Cockpit fuel lines and fire prevention

[Phil]

Like many others, I'm not putting a single hard line anywhere in my airplane.

Not because they aren't really capable of living a long and useful life, but because I know I'm not really capable of building a line I'd be proud of putting in my airplane. The margin for creating the perfect line is thin and it's something you can waste many weeks of evenings tweaking and rebuilding.

Even after building the perfect line, I'd still be paranoid. Been there and done that with the brake lines originally.

For me the machined fit of a teflon/braided/sleeved (on fuel) hose is idiot proof. That means it's perfect for someone like me.

Phil

[szicree]

Regarding flex lines, be advised that the hard lines tend to pinch shut when torn apart in a wreck; not so with rubber hose.

It's worth noting that much of the "re-engineering" that is being suggested has already been tried over the last 100 years and was found to be inferior to modern standard aircraft methods. We really should look to what has worked historically and stop trying to reinvent the wheel. Having said that, putting fuel lines and a sparky little motor in the same small box is an I.E.D. just waiting to explode.

[DanH]

Originally Posted by TSwezey

...our boost pumps were after the valve running at 60 PSI.

"Pumps", plural, more than one? Self regulated, or were there also full flow return lines from separate pressure regulators at the engine fuel rails?

Perhaps we should document the failed system before further speculation about the stock RV-10 fuel system.

Todd, can you post a system diagram please? And perhaps build log photos of your completed tunnel package?

[apkp777]

Does anyone know which stainless tubing from Spruce would be suitable for fabbing fuel lines. Even though I am happy with my 3003 aluminum, I might change the line from the pump to the gascolator. Mostly because my son (co-pilot) has really long legs and I can see him pushing on the line.

[L.Adamson]

Originally Posted by Phil

Like many others, I'm not putting a single hard line anywhere in my airplane.

Not because they aren't really capable of living a long and useful life,

snipped

One advantage of a hard line ...........is the life of the part. I'd say that many hard lines could easily last the life span of the airframe.

Yet, flexible lines have shelf life, as well as a service life. You'll just have to keep inspecting, or replace at 5-8 years. And firesleeve makes the inspection even tougher.

L.Adamson --- RV6A

[skylor]

Todd's incident has scared a lot of people, and rightfully so. However, as others have already pointed out, we really need to think and proceed cautiously before we start redesigning entire fuel systems because of this incident. If we simply start replacing every aluminum part on our planes that makes us nervous with steel parts, our aircraft will be too heavy to get off the ground. Hey, there's been it least one in-flight break up of an RV due to spar failure (N58RV)...why not replace our spars with something stronger like steel? Our machines will be too heavy to fly, but at least they'll be safe!

OK, in all seriousness certified aircraft have been using aluminum components for the fuel system throughout the aircraft and fuselage for years without too many issues...and most issues are the result of poor maintenance. In the last couple of weeks I've looked closely at both an older Cessna 310 and a 60's era Piper Aztec-Geronimo that were undergoing annuals. Both of these planes have aluminum fuel plumbing throughout (including lines running to the nose mounted gas heater) and have been flying for many years without fires or explosions. These aircraft even have aluminum fuel fittings fire-wall forward.

My own personal construction choice that I made 4 or 5 years ago on my RV-8 was to throw away the Van's supplied "soft" tubing and to use 5052-0 for all fuel and hydraulic plumbing aft of the firewall. I used 5052-0 not so much because of its increased strength, but because it has vastly superior fatigue resistance over the soft tube. Secondly, I have paid careful attention to fabricating and installing all of these lines properly to avoid unnecessary stresses and chafing. Finally, I pressurized every leg of pluming in my aircraft with shop air using a gauged leak test device and performed decay checks on everything as well as bubble checking all fittings and joints while they were under pressure.

In addition, I believe that minimizing high-pressure plumbing inside the cockpit/cabin is probably more realistic and useful than trying eliminate all fuel plumbing inside of our aircraft. A small fuel leak in the low pressure plumbing will be more likely to result in air drawn into to the line rather than large amounts of fuel leaking out of the line in our aircraft.

I think we would all be better served to pay close attention to using standard practices and materials in the correct fashion in our aircraft, instead of starting to redesign whole systems and use non-standard materials (for light aircraft). Of course, if any one does figure out a way to improve fuel system safety without increasing airframe weight, drag, or complexity, I'm all for it!

Skylor
RV-8 QB, Final Assembly

[logansc]

When did it start raining flaming RV's all over the world? I must have missed that...


Lee...

[Toobuilder]

Originally Posted by apkp777

Does anyone know which stainless tubing from Spruce would be suitable for fabbing fuel lines. Even though I am happy with my 3003 aluminum, I might change the line from the pump to the gascolator. Mostly because my son (co-pilot) has really long legs and I can see him pushing on the line.

http://www.aircraftspruce.com/catalo...lesstubing.php

[apkp777]

Originally Posted by Toobuilder

http://www.aircraftspruce.com/catalo...lesstubing.php

Mike,

The 304 seamless? I don't remember the stainless I used in the past being .035 wall thickness. Maybe it was, just seems awfully thick.

[Toobuilder]

Originally Posted by Phil

Like many others, I'm not putting a single hard line anywhere in my airplane.

Not because they aren't really capable of living a long and useful life, but because I know I'm not really capable of building a line I'd be proud of putting in my airplane. The margin for creating the perfect line is thin and it's something you can waste many weeks of evenings tweaking and rebuilding.

Even after building the perfect line, I'd still be paranoid. Been there and done that with the brake lines originally.

For me the machined fit of a teflon/braided/sleeved (on fuel) hose is idiot proof. That means it's perfect for someone like me.

Phil

OK, couple of comments, not the least of which is the fact that you are afraid of properly bending and flaring hard line, yet you are constructing a four passenger aircraft... Do you see the irony here?

To more practical comments:

If you do "all braided hose" you are signing up to:

1. About a 10-12 pound decrease in useful load;
2. Significant unnecessary expense;
3. A complete fuel line replacement schedule every few years;
4. A packaging nightmare;
5. Decreased reliability (hose does fail, degrade, chafe, cause damage and LEAK!.)

I wholeheartedly echo those here who call to not "reinvent the wheel". Flex hose has its application in standard aviation practices, (but it's usually a LAST resort), as does other material. We're building aircraft here, so it's best to follow "aircraft standards" don't you think? The standards for proper fluid systems are readily available to all of us and are fairly easy to understand. Most "standard practices" can be found in AC43-13, and the T.O.s 1-1A-1 and 1-1A-8.

The purpose for building amateur built airplanes is to learn... Don't sell yourself short on the experience of learning how to fabricate a few hard lines.