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WIederling
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Re: Few questions about the A310 (and A300)

Tue Mar 02, 2021 6:24 pm

Starlionblue wrote:
Airbus went with an unbroken flapline for better low-speed performance on the A330/A340 (and subsequently on the A380 and A350). The downside is the need for a stiffer (and thus heavier) wing to counteract aileron reversal.

Clean Wing: they seem to have put quite the effort into that. no thrust gates ..

Then:
Airbus seems to ( OK, I am certain :-) use thicker profiles that are stil perfectly supercritical.
Static height brings stiffness with the 4th exponent?

MY tentative guess is that the Airbus wing is lighter _and_ stiffer for comparable lift.

Especially the bendy 787 wings need thicker skins to carry moment forces along the wing.
Murphy is an optimist
 
VSMUT
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Re: Few questions about the A310 (and A300)

Tue Mar 02, 2021 10:25 pm

WIederling wrote:
Starlionblue wrote:
Airbus went with an unbroken flapline for better low-speed performance on the A330/A340 (and subsequently on the A380 and A350). The downside is the need for a stiffer (and thus heavier) wing to counteract aileron reversal.

Clean Wing: they seem to have put quite the effort into that. no thrust gates ..

Then:
Airbus seems to ( OK, I am certain :-) use thicker profiles that are stil perfectly supercritical.
Static height brings stiffness with the 4th exponent?

MY tentative guess is that the Airbus wing is lighter _and_ stiffer for comparable lift.

Especially the bendy 787 wings need thicker skins to carry moment forces along the wing.


I don't think you are right there. Boeing is generally known for having lighter, but slightly less efficient wings. That is why they are floppy, and floppy is why they are less efficient. Airbus is the opposite. Stiffer and therefore heavier, but slightly more efficient. In the end the two methods achieve the same.
 
WIederling
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Re: Few questions about the A310 (and A300)

Wed Mar 03, 2021 11:07 am

VSMUT wrote:
I don't think you are right there. Boeing is generally known for having lighter, but slightly less efficient wings. That is why they are floppy, and floppy is why they are less efficient. Airbus is the opposite. Stiffer and therefore heavier, but slightly more efficient. In the end the two methods achieve the same.


first order approximation is an I beam.

vary the height of the webbing.

for the same moment (bending force ) carried:
increasing the webbing height reduces forces in the flanges.
to carry the same load lower webbing demands thicker flanges.
BUT:
The bending limit is forced by the limits of elastic deformation (upper versus longer flange resp wing skin.)
the same elastic deformation limit will show much more bending displacement on a lower beam resp. thinner wing.

flange resp. skin thickness is forced via max stresses that have to be carried at their respective displacements.

imu: a bendy wing looks much more sexy is but is a suboptimal design.
The win from being able to make a thicker wing profile behave supercritial is enormous.

just compare OEW for A359 vs. 7810 ( keep in mind the size of the wingbox and wing.
Murphy is an optimist
 
VSMUT
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Re: Few questions about the A310 (and A300)

Wed Mar 03, 2021 4:21 pm

WIederling wrote:
just compare OEW for A359 vs. 7810 ( keep in mind the size of the wingbox and wing.


But you can't just draw that conclusion from the OEW alone. The 787-10 has 1.5 meters more fuselage to drag around than the A350-900. That weighs a fair bit in itself. If I'm not mistaken, the A350 also has a greater composite content, with the wings in particular making the big difference.
 
WIederling
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Re: Few questions about the A310 (and A300)

Sat Mar 06, 2021 10:42 am

VSMUT wrote:
WIederling wrote:
just compare OEW for A359 vs. 7810 ( keep in mind the size of the wingbox and wing.


But you can't just draw that conclusion from the OEW alone. The 787-10 has 1.5 meters more fuselage to drag around than the A350-900. That weighs a fair bit in itself. If I'm not mistaken, the A350 also has a greater composite content, with the wings in particular making the big difference.


The 787 is the all plastic plane. A350 is just a panelliner :-)
The A350 has the wider fuselage.
The A350 has much more wing.
The A350 has much higher MTOW.

You get at weight per fuselage meter via the 789 to 7810 OEW changes. ( as the two types are minimum change )
per meter fuselage probably ~1.. 1.5t ( including pax stuffings.)

Then compare wing area, MTOW :-)
The A350 seems to be the structurally (significantly) more efficient airframe.
Murphy is an optimist
 
VSMUT
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Re: Few questions about the A310 (and A300)

Sat Mar 06, 2021 11:31 am

WIederling wrote:
The 787 is the all plastic plane. A350 is just a panelliner :-)


Slightly less than the A350 actually. The 787 is ahead on the fuselage construction (1 barrel vs panels), but Airbus is ahead of Boeing on the composite content in the wing. Boeing uses somewhat more traditional materials in the structure of the wing than Airbus does. The overall figures are 50% composite for the 787 and 53% for the A350.


WIederling wrote:
You get at weight per fuselage meter via the 789 to 7810 OEW changes. ( as the two types are minimum change )
per meter fuselage probably ~1.. 1.5t ( including pax stuffings.)


The 787-10 is listed on Wikipedia with an OEW of 6650 kg more than the 787-9, so 1215 kg per meter.


WIederling wrote:
The A350 seems to be the structurally (significantly) more efficient airframe.


Efficient at what? Long range cruise the big wing wins. Short haul the smaller and lighter wing wins. It's like the 757 vs A321.
 
WIederling
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Re: Few questions about the A310 (and A300)

Sat Mar 06, 2021 1:33 pm

VSMUT wrote:
WIederling wrote:
The 787 is the all plastic plane. A350 is just a panelliner :-)


Slightly less than the A350 actually. The 787 is ahead on the fuselage construction (1 barrel vs panels),

My guess is that you'll never see a cylindrical barrel section from Boeing again.
They had rather public difficulty making the sections fit early on and they seem to have generated
a rather expensive to solve problem over most of the manufactured frames till today.

VSMUT wrote:
But Airbus is ahead of Boeing on the composite content in the wing. Boeing uses somewhat more traditional materials in the structure of the wing than Airbus does. The overall figures are 50% composite for the 787 and 53% for the A350.

3% difference in materials won't be all to significant in outcome.

VSMUT wrote:
The 787-10 is listed on Wikipedia with an OEW of 6650 kg more than the 787-9, so 1215 kg per meter.


WIederling wrote:
The A350 seems to be the structurally (significantly) more efficient airframe.


Efficient at what? Long range cruise the big wing wins. Short haul the smaller and lighter wing wins. It's like the 757 vs A321.

Wings: weight vs size . Start of discussion.
787 has a smaller wing that equals the A350 wing in weight.
The theory floated was that the B wing was lighter because it was more flexing.
Murphy is an optimist
 
VSMUT
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Re: Few questions about the A310 (and A300)

Sat Mar 06, 2021 2:07 pm

WIederling wrote:
My guess is that you'll never see a cylindrical barrel section from Boeing again.
They had rather public difficulty making the sections fit early on and they seem to have generated
a rather expensive to solve problem over most of the manufactured frames till today.


How did the Russians and Chinese do it on their latest aircraft? Panels or barrels?


WIederling wrote:
The theory floated was that the B wing was lighter because it was more flexing.


Other way round. It is lighter (less structure and stiffening), so it flexes. A flexing wing is less efficient, because the total lift acts at a 90 degree angle to the wing, and so a flexed wing wastes some of its total lift on a horizontal component.
 
WIederling
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Re: Few questions about the A310 (and A300)

Sat Mar 06, 2021 4:38 pm

VSMUT wrote:
WIederling wrote:
My guess is that you'll never see a cylindrical barrel section from Boeing again.
They had rather public difficulty making the sections fit early on and they seem to have generated
a rather expensive to solve problem over most of the manufactured frames till today.


How did the Russians and Chinese do it on their latest aircraft? Panels or barrels?

what I could find:
MC-21 is Al/Li metal fuselage
Sukhoi_Superjet seems to be Al
C919 is Al/Li
Mitusbishi SpaceJet is Al/Li

WIederling wrote:
The theory floated was that the B wing was lighter because it was more flexing.


Other way round. It is lighter (less structure and stiffening), so it flexes. A flexing wing is less efficient, because the total lift acts at a 90 degree angle to the wing, and so a flexed wing wastes some of its total lift on a horizontal component.


let me repeat: E-Modulus and max elastic deformation is given by the material. CFRP.
bending limits are dependent on these material properties.
a thinner profile will show more bending under these load conditions.
upper and lower skins are nearer to each other and thus the same deformation leads to a larger displacement.
BUT
a thinner wing needs much thicker wing skins to carry the same forces.
a thinner wing with comparable planform and area will thus be heavier.
Murphy is an optimist
 
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SQ22
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Comparing Boeing 787 and Airbus A350 wing design

Sun Mar 07, 2021 9:05 am

I have moved the ongoing discission in a separate thread. Feel free to continue your discussion here.
 
WIederling
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Re: Comparing Boeing 787 and Airbus A350 wing design

Sun Mar 07, 2021 5:47 pm

SQ22 wrote:
I have moved the ongoing discission in a separate thread. Feel free to continue your discussion here..


Thanks for the constructive moderation.
Murphy is an optimist
 
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jetmech
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Re: Few questions about the A310 (and A300)

Mon Mar 08, 2021 9:57 am

WIederling wrote:
Starlionblue wrote:
Static height brings stiffness with the 4th exponent?

For a simple cantilever beam of rectangular cross section acted upon by a point load at the free end, the deflection is given by PL^3 / 3EI; with P being the magnitude of the point load, L the length of the cantilever, E the Modulus of elasticity and I the second moment of area.

The second moment of area for a rectangular section is (breadth x height^3) / 12. So stiffness should scale with the static height to the 3rd exponent.

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
WIederling
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Re: Few questions about the A310 (and A300)

Mon Mar 08, 2021 11:36 am

jetmech wrote:
WIederling wrote:
Starlionblue wrote:
Static height brings stiffness with the 4th exponent?

For a simple cantilever beam of rectangular cross section acted upon by a point load at the free end, the deflection is given by PL^3 / 3EI; with P being the magnitude of the point load, L the length of the cantilever, E the Modulus of elasticity and I the second moment of area.

The second moment of area for a rectangular section is (breadth x height^3) / 12. So stiffness should scale with the static height to the 3rd exponent.


First order approximation is an I-Beam ( wing skins as flanges, webbing as sidewalls to wingbox.)
or a square hollow tube.

Second order approx. would be tapering the arrangement.

But you get the basics exposed via looking at the i-beam thing fixed one side into a wall or double length with center support and end symmetric point loads
Murphy is an optimist
 
flipdewaf
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Comparing Boeing 787 and Airbus A350 wing design

Mon Mar 08, 2021 7:50 pm

WIederling wrote:
jetmech wrote:
WIederling wrote:

For a simple cantilever beam of rectangular cross section acted upon by a point load at the free end, the deflection is given by PL^3 / 3EI; with P being the magnitude of the point load, L the length of the cantilever, E the Modulus of elasticity and I the second moment of area.

The second moment of area for a rectangular section is (breadth x height^3) / 12. So stiffness should scale with the static height to the 3rd exponent.


First order approximation is an I-Beam ( wing skins as flanges, webbing as sidewalls to wingbox.)
or a square hollow tube.

Second order approx. would be tapering the arrangement.

But you get the basics exposed via looking at the i-beam thing fixed one side into a wall or double length with center support and end symmetric point loads

I was planning on posting some long winded stuff about wing design and t/c and wing area vs thickness affect on Mcrit and weight estimation but work happened and then I read this post and dragged out a sheet from a couple of years ago that describes what you say right here. As you can see it is quite organic but goes some way to estimating wing weight and shows the underlying trends being described.

https://drive.google.com/file/d/1BE7vpY ... sp=sharing

Fred

Edit: not sure if that link works or not, Dropbox doesn’t like me so I had to try google drive.


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flipdewaf
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Re: Comparing Boeing 787 and Airbus A350 wing design

Mon Mar 08, 2021 8:50 pm

https://www.dropbox.com/s/2e7v2qsid4o19 ... .xlsx?dl=0

Maybe this is better.


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WIederling
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Re: Comparing Boeing 787 and Airbus A350 wing design

Tue Mar 09, 2021 7:52 am

flipdewaf wrote:
https://www.dropbox.com/s/2e7v2qsid4o19dn/Wing%20bending.xlsx?dl=0

Maybe this is better.


Great!

I can access it. thanks ( and a good morning! )

That'll take a bit for me to wrap my mind around it.
I am more of an equations guy than a spread sheeter.
Murphy is an optimist
 
VSMUT
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Re: Few questions about the A310 (and A300)

Wed Mar 10, 2021 9:51 am

WIederling wrote:
what I could find:
MC-21 is Al/Li metal fuselage
Sukhoi_Superjet seems to be Al
C919 is Al/Li
Mitusbishi SpaceJet is Al/Li


Interesting. It supports the theory that CFRP doesn't scale down very well.


WIederling wrote:
let me repeat: E-Modulus and max elastic deformation is given by the material. CFRP.
bending limits are dependent on these material properties.
a thinner profile will show more bending under these load conditions.
upper and lower skins are nearer to each other and thus the same deformation leads to a larger displacement.
BUT
a thinner wing needs much thicker wing skins to carry the same forces.
a thinner wing with comparable planform and area will thus be heavier.


But the skin isn't everything. What about the internal structure that supports it, the spar and wing box in particular? We know weight is added when wings are made stiffer, in order to provide wing bending relief.
 
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Starlionblue
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Re: Few questions about the A310 (and A300)

Wed Mar 10, 2021 10:19 am

VSMUT wrote:

WIederling wrote:
let me repeat: E-Modulus and max elastic deformation is given by the material. CFRP.
bending limits are dependent on these material properties.
a thinner profile will show more bending under these load conditions.
upper and lower skins are nearer to each other and thus the same deformation leads to a larger displacement.
BUT
a thinner wing needs much thicker wing skins to carry the same forces.
a thinner wing with comparable planform and area will thus be heavier.


But the skin isn't everything. What about the internal structure that supports it, the spar and wing box in particular? We know weight is added when wings are made stiffer, in order to provide wing bending relief.


Isn't that more like "wing bending resistance"?

Wing bending relief is a counterweight like an engine.

Or am I overthinking this?
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
WIederling
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Re: Few questions about the A310 (and A300)

Fri Mar 12, 2021 8:33 am

VSMUT wrote:
WIederling wrote:
what I could find:
MC-21 is Al/Li metal fuselage
Sukhoi_Superjet seems to be Al
C919 is Al/Li
Mitusbishi SpaceJet is Al/Li


Interesting. It supports the theory that CFRP doesn't scale down very well.


Regular run of things new:
unknown,
new, upcoming,
viewed as next best thing to slices bread and will replace everything,
downsides exposed and some faces but PR and fans will ignore it,
$newstuff has found its place being better in some places while underperforming in others.
no quantum step changes visible.:-)

WIederling wrote:
let me repeat: E-Modulus and max elastic deformation is given by the material. CFRP.
bending limits are dependent on these material properties.
a thinner profile will show more bending under these load conditions.
upper and lower skins are nearer to each other and thus the same deformation leads to a larger displacement.
BUT
a thinner wing needs much thicker wing skins to carry the same forces.
a thinner wing with comparable planform and area will thus be heavier.


But the skin isn't everything. What about the internal structure that supports it, the spar and wing box in particular? We know weight is added when wings are made stiffer, in order to provide wing bending relief.


Wingskin is structure and load bearing.
( the torsion resistant wingbox profile is set up from upper, lower wing skin, 2 or 3 spars.
profile kept open by frames in regular intervals. ( highlift and stuff attached to front and rear of wingbox.))

you have two options for increasing torsion resistance ( and bending effects )
make the material thicker all around. ( linear weight::linear stiffness gain)
increase profile height and depth ( i.e. increase the area covered by the frames. (IMU linear+ weight ::exp_3 stiffness gains.)
Murphy is an optimist
 
IADFCO
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Re: Comparing Boeing 787 and Airbus A350 wing design

Fri Mar 12, 2021 10:10 pm

A potentially interesting twist (pun intended!) is that with composites, if the laminates are arranged properly, it is possible to generate useful bending-torsion couplings such as, for example, as the wing bends up, it also twists nose-down. This is a type of "aeroelastic tailoring" that could be used to change the twist distribution of a wing as a function of aircraft weight.

I don't know whether something like this is used in commercial airliners because I don't work in that field, but a well-known example is the Grumman X-29 https://en.wikipedia.org/wiki/Grumman_X-29, where aeroelastic tailoring was leveraged to protect against static aeroelastic instability (divergence) with a forward swept wing.

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