See the ping-pong valve described here:

    https://tinyurl.com/y5ukveyb

see fig 4

    Steve

On 18/07/2020 18:53, Jerry via groups.io wrote:

It seems like over inflation is a common problem.  Could we come up with a simple (and light) pressure releif valve that is inseted in the fill tube?  Maybe something that could be 3d printed.  You could also use overfill for a faster initial climb.  It might save a lot of balloons. 

Jerry

On Sat, Jul 18, 2020 at 10:31 AM, Michael

<mw@...> wrote:

Hi All,

I plotted the ascent and unexpected descent of the GPSL K5NOT-11 WSPR balloon I sent up. It was a WSPR Skytracker and SBS-13 balloon of which I had trouble sealing - the sealing unit recommended was not available and an equivalent unit melted the neck right off. The equivalent unit was likely defective and too hot. I had eventually sealed the neck and folded it up like we do with latex balloons. I felt it was probably OK to fly. However, after a short time at 43,000 ft float level the balloon came back down. I assumed the premature descent to be caused from where I sealed it.

However, something about the descent did not make sense. If the leak was at the bottom - at the seal, I would expect the balloon to descend some portion and then somewhat stabilize at a fair altitude as the helium would want to stay at the top of the envelope and not flow down and out at the filling neck. Instead it descended all the way on a very linear line. I now highly suspect the leak actually was a pinhole or larger that developed in flight at or near the top of the envelope as a very under-inflated envelope with positive buoyancy took the payload aloft. The balloon was filled to 7 grams of positive lift.

According to the ascent table provided by Scientific Balloons - who makes the SBS-13, 5-8gr of lift is the sweet spot. I measured the lift in several different ways and confirmed 7 gr lift. However, based on the table also provided by Scientific Balloons, the 7gr of lift should result in less than 1.3 meters of ascent rate. When I calculated the time from launch to float I came up with 1.77 meters / second ascent rate which does not agree with the 1.3 meters targeted, but rather reflects over 10 gr but less than 12 gr of free lift which is too much.

What I learned from premature descent of the K5NOT-11 balloon via the NTSB (North Texas Squirrely Balloon) analysis:

• Free lift was most likely the culprit causing an over pressure envelope failure at the top of the envelope and not caused by a bad seal at the neck. The free lift was measured with a 0.1gr repeatable accuracy, but does not match up with the tables provided by Scientific Balloons, so an error / discrepancy / calibration issue crept in here in some manner.
  
• Even though the sealer was a bear, it eventually sealed - and folding and taping probably was good as extra insurance.
  
• When you seal one of these balloons, try sealing on the very end of the neck first to prove the seal process before sealing where you actually want the seal.
• Science can be fun until your hope of achievement is overwhelmed by the realization of complete failure.
  

--Michael

Virus-free. www.avg.com

On Sat, Jul 18, 2020 at 10:31 AM, Michael

<mw@...> wrote:

Hi All,

I plotted the ascent and unexpected descent of the GPSL K5NOT-11 WSPR balloon I sent up. It was a WSPR Skytracker and SBS-13 balloon of which I had trouble sealing - the sealing unit recommended was not available and an equivalent unit melted the neck right off. The equivalent unit was likely defective and too hot. I had eventually sealed the neck and folded it up like we do with latex balloons. I felt it was probably OK to fly. However, after a short time at 43,000 ft float level the balloon came back down. I assumed the premature descent to be caused from where I sealed it.

However, something about the descent did not make sense. If the leak was at the bottom - at the seal, I would expect the balloon to descend some portion and then somewhat stabilize at a fair altitude as the helium would want to stay at the top of the envelope and not flow down and out at the filling neck. Instead it descended all the way on a very linear line. I now highly suspect the leak actually was a pinhole or larger that developed in flight at or near the top of the envelope as a very under-inflated envelope with positive buoyancy took the payload aloft. The balloon was filled to 7 grams of positive lift.

According to the ascent table provided by Scientific Balloons - who makes the SBS-13, 5-8gr of lift is the sweet spot. I measured the lift in several different ways and confirmed 7 gr lift. However, based on the table also provided by Scientific Balloons, the 7gr of lift should result in less than 1.3 meters of ascent rate. When I calculated the time from launch to float I came up with 1.77 meters / second ascent rate which does not agree with the 1.3 meters targeted, but rather reflects over 10 gr but less than 12 gr of free lift which is too much.

What I learned from premature descent of the K5NOT-11 balloon via the NTSB (North Texas Squirrely Balloon) analysis:

• Free lift was most likely the culprit causing an over pressure envelope failure at the top of the envelope and not caused by a bad seal at the neck. The free lift was measured with a 0.1gr repeatable accuracy, but does not match up with the tables provided by Scientific Balloons, so an error / discrepancy / calibration issue crept in here in some manner.
  
• Even though the sealer was a bear, it eventually sealed - and folding and taping probably was good as extra insurance.
  
• When you seal one of these balloons, try sealing on the very end of the neck first to prove the seal process before sealing where you actually want the seal.
• Science can be fun until your hope of achievement is overwhelmed by the realization of complete failure.
  

--Michael

UPDATE:

KM6BWB-10 returned to California today after a big loop into Mexico and out into the Pacific near Baja. Still flying high !!!

- Bill WB8ELK

-----Original Message-----
From: Bill Brown via groups.io <wb8elk@...>
To: gpsl@groups.io <gpsl@groups.io>
Sent: Thu, Jul 16, 2020 11:06 am
Subject: [GPSL] GPSL Pico balloons status updates

Out of the 10 Pico Balloons that were launched last Saturday for GPSL (2 on Sunday), one is currently being received as it flies over Bulgaria (KC7VQR-11) and two more may still be flying but out of range of APRS ground stations. Here's the status of all of the balloons so far:

Still flying or potentially still flying:

KC7VQR-11 (APRS Skytracker with SBS-13 balloon) - Currently flying over Bulgaria. 7 grams of free lift with helium.

KM6BWB-10 (APRS Skytracker with two silver foil balloons - Last heard in Mexico, if it is still flying it should show up back in CA/AZ on 7/18 @ 2200z.

KK6UUQ-7 (APRS SKytracker with single foil balloon - Launched, burst, recovered from a field then flown again within a few hours and last heard SW of New Orleans. Predicted to show up 7/18 @ 1200z in east TX

On the ground:

VA5BNC-15 (APRS custom built by Bruce VE5BNC - 25 grams on a single foil balloon) - Landed in east GA, then took off again the next morning and landed near Orangeburg SC.

WB8ELK-10 (APRS Skytracker on a single silver foil balloon) - Hit bad storms along NC coast not far from Kitty Hawk and looks like it splashed down a half mile from shore.

KM4ZIA-2 (WSPR Skytracker on SBS-13 balloon) - Hit bad storms off the coast of NC and probably splashed down in the Atlantic.

KM4BUN-1 (WSPR Skytracker on SBS-13 balloon) - Hit bad storms off the coast of NC and probably splashed down in the Atlantic.

K5NOT-11 (WSPR Skytracker on SBS-13 balloon) - Had trouble heat sealing the filling port so likely caused leak after 20 minutes of float time. Landed in central TX.

W5HRH-15 (WSPR board on SBS-13 balloon) -  10 grams of free lift, anything over 8 grams has more risk. if it works it will work very well but increased risk of leaking as it achieves float altitude. It burst and came down in South Texas. I did have one work great with 11 grams of free lift but that's the upper limit. The most recent successes I have observed have had between 6.5 and 7.5 grams free lift.

Not Sure if still flying:

K7HAK-11 (APRS Skytracker with two silver foil balloons) - Likely landed in SC where there were a lot of storms. Didn't show up over Newfoundland per prediction but may still be aloft. If it doesn't show up in Europe within two days from now then it probably landed in SC.

GPSL balloons launched on Sunday:

Also W7EEU-11 launched an APRS Skytracker on a single silver foil balloon on Sunday since he couldn't launch on Saturday during our big event. It had a wild roller coaster ride after picking up some icing but finally reached a stable float on the second day. It was heading into northern Canada and may show up again in a few days in Europe if it is still flying.

K6STS launched a WSPR payload on an SBS-13 on Sunday as part of GPSL but it came down shortly about 2 miles from his house. He has recovered it and will fly again soon.

- Bill WB8ELK