My summary of all posts as of 5th November 2022 here: https://groups.io/g/picoballoon/search?p=recentpostdate%2Fsticky%2C%2CYokohama%2C20%2C2%2C100%2C0&jump=1
Clear version: https://yokohamaballoon.com/products/sphere-balloon32inch?variant=41763086729369
Material： Nylon, Polyethylene
Due to the characteristics of the plastic film, if the balloon is inflated with gas in a cold or dry environment, the film may not stretch, and the balloon may burst before forming a round shape. Humidify the environment a few days before you wish to blow up the balloon. Inflate the balloon about 85% with gas, working in a warm environment. Leave the balloon untouched for a few hours, before inflating it the remaining 15% to create a beautiful spherical shape.
Yokohama claim 32inch, 113cm, 80cm, 270litres
Balloon empty weight: 48.6g
The volume of a Yokahama is around 0.25 cu m with stretching.
5g / 6g / 7g / 8.5g (10g too much)
Free lift for the clear 8.5gram, if I would release a silver I would keep the free lift to around 4.8-5g to keep it on the safe side due to the extra heating of the silver coloured ones.
The UAH students pressure tested our recent Yokohama balloon with compressed air to 0.4 PSI. The burst pressure is around 0.55 PSI so I would recommend 0.3 PSI to be safe.
Pre-stretched at 0.45psi for 24 hours. Stretching assisted by misting the expanding balloon with a water spray and careful work with a hair dryer. Not all of the seams were completely smooth though.
Before flight it was pumped to 0.45psi for an hour.
Did my 4th test to failure of the Yokohama balloons. This one was left at room humidity and temperature. Just a normal day at around 65F. Filled the balloon to .41 psi and held it at that pressure for about 4 days. Circumference was about 99 inches. It seemed quite stable. Yesterday I raised the pressure to .51 psi and held it overnight. The circumference increased to about 102". Today the film had developed a pinhole leak. The seams are OK but a pinhole failure. From my testing, it suggests that a pressure over .5 psi is risky or that a circumference beyond 100 inches is risky.
Tested three Yokohama balloons to failure (nylon) and moisture is an issue I don't think we have a firm handle on. I tested 2 while wet and both failed at around .3 psi The third test was dry and it failed at .52 psi. For the Yokohama balloons, it looks to me like a circumference of 110 inches might be too much. 100 inches seems safe.
I did a stretching test of the Yokohama balloons and had my first seam failure, Started on 4/27 at .165 psi. The circumference initially expanded to 92.5 inches. Held that pressure. By 4/29 the circumference had reached 94 and appeared stable. Increased the pressure to .25 psi and the circumference reached 98 by 5/1 and seemed stable. Increased the pressure to try about .3 psi and had a seam pull open. Through all this testing I kept the balloon moist with a hand sprayer and a sheet of painters poly over it. The surface was always moist. The room temperature was just below 70F.
I repressurized to failure my second Yokohama balloon. It failed at roughly 0.52 psi. When I reached 0.43 psi the circumference had reached the previous circumference of 100". As the pressure increased so did the circumference. At .52 psi the wrinkles on the seams had vanished and the circumference reached 103.75". What was curious was the balloon continued to expand at .52 and grew to 108.5" at my last measurement. It looks like the tension on the film had reached a point where it was stretching to failure. Then it popped. I presume the circumference probably reached 109" at the point of failure. Watching the pressure at .52 psi, it fluctuated and I presume the film was stretching and increasing the volume at the rate my air could enter the balloon. When it was fluctuating I suspected a leak I looked for leaks and did not find any, Most likely it was an enlarging balloon. The failure seems to be at the seams, not from thinning of the film.
You must pump the balloon up to at least 0.300 psi before launch, I recommend 0.400psi, do not launch a balloon that have not been prepumped on ground, it will fail.
Polystyrene fill tube by Evergreen model 225 It is 5/16" OD. It is slick and won't stick and mess up the fill valve. https://evergreenscalemodels.com/products/225-156-4-0mm-od-tubing
Beacon Foam-Tac glue
I am using the usual 300 watt impulse sealer. The heat is on for about 2 seconds and I hold the clamp in place for maybe 10 seconds. The setting is full scale for the 2 seconds and I heat it once before the actual seal.
Clean the paint off the seal with acetone. Alcohol works but acetone is quicker and seems better.
Mikael - I don't remove any paint and use cyanoacrylate based glue.
I cleaned the paint and sealed the outboard part of the original heat seal seam and two other places downstream. After the band sealing I put rubber cement in the rest of out board port and folded it and taped it with Tyvek tape.
Sealed with 5 minute araldite epoxy applied with a cotton tip pushed into the balloon neck and allowed to dry. The neck was then folded and sealed with a strip of Tyvek Sheathing Tape.
I used regular superglue and after I got the glue up the nozzle I folded the inlet and held the fold in place with some Kapton tape, it have worked fine on several flights,
A heat seal worked (I removed the internal paint first) - but the neck is very short and does not leave much room for error. My feeling is that if these can be reliably glued that would be the better solution. I'm pretty sure the valves are made of Polyethylene (PE) - which is difficult to bond reliably with glues. Some folk have been using contact adhesives - and these have worked - but my experience with contact adhesive & PE has not been good longer term. Superglue (Cyanoacrylate - CA) seems to have worked for a couple of folk - but in my testing with the necks I've found the bond poor. CA bonds to the internal paint in the valves - but the paint then seems to be able to separate from the PE. CA has a poor bond with the PE of the neck itself. I have found some special CA primer for PE. The join surface is first primed fro about a minute (it evaporates) and then glued with CA this gives a much better bond (to the point where the PE is failing before the bond) - so my current testing is with that (looking good so far).
Trying: https://www.amazon.co.uk/dp/B00EV5DYJY?psc=1&smid=AEZQ14FRKLF1N&ref_=chk_typ_imgToDp
Could try: https://www.ebay.co.uk/itm/283070037373 or https://www.ebay.co.uk/itm/185468729471
0.5g magnet to pull the tilted solar cells to the south