As in, will it be a long narrow body or a very short wide body? (Or rather, what do you guys think it'll be?)

Hard to say when there is very few info out in the public domain other than the concept pic floating in the net since last year. Your guess is good as anyone's and if I were to guess, it will most likely be somewhere between the two.

http://ihaveaplanetocatch.com/2017/06/2 ... f-the-797/

Most people expect wide body 2-3-2.



The concept to beat is long 3-3 fuselages.

Maybe it can become something inbetween, offering advantages of both 3-3 and 2-3-2.

Hey, guys, what is "in between a narrow body and a wide body"? A description - or better a diagram - might help those like me to struggle with this in between notion

By the way, do we really need this, yet another 797 thread? I think not

I think a better definition (other than narrow and wide body) is single aisle and twin aisle.

sassiciai wrote:

Hey, guys, what is "in between a narrow body and a wide body"? A description - or better a diagram - might help those like me to struggle with this in between notion

By the way, do we really need this, yet another 797 thread? I think not

E.g. 2 aisles in front to give everyone aisle access and a single wide (1.5) aisle in the back, to speed up boarding / deboarding when operating shorter flights.



Goal would be to get towards a serious 200-220 dual class configuration without getting into typical twin aisle cost level situations.

Where's the "it'd look like a 767" option, giving a 767 the A350mk1 treatment with enough tweeks for 8-abreast Y sounds like the most probable scenario for me.

StTim wrote:

I think a better definition (other than narrow and wide body) is single aisle and twin aisle.

it is my impression that the two definitions are identical:
narrow body = single aisle
wide body = twin aisle

...at least, I never read/heard anything different from this.

please, let me know if I am wrong!

Personally I'm imagining it as a widebody MC-21 :p

Can't see a short-and-fat design like the A310 or B762 - increasing fuselage diameter increases drag, which needs to be offset both aerodynamically (eg by increasing overall wetted area) and financially (increasing capacity), and I think the business case for two aisles and ULD capability will rule out a B753-style "pencil" design.

I see it as a scaled down 787. Like the 787 and the A350, manufactures are making the cabins wider. Now how wide would you go, as the article above talks about drag. But it would be nice to have a wider cabin with wider seats for a narrowish body aircraft that can go long distances.

To be honest I am kind of glad to see a thread dedicated to this topic since it is probably the most discussed part of the proposed 797/NMA/MOM.

Wider is heavier, but shorter is lighter. It takes a team of engineers who actually know all the constraints to determine what is actually most efficient, but that doesnt stop a healthy discussion from armchair engineers who design in photoshop.

Beatyair wrote:

I see it as a scaled down 787. Like the 787 and the A350, manufactures are making the cabins wider. Now how wide would you go, as the article above talks about drag. But it would be nice to have a wider cabin with wider seats for a narrowish body aircraft that can go long distances.

I think e.g. A321 seats & aisle are significantly wider than on a 9 aabreast 787 or 10 abreast 777. A wide cabin is nice, unless you stuff it with an extra seat per row and shrink seat width, armrests and aisles. And that's exactly what happened.



A slightly wider narrowbody fuselage could become a way to open more capacity for efficient NB's, by eliminating long boarding time restrictions and structural in-efficiency of long tubes. Plus it would fill in aisle excess requirements for business class and open up space for more cargo in an efficient, standard containerized way.

I assume a possible 797 will have a new optimized wing anyway. It will be dimensioned based on MTOW, mission profile, range, engine requirements and handling characteristics.

Personally I hope the design comes out looking at least in some way like a natural 757 successor. Failing that and if going wide, like a 762 Max concept.

keesje wrote:

sassiciai wrote:

Hey, guys, what is "in between a narrow body and a wide body"? A description - or better a diagram - might help those like me to struggle with this in between notion

By the way, do we really need this, yet another 797 thread? I think not

E.g. 2 aisles in front to give everyone aisle access and a single wide (1.5) aisle in the back, to speed up boarding / deboarding when operating shorter flights.

.

I don’t think it is actually written in AC25-17A, but I think the FAA would object to a configuration where the aisles did not run the entire length of the airplane.

https://www.faa.gov/documentLibrary/med ... 25-17A.pdf

I am picturing a problem if there is an evacuation where the configuration transitions from two aisles to one if the exits in that location are blocked. A dead end aisle with an exit blocked in that area could be a death zone. A dark smoke filled cabin where the aisle doesn’t run the full length of the plane could cause a big safety problem.

I also wonder how the flight attendant visibility requirements would be satisfied

https://www.faa.gov/documentLibrary/med ... 785-1B.pdf

In general I see some regulatory barriers to having a hybrid partial single aisle partial dual aisle configuration

keesje wrote:

I think e.g. A321 seats & aisle are significantly wider than on a 9 aabreast 787 or 10 abreast 777. A wide cabin is nice, unless you stuff it with an extra seat per row and shrink seat width, armrests and aisles. And that's exactly what happened.



A slightly wider narrowbody fuselage could become a way to open more capacity for efficient NB's, by eliminating long boarding time restrictions and structural in-efficiency of long tubes. Plus it would fill in aisle excess requirements for business class and open up space for more cargo in an efficient, standard containerized way.

I assume a possible 797 will have a new optimized wing anyway. It will be dimensioned based on MTOW, mission profile, range, engine requirements and handling characteristics.

I think the reason your design has never been done before is because it may be uncertifiable. The AC covering cabin crashworthiness is over 800 pages. 100 of those pages is dedicated to aisle spacing and cross aisle width and exit configuration. It is highly regulated.

Looks like the 797 will be something different to what many of us had envisioned. We had thought of a modernized 757 but looks like they want to build a totally different airplane. Looks like at the end it may be a short 787 what we may get. All I want is that they use the 787 windshield style on it. I can't wait to see it flying at last. Good luck Boeing, you'll do great.

keesje wrote:

sassiciai wrote:

Hey, guys, what is "in between a narrow body and a wide body"? A description - or better a diagram - might help those like me to struggle with this in between notion

By the way, do we really need this, yet another 797 thread? I think not

E.g. 2 aisles in front to give everyone aisle access and a single wide (1.5) aisle in the back, to speed up boarding / deboarding when operating shorter flights.



Goal would be to get towards a serious 200-220 dual class configuration without getting into typical twin aisle cost level situations.

Does it also include the giant fly under the port wing?

NYPECO wrote:

Does it also include the giant fly under the port wing?

It's shown that way to indicate that this design is air-worthy even with the loss of one fly. This is known in the industry as Enormous Fly On Port Side, commonly called EFLOPS.

Newbiepilot wrote:

I don’t think it is actually written in AC25-17A, but I think the FAA would object to a configuration where the aisles did not run the entire length of the airplane.

https://www.faa.gov/documentLibrary/med ... 25-17A.pdf

I am picturing a problem if there is an evacuation where the configuration transitions from two aisles to one if the exits in that location are blocked. A dead end aisle with an exit blocked in that area could be a death zone. A dark smoke filled cabin where the aisle doesn’t run the full length of the plane could cause a big safety problem.

I also wonder how the flight attendant visibility requirements would be satisfied

https://www.faa.gov/documentLibrary/med ... 785-1B.pdf

In general I see some regulatory barriers to having a hybrid partial single aisle partial dual aisle configuration

FWIW There is at least one configuration out there which uses a mix of one and two aisles, the upper deck of the Etihad A380. And any A330 which shifts from a 2-2-2 business class configuration to 2-4-2 in economy is going to have a significant offset in those aisles such that the aisle is nowhere close to being a straight line down the cabin.

2-4-2 for 220-270 seems kind of wide and stubby isn’t it? (Not like I know the dimensions, though). I think the “too much capacity for a narrow body but not enough for a wide body” argument comes into play here. It’s clear to me that 2-3-2 isn’t very popular (only to PAX), but to get that target capacity amount, you’d need a wide, stubby aircraft (which, like the a310, 747SP, and a318 have proven, are very successful), or a longer but not as wide wide body. Aren’t longer aircraft better with (frontal area) drag? I think yes.

I think discussion on this site has asserted that frontal drag is less a factor for drag than weight and wetted area. Perhaps someone more technical can offer a brief summary, or links to the discussions.

I'd bet GOOD Money it will be a replacement for the B767-300ER and probably with the Same or similar Fuselage dimensions except with new all digital systems a composite Wing and true Fly By wire flight controls for a smoother ride. It will set the bar for every new narrow body Boeing produces to replace the B737 and the B757 (and Yes they will eventually replace the B757 and NOT with any B737 Design!)

I think dependent on materials, cross section, there is a limit to where 3-3 is the best idea. Above 200 seats proves doable, e.g. 400 seats is theoretically possible but very heavy to preserve integrity and critical RE: the 80x80m airport restrictions and boarding.

Somewhere inbetween there is a maximum. A 10-12 inch wider than A320 fuselage opens up new territory in terms of cabin flexibility, (de)boarding speed, fuselage stifness/ strenght and most importantly; additional seatrows & AKH's in a light fuselage.

Newbiepilot wrote:

I don’t think it is actually written in AC25-17A, but I think the FAA would object to a configuration where the aisles did not run the entire length of the airplane.

https://www.faa.gov/documentLibrary/med ... 25-17A.pdf

I am picturing a problem if there is an evacuation where the configuration transitions from two aisles to one if the exits in that location are blocked. A dead end aisle with an exit blocked in that area could be a death zone. A dark smoke filled cabin where the aisle doesn’t run the full length of the plane could cause a big safety problem.

I also wonder how the flight attendant visibility requirements would be satisfied

https://www.faa.gov/documentLibrary/med ... 785-1B.pdf

In general I see some regulatory barriers to having a hybrid partial single aisle partial dual aisle configuration


I think the reason your design has never been done before is because it may be uncertifiable. The AC covering cabin crashworthiness is over 800 pages. 100 of those pages is dedicated to aisle spacing and cross aisle width and exit configuration. It is highly regulated.

To solve the "dead end aisle" issue, couldn't you just have an exit door at the transition point? I assume that the MOM/797 would have L2 boarding to make enplaning and deplaning more efficient. First row aft of L2 gets extra legroom.

keesje wrote:

Somewhere inbetween there is a maximum. A 10-12 inch wider than A320 fuselage opens up new territory in terms of cabin flexibility, (de)boarding speed, fuselage stifness/ strenght and most importantly; additional seatrows & AKH's in a light fuselage.

I am not trying to be rude, but Are you repeating the same nonsense regarding improved structural efficiency from a wider aisle? You waived the white flag in this thread from 6 months ago because you couldnt support or justify that statement at all.

viewtopic.php?t=1362655&start=750

keesje wrote:

Newbiepilot wrote:

How is anything that you posted relevant to your comment "A 10 inch wider fuselage also does wonders for structural efficiency / weight when going beyond 35 seat rows."

No one has posted any credible evidence or engineering rationale that a 10 inch wider fuselage has any positive structural benefit other than weighing more and increasing drag.

I legitimately tried flicking the fly off the one picture thinking it landed on my phone screen...

frmrCapCadet wrote:

I think discussion on this site has asserted that frontal drag is less a factor for drag than weight and wetted area. Perhaps someone more technical can offer a brief summary, or links to the discussions.

The discussion was in this thread: Aircraft 2-3-2 Cabin, more space & speed?

Some hard numbers are listed at Bjorn’s Corner: Aircraft drag reduction, Part 20.

In level flight at FL370, our cruise drag, at our cruise speed of M0.78 and average mission weight, is 7,900lbf. This means our engines need to produce 3,950lbf each to keep a constant Mach of 0.78.

The 7,900lbf of drag is composed of 4,700lbf of Parasitic drag or drag independent of lift and 3,200lbf of Induced drag or drag caused by lift.
...
Form drag would be around 7% of Parasitic drag, mainly coming from airflow which is disturbed by air-conditioning inlets and outlets and airflow separations caused by the upsweep and contraction of the tail of the aircraft. Separations are also caused by gaps around ailerons/rudders/flaps and the end of flap fairings and engine pylons/nacelles.
...
This means 75% of our Parasitic drag is made up of air friction drag against the aircraft’s wetted surface.

(I'm assuming that "frontal drag" was meant to indicate "form drag".)

Newbiepilot wrote:

keesje wrote:

Somewhere inbetween there is a maximum. A 10-12 inch wider than A320 fuselage opens up new territory in terms of cabin flexibility, (de)boarding speed, fuselage stifness/ strenght and most importantly; additional seatrows & AKH's in a light fuselage.

I am not trying to be rude, but Are you repeating the same nonsense regarding improved structural efficiency from a wider aisle? You waived the white flag in this thread from 6 months ago because you couldnt support or justify that statement at all.

viewtopic.php?t=1362655&start=750

keesje wrote:

Newbiepilot wrote:

How is anything that you posted relevant to your comment "A 10 inch wider fuselage also does wonders for structural efficiency / weight when going beyond 35 seat rows."

No one has posted any credible evidence or engineering rationale that a 10 inch wider fuselage has any positive structural benefit other than weighing more and increasing drag.

Hi Newbe pilot, I (and others posters #781, 782) explained you multiple times and you keep asking the same question. I gave up explaining again, that´s why the white flag.
https://www.airliners.net/forum/viewtopic.php?t=1362655&start=750#p19987987

Hi Newbie if a fuselage has a 10 inch wider fuselage, the same loads have a longer arms which leads to lower stains. It improves area moment of inertia of an aircraft fuselage cross section. Alternative you can lower the dimensions of fuselage structure and skin (weight saving) or e.g. make the fuselage longer and stay within the allowed load envelope. A bigger (average) radius helps to the fourth power improving Polar moment of inertia of a tube leaving room for weight reduction if the load stays ~ the same. Which is the case if e.g. a cabin stays 3-3 abreast + AKH container.

keesje wrote:

Newbiepilot wrote:

keesje wrote:

Somewhere inbetween there is a maximum. A 10-12 inch wider than A320 fuselage opens up new territory in terms of cabin flexibility, (de)boarding speed, fuselage stifness/ strenght and most importantly; additional seatrows & AKH's in a light fuselage.

I am not trying to be rude, but Are you repeating the same nonsense regarding improved structural efficiency from a wider aisle? You waived the white flag in this thread from 6 months ago because you couldnt support or justify that statement at all.

viewtopic.php?t=1362655&start=750

keesje wrote:

No one has posted any credible evidence or engineering rationale that a 10 inch wider fuselage has any positive structural benefit other than weighing more and increasing drag.

Hi Newbe pilot, I (and others posters #781, 782) explained you multiple times and you keep asking the same question. I gave up explaining again, that´s why the white flag.
https://www.airliners.net/forum/viewtopic.php?t=1362655&start=750#p19987987

Hi Newbie if a fuselage has a 10 inch wider fuselage, the same loads have a longer arms which leads to lower stains. It improves area moment of inertia of an aircraft fuselage cross section. Alternative you can lower the dimensions of fuselage structure and skin (weight saving) or e.g. make the fuselage longer and stay within the allowed load envelope. A bigger (average) radius helps to the fourth power improving Polar moment of inertia of a tube leaving room for weight reduction if the load stays ~ the same. Which is the case if e.g. a cabin stays 3-3 abreast + AKH container.

Thanks for the image that reminds me of freshman statics. I also learned way back in that class that a dimensionless chart or equation can’t be used to optimize a real object. For example when designing a truss, the more joints you have, theoretically the higher the strength. I remember in a lab class building a truss around one set of equations which led us to put in many joints close together. We then tested them to failure and learned that at some point you have to add a bending moment in to the equation which can cause the whole truss to twist. None of us figured out how to do that, but it was because we weren’t using higher level math and differential equations and matrix algebra, but that is what they do to you in freshman statics.

The logic you used supports a wider fuselage but tells us nothing about whether a 10 inch wider narrowbody or a 30 inch wider 7 abreast design is better. Aluminum and carbon fiber have different strength to weight ratios. A carbon fiber fuselage may be optimized to be a different width and length To fit in the same number of seats. You would have some credibility if you actually had some numbers, weights, lengths, etc. All you keep doing is talking about optimizing a single number (width) and generalizing about every other dimension. That is not how engineering works.

Newbiepilot wrote:

keesje wrote:

Hi Newbie if a fuselage has a 10 inch wider fuselage, the same loads have a longer arms which leads to lower stains. It improves area moment of inertia of an aircraft fuselage cross section. Alternative you can lower the dimensions of fuselage structure and skin (weight saving) or e.g. make the fuselage longer and stay within the allowed load envelope. A bigger (average) radius helps to the fourth power improving Polar moment of inertia of a tube leaving room for weight reduction if the load stays ~ the same. Which is the case if e.g. a cabin stays 3-3 abreast + AKH container.
https://www.engineersedge.com/imagefiles/polar-moment-of-inertia.png

Of course there are other loads the fuselage has to take, but those are often more limiting factors for widebodies, that can theoretical have thin skins from a bending standpoint but still need to withstand e.g. hail & scrapnel loads
.

How is anything that you posted relevant to your comment "A 10 inch wider fuselage also does wonders for structural efficiency / weight when going beyond 35 seat rows." What is special about 35 rows to make a wider fuselage more structurally efficient?

In one post you say widebodies can't compete with narrowbodies in efficiency. Then in another you say that current narrowbodies are too narrow and need to be wider to be more efficient. You seem to have decided that 178 inches is some magic number, yet provide no analysis why.

I understand how a beam works, but not how you are coming up with numbers showing that 178 inches is the ideal diameter for a plane that is 55 meters long. Why is 178 inches better than 196 inches or 164 inches? Nothing that you posted backs up the claim that 178 inch diameter fuselage will be lighter than a 164 inch fuselage since it is all theory. Going on the wider is better motif, why not make the airplane a 7 abreast widebody that is 196 inches wide?

It sounds like there is some kind of agenda going on about wider aisle narrowbodies, but I can’t figure it out.

The logic you used supports a wider fuselage but tells us nothing about whether a 10 inch wider narrowbody or a 30 inch wider 7 abreast design is better.

Because with a 7 abreast cross section you significant increase loads (the 7th passenger) e.g. bending moment. When you stay 3-3, you don't significantly increase (pay) loads while lowering tension loads in the crown and compression loads at the bottom. Specially when you are designing a long, high capacity fuselage, where you need to limit fuselage flexing (Ref 753, M90, A346) .



.

manicottiK wrote:

NYPECO wrote:

Does it also include the giant fly under the port wing?

It's shown that way to indicate that this design is air-worthy even with the loss of one fly. This is known in the industry as Enormous Fly On Port Side, commonly called EFLOPS.

thank you for making me actually laugh out loud!
maximum levity is needed to tolerate yet another speculative MoM/797 thread.

FlyHappy wrote:

manicottiK wrote:

NYPECO wrote:

Does it also include the giant fly under the port wing?

It's shown that way to indicate that this design is air-worthy even with the loss of one fly. This is known in the industry as Enormous Fly On Port Side, commonly called EFLOPS.

thank you for making me actually laugh out loud!
maximum levity is needed to tolerate yet another speculative MoM/797 thread.

Yes, a screaming shortage of airline feedback, design concepts, Udvar opinions is becoming visible. The x-teenth Airline XYZ saying they might be interested in an NMA is empty box material too. Even John Ostrower is turning to questionable sources. https://jonostrower.com/2018/04/toddler-helped-explain-boeings-nma-fuselage/

Maybe Boeing are saving news for Farnborough? Of course I fully understand Boeing keeping quiet as we speak, alternative they are in a deadlock ("can't close the business case") and have nothing positive to communicate..



Lets hope Airbus meanwhile hasn't been progressing A321Plus behind the curtains. An A320Plus might shorten the 737MAX product live cycle so much, medium term strategic priorities (also NMA) have to be reviewed.

keesje wrote:

The logic you used supports a wider fuselage but tells us nothing about whether a 10 inch wider narrowbody or a 30 inch wider 7 abreast design is better.

Because with a 7 abreast cross section you significant increase loads (the 7th passenger) e.g. bending moment. When you stay 3-3, you don't significantly increase (pay) loads while lowering tension loads in the crown and compression loads at the bottom. Specially when you are designing a long, high capacity fuselage, where you need to limit fuselage flexing (Ref 753, M90, A346) .

.

I find your engineering logic rather comical for why 178 inch 6 abreast fuselage width is optimal over 168 6 abreast or 196 7 abreast.

keesje wrote:

Lets hope Airbus meanwhile hasn't been progressing A321Plus behind the curtains. An A320Plus might shorten the 737MAX product live cycle so much, medium term strategic priorities (also NMA) have to be reviewed.

We had a whole thread discussion how the Chief Commercial Officer of Airbus told us the A320plus has been shelved for now.

From This Thread:
viewtopic.php?f=3&t=1391201&start=250

keesje wrote:

I think we shouldn't read too much in this rumoured to be shelved plus study. Airbus for now is the market leader, with 321LR soon entering service. A moderately upgraded A322 could be ready in 4 yrs. Most probably way cheaper and lighter than any 797 and with a karge commonakity with 6000 NEO's currently on order.

Airbus refocusing on production is not a rumor, especially when Eric Schultz (Chief Commercial Officer of Airbus) is talking about it. What shelve actually means is up for determination. Airbus explicitly said they are focusing on delivering what they committed to before moving to an upgrade. Just because you may not like it, doesn’t mean we shouldn’t read into these statements.

Post #78 from this same thread with actually quotes from Airbus:

Revelation wrote:

mmo wrote:

Here is a much better synopsis of what is going at Airbus with respect to the 32X production and the Plus and Plus Plus programs.

http://aviationweek.com/commercial-avia ... pgrade-now

The most interesting stuff to me was the direct quotes.

“We cannot fix everything at the same time,” Airbus chief commercial officer Eric Schulz said, referring to the in-service issues, the possible production rate increases and potential product development. Airbus’ management has come to the conclusion that “we need to deliver what we committed to first” before moving on to an A320neo family upgrade.

And later in the article:

Schulz conceded that “we are in a difficult situation today” and decisions have to be made “step-by-step” rather than all at once.

Total difference in tone from Leahy et al, IMHO.

I can't picture the same words coming from Leahy's mouth.

CowAnon wrote:

frmrCapCadet wrote:

I think discussion on this site has asserted that frontal drag is less a factor for drag than weight and wetted area. Perhaps someone more technical can offer a brief summary, or links to the discussions.

The discussion was in this thread: Aircraft 2-3-2 Cabin, more space & speed?

Some hard numbers are listed at Bjorn’s Corner: Aircraft drag reduction, Part 20.

In level flight at FL370, our cruise drag, at our cruise speed of M0.78 and average mission weight, is 7,900lbf. This means our engines need to produce 3,950lbf each to keep a constant Mach of 0.78.

The 7,900lbf of drag is composed of 4,700lbf of Parasitic drag or drag independent of lift and 3,200lbf of Induced drag or drag caused by lift.
...
Form drag would be around 7% of Parasitic drag, mainly coming from airflow which is disturbed by air-conditioning inlets and outlets and airflow separations caused by the upsweep and contraction of the tail of the aircraft. Separations are also caused by gaps around ailerons/rudders/flaps and the end of flap fairings and engine pylons/nacelles.
...
This means 75% of our Parasitic drag is made up of air friction drag against the aircraft’s wetted surface.

(I'm assuming that "frontal drag" was meant to indicate "form drag".)

Thanks for sharing this. I missed it earlier, but it makes the idea of a wider narrowbody less viable since the parasite drag increases.

It is looking more and more like the 797/NMA/MOM is going to look quite similar to a 767-200 and 767-300. Very similar capacities. The larger of the new planes will be pretty similar in capacity to a 787-8, but have a smaller wing, be much lighter and have lower acquisition costs than the 787-8. That should make it attractive for regional short to medium range routes. Between the 797 and 787, I would think the A330neo may get entirely pushed out of the market.

Newbiepilot wrote:

It is looking more and more like the 797/NMA/MOM is going to look quite similar to a 767-200 and 767-300. Very similar capacities. The larger of the new planes will be pretty similar in capacity to a 787-8, but have a smaller wing, be much lighter and have lower acquisition costs than the 787-8. That should make it attractive for regional short to medium range routes. Between the 797 and 787, I would think the A330neo may get entirely pushed out of the market.

Last year you said cabin width really isn't much of an issue.

It isn't that hard for the product development engineers at Boeing to layout a 6 abreast, 7 abreast and 8 abreast cabin to see which is the lightest. Cabin width just isn't a critical factor as deciding engine thrust, payload, range and wingspan.

https://www.airliners.net/forum/viewtopic.php?f=3&t=1357237&start=300#p19414253

I think it is. And a WB will costs associated would leave open a very big segment for Airbus to harvest without competition.. I doubt it.

I have no idea why Kessje here is so obsessed with the idea of a flying pencil narrowbody NMA. Maybe it's because that's the method by which Airbus can make a quick response?

In order to get a decent buffer between the NMA and any type of A320-stretch. The cabin area will have to be ~180m^2++. Even with the MC-21's cabin width (3.81m), the cabin length needs to be longer than 47 meters. Well past the point where bending loads start favoring a shorter, wider fuselage for the same area w.r.t weight and drag.

I don't think it will be a direct 767 replacement, seeing how the 767 is still in production. I don't think it will be a 757 replacement, seeing how the 737MAX-10 is less than 4 meters short of the 757-200. It wouldn't make sense to put all that money into the 737MAX-10 only to turn around and spend double for another 757 replacement. With the 757 being replaced by the 737MAX-10, the 767 still in production, the 777X coming soon, and the 787 going strong, I honestly don't see a need for the 797 right now.

Apparently, Boeing will launch a twin aisle and not a single aisle _ IF it launches anything, and plans to do so by 2025

"Ihssane Mounir, senior vice-president for commercial sales and marketing at Boeing, told French journalists Boeing would "protect" the targeted 2025 date for entry to service, which some analysts see as ideal for planned replacement cycles.

He declined to say when Boeing could make a decision on the possible twin-aisle plane, which has been the source of speculation among airlines and investors for around two years.

Mounir, who has led Boeing sales since Oct 2016, said "conservative" estimates showed global demand for 4,000 to 5,000 middle-of-the market jets over a 20-year period.".

https://finance.yahoo.com/news/boeing-s ... 34836.html

It will look like the 2707, non-existent.

XAM2175 wrote:

Personally I'm imagining it as a widebody MC-21 :p

Can't see a short-and-fat design like the A310 or B762 - increasing fuselage diameter increases drag, which needs to be offset both aerodynamically (eg by increasing overall wetted area) and financially (increasing capacity), and I think the business case for two aisles and ULD capability will rule out a B753-style "pencil" design.

Will the weight savings of CFRP on a fuselage of similar dimensions be enough to counter the drag? Not to mention the overall jumps in technology and aerodynamics since the 767 came out.

TWA772LR wrote:

Will the weight savings of CFRP on a fuselage of similar dimensions be enough to counter the drag?

Oh probably, yeah - B788 is a decent-enough example there, I think. Can't say to what extent though.

Jayafe wrote:

It will look like the 2707, non-existent.

If the segment is really 4000 to 5000 frames , it will look like something you really won't like. and neither will Airbus.

more from Mounir (must be the same interview):

https://www.ainonline.com/aviation-news ... nma-design

https://www.reuters.com/article/us-boei ... SKBN1JG23Y

Interesting they are now mentioning saving costs on the electronics by outsourcing. Shades of the 787 again, but hopefully they've learned their lesson this time.

And now the question to the thread title has been answered by a Boeing executive (yet again).

Newbiepilot wrote:

A dead end aisle with an exit blocked in that area could be a death zone. A dark smoke filled cabin where the aisle doesn’t run the full length of the plane could cause a big safety problem.

Why a dead end aisle? Can not the center section taper until the left and the right aisle join? Maybe the seatmap you were picturing is not the only way to accomplish a two-to-one-aisle transition.

Newbiepilot wrote:

No one has posted any credible evidence or engineering rationale that a 10 inch wider fuselage has any positive structural benefit other than weighing more and increasing drag.

It requires not much technical knowledge to understand, that a wider tube is stiffer than a narrow one. So to get the same sturdiness you can use thinner metal sheets, weaker stringers and frames. That is structural efficiency.

Mentioning "weighting more" and "increasing drag" you are mixing unrelated things. Even "weighting more" is not structural efficiency because efficiency describes a relation. Structural efficiency could e.g. be "added diameter per added weight".

rheinwaldner wrote:

Newbiepilot wrote:

A dead end aisle with an exit blocked in that area could be a death zone. A dark smoke filled cabin where the aisle doesn’t run the full length of the plane could cause a big safety problem.

Why a dead end aisle? Can not the center section taper until the left and the right aisle join? Maybe the seatmap you were picturing is not the only way to accomplish a two-to-one-aisle transition.

Newbiepilot wrote:

No one has posted any credible evidence or engineering rationale that a 10 inch wider fuselage has any positive structural benefit other than weighing more and increasing drag.

It requires not much technical knowledge to understand, that a wider tube is stiffer than a narrow one. So to get the same sturdiness you can use thinner metal sheets, weaker stringers and frames. That is structural efficiency.

Mentioning "weighting more" and "increasing drag" you are mixing unrelated things. Even "weighting more" is not structural efficiency because efficiency describes a relation. Structural efficiency could e.g. be "added diameter per added weight".

Rheinwalder, I wouldn't spend to much energy on this. Proof will be demanded & then ignored.

https://www.airliners.net/forum/viewtopic.php?t=1362655&start=750#p19987987

If the segment is really 4000 to 5000 frames you have to ask why it is taking so long to close the business case.

StTim wrote:

If the segment is really 4000 to 5000 frames you have to ask why it is taking so long to close the business case.

I think because who has the 757s keeps em like pure gold, others use A321s that are good-ish on medium haul.
The rest works it out with 737s, or 320s, that aren't really as good as a 753, but I don't see Southwest or Ryanair really complaining about anything on their 737s.

StTim wrote:

If the segment is really 4000 to 5000 frames you have to ask why it is taking so long to close the business case.

there is a business case but you need to assess it carefully other way you might loose the biggest part of the market.

It is my understanding that boeings need to balance at least:
- range somewhere between 2000nm and 5000nm. You cannot have everything: you need to choose which part is the most relevant for this market segment.
- cabin size for about 230 to 280 people. It is not the same aircraft and, related to this...
- ...how much belly cargo space will be offered.

Boeing needs to evaluate which segment of that market is the most relevant as per Return On Investment (ROI). For example: low cost carriers need 280 but not really cargo belly whereas other carriers might want to consider the cargo belly too (like Lufthansa). First case would be a narrowbody (if the fuselage is not too long) and probability not the longest range possible, second case is clearly a wide body and probability a more balanced range is preferred due to the variety of missions.
Range will affects wing shape and the number of expected cycles. High cycles means the landing gear gets more stressed. Regarding wing shape, if you have high cycles you can compromise a little to have better performance for take off / landing but worse on cruise for longest range routes. Also, you need to consider if you want wingtips like B787 or like B737 (one better of high cycles, one better for long flying time). In a similar fashion you also need to consider the engine nacelle shape.

That is already quite many key aspect to evaluate and Boeings wants to make sure to sell thousands of units, not just a couple hundreds.

edit to add a note: the numbers, expecially the range, are pure example from my side.

vahancrazy wrote:

StTim wrote:

If the segment is really 4000 to 5000 frames you have to ask why it is taking so long to close the business case.

there is a business case but you need to assess it carefully other way you might loose the biggest part of the market.

It is my understanding that boeings need to balance at least:
- range somewhere between 2000nm and 5000nm. You cannot have everything: you need to choose which part is the most relevant for this market segment.
- cabin size for about 230 to 280 people. It is not the same aircraft and, related to this...
- ...how much belly cargo space will be offered.

Boeing needs to evaluate which segment of that market is the most relevant as per Return On Investment (ROI). For example: low cost carriers need 280 but not really cargo belly whereas other carriers might want to consider the cargo belly too (like Lufthansa). First case would be a narrowbody (if the fuselage is not too long) and probability not the longest range possible, second case is clearly a wide body and probability a more balanced range is preferred due to the variety of missions.
Range will affects wing shape and the number of expected cycles. High cycles means the landing gear gets more stressed. Regarding wing shape, if you have high cycles you can compromise a little to have better performance for take off / landing but worse on cruise for longest range routes. Also, you need to consider if you want wingtips like B787 or like B737 (one better of high cycles, one better for long flying time). In a similar fashion you also need to consider the engine nacelle shape.

That is already quite many key aspect to evaluate and Boeings wants to make sure to sell thousands of units, not just a couple hundreds.

edit to add a note: the numbers, expecially the range, are pure example from my side.

And to that point I do not think there is a single segment for that number. There is instead a large number of different segments which could in total be 4000 to 5000 frames but to do that would require multiple different solutions. Could a big enough part of it be captured by a single solution that can be produced at a price point the airlines are willing to pay.

StTim wrote:

If the segment is really 4000 to 5000 frames you have to ask why it is taking so long to close the business case.

because

1. That's just nonsense numbers.
2. Airlines are apparently saying they won't pay the kind of pricing Boeing needs to justify it
3. China is about to take a big fat dump in the MOM sector by launching the CR-929 with Russia.

Item 3 is the most important as it means 50% or more of the predicted sales in China and Russia won't happen.

There is an Item 4 which is Airbus, however keeping this discussion just to Boeing then those three factors are stopping any business case closing.

StTim wrote:

vahancrazy wrote:

StTim wrote:

If the segment is really 4000 to 5000 frames you have to ask why it is taking so long to close the business case.

there is a business case but you need to assess it carefully other way you might loose the biggest part of the market.

It is my understanding that boeings need to balance at least:
- range somewhere between 2000nm and 5000nm. You cannot have everything: you need to choose which part is the most relevant for this market segment.
- cabin size for about 230 to 280 people. It is not the same aircraft and, related to this...
- ...how much belly cargo space will be offered.

Boeing needs to evaluate which segment of that market is the most relevant as per Return On Investment (ROI). For example: low cost carriers need 280 but not really cargo belly whereas other carriers might want to consider the cargo belly too (like Lufthansa). First case would be a narrowbody (if the fuselage is not too long) and probability not the longest range possible, second case is clearly a wide body and probability a more balanced range is preferred due to the variety of missions.
Range will affects wing shape and the number of expected cycles. High cycles means the landing gear gets more stressed. Regarding wing shape, if you have high cycles you can compromise a little to have better performance for take off / landing but worse on cruise for longest range routes. Also, you need to consider if you want wingtips like B787 or like B737 (one better of high cycles, one better for long flying time). In a similar fashion you also need to consider the engine nacelle shape.

That is already quite many key aspect to evaluate and Boeings wants to make sure to sell thousands of units, not just a couple hundreds.

edit to add a note: the numbers, expecially the range, are pure example from my side.

And to that point I do not think there is a single segment for that number. There is instead a large number of different segments which could in total be 4000 to 5000 frames but to do that would require multiple different solutions. Could a big enough part of it be captured by a single solution that can be produced at a price point the airlines are willing to pay.

Very very possible! With so many variable numbers it might even account for two aircraft family with similar pax size but different mission requirements. If the market was actually over 3000 frames, 2 families might already work. The new challenge would be: how to develop them economically and timely?
That's why, all in all, I expect Boeing to come up with just 1 product (not 2 as B757+B767) and, subsequently the problem of balancing the product. Thus, the extensive studying time we see right now.