Balloon tank construction

LAST EDITED ON Mar-22-04 AT 08:01 PM (CDT)
 
In another thread, drawings and explanation were requested on how to make a balloon tank. So here it is:

Basically you are using a helium quality balloon from a florist or craft store as a fuelproof bag. You want to leave it floppy, not generate pressure. So, select a balloon of an appropriate size. For 1/2A, you only need hold an ounce or therabouts, and small balloons are just fine.

Take a piece of fuel hose about 2" long, and shove a 3/4" piece of brass tube in it to reinforce the binding area, and act as a coupler to the hose to the engine. Cut holes in the side of the tube at several spots to make sure the fuel pickup can not seal against the rubber. Since there is nothing but fuel in the tank, this actually works great.

Bind the balloon over the brass reinforced section.

You are done! See, that wasn't too bad.

BTW, draw all the air out of the balloon with your syringe before filling. The object is to have nothing that can foam. I find that if you keep the tank out of the sun, they last a very long time, as much as a year! And they are cheap!

Larry,
Great idea!
Could a fill tube be added that could be plugged before flight? That would make filling the tank a bit easer and the reed valve should close off to allow you to suck the air out of the balloon before filling.
Rob Johnson
Orange,CA.

Any body have an opinion if this setup could be used with a diesel? I have played with .15 diesel combat and think this could solve some problems. I think, however, that Ether is a superior solvent? Opinions?

The Brits have used balloon tanks with diesels. Don't know how well they worked.

The principle would work well, but the balloons I have tried go very strange when hit by diesel fuel. I would love to know if there are other materials. You certainly could seal polyethylene (plastic bag material to make a proper balloon for this purpose.

The reed valve has nothing to do with it, as the needle assembly is open to the air through the venturi. As such, you won't be able to pull a vacuum on the tank.

I suspect you will flood the engine when filling, too.

A related question. Will a reed valve engine work on a low pressure (thin wall surgical tubing) bladder? I was always told it would not. But DesingMan will know for sure.

Short answer: Yes. Makes for much more consistent runs, too. I have 2 Black Widows set up for surgical-tubing pressure tanks. I just bent one vent tube inside the tank so as to get a piece of fuel line on it, which I then connected to the NV assembly. Then hook your pressure tank to the outer end of the vent. Voila! And no permanent damage done to the stock tank, either.
--Ray

Instead of a balloon you can use a liner from a baby bottle. Fuel proof and easy to adjust the volume. Not sure if Diesel affects the plastic.

Randy Heydon pointed out that surgical gloves are available in Nitrile, a pretty everything-proof elastomer. The fingers ought to make superb tanks, even for diesel fuel!

I have to try it!