Taxi645 wrote:

The A380Mk2 vs. The CEO and the 777x:



So anyone who drags out the old and tired well the A380CEO didn't do well so a Mk2 can't do well either is unable to grasp and/or acknowledge the huge difference in fuel seat per mile cost and resulting market dynamics in the 773/A380 (equal at equal seating density) vs. 779/A380Mk2 (-25%) scenario clearly shown in the above table.

I know you took them from Leeham, but that spreadsheet assumes the 779 would consume more trip fuel over the 77W over a 15 hour flight, I don't think this assumption holds much water given that the 779 has at least 5% improvements in both SFC and L/D, the only way for such a figure to pan out would be for the 779 to be significantly heavier than the 77W at takeoff, which would imply something like a 10% OEW delta between the 779 and the 77W, which is hard to believe to say the least, and certainly wouldn't justify the orders the 777X has gotten from numerous 10-abreast (or soon to be) 77W operators.

JustSomeDood wrote:

I know you took them from Leeham, but that spreadsheet assumes the 779 would consume more trip fuel over the 77W over a 15 hour flight,

Correct, I didn't closely read these tables because of my doubts on the theoretical model. Bjorn specifically says in the comments to that table that a typo exaggerated 779's fuel burn by ~20%.

Taxi645 - here's another (very) rough cut at your A380-850X proposal.
Here's how I suggest a quick(ish) estimation loop starting from ballpark end-parameters and cross-checking for constraints. Basically you run a couple "loops" between MTOW and structure:

• Set your new SFC. Let's say -17.5% vs. A380.
• Guesstimate a new wing area and effective span. Let's say 280ft effective span with winglets (hereinafter just "span) and 7,000ft2 wing.
• Guesstimate an empennage delta ~proportional to your wing area delta: -20%; guesstimate an empennage weight delta ~proportional to area
• Guesstimate a conservative engine thrust delta - say -20% - and an engine weight delta proportionate to thrust

[/list]

Now you can estimate an L/D delta from the square root of Wetted Aspect Ratio (WAR) = span^2 / wetted area.
A380's total Swet is ~4,0000m2. So let's add our negative deltas to our new span and compute:

• Wing shrinks by 2,100ft2, but only 86% counts (the rest is "virtual wing" under the fuselage). Delta to Swet = ~340m2
• A388's empennage Swet of ~660m2 shrinks by 20%: ~132m2 delta
• For now say engine Swet remains the same (it will probably shrink even with higher BPR)
• Span (effective) increases from 267ft to 280ft

A380X's WAR = 2.07. A388's WAR = 1.66. A380X's L/D is ~11.7% higher than A388.

Weight deltas:

• Empenagge ~ 8% of OEW. -20% delta = ~10,000lbs
• Wing area delta: Wing is ~35% of OEW; area-dependent is ~60% of wing; -22% area delta = ~28,000lbs
• Wing CFRP delta = ~10% of (revised) wing weight = ~19,000lbs
• Engine system weight delta = 1.5 * engine dry weight * .2 = ~16,000lbs
• So far, total weight delta is -82,000lbs. New OEW is 534,000lbs.

NOTE - at this point I realize I'm doing an -800X instead of -850X. Not going to redo the post but we can extrapolate to -850 pretty easily. And we should see it's not necessary...

NOW FIGURE MTOW by Breguet Range equation where A388 and A380X have equal range at 525 pax.
Range is proportional to

..........Speed * L/D * Ln ( MTOW / Wlanding ) / SFC

As you can see, we substitute our ratios of L/D and SFC, plug in our (OEW+Payload) for Wlanding, and solve for MTOW from A388.

The result is 977,000lbs MTOW. We now have about the same wingloading and T/W as A380, so takeoff roll should be about the same. [if anybody wants a simple Excel tool for this calc, I'll post a Google doc].

But that's not the end, we have another set of loops we can do. For now let's just do one more:

• MLG delta: assuming MLG is ~4% of MTOW, weight delta = ~5,700lbs
• Fuselage delta: Fuse responds to MTOW via the aero loads from empennage and from taxi bump stress case. Estimates are hard to come by but 4,000lbs is a conservative estimate.
• Let's forget about the 210,000lb max payload. The most we'll ever carry is ~720 pax (162,000lbs) which leaves space for ~15,000lbs cargo. Let's say 185,000lbs max payload.
• At this point we should check our bending moments but it should be neutral even after effective span gain (should have looked at that earlier- this is easier in a spread sheet).
• New OEW is 524,000lbs.

Solving our Breguet equation again, we get an MTOW of 962,000lbs. So we can go back and shrink the wing, engines, empennage, MLG again.
We should also apply a tech and lever factor to empennage - as discussed in my OP, relaxed stability and shifting pressure centers allow for a smaller, lighter empennage than sketched so far, which is worth serious L/D and weight benefit. Then we go back and find our new MTOW and we again shrink the wing, engines, empennage, MLG. (Lower weight, higher L/D)

We don't have the ability to be precise, but this iterative process should settle at MTOW 900-950,000lbs and trip fuel delta of ~40-45%.

For max precision we could add deltas for pax systems (limiting capacity to ~700= fewer aircon packs), for hydraulic systems (especially for smaller control surfaces and MLG), for cabin BFE efficiencies, for whatever structural margins Airbus hasn't bothered harvesting in the moribund A380 (Leahy once alluded to such weight, but said Airbus wouldn't spend $millions taking out a few tonnes.)

For those reasons I wouldn't be surprised by an MTOW south of 900k lbs for -800X, probably ~5% greater for -850X.

Taxi645 - for your OEM business case you'd then want to consider the production impact of these changes. Long/short the X should be much cheaper to build than A388 even after CFRP wing expense. Engines are ~1/3 of cost and they'd shrink by 25-30%. MLG is very costly and would similarly shrink. Empennage shrinks. Complex flight control systems and associated hydraulic networks shrink. These would far outweigh the incremental cost of a smaller CFRP wing.

Those production cost factors allow you to build your -850X for less than A388 and sell it for more.

...which is why I still see some hope for an A380X some day. But not THAT much hope unless Airbus has a change of heart. And I'd rather see a clean sheet VLA in 2028 than an A380X in 2026.

JustSomeDood wrote:

I don't think this assumption holds much water given that the 779 has at least 5% improvements in both SFC and L/D, the only way for such a figure to pan out would be for the 779 to be significantly heavier than the 77W at takeoff, which would imply something like a 10% OEW delta between the 779 and the 77W, ..........

OEW +20..25t is the current estimation afaik. A bit more than 10%. ( ~12%)

Matt6461 wrote:

[*]You ignore the empennage. Even the belated NEO proposals modified the empennage; this is lower-hanging fruit than MLG/cargo revisions.

I only ignored it in my presentation not the calculation, because I wanted to focus on the implications of the update and open peoples eyes rather than filling the screen with a sea of figures.

[*]What's your OEW, L/D, and SFC. You can state the latter two as a ratio to A388. It's impossible to judge the feasibility of a proposal without some reasonable range for those three basic parameters.

L/D I took -6%. It my new calculation based upon WAR (as you suggested) I end up with -11.1% (close to your estimate). Although I think this also is a strong simplification considering the change in drag composition during flight.

SFC I took -15%, I preferre to stay on the conservative side here.

OEW, I'll redo it later as per your suggestion.

[*]You're still on this "induced drag" thing. Maybe look back at our TechOps thread on this. L/D is non-dimensional; unrelated to actual weight (with some slight caveats).

AR changed as can be seen in the table, more later.

[*]Please address the relative cost/benefit of rebuilding ~30% of the lower fuselage to enable +6 LD3's. This is a massive revision and cargo just isn't THAT valuable.[/list]

You keep looking at this in isolation. It is not about a single benefit. It's about designing a efficient/economic configuration for a 10+8 tube within a 80m box with the benefit of ultrafan type engines.

In my view this is around around 505t MTOW because this allows both for a competive effective AR of around 9.8 within the 80m box as well as a reduction in size and weight of the MLG, the former improving cargo space. Furthermore 505t MTOW allows engines to be shared with an A330 successor.

If 505t means it can be stretched more than the proposed 2,7m, then by all means. I don't care too much about the exact amount of stretch too as long as the MTOW ends up at 505t max.

Finally, to the extent that you present this as an alternative to an A380NEO, notice that your trip fuel is higher than for my above-sketched A380-900NEO. If I'm right about the -900NEO, why would Airbus spend more to build a worse product?

Of course feel free to tell me I'm dead wrong about the -900NEO. But please show your work.

My suggestion was not calculated the same way as yours so one can not sensibly compare those. I'll try to work out a bit more later.

JustSomeDood wrote:

I know you took them from Leeham, but that spreadsheet assumes the 779 would consume more trip fuel over the 77W over a 15 hour flight, I don't think this assumption holds much water given that the 779 has at least 5% improvements in both SFC and L/D, the only way for such a figure to pan out would be for the 779 to be significantly heavier than the 77W at takeoff, which would imply something like a 10% OEW delta between the 779 and the 77W, which is hard to believe to say the least, and certainly wouldn't justify the orders the 777X has gotten from numerous 10-abreast (or soon to be) 77W operators.

Matt6461 wrote:

JustSomeDood wrote:

I know you took them from Leeham, but that spreadsheet assumes the 779 would consume more trip fuel over the 77W over a 15 hour flight,

Correct, I didn't closely read these tables because of my doubts on the theoretical model. Bjorn specifically says in the comments to that table that a typo exaggerated 779's fuel burn by ~20%.

Thank you for pointing that out.

Leeham says they wrongly listed as 120,5t in stead of 102,5. In the new table I will post later I adjusted the 777x fuel use by -15% (102,5/120,5).







On the engine side I want everyone to consider the numbers if shared with a A330NEO succesor.

Let's assume 1.000 copies sold for the A330 successor, that means 2.000 engines.

Let's assume 500 copies sold for the A380mk2, that again means 2.000 engines.


So in total we are looking at a potential market for 4.000 widebody engines! I'll let that sink in a bit...

Consider the economies of production scale for such an engine and how hard engines OEM's would want to be on such a program. They would do everything to get on board including taking up a large part of the bill.

Taxi645 wrote:

It my new calculation based upon WAR (as you suggested) I end up with -11.1% (close to your estimate). Although I think this also is a strong simplification considering the change in drag composition during flight.

The theoretical underpinning of using SQRT(WAR) is an assumption that the planes being compared each see max L/D where Di=Dp. A bit of calculus gets you the rest of the way. You're right it's simplified, but so is any A.net post compared to a multi-year, multi-$million process of interrogating these questions. (of course you know that... just for the gallery). It's a small, lazy short cut over the drag composition approach but in my experience tracks A380 modifications pretty well because the A380 has ~50% Di.

Taxi645 wrote:

I only ignored [the empennage] in my presentation not the calculation, because I wanted to focus on the implications of the update and open peoples eyes rather than filling the screen with a sea of figures.

Is this some advice for me?

Taxi645 wrote:

It is not about a single benefit. It's about designing a efficient/economic configuration for a 10+8 tube within a 80m box with the benefit of ultrafan type engines.

6 LD3's seems too little to justify significantly higher MTOW, even if the additional benefit is a shared A330-R engine. Just a suggestion; I'll be interested to see the rest of the project idea.

Here's a different cut at stepping back from "isolation":
You've got a $10bn budget for a 500-plane program with shared engines. Is there a route to making this a 750+ sales program on a $15bn budget? I actually think so: 10-6 or 9-6 clean-sheet double-decker. That plane effectively becomes a replacement for much widebody traffic, including many A330's, all 777's. I bring that up here not to change the subject, but to raise the issue of Boeing competitive response. If your/my A380X launches and demonstrates a highly-profitable VLA market while damaging/killing the 777X, we could expect a Boeing response in that space or (more likely) slightly below it. The A380X, while a great plane, would be difficult to future-proof due to its (mostly) metal fuselage whose form is optimal for 650+ seats. If you're going to spend $10bn on a plane that might be obsolesced by competition shortly after EIS, it's probably better to spend $15bn on a better product that can withstand competition.

In another thread, Revelation cited an AvWeek email stating that a 75k Ultrafan engine will have 140in fan. viewtopic.php?f=3&t=1374685&hilit=boeing+officially+forms&start=1100#p20181211

In my OP, I postulated 68k engines for slightly-lower -900NEO MTOW. However:

• Assuming thrust is ~proportional to SQRT (Fan Diameter ), this implies a ~133in fan, slightly bigger than GE9X.
• That would imply significantly more engine drag than I modeled, even with a shorter nacelle - one which would have to bear higher Cdp for lower fineness (nacelle is modeled like a short fuselage with max Cdp value ~2, per Stanford Aero class notes)
• Higher engine drag would imply slightly higher thrust for higher MTOW and cruise drag + wing loop.

My model is only an approximation of course, but it doesn't require any high precision to see that an A380-900NEO might not be able to fit an Ultrafan-type engine on the current wing/MLG. The wing is already gulled to accommodate engines, likely no room for ~20in more under the wing.

That implies either (1) revised MLG or (2) a smaller -850NEO that doesn't fully utilize the A380's capabilities. Either way it's a more costly project and/or a less attractive product if ~70k engines are ballpark for a -900NEO.
----------------------

On a different note, I wonder what this implies for projects 787MAX and A350NEO, which I envisioned coming in the second half of next decade - likely spurred by CRAIC C929's threat to capture a huge chunk of the Sinosphere market absent A/B action (sort of like how CSeries spurred NEO/MAX without actually taking many orders). If A350-2000 would need ~100k engines, we're talking 160+ in fan. No way that fits the wing/MLG. Same could be said of a 787-11MAX.

Do Ultrafan-type engines augur the return of the quad? I'm thinking of an asymmetric quad that:

• Has two big and two little engines of ~3-1 SLS thrust ratio.
• Quad OEI performance allows removal of 2nd segment climb constraint, reducing total thrust by, say, 6-10%.
• Big engine is fully-optimized long haul Ultrafan, little engine saves ~35% of engine drag by using smaller fan around modern core. Little engine is highly-loaded (~6 T/W) and optimized for lower mx cost (fewer clearance control valves, for instance).
• Big engine could suppy 85-90% of cruise thrust with little engine at ~50% max rpm - still within the cruise SFC bucket.
• At 88/12 cruise work division, cruise SFC suffers only 1% if little engine has 8% higher SFC

So at a cost of ~1% cruise SFC (and ~3% climb SFC), you could see the following benefits:

• 6-10% lower overall thrust versus twin, with attendant weight/drag effects (~1% Dp delta, ~1% weight delta)
• ~35% reduction in OEI yaw moment, allowing tail-fin shrinkage (worth ~1% weight and Dp)
• As little engine is not critical in OEI case, it can be pushed further out on wing to provide bending relief and weight savings
• Potential for savings on total engine acquisition and mx costs, though - in order to recover development expenses - OEM building two engines would likely require twin-equivalent unit profits despite lower recurring production/mx costs. Whoever builds a narrowbody Ultrafan-gen engine could be approached to "Frankenstein" our little engine on the relative cheap while developing the main engine.

Just a thought, might start a different thread on it if any interest.

Matt6461 wrote:

On a different note, I wonder what this implies for projects 787MAX and A350NEO, which I envisioned coming in the second half of next decade - likely spurred by CRAIC C929's threat to capture a huge chunk of the Sinosphere market absent A/B action (sort of like how CSeries spurred NEO/MAX without actually taking many orders). If A350-2000 would need ~100k engines, we're talking 160+ in fan. No way that fits the wing/MLG. Same could be said of a 787-11MAX.

Do Ultrafan-type engines augur the return of the quad? I'm thinking of an asymmetric quad that:

I see this being a very big issue and it will mean the end of the line for most aircraft designs.

Boeing and Airbus would know that engine diameters would be increasing for any given thrust levels. The problems with the 737's low ground clearance will become a problem with all current models.

As engine fuel efficiency increases the range of the aircraft will also increase. So the aircraft could be lighter to perform the same flight requiring less thrust. So instead of increasing maximum takeoff weight we might see reducing maximum takeoff weights of the current designs and big weight reduction programs. Lower thrust requirements means you can run a higher bypass engine while keeping diameter the same. Think of the Trent 700 and Trent 500 same fan size but the Trent 500 has a higher bypass ratio with less thrust.

Airbus with the A350 has gone the wrong way by increasing weight which will prevent them from fitting high bypass engines in the future as you pointed out.

This is why I see the 787 forming the basis of the MOM. It would retain ground clearance of the heavier models to allow next gen engines.

A 180T max takeoff weight lightweight 787-8 (787-3) would need only 55,000lb of thrust. Based on the ultrafan that would need a 120inch fan which would fit no problems. If engine SFC is 10% better the payload range probably won't reduce that much from the current 787-8.

Thank You Matt for doing this very interesting thread.

Airbus has a lot of workforce coming out of programs that are finished, and they have the time to make a working proposition of the Whalejet, but the most important part is missing : ENGINES, as soon as GE,RR,PW or somebody has a new engine and delivers circa 2026 a product that has at least a high one digit advantage over the best engines now or better, the A380 will remain as it is. If they commit I bet Airbus will promise the engine manufacturer at least 2000 engines sold.... billions at stake here on both sides so nobody is going to go as crazy as Airbus did in 2000....
The old saying says: once bitten twice shy, so I think your post is wonderful on many calculations and economics, but as long as there is no engine ... we will be in the doldrums.
I really hope Airbus makes the A380 mkII a reality.

TRB

TheRedBaron wrote:

If they commit I bet Airbus will promise the engine manufacturer at least 2000 engines sold

2,000 engines promise? Seems excessive. The upside of a -900NEO is 45/year; Airbus wouldn't bet the farm on the best-case scenario.
Airbus may have to do some profit-sharing with an engine OEM to get new engines; that wouldn't necessarily kill a business case.
My OP uses conservative estimates of the performance delta. I could see a version of the -900NEO with 295ft effective span (very big winglets) and ~10,000 lower OEW than I estimate here. That would enable a lower MTOW and lower thrust requirements. Then again, I could just as likely be off in the opposite direction.

If the upside of performance/weight modelling is true (say 40% per-pax fuel delta), then Airbus probably has room to share $1bn or so in profit with an engine OEM to get this program off the ground.

But here's the big sticking point, IMO: A world in which airlines see broad value proposition in a -900NEO is a world in which VLA's look good again. The A380 will be an old, suboptimal design by 2026 - even with my sketched revisions - and Boeing could kill it off by launching its own 777-9 successor as a 2-deck VLA of both lower capacity and lower unit costs than a -900NEO. That's a recipe for program disaster.

The only way I see a -900NEO happening is if it is some sweet spot where sufficient demand for it exists, but nobody perceives sufficient demand for clean-sheet competition. The thing is, that's a pretty thin chance IMO. If airlines place 400 orders for a -900NEO, Boeing should see that a 500-seater with lower unit costs would sell 1,000 frames.

My hope is that Airbus launches the -900NEO, demonstrates a VLA market, and that we get a truly optimal VLA as a competitive response. Maybe the response could come from COMAC/CRAIC if their learning curve on C929 goes well.

A quick rendition of the A380 with above improvements.

...and I think the aesthetics in general are better with the adjustments, using a full service carrier as an example it just looks less stubby and more purposeful.

Eurofusion wrote:

...and I think the aesthetics in general are better with the adjustments, using a full service carrier as an example it just looks less stubby and more purposeful.

Looks really good!

You clearly know way more about all of this than I do; your analysis is most impressive. I do have one question that might make me look like an imbecile, but here goes. You say we are looking at the EK A380 with 437 seats. The Seatguru diagram you used is an EK two class bird. She already seats 615 (!). Doesn't that throw the whole analysis off kilter, especially from an exit limit perspective? Thank you very much for all of this insight! I love reading from well informed contributors, such as yourself.

Slug71 wrote:

Eurofusion wrote:

...and I think the aesthetics in general are better with the adjustments, using a full service carrier as an example it just looks less stubby and more purposeful.

Looks really good!

Thanks Slug71, I won't give up my day job, but much appreciated!

AA777223 wrote:

You say we are looking at the EK A380 with 437 seats. The Seatguru diagram you used is an EK two class bird. She already seats 615 (!).

437 on the lower deck, not the whole plane. On the UD I went with SQ's UD layout plus a premium economy section occupying the stretch. So we get a ~700-seat 4-class plane. Much more revenue potential than a 615 seat 2-class plane.
As I say, however, the optimal layout probably wouldn't be at 700 seats. It would instead give more space to premium classes.

Eurofusion - thanks! Looks great!
The only minor revision I'd add is the stretch should be greater aft than foreward. The smaller empennage and relaxed stability margin should enable this. Might make the aesthetics a little worse (stubbier forward fuse) but significantly improves the economics.

Matt6461 wrote:

AA777223 wrote:

Eurofusion - thanks! Looks great!
The only minor revision I'd add is the stretch should be greater aft than foreward. The smaller empennage and relaxed stability margin should enable this. Might make the aesthetics a little worse (stubbier forward fuse) but significantly improves the economics.

Much appreciated, so are you saying 4 frames fore and 6 frames aft (overall 79.4 metres)? The additional length BTW may require an additional exit. The above rendition and even with your changes would have Etihad rethink the residence which was a creative use of dead space - anyone want to rent an A380 attic. The top deck's additional foreward door and the new stair 'enabler' this becomes a crew sleeper and galley gaining yet more space in the conventional cabin.

Eurofusion wrote:

so are you saying 4 frames fore and 6 frames aft (overall 79.4 metres)?

Yep.

Eurofusion wrote:

The additional length BTW may require an additional exit.

Cabin length would be fine for MD with 5 doors. On UD, 3 doors work spaced 60ft apart with the last ~40ft of UD using the rear stairs as its aft "exit".

Eurofusion wrote:

The top deck's additional foreward door and the new stair 'enabler' this becomes a crew sleeper and galley gaining yet more space in the conventional cabin.

I'd still envision crew rests in the expanded belly hold. But you're right that I didn't explicitly account for added UD space from stair revision in my OP. My unstated assumption was the extra space is sufficient to hold galley/lavs for the added PY cabin.

Etihad wrote:

The above rendition and even with your changes would have Etihad rethink the residence which was a creative use of dead space - anyone want to rent an A380 attic

My proposed layout negates The Residence as currently configured - but uses space more efficiently.
This plane would significantly change the economics of cabin room, however, allowing much more creativity for F pax. At this level of fuel efficiency, cabin crew and pax weight becomes a much higher portion of trip cost. If an airline simply doubled the floor area apportioned to an F seat, while maintaining current "soft product", the actual impact on cost/seat would be on the order of ~50%. Think two new-SQ-A380 F suites combined. Given -900NEO's efficiency, cost/F-seat would be competitive with a 777 while offering twice the space.

Another idea would be to turn the last ~25ft of MD into a "charter cabin." Given ~500ft2, you could fit a bedroom, nice lav, full living room, and bar/galley into that space. Charge $40k one-way for 12hr flight and you're still far, far cheaper than a G650 or other private jet (~$8k/hr for a large cabin jet). Use a personal service vehicle to take "charter" passengers to the private cabin without encountering the unwashed masses in the airport/cabin. That means your extra capacity has less impact on yield, as your charter cabin is competing in a non-airline market.

Eurofusion wrote:

A quick rendition of the A380 with above improvements.

Knowing how big an A380 is, those winglets must be massive

JustSomeDood wrote:

Knowing how big an A380 is, those winglets must be massive

I posited 21ft (up+down) in my OP; given that A380 fuselage is 28ft high, looks like the render pretty much went with that.
21/262 is the same winglet/span proportion as the 737MAX (9.5/118).
But there are many plausible reasons that the A380's winglet proportions would be higher at the optimal point:

• A380's induced drag component is much higher than 737MAX (any model).
• A380's AR is much lower than 737MAX; more room for bigger winglets in the weight and Swet vs. L/D tradeoff

If we kicked up effective span to 300ft (36 ft tall winglets), we'd get ~3.4% better L/D. Additional weight would be probably ~5,000lbs. On a max range trip that implies ~3% lower fuel burn and greater range. Or we could further decrease MTOW and thrust to further shrink the empennage at equal max range (probably the better choice, as there aren't many 17hr routes).

Eurofusion wrote:

Much appreciated, so are you saying 4 frames fore and 6 frames aft (overall 79.4 metres)?

Third item

Thanks @Matt6461. Here is the update based on 4 frames fore and 6 frames aft, still looks in better proportion than the current 800. I wonder what the market is for 'Cabin' class - don't just book a seat, book a room. ETD only have limited destinations and are notoriously secretive with their books but it's a good PR stunt if nothing else. How would a LAX>LHR yield though? Probably another stream on this.

@WIederling. I did see that and in fact did some of my work with it and other sources but Matt6461 is suggesting changing the tail and wing design.

Eurofusion wrote:

Thanks @Matt6461. Here is the update based on 4 frames fore and 6 frames aft, still looks in better proportion than the current 800

Thanks!
Yep the aesthetic suffers a little bit the less it's stretched forward. But I agree - still a lot better than A388 and still a handsome plane.
The reason A380's forward fuselage looks so stubby (besides its fineness ratio) is that the wing is swept more than usual and it's chord-length is much higher than usual. The former means that the center of pressure is further aft of the leading edge at fuselage junction. The latter means that fuselage root chord is just astoundingly long. ~60% greater than on 777.

Only if it is a quick draw (I know nothing about these programs), it'd be interesting to see the look with the 31ft winglets I speculated over.
Another benefit of winglets I forgot to mention: Most likely the A380 is climb-limited at takeoff. That's unusual for a quad but the enormous weight, mediocre span, low takeoff L/D, and low T/W ratio probably mean it barely has the required 3% excess thrust after losing an engine during takeoff. I'm more confident in that guess given that Airbus chose the droop nose leading edge device, and specifically said it helped by reducing drag. That only matters if second-segment climb with OEI is an active constraint (slats would retract at 1,000ft), so we can be pretty confident that takeoff performance is climb-constrained.
Large winglets would basically remove this constraint due to their larger impact on L/D at takeoff versus cruise. So we could shrink the engines (and tail fin) even further due to winglets. According to Ferpe, the A380 is one of the quickest climbers so we there's room for smaller engines without impacting cruise FL.

Eurofusion wrote:

I wonder what the market is for 'Cabin' class - don't just book a seat, book a room. ETD only have limited destinations and are notoriously secretive with their books but it's a good PR stunt if nothing else. How would a LAX>LHR yield though? Probably another stream on this.

Yeah we'd probably need another thread to hash this out well. But here's a few thoughts for now:

• Etihad probably sees some difficulty attracting F pax aside from AUH/DXB and Australia-bound passengers. Extremely wealthy people have a high cash-value for time; they have direct service options available from most big cities.
• For cities like LON, NYC, LAX, SIN, HKG, TYO, SYD, Paris, there's probably scores of multi-millionaires flying direct between them on private flights. You need to attract only a few of them to get decent load factor for a "charter cabin." These folks are rich but saving $50k per flight and/or getting 500ft2 of space instead 300ft2 on the biggest (non-BBJ) planes should be attractive.
• Instead of booking directly through the airline, we could set a deal with NetJets or similar services whereby membership hours could be redeemed by booking an airliner cabin instead of a private jet. That would save NetJets thousands of dollars while offering extra space (but lower flexibility) to members. NetJets could arrange another private jet for members traveling onward regionally from the destination hub (they already do this).
• This kind of arrangement might be profitable on a 777X or A350 and I've always wondered whether airlines have held partnership discussions with NetJets. Etihad already has partnered with a private jet broker to book The Residence (but even The Residence is a big step down from a large-cabin jet). The business case becomes much, much better with a VLA whose marginal capacity cost is ~50% of the CASM of the most efficient plane flying (a metric -900NEO meets, though barely).

Matt6461 wrote:

Only if it is a quick draw (I know nothing about these programs), it'd be interesting to see the look with the 31ft winglets I speculated over.

Well she's a beasty if ever I saw one!


Cabin class
I suspect that you would end up with perks and miles clientele in the cabin class, probably what Etihad are catering to. VVIPs have an entourage plus security is a high concern unless you could prove that case on the airlines budget. So really it will be the honeymooners and celebs who have something to prove - that may be good business. The scheduling and city pairs are key for serious VIP exec jetists and this behemoth compromises both so you put up with the cabin for the mission. I suspect it's a marketing tool for the airline, a seduction tool for the lonely millionaire and an enticement for closing contracts. I suspect we all want to see though even if we never travel in it.

...Incidentally the engines are still massive on this I had increased them to 150 inch fans and they are well forward and follow the profile of the A350/73ng profile, so I'll remodel that at some stage.

The current A380 is much for airlines. Why would a stretch be built?

BA re-imagined. A bit of troll fodder.

Eurofusion wrote:

Slug71 wrote:

Eurofusion wrote:

...and I think the aesthetics in general are better with the adjustments, using a full service carrier as an example it just looks less stubby and more purposeful.

Looks really good!

Thanks Slug71, I won't give up my day job, but much appreciated!

No prob. Oh you did good, wish I could do that!

Eurofusion wrote:

Thanks @Matt6461. Here is the update based on 4 frames fore and 6 frames aft, still looks in better proportion than the current 800.

Looks even better IMO.

OA940 wrote:

The current A380 is much for airlines. Why would a stretch be built?

Better CASM and shrinks don't work well in just about every type. Just look at the 737-600/700, MAX7, A318, A319, A319NEO, A338, A358, 788, 778X...No exception to the A380. It would be more efficient if stretched and would work better to reduce frequency.

Eurofusion wrote:

BA re-imagined. A bit of troll fodder.

That looks damn good!

IMO Airbus should have raised the cockpit slightly. I think it would look really good if the cockpit windows were just below the second deck windows.

Eurofusion wrote:

Well she's a beasty if ever I saw one!

Yeah she is! But in my beholding eye, efficiency is beautiful. That's a damn beautiful plane, abnormal winglets notwithstanding.

Eurofusion wrote:

BA re-imagined. A bit of troll fodder.

Lol.
BA would be a big fan of this IMO.
It's my prediction that longaul - at least TATL-length trips - will suffer the same fate as shorthaul: convergence on actual cost through LCC and other lower-cost competition (Norwegian, Chinese airlines, ME3, Indian airlines).
BA's profit maximization strategy in the current non-competitive environment is to emphasize yield management; that won't work once Norwegian and others move the industry down the price/demand curve.
BA and other legacies can only counter with greater economies of scale through their megahubs. One-stop flying is not going to die and, as EK demonstrates, an airline can make $billions by emphasizing greater quantity at lower prices (RyanAir has the world's highest profit margin in fact).
None of that happens if all longhaul LCC's fail and if protectionism is resurgent, but I'd bet the other way.

Eurofusion wrote:

VVIPs have an entourage plus security is a high concern unless you could prove that case on the airlines budget. So really it will be the honeymooners and celebs who have something to prove - that may be good business.

Let me revise my initial cabin size to 10% of -900NEO's floor area. That's ~750ft2, about as big as the usable space in a BBJ 2 (private 737-800). Now we have a cabin easily big enough to accommodate an entourage. BBJ2 has two bedrooms, a living room, 2 lavs, galley, and a conference room. Space could be used more efficiently on A380 MD because shorter aisle length.
Security is largely a matter of privacy for proprietary info/communication/discussions. This cabin would be totally private (but for probably a mandatory FA during takeoff/landing). You're not trying to capture the entire world of VVIP destinations, you just want to capture the big premium routes between global alpha-cities on which the luminaries of finance, politics, entertainment frequently travel. As you'll see below, it would be cheaper - and more spacious - to fly airline charter and leave your private jet sitting idle than to pay the jet's variable costs.
For fractional-jet-ownership members who buy a certain number of hours per year through NetJets and others, it's a choice between flying a ~200ft2 plane or a ~750ft private cabin on the routes where -900NEO flies. Where it doesn't fly, they just stick with the status quo of a relatively cramped, likely more expensive trip. NetJets could provide onward connection for a short hop from a hub. I'm sure a sizable portion of their customer base wouldn't mind adding an hour to their trip for something more than 7ft-wide cabin. That's why I see airline tie-in with private charter companies as essential (as Etihad is doing with The Residence).

BBJ2's direct operating cost per hour is at least $10,000 dollars (depending on how you spread acquisition cost - $8,000/hr variable cost). It's higher for a private jet because you have budget for accommodations for crew.
Operating cost of the -900NEO would be ~$17k/hr. If we apportion 10% of that to charter cabin, that's $1,700/hr - one-sixth of minimum BBJ2 cost.
If we sell our charter cabin for half of BBJ2 price - $5k/hr - our break-even load factor is ~30%.
Beyond direct-selling to charter pax, you'd reward loyal F/J customers - as you suggest. Loyalty miles are a huge liability on network carriers' balance sheets; convincing an F/J passenger to fly his whole family and/or friends on the trip of a lifetime (surely memorialized in selfies etc.) would be huge for the airline if the executive forked over, say, 3 free F fares in loyalty miles.

Beyond honey-mooners, I could see groups of friends splurging on a private cabin for a long-planned trip or a bachelor/bachelorette party. Also a market-stimulative effect: Imagine a team of lawyers and/or bankers - usually J passengers - travelling NYC-HKG to close a deal. As J pax, they can't discuss their case or talk with clients en route due to lack of privacy. In our BBJ2 cabin, they have not only privacy, but also a conference room for large meetings to put the final touches on their pitch/strategy, or to speak confidentially with clients. 16hrs of dead time becomes hours of billable time. For Wall Street lawyers that's $1,000/hr per lawyer.

Your objections are well-taken, especially regarding corporate security policies. I just think there are workarounds given enormous cost-savings and/or game-changing cabin space at equal price.

OA940 wrote:

The current A380 is [too] much for airlines. Why would a stretch be built?

Forgive me for my tone if I get a little saucy. I don't mean to attack you personally, but this idea comes up so often, and is so obviously wrong-head... A simple thought-experiment illustrates why:

• Suppose Airbus magically found a way to increase the A350's capacity to A380-size, but without impacting trip cost. Call it the A350-380.
• The A350-380 is now just as big as the A380 and therefore, by your logic, "too big."
• But that's obviously absurd. Nothing about the extra seats costs airlines any money; if they sell extra seats for $1, or if they gives 2x the space/seat for a $1 premium, they're ahead of the game.

This should illustrate that what we really mean when we talk about right-sizing is TRIP COST NOT CAPACITY.

Now play with my example a little more: A350-380 has 10% higher trip cost for twice the capacity. My guess is Airbus wouldn't sell a single A359 or A35K - only A350-380's. If you can't get 10% more revenue with twice the seats/space, you're a terrible airline.

How about 20% trip cost delta?
Probably a few airlines wouldn't see any benefit in the bargain but still 90% of A350 sales would be -380's.

30% trip cost delta?
I'm still guessing the majority of orders are for -380's.

50% trip cost delta?
Now the added seats cost half as much as seats on A359. Many operators could only fill those seats with lower-yield transfer pax; many airlines would stick with smaller A350's. But many operators would buy A350-380 as well. especially those with large O&D markets - airline can profitably grab market share by offering a 20% discount against the competition and/or by offering 25% more space/pax.

80% trip cost delta?
Here there's not much room to discount profitably or to board lower-yielding pax. So I'd expect not many A350-380 sales.
And guess what? That's about the A388's situation: added seats over a 77W cost ~80% of the 77W's per-seat cost.

THAT'S what explains the A388's failure; not simply its size.

IMO something like 50% marginal capacity cost (versus contemporary planes) is needed for decent VLA sales.
Which brings us back to your "Why the stretch?":
Only the stretch enables ~50% marginal capacity cost versus a 777-9 and smaller planes (assuming we're keeping the current wing and MLG).

slug71 wrote:

IMO Airbus should have raised the cockpit slightly.

Since flattery gets you everywhere, I've remodelled it incorporating some of the A350's rakish looks. A B777 after Christmas dinner. The improved drag coefficient would have to be phenomenal to overcome the development cost and cabin compromise though.



Thanks once again for your comprehensive answer.

Matt6461 wrote:

BA's profit maximization strategy in the current non-competitive environment is to emphasize yield management; that won't work once Norwegian and others move the industry down the price/demand curve.

I already fly Norweigian premium TATL then spoke to my destination. There is also something to be said walking on to a wide body and taking a left. So you're quite right I'll compromise destination for a better price:product ratio so hub and spoke isn't dead yet. For short haul I'll grin and bear it, cheapest fare wins. However business travelers, by that I mean paid for by businesses, the model is slightly different. There are negotiated rates designed to offer a savings over an entire network, particularly advantageous on monopolised routes. These deals however rely on everyone booking through an approved customised OBT (online booking tool). I do a lot of work for a significant TMC (Travel Management Agency) and what we see is people going 'rogue' all the time. In part the OBT is clunky, in part everyone is a savvy consumer these days they see a better price and think they're saving money for the company but in reality they're disrupting a $20m savings bond they have with a preferred supplier. This model is changing and the rise of AirBnB, Uber and the like is creating better products at a better price and everyone is winning except for the Goliaths. What the German's refer to as Mittelstand. So the legacy carriers need to adapt, yes it's the yield management but also the established network.

I love your exclusive section concept. I do think though it would need to be modular so it could so it could be adapted for purpose it ought to be near the lux F/J cabin so you could utilise the F suites for a standard flight then cordon off sections depending on who is invited to the venue space. Then you can rent that area dynamically as a meeting room, bar, product promotion etc. So lawyers want 5 hours the bachelor party 3 hours or block book it during a flight - then leave it as a bar/coffee shop by default. I know this isn't your concept entirely but rather doing a penthouse apartment with business facilities, but airlines may prefer the latter to mitigate risk unless the model can be proven. On paper it makes sense and I see your rationale.

I see this aircraft more as an enabler for a mid-market offer, running a very competitive long haul all biz/eco prem+ flat-bed seats. Yes it's been done and failed, but not on the right aircraft. I would pay $100 more for a flat bed on NOR routes or a zero gravity position (As per Emirates), I'm still quids in and far more comfortable than on a standard coach cabin with a legacy. As a legacy you could run it at your worst slot, to your furthest destination with a reduced service and call it 'The Sleeper'. Potentially not disrupting your business market and stealing share from the LCCs. The worst thing about the rare treat of travelling J/F is missing the perks beyond the seat by going to sleep, this way the perk is the sleep.

Again Matt6461 thanks for you thoughtful insight.

slug71 wrote:

IMO Airbus should have raised the cockpit slightly.

Since flattery gets you everywhere, I've remodelled it incorporating some of the A350's rakish looks. A B777 after Christmas dinner. The improved drag coefficient would have to be phenomenal to overcome the development cost and cabin compromise though.



Thanks once again for your comprehensive answer.

Matt6461 wrote:

BA's profit maximization strategy in the current non-competitive environment is to emphasize yield management; that won't work once Norwegian and others move the industry down the price/demand curve.

I already fly Norweigian premium TATL then spoke to my destination. There is also something to be said walking on to a wide body and taking a left. So you're quite right I'll compromise destination for a better price:product ratio so hub and spoke isn't dead yet. For short haul I'll grin and bear it, cheapest fare wins. However business travelers, by that I mean paid for by businesses, the model is slightly different. There are negotiated rates designed to offer a savings over an entire network, particularly advantageous on monopolised routes. These deals however rely on everyone booking through an approved customised OBT (online booking tool). I do a lot of work for a significant TMC (Travel Management Agency) and what we see is people going 'rogue' all the time. In part the OBT is clunky, in part everyone is a savvy consumer these days they see a better price and think they're saving money for the company but in reality they're disrupting a $20m savings bond they have with a preferred supplier. This model is changing and the rise of AirBnB, Uber and the like is creating better products at a better price and everyone is winning except for the Goliaths. What the German's refer to as Mittelstand. So the legacy carriers need to adapt, yes it's the yield management but also the established network.

I love your exclusive section concept. I do think though it would need to be modular so it could so it could be adapted for purpose it ought to be near the lux F/J cabin so you could utilise the F suites for a standard flight then cordon off sections depending on who is invited to the venue space. Then you can rent that area dynamically as a meeting room, bar, product promotion etc. So lawyers want 5 hours the bachelor party 3 hours or block book it during a flight - then leave it as a bar/coffee shop by default. I know this isn't your concept entirely but rather doing a penthouse apartment with business facilities, but airlines may prefer the latter to mitigate risk unless the model can be proven. On paper it makes sense and I see your rationale.

I see this aircraft more as an enabler for a mid-market offer, running a very competitive long haul all biz/eco prem+ flat-bed seats. Yes it's been done and failed, but not on the right aircraft. I would pay $100 more for a flat bed on NOR routes or a zero gravity position (As per Emirates), I'm still quids in and far more comfortable than on a standard coach cabin with a legacy. As a legacy you could run it at your worst slot, to your furthest destination with a reduced service and call it 'The Sleeper'. Potentially not disrupting your business market and stealing share from the LCCs. The worst thing about the rare treat of travelling J/F is missing the perks beyond the seat by going to sleep, this way the perk is the sleep.

Again Matt6461 thanks for you thoughtful insight.

Eurofusion wrote:

slug71 wrote:

IMO Airbus should have raised the cockpit slightly.

Since flattery gets you everywhere, I've remodelled it incorporating some of the A350's rakish looks. A B777 after Christmas dinner. The improved drag coefficient would have to be phenomenal to overcome the development cost and cabin compromise though.

Now that looks sexy!!

But agreed. The development cost more than likely would not offset the drag coefficient. I actually think you would gain a tiny bit of cabin area by raising the cockpit slightly though. It would be tight, but I think it would allow enough room for the flight crew rest area to be moved below the cockpit vs behind it. But that's just an uneducated guess from looking at some cutaway pictures online.

Eurofusion wrote:

Thanks once again for your comprehensive answer.

Thank you for the stimulating discussion. Thanks to everyone who's joined in here.
I'll discuss your points in separate replies, depending on time (typing on my phone as I run errands).

Slug71 wrote:

I actually think you would gain a tiny bit of cabin area by raising the cockpit slightly though.

Eurofusion wrote:

A B777 after Christmas dinner. The improved drag coefficient would have to be phenomenal to overcome the development cost and cabin compromise though.

This is spilled milk but I'm gonna cry about it: Airbus should have used a (slightly-below) UD cockpit. It's possible if you (1) center the nose-cone in the middle of the vertical axis, (2) use MD height of ~6.25ft under the cockpit instead of 8ft (3) use ~5in floor under cockpit instead of ~13in under UD (~30in lower than UD floor). This should yield ~12m2 of additional MD space (~2% floor area bump on A388). In addition, the MD reaches full height earlier and probably gains length even after adding the cockpit (B744's UD starts ~16ft from nose after cockpit; A380 UD starts with reduced height at ~21ft from nose). MD can also reach max width earlier. This should add another ~1% floor area at constant capacity.
Now it's true that we can't put seating ahead of doors and that 6.25ft height is too small for good pax accommodation. Instead, let's put a galley with 16 carts and 2-4 lavatories fore of D1. That move frees up space for ~20 more Y seats.
Airbus probably didn't do this because (1) it rules out your forward grand staircase and (2) it likely costs 2 LD3's due to more taper length in the belly. Re (1) - the grand staircase is stupid economically (As the A380Plus recognizes). Re (2) even the lowest-yielding pax are better than cargo; the lost LD3 space is still useful for bulk bags, freeing up probably 80% of lost LD3 space.
OTOH I think this would cost a little bit of drag, not reduce it. You'd lose the tiny amount of fuselage lift forward, which would mean more tail force in cruise. But we're talking like 0.01% impact.

Eurofusion wrote:

slug71 wrote:

IMO Airbus should have raised the cockpit slightly.

Since flattery gets you everywhere, I've remodelled it incorporating some of the A350's rakish looks. A B777 after Christmas dinner.

IMU the A380 cockpit /nose design already is at the right place for an A350 comparable aero.
Only difference to the later model is no conformal windows.
( Overlay the properly scaled A380 side view with an A350XWB side view.
I remember some pdf that explained the layout reasoning for the A380.)

Thanks @Matt6461, great thread well thought out and compelling arguments, enjoyed that.

Incidentally the BA aircraft is named after a Plantagenet - would be King.

Eurofusion wrote:

would need to be modular so it could so it could be adapted for purpose it ought to be near the lux F/J cabin so you could utilise the F suites for a standard flight then cordon off sections depending on who is invited to the venue space.

Love this idea. I had thought of placing the conference room at the fore of private cabin, allotting complementary hours to private cabin and then renting conference room to F/J pax (should be able to get at least $1k/hr). You could place the private cabin's bar and living room such that it could function as bar/coffee/snacks + lounge for F/J/PY on routes with lower charter demand. Maybe rent out product offering to Starbucks or boutique coffee/spirits/charcuterie/restaurant for exposure to a high-wealth captive audience. Then maybe rent out the 2 bedrooms separately. Charge for in-flight showers in the larger lav. Lots of possibilities for modular without ruining appeal when sold as a unitary private cabin.

Eurofusion wrote:

I see this aircraft more as an enabler for a mid-market offer, running a very competitive long haul all biz/eco prem+ flat-bed seats

That's possible but I'd guess this plane would always carry a substantial component of "garbage-yield" basic-Y pax. It changes the rules of the game: where basic Y is filler right now, it would be immensely profitable at current market prices, still-profitable if Y prices drop by 30% (as they would in a new competitive equilibrium). SQ could brand Basic Y as Scoot, BA as Level, Lufthansa as Eurowings, Korean as Joon, Emirates as FlyDubai etc. Basic Y cabin crew could wear the respective LCC uniform to prevent conflation of low-price product with mainline.
This allows megahub airlines to basically own the one-stop Y market: Even long/thin 787 routes like NRT-DEN or XMN-NYC rely on one/two-stoppers to fill at least half the seats. Every connecting pax would choose one/two stops via a megahub (far cheaper on -900NEO) over more-expensive flights via a smaller hub (also more regional frequency, less average layover time at the megahub).

As a result, the business case for many long thin routes would evaporate, as no long-thin route has sufficient O&D to fill even a 788.

But you're right: airlines would likely combine "garbage yield" strategy with a "more space for equal price" strategy for mid-yield, comfort-sensitive pax. I haven't done my promised total cost analysis yet, but -900NEO would see ~35% lower cost-per-m2/ft2 than A359/787. If we keep galley/lav space/pax constant, -900NEO could allot ~80% more space/seat at equal cost/seat. That means PY becomes lie-flat beds in "herringline" configuration, perhaps with a "couples suite" making it 9-abreast on MD with a couple sharing aisle access. $2k for a lie-flat, direct-aisle seat on an intercontinental flight? I see a big market. We could avoid J substitution by offering that deal only to vacationers with a week+ return date and by keeping soft product to PY standard. Above Basic Y, mainline Y could turn into "PY-" 9ab on MD or 7ab on UD with 37in pitch. Sell at market price for FSC Y and you'll capture the whole comfort-sensitive Y market.

------------------------------------------------------------------------------------------------------------------
Another point: The economics of this plane would make it useful on shorthaul to boost utilization. China Southern was losing money with A388's on PEK-CAN, but they must at least covered variable costs (otherwise you just park the asset). Given that acquisition cost is, at most, 25% of A380 DOC, and given that -900NEO should have ~25% lower CASM at equal utilization rate, shorthaul hops between longhaul is now profitable. I could see UA, for example, running planes on a SFO-NRT/PVG/PEK/HKG-EWR-SFO circuit, which could elevate utilization to ~16hrs/day instead of the normal ~13hrs for A388. BA could add a short turn to CDG, FRA, MXP, IST, etc. between longhaul -900NEO trips. These shorthaul trips could beat RyanAir/Wizz/EasyJet fares/comfort while flying out of LHR instead of STN/LTN/LGW.

Final point (for now): Door and cabin layout could have huge impact on turnaround time, making shorthaul -900NEO trips very attractive.

Say we go with 4 doors on UD:

• First door (D6) is ~10ft aft of UD start, allowing space for galleys/lavs.
• D7 is 60ft aft of D6, allowing ~180 Y seats between D6 and D7.
• Aft of D7 are ~230 Y/Y+ seats (~410 Y seats easily fit on the stretched UD).
• On MD, we have ~240 basic Y seats between D1 and D2.
• Aft of D2 are all F/J (and maybe private cabin) seats. Say 80 seats.
• With 4 doors on UD, we can probably get ride of rear stairs, leaving one A380Plus-style shrunken staircase (shared with crew rest access). That allows for galley/lavs at rear of both decks.

Now consider the boarding/deplaning flows at each seat:

• D6 serves ~180 pax
• D7 serves ~230 pax
• D1 serves ~240 pax
• D2 serves ~80pax. [D5 serves private cabin via designated vehicle, where applicable]

Assuming the critical path is pax deboarding, our turnaround time is dictated by D1 flow. Here we have LCC ~A321 volume but with two aisles versus one. In short our turnaround time can be better than A321 unless cargo/bags unloading becomes the critical path.
We could further decrease turnaround time by distributing Y+/PY such that no passenger/door flow exceeds ~200 pax. Then we'd be at ~LCC A320 turnaround time given our two aisles.
Compare that to A388, where critical path is boarding/deplaning up to 370 pax from D2.
Possible objection: Per ACAP, A380's TRT is dominated by refueling. That wouldn't be the case with shorthaul, plus our -900NEO has significantly lower trip fuel burn than A388.
A388 doesn't work well on short routes because of both high operating cost (vs. NB's) and long turnaround time. We've fixed both problems; we now have a perfect solution for slot-congested hubs like LHR, EWR, SFO, HKG, HND. And for low-cost shorthaul on trunk routes regardless of slot congestion.
Minor objection might be that F/J isn't at the pointy end. IMO that wouldn't matter. It's already the case with several operators (e.g. EK's 2-class A380, Air China's 748) and we can build a grand, exclusive entryway for F/J midway on the MD.
I could see the -900NEO dominating market share on congested, super-dense shorthaul (with frequency supplementation by NB's/RJ's). Think HND-FUK/CTS, HKG-TPE, PEK-CAN/PVG, SFO/LAX/ORD/DFW-NYC (UA could build EWR into a megahub for one-stop flights to Europe - would dominate AA's PHL TATL hub).

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

OK I lied- one more thought (enjoying this exchange...).
How about a MD baggage/cargo compartment?
Why? Well cargo/bags stack better on MD than in the belly; belly floor area is bigger and can hold galleys/lavs/rest/amenities.
Here's a sketch:

• Airbus previously discussed raising the MD floor by 3in to enable 11ab. So it's possible (though for now even small A388 development cost is unjustified).
• The belly hold currently has 5ft 9in height; raising MD floor by 3in gives you 6ft height below. Incidentally, it reduces the amount of "sidewall" sculpting for 11ab.
• The forward part of rear hold is 8ft wide. That's perfect for a large galley with 2 rows of 2-deep trolleys. Lack of pax interference would allow staff/AIrobot to shuffle carts as needed. Two lifts would supply carts to MD and UD. Assuming you want to keep a full meal service on-deck, and that long-haul config requires storage of 3 meal services, we can reduce our cabin galley footprint by 2/3 (more if we use the lifts during meal service). This allows ~5% more seats. This 8ft-wide area is ~32ft long, which means we could stow up to 120 carts in it (allowing 2ft for 2 double-wide lifts). Total carts shouldn't exceed 120. This opens another opportunity discussed below.
• With our 18ft rear stretch, we have 43ft of ~10.5ft wide, 6ft high belly space: ~450ft2 floor space. That's enough to easily hold 8 F/J lavs (2-abreast, 4.5x4ft each).
• We still have ~27 ft of belly length after the 8 lavs. Assuming crew rest occupies ~12ft, we have 15ft remaining. say 2ft goes to stairs. In our remaining ~135ft2, we could put: (1) a conference room and/or (2) attach showers to lavs, charge for showers and/or give them as perks and/or (3) put the premium bar down there if we don't apply our modular private cabin concept. The central aisle floor could be lowered by 6in, enabling 6'6" height above the aisles for passengers.
• Assume we want to replace our lost belly volume (~22 LD3's for my -900NEO) with MD bags/cargo compartment at MD rear. Our MD is now 7'9" high. Assuming 135ft3 internal volume per LD3, our MD compartment needs ~390ft2 of floor space: ~5% of floor space.
  
  
  Now count up the tradeoffs:
  
  • We lose 5% of floor area to MD baggage compartment.
    
  • We gain at least 5% of floor area by shrinking cabin galleys. Already a neutral on pax/cargo space.
  • We move ~8 lavs to belly (~2% cabin area delta)
  • We gain ~135ft2 (~2% of cabin area) of belly cabin for showers/bar/private conference rooms/private sleeping areas (family bunks anyone?). Hard to approximate the revenue impact but if 50% as lucrative as seating, we have 1% trip revenue delta. My guess is that private offices for those high-rate lawyers/bankers might actually exceed seat revenue/m2 in many circumstances.

...so in sum these alterations add at least 3% trip revenue potential for little incremental trip cost.

And there are further possible benefits:

• We could lose one MD exit pair and a belly cargo door - probably at least weight-neutral with a large MD cargo door. And/or we could add a (smaller than cargo) catering door to belly galley, enabling quick catering replenishment on a path that doesn't interfere with cabin cleaning between deplaning/boarding, further reducing our turnaround time. In fact, because we sketched belly cargo room for 120 carts, staff could move all carts to the belly after final meal service but before landing, then exchange them en masse through a single belly door, thus zero catering interference with the deplane-clean-board critical path, and further turn-around time reduction.
• The weight of galley/lavs/offices would be far less than max-density cargo; we can lose weight on belly floor structure sufficient to at least offset reinforcement under MD cargo compartment.
• If we adopt our modular private cabin idea, and place it on MD, belly can house bedrooms, galley, lavs for it. Thus we can shrink private cabin's footprint and/or offer an even bigger private cabin.
• I sketched an MD compartment with ~3,000ft3 cargo/bags volume. If we make it 2,000ft3, we lose ~7 LD3-equivalents but gain ~1.6% cabin area.
• We could further optimize the MD hold: Airbus intended higher effective MD height for A380F by removing pax platform from floor material (e.g. seat rails, padding, seating substrates). We could do the same in our MD hold, increasing effective height to 8.5ft or slightly more. As the MD hold contains only bags, we can use an A380-only bags container that utilizes the concave bulge of the fuselage. Combined these two changes decrease MD-hold floor area by ~15% at constant volume. Now our passenger revenue delta is ~5%.
• MD hold needs a partition under UD and on MD foreward of hold. But that's a much smaller area than the ~70ft-long partition between belly and MD. So we save a little weight complexity there.
• CoG shouldn't be an issue: MD hold is full only if forward hold is full of cargo/bags (~45,000lbs including LD3 tare weight). Even with 30k lbs in (biggest) rear hold, you should maintain balance after accounting for displacement of MD pax/furnishings by baggage hold.

In sum I see a feasible >5% delta to pax revenue at a cost of 7LD3, or >3.5% delta at cargo neutrality.

How about a MD baggage/cargo compartment?

There are some genius ideas here. I won't mind taking some time to actual model this - I'll get back to you.

Eurofusion wrote:

I won't mind taking some time to actual model this - I'll get back to you.

Thanks, looking forward to it.

Tailcone baggage/cargo compartment

A380's tailcone runs ~43ft past the aft cabin bulkhead. If we shrink the tailplane area by ~33% and keep its current span and trailing edge*, then we move the tailplane trim actuation point ~15ft further aft. We now have ~18ft length of potentially empty and voluminous tailcone space. It would be expensive, complicated, and heavy to pressurize this non-circular compartment for a "mezzanine level" single-deck cabin extension, but baggage needs only heat and maybe mild pressurization.

*Higher-AR tailplane means a little less weight savings but gives more effective lift and less tailplane induced drag, which should allow less tailplane area and/or slightly better takeoff L/D = slightly lower thrust requirement. 777X's new tailplane is higher-AR, perhaps for those reasons. Plus my OP didn't account for making the new stabilizers' internal structure out of CFRP so we have room to play with.

Our new tailcone compartment would look something like this:


The tailcone is ~20ft wide aft of cabin, tapering to ~13ft wide over the next ~18ft (we'd have to adjust area-ruling for new smaller tailplane so we're basically rebuilding the tailcone but keeping overall length and sweep). By rough estimate a ~2,500ft3 contoured compartment with ~15ft average width (18*15*10=2,700). That's enough space for ~500pax' bags, which frees ~20LD3 for cargo or the entire rear belly for galley/lavs/amenities.

A 15ft stretch to the belly rear belly/fuselage (less than OP's 18ft rear stretch to maintain CoG) gives ~750ft2 of cabin space with 6'3" height. In my MD cargo post I positied 6ft belly height after 3in MD-raise but look at the A380's cargo belly:



We can remove a few inches from the floor for cargo rollers and lower-maxcargo-weight; we can remove some from the ceiling for fire-suppression systems and cabin/belly partition.

So if this revision is plausible, operators could be given an option of either:
1. Effectively 20 LD3's of cargo space delta (brining -900NEO to 70LD3's).
2. Effectively 11% more cabin room, most of which will be used with equal - or better - space efficiency vs. MD/UD for trolley storage (better if consolidated into 2 banks of 2-deep rows) and lavs (should be about equal).

Weight of compartment:

• Say floor beams are lighter than pax beams because they need not survive a 16g-crash landing, only ~4g static maneuver resilient (the tailcone could shear off on 16g crash as engines do with water landings.) At ~4lbs/ft2 we have have ~1,000lbs of floor beams.
• We'll need an airtight, lightly pressurized compartment for bags, with a hookup to heating/pressure air. Also fire suppression systems. With, say, 20,000ft pressure altitude, our relatively small compartment's pressure weight shouldn't be much - 3,000lbs? Say another 1,000lbs for fire/heat/air.
• We'll need to reinforce the tailcone. No idea on weight delta: 2,000lbs? (big moment of inertia for our big tailcone, small lever arm for the baggage, so shouldn't have terrible weight impact)

My guess is ~7,000lb OEW delta (~1.1%). We're gaining ~11% capacity or ~20LD3's so a substantially greater weight delta should be worth it.

Reasons we might omit the option for 70LD3's and make belly cabin mandatory:

• minimizes CoG and fuse bending moment impacts by merely shifting aft belly cargo further aft, instead of adding highly-levered weight to the mix at max loading.
• Fully utilizing 70LD3's would require more payload, implying heavier wings and fuselage and probably greater MTOW, with knock-on effects on new engines and new empennage.
• With 28 LD3's in the forward belly hold, we have cargo usable cargo capacity already (~40,000lbs at average density); belly load factors/yields are low.

This proposal largely fixes two suboptimal problems with the A380 fuselage design: The too-large, no-revenue tailcone/empennage and the too-tall belly area, which is designed to hold pax facilities but can't without entirely foregoing cargo.

I have a few more possibly feasible/cheapish ideas for -900NEO but wanted to get your thoughts on this one.

The big issue with a mid-level cargo compartment in the tail is the reinforcement of the rear bulkhead for crashworthiness. Multiply the weight of those containers by 16, and then find a way to hold that load back in a crash. If it made sense, they would have tried it already.

@LH707330 In case you missed it (long reply), I tried to address this already:

Say floor beams are lighter than pax beams because they need not survive a 16g-crash landing, only ~4g static maneuver resilient (the tailcone could shear off on 16g crash as engines do with water landings.)

This would be a showstopper if we had pax in the tailcone, but - haven't checked the regulations - pretty sure it's okay if bags don't survive a crash. My intuition is there's a fairly simple engineering solution where the tailcone is fine during ~4g force of static maneuver but shears off in a 16g crash.

LH707330 wrote:

If it made sense, they would have tried it already.

The MRJ (other RJ's?) basically does:


From the drawing, MRJ's bags hold goes right up to tailplane trim actuator, whose machinery/hydraulic reservoir would sit just fore of the tailplane's root chord.

There's another good reason this hasn't been done on mainliners before: can you think of a case in which a plane suddenly gained ~2,500ft3 of potential baggage space via aft relocation of the tailplane's leading edge? For most planes, the distance bulkhead-->trim actuator looks only a few feet. It wouldn't be worth extra complexity, cost, and weight of cargo doors/floors to fit a dozen or so bags in the tailcone. Probably better for maintenance ease make access to the trim actuator/hydraulics easier and maybe put other systems back there. This area could be like the crown of a widebody: big but only useful for crew rests, necessary for aero/pressure shape, so not much priority in maximizing its space efficiency (as Boeing's ability to (belatedly) reorganize 748's crown for Skybunks etc shows).

What else is typically in a tailcone, btw? The APU is usually aft of the stabilizers - I'm wondering about the (seemingly small) space from aft bulkhead to trim actuator.

I guess my issue is with the cumulative weight. If you could get it to shear at ~4g, then it'd work out, I just wonder if the cert agencies would bless it. If so, then no issues. I, for one, would not want to sit in the row right afore the bulkhead during a prang, knowing all that junk is right aft.

My picture from last post disappeared; here's a better link:

LH707330 wrote:

I guess my issue is with the cumulative weight. If you could get it to shear at ~4g, then it'd work out, I just wonder if the cert agencies would bless it.

Re cumulative weight the scheme adds ~35,000lbs (cargo+containers+infrastructure). MZFW is ~830,000lbs so doesn't seem an impractical delta.
Re agencies, I'd bet they'd see reason if the engineers have a solution. Wings would reliably snap off at ~8g; same could be designed for tailcone.
For your aft-pax worries, seems possible to have a load path that cleanly transfers at cone/fuse junction to a transfer path (fuse-cone) that is independent of each, is strong enough for, say, 5g but fails completely at 6g (some strong but brittle material with a known fail-point). Load-transfer path would add some weight but we're talking 11% capacity delta on ~290t plane, so not insuperable.

To be clear, I get your intuition that we'd have seen this before it were possible. This is a suboptimal use of fuselage space and it's unlikely on a clean-sheet widebody. With a higher NEO budget we'd want to re-contour the rear fuse taper to use the extra 15ft for 2-deck space. But I'm trying to keep this proposal to what Airbus could feasibly do with ~$4bn.

One other note on volume of tail-cone space. If we want more volume, or have doubts about my 2,500ft3, we could make the rear bulkhead flat (A340 did it post-EIS, IIRC) with a small weight penalty. Upthread I've explained that we don't need rear stairs with 4 UD doors; nly thing using the concave bulkhead is those stairs.

UD sidewall sculpting for 9ab

A380's UD is effectively 208in wide for seating. To gain effective inches, we need to add space at shoulder/head level.
Let's say the minimum acceptable seating standard for mainline, longhaul Y is the 77W at 10 ab: 17in seat with 2in armrest.
By that standard, our minimum 9ab effective width 212in is (231in -19in). That's 3-4 in less than 787 (787 seating is wider than 777 10ab).

The OP lays out why 33% narrower MD sidewalls could enable 11ab for acceptable weight penalty (.7-1t).
On the UD, we have thinner sidewalls but we get more space for each inch of sidewall shaving due to fuse curvature:



Per my miserable attempt at graphic design, the horizontal cabin-width axis intersects the sidewalls at ~30degree average angle (varying with measured height). Thus we get:

• ~1.15in of cabin width each side (cos(30)) per inch of sidewall shaving = ~2.3in total cabin delta per -1in sidewall-thickness delta
• To reach 212in cabin width we need ~1.7in sidewall delta.
• If sidewalls are ~8in at this point, then ~22% less thickness implies ~27% more frame material.
• Per my estimate (see photo), affected fuselage permiter is ~7ft or ~9% of total permiter.
• If frames are ~20% of total fuselage weight (175,000lbs), then weight delta is only ~850lbs. (175,000 * .2 * .09 * 1.27)

850lbs barely registers and 212in is pretty tight for 9ab, so let's say 215in and 2,000lbs weight delta (~3in sidewall shave).

This revision widens UD by ~3.4% and makes the A380's UD Y-seating ~10% more space-efficient than currently.
Now my all-Y UD is more efficient, 8ab Y+ is better, and there's space for Zodiac Optima 8ab "Herringline" seats (UA's 77W Polaris but at slightly longer pitch).

Next arguably feasible and cheap idea:

Non-uniform engine thrust

The rationale is to shrink the V-stab, which even after OP's revisions is ~50% bigger than 777-8's despite much longer lever arm.
V-stab is sized for one-engine-out (OEI) conditions; the critical engine is either outer engine due to their longer lever arm for yaw moment and lower distance from Vstab's center of pressure (due to wing sweep).

Here's how it works:

• Keep all engines physically identical - same family - but uprate the inner engines' max TO thrust and derate the outer engines.
• Outer engines have ~80% greater lever arm than inner - they're still the critical engines but create less yaw moment.
• Across engine families, ~35% seems a high but doable spread for thrust ratings.
• Our lower-MTOW -900NEO needs ~260k T
• Outer engines have 56k lb-T, inner have 74k (~32% spread)

Compared to even thrust spread, max OEI yaw moment (and thus V-stab size) is ~14% lower versus even thrust (56/65).

Deltas from V-stab shrinkage:

• ~35m2 Swet (~0.9% Dp reduction)
• ~1,000lbs (assuming ~14% weight reduction from our previously-shrunken V-stab)

Another benefit is potentially smaller engine system (by area and weight, not thrust), due to higher average T/W ratio (depends on spread of derate/uprate versus a baseline even engine thrust).

Drawbacks/Issues so far:

• What about engine mx? These are basically identical engines, just one is programmed to run at higher RPM during takeoff. The mx delta would be should be small: uprated engine will be more but derated less. On net it would be positive delta though. To minimize mx and on-wing life impact, we'd rotate engines every year or whenever is convenient during heavy maintenance checks.
• What about SFC? The uprated engine will have lower SFC during takeoff/climb, as its fan will be spinning faster than optimal. During cruise, however, all engines would run at equal N1 and equal SFC (by my understanding of uprating/derating - correct me if you know better).
• What about engine purchase/development cost? It should cost the OEM some delta to program and certify two thrust versions instead of one, but this seems minimal overall and would be mandated in Airbus/OEM contract to fly on -900NEO. If OEM prices engines linearly on thrust, buyer price is equal but production cost of smaller engines could be lower.
• What about thrust growth for stretch/shrink? It's largely ruled out by perfect match of engines and empennage. IMO a -900NEO has to be maximally-optimized, single-family plane. There's really no room for a family of suboptimal VLA's based on A380.
• Why haven't we seen this yet? Hmmm... 3 modern quads: 744, A340NG, A380. The latter two were (supposed to be) parts of families; they had empennages suitable for shorter lever arm (A345/6) or else V-stabs sized for growth (A380F). Re 744, idk. Maybe wasn't worth design complexity at the time (different economic environment).

Our Swet and weight deltas should yield ~1% lower fuel burn after iterative loops (that would also impact - slightly - engine thrust, mx, and production cost). Delta to engine mx (~5% of life-cycle cost) should be low-single digits. Seems worth it.

Please point out where I'm missing stuff or suggest additional considerations/improvements.

There are be a few more feasible and cheap-ish -900NEO possibilities to explore (e.g. even larger winglets, greater use of GLARE and accounting for its predominance in the stretched sections, plausible opportunities to use other advanced materials cheaply, whatever y'all suggest).

After, hopefully, discussion of these revisions and maybe a few minor ones, I'd like to proceed to analyzing the DOC/CASM of this plane, its production cost versus A388, and explore the business case.

Preview: With optimistic but defensible projections, this plane could exceed 35% CASM reduction vs. A388 - far more than I projected at the start of this thread. That means lower trip cost but up to 35% more capacity/cabin area. For ~20% more trip cost than 777-9 you'd get at least twice the seats . Or, more likely, some combination of trip-cost-saving lower-density (more space for higher yield) and more seats.

My issue is that the changes that should be done start adding up real quick to "why not a new plane".

One thing I haven't seen is a new wing to save on its insane construction costs. Its one of the worst things about the insane A380 supply chain. 3D milling the wing skins sounds good till you have to pay for it. Then the specialty barges and ships. And the ground convoys. Give the UK something else manufacturing wise and do final assembly of a carbon wing at the A380 plant. The design and expertise can live in the UK just fine.

Matt6461 wrote:

LH707330 wrote:

I guess my issue is with the cumulative weight. If you could get it to shear at ~4g, then it'd work out, I just wonder if the cert agencies would bless it.

Re cumulative weight the scheme adds ~35,000lbs (cargo+containers+infrastructure). MZFW is ~830,000lbs so doesn't seem an impractical delta.
Re agencies, I'd bet they'd see reason if the engineers have a solution. Wings would reliably snap off at ~8g; same could be designed for tailcone.
For your aft-pax worries, seems possible to have a load path that cleanly transfers at cone/fuse junction to a transfer path (fuse-cone) that is independent of each, is strong enough for, say, 5g but fails completely at 6g (some strong but brittle material with a known fail-point). Load-transfer path would add some weight but we're talking 11% capacity delta on ~290t plane, so not insuperable.

Regarding the aft cargo area loadpath, it might make sense, might not, I'm not a structures guy, so I couldn't tell you, but good that you're considering it.

Matt6461 wrote:

One other note on volume of tail-cone space. If we want more volume, or have doubts about my 2,500ft3, we could make the rear bulkhead flat (A340 did it post-EIS, IIRC) with a small weight penalty.

You got a ref for the A340 bulkhead? That's the first I've heard of it.

Matt6461 wrote:

Next arguably feasible and cheap idea:

Non-uniform engine thrust

The rationale is to shrink the V-stab, which even after OP's revisions is ~50% bigger than 777-8's despite much longer lever arm.
V-stab is sized for one-engine-out (OEI) conditions; the critical engine is either outer engine due to their longer lever arm for yaw moment and lower distance from Vstab's center of pressure (due to wing sweep).

Here's how it works:

• Keep all engines physically identical - same family - but uprate the inner engines' max TO thrust and derate the outer engines.
• Outer engines have ~80% greater lever arm than inner - they're still the critical engines but create less yaw moment.
• Across engine families, ~35% seems a high but doable spread for thrust ratings.
• Our lower-MTOW -900NEO needs ~260k T
• Outer engines have 56k lb-T, inner have 74k (~32% spread)

Compared to even thrust spread, max OEI yaw moment (and thus V-stab size) is ~14% lower versus even thrust (56/65).

Deltas from V-stab shrinkage:

• ~35m2 Swet (~0.9% Dp reduction)
• ~1,000lbs (assuming ~14% weight reduction from our previously-shrunken V-stab)

Another benefit is potentially smaller engine system (by area and weight, not thrust), due to higher average T/W ratio (depends on spread of derate/uprate versus a baseline even engine thrust).

Drawbacks/Issues so far:

• What about engine mx? These are basically identical engines, just one is programmed to run at higher RPM during takeoff. The mx delta would be should be small: uprated engine will be more but derated less. On net it would be positive delta though. To minimize mx and on-wing life impact, we'd rotate engines every year or whenever is convenient during heavy maintenance checks.
• What about SFC? The uprated engine will have lower SFC during takeoff/climb, as its fan will be spinning faster than optimal. During cruise, however, all engines would run at equal N1 and equal SFC (by my understanding of uprating/derating - correct me if you know better).
• What about engine purchase/development cost? It should cost the OEM some delta to program and certify two thrust versions instead of one, but this seems minimal overall and would be mandated in Airbus/OEM contract to fly on -900NEO. If OEM prices engines linearly on thrust, buyer price is equal but production cost of smaller engines could be lower.
• What about thrust growth for stretch/shrink? It's largely ruled out by perfect match of engines and empennage. IMO a -900NEO has to be maximally-optimized, single-family plane. There's really no room for a family of suboptimal VLA's based on A380.
• Why haven't we seen this yet? Hmmm... 3 modern quads: 744, A340NG, A380. The latter two were (supposed to be) parts of families; they had empennages suitable for shorter lever arm (A345/6) or else V-stabs sized for growth (A380F). Re 744, idk. Maybe wasn't worth design complexity at the time (different economic environment).

Our Swet and weight deltas should yield ~1% lower fuel burn after iterative loops (that would also impact - slightly - engine thrust, mx, and production cost). Delta to engine mx (~5% of life-cycle cost) should be low-single digits. Seems worth it.

Please point out where I'm missing stuff or suggest additional considerations/improvements.

This is an interesting idea, but I think you're overthinking it. The limiting conditions are v1 OEI and vmca. The only thing you'd have to do is cap the thrust on the outboards below a certain speed (vmca) as is done on three-engine ferry flights, then once past v1, throttle them up while throttling down the inboards so that they all make the same total thrust. By the time your gear is coming up, you're going fast enough that they can all be making the same thrust, and can keep doing so for the rest of the flight. Computers and A/T would make this pretty simple.

Now the question about why we have not seen it yet? My guess is that the field performance hit results in too much payload loss. If you deliberately derate your outboards to shave 1% of your stab weight, your field performance gets worse than it would with full thrust/big stab, which means you lose available payload capability off that runway. Put differently, if I buy the "small-tail" version, I might be tempted to think "Shit, I'd take a 1% fuel hit to get 5% more revenue payload." If it's the case that all A380 fields are longer than needed, then the simple answer would be to make all engines physically smaller because the thrust is excessive.

One other thing to consider: until the A340, all quads had the most powerful engines available at their time, including the 744. That was the biggest you could do in 1988, and they needed all that thrust

Regarding the problems with the recent quads:
A380: overbuilt, see thread topic
A345/6: a stretch too far. The pizza slice wing lost a lot of the qualities that made the 1.0 wing so good in the name of fuel storage, namely aspect ratio and T/C (proof in pudding is that it still soldiers on with a new winglet in the neo). The 343 was a structurally pretty well optimized frame, so messing with it involved a lot of consequences. Regarding the tailfeathers, the 500/600 empennage was actually larger than the 300 by a decent margin because of the higher thrust and weights.
744: couple thing going on with this:
1. 1960s wing design meant suboptimal AR in the late-80s, even with the winglets. There was a good thread on here a year or two back where zeke posted some brochures about how much better the 343 aero was relative to the 744, which has a better T/W
2. Code E sizing meant the wingtips could not go outside their 211 ft 5 size

LH707330 wrote:

You got a ref for the A340 bulkhead?

Post-EIS bulkhead flattening was actually the 737NG (and maybe others):

The flat bulkhead will become standard on all 737's from 2006

http://www.abovetopsecret.com/forum/thr ... rshift=yes

LH707330 wrote:

it might make sense, might not

Right. My goal here is to consider what's arguably feasible and cheap-ish on -900NEO. All here subject to doubt. Even for experts the details can screw the initial projections. E.g. most industry observers expected Al-Li for 777X; after study Boeing concluded it would be too difficult.

LH707330 wrote:

The limiting conditions are v1 OEI and vmca.

Don't forget V2 (winglets should remove that constraint).
Vmcg is more likely operative than Vmca. With engine-out post-V1, you're still accelerating on the ground for some time. Here speed is lower and thrust is greater (less lapse) than after Vmu. Highest yaw moment at lowest speed is what sizes the Vstab; that's likely Vmcg (front LG is steerable but how much can it do safely?). Plus it's fine to sideslip in the air a little, not so much on the runway. I believe this is why Vmcg<V1.

LH707330 wrote:

By the time your gear is coming up, you're going fast enough that they can all be making the same thrust, and can keep doing so for the rest of the flight.

Assuming MTOW and OEI from just after V1, you need full thrust from all engines until 1,000ft, then retract flaps and accelerate. Even engine thrust probably wouldn't happen until cruise, as TOC climb thrust = ~10-15% more than initial cruise thrust. I'm envisioning up-rating two engines past "normal" for climb as well as TO. Outer engines would have "normal" intensity for climb, inner engines slightly higher intensity (=slightly worse climb SFC but higher engine T/W and less nacelle drag).

LH707330 wrote:

1% of your stab weight

14% of stab weight and drag; rough estimate of 1% delta to trip cost.

LH707330 wrote:

My guess is that the field performance hit results in too much payload loss.

I probably didn't do the setup clearly enough. We're using equal thrust (260k), just differently distributed. If an outer engine fails, we've lost less thrust than with uniform engines, so field performance would be better than default. If the inner engine fails at V1 (critical engine for BFL, not for engine sizing), then we have ~4.6% less thrust than default.

But:

• 1. Given our low wingloading, V1 and Vlof happen far down the runway - say 75% of BFL (slower plane stops more quickly).
• 2. The necessary delta to kinetic energy for liftoff post-V1 is ~10% (less time on ground, lower thrust rates due to lapse).
• 3. -4.6% delta to thrust is -0.46% delta to kinetic energy; but say it's 1%:
• 4. Now our smaller Vstab comes into play. If Vmu is critical, we're at least 1% lighter at MTOW, kinetic energy is fine for liftoff. If V2 remains critical, our Vstab induced drag (very substantial if outer engine is out) is ~40% lower due to half the yaw-moment lever arm.

I maybe should have made the weight/drag implications of 14% smaller Vstab more explicit - but my posts are already long haha. I'm probably underestimating a bit the direct Vstab shrinkage impact and didn't do iterative loops from it. Engines shed lbs and Swet at expense of mx cost; airframe sheds weight in MLG, wing.

@LH707330 and others still following, further rough quantification of the OEI Vstab induced drag effects:

• First, the effect is from shifting critical engine from outer to inner, not from lower Dp from smaller Vstab (low impact of Dp at takeoff).
• With default uniform engine thrust, outer engine failure is the critical BFL case.
• Per ACAP, outer engine is ~84ft from centerline. On -900NEO, it's ~125ft from Vstab center of pressure (Cp).
• Default 65k engine generating 80% SLS thrust at V1 failure means we need ~35k-lbs lift from Vstab [84/125*.8*65] to keep straight.
• Low-AR Vstab's L/D at takeoff speed is ~4, so ~9k-lbs induced drag from Vstab.
• With failure of uneven inner-engine: 80% of 74k lbs-T, 46.5ft from center, 135ft from Vstab Cp (wing sweep delta from outer), Vstab generates ~20k-lbs lift and ~5k-lbs drag.
• -4k-lbs drag delta from default is ~2% of OEI thrust [ 4 / (.8*260) ]

Versus default condition, our net thrust delta with OEI at V1 is ~2.6% (4.6-2). This is all very rough of course...

And the reason I think a net -2.6%, post-V1 thrust delta fine and we'd actually see lower BFL is:

• as stated upthread, winglet-enabled effective span increase and MTOW delta reduces takeoff Di by 30-40%
• Because A388's BFL appears climb-limited (as explained above), and because Di delta removes/eases 2nd-segment climb constraint, we can lift off safely at lower speed than does A388 (A388 can most likely physically lift off the ground at speeds below its current V2/1.05 - V2 can't exceed Vlof by >5%.)
• If we want improved BFL versus A388 rather than Vstab-shrinkage-enabled better efficiency, than we'd have to reduce outer-inner differential a bit and shrink Vstab by, say, 10% instead of 14%. But a -900NEO will only operate from the biggest airports, most of which don't materially restrict payload/range performance.

Ultimately, -900NEO's engines will be (top of) climb-constrained, not takeoff constrained (assuming big winglets). We have more room to shrink below 260k but I'm not sure by how much - depends on A388's V2/Vmu ratio, its exact drag at TOC, and the -900NEO's TOC drag/FL.

Whichever climb-constrained engine power works, there's room for uneven thrust and Vstab shrinkage at constant A388 BFL.

Hi @matt6461 an unrelated technical question. I've hooked onto the sub deck amenities concept and particularly the notion of already having trolleys loaded and ready to be exchanged at luggage deplaning moment i.e they've been packed and stored in that area. In part you could argue this technology could be cascaded, so not entirely an A380NEO programme burden. However certification might only allow that any trolley in a cabin must be able to be stored safely within 60ft on a flat plane. In an emergency I can't see trolley lifts being a priority and I expect loose trolleys in a 12g exchange with the landscape not being a welcome gift although probably not your primary concern. That said the galley can be reduced to hold at least a single light service at any given time exchanging as they go reducing the holding area significantly. Service will be slow and there will be a lot of running up and down the plane especially if it's not an optimised central point. So a suggestion:

Is this an accurate model of the current A380 hold area?


I think compartment 2 is this best candidate for the extended passenger area, move the bulk head forward to delineate compartment 1 and 2. The fore and aft of compartment 3 extended to lavs and trolley lifts full width, whilst using the length of compartment 3 for trolley store. The loading could be through the back hold door and I notice there is a bulk loading area in the tail incidentally. Then you have your venue space under the premium cabin area. However with no engineer training this maybe a cost too far. Jumping on the asymmetric theme there maybe qualities in supplying the rear of the aircraft with additional trolleys? Or flushing economy quickly as per your original concept.