Fuel tank filling pipe

[Tony Read 2]

I've always fitted the tank filler pipe pointing up to the top of the tank, but is this necessary?

I have acquired a second hand model and it looks to be a bit of a pain to get to the clunk pipe to pump out any residue fuel after a flying session. It might not be always convenient to run the engine until the tank is empty, so I wondered if it would be a good idea to point the filler pipe down, possibly with a bit of flexible clunk tube on it. I could then connect my pump and remove the fuel.

The disadvantages that I can see are that the tank may syphon if the stopper comes out of the pipe and the clunk pipe could be twisted around the filler if I am not careful.

Anyone tried this?

[Peter Christy]

If you only have two pipes (filler and engine feed), I can see you having trouble *filling* the tank at all! Where will the displaced air go?

Many tanks use 3 pipes, with one often used for exhaust pressure. The clunk goes to the engine, but of the other two, one can indeed go to the bottom, as long as the other goes to the top to let the air out when filling the tank!

But if your clunk is not completely draining the tank, do you not risk running out of fuel in flight - even though there is still some left in there?

Sounds like you need to re-plumb your clunk!

--

Pete

[Jon Laughton]

Hi Tony

For quite a few years now I have set up all my fuel tank internal fail/unfill line the same as my fuel feed to the engine i.e. with a length of fuel tubing and a clunk. This means there are two clunks in the tank but I have never ever had a problem..

But note that all my tanks on two strokes are pressurised by a third line from the exhaust muffler

Hope this helps?

Jon

[Shaunie]

The way I read your post Tony is that there is nothing wrong with your feed pipe/clunk, just that it's difficult to access.

I see no problem with what you propose, providing that there is a third pipe for exhaust pressure (or venting). If you were to invert the pipe and extend it with some tube to the bottom of the tank it will do what you want. Yes it could siphon if the bung comes out, but how often has that ever happened to you? you'd be in trouble with a lean running engine anyway, regardless of fuel loss.

Don't think you need to bother with a clunk though, the plane is always upright on the ground when you de-fuel it, just cut the pipe accurately so it lays on the bottom of the tank at the lowest point.

Shaunie.

Edited By Shaunie on 01/08/2016 16:18:53

[Nigel R]

maybe too simple an idea, but turning the model upside down always worked for me...

[Shaunie]

There's always a Clever Dick in any forum .

Seriously though, not always practical with something large.

Shaunie.

[Jon Laughton]

Posted by Shaunie on 01/08/2016 16:16:21:

The way I read your post Tony is that there is nothing wrong with your feed pipe/clunk, just that it's difficult to access.

I see no problem with what you propose, providing that there is a third pipe for exhaust pressure (or venting). If you were to invert the pipe and extend it with some tube to the bottom of the tank it will do what you want. Yes it could siphon if the bung comes out, but how often has that ever happened to you? you'd be in trouble with a lean running engine anyway, regardless of fuel loss.

Don't think you need to bother with a clunk though, the plane is always upright on the ground when you de-fuel it, just cut the pipe accurately so it lays on the bottom of the tank at the lowest point.

Shaunie.

Edited By Shaunie on 01/08/2016 16:18:53

Shaunie is right you don't have to bother with a clunk but it does make sure you get the maximum fuel out of the tank as you can lift the nose to ensure the clunk is in the fuel.....not essential but a tad more effective

[Shaunie]

Aaah, but I've never got enough clunks for the tanks I have, let alone two for each.

I have one plane with this problem, I put a fuel dot in. Some people have had problems with air leaks but mine has been fine. I put a remote glow on the same plate, works really well.

shaunie.

[cymaz]

This may help....or not

[Tony Read 2]

Thanks guys. Forgot to mention that it is a three pipe system. Will try Jon's or Shaunie's solution.

[Tony Read 2]

BTW I serviced two of my models this weekend. When I took the fuel tank bungs out the bent brass pipes just crumbled in my hand! The straight ones were tarnished but fine. I empty the tanks at the end of every session, but I suspect that the fuel, when contaminated with residue from the exhaust pressure, still has time to react with the brass, especially where stress has been placed in the metal. Will try aluminium pipes and see what happens.

[Ace]

What has worked reliable (for me anyway) is to add a short length of fuel tubing to the upturned breather so it just reaches the top, DON'T forget cut a V in the end so it can't vacuum stick as you draw off fuel. Bonus is you get a full tank every time. Do the same for the down turned fill pipe to the bottom and by tipping your plane slightly forward on its wheels all fuel will be pumped out. Ace

Edited By Ace on 02/08/2016 14:32:37

Edited By Ace on 02/08/2016 14:33:59

[Keith Evans 3]

I tend to use SLEC tanks where there is no internal plumbing apart from the fuel feed line and clunk .Both the exhaust and filler vents are right at the top front face of the tank . Holding the plane vertical gets all the fuel out with no problems .There are no large bungs and extra pipe work to contend with .

[Steve Hargreaves - Moderator]

I'm a two clunk man myself......one on the feed pipe & one on the filler with the third pipe to the muffler......drain through the filler (IYSWIM) & then run the engine until it stops from lack of fuel.....a few drops of after run & Roberts yer mums brother.

[Shaunie]

Of course with a SLEC tank you can block one of the top pipes and drill out the blanked fitting at the bottom that is intended for a level pipe and use that for a fill/drain.

Shaunie.