Quoting Clipper101 (Reply 235):

Quoting Amiga500 (Reply 233):

Quoting Clipper101 (Reply 203):

Quoting Clipper101 (Reply 245):

Quoting Amiga500 (Reply 191):

Quoting Clipper101 (Reply 240):

From my search into resources I have from the 2001-era, Airbus plan appears to have been introducing the -800 around 2005, introducing the -800F around 2008 then to use -800F strengthened wings & body structure further in an A380 stretched into -900.

But, in my re-collection I still remember clearly that Airbus stopped promoting its -900 after WTT results indicated increase in fuselage induced drag due to the stretch of -900 would result in less favourable CASM, most probably could be in conjunction with weight gained from requiring a strengthened structure; I know I read that somewhere but still could not find it to support myself tangibly (again I will keep in mind to find it, I guess WTT was around 2004 - 2005, so -/+ 1 year will make me look in a period between 2003 - 2006).

Common sense also plays its part here since tracking the A380 program throughout its history it is apparent how A380 was sensitive to weight increase, any drop in weight was highly welcomed; if you happen to have an encounter with the A380 you would sense this fact. Some historic accounts in that regard which I could think of: Airbus re-designed Fwd nose section from landing gear area, removing outer thrust reversers (basically there was initially an intent to remove all however it was decided later to only keep the inner) & doing some structural re-design of tail fin (please do not ask me for sources !!).

So, came my question how would we know a new engine may only regain some of the efficiencies lost going to a -900 without necessarily give additional efficiency enhancements, which would lead me to think of a -800neo as the most possible candidate; if it comes with a new wing then I even can see it as a very sharp aircraft: it should have a higher performance wing only customised to a -800, hence would be of less weight. In terms of passenger capacity, I do not see it a point to worry about, it would be a chance for Airbus to press for the 11-abreast economy on main deck as a standard as opposed to being an option nowadays, and you have even more efficiencies.

Yes sharp aircraft, but does Airbus have the financial resource to step into it? In my opinion I see the situation in same manner as with interest rates issue now adays: Everybody is waiting for the Fed to raise them, but when? Towards end of the day it will happen, when its time comes.

[Edited 2015-10-22 06:11:23]

[Edited 2015-10-22 06:16:30]

Quoting Clipper101 (Reply 250): But, in my re-collection I still remember clearly that Airbus stopped promoting its -900 after WTT results indicated increase in fuselage induced drag due to the stretch of -900 would results in less favourable CASM, most probably could be in conjunction with weight gained from requiring a strengthened structure; I know I read that somewhere but still could not find it to support myself tangibly (again I will keep in mind to find it, I guess WTT was around 2004 - 2005, so -/+ 1 year will make me look in a period between 2003 - 2006).

That time frame, however, also overlaps when the A380 was going through all its major production troubles. I am more inclined to believe that Airbus stopped promoting the -900:
A) so they could focus more on getting out the A388, which is of course why they stopped development on the A388F
B) because it was clear that any A389 was going to be a while out
C) to reduce the amount of attention the A380 was getting.

Remember, at the time Airbus was very secretive about what was going wrong with the A388, and it was really until after the fact that it was revealed how/why the program was so horribly screwed up (and how it was clear that Airbus was completely underselling the A380's issues as soon as final assembly started). In fact in the early days of the 7E7/787 program Boeing was being praised for being so open and honest in comparison to Airbus until the 787 troubles became clear   

Airbus has smart engineers, they could come up with a way to make the economics of the stretch work. Not necessarily the business case though.

Quoting Clipper101 (Reply 250): But, in my re-collection I still remember clearly that Airbus stopped promoting its -900 after WTT results indicated increase in fuselage induced drag due to the stretch of -900 would result in less favourable CASM

Sorry but I don't believe this for a second. The -800 fuselage is actually much less ideal than a -900 from a finesse ratio perspective.

Yes, there will be higher induced drag throughout flight.... if MTOW increases. If it doesn't, then the drag increase will only become noticeable as you burn off fuel weight (i.e. work nearer to OEW which would favour the -800).


But, if Airbus build a -900 with the same MTOW and engines as -800, you'll definitely get better CASM (albeit with reduced range).

Quoting KarelXWB (Reply 248): Yup, though that doesn't change the fact that the A333ceo goes out of production.

Which I think was the original point and one that you have made upthread...I see your point now  

Moving on!

tortugamon

Quoting Polot (Reply 251): Airbus has smart engineers,

This is a fact no two can argue about

Quoting Polot (Reply 251): they could come up with a way to make the economics of the stretch work

This is what I am saying, how would you know that stretching would not end up ecountering complexities that would require a resolution (See my Reply 157). Learning curve on current fuselage as it is now should already be flat plus other things that play in favour of a -800neo.

Quoting Amiga500 (Reply 252): The -800 fuselage is actually much less ideal than a -900 from a finesse ratio perspective.

Do you have a comparison?

Quoting Clipper101 (Reply 255): Do you have a comparison?

What do you mean? Compare it to any other commercial airliner in the sky.

If you can, grab a book on preliminary aircraft design, Jenkinson "Jet Aircraft Design" or similar.

There are parametric sizings of fuselages based on decades of experimental data and experience; all of which will say the -800 fuse is too short for its diameter.

Compared to other twin/long range aircraft:


A380-800 length: 72.7m
A380-800 dia: 7.8 (average)
ratio: 9.3

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

A330-200 length: 58.8m
A330-200 dia: 5.64m
ratio: 10.43

A330-200 length: 63.7m
A330-200 dia: 5.64m
ratio: 11.29

777-200 length: 63.7m
777-200 dia: 6.2m
ratio: 10.27

777-300 length: 73.9m
777-300 dia: 6.2m
ratio: 11.92

Quoting KarelXWB (Reply 187):

apologies I didnt reply earlier, hadnt read the thread for a few days.
it is an opinion based on experiance, minor changes to the blades can have a dramatic effect on performance.
one thing to make a new part with new materials, it's another to get the same performance.
on the current blades they flex on take off, i have heard figures of 7 fo 12 degres of twist unwind. then in cruise they are less distorted. so the static shape and skin thicknesses influence the shape on take off and in cruise. this has been optimised over the years by people a lot cleverer than me.
The Cti blade is going to react completely differently, thats for sure. can you get optimum shape for cruise, take off and what shape does it need to be static to get that will all have to be relearnt.
it is not as simple as some may think.
i have worked on a blade change where the manufacturing method was changed, significant performance was lost, in the region of 10%

like i say its an opinion, I have no idea how the ALPS project is going.

Quoting Clipper101 (Reply 250): WTT results indicated increase in fuselage induced drag due to the stretch of -900 would result in less favourable CASM

As I wrote above, I could definitely see the -900 stretch being less fuel-efficient than many here assume. Folks often forget that induced drag rises with the square of weight, and that a certain percentage weight gain is much worse for the A380-900 than for other stretches because induced drag is so dominant in A380's drag buildup.

Quoting Clipper101 (Reply 250): if it comes with a new wing then I even can see it as a very sharp aircraft: it should have a higher performance wing only customised to a -800, hence would be of less weight.

I agree! I've put a bit of thought into this, if you care to check it out. TBH I've been learning as I go along, but these threads contain one amateur's attempt to sketch out what an "A380X/NWO" would look like. I have a strong suspicion that a rewinged A380 would be an absolute world-beater.

A380NEO: Revisions And BizCase Unclear,2020-25EIS (by Matt6461 Jul 23 2015 in Tech Ops)
A380X Part 3: Business Case (by Matt6461 Mar 2 2015 in Tech Ops)

Quoting Clipper101 (Reply 254): Quoting Amiga500 (Reply 252): The -800 fuselage is actually much less ideal than a -900 from a finesse ratio perspective. Do you have a comparison?

Amiga makes good points. There is some optimal "fineness ratio," and the A380 is likely below it. In addition to fineness ratio, there's a factor I call "taper ratio": what portion of the fuselage is the most efficient parallel part versus what portion is tapered. This seems to be another way that the A380-800 suffers from the -900's legacy: If Airbus had wanted to build a 500-seater, they could have built a narrower, finer, less-tapered fuselage. It would have been more efficient on drag and weight, most likely.

But Amiga500 - might a double-decker likely have lower optimal fineness ratio? Its fuselage is going to be denser due to efficient volume usage, but this means greater bending moments for a given fineness ratio. Optimal fineness ratio is heavily influenced by a tradeoff between weight (long, thin, bending, but lower drag) and drag (shorter, stronger, less bending, but more drag). If you're double-stacking payload, floor beams, furnishings, and systems in double-decker, you start to get serious bending moments at lower fineness than you would in a single deck.

I have pasted below something I wrote elsewhere about the A380's unusually high taper ratio.

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


The A380, however, is an unusually tapered fuselage, even for its low fineness ratio. Its fuselage is constant width for only 40% of its length (93/231).

The B772, for example, has 10/1 fineness ratio (versus 9/1 for A380-800), yet is parallel for ~56% of its length.

The 788 has ~9.5/1 fineness ratio, and is parallel for ~50-55% of its length.

[I got both of these figures by eye-balling from ACAP manuals]

Airbus wanted to satisfy operators seeking to cruise up to M=.89. Thus designers streamlined the fuselage for no supersonic flows until M=.85 and no wave drag until M=.89.

Quote:
“Some of our customers want to belt along at M0.89, so we’ve deliberately gone out to make sure we’re shock free. We ended up playing tricks with the ovoid cross-section to get the flow to ‘go bad’ at M0.93. You have more ‘fatness’ up and down than you do in width, and the acceleration of the air from the nose is dependent on the curvature of the front fuselage. So we had to tailor the distribution of the curvature of the fuselage to maintain this acceleration,” he says. “We tried to make sure the velocity near the doors is as low as possible because the door areas can be susceptible to leaking and noise.”
http://www.flightinternational.com/A...n/180/199071/Creating+A+Titan.html

I wonder if that desire for M.89 cruise resulted in the highly-tapered design? In the low-fuel price environment in which A380 was born, this might have made more sense than it does today.

[Edited 2015-10-22 10:27:35]

Quoting Matt6461 (Reply 258): But Amiga500 - might a double-decker likely have lower optimal fineness ratio? Its fuselage is going to be denser due to efficient volume usage, but this means greater bending moments for a given fineness ratio. Optimal fineness ratio is heavily influenced by a tradeoff between weight (long, thin, bending, but lower drag) and drag (shorter, stronger, less bending, but more drag). If you're double-stacking payload, floor beams, furnishings, and systems in double-decker, you start to get serious bending moments at lower fineness than you would in a single deck.

Fineness ratio is an aerodynamic term only.



In terms of structural efficiency:
stress = moment * distanceFromNeutralAxis / I

I = second moment of area = (PI/4) * R^4 (for a circular cross section)

So, while distanceFromNeutral axis is linear with increased fuselage radius R, I is proportional to R^4.

Moment scales linearly with fuselage length. i.e. M = force*L

Meaning stress drops by a cubic function with increased fuselage radius and increases by a linear function of fuselage length.



So yes, I suppose trading aerodynamics for weight, you might end up with a fatter than normal fuselage - BUT - A380 was designed from the get-go for the -900, this will include the main fuselage longerons/ribs - so your already carrying that additional weight.

Quoting Matt6461 (Reply 258): I wonder if that desire for M.89 cruise resulted in the highly-tapered design? In the low-fuel price environment in which A380 was born, this might have made more sense than it does today.

I recall Tim Clarke saying something along the lines that "the faster it flies, the more efficient it is" - suggests optimum speed for fuel efficiency is at the high end of what is possible

Quoting JerseyFlyer (Reply 260): I recall Tim Clarke saying something along the lines that "the faster it flies, the more efficient it is" - suggests optimum speed for fuel efficiency is at the high end of what is possible

I remember that quote from him very well.

He stated this in the article which can be read here: http://aviationweek.com/awin-feature...ory/emirates-a350-1000-order-limbo.

There was also a thread about it here: A380 Overperforms Says Tim Clark Of EK (by art Nov 22 2012 in Civil Aviation)

I am sure someone cleverer than me can work out exactly what the NEO will be.So much has been 'leaked' and some of the logic is so compelling that the rest should be 'workoutable' IMHO.
We know
The wing is larger than optimal and has a sub optimal aspect ratio.
The existing engines will be (by NEO) 16 years old EIS (and older from design) therefore require a new engine.
Emirates and others state they would like some more Pax capacity
The plane lacks cargo capacity.

So
1.You stretch the aircraft.Airbus has now openly spoken about a 'small' stretch some have stated it would add about 50/60 pax (y I presume).This makes the wing body ratio's better and utilizes the lifting ability of the wing better.I bet it will be done so no major structural changes are necessary inc landing gear.
2.The only possible new engines are XWB's.But you 'semi advance' them (as being tested on an XWB right now)- 7-8% improvement? Sir Tim has openly spoken about the XWB option already.
3.The last 15 years has (particularly for Airbus) has seen an exponential growth in understanding about blended winglets.Airbus has said they will be doing 'something'- what else would a cheap modification be?
So the outer 10 foot of the wing is modified.It won't be 100% perfect but would probably yield 2-3% improvement? They work especially well on longer 'cruise' flight patterns. B Winglets will also improve the overall aspect ratio of the wing as well.
4.Cargo. The exact amount of stretch will depend on what is 'cargo optimal'.I know nothing about cargo.But I imagine it would be a length so that (perhaps) an extra pair (more?) of LD36's or whatever can be carried or whatever is optimal for the said stretch.The wing can lift them thats for sure and you will be carrying less fuel anyway.
Added together (improvements plus pax capacity increase) you should be able to find a 15% (max) improvement I would have thought.

Note the 'new XWB' engine could be offered at a later date on the 359 as a 'pip'.

Quoting Matt6461 (Reply 258): "fineness ratio,"

Agree, but I thought the fineness ratio term is supposed to correlate more to fuselage pressure drag, and we are discussing effect of fuselage induced drag on stretched A380, so I do not know why it is brought into the discussion.

Anyways, I managed to find another thread with some parameters comparison study in:

A380 Wing High Efficiency Vs Mediocre Aspect Ratio (by faro May 4 2013 in Tech Ops)#34

If you go to (Reply 19), still I see a little jump in Pressure Drag from A380-800 over to A380-900, or as this table in above thread indicates.

Quoting JerseyFlyer (Reply 260): I recall Tim Clarke saying something along the lines that "the faster it flies, the more efficient it is"

Good point, I also remember that

Quoting parapente (Reply 262): So 1.You stretch the aircraft

If more than one customer signed on for this aircraft is serious numbers I imagine we would be seeing it but as it appears based on those same leaks, no one other than EK seems to be stepping up. Hence Airbus asking EK to finance it. I believe that is the current rub.

tortugamon

Quoting parapente (Reply 262):
So
1.You stretch the aircraft

If more than one customer signed on for this aircraft is serious numbers I imagine we would be seeing it but as it appears based on those same leaks, no one other than EK seems to be stepping up. Hence Airbus asking EK to finance it. I believe that is the current rub.

tortugamon

I fully agree.That does indeed appear the case - although clearly there a quite a few existing users that will want some down the line.
But if you don't (half) stretch it what 'existing' engine is out there that could be used as a NEO base and how would you possibly make the 13% plus that Sir Tim says he needs? Cant see a T1000 in any guise producing the thrust required for a 'standard' -800 .

Would this be some variation of a 'take or pay' contract. Say Airbus needs to sell 250 NEOs to cover their and subs development costs at say $12 million per.


If EK were itself buying 200 planes they really would only be on the hook for 50 planes R and D. This does not sound unduly expensive, and Airbus likely would sell 50 to other carriers.

Quoting Amiga500 (Reply 259): Fineness ratio is an aerodynamic term only.

Quoting Clipper101 (Reply 263): Agree, but I thought the fineness ratio term is supposed to correlate more to fuselage pressure drag, and we are discussing effect of fuselage induced drag on stretched A380, so I do not know why it is brought into the discussion.

If structural engineers have a term that conveys the weight-gain tendency of a longer, thinner body of equal volume, and carrying the same "contents" (payload, floor beams, systems, furnishings), then we should use that term. Is there one?

Otherwise it seems borrowing the aerodynamic term gives a shorthand for predicting the weight gain that results from stretching a fuselage to gain capacity, rather than using a bigger diameter. I realize it's not the right technical jargon but seems useful...
From that insight I was bringing induced drag into the discussion because Di escalates with weight.

Quoting Clipper101 (Reply 263): If you go to (Reply 19), still I see a little jump in Pressure Drag from A380-800 over to A380-900, or as this table in above thread indicates.

Agreed. The A389 would be enormously efficient on parasitic drag. Unfortunately that would be a relatively small part of the story for it.

Quoting Amiga500 (Reply 259): In terms of structural efficiency:...

Thanks. Glad to have you here. A few more questions if you don't mind...

Quoting Amiga500 (Reply 259): I = second moment of area = (PI/4) * R^4 (for a circular cross section)

Basic question:
How does an ellipse vs. circle effect I?

I've read stuff suggesting that the A380 has better bending resistance because it's thicker vertically than horizontally.

That makes intuitive sense to me... If I scrunch a paper-towel cylinder and try to balance something on it, it buckles more easily if placed on the "flat" side.

Quoting Amiga500 (Reply 259): A380 was designed from the get-go for the -900, this will include the main fuselage longerons/ribs - so your already carrying that additional weight.

I thought stretches typically added and/or beefed up longerons/stringers versus the base model.
Seems like an easy modification for bending stress...

Do ribs have a function for bending stress as well? I thought they were for pressurization? I'm thinking of fuselage frames here. That may not be what you mean... So what are fuselage ribs?

Quoting JerseyFlyer (Reply 260): I recall Tim Clarke saying something along the lines that "the faster it flies, the more efficient it is"

Quoting JerseyFlyer (Reply 260): He stated this in the article

He mentions M.86 versus M.83 though. Airbus designed the fuselage for efficiency at M.89, I doubt EK is going to that fast regularly.

Induced drag declines with the square of speed, form drag has the opposite relation.
So I wouldn't be surprised if the A380's best speed is slightly higher than most aircraft.
But M.85 is usually Mdd (Mach for drag divergence) for modern critical airfoils.
Above Mdd wave drag increases dramatically on the wing. So I'm not sure fuselage efficiency at that speed matters much. Unless fuel is at 2000 prices.

Quoting parapente (Reply 262): So the outer 10 foot of the wing is modified.It won't be 100% perfect but would probably yield 2-3% improvement? They work especially well on longer 'cruise' flight patterns. B Winglets will also improve the overall aspect ratio of the wing as well.

Perhaps Airbus could add folding winglets to significantly extend span.
The 77W/L project added 13ft of span without changing the basic architecture of the wing.
On A380, a proportional extension would be ~16 feet. But A380's tip chord is thicker, probably they could add more.
If new winglets had same proportion to Code F box as 777X has to Code E, span would be ~288ft.
New aspect ratio would be ~18% higher.
L/D would improve by ~10%.

Combine that with new engines and a "half stretch," and per-seat fuel burn improves by perhaps ~25%, depending on weight gain.

This would be much cheaper than a new CFRP wing, but more expensive than a NEO.
Not sure if it's technically feasible, and would almost certainly require aileron/slat rework outboard.

Quoting parapente (Reply 262): Note the 'new XWB' engine could be offered at a later date on the 359 as a 'pip'.

Maybe. The RR Advance's HP spool has several more stages, will be heavier.
Not sure it would be replaceable on the wing.

But if it could be, that would be a great boon to the NEO business case and the A350 as well.

[Edited 2015-10-23 09:57:59]

Quoting parapente (Reply 262): 4.Cargo.

A ~3m stretch will give you 2 more LD3 pairs, 4 LD3's.
But the bags of 50-60 pax will occupy 2 of those. You gain 2 LD3 net for revenue cargo.

Cargo yield is about 1/5 of passenger yield by weight. See, e.g., http://airlines.org/data/a4a-monthly...er-and-cargo-yield-fares-per-mile/

One LD3 has 139.5ft3 usable volume, and cargo density is typically ~11lbs/ft3.
So one LD3 only gives the revenue of ~1.5 pax.
For the A380, this is rounding error.

For an 35J, the ~30 free LD3 slots give 45 pax-equivalents of revenue. Or about 15% total of total revenue capacity at typical seat configuration.

The A380 will never be good on cargo because, as a double decker, its pax-relative cargo capacity is always going to be small. Unless it's a combi...

Quoting Matt6461 (Reply 267): If structural engineers have a term that conveys the tendency or a longer, thinner body of equal volume, and carrying the same "contents" (payload, floor beams, systems, furnishings), then we should use that term. Is there one?

No, structural engineers are in the habit of designing efficient structures, if you want to carry, or transport something, that is no longer a structural engineer. Another engineer will give a structural engineer constraints to meet that requirement. The structural engineer will make their design less efficient to meet that requirement.

Quoting Matt6461 (Reply 267): From that insight I was bringing induced drag into the discussion because Di escalates with weight.

These sort of generalizations just dont work with airlines in a transonic cruise at flight levels.

Quoting Matt6461 (Reply 267): I thought stretches typically added and/or beefed up longerons/stringers versus the base model.

Actually the key is not in the frame, it is in the skin. For the higher weight, they planned to to for GLARE, but they did that anyway.

Quoting Matt6461 (Reply 267): Induced drag declines with the square of speed, form drag has the opposite relation.

Again, we don't care that much about what happens for takeoff or landing, its the cruise where an airliner will sit most of the time.

Quoting Matt6461 (Reply 267): The RR Advance's HP spool has several more stages, will be heavier.

Not true, as we have seen with engine developments over the years, the density of jet engines has been reducing on a trend for the past 50 years. Lighter materals, higher bypass ratios.

Quoting Matt6461 (Reply 268): Cargo yield is about 1/5 of passenger yield by weight. See, e.g., http://airlines.org/data/a4a-monthly...mile/

That is rubbish data for the A380, the A380 is a ULH machine, that data is skewed to narrow body short/medium haul (US domestic routes). Cargo yield ULH is lower, because it costs a lot more fuel to carry that weight in a pax aircraft, it is more efficient in a cargo aircraft where you can land and refuel more often.

Quoting zeke (Reply 269): Quoting Matt6461 (Reply 267): From that insight I was bringing induced drag into the discussion because Di escalates with weight. These sort of generalizations just dont work with airlines in a transonic cruise at flight levels.

Quoting zeke (Reply 269): Quoting Matt6461 (Reply 267): Induced drag declines with the square of speed, form drag has the opposite relation. Again, we don't care that much about what happens for takeoff or landing, its the cruise where an airliner will sit most of the time.

I don't get your point here.

Are you saying a heavier plane doesn't have higher induced drag in cruise? And are you saying that induced drag doesn't matter for cruise?

I agree that cruise is where most of the fuel is burned, but I'm pretty sure weight and induced drag matter quite a bit during cruise.

Quoting zeke (Reply 269): Actually the key is not in the frame, it is in the skin. For the higher weight, they planned to to for GLARE, but they did that anyway.

Well that's sort of my intuition - that fuselage frames don't help resist bending, but are for pressurization strength.

I agree that skin thickness is at issue for bending strength as well.
But when aircraft are stretched, I wonder if skin thickness is varied. Or do longerons/stringers take the added bending moment? Both?
It would seem easier to simply beef up longerons/stringers than to change skin thickness. If you can do so.
Not sure though. Maybe Amiga500 can tell us.

Quoting zeke (Reply 269): Quoting Matt6461 (Reply 267): The RR Advance's HP spool has several more stages, will be heavier. --------------------- Not true, as we have seen with engine developments over the years, the density of jet engines has been reducing on a trend for the past 50 years. Lighter materals, higher bypass ratios.

The T7000 will be heavier than the T700. The LEAP will be heavier than the CFM56. MAX's and NEO's are going to be heavier than their predecessors as a result.

Your 50-year trend line may be correct, but the specific trend of increased core stages seems to increase engine dry weight.

Quoting zeke (Reply 270): That is rubbish data for the A380, the A380 is a ULH machine, that data is skewed to narrow body short/medium haul (US domestic routes). Cargo yield ULH is lower, because it costs a lot more fuel to carry that weight in a pax aircraft, it is more efficient in a cargo aircraft where you can land and refuel more often.

Zeke feel free to provide your own data for cargo yield.
The link I provided specifically breaks out international versus domestic operations.
I agree it's probably weighted more towards NB ops (Caribbean, Canada), but the international data would include all U.S. WB ops.

In any event, I used a figure of 1/5 cargo yield by weight, relative to pax.
That came directly from Bjorn/Ferpe at Leeham (behind a paywall or I'd provide a link).

Do you dispute the 1/5 figure? Which would you use? On what empirical basis?
It's very difficult to find widebody and ULH-specific data for cargo yield, which is why I'm taking Bjorn's 1/5 figure.
So again, if you have your own data, your own links, providing that would be greatly appreciated.

Quoting Matt6461 (Reply 271): Are you saying a heavier plane doesn't have higher induced drag in cruise? And are you saying that induced drag doesn't matter for cruise?

No, induced drag is most noticeable at lower speeds. Larger aircraft do not behave like a C172 in cruise as designers deliberately manipulate the lift distribution in cruise to reduce the induced drag. That is the whole reason why the 787/A350 went to the next step for variable camber in cruise.

Quoting Matt6461 (Reply 271): But when aircraft are stretched, I wonder if skin thickness is varied. Or do longerons/stringers take the added bending moment? Both?

Both, but the majority will be taken in the skin. The fuselage can be modeled as an ideal elliptical beam.

Quoting Matt6461 (Reply 271): The T7000 will be heavier than the T700. The LEAP will be heavier than the CFM56. MAX's and NEO's are going to be heavier than their predecessors as a result.

"will be" but none of the data is available .....

Quoting Matt6461 (Reply 272): The link I provided specifically breaks out international versus domestic operations.

For a handful of US carriers, none of which operate mainly in the ULH territory.

Quoting Matt6461 (Reply 272): I agree it's probably weighted more towards NB ops (Caribbean, Canada), but the international data would include all U.S. WB ops.

Which includes a very small percentage of ULH flying in comparison. Have a look at the EWR HKG flight to see how many seats they block off because they cannot take full pax payload.

Quoting Matt6461 (Reply 272): Do you dispute the 1/5 figure? Which would you use? On what empirical basis?

Of course, when operating ULH you ate looking at operating aircraft close to max range, and you should know the OEM range payload graphs dont include any cargo, let alone catering and all the other equipment airlines install.

Quoting zeke (Reply 273): No, induced drag is most noticeable at lower speeds

Of course but so what?

That induced drag is more noticeable at low speed doesn't mean it's irrelevant at high speed. The A380's induced drag at cruise is over half of its total drag. At takeoff it's 90% of total drag.



I still don't get your point here. I said weight increases induced drag. That's not really disputable...

Quoting Matt6461 (Reply 271): I don't get your point here.

I do not either, we supposedly are talking fuselage induced drag all along (again, when A380 fuselage is stretched from -800 to -900) & not with wings, in my understanding zeke posts are getting wings into it

[Edited 2015-10-23 12:02:49]

[Edited 2015-10-23 12:07:07]

Quoting Matt6461 (Reply 274): The A380's induced drag at cruise is over half of its total drag.

False, skin friction would be more like 50%, and induced more like 20-30%.

Quoting Clipper101 (Reply 275): I do not either, we supposedly are talking fuselage induced drag all along (again, for an A380 stretched from -800 to -900) & not with wings

Do you not get my point, or do you not get Zeke's point?

I'll assume it's mine, and that you don't understand why I'm bringing wings into a discussion of fuselage drag.**

**Sidenote - you say "fuselage induced drag," which I take to mean fuselage drag generally. Because the fuselage has a small component of lift, it does create some induced drag. But most fuselage drag is pressure drag.

So here's why:

-The intuition is that a -900 stretch would work as well as, e.g., the 787-10 stretch

-We can't just look at the fuselage in isolation, however. An airplane is an interdependent system, and how a stretch performs depends on the system's characteristics

-Here, two considerations suggest that a -900 stretch would not perform as well as one might think, simply looking at the fuselage:

(1) Simple stretches have a bigger impact on induced drag than on parasitic drag. The added wetted area is very efficient at enclosing the weight of payload/fuselage/beams/systems/furnishings. And the increased fineness ratio further mitigates parasitic drag rise. Structural efficiency generally improves as well, but not to the same extent as parasitic drag efficiency.

(2) The A380's drag profile is disproportionately weighted towards induced drag. Although a -900 stretch would impact each component of drag similarly to, e.g., 787-10, the differing proportions that those components represent for A380 versus 787 must be considered.

...leading to the conclusion that a -900 sees less efficiency gain than simple analogy to other stretches might suggest.

Quoting zeke (Reply 276): False, skin friction would be more like 50%, and induced more like 20-30%.

Take a look at Ferpe's table, specifically Column AD, Rows 176-78.

Consider this public quote from LeehamNews, also likely authored by Ferpe without authorial credit:

Quote: This forced Airbus to build the A380 with a two stories fuselage and with a wing with an unusually low aspect ratio. At 7.8, it is well below the present state of the art, which is more like 9.0 (777-300ER) or 9.5 (787, A350). The drag due to weight (induced drag) is therefore higher than normal. This is compensated by good values for the normally dominant drag component, the drag due to size (wetted area and form drag). In fact, the figures for drag show the reverse trend compared to normal airliners with drag due to weight dominating with 50% at average cruise weight and the drag due to size down at 40%.

http://leehamnews.com/2014/02/03/upd...-a-neo-version-and-whats-involved/
I realize that you are a pilot, Zeke. But the etiquette of this forum requires that we provide some proof of our assertions. Without this requirement, people tend to state naked opinion and much time and space is wasted on poor conversation where simple evidence would have worked. If you disagree with Ferpe, please explain why and provide some kind of evidence for your contentions.

[Edited 2015-10-23 12:31:23]

Quoting Matt6461 (Reply 278): I realize that you are a pilot, Zeke. But the etiquette of this forum requires that we provide some proof of our assertions. Without this requirement, people tend to state naked opinion and much time and space is wasted on poor conversation where simple evidence would have worked.

The audacity of such a lecture is quite astonishing when you yourself make so many assertions with no supporting evidence whatsoever. For example:

Quoting Matt6461 (Reply 271): The T7000 will be heavier than the T700. The LEAP will be heavier than the CFM56.

Instead of lecturing others about forum etiquette, perhaps you should look at the forum rules, especially the ones regarding remaining on-topic. You have, once again, like with so many other A380 threads, dragged this one off into technical discussions about your perceived A380 design deficiencies and aerodynamics, and plugs for you pet A380X "project".

Quoting Matt6461 (Reply 277): drag generally. Because the fuselage has a small component of lift, it does create some induced drag.

   Off course, for non-pefectly circular cross section (like that of the A380), yes it should have & we had that one cleared from the beginning ...

Quoting Matt6461 (Reply 277): But most fuselage drag is pressure drag.

   We came into terms on that when "fineness ratio" was raised ...

Quoting Matt6461 (Reply 277): you say "fuselage induced drag," which I take to mean fuselage drag generally

   Yes ... perfect

Quoting Matt6461 (Reply 277):

Yes, looks like we understood each other point of views now  

[Edited 2015-10-23 13:18:24]

[Edited 2015-10-23 13:19:06]

Quoting speedbored (Reply 279):

Ah and you're back to your favorite pet project: disagreeing with whatever I say and trying to tamp down any discussions of the A380's flaws. It's nice to have a fan club though. The prominence of place I hold in your mind is quite flattering.   

Lots of people here like to discuss what a revised A380 might include. Your attempts to limit the discussion to boundaries you find acceptable will never succeed. But I'm sure you'll keep trying.

[Edited 2015-10-23 13:39:39]

Quoting Matt6461 (Reply 281): Lots of people here like to discuss what a revised A380 might include.

Then feel free to go and discuss it in a thread about that topic instead of derailing every other A380 thread.

Quoting speedbored (Reply 282): Then feel free to go and discuss

...and by all means feel free to actually discuss the A380neo. Got anything to say? Or are you just here for your personal issue with me?

I just checked, btw, and there was no mention of an A380X until Reply 258. That came in response to another poster raising the possibility of a new CFRP wing. I'm going to guess that poster appreciated the link to other people's thoughts about the issue.

Apologies, fellow members, for this diversion between me and speedbored. It's generally my policy to respond to one of every six or so of his posts on the subject of Matt6461.

Please continue discussion in the following thread:
Airbus Presses EK To Finance A380neo Part 2 (by lightsaber Oct 23 2015 in Civil Aviation)

Quoting Matt6461 (Reply 278): But the etiquette of this forum requires that we provide some proof of our assertions. Without this requirement, people tend to state naked opinion and much time and space is wasted on poor conversation where simple evidence would have worked. If you disagree with Ferpe, please explain why and provide some kind of evidence for your contentions.

Have a look this Boeing aero news, skin friction on the 737 is 53% of the total drag, and induced drag 29%. My ball park are in line with exactly what the manufacturers are saying, yours are not.

http://www.boeing.com/commercial/aer...ticles/2013_q1/pdf/AERO_2013q1.pdf