Making the Envelope....

We have completed the building of a balloon envelope intended for filling with steam. The material used is the Gelvenor material described here, which, at least when new, appears to be substantially impervious to steam, i.e. impervious enough for this application. The volume of our envelope is 600 m3 and the area is 400 m2; it is 19 meters high and 8.4 meters in greatest diameter, and it weighs 38 kg. By hot-air balloon standards the construction is very strong. We used eighteen continuous vertical gores, and sewed load tapes top to bottom. We did not provide any horizontal load tapes, because in the case of a steam balloon they do not seem worthwhile.

At the top of the envelope there is a hole 1 meter in diameter, with a 1 meter long vent tube of the same fabric sewn to it, piped around its free end. To seal the envelope we tuck the vent tube inwards and tie it closed with a bit of weak break-cord. The ripcord is tied to the break-cord and comes out at the bottom of the envelope. This simple ripping system seems to work very well indeed - probably because the fabric is so slippery.

The bottom of the envelope comes down to a hole 66 cms in diameter, with one side of a detachable zip sewn round it. The drainage contraption to be zipped on is described later. Near the bottom we put a couple of plastic windows and (for entry) a 140 cm waterproof zip from a diver's dry suit.

Terry Price is a legend in the UK ballooning world. We were very lucky to obtain her services for building our balloon..... .

Here Terry is slaving away over a hot sewing machine.....

This is the final result..... laid out in the park, but not (yet) inflated....

The next test was to inflate it in the Scout Hall, as much as we could. That was kind of a laugh.... We used the bouncy-castle blower. Here's a panorama....

It got bigger....

and bigger....

and bigger....

and bigger....

and bigger !

It looked pretty through the door....

And even prettier from inside!



Next we proceeded to outdoor inflation.... see the next section ....



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