Fuel line fittings
Posted: Tue Sep 28, 2021 7:26 pm
by wingnut99
I’m having trouble finding the appropriate fittings for my fuel line. I’ve ordered several 90° elbows from Aircraft Spruce and from Amazon with all of them being wrong. The fuel tank has a 3/8" fitting in the bottom which is the same as the gascolator. Unfortunately if I order a 3/8" pipe fitting the flared portion is only 1/4" and if I order a 3/8" flare to accept the 3/8" fuel line then the pipe thread end is 1/2." I can’t find a 3/8" pipe to 3/8" flare elbow. I don’t really want to use a bunch of reducers or adapters to get everything to work. To many potential leaks. Any ideas?
Re: Fuel line fittings
Posted: Wed Sep 29, 2021 9:50 am
by racaldwell
HI WN99,
ACS has AN816 in 6-6D size. The 6 means 3/8 so this one is 3/8 thread and 3/8 tube. The D is aluminum. AN816 is a straight nipple.
Rick Caldwell
Xenos 0057
Re: Fuel line fittings
Posted: Thu Dec 16, 2021 9:42 am
by wingnut99
I moved on to engine installation and wiring. I’ll be back to the fuel system soon so thanks for the clarification. I’m seriously considering pulling the altitude compensating carb off for simplicity. I can get rid of 2 fuel pumps and a carburetor heat system and the only addition will be a mixture control. I hate pulling brand new parts off and spending another $500 to replace them but I think it’s worth it to speed up the process and eliminate complexity.
Re: Fuel line fittings
Posted: Thu Dec 16, 2021 3:26 pm
by Scott Todd
After building 3 airplanes and working on dozens more, here is some probably controversial advice; NEVER, NEVER, NEVER use 90 NPT fittings for anything! Its always just a pain in the a$$. Use straight NPT ones so you can get them the right torque and then make or have the other lines made with AN 90 fittings on them. Its WAY easier to get them all tightened and lined up correctly.
Re: Fuel line fittings
Posted: Thu Dec 16, 2021 8:47 pm
by sonex1374
I buy all by AN fittings through Jegs. They have a great selection, quality is good, and the descriptions and pictures help assure you get the right parts.
https://www.jegs.com/i/JEGS/555/100146/10002/-1
Jeff
Re: Fuel line fittings
Posted: Thu Dec 16, 2021 9:18 pm
by Rynoth
Scott Todd wrote:After building 3 airplanes and working on dozens more, here is some probably controversial advice; NEVER, NEVER, NEVER use 90 NPT fittings for anything! Its always just a pain in the a$$. Use straight NPT ones so you can get them the right torque and then make or have the other lines made with AN 90 fittings on them. Its WAY easier to get them all tightened and lined up correctly.
When space is available, I totally agree. All too-often you have to choose between slightly-undertorqued or over-torqued to get the thing to line up correctly.
Re: Fuel line fittings
Posted: Fri Sep 02, 2022 3:00 am
by Skippydiesel
wingnut99 wrote:I’m having trouble finding the appropriate fittings for my fuel line. I’ve ordered several 90° elbows from Aircraft Spruce and from Amazon with all of them being wrong. The fuel tank has a 3/8" fitting in the bottom which is the same as the gascolator. Unfortunately if I order a 3/8" pipe fitting the flared portion is only 1/4" and if I order a 3/8" flare to accept the 3/8" fuel line then the pipe thread end is 1/2." I can’t find a 3/8" pipe to 3/8" flare elbow. I don’t really want to use a bunch of reducers or adapters to get everything to work. To many potential leaks. Any ideas?
Maaaate! Go “rubber” all the way. No elbows. No Flares. No expensive fittings that may leak. One length between applications, no joins. No vibration issues. Way way less cost. Sure you should replace every 5 years as per Rotax recommendations but its easier than it sounds (could do mine in a morning). Purchase quality fuel hose from your Auto shop - I use Gates hoses. You can look up the specifications for Gates, not so for many auto hoses.
If you do go rubber - make sure you use the latest automotive style spigots (push on fittings) not the old stile multi barb fittings AND never overtighten the hose clamps (which should be the fuel injector style). The hose clamp is a security devise NOT a leak preventer. Make sure your hoses ID is compatible with the spigot OD and you will not have leaks.
Re: Fuel line fittings
Posted: Fri Sep 02, 2022 4:18 pm
by karmarepair
Skippydiesel wrote:Maaaate! Go “rubber” all the way.
Me, if I were to start all over again, would got with a hard line all the way from the shutoff valve to a SHORT section of flex hose just before the AeroInjector. NO other filters or fittings, and I’d rig up a proper bulkhead grommet for the firewall penetration. Reasoning is that anything that can pass the finger strainer will pass the needle on the AeroJector, and if you keep the fuel tank full all the time, there is literally no way for water to get in the tank, protected as it is from rain by a tight cap AND the fuel door.
I don’t like how close to the exhaust my fuel line runs, from the gascolator a previous builder installed to the AeroInjector, and the multiple 90 degree fittings in my installation have all the problems mentioned, plus one AN fitting is on the BACK side of the firewall where it’s all but inaccessible.
At least one Sonex I know of is running this way I described successfully.
Re: Fuel line fittings
Posted: Fri Sep 02, 2022 4:43 pm
by Bryan Cotton
I did a combination of hard line and braided line - all AN fittings. Documented on page 102 of my thread:
viewtopic.php?f=39&t=578&start=1010
It all runs downhill, and there is a filter on the engine side of the firewall.
The original hard plumbing was redone with the angle shim pictured. There are two layers of firesleeve firewall forward, so you can’t see the filter or line. I figure it’s as much insulation as it is protection.
No rubber hoses for me.
Re: Fuel line fittings
Posted: Fri Sep 02, 2022 7:07 pm
by Skippydiesel
karmarepair wrote:
Skippydiesel wrote:Maaaate! Go “rubber” all the way.
Me, if I were to start all over again, would got with a hard line all the way from the shutoff valve to a SHORT section of flex hose just before the AeroInjector. NO other filters or fittings, and I’d rig up a proper bulkhead grommet for the firewall penetration. Reasoning is that anything that can pass the finger strainer will pass the needle on the AeroJector, and if you keep the fuel tank full all the time, there is literally no way for water to get in the tank, protected as it is from rain by a tight cap AND the fuel door.
I don’t like how close to the exhaust my fuel line runs, from the gascolator a previous builder installed to the AeroInjector, and the multiple 90 degree fittings in my installation have all the problems mentioned, plus one AN fitting is on the BACK side of the firewall where it’s all but inaccessible.
At least one Sonex I know of is running this way I described successfully.
Why?
What advantage do metal lines confer in our class of aircraft?
Where not possible to rout fuel lines away from hot components, heat shields can be easily custom made using builders malleable aluminium flashing, exhaust wrap and high temp silicon gasket goo. Cut aluminium to length/width (always allow extra to do a final trim) Cut exhaust wrap into strips appropriate to aluminium sheet (I like to stop wrap just before edges of aluminium by about 5mm). Using liberal amounts of silicon , glue wrap to aluminium. Leave to set overnight. Wrap “sandwich” around hose/pipe & secure with safety wire or hose clamp (extra weight & cost).
Re: Fuel line fittings
Posted: Sat Sep 03, 2022 3:33 pm
by karmarepair
Bryan Cotton wrote:I did a combination of hard line and braided line - all AN fittings. Documented on page 102 of my thread:
http://www.sonexbuilders.net/viewtopic. … start=1010
This is very much like the arrangement on my plane. That hard line from the valve to the firewall took be the better part of a day to get right. The length and the bend need to be quite precise, and you need to assemble both ends, and flare them. Once you have the fittings on, little micro adjustments are TOUGH without collapsing the tubing. And tightening the aft flare fitting at the firewall was a Bee-Yatch.
The plans just have a hard line running through a hole in the firewall. ANY connection you need to make happens where it is easy to see, easy to reach, and you don’t have to work to tight tolerances. Keeping the firewall from chafing through the aluminum tubing, while keeping the fire and heat on the engine side is the only challenge, and Bingelis has suggestions on that front.
I’m not knocking what you did, it’s all to “code”, and it’s VERY much like I did, but as I say, I would NOT do it that way again if I was starting from scratch.
Re: Fuel line fittings
Posted: Sat Sep 03, 2022 3:41 pm
by Bryan Cotton
We all have our preferences. Mine took many iterations and I would do the same thing again.
Re: Fuel line fittings
Posted: Sat Sep 03, 2022 5:26 pm
by GraemeSmith
Bryan Cotton wrote:We all have our preferences. Mine took many iterations and I would do the same thing again.
OK - just to get the popcorn machine going a bit more… 
The metal shallow “S” bend in Bryan’s picture.
I have a thought that in the event of a crash and firewall deformation - that metal “S” bend is relatively hard compared to the softer tank and might be too rigid - causing the shut off valve and tank fitting to tear the bottom of the tank. Fuel leak resulting.
I have replumbed that “S” in flexible fuel line in the hope the line will flex in a firewall deforming crash and the tank fittings will stay in the tank.
My 2c.
YMMV
Re: Fuel line fittings
Posted: Sun Sep 04, 2022 11:01 am
by GordonTurner
Actually Graeme, my equally unscientific take on it is that the bends in the tube offer very little resistance to just bending more. To me it looks like in the event you are concerned about the tubing will be the weak link, it will bend further and kink, but is not likely to actually fail and i think very unlikely to impart a very significant force to the valve/tank fitting. Both of us can’t be right
Gordon
Re: Fuel line fittings
Posted: Sun Sep 04, 2022 1:15 pm
by Bryan Cotton
If the impact is enough to bring the tank and firewall closer together, it’s likely to be fatal anyway. Hopefully none of us will go there.
In terms of service life, the aluminum tube doesn’t really age. By making that a hard line I was able to ensure the fuel flows downhill all the time, even in the 3 point attitude.
My fuel system was not expensive.
Re: Fuel line fittings
Posted: Sun Sep 04, 2022 7:27 pm
by Skippydiesel
[
In terms of service life, the aluminum tube doesn’t really age. By making that a hard line I was able to ensure the fuel flows downhill all the time, even in the 3 point attitude.
It may not “age” as in corrosion but it can certainly fatigue and threaded caps can loosen.
“hard line I was able to ensure the fuel flows downhill” - surely you make this point in jest.
My fuel system was not expensive.[/quote]
" not expensive" this is a comparative statement, so to what are you comparing the cost of your tube to? It cant be rubber hose, as aluminium tube & required fittings are many times the cost of rubber. I have no doubt that over a very very very long operational life, the cost of replacing rubber every 5 years (as per Rotax suggested intervals) would equal and may exceed the cost of aluminium but in this speculative time span I have little doubt at least some of the aluminium would also have been replaced.
Re: Fuel line fittings
Posted: Sun Sep 04, 2022 10:48 pm
by Bryan Cotton
Skippydiesel wrote:It may not “age” as in corrosion but it can certainly fatigue and threaded caps can loosen.
I have little doubt at least some of the aluminium would also have been replaced.
In a prior life I rebuilt a 1946 Cessna C140. I had do do major surgery to fix spar attach points and I replaced the hard fuel lines, though they could have been reused. I did reuse some of the 60+ year old fittings. I am sure those were the original fuel lines as I was into parts of the airplane never meant to be seen again. 60+ years is good enough for me. Plus I used to work at Sikorsky and plumbing there, on Blackhawks and the X2 technology demonstrator was generally hard lines and rubber lines were verboten. I actually plumbed the Waiex with leftover tube that I bought for the C140 project.
Skippydiesel wrote:“hard line I was able to ensure the fuel flows downhill” - surely you make this point in jest.
If you read through the forums, it comes up often as one of the ways to mitigate burps. Plus ensures there is no way for water to collect upstream if you are not running a gascolator. No jest. I think it may have been a statement from Sonex on the old Yahoo groups too.
Skippydiesel wrote:" not expensive" this is a comparative statement, so to what are you comparing the cost of your tube to? It cant be rubber hose, as aluminium tube & required fittings are many times the cost of rubber.
Here is my firewall aft costs as shown in the picture. Total is $17.07 plus tax and shipping. I don’t consider that expensive.
Edit - tools cost for the AN flares are not shown. But, as we all know, the purpose of the hobby is to buy tools.
Re: Fuel line fittings
Posted: Sun Sep 04, 2022 11:20 pm
by Skippydiesel
In US dollars it doesn’t look/sound expensive however your origional statement was one of comparison - where is the cost in rubber hose???
Re: Fuel line fittings
Posted: Sun Sep 04, 2022 11:33 pm
by Bryan Cotton
Skippydiesel wrote:In US dollars it doesn’t look/sound expensive however your origional statement was one of comparison - where is the cost in rubber hose???
Aluminum hose fitting $5.80
Hose, 1’ $2.95
Not sure what you would use to penetrate the firewall. I couldn’t find anything at Aircraft Spruce. So the rubber hose stuff behind the firewall is $8.75 plus maybe $5 for a firewall connector so $13.75 vs $17.07.
I wasn’t really making a comparison, but my hard plumbing is less than a tank of gas for my Yamaha.
Re: Fuel line fittings
Posted: Mon Sep 05, 2022 3:38 am
by Skippydiesel
Bryan Cotton wrote:
Skippydiesel wrote:In US dollars it doesn’t look/sound expensive however your origional statement was one of comparison - where is the cost in rubber hose???
Aluminum hose fitting $5.80
Hose, 1’ $2.95
Not sure what you would use to penetrate the firewall. I couldn’t find anything at Aircraft Spruce. So the rubber hose stuff behind the firewall is $8.75 plus maybe $5 for a firewall connector so $13.75 vs $17.07.I wasn’t really making a comparison, but my hard plumbing is less than a tank of gas for my Yamaha.
What 1 ft of hose is all you need ? - no boost pump/line, not return from main pump, no breather, no auxiliary. If this be the case, I loose my argument, as 1 ft of anything is going to be “in the ball park” no matter if its gold plated or just plain rubber.
As for firewall penetration - I have used electricians gland (can be had in plastic stuff or metal) to good effect. Can also be used for cable buddles and come in a wide range of sizes.
Re: Fuel line fittings
Posted: Mon Sep 05, 2022 10:24 am
by GordonTurner
There is so little plumbing in this plane that cost should not even be a factor, only quality. It’s homebuilding, so quality is in the eye of the individual builder.
Skippy, we all appreciate your opinions on things, but if you want to argue then it would be more helpful if you provide specific facts and details instead of unprovable generalities. And tell us specifically what this electricians thing is???
I personally would prefer to see this discussion return to the technical advantages and alternative methods, and particularly a discussion of the safety durability and operational characteristics of different systems.
Build on. We’re all friends here. Gordon
Re: Fuel line fittings
Posted: Mon Sep 05, 2022 10:07 pm
by Skippydiesel
GordonTurner wrote:There is so little plumbing in this plane that cost should not even be a factor, only quality. It’s homebuilding, so quality is in the eye of the individual builder.
Hi Gordon,
The quantity of plumping will vary between Sonexs - eg my one has wing tanks, associated breather, fuel transfer lines and because its Rotax powered, has both boost pump line & return fuel line - many meters of fuel line.
Cost should always be a factor as long as safety is not compromised. I for one do not wish to spend any more than is necessary to achieve an efficient/safe/airworthy aircraft.
I agree with your sentiment on home building - it is a wonderful opportunity/challenge/achievement to build & fly your own aircraft - my commentary is just to inform not dictate. In my view, building an experimental is an opportunity to at least consider non aviation materials but only if there is good evidence to show that functional safety is not being compromised.
Skippy, we all appreciate your opinions on things, but if you want to argue then it would be more helpful if you provide specific facts and details instead of unprovable generalities. And tell us specifically what this electricians thing is???
Actually I did specify - where I come from they are called Electrical Glands - Google that and you will get a host of variants/sizes. They are made to facilitate the penetration, by cables or conduit, of a thin wall (most often metal) so are eminently suited to hose or pipe..
I personally would prefer to see this discussion return to the technical advantages and alternative methods, and particularly a discussion of the safety durability and operational characteristics of different systems.
From my perspective the technical attributes of “rubber” hose are:
Single run - in most instances a single hose can be employed between delivery & receival points. Metal hoses often require several joins in a run (eg penetration of a fire wall)
Reduced fittings minimises potential failure/leak points.
Ease of installation, no bending, no flaring, just push on.
When correctly installed, there is no concerns of fretting/resonance/gross movement damage.
No corrosion potential internally or externally.
Cost- considerably cheaper per unit, than aluminium pipe.
Deterioration due to aging (mainly exposure to fuel) is a concern, hence the Rotax advise to replace all rubber components, exposed to fuel, every 5 years.In my limited experience, I have found good quality rubber hose (I use Gates products) to be easy/fast to install, leak proof when the correct ID hose is specified for the OD of the spigot. The old hose (5 year replacement) is still good enough to be recycled for use on mowers/tractors/etc.
I use the latest automotive style spigot usually with just the one raised safety collar and fuel injection style hose clamps that give 360 degree even pressure. Clamps are for security, not for leak prevention, so should never be tightened such that they cause distortion or pinching of the hose.Build on. We’re all friends here. Gordon
Re: Fuel line fittings
Posted: Wed Sep 28, 2022 8:16 pm
by Skippydiesel
Came up with another positive for rubber hose compared with the traditional aluminium:
Tools:
Aluminium pipe requires expensive bending, flaring, cutting equipment and then at least three spanner sizes to install
Rubber hose requires a cheap cutter (for nice “square” particle free cuts), a screw driver and or pliers (can go fancy & purchase special spring clamp pliers) for retainer installation.