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Faro
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A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Sat May 04, 2013 9:32 am

IIRC, the A380 has today the lowest CASM of any operational airliner. Its wingspan is also constrained by regulatory gate width requirements so that it has a relatively stubby wing.

How is such a low CASM achieved despite an aspect ratio of around 7.5. Comparatively, most newer airliners have AR ratios around 9 or higher. An AR of 7.5 is comparable to the L1011-500 and VC-10, some rather outdated aircraft.

What is it about the A380's wing that counters its relatively low AR? In terms of lift to drag ratio, is it more or less efficient than the 77W's wing?


Faro
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Stitch
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Sun May 05, 2013 4:01 am

What help's the A380's CASM is the large number of seats you can put in it.  
 
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Sun May 05, 2013 2:40 pm

AR is certainly important, but it is not the only measure of efficiency. I'd bet that despite the similar aspect ratio the A380 wing utilizes many aerodynamic advances that make it far more efficient than any other jetliner wing of similar aspect ratio. That said, a higher aspect ratio would certainly have had aerodynamic benefits (though the structure of the shorter wing is lighter).

Combined with other new materials and systems--plus, as above, the economies such a large aircraft--and the A380 is incredibly efficient. Certainly not having the constraint on span would have offered other opportunities for further improvements, but like all designs it was a trade off, and apparently still good enough.
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ferpe
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Sun May 05, 2013 7:35 pm

As I have this all in a large excel model, the easiest is to copy the relevant parts including some other notable frames and then look at the different values. I have not studied this before and not looked beyond a quick glimpse so everyone comment. I will leave my first thoughts below the table:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/A380wingversusothers_zpsf8fee3d5.jpg


1. This part of my airframe model shows wing data but also drag and lift values on an overall frame level.

2. What one can see is that only the latest frames of the longhaulers have better aspect ratio then the A380. If we would look at only a wing level we would see a L/D (the true figure of merit as it shows how much drag is created for the lift you need to fly level) that was clearly worse for the A380 then e.g. 788, 359 and -9X.

3. What you see in the table is the drag created on an airframe level when lifting the aircrafts weight. Here the very efficient packaging on the A380 benefits the OVERALL L/D as the dominant drag components, parasitic drag (where skin friction drag is dominating) is relatively lower for the A380, it has a low wetted surface per transported pax due to it's whale like packaging. So the frame L/D when cruising at Cl 0.5 (I have put all at Cl 0.5 at FL370 by adjusting the weights so that we can compare better, except for 320 and 738 as they seems to be designed for a higher Cl cruise) is only 1 unit lower then the soaring eagle -9X  .


So the A380 is doing pretty well on an overall L/D despite its stubby wing, part of that is low wingloading and a good transonic design = low compressibility drag and then the low overall parasitic drag. These two compensate a somewhat higher induced drag level (Dp is all drag independent of lift and Di is all drag dependent on lift, i.e. also compressibility drag) .


Edit: Just a caution, don't look at the drag per pax etc figures (oops, should have taken them out). FL370 is the average weight FL for the A380, some other frames like the 748i has this FL as the last just before it is time to descent. No wonder they have a lower overall drag level per pax as the frame is at 69% of MTOW vs 78% for the A380. I can't show different frames on different flight levels easily so that is why I adjusted the weight to get them all at the same loading of the wings at FL370. The picture only tells a good story around L/D at that FL. The drag coefficients and the basic wing data (effective span including wingtip devices, wingloading, spanloading etc) is OK to compare as well.

[Edited 2013-05-05 13:04:31]
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ferpe
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Mon May 06, 2013 7:04 am

As I have the wetted areas for the frames (you need them to calculate the dominant drag factor, skin friction drag which is the major part of the parasitic drag (or drag independant of lift)) I revised the table to include the frames total wetted area and then I divided it with the cabin area that the airplane transports. I did not use Pax count as these are not calculated using the same standards (ref the A380 vs 748i debate re seating).

While I guessed on the low wetted area per pax in the previous post it was quite interesting to see the result, it is highlighted (click on the tables to get them in sharp resolution):

http://i298.photobucket.com/albums/mm262/ferpe_bucket/A380wingversusotherswithwettedareaperm2cabin_zps1d0be360.jpg

Here we see that while the A380 might not be top at induced drag reduction is in a class of it's own when it comes to avoiding the most prevalant drag, skin friction. Normally induced drag (the compression drag is tiny in the Cdi so it is essentially only induced drag) is from 45% down to 1/3 of the drag as the frame gets lighter, we can see that at average cruise weight it is 50-50 for the A380. It compensates by being efficient in other corners.

One can also see why the 748i can't compete, neither with the tube+wings (787 to -9X) nor with the double decker A380. it is simply to much wetted area for what it does, it is an inefficient single level frame with the hump making it double decker on to short a distance, lots of wetted area not contributing to the cabin floor area. As a part double decker it should have a lower factor then the -9X, it does not. And while the wing is a shade better on aspect ratio and span loading then the A380 it is to little to help. Both the A380 and 748i lacks span compared to the new DA crop, A380 because of the 80m dilemma, 748i because it is a base design which is 40 years old.

[Edited 2013-05-06 00:22:59]
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r2rho
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Mon May 06, 2013 11:35 am

Very interesting analysis ferpe.

Another thing to note is that the A380 wing was designed to eventually carry the weight of the -900, which is another constraining factor leading to more "stubbiness" (an A388-only wing could have surely been shorter at the root). That despite that the A388 has turned out so efficient shows that they must have really optimized the aerodynamics to extract the best out of the given constraints. Even then, it looks like Airbus have found they can optimize further, as is shown by the new wing twist applied to the BA frames and onwards.
 
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Mon May 06, 2013 11:24 pm

Thank you very much, ferpe, for an extremely interesting analysis.

Just one extra comment: The low wetted area of the A380 comes at a price. It has a relatively small cargo volume.

Cargo volume offers potential airline revenue just like cabin floor area does. The large Boeing planes (744, 748i, 773ER) offer a substantially larger cargo volume to cabin floor ratio.

The A380 was made as a pax plane - pax and their baggage. That's perfect when that is your customer base. If, however, your customer base is pax + baggage + substantial high volume cargo on sectors considerably shorter than max range, then the A380 is soon maxed out and loses points to the competition.
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ferpe
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Tue May 07, 2013 5:26 pm

Quoting prebennorholm (Reply 6):
Just one extra comment: The low wetted area of the A380 comes at a price. It has a relatively small cargo volume.

You are right, the double decker layout gives only half the length to the underfloor area. But that is not all, the A380 engineers seems to have chosen a MLG design that worsened this problem even further, the design impinged on the cargo area at great length:



The MLG is staggered behind each other and protrudes therefore into the cargo area over a long distance (on an already short under the floor area) and made it 1 abreast LD3, 748i and normal tube designs avoided that by focusing the MLG directly behind the center wingbox, for the 748i even when it had a 4 strut MLG like the A380 to spread the pavement loading:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/747MLGstowage_zps5b1cd99d.jpg


Here not to scale screen-shots from the ACAPs with an LD3 summary for each frame type that I added:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/A380cargocapacityvs748and77W_zpsbd98bd02.jpg

The grey area shows the stowage space for the MLG in the underbelly.
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astuteman
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Thu May 09, 2013 7:33 pm

Quoting ferpe (Reply 4):
Here we see that while the A380 might not be top at induced drag reduction is in a class of it's own when it comes to avoiding the most prevalant drag, skin friction

It would be interesting to see how the 79m A380-900 might model ...........  

Rgds
 
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Thu May 09, 2013 7:41 pm

Quoting astuteman (Reply 8):
It would be interesting to see how the 79m A380-900 might model ...........

OK, tell me the MTOW that I shall use and I will include that column.
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Aviaponcho
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Thu May 09, 2013 8:56 pm

590 t ?

Ferpe, there's a fifth position reserved for a central main landing gear for growth on the A380 ! (4 wheels)

And it might be interesting to drop LD3 for all non luggage and put in 88*125 or 96*125 pallets... you can fit some between the landing gear... (6 precisely)

[Edited 2013-05-09 13:59:21]
 
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Thu May 09, 2013 11:24 pm

Quoting aviaponcho (Reply 10):
Ferpe, there's a fifth position reserved for a central main landing gear for growth on the A380 ! (4 wheels)

What is the current gear good for? I heard 640t (with the brakes good for 625t with brakes on all 20 main wheels).
 
astuteman
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Fri May 10, 2013 4:36 am

Quoting ferpe (Reply 9):
OK, tell me the MTOW that I shall use and I will include that column.

My guess would be the launch weight of the 388 plus 30t - i.e. 599 tonnes

Rgds
 
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Fri May 10, 2013 3:31 pm

Quoting Stitch (Reply 11):
What is the current gear good for? I heard 640t (with the brakes good for 625t with brakes on all 20 main wheels).

If I recall correctly, the main limitation was not primarily the landing gear itself but pavement loading.

Which was also why the A388F was supposed to get that additional center bogie, just like the A389 later on.

Quoting ferpe (Reply 7):
the A380 engineers seems to have chosen a MLG design that worsened this problem even further, the design impinged on the cargo area at great length:

What would have been a realistic alternative?

When looking at the (excellent) comparison of the floor plans I believe one thing to remember is that in the 747 the lower deck occupies almost half of the main cross section versus less than a third in the A380. Plus the six-wheel A380 body bogies simply couldn't be stowed near-upright like the shorter 747 ones.

Keeping the center area flexible for use either for additional cargo space in the lighter version(s) or for an additional wheel well in the heavier ones looks like a pretty decent concept given the needs and circumstances.

An A389 would probably take away some space for the additional MLG leg there, but if the total length is sufficient, it should still provide somewhat decent cargo space, even if the increased passenger load with their luggage will keep eating into it. But how could a full double decker ever be a first-rate cargo hauler anyway?

Effectively you're paying for the somwhat better cargo ratio in the 747 with the empty crown space above the cabin you can't use.

The wing was already designed for the larger version from the start, as was the MLG layout. Effectively the A388 is already a somewhat compromised shrink of the initial, full design. They already had their hands full with pushing the 80m box to its limits airport-wise with the initial version (let's ignore the originally proposed even shorter double-shrunk -700 for now), but the design clearly points to an A389 being the full implementation.

That the A388 today is already quite efficient even while having to haul around much of the structure of a future A389 looks like a pretty aggressive but forward-looking design strategy to me.

[Edited 2013-05-10 08:38:00]
 
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Fri May 10, 2013 6:19 pm

The A380 wing was optimised for stretched A380-900 variant which could possibly launched in the future
 
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Fri May 10, 2013 7:47 pm

Quoting Klaus (Reply 13):
If I recall correctly, the main limitation was not primarily the landing gear itself but pavement loading.

Which was also why the A388F was supposed to get that additional center bogie, just like the A389 later on.

The A380-800F would not have had a center bogie according to the A380 ACAPs. And one of the A380-800 test airframes performed a take-off at 596.5t and then landed at 590t.
 
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Fri May 10, 2013 7:56 pm

Quoting Stitch (Reply 15):
The A380-800F would not have had a center bogie according to the A380 ACAPs. And one of the A380-800 test airframes performed a take-off at 596.5t and then landed at 590t.

I can't say I remember this really well; It may have been just speculation about an HGW F version back then.
 
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Fri May 10, 2013 8:44 pm

Quoting ferpe (Reply 7):
Here not to scale screen-shots from the ACAPs with an LD3 summary for each frame type that I added:

So the 777 is so excellent that bends even the math!
2*12+2*8 = 40 (not 44)
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ferpe
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Fri May 10, 2013 8:49 pm

Quoting Aquila3 (Reply 17):
So the 777 is so excellent that bends even the math!
2*12+2*8 = 40 (not 44)

Yeah , there is a fault in the last line in the picture (my addition and fault), read the fine print (Boeing facts) and you find it should have been 10*2 LD3s, ie 44 in total.
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ferpe
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Sat May 11, 2013 10:30 pm

Quoting astuteman (Reply 12):
My guess would be the launch weight of the 388 plus 30t - i.e. 599 tonnes
OK, so here the table with a projected A380 in 3 versions, std, -900 with the -800 wing and finally -900 with sharklets:

http://i298.photobucket.com/albums/mm262/ferpe_bucket/A380wingversusotherswithwettedareaperm2cabin-900and900sl_zpsf71fb33c.jpg

The total wetted area increases (fuselage length in red increases) therefore the parasitic drag increases and the L/D decreases somewhat. The sharklet equipped A380-900X claw back half of that by reducing drag due to lift, see the effective wingspan and aspect ratio in red. That a full doubledecker is an effective transport form for pax is seen when we divide the total wetted area with the cabin area, we are now at a sensational 4.9 m2 wetted area per m2 of cabin space (click on the table to see better).

It still does not make sense to look at total drag per m2 cabin area as I have the different birds at very different weight in order to get them to Cl 0.5 at FL370. We could look at drag independent of lift (and therefore weight) divided by cabin area, you could do that exercise. It will track our wetted area per m2 cabin closely as skin friction drag is the dominant part of the non lift (=parasitic) drag.

One interesting drag factor which decreases is the fuselage pressure drag factor or the form factor drag. This is modeled as an increase of the skin friction drag due to airstream overspeed to get around the fuselage (there is no such thing as drag due to frontal area, it is called pressure drag and is taken as the increased speed needed to traverse that whale body with all it's twist and turns. We can see that this drag likes the longer and slimmer body (better finesse ratio which is fuselage dia to length)).

If you look at the range you see I took an existing -900 column I had which had TXWB engines (TSFC around 0.52 instead of 0.56 ), that is why these ladies fly some 200nm longer then the -800 despite being heavier and having higher drag  .

[Edited 2013-05-11 15:51:43]
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Sun May 12, 2013 4:37 am

Quoting Klaus (Reply 13):
If I recall correctly, the main limitation was not primarily the landing gear itself but pavement loading.

Interestingly, the A388 has a lot of room to grow in pavement loading. 569 tons on 20 wheels is only 28.5 tons per wheel, well shy of the 32 routinely seen on other aircraft. 32 x 20 = 640 tons before you need a fifth leg... My numbers may not be all that accurate, but for sure it has plenty of room to grow.
 
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Sun May 12, 2013 11:12 am

Ferpe, i've got 298 t oew in an air et cosmos hors serie (and 286 t for the -800er)
14200 km range with 656 pax
Not equipped today for brownsing through your wonderful tabs.
 
Klaus
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Sun May 12, 2013 2:20 pm

Quoting WingedMigrator (Reply 20):
Interestingly, the A388 has a lot of room to grow in pavement loading. 569 tons on 20 wheels is only 28.5 tons per wheel, well shy of the 32 routinely seen on other aircraft. 32 x 20 = 640 tons before you need a fifth leg... My numbers may not be all that accurate, but for sure it has plenty of room to grow.

As far as I'm aware it's not just the weight per wheel but also the area the wheels are distributed across which is constrained.
 
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Sun May 12, 2013 8:33 pm

Quoting aviaponcho (Reply 21):

Oh and 277 t OEW for the A380-800 in this source... last ACAPS was 270.5 t
And 600 t for the heaviest Freighter (with the same landing gear)

By the way the A380-800 is 525PAX normally (even if it stays 555 on acaps... quoted range for airbus is for 525).

I can't find the lines with normalized consumption per m² or per pax ?
 
astuteman
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Thu May 16, 2013 5:01 pm

Quoting ferpe (Reply 19):
OK, so here the table with a projected A380 in 3 versions, std, -900 with the -800 wing and finally -900 with sharklets:

Many thanks my friend. I and one or two others used to model this sort of stuff, but I've stopped now - yours are so thorough.

I've always been of the view that when (and if) an A380-900 (as originally described by Airbus) was launched, it would end up outranging the A380-800 a bit, whilst offering 14%-15% more capacity.
I don't see much of a movement in trip cost either, especially if one assumes TXWB's

thanks again

Rgds
 
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Sat May 18, 2013 5:36 am

Quoting astuteman (Reply 24):
Many thanks my friend. I and one or two others used to model this sort of stuff, but I've stopped now - yours are so thorough.

Well modeling the way you did it (and I as well before taking it to a full drag model) makes a log of sense, it can bring a pretty close understanding of a frames performance. The seemingly impossible engine size of the 777X brought me to actually seek numbers for the forces involved. Once done it is amazing how little I have to tune those aerodynamic constants and the equations that control how they scale with weight or other dimensions.

If the spec range does not fit for a frame I usually find something else that is not trustworthy such as stated TSFC (a fault big factor and why I now also model the engines to do reality checks on these figures) and the empty weights. A fault of 2% on the A380 empty weight gives you 250nm payload-range fault, a 0.01 fault in TSFC 150nm. A fault in a aero constant might give you a 50nm fault like if the interference drag is 25% to high (actually checked it, increase that drag 25% and you loose 40nm   ).

[Edited 2013-05-17 23:25:55]
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Sat Oct 19, 2013 6:56 am

Ferpe - thanks for posting this. Can you share your excel sheet? Also, are you using a program? How are you coming to your numbers?
 
ferpe
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Mon Oct 21, 2013 10:26 pm

Quoting Matt6461 (Reply 26):
Can you share your excel sheet? Also, are you using a program? How are you coming to your numbers?

Hi, I have been advised to not share the model I have made but it is not very difficult to do one for yourselves. I pretty much gave a cook-book description on how to make a model using excel in this thread:

Boeing Vs. Airbus Wing Design Philosophies (by ferpe Apr 16 2012 in Tech Ops)

A few tips about using excel to make the model:

1. You have to start collecting the principal parameters. The one you need is part of the Standford course I reference. Start small and expand gradually.

2. Use named parameters where-ever you can (in fact everywhere). My sheet call the specifix weight of JetA1 just that and not cell U3 and when I want to have the weight of the fuel the formula looks like Fuel_weight =tank_volume*JetA1 on the row for fuel weight in the 788 column. I did not know everything about named cells and columns when I started and had the typical B174 = B172 * U3 which soon becomes a nightmare.

3. Activate iterative calculation to do the route reserves part, standard is 5% of route fuel.

4. To get your atmospheric constants (viscosity etc) use this site:

http://www.aerospaceweb.org/design/scripts/atmosphere/

5. Use PianoX as your reference when you develop your model, you can check almost everything you do with a airplane that is modeled in PianoX. The 788 is especially well covered. In fact if you don't know how a civil airliners 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 aircrafts, not even if you had my excel:

http://www.lissys.demon.co.uk/PianoX.html

[Edited 2013-10-21 15:39:18]
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Pihero
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Tue Oct 22, 2013 11:44 am

Hi, Guys !
There's a very good illustration of the A380 wing efficiency, through a picture I discovered on Flicker :

A380 humid air takeoff
Here we see that aerodynamics are not that arcane a science as it can be illustrated in everyday's life   

See the depression on top of the wing causing water vapor to be visible, thus giving a - very - clear picture of the lft repartition at Flap 2 config.
See also that , with the drooped ailerons, we have a full span trailing edge high lift flap system and the almost complete absence of tip or flap-break vortices.

Airbus seems to have managed a very clean airflow ( which also illustrates why the airplane is so quiet )

I would think that the A350, with a higher aspect ratio and winglets would do even better.

I'd be grateful if someone could upload this pic on this thread.

Rgds
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ferpe
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Tue Oct 22, 2013 11:50 am

Quoting Pihero (Reply 28):
I'd be grateful if someone could upload this pic on this thread.

Wilco!

http://i298.photobucket.com/albums/mm262/ferpe_bucket/A380startinginwetweather_zps0b14fe94.jpg

(fantastic picture  )

[Edited 2013-10-22 04:51:32]
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KarelXWB
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Tue Oct 22, 2013 12:05 pm

Than you will also like this one:


F-WWDD sous le plafond by Killian Mouden, on Flickr

Note there is more fog on the left-hand side wing.

[Edited 2013-10-22 05:09:05]
Close, but no cigar http://vine.co/v/OjqeYWWpVWK
 
Pihero
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Tue Oct 22, 2013 1:08 pm

Quoting ferpe (Reply 29):
Wilco!

Ferpe, you're a prince !

Quoting KarelXWB (Reply 30):
Note there is more fog on the left-hand side wing.

It's quite normal : the drooped ailerons are in line with the flaps while on the low wing side - starboard - , as expected, the ailerons, at least the inner portion , are up : note the dip in the depression ( hence lift ) at that inner aileron point.

Superb photos !

[Edited 2013-10-22 06:09:43]
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ferpe
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Tue Oct 22, 2013 6:34 pm

Quoting Pihero (Reply 31):
Superb photos !

Now we only need them with no high lift deployed and we could start discussing Airbus change in wingtwist 
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TheRedBaron
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Sun Sep 06, 2015 2:04 am

Thanks for the very informative thread and fantastic Photos...

Best Regards

TRB
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Fri Nov 06, 2015 4:01 pm

Quoting astuteman (Reply 24):
ve always been of the view that when (and if) an A380-900 (as originally described by Airbus) was launched, it would end up outranging the A380-800 a bit, whilst offering 14%-15% more capacity.
I don't see much of a movement in trip cost either, especially if one assumes TXWB's

(Please forgive my laymen questions)

Does the -900 have additional fuel tanks? Otherwise, how is the range more than a lighter sibling?

Also, if the trip costs are similar, and range isn't compromised on the larger whale, what was the advantage of releasing the -800 first?
.
 
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Fri Nov 06, 2015 8:23 pm

Quoting luv2cattlecall (Reply 34):
(Please forgive my laymen questions)

Does the -900 have additional fuel tanks? Otherwise, how is the range more than a lighter sibling?

Also, if the trip costs are similar, and range isn't compromised on the larger whale, what was the advantage of releasing the -800 first?

See this:

Quoting ferpe (Reply 19):
If you look at the range you see I took an existing -900 column I had which had TXWB engines (TSFC around 0.52 instead of 0.56 ), that is why these ladies fly some 200nm longer then the -800 despite being heavier and having higher drag

Also, the higher certified weights on the 900 would allow more fuel to be carried. I think the 380 is more weight-limited than fuel-limited, but that's just a guess.
 
WIederling
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Sat Nov 07, 2015 7:35 pm

Quoting LH707330 (Reply 35):
I think the 380 is more weight-limited than fuel-limited, but that's just a guess.

Available tankage in the center wing box is currently unused.

copied from a conversation on PPRUNE:
When the center tank is not installed the total usable fuel volume is 315,354 liters.
With the center tank installed the total usable fuel volume is 357,054 liters.

Airbus conducted tests with MTOW increased to 600t.
That is probably not the limit. all brakes installed would allow 625t.
Murphy is an optimist
 
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DocLightning
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Sat Nov 07, 2015 8:47 pm

Quoting KarelXWB (Reply 30):
Note there is more fog on the left-hand side wing.

It's a brilliant picture. You can see how the low pressure distribution on the starboard wing ends just at the start of the aileron section as the function of the ailerons is to decrease the lift on the downward-banking wing and to increase it on the upward-banking wing.

Slightly off-topic, but I wonder why in that same photo there also seems to be a low pressure zone above the tailplane. This would make sense if the cockpit crew had just commanded a downward change in pitch, but otherwise my understanding is that the tailplane would normally be producing a downward lift.

Any ideas why that is there?
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Starlionblue
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Sat Nov 07, 2015 9:25 pm

Quoting DocLightning (Reply 37):
Slightly off-topic, but I wonder why in that same photo there also seems to be a low pressure zone above the tailplane. This would make sense if the cockpit crew had just commanded a downward change in pitch, but otherwise my understanding is that the tailplane would normally be producing a downward lift.

AFAIK many modern airliners have tailplanes that produce upward or downward lift depending on CG position.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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DocLightning
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Sat Nov 07, 2015 11:15 pm

Quoting Starlionblue (Reply 38):
AFAIK many modern airliners have tailplanes that produce upward or downward lift depending on CG position.

The lift can be controlled by trimming the tailplane, but all airliners maintain a CG slightly forward of the CL and MLG so that they will rest on all three gear while on the ground. So the tailplane must produce a downward force to prevent the aircraft from nosing down.
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WIederling
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Sun Nov 08, 2015 9:08 am

Quoting DocLightning (Reply 39):
So the tailplane must produce a downward force to prevent the aircraft from nosing down.

you fix that by arranging the gears properly.

you need negative lift for _passive_ stable flight.
( nose down increases negative lift, nose comes back up
nose up decreases negative lift, nose comes back down )
Murphy is an optimist
 
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Matt6461
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RE: A380 Wing High Efficiency Vs Mediocre Aspect Ratio

Mon Nov 09, 2015 11:56 pm

Just for future reference re this thread, which is an all-time great and frequently referenced elsewhere.

There's a simple, but significant error in our dear, departed Ferpe's spreadsheet:

The values for wetted area are too low by approximately a factor of wing exposed area.

For A380, for example, Ferpe's Swet value is 2878m2. All other published estimates of the A380's Swet are ~3,600m2.
http://www.dept.aoe.vt.edu/~mason/Mason_f/A380Berger.pdf

Same for 777. The 77W's Swet is usually given at ~2600m2, Ferpe gives 2107m2.

One can see the error without outside support if one simply adds, e.g., 2x the A380's exposed wing area of 710m2 to its fuselage area of 1564m2 - you're already above the 2878m2 figure.

The discrepancies between Ferpe's figures and the published figures disappear if one simply adds exposed wing area to the calculation again. And indeed, in one of Ferpe (a.k.a. Bjorn)'s analyses on Leeham (behind a paywall), he appears to have noticed the error and corrected it - as the 773 has ~2,600m2 Swet.

This correction would slightly change the calculations for models here. The A380, for example, would gain ~25% more wetted area, while the 777-9 would gain only ~20% - more of the A380's Swet is in its wings due to the superb fuselage.

Relatively speaking, this would contribute ~2% negative delta to a ratio between the L/D's of the A380 and 777-9.

None of this is to suggest that Ferpe's spreadsheet isn't otherwise excellent. If there is an A.net Hall of Fame or canonization process he's my first nominee. It's a simple "forgot to carry the one" error that is easy to make on a spreadsheet as comprehensive as Ferpe's, but still something to note for future reference.

[Edited 2015-11-09 15:59:43]

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