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  #31  
Old 02-19-2014, 10:18 AM
jj_jetmech jj_jetmech is offline
 
Join Date: Aug 2013
Location: Klgb
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Are some people just hoping for a short cut for fear of drilling out a few more rivets? You already took the tail off, how about spend a few more hours and actually comply with the SB. Vans for me!
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  #32  
Old 02-19-2014, 04:38 PM
glenn654 glenn654 is offline
 
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I'm not taking a stand either for or against since I don't have a dog in this fight but it would be interesting to know if a simulation for testing this part/material could be performed to see if it is as suitable as Vans.

But Van's would be the one to do this and I seriously doubt that will happen.

Glenn Wilkinson
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  #33  
Old 02-20-2014, 12:47 AM
SvingenB SvingenB is offline
 
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Galvanic corrosion between stainless and aluminum always ends up with aluminum being sacrificially corroded. Stainless is the more "noble" material. Passivating the stainless help nothing to prevent this, if anything it will make the matter worse. This is only a problem in marine environments. Without salt the combination of stainless and aluminium is perfectly safe.
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  #34  
Old 02-20-2014, 07:13 AM
krw5927 krw5927 is offline
 
Join Date: Aug 2010
Location: Wichita, KS
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Quote:
Originally Posted by SvingenB View Post
Galvanic corrosion between stainless and aluminum always ends up with aluminum being sacrificially corroded. Stainless is the more "noble" material. Passivating the stainless help nothing to prevent this, if anything it will make the matter worse. This is only a problem in marine environments. Without salt the combination of stainless and aluminium is perfectly safe.
Exactly. Passive 301 stainless is further away from 2024 Aluminum on the galvanic series than active 301 stainless. Meaning greater galvanic potential and corrosion risk.
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  #35  
Old 02-20-2014, 01:54 PM
vgb vgb is offline
 
Join Date: Aug 2007
Location: northern Cal
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I wonder why these cracks started in the first place if the engineering and stress tests where done?
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  #36  
Old 02-20-2014, 02:28 PM
Geeman Geeman is offline
 
Join Date: Apr 2010
Location: Novato, CA KDVO
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Talking Not an exact science

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Originally Posted by vgb View Post
I wonder why these cracks started in the first place if the engineering and stress tests where done?
Because engineering is not an exact science and not every calculation results in the exact answer. Too many variables. Kinda of why their are test pilots
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  #37  
Old 02-20-2014, 04:02 PM
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JanRV6UK JanRV6UK is offline
 
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Quote:
Originally Posted by Geeman View Post
Because engineering is not an exact science and not every calculation results in the exact answer. Too many variables. Kinda of why their are test pilots
and sometimes cracks ... ;-)
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  #38  
Old 02-20-2014, 05:19 PM
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kinger kinger is offline
 
Join Date: Jan 2007
Location: USA
Posts: 256
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Quote:
Originally Posted by Walt View Post
I normally try to refrain from entering discussions like this but what the heck, my wife tells me all the time I don't have any "filters" since retiring so I'm gonna throw my 2c in here

I would highly recommend owners just bite the bullet and install the Van's approved SB with no deviations and do it exactly as written. I've seen quite a few major repairs in my day and the Van's fix looks like what I would expect a typical repair to look like. On the other hand, Alan's repair does not even follow what I would consider to be standard practice from 43-13.

I appreciate the effort and ingenuity that Allan put into this, but this is not a mod/fix I would endorse.

But do we prime the SB parts???
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  #39  
Old 02-20-2014, 05:29 PM
Epepperman Epepperman is offline
 
Join Date: May 2011
Location: Whitetop Nebraska
Posts: 30
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Speaking of the possible galvanic action of stainless and aluminum...
What is our firewall made of again, and what fasteners do we use to rivet them on with? Is this really an issue? Someone is offering a substitute, take it or leave it but don't bash him for offering it.
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  #40  
Old 02-20-2014, 09:59 PM
SvingenB SvingenB is offline
 
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Quote:
Originally Posted by Epepperman View Post
Speaking of the possible galvanic action of stainless and aluminum...
What is our firewall made of again, and what fasteners do we use to rivet them on with? Is this really an issue?
If it is an issue or not depends on where you are going to fly. Galvanic corrosion problems in aluminum is generally no issue at all, or only a minor issue. However, in marine environments, galvanic corrosion problems is THE issue of ALL corrosion issues. This is common knowledge to every boat owner (salt waters), and to the US Navy.
Quote:
An estimated 90% of corrosion damage to our F/A-18 aircraft is due to galvanic interactions
The point is that galvanic corrosion, if left to develop, can destroy parts within a few months close to the sea, days even. Still, only a few miles inland and the problem is non existent.

The combination of aluminum and stainless is a special case, this combination is 100% safe away from the sea (no salt). These alloys will not interact in fresh water environments even though the galvanic potential between them is larger than aluminum and copper. In a marine atmosphere they will interact instantly where aluminum will corrode rapidly.

Besides, 301 stainless will not last long in a marine environment if left untreated, passivated or not. It is definitely not a metal you would ever put on the deck of a boat (316 stainless and lots of other alloys are made for marine use). Untreated 6061 aluminum will last for years and years in marine environments, but connect it with a piece of 301 stainless and corrosion starts within days. I have a test piece of 6061 riveted with 304 stainless using various protection methods that will be permanently fitted to my boat for some years, just to see how it develops.

Corrosion of aluminum is entirely decided by the environment. Practically speaking it is a problem that exist exclusively for marine environments. Inland, the problems are virtually non existing.
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