you would need from the core would be massive. Either you make the core much larger, which runs into all sorts of scaling problems with aeromechanics and what not or you run the engine much hotter, which we currently are nowhere near the ability to do due to material constraints.

It would be a massive undertaking for sure.
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SchorschNG
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RE: What If Boeing Was To Make A Super Twin?

Sat Jul 09, 2011 2:35 pm

Quoting astuteman (Reply 15):
mmm
14 replies and nobody's mentioned the Ecoliner concept....

http://www.youtube.com/watch?v=CVWQ5h5UOfk

Rgds

Because it probably is a dead end.
Double deck cross sections are a night mare. There is one cross section that works quite OK, we are calling it A380.
Making it smaller only makes the upper deck less attractive or will increase structural weight.
Many more issues come to my mind:
- evacuation
- cargo capacity
- freighter conversion

The most suitable B777 replacement would be a 6.8m wide round fuselage (full 10-abreast economy, 11 abreast "small" economy). If you use the entire 80m box, you easily get 450 people inside, especially with some creative monument placing.
The aircraft has massive cargo capacity.

Engines: the landing gear has to be long anyway, and if engines are hard to fit you need to be a bit more creative in wing design. Increase dihedral or put the engines farer to the outside.

The aircraft would kill the A380-800 in CASM.
Problem: it would kill the B747-8 and B777-300ER first.
From a structural standpoint, passengers are the worst possible payload. [Michael Chun-Yung Niu]
 
wn700driver
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RE: What If Boeing Was To Make A Super Twin?

Sun Jul 10, 2011 12:02 am

Quoting SchorschNG (Reply 19):
Many more issues come to my mind:
- evacuation
- cargo capacity

Highly debatable. If they 380 can squeak by one these issues, then yes, it is a no brainer on a twin.

Quoting SchorschNG (Reply 19):
If you use the entire 80m box, you easily get 450 people inside, especially with some creative monument placing.

The 777-300 can already do this as it is. Actually, it can get to 550 if need be, though I do not know how they would do this. 472 is the most I've heard of. As that is, it is already a better CASM than the 380. I wouldn't want to fly it that way though.

Quoting SchorschNG (Reply 19):
Increase dihedral or put the engines farer to the outside.

Hmmm... Perhaps. But how far is too far I wonder... I'll bet that a wing with a lot of built in dihedral could support an engine perhaps out to 60% the distance from root to tip, but how aerodynamically wise is that? I'd still not rule out a tail mounted configuration...

Quoting SchorschNG (Reply 19):
The aircraft has massive cargo capacity.

Maybe below decks, but like the 380, it would be undesirable at best to go for cargo ops. There are too many issues with structural design and wasted space for it to be profitable. But then again, with only two engines to feed, it may be more an acceptable option to have a three deck parcelor. I don't know...
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astuteman
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RE: What If Boeing Was To Make A Super Twin?

Sun Jul 10, 2011 4:49 am

Quoting SchorschNG (Reply 19):
Double deck cross sections are a night mare. There is one cross section that works quite OK, we are calling it A380.

The worst thing for me in the Ecoliner concept is that they ignore one of the biggest nightmares of a twin-deck approach - where do you cram that intensity of systems. There's a reason the A380 has the cross-section it has, and it STILL has integration problems

Quoting wn700driver (Reply 20):
Actually, it can get to 550 if need be, though I do not know how they would do this. 472 is the most I've heard of. As that is, it is already a better CASM than the 380

But in what configuration?
I'd like you to point me to anything flying that will get remotely close to the CASM of Air Austral's 840 seat A380's (which incidentally still offers more space per passenger than a 550 seat 773)

Rgds
 
SchorschNG
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RE: What If Boeing Was To Make A Super Twin?

Sun Jul 10, 2011 10:42 am

A 6.8m cross section offers a A380-like economy. The B777 is too small to house a competitive 10-abreast economy, many airlines don't care and offer it anyway. The A380 is - when you look at it - plagued with many compromises. Double deck is the last resort.
From a structural standpoint, passengers are the worst possible payload. [Michael Chun-Yung Niu]
 
qfa787380
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RE: What If Boeing Was To Make A Super Twin?

Mon Jul 11, 2011 12:54 am

Quoting astuteman (Reply 15):
But they'll build a 773ER stretch ....

Which, of course, I did mention as a 3-4 row stretch of the 77W.
 
keesje
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RE: What If Boeing Was To Make A Super Twin?

Tue Jul 12, 2011 10:21 pm

I think adding a 40 klbs engine in the tail is easier to realize then creating a from 0 a 160 klbs engine & putting it under a wing.

A trijet (2.5 jet) would need less control surface (less asymmetric in case of a V1 shutdown), have substantial lighter wingstructure, no ETOPS restriction and could use existing engines (e.g. GE90-11X, GTF).

Quoting SchorschNG (Reply 19):
Making it smaller only makes the upper deck less attractive or will increase structural weight.

Don't think so it would have 3 aisles for 16 abreast (10 abreast potential on maindeck like 777). It would be aimed at the segment inbetween the 773 and A380, the 400-500 3 class seat segment, a kind of 1:1 747 replacement.

"Never mistake motion for action." Ernest Hemingway
 
thegeek
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RE: What If Boeing Was To Make A Super Twin?

Wed Jul 13, 2011 2:53 am

Quoting keesje (Reply 24):
I think adding a 40 klbs engine in the tail is easier to realize

Possibly it is, but a 40klbs engine is bigger than a CFM56. Would this Thrusting APU then require an additional APU? Also no engines are made in that thrust class. Perhaps a CFM56 size would be more achievable. But the major problem with adding thrust to the 777 (and then stretching it) is the landing gear which has no room for growth. The major benefit to this plan would be that the middle engine could in theory be shut down for cruise and work the other engines harder for more efficiency.

Seems unlikely, and won't happen for the 777.

Quoting keesje (Reply 24):
no ETOPS restriction

Does that still apply? I thought they changed the rules to make trijets and quads the same as twins, with some jurisdictions grandfathering in the old rules for existing quads/trijets.
 
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Stitch
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RE: What If Boeing Was To Make A Super Twin?

Wed Jul 13, 2011 5:04 am

Quoting thegeek (Reply 25):
Does that still apply? I thought they changed the rules to make trijets and quads the same as twins, with some jurisdictions grandfathering in the old rules for existing quads/trijets.

LROPS have put into place for trijets and quads many of the requirements ETOPS had for things like on-board medical support and cargo hold fire suppression.

ETOPS-330 should also pretty much put the entire planet within diversion range.
 
SchorschNG
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RE: What If Boeing Was To Make A Super Twin?

Wed Jul 13, 2011 6:47 am

Quoting keesje (Reply 24):
I think adding a 40 klbs engine in the tail is easier to realize then creating a from 0 a 160 klbs engine & putting it under a wing.

A trijet (2.5 jet) would need less control surface (less asymmetric in case of a V1 shutdown), have substantial lighter wingstructure, no ETOPS restriction and could use existing engines (e.g. GE90-11X, GTF).

Don't think so it would have 3 aisles for 16 abreast (10 abreast potential on maindeck like 777). It would be aimed at the segment inbetween the 773 and A380, the 400-500 3 class seat segment, a kind of 1:1 747 replacement.

A Trijet is definite no-go, especially with two different types of engine. Remember: this aircraft needs to compete with the two most efficient aircraft in terms of CASM (B773ER and A388), a funny mix of engines will probably be efficient in terms of fuel burn, but not in total cost of operation.
The cabin looks nice as cross section, but the overall fuselage would look ugly. Despite the structural implications, you would lose lots of cargo volume, need additional ground service equipment and probably require lots of additional infrastructure.
Now, people may argue, that same applies for A380. Yes, true, but the A380 is a game changer, the "Ecoliner" is not.

And the competing 450-seater is 80-85m long, uses a 6.8-7m cross section, has tremendous cargo volume and can be plugged into existing infrastructure without problems. Only issue is length, but most airports have no issue with that. Span is critical.
From a structural standpoint, passengers are the worst possible payload. [Michael Chun-Yung Niu]
 
keesje
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RE: What If Boeing Was To Make A Super Twin?

Wed Jul 13, 2011 9:04 am

Quoting SchorschNG (Reply 27):
A Trijet is definite no-go

I think there are no definite no-go's in aerospace. A case is made for each requirement. Solutions that used to be "no-go" once, can become feasible because of changing circumstances, technology, conditions, requirements, priorities. E.g. likely big noisy props will be back on big aircraft in the next decade, after 50 yrs.

Quoting SchorschNG (Reply 27):
Remember: this aircraft needs to compete with the two most efficient aircraft in terms of CASM (B773ER and A388), a funny mix of engines will probably be efficient in terms of fuel burn, but not in total cost of operation.

If they are existing engines, it's a low risk, probably more efficient solution. Boeing seriously considered it as recent as 1998 but convinced GE to boost the GE90 by ~15%. http://i191.photobucket.com/albums/z...keesje_pics/ATPU777concpet1998.jpg

Another 30% for the GE90 by 2020, for a previous generation engine, seems unfeasible. An entirely new engine would be a very difficult business case. The numbers would never be in the thousands..

Quoting SchorschNG (Reply 27):
The cabin looks nice as cross section, but the overall fuselage would look ugly.

Irrelevant IMO. http://1.bp.blogspot.com/_-Oqf_vOman...MiWns/s1600/AirFrance_Ecoliner.JPG

Quoting SchorschNG (Reply 27):
Despite the structural implications, you would lose lots of cargo volume, need additional ground service equipment and probably require lots of additional infrastructure.

You would have limited cargo space, similar to the A380. Moving cargo on passenger aircraft is in decline. It's costly, hopping between crowdy, expensive passenger hubs airports iso of cargo hubs. Hard to compete with an old, stuffed, less schedule tight Atlas 747Fs stopping at all the right places at the right (cheaper) times (e.g. Shenzhen, Anchorage, DXB or MEM).

Quoting SchorschNG (Reply 27):
And the competing 450-seater is 80-85m long, uses a 6.8-7m cross section, has tremendous cargo volume and can be plugged into existing infrastructure without problems

It would miss the ICAO box. It would have lots of cargo volume, and a giant empty attic. If this space could be used in an efficient way is the big question, cargo containers are predefined (LD3) and airlines want revenue generation volume, no upper deck bars, lounges, offices etc. Ask Boeing (fancy 747-8i ideas).

http://i191.photobucket.com/albums/z160/keesje_pics/12abreastcabin.jpg
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SchorschNG
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RE: What If Boeing Was To Make A Super Twin?

Wed Jul 13, 2011 7:47 pm

Dead volume isn't as bad as it seems. If the structure surrounding it is more efficient who cares.
The twin deck might look as very innovative solution, but innovation doesn't make money by itself.
A classic single deck aircraft still is easiest when it comes to turn-around and system arrangement.
A very long cylindrical section also reduces manufacturing costs.
Such an aircraft is easy to stretch and shrink.

When aiming at a 3-4-3 premium economy and 3-5-3 cattle class, you can possibly install a 2-2-2-2 business class (means triple aisle) and a 1-2-2-1 first class. Monuments can be shifted in the lower deck, especially lavatories. The upper dead volume (which is massive) can be occupied by crew rest and maybe even some kind of galley (problematic due to weight).
Such an aircraft comes out better weight-wise and still offers sufficient floor area.

Sure, you can go twin-deck, but I doubt such design wouldn't survive the direct comparison to the single deck solution.

The B777-300 is a "350-seater". Going 11-abreast in economy with an 17.5inch seat would require a 6.45m wide cabin, so the approximately 6.8m wide fuselage I talked about. A 2-2-2-2 business class with 22inch seat would require a 6.6m cabin width, going 21.25inch seat width would reduce that to 6.45m.
From a structural standpoint, passengers are the worst possible payload. [Michael Chun-Yung Niu]
 
keesje
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RE: What If Boeing Was To Make A Super Twin?

Wed Jul 13, 2011 8:51 pm

SchorschNG, a widebody circulair fuselage would have similar cargo capasity as a A330 or 787, 2 LD3s side by side. The Ecoliner concept is 9 abreast maindeck (6.4 m) and would probably have a similar total cross section as a 6.8 circular cross section.. but 5 more seats and more flexibilty (e.g. premium upperdeck like A380).



Little dead cross section that has to be pushed through the atmosphere for 100.000 hours.. That's why Airbus went twin deck.. given all restrictions, it was the least inefficient cross section for moving 600 people in the 80x80 ICAO box.

http://www.youtube.com/watch?v=2yh6kL7rxVc

Boeing considered a big maindeck and shelved the idea..
http://i191.photobucket.com/albums/z...eesje_pics/Boeing763_246Ctotal.jpg

[Edited 2011-07-13 13:56:39]
"Never mistake motion for action." Ernest Hemingway
 
thegeek
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RE: What If Boeing Was To Make A Super Twin?

Thu Jul 14, 2011 1:41 am

Quoting keesje (Reply 28):
Moving cargo on passenger aircraft is in decline

My understanding was the exact opposite. Do you have a link? Perhaps it is market specific.

Quoting keesje (Reply 30):
That's why Airbus went twin deck.. given all restrictions, it was the least inefficient cross section for moving 600 people in the 80x80 ICAO box.

Note though that a number of quite reputable people are calling for Airbus to breach the 80x80 box for the A389. Is this really such an issue? An A380 size single deck 10 abreast airliner would be incredibly long and therefore require strengthening. I'd say this is the main reason for the double deck.
 
rheinwaldner
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RE: What If Boeing Was To Make A Super Twin?

Thu Jul 14, 2011 7:20 am

Quoting SchorschNG (Reply 29):
The twin deck might look as very innovative solution, but innovation doesn't make money by itself.

The "number of seats/diameter"-ratio or "seats/area of cross section"-ratio is extremely valuable to make money. And double deckers are unbeatbale regarding these metrics.

Quoting SchorschNG (Reply 29):
A classic single deck aircraft still is easiest when it comes to turn-around and system arrangement.

Why? To me it seems that easy and even more efficient boarding solutions can be achieved.

System arrangement usually not drives the rest. It can be adopted to any given layout.

Quoting SchorschNG (Reply 29):
A very long cylindrical section also reduces manufacturing costs.

Why? Very long cylindrical sections tend to bend (and thus require heavier structure).

Quoting SchorschNG (Reply 29):
Such an aircraft is easy to stretch and shrink.

Why? Any steady cross section should be extendable equally easy. A double decker has the best "added seats/per stretched meter"-ratio. This makes it easy too (less enforcements due to the smaller length increases).
 
SchorschNG
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RE: What If Boeing Was To Make A Super Twin?

Thu Jul 14, 2011 8:14 am

Quoting keesje (Reply 30):
Little dead cross section that has to be pushed through the atmosphere for 100.000 hours.. That's why Airbus went twin deck.. given all restrictions, it was the least inefficient cross section for moving 600 people in the 80x80 ICAO box.

http://www.youtube.com/watch?v=2yh6k...7rxVc

If you look at your posted link, the 450P aircraft is single deck.
Twin deck becomes a useful solution above 500-530 pax three class.
But the more attractive market is 350-450 Pax, expect a volume of several hundred units in the next 20 years.
Currently this market is served by the B747-8 only, a not very attractive aircraft.

By the way: the Boeing "idea" is a patent for overhead sleeping bunks, I know this patent for some time. Nothing is said about the usefulness of a particular cross section for a particular capacity. These patents are generally not very helpful in estimating the level of research of a manufacturer.

Dead volume costs nothing in the first place, surface (>drag) and structure (>weight) cost. Weight-wise a round fuselage beats an oval fuselage. Surface-wise the little savings do not really change the big picture.

Quote:
The "number of seats/diameter"-ratio or "seats/area of cross section"-ratio is extremely valuable to make money. And double deckers are unbeatbale regarding these metrics.

The seats per cross sectional area are a very rough and by no standards ideal measure for efficiency, a very crude preliminary design method. In the end weight per installed seat counts, and the A380 for example doesn't really set a new mark here, neither does the B747-8. The B777-300 is more efficient than either of them.

Quoting rheinwaldner (Reply 32):
Why? Very long cylindrical sections tend to bend (and thus require heavier structure).

Get busy on aircraft design before making those statements!
Of course the structural stresses increase, but depending on the ratio between diameter and length they do not pose a big problem. Usually pressurization sizes the structure, you might have some buckling sized panels on the upper side, but that doesn't ruin the day. A non-cylindrical fuselage comes out extremely bad in pressurization, and that from the first to the last frame!
A 84m fuselage with 6.8m diameter has a fitness ratio of 12.4, so only slightly more than the B777-300.

Quoting rheinwaldner (Reply 32):
Why? To me it seems that easy and even more efficient boarding solutions can be achieved.

I doubt you successfully integrate all the doors. See also my comments at the bottom.

Quoting rheinwaldner (Reply 32):
Why? Any steady cross section should be extendable equally easy. A double decker has the best "added seats/per stretched meter"-ratio. This makes it easy too (less enforcements due to the smaller length increases).

And why does this "ratio" have any relevance? Structurally, when we talk about 6.8-7m diameter, structural strength is not a big issue. Pressurization is the biggest issue. Double deck means huge problems with door locations (see A380), a high proportion of "non regular" fuselage parts (especially a relatively long center section).

The "Ecoliner" would have a prohibitively long wing root chord. You cannot service the upper deck at all, evacuation looks extremely doubtful.
That is because the "Ecoliner" isn't an engineered aircraft design, it is a number of nice looking pictures. I haven't seen anything like a reasonable 3-view showing me locations of wing box, cargo doors, passenger doors, a cabin floor plan. Many aspects are just speculation, the rendered pictures imply a higher level of engineering than is actually located behind it. Because there is pretty much zero.

If someone wants to be innovative, try to clear the main deck of all unnecessary things except seating. Galleys, crew rest, lavatories, put the most into the lower deck ... or the dead volume above the cabin.
From a structural standpoint, passengers are the worst possible payload. [Michael Chun-Yung Niu]
 
keesje
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RE: What If Boeing Was To Make A Super Twin?

Thu Jul 14, 2011 7:43 pm

To avoid risks I took the 777 lower part of the fuselage / wing/ wingbox and blew up to upper half that is pretty much there already on the 777, but empty. Length was 68m, to keep everything light but still accommodate 500 people.

http://i191.photobucket.com/albums/z...0/keesje_pics/Ecoliner1concept.jpg

Quoting SchorschNG (Reply 33):
If someone wants to be innovative, try to clear the main deck of all unnecessary things except seating. Galleys, crew rest, lavatories, put the most into the lower deck ... or the dead volume above the cabin.

Innovative? It's been done for decades on DC10, 747, A340, Stratocruiser etc. .

Quoting SchorschNG (Reply 33):
Dead volume costs nothing in the first place, surface (>drag) and structure (>weight) cost.


?! less volume reduces frontal surface, that helps a lot reducing drag and fuel consumption.

"Never mistake motion for action." Ernest Hemingway
 
tdscanuck
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RE: What If Boeing Was To Make A Super Twin?

Thu Jul 14, 2011 9:23 pm

Quoting keesje (Reply 34):
Quoting SchorschNG (Reply 33):
Dead volume costs nothing in the first place, surface (>drag) and structure (>weight) cost.

?! less volume reduces frontal surface, that helps a lot reducing drag and fuel consumption.

Total drag is a relatively weak function of frontal area vis a vis decks. It has no effect on parasitic drag (that's a surface area function) and, although you do multiply Cd by frontal area to get form drag, aerodynamic shaping has a much larger effect on Cd. A good aerodynamic form can have way lower drag even with a higher frontal area. A teardrop shape can be 50% larger than a ball and have lower drag. And fuselage frontal area has no impact on induced drag.

Tom.
 
keesje
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RE: What If Boeing Was To Make A Super Twin?

Thu Jul 14, 2011 10:25 pm

If you compare a circular cross section of 6.8m to a similar one of 6.4m, the resulting frontal area is

(46.24 - 40.96)/40.96 *100% = 12-13% higher.

Given the same state of technology for the rest of the airframes,that is significant. E.g. winglets do 3-5%.

IMO it's one of the reasons the similar capacity A330-300 drove the 777-200ER out of the market when it got more range/improved engines. And why the 787-9 & 10 replacing the 777 will be narrower, making better use of the available cross section.

Reasonable efficient cross sections are created by preventing pressure cabin induced bending in the fuselage by redirecting forces through decks.. e.g. 747, E190, A380, Q400, and .. 707/737/757

Other examples..


Circular cross sections are theoretical ideal, but better utilization requirements mostly leads to compromises.
"Never mistake motion for action." Ernest Hemingway
 
SchorschNG
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RE: What If Boeing Was To Make A Super Twin?

Fri Jul 15, 2011 6:20 am

Quoting keesje (Reply 34):
To avoid risks I took the 777 lower part of the fuselage / wing/ wingbox and blew up to upper half that is pretty much there already on the 777, but empty. Length was 68m, to keep everything light but still accommodate 500 people.

You will need more wing area, as your aircraft will be heavier. Means longer root chord, means trickier fuselage design.

Quoting keesje (Reply 34):
?! less volume reduces frontal surface, that helps a lot reducing drag and fuel consumption.

Actually, in aircraft design the wetted surface is the figure of merit. Now, easy geometry if we assume the aircraft to be a cylinder:
frontal area: r_fus^2 * pi
fuselage wetted area: 2*pi * r_fus * l_fus
fuselage cabin area: 2 * r_fus * l_cab (at armrest level)
fuselage volume: r_fus^2 * l_fus * pi

The drag increases linearly with the diameter, not as quadratic function. Apart from these preliminary design methods, the actual shaping of the fuselage is important. Theoretically, a very long and slander aft section is of advantage. Area ruling in the center section has large effect on transonic performance (see A380).

Another advantage of a long cylinder is the indirect effect in tail size and wight: tail surfaces become smaller due to longer lever arm. Weight-wise a small gain, but wetted surface counts.

Quoting keesje (Reply 36):
IMO it's one of the reasons the similar capacity A330-300 drove the 777-200ER out of the market when it got more range/improved engines. And why the 787-9 & 10 replacing the 777 will be narrower, making better use of the available cross section.

Sure enough not because of frontal area. The A330-300 is right-sized for a particular mission, which is the 3000-5000nm mission. The B777-200(ER) just is a bit oversized for that. On the other hand, it can do 6000nm with basically full load. Additionally, the A330 cross section offers a better opportunity for a good cabin. The B777 for example is too large for a 2-2-2 business class, and a 2-3-2 business class isn't a really competitive product. So as airline, you cannot truly harvest the additional fuselage diameter of the B777, only when it comees to economy seating. That's why Airbus came around with the A350 cross section: 2-2-2 in business, 3-3-3 in economy.
The B777 is a well conceived design, but with a different heritage. We shouldn't forget it was invented in the mid 80ies and standards were different those days. The fact that the A330 cross section fits perfectly to common market needs is merely luck.

From aerodynamics point of view I would assume both are well designed, the B777 has a slightly better M*L/D. However, the A330/340 wing is very efficient also for today's standards.

Quoting keesje (Reply 36):
Reasonable efficient cross sections are created by preventing pressure cabin induced bending in the fuselage by redirecting forces through decks.. e.g. 747, E190, A380, Q400, and .. 707/737/757

Your posted picture is so to find in "Torenbeek - Synthesis of Subsonic Aircraft Design". These cross sections shown are studies by Douglas from the early 60ies, non was build except the upper left one (which is the B707). I further wouldn't throw aircraft like A380 and E190 into one basket: the former weight 10-fold of the latter. Sizing loads change with increasing size: while smaller aircraft's fuselages are more prone to be sized by maneuver loads, larger aircraft are sized by fatigue loads. Therefore, larger aircraft have more benefit from strictly circular cross sections. By the way, one of the big killers of the Blended Wing Body.

When going big a circular cross section usually is the minimum weight alternative. For some capacities like the 500-650 of the A380 family there is no way how you can achieve that with a circular cross section. For a 400-500 passenger aircraft you can, while the upper end would stretch the limits. However, it works.
From a structural standpoint, passengers are the worst possible payload. [Michael Chun-Yung Niu]
 
tdscanuck
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RE: What If Boeing Was To Make A Super Twin?

Fri Jul 15, 2011 10:37 am

Quoting keesje (Reply 36):
If you compare a circular cross section of 6.8m to a similar one of 6.4m, the resulting frontal area is

(46.24 - 40.96)/40.96 *100% = 12-13% higher.

Given the same state of technology for the rest of the airframes,that is significant.

It's only significant if you're ignoring all the other implications. A circular cross section of 6.25% more diameter (6.8m vs 6.4m) does have ~12% more frontal area. But that means 12% more stuff you can put in there, so the frontal drag increment which might be 3% of the overall aircraft drag gives you 12% more space to put payload. On top of that, it's 27% stiffer, which means it can be lighter, which means less induced drag on the wing, and induced drag is a far larger contributor to drag than frontal area.

Tom.
 
keesje
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RE: What If Boeing Was To Make A Super Twin?

Fri Jul 15, 2011 9:03 pm

Quoting tdscanuck (Reply 38):
But that means 12% more stuff you can put in there, so the frontal drag increment which might be 3% of the overall aircraft drag gives you 12% more space to put payload.

If that only was true.. but it isn't. You can't add half a LD3 or introduced dozens of overhead crew rests in a profitable way. Boeing proved that with the 777 and 747-8i.

If you increase the diameter of a circulair fuselage beyond e.g a 777, you are creating a double deck anyway, flying it around without extra payload at all, below as well as above the passenger cabin.

http://i191.photobucket.com/albums/z160/keesje_pics/extrawide10abreastsingledeckWB84mlongcrosssection.jpg

Stretching such an aircraft to e.g. 84m, 10 m longer then a 777-300ER, creates a 747 replacement. Still less seats then the existing twin deck 747-8i and a requirement for a brand new 170(?)klbs engine if it has to be twin engined aircraft. Tail strike considerations would require a compromised wing or very long landing gears.

http://i191.photobucket.com/albums/z160/keesje_pics/extrawide10abreastsingledeckWB84mlong.jpg
"Never mistake motion for action." Ernest Hemingway
 
SchorschNG
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RE: What If Boeing Was To Make A Super Twin?

Sat Jul 16, 2011 9:01 am

The 6.8m single deck aircraft will gain capacity by several small things:
- Your layout shown above gives us a B777 with 10-abreast seating. A 6.8m fuselage would house an 11-abreast at similar standards. Your 388 economy seats would become ~430.
- The galley consumes quite some area. I know lower deck galleys do not win hearts and minds of airlines easily, but a twin deck is more complicated. Therefore, getting some galleys and lavatories downstairs will free up additional area. I would assume some 3-5% more seating.
- Your business class seating shows angled flat beds, a very good decisions for a fuselage diameter like that of the B777, where regular seats in 2-2-2 would waste area. Now, these angled seats can be angled even more or arranged differently and you could install more seats at similar standard. So the 30 business class eats become 35 or more.
- The LD-3 container is handy and established, but many items travel on pallets. Providing a larger cargo hold probably doesn't work with LD-3, but it works with other containers.

Correct: the upper lobe volume is pretty much wasted. But as Tom and me stated, that doesn't mean a disadvantage in itself. When this solution comes out with lower/equal efficiency (that is drag & weight plus snowball effects), it is the option of choice. The twin deck solution has to be substantially better to be preferred, that was the case for the A380.

For 450 seats (3-class) this is a narrow choice, but I bet the single deck aircraft still comes out ahead.

What the B747 gains through its upper deck, it wastes elsewhere.
The B747 solution was chosen for easy cargo loading, and actually it was chosen over a twin deck in 1966.
From a structural standpoint, passengers are the worst possible payload. [Michael Chun-Yung Niu]
 
keesje
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RE: What If Boeing Was To Make A Super Twin?

Sat Jul 16, 2011 9:12 pm

Quoting SchorschNG (Reply 19):
The most suitable B777 replacement would be a 6.8m wide round fuselage (full 10-abreast economy, 11 abreast "small" economy).
Quoting keesje (Reply 28):
You would have limited cargo space, similar to the A380. Moving cargo on passenger aircraft is in decline. It's costly, hopping between crowdy, expensive passenger hubs airports iso of cargo hubs.
Quoting keesje (Reply 28):
It would miss the ICAO box. It would have lots of cargo volume, and a giant empty attic. If this space could be used in an efficient way is the big question, cargo containers are predefined (LD3) and airlines want revenue generation volume, no upper deck bars, lounges, offices etc.
Quoting SchorschNG (Reply 29):
A very long cylindrical section also reduces manufacturing costs.
Quoting tdscanuck (Reply 38):
It's only significant if you're ignoring all the other implications. A circular cross section of 6.25% more diameter (6.8m vs 6.4m) does have ~12% more frontal area. But that means 12% more stuff you can put in there, so the frontal drag increment which might be 3% of the overall aircraft drag gives you 12% more space to put payload. On top of that, it's 27% stiffer, which means it can be lighter, which means less induced drag on the wing, and induced drag is a far larger contributor to drag than frontal area.
Quoting SchorschNG (Reply 40):
- The LD-3 container is handy and established, but many items travel on pallets. Providing a larger cargo hold probably doesn't work with LD-3, but it works with other containers.
Quoting keesje (Reply 28):
It would miss the ICAO box.
Quoting SchorschNG (Reply 37):
When going big a circular cross section usually is the minimum weight alternative. For some capacities like the 500-650 of the A380 family there is no way how you can achieve that with a circular cross section.
Quoting keesje (Reply 39):
You can't add half a LD3 or introduced dozens of overhead crew rests in a profitable way.

  

http://i191.photobucket.com/albums/z160/keesje_pics/extrawide10abreasttwindeckWB80mlongcrosssection.jpg

[Edited 2011-07-16 15:13:42]
"Never mistake motion for action." Ernest Hemingway
 
tdscanuck
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RE: What If Boeing Was To Make A Super Twin?

Sun Jul 17, 2011 6:24 am

Quoting keesje (Reply 41):
  

I see a lot of quotes and a very artistically rendered doodle. Care to enlighten us on the connection?

Tom.
 
SchorschNG
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RE: What If Boeing Was To Make A Super Twin?

Sun Jul 17, 2011 2:54 pm

The aircraft doesn't start when capacity definition is finished, but it rather is a trade.
Some passenger capacities are not served as the resulting aircraft would look funny or have disadvantages.
There are blind spots, noticeably:
- the 220-260 seat region in short range, where single aisles are too small and twin aisles too large (at least would each design have a substantial disadvantage, very handy to compare B757 and 767 in that respect)
- the 450-550 seat region in long range, where a twin deck doesn't work and a single deck neither.
From a structural standpoint, passengers are the worst possible payload. [Michael Chun-Yung Niu]
 
rheinwaldner
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RE: What If Boeing Was To Make A Super Twin?

Tue Jul 19, 2011 12:53 pm

Quoting tdscanuck (Reply 35):
Total drag is a relatively weak function of frontal area vis a vis decks. It has no effect on parasitic drag (that's a surface area function) and, although you do multiply Cd by frontal area to get form drag, aerodynamic shaping has a much larger effect on Cd. A good aerodynamic form can have way lower drag even with a higher frontal area. A teardrop shape can be 50% larger than a ball and have lower drag. And fuselage frontal area has no impact on induced drag.

I assume that all of these things are not discriminators. An equally good form can be applied to any fuselage. All fuselages are more teardrops than balls.

Thus seats per sqm of a cross-section remains the most discriminating factor.

Kessje is right. The 777 will have the largest 9 abreast cross section. And it will be the worst. Partly because of that. Even Boeing sees the 789 as 772ER replacement. Also because the large 777 cross section cause an inherent penalty vs the more sleek 787.
 
tdscanuck
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RE: What If Boeing Was To Make A Super Twin?

Tue Jul 19, 2011 11:59 pm

Quoting rheinwaldner (Reply 44):
I assume that all of these things are not discriminators. An equally good form can be applied to any fuselage. All fuselages are more teardrops than balls.

This is true. But this is not:

Quoting rheinwaldner (Reply 44):
Thus seats per sqm of a cross-section remains the most discriminating factor.

What's being missed is how frontal drag plays into the overall aircraft drag and weight. In terms of pure fuselage form drag, seats per cross-section is a reasonable metric. But that's a terrible metric for the overall aircraft because:
-Fuselage form drag is a relatively small portion of overall drag (and the bigger portion, skin drag, improves with round cross sections)
-Cross section has a major effect on fuselage stiffness, and hence structural weight
-Cross section has a major impact on systems routing, which is a very complicated trade space
-Fuselage structural weight goes directly to wing induced drag, which is a bigger contributor to overall drag than fuselage form drag
-Fuselage cross-section has a very complicated interaction with the wing-body join, driving a lot of the shape (weight, form drag, parasitic drag) of the wing-body fairing.

To reduce the problem to "less frontal area = good" is massively oversimplifying a very complicated problem. The two most critical things in airliner design are the cross section and the payload range curve. The fact that all OEM's reach different solutions is obvious proof that there are no simple rules to it.

Tom.
 
rheinwaldner
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RE: What If Boeing Was To Make A Super Twin?

Wed Jul 20, 2011 7:39 am

Quoting tdscanuck (Reply 45):

Again you correctly list 5 areas where the cross section has an impact.

And again none of them inherently benefits more from a single deck fuselage than than from a double decker. Overall most (or even all) of these critical points can be solved equally good regardless of the numbers of floors.

Quoting tdscanuck (Reply 45):
-Fuselage form drag is a relatively small portion of overall drag (and the bigger portion, skin drag, improves with round cross sections)

Hoe does a round cross section improve skin drag?

I would say that stuffing X people into a tube yields the lowest skin drag if the wettet area is the smallest. And the wetted area will be smallest when that tube is the shortest. And the tube will be the shortest if the number-of-seats per cross section will be the largest. As I said.

This metric is paramount - especially for skin drag.

I have only a source in German but this document: ...
http://www.mp.haw-hamburg.de/pers/Sc...lz/arbeiten/TextClausen-Hansen.pdf

... tells this on page 48:

Quote:
(translated by me)despite that a circle is the lightest option, a minimized circumference has such a large positive impact on the drag that overall a more efficient aircraft has been created.

...on page 52 you can see that a non-circular, optimized 7 abreast cross section can lower skin drag by almost 4% (and why on earth is the 767 fuselage higher than wide?!).

You surely won't tell me that any of the points you listed would be handicapped by 4% if the cross section would not be circular and single-deck?

B.t.w. the link shows a nice draft for a larger, twin-aisle short range jet. The document has been created at the Airbus' Future Project Office.

Another comparison:

777:
width=6.19/circ=19.45/seat_abreast=9/rel_wetted_area_per_seat=2.161/wetted_area_per_seat=100%/skin_drag_per_seat=100%

A380:
width=7.14/height=8.47/circ=24.56/seat_abreast=18/rel_wetted_area_per_seat=1.42/wetted_area_per_seat=66%/skin_drag_per_seat=66%

Summary: the 777 cross section has terrible skin drag characteristics (per seat) compared with an A380.

Questions?
 
tdscanuck
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RE: What If Boeing Was To Make A Super Twin?

Wed Jul 20, 2011 8:20 am

Quoting rheinwaldner (Reply 46):
And again none of them inherently benefits more from a single deck fuselage than than from a double decker.

I don't think that's true...although in theory cross-sections can vary arbitrarily, the required cabin height forces them to "step" at certain points. Fineness ratio pins down the length vs. width of the fuselage into a fairly narrow range, so for a given floor area you get discontinuous jumps in possible cross sections with acceptable characteristics. For certain floor areas you'll get an inherently bad single-deck solution and an inherently good double-deck solution. For other floor areas the trade will flip.

Quoting rheinwaldner (Reply 46):

Hoe does a round cross section improve skin drag?

For a given volume, it has lowest circumference.

Quoting rheinwaldner (Reply 46):
I would say that stuffing X people into a tube yields the lowest skin drag if the wettet area is the smallest. And the wetted area will be smallest when that tube is the shortest.

That's true, but now you're trading skin drag against form drag. Your form drag goes through the roof if the fineness ratio gets too low (i.e. short tube).

Tom.
 
wn700driver
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RE: What If Boeing Was To Make A Super Twin?

Fri Jul 29, 2011 3:14 am

Quoting astuteman (Reply 21):

But in what configuration?
I'd like you to point me to anything flying that will get remotely close to the CASM of Air Austral's 840 seat A380's (which incidentally still offers more space per passenger than a 550 seat 773)

Rgds

Costs lower than Austral's 840 seater? I don't know, but I'm willing to bet that ANA's domestic 773s may still have an edge given the fact that they burn about 65% of the fuel but carry over that percentage of PAX. I guess that one would boil down to LFs.
Plus even a high density 773 can carry a bit more belly cargo than a 388, IIRC, adding to the bottom line.

Austral's config is about the closest to what I've seen in terms of the A380's best usage. Hope it works out well for them. But the other issue is what exactly composes total ops cost. We talking just fuel? Or MX, crewing etc, too? If so, it still takes a config much greater than the current seating configs (WRT A380) to become the CASM "Champ." I know a lot of airlines can charge premiums for the routes A380s "happen" to fly, and this offsets operational costs some, but I have a hard time understanding, for example, how a KE 380 configured for 407 PAX is any better than a World Airways MD-11 on a straight per seat basis.

This is why my bias is toward the larger twins. Used correctly, they're pretty tough to beat. Even if they don't have supermisty showers and duty free on board...
Base not your happiness on the deeds of others, for what is given can be taken away. No Hope = No Fear
 
flipdewaf
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RE: What If Boeing Was To Make A Super Twin?

Fri Jul 29, 2011 8:40 am

Quoting rheinwaldner (Reply 46):
(and why on earth is the 767 fuselage higher than wide?!).

You can save weight with the fuselage being taller making it stiffer (higher second moment of area and all that) for the vertical forces from the Tailplane.

Quoting tdscanuck (Reply 47):
That's true, but now you're trading skin drag against form drag. Your form drag goes through the roof if the fineness ratio gets too low (i.e. short tube).

Just Like 99% of all fish Are 4 times as long as they are wide.

Quoting wn700driver (Reply 48):

SQ stated that their A380s are around 20% cheaper per seat to operate than the 77W.

Fred
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