Category: Solar Balloon
With our last balloon drifting through the stratosphere, it is now time for us to look forward to our next project.
The first thing to work on is obviously the quality of our tether rope. Just out of simplicity, I think we have decided to use paracord to hold out next balloon, partly because it is so light, and partly because it can hold so much weight before it brakes. We may also look into the possibility of a second safety line or an anchor that can act as a fail-safe, just in case.
The next thing that we will be changing is the design of the balloon itself. As I mentioned before, a sphere is a very good shape to use on paper, but the problem is it is very hard to produce, making the construction phase take far to long to complete. To try to solve this problem, we decided to change the shape into the cube. A cube is geometrically similar in shape to a sphere but is also much easier to produce. Another way we are going to make the building process easier is by increasing the size of our plastic. We decided to buy some painting drop cloth, which we will use to make the walls of our balloon. this way we only need to fuse two pieces of plastic instead of +50. Because our drop cloth is clear, we are also going to be covering the inside with black paint pigment. It can be bought at Walmart for an only a few dollars and can make our balloon black and so able to absorb the sun’s energy as well, if not better, then the trash bags.
The next modification we wanted to try is one that we have seen on professional balloons but have not tried ourselves yet. That is to put a clear balloon over the black one. This will help us because as the black balloon absorbs the sun’s energy, it will radiate that heat in two directions, in and out. The heat radiated in is already being collected by the black balloon but right now all the energy being radiated out is simply lost energy. By adding a clear balloon outside the black one, we can collect the energy being radiated out as well, increasing the efficiency of our balloon.
The final thing we want to add to our balloon is a black box. Though we do not intend to lose a balloon again, our last outing has taught us that anything can happen. Because of that, we decided to add a sensor package to our balloon so that if we do lose our balloon again, we can find it when it lands. Our box will have several sensors to help know what our balloon is doing at all times.
- A radio tower based tracker. This is similar to what professional weather balloons use, it allows us to track the balloon based on what radio signals are picking it up. We decided to use this tracking device because it is more versatile than a GPS tracker and is also cheaper.
- A camera. One of the main goals of our last balloon was to be able to hold a camera so we can take pictures from 300 feet, just because it would be cool. Because we still want to do this, we are getting a cheap Go-Pro and putting it in our balloon, so that as we fly we can record our flight and hopefully get some good pictures. we chose a Go-Pro because it is smaller and tougher then other cameras and so can survive an impact better. (Even though we hope it never will need to)
- An altimeter. Though we hope to never lose another balloon, we do want to prepare for the possibility. To accommodate that wish, we decided to track our height so if we do lose another balloon and we recover it, we can at least know how high we went.
- A thermometer. Because temperature is so important in calculating our lift, we decided it would be beneficial to add a thermometer to both measures the temperature of the air inside and outside the balloon. This way, we can start to get a better idea of what temperatures we should use in our future calculations.
Because finals are rapidly approaching, both I and Andy agreed that we were too busy to build our next balloon right away. When we do, these are some of the changes we will be making and hopefully, we will get another successful flight. Until then, good luck with your projects and Happy Tinkering!
The day is finally here, the day that we have been dreaming of for months now. It was time to fly our solar balloon! The sun is hot, the wind is present but manageable, and the skies are clear. We arrived at a local park at about noon on Saturday and immediately started filling up the balloon with an nervous excitement that is to be expected with a maiden voyage. The wind was slightly gusty so while we were waiting for the wind to die down, we scoured the surface of the balloon, patching any holes we could find. Because the wind was blowing decently strong so we were forced to hold the balloon down in an effort to limit the pull the wind had on the large surface of the balloon, however, as a result, we couldn’t get a good idea of exactly how much lift was being generated. In fact, we were considering refilling the balloon with hot air to try to boost the lift a little higher. We honestly didn’t think it would fly very well, not with the thermal test from last week and the amount of air that had leaked out of the balloon by this point. By rough estimate, the balloon was only about 3/4 full when the wind finally let up enough for us to give it a test flight. We made sure the balloon was tied to the fishing line which was attached to the fishing pole we used to control the balloon while it was in the air, and it was time for a test!
When we finally let the balloon go, it beautifully formed into a sphere and instantly started rising, much faster then our last balloon did. We knew that we needed to keep the balloon under 300 feet for legal reasons so after only going up maybe 200 feet, we locked the fishing line so it wouldn’t fly any higher and that is when it happened.
At first, I didn’t know what happened but it soon became apparent that our fishing line broke and as a result, we had lost control of the balloon. In hindsight, using a small Gage fishing line to hold a balloon designed to lift at least several kilograms was not a very smart idea, but this balloon was about the same size as our last balloon and that sting had handled the stress beautifully so we didn’t think anything about it. In desperation we chased after our balloon as it continued to rise, hoping that it would sink to an altitude that we would be able to recapture it. It quickly became apparent that not only were we not running fast enough to catch the balloon, but it had no intentions of returning to the earth anytime soon. Even chasing it in a car would not have been plausible as it quickly rose higher and higher, quickly shrinking unto the blue sky, leaving us with nothing to do but take pictures.
Our feelings at this moment were very mixed as the balloon worked much better then either of us had predicted it would. As I said earlier, just before we released the balloon, we were about to go reinflate it with hot air to try to make it fly better. The fact that it had enough lift to break our line was exciting because that meant that our balloon was working as good, if not better then intended. That feeling was mixed however as we were watching over 7 hours of hard work float away into the sun.
The experience was not a total waste either because we now know that, while a sphere generates the most lift of all the shapes we could have used, it is not the easiest to make. Andy has, on his own, make rectangular balloons of similar size in only a few hours while a sphere took two people over 7 hours to complete. Also, we now know that we need a stronger rope to hold our balloons how with. Right now we are researching the possibility of using paracord or deep sea fishing line for our next balloon. In the meantime, however, we got to enjoy watching our balloon shrink into a dot in the distance and then finally disappear in the clear blue sky. I hope you found this post interesting, we will be doing more building in the next Solar Balloon post so if you are interested in that then I hope to see you in the next one. Untill then, Happy Tinkering!
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!
This week me and Andy wanted to start construction of a new solar balloon using the new numbers that we had run in the last solar balloon post. one of the things that we bost agreed was the downfall of the first solar balloon was the weight added by all the tape used in construction and patching or holes. Because of this, we wanted to see if we could find a new and lighter way to seal everything together. We wanted to see if we could get a method of fusing the plastic together to work. The idea is that we would use heat to make both layers of plastic melt slightly so when they cooled back down they would be melted together and therefore fused without adding any of the weight that would come from using tape.
Because one of the major design goals for this balloon is to keep the cost at a minimum, we have decided to build our balloon, at least for now, out of cheap plastic trash bags. One of the advantages of this is they have a very low melting temperature making fusing easier. The next thing we needed was a heat source. We decided to try a cheap iron like the one that can be bought at Walmart for ironing your clothes. we went with this because it has multiple heat settings that will help us to while in on the ideal heat for fusing but not melting the plastic.
the next thing that we needed to address was the rate at which the heat was being transferred to the plastic. Even at the lowest setting, the iron can easily melt straight through the plastic if you are not careful. We received a tip that placing a layer of parchment paper between the plastic and the iron will help to slow the heat transfer rate to a degree that it becomes more manageable.
With all this together, all that was left was to find the exact temperature setting for our iron. If you are going to be duplicating this technique for one of your own projects then keep in mind that not only will your iron be behaving differently but also the heat required to melt different plastics is drastically different so you will need to find your own heat settings for your situation. what worked for us was to turn the heat all the way up then take one or two quick passes over where you want to fuse the plastic together. Any longer and the plastic ends up melting holes in itself and any colder and the two layers don’t actually fuse. done right and you end up with a lightweight bond with few to no holes and yet just as tough if not tougher then the original plastic.
I hope this post was interesting and helpful to you. We certainly learned a lot about it and super excited to start building the mid-scale balloon very soon. until then, good luck with your own projects and Happy Tinkering!
*A note from future me. Though this technique of fusing did work, we found that it still had some major flaws that will need to be worked out before going full scale. I will be talking about some of these in the next Solar Balloon post but keep in mind that this is not a perfect technique and so feel free to experiment on your own to see if there is a better option that we haven’t thought of yet.
The solar balloon is by far the largest project I have ever attempted and so an element of risk comes with it. I usually don’t like doing math when I do my tinkering projects, however, both me and Andy decided that if we were going to be making a full-scale solar balloon capable of carrying one or two people then we might want to take some safety precautions. One of the first precautions we wanted to take was to know the math so that we would at least know that our paper works on paper. If you find math to be very boring then you might want to move on to the next post but if you find this interesting or you are attempting this yourself then you should stick around.
The math behind a solar balloon or any hot air balloon is very similar to a boat. the reason is a lighter than air device like a balloon literally floats on top of the air like a boat floats on water. to solve for this, we can use the buoyancy equation which says that the buoyancy force on an object is equal to the weight of the air (or water) that you displace. in math-speak that is:
or the pressure of the displaced air (P) multiplied by the pull of gravity (G) and the volume of displaced air (V). For our solar balloon that is modified to:
(Po= outside pressure and Pi= inside pressure)
or the difference in the density between the air outside of the balloon and inside the balloon (Po-Pi), multiplied by gravity (G) and the volume (V). Though this will get you the buoyant force, we wanted the only variable to be the temperature of the air and to incorporate this we use the ideal gas law which is:
or the pressure of the gas (P) multiplied by the volume of gas in question (V) is equal to the amount you have (the number of moles)(N) multiplied by a constant (the ideal gas constant)(R) and by the temperature of the air (in Kelvin )(T). When you combine this with the buoyancy equation you get:
Once we had this equation, Andy, who knows programming, but this into a program so we could easily modify the terms and find a volume that works for our purposes. The code he wrote looks like this.
we then did some research and found the lowest temperature difference recorded in a solar balloon was about 2 degrees and so decided to use that as our test temperature. we will probably get more heat than that in our balloon and our next balloon is going to be a test platform to find out stuff like this but for now, we figured that this would be a good baseline. We started to test the program at different volumes and these are the numbers we came up with.
- A spherical balloon with a 5-foot radius (or 10 feet across) with 1 degree of temperature difference will lift 0.594 kg and with 2 degrees of temperature difference will lift 1.185kg
- A spherical balloon with a 10-foot radius (or 20 feet across) with 1 degree of temperature difference will lift 4.754 kg and with 2 degrees of temperature difference will lift 9.487kg
- A spherical balloon with a 25-foot radius (or 50 feet across) with 1 degree of temperature difference will lift 74 kg and with 2 degrees of temperature difference will lift 148kg
This data shows that a balloon with a 2-degree temperature difference and a 25-foot radius will lift a 220 lb person with ease. This is fun to imagine but for now, we will be making a 5-foot radius balloon and its cargo will be a video camera (mostly because we wanted a cargo and though that pictures might be kinda fun). this balloon is probably going to be much too big for just lifting a camera but that means that we can use it as a test balloon for a long time coming.
I recognize that math can be very boring but we decided that it was worth knowing so we don’t take weeks making a balloon that doesn’t work. I hope this post was insightful to you and happy tinkering!
I recently started a project with a friend to make whats called a solar balloon. The concept is to make a hot air balloon that uses no heat source other than the power of the sun. There have been various attempts over the past few years. Most of them have been small toys or science experiments but some people have able to get full-scale versions capable of carrying a person. If you are interested In learning more, look at this website of one that flew for 2 hours.
My friend, Andy, has been making these for a while and invited me to see what he was working on. We met up at a field one cold morning and spent several hours working to get his Solar Balloon flying. I was impressed how small the whole thing was. deflated, it was smaller than a breadbox but inflated it grew to be as tall as me and much too big to fit my arms around.
we inflated it by means of a hair dryer and kept control of it by means of a fishing pole and fishing line. We had various problems that made flying it much harder than we anticipated, stuff like the tape we used to fill the seams of the trash bags that make up the skin of the balloon coming loose, to the wind making the balloon virtually uncontrollable. After many hours of work, we finally succeeded in getting it flying!
if you want to do the math to find out how high the baloon went, both me and andy are about 6 feet tall.
It was the only flight we got that day and we had a lot of fun getting it to work but we both agreed that there was room for improvement. The next series of posts will be about our process as we strive to improve upon our last flight and to hopefully make one big enough to fly in one day (that’s the goal at least). Some of the things we decided to work on was
- A better method for joining the trash bags together. Ideally, we would like to use a heat seal like in vacuum packing but if that doesn’t work then possibly double-sided tape.
- We need to decide what shape would produce the best lift per gram of weight for our balloon.
- We wanted to see if there was a mathematical way to know how much our balloon will lift so that we know if it will both lift itself but also a cargo (like a person).
- We need to know how hot the balloon is getting on the inside so that we can get trash bags that can handle the heat
- We want to know if it is better to have the back of the balloon be reflective to help trap the heat or if it would be better to keep it all black
- Or is it better to have the side facing the sun be clear like a car window
When we start getting ready to go full scale
- We need to have a way to control of our orientation to the sun and our ascension/descent (up/down)
- We will need to know weather pattern and how things behave differently at altitude
- We will need to know what paperwork we need to do with the FAA (Federal Aviation Administration) and the NTSB (National Transportation Safety Board) so that we know that no airliner will be flying into us while we are testing our balloon.
While we are working toward a full-scale model, we decided to set ourselves intermediate goals (we are guys but we are not complete idiots) and so the immediate goal is to have a balloon that can carry a remotely-controlled camera to a decent altitude and then take pictures for the heck of it. This project will take a while and we will be taking lots of safety precautions so I will be reporting on our progress over the next while. In the meantime, thanks for joining me and happy tinkering!