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

Steve G8KHW / AJ4XE

My guess would be that the pressure drops as the balloon is released because the envelope is under less tension - held to the ground the full lift of the balloon is transferred into envelope tension - when in free flight the tension is reduced to that of just the payload weight. The difference is the result of the drag force as the balloon moves through the air - balloon shape differences too due to the movement.

    Steve G8KHW/AJ4XE

On 02/07/2019 22:22, Jerry via Groups.Io wrote:
Now that I am back from my 4995 mile trip to GPSL, I thought I would finish out this thread by posting my graphs from my internal pressure measurements.  Below is the original email and the attached graphs.  Since this was written I think the best explanation is that I had the outside measure port just below the balloon.  It should have been outside the influence of the balloon.  The graph does show a pretty significant rise in differential pressure just before burst.  If the amount of helium (or hydrogen) cannot overcome this pressure increase to maintain the lift, the balloon will float.

Original post:

I finally have the data on the differential pressure during a flight.  This was a 1000 gram balloon.  The ascent was about 1100 Ft/Sec with a burst altitude of 87,000 feet.

The pressure and temperature was measured at the end of a tube that went about 20 inches into the balloon.  The tube fed the pressure to a differential pressure transducer outside the neck of the balloon.

As expected there was a peak pressure as the balloon started to inflate.  This quickly started to drop off as the balloon inflated as expected.

At launch the pressure suddenly dropped 0.003 PSI.  I suspect that was due to the acceleration possibly on the actual transducer.  If anyone has another explanation I would love to here it.

Again as expected the pressure dropped as the diameter increased. 

As the balloon approached burst the pressure did increase as expected.  The increase from the minimum was about 0.008 PSI.  I don't think we can judge how this compares to the initial peak because of the offset during Ascent.

The temperature was probably as expected.  During fill the internal temp was a little lower than the outside temp which can be explained by the cooling from the helium pressure change.  Once in flight the internal temperature lags a little but not by a significant amount.

I think some other groups measured internal pressures and would love to know how these compared.

Graphs should be linked to this email.


On Tuesday, June 25, 2019, 6:44:51 PM MST, Jerry via Groups.Io <jerrygable@...> wrote:

As a friend of mine likes to say:  If its worth engineering it is worth over engineering.  He has been working on his automated can crusher for at least 3 years.

 I am interested in what makes the flights behave the way they do.  That is why I wrote the prediction software.  Back when Ron Meadows had a latex balloon make it to Morocco there was interest in making latex floaters.  Soon after that the mylar pico balloons got popular and the latex floater interest died out. 

As Bill pointed out most of the latex floaters have been big balloons.  I think that is because the trackers were a lot heavier.  Now with the pico trackers being used I would think smaller latex should work as Gur found out.  One thing that I would like to understand is the amount of degradation UV actually does.  Ron's balloon stayed up a week or more and I have had balloon shards that spent the summer in the AZ desert that seemed in pretty good shape.  Maybe I should try some timed exposures in the desert and see if I can measure the change over time.  

Jerry Gable
Balloon Flight Prediction tools

On Tuesday, June 25, 2019, 8:49:05 AM MST, Michael Hojnowski <kd2eat@...> wrote:

I wonder if all the "sciencing" is overkill.  Couldn't you just fly it like a standard pico.  Give yourself 5-10 grams free lift, let go, and walk away?   It'll either burst or it won't.  Any less free lift than that is untenable, so if it bursts, then floaters with latex would be an unreliable thing for sure.  If it works, then you can start worrying about how long they last due to UV, etc.

Mike / KD2EAT

On 6/25/2019 11:08 AM, Joe WB9SBD wrote:
I have Jerry's data here somewhere also. I'll also try to find it.

One thing I do remember tho, the differential was very very small.  Which makes total sense, if you do the math by taking the tensile strength of the latex, and calculate what the surface tension on that latex would be at it's failure point the pressure differential is very small.

I remember when I did the calculations using the math way, it came in like within 1% of what Jerry actually measured.

Near Space Sciences
30 years and 70 flights,,, 

The Original Rolling Ball Clock
Idle Tyme

On 6/25/2019 9:40 AM, Jerry via Groups.Io wrote:
I did some measurements on balloons that were discussed on the list but never presented anything at gpsl.  I flew a flight with a differential pressure sensor on the balloon and measured the pressure curve.

I'm still on the road after GPSL but will dig up what I did when I get home next week.

Jerry Gable
Balloon Flight Prediction tools

On Tuesday, June 25, 2019, 5:13:04 AM MST, BASE_DePauw <hlbrooks@...> wrote:

I don't have a copy of the paper, but recall James Flaten of U Minnesota talking about internal and external pressure of a latex balloon back in 2011. Shortly before burst the internal pressure exceeds the external. James thought that it could be possible to use this difference to cut away from the balloon just before burst to avoid post burst chaos.

My students and I talked about floating large payloads at 20 km at GPSL2017 in Hutch.


On Tue, Jun 25, 2019, 12:27 AM Bill Brown via Groups.Io <> wrote:
Hi Gur,

  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

-----Original Message-----
From: BASE_DePauw <hlbrooks@...>
To: GPSL <>
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


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

Steve Randall
Random Engineering Ltd
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