I have received lots of questions on the actual design of the cluster, and how I will handle release of individual cells.
I’ve considered a couple of designs.
The most basic design. Have 55 balloons, with 55 ropes. Each balloon is tied to the gondola. But, what a mess. In theory, you could cut any individual balloon from the gondola for a 219 cu/ft helium ‘vent’-- but who knows if the balloon would pull free from all the other cords.
It could be like sliding one stick of uncooked spaghetti out from the package-- nice and smooth. Or, it could be like trying to pull one piece of cooked spaghetti out from the bowl-- intertwined, sticky, and altogether less successful.
I didn’t really consider this option.
My gondola has 8 carabineer attach points, and the first cluster design was essentially an octopus. Each carabineer got a tall 7-tier stack of balloons, attached vertically to one to another in a daisy chain fashion. Each ‘arm’ was a tall column of balloons, independent of all other arms. I could imagine the individual arms, waiving about. Didn’t sound good.
Balloons could only be released by cutting an entire 7-balloon ‘arm’ from the gondola. And, the arm would only release if they hadn’t become tangled with other balloons in other columns. (This would also be a giant helium vent-- cutting an entire column.)
Each cable in the octopus arm was to be the same-- an 8-foot plastic coated steel flexweave cable. Because each ‘arm’ of the octopus attached to the carabineers on the gondola, the bottom-most cable had the strain of the entire ‘arm’ or tower of balloons. These flexweave steel cables failed in testing,
I had my chair rigged, hanging under my deck, and I was bouncing around along with 140 pounds of water ballast. I was actually standing in the chair, to see if I could reach the imaginary bottom tier of balloons, above my head. I was standing in the chair and I heard this ‘POP!” And then: “POP!POP!” One cable failed-- and as soon as it did, the next two followed suit.
I was sent flipping backwards, head-over-heels, tumbling out of my chair, and on the way down I hit the ballast tanks, and my water ballast came dumping down on me, as I crashed into the grass on my back. True story, that.
I dumped the cables.
I can’t think of many good things to say about this octopus design. Balloons couldn’t be released individually, it was very tall, and I’m glad to be past it.
Stack of Donuts:
When working with small sets of balloons, groups of 7 form into very nice little clusters. It is like a ring, or donut, with one ‘donut hole’ stuck into the middle of the ring.
I considered using an 8-high stack of these donuts, making a tower, or a Stack of Donuts.
The attached adobe .pdf docs show the component breakout of the stack, as well as the stack combined into its tower.
The lowest 7-balloon tier in the stack would have micro-vents, to allow controlled release of gas from any of the 7 balloons in the bottom tier.
The next several tiers are also in groups of 7, attached to the gondola by progressively longer straps. Each strap has a carabineer ‘ring’ on top, and the 7 balloons flower out on individual lines from the carabineer. The strap for the next tier runs up through the prior level’s 7-cluster, and blossoms into another 7-cluster, one right on top of the other.
The cells in the very top tier would be individually tied to the gondola, using long stretches of 3mm climbing utility cord. These are the ‘donut holes’ floating on the very top of the stack, and would allow for 219 cu/ft venting off the top of the stack.
The next 7-balloon tier would be a quick-release tier. This is essentially a powerline landing tier: cut the whole tier, causing an emergency descent, entering near-freefall. This would only be for low-altitude powerline type situations, where you need to plunk the aircraft down ‘now.’
One problem with this quick-release tier is that every balloon in the tier above, the individual ‘donut holes’, would already have to have been released. In a real powerline situation, it would mean making sure all individual release balloons had already been cut, and then pulling the quick release on the 7th tier. With only a brief time to act, this delay could be fatal.
Other questions include the spaghetti question above. Would the top level donut holes really pull out and release, all the way up through the stack?
The tower is also very tall, with crown of the top balloon topping out 72 feet above the attach point on the gondola.
When playing with configurations, I built little models from piballs. It was interesting to note the lift produced by the cluster, and what happens when removing one balloon from the group. The ‘vent’ size to invoke a descent is very, very small. Tiny vents (removing one half-inflated balloon from the weighted piball cluster) caused descent. Tiny weight removal (a rubber band) caused a steady climb to begin. Of course, these are only piball models, but it was useful to observe. Tiny vents! Tiny ballast drops!
Some models and photos attached.
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Thank you very much,
Jonathan R. Trappe