atlturbine
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Advantage Of Rear Preassure Dome Vs Flat Bulkhead

Wed Oct 01, 2008 2:10 am

Other than space advantage what is the substantial differences structurally or otherwise?

[Edited 2008-09-30 19:11:17]
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474218
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RE: Advantage Of Rear Preassure Dome Vs Flat Bulkhead

Wed Oct 01, 2008 2:20 am



Quoting Atlturbine (Thread starter):
Other than space advantage what is the substantial differences structurally or otherwise?

One word "weight".
 
atlturbine
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RE: Advantage Of Rear Preassure Dome Vs Flat Bulkhead

Wed Oct 01, 2008 3:12 am

Wow..thanks..that seems simple enough. Thanks for the info.
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atlturbine
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RE: Advantage Of Rear Preassure Dome Vs Flat Bulkhead

Wed Oct 01, 2008 3:16 am

So why ever use a pressure dome to begin with I wonder?
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Starlionblue
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RE: Advantage Of Rear Preassure Dome Vs Flat Bulkhead

Wed Oct 01, 2008 4:20 am

As I see it, a dome can be made less heavy for the same strength given its shape.
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acNDTTech
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RE: Advantage Of Rear Preassure Dome Vs Flat Bulkhead

Wed Oct 01, 2008 4:52 am

This is just a guess. Maybe because of the strength of a sphere vs. the strength of a flat panel, a dome may be stronger than a flat bulkhead?  Confused
 
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Starlionblue
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RE: Advantage Of Rear Preassure Dome Vs Flat Bulkhead

Wed Oct 01, 2008 5:06 am



Quoting AcNDTTech (Reply 5):
a dome may be stronger than a flat bulkhead?

Given the same weight of material yes.
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tdscanuck
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RE: Advantage Of Rear Preassure Dome Vs Flat Bulkhead

Wed Oct 01, 2008 6:28 am



Quoting Atlturbine (Thread starter):
Other than space advantage what is the substantial differences structurally or otherwise?

Different loading. A dome is in pure tension (away from the rim), a flat bulkhead is in bending. That's the main reason the flat bulkhead is heavier.

Tom.
 
MD11Engineer
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RE: Advantage Of Rear Preassure Dome Vs Flat Bulkhead

Wed Oct 01, 2008 2:16 pm

Also, there is generally no space advantage involved with a domed pressure bulkhead. The space inside the bulkhead is normally wasted and empty.
A flat pressure bulkhead is also easier to manufacture, since it doesn't contain 3d curves.

Jan
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atlturbine
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RE: Advantage Of Rear Preassure Dome Vs Flat Bulkhead

Wed Oct 01, 2008 5:41 pm



Quoting MD11Engineer (Reply 8):
Also, there is generally no space advantage involved with a domed pressure bulkhead. The space inside the bulkhead is normally wasted and empty.

My bad MD11Engineer. When I started the thread I should have said space advantage for the flat pressure bulkhead.  Yeah sure

It seems that some of the more nightmarish jobs in my aviation career have involved working aft of flat pressure bulkheads (DC-9's, MD-88's & 727's specifically) Those jobs could be the subject of a new thread I am certain!

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RE: Advantage Of Rear Preassure Dome Vs Flat Bulkhead

Wed Oct 01, 2008 7:23 pm



Quoting MD11Engineer (Reply 8):
Also, there is generally no space advantage involved with a domed pressure bulkhead. The space inside the bulkhead is normally wasted and empty.



Quoting Atlturbine (Reply 9):
My bad MD11Engineer. When I started the thread I should have said space advantage for the flat pressure bulkhead.

A flat bulkhead has a space advantage. It is 2-4 galley carts on a 737. That's enough to allow relocation of the lavatories and up to 6 more seats. That's worth a weight penalty.
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tdscanuck
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RE: Advantage Of Rear Preassure Dome Vs Flat Bulkhead

Wed Oct 01, 2008 10:01 pm



Quoting MD11Engineer (Reply 8):
Also, there is generally no space advantage involved with a domed pressure bulkhead. The space inside the bulkhead is normally wasted and empty.

There is no space advantage to the curved bulkhead (a flat one provides more cabin room) but it's not true that the space inside the bulkhead is wasted and empty...the rear galley on many aircraft is curved at the back to fit partially into the dome.

Tom.
 
pmk
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RE: Advantage Of Rear Preassure Dome Vs Flat Bulkhead

Fri Oct 03, 2008 1:59 am

Not to impugn the others but there is another important reason.

Pressure containers, of any kind, operate best when the metal or frankly any other material does not have a 90 degree angle; this creates a fatigue point is generally to be avoided. Hence the reason that propane tanks, champagne bottles, soda pop cans, submarine pressure hulls, spacecraft, and other pressure vessels are ideally round or have hemispherical ends.

There are formuli that explain this in depth but suffice it to say rounder is better.

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474218
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RE: Advantage Of Rear Preassure Dome Vs Flat Bulkhead

Fri Oct 03, 2008 2:11 am



Quoting Pmk (Reply 12):
Pressure containers, of any kind, operate best when the metal or frankly any other material does not have a 90 degree angle; this creates a fatigue point is generally to be avoided. Hence the reason that propane tanks, champagne bottles, soda pop cans, submarine pressure hulls, spacecraft, and other pressure vessels are ideally round or have hemispherical ends.

All this is true and that is why the flat bulkhead have to made from thicker material with lots of stiffing and thus are much heaver.
 
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jetmech
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RE: Advantage Of Rear Preassure Dome Vs Flat Bulkhead

Sat Oct 04, 2008 8:41 am



Quoting Tdscanuck (Reply 7):
Different loading. A dome is in pure tension (away from the rim), a flat bulkhead is in bending. That's the main reason the flat bulkhead is heavier.



Quoting Pmk (Reply 12):



Quoting 474218 (Reply 13):

I think the bending issue is the main reason flat bulkheads are far more robust structures compared with a pressure dome. Applying bending loads means you have to deal with compressive loads as well as tensile loads.

Tensile loads are a stable configuration, and are relatively easy to design for. The problem with bending is the compressive part of the loading. You have the additional scenario of buckling and instability to deal with, which is trickier to design for, and often requires additional material mass to ensure stability.

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atlturbine
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RE: Advantage Of Rear Preassure Dome Vs Flat Bulkhead

Sun Oct 05, 2008 5:38 am

Thanks for all the great input! Adding to this..we are all aware of some infamous failures of P domes in the past (JAL 123 for example). Is anyone aware of a "flat pressure bulkhead" inflight failure?
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Starlionblue
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RE: Advantage Of Rear Preassure Dome Vs Flat Bulkhead

Sun Oct 05, 2008 5:48 am



Quoting Atlturbine (Reply 15):
Is anyone aware of a "flat pressure bulkhead" inflight failure?

Nope. There is one famous one for a classic bulkhead, the JAL 747 accident.
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