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lacontrabarra
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Interior modules expansion due to pressurization effects

Sun Feb 23, 2020 8:45 am

Hi all,

Good on paper, but in practice...would an operative galley, lav door, closet, or bin on the ground, being close or out of to its min clearance tolerance, be jammed in flight due to physical changes in the furniture module by pressurization effects.

Did anyone experienced that? (Besides from nonsense write ups)
 
unimproved
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Re: Interior modules expansion due to pressurization effects

Sun Feb 23, 2020 10:51 am

The fuselage expands during pressurization so it'd be the other way around. No clearance checks are done in the air however, so it'll always be adjusted to ground situation.
 
lacontrabarra
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Re: Interior modules expansion due to pressurization effects

Sun Feb 23, 2020 11:55 am

Agreed. Thanks a lot for the explanation. Heard both versions.The contraction theory didn’t really fit my logic. Plus I never heard of that in practice. That’s why the post...
 
mxaxai
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Joined: Sat Jun 18, 2016 7:29 am

Re: Interior modules expansion due to pressurization effects

Sun Feb 23, 2020 12:23 pm

Anything inside the aircraft will usually move with the fuselage, as galleys, lavs etc are not designed to be load-bearing structures. Overhead bins, for example, have one fixed bearing and one moving bearing.
 
lacontrabarra
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Re: Interior modules expansion due to pressurization effects

Sun Feb 23, 2020 1:11 pm

mxaxai wrote:
Anything inside the aircraft will usually move with the fuselage, as galleys, lavs etc are not designed to be load-bearing structures. Overhead bins, for example, have one fixed bearing and one moving bearing.


True, but my question was more directed towards the importance of keeping i.e a lav door serviceable. I was quite stunned by a colleague’s statement, that if say a door gotta have a clearance of 3mm from the frame, and it has say 2mm, it will work on ground and you’ll sign it off as ops ck ok, but it will jam or not operate smoothly in flight. Another colleague, an actual interior guy stated it was quite the opposite, same as the first fella who replied to my post...
 
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Starlionblue
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Re: Interior modules expansion due to pressurization effects

Sun Feb 23, 2020 4:08 pm

AFAIK the interior fittings are not rigidly attached to the fuselage. If you look at the overhead bins in moderate turbulence you'll notice they shake out of sync with the fuselage. This is to allow for expansion, contraction, movement. Look down a long narrowbody and you can sometimes see the seats move as the fuselage twists in turbulence, which moves the floor. meanwhile the overheads go in another direction.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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dennypayne
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Re: Interior modules expansion due to pressurization effects

Sun Feb 23, 2020 5:27 pm

Starlionblue wrote:
Look down a long narrowbody and you can sometimes see the seats move as the fuselage twists in turbulence, which moves the floor.


I used to love sitting in the back of the stretch DC-8s in turbulence and watch the tops of the front seats twist one direction while the rear ones went the opposite way.

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JayinKitsap
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Re: Interior modules expansion due to pressurization effects

Sun Feb 23, 2020 8:11 pm

Thin wall circular tubes (airplanes, pipes, and submarines all fit this category) are able to be modeled on the principal stresses only, neglecting out of plane flexure. Thick wall tubes must account for that, a good example is a 1,000 PSI tank 3 feet in diameter with 2 inch wall thickness. There is also an intermediate range. Even though subs have a shell thickness of several inches, that is small compared to the 500 inch diameter, but subs actually are in the intermediate range.

Anyway, shells under pressure will expand, things like floor beams, luggage bins, toilet and galley compartments, etc must allow for the full shell expansion and movements under shell hoop pressures as well as axial flexure. Otherwise the shell loads will jump to the restraining part making it part of the structure until it slips or fails. There are horrible stress risers in the shell by such attachments, so they must be avoided.

So these secondary partitions etc, the joint sizes are established to cover the expansion, contraction, racking, and tolerances. The big issue on such parts is the different thermal and humidity changes in the material. A plastic panel with an aluminum perimeter frame could see significant changes from being parked in the arctic compared to a hot day in Guam.
 
basspaul
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Re: Interior modules expansion due to pressurization effects

Mon Feb 24, 2020 1:22 pm

Starlionblue wrote:
AFAIK the interior fittings are not rigidly attached to the fuselage. If you look at the overhead bins in moderate turbulence you'll notice they shake out of sync with the fuselage. This is to allow for expansion, contraction, movement. Look down a long narrowbody and you can sometimes see the seats move as the fuselage twists in turbulence, which moves the floor. meanwhile the overheads go in another direction.


This, and when we get it wrong, doors do, and have jammed in surface. Especially a problem in biz jets as the customer expects very small gaps around doors as compared to what is acceptable to commercial operators. Also, many biz jets have pressurized floors over/near the wings. This floor moves down with pressurization while the fuselage grows out. I worked on one project where this effect was in the magnitude of .25-30 inch when combined.
 
lacontrabarra
Topic Author
Posts: 4
Joined: Sun Feb 23, 2020 8:18 am

Re: Interior modules expansion due to pressurization effects

Mon Feb 24, 2020 2:51 pm

basspaul wrote:
Starlionblue wrote:
AFAIK the interior fittings are not rigidly attached to the fuselage. If you look at the overhead bins in moderate turbulence you'll notice they shake out of sync with the fuselage. This is to allow for expansion, contraction, movement. Look down a long narrowbody and you can sometimes see the seats move as the fuselage twists in turbulence, which moves the floor. meanwhile the overheads go in another direction.


This, and when we get it wrong, doors do, and have jammed in surface. Especially a problem in biz jets as the customer expects very small gaps around doors as compared to what is acceptable to commercial operators. Also, many biz jets have pressurized floors over/near the wings. This floor moves down with pressurization while the fuselage grows out. I worked on one project where this effect was in the magnitude of .25-30 inch when combined.


I understand you said that the doors jam while the airplane is on the gnd?

My colleague who works on Bizjets as well said that the lav modules actually become loose in the air if not adjusted to proper specs on gnd. And the squeaky noises are actually normal on the gnd, while they do go away in the air.
 
basspaul
Posts: 32
Joined: Fri Jan 26, 2018 8:18 pm

Re: Interior modules expansion due to pressurization effects

Mon Feb 24, 2020 4:51 pm

lacontrabarra wrote:
basspaul wrote:
Starlionblue wrote:
AFAIK the interior fittings are not rigidly attached to the fuselage. If you look at the overhead bins in moderate turbulence you'll notice they shake out of sync with the fuselage. This is to allow for expansion, contraction, movement. Look down a long narrowbody and you can sometimes see the seats move as the fuselage twists in turbulence, which moves the floor. meanwhile the overheads go in another direction.


This, and when we get it wrong, doors do, and have jammed in surface. Especially a problem in biz jets as the customer expects very small gaps around doors as compared to what is acceptable to commercial operators. Also, many biz jets have pressurized floors over/near the wings. This floor moves down with pressurization while the fuselage grows out. I worked on one project where this effect was in the magnitude of .25-30 inch when combined.


I understand you said that the doors jam while the airplane is on the gnd?

My colleague who works on Bizjets as well said that the lav modules actually become loose in the air if not adjusted to proper specs on gnd. And the squeaky noises are actually normal on the gnd, while they do go away in the air.


It can go both ways: rigged to perfection on the ground, problems in the air. Get it working the air, everything jams on the ground. You need to design in flexible & slip features to avoid this. And sometimes the plane will flex in just a slightly different way than expected in the FEM and can be a pain to figure out what is actually moving.

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