Re: KD0VJI11 latex floater over North Dakota Athens AL N4SEV11 floater and PB0AHX1 floater with APRS and RTTY
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Jerry
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. Jerry
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.
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. Joe WB9SBD Near Space Sciences 30 years and 70 flights,,, The Original Rolling Ball Clock Idle Tyme Idle-Tyme.com http://www.idle-tyme.com 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.
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.
Howard
On Tue, Jun 25, 2019, 12:27 AM Bill
Brown via Groups.Io <wb8elk=aol.com@groups.io>
wrote:
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