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Thoughts On The 787 Wingox...  
User currently offlineElpinDAB From United States of America, joined Apr 2005, 485 posts, RR: 4
Posted (5 years 3 weeks 4 days 18 hours ago) and read 6480 times:

Here are my thoughts...

First, why didn't they make it subtly area-ruled like the A-380's wingbox? It's optimized for about the same range and cruise speed.

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Next, could Boeing enlarge the wingbox, to make it sag more below the fuselage, like the A330, or to be more extreme, the Citation X, making it stronger? Lowering the attachment point of the wing would solve issues of having to re-design the landing gear to arrange for increased engine clearance, while giving the aircraft more space to arrange for the high load demands of a large, flexible wing?


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It seems as if the 787's wing and wingbox is tucked way up within the fuselage. How could this be beneficial? Aerodynamics might have been a factor, but a skillfully designed, drooping wingbox might have solved any aerodynamic drawbacks, while creating more space for strengthening structural components, in a addition to increased cargo and baggage capacity.

My analysis is hardly even ameteur. I'd like to hear any of your own technical ideas why the current 787 wingbox isn't working.

10 replies: All unread, jump to last
 
User currently offlineBri2k1 From United States of America, joined Dec 2004, 988 posts, RR: 4
Reply 1, posted (5 years 3 weeks 4 days 3 hours ago) and read 6329 times:

Probably the main reason is the 787's use of 50% composites in the fuselage.

Quoting ElpinDAB (Thread starter):
First, why didn't they make it subtly area-ruled like the A-380's wingbox?

Range and cruise speed aside, what about dimensions and capacity? Shouldn't those have a significant role in the size and location of structural components? And they are vastly different between the A380's max 656-seat design capacity with a 261-foot wingspan, and the 787's 296 seats and 208-foot maximum wingspan. Not to mention the number of engines...

Quoting ElpinDAB (Thread starter):
Next, could Boeing enlarge the wingbox, to make it sag more below the fuselage, like the A330, or to be more extreme, the Citation X, making it stronger?

Yes. But design without purpose is like form without function, and neither are appealing to me or many of my aviator friends.

Quoting ElpinDAB (Thread starter):
a skillfully designed, drooping wingbox might have solved any aerodynamic drawbacks

Not if it wasn't producing more lift than the drag it was inducing.

Quoting ElpinDAB (Thread starter):
My analysis is hardly even ameteur.

I am not trying to be rude, but you misspelled "amateur." This does not lend itself to your credibility. I believe it's the spirit (and rules) of the forum to present opinions as opinions and facts as facts, citing sources where applicable. Your profile lists your occupation as "Serbian Psychiatrist," and whether it's true or not, it would appear without further data that your analysis is, indeed, amateur.

I was fortunate enough to take the Boeing factory tour in early June of 2007 and saw the very first production 787 on the assembly line (albeit from a distance). I can assure you, the form and function of the major structural components are as aesthetically pleasing to any engineer as the elegant simplicity of the Wright Flier or the bodacious performance of the Citation X. I'm one of those guys who tries to outsmart the automotive engineers, adding aftermarket parts to my car, but I know I'm not qualified to armchair-engineer the world's most technologically advanced airliner.



Position and hold
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 2, posted (5 years 3 weeks 3 days 21 hours ago) and read 6253 times:



Quoting ElpinDAB (Thread starter):
First, why didn't they make it subtly area-ruled like the A-380's wingbox?

You don't area rule a wing-box. What you're looking at on the A380 is the wing-to-body fairing. The wing box on the A380 is very simlar (in geometry) to all other large commercial jets, just scaled.

Area ruling also applies to the whole area, not specific parts, so you need to include everything at that station...when you're around the wings, wing/body interaction can overrule area ruling, and you can't tell what the fairing above the wing is doing.

Also, area ruling is really a huge deal for supersonic...in transsonic it's much less clear.

Quoting ElpinDAB (Thread starter):

Next, could Boeing enlarge the wingbox, to make it sag more below the fuselage, like the A330, or to be more extreme, the Citation X, making it stronger?

There's nothing about the Citation X construction that's stronger, it's just way easier to assemble and gives you more cabin space. That's a huge issue on a biz jet...on a transport aircraft, the wing goes through the cargo bay anyway do it doesn't change cabin area.

Quoting ElpinDAB (Thread starter):
Lowering the attachment point of the wing would solve issues of having to re-design the landing gear to arrange for increased engine clearance, while giving the aircraft more space to arrange for the high load demands of a large, flexible wing?

How would lowering the wing fix the the landing gear issue? It seems to me it would make it worse because the geometry between the wheel well and the wing would get really strange.

Quoting ElpinDAB (Thread starter):
It seems as if the 787's wing and wingbox is tucked way up within the fuselage.

They are. As are all current Boeing and Airbus jets.

Quoting ElpinDAB (Thread starter):
How could this be beneficial?

Better aerodynamics (no big hump sticking off the bottom of the fuselage), lower fuselage (easier servicing), easier gear geometry.

Quoting ElpinDAB (Thread starter):
Aerodynamics might have been a factor, but a skillfully designed, drooping wingbox might have solved any aerodynamic drawbacks, while creating more space for strengthening structural components, in a addition to increased cargo and baggage capacity.

I don't really get how it increases space for strenthening...the fuselage is built around the wing, not the other way around. You would get more cargo space, but with a pretty hefty drag penalty I suspect. The wing box on something like the 787 is about 6 feet thick...that's a lot of frontal area hanging out in the breeze. Plus, you'd have to relocate all the stuff that currently lives under the wing (most of the ECS).

Quoting ElpinDAB (Thread starter):
My analysis is hardly even ameteur. I'd like to hear any of your own technical ideas why the current 787 wingbox isn't working.

Why do we think it's not working? As far as I can tell, the 787 hasn't done anything different with the wing box than prior Boeing jets, and those work just fine.

Tom.


User currently offlinemusang From United Kingdom, joined Apr 2001, 872 posts, RR: 7
Reply 3, posted (3 years 11 months 3 weeks 5 days 9 hours ago) and read 5028 times:

Bri2k1

Quoting Bri2k1 (Reply 1):
I am not trying to be rude, but you misspelled "amateur." This does not lend itself to your credibility

I am not trying to be rude either, but you misspelled "Flyer". This does not in any way affect my opinion of your credibilty any more than it affects my opinion of your sense of balance, taste in music etc..

One of "the rules" shown above the reply field, is "No hostile language or criticizing of others". Don't you think you were a little intolerant and contemptuous of our Serbian contributor's question? Everyone makes spelling mistakes, and English is possibly not even his first language. We're not all rocket scientists like yourself, and I would respectfully suggest that so-called "amateurs" would far more appreciate replies like the one which followed yours!

Regards - musang


User currently offlinePihero From France, joined Jan 2005, 4619 posts, RR: 77
Reply 4, posted (3 years 11 months 3 weeks 5 days 7 hours ago) and read 4971 times:
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Quoting Tdscanuck (Reply 2):
area ruling is really a huge deal for supersonic...in transsonic it's much less clear.

I beg to differ. The area rule was initially put on designs that couldn't be supersonic. The best example was the YF-102 which couldn't pass the *sound barrier* until they reworked the fuselage into the so-called *coke bottle rule*. So the transsonic domain was where the rule was the most useful.
With a very modest thrust increase, the prototype went from an unsurpassable .98M to 1.22.
See below :
the F102 story

Quoting Tdscanuck (Reply 2):
.when you're around the wings, wing/body interaction can overrule area ruling, and you can't tell what the fairing above the wing is doing.

I agree it's difficult but we've had so much progress in three-dimensional aerodynamics that's it's now feasible...It's even patented !

(edit) : a wiki short and clear history / advantages of the thing :
Area rule

[Edited 2010-12-01 09:08:38]


Contrail designer
User currently offlineFly2HMO From , joined Dec 1969, posts, RR:
Reply 5, posted (3 years 11 months 3 weeks 5 days 5 hours ago) and read 4934 times:

Quoting ElpinDAB (Thread starter):

First, why didn't they make it subtly area-ruled like the A-380's wingbox?

If it works, don't fix it. As simple as that. They obviously did the math and know the current design is the best.


User currently offlinemusang From United Kingdom, joined Apr 2001, 872 posts, RR: 7
Reply 6, posted (3 years 11 months 3 weeks 4 days 7 hours ago) and read 4695 times:

Other examples which spring to mind are the fuselage abeam the engines on (among other Dassaults) the Falcon 900,


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the rear fuselage at the base of the fin on the production and pre-production Concordes,


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and the fuselage of the Blackburn Buccaneer.


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Regards - musang


User currently offlineWingscrubber From UK - England, joined Sep 2001, 852 posts, RR: 0
Reply 7, posted (3 years 11 months 2 weeks 3 days 7 hours ago) and read 4259 times:

FYI, the Citation X area-ruled wing-body fairing has everything to do with its speed, as does the 'pinch' between the engines at the rear. The 'finger fairing' ahead of the wing box area was required to help achieve the cruise speed targets during the X's development which has a knock-on effect on efficiency.

The central wing box on the Citation X actually has a deep u-shaped curve in it where it mates to the fuselage so the main spar doesn't cut across the cabin floor like it does in some of the smaller Citations, this means the entire uninterupted central wing box is used for fuel storage, and all the fairing space around it is packed tightly with hydraulic and pneumatic lines, wire bundles and anti-ice ducting. The PTU and EMP are down there too.

ElpinDAB, your analysis is spot-on IMO, Bri2K1's elitist comments probably stem from a misunderstanding of 'hardly even amatuer' which is a clear statement of modesty and not arrogance as Bri2k1 misinterpreted.

The 787 wing-body fairing around the central wing box does have pretty terrible area ruling which means there are some potential drag reductions there which Boeing didn't capitilize on, BUT by not straking those fairings forward and aft of the main wing they probably do save some weight and I suspect there are possible some 767 part numbers being re-used which might have helped save some NRE cost on an already extravagent development program, but I've never worked for Boeing so I don't know.



Resident TechOps Troll
User currently offlinealwaysontherun From Netherlands Antilles, joined Jan 2010, 464 posts, RR: 0
Reply 8, posted (3 years 11 months 2 weeks 3 days 6 hours ago) and read 4221 times:

Quoting Tdscanuck (Reply 2):
Better aerodynamics (no big hump sticking off the bottom of the fuselage), lower fuselage (easier servicing), easier gear geometry.


Does that additional hump on the A330F affects aerodynamics by much?

On my LSA plane covering the all wheels with a fairing already saves me a few MPH cruise speed, apparently.


[quote=Bri2k1,reply=1]I am not trying to be rude, but you misspelled "amateur." This does not lend itself to your credibility.

And yet it´s rude……….

Quoting musang (Reply 3):
I am not trying to be rude either, but you misspelled "Flyer". This does not in any way affect my opinion of your credibilty any more than it affects my opinion of your sense of balance, taste in music etc..

That must hurt………..

Quoting musang (Reply 3):
One of "the rules" shown above the reply field, is "No hostile language or criticizing of others". Don't you think you were a little intolerant and contemptuous of our Serbian contributor's question? Everyone makes spelling mistakes, and English is possibly not even his first language. We're not all rocket scientists like yourself, and I would respectfully suggest that so-called "amateurs" would far more appreciate replies like the one which followed yours!

Amen, you are rapidly approaching my RU list!

###"I´m always on the Run"###



"Failure is not an option, it comes standard in any Windows product" - an anonymous MAC owner.
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 9, posted (3 years 11 months 2 weeks 1 day 22 hours ago) and read 3987 times:

Quoting alwaysontherun (Reply 8):
Does that additional hump on the A330F affects aerodynamics by much?

It's definitely got some effect, but I'd bet it's tiny.

Quoting alwaysontherun (Reply 8):
On my LSA plane covering the all wheels with a fairing already saves me a few MPH cruise speed, apparently.

True, but the change in Cd between a "block" (what a wheel nearly is) and a fairing is *huge*. The change between an angled plate (the original A330 lower nose) and and a curved angled plate (the "bump" on the A330F) is much much smaller. Drag coefficients are incredibly non-linear. Modern commercial jets can't get away with crappy aerodynamics anywhere, so they're all playing down in the weeds of nearly-optimal-shapes most of the time.

One factor that kicks in on big jets that you don't see on little things like LSA's is the thickness of the boundary layer. At the back end of a large jet, it can be several inches thick...that's why you can get away with things like button-head rivets at the tail end without any meaningful drag penalty.

Tom.


User currently offlineBMI727 From United States of America, joined Feb 2009, 15809 posts, RR: 27
Reply 10, posted (3 years 11 months 2 weeks 1 day 17 hours ago) and read 3909 times:

Quoting ElpinDAB (Thread starter):
First, why didn't they make it subtly area-ruled like the A-380's wingbox?

Well, the extra two engines are going to make a nice dent in the x-sec area too.

Quoting Tdscanuck (Reply 2):
.on a transport aircraft, the wing goes through the cargo bay anyway do it doesn't change cabin area

Well, there is the BAe-146. Should you find yourself in a seat under the wing, you'll be hard pressed to put anything larger than a Harry Potter book in the overhead. But on most airliners, the wings do not protrude into the cabin at all.

Quoting Fly2HMO (Reply 5):
If it works, don't fix it. As simple as that. They obviously did the math and know the current design is the best.

Pretty much. If something is blatantly area ruled (like the CV-990's anti-shock bodies) it probably wasn't quite right to start with. These days, area ruling is well understood and rolled into designs from the start rendering such things unnecessary. So if I had to guess, I'd say that the 787 probably follows the area rule about as well as any other modern airliner, but just doesn't have any features that clearly were designed to fulfill the area rule. Not that using such features indicates a screwup, just that Boeing arranged it so they didn't need it.

Wikipedia probably says it better than I just did:

Quote:
Although the rule still applies, the visible fuselage "waisting" can only be seen on a few aircraft, such as the B-1B Lancer, Learjet 60, and the Tupolev Tu-160 'Blackjack' — the same effect is now achieved by careful positioning of aircraft components,
Quoting alwaysontherun (Reply 8):
Does that additional hump on the A330F affects aerodynamics by much?

Not enough to justify changing the whole nose gear. Really, it didn't seem that large to me.



Why do Aerospace Engineering students have to turn things in on time?
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