Boeing 797 Discussion Thread - 2018

SonOfABeech · Tue Sep 26, 2017 2:50 pm

I'm just an armchair engineer, but I'm skeptical of a widebody MOM unless it's something like a 788 with slashed weights,

JetBuddy · Tue Sep 26, 2017 3:08 pm

Newbiepilot wrote:
JetBuddy wrote:
I don't understand those who claim that 4500nm range will be perfect. In my opinion that is 1000nm too short. It leaves out a lot of TATL and Intra-Asian routes. If they're going to spend billions on making an all new airliner, designing it with too short range would be a massive waste.

It could be but look at the huge market between the Middle East and India and flights under 6 hours in Asia. If the airframe is too heavy with 5500nm range, it might not have low enough operating costs or acquisitions costs to undercut the A330 in the Asia and Middle Eastern markets.

Yes there's a huge sub 4500nm market, but it's a market that can be filled by the main competitor A321LR - at least up to 4200nm on paper. If range could be increased to 5500nm, it would open up the possibility for a lot of new routes that are non-existant today. Just like the 787 was a trailblazer for new long range routes, the 797 could do the same thing for medium range routes.

Another option would be to design a lighter standard version with 4500nm range, and a slightly heavier ER version with 5500-6000nm range. It would be smart to at least design the aircraft in a way that leaves that option open.

flipdewaf · Tue Sep 26, 2017 3:43 pm

Newbiepilot wrote:
In the bigger picture, the fuselage structure is just 10-15% of the entire airframe weight

so you are saying the airframe will weight 10x the fuselage weight? sounds like fuselage weight savings are important as they multiply up when you build a frame around it.

outside of the technical stuff I would have expected a project office to have been put to this already, it seems strange to mention it or indeed to have it mentioned. Like they really need to tell people they are serious about this.

Fred

Revelation · Tue Sep 26, 2017 4:06 pm

keesje wrote:
ElroyJetson wrote:
200-250 pax range 4000-4500nm and CASM at least 10% lower than the A321 neo or 737-10 MAX with equal or lower trip costs.

Do that and you have a winner.

Agree, they'll have to resist overspecification.

An oval cross section seems a kind of bad-ish idea from a structural weight / costs point of view, compared to a (near) cylindrical one.

Guess that means Boeing is full of ignorant engineers who don't know this, or they're confident they found a way to do an oval cross section with an acceptable trade off between volume and weight :scratchchin:

parapente · Tue Sep 26, 2017 4:08 pm

If we accept the fuse will be (drag reducing) ovoid (doesn't have to be that's the strong rumour-and it's far easier with carbon composite).If it were to be -as many here suggest-2X4x2,but with 17"economy seats (not Airbus 18")and of course the much thinner side walls that the Boeing mandril method allows for.Then indeed with 250-275 (one class) sizes (29-30" pitch) you may have a very efficient a/c over a 5knm typical route.Note ' all electric'for low maintenance.

It's not going to 'more' efficient than a super stretched rewinged ,metal fuse A322 (same engines assumed).But which a/c would you choose?

bigjku · Tue Sep 26, 2017 4:23 pm

parapente wrote:
If we accept the fuse will be (drag reducing) ovoid (doesn't have to be that's the strong rumour-and it's far easier with carbon composite).If it were to be -as many here suggest-2X4x2,but with 17"economy seats (not Airbus 18")and of course the much thinner side walls that the Boeing mandril method allows for.Then indeed with 250-275 (one class) sizes (29-30" pitch) you may have a very efficient a/c over a 5knm typical route.Note ' all electric'for low maintenance.

It's not going to 'more' efficient than a super stretched rewinged ,metal fuse A322 (same engines assumed).But which a/c would you choose?

A silly question but what if you are able to increase body lift by shaping and reduce wing size?

Newbiepilot · Tue Sep 26, 2017 4:36 pm

flipdewaf wrote:
Newbiepilot wrote:
In the bigger picture, the fuselage structure is just 10-15% of the entire airframe weight
so you are saying the airframe will weight 10x the fuselage weight? sounds like fuselage weight savings are important as they multiply up when you build a frame around it.

outside of the technical stuff I would have expected a project office to have been put to this already, it seems strange to mention it or indeed to have it mentioned. Like they really need to tell people they are serious about this.

Fred

The wings, engines, systems and gear make up the majority of the weight of the airframe. The engines weigh about the same as the entire fuselage structure. These factors are all dependent on MTOW and payload figures. Once the architecture of the wing, gear and engines are laid out with target weights, electrical, flight controls and hydraulics are sized around them. The furnishings, water/waste, lighting, pneumatic, and air conditioning systems are fuselage size dependent.

The driving force behind fuel burn is how much the airplane weighs. Weights are determined by how much payload is going to be carried. That payload can be fuel, passengers and cargo. Different fuselage lengths can be specified based on the payload or range targets that airlines are interested in. Airlines typically want a given number of seats and range and that determines payload requirement. As an example, JAL might want 300 seats over 500 miles whereas UA wants 180 seats over 4500 miles. 6, 7, 8 or 9 abreast isn't driving the requirements, weight is and it's possible the same wing and engine combo can fit the needs of both JAL and UA since 300-350k lbs MTOW would be perfect for both those missions. It's most likely worthwhile to have a slightly less efficient short widebody for UA than an ultra long widebody requiring a taller heavier gear for JAL. That's why I think it will be a smaller widebody personally.

texl1649 · Tue Sep 26, 2017 5:07 pm

Conformal fuel tank concepts (similar to F-16 and F-15) would seem to be possible for a modern CFRP frame without, necessarily, changing the wing box or wings themselves. Particularly for an ovoid design, this would be true. Of course, different MLG configurations might be needed (and/or folding tips, engine ratings, etc).

It's sort of fascinating to consider given the possibility of a limited cargo hold for this second generation carbon framed widebody; (a) folding tips optional, (b) heavier/additional stages for engines available), (c) different bogey configurations (MLG), and (d) additional tanks around fuselage-wing areas. It all makes me think Boeing might launch, initially, with 3 variants, as they originally did/tried with the 787 (the -3 variant being essentially non-competitive/over-built winding up cancelled).

Not that much additional structure has to be built into the basic, shortest range, longer fuselage, no additional tanks "stripper model" 797-10, versus an "ER" (6-8 rows shorter frame) up tanked frame.

flipdewaf · Tue Sep 26, 2017 6:22 pm

Newbiepilot wrote:
The wings, engines, systems and gear make up the majority of the weight of the airframe.

totally agree, all in order to get the fuselage full of pax and cargo off the ground.

Newbiepilot wrote:
The engines weigh about the same as the entire fuselage structure

exactly, and if the fuselage is heavier those pieces will have to be heavier as well to lift it.

Newbiepilot wrote:
These factors are all dependent on MTOW and payload figures.

but MTOW isn't dependent on the weight of the main structural components?

Newbiepilot wrote:
6, 7, 8 or 9 abreast isn't driving the requirements,

but the number abreast drives the width and the width drives the weight and

Newbiepilot wrote:
The driving force behind fuel burn is how much the airplane weighs

Fred

strfyr51 · Tue Sep 26, 2017 6:34 pm

HTCone wrote:
It's going to be a very difficult aircraft to get right isn't it? Too big/heavy, could eat 787 sales, and A330Neo MAY take too many of it's sales to make it as profitable as it could be. Not capable enough, ditto with the A321LR, or inevitable A322. Interesting times ahead. Looking forward to seeing what they come up with.

Is that what you Know?? Or what you HOPE?? Because it Certainly isn't anything you can Prove!!

strfyr51 · Tue Sep 26, 2017 6:49 pm

Designing a Middle of the Market airplane in the B797, the question IS?? Where if the Middle of the market?? I submit it is just longer than the B767-200 and
B767 300, within a few miles. However, What Boeing states the range to BE and what it actually IS?? Might be 2 separate ranges of which I seriously doubt it will be LESS than the B767-300ER. But it will NOT be the same as the B787-8. ..

strfyr51 · Tue Sep 26, 2017 7:11 pm

The optimum Between the Single aisle of the B757-300 and the B767-300 or B767-400 makes the twin aisle the better fuselage base because of the ease of Loading and unlading passengers and LD2 or LD3 containers.
It will be faster to load cargo with fewer people and have a greater freight base for revenue cargo than the B757.passengerliner has.
I think Boeing could still update and build the B757 sized airplane in the future...

Newbiepilot · Tue Sep 26, 2017 7:21 pm

flipdewaf wrote:
Newbiepilot wrote:
The wings, engines, systems and gear make up the majority of the weight of the airframe.
totally agree, all in order to get the fuselage full of pax and cargo off the ground.
Newbiepilot wrote:
The engines weigh about the same as the entire fuselage structure
exactly, and if the fuselage is heavier those pieces will have to be heavier as well to lift it.
Newbiepilot wrote:
These factors are all dependent on MTOW and payload figures.
but MTOW isn't dependent on the weight of the main structural components?
Newbiepilot wrote:
6, 7, 8 or 9 abreast isn't driving the requirements,
but the number abreast drives the width and the width drives the weight and
Newbiepilot wrote:
The driving force behind fuel burn is how much the airplane weighs

Fred

The differences in fuselage weight between a 6 abreast airplane that is 18% longer than a 7 abreast plane or 33% longer than an 8 abreast airplane aren't that huge in the grand scheme of things. Perhaps 1-2% difference in airframe weight. That's why cabin width isn't as crucial as some here act like it is (not you). The penalties of having 2 aisles in a 7 abreast layout aren't that terrible if it allows the airframe to be stretched longer for higher capacity stretched configurations without needing taller gear or poor takeoff performance. 7 abreast may not be ideal, but it isn't a prohibitive setup making the 797 nonviable. It's an option depending on capacities that airlines want. Hopefully that makes some sense.

I think figuring out what payload to optimize the wing and engine combination for is the big challenge.

nine4nine · Tue Sep 26, 2017 7:23 pm

Perhaps similar to the 757 but a 2x2x2 twin aisle? The fuselage would be a tad wider than 757 and also ease the boarding process at the same time and be able to reasonably fit into airports the 757's currently fly into (SNA for instance) whereas a 767 size plane cannot. That's my guess....

PlanesNTrains · Tue Sep 26, 2017 7:44 pm

strfyr51 wrote:
Designing a Middle of the Market airplane in the B797, the question IS?? Where if the Middle of the market?? I submit it is just longer than the B767-200 and
B767 300, within a few miles. However, What Boeing states the range to BE and what it actually IS?? Might be 2 separate ranges of which I seriously doubt it will be LESS than the B767-300ER. But it will NOT be the same as the B787-8. ..

strfyr51 wrote:
The optimum Between the Single aisle of the B757-300 and the B767-300 or B767-400 makes the twin aisle the better fuselage base because of the ease of Loading and unlading passengers and LD2 or LD3 containers.
It will be faster to load cargo with fewer people and have a greater freight base for revenue cargo than the B757.passengerliner has.
I think Boeing could still update and build the B757 sized airplane in the future...

Is that what you Know?? Or what you HOPE?? Because it Certainly isn't anything you can Prove!! :-)

Polot · Tue Sep 26, 2017 7:45 pm

nine4nine wrote:
Perhaps similar to the 757 but a 2x2x2 twin aisle? The fuselage would be a tad wider than 757 and also ease the boarding process at the same time and be able to reasonably fit into airports the 757's currently fly into (SNA for instance) whereas a 767 size plane cannot. That's my guess....

Airlines would just go 3-3.

Also SNA can handle 767 sized planes, FedEx use to (maybe still does, idk) fly A300/A310s there.

Revelation · Tue Sep 26, 2017 8:40 pm

Newbiepilot wrote:
I think figuring out what payload to optimize the wing and engine combination for is the big challenge.

I think what you're writing is going right over the heads of most of the posters here.

It bears repeating, with some emphasis:

Newbiepilot wrote:
Airliners.net spends a lot of time talking about cabin width. A lot of casual aviation fans don't see much more than the interior of an airplane and a paint scheme from afar. I think that might be why there is so much discussion on width of the cabin and efficiencies from 6, 7, 8 etc abreast seating and 17inch vs 18 inch wide seats. What else are you going to think about while on a long flight sitting in economy? Not as many people pay close attention to the exact geometry of the wing, how many spoilers there are, if the flaps are double slotted and how the wing high lift devices work at low speeds to maximize payload.

In the bigger picture, the fuselage structure is just 10-15% of the entire airframe weight. The added weight of a 7 abreast cabin vs 6 abreast is going to be very small. The engineers can optimize the length, width and diameter of the fuselage for the number of passengers they intend to carry. There is lots of flexibility and shorter fuselages have some positive features as well as narrower fuselages.

What I think really maters is payload and that depends on size of the wing and engines chosen. The 787 wing is 3 times the size of the 737 and the engines have almost 3 times as much thrust. That is where there is a huge gap. Splitting the difference in wing area with a 2500 sq ft wing and engines with 50k lbs thrust could allow a smaller version to have close to the range of a 767 and a larger version to have less range but very low CASM on missions under 2500 miles.

A MTOW in the 250-350K range could open up a lot of sales opportunities for the Asian market. The Asian market that we have today barely existed when the A300 and A310 were designed (Beijing's airport had 12 gates when the A300 entered service and now has over 100). The result is that there are A330s, 787s, and 777s being used on flights under 2000 miles all across Asia. These airplanes have overpowered engines and too large of wings to be efficient in this segment compared to a clean sheet design. Even without step changes in engine technology and optimized wing and engine combo could sell very well.

I think we probably will see a widebody design so that the airplane can have enough capacity to compete against an A330neo flying regional flights between the Middle East and India or regionally in East Asia between destinations like SIN, HKG, TPE, PVG, PEK, CAN, ICN, NRT, KIX, HND etc. The Japanese airlines will have a plane better suited for their short haul market while US carriers will have a lower capacity version best suited for point to point transatlantic and Hawaii.

flipdewaf · Tue Sep 26, 2017 8:45 pm

Newbiepilot wrote:
I think figuring out what payload to optimize the wing and engine combination for is the big challenge.

I agree, framing the problem correctly and solving fro the actual issue and not the perceived issues (the most important and hardest part of problem solving is to know what the problem is). I do think though that once you have solved that the fuselage has to be designed through decisions whereas the thrust levels and wing area will all but fall out of a properly constructed constraints diagram, the maths tells you how big your wing should be and how much thrust you need. This is the way I was tought.

Fred

william · Tue Sep 26, 2017 9:07 pm

Boeing knows what it is up against in regards an Airbus response. Boeing has run the numbers on a lengthened A321 with a new wing and engines. Its against that aircraft Boeing is making sure this aircraft will compete against. On the flip side Airbus is taking the same info read here on Anet and have ran simulations on oval twin aisles and wider single aisles. They have an idea just how efficient this MOM can be.

aviationjunky · Tue Sep 26, 2017 9:23 pm

So, essentially they want a 767 replacement? According to the charts above, that is the MoM right now. But isn't the 767 still in production, just with no orders or anything? Wouldn't it be easier and cheaper to just update the current 767, and save the 797 model for something completely different?

william · Tue Sep 26, 2017 9:32 pm

aviationjunky wrote:
So, essentially they want a 767 replacement? According to the charts above, that is the MoM right now. But isn't the 767 still in production, just with no orders or anything? Wouldn't it be easier and cheaper to just update the current 767, and save the 797 model for something completely different?

There are numerous posts on this subject. The short story is even if you put a new wing, engines and avionics on the 767, it would still be too heavy to be competitive. Not to mention Boeing offered this to the airlines and they stated not interested.

Stitch · Tue Sep 26, 2017 9:50 pm

nine4nine wrote:
Perhaps similar to the 757 but a 2x2x2 twin aisle? The fuselage would be a tad wider than 757 and also ease the boarding process at the same time and be able to reasonably fit into airports the 757's currently fly into (SNA for instance) whereas a 767 size plane cannot. That's my guess....

Well Boeing would have direct knowledge of the McDonnell-Douglas DC-XX, which was their answer to the Boeing 757. Derived from the ATMR (Advanced Technology, Medium Range) studies it would have used the PW2000 engine combined with a smaller, but higher-aspect ratio wing and offered 3+3, 2+2+2 or 2+3+2 seating in a cabin 439cm wide (compared to the 757's 376cm). McD figured it would weigh less than a 757-200 and burn 8-10% less fuel.

nine4nine · Tue Sep 26, 2017 10:42 pm

Polot wrote:
nine4nine wrote:
Perhaps similar to the 757 but a 2x2x2 twin aisle? The fuselage would be a tad wider than 757 and also ease the boarding process at the same time and be able to reasonably fit into airports the 757's currently fly into (SNA for instance) whereas a 767 size plane cannot. That's my guess....

Airlines would just go 3-3.

Also SNA can handle 767 sized planes, FedEx use to (maybe still does, idk) fly A300/A310s there.

Cargo ops are one thing pax ops are different. Those fed ex birds ferry out empty to LAX and have dedicated ramp markings separate the terminals. Also you can't park a 763 or A300 at the gate at a place like SNA etc....Most airports the size of SNA where the 757 operates as the largest pax aircraft have limited gate space and ramps are marked accordingly. Too big of a plane would make many airports inoperable.

keesje · Tue Sep 26, 2017 11:06 pm

Personally I'm not blown away by the innovation I've heard about / seen sofar on a possible 797.

Obviously we are seduced by great concepts proving the enormous leaps forward, only to be presented more of the same at launch.

I know I know I see this totally wrong.. or at least 85%

:wink2:

Newbiepilot · Tue Sep 26, 2017 11:39 pm

keesje wrote:
Personally I'm not blown away by the innovation I've heard about / seen sofar on a possible 797.

Obviously we are seduced by great concepts proving the enormous leaps forward, only to be presented more of the same at launch.

I know I know I see this totally wrong.. or at least 85%

Sticking green symbols on pictures of concept designs doesn't make them more practical. There is a reason why most planes are twin engine with a conventional tail.

PlanesNTrains · Wed Sep 27, 2017 1:00 am

Newbiepilot wrote:
keesje wrote:
Personally I'm not blown away by the innovation I've heard about / seen sofar on a possible 797.

Obviously we are seduced by great concepts proving the enormous leaps forward, only to be presented more of the same at launch.

I know I know I see this totally wrong.. or at least 85%

Sticking green symbols on pictures of concept designs doesn't make them more practical. There is a reason why most planes are twin engine with a conventional tail.

What about a fly?

Revelation · Wed Sep 27, 2017 1:29 am

keesje wrote:
Personally I'm not blown away by the innovation I've heard about / seen sofar on a possible 797.

I wonder if people at Boeing are deeply hurt by your disapproval? :scratchchin:

I hope they have access to good therapists. :wink2:

Devilfish · Wed Sep 27, 2017 1:53 am

keesje wrote:
Personally I'm not blown away by the innovation I've heard about / seen sofar on a possible 797.

Inasmuch as web images are already being posted, maybe you would agree this is breaking the mould enough should Boeing proffer it as their MoM concept?.....

http://aviationweek.com/site-files/avia ... otor-3.jpg

http://awin.aviationweek.com/Portals/AW ... otor-2.jpg

Across the pond, Airbus was toying with other ideas..... :eyepopping:

.....

https://i.pinimg.com/originals/7b/0a/3d ... 694a0d.jpg

Byron1976 · Wed Sep 27, 2017 2:04 am

The key of the MOM, is the fuselage section. It has to be wider than the Airbus fuselage. The 21th century average man is "bigger" than the 50's man. If Boeing do wrong on this ítem, the MOM, will be a failure.

RJMAZ · Wed Sep 27, 2017 2:45 am

aviationjunky wrote:
So, essentially they want a 767 replacement?

The MOM will not be a 767 replacement. It will be a 737 and A320 replacement on thick congested routes.

There are a lot of destination pairs that operate 10+ narrowbody flights per day. With shortages of gates in Asia they frequently use widebody aircraft for short 1000nm trips. It costs them more to do this but they have no choice. This shortage of gates will increase in the future and the MOM will take full advantage of this.

RJMAZ · Wed Sep 27, 2017 3:02 am

JetBuddy wrote:
I don't understand those who claim that 4500nm range will be perfect. In my opinion that is 1000nm too short. It leaves out a lot of TATL and Intra-Asian routes. If they're going to spend billions on making an all new airliner, designing it with too short range would be a massive waste.

5500nm is too long. That is the exact trap Boeing has to avoid. The extra structure and fuel capacity to get that extra 1000nm is just dead weight in routes below 4000nm. It will destroy any chance of competing on CASM with the narrowbodies. This is where 1000 frames can be sold to airlines with gate shortages. Plenty of airlines are operating 10+ daily narrowbody flights between destination pairs. The MOM will capture a huge percentage of this short thick market.

On the other end of the spectrum you are getting close to the medium haul CASM monster known as the 787-10. With its range of 6430nm it will be the aircraft of choice for those long distance TATL routes. It would be impossible for such a long range MOM to come close to the CASM of the 787-10.

JHwk · Wed Sep 27, 2017 3:21 am

It will be interesting to see what Boeing comes up with.

I would think that gate constraints would favor 737 lengths and (folded) wingspans with an 8-abreast section optimal, and I guess the fan diameter is somewhere around 92-100".

Could we see a more unique wing-body join like this?

StudiodeKadent · Wed Sep 27, 2017 4:44 am

strfyr51 wrote:
Designing a Middle of the Market airplane in the B797, the question IS?? Where if the Middle of the market?? I submit it is just longer than the B767-200 and
B767 300, within a few miles..

Yeah, that's basically it.

The 787-8 replaces the 767 ER models, the 787-9 basically provides A330-capacity at 777-300ER ranges, and the 787-10 replaces shorter-range 777s

But there's still a gap in the market. Basically, 200-269 pax/4000-5000nmi. The A330-200 and A330-800 are inefficient designs particularly at such ranges. The A330-300 is a larger size category. The non-ER 767s are obsolete, and the A321neoLR only barely reaches the very minimum for that market space.

If the 797 is a replacement for 767-200/767-300 jets, there aren't going to be any really competing products.

I think we already know the 797 will be a 7-abreast twin aisle aircraft with two models... an optimized base model and a simple stretch. Let's call these the 797-9 and 797-10. I'd predict the -9 would have around 240pax/5000ish nmi (probably a bit more than 5000... but certainly no more than 5500), and the -10 would be 270pax/>4000nmi (probably around 4200nmi or so for denser TATL routes).

iamlucky13 · Wed Sep 27, 2017 8:23 am

keesje wrote:
Personally I'm not blown away by the innovation I've heard about / seen sofar on a possible 797.

Why would you expect to be blown away? Almost all of the discussion with regards to the MoM concept from Boeing has been laced with an understanding that it won't be focused on radical innovation but on applying their existing technology and carefully chosen incremental improvements to create new model at modest development cost.

seahawk · Wed Sep 27, 2017 9:04 am

The industry has no appetite for moon shots at the moment. I would not even be surprised if the 797 would feature a conventional fuselage or maybe a A350 like solution.

keesje · Wed Sep 27, 2017 9:26 am

As long as we fully understand & embrace taking the development directions we see on new aircraft, we are doubling air pollution in the next 20 years (assuming traffic keeps doubling every 15 yrs).

Boeing (& Airbus) are pursuing innovation and leadership that will build a brighter, more sustainable future for employees, customers, communities and industry. It seems the global pollution has lower priority.

Just observing :veryhappy:

Good thing is, we as an industry know what we are doing, so we can explain later on why we cooperated !

seahawk · Wed Sep 27, 2017 9:33 am

The technology shown in the studies will not be ready by 2025. It will come around 2030 and later. The question is how sustainable a new aircraft project is, when we are expecting new disruptive technologies to mature less than a decade after launch of this new plane,

SomebodyInTLS · Wed Sep 27, 2017 9:44 am

Newbiepilot wrote:
The differences in fuselage weight between a 6 abreast airplane that is 18% longer than a 7 abreast plane or 33% longer than an 8 abreast airplane aren't that huge in the grand scheme of things. Perhaps 1-2% difference in airframe weight. That's why cabin width isn't as crucial as some here act like it is (not you). The penalties of having 2 aisles in a 7 abreast layout aren't that terrible if it allows the airframe to be stretched longer for higher capacity stretched configurations without needing taller gear or poor takeoff performance. 7 abreast may not be ideal, but it isn't a prohibitive setup making the 797 nonviable. It's an option depending on capacities that airlines want. Hopefully that makes some sense.

I think figuring out what payload to optimize the wing and engine combination for is the big challenge.

You're missing Fred's point... cabin width DETERMINES THE PAYLOAD (then additional aisles etc. add a penalty).

Newbiepilot · Wed Sep 27, 2017 10:41 am

SomebodyInTLS wrote:
Newbiepilot wrote:
The differences in fuselage weight between a 6 abreast airplane that is 18% longer than a 7 abreast plane or 33% longer than an 8 abreast airplane aren't that huge in the grand scheme of things. Perhaps 1-2% difference in airframe weight. That's why cabin width isn't as crucial as some here act like it is (not you). The penalties of having 2 aisles in a 7 abreast layout aren't that terrible if it allows the airframe to be stretched longer for higher capacity stretched configurations without needing taller gear or poor takeoff performance. 7 abreast may not be ideal, but it isn't a prohibitive setup making the 797 nonviable. It's an option depending on capacities that airlines want. Hopefully that makes some sense.

I think figuring out what payload to optimize the wing and engine combination for is the big challenge.

You're missing Fred's point... cabin width DETERMINES THE PAYLOAD (then additional aisles etc. add a penalty).

Cabin width doesn't determine payload in the design phase. The engineers start with the number of passengers to be carried as decided by the marketing and configuration teams based on airline input, convert that to payload in the form of weight combined with fuel/range requirements to specify engine and wing requirements. Length and width of the fuselage can be optimized around the various passenger count targets. The design process doesn't start with choosing a cabin width and designing the plane around that. It starts with range and payload charts based on what airlines want.

flipdewaf · Wed Sep 27, 2017 11:00 am

SomebodyInTLS wrote:
Newbiepilot wrote:
The differences in fuselage weight between a 6 abreast airplane that is 18% longer than a 7 abreast plane or 33% longer than an 8 abreast airplane aren't that huge in the grand scheme of things. Perhaps 1-2% difference in airframe weight. That's why cabin width isn't as crucial as some here act like it is (not you). The penalties of having 2 aisles in a 7 abreast layout aren't that terrible if it allows the airframe to be stretched longer for higher capacity stretched configurations without needing taller gear or poor takeoff performance. 7 abreast may not be ideal, but it isn't a prohibitive setup making the 797 nonviable. It's an option depending on capacities that airlines want. Hopefully that makes some sense.

I think figuring out what payload to optimize the wing and engine combination for is the big challenge.

You're missing Fred's point... cabin width DETERMINES THE PAYLOAD (then additional aisles etc. add a penalty).

A cabin of identical area (175m^2) at 7 abreast twin aisle by my calculations works out to be ~13% heavier per seat than single aisle 6 abreast.

Obviously there may be some issues with a 59m narrow body rotating at T/O although there is a good case to say that the continuing increase in fan diameters means that legs are going to have to get longer anyway.

Fred

Newbiepilot · Wed Sep 27, 2017 11:10 am

flipdewaf wrote:
SomebodyInTLS wrote:
Newbiepilot wrote:
The differences in fuselage weight between a 6 abreast airplane that is 18% longer than a 7 abreast plane or 33% longer than an 8 abreast airplane aren't that huge in the grand scheme of things. Perhaps 1-2% difference in airframe weight. That's why cabin width isn't as crucial as some here act like it is (not you). The penalties of having 2 aisles in a 7 abreast layout aren't that terrible if it allows the airframe to be stretched longer for higher capacity stretched configurations without needing taller gear or poor takeoff performance. 7 abreast may not be ideal, but it isn't a prohibitive setup making the 797 nonviable. It's an option depending on capacities that airlines want. Hopefully that makes some sense.

I think figuring out what payload to optimize the wing and engine combination for is the big challenge.

You're missing Fred's point... cabin width DETERMINES THE PAYLOAD (then additional aisles etc. add a penalty).

A cabin of identical area (175m^2) at 7 abreast twin aisle by my calculations works out to be ~13% heavier per seat than single aisle 6 abreast.

Obviously there may be some issues with a 59m narrow body rotating at T/O although there is a good case to say that the continuing increase in fan diameters means that legs are going to have to get longer anyway.

Fred

That is a pretty hard calculation since it isn't just comparing cylinders. Weight is not linear with length. Longer planes also means longer electrical wiring runs, fuel tubes, hydraulic tubes, pneumatic ducts,etc that go up in weight for a longer plane but not wider plane. Gear also gets taller which is the densest metal on the airplane since it is steel.

SomebodyInTLS · Wed Sep 27, 2017 11:43 am

I'd like to add that I wanted to go back and delete my comment after seeing the rest of the discussion but it wouldn't let me.

I'd rather have said something like cabin width is a factor in determining the payload instead of giving the impression it's the key value.

flipdewaf · Wed Sep 27, 2017 12:42 pm

Newbiepilot wrote:
flipdewaf wrote:
SomebodyInTLS wrote:

You're missing Fred's point... cabin width DETERMINES THE PAYLOAD (then additional aisles etc. add a penalty).

A cabin of identical area (175m^2) at 7 abreast twin aisle by my calculations works out to be ~13% heavier per seat than single aisle 6 abreast.

Obviously there may be some issues with a 59m narrow body rotating at T/O although there is a good case to say that the continuing increase in fan diameters means that legs are going to have to get longer anyway.

Fred

That is a pretty hard calculation since it isn't just comparing cylinders. Weight is not linear with length. Longer planes also means longer electrical wiring runs, fuel tubes, hydraulic tubes, pneumatic ducts,etc that go up in weight for a longer plane but not wider plane. Gear also gets taller which is the densest metal on the airplane since it is steel.

It was calculated using the stamford weight breakdown estimation method which I have used successfully in the past and have calibrated against current airliners and it seems to have good accuracy (1-2%).

Fred

keesje · Wed Sep 27, 2017 1:31 pm

flipdewaf wrote:
Newbiepilot wrote:
flipdewaf wrote:

A cabin of identical area (175m^2) at 7 abreast twin aisle by my calculations works out to be ~13% heavier per seat than single aisle 6 abreast.

Obviously there may be some issues with a 59m narrow body rotating at T/O although there is a good case to say that the continuing increase in fan diameters means that legs are going to have to get longer anyway.

Fred

That is a pretty hard calculation since it isn't just comparing cylinders. Weight is not linear with length. Longer planes also means longer electrical wiring runs, fuel tubes, hydraulic tubes, pneumatic ducts,etc that go up in weight for a longer plane but not wider plane. Gear also gets taller which is the densest metal on the airplane since it is steel.

It was calculated using the stamford weight breakdown estimation method which I have used successfully in the past and have calibrated against current airliners and it seems to have good accuracy (1-2%).

Fred

It seems 767-200 - 757 comparisons confirm this. Same technology aircraft launched by the same OEM at the same time.
This time around, groundbreaking technology changing the balance between wider and longer might again not be available.

Revelation · Wed Sep 27, 2017 2:27 pm

keesje wrote:
It seems 767-200 - 757 comparisons confirm this. Same technology aircraft launched by the same OEM at the same time.
This time around, groundbreaking technology changing the balance between wider and longer might again not be available.

It seems the steady stream of good news about the progress of the program suggests that it might be available. :scratchchin:

JetBuddy · Wed Sep 27, 2017 3:11 pm

RJMAZ wrote:
JetBuddy wrote:
I don't understand those who claim that 4500nm range will be perfect. In my opinion that is 1000nm too short. It leaves out a lot of TATL and Intra-Asian routes. If they're going to spend billions on making an all new airliner, designing it with too short range would be a massive waste.

5500nm is too long. That is the exact trap Boeing has to avoid. The extra structure and fuel capacity to get that extra 1000nm is just dead weight in routes below 4000nm. It will destroy any chance of competing on CASM with the narrowbodies. This is where 1000 frames can be sold to airlines with gate shortages. Plenty of airlines are operating 10+ daily narrowbody flights between destination pairs. The MOM will capture a huge percentage of this short thick market.

On the other end of the spectrum you are getting close to the medium haul CASM monster known as the 787-10. With its range of 6430nm it will be the aircraft of choice for those long distance TATL routes. It would be impossible for such a long range MOM to come close to the CASM of the 787-10.

That must be why every single aircraft type in/around this segment only started selling when they offered better range? Your argument is flawed. Look at the A300/A310, A330, 757 and 767. The initial low range models sold poorly, but they sold a lot better when they were offered with more range.

Like I mentioned earlier, designing the aircraft with better range from the start is the key to success. At least design the aircraft so that an ER version could be offered upon demand.

Offering only 4500nm, where less than 4000nm are actually useful will be a major flaw. 5500nm opens up new routes between the US and Eastern Europe, North Africa, deeper into South America, and also a lot of Intra-Asian routes. The 797 has the possibility to be a trailblazer like the 787 was. But not with 4500nm range.

Revelation · Wed Sep 27, 2017 3:21 pm

JetBuddy wrote:
RJMAZ wrote:
JetBuddy wrote:
I don't understand those who claim that 4500nm range will be perfect. In my opinion that is 1000nm too short. It leaves out a lot of TATL and Intra-Asian routes. If they're going to spend billions on making an all new airliner, designing it with too short range would be a massive waste.

5500nm is too long. That is the exact trap Boeing has to avoid. The extra structure and fuel capacity to get that extra 1000nm is just dead weight in routes below 4000nm. It will destroy any chance of competing on CASM with the narrowbodies. This is where 1000 frames can be sold to airlines with gate shortages. Plenty of airlines are operating 10+ daily narrowbody flights between destination pairs. The MOM will capture a huge percentage of this short thick market.

On the other end of the spectrum you are getting close to the medium haul CASM monster known as the 787-10. With its range of 6430nm it will be the aircraft of choice for those long distance TATL routes. It would be impossible for such a long range MOM to come close to the CASM of the 787-10.

That must be why every single aircraft type in/around this segment only started selling when they offered better range? Your argument is flawed. Look at the A300/A310, A330, 757 and 767. The initial low range models sold poorly, but they sold a lot better when they were offered with more range.

Like I mentioned earlier, designing the aircraft with better range from the start is the key to success. At least design the aircraft so that an ER version could be offered upon demand.

Offering only 4500nm, where less than 4000nm are actually useful will be a major flaw. 5500nm opens up new routes between the US and Eastern Europe, North Africa, deeper into South America, and also a lot of Intra-Asian routes. The 797 has the possibility to be a trailblazer like the 787 was. But not with 4500nm range.

As above, "The 787 wing is 3 times the size of the 737 and the engines have almost 3 times as much thrust", so how much weight/thrust are you willing to add to the 4500nm model to get that extra 1000nm range? The additional weight added to get additional range curve is flatter than it was back in the 80s but it's still not flat. It'll be interesting to see what Boeing ends up presenting.

JetBuddy · Wed Sep 27, 2017 3:42 pm

Revelation wrote:
JetBuddy wrote:
RJMAZ wrote:

5500nm is too long. That is the exact trap Boeing has to avoid. The extra structure and fuel capacity to get that extra 1000nm is just dead weight in routes below 4000nm. It will destroy any chance of competing on CASM with the narrowbodies. This is where 1000 frames can be sold to airlines with gate shortages. Plenty of airlines are operating 10+ daily narrowbody flights between destination pairs. The MOM will capture a huge percentage of this short thick market.

On the other end of the spectrum you are getting close to the medium haul CASM monster known as the 787-10. With its range of 6430nm it will be the aircraft of choice for those long distance TATL routes. It would be impossible for such a long range MOM to come close to the CASM of the 787-10.

That must be why every single aircraft type in/around this segment only started selling when they offered better range? Your argument is flawed. Look at the A300/A310, A330, 757 and 767. The initial low range models sold poorly, but they sold a lot better when they were offered with more range.

Like I mentioned earlier, designing the aircraft with better range from the start is the key to success. At least design the aircraft so that an ER version could be offered upon demand.

Offering only 4500nm, where less than 4000nm are actually useful will be a major flaw. 5500nm opens up new routes between the US and Eastern Europe, North Africa, deeper into South America, and also a lot of Intra-Asian routes. The 797 has the possibility to be a trailblazer like the 787 was. But not with 4500nm range.

As above, "The 787 wing is 3 times the size of the 737 and the engines have almost 3 times as much thrust", so how much weight/thrust are you willing to add to the 4500nm model to get that extra 1000nm range? The additional weight added to get additional range curve is flatter than it was back in the 80s but it's still not flat. It'll be interesting to see what Boeing ends up presenting.

I'm no expert in aerodynamics or aircraft design. I do understand your point, but comparing a long range widebody aircraft like the 787 with a short/medium range narrowbody aircraft like the 737 isn't really fruitful. Of course the 787 wings are 3 times the size of the 737 wings.

I'm talking about adding 20% more range in the same aircraft model (797/MOM 4500nm baseline suggestion), not tripling or quadrupling the range and doubling the pax capacity as is the case between the 737 and 787.

Revelation · Wed Sep 27, 2017 3:47 pm

JetBuddy wrote:
Revelation wrote:
JetBuddy wrote:

That must be why every single aircraft type in/around this segment only started selling when they offered better range? Your argument is flawed. Look at the A300/A310, A330, 757 and 767. The initial low range models sold poorly, but they sold a lot better when they were offered with more range.

Like I mentioned earlier, designing the aircraft with better range from the start is the key to success. At least design the aircraft so that an ER version could be offered upon demand.

Offering only 4500nm, where less than 4000nm are actually useful will be a major flaw. 5500nm opens up new routes between the US and Eastern Europe, North Africa, deeper into South America, and also a lot of Intra-Asian routes. The 797 has the possibility to be a trailblazer like the 787 was. But not with 4500nm range.

As above, "The 787 wing is 3 times the size of the 737 and the engines have almost 3 times as much thrust", so how much weight/thrust are you willing to add to the 4500nm model to get that extra 1000nm range? The additional weight added to get additional range curve is flatter than it was back in the 80s but it's still not flat. It'll be interesting to see what Boeing ends up presenting.

I'm no expert in aerodynamics or aircraft design. I do understand your point, but comparing a long range widebody aircraft like the 787 with a short/medium range narrowbody aircraft like the 737 isn't really fruitful. Of course the 787 wings are 3 times the size of the 737 wings.

I'm talking about adding 20% more range in the same aircraft model (797/MOM 4500nm baseline suggestion), not tripling or quadrupling the range and doubling the pax capacity as is the case between the 737 and 787.

Sure, and I'm no expert either, but weight growth is not really linear because to add fuel you need to add strengthening which adds weight, so you need to add more thrust which also adds weight, so you need to add more fuel for the same range, and now we're in a negative feedback loop.

NYCRuss · Wed Sep 27, 2017 4:05 pm

Revelation wrote:
JetBuddy wrote:
Revelation wrote:

As above, "The 787 wing is 3 times the size of the 737 and the engines have almost 3 times as much thrust", so how much weight/thrust are you willing to add to the 4500nm model to get that extra 1000nm range? The additional weight added to get additional range curve is flatter than it was back in the 80s but it's still not flat. It'll be interesting to see what Boeing ends up presenting.

I'm no expert in aerodynamics or aircraft design. I do understand your point, but comparing a long range widebody aircraft like the 787 with a short/medium range narrowbody aircraft like the 737 isn't really fruitful. Of course the 787 wings are 3 times the size of the 737 wings.

I'm talking about adding 20% more range in the same aircraft model (797/MOM 4500nm baseline suggestion), not tripling or quadrupling the range and doubling the pax capacity as is the case between the 737 and 787.

Sure, and I'm no expert either, but weight growth is not really linear because to add fuel you need to add strengthening which adds weight, so you need to add more thrust which also adds weight, so you need to add more fuel for the same range, and now we're in a negative feedback loop.

Do we know for sure that a 5500nm design would create that negative feedback loop?

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