Burst altitude
Joe WB9SBD
Hi Steve,
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Thanks for making the confirmation on my calculations. I was amazed that that little balloon granted with no work to do could reach as high as it was calculating to be. I was close, I was about 2K higher. BUT we and I do not know why, but our Lift provided by H2 per volume is slightly different. And thus the difference in burst altitude. I have been using oz per cuft. with yours numbers that comes out to 1.184153533..... oz per cuft. For decades I have been using a number that I came up with in the 1980's as 1.216 oz per cuft. I honestly do not know where that number came from. It's been 30+ years! Thanks for confirming my calculations. Joe WB9SBD
On 9/6/2020 4:40 AM, Steve G8KHW /
AJ4XE wrote:


Steve G8KHW / AJ4XE
Hi Joe  Assuming this is not a trick question (if a balloon is neutrally buoyant it won't ascend  so won't ever burst). Assuming you mean if something else was pulling it up: The 100g Kaymont (KCI100) is a rebadged Totex TA100 and has a burst diameter of 1.96m (6.4ft) and an average weight of 100g Ignoring the constraining effects of the latex increasing pressure at fill: A 100g balloon will need 100g of lift to make it neutrally buoyant. Pure H2 gives a lift of 1.18552 g/L (Air 1.225 g/L
less H2's 0.08988 g/L both STP) hence requiring 100/1.18552 = 84.3511707L = 0.0843511707 cu m = 2.978833cu ft of H2 to make it neutrally buoyant. 0.0843511707 cu m of Hydrogen will have a mass of 7.58148g ( 84.3511707L * 0.08988 g/L) the overall mass will be 100g + 7.58148 = 107.58148g Assuming a sphere at burst the TA100 will have a volume of
2.217631 cu m (4/3 Pi r^3) so for neutral buoyancy the question comes down to at what
altitude does 2.217631 cu m displace 107.58148g of air or at what altitude does air density become 48.51189g / cu m (107.58148 / 2.217631) using the NASA 1960s air density model that gives an altitude of about 23.85Km (78100ft) Hope that helps Steve G8KHW / AJ4XE
0.0843511707 cu m at STP become 2.217631 cu m  a ratio of
1:26.29046 using the NASA air density model that gives an altitude of 22.3Km (73144ft) What this doesn't account for is the pressure increase due to the
elastic tension of the envelope
On 06/09/2020 03:18, Joe WB9SBD wrote:
It has been a LONG LONG time since I have calculated a burst altitude.


Joe WB9SBD
It has been a LONG LONG time
since I have calculated a burst altitude.
Let me see if I am STILL doing it correctly.. I did a calculation on a tiny 100 gram Kamont balloon. Now i know in theroy this won't work. But fill it with H2, so it is neutral buoyant. With those paramaters. what altitude would it pop at? Joe WB9SBD

