Art of the Hands

Time to Tinker

Tag: Solar Balloon

Solar Balloon Part 6-What next?

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.

  1. 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.
  2. 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)
  3. 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.
  4. 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!

Solar Balloon Part 2-lets do the math

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:

B=PGV

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:

B=(Po-Pi)GV

(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:

PV=NRT

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:

B=PVG/(R(Tf-Ti))

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.

  1. 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
  2. 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
  3. 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!

Solar Balloon Part 1-The Beginning

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!

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