Zenith Aircraft Builders and Flyers
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Fuel lines - rubber, Teflon, or aluminum?
It's time to replace my old rubber fuel lines and I'm considering switching to aluminum or braided steel/Teflon so I don't have to do this again in five years. Has anyone studied the merits of each hose type? Intuitively, the braided steel with Teflon seems like it would be the most crash/fire resistant, but at ten times the cost of the other options I'd like to see some data to back that up. I did a bit of searching online but couldn't find anything... I don't really know where to begin looking for that sort of thing though.
I'm currently leaning towards aluminum because it's good enough for certified aircraft and relatively cheap and easy to work with, but I'm open to being persuaded in a different direction.
Oh, and in case anyone is installing rubber hoses, I saw someone recommend lubricating the fittings before installing the hose (I think it was Jan E. in one of the Homebuilt Help tips of the week on YouTube). I've had to destroy some fittings to remove my rubber hoses, so that's probably good advice!
Thanks
Replies to This Discussion
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Permalink Reply by Perry Delano on
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Hi Matt,
I Used 1/2 inch aluminum behind firewall, c/w Earls style fittings, Parker lines, stock on New Rotax forward of firewall. Couple of tips here: you can straighten coils of aluminum tube using a diy device using rollerblade wheels, I think it’s in my photos on this site, speedshop version about $300 can send you a pic if you can’t find it. For oil lines I used hoses with Aeroquip push on fitting. If you need to remove a fitting use a soldering gun with cutting bit not a hacksaw, cut axially along fitting over barbs which will save the fitting. Someone posted a video of this on YouTube. Extremely helpful. I used a heat gun to warm the hoses a bit before pushing them on.
Plane not in the air yet or fuel flow test done so efficacy of above remains to be seen.
Perry
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Permalink Reply by Matt Pope on
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Very cool, Perry - I'll look for the straightener photos.
I hadn't thought of using heat to get those fittings off... Unfortunately the problem fittings are in the wing tanks and I'm a bit concerned I might blow myself up if I try that. It's probably a pretty small risk, but I think I'll just eat the cost of a few more fittings.
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One more thing. automotive speed shops and hose shops/supplier may be cheaper than aviation sources.
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Permalink Reply by John Austin on
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If you plan to keep the plane for any length of time, I'd definitely go with something other than rubber - it'll have to be replaced again, eventually.
Nothing wrong with aluminum lines, but one thing to consider is will it be difficult to replace the lines on a fully constructed airplane? They're fairly easy to install during construction, but once construction is complete, you may find you have to use shorter runs/more connections to route the new lines.
I'm biased as I have stainless braided PTFE lines. They have the advantage that they are flexible, so new lines could be routed a bit easier than hard aluminum lines. Like aluminum, they are also considered permanent and won't need future replacement. Can't quote data, but braided stainless lines are TOUGH - likely would be the last thing to break in a crash! Also, when used with quality AN fittings, they are least likely to leak - I've had the lines for 10 years, they run through the cabin of my STOL750, and I've never even had a whiff of gas fumes - ever. They also tolerate all fuels well - after all, they're used in top fuel dragsters to run nitromethane!
If you go the stainless braided PTFE route, use quality lines and connectors. Avoid the cheapy Chinese stuff and be sure the PTFE is carbon impregnated (usually the liner will be gray or black) to avoid static build-up in the lines that can damage the liner. I fabricated my own lines using Earl's components obtained from ANPlumbing.com. They have lots of how-to videos and can also give good advice on the phone. You can also have the lines pre-fabricated from sources such as Aircraft Specialty.
John
N750A
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Hi John - thanks for your take, and good point about it being difficult to retrofit with hard tubing.
I was considering using Earl's UltraPro, which is maybe what you used, but they don't seem to make NPT fittings that fit that hose and I thought maybe it was a bad idea to double the number of connections by connecting NPT fittings to the regular hose ends. It's good to hear that you've never had any leaks though. Do you remember how you handled that?
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I'm not familiar with the UltraPro. As I recall, I used Earl's "Speed-Seal" hose and AN fittings and they have NPT adaptors for AN fittings here.
Properly installed and sealed (NPT requires sealant but not the AN fittings), very little risk of leaks!
John
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Thanks, John - I hadn't seen the Speed-Flex hose and Speed-Seal hose ends before. It looks like that hose is about 25% cheaper than the UltraPro and it has the conductive PTFE, so definitely worth a look.
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Permalink Reply by John "Allen" Walker on
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I went aluminum all the way. With the Aeromomintum engine you must run your return lines back to the wing tanks. So, no way was I going to run rubber or even braided covered rubber lines.
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Yeah, it seems like aluminum is about the same cost as rubber, but much lighter - especially if you're adding return lines.
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Permalink Reply by Patrick Hoyt on
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I originally used Braided Steel lines in my airplane. Not being able to inspect the interior hose within the braided steel lines never really sat well with me, because at the end of the day they're still rubber or "rubber-like" hoses underneath that braided steel sheath...
While rebuilding my airplane I removed all the braided steel lines. I was quite surprised how heavy the braided steel lines (and their associated fittings) were when I had them all together on my workbench. I never really noticed all the weight when I was fabricating and installing those hoses one-at-a-time.
Also discovered Fuel Injection Hose during this time. After working with that, I don't know that I would go back to the braided steel lines.
On my upcoming next project I'm seriously considering running Aluminum lines inside the wings (in the areas that are difficult to inspect), and Fuel Injection Hose everywhere else - where I can inspect.
- Pat
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Patrick,
I agree braided ss lines are, in general, heavier, but we were talking about PTFE lines - they do NOT have a rubber or "rubber like" lining - it's PTFE: polytetrafluoroethylene, a fluoropolymer. This is strictly an aerospace-spec and quality liner and is considered "permanent," unlike rubber. It's used throughout the aerospace industry and is chemically resistant to almost everything - especially fuels.
I think there are braided rubber lines - sometimes used as oil lines, etc., but I wouldn't use those for fuel. I'm guessing the rubber lines have thicker walls and are likely heavier than PTFE liners, but aluminum lines are going to be lighter but more fragile than braided stainless steel.
John
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