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  #1  
Old 05-31-2018, 12:01 PM
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Hartstoc Hartstoc is offline
 
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Default An Alternate routing for the rear-governor SS oil line.

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/go...ine/?view=roll

Note: A concluding note has been addded at the bottom of page 2.
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Last edited by Hartstoc : 06-04-2018 at 10:43 AM.
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  #2  
Old 05-31-2018, 12:20 PM
David Paule David Paule is offline
 
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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
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  #3  
Old 05-31-2018, 01:08 PM
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Hartstoc Hartstoc is offline
 
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Quote:
Originally Posted by David Paule View Post
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/go...003.html#media
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Last edited by Hartstoc : 05-31-2018 at 09:16 PM.
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  #4  
Old 05-31-2018, 01:20 PM
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rocketbob rocketbob is offline
 
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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.
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  #5  
Old 05-31-2018, 03:01 PM
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Quote:
Originally Posted by rocketbob View Post
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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RV-7A (bought)
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-2021 VAF donation!!-
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Last edited by Hartstoc : 05-31-2018 at 08:38 PM.
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  #6  
Old 05-31-2018, 04:32 PM
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Steve Melton Steve Melton is offline
 
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what about a rubber grommet vs the alum bushing to pass thru the baffle?
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  #7  
Old 05-31-2018, 08:37 PM
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Hartstoc Hartstoc is offline
 
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Quote:
Originally Posted by Steve Melton View Post
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/go...818347013.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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RV-7A (bought)
Built Monnett Moni
Frmr Test Pilot/Author CAFE APR's:
RV-8A, S-7C, Europa, Glastar.
-2021 VAF donation!!-
"RV-Fun is inversely proportional to RV-Weight!"

Last edited by Hartstoc : 05-31-2018 at 09:02 PM.
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  #8  
Old 05-31-2018, 11:50 PM
PCHunt PCHunt is offline
 
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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!
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  #9  
Old 06-01-2018, 06:18 AM
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Steve Melton Steve Melton is offline
 
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looks good. make sure it can slide thru the silicon if it needs to grow thermally.

Quote:
Originally Posted by Hartstoc View Post
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/go...818347013.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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Cincinnati, OH
RV-9A, Tip-up, Superior O-320, roller lifters, 160HP, WW 200RV, dual impulse slick mags, oil pressure = 65 psi, EGT = 1300F, flight hours = 900+ for all

Simplicity is the art in design.
I was born an airplane nut. I have no explanation for it.
My Artwork is freely given and published and cannot be patented.
www.rvplasticparts.com

Last edited by Steve Melton : 06-01-2018 at 06:23 AM.
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  #10  
Old 06-01-2018, 09:57 AM
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Quote:
Originally Posted by Steve Melton View Post
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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Otis Holt-
RV-7A (bought)
Built Monnett Moni
Frmr Test Pilot/Author CAFE APR's:
RV-8A, S-7C, Europa, Glastar.
-2021 VAF donation!!-
"RV-Fun is inversely proportional to RV-Weight!"

Last edited by Hartstoc : 06-01-2018 at 12:27 PM.
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