MJD

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Hi folks,

I'm posting my first draft of this here before the Christmas decorating, shopping, cooking, sleeping (?), etc. takes over for the next few days. There are likely some omissions and whatnot, but I will scan over it and make changes as I discover them. These are just some ideas I've used that so far have allowed me to whip up nice, light, functional 1/2A tanks for pennies. And to make a bladder tank that is simply not commercially available. For the acid test I used one on my Blink model with VA .049 MkII with muffler pressure, and it works just like the big ones do. I sent a couple to CP for evaluation, he liked 'em, and I promised a couple more here and there which are almost done and will be this week - really!

Your input is most welcome.

Mike D aka MJD
MikesRC

MJD

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I stared at a pile of bits for a while, thinking about how to turn my usual way of doing things this way and that into an orderly how-to procedure. I then realized that what was probably more important than a “here is a tank type A step by step”, was to talk about the tools and methods and just show some examples of what you can do with them.

The Fuji film can seems to have been designed for the 1/2A tinkerer. Made of low-density polyethylene, it is tough (enough), flexible and light, and holds close to an ounce of liquid. They are readily scrounged from camera counters. The down sides are that nothing you can find on the shelf sticks to it period – it is a “low surface energy” plastic that simply waves off conventional solvents and adhesives. Silicones and other elastomers will conform to it and seal against it, but any semblance of bond strength is mere “stickiness”, not a chemical or mechanical bond of any worth.

So the biggest issue facing the would-be tank builder is access fittings. I screwed around with a few different methods, and made a number of tanks that worked fine but I am not sure how many identical examples there are as I was always tinkering with the tools and methods. I have a fine collection of Spaenaur miniature barb fittings and the like, and used many of them successfully as access fittings and whatnot. But it was easy for me to get them through work, and not everyone has that convenience.

In the end, one method turned out to be the most reliable and repeatable for creating a tight seal using the kinds of flotsam & jetsam most of us have lying around in our work shops or can scrounge at the hobby store.

Tools and Materials

Here is a list of the basics you’ll need to get anything done:

- Fuji film cans. Find a few, you need a couple extra for practice.
- Small and medium silicone fuel tubing.
- 3/32” brass and aluminum K&S tubing
- X-acto knife with sharp #11 blade, or my favourite a loose Olfa utility knife blade.
- Vinyl tape.

Plus assorted basic hobby tools other than the X-acto/#11 combo

Optional:

- A punch set for craft work. The set I use came from Dollarama, and I bought two sets. I cleaned them up a bit. 1/16” – 3/16” is the range of hole sizes that will cover anything I can think of.


RULE #1

EXPERIMENT!

Get extra everything and make a few mistakes – you’ll learn faster doing that than by reading endless “how-to” tips!

MJD

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#1 – cutting tubing

The first thing you need to be able to do is to cut small metal tubing nicely. In descending order of personal preference, a sharp Olfa refill blade, a single-edge razor blade or an X–acto #11 work well.

The pics are almost self-explanatory. I set the tubing down on a smooth but not slippery surface, then holding a sharp blade vertically and exactly at right angles to the tube, I lightly roll back and forth a few times. If you hold the blade at an angle, the cut will end up as a helical spiral. Practice.

Normally, I am through the Al tube in 2-3 seconds. Brass takes a few more rolls, and generally I do not cut all the way through the brass, but score it deeply, then snap it off clean – it works.

After cutting the edges are rough and will ruin your day by nicking fuel tubing and tank access holes. So they need to be cleaned up. Chuck the cut piece of tube in a Dremel or hand drill, spin it and dress the ends on a piece of sandpaper 180-200 for removing burrs and 320-400 to smooth and radius the corners.

If the tubing itself needs some TLC due to nicks, scratched or spooge, you can clean up the exterior of the tube with 400 grit paper, or a Scotch-brite pad which I prefer for this job.

MJD

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#2 - Making holes

Making holes is easy. Making holes that seal when you shove something through them takes only a bit more care. Luckily, one of the redeeming virtues of LDPE is it’s flexibility and softness, so it is quite accommodating when it comes time to seal against something else.

Three methods have worked for me:

a. Punching

Using a cheapy craft hole punch so far has been the easiest way to make repeatable and functional access holes. I have a scrap block of polyethylene plastic I use as a base, or use something else you have around that seems to work well when you test it, and doesn’t bugger up your punches. I had to chuck each of the Dollarama-special punch tips in a 3/8” drill, and spin them against some fine sandpaper to clean up the cutting edges, but a with a couple of minutes effort they looked and worked fine.

MJD

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b. Drilling

“Drilling” per se does not involve regular drill bits, you can put those away.

Because of the buttery soft nature of LDPE, you can cut through it very easily with homemade cutters fashioned from plain old brass tubing.

I have had success by sharpening a piece of brass tubing to use as a hole cutter. First, I cut a piece of the tubing to length using the rolling blade technique, then I sharpen the end by spinning it at high speed against a fine file or sanding block. I sharpen to the inside if I want the hole smaller than the tube, otherwise outside works too.

Finally, you can gently drill through the plastic using moderate speed, using a Dremel tool or drill press. Use balsa or something soft underneath so you do not ruin your cutter every time you use it.



(the picture shows aluminum tube being bevelled on a piece of sandpaper. Pretend it is brass colored.)

MJD

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c. Melting

I worked with this idea for a while, and was able to fairly reliably make decent holes. While the appeal of the smooth melt-cut surface and the ease that you can melt LDPE was appealing, in the end I realized that a lot of finesse was needed, and that punching or drilling the holes was in fact more repeatable and reliable.

To do this, I used 2-3” sections of Al tube – not brass – because they only stay at melt temp for a second or two. This proved to be important, as radiant heat form the tool can enlarge or distort the hole. The tube was heated with a small torch but nowhere near red heat – LDPE starts to melt at around 275F so you do not need, nor do you want, excessive temperature or heat. The ends of the tube should be cut true and neatly, and cleaned up with fine sandpaper before starting.

Here’s the trick I found that helped me greatly in consistency if you want to try - I heat the tube in the flame until it just seems hot enough, then push it gently through the plastic, but keep pushing it through in a steady motion until the cool part of the tubing passes through the hole. Don’t dwell at all with the hot part in the hole – keep moving.

I did not get pics of this technique, but I didn’t figure it was a candidate except for die-hard tinkerers. It will work, but the other methods are quick and less fiddly and work well.

MJD

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#2 - Access fittings


As I said before, I putzed around with Spaenaur miniature barb fittings, and they rock, and if you feel like snagging some fitting and messing around – go for it. With the techniques here for hole making and some modelling ingenuity, all sorts of things are possible.

These fittings include threaded barb fittings – for example, one type has 10-32 thread by 3/32” barb – cool! Add a nut to the back and you have a solid connection. You need a gasket or silicone to make a reliable seal. All this stuff is off the online shelf at McMCaster-Carr.

BUT – this is all nice, but a hassle for a little 1/2A tank when you can use hobby shop/workshop materials and do a decent job. So I won’t dwell on the fittings issue. If you’re interested, I bet you can look through the available stuff and figure out what you’d like to fool with. This part is not rocket science and lends itself well to impulse buying once you see all the cool bits you can get. You figure it out.

Now I generally just use tubing for small stuff.

For 1/2A tanks, I like to use 3/32” aluminum tubing. It’s light, cuts easily, lasts longer than anything else on the aircraft or fuel system and is available at your LHS.

MJD

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#3 - Sealing

a. Metal/plastic

LDPE is a soft plastic, and with an interference fit hole to a piece of smooth walled tubing usually makes a good gas- and liquid-tight seal. Therefore one method that works well is to punch an undersize hole in the plastic, then push the tubing directly though the plastic. It seems to me that the plastic in the lids is a bit softer, perhaps as it is required to conform to the can itself. So while this method can make an excellent seal in any location, it seems to work best in the lid itself.

Once I fitted the tubing to this lid, I anchored it a bit more securely with two small sections of small silicone tubing as shown here:

This access fitting as shown can withstand a load of about 1kg/2.2 pounds (see pic) before moving; I tested this on a digital balance. This is plenty to resist any movement in use. However, it is not always enough to withstand heavy-handed tubing mounting forces, so I suggest you fit a length of fuel line before installing it so you can hold on to things to manage the process without buggering it all up. It can be a shorter piece to which you later couple some more with a piece of Al tubing, or full length right now – you decide. While I was doing this, I noticed it is my habit to moisten the fittings and tubing before pushing them together (I know how they all taste now) as this greatly reduces the force needed, yet seems to go away after a short time and leave things snug as they should be.

MJD

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b. Metal/silicone tubing/plastic

Silicone tubing is a very accommodating material – great flexibility at all working temps, fuel proof, cuts easily, and makes a great seal against many substrates with only moderate pressure.

The single most reliable method I have used to seal access fitting to tanks is to punch an undersize hole to tightly fit silicone tubing, then work the metal tubing through this. The silicone tubing compresses against the soft tank and the tubing to make a perfect seal pretty much every time.

For this method, you need to punch a hole bigger than the ID of the silicone tube, but smaller than the OD. To get enough compression for a tight seal, I suggest you try for a hole about halfway between the ID and OD. You can figure this out, I doubt we have the same tools or even the same brand of tubing - again, experiment and make all the mistakes on some practice parts.

Wetting the tubing eases the job of pushing it through.

- if the hole is too tight, it’s a pig getting the soft tubing through. But a 45° cut on the inside end (which you can trim off after if you wish) makes it easier.

- if the hole is too loose, I think you can imagine the issues.

Oh yeah.. the breakout force of this assembly is similar to the other, about 2 pounds.

MJD

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c. Silicone tubing directly into the tank

This works well too, but I only use this method for vent fittings, as it does squeeze the ID down a bit thereby restricting flow. This is not an issue for vent/muffler pressure fittings, and in fact Jett Engineering bladder tanks use this method on the vent.

It’s stupid easy - make a hole smaller than the tubing and push it through. Hole size is the same as for method (b.) above. Cut an angle on the end for easier insertion if you wish. Occasionally, I reach inside and pull when things are stubborn. Careful not to hurt the tubing though.

For positive retention, I suggest a short piece of appropriately sized Al or plastic tubing – ¼” or so, pushed into the inside end then drawn up to the hole. You’ll need to push some extra tubing through to get at it. Submerge the piece of hard tubing in the fuel tubing to eliminate any internal edges (think bladder tanks) and to let the end of the silicone tube shrink over the end for more positive retention.

If you use a short piece of tubing of course you can splice in more vent line later, same deal as for the fuel line.

Here is a tank body with a vent fitting in the rear done this way.

MJD

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So what do I make with this?

Whatever you want or need! I’m not here to explain tank basics, so if you are doing this you best be familiar enough with engines and fuel systems to make your own decisions along the way. But I’ll show you two examples that work great.

MJD

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Clunk tank:

This tank holds 25cc of fuel, and has a flexible clunk line made from latex tubing. Egads! Latex degrades with glow fuel! Well, it does, slowly, but you can get a season or more from one assembly. The reason I use latex is that even small silicone tubing is not flexible enough to use with light clunks weights – it will hold the weight straight out against gravity over these short lengths. If you use a regular tank clunk, samples of which I have weighed in at 5-6 grams, then silicone will work.

So you can choose between a 10-11 gram tank with latex clunk line, or a 15-17 gram tank with silicone. That’s still only just over 1/2 ounce, but as an example that is 6% of the weight of my 1/2A Squirt model.. it adds up!

After it is all assembled, I wrap the lid with tape – I thought I’d use hockey tape since we invented the game – but electrical works okay too. Smooth the edges down tightly so spilled fuel won’t creep under and bugger up the adhesive.

You can see here how I used some small pieces of silicone tubing as clamps over the clunk line, spreading them with needle nose pliers. I broke a couple, no worries.

MJD

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more pics, one more to go..

MJD

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...

MJD

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Bladder tank:

Ah, now we’re talking! 1/2A bladder tanks? Yep – they work great.

Buy some 12” helium quality balloons if you don’t have them already.

See pics! Easy! Stretch the bit of neck over the lip of the film can after you insert it, then work them down the sides a bit to tidy everything up. Pop the lid on, but wet the shoulder of the lid first if you like, it makes it easier.

Small sections of silicone tube fit over the ends of the acces fitting internally can be used to prevent nicking the bladder. Because the bladder in theory has no air, you don't really need any kind of special pickup tube inside it, but a short piece of fuel tube with the end cut on an angle, perhaps a V-notch, can help prevent the bladder blocking the inlet. I've never seen that happen, but it seems like a good idea. I note that the Jett tanks have a length of tubing to the center of the tank - I do not know if the last part of the fuel draw sees any issues with the big wrinkly bladder and this helps, or..?

Weighing picture #1 is the empty weight of the tank.

#2 shows the scale zeroed again, then the tank filled with water. It shows 25cc capacity, with about 1-1.3cc left in the tank after I blew the water out with the vent line. Works for me.

OOPS - pictures out of order. It was 1.8 grams of fuel left as you can see. Pic 1 is the fuel left.

MJD

chevy43

Great how to - thank you!

A while ago I realized how nice and light these fugi tanks are!

I bought a whole box of Fugi cans on the big auction site for cheap.

You thought of a lot of ways of using them!

I like the uniflow set up for tanks - it keeps fuel pressure stable and works fine without tank pressure:
http://www.fraserker.com/heli/uniflo....htm#practical

MJD

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Someone read this - wow!

Have you made a film can uniflow tank yet? I'd probably start with latex tubing internally myself, to get the clunk flexibility.

MJD

Yuu

Great procedure, and Great presentation. Yes, we were reading along. Your work did not go to waste. Thanks!