I am sure if you have seen one of these in action then you must have wanted to try it for yourself. I am talking about Sky Lanterns. Those lovely miniature hot air balloons that the Thais believe are symbolic of problems and worries floating away. They are constructed from oiled rice paper on a bamboo frame, and contain a small candle or fuel cell composed of a waxy flammable material. When lit, the flame heats the air inside the lantern, thus lowering its density causing the lantern to rise into the air. The sky lantern is only airborne for as long as the flame stays alight, after which the lantern floats back to the ground. Sure you can buy these online but for those of you who would like to build it rather than buying please keep on reading and I assure you, you will be flying your very own sky lantern in no time at all.

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Sky Lantern Autopsy

A little reverse engineering revealed:
Weight of a flying lantern	2.7 ounces
Thin bamboo hoop at bottom	45.75? circumference, 14.56? diameter
Weight of hoop	0.3 ounces (with a little paper and glue still hanging onto it)

Bamboo is about 1/16? x 1/8?

X of thin wire tied to hoop

X of wire is “woven” through waxed cloth and paper “burner”

The burner is composed of a 2.5? x 17? piece of wax-impregnated cloth, folded in Z-fashion back on itself 5 times.

In between each Z-fold of the waxed cloth are five 2.25? x 3? pieces of thin, coarse-fiber paper, about the weight of 40# kraft paper.

(The cloth/paper burner smells “nice,” sort of like the scent of roses. Maybe the young Chinese lady who made this one was wearing some fragrant perfume.)

Note: I have also seen sky lantern burners, which resemble fiber-reinforced blocks of wax. I don’t know how they are made and have not tried to duplicate them.

The “bag” of the balloon is made up of white tissue paper. This paper has been treated with a fire retardant; it does not catch fire when touched by a flame. It just scorches a bit.

The tissue paper bag weighs 1.5 ounces.

There are four panels (called gores in the ballooning world) that make up the balloon, and they are glued together and to the bamboo hoop.

Here’s a sketch of one of the gores, with a bit added to the edges to allow for gluing.

I flew one of these fire-lanterns in my high-tech, windless wind-tunnel (actually my garage, emptied of any gas cans or other combustibles). I tethered the Chinese lantern to a weight with some very thin, light string as it burned. The fuel pack burned for 4.5 minutes.

I added 0.05-ounce pieces of wire, one at a time, to the bottom wire “X” of the balloon as it “flew,” and found it would carry 0.25 ounce of payload before starting to sag toward the ground garage floor. That 0.25 ounce, added to the paper-lantern’s original weight of 2.7 ounces, added up to a maximum flying weight of 2.95 ounces for a lantern with this internal volume.

It is the internal volume of a paper hot-air balloon, and the heated air it can contain as well as how much that air is heated, which determines its maximum carrying capacity.

Note: The information above is important. These flying lanterns are delicately balanced for flight, and they are just light enough to allow them to fly. If they were much heavier, they would not leave the ground. Due to some circumstances, which I describe below, my first balloon ended up weighing 3.9 ounces, and obviously would not have flown.

So, let’s make a paper sky lantern

I went up to my local Hallmark store and bought some nice tissue paper in different colors.

Some checking online produced some leads on products designed to flameproof paper. One company, Universal Fire-Shield (www.firechemicals.com), sells a product, Universal Paper Shield P-3000, designed to fireproof paper products. I ordered some. They sell a quart spray bottle for about $30, including shipping. This would be enough to treat about a dozen paper hot-air balloons.

I hung 4 pieces of the red tissue paper on a clothesline, and sprayed them with the Paper Shield until they were saturated. After they were dry, I tried to burn a little piece of the paper, and it only scorched like the original fire-lantern paper, but it would not burn.

Note: On my third attempt to make one of these paper lanterns, I decided to try to spray the untreated bottom half of the balloon after it was assembled, in order to skip the step described above. I hung it up, slightly inflated it with my heat-gun, and started spraying it. The tissue paper soon started to weaken, sag, and tear, ruining the balloon. Crud! Another lesson learned.

I decided that the process of hanging the panels like laundry works best. The upper corners of the sheets will be cut off when the gores are cut out, so I don’t spray those areas because they get weak when they are wet, and allow the clothespins to tear through the paper and sometimes that has the paper to tear loose from the string.

Warning: Paper Shield has an acid in it, and it will damage a concrete garage floor slightly. It’s best to have a plastic drop cloth under the clothesline to protect the floor. Don’t breathe its fumes or get it on your skin.

The red tissue will be the bottom of the paper hot-air balloon, which will be the only part that gets exposed to the flame. The top of the balloon will be blue paper, and it does not need to be treated.

I glued a piece of the red paper to a piece of the blue with thin stripes of Elmer’s, and I did that four times for the four panels, and let the panels dry.

Note: The Elmer’s glue tends to wet the tissue paper, bleeds through, and tries to stick to the other stuff around it. In an attempt to avoid this problem, I used hot glue when building my first balloon. This worked nicely during construction, but when I fired that baby up, the hot-glued seams at the top of the balloon let go completely. I did not think the internal temperature would get high enough to cause this problem. I was wrong. (My wife, Molly, told me later on that she wondered about me using the hot glue, and that she thought it would melt when the burner was lit. Oh, well.) The hot glue, which is significantly heavier than the dried Elmer’s, also contributed to the excess weight of the first model.

After gluing the red and blue sheets together and letting them dry, I cut the four panels out with scissors, using a kraft paper template that I made based on the sketch above. Folding the kraft paper in half lengthwise, and then every 6? made the pattern transfer easy.

Then it was time to glue the lantern gores together to form the Thai-lantern’s “bag.” I laid one of the gores, unfolded and open, on the worktable with the inside up. (The outside of the gore is simply the side that I think looks best.) Then I laid a gore, outside up, on top of the first gore, weighed the two down, and glued the right sides together with a thin stripe of Elmer’s. The table had waxed paper on it so that any glue that seeps through wouldn’t stick to it.

I then folded the top gore’s loose side over on itself, so that half’s inside was facing up, inserted some waxed paper between the glued side and this loose side, and laid the third gore on top of that one. I glued those two loose edges together, inserted more waxed paper, folded the loose half of the third gore over, laid the fourth and final panel on top, and glued those loose edges.

Then the last step was to fold the loose half of the top, fourth gore, over on itself, and fold the loose half of the bottom, first gore over onto it, and glue the loose halves together. (This all sounds much more complicated than it actually is. Once you try it, it’ll all make sense.)

Then I pulled the glued edges up and off all the waxed papers, propped the panels apart from each other and from the table, and allowed the seams to dry.

Another Failure Note: On my first attempt to build one of these, I tried gluing the bag together with the panels inside out. I let the seams dry, and then I tried to turn the bag right side out, so that the seams would be hidden. This probably would have worked OK, but the fireproofed red tissue paper was somewhat brittle because of the fire-treatment, and as I tried to turn it inside out, it started to tear and crack at the bends and creases. I had to try to repair these tears with clear packing tape, which increased the lantern’s weight, and made it ugly, and not something to be proud of. I decided to simply allow the seams to be on the outside of the bag in future models, and avoid the “turning inside-out” step.

Making the sky lantern’s bamboo hoop

Home Depot had some 1? diameter bamboo poles in their lawn and garden department. I bought one and carefully split it into thin strips. I took one of the strips and smoothed it with sandpaper and a razor knife until it was about the dimension of the original lantern’s bamboo. I only sanded the “interior” side of the bamboo because I did not want to weaken the smooth, exterior side of it. Then I glued it into a hoop with the same circumference of the original.

Another source of good bamboo strips is from a “Tiki-Torch” pole. These are often split to obtain bamboo strips for girandola frames, wheel frames, and the like. (Or you can steal some green bamboo from Harry Gilliam’s bamboo-infested front yard.)

Making the Sky Lantern Burner

I had some blue, industrial paper-towels, and I decided to melt some grocery-store canning-wax, and impregnate the towels with the wax in an attempt to duplicate the waxed fabric that I found in the original fire-lantern’s burner.

Warning: Canning (paraffin) wax is very flammable, and should only be melted over low heat in a double boiler. It should never be exposed to open flames or high heat.

I took a strip of this waxed paper towel, and burned it alongside a strip of the waxed material from the original lantern’s burner. Both samples burned identically and for the same amount of time.

I had some coarse, recycled kraft paper, and cut it into rectangles to match the original burner’s paper layers. Then I cut some strips of the waxed paper towel to match the original burner, and sandwiched 5 pieces of the kraft paper in between each layer of the waxed paper-towel.

Then I stacked the layers of the burner together, punched 4 holes through all the layers with an awl, and threaded two pieces of wire through the holes.

The ends of the wire were then wrapped around the bamboo hoop and twisted tightly to secure the ends. The hoop was then carefully glued into the end of the lantern’s tissue paper bag, and the glue was allowed to dry.

A simple alternative burner can be made by simply installing a plain X of wire on the bamboo hoop. Then strips of cotton-ball like material can be saturated with rubbing alcohol, draped over the center of the wire X, and ignited when launching the balloon. But keep in mind, you have to use this method right away; the alcohol fuel evaporates, and these have no “shelf life.”

All that remained, then, was the installation of the “FAA” aircraft identification numbers, and a flight in the “test chamber.”

This paper hot-air balloon’s final weight was 3.0 ounces. At about 50-degrees F in my garage, it was able to carry a payload of .55 ounces of the wire pieces before it started to sag toward the ground.

After this testing, some soot and moisture condensed on the inside of the lantern. I was able to allow it to dry out, attach a new burner, and fly it outdoors for real. It was about 40-degrees F outside on the evening that we flew it, and it really took off for the heavens very quickly.

Note: The flying lantern in on the right, Molly is on the left. The fact that Molly’s attire matched the balloon she was launching was entirely coincidental. That’s my story and I’m sticking to it.