Fuel Line

[Mike Clayton]

I am rebuilding a Kitfox II which was badly damaged in an accident. The remains had no fuel lines installed anywhere, except for a short piece from the wing tank. I assume it may have been connected to aluminum fuel line, but there is no evidence to support that assumption. I have installed a new header tank, located behind the seat. I will be installing a Facet pump between the header tank and the gascolator, or perhaps between the gascolator and the pulse pump, which is located on the firewall. I am trying to decide if there is any problem with use of flexible fuel line such as the Bing blue line between the wing tank and the header tank, and between the header tank and the firewall, as well as in the engine compartment. The line has a temperature rating of 250 deg F, and a pressure rating of 80 lbs/sq in. The pressure rating is fine for this installation, as the maximum pressure is on the order of 2-3 lbs/sq in. I know certified aircraft use solid fuel line prior to the firewall, but given a number of considerations, I would prefer using the flexible line. If need be, I can protect the line from getting pinched prior to the firewall by careful routing, or by using a short section of solid line in areas where this might be a significant risk.

I am looking for ideas and opinions before I make a decision. Thanks in advance.

[CraigCantwell]

I'm not a fan of flexible lines in the cabin, especially when you add a fuel pump to the mix. It might be a little harder to figure out and route a hard line now, but what are you going to do in a couple of years when you need to replace that flex line? Why not install hard line now and not have to worry about it?

[Dave Prizio]

Flexible fuel lines have a limited life. Thus any permanent installation that does not require flexibility should be done with solid aluminum lines. This minimizes future maintenance and protects against fuel line leaks or failures as the flexibly hose ages.

The fuel line from the gascolator to the engine needs to be flexible to allow for engine movement, but it it very important to have that line protected with a product like Aeroquip Fire Sleeve.

[turtle]

If a fire in the cockpit started, for whatever reason, what stops the plastic line from melting and adding fuel to the fire right underneath you?

[steveinindy]

I'm not a fan of flexible lines in the cabin

There's no good justification for routing a fuel line of any variety through the cockpit.

If a fire in the cockpit started, for whatever reason, what stops the plastic line from melting and adding fuel to the fire right underneath you?

Which is why a few extra dollars for a fire-resistant fuel line is a good idea along with fuel shut-off valves between the tank and the cockpit. Also, there are very few in-cockpit fires (that aren't fueled by spilled gasoline, etc in the post crash environment) that can't be controlled by isolating the electrical components. This is one of the major reasons why being a little cautious about your choice of materials (structural and insulation as well as things like fuel and electrical lines), the layout of systems, etc can make a huge difference in whether a crash is survivable or not.

Thus any permanent installation that does not require flexibility should be done with solid aluminum lines

Or something more resilient than a simple plastic line. Aluminum lines tend to increase the forces applied to the tank if a wing is sheared off and can actually cause more problems from a fire safety perspective than they solve. There are plenty of better options in any aircraft supply catalog such as Aircraft Spruce.

[Frank Giger]

Hmmm, I was thinking copper....

[Racegunz]

Not sure with wing tanks or a behind the seat header you could avoid fuel lines routing through the cockpit?????? Anyhow stainless braided fuel line with an fittings is a much better choice than the blue bing line although that is exactly what I had in my first experimental and it was not a problem, I think alot of the avid's/kitfoxes use that line with no issues just route it to protect from pinching and chaffing.

[steveinindy]

Not sure with wing tanks or a behind the seat header you could avoid fuel lines routing through the cockpit??????

Just my two cents (based largely off of the US Army crash survival research related to fuel tanks for light aircraft and helicopters) but the only thing dumber than a fuel line through the cockpit is a fuel tank in the cockpit.

With wing tanks, keeping the fuel lines out of the cockpit is pretty easy if you're willing to put some effort into the design. Sadly, with a lot of the kit and plans built designs out there it seems like once the designer(s) got past the aerodynamics phase they took the path of least resistance and didn't give much thought to any of the subsystems beyond "Eh....that'll work".

[Mike M]

I am trying to decide if there is any problem with use of flexible fuel line such as the Bing blue line ...I am looking for ideas and opinions

seems like you got your wish, ideas and opinions, but some drifted way off the question you asked. i'll assume you're not intending to redesign the entire aircraft to incorporate all the esoteric solutions to perceived problems you didn't mention.

i am familiar with the way kitfoxes are normally built. early models used bing blue fuel line, later models used mil-h-6000 "rubber" hose. i built and flew an avid flyer for over ten years. i installed bing blue fuel line throughout as per the kit contents and instructions. it is advertised as, and proved to be, compatible with autogas or avgas. the aircraft was hangared when not flown. there was no noticeable deterioration of the blue line in that ten years. it was still flexible and did not crack at the ends like rubber fuel line tends to do. in short, it did what it was supposed to do reliably over time. i see no problem with using it as the manufacturer recommends and as the kitfox assembly manual recommends.

if you intend to use autogas but don't want to use bing blue tubing, i recommend avoiding mil-h-6000. i have seen it deteriorate within mere months of using premium autogas. it's not supposed to, but it did. i recommend automotive fuel line instead. NAPA's has proved compatible with autogas and avgas over the last 11 years in my applications.

your mileage may vary.

[steveinindy]

but some drifted way off the question you asked.

Sorry about that.

USED to be, maybe. now i'm paid to say NO.

Ah....I guess it depends on which service you fly for but I hope the approach your company takes continues as a permanent trend even after the attention from all the deaths a few years back fades out. I never want to attend that many funerals of friends in a single year ever again.

But if you DO encounter those circumstances...you'd really wish you'd accepted the complexity.

Points taken. However, I honestly believe that given a little time, I could build a crash resistant fuel tank that could be safely put into an aircraft like the Fly Baby.

I mean, we already have a design that exceeds the US Army standards for helicopter fuel tanks. It's going into our LSA design. One of the tests we're planning is to build a break-away rig for the bed of a pickup truck and to slam this tank (filled with water) into a scrapped telephone pole (one of the local energy companies has offered to donate one for the test) at a speed probably close to 65 mph. It's designed (on paper) to withstand a 80+ mph impact but I'm not sure we could safely test that with the gear we have available to us. Honestly, the fuel tank and seat designs were the only reason I even bothered with an LSA design. It's nothing more than a testbed for subsystems that will be scaled up for our real project. It's just a heck of a lot cheaper to abuse and destroy a dozen or so 6 gallon tanks than to do the same to even the smallest tank for the larger design.