23 April 2011

The Great Hot Air Balloon Failure

My kids are a curious lot, perpetually  interested in making things, destroying things, changing the shape and/or color of things that I would rather they have left alone, and so on. We give them a lot of freedom in this respect, as we consider experimentation an important part of a quality General Education. As part of this philosophy, we homeschooled them until we got too many to keep up with. I suppose lots of what we try to do with them still constitutes experimental education, from “Adventures in Rhetoric” with my Number One Daughter, to “Don’t Set That on Fire, It Will Explode” with my Number Two Son. But one of the things we do a lot of is just basic experimenting.
Experimentation is the best way to learn about the world, in my opinion, and is one of the things that make Quakerism significant to me. After all, one of the foundations of Christian Unprogrammed Quakerism is that personal experience lies at the base of all knowledge of God. Of course, most all interpreters of Christianity will say that, but they will usually add “. . . and this other person’s personal experience is the one you should listen to . . .” My lovely wife and I take a different approach to the matter, sometimes intentional, sometimes accidental. Rather than learn about the Creation from the hoary experts in their ivory towers, or from the hoary authorities in their cloistered rectories, I try to let my kids learn as much about the world as they can directly, from the hoary world itself. And of course, they always have their hoary father around to assist them in avoiding the incineration of their home and other such unintentional consequences.
Our kids are especially fond of bright colors, paper, defying gravity, cutting things up, destroying solid objects, and discovering new uses for fire. So one day last week, I considered that it was time to teach the children something useful about all of these things. How, I wondered, could I possibly fit all this into a single day? Fitting it into a single day is important, because driving a truck for a living means that my home time is extremely limited. We’re still waiting for the opportune moment to glue the masts onto the ships they built inside old whiskey bottles the time I was home before last. I didn’t quite ream out the holes in the wooden hulls big enough before we glued them inside the bottles. Manipulating the masts and sails into place at the end of long , slender drinking straws turned out to be more difficult than I expected, and we ran out of time before I could come up with an alternative technology. But not to worry, all I have to do is sneak a few more whiskey bottles past my wife, and we’re ready to try again.
Anyway, I hit onto the solution to the current problem while driving across Wisconsin, and immediately called Shawna to make the necessary arrangements.
“I need you to buy some stuff for me for when I get back.”
“What stuff?”
“Well, I need some long tissue paper, some tomato paste in the small cans, some glue sticks, and some 90 percent isopropyl alcohol.”
“Why should I help you build a bomb? We can’t afford insurance.”
“It’s not for a bomb. We’re all going to build a Hot Air Balloon. And I just want the cans for the burners.”
“You mean you’re going to throw away perfectly good tomato paste?”
“You can make spaghetti for dinner.”
And there you have it. A quick project that involves the exercise of solid geometry, convection, a bit of history, requires the uses paper, glue, an electric drill, perhaps, and would result in a spectacular and emotionally satisfying visual extravaganza to seal the lessons into the malleable and receptive minds of my five children. It would also show my lovely wife that I could actually do more during my 72 hours at home than just sit on the couch rolling lint out of my navel. Yes, such are the dreams of mice and men, but little did I realize how soundly my hopes would be dashed by the cold hard reality of nature and nature’s laws. But I digress.
I arrived home to discover a complication already waiting for me.
“Your son’s science teacher said to use Sterno for the heat source, so that’s what I got.”
“Sterno? That won’t work,” I said, hefting one of the heavy cans filled with an evil-smelling pink gel. “Why couldn’t you just buy the tomato paste and alcohol?”
“Stuff it.”
So we made another trip to the grocery store in the next town, my wife having washed her hands of this stage of the affair. At lunch at the McDonald’s, I grilled my Number One Daughter on her geometry skills, because at the age of 13, it would be her responsibility to supervise the design of the gas envelope.
“Devra, what is the value of pi, to eight decimal places?”
“Three point one four one five nine.”
“That’s only five,” I said. “What are the next three?”
“How should I know? I can’t remember. Two six nine, maybe.”
“Wrong! Two six five!”
I consider pi to be an important number for children to know, and make sure that its value is included in their education somewhere. After all, it’s a necessary number for making Hot Air Balloons, as well as for many other household tasks, such as determining the amount of cornbread batter to prepare for a round baking pan if you want the cornbread to be a certain thickness. You know, important stuff.
“Okay, if you want to make a round balloon about three feet in diameter, how many one-foot wide panels do you have to cut?”
“And if you want the balloon to have a one-foot hole in the bottom, how wide do the panels have to be at the bottom?”
“Um, three feet divided by nine? Four inches?”
“And what is the angle of the top of the panels, to make them fit together right?”
“How do you do that?”
“You take the number of degrees in a circle, and divide it by the number of panels.”
“Um, forty degrees?”
We were all set.
Constructing a hot air balloon is something everybody should do at some point in their lives. Building a lighter-than-air craft, even in miniature, is an interesting lesson in convection, in relative air density, in buoyancy, and in history too, for that matter, as well as being fun. After all, the first man-made vehicles to venture off the earth’s surface were the hot air balloons of those old Montgolfier brothers, and the technology has been fundamentally the same ever since. My own experiments as a teenager in England used lightweight tissue paper for the gas bag, but my wife explained that tissue only came in small sheets in America these days. Innocently, I chose to substitute longer gift-wrapping paper. This was my first mistake, but it would be a while before this one came to light, and in the meantime there was plenty of opportunity for making others.
Most immediate was my preoccupation with burner construction. To make a good burner for a hot air balloon, just take a small tomato paste can (or similar), stick it over the end of a piece of wood, and drill a whole bunch of quarter-inch holes in it. Leave enough non-perforated space at the bottom to hold some alcohol, and attach a loop of flame-proof bailing wire at the top to hang it from under the balloon. Voila! Instant burner! A bit heavy, though, I thought. In England, I had used aluminum pill bottles when I did it, but those are hard to come by in Appalachia. We set the tomato paste can on a flat rock on the dining room table, poured in some alcohol, and I dropped in a match.
“Is that all it does?” My Number One Son Griffin queried us skeptically from his position of safety behind the fire extinguisher in the kitchen. Griffin is fairly blasé about fire. In fact, he was the trigger man in the Great Hilltop Grassfire a few years ago that taught my city-slicker wife how unexpectedly exciting it can be to try to burn a dried-up old Christmas tree in a dried-up old hayfield next to your dried-up old house. Which is another story, but one that may never be told for diplomatic reasons. But truly, the burning rubbing alcohol was not a very impressive sight—a tall, cool, yellow flame that smoked and didn’t seem to put out much heat at all.
“Give it some time to warm up and start boiling the alcohol into a vapor, “I suggested hopefully. “I remember the flame making a tight cone of purple fire that really put out the BTUs when I did it.”
After a while it did get a little better, but not much. Another mistake. Puzzled, I thought about why it wasn’t burning like I remembered. Then I remembered that I had used methanol in my own attempts, years ago.
Methanol. Wait a minute—that was the answer. There had been no water in the fuel I had used, it had been pure wood alcohol. Thinking about it, I realized that a 91-percent isopropyl flame would never get really fierce, because boiling the water mixed into the rubbing alcohol was absorbing the heat produced by the combustion, making steam instead of hot air, and decreasing the heat available for raising the temperature of the air going into the balloon. Heat of vaporization and all that. Not good. A better fuel was necessary.
“We need some meth,” I said.
“Excuse me?” replied Shawna.
“Methyl alcohol, you know, methanol, methylated spirits. I need to get some at the apothecary.”
“The fact that you buy it at ‘the apothecary’ is an indicator that you aren’t likely to find what you need around here. This isn’t England anymore.”
But another trip to town netted a small can of pure wood alcohol from the paint section of the hardware store. Refueling the burner with the methanol brought a dramatic change, and a tight purple cone of hot, hot flame hissed gently above the top of the tomato paste cans, just as I remembered. We were in business.
In the meantime, my daughters were busily snipping out panels for the balloon, using a large pattern cut from a cardboard box we’d salvaged from behind the drugstore (not from the apothecary, note.)
“How many do we need?” asked Paoli. Daughter Number Two is likely to turn into an artist like her mother, and was instantly involved in the patterning and cutting of the panels. This was her element. She’s also a literary type, so I’m making plans for a future project to capitalize on that. In the meantime, a three foot balloon will need pi times 3 (or so) panels to get all the way around.
“Nine panels for each balloon. Let’s make just one first, and see how it goes.”
Fitting the panels together was sort of like building a giant paper fan, except that the glue sticks didn’t seem up to the task of holding the paper together, in the neat edge-to-edge match necessary to produce a clean, prolate spheroid when unfolded. Another mistake, I realized. But with a judicious application of packing tape and staples, we managed to produce something that looked like a cross between Humpty Dumpty and one of my grandmother’s cotton quilts. A ring of bailing wire at the bottom to suspend the burner was installed, a round paper cap at the top to seal the crown, and the balloon was done! A bit heavy, I thought innocently, not yet having perceived my technological humiliation rapidly approaching from the far distance.
“Hold this up, “I said to Shawna. “I need to see into it to center the hook so we don’t set it on fire when we light it.”
“On fire?” asked Griffin, still in control of the fire extinguisher. “Aren’t you going to take it outside to test it?”
“Nope. Too windy. We’ll just fill it a little and try it here in the dining room.”

“Can you do that? Did you do that when you built yours?”
“Of course,” I explained, neglecting to mention how my own balloon had met its dramatic fiery end in the basement bathroom of my London high school.
“Can I have a can of Sterno?” asks Starbuck. He will soon be nine, and playing with matches is a wonderful way to anticipate a birthday. Playing with a can filled with napalm is even more interesting.
“You can’t take it away, but you can light it here if you want to watch.” I decide that gathering all the pyros into one place would concentrate the danger, and would likely make adequate response more timely.
“Can I have the other can?” asks six-year-old Golden.  I nod. Starbuck and Golden are close enough in age to plot together at acts of destruction. Luckily Golden’s attention span isn’t as long as Starbuck’s. When he catches up, I imagine that all the remaining screws holding the doorknobs to the doors will disappear to wherever Starbuck put the first ones. And the bolts holding the bunk beds together. And everything else he has taken apart since he discovered how to use a wrench and a screwdriver. Golden is still in the more direct hammer-and-hatchet phase, and has blazed every wooden object near the house with his signature series of gnawing rodent imitations, including the porch railings and the bench by the front door.
But now we’re ready for the big moment, the moment when I shine in front of wife and children, when obscure and mundane components unite in a miracle to vindicate my claim that Dad Really Does Know Something Interesting After All. My time had come.
“Shawna, stand on top of this milk crate and hold the balloon up, so I can light it from below.”
Obligingly, Shawna takes hold of our alcohol bomb and I get down on my hands and knees to light the burner hanging underneath. (She’s sort of short, even standing on the milk crate.) After a moment, I step back, and the little burner hisses out its little purple cone again, this time directing the heated air straight up into the one-foot wide basal orifice of the magnificent Hot Air Balloon.
And then we wait. And wait some more. A little too long, I think. It wasn’t going up.
“It’s not going up,” Shawna observes.
“Let me hold it a minute,” I suggested.
“I can feel the heat coming out of the holes in the top. It’s burning fine. And look at the ceiling.”
Holding the balloon by its crumpled crown, I can feel the heated air slipping out between the badly glued edges, past the many staples, and past the packing tape patches, then escaping to the ceiling. Looking up, I see ring after ring of concentric diffraction shadows rippling across the ceiling just above the balloon, proof that the hot air was pumping out of the burner. Just not enough to lift the leaky balloon, which by this time was getting pretty heavy, what with me having to hold it up in the air. Obviously, we had a weight problem, combined with excessive leakage.
“Okay. Let’s think about this.”
While I thought about it, Griffin returned the fire extinguisher and sat down in front of the computer to slaughter as many Third World mercenaries as he could in his new video game. Starbuck and Golden disappeared to burn up the Sterno in unsupervised privacy. I sat with the two girls looking at the failed balloon.
“Just not light enough, I think. The tissue paper version was lots lighter. And I used balsa wood to reinforce the opening in that one, not bailing wire.”
“Should we make another?” asks Paoli.
“No. Go get a garbage bag, and we’ll test whether the burner is up to the job.”
So there in the kitchen, we built another balloon, smaller and lighter, this time. I couldn’t help but think of Daniel Defoe’s Robinson Crusoe, laboriously building his first boat so large that he was unable to launch it, and had to build a smaller, lighter one, nearer to the sea. This new balloon was just a simple lightweight garbage bag, with a ring of wire at the bottom holding the same burner. I filled the burner, lit it, and held the bag up over the gently roaring flame.
“Look! It’s lifting!”
And it was, but that was all it did. The lightweight garbage bag filled into a satisfying balloon of heated lighter-than-air air, strained to the ends of its tether, and floated in mid-air over the burner, which still sat solidly on the wooden boards of the kitchen floor. We had fuel, we had ignition, we had containment, but we had no lift off.
And that is where we ran out of time.
So at this point, the Great Hot Balloon Project is still in stasis, as I write these words to the sound of the rumbling diesels alongside me in this small Oklahoma truck stop, ten days out from the house. The procedures have worked well enough to vindicate science, but not well enough yet to vindicate our interpretation of the technology. We have heat, probably enough, but we have too much weight, or we have too little volume, or both. Alternatively, perhaps what we need is a steeper density gradient. Perhaps if we had taken the balloon and tested it in the colder cellar, the difference in weight between the inflated balloon and the cold air it displaced would have been enough to generate sufficient lift to raise it, possibly to the point from which it could have ignited the kitchen floor from underneath. Perhaps it was all a combination of these things. Perhaps the stiffness of the wrapping paper envelope prevented it from expanding into a large enough volume to hold adequate heated air (it was open on the bottom, after all, and could only hold so much).
So, for the next iteration of this continuing project, we are first going to conduct a post mortem with the children, and enlist their help in the design of the Great Hot Air Balloon, Mark II. Probably we’ll return to the lighter and more flexible tissue paper, but if we do we’ll have to build the panels from multiple pieces. Probably we’ll make the balloon bigger, which will make it that much more impressive if it works. We seem to have reached a technological ceiling with the burners, except for further experimentation with the small aluminum prune juice cans that are much lighter than the tomato paste versions. Maybe we could use a better fuel, after all. I had briefly considered using nitromethane, but decided that race-car fuel would not be a safe heat source. But maybe being wise wasn’t so smart, after all. I'd also thought about generating hydrogen using water and an automotive battery charger, as the old method of dropping iron into sulfuric acid was likely too hazardous, even for us. And perhaps we’ll dispense with the bailing wire, except for the components directly in line with the flame.
In the end, there’s no telling what we’ll do. After all, this is Experimental Learning, and therefore a failure is just as informative as a success. It just doesn’t make Dad look as good, you know.
Maybe we should try making black gunpowder next.