Clunk Line

[StevL]

Yesterday I was flying my 50cc yak and everything seemed fine. We did a little hovering, rolling circles, harrier, pattern stuff and just punching holes in the sky. Suddenly without notice I was doing a very low inverted pass and started to pull a up line (near straight up). Suddenly the engine started coughing and almost shut down.

After landing, check the fuel, it was fine and still a half tank. Put about a 1/8 turn richer on the carb, both high and low thinking this is the coolest weather I've flown in since last year (high 55).

Another flight doing some hole punching (at about 4 minutes into the flight) it coughs and dead sticks.

I checked the clunk line and it is very stiff. It will not fall 1/4 the way to the bottom (top) of the tank when turned inverted. I'm using Tygon fuel line and it is only about 3 months old.

What do you guys use for the clunk line? Anything that stays more flexible?

[exeter_acres]

I use Tygon... what was the temperature.. it will be a bit stiffer in the cold...
I do change the line about once a year

[rcign]

One more time..
Hayes molded neoprene from Tower..One size fits all, no barbs needed, won't fall off a straight brass tube..Never gets hard....Hayes is the ONLY neoprene that works...Small (about 1/16) diameter will run a DA 150 gasser with no problem......Or 3W 170..Or anything else you can put on your airplane....

[StevL]

rcign,

I just found the thread where you guys been over this. I'll give it a try!

I did have a problem that cost me an airframe using the Hayes on a glow set up running 30% fuel. The Hayes expanded and slide off the brass tubing while in a low hover

Thanks for the tip!

[rede2fly]

	Quote: Originally Posted by rcign
	One more time.. Hayes molded neoprene from Tower..One size fits all, no barbs needed, won't fall off a straight brass tube..Never gets hard....Hayes is the ONLY neoprene that works...Small (about 1/16) diameter will run a DA 150 gasser with no problem......Or 3W 170..Or anything else you can put on your airplane....

	Quote: Originally Posted by StevL
	rcign, I did have a problem that cost me an airframe using the Hayes on a glow set up running 30% fuel. The Hayes expanded and slide off the brass tubing while in a low hover Thanks for the tip!

oops might rethink it

[StevL]

On glow I would certainly use a barb and wire tie it. I'll do that on the gassers too, just makes me feel safer.

Hayes is good stuff, it just expanded on the high nitro stuff, but it stays very flexible.

[rcign]

Hayes is NOT for glow, gas only...Silicone is for glow...

[RCAddiction]

Hayes neoprene line is supplied with the Hayes 2-16 oz glow fuel tanks. If it's not intended for glow, the Hayes folks don't know that ;l-). Viton tubing from McMaster works well for gas....lasts longer for me than the Hayes line and is more tear resistant. Yup, silicone for glow.

[Al Lewis]

About 40 years ago they dug a WWII fighter out of the ice and shipped it back to the states. When they took the engines apart every neoprene seal on it was still good. Great stuff with gas.

[RCAddiction]

Apparently my problem is that I don't fly under the ice. I knew it.

Actually, neoprene is really good for certain gasolines but not all blends and additives used today. That's why it is not used much for automotive fuel systems today. Everything I designed for Ford, Jag, Saturn, Chrysler, Honda, Bosch, Walbro 18-20 yrs ago was using Viton or Fluorosilicone. There was one buna-N part that Chrysler made me swap out from Viton as a cost reduction to save a dime in a 10$ product. They failed later and made the fuel pump modules noisy.

[Al Lewis]

	Quote: Originally Posted by RCAddiction
	Apparently my problem is that I don't fly under the ice. I knew it. Actually, neoprene is really good for certain gasolines but not all blends and additives used today. That's why it is not used much for automotive fuel systems today. Everything I designed for Ford, Jag, Saturn, Chrysler, Honda, Bosch, Walbro 18-20 yrs ago was using Viton or Fluorosilicone. There was one buna-N part that Chrysler made me swap out from Viton as a cost reduction to save a dime in a 10$ product. They failed later and made the fuel pump modules noisy.

No wonder they're going bankrupt. BunaN can be dissolved by gasoline, as I'm sure you know. I use a lot of Viton in designs at work but it is pricey. Still, it is the best thing around hydrocarbons.

[Truckracer]

I like Hayes tubing but I have had it slip off of brass tubing.... and so have other users here in my area. So I barb and tywrap it just like I would Tygon. Have to disagree about using it with glo fuel though ... many people use it with great results and it is supplied as a clunk line for Hayes tanks.

[RCAddiction]

Al, actually the Japanese carmakers were sticklers for fluorosilicone (Viton is fluorocarbon) and liked to use LCP (liquid crystal polymer) for pump inlets since while expensive, it was dimensionally extremely accurate and chemically resistant.

Not saying these are accurate today, but they were in 1990:
Ford - get it done right
GM - get it done on time
Chrysler - get it done cheap - hence the Buna-N. Stupid decision, parts failed within 6 months.

[Al Lewis]

I use quite a lot of BunaN. We mill our own for some applications but certain things I design for are very particular about what gets near them so Viton is also used a lot.

[RCAddiction]

Viton is great, except when cold. That's was the main advantage of Fluorosilicone, lower temp capability and lower durometers possible than Viton.