swallow
Posts: 182
Joined: Wed Jul 11, 2007 12:23 am

RE: A380 Overperforms Says Tim Clark Of EK

Thu Nov 22, 2012 6:21 pm

Quoting KC135TopBoom (Reply 33):
I just don't see where cruising at .86M as opposed to .83M will save fuel

I found this explanation on another website. Hope it makes sense.

The A380 was designed to have an economical cruise speed, and a high speed cruise. The design turned out such that the fuel burn was higher than expected at the economical cruise speed (due to the lower than desired aspect ratio of the wing) and so they tend to only use the high speed cruise of around 0,86. There are no/ minimal gains by cruising slower in the A380 unless the aircraft is partially filled. You will see that Airbus is changing the wing twist from next year, and increasing the washout by another 1.5 degrees in order to try and resolve this problem.

The basic problem stems from the fact that you want to carry 555 pax, making this a large aircraft, so you need a certain wing area, but you are restricted in span due to existing airport infrastructure. The net result is that the wing chord is increased, with a fixed span, so the aspect ratio of the wing reduces. Induced drag is inversely proportional to aspect ratio. So they have a bit of a problem!


Source: http://www.avcom.co.za/phpBB3/viewtopic.php?f=1&t=98712
The grass is greener where you water it
 
art
Topic Author
Posts: 3037
Joined: Tue Feb 08, 2005 11:46 am

RE: A380 Overperforms Says Tim Clark Of EK

Thu Nov 22, 2012 6:43 pm

Quoting swallow (Reply 50):

Thanks. I think I may be starting to understand.  
 
User avatar
Stitch
Posts: 26588
Joined: Wed Jul 06, 2005 4:26 am

RE: A380 Overperforms Says Tim Clark Of EK

Thu Nov 22, 2012 7:11 pm

So the fuel savings from the wing twist comes from allowing a slower cruise speed, which reduces engine thrust and SFC?
 
User avatar
Revelation
Posts: 22242
Joined: Wed Feb 09, 2005 9:37 pm

RE: A380 Overperforms Says Tim Clark Of EK

Thu Nov 22, 2012 7:30 pm

Quoting HiJazzey (Reply 13):
True, although they're flying longer these days. The newer generation NBs like the NEOs and Max's should probably be optimised for longer stage lengths

Might be why Boeing is finding it worthwhile to clean up the tail cone on the 737.

Quoting sunrisevalley (Reply 31):
For what it terms a "reu" version with 840- seats, 282t.

I imagine the name came from the company that planned to fly two A380s in cattle-class configuration to Reunion Island.
Wake up to find out that you are the eyes of the world
The heart has its beaches, its homeland and thoughts of its own
Wake now, discover that you are the song that the morning brings
The heart has its seasons, its evenings and songs of its own
 
mauriceb
Posts: 2150
Joined: Tue Aug 10, 2004 2:50 am

RE: A380 Overperforms Says Tim Clark Of EK

Thu Nov 22, 2012 8:02 pm

Maybe the fact that it performs better at a higher mach. number comes from the fact that the faster a plane is able to fly, the less induced drag it creates. Higher speed also means that the profile drag numer is higher. But probably the plane is so aerodynamic that the extra speed+less induced drag makes up for the extra profile drag.

Incredible it only performs 1% less after years of operation, shows once again that the A380 is a game changer.

I can imagine that future, composit planes, will also have less degradation in performance as it is less funurable to damage due to rocks, weather, and fluctuating cabin pressure...


Let's see if the 787 will perform even better!


Maurice
 
art
Topic Author
Posts: 3037
Joined: Tue Feb 08, 2005 11:46 am

RE: A380 Overperforms Says Tim Clark Of EK

Thu Nov 22, 2012 8:26 pm

Quoting Revelation (Reply 53):
Quoting sunrisevalley (Reply 31):
For what it terms a "reu" version with 840- seats, 282t.

I imagine the name came from the company that planned to fly two A380s in cattle-class configuration to Reunion Island.

"Cattle class" sounds disparaging to me. I know the term is used but one should not forget that 50 years ago air travel was very, very expensive in Europe and had it remained so, there would be relatively few travellers and hundreds of thousands/millions less people employed in the aviation industry . If cramming 840 people into an A380 saves each pax $200 for 20 hours flight, I think most of those pax would be very pleased to experience the additional discomfort. For some it would make the difference between taking the trip/not taking the trip.
 
tommytoyz
Posts: 1195
Joined: Thu Jan 18, 2007 9:08 am

RE: A380 Overperforms Says Tim Clark Of EK

Thu Nov 22, 2012 10:48 pm

The SR-71 burned less fuel per mile traveled the faster it flew. Going Mach 3.5 was more economical than flying at Mach 3.2.

Why? Beats me. No idea.

But that's a huge speed differential of Mach 0.3. Here with the A380 it's only a speed differential of Mach 0.03.

To turlte:

The wrinkles on the B-52 have been there since she rolled out of the factory:

the conspicuous skin wrinkles, which are often mis-identified as evidence of aging, but were actually present when factory fresh and are due to tension from wing flex and weight (called Wagner Tension Field).
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: A380 Overperforms Says Tim Clark Of EK

Thu Nov 22, 2012 11:20 pm

Quoting art (Thread starter):
Seems remarkable that the the aircraft burns less fuel at mach 0.86 than at mach 0.83. How does that come about?

ASM production goes up more (due to higher speed) than CASM (due to higher fuel burn).

Quoting art (Reply 10):
I see narrowbodies tend to have m 0.8 as their advertised cruise speed. Can they also be flown faster without increasing fuel burn from A to B

Typically not.

Quoting art (Reply 10):
I don't understand why the advertised cruise speed would be less than the speed.that burnt the least fuel between origin and destination. Lower engine maintenance cost? Some other factors?

Design cruise speed was selected *way* back in the development phase before all the testing (especially NAMS) was completed.

Quoting autothrust (Reply 44):
The upper shells/skins are GLARE not aluminium.

GLARE is an aluminum/fiberglass laminate. So it's correct to refer to it as composite, but not correct to say it doesn't have any aluminum.

Quoting autothrust (Reply 44):
However anyone has some info about the Wagner Tensions Field?

Here's a good paper:
http://diablo221.altervista.org/Tension-field%20Theory.pdf

It's also called "diagonal tension" or "intermediate diagonal tension". It's been used in aircraft design for decades. It works really well when you're not so worried about displacement as strength.

Quoting MauriceB (Reply 54):
Maybe the fact that it performs better at a higher mach. number comes from the fact that the faster a plane is able to fly, the less induced drag it creates.

Be careful; the faster you fly, the less induced drag *coefficient* it creates. The induced drag force goes up because the dynamic pressure goes up faster than the induced drag coefficient drops.

Quoting tommytoyz (Reply 56):
The SR-71 burned less fuel per mile traveled the faster it flew. Going Mach 3.5 was more economical than flying at Mach 3.2.

Why? Beats me. No idea.

At those speeds, the SR-71 was in pure ramjet mode. Ramjet efficiency goes up with increasing speed. So, as the airplane accelerated, the engine thrust could go up faster than the drag.

Tom.
 
musang
Posts: 792
Joined: Sun Apr 08, 2001 4:11 am

RE: A380 Overperforms Says Tim Clark Of EK

Thu Nov 22, 2012 11:30 pm

Quoting lightsaber (Reply 20):
Aircraft put on a tremendous amount of weight (tons) per year

In the mid '80s AirLanka was using one of Royal Jordanian's TriStar 500s. It became apparent during an overhaul that there was (I'm sure any figure bandied around at the time was exaggerated) a rediculous amount of sand in the belly, presumably dropped off ULDs, pallets and ground staff shoes over the years.


View Large View Medium
Click here for bigger photo!

Photo © AlainDurand



musang
 
User avatar
flyingturtle
Posts: 5720
Joined: Mon Oct 31, 2011 1:39 pm

RE: A380 Overperforms Says Tim Clark Of EK

Thu Nov 22, 2012 11:46 pm

Quoting tommytoyz (Reply 56):


For a thorough discussion of the topic at hand, please refer to my posting #39.   




David
Reading accident reports is what calms me down
 
User avatar
zeke
Posts: 14381
Joined: Thu Dec 14, 2006 1:42 pm

RE: A380 Overperforms Says Tim Clark Of EK

Fri Nov 23, 2012 8:31 am

Quoting francoflier (Reply 2):

The extra fuel flow required to go faster is lower is compensated by the shorter flight time.

That is part of it, with the newer aircraft they have transonic wings and have rather flat drag polars, M0.83 would be closer to maximum endurance for the A380, and 0.86 closer to normal long range cruise, i.e. best MxL/D.

Quoting francoflier (Reply 2):

I didn't think the A380 would be 'comfortable' .86 cruiser. I imagined it more in the .84~.85 range.

The A380 was designed for a long range cruise of 0.85/FL360, it might have turned out a bit better than design, i.e. 0.855/0.86.

Quoting JU068 (Reply 4):
What about the other operators? Have any of them been this impressed by this bird?

QF & SQ have made similar comments before.

“In terms of technical performance, specifically fuel burn, the aircraft is performing better than Airbus promised. In seat/mile terms we achieve overall a 20% better fuel burn than our 747-400s.“ Chew Choon Seng, CEO Singapore Airlines ATW online, Dec 13th 2007

“The A380 has met or exceeded all the original performance, noise and fuel burn guarantees made by Airbus at the time the aircraft purchase decision was made.” Lyell Strambi, Group Executive - Qantas Airlines, Operations Airline Fleet Management , July 2009

Quoting flyingturtle (Reply 16):
How does that happen?

The airframe degrades over time, a number of items that change over time include the paint, seals on the slats, damage from lightning strikes/birds, damage from ground equipment, erosion in the engine, etc.

Quoting flyingturtle (Reply 46):
Now, what exactly is optimized when the A380 is flown at 0.86 M vs. 0.83 M? Tim Clarke mentions fuel efficiency, but what is the exact metric?

0.86 would be close to the tangent to the drag polar, which is the best specific range (nil wind).

To work this out, the aircraft automatically records the engine and airframe parameters during the cruise, these parameters are sent back to the operator back via ACARS/QAR data. Airbus produces as part of the performance engineering software a inflight flight planning (IFP) software, that is the baseline virtual "A380" which every operator bases their flight planning on.

The performance monitoring software takes a whole series of the aircraft parameters, weight, altitude, TAS, and mach, N1, from various flights, weights, times, conditions from that it will look at the IFP to come up with the theoretical fuel flow (FF) for those parameters. Next it takes the same parameters, this time using the actual N1, and uses a theoretical engine for that altitude and mach to come up with a new calculated FF, the calculated FF is compared to the theoretical FF, the difference in the model is the airframe degradation (i.e. a given amount of thrust at a given altitude is required to overcome the drag in the IFP). It does another loop where the actual FF is compared to the theoretical FF, we already know what the airframe degradation is from the previous step, so any additional fuel flow is the engine degradation contribution.

This is a very statistical approach, both for generating the engine and airframe model in the IFP as well as the recording the in service data. The data shows trends, not absolutes. Also I believe the wing and some of the fairings on the initial test aircraft were slightly different to the production aircraft, which would result in some of the flight test data being a little more conservative.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
maxter
Posts: 197
Joined: Sun May 24, 2009 2:23 am

RE: A380 Overperforms Says Tim Clark Of EK

Fri Nov 23, 2012 8:45 am

Quoting flipdewaf (Reply 8):
This seems like good news for the whale but Tim Clark always seems to have a reason up his sleeve for saying things.

For goodness sake, can't we just accept that this aircraft may just be all TC and many others say it is rather that somehow cast doubt as to it's actual abilities by insinuating that TC might not be on the level?
maxter
 
User avatar
autothrust
Posts: 1468
Joined: Sun Jun 11, 2006 8:54 pm

RE: A380 Overperforms Says Tim Clark Of EK

Fri Nov 23, 2012 9:33 am

Quoting tdscanuck (Reply 57):
GLARE is an aluminum/fiberglass laminate. So it's correct to refer to it as composite, but not correct to say it doesn't have any aluminum.

I haven't said it doesn't have any aluminium. I was just pointing out the upper shells not being normal aluminium so less prone to Wagner Tension Field.



Anyone knows if GLARE 2 will be used on the next A380's?
Flown on: DC-9, MD-80, Fokker 100, Bae 146 Avro, Boeing 737-300, 737-400, 747-200, 747-300,747-400, 787-9, Airbus A310, A319, A320, A321, A330-200,A330-300, A340-313, A380, Bombardier CSeries 100/300, CRJ700ER/CRJ900, Embraer 190.
 
PlaneInsomniac
Posts: 418
Joined: Tue Nov 20, 2007 7:34 am

RE: A380 Overperforms Says Tim Clark Of EK

Fri Nov 23, 2012 9:57 am

Quoting maxter (Reply 61):
For goodness sake, can't we just accept that this aircraft may just be all TC and many others say it is rather that somehow cast doubt as to it's actual abilities by insinuating that TC might not be on the level?

Well, yeah, remember that this is about the A380.

According to some poeple:
If somebody who really should know what he's talking about says the plane is consistently performing better than projected, this can only mean:
a) the plane is really underperforming for some bizarre, illogical "technical" reason or
b) that person is lying for political reasons.

Nothing new, really. The same game we have played here for a decade or so. Some people just never get tired, I guess.
Am I cured? Slept 5 hours on last long-haul flight...
 
User avatar
flyingturtle
Posts: 5720
Joined: Mon Oct 31, 2011 1:39 pm

RE: A380 Overperforms Says Tim Clark Of EK

Fri Nov 23, 2012 10:09 am

Keep clicking through, there will be some diagrams about the Wagner tension field:

http://www.docstoc.com/docs/74843498...S-OF-DIAGONAL-TENSION-FIELD-ACTION

Quoting autothrust (Reply 62):

You have confused me by mentioning "upper shells"... huh, what part of the A/C is that? It can't be part of the fuselage...    
Quoting zeke (Reply 60):

Thank you for sharing your knowledge!


David

[Edited 2012-11-23 02:11:33]
Reading accident reports is what calms me down
 
User avatar
N14AZ
Posts: 3971
Joined: Sat Feb 24, 2007 10:19 pm

RE: A380 Overperforms Says Tim Clark Of EK

Fri Nov 23, 2012 11:11 am

Quoting swallow (Reply 50):
I found this explanation on another website. Hope it makes sense.

The A380 was designed to have an economical cruise speed, and a high speed cruise. The design turned out such that the fuel burn was higher than expected at the economical cruise speed (due to the lower than desired aspect ratio of the wing) and so they tend to only use the high speed cruise of around 0,86. There are no/ minimal gains by cruising slower in the A380 unless the aircraft is partially filled. You will see that Airbus is changing the wing twist from next year, and increasing the washout by another 1.5 degrees in order to try and resolve this problem.

The basic problem stems from the fact that you want to carry 555 pax, making this a large aircraft, so you need a certain wing area, but you are restricted in span due to existing airport infrastructure. The net result is that the wing chord is increased, with a fixed span, so the aspect ratio of the wing reduces. Induced drag is inversely proportional to aspect ratio. So they have a bit of a problem!
Quoting Stitch (Reply 52):
So the fuel savings from the wing twist comes from allowing a slower cruise speed, which reduces engine thrust and SFC?

Given the fact that I was lousy in Physics I also would appreciate if somebody could explain the link between the wing twist and the speed.

So if Airbus now ncreases the wing twist by 1.5 degree, the wing span is actually a little bit smaller, correct? (seems as if I was lousy in mathemtics as well...).
 
User avatar
lightsaber
Moderator
Posts: 18639
Joined: Wed Jan 19, 2005 10:55 pm

RE: A380 Overperforms Says Tim Clark Of EK

Fri Nov 23, 2012 1:51 pm

Quoting francoflier (Reply 2):
Quoting musang (Reply 58):
In the mid '80s AirLanka was using one of Royal Jordanian's TriStar 500s. It became apparent during an overhaul that there was (I'm sure any figure bandied around at the time was exaggerated) a rediculous amount of sand in the belly, presumably dropped off ULDs, pallets and ground staff shoes over the years.

My prior employer purchased a used 747 for ground based testing. When it took too long to prepare the aircraft, they weighed the trash cans of scapped off food (tarred for a empty trash can) to show the executives why we were behind schedule. 3.5 TONS of scrapped food later, it was ready.

And by yuck on the carpets... absorbed food and such. They weighed about twice what they did when installed.

Note: I don't know about the seats. They were worth money and thus removed as we weren't going to pay what they were worth.

Quoting imiakhtar (Reply 21):
It would be interesting to see how the GP7200 compares.

   And the Trent too... But the real numbers will be hard to find.

Quoting maxter (Reply 61):
For goodness sake, can't we just accept that this aircraft may just be all TC and many others say it is rather that somehow cast doubt as to it's actual abilities by insinuating that TC might not be on the level?

There is certainly enough sales demand, for the long lead times, to imply the A380 will make money.   

Lightsaber
IM messages to mods on warnings and bans will be ignored and nasty ones will result in a ban.
 
swallow
Posts: 182
Joined: Wed Jul 11, 2007 12:23 am

RE: A380 Overperforms Says Tim Clark Of EK

Fri Nov 23, 2012 2:07 pm

Quoting N14AZ (Reply 65):
Given the fact that I was lousy in Physics

Me too   

Quoting N14AZ (Reply 65):
I also would appreciate if somebody could explain the link between the wing twist and the speed

My layman understanding is that wing twist decreases induced drag at cruise. Adding twist makes the wing more efficient.

I suppose it follows that less induced drag translates into faster speed.

Quoting Stitch (Reply 52):
So the fuel savings from the wing twist comes from allowing a slower cruise speed, which reduces engine thrust and SFC?

Methinks the fuel savings come from lower induced drag at cruise, but I'll defer to the engineers on this board.

[Edited 2012-11-23 06:08:41]
The grass is greener where you water it
 
2175301
Posts: 1611
Joined: Wed May 16, 2007 11:19 am

RE: A380 Overperforms Says Tim Clark Of EK

Fri Nov 23, 2012 2:29 pm

Quoting lightsaber (Reply 66):
There is certainly enough sales demand, for the long lead times, to imply the A380 will make money.

At least for most of the companies operating them.


Have a great day,
 
User avatar
Stitch
Posts: 26588
Joined: Wed Jul 06, 2005 4:26 am

RE: A380 Overperforms Says Tim Clark Of EK

Fri Nov 23, 2012 2:56 pm

Quoting Stitch (Reply 52):
So the fuel savings from the wing twist comes from allowing a slower cruise speed, which reduces engine thrust and SFC?
Quoting swallow (Reply 67):
Methinks the fuel savings come from lower induced drag at cruise, but I'll defer to the engineers on this board.

Which is essentially what I meant, I just worded it poorly.
 
User avatar
autothrust
Posts: 1468
Joined: Sun Jun 11, 2006 8:54 pm

RE: A380 Overperforms Says Tim Clark Of EK

Fri Nov 23, 2012 3:05 pm

Quoting flyingturtle (Reply 64):
You have confused me by mentioning "upper shells"... huh, what part of the A/C is that? It can't be part of the fuselage..

Sorry for confusing  
Quoting flyingturtle (Reply 64):
there will be some diagrams about the Wagner tension field:

Thanks for the Links.
Flown on: DC-9, MD-80, Fokker 100, Bae 146 Avro, Boeing 737-300, 737-400, 747-200, 747-300,747-400, 787-9, Airbus A310, A319, A320, A321, A330-200,A330-300, A340-313, A380, Bombardier CSeries 100/300, CRJ700ER/CRJ900, Embraer 190.
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: A380 Overperforms Says Tim Clark Of EK

Fri Nov 23, 2012 3:33 pm

Quoting zeke (Reply 60):
The A380 was designed for a long range cruise of 0.85/FL360, it might have turned out a bit better than design, i.e. 0.855/0.86.

This seems to have been a trend since the mid 90's for both OEM's. I think that better CFD tools (they're really really good for high speed aerodynamics now) haven't quite caught up with the conservatism from the aerodynamics guys. Always a pleasant surprise when you get to actual testing.

Quoting autothrust (Reply 62):
I haven't said it doesn't have any aluminium. I was just pointing out the upper shells not being normal aluminium so less prone to Wagner Tension Field.

Diagonal tension is an intentional design; it's nothing particular to aluminum. As far as I know, nobody is currently building large airliners with diagonal tension skins so the fact that you don't see wrinkles isn't because it's GLARE, it's because they didn't design it in. Several current design do go into diagonal tension when they're over limit load but you never see that in service.

Quoting N14AZ (Reply 65):
Given the fact that I was lousy in Physics I also would appreciate if somebody could explain the link between the wing twist and the speed.

Wing twist determines how much lift each piece of the wing is generating. This, in turn, determines the spanwise lift distribution, which determines induced drag. So altering the wing twist can alter the induced drag for the same amount of lift. The normal induced drag expression is:
C_di = C_l^2 / pi / Aspect Ratio / e

e is called "Oswald's Efficiency Factor" and is where you roll in all the effects of twist, sweep, taper, planform, etc.

Quoting swallow (Reply 67):
Methinks the fuel savings come from lower induced drag at cruise, but I'll defer to the engineers on this board.

Lower induced drag *coefficient*. Absolute induced drag still goes up but not enough to offset the faster trip (you burn more fuel per unit time but do it for less time).

Tom.
 
User avatar
flyingturtle
Posts: 5720
Joined: Mon Oct 31, 2011 1:39 pm

RE: A380 Overperforms Says Tim Clark Of EK

Fri Nov 23, 2012 6:26 pm

Quoting tdscanuck (Reply 71):
Diagonal tension is an intentional design; it's nothing particular to aluminum. As far as I know, nobody is currently building large airliners with diagonal tension skins so the fact that you don't see wrinkles isn't because it's GLARE, it's because they didn't design it in. Several current design do go into diagonal tension when they're over limit load but you never see that in service.

How are E-2 Hawkeyes and B-52 built, if they form these wrinkles? I'm looking for "stringers B-52", but can't find anything...


David
Reading accident reports is what calms me down
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: A380 Overperforms Says Tim Clark Of EK

Fri Nov 23, 2012 7:07 pm

Quoting flyingturtle (Reply 72):
How are E-2 Hawkeyes and B-52 built, if they form these wrinkles?

The wrinkles don't form until you load the structure. They're build with normal skins and techniques. The difference between this and more conventional semi-monocoque structures is whether you let the skin go past its buckling load...if you do, it wrinkles. Sometimes you'll only see the wrinkles when the load is on and they'll come out when it relaxes. Sometimes it doesn't come out and you see airplanes that are "permanently" wrinkled. It's not really permanent, in the sense that the material never went past it's yield point, but the structure never relaxes enough for the wrinkles to come out. At least in theory, if you could return the aircraft to jig position, the wrinkles would come out.

Quoting flyingturtle (Reply 72):
I'm looking for "stringers B-52", but can't find anything...

Search on "intermediate diagonal tension" and you'll get lots of hits. The stringers aren't winkling, it's the skin that's wrinkling. The skin basically gives up all compression capability in one direction (perpendicular to the wrinkles) and that compressive load tranfers into the stringers and frames. The skin is carring predominantly tension (parallel to the wrinkles). In a diagonal tension design, if the stringers or frames buckle (wrinkle) you're screwed because now you've got nothing to carry compression. In theory, you could have intermediate diagonal tension beams for stringers or frames but I'm not aware of any design actually doing that.

Tom.
 
User avatar
autothrust
Posts: 1468
Joined: Sun Jun 11, 2006 8:54 pm

RE: A380 Overperforms Says Tim Clark Of EK

Fri Nov 23, 2012 7:25 pm

Quoting tdscanuck (Reply 71):
Diagonal tension is an intentional design; it's nothing particular to aluminum. As far as I know, nobody is currently building large airliners with diagonal tension skins so the fact that you don't see wrinkles isn't because it's GLARE, it's because they didn't design it in. Several current design do go into diagonal tension when they're over limit load but you never see that in service.

Thanks for the explanation.

Wouldn't you see wrinkles in a 787?
Flown on: DC-9, MD-80, Fokker 100, Bae 146 Avro, Boeing 737-300, 737-400, 747-200, 747-300,747-400, 787-9, Airbus A310, A319, A320, A321, A330-200,A330-300, A340-313, A380, Bombardier CSeries 100/300, CRJ700ER/CRJ900, Embraer 190.
 
User avatar
flyingturtle
Posts: 5720
Joined: Mon Oct 31, 2011 1:39 pm

RE: A380 Overperforms Says Tim Clark Of EK

Fri Nov 23, 2012 9:56 pm

Quoting tdscanuck (Reply 73):
The stringers aren't winkling, it's the skin that's wrinkling.

Thank you, your answer is really helping me to understand. I was looking for a picture of a "skinned" B-52 or E-2, and I was wondering if the stringers and longerons are placed differently in comparison to, say, a 777 or a 330. The latter ones don't seem to wrinkle...

So it only depends on how much load the skin is carrying, in comparison to the internal structure like stringers and longerons?



David
Reading accident reports is what calms me down
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: A380 Overperforms Says Tim Clark Of EK

Sat Nov 24, 2012 6:31 pm

Quoting autothrust (Reply 74):
Wouldn't you see wrinkles in a 787?

You shouldn't. As far as I know, the 787 doesn't have any intermediate diagonal tension design in the composite. It's all shear-resistant. Also, when you have the ability to tailor directional strength with fibers (as you do in GLARE or CFRP) then weight advantage isn't as large.

Quoting flyingturtle (Reply 75):
I was looking for a picture of a "skinned" B-52 or E-2, and I was wondering if the stringers and longerons are placed differently in comparison to, say, a 777 or a 330. The latter ones don't seem to wrinkle...

As far as I know, the placement (in terms of frame or stringer spacing) isn't significantly different. The major difference would be skin thickness relative to stringer/frame spacing...for similar loading with a diagonal tension design, you'd have either a significantly thinner skin or significantly more spaced out frames/stringers but not necessarily both.

Quoting flyingturtle (Reply 75):
So it only depends on how much load the skin is carrying, in comparison to the internal structure like stringers and longerons?

It depends on how much load the skin is carrying relative to its bucking load. In a shear resistant design, you keep the skin loads below the skin bucking load so it doesn't wrinkle (wrinkling is the 2D version of 1D column buckling). In a diagonal tension design you intentionally let the skin go above buckling load so it wrinkles; the skin loses it's ability to handle compression perpendicular to the wrinkles so you need stringers/frames that can handle the shifted compression load. In return, you can use a much thinner skin and, in general, you don't need to increase the stringer/frame weight as much as you save on the skin. So you have an overall lighter structure for a given load capability. This is especially useful when you're covering the gap between limit and ultimate load; if you are shear-resistant up to limit load you can get a lot of post-limit capability via diagonal tension and so make it all the way to ultimate load without a lot more structure. Since, at least in theory, you'll never go over limit load in service, the presence of wrinkling usually isn't that big a deal. You see this concept a lot in, for example, floor beams.

You typically don't see this type of design outside aerospace because the wrinkling results in large deflections...in something like a building or bridge those are highly undesirable (and weight savings isn't nearly so important).

Many of the current types, including 787/A350/A380 may exhibit this wrinkling behavior between limit and ultimate load but you're unlikely to ever see it in normal operation. For aerodynamic reasons, you don't want skin wrinkles in normal operation. The B-52 had...less stringent...fuel burn requirements.

Tom.
 
ferpe
Posts: 2667
Joined: Tue Nov 30, 2010 7:44 am

RE: A380 Overperforms Says Tim Clark Of EK

Sat Nov 24, 2012 8:48 pm

Quoting flyingturtle (Reply 46):
Now, what exactly is optimized when the A380 is flown at 0.86 M vs. 0.83 M? Tim Clarke mentions fuel efficiency, but what is the exact metric?

Tom has answered that in a brief way, here a bit more on why the A380 can be more efficient when flown at 0.86 instead of 0.83:

In general the drag on an aircraft has this dependence of speed (from one of the aircraft design books):

http://i298.photobucket.com/albums/mm262/ferpe_bucket/Totaldragcurve.jpg

As can be seen induced drag (or drag due to lift) is dominating at low speed (it is 80% of the problem at start for instance) and parasitic drag (or drag independent of lift, mainly friction drag ) raises as your speed increases. This diagram ignores one important drag component however, transonic drag. This stays really low (under 1% of total drag) up to cruise speeds and then shoots up very steeply at or just after max cruise speed (due to the stronger wing shockwaves beating the boundary layer to let go) .

Now the A380 has 2 specific characteristics, it has a rather big wing area (good for transonic drag rise if you do the profile right) and rather short span (for a modern wing ) due to the 80m restriction. So induced drag is higher then normal and transonic drag has the potential to be kept low longer then normal (which A seems to have achieved). So by flying faster you increase the parasitic drag as normal, you lower the induced drag more then normal and your transonic drag does not shoot up as usual, voila the TC effect  Wow!  . Of course your total drag increases and therefore you need more engine = higher fuel burn but the time decrease for the leg compensate as others have explained.

Here as a reference the drag data for the A380 at cruise compared to the 787, both modern wings (look at the ratios not the absolute values):

Drag lbf..........Induced...%.....Parasitic..%...Transonic..%
A380...............25,000...48......26,000...50........1,000...2
787...................8,700...37......14,300...61...........500...2


What A is now trying to do with the added wing twist is to lower the high induced drag of the A380 as much as the wing allows, apparently their flight test data told them they could tweak the e (the Oswald thing per Toms post) a tick further   .

[Edited 2012-11-24 13:10:54]
Non French in France
 
astuteman
Posts: 7010
Joined: Mon Jan 24, 2005 7:50 pm

RE: A380 Overperforms Says Tim Clark Of EK

Sun Nov 25, 2012 7:50 am

Quoting ferpe (Reply 77):
transonic drag has the potential to be kept low longer then normal (which A seems to have achieved).

They did.
During flutter testing, they were expecting to have to dive at a 6 degree angle to achieve M0.96, but only required a 4 degree angle.

I have no link, but I've been advised that part of this was also due to the (infamous) long forehead working better than was predicted to avoid transonic shock waves as the air was accelerated over that huge fuselage..

(during testing they also reduced take-off and landing speeds by 4 kts, but that's a different matter)

Rgds
 
kaitak
Posts: 9756
Joined: Wed Aug 18, 1999 5:49 am

RE: A380 Overperforms Says Tim Clark Of EK

Sun Nov 25, 2012 9:38 am

Emirates pushing for A389?

http://www.arabianbusiness.com/emira...-for-up-800-passengers-480685.html

Although the -900 isn't specifically mentioned, an 800 seater (triple deck!) aircraft is; the EK executive concedes that the technology for such an aircraft is over a decade away, but K will be interested in it when it happens.

Does anyone know if there is any firm detail yet on the A380, e.g. dimensions (or length of the intended fuselage plugs to lengthen the A388?).

It would surprise me very much if EK were not at the head of the queue for the A389, particularly with so many undelivered A388s, orders for which would be converted to A389s?

I guess the big issue there would be whether other carriers would be willing to take that jump; CX and VS have expressed interest in the -900, though I think it's anyone's guess whether VS actuall flies any A380s at all.
 
User avatar
Zkpilot
Posts: 4380
Joined: Wed Mar 08, 2006 8:21 pm

RE: A380 Overperforms Says Tim Clark Of EK

Sun Nov 25, 2012 9:53 am

Quoting kaitak (Reply 79):

I guess the big issue there would be whether other carriers would be willing to take that jump; CX and VS have expressed interest in the -900, though I think it's anyone's guess whether VS actuall flies any A380s at all.

Me thinks part of the reason why QF deferred its last 8 A380 deliveries to the end of the decade was to get the A389...
64 types. 44 countries. 24 airlines.
 
User avatar
scbriml
Posts: 18096
Joined: Wed Jul 02, 2003 10:37 pm

RE: A380 Overperforms Says Tim Clark Of EK

Sun Nov 25, 2012 10:03 am

Quoting kaitak (Reply 79):
It would surprise me very much if EK were not at the head of the queue for the A389, particularly with so many undelivered A388s, orders for which would be converted to A389s?

IMHO, Airbus would be insane to launch the -900 for EIS before EK has taken delivery of nearly all their A388s.
Time flies like an arrow. Fruit flies like a banana!
There are 10 types of people in the World - those that understand binary and those that don't.
 
art
Topic Author
Posts: 3037
Joined: Tue Feb 08, 2005 11:46 am

RE: A380 Overperforms Says Tim Clark Of EK

Sun Nov 25, 2012 10:05 am

Quoting kaitak (Reply 79):
It would surprise me very much if EK were not at the head of the queue for the A389, particularly with so many undelivered A388s, orders for which would be converted to A389s?

I guess the big issue there would be whether other carriers would be willing to take that jump; CX and VS have expressed interest in the -900, though I think it's anyone's guess whether VS actuall flies any A380s at all.

It's been debated but the big issue for Airbus may be that airlines ordering A389 would have ordered A388 anyway.
 
User avatar
Stitch
Posts: 26588
Joined: Wed Jul 06, 2005 4:26 am

RE: A380 Overperforms Says Tim Clark Of EK

Sun Nov 25, 2012 3:37 pm

There will be no real need for Airbus to launch an A380-900 until a smaller plane equals or beats it's CASM and I don't expect that to be possible until Boeing launches their next generation large widebody twin (the Y3).

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