Helium is the key to getting your weather balloon to the edge of space. It weighs roughly 7 times less than air and can thus provide a lot of buoyancy. It’s also colorless, odorless and non-flammable.
Locating helium is not nearly as difficult as it might sound. Helium is used in the party, promotions and welding industries. Most party rental stores such as Party City and iParty rent out helium gas cylinders. One of the quickest ways to locate helium is to go to Google Maps, zoom in over your city, and type “helium” or “helium rental” into the search box. Shop around to see who will give you the best rates. A 200 cft helium gas cylinder rental can cost anywhere from $60 to $120. Keep in mind that some party rental stores will also require a $100 to $200 deposit on their gas cylinders.
How Much Helium Should I Get?
Helium gas cylinders come in many different sizes. Typical sizes available are 50, 80, 125, 200, and 300 cft gas cylinders. If launching our Eagle Kit with a 600 g weather balloon, you can fly on as little as 80 cft. If you want to be precise and calculate exactly how much helium you need, first calculate how much total lift you need.
Total Lift Required = Weight of Payload + Weight of Balloon + Positive Buoyancy
You get to choose how much Positive Buoyancy you want. The more you add, the faster your balloon will climb, but it comes at a cost. Adding more Positive Buoyancy means you're adding more helium which means your balloon will burst at a lower altitude. We recommend adding 500 g of Positive Buoyancy when flying the Eagle..
Now that you know what your Total Lift Requirement is, you need to convert it into Cubic Feet Helium Required. To do this, simply multiply Total Lift Required (in grams) by 0.035.
Cubic Feet Helium Required = Total Lift Required (in grams) * 0.035
As an example, if your payload was is Eagle (700 g) and you are flying it with a 600 g balloon:
Total Lift Required = 700g + 600g + 500g = 1800g.
Cubic Feet Helium Required = 1800g * 0.035 = 63 cft
If Renting From a Party Supply Store
Most welding supply stores will know what you are asking for when you ask them if they carry a 125 cft helium gas bottle. Unfortunately party rental stores do not work in cft. They instead quote the price and size of their gas cylinders based on how many party balloons it will fill. This can be even more confusing because they all base the number of balloons they can fill on different size balloons. Use the chart to the left to decipher exactly what it is they are trying to rent out to you..
When you call the party rental store and ask them what size helium gas cylinders they carry, they are most likely going to respond by asking you how many balloons you are trying to inflate. If they do, and you want to rent a tank that holds 125 cft, tell them you want to inflate approximately 250 twelve-inch balloons (450 nine-inch balloons). Numbers in the chart are approximate, so if their tank only fills 230 twelve-inch balloons, chances are it is still a 125 cft tank.
How to Inflate a Weather Balloon