Print from Airliners.net discussion forum
http://www.airliners.net/aviation-forums/tech_ops/read.main/147672/

Topic: How Flexible Is An Aircraft's Fuselage?
Username: Speedracer1407
Posted 2006-03-09 08:36:10 and read 8681 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]

Topic: RE: How Flexible Is An Aircraft's Fuselage?
Username: AmericanB763ER
Posted 2006-03-09 11:28:59 and read 8661 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

Topic: RE: How Flexible Is An Aircraft's Fuselage?
Username: 2enginesonly
Posted 2006-03-09 13:23:57 and read 8630 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

Topic: RE: How Flexible Is An Aircraft's Fuselage?
Username: A300605R
Posted 2006-03-09 13:41:22 and read 8624 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 

Topic: RE: How Flexible Is An Aircraft's Fuselage?
Username: FLY2HMO
Posted 2006-03-10 01:47:02 and read 8510 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.

Topic: RE: How Flexible Is An Aircraft's Fuselage?
Username: Sfomb67
Posted 2006-03-10 05:42:25 and read 8458 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.

Topic: RE: How Flexible Is An Aircraft's Fuselage?
Username: Buzz
Posted 2006-03-10 06:09:04 and read 8448 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

Topic: RE: How Flexible Is An Aircraft's Fuselage?
Username: Pilotaydin
Posted 2006-03-10 07:03:38 and read 8442 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....

Topic: RE: How Flexible Is An Aircraft's Fuselage?
Username: 777WT
Posted 2006-03-10 09:01:28 and read 8419 times.

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

Topic: RE: How Flexible Is An Aircraft's Fuselage?
Username: Speedracer1407
Posted 2006-03-10 10:22:24 and read 8405 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

Topic: RE: How Flexible Is An Aircraft's Fuselage?
Username: Starlionblue
Posted 2006-03-10 14:28:52 and read 8375 times.

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

Topic: RE: How Flexible Is An Aircraft's Fuselage?
Username: Chema
Posted 2006-03-10 16:33:25 and read 8332 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

Topic: RE: How Flexible Is An Aircraft's Fuselage?
Username: Lehpron
Posted 2006-03-11 01:16:48 and read 8251 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.

Topic: RE: How Flexible Is An Aircraft's Fuselage?
Username: Flashmeister
Posted 2006-03-11 09:40:23 and read 8192 times.

Sit at the back of a 757-300 and fly through turbulence... you'll see the flex for sure.

Topic: RE: How Flexible Is An Aircraft's Fuselage?
Username: EmiratesA345
Posted 2006-03-11 10:06:00 and read 8187 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

Topic: RE: How Flexible Is An Aircraft's Fuselage?
Username: WickedPenguin
Posted 2006-03-26 17:10:26 and read 7871 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.

Topic: RE: How Flexible Is An Aircraft's Fuselage?
Username: 2H4
Posted 2006-03-26 17:26:36 and read 7868 times.



A study in wrinkled fuselage skin:


View Large View Medium
Click here for bigger photo!

Photo © Michael Baldock
View Large View Medium
Click here for bigger photo!

Photo © Howard J Curtis




View Large View Medium
Click here for bigger photo!

Photo © Daniel Butcher - UK Airshow Review




View Large View Medium
Click here for bigger photo!

Photo © Roel Kroes
View Large View Medium
Click here for bigger photo!

Photo © DAI - Dutch Aviation Images






2H4


Topic: RE: How Flexible Is An Aircraft's Fuselage?
Username: HAWK21M
Posted 2006-04-01 18:08:35 and read 7703 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

Topic: RE: How Flexible Is An Aircraft's Fuselage?
Username: ANother
Posted 2006-04-03 11:52:57 and read 7586 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.


The messages in this discussion express the views of the author of the message, not necessarily the views of Airliners.net or any entity associated with Airliners.net.

Copyright © Lundgren Aerospace. All rights reserved.
http://www.airliners.net/