High-Altitude Balloon Lift
After conducting many launches and seeing high-altitude balloons tangled in trees, buildings and power lines minutes after launch, I would like to share some of the techniques I use to calculate lift of a high-altitude balloon.
The general rule for determining lift need for a high-altitude balloon to carry a payload into Near-Space is to multiply the entire payload weight by 1.5. (e.g. a 10 lb payload would require the balloon lift to be 15 lbs.) The lift need to carry the payload is also referred to as nozzle lift.
When you have the nozzle lift for your high-altitude balloon you will need a way to measure this lift. There are a number of ways of doing this but I will explain two.
The first method of determining nozzle lift uses a digital fish scale you can find at most sporting good stores. See picture below:
Tie a line from a heavy object at your launch site, which will most likely be your helium tank to the bottom of the digital fish scale. Tie another line from the top of the digital fish scale directly to the neck of the balloon. When filling the high-altitude balloon periodically stop filling, pull the helium nozzle from the balloon and seal the balloon neck with your fingers and check the lift indicated on the digital scale. This method of checking lift works well with little to no wind. In windy conditions the balloon will pull as it is blown side to side giving a false reading on the digital scale.
The second method of measuring nozzle lift is to fill containers with water to equal the nozzle lift required. If the nozzle lift is 15 lbs fill milk jugs or a 5 galloon bucket with water to equal 15 lbs (1 gallon of water is apox. 8.35 lbs.) Tie this container to the neck of the balloon. When the container is lifted off the ground you have met your nozzle lift. This method works well in windy conditions and also can be used for more advanced Near-Space explorers for precise low ascend rate flights.
Jason Krueger
The general rule for determining lift need for a high-altitude balloon to carry a payload into Near-Space is to multiply the entire payload weight by 1.5. (e.g. a 10 lb payload would require the balloon lift to be 15 lbs.) The lift need to carry the payload is also referred to as nozzle lift.
When you have the nozzle lift for your high-altitude balloon you will need a way to measure this lift. There are a number of ways of doing this but I will explain two.
The first method of determining nozzle lift uses a digital fish scale you can find at most sporting good stores. See picture below:
Tie a line from a heavy object at your launch site, which will most likely be your helium tank to the bottom of the digital fish scale. Tie another line from the top of the digital fish scale directly to the neck of the balloon. When filling the high-altitude balloon periodically stop filling, pull the helium nozzle from the balloon and seal the balloon neck with your fingers and check the lift indicated on the digital scale. This method of checking lift works well with little to no wind. In windy conditions the balloon will pull as it is blown side to side giving a false reading on the digital scale.
The second method of measuring nozzle lift is to fill containers with water to equal the nozzle lift required. If the nozzle lift is 15 lbs fill milk jugs or a 5 galloon bucket with water to equal 15 lbs (1 gallon of water is apox. 8.35 lbs.) Tie this container to the neck of the balloon. When the container is lifted off the ground you have met your nozzle lift. This method works well in windy conditions and also can be used for more advanced Near-Space explorers for precise low ascend rate flights.
Jason Krueger
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Comment
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Comment by Jason Krueger on September 28, 2009 at 10:25am -
There are a couple of factors which could have contributed to the low ascent rate. I have occasionally noticed the large helium tanks to be under filled coming from the supplier. If you notice your starting tank pressure is low (I believe a full tank is around 2500 PSI) then you will not have as much lift. The second factor which could have influenced the low ascent rate is the weight of the payloads. It is important to use a precise scale which you might find in a lab to weigh everything but the high-altitude balloon to determine your final payload weight. I have worked with Universities where students add things to their payloads last minute and this will drastically affect your accent rate even if it is only a few ounces.
I watched your flight and the funny thing is many more advanced high-altitude balloon teams try for ascent rates of 550 ft/min to get more time in Near-Space and you have done it on one of your first launches.
Keep up the good work,
Jason
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Comment by Steve Spicklemire on September 27, 2009 at 6:24pm -
Hi Jason,
This weekend we put 2 full tanks of He into a 1200g balloon. We only measured about 13.5 lb of lift. (we had approximately 9lb of total payload so we thought we were OK.) We ended up with an ascent rate of about 550 ft/min... 2.5hr until burst! Any idea what went wrong?
thanks!
-steve
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