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I presented some data on measurements at the neck of a balloon during the flight quite some time back. I did not equate it to floater success as success was not yet achieved with our tests, :) but it made for a very interesting observation of what pressure is seen at the neck of the balloon. In short, the pressure at the balloon neck is fairly high at initial fill, drops to near zero or at zero at altitude and then spikes up noticeably at the point of mechanical maximum right before burst. It was our intention to sence that spike, release some helium and achieve near neutrality for radio contacts in an on board repeater, followed by outgassing enough to return to earth at a fixed rate. Work got in the way of continuing this effort. :)
On Jun 24, 2019, at 11:17 PM, Bill Brown via Groups.Io <wb8elk@...
Empirically, I have planned quite a few latex floater flights using lightweight payloads and low free lift. My best success has been with payloads under 2.5 pounds and just a few ounces of positive lift. Less than 250 ft/min ascent rate can often achieve float with lightweight payloads. However, the best balloons to use for this are 1200 gram or larger. NG0X managed to float a payload on a 1000 gram balloon. However, this balloon (KD0VJI-11) was just a small 600 gram balloon. But the total flight train weight was just over 2 ounces with about 3 ounces of free lift and it worked great, which is quite an accomplishment for such a small balloon and an amazing peak altitude for a 600 gram balloon as well (101,430 feet).
But apparently the amount of lifting gas was below the breaking force of the latex until the UV radiation eventually degraded the latex after a day or two.
There was a paper presented at GPSL a few years ago describing this effect to predict the success conditions for floating a latex balloon measuring the internal pressure of the balloon during flight. Does anyone remember who gave that talk or have a copy of it?
- Bill WB8ELK
From: BASE_DePauw <hlbrooks@...
To: GPSL <GPSL@groups.io
Sent: Mon, Jun 24, 2019 9:19 am
Subject: Re: [GPSL] KD0VJI11 latex floater over North Dakota Athens AL N4SEV11 floater and PB0AHX1 floater with APRS and RTTY
The latex in the balloon stretches like a spring obeying Hooke's law. The more that the balloon is stretched the more force that is needed to stretch it further. Additionally, the spring constant for latex is not constant, but actually increases dramatically in the last few centimeters of stretch before the latex breaks (and the balloon bursts).
When small amounts of lifting gas, either hydrogen or helium, are in a large balloon, there are not enough gas molecules to exert the required force to stretch the balloon to the breaking point.
On Mon, Jun 24, 2019 at 12:04 AM Gur Lavie <gurlavie@...
Whats the physics behind a Latex becoming a floater ?
Does it mean it was completely “under” filled ?
Can this be intentionally planned and launched ?
On Sun, 23 Jun 2019 at 22:10 Bill Brown via Groups.Io <email@example.com
Fascinating flight. I believe this is the smallest balloon (600 gram) to achieve a stratospheric float. They are flying a Skytracker board without the solar panels but with a 4 AAA lithium battery pack. It worked through the entire night at -50 deg C or below and is still doing great after 27 hours aloft. After the foamcore, tape and bubble wrap the payload came in at 65 grams (about 2.3 ounces). They put 140 grams (about 5 ounces) neck lift into the 600 gram latex balloon. The ascent rate was below 250 ft/min most of the flight and it floated around 101,000 feet. It is still flying over North Dakota and has made it through mid-day so far.
We also launched a Skytracker from the Athens AL Field Day site this morning and it is floating nicely heading over central TN at the moment (Callsign: N4SEV-11).
Also, PB0AHX-1 is flying over Germany at the moment with a Skytracker that I modified to output 50 baud RTTY after the second APRS transmission. You can hear it on 145.300 MHz via one of the many websdr.org
receivers in Europe. I could hear it well from a couple of websdr radios in western Germany this morning.
- Bill WB8ELK
From: Jim Reed <jim.reed@...
To: GPSL <GPSL@groups.io
Sent: Sun, Jun 23, 2019 9:15 am
Subject: [GPSL] Floater - was not the plan
Our local HAM radio club asked us to put a balloon they could track for their field day. I guess we messed up in the helium calculation. 😊
It turned into a floater. It is a 600 gram latex balloon flying one of Bill’s skytrackers. Been floating for about a day now at 100k. Kinda neat to see the track.
Just thought I would share for those that are into that stuff.
Howard L. Brooks
Professor of Physics and Astronomy
241 Julian Science and Mathematics Center
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Greencastle, IN 46135hlbrooks@...
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