Re: KD0VJI11 latex floater over North Dakota Athens AL N4SEV11 floater and PB0AHX1 floater with APRS and RTTY



My students investigated this phenomena a few years ago, inspired by Ron K6RPT ( and his transoceanic flights plus a near floater of our own that carried a load of 3 kg (BASE 67 in 2011).

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.

Howard, KC9QBN
BASE, DePauw

On Mon, Jun 24, 2019 at 12:04 AM Gur Lavie <gurlavie@...> wrote:
Hei Bill,

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 <> wrote:
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.

Callsign: KD0VJI-11

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 receivers in Europe.  I could hear it well from a couple of websdr radios in western Germany this morning.

The RTTY telemetry is displayed on under the callsign PB0AHX.

- Bill WB8ELK

-----Original Message-----
From: Jim Reed <jim.reed@...>
To: GPSL <>
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
DePauw University
602 S. College Street
Greencastle, IN 46135
Office: (765) 658-4653
FAX: (765) 658-4732

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