Exploring the Envelope Model

In preparations of our next stage I thought it would be good to have a scaled down envelope model we can send over to the Windreiter team to make sure that whole that concept is well understood.

Initial sketch of the envelope model showcasing the modular design and providing us with ~26kg buoyancy:

Initial sketch of the envelope model

When visualized in OpenSCAD, that front part (EDF intake) looks like this:

EDF intake

And then the overall view of a one envelope with a part of inner structure is planned like below:

Started with some scratches on a cardboard paper and looking for a material and ended up picking the LLDPE plastic bin-bags as a first go. Tried multiple glues for gluing it through past months, but none of those did well. So when looking for our options I ended up finding a website Welding Plastic Bags which provides very simple way to solve this. Long story short it goes like this:

1/ You need a baking paper and a soldering iron with a flat tip and temperature control.

2: Stack Materials – The welding process is commenced by preparing the Mylar sheets, ensuring they were free of dust and oils. Then make a material sandwich as baking paper, plastic sheet A, plastic sheet B, baking paper.

Nonsense image of how that quote from above is represented by DALL-E 3 😀

3: Welding the Seam – Use pressure on the soldering iron and move it along the seam to melt the sheets. Tip of the iron needs to be so that the whole surface of the tip makes contact with the paper. Heat gun will fuse plastic sheets together, forming a strong bond. This step was critical in ensuring the envelope’s durability and airtightness.

DALL-E actually did pretty well here … with bit of imagination 😀

Testing it on couple tiny objects we managed to manufacture following experimental balloon:

Seeing that doing reasonably ok, still that material seemed to be too thin and we’ve got many accidents burning through it. Seb then came with an idea to get back to a leftover of the Mylar (wide silver reflective film roll with tough black backing), which we tested instantly and that really started look pretty good! So we decided to go with that one.

Then it took pretty much couple weekends of cutting and welding.

But the result is worth it!

The last part was to do some weighing.

As you can see, scales say that it comes up with 235g. I think we used roughly about 1m2 of material so with our planned envelope of 70m2 it would take 16+ kgs. That’s unfortunately too much for our leftover weigh budget of ~12kg.

As always, we welcome insights or experiences from others working on similar projects. Feel free to share your thoughts in the comments below.

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