More Bad Flares on Fuel Lines Found, What's up with this?

[swisseagle]

Hello

In switzerland we lost the first RV-9 due to a bad flare, after about 40h.

The repport you can find here: http://www.bfu.admin.ch/common/pdf/u1987_d.pdf Page 9, 10, 11.

The problem is, when you make the flare to big, the material is thinned out and hardened. Thats where the Norm come handy to prevent that.

Interestingly, there is a Norm to manufacture these flarings, SAEJ533, even more interestignly is, that nearly nobody know that and inform about that, not Vans, not in the EAA video, not the supplyer of the tools!?

So how could a builder find the source and can do it propperly?

From a not officially source:


There is also a different torque for aluminum fittings (which you use with rubberhose thogether) and aluminum tubing!

You will crack the tubing (3003 only), even when you will use the correct torque, but allow the tubing to rotate with the nut, when you tighten it! It will squeeze the flaring even more and the material let go and getting thinner and harder.

There are other places where it is nearly the same, an example are the Fuel-Pump-Fittings with the O-Ring. Many, many threads are adressing that nobody know the torque to apply!?

I bought the 5XXX tubing vom Spruce and let them send to Vans, so they included it in my box, this way it was much cheaper than letting send the straight tubes to europe.


Regards, Dominik

[L.Adamson]

Originally Posted by rhill

The story of the 8 pilot jumping without a chute is enough for me,

Except that had nothing to do with fuel lines supplied by Van's, or any fuel lines period. The overhauled engine failed at 35 hrs, knocking a hole through the case.

L.Adamson

[Alan Carroll]

Originally Posted by Ironflight

I have thrown away LOTS of pieces that didn't quite meet standards for fit and quality in the airplanes. (...and when you screw one up, don't throw it away immediately - cut it up into pieces to use for flaring practice!)

Ditto. On the fuel lines I probably made 5 pieces for every one that ended up installed in the airplane. Certainly I made hundreds of "practice" flares. All 3003, no leaks or failures yet (700+ hrs).

[Dundee Downunder]

Our SAAA Chapter 13 guru, Fred Moreno, conducted a series of
experiments to determine the likely cause of Hydraulic Fitting failures.
Their conclusions were "These fittings are very sensitive to extrusion of
the tube by over tighening of the AN-818 nut. It only takes a onetime 50% loading to damage the tubing flare. A few cycles of overload at less than 50%excessive torque can compromise the strength sufficiently that a flare which may appear to be in good condition can fail when hydraulic pressure is applied, especially with 1/4" tube." How does this happen?...usually by
one giving it an extra tug "just to be sure" or your assistant "double checking"
the nut.
The solution...Buy a set of crows feet for your torque wrench for AN 818 nuts
and DO NOT make it " just a little tighter just to be sure".
Ref. Airsport SAAA Australia November 2010 p.9 for the full article.

[Dundee Downunder]

Our SAAA Chapter 13 guru, Fred Moreno, conducted a series of
experiments to determine the likely cause of Hydraulic Fitting failures.
Their conclusions were "These fittings are very sensitive to extrusion of
the tube by over tighening of the AN-818 nut. It only takes a onetime 50% loading to damage the tubing flare. A few cycles of overload at less than 50%excessive torque can compromise the strength sufficiently that a flare which may appear to be in good condition can fail when hydraulic pressure is applied, especially with 1/4" tube." How does this happen?...usually by
one giving it an extra tug "just to be sure" or your assistant "double checking"
the nut.
The solution...Buy a set of crows feet for your torque wrench for AN 818 nuts
and DO NOT make it " just a little tighter just to be sure".
Ref. Airsport SAAA Australia November 2010 p.9 for the full article.

[Tandem46]

Originally Posted by swisseagle

In switzerland we lost the first RV-9 due to a bad flare, after about 40h.

The repport you can find here: http://www.bfu.admin.ch/common/pdf/u1987_d.pdf Page 9, 10, 11.

Good grief!!! Bad flare? How about bad tubing bends!! See bends on pg 10 and 11.

[az_gila]

Originally Posted by tobinbasford

Good grief!!! Bad flare? How about bad tubing bends!! See bends on pg 10 and 11.

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"....

[nauga]

Originally Posted by rhill

The story of the 8 pilot jumping without a chute is enough for me...

There was no tubing or flaring technique that I'm aware of that would've prevented the engine from eating itself in that example.

[rhill]

Originally Posted by nauga

There was no tubing or flaring technique that I'm aware of that would've prevented the engine from eating itself in that example.

MY Bad,repeating a story told to me at a fly-in,I will check my facts next time.My point is this is a very inexpensive area of the build, Great idea for a EAA video,great demo for fly in's and chapter meetings,anything that could lower the accident rate,if it improves the odds even 1 in a thousand its worth the price of 5052 over the stock tubing.

[F1R]

I have seen some RV's and Rockets with Braided SS /Teflon lines from the fuel tanks all the way to the fuel spider. My own rocket is this way. I am not advocating it for everybody, but it does provide an option for those not keen on a rigid tubing job. Summit Racing in the USA has realms of SS & AN fittings for the various line sizes. I use it for brake lines, manifold pressure and fuel lines. The various sizes of line is all pressure & temperature rated. It is quite easy to build quality hoses with using the proper fittings.

In the end, rigid tubing or otherwise, quality workmanship, routing and vibration protection, inspection and maintenance is required to keep any system safe. See post #21 on this thread.