Balloon Burst

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Sasha Tim

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May 26, 2023, 12:07:51 PM5/26/23
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Hi all,

Following up on a recent flight by CUSF... how can I make sure that I have enough helium for my balloon to burst, given the balloon diameter and payload weight? 

73,

VE3SVF

John Laidler

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May 26, 2023, 12:19:59 PM5/26/23
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I used the calculator at the bottom of this page on the Random Engineering website.


If you feed in the details of the balloon, gas used and the payload weight then set an ascent rate of say 5m/s you can be very confident the balloon will burst at the expected altitude. There may be occasions where you might want to increase the ascent rate.  By increasing the ascent rate the balloon will not only rise faster but it will burst at a slightly lower altitude. This is a legitimate tactic if predictions suggest the balloon might fall into the sea if it stays aloft too long. 

The calculator gives the neck lift which is the upward force exerted by the balloon without the payload attached.  You can put water in a plastic bottle until the total weight is equal to the desired neck lift.  Then attach this to the balloon and fill with gas until it just manages to achieve neutral buoyancy.

John
M0WIV 

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Steve

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May 26, 2023, 12:20:59 PM5/26/23
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Use one of the burst calculators and aim for 5m/sec ascent rate - e.g. https://sondehub.org/calc/   - less than about 3.5m/sec is float territory. 

Pre-calculate how much helium you will need and make sure you bring a cylinder with more than enough.  Also be sure of the purity of the gas you have obtained - there are quite a few diluted Heliums around.

Don't skimp on gas and don't be worried about overfill - add a few extra squirts of gas if needed to be sure (traditionally measured in Stirks).

When you fill the balloon make sure it has the required neck lift and your not being fooled by the wind.  Make sure the test weight is lifted continuously off the ground.

    Steve G8KHW

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Mike Sharps

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May 26, 2023, 1:31:02 PM5/26/23
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Excellent article by Dave Ackerman explaining the whole process if you haven’t read it already May I also suggest you have a play around with the CUSF flight predictor as this will give you more idea of flight distances vs burst altitudes and ascent / descent rates. There are quite a few variables to consider and it takes a while to get your head around everything.

On Fri, 26 May 2023 at 17:07, Sasha Tim <sasha...@gmail.com> wrote:
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Mark Jessop

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May 26, 2023, 6:39:27 PM5/26/23
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I'm also curious as to what balloon you are planning on using, as in previous conversations you seemed to suggest you would just be using party balloons.

73
Mark VK5QI

Shivaram S P

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Aug 5, 2023, 5:14:50 AM8/5/23
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But how to check neck lift on a windy day? when the weight keeps fluctuating in the machine. 

David Akerman

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Aug 5, 2023, 5:58:48 AM8/5/23
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Like Steve said, make sure the balloon is lifted continuously off the ground; it's not enough if it lifts then drops back to the ground.  And also as Steve said, add a few more "Stirks" (a Stirk is an undefined number, but basically "several", seconds of gas).

Always best to aim for more gas than you need.

If you can find shelter from the wind that can help a lot.  My launch site is on a hill and rather exposed, so if it's windy we walk down the hill to some cover next to a copse.  Or find a building to fill next to.  Or perhaps wait for the wind to die down.  Or worst case, launch another day; it's not just the filling that's an issue it's letting go of the balloon without the payload crashing into the ground.  We've all been there with that one.

Dave

Steve

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Aug 5, 2023, 6:08:55 AM8/5/23
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" weight keeps fluctuating in the machine" sounds like you are using some form of lift scales? - and not the test weight suggested. 

In my view the test weight is easier to use in the wind as you are not trying to mentally average a reading.

The professionals (weather services etc.) use purpose built buildings in which to inflate the balloon and measure lift out of the wind - the buildings have large doors through which to exit the balloon. Some go so far as to have doors on all 4 sides of the building so you can always exit downwind.

Failing that, fill and launch on the leeward side of a building or other obstruction such as tall trees.  Where that's not possible I've gone so far as to build a windbreak (middle of Dartmoor):

    https://www.youtube.com/watch?v=z1z3z2S18Co

Some groups have gone even further and use a gas flow meter to measure the amount of gas fill - and fill under a bag:-

    https://www.youtube.com/watch?v=khmw7tsiZ-8

You can also roughly measure the amount of gas used by the  pressure drop method.  

IMO The test weight method is more accurate in low wind conditions - the gas flow meter and pressure drop methods of measuring fill (and hence lift) might be more applicable to windy conditions.

    Steve

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Mark Goergen

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Aug 5, 2023, 7:46:51 AM8/5/23
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For balloon filling, we go to the leeward side of our house. We have a 3d-printed neck insert that is threaded to take a Colder PLCD 24006 MNPT threaded coupler (quick disconnect). My supply hose has a Colder PLCD17006 barbed coupler on the end. These each close when disconnected. We attach four zip ties to the neck as shown in the images below. Our neck lift is measured by a partially-filled 1 US gallon (3.8L) water bottle, which is clipped to one of the looped zip ties. When we think we are at the correct fill, we disconnect the couplers and see if we have buoyancy.  
We generally avoid launching above 4 m/sec wind speed. Luckily in the US, under 1814g we do not need to notify anybody and can launch at will, so rescheduling is not the nightmare you need to deal with. Our payload comes in just under 1800g.
I used the neck from a previous flight to illustrate our connections.
Mark
20230512_111112.jpg20230511_221547.jpg45f3469d-73dc-41c9-b1b2-80be964536a3.jpg

On Sat, Aug 5, 2023 at 7:03 AM 'noddym' via UKHAS <uk...@googlegroups.com> wrote:
02a47efb-32da-4881-bec9-be17c3da9cb5.jpeg9ad6e19b-dd4b-469f-a0ef-3f69119bd30a.jpeg888c8d54-1175-481c-99cd-da3b504ccb7d.jpegAs the chaps at Cambridge found out, it can be a bit hit and miss… too much and it bursts too soon, and if you under inflate it, it becomes a floater and you can say bye-bye. So, the challenge is to get an accurate(ish) 5m/s rate of ascent. Fortunately, being a genius(😂), I have devised a cunning plan!…

An air valve for an inflatable boat/kayak that goes inside the neck of the balloon and cable-tied to provide a tight seal. I got one with a small collar so the cable tie can’t slip). The valve is a simple ‘press valve’ so I got 3m of flexible hose and a foot pump connector and put them together…

So, once connected to the helium cannister we can fill as required…
To check we’ve fot the right ascent rate, the water bottle ‘payload can be reduced by the weight of the valve and we can then disconnect the black hose and release the balloon on a tether (attached to the valve) and time the ascent. I’ve measured out a 40m lightweight nylon tether so at full extend it should be about 8 seconds. If we need to add some helium then we just attach the black hose and keep filling, however crucially, if we need to remove some helium, then we just press the valve in to let it escape.once we’re happy with the rate, the neck can be sealed further up than the valve, payload attached, valve can then be removed and away we go, confident we have the correct rate of ascent. And of course, the valve is reusable, so I made a nifty little storage/winder thingy.

Anyway… it seemed to work pretty well

noddym

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Aug 5, 2023, 7:49:01 AM8/5/23
to UKHAS
888c8d54-1175-481c-99cd-da3b504ccb7d.jpeg9ad6e19b-dd4b-469f-a0ef-3f69119bd30a.jpeg02a47efb-32da-4881-bec9-be17c3da9cb5.jpegAs the chaps at Cambridge found out, it can be a bit hit and miss… too much and it bursts too soon, and if you under inflate it, it becomes a floater and you can say bye-bye. So, the challenge is to get an accurate(ish) 5m/s rate of ascent. Using the principle of ‘keeping it simple’, we devised a cunning plan!…

An air valve for an inflatable boat/kayak that goes inside the neck of the balloon and is cable-tied to provide a tight seal (I got one with a small collar so the cable tie can’t slip). The valve is a simple ‘press valve’ so I got 3m of flexible hose and a foot pump connector and put them together…

So, once connected to the helium cannister we can fill as required…
To check we’ve got the right ascent rate, the water bottle ‘payload’ can be reduced by the weight of the valve and we can then disconnect the black hose and release the balloon on a tether (attached to the valve) and time the ascent. I’ve measured out a 40m lightweight nylon tether so at full extend it should be about 8 seconds. If we need to add some helium then we just attach the black hose and keep filling, however crucially, if we need to remove some helium, then we just press the valve in to let it escape. Once we’re happy with the rate, the neck can be sealed further up than the valve, payload attached, valve can then be removed and away we go, confident we have the correct rate of ascent. And of course, the valve is reusable, so I made a nifty little storage/winder thingy.

Anyway… it seemed to work pretty well

On Saturday, August 5, 2023 at 11:08:55 AM UTC+1 G8KHW wrote:

Steve

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Aug 5, 2023, 8:16:21 AM8/5/23
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Nice double check on ascent rate - should be OK in light winds - but in medium/strong winds your need to run (like the wind) to keep under the balloon.

    Steve

On 05/08/2023 12:03, 'noddym' via UKHAS wrote:
02a47efb-32da-4881-bec9-be17c3da9cb5.jpeg9ad6e19b-dd4b-469f-a0ef-3f69119bd30a.jpeg888c8d54-1175-481c-99cd-da3b504ccb7d.jpegAs the chaps at Cambridge found out, it can be a bit hit and miss… too much and it bursts too soon, and if you under inflate it, it becomes a floater and you can say bye-bye. So, the challenge is to get an accurate(ish) 5m/s rate of ascent. Fortunately, being a genius(😂), I have devised a cunning plan!…

An air valve for an inflatable boat/kayak that goes inside the neck of the balloon and cable-tied to provide a tight seal. I got one with a small collar so the cable tie can’t slip). The valve is a simple ‘press valve’ so I got 3m of flexible hose and a foot pump connector and put them together…

So, once connected to the helium cannister we can fill as required…
To check we’ve fot the right ascent rate, the water bottle ‘payload can be reduced by the weight of the valve and we can then disconnect the black hose and release the balloon on a tether (attached to the valve) and time the ascent. I’ve measured out a 40m lightweight nylon tether so at full extend it should be about 8 seconds. If we need to add some helium then we just attach the black hose and keep filling, however crucially, if we need to remove some helium, then we just press the valve in to let it escape.once we’re happy with the rate, the neck can be sealed further up than the valve, payload attached, valve can then be removed and away we go, confident we have the correct rate of ascent. And of course, the valve is reusable, so I made a nifty little storage/winder thingy.

Anyway… it seemed to work pretty well



On Saturday, August 5, 2023 at 11:08:55 AM UTC+1 G8KHW wrote:

Steve

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Aug 5, 2023, 8:26:01 AM8/5/23
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Likewise - Up to 10mph is fine much above that and its getting quite
challenging.

De-reelers seem to be the answer for windy conditions.

    Steve

On 05/08/2023 12:46, Mark Goergen wrote:
> We generally avoid launching above 4 m/sec wind speed.

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