Tank Adjustment for Plastic Tanks with Uniflow Setup

[JHildreth]

What is the proper adjustment direction of the uniflow tube for a plastic tank?  I have searched this site, unsuccessfully, for an answer to this question.  The typical comment is to turn the uniflow tube to adjust.  That is O.K., but which direction?

I am flying and ARF SV-11, and I am experiencing the engine going lean inverted.  The tank is a Sullivan 8 oz rectangular (not a slant tank).  The uniflow setup is like has been discussed in previous topics, but I could not find any statements on the direction to move the end of the uniflow vent to correct differences in engine run, upright vs inverted.

The normal tank adjustment when physically moving the tank is to shim the tank farther away from the engine bearers if the engine goes lean inverted.  If you don't physically move the plastic tank, do you move the end of the uniflow vent in the tank the same direction you would shim the tank?  Specifically, should I turn the end of the uniflow vent away from the engine bearers to correct the engine going lean inverted?

Joe

[Dan McEntee]

  I think it's best to shim the tank as if it were a metal tank, just as you describe. But if  f or some reason you can't do this, rotate the cork/stopper in the same direction, and about the same amount you needed to shim the tank. I hope this helps.
  Type at you later,
  Dan McEntee

[pmackenzie]

You move the uniflow vent in the same direction you would have moved the whole tank.

[JHildreth]

Thanks for the replies.

Joe

[BillLee]

If you think about it, moving the whole tank is the same as moving the uniflow vent: the "point of regulation" (i.e., the end of the uniflow vent inside the tank) is changing position relative to the engine. That's what you want to have happen.

[John Lindberg]

John Miller  (I believe it was John Miller) had a diagram for a plastic tank on the now defunct "Stuka Stunt", he separated the uniflow tube from the pick-up tube, and then rotated just the uniflow tube for adjustments, I tried this, it works with the Sullivan 8 ounce plastic tank! 

[Tim Wescott]

If you think about it, moving the whole tank is the same as moving the uniflow vent: the "point of regulation" (i.e., the end of the uniflow vent inside the tank) is changing position relative to the engine. That's what you want to have happen.

That.

John Miller  (I believe it was John Miller) had a diagram for a plastic tank on the now defunct "Stuka Stunt", he separated the uniflow tube from the pick-up tube, and then rotated just the uniflow tube for adjustments, I tried this, it works with the Sullivan 8 ounce plastic tank! 

On metal tanks at least, I find that a fixed uniflow with an "ordinary" clunk works great.  Just be careful that the clunk doesn't get tangled in the uniflow.

[EricV]

Yes to all the above. Its been a while but I always used to hard plumb the uniflow in clunk tanks, and swedge the copper to hug the outer wall and stop it well short of the clunk pickup, so it becomes impossible for the clunk to hit the uniflo. Uniflow doesn't need to go all the way back, your fuel isn't there in flight most of the run anyway, at least not if the plane is trimmed right  Moving the uniflow up or down changes the apparent tank height to the engine, but I prefer to shim the tank, or on profiles just silicone the tank to piece of thin ply, with slots on the ends for mounting screws and adjust the tank up or down that way. Much easier than trying to mess with the stopper or tubing, since they swell up. Another trick is to replace the stock Philips screw with a hex head self tapping screw from Microfasteners, so you can use a ball driver at an angle instead of trying to get a Philips in there between the tubing, makes life a fair bit easier. Hope that helps.
EricV

[John Miller]

I would have been here sooner, but I had to search for the drawing of the RC uniflow clunk tank.

I've used this system in every installation, except one since the mid-late eighties. That was when Allen Brickhause showed, and explained to me, his use of RC tanks converted to uniflow CL use.

Over time, I've made a few small improvements, but, this is pretty well what Allen explained to me.

It works, and works very well. You do not have to rotate the stopper. Just loosen it a little, if it's too tight and won't move, then, rotate the uniflow only.

You should not tie, or connect the uniflow and pickup together because when they move together, it changes the positional relationship of the uniflow in the tank. This can "mess up" the apparent tank height when the clunk moves.

Having the uniflow located as shown works, as also testified in others experience. Rotating the end inside the tank does change the apparent center of the tank, and moving it up or down, will change the quality of the engine run, upright and inverted. The tank can be mounted solidly in the fuse, or on the side of a profile, and it will work fine.

The illustration shows how to set the tank up, and I hope it is clear to all who study it.

Cheers, John Miller

[John Skukalek]

Thanks for the illustration John. I have a question. In the Top View, the pick up line appears to be inboard of the other 2 lines where they pass through the stopper. If the other view is from the front, the pick up doesn't appear to be in that position?  Or am I looking at it wrong? 

[John Miller]

Hi John,

What you're looking at in the illustration, is a straight orthographic projection. It might be better realized if it was turned 90 degrees with the front view on the bottom, and the top view above.

That being as it is, look closely at the front view. The tubes are arranged in a triangle shape, as allowed by the RC tank stopper. The widest sides are the top and bottom of the tank. Mentally rotate the illustration so the tank is oriented with the wide side on the bottom.

Now, notice that the Uniflow line is at your left corner of the triangle. Looking down at the top view. you'll see that the uniflow line goes to about the middle of the tank,  Back to the front view. Move your eye over to the other bottom, or triangle base corner. This is where the fuel pickup line, the clunk line is arranged.

Note, that unlike the uniflow line, which has a rather large bend to direct the uniflow end to the side of the tank, the pickup line has a much smaller bend that lines the pickup to the outside corner. I like to use a sintered bronze clunk, rather than the chromed brass one that comes with the tank. I've been using this style of clunk for a long time without any problems. I also draw my fuel, through a sintered bronze filter in the fuel jug, and having a second one in the tank, acting as a clunk, has kept me from crud problems for years. I highly recommend you consider doing this also.

The overflow line is at the top or peak of the triangle. Take the time to bend this tube so it winds up close to the top inner corner as shown.

It's not necessary to really torque down on the screw that expands the stopper to seal it in place. Just make sure it's sealed. I've found, that it's often the case, that with a little effort you can adjust the uniflow without having to loosen up the center screw.

I use muffler pressure with my tanks set up this way without problems.

Best of luck with your new tank

John Miller

[John Skukalek]

Got it! Thanks for patiently explaining it John.

[John Miller]

Happy to be of help.

Best luck with your tank.

John Miller

[John Skukalek]

John, this set up is working great on my 40 size(Brodak) profile. I have a "fine tuning" question. On a profile, does it make a difference how the end of the uniflow line is oriented outside of the tank? Should it be in or out of the air stream? Thanks again.

[John Miller]

John, this set up is working great on my 40 size(Brodak) profile. I have a "fine tuning" question. On a profile, does it make a difference how the end of the uniflow line is oriented outside of the tank? Should it be in or out of the air stream? Thanks again.

John, I'm happy to hear that the tank is working well for you. I do believe it does make a difference in how the uniflow end is related to the passing airstream. At 90 degrees, to pointing so that the end is downstream from the airflow, you can get negative, air pressure (suction). Directing the uniflow end into the incoming air results in positive pressure, but the pressure varies with the airspeed, which could vary the engine speed when you may not want it to. I've connected muffler pressure to the uniflow for years with this setup, and have enjoyed consistent runs by doing so. Some shield the uiniflo0w end so it's out of the airflow with decent success, and maybe something to try if you can not make other solutions work for you.

Best wishes, John Miller

[Ken Culbertson]

I would have been here sooner, but I had to search for the drawing of the RC uniflow clunk tank.

I too have used this setup exclusively since the square plastic clunk tank was introduced.  Before that I ran brass "clank" tanks but that is a different story.  It has worked great except for one OSLA46 that absolutely refused to run on uniflow.  I flipped the muffler pressure to the overflow vent and capped the uniflow -  shazam, perfect runs.  Since I always install tanks at least 1oz larger and measure fuel this kept the fuel away from the overflow when setting the NV.  Easier to add an extra 1/2oz than screw with the venturi when the weather wants to shut you down in the clover at a contest.

One thing I did on profiles was to mark the position of the Uniflow on the tank.  I had to fill mine through the muffler pressure hose connected to the uniflow and it was too easy to move it if you weren't careful.  Served me well for a long time until one day a few years back I was visited by the Energizer Bunny.

Ken

[Frank Donnelly]

John,
Thanks for the illustration and the additional clarification. I do have one question. I can see the position of the end of the uniflow line inside the tank with respect to the sides, front and back. What about the elevation? Should you start at the center and move it up and down as needed?
Thanks,
Frank

[John Miller]

John,
Thanks for the illustration and the additional clarification. I do have one question. I can see the position of the end of the uniflow line inside the tank with respect to the sides, front and back. What about the elevation? Should you start at the center and move it up and down as needed?
Thanks,
Frank

Frank, you've got the right idea. Centered usually eventually requires the internal end of the uniflow to be raised slightly. the first flights will get the location as you adjust.

Best wishes, John Miller