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".

[Racegunz]

Well every piper cub and aeronca champ and tens of other designs have header tanks right there to smash into you if you crash, so I guess i just won't crash with any fuel left.:P I see the logic, but small aircraft have little other choice. So just for conversation sake what small tractor engine design doesn't have at least fuel lines through or under the cockpit?

[steveinindy]

So just for conversation sake what small tractor engine design doesn't have at least fuel lines through or under the cockpit?

Under isn't so much of a problem if you properly shield the fuel lines. It's yet another use for thick-walled aluminum tubing or something similar ;) In my LSA design, the fuel tanks inside the structural protection of the wing box (which is design to stay intact up to a 40 g vertical impact and roughly 90 g longitudinal impact because the seats are attached to it and because it protects the fuel lines along with providing a large part of the structural integrity to the cockpit roll cage) and then forward of the firewall. There are four self-sealing quick disconnect valves on each line: one at the tank, one at the junction of the wing and fuselage, one at the posterior side of the firewall and then one right before the fuel line enters the engine. The one at the posterior firewall can also be triggered by the pilot to seal off fuel flow to the engine compartment in the event of a fire.


I see the logic, but small aircraft have little other choice

Honestly, especially in the homebuilt community, there are plenty of better choices but so many of us get hung up on the idea of expediency (read as: "wet wings") or tradition (read as: header tanks and plastic fuel lines)


Well every piper cub and aeronca champ and tens of other designs have header tanks right there to smash into you if you crash, so I guess i just won't crash with any fuel left.

Touche, but just because a design is a classic and sold well doesn't mean it is something to be emulated in every detail. All designs have room for improvement. That said, I'm looking forward to getting my taildragger endorsement this summer in an Aeronca. :D

The one advantage of a partially full aluminum header tank is that the grade of material many of them are made out of is one of the best metals to use to form an energy absorbing impact surface for one's face. (No, I'm not kidding but I'm also not actually suggesting a cockpit mounted fuel tank as a safety measure either).

[Frank Giger]

My Nieuport has an aluminum tank that sits right behind the firewall and over the pilot's legs simply because there is no place else to fit it.

One of the factors in placement, of course, is flight parameters. In Champs, Cubs, and my little biplane the speeds and mass of the aircraft factor in with the safety of the decision if in a wreck.

A wreck that involves enough force to actually make the tank a factor are already catastrophic to the point that it doesn't matter; the pilot has already been killed by the engine.

Assuming less than a nose dive into the ground or full speed into a cliff, the airframe will take enough of the force that the fuel tank won't be touched. The lines and their routing, if prudent, should likewise be minor.

A very neat thing about my plane's aluminum tube and gusset design is that it deforms very nicely. There's a video where a guy has his tail feathers cut clean off of his scaled Nieuport 11 by another plane at 100 feet AGL and does a nose dive into the grass; the pilot suffered a broken leg and soiled trousers.

Steve, you're going to absolutely fall in love with the Champ! Mark One Eyeball Altimeter/Airspeed Indicator, Wind On Cheek/Butt Slide Slip Indicator, Sound and Vibration Tach systems are how it is meant to be.

[rwanttaja]

Another factor to consider in the fuel-tank-in-the-cabin issue is whether putting it ELSEwhere might increase the potential for an accident.

A Fly Baby might be a good example. Putting fuel tanks in the wings would be the only other option. But splitting one tank into two means the pilot now has the opportunity to mismanage the fuel valve and run one tank dry at the wrong moment. Putting the tanks in the low wings means that the airplane needs a fuel pump to get the gas to the engine. Another potential failure point.

Remember, the P-51 had a fuel tank right behind the pilot...

Ron Wanttaja

[steveinindy]

Remember, the P-51 had a fuel tank right behind the pilot...

There's also the slight issue of a P-51 being a little more sturdily built than your average homebuilt. The fact that the thing had self-sealing tanks also mitigated the risk somewhat.


But splitting one tank into two means the pilot now has the opportunity to mismanage the fuel valve and run one tank dry at the wrong moment.

Point taken although there is the option of putting in a fuel pump which draws from both tanks simultaneously. Think a header tank effect without the header tank.


Putting the tanks in the low wings means that the airplane needs a fuel pump to get the gas to the engine. Another potential failure point.

What is the actual documented failure rate for a certified fuel pump that isn't due to improper maintenance, botched installation, etc? Has anyone actually looked into that? I'm not being argumentative, I am seriously curious about that. I've never seen any hard data on it.

So far as I am concerned is offset by the benefit of the plane being less likely to turn turtle in a hard or forced landing scenario etc. I have a learned aversion to an aircraft with most of the mass above and/or behind the pilot(s) and passengers.

[steveinindy]

A wreck that involves enough force to actually make the tank a factor are already catastrophic to the point that it doesn't matter; the pilot has already been killed by the engine.

Actually, you'd be damn surprised how many crash fatalities have NO traumatic injuries whatsoever other than their burns. Eliminating deaths due to smoke inhalation, burns and post-crash drowning (the three most common easily preventable causes of death in crashes or their immediate aftermath) would reduce GA aviation fatalities about 30-40%.

It's a very common misconception that most crashes that kill people are utterly non-survivable. It's kind of the same attitude people had about car accidents (which at highway speeds frequently involve a similar amount of force when measured at the structure closest to the impact before the energy absorbing features have a chance to do their thing) in the 1950s and 1960s. If I had to put money on it, there are probably 1/5 to 1/4 of crashes (depending largely on the type of aircraft) that are going to kill everyone on board without question and there's little to do other than avoid them. The rest could have survival improved- although not assured- through some rather minor modifications to designs.

The thing is that this is not a push to ground or force modifications to existing aircraft or even a criticism of them (well with a couple of major exceptions but that's a topic for another thread or for PMs). It's one of a desire to continue forward with the progression of technology at all levels of aircraft design. There are things that can be done in the Cub clone taildraggers, the RV series, the high performance boys like the Lancair and even the ultralight crowd. People grouse and moan about we don't respect where we have come from and the "spirit of homebuilding"- the creative, energetic and passionate spirit- is dead. It's not dead. Far from it as a matter of fact. The thing is that we just need a focus and a goal that can bring all of us together- from the ultralight junkies to the guys in the ultra-suped up Lancairs.

I actually submitted a series of articles to Chad Jensen about this very subject and how the quickest way for us to get the NTSB and FAA off of our collective asses is to give them a reason to do exactly that. Trust me, as much as I catch crap on here for advocating for staying away from non-certified parts and such, the last thing I want is MORE oversight. The way we do this and the way I suggest a new goal for the creative and somewhat quixotic minds of experimental aviation to work together and stop bickering in a petty turf war of sorts is to make safety our focus.

We are the only branch of aviation with sufficient leeway in the regs to pretty prove that safety and performance are not contradictory and that homebuilt aircraft are on par with anything coming out of the factories in Wichita, Duluth and elsewhere. Instead of being looked at as a bunch of weird folks who like to tinker in our garages and hangars (even thought a lot of us, myself included, are weird folks who like to tinker), let's use our collective experience, knowledge and creativity to figure out new ways to make better intrusion prevention, better restraints (lower rates of them separating from their mounts would be a great start), improved lightweight energy absorbing seats, better fuel tanks, etc.

If we knock our fatal crash rate down by 10% through better construction in concert with continued pilot education, we have removed one of the major reasons for the FAA to scrutinize us like they have been doing lately. I believe this is an achievable and reasonable goal.

Policing of our own ranks must also be part of our efforts. That is, putting your foot down and saying something when you see a fellow pilot about to do something stupid or after they've done something stupid but "gotten away with it". None of us wants to be a jerk or overstep our bounds but if we don't speak up to protect our brother and sister pilots and their passengers, who is going to do so in a way that we aren't going to hate a lot more?

If anyone would like, I'm happy to provide a PDF of the medical records and autopsy report release form my research company uses to gain access to data for our crash safety research (for survivors and fatalities respectively). Handing one of those to a pilot about to do something boneheaded (like the guy I helped stop from taking off into freezing rain in a 172) tends to give someone pause.....especially if you hand one to his wife or other passengers as well. It's an option of last resort obviously but it generally make them rethink their cunning plan.


Just my two cents....feel free to ream me for this post....

[Frank Giger]

Naw, no reaming...I can't disagree with any particular point.

The crux is working the cost-benefits of design decisions, as all designs involve prudent compromises between safety and perfomance.

Restraints are a great example, as you mentioned. I'll be spending a bit more in money and time than I really like on a five point restraint system because I view it as the first line of surviveability in a wreck. Since my plane is open cockpit, I'll be wearing a helmet during the first 40 and beyond; looking doofy in the cockpit is better than looking good in a casket.

However, the location of the fuel tank is pretty much non-negotiable based on basic design and dimensions of the aircraft; installation and fuel line routing is going to be in the cockpit. That just means that a lot of attention to detail and foresight has to be put into them for safety.

[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.

[Mike M]

Remember, the P-51 had a fuel tank right behind the pilot...

Ron Wanttaja

at the risk of being misinterpreted because print doesn't convey a wink and a nod very well,

remember that P-51 pilots were paid to take crazy risks.

[Samyguy]

Tygon fuel line from Graingers has lasted 15 years for me. With no sign of deteriortion.

[steveinindy]

I'll be wearing a helmet during the first 40 and beyond; looking doofy in the cockpit is better than looking good in a casket.

Of course, there's a lot of folks who joke that helmets are there to allow a good appearance in the casket but I digress..... ;)


However, the location of the fuel tank is pretty much non-negotiable based on basic design and dimensions of the aircraft; installation and fuel line routing is going to be in the cockpit. That just means that a lot of attention to detail and foresight has to be put into them for safety.

Then please, as your friend, I ask that you use a braid steel or similarly tough fuel line with a couple of quick disconnects to minimize the risk of spills. Placing the fuel tank as far back as the CG will allow is also a good idea. :)

[steveinindy]

remember that P-51 pilots were paid to take crazy risks.

Kind of like HEMS pilots ;)

[Mike M]

Kind of like HEMS pilots ;)

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

[rwanttaja]

at the risk of being misinterpreted because print doesn't convey a wink and a nod very well,

remember that P-51 pilots were paid to take crazy risks.

And here I thought that my checks were just 30 years behind. :-)

I can appreciate Steve and others' arguments for keeping the fuel out of the fuselage. I certainly grant the safety benefits.

But for the fuselage fuel tank to make a difference, I have to crash. After that, to make a difference, the crash has to be such that the fuel tank is broached. After that, the crash has to be such that I am incapacitated. And after that, the fuel has to be ignited.

I certainly agree with the possibility... we had an accident in the Fly Baby community about ten years ago that went about 95% through this sequence.

http://www.bowersflybaby.com/safety/horsten.html

Fuel-System mechanical problems or pilot fuel-system management issues contribute to about 8% of homebuilt accidents, but of course, the above sequence can occur in any accident. It's impossible to quantitatively compare the approaches... Reduce (slightly) the overall number of accidents due to fuel system or fuel management problems, or reduce (slightly) the risk of burning to death if you crash, if the fuel tank is ruptured, if you're trapped, and if it catches fire.

Good subject for arguing over a couple of beers at the bar, but impossible to settle (short of a thumb-wrestling tourney).

Putting the fuel tanks in the wings results in a more-complex aircraft. If you don't install something, you can't install it wrong, the parts can't wear and fail, and later maintainers can't botch the wrenchwork.

Adding the complexity to move the fuel tank out of the fuselage reminds me of ballistic parachutes. It takes more building effort to install, it reduces performance, it makes things more complex to maintain, and really is only useful in a fairly narrow range of circumstances.

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

Ron Wanttaja

[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.

[Bob H]

I worked with a friend with Kitfox and 912 engine and I have a 912 in Pulsar. If you are using mogas, stay away from blue vinyl lines and use automotive fuel hoses as they are formulated to withstand mogas with ethanol. I have never had an issue with auto hoses but replace them every 5 yrs and my CA mogas has 10% ethanol. Never saw any sign of deterioration but do it as precaution and it's both easy and inexpensive to do. There is no preload issue or fatigue issue with a rubber line as you can have with aluminum tubing nor a weight hit as with braided SS with AN fittings. I would go with what is safe and convenient to install and maintain.

[BushCaddy]

Some people never finish their airplanes because they search for perfection and it doesn't exist. Some people over-analyze and over-engineer every aspect and that's ok...it's their choice and perhaps they prefer building to flying...that's ok too. But it's not for me. In the real world the more pragmatic approach is take what has consistently worked in certified designs and incorporate them into your aircraft w/o over-complications and added potential points of failure. There is nothing unsafe or unreasonable about unshielded hard alumium fuel lines in the cockpit...just about every high wing airplane flying has them. No airplane can be 100% safe in every circumstance because it's an impossible task. At some point you just have to take what has succeeded time and time again in the past and move on.

My $.02