Fuel line fittings

[karmarepair]

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.

[Bryan Cotton]

We all have our preferences. Mine took many iterations and I would do the same thing again.

[GraemeSmith]

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

[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

[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.

[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.

[Bryan Cotton]

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.

"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.

" 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.

[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???

[Bryan Cotton]

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.

[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???

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.