GearDownFlaps30
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Boeing 747-8i Questions

Sat Sep 18, 2010 7:31 pm

Hi all, I'm Steven and this is my very first post here on Airliners net. After contemplating all those great photos and reading all those compelling topics for the last 5 years, I eventually joined the "community".

My first post is related to the supreme 747-8i, precisely the rear section of its wing/fuselage fairing. I know the rear fuselage section is stretched by 1.524m around the wing trailing edge but is the rear section of its wing/fuselage fairing stretched as well, or is it the same length as on the 747-400?

Then the wings. Boeing says they are "relofted", I understand their airfoil sections are new, not forgetting the new double-slotted inboard and single-slotted outboard flaps, new leading edge devices and of course the smart-looking new wingtip extensions but how about the wing shape from the top view? Is it identical to that of the 747-400, not taking into consideration the wingtips? Or are the trailing edges "smoothened" as on the 787s wings (smooth-curvy transition between the inboard flaps/aileron/outboard flaps/aileron)?

Thanking you all in advance!
Ciao, Steven
 
tdscanuck
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RE: Boeing 747-8i Questions

Sat Sep 18, 2010 10:41 pm

Quoting GearDownFlaps30 (Thread starter):
Hi all, I'm Steven and this is my very first post here on Airliners net.

Welcome!

Quoting GearDownFlaps30 (Thread starter):
I know the rear fuselage section is stretched by 1.524m around the wing trailing edge but is the rear section of its wing/fuselage fairing stretched as well, or is it the same length as on the 747-400?

As far as I can tell, no. The extension appears to be in the constant cross-section portion aft of the fairing, so the fairing itself didn't change length.

Quoting GearDownFlaps30 (Thread starter):
Then the wings. Boeing says they are "relofted", I understand their airfoil sections are new, not forgetting the new double-slotted inboard and single-slotted outboard flaps, new leading edge devices and of course the smart-looking new wingtip extensions but how about the wing shape from the top view? Is it identical to that of the 747-400, not taking into consideration the wingtips? Or are the trailing edges "smoothened" as on the 787s wings (smooth-curvy transition between the inboard flaps/aileron/outboard flaps/aileron)?

Yes, the wing planform also changed shape. Compare these two scale drawings:
747-8: http://www.boeing.com/commercial/airports/acaps/7478sec9.pdf (pg. 3)
747-400: http://www.boeing.com/commercial/airports/acaps/7474sec9.pdf (pg. 3)

Tom.
 
GearDownFlaps30
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RE: Boeing 747-8i Questions

Sun Sep 19, 2010 5:18 am

Hi and thank you for your message.

Quoting tdscanuck (Reply 1):
As far as I can tell, no. The extension appears to be in the constant cross-section portion aft of the fairing, so the fairing itself didn't change length.

Ok, thank you, I thought they would have taken the opportunity to redesign the fairing in order to gain a few percentages here and there (as did Airbus on their A340-500 and -600, featuring a longer/deeper/fatter fairing than on the A340-200 and -300).

Quoting tdscanuck (Reply 1):
Yes, the wing planform also changed shape. Compare these two scale drawings:

Outch, I can count no less than 4 "kinks" on the trailing edge (inboard aileron, outboard flaps, outboard aileron and wingtip) versus 1 kink on the 747-400s wing trailing edge.

Can we trust these drawings, or are they simplified ones?
Ciao, Steven
 
SchorschNG
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RE: Boeing 747-8i Questions

Sun Sep 19, 2010 9:09 am

Quoting GearDownFlaps30 (Reply 2):
Outch, I can count no less than 4 "kinks" on the trailing edge (inboard aileron, outboard flaps, outboard aileron and wingtip) versus 1 kink on the 747-400s wing trailing edge.

Can we trust these drawings, or are they simplified ones?

I wouldn't trust them too much when it comes to details.

The B747-8 was supposed to use similar wing planform to re-use jigs. While usually a "wing relofting" is something you don't do, the gain was large as the B747-400 still flew the non supercritical wing of the 1960ies.
However, with changed profile and high-lift devices come new list distribution and loads, that require new structure added as some key structural features cannot be changed (for example engine position). But usually all issues can be resolved with some extra weight. Carrying some "ballast" in the wings to counter flutter is common occurrence on some Airbus and Boeing aircraft, including the B747.

Interesting to note that the B747-8I has serious issues with its wing (flutter and vibration), and that might delay the program, some people are saying up to half a year.
From a structural standpoint, passengers are the worst possible payload. [Michael Chun-Yung Niu]
 
GearDownFlaps30
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RE: Boeing 747-8i Questions

Sun Sep 19, 2010 11:20 am

Hello, thank you for your reply.

Quoting SchorschNG (Reply 3):
the B747-400 still flew the non supercritical wing of the 1960ies.

Yes, I was always surprised it was reused almost identically with just the addition of the wingtip extension and winglet on the 747-400, I wonder if the wing design was ahead of its time in the 60-70s, a design THAT good in the 60-70s that it was still good on the 90s for the 747-400? I never read a comment saying the 747-400 was let down by its "old tech" wing, unlike the MD-11.

Quoting SchorschNG (Reply 3):
Interesting to note that the B747-8I has serious issues with its wing (flutter and vibration), and that might delay the program, some people are saying up to half a year.

I read that too, something to do with one portion of the wing ldg door causing flutter to the newly designed inboard double-slotted flaps. I hope the programme do not get too delayed, it is not like if they had hundreds of airframes sold and dozens of loyal customers, they only have one firm customer in the name of Lufthansa.

Have a nice day all!
Ciao, Steven
 
tdscanuck
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RE: Boeing 747-8i Questions

Sun Sep 19, 2010 2:19 pm

Quoting GearDownFlaps30 (Reply 2):
I thought they would have taken the opportunity to redesign the fairing in order to gain a few percentages here and there

Oh, they did redesign the fairing...the wing changed airfoil, therefore the fairing must have changed. I thought you were asking if the fairing got longer as a result of the fuselage extention.

Quoting GearDownFlaps30 (Reply 2):
Outch, I can count no less than 4 "kinks" on the trailing edge (inboard aileron, outboard flaps, outboard aileron and wingtip) versus 1 kink on the 747-400s wing trailing edge.

Can we trust these drawings, or are they simplified ones?

For major stuff like planform they're good (they're scale drawings used by airports for planning, so gross dimensions are accurate). Although I'm not sure number of kinks is a particularly good metric.

Quoting SchorschNG (Reply 3):
Interesting to note that the B747-8I has serious issues with its wing (flutter and vibration)

The 747-8I has no flutter issues that we know of...it hasn't even flown yet. The 747-8F has issues but, since flutter is an aerodynamic-structural coupling and since the 747-8I has different aerodynamics, it's too early to tell about the -8I.

Quoting GearDownFlaps30 (Reply 4):
they only have one firm customer in the name of Lufthansa.

Eight, actually. I understand why people keep forgetting the BBJ's, but why does everyone keep forgetting Korean?

Tom.
 
GearDownFlaps30
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RE: Boeing 747-8i Questions

Sun Sep 19, 2010 5:31 pm

Quoting tdscanuck (Reply 5):
Oh, they did redesign the fairing...the wing changed airfoil, therefore the fairing must have changed. I thought you were asking if the fairing got longer as a result of the fuselage extention.

Thank you, it is now clear to me that the rear section of the fairing was not stretched, and that the whole fairing was actually slightly revised.

Quoting tdscanuck (Reply 5):
For major stuff like planform they're good (they're scale drawings used by airports for planning, so gross dimensions are accurate). Although I'm not sure number of kinks is a particularly good metric.

Regarding the trailing edge kinks, I will have to check photos to be sure.

Quoting tdscanuck (Reply 5):
The 747-8I has no flutter issues that we know of...it hasn't even flown yet. The 747-8F has issues but, since flutter is an aerodynamic-structural coupling and since the 747-8I has different aerodynamics, it's too early to tell about the -8I.

Speaking of the 747-8i in that case was a typo but I do hope the passenger version will not reproduce the problems the freighter version is encountering.

Quoting tdscanuck (Reply 5):
Eight, actually. I understand why people keep forgetting the BBJ's, but why does everyone keep forgetting Korean?

I thought Lufthansa was the sole customer for the 747-8i but I forgot Koreans order and BBJs as well.

Hey, many thanks for your help!
Ciao, Steven
 
ANITIX87
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RE: Boeing 747-8i Questions

Mon Sep 20, 2010 4:53 pm

Steven, Welcome!

I don't mean to hijack your thread, but this yielded some questions from me, too.

Tom, does the 748 not have inboard high-speed ailerons? The PDF you linked doesn't show any.

Do the primary aerodynamic differences you mentioned (when talking about the flutter issues) stem mainly from the extended upper deck? I assume the wing and gear are the same, and that this wouldn't change the aerodynamics much, but I don't know a whole lot about the 748, to be honest.

Thanks.

TIS
www.stellaryear.com: Canon EOS 50D, Canon EOS 5DMkII, Sigma 50mm 1.4, Canon 24-70 2.8L II, Canon 100mm 2.8L, Canon 100-4
 
SchorschNG
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RE: Boeing 747-8i Questions

Mon Sep 20, 2010 8:47 pm

Quoting tdscanuck (Reply 5):

The 747-8I has no flutter issues that we know of...it hasn't even flown yet. The 747-8F has issues but, since flutter is an aerodynamic-structural coupling and since the 747-8I has different aerodynamics, it's too early to tell about the -8I.

The -8I gonna have the same wing as the -8I, they have similar weights. So what's your point?
The B747-8 does have some problems.
From a structural standpoint, passengers are the worst possible payload. [Michael Chun-Yung Niu]
 
Vmcavmcg
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RE: Boeing 747-8i Questions

Mon Sep 20, 2010 9:10 pm

Quoting SchorschNG (Reply 8):
The -8I gonna have the same wing as the -8I, they have similar weights. So what's your point?
The B747-8 does have some problems.

The flutter is the resutl of the short upper deck on the 748F compared with the longer upper deck on the 748I.
If we weren't all crazy, we would go insane!
 
tdscanuck
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RE: Boeing 747-8i Questions

Tue Sep 21, 2010 12:34 am

Quoting ANITIX87 (Reply 7):
Tom, does the 748 not have inboard high-speed ailerons? The PDF you linked doesn't show any.

They're the gap between the inboard and outboard flaps. You can see them in this CG rendering:
http://www.boeing.com/commercial/startup/pdf/freighters/747-8F_ext.pdf
or the real thing here:
http://www.airliners.net/photo/Boein...d=29df1554680121211bbb71976f329d02

The scale drawings (the original PDF link) are good for gross dimensions, but pretty useless for technical details.

Quoting ANITIX87 (Reply 7):
Do the primary aerodynamic differences you mentioned (when talking about the flutter issues) stem mainly from the extended upper deck?

Yes. There are also structural differences because of the higher MLW on the freighter.

Quoting SchorschNG (Reply 8):
The -8I gonna have the same wing as the -8I, they have similar weights. So what's your point?

That the aerodynamics aren't the same. Flutter is a fairly complicated aerodynamic/structural coupling, and it's extremely configuration sensitive. The -8I has a pretty major aerodynamic change with the extended hump. I wouldn't be at all surprised if the -8I has similar issues to the -8F, but it's way to early to say that it automatically must.

Tom.
 
SchorschNG
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RE: Boeing 747-8i Questions

Tue Sep 21, 2010 5:54 pm

Quoting tdscanuck (Reply 10):
That the aerodynamics aren't the same. Flutter is a fairly complicated aerodynamic/structural coupling, and it's extremely configuration sensitive. The -8I has a pretty major aerodynamic change with the extended hump. I wouldn't be at all surprised if the -8I has similar issues to the -8F, but it's way to early to say that it automatically must.

Fully agree, predicting flutter is hell of a job.
Actually, I didn't think about the effect of the hump in transonic regime.
I guess the issues with the B747-8F will be sorted out with the magic of some extra kg, and the -8I will probably not have any additional delay due to it.

Quoting tdscanuck:
They're the gap between the inboard and outboard flaps. You can see them in this CG rendering:

Quite surprised it still uses high-speed ailerons. I thought that was old fashioned.
Does it because Boeing think high-speed ailerons are superior, or because the B747-400 wing planform restricted the changes in trailing edge devices.
Airbus does use full length high lift devices, with one, two or three outer wing ailerons on A320, A330/340 or A380, respectively.
From a structural standpoint, passengers are the worst possible payload. [Michael Chun-Yung Niu]
 
SchorschNG
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RE: Boeing 747-8i Questions

Tue Sep 21, 2010 5:57 pm

Just checked visually: the B787 does seem to have high speed ailerons, too.
From a structural standpoint, passengers are the worst possible payload. [Michael Chun-Yung Niu]
 
tdscanuck
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RE: Boeing 747-8i Questions

Wed Sep 22, 2010 12:42 am

Quoting SchorschNG (Reply 11):
Quite surprised it still uses high-speed ailerons. I thought that was old fashioned.

It's not so much old fashioned as just different. The 777 and 787 retained them, even though they're far newer.

Quoting SchorschNG (Reply 11):
Does it because Boeing think high-speed ailerons are superior, or because the B747-400 wing planform restricted the changes in trailing edge devices.

The planform changed with the 747-8, so that wasn't the restriction. I suspect it was to keep the number of changes to a minimum. The 747-8 has to fly like the 747-400 to retain common type rating, and it probably would have taken a lot more effort to retain the same flight characteristics with the inboard ailerons gone.

Quoting SchorschNG (Reply 11):
Airbus does use full length high lift devices, with one, two or three outer wing ailerons on A320, A330/340 or A380, respectively.

Exactly, it's just two sides of a trade study. Having only one aileron (on each side) means that it has to be bigger and you need to be better about your gain scheduling vs. speed, but you've only got one system to deal with. You do pick up some sonic issues because now you've got flaps potentially hanging in the engine wake. Having two ailerons increases part count,but means the individual parts are smaller, the gain scheduling is easier to implement, and keeps your flaps out of the engine wake.

Quoting SchorschNG (Reply 12):
Just checked visually: the B787 does seem to have high speed ailerons, too.

Technically, they're flaperons. They move together as part of the high-lift system, and move differentially for roll control.

Tom.

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