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  #61  
Old 10-29-2011, 03:04 PM
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rv8ch rv8ch is offline
 
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Default English version

Quote:
Originally Posted by az_gila View Post
I though the Page 10 tube defects might have been accident related, but Google translates the comment on figure 5 to "defective production of tube bending"....
There is also an english version of the report here: http://www.bfu.admin.ch/common/pdf/1987_e.pdf
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  #62  
Old 10-29-2011, 03:51 PM
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Default Thanks for the english link!

Hello Mickey

Thanks for the english link! Did not know, that they also translate it to a non official language for switzerland.

The tube was bent by the impact!

The pilot walked away, the parked cars and the structure of the plane reduced the g load to a level where it was survivable.


Regards, Dominik
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  #63  
Old 10-29-2011, 05:11 PM
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Quote:
Originally Posted by swisseagle View Post
The tube was bent by the impact!
The first sentence on page 10 states "No traces of an external violent force could be found either on the fuel selector casing or on the separated line."

Furthermore, as Gil points out, figure 5 on pg 10 has arrows pointing to the bends in the tubing with accompanying text "mangelhafte herstellung der rohrbiegung" which translates to "defective manufacture of the pipe bend".

What is strange is that the English version of the report leaves out both the arrows and the text.
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  #64  
Old 10-29-2011, 05:25 PM
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Quote:
Originally Posted by tobinbasford View Post
.....
What is strange is that the English version of the report leaves out both the arrows and the text.
That was the first thing I noticed too - thank goodness for Google translators...
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  #65  
Old 10-29-2011, 09:45 PM
Captain Avgas Captain Avgas is offline
 
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Quote:
Originally Posted by Dundee Downunder View Post
Our SAAA Chapter 13 guru, Fred Moreno, conducted a series of
experiments to determine the likely cause of Hydraulic Fitting failures.
This is a link to the report mentioned above.

http://forums.matronics.com/download...43a40358ba848e

It makes for an interesting read. But it is relevant that the report does not state what grade of alloy tubing was being used in the tests.

When RV builders use the torque values for AN-818 nuts onto aluminium tube as per AC43.13 it should be understood that those specified torques are for grade 5052 alloy.....NOT for 3003 alloy which is much softer.

Here is another good read for builders who really want to understand the subject: Aluminium Tubing Strength for Mechanics.
It states that 5052 is the tube alloy of choice for aviation applications (fuel and hydraulics). Note the comments on 5052 having "the best fatigue strength of any of the non-heat treat aluminium alloys".

http://www.mechanicsupport.com/tube_strength.html

And finally, according to the Standard Aircraft Handbook:

"Aluminum alloy tubing, 1100 (1/2-hard) or 3003 (1/2-hard), is used for general-purpose line of low or negligible fluid pressures, such as instrument lines and ventilation conduits. The 2024-T and 5052-0 aluminum alloy materials are used in general-purpose systems of low and medium pressures, such as hydraulic and pneumatic 1000- to 1500-psi systems and fuel and oil lines. Occasionally, these materials are used in high-pressure (3000 psi) systems."

I think there must now be considerable doubt about the wisdom of Vans supplying grade 3003 tubing for the brake lines based on both available technical data and on the brake failure rate in RVs.
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  #66  
Old 10-29-2011, 09:55 PM
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Quote:
I think there must now be considerable doubt about the wisdom of Vans supplying grade 3003 tubing for the brake lines based on both available technical data and on the brake failure rate in RVs.
Just one question.

How many RV brake failures have been from split aluminum tubing? Most that I see, have to do with improper flares, and breaking at the B-nut. Perhaps the evidence is there. I just haven't seen it all.

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  #67  
Old 10-29-2011, 11:20 PM
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Quote:
Originally Posted by L.Adamson View Post
Just one question.

How many RV brake failures have been from split aluminum tubing? Most that I see, have to do with improper flares, and breaking at the B-nut. Perhaps the evidence is there. I just haven't seen it all.

L.Adamson
Reading the data presented in this thread, you could make a reasonable arguement that the two are related - breaks at the B-Nut and use of 3003-0 tubing - based on the lower, non-specified torque that should be used with the much softer 3003-0 tubing...
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  #68  
Old 10-30-2011, 04:43 AM
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Default I'm convinced

I'll order some 5052 tubing today and use what Van's sent for practice, with one exception. I think I will use the 3003 tubing for the fuel vent line. I'm not ready to bash Van's for a poor material choice, as I suspect the material can be used successfully. It does appear less forgiving of mistakes (Gil's comment seems to nail this point) and I am an amateur at this. Given the modest cost of using 5052 tubing and considering I'm going with FI, it just makes sense.
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  #69  
Old 10-30-2011, 07:39 AM
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Without arguing the merit of different tubing materials (the flares that were found cracked that I started this tread with were NOT 3003), the fact remains it was the improper manufacturing that caused the cracking, not the materail choice (this was also a very low time aircraft so it was not fatigue or overtorquing the fitting).

So regardless of what material you elect to use the, the tools, methods and quality control is the determining factor of whether or not you will end up with a good part.

Merely switching from 3003 to 5052 will not fix this problem
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  #70  
Old 10-30-2011, 08:28 AM
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Quote:
Originally Posted by Walt View Post

Merely switching from 3003 to 5052 will not fix this problem
Really Walt, I wasn't proposing to deliberately use poor technique and expect the 5052 to take care of the problem or to not carefully inspect the work I do before deciding it is serviceable.
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