Have to wonder if some of these could have been sold with the big china sale today, had Airbus just redesigned the wings and lightened where possible.

Might even be worthwhile to do a buy back of A380s and refit them with the new wings and wingbox for resell. Possibly for SR use with smaller tanks.

Bjorn/Ferpe also reiterates that the A380's drag composition is such that induced drag is 20% greater than parasitic. Last time I pointed this out I think SomebodyinTLS asked whether that could be True, given that it implies the A380 flies on the back end of the drag curve. I think the explanation is the typical drag minimum at Di=Dp holds only when we ignore transonic effects. Were the A380 able to fly at Mach .98 the induced drag would come down and parasitic would go up so that the typical minimum would hold. Obviously that's not possible without incurring a huge wave drag penalty, thus the A380 cruises with an odd drag composition due to its form. As Bjorn also reminds us, the 2deck fuse is very efficient on wetted area and therefore parasitic drag; the wings are stubby and therefore bad on induced drag.

It was my hobbyhorse for a few years here to call for a new wing; now that's been replaced by a new VLA fantasy (A360 or A390?).

Anyway that great fuse plus bad wing issue will always hamper this plane absent big investment; Bjorns post is a good reminder why the A380 is both currently suboptimal and reservoir of tantalizing potential.

It doesn't require a new wing to reduce the drag percentage. If Airbus would stretch the A380, they could use a smaller empenage, which means less drag. Of course the longer fuselage will increase the drag slightly, but the double-deck hull shape of the A380 has a very good drag per seat ratio.
Overall a stretch would reduce the drag per seat a lot and if the MTOW is not increased, it wouldn't have any drawbacks except a reduced range. But for most routes reduced range wouldn't be an issue, because the A380 has much more range than needed (DXB-Europe or LHR-JFK).

JoergAtADN wrote:

It doesn't require a new wing to reduce the drag percentage. If Airbus would stretch the A380, they could use a smaller empenage, which means less drag.

Simply less drag per seat isn't the right question to ask.
Rather, you want to work backwards from the economics: what efficiency delta would justify the risk/capacity/efficiency tradeoff of a bigger A380?
IMJ you need to be at around 50% trip cost delta per capacity delta for a stretch to be widely popular (I base this off efficiency comparisons between bigger and smaller planes for ~equal range). That's 50% versus smaller competition (i.e. 777-9), not 50% versus A388. Pick your own efficiency target if you like.
Only once you've picked your efficiency target should you begin working backwards from there to investigate whether the technical/aero solution meets your target.

Can you achieve that kind of game-changing efficiency delta via a smaller empennage and slightly less fuselage drag per pax? Almost certainly not.

Matt6461 wrote:

JoergAtADN wrote:

It doesn't require a new wing to reduce the drag percentage. If Airbus would stretch the A380, they could use a smaller empenage, which means less drag.

Simply less drag per seat isn't the right question to ask.
Rather, you want to work backwards from the economics: what efficiency delta would justify the risk/capacity/efficiency tradeoff of a bigger A380?
IMJ you need to be at around 50% trip cost delta per capacity delta for a stretch to be widely popular (I base this off efficiency comparisons between bigger and smaller planes for ~equal range). That's 50% versus smaller competition (i.e. 777-9), not 50% versus A388. Pick your own efficiency target if you like.
Only once you've picked your efficiency target should you begin working backwards from there to investigate whether the technical/aero solution meets your target.

Can you achieve that kind of game-changing efficiency delta via a smaller empennage and slightly less fuselage drag per pax? Almost certainly not.

What else does matter than drag per seat? The only other thing that comes to mind are engines. If the numbers are against your ideas you try to move the equitation.

If the A380 has less drag per seat than a 777-9, the 777-9 than has to have superior engines to draw even. If than the A380 goes to a similar engine generation the advantage of the 777 is gone. It is the same with seat density. The 777-9 is always counted with a high seat density, I never heard you comment on that, but the moment somebody talks about increased seat density on the A380, you cry sham.

The point is, that most operators of the A380 did not go for a high seat density but rather comfort and prestige. Emirates runs it's highest density A380 at 615 pax and still goes there for a lower density than on their 777.

I agree that the A380 does not sell, but the problem is not CASM, but that it is to large for most airlines. A situation I see coming for the 777-9 too.

What strikes me on these internal layouts whether it be circa 500 or circa 600 pax is the proportion of high yield.With such a high proportion First,Biz-and Premium,if you can get high load factors you are going to print money whether the length of journey is optimal or indeed the aircraft itself.
No doubt 'every little helps' whether it is internal packaging or external physical improvements.But the key as always with this aircraft is filling it on a regular basis particularly with the aforementioned high yield seats.
Not meany airlines can.That problem is not going away (it was equally true of the 747 before it).

Matt6461 wrote:

Bjorn/Ferpe also reiterates that the A380's drag composition is such that induced drag is 20% greater than parasitic. Last time I pointed this out I think SomebodyinTLS asked whether that could be True

Must have been someone else. Aerodynamics was literally my worst subject at uni - I'm left with a general understanding but I never pretend to know much about it.

SomebodyInTLS wrote:

Matt6461 wrote:

Bjorn/Ferpe also reiterates that the A380's drag composition is such that induced drag is 20% greater than parasitic. Last time I pointed this out I think SomebodyinTLS asked whether that could be True

Must have been someone else. Aerodynamics was literally my worst subject at uni - I'm left with a general understanding but I never pretend to know much about it.

I think it may have been me:

VirginFlyer wrote:

Matt6461 wrote:

There's actually a similar thing happening with airliners. Most drag is related to size (parasitic) instead of weight (induced) for most airliners.
That's actually not true of the A380, however. The whale is quite efficient on size despite the big wing because its double-deck fuselage has only ~25% more wetted area than a 77W.
But the whale is quite heavy and compounds that problem with insufficient span - thus a lot of induced drag ( ~ lift ^ 2 / span ^ 2 )

I would find it incredibly surprising if in cruise parasite drag is not the greater source ofdrag. Induced drag reduces at a square of speed, while parasite drag increases at a square of speed. While you may be right (or you may not - I would want to see hard data here) that at a given speed in the cruising range an A380 would producd more induced drag when expressed as a percentage of parasite drag at that speed, compared to a 777, in both cases that percentage would be less than 100. Otherwise if what you are saying is correct, that in cruise induced drag is greater than parasite drag, then that means the aircraft is flying on theback (or left hand side) ofthedragcurve, and that would be rather surprising in itself.

Airbus A380 MidLife Upgrade, 2021? (page 3) - post #144

V/F

VirginFlyer wrote:

I think it may have been me

Hopefully Bjorn's aerodynamic expertise is sufficient to convince you on the drag composition issue.

Revelation wrote:

mjoelnir wrote:

Revelation wrote:

Indeed true, but after TXWB it seems on T7000 RR made a change that they had to back out late in the game, which meant a lot of costly re-testing, which also messed up the schedule. I raise this point not to denigrate RR (such things happen in development...), but to show that their spending has been greater than anticipated, which might explain why they decided against coming up with an engine for A380NEO. I don't know if it was known at the time, but we now know the last T900 PIP didn't go according to plan either, which presumably also meant more spending than intended.

I thought the T7000 followed corresponding changes and delays on the T1000ten, being a derivative of that engine, just with additional bleed and smaller power take off.

I can't remember where I read a more detailed story, but https://www.bloomberg.com/news/articles ... icing-snag says:

Delays to the first flight of Airbus SE’s revamped A330neo jetliner stem from an unexpected requirement for extra testing of the model’s Rolls-Royce Holdings Plc engines, according to the planemaker.

... and my recollection is that this 'extra testing' came from a change they made late in the development cycle. Or I could be mixing things up. In any case, it's extra testing which adds extra costs and delays deliveries which delays revenues, which is the main point.

This needs some explaining as well because it's pretty complicated.

It started with the T1000-TEN engine that was delayed by 12 months:

Rolls-Royce confirms that an upgraded version of the Trent 1000 engine for the Boeing 787 fleet will be delayed one year before entering service and reducing fuel burn levels to the originally promised standard.

Ref https://www.flightglobal.com/news/artic ... 17-423434/

Reason for delay:

Last year, R-R discovered that a new, cost-saving material used to make the banded stators in the compressor was not ready for operational service, so the company redesigned the component with a conventional metal, Moore says.

“That was a cost reduction opportunity and on the basis of the test results it didn’t work out as we thought it would,” he says. “We took time to fix that. Certification is an important milestone but what you want is a robust product and something the customer can use as an everyday, reliable machine.”

Moreover, fatigue testing on the Trent 1000-TEN revealed cracking in the intercase about one-third of the way through the 3,000h-cycle, Moore says. In that case, a pedestal attaching a solenoid to the intercase cracked under the pressure. After tearing down the engine, R-R discovered that the out-of-balance testing conditions had exceeded the design parameters, so the components were being shaken harder than the engine was expected to experience in service. R-R’s engineers have slightly lowered the pedestal to prevent cracking and the redesigned component should re-enter testing by July, Moore says.

Ref https://www.flightglobal.com/news/artic ... pr-426468/

Being a derivative the TEN delay cascaded on the T7000. RR made an error with a new material in the low pressure staters and it was subject to fatigue. The test data of the ground tests invalidated, forcing RR to change materials and revalidatie all data.

RR also unveiled that regulators are asking additional testing on icing conditions on the wing.

All together, there was a delay and additional test capacity was required, something RR didn't account for.

Agreed.
It would definitely be better to be done in tandem. Certainly more cost effective. But it still keeps the NEO option open for evolution at least. If the engine is likely to be a variant of the Advance, RR should have enough specs to share for design consideration of the new wing.

Hopeful I know. Be sad to see the A380 go so soon though.

dubaiamman243 wrote:

Quote:
"Beyond the new tweaks, the health of the programme depends on getting costs low enough so that Airbus can keep output ticking over at 12 a year without losing money, while it waits for what it hopes will be a rise in demand as air travel grows."

aka. Airbus lost money on the a380 and is trying to make money.

CFRP would lower cost.
It could use the diet too.

Might be a good time to work out the details for a freighter version again.

I think the A380plus is a stopgap in order to attract orders from Emirates and others so that the A380 production line can be kept open while Airbus is waiting for the RR Ultrafan. Ultrafan will be available after 2025. With a production of 12 A380's per year, and taking the current backlog into consideration, subtracting firm orders that is likely to be canceled, Airbus needs maybe 50 new orders to keep production going to 2025 at current levels.

For the A380 program to continue in the decades to come, Airbus needs to do what Boeing is currently doing to the 777. Boeing is upgrading the 777: 1) new CFRP folding wings, 2) doing a re-engine, and 3) stretching the fuselage.

The A380 wings are suboptimal in order to fit into the 80 meters box (code F aircraft). New advanced materials (CFRP), technology advances like folding wings and variable camber etc. are now ready for application. These would benefit the A380 tremendously. Together with new RR Ultrafan engines this could make the A380 a great success. There is no doubt that air traffic will grow, and the A380 fuselage, with its relatively small wetted area and high passenger volume, could be CASM king by a huge margin. It's a big bet, but the only way the A380 could have a future beyond 2025.

The EU should put some "light pressure" on the gulf carriers. If they don't order more A380s soon, they can expect a future where their access to EU airspace and airports will be severely limited. If they think that they can fly into EU with only 777s, think again.

Slug71 wrote:

CFRP would lower cost.
It could use the diet too.

Might be a good time to work out the details for a freighter version again.

CFRP would not lower costs for Airbus. CFRP is not cheap, and neither is redesigning parts to add it to the aircraft.

2175301 wrote:

I think that the evidence is that the B777 is out competing the A380.

Things in the mirror may be ...

With every A380 you push a nominal batch of 550 seats into the market.
That is nearly twice as much as you provide via a 77W.

A large segment of the market just does not stage A380 against 77W ( or other similar sized "lesser" frames.)

reidar76 wrote:

The EU should put some "light pressure" on the gulf carriers. If they don't order more A380s soon, they can expect a future where their access to EU airspace and airports will be severely limited. If they think that they can fly into EU with only 777s, think again.

Surely this must be a joke.

Polot wrote:

Slug71 wrote:

CFRP would lower cost.
It could use the diet too.

Might be a good time to work out the details for a freighter version again.

CFRP would not lower costs for Airbus. CFRP is not cheap, and neither is redesigning parts to add it to the aircraft.

CFRP is cheaper to produce than GLARE. Besides the wing, there shouldn't be much redesign needed.

Slug71 wrote:

Polot wrote:

Slug71 wrote:

CFRP would lower cost.
It could use the diet too.

Might be a good time to work out the details for a freighter version again.

CFRP would not lower costs for Airbus. CFRP is not cheap, and neither is redesigning parts to add it to the aircraft.

CFRP is cheaper to produce than GLARE. Besides the wing, there shouldn't be much redesign needed.

unknown.

What happend was that GLARE did not show the expected exponential decrease in pricing.
This could be due to tech issues but it could also be due to a patent holder monopolist
being unwilling to to yield on price.

The A380 was built too big.Not a little too big,way too big.Nothing you do to the aircraft alters that fact.

parapente wrote:

The A380 was built too big.Not a little too big,way too big.Nothing you do to the aircraft alters that fact.

Disagree.
The size is fine. Many airports just spent billions to accommodate it. It's just overbuilt. The -800 should have been the base model. Economics spoiled it's success, but it can be corrected. Economies are rebounding and oil prices are expected to stay down long term.

caoimhin wrote:

reidar76 wrote:

The EU should put some "light pressure" on the gulf carriers. If they don't order more A380s soon, they can expect a future where their access to EU airspace and airports will be severely limited. If they think that they can fly into EU with only 777s, think again.

Surely this must be a joke.

I think the gulf carriers (especially EK) have done way more than their share to keep the A380 afloat.

Maybe the EU should put some "light pressure" on EU airlines to do their share.

Of course, if it made financial sense to do so, the EU airlines would have already ordered more A380s.

BTW, has ANY airline expressed interest in the A380 PLUS? -ir

IslandRob wrote:

BTW, has ANY airline expressed interest in the A380 PLUS? -ir

No specific airlines so far. Closest is the "discussions" with China over A380's - those would presumably be PLUS versions.
The worst thing about this PLUS proposal is it threatens several more years - and threads - touting A380 sales campaigns to no avail.

That said, if there's any chance of non-EK orders it would probably be to China as part of some political package.

Slug71 wrote:

Disagree.
The size is fine. Many airports just spent billions to accommodate it.

Hmmmm, Airbus is on record that airports that could accommodate the 747 could accept the A380 with minimal to no change, so for the billions you are talking about all airports combined that had to widen taxiways, right?

par13del wrote:

Slug71 wrote:

Disagree.
The size is fine. Many airports just spent billions to accommodate it.

Hmmmm, Airbus is on record that airports that could accommodate the 747 could accept the A380 with minimal to no change, so for the billions you are talking about all airports combined that had to widen taxiways, right?

I guess it comes down to what their definition of "accommodate" is. Can an A380 land, taxi and unload passengers at all airports where 747's operate -- probably. Can they do it smoothly without any interference or special requirements -- probably not. KSEA is a prime example -- an A380 could land and deplane passengers (somewhere) but would cause issues with the normal operations unless it was the middle of the night.

Egerton wrote:

However, I do find it strange that the engine triumvirate have a business model involving initial heavy loss making over many years. This cannot continue.

It's been continuing for many years, and as engine makers take over ever more of aftermarket support, it seems even more likely to continue.

I would like someone to explain to me how an aircraft that only works economically seating circa 550-650 pax is right sized.
Take away Emirates (a one off specialist global hub operator) and take a look.
But don't worry about 600 don't even worry about 500 let's go right down to 400! The 779 (right now) is dependant on exactly the same one off global hub operator.
The market is ok with 400 pax as a very top end.The A380 was a mistake that's all.We all make mistakes and Airbus made one -it happens.

I don't think the fuselage size is the problem, but Airbus definitely overdid the wing and empennage but sizing it for the stretch. Even if Airbus do stretch it in the future the technology improvements made since ~2000 mean the plane will never have a need for the full MTOW it was designed for.

It is not that the wing is too large, it is the -900 for that wing which never came in the end

Polot wrote:

I don't think the fuselage size is the problem

The A380 has the most efficient fuselage ever built but it could be better for its capacity.
A few strategic decisions hampered fuselage efficiency:

• In selecting 650-seats as the optimal size, Airbus used a fuselage that was much taller than optimal - in order to provide sufficient stiffness for 80m+ stretch.
• Airbus optimized for identical-width 10ab and 8ab layouts for UD and MD. That created inefficiency whereby the broadest point is at eye-level on MD.
• Airbus designed room for pax amenities in the belly - completely unnecessary given the already reduced cargo capability.
• In general, fuselages are optimal at ~11 fineness, though maybe less for a 2-decker. A388 is <9 due to optimization for 650 seats. This means much larger fore and aft tapering sections, which are less efficient on weight and wetted area per pax.
• Related to the above, Airbus had to place the rear bulkhead ~47ft from fuselage tail end in order to accommodate the massive horizontal stabilizer and its activator. That figure is ~33 for the 777 and was shorter for the MD12. The Hstab is as big as the A310's wing so it needs a massive tailcone. Again, this suboptimal constraint derives from building a 650-seater at 2000 tech.

It isn't very difficult to imagine a 550-seat 2-deck fuselage with far less wetted area and weight than today's A388. Depending on your assumptions about side walls, an optimal 550-seat fuse should have 1350-1400m2 wetted area against the A388's 1564m2 (10-14% reduction).

For example, use a triple-bubble with the following main dimensions:

• MD bubble 269in (22'5")
• UD bubble of 231in (19'3")
• Belly bubble that cuts off the the MD bubble below the MD floor, limiting its size to LD3 depth.
• If we assume 7in sidewalls, the MD is wider 7in wider at armrests than A380, the UD has equal width

The perimeter of that design is equivalent to a 24.08ft circle - ~7% less than A380 (Estimated at 25.8 equivalent).
It is two feet shorter than A380 and one foot skinnier.

With perfect hindsight given A380's experience, we could design the UD and fuselage such that the UD is only expected to carry premium classes. That would reduce weight in UD floor beams and enable thinner/lighter MD sidewalls. Premium seats weigh ~100lbs more than economy but spaced at ~4x less dense the overall load is much lighter.

In addition, we'd want to shorten the empty tail cone and would be able to, given the much smaller empennage. If we pull equal to 777, that would add 14ft of cabin length for no wetted area cost (small cost in additional pressure structure). If we pull even to the MD12 it adds ~17ft of cabin length.

It would probably also be wise to center the nose cone higher to allow a longer upper deck with a smaller cockpit located up there a la 747. A380 likely didn't use this because it would have penalized cargo and nose landing gear - plus the marginal benefit for an 80m design would be quite low. It would be fairly significant for a shorter design, however.

All in, you could probably build such a fuselage for about the same wetted area as the 777-9 (1339m2) with at least 40% more capacity. Given CFRP construction and shorter bending moments, it would likely be significantly lighter. Extrapolate the rest of the plane from the thing you're lifting (fuselage+contents) and you could have lower trip fuel cost than the 777-9 given 2025 engine tech and an 80m wing.

That's the plane that seems possible with 2025 tech but we'll never see it as long as Airbus is shackled to the whale's bloated corpse.

Matt6461, I liked the discussion you were having here:

viewtopic.php?t=775819

The Ecoliner that Keesje proposed was a very attractive idea and I'd love to see something like that come down the pike.

Matt6461 wrote:

Polot wrote:

I don't think the fuselage size is the problem

The A380 has the most efficient fuselage ever built but it could be better for its capacity.
A few strategic decisions hampered fuselage efficiency:

• In selecting 650-seats as the optimal size, Airbus used a fuselage that was much taller than optimal - in order to provide sufficient stiffness for 80m+ stretch.
• Airbus optimized for identical-width 10ab and 8ab layouts for UD and MD. That created inefficiency whereby the broadest point is at eye-level on MD.
• Airbus designed room for pax amenities in the belly - completely unnecessary given the already reduced cargo capability.
• In general, fuselages are optimal at ~11 fineness, though maybe less for a 2-decker. A388 is <9 due to optimization for 650 seats. This means much larger fore and aft tapering sections, which are less efficient on weight and wetted area per pax.
• Related to the above, Airbus had to place the rear bulkhead ~47ft from fuselage tail end in order to accommodate the massive horizontal stabilizer and its activator. That figure is ~33 for the 777 and was shorter for the MD12. The Hstab is as big as the A310's wing so it needs a massive tailcone. Again, this suboptimal constraint derives from building a 650-seater at 2000 tech.

It isn't very difficult to imagine a 550-seat 2-deck fuselage with far less wetted area and weight than today's A388. Depending on your assumptions about side walls, an optimal 550-seat fuse should have 1350-1400m2 wetted area against the A388's 1564m2 (10-14% reduction).

For example, use a triple-bubble with the following main dimensions:

• MD bubble 269in (22'5")
• UD bubble of 231in (19'3")
• Belly bubble that cuts off the the MD bubble below the MD floor, limiting its size to LD3 depth.
• If we assume 7in sidewalls, the MD is wider 7in wider at armrests than A380, the UD has equal width

The perimeter of that design is equivalent to a 24.08ft circle - ~7% less than A380 (Estimated at 25.8 equivalent).
It is two feet shorter than A380 and one foot skinnier.

With perfect hindsight given A380's experience, we could design the UD and fuselage such that the UD is only expected to carry premium classes. That would reduce weight in UD floor beams and enable thinner/lighter MD sidewalls. Premium seats weigh ~100lbs more than economy but spaced at ~4x less dense the overall load is much lighter.

In addition, we'd want to shorten the empty tail cone and would be able to, given the much smaller empennage. If we pull equal to 777, that would add 14ft of cabin length for no wetted area cost (small cost in additional pressure structure). If we pull even to the MD12 it adds ~17ft of cabin length.

It would probably also be wise to center the nose cone higher to allow a longer upper deck with a smaller cockpit located up there a la 747. A380 likely didn't use this because it would have penalized cargo and nose landing gear - plus the marginal benefit for an 80m design would be quite low. It would be fairly significant for a shorter design, however.

All in, you could probably build such a fuselage for about the same wetted area as the 777-9 (1339m2) with at least 40% more capacity. Given CFRP construction and shorter bending moments, it would likely be significantly lighter. Extrapolate the rest of the plane from the thing you're lifting (fuselage+contents) and you could have lower trip fuel cost than the 777-9 given 2025 engine tech and an 80m wing.

That's the plane that seems possible with 2025 tech but we'll never see it as long as Airbus is shackled to the whale's bloated corpse.

To me this seams great on paper, but I fear that there would be too little cargo room left if it was a 'short' double decker - still roughly equal pax bags as todays A380 since those have around 540-560 pax average seating. And it would seam impossible to have a lower trip fuel burn than the 779 since I imagine this beast would have a fair bit higher MTOW, even with the bigger wing, but it would probably be quite close, mostly because I'd still imagine it to be a quad.

I would suggest making it a little slimmer than it is today so it has 10Y seating on MD, meaning only very slightly wider than the 777 fuse (and not almost 11Y) and also have the A330 fuse width on UD so all of the current wasted space would be eliminated. That alone would bring the empty weight down enough for it to be competetive with the 779 IMO. Also IMO, there is not much point going to a significantly smaller design since it would be getting close enough to the largest possible twins that it would be counterintuitive with all the extra stucture that is needed for the double decker design.

350helmi

350helmi wrote:

To me this seams great on paper, but I fear that there would be too little cargo room left if it was a 'short' double decker

Immaterial. If VLA fuel trip cost is in the area of 777-9, you'd be happy to carry even the lowest-yielding passenger instead of belly cargo, which average ~1/5th the yield per weight. If that economic equation somehow changes, you just use some main deck space for cargo/bags. The fact that nobody (aside from a few KLM frames) uses combis should tell you that cargo isn't your first priority.

I suspect folks like to cite cargo as an issue because they've heard airlines say it. They forget that airlines care about $$$$$$$, not cargo or passengers.

350helmi wrote:

I would suggest making it a little slimmer than it is today so it has 10Y seating on MD, meaning only very slightly wider than the 777 fuse (and not almost 11Y) and also have the A330 fuse width on UD so all of the current wasted space would be eliminated.

There are a lot of solutions here, including something like Keesje's ecoliner. IMO you'd want the option for a viable 11ab for high-density, lower-yielding cattle class. At the economics I'm arguing are possible, you make $$$$ off of cheap Y longhaul fares. Just as the mainline airlines have learned to make money off basic economy.

350helmi wrote:

all the extra stucture that is needed for the double decker design.

What extra structure? I already accounted for floor beams, furnishings/systems, and increased bending moments. The only additional consideration is the amount of sidewall strength required to maintain survivability under certain crash landing conditions. I am not certain of the impact of that constraint (can anyone chime in?) but I get the same result as above when I model from the A380, whose design is constrained by the crash consideration.

350helmi wrote:

it would be getting close enough to the largest possible twins that it would be counterintuitive

I have one very urgent condition to beg of you: be willing to question your intuitions based on a string of arithmetical or other logic. The reasons for my conclusions are set out in my posts; to simply fall back on background intuitions makes all that effort - mine to write and yours to respond - worthless.

PlanesNTrains wrote:

Matt6461, I liked the discussion you were having here:

viewtopic.php?t=775819

The Ecoliner that Keesje proposed was a very attractive idea and I'd love to see something like that come down the pike.

Thanks. Feel free to chime in on the thread then!

Ecoliner is a good first-order concept - basically just a smaller 2-decker as I have been saying.
It's frustrating, however, that Keesje tends to prefer pictures to harder analysis, and tends to back away from technical discussions.

Hard analysis.
If you are looking for the perfect 744 replacement for pax and cargo can anybody tell me what's wrong with the 779?It looks like a perfect replacement today.The only question perhaps is whether it's too big for today's sweet spot (see 350-1000).If you were looking for something possibly better at the same size then it would surely be the 350-1100.
If (for whatever reason) you wanted to go into the elephants graveyard (i.e. Bigger again) then the obvious answer (considering the clear small market size) would be a derivative (i.e. Keeping costs in proportion to potential limited sales).Well we know the answer to that too.Its the 777-10 at 450 pax.No one on earth is going to make the same mistake (for a third time) and go even bigger still!

It's clearly in Airbus' interest to try as hard as they can to keep Emirates buying the A380 because each one sold diminishes the economic chances of a 777-10 stretch being built (at least in the medium term).Whether they can achieve this who knows.

The reason Airlines did not buy the 380 in large numbers was not because it did not have perfect efficiency ,it was because they did not (and do not/will not) have the routes where they can fill it up on a regular basis.Its too big.

Slug71 wrote:

CFRP would lower cost.
It could use the diet too.

No it would not, and I doubt you would save much weight anyway.

Were you aware that two of the largest CFRP components flying are the A380 centre-wingbox and rear pressure bulkhead? There are composites all over the A380 already so these things have been considered. The current GLARE upper fuselage panels are an advanced composite so CFRP is unlikely to improve things much there.

Then add the massive redevelopment and manufacturing costs of changing over to CFRP and it's a totally dead duck.

SomebodyInTLS wrote:

Slug71 wrote:

CFRP would lower cost.
It could use the diet too.

No it would not, and I doubt you would save much weight anyway.

Were you aware that two of the largest CFRP components flying are the A380 centre-wingbox and rear pressure bulkhead? There are composites all over the A380 already so these things have been considered. The current GLARE upper fuselage panels are an advanced composite so CFRP is unlikely to improve things much there.

Then add the massive redevelopment and manufacturing costs of changing over to CFRP and it's a totally dead duck.

Agreed re feasibility of CRRP'ing the A380. That's probably more complicated than clean sheet given the need to integrate different materials.

Don't underestimate CFRP's potential for an A380 replacement (or GFRP). GLARE is only in upper fuse panels towards fore and aft. Those are the thinnest, least-loaded parts of the fuse.

I'm going to apologise before I start typing this Matt, I promise that I'm not picking on you but you do generate some interesting points so I feel I should come and discuss them.

Matt6461 wrote:

The A380 has the most efficient fuselage ever built but it could be better for its capacity.

Won't disagree there, it has a very efficient cross section but because it's so short (relatively) the cross section doesn't have enough room to promote its efficiency.

Matt6461 wrote:

In selecting 650-seats as the optimal size, Airbus used a fuselage that was much taller than optimal - in order to provide sufficient stiffness for 80m+ stretch.

The cross section wasn't created that high to get sufficient cross section height for creating stiffness for a stretch, it was made that big to allow people to stand up. The fuselagfe would be well over 100m before it became bending dominated.

Matt6461 wrote:

Airbus designed room for pax amenities in the belly - completely unnecessary given the already reduced cargo capability

One of the driving factors for the belly depth was the wing root thickness, having a spar going right through the cabin a la jetstream 31 was probably frowned upon.

Matt6461 wrote:

In general, fuselages are optimal at ~11 fineness, though maybe less for a 2-decker. A388 is <9 due to optimization for 650 seats. This means much larger fore and aft tapering sections, which are less efficient on weight and wetted area per pax.

Agree here, the fineness as with the AR seem out of step with the norm.

Matt6461 wrote:

The Hstab is as big as the A310's wing so it needs a massive tailcone. Again, this suboptimal constraint derives from building a 650-seater at 2000 tech.

Its like this was a compounding problem design the wing for the longer/heavier model and then you are stuck with the length of the shorter model for the moment arm.

Matt6461 wrote:

It isn't very difficult to imagine a 550-seat 2-deck fuselage with far less wetted area and weight than today's A388. Depending on your assumptions about side walls, an optimal 550-seat fuse should have 1350-1400m2 wetted area against the A388's 1564m2 (10-14% reduction).

Do you have a diagram or dimensions to show how you got to this figure? Id love to put you expected dimensions in to my weight (and now aero) estimator

Matt6461 wrote:

With perfect hindsight given A380's experience, we could design the UD and fuselage such that the UD is only expected to carry premium classes. That would reduce weight in UD floor beams and enable thinner/lighter MD sidewalls. Premium seats weigh ~100lbs more than economy but spaced at ~4x less dense the overall load is much lighter.

I'd go with airbus on this one, there probably isn't that much to save on the floor weight and to lose flexibility for the airlines and effectively telling them where they can put certain seats would be pushing it.

Matt6461 wrote:

It would probably also be wise to center the nose cone higher to allow a longer upper deck with a smaller cockpit located up there a la 747. A380 likely didn't use this because it would have penalized cargo and nose landing gear -

The forehead-itis that the A380 suffers (also the 787 but people seem to let that on go) are incredibly important for the cruise drag perspective from what I recall.

Matt6461 wrote:

All in, you could probably build such a fuselage for about the same wetted area as the 777-9 (1339m2) with at least 40% more capacity. Given CFRP construction and shorter bending moments, it would likely be significantly lighter. Extrapolate the rest of the plane from the thing you're lifting (fuselage+contents) and you could have lower trip fuel cost than the 777-9 given 2025 engine tech and an 80m wing.

Again, you'll have to show diagrams or at least dimensions of how you get to that figure (and fit the people in (with their heads))

Matt6461 wrote:

If that economic equation somehow changes, you just use some main deck space for cargo/bags. The fact that nobody (aside from a few KLM frames) uses combis should tell you that cargo isn't your first priority.

Regulatory hurdles around fire is the big issue if I recall, cargo is no longer allowed to share the same deck as PAX, grandfathering is allowed for this.

Matt6461 wrote:

What extra structure? I already accounted for floor beams, furnishings/systems, and increased bending moments.

I think we need more details of how that was accounted for, have you accounted for the extra length of the nose and tail sections. There is a lot of " the weight would remain static when we add capability because CFRP" around a.net.

I'd love for you to supply some dimension data for me to analyse so that we can put real figures to things.

Fred

We can start redesigning the A380 every day of the week or we can look at the proposed changes for the A380plus. According to Leeham the proposed changes do bring the A380 level with the estimated CASM of the 777-9. If we talk about a bigger frame needing a better CASM, we could back strait down to the A350-1000/900 or on the Boeing side 787-9 and -10. The only thing both the 777-9 and to a far bigger degree the A380 have, is size.

Furthermore if the plus changes brings the A380 on par with the 777-9, a new engine, and be it only an engine on par with the GE9X, something like the Trent advanced, would bring the A380 in front regarding CASM, no new wing no stretch needed.

flipdewaf wrote:

I'm going to apologise before I start typing this Matt, I promise that I'm not picking on you but you do generate some interesting points so I feel I should come and discuss them.

Zero apologies needed. As long as we stick to questioning ideas be as ruthless and brutal as necessary with anything I say.
I appreciate your request for more details. Sometimes I'll post a load of arithmetical analysis to little apparent reception so I've held back on that for time's sake increasingly. But always happy to oblige when the work schedule permits.

So here's a spreadsheet of my fuselage model: https://docs.google.com/spreadsheets/d/ ... sp=sharing

The spreadsheet model is a little messier than if I were presenting professionally but should be understandable. I'd be happy to collaborate on making a cleaner version for general a.net use. Here's an explanation of how it works:

• Set parameters like fuse radius, deck heights and thicknesses, sidewall thickness
• Manipulate vertical elevation of each deck/bubble via "MD below center" - that positions the MD floor at the given amount of inches below the MD bubble's center.
• Use simple pythagorean theorem to calculate cabin/fuse width at given points by using radius as the hypotenuse: Width = 2 * SQRT ( (R-SideThick)^2 - (vertical position of reference point)^2)
• Use ArcTan/ArcSin/ArcCos functions to calculate the degrees through which each "bubble" revolves
• The UD bubble is set at 180 degrees
• The belly bubble calculation is set so that the cargo floor base displacement form MD bubble's center is a given. You then just increase the diameter of the belly bubble until its width at MD floor is equal to the MD's bubble's width at that point. A separate cell calculates the belly bubble's degrees of rotation.
• Prorate the perimeter/circumference contribution of each "bubble" according to their degrees of rotation and individual circumference
• Add them up

As you can see, this is just simple grade school math...

In this version of the model, I have three bubbles for belly, MD, and UD.
Their radii are 195in, 134.5in, and 115.5in respectively.
Degrees of rotation are ~125, ~82, and 180 respectively - the MD bubble actually the smallest perimeter constituent.
Contra my earlier post, the diameter-equivalent perimeter is 23.95ft - I found a small error in the calc.

Between the UD and MD is a vertical 13in section matching the floor beam thickness and reinforced by it. I assume this would be faired via a few inches of floor beam reinforcement contained in the upper area of MD and unused lower/outer portions of UD. I didn't actually calculate the fairing's impact on perimeter because it seems fairly small and I just don't want to put that much work in. Circles and right triangles are enough for this words guy.

If you get into the nitty-gritty, you'd probably quibble with a few details. I set the MD floor thickness at 8 inches, for example, and MD internal height at 93in (3in shorter than A380). 8in is probably a bit thinner than A380's MD floor beams but I reason this would apply only over the LD3 span so could be optimized for that section. I also figure that losing 3in of cabin height on the MD isn't a big deal. Maybe others disagree. IMO cabin space per pax is more important to PaxEx than cabin height; a shorter cabin allows more space for a given price. And MD should be mainly economy.

Very interested to hear whether you're able to plug this doodle into your weight model. Happy to help make things more clear if this isn't.

Re your other points...

flipdewaf wrote:

One of the driving factors for the belly depth was the wing root thickness, having a spar going right through the cabin a la jetstream 31 was probably frowned upon.

Not sure about this. I definitely recall Airbus marketing materials touting pax amenities in the belly. Anyone have a quick cite?
In any event, wing thickness far exceeds belly depth already - thus the very large wing fairing. If Airbus didn't consider it worthwhile to extend the belly to match the wing already, why would it have been held back from further reductions in belly depth for wing/body reasons?
And for a clean sheet, this wouldn't be a problem. Wing will be much smaller and therefore thinner at equal t/c.

flipdewaf wrote:

I'd go with airbus on this one, there probably isn't that much to save on the floor weight and to lose flexibility for the airlines and effectively telling them where they can put certain seats would be pushing it.

I'd go with Airbus' response to airlines' response after being informed of the potential flexibility/efficiency tradeoffs. Thing is, that tradeoff appears not to have been offered in 2000. Airbus clearly wanted to offer the 853-seat version so it wasn't on the table. Maybe the idea works out, maybe it doesn't.

Do you have any particular insight, btw, on the effect of UD weight on the A380's very high sidewall thickness? I have heard it's due more to non-circular shape than UD weight and crash landing constraints, but not sure about that.

flipdewaf wrote:

I think we need more details of how that was accounted for, have you accounted for the extra length of the nose and tail sections. There is a lot of " the weight would remain static when we add capability because CFRP" around a.net.

Ok that's a bigger request. I owe you a response but the current model is only legible to me so give me some time to put something together.

At a more basic level, however, just consider this proposal:

• Take A380's cabin lengths * width and divide by floor area of 545m2 (per Ferpe). That gives me a ~93% "block coefficient" of actual cabin area compared to a simple LxW calc.
• Take my proposed VLA cross section, posit cabin lengths, fuse widths, and apply roughly the same "block coefficient."
• When I do this calculation, I assume that the shorter tailcone allows the cabin to reach within 33 of the tail, that we recover 4ft of "wasted" length on the UD, and 6ft on the MD (due to cockpit relocation). This gets me an A380-sized cabin with a fuselage that is ~217ft long and ~24ft circumference (equivalent).
• Applying the circumference and length ratios to the 777-9's fuselage at 1339m2, I get a fuselage Swet of ~1370m2 (777-9 is 246.5ft long and 20.33ft wide circular).

From there I estimate floor beams for both A380 and "A390" at equal weight, subtract some weight for modern systems/furnishings, and estimate bending moments based on length and weight of fuselage pressure structure + contents. (This is just a ratio to A380, btw. I don't have a model to invent weights from scratch).

EDIT - there are some additional subtle revisions to account for. E.g. my thinner, shorter fuse has more constant proportional length and therefore probably a higher "block coefficient." But it also takes a penalty for being shorter than A380 and therefore less stiff. Its lower internal volume should mean less pressure stress (Right? Not entirely certain on the volume-stress relationship here but I think that's right).

mjoelnir wrote:

According to Leeham the proposed changes do bring the A380 level with the estimated CASM of the 777-9.

How will purchase price for a A380+ and B779 be per unit and per seat?

If CASM is similar and a A380+ with similar costs as todays A380 compared to a B779 with big investments in new wing etc the A380+ should have a advantage at EK etc after initial pricing for the B779 is over.

Matt6461 wrote:

So here's a spreadsheet of my fuselage model:

Much appreciated, from what I see and from what you type its a numerical representation of the geometry of the fuselage ( I couldnt quite get the numbers then I realised you were using feet and inches and it made a lot more sense). for that piece you are much better to download a free cad program and draw what you are describing in the spreadsheet.
a. you get the same information
b. its quicker to iterate and make new designs
c. You can see why it might not work rather then the numbers telling you it is good.
d. Much better for a discussion on a.net.

I struggle with the picture thing because my computer is in the room next to 15 month old daughter so only can post off work computer which now doesn't have autocad so i cant complain too much.

Matt6461 wrote:

If you get into the nitty-gritty, you'd probably quibble with a few details.

It's not that its the details but that the level of detail is almost too great in a specific area whilst neglecting others. I know I might be repeating myself but the fact that the assumption of the floor being 8 inches vs 12 inches is as important than if people actually fit in it.... If you can it would be useful to drive the cabin width in your equations from width at shoulder level.

Matt6461 wrote:

Happy to help make things more clear if this isn't.

The drivers for getting a good fuselage weight estimation are height width and length. if it turns out that its a bending dominated fuselage (it probably isn't, this thing is taller than a T7 and less than 80m) then you need other parameters such as root chord length engine weight and a few others.

Am I right in thinking you're overall width is 269inches and the height is 251inches?

Matt6461 wrote:

And for a clean sheet, this wouldn't be a problem. Wing will be much smaller and therefore thinner at equal t/c.

Agreed, the wing is far too big and creates issues even there.

Matt6461 wrote:

Do you have any particular insight, btw, on the effect of UD weight on the A380's very high sidewall thickness?

Nothing on that one sorry

Matt6461 wrote:

Take A380's cabin lengths * width and divide by floor area of 545m2 (per Ferpe). That gives me a ~93% "block coefficient" of actual cabin area compared to a simple LxW calc.

I like the "block coefficient" value but to do it properly we should understand what drives the block efficiency number (actual to useful floor area) if your model doesn't encompass this then we could easily have a scenario where we are out on useful cabin area by 10%.

Matt6461 wrote:

When I do this calculation, I assume that the shorter tailcone allows the cabin to reach within 33 of the tail,

I would say the long tailcone is more to do with fuselage height than width, you should scale this with fuselage height.

Fred

flipdewaf wrote:

Matt6461 wrote:

And for a clean sheet, this wouldn't be a problem. Wing will be much smaller and therefore thinner at equal t/c.

Agreed, the wing is far too big and creates issues even there.

When you guys say the wing is far too big, to what are you referring exactly? I am asking because the wingloading is not that low, so the wing area seems appropriate even for this (non-stretched) MTOW.

flipdewaf wrote:

Am I right in thinking you're overall width is 269inches and the height is 251inches?

No but that's my fault. I did a quick half-clean-up and deleted one of the cells that should have been added to fuselage height.
Total height is 339.3in per the model (edited in the link now).

flipdewaf wrote:

If you can it would be useful to drive the cabin width in your equations from width at shoulder level.

Cell H12 controls the vertical elevation within the UD bubble at which seat height is measured. I currently have it at 36in - a bit less than seated shoulder height but to allow including 4 inches of armrest width.
If you change Cell H12 from 36in to 60in you get an effective width only two feet shorter than at 36in reference height. So one foot inboard of the outer armrest point on each side, pax have 5ft of headroom. A further foot inboard and they have 76in. That should be more than sufficient to seat window pax. Only the tallest folks would have to watch out entering/exiting window seats.
Cell C9 controls vertical elevation of MD seating width reference point. On the MD - where fuse isn't curving in on the shoulders in a significant way - I assume armrest height is the appropriate point for width calculation (I use 27in height).

flipdewaf wrote:

I like the "block coefficient" value but to do it properly we should understand what drives the block efficiency number (actual to useful floor area) if your model doesn't encompass this then we could easily have a scenario where we are out on useful cabin area by 10%.

There are definitely further refinements to describe. I have a spreadsheet that uses a parabolic(ish) modeling of nose/tail-cones that estimates cabin widths for those areas. For the area gained by relocating the cockpit, I exclude it from L*W*BlockCoefficient calc, estimate its area at ~10m2, and add it back. While some error inheres in the method I describe, I can't see my design's block coefficient being more than a few % plus or minus the A380. Given that tapered section is only ~40% of A380 cabin length, a 10% error in block coefficient would mean 25% more severe tapering in my design. I can't imagine a reason to think that so. In fact, my design would have proportionately higher parallel section due to lower max width and a higher location of the nose centerline (less nose cone tapering length). I haven't accounted for that fact in using the A380's "block coefficient" so I figure I'm being conservative.

flipdewaf wrote:

I would say the long tailcone is more to do with fuselage height than width, you should scale this with fuselage height.

That might be true of the A380 but it might also be something they accepted as a consequence of fuselage form, given the need for a massive tailcone anyway.
The advantage of a design where max width is closer to cabin level is that tapering has a less severe effect on cabin width.
In fact, I would envision retaining the higher height-width ratio of this fuselage all the way to the end so that both decks taper without becoming unusable as in the A380. That mandates a blade-ending instead of the A380's cone - might be slightly more aerodynamic anyway.
This is what the MD12 appears to have done, resulting in usable cabin space far further aft than A380:




The other consideration is rotation angle. A380 was meant to stretch to 80m, MD12 and my proposal would not. Therefore A380 requires more aft fuselage upsweep than MD12 or a smaller 2-decker would. Removing that constraint has meaningful impact on potential fuselage efficiency.

Taxi645 wrote:

flipdewaf wrote:

Matt6461 wrote:

And for a clean sheet, this wouldn't be a problem. Wing will be much smaller and therefore thinner at equal t/c.

Agreed, the wing is far too big and creates issues even there.

When you guys say the wing is far too big, to what are you referring exactly? I am asking because the wingloading is not that low, so the wing area seems appropriate even for this (non-stretched) MTOW.

If you compare the A380 to its contemporaries (77W, A340NG), the wingloading is significantly higher. The more recent twins have a lower fuel percentage of MTOW and therefore lower wingloading at MTOW for a given range - you don't want to shrink the wing of A350/787/777X because AR would be fairly constant and you'd therefore be shrinking span and hurting L/D and fuel efficiency.

You also shouldn't be looking at wingloading in a vacuum. Wingloading is the product of all other design decisions/tradeoffs made in the program. Were the A380 optimized for -800 size, the engines, wing, empennage, landing gear, and fuselage would be smaller/lighter. As a result you'd have maybe the same wingloading but a smaller wing.