Solar Balloon Part 4-lets get to building
Now that all the math and production procedures are all worked out, it is finally time to start building my first solar balloon. The first thing that We needed to work out was how we were going to cut out the pattern correctly. We brainstormed using a projector and tracing that line to make out the pattern. This idea was quickly disregarded because the scale needed and the relatively small work area we would be working in made us doubt that any projector has an area of vision that big. Even if it did, both me and andy agreed that there would likely distortions in the pattern as we got to the end of the image so a projector was out of the picture. The only thing we could think of that would let us duplicate a shape big enough was to use some kind of a template. This idea also had problems because of the sheer size we are talking about. In case you don’t remember from some of my previous posts on the solar balloon, our solar balloon is designed to be 10 feet across and so, if we do the math, we need a template about 5 feet wide and 15 feet long. Funny thing, you cant go down to a craft store and pick up a 15-foot long template for a sphere, that kind of thing is just not made anywhere we could find. because of this, we were forced to make our own. our first idea was to get an image from the internet and then printing it ours on a mega scale printer located in the printer of the library where we both go to school. Turns out trying to print a piece of paper this big would cost us over 100 dollars, which is obviously out of the question for a build that is supposed to be a very cheap project. Finally, we got the idea (from my Mom) to use a painters drop cloth. a quick trip to LOWES found us with a piece of plastic measuring about 10 feet wide and 20 feet long, just the right size for our template.
The next challenge was to put the pattern on our template. We couldn’t use a projector, for reasons mentioned earlier, so we decided to the math and draw the shape ourselves. Because we decided to make our balloon out of pieces of this template, all we needed to do was a little math and in no time we had ourselves a template. we folded the plastic in quarters just to expedite the cutting process and made sure to include a hole in the bottom so we could fill it up with air before take off.
With the template ready to go, we started an assembly line with Andy making giant sheets of plastic by fusing about 8 disassembled trash bags into one giant sheet which I then used the template to cut the sheets into balloon parts. In case you were wondering why there is a hole in the nose of our template, that was an accident where we accidentally melted our sheet of plastic to the template and was forced to cut that part away from the template and plastic sheet in order to separate the too. As an upside, the template now looks like a rocket ship!
After we completed six of these balloon parts, the next step was to fuse them into a sphere. To tackle this, me and Andy set up a system to make creating a 3D object on a 2D floor easier. we started joining each section by first joining the middle and then moving to the nose (where the hole is in the template) with Andy fusing while I was putting each piece in place so they would be ready for fusing. once we reached the nose, we then repeated the process moving about 1/2 to 2/3 of the way down the tail. We didn’t completely finish it for reasons that will soon become clear. with one side of the plastic balloon part fused, we repeated that process five more times until finally, we were at the final seam. Because this seam was the one that closed the balloon making into a sphere, we needed a different plan of attack for how to finish this. What we finally decided on was Andy was going to crawl into the balloon and I was going to drag the cloth over his back so he could position it for fusing. I was also in charge of making sure he had enough air to breath as neither of us thought to bring a fan for ventilation.
This image is a picture of Andy inside the balloon and hopefully, this shines some light on just how big this thing was. With this final seam, we started at the nose and worked our way back until we got to the tail and this is where leaving the remainder of the tail’s unfused was a good idea because it created a hole big enough for andy to work in. Once andy was out of the balloon, the only thing left to do was fuse the tails and give it a test.
In case you still haven’t gotten the scale of this balloon, your tallest friend could, if we made a hole for him, crawl inside this balloon and stand straight with feet of clearance between their head and the top of the balloon. Also, if you were wondering why were wearing hearing protection, my boss was amazing and let us use one of the backpack leaf blowers that we use for work and it is was so powerful that it filled the balloon in just minutes while still running on idle. There was hardly any sun that day so we didn’t really expect to get it flying but we still wanted to see it inflated and get some information about how hot it was inside the balloon even with almost no sun. when we inflated it, we found that our method of fusing had malted dozens or hundreds of holes in the ballon of various sizes that all needed to be taped together so it would be mostly airtight. also, we tested the temperature difference between the outside air and the inside air and came to about 5 degrees of temperature. This was worrying because our math had said that a balloon this size should be lifting almost 1 kilogram with only 2 degrees of temperature difference but in hindsight, the fact that the balloon was not flying yet was not entirely surprising because of 2 reasons.
- the balloon was probably slightly smaller than we intended it just due to manufacturing imperfections that were unavoidable
- The balloon was not full of air like the math required, it was probably only 80% full at the time we measured the temperature so the total lift would have been reduced because of that
Though this result surely surprised and worried us, we soon found that this was not going to be a problem in the slightest. If you remember, one of the purposes of this balloon was to decern an approximant temperature difference we will be getting in our balloons so we have a base for our future calculations. Because of this, we over-engineered this balloon so that it should work in almost any condition, and indeed we will see in the next Solar Balloon post that our earlier concerns were unfounded.
I hope that you have enjoyed this post. If you are attempting to build one of these Balloons yourself than plan for this build to take you multiple hours to complete, it took us approximately 10+ hours split over two days, so plan for either more people or similar build times when you do yours. Either way, I hope this post was helpful for you and until next time, Happy Tinkering!