I was reading an article in this month's "Flying Models" about using balloons for pressurized, collapsable fuel cells. The article was mostly aimed at the smaller 1/2A size engines, but I was thinking it might work on larger ones as well. The question I have is wouldn't the balloons eventually lose their elasticity? The whole thing was about keeping constant fuel flow without having to rely on the exhaust or gravity. I'm sure they make them, but on something that small, I would think a pump would be a waste of space and weight. Does anyone make a collapsable, self pressurizing fuel cell for larger planes? If so, what are they made of, and how long do they last?

Later trends tend to use surgical tubing for the actual cell with a balloon over the outside to stabilize the pressure and act as a safety device to catch the fuel in case the tubing breaks.

You fill the fuel cell with your fuel pump

Bladder type fuel tanks are not common enough yet.

Currently, most are designed for racing and are made by (for) racing engine manufacturers, like Jett and Nelson.
Tettra also makes them.

Most of those offered are of small capacity (4-6.5 oz.) and carry a price 4-5 times their normal, same capacity equivalents.


A bladder tank is impervious to fuel-foaming, to clunk-hop (no clunk) and to bubbles in the fuel-line and fuel pressure is affected to a lesser degree, by the level of the fuel in the tank. They don't need much padding around them to counter air-frame vibration.
Exhaust gasses are never ingested into the engine.

The latex bladder, however, is more prone to wear and perforation, necessitating periodic replacement.


If a wider range of sizes is available, at twice the normal cost, I would buy it no-doubt, for all my planes.

...Many RCU threads would not need to be opened...

You can use Nitrle rubber and it would last way longer.. I make 1/2 A tanks out of nitrle glove fingers I cut off of gloves. They save me alot of weight compared to the plastic tanks...

When I was flying CL combat with glow engines in the UK we used babies dummies as tanks. Just stick the fuel tubing in, wrap with thread and glue to hold at the neck and inflate with a syringe full of fuel. Do this twice before use to relax the rubber.

When set up it gives a very consistant engine run even at the incredible G forces attained in a bout.

> The question I have is wouldn't the balloons eventually lose their elasticity? <

The tank in the article you are referring to is pressurized by the muffler and fuel supply does not depend on elasticity of the balloon.

Well, actually, if you look at the illustrations of the build, the inner balloon holds the fuel and the outer balloon is pressurized by the exhaust. i know they weren't meant to last forever, but eventually, the outer balloon would get easier and easier to inflate. It seems to me this would decrease the pressure on the inner balloon unless the whole cell was in some kind of container.

I guess maybe by the time they're mainstreamed into the rest of the RC community they'll be a little longer lasting and less expensive. I'd pay $20 for a 12 oz tank that's foam free, no possibility for fuel contamination, and not having to worry about the clunk getting clogged up.

I've been building models for over 55 years and bladder type tanks have been around that long. I remember them when I was a kid. They used to use fountain pin bladders in the 50's.

Broke,


That is plain wrong! Any enclosed volume will have the same pressure as its source.

The muffler has an average of 0.5 psi and the outer tank is made of of poly-propylene, of poly-ethylene, which are semi-rigid plastics - not an 'external balloon'...

The pressure in the bladder will be the same as in the external tank, or just marginally lower (-0.01 psi), as fuel is constantly drawn from it.