JOAL17- Help requested

92 views
Skip to first unread message

JohnM SSC

unread,
Jun 2, 2020, 5:16:23 AM6/2/20
to UKHAS
Hi Folks

There was some discussion on IRC yesterday as to the legality of our flight and a lot of the speculation is wide of the mark.  So here are a few facts.


The configuration
  • The envelope-  Pawan 100 (selected as only company specifying burst dia <2m.) The payload is approx the size of two stacked cig packets .
  • The bottom 40mm of the envelope neck is cut off and the payload mounted so that it hangs no lower than the uncut neck would have done.
  • The antenna is only approx 8cm as we use 869MHz and is mounted vertically inside the envelope.
  • The parachute is inside the envelope.
  • Our total payload weight including chute etc is approx. 70gm.
  • We underfilled yesterday to reach a higher altitude.
  • We use a modified version of  Dave Akerman's uplink software to retransmit missing image packets.
  • The 'moon like'  object visible in the high altitude images is the bottom of the envelope.  The splodges are actually biro ink on the inside of the envelope (don't ask!).

Request for help

We would like a helium vent valve that we can control with our uplink.  Any ideas as to existing hardware that weighs <10gm that would do the job would be much appreciated.  We are speculating as to whether we might get to 100,000ft ( in old money).

cheers
John of JOAL

Steve

unread,
Jun 2, 2020, 7:42:44 AM6/2/20
to uk...@googlegroups.com

Here is a quick video of my balloon vent valve that I used on flights way back - just a small RC servo lifting a slightly spring loaded sealing plate.  It certainly worked at venting within a reasonable amount of time**. 

    https://www.youtube.com/watch?v=eahxgo7u5nI

It was designed for balloons 1200g and up - but you could certainly build a small variant for the Pawan CPR-100.  A 10g valve seems possible using a small 3 or 4g RC micro servo.

** part of the problem in venting large balloons is the shear volume and low differential pressure - you need a fairly big orifice to vent in a reasonable time (minutes).  Smaller balloons will have more differential pressure - so you might be able to cut down on size considerably.  There is a way to calculate balloon pressure and orifice size to work out the scaling.


It's possible with small balloons that some venting at high altitude would get you a bit higher - trading some of the increased ascent rate for higher altitude. Its worth a try.  I do know for bigger balloons it probably wouldn't work. E.g. with the HY-1600 there is a optimum fill - more and you ascend faster and burst lower, less and it either enters a float or ascent slows down significantly at high altitude (approaching a float) - either way it doesn't burst as high.


Fine work achieving 27420m (almost 90,000ft) on a CPR-100. 


If you do the maths and use the NASA air density model you find that the volume a 2m sphere at 100,000ft will not support more than 68g

    The NASA model has air density at 100,000ft (30.48Km) as 0.01614Kg per cubic meter, a 2m sphere is 4.18933 cu m - meaning at a 2m balloon will displace 68g of air at that altitude.

That 68g includes the balloon, payload and assumes a zero density lifting gas - so I can say with some certainty that 70g of payload + (say) 120g of balloon using 97% pure helium cannot achieve 100,000ft without being bigger than 2m across.

    Steve

--
You received this message because you are subscribed to the Google Groups "UKHAS" group.
To unsubscribe from this group and stop receiving emails from it, send an email to ukhas+un...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/ukhas/e210fc77-df33-466f-a34c-6803be5e265c%40googlegroups.com.

Virus-free. www.avg.com

Nick McCloud

unread,
Jun 3, 2020, 4:47:46 PM6/3/20
to UKHAS


On Tuesday, 2 June 2020 10:16:23 UTC+1, JohnM SSC wrote:
There was some discussion on IRC yesterday as to the legality of our flight and a lot of the speculation is wide of the mark.  

There was discussion about flights under 2m burst as a flight not in the diary commenced but was announced on IRC post launch with a quoted target burst altitude outside the range of a small balloon.

We weren't the Spanish Inquisition, there was no speculation, close to or wide of the mark, just a discussion.

I enquired about the NOTAM status as I'm a licensed pilot, I have notaminfo.com close to hand & use it several times a week.

Steve

unread,
Jun 3, 2020, 6:27:48 PM6/3/20
to uk...@googlegroups.com

A few points I'd like to make about this:

    * The burst calculator (my own and the many variants based on it) produce results that are noticeably lower than the actual burst altitudes for these small balloons.  I know there is an issue and I have been meaning to fix it for some time.

    * That said, in this case (CPR-100) either the manufacturer burst diameter is lower than the actual burst diameter by a few tens of percent - or the NASA air density model is significantly wide of the mark  by a few hundred percent (unlikely).

    * I have spoken to the manufacturer today - and they confirm that they know the burst diameter on the CPR-100 has improved but they have no immediate plans to change their existing specification of 1.85m.

    * Based on the above and the flight results it is my belief that a significant proportion of these balloons are bursting above 2m diameter.


Its worth remembering that the definition of small balloon and hence exemption from much of the UK air navigation order is:


    “Small balloon” means a balloon of not more than two metres in any linear dimension at any stage of its flight, including any basket or other equipment attached to the balloon; 

     

there is no specification of the balloon burst diameter - although obviously in free flight the balloon (plus neck length) must not exceed 2m at burst. 

It's up to the flyer to ensure these conditions are met if they are flying without a CAA Permit.

    Steve G8KHW

--
You received this message because you are subscribed to the Google Groups "UKHAS" group.
To unsubscribe from this group and stop receiving emails from it, send an email to ukhas+un...@googlegroups.com.

Richard Ibbotson

unread,
Jun 3, 2020, 7:11:47 PM6/3/20
to UKHAS
I do not think that the requirement for CAA approval or a NOTAM should be seen as as significant barrier to any flight opportunity. The CAA appear supportive of amateur ballon flights and quick to respond to requests.
The official CAA line appears to now follow the EU rules and there is no recognition of the size limit. They still are happy to approve flights of smaller balloons if safety standards can be shown. It is of course up to individual risk assessments, external constraints, and conscience, as to which rules we follow or ignore.

David Akerman

unread,
Jun 4, 2020, 1:38:56 AM6/4/20
to UKHAS
Well, the small balloon exemption does have some advantages, such as being able to send up a balloon at short notice e.g. to photograph what looks to be a nice sunset.  The problem though appears to be that these 100g balloons outperform their specification enough that they aren't always actually exempt.  You can see this by calculating the actual burst diameter from the burst altitude etc.

Steve, are there any slightly smaller balloons available around the 70g mark that should always burst comfortably below 2m diameter?

On Thu, 4 Jun 2020, 00:11 Richard Ibbotson, <richard.i...@gmail.com> wrote:
I do not think that the requirement for CAA approval or a NOTAM should be seen as as significant barrier to any flight opportunity. The CAA appear supportive of amateur ballon flights and quick to respond to requests.
The official CAA line appears to now follow the EU rules and there is no recognition of the size limit. They still are happy to approve flights of smaller balloons if safety standards can be shown. It is of course up to individual risk assessments, external constraints, and conscience, as to which rules we follow or ignore.

--
You received this message because you are subscribed to the Google Groups "UKHAS" group.
To unsubscribe from this group and stop receiving emails from it, send an email to ukhas+un...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/ukhas/12516259-4485-4755-aa27-5adf1cd9c737%40googlegroups.com.

Steve

unread,
Jun 4, 2020, 5:15:07 AM6/4/20
to uk...@googlegroups.com

Pawan do a 70g balloon but the nearest other manufacturers come are 50 and 60g balloons.

However (forgive me if I'm wrong) I don't think this is John and Alan's aim - I think they see being able to achieve 100,000ft as a desirable feature of their system. Likewise not having to request a permit. 

But as Scotty would say "ye cannae change the laws of physics":

    it is not possible to reach 100,000ft with a 100g balloon (typically actually weighing 125g), 70g payload using 97% helium and have the balloon less than 2m in diameter.

    Steve

Nick McCloud

unread,
Jun 4, 2020, 5:16:31 AM6/4/20
to UKHAS


On Thursday, 4 June 2020 06:38:56 UTC+1, David Akerman wrote:
Well, the small balloon exemption does have some advantages, such as being able to send up a balloon at short notice e.g. to photograph what looks to be a nice sunset. 

Or seize the day when a school can let the students out for the day.


 
Steve, are there any slightly smaller balloons available around the 70g mark that should always burst comfortably below 2m diameter?

Subject to shelf life, I'd happily have 20+, I could easily see me launching a small balloon once a month.

Nick McCloud

unread,
Jun 4, 2020, 9:37:30 AM6/4/20
to UKHAS
Rather than a servo, how about tying a cord on the inside of the balloon at the top and have a 2m length that is tied to sprung loaded release valve at the neck - when the balloon gets to 2m, it opens the valve automagically.

Not sure if this is a recipe for a floater though ...


Alternatively use Dave's magic pyrotechnics and the cord could blow a hole in the balloon, maybe best to use hydrogen for a decisive effect so the latex doesn't wrap around the payload.

Nick McCloud

unread,
Jun 4, 2020, 9:40:04 AM6/4/20
to UKHAS


On Thursday, 4 June 2020 10:15:07 UTC+1, G8KHW wrote:

Pawan do a 70g balloon but the nearest other manufacturers come are 50 and 60g balloons.

However (forgive me if I'm wrong) I don't think this is John and Alan's aim - I think they see being able to achieve 100,000ft as a desirable feature of their system. Likewise not having to request a permit.  


I'm not bothered about the actual details of the size of the balloon and I'm not looking to head to 100,000ft, that can be a stretch* goal, I just would really really like to be able to launch when I want to suit school timetables or for an amazeballs prediction.


* Boom-tish

Nick McCloud

unread,
Jun 4, 2020, 11:37:11 AM6/4/20
to UKHAS
Still thinking ...

Maybe with the 100g balloons we (or at least I have), I could cable tie off the top to reduce its overall size or with gloves on, stretch the top & tie a knot in it.

What sort of bar/psi would be needed at ground level to give this a try to test the burst?

Steve

unread,
Jun 4, 2020, 11:41:14 AM6/4/20
to uk...@googlegroups.com

Pressure wise - not a lot - in the region of 10KPa (1.5 psi).

    Steve

--
You received this message because you are subscribed to the Google Groups "UKHAS" group.
To unsubscribe from this group and stop receiving emails from it, send an email to ukhas+un...@googlegroups.com.

Steve

unread,
Jun 4, 2020, 11:42:41 AM6/4/20
to uk...@googlegroups.com

You can burst them with a leaf blower.  Got a video somewhere ....

    Steve

Steve

unread,
Jun 4, 2020, 11:53:46 AM6/4/20
to uk...@googlegroups.com

Ere tis - this was about a 50g balloon (hence burst pressure higher than 100g).

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

twas a bit of a bang.

    Steve

Nick McCloud

unread,
Jun 4, 2020, 2:27:19 PM6/4/20
to UKHAS


On Thursday, 4 June 2020 16:41:14 UTC+1, G8KHW wrote:

Pressure wise - not a lot - in the region of 10KPa (1.5 psi).


The big compressor & airline are in storage but I'm sure I can rig something up with the heavy-duty tyre compressor - sadly will be next week as it's another round of removals this weekend.

Steve

unread,
Jun 4, 2020, 2:52:48 PM6/4/20
to uk...@googlegroups.com

Great - let me know how it goes when you get round to it - please assess the neighbors annoyance factor of the burst bang  :-)  

Based on the 50g (note the impact on camera man in the clip) I decided not to do a 100g - but bang might be less as the burst pressure is less but the volume will be more.

    Steve

--
You received this message because you are subscribed to the Google Groups "UKHAS" group.
To unsubscribe from this group and stop receiving emails from it, send an email to ukhas+un...@googlegroups.com.

Nick McCloud

unread,
Jun 5, 2020, 5:40:47 AM6/5/20
to UKHAS
Camera man will be a tripod and as there are two under fives next door, I'll give them heads up.

I'll organise a couple of tape measures as well.

Just need to find where I put my box of balloons.

Nick

John Laidler

unread,
Jun 5, 2020, 7:00:44 AM6/5/20
to uk...@googlegroups.com
If you do it with the sun shining and no wind you could lay the tape measure on the ground below the balloon and be able to measure the distance by viewing the video at the point of it bursting. 

John

--
You received this message because you are subscribed to the Google Groups "UKHAS" group.
To unsubscribe from this group and stop receiving emails from it, send an email to ukhas+un...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/ukhas/20cc4099-870f-4c0a-838a-3b653ba0789do%40googlegroups.com.
Reply all
Reply to author
Forward
0 new messages