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keesje
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Aircraft 2-3-2 Cabin, more space & speed?

Sun Mar 11, 2018 1:18 pm

I wonder if a lean 2-3-2 cabin has the speed and space advantages widely assumed.

Image

Above the 2 window seats, probably there is not enough space to put a cabin trolley wheels first/ on its side. A NB 3-3 can handle this easily.

Image

Above the 3 seater in a 2-3-2 there are left & right bins. But not deep ones either. A lot of space is used for the two aisles. Also higher in the cabin.

Speed, as to 2 narrow aisles, if 3 persons are blocking a narrow aisles, nobody goes anywhere. With one wide (e.g 30 inch) aisle, they pass those 6 non moving people. Resulting in a more constant stream of people entering /exiting the single front door.

Image
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StTim
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Sun Mar 11, 2018 1:23 pm

That MOM7 section you have highlights why it would be a poor cargo hauler. Passenger bags will take more of the available LD3-45 space.

I also see the floor structure as significantly heavier to cope with the compression loads. All others are in tension when the cabin is pressurised.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Sun Mar 11, 2018 2:35 pm

Another hypothetical mom thread...
 
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william
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Sun Mar 11, 2018 2:44 pm

keesje wrote:
I wonder if a lean 2-3-2 cabin has the speed and space advantages widely assumed.

Image

Above the 2 window seats, probably there is not enough space to put a cabin trolley wheels first/ on its side. A NB 3-3 can handle this easily.

Image

Above the 3 seater in a 2-3-2 there are left & right bins. But not deep ones either. A lot of space is used for the two aisles. Also higher in the cabin.

Speed, as to 2 narrow aisles, if 3 persons are blocking a narrow aisles, nobody goes anywhere. With one wide (e.g 30 inch) aisle, they pass those 6 non moving people. Resulting in a more constant stream of people entering /exiting the single front door.

Image


1. I would think people on this site would remember the 7j7 from the eighties, this is not a a new concept for Boeing.
viewtopic.php?f=3&t=1384921&p=20134003&hilit=7j7#p20134003

2. The more I see the oval concept the more I am convinced this is tied in with the 737 replacement. Develop the 797, and the 737 replacement is halfway there (smaller wings and engines). And if you doubt me look at #1 again.

3. If an airline needs more cargo capability good deals can be found on A330s and 787s.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Sun Mar 11, 2018 4:34 pm

keesje wrote:
I wonder if a lean 2-3-2 cabin has the speed and space advantages widely assumed.]


It is not just assumed, it is documented in the ACAPS.

Boeing actually provides boarding and deboarding rates in their ACAPS. The 737 boards are 12 passengers per minute and passengers deboard at 18 passengers per minute. The 767 boards at 20 passengers per minute and passengers deboard at 25 passengers per minute, using one door but two aisles. Both ACAPS only have passengers boarding through L1. The additional aisle doesn’t double boarding speed. But it certainly increases it. The 757-300 is even worse. Due to the airplane length, for a plane boarding through L1, only 9 passengers per minute board.

According to the published ACAPS:

A 737-900ER with 177 passengers on the plane typically requires a minimum of 40 minutes to turn (including 10 deplaning, and 15 for boarding)

A 767-200 with 216 passengers only requires 35 minutes (including 9 for deplaning and 11 for boarding)

A 757-300 with 243passengers takes 55 minutes to turnaround (including 14 for deplaning and 27 for boarding)

Given all this published in the ACAPS it seems like this thread is just meant to cast shade on the proposed 797 concept. The boarding speed assumptions of 2-3-2 are documented. You can agree or disagree and specific rates vary by location, airline procedure and season, but it is hard to disagree entirely with the airport compatibility engineers when comparing different planes.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Sun Mar 11, 2018 4:59 pm

 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Sun Mar 11, 2018 5:07 pm

keesje wrote:
I wonder if a lean 2-3-2 cabin has the speed and space advantages widely assumed.

Image

Above the 2 window seats, probably there is not enough space to put a cabin trolley wheels first/ on its side. A NB 3-3 can handle this easily.



So what? The pivot bins of a 767 - see Delta's refitted 767-300ERs - have space for a bag on its back, plus there's space in center bins.

What would be necessary to get you to understand that two-aisle passenger loading is faster than single-aisle loading? Let's start there, because the rest of this seems a foolish waste of time.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Sun Mar 11, 2018 5:19 pm

William.Its a fair way into the future but on the basis that this (ovoid2x3x2) is what gets built,then yes it may well potentially feature in a 737 replacement.One has to peer quite a long way into the future of course and much can change.But the exponential growth of regional flying has been (and still is) extraordinary.We know that already LCC's are using A321NEO 's and will be packing them with 230+ pax;and that's today!

I think it's well possible that Airbus will bring out a 322 'plus' -a small stretch to 250 pax (let's say 29" pitch).as a regional a/c.

So this 2x3x2 config would work well in that environment.As newbepilot has stated the facts are that a twin aisle is a better config for boarding and deplaning.it becomes critical at these numbers.It also gives the a/c a better finesse ratio.
But first things first!Lets see what Boeing brings to the party!
 
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keesje
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Sun Mar 11, 2018 6:02 pm

Speed, as to 2 narrow aisles, if 3 persons are blocking a narrow aisles, nobody goes anywhere. With one wide (e.g 30 inch) aisle, they pass those 6 non moving people. Resulting in a more constant stream of people entering /exiting the single front door.


It is not just assumed, it is documented in the ACAPS.


Can you also link the ACAPS for the wide aisle I mention? Otherwise we are doing the apples-oranges thing.
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Andy33
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Sun Mar 11, 2018 7:16 pm

Although lots of a-net members are probably used to boarding/alighting narrowbodies using a single jetbridge at Doors L1, in large parts of the world it is more likely that the rear door will also be used with airstairs. This why Ryanair, for example can turn a 189 seat 738 in 25 minutes from doors open to doors closed, which is theoretically impossible using Boeing's ACAPS figures quoted above. Yet they do this several hundred times a day across Europe.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Sun Mar 11, 2018 7:41 pm

Is that a midget in the last picture?
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Sun Mar 11, 2018 7:44 pm

keesje wrote:
I wonder if a lean 2-3-2 cabin has the speed and space advantages widely assumed.

Image

Above the 2 window seats, probably there is not enough space to put a cabin trolley wheels first/ on its side. A NB 3-3 can handle this easily.

Image

Above the 3 seater in a 2-3-2 there are left & right bins. But not deep ones either. A lot of space is used for the two aisles. Also higher in the cabin.

Speed, as to 2 narrow aisles, if 3 persons are blocking a narrow aisles, nobody goes anywhere. With one wide (e.g 30 inch) aisle, they pass those 6 non moving people. Resulting in a more constant stream of people entering /exiting the single front door.

Image



Ok that 787 diagram is off. They do not have 18" seats with a 22" isle on 9x layout. they have 17.2" seats with 19" isles. the cabins only 18' wide.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Sun Mar 11, 2018 8:59 pm

keesje wrote:
Speed, as to 2 narrow aisles, if 3 persons are blocking a narrow aisles, nobody goes anywhere. With one wide (e.g 30 inch) aisle, they pass those 6 non moving people. Resulting in a more constant stream of people entering /exiting the single front door.


It is not just assumed, it is documented in the ACAPS.


Can you also link the ACAPS for the wide aisle I mention? Otherwise we are doing the apples-oranges thing.


You can get the 767 & 787 ones from the same Boeing site, but there are non for the MOM as it does not exist yet.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Sun Mar 11, 2018 9:03 pm

Varsity1 wrote:
Is that a midget in the last picture?


No it was a child & an adult. Be nice please.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Sun Mar 11, 2018 9:15 pm

For boarding it will work fine, what it imho will not have is the promised "twin aisle passenger comfort". As anybody who flew on a 787 in 9 abreast with a small aisle, the small aisle means you are constantly disturbed by the passenger service and other passengers bumping into you.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Sun Mar 11, 2018 10:20 pm

Varsity1 wrote:
Is that a midget in the last picture?

No it's a child or a teen.
Well uh, I obviously decided to refine this but i dont know how.
 
RJMAZ
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Sun Mar 11, 2018 10:22 pm

A tight 7 abreast oval the side storage bins would be useless. It can't work. The middle bins would be too small. You have just highlighted why it won't happen.

An 8ab double bubble provides more height and allows full sized middle bins and side bins. They can fit LD3-45's or bulk load if they need more space.

Image



If Boeing wants to really incresse cargo capacity they could go a simple low risk circular fuselage. Add a couple inches of width to the 767 allows 8ab and also keeps the LD2's.

Image
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Mon Mar 12, 2018 10:35 am

PanzerPowner wrote:
Varsity1 wrote:
Is that a midget in the last picture?

No it's a child or a teen.


This is an Easyjet A320 cabin with relative narrow seats (17.x inch like 737) and a slight wider aisle (23 inch iso 19inch?).

Apparently they concluded for their (short haul) operations having a little more aisle is more valuable than offering extra seat width comfort.

https://youtu.be/N6-gFNw62l8?t=1m5s

IMO if you specify a 30 inch aisle, passing becomes easy, the cabin dynamics totally changes, making longer 40+ rows cabins feasible.
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Mon Mar 12, 2018 1:42 pm

RJMAZ wrote:
A tight 7 abreast oval the side storage bins would be useless. It can't work. The middle bins would be too small. You have just highlighted why it won't happen.

An 8ab double bubble provides more height and allows full sized middle bins and side bins. They can fit LD3-45's or bulk load if they need more space.

Image



If Boeing wants to really incresse cargo capacity they could go a simple low risk circular fuselage. Add a couple inches of width to the 767 allows 8ab and also keeps the LD2's.

Image


1. Boeing has been working on this seating config for 30 years , I am sure they can find a solution for some roller bags.

2. The oval solution ties this project with the 737 replacement, if they go larger you loose that connection and it becomes a stand alone project.

3. Going larger looses the "narrow body" economics and any hope of matching the per seat costs of the A321. And believe the top of and part of the A321 market is the target for this aircraft.

4. If it is so 'easy' and 'cheap' for Airbus to put a new wing and engines on the A330, why not the 787?
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Mon Mar 12, 2018 2:45 pm

william wrote:

4. If it is so 'easy' and 'cheap' for Airbus to put a new wing and engines on the A330, why not the 787?


Not easy & cheap, but way cheaper than something entirely new.

Apart from lower development costs, an existing supply chain and aircraft cockpit commonality are very positive.

Airbus could either "A310" the A330 or "777X" the A321.

That said I haven't seen any reference to a new wing / engine / LDG for a lower weight A330 version..

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Re: Aircraft 2-3-2 Cabin, more space & speed?

Mon Mar 12, 2018 4:09 pm

RJMAZ wrote:
A tight 7 abreast oval the side storage bins would be useless. It can't work. The middle bins would be too small. You have just highlighted why it won't happen.

An 8ab double bubble provides more height and allows full sized middle bins and side bins. They can fit LD3-45's or bulk load if they need more space.


If Boeing wants to really incresse cargo capacity they could go a simple low risk circular fuselage. Add a couple inches of width to the 767 allows 8ab and also keeps the LD2's.



Just from a layman's perspective, I'd think they'd be trying very hard to get LD3s in. The LD2 is largely 767-specific and you'd therefore be creating a barrier for the purchase of the new plane by continuing on that route. On the contrary, going LD3 would greatly expand commonality across fleets. I can't immediately think of a 767 operator that doesn't also operate a type that takes LD3s already, whereas there are a ton of carriers that use LD3s and not LD2s.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Mon Mar 12, 2018 4:59 pm

IADCA wrote:
RJMAZ wrote:
A tight 7 abreast oval the side storage bins would be useless. It can't work. The middle bins would be too small. You have just highlighted why it won't happen.

An 8ab double bubble provides more height and allows full sized middle bins and side bins. They can fit LD3-45's or bulk load if they need more space.


If Boeing wants to really incresse cargo capacity they could go a simple low risk circular fuselage. Add a couple inches of width to the 767 allows 8ab and also keeps the LD2's.



Just from a layman's perspective, I'd think they'd be trying very hard to get LD3s in. The LD2 is largely 767-specific and you'd therefore be creating a barrier for the purchase of the new plane by continuing on that route. On the contrary, going LD3 would greatly expand commonality across fleets. I can't immediately think of a 767 operator that doesn't also operate a type that takes LD3s already, whereas there are a ton of carriers that use LD3s and not LD2s.


I think the LD3's are too big to make a NMA real lean and the LD3-45/AKH to small to efficient use the space under 7 seats/2 aisles..

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Re: Aircraft 2-3-2 Cabin, more space & speed?

Mon Mar 12, 2018 9:32 pm

IADCA wrote:
Just from a layman's perspective, I'd think they'd be trying very hard to get LD3s in.

I've heard this a dozen times.

LD3's require a 9ab cabin. So pretty much a 787 width. You could only go a few inches narrower than a 787 before the LD3's won't fit.

Boeing won't make a fuselage a few inches narrower than the 787 to save a tiny bit of drag and weight just so they can still fit LS3's. That few inches would mean they loose a full seat in the width compared going added a few inches and going with the 787 cross section.

No cleansheet design will use LD3 containers. It will either be a lightweight 787 or a cleansheet using LD3-45 or LD2's.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Mon Mar 12, 2018 9:56 pm

RJMAZ wrote:
IADCA wrote:
Just from a layman's perspective, I'd think they'd be trying very hard to get LD3s in.

I've heard this a dozen times.

LD3's require a 9ab cabin. So pretty much a 787 width. You could only go a few inches narrower than a 787 before the LD3's won't fit.

Boeing won't make a fuselage a few inches narrower than the 787 to save a tiny bit of drag and weight just so they can still fit LS3's. That few inches would mean they loose a full seat in the width compared going added a few inches and going with the 787 cross section.

No cleansheet design will use LD3 containers. It will either be a lightweight 787 or a cleansheet using LD3-45 or LD2's.


Well, the Airbus WB cross-section takes LD3s, so you clearly don't need something as wide as the 787, but I understand your point. Maybe 3-45s are the answer, but that implies potentially a very different fuselage shape. I've seen and heard enough complaints about the lack of commonality of LD2s (not just on here) so it strikes me as something they would probably rather address than not, but it equally seems like airplane should drive containers, not the reverse.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Mon Mar 12, 2018 10:30 pm

IADCA wrote:
Well, the Airbus WB cross-section takes LD3s, so you clearly don't need something as wide as the 787, but I understand your point. Maybe 3-45s are the answer, but that implies potentially a very different fuselage shape. I've seen and heard enough complaints about the lack of commonality of LD2s (not just on here) so it strikes me as something they would probably rather address than not, but it equally seems like airplane should drive containers, not the reverse.

The A330 is only 5inchs narrower than the 787 yet looses a full seat width. That's a big cost 11% reduction in seats for a 2% reduction in width.

The bigger diameter of the 787 cross section allows the LD3 containers to sit lower down. The floor level of the passenger cabin can then be lower. The widest point of the cabin is at elbow level on the 787 instead of floor level on the A330. The A330 cabin width then becomes significantly narrower at shoulder level compared to the 787. The 787 is actually 12inchs wider at shoulder level which is the what really counts.

You could in theory go another 5inchs narrower than the A330 fuselage and still fit LD3's but the passenger cabin floor would be so high up you would probably need to consider 7ab.

This is why the LD2's work good. Being narrower than LD3's it allows them to sit lower down in the circle of the fuselage. This allows the passenger floor to be lower so the widest point of the cabin is higher up. It would allow a tight 8ab cabin and lots of cargo.
 
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Matt6461
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Mon Mar 12, 2018 11:14 pm

RJMAZ wrote:
An 8ab double bubble provides more height and allows full sized middle bins and side bins. They can fit LD3-45's or bulk load if they need more space.


I saw your sketch earlier, where'd it go?
Your design demonstrates the efficiency of tight 8ab. I've previously written that a ~204in circle (with sidewall sculpting) fits a tight 8ab and easily fits belly LD3-45's; if your double-bubble saves ~5% fuselage perimeter then NMA is more space-efficient in Y than A320, almost as efficient as 737.

william wrote:
3. Going larger looses the "narrow body" economics and any hope of matching the per seat costs of the A321. And believe the top of and part of the A321 market is the target for this aircraft.


What's this statement based on? Some intuition connected to the mental categories "narrow body" and "widebody"?
If so, that's just not valid reasoning. If not, please show your work.
A320 has an effective diameter of ~159in. A double-bubble 8ab should have effective diameter of ~195in. In the constant sections, that's 26.5in/seat for A320 family, 24.4in/seat for NMA. NMA's lower fineness ratio will total fuselage Swet per seat about equal.

But that's just the fuselage. NMA will a 5th-gen CFRP wing with greater effective span, AR, and lower wingloading (increases L/D and reduces cruise SFC by reaching stratosphere).
Engine baseline will be ~15% lower SFC than A320NEO.

I'm willing to consider your argument that 8ab (or 7ab) can't beat CASM of A321LR, but I see absolutely no fracking way you're right. Boeing would be ridiculously stupid to build NMA larger than A321LR with higher CASM, so they disagree as well.

IADCA wrote:
seems like airplane should drive containers, not the reverse.


Right? NMA will be fine carrying bags plus maybe a little bit of cargo. Gunning for higher cargo capacity is stupid for many reasons:

  • belly cargo yields are low and LF is typically around 40%.
  • NMA will be relatively light airplane with high-AR. Added payload capacity will disproportionately impact empty weight, MTOW, empennage and engine size, wing bending material (which is disproportionately significant for a high-AR wing).

Given the foregoing, it wouldn't be stretch to see 10% higher CASM if you shoot for LD2's or LD3's. Average trip cargo revenue delta would be not reach even 5%.
Asian airlines have apparently been telling Boeing they want NMA with cargo capacity. I say call their bluff; see if they'll pass on a super-efficient hub hauler due to missing a few percentage points of trip revenue from cargo.

Keesje wrote:
the LD3-45/AKH to small to efficient use the space under 7 seats/2 aisles..


Show your work.
Given prevailing belly yields and LF's, what tradeoff between cargo revenue and DOC informs your judgment that -45's are too inefficient?

Keesje wrote:
A NB 3-3 can handle this easily.


You're adding ~13in to A320's effective diameter of ~159in. At 6ab, you have ~28.7in/seat. You now have literally the least-efficient passenger cross section in the world, nearly tied with 7ab 767 (~204in effective diameter).
Have you ever done this math? I might be off by an inch one way or the other (haven't seen your exact design proposal, if there is one), but your most optimistic case is to match an 8ab A330 (except without the belly capacity).
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Mon Mar 12, 2018 11:18 pm

william wrote:
4. If it is so 'easy' and 'cheap' for Airbus to put a new wing and engines on the A330, why not the 787?

I strongly believe that is exactly what Boeing is doing.

The 787-8 is the lowest profit version of the family due to it using inefficient out of date production techniques. It shares very little parts with the 787-9 and 787-10.

Boeing will launch a lightweight 787 very similar to the 787-3. It will be significantly lighter using the in service experience and production knowledge gained. The 787-3 was a good original concept but cost cutting meant it was changed to share all the heavy parts of the standard 787-8. This extra weight killed the efficiency on short trips and the smaller wing could no longer work. It's easy to make carbon fibre items lighter by reducing the number of layers. If the maximum takeoff weight is reduced then the loads also reduce, so using software analysis they can work out where they can reduce layers.

A-netters will all cry when all the mom rumours, oval designs and fancy concepts turn out to be nothing more than a 787 :weeping:

In terms of new engines for a lightweight 787, they already exist in some shape or form.

Engine development usually goes as follows spread out by more than a decade.
1) New designs are created on software.
2) Test engine gets built, it gets run at lower thrust levels showing improved fuel burn.
3) Tweaks are made to increase thrust and durability at the higher thrust levels.
4) The engines enter service at initial thrust level.
5) Higher thrust versions come after the engine core matures.

Rolls and GE both have engines at step 1-2 for replacement of the 787's current engines in 10-15 years times. To get reliable thrust levels required for step 4 to power a heavy 787-9 the engines might need a further 5+ years of development. But the lower thrust requirements of a 787-3 would mean the same engine at the point of step 2 of the development cycle could be used. This would significantly bring forward the entry to service date.

The leap core now at stage 4 could be ready to move up to stage 5 with a 50% higher thrust version using a larger fan and another LP compressor stage to supercharge the current core. This could power a very light 787.

The Pratt GTF now moving between step 3 to 4 could also provide the thrust required. A higher ratio gearbox which I believe they have already tested would allow for a 90+inch fan and for 45,000lb of thrust without much being done to the core.
 
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keesje
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Mon Mar 12, 2018 11:47 pm

Keesje wrote:
A NB 3-3 can handle this easily.

Matt6461 wrote:
You're adding ~13in to A320's effective diameter of ~159in. At 6ab, you have ~28.7in/seat. You now have literally the least-efficient passenger cross section in the world, nearly tied with 7ab 767 (~204in effective diameter).
Have you ever done this math? I might be off by an inch one way or the other (haven't seen your exact design proposal, if there is one), but your most optimistic case is to match an 8ab A330 (except without the belly capacity).


Nope, two 20 inch aisles on a 2-3-2 is 5.7 inch per seat, one 30 inch aisle on a 3-3 is 5 inch per seat. The frontal area / drag is lower, (de) boarding might be faster, bigger bins are possible and LD3-45's fits under the passenger floor neatly. More LD3-45's than under a same capacity 2-3-2 fuselage. For the premium cabin you could still go twin aisles, 1-2-1 or 1-1-1.

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Hello 2007 :wink2:
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Matt6461
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Tue Mar 13, 2018 12:10 am

Keesje wrote:
Nope, two 20 inch aisles on a 2-3-2 is 5.7 inch per seat, one 30 inch aisle on a 3-3 is 5 inch per seat.


No.
You're apparently just looking at aisle-space per seat. Look at the entire fuselage. Drag is a matter of fuselage Swet, aisles have zero drag unless there's an aisle for skywalkers outside the plane.
The A320 adds fuselage drag to accommodate LD3-45's; NMA-8ab would save fuselage drag to limit belly to -45's.

The calculation you want is #seats/perimeter, not number of seats/aisle width. Under your calculation, the A330 carries no drag penalty for the fuselage being ~10% greater than necessary - due to cabin floor level and LD3 hold. That's illogical.

What is the perimeter of your fuselage, or the effective diameter (perimeter/pi)?

Keesje wrote:
The frontal area / drag is lower


There is no such thing as free-standing "frontal area drag."

To the extent "frontal area" matters, it is mainly in determining fuselage coefficient of parasitic drag (Cdp) via fineness ratio.
Most of Cdp is simply skin friction, which is determined by wetted area. Increasing fuselage fineness from 9 to 11 gives only ~2% lower Cdp. So making 22% wider fuse costs 2% drag at equal fuse Swet. Small potatoes. Almost always outweighed by increased bending stress and weight (though there's also an empennage impact).

Keesje wrote:
Hello 2007 :wink2:


Yep you're a veteran! And you've given us stimulating ideas now for decades.

But that's why I push you to start from numbers and aero/engineering laws and then illustrate with drawings. You've been here long enough to know that the numbers matter more than pictures and generalities.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Tue Mar 13, 2018 12:35 am

RJMAZ wrote:
The 787-3 was a good original concept but cost cutting meant it was changed to share all the heavy parts of the standard 787-8. This extra weight killed the efficiency on short trips and the smaller wing could no longer work. It's easy to make carbon fibre items lighter by reducing the number of layers. If the maximum takeoff weight is reduced then the loads also reduce, so using software analysis they can work out where they can reduce layers.


As I always say, please show your work.
MTOW's impact on wing weight is secondary. For modern High-AR, M.85 wings (i.e. thin), the weight of [fuse+maxpayload+empennage] dominates over MTOW. Given denser pax seating and same belly-hold, you can't reduce the 787SR's payload. You barely impact empennage weight; you lose a little weight in the fuse with lower max thrust.
I'd be surprised if you can reduce OEW by 10%, which would still leave you much heavier per seat than A321LR.
You could shrink the wing for further OEW reduction, but then you're hurting L/D. The optimal span and area could be lower than 787-8/9/10, but probably not as much as you seem to think. A 170ft wing, for example, means ~34% higher Di/Kg during cruise. It takes A LOT of structual weight delta to overcome such a large drag penalty.

If you can estimate a reasonable projection of weight, optimal span, and wing area, and show that it meaningfully improves trip cost, then I'll be happy to join your cause - business case would certainly be a lot easier for a 787SR. I just don't see it on my initial scan of aero/engineering project. But it's your project, I haven't looked too deeply. What are your weight/span projections and how did you get there?
 
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keesje
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Tue Mar 13, 2018 12:40 am

For drag calaculations, the reference area depends on what type of drag coefficient is being measured. For aircaft and many other objects, the reference area is the projected frontal area of the vehicle (A).

Image

The bigger the reference area, the higher the drag force. Which shouldn't come as a surprise.

The biggest NB under development, the longer MS21-400 has a wide aisle. For a reason.

Image
"Never mistake motion for action." Ernest Hemingway
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Tue Mar 13, 2018 1:33 am

Matt6461 wrote:
But it's your project, I haven't looked too deeply. What are your weight/span projections and how did you get there?

We do have a quite a few examples where the maximum takeoff weight has been increased and it came with an increase in empty weight due to strengthening.

Some rules of thumb.
1) Lift to drag ratio improves the bigger you make the wing.
2) Empty weight increases the bigger you make the wing.
3) Short range fuel efficiency improves as the empty weight decreases.
4) Long range fuel efficiency improves the better the lift to drag ratio.

You won't see an aircraft with A380 wings with a A320 fuselage, nor will you see an aircraft with A320 wings with a A380 fuselage. There is an optimal wing size and that is determined by the flying weight of the aircraft.

By reducing the range requirement, it reduces the fuel need, which reduces the maximum takeoff weight which reduces the optimal size of the wing and significantly reduces the size and weight of the landing gear and wingbox.

To clearly display this in a black and white way, let's say you had a 787-8 that would only operated short 500nm flights for the rest of its life. It would never take off at a weight over 160T approx two thirds of its maximum takeoff weight. Boeing could shave 1000kg off the landing gear struts and bogies. As the aircraft would do derated takeoffs they could fit smaller/lighter genX2b's saving another 1000kg. Boeing could also rip out the plumbing for all but one of its fuel tanks saving more weight. The lift to drag ratio of this example would not change as the wing is unchanged. Weight reduces which means a guaranteed fuel burn saving.

The best modern example is the A300, A310 and A330-200. You can accurately calculate how much they would weigh if they were shrunk or stretched to the same fuselage length. You can also accurately calculate fuel burn using equal SFC and figures in the ACAPs.

The A300 weighs 75% of the empty weight of a A330 of similar length. Adding 30T payload and 10T of fuel to fly 500nm it is now 80%. Even with a lower lift to drag ratio the empty weight would show a 5% trip fuel burn advantage to the lighter A300.

If you put 40T of fuel in both aircraft the A300 is taking off 85% lighter than the A330. The lower lift to drag ratio of the smaller A300 wing puts them at equal fuel burn on a trip around 3000nm. Any more fuel than this and the A330 wing provides a fuel burn advantage as the flying weight is now optimal for its larger wing.

The same process would apply to a lightweight smaller winged 787-8. There will also be a crossover point where the original 787-8 will be more efficient but if designed correctly this point will be up around 3000nm. If the engines are half a generation newer maybe even up to 4000nm.

So to produce a 787 that burns less fuel under 4000nm is exactly what they need. The advantage against the normal 787-8 grows the shorter the flight.

If Boeing goes to the effort of getting engines half a generation newer I would expect them to produce two lengths of this lightweight 787 version.

787-2 - 50m - 180T - 5500nm
787-3 - 56m - 180T - 4500nm
787-9 - 62m - 242T - 7635nm
787-10 - 68m - 242T - 6430nm
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Tue Mar 13, 2018 1:57 am

Keesje wrote:
For aircaft and many other objects, the reference area is the projected frontal area of the vehicle (A).


Are you sure you're reading about airplanes and not road vehicles? In a brief google search, I only found reference to your formula under automobile aerodynamics. And even there it appears that:

Drag coefficient (Cd) is a commonly published rating of a car's aerodynamic smoothness, related to the shape of the car. Multiplying Cd by the car's frontal area gives an index of total drag. The result is called drag area, and is listed below for several cars. The width and height of curvy cars lead to gross overestimation of frontal area.


https://en.wikipedia.org/wiki/Automotive_aerodynamics

I can guess some reasons why this rough estimate works for many automobiles but not for planes: Cars/small trucks usually have very low fineness ratios of ~2-3. At this low level of fineness, Cdp will decrease in approximate relation to inverse of length. In addition, the "block form" of a car/truck means you have very-low pressure "vaccuum" behind the vehicle, and a very-high pressure gradient on the engine grill/wheels/windshield. This creates enormous aerodynamic drag. Not so with airplanes, which invariably have streamlined tail- and nose-cones. Given that aerodynamic drag is far less significant than wheel bearing friction (and kinetic energy lost to tire compression), it rarely makes sense to build a streamlined nose/tail fore and aft of your blockish automobile. Too much production cost, weight, impracticality (try parking an SUV with 15feet extra vehicle length for streamlining.)

In fact serious streamlining only makes sense when (1) your vehicle is meant for very high speeds - think of race car streamlining - or (2) when a cone is immaterial to vehicle weight and provides great benefits - perfect example is an 18-wheeler freight truck with a foldable cone-ish structure at the rear of the trailer. Per the above quote, your formula for drag index would miss these cases. It's a bad formulas for cars, let alone airplanes.

Can you cite any serious *Airplane* aerodynamics article that uses your "Frontal Area" formula to estimate drag? I bet you can't.

Rather than using a deeply flawed formula for estimates of road performance, you should learn the fundamentals from real airplane experts. For example, Bjorn at Leeham:

This means 75% of our Parasitic drag is made up of air friction drag against the aircraft’s wetted surface.

There are other drag factors, but these are the main ones and the ones we have discussed. The important ones are Air friction drag and Induced drag. These represent 85% of total drag of an aircraft.

This is why aircraft designers try to minimize the total surface of the aircraft at the same time as they try to make the wingspan as wide as possible.


https://leehamnews.com/2018/03/09/bjorn ... more-26557

You should go back and read Bjorn's entire series on aircraft drag (free content).

Your frontal area formula implies that A346 fuselage has the same drag as A332's fuselage. Hopefully you realize how preposterous that is. The key to understanding why you (hopefully) share my intuition is to realize (1) that fuselage Swet is the dominant Dp factor and (2) that frontal area, given constant Swet, only secondarily impacts Dp via fineness factor's small impact (above fineness = ~7) on Cdp.

You've been here a long time and have invested serious time/attention to airplanes. Do yourself (and us) a favor and learn the basics of airplane aerodynamics.

Keesje wrote:
The biggest NB under development, the longer MS21-400 has a wide aisle. For a reason.


Yeah the reason is extra space for quicker turnaround and/or wider seats.
But it comes at a cost. Quoting Bjorn again:

The MC-21 has a wider fuselage than the A320. This is a positive as it allows passengers to pass each other in the aisle of the cabin.
The drawback of the wider fuselage is a bit higher aircraft drag.
Coupled with a lower wing aspect ratio, the lighter MC-21 cannot open a fuel consumption advantage over the A320neo, despite being a more modern [and larger] design.


Your design would make a similar tradeoff: losing a good deal of tech advances to greater fuselage friction.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Tue Mar 13, 2018 2:44 am

RJMAZ wrote:
Some rules of thumb.


Yikes.
If you mean "A.net rules of thumb" I'm already expecting nonsense. Most folks here, even many long-time, frequent posters, appear to be ignorant of basic aerodynamics.
Even beyond A.net, finance publications and industry-observer blogs regularly publish complete nonsense (Seeking Alpha is one of the worst).

Sure enough, you've imbibed nonsensical rules of thumb:
RJMAZ wrote:
3) Short range fuel efficiency improves as the empty weight decreases.
4) Long range fuel efficiency improves the better the lift to drag ratio.


Absolute nonsense. Boeing admitted that 787-3's fuel burn would be worse than 788's. The heavier 77W burns less fuel on short trips than the lighter 773. (google for the a.net thread)

Short-range lightness is not to improve fuel efficiency, rather it's because fuel isn't as dominant on short-haul and lower weight saves on airplane cost, maintenance, landing fees. Those three factors are ~60% of operating cost on shorthaul; fuel is ~20%.

Fuel burn is actually pretty simple at high-level. It's always determined by SFC, weight, and L/D. Span-dependent wing weight is usually only ~15% of OEW: there are few span/weight tradeoffs that don't improve fuel efficiency. It's just a matter of whether the heavier plane's fuel efficiency outweighs the lighter plane's non-fuel efficiency. On shorthaul the crossover point for total cost happens at lower weight than on longhaul.

Sorry, btw, for coming across as bellicose. I just want to project that I'm totally confident in calling BS on these rules of thumb. That misconception is so common on A.net that you have to sort of shout above the din to be heard amidst the rabble. For every poster telling you what I'm saying there will be 100 with the opposite view - who hold it because they heard it from 10,000 other a.nuts.

RJMAZ wrote:
By reducing the range requirement, it reduces the fuel need, which reduces the maximum takeoff weight which reduces the optimal size of the wing and significantly reduces the size and weight of the landing gear and wingbox.


I agree with almost all of that, I just would like some reasonably mathematical projection of the tradeoffs.
My main reservation is with "lower MTOW = smaller wing." That's mostly true of most designs but not if we have a maximum value for AR. In that case, you might "pay" a wing area/weight penalty to get higher span (many folks don't realize that Di is a matter of span, not AR). A wing that is "too big" (weight and area) at 8AR might be optimal at 12AR. The bigger wing has many benefits besides Di reduction:

  • Most modern airliners have ~65/35 Dp/Di breakdown. A larger wing means higher cruise FL, which increases your L/D until Di=Dp.
  • If your engines are sized for takeoff, a bigger wing can mean smaller, lighter, cheaper engines.
  • The bigger your wing, the more bending relief it provides. Go too high on ratio of (fuse+contents) / (wing+engines) and your wing is disproportionately impacted by MZFW static maneuver bending condition. In effect this means extra wing is "cheaper" (weight-wise) when that ratio is high. That's my concern with a short/small-winged 787: you're not going to save as much wing weight as a straightforward span and area estimate would lead you to believe.

RJMAZ wrote:
It would never take off at a weight over 160T approx two thirds of its maximum takeoff weight. Boeing could shave 1000kg off the landing gear struts and bogies.


I agree in principle but let's try to quantify: LG is usually ~4% of MTOW. Use that estimate to quantify the impact (your estimate is actually conservative).
You can better estimate your MTOW by the Breguet Range equation. Leaving out constant terms:

Range = L/D * ln (MTOW / Wlanding) / SFC

Make two Brequet equations, use a ratio of 787SR to 787-8 (use 1 for 787-8) in place of actual L/D, SFC, and range then solve the equations for MTOW. (EXP( x ) in Excel will remove the ln function and turn it into MTOW / Wlanding
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Tue Mar 13, 2018 3:35 am

Keesje wrote:
The biggest NB under development, the longer MS21-400 has a wide aisle. For a reason.


I'm still waiting for your fuselage diameter, btw. Please no more pictures.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Tue Mar 13, 2018 4:16 am

Matt6461 wrote:
RJMAZ wrote:
3) Short range fuel efficiency improves as the empty weight decreases.
4) Long range fuel efficiency improves the better the lift to drag ratio.


Absolute nonsense. Boeing admitted that 787-3's fuel burn would be worse than 788's. The heavier 77W burns less fuel on short trips than the lighter 773. (google for the a.net thread

Your opinion is formed because you create unrealistic and conservative empty weight numbers. As you scale a design down you are creating an empty weight delta. The aircraft is becoming more and more overweight and underwinged as it is scaled down.

Removing empty weight from a design DOES improve short haul short efficiency. If you remove payload from an aircraft it flies further with the same fuel. Removing payload is the same as removing empty weight. The wing does can have a lower angle of attack the lighter the flying weight becomes.

You can also remove empty weight while keeping the same lift to drag ratio. You assume lift to drag wiill always reduce and create a delta difference. The weight saving from the 787-3 is coming from removing range capability, fuel capacity, thrust, landing gear strength. The wing can then be made smaller and still maintain the same lift to drag of the original long range design. You then start an optimisation loop. Now that the wing is smaller it reduced weight even more, so landing gear, thrust and fuel capacity can reduce a bit more. You can run this loop many times. The first loop might remove 10% empty weight, the second loop 5%, the third loop 2.5%. So you don't stop at 10% and call it a day.

The original optimised 787-3 was sold to JAL as having better fuel efficiency on all flights below 2000nm. Cost overuns and delays in the 787-8's development caused Boeing to take short cuts on the 787-3. The 787-3 could no longer have unique lightweight bulkheads and structure and it was forced to share the 787-8's heavier components. This increased the empty weight by some 5T without adding any more wing.

The original clipped wing was sized pretty well for the original weight but that extra dead weight killed the efficiency crossover point down from 2000nm to only 300nm. Boeing then cancelled development once they realised they had to do the 787-3 properly or not at all. Bringing up the non optimised heavy 787-3 as proof is not a valid argument. Done today Boeing would be able to get it lighter than even the original 787-3. In service experience would allow them to know where the loads are and where they can remove that extra 1% weight. Adding engines half a generation newer would hit it out of the ball park.

Weight reduction in the fuselage reduces wing root bending moment to also reduce. This allows the wingbox to be much lighter. The biggest payload in the fuselage is fuel. This is why aircraft burn the fuel in the centre tank first to reduce loads and improve fatigue life. In the lightweight 787-3 Boeing could remove all fuel from the centre section. This would allow the wingbox to be much lighter. Lots of designed have had optional centre tanks like the 767 ER models and it needed lots of strengtheing to support that weight. The 767-300 to 300ER gained 4% in empty weight just for the extra strengthening for the wing box tank. The non ER could have run lighter landing gear and would have been even lighter if it went through the optimisation loop a few times as a cleansheet.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Tue Mar 13, 2018 5:19 am

RJMAZ wrote:
The wing does can have a lower angle of attack the lighter the flying weight becomes.


No. Not in cruise. All modern airliners cruise as high as they can. Unless their climb is engine-limited (true of A343 iirc), the cruise FL limit is dictated by the onset of buffet. For modern airliners, that means Cl = ~.5 (slightly higher for thicker-winged and slower NB's), which means a lighter wing cruises higher to reach its buffet limit. In short, airliners have a maximum Cl and nearly always climb until they hit that limit at level cruise. Equal Cl means equal angle of attack (in cruise configuration). This is why an airliner's initial cruise on a max-range mission is lower than on a shorter-range mission (if you don't believe, go on FlightAware and look at the flight logs for, say, a 77W on DXB-ORD versus on DXB-BOM.).

RJMAZ wrote:
Removing empty weight from a design DOES improve short haul short efficiency.


OF COURSE IT DOES! Nobody disputes that. But the weight effect holds to the same extent for longhaul. Remove 1% weight from E175 and 1% from 77L and you have the same percentage impact on trip fuel burn - assuming OEW/payload ratio is identical for both.

In fact, however, shorthaul planes are lighter and have denser cabins so the effect of 1% weight burn is lower for, e.g., RyanAir 738's than for ANA 77W's. (pax-only missions).

You must be able to hold in your head a tradeoff between two items: L/D and weight. Instead you're looking at only item (weight) and are ignoring - or are incapable of readily conceiving - the interplay between L/D and weight.
Here I'm only talking about longer/bigger versus shorter/smaller wings only. A full analysis would reach the knock-on effects of higher L/D or lower weight on engines/empennage/LG (and a small effect on fuselage weight).

RJMAZ wrote:
The wing can then be made smaller and still maintain the same lift to drag of the original long range design


Yes, the wing COULD be made smaller at constant L/D. (If empennage/engine shrinkage outweighs wing shrinkage)
But you may have a fundamental misconception of what L/D is. It IS NOT impacted by weight AT ALL.
Your plane will reach optimal L/D at Cl=~.5. Whether that occurs at FL31 (heavier payload and/or longer mission) or FL37(lighter payload and/or shorter mission) does not matter. L/D will always be the same; weight (=lift at cruise) and therefore drag will be higher the lower you cruise.

RJMAZ wrote:
Weight reduction in the fuselage reduces wing root bending moment to also reduce. This allows the wingbox to be much lighter. The biggest payload in the fuselage is fuel.


Very basic point: the wing is tested for bending moment at Maximum Zero Fuel Weight - fuel in the fuselage does not matter when your testing condition stipulates ZERO FUEL.*

*some small reserve is assumed, but those last drops of fuel would NEVER be stored in the center wingbox.


RJMAZ wrote:
You can run this loop many times. The first loop might remove 10% empty weight, the second loop 5%, the third loop 2.5%. So you don't stop at 10% and call it a day.
[/quote]

Dude I have posted enormously byzantine (by a.net standards) spreadsheets that run this loop via iterative Excel calculations. I am very familiar with the concept.
--------------------------------------------------------------------------------------------------------------------------

Most else you say goes to empty weight, not a weight/L/D tradeoff re wing span and size.
I like your enthusiasm here and I don't intend meanness in saying this, but I can't have a dialogue with you where we disagree about the nature of L/D.
Stanford Aerodynamics Department used to have a course summary with lecture notes to which I could refer anyone for basic aero/engineering stuff (and from which I started to learn this stuff). It disappeared last year. For now, the best "Airplanes 101" I can recommend is Leeham Bjorn's series, linked to in my reply to Keesje.

As someone who spent years and hours trying to figure this stuff out, all the while posting some nonsense here (I can link to embarrassing posts by me if you'd like), I can't strongly enough reccommend renting/buying an aerodynamics textbook and investing some hours into it.


---------------------------------------

On the ultimate issue, I don't disagree that a short-range B787 could be a good MoM entry. As you say, lowering MTOW (due to both range and SFC) will save weight in wing, engines, empennage, and landing gear. It will decrease Swet in engines (maybe? - Ultrafan will have huge nacelles) and in empennage - thereby increasing L/D. And I agree the 787-3 could have been better had Boeing invested $billions in giving it a customized fuselage/empennage/LG/engines/wing.

The only thing I disagree with you about - aside from how planes fly lol - is whether and to what extent the wing's planform (span, sweep, area) should change. That's issue turns on weight vs. L/D tradeoffs. It just does, sorry if you don't see that.

The marginal benefit of shorter, lighter, smaller wing might not be sufficient to justify an extra $3bn in development cost and the airline acquisition cost delta necessary to justify the investment.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Tue Mar 13, 2018 10:32 am

Matt6461 wrote:
On the ultimate issue, I don't disagree that a short-range B787 could be a good MoM entry. As you say, lowering MTOW (due to both range and SFC) will save weight in wing, engines, empennage, and landing gear. It will decrease Swet in engines (maybe? - Ultrafan will have huge nacelles) and in empennage - thereby increasing L/D. And I agree the 787-3 could have been better had Boeing invested $billions in giving it a customized fuselage/empennage/LG/engines/wing.

As your knowledge is greater than mine. I have a few questions regarding what a lightweight 787 would look like.

Could a fully optimised 787-3 with a maximum range of only 4000nm have lower fuel burn than a 787-8 on a 1000nm flight?

Landing gear, wing, engines and wingbox are all 100% optimised for the 4000nm and lower fuel load.

If so what would the wing look like and what would be the estimated empty weight?

I assume the perfect wing will be smaller due to the lower empty weight and fuel load.

My answer is 100T empty, with a wing 75% of the area, similar aspect ratio and 5° less sweep accepting a slightly lower cruising speed to gain more efficiency.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Tue Mar 13, 2018 10:59 am

RJMAZ wrote:
Could a fully optimised 787-3 with a maximum range of only 4000nm have lower fuel burn than a 787-8 on a 1000nm flight


I'd be shocked if it didn't. Even absent a new wing, we'd see massive weight/drag savings in engines, empennage, LG, fuselage (mostly correcting 788's flaws), wing (secondary MTOW effect and less tankage).

Modelling this is in a form comprehensible to others is a huge task: I have either narrate the changes and iterate the loops or clean up my messy spreadsheets for so others can read them.

My reservations about 787-3 are significant: smallest possible model is at very top MoM capacity; even with aggressive estimates it will be difficult to achieve outstanding cash operating economics that clean sheet would deliver. OTOH if Boeing can produce 789's for ~$90mn, 787-3 production cost could be ~$75mn. Given lower development cost than NMA, it could be a real A330 replacement and grow that market segment.

I see this as Boeing's fallback plan if NMA biz case doesn't close. Not a bad fallback though.

I'm interested enough to attempt a model but might be a month from now.

Just briefly re wing size: 25%smaller at constant AR means ~150ft wingspan. That's less span 763ER; just can't imagine that penciling out.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Tue Mar 13, 2018 3:55 pm

Matt6461 wrote:
RJMAZ wrote:
Could a fully optimised 787-3 with a maximum range of only 4000nm have lower fuel burn than a 787-8 on a 1000nm flight


I'd be shocked if it didn't. Even absent a new wing, we'd see massive weight/drag savings in engines, empennage, LG, fuselage (mostly correcting 788's flaws), wing (secondary MTOW effect and less tankage).

Modelling this is in a form comprehensible to others is a huge task: I have either narrate the changes and iterate the loops or clean up my messy spreadsheets for so others can read them.

My reservations about 787-3 are significant: smallest possible model is at very top MoM capacity; even with aggressive estimates it will be difficult to achieve outstanding cash operating economics that clean sheet would deliver. OTOH if Boeing can produce 789's for ~$90mn, 787-3 production cost could be ~$75mn. Given lower development cost than NMA, it could be a real A330 replacement and grow that market segment.

I see this as Boeing's fallback plan if NMA biz case doesn't close. Not a bad fallback though.

I'm interested enough to attempt a model but might be a month from now.

Just briefly re wing size: 25%smaller at constant AR means ~150ft wingspan. That's less span 763ER; just can't imagine that penciling out.


I agree with that assesment, but it would not be the aircraft that got DL, UA and Qantas excited about it. A franken 787 may be more efficient than an A330 but will not be close to the A321 in seat costs. If the Asian carriers want it then Boeing will expect to see some major launch orders from that region.

My opinion on the 7 vs 8 abreast is based on drag. Every inch added to the width increases drag,
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Tue Mar 13, 2018 8:09 pm

William wrote:
Every inch added to the width increases drag,


Luckily I just created thread to store replies to points like this:

2. What determines parasitic drag (Dp)?

My answer: Dp is largely a matter of wetted area, which causes skin friction, which dominates Dp.

Reference:
This means 75% of our Parasitic drag is made up of air friction drag against the aircraft’s wetted surface.
There are other drag factors, but these are the main ones[]. The important ones are Air friction drag and Induced drag. These represent 85% of total drag of an aircraft.
This is why aircraft designers try to minimize the total surface of the aircraft at the same time as they try to make the wingspan as wide as possible.


https://leehamnews.com/2018/03/09/bjorn ... more-26557

Common A.net myth: There is such a thing as "frontal area drag" and it is REALLY important.
Truth: There is no such thing as frontal area drag for airliners. Frontal area impacts drag via the fineness ratio (Fuselage LOA / diameter). A higher fineness ratio means a higher Coefficient of Parasitic Drag (Cdp). The difference between the finest (e.g. 757-300 or DC-8-73) and the stubbiest fuselages (e.g. A310 or 787-8) rarely exceeds 5% Cdp ratio, and is around 2% for 10 versus 12 fineness (approximately A350-900 versus A350-1000).

Frontal area also has some effect on area-ruling for transonic airliners (all contemporary jet airliners). That is usually handled with fairings to avoid excessive local velocities and nearly all modern airliners avoid wave drag except on the wing crests.

None of these considerations mean frontal area drag is some independent drag component. Frontal area has some relatively small knock-on effects on the main drag components, but shouldn't considered in isolation.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Tue Mar 13, 2018 8:11 pm

Matt6461 wrote:
Keesje wrote:
The biggest NB under development, the longer MS21-400 has a wide aisle. For a reason.


I'm still waiting for your fuselage diameter, btw. Please no more pictures.


still waiting...
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Tue Mar 13, 2018 9:44 pm

Matt6461 wrote:
Matt6461 wrote:
Keesje wrote:
The biggest NB under development, the longer MS21-400 has a wide aisle. For a reason.


I'm still waiting for your fuselage diameter, btw. Please no more pictures.


still waiting...


Irkut MS-21 cross section, it took me like 40 seconds to find :beady: What's the point?

Image
"Never mistake motion for action." Ernest Hemingway
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Tue Mar 13, 2018 10:00 pm

Keesje wrote:
Irkut MS-21 cross section


So is the MC-21 cross section identical to your proposed wide-aisle NMA? MC-21 can't hold 2-aisle J per your diagram.
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Tue Mar 13, 2018 11:26 pm

Matt6461 wrote:
Keesje wrote:
Irkut MS-21 cross section


So is the MC-21 cross section identical to your proposed wide-aisle NMA?


No?

Matt6461 wrote:
MC-21 can't hold 2-aisle J per your diagram.


Indeed.. but it is 5 inch wider then many other aisles.

Image
"Never mistake motion for action." Ernest Hemingway
 
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Wed Mar 14, 2018 6:57 am

Keesje wrote:
No?


Dude are you just trolling us?
I've asked you several times what your proposed diameter is. Answer the question.
 
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keesje
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Wed Mar 14, 2018 7:31 am

Matt I think everybody reading your question can see you asked for the MS-21 cross section, you should be more clear if you something else. If you refer to a possible 30 inch aisle cross section, you should better look at the the pictures, 168 inch (outer), ~155 (cabin)..

Image
"Never mistake motion for action." Ernest Hemingway
 
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Matt6461
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Wed Mar 14, 2018 8:19 am

Keesje wrote:
Matt I think everybody reading your question can see you asked for the MS-21 cross section


Sure. Note that your diagram did not appear in this thread and I'm not searching a million MoM/NMA threads to find some version of your proposal, after which I'd still have to ask if it's your current version. Please do us the courtesy of always typing 5 more digits to provide fuselage diameter.

With a 168in diameter you have 28in diameter/seat. That's slightly worse than 8ab A330's 27.75in/seat (and 10ab 777 is 24.3in/seat). You have 20% more fuselage drag/pax and structure/pax than 737 in the Y cabin. So you've gone from narrowbody advantage on wetted area to a substantial disadvantage.

Please remember we're talking about airplanes not an SUV, so Swet is what matters, not frontal area (that's a bad formula for cars, an irrelevant one for planes).

Compare that to an 8ab, 208in effective diameter NMA (27in/seat). If Boeing has the oval down, a 7ab can roughly match 8ab's fuselage efficiency. In both cases, the widebody gives a greater moment of inertia and shorter lever arm per pax than your big single-aisle: weight savings on fuselage bending reinforcement and greater family capacity growth potential.

You're forcing two "excuse me" exchange for lav trips, versus average of .5 on 8ab and fewer on 7ab.
You think turnaround will be lower than 8 or 7ab, but have no evidence/studies to show it.
I just don't see any sensible tradeoff here.

If you still think you're right about your truck drag approximation (you're not), let's be merciful to one another and just let that rest.
 
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keesje
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Wed Mar 14, 2018 8:30 am

Matt6461 wrote:

With a 168in diameter you have 28in diameter/seat. That's slightly worse than 8ab A330's 27.75in/seat (and 10ab 777 is 24.3in/seat). You have 20% more fuselage drag/pax and structure/pax than 737 in the Y cabin. So you've gone from narrowbody advantage on wetted area to a substantial disadvantage.



You are carefully avoiding the 2-3-2 NMA inch/ seat on topic in your story line. Noticed! :wink2:
"Never mistake motion for action." Ernest Hemingway
 
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Matt6461
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Re: Aircraft 2-3-2 Cabin, more space & speed?

Wed Mar 14, 2018 8:43 am

keesje wrote:
Matt6461 wrote:

With a 168in diameter you have 28in diameter/seat. That's slightly worse than 8ab A330's 27.75in/seat (and 10ab 777 is 24.3in/seat). You have 20% more fuselage drag/pax and structure/pax than 737 in the Y cabin. So you've gone from narrowbody advantage on wetted area to a substantial disadvantage.



You are carefully avoiding the 2-3-2 NMA inch/ seat on topic in your story line. Noticed! :wink2:


If you're sayung you agree that it's effective diameter/seat and not aisle inches per seat or frontal area than we're making serious progress! :)

Do you agree?

If so I'll try to model an 7ab oval tomorrow. Surprisingly the calculation for conical ellipse perimeter is difficult. I'm avoiding it out of laziness. There's no point doing the work if you still want to pretend airplanes behave like F-150's.

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