air in fuel line of glow engine

by rick
(urbana)

For some reason I keep getting air in the fuel line of my RC plane's glow engine. Unfortunately this always leads to a dead stick landing or worse, a crash!

I just don't get it. I have changed all fuel lines, tubes, the top part that supports fuel tubes and I'm still getting air into the inlet fuel line.

Can you please help before I crash this thing?

Thank you

Matt's Reply: No, don't crash!

Hi Rick,

Unfortunately I can't keep ya from crashing the thing, but may be able to help you figure out this air problem of yours.
RC airplane fuel tank clunk

Take a look at the image below. Make sure the exhaust line is but upwards like in the picture. I am sure you have check this already, but I just want to cover all the bases.

Vibration can also cause the fuel to foam leading to air in the fuel line. Make sure the tank is wrapped in foam if you have the room. Also make sure the prop is balanced to prevent excessive vibrations.

I have heard of people adding a drop or two of Armor oil to prevent fuel from foaming. But I believe most fuels these days already have additives to help minimize the foaming.

You may also have a pin hole in the tank or the new tubing and fuel line. It's rare, but you could have a hole in the new tubing and lines you just installed. It's good to check everything.

A good way to test is to fill your sink or a bucket with water. Submerge the entire tank and fuel lines under the water. Pinch the exhaust tubing closed and blow into the fuel line and watch for air bubbles (or vise versa).

Please let us know what you find!

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air in fuel line of glow engine

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air in fuel line
by: rick

Thanks Matt for comment.

Does the fuel tubes have to be aluminum? The fuel lines on my RC plane are brass. I did perform the leak test and the tank passed this test with flying colors.

Although I do have an old 60 size Towers Hobbies trainer. The tank fit is so tight that it is impossible to wrap foam around it unless I do some serious restructuring.

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aluminum or brass, doesn't matter.
by: Matt

It doesn't really matter if it's brass or aluminum, as long as it's air tight.

Is the air in the line before or after the high speed needle?

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air in fuel line
by: Anonymous

My airplane's engine is about 7or 8 years old. It has one line to the needle valve and one line two the exhaust.

When I took the tank out of airplane I'm wondering if the fuel line that is inside the tank slipped or was pulled by the clunk part, and hitting back part of tank.

I'll find out tomorrow when I check it out. It rained all day yesterday and today. But anyway, the air bubbles that I noticed were visible before the needle valve. I couldn't tell if they were before the inline filter.

The day I was flying the plane it shut down 3 different times all in mid flight. I would really like to find the cause.

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filled tank?
by: Anonymous

Are you filling the tank until gas comes out the xaut line? Make sure you are filling the tank to push all the air out

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