Balloon Performance Calculator Tutorial
Before you use our Balloon Performance Calculator it is important to us that you understand exactly how it works. The Balloon Performance Calculator starts by collecting three pieces of information: the size of your weather balloon, your payload's weight, and how much positive lift you want to use. With these three values, the Balloon Performance Calculator determines exactly how much helium you need. To accomplish this the calculator adds the weight of the balloon, the weight of the payload, and the positive lift. It then divides this summation by 27.82 to get the amount of helium you need in cubic feet (1 cu.ft. helium can conservatively lift 27.82 grams). Next the Balloon Performance Calculator calculates the altitude at which the balloon will burst. It already knows what the initial volume of the balloon is at launch in cu.ft. and can therefore predict at what altitude the balloon will be when it reaches its maximum volume. The smaller the balloon's initial volume, the higher it will go before it reaches its burst volume. Keep in mind that this is a conservative estimate only.
Link to Balloon Performance Calculator
What You Need
- The size balloon you intend to use - Our Balloon Performance Calculator works with our 350, 600, and 1200 g balloon sizes.
- The weight of your payload in grams - This is the weight of everything suspended below the balloon including the parachute. You can use the launch scale included with our Inflation System Kit. to get an accurate measurement. The weight of the payload does NOT include the weight of the balloon.
- Your positive lift in grams - This number will make more sense as you learn how to use our Balloon Performance Calculator. For now just start with an initial guess of 100 grams. You can always change this number based on the results you get from the calculator.
What is Positive Lift?
Positive lift is the extra lift your weather balloon needs to rise upward in addition to the lift needed to carry the weight of your payload and the weight of the balloon itself. As an example, let's say you want to launch a payload that weighs 1200 grams (including the weight of the parachute, rigging, etc.). Let's also assume you are using our 1200 g weather balloon (which also weighs 1200 grams). You calculate how much helium you need to launch your payload with the knowledge that 1 cu.ft. of helium will lift 28 grams. You divide the weight of your balloon and payload (2400 g) by 28 g/cu.ft. to get the total number of cubic feet of helium required for your launch (2400 g ÷ 28 g/cu.ft = 86 cu.ft.). You inflate your balloon with 86 cu.ft. of helium and release your payload. To your surprise it doesn't climb. It just floats right in front of you, neither climbing nor descending. This is because your balloon has only enough helium to lift its own weight and the weight of the payload. It's at perfect equilibrium. You need a force that will make the balloon and payload rise upward. The easiest solution is to add more helium to the balloon. This additional helium will provide the extra lift you need to make your balloon climb. The lift force created by this additional helium is called positive lift. The more helium you add to your balloon in addition to the helium used to lift the weight of the payload and the balloon itself, the more positive lift you will have. The more positive lift you have, the faster your payload will climb.
Things to Keep In Mind
- Our Balloon Performance Calculator is conservative when calculating predicted burst altitude. We want our customers to be pleased with their achieved altitude and not be disappointed because they never reached a theoretical altitude generated by our calculator.
- Two identical size balloons made by the same manufacturer will typically burst at the same diameter/volume. More expensive balloons have a greater burst diameter/volume than those made by a cheaper manufacturer.
- Balloon sizes are measured by their weight in grams. A 350 g weather balloon weighs ~ 350 grams. A 1200 g weather balloon weighs ~ 1200 grams.
- The larger the balloon size (the more it weighs), the larger its diameter/volume will be before it bursts.
- If you launch two payloads with the same size balloon, the balloon with the least amount of helium will burst at the higher altitude.
Step 1 - Input your balloon size, payload weight, and positive lift of 100 g into the calculator. Select your balloon size from the drop down menu and input your payload weight (everything suspended below the balloon including parachute, rigging, cameras, etc.). Because we're not sure how much positive lift we need yet we'll just enter 100 g for now. For this tutorial we'll use our 600 g Weather Balloon and our Eagle Pro Kit which weighs ~ 600 g (including batteries, a GoPro, parachute, Radio Bug, etc.). Our Weather Balloon Inflator kit includes a launch scale which you can use to measure the weight of your particular payload setup. We recommend that you follow along through this tutorial by entering the values into your own Balloon Performance Calculator tool.
Step 2 - Calculate. Click Calculate. Under the Output side of the calculator you'll see how much helium you need, your estimated burst altitude, average ascent rate, and ascent time (time it would take your balloon to travel from 0 m altitude to estimated burst altitude). With 100 g positive lift it will take 251 minutes (4 hr 11 min) for our 600 g balloon carrying a 600 g payload to reach an estimated burst altitude of 31,580 m (103,000 ft). Although we are happy to see our balloon bursting at an altitude of over 100,000 ft, the battery on our GoPro lasts just under three hours. Assuming the payload takes 35 to 45 minutes to descend under parachute once the balloons bursts, we need our ascent to take no more than 120 minutes if we want to capture the entire flight on video. Our average ascent rate is too slow.
Step 3 - Increase your positive lift. We decide to see what happens if we increased our positive lift from 100 g to 1,000 g and recalculate (enter a new Positive Lift value of 1,000 g and click Calculate). Our ascent time is now only 84 minutes (1 hr 24 minutes). The ascent time is below our 120 minute target, but our burst altitude has decreased from 31,580 m to 28090 m (92,000 ft). There's an even bigger problem. Our average ascent rate is over 5 m/s. Any ascent rate over 5 m/s significantly increases our risk of the balloon creating unsteady oscillating drag in its wake as it ascends though the atmosphere. This will cause our payload to swing about violently and could cause damage to the payload and balloon. Our average ascent rate is now too fast.
Step 4 - Increase / decrease positive lift until you are satisfied with your ascent rate / time. We know we need a positive lift of between 100 g and 1,000 g. Our goal is to have an ascent time of 120 minutes and have an ascent rate under 5 m/s. We experiment with different positive lift numbers (just enter different Positive Lift values between 100 and 1,000 g and click Calculate) until we find 460 g gives us an ascent time of exactly 120 minutes. Our burst altitude is 29,950 m. This is less than the 100,000 ft we were hoping for, but the calculator is conservative so our chance of reaching 100,000 ft is still high (we had a customer reach 115,000 ft using 100 g positive lift even though the calculator estimates a burst altitude of only 103,000 ft for this setup). Our average ascent rate is well below 5 m/s and we need 60 cu.ft. helium for our launch.
Step 5 - Taking it further. The local party supply store rents out 55 cu.ft. helium tanks (a common size for Party City). We need 60 cu.ft. for our launch, but what if we don't want to spend the money to rent an additional 55 cu.ft tank when we only need 5 extra cu.ft? We decrease our positive lift until our calculator tells us our setup requires 55 cu.ft for the launch. With a positive lift of 330 g we need exactly 55 cu.ft. This increase our ascent time from 120 minutes to 140 minutes. It also increases our burst altitude to 30490 m which is ~100,000 ft. We don't like adding 20 minutes to our ascent time. What other options do we have?
Step 6 - What if we reduced our balloon size? We decide we don't want to rent two 55 cu.ft. helium tanks. What happens if we reduce our balloon size from 600 g to 350 g? After calculating different positive lift values we find that 290 g positive lift gives us the 120 minute ascent time we are looking for and our total helium required is only 45 cu.ft. Our estimated burst altitude however has dropped to 26,060 m. This is less than the 30,000 m ~100,000 ft we were hoping for. Here are just a few options you might have. If you get creative you could probably think of even more options.
- Rent two 55 cu.ft. helium tanks for our 600 g weather balloon and reach 30,000 m in 120 minutes so we can capture the entire flight on our GoPro.
- Rent only one 55 cu.ft. helium tank with our 600 g weather balloon and fly even higher, but risk not capturing the entire flight on our GoPro.
- Rent only one helium tank and use the smaller 350 g balloon, not fly as high, but still capture the entire flight on our GoPro.
- Use our 600 g weather balloon and find a way to reduce the weight of our payload so we can reach our burst altitude in 120 minutes on 55 cu.ft. Play around with the Balloon Performance Calculator and see if you can figure out how much your payload would have to weigh to reach the estimated burst altitude in 120 minutes with 55 cu.ft helium. The answer is at the bottom of this webpage*.
- Move your launch site from sea level (calculator assumes you launch at an elevation of 0 m) to a higher elevation. Here in Colorado High Altitude Science typically launches at an elevation of 2,200 m. At an average ascent rate of 3.6 m/s it will reduce our ascent time by 10 minutes (2200 m divided by 3.6 m/s divided by 60s/min = 10.2 minutes).
Which option would you chose?
*The answer to option 4 in Step 6 - Using a 600 g weather balloon and 55 cu.ft. your payload would have to weigh 480 g and you would need a positive lift of 450 g to reach the estimated burst altitude in 120 minutes.