Let’s Talk Fuel Lines!

[AKNick]

I've seen that video before too. But every application is different, like for example a heavy clunk with soft tubing is more prone to kink/fold over, which is a reason in itself for adding a straw or copper tubing. This could happen in a negative G style maneuver (tail slide?) possibly as well. I've seen it happen where the plane noses over on the ground, and the clunk fall forward to the top of the tank. Just a extra measure of security.

 

[stangflyer]

I've seen that video before too. But every application is different, like for example a heavy clunk with soft tubing is more prone to kink/fold over, which is a reason in itself for adding a straw or copper tubing. This could happen in a negative G style maneuver (tail slide?) possibly as well. I've seen it happen where the plane noses over on the ground, and the clunk fall forward to the top of the tank. Just a extra measure of security.

Exactly. That is why I like the heavy clunk. 99% of the time, that clunk will always be in fuel.

 

[sailr]

I did some research on this a while back. One guy (Jharkin) dug up most of this on the other site. Every tubing has it's purpose. whether it's heat resistant, flexible, fuel/ethanol resilience.

Viton = (thick wall and black unless it's the Sullivan Pro-Flex version of the stuff which is tan) best for inside the tank. It's expensive, but will last forever. PSP sells the right stuff in a thicker wall, wont kink as easy.

Tygon = commonly found, cheap, and overtime gasoline will make it harden... change it every couple years

Tygothane/Polyurethane - good alternative to tygon, lasts longer. TDRC sells this stuff in blue and red. helps to soften the tubing with heat prior to putting over a barb, and it is hard to remove... very hard to remove.

Blue Flurosilicone - ??EasyLFex?? never heard of it.

Neoprene - softens over time.

Fluran 5500 - fluorielastomer -40-400F resists oil and fuel. http://www.teastech.ie/wp-content/uploads/2013/09/FT-Fluran-F5500A.pdf
pretty interesting stuff, never heard of it.

I've been noticing that people are starting to put their in tank fuel pickup lines through straws or connected to a brass tubing to keep the line from kinking or falling to the front of the tank. Also instead of zip ties, or wire, people are stetching an additional piece of tubing (1/8") over top of the barbed area, keeps a little extra tension for an air tight seal.

 

[Yakman]

Was out for a couple of flights this afternoon with my Edge 540, got all new Tygon lines last summer. At 39 degrees they seemed awful stiff. I need to look at line inside of fuel tank, since i fly during winter also.

 

[Snoopy1]

I am really glad this got brought up. I had thought I would look at alternative tubing for my setups. But then I got to thinking of two things that keep stopping me. The first being foremost in my mind. I make it a point to check my fuel lines each end of season and then again each beginning of season. So far, I have replaced only the tubing in my SD 260 once in five years. Yet I firmly believe preventative maintenance is a must to keep our planes flying without disaster. So a little time inspecting and replacing it is not a problem to me. It gives me the chance to really look everything over real well as anyone would do with a regular "yearly" on a full scale. So far all the Tygon I have put in my planes still seems to be as plyable as when it was first installed. The second thing that stops me is "if it ain't broke, don't fix it". I too use the stretched fuel ring over the fuel tubing to act as a clamp band on fuel lines. I have used zip ties before but I am really liking the alternative method lately. I do however do something that not a lot of people do in regards to the carb line and klunk. I use the Sullivan Super Klunks.
https://www.ebay.com/p/Sullivan-Super-Klunk-Large-Tanks-S396-Clunk/1027566138
They are quite heavy and have been doing an awesome job for me. I know many guys use a brass tube in the carb line to keep the line from falling forward in their tank. But my theory is this: On a down line using higher throttle settings, I would think an engine would starve of fuel if the line stays at the back of the tank. With the Sullivan Super Klunks, they are heavy enough with Tygon fuel line that they will in fact fall forward and constantly keep the line in fuel. And when going back to an upline, the fuel line then goes back to the rear of the tank. Also, with extremely high "G" maneuvers and due to the centrifugal force, an inertial force it pulls the fuel line out to constantly be submerged in fuel. I guess it must be working because I have never had an engine die from fuel starvation. I saw a YouTube video not long ago that debunked the theory of fuel being "sucked" to the back of the tank in a down line. It clearly showed the fuel falling to the front of the tank and the "stiffened" fuel line and clunk being left subject to open air and no fuel. I would think in order for the fuel to be able to overtake gravity, a falling object would have to be moving pretty fast and for a long time to have the fuel become weightless and stay at the rear of the tank.

I agree with all you have said above but need to make one point I have at one time not made a very graceful landing and the fuel clunk got thrown to the front of the tank and it stayed there. After several dead stick landings I discovered that the clunk was stuck up front. And after shaking the plane up and down the clunk was free again and all was good. So when you do your flying do feel that the clunk drops to the front of the tank. Have you checked it. Now that I think of the size of tanks that you are using with those gorgeous redheads it probably has sufficient space to drop forwards and backwards.

 

[stangflyer]

I agree with all you have said above but need to make one point I have at one time not made a very graceful landing and the fuel clunk got thrown to the front of the tank and it stayed there. After several dead stick landings I discovered that the clunk was stuck up front. And after shaking the plane up and down the clunk was free again and all was good. So when you do your flying do feel that the clunk drops to the front of the tank. Have you checked it. Now that I think of the size of tanks that you are using with those gorgeous redheads it probably has sufficient space to drop forwards and backwards.

They do. Drop backwards that is. Part of it is also due to the size and weight of the clunk itself. I have tested many clunks. Some are large, yet have no weight to them. Some are just way too small to even consider. While others have an opening that not even a sewing needle could pass through. The Sullivan Super Klunks #S396 if I remember correctly... seem to do a really good job. That added to the size of the tank helps too. I will go so far as to say also, that most my planes are stored on their nose. Hence the clunks fall to the front of the tank. When I take one of them out flying, I make darned sure the clunk is back at the back of the tank before I even fuel the plane. I truly have considered the hard tube in the middle of the carb pick up line. I just keep coming back to the same things that have always been consistent. "If it ain't broke, don't fix it". And the other being I have yet to ever have a problem so I am not going to alter it. In fact, I just built a brand new TDRC tank for the baby Yak last night. Yup, you guessed it...Sullivan Super Klunk with no hard line between the clunk and the cap fitting. Something else I have noticed. The tank in the Pitts is a smaller one. I think it is like 17 ounces. So the area is quite cramped for a clunk to fall forward. Unless of course you have a hard nose landing or what not.... But other than that, I stand it also on the nose and the clunk stays put. I dunno.... I see the logic behind the hard line. I just have a really-really hard time changing something that works.

 

[Snoopy1]

Ok this is some new gas fuel line that I was introduced to at JoeNall. Been using since early spring and up to now I believe it is best I have tried ie Tygon, Viton and a few others I must say up to now this is the best tubing I will be switching over to. It is not cheap.

 

[Bruce Swartfager]

Reference fuel clunks I have been using Walbro Felt clunks in all my gassers . I was advised not to use the knockoff style or brands made in China. I have never had any problems since switching to the Walbro Felt clunks. I get them from ValleyViewRc they are around $5 per piece, a little pricey but I think it is well worth the money.

 

[AKNick]

View attachment 99896 Ok this is some new gas fuel line that I was introduced to at JoeNall. Been using since early spring and up to now I believe it is best I have tried ie Tygon, Viton and a few others I must say up to now this is the best tubing I will be switching over to. It is not cheap.

The Sullivan S216 claims it it Fluoroelastomer, guess what Viton line is... Fluoroelastomer! It might be altered a bit, but I'm guessing it's Fluorelastomer died yellow with their chosen ID/OD.

 

[Snoopy1]

The Sullivan S216 claims it it Fluoroelastomer, guess what Viton line is... Fluoroelastomer! It might be altered a bit, but I'm guessing it's Fluorelastomer died yellow with their chosen ID/OD.

It my be a derivative of it or something but I have had Viton and this is similar but not the same I do prefer it up to now.