JustSomeDood
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Hypothetical windowless airliner questions (technical)

Fri Nov 24, 2017 4:25 pm

Hi, first post here so I hope this is the right section to post this:

Say, hypothetically, if A/B can make a window-less version of any model of their aircraft lineup (e.g Windowless A350/787), while re-optimizing the aircraft's structure for window-less design (i.e taking out reinforcements, less wing etc), what's the sort of weight savings that can be made (assuming identical capabilities)?

Secondly, for some reason, every single-deck aircraft places the window line near half-way down the fuselage, leaving the main floor quite low in the fuselage, in a window-less design, would it be possible to move up the main deck in such a way that the aircraft can fit 2 decks of passengers in the same height of fuselage? (Think 777/787/A350 fuselages, obviously, cargo is disregarded).

Detailed answers/discussion to both questions would be helpful, thanks.
 
Armadillo1
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Re: Hypothetical windowless airliner questions (technical)

Fri Nov 24, 2017 6:41 pm

i think 6+9 +ld3/45 can be put in fuselage 6.5-6.7m diameter
cargo cant be totaly disregarded.

passenger deck must be 70sm over fuselage bottom.
it is unclear about sides of fuselage

look at this patent for example
https://www.google.com/patents/US20100187352


also, i dont think windows obstruct placing passenger deck anywhere
 
VSMUT
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Re: Hypothetical windowless airliner questions (technical)

Fri Nov 24, 2017 7:22 pm

JustSomeDood wrote:
Secondly, for some reason, every single-deck aircraft places the window line near half-way down the fuselage, leaving the main floor quite low in the fuselage, in a window-less design, would it be possible to move up the main deck in such a way that the aircraft can fit 2 decks of passengers in the same height of fuselage? (Think 777/787/A350 fuselages, obviously, cargo is disregarded).

Detailed answers/discussion to both questions would be helpful, thanks.


As long as you can satisfy the emergency evacuation requirements, I don't see why not? Problem is, however, that the space is of very limited value. The walls lean in so much that you can't really fit any meaningful number of seats in. The weight and cost increases, certification and engineering hurdles are probably more than what the few extra seats will add in value.
 
CowAnon
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Re: Hypothetical windowless airliner questions (technical)

Thu Jan 11, 2018 2:20 am

JustSomeDood wrote:
Hi, first post here so I hope this is the right section to post this:

Say, hypothetically, if A/B can make a window-less version of any model of their aircraft lineup (e.g Windowless A350/787), while re-optimizing the aircraft's structure for window-less design (i.e taking out reinforcements, less wing etc), what's the sort of weight savings that can be made (assuming identical capabilities)?

Secondly, for some reason, every single-deck aircraft places the window line near half-way down the fuselage, leaving the main floor quite low in the fuselage, in a window-less design, would it be possible to move up the main deck in such a way that the aircraft can fit 2 decks of passengers in the same height of fuselage? (Think 777/787/A350 fuselages, obviously, cargo is disregarded).

Detailed answers/discussion to both questions would be helpful, thanks.

Can't answer anything, but I've been wondering about the possibility of double-decking existing widebodies as well. Theoretically a 787 has space for a 3-3 configuration on an upper deck and either a 2-3-2 or a tight 2-4-2 on the lower deck, if you vertically stagger the outer seat groups upward (for example, the flooring for the outer aisle seat being 7" higher than the aisle floor, and then flooring for the adjacent window seat being an additional 7" higher, similar to what is shown in the patent link's images). That would probably require eliminating overhead stowage bins above the outer seats, but the bins above the inner seat group would have enough room, or you could even use the floor space next to the upper deck's window seats (which is large but unusable for seating because of the fuselage curvature) for bin stowage. You'd then have to add room for a staircase and put the cargo at the back of the fuselage (like the Mitsubishi regional jet does), but combined with the 13-to-14 seats abreast (+above/below) for the double deck configuration, the amount of wetted area per seat would still be much less than with a typical 8-9 abreast 787 single decker setup.

Had the 787 program not been fouled up for so long, maybe Boeing could've considered a double-deck 787 program (using the existing 787-8/9/10 fuselage lengths) with new wings to replace the larger-capacity 777 classic, rather than doing the 777-X. Or maybe Airbus could've double-decked the 350-900 fuselage for additional seating instead of doing a 350-1000 stretch, which goes beyond the upper optimum fineness ratio of 12. I'm also wondering how short you could make a double-deck 787 if you wanted it to be the NMA/MOM. A double-deck 787 with 18 rows at 30" seat pitch would hold 234 passengers in the [3-3]/[2-3-2] configuration or 252 passengers in the [3-3]/[2-4-2] configuration, only take up 45' of fuselage length, and allow quick embarking and disembarking. According to the Hamburg Open Online University (HOOU) aircraft design course's chapter on fuselage design, (http://www.fzt.haw-hamburg.de/pers/Scho ... selage.pdf), planes with a fineness ratio of 5 have been tried. For the 787, that would mean an aircraft length of 95'. Would you be able to fit a 45' seating area, lavatories, galleys, cargo, cockpit, empennage, and wings onto such a short, stubby plane? Although the cross section is twice that of a narrowbody plane, the amount of fuselage wetted area would be slightly less than the A321, and isn't skin friction the most important factor in drag?
 
JustSomeDood
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Re: Hypothetical windowless airliner questions (technical)

Thu Jan 11, 2018 8:53 am

CowAnon wrote:
JustSomeDood wrote:
Hi, first post here so I hope this is the right section to post this:

Say, hypothetically, if A/B can make a window-less version of any model of their aircraft lineup (e.g Windowless A350/787), while re-optimizing the aircraft's structure for window-less design (i.e taking out reinforcements, less wing etc), what's the sort of weight savings that can be made (assuming identical capabilities)?

Secondly, for some reason, every single-deck aircraft places the window line near half-way down the fuselage, leaving the main floor quite low in the fuselage, in a window-less design, would it be possible to move up the main deck in such a way that the aircraft can fit 2 decks of passengers in the same height of fuselage? (Think 777/787/A350 fuselages, obviously, cargo is disregarded).

Detailed answers/discussion to both questions would be helpful, thanks.

Can't answer anything, but I've been wondering about the possibility of double-decking existing widebodies as well. Theoretically a 787 has space for a 3-3 configuration on an upper deck and either a 2-3-2 or a tight 2-4-2 on the lower deck, if you vertically stagger the outer seat groups upward (for example, the flooring for the outer aisle seat being 7" higher than the aisle floor, and then flooring for the adjacent window seat being an additional 7" higher, similar to what is shown in the patent link's images). That would probably require eliminating overhead stowage bins above the outer seats, but the bins above the inner seat group would have enough room, or you could even use the floor space next to the upper deck's window seats (which is large but unusable for seating because of the fuselage curvature) for bin stowage. You'd then have to add room for a staircase and put the cargo at the back of the fuselage (like the Mitsubishi regional jet does), but combined with the 13-to-14 seats abreast (+above/below) for the double deck configuration, the amount of wetted area per seat would still be much less than with a typical 8-9 abreast 787 single decker setup.

Had the 787 program not been fouled up for so long, maybe Boeing could've considered a double-deck 787 program (using the existing 787-8/9/10 fuselage lengths) with new wings to replace the larger-capacity 777 classic, rather than doing the 777-X. Or maybe Airbus could've double-decked the 350-900 fuselage for additional seating instead of doing a 350-1000 stretch, which goes beyond the upper optimum fineness ratio of 12. I'm also wondering how short you could make a double-deck 787 if you wanted it to be the NMA/MOM. A double-deck 787 with 18 rows at 30" seat pitch would hold 234 passengers in the [3-3]/[2-3-2] configuration or 252 passengers in the [3-3]/[2-4-2] configuration, only take up 45' of fuselage length, and allow quick embarking and disembarking. According to the Hamburg Open Online University (HOOU) aircraft design course's chapter on fuselage design, (http://www.fzt.haw-hamburg.de/pers/Scho ... selage.pdf), planes with a fineness ratio of 5 have been tried. For the 787, that would mean an aircraft length of 95'. Would you be able to fit a 45' seating area, lavatories, galleys, cargo, cockpit, empennage, and wings onto such a short, stubby plane? Although the cross section is twice that of a narrowbody plane, the amount of fuselage wetted area would be slightly less than the A321, and isn't skin friction the most important factor in drag?


Using the 787 fuselage, double-decking it as a basis for a ludicrously stubby NMA seems way out there, although I'd love to see such a plane fly :)

That said, modern widebodies (787/A350/777X) have so much crown space above the main passenger deck that there has to be a more profitable way to utilize such space than crew rests that will be empty on non-longhaul flights. An 8-6 cross section on a 787/A350 (more for a 777X) with a slightly lower passenger main deck would be a dang good people-hauler, the LH-oriented wings can be put to good use hauling higher MZFWs. Payload-range of course takes a significant hit, but many airlines don't seem to be hitting the range limits of their long-haul widebodies anyways...
 
WPvsMW
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Re: Hypothetical windowless airliner questions (technical)

Thu Jan 11, 2018 8:08 pm

Sell reservations in the "sleeperettes" above the main cabin on short-haul.
 
Nean1
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Re: Hypothetical windowless airliner questions (technical)

Fri Jan 12, 2018 1:42 am

I remember reading somewhere that when Embraer perfected the Lineage 1000 creating the 1000E one of the modifications consisted of removing some windows, to reduce weight and drag.

A windowless airplane would be lighter and more aerodynamic, with less parasitic drag. Perhaps someone could think of increasing cabin pressurization, allowing flights at higher altitudes and more comfort.

Panels could give a sense of the outside view and attitude of the aircraft. But the nome of the seats would have to change from window to wall... Ultra low cost carrier dream.
 
gloom
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Re: Hypothetical windowless airliner questions (technical)

Fri Jan 12, 2018 9:16 am

Remember two things.
One: for a doubledecker, you'll need so much more weight. Second floor capable to handle weight. Extra seats. Alternate bin space. I believe whole operation could land the weight per length anywhere between 60 and 100 percent extra. We're talking probably 30-40 % higher OEW here.
Two: Once you have the structure, you'll land probably 60-70% more passenger. Assuming standard 300 widebody, you raise it with 200 persons. Another 40.000 lbs.

Both will have huge impact on wing load. Sure, on short to medium one can surely use A321/B739ER concept - high takeoff/landing speeds, short flap speeds etc. Plane characteristics will not be perfect, ground service could take longer, but man it will fit those passengers, and wings will do. However, since planes are already quite limited on payload (especially LR/ULR), I don't see anything beyond 3000nm going doubledecker. And I have serious doubts whether such a solution would end up like A380 - extra weight to carry persons and loss of effectiveness due to higher required lift from wings could mean one doubledecker 787/350 would work worse than two onedeckers.

Also, there's one more reason to reckon. A380 was not killed by economics. It was killed by surrounding infrastructure and lacks for hub concept anyways. Doubledecker will always be heavy and number of passengers WILL require lots of new infrastructure as well. Both on runways/taxiways (PCN etc) and boarding/deboarding effectively. We also see the best value now in market of 250-300, even 777X seems to be too large for most operators. I don't see it turning, so why going even bigger?

So, basically. While technically possible, and maybe even economically viable, it seems just a possibility, and I don't see anyone doing such plane, otherwise than for some special purposes (cargo doubledecker could be viable, VIP plane - perhaps).

Cheers,
Adam
 
Armadillo1
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Re: Hypothetical windowless airliner questions (technical)

Sat Jan 13, 2018 10:33 am

gloom wrote:
We're talking probably 30-40 % higher OEW here.
Two: Once you have the structure, you'll land probably 60-70% more passenger. Assuming standard 300 widebody, you raise it with 200 persons. Another 40.000 lbs.

facepalm

its not about fitting 789 as dd's with old wing.

its about placing 777 load in 767|787 size fuselage

so dd's with 777x load will be 781 MTOW, perfectly fitting in existing infrastructure.
(few issues like boarding can be easely solved)

most problem i can see are difficulty with changing seating. less volume for 1st class, less flexibility in cabin, making aircraft builded for single role.
 
gloom
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Re: Hypothetical windowless airliner questions (technical)

Sat Jan 13, 2018 5:47 pm

Armadillo1 wrote:
facepalm


Any reasoning, or just bashing?

its not about fitting 789 as dd's with old wing.

its about placing 777 load in 767|787 size fuselage


Both are quite the same.
I'm not considering geometrical shape here, just weights.

I can think of two scenarios:

NB expanded to 250-300 places (from current standard 180-200).
WB expanded to 450-500 places (from current standard of ~300).

Both by probably a factor of 50-60%. Main deck lowered (and probably shape more ovoidal cross-section to accomodate cargo on the belly as usually, but that's just remark, nothing really difficult here), new one above.

So basically, what we have here is:
1. extra weight (structural): new floor, more seats, lavatories, galleys etc.
2. extra weight (pax): 1 ton for each 10 pax extra. That will be up to 10 tons extra for NB, with around 90t MTOW for A321 nowadays - you realize that? WBs are easier, since one can dump fuel and make it medium range plane, but it's also 15-20t extra - especially for landing.
3. That weight is both on wings AND landing gear. Effecting PCN and many more (infrastructure).
4. Costs might be reduced a bit on fuel, but fees and crew will cost the same to the comparable onedecker (comparable = similar seat number).

I'll keep my case as still effective. While possible technically, and maybe also economically CASM will go by a small factor, but other problems make it just a concept, not to be seen in real aviation. Small plane with large wings and large gear to keep weight to lift right, will not work better than longer hull with one deck. And complexity increase over current concept will cost extra.

I just don't see it coming. And certainly not in you weight class (777x load in 781 weight? c'mon).

Cheers,
Adam
 
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Re: Hypothetical windowless airliner questions (technical)

Sun Jan 14, 2018 9:24 am

CowAnon wrote:
Can't answer anything, but I've been wondering about the possibility of double-decking existing widebodies as well.

I was actually thinking about this for the 777.

Adding a 747 style hump forward of the wing for a first class cabin. Then add a 3m stretch behind the wing for weight distribution bringing the length to 80m. The wing seems big enough and it would make a great twin engine lightweight 747.

Range would be reduced unless they up the maximum takeoff weight significantly. However as the payload range of the 777-9 is already exception trading payload for fuel would still result in an extra with 6500nm range. Removing the centre fuselage fuel tank would offset most of the extra fuselage weight in terms of loads on the centre wing box.
Last edited by RJMAZ on Sun Jan 14, 2018 9:41 am, edited 1 time in total.
 
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Re: Hypothetical windowless airliner questions (technical)

Sun Jan 14, 2018 9:41 am

RJMAZ wrote:
CowAnon wrote:
Can't answer anything, but I've been wondering about the possibility of double-decking existing widebodies as well.

I was actually thinking about this for the 777.

Adding a 747 style hump forward of the wing for a first class cabin. Then add a 3m stretch behind the wing for weight distribution bringing the length to 80m. The wing seems big enough and it would make a great twin engine lightweight 747. Range would be reduced unless they up the maximum takeoff weight significantly


Boeing tried the "adding a hump" concept with with the 767-X, but then they came to their senses and designed the 777 from scratch. And then everyone agreed never to speak of what became known as "The Hunchback of Mukilteo" ever again. Ever... :D

Image
Image
Image
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RJMAZ
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Re: Hypothetical windowless airliner questions (technical)

Sun Jan 14, 2018 10:26 am

Starlionblue wrote:
Boeing tried the "adding a hump" concept with with the 767-X

I'm thinking something like this.

Image

A new nose and a very subtle hump. High commonality with the 777-9.

Wings, wingbox, engines, tail, landing gear, rear fuselage and cockpit all shared with the 777X.
 
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Re: Hypothetical windowless airliner questions (technical)

Sun Jan 14, 2018 11:26 am

Image
 
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Starlionblue
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Re: Hypothetical windowless airliner questions (technical)

Sun Jan 14, 2018 11:56 am

RJMAZ wrote:
Starlionblue wrote:
Boeing tried the "adding a hump" concept with with the 767-X

I'm thinking something like this.

Image

A new nose and a very subtle hump. High commonality with the 777-9.

Wings, wingbox, engines, tail, landing gear, rear fuselage and cockpit all shared with the 777X.


Fair dinkum. However I have a feeling that adding a 3.5 meter plug (to stay within 80m) would give you almost as many seats with much less complication.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
RJMAZ
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Re: Hypothetical windowless airliner questions (technical)

Sun Jan 14, 2018 12:42 pm

A simple 3.5m extension would give 20.5m2 of extra cabin area. That's only a 5% increase in cabin area over the 777-9. The 777-8 to 777-9 is a larger 10% difference.

The upper hump would create over 60m2 of extra cabin area in addition to the 20m2 added in the stretch. That is a big increase.

If the fuel load is reduced to keep a similar MTO it would result in an aircraft with extremely good CASM and be a very light aircraft per passenger. Of course this comes at the expense of range. But on any flight where this 777-10 could reach it would be unstoppable. For the really thick trunk routes it would be the best solution.

If it is 90% as good as a clean sheet VLA while costing only 10% of the price to develop then it is a very possible solution.
 
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Starlionblue
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Re: Hypothetical windowless airliner questions (technical)

Sun Jan 14, 2018 12:46 pm

Fair enough. However the aerodynamic considerations, structural considerations and increased construction complexity would be considerable compared to a simple plug, and with a 747 style hump there is some "dead" area along the walls which would come off the 60 square meters.

I'm not saying it isn't doable. I'm saying it probably isn't quite that simple.
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JustSomeDood
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Re: Hypothetical windowless airliner questions (technical)

Sun Jan 14, 2018 2:18 pm

Actually, how feasible would it be to "hollow out" much of the crown space above the main deck to be used as flat beds for premium class? from this picture of an A350, the crew rest areas only take up a small amount of a widebody's fuselage length, have J/F passengers sit on much smaller footprint W-ish seats during take-off/landing before they head up for the majority of the flight, it certainly doesn't seem to be a huge engineering endeavour (relatively speaking) to relocate the crew rest areas into cargo hold areas for more premium seats/long haul configurations where cargo holds are mostly empty anyways.

Image
 
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zeke
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Re: Hypothetical windowless airliner questions (technical)

Sun Jan 14, 2018 3:15 pm

If your going windowless, why stick with a tube with wings ?
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JustSomeDood
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Re: Hypothetical windowless airliner questions (technical)

Sun Jan 14, 2018 10:51 pm

zeke wrote:
If your going windowless, why stick with a tube with wings ?

The implied assumption is that A/B/somebody else don't have the sort of risktaking appetite to make a design that radically deviates from tube + wings.
 
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Starlionblue
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Re: Hypothetical windowless airliner questions (technical)

Mon Jan 15, 2018 1:11 am

JustSomeDood wrote:
Actually, how feasible would it be to "hollow out" much of the crown space above the main deck to be used as flat beds for premium class? from this picture of an A350, the crew rest areas only take up a small amount of a widebody's fuselage length, have J/F passengers sit on much smaller footprint W-ish seats during take-off/landing before they head up for the majority of the flight, it certainly doesn't seem to be a huge engineering endeavour (relatively speaking) to relocate the crew rest areas into cargo hold areas for more premium seats/long haul configurations where cargo holds are mostly empty anyways.

Image


Using crown space is certainly feasible, but there's not as much space up there as one might think. The 777 or 350 crew bunks are not for the claustrophobic. And to my knowledge cargo holds are not mostly empty on long haul.

Boeing did have the Aeroloft concept for using crown space a while back. Image
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CplKlinger
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Re: Hypothetical windowless airliner questions (technical)

Mon Jan 15, 2018 1:26 am

Not having the mechanics perspective on this, but isn't there a fair amount of stuff running above the ceiling in the crown space, like cabling, ductwork, SATNAV/WiFi Receivers? That stuff is going to have to go somewhere, and as others have said, you may not get the amount of space you think you'll get. Why try reinventing the wheel?
 
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Re: Hypothetical windowless airliner questions (technical)

Mon Jan 15, 2018 2:32 am

Starlionblue wrote:
RJMAZ wrote:
CowAnon wrote:
Can't answer anything, but I've been wondering about the possibility of double-decking existing widebodies as well.

I was actually thinking about this for the 777.

Adding a 747 style hump forward of the wing for a first class cabin. Then add a 3m stretch behind the wing for weight distribution bringing the length to 80m. The wing seems big enough and it would make a great twin engine lightweight 747. Range would be reduced unless they up the maximum takeoff weight significantly


Boeing tried the "adding a hump" concept with with the 767-X, but then they came to their senses and designed the 777 from scratch. And then everyone agreed never to speak of what became known as "The Hunchback of Mukilteo" ever again. Ever... :D

Image
Image
Image


Those are great pictures, especially that CX Bird. Love that they went RR on it too. You don't know if someone's making those models, do you?

Starlionblue wrote:

Using crown space is certainly feasible, but there's not as much space up there as one might think. The 777 or 350 crew bunks are not for the claustrophobic. And to my knowledge cargo holds are not mostly empty on long haul.


And that was the point I actually showed up to make. I totally agree with this. I'm only 6'4", but it is not close to possible for me to stand up striaght in either of the 77W's crew rest areas. And that's even with the sunken floor the aft one has running down the spine of the OHBs below.


CplKlinger wrote:
Not having the mechanics perspective on this, but isn't there a fair amount of stuff running above the ceiling in the crown space, like cabling, ductwork, SATNAV/WiFi Receivers? That stuff is going to have to go somewhere, and as others have said, you may not get the amount of space you think you'll get. Why try reinventing the wheel?


Some. But overall, it wouldn't be that difficult to rework. Consider that on the 77W, the aft crew rest module runs the entire legnth of the crown between doors 4L/R and 5L/R as it already is.
Much like a GE90, I'm a huge fan of Big Twins...
 
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Starlionblue
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Re: Hypothetical windowless airliner questions (technical)

Mon Jan 15, 2018 2:42 am

I get the feeling the CX one was made by starting out with a 767 kit and modifying it. The Boeing livery model is from the Boeing factory I think. Probably a custom job.
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RJMAZ
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Re: Hypothetical windowless airliner questions (technical)

Mon Jan 15, 2018 2:44 am

Starlionblue wrote:
and with a 747 style hump there is some "dead" area along the walls which would come off the 60 square meters.

This dead space is absolutely perfect for premium business and first class seating. They can be used for storage, or angled bed seats can extend into this space.

The overhead bins could be then be moved to the lower wall which would help with the low ceiling height and improve cosmetics. Nearly all 747 and A380's have a decent amount of bed/flat business class seats. These can all be placed on the upper deck which would appear prestigious and be very private.

JustSomeDood wrote:
Actually, how feasible would it be to "hollow out" much of the crown space above the main deck to be used as flat beds for premium class?

You cant stand up even at the highest point. It would need a need a hump to make it work. Something about half the height of the 747's hump would be the bare minimum to allow you to stand up.

It would make more sense to jeep then as pilot and crew rest areas and relocate the toilets and food services below deck.
 
CowAnon
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Re: Hypothetical windowless airliner questions (technical)

Wed Jan 17, 2018 8:54 am

Armadillo1 wrote:
i think 6+9 +ld3/45 can be put in fuselage 6.5-6.7m diameter
cargo cant be totaly disregarded.

You're right. I became curious and sketched a possible arrangement for the aft (non-hump) cross section of a 747, which is 256" (6.50 m) wide. Assuming the height is at least equal to the width, the 747 can fit 3-3 upper deck seating, 3-4-3 lower deck seating (where the outer seat groups are elevated), and an LD3-45 container underneath, with 18" seats, 1.5" armrests, 7'0" or higher aisle clearances, and 19" aisles throughout.

If you don't worry about fitting an LD3-45 under the lower deck of seats, you can do a 2-4-2 upper/2-5-2 lower seating arrangement (or vice-versa), resulting in 17 seats abreast instead of 16 abreast with the LD3-45. Since you'd have to find a place for additional storage anyway, I'd just dedicate a certain portion of the aft fuselage to cargo. The resulting drop in the wetted area per seat wouldn't be too significant. So Boeing could've removed the hump and still created a full double-deck version of the 747!
 
CowAnon
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Re: Hypothetical windowless airliner questions (technical)

Wed Jan 17, 2018 9:48 am

gloom wrote:
Armadillo1 wrote:
its not about fitting 789 as dd's with old wing.

its about placing 777 load in 767|787 size fuselage


Both are quite the same.
I'm not considering geometrical shape here, just weights.

I can think of two scenarios:

NB expanded to 250-300 places (from current standard 180-200).
WB expanded to 450-500 places (from current standard of ~300).

Both by probably a factor of 50-60%. Main deck lowered (and probably shape more ovoidal cross-section to accomodate cargo on the belly as usually, but that's just remark, nothing really difficult here), new one above.

So basically, what we have here is:
1. extra weight (structural): new floor, more seats, lavatories, galleys etc.
2. extra weight (pax): 1 ton for each 10 pax extra. That will be up to 10 tons extra for NB, with around 90t MTOW for A321 nowadays - you realize that? WBs are easier, since one can dump fuel and make it medium range plane, but it's also 15-20t extra - especially for landing.
3. That weight is both on wings AND landing gear. Effecting PCN and many more (infrastructure).
4. Costs might be reduced a bit on fuel, but fees and crew will cost the same to the comparable onedecker (comparable = similar seat number).

I'll keep my case as still effective. While possible technically, and maybe also economically CASM will go by a small factor, but other problems make it just a concept, not to be seen in real aviation. Small plane with large wings and large gear to keep weight to lift right, will not work better than longer hull with one deck. And complexity increase over current concept will cost extra.

I just don't see it coming. And certainly not in you weight class (777x load in 781 weight? c'mon).

Cheers,
Adam

Adam, thanks for your detailed input here and above. I'm sure you're final conclusion is correct (about these types of planes not being built). However, my idea doesn't put cargo in the belly, so the extra weight of floors/seats/lavs would be offset to some degree by the lack of cargo. Also you thought that boarding/deboarding might be more difficult, but the possible seating configurations for the two-deck 787/350/777 planes are very nice: 2-2-2 / 2-3-2, 2-3-2 / 2-3-2, and 2-3-2 / 2-4-2, respectively. Those configurations mean passengers are at most one seat away from the aisle in 13-15 seat abreast setups, whereas on a 380, 4 of the 19 passengers abreast are two seats away from the aisle.

I'm glad Armadillo1 brought up the 767. I initially thought it was too small to be a double decker, but actually it may be the perfect double-decker airplane, since it can hold a 2-2 upper deck / 2-2-2 lower deck. With no middle seats, the 2-deck 767's blemishes are just the elevated side seats on the lower deck, and one of the decks having only a 6'11" aisle height instead of 7'0" or above. Although I would probably go with a clean sheet plane that's skinnier (182" instead of 198" wide, which means going with a 3-3 instead of 2-2-2 on the lower deck :( ) and add one inch to the height (to 214") to get the full 7'0" aisle heights. That means if you want to position it as the MOM to match the A321's passengers capacity (240 passengers at 28" pitch) and cylindrical surface area (146" length for a 155.5" wide by 163" high tube), you get a seating area length of 56' and a total fuselage length of up to 117" (similar to the 737-7 MAX). This results in a fineness ratio of 6.56, which is smaller than the BAE146-100, but still close if I'm interpreting Fig. 6.1 of the HOOU document correctly.

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