Twist the tie tighter.  Or use a rubber band, multiple wraps.

Bob,
I have solved the leaking problem this way.
Like you, I place a short piece of copper or brass tubing at the neck. I then cover this splice with a 1/2'' long piece of large diameter silicone fuel tubing. This increases the diameter of the neck reducing the number of folds in the balloon neck when bound. Instead of wire or rubber bands, I buy a quantity of small nylon cable ties and use one per balloon. These can be cinched up tight by hand. The ties working against the flexible large diameter silicone tube at the neck gives a perfect seal every time.

Orv.

Thamk you for the information.  I will try the fuel tubing under the ties first.  It looks like the easy way to tighten the seal.  Once again your help is great to a retread like me.

Bob

Most all my .049s seem pretty tolerant of tank height, anything reasonably close to centered works well.  Probably because we don't use a 4/2/4 break, but peaked out pretty close to max.  Seems like that makes them less critical of fuel pickup location. Once peaked out they just stay there, upright or inverted--unless you're talking about an extreme tank misalignment!

                How many flights are you guys getting before you have to replace the balloon tank ?
                            Bill

Bill, i have had some last as long as 6 months and some as long as 6 days. For the price there may be a small quality issue sometimes,, but over all they can't be beat  ,,  yet!! I do run some balloon tanks on the platters with the motor running very rich at launch in order to do a 4-2 break for training maneuvers and some will tend to vary the runs between upright and inverted flight according to the tank height, but for general purpose slightly rich 2 cycle running  the tank height is not so critical. I have as many as 7 or 8 ready to go at anytime..  Keep working with your setups and i believe you will find one to suit your flying.  These "tanks" and a decent running engine are way too much fun!!!! 

 Tim Wescott, is that a pill bottle for the tank container?  If not what then?  Thanks a lot

Did you know that ping-pong balls are very soluble in model airplane fuel?

No I didn't.  I was of the understanding that ping pong balls were celluloid which would resist fuel, but I never tried an experiment.

Phil

In my second photo above, you can see a balloon surround that's made out of plywood -- it's lite-ply top & bottom, with 1/64" ply wrapped around that.  Originally I had cut a circle out of the fuselage just big enough to hold a ping-pong ball, with the firewall neatly glued to that, and braces, and all that lovely stuff.  Only after I had everything nice and finished and pretty, with a balloon stuffed into the ping-pong ball and everything, did I slosh some fuel on it and watch the thing just absolutely melt in front of my eyes.

"Frustration" does not quite capture the feeling I was experiencing at that moment.

That is an elegant cavity.  I was not sure what I was looking at before! 

Yes, verify then use.  I have been doing that with various paints since dope is hard to get for me.

Phil

Some informative pictures:

I like it! But how do you get the balloon in and out?  Also dose oil from the 2-cycle fuel collect in the cavity?

There's holes in the bottom to let excess fuel weep out, and to let the air out as the balloon fills.

And yes, the inside's painted with epoxy.