There are two kinds of balloon that you can use:
- Sounding balloons
- Cold Weather balloons
Sounding balloons will typically weigh in at 200 grams to a full kilogram and lift 250 grams of payload. They will also go up to 20 – 30 km.
The cold weather balloons can carry a good kilogram and are made to go to the stratosphere (from 10 to 50 kilometers high where temperatures can be lower than -75 degrees C)
Kaymont’s balloon has a 12 cm long thick neck used to fill the balloon and attach the load lines.
When you manipulate the balloon, I highly recommend that you use latex gloves. It’s not to protect you but to prevent you from damaging the balloon with your nails and your sweat.
Remember: The balloon is very fragile. Find an area that’s very protected from the wind otherwise, it will bounce against you and the ground a lot and may be damaged before even launching it. Because it’s so fragile, you must launch it from somewhere with no possible contact with fences, trees, phone or electric lines.
How much Helium?
To fill the balloon, I highly recommend to use Helium over Hydrogen.
Hydrogen is lighter than Helium but the difference is ridiculous when you think about the risks. Hydrogen is extremely flammable whereas helium is an inert gas. Moreover Helium is easy to obtain and you do not need any special permits if you decide to start transporting several tanks of it around in your truck.
You can find helium tanks at local party stores or welding supply stores.
I found mine at SF Party in San Francisco.
One cubic foot of helium will lift about 28.2 grams. Kaymont recommends a gross lift of 3440g. So I needed 3440/28.2= 122 cf of helium. I took the 244cf tank + a dolly. It cost me $148. Be careful the tank is very heavy.
How to to fill the balloon from the Helium Tank?
Helium tanks from party stores usually come with special regulators for party balloons. It’s not the best thing in our case because the flow rate is low, you need to constantly bend the valve and consequently it slows the filling process down.
The obvious issue is to link the small regulator’s mouth to the 3 cm wide balloon’s neck. You need to build the joint/adaptor yourself.
- A plastic tube (3 to 6 feet long)
- A 1 inch PVC 90 degrees Elblow
- A 1 inch female PCV tube
- Some scotch tape
To make sure the dimensions are correct, bring with you the balloon and the regulator when you go shopping. You can find the materials at Lowe’s or Home Depot.
The reason you want to a long plastic tube is to be able to inflate the balloon on a clean plastic cover away from everything.
The balloon’s neck is about 3cm (1.2 inch) wide, a 1inch wide PVC tube is large enough to keep it tight. Make sure to secure it with 2 tie wraps and a solid pair of hands.
Since the inflating process can take up to one hour, the person responsible for the balloon can get very tired. The reason you want an Elbow shape is to attach the inflating balloon to something heavy to prevent it to fly away and to measure the lift.
How much Helium is enough?
The tank regulator may or may not have a volume gauge. To measure the balloon’s lift, I found very hard to use a hanging scale. It’s great to weight your payload but absolutely not convenient to measure the lift. The scale is not accurate if there is any wind. It requires at least 2 person and tends to recalibrate itself each time you switch it on.
The best way I found was to attach the regulator joint to a jug of water. Add the desired amount of water to match the lift (3440g -> 3.5 liters). When the balloon is at equilibrium you know you have reached the desired lift.
Remember: It’s always better to have more lift that not enough. (More Lift = Faster ascent rate = Shorter flight time = Fewer problems)
About sealing the balloon, Dave Mullenix has the best instructions: using tie wraps or heavy twine, tie the balloon neck off tightly above the filling adaptor. Remove the joint. Tie the neck again, four to six inches below the first piece of twine. Tie your payload cord to the neck between these two pieces of twine. Now bend the neck over double and tie it again, twice. You will now have the neck of the balloon bent over double, with the payload suspension cord nestled in the bottom of the bend and the whole thing securely tied.
You’re ready to go over your pre flight checklist.