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Old 02-25-2010, 07:50 AM   #1
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Default Why is the 757 fuselage fatter behind the wings?

This is something I only recently noticed, usually most frames have similar sizes at the front and the back of the wings, but the 757 doesn't, is there any reason for that? Aerodynamics? Weight repartition?
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Old 02-25-2010, 07:59 AM   #2
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Default Re: Why is the 757 fuselage fatter behind the wings?

I worked as an engineer for Boeing and I have no idea what you are talking about. The 757 has the same constant cross-section both in front of the wing as it does behind the wing (neglecting the tapering sections). What makes you think that the fuselage is wider behind the wing?
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Old 02-25-2010, 08:11 AM   #3
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Default Re: Why is the 757 fuselage fatter behind the wings?

I'm sorry I should have clarified that I was referring to the vertical cross section (top to bottom, not left to right) Does this make it clearer? I'm gonna find a photo to show what I mean if not. The back of the 757 is closer to the ground than the part in front of the wings.
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Old 02-25-2010, 08:55 AM   #4
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Default Re: Why is the 757 fuselage fatter behind the wings?

Trust me....the fuselage is the same cross-section.
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Old 02-25-2010, 09:20 AM   #5
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Default Re: Why is the 757 fuselage fatter behind the wings?

I'm looking forward to seeing this picture...
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Old 02-25-2010, 09:39 AM   #6
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Default Re: Why is the 757 fuselage fatter behind the wings?

There, do you guys see what I mean now? I drew a line as straight as I could to illustrate my point. In front of the wings there's a gap between the line and the fuselage. Behind the wings the line touches the fuselage inferring that is is "wider vertically"

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Old 02-25-2010, 10:01 AM   #7
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Default Re: Why is the 757 fuselage fatter behind the wings?

You need to view from the side (perpendicular). What you are seeing is that the nose gears sits the front of the a/c a bit higher. But if you perfer to believe that the fuselage is wider (or taller) in the rear than it is in the front...go right ahead.
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Old 02-25-2010, 10:34 AM   #8
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Default Re: Why is the 757 fuselage fatter behind the wings?

Hmm...I think I'm going to have to agree with AC881 here. I just finished comparing several side-view photos in Paint Shop Pro, and they all are showing the fuselage aft of the wing root fairing as being larger, top to bottom, than the fuselage forward of the wing, similar to the 727-200, for example.
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Old 02-25-2010, 11:14 AM   #9
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Default Re: Why is the 757 fuselage fatter behind the wings?

Like I said above...the fuselage cross-section is the same on either side of the wing. If you want to include the wing/body fairing, that is not considered part of the fuselage (i.e. primary structure) But yes the fairing is larger behind the wing. That gets into the topic of area ruling. Google that for more information.
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Old 02-25-2010, 11:44 AM   #10
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Default Re: Why is the 757 fuselage fatter behind the wings?

Quote:
Originally Posted by JSchultz View Post
You need to view from the side (perpendicular). What you are seeing is that the nose gears sits the front of the a/c a bit higher. But if you perfer to believe that the fuselage is wider (or taller) in the rear than it is in the front...go right ahead.
OK JSchultz let me make this simpler and answer me this one question:

Consider the distance between:
A: the top and the bottom of the fuselage at the front (say around doors L2/R2)
B: the top and bottom of the fuselage at the back (around the second cargo door)

Are those distances similar??

I'm not trying to start a conspiracy theory or believe what doesn't exist. But I've looked at several pictures on A.net, I have NINE Gemini 200 757's and ALL of them show that the rear part of the fuselage (behind the wing/body fairing) is "thicker"

I'm going to take a pic of one of my models since apparently my point is not understood...
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Old 02-25-2010, 12:12 PM   #11
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Default Re: Why is the 757 fuselage fatter behind the wings?

That picture clearly shows that the aircraft is "thicker" even behind the fairing.
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Old 02-25-2010, 12:13 PM   #12
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Default Re: Why is the 757 fuselage fatter behind the wings?

Dear AirCanada881...your point is clear. Unfortunately you are incorrect in your assumptions and perception. I'll check what info I have at home that is not proprietary and post later today.
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Old 02-25-2010, 12:27 PM   #13
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Default Re: Why is the 757 fuselage fatter behind the wings?

Quote:
Originally Posted by JSchultz View Post
Dear AirCanada881...your point is clear. Unfortunately you are incorrect in your assumptions and perception. I'll check what info I have at home that is not proprietary and post later today.
OK I'm not sure why you're giving me an attitude here I asked a simple question and as you can see I am not the only one who is noticing what I am noticing, but since you're insisting here are photos I took of my Gemini 200 model of a US Airways 757. To me the difference between front and back is obvious:











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Old 02-25-2010, 12:47 PM   #14
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Default Re: Why is the 757 fuselage fatter behind the wings?

Quote:
Originally Posted by JSchultz View Post
Like I said above...the fuselage cross-section is the same on either side of the wing. If you want to include the wing/body fairing, that is not considered part of the fuselage (i.e. primary structure) But yes the fairing is larger behind the wing. That gets into the topic of area ruling. Google that for more information.
Um, I WASN'T including the fairing. Why would I do that? I was saying that from the numerous photos I checked, the fuselage AFT of the fairing is larger, top to bottom, than the fuselage forward of the wing. That was all.

Quote:
Originally Posted by AirCanada881 View Post
OK I'm not sure why you're giving me an attitude here I asked a simple question and as you can see I am not the only one who is noticing what I am noticing, but since you're insisting here are photos I took of my Gemini 200 model of a US Airways 757. To me the difference between front and back is obvious:
AC, I probably would exclude models from this conversation
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Old 02-25-2010, 12:53 PM   #15
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Default Re: Why is the 757 fuselage fatter behind the wings?

In The Photography World, There Are "Optical Illusions" That Are Caused By A Variety Of Reasons And There Are Several Types Of Optical Distortion.
The Two Most Common Are Barrel Distortion And Pincusion Distortion.

Barrel Distortion Is Caused By Wideangle Lenses. I'm Sure Many Of You Have Seen The Results Of A "Fisheye" Lens. Fisheye Lenses Are Extreme Examples Of Barrel Distortion, But Is Often Very Notable With 18,24,28 & 35 MM Lenses.
An Example Is Taking A Photo Of The Nose Section At The Gate. You Need To Adjust Your Zoom To A Wideangle Setting So That You Can Cover The Entire Aircraft In One Shot. Notice The Nose Is Bulbous And Distorted And The Fuselage Is Elongated, The Aft Section Is Further Back Than It Really Is And Looks Very Tiny.

Pincusion Distortion Is The Opposite Effect And Is Caused By Long Telephoto And Zoom Lenses, Typically Noticed Beyond 200mm. Pincusion Distortion Is Also Referred To Compression Effect.
This Kind Of Distortion Is Noticed Mostly When Taking Frontal Views Such As Taking A Photo Of A Plane Landing Or Taking Off From Front On.
If You Spend Time On Airliners Dot Net, You Will See Such Shots Where The Aft Section Of The Fuselage Appears Larger In Diameter Than The Front. This Is Another Example Of Pincusion Distortion. And The Longer The Lens, The Greater The Effect.

In This Particular Scenario, The Effect Is Negligible. Going By My Own Experience, The Setting In This Photo Appears To Be In The 70-100mm Range. Not Much Optical Distortion, But All Lenses Regardless Of Focal Length Have Distortion To Some Degree.
Even Standard 50mm Lenses That Have The Least Amount Of Distortion Can Show Signs Of Distortion. (Ever Shoot A Building Looking Up? Notice It Gets Smaller Real Quck As It Goes Higher? That's Optical Distortion And There's No Way Around It Unless You Buy A View Camera Or Shift Lens. But Even Then There's Always Some Minor Distortion)
ASFASIK, The Fuselage Cross Section (Vertical Or Horizontal) Are The Same.
It Would Cost 100 Million Dollars For Boeing In Tooling To Have The Fuselage Cross Sections Different Diameter Or Height, So I Seriously Doubt They Are Different.

Also Position Of Camera Relative To The Subject Affects The Optical Distortion.
Is The Camera Dead Center Of The Fuselage? What If The Nose Section Is 3 Feet Closer To The Camera Than The Aft Section? Can You Tell By Looking At This Photo? With All My 24 Years Of Photography Experience, I Can't.
Contrary To Popular Belief, Photography Is NEVER An Exact Science And You Can Never Use It As A Tool For Measuring Precision. But It Seems Just About Everyone On This Site Does.
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Old 02-25-2010, 12:59 PM   #16
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Default Re: Why is the 757 fuselage fatter behind the wings?

The fuselage looks consistent front to rear to me.



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Old 02-25-2010, 01:07 PM   #17
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Default Re: Why is the 757 fuselage fatter behind the wings?

Quote:
Originally Posted by AirCanada881 View Post
OK I'm not sure why you're giving me an attitude here I asked a simple question and as you can see I am not the only one who is noticing what I am noticing, but since you're insisting here are photos I took of my Gemini 200 model of a US Airways 757. To me the difference between front and back is obvious:
Well, I think a big reason he is giving an attitude is simply because you seem to be arguing the guy's credentials. The guy says he was an Engineer for Boeing (meaning he went to school to study how to design parts of these things, and likely has a trained eye to notice things that you wouldn't, and likely could have had something to do with the 757 when he worked there). Using a scale model, that may have a flaw when it was made might not be the best idea, but rather some Engineering Drawings/Blueprints could do the trick. I'd recommend searching up for those online.

I think one thing that no one has considered yet, and looking at the photo that you showed of the actual thing, did you ever consider that the aircraft could be heavier in the back (especially when empty), and therefore cause the nose to go up a certain angle, where it wouldn't be noticeable in a small distance, but at a larger distance would be just slightly so? I also notice that there is a large distortion in the "line" you used to prove this, as it is not very parallel with the fuselage and actually goes up in the y direction about 4 or 5 pixels. It may not sound like a large amount, but it is pretty noticeable when you have a look at it.
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Old 02-25-2010, 01:07 PM   #18
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Default Re: Why is the 757 fuselage fatter behind the wings?

Thank you for the very informative detailing L-1011, the thing is when I look at any other plane, may it be the 747,767,777, A320 or even the A330/340 I do not notice any difference, but in this particular example of the 757, I do see the difference and it's not a small difference at all.

Maybe a better visual example would be the 757-300, look at this photo and tell me you don't notice a substantial difference between front and aft fuselage vertical cross sections. Yes I realize the photo is taken at an angle but I can't believe distortion would amount to this much difference.

Photos: Boeing 757-330 Aircraft Pictures | Airliners.net
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Old 02-25-2010, 01:13 PM   #19
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Default Re: Why is the 757 fuselage fatter behind the wings?

Quote:
Originally Posted by AirCanada881 View Post
Thank you for the very informative detailing L-1011, the thing is when I look at any other plane, may it be the 747,767,777, A320 or even the A330/340 I do not notice any difference, but in this particular example of the 757, I do see the difference and it's not a small difference at all.

Maybe a better visual example would be the 757-300, look at this photo and tell me you don't notice a substantial difference between front and aft fuselage vertical cross sections. Yes I realize the photo is taken at an angle but I can't believe distortion would amount to this much difference.

Photos: Boeing 757-330 Aircraft Pictures | Airliners.net
Again, get an Engineering drawing, not a photo. The problem with photos is that the angles they are taken at will help give a distortion to what is actually there. An Engineering Drawing/Blueprint typically will take a nice, even cross sectional view without any of that un-needed distortion that would be caused by a photograph of the actual 1:1 scale thing.
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Old 02-25-2010, 01:17 PM   #20
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Default Re: Why is the 757 fuselage fatter behind the wings?

I've serviced plenty of 757's to know that there is no differance in the diameter or circumfrence of the rear and forward fuselages.
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Old 02-25-2010, 01:17 PM   #21
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Default Re: Why is the 757 fuselage fatter behind the wings?

I'm Looking At A Lot Of Photos Of The 757 Now. It Does Appear That The Aft BELLY Section BELOW The Lobe Line Is Bigger, But The Fuselage Cross Section Height Above The Lobe Line Is Still The Same Throughout.
However The Real Proof Is Only In Schematics. Until Then, I'm Still Going With The Optical Illusion Theory.

Regardless, The Optical Distortion Described Above is 100% Valid.
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Old 02-25-2010, 01:18 PM   #22
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Default Re: Why is the 757 fuselage fatter behind the wings?

AirCanada881...please accept my apology. I did not mean to come across with an attitude. I think you have your answer.
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Old 02-25-2010, 01:22 PM   #23
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Default Re: Why is the 757 fuselage fatter behind the wings?

Well I'm very confused. I never thought this thread woud have divergent answers, I was so sure that the 757 had a fatter back, I mean from all the ones I've seen in real life and in photos... But I could very well be wrong... It's just hard to believe since I can really see the difference... But you can't argue with science, if anyone has blue prints of the said model, I'd love to see them, thanks to everyone for participating this has been real informative for me :-)
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Old 02-25-2010, 01:27 PM   #24
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Default Re: Why is the 757 fuselage fatter behind the wings?

Here's a PERFECT Example Of Optical Distortion.

Notice On This 757, The Fuselage Appears Very Narrow Near The Wing/Body Fiaring (See Near Engines) Now Notice The Fuselage Actually Appears To Curve And The Forward Section Of The Fuselage Appears Larger In Curcumference Near The Forward Door.
Also The Aft Section No Longer Appears Larger.
This Is Pincusion Distortion, Noted By How the Fuselage Curves.
Appears To Be 300mm Or Possibly Longer.

Click Large.

http://upload.wikimedia.org/wikipedi...tf-fiv.arp.jpg
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Old 02-25-2010, 01:28 PM   #25
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Default Re: Why is the 757 fuselage fatter behind the wings?

Quote:
Originally Posted by AirCanada881 View Post
Well I'm very confused. I never thought this thread woud have divergent answers, I was so sure that the 757 had a fatter back, I mean from all the ones I've seen in real life and in photos... But I could very well be wrong... It's just hard to believe since I can really see the difference... But you can't argue with science, if anyone has blue prints of the said model, I'd love to see them, thanks to everyone for participating this has been real informative for me :-)
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Old 02-25-2010, 01:29 PM   #26
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Default Re: Why is the 757 fuselage fatter behind the wings?

I found this if anyone is interested:

Photobucket
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Old 02-25-2010, 02:17 PM   #27
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Default Re: Why is the 757 fuselage fatter behind the wings?

I have to agree with Air Canada, the fuselage is definitely larger after the wing fairing. It's no illusion. The diagram above perfectly shows this. I don't know if people are blind or what, but really just look at that, it's obviously larger. The line that shows the length of the aircraft is completely Parallel to the top of the aircraft, yet if you draw a straight line on the underside, the front and aft don't match up. There is definitely some difference there.
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Old 02-25-2010, 02:32 PM   #28
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Default Re: Why is the 757 fuselage fatter behind the wings?

I drew this out so the people who don't understand can see

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Old 02-25-2010, 02:34 PM   #29
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Default Re: Why is the 757 fuselage fatter behind the wings?

Quote:
Originally Posted by tactnpldn767 View Post
I have to agree with Air Canada, the fuselage is definitely larger after the wing fairing. It's no illusion. The diagram above perfectly shows this. I don't know if people are blind or what, but really just look at that, it's obviously larger. The line that shows the length of the aircraft is completely Parallel to the top of the aircraft, yet if you draw a straight line on the underside, the front and aft don't match up. There is definitely some difference there.
I Don't Think Anyone Said They Don't See It. I See It.
Not Arguing That Point. But That Diagram Is An Artists Graph, Not A Blueprint.
What If That Artist Sees What Everyone Else Sees? An Optical Illusion.
If That Drawing Had Actual Measurements, I'd Agree, But Where Are The Measurements To Back Up The Drawing?

Blueprints Please, Not Artists Drawing.
If You Had Any Mecahincal Parts/Service Manual Drawings Background, You'd Know Never To Rely On These Kinds Of Graphs Unless They Have Specs To Match.
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Old 02-25-2010, 02:46 PM   #30
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Default Re: Why is the 757 fuselage fatter behind the wings?

Quote:
Originally Posted by tactnpldn767 View Post
I drew this out so the people who don't understand can see

Having finally gotten a good look at the decent cross sectional drawing provided by AC881, I was able to do a good and quick measurement comparison with 3 regions (1 in front, 2 in the back) using a very thick, straight datum line located on the ground and measurements in pixels. Results came back with AC881 may be onto something, with the front section being 36 pixels from bottom of the fuselage to ground, and the rear 2 regions being 34 pixels from the same said points.


Of course, this could be more like how Rick said, it could also be not a very accurate description. Actual blueprints could definitely be more helpful than this, as they have a the most accurate view of what is actually going on in the design.
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Old 02-25-2010, 02:48 PM   #31
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Default Re: Why is the 757 fuselage fatter behind the wings?

You can trust a picture of a measurement ...
But ... NEVER trust the measurement of a picture ...

... or a drawing.
... or a model.

Something from a long ago school memory ...

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Old 02-25-2010, 02:56 PM   #32
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Default Re: Why is the 757 fuselage fatter behind the wings?

I don't know if this adds credit to the drawing I found but I found it on this website:

Boeing 757-300
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Old 02-25-2010, 03:12 PM   #33
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Default Re: Why is the 757 fuselage fatter behind the wings?

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I don't know if this adds credit to the drawing I found but I found it on this website:

Boeing 757-300
What is your point now ?

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Old 02-25-2010, 03:20 PM   #34
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Default Re: Why is the 757 fuselage fatter behind the wings?

OK so I found this on the Boeing website which if you look at page 7 will discredit my assumption that the aft part of the fuselage is fatter... These optical illusions sure take you on for a spin sometimes!!

http://www.boeing.com/commercial/air...ps/753sec2.pdf

OK I just relooked at the document and on page 22 the drawing of the 757-300 AGAIN shows a difference in thickness!!!

This is going to drive me insane if I don't get a straight answer, someone please help...
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Old 02-25-2010, 05:44 PM   #35
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Default The official Answer

I just got home and checked the engineering.....AirCanada881 you are correct! I admit I was wrong. I "spoke" too soon and I should have checked the engineering before posting. I always worked the wide bodies so I've learned something new too.
The Answer:The bottom of the lower lobe of the fwd fuselage is at WL 148.50 while the aft is at WL 130.0 (a difference of 18.5 inches).

Case settled! Now back to collecting...
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Old 02-25-2010, 06:08 PM   #36
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Default Re: Why is the 757 fuselage fatter behind the wings?

Well done AC881!
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Old 02-26-2010, 04:38 AM   #37
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Default Re: Why is the 757 fuselage fatter behind the wings?

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Originally Posted by LOT 737-300 View Post
AC881 may be onto something.
I knew I wasn't nuts :-)

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I just got home and checked the engineering.....AirCanada881 you are correct! I admit I was wrong. I "spoke" too soon and I should have checked the engineering before posting. I always worked the wide bodies so I've learned something new too.
The Answer:The bottom of the lower lobe of the fwd fuselage is at WL 148.50 while the aft is at WL 130.0 (a difference of 18.5 inches).

Case settled! Now back to collecting...
Well just for the record I never questioned your engineering credentials, just what my eyes were seeing, I'm just baffled that I was the only one who assumed right from the getgo that there was a difference... To me the difference in depth was trivial...

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Well done AC881!
Thanks man, but I really wasn't trying to win an argument. If you look at my first post I went into this assuming the difference in depth was an acceptable fact!

So my initial question still remains unanswered lol, WHY are the depths different? Weight restrictions? Aerodynamics?
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Old 02-26-2010, 04:50 AM   #38
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Default Re: Why is the 757 fuselage fatter behind the wings?

Glad we all came to a determination regarding the fuselage. Now I can go to sleep
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Old 02-26-2010, 05:16 AM   #39
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Default Re: Why is the 757 fuselage fatter behind the wings?

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Glad we all came to a determination regarding the fuselage. Now I can go to sleep
At 05:16 in the morning I would sure hope so!
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Old 02-26-2010, 07:09 AM   #40
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Default Re: Why is the 757 fuselage fatter behind the wings?

Same thing on my 1:650 B757... the aft seems a little bulgy.
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Old 02-26-2010, 08:24 AM   #41
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Default Re: Why is the 757 fuselage fatter behind the wings?

perhaps the wing box has something to do with said bulge ?
just my .01 adjusted for inflation
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Old 02-27-2010, 03:01 AM   #42
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Default Re: Why is the 757 fuselage fatter behind the wings?

I have checked too and found that Sec. 46 gets up to WL138.5, making a difference of 10in between body section heights. For all that's worth at 1/200, you had better make sure Gemini gets precisely 0.05in difference between the front and back sections.

For a good explination for the difference, check OldAeroGuy's response in the "corresponding" A.net thread, reply 13.
http://www.airliners.net/aviation-fo...d.main/271973/

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Old 02-27-2010, 12:27 PM   #43
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Default Re: Why is the 757 fuselage fatter behind the wings?

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I have checked too and found that Sec. 46 gets up to WL138.5, making a difference of 10in between body section heights.
Where is Sec. 46? I'm curious where this third figure is located on the aircraft.
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Old 03-01-2010, 10:02 PM   #44
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Default Re: Why is the 757 fuselage fatter behind the wings?

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Where is Sec. 46? I'm curious where this third figure is located on the aircraft.
Sec. 46 starts just before the trailing edge of the wing and goes just a little ways behind the last door where the rear pressure bulkhead is. The WL138.5 figure, I think, replaces the WL130.0 figure , so there are only two different cross sections.

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Old 03-01-2010, 10:18 PM   #45
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Default Re: Why is the 757 fuselage fatter behind the wings?

Here's the short version:

Everyone knows that all the narrowbody Boeings share the same fuselage WIDTH. Fewer people know that there are two different HEIGHTS. Above the cabin floor, they're all identical. Below the floor, there are two different depths, one is 10 inches deeper than the other. And some planes are made with different depths. The split always occurs at the wings, and the transition is covered by the wing-body fairing so it's harder to see. (but if you compare the location of the bottom of the fuselage to the bottom of the WBF, it should be apparent there's a difference front/rear). So, fore/aft, whether a Boeing has a shallow or deep fuselage:

707 is deep/deep
727 is shallow/deep
737 is shallow/shallow
757 is shallow/deep

There you go. A 757 fuselage *is* 10 inches deeper aft of the wing. And so is the 727.
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Old 03-02-2010, 09:19 PM   #46
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Default Re: Why is the 757 fuselage fatter behind the wings?

Good thing I noticed this great thread today because I have slept well. Tech talk aside, the 757 is a sweet looking bird. Like the Connie, the tall nose gear gives it a dainty appearance. Still, when it comes to porn on wheels, the 727 reigns supreme!
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Old 03-02-2010, 11:48 PM   #47
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Default Re: Why is the 757 fuselage fatter behind the wings?

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Still, when it comes to porn on wheels, the 727 reigns supreme!
Hell yes!
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Old 03-03-2010, 04:54 AM   #48
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Default Re: Why is the 757 fuselage fatter behind the wings?

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Good thing I noticed this great thread today because I have slept well. Tech talk aside, the 757 is a sweet looking bird. Like the Connie, the tall nose gear gives it a dainty appearance. Still, when it comes to porn on wheels, the 727 reigns supreme!
You just made my day with this comment :-)
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Old 06-24-2014, 09:18 PM   #49
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Default Re: Why is the 757 fuselage fatter behind the wings?

It is my understanding that the 757 uses the 727 fuselage forward of the wings and the 707 fuselage aft of the wings.
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Old 06-26-2014, 01:19 AM   #50
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Default Re: Why is the 757 fuselage fatter behind the wings?

I just noticed that I am a bit wider on my lower part of the thorax, just like the 757-200

. . how cool is that!!!
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