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morrisond
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Re: Cabin configurations, fuselage weight model

Sat Feb 20, 2021 1:18 pm

SteinarN wrote:
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


That is the figure for both ends. The Cabin on the 2x3x2 in a 2 class configuration equivalent to a Theoretical A322 of about 45/46m would be about 26.4M and the front (Nose section from where it starts tapering just forward of the Cabin to the tip of the Radome) and rear section (just aft of the cabin where it starts tapering to the tip of the tail) would in combination be 13.2 M.

The A320/321 have ends that are 12M long. The 2x3x2 would have extra floor space in the ends as they are wider but we are ignoring that here. If the ends of the 2x3x2 were 17M they would have a ton of extra floor space meaning the Cabin could encroach even more into the the "Ends" (vs the 13.2M ends model) and the Cabin could be even shorter. This Short and stubby fuselage would have about 9% less skin area and about 2% less volume than the A322 - but probably needs slightly larger tail surfaces to account for the stubbiness. Not necessarily a longer tail. However you might chose to have a slightly longer tail on the base model as then your control surfaces could be smaller (and lighter) offsetting the weight increase from the extra length - which at 13.2 ends they would be longer than necessary - by a least 1.2M - probably closer to 2M. It would be a tradeoff between weight and drag. Or if you wanted to size it to take into account future models of different capacities where a longer or shorter tail may be more optimal you might choose something else. However this model is I believe assuming the perfect size ends and control surfaces everywhere along the curve.

So basically I am suggesting a length of somewhere around 39.4M total length for the 2x3x2 is more appropriate to compare it with an 45/46M A321/A322 but because it is being artificially handicapped in the model with way too long end lengths (total length in the model of 43M)which adds a ton of weight the model is probably calculating that it needs a bigger wing/gear/engines as well - further handicapping the 2x3x2.

It's a great Model - Fred has done some great work - but maybe some of the assumptions should be revisited. This 2x3x2 is not a wide body and it's not a Narrowbody it is somewhere in between.
 
flipdewaf
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Re: Cabin configurations, fuselage weight model

Sat Feb 20, 2021 2:53 pm

SteinarN wrote:
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

In the calculations I have done this figure would refer to the length calculated by the number of rows multiplied by the pitch in order to get the length of the aircraft. Whilst superficially it might appear to be the length of the tapered sections it isn’t in the model.

I am currently working on a suitable algorithm for estimating space available in the tapered section so that these can compared on a suitably comparable basis letting the numbers rather than extended verbiage do the talking.

I am currently at the stage of determining how to establish the longitudinal position of a give to shape that fits inside the ellipse of given size.

Fred


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LH707330
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Re: Cabin configurations, fuselage weight model

Sat Feb 20, 2021 8:24 pm

morrisond wrote:
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.

I missed the 17m vs 12m ends, thought those were adjusted in Fred's latest model. While I suspect that the area on the 2-3-2 might be less than the 3-3, the overall weight and form drag might not. Do you have a table of assumptions for those inputs to compare them?
 
morrisond
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Re: Cabin configurations, fuselage weight model

Sat Feb 20, 2021 8:40 pm

LH707330 wrote:
morrisond wrote:
LH707330 wrote:
...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.

I missed the 17m vs 12m ends, thought those were adjusted in Fred's latest model. While I suspect that the area on the 2-3-2 might be less than the 3-3, the overall weight and form drag might not. Do you have a table of assumptions for those inputs to compare them?


No I don't - Who knows on the weight.

The 2x3x2 also has 20% fewer frames, stringers and floor beams in the cabin due to the shorter cabin length at the same capacity. It should be fewer parts to assemble it - lowering production/labour costs.

Assuming it is built out of carbon - we have also read that at the strength needed for SA - Carbon skins are thicker than necessary to deal with things like ramp rash. With a 2x3x2 and its non standard shape that extra stiffness/strength could be used in lieu of heavier stronger frames/floorbeams, stringers and longerons that might be needed with an metal design. Plus there is about 9% less skin on the 2x3x2.

In the end the weight penalty may not be so big as people are assuming and maybe within the delta between the A320 and 737 Fuselages.

In the end it may not be quite as efficient as 3x3 when you take everything into account - by it could be close enough to offset the disadvantages and no worse than 320 over 737.
 
Sokes
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Re: Cabin configurations, fuselage weight model

Sat Feb 20, 2021 9:39 pm

morrisond wrote:
Carbon skins are thicker than necessary to deal with things like ramp rash. With a 2x3x2 and its non standard shape that extra stiffness/strength could be used in lieu of heavier stronger frames/floorbeams, stringers and longerons that might be needed with an metal design. Plus there is about 9% less skin on the 2x3x2.

Since Boeing sticks to Al for the B777X I doubt a 7 abreast plane would use a carbon fibre fuselage.

An A310 is 46,66m long, 8,3 x diameter.
The B767-200 is 48,51 m long, 9,6 x width, 9,0 x hight.
(B767 fuselage: 17 ft 9 in / 5.41 m height, 16 ft 6 in / 5.03 m width)
Why can't the world be a little bit more autistic?
 
IADFCO
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Re: Cabin configurations, fuselage weight model

Sun Feb 21, 2021 1:00 am

flipdewaf wrote:

[...]

I am currently working on a suitable algorithm for estimating space available in the tapered section so that these can compared on a suitably comparable basis letting the numbers rather than extended verbiage do the talking.

[...]



When you have a moment consider adding to the plots some points representative of actual existing aircraft. That would be helpful in validating the methodology.
 
morrisond
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Re: Cabin configurations, fuselage weight model

Sun Feb 21, 2021 1:36 pm

Sokes wrote:
morrisond wrote:
Carbon skins are thicker than necessary to deal with things like ramp rash. With a 2x3x2 and its non standard shape that extra stiffness/strength could be used in lieu of heavier stronger frames/floorbeams, stringers and longerons that might be needed with an metal design. Plus there is about 9% less skin on the 2x3x2.

Since Boeing sticks to Al for the B777X I doubt a 7 abreast plane would use a carbon fibre fuselage.

An A310 is 46,66m long, 8,3 x diameter.
The B767-200 is 48,51 m long, 9,6 x width, 9,0 x hight.
(B767 fuselage: 17 ft 9 in / 5.41 m height, 16 ft 6 in / 5.03 m width)


Boeing kept to AI on the 777X to be able to use the same production equipment and have it considered as a derivative. Changing the Fuselage material would have been considered a new type I think it is safe to definitively say.

I also think Fred's models - which I believe are assuming that AI is being used for the 2x3x2 is showing that AI would be quite heavy. Complex Carbon structures must be really hard to model requiring very sophisticated models and very powerful computers in order to get the weight to acceptable levels.

To save a lot of Grief (and work) - I would suggest that Fred just model Round cross sections using AI of equivalent circumference then we should be able to look at them and make an intuitive guess that if Boeing (or Airbus if they choose to do so) can keep the weight within x% of that AI Round model in a Carbon Ovalish design it could work at that capacity.

A 2-3-2 at 168"H ( 4.27M)x 185" W (4.7M) (18" aisles using 777X seat sets and assuming side walls 1" thinner than 777X) and 39.6 M long (13.2M ends) would be 9.27x Height and 8.42X width - somewhere around 8.9x averaged out.

It's not that far out and we know this would never be the shortest variant and possibly not a bad starting point, especially if it is a full clean sheet with 2020's full electric vs 1980's systems architecture and things like a more Aero nose than a probable rewinged A320/321 based competitor to offset that extra 50-100 lbs of fuselage form drag.

I would assume that a revamped A320 would have equivalent aero in terms of wings/tail and the engines would have similar TSFC - it's just whether or not the regulators would allow that to be certified as a derivative. Given what is happening with 777X which has been a similar development - I'm not sure they would.
 
flipdewaf
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Re: Cabin configurations, fuselage weight model

Mon Feb 22, 2021 11:41 am

morrisond wrote:
Sokes wrote:
morrisond wrote:
Carbon skins are thicker than necessary to deal with things like ramp rash. With a 2x3x2 and its non standard shape that extra stiffness/strength could be used in lieu of heavier stronger frames/floorbeams, stringers and longerons that might be needed with an metal design. Plus there is about 9% less skin on the 2x3x2.

Since Boeing sticks to Al for the B777X I doubt a 7 abreast plane would use a carbon fibre fuselage.

An A310 is 46,66m long, 8,3 x diameter.
The B767-200 is 48,51 m long, 9,6 x width, 9,0 x hight.
(B767 fuselage: 17 ft 9 in / 5.41 m height, 16 ft 6 in / 5.03 m width)


Boeing kept to AI on the 777X to be able to use the same production equipment and have it considered as a derivative. Changing the Fuselage material would have been considered a new type I think it is safe to definitively say.

I also think Fred's models - which I believe are assuming that AI is being used for the 2x3x2 is showing that AI would be quite heavy. Complex Carbon structures must be really hard to model requiring very sophisticated models and very powerful computers in order to get the weight to acceptable levels.

What they show is the inherent disadvantages and advantages of different cross sections for different pax capacities in terms of weight. What they absolutely don’t show is that Al is heavy. Carbon structures don’t need magic special computers but complex structures do (I believe you are referring to FEA). Al is chosen because of its more ubiquitous nature and that the reference properties are easier and more reliable to come by. The detailed design choices might be slightly different based on the materials but the drivers as shown in my models are absolutely the drivers for all materials. Computers don’t break physics, even if they are working on magic carbon.

Just out of interest, how much weight did the 787 or A350 save over their Al rivals (A330 &777) by using majority carbon structure?

morrisond wrote:
To save a lot of Grief (and work) - I would suggest that Fred just model Round cross sections using AI of equivalent circumference then we should be able to look at them and make an intuitive guess that if Boeing (or Airbus if they choose to do so) can keep the weight within x% of that AI Round model in a Carbon Ovalish design it could work at that capacity.

Instead of an intuitive guess, why don’t we use the model that is already working? The model is absolutely set up to use ellipses and whilst not an exact representation of the aircraft being mentioned it does provide a closer reflection of reality.

I find it strange however that you suddenly want to go back to modelling it as a cylinder even though that isn’t an issue for my model? I was under the understanding that the raison d'être for your ugly baby was the fact that it absolutely was not a circle however but now you are seeing that this is hampering it from a weight perspective you want to move away from that? To save grief? I do have to wonder who’s grief is going to be saved...

morrisond wrote:

A 2-3-2 at 168"H ( 4.27M)x 185" W (4.7M) (18" aisles using 777X seat sets and assuming side walls 1" thinner than 777X) and 39.6 M long (13.2M ends) would be 9.27x Height and 8.42X width - somewhere around 8.9x averaged out.



Don’t you worry, I am working on a way to suitably model the available space in the tail whereby the maths takes care of it.
morrisond wrote:

It's not that far out and we know this would never be the shortest variant and possibly not a bad starting point, especially if it is a full clean sheet with 2020's full electric vs 1980's systems architecture and things like a more Aero nose than a probable rewinged A320/321 based competitor to offset that extra 50-100 lbs of fuselage form drag.

Don’t worry, I’ll start an aero thread.
morrisond wrote:

I would assume that a revamped A320 would have equivalent aero in terms of wings/tail and the engines would have similar TSFC - it's just whether or not the regulators would allow that to be certified as a derivative. Given what is happening with 777X which has been a similar development - I'm not sure they would.

The theory behind use of the supplemental type certificate has not changed (unless you have evidence to the contrary) the delay in the 777X as far as I can tell is the result of the realisation of the FAA that their oversight into the process was not suitable and the due diligence was not adhered to suitably.


I have completed the addition of the length calculation utilising the available end space. The model determines at what scaled variant of the cross sectional ellipse a consistently sized shape (consistent across the whole model, between configurations (2m x 2m) will fit. This is then used to determine how far down the tapered cross section space could be used. The tail taper ratio (consistent across all configurations) can then be used to calculate the available area in the tail tapered section (Assuming a trapezoidal shape). The length of the fuselage required for seating is simply the number of seats divided by the number accross to get the number of Rows and then multiplied by the seat pitch
The area required for the ancillary items in the cabin (toilets, galleys, closets etc) are calculated at 0.2m^2 per pax. The available space in the tail is then removed from this figure to leave the remaining constant cross section space to be taken up by the ancillaries. The constant cross sectional ancillary area is then divided by the available width to get the length of the constant cross section required by the ancillaries. This length is then added to the seat Rows X pitch to get the length of the constant section. The constant cross section then has 4 x Ramanujan perimeter based equivalent width added (1.5 nose +2.5 tail).

This is the resulting chart using the above assumptions on length is below ( at 32" pitch)
Image

For reference at 206 seats the A32X cross section is at 43.4m and the Wide oval is at 40.7m

Fred
Image
 
morrisond
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Re: Cabin configurations, fuselage weight model

Mon Feb 22, 2021 1:22 pm

Hi Fred - That is a very civil response.

It seems like the A350 saved quite a bit of weight over the 777.

I was just suggesting to model Circle's vs Ovals to save you some work. That is all.

Your model is assuming a difference in length of 2.7M - I think it should be about 2x that - but that is close enough. One can look at how the graphs have evolved and figure out somewhere around 206-250 seats the lines would cross if you used my shorter idea and the delta over 200 seats is not much different than A320 vs 737.

It is not a show stopper.

Thank you for your work.
 
flipdewaf
Topic Author
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Re: Cabin configurations, fuselage weight model

Mon Feb 22, 2021 2:12 pm

morrisond wrote:
Hi Fred - That is a very civil response.

It seems like the A350 saved quite a bit of weight over the 777.

The A359 manages to save a whopping 3t OWE over the 772 in an airframe that has a 20t lower MTOW, slightly higher wingspan and slightly norrower fuselage. Its hardly the wonder material its made out to be from a weight perspective, useful? yes. A paradigm shift in aircraft weight. Not a chance.
morrisond wrote:

I was just suggesting to model Circle's vs Ovals to save you some work. That is all.

Once the model is there I just put the inputs in and press go.
morrisond wrote:

Your model is assuming a difference in length of 2.7M - I think it should be about 2x that

5.4m less?Based on what?

If you add up the area of the 185" wide cabin and use ALL of the tail in a 5.4 m shorter fuselage you still have 6m^2 less Total than if you used 1/2 the taper of the single aisle. AND you think you are going to put an extra aisle in it and then the pax are going to love it because its got 2 aisles?

Go and sit down with a pencil and paper and a ruler and draw the thing!

morrisond wrote:
- but that is close enough. One can look at how the graphs have evolved and figure out somewhere around 206-250 seats the lines would cross if you used my shorter idea and the delta over 200 seats is not much different than A320 vs 737.

These charts do not add the additional weight for the floor being in compression rather than tension.

Aside from that the charts represent the differences in fuselage and that would indeed have an impact on the complete aircraft and a comparable impact 'all things being equal', except that as the phrase goes, all things are not equal. The 737 is somewhat hampered by its low design and as such the benefits that the lower weight fuselage are not born out an an aircraft level, the additional propulsive efficiency gained by the larger engines of the A32XNEO are certainly beneficial to the point that the lower weight is nullified, the MAX the additional weight of having to integrate the larger engines has almost completely removed the weight advantage the the 737 had.

All that talk is rather fun comparing the existing models but the NMA/MOM/797 Ovular machine isn't only competing against the A32XNEO, it is also competing internally against the narrow body version of itself whereby the technology level is identical
morrisond wrote:

It is not a show stopper.
Indeed, it may well be heavier and cause more lift independent drag but at least its less comfortable to make up for it.

Fred
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morrisond
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Re: Cabin configurations, fuselage weight model

Mon Feb 22, 2021 6:53 pm

Huh - it seems like a double circle is not so hard from a pressurization standpoint after all. Here is a study on basically what Ostrower is saying it is - for the pressurized part - the difference being the NMA would not have the Bottom non-pressurized cargo comparment - NMA would incorporate that in the Floor Beams https://www.dlr.de/fa/en/Portaldata/17/ ... srw_08.pdf

And no Carbon is not a wonder material - but it is lighter and does have some advantages that can be taken advantage of in non-circular fuselage shapes. But yes a clean sheet 3x3 could take advantage of that.

On the 772 vs 359 - the 772ER is only capable of about 80% the range of the A359.

On the ends a 2x3x2 the passenger cabin would be at minimum 16.7% less long - using your own numbers and they seem to be what the ACAPs show on the A320 you have about an 31.4M Passenger section with I assume 12M ends.

The NMA passenger section would therefore be about 26.15M long - 12 M ends would have more floor space as they are wider - yet you seem to want to put 14.55M ends on it which would have even more floor space. That doesn't seem like a fair comparison. So 2.55M - but you are using a shorter length for the A322 now than you were before and that is why the numbers don't line up.
 
flipdewaf
Topic Author
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Cabin configurations, fuselage weight model

Mon Feb 22, 2021 9:12 pm

morrisond wrote:
Huh - it seems like a double circle is not so hard from a pressurization standpoint after all. Here is a study on basically what Ostrower is saying it is - for the pressurized part - the difference being the NMA would not have the Bottom non-pressurized cargo comparment - NMA would incorporate that in the Floor Beams https://www.dlr.de/fa/en/Portaldata/17/ ... srw_08.pdf

Of course it’s not hard, it’s just heavy. That article/paper whilst interesting is not showing what you think it might be, did you see the size of the floor beams?

morrisond wrote:

And no Carbon is not a wonder material - but it is lighter and does have some advantages that can be taken advantage of in non-circular fuselage shapes. But yes a clean sheet 3x3 could take advantage of that.

On the 772 vs 359 - the 772ER is only capable of about 80% the range of the A359.

And you think that’s down to cfrp structure? I’ll give you a clue, the big hot bits on the wings make up the bulk of it...

morrisond wrote:
On the ends a 2x3x2 the passenger cabin would be at minimum 16.7% less long - using your own numbers and they seem to be what the ACAPs show on the A320 you have about an 31.4M Passenger section with I assume 12M ends.


Then you put to stop assuming. I have explained above exactly how the determination of length for the model was done. If you haven’t understood ( which appears to be the case) the read it again and if you have questions about the methodology then ask.

morrisond wrote:

The NMA passenger section would therefore be about 26.15M long - 12 M ends would have more floor space as they are wider - yet you seem to want to put 14.55M ends on it which would have even more floor space. That doesn't seem like a fair comparison. So 2.55M - but you are using a shorter length for the A322 now than you were before and that is why the numbers don't line up.


At 240 pax @ 28” the length of cabin taken by seating is 28.448m
The 7 abreast model would be 24.384m.
The additional area required for 240 pax for ancillary items is 4.8m^2. In both cases.
The area available in the tail of the A32X is 7.5m^2 which suggest around 0.5m of seating going in to the tail and a length of 2.96m of linear availability in the tail. For the Oval the length in the tail is 4.4m with an area of 11.5m suggesting that there is about 1.1 meters of seating in the tail taper.

So the constant section of the A32x @240x 28” is 28.448-0.5 and the mom is 24.348-1.1.

To make whole length we add 4x the normalised diameter. I have chosen to normalise around surface area using ramunajan ~16m for the A32x and ~ 19m for the mom.

You appear to be under the impression that I am making choices between the aircraft whereas I am not.

Fred


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morrisond
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Re: Cabin configurations, fuselage weight model

Tue Feb 23, 2021 1:18 am

flipdewaf wrote:
morrisond wrote:
Huh - it seems like a double circle is not so hard from a pressurization standpoint after all. Here is a study on basically what Ostrower is saying it is - for the pressurized part - the difference being the NMA would not have the Bottom non-pressurized cargo comparment - NMA would incorporate that in the Floor Beams https://www.dlr.de/fa/en/Portaldata/17/ ... srw_08.pdf

Of course it’s not hard, it’s just heavy. That article/paper whilst interesting is not showing what you think it might be, did you see the size of the floor beams?

morrisond wrote:

And no Carbon is not a wonder material - but it is lighter and does have some advantages that can be taken advantage of in non-circular fuselage shapes. But yes a clean sheet 3x3 could take advantage of that.

On the 772 vs 359 - the 772ER is only capable of about 80% the range of the A359.

And you think that’s down to cfrp structure? I’ll give you a clue, the big hot bits on the wings make up the bulk of it...

morrisond wrote:
On the ends a 2x3x2 the passenger cabin would be at minimum 16.7% less long - using your own numbers and they seem to be what the ACAPs show on the A320 you have about an 31.4M Passenger section with I assume 12M ends.


Then you put to stop assuming. I have explained above exactly how the determination of length for the model was done. If you haven’t understood ( which appears to be the case) the read it again and if you have questions about the methodology then ask.

morrisond wrote:

The NMA passenger section would therefore be about 26.15M long - 12 M ends would have more floor space as they are wider - yet you seem to want to put 14.55M ends on it which would have even more floor space. That doesn't seem like a fair comparison. So 2.55M - but you are using a shorter length for the A322 now than you were before and that is why the numbers don't line up.


At 240 pax @ 28” the length of cabin taken by seating is 28.448m
The 7 abreast model would be 24.384m.
The additional area required for 240 pax for ancillary items is 4.8m^2. In both cases.
The area available in the tail of the A32X is 7.5m^2 which suggest around 0.5m of seating going in to the tail and a length of 2.96m of linear availability in the tail. For the Oval the length in the tail is 4.4m with an area of 11.5m suggesting that there is about 1.1 meters of seating in the tail taper.

So the constant section of the A32x @240x 28” is 28.448-0.5 and the mom is 24.348-1.1.

To make whole length we add 4x the normalised diameter. I have chosen to normalise around surface area using ramunajan ~16m for the A32x and ~ 19m for the mom.

You appear to be under the impression that I am making choices between the aircraft whereas I am not.

Fred


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Yes - I saw the shape of the Floor Beams - however that structure between the top and bottom surfaces of the beam could be very light weight rigid styrofoam or something similar sandwiched with Carbon. You would also have a flat surface for the walls of cargo hold to attach to which could further stiffen the structure if the walls were rigidly attached - essentially making one very large LD3-45 or larger Keel Beam. You could get access to the voids beside the cargo area for heavy maintenance by removing the floor of the cabin. The cargo area would only be 50% of the length of the aircraft in the examples we are looking at taking into account the wingbox area - which is no different than other aircraft as it just has a half circle above it - and the ends which with all the walls and bulk heads for things like Gear wells and Equipment bays should be a lot easier to figure out.

They are ways to do it. If I can think of a few - I'm sure Aerospace engineers could and I'm sure if you put your mind to it you could come up with some creative ideas as well.

Yes I'm quite aware that the 772ER engines are not as good - but I don't think they are worse enough to make up the differential in range and the larger engines on the 359 are probably heavier.

We are close enough on the length - I will drop it. I'm sure in the end it could go one way or other - probably more dependent if they have to account for various other lengths in the future.
 
LH707330
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Re: Cabin configurations, fuselage weight model

Tue Feb 23, 2021 5:26 am

morrisond wrote:
LH707330 wrote:
morrisond wrote:

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.

I missed the 17m vs 12m ends, thought those were adjusted in Fred's latest model. While I suspect that the area on the 2-3-2 might be less than the 3-3, the overall weight and form drag might not. Do you have a table of assumptions for those inputs to compare them?


No I don't - Who knows on the weight.

The 2x3x2 also has 20% fewer frames, stringers and floor beams in the cabin due to the shorter cabin length at the same capacity. It should be fewer parts to assemble it - lowering production/labour costs.

Assuming it is built out of carbon - we have also read that at the strength needed for SA - Carbon skins are thicker than necessary to deal with things like ramp rash. With a 2x3x2 and its non standard shape that extra stiffness/strength could be used in lieu of heavier stronger frames/floorbeams, stringers and longerons that might be needed with an metal design. Plus there is about 9% less skin on the 2x3x2.

In the end the weight penalty may not be so big as people are assuming and maybe within the delta between the A320 and 737 Fuselages.

In the end it may not be quite as efficient as 3x3 when you take everything into account - by it could be close enough to offset the disadvantages and no worse than 320 over 737.

Carbon may well be slightly suboptimal for a 3-3 layout vs aluminum, but how much do you think that calculus changes with a narrow 2-3-2? As Fred's pointed out in comparing the 777/350 and the 330/787, CF widebodies, where the CF is supposedly more helpful, don't have that much of a weight advantage due to the CF, so scale that down to 2-3-2 and I think it's tricky to square that circle.

A shorter fuselage will also require bigger tail feathers due to the shorter moment arms in pitch and yaw, so even if the 2-3-2 tube turns out better, which I'm still unconvinced of, you'd need to deal with the weight and higher Di and Dp of the stabilizers, which would further hurt the case.

Regarding the non-cylindrical shape with the floor beams in compression, I'd like to think about this in a different way: if it's a worthwhile idea, why has it not been tried on a previous design? It seems the only benefit you gain is a bit less frontal area at the expense of an increase in structural weight and a length limit dictated by vertical fineness ratio.

morrisond wrote:
They are ways to do it. If I can think of a few - I'm sure Aerospace engineers could and I'm sure if you put your mind to it you could come up with some creative ideas as well.


I don't think anybody's doubting whether it's possible. What's in question is whether it makes sense, and the prevailing wisdom on this thread and the world of successfully-produced aircraft appears to show that it doesn't.
 
flipdewaf
Topic Author
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Re: Cabin configurations, fuselage weight model

Tue Feb 23, 2021 11:47 am

morrisond wrote:

They are ways to do it. If I can think of a few - I'm sure Aerospace engineers could and I'm sure if you put your mind to it you could come up with some creative ideas as well.

Its the Dunning-Kruger effect
morrisond wrote:
Yes I'm quite aware that the 772ER engines are not as good - but I don't think they are worse enough to make up the differential in range and the larger engines on the 359 are probably heavier.

Ge90-85b -7892kg
Trent XWB 84 - 7277kg

A standard 1% year TSFC improvement from 1997->2015 would give you an additional 16% improvement in fuel burn from the engines. the 7065nm range of the 772 would get you 8195nm.
SFC numbers are hard to come by but I would expect the number for the Ge90-85b to be around 0.56 and the XWB to be ~0.5 or a reduction of ~11%. An 11% reduction would give about 7842nm.

It seems to me that the engine is doing the heavy lifting of improving range.

morrisond wrote:

We are close enough on the length - I will drop it. I'm sure in the end it could go one way or other - probably more dependent if they have to account for various other lengths in the future.


Who's this 'we'? 'I'm glad your sure but if ever I have a flight on it I'll be sure to book one of the seats inside the plane.

Fred
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morrisond
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Re: Cabin configurations, fuselage weight model

Tue Feb 23, 2021 4:20 pm

LH707330 wrote:
morrisond wrote:
LH707330 wrote:
I missed the 17m vs 12m ends, thought those were adjusted in Fred's latest model. While I suspect that the area on the 2-3-2 might be less than the 3-3, the overall weight and form drag might not. Do you have a table of assumptions for those inputs to compare them?


No I don't - Who knows on the weight.

The 2x3x2 also has 20% fewer frames, stringers and floor beams in the cabin due to the shorter cabin length at the same capacity. It should be fewer parts to assemble it - lowering production/labour costs.

Assuming it is built out of carbon - we have also read that at the strength needed for SA - Carbon skins are thicker than necessary to deal with things like ramp rash. With a 2x3x2 and its non standard shape that extra stiffness/strength could be used in lieu of heavier stronger frames/floorbeams, stringers and longerons that might be needed with an metal design. Plus there is about 9% less skin on the 2x3x2.

In the end the weight penalty may not be so big as people are assuming and maybe within the delta between the A320 and 737 Fuselages.

In the end it may not be quite as efficient as 3x3 when you take everything into account - by it could be close enough to offset the disadvantages and no worse than 320 over 737.

Carbon may well be slightly suboptimal for a 3-3 layout vs aluminum, but how much do you think that calculus changes with a narrow 2-3-2? As Fred's pointed out in comparing the 777/350 and the 330/787, CF widebodies, where the CF is supposedly more helpful, don't have that much of a weight advantage due to the CF, so scale that down to 2-3-2 and I think it's tricky to square that circle.

A shorter fuselage will also require bigger tail feathers due to the shorter moment arms in pitch and yaw, so even if the 2-3-2 tube turns out better, which I'm still unconvinced of, you'd need to deal with the weight and higher Di and Dp of the stabilizers, which would further hurt the case.

Regarding the non-cylindrical shape with the floor beams in compression, I'd like to think about this in a different way: if it's a worthwhile idea, why has it not been tried on a previous design? It seems the only benefit you gain is a bit less frontal area at the expense of an increase in structural weight and a length limit dictated by vertical fineness ratio.

morrisond wrote:
They are ways to do it. If I can think of a few - I'm sure Aerospace engineers could and I'm sure if you put your mind to it you could come up with some creative ideas as well.


I don't think anybody's doubting whether it's possible. What's in question is whether it makes sense, and the prevailing wisdom on this thread and the world of successfully-produced aircraft appears to show that it doesn't.


We will see what Boeing ends up producing. Yes Carbon may not save that much weight but it may make more complex shapes possible if you are thinking outside the box a little.
 
flipdewaf
Topic Author
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Re: Cabin configurations, fuselage weight model

Tue Feb 23, 2021 10:15 pm

morrisond wrote:
flipdewaf wrote:
morrisond wrote:

At least it would be very aero.

And what are your calculations for the A321 then including the Nose?

If we calculated it in the same way:
44.5 m total, 6.06m for the nose leaving ~38.5 left behind of which 10.1 is in the tail leaving a constant section of 28.4m. 28.4 * 3.75 = 106.5m^2 in the constant section and 0.5*10.1*4.04 in the tail (20.4m^2)

Edit: For my 6m difference I had used fuselage width not cabin width.

Fred


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So we are back to 5.4M difference. The other day you had the A321 at 43.4 and the MOM at 40.4 which did not make sense to me. Did you maybe just mistype something? Was 43.4 supposed to 45.4? You ave been going back and forth between 206 and 212/216 seats or so.

I agree these new numbers make a lot more sense.

So basically you are saying your model says a 2-3-2 with the same capacity and the same space for Galleys/ LAVs and two aisles has about 3-4% less floor area and by my calculations about 9% less skin area and 2% less volume and at its aero sections are more tapered leading to possible aero advantages.

Ignoring the unknown (How much of a weight penalty would a double circle take) that seems pretty efficient to me and not something impossible to overcome with design choices/inherent properties of some materials elsewhere. It is definitely in the ballpark and by your own model within the Delta of A320 vs 737 at about 322 seat capacity.

As it is a lot shorter you would save a bunch with shorter gear due to the shorter length and longer tapered rear.

Good model. Good work.


I think there is some confusion, and I understand that there are lots of things going on so its hard.

My model that has been used to compare weights per pax in the fuselage works by:
a. Calculating the length required to carry the seats ((Number of seats/Number of seats abreast)*Seat pitch)
b. It also calculates the distance along the elliptical tapered section into which a rectangle of a predefined dimension will fit. at a certain size it becomes too small to do anything useful in (this is the case regardless of the aircraft. This is done by writing a function that determines when all four corners of the rectangle will be in contact with an ellipse of the same height to width ratio as the main fuselage and then determines the ratio of scales of those ellipses (Main fuselage to the minimum cabin width) to determine the fraction of the tail that the cabin can take up.
c. we know that the taper ratio (the number of effective fuselage widths per length of the taper) which is set at 2.5 will then allow us to work out the length of the cabin in the tail.
d. As we have the width of the cabin, the length of the cabin in the tail section and the minimum width we have the ability to work out the area available in the tapered tail section as well as an approximate aisle to seat width ratio (It'll be clear why we do this in a minute).
e. If we take a standard amount of area per pax (0.2m^2) for ancillary items (Galleys, Toilets, closets etc) then we can work out the amount of additional area required beyond the seating to form a 'cabin' and we subtract the are in the tail that we have already established we are left with a figure for how much additional cabin area we need to fit in to the constant cross section part of the fuselage. If we divide that area by the useful width (seats = useful, aisles = not) then you have a length over constant cross section that we need for said ancillaries. The reason for the "useful width" is that galleys and toilets can't be in the aisles.
e. once we have the length of the seated bits and the ancillaries in the constant cross section we add them together to get the total length of the constant cross section and then add 1.5*normalised diameter for the nose and 2.5 * normalised diameter for the tail. I had used the Ramunajan method for that and then realised that aerodynamically it should be done for area not perimeter but as these aren't very high ratio ellipses the changes were in the seconds decimal place at most so not worth changing the charts,

So you can see that the model works in reverse in terms of length, it uses the pax capacity and the cross section to calculate the length rather than taking a length and seeing what capacity fits in. As there have been some revisions over time in terms of how certain aspects were calculated (going from round to elliptical, assessing cabin space in the tail etc etc.) then the values that it spits out will vary.

With regards to the value of floor area that you mention it was not a 'model' made in the same way but starting from the assertion that the mom would be 5.4m shorter. I then reversed some of the calculations to determine what the cabin floor area would be based on a similar method of tail area and constant section. If we know the length and the width and the height then the floor area calculation is relatively easy. it was done to demonstrate that if you did use the length you suggested then the ability to carry the same passenger load was lost.

I guess that when the model is up and running and all you have to do is change the seat pitch and capacity and it'll spit numbers at you then you end up playing with it so see the interesting things happen. Inevitably you lose track of which numbers were in where.

Fred
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morrisond
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Re: Cabin configurations, fuselage weight model

Tue Feb 23, 2021 10:46 pm

Makes sense to me - and I'm being honest here - Great work Fred - that is a lot of effort.

Any idea if my idea of basically creating a giant keel beam by rigidly attaching the cargo hold walls to the monolithic floor/lower frame beams to offset the bending moment of the fuselage as it is wider than higher has any merit?

Is it done already? - Would this bot be a great use of carbon? Get something for almost nothing as you need the cargo walls anyways and it would not be that difficult to have access ports to the aresa beside the Cargo area as that would not really wreck the strength of the walls.

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