Ballon Bladder Tank

Here is something I've been experimenting with: A ballon Bladder tank. Slip a ballon over the pickup tube/clunk and stopper of a clunk tank, pull the vent tube out until it is flush with the inside surface of the stopper and put the ballon and stopper in the plastic body. Drill some air holes in the plastic body of the tank. The plastic body of the tank is there just to protect and constrain the bladder. Fill it through the pickup tube exhausting all air through the vent tube. Cap the vent tube and connect the fuel line to the engine. Since the ballon is as large as the plastic body of the tank there is no pressure. But, there is no air in the fuel supply volume since the bladder collapses as fuel is consumed and the pick up remains submerged. Engine runs have been solid, consistant and reliable...

You can use any convenient fuel cell container with bladder tanks. Only the highest pressure types have anything like a required shape. Surgical tube bladders may last longer and be less likely to develop weak spots if restrained from reaching their maximum expansion in cross-section, so semi-rigid tubes may be built into a combat plane.

An ideal "clunk" inside this type of low, or no-pressure (if you have a large enough balloon), type of bladder is the DuBro # TF-1 "Tank Filter". There is a slight chance that the balloon wall could block a regular clunk's inlet hole, but this device HAS no one hole into it.

The K.

Check out http://www.darrolcady.com/Tettra_Tanks/tettra_tanks.html also http://www.jettengineering.com/ and click on "Mufflers and Accessories". I think these work the same as what you have described. I've been intrigued by the concept but the relatively high cost of them, my relatively low level of flying expertise and the fact that thus far, muffler pressure on uniflo gives me no problems have combined to keep me from ordering one. What sort of balloons do you use?

Best, Hoovie

I keep meaning to try a balloon tank. Your setup sounds well thought-out. There are a couple of British OTS airplanes, the Juggler and the Twister (not the Sig Twister, of course), which had balloon tanks loose inside a fuselage compartment.

we used this kind of tank on slow combat planes back in the '80's. I also used it on some profile scale planes. It works well, as long as the motor will tolerate the mixture change from full to empty. Like an open-vented stunt tank, the motor tends to start rich and gradually lean out as the tank empties. It usually isn't a problem on stunt-type planes, but can be on stuff with more wide open engines.

Make sure ALL the air is out of the balloon! The tiniest bubble seems to find its way to the fuel line and kill the motor. Also, sometimes the balloon will collapse on the fuel line while there is still fuel available. We used to cut V notches in the fuel pickup line so it wouldn't get block until virutally all the fuel was used.

>we used this kind of tank on slow combat planes back
>in the '80's.

> (...) Like an open-vented stunt tank, the motor tends
>to start rich and gradually lean out as the tank empties.
>
To reduce that effect, put the fuel cell container on the inboard side.
>
>Make sure ALL the air is out of the balloon! The tiniest
>bubble seems to find its way to the fuel line and kill the
>motor. Also, sometimes the balloon will collapse on the
>fuel line while there is still fuel available. We used to
>cut V notches in the fuel pickup line so it wouldn't get
>blocked until virutally all the fuel was used.

As per the above message of mine: An ideal "clunk" inside this type of low, or no-pressure (if you have a large enough balloon), type of bladder is the DuBro # TF-1 "Tank Filter". There is a slight chance that the balloon wall could block a regular clunk's inlet hole, but this device HAS no one hole into it (it's made from a porous metallic material).

K.

Is this the same thing that the late Jimmy Walker used on the
Fire Baby? If it is it worked very well,but you had to get all
the air out.
Evan Jones

Larry Renger has an article "Tanks for Nuttin" in tne April, 2002 issue of Flying Models Magazine. He describes a similar tank in the article which is pressurized by muffler pressure. Other than that it sounds like the same setup. He also mentions you should use balloons for helium inflation. He says thay are better quality, heavier rubber and less likely to be porous as well as appartnely fuel proof. Interesting article.

That sounds just like my 1952 Firebaby and Spitfire set up. It worked. In fact I am looking for a plastic canopy for my Firebaby. The ballon tank is rotted, but still there.

Yup.. In the AMA museum, there's a plane from the 1940s with a ballon tank in the canopy.

As someone else mentioned - these things were in vogue back in the early 80s in Slow Combat. The main problem was the pressure change as the hydraulic head changed. The solution was to use a shallow container. The problem was that you need a good 5 oz. of fuel to fly Slow Combat for 5 minutes. That's a big balloon. Aside from rubber balloons, people also used plastic bags (the sort you get for use as disposable baby bottles). These tanks graduallty fell out of favor after 2-3 years due to all the hassles and everyone went back to metal uniflo chicken hoppers.

Lo and behold - a few years ago, the RC Pylon crowd started using them. Initially, these were sold by Tettra, but now some people make their own. They're usually a lot bigger than ours were (about 6-8 oz) and they use plastic fuel tanks to house them. A couple years ago there was a "how to make" article in Model Aviation, in the Pylon column. I guess what goes around comes around.

Here's how we made them. The pickup tube inside the tank was perforated. When filling the tank, make sure all the air is taken out. This requires the use of a syringe (which is why you see syringes everywhere if you visit Pylon at the Nats these days). Use a hemostat on the fuel line until you're ready to start, or you'll end up with a flood.

I suspect one way to get around the leaning out problem is to fix the neck of the balloon in some position, probably towards the outboard side of the tank. Dan Miles experimented with supergluing the balloon to the outboard surface of the container he was using. He said he didn't have any leaning-out problems after that.