Why let the government have all the fun with UFOs? Build your own!
I am continuously inspired by the weird beauty of deep-sea creatures. My intent with this creature was to create a kinetic public sculpture that would capture some of the alien wonder of the deep-sea environment.
As an amateur drone pilot I also recognized the many advantages of balloon-based photography:
1) The ability to fly continuously for many days without the need for batteries.
2) Safety (no dangerous spinning parts).
3) The ability to run constant power up the tether to the camera (long captures; essentially creating a very-low-orbit satellite).
4) Balloon operation is less regulated than drone operation and generally receives less negative attention.
Step 1: Pick Your Design!
My first balloon creature was made from a single 4' diameter radar balloon which I purchased from: Meteorological Products Inc.
This design was lightweight and simple but the sphere produced a great deal of drag in the wind, pushing the creature downwards.
For my second design I added lightweight balsa-wood and mylar kite wings. This design is called a "kytoon" or kite-balloon hybrid, and is a popular design for flying antennas, called aerostats. My kytoon design produced a great deal of lift in light wind but was also heavier, countering the effect of the buoyant helium.
In order to design a kytoon that will remain buoyant without the help of lifting wings the designer needs to understand the buoyancy equation:
Fb: The buoyant force created by displacing the air.
ρm: The density of the medium being displaced (air).
V: Volume of air displaced.
One challenge of ballooning is air contamination inside the envelope. Although helium is ~98% pure out of the bottle, there will always be air left over inside the envelope which will reduce the total amount of air displaced by the balloon.
The weight of the balloon, the tether, any wings or other decorations, the camera, and the weight of helium itself will counter the buoyant force. By adding these factors to the equation we can calculate the weight of the payload our balloon can lift.
Fp: The total lift, or payload capacity.
Fb: The buoyant force (derived above).
ρh: The density of helium.
Wt: Weight of tether (the higher the balloon flies the more tether weight will need to be supported)
Wb: Weight of balloon.
Wo: Other decorations, kite poles, camera, etc.
I attached a handy excel spreadsheet that I made to calculate the buoyant forces and material weights.
Step 2: Pick Your Materials!
As we saw in the previous step, the payload capacity is dictated by the weight. Heavier balloon materials will weigh the project down.
Balloon mylar is one of the best materials for balloons because it is extremely lightweight and also (due to the aluminum coating which gives it its appearance) highly impermeable to helium. Balloon mylar is a composite material made from polyester with a mettalized aluminum coating and a nylon film backing. When the nylon sides are pressed together with heat they become welded together and can hold gas (see image of balloon mylar with matte and shiny sides).
The downside of balloon mylar is that it is extremely hard to purchase.
I have purchased the material from mylar balloon makers in China through Alibaba and as a sample from DuPont Teijin Films. Another option is to purchase pre-made mylar balloons and attach them together (like my 4' balloon from Meteorlogical Products) The problem with most party-store balloons is that their volume to surface area is poor, meaning that they produce very little lift. A single large gas envelope is more efficient than many smaller balloons attached together.
I have also experimented with using TPU film (purchased from this company) and a standard impulse bag sealer to create an envelope. This material is slightly more permeable to helium than mylar but is also much stronger and relatively lightweight.
Step 3: Heat-sealing Balloon Mylar!
1) Stretch and tape the mylar onto an ironing board. Be careful to avoid wrinkles because they will leak!
2) Place a fabric sheet over the work and apply the iron on high heat.
3) I like to create nice wide seams and trim them down.
I made this dodecahedron with my friend using this process.
Step 4: Assemble the Balloon!
I used mylar tape from Uline to tape the balloons and tentacles together. This tape is extremely strong and lightweight!
Here you can see some of the 3D printed joints I made to attach my balsa wood kite poles together.
The mylar tentacles of my creature contain a series of helium-filled latex balloons for additional lift.
Step 5: Fly Your Creation!
The great advantage of inflatables is that they are extremely transportable (the entire 25' long squid creature can be crumpled up into a 4' long bundle).
This makes it easy to transport them to many destinations and spread rumors of global alien invasion!
Remember to keep away from power lines! ;D