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

Flares according to SAEJ533!

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:
Flare.jpg



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
 
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rhill said:
The story of the 8 pilot jumping without a chute is enough for me,
Click to expand...

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
 
Ironflight said:
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!)
Click to expand...

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).
 
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.
 
Aussie Experiments

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.
 
tobinbasford said:
Good grief!!! Bad flare? How about bad tubing bends!! See bends on pg 10 and 11.
Click to expand...

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"....:eek:
 
nauga said:
There was no tubing or flaring technique that I'm aware of that would've prevented the engine from eating itself in that example.
Click to expand...

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.
 
Braided SS / Teflon

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.
 
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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
 
swisseagle said:
The tube was bent by the impact!
Click to expand...

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.
 
Dundee Downunder said:
Our SAAA Chapter 13 guru, Fred Moreno, conducted a series of
experiments to determine the likely cause of Hydraulic Fitting failures.
Click to expand...

This is a link to the report mentioned above.

http://forums.matronics.com/download.php?id=23055&sid=998c1b21e83aea09bc43a40358ba848e

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.
 
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.
Click to expand...

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
 
L.Adamson said:
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
Click to expand...

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...
 
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.
 
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 :eek:
 
Walt said:
Merely switching from 3003 to 5052 will not fix this problem :eek:
Click to expand...

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.
 
AlexPeterson said:
A perfectly flared, properly torqued tube can crack if there is not good alignment. In other words, the B nut should thread on by hand. If it isn't easy to do so, the tube is probably not aligned. Now add a little cyclic loading, either bending or tension, and it will fatigue crack. I'm guessing the tube in the first picture was not cracked at the time of flare or tightening. I certainly could be wrong.
Click to expand...

I thought this might stir some responses??
 
Walt said:
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.
Click to expand...

I would have thought that "quality control" specifically means using the correct material in the manufacture of any product. All industry documents that I have read would seem to indicate quite clearly that grade 3003 tubing is not recommended for brake lines on aircraft.

While I agree that correct flaring technique is thoroughly important (obviously), I don't think there is any proof available that all of the RV brake line failures can be attributed solely to poor flaring technique. Misalignment of the flare and/or overtorquing of the B-nut during repetitive reassembly may account for many of the failures. Consider that the flare at the top of the brake line on RVs never seems to fail....only the bottom flare. Could it be that the bottom flare is always the one that is poorly fabricated. That is not likely.

More likely is that the bottom flare is potentially subjected to more cycles of reassembly misalignment and/or overtorquing as it is the connection that is constantly being disconnected for maintenance. Each misalignment and/or overtorquing may deform the flare progressively until it eventually fails in service.

My argument is that 5052 is arguably less critical to flare in the first instance than 3003 (at least in my experience), less susceptible to damage from multiple retorquing (it's harder), and less likely to fail due to the cyclical stresses placed on it due to RV gear movement (has a higher fatigue strength).

In the hands of an amateur builder who may do no more than a couple of dozen flares in his life there is probably a lot more safety factor in opting for 5052 alloy than the 3003 alloy that no mainstream technical aviation document recommends.

In terms of the dangers of repetitive overtorquing of tubing flares I refer again to the document by Fred Moreno:
http://forums.matronics.com/download.php?id=23055&sid=998c1b21e83aea09bc43a40358ba848e

Having said all of this I must admit that I did not use any type of tubing at the brake caliper on my RV7A. I used high pressure hose. I think Vans design is flawed in that area and the fact that so many other builders use hose in that location as well means that many obviously agree with me.

When there is any doubt in my mind on crucial design issues I tend to have a good look at several certificated aircraft to ascertain what constitutes best practice before I proceed.
 
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Been following this closely - my conclusions:

3003 is a servicable choice done well. 5052 is a better one. In either case, your flares better be of high quality and your B-nuts not over tightened. 5052 would seem to provide a higher margin for less than professional craftmanship.

I am an engineer. I have a background in professional aviation and quality control. Even with that, I judge my personal level of workmanship to be only a 6.5 out of 10. My tube bending and flaring were done at that same level of "servicable but not great" workmanship. That tubing has served well in 200+ hours of service.

This thread has given me reason to look again at the quality of this critical system where I (like most builders) used a less than optimum material put together with less than optimal skills.

Now armed with a copy of SAEJ533, I will inspect my fuel tubing system (fuel injection with AFP pump and filter) for quality - with the expectation that I will probably be re-doing this critical system with 5052 and much improved quality and workmanship.

This will cost only a few $'s and a weekend's time.

I relate all of this because I suspect that I am about the "norm" for builders out there, and if I think this is a prudent course (knowing so much more now than I knew before), then it is probably a prudent course for lots of other builders.

That is the value of this forum. This is the type of cultural knowledge and standards that we can foster in our community that will create safer builders, airplanes and fewer accidents. Walt is setting a higher, more professional standard for us all to follow.

Current builders - proceed with 3003 but understand that quality craftsmanship and care is essential in this critical area to ensure safe results.
Hacks like me - redo better the second time (and while your at it, why not use the better material).

Thanks for starting the thread and thanks for all the thread contributions that led to improved knowledge.
 
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Has anyone figured out the weight penalty for flex lines versus 3003 or 5052? From what I've read, the downside to flex lines is limited life and weight. But how much more does a full set of flex lines (aft of firewall) really cost in terms of weight?
 
Most important thread in long time

Really glad to see this thread. I don't want to see it reduce to this vs that. The subject is crappy flares & tube fitting. Not material or flex vs tube. Crappy flares & fit. A good flare that is properly aligned can stand some torque abuse, etc. I've seen perfectly flared SS tubes fail from stress & vibration. That's engineering and trial by fire. Half the equation. The other half is......crappy flares.
 
CharlieWaffles said:
Has anyone figured out the weight penalty for flex lines versus 3003 or 5052? From what I've read, the downside to flex lines is limited life and weight. But how much more does a full set of flex lines (aft of firewall) really cost in terms of weight?
Click to expand...

The flex lines used are usually Teflon which should not have any limited life issues.
 
az_gila said:
The flex lines used are usually Teflon which should not have any limited life issues.
Click to expand...

Well Gil, I don't usually disagree with you, but at Oshkosh last year, i talked with a couple of different manufacturers of Teflon hoses, and both said that they need to be replaced at intervals "set by the airframe manufacturer". Neither one indicated that their lifetime is indefinite.

Paul
 
CharlieWaffles said:
Has anyone figured out the weight penalty for flex lines versus 3003 or 5052? From what I've read, the downside to flex lines is limited life and weight. But how much more does a full set of flex lines (aft of firewall) really cost in terms of weight?
Click to expand...

Part by part, inch by inch, I don't have any numbers. However, I removed most of the flex hose FWF on the -8 and replaced it with stainless hard lines. Where I was forced to run flex hose due to component movement, I kept it as short as possible. I'm guessing this -8 was a "typical" example of a fuel injected RV.

Going to SS hardline I saved an incredible 7 pounds. The trash bag full of discarded firesleved hose was really something to behold.
 
Weight v.cost

More than cost of the weight is the weight of the cost.

First off, Vans own airplanes have accumulated well over 20,000 hrs using the soft 3003 fuel line supplied in our kits. Learn how to properly flare and torque the B nuts and you have nothing to worry about.

Not only are hoses impractical in many tight locations due to a larger bend radius but hoses are also too fat to fit in many locations behind the firewall. Weight of those hoses is just one of the downsides but the cost of a complete set of hoses could easily be more than 10 times the cost of aluminum tubing.
Even with unavoidable trial pieces that most of us create when doing fuel lines it would be difficult to exceed a cost of $50.-in material. You can buy
2 hose fittings for that price and you can figure out the rest for yourself.

The picture in the original post shows an "acceptable flare" with sufficient wall thickness but sharp edges and a crack probably the result of missalignment or vibration.
I use a scotch brite pad to smooth out the edges of flares and I never miss an opportunity to install an adel clamp on a nut plate for support.
One thing that bothered me on the RV-10 fuel system behind the tunnel was the oil canning of the firewall. In essence that wobbly surface would transmit the engine vibrations throught the fuel hose and the bulkhead fitting to the back of the firewall fuel lines and thus cause potential for cracked aluminum
flares.
Here is what I did to alleviate the problem.

Photo%252520%25252031.JPG
 
If you could, please take a look here any provide positive/negative comments about how I made up my flares.

Thanks in advance for your time!

-Jim
 
Ironflight said:
Well Gil, I don't usually disagree with you, but at Oshkosh last year, i talked with a couple of different manufacturers of Teflon hoses, and both said that they need to be replaced at intervals "set by the airframe manufacturer". Neither one indicated that their lifetime is indefinite.

Paul
Click to expand...

CYA? While the airframe manufacturer requirements always rules for STC or certified applications, the FAA and hose manufacturers have published otherwise. Note that inspections are required...

Teflon™ is the DuPont trade name for tetrafluoroethylene
resin. It has a broad operating temperature range
(−65 °F to +450 °F). It is compatible with nearly every
substance or agent used. It offers little resistance to
flow; sticky, viscous materials will not adhere to it. It
has less volumetric expansion than rubber, and the shelf
and service life is practically limitless. Teflon™ hose
is flexible and designed to meet the requirements of
higher operating temperatures and pressures in present
aircraft systems. Generally, it may be used in the same
manner as rubber hose. Teflon™ hose is processed and
extruded into tube shape to a desired size. It is covered
with stainless steel wire, which is braided over the
tube for strength and protection. Teflon™ hose is unaffected
by any known fuel, petroleum, or synthetic base
oils, alcohol, coolants, or solvents commonly used in
aircraft. Teflon™ hose has the distinct advantages of
a practically unlimited storage time, greater operating
temperature range, and broad usage (hydraulic, fuel,
oil, coolant, water, alcohol, and pneumatic systems).

Above from FAA document http://www.faa.gov/library/manuals/aircraft/amt_handbook/media/FAA-8083-30_Ch07.pdf

From www.amtonline.com

The Air Force requires all rubber hose assemblies be replaced after 10 years from date of assembly manufacture, and PTFE hose assemblies shall be replaced “on-condition.”

An Aeroquip document -

The effect of heat on Teflon hose is completely different from that of rubber hose. Unlike the more common organic rubber compounds, Teflon or "Tetrafluorethylene", as it is more properly known, does not harden when being used at elevated temperatures (-SJCF to +400°F), but stays uniform in texture and consistency.

From an Eaton hose document - http://vargaair.com/admin/wp-content/uploads/2009/08/tf100-31_aluminum_compression_fittings.pdf

Service and shelf life of Eaton’s
Aeroquip Brand Teflon hoses
are unlimited for all practical
purposes. However, experience
has shown that service life on
impulsing applications may eventually
be limited by fatigue in the
wire reinforcement. Maximum
service life on such applications
is best determined by the operator,
based on his experience.

It was not my personal random comment....:)

I belief in our relatively easy RV applications they have an essentially unlimited life if inspected carefully every annual.
 
I knew I'd pry more research out of you with that comment Gil - thanks! ;)

The only thing I'd continue to press is...how do you determine the condition of the interior of a Teflon hose to ddetermine if it is in need of replacement? You can flex it and see if it is getting crispy, but can't tell what's going on inside. And no one will give a ballpark figure. It's just something to consider.

Don't get me wrong - Teflon hases are FAR superior to rubber hoses in every way. But I don't think thre is enough evidence yet on ultimate life.
 
Ironflight said:
I knew I'd pry more research out of you with that comment Gil - thanks! ;)

The only thing I'd continue to press is...how do you determine the condition of the interior of a Teflon hose to ddetermine if it is in need of replacement? You can flex it and see if it is getting crispy, but can't tell what's going on inside. And no one will give a ballpark figure. It's just something to consider.

Don't get me wrong - Teflon hases are FAR superior to rubber hoses in every way. But I don't think thre is enough evidence yet on ultimate life.
Click to expand...

There is an inspection procedure document, but it is a newer AS document that costs $$$ and is not on-line as far as I could find...:(

Don't know about a "ballpark" figure, but the FAA words are -

...service life is practically limitless...

Sounds good enough for me in our typical applications when used as a replacement for a rubber hose...:)
 
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az_gila said:
There is an inspection procedure document, but it is a newer AS document that costs $$$ and is not on-line as far as I could find...:(

Don't know about a "ballpark" figure, but the FAA words are -

...service life is practically limitless...

Sounds good enough for me in our typical applications when used as a replacement for a rubber hose...:)
Click to expand...

Thread is drifting a bit but this topic is important.
I hope we can get our hands on that document at some point. The worry I have is that unlike rubber hoses, that had a measurable service life and showed signs before failure, how do you know if you have a teflon hose going bad? I had a teflon hose failure on the Bucker. It was a simple drain line from the bottom of the fuel tank in the cockpit area, no heat, no pressure... The inside of the hose about mid way just collapsed after about 10 years, 130 hours or so. You could not see it at all from the outside. I will assume it was defective from the start but who knows.
 
One comment on teflon--

Teflon, like other hose liners, will take a set over a period of time, due to heat and fluid cycles. Like Aeroquip 303 style hose, once teflon has been in service, dont take it off and flex it, or try to straighten it out to inspect it. Even though we dont have the temperatures that the hoses were intended for, you can still damage the liner or cause cracks that may not be able to see. If you need to remove them, (and you are going to reinstall them), support them so you can maintain the bends that they have.
Running oil temps to 250* is not a problem for teflon, as this is well within its intended temperature range.
Having seen some teflon hoses that were subjected to heat (exhaust), and abrasion, the liners are very durable. BUT, they will not take abuse, such as non-firesleeved appications laying on hi-heat exhaust. The stainless braid will fail, and the liner will be directly affected by the heat.
If you plan your hose routings correctly, your hoses will last the lifetime of your airframe. This has been proven in commercial and military applications,
Tom
 
JonJay said:
Thread is drifting a bit but this topic is important.
I hope we can get our hands on that document at some point. The worry I have is that unlike rubber hoses, that had a measurable service life and showed signs before failure, how do you know if you have a teflon hose going bad? I had a teflon hose failure on the Bucker. It was a simple drain line from the bottom of the fuel tank in the cockpit area, no heat, no pressure... The inside of the hose about mid way just collapsed after about 10 years, 130 hours or so. You could not see it at all from the outside. I will assume it was defective from the start but who knows.
Click to expand...

Several of the documents previously listed stated that the smooth bore Teflon hoses can be kinked in handling. Perhaps this is what happened to yours?

My previous post mentioned "long life" but in the context of a rubber hose replacement - ie, under the same operating conditions. Higher stresses, such as heat, certainly would reduce hose life spans.
 
SAE Standards

az_gila said:
I think this is the document

SAE AIR Report ARP 1658, "Hose Assemblies, Installed, Visual Inspection Guide"

http://standards.sae.org/arp1658b/
Click to expand...

Unfortunately, many of the old AN, MS, NAS documents which were public domain, are being obsoleted and SAE (Society of Automotive Engineers) has been recreating them as AS, ARP and various other standards. These are not public domain, and so we as users have to pay a substantial amount to purchase them. Fortunately, most of the AN, MS and NAS parts are still recognized and manufactured, but for standards such as the teflon hose inspection standard, we're probably have to pay $$
 
Thanks

I started plumbing this afternoon and because of the comments here I probably proceeded with more than an average amount of care and caution. I mike'd each flare to be sure it wasn't over done and I inspected each flare carefully under bright lights and with magnification. I rejected my first 4 flares and then proceeded to produce acceptable flares pretty consistently...if only I could consistently get the sleeve on in the right direction or not cut a tube a half an inch short. More practice.

I try to be careful and pay attention to detail in everything I do on the 9, but sometimes, I simply don't know what it is I don't know. Flaring tubing and especially not over-torquing the fittings were a couple of the things I didn't know well enough. This thread alone was sufficient to justify my $25 contribution to Doug. Thanks one and all.
 
Haven't done much in the way of flaring on my kit thus far, but my brother has quite a bit of his plumbing completed: www.our7a.com. He's been really picky about the tubing; probably has gone through 2-3 rolls (in addition to what comes with the kit)... Those tubing bends & flares sure do look nice though!

Chris
 
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