Author Topic: Plastic clunk tank uniflow set up (Read 5026 times)

Brian Hampton · « **Reply #50 on:** December 06, 2023, 01:10:31 PM »

Quote from: John Skukalek on December 06, 2023, 09:02:20 AM

When I rotate the uniflow line from outside the tank, it moves the fixed uniflow line inside the tank up or down because its a hard line bent so that the end is close to the tank wall about half way back. This changes the effective height of the tank without moving the tank or rotating the tank cap. Very convenient. this is on profile stunters.

That's almost exactly the way I do it too. Only real difference is that I run the solid uniflow line to roughly 1/2" back from the clunk and pack the tank so the rear is maybe about 1/4" further outboard than the front of the tank. That keeps the uniflow action working until the last dregs of fuel uncover the uniflow giving about the last lap or so of a somewhat leaner warning that the engine is about to quit. Outside the stopper I bend the end of the uniflow line for some leverage to turn it up or down inside the stopper. This is with full fuselage stunters.

Steve Dwyer · « **Reply #51 on:** December 07, 2023, 12:12:42 PM »

To fully understand your question: Please confirm: You are basically using 2 clunks .. One for feed and 1 for uniflow. Those clunks are connected so the uniflow follows the feed and vice versa.

Paul,

I'm using a single very flexible line to the one and only clunk pick up. To elaborate, the line must travel evenly along the rear outer edge of the tank as close as possible without contacting the rear of the tank when holding the model upright and inverted. The vent is a hard brass tube with a small piece of flex tube on the end. This vent is positioned at the midpoint of the tank outer wall looking from front to rear and top to bottom. The actual contact point of the vent is visible from outside of the tank and is verified by marking a reference line on the tank. The overflow is in contact with the top front of the tank also with a small piece of flex tube cut at an angle. Everything is configured as shown in the sketch above.

Steve

Steve Dwyer · « **Reply #52 on:** December 07, 2023, 01:25:26 PM »

Is it possible that this imaginary force in the equation that you believe in, is a misunderstanding coming from those using a clunk tank with a single clunk for pickup and a stiff inflow tube? with those, you can raise/lower the end of inflow tube end by turning the rubber cap and have some sort of adjustment for level/inverted speed. I've never tried it, maybe it works. The whole issue is somehow uncertain and un-elegant for me, so I believe in symmetry. Less surprises that way. L

Lauri,

There's nothing IMAGINARY here, the external end of the uniflow vent line exiting the tank that is positioned in a forward direction on the front inside of the model (most laminar area) acts similar to a pitot tube. The open end of the tube sees Total Pressure which is comprised of Static and Dynamic Pressure. Internally the head of the liquid and partial vacuum above is countered or affected by the dynamic pressure. When you add muffler pressure eliminating the external opening to the tank the system pressure simply increases while in both cases a constant flow (at a different rate) exits the tank.

Changing the vertical position of the vent inlet or what some like to call changing the "effective" height of the liquid changes very slightly the pressure at the spray bar having a change on engine run. Additionally rotating the cap while holding the vent at its same reference position (mark on the exterior of the tank) also changes the exit pressure to the spray bar by changing the fluid head also changing the engine run. That's what I believe!

Steve

Lauri Malila · « **Reply #53 on:** December 07, 2023, 11:29:59 PM »

Steve,

I (think) I understand your logic, and I have made the same mistake myself, imagining interactions where there is not, and missing the real one(s). I wasted lots of time moving the remote valve around, just to find out that it does not matter.
But in this kind of experimental work also no result is a result, you have to walk that road.
Where the fuel line goes between pick-up point and spraybar, does not matter. Also the inflow vent inlet, it is filled with air so there is not much of a fuel head to talk about. L

Ken Culbertson · « **Reply #54 on:** December 08, 2023, 07:22:56 AM »

I have never been able to make uniflow work but now I understand why and if I ever fly IC again I will use it like explained here. Thanks for the in-depth discussion.

But, now that we have solved another one of life's mysteries, can you gentlemen explain to me why an oversized (never full) non uniflow clunk with muffler pressure outside of the fuel produces a perfect run? The pickup in the tank is almost never in line with the spray bar.

Ken

Dennis Toth · « **Reply #55 on:** December 08, 2023, 07:54:01 AM »

Ken,
The short answer is luck! A more detail might be that the tank is not very wide (like the old original Nobler tank) and the engine is choked down a bit (like using an oversize spraybar) with just the right prop load that leans just a bit as it gets near the end of the run. Lots of stunt flyers won many contests with conventional vented tanks adding the muffler pressure adds a little more push at the beginning of the flight and less as the tank gets full of air and this is possibly off set by the fuel head decreasing as the flight goes on.

Some flyers just liked to have the slightly leaner run as they got to the more power demanding maneuvers at the back part of the pattern. There were tank designs that had the vent lines positioned to uncover after 1/2 to 3/4 of the fuel was drawn out. Lots of ways to plumb these things if you want to spend the time to play and adjust. Uniflow is just a straightforward way for most 2 strokes. 4 Strokes are a different story as they like the conventional venting with muffler pressure for sure.

Best, DennisT

Lauri Malila · « **Reply #56 on:** December 08, 2023, 08:50:28 AM »

Question; why do 4-strokes like more "conventional" venting? I would imagine that same rules apply, you want consistent fuel supply through the flight. The need to make it leaner towards the end of flight sounds like from the time before trimming was invented.
Another point is to recognise what actually is happening during the flight. It is true that Inflow has often a small tendency to get a little richer towards the end, but it's nothing so dramatic that couldn't be fixed with fine-tuning the plumbing and lateral placement of tank.
A problem we see more often is richening due to insufficient thermal insulation of fuel tank.
Another thing that is basically never discussed here, is the lateral placement of tank for correct power management. especially with classic 2-strokes, it is an absolutely essential trimming tool, especially if you want to be competitive against other powerplants. That is, to use only the necessary amount of power in an intelligent way. L

Steve Dwyer · « **Reply #57 on:** December 08, 2023, 09:48:45 AM »

Uniflow tanks in my opinion offer many more benefits than metal. Supplying fuel through a tiny spray bar eductor from an adjacent tank being subjected to a number of forces is a wonder we can get a consistent engine run. It's time for me to go back to the field and verify some thoughts and try some ideas brought out here. Unfortunately the weather here in upstate NY is not cooperating. For anyone coming away from all this, thinking negatively about using UF I'd urge you to reconsider. They are an achievement and benefit to CL modeling.

Steve

Colin McRae · « **Reply #58 on:** December 08, 2023, 10:10:17 AM »

Quote from: Steve Dwyer on December 08, 2023, 09:48:45 AM

Uniflow tanks in my opinion offer many more benefits than metal. Supplying fuel through a tiny spray bar eductor from an adjacent tank being subjected to a number of forces is a wonder we can get a consistent engine run. It's time for me to go back to the field and verify some thoughts and try some ideas brought out here. Unfortunately the weather here in upstate NY is not cooperating. For anyone coming away from all this, thinking negatively about using UF I'd urge you to reconsider. They are an achievement and benefit to CL modeling.

Steve

All of the metal tanks I use are uniflow designed tanks I got from Brodak. I have used both their oval profile and wide wedge uniflow tanks. Once I obtain the correct tank height relative to the spray bar, I get consistent engine runs and equal lap times when inverted.

Brodak makes metal tanks in both standard vent and uniflow designs.

Brett Buck · « **Reply #59 on:** December 08, 2023, 12:04:06 PM »

Quote from: Steve Dwyer on December 08, 2023, 09:48:45 AM

Uniflow tanks in my opinion offer many more benefits than metal. Supplying fuel through a tiny spray bar eductor from an adjacent tank being subjected to a number of forces is a wonder we can get a consistent engine run. It's time for me to go back to the field and verify some thoughts and try some ideas brought out here. Unfortunately the weather here in upstate NY is not cooperating. For anyone coming away from all this, thinking negatively about using UF I'd urge you to reconsider. They are an achievement and benefit to CL modeling.

Almost everyone in competition uses metal or carbon fiber uniflow tanks either with pipe pressure or open (and some of us switch from open to pressure depending on the conditions). Most of them are conventional wedge shape. Those who do not , use clunk tanks of various materials, usually uniflow. During the brief second "4-stroke revolution" I made a lot of people metal clunk tanks - clunk because 4-strokes seem to need them (it is nearly miraculous how much better it is), and metal to make them fit in the airplane.

I am not sure what distinctions you are attempting to make between metal and uniflow, the material it is made from makes absolutely no difference. It is a useful adjustment to be able to switch between the four combinations - open/uniflow, open/suction, pressure/uniflow, and pressure/suction depending on what the engine needs in particular conditions. My system was long set up to be able to change between any of these "on the fly" with just changing where the external soft tubes go, and I have switched between various versions seconds before a flight.

Brett

Steve Dwyer · « **Reply #60 on:** December 08, 2023, 12:30:51 PM »

Quote from: Colin McRae on December 08, 2023, 10:10:17 AM

All of the metal tanks I use are uniflow designed tanks I got from Brodak. I have used both their oval profile and wide wedge uniflow tanks. Once I obtain the correct tank height relative to the spray bar, I get consistent engine runs and equal lap times when inverted.

Brodak makes metal tanks in both standard vent and uniflow designs.

Colin, I have both metal uniflow and straight vented wedge, oval and square tanks from Brodak. Various tanks are on profiles and full fuse models. I too have had good metal tank engine runs with and without ending lean outs. The benefits I see with clear plastic stoppered tanks is the ability to clean the tanks, no chance of corrosion, leaking solder and seeing that all the fuel has emptied before putting the model away. There's no argument here worth attempting to delve into, most all style tanks work if installed correctly. Everyone has there personal preference. Amen.

Paul Van Dort · « **Reply #61 on:** December 11, 2023, 07:39:48 AM »

Quote from: Brett Buck on December 08, 2023, 12:04:06 PM

Almost everyone in competition uses metal or carbon fiber uniflow tanks either with pipe pressure or open (and some of us switch from open to pressure depending on the conditions). Most of them are conventional wedge shape. Those who do not , use clunk tanks of various materials, usually uniflow. During the brief second "4-stroke revolution" I made a lot of people metal clunk tanks - clunk because 4-strokes seem to need them (it is nearly miraculous how much better it is), and metal to make them fit in the airplane.

I think that the fact that in 4 stokes, the mixture enters the combustion directly, leaves no room for a short interrupted fuel supply. In 2 strokes, the mixture passes the engine's carter, acting as a buffer. Small fuel interrupts are not having a big effect on the engine as compared to 4 strokes. Just my 2 cent. I cannot prove it :-)

Steve Dwyer · « **Reply #62 on:** December 12, 2023, 08:08:08 AM »

Paul,

Interesting, I'm sure some of the engine gurus here could easily respond to your question. I'd suspect if the fuel is flashing vs entering the combustion chamber as more a liquid/air mixture impacts the engine performance (lean vs rich). 4 vs 2 strokes I have no idea.

Steve

Colin McRae · « **Reply #63 on:** December 12, 2023, 08:53:26 AM »

I have a real-world example.

My Vector 40 with OS 46LA had a metal 4 oz wide wedge uniflow tank. I was not getting equal lap times when inverted. I could not raise the tank inside the fuselage as the tank was already up against the wood motor mounts.

So as an experiment I in installed a Sullivan 4 oz rectangular flex tank. (The flex tank material allowed me to get the tank inside the tight space.) I made up the tank tubing pretty much exactly as the pdf shows at the beginning of this post. I adjusted the uniflow vent exit in the tank approx 1/4" higher than the engine spray bar.

Low and behold now equal lap times. Success, I guess.

Steve Dwyer · « **Reply #64 on:** December 12, 2023, 09:28:06 AM »

Yup that's how a uniflow tank vent works. Now if you can raise and lower the flex tank within the space you will see a run change as well. OR to the point we went around earlier here for hours, if you rotated the tank cap changing the height position of the fuel outlet relative to the spray bar AND repositioned the vent to the same exact position it was before you rotated the cap you will also see a change in the engine run. It's been from my experience this works as well. But to the point of others it easier to move the vent position than rotating the cap and playing with the cap screw.

Steve

Colin McRae · « **Reply #65 on:** December 12, 2023, 11:15:26 AM »

Quote from: Steve Dwyer on December 12, 2023, 09:28:06 AM

Yup that's how a uniflow tank vent works. Now if you can raise and lower the flex tank within the space you will see a run change as well. OR to the point we went around earlier here for hours, if you rotated the tank cap changing the height position of the fuel outlet relative to the spray bar AND repositioned the vent to the same exact position it was before you rotated the cap you will also see a change in the engine run. It's been from my experience this works as well. But to the point of others it easier to move the vent position than rotating the cap and playing with the cap screw.

Steve

On my Vector, can't move the tank around as the Vector has a relatively small tank bay. But the 4 oz Sullivan flex tank just fits in. But I don't need to move it as the UF vent 1/4" above the spray bar fixed my original inverted lap time issue.

And I built the UF tube with a short 90 deg turn just outside the stopper (just like the pdf shows). I can easily move the UF vent outlet height inside the tank by rotating the UF tube itself from the outside. I do not need to rotate the stopper.

Steve Dwyer · « **Reply #66 on:** December 12, 2023, 02:49:14 PM »

Understand, I have read some guys have actually soldered a small tab on the vent outlet making rotation easier. And it acts as a good reference tab for the vent position when you cant easily see inside the tank as in your case in the Vector.

Colin McRae · « **Reply #67 on:** December 12, 2023, 06:37:02 PM »

Quote from: Steve Dwyer on December 12, 2023, 02:49:14 PM

Understand, I have read some guys have actually soldered a small tab on the vent outlet making rotation easier. And it acts as a good reference tab for the vent position when you cant easily see inside the tank as in your case in the Vector.

I guess I was a bit lucky. The Sullivan flex tank material is somewhat clear so easy to see where the vent is located. I initially set my UF vent outlet at 1/4" above the engine spray bar. And I got the inverted lap time issue resolved. No further need to adjust.

Author Topic: Plastic clunk tank uniflow set up (Read 5026 times)

Brian Hampton

Re: Plastic clunk tank uniflow set up

Steve Dwyer

Re: Plastic clunk tank uniflow set up

Steve Dwyer

Re: Plastic clunk tank uniflow set up

Lauri Malila

Re: Plastic clunk tank uniflow set up

Ken Culbertson

Re: Plastic clunk tank uniflow set up

Dennis Toth

Re: Plastic clunk tank uniflow set up

Lauri Malila

Re: Plastic clunk tank uniflow set up

Steve Dwyer

Re: Plastic clunk tank uniflow set up

Colin McRae

Re: Plastic clunk tank uniflow set up

Brett Buck

Re: Plastic clunk tank uniflow set up

Steve Dwyer

Re: Plastic clunk tank uniflow set up

Paul Van Dort

Re: Plastic clunk tank uniflow set up

Steve Dwyer

Re: Plastic clunk tank uniflow set up

Colin McRae

Re: Plastic clunk tank uniflow set up

Steve Dwyer

Re: Plastic clunk tank uniflow set up

Colin McRae

Re: Plastic clunk tank uniflow set up

Steve Dwyer

Re: Plastic clunk tank uniflow set up

Colin McRae

Re: Plastic clunk tank uniflow set up