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An Alternate routing for the rear-governor SS oil line.

Hartstoc

Well Known Member
I needed to fabricate a stainless steel oil line for the installation of my new Hartzell Composite propellor. The usual pathway below the cylinders was daunting, so I came up with an alternate route that turns out to have quite a few advantages over the standard approach.

It is much easier to fabricate and install, is fully accesible with top cowl removed, has fewer bends, is far more rigid, purges air much better Because it runs uphill as much as possible from the front section, does not require an elbow at the front end, and serves as a beautiful mounting point for keeping ignition wires and, in my case, the Lightspeed sensor wires, well away from the hot jugs!

This link will take you to series of photos with captions. They provide quite a bit of detail so please do read through them before posting any questions or comments. Thanks for looking- Otis

https://public.fotki.com/Hartstoc/governor-oil-line/?view=roll

Note: A concluding note has been addded at the bottom of page 2.
 
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That's a lot of unsuported overhang for that oil line. It's a vibration failure just waiting to happen.

Huge_Overhang.jpg


It needs some support, perhaps at two points in these sections, one way or another.

Dave
 
That's a lot of unsuported overhang for that oil line. It's a vibration failure just waiting to happen.

It needs some support, perhaps at two points in these sections, one way or another.

Dave

The run may look longer in the photo than it really is, but It is well supported against vibration along its full length. Just out of the picture to the right is where it is RTV-potted into the very sturdy welding flange that attaches it to the solidly mounted rear baffle. This RTV “bushing” not only holds a firm grip on the heavy-wall Stainless steel tube, it also makes an excellent vibration damper, far superior in every regard to Adel clamps. You would agree if you were able to prod it a bit in person.- the stock Lycoming part properly installed is sloppy by comparison. Thank you very much for expressing your concern, though. Otis

Later edit: the first thing I did when back at the hangar was to use a spring- scale to side load the span midpoint to 15#, which resulted in a delfection of no more than 1/16”, confirming the rigidity of the line. That said, a stiff line feeding the pressure sending unit mounted on the firewall passes right by that point, so I coupled the two with an adel clamp assembly as shown here just to kill any possibility of resonant harmonic excitation of the line. You can’t be too careful, So thanks, Dave!- Otis

https://public.fotki.com/Hartstoc/governor-oil-line/1527818352003.html#media
 
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Curious why you made your own line vs. using the stock Lycoming part. Cost? Some of the reasons you mention are generally not of concern with the stock line.
 
Curious why you made your own line vs. using the stock Lycoming part. Cost? Some of the reasons you mention are generally not of concern with the stock line.

Well, I don’t have a good justification, but I really did end up feeling like this installation gives me some advantages as listed listed over the Lycoming part, which has always seemed a bit too contorted to me, especially the way it wriggles around the motor mount. Also, I had the right tools and was entrigued by the challenge. In short- no good excuses!

I know many are using flexible lines these days, but I did want to stick with rigid lines to prevent any volumetric flexibility that might contribute to erratic pitch behavior.
 
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what about a rubber grommet vs the alum bushing to pass thru the baffle?

Great question!- I regarded the Bulkhead pass-through as an important support point for the oil lin for the very reason that Dave pointed out a few entries back. The baffle is securely bolted to the crankcase just a few inches from the passthrough point, and the drilled-out welding flange packed with RTV makes a beautiful flex-joint, sort of like being welded on but still having a little give.

https://public.fotki.com/Hartstoc/governor-oil-line/1527818347013.html

A grommet would be fine for cushioning and sealing but would not impart the stability of the baffle to the oil line. If you look around the suspension systems of most modern cars you can find analogous joints, where two components are securely bolted together, but the bolt passes through a section of tube that passes through a larger hole in the second component, and the space butween the tube and the hole is filled with a firm but flexible rubbery substance.-Otis
 
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This may well be an OWT, but I recall being warned against using the pushrod tubes for support. They are relatively thin-walled aluminum, and may not be the best support.

And vibration support is much different from physical support. A tube can feel very secure to the "wiggle", but when the engine is running, the vibration forces can be much different.

The portion of your tubing from the governor to the pass-thru fitting on the baffle appears to be susceptible to vibration, at least from the photos. And the baffle itself may vibrate.

And, obviously, you will have to remove the tubing if and when you remove the engine from the mount. (Hopefully not a frequent event!)

My question is: Why change something that is proven, and take even a small chance that something might go wrong? Unless there is a clear and measurable benefit, of course.

Cheers!
 
looks good. make sure it can slide thru the silicon if it needs to grow thermally.

Great question!- I regarded the Bulkhead pass-through as an important support point for the oil lin for the very reason that Dave pointed out a few entries back. The baffle is securely bolted to the crankcase just a few inches from the passthrough point, and the drilled-out welding flange packed with RTV makes a beautiful flex-joint, sort of like being welded on but still having a little give.

https://public.fotki.com/Hartstoc/governor-oil-line/1527818347013.html

A grommet would be fine for cushioning and sealing but would not impart the stability of the baffle to the oil line. If you look around the suspension systems of most modern cars you can find analogous joints, where two components are securely bolted together, but the bolt passes through a section of tube that passes through a larger hole in the second component, and the space butween the tube and the hole is filled with a firm but flexible rubbery substance.-Otis
 
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looks good. make sure it can slide thru the silicon if it needs to grow thermally.

Actually, the baffle has ample freedom of movement in that one axis to acommodate thermal expansion. It is the in-plane stability that I wanted to impart to the oil line, and the RTV is hard-cured to both the oil line and the aluminum welding flange To insure this. The line can be easily removed by un-bolting the flange from the baffle. O
 
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This may well be an OWT, but I recall being warned against using the pushrod tubes for support. They are relatively thin-walled aluminum, and may not be the best support.

And vibration support is much different from physical support. A tube can feel very secure to the "wiggle", but when the engine is running, the vibration forces can be much different.

The portion of your tubing from the governor to the pass-thru fitting on the baffle appears to be susceptible to vibration, at least from the photos. And the baffle itself may vibrate.

And, obviously, you will have to remove the tubing if and when you remove the engine from the mount. (Hopefully not a frequent event!)

My question is: Why change something that is proven, and take even a small chance that something might go wrong? Unless there is a clear and measurable benefit, of course.

Cheers!

Yes- but note that the forward fitting is just a few inches away, so the pushrod tube is being only being used as a minor stabilizer here- no significant loads are being imposed upon it. Its primary function is to prevent the two tubes from chafing one another. This stainless tubing is very stiff and rugged stuff- nothing like the aluminum we use for fuel lines. As you say- vibration support is very different from structural support- preventing excitation though damping can be a lot easier than stopping it with brute force. The baffle pass- through is, by contrast, very structural in this application, and the baffle won’t vibrate in the critical axis’.

Your question is a good one- and one that can be asked of many choices made on experimental aircraft. Often these require a large measure of confidence in one’s ability to innovate without gettiing into trouble. The standard Lycoming oil line has to be installed so that it works with all installations and can be shipped fully assembled. Solving the same problem with an existing installation can open the door to alternate solutions. I’ll be doing a lot of video-recorded ground testing of this installation before flying it, and will unhesitantly go back to the tried and true if any doubt emerges.

The comments and questions here really underline the value of VAF! It not only offers a forum for sharing innovative ideas, it exposes them to the scrutiny of a veritable army of very sharp, experienced thinkers. That is something to be grateful for!- Otis
 
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.... a stiff line feeding the pressure sending unit mounted on the firewall passes right by that point, so I coupled the two with an adel clamp assembly as shown here just to kill any possibility of resonant harmonic excitation of the line. You can’t be too careful, So thanks, Dave!- Otis

https://public.fotki.com/Hartstoc/governor-oil-line/1527818352003.html#media

It appears as if you tied that oil line to a flexible hose that's restrained at one end away from the engine. If that's correct, you added mass to the oil line, rather than stiffness. It would have been much better to securely fasten it to some stiff places on the engine. As it is, you went backwards, adding mass instead of stiffness.

Considering the iterations Lycoming went through to make their version safe and reliable, your new version seems like it will, at some point, give problems.

Dave
 
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It appears as if you tied that oil line to a flexible hose that's restrained at one end away from the engine. If that's correct, you added mass to the oil line, rather than stiffness. It would have been much better to securely fasten it to some stiff places on the engine. As it is, you went backwards, adding mass instead of stiffness.

Considering the iterations Lycoming went through to make their version safe and reliable, your new version seems like it will, at some point, give problems.

Dave

Hmmn- If you study the installation with care, and imagine a triangle that the soft-coupling of these two lines forms between the midpoint of the exposed 13.5” free span of the stainless tube, the engine itself(midway between the span’s support points)and the flair coupling of the oil pressure line at the engine, you can see a relationship that stabilizes but is not intended restrict all movement, nor to add any stiffness to the enviable amount already in the tube(that was a joke). In fact, the flex line will impart a tiny bit of movement to the rigid line that it can easily tolerate, but it will place a limit upon its range and, most importantly, prevent any possibility of destructive harmonic resonance of the rigid line(which does have a mid-span bend that could be of concern). I was spurred to add this while looking for potential problems with the installation after your original comments earlier in this thread. I cannot say if I would have done this otherwise or not, So thanks again for your original comment as this is definitely better even if not really needed.

Your prediction of the failure of this installation is less helpful, but learning that I have somehow reduced the mass of the pre-existing flex-line by gently coupling it to my new oil line will provide me with something to ponder.

I take all comments and suggestions with deadly seriousness. It then becomes my job to re-analyze my own work in light of those comments and make modifications if I deem them to have merit with respect to my particular installation. THAT is the beauty of this forum. Let’s please be careful, though- I don’t think we want VAF morphing into a new FAA- just one of those is quite adequate, thank you.- Otis
 
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Hmmn- If you study the installation with care, you will see that the soft-coupling of these two lines forms a triangle with the midpoint of the exposed 13.5? free span of the stainless tube(which has absolutely rigid support at both ends of this short span), the engine itself, and the flair coupling of the oil pressure line at the engine end as its three corners. This relationship is not intended restrict all movement, nor to impart any additional stiffness to enviable amount already there(that was a joke). In fact, the flex line will impart a tiny bit of movement to the rigid line that it can easily tolerate, but it will place a limit upon its range and, most importantly, prevent any possibility of destructive harmonic resonance of the rigid line. It does have a mid-span bend that could be of concern. I was spurred to add this while looking for potential problems with the installation after your original comments earlier in this thread. I cannot say if I would have done this otherwise or not, So thanks again for your original comment as this is definitely better even if not really needed.

Your prediction of the failure of this installation is less helpful, but learning that I have somehow reduced the mass of the pre-existing flex-line by gently coupling it to my new oil line will provide me with something to ponder.

I take all comments and suggestions with deadly seriousness. It then becomes my job to re-analyze my own work in light of those comments and make modifications if I deem them to have merit with respect to my particular installation. THAT is the beauty of this forum. Let?s please be careful, though- I don?t think we want VAF morphing into a new FAA- one of those is just right.-Otis

So did you run this new line through anything like FEM or other analysis, or was it all done TLAR? There seems to be a lot of "intended to"s and "should"s and such in your thinking here.

Given that a) Lycoming's solution is battle-tested on a gazillion installations, and b) a failure here *will* result in complete engine failure in short order as all of your oil gets pumped overboard (including the possible fire hazard), this seems like some pretty serious experimental aviation that might warrant concomitant serious engineering analysis. It might all be fine, but I'd want to run actual vibration analyses and such to be sure before I deviated from the factory solution.
 
Otis, thanks for your detailed reply, previously.

My question was: Why change something that is proven, and take even a small chance that something might go wrong? Unless there is a clear and measurable benefit, of course.

My next question, yet unanswered, is: What is the clear and measurable benefit of your installation over the standard one?

Thanks for a good discussion......
 
Otis, thanks for your detailed reply, previously.

My question was: Why change something that is proven, and take even a small chance that something might go wrong? Unless there is a clear and measurable benefit, of course.

My next question, yet unanswered, is: What is the clear and measurable benefit of your installation over the standard one?

Thanks for a good discussion......

Well, I wish I could invite all of you guys over to poke and prod this thing to your heart?s content. It?s an oil line, and I think you would walk away feeling like it is a damned good one, just as good as the Lyc version. It?s been pretty deeply integrated into my engine, providing a very good support to several cables and components for the ignition system, but I?m not married to it. I?ll report back after I?ve done some ground testing and run it past a few other mechanics I respect. There are usually a few cat-skinning options!-
 
OK- UNCLE!

OK, Uncle! I?m happy with this installation, but cannot ignore the consistent cautionary sentiments of a bunch of guys who?s sole motives are keeping one another out of trouble.

Fortunately, there is an easy way to fix this. I just removed the magneto on that side to install the first of two Lightspeeds, so now there is a dummy cover but the studs are still there, and will provide ideal anchor points for a bi-pod pair of struts that will support the mid-point of the offending span aft of the baffle with absolute rigidity. The line is already as stiff as the standard Lyc oil line, but will be pretty much welded to the engine on 7? centers with this addition.

Will post a pic here when done- Otis
 
Experimenting

You've already received lots of comments on this, and we all certainly recognize the benefits of amateur-built aviation, one being to make modifications a whole lot faster than in the certified world. I thinkn what people are trying to say here, though, is that sometimes the benefits of a change COULD be outweighed by the risk.
In this case we all know that at one time even in the current location there was an AD to change this line to a stainless line due to cracking. Was it the way it was supported, or was it long-term harmonics? We probably don't know. We do know they ALL weren't failing, just enough to warrant an AD.

I do know I have seen RV's that were built somewhat the same way (no 2 are really alike), and yet on on some I see cracking of various components in the firewall forward area, and none on others. It's really hard to tell it is workmanship (other than the obvious poor workmanship) or is it something else insidiously at play, such as harmonics. I know I also see less cracking with RV's that have composite props as opposed to metal props. Harmonics at play? Who knows.

The point is that making a chance in such a key piece that could have catastrophic results to the aircraft, and potentially people, should give one great pause. It could be the failure that sneaks up on you in the middle of the night 300 hours from now, yet 200 hours from now you will have deemed it a success. There are probably millions, and even billions, of hours on the compnents in the certified fleet, and yet we still see AD's issued on them.

So, tread carefully, and never trust it.

Vic
 
....you can see a relationship that stabilizes but is not intended restrict all movement, nor to add any stiffness....

They are not supports. Relationships of this nature are not considered, in the jargon of a dynamicist, to constrain the system.


....prevent any possibility of destructive harmonic resonance of the rigid line....

It won't. It will shift the frequency of that, though. For better or for worse, how will you know?


....learning that I have somehow reduced the mass of the pre-existing flex-line by gently coupling it to my new oil line....

Sorry, that was not my intent, and I didn't mean to inadvertently give that impression.


Give the history of the original oil line, a reasonable approach to a replacement would be to first analyze the final version of Lycoming's and then to attempt to duplicate those results with this new one. This will take a dynamic analysis using FEA on both Lycoming's version and yours.

Dave
 
Bace turned out to be easy-peazey.

Oop- Bace should be “Brace” above, can’t edit header-

It turned out that the studs securing my B&C spline-drive primary alternator were of sufficient length to also secure a simple aluminum strut that lined up beautifully with the mid-piont of the span. It is now dead-rigid along its entire length. This photo and caption have been added to the album:

https://public.fotki.com/Hartstoc/governor-oil-line/bracing-strut.html

I really do appreciate the comments generated by this thread, and they did lead me to find a way to erase all doubt about the part, at least for me.

I’m now prepared to declare unequivocally that for my application, this heavy wall-stainless steel oil line is now superior in every regard to the stock lycoming part. It is vastly more rigid along its entire length. It has fewer bends, replaces the 90° flair fitting at the forward end with a far sturdier, simpler, more elgant, and less flow-restrictive straight steel fitting that promotes the purging of air by maintaining an uphill path for nearly two feet upon leaving that fitting. It is fully visible for scrutiny as part of every pre-flight inspection. It has cleaner, better executed flairs than those on the stock lines I’ve seen. Its shape and path intrinsically acommodates thermal expnsion and contraction without placing undue stress upon the flair couplings yet it lives in a far more benign environment than does the Lycoming part.. It does NOT require any sophisticated vibrational analysis for the simple reason that it Is fully constrained or heavily damped along its entire length. There is no other part or component on my aircraft in which I have greater confidence than I do for this one.

Lycoming is stuck with the requirement that their line be pre-installed on new engines and compatible with a wide variety of engine mounts and installations. To acommodate these requirements, they found it necessary to place it in an extraordinarily hostile environment. I was not constrained by such concerns.- Otis
 
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Big improvement.

I'm glad that you kept after this.

Your workmanship was not in question. However, there is a large difference in designing for vibration rather than for strength. Your brace will help.

Whether or not your design is superior to Lycoming's is something that only service experience will reveal. Probably a good idea to remain cautious about this and inspect it often, particularly as you add hours.

I think that if you hit edit, then "go advanced," that you will have the opportunity to change the title. I just found that out this last week.

Dave
 
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Oop- Bace should be “Brace” above, can’t edit header-

It turned out that the studs securing my B&C spline-drive primary alternator were of sufficient length to also secure a simple aluminum strut that lined up beautifully with the mid-piont of the span. It is now dead-rigid along its entire length. This photo and caption have been added to the album:

https://public.fotki.com/Hartstoc/governor-oil-line/bracing-strut.html

I really do appreciate the comments generated by this thread, and they did lead me to find a way to erase all doubt about the part, at least for me.

I’m now prepared to declare unequivocally that for my application, this heavy wall-stainless steel oil line is now superior in every regard to the stock lycoming part. It is vastly more rigid along its entire length. It has fewer bends, replaces the 90° flair fitting at the forward end with a far sturdier, simpler, more elgant, and less flow-restrictive straight steel fitting that promotes the purging of air by maintaining an uphill path for nearly two feet upon leaving that fitting. It is fully visible for scrutiny as part of every pre-flight inspection. It has cleaner, better executed flairs than those on the stock lines I’ve seen. Its shape and path intrinsically acommodates thermal expnsion and contraction without placing undue stress upon the flair couplings yet it lives in a far more benign environment than does the Lycoming part.. It does NOT require any sophisticated vibrational analysis for the simple reason that it Is fully constrained or heavily damped along its entire length. There is no other part or component on my aircraft in which I have greater confidence than I do for this one.

Lycoming is stuck with the requirement that their line be pre-installed on new engines and compatible with a wide variety of engine mounts and installations. To acommodate these requirements, they found it necessary to place it in an extraordinarily hostile environment. I was not constrained by such concerns.- Otis

Im not sure how I stumbled on this old thread, but it is fascinating. So the question I have is, how has she held up after 4+ years since the OP? Im really curious as your workmanship building this oil line is impeccable and I am a huge fan of the thought and analysis that went into this, as well as a big believer in rigid oil lines as well.

But the question remains, how has it been after all these years? Are you still running it? Has it posed any issues since installation?
 
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