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Re: The Airbus A380 Turns 15 Today (April 27)

Wed Oct 21, 2020 6:11 pm

lightsaber wrote:
LH707330 wrote:
lightsaber wrote:
There is an economy of scale in maintenance. Due to the large freight fleet (744F+747SF+748F) and for engines, the 787 fleet or 767 fleet, parts are readily available for a 747. RR brought down maintenance costs on the T500 but there just isn't as much commonality as RR advertised. This means an A346 opperator must stockpile more parts, which is an expense.

Serious question, does the A346 have unique tires and brakes? If so, that becomes a challenge.

Aviation is becoming more and more about economics of scale.

Lightsaber

I don't think the tires and brakes are unique, they're shared with the shorter 340 and 330 variants. The center gear strut and bogie is unique, and the wheels on it have brakes (the 342/343 don't, which is why they don't get dusty as fast), but I'm pretty sure they're all the same.

The T500 must be really bad on maintenance if they're yanking the 346 over the 744, the 346 has ~10% better fuel burn, and is slightly smaller, which would be a good thing in the reduced-pax environment.

The maintenance costs on the T500 engines are stunningly bad. I worked the Pratt engine bid for the A345/6 and I cannot believe RR was allowed to charge what they do for parts. Now part of the issue is RR prevented repairs on the T500 parts until a large number of airframes were parked. Those parked airframes provided enough cheap parts that repairs haven't been developed (or more precisely, not enough).

Normally the profit center for LH on engine overhauls is parts repairs. It costs millions to develop the repairs and certify them. It is too late Normally at the overhaul centers they develop a few repairs per year as the stockpile of repairable parts(based on prior repairs) grows.

Too late. This is a side effect of just not selling enough T500s

The time period dates back to when RR were trying to incentivise operators to lock in lifetime maintenance contracts, which they did largely with blunt force - high parts prices.

Later the approach was more subtle, with the leasing and finance players wooed to insist on packaged engine maintenance, AND higher parts prices for those who decided to go it alone.

The problem for those who rejected the deal when acquiring new, is it costs to buy into the maintenance club post purchase.
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Wed Oct 21, 2020 6:25 pm

Sokes wrote:
Revelation wrote:
https://www.icas.org/ICAS_ARCHIVE/ICAS2 ... RS/806.PDF shows all the different cross sections they tried and how they sorted them out.

They ended up with 10+8 mainly because they defined their core market as 550-650 seats with room for growth beyond 650.

Funny, the B747 cross section seemed to be bad, as it wasn't considered further. But nobody speaks of retiring B747-8i.

What is a core market? A good plane makes its own demand. It doesn't matter if it's 400 or 600 seats.

I speculate that Airbus looked at demand and cost savings versus prior generation. By demand, I mean how many airframes would sell. Since at A380 launch I was working a program with the working midel # of A305, an aluminum winged 787 competitor, just with a little less range (as CFRP gives free range). So Airbus knew the risk of point to point.

However, because of the points I made above the detail design of the 2 decker wasted too much space which increased the cost per passenger. I know there is resistance to talking CASM, but if a bigger plane doesn't carry a passenger for substantially less than a smaller plane, airlines buy the smaller plane. Wasted space is wasted cost.

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Re: The Airbus A380 Turns 15 Today (April 27)

Wed Oct 21, 2020 6:57 pm

lightsaber wrote:
However, because of the points I made above the detail design of the 2 decker wasted too much space which increased the cost per passenger. I know there is resistance to talking CASM, but if a bigger plane doesn't carry a passenger for substantially less than a smaller plane, airlines buy the smaller plane. Wasted space is wasted cost.

Seems Airbus talked itself into thinking it had the VLA market to itself so it could afford the grand staircase, the big crew rest area, the tall main deck for future 8x8 cargo platforms, 20 wheels so they would not have to struggle to make the A380-900 work, growth to 650 passengers and beyond.

It seems they felt the VLA was a market to itself and did not see big twins as a threat.
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Re: The Airbus A380 Turns 15 Today (April 27)

Thu Oct 22, 2020 1:17 am

From my recollection of the discussions on this forum around the time the A380 (or A3XX) was gestating, Airbus was fed up with Boeing selling package deals of 747s and other types; and they felt Boeing was able to cross-subsidize the smaller planes with excess profits from the 747, which had no direct competitor. The sense was that Airbus wanted to put a stop to that by having a big plane better than the 747.
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Thu Oct 22, 2020 1:40 am

Revelation wrote:
Sokes wrote:
What is a core market? A good plane makes its own demand. It doesn't matter if it's 400 or 600 seats.

Not really. There are only so many pax on a given day who want to go from A to B and are willing to pay market rates to do so.

One more reason to favour the B747 cross section.

Anybody knows if the B747 wingbox is high enough to fit a 80m carbon wing? Or at least a folding wing like B777X?

If we ignore engine issues for a moment:
I really like the B747 fuselage. I think the B777 wastes space.
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Re: The Airbus A380 Turns 15 Today (April 27)

Thu Oct 22, 2020 7:54 pm

Areopagus wrote:
From my recollection of the discussions on this forum around the time the A380 (or A3XX) was gestating, Airbus was fed up with Boeing selling package deals of 747s and other types; and they felt Boeing was able to cross-subsidize the smaller planes with excess profits from the 747, which had no direct competitor. The sense was that Airbus wanted to put a stop to that by having a big plane better than the 747.


I've seen this argument several times; it always seemed like bad or retrospective justification.

The A380 program lost at least $25bn and produced 240 frames. So instead of countering 747 sales with the A380, Airbus could have paid airlines $100mn for each plane they intended to buy.

SQ wants 20 747's? How about 10 A340's and 20 free A340's instead?

It's just never a good idea to respond to a good product with a bad product.
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Thu Oct 22, 2020 8:00 pm

Sokes wrote:

If we ignore engine issues for a moment:
I really like the B747 fuselage. I think the B777 wastes space.


First, for most of its length the 747 wastes more space than 777: Both fit 10ab and 2 LD3 but the 747 is wider/taller. 747 is also non-circular in its crown, meaning more weight.

Second, 747's empty tailbone is longer, that space is also wasted.

The partial UD barely evens things up in terms of surface area per seat.
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Thu Oct 22, 2020 8:03 pm

Lightsaber wrote:
However, because of the points I made above the detail design of the 2 decker wasted too much space which increased the cost per passenger


Do you mean you were working on a 787-size double decker?
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Fri Oct 23, 2020 5:16 am

Matt6461 wrote:
First, for most of its length the 747 wastes more space than 777: Both fit 10ab and 2 LD3 but the 747 is wider/taller. 747 is also non-circular in its crown, meaning more weight.

Second, 747's empty tailbone is longer, that space is also wasted.

cabin width:
A350: 5,61m
B777: 5,86m
B747: 6,10m
A380: 5,92m/ 6,58m

I conclude 10 abreast B747 is like 9 abreast A350.
However the A380 should be 9 or 10 abreast on the upper and 11 abreast on the lower deck. Otherwise it's at least 50 cm too wide.


But the 5,61m cabin width of A350 may indeed be better with a 6 abreast upper deck for a transpacific plane.

The partial UD barely evens things up in terms of surface area per seat.

This refers to which B747 model compared to which plane?
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Re: The Airbus A380 Turns 15 Today (April 27)

Fri Oct 23, 2020 1:49 pm

Matt6461 wrote:
Lightsaber wrote:
However, because of the points I made above the detail design of the 2 decker wasted too much space which increased the cost per passenger

Do you mean you were working on a 787-size double decker?

I think he's referring to the stuff I quoted in #253 above.

It seems Airbus was determined to have itself the biggest plane ever, regardless of the actual market to support all the growth variants and the cost of the exotic materials needed to prevent the trip costs from ballooning too much. Once they had the huge plane they didn't feel the need to optimize things such as staircases and crew rests. As your earlier threads point out, they could have had much better casm, but that didn't seem to be a primary driver of the program. This interview confirms a lot of what we knew, and adds some interesting things we didn't.
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Re: The Airbus A380 Turns 15 Today (April 27)

Fri Oct 23, 2020 5:31 pm

Remember, Boeing at the time was doing the various 747 studies to extend to top passenger deck, there were the discussions on doing an A-B JV for a VLA etc. Airbus probably felt they needed to carry more than any of these studies, otherwise B could counter with a similar size.

In hindsight it seems quite apparent that doing a 744+ 120 seats was a practical maximum. A had to fight the 80M box to fit their plane, adding area to wings without added length, etc.
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Fri Oct 23, 2020 6:39 pm

Revelation wrote:
Once they had the huge plane they didn't feel the need to optimize things such as staircases and crew rests. As your earlier threads point out, they could have had much better casm, but that didn't seem to be a primary driver of the program. This interview confirms a lot of what we knew, and adds some interesting things we didn't.


Some of the marketing around the A380 prior to delivery also pointed in that direction. VS, for example, planned gyms, casinos, and beauty salons on the A380s they ordered. Not that they ever actually took delivery, but the message indicates the airline didn't necessarily need the space for more seats. Who knows if VS's order was anything more than a colossal marketing stunt?
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Sat Oct 24, 2020 10:41 am

JayinKitsap wrote:
Remember, Boeing at the time was doing the various 747 studies to extend to top passenger deck, there were the discussions on doing an A-B JV for a VLA etc. Airbus probably felt they needed to carry more than any of these studies, otherwise B could counter with a similar size.


Remember that anybody can build the world's largest plane; the goal is to build a plane that airlines actually want.

Were Boeing dumb enough to try inflating a 1960's plane beyond the size of a good modern VLA, they'd have wasted their money.

That may seem obvious but if you're early-century Airbus you're not thinking right - perhaps not all - so the mega-747 seems an actual threat.

Revelation wrote:
I think he's referring to the stuff I quoted in #253 above.


Ah that's probably right.

Sokes wrote:
A350: 5,61m
B777: 5,86m
B747: 6,10m
A380: 5,92m/ 6,58m

I conclude 10 abreast B747 is like 9 abreast A350.


I conclude that's irrelevant. The question is about aero/structural efficiency; it's not an SAT analogy test. The 747 is no more aero-structurally efficient than the 777.

A Boeing executive actually stated that the 77W has better unit costs than 748 - despite engines significantly newer. I realize there are emotional attachments to the Queen but I'd suggest looking at the matter analytically and with reference to aero/structural fundamentals.

Lightsaber wrote:
In my opinion, the packaging of the front and rear staircases was done poorly. I also consider the crew rest options not well thought out and space inefficient. That alone destroyed the economics per passenger.


I'd be very curious to hear your alternate arrangement if it's not proprietary. The belated A380+ revisions to staircases added only ~3% capacity IIRC.

From Airbus statements there seemed an implication that a UD cockpit didn't happen because they wanted to streamline the fuselage sufficiently for operation up to .89M. As a UD cockpit should be worth ~2% capacity and .89M cruise is useless, that seems a bad tradeoff.

A380 also seems to carry an abnormally large empty tailcone even for its height. That seems necessary given the massive tailplane, which is necessary due to all the other wasteful decisions.
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Sat Oct 24, 2020 12:58 pm

Matt6461 wrote:
Sokes wrote:
A350: 5,61m
B777: 5,86m
B747: 6,10m
A380: 5,92m/ 6,58m

I conclude 10 abreast B747 is like 9 abreast A350.

I conclude that's irrelevant. The question is about aero/structural efficiency; it's not an SAT analogy test. The 747 is no more aero-structurally efficient than the 777.

I don't know what is a SAT analogy.
I discussed fuselage cross sections and you argue that the B747 is not more aero structurally efficient than B777. I assume that includes the wing which wasn't part of my discussion?
Do you think the B747 fuselage is too heavy or not good from an aerodynamic point of view?

A Boeing executive actually stated that the 77W has better unit costs than 748 - despite engines significantly newer.

Do you mean cost per seat of sale price or operating cost per seat mile?

The B777-300ER engines turned out to be extraordinary good. Then there are two versus four engines. The B747-8i wing is too short.
Even better: The new B777-9X has a longer wing than the B747-8i. How should the later be aero structurally efficient?

My discussion refers to a hypothetical B747-8i with 80 m carbon wing or a new plane with a continuous upper deck. I don't know if the wingbox could support such a wing.

I may well be wrong. But I have a suspicion that's because of the need for four engines, not because of structural weight or aerodynamic inefficiency of my proposed fuselage.
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Re: The Airbus A380 Turns 15 Today (April 27)

Sat Oct 24, 2020 2:18 pm

Sokes wrote:
Do you think the B747 fuselage is too heavy or not good from an aerodynamic point of view?

The 747 fuselage is not good in either. It's too wide and tall for the 10-abreast seating, which adds weight and drag. Especially the rear fuselage, behind the upper deck, has lots of unused volume. The nose is shaped to accomodate the upper deck cockpit and is also based on 1960s aerodynamics. The single-aisle upper deck requires a double-bubble fuselage shape; it's not the only aircraft to use that but it adds weight in the floor and can cause extra drag if the fairing isn't optimized.

If you compare the 77W and 748 OEW, the 77W is lighter per passenger. In the Boeing reference configuration that difference is relatively small (~ 3%) but for real-world configurations, e. g. the CA 748 vs 77W, it's over 10% difference.

Sokes wrote:
My discussion refers to a hypothetical B747-8i with 80 m carbon wing or a new plane with a continuous upper deck. I don't know if the wingbox could support such a wing.

Boeing wanted to avoid certification issues by retaining the original 747 wing layout for the 747-8. The 747, like the 737, is fundamentally a very old design and there is a risk that major aerodynamic changes in one part would require significant re-work in other parts too.

An 80m wing would have run into the same fears and problems that accompanied the A380 program. The 748 as it is avoids that by being "just slightly" outside the 65m envelope. The 779 requires folding wingtips.

A continuous upper deck would have been a major redesign. You'd have to design a completely new tail cone, make sure to keep the center of gravity in the right place (potentially move the wing further back), likely require a new, larger stair case and/or upper deck boarding, ... basically it'd be a 90% new aircraft. Add a clean-sheet CFRP wing and a new cockpit and you're close to 100%.
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Sat Oct 24, 2020 2:45 pm

mxaxai wrote:
Sokes wrote:
Do you think the B747 fuselage is too heavy or not good from an aerodynamic point of view?

The 747 fuselage is not good in either. It's too wide and tall for the 10-abreast seating, which adds weight and drag. Especially the rear fuselage, behind the upper deck, has lots of unused volume.

It's not too wide for 10 abreast, unless you consider A350 too wide for 9 abreast.
But as I earlier said, 9 abreast main deck, 6 abreast upper deck may be better.

Interesting that the main deck is too high. So both A380 and B747 have too high main deck because of cargo operations.
How much height could be reduced in a new design?
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Re: The Airbus A380 Turns 15 Today (April 27)

Sat Oct 24, 2020 2:54 pm

Matt6461 wrote:
From Airbus statements there seemed an implication that a UD cockpit didn't happen because they wanted to streamline the fuselage sufficiently for operation up to .89M. As a UD cockpit should be worth ~2% capacity and .89M cruise is useless, that seems a bad tradeoff.

One more quote from the interview regarding speed:

Interviewer: "... The A380-800, in this form, wasn't the aircraft the airlines demanded. In the end - one must almost say tragically - all the potential built into it, that had to be carried around and made the -800 less attractive, less economical, couldn't be used because the planned stretch never came."

Thomas: "Considering all that one knows or has heard of the A380-800 - I'm not a pilot myself but I've flown with it a few times with our chief pilot Fernando Alonso, we flew some small maneuvers. I was always interested where Airbus was world champion when we had a cruise speed of Mach 0.85; with the A330, A340 we sadly had only Mach 0.83 (!), that hadn't been a good decision either. Though, nowadays if you have a certain cruise speed, lets say Mach 0.85, and you have a problem due to a late departure or strong headwinds then the pilot can go up to MMO, Maximum Operating Limit, but the fuel burn goes up. Obviously you can't fly too fast and risk not arriving [due to the increased fuel burn]. However, the A380 is the most well-mannered aircraft. I sat there, and there's a small dial and you turn it when you're flying 0.85 and you go up to 0.86, 0.87 and the fuel burn increased very moderately. I didn't go to sleep that night, it was during the flight test campaign and Fernando wanted to show me this, so that I would see it for myself. "

"I''ve never seen this show up in any brochures or anything. It's because of the large wing. We told ourselves: "We need to avoid this. The A310 had a too small wing and the A340 had a too small wing." Well, first the A340-300 but the -600 later too. We had a wing with 840 m^2 and that allowed a very low landing speed, 135 knots. The 747 had a landing speed of 175 knots. First of all, the crew, especially at more difficult airports, felt better if they can approach slower, which gives them more time to react than at high speeds. The other thing is, when you touch down, 175 and 135 are worlds apart. With regards to the energy that the gear has to dissipate it's [a difference of] 40%. This was never really used [by marketing] to tell the customers "Listen, your approach speed is so low with this fantastic aircraft, this will have numerous benefits". I don't know why we didn't, but we should've cared more about our customers."

--------
I think it's worth remembering at this point that Boeing at this time very seriously considered the sonic cruiser. It would not suprise me if airlines demanded a higher-than-normal speed just in case the sonic cruise with Mach 0.95+ cruise became a success. Obviously, in hindsight speed and comfort proved to be less important than efficiency. Additionally, advances in aerodynamics allowed the 787 and A350 to cruise at M0.85 as well without a major hit to fuel burn. So the A380's cruise speed was an advantage against the A330 and 777 but not against the later smaller twins, which is probably why Airbus never bothered to highlight it.
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Sun Oct 25, 2020 7:57 am

mxaxai wrote:
"Listen, your approach speed is so low with this fantastic aircraft, this will have numerous benefits". I don't know why we didn't, but we should've cared more about our customers."


First, thank you once more for the transcription. That said, regarding this quote:

Who the heck cares?

To make it more explicit, how much more would customers pay for a lower approach speed? How many customers even know what approach speed means?

It's engineering ingenuity taking over due to strategic leadership's vacuum/stupidity. Engineers can tell you how to do something, executives need to tell you whether doing something is worthwhile. That cost/benefit analysis appears to have been completely absent in the A380 program. The 77W has a very high approach speed and seems never to have suffered any for it. Who cares about the last 30 seconds of a 14-hour flight?

mxaxai wrote:
Obviously, in hindsight speed and comfort proved to be less important than efficiency.


I would guess that the tradeoff implicit in your statement was never weighed seriously.

To have conducted a strategic analysis of speed/comfort vs. efficiency would have required basic strategic coherence entirely lacking from the program from its very inception. They probably never directly considered the tradeoff - just assumed a "market" existed for an airplane of giant size based on a teenager's reading of trend curves. They did not examine the dynamics underlying those trend curves, and whether those curves may be shifting. Abominable. It annoys me to no end that such stupidity was compensated so well.

Sokes wrote:
Do you think the B747 fuselage is too heavy or not good from an aerodynamic point of view?


Yes. Fuselage drag efficiency is basically a matter of surface area versus capacity. Yes, it's mostly that simple (there are myriad complications on which thousands of careers are built but at our level of analysis that's all you need to know).

Sokes wrote:
Why can't the world be a little bit more autistic?


Agreed. If Airbus had proceeded on cold logical terms the A380 would have been far different or not launched at all.

No autistic person could have approved the A380 program; only highly-socialized executives who knew how to game the public financing system could have done so.
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Sun Oct 25, 2020 11:37 am

mxaxai wrote:
I think it's worth remembering at this point that Boeing at this time very seriously considered the sonic cruiser.

Ah, it was about keeping up with the Jones.

Wasn't the B747 supposed to become a freighter because of a future of faster travel?

Boeing got it right, later got it wrong and Airbus decided to follow. With the difference that Boeing dismissed the sonic cruiser.
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Re: The Airbus A380 Turns 15 Today (April 27)

Sun Oct 25, 2020 2:29 pm

Matt6461 wrote:
mxaxai wrote:
"Listen, your approach speed is so low with this fantastic aircraft, this will have numerous benefits". I don't know why we didn't, but we should've cared more about our customers."


First, thank you once more for the transcription. That said, regarding this quote:

Who the heck cares?

To make it more explicit, how much more would customers pay for a lower approach speed? How many customers even know what approach speed means?

It's engineering ingenuity taking over due to strategic leadership's vacuum/stupidity. Engineers can tell you how to do something, executives need to tell you whether doing something is worthwhile. That cost/benefit analysis appears to have been completely absent in the A380 program. The 77W has a very high approach speed and seems never to have suffered any for it. Who cares about the last 30 seconds of a 14-hour flight?

Agree, only engineers truly care about that. A low approach speed allows weaker and fewer brakes, less brake and tyre wear, faster runway vacation and turnaround, no thrust reverse on the outer engines and lowers aerodynamic loads. But ultimately it's an engineering trade-off and the end result, a change in operating cost, is all that matters to the accountants that buy the aircraft. You can't look at a single component and call it "perfect" when the rest of the product suffers.

I doubt that Airbus designed the wing around the approach speed of the -800, it's just a side effect of the large wing, which itself was motivated by take-off conditions (and the planned 600t stretch/F).

The 77W does face a few issues, like limitations at short runways or weak pavements. That's only a miniscule part of the airports that can support aircraft of this size, though, so it's not a big deal for most airlines. It's also more related to takeoff at MTOW than landing. For example, GA can't fly nonstop DPS-AMS because DPS only has 2984m of runway.
Additionally, the 77W has a relatively complex flap system compared to the A380. Perhaps Airbus would have been better off with double-slot flaps and a smaller wing?

An aircraft that has truly suffered from high landing speeds is the MD-11 with its large number of landing accidents.

Sokes wrote:
mxaxai wrote:
I think it's worth remembering at this point that Boeing at this time very seriously considered the sonic cruiser.

Ah, it was about keeping up with the Jones.

Speed does matter for airlines. Higher speed allows for higher utilization and/or better on-time performance.

A good example is the ATR vs Dash8 vs CRJ/ERJ. The ATR is the most efficient of the 3 but also the slowest. That makes it a great choice for short, low yield routes in southern Asia. The CRJ/ERJ are the fastest and most expensive to operate, so they are best used in high yield, high utilization markets like the USA. The Dash 8 finds itself inbetween, and nowadays sells only in markets with medium yields, medium utilization but long range like Eastern Africa or the US&Canada Pacific Northwest.

It's not a coincidence that newer widebodies all have higher cruise speeds. Finding the sweet spot is a job for both engineers and accountants combined, however, and if the A380 could have been more efficient at M0.84 and a MMO of M0.87 they should have chosen that instead.
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Sun Oct 25, 2020 5:36 pm

The approach speed is relevant insofar as it impacts runway performance and the ability of the aircraft to stop in the promised distance. As Thomas points out in the interview, the 380's lower speed means it gets to the runway with something like 40% less energy to dissipate. I recall reading an anecdote about an exchange between Juan Trippe and Joe Sutter where they were discussing the 747's triple-slotted flaps. Sutter asked if they could go double-slotted, and Trippe replied along the lines of "do whatever you want, just make sure you hit the approach speed spec we agreed upon," and they went triple in the end. Had they gone double, it would have been less weight and cheaper maintenance, but then versatility would have suffered.

My takeaway listening to that podcast was two-fold:
1. Thomas was overemphasizing the part that the engine OEMs played in the 380's failure, in my opinion blaming them unfairly.
2. Airbus was too obsessed with the 340 development being boxed in that they went whole hog on the 380 to make it a jack of all trades. This cost them in several respects that Thomas noted: too-high roof for the containers, too big engines for LHR (.8% fuel burn IIRC), too heavy for baked-in stretch, etc.

The A340-300, per one of our old threads here, was structurally more efficient than the 777-200ER, and was hamstrung by having suboptimal engines. The main issue facing Airbus in that regard was that the engine OEMs didn't take them seriously enough to invest the resources in a better engine. When Boeing launched the 777 in 1990, they probably knew that they had ~10% to work with on the new engines, and could afford to sacrifice a few percent overbuilding the 200 for an eventual stretch with better engines, much like they did with the 767. As such, the takeaway for Airbus should have been that they had the right idea, but lacked the clout in 1987. Had they made the 343 slightly larger and given it bigger engines (they were considering the PW2000 and RB211-535 from the 757), it would have been too heavy and lost enough efficiency to make the MD-11 competitive again. Given their options at the time, they made the right play call.

I'd be curious to know why Thomas thought the 346 wing was too small, it's similar in size to the 777-300ER, and they designed more fuel and speed into it from day 1. The failure of the 346 was too heavy due to overstretching, and the knock-on effect that PW and GE correctly concluding it wouldn't do well as a result. It probably didn't help that GE had its eyes on the 777-300ER, and didn't want to build two competing products.

In retrospect, I think the 380 could have been better had they focused on a narrower set of requirements and optimized for those. The fact that they spent so much time running around between prospects and pulling the scope this way and that should have been their first clue that it might not be the right idea.
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Mon Oct 26, 2020 1:47 am

mxaxai wrote:
Speed does matter for airlines. Higher speed allows for higher utilization and/or better on-time performance.

A good example is the ATR vs Dash8 vs CRJ/ERJ. The ATR is the most efficient of the 3 but also the slowest.
...
and if the A380 could have been more efficient at M0.84 and a MMO of M0.87 they should have chosen that instead.

Here a web page with different cruise sperds of airliners:
https://www.statista.com/statistics/614 ... per%20hour.

From Wiki:
Cruise speed:
ATR: 510 km/h (320 mph, 280 kn)
Dash 8: 556 km/h, 300 kn

E 175: Mach .75 (430 kn; 797 km/h; 495 mph)
E190: Mach .78 (447 kn; 829 km/h; 515 mph)
A330: Mach 0.82 (470 kn; 871 km/h),
B777: Mach 0.84 (482 kn; 892 km/h)
A380: Mach 0.85, 903 km/h (561 mph, 488 kn)

While there is a lot of difference between turboprop and jet speed, widebody optimum cruise speed varies within 4%. If a certain city pair needs an additional pilot for the 15 min slower plane I believe time matters, otherwise not so much.
The A330 sold o.k. .

An ATR has low wing loading. It's a bumpy ride. So I believe the preference for jets over props has more to do with comfort and anxieties than time savings.
I may be wrong if the jet can make an additional daily flight,
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Re: The Airbus A380 Turns 15 Today (April 27)

Mon Oct 26, 2020 4:56 am

mxaxai wrote:
Perhaps Airbus would have been better off with double-slot flaps and a smaller wing?


Probably but then the -900 might have needed triple-slotted or might have been unfeasible.

The -900's freakish size is what really drove everything. It forced the massive wing, which torpedoed the aerodynamics - especially after ICAO adopted the 80m constraint. The big wing made the engines and empennage bigger, the latter being underrated as factor in A380's failure. If anything sums up this program, it's John Leahy touting A380's massive tailfin as if that was something to highlight instead of hide.
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Mon Oct 26, 2020 3:05 pm

LH707330 wrote:
In retrospect, I think the 380 could have been better had they focused on a narrower set of requirements and optimized for those. The fact that they spent so much time running around between prospects and pulling the scope this way and that should have been their first clue that it might not be the right idea.

I think the big mistake is the focus on pax counts between 550 and 650. I don't think I'd say the problem is the range should be more narrow, I'm more inclined to say the target was wrong.

It seems that simplifying the program by never targeting a freighter might have helped but they still planned to build the -900 and it's clear from the interview that they were going to make that as simple as possible even if that meant burdening the 800. The freighter did add the taller main deck so that too was a burden but probably not a game changer.

Turns out the freighter wasn't all that important to have. FX bought 777F, UP bought 748F, EK went with belly freight and all is well with the world.

The original 747 was able to target an after life as a freighter because it came with breakthrough technology, the high bypass turbofan, so it was OK to over shoot the mark. A380 never had such luxury. In particular its engines were not much of an advance in terms of efficiency above others on the market at the time.
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Re: The Airbus A380 Turns 15 Today (April 27)

Mon Oct 26, 2020 8:22 pm

Revelation wrote:
LH707330 wrote:
In retrospect, I think the 380 could have been better had they focused on a narrower set of requirements and optimized for those. The fact that they spent so much time running around between prospects and pulling the scope this way and that should have been their first clue that it might not be the right idea.

I think the big mistake is the focus on pax counts between 550 and 650. I don't think I'd say the problem is the range should be more narrow, I'm more inclined to say the target was wrong.

It seems that simplifying the program by never targeting a freighter might have helped but they still planned to build the -900 and it's clear from the interview that they were going to make that as simple as possible even if that meant burdening the 800. The freighter did add the taller main deck so that too was a burden but probably not a game changer.

Turns out the freighter wasn't all that important to have. FX bought 777F, UP bought 748F, EK went with belly freight and all is well with the world.

The original 747 was able to target an after life as a freighter because it came with breakthrough technology, the high bypass turbofan, so it was OK to over shoot the mark. A380 never had such luxury. In particular its engines were not much of an advance in terms of efficiency above others on the market at the time.

Matt6461 wrote:
mxaxai wrote:
Perhaps Airbus would have been better off with double-slot flaps and a smaller wing?


Probably but then the -900 might have needed triple-slotted or might have been unfeasible.

The -900's freakish size is what really drove everything. It forced the massive wing, which torpedoed the aerodynamics - especially after ICAO adopted the 80m constraint. The big wing made the engines and empennage bigger, the latter being underrated as factor in A380's failure. If anything sums up this program, it's John Leahy touting A380's massive tailfin as if that was something to highlight instead of hide.


I think you two are on the money: the 900 was too big for the market, and the desire to do it drove the rest of the wrong decisions. Had they focused on a 450-550 pax plane in two versions with a payload/range trade for APAC carriers and a trunk version for the Europeans, they could have done an 8+6 or a different cross section with smaller tail surfaces, lower weight, and then in turn better AR within the 80m box.

Matt, I know you modeled a lighter A380 a few years back, did you also look at an 80x80 optimized 550-seater? Curious to know how a 450/8000 nm short and 550/7000 nm long plane would have turned out from a weight and efficiency standpoint.
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Tue Oct 27, 2020 12:36 am

mxaxai wrote:
I think it's worth remembering at this point that Boeing at this time very seriously considered the sonic cruiser. It would not suprise me if airlines demanded a higher-than-normal speed just in case the sonic cruise with Mach 0.95+ cruise became a success. Obviously, in hindsight speed and comfort proved to be less important than efficiency.


Well, I have said this before, but I think a key reason why Boeing proposed the Sonic Cruiser was related to airline economics back in the late 1990s while that program was under development. That period was marked, at least in the U.S., by relatively high labor costs for the network carriers and very low fuel costs. In 2000, UA's labor costs were 35% of their overall operating expenses, while fuel was only 13%. If you could go 15% faster (M0.95 vs. M0.83) you'd reduce overall labor costs by more than the 20% in fuel used. If you could get an extra segment a day out of the aircraft, that'd be a bonus. The extra speed would have just been a marketing bonus.

IMO the capability for higher cruise speed was more about outdoing the 747, since it had the highest cruise speed of intercontinental jets in operation at the time if memory serves.
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Tue Oct 27, 2020 3:14 am

LH707330 wrote:
Matt, I know you modeled a lighter A380 a few years back, did you also look at an 80x80 optimized 550-seater?


Not sure I ever modeled an 80x80 optimized plane. Closest would be -900NEO which isn't optimal, though it could have been a great plane with really aggressive winglets. viewtopic.php?f=5&t=1384423 Even a suboptimal double-decker (>450 seats) has massive advantages; only a disastrous strategic concept can screw it up.

IMJ any optimal double-decker has a span:length ratio >1. If the fuse length catches up to nominal span then you need aggressive winglets, which obviously isn't optimal.

LH707330 wrote:
Curious to know how a 450/8000 nm short and 550/7000 nm long plane would have turned out from a weight and efficiency standpoint.


I never modeled a double-decker family, just optimal single-member family planes. IMJ multiple members is unnecessary to program success and would likely be more expensive than the additional OEM revenue generated.

At least that's how the numbers seemed when working on ~2025 EIS. For a designer in 2000 things might have been different. Why? Well with 2025 engine tech (Ultrafan at ~.45 SFC) and with double-decker aerodynamics (L/D ~24), even the 8000nm model is only ~30% fuel at MTOW (A380 is ~43%). [These numbers are easy to check with the basic version of the Breguet Range Equation]. Therefore the 7000nm model's MTOW is only ~4-5% lower than if 8000nm. The basic idea is that the "range penalty" is significantly decreasing with better aero/SFC properties.

A designer in 2000 would have faced worse engine tech and slightly lower L/D; a two-member family MIGHT have been justified back then.

Any way I look at the fundamentals, however, the optimized double-decker should be so far ahead of single deckers that even the 8000nm plane is more efficient than a narrowbody on short flights. This is particularly true once we consider slot costs (either traded slot costs or the opportunity cost of slots at high-demand airports). I've ridiculed Airbus slot-cost rationale for the A380 and maintain that stance regarding intercontinental flights where slot costs are a negligible part of DOC. On short flights, however, slot costs can be up to 50% of total cost for NB operations.

Furthermore, the benefits of a stretched double-decker are on the "normal" capacity/efficiency curve (actually slightly below for various reasons). Each blip traveled on the normal capacity/efficiency curve diminishes the double-decker's performance on what I consider the really decisive curve: Marginal Capacity Cost (MCC) = [Marginal Seats] / [Marginal Cost]. The optimized double-decker's MCC versus, e.g., 77W should be ~25%. With a little arithmetic it's easy to see that a stretched double-decker's MCC will be worse than the basline model's, even if the stretch has 10% lower CASM. Again the stretch is travelling down the normal capacity/efficiency curve whereas the jump between single- and double-decker has a dramatic kink in that curve.
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Tue Oct 27, 2020 3:41 am

Matt6461 wrote:

LH707330 wrote:
Curious to know how a 450/8000 nm short and 550/7000 nm long plane would have turned out from a weight and efficiency standpoint.


I never modeled a double-decker family, just optimal single-member family planes. IMJ multiple members is unnecessary to program success and would likely be more expensive than the additional OEM revenue generated.


I have a theory that would undercut what I wrote above, justifying stretches that I never modeled beyond an optimized single-member double-decker "family." It goes like this:

  • An optimal double-decker would cut long-haul CASM by ~40% compared to a 2019 global average roughly equivalent to the 77W's CASM. [A350/787 have lower cash operating costs but until they're depreciated are about as efficient as an old 77W]
  • Under the current (pre-COVID) market equilibrium, the mass of middle class travelers generally choose the cheapest flight and airlines lose money by giving Y another inch here and there. PY and Y+ are a small but growing segmentation of the middle class market.
  • Under a possible 2025 double-decker equilibrium, however, standard Y seats would become sufficiently cheap that airlines could offer middle class pax twice the space for only ~$15 per hour of flight. For a TATL flight that means only ~$300 more for an '90's style J-class recliner seat, compared to standard Y.
  • A very large sector of today's Y-class herd would throw down $300 extra in that new economic equilibrium. Very likely they would also prefer a one-stop in '90's J-class to nonstop in today's Y.
  • The Y-pax who've moved up to '90's J would be replaced by less-affluent folks paying cheaper prices.

The FL30 view is that double-decker economics, combined with generally higher levels of tech, would (1) transform flying similarly to what we see now (top ~10% of world flying regularly) versus what we saw in the '70's (top ~1% flying regularly) and (2) transform the relative salience of airline "hotel" function versus "get me there" function.

In that transformed market, the double-decker would set the equilibrium and would be competing - potentially or in reality - against other double deckers. It would therefore be appropriate to design a stretch with only 5-10% better CASM, either to service the now-large double-decker market or to preempt a competitor launching his own double-decker that hurts the OEM's profit stream.
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Tue Oct 27, 2020 4:53 am

LH707330 wrote:
Curious to know how a 450/8000 nm short and 550/7000 nm long plane would have turned out from a weight and efficiency standpoint.


I skipped over making a more direct point and jumped into broad theoretical points, as is my wont.

A short answer is that a simple stretch of an optimized 2-decker would trade range severely:

  • As stated above, 2-decker's high L/D means a very shallow payload/range curve.
  • But the 2-decker is also more structurally efficient due to shorter, higher fuselage (less bending). ...which cascades into wing bending weight, engines, empennage, landing gear, etc.
  • Because of higher structural efficiency, the standard pax payload is higher % of OEW. I'd guess an optimal 500-seat A380 would weigh <500k lbs. That means a 10% capacity increase moves farther on the x-axis of a payload range curve than for a typical plane.
  • Combining these two dynamics means that for a given % capacity stretch we're moving relatively farther on the x-axis of an abnormally shallow payload-range curve.

I haven't run the numbers but I'd guess a 550-seat simple stretch of an 8,000nm 450-seat 2-decker would have only ~5,000nm range.
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Wed Oct 28, 2020 3:52 am

Matt6461 wrote:
LH707330 wrote:
Matt, I know you modeled a lighter A380 a few years back, did you also look at an 80x80 optimized 550-seater?


Not sure I ever modeled an 80x80 optimized plane. Closest would be -900NEO which isn't optimal, though it could have been a great plane with really aggressive winglets. viewtopic.php?f=5&t=1384423 Even a suboptimal double-decker (>450 seats) has massive advantages; only a disastrous strategic concept can screw it up.

IMJ any optimal double-decker has a span:length ratio >1. If the fuse length catches up to nominal span then you need aggressive winglets, which obviously isn't optimal.

LH707330 wrote:
Curious to know how a 450/8000 nm short and 550/7000 nm long plane would have turned out from a weight and efficiency standpoint.


I never modeled a double-decker family, just optimal single-member family planes. IMJ multiple members is unnecessary to program success and would likely be more expensive than the additional OEM revenue generated.

At least that's how the numbers seemed when working on ~2025 EIS. For a designer in 2000 things might have been different. Why? Well with 2025 engine tech (Ultrafan at ~.45 SFC) and with double-decker aerodynamics (L/D ~24), even the 8000nm model is only ~30% fuel at MTOW (A380 is ~43%). [These numbers are easy to check with the basic version of the Breguet Range Equation]. Therefore the 7000nm model's MTOW is only ~4-5% lower than if 8000nm. The basic idea is that the "range penalty" is significantly decreasing with better aero/SFC properties.

A designer in 2000 would have faced worse engine tech and slightly lower L/D; a two-member family MIGHT have been justified back then.

Any way I look at the fundamentals, however, the optimized double-decker should be so far ahead of single deckers that even the 8000nm plane is more efficient than a narrowbody on short flights. This is particularly true once we consider slot costs (either traded slot costs or the opportunity cost of slots at high-demand airports). I've ridiculed Airbus slot-cost rationale for the A380 and maintain that stance regarding intercontinental flights where slot costs are a negligible part of DOC. On short flights, however, slot costs can be up to 50% of total cost for NB operations.

Furthermore, the benefits of a stretched double-decker are on the "normal" capacity/efficiency curve (actually slightly below for various reasons). Each blip traveled on the normal capacity/efficiency curve diminishes the double-decker's performance on what I consider the really decisive curve: Marginal Capacity Cost (MCC) = [Marginal Seats] / [Marginal Cost]. The optimized double-decker's MCC versus, e.g., 77W should be ~25%. With a little arithmetic it's easy to see that a stretched double-decker's MCC will be worse than the basline model's, even if the stretch has 10% lower CASM. Again the stretch is travelling down the normal capacity/efficiency curve whereas the jump between single- and double-decker has a dramatic kink in that curve.


Good point on the MCC piece, I think you're probably right about the one-family model there. If you target a range at MZFW around 5500 nm as appears to be the sweet spot for most larger widebodies, you end up with something like 8,000 brochure range, so that sounds about on the money. If we agree that something in the 80m box needs to have more efficient span loading and that the optimal pax count is between 450-550, then I wonder if a longer 6+8 or 6+9 would solve the empennage weight problem while also being tall enough to counteract bending moments. Why do you think it needs to have >1 span/length? A narrower tube would result in a longer tube. My guess is that you'd get pretty close to 80x80 when all is said and done.
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Wed Oct 28, 2020 7:52 am

LH707330 wrote:
Why do you think it needs to have >1 span/length? A narrower tube would result in a longer tube. My guess is that you'd get pretty close to 80x80 when all is said and done.


That's what I, too, am curious about. Maybe his assertion takes into account folding wingtips.

But still, one has to wonder if 10+6 / 8+6 / 9+7 or whatever abreast is truly more efficient than an optimized 10+8 abreast fuselage. I'm thinking, 18 abreast fuse = less length and thus less wetted area so less drag overall. I'm guesstimating that shortened length is sufficient enough to more than cancel out the circumference difference, but I'd be interested to know how the math pans out more specifically when bending moment etc. come into play.

And on top of that, we don't really have any sufficient J class product to put in in that 6-across UD do we?
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Wed Oct 28, 2020 8:08 am

Matt6461 wrote:
An optimal double-decker would cut long-haul CASM by ~40% compared to a 2019 global average roughly equivalent to the 77W's CASM. [A350/787 have lower cash operating costs but until they're depreciated are about as efficient as an old 77W]

Do you mean compared to the average B777-300ER? 40% sounds a lot.
Can you expand?
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Re: The Airbus A380 Turns 15 Today (April 27)

Wed Oct 28, 2020 8:51 am

PolarRoute wrote:
LH707330 wrote:
Why do you think it needs to have >1 span/length? A narrower tube would result in a longer tube. My guess is that you'd get pretty close to 80x80 when all is said and done.


That's what I, too, am curious about. Maybe his assertion takes into account folding wingtips.
...
I'm thinking, 18 abreast fuse = less length and thus less wetted area so less drag overall.
...
And on top of that, we don't really have any sufficient J class product to put in in that 6-across UD do we?

The two B777x models have roughly 70m and 77m length with a wingspan of roughly 72 m. If there had to be no hinge system, would Boeing have chosen 74 m wingspan?
The A380 is roughly 73m long with roughly 80m wingspan. Obviously Airbus chose the wingspan because of the 80m x 80m box.
I therefore assume that even a B747 should have a wingspan greater than length.

Your 18 abreast tube may have less wetted fuselage, but in days with fewer passengers, where to put freight?

An airline that offers a daily city pair could of course alternate A380 and A330. Economy passengers would get good priced seats only every alternate day. I believe that's o.k. for intercontinental flights. In this case I agree with you.

Concerning business class product: one can also put economy passengers on top.
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Re: The Airbus A380 Turns 15 Today (April 27)

Wed Oct 28, 2020 1:15 pm

Sokes wrote:
PolarRoute wrote:
LH707330 wrote:
Why do you think it needs to have >1 span/length? A narrower tube would result in a longer tube. My guess is that you'd get pretty close to 80x80 when all is said and done.


That's what I, too, am curious about. Maybe his assertion takes into account folding wingtips.
...
I'm thinking, 18 abreast fuse = less length and thus less wetted area so less drag overall.
...
And on top of that, we don't really have any sufficient J class product to put in in that 6-across UD do we?

The two B777x models have roughly 70m and 77m length with a wingspan of roughly 72 m. If there had to be no hinge system, would Boeing have chosen 74 m wingspan?
The A380 is roughly 73m long with roughly 80m wingspan. Obviously Airbus chose the wingspan because of the 80m x 80m box.
I therefore assume that even a B747 should have a wingspan greater than length.

Your 18 abreast tube may have less wetted fuselage, but in days with fewer passengers, where to put freight?

An airline that offers a daily city pair could of course alternate A380 and A330. Economy passengers would get good priced seats only every alternate day. I believe that's o.k. for intercontinental flights. In this case I agree with you.

Concerning business class product: one can also put economy passengers on top.

Optimal wingspan is a function of loading (weight) as the material the wing is made from determines the optimal aspect ratio and since we want to cruise in thinner air, that means a wing area for weight. The length if a plane has nothing to do with optimal wingspan.

Now cruise altitude is somewhat limited by the ability to safely descend quickly, wing loading.

I looked at a bunch of planes and on current technology, wings are converging:

Plane: 779 A388 A35K 789/x
Wing area (m^2): 516.7 845 464.3 377
Wing aspect ratio: 9.96 7.5 9.03 9.59
MTOW (1000kg): 351.5 575 316 254
Wing loading (tons/m^2): 0.680 0.680 0.681 0.674


From the above, we see wings are growing in aspect ratio, but compromises are done for gates. The wing loading at MTOW is almost the same. The 787 could gain a few tons of MTOW by wing loading, but is limited by the gear.

The A35K's aspect ratio is compromised to fit in a 77W gate. Note: The 77W had high wing loading (0.805 tons/m^2 at MTOW) due to gate limits.

High aspect ratio wings enable underside laminar flow (a post A380 technology). In general, flying higher is better (low wing loading), so between aspect ratio and wing area, wing area is a 1st order effect, underside laminar flow a 2nd order effect (important, but less impact on mission fuel burn than getting up into less dense air). That FL430.

Question, is Wikipedia correct in that the A350-1000 and A339 have lower FL410 ceilings? It never occurred to me anyone would willingly take another almost 9% increase in drag for end of cruise. Can anyone confirm?

I see all the discussion on the A388 being over winged... and I respectfully disagree.

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Re: The Airbus A380 Turns 15 Today (April 27)

Wed Oct 28, 2020 1:21 pm

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Re: The Airbus A380 Turns 15 Today (April 27)

Wed Oct 28, 2020 1:24 pm

lightsaber wrote:


Question, is Wikipedia correct in that the A350-1000 and A339 have lower FL410 ceilings? It never occurred to me anyone would willingly take another almost 9% increase in drag for end of cruise. Can anyone confirm?

Yes, according to the EASA type certificates the A350-1000 and A330 (all variants except the Beluga, which has a lower ceiling) have a max altitude of 41,450 ft.

The A359 can go up to 43k ft.
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Wed Oct 28, 2020 2:42 pm

Lightsaber wrote:
In general, flying higher is better (low wing loading)


AFAICS this is true on account of 2 dynamics:

  • 1. Parasitic drag is usually predominant and is linear with air density (induced drag, usually smaller than parasitic, is inversely linear with density).
  • 2. Engines run more efficiently in colder air.

Neither condition, however, really favors flying above FL37 for the A380.

Re (1), Di's predominance for A380 means its L/D actually decreases as it ascends.

Re (2), above FL37 or so the stratosphere is isothermic and the engine efficiency benefit runs out.

A380 reaches FL37 pretty quickly, after which ascent only means lower true air speed (due to compressibility effects) and slightly worse L/D.

LH707330 wrote:
I wonder if a longer 6+8 or 6+9 would solve the empennage weight problem while also being tall enough to counteract bending moments.


It probably would be tall enough: 8/9+6 is only slightly less tall than a good 10+8 because deck/hold height sets the vertical dimension. The slightly longer fuse helps with empennage size too of course.

Here's a confession: I haven't been completely honest about my criticism of 10+8 in preference to 8/9+6 for new design. When I've done a little modeling, a good 10+8 can pencil out better than 8/9+6 even for 500 seats. The key is that, as mentioned, deck height controls the vertical dimension so additional width comes at little cost in Swet. Total fuse Swet is, as PolarRoute suggests, meaningfully more efficient with 10+8. And a less oblong cross-section gives some small benefit in Cdp.

My lack of candor owes to laziness rather than trying to pull one over on y'all: explaining at length would have required more work and more anti-A380 invective. Basically the A380's 10-8 is an extremely inefficient 2-deck cross-section (despite being by the most efficient cross section ever actually built). Excessive MD and belly height is a main culprit (motivated by cargo per Father A380). Equally important, max cabin width is up around MD shoulder level. Plus the extreme sidewall thickness that a modern 10+8 design would ameliorate with 777X-style sidewall shaving at key points and/or thinness enabled by CFRP. A double-bubble is far more efficient for cabin space but less so for bending resistance. I'd guess that's the main reason for not going double-bubble on the A380: if you need to stretch it to 80m the bending stress becomes more dominant.

But it's not just the cross section: A380's fuse Swet is further harmed by the 43ft empty tailcone. For comparison, the MD-12 design had a ~21ft empty tailcone and similar large cross section. So fuse height alone can't explain that tailcone length. Rather it seems the massive tailcone is necessary to fit the massive tailplane, whose massive elevation machinery sits ahead of the massive tailplane. The more I learn about this program, the less surprised I'd be to find out the tailcone is massive because, "meh, it'll sell anyway because it's big." I.d. Airbus just wasn't trying very hard.

In sum I'd say a new 2-decker is probably optimal at 10-8 for 500 seats, maybe not for 450 seats but probably still is. As 450 seats seems around the "kink" where the capacity-efficiency curve transitions from single to double decker, we can see very significant variations in efficiency at this point between double-deckers. So the MCC of a 10-8 500-seater may be attractive, compared to a 8/9-6 450-seater. I'm far less confident about that judgment though, would require more resolution than I have from the fundamentals.

For the A380, however, anything that forced Airbus to abandon the 650-seat target would have been an incredible boon to the program, even if it turned out that 8/9-6 was slightly less efficient than a notional 10-8. That's because re A380 we're not analyzing a notional 10-8, we're analyzing the actual A380 cross section that wasted space/weight/drag in the vertical axis and placed max width at a useless elevation. A good 8-6 would have been far better than the A380 but not necessarily because 8-6 is inherently better than 10-8.

Another difference between analyzing a contemporary optimized 2-decker versus analyzing alternate A380 designs is the differing predominance of the empennage factor. For equal capacity and range, an optimal 2000 design will have a larger empennage than an optimal 2025 design (higher operating weights and bigger engines means bigger control surfaces). The older design would place more emphasis on fuse lever arm to minimize empennage size than would the newer. So 8-6 could have been optimal in 2000 without implying it's optimal now.

LH707330 wrote:
Why do you think it needs to have >1 span/length?


The reasoning incorporates the above analysis of 10-8 vs. 8/9+6. If your optimization loop spits out the capacity of an 80m 8/9+6 you've already got something larger than A388: cabin length is going to be ~230ft vs. ~165 (IIRC) for A388 because you reclaim empty tailcone space in the optimal design. So even if 8+6's combined cabin width is only 70% of A380's two decks, total deck space is at least as big (aside from longer, less of the 8+6 cabin is tapered). At that size (~550 seats) I'm fairly certain that 10+8 is more efficient overall, even with a slightly bigger empennage than 8+6 (again for contemporary design, not necessarily for 2000). If you want smaller capacity then it's not 80m length. Maybe the wing shrinks in line with fuselage length but 80m seems optimal for contemporary design even if the 8-6 fuselage is only 240ft long. If you pencil around with 2025 projections of an optimized 2-decker, it becomes clear that payload weight is more significant than usual. So you need a big wing to carry lots of people and any cargo. There's diminishing returns to structural efficiency unless you can discriminate against fat passengers (maybe a small-wing subvariant for East Asia?).

Sokes wrote:
Do you mean compared to the average B777-300ER? 40% sounds a lot.
Can you expand?


It's a lot but start from saving 40% of fuselage drag per pax and work your way around the fundamentals. Add in Ultrafan and it's conservative, IMO.

Google matt6461 and "A380NEO," "A380X," and "A380NWO" for my old threads in TechOps. The older a thread is, the less I knew when I wrote it. The A380-900NEO probably has my least ignorant analysis but in each thread the fundamentals discussions are fairly accurate.
 
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PolarRoute
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Re: The Airbus A380 Turns 15 Today (April 27)

Wed Oct 28, 2020 6:40 pm

lightsaber wrote:
Plane: 779 A388 A35K 789/x
Wing area (m^2): 516.7 845 464.3 377
Wing aspect ratio: 9.96 7.5 9.03 9.59
MTOW (1000kg): 351.5 575 316 254
Wing loading (tons/m^2): 0.680 0.680 0.681 0.674


Thanks for the hard numbers. Interesting to note that somehow all the wing loadings figures come down to around .68 and 789/X actually has the lightest-loaded wing.
I thought Boeing did high-loaded wings relative to Airbus due to their elastic wings eating into effective wing span?

I see all the discussion on the A388 being over winged... and I respectfully disagree.


Now that I have the hard figures in front of my eyes I see where you're coming from.
But if memory serves, wasn't the assertion mostly about the stubby aspect ratio and -900 being structurally baked in resulting in more weight than necessary, rather than wing area itself?

Unless you have more to say about that than what I, admittedly shallowly, know.

Matt6461 wrote:
The more I learn about this program,


the more I become puzzled.

In sum I'd say a new 2-decker is probably optimal at 10-8 for 500 seats


If true, then the A380 we have today is pretty well optimized, at least with its fuselage - a 500-seater with 10-8 abreast seating.
Yes there is the deck height that's been compromised in favor of the ill-fated freighter version, but as per 'the Father', that's only 1.5% delta.

For comparison, the MD-12 design had a ~21ft empty tailcone and similar large cross section.


And quick google search gives me that MD-12 only had an MTOW of 949,000lbs with OEW at only 429,000.
....Should we have been better off with the MD-12?

I mean, was the -900 baked in THAT much? What was it that went through their minds to let this big of a difference actually materialize with nobody objecting until so and thought 'this is the way to go'?
I love Airbus don't get me wrong, especially their heart to come out big and take on the risk. But this is just..
 
tomcat
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Re: The Airbus A380 Turns 15 Today (April 27)

Wed Oct 28, 2020 7:07 pm

Matt6461 wrote:
Areopagus wrote:
From my recollection of the discussions on this forum around the time the A380 (or A3XX) was gestating, Airbus was fed up with Boeing selling package deals of 747s and other types; and they felt Boeing was able to cross-subsidize the smaller planes with excess profits from the 747, which had no direct competitor. The sense was that Airbus wanted to put a stop to that by having a big plane better than the 747.


I've seen this argument several times; it always seemed like bad or retrospective justification.

It's just never a good idea to respond to a good product with a bad product.


I have seen this argument more than 20 years ago in French aviation magazines like Air & Cosmos. Thanks to a little Google search I have found one occurrence of this argument dating from January 1998 in the magazine "Aviation Civile" #289. It reads like this:

Since its launch in the late 1960s, Airbus has succeeded in a daring gamble by taking around 30% market share, despite its absence from the very large segment where Boeing enjoys a monopoly position with the B747. First with the A300-A310, then with the A320 and its A321 and A319 derivatives, and finally with the A330-A340, Airbus has built its range, its experience and its reputation. However, the shortcoming of this range leaves Boeing in a comfortable position thanks to significant margins on the B747 which allow it to develop very aggressive competition on the rest of its production. A comfortable situation, but which nevertheless relies on the quality of the B747 and also on the saturation of the airports, which allows Boeing to sell it at a price per seat (criterion of the client companies) sufficiently attractive compared to lower capacity planes.


https://en.calameo.com/read/0051166333699c63868d6
 
tomcat
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Re: The Airbus A380 Turns 15 Today (April 27)

Wed Oct 28, 2020 7:34 pm

PolarRoute wrote:

Matt6461 wrote:
In sum I'd say a new 2-decker is probably optimal at 10-8 for 500 seats


If true, then the A380 we have today is pretty well optimized, at least with its fuselage - a 500-seater with 10-8 abreast seating.
Yes there is the deck height that's been compromised in favor of the ill-fated freighter version, but as per 'the Father', that's only 1.5% delta.


It appears that Airbus also had P2F conversion in mind when they set the deck height which makes it even more painful to see young A380s being retired and going straight to recycling while the express market is booming.

PolarRoute wrote:

Matt6461 wrote:
For comparison, the MD-12 design had a ~21ft empty tailcone and similar large cross section.


And quick google search gives me that MD-12 only had an MTOW of 949,000lbs with OEW at only 429,000.
....Should we have been better off with the MD-12?

I mean, was the -900 baked in THAT much? What was it that went through their minds to let this big of a difference actually materialize with nobody objecting until so and thought 'this is the way to go'?
I love Airbus don't get me wrong, especially their heart to come out big and take on the risk. But this is just..


It could be that they didn't want to go head to head with a cheap upgrade of the 744 (like an early 747-8). They have sized the A380 in a way that was out of reach of the 747 and they thought that this size would naturally make the A380 more efficient than anything smaller. The fact that they went the A342/3 way and then the A345/6 way shows that they never concluded that a large long range twin was a viable option until Boeing proved them wrong twice (with the 772ER and then with the 77W). My take is that Boeing was more familiar than Airbus about the potential of the large engines. The leader in the field is GE (or at least not any European engine maker) and together with the NASA, GE had been paving the way for a large engine since the early 80s. I cannot conceive that the US taxpayer money could benefit a non-US plane maker in the same timeframe than Boeing.
 
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lightsaber
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Re: The Airbus A380 Turns 15 Today (April 27)

Wed Oct 28, 2020 9:40 pm

PolarRoute wrote:
lightsaber wrote:
Plane: 779 A388 A35K 789/x
Wing area (m^2): 516.7 845 464.3 377
Wing aspect ratio: 9.96 7.5 9.03 9.59
MTOW (1000kg): 351.5 575 316 254
Wing loading (tons/m^2): 0.680 0.680 0.681 0.674


Thanks for the hard numbers. Interesting to note that somehow all the wing loadings figures come down to around .68 and 789/X actually has the lightest-loaded wing.
I thought Boeing did high-loaded wings relative to Airbus due to their elastic wings eating into effective wing span?

I see all the discussion on the A388 being over winged... and I respectfully disagree.


Now that I have the hard figures in front of my eyes I see where you're coming from.
But if memory serves, wasn't the assertion mostly about the stubby aspect ratio and -900 being structurally baked in resulting in more weight than necessary, rather than wing area itself?

Unless you have more to say about that than what I, admittedly shallowly, know.

Matt6461 wrote:
The more I learn about this program,


the more I become puzzled.

In sum I'd say a new 2-decker is probably optimal at 10-8 for 500 seats


If true, then the A380 we have today is pretty well optimized, at least with its fuselage - a 500-seater with 10-8 abreast seating.
Yes there is the deck height that's been compromised in favor of the ill-fated freighter version, but as per 'the Father', that's only 1.5% delta.

For comparison, the MD-12 design had a ~21ft empty tailcone and similar large cross section.


And quick google search gives me that MD-12 only had an MTOW of 949,000lbs with OEW at only 429,000.
....Should we have been better off with the MD-12?

I mean, was the -900 baked in THAT much? What was it that went through their minds to let this big of a difference actually materialize with nobody objecting until so and thought 'this is the way to go'?
I love Airbus don't get me wrong, especially their heart to come out big and take on the risk. But this is just..

Boeing ran out if landing gear capability on the 787. That is the only reason the 789/78x has a 1% lower wing loading.

The A388 wing does have weight to enable MTOW increases (heck, it already grew to 575). But there were discussions on it having an unusually high wing area for the A389. That I disagree with.

It is a small aspect ratio wing for the area. That was the 80m box compromise. Any future double decker will have a cfrp wing and folding wingtips for 80m (or less) at the gate, but 85 to 90m on the runway.

Paper airplanes always defeat real aircraft. I liked the MD-12 concept, but it wasn't to be made out of unicorn horn...

Lightsaber
Winter is coming.
 
Antarius
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Re: The Airbus A380 Turns 15 Today (April 27)

Wed Oct 28, 2020 10:24 pm

tomcat wrote:
PolarRoute wrote:

Matt6461 wrote:
In sum I'd say a new 2-decker is probably optimal at 10-8 for 500 seats


If true, then the A380 we have today is pretty well optimized, at least with its fuselage - a 500-seater with 10-8 abreast seating.
Yes there is the deck height that's been compromised in favor of the ill-fated freighter version, but as per 'the Father', that's only 1.5% delta.


It appears that Airbus also had P2F conversion in mind when they set the deck height which makes it even more painful to see young A380s being retired and going straight to recycling while the express market is booming.

PolarRoute wrote:

Matt6461 wrote:
For comparison, the MD-12 design had a ~21ft empty tailcone and similar large cross section.


And quick google search gives me that MD-12 only had an MTOW of 949,000lbs with OEW at only 429,000.
....Should we have been better off with the MD-12?

I mean, was the -900 baked in THAT much? What was it that went through their minds to let this big of a difference actually materialize with nobody objecting until so and thought 'this is the way to go'?
I love Airbus don't get me wrong, especially their heart to come out big and take on the risk. But this is just..


It could be that they didn't want to go head to head with a cheap upgrade of the 744 (like an early 747-8). They have sized the A380 in a way that was out of reach of the 747 and they thought that this size would naturally make the A380 more efficient than anything smaller. The fact that they went the A342/3 way and then the A345/6 way shows that they never concluded that a large long range twin was a viable option until Boeing proved them wrong twice (with the 772ER and then with the 77W). My take is that Boeing was more familiar than Airbus about the potential of the large engines. The leader in the field is GE (or at least not any European engine maker) and together with the NASA, GE had been paving the way for a large engine since the early 80s. I cannot conceive that the US taxpayer money could benefit a non-US plane maker in the same timeframe than Boeing.


I'd argue Airbus proved themselves wrong with the a330 series.

Sure, it isn't a VLA, but the a330 series has been widely successful for Airbus across many market segments. So while I agree the 777 also proved them wrong, they ignored data they had themselves.
2020: SFO DFW IAH HOU CLT MEX BIS MIA GUA ORD DTW LGA BOS LHR DUB BFS BHD STN OAK PHL ISP JFK SJC DEN SJU LAS TXL GDL
 
LH707330
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Re: The Airbus A380 Turns 15 Today (April 27)

Thu Oct 29, 2020 3:32 am

Polot wrote:
lightsaber wrote:


Question, is Wikipedia correct in that the A350-1000 and A339 have lower FL410 ceilings? It never occurred to me anyone would willingly take another almost 9% increase in drag for end of cruise. Can anyone confirm?

Yes, according to the EASA type certificates the A350-1000 and A330 (all variants except the Beluga, which has a lower ceiling) have a max altitude of 41,450 ft.

The A359 can go up to 43k ft.

For the 35K it's supposedly because the spoilers (common to the 900) are too small to dissipate the higher potential energy in an emergency descent. The 748 is similar in that regard, but it also got a wing reloft which marginally improved L/D.

On the 339 I'm not entirely sure as to the reasoning, after all it's got a pretty big wing for the weight because it's shared with the 340 that went all the way to 276t. Maybe it's a system design issue, or it wasn't worth futzing with it to make the change.

Matt6461 wrote:

LH707330 wrote:
I wonder if a longer 6+8 or 6+9 would solve the empennage weight problem while also being tall enough to counteract bending moments.


It probably would be tall enough: 8/9+6 is only slightly less tall than a good 10+8 because deck/hold height sets the vertical dimension. The slightly longer fuse helps with empennage size too of course.

Here's a confession: I haven't been completely honest about my criticism of 10+8 in preference to 8/9+6 for new design. When I've done a little modeling, a good 10+8 can pencil out better than 8/9+6 even for 500 seats. The key is that, as mentioned, deck height controls the vertical dimension so additional width comes at little cost in Swet. Total fuse Swet is, as PolarRoute suggests, meaningfully more efficient with 10+8. And a less oblong cross-section gives some small benefit in Cdp.

My lack of candor owes to laziness rather than trying to pull one over on y'all: explaining at length would have required more work and more anti-A380 invective. Basically the A380's 10-8 is an extremely inefficient 2-deck cross-section (despite being by the most efficient cross section ever actually built). Excessive MD and belly height is a main culprit (motivated by cargo per Father A380). Equally important, max cabin width is up around MD shoulder level. Plus the extreme sidewall thickness that a modern 10+8 design would ameliorate with 777X-style sidewall shaving at key points and/or thinness enabled by CFRP. A double-bubble is far more efficient for cabin space but less so for bending resistance. I'd guess that's the main reason for not going double-bubble on the A380: if you need to stretch it to 80m the bending stress becomes more dominant.

But it's not just the cross section: A380's fuse Swet is further harmed by the 43ft empty tailcone. For comparison, the MD-12 design had a ~21ft empty tailcone and similar large cross section. So fuse height alone can't explain that tailcone length. Rather it seems the massive tailcone is necessary to fit the massive tailplane, whose massive elevation machinery sits ahead of the massive tailplane. The more I learn about this program, the less surprised I'd be to find out the tailcone is massive because, "meh, it'll sell anyway because it's big." I.d. Airbus just wasn't trying very hard.

In sum I'd say a new 2-decker is probably optimal at 10-8 for 500 seats, maybe not for 450 seats but probably still is. As 450 seats seems around the "kink" where the capacity-efficiency curve transitions from single to double decker, we can see very significant variations in efficiency at this point between double-deckers. So the MCC of a 10-8 500-seater may be attractive, compared to a 8/9-6 450-seater. I'm far less confident about that judgment though, would require more resolution than I have from the fundamentals.

For the A380, however, anything that forced Airbus to abandon the 650-seat target would have been an incredible boon to the program, even if it turned out that 8/9-6 was slightly less efficient than a notional 10-8. That's because re A380 we're not analyzing a notional 10-8, we're analyzing the actual A380 cross section that wasted space/weight/drag in the vertical axis and placed max width at a useless elevation. A good 8-6 would have been far better than the A380 but not necessarily because 8-6 is inherently better than 10-8.

Another difference between analyzing a contemporary optimized 2-decker versus analyzing alternate A380 designs is the differing predominance of the empennage factor. For equal capacity and range, an optimal 2000 design will have a larger empennage than an optimal 2025 design (higher operating weights and bigger engines means bigger control surfaces). The older design would place more emphasis on fuse lever arm to minimize empennage size than would the newer. So 8-6 could have been optimal in 2000 without implying it's optimal now.

LH707330 wrote:
Why do you think it needs to have >1 span/length?


The reasoning incorporates the above analysis of 10-8 vs. 8/9+6. If your optimization loop spits out the capacity of an 80m 8/9+6 you've already got something larger than A388: cabin length is going to be ~230ft vs. ~165 (IIRC) for A388 because you reclaim empty tailcone space in the optimal design. So even if 8+6's combined cabin width is only 70% of A380's two decks, total deck space is at least as big (aside from longer, less of the 8+6 cabin is tapered). At that size (~550 seats) I'm fairly certain that 10+8 is more efficient overall, even with a slightly bigger empennage than 8+6 (again for contemporary design, not necessarily for 2000). If you want smaller capacity then it's not 80m length. Maybe the wing shrinks in line with fuselage length but 80m seems optimal for contemporary design even if the 8-6 fuselage is only 240ft long. If you pencil around with 2025 projections of an optimized 2-decker, it becomes clear that payload weight is more significant than usual. So you need a big wing to carry lots of people and any cargo. There's diminishing returns to structural efficiency unless you can discriminate against fat passengers (maybe a small-wing subvariant for East Asia?).

I guess that makes sense. Given that the 779 is ~400 passengers on a single deck at 76m, I doubt you'd need that much length to get in 550 on an 8+6, which gives you 40% more seats per row.

Now I'm curious to know more about how an MD-12 would have turned out, maybe that was the right way to go in the mid-90s.
 
Sokes
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Re: The Airbus A380 Turns 15 Today (April 27)

Thu Oct 29, 2020 12:04 pm

For skin friction drag 10+8 may be better, but for cargo capacity 9+6 is better.
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mxaxai
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Re: The Airbus A380 Turns 15 Today (April 27)

Thu Oct 29, 2020 2:35 pm

Matt6461 wrote:
A good 8-6 would have been far better than the A380 but not necessarily because 8-6 is inherently better than 10-8.

Personally, a 6-abreast upper deck would make me concerned about passenger comfort and boarding/deboarding time. A full-length 6-abreast upper deck would be about 55-60m long, twice as long as common narrowbody cabins. It would feel like a very long and narrow tube. In a full economy layout, you might have to board and deboard 250-300 passengers through a single door and single aisle.

Not saying that this is why the 10-8 layout was chosen by Airbus, just a thought by myself.
 
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Re: The Airbus A380 Turns 15 Today (April 27)

Fri Oct 30, 2020 10:11 am

LH707330 wrote:
Now I'm curious to know more about how an MD-12 would have turned out, maybe that was the right way to go in the mid-90s.


I've discussed the MD-12 a bit in the past:
viewtopic.php?t=1389931
viewtopic.php?t=776333&start=50

Its gate constraint was far worse than A380's yet it claimed -12% fuel/pax vs. 747. That's on par with what the A380 achieved, adjusted for older engines. Of course that was just the claim...

IMO the MCC wasn't quite there for it. -12% fuel/pax and +30% pax (vs. 744) barely hits the 50% MCC benchmark but only for fuel, which was cheap back then and only ~25% of DOC.

But the MD12 was such a ridiculously-constrained design that IMO its efficiency is powerful evidence of the 2-decker's promise.

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