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.
On 02/07/2019 22:22, Jerry via
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.
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
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
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
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.
On Tuesday, June 25, 2019, 8:49:05 AM MST,
Michael Hojnowski <kd2eat@...>
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,
Mike / KD2EAT
On 6/25/2019 11:08 AM, Joe WB9SBD wrote:
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,,,
Original Rolling Ball Clock
6/25/2019 9:40 AM, Jerry via Groups.Io
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
On Tuesday, June 25, 2019, 5:13:04
AM MST, BASE_DePauw <hlbrooks@...>
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
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
But apparently the
amount of lifting gas was
below the breaking force of
the latex until the UV
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
Subject: Re: [GPSL]
KD0VJI11 latex floater
over North Dakota Athens
AL N4SEV11 floater and
PB0AHX1 floater with APRS
The latex in the balloon stretches like a
The more that
the balloon is
more force that
is needed to
latex is not
the last few
the latex breaks
(and the balloon
When small amounts of lifting gas, either
helium, are in a
there are not
to stretch the
balloon to the
Mon, Jun 24,
2019 at 12:04 AM
Gur Lavie <gurlavie@...
mean it was
Can this be
Sun, 23 Jun
2019 at 22:10
Bill Brown via
are flying a
with a 4 AAA
at -50 deg C
or below and
is still doing
great after 27
in at 65 grams
put 140 grams
lift into the
600 gram latex
was below 250
ft/min most of
the flight and
feet. It is
Dakota and has
Field Day site
and it is
TN at the
Germany at the
moment with a
output 50 baud
RTTY after the
You can hear
it on 145.300
MHz via one of
the many websdr.org
could hear it
well from a
From: Jim Reed
To: GPSL <GPSL@groups.io
Sent: Sun, Jun
23, 2019 9:15
- was not the
asked us to
put a balloon
day. I guess
we messed up
in the helium
turned into a
floater. It is
a 600 gram
flying one of
for about a
day now at
neat to see
for those that
are into that
602 S. College
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