Uniflow Clunk-Tank question..

[Joe Yau]

Just wondering which one works the best?   To run a fixed tube in the middle of the tank on the outboard side (as shown below), or piggy back the uniflow tube on the fuel pick up about mid way in position of the tank.

Thanks in advance

[FLOYD CARTER]

Joe.  I've set them up both ways, and either one seems to work OK.  The problem with soldering the uniflow tube to the clunk is the two hoses reduce the flexibility of the clunk, unless it is very heavy!  If you can find some very flexible fuel hose, it might work.

Floyd

[Brett Buck]

Joe.  I've set them up both ways, and either one seems to work OK.  The problem with soldering the uniflow tube to the clunk is the two hoses reduce the flexibility of the clunk, unless it is very heavy!  If you can find some very flexible fuel hose, it might work.

   You need to use a loop of wire around the 'free" end of the uniflow to let it slide relative to the clunk, instead of soldering it directly to the clunk. Peter "Greasy Pete" Deane clued me in to that one, great idea.

  However, I much prefer the fixed uniflow as shown in the drawing. It permits you to control the effective tank height by monkeying with the position of the tube in the tank and greatly relieves the need to get the tank in exactly the right height. Just twist the tube in the stopper to move the vent up or down. The only problem is that it can tend to adjust itself if you manipulate the tank or the tubes very much. We used to make a little brass triangle with 3 holes in it and then solder the tube to the triangle to keep it from moving.

   Brett

[Joe Yau]

However, I much prefer the fixed uniflow as shown in the drawing. It permits you to control the effective tank height by monkeying with the position of the tube in the tank and greatly relieves the need to get the tank in exactly the right height. Just twist the tube in the stopper to move the vent up or down. The only problem is that it can tend to adjust itself if you manipulate the tank or the tubes very much. We used to make a little brass triangle with 3 holes in it and then solder the tube to the triangle to keep it from moving.

   Brett

   Brett

Just to get it in perspective..  the fuel pick up is always either at the bottom or the top of the tank, and never in the middle.  So, to adjust the uniflow tube as to compares to changing the tank's height..   by moving the uniflow tube closer towards (either more to the top or bottom) the pick up will increase the preasure which will make it run richer?   do I have this right?

[Tim Wescott]

Just to get it in perspective..  the fuel pick up is always either at the bottom or the top of the tank, and never in the middle.  So to adjust the uniflow tube as to compares to changing the tank's height.   By moving the uniflow tube closer towards the pick up will increase the preasure which will make it run richer?   do I have this right?

Moving the uniflow up with respect to the needle valve makes it richer -- with a uniflow tank the thing that dictates lean/rich is the amount of drop from the uniflow vent in the tank to the needle valve.  That's why it's "uniflow" -- the flow doesn't change as the amount of fuel in the tank drops.  In theory, if you kept the uniflow pickup in one spot with respect to the airframe, you could move the tank in, out, up, down, forward or back, and until the uniflow pickup was uncovered, the flow characteristics would remain the same.

[Joe Yau]

Moving the uniflow up with respect to the needle valve makes it richer -- with a uniflow tank the thing that dictates lean/rich is the amount of drop from the uniflow vent in the tank to the needle valve.  That's why it's "uniflow" -- the flow doesn't change as the amount of fuel in the tank drops.  In theory, if you kept the uniflow pickup in one spot with respect to the airframe, you could move the tank in, out, up, down, forward or back, and until the uniflow pickup was uncovered, the flow characteristics would remain the same.

Thanks Tim, that make sense. so its relative to the NV position.

[Robert Zambelli]

Joe - I have been running the uniflow tube exactly like you show it and the results are GREAT.
As such, I have have some of the best 4-stroke runs ever.

Bob Z.

[Joe Yau]

Thanks All for the replies. 

I will give the one in the drawing a try.. I like the fact that its easily adjustable.

[Bill Little]

Just to get it in perspective..  the fuel pick up is always either at the bottom or the top of the tank, and never in the middle.  So, to adjust the uniflow tube as to compares to changing the tank's height..   by moving the uniflow tube closer towards (either more to the top or bottom) the pick up will increase the preasure which will make it run richer?   do I have this right?

hi Joe,

I have thought about the clunk position "in the tank" during flight.  Seems the "C" fore that is in effect while in flight (centrifugal or centripetal ) will cause the pick up to migrate towards the middle of the outside of the tank like the fuel does.

Seems a real flexible pick up line could be more detrimental than helpful.

Brett, Howard, Ted, where are you guys?

Big Bear

[Dennis Moritz]

I've a uniflo clunk on a kit bashed Tanager, a tank fabricated by Dan Banjok. The stopper is turned so that the uniflo vent and pickup vent are centered. Dany filed a flat on the outboard side of the brass clunk which allows it to suck, in theory, near the last drop. The uniflo pickup is bound with copper wire and soldered to the inside of the clunk, about 3/8" back from the fuel pickup opening. (3/8" is one of those magic numbers we love in CL Stunt.) The tank works very well. Very consistent run and shut off. The flex tubing is pink silicon, curl angled out. Uniflo is hooked to muffler pressure. I use muffler pressure on all my tank hook ups. This provides, I believe, a stable venting. Exterior venting varies upwind and down etc.

[Bill Allen]

Joe: Along with positioning of the tubes is the clunk itself...I'm using the clunk offered by DU-BRO which is 2 grams (8G) heavier than the one supplied in the RST tank by Sullivan.  It makes a difference.        BILL ALLEN     

[Brett Buck]

I have thought about the clunk position "in the tank" during flight.  Seems the "C" fore that is in effect while in flight (centrifugal or centripetal ) will cause the pick up to migrate towards the middle of the outside of the tank like the fuel does.

Seems a real flexible pick up line could be more detrimental than helpful.

Brett, Howard, Ted, where are you guys?

  Hey big guy, I already posted in this thread!  If I understand the question, yes, the clunk will end up against the outside wall of the tank. It will almost always end up in one of the corners, top or bottom, because there's always a fair bit of acceleration up or down. In level flight, for instance. you have about 2.5 gs to the outside and 1 g down - so it's not just plastered flat against the outside wall. It gets pretty flat against the top and bottom in the maneuvers. A square corner is about 15 Gs so that makes is mostly at the bottom.

    Brett

[Bill Little]

  Hey big guy, I already posted in this thread!  If I understand the question, yes, the clunk will end up against the outside wall of the tank. It will almost always end up in one of the corners, top or bottom, because there's always a fair bit of acceleration up or down. In level flight, for instance. you have about 2.5 gs to the outside and 1 g down - so it's not just plastered flat against the outside wall. It gets pretty flat against the top and bottom in the maneuvers. A square corner is about 15 Gs so that makes is mostly at the bottom.

    Brett

LOL!!!!!!!!  I saw that post, but I wanted one of you guys to answer my "question".

Have you ever had a clunk flip to the front of the tank and get hung there?  It happened to me "once".  I had a long length of that really flexible "almost clear" silicone tuning.  Had to cure that......

Thanks!
Bill

[john e. holliday]

Yes,  I put a length of brass tubing in the line inside the tank.   This was when I few the twiddly stick stuff.