Calculating Ascent Rate and Peak Altitude of a High Altitude Balloon

[thespaceman]

Howdy,
I am looking to find the rate of ascent for a weather balloon filled with helium. My assumptions as of now are total payload weight=10lbs, total balloon weight=2lbs, total balloon volume(at launch)=150ft^3, balloon diameter(at launch)=6ft.
Also, how does the rate of ascent change with altitude?
And lastly, what is the peak altitude it will reach?
Any help will be greatly appreciated. :)
-thespaceman

 

[Johnson]

Hey thespaceman,

I actually have some experience with weather balloons, so thought I'd post what I know. Give consideration that this is taken from practical experiments personally and not from literature.

Your first question about ascent change with regards to altitude. It should not change depending on altitude, because as the pressure gets less and less, the balloon is expanding, giving the same ratio of helium displacement over air. Of course, wind currents, and temperature fluctuations can offset your rate of ascent by a small amount, but nearly impossible to calculate. Some fluctuations will cause the rate of ascent to speed up, others will slow it down. On average the ascent rate should not fluctuate more than 10%.

As with your second question, the peak altitude really depends on the material of your weather balloon and where you get it from. High altitude weather balloons can go 30-37km in height, with some amateur hobbyists boasting of nearly 40km. Personally 33km was the highest I've ever gotten one, but I'm working on a budget of about $200 per flight (with many reusable parts).

Hopefully this helped, best of luck.

 

[thespaceman]

That is extremely helpful thank you. What I am trying to do now is to calculate the ascent rate that my balloon will have. I calculated an approximate peak altitude already to be 26km, but what I would like to calculate by hand is how long it will take to get there. What is really important is how long I will be above the tropopause.