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RV-6A fuel line solution needed

sparkcrafter

Active Member
I'm in the process of getting back to my RV-6A project after 10 years or so of having it mothballed. There are a few items on the plane that I look at now and would like to improve how I originally installed them. For example, the fuel line connection from the firewall to the filter was originally configured as an aluminum tube:

IMG_20150223_094857.jpg



I'd like to replace that tube with something more robust, while minimizing the ripple effect of moving too many parts around. The problem is that the distance from flange to flange is only about 4 inches, so it's really too tight to connect from flange to flange using a hose with a 90deg fitting on the end that would connect to the firewall fitting.

The options I've come up with so far are:

1) Move the filter to a different location further away from the firewall fitting. The downside to this is the ripple effect on other parts and I'd have to remake the heat shroud for the filter. Doable, but hoping for an easier solution.

2) Make a tube similar to my aluminum tube, but made out of stainless. Tom at TSFLIGHTLINES has offered to make this up at a reasonable cost. Only issue I can see with this is whether or not there would be a problem with vibration stress cracking over time.

3) Make a "U" shaped hose with 90 degree fittings on each end. Other than the cost, this seems like it would work.


Anyone have thoughts on which way to go with this connection?

-Jerald
 
"Anyone have thoughts on which way to go with this connection?"

4) Put a 90 deg AN-fitting on the filter input, and use a slightly longer 'hose' solution end-to-end (u-shape). The 'bottom' of the U in the hose would be near enough to the engine mount to secure it with an Adel clamp combination.

gary
 
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Where's the problem...??

Jerald, not sure I see the problem with the aluminum tube. Looks pretty good to me. Short enough to avoid vibrations. No relative motion between bulkhead fitting and filter.

I would be more concerned about what looks like a 4 gage cable passing through the firewall with just a loose plastic snap bushing. Firewall pass-throughs need to be smoke/flame tight. Cannot tell from photo, but it looks like engine rocking motion would create sawing motion at this pass-thru...

BTW, welcome to VAF!

- Roger
 
Welcome Back Jerald!

I like the idea of the stainless. You probably would not have a fatigue issue with that

If you wanted "cleaner look", you could consider the bulkhead fitting with the 90 deg on the firewall side. This will clearly make the inside an area to modify in the "cascade" of change.

I wonder if there is a 90 deg fitting with a captured B nut on one leg that could be used for this, resulting in a 90 deg on both sides of the FW?

Always things to do - - keep us posted on your project.
 
Thanks for the warm welcome!

Several good suggestions to ponder within minutes of posting the question... what a great forum.

Roger,
No worries on the firewall hole. That hole has a rubber grommet and fireshield that I temporarily removed while playing with different wire routing options. The bushing is just there to prevent chafe while the grommet and fireshield are off.

-Jerald
 
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CAT - Bulkhead Passthrough Fitting

Cleaveland Aircraft Tool - Search "Bulkhead Passthrough Fitting" and see if this is what you had in mind.

HFS
 
Jerald,
What about changing the firewall fitting to a 90?, pointing up? The existing tube would be essentially the same shape, but you will likely have to make a new one for proper fit. Once installed, put an adel clamp with a spacer at the top of the loop securing it to the firewall for stability. IMHO, you really don't need a stainless tube, as if you secured it to the firewall it will be quite stable.
This installation would get the loop out of the way, and it will not be leaned on, bent, etc.
 
Since it is in the engine compartment, I think I would just make another fuel line hose like all the others and maybe put a 45 degree fitting at the filter end of the hose. Fire sleeve the hose if you like but I don't think it is necessary in that location.
 
Go flexible

Had a similar looking setup in the rv-4 I bought. The aluminum tube fatigued in flight, the engine sucked air and quit. The electric fuel pump re-pressurized the line, the engine restarted, and I asked ATC for a direct route home instead of the standard route. The engine quit again as soon as I got to the hangar. Turns out the electric pump was pumping a gallon a minute into the engine compartment with exhaust stacks ten inches to either side.

Aluminum tube? No way. Folks advocating aluminum? Violently disagree. Stainless? Nah, flexible with fire sleeve is standard and a fuel line is not where I'd choose to experiment.

BTW, one of the early rv-8s had an engine compartment fire and the pilot bailed out at 200 feet without a parachute, apparently aiming for a body of water. And I had a friend who did not survive burns from a Harmon Rocket engine fire that burned through the floorboards.
 
My first question is, will you / have you installed an engine with fuel injection? If not, you really need a gascolator to trap any water. If carbureted, install one of Van's gascolators at the firewall, where the line comes out.

If injected and you are going to keep the filter in that location, then I would worry about that section of tubing vibrating and cracking. As suggested, put in a 90* bulkhead fitting, pointing up, and make a new aluminum line to go to your filter WITH fire sleeve insulation. I had a similar U in my line running from the gascolator up to the fuel flow meter and had four engine stoppages before I realized that it needed to be insulated.
 
The plane has fuel injection. Based on the feedback, I'm thinking I will replace the firewall fitting with a 90 deg elbow that points toward the fuel filter, then use a short fire-sleeved hose to connect the elbow to the filter. The only potential issue with this is the short distance of hose won't tolerate much misalignment of the fittings, but I think I can get them aligned pretty close.

Great feedback, guys. Thanks!

Jerald
 
I realize I am coming in late to this conversation but I would like to make a couple suggestions anyway. First, is the possibility of flipping the filter over- which puts the inlet end further away from the outlet coming out with the firewall and may allow a flexible hose to be used without violating the minumum radius rule. The second suggestion is to purchase some of the red silicon dip and dip the fire sleeve matetial end before installing. The bare fiberglass is going to absorb fuel/greese/dirt and look not very nice after a while. Just tought I'd throw those out.
 
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