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keesje
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Re: NMA/MOM/797 variant performance analysis

Wed Feb 12, 2020 9:07 pm

A 7 abreast cross section will be significant heaver because the higher loads of 7 passengers and the bigger spans / moments they create.

Although a bad comparison, the same technology, same manufaturer, same seat capacity, same engine 767-200 and 757-300 differ significantly in empty weight. 64 vs 80t.
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oschkosch
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Re: NMA/MOM/797 variant performance analysis

Wed Feb 12, 2020 9:13 pm

Nma will never be 7W, absolutely no point in doing so.

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keesje
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Re: NMA/MOM/797 variant performance analysis

Wed Feb 12, 2020 9:58 pm

The 757-300 is 6m, 7 rows longer than the 767-200. Has longer landing gear, still 3400NM range. Much smaller tail section than 762.

The slightly shorter, wider fuselage, far more modern A321XLR is 20% lighter than the 1980 757-200, while offering 15% more range.

No wonder airliners are jumping on it
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seahawk
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Re: NMA/MOM/797 variant performance analysis

Thu Feb 13, 2020 6:16 am

morrisond wrote:
flipdewaf wrote:
morrisond wrote:

Humor me - what happens if you keep the Fuselage weight the same? We are all making large assumptions about how much heavier Ovalish Cross Section would weigh.

I still can't believe the tail gets that much heavier


It scales on many things, wing area, h-tplane area, v-tplane area, g loading. Taper, sweep, span. Whilst it’s possible to change all of these I have simply chosen to base the current ones off the the afformentuined Boeing planes that fit within the right category. Effectively it happens because as the area increases so does the span and Just like a wing (because that’s what it is) it’s weigh is hugely impacted by span. The A380 for example has nigh on 20t of weight attributed to the tail surfaces in one form or another, we’re talking ~4t here.

Effectively read the Stanford course notes and you’ll get it, it’s about a comprehensive read on aircraft design you can get. Then read torenbeek, then read Raymer.

And I don’t regard your statement of “all making assumptions” as an even remotely fair assessment, not all assumptions are equally valid.

Your previous triumphalism incorrectly pointing at my work as proof of your position in a different thread dissuades me from dancing to your tune anymore. I do not wish to be associated with that behaviour.

Fred


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Fred - you were the one pointing out that as the Fuselage was 9% heavier everything else increases as well. I pointed out that you have to look at the weight of the loaded fuselage which would only be 2.5% more in an all Y configuration and you have been backpedaling ever since and have not refuted that position.

I appreciate the effort you put in but let's just agree to disagree and not make this a thing.

Thank you for trying.


Again you are mixing requirements and results. Payload is a requirement as is range. From then on it is an iterative process, after you defined the form of the fuselage and have set the requirements, all other things are easily calculated by using formulas around since decades and still good enough to match reality with a small margin of error. As the model has been calibrated by showing correct results for existing planes, there is no reason to believe the results could be fundamentally wrong.
 
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Re: NMA/MOM/797 variant performance analysis

Thu Feb 13, 2020 7:40 am

seahawk wrote:
morrisond wrote:
flipdewaf wrote:

It scales on many things, wing area, h-tplane area, v-tplane area, g loading. Taper, sweep, span. Whilst it’s possible to change all of these I have simply chosen to base the current ones off the the afformentuined Boeing planes that fit within the right category. Effectively it happens because as the area increases so does the span and Just like a wing (because that’s what it is) it’s weigh is hugely impacted by span. The A380 for example has nigh on 20t of weight attributed to the tail surfaces in one form or another, we’re talking ~4t here.

Effectively read the Stanford course notes and you’ll get it, it’s about a comprehensive read on aircraft design you can get. Then read torenbeek, then read Raymer.

And I don’t regard your statement of “all making assumptions” as an even remotely fair assessment, not all assumptions are equally valid.

Your previous triumphalism incorrectly pointing at my work as proof of your position in a different thread dissuades me from dancing to your tune anymore. I do not wish to be associated with that behaviour.

Fred


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Fred - you were the one pointing out that as the Fuselage was 9% heavier everything else increases as well. I pointed out that you have to look at the weight of the loaded fuselage which would only be 2.5% more in an all Y configuration and you have been backpedaling ever since and have not refuted that position.

I appreciate the effort you put in but let's just agree to disagree and not make this a thing.

Thank you for trying.


Again you are mixing requirements and results. Payload is a requirement as is range. From then on it is an iterative process, after you defined the form of the fuselage and have set the requirements, all other things are easily calculated by using formulas around since decades and still good enough to match reality with a small margin of error. As the model has been calibrated by showing correct results for existing planes, there is no reason to believe the results could be fundamentally wrong.


You are right, none of the equations are particularly difficult, the key thing that the spreadsheet/model enables is that it prevents you from ever thinking about a single parameter in isolation and as keesje says, everything is a compromise in aircraft design and it allows you to watch the compromises play out, exactly as it has done here.

I would love to recode a lot of it to work through a different data analysis program I use (sas jmp) as that is super quick but I doubt I’ll ever find the time.

Fred


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AvgWhiteGuy
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Re: NMA/MOM/797 variant performance analysis

Thu Feb 13, 2020 1:23 pm

Re: skin friction drag. When I ran the numbers in my airline's "OPC" for both 700's and 800's at identical weights, altitudes, speeds, temperatures, bleed configuration and wingtip device configuration, the cruise fuel flow was always identical for the same weight, regardless of whether it was a 700 or 800. Not trusting the numbers, I ran them probably a dozen times when bored at cruise and I contacted the person who works with Boeing on our aircraft performance and he said the effect of skin friction drag was "negligible." I wouldn't put too much emphasis on skin friction drag on stretches of an otherwise identical fuselage.
 
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Re: NMA/MOM/797 variant performance analysis

Thu Feb 13, 2020 5:00 pm

Image

So A slightly updated set of analysis. I had to redo the MTOW piece as I had it set low for the WB and nowhere near what would be required (115t I think) and I updated the HTP and VTP area calculators so that they scale with those on the NB version. The area is scaled on a function and the linear dimensions are scaled ^(1/2) to maintain geometry.

The VTP area scales with (thrust Ratio)*(fuselage length ratio)*(Wingspan ratio)*(NB VTPArea)

The HTP area scales with (Fuselage length ratio)*(Ratio of wing area)*(NB HTP area)

Fred
Last edited by flipdewaf on Thu Feb 13, 2020 5:03 pm, edited 1 time in total.
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keesje
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Re: NMA/MOM/797 variant performance analysis

Thu Feb 13, 2020 5:02 pm

AvgWhiteGuy wrote:
Re: skin friction drag. When I ran the numbers in my airline's "OPC" for both 700's and 800's at identical weights, altitudes, speeds, temperatures, bleed configuration and wingtip device configuration, the cruise fuel flow was always identical for the same weight, regardless of whether it was a 700 or 800. Not trusting the numbers, I ran them probably a dozen times when bored at cruise and I contacted the person who works with Boeing on our aircraft performance and he said the effect of skin friction drag was "negligible." I wouldn't put too much emphasis on skin friction drag on stretches of an otherwise identical fuselage.


Thanks! Welcome.
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morrisond
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Re: NMA/MOM/797 variant performance analysis

Fri Feb 14, 2020 7:49 pm

Ok Fred - run the WB and NB (the 28" Wide aisle one (Kessje's Model - however his is an 168" Circle which presumably could be heavier than the WB) at the same weight sans tails and what do you get?

Why the 28" one? - same ease of getting around the cabin as a 2 aisle as Keesje keeps pointing out and loading/unloading - no one would accept one 16" aisle with 300 Y seats - it would probably have a really hard time passing the evac rules unless riddled with exits.
 
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Re: NMA/MOM/797 variant performance analysis

Fri Feb 14, 2020 7:57 pm

morrisond wrote:
Ok Fred - run the WB and NB (the 28" Wide aisle one (Kessje's Model - however his is an 168" Circle which presumably could be heavier than the WB) at the same weight sans tails and what do you get?

Why the 28" one? - same ease of getting around the cabin as a 2 aisle as Keesje keeps pointing out and loading/unloading - no one would accept one 16" aisle with 300 Y seats - it would probably have a really hard time passing the evac rules unless riddled with exits.

Nah, let’s assume they are both equal for loading. You know, for the sake of comparisons. It is after all the only way to do it...


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morrisond
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Re: NMA/MOM/797 variant performance analysis

Fri Feb 14, 2020 8:45 pm

flipdewaf wrote:
morrisond wrote:
Ok Fred - run the WB and NB (the 28" Wide aisle one (Kessje's Model - however his is an 168" Circle which presumably could be heavier than the WB) at the same weight sans tails and what do you get?

Why the 28" one? - same ease of getting around the cabin as a 2 aisle as Keesje keeps pointing out and loading/unloading - no one would accept one 16" aisle with 300 Y seats - it would probably have a really hard time passing the evac rules unless riddled with exits.

Nah, let’s assume they are both equal for loading. You know, for the sake of comparisons. It is after all the only way to do it...


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Yes I'm sure you will be able to load an 16" wide single aisle 300 seat aircraft as fast as an 2 16" aisle 300 seat aircraft from one door.

If Boeing was going to go down the route of the NNB they would just keep the 737 cross section. Good luck with getting any containers or much Cargo in that NNB belly with a fuselage height 9" less than an 737 or 16" less than an A321.

It would probably hold 50-60% less cargo than the WB even taking into account the longer length of the NNB. No that isn't a disadvantage at all. I'm sure Airlines would love to go from an 45" tall LD3-45 to an 29" tall one and possibly a few inches narrower.

If you want to compare things properly you would have to flatten out the WB belly more to get the same Cargo Capacity - of course saving weight on WB vs NB and WB vs NNB.
 
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Re: NMA/MOM/797 variant performance analysis

Fri Feb 14, 2020 9:05 pm

morrisond wrote:
flipdewaf wrote:
morrisond wrote:
Ok Fred - run the WB and NB (the 28" Wide aisle one (Kessje's Model - however his is an 168" Circle which presumably could be heavier than the WB) at the same weight sans tails and what do you get?

Why the 28" one? - same ease of getting around the cabin as a 2 aisle as Keesje keeps pointing out and loading/unloading - no one would accept one 16" aisle with 300 Y seats - it would probably have a really hard time passing the evac rules unless riddled with exits.

Nah, let’s assume they are both equal for loading. You know, for the sake of comparisons. It is after all the only way to do it...


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Yes I'm sure you will be able to load an 16" wide single aisle 300 seat aircraft as fast as an 2 16" aisle 300 seat aircraft from one door.

As sure as you are that the WB would weight the same as the NB or not?
morrisond wrote:

If Boeing was going to go down the route of the NNB they would just keep the 737 cross section.

Arguable.
morrisond wrote:
Good luck with getting any containers or much Cargo in that NNB belly with a fuselage height 9" less than an 737 or 16" less than an A321.

Please see the opening post of this thread where the diagram is shown.
morrisond wrote:
It would probably hold 50-60% less cargo than the WB even taking into account the longer length of the NNB.

I thought the ovoid was because it wasn’t for cargo and to use nb containers?
morrisond wrote:
No that isn't a disadvantage at all. I'm sure Airlines would love to go from an 45" tall LD3-45 to an 29" tall one and possibly a few inches narrower.

If you want to compare things properly you would have to flatten out the WB belly more to get the same Cargo Capacity - of course saving weight on WB vs NB and WB vs NNB.


A JCB will help you dig faster.

Fred



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Re: NMA/MOM/797 variant performance analysis

Sat Feb 15, 2020 12:07 am

I'm not sure a 300 seat option would be possible with a narrow narrow body, the third option.

It think a significant wider aisle is required for up to 50 rows, 5000NM.

Purely from an area moment of inertia, stiffness, weight perspective of a very long fuselage (57m?).

Apart from that most passengers go to the lav during >5 hour flights and multiple catering rounds would be served from a single aisle. It helps sevices if 2 people, 2 trolleys can pass each other.

A single, narrow, no-pass aisle probably becomes a real irritator, stumbling block on long full flights.

For >6 hr flight business class, requirements are flat bed and direct aisle access. To be really interchangeable, common with widebodies of the operators it would be a big plus.

A wider aisle also creates a better space experience and/ or bigger bins, which make it more acceptable for longer flights.

It might be an operational requirement instead of wasted space, for a 50 row, 5000NM specification.

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morrisond
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Re: NMA/MOM/797 variant performance analysis

Sat Feb 15, 2020 1:24 am

keesje wrote:
I'm not sure a 300 seat option would be possible with a narrow narrow body, the third option.

It think a significant wider aisle is required for up to 50 rows, 5000NM.

Purely from an area moment of inertia, stiffness, weight perspective of a very long fuselage (57m?).

Apart from that most passengers go to the lav during >5 hour flights and multiple catering rounds would be served from a single aisle. It helps sevices if 2 people, 2 trolleys can pass each other.

A single, narrow, no-pass aisle probably becomes a real irritator, stumbling block on long full flights.

For >6 hr flight business class, requirements are flat bed and direct aisle access. To be really interchangeable, common with widebodies of the operators it would be a big plus.

A wider aisle also creates a better space experience and/ or bigger bins, which make it more acceptable for longer flights.

It might be an operational requirement instead of wasted space, for a 50 row, 5000NM specification.

https://www.flickr.com/photos/rtm67/355 ... ed-public/


Keesje,

Is there anyway you can get an LD3-45 in the NNB with 16" less fuselage height than an A320?
 
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Re: NMA/MOM/797 variant performance analysis

Sat Feb 15, 2020 7:17 am

morrisond wrote:
Is there anyway you can get an LD3-45 in the NNB with 16" less fuselage height than an A320?

Of course you can. You can put the passenger floor as high as you want to fit containers underneith.

The problem that creates is the widest part of the cabin will now be very close to floor level. At shoulder level that results in around 6inch of reduced cabin width.

So you have two choices:
1) Fit 18inch seats and have no LD3-45 containers.
2) Fit 17inch seats and raise the floor a foot to fit containers.

Do you want containers or wider seats? You can't have both unless you increase the cross section circumference.
 
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Re: NMA/MOM/797 variant performance analysis

Sat Feb 15, 2020 7:48 am

RJMAZ wrote:
morrisond wrote:
Is there anyway you can get an LD3-45 in the NNB with 16" less fuselage height than an A320?

Of course you can. You can put the passenger floor as high as you want to fit containers underneith.

The problem that creates is the widest part of the cabin will now be very close to floor level. At shoulder level that results in around 6inch of reduced cabin width.

So you have two choices:
1) Fit 18inch seats and have no LD3-45 containers.
2) Fit 17inch seats and raise the floor a foot to fit containers.

Do you want containers or wider seats? You can't have both unless you increase the cross section circumference.


You are totally right. The drawings I did on CAD show this exact issue for both the NNB and the Ovid.

It’s more of an issue for the NNB than for the ovid at shoulder/head height because of the tighter radius.

If I were to argue where/how a NB should be dimensioned I fear it would come out perilously close to an A32x for the fuselage and I don’t want to go there in this thread just yet, some a.net members are not ready.

Fred


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morrisond
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Re: NMA/MOM/797 variant performance analysis

Sat Feb 15, 2020 11:03 am

Good luck with standing in that Aisle - and now the Overhead bins are right on top of the seats. There is not enough room.

And BTW - I think the comparison with the A320 is valid as this is most likely what Boeing would be competing with. Of course that would be built out of Aluminum which has a 1,200KG weight penalty as I posted in that research paper I linked too.
 
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Re: NMA/MOM/797 variant performance analysis

Sat Feb 15, 2020 1:39 pm

morrisond wrote:
Good luck with standing in that Aisle - and now the Overhead bins are right on top of the seats. There is not enough room.

That’s a good point, I will see if i can get some scaled drawings of people to put in to the drawings to give a better appreciation of scale.

morrisond wrote:
And BTW - I think the comparison with the A320 is valid as this is most likely what Boeing would be competing with. Of course that would be built out of Aluminum which has a 1,200KG weight penalty as I posted in that research paper I linked too.


The A320 piece was more to do with the scale and applicability of reasonable sized seats and aisles.
1200kg. A figure not born out at an aircraft level though. How’s the CFRP helping the weight on the 787 compared to the A330...

Fred


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keesje
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Re: NMA/MOM/797 variant performance analysis

Sat Feb 15, 2020 5:39 pm

flipdewaf wrote:
morrisond wrote:
Good luck with standing in that Aisle - and now the Overhead bins are right on top of the seats. There is not enough room.

That’s a good point, I will see if i can get some scaled drawings of people to put in to the drawings to give a better appreciation of scale.

morrisond wrote:
And BTW - I think the comparison with the A320 is valid as this is most likely what Boeing would be competing with. Of course that would be built out of Aluminum which has a 1,200KG weight penalty as I posted in that research paper I linked too.


The A320 piece was more to do with the scale and applicability of reasonable sized seats and aisles.
1200kg. A figure not born out at an aircraft level though. How’s the CFRP helping the weight on the 787 compared to the A330...

Fred

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The CFRP weight advantage doesn't seem significant (2016 pic).

Image

I think specialists have some concerns on producing 2 CFRP aircraft a day. Lay up speed hasn't boomed. So you need real big, clean factories..
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seahawk
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Re: NMA/MOM/797 variant performance analysis

Sat Feb 15, 2020 6:52 pm

flipdewaf wrote:
RJMAZ wrote:
morrisond wrote:
Is there anyway you can get an LD3-45 in the NNB with 16" less fuselage height than an A320?

Of course you can. You can put the passenger floor as high as you want to fit containers underneith.

The problem that creates is the widest part of the cabin will now be very close to floor level. At shoulder level that results in around 6inch of reduced cabin width.

So you have two choices:
1) Fit 18inch seats and have no LD3-45 containers.
2) Fit 17inch seats and raise the floor a foot to fit containers.

Do you want containers or wider seats? You can't have both unless you increase the cross section circumference.


You are totally right. The drawings I did on CAD show this exact issue for both the NNB and the Ovid.

It’s more of an issue for the NNB than for the ovid at shoulder/head height because of the tighter radius.

If I were to argue where/how a NB should be dimensioned I fear it would come out perilously close to an A32x for the fuselage and I don’t want to go there in this thread just yet, some a.net members are not ready.

Fred


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The A320 fuselage cross section should be the baseline, it is extremely efficient when using LD3/45s, as the container was designed for it.
 
RJMAZ
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Re: NMA/MOM/797 variant performance analysis

Sun Feb 16, 2020 2:06 am

seahawk wrote:
The A320 fuselage cross section should be the baseline, it is extremely efficient when using LD3/45s, as the container was designed for it.

Any future Boeing 6ab would definitely have a cross section within an inch or two of the A320. Just like how all aircraft are a tube with wings.
 
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Re: NMA/MOM/797 variant performance analysis

Sun Feb 16, 2020 5:52 am

As Boeing plots their next move, how likely is it that Airbus will do an all new wing and re-gear the A321 for a 120t aircraft, or will they decide to go clean sheet at that point? I could see a A321 stretch to the A322 at 101t, engine improvements or folding wingtips, but the next investment beyond that is a big one. Like the 777x, just because it's there doesn't make it the optimal choice of fuselage.
 
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Re: NMA/MOM/797 variant performance analysis

Sun Feb 16, 2020 7:57 am

For using LD3/45s it is close to a perfect solution, as the LD3/45s was designed to fit the cross section.
 
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Re: NMA/MOM/797 variant performance analysis

Sun Feb 16, 2020 9:07 am

DenverTed wrote:
As Boeing plots their next move, how likely is it that Airbus will do an all new wing and re-gear the A321 for a 120t aircraft, or will they decide to go clean sheet at that point? I could see a A321 stretch to the A322 at 101t, engine improvements or folding wingtips, but the next investment beyond that is a big one. Like the 777x, just because it's there doesn't make it the optimal choice of fuselage.


I’m not sure what the maximum you can go to before going to a 4wheel bogey. There is a piece at the back of my head that for a first pass guess at the number of wheels required was to divide the MTOW by 30t and start there. Obviously there are other considerations such as the sizes and wheel spacing (A359 goes to 35t/tyre) and the black art of ACN/PCN. It may be that airbus can take the current gear up to 105t or even 110? At both those weights a 41m wing could take them an awful long way. The bigger issue may well be how to integrate it in to current production processes and maintain the cost advantage of the 32x series production scale.

Fred


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Re: NMA/MOM/797 variant performance analysis

Sun Feb 16, 2020 11:39 am

flipdewaf wrote:
It may be that airbus can take the current gear up to 105t or even 110? At both those weights a 41m wing could take them an awful long way. The bigger issue may well be how to integrate it in to current production processes and maintain the cost advantage of the 32x series production scale.


Can airbus move the individual wheels on a gearleg further apart to achieve wider track?

Other opt. would be larger tires or tech improvements in the tire layup.
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morrisond
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Re: NMA/MOM/797 variant performance analysis

Sun Feb 16, 2020 1:02 pm

flipdewaf wrote:
DenverTed wrote:
As Boeing plots their next move, how likely is it that Airbus will do an all new wing and re-gear the A321 for a 120t aircraft, or will they decide to go clean sheet at that point? I could see a A321 stretch to the A322 at 101t, engine improvements or folding wingtips, but the next investment beyond that is a big one. Like the 777x, just because it's there doesn't make it the optimal choice of fuselage.


I’m not sure what the maximum you can go to before going to a 4wheel bogey. There is a piece at the back of my head that for a first pass guess at the number of wheels required was to divide the MTOW by 30t and start there. Obviously there are other considerations such as the sizes and wheel spacing (A359 goes to 35t/tyre) and the black art of ACN/PCN. It may be that airbus can take the current gear up to 105t or even 110? At both those weights a 41m wing could take them an awful long way. The bigger issue may well be how to integrate it in to current production processes and maintain the cost advantage of the 32x series production scale.

Fred


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They had a 4 wheel bogie option that Air India used viewtopic.php?t=755991

But as they would be doing a new wing and new wing box a new gear that wouldn't be that big a deal - they might need longer gear as well of they are thinking of an A323.

They build A320 series in so many places - it wouldn't be hard to convert one to New Wing building.

However I believe Boeing builds 777W and X's on the same line with different wings so it should not be impossible. The folding tips may be what allows this.
 
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Re: NMA/MOM/797 variant performance analysis

Sun Feb 16, 2020 2:17 pm

morrisond wrote:
They had a 4 wheel bogie option that Air India used viewtopic.php?t=755991


IMU that was never certified beyond the initial MTOW of the A320-200 .
And the wheels are really small: 36x11 vs 49x17 ( some variants ) for the single axle MLG

newer A321(CEO/NEO) have 1270X455R22 ( metric dims. ~~50x18 )
ref: https://www.bridgestone.com/products/sp ... ations.pdf

What I could find:
The 36x11 type seems to max out at ~35klbs * 4 * 2 *.454 ~= 125t
The 1270X455R22 type seems to max out at ~55klbs * 2 * 2 *.454 ~= 100t
https://www.jupitor.co.jp/pdf/michelin_aircraft.pdf p22, p26

errors? squawk!
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flipdewaf
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Re: NMA/MOM/797 variant performance analysis

Mon Feb 17, 2020 1:12 pm

So I did this from your info. As ever please ask questions.
Image

The dimensions for the seats an aisles are the same as in the previous example, 17" seats and 16" aisles. The Overall fuselage diameter comes out at near enough 5.1m. The drawing shows LD2 containers. I haven't drawn overhead bins because CAD takes me too long and I'm impatient.

The otehr pieces of data I put together show a need for a wing of about 220m^2 and an MTOW of 142-143t
The shorter version has a max exit limit set of 300 and the larger or 350 but you can see in teh mission data I have assumed 100kg per pax and with the pax info you supplied for both variants. The length of the two variants correspond to the 762 and 763 and the DOW for the larher variant is ~81t and the smaller version ~76t.
The missions are the same as the previous.
Image

Fred
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Re: NMA/MOM/797 variant performance analysis

Mon Feb 17, 2020 8:37 pm

That is not too umcompetetive if you consider the extra revenue potential compared to the 7w ovid.
 
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Re: NMA/MOM/797 variant performance analysis

Mon Feb 17, 2020 10:14 pm

seahawk wrote:
That is not too umcompetetive if you consider the extra revenue potential compared to the 7w ovid.

I agree, the issue may come with potential cannibalisation of the 787 but if that were to be re-engined the -8 might well be out of the picture anyway.

Fred


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RJMAZ
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Re: NMA/MOM/797 variant performance analysis

Mon Feb 17, 2020 11:09 pm

flipdewaf wrote:
So I did this from your info. As ever please ask questions.

Exceptional work.

I remember saying last year that I was 80% certain it was going to be a circular 8ab exactly as pictured. The remaining 20% covers ovoid 8ab, ovoid 7ab and wide aisle 6ab.

That fuel burn per square metre of cabin area actually looks exceptional for that tight circular 8ab which is why it makes the most sense.

One think worth noting is the 797 seating capacity is closer together in size than the 767-200 and 767-300. 17% capacity difference versus 22% capacity difference.

So the larger 797-7 would probably be one metre shorter than the 767-300. This should reduce DOW and fuel burn by a couple percent.

797-6 48.5m
797-7 54m
 
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Re: NMA/MOM/797 variant performance analysis

Tue Feb 18, 2020 7:51 am

Also what wingspan and engine thrust did you use for your calculations?

I assume it would be around 48metres and 48,000lb of thrust?
 
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keesje
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Re: NMA/MOM/797 variant performance analysis

Tue Feb 18, 2020 8:21 am

The landing weight seems higher than an A321XLR MTOW. That's translating in costs at all levels.
Curvature, 17 inch seats combined with 16inch aisles would have people hang into the aisles and being bump by troleey and everyone.

I think this aicraft would be expensive & quickly get famous for the wrong reasons.
LD2 is the odd standard specailly for 767.
Leisure airlines use(d) 2-4-2- on the 767 airlines and moved bak to 2-3-2 after passeneger and crew feed back.

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JustSomeDood
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Re: NMA/MOM/797 variant performance analysis

Tue Feb 18, 2020 1:25 pm

Really interesting stuff here, just want to ask a couple of things:

SFC has been set to 0.49 in all scenarios, this is obviously a fuel consumption/thrust figure of some sort but how does it compare to other contemporary A/C? (A320neo/B787/A350/777X et al)

What assumptions, if any, does this model make for cruise Mach? Don't know if your model accommodates this, but given the NMA is supposed to be flexible flying between short and mid ranges, what sort of trip fuel delta would a reduction in Mach speed (say .85 to .83) bring?

Taking your "wide narrowbody" as the baseline, by how much would the important parameters (MTOW/DOW/fuel consumption) change if trip length needs to be pushed to 5200nm (East Asia -> Europe) for both sizes, if we assume payload drops 20% from your baseline (20t/25t->16t/20t, think more premium seat layout)?
 
CowAnon
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Re: NMA/MOM/797 variant performance analysis

Tue Feb 18, 2020 8:11 pm

JustSomeDood wrote:
Really interesting stuff here, just want to ask a couple of things:

SFC has been set to 0.49 in all scenarios, this is obviously a fuel consumption/thrust figure of some sort but how does it compare to other contemporary A/C? (A320neo/B787/A350/777X et al)


From PD-14: New-generation engine for MC-21 (Dec. 2011 article), the specific fuel consumption is 0.51-0.53 (in lbs-fuel / lbf-thrust / hour, or kg/kgf/hr) for comparable narrowbody engines. The SFC will be a little lower for large widebody engines, but I don't know the exact values.
 
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Re: NMA/MOM/797 variant performance analysis

Tue Feb 18, 2020 8:57 pm

JustSomeDood wrote:
SFC has been set to 0.49 in all scenarios, this is obviously a fuel consumption/thrust figure of some sort but how does it compare to other contemporary A/C? (A320neo/B787/A350/777X et al)

0.49 is actually conservative.

Trent XWB is listed at 0.478.
Trent 1000 is 0.506.
CFM LEAP is 0.51

Going bigger with the same level tech often results in better fuel consumption. The XWB has the best tech and us bigger.

I would say simply scaling up LEAP to 48,000lb the SFC would drop below 0.50. Adding minor tech improvements would see it hit 0.49. If it uses Pratts 5 and the GE9x core tech it will hit 0.48 easily.

JustSomeDood wrote:
Taking your "wide narrowbody" as the baseline, by how much would the important parameters (MTOW/DOW/fuel consumption) change if trip length needs to be pushed to 5200nm (East Asia -> Europe) for both sizes, if we assume payload drops 20% from your baseline (20t/25t->16t/20t, think more premium seat layout)?

That 4700nm mission profile had a MTOW of only 138t. A MTOW of 144t would see it hit 5200nm easily. This aircraft will easily fly Asia to Europe. That is still using relatively high seating density compared to long haul widebody standards. We see 787-9's with under 250 seats fairly often. That density would result in only 160 seats on the 797-6 that would give a big range boost of easily another 500nm. This will open up all of East Asia with Europe. It will also become a pacific rim aircraft. Japan to US west coast would be no problem.
 
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Re: NMA/MOM/797 variant performance analysis

Tue Feb 18, 2020 10:57 pm

keesje wrote:
The landing weight seems higher than an A321XLR MTOW. That's translating in costs at all levels.

It is much lower costs than the thousands of other widebody aircraft. Lower costs at all levels.

The 797-7 proposed actually has better econimics per passenger than the A321. We are looking at a 4.95m wide passenger cabin that is 23cm wider than the 767. The cabin length for the 797-7 is equal to the 767-300 at 40.36m. Cabin area is then 200m2.

The A321 has a cabin area of only 127m2. The 797-7 has a cabin area 57% larger. The DOW is also 57% higher once you add the ACT or RCT weight to the A321. This has satisfied the widebody with narrowbody economics. The 797-7 will not have a wing limited to code C gates, it will have a higher aspect ratio wing and better lift to drag ratio. It will not be stuck cruising at 28,000ft for hours like the A321. Fuel burn per passenger will be better.



keesje wrote:
Curvature, 17 inch seats combined with 16inch aisles would have people hang into the aisles and being bump by troleey and everyone
This is not a 75m long widebody. Consider the 2-4-2 cabin as two 2-2 cabins of a Q400 and the 16inch aisle is now fine. That is a total of 32inch of aisle for 8 passengers. The A321 has only 22inch of aisle for 6 passengers.



keesje wrote:
I think this aicraft would be expensive & quickly get famous for the wrong reasons.
LD2 is the odd standard specailly for 767.
Leisure airlines use(d) 2-4-2- on the 767 airlines and moved bak to 2-3-2 after passeneger and crew feed back.

LD2 is great as you can also put LD3 sideways. Even with LD3 containers wasting space they would still have more than enough volume for passenger bags. This is very versatile when you get cargo already in a LD3 it can be placed straight onto this 797 design. The A321 would probably struggle for room even if it was placed into a LD3-45. The A321 barely has enough space to fit passenger bags.

Containers are very cheap.
 
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Re: NMA/MOM/797 variant performance analysis

Wed Feb 19, 2020 1:43 am

flipdewaf wrote:
So I did this from your info. As ever please ask questions.
Image

The dimensions for the seats an aisles are the same as in the previous example, 17" seats and 16" aisles. The Overall fuselage diameter comes out at near enough 5.1m. The drawing shows LD2 containers. I haven't drawn overhead bins because CAD takes me too long and I'm impatient.

The otehr pieces of data I put together show a need for a wing of about 220m^2 and an MTOW of 142-143t
The shorter version has a max exit limit set of 300 and the larger or 350 but you can see in teh mission data I have assumed 100kg per pax and with the pax info you supplied for both variants. The length of the two variants correspond to the 762 and 763 and the DOW for the larher variant is ~81t and the smaller version ~76t.
The missions are the same as the previous.
Image

Fred


It is really close to a 767. 0,05 m, 2 inch,

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reidar76
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Re: NMA/MOM/797 variant performance analysis

Wed Feb 19, 2020 7:30 am

RJMAZ wrote:
Consider the 2-4-2 cabin as two 2-2 cabins of a Q400 and the 16inch aisle is now fine.


Yes, I agree. The seating comfort of this proposed NMA cross section would be very similar to the Q400.

This aircraft would give 9 abreast A330s in Asia serious competition. In the US and in most other places it would be a 7 abreast aircraft, except for maybe European leisure travel companies etc.

keesje wrote:
It is really close to a 767. 0,05 m, 2 inch,


Yes, it is basically a 8 abreast 767 reincarnated.
 
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keesje
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Re: NMA/MOM/797 variant performance analysis

Wed Feb 19, 2020 8:28 am

I think a Q400 has no middle seats, extensive catering services and seldom flies longer than 100 minutes..
Lets not stick a region /leisure specification and a mainline widebody..

There a reason Boeing spends tons of money widening the 777X cabin while most 77W have 10 abreast already.

16 Inch aisle, is that the type where you walk sideways?
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flipdewaf
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Re: NMA/MOM/797 variant performance analysis

Wed Feb 19, 2020 10:35 am

RJMAZ wrote:
keesje wrote:
The landing weight seems higher than an A321XLR MTOW. That's translating in costs at all levels.

It is much lower costs than the thousands of other widebody aircraft. Lower costs at all levels.

Im not sure whether comparing to other widebodies is really that useful, flying is generally a commodity affair these days and those who know to look for comfort aren't going to choose 17" seats and 16" aisles

RJMAZ wrote:
The 797-7 proposed actually has better econimics per passenger than the A321. We are looking at a 4.95m wide passenger cabin that is 23cm wider than the 767. The cabin length for the 797-7 is equal to the 767-300 at 40.36m. Cabin area is then 200m2.

Better economics would suggest that there is more than just fuel burn, The major benefit the A321 has in its favour is the ~10k other examples of the same family flying and being produced. If we were to expect the 797-6/7 to be produced at 10/mo. I expect purchase costs to go somewhat in line with OWE so the cost per seat would be some 4% higher on a like for like basis and the the A32X is running at rate 60 then you have a ~33.5% efficiency of production deficit to make up per seat. I don't see Boeing having this level of production advantage to gain, of course going for NB they gain advantages by using the same cross section as a new high rate model.
RJMAZ wrote:
The A321 has a cabin area of only 127m2. The 797-7 has a cabin area 57% larger.

it has a 57% larger cabin for 50% extra, less comfortable, seating 2-4-2 vs 3-3.
RJMAZ wrote:
The DOW is also 57% higher once you add the ACT or RCT weight to the A321. This has satisfied the widebody with narrowbody economics. The 797-7 will not have a wing limited to code C gates, it will have a higher aspect ratio wing and better lift to drag ratio. It will not be stuck cruising at 28,000ft for hours like the A321. Fuel burn per passenger will be better.

The limitations on height are not about L/D ratio, its about available buffet margin.

RJMAZ wrote:
That is a total of 32inch of aisle for 8 passengers. The A321 has only 22inch of aisle for 6 passengers.

That's a very clumsy comparison to make. if we were to take it at a base level then the 2-4-2 has 4 inches per seat and the 3-3 is 3.67 per seat.

If we are to assume that is a reasonable means of comparison then we could go to 5 inches per seat at 8 abreast (by definition better) and have a 1-1-1-1-1-1-1-1 arrangement with 5.7" aisles.
Whilst this is an extreme example I think it demonstrates that the simple arithmetic does not suitable convey the benefits. A single blocked 16" aisle stops halt the cabin on the 2-4-2 (you do not have choice of aisles) a blocked aisle on the 3-3 blocks 100% of the passengers... but is the aisle less likely to be blocked because of its increased size? I'd wager that 1" added to the single aisle is of more benefit than 0.5" added to each of the aisles. Aisles and seat width s may be continuous variables, people aren't.

Fred
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Re: NMA/MOM/797 variant performance analysis

Wed Feb 19, 2020 10:40 am

Keesje, for years you have said it impossible the achieve the "widebody with narrowbody economics".

The information provided by flipdewaf proves it is clearly possible. Weight per square metre of cabin area is a primary metric for short haul efficiency and they are the same as the best narrowbody on the market. Instead of accepting that you now are trying to say that it is not comfortable enough. That is absolutely wrong.

With 2-4-2 that means 6 out of 8 seats are window or aisle seats. The A321 has 4 out of 6 seats. That is 75% vs 66%.

With 3-3 the window seat has to cross 2 passengers which is also a huge negative for comfort.

The 767 has 31cm of sidewall. The 737 has 22cm of sidewall. The 777X has 25cm of sidewall. So the 797 with "near enough 5.1m" will be much wider inside than a 8ab 767 reincarnated. The seats he used are standard Boeing 17inch. They are not the narrow 16inch seats used in 9ab A330's or 8ab 767.
 
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keesje
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Re: NMA/MOM/797 variant performance analysis

Wed Feb 19, 2020 12:33 pm

RJMAZ wrote:
Keesje, for years you have said it impossible the achieve the "widebody with narrowbody economics".

Correct. And some others learned a lot too, so they say. https://aviationweek.com/aerospace/boeing-hints-new-direction-nma-refocus

RJMAZ wrote:
The information provided by flipdewaf proves it is clearly possible. Weight per square metre of cabin area is a primary metric for short haul efficiency and they are the same as the best narrowbody on the market. Instead of accepting that you now are trying to say that it is not comfortable enough. That is absolutely wrong.

Hijacking Q400 17 inch seats with 16inch aisles specs and put them on a 4000NM WB & comparing the to a A321 is a nice thought experiment, but nothing more.

RJMAZ wrote:
With 2-4-2 that means 6 out of 8 seats are window or aisle seats. The A321 has 4 out of 6 seats. That is 75% vs 66%.

So ?

RJMAZ wrote:
With 3-3 the window seat has to cross 2 passengers which is also a huge negative for comfort.

It has. But people are kind of used to it, 747s, 777s & A380s have it too. As long as you have some decent width, knee room / living space..

RJMAZ wrote:
The 767 has 31cm of sidewall. The 737 has 22cm of sidewall. The 777X has 25cm of sidewall. So the 797 with "near enough 5.1m" will be much wider inside than a 8ab 767 reincarnated. The seats he used are standard Boeing 17inch. They are not the narrow 16inch seats used in 9ab A330's or 8ab 767.


You need to include the armrest. Some "smart" people halfed them in width. That doesn't help you shoulders, or create any comfort. Same for the aisle, don't have the illustion it doesn't effect seat comfort.

Divide the cabin width at shoulder height by the number of seats per row. That gives a good indication, the rest is marketing, confusiion and perception management., believe me.

Same for wall thickness, all trade-offs, it's like that for a reason. Maybe thinner means noisier, colder, more expensive, heavier, smaller windows too.
"Never mistake motion for action." Ernest Hemingway
 
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Stitch
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Re: NMA/MOM/797 variant performance analysis

Wed Feb 19, 2020 4:43 pm

I don't see 16-inch aisles working on a two-aisle airframe. The 777 is 17 inches in a 3+4+3 configuration, which is the absolute minimum I would expect (the 787 and A350 are 18 inches at 3+3+3).
 
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Re: NMA/MOM/797 variant performance analysis

Wed Feb 19, 2020 7:33 pm

keesje wrote:
RJMAZ wrote:
With 2-4-2 that means 6 out of 8 seats are window or aisle seats. The A321 has 4 out of 6 seats. That is 75% vs 66%.

So ?

[


Yes - So what - 7W is 6 out of 7 or 85.7% even better.
 
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NMA/MOM/797 variant performance analysis

Wed Feb 19, 2020 7:45 pm

morrisond wrote:
keesje wrote:
RJMAZ wrote:
With 2-4-2 that means 6 out of 8 seats are window or aisle seats. The A321 has 4 out of 6 seats. That is 75% vs 66%.

So ?

[


Yes - So what - 7W is 6 out of 7 or 85.7% even better.

Beechcraft 1900 and the conversation ends lol! Every seat both an aisle and a window plus you can see out the from too!

Fred


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morrisond
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Re: NMA/MOM/797 variant performance analysis

Wed Feb 19, 2020 8:03 pm

flipdewaf wrote:
morrisond wrote:
keesje wrote:

So ?

[


Yes - So what - 7W is 6 out of 7 or 85.7% even better.

Beechcraft 1900 and the conversation ends lol! Every seat both an aisle and a window plus you can see out the from too!

Fred


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Yes that Wins.

That reminds me of my personal favourite flight as a passenger on a Cessna Caravan Flight from Maui to Oahu last year - I had the front right seat and could see right into the cockpit and see all the cockpit displays. Cruise speed on a Caravan is not very impressive...
 
RJMAZ
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Re: NMA/MOM/797 variant performance analysis

Wed Feb 19, 2020 8:25 pm

morrisond wrote:
keesje wrote:
RJMAZ wrote:
With 2-4-2 that means 6 out of 8 seats are window or aisle seats. The A321 has 4 out of 6 seats. That is 75% vs 66%.

So ?

[


Yes - So what - 7W is 6 out of 7 or 85.7% even better.

No doubt the 2-3-2 is even more comfortable. But 2-4-2 is far more comfortable than the 3-3 if the seat size is equal. This means if we are trying to compare equal comfort for a fair comparison then the 2-4-2 has to run smaller seats to make this happen.

When you take into account the vast majority of people fly individually or in pairs 3-3 is a bad choice.

Likewise if we want to have similar boarding time. The twin aisle NMA will board much faster. To make boarding time equal for a fair comparison the twin aisle must run narrower aisles.

flipdewaf wrote:
Beechcraft 1900 and the conversation ends lol! Every seat both an aisle and a window plus you can see out the from too!

Maybe with that 8ab cross section you could add an inch to each aisle and half an inch to each seat so that keesje can't complain that it has less comfort. The widebody does appear to easily match narrowbody economics with your numbers.

57% more cabin area for 57% more DOW is impressive. It appears the fuel used is extremely low on the 8ab widebody. If we assume a full RCT in the A321XLR that means the 8ab widebody burns only 40% more fuel for 57% more cabin area. Your design has clearly added a bit of extra wing at the expense of extra empty weight like the 777X, it clearly pays off on longer flights.

It is highly likely that even with 4 inchs added to the cross section that the 8ab will easily match the A321 fuel burn per passenger.
 
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Re: NMA/MOM/797 variant performance analysis

Wed Feb 19, 2020 10:09 pm

Then we would end up with an A300 like 8 abreast, medium range aicraft. 35-40t higher empty weight than an A321. But able to carry LD3s..
"Never mistake motion for action." Ernest Hemingway
 
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Re: NMA/MOM/797 variant performance analysis

Thu Feb 20, 2020 9:02 am

In the past (7J7) Boeing looked at "fat" NB configurations offering a wider aisle.

I think the "fat" is needed for a workable NB >230 seats service concepts over longer distances.

Boeing took "767" sized seats as starting point.

Image
https://twitter.com/jonostrower/status/ ... 8541470720

And I believe weight, operating cost and flexibility will be superior to skinny twin aisles. As will comfort.

Even if you look at a lightened, modernized smaller wing A300, the A310, it is still 20-25t heavier than a a321xlr.

You won't CRFP that away. CRFP didn't do miracles is terms of weight and has drawback$ too.
.
An A322 would have restricted range, no real TATL capability, compromized premium cabins and blinding low operating costs.

Boeing knows better than anyone except Airbus and will take that into account. They have to go moonshot lean & mean.
"Never mistake motion for action." Ernest Hemingway

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