Clink yer Clunk

[John Carrodus]

Am losing the will to live messing with metal tanks and their raft of associated problems- rusting, leaking, is it uniflow?, suck?, crud and snot floating inside etc etc. So, converting my profiles to RC clunk tanks set up as uniflow. Baba-ding! Most problems gone. BUT..........My friend was flying one of my hack profiles, had flown a lazy8 and was inverted climbing out at the top...splutterpop-dead. Lines went soft and model stalled in with resulting tail and wingtip damage. ( Would have been nasty , however we fly over the green stuff in NZ )
Moral - check yer clunk clinks! During fueling, the feed line clunk bulb had been pushed against the rear wall and jambed solid. A good reminder. I know this is mentioned elsewhere, but worth repeating here again as a caution with using clunk tanks. ( I can hear the metal guys saying, 'That wouldn't have happened with tin plate and copper tubing!")

[De Hill]

Did you refuel by injecting fuel into the feed line?

[John Carrodus]

Presactly Dee. That's why there is a blob of white glue glue now on the fuel feed copper tube to stop it moving backwards again. ( The origin of the white glue is another interesting story )

[Dennis Toth]

Good point, most of the time when this happens its either from a rough landing where the nose goes in and flips the ship while it's still at a good forward speed or when the ship is carried nose down. If the tubing is that flexible it is a good clunk but you need to check before a flight as you suggested.

Best,    DennisT

[kevin king]

That wouldnt have happened with a metal tank! 😁

[aj bagg]

I agree, metal tanks are not worth the hassle. I've achieved my best runs using round clunk tanks. Over the years I've found several set up details that improve the clunk tank performance.

Rework the clunk. The hose barb on the Sullivan brand I use is to large in diameter and to sharp. The flexible tube will develop a hole at the junction of it and the barb in a short year or two, reworked they are trouble free for twenty years or more. Solder in a short piece of tubing to neck it down and carefully round the end to fix this.

Do not use the wire hose clamps. Instead make sure your cut off on the flexible tube is square and that the flexible tube is pushed on the fittings all the way.

Use the plastic tube! it is lighter and cleaner than the brass but the main benefit is the internals are more accurate. The plastic will distort during tank assembly then spring into position after it's rubber mount is seated. This spring action also allows all three holes in the tank to be used... the third being a vent line that allows filling the tank with the plane sitting flat and not having to hold the plane in some awkward position to achieve a fill. I set up the with a pickup line, a uniflow line to the "bubble" in the tank, and the third a vent to the forward top corner of the tank. Filling is accomplished with the fuel being injected properly on the far side of the fuel filter. To fill park the plane on the stooge, pull the third vent line cap off ( I use a piece if tube instead of a cap and simply have this tube stuck onto a blind standoff which I just pull the line off before fill and back on after filling.)Then fill into the uniflow line. The fuel supply line should be clamped during the fill. either have a set of hemostats handy, like attached to the glow driver so when done filling and ready to start you remove the hemostat and your glow driver is already there. This saves losing the hemostat also! OR you can just leave a small loop in the fuel line that can be easily grabbed and pinched kinking off the fuel line during the fill.

After the flight when you pick up your plane as you pick it up, hold it nose up vertical and "rattle" the clunk so you can hear the clunk banging the sides of the tank. This is a good habit that assures the clunk is in the proper position for the next run.

Store your aircraft hanging vertically. I hang mine by the tightening hole in the spinner. Hanging in this manner assures the fuel line and clunk does not take on a memory of being in an improper position.

If possible recess your tank into the fuselage on profiles. This makes for a more consistant run. The "demand" point for fuel is the orifice in the spray bar. The "supply" is the hole in the clunk. The relative position of the "demand" to the "supply" as it relates to the flying circle radius is important for consistant run through the flight. This relationship determines if the fuel will flow downhill or have to be pumped back uphill. I try to keep the "supply" less than an inch outside the "demand"

Have fun!
AJ

[aj bagg]

I should have added that for perfect bends in the plastic lines, slide weed eater string or a wd40 straw into the plastic and heat with a heat gun to bend. then pull out when cool.

[Brett Buck]

Am losing the will to live messing with metal tanks and their raft of associated problems- rusting, leaking, is it uniflow?, suck?, crud and snot floating inside etc etc.

   I have no problem with you using what you want, but - if you can't get conventional tanks to work, there's something else wrong, too. I presume you are referring to commercial pre-made metal tanks?  If so, yes, you might have a lot of problems. But most people make or buy their own tanks designed to their requirements.

   The big issue with clunk tanks is the cutoff. A proper tank will run with *no* change in the run until it is completely out of fuel unless you are maneuvering, and will make it through a 4-leaf without going lean with 2-3 laps of fuel, or be able to be cut off 2 laps early to set up your landing approach. I have never found any easy way to ensure that with a clunk tank and they are notoriously difficult to cut off - usually you start getting funnies in the maneuvers as early as the hourglass, then an extended period of speed up and slow down as the fuel sloshes back and forth.

     If you are having problems with tanks, we can certainly help you address them.

    Brett

[Dave Harmon]

Well said Brett.
With all the disparaging comments regarding metal tanks I was sitting on my hands for a couple of days to be sure I calmed down a bit and didn't say something nasty.

I have never had any problems with a metal tank that was properly assembled and soldered.
This is the reason I get the Brodak wide Uniflow tank kits and assemble them myself.
I have a slightly different uniflow tube position that avoids going rich when the tube is uncovered....my arrangement keeps a good steady run going until the end...then it burps twice and quits.
This is with the open uniflow setup for a good 4 2 4 run.
The ROJETT 67 runs pretty steady with just a slight 4 stroke...sounds wonderful!

[John Carrodus]

Heaps of thanks guys. Lots of good ideas- eg ag WD tube inside copper tube while bending.
Brett- Yes - had a heap of trouble with leaking made up metal tanks and old second hand gungies. Yes the last few laps are often ( not always) a gasp and splutter affair, however on balance, I think I'd rather put up with that than the faffing about I've endured over the last few years. One of my mates puts his tanks inboard on all his profiles and swears by it.

[Brett Buck]

Heaps of thanks guys. Lots of good ideas- eg ag WD tube inside copper tube while bending.
Brett- Yes - had a heap of trouble with leaking made up metal tanks and old second hand gungies. Yes the last few laps are often ( not always) a gasp and splutter affair, however on balance, I think I'd rather put up with that than the faffing about I've endured over the last few years. One of my mates puts his tanks inboard on all his profiles and swears by it.

   Again, I am not trying to talk you out of anything, but almost everyone competitive uses metal tanks, with no issues whatsoever.

     Brett

[Steve Glass]

I have a slightly different uniflow tube position that avoids going rich when the tube is uncovered....my arrangement keeps a good steady run going until the end...then it burps twice and quits.

Can you please elaborate on this.

Steve

[Dave Harmon]

Can you please elaborate on this.

Steve

The uniflow tube is on top and the inlet is at least 1/8" lower than the usual position of on top of the pickup tube.
As long as the uni tube is immersed in fuel the engine will not go rich....it will maintain however you have it set before takeoff.
The uni tube is 3/32" from the back cover and the pickup tube is 1/2" forward of the uni inlet.
These tube inlets are far enough apart to prevent the pickup tube from sucking bubbles from the uni....if there are any.
The run time is very predictable and at the end of the flight I cannot suck any fuel from the tank from the pickup tube.
I got tired of the last 10 or 15 laps being hawg rich and then farting and wheezing for a couple more before it quit.
So....I made some experiments and this config works great without any of the nonsense others have described.
Try it!

Bend the tubes and punch the tank holes first.
Trial fit it so that it lays in the tank nicely, then clean the tubes with lacquer thinner, then tin the tubes with solder as shown, then hold the tubes together with a clothes pin and solder as shown.
Then insert the tubes into the holes and solder to the V of the tank.

Earlier I wrote...."avoids going rich when the tube is uncovered".
What I meant to say is....avoids going rich because the tube is never uncovered.

[Steve Glass]

Try it!

I will, thanks

Steve

[John Carrodus]

Dave- many many thanks. What a good idea. I will try it - possibly figure out a way to set up the same twin soldered air in - fuel out weighted clunk, in a plastic RC tank.

[Dave Harmon]

Dave- many many thanks. What a good idea. I will try it - possibly figure out a way to set up the same twin soldered air in - fuel out weighted clunk, in a plastic RC tank.

Hi John....
You're welcome!

I must say though that the 'paired' uni line and pickup line in an R/C plastic tank has not worked for me.
Yeah....it works fine if you just go around and around in circles but what Brett has written above is the dyin' trut!
Just remember that whatever tank config you have...plastic or metal....BOTH the uni and pickup tube must be immersed in the fuel at the same time....all the time....or you will have an unstable engine run.
Pretty hard to do if a clunk is flying around.
Give the metal tank another try but don't leave any fuel in it after the flying session.
I notice that there is fuel in the tank in the picture you posted.

[aj bagg]

I’ve pondered a few days about posting more detail on my clunk tank set-ups. With all these great ideas and Brett’s analytical mind on the job to keep everything real, why not? This place is great!
For the record I have no problem with metal tanks except my own laziness. Issues of forgetting to clean them and that model sets for 6 months or 2yrs. and now it’s full of crud. I still have and use, now and then, the tooling I made for making tanks 40yrs. ago. Back then I made the tanks with lacquer thinner cans and a screw on cap from cox fuel cans or marvel mystery oil cans. Now it’s very hard to find the small diameter screw on tops. Also several of my customers back then had plating and or powder coat facilities which made my tanks have bling. I still have some of the tanks from back then. Now I just like to see whats going on in my tank so I use these clunk tanks.

Quote from Brett;“   The big issue with clunk tanks is the cutoff. A proper tank will run with *no* change in the run until it is completely out of fuel unless you are maneuvering, and will make it through a 4-leaf without going lean with 2-3 laps of fuel, or be able to be cut off 2 laps early to set up your landing approach. I have never found any easy way to ensure that with a clunk tank and they are notoriously difficult to cut off - usually you start getting funnies in the maneuvers as early as the hourglass, then an extended period of speed up and slow down as the fuel sloshes back and forth. “

I agree clunk tanks go funky late in the run. I like the idea of the double line to the clunk. Worth exploring, maybe some 1/2a fuel line to keep it flexible?

I took a different approach to getting a consistent run with the clunk. I looked at the shape, size, and position of the fuel “puddle” in the tank as it approached empty. To picture my theory imagine a bottle approx. the shape of our round clunk tank. We put a small amount of liquid in this bottle and lay it on it’s side. The liquid forms a long skinny column in the jar. If this was our tank and fuel this long skinny column sloshing about in our tank as it approaches empty and this clunk trying to pick up fuel from this skinny column. Add to the equation the clunk swings on an arc dipping shallower and deeper. When you look at this fuel pick up as we near the end our run in detail we see why we get funky as we approach empty.

Now take our demo bottle of liquid and pick up one end slightly, the liquid goes from a long skinny column to an approximation of a round puddle. So we put “wedge” in our clunk tank to change the shape of our puddle in order to have a puddle more available to the clunk. Further make the puddle bigger by shortening the pick up line a sixteenth or three thirtyseconths to leave a couple of teaspoons of fuel in the tank after the run. By having a relatively large round puddle for the clunk to sip from at the time the clunk can no longer “reach” the fuel makes for a far more consistent run. Set up this way, approximately 3 laps from cutoff I get the slightest pick up in rpm, one lap to go it will lean out noticeably and quit one lap later in the same spot it went lean. I haven’t figured out how to post video here easily, we videoed three flights yesterday with my new Os 46la powered Pathfinder and six ounce clunk tank showing perfect runs with predictable cutoffs using this set up. On this plane the tank is mounted recessed through the fuselage so that “supply” is only ¼” outside “demand”. Also the tank has 5/32” “wedge”.

AJ   

[Dave Harmon]

I have tried this version of the clunk tank setup as well...and it didn't work for me.
Scroll down to the bottom pix showing the slip loop on the clunk.
The whole 'secret' to making this work is to keep the uniflow and the clunk immersed in the fuel at the same time....all the time.

http://www.tulsacl.com/ClunkTank.html

[Dan McEntee]

  One of the keys to having any tank, especially a uniflow of any kind, is to make sure the tank is oriented correctly in the model and while it is flight. This usually boils down to having a slight cant in the tank where the back outboard corner of it is farther outboard of the right front corner. Some don't take this into account and in the process of trimming out a new model, they have excessive offset to the engine, rudder and lead outs to where the plane is actually flying with the nose quite a bit out. Think about what that does to the position of the tank, no matter what kind it is, and the fact that as the tank load runs down, centrifugal force can tend to make the fuel run away from the pick ups for both the fuel and uniflow. Fuel can actually try to run to the FRONT of the tank, and if things are borderline, it can flow back and forth depending on what gyrations the model is going through. I have fixed erratic engine runs just by stuffing a thick shim behind the back end of a tank on a profile model. If it's a full fuselage model, make sure you have enough room to cock the tank a bit when building the fuselage , or build a tank for it that is wider at the back than it it in front.  This is one of the little things that adds up to having the whole model perform correctly.
  Type at you later,
  Dan McEntee

[Dave Harmon]

centrifugal force can tend to make the fuel run away from the pick ups for both the fuel and uniflow. Fuel can actually try to run to the FRONT of the tank

Exactly Dan.....
That's why you can see on several websites showing metal uniflow tanks with the uniflow tube in the front right part of the tank.
As soon as you see this....just move on because you just know that the guys airplane is flying in a huge skid instead of having a proper setup.
As an aside....I have never had to shim the rear corner of the tank to make it feed properly.....but I know that there is no penalty to do it...a little insurance is always good.

[Brett Buck]

I have tried this version of the clunk tank setup as well...and it didn't work for me.
Scroll down to the bottom pix showing the slip loop on the clunk.
The whole 'secret' to making this work is to keep the uniflow and the clunk immersed in the fuel at the same time....all the time.

http://www.tulsacl.com/ClunkTank.html

   If you are going to have the uniflow move, too, then Bob Reeves' example is the one you want to use, because it doesn't bind up the clunk motion.  Also, I suggest Sullivan Proline tubing for the clunk line, it is much more flexible.

     When I was running clunk tanks, I had *much better luck* allowing the clunk to move, but using a rigid uniflow vent (just a tube bent to go along the outside edge of the tank and, of course, out of the swing path of the clunk itself). That way you could still adjust the inside/outside speed by moving the vent tube by twisting it in the stopper. Still has the same cutoff problem.

    I will also admit I never mastered the art of an outside bunt to pin the clunk at the top of the tank to get it to run out when I wanted.

    The other big problem with plastic clunk tanks is fitting them into the fuselage. To get around that, I made several metal clunk tanks for 4-stroke runners that were custom fit and size, and you can positively locate the vent tube position by soldering it to the inside of the tank.  Silicone or ProLine is plenty durable enough to seal up semi-permanently, at least long enough for the fad to pass.

      Brett

[Brett Buck]

Exactly Dan.....
That's why you can see on several websites showing metal uniflow tanks with the uniflow tube in the front right part of the tank.

   Or why many/most of them are tapered in planform, or have the rear end kicked out, to force the fuel to the back under normal operation. You can't possibly put enough taper in it to keep the fuel at the back on maneuver entry, as soon as you touch the controls, the deceleration (maybe around 1-1.5Gs or more) slings it toward the front. *That's* why you have "chicken hoppers" or vertical baffles, if anything, and why longitudinal baffles (like in the old Fox wedge/T-21 style) tank didn't do anything useful, and when they broke loose, the only downside was the rattling noise.

     Brett

[Dan McEntee]

   If you are going to have the uniflow move, too, then Bob Reeves' example is the one you want to use, because it doesn't bind up the clunk motion.  Also, I suggest Sullivan Proline tubing for the clunk line, it is much more flexible.

     When I was running clunk tanks, I had *much better luck* allowing the clunk to move, but using a rigid uniflow vent (just a tube bent to go along the outside edge of the tank and, of course, out of the swing path of the clunk itself). That way you could still adjust the inside/outside speed by moving the vent tube by twisting it in the stopper. Still has the same cutoff problem.

    I will also admit I never mastered the art of an outside bunt to pin the clunk at the top of the tank to get it to run out when I wanted.

    The other big problem with plastic clunk tanks is fitting them into the fuselage. To get around that, I made several metal clunk tanks for 4-stroke runners that were custom fit and size, and you can positively locate the vent tube position by soldering it to the inside of the tank.  Silicone or ProLine is plenty durable enough to seal up semi-permanently, at least long enough for the fad to pass.

      Brett

   When I use a plastic tank, this is pretty much what I set up. I think I have made clunk tanks just about every way possible and this type has been the most consistent.  I have one in a beater model ( a Legacy .40  with a LA.46 in it) that is just about perfect. It runs to the last second and drop of fuel with a nice steady run and then just stops! It has a six ounce RST tank that is canted just a bit. You still can't do a cut off loop, I feel that is just the nature of the beast and monitor my fuel load and run times closer. Clunk tanks are cheap and easy to build, clean, modify and replicate, but you have to understand it's limitations and the whole big picture of what is going on during flight. Some one on here has posted good video of what happens to the fuel load  in a clunk tank while in flight and now would be a good time to post that again if some one can find it.

  Type at you later,
 Dan McEntee

[Dave Moritz]

Dave:

I'm really grooving on your uni-tank plumbing approach shown above. Very nice workmanship as well. The photo shows the tank's forward end with two exit holes. It looks like either you've soldered the tubes in with very short extensions or you've installed some kind of shoulders in the holes. Would you kindly elaborate?

Thanks.

Dave Mo...

[De Hill]

Bob Reeves did a couple of youtube videos on controls and tanks in flight.

Go to youtube and enter TwistMastertank for the tank,
and TwistMastercontrols for control movements.

This video was made at our old field on  our late member Jerry Neafus's land.

[Brett Buck]

Bob Reeves did a couple of youtube videos on controls and tanks in flight.

Go to youtube and enter TwistMastertank for the tank,
and TwistMastercontrols for control movements.

This video was made at our old field on  our late member Jerry Neafus's land.

   It was really good and very useful for purposes of analysis. What it told me is that even in a clunk tank that is basically just a square plastic box, the slosh frequency was very high and the damping was really high. The effect is that the fuel more-or-less quickly ends up where the acceleration vector would suggest, and it stays there until the acceleration vector changes. Point being, you could just look at the direction of the acceleration, and the fuel surface would be perpendicular to it for all practical purposes, and you didn't have to concern yourself over "settling" for any appreciable length of time.

     Brett

[Dave Harmon]

Dave:

I'm really grooving on your uni-tank plumbing approach shown above. Very nice workmanship as well. The photo shows the tank's forward end with two exit holes. It looks like either you've soldered the tubes in with very short extensions or you've installed some kind of shoulders in the holes. Would you kindly elaborate?

Thanks.

Dave Mo...

Hey Dave....thanks a lot!
In the pix I posted, the holes are punched from the inside of the end cap.

The way I do it is....
Locate the holes on the tank end cap or for the overflow....
Then drill a small hole in each location....never use a awl...that's one of the things that's wrong with mfgd tanks....they leak here when the solder has to close up a huge hole.

Then....using a piece of hardwood...I use a chunk of maple...drill a slightly larger hole than 1/8" in the maple.
Drill a #26 hole in the maple for the 1/8" sharpened music wire punch.

I use a 2" piece of 1/8" music wire sharpened in a drill press....
Then position the work over the hole in the wood and using a hammer, punch the hole from the inside of the tank piece.
This will give you a nice, tight flange that won't leak....this is the extension shown in the pix.

Of course, chuck up some 1/8" copper tubing and spin it clean with perhaps 400 grit or whatever.
Then bend the tubes to shape and do a final clean with contact cleaner, or lacquer/dope thinner.
I use liquid flux to tin the copper tubes as shown then wipe clean with a paper towel while still molten.
Then clip together, apply more liquid flux and use a 100w stick iron.

It goes real quick with high heat and does not heat up the whole tank when soldering the seams.
When done...use lacquer thinner right away to clean and flush the tank to get the flux out before it gets hard.

[Dan McEntee]

Hey Dave....thanks a lot!
In the pix I posted, the holes are punched from the inside of the end cap.

The way I do it is....
Locate the holes on the tank end cap or for the overflow....
Then drill a small hole in each location....never use a awl...that's one of the things that's wrong with mfgd tanks....they leak here when the solder has to close up a huge hole.

Then....using a piece of hardwood...I use a chunk of maple...drill a slightly larger hole than 1/8" in the maple.
(I will edit the drill size later today)

I use a 2" piece of 1/8" music wire sharpened in a drill press....
Then position the work over the hole in the wood and using a hammer, punch the hole from the inside of the tank piece.
This will give you a nice, tight flange that won't leak....this is the extension shown in the pix.

Of course, chuck up some 1/8" copper tubing and spin it clean with perhaps 400 grit or whatever.
Then bend the tubes to shape and do a final clean with contact cleaner, or lacquer/dope thinner.
I use liquid flux to tin the copper tubes as shown then wipe clean with a paper towel while still molten.
Then clip together, apply more liquid flux and use a 100w stick iron.

It goes real quick with high heat and does not heat up the whole tank when soldering the seams.
When done...use lacquer thinner right away to clean and flush the tank to get the flux out before it gets hard.

   I searched the world over to find the ultimate tool for making holes in tank material and managed to collect up a few. Good old fashioned ice picks, the older the better !! The old ones were made out of really good carbon steel, were tapered for their entire length, and are as sharp as a sewing needle and stay that way. You can buy ice picks just about anywhere, but they are usually just made from 5/32" or 3/16" steel rod with a steep taper point on one end. The old ones were made the way they are for a reason that makes them ideal for making tanks. I locate the position for the tube, then just poke the ice pick through and work it through until the tube just fits through with some friction. I usually mark the pick I'm using marked with a sharpie in the area I need to stop at. This leaves a flange that goes into the tank so you get a vice , flowing solder joint on the outside. It takes almost no effort to poke the hole through ( that's why hit men used them for their nefarious purposes!) and I usually do it after I have the front end cap of the tank soldered on. I use a 40 or 60 watt iron with a big wide tip, which transfers a lot of heat fast like you suggest. I have some of the really old big irons with genuine cloth insulation, but don't use those because they are too long and heavy for small tanks. Wattage isn't as important as the size of the tip and tip shape. For solder I just use 1/32" rosin core and just a touch of Ruby Fluid paste flux on the outside only. This is the best flux I have ever used for sheet metal of any kind. A little goes a long way and it's easy to flush off afterwards. It's just hard to find some times.
  Type at you later,
    Dan McEntee

[Dave Harmon]

Dan....thanks for reminding me that the small flange on the holes need to go the other way.
I'll punch from the outside next time.

[Brett Buck]

These tube inlets are far enough apart to prevent the pickup tube from sucking bubbles from the uni....if there are any.
The run time is very predictable and at the end of the flight I cannot suck any fuel from the tank from the pickup tube.
I got tired of the last 10 or 15 laps being hawg rich and then farting and wheezing for a couple more before it quit.
So....I made some experiments and this config works great without any of the nonsense others have described.
Try it!

  That is pretty much exactly the way I make mine, for the same reason. My uniflow outlet is much closer to the pickup than that, but it has to be because my tank is tapered.

      Brett

[John Carrodus]

A thought
Rging ging e gasping and burping the last few drops in the tank.

Has anyone tried stuffing stainless stell wool into the rear end of the tank?
It might stop slopping and surging of fuel during stunt also?

[John Carrodus]

Re gasping and surging...( sorry - sticky keys! )

[Dave Moritz]

Dave:

Much obliged for your clear explanation. Thanks to your generosity, this will greatly enhance my tank building techniques for use next Winter.

Dave Mo...

[Dave Harmon]

Dave:

Much obliged for your clear explanation. Thanks to your generosity, this will greatly enhance my tank building techniques for use next Winter.

Dave Mo...

Glad to help out where I can.....
Come to Tulsa...we have a great site!