Clunk Line Question
 

Greetings!

I am wondering why often times a special type of fuel line is included to hook the clunk to. (in glow fuel tanks) Sometimes this tubing is black or sometimes clear. Why not simply use std silicone tubing inside of the tank for the clunk?

Ernie

Clunk Line Question
 

Some tanks need the increased flexibility. If you are nose down with less than half a tank of fuel, the standard fuel tubing may not allow the clunk to drop all the way to the nose of the tank. The air it picks up just doesn't burn and you get to practice dead-stickin' :eek: The dreaded stuck clunk is also fun. Once had a guy at our field spend three weekends trying to figure out why his engine stalled after 2 to 3 minutes of flying time. (Okay, it was me :D ) The clunk was stuck just about halfway up the from wall of the tank. I got awfully good at dead-stickin' that trainer. If standard fuel tubing will allow the clunk to travel the full range of your tank without sticking, it is fine to use it. Just rotate the assembled tank outside the plane and watch the clunk movement. Shake it around a bit to simulate plane movements to ensure it won't get stuck in actual use.

Clunk Line Question
 

Good answer, except for one thing.

The clunk should NOT be able to swing forward in a standard tank. Very often, tank MFGs will include a stiff plastic tubing to be inserted in the tanks feed line to prevent the clunk from swinging forward and getting stuck.

As far as the feed line sucking air while nose down, it just doesn't happen (at least not in most cases) due to the fact that the plane is moving forward, thus pushing the fuel to the back of the tank. If some air IS fed into the line, it will pass through the carb much faster than fuel will, so you may get 1 or 2 lean "pops" out of your engine, but when you consider how many "pops per second" you're getting, they will go by in the blink of an eye and usually won't even be noticed.

Clunk Line Question
 

After pulling my hair out trying to figure out why one of my engines wouldn't run full throttle, it was therorized that the chincy thin fuel line supplied with the cheapo TT tank I bought was actually collapsing. I swapped it out with regular fuel line and all was well. I've never used the supplied clunk line since with any tank...I always use the same fuel line I use on the outside of the tank.

Clunk Line Question
 

Had the same thing happen to me also, When I changed lines, to just the "regular" blue fuel line, everything was happy!

:)

Clunk Line Question
 

The clunk should NOT be able to swing forward in a standard tank

Minnflyer, I think you are on to something here and I wonder how many folks are hip to this. For example, the illustration you gave shows a stiff piece of tubing in the clunk line to keep it from going foreward in the tank and kinking. How many people (especially the ones who use std silicone tubing) actually do this??? It appears that we all should.

Okay, so the funky clunk tubing supplied by tank mfg's is actually LESS flexible than standard tubing..... and now we know why...

Thanks a whole bunch!

Ernie

Clunk Line Question
 

Again MinnFlyer comes up with another great illustration (I love them cause they are so easy to follow).

I have used the method that Minn demonstrated and it works like a charm!

My first thought on this though was that perhaps the black tubing was for gas (not sure if that is the case as those kits are usually sold seperately).

I've not bought any tanks recently so I don't know if they are being sold with the hardware to run gas and glow fuels...

Anyone?

Thanks....
 

Thanks for all the great replies to my origional question guys. I tried using a piece of stiff tubing in the middle of the clunk line but found that it made things a little "too stiff". The clunk did not want to move freely. This might be attributed to the fact that the tank is not too huge, about 10 ounces. I would up (so far!) using a three line setup (with 2 clunks) and using standard blue silicone tubing on both clunks. They move freely around the rear of the tank area and I could not possibly get them to kink and go to the front part of the tank. It's sure something to keep an eye on after a crash or if the blue tubing gets more flexible under other conditions.

Gee whiz, it never did occur to me that the black tubing sometimes included with tank kits was for gasoline ONLY! Gulp, maybe I have used it.....

Thanks again,

Ernie

2 clunks
 

...... Also..... I am wondering how likely it is for my 2 clunks to get twisted around each other??? Doesn't seem likely so far.

Ernie

Clunk Line Question
 

I don't think that you will have a problem.

If it was too stiff with the method Minn posted, then it's probable that the stiff portion was too long. You only need a short portion of the stiff stuff to avoid the kinks and maintain the effect.

Don't worry about using the black stuff (even if it's for gas).
My understanding is that the black stuff is good for everything Gas / Smoke / Glow) but the regular silicon will get eaten by the gas / smoke fuels. (someone PLEASE correct me if that is not accurate).

I don't think you have done anything wrong. I've never run two clunks so that may just be an innovative solution. However, to me it seems like overkill and could cause some issues in the future (like twisting). Perhaps Minn knows a pro vs con against multiple clunks. Not my area of expertise. Anyway, the key is that you don't have a problem with the kinks. I would still try to find the "happy place" with the small portion of stiff tubing in the tank that allows freedom without the kinks.

It will help out in future models for sure. I don't think that dual clunks will be practical from here until the day that you stop flying.

Clunk Line Question
 

I don't think that dual clunks will be practical from here until the day that you stop flying.

I got the 2 clunk (three line setup) idea from the guys here. It seems to me that a 2nd clunk will actually drain the fuel better (at the end of the flying session) than bent tubing inside of the tank.... but maybe not. It sure was easier though than bending tubing and getting it as close to the bottom of the tank as possible.

Hmmm time will tell. Has anyone had a problem with a 2 clunk setup?

Ernie

Clunk Line Question
 

Like I said, if someone here gave you that advice then stick with it.

I've been out of the hobby for a while so a lot has changed. I would definitely not tell you to change anything as I'm still learning stuff everyday. That's why I thought it was an innovative idea. I don't have first hand knowledge of it and haven't read it here (yet). That's the only reason I thought it may have been overkill.

Don't worry about little ole me. :) I'm sure there are alot of things that I'm not correct about. That's why I like this place so much. I would wait for Minn or another poster to shed some light (as you are doing).

Good luck and let us all know if that setup is working for you. Heck I might even try it someday if the need arises.

Clunk Line Question
 

Hi Ernie Miser, I use the three line two clunk system on all my cowled glow engines,never had a problem,I use regular glow line in the tank with a piece of plastic drinking straw inserted over part of the line,it keeps the clunks from moving to the front of the tank.

Clunk Line Question
 

Ernie:

Two clunks are common on the three line system. Problems do not arise.

I have dual clunks in some planes too, but I am using them to feed two engines from a single tank. Had problems getting equal feed to both from a single clunk, twin engines, twin clunks, single tank.

Twin engines, double clunk. Without pumps it runs like junk.

Bill.

Clunk Line Question
 

Don't worry about little ole me. I'm sure there are alot of things that I'm not correct about. That's why I like this place so much. I would wait for Minn or another poster to shed some light (as you are doing).

You guys are great. I can't imagine another place in the world where we could share so much information. FunK, I do appreciate your input a lot. It does look like the two clunk lines will work great now, but you sure did get me to questioning it - and I even had a nightmare last night that they were getting tangled inside of the tank. It was awful.... they were tying themselves in knots and everything! It is this kind of questioning that gets us to take a close look at things in the building stage when it should be done.

A question for the two clunk guys..... Do you make both clunks equally long so they both sit at the rear of the tank?

Ernie

Clunk Line Question
 

Yes,I do it that way to remove as much fuel as possible from tank.

Clunk Line Question
 

Ernie:

I make the clunk line for the right engine a hair shorter than the one for the left. With conventional rotation a twin is easier to fly with the right engine dead than the other way around. So if I go dead engine I'd rather run the r/h engine dry first. But the tanks are big enough that I've not had to test the theory.

If you're running two clunks for defueling ease, do as John said; equal lengths.

Run your engines out of fuel, FAA says you're a fool.

Bill.