nippaero

nippaero

Well Known Member
I'm getting ready to hook up all my hoses and I have been reading through the archives about AN fittings. I already have the aluminum ones. It seems like a lot of people are suggesting to use steel fittings because of safety. Now I am wondering if I should use steel ones. Any guidance here would be appreciated. :confused:
 
I followed what I consider rule of thumb for hoses attached to shaking engines...

Any hoses connected directly to the engine should have steel fittings.

There's a lot of mass to a fluid filled hose. In my opinion, It's also a good idea to support the hose a few inches back from the fitting. Think of the engine trying to wag that hose like a dog wagging it's tail. You don't want them to be loosening or cracking.

Bevan
 
My preference:
Steel on the engine for strength
Steel in aluminum to prevent galling (especially in engine case and oil cooler).

In reference to clamping hoses, be careful not to clamp engine hoses to fixed structure like engine mounts, hoses need to be able to flex and move about without causing undue strain or tension on them.
 
Walt said:
In reference to clamping hoses, be careful not to clamp engine hoses to fixed structure like engine mounts, hoses need to be able to flex and move about without causing undue strain or tension on them.
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Agreed and should have mentioned that as it may not be obvious to all.

Bevan
 
Vans supplies aluminum fittings for the oil cooler. Both ends. Lycoming installed a 45 deg steel (corrected) fitting on the engine. I went by the book on this, but do wonder if there is a documented failure of a factory installation.

The hoses do have mass, but are still hoses even if rather stiff. I can not see any way to secure them from the cooler to the engine on supply or return.

I have installed all steel fittings for the fuel supply starting at the bulkhead firewall fitting.

Correction : I have been installing FWF stuff and checked the oil supply 45 deg fitting supplied on the M1B. It is Steel. I was wrong about that one, but the straight return fitting is aluminum.
 
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All the fittings on my IO-320 are steel. After I saw the not-pretty forced landing of a p-51 at Reno a few years ago, and found out the cause was a complete loss of oil due to the failure of a blue AN fitting on an oil hose, the decision to go with steel fittings was easy.
 
Aluminum or steel fitting on engine for oil cooler

BillL said:
Vans supplies aluminum fittings for the oil cooler. Both ends. Lycoming installed a 45 deg aluminum fitting on the engine. I went by the book on this, but do wonder if there is a documented failure of a factory installation.

The hoses do have mass, but are still hoses even if rather stiff. I can not see any way to secure them from the cooler to the engine on supply or return.

I have installed all steel fittings for the fuel supply starting at the bulkhead firewall fitting.
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Well is there any further thinking on whether the aluminum fitting from Van's for the oil cooler should be steel? I'm about to install mine.

I noticed Lycoming has already installed the 45 degree elbow fitting and it is painted so I can't tell if it is steel or aluminum. Looks like steel. Should I put steel fitting in for the other oil cooler connection to engine?

The pressure fittings are steel that go on the engine.
 
Huh

If the Aluminum fitting isnt strong enough to hold the hose attached to it, why are they even manufactured..

I believe its more a matter of line pressure...

As far as a failed fitting in a P-51...maybe it was damaged some how...

Cm
 
Christopher Murphy said:
If the Aluminum fitting isnt strong enough to hold the hose attached to it, why are they even manufactured.
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Because aluminum has no fatigue limit. With steel, so long as the stresses are under about 40% of the yield stress, the part lasts virtually an infinite number of cycles. With aluminum there is no such limit. An infinitesimal force applied some finite (but large) number of times causes the part to fatigue and break.

Thanks, Bob K.
 
Bob Kuykendall said:
Because aluminum has no fatigue limit. With steel, so long as the stresses are under about 40% of the yield stress, the part lasts virtually an infinite number of cycles. With aluminum there is no such limit. An infinitesimal force applied some finite (but large) number of times causes the part to fatigue and break.

Thanks, Bob K.
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I guess I dont understand...if the aluminum fitting is so deficient. Why are they even manufactured..?

Cm
 
Hey Bob,

The phrasing 'has no fatigue limit', while accurate, might be a bit confusing (I had to parse it 2 or 3 times to get your meaning).

How about, 'aluminum always has a limited fatigue life, regardless of stress, unlike steel, which has unlimited fatigue life if kept under its fatigue limit'?

Having said that, isn't it an argument that's made without enough conditions attached? For example, RV spars are not only aluminum, they are anodized (not alodined), which, if I've been correctly informed, halves their fatigue life. No one panics about that, because the number of cycles required to reach life limit exceeds the total likely to be achieved in a typical RV's lifespan. (That may change when hours on RV's start approaching those of some civil/military a/c that have had fatigue failures...)

From earlier posts: I understand the concern with galling with aluminum on aluminum, but isn't that more or less limited to pipe threads? Otherwise, we'd be having galling problems with all our aluminum flair fittings.

Charlie
 
Where do the lines fall in aluminum vs brass fittings?
I recently connected the check valve drain on the bottom of my IO 360. With the exhaust mounted I had to use a 45 degree "street el" fitting that I could only find in aluminum or brass. I installed the aluminum one because I could not find much data on the brass ones. I hope this makes since.
 
I avoid aluminum fittings -4 and smaller, especially long sweep hose ends, the curved tube is too thin.
I also don't like swivel hose ends, in my experience, they leak (seep).
I use aluminum fittings. I won't use worn or old ones, especially around heat, vibration or near the rated pressure. There was a discussion around here on Automotive aftermarket hose & fittings, worth reading.
You might be running 250 psi oil pressure max on a cold start, -8 (1/2") Russell ProFlex hose is rated 1000 PSI, a 4:1 safety margin for a home assembled hose.
 
Just to complicate things...

I have high quality Teflon/stainless hoses. Having problems tightening without the fitting galling and twisting the hose the last 1/4 turn or so. I went with these for the exact reason the OP asked about. No aluminum FWF. Strength and melting point. But I'm not convinced stainless plays nice.
 
So I have this oil cooler that came off a 50 year old plane....the -8 fitting is aluminum....is it going to fail at any moment? after thousands of hours?
 
Gentlemen, Bob is trying to give you a reasoned answer, based on established engineering principle. Ragging him with rhetorical nonsense just helps dumb down the forums, because pretty soon, smart people won't answer questions.

Perhaps one might Google cycles, stress, and the SN curves for steel and aluminum.
 
I'm bi-metallic. I used all steel fittings for my 3/8" fuel lines, and aluminum fittings on my 1/2" oil lines to the oil cooler. The manufacturer of my JPI EDM-700 fuel flow transducer cautions: "Do no use aluminum fittings." They don't say why not.
 
I hope this isn't considered snarky, because I do mean it sincerely, but aside from the P-51, do we know of any incidents or accidents caused by broken AN fittings FWF? I tried to search the NTSB database with a number of search terms, and found 3, all of which involved improper stresses or maintenance - one was an improperly installed Tee fitting for fuel pressure that was being pulled to the side with a zip-tie; the 2nd was a carb inlet fitting that somebody had added a 4" long fuel flow transducer to the end of, and the third was a fitting that had been previously deformed.

I don't doubt the science being discussed - steel is certainly stronger and probably better suited for these FWF applications. If I had both in my hand, I would probably use steel, too. But, if properly installed AL fittings aren't actually failing in practice, it is mostly an academic argument, it would seem. I'm ready to eat crow and change fittings if I am missing something, here though.

Chris
 
timely discussion

I'm about to hang my engine (rv10) in the next few weeks and came here because I noticed my FWF kit comes with a lot (maybe all) AL fittings. And I think someone earlier mentioned that his engine came from the factory with AL fittings. For me, wiring the panel by myself was a no-brainer. It's FWF that keeps me up at night. I don't even know what I don't know.

Given the cost of everything in the kits and that very expensive IO540 in my garage it's hard to imagine Van's or Lycoming using AL fittings just to save cost. I have to believe there is some science behind their decisions. Now this isn't at all to discount the discussion going on here. The opposite, in fact. As stated, I don't even know what I don't know. And using steel does seem intuitive for many of the reasons mentioned. It just gnaws at me that maybe there's some unintended consequence of using steel where Vans and Lycoming use AL. Or maybe is it just engineering tradition with some preferring one trade-off over another, where both have their strengths. I really wish I knew. But in this FWF department I do know I can't lightly go against what Vans and Lycoming specify.

I will be following this thread very carefully and I appreciate all the contributions being made.
 
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Like Joe suggests above, there were no hoses with steel fittings in anything Vans sent me in my vintage 2007 FWF kit. Off the top of my head, I can't think of it including a single steel (non-hose) fitting either. Everything seemed to be aluminum.

Not sure what that means or implies, except to say that Van's apparently did not think that an exclusive use of steel fittings FWF was necessary. From Joe's experience, it suggests that they still don't.
 
Alot of OE-

planes have aluminum AN fittings installed. Many have been flying for decades with no issues. As Bob stated above, there are stresses involved where steel is probably a better choice than aluminum. There are locations where aluminum may be better than steel. We typically use steel in FWF applications ON THE ENGINE, with exception being -10 oil fittings due to weight.

Aluminum is 'generally' fine for our use, if it is AN quality.
My .02 worth only----
Tom
 
TS Flightlines said:
planes have aluminum AN fittings installed. Many have been flying for decades with no issues. As Bob stated above, there are stresses involved where steel is probably a better choice than aluminum. There are locations where aluminum may be better than steel. We typically use steel in FWF applications ON THE ENGINE, with exception being -10 oil fittings due to weight.
My .02 worth only----
Tom
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I concur with Tom. MY decision to go with steel fittings on the engine entailed only 6 fittings. Like a lot of other build decisions we make, "Why would I obsess about a potential safety improvement that comes at such a small cost?" Is it guaranteed the change to six steel fittings will make me safer? Heck no. But at that minuscule cost, why not ?!?!
 
I was in this same boat a short while ago... My brand new engine had, fresh from the Lycoming factory, aluminum fittings installed. I spent the extra cash to acquire new steel fittings.

Why?

Because somewhere in my little junk pile is a cracked aluminum AN-6 fitting.

It came into my possession many years ago when I was a lowly line boy, tasked with cleaning up the oil spill under an airplane in the hangar. The source of the oil spill was this cracked fitting. The mechanic handed me the fitting, telling me to put it in the vise and crush it so nobody else would ever come that close to an in-flight engine stoppage from oil starvation. I kept the fitting as a reminder...
 
Rupester said:
I concur with Tom. MY decision to go with steel fittings on the engine entailed only 6 fittings. Like a lot of other build decisions we make, "Why would I obsess about a potential safety improvement that comes at such a small cost?" Is it guaranteed the change to six steel fittings will make me safer? Heck no. But at that minuscule cost, why not ?!?!
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The assumption here is that steel is a safety improvement. Admittedly, this seem intuitive. But if steel fittings is such an obvious safety enhancement at such a low cost why does Lycoming ignore it? Again, I genuinely have no opinion. It's just that the manufacturer of a very expensive engine (who has been doing it for a very long time) neglects to use parts which would add only a tiny fraction of the overall cost (which we pay anyway). Why? They must have a reason. ... It wouldn't be the first time changes are made to fix one perceived problem only to cause some other real problem. I'm just very reticent to change out all my AL fittings without some input from the manufacturer.

Does anyone have any contacts with Lycoming they can have look into this?
 
jwilbur said:
I'm just very reticent to change out all my AL fittings without some input from the manufacturer.
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Why? Because it takes a few dollars, some time, and might be a little messy?

When I un-wrapped my brand new Titan O-340 engine, I immediately noticed that the large oil line fittings were aluminum. A quick email Titan outlining the plan to change to steel fittings, using Loctite 567 on NPT threads, got me written approval and assurance that doing so would not void the warranty.

They do it to save a few bucks, that's all.
 
krw5927 said:
Why? Because it takes a few dollars, some time, and might be a little messy?

When I un-wrapped my brand new Titan O-340 engine, I immediately noticed that the large oil line fittings were aluminum. A quick email Titan outlining the plan to change to steel fittings, using Loctite 567 on NPT threads, got me written approval and assurance that doing so would not void the warranty.

They do it to save a few bucks, that's all.
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They wouldn't do it to "save a few bucks" if it exposed themselves to more liability. Someone deemed the aluminum to be just fine, and with the one exception of the P51 incident, which was a totally different application, I have never heard of an aluminum fitting fail on an oil cooler line. Why would the manufacturer take that kind of a risk?
 
krw5927 said:
Why? Because it takes a few dollars, some time, and might be a little messy?

When I un-wrapped my brand new Titan O-340 engine, I immediately noticed that the large oil line fittings were aluminum. A quick email Titan outlining the plan to change to steel fittings, using Loctite 567 on NPT threads, got me written approval and assurance that doing so would not void the warranty.

They do it to save a few bucks, that's all.
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My point is are you sure there isn't some unintended consequence to doing it? If it's so much safer, why doesn't the manufacturer use them? Saving a few bucks that we pay for anyway makes very little sense - especially when it would open them up to lawsuits.
 
The (unofficial... see my signature) Van's Aircraft position is that in all applications on RV's the larger sized (-6 and -8) fittings are under very low load / vibration stress. In most applications the fittings are used on both ends of a hose that has no relative motion between its two ends.
Example - hose from engine drive fuel pump to fuel servo or carburetor.... both components are attached to the engine so there is no relative motion between the two other than the small amount of movement that may occur in the hose due to vibration.
Same case with the oil cooler lines if the cooler is baffle mounted. Even if it is firewall mounted, the relative motion is very small because the engine fittings are on the back of the engine centered between the 4 vibration isolators.

Because the -4 fittings are much less massive, Van's uses a steel fitting for the oil pressure / restrictor fitting. It is located right adjacent to a vibration isolator so relative motion is probably near zero, but there could be some high freq. vibration induced in the fitting with the hose routing to a sensor mounted on the firewall so a steel fitting is used for some additional insurance. An aluminum AN816-4D is used for the manifold pressure port on an engine cyl. There is definitely some relative motion out on the end of the cyl. but there is a lot of history showing that the short length of the aluminum 816 fitting makes it durable in this location. This is the only one I can see as possibly justified to use steel from a durability standpoint.

Aluminum fittings not being fire proof often comes into these discussions, and it is a valid point. The problem with that is most of the common -6 and -8 hose ends are aluminum, so even if the fitting it attaches too is steel, you will still have an aluminum nut on the hose fitting that is not covered with fire sleeve.

The only good argument (in my opinion) for using steel fittings is that steel NTP fittings threaded into aluminum ports (such as in the engine, oil cooler, etc) are far less likely to gall and get stuck than the aluminum fittings are. Especially if an amateur (what we all are at one point, right?) over torques it trying to get the clocking/alignment they need. Using a good quality thread sealant (loctite 565, etc) goes a long way towards preventing this. If installed properly, aluminum fitting work just fine, and are lighter and cheaper (often times less than half the price depending on size).

So, having said that.... someone contemplating changing out their aluminum fittings because they have been led to believe they are not safe could actually be setting them self up for an undesirable and possibly expensive repair when the threads in the oil cooler or engine case get destroyed while removing the aluminum fitting that was tightened to some unknown torque value by a different amateur.

Food for thought....
 
JonJay said:
They wouldn't do it to "save a few bucks" if it exposed themselves to more liability. Someone deemed the aluminum to be just fine, and with the one exception of the P51 incident, which was a totally different application, I have never heard of an aluminum fitting fail on an oil cooler line. Why would the manufacturer take that kind of a risk?
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The engine manufacturer isn't the one attaching a big, heavy, floppy hose to the fitting. That's the airframe manufacturer (us). Therefore they don't carry the liability.
 
Sorry; didn't mean to offend. Should have included the obligatory 'smiley'.

Point is, if there's a lawsuit, everybody gets sued. And Lyc has a much bigger bullseye than a lowly homebuilder.

Charlie
 
rv7charlie said:
Sorry; didn't mean to offend. Should have included the obligatory 'smiley'.

Point is, if there's a lawsuit, everybody gets sued. And Lyc has a much bigger bullseye than a lowly homebuilder.

Charlie
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Tiny edit on this - everyone who has $$ gets sued. :eek:
 
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