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753 Fuselage Warp/Torsion?  
User currently offlinesqa380fan From United States of America, joined Nov 2008, 35 posts, RR: 1
Posted (2 years 5 months 5 days 3 hours ago) and read 3629 times:

Hi,
This is my first time posting in the forums but I've been meaning to ask about this particular picture ever since I saw it a year or so ago:


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Photo © Daan Krans - AirTeamImages



One can clearly see that the window line along the left side is severely warped, and droops toward the front and rear. I'm assuming that this is due in part to the length of the 753's fuselage, but it still seems pretty crazy to me... so my question is, how often does this happen? And why? Could this possibly be some photographic illusion? It seems to me that the plane is pretty clearly 'bent'...

Thanks!

14 replies: All unread, jump to last
 
User currently offlineamccann From United States of America, joined Mar 2008, 175 posts, RR: 0
Reply 1, posted (2 years 5 months 5 days 3 hours ago) and read 3516 times:

Quoting sqa380fan (Thread starter):
I'm assuming that this is due in part to the length of the 753's fuselage, but it still seems pretty crazy to me... so my question is, how often does this happen? And why?

I would have to say you are correct, the fuselage is indeed bent. You can imagine the fuselage of an aircraft as beam, supported only in the middle. The horizontal tail produces a down force on the rear of the fuselage, and the weight of the fuselage itself also produces a down force on both the front and rear of the fuselage. Again, using the beam analogy, a fuselage can be imagined as a beam supported in the middle with loads applied on the ends.

Additionally because the cross sectional area of the 757-300 is relatively low, when compared to other aircraft of long fuselage, the bending stiffness is lower and therefore the bending deflection is higher. The DC-8-60 series experienced a similar bending phenomenon.



What one person receives without working for, another person must work for without receiving. - Ronald Reagan
User currently offlinetb727 From United States of America, joined Jun 2005, 1572 posts, RR: 9
Reply 2, posted (2 years 5 months 5 days 2 hours ago) and read 3417 times:

If it didn't bend it would break. You'd be surprised at how much stuff moves!


Too lazy to work, too scared to steal!
User currently offlinesqa380fan From United States of America, joined Nov 2008, 35 posts, RR: 1
Reply 3, posted (2 years 5 months 5 days 2 hours ago) and read 3342 times:

Thanks for the replies! I do realize that wings are designed this way for obvious reasons, guess it just had never occurred to me that the same could be true for the fuselage. I suppose the amount exhibited in the picture just really caught my attention... had no idea it could bend *that* much.

User currently offlineXFSUgimpLB41X From United States of America, joined Aug 2000, 4189 posts, RR: 37
Reply 4, posted (2 years 5 months 5 days 2 hours ago) and read 3342 times:

When sitting in the back of the 753 and looking forward you can see the fuselage wiggle in turbulence. It's quite the sight!


Chicks dig winglets.
User currently offlineHAWK21M From India, joined Jan 2001, 31660 posts, RR: 56
Reply 5, posted (2 years 5 months 5 days 2 hours ago) and read 3294 times:

Aluminium alloy stretches & bends.......


Think of the brighter side!
User currently offlinetb727 From United States of America, joined Jun 2005, 1572 posts, RR: 9
Reply 6, posted (2 years 5 months 5 days 2 hours ago) and read 3294 times:

The other day I was in the back during flight(a freighter) and we were going through a little light chop so I tried to look down the side to see if the fuselage was flexing or twisting any but I don't think it was rough enough. Of course if it gets too rough, I don't think I'll be in the back to see it, I'd be buckled in up front.


Too lazy to work, too scared to steal!
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16975 posts, RR: 67
Reply 7, posted (2 years 5 months 5 days 2 hours ago) and read 3252 times:

Not only does it bend but it also twists. This is quite noticeable in a 757. If you sit in the back during turbulence you can really see it.


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently onlineMax Q From United States of America, joined May 2001, 4311 posts, RR: 19
Reply 8, posted (2 years 5 months 4 days 23 hours ago) and read 3193 times:

Quoting tb727 (Reply 6):


The other day I was in the back during flight(a freighter) and we were going through a little light chop so I tried to look down the side to see if the fuselage was flexing or twisting any but I don't think it was rough enough. Of course if it gets too rough, I don't think I'll be in the back to see it, I'd be buckled in up front.

I don't think you will see that in the B727, the fuselage is built like a tank, the wings take all the load and they flex significantly, that's why she has such a smooth ride.


The 753 fuselage is very long and limber, it also flexes significantly, that is why it has a much better ride than a -200.


It is also a much nicer flying Aircraft, although I seem to be in the minority on that opinion !



The best contribution to safety is a competent Pilot.
User currently online747classic From Netherlands, joined Aug 2009, 2076 posts, RR: 14
Reply 9, posted (2 years 5 months 4 days 20 hours ago) and read 3107 times:

I experienced the same fuselage bending and twisting on a extremely bumpy crew positioning flight with a KLM DC8-63 (the flying pencil) during the seventies.
Sadly I never operated that aircraft type myself.

[Edited 2012-02-06 04:08:41]


Operating a twin over the ocean, you're always one engine failure from a total emergency.
User currently offlinerfields5421 From United States of America, joined Jul 2007, 7494 posts, RR: 32
Reply 10, posted (2 years 5 months 4 days 18 hours ago) and read 3021 times:

Quoting amccann (Reply 1):
The DC-8-60 series experienced a similar bending phenomenon.

Back in the summer of 1972 - on a long MAC charter flight from Travis AFB to Southeast Asia - I was amazed to see how much the DC "Stretch" 8 flexed. I was seated on the next to last row of the one-class aircraft in the aisle seat. At times the aisle looked like it belonged in a carnival fun-house.


User currently offlineBAe146QT From United Kingdom, joined Sep 2006, 996 posts, RR: 0
Reply 11, posted (2 years 5 months 4 days 12 hours ago) and read 2802 times:

Quoting tb727 (Reply 2):
If it didn't bend it would break. You'd be surprised at how much stuff moves!

I'm no aircraft engineer, but that is a definitive answer from a structural point of view...up to a point.

Not trying to resist flex or tortional force can make a structure more durable. It's a basic principle in skyscrapers. But allowing harmonic rhythm can make things worse - which is what happened at the Tacoma Narrows.

So the fact that an airliner bends, flexes, swells and contracts in flight - and that this is planned for - is no surpise. It's *really* obvious if you sit at the back of a descending 747.



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User currently offlinevikkyvik From United States of America, joined Jul 2003, 9694 posts, RR: 27
Reply 12, posted (2 years 5 months 4 days 12 hours ago) and read 2777 times:
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Quoting sqa380fan (Thread starter):
Could this possibly be some photographic illusion? It seems to me that the plane is pretty clearly 'bent'...

Just to add a bit - although the effect is very real, the angle of the photograph makes it appear more significant that it probably is.

It looks like the max deflection is in the vicinity of 1 window-height. I'll assume a window is 18" tall, though I actually have no idea. I'll also assume that the first and last windows are about 140' apart (so I'll use 70' for half of the windows). That gives me a deflection angle of about 1.2 degrees. Noticeable, but small.



"Two and a Half Men" was filmed in front of a live ostrich.
User currently offlineseabosdca From United States of America, joined Sep 2007, 5274 posts, RR: 4
Reply 13, posted (2 years 5 months 4 days 9 hours ago) and read 2678 times:

Quoting vikkyvik (Reply 12):
Just to add a bit - although the effect is very real, the angle of the photograph makes it appear more significant that it probably is.

Very true. The OP's photo really doesn't give any hint of the massive length of the 753. Try to juxtapose it with this one in your mind's eye...


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Photo © Mathias Henig




Most gorgeous aircraft: Tu-204-300, 757-200, A330-200, 777-200LR, 787-8
User currently onlineMax Q From United States of America, joined May 2001, 4311 posts, RR: 19
Reply 14, posted (2 years 5 months 4 days 3 hours ago) and read 2535 times:

The Md80 bends like Gumby as well !


The best contribution to safety is a competent Pilot.
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