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03-12-2015, 06:03 PM
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Join Date: Sep 2005
Location: Maple Grove, MN
Posts: 2,333
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It may be that the tube was a little short, and the B-nut put tension on the tube as it was tightened. It seems to explain the stepped flare (different angle below the crack) that we see in the picture.
As one is tightening them, B-nuts should go from loose to very snug in a very small number of flats of the nut. If they seem to start building up torque slowly, there may be aluminum deformation going on. The flare of the tube should rest against the male fitting and be co-axially aligned prior to tightening the B-nut.
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Alex Peterson
RV6A N66AP 1700+ hours
KADC, Wadena, MN
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03-12-2015, 06:12 PM
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Join Date: Dec 2011
Location: Livermore, CA
Posts: 6,797
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Quote:
Originally Posted by BobTurner
To my eye there appears to be a change in the flare angle, starting at the crack. Are you sure you used an aviation flare, not an automotive one? They're different angles.
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I looked again, and I take my post back.
I agree with others here, it was over-flared (should fit thru the B nut threads) and over-torqued.
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03-12-2015, 07:04 PM
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Join Date: Apr 2008
Location: Lake Havasu City AZ
Posts: 2,393
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Tubing
The mutilation on the OUTSIDE of the tube is completely unacceptable. If any of this existed before the material was flared, the crack may have started in one of these deep scratches.
Regarding Tom Swearengen's comments on tubing, I only use 5052-O. With all due respect I would not use 3003 on a tractor.
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03-12-2015, 07:26 PM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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Quote:
Originally Posted by jrs14855
I only use 5052-O. With all due respect I would not use 3003 on a tractor.
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Everyone is entitled to their own opinion, but lets not loose site of the fact that what ever material is used to do a specific job, it still requires proper processes and techniques be used for it to perform well.
Someone could pend a fortune using the materials they used on the space shuttle, but if not used properly, there is no assurance that it will perform well.
Actual service history says a lot.... there are literally thousands of RV's safely flying with lines made from 3003 tubing....
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.
Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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03-12-2015, 07:40 PM
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Join Date: Oct 2005
Location: Melbourne, Australia
Posts: 1,868
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Quote:
Originally Posted by jrs14855
The mutilation on the OUTSIDE of the tube is completely unacceptable. If any of this existed before the material was flared, the crack may have started in one of these deep scratches.
Regarding Tom Swearengen's comments on tubing, I only use 5052-O. With all due respect I would not use 3003 on a tractor.
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Same here. Only 5052-0 for me (both fuel and hydraulic lines). The 3003 is too soft. This has been discussed in detail on VansAirforce before.
My best guess is Vans supplies the 3003 because it is cheap cheap cheap and because it comes in rolls so is easy to freight. The 5052 is far superior but it comes in long straight lengths so there are logistical problem in transporting it.
Of course I agree with Scott in that it is useless buying superior tubing if you have totally inadequate fabrication skills.
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You’re only as good as your last landing 
Bob Barrow
RV7A
Last edited by Captain Avgas : 03-12-2015 at 07:46 PM.
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03-12-2015, 07:46 PM
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Join Date: Jan 2010
Location: Ottawa, Ks
Posts: 2,188
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I'm fairly sure now that I over-flared the tubing by using the clutch mechanism as my stopping point. I found this reference online,
My flair is over the max diameter, sticking past the sleeve
As much as I hate to say it, looks like I'm going to be redoing all my hard fuel lines  .
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RV 7 400 hours and counting
19 donation done
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03-12-2015, 08:06 PM
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Join Date: Jun 2006
Location: Castaic, CA
Posts: 549
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I routinely use the Rigid RFT37 at work with 3/8" .028" Stainless so I'm familiar with it. The few times I have done copper line with it, It always over flares. I believe the clutch mechanism is simply too tight for soft material. While the clutch mechanism is a nice feature that allows you to burnish the inside face for the flare, I don't find that necessary when doing soft tube like copper or aluminum. I would suggest trying a different flare tool, I get good results with the Parker Rolo Flare. This tool does not have a clutch, so you will need to practice on a few pieces to get the feel of how tight to thread the flaring cone down.
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Mike Sumner
Castaic, Ca
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03-12-2015, 08:24 PM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,652
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Quote:
Originally Posted by rvbuilder2002
...Actual service history says a lot.... there are literally thousands of RV's safely flying with lines made from 3003 tubing....
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There are probably plenty still flying around with the plastic brake pressure lines too... But that doesn't mean we ignore a more suitable material.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
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Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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03-12-2015, 08:42 PM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,516
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Quote:
Originally Posted by crabandy
I'm fairly sure now that I over-flared the tubing by using the clutch mechanism as my stopping point. I found this reference online,
My flair is over the max diameter, sticking past the sleeve
As much as I hate to say it, looks like I'm going to be redoing all my hard fuel lines  .
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Good work getting to the root cause! Stuff happens, on the plus side, your due diligence found a solution quickly.
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Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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03-12-2015, 09:01 PM
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Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 9,035
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Quote:
Originally Posted by Toobuilder
There are probably plenty still flying around with the plastic brake pressure lines too...
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Your right, there are. Probably thousands.
Nothing wrong with people wanting to use something different ( and others making a business out of fulfilling that desire), but I get tired of the suttle implications that others who do not choose to do the same, are fools.
__________________
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.
Scott McDaniels
Van's Aircraft Engineering Prototype Shop Manager
Hubbard, Oregon
RV-6A (aka "Junkyard Special ")
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