Constraining a latex balloon inside a nonelastic monocoque outer canopy

[Oliver de Peyer]

What would happen if I put a latex balloon inside another canopy that was not elastic?

Now, it seems to me that usually the latex balloon expands and e‎xpands until it bursts.

If you stopped it expanding... it wouldn't burst?

I was trying to think of ways of making big superpressure balloons that float, without needing custom mylar canopies etc.

Moreover, the outer canopy would be loadbearing ‎(hence I believe monocoque is the appropriate term) but wouldn't have to be gastight, and so would be considerably easier to construct (you could even perhaps tape the seams, as some solar balloonists do)

‎Would this work?

Thanks

Ol

M0LVR

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[Leo Bodnar]

Hi Oliver,

If you are aiming for superpressure envelope then this would work - if made practical.

I have launched a few latex balloons constrained inside non-elastic netting in 2014 but none of them were successful - possibly due to very difficult launch procedures and ensuing microdamage.

Netting was quite coarse, tangly and hard to sew around the latex

Cheers

Leo

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[Oliver de Peyer]

Thanks Leo

I was thinking more of a geodesic mylar sphere. In this case the mylar could be cut as polyhedra with straight edges, which would be easier than cutting and sealing curved gourds. Since the mylar doesn't need to be gastight, you could fold it up for transport without having to worry about pinholes developing in the creases.

You could probably test this with quite a small sphere initially. It will probably burst (the smaller the sphere, the higher the pressure in the latex inner) but at least would give proof of principle before one tries to build a 10m mylar monster. Actually at some point of course the latex balloon will not be able to carry the weight of the mylar sphere. Hmmm. Some sums to be done.

I imagine the latex might have been bulging through the holes in your netting Leo, ‎causing localised areas of high stress. Similarly I imagine the latex will bulge into the internal angles between the polyhedra of a sphere.

It may be a silly question, but how wide is the latex balloon at launch?

‎BW

Ol

M0LVR

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From: Leo Bodnar Sent: Saturday, 9 June 2018 09:53 To: uk...@googlegroups.com Reply To: uk...@googlegroups.com Subject: Re: [UKHAS] Constraining a latex balloon inside a nonelastic monocoque outer canopy

[Steve Aerospace]

One of my balloon customers buys my largest latex balloons to go inside small hot air balloons to demonstrate them - works quite well.  I can't see any reason why something similar could not be used for a super-pressure balloon - the outer skin will also protect the latex balloon from direct UV.

As an example:

    taking a 10m diameter balloon - 314sq m of surface area - 523cum volume

    covered with 22gsm (grams per square m) ripstop fabric - the fabric weighs about 7Kg

    lets assume a 3000g balloon

    say 1Kg payload - so overall weight 11Kg

    say 13 cu m of helium to lift off and ascend.

Gives a float altitude of 25,000m (82,000ft)

Might be a bit optimistic but seems to work as an idea.

    Steve

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[Oliver de Peyer]

Sounds promising!

So how much does the 3000g balloon cost?

Do you think the latex balloon has to already fill the outer at launch?

Otherwise presumably the outer will collapse on top of the latex balloon and all the stress will be on the top to begin with.

This can all be tested initially on a smaller scale - smaller balloon and smaller outer canopy etc, just to see what happens.

My own angle is a self-sterilising outer canopy, for instance copperised mylar. If it doesn't have to be gastight then it is much easier to do.

Thanks

Ol

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From: Steve Aerospace Sent: Saturday, 9 June 2018 11:06

[Steve Aerospace]

3000g latex balloon in the UK? - depends on the brand - but say around £300

The nylon fabric you are going to need say 400+sq m - so you can recon on £2,000+

But the outer canopy is potentially re-usable.

I was thinking the fabric balloon would be made sticky side and seams outside to allow the inner latex balloon to slip over the fabric as it expands inside. You would have something that looked like a zero pressure balloon shape at launch.

For safety you would want the ability to terminate the flight by releasing the gas - so have the balloon neck with a remotely controlled valve - but bring the neck out of the top of the fabric balloon.

With latex you are going to get noticeable gas diffusion - but based on CNSP flights it must be good for a few days.

    Steve

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[Joe]

Actually Leo's Netting IS a excellent approach! It greatly lessens the surface tension effect on the netting.

It is somewhat like a "Pumpkin" Balloon system.

Joe WB9SBD

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[Steve Shuff]

hi , hust a quick one.  I seem to recall seeing the balloons with a net over them but this was going back to my childhood days. In theory with todays technology there is likely a material in which a very lightweight net could be constructed. 

[Joe]

Yes that would work BUT... and there always is a BUT isn't there?

I do not have the math handy, But the strength it needs to be is incredible! The "Surface Tension" Is UN-believably high!

So high that I gave up pursuing that route.

Instead I tried twice the Anchor Balloon method instead. With mixed results. Seemed to have worked but payloads malfunctioned or just plain died so full telemetries we did not get.

Joe WB9SBD

The Original Rolling Ball Clock
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[Joe]

Crunch the numbers first.

And even these the fill MUST be minimal positive buoyancy. To be able to cancel up the power of the lift the balloon has to get pressurized. and with these diameters the pressure seems minimal, but when you calculate the surface tension the rip stop must endure is incredible! Hundreds or even thousands of pounds even!

Joe WB9SBD

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[Oliver de Peyer]

Largeish homemade mylar balloons have already been made, for instance by CUSF (in that case a "conventional" heatsealed gourd design). So it would seem possible to indeed build your own superpressure balloon.

So something similar should presumably be able to take the tensile stress of a latex balloon expanding inside it - either way the pressure applied is the same.

But from what I heard, the CUSF balloon was very fiddly to make, hence the idea of making it all a bit easier by using a commercial latex balloon as the actual gastight bit and something else for the outer monocoque.

It could be netting, or mylar, but it would not need to be totally gastight and it would not even need to have totally continuous seams.

For some of my experiment concepts that I have developed over the years, a large floating balloon would be needed for long duration experiments, preferably many weeks.

For others, where I am sampling air, I still would need a flight time of several days to pump enough air through the sampler so as to make it worthwhile.

If anything the floaty bit is not so important to me, the real stumbling block for me for years has been to get a sterile surface chemistry on the balloon that I am happy with and can afford on a hobbyist's budget. I think this is easier to do with a monocoque outer of a separate material.

BW

Ol

M0LVR

[Steve Aerospace]

Thanks Joe - I have crunched the numbers and my conclusion is that its doable.

I come up with about 71kgf/m = 48lbf/ft for the tension in the balloon skin in the example given,  That is a 1ft width of envelope material must hold 48lb without tearing.  It sounds feasible to me - certainly considering some of the tension will be taken by the latex balloon and some by the fabric.  I haven't been able to find much data on ripstop nylon - so I will conduct some tests over the next few days.

Here is how I came up with the figures:   

    https://ukhas.org.uk/ideas:super-pressure_balloon_skin_tension_calculations

    Steve G8KHW

[John Underwood]

Typical engineering ripstop Nylon (MIL-C-44378) has a mass of about 1.2 oz/sq yard (38 gsm) and a breaking strength of 45 lbf/in (7500 N/m). If you take account of joint strength (you will be lucky to beat 80% unless you know what you are doing) it isn't quite strong enough.

MIL-C-7350 is slightly stronger but also heavier.

All the specs are available on the internet.

Hope this helps.

John

[John Underwood]

Oops. Decimal point in the wrong place. It's plenty strong enough! I hate kgf.

MIL-C-44378 is already quite lightweight. I think you can get material of about half the weight but I haven't seen specifications. Joining very lightweight materials effectively (and designing your cover without stress raisers) will be a challenge.

[Steve Aerospace]

Thanks John - good news.    I over estimated the size of the balloon in the original post and didn't take fabric stretching into account - so there is some extra weight budget too.

From a purely calculation point of view Newtons are great to work with,  but if I need to visualize something then I divide by 10 and think Kg.

Steve

[stephen billings]

I don't know if you can get untreated MIL-C-44378, as that would make it lighter still.  Not by much, but when weight is an issue, it all counts.

I know that untreated is still strong, as I use it for parachutes, for my teddy bears.

Joining it is easy, if you know how.  You will need some of the Pritt type glue sticks.

Run it along one of the edges you want to join.

Then place the other on top, and weight down with something.

When stuck,you can sew the parts together, with a sewing machine.

Hope this will help.

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[Oliver de Peyer]

What about mylar?

I was concentrating on that as a material because it can be purchased copperised.

Thanks

Ol

M0LVR

[Steve Aerospace]

Have you got a spec - weight (with coating) and thickness and or strength - then I can work out if its feasible.  What altitude do you want to float at?

    Steve

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[Steve Aerospace]

Oh and payload weight.

    Steve

[Oliver de Peyer]

Thanks Steve, that's a thought provoking list of parameters.

O.K, payload weight: 
What is the max allowed by CAA? I had it in my mind that it was 1.8kg/4Ib. Whatever the max is anyway, some of my payload concepts tend to run quite heavy.

Float height: 30km
But floating is not essential to me, it is nice (for instance we were looking at a 100 day duration floater with my old NASA colleagues) but it is more important to just get a sterilising canopy to altitude somehow, even if it turns out to be a straight up and down.
‎
Mylar spec:
Please just spec for standard aluminised mylar in the first instance - whatever has been used for picos for instance because we know that floats.
‎
Copperised mylar is hard to get hold of and tends to show up as bulk industrial purchases in the outer reaches of AliBaba. Even then it can be fleeting (you go back to look at a given Chinese manufacturer and find they no longer exist, etc). It would require a significant lump of cash and more importantly I would need somewhere to stash a 500kg reel of mylar! A hackspace perhaps. 
Various people will do custom coatings in which case it is "simply" the case of substituting a vat of molten copper in place of molten aluminium in your PVD vacuum chamber as the mylar film is spooled ‎through. In which case, the surface coating thickness might be identical between aluminised and copperised mylar, although the kg/m2 might alter.
‎
So in the first instance it would be enough to see if aluminised mylar actually ‎could compare to ripstop and see if anybody could build a geodesic sphere from ripstop or mylar and see if would actually fly (or ripstop for structural strength and then a very thin outer copperised mylar?? Now there's an idea)

Many thanks
BW

Ol‎

‎

[Steve Aerospace]

I don't think there is an upper limit on the payload - but the CAA will
require you to do more and more things to mitigate risks the heavier you
go.  SERA/ICAO rules now apply (see my presentation at the 2016
conference https://www.youtube.com/watch?v=PQJAjDEq5AA&t=1h47m17s).
Below 2Kg is simplest - the only requirement is that the line requires
less than 230N (23.4kgf) impact force to detach payload from balloon. 
Anything with a combined mass of greater than 4Kg gets quite
complex/difficult to launch.

Aluminum Mylar (BoPET):  The sample aluminumised PET I have to hand
(don't think its a true BoPET but is similar density) is 12.5um thick
and about 19gsm - so that's a bit lighter than the ripstop we have been
talking about.  Mylar strength at 5% stretch is about 100MPa - which is
equivalent (if I have my sums right) to 1,250N/m for 12.5um thick
material.  This seems to be in the right ball park - but could do with
being a bit thicker.

I will put a spreadsheet together so folk can try some what if scenarios.

    Steve

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[Steve Aerospace]

I don't think there is an upper limit on the payload - but the CAA will
require you to do more and more things to mitigate risks the heavier you
go.  SERA/ICAO rules now apply (see my presentation at the 2016
conference https://www.youtube.com/watch?v=PQJAjDEq5AA&t=1h47m17s).
Below 2Kg is simplest - the only requirement is that the line requires
less than 230N (23.4kgf) impact force to detach payload from balloon. 
Anything with a combined mass of greater than 4Kg gets quite
complex/difficult to launch.

Aluminum Mylar (BoPET):  The sample aluminumised PET I have to hand
(don't think its a true BoPET but is similar density) is 12.5um thick
and about 19gsm - so that's a bit lighter than the ripstop we have been
talking about.  Mylar strength at 5% stretch is about 100MPa - which is
equivalent (if I have my sums right) to 1,250N/m for 12.5um thick
material.  This seems to be in the right ball park - but could do with
being a bit thicker.

I will put a spreadsheet together so folk can try some what if scenarios.

    Steve

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[Oliver de Peyer]

Many thanks again Steve

Due to commitments with the xyl and yl, I haven't been able to get to my computer today but have done many a Google and AliBaba search on my phone.

As I feared, most copper mylar suppliers are quite opaque as to whether it is actually copper, or just "copper coloured mylar" - some copper coloured mylar is actually gold! Also, they don't all have tension ratings etc, often they are polylaminates (I need a bare metal surface) and the minimum order sizes and costs are (for personal use) immense.

However, digging a bit further, it soon became apparent that adhesive copper tapes are more "mainstream" - both cheaper and crucially readily stocked for retail use in the west. Digikey and Mouser stocks a wide range of 3M copper tapes for instance, in widths of up to 23" (so a sheet really not a tape).
Typical thicknesses are 0.1mm.

Here is 3M 1245 for instance:
Backing thickness 1 1.4 mil (0,04mm) Total thickness (backing plus adhesive) 4.0 mil (.101mm) Breaking strength 1 25 lb./in (44 N/10mm) Adhesion to steel 1 35 oz/in (3.8 N/10mm‎)

So that's 4400N/m, correct?
Not too bad.

Of course, you are stuck with an adhesive layer, but you use this as a feature instead of a bug:

1) Thin ripstop geodesic ‎polyhedra for sphere - pritsticked and then sewn together (suits a cottage industry amateur HABber working from his bedroom. Knew that sewing machine the xyl bought would come in handy one day)
2) Ripstop is a fairly good semiporous rough ‎surface for bonding the adhesive copper foil sheets.
3) The foil sheets and the adhesive/ripstop layer provide most of the structural strength. It is a bit like a doped fabric-metal laminate.

Of course - would it be too heavy? You can of course just make your balloon bigger and bigger and use hydrogen to reduce lifting gas costs. It doesn't have to be strong ripstop any more, anything will do. But I imagine the foil sheets will be the real cost (ironically then probably better to order from AliBaba)

The ripstop is probably much easier to work with than mylar.

The other alternative is very thin flexible copper clad PCB boards. I have some 0.1mm Pulsar ones at home for instance. But now you practically have a rigid zeppelin! I will weigh one of the Pulsars when I get home. I imagine most of the weight and rigidity is the phenolic board. Maybe a copper foil tape/sheet would actually weigh less and be more ductile for the same thickness.

It hovers on the edge of doable or is at least very intriguing. You could go lower and lower for target altitude to help with getting it airborne, anything above the tropopause would have some astrobiological value.

I don't have the specs for different types of ripstops‎ etc so I can't work out for now the relative strengths and weights of ripstop/adhesive foil sheet composites.

I wonder if you would need a parachute still? Arguably it will have a huge surface area even after the latex inner canopy bursts.

Bw

Ol

[Joe]

It has been too long of a time for me to remember, But I think you are missing a step in your math calculations.

Being one that has pursued this for close to 3 decades, and worked closely with the developer of the "Pumpkin" style of Balloon with the designer at NASA. I think you are missing a major step in the calculations. Because when we ran the numbers on typical Amateur Size payloads and flight systems, there were little to no materials available that would do the job, and NONE that if could do the task could be sewn or bonded together. The seams always would fail.

Joe WB9SBD

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[Oliver de Peyer]

Dear Joe

Many thanks for your advice backed by many decades of experience!

I think the key here is your phrase "amateur size... flight systems". I rather suspect that monocoque designs etc are possible but by the time you have a built a balloon big enough to be carry the weight of the outer canopy, it is so big that it is not really "amateur size". Ironically though it might still be capable of being fabricated by amateurs. 

If‎ you have a balloon when the CANOPY weighs 100kg but the payload weighs 1kg, can it still get CAA or FAA permission?....

To spare my blushes somewhat, one could argue that (for instance) the 3M sheets are new materials and in particular the polyacrylic glues used are new and probably add a lot of the structural strength themselves. Indeed, a strong glue might give a seam strength not previously possible. It would be fun to try taping some test seams just to see what happens.

The 3M adhesive sheets are, it turns out, very expensive in any usuable sizes (such as their 23" widths) so back to the drawing board... intriguingly though copper foil seems quite cheap, cheaper than mylar for instance.

Remember, for my own purposes floating is not essential but would be nice.

A straight up and down flight with a latex inner canopy that in fact bursts after all would be astrobiologically valid as long as the flight would be long enough that you could claim that the canopy had feasibly sterilised itself in flight.

It is very tempting to see if a foil outer canopy would work, and might even be made fully gastight, since it has in fact been tried successfully before (for instance the ZMC2 airship) - although not applied to stratospheric flight.

BW

Oliver

Radio callsign: M0LVR

[Steve Aerospace]

Thanks Joe - while I'm sure your right about "Pumpkin" type balloons being needed for large NASA payloads I'm less convinced at a smaller scale,  after all under the right conditions its quite possible to get a  sealed (hence super-pressure) Hwoyee 1600g to float for several hours in sunlight at around 38Km (approx 10m diameter) - I can see nothing special about latex strength in comparison with other envelope materials.

I can't see any missing steps in my calculations but I'm happy for anyone to point out any omissions:

    1) Calculate the air Density, Pressure and Temperature at the intended float altitude (I'm currently using the 1962 NASA atmospheric model).

    2) Estimate the size of the balloon at float and hence the size and weight of the fabric envelope.

    3) Calculate the amount of gas needed to lift the weight of:   Latex Balloon + constraining fabric envelope + Payload + Free lift

    4) Calculate the total weight of the balloon system - that is:  Latex Balloon + constraining fabric envelope + payload + gas.

    5) Using density from 1) work out the displacement volume of the balloon at float equal to the total weight (latex balloon + fabric envelope + payload + gas)

    6) from the balloon volume calculate the balloon radius assuming a sphere.

    Iterate steps 2 to 6 each time getting a better estimate of balloon size - until the solution converges- then:

    7) calculate the internal pressure of the balloon at float from the mass of gas at launch (mols), internal gas temperature at (assume some thermal gain) and the size of the balloon at float

    8) work out the differential pressure (internal pressure - atmospheric pressure) at float

    9) from differential pressure and balloon radius using the sphere surface tension/hoop stress equation calculate the tension in the balloon + fabric skin combination

    10) see if the solution is viable  - i.e. the tension is significantly less than the strength of fabric being used.

Bear in mid we are not after absolute accuracy - just to see if the solution is in the right ball park to be viable.

    Steve

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[Leo Bodnar]

Great to see superpressure balloons getting some press!

sealed (hence super-pressure)

I think superpressure balloon is usually defined by reasonably constant volume envelope and, in general, almost complete irrelevance of its internal gas pressure, as long as it is higher than ambient.

I don't know the value of superpressure in latex balloon at float altitude but I reckon it is tiny.

Reaching floating attitude is not a big problem, staying at it - is.  Vertical drafts of either direction, water condensation, moisture absorption, supercooling, skin gas migration are just a few things to look out for.  They all have conflicting requirements for value of superpressure.

Leo

On 17 Jun 2018, at 13:47, Steve Aerospace wrote:

Thanks Joe - while I'm sure your right about "Pumpkin" type balloons being needed for large NASA payloads I'm less convinced at a smaller scale,  after all under the right conditions its quite possible to get a  sealed (hence super-pressure) Hwoyee 1600g to float for several hours in sunlight at around 38Km (approx 10m diameter) - I can see nothing special about latex strength in comparison with other envelope materials.

I can't see any missing steps in my calculations but I'm happy for anyone to point out any omissions:

    1) Calculate the air Density, Pressure and Temperature at the intended float altitude (I'm currently using the 1962 NASA atmospheric model).

    2) Estimate the size of the balloon at float and hence the size and weight of the fabric envelope.

    3) Calculate the amount of gas needed to lift the weight of:   Latex Balloon + constraining fabric envelope + Payload + Free lift

    4) Calculate the total weight of the balloon system - that is:  Latex Balloon + constraining fabric envelope + payload + gas.

    5) Using density from 1) work out the displacement volume of the balloon at float equal to the total weight (latex balloon + fabric envelope + payload + gas)

    6) from the balloon volume calculate the balloon radius assuming a sphere.

    Iterate steps 2 to 6 each time getting a better estimate of balloon size - until the solution converges- then:

    7) calculate the internal pressure of the balloon at float from the mass of gas at launch (mols), internal gas temperature at (assume some thermal gain) and the size of the balloon at float

    8) work out the differential pressure (internal pressure - atmospheric pressure) at float

    9) from differential pressure and balloon radius using the sphere surface tension/hoop stress equation calculate the tension in the balloon + fabric skin combination

    10) see if the solution is viable  - i.e. the tension is significantly less than the strength of fabric being used.

Bear in mid we are not after absolute accuracy - just to see if the solution is in the right ball park to be viable.

    Steve

On 16/06/2018 13:56, Joe wrote:

It has been too long of a time for me to remember, But I think you are missing a step in your math calculations.

Being one that has pursued this for close to 3 decades, and worked closely with the developer of the "Pumpkin" style of Balloon with the designer at NASA. I think you are missing a major step in the calculations. Because when we ran the numbers on typical Amateur Size payloads and flight systems, there were little to no materials available that would do the job, and NONE that if could do the task could be sewn or bonded together. The seams always would fail.

Joe WB9SBD

<CLEAN-IDLE-TYME-LOGO-120x96.jpg>

[Steve Aerospace]

Thanks Leo - perhaps that is the missing aspect - enough extra pressure to ensure a constant volume envelope day and night.  

I'm mostly concerned with the logic of the calculations and/or any missing steps.

One can always put more gas in (extra free lift) - this will result in faster ascent and extra pressure at float.  I guess the float may be lower due to the extra mass of gas - but probably offset somewhat due to envelope stretching because of the extra pressure.  What isn't modeled is elasticity of the envelope.

Pressure inside a HY-1600 Latex balloon at 38Km float?   Lets say 1700g for the balloon (1700g would be typical for a HY-1600 balloon) + 200g Payload + 1.8cu m of Hydrogen would be typical for a float.  My calculations come out at balloon diameter 9.0m internal pressure 0.497KPa External 0.379kPa - differential 0.118kPa - about 0.017psi.   Sounds about right for the burst pressure data I've seen.

    Steve

[Oliver de Peyer]

Thanks Leo for the tips. It would seem to me that an inner canopy and an outer canopy would solve some of these problems, since the outer would physically protect and insulate the inner.

Whether this is worth the weight penalty is the question.

My thinking process for all this started from the premise than large superpressure balloons would be very hard to make and so using a latex inner canopy with a monocoque outer canopy might be a shortcut.

I don't even know what you would call it... a monocoque outer canopy balloon?

Would you let the latex balloon expand to near-bursting, or would you keep it smaller than that?

One way or another you can test this, since the latex balloon is literally off the shelf and the outer canopy doesn't need to be gastight so is suddenly much easier to make. 

Ol

[Steve Aerospace]

Generally when folk suggest ideas like this I think :- Amateur HABing has been around 50+ years, if it was that simple it would have been done already.   However with this one I'm not so sure.

    Steve

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[Oliver de Peyer]

My "conscience" is clear ;-) ... I am not being a crank with no aeronautical training claiming I have made an unsubstantiated marvellous invention, possibly I am being ‎a crank with some astrobiological training instead ;-)

But once I got thinking I began to wonder what might happen and if I had gone a roundabout way to making a superpressure thingy of some sort.

‎I would be happy if I could just find a way of flying custom outer canopies around reliable latex inners (and without bursting the inner too soon) even if they don't float. I think I will try getting hold of some odd canopy materials (such as metallic foil perhaps) and seeing if I can bond some polyhedra together.

People with more competence than I in such things might want to try more realistic materials such as ripstop.

Anyway it is something we can actually test fairly easily, as long as the balloon‎ can actually lift the outer canopy - and Steve's sums give some clear parameters to work with.

Ol

[Joe]

This may be where I was getting much higher numbers in my calculations. Having enough lift to keep aloft after the solar energy goes away at sundown.

This is not a small amount either! A Minimum of 10% of the total lift. Averaging between 10 & 15 percent.

So to cancel the extra 15% lift during the day is HARD!

This might be what was missing.

Joe WB9SBD

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[Joe]

Yup you can test this on the ground. if you know the pressure it has to hold, you can simply fill it with air and pump it up to the desired pressure, and see if it holds.

One caution, the restrictor bag, has to be as smooth as a newborns babys bottom. a single rough area and the balloon will fail.

Joe

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[Joe]

Like I said.

Ive been trying for 30 years, come close, Never with as being described. But close with Earthwinds technology.

Two flights seemed to have worked, but sadly the payloads had failed to know how long it actually stayed up.

Joe WB9SBD

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[Joe]

See below for comments,,,

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On 6/17/2018 5:49 AM, 'Oliver de Peyer' via UKHAS wrote:

Dear Joe

Many thanks for your advice backed by many decades of experience!

I think the key here is your phrase "amateur size... flight systems". I rather suspect that monocoque designs etc are possible but by the time you have a built a balloon big enough to be carry the weight of the outer canopy, it is so big that it is not really "amateur size". Ironically though it might still be capable of being fabricated by amateurs.

Size is all relevant. With the huge amount of these small foil long duration flights, any latex is a large balloon.
Here at Near Space Sciences we have flown even the 3000 gram sized balloons. That's a burst diameter of over 40 feet in diameter, so what is "Amateur Sized?"

How about one we have, a PE Balloon that has a 300,000 cubic foot volume. Now that's BIG.

If‎ you have a balloon when the CANOPY weighs 100kg but the payload weighs 1kg, can it still get CAA or FAA permission?....

FAA says nothing about balloon weights, Funny, I could fly one of those pico payloads ( less than one ounce) on that giant balloon that weighs 30+ pounds and be legal.

To spare my blushes somewhat, one could argue that (for instance) the 3M sheets are new materials and in particular the polyacrylic glues used are new and probably add a lot of the structural strength themselves. Indeed, a strong glue might give a seam strength not previously possible. It would be fun to try taping some test seams just to see what happens.

 How Big of a Sphere do you plan on trying to make?  I may have an Idea for you to test, that puts far far less stress on the restriction bag.

The 3M adhesive sheets are, it turns out, very expensive in any usuable sizes (such as their 23" widths) so back to the drawing board... intriguingly though copper foil seems quite cheap, cheaper than mylar for instance.

Makes ya wonder what it is made of.

Something else to remember also that we ran into in our efforts. A glue may seem perfect, BUT.... and there always is a BUT isn't there? How does it perform at -70 degrees F? Many we thought would work failed miserably when got cold.

Remember, for my own purposes floating is not essential but would be nice.

A straight up and down flight with a latex inner canopy that in fact bursts after all would be astrobiologically valid as long as the flight would be long enough that you could claim that the canopy had feasibly sterilised itself in flight.

What is the purpose of the restrictor then if not to prolong the flight?

It is very tempting to see if a foil outer canopy would work, and might even be made fully gastight, since it has in fact been tried successfully before (for instance the ZMC2 airship) - although not applied to stratospheric flight.

What level of lift are you using in your calculations? and what amount of internal pressure are you generating to cancel out the lift?

Joe WB9SBD

BW

Oliver

Radio callsign: M0LVR

[Oliver de Peyer]

Dear Joe

The outer canopy - the restrictor bag - is there to ensure perpetual biological sterility for air sampling missions‎. There are various ways this could work, a copper metallic canopy being one of them. This was the original idea of the outer canopy, only later did I begin to wonder what would happen in terms of superpressure etc.

I will go into this in more depth and reply to your other comments in another email.

BW

Oliver

[Joe]

ahhh I see he he he

Joe

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[Oliver de Peyer]

Dear Joe

In answer to your other questions:

Some of the other perpetually sterile balloon concepts I came up with went very, very big - say a 30m radius with a hundred thousand cubic metre volume. See footnote 1 below.

Some such sizes are no doubt totally impractical but perhaps it would be fun for someone to find out just how big you could go.

For my own stuttering efforts however I am quite sure that I will not have the resources, time or physical space to go anywhere near that big. How do you make a gastight do-it-yourself canopy for instance?

Therefore I would coalesce around the largest possible ‎latex balloon, such as the 3000g one, and work back from there (i.e the latex balloon size dictates the rest). Outer canopies of any sort are much easier to make than true gastight canopies, it seems to me. The questions are:

Will they be too heavy to fly?

As restrictor bags, do they buy you anything useful in terms of achieving superpressure etc?

I have put in a request to 3M to find the temperature range of their tape glues.

I guess you are really paying for the glue, which is a metal-to-metal glue. Copper tape is mainly used for RF shielding etc.

I rather suspect that copper foil is easier to make than even boPET film etc - you just keep rolling it and rolling it, thinner each time. It is actually cheaper than aluminised mylar etc. Even artisanal copper leaf (which is hammered by hand to its final thickness) is not actually that expensive‎.

So copper foil is worth a punt for my purposes, maybe with copper tape along the seams.

I imagine‎ the foil and tape edges will be quite sharp, so we might need a very thin intermediate THIRD layer, such as muslin.

Finally, if this is a geodesic structure of polyhedra (straight edges easier to cut and tape), we cannot actually assume it will sag around the latex balloon inside. If I have this right in my head, a geodesic structure is self supporting, correct?

In which case, the latex inner balloon might be at highest stress pressed up against the inside top of the outer sphere which will remain semi-rigid.

As a further project in the distant future it would be even tempting to try a gastight metal foil balloon, since it has actually be done in the past with the ZMC2 (multilaminate aluminium foil with the foil panels stitched together with three lines of aluminium thread! Helium permeability was very low).

Regarding lift, inner pressure etc I am totally winging it so I would‎ defer to Steve's figures in an earlier email (85,000ft float, 13 cubic metres of hydrogen, 3000g balloon constrained at near maximum diameter (10m))

BW

Oliver

1 For instance one idea was a balloon with an outer foam layer soaked in dilute hydrogen peroxide. I even found a bemused foam manufacturer who could have sold me large foam sheets with a gas impermeable base.

However a ten centimetre square of this stuff‎ weighed about 250g wet. So you had to have a huge balloon to lift the balloon when wet.

Whilst not impossible to build, and maybe not even impossible to fly (using hydrogen), it would have dripped about a ninety metric tonnes of hydrogen peroxide into the environment during flight, which would no doubt be totally banned. I have no idea of what the environmental consequences of a ninety tonne peroxide spill are, even if only at 3% strength.

[Joe]

Hi Oliver,

Something you may want to try. We have done it twice so far, and both times it did seem to reach the desired float altitudes. But how long, I do not know because both payloads  froze during the cold night and never came back later on the next day.

They made it past dark and stayed aloft, level flight. But froze like at 3 or 4 am, never to come back alive after sunup.

But the design is something you might want to think about the pressure is far less, and you can actually control it and set it to park at the desired altitude too if you wish to be at a certain one.  Here is a page about the project.  We called it "EarthBreeze" after the "Technology used in the "EarthWinds" project.
http://www.qsl.net/nss/earthbreeze.html

Joe WB9SBD

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[Steve Aerospace]

Its an interesting design Joe.   I remember it took some time to get my head round it when you launched EarthBreeze II back in 2012.  The way I like to think of it is that although the weight of the overall system remains the same the  pumpkin provides negative buoyancy once the balloon inside it starts to become constrained by the fabric envelope**.  With the right amount of gases one can arrange float when the buoyancy of the Top latex balloon plus the negative buoyancy of the pumpkin matches the weight of the overall system.

I'm not sure how long the top balloon will last in all that UV - maybe a day or two.  It certainly deserves another try.

    Steve

** In fact with an air fill I think the pumpkin is providing a small amount of negative buoyancy all the way from launch - but the negative buoyancy goes up rapidly once the lower ballooon starts to become constrained by the fabric envelope.

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[Oliver de Peyer]

Dear Joe,

I was interested in your use of parachutes as off-the-shelf restrictor bags (i.e using two parachutes sewn together).

How big do parachutes get?

What are the biggest sizes sold for hobbyist use? 

What are the biggest sizes that you sell, Steve?

It is perfectly possible to find second hand parachutes on eBay, but if they are actual working parachutes (for instance for skydiving) they have "unhelpful" vents and so on which are no doubt good for working as a parachute but not for readily turning into restrictor bags. I also imagine the fabric will be too heavy duty for this application.

It is one of those things where do you build your own canopy (need to be handy with your sewing machine and can you afford the fancy MILspec fabric?) or do you cobble together something else? (e.g existing balloon or model rocket chutes, or other things like kids' "wind tents" - but all of which tend to be fairly small)

It would be a nice one for someone to try on a small scale - i.e two largeish parachutes from Steve's stock plus whatever latex balloon would feasibly fit inside.

For my own particular application, once I have a passable restrictor bag I can then start sticking copper foil on the outside etc (although it might end up too heavy to fly).

BW

Oliver

[Joe]

See Below for answers.

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On 6/19/2018 5:56 AM, 'Oliver de Peyer' via UKHAS wrote:

Dear Joe,

I was interested in your use of parachutes as off-the-shelf restrictor bags (i.e using two parachutes sewn together).

How big do parachutes get?

As big as you can afford! he he he...

What are the biggest sizes sold for hobbyist use?

I honestly do not know the answer to this question. In our two experiments, we tried a 15 footer on the first flight, and like a 25 footer on the second one.

I got them from a "Surplus" place. Problem is their supplies vary constantly. You can look one day and see them there, and say cool I'll get some. And go back a few days later and all sold out. Or the other way around too. Look and nothing good for your application, Like 80 foot made to drop Jeeps or some crazy thing, but none suitable, yet the next day ones that are good appear. ya have to look almost daily. their address is,

https://colemans.com/

 

What are the biggest sizes that you sell, Steve?

I am interested also....

It is perfectly possible to find second hand parachutes on eBay, but if they are actual working parachutes (for instance for skydiving) they have "unhelpful" vents and so on which are no doubt good for working as a parachute but not for readily turning into restrictor bags. I also imagine the fabric will be too heavy duty for this application.

Yeah the two that I found at Colemans did now have the spill hole. Well they did, but they were very very small, like only an inch in diameter, which was perfect! I covered one and the balloon neck exited the other.

It is one of those things where do you build your own canopy (need to be handy with your sewing machine and can you afford the fancy MILspec fabric?) or do you cobble together something else? (e.g existing balloon or model rocket chutes, or other things like kids' "wind tents" - but all of which tend to be fairly small)

Yeah you need the VOLUME  for it to work. too small and you can not generate enough ballast weight.

It would be a nice one for someone to try on a small scale - i.e two largeish parachutes from Steve's stock plus whatever latex balloon would feasibly fit inside.

I'm Game again, if I can find a reasonably sized sphere and weight. and of course cost.

For my own particular application, once I have a passable restrictor bag I can then start sticking copper foil on the outside etc (although it might end up too heavy to fly).

what is the bag?

Joe WB9SBD

BW

Oliver

[Oliver de Peyer]

Dear Joe

Right now there are lot of chutes on the Colemans site, many thanks for the link.

Much too big for most HAB payload return applications but about right for larger restriction bags! (e.g 30 footers)

It is odd to see British parachutes on a U.S surplus site, I wonder if anybody knows where they might turn up in the U.K?

(Steve did you ever think of getting into the surplus parachute trade... ;-) ? )

For myself, if I ever get hold of a decent bit of copper foil or tape, the next thing would be to try to stick it or sew it to a parachute canopy etc and see what the all-up weight is per unit surface area (kg/m3). Then I could start working out how large the balloon has to be.

I did request a 3M sample but they might not think I am a serious user.

BW

Oliver

[Steve Aerospace]

I added my answers to Joe's

    Steve

On 19/06/2018 13:49, Joe wrote:

See Below for answers.

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On 6/19/2018 5:56 AM, 'Oliver de Peyer' via UKHAS wrote:

Dear Joe,

I was interested in your use of parachutes as off-the-shelf restrictor bags (i.e using two parachutes sewn together).

How big do parachutes get?

As big as you can afford! he he he...

What are the biggest sizes sold for hobbyist use?

SR: The biggest that Spherachutes make as standard is 192" (16ft) - but I'm sure they would make bigger if you crossed their palm with money.  A pair of 192in Sphereachutes would set you back about £700 imported into the UK.  Spherachutes are the ideal shape as they are 1/2 spheres - but they do have a spill hole you would need to cover:-  http://spherachutes.com/main%20spherachutes%20168-3sm.jpg .  The size measurement is across the top - so a 192" chute will give you a 250in diameter sphere.  Spherachutes are made to order - so I'm sure I could get one made with a smaller or no spill hole.

I honestly do not know the answer to this question. In our two experiments, we tried a 15 footer on the first flight, and like a 25 footer on the second one.

I got them from a "Surplus" place. Problem is their supplies vary constantly. You can look one day and see them there, and say cool I'll get some. And go back a few days later and all sold out. Or the other way around too. Look and nothing good for your application, Like 80 foot made to drop Jeeps or some crazy thing, but none suitable, yet the next day ones that are good appear. ya have to look almost daily. their address is,

https://colemans.com/

 

What are the biggest sizes that you sell, Steve?

SR: See above.   Contact me off group if you want to discuss having some made.

I am interested also....

It is perfectly possible to find second hand parachutes on eBay, but if they are actual working parachutes (for instance for skydiving) they have "unhelpful" vents and so on which are no doubt good for working as a parachute but not for readily turning into restrictor bags. I also imagine the fabric will be too heavy duty for this application.

Yeah the two that I found at Colemans did now have the spill hole. Well they did, but they were very very small, like only an inch in diameter, which was perfect! I covered one and the balloon neck exited the other.

SR: I do have 1 x 168in(14ft)  in stock right now - bought for a big job (but we ended up using a 12ft Rocketman for drift reasons) - I could do a deal if bought with a 2nd.

It is one of those things where do you build your own canopy (need to be handy with your sewing machine and can you afford the fancy MILspec fabric?) or do you cobble together something else? (e.g existing balloon or model rocket chutes, or other things like kids' "wind tents" - but all of which tend to be fairly small)

Yeah you need the VOLUME  for it to work. too small and you can not generate enough ballast weight.

SR: The hemispherical gore pattern is available online if you want to make your own.

It would be a nice one for someone to try on a small scale - i.e two largeish parachutes from Steve's stock plus whatever latex balloon would feasibly fit inside.

I'm Game again, if I can find a reasonably sized sphere and weight. and of course cost.

For my own particular application, once I have a passable restrictor bag I can then start sticking copper foil on the outside etc (although it might end up too heavy to fly).

what is the bag?

Joe WB9SBD

BW

Oliver

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[Steve Aerospace]

I have added a surface tension calculator spreadsheet to the bottom of the wiki page: https://ukhas.org.uk/ideas:super-pressure_balloon_skin_tension_calculations

    Steve

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[Steve Aerospace]

Sure - I was already thinking I would do one - I'll make the choice of anchor balloon gas flexible - as I was wondering what other gases might do.

Steve

On 21/06/2018 13:52, Joe wrote:

Steve,

Could you make up a similar calculator that works with my idea of the "EarthBreeze" method? Using "AIR" as the anchor balloon "GAS"?

Joe WB9SBD

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[Joe]

It would be interesting to see what performance differences would be with different gasses.

"AIR"
CO2
Nitrogen
SF6
etc.

Joe WB9SBD

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[Joe]

Steve,

Could you make up a similar calculator that works with my idea of the "EarthBreeze" method? Using "AIR" as the anchor balloon "GAS"?

Joe WB9SBD

The Original Rolling Ball Clock
Idle Tyme
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