What Fuel tubing to use inside gas tank
 

Hi
I have just finished a Goldberg Super Chipmunk and a Evolution 61 engine flies it. The engine runs great. But at half tank I experience the engines dies after a nose down orientation. When i land i see air in the line and have to prime to start the engine again. The clunk in the tank tank does not fall down and follow the fuel, it is normal fuel tubing but it must be too stiff. So the clunk stays in the air when the plane dives. Is the clunk suppose to make a u and follow the fuel. Can any one recommend a solution, or a very flexable fuel tube i can use. I use a 12 oz fuel tank. Thank you for advice in advance.

RE: What Fuel tubing to use inside gas tank
 

jwfswart,

Use regular silicone fuel tubing and make the length just short of the rear of the tank with the clunk on. The problem your having is the clunk is getting hung up and can't come back to the bottom of the tank where the fuel is. This should solve your problem.

Gibbs

RE: What Fuel tubing to use inside gas tank
 

no the clunk should not make a u it should just satay at the rear of the tank and move freely side to side and top to bottom.the tubing should be flexible enough to allow the clink to rest on the bottom of the tank.it should be about 3/8 of an inch from the rear of the tank.

RE: What Fuel tubing to use inside gas tank
 

Here is a trick that might help you, take your tank out and hold it verticle so that the clund is at the bottom of the tank now hold it up to the light it should not touch the bottom of the tank if it does that your problem

RE: What Fuel tubing to use inside gas tank
 

I thank you for the responses.
The clunk can move freely left and right up and down. It is a 1/4 inc roughtly from the back when i hold it vertically hanging down.
BUT when i hold the tank vertically upsidedown the clunk rests against a side and with a half tank of gas will be out of the gas and then draw air. I am using regular fuel tubing. I was contimplating two pick ups, one in the back and one in the front. But with half a tank flying up the front pickup will suck air.
Any further advice.

RE: What Fuel tubing to use inside gas tank
 

All
I will also shorten the fuel tube a little more and test again.
Thank you.

RE: What Fuel tubing to use inside gas tank
 

Actually, a clunk is almost always moved around in the tank by more than 1g of force. So lot's of times, it'll go where the fuel goes and find it's way easier than it does when we're holding the tank in our hands looking at what 1g will do.

You're spot on about two pickups. You're just increasing the opportunity to draw air with two pickups. Air is easier to draw than fuel. It'll always be drawn first.

If the clunk is 1/4" from the back when the airplane is flying straight up, but is blocked by the end of the tank when the airplane is flying inverted, then the pickup line carrying that clunk is way off center. Use the tubing that sticks through the stopper to reach to the center of the tank. Do it with a short reach of tubing, but have the flexible line centered in the tank. Then the clunk will reach all around the back equally.

RE: What Fuel tubing to use inside gas tank
 

in flight the fuel seldom moves to the front of the tank while the plane is in motion.I would start looking for a pin hole in your engine feed line or simply replace it.acceleration keeps the fuel to the rear,when you start to dive the plane is accelrating and gravity is pulling at the fuel but they cancel each other out as long as the plane is in motion.

RE: What Fuel tubing to use inside gas tank
 

Fuel always moves to the front of the tank on a downline; rarely does a downline last more than a few seconds so check to see if your engine stays running after holding it down to a count of three or four. the engine keeps running on the residual fuel in the system. There is a video on RCU showing an externally mounted tank which proves this. Can't remember the post, it was earlier this year.

RE: What Fuel tubing to use inside gas tank
 

If your running out of fuel on the down line I would put a loop in your line from the tank to the Carb. that will give you more time on your down line without running out of fuel.That should fix the problem.

RE: What Fuel tubing to use inside gas tank
 

Thank you all very much for the excellent experienced information. I will use all of the advice and refit the fuel lines in the tank.

RE: What Fuel tubing to use inside gas tank
 

something else.... All the tanks I have had, the line inside going to the clunk is much thinner than regular fuel tubing, and a Lot more flexible. If you use regular tubing, it might be too stiff to hang down to the bottom of the tank when its horizontal. Try and find the thinnest (thin walls not inner diameter) tubing available and it should work better.

RE: What Fuel tubing to use inside gas tank
 

There are also clunks that can be bought separately that are MUCH heavier than the stock one that comes with the tank. Maybe your stock clunk just isn't heavy enough?

RE: What Fuel tubing to use inside gas tank
 

If it is too stiff then it isn't normal fuel tubing. What specific tubing are you using?

Just out of curiosity, how far inside the tank does the brass tubing on you clunk line go? It should only extend into the tank (past the stopper) about a half an inch or so.

RE: What Fuel tubing to use inside gas tank
 

No the fuel will stay in the back of the tank on a down line unless you have discovered a way to put the brakes on. Gravity lets everything fall at the same speed. In addition the prop is still pulling and adding to the pull of gravity.

However the clunk must go to the bottom of the tank and to the top of the tank when upside down.

Something else is wrong. Sounds a little like the clunk fell off or is stuck in the front of the tank.

Bill

RE: What Fuel tubing to use inside gas tank
 

Everything does not fall at the same speed due to gravity; drop a feather and a rock and see which drops faster.

RE: What Fuel tubing to use inside gas tank
 

scratchonly ,
"Everything does not fall at the same speed due to gravity; drop a feather and a rock and see which drops faster."

you were obviously asleep in physics class.a feather has resistance to the air a rock does not,in a vacum they will fall at the same rate.
the rock if it weighs more than the feather(mass)will have more energy than the feather

RE: What Fuel tubing to use inside gas tank
 

Correct!! The plane has air resistance and the fuel does not; glad to see we agree.

RE: What Fuel tubing to use inside gas tank
 

First of all who was complaining about to sti.... never mind

some tanks come with a softer and more flexable tubing for the clunk so if its a new tank stick with that otherwise time for a trip to the LHS...as if you needed an excuse!:D

RE: What Fuel tubing to use inside gas tank
 

I used normal fuel tubing and the bras tube extends about 3/4 inc. On my trainer from World Models the fuel tank tubing came with the tank and it was thin walled tubing. The clunk is moving freely from side to side up and down. But do not fall forward, gets propped up against the walls. Clunk is 1/4 inc from back.
Thanks for all the advice.