Basic comparison of copper mylar vs aluminium mylar

[Oliver de Peyer]

Dear all, and especially Steve,

I have been getting enthused about experimenting with copper Mylar so have been working out if it is a practical material for balloons.

Here are some sums roughly comparing Copperised and Aluminised Mylar, for the thinnest Cu-Mylar I could find. I have done sums for 1kg and 25kg of the stuff:

Copperised Mylar:

Densities:
PET is 1.38g/cm3 
Cu is 8.96g/cm3

Thicknesses:
0.012mm Cu
0.015mm PET

Aluminised mylar:

0.0015 of an inch thick which is
0.04mm (0.0381mm to be more exact)

Al is 2.7g/cm3

So, a typical aluminised mylar balloon (according to nabas.co.uk) is 0.0381/0.012 = 2.7 time thicker in terms of Al layer than thinnest Cu layer available

8.96/2.7 = copper is 3.32 times denser than aluminium

3.32/2.7 = the metal layer is 1.23 times heavier for Cu at 12um thick than for a typical Al mylar film at 38um thick
- not too bad.

What we don't know is how thick the layer of PET is on a typical aluminised mylar balloon - or how much strength the different types of metal layers give the balloon (is Cu stronger and more leakproof than Al or vice versa?)

How much does a sheet of copperised mylar weigh?

Convert everything to cm

0.0012cm thick Cu x 8.96 = 0.0108 g per cm2
0.0015cm thick PET x 1.38 = 0.00207 g per cm2

So the metal layer weighs about 5x more than the PET layer (same would be true for 38um Al)

Grand total for a square cm of Cu-Mylar:
0.0108 + 0.00207 = 0.01287 g

So, if 1kg is the minimum order for Cu-Mylar:

1000g/0.01287 = 77700 cm2
This is 7.77m2
This corresponds to a sphere with a radius of 0.7863m - not a bad size for a CAA-exempt balloon

This would have a volume of 2.04m3

1m3 of helium at 1 bar (i.e a fully inflated balloon at ground level) can lift 1kg - correct me if I am misrecollecting this please

So, 1kg of Cu-Mylar of the above specs can comfortably lift itself plus another kg of payload
(obviously you would inflate the balloon much less fully with a much lower payload to achieve a decent altitude before bursting)

So, it will certainly fly, but it would be worth ordering much more than 1kg since 1kg is basically only one balloon's worth, and not even a full 2m CAA-exempt canopy size.

Might go for 25kg initially since it can still be manhandled (weight same as 8 year old nipper) and probably wouldn't break your toes if you dropped it!

It comes on a 41cm wide reel

77700/41
=1895cm long sheet for a 1kg order
Just shy of 19m
Or 474m or so for 25kg

What is the diameter of this?

Combined thickness of Cu and PET is 0.0027cm
And a 1cm2 square weighs 0.01287g

So a 1cm3 cube weighs (1/0.0027) x 0.01287 =4.7666g

So 1kg has a volume of 1000/4.7666 = 209.8 cm3
25kg has a volume of 5245 cm3

The bare reels from the supplier have a diameter of 76mm, so 3.8cm radius
So the bare reel itself is a cylinder of volume 3.8 x 3.8 x pi x 41 = 1860cm3

So, working back for a cylinder of total volume 1860 + 209.8 = 2070cm3, this is a reel of diameter 80mm (so barely 2mm of mylar on the reel) for 1kg

For 25kg it's 7105cm3 not 2070, which is a reel of diameter 149mm

So a tube 15cm wide standing 41cm high and weighing 25kg... can probably hide that in the corner ;-)
25kg would cost about $250 without discount.

Please let me know if any of my sums are wrong!

1kg for a 1.6m wide balloon seems disappointing but how much does a 1.6m wide aluminised mylar balloon weigh? Thinking about it, a party balloon might be 0.079m in radius not 0.79m, so weigh a hundred times less, so 10g not 1kg... probably not far off. NABAS suggests 38um for the thickness of the Aluminium, and they probably know their stuff. As above this would seem to indicate that Cu vs Al doesn't make much difference given the differences in thickness. It would be intriguing to know if much thinner Al layers are available on Alibaba somewhere. What is the empty weight of the 36" Qualatexs for instance?

Now to get my XYL to translate a quote request for the relevant supplier of Alibaba. Plus dinner and flowers to persuade her to let me buy it...

BW

Oliver

M0LVR















‎

Sent from my BlackBerry 10 smartphone on the EE network.

[Stuart Robinson]

On Saturday, September 17, 2016 at 4:47:53 PM UTC+1, Oliver de Peyer Astrobiologist wrote:

>What is the empty weight of the 36" Qualatexs for instance?

38.25g

[Steve Aerospace]

Oliver,

“Mylar” balloon materials are normally made of a number of layers - US patent 20040226649 A1 is a good source of info.  

Using your figures I came up with 128g per square meter (gsm) for the combined PET+Cu (27 micron) material - which gives about 1Kg for a 1.6m diameter sphere (8.04sq m surface area 2.14 cu m volume).

Checking this against a scaled up 36” Qualtex (about 40 micron thickness) suggests that the aluminium layer must be quite a lot thinner than your nabas.co.uk source.

Steve

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Steve Randall

Random Engineering Ltd

st...@randomaerospace.com

+44 7802 242135

[Oliver de Peyer]

Dear Steve,

Very interesting - to be glass half full it suggests that Cu-Mylar is thicker and more robust than most Al-Mylar balloons we've tried using so far.

What is the cost for 1 cubic metre of Helium these days?

It seems worthwhile trying to make a modest low altitude floater first, and then if it proves gasworthy etc, trying to ‎build something much bigger.

I'll get a price off AliBaba and get back to you.

BW

Oliver

Sent from my BlackBerry 10 smartphone on the EE network.

From: Steve Aerospace Sent: Sunday, 18 September 2016 13:19 To: uk...@googlegroups.com Reply To: uk...@googlegroups.com Subject: Re: [UKHAS] Basic comparison of copper mylar vs aluminium mylar

[Steve Aerospace]

A single 1.8cu m balloon grade cylinder (you collect rather than home delivery) is about £75 (so about £42 / cu m).  But you can get it much cheaper if you get bigger cylinders.

Steve

[Oliver de Peyer]

Thanks Steve

How about Hydrogen?

(For a small balloon it seems safe enough, but if you've ever sat through the talk in the Science Museum when they put a match to a small latex balloon of hydrogen, it does give one pause for thought!‎)

BW

Oliver

Sent from my BlackBerry 10 smartphone on the EE network.

From: Steve Aerospace Sent: Sunday, 18 September 2016 15:52

[Steve Aerospace]

Hydrogen in large, heavy cylinders works out very cheap - about £10 per cubic meter IIRC.  Man handling these 75Kg cylinders is however a real issue.  These days I tend to use the easy to handle BOC genie 5.2cu m G20 cylinders (25Kg) for both Helium and Hydrogen.   Because re-salers (Click4balloons and BalloonHelium)  get a large discount, Helium works out at a very similar price to BOC Hydrogen in G20s - I think last time I checked Hydrogen in G20s worked out about 80% of the price of Helium.

Steve

[Steve Aerospace]

Oh - I forgot to say BOC sell small, lightweight 1.8cu m ZH Hydrogen cylinders with integral regulator for their HYMERA fuel cell system - worth checking current prices, but from what I remember it was actually a similar price to a similar sized Helium cylinder. 

Steve