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How Flexible Is An Aircraft's Fuselage?  
User currently offlineSpeedracer1407 From United States of America, joined Dec 2004, 333 posts, RR: 0
Posted (8 years 4 months 3 weeks 2 days 14 hours ago) and read 8660 times:

I've heard often on these forums that a keen eye can notice some fuse flex during turbulence, as long as that eye is seated towards the rear of the plane, thus looking down the majority of the tube. Seems sensible to me, though I've tried many times and failed to detect it. Thus, I wonder just how much things flex. I'm reminded of the automotive industry's recent (last 10 years or so) attention to publicizing dramatic increases in chassis stiffness, thus making it yet another well-known factor of proper driving dynamics. But the figures in this case are something like tens of thousands of newton-meters per inch of tortional deflection; nobody can really detect it, unless they drive a convertible on a rough road and whitness a tiny bit of cowl shake.
Naturally, a multi-hundred-ton airplane is a different story, at least as far as the visible amount of fuse flex. But I'm curious about the figures involved. Do manufacturers measure fuse flex the same way auto manufacturers do? What are the figures? Is there a range of flexibility that's optimal? Or does it vary dramatically from plane to plane based on manufacturer philosophy.

Also, please keep in mind that I'm not talking about wing flex, as I feel somewhat more comfortable with that concept.

O

[Edited 2006-03-09 08:39:10]


Dassault Mercure: the plane that has Boeing and Airbus shaking in their boots.
18 replies: All unread, jump to last
 
User currently offlineAmericanB763ER From Luxembourg, joined Sep 2005, 166 posts, RR: 0
Reply 1, posted (8 years 4 months 3 weeks 2 days 12 hours ago) and read 8640 times:

Fuselage flex is easily noticeable when you're standing at the gate with the aircraft parked in front of you - just look down the window row and you'll see where the fuselage is bending (the portion above the wing box is slightly higher than both ends of the fuselage due to gravity)

The longer the fuselage the more visible it is but it also depends a lot on the aircraft type - out of my experience it's most visible on Boeing 767-300's (also from the inside you'll notice the 'wobbling' while taxiing + during turbulence).



Marco


User currently offline2enginesonly From Netherlands, joined Jun 2005, 91 posts, RR: 0
Reply 2, posted (8 years 4 months 3 weeks 2 days 10 hours ago) and read 8609 times:

Fuselage flexing is extremely noticable during a high power testrun when your at the headset and standing in front of the aircraft.
I've seen Fokker 50 tails rotating the opposite direction of the wings ( torsion ) and this at a rate 60 times a minute ( lh wing down and lh stabilizer up and vice versa ).
This severe flexing is also very noticable on the B752 during a high power testrun.
You really have to see this to believe it  Smile

The flexibility of a wing is just the same: if you're standing at the wingtip ( in a cherrypicker or something ) it takes almost no effort to move the wing up and down....even if there's 15 tons of fuel in it ( Boeing 763ER ).

Arjan


User currently offlineA300605R From Germany, joined Nov 2005, 136 posts, RR: 0
Reply 3, posted (8 years 4 months 3 weeks 2 days 9 hours ago) and read 8603 times:

I could clearly see fuse flex once while climbing out of DOH on a QR A300.
As I was sitting over the wings I could see that the overhead bins of the forward section seem to move. I guess the reasons were a steep departure together with turbulences.
But I can't quantify the movement anyway.
Was interesting to see, but was the first and the last time that I saw it on an aircraft as well.
 wave 



300 319 320 321 332 733 734 735 738 753 763 F27 M83
User currently offlineFLY2HMO From , joined Dec 1969, posts, RR:
Reply 4, posted (8 years 4 months 3 weeks 1 day 21 hours ago) and read 8489 times:

I was sitting in the very rear of an MD88 a while ago and we passed rather fast over some pretty nasty bumps in the taxiway. I dare say it flexed almost a foot up and down at the center!!!  eyepopping 

I've noticed that its very easy to see this in the longer mad-dogs.


User currently offlineSfomb67 From United States of America, joined Dec 2005, 417 posts, RR: 0
Reply 5, posted (8 years 4 months 3 weeks 1 day 17 hours ago) and read 8437 times:

I was always told that if you were seated in the rear of a stretch 8 (-71,73), you can look up the isle during take-off, and see the flex, although I never looked for it. Also, it's evident during jacking on many aircraft. The 747 fuselage will develop wrinkles aft of the MLG at about 10:00 & 2:00 position. The control cables to the tail will also loose about half their tension on a 747 when jacked.


Not as easy as originally perceived
User currently offlineBuzz From United States of America, joined Nov 1999, 697 posts, RR: 22
Reply 6, posted (8 years 4 months 3 weeks 1 day 17 hours ago) and read 8427 times:

Hi Speedracer1407, Buzz here. Ever walk up and down the aisle of an empty airliner? When I walk aft on a 757 I feel the airplane bounce up and down a bit... maybe half an inch as 200+ lbs of mechanic (and tools) rhythmically step down the aisle.
When the airplane is pressurized it puts the structure in tension, which would stiffen it a bit.
And on the ground you see skin wrinkles in the 737 and 757's, I hear that when the skin stretches (about 1/16 inch when you rig a Boeing cabin door) the wrinkles disappear. Different set of wrinkles on a B-52, that part of the fusel-sausage isn't pressurized.
g'nite


User currently offlinePilotaydin From Turkey, joined Sep 2004, 2539 posts, RR: 51
Reply 7, posted (8 years 4 months 3 weeks 1 day 16 hours ago) and read 8421 times:

I just saw a picture of a 737 fuselage that buckled and then fractured because th pushback tug pushed the a/c back with its parking break set....


The only time there is too much fuel onboard, is when you're on fire!
User currently offline777WT From United States of America, joined Jan 2005, 875 posts, RR: 1
Reply 8, posted (8 years 4 months 3 weeks 1 day 14 hours ago) and read 8398 times:

Sit in the back of a A340-600 and look towards the front in flight, that's one lonnnngggg plane  Wink

User currently offlineSpeedracer1407 From United States of America, joined Dec 2004, 333 posts, RR: 0
Reply 9, posted (8 years 4 months 3 weeks 1 day 13 hours ago) and read 8384 times:

Thanks for the replies. I guess I must be looking in the wrong places or something. I always figured bouncing around while boarding was due mostly to tire flex and minor landing gear strut compression. I guess I just need to suck it up and get a seat in back next time.

O



Dassault Mercure: the plane that has Boeing and Airbus shaking in their boots.
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17000 posts, RR: 67
Reply 10, posted (8 years 4 months 3 weeks 1 day 9 hours ago) and read 8354 times:

I've seen 757s twist in turbulence, that is the front would roll one way and the rear another. Pretty cool.


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineChema From Spain, joined Mar 2004, 17 posts, RR: 0
Reply 11, posted (8 years 4 months 3 weeks 1 day 7 hours ago) and read 8311 times:

In this video you can see the fuselage flexing like crazy. I read somewhere that the tail of the aircraft was replaced and it continued flying as a test plane, so I assume that the rest of the fuselage wasn´t damaged by the massive flexing.

http://www.youtube.com/watch?v=uYAVLfuUjPA&search=landing%20accident


User currently offlineLehpron From United States of America, joined Jul 2001, 7028 posts, RR: 21
Reply 12, posted (8 years 4 months 3 weeks 22 hours ago) and read 8230 times:

On of the reasons a canard surface was placed on preliminary SST studies from Boeing in the 60'd and NASA/Boeing concepts of the late 1990's because the long fuselage would bend too much. In some of those designs, the pilot sat almost 90 feet from the nose wheel! Even if it were a few inches, a 300-foot plane would sway up and down on landing and takeoff like a bridge in the wind.


The meaning of life is curiosity; we were put on this planet to explore opportunities.
User currently offlineFlashmeister From United States of America, joined Apr 2000, 2900 posts, RR: 6
Reply 13, posted (8 years 4 months 3 weeks 13 hours ago) and read 8171 times:
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Sit at the back of a 757-300 and fly through turbulence... you'll see the flex for sure.

User currently offlineEmiratesA345 From Canada, joined Jun 2003, 2123 posts, RR: 9
Reply 14, posted (8 years 4 months 3 weeks 13 hours ago) and read 8166 times:

When i flew on the Concorde I sat at the very back in the aisle seat. The whole flight you could see the cockpit door moving up and down.

Mark



You and I were meant to fly, Air Canada!
User currently offlineWickedPenguin From United States of America, joined Nov 2003, 4 posts, RR: 0
Reply 15, posted (8 years 4 months 6 days 6 hours ago) and read 7850 times:

On our last trip to Europe, my wife and I were sitting in the last row of a Virgin A340-300.

On approach into Heathrow, we kept hearing these awful groans and creaks. I asked the flight attendant sitting next to us what those were (though I already had a pretty good idea).

When he confirmed that it was fuselage flexing, I made a mental note to avoid A340's if possible. I mean, the thing sounded like it was crying!  Silly

I've flown all my life (both my parents are in the airlines) and never heard anything quite like it on any other aircraft. I can only imagine what those sounds would do to someone who was afraid of flying.


User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 16, posted (8 years 4 months 6 days 6 hours ago) and read 7847 times:
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A study in wrinkled fuselage skin:


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Intentionally Left Blank
User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 17, posted (8 years 4 months 5 hours ago) and read 7682 times:

Quoting Pilotaydin (Reply 7):
I just saw a picture of a 737 fuselage that buckled and then fractured because th pushback tug pushed the a/c back with its parking break set....

What Section.
regds
MEL



Think of the brighter side!
User currently offlineANother From , joined Dec 1969, posts, RR:
Reply 18, posted (8 years 3 months 4 weeks 12 hours ago) and read 7565 times:

Quoting Sfomb67 (Reply 5):
I was always told that if you were seated in the rear of a stretch 8 (-71,73),

Flew DC8-63s (73s were just re-engined 63s) quite a few times. Through rough weather the flex was VERY obvious.


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