Moderators: richierich, ua900, PanAm_DC10, hOMSaR

 
User avatar
DocLightning
Posts: 21971
Joined: Wed Nov 16, 2005 8:51 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Sun Aug 16, 2015 6:56 am

Quoting Matt6461 (Reply 196):
Welcome to the discussion Lightsaber. Lots of folks raise this issue of the taxiway/runway spacing. My intuition has always been that, because A380 would - like 777X - only unfold wings for takeoff run, and would fold immediately after landing, it's not that big of a deal. It seems unlikely that planes landing or taking off would be so close to taxiing planes that ~15ft of span on one side would matter. But is it different at some airports like LAX?

A folding wing for the A380 would have some serious challenges to overcome.

Presumably the point of a folding wing would be to increase the total span to beyond 80m and that's where we have a problem.

No, you can't unfold the wings once you are on the runway because you have other aircraft on the parallel taxiway. There are very few airports in the world where there would not be a risk of a devastating high-speed tip strike between, say, an A380 and the A380NEO roaring down the runway at over 100kt.

So the A380 would have to be designed to take off with the tips folded and then extend them when the gear are retracted. They would then have to be fully folded before crossing the threshold. That would require a very robust actuator and a very good plan in case of a folding failure on approach.

But even if this were all technically feasible (and it should be; flap mechanisms operate under high aerodynamic stress without a problem), it would mean that the benefit of that increased span would be lost until the aircraft was already airborne. That means higher engine settings for the takeoff roll and the terminal phase of landing. So we have a setting of increasing costs in a setting of diminishing returns. It's already tricky enough to taylor a wingtip device to add additional benefit without increasing wetted area, weight, and structural stress beyond the "payback" point. To do that with a heavy-duty actuator for a device that wouldn't even be usable until after rotation is going to be nigh well impossible.
-Doc Lightning-

"The sky calls to us. If we do not destroy ourselves, we will one day venture to the stars."
-Carl Sagan
 
User avatar
seahawk
Posts: 9867
Joined: Fri May 27, 2005 1:29 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Sun Aug 16, 2015 9:12 am

Yes, it would be like an AN-225 thrown in on the busiest hubs in the world.
 
tommy1808
Posts: 13983
Joined: Thu Nov 21, 2013 3:24 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Sun Aug 16, 2015 9:29 am

Quoting DocLightning (Reply 200):
No, you can't unfold the wings once you are on the runway because you have other aircraft on the parallel taxiway. There are very few airports in the world where there would not be a risk of a devastating high-speed tip strike between, say, an A380 and the A380NEO roaring down the runway at over 100kt.

Maybe 3.8.7 of the ICAO Aerodrome operations standards hold the answer to that Problem. Minimum separation can be lower than defined by the standard, if it doesn´t adversely effect operational safety.
Hence maybe the FBW system can hold the key to going beyond 80 meters wingspan on the runway. If one can guarantee that the aircraft will stay within x distance of the centerline, the wingspan should be able to increased by the amount of permissible center line deviation the system reduced.

best regards
Thomas
Well, there is prophecy in the bible after all: 2 Timothy 3:1-6
 
mmo
Posts: 2059
Joined: Thu Apr 18, 2013 3:04 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Sun Aug 16, 2015 11:26 am

Quoting DocLightning (Reply 200):
So the A380 would have to be designed to take off with the tips folded and then extend them when the gear are retracted. They would then have to be fully folded before crossing the threshold. That would require a very robust actuator and a very good plan in case of a folding failure on approach.

I have to ask, if you can takeoff and land at MTOW then why do you need to have a wing span that requires tips folded? That defeats the purpose doesn't it? After all, you are merely adding weight you don't need.
If we weren't all crazy we'd all go insane!
 
User avatar
Stitch
Posts: 27367
Joined: Wed Jul 06, 2005 4:26 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Sun Aug 16, 2015 3:22 pm

Quoting DocLightning (Reply 200):
No, you can't unfold the wings once you are on the runway because you have other aircraft on the parallel taxiway. There are very few airports in the world where there would not be a risk of a devastating high-speed tip strike between, say, an A380 and the A380NEO roaring down the runway at over 100kt.

Well what kind of span are we discussing here? 85m? 90m? 95m? 100m?

I have to believe that even at the current 80m, an A380's wingtip on the active runway is not within 5-10m of the wingtip of a plane with a 65m span on the parallel taxiway. So I have to believe that Airbus could go with a 5-10m span increase without worries of encroaching on the parallel.

A more likely scenario I could see is, depending on the span, that the A380 cannot deploy her wingtips until she's lined-up on the active, which will result in a delay. And if she cannot retract her tips after landing and entering a high-speed taxiway, it could be necessary to have a Follow Me truck take her to an area where they can park her, unload pax, and then fix the issue before tugging her back to her gate.

Both of which would be impactive (very, in the latter case) to airport and airline scheduling.
 
User avatar
Matt6461
Topic Author
Posts: 2991
Joined: Wed Oct 16, 2013 9:36 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Sun Aug 16, 2015 6:28 pm

Quoting DocLightning (Reply 200):
No, you can't unfold the wings once you are on the runway because you have other aircraft on the parallel taxiway.

The quickest bit of research tells me that, for new runways of large-size aircraft, the FAA requires minimum parallel taxiway-runway separation of 500-550 feet:

Quote:

ii) For CAT II/III operations involving Group V aircraft or CAT I operations involving Group
VI aircraft, a 500 ft runway / parallel taxiway separation standard will apply to any airport
electing to proceed with construction.
iii) For Cat II/III operations involving Group VI aircraft, a 550 ft runway / parallel taxiway
separation

https://www.faa.gov/about/office_org/headquarters_offices/arc/programs/aosc/media/AOSC_DD_04_Summary.pdf

With 550 feet separation, two A380's passing each other on takeoff/taxi will have ~300 feet between them if each is on the extreme inner edge of its respective runway/taxiway. A 10m span extension would reduce that separation by ~10-12%.

This regulation supports my intuition that runway-taxiway separation distances are greater than needed to avoid an incidental wing/wingtip strike. The greater distance is probably there for other safety constraints. E.g. a plane landing out alignment unexpectedly, and slightly deviating from runway. If taxiing planes were parked on the runway's "curb," so to speak, every slightly poor landing, every roll into the grass, would be a calamitous collision of two loaded airliners.

I'd be surprised if parallel separation distance was drastically lower before the above-quoted 2005 revision. Even at LAX. But maybe someone has some hard data?

Quoting Stitch (Reply 204):
Well what kind of span are we discussing here?

I'm talking about 90m span, which would add ~16ft on either side to A380. This revision seems well nigh insignificant with 550ft runway-taxiway separation.

Incidentally, youd don't need to do a new *folding* wing: the A380 would greatly benefit from a new, much-smaller CFRP wing of 80m span and winglets. If you go down to 6700ft2 wing area, you can take a tremendous amount of weight out of the plane. That combined with smaller/lighter engines and empennage could enable ~8,000nm range at ~940,000lbs MTOW, so wing loading would be only ~1-2% higher than for CEO. You have lower induced drag due more to weight reduction than span increase, while parasitic drag has decreased with smaller wing/engines/empennage.

This version of the A380NWO - 80m wing version - might actually be best because it's likely cheaper to build. It's not quite as fuel-efficient as with the longer wing, but could be better on DOC for shorter missions.

EDIT - was scrolling through the forum archive on a hunch... This thread appears to be now the longest in Tech Ops in well over two years. Thanks to everyone who has contributed substantive, interesting discussion.  Smile

[Edited 2015-08-16 11:40:11]

[Edited 2015-08-16 12:15:13]
 
User avatar
Matt6461
Topic Author
Posts: 2991
Joined: Wed Oct 16, 2013 9:36 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Sun Aug 16, 2015 8:51 pm

Quoting Stitch (Reply 204):
A more likely scenario I could see is, depending on the span, that the A380 cannot deploy her wingtips until she's lined-up on the active, which will result in a delay.

This is true, but:

-IIRC 777X's wing unfold is only ~10 seconds.

-Seems like a ~10 second delay for wing unfold will be greatly outweighed by the reduction of separation distances enabled by the massive (40-50%) reduction of induced drag at takeoff (greater span plus lower weight = much lower Di).

Quoting Stitch (Reply 204):
And if she cannot retract her tips after landing and entering a high-speed taxiway, it could be necessary to have a Follow Me truck take her to an area where they can park her, unload pax, and then fix the issue before tugging her back to her gate.

Also true but Boeing is aiming for 1/1000 failure rate for deployment, 1/10,000 for retraction.

Failure to deploy isn't as big of an issue for the airport: The plane just taxis back as a "normal" Code F plane. Or maybe, like the 777X, it completes the mission with ~3-4% higher fuel burn - assuming it's a less-than-MTOW mission for which revving the engines harder than planned gets it off the ground. At 1/1000, this happens once over 2-3 years. It's a pain but manageable.

Failure to retract would be more problematic as you describe. But at 1/10,000 we're talking 2-3 incidents per frame over 20 years. Seems manageable.
 
User avatar
Stitch
Posts: 27367
Joined: Wed Jul 06, 2005 4:26 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Sun Aug 16, 2015 11:25 pm

Quoting Matt6461 (Reply 206):
Failure to deploy isn't as big of an issue for the airport: The plane just taxis back as a "normal" Code F plane.

Code F is between 65 and 80 meters so if she can't retract, she's going to now be a "Code G" plane.  

Based on comments I have read, I am to understand that some A380 airports have special procedures to accommodate her 80m span. Another 10m may not be an issue within those procedures, but if it is...

All that being said, I do agree that it likely would be a very rare occurrence so even if it does present an issue, it's one that will be a momentary pain point over the annual operations of an airport and airline.
 
Pihero
Posts: 4318
Joined: Mon Jan 31, 2005 5:11 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Sun Aug 16, 2015 11:29 pm

Quoting Matt6461 (Reply 194):
According to the wing weight index worked out by Standford aerodynamics Professor Kroo, wing weight trends upwards with the inverse of the cosine of the dihedral angle.

1/- AAFAIK, your link does not mention dihedral effect.

2/- The actual dihedral of the A3.80 is 5.6°. The effect of cos 5.6° to let's say 4.6° is from 1.004795 to 1.003232 thus .001563 or .16% or 1.6 kg /t of wing structure.
That dihedral doesn't come from nowhere : "éExternally, the most distinctive aspect of the wing, aside from its size and 79.7m span, is the pronounced “gulling’”effect and its 5.6° dihedral. “This was set by the stability requirements of the aircraft. We didn’t want it too high, making it too stable, or too low, making it unstable. Plus, we needed to set it for adequate engine ground clearance, particularly in the case of the aircraft rolling around on its undercarriage."

Quoting Stitch (Reply 204):
Well what kind of span are we discussing here? 85m? 90m? 95m? 100m?

Welcome me to your club, 'cause I'm lost.

Quoting Matt6461 (Reply 205):
I'm talking about 90m span, which would add ~16ft on either side to A380. This revision seems well nigh insignificant with 550ft runway-taxiway separation
Quoting Matt6461 (Reply 205):
the FAA requires minimum parallel taxiway-runway separation of 500-550 feet:

That has nothing to do with wingtip clearances : It's about cat II /III approaches obstacle protection and, incidently Cat II/III ILS beams protection.

Quoting Matt6461 (Reply 205):
Incidentally, youd don't need to do a new *folding* wing: the A380 would greatly benefit from a new, much-smaller CFRP wing of 80m span and winglets.

So...

Quoting Matt6461 (Reply 205):
If you go down to 6700ft2 wing area, you can take a tremendous amount of weight out of the plane.
Quoting Matt6461 (Reply 205):
Quoting Matt6461 (Reply 205):
so wing loading would be only ~1-2% higher than for CEO

Let's put all these into perspective, shall we ?
New wing :
Span = 80 m
Area = 622.5 m^2 ( from 6700 ft^2 )
The numbers come out then as Aspect ratio = Span ^2 / Area ==> 6400 / 622.5 = 10.28, which compares very favourably to the highest aspect ratio of 9.77 for the A350 and the 777X of 9.77.
But then, the torsion loads would be quite higher.
We'll see that later.
Now, we come to the crunch : the A380 wing loading is 680 kg/m^2
Taking your 2% increase with the new wing, it comes to 680 x 102% = 693.6Kg/m^2
and with an area of 622.5 m^2, the MTOW becomes 693.6 x 622.5 = 431 766 kg
Therefore, you managed to shave 143.2 tonnes on the actual 575 t of the A380 !... That's nearly 320 000 pounds !

Don't wonder why I've called this thing just a dream, without nor thought or technical basis.

So let's stop dreaming, or if we couldn't deal with maths and physics, let's stop this nonsense of a thread altogether.

As a final point, I'd like to refer to Mr Guy Norris, of Flight International : (link in post #185 by Speedbored )

" “Ideally we would like to have optimised the wing for an 82.5m span, but that’s outside the box so we couldn’t do that, therefore we added the 2.4m-high winglets,” says Ogilvie.
Although the original concept was for 3m-plus winglets, these were reduced when loads analysis revealed that additional strengthening of the outboard wing section would be required, and the added weight would therefore outdo any lift and drag benefit. The final size of the winglet, which is based on the original A320 shape patented by BAE Systems’ Jeff Jupp and Peter Reese, was calculated using theorems originally developed by legendary German aerodynamicist Max Munk.
"

Quoting Matt6461 (Reply 205):
This thread appears to be now the longest in Tech Ops in well over two year

Yeah ! the old discusion about quantity vs quality.   
Contrail designer
 
User avatar
TheRedBaron
Posts: 3276
Joined: Tue Mar 29, 2005 6:17 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Mon Aug 17, 2015 1:36 am

Quoting Matt6461 (Reply 48):
You and Airmagnac may have a lot of knowledge and a lot to say, but you're missing the forest for the trees. You're obfuscating the central issue of whether a simple NEO will make the A380 attractive; you're avoiding any discussion of what efficiency improvement is required; you're not providing any proposals yourself.

They have by telling you make wrong assumptions.

Quoting Matt6461 (Reply 67):
This sounds like a conspiracy theory. Have any evidence that A380 has no larger wake vortices than a 747?

If you are going to doubt very knowledgeable people here, what is the point on posting.

Quoting Pihero (Reply 69):
The better question is "Have you any evidence that the A380 has a larger wake than the 748 ?"... and yes I have that evidence, from the test director himself.

There is your answer.

Quoting Matt6461 (Reply 72):
As I said, the 748's wing is a reloft on "old bones." I agree that a ton of new - and very expensive - features went into the 748 version of the wing. But these don't change the fact that 748 shares with the A380 a fatal flaw: low aspect ratio.

Sometimes I really believe you think the guys at Everett, Filton, and Hamburg, really know nothing about airfoil design !

Quoting seahawk (Reply 74):
CASM is a result of the decision making process, not a parameter to base the decision on.

  

This is a very informative post, thanks for the data and the info... Pihero, Stitch, Lightsaber, Speedbored et al.

TRB
The best seat in a Plane is the Jumpseat.
 
User avatar
DocLightning
Posts: 21971
Joined: Wed Nov 16, 2005 8:51 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Mon Aug 17, 2015 1:37 am

Quoting Matt6461 (Reply 205):
The quickest bit of research tells me that, for new runways of large-size aircraft, the FAA requires minimum parallel taxiway-runway separation of 500-550 feet:

For new, yes. But then most major airports are not new. So if you're going to design an aircraft that can only operate out of new airports, that doesn't help your business case very much. I doubt Taxiways C and F at SFO are that far from their respective runway 28s.

Quoting Stitch (Reply 204):
I have to believe that even at the current 80m, an A380's wingtip on the active runway is not within 5-10m of the wingtip of a plane with a 65m span on the parallel taxiway.

You have to assume that there will be another A380 on the taxiway. Otherwise you are into a whole world of logistical issues with timing how many A380s can depart when and how.

Quoting tommy1808 (Reply 202):
Maybe 3.8.7 of the ICAO Aerodrome operations standards hold the answer to that Problem. Minimum separation can be lower than defined by the standard, if it doesn´t adversely effect operational safety.
Hence maybe the FBW system can hold the key to going beyond 80 meters wingspan on the runway. If one can guarantee that the aircraft will stay within x distance of the centerline, the wingspan should be able to increased by the amount of permissible center line deviation the system reduced.

You can't make that guarantee on landing, though.
-Doc Lightning-

"The sky calls to us. If we do not destroy ourselves, we will one day venture to the stars."
-Carl Sagan
 
WingedMigrator
Posts: 1771
Joined: Wed Oct 26, 2005 9:45 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Mon Aug 17, 2015 2:42 am

Quoting DocLightning (Reply 200):
it would mean that the benefit of that increased span would be lost until the aircraft was already airborne

While there are no doubt many arguments against airborne-actuated folding wing tips, lost benefit during takeoff is not one of them. The extra span wouldn't be needed during takeoff and landing; the existing wing is plenty capable of producing the necessary lift. The drag benefit of the extended wingtip accrues over hours of cruise, not the brief and draggy (flaps and slats, ugh!) portions of a flight cycle.
 
tommy1808
Posts: 13983
Joined: Thu Nov 21, 2013 3:24 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Mon Aug 17, 2015 6:36 am

Quoting DocLightning (Reply 210):
You can't make that guarantee on landing, though.

With drones landing on aircraft carriers, i am fairly sure we can, given a certain definition of environmental conditions.
Keep in mind, for that to work, it doesn´t need the sub-inch precision demonstrated by the X-31 program (aircraft position, not landing spot), it just needs to be better than human landings. That improvement can directly move into wingspan, w/o decreasing the operating safety.

best regards
Thomas
Well, there is prophecy in the bible after all: 2 Timothy 3:1-6
 
User avatar
seahawk
Posts: 9867
Joined: Fri May 27, 2005 1:29 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Mon Aug 17, 2015 7:13 am

Should we not wait with that discussion when we know if the increased wing span is really needed. Especially considering that the folding mechanism will come with its own drawbacks and that aspect ratio is not the holy grail of wing design (from parasitic drag to loss in internal volume and more challenging ), if you look at the wetted aspect ration the A380 is pretty good.

Ferpe did some good work on that back in 2013.
 
User avatar
speedbored
Posts: 2230
Joined: Fri Jul 19, 2013 5:14 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Mon Aug 17, 2015 7:30 am

Quoting Matt6461 (Reply 194):
I asked you for a case where two widebodies with significantly different CAxM on a given longhaul route have an inverted relationship of CAxM differential on another long haul route.

No you didn't, please stop changing the argument every time you are caught out. The request I replied to was "a single example of where the varying variances - between widebodies - would render high-level CAMM comparisons meaningless" and I have given you the simplest possible example. You are doggedly determined not to get the point that looking at costs on a per-anything basis can render your comparisons meaningless. Airlines do not use such a comparison for good reason. Why is that so impossible for you to accept?

Quoting Matt6461 (Reply 194):
you're back to your old evasions:

No, I am still waiting for you to provide a workable definition for CAxM. But you keep ignoring every single inconvenient question that is posed to you.

Quoting Matt6461 (Reply 194):
My simple request is that you stop constantly interjecting with an objection that you can't compare planes based on unit efficiency.

I will do that as soon as you stop incorrectly insisting that you can.

Quoting Matt6461 (Reply 194):
trying to evade the question by accusing me of something or other.

I am doing nothing of the sort. I answered the specific question that you asked. If you wanted an answer to a different question then, perhaps, you need to ask that instead?

Quoting Matt6461 (Reply 194):
Kids on the playground say to each other, "That's just your opinion," as if it were dispositive. I never found it dispositive as a kid and I don't now.

I don't go playing with kids in playgrounds so I wouldn't know. But it is in the forum rules that you must back up statements, or make it clear that they are just opinions.

Quoting Matt6461 (Reply 194):
Nobody's saying that.

Maybe not but, historically, it is almost always exactly what has happened.

Quoting Matt6461 (Reply 194):
which is accounted for by escalating structural weight in proportion to cube of span.

But that is to account for the stuctural weight of the wing itself. I'm not talking about additional structure required because of making the wing longer; I'm talking about additional structure that will be required because of your plan to make the wingbox shorter. The forces going through the wingbox are many, and interact in very complex ways. Making the wingbox shorter will reduce the lever arm available within the wingbox to cope with some of these forces, especially twisting and bending ones.

Quoting Matt6461 (Reply 194):
New engines could perhaps have as little as 50k thrust, much smaller than either T1000 or T7000.

I'd be very surprised if you could manage around three times the percentage thrust reduction that Boeing are managing with the 779, but the smallest T1000 is only 53k. Even if, by some miracle, you could get thrust requirements right down to GTF range, and re-use the A321 engines, you'll still gain less than 18 inches of extra clearance.

Quoting Matt6461 (Reply 199):
This all seems too obvious to point out - that unit costs matter.

Yes, so obvious that no airline I have ever worked with has been clever enough to see it. They can only fly aircraft in whole units of 1 aircraft. They cannot fly single seats or single square metres of floor. They are interested only in how much money they will make for their shareholders, as they are legally obliged to be.

Quoting TheRedBaron (Reply 209):
Sometimes I really believe you think the guys at Everett, Filton, and Hamburg, really know nothing about airfoil design

Or maybe they just use different textbooks  
Quoting DocLightning (Reply 210):
You have to assume that there will be another A380 on the taxiway. Otherwise you are into a whole world of logistical issues with timing how many A380s can depart when and how.

True. There's also the possibility that you might have to close a runway or two while retrieving an A380 that is unable to retract the wingtips, when the only available taxiway is too close.

Most of the worlds largest/busiest airports are already very space constrained, many of them still have significant numbers of important taxiways that cannot be used by code F aircraft. I can certainly see them being extremely resistant to having to make further changes to cope with aircraft larger than code F on a regular basis.

Quoting WingedMigrator (Reply 211):
While there are no doubt many arguments against airborne-actuated folding wing tips

I suspect that, at many airports, noise could be a significant factor.
 
User avatar
Matt6461
Topic Author
Posts: 2991
Joined: Wed Oct 16, 2013 9:36 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Mon Aug 17, 2015 3:14 pm

Quoting Pihero (Reply 208):
The FAA requires minimum parallel taxiway-runway separation of 500-550 feet:
That has nothing to do with wingtip clearances : It's about cat II /III approaches obstacle protection and, incidently Cat II/III ILS beams protection.

Can you say more about this? Do you really think wingtip clearance is irrelevant? This is another case where I'd love for you to be right.

Quoting Pihero (Reply 208):
Let's put all these into perspective, shall we ?

You go to a lot of trouble deriving an MTOW number that appeared in my post.   I'm going to run the 80m wing through my estimator and post it here shortly.

Quoting Pihero (Reply 208):
1/- AAFAIK, your link does not mention dihedral effect.

2/- The actual dihedral of the A3.80 is 5.6°. The effect of cos 5.6° to let's say 4.6° is from 1.004795 to 1.003232 thus .001563 or .16% or 1.6 kg /t of wing structure.
That dihedral doesn't come from nowhere

The symbol for dihedral is defined elsewhere in the course notes.

I specifically use the term "dihedral/gulling" instead of merely dihedral. The gulled wing describes an arc, travel along which is longer than would be a straight line from root to wing tip. Therefore, the pronounced gulling effect of A380's wing appears to add more structural length per span than even its slightly higher dihedral would suggest.

And yes, I recognize that this is at most a few percentage points in wing bending weight.

Per the article, I correctly identified the reasons for dihedral...

Quoting TheRedBaron (Reply 209):
If you are going to doubt very knowledgeable people here, what is the point on posting.

"In God we trust. All others must bring data."

There are some knowledgeable people who disagree with each other here. There are also knowledgeable people saying crazy things. There are knowledgeable people saying things that might be true, but lack the support of data.

It appears your method of decision, given such ambiguities, is to believe whoever supports the A380. I have a more rigorous cast of mind. The forum, especially TechOps, works best when folks make points tied to specifically cited data.

Quoting DocLightning (Reply 210):
For new, yes. But then most major airports are not new.

I only have data on runway separation for the new regs. My intuition is that reducing separation distance by even 150 feet might not make the wingtip clearance issue determinative. This is just an intuition, I'm open to a good hard explanation of why it's wrong, backed up by regs or ineluctable logic...

But if Pihero is correct as quoted above, the separation distances are about obstacle clearance anyway - not wingspan. This could make sense: an aircraft yawing a bit during engine-out takeoff must climb over the vert-stabs of parallel-taxiing planes. Regulatory minimum climb rate is ~20% IIRC, so leaving 500 feet to climb over a 70ft stabiliser - maybe that motivates the separation distance and not the wingspan.

I don't know. Pihero- do you have any citations to back up your claim that wingspan doesn't control separation distance?

Quoting WingedMigrator (Reply 211):
Quoting DocLightning (Reply 200):
it would mean that the benefit of that increased span would be lost until the aircraft was already airborne
While there are no doubt many arguments against airborne-actuated folding wing tips, lost benefit during takeoff is not one of them.

I agree that, were loaded wingtip actuation possible, we'd lose very little trip efficiency from a marginally more costly takeoff. Fuel burn during climb and cruise far predominates. Engine setting would be higher but- "paper" derates of widebodies for regional flying typically save less than 1% of operating cost, no? Here we'd have the inverse of a ~5% derate to overcome higher induced drag at V2, and to attain the higher V1 speed required by (very slightly) lower wing area.

I'd love to take your prescription for the wingtips, Doc.

My doubt is this: you analogize to flaps, which indeed are actuated under high loading. But:

-The lever arm for 777X wingtip actuation is within the airfoil. Absent flight loads, the attendant short arm is adequate to actuate. I doubt it would be with full flight loads.

-The necessary lever arm for more highly-loaded flaps typically extends beyond the airfoil, and is encapsulated in a fairing. The fairing is oriented chord-wise, enabling high fineness ratio in the streamwise flow direction.

-If we tried to build an extra-airfoil lever arm for actuating a folding wingtip, this lever and its fairing would be oriented span-wise instead of chord-wise. Unlike for flap track fairings, it would be impossible to create a fine and streamlined fairing. It would likely contribute a lot of interference and/or parasitic drag, as well as a lot of weight.

These are just first-take intuitions though. If there were an efficient solution to in-flight actuation, many of the problems we're discussing would be solved.

But if they can't be solved, then there's still the option of an 80m CFRP wing plus winglets. I'm going to run this through my estimator and post the results. As always, any critiques of my estimator are welcome. Aside from generic "that's stupid" comments that don't point to specific errors or improvements. But I expect some of those anyway. C'est la vie d'Internet.
 
Pihero
Posts: 4318
Joined: Mon Jan 31, 2005 5:11 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Mon Aug 17, 2015 6:01 pm

Quoting Matt6461 (Reply 215):
Can you say more about this?

Just read the text you linked to.

Quoting Matt6461 (Reply 215):
You go to a lot of trouble deriving an MTOW number that appeared in my post.

No, it took me just under a minute on thge back of an envelope.

You might have noticed that in fact my figures are more accurate than your 940 000 lbs that come out of nowhere.

Quoting Matt6461 (Reply 215):
I'm going to run the 80m wing through my estimator and post it here shortly.

Please do and let's have a laugh.

Quoting Matt6461 (Reply 215):
The symbol for dihedral is defined elsewhere in the course notes.

So why can't you quote the page where it's at ?
I have the feeling that you mistook dihedral with sweep back ( structural effect of sweep back proportional to 1/cos^2 angle of sweep ).

Quoting Matt6461 (Reply 215):
The symbol for dihedral is defined elsewhere in the course notes.

I'm not interested in symbols but facts and figures.

Quoting Matt6461 (Reply 215):
Therefore, the pronounced gulling effect of A380's wing appears to add more structural length per span than even its slightly higher dihedral would suggest.

  

Quoting Matt6461 (Reply 215):
And yes, I recognize that this is at most a few percentage points in wing bending weight.

I don't understand the concept of *bending weight*.

A few percentage points ?
My maths recognize 2/10 of a percent. I admire your generosity with figures.

Quoting Matt6461 (Reply 215):
This could make sense: an aircraft yawing a bit during engine-out takeoff must climb over the vert-stabs of parallel-taxiing planes.

Define *a bit* and *over the verttical stab* (is that a fin, by any chance ?). I have a feeling that you're going to meet some drastic obstacle clearance figures, here.

Quoting Matt6461 (Reply 215):
Regulatory minimum climb rate is ~20% IIRC,

A climb rate is given in ft/min, meter /sec...inches per hour... whatever.
Yes, a climb GRADIENT is given as a percentage - obviously, being the ratio of two values of the same unit, it has no dimension.
And no : at takeoff the net gradient for a quad is 2%, not 20%.
Contrail designer
 
User avatar
Matt6461
Topic Author
Posts: 2991
Joined: Wed Oct 16, 2013 9:36 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Mon Aug 17, 2015 7:56 pm

Here's an estimate of an A380 with a new CFRP 80m wing with winglets. A few things about this estimate:

It applies the simple empirical research formulae for estimating wing weight developed by professor Ilan Kroo of Stanford University. http://adg.stanford.edu/aa241/AircraftDesign.html. It is an estimate.

As I've said earlier, my goal is to try to apply some first-order basic principles to get an estimate of how the wing would work. Ideas for refinement and revision are welcome.

Basic assumptions/parameters from the model:

("~" means "proportional to)

-wing weight is 40% span-dependent and 60% area-dependent
-span dependent wing weight (SPWW) ~ span^3
-SPWW ~ ultimate load
-SPWW ~ SQRT(MTOW/MZFW) - this term estimates structural cost of carrying more/less fuel in wings
-ultimate load calculated as fuselage payload empennage minus wing/engine bending relief
-wing/engine bending relief calculated by estimated center of weight versus center of lift
-area-dependent weight ~ wing exposed area

For empennage, I simplified a little bit:
-area of vert-stab and tailplane assume to be ~ max lift required for critical flight conditions (engine out yaw force for vert.stab., force of rotation for tailplane)
-weight of empennage, as cantilevered lifting surfaces, moves somewhat more than linearly with empennage area. I used an exponent of 1.2 to estimate weight reduction.

Landing gear weight ~ MTOW. Baseline A380 MLG estimated at 3.5% of MTOW.

Dry engine weight ~ thrust. Total propulsion system weight = 1.6*(dry engine weight)

I DID NOT model the reduction in fuselage weight that would likely come from smaller aerodynamic loads from lower MTOW and thrust. I also didn't change wing sweep or dihedral, both of which could perhaps be altered for further optimization. Mostly just being lazy...

I modeled new MD-12/737MAX-style split-scimitar winglets as conferring effective span of 273ft against A380CEO's effective span of 266ft (per Ferpe). This confers a ~2% fuel burn delta, which seems reasonable to me but I'm open to other suggestions as with everything else here.

New engines have -11% SFC delta over CEO engines in this model. These would have to be clean sheet engines, a ~2021 NextGen GTF seems like the best candidate. I recognize that, as with the NEO, convincing an OEM to power this aircraft would be central to the business case.

The aerodynamics are as previously stated:

Quoting Matt6461 (Reply 171):
We know that 90 % of drag comes from two types: parasitic/form drag and induced drag. The next biggest portion is either wave drag or trim drag.

To make things simpler for wing comparisons that primarily alter span, weight, and area, I propose focusing on the following relationships:

Induced drag = Di ~ (span^2)/(lift^2)/(air density) http://en.wikipedia.org/wiki/Lift-induced_drag

Parasitic/form drag = Dp ~ (wetted area)*(Cdp coefficient)*(air density)

Air density at cruise ~ wing loading

For wave drag: most wave drag occurs on the airfoil surfaces. This is especially true of the A380, whose fuselage is designed for 0 wave drag up to M=.89 (again, it's that great fuselage)

Therefore, I propose roughly estimating wave drag as ~ (wing area plus empennage area)

The drag buildup gives a fuel burn figure. That fuel burn figure is then plugged into Leeham's figures for A380 DOC, with adjustments for our new engine thrust (linear with mx), wetted area (linear with frame mx), MTOW (relates to en routes fees by cube root, per Leeham estimate), and capital cost. So this last part is just arithmetic; one can skip the aerodynamics just enter a fuel burn and capital cost delta, specify a gas price, and you'll see a different DOC trip cost.

That's all there is to it folks. It's a little bit harder to follow in spreadsheet form, but questions are welcome.

*Note: I've issued a call for help modelling fuselage lift, still working on my estimated approach to that (help would still be appreciated), but including would almost certainly make a new wing more attractive: we're keeping the same fuselage, therefore keeping its lift. However, I'm estimating lift as if we're losing lift in proportion to wing area at given speed/air density. Including fuselage lift would allow for an even smaller, lighter wing as a result.

Here's the A380NEO modeled with 80m wing and winglets. Wing area is 6900ft2, thrust is ~196k lbs, MTOW is 970,000lbs, OEW is ~513,000lbs. The wing is 48,000lbs lighter, the engine system ~25,000lbs lighter, empennage ~19,000lbs lighter, landing gear ~10,000lbs lighter.

On a 6,000nm trip and using Leeham's cost proportions, its trip cost is ~19% lower than than CEO's if sold at $460mn per frame.

http://docs.google.com/spreadsheets/...OrPyGiSlUq2DdRt1Y/edit?usp=sharing

[Edited 2015-08-17 13:24:27]
 
User avatar
Matt6461
Topic Author
Posts: 2991
Joined: Wed Oct 16, 2013 9:36 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Mon Aug 17, 2015 10:09 pm

Previous post presented an estimate, based on best-available model of operating weight, and based on a few fundamental parameters of drag, that an A380 with a new 80m CFRP wing/winglets would have ~19% lower trip cost on a 6000nm mission. For shorthand, in this post I'll call that plane the A380NWO ("New Wing Option").

Is there a business case for such a revision? My intuition is yes, here's why:

-Development cost for this version should be no more than $5bn. It has new wing, empennage, engines, and landing gear. 777X is supposed to cost around $5bn; let's compare the difference between the revisions:

-A380NWO adds new landing gear (777X has new engine, wing, and empennage)

-777X adds two fuselage stretches, and requires certification of two airframe arrangements, including certifying wing for -8X and -9X at different MZFW critical load conditions.

What would cost more? Certification and rework of two fuselage stretches, plus additional wing certification requirements for two models, or development of new landing gear? Honestly not sure, but seems like new landing gear wouldn't be drastically more expensive than the 777X's additional work.

For $5bn development cost, what ROI might Airbus expect?

Suppose they are able to sell and deliver 700 A380NWO's from 2021-2035. That's ~50 frames/year over 15 years, given a decent ramp up in 2021-23.

In my spreadsheet, I fixed sales price at $460mn.

-I estimated that moving production rate from 30 to 50/year would decrease unit price by ~9%.
-I estimated that production price/cost at break even for A380CEO is apportioned 2/3 to frame and 1/3 to engines.
-I estimated that engine price would decrease linearly with thrust, plus 5% for tech delta
-I estimated that frame price would decrease with weight, plus 5% for tech/materials delta (CFRP)

Based on these assumptions, and assuming that the A380 is breaking even on production at its current sales price, I estimate ~$70mn profit per plane at $460mn list price and 45% standard discount from list.

What kind of ROI do we think would justify an airliner business case? Say we're highly risk averse and need to see a 50% projected ROI, such that two years of full production recovers nominal investment. That would require a $2.5bn profit stream and $50mn per frame at 50 frames/year. So there's room in my production cost estimate for error - it's a very rough estimate.

Now the $5bn question - could an A380 with ~20% lower operating cost sell in the neighborhood of 50/year? Would airlines want 700 such planes from 2021-2035? My gut feeling is yes:

Per Leeham's figures, A380CEO's DOC trip cost on a 6000nm flight is ~$290,000. If it does one such flight per day, 365 days per year, its annual DOC is $105mn. Saving ~20% of that is ~$20mn per plane. For BA and QF with 12 frames, switching A380CEO to NWO would be worth $240mn added annual profit. That's 15% of IAG's 2014 profit. http://www.nytimes.com/2015/02/28/bu...rent-of-british-airways.html?_r=0. It's about a quarter of Qantas' expected 2014/15 annual profit. http://www.news.com.au/finance/busin...ntas/story-e6frfkur-1227474683211. For SQ with ~20 frames, that's $400mn added annual profit, well in excess of recent quarterly profit results. http://centreforaviation.com/analysi...the-farm-on-premium-economy-208677

For EK with 65 frames, that's $1.3bn added profit, basically doubling its profit.

So I'd expect current operators to replace their CEO's with NWO's, and expand their fleets.

But it's gotta sell better than the CEO of course. And that's the argument we've had for a while here... Does ~20% trip cost reduction broaden market appeal? I think it does, but... well we can debate. And I've already written a lot, will perhaps return to this point again.

EDIT: I just wante to add one simple point. By even Amedeo's stats, the A380 will have ~50% greater trip cost than 777-9. www.amedeo.aero/a380. A 20% reduction in trip cost means the A380NWO's trip cost would be only 20% greater than 777-9. [.8*1.5=1.2]

Gut theory: A plane with 20% higher trip cost than competition is fundamentally different to the market than a plane with 50% higher trip cost.

2nd gut theory: A plane with 40% higher trip cost is not fundamentally different from one with 50% higher trip cost. A380NEO will only lower trip cost ~6-7% at most, thus ~40% higher trip cost.

Corollary to two proceeding gut theories: A380NWO is a fundamentally different value and risk proposition from A380CEO or NEO.

[Edited 2015-08-17 15:30:23]
 
User avatar
speedbored
Posts: 2230
Joined: Fri Jul 19, 2013 5:14 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Tue Aug 18, 2015 12:06 am

Quoting Pihero (Reply 216):
I have the feeling that you mistook dihedral with sweep back ( structural effect of sweep back proportional to 1/cos^2 angle of sweep ).

I'm sure you are right:
http://adg.stanford.edu/aa241/wingdesign/wingparams.html
http://adg.stanford.edu/aa241/structures/componentweight.html
I can't find any reference to dihedral anywhere.

Quoting Pihero (Reply 216):
Quoting Matt6461 (Reply 215):
This could make sense: an aircraft yawing a bit during engine-out takeoff must climb over the vert-stabs of parallel-taxiing planes.

Define *a bit* and *over the vertical stab* (is that a fin, by any chance ?). I have a feeling that you're going to meet some drastic obstacle clearance figures, here.

 
 
User avatar
Matt6461
Topic Author
Posts: 2991
Joined: Wed Oct 16, 2013 9:36 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Tue Aug 18, 2015 1:14 am

Quoting speedbored (Reply 219):
I can't find any reference to dihedral anywhere.
Quoting Pihero (Reply 216):
I have the feeling that you mistook dihedral with sweep back

My fanclub keeping me honest.  

I remembered the relationship but gave the wrong source. Hard to remember which squiggly is sweep and which is dihedral, it's all Greek. See Page 238 here: http://bit.ly/YCu6gn

Quote:
The effective wing planform area as a function of
dihedral angle is determined as follows:

Effective wing area = cos(dihedral angle)*wing reference area

The entire wing area, not just span, effectively decreases with the cosine of the dihedral. Thus dihedral would have a more pronounced effect on structural weight for a given wing area than I stated initially, and in relation to cosine of the angle itself.

The effect is still small, and thus I haven't bothered with it any of the models I've presented. I've just noted it as one of those details one could tweak for a fine-level analysis, depending on how stability and engine ground clearance works out with the new wing.

Thank you both for your attentiveness to proper citation.
 
User avatar
seahawk
Posts: 9867
Joined: Fri May 27, 2005 1:29 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Tue Aug 18, 2015 5:18 am

Maybe this thread helps a bit:

A380 Wing High Efficiency Vs Mediocre Aspect Ratio (by faro May 4 2013 in Tech Ops)#1

As we see, the whole airframe is not as bad as the wign alone makes it seem.
 
User avatar
Matt6461
Topic Author
Posts: 2991
Joined: Wed Oct 16, 2013 9:36 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Tue Aug 18, 2015 5:43 am

Quoting seahawk (Reply 221):
As we see, the whole airframe is not as bad as the wign alone makes it seem.

I've already linked images from this thread a couple times here.

As you'll see from Ferpe's analysis therein, the A380 has only slightly worse L/D than contemporary airliner competition. So in the sense that it's only slightly worse, I guess you're right that it's "not as bad as the wing makes it seem."

But that's a tragedy. The A380's fuselage is outstanding. Low wetted area, no wave drag, good weight per passenger. It should have THE BEST L/D, not the worst. The wing pulls this all this great engineering back below average, leaving the A380 barely more efficient than modern big twins.

Modernize/fix the wing and you've probably got a great plane. That's all I'm saying here. ...and trying to work out just how great.
 
User avatar
speedbored
Posts: 2230
Joined: Fri Jul 19, 2013 5:14 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Tue Aug 18, 2015 7:51 am

Quoting Matt6461 (Reply 220):
The entire wing area, not just span, effectively decreases with the cosine of the dihedral. Thus dihedral would have a more pronounced effect on structural weight for a given wing area than I stated initially, and in relation to cosine of the angle itself.

Yes, but in totally the opposite direction from what you claim. "Wing area effectively decreases" and "Effective wing area decreases" are not at all the same thing.

The calculation is to make allowance for the fact that the adding dihedral angle changes the angle at which lift forces act and, therefore, reduces the actual[b] amount of lift that is available from a given wing to keep the aircraft in the air. "Effective wing area", in this context, means the equivalent size of wing with zero dihedral that would be required to produce the same lift as a wing with the given dihedral.

With a zero dihedral angle, all of the lift forces are acting in the vertical plane so all of the generated lift is available to keep the aircraft airborne. At this angle, effective wing area = actual wing area.

At, say, a 25 degree dihedral angle, some of the lift is now acting in the horizontal plane, so is wasted. At this angle, [b]effective
wing area = ~90% of actual wing area. Given that you want your aircraft to stay in the air you would, all else being equal, need to increase the actual wing area by ~10%, to produce the same amount of lift as when it had a zero dihedral.

Nice to see, though, that you have chosen to base your weight calculations, for an all-new CFRP wing, on equations determined via analysis of all metal wing designs, on aircraft ranging from DC8s and 707s, to modern wonders such as the 747-100, DC10 and L1011. Good thing that real-world wing design hasn't moved on much since 1972.
 
Pihero
Posts: 4318
Joined: Mon Jan 31, 2005 5:11 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Tue Aug 18, 2015 11:18 am

That so-called "study" i so full of errors,false assumptions and such mediocre knowledge of physics that I don't know where to start.

Quoting Matt6461 (Reply 220):
The entire wing area, not just span, effectively decreases with the cosine of the dihedral.

You may also consider that modern wings show a lot of *dihedral* through their flexibility, as demonstrated here :

View Large View Medium
Click here for bigger photo!

Photo © Brian Losito


yet it hasn't been taken care of in your sheet ( or in Ferpe's Excel, btw)

Quoting Matt6461 (Reply 217):
Induced drag = Di ~ (span^2)/(lift^2)/(air density)

If we believed that proportionality, the shortest possible wingspan will have the lowest induced drag !.. That's very new to me.
In fact, taking the equation you found on wiki :
Di = L^2 / (K x V^2 x S X Ar)
where L is lift, Ar the aspect ratio and V the equivalent airspeed.
As we know that Ar = b^2 / S, with S the wing area, the equation becomes :
Di = L^2 / (K X V^2 X b^2), which puts things in their right place.

So, taking the same notation you used : Di ~ (lift^2) / (span^2) ... and forget air density as it is a constant in these conditions.

So that very important aspect of your sheet is in error...badly.

(btw, K is the product of 1/2 r x pi x e ) all being constants : r is air density, pi is pi, e is the wing efficiency.

Quoting Matt6461 (Reply 217):
Air density at cruise ~ wing loading

Rubbish : at cruise Weight = Lift = weight =S x Wing loading . Wing loading at level cruise has nothing to do with aerodynamics... it is at any given moment a constant.

And why, may I ask all aircraft flying at the same altitude, the same Mach numlber, the same temperature will have different values of air density ?

Quoting Matt6461 (Reply 222):
As you'll see from Ferpe's analysis therein, the A380 has only slightly worse L/D than contemporary airliner competition.

I went back to that thread, and of course found out about Ferpe's method :
He went to same conditions ( FL 370, M.85 ) and looked for the weight at which Cl = .50... From that point, he computed the drag, hence the Cd and derived the lift-to-drag ratio.
He explained it rather clearly, so as a matter of fact the Cl/Cd of his Excel sheet has nothing to do with either best L/D, or best cruise alpha. It is just an illustration of a very specific point in the aircraft utilisation... meaning you cannot, in intellectual honesty, take these figures as criteria of superiority of a design on another. For that, you'll have to integrate the whole flight.... and these airfoils certainly don't match.
(I'm quite sure that modernj / high aspect ratio designed wings will have an advantage... but have you taken into account the influence of early cruise steps, *commercial speed*....etc...

Taking all the above, I very much doubt the validity of your study... There are too many errors, too many intuitive assumptions for it to be of any value.

Ferpe warned you - personally -of the difficulty of that study. These are his exact words :
" In fact if you don't know how a civil airliner is flown and why, (step cruise etc), run every aspect of PianoX and learn to understand why it does what it does. If you don't understand that you can't model airplanes, not even if you had my excel..."

You should have listened.

[Edited 2015-08-18 04:22:02]

[Edited 2015-08-18 04:34:04]
Contrail designer
 
rheinwaldner
Posts: 1865
Joined: Wed Jan 02, 2008 4:58 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Tue Aug 18, 2015 1:20 pm

Guys are still not getting the big picture.

Even roughly estimated overall CASM values explain why some aircraft today sell better than others. I don't have to check any other parameter to recognize that. The correlation between aircraft efficiency (=CASM) and market share is often so striking, that in some cases you can even derive fleet wide CASM figures by just checking how much an aircraft was sold.

I have a book here called "Aircraft Finance" with 384 pages.

The term asm and casm are mentioned all over especially to compare different aircraft on all levels. Therefore speedbored's refusal to accept one of the mentioned CASM definitions comes across really strange.

In the book e.g. this sentence is written in the chapter "Aircraft Efficiency: Operating and Financial Metrics":
"With greater fuel efficiency and longer average stage lengths, the 737-700 has a CASM of 8.18 cents per seat mile while the A319 has a CASM of 9.39 cents per seat mile."

So dear speedbored, do you still insist that you have no clue what could be meant by this sentence? You have no idea how CASM should be understood here?

Chapter 10 is called "Airline Fleet Selection Process". There you find in the "Cost efficiency" section the following quote:
Armed with technical and operating data, an airline can undertake further analysis of aircraft choices by looking at the trade-off between key metrics, including CASM, seat capacity, and range (see Figures 10.5-10.13). Figure 10.5-10.6 compare the seat capacity of different aircraft types and their corresponding CASM.

Airlines don't evaluate based on CASM? That claim was nothing than embarassing. CASM is a key metric for aircraft evaluation.

So we have CASM as a strong indicator how good an aircraft will sell. And we have the today A380, see the correlation between its success and the lack of a distinct efficiency improvement against the 777. And nobody denies that it has wonderfully designed wings which are very good despite the AR. But the question remains how much better would it be if the wingspan would be larger? IMO a valid and rather easy to be answered question. The more tricky part would be to predict the resulting market share, if e.g. this new A380 would be 20% more efficient per seatmile than the 779X (20% is an example, put in whatever you think to be valid)? About that I could undertstand to have disagreements then...

Quoting Pihero (Reply 224):
So, taking the same notation you used : Di ~ (lift^2) / (span^2) ... and forget air density as it is a constant in these conditions.

So increasing the span would really help the A380 right? Regardless how good the wings are today. Increasing the span reduces Di by the power of two. Would that not be an argument for Matts "larger span" proposals?
Many things are difficult, all things are possible!
 
User avatar
speedbored
Posts: 2230
Joined: Fri Jul 19, 2013 5:14 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Tue Aug 18, 2015 2:25 pm

Quoting rheinwaldner (Reply 225):
I have a book here called "Aircraft Finance" with 384 pages.

Oh dear, someone else who thinks that textbooks reflect the real world.

Quoting rheinwaldner (Reply 225):
Therefore speedbored's refusal to accept one of the mentioned CASM definitions comes across really strange.

Well, so far, I have only been presented with one definition for CASM and, embarrassingly, it did not contain any mention of a definition for the number of miles, without which it is completely useless, as no figure can be calculated. So, of course I did not accept it.

Quoting rheinwaldner (Reply 225):
So dear speedbored, do you still insist that you have no clue what could be meant by this sentence? You have no idea how CASM should be understood here?

Yes, I fully understand that sentence and, unlike many people here, I also fully understand exactly what CASM can and cannot be used for. But, it seems, you do not. You seem to have failed to notice the "longer average stage lengths" qualifier on the 737 number, which renders any comparison between the two figures apples to oranges.

Quoting rheinwaldner (Reply 225):
Airlines don't evaluate based on CASM? That claim was nothing than embarassing. CASM is a key metric for aircraft evaluation.

Well it is very hard to comment without being able to see the book that you claim to be looking at. But do you have any evidence that any airline has ever used that book?

I have real experience, working with 72 different real airlines, on real aircraft acquisition projects. Not one of them has ever used CASM, or any remotely related metric, to make an aircraft purchase decision. I fail to see why relating my real experiences should be "embarrassing".

Quoting rheinwaldner (Reply 225):
So we have CASM as a strong indicator how good an aircraft will sell.

"in your opinion". I, many others, and all of the airlines I have ever worked with, prefer to look at more pertinent and meaningful numbers.

I have yet to see a fair definition of CASM that can be used by an airline to make such a comparison. Of course, after collecting their own proposed route data, applying their own seating configurations, and working out their own costs, airlines could calculate CASM for each of the options they are considering and decide purely on that basis (though they would still be taking a huge risk on revenue/profit if there were more than insignificant seat count differences). But this would be on the basis of an airline specific definition of CASM, and add a legally unacceptable risk to the decision if there were seat count differences.

The best evidence that I have for the fact that CASM is not useful for such a comparison is that, when it comes to narrowbodies, both Airbus and Boeing claim to have the CASM advantage - that just goes to show how easily it can be manipulated to give the wrong answer.

I have already asked this at least twice but have yet to receive a reply, so I'll ask again:
Given that, for publicly listed airlines, management are legally obliged to only make decisions that they believe will maximise shareholder value, how exactly can they show that they have fulfilled that obligation if they make an aircraft purchase decision on the basis of CASM?

Quoting rheinwaldner (Reply 225):
So increasing the span would really help the A380 right?

Not if it means that it cannot be operated at many of the airports that it currently serves. There are good reasons why the Airbus designers kept it within the 80m box, many of which cannot be met even by the addition of folding wingtips.
 
Pihero
Posts: 4318
Joined: Mon Jan 31, 2005 5:11 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Tue Aug 18, 2015 4:18 pm

Quoting rheinwaldner (Reply 225):
In the book e.g. this sentence is written in the chapter "Aircraft Efficiency: Operating and Financial Metrics":
"With greater fuel efficiency and longer average stage lengths, the 737-700 has a CASM of 8.18 cents per seat mile while the A319 has a CASM of 9.39 cents per seat mile."

Why do you shoot your own foot ?
With that casm disadvantage, how do explain that the 319 has outsold the 737-700 ; 1472 to 1114 that's 57 vs 43 %. at end of July 2015 ?

Quoting rheinwaldner (Reply 225):
The correlation between aircraft efficiency (=CASM) and market share is often so striking, that in some cases you can even derive fleet wide CASM figures by just checking how much an aircraft was sold.

Doesn't look like it's the case, does it ?

Quoting rheinwaldner (Reply 225):
So increasing the span would really help the A380 right?

I never said otherwise, but I looked at the ways to implement that... and I don't see how, for the moment.
1/- Our friend has *proven* otherwise ( see my post above) and probably based his demo on that premice, among others.
I'm not buying that sort of thing without a detailed computation... Just showing bare results on a spreadsheet in which I have demonstrated at least three glaring errors of postulate doesn't get my vote.
2/- I'm way past the time I believed in Father Xmas :

Quoting Matt6461 (Reply 217):
Here's the A380NEO modeled with 80m wing and winglets. Wing area is 6900ft2, thrust is ~196k lbs, MTOW is 970,000lbs, OEW is ~513,000lbs. The wing is 48,000lbs lighter, the engine system ~25,000lbs lighter, empennage ~19,000lbs lighter, landing gear ~10,000lbs lighter.
102 000 lbs saved on the OEW, which then become 310 000 lbs saved on MTOW (btw, where is the MZFW ?.. very very important, you know ) on a 6 000 nm flight ?...
As an A380 fan, I really would like to see that... in Xmas 2215 very probably.

Sorry, I'm less and less interested in buying your project.
Contrail designer
 
User avatar
Matt6461
Topic Author
Posts: 2991
Joined: Wed Oct 16, 2013 9:36 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Tue Aug 18, 2015 4:47 pm

Quoting speedbored (Reply 223):
The calculation is to make allowance for the fact that the adding dihedral angle changes the angle at which lift forces act and, therefore

You're not saying anything different here, despite your use of bold.

Quoting Pihero (Reply 224):
If we believed that proportionality, the shortest possible wingspan will have the lowest induced drag !

You've identified a glaring clerical error in my post, not in my spreadsheet. This is the problem with my fanclub here:

You guys represent that portion of the internet that isn't interested in cooperative dialogue, you're just out to criticize and/or self-aggrandize. You haven't made one positive, constructive suggestion. You haven't even looked at the spreadsheet yet you spend a lot of time criticizing. You know that I know that Di decreases with span - that's the whole reason for the folding wing. If you had bothered to look at the spreadsheet you would have seen that the relationship is correct in it.

If you were a decent person trying to help things along, a simple "I think you misspoke here" would have been what you have said. Instead you either pretend or deceive yourself that I have created a spreadsheet model that directly contradicts everything I have been saying over 200 posts - that induced drag gets worse as span increases. You should reconsider why you participate in these forums and what your goals are.

Quoting Pihero (Reply 224):
And why, may I ask all aircraft flying at the same altitude, the same Mach numlber, the same temperature will have different values of air density ?

They don't.

Quoting Pihero (Reply 224):
I went back to that thread, and of course found out about Ferpe's method

I don't think you understand what the model does. Unlike Ferpe's model, it compares a few variables throughout the flight regime. I don't need to know every fine detail if I'm only tweaking a few variables - unless there is something that I've left out that is correlated AGAINST the improvement I'm trying to show. The missing values would be statistical noise or opportunities for further delta that I've passed up.

I'd go into further detail if I thought you were in good faith here.

Quoting Pihero (Reply 227):
2/- I'm way past the time I believed in Father Xmas :
Quoting Pihero (Reply 227):
102 000 lbs saved on the OEW, which then become 310 000 lbs saved on MTOW (btw, where is the MZFW ?.. very very important, you know ) on a 6 000 nm flight ?...

Same response. I'd go into further detail if I thought you were in good faith. I've presented, very transparently, how the model works. If you have any specific, substantive points, we can engage.

[Edited 2015-08-18 10:08:16]
 
User avatar
Matt6461
Topic Author
Posts: 2991
Joined: Wed Oct 16, 2013 9:36 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Tue Aug 18, 2015 4:55 pm

Quoting speedbored (Reply 226):
Oh dear, someone else who thinks that textbooks reflect the real world.

Gross.

Quoting speedbored (Reply 226):
I have real experience, working with 72 different real airlines, on real aircraft acquisition projects. Not one of them has ever used CASM, or any remotely related metric, to make an aircraft purchase decision. I fail to see why relating my real experiences should be "embarrassing".

2 main reasons why it's embarrassing:

(1) It's flatly contradicted by real-world facts, in which high-level comparisons of similar widebodies always favors the one with lower CASM, and in which no higher-CASM, higher-capacity airliner ever excells against lower-CASM, lower-capacity competition

[Edited 2015-08-18 10:40:51]
 
User avatar
Matt6461
Topic Author
Posts: 2991
Joined: Wed Oct 16, 2013 9:36 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Tue Aug 18, 2015 4:58 pm

Continued from above...

(2) Given the obvious wrongness of (1), one wonders why you stick with it. Perhaps it's because advancing argument (1) enables you to remind A.netters of your personal credentials. "Did I mention I've been involved in real world purchasing decisions and we don't use something named CASM?" "Hey guys did I mention something about my experience yet?" This is embarrassingly needy, validation seeking behavior, especially for someone in their 50s.
 
User avatar
Stitch
Posts: 27367
Joined: Wed Jul 06, 2005 4:26 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Tue Aug 18, 2015 5:39 pm

Quoting speedbored (Reply 226):
I have real experience, working with 72 different real airlines, on real aircraft acquisition projects. Not one of them has ever used CASM, or any remotely related metric, to make an aircraft purchase decision. I fail to see why relating my real experiences should be "embarrassing".
Quoting Matt6461 (Reply 229):
(1) It's flatly contradicted by real-world facts, in which high-level comparisons of similar widebodies always favors the one with lower CASM, and in which no higher-CASM, higher-capacity airliner ever exceeds against lower-CASM, lower-capacity competition...

Without infringing on any NDAs or proprietary/confidential information, could you give us an idea of what criteria the airlines you have worked with have used to make their decisions?

It strikes me as reasonable that many of those criteria in some way would positively influence "CASM" and that the axiom that "lowest CASM wins RFPs" is a by-product of the actual criteria rather than the criteria itself.

In which case, both of you are correct and we can move on. 
 
User avatar
Matt6461
Topic Author
Posts: 2991
Joined: Wed Oct 16, 2013 9:36 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Tue Aug 18, 2015 7:36 pm

Quoting Stitch (Reply 231):
It strikes me as reasonable that many of those criteria in some way would positively influence "CASM" and that the axiom that "lowest CASM wins RFPs" is a by-product of the actual criteria rather than the criteria itself.

This is the argument that I've been making to Speedbored for a while now: that he's looking for something named "CASM," while ignoring the fact that all the supposedly "non-CASM" factors he cites are components of CASM as computed in the OP's linked stories and related model: fuel, capital, mx, labor, and fees.

I appreciate your contributions, Stitch and Rheinwaldner, but I'd suggest this is a pointless debate by now. Speedbored has said as much:

Quoting speedbored (Reply 193):
"I'm wrong, you are right". Well you'll never get that.

There's no point arguing with someone who says he'll never admit he's wrong- they're no longer arguing in a spirit of truth and intellectual curiosity. They're playing a different game that isn't susceptible to reasoned argument, and playing their game will waste your time. This is why I didn't respond to his last post about CASM; I'd advise the same for everyone.

EDIT - I only mean the "CASM doesn't matter" debate is pointless. The real discussion - whence with the A380 and how? - that should continue.  Smile

[Edited 2015-08-18 12:38:11]
 
User avatar
Matt6461
Topic Author
Posts: 2991
Joined: Wed Oct 16, 2013 9:36 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Tue Aug 18, 2015 9:28 pm

Quoting Pihero (Reply 224):
Wing loading at level cruise has nothing to do with aerodynamics

This is a patently false statement. Wing loading influences, inter alia, the best altitude for cruise, which strongly influences cruise L/D. Generally speaking, the higher the cruise altitude, the better the cruise L/D.

Quoting Pihero (Reply 224):
[wing loading] is at any given moment a constant.
Quoting Pihero (Reply 224):
And why, may I ask all aircraft flying at the same altitude, the same Mach numlber, the same temperature will have different values of air density

We may be having language difficulties. It seems you think all aircraft are flying at the same altitude? And it seems that you think I am saying that wing loading somehow changes the air's density at constant altitude?

Let me explain, in case this wasn't clear to others as well:

The model assumes that planes with lower wing loading cruise at higher altitude. Specifically, they will climb, relative to a higher-loaded wing, until lift/wingM2=weight/wingM2. Holding speed and Cl constant, a lower-loaded wing has to cruise in lower air density, i.e. at higher cruise altitude.

Quoting Pihero (Reply 227):
I have demonstrated at least three glaring errors

As I detailed above, one of the "glaring errors" was just a typo in the post, not the spreadsheet. And your refusal to see it as a typo, after I've said repeatedly that greater span reduces induced drag (not the opposite), demonstrates that you're approaching this discussion in bad faith: rather than really discussing how to model airliner performance, you're just looking for chances to attack me.

What are the other supposed errors? As I demonstrate above, you have a fundamental misconception of how air density works in this model, and you seem to fundamentally misunderstand wing loading if you think it irrelevant to aerodynamics. But you probably haven't even looked at the spreadsheet?

I don't really care about attacks, my self-esteem isn't dependent on anonymous airline forums where I'm pursuing intellectual curiosity as an amateur. When you said I will have "egg all over my face" I actually found that honest aggression kind of endearing for its transliterated childishness. If you give honest attention to ideas, you can pretty much call me whatever names you want. I am, however, annoyed when I think I'm in a discussion based on intellectual curiosity and suddenly it's just a pissing contest. Let's avoid that. Either make a serious effort to understand what I'm actually saying or what's the point here? Easy to just ignore the thread.

[Edited 2015-08-18 14:31:24]
 
Pihero
Posts: 4318
Joined: Mon Jan 31, 2005 5:11 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Tue Aug 18, 2015 10:25 pm

Quoting Matt6461 (Reply 228):
You guys represent that portion of the internet that isn't interested in cooperative dialogue, you're just out to criticize and/or self-aggrandize.

Pots and kettles, methinks...

You've come to this thread with the great news that you have solved Airbus problem, albeit at a price, with an unbeatable
solution : change the wing and everything will derive from that : hundreds and thousand pounds of shaved weight, incredible specific consumption with much smaller engines, etc...

Problem is that I'm a technician and I've studied a lot of aerodynamics, I've taught performance / flight planning and management and I'm quite familiar with regulations and certification problems.

Your study has many elements that don't add up, probably the reason why you're just publishing ratios ( NWO vs CEO).
So let's take your spreadsheet :
1/- You advertise MTOW = 970 000 lbs, but you start your study at 973 728 lbs
2/- Your final weight is 638 020 lbs
so I presume that the weight delta is due to Fuel Burnoff => 973 728 - 638 020 = 335 708 lbs
That's an interesting figure, especially when mixed with OEW =============> 513 000 lbs... and ...
your traffic load of 534 passengers that you estimated at TL ==============> 120 150 lbs
.............................................................................TOTAL ==================> 968 858 lbs
... which compared to the TOW 973 728 - 968 858 = Fuel remaining ========= > 4 870 lbs
considering that as the sum of the remaining reserves ( 5% burnoff + 45 minutes at 1500 ft, roughly 25 000 lbs), you are way out of the legal requirements.
3/- The trip you considered is just 6 000 nm ... That means that with a full passenger load, no cargo and basically minimal baggage you are at the very end of your aircraft performance. ( the A388 flies 8 000 nm, with reserves with that payload....+ luggage ).

Is CASM still the almighty criterium ? Who wants an aircraft only capable of carrying 534 pax on a 5 500 nm sector, with no cargo and no frills ?

Quoting Matt6461 (Reply 228):
Quoting Pihero (Reply 224):
And why, may I ask all aircraft flying at the same altitude, the same Mach numlber, the same temperature will have different values of air density ?

They don't.

Oh ! but you write and compute otherwise in your spreadsheet : column *U* = "Air density ratio", in which you take the A380 as a baseline, an aspect that confirms your :

Quoting Matt6461 (Reply 171):
To make things simpler for wing comparisons that primarily alter span, weight, and area, I propose focusing on the following relationships:

[note "~" means "proportional to"]

Induced drag = Di ~ (span^2)/(lift^2)/(air density) http://en.wikipedia.org/wiki/Lift-induced_drag

Parasitic/form drag = Dp ~ (wetted area)*(Cdp coefficient)*(air density)

Air density at cruise ~ wing loading

ignoring your *clerical mistake*, one can see that Di and Dp actually are real parameters affected by air density, which changes with pressure - i.e altitude - and temperature... Nothing else... You cannot allocate in the same conditions different values - let alone ratios of values - to the A380 and its successor.
And I reiterate, wing loading is the ratio W/S ( weight over wing area, however you consider that value : Airbus, exposed....).

The last point is that you have never considered how strongly that wing is going to be built : it has to withstand a load factor of 3.75, meaning 3.75 the nominal wing loading ( it's 1.5 times the 2.5 max load factor, to destruction).
At that sort of load, all your wing structure will find increased shear / torsion / compression loads that require studies way above my pay grade and equipment... and you cannot derive that structure strength from the A380 data : the loads will be relatively much higher as the wing is smaller, narrower, the material is different... and much different in their respective importance. Torsion loads will be probably be very important, so maybe - just maybe you'd have to consider a metal box and spars...

That's why I asked you what MZFW you were considering.

Last comment : your burnoffs are wayyyyyyyy out what we see actually ; it's here that I'm using an accurate parameter that we call in France *Transport coefficient*.
It is simply the ratio TOW / LW in which LW + Fuel Burnoff = TOW.
It does of course depend on the sector length ( or more accurately sector time ). For a 12 hour flight, it is ~ 1.40, which means, if your airplane is at least as efficient as a 777w or an A333.
In this case Boff = TOW x (1 - K) / K = TOW x .4 /1.4 ==> 973 728 X 2/7 = 278 208 lbs, which compared to your Boff of 335 708 lbs is some 57 500 lbs lower ; That figure brings us much closer to reality. ( your transport coefficient is exactly 1.53, which is very very very poor, 707 like )

So I have a feeling that you'd have to go back to your sheet, 'cause your project doesn't seem to be that efficient.
(Which demonstrates that, again, casm is certainly not the main criterium)

BTW, your derived K for the A388 is K = 1 268 000 / 746 350 = 1.70, which is a ridiculous value, not even worthy of an old Comet.
Contrail designer
 
User avatar
speedbored
Posts: 2230
Joined: Fri Jul 19, 2013 5:14 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Wed Aug 19, 2015 12:52 am

Quoting Matt6461 (Reply 228):
You guys represent that portion of the internet that isn't interested in cooperative dialogue

No, we represent the portion of the internet that is interested in facts. There are plenty of other websites out there for fantasists.

Quoting Matt6461 (Reply 228):
If you have any specific, substantive points, we can engage.

Almost every one of Pihero's posts contains specific, substantive points. Just because you don't like what he is saying doesn't mean it is not there.

Quoting Matt6461 (Reply 229):
It's flatly contradicted by real-world facts, in which high-level comparisons of similar widebodies always favors the one with lower CASM, and in which no higher-CASM, higher-capacity airliner ever exceeds against lower-CASM, lower-capacity competition

There you go changing the argument again. Now, having had a narrowbody example, that disproves your assertion, posted by one of your "supporters", you're only interested in widebodies. And it is also now "exceeds" instead of "succeeds".

Please explain why exactly it is that CASM is only a valid metric now for comparison of widebodies, not narrowbodies?

Quoting Matt6461 (Reply 230):
Given the obvious wrongness of (1)

Yes, I agree, your first reason is quite obviously wrong.

Quoting Matt6461 (Reply 230):
Perhaps it's because advancing argument (1) enables you to remind A.netters of your personal credentials. "Did I mention I've been involved in real world purchasing decisions and we don't use something named CASM?" "Hey guys did I mention something about my experience yet?" This is embarrassingly needy, validation seeking behavior, especially for someone in their 50s.

Oh give the personal attacks a rest - they're really getting tiresome and they do absolutely nothing to improve your credibility. I've been around long enough to really not give a damn what people think about me, and I have absolutely no need at all to impress anyone.

Quoting Matt6461 (Reply 232):
all the supposedly "non-CASM" factors he cites are components of CASM

Not even close to true.

Quoting Matt6461 (Reply 232):
fuel, capital, mx, labor, and fees.

Also not true. I have never claimed that any of those are not components of CASM.

Quoting Matt6461 (Reply 232):
There's no point arguing with someone who says he'll never admit he's wrong

I have never said anything of the sort. I said only that I will not say that I am wrong about my claim that airlines do not base their purchase decisions on CASM, because I am in no doubt whatsoever that I am right on that. When I am wrong, I admit it - it makes life a lot easier than this nonsense, after all.

Quoting Matt6461 (Reply 232):
they're no longer arguing in a spirit of truth and intellectual curiosity.

All I am interested in is the truth. And this is where we differ - before I post facts, even those that I am pretty certain of, I almost always do some quick research to check that I actually remember things correctly. You, on the other hand, just go ahead and post things as fact without even a cursory check (see your claims on wing-twist, dihedral, engine-out-yaw reason for runway-taxiway clearance, for particularly humorous examples).

Quoting Matt6461 (Reply 232):
This is why I didn't respond to his last post about CASM

Yes, of course. It couldn't be because I asked the same inconvenient question that you have now failed to answer 3 times, could it?

Quoting Matt6461 (Reply 233):
This is a patently false statement.

No, Pihero is correct. Wing loading is a very simple calculation - loaded weight divided by wing area. It doesn't matter what the wing aerodynamics are like, they will not alter the wing loading. Wing loading reduces gradually during a flight, as weight is thrown away by the engines, and will also increase or decrease slightly in accordance with the vertical acceleration whenever the aircraft alters its rate of climb or descent.

Quoting Matt6461 (Reply 233):
We may be having language difficulties.

Have you considered that it might help if you stopped using so much esoteric language and legalese? It doesn't impress anyone. This is, after all, a global aviation website with very many contributors and readers who do not have English as their first language.

Quoting Matt6461 (Reply 233):
It seems you think all aircraft are flying at the same altitude?

I'm certain Pihero knows that that is not the case. It does, however, seem that you think that all aircraft are allowed to fly at their natural cruise altitude, which is simply not true. Pihero did point you at Ferpe's warning - you really should not have ignored it.

Quoting Matt6461 (Reply 233):
And it seems that you think I am saying that wing loading somehow changes the air's density at constant altitude?

Maybe that is because it is what you said:

Quoting Matt6461 (Reply 171):
Air density at cruise ~ wing loading

The only commercial aircraft that I am aware of that was actually permitted to keep climbing and accelerating, until it hit its own natural speed and altitude limits, was Concorde. Every other commercial aircraft has to adhere to the flight levels that are assigned/permitted by ATC, and/or as defined by flightpath rules in uncontrolled airspace, and/or by certification limits.

Cruise altitude is rarely, if ever, the maximum altitude that an aircraft can achieve, even when an aircraft is permitted to climb to the highest achievable flight level, this could still be considerably lower than the highest altitude it could achieve (due to flight level separation requirements). Also, every commercial aircraft will have a maximum certified flight level, regardless of what the wing could actually achieve, due to the min-time/max-speed requirements for a descent in the case of a depressurisation.

Quoting Matt6461 (Reply 233):
The model assumes that planes with lower wing loading cruise at higher altitude.

Then the model is incorrect on that point. It is also incorrect to assume that all aircraft cruise at the same airspeed.

Quoting Matt6461 (Reply 233):
I don't really care about attacks .... I am, however, annoyed when I think I'm in a discussion based on intellectual curiosity and suddenly it's just a pissing contest. Let's avoid that.

Your hypocrisy really is impressive. Just in this thread, you have labelled me:
"ungenerous", "not enough of a man", "too deep in the weeds", "pedantic", "simplistic", "ridiculous", "not credible", "underwhelming", "unable to maintain conceptual distinctions", "insecure", "vain", "embarrassingly needy", "validation seeking", "bullshitter" and "stupid" (though the mods deleted those last two). And that is on top of the previous PMed insults, such as "combine being unpleasant with being, frankly, stupid", "you're either not really in the airline business or else that, wow, there are some dumb people in that business", "that just facially wrong, moronic comment" or "all the nonsensical, bitter, pedantic shit you spew".

If you want to avoid it then, perhaps, you should not be dishing it out.

I suspect that you are making these personal attacks, and then playing the victim, in the hope of making people who disagree with you, or point out the holes in your arguments, give up and go away, and to elicit sympathy from others. Or maybe you hope to trigger some sort of reaction that would get us banned. It's not going to work - insults are of absolutely no consequence to me unless they come from someone I respect.
 
User avatar
Matt6461
Topic Author
Posts: 2991
Joined: Wed Oct 16, 2013 9:36 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Wed Aug 19, 2015 12:52 am

Quoting Pihero (Reply 234):
3/- The trip you considered is just 6 000 nm ... That means that with a full passenger load, no cargo and basically minimal baggage you are at the very end of your aircraft performance. ( the A388 flies 8 000 nm, with reserves with that payload.... luggage ).

A lot of your post involves a simple misunderstanding:

The numbers I posted represent a max range trip for both aircraft, but the model is easily adjusted for shorter trips. I posted the max range trip to demonstrate the MTOW constraint.

To estimate a 6,000nm trip, you just change mission TOW in cell O131, then "fuel burn increment" in cell O21. I estimated 6,000nm by using a CEO TOW of 1,100,000lbs. This changes the fuel delta slightly, by about .5%, which changes the trip cost delta by even less. I quoted a trip cost delta of "~19%," which remains true (19.2% to be exact per the model).

Quoting Pihero (Reply 234):
1/- You advertise MTOW = 970 000 lbs, but you start your study at 973 728 lbs

I accept a slightly lower nominal range for the A380NWO, but increasing MTOW to 974,000lbs would barely change the results. If the A380's nominal range is 8200nm, this model shows the NWO at ~8100nm. Not a big deal.

The reason for accepting slightly lower nominal range is that the NWO could trade payload for range "much more cheaply." I.e. because gallons/mile is much lower than for CEO, dumping 1,000lbs of payload gets you a lot more range. Per the model, dumping 10 pax gets you down to 970,000lb mission TOW at CEO's max range. So few of CEO's real missions are payload-restricted that I don't see this as a huge issue. Meanwhile, dumping 50 pax would get it to 9,000nm range, while still having far better CASM than 777-8. The A380 can't carry much cargo, so excessive range, which might otherwise come into play at MZFW, isn't as beneficial for it.

That's a judgment call about payload/range, whether MTOW is set 5,000lbs higher or lower isn't a big deal.

Quoting Pihero (Reply 234):
You cannot allocate in the same conditions different values - let alone ratios of values - to the A380 and its successor.

I'm having trouble understanding what you mean here. Please explain what you think I am doing, and how it is incorrect.

Quoting Pihero (Reply 234):
The last point is that you have never considered how strongly that wing is going to be built

I have been very transparent about the weight model I am using - the wing weight index I linked above several times. If you want to suggest a better model, or specific refinements to it with justified reasoning, you are welcome to do so.

Quoting Pihero (Reply 234):
That's why I asked you what MZFW you were considering.

I've mentioned the payload before - 170,000lbs - and have provided an OEW. It's also in the spreadsheet on page 2. MZFW is just payload+OEW.

Quoting Pihero (Reply 234):
Last comment : your burnoffs are wayyyyyyyy out what we see actually

I may have underestimated DOW for both planes. I added unusable fuel and 6,000lbs for miscellaneous items to both planes. If there is an error, it shouldn't massively effect the comparative picture - both planes may have too high a fraction of fuel weight.

Which values would you assign for unusable fuel and for non-OEW items to get DOW?
 
User avatar
speedbored
Posts: 2230
Joined: Fri Jul 19, 2013 5:14 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Wed Aug 19, 2015 12:56 am

Quoting Stitch (Reply 231):
Without infringing on any NDAs or proprietary/confidential information, could you give us an idea of what criteria the airlines you have worked with have used to make their decisions?

Well, as you ask so nicely, sure I can.  

I've already mentioned quite a few but, rather than attempt to post anything more here, given Matt's continued hostility, I will spend a little time considering how to present it clearly, with examples, and start a separate thread on it.

Quoting Stitch (Reply 231):
It strikes me as reasonable that many of those criteria in some way would positively influence "CASM" and that the axiom that "lowest CASM wins RFPs" is a by-product of the actual criteria rather than the criteria itself.

True, and I have already said as much, with provisos, myself. Though there are still many very important factors that do not influence CASM in any way. Availability, for example, is almost always dismissed as irrelevant but factors in very many more RFPs than most people seem to assume.

Unfortunately, this axiom only really holds true when comparing similar aircraft, with broad market appeal, so that otherwise significant airline/route differences average themselves out. When one or both of the aircraft being compared could be considered "niche" (e.g. is limited in the number of routes that it can viably operate on, or has "special" performance characteristics) then this most certainly is not true. The subject of this thread definitely falls into this particular category.

I'll see what I can come up with.
 
User avatar
Matt6461
Topic Author
Posts: 2991
Joined: Wed Oct 16, 2013 9:36 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Wed Aug 19, 2015 1:41 am

Quoting speedbored (Reply 237):
I will spend a little time considering how to present it clearly, with examples, and start a separate thread on it.

Great idea for another thread. I look forward to it.

Quoting speedbored (Reply 235):
Quoting Matt6461 (Reply 232):
fuel, capital, mx, labor, and fees.
Also not true. I have never claimed that any of those are not components of CASM.

I have to point out that you claimed exactly this, and were *shocked* I didn't know it:

Quoting speedbored (Reply 154):
Quoting Matt6461 (Reply 129):
Such as? On the cost side, these are?

Again, you seriously have to ask? En-route costs, landing fees,


[Edited 2015-08-18 18:44:18]
 
User avatar
seahawk
Posts: 9867
Joined: Fri May 27, 2005 1:29 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Wed Aug 19, 2015 5:11 am

Am I the only one that thinks that making a VLA more payload restricted is a bit of moving in the wrong direction?

Also I highly doubt the reduction of MOEW given, considering that the longer wing will mean that the fuselage will have to accept stronger loads from the wing due to the increased wing span.

And finally I am waiting to be shown howyou would do the new wing with the existing wingbox. Imho we would be taking about a completely new aircraft. It might look a bit like an A380, but new wing, new wing box, new gear, different materials and a new landing gear, means that practically every major component will be new.

I also fail to understand what is an Air Density Ratio (air density should be constant for the purpose of the discussion) and how the form and roughness factor was calculated. Because the leading edge (the part which creates most drag) was increased by 13%, yet this increase in drag is nowhere to be found.
 
User avatar
speedbored
Posts: 2230
Joined: Fri Jul 19, 2013 5:14 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Wed Aug 19, 2015 5:36 am

Quoting Matt6461 (Reply 238):
I have to point out that you claimed exactly this, and were *shocked* I didn't know it:

Quoting speedbored (Reply 154):
Quoting Matt6461 (Reply 129):
Such as? On the cost side, these are?

Again, you seriously have to ask? En-route costs, landing fees,

Nice try but you really aren't fooling anyone except yourself. Given that your "such as?" question was posed in response to my initial statement that:

Quoting speedbored (Reply 121):
there are also many other route-related factors that affect CASM, many of which can vary with aircraft type.

Perhaps you could explain to us how exactly you think that "factors that affect CASM" can ever possibly be interpreted as claiming that those factors are "not components of CASM"? You've made many very strange claims in this thread but that one is truly ludicrous.
 
User avatar
Matt6461
Topic Author
Posts: 2991
Joined: Wed Oct 16, 2013 9:36 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Wed Aug 19, 2015 6:15 am

Quoting seahawk (Reply 239):

Am I the only one that thinks that making a VLA more payload restricted is a bit of moving in the wrong direction?

The model showed a ~100nm reduction in pax bags range. But an increase in range with, say, 80% of pax, at which it would have better CASM. All that can be changed quite easily - gaining 100nm range isn't very expensive in operating cost.

EDIT - the forum somehow cut off some text here.

The intuition for lower nominal range for A380 is this: A380 doesn't have the ability to use "excess range" for hauling cargo. It's rarely weight-limited, mostly volume-limited. Whereas gaining 100nm of MZFW range for 777X would mean hauling a significant portion of trip revenue in cargo over a greater distance, extending the A380's MZFW range means hauling absolutely less cargo, which represents a relatively lower fraction of trip revenue. IMJ the A380 wouldn't gain much in marginal sales by extending its Pax+bags range. QF's DAL-SYD leg is the only one that I know to be payload-restricted for passengers. IMG it's better to give up a bit of nominal range for better efficiency than to present a marginally better sales proposition to one or two customers. But this is really fine detail stuff and if you wanted to increase MTOW by ~5,000lbs it wouldn't change much.

Quoting seahawk (Reply 239):
Also I highly doubt the reduction of MOEW given, considering that the longer wing will mean that the fuselage will have to accept stronger loads from the wing due to the increased wing span.

You're talking about wing-body join. I think that aspect of weight is ambiguous, as I'll explain.

But first, there's also the factor of fuselage loads from empennage:
Load from vertical stablizer is lower due to (1) lower thurst=lower moment from engine-out conditions and (2) lower gust-force due to smaller vertical stabilizer.
Load from from horizontal stabilizer is lower because HorStab is smaller due to lower weight, which means lower rotation requirement. Smaller HorStab means lower max loading in gust conditions.

Back to wing-body:
-the -1G flight condition is a big constraint - it's not just MZFW bending moment. In this condition, the lower MTOW and wing wing weight means there's less shearing force from the downward deflection of the wings. This condition definitely has some implications for weight: Airbus had to reinforce wing-body join when it upped A380 MTOW.
-If we're only talking about the 80m version of the A380NWO, the bending moments at wing-body join will actually be smaller: payload is restricted and lighter landing gear and empennage decrease bending moment. For the 80m version, at least, which might be better than the folding-wing version, the fuselage join should be lighter

Quoting seahawk (Reply 239):
And finally I am waiting to be shown howyou would do the new wing with the existing wingbox.

Wingbox would be redesigned. Do you mean how I would fit it within the current fuselage? Well the CEO's wing shortens the wing box by "kinking" the front spar "prematurely." You can see this effect here:
http://i15.photobucket.com/albums/a357/thezeke/350xwb/1a6750af.png

Getting rid of the "kink" could extend the front spar to the front of a wingbox of equal dimensions to the current wingbox. It would also probably save weight in the outer wing box: the "kink" isn't free structurally; it's a design decision made to allow a shorter center wingbox and thereby greater room for cargo.

Quoting seahawk (Reply 239):
I also fail to understand what is an Air Density Ratio (air density should be constant for the purpose of the discussion)


Air Density varies with altitude, thus it is not constant throughout a flight regime.

But Air Density Ratio should probably be Air Pressure Ratio. I started using "Air Density" in an early version and for som reason stuck with it. But Air Pressure is related to Air Density and Temperature. Temperature doesn't vary much above FL 37, and most of the CEO/NEO/NWO's flight regime is above FL 37. So it's not a huge issue - Air Density would capture most of the effects I think.

In any event, Air Density/Pressure is just a proxy for cruise altitude. Because my model is purely comparative, I didn't calculate the actual flight levels for either CEO or NWO/NEO. I sought to capture the *relative* effects of different flight levels by comparing the density/pressure of air at which they fly. This factor has straight-forward effects on drag.

The total effect is also ambiguous depending on whether we're talking about the 80m+ or 80m NWO version. It helps the 80m+ version of the NWO, which has a lower wing loading than CEO therefore flies higher for most of a max-range mission. But it hurts the 80m version of the NWO, which has slightly higher wing loading than CEO and therefore flies lower than CEO (per the model).

TBH I'm least satisfied with how I modeled cruise altitude. I'm pretty satisfied that wing-loading generally correlates with cruise altitude, but the relationship is quite rough for many reasons. Regulatory restrictions limit cruise altitudes to 2,000ft increments, emergency descent requirements play a further role.

But, given that the 80m version achieves ~20% CASM delta despite being *adversely* effected by cruise altitude, this is another case where it's not necessary to my hypothesis that a new wing could give great benefit. Higher cruise altitude (~wing loading in my model) means better fuel efficiency. If that's dead wrong then the 80m version is even better than the model predicts. Even for the 80m+ version the differences aren't that great: if flying higher is impossible, then optimal solution is to shrink the wing further, saving weight.

I don't think it's dead wrong; I do think it's a little less accurate than ideal. Any suggestions for improvement?

No matter how the particulars shake out - lower wing loading for higher cruise or smaller, lighter wing for lower cruise - the trip fuel burn delta for A380NWO should still be in the neighborhood of 35% under the model. That's somewhat of a "magic number" that, in conjunction with smaller engines (lower mx) and lighter MTOW (lower fees), allows for ~20% CASM/trip cost delta. That 20% number is shorthand for a step-change that allows the A380 to present a fundamentally different value proposition. And that's what I think Airbus needs to target with any new A380. Not incremental revision to a product that isn't selling, but transformational change.

Quoting seahawk (Reply 239):
and how the form and roughness factor was calculated.

I didn't include those calculations in this version of the model. Note that I give the NWO a 1.8% advantage on this factor, which only effects Cdp, and therefore gives only a ~1% advantage.

But here's why:
-Ferpe fixes roughness for CFRP at 1.04; fixes Aluminum at 1.08. This explains a lot of the delta. As I said upthread, I'm not certain that these rosy predictions for CFRP smoothness have held.
-Wing Cdp is higher than fuselage Cdp per Ferpe and my own calculations. This is somewhat counterintuitive, but is attributable to the characteristics of bodies of rotation versus planar bodies. The NWO, with a smaller wing, has a lower proportion of higher-Cdp wing area, versus lower-Cdp fuselage area.
-Engines have much higher Cdp than either wing or fuselage. The NWO has much smaller engines, thus lower average Cdp.
-When I ran these numbers, it worked out to -1.8% Cdp delta. If anyone is interested in seeing the specific figures, I can reformat them for public consumption and post them.

Quoting seahawk (Reply 239):
Because the leading edge (the part which creates most drag) was increased by 13%, yet this increase in drag is nowhere to be found.

EDIT - meant to respond here...Why would the leading edge create most of the drag? It doesn't add induced drag, parastic drag is more a function of wetted area, and wave drag occurs at/behind the crest of the airfoil. Perhaps interference and control surface gap drag are highest at the leading edge (due to slat discontinuities in smoothness), but these forms of drag are far from predominant.

But if you're alluding to something I don't know - pray tell.

[Edited 2015-08-18 23:28:23]

[Edited 2015-08-18 23:38:43]
 
User avatar
seahawk
Posts: 9867
Joined: Fri May 27, 2005 1:29 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Wed Aug 19, 2015 6:54 am

Okay, I am done. What you propose is a new plane.
 
User avatar
speedbored
Posts: 2230
Joined: Fri Jul 19, 2013 5:14 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Wed Aug 19, 2015 8:29 am

Quoting Matt6461 (Reply 241):
with, say, 80% of pax, at which it would have better CASM.

Is this an attempt to disprove your own argument about the usefulness of CASM? Why not go even further and maximise CASM by flying the aircraft around empty?

Quoting Matt6461 (Reply 241):
If we're only talking about the 80m version of the A380NWO

He wasn't. That was why he said:

Quoting seahawk (Reply 239):
the longer wing
Quoting Matt6461 (Reply 191):
A new wing would have a shorter wing box

quote=Matt6461,reply=241]a wingbox of equal dimensions to the current wingbox.[/quote]
Seems even you are confused now.

Quoting Matt6461 (Reply 241):
as I'll explain.

So we now have an aircraft with:
a) longer wings that will push the centre of lift rearwards
b) wings with "the kink" removed, which will push the CoL a considerable distance further to the rear.
c) a lighter empennage which will push the centre of gravity forward
d) a smaller "HorStab" to maintain trim even though the the CoG and CoL are now quite a distance apart.
Seems to me that's going to make it very difficult for the pilots to keep it in the air. Assuming they can actually get off the ground in the first place.

Quoting Matt6461 (Reply 177):
sweep, thickness/chord, and airfoil profile, no? I'm keeping all those equal in my model.

You'll find this extremely difficult to manage after you take that "kink" out, btw.

Quoting Matt6461 (Reply 241):
the bending moments at wing-body join will actually be smaller

How can you be sure of that without doing the calculations? Lower mass can create greater forces if you increase the lever arm. Even with the 80m wing, the changed geometry will seriously impact the amount of fuel that can be carried in the wing to counteract some of the wing bending forces.

Quoting Matt6461 (Reply 241):
it's a design decision made to allow a shorter center wingbox and thereby greater room for cargo.

Ah, so it is not to provide increased fuel capacity, or to increase tailstrike clearance during rotation, or to make it easier to attach the undercarriage, or ...?

Almost every design decision has multiple drivers, and it is very rare for it to not involve compromise.

Quoting Matt6461 (Reply 241):
You can see this effect here

Nice picture of an A350 wing.

Quoting seahawk (Reply 242):
What you propose is a new plane.

No, I think he really is only proposing a changed plane. Seems to me that a new plane would probably be cheaper, though.
 
User avatar
Matt6461
Topic Author
Posts: 2991
Joined: Wed Oct 16, 2013 9:36 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Wed Aug 19, 2015 1:55 pm

Quoting speedbored (Reply 243):
CoG and CoL are now quite a distance apart.

This CoG and CoL worry me least about this design. A simple stretch of the aft fuselage would address it if needed. It would also allow an even smaller empennage. And we still have multiple other options to address the issue, such as deceasing sweep.

Quoting speedbored (Reply 243):
How can you be sure of that without doing the calculations?

I did the calculations. See Sheet 2.

Quoting speedbored (Reply 243):
impact the amount of fuel that can be carried in the wing to counteract some of the wing bending forces.

For the 80m version I was talking about, I did estimate that ZFW critical load bending moment at root is 4% percent higher (sheet 2). And paid for that in increased weight. Fuel bending relief is irrelevant at ZFW, obviously. The other bending cases, such -1G gust, are alleviated by lower fuel weight.

Quoting speedbored (Reply 243):
Seems even you are confused now.

Remember earlier when I mentioned a shortened wingbox as one *option* to deal with CoG/CoL issues? Well, here's a different reason not to use that particular option.

I generally appreciate your input on the design aspects of this thread, thank you. But saying things like "you're confused" when going through a multivariate, multi-path process - even radically simplified as here - that language goes back to a really unproductive posture doesn't it?

Throughout this process, from start to finish, I have said revisions are welcome. Would you like to suggest any specific revisions?

Quoting speedbored (Reply 243):
Almost every design decision has multiple drivers

Yeah even you're just half-designing a paper revision.

[Edited 2015-08-19 07:01:08]
 
Pihero
Posts: 4318
Joined: Mon Jan 31, 2005 5:11 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Wed Aug 19, 2015 2:55 pm

Quoting seahawk (Reply 239):
Am I the only one that thinks that making a VLA more payload restricted is a bit of moving in the wrong direction?

Count me in your club, please !

Quoting Matt6461 (Reply 236):
A lot of your post involves a simple misunderstanding:

The numbers I posted represent a max range trip for both aircraft, but the model is easily adjusted for shorter trips. I posted the max range trip to demonstrate the MTOW constraint.

That's just rubbish !
Max range , How much is it ? and for whom ?*A* max range isn't just enough for us. Give us the figure as it could be computed (hint : the Breguet equation).

Quoting Matt6461 (Reply 236):
I accept a slightly lower nominal range for the A380NWO, but increasing MTOW to 974,000lbs would barely change the results. If the A380's nominal range is 8200nm, this model shows the NWO at ~8100nm. Not a big deal.

Didn't see the proof of that...

Quoting Matt6461 (Reply 236):
Quoting Pihero (Reply 234):
The last point is that you have never considered how strongly that wing is going to be built

I have been very transparent about the weight model I am using - the wing weight index I linked above several times. If you want to suggest a better model, or specific refinements to it with justified reasoning, you are welcome to do so.

Going to your sheet, page 2 - "Wing and structure", what you call "Wing ultimate load analysis" is just *the bending moment*.
We've tried to tell you that in fact the charges on that wing should be computed with a load factor of 3.75 , in other words 3.75 times your beloved 1 g wing loading.
That study, which involves far higher figures, is not in your sheet.

Quoting Matt6461 (Reply 236):

Quoting Pihero (Reply 234):
Last comment : your burnoffs are wayyyyyyyy out what we see actually

I may have underestimated DOW for both planes. I added unusable fuel and 6,000lbs for miscellaneous items to both planes.

Once again, where are these values ? What are these values of *miscellaneous items* for ?

Quoting Matt6461 (Reply 241):
n any event, Air Density/Pressure is just a proxy for cruise altitude. Because my model is purely comparative, I didn't calculate the actual flight levels for either CEO or NWO/NEO. I sought to capture the *relative* effects of different flight levels by comparing the density/pressure of air at which they fly.

For your study to be reliable and acceptable, you'd have to adhere to the real world constraints : Cruise flight level management / Step climbs / Max and optimum flight levels....
If you allocate one flight level to the higher-cruising aircraft, it follows that you are stuck with the available nearest level to your level for *air density ratio* . For example taking the last slice of your study, you allocate a ratio of 1.1254.
We can ( if we take your max range idea at face value ) say that the A388 will be at FL 430, i.e 43 000 ft., where density is .261 066. The levels then available with a lower-performing aircraft are FL 410, then 390, then370...etc...
Estimating in the best case that they are in RVSM space, let's find out the FL for .261 066 x 1.1254 = .293 804... and OOooooPs you can't take FL 410 as density is .287... hence you'd have to descend -or use - FL 390 as your max alt.
Therefore, your assumption is wrong... you'd have to consider a very clever strategy of step-cruise levels.

Quoting Matt6461 (Reply 233):
the model assumes that planes with lower wing loading cruise at higher altitude. Specifically, [b]they will climb, relative to a higher-loaded wing, until lift/wingM2=weight/wingM2. Holding speed and Cl constant, a lower-loaded wing has to cruise in lower air density, i.e. at higher cruise altitude.

I fail to understand the logic of that : At all times in cruise Lift = Weight and the parameters you discard - speed and Cl - are in fact the ones that you should really be working on.

Which brings me to asking you to demonstrate the influence of wing loading on cruise performance. There are several very simple equations to consider.

You asked us to have a look at your sheet.
I did, but I'm not impressed, because a lot of key figures are missing.
But, on page 4 I really gave up : Thrust-to-weight ratio is in fact weight-to-thrust and I can't be bothered to go any further, especially when there are no figures for V1 ( the same, different and how ?).

[Edited 2015-08-19 07:57:21]

[Edited 2015-08-19 08:09:15]

[Edited 2015-08-19 08:17:01]

[Edited 2015-08-19 08:18:42]
Contrail designer
 
User avatar
Matt6461
Topic Author
Posts: 2991
Joined: Wed Oct 16, 2013 9:36 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Wed Aug 19, 2015 5:04 pm

Quoting Pihero (Reply 245):
Max range , How much is it ?

I was using the Breguet range equation, as you suggest. Between an MTOW of 970k lbs and 974k lbs, the ln(Wto/Wlanding) term varies by 1%. At 974k lbs, the NWO matches the A380's nominal range per the model. If A380CEO's nominal range is 8200nm, we get: .99*8200=8120nm. I quoted ~8100nm.

Quoting Pihero (Reply 245):
"Wing ultimate load analysis" is just *the bending moment*.

I think one must separate "bending moment" from "ultimate load." Bending moment is a factor of ultimate load and lever arm (span). The wing weight index separates these two as well.

To make this concrete, an example of how I think these different:

Consider a hypothetical material "Supernium." Supernium has a density of .000000000000000000000000001 lbs/ft3, but the strength of CFRP.

Now consider two planes, both of which have wings and engines made of Supernium. Both planes have the same fuselage and payload, which weigh 500,000lbs.

Plane A has Supernium wings of span 300ft.

Plane B has Supernium wings of span 150ft.

Planes A and B have basically same ultimate load, but have different bending moments. Why?

-Ultimate Load is the weight of material causing bending stress, minus bending relief from wing and engines. Because Supernium is so light, there's basically no bending relief to calculate. Thus the "ultimate load" for both A and B is the weight of fuselage plus payload.

-But the bending moment of planes A+B differs: plane B's wing is longer. Thus the "lever arm" of its lift is longer, and the bending moments as well. Plane B would need more Supernium in its wing for greater bending moment.

Intuitively, this makes sense to me. Here there are two separate effects that could make a wing heavier or lighter: (1) changing span and (2) carrying a heavier/lighter fuselage/payload. One must separate out (1) how much are we lifting? and (2) how big a lever are we using?

The wing weight index that I linked also separates these effects by making wing weight proportional to both (1) span^3 and (2) ultimate load. See http://adg.stanford.edu/aa241/AircraftDesign.html - Section 10.3.1 [Nult=ultimate load]

Quoting Pihero (Reply 245):
What are these values of *miscellaneous items* for ?

Catering, cargo tares, magazines, toilet paper, etc. I remember Ferpe trying to estimate the other items, beyond OEW, that fly on a typical mission. I don't know quite how to do this so I just used 6,000lbs for both planes. I'm sure that's not exactly correct. But I applied the 6,000 to both so it's not really affecting the comparative picture much.

Quoting Pihero (Reply 245):
Once again, where are these values ?

See Column I, labeled "Misc Items."

Quoting Pihero (Reply 245):
For your study to be reliable and acceptable, you'd have to adhere to the real world constraints : Cruise flight level management / Step climbs / Max and optimum flight levels....

For my study to be totally precise, yes, you're correct. But as I've said repeatedly, this is an estimate. If you can think of a way to easily set flight levels, I would greatly appreciate it.

In the absence of actual flight levels, however, a *relative* estimate is the best I can think of to compare *relative* performance. The abstraction that I have made doesn't favor the CEO over the NWO or vice versa. And to me that's what matters: That I'm giving a fair portrait of both planes. Could it be a little more detailed? Yes, absolutely. But unless the model is somehow skewed towards better results for the NWO, the objection is on grounds of precision.

Quoting Pihero (Reply 245):
There are several very simple equations to consider.

Which ones? Besides the relationships I laid out regarding air density?
 
User avatar
seahawk
Posts: 9867
Joined: Fri May 27, 2005 1:29 am

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Wed Aug 19, 2015 5:31 pm

Ultimate Load is a result of the Bending moment. The material does not care if the load is created by a momentum, or by direct force. However the lever arm of force for the wing with more wingspan is longer, therefore for a similar wing load, the force created at the wingroot is bigger.
 
User avatar
Matt6461
Topic Author
Posts: 2991
Joined: Wed Oct 16, 2013 9:36 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Wed Aug 19, 2015 5:40 pm

Quoting Pihero (Reply 245):
But, on page 4 I really gave up : Thrust-to-weight ratio is in fact weight-to-thrust and I can't be bothered to go any further, especially when there are no figures for V1 ( the same, different and how ?).

Weight to thrust ratio is indeed mislabeled. Thanks, you've found another typo.

In the model, however, the typo doesn't matter because it's used as intended. Allow me to explain the reasoning. It's important to remember that this is entirely a *relative* picture.

-I estimate relative V1 according to relative wing loading. At equal Cl, lift ~ S*v^2. If we have 5% higher wing loading at MTOW, then we need 5% more lift per wing ft2. If we need 5% more lift per wing ft2, then we need V1 to increase by SQRT(1.05). That's how I set V1.

-To determine balanced field length: I set acceleration equal to weight/thrust ("W/T"). I estimate time to reach each plane's respective V1 based on V1/(W/T): at constant acceleration, Speed=Time*Acceleration. To make this really precise I'd have to adjust for the rate of thrust lapse between each plane's engines.

-Given each plane's respective time to reach V1, we know its relative distance traveled at V1. This is proportional to the square root of speed at V1 (assuming constant acceleration).

-Given relative speed at V1, we also know relative breaking distance for a rejected takeoff: This is proportional to the square of speed.

-Adding relative distance to reach V1 and relative breaking distance gives us relative balanced field length.

-As you'll see, the model gives the 80m NWO a 4% longer balanced field length than the CEO. I judged this acceptable because the CEO's balanced field length, 9,600ft at ISTAT conditions, is relatively short. Its higher thrust is probably more a matter of V2 climb gradient constraint.

-I didn't model V2 climb gradient here, because NWO, either 80m or 80m+, will easily beat CEO here - it's not the important constraint. Why? Well at takeoff ~90% of drag is induced. The NWO is going to have 40-50% lower lower induced drag, only ~25-30% lower thrust. Between V1 and V2, V1 seems much more likely to be the operative constraint.
 
User avatar
Matt6461
Topic Author
Posts: 2991
Joined: Wed Oct 16, 2013 9:36 pm

RE: A380NEO: Revisions And BizCase Unclear,2020-25EIS

Wed Aug 19, 2015 5:45 pm

Quoting seahawk (Reply 247):

Ultimate Load is a result of the Bending moment.

I don't think this is correct for the reasons I outlined above, and based on the wing weight index that I linked. I'm open to reconsidering my opinion, but do you have a source?

Based on the equations I've seen, it makes more sense to me that:

-Ultimate load tells you how much you're lifting, while

-span and lift distribution tell you the lever arm of lift

Multiplying those two together would give the bending moment.

If you don't have a separate term for "how much are we lifting?" then how do compute bending moment? You can't do it from span and lift distribution alone. Putting an A380 fuselage onto the 737's wings, for example, wouldn't change the lever calculus, but it certainly would change the "how much are we lifting" calculus. That latter part - the A380's fuselage instead of the 737's in this example - is what I think ultimate load captures.

Who is online

Users browsing this forum: No registered users and 22 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos