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Advantage Of Rear Preassure Dome Vs Flat Bulkhead  
User currently offlineAtlturbine From United States of America, joined Aug 2008, 158 posts, RR: 14
Posted (5 years 11 months 2 weeks 6 days ago) and read 4551 times:

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

[Edited 2008-09-30 19:11:17]


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16 replies: All unread, jump to last
 
User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 1, posted (5 years 11 months 2 weeks 6 days ago) and read 4545 times:



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

One word "weight".


User currently offlineAtlturbine From United States of America, joined Aug 2008, 158 posts, RR: 14
Reply 2, posted (5 years 11 months 2 weeks 5 days 23 hours ago) and read 4531 times:

Wow..thanks..that seems simple enough. Thanks for the info.


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User currently offlineAtlturbine From United States of America, joined Aug 2008, 158 posts, RR: 14
Reply 3, posted (5 years 11 months 2 weeks 5 days 23 hours ago) and read 4527 times:

So why ever use a pressure dome to begin with I wonder?


To the World you might be One Person but to One Person you might be the World
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17038 posts, RR: 66
Reply 4, posted (5 years 11 months 2 weeks 5 days 22 hours ago) and read 4513 times:

As I see it, a dome can be made less heavy for the same strength given its shape.


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineAcNDTTech From United States of America, joined Jul 2008, 338 posts, RR: 0
Reply 5, posted (5 years 11 months 2 weeks 5 days 21 hours ago) and read 4504 times:

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

User currently offlineStarlionblue From Greenland, joined Feb 2004, 17038 posts, RR: 66
Reply 6, posted (5 years 11 months 2 weeks 5 days 21 hours ago) and read 4497 times:



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

Given the same weight of material yes.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 7, posted (5 years 11 months 2 weeks 5 days 20 hours ago) and read 4482 times:



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.


User currently offlineMD11Engineer From Germany, joined Oct 2003, 14026 posts, RR: 62
Reply 8, posted (5 years 11 months 2 weeks 5 days 12 hours ago) and read 4412 times:

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


User currently offlineAtlturbine From United States of America, joined Aug 2008, 158 posts, RR: 14
Reply 9, posted (5 years 11 months 2 weeks 5 days 9 hours ago) and read 4376 times:



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!

Mitch



To the World you might be One Person but to One Person you might be the World
User currently offlineRoseFlyer From United States of America, joined Feb 2004, 9633 posts, RR: 52
Reply 10, posted (5 years 11 months 2 weeks 5 days 7 hours ago) and read 4335 times:



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.



If you have never designed an airplane part before, let the real designers do the work!
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 79
Reply 11, posted (5 years 11 months 2 weeks 5 days 4 hours ago) and read 4282 times:



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.


User currently offlinePmk From United States of America, joined May 1999, 664 posts, RR: 2
Reply 12, posted (5 years 11 months 2 weeks 4 days ago) and read 4155 times:

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.

PMK


User currently offline474218 From United States of America, joined Oct 2005, 6340 posts, RR: 9
Reply 13, posted (5 years 11 months 2 weeks 4 days ago) and read 4151 times:



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.


User currently offlineJetMech From Australia, joined Mar 2006, 2699 posts, RR: 53
Reply 14, posted (5 years 11 months 2 weeks 2 days 18 hours ago) and read 4054 times:



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.

Regards, JetMech



JetMech split the back of his pants. He can feel the wind in his hair.
User currently offlineAtlturbine From United States of America, joined Aug 2008, 158 posts, RR: 14
Reply 15, posted (5 years 11 months 2 weeks 1 day 21 hours ago) and read 3970 times:

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?


To the World you might be One Person but to One Person you might be the World
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17038 posts, RR: 66
Reply 16, posted (5 years 11 months 2 weeks 1 day 21 hours ago) and read 3965 times:



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.



"There are no stupid questions, but there are a lot of inquisitive idiots."
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