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A380 Wing High Efficiency Vs Mediocre Aspect Ratio  
User currently offlinefaro From Egypt, joined Aug 2007, 1515 posts, RR: 0
Posted (11 months 2 weeks 5 days 5 hours ago) and read 10836 times:

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 An AR of 7.5 is comparable to the L1011-500 and VC-10, some rather outdated aircraft.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


The chalice not my son
32 replies: All unread, showing first 25:
 
User currently offlineStitch From United States of America, joined Jul 2005, 29674 posts, RR: 84
Reply 1, posted (11 months 2 weeks 4 days 11 hours ago) and read 10625 times:
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What help's the A380's CASM is the large number of seats you can put in it.  

User currently offlinedw747400 From United States of America, joined Aug 2001, 1254 posts, RR: 1
Reply 2, posted (11 months 2 weeks 4 days ago) and read 10483 times:

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.



CFI--Certfied Freakin Idiot
User currently offlineferpe From France, joined Nov 2010, 2792 posts, RR: 59
Reply 3, posted (11 months 2 weeks 3 days 19 hours ago) and read 10376 times:

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]


Non French in France
User currently offlineferpe From France, joined Nov 2010, 2792 posts, RR: 59
Reply 4, posted (11 months 2 weeks 3 days 8 hours ago) and read 10207 times:

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]


Non French in France
User currently offliner2rho From Germany, joined Feb 2007, 2497 posts, RR: 1
Reply 5, posted (11 months 2 weeks 3 days 3 hours ago) and read 10116 times:

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.


User currently offlineprebennorholm From Denmark, joined Mar 2000, 6289 posts, RR: 54
Reply 6, posted (11 months 2 weeks 2 days 15 hours ago) and read 9921 times:

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.



Always keep your number of landings equal to your number of take-offs, Preben Norholm
User currently offlineferpe From France, joined Nov 2010, 2792 posts, RR: 59
Reply 7, posted (11 months 2 weeks 1 day 21 hours ago) and read 9789 times:

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.



Non French in France
User currently offlineastuteman From United Kingdom, joined Jan 2005, 9834 posts, RR: 96
Reply 8, posted (11 months 1 week 6 days 19 hours ago) and read 9517 times:
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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


User currently offlineferpe From France, joined Nov 2010, 2792 posts, RR: 59
Reply 9, posted (11 months 1 week 6 days 19 hours ago) and read 9516 times:

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.



Non French in France
User currently offlineaviaponcho From France, joined Aug 2011, 580 posts, RR: 8
Reply 10, posted (11 months 1 week 6 days 18 hours ago) and read 9504 times:

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]

User currently offlineStitch From United States of America, joined Jul 2005, 29674 posts, RR: 84
Reply 11, posted (11 months 1 week 6 days 15 hours ago) and read 9470 times:
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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).


User currently offlineastuteman From United Kingdom, joined Jan 2005, 9834 posts, RR: 96
Reply 12, posted (11 months 1 week 6 days 10 hours ago) and read 9428 times:
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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


User currently offlineKlaus From Germany, joined Jul 2001, 21353 posts, RR: 54
Reply 13, posted (11 months 1 week 5 days 23 hours ago) and read 9280 times:

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]

User currently offlinecobra27 From Slovenia, joined May 2001, 1003 posts, RR: 0
Reply 14, posted (11 months 1 week 5 days 20 hours ago) and read 9241 times:

The A380 wing was optimised for stretched A380-900 variant which could possibly launched in the future

User currently offlineStitch From United States of America, joined Jul 2005, 29674 posts, RR: 84
Reply 15, posted (11 months 1 week 5 days 19 hours ago) and read 9207 times:
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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.


User currently offlineKlaus From Germany, joined Jul 2001, 21353 posts, RR: 54
Reply 16, posted (11 months 1 week 5 days 19 hours ago) and read 9205 times:

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.


User currently offlineAquila3 From Italy, joined Nov 2010, 243 posts, RR: 0
Reply 17, posted (11 months 1 week 5 days 18 hours ago) and read 9189 times:

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)



chi vola vale chi vale vola chi non vola è un vile
User currently offlineferpe From France, joined Nov 2010, 2792 posts, RR: 59
Reply 18, posted (11 months 1 week 5 days 18 hours ago) and read 9187 times:

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.



Non French in France
User currently offlineferpe From France, joined Nov 2010, 2792 posts, RR: 59
Reply 19, posted (11 months 1 week 4 days 16 hours ago) and read 8973 times:

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]


Non French in France
User currently onlineWingedMigrator From United States of America, joined Oct 2005, 2132 posts, RR: 56
Reply 20, posted (11 months 1 week 4 days 10 hours ago) and read 8894 times:

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.


User currently offlineaviaponcho From France, joined Aug 2011, 580 posts, RR: 8
Reply 21, posted (11 months 1 week 4 days 3 hours ago) and read 8814 times:

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.


User currently offlineKlaus From Germany, joined Jul 2001, 21353 posts, RR: 54
Reply 22, posted (11 months 1 week 4 days ago) and read 8783 times:

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.


User currently offlineaviaponcho From France, joined Aug 2011, 580 posts, RR: 8
Reply 23, posted (11 months 1 week 3 days 18 hours ago) and read 8716 times:

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 ?


User currently offlineastuteman From United Kingdom, joined Jan 2005, 9834 posts, RR: 96
Reply 24, posted (11 months 6 days 22 hours ago) and read 8369 times:
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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


25 Post contains images ferpe : 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 understandin
26 Matt6461 : Ferpe - thanks for posting this. Can you share your excel sheet? Also, are you using a program? How are you coming to your numbers?
27 Post contains links ferpe : 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 desc
28 Post contains links and images Pihero : 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 se
29 Post contains links and images ferpe : Wilco! (fantastic picture )[Edited 2013-10-22 04:51:32]
30 Post contains links and images KarelXWB : 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 2013-1
31 Pihero : Ferpe, you're a prince ! It's quite normal : the drooped ailerons are in line with the flaps while on the low wing side - starboard - , as expected,
32 Post contains images ferpe : Now we only need them with no high lift deployed and we could start discussing Airbus change in wingtwist
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