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Sokes
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Wing length and economy of scale in aircraft manufacturing

Fri Jan 24, 2020 9:52 am

Anybody knows why the OEW of A380 is so high? I would expect economy of scale to lower the weight/ seat compared to an A350.
A380: 277t/ 853 seats = 325 kg/ seat
A350-900: 142,4t/ 440 seats = 324 kg/ seat
A330-200: 120,6t/ 406 seats = 297 kg/ seat
A320: 42,6t / 190 seats = 224 kg/ seat

Does crossing a certain wingspan require so much added wing weight that economy of scale doesn't apply?
What is this wing span: rather 60m (B787), 65m (A330Neo, A350) or 72m (B777X)?
Or is it not the wing's fault that A380 is so heavy?
Why can't the world be a little bit more autistic?
 
Zeke2517
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Re: Wing length and economy of scale in aircraft manufacturing

Fri Jan 24, 2020 11:45 am

Not an engineer, but I’m pretty sure that the 380 wasn’t able to have the wingspan that it should have because it had to fit into existing gates at airports. Therefore it was kind of doomed from the start, which is why they don’t make ‘em anymore.
 
unimproved
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Re: Wing length and economy of scale in aircraft manufacturing

Fri Jan 24, 2020 1:26 pm

Zeke2517 wrote:
Not an engineer, but I’m pretty sure that the 380 wasn’t able to have the wingspan that it should have because it had to fit into existing gates at airports. Therefore it was kind of doomed from the start, which is why they don’t make ‘em anymore.

If it didn't have the wingspan it needed then it wouldn't fly at all.

It was doomed because it has the operating costs of close to two twinjets stacked on top of eachother, without the fleet planning advantage of having two actual aircraft. They work very well for airlines needing to move a lot of people to their hub at once (ME3 transfer flights for example, where everything arrives around midnight and then leaves again an hour or two later) but that's it.
 
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SheikhDjibouti
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Re: Wing length and economy of scale in aircraft manufacturing

Fri Jan 24, 2020 1:40 pm

Sokes wrote:
Anybody knows why the OEW of A380 is so high? I would expect economy of scale to lower the weight/ seat compared to an A350.

Or is it not the wing's fault that A380 is so heavy?

Wikipedia is a much maligned source, but I find it invaluable. And I'm not ashamed to admit it either.

Wikipedia wrote:
The A380's wings are sized for a maximum takeoff weight (MTOW) over 650 tonnes to accommodate future versions,
i.e. 75 tonnes more than A380-800 MTOW of 575t

Wikipedia wrote:
The optimal wingspan for this weight is about 90 m (300 ft), but airport restrictions have limited it to less than 80 m (260 ft), thereby lowering the aspect ratio to 7.8 which reduces fuel efficiency

So, less than optimal wingspan, and also designed for an even bigger model that never got off the ground.
Nothing to see here; move along please.
 
WIederling
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Re: Wing length and economy of scale in aircraft manufacturing

Fri Jan 24, 2020 6:58 pm

SheikhDjibouti wrote:
So, less than optimal wingspan, and also designed for an even bigger model that never got off the ground.


if you go over all existing types you'll find that MTOW and wingspan have some exponential relation.

scaling the wing in a more linear fashion incurs massive weight costs CFRP seems to not improve all too much.

A380: OEW 277, MTOW 575, ratio 0.482, span 79.75
777X: OEW 181, MTOW 353, ratio 0.512, span 71.8
A359: OEW 134, MTOW 280, ratio 0.478, span 64.75
787-9: OEW 128, MTOW 253, ratio 0.505 span 60.12
Murphy is an optimist
 
Sokes
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Re: Wing length and economy of scale in aircraft manufacturing

Sat Jan 25, 2020 6:00 pm

WIederling wrote:
...
scaling the wing in a more linear fashion incurs massive weight costs CFRP seems to not improve all too much.

A380: OEW 277, MTOW 575, ratio 0.482, span 79.75
777X: OEW 181, MTOW 353, ratio 0.512, span 71.8
...


AFAIK double the wing length is four times the lift, but eight times the material required.
As the A380 wing is too short (80m gate) one should expect the OEW/ seat to be lower. But mainly I refer to the fact that the A380 has two passenger decks. I would expect it to be lighter/ seat even after accounting for stairs.
Good question how much weight CFRP can save. Anybody has a percentage number?
Why can't the world be a little bit more autistic?
 
WIederling
Posts: 9291
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Re: Wing length and economy of scale in aircraft manufacturing

Sat Jan 25, 2020 6:15 pm

Sokes wrote:
WIederling wrote:
...
scaling the wing in a more linear fashion incurs massive weight costs CFRP seems to not improve all too much.

A380: OEW 277, MTOW 575, ratio 0.482, span 79.75
777X: OEW 181, MTOW 353, ratio 0.512, span 71.8
...


AFAIK double the wing length is four times the lift, but eight times the material required.
As the A380 wing is too short (80m gate) one should expect the OEW/ seat to be lower. But mainly I refer to the fact that the A380 has two passenger decks. I would expect it to be lighter/ seat even after accounting for stairs.
Good question how much weight CFRP can save. Anybody has a percentage number?


What I've seen goes all over the place.
One information is specific strength: hang a wire of the stuff and see at which length it breaks.
Al ~22km, Matrix embedded CF ~80km :-)
Best place to bring that to bear is solid structures. ... Like wings
same strength CFRP should show drastically lower buckling performance.

reality: the new planes using CFRP are not significantly lighter than their fully Al brethren.
Murphy is an optimist
 
mxaxai
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Re: Wing length and economy of scale in aircraft manufacturing

Sun Jan 26, 2020 1:01 am

The A380 (and the A350-900) has massive range compared to the A330 and A320. Carrying around all that fuel doesn't come for free, you need a larger wing, more powerful engines, stronger gear etc. So that's at least part of the difference. Another aspect for A350 vs. A380 in particular is probably AL vs CFRP as their range is similar.

Also the new engines are heavier despite their increased efficiency, which eats up some of the weight gains made in other areas. Same applies to other areas, to some extent, where new materials are used to keep weight steady while improving other features like aerodynamics, manufacturing, comfort ... e. g. the 77X has a new wing that isn't actually much lighter, if any, despite new materials but does improve aerodynamics through increased span and revised geometry.
 
WIederling
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Re: Wing length and economy of scale in aircraft manufacturing

Sun Jan 26, 2020 9:21 am

mxaxai wrote:
...........the 77X has a new wing that isn't actually much lighter, if any, despite new materials but does improve aerodynamics through increased span and revised geometry.


The 777-9 gained ~~20t OEW. major increase in the wings.

A350, A380 actually are light ( OEW ) for their MTOW capability.
Then for per seat weight you have to use a comparable density pax layout.
( take a one class economy layout?)
Murphy is an optimist
 
Sokes
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Re: Wing length and economy of scale in aircraft manufacturing

Sun Jan 26, 2020 4:40 pm

WIederling wrote:
mxaxai wrote:
...........the 77X has a new wing that isn't actually much lighter, if any, despite new materials but does improve aerodynamics through increased span and revised geometry.


The 777-9 gained ~~20t OEW. major increase in the wings.

A350, A380 actually are light ( OEW ) for their MTOW capability.
Then for per seat weight you have to use a comparable density pax layout.
( take a one class economy layout?)


A330-300: OEW / MTOW = 242t / 129,4t = 53%
Using your earlier post all widebodies have an OEW which is 48-53% of MTOW. The A380 is on the lower end, but I would have expected it still lower.
If one considers how well the B787 does with it's short wing and if one considers the weight increase of the B777X I assume the exponential weight increase with wing length limits the useful wing length. If this assumption is correct there is a limit in economy of scale in plane size.
I assume where this limit is depends on available engines. A lot of assumptions, but I feel my question is answered.
Why can't the world be a little bit more autistic?
 
WIederling
Posts: 9291
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Re: Wing length and economy of scale in aircraft manufacturing

Sun Jan 26, 2020 5:49 pm

Sokes wrote:
WIederling wrote:
mxaxai wrote:
...........the 77X has a new wing that isn't actually much lighter, if any, despite new materials but does improve aerodynamics through increased span and revised geometry.


The 777-9 gained ~~20t OEW. major increase in the wings.

A350, A380 actually are light ( OEW ) for their MTOW capability.
Then for per seat weight you have to use a comparable density pax layout.
( take a one class economy layout?)


A330-300: OEW / MTOW = 242t / 129,4t = 53%
Using your earlier post all widebodies have an OEW which is 48-53% of MTOW. The A380 is on the lower end, but I would have expected it still lower.
If one considers how well the B787 does with it's short wing and if one considers the weight increase of the B777X I assume the exponential weight increase with wing length limits the useful wing length. If this assumption is correct there is a limit in economy of scale in plane size.
I assume where this limit is depends on available engines. A lot of assumptions, but I feel my question is answered.


The limit is not with engines but with material strength. if you can build a higher aspect ration wing for the same weight ...
Scaling effects work against aerodynamic optima here. ( exponential, no hard corner )

Another thing that incurs weight penalty is a thinner profile ( causes that wonderful flex on the 787.)
The 777X wing is said to be a scaled 787 wing.

In a first order abstraction a wing is an H-beam, profile height is the webbing, wingskin the flanges.
With a higher webbing the flanges can be thinner for the same load bearing capability
and deflection from loads decreases. A high profile wing is stiffer and lighter.
Better abstraction would include taper factor and such.
But a constant section beam is a good start point to look at.
Murphy is an optimist
 
Sokes
Topic Author
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Re: Wing length and economy of scale in aircraft manufacturing

Mon Jan 27, 2020 1:44 am

WIederling wrote:
Another thing that incurs weight penalty is a thinner profile ( causes that wonderful flex on the 787.)
The 777X wing is said to be a scaled 787 wing.



I didn't knew. As always great info. Thanks.
If that is so my earlier conclusions are probably not valid. I guess it also means the B777X should have a bright future.
Suppose you had to run an airline: With all the trouble new engine technology is facing, would you order the B777X now or would you wait to see how GE's new engine will perform?
Anybody knows if the A220 wing is similar slim?
Why can't the world be a little bit more autistic?
 
JayinKitsap
Posts: 2166
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Re: Wing length and economy of scale in aircraft manufacturing

Mon Jan 27, 2020 7:22 am

For a cantilever beam with a uniform load (it is actually tapered which complicates things, lower moment for same area and wing pressure) the moment is a function of the length squared, deflection is based on the length to the 4th power. So double the length, the moment goes up by 4x and the deflection by 16x.

The beam stiffness I is based on sum Aflanges * y^2 + web width * depth^3/12. The section modulus S is I/ (d/2) with M/S giving the peak bending stress.

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