tryingagain

Hi all, I recently completed an older Falcon 56 kit. I have installed a Dubro 8 oz tank on its' side in the aircraft. One of the guys at the field is appalled and says it will cause problems. For the life of me I can't see what. Isn't the idea of a clunk tank that it will supply fuel no matter what its' orientation. I await your wisdom.

Cheers

Gord

DavidAgar

My Feedback: (108)

As long as the clunk is on the bottom and the vent is in the top of the tank, you should not have any problems with your set up. Good Luck, Dave

badger5964

My Feedback: (6)

No problems. I have done this twice with a 10 and 16 oz tanks. Flew like every other plane. I like an oversized tank so putting them on their side allows them to fit in a narrow fuselage.

RCKen

My Feedback: (9)

As was said above, as long as the clunk and vent line are properly installed the tank will work no matter how you place it. I've had several planes that I've mounted the tank on it's side, and they work flawlessly!!!

Ken

jaka

Hi!
He can't have been in this hobby long if he thinks mounting a tank on its side is something to be appalled about!!!
Just go ahead! As long as you mount the tank with the fuel pick-up tube to the bottom and vent at top ...it work just fine.

A tip!
Use two clunks (one to silencer pressure and one to carb ) that way you get a Uni-flow tank ...and you get a more even fuel flow to the carb.

tryingagain

Thanks guys,

The width was exactly why I did it. It fit beautifully on its' side but didn't have a chance the other way.

Cheers

Gord

Gray Beard

My Feedback: (-1)

Jaka, I don't get it, you have a pressure line going to the muffler already, are you also installing the third line with the clunck as a pressure line too?? I run the three line system and add a clunck too but that's my fill and drain line then I have the main line with a clunck to the carb and the third line is my pressure/over flow line that goes to the muffler.

JollyPopper

My Feedback: (6)

Gray Beard:

I'm guessing that what Jaka is doing is running a line from the muffler to a line with a clunk on it. The second line with clunk goes to the carburetor. The third line, vent, is simply open to the air or maybe has a line running to some place that is open but protected from dust, etc. That way, muffler pressure is introduced directly into the fuel because the clunk will keep the line submerged. With this setup, I guess the tank could be filled from the carb line or the muffler line. Just a guess. It could be all wrong.

JollyPopper

My Feedback: (6)

On second thought, wouldn't exhaust gas directly in the fuel cause bubbles? I'm confused.

Ed Smith

Jakka has described the "Uniflow" fuel tank. Except for the "Bubbleless" type tank the "Uniflow" is the best tank system for non pumped engines. Go here for the full explanation. of how it works.

http://www.fraserker.com/heli/uniflo...flow_works.htm

Ed S

Gray Beard

My Feedback: (-1)

I read it, I understand the thinking, just can't see it as a lot better then the normal three line system with the pressure being pushed in from the top. I will give it a try with one of my planes/tanks I have been having a problem with. I was going to go to a bubbless tank but I may as well see if this works for me or not.
Popper, if you have an open vent in your tank any pressure being pushed in would just flow right out the opened vent. My OS pumpers require an open vent because they suck the fuel from the tank. My YS engines require a closed system because they use positive pressure and pump about 7 or 8 pounds into the fuel tank, don't run fer beans without that pressure in there!!
As for bubbles from the pressure, the fuel would never notice it. You would get more bubbles from vibration and sloshing around durning flight. The anti foaming agents used in fuel these days seems to work pretty well.
Wish someone would put that in flight video of the fuel tank showing what happens during flight on a sticky!!! It's a real eye opener.
I will get my tank set up something this week and give it a try.

DGrant

My Feedback: (4)

You can't run any clunk line to your muffler with an open air vent... unless you want your fuel to siphon into your muffler and fill it up.. and run all over the table. That's the difference in the "uniflow" set-up, and a coventional 2-clunk set-up. With the uniflow you only vent the tank for fueling/defueling... other then that.. the vent stays closed.

Sandmann_AU

I understood the logic of how it worked when I first heard about it, but like you couldn't see how it would provide any real benefit, until I emailed someone who'd done a big write about it with my arguments and they explained it in a slightly different way which made sense. Imagine you have a barrel of water and a piece of garden hose. If you put the end of the garden hose into the first inch or two of the water and blow through it it'll be fairly easy to make bubbles but if you put it at the bottom of the barrel and blow it'll take a lot more effort, due to the air you're blowing pushing against the pressure of the water above the end of the hose. If you open a tap on the barrel and continue blowing it'll get easy as the barrel empties.

That same pressure is pushing fuel into the carb on your engine, but as it reduces due to the tank emptying the pressure from the exhaust has more impact which counters the reduction in impact of the fuel's inherent pressure. It's not about creating more pressure, but rather keeping the pressure constant so the mixture doesn't vary as much as the tank empties.

Having said that - I don't use uniflow systems as I like ezy-fill fittings (despite the popular opinion against them on here), and I really don't want to install a tank vent AND the filler. It's usually safer and easier (in my opinion) to have a larger than required tank and land with it still 1/3 full, which not only lessens the impact of reducing pressure but also gives you plenty of scope for aborted landings etc (albeit at the cost of a little extra wet weight). That way I land when I want to, not when I have to.

jaka

Hi!
The Uni-flow tank is like any other tank! You fill it as usual trough either the silencer clunk line...or through the fuel line that goes to the carb!
As you do you have the vent line open!
When you have filled the tank you close the vent line. Usually I use a 3mm screw for this. See picture below.

JollyPopper

My Feedback: (6)

and having the vent line closed and pressure going into the fluid does not cause bubbling?

Sandmann_AU

It will cause bubbles, of course, but to such a small degree as to be irrelevant compared to the frothing from the engine's vibrations. Think about it, the tank's a sealed unit so the exhaust can only pump gas into the tank at the same rate as it draws liquid out. You might get a small bubble every 10 seconds or so and unlike the frothy bubbles caused by vibration the exhaust's bubbles will be larger single bubbles which would just go straight to the surface and pop. Also, fuel's a very thin medium (unlike oil etc) so bubbles will be more likely to stay at the surface rather than staying in suspension. Because the fuel line has a clunk it's as far away from the bubbles as possible, and can only draw them when the fuel's so low that you should already be on the ground. It's a non-issue.

JollyPopper

My Feedback: (6)

I'm embarrassed. Of course the vent would have to be closed except when fueling up. What good would it do to put pressure in the tank if it had an open vent? Not the first time I ever said something stupid before I thought it through.