I just tried out a balloon tank today, since I'm just not getting joy with trying to make a Golden Bee tank work inverted (I know: this should work.  I may start a thread on it).

As far as the "works at any attitude" it's great, but I have some questions.

I "mounted" the tank by making a cylinder of acetate about 1" in diameter, and nailing it down to the plane wing with a bit of plywood to spread the forces, and a pair of #2 screws.  My problems with this are twofold, with both filling and holding the tank in position.

In filling, I need to disconnect the fuel tube from the tank inlet tube, but everything is squirmy and not nailed down (and now it's all fuel soaked, to boot).

In flight, the tank just extends through my (hollow) tube and flaps out the back.  I think this latter problem can either be fixed by putting a back onto my tank mount, or by ignoring the problem, but it'd be nice to have things nailed down.

So -- how to do this?  I know that Ray uses 35mm film cannisters.  That's just exceedingly cool, but I didn't save mine and they're kind of rare.  I'm thinking of doing something like soldering a brass strap onto a bit of fuel tubing, to be held down by one of the engine mounting screws or by a screw to the airframe.

Does my method make sense?

Is there an easier way?

Thanks.

You could close the end of the plastic tube with a peice of balsa.   

Tim, that looks like it should work fine. If you want some film cannisters let me know your address in a pm and i will send you a few. I have saved different size bottles for a couple of years now. I do like to use the Sig 6 inch clear canopies when i have the room.

Both the Sky Sport and Sky Streak have balloon tank compartments built in.  Balsa works fine, just epoxy coat the inside!  The balloons only want to slither out the back, not the front, it seems.

I think if I had an engine with a convenient fill nipple on it I wouldn't have a big issue.  The engine is an old Cox "product" engine, and it's hard to get fuel tubing onto the nipple -- so I don't want to have to either mess around with a floppy balloon, or with ever taking the tube off the engine.

So the hard mount appeals to me.  We'll see how it does in practice.  Here's the final version, which brings the bottom of the tubing up at least a fraction of an inch above ground level.

You can barely see the plastic in the picture -- it's round, and it reflects the balloon color which is itself natural latex and not too different from the balsa.  It's a bit more evident in the first set of pictures.

Landing gear adds weight and drag, and this plane already has a ton of weight in the tail.  I did consider it, though.