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flipdewaf
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Cabin configurations, fuselage weight model

Fri Feb 12, 2021 11:13 pm

So...

I decided, as is my way, to create a spreadsheet model to describe the way in which aircraft perform. At the moment with the NMA/MOM/797 discussions coming back and the debates around fuselage configuration rearing it’s head I was drawn to creating a study in to the inherent widths, aisles lengths debate that ensues.

I set up a model looking at the metric of weight per passenger based on a simple model combining both stresses from pressurisation and from bending.

The model sets up with some standards on seat width and pitch as well as aisle width. Seats and aisles are 20” wide each and 5” of wall added to create the outer diameter. The seat pitch determines the length of the cabin and in this case is set as 32”. The overall aircraft length is determined by the cabin length + 6x width (addition for nose and tail). The stresses established by hoop stress and bending are combined and a skin thickness determined which is multiplied by the length x circumference x al density to get an overall weight. This weight is divided by the number of pax to get a comparable weight. The model is run from 50 to 650 seats and 4 abreast to 11 abreast. From 7 abreast and up the configurations have 2 aisles.

The out put of the model as it stands is below:
Image

Overall the model shows that as the pax capacity increases the optimal (lowest weight per pax) moves to wider aircraft.

The gap in the pattern between the narrow body and wide body aircraft is evident in the output with the 3x3 showing the largest area of being the most optimal solution (140-300pax).

The additional aisle of the wide body aircraft, as expected, increases the weight per pax due to the less optimal use of space. The 8 abreast configuration has a reduced area of being optimal but the 7 abreast configuration is the optimal solution at no capacity.

The model appears to show that the c-series, A320/737 and 787/A350 are well placed for their configuration/capacity. The 777X looks like the 778X may be undersized and the 771X may well be a good idea. The A330 shows its issues here especially vs the tighter 787. Finally a 7 abreast aircraft appears not worth worrying about, a transition from 6 abreast to 9 abreast seems to not leave a lot of a niche.

I will put genuine aircraft configurations (widths/capacities) on to the chart going forward so we can see both the theory and how the market works with the genuine gaps.

As ever feedback and discussion is very welcome.

Fred


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Image
 
SteinarN
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Re: Cabin configurations, fuselage weight model

Sat Feb 13, 2021 9:54 am

Interesting topic.
But the chart is very hard to read. Can you put in a higher resolution picture, or a clickable picture?
 
flipdewaf
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Re: Cabin configurations, fuselage weight model

Sat Feb 13, 2021 10:26 am

SteinarN wrote:
Interesting topic.
But the chart is very hard to read. Can you put in a higher resolution picture, or a clickable picture?

Apologies, posting the pics from iPad so difficult to ensure it’s correct.

Image
photo hosting sites reviews

Does this look ok?

Fred


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Image
 
SteinarN
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Re: Cabin configurations, fuselage weight model

Sat Feb 13, 2021 12:21 pm

@flipdewaf
Thank you! It is perfect now.

Your formula seems to suggest that a 6 abreast is the lightest fuselage all the way up to 300 seats in single class. That's an awfully long fuselage.
The weight in your chart, is that the weight of the outer skin only?
Interesting to see the step change in weight from 6ab single aisle to 7ab dual aisle.
A 7ab dual aisle MOM seems to be a design which is very difficult to make weight efficient.
 
morrisond
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Re: Cabin configurations, fuselage weight model

Sat Feb 13, 2021 1:34 pm

Hi Fred,

As always - you do some great work.

I was playing with some numbers as well this morning.

Yes - I believe that a 7W NMA may not be as weight efficient as a 6W - but it may not as big as a penalty as you think it may be.

Remember the bare fuselage weight is somewhere around 5% of MTOW and there may be some inherent advantages of Carbon that make up some of the structural cost due to Skins having to be thicker than necessary for things like Ramp Rash. Carbon could be wasted on a 3x3 but make perfect sense on a 2x3x2.

The one interesting change to your graph would be to look at two narrower aisles vs one wider one.

I did some math this morning at equivalent capacity (adjusting length for the same number of seats) in a two class configuration (the Aviation Week article calls NMA 2 class).

Assuming narrower aisles on a 2x3x2 - call it 17" - One inch less than 777x vs 19" on an A320 the 2x aisle uses up 43% more floor space for aisles before adjusting for the extra space you pick up at the ends in the galleys.

That is the equivalent of going from a 19" Single Aisle to about a 27" Aisle - which if you are talking about a capacity of A322 + you may need extra width just so people can pass a cart - or what it is going to be like trying to deplane a SA with 270 passengers(NMA -6/7) in 2040?

What happens to your graph when you assume a 2x3x2 with 2x 17" Aisles vs one at say 27".

What cross sections are you using? WxH?
 
morrisond
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Re: Cabin configurations, fuselage weight model

Sat Feb 13, 2021 5:04 pm

Also please explain what you are getting that extra 15' of Fuselage length? Yes the tail might have to be slightly longer (but I think your model is taking into account a circular fuselage not Ovalish fuselage that is basically the same height (maybe a little more than a 3x3) that is basically just a 3x3 and bulged out 15-16" on each side) - but if you split that 15' between front and back and say it's 3' longer tail - that gives 6' of usable space inside then that could mean you get an extra set of 1x1x1 in the front and maybe a couple of rows of 2x2x2 in the back - meaning fuselage shorter for the same capacity.

You are also ignoring that due to the extra width the galleys in the front and back could be shorter - offset by the extra aisle entrance at both ends.

No wonder your model is so disadvantaging 2x3x2. It's a great model but may need tweaks.

Personally I would be comparing 2x17" aisles vs 1x 19" and the tails of the airplane the same length. You save a little bit in the galleys but can then make the tail a little longer and taper over a greater length.

What is more aero - a Teardrop or a pencil?
 
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seahawk
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Re: Cabin configurations, fuselage weight model

Sat Feb 13, 2021 5:47 pm

Thank you for the chart. Great post.

SteinarN wrote:
@flipdewaf
Thank you! It is perfect now.

Your formula seems to suggest that a 6 abreast is the lightest fuselage all the way up to 300 seats in single class. That's an awfully long fuselage.
The weight in your chart, is that the weight of the outer skin only?
Interesting to see the step change in weight from 6ab single aisle to 7ab dual aisle.
A 7ab dual aisle MOM seems to be a design which is very difficult to make weight efficient.


Not that unrealistic, the 757-300 was known to be a CASM monster before the A321NEO.
 
JayinKitsap
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Re: Cabin configurations, fuselage weight model

Sun Feb 14, 2021 6:27 pm

Some questions &/or comments to your excellent but simple model. It really fleshes out the potentials of various sides.

1. Your 3D for the nose, that is 3 diameters ahead of the first seat row, but includes the pair of doors, the galley and closets as well as the cockpit and nose. Is there the weight of the end cap too. Is 3D representative of actual planes verses say 2.5D. I use a similar approach on fiberglass tanks with decent results in getting the initial weight.

2. Your 3D for the tail, is that representative of current planes or is it more like 2.5D also. It seems like there is at least 2D from the bulkhead to the tail tip.

3. This is probably suitable for circular and double bubble cross sections. However, the larger the hull radius the thicker the skin as there are compression load cases in both the hoop and axial direction. Some tuning based on actual planes (say 77W) would improve the information.

4. Could add easily the frontal and rest of the wetted area to fill a 2nd chart.


My take is that around 260-280 passengers the 7ab is as efficient at 6ab weight wise, technically it is over 300 where they cross, but as noted above the flexure cases when long would require thicker skins in the crown.
 
LH707330
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Re: Cabin configurations, fuselage weight model

Sun Feb 14, 2021 9:25 pm

Fred, thanks for putting this together, great work! This really calls into question the design thinking behind the 767: why did they pick that diameter if they could have done a 757-300 with a bigger wing and saved weight and development cost? I suspect it may have been the case that the 767, like the A300, were designed backward from the question "what's the biggest twin we can do with two of the 1970s strongest engines?" Boeing went for range over payload, while Airbus went the other way in picking their diameter. It also implies that MD and Lockheed picked a good diameter for the DC-10 and L1011, although the trijet layout was the least efficient structurally.

Another comparison I'd be keen to see is how the 330/340/787/777 stack up against that theoretical model: it almost seems to me that B could have made the 777 a bit wider for comfortable 10Y, or narrower to compete with the 330/340. I've read that A had better fuselage weight, which is why the 330 did better in market and the 340 was able to hang on for some time despite older engines.
 
LH707330
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Re: Cabin configurations, fuselage weight model

Sun Feb 14, 2021 9:30 pm

[quote="morrisond"
Yes - I believe that a 7W NMA may not be as weight efficient as a 6W - but it may not as big as a penalty as you think it may be.

Remember the bare fuselage weight is somewhere around 5% of MTOW and there may be some inherent advantages of Carbon that make up some of the structural cost due to Skins having to be thicker than necessary for things like Ramp Rash. Carbon could be wasted on a 3x3 but make perfect sense on a 2x3x2.
[/quote]

The problem with the 5% argument is that if you made a heavier fuselage for 7Y, the variables begin chasing one another. Let's say your tube is 5%, and making wider would make it 6% of MTOW if you don't touch anything else. That may be a 1 pp difference in total, but it's a 20% jump at the component level. If you want to retain range, you now need to support that heavier fuselage with a bigger wing, stronger gear, bigger engines, etc. Pretty soon, the vehicle weight has gone up a bit as well and your 1 pp initial difference for the fuselage has turned into a multi-pp difference overall.
 
RJMAZ
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Re: Cabin configurations, fuselage weight model

Sun Feb 14, 2021 10:12 pm

As I expected 7ab is the only cross section that is never the most optimal.

Between 300 and 360 seats your graph shows 8ab is the most optimal. This is target seat capacity for the 797. With the A321 seating 240 seats single class I'd expect the short 797 to be 25% bigger and the long 797 50% bigger. This exactly 300 and 360 seats.

Budget airlines have already squeezed 8ab into the 767. So with a clean sheet design and simply add 6inchs to the cabin width of the 767 and keep LD2's.

It wouldn't surprise me if Boeing did 777X upgrade style to the existing 767. Carbon wing, cleansheet engines and sculpted cabin side walls to squeeze in an extra seat.
 
Sokes
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Re: Cabin configurations, fuselage weight model

Mon Feb 15, 2021 12:24 am

I wanted to start a new topic, but it fits well here.

I wondered if for a VLA an elliptical shape like the A380 or a double bubble like B747 is structurally more efficient.
Double deck planes tend to be too high. Not to add height for overhead bins I consider only 6 abreast suitable on upper deck.

The B787 has a cabin width of 549 cm,
the A350 of 561 cm,
the B777X of 596 cm,
the B747 of 608 cm and
the A380 of 6,58 cm.

For double bubble the B747 looks good. The lower and middle floor make a nice circle.

For elliptical with six abreast on top I have Keesje's Ecoliner in mind. The main deck would be nine abreast. So the 5,61m of A350 should do.

The A380 is an eleven abreast plane. It's a meter broader. I wonder what the floors alone weigh? With structural requirements for the floor increasing square with width: 6,6m/5,6m = 1,8 ; 1,8x1,8 = 1,39

Or was the double bubble of B747 good as it was? After all it's the right width for 10 abreast.

Cross section of Keesje's Ecoliner:
viewtopic.php?t=775819

Where is Keesje by the way?
Why can't the world be a little bit more autistic?
 
Sokes
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Re: Cabin configurations, fuselage weight model

Mon Feb 15, 2021 12:40 am

flipdewaf wrote:
...
The overall aircraft length is determined by the cabin length + 6x width (addition for nose and tail).
...
Fred

I believe aircrafts are usually 9-12 times as long as wide. I assume 6x width for nose and tail is too much.
Here a B777-200:
Image
https://de.wikipedia.org/wiki/Boeing_777

Length is 63,7 m/ fuselage diameter 6,2 m = 10,3

And a -300:
Image
Same source

Length is 73,9 m/ 6,2 m = 11,9
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flipdewaf
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Re: Cabin configurations, fuselage weight model

Mon Feb 15, 2021 4:42 pm

I have done a slightly updated model. I have put in it fuselage dimensions from existing rather than just using seat width + aisle width as a predictor. They are modeled now as ellipses as opposed to circles and to keep it even slightly manageable I have kept the axis for the second moment of are about the centre of the ellipse (its probably slightly lower?) I have stopped the fuselages when they get to a fineness ratio of 14 or if they go over 80m.

Image

I have done a quick correlative study on the availability of space in the tail and the cabin vs fuselage length came to : Fuselage length = 7.6480704 + 1.0906144*Length of cabin (m) I have not yet implemented that in to this model yet. The otehr way of implementing could be that it is close to 2.4 fuselage widths of fuselage beyond the length of the cabin in widebodies and about 2.7 in narrowbodies. the current model has it at 5X for all.

Fred
Image
 
morrisond
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Re: Cabin configurations, fuselage weight model

Mon Feb 15, 2021 5:19 pm

flipdewaf wrote:
I have done a slightly updated model. I have put in it fuselage dimensions from existing rather than just using seat width + aisle width as a predictor. They are modeled now as ellipses as opposed to circles and to keep it even slightly manageable I have kept the axis for the second moment of are about the centre of the ellipse (its probably slightly lower?) I have stopped the fuselages when they get to a fineness ratio of 14 or if they go over 80m.

Image

I have done a quick correlative study on the availability of space in the tail and the cabin vs fuselage length came to : Fuselage length = 7.6480704 + 1.0906144*Length of cabin (m) I have not yet implemented that in to this model yet. The otehr way of implementing could be that it is close to 2.4 fuselage widths of fuselage beyond the length of the cabin in widebodies and about 2.7 in narrowbodies. the current model has it at 5X for all.

Fred


How does an 767 which has a cross section somewhere around 30% more than an MOM/NSA - has a lot more range and can take a much larger container weigh less per passenger?

What MOM cross section are you using? 170x190?
 
flipdewaf
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Re: Cabin configurations, fuselage weight model

Mon Feb 15, 2021 5:31 pm

morrisond wrote:
flipdewaf wrote:
I have done a slightly updated model. I have put in it fuselage dimensions from existing rather than just using seat width + aisle width as a predictor. They are modeled now as ellipses as opposed to circles and to keep it even slightly manageable I have kept the axis for the second moment of are about the centre of the ellipse (its probably slightly lower?) I have stopped the fuselages when they get to a fineness ratio of 14 or if they go over 80m.

Image

I have done a quick correlative study on the availability of space in the tail and the cabin vs fuselage length came to : Fuselage length = 7.6480704 + 1.0906144*Length of cabin (m) I have not yet implemented that in to this model yet. The otehr way of implementing could be that it is close to 2.4 fuselage widths of fuselage beyond the length of the cabin in widebodies and about 2.7 in narrowbodies. the current model has it at 5X for all.

Fred


How does an 767 which has a cross section somewhere around 30% more than an MOM/NSA - has a lot more range and can take a much larger container weigh less per passenger?

What MOM cross section are you using? 170x190?


186x168. The reason its heavier is that the lower radii of the fuselage in the crown and belly (I am assuming ellipse for ease of calculation) means that the required strength for pressurization requirements are very high. Then when the length starts to increase the fact that is significantly lower in profile than the 767 means that it has a lower second moment of area and so doesn't handle bending loads as well.It s a simplistic model and I would wager there's more to go at here.

Fred
Image
 
flipdewaf
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Re: Cabin configurations, fuselage weight model

Mon Feb 15, 2021 7:35 pm

RJMAZ wrote:
Between 300 and 360 seats your graph shows 8ab is the most optimal. This is target seat capacity for the 797. With the A321 seating 240 seats single class I'd expect the short 797 to be 25% bigger and the long 797 50% bigger. This exactly 300 and 360 seats.

Budget airlines have already squeezed 8ab into the 767. So with a clean sheet design and simply add 6inchs to the cabin width of the 767 and keep LD2's.

I took 18.2" from the size of the 787 and kept the height to width ratio the same, this is the result:
Image
I have bolded 787 - Black
A32X -green
242 mom - Blue

Whilst its better than the MOM example it seems to me that the 787 cross section is already there, it can do 9 abreast and that slightly more efficient use of floor space makes up for the better weight per floors pace. The area around the top end of the narrow bodies seems very congested.

Fred
Image
 
RJMAZ
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Re: Cabin configurations, fuselage weight model

Mon Feb 15, 2021 9:06 pm

flipdewaf wrote:
I took 18.2" from the size of the 787 and kept the height to width ratio the same, this is the result:

Whilst its better than the MOM example it seems to me that the 787 cross section is already there, it can do 9 abreast and that slightly more efficient use of floor space makes up for the better weight per floors pace.

This second graph just proves your first graph wrong.

Your first graph shows 8ab as lighter than 9ab between 300 and 360 seats. The first graph would assume equal construction technology for each.

For your second graph to have the 787 9ab lighter than 8ab. You have clearly put the 787 as having better or lighter construction. So you are just making these graphs up?
 
flipdewaf
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Re: Cabin configurations, fuselage weight model

Mon Feb 15, 2021 9:16 pm

RJMAZ wrote:
flipdewaf wrote:
I took 18.2" from the size of the 787 and kept the height to width ratio the same, this is the result:

Whilst its better than the MOM example it seems to me that the 787 cross section is already there, it can do 9 abreast and that slightly more efficient use of floor space makes up for the better weight per floors pace.

This second graph just proves your first graph wrong.

Your first graph shows 8ab as lighter than 9ab between 300 and 360 seats. The first graph would assume equal construction technology for each.

For your second graph to have the 787 9ab lighter than 8ab. You have clearly put the 787 as having better or lighter construction. So you are just making these graphs up?


In a sense I am just making them up but I see your point so something might be amiss. In the first chart I used 20" per seat and 20" per aisle plus plus 10" total for the wall. and circular cross sections. In the second chart I had updated the sheet to use ellipse cross sections and for the width of he 8 abreast I basically took 18.2" from the 787 width but kept the x-section the same ratio of height to width.

I would be inclined to agree with you as i have used the 787 as the base they should be similar, I'll have a dig through the spreadsheet and see why it might be going differently than we would expect, (might be right but It may be my assumptions or calcs.

Fred

Edit: So I went back and looked and the issue is two fold, one is the use of circular vs high ellipse in the model, the more off circle the ellipse the higher the weight at short lengths the taller the ellipse the lower the slope at the longer end. The "rounder" the fuselage the lighter at short weights, but the taller it is the more "stretchable" it is. (or the baked in stretch causes less additional weight at the short end).

Fred
Image
 
flipdewaf
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Re: Cabin configurations, fuselage weight model

Mon Feb 15, 2021 9:46 pm

RJMAZ wrote:
flipdewaf wrote:
I took 18.2" from the size of the 787 and kept the height to width ratio the same, this is the result:

Whilst its better than the MOM example it seems to me that the 787 cross section is already there, it can do 9 abreast and that slightly more efficient use of floor space makes up for the better weight per floors pace.

This second graph just proves your first graph wrong.

Your first graph shows 8ab as lighter than 9ab between 300 and 360 seats. The first graph would assume equal construction technology for each.

For your second graph to have the 787 9ab lighter than 8ab. You have clearly put the 787 as having better or lighter construction. So you are just making these graphs up?


Image

I took the numbers of the autocad model I made of your suggested aircraft about 1 year ago. 5.098m circular.

Fred
Image
 
LH707330
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Re: Cabin configurations, fuselage weight model

Mon Feb 15, 2021 10:44 pm

Two possible things I can think of looking at this:
1. The seats/aisle problem shows that a tight 9Y 787 is the most efficient formula and there's not much point in going with a 7Y or 8Y for a new design under these assumptions. Assuming that Fred's checks don't reveal any serious issues with the model, this would confirm my hunch that the MoM "gap" is not so much a gap as a physics-limited space that one can't fill effectively. Recall also that the A310, A300-600, and early A330-300 didn't sell very well because they lacked range, and hence flexibility. The A332, 233t A333, and 767-300ER sold much better than their shorter-ranged siblings, showing that a small loss in efficiency in exchange for flexibility is worthwhile. The 767-400ER also sold poorly against the A332 despite having a slightly better CASM, again due to range flexibility.
2. This model focuses on an all-Y setup for seats. Many carriers have close to half their cabin length taken up by premium classes, meaning the effect of the efficient 9Y would be diminished. If a carrier wants to put in a 1-2-1 business class, would an A330 and a 787 have about the same layout? If so, the 787's forward section would be "too wide," and hence be wasted space and weight. Could you get a comfortable 2-4-2 PY in a 787, or would you have to go down to a 2-3-2 for that?
 
morrisond
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Re: Cabin configurations, fuselage weight model

Tue Feb 16, 2021 1:43 am

flipdewaf wrote:
I have done a slightly updated model. I have put in it fuselage dimensions from existing rather than just using seat width + aisle width as a predictor. They are modeled now as ellipses as opposed to circles and to keep it even slightly manageable I have kept the axis for the second moment of are about the centre of the ellipse (its probably slightly lower?) I have stopped the fuselages when they get to a fineness ratio of 14 or if they go over 80m.

Image

I have done a quick correlative study on the availability of space in the tail and the cabin vs fuselage length came to : Fuselage length = 7.6480704 + 1.0906144*Length of cabin (m) I have not yet implemented that in to this model yet. The otehr way of implementing could be that it is close to 2.4 fuselage widths of fuselage beyond the length of the cabin in widebodies and about 2.7 in narrowbodies. the current model has it at 5X for all.

Fred


Hi Fred,

So at something like 216 seats (A322 32" Y seat Capacity assuming two extra rows I think) - where is the A320 at in Total Length and where is the MOM?

The spreadsheet is a great effort but it seems really sensitive to the shape. What happens to MOM with a change to 170"x184" (or even just set it as round at about 177x177) which is only a 2" difference but it may give you an additional clue to what is happening with the model.
 
RJMAZ
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Re: Cabin configurations, fuselage weight model

Tue Feb 16, 2021 1:56 am

flipdewaf wrote:
Image

I took the numbers of the autocad model I made of your suggested aircraft about 1 year ago. 5.098m circular.

Excellent. These are the numbers I expected and confirms my analysis. A tight 8ab with LD2 containers is an excellent cross section for the 797 based on the seat numbers we have been given. This is 92% of the diameter of the A330 cross section. It is the lightest cross section for aircraft that has 25 to 50% more seats than the A321. This also works out to be 60 to 80% of the seats of a max density 787-8. Perfectly in the middle of the MOM space.

Cabin area
A321: 127m2
797 plus 25%: 159m2
797 plus 50%: 190m2
787-8: 232m2
787-9: 265m2

The 767-200 and 767-300 are 160m2 and 190m2 cabin area respectively. So the two 797 models are effectively a row or so shorter than the 767 200 and 300 but with a cabin a few inches wider to squeeze in an 8th seat. This is still well under the 787-8 size.

7ab in the 767 is by far the most comfortable cabin on the market. I would say it is too wide for 7ab by today's standards. But 8ab in the 767 is also the tightest and least comfortable cabin on the market and is only used by one charter airline. If the 767 had 5inch of extra cabin width then its 8ab cabin is now equal to 9ab in the A330 in terms of comfort. This comfort level seems to be acceptable for low cost carriers. I then propose 6inch of extra cabin width over the current 767 so it is ever so slightly more comfortable than 9ab in the A330. As the 797 will be doing lots of shorter routes I think this comfort level would be acceptable by most main airlines.

2-4-2 is also much more comfortable than 3-3-3 if the same seats are used. On paper a 6inch wider 767 should have worse comfort than 9ab in the 787. I think 17inch seats in 2-4-2 should provide a similar comfort level to 17.5inch seats in 3-3-3.

Can Boeing get 6inch of extra cabin width out of the 767 cross section? That is making the cabin walls half as thick which doesn't seem possible. The 777X gained 3inchs but I do not think this would allow 8ab to fit in the 767 with acceptable comfort. This would save a lot in development cost. Effectively Boeing just needs to put a higher aspect ratio carbon wing on the existing 767 with the same lift/drag but with lower weight. Forget the overweight, derated and half a generation old 747-8 engines. Put a LEAP engine scaled to the exact power required so there is no easy performance on the table.

I think the 767-400 freighter and 767NEO rumours could actually be the same aircraft as this mystery 797. Boeing could have planned all along to do the 767X
 
morrisond
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Re: Cabin configurations, fuselage weight model

Tue Feb 16, 2021 3:49 am

RJMAZ wrote:
flipdewaf wrote:
Image

I took the numbers of the autocad model I made of your suggested aircraft about 1 year ago. 5.098m circular.

Excellent. These are the numbers I expected and confirms my analysis. A tight 8ab with LD2 containers is an excellent cross section for the 797 based on the seat numbers we have been given. This is 92% of the diameter of the A330 cross section. It is the lightest cross section for aircraft that has 25 to 50% more seats than the A321. This also works out to be 60 to 80% of the seats of a max density 787-8. Perfectly in the middle of the MOM space.

Cabin area
A321: 127m2
797 plus 25%: 159m2
797 plus 50%: 190m2
787-8: 232m2
787-9: 265m2

The 767-200 and 767-300 are 160m2 and 190m2 cabin area respectively. So the two 797 models are effectively a row or so shorter than the 767 200 and 300 but with a cabin a few inches wider to squeeze in an 8th seat. This is still well under the 787-8 size.

7ab in the 767 is by far the most comfortable cabin on the market. I would say it is too wide for 7ab by today's standards. But 8ab in the 767 is also the tightest and least comfortable cabin on the market and is only used by one charter airline. If the 767 had 5inch of extra cabin width then its 8ab cabin is now equal to 9ab in the A330 in terms of comfort. This comfort level seems to be acceptable for low cost carriers. I then propose 6inch of extra cabin width over the current 767 so it is ever so slightly more comfortable than 9ab in the A330. As the 797 will be doing lots of shorter routes I think this comfort level would be acceptable by most main airlines.

2-4-2 is also much more comfortable than 3-3-3 if the same seats are used. On paper a 6inch wider 767 should have worse comfort than 9ab in the 787. I think 17inch seats in 2-4-2 should provide a similar comfort level to 17.5inch seats in 3-3-3.

Can Boeing get 6inch of extra cabin width out of the 767 cross section? That is making the cabin walls half as thick which doesn't seem possible. The 777X gained 3inchs but I do not think this would allow 8ab to fit in the 767 with acceptable comfort. This would save a lot in development cost. Effectively Boeing just needs to put a higher aspect ratio carbon wing on the existing 767 with the same lift/drag but with lower weight. Forget the overweight, derated and half a generation old 747-8 engines. Put a LEAP engine scaled to the exact power required so there is no easy performance on the table.

I think the 767-400 freighter and 767NEO rumours could actually be the same aircraft as this mystery 797. Boeing could have planned all along to do the 767X


Except Boeing seems to have a new plan with NMA-5 at about anticipated 322 capacity of 321 plus 2 rows. A lot smaller than the old NMA-6/7. The rumour is Boeing is basically targeting replacing 752/753. Look at the AvWeek article.

https://aviationweek.com/air-transport/ ... titor-plan
 
RJMAZ
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Re: Cabin configurations, fuselage weight model

Tue Feb 16, 2021 6:19 am

morrisond wrote:
The spreadsheet is a great effort but it seems really sensitive to the shape. What happens to MOM with a change to 170"x184" (or even just set it as round at about 177x177) which is only a 2" difference but it may give you an additional clue to what is happening with the model.

His model is determining fuselage weight and accurately takes into account the shape. A perfectly circular fuselage 180" in diameter will weigh less than a reduced height fuselage that is the same 180" width but only 160" high. The loading of the fuselage tube is primarily vertical.

The reduced height cross section would have less frontal area and less drag from the fuselage tube but the increased weight of the fuselage will cause more lift and drag from the wings.

Flipdewaf might be able to give his opinion. Will a reduced height fuselage actually have less drag? Does the drag saved from the fuselage exceed the extra drag on the wings?

My opinion is there is no total drag saving from reduced height. At best the drag is equal. So it is better to just have a circular fuselage and gain free cargo volume without any drag penalty.
 
flipdewaf
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Re: Cabin configurations, fuselage weight model

Tue Feb 16, 2021 12:43 pm

RJMAZ wrote:
Cabin area
A321: 127m2
797 plus 25%: 159m2
797 plus 50%: 190m2
787-8: 232m2
787-9: 265m2


be careful though because 'useful' cabin area is different, the 2-4-2 is about 20% aisle and the 3-3 is about 14% aisle. If we say that aisle widths and seat width is about the same (because that makes maths easier) then the 127m^2 A321 is about 109m^2 of seat space and the 797+25% is about 127m^2 which is about 17% more seating space.

morrisond wrote:
The spreadsheet is a great effort but it seems really sensitive to the shape.
Yes, it is quite sensitive to shape but so are real aircraft. You want to build them tall if possible, I have put the A380 in to this model and it is and that ugly fuselage is an absolute structural dream (unfortunately the beautiful wings were an aerodynamics nightmare).

RJMAZ wrote:
His model is determining fuselage weight and accurately takes into account the shape. A perfectly circular fuselage 180" in diameter will weigh less than a reduced height fuselage that is the same 180" width but only 160" high. The loading of the fuselage tube is primarily vertical.
to be honest I have no way of knowing the absolute accuracy of the model (no suitable reference) and it clearly leaves a lot of things out. Id say what it does do is demonstrate the relative performance between configurations for comparative purposes.

Fred
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morrisond
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Re: Cabin configurations, fuselage weight model

Tue Feb 16, 2021 1:59 pm

RJMAZ wrote:
morrisond wrote:
The spreadsheet is a great effort but it seems really sensitive to the shape. What happens to MOM with a change to 170"x184" (or even just set it as round at about 177x177) which is only a 2" difference but it may give you an additional clue to what is happening with the model.

His model is determining fuselage weight and accurately takes into account the shape. A perfectly circular fuselage 180" in diameter will weigh less than a reduced height fuselage that is the same 180" width but only 160" high. The loading of the fuselage tube is primarily vertical.

The reduced height cross section would have less frontal area and less drag from the fuselage tube but the increased weight of the fuselage will cause more lift and drag from the wings.

Flipdewaf might be able to give his opinion. Will a reduced height fuselage actually have less drag? Does the drag saved from the fuselage exceed the extra drag on the wings?

My opinion is there is no total drag saving from reduced height. At best the drag is equal. So it is better to just have a circular fuselage and gain free cargo volume without any drag penalty.


Luckily then Boeing isn't looking at pure elipses. No spreadsheet - however good it is will have a very easy time dealing with some of the more complex shapes that are rumoured. Plus we are talking about comparing it to an Narrowbody like the A320 at 163". I'm suggesting the NMA is somewhere around 168" - Leeham has it at 170" so they do have the advantage of extra height over a narrow body.

If round was the right answer - I highly doubt we would be hearing all the rumours about these non-standard cross sections.

I'm sure Airbus would be quite capable of cranking out something similar. 2-4-2 with LD2's will have a very hard time competing with a rewinged A322 at similar capacity.
 
morrisond
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Re: Cabin configurations, fuselage weight model

Tue Feb 16, 2021 2:05 pm

flipdewaf wrote:
RJMAZ wrote:
Cabin area
A321: 127m2
797 plus 25%: 159m2
797 plus 50%: 190m2
787-8: 232m2
787-9: 265m2


be careful though because 'useful' cabin area is different, the 2-4-2 is about 20% aisle and the 3-3 is about 14% aisle. If we say that aisle widths and seat width is about the same (because that makes maths easier) then the 127m^2 A321 is about 109m^2 of seat space and the 797+25% is about 127m^2 which is about 17% more seating space.

morrisond wrote:
The spreadsheet is a great effort but it seems really sensitive to the shape.
Yes, it is quite sensitive to shape but so are real aircraft. You want to build them tall if possible, I have put the A380 in to this model and it is and that ugly fuselage is an absolute structural dream (unfortunately the beautiful wings were an aerodynamics nightmare).

RJMAZ wrote:
His model is determining fuselage weight and accurately takes into account the shape. A perfectly circular fuselage 180" in diameter will weigh less than a reduced height fuselage that is the same 180" width but only 160" high. The loading of the fuselage tube is primarily vertical.
to be honest I have no way of knowing the absolute accuracy of the model (no suitable reference) and it clearly leaves a lot of things out. Id say what it does do is demonstrate the relative performance between configurations for comparative purposes.

Fred


Can you put a round cross section of a 2x3x2 at something like 177" in just for reference purposes? Adjust the the cabin length shorter by about 20% (for a 2 class cabin vs 3x3) and use nose and tail of about the same length as A321 or not that much longer?
 
flipdewaf
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Re: Cabin configurations, fuselage weight model

Tue Feb 16, 2021 2:27 pm

morrisond wrote:
flipdewaf wrote:
RJMAZ wrote:
Cabin area
A321: 127m2
797 plus 25%: 159m2
797 plus 50%: 190m2
787-8: 232m2
787-9: 265m2


be careful though because 'useful' cabin area is different, the 2-4-2 is about 20% aisle and the 3-3 is about 14% aisle. If we say that aisle widths and seat width is about the same (because that makes maths easier) then the 127m^2 A321 is about 109m^2 of seat space and the 797+25% is about 127m^2 which is about 17% more seating space.

morrisond wrote:
The spreadsheet is a great effort but it seems really sensitive to the shape.
Yes, it is quite sensitive to shape but so are real aircraft. You want to build them tall if possible, I have put the A380 in to this model and it is and that ugly fuselage is an absolute structural dream (unfortunately the beautiful wings were an aerodynamics nightmare).

RJMAZ wrote:
His model is determining fuselage weight and accurately takes into account the shape. A perfectly circular fuselage 180" in diameter will weigh less than a reduced height fuselage that is the same 180" width but only 160" high. The loading of the fuselage tube is primarily vertical.
to be honest I have no way of knowing the absolute accuracy of the model (no suitable reference) and it clearly leaves a lot of things out. Id say what it does do is demonstrate the relative performance between configurations for comparative purposes.

Fred


Can you put a round cross section of a 2x3x2 at something like 177" in just for reference purposes? Adjust the the cabin length shorter by about 20% (for a 2 class cabin vs 3x3) and use nose and tail of about the same length as A321 or not that much longer?

1. You ain’t fitting 7 abreast in that.
2. 14% more seating area across but yet 20% shorter?
3. Why would the nose and tail of a bigger plane be the same length as the smaller one?

Fred


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morrisond
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Re: Cabin configurations, fuselage weight model

Tue Feb 16, 2021 4:17 pm

flipdewaf wrote:
morrisond wrote:
flipdewaf wrote:
be careful though because 'useful' cabin area is different, the 2-4-2 is about 20% aisle and the 3-3 is about 14% aisle. If we say that aisle widths and seat width is about the same (because that makes maths easier) then the 127m^2 A321 is about 109m^2 of seat space and the 797+25% is about 127m^2 which is about 17% more seating space.

Yes, it is quite sensitive to shape but so are real aircraft. You want to build them tall if possible, I have put the A380 in to this model and it is and that ugly fuselage is an absolute structural dream (unfortunately the beautiful wings were an aerodynamics nightmare).

to be honest I have no way of knowing the absolute accuracy of the model (no suitable reference) and it clearly leaves a lot of things out. Id say what it does do is demonstrate the relative performance between configurations for comparative purposes.

Fred


Can you put a round cross section of a 2x3x2 at something like 177" in just for reference purposes? Adjust the the cabin length shorter by about 20% (for a 2 class cabin vs 3x3) and use nose and tail of about the same length as A321 or not that much longer?

1. You ain’t fitting 7 abreast in that.
2. 14% more seating area across but yet 20% shorter?
3. Why would the nose and tail of a bigger plane be the same length as the smaller one?

Fred


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1. I understand that you can't put 2x3x2 in it. I was just suggesting it as basically the same circumference as an 168x186" Elipse ( and I think they might be able to pare that down to about 183" assuming same seats/aisle width as 777X and 1" thinner Walls than 777X) - and see what your model pops out so at least we can understand how something of that cross section would do. Your model might have an easier time with round cross sections.

2. Last time I checked 6W to 7W is 16.7% more seating across in Y and it could be 50% more in the front in 2x2x2 or 1x1x1 - which is how you get about 20% shorter in the cabin. It's wider - but the reduction in Cabin length saves you more in Volume/Skin area due to the shape.

3. That 2x3x2 would actually have about 9% less skin and 2% less internal volume - it is not larger. It will be stubbier - but you also have that extra width in the ends and ignoring aero you could technically be shorter if you want the equivalent space for Cockpit/Lavs galleys.
 
flipdewaf
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Cabin configurations, fuselage weight model

Tue Feb 16, 2021 7:17 pm

morrisond wrote:
flipdewaf wrote:
morrisond wrote:

Can you put a round cross section of a 2x3x2 at something like 177" in just for reference purposes? Adjust the the cabin length shorter by about 20% (for a 2 class cabin vs 3x3) and use nose and tail of about the same length as A321 or not that much longer?

1. You ain’t fitting 7 abreast in that.
2. 14% more seating area across but yet 20% shorter?
3. Why would the nose and tail of a bigger plane be the same length as the smaller one?

Fred


Sent from my iPad using Tapatalk


1. I understand that you can't put 2x3x2 in it. I was just suggesting it as basically the same circumference as an 168x186" Elipse ( and I think they might be able to pare that down to about 183" assuming same seats/aisle width as 777X and 1" thinner Walls than 777X) - and see what your model pops out so at least we can understand how something of that cross section would do. Your model might have an easier time with round cross sections.

2. Last time I checked 6W to 7W is 16.7% more seating across in Y and it could be 50% more in the front in 2x2x2 or 1x1x1 - which is how you get about 20% shorter in the cabin. It's wider - but the reduction in Cabin length saves you more in Volume/Skin area due to the shape.

3. That 2x3x2 would actually have about 9% less skin and 2% less internal volume - it is not larger. It will be stubbier - but you also have that extra width in the ends and ignoring aero you could technically be shorter if you want the equivalent space for Cockpit/Lavs galleys.

The model is fine with the ellipse, the weight is down to the choice of configuration.

I can show any plane to do anything in my models if I assume it’s weight based on one configuration, it’s aero on another and capacity on yet another. It’s just not helpful.

The problem with the wide ovary ostrowers child configuration is It’s heavy, The horse is dead, stop flogging it.

We call it ugly baby syndrome where I work, people don’t let their ideas go and through emotional attachment and experience cognitive dissonance.

Fred




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morrisond
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Re: Cabin configurations, fuselage weight model

Tue Feb 16, 2021 8:05 pm

flipdewaf wrote:
morrisond wrote:
flipdewaf wrote:
1. You ain’t fitting 7 abreast in that.
2. 14% more seating area across but yet 20% shorter?
3. Why would the nose and tail of a bigger plane be the same length as the smaller one?

Fred


Sent from my iPad using Tapatalk


1. I understand that you can't put 2x3x2 in it. I was just suggesting it as basically the same circumference as an 168x186" Elipse ( and I think they might be able to pare that down to about 183" assuming same seats/aisle width as 777X and 1" thinner Walls than 777X) - and see what your model pops out so at least we can understand how something of that cross section would do. Your model might have an easier time with round cross sections.

2. Last time I checked 6W to 7W is 16.7% more seating across in Y and it could be 50% more in the front in 2x2x2 or 1x1x1 - which is how you get about 20% shorter in the cabin. It's wider - but the reduction in Cabin length saves you more in Volume/Skin area due to the shape.

3. That 2x3x2 would actually have about 9% less skin and 2% less internal volume - it is not larger. It will be stubbier - but you also have that extra width in the ends and ignoring aero you could technically be shorter if you want the equivalent space for Cockpit/Lavs galleys.

The model is fine with the ellipse, the weight is down to the choice of configuration.

I can show any plane to do anything in my models if I assume it’s weight based on one configuration, it’s aero on another and capacity on yet another. It’s just not helpful.

The problem with the wide ovary ostrowers child configuration is It’s heavy, The horse is dead, stop flogging it.

We call it ugly baby syndrome where I work, people don’t let their ideas go and through emotional attachment and experience cognitive dissonance.

Fred




Sent from my iPad using Tapatalk


And faced with data (20% less cabin length in 2 class, 9% less skin area and 2% less Volume) - what you are doing is called?

Answer one simple question - at A322 rumoured Capacity (A321+ 2 Rows) an A322 would seat about 216 in Y at 32" pitch, or about 24 up front (2x2 by 6 rows at about 38-39" pitch and about 174 in the back - 198 Combined) and be about 151' long. - What length is your MOM?
 
RJMAZ
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Re: Cabin configurations, fuselage weight model

Tue Feb 16, 2021 8:59 pm

morrisond wrote:
Answer one simple question - at A322 rumoured Capacity (A321+ 2 Rows) an A322 would seat about 216 in Y at 32" pitch, or about 24 up front (2x2 by 6 rows at about 38-39" pitch and about 174 in the back - 198 Combined) and be about 151' long. - What length is your MOM?

The rumoured A322 has less than 10% additional seats. At that seat number 6ab would be the only option. So any Boeing MOM at that seat capacity would have the same cabin width and length as the A322.

It is only once you get near 757-300 length does it make sense to consider twin aisle. All of the Boeing MOM seat numbers have been more than 25% higher than the A321 capacity. The smaller NMA-6 2 class seating capacity previously provided by Boeing was the same as the 2 class capacity of the 8AB A310 and even slightly higher than the 7ab 767-200. All of the previous analysis was done around this larger capacity.
 
flipdewaf
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Re: Cabin configurations, fuselage weight model

Tue Feb 16, 2021 9:44 pm

morrisond wrote:
flipdewaf wrote:
morrisond wrote:

1. I understand that you can't put 2x3x2 in it. I was just suggesting it as basically the same circumference as an 168x186" Elipse ( and I think they might be able to pare that down to about 183" assuming same seats/aisle width as 777X and 1" thinner Walls than 777X) - and see what your model pops out so at least we can understand how something of that cross section would do. Your model might have an easier time with round cross sections.

2. Last time I checked 6W to 7W is 16.7% more seating across in Y and it could be 50% more in the front in 2x2x2 or 1x1x1 - which is how you get about 20% shorter in the cabin. It's wider - but the reduction in Cabin length saves you more in Volume/Skin area due to the shape.

3. That 2x3x2 would actually have about 9% less skin and 2% less internal volume - it is not larger. It will be stubbier - but you also have that extra width in the ends and ignoring aero you could technically be shorter if you want the equivalent space for Cockpit/Lavs galleys.

The model is fine with the ellipse, the weight is down to the choice of configuration.

I can show any plane to do anything in my models if I assume it’s weight based on one configuration, it’s aero on another and capacity on yet another. It’s just not helpful.

The problem with the wide ovary ostrowers child configuration is It’s heavy, The horse is dead, stop flogging it.

We call it ugly baby syndrome where I work, people don’t let their ideas go and through emotional attachment and experience cognitive dissonance.

Fred




Sent from my iPad using Tapatalk


And faced with data (20% less cabin length in 2 class, 9% less skin area and 2% less Volume) - what you are doing is called?

Answer one simple question - at A322 rumoured Capacity (A321+ 2 Rows) an A322 would seat about 216 in Y at 32" pitch, or about 24 up front (2x2 by 6 rows at about 38-39" pitch and about 174 in the back - 198 Combined) and be about 151' long. - What length is your MOM?


Image

The x axis is pax number so directly comparable
The image attached shows the line of 216 so you can compare.

I had to dig in to the workings as the direct fuselage length was not immediately available but the A32X scale fuselage was 45m the mom was 43m.

Fred


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morrisond
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Re: Cabin configurations, fuselage weight model

Tue Feb 16, 2021 10:31 pm

Thanks Fred - that makes a lot more sense - not much more than the delta between A320/737.

Did something happen to the 2-4-2 line?
 
morrisond
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Re: Cabin configurations, fuselage weight model

Tue Feb 16, 2021 10:41 pm

RJMAZ wrote:
morrisond wrote:
Answer one simple question - at A322 rumoured Capacity (A321+ 2 Rows) an A322 would seat about 216 in Y at 32" pitch, or about 24 up front (2x2 by 6 rows at about 38-39" pitch and about 174 in the back - 198 Combined) and be about 151' long. - What length is your MOM?

The rumoured A322 has less than 10% additional seats. At that seat number 6ab would be the only option. So any Boeing MOM at that seat capacity would have the same cabin width and length as the A322.

It is only once you get near 757-300 length does it make sense to consider twin aisle. All of the Boeing MOM seat numbers have been more than 25% higher than the A321 capacity. The smaller NMA-6 2 class seating capacity previously provided by Boeing was the same as the 2 class capacity of the 8AB A310 and even slightly higher than the 7ab 767-200. All of the previous analysis was done around this larger capacity.


It would not be 6AB if you ever wanted to stretch it beyond A322 - and that is assuming that Boeing hasn't found something (and Airbus has really smart people as well - they would be able to do the same thing) - that makes the weight penalty not so bad.

Boeing is talking about NMA as 757-200/300 capacity according to the latest reports.

I still think the whole thing is a lot smaller than both of you. My 2-3-2 would have about 6M less of cabin length (in a 2 class) - but Fred's model is assuming it's only 2m overall length shorter.

An A321 is about 30M of Cabin and 14 M of Nose and Tail - the Model has my MOM at about (assuming all Y) - at about 25M of cabin and 17M of nose and tail. Even if you stick all that on the tail you have the extra width in the ends which means seats can creep the ends a bit so the cabin would be shorter.

The way it is right now doesn't seem optimal and is making the 2-3-2 heavier than it needs to be. Who would ever build something like that?
 
flipdewaf
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Re: Cabin configurations, fuselage weight model

Tue Feb 16, 2021 10:48 pm

morrisond wrote:
Thanks Fred - that makes a lot more sense - not much more than the delta between A320/737.

Did something happen to the 2-4-2 line?

Yep, I was adding in figures for c-series/A220 and I just hadn’t changed the label yet.

Fred


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flipdewaf
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Re: Cabin configurations, fuselage weight model

Tue Feb 16, 2021 11:27 pm

morrisond wrote:
RJMAZ wrote:
morrisond wrote:
Answer one simple question - at A322 rumoured Capacity (A321+ 2 Rows) an A322 would seat about 216 in Y at 32" pitch, or about 24 up front (2x2 by 6 rows at about 38-39" pitch and about 174 in the back - 198 Combined) and be about 151' long. - What length is your MOM?

The rumoured A322 has less than 10% additional seats. At that seat number 6ab would be the only option. So any Boeing MOM at that seat capacity would have the same cabin width and length as the A322.

It is only once you get near 757-300 length does it make sense to consider twin aisle. All of the Boeing MOM seat numbers have been more than 25% higher than the A321 capacity. The smaller NMA-6 2 class seating capacity previously provided by Boeing was the same as the 2 class capacity of the 8AB A310 and even slightly higher than the 7ab 767-200. All of the previous analysis was done around this larger capacity.


It would not be 6AB if you ever wanted to stretch it beyond A322 - and that is assuming that Boeing hasn't found something (and Airbus has really smart people as well - they would be able to do the same thing) - that makes the weight penalty not so bad.

Boeing is talking about NMA as 757-200/300 capacity according to the latest reports.

I still think the whole thing is a lot smaller than both of you. My 2-3-2 would have about 6M less of cabin length (in a 2 class) - but Fred's model is assuming it's only 2m overall length shorter.

An A321 is about 30M of Cabin and 14 M of Nose and Tail - the Model has my MOM at about (assuming all Y) - at about 25M of cabin and 17M of nose and tail. Even if you stick all that on the tail you have the extra width in the ends which means seats can creep the ends a bit so the cabin would be shorter.

The way it is right now doesn't seem optimal and is making the 2-3-2 heavier than it needs to be. Who would ever build something like that?


When the capacity is set as 245 and 290 with 32” pitch the overall length of the 767 in my model are within 1 meter of the 762 and 763 respectively.



Fred


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Re: Cabin configurations, fuselage weight model

Tue Feb 16, 2021 11:47 pm

morrisond wrote:
It would not be 6AB if you ever wanted to stretch it beyond A322

Sounds like the A380. Building an inferior cross section in preparation for a stretch.

7AB does not pass any current engineering or economic analysis. One reason 7AB was used in the 767 was because the comfort standards for economy passengers were much higher 40 years ago. A second reason is there was no engine big enough to make a 6000nm 8AB twin engine aircraft. 10 years later when the A330-200 arrived the demand was huge.

Both of these reasons for 7AB no longer apply. Any technology used on a 7AB aircraft could be used on an 8AB and gain 5+% efficiency per seat. If the aircraft needs to be smaller than the 8AB A310 a designer would go straight to a 6AB 757-300 fuselage and skip 7AB entirely.

It is the minimum aisle size that kills 7AB. You need two 16inch aisles or 32inch in total. A 6AB could have a 20inch aisle. The 7AB gains 16.6% more seats over 6AB but needs 60% more aisle. 8AB gains 33% more seats over 6AB for that same 60% aisle increase. Boarding times are not an issue.
 
morrisond
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Re: Cabin configurations, fuselage weight model

Wed Feb 17, 2021 1:50 am

RJMAZ wrote:
morrisond wrote:
It would not be 6AB if you ever wanted to stretch it beyond A322

Sounds like the A380. Building an inferior cross section in preparation for a stretch.

7AB does not pass any current engineering or economic analysis. One reason 7AB was used in the 767 was because the comfort standards for economy passengers were much higher 40 years ago. A second reason is there was no engine big enough to make a 6000nm 8AB twin engine aircraft. 10 years later when the A330-200 arrived the demand was huge.

Both of these reasons for 7AB no longer apply. Any technology used on a 7AB aircraft could be used on an 8AB and gain 5+% efficiency per seat. If the aircraft needs to be smaller than the 8AB A310 a designer would go straight to a 6AB 757-300 fuselage and skip 7AB entirely.

It is the minimum aisle size that kills 7AB. You need two 16inch aisles or 32inch in total. A 6AB could have a 20inch aisle. The 7AB gains 16.6% more seats over 6AB but needs 60% more aisle. 8AB gains 33% more seats over 6AB for that same 60% aisle increase. Boarding times are not an issue.


You better educate Boeing then that a 7AB Double Circle doesn't work. If you do a fair analysis and stop thinking of the NMA as a Widebody and start thinking about as a bulged out SA and stop handicapping it with ridiculously long ends. How else do you think Boeing is going to get SA economics with Widebody comfort?

We are not talking about an Elipse. Your argument for 8W doesn't make any sense as then you might as well stick with the very efficient 787 9W and use LD3's.

Actually when you adjust for similar capacity 2x17 (only 1" less than 777X and fine for shorter missions) vs 1X19 is only 40% more and equivalent to a 1x27".
Last edited by morrisond on Wed Feb 17, 2021 2:09 am, edited 1 time in total.
 
morrisond
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Re: Cabin configurations, fuselage weight model

Wed Feb 17, 2021 2:06 am

flipdewaf wrote:
morrisond wrote:
RJMAZ wrote:
The rumoured A322 has less than 10% additional seats. At that seat number 6ab would be the only option. So any Boeing MOM at that seat capacity would have the same cabin width and length as the A322.

It is only once you get near 757-300 length does it make sense to consider twin aisle. All of the Boeing MOM seat numbers have been more than 25% higher than the A321 capacity. The smaller NMA-6 2 class seating capacity previously provided by Boeing was the same as the 2 class capacity of the 8AB A310 and even slightly higher than the 7ab 767-200. All of the previous analysis was done around this larger capacity.


It would not be 6AB if you ever wanted to stretch it beyond A322 - and that is assuming that Boeing hasn't found something (and Airbus has really smart people as well - they would be able to do the same thing) - that makes the weight penalty not so bad.

Boeing is talking about NMA as 757-200/300 capacity according to the latest reports.

I still think the whole thing is a lot smaller than both of you. My 2-3-2 would have about 6M less of cabin length (in a 2 class) - but Fred's model is assuming it's only 2m overall length shorter.

An A321 is about 30M of Cabin and 14 M of Nose and Tail - the Model has my MOM at about (assuming all Y) - at about 25M of cabin and 17M of nose and tail. Even if you stick all that on the tail you have the extra width in the ends which means seats can creep the ends a bit so the cabin would be shorter.

The way it is right now doesn't seem optimal and is making the 2-3-2 heavier than it needs to be. Who would ever build something like that?


When the capacity is set as 245 and 290 with 32” pitch the overall length of the 767 in my model are within 1 meter of the 762 and 763 respectively.



Fred


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If the ends are 17M vs 12M on the A321 then you could use that extra 5M = 16.4' for something like a 5' longer nose section and 5' more in the rear taper before the bulkhead with a 6' longer tail (before the rear bulkhead) which seems reasonable.

BTW the 250T 787 looks like it is only about 20M for the ends.

In that extra 5 feet up front you could get another set of 1x1x1 and call it two sets of 2x2x2 in the back - meaning the barrel could be correspondingly shorter at the cost of 2 seats due to the rear taper (but you would not really lose those two as you still have that extra space in the wider ends vs SA for Galleys/Lavs/Cockpits) that could be used.

That would put the NMA at 39M vs 44M for the A320 and probably put the weight per passenger delta to less than the difference between 320 and 737.

On the good side with all that extra length in the ends for the NMA - Aero should be pretty good!

I kind of think of the NMA as a SA with Conformal Fuel tanks - which from Reports only impose a very minor drag penalty.
 
flipdewaf
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Cabin configurations, fuselage weight model

Wed Feb 17, 2021 7:39 am

The things you mention are all valid in terms of what you can use the tapering areas for but why can’t you do exactly the same for a narrow body? It’s simultaneously only a little bit wider so not too much of a hit to weight but yet soo much wider it’s a revolution in being able to put things in it.

The extra length on the model is not specifically for nose and tail, it basically is there to estimate the length of the fuselage compared to the number of rows * pitch. It represents all length not used for pax purposes (galleys, toilets, closets cockpits, non pressurised sections etc.) The fact that it does represent length for existing configurations leads me to believe it’s a fairly good estimate.

Conformal fuel tanks? I mean by all means start your own thread to flog that but I think that horse is dead on arrival.

Fred


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morrisond
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Re: Cabin configurations, fuselage weight model

Wed Feb 17, 2021 1:28 pm

Hi Fred - I was joking on the CFT thing - but from an aero standpoint it's not that far removed from that.

Sure you could do the same thing (stuff more seats in the taper part of the SA - if you put put the ends at the same proportion as the MOM - in this case the ends would be somewhere around 20% longer than MOM (as MOM cabin length is about 20% less) up around 21M - or longer than an 787. Using actual Math the SA would have a total length of 53.757M. However lets assume we are not going to do that.

Using the A322 length from your Model at about 45M (Close to real as the A321 is 45M long plus two rows = 46M) long the ends are about 36.4% of the Cabin length (12/33M). If you were to apply the same standard to an MOM at a Cabin length or approximately 20% less or 26.4M (and pretty close to your 43M - 17M = 26M) - you would get end lengths of about 9.6M or about 36M total length vs 43m as your model has it. Now of course 9.6M ends are ridiculously short.

However your model is using a ratio of 62.9% (17/43M) for the approximately only 30" wider MOM. That seems really extreme.

If you use the same Nose/end length as the A321 of 12M (which does give you extra space in the ends with the MOM) you get a MOM length of about 38M. That doesn't quite right either as you do need some more taper to account for the different cross section.

You are arbitrarily using width as the determining factor of nose and end lengths. You are comparing to what is out there already. The point is MOM is something new and can't be compared. It is not gaining as much cross section as a circle so the total taper does not need to be as great.

Instead of width how about you use Circumference? There is only about a 10% difference between the two. So the 12M A321 ends become 13.2M ends on the MOM - add that to 26 or 26.4 and you get 39.2-39.6M. Or adjust the 36.4% up by 10% to 40% and you get get end lengths of 10.5M (and give you about the same floor area as the 20% narrower SA) for a total length of about 37.1M. But that seems extreme as more taper would help aero

I think taking the A320 lengths and adding 10% on for the larger circumference makes more sense and puts the Ends length ratio at almost spot on 50% (13.2M/26.4M) vs 36.4% for the A321/322 or the 62.9% you are using for the MOM model. That seems more reasonable to me.

The other way to look at it is if it were a Vertical 183-186"H x 168"W Cross section - only a foot wider than A320 (7.7% more) - would it need ends 17M vs 12M?
 
morrisond
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Re: Cabin configurations, fuselage weight model

Fri Feb 19, 2021 1:28 am

The silence on this thread has me thinking that a 2x3x2 with 13.2M ends is pretty close to 3x3 at 216 seats and could be better above.
 
flipdewaf
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Cabin configurations, fuselage weight model

Fri Feb 19, 2021 1:29 am

morrisond wrote:
The silence on this thread has me thinking that a 2x3x2 with 13.2M ends is pretty close to 3x3 at 216 seats and could be better above.

Or my father in law is Ill and I’m having to look after the farm....


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LH707330
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Re: Cabin configurations, fuselage weight model

Fri Feb 19, 2021 3:50 am

morrisond wrote:
The silence on this thread has me thinking that a 2x3x2 with 13.2M ends is pretty close to 3x3 at 216 seats and could be better above.

...or that people are unwilling to continue engaging the 2-3-2 idea when most cited tech reasons that it could be better could also be applied to 3-3. Where's your spreadsheet, and what are all the assumptions going into it?

Fred's posted a model with some assumptions, has made some revisions, and has reached conclusions. When you post an even apples-to-apples model, we'll consider it.
 
morrisond
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Re: Cabin configurations, fuselage weight model

Fri Feb 19, 2021 1:38 pm

flipdewaf wrote:
morrisond wrote:
The silence on this thread has me thinking that a 2x3x2 with 13.2M ends is pretty close to 3x3 at 216 seats and could be better above.

Or my father in law is Ill and I’m having to look after the farm....


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I'm sorry to hear that Fred. I hope he gets better soon.
 
morrisond
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Re: Cabin configurations, fuselage weight model

Fri Feb 19, 2021 3:26 pm

LH707330 wrote:
morrisond wrote:
The silence on this thread has me thinking that a 2x3x2 with 13.2M ends is pretty close to 3x3 at 216 seats and could be better above.

...or that people are unwilling to continue engaging the 2-3-2 idea when most cited tech reasons that it could be better could also be applied to 3-3. Where's your spreadsheet, and what are all the assumptions going into it?

Fred's posted a model with some assumptions, has made some revisions, and has reached conclusions. When you post an even apples-to-apples model, we'll consider it.


Look in the other thread - a lot of data on 2-3-2 vs 3x3. A comparable capacity at about that 216 Y seats 32" seat pitch would have the 2-3-2 at about 9% less skin and 2% less internal volume and only a 10% greater circumference, and with a cabin 20% less in length than an A321/A322 - yet for some reason it needs ends that are 17M vs 12m for the narrow body. What aircraft designer would handicap their base design with a decision like that?

How is that Apples to Apples - that is Apples to Grapefruits.

But as Fred stated he is busy so maybe he hasn't had the time to look at it/consider it.

Do I think it will be as good as the A320 fuselage at that size(216 Seat Y seats)? Probably not as the structural weight per Cubic Volume will be higher due to the complex shape - but it may not be that different than the delta between A320 and 737 and the A320 seems to be fine with that handicap.

If it is 3x3 what I have come to the conclusion that the A320 is about the perfect size. It needs to be that width for LD3-45 - and if you want better boarding/deplaning - put 737 Seat sets in it - and have a 25" aisle. However you then have a me to product that doesn't have any differentiation in a market that could have a very strong 3rd competitor after this new design could possibly EIS (C919) that will most likely be priced to take market share even at a big loss. Anything larger than A320 is inefficient and I don't think you can make it smaller if you want it to hold an LD3-45.
 
Sokes
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Re: Cabin configurations, fuselage weight model

Sat Feb 20, 2021 10:57 am

morrisond wrote:
The silence on this thread has me thinking that a 2x3x2 with 13.2M ends is pretty close to 3x3 at 216 seats and could be better above.

What does 13,2M mean?
Why can't the world be a little bit more autistic?
 
SteinarN
Posts: 192
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Re: Cabin configurations, fuselage weight model

Sat Feb 20, 2021 11:44 am

Sokes wrote:
morrisond wrote:
The silence on this thread has me thinking that a 2x3x2 with 13.2M ends is pretty close to 3x3 at 216 seats and could be better above.

What does 13,2M mean?


I think he means that the distance from start of fuselage taper and to the very front and back end is 13,2 meters. So, say 30 meter fuselage, 13,2 meter tail and 13,2 meter front for a total length of 56,4 meters

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