Here’s the instructional video from the workshop on heat seaming balloons. If you have the space and equipment, this will produce a lighter, more air-tight balloon.
Grassroots Mapping PDX 6/26/2010: heat seaming from mathew lippincott on Vimeo.
Grassroots Mapping PDX: Taping up balloons
I’ve finally collected and edited the workshop’s videos and instructions:
Taping Instructions
Follow the first two pages of my Balloon Building Guide to make a tetrahedron balloon. Tape carefully.
My balloon guide’s rigging is for short flights in confined urban areas. We’re going to use a different rigging for aerial photography.
One corner of the balloon is used for filling, and is tied off, like a trash bag. A second corner is re-enforced, and a loop of tape attached. To the tape is tied a short length of line. The knot used is a Bowline.
Grassroots Mapping PDX 6/26/2010: Rigging a balloon for flight from mathew lippincott on Vimeo.
attach a swivel to the balloon so that any spinning won’t twist the line or the camera.
warhol while you wait
I’ll have photos and videos from Grassroots Mapping up soon, Special thanks to Dustin Zemel for documenting.
in the mean time, enjoy an entire Andy Warhol installation, reproduced and on sale from a Chinese wholesaler.
Today went great
Thanks Sabrina Lindsey & Molly for bringing food, Dustin & Jane for documenting, Robby, Anna, Wade, Tuuli, Joel, Samantha, Dennis, & Scott for making the workshop awesome.
Helium Dispersion Through HDPE
In conversations on the Grassroots Mapping google group we’ve been wondering how long a homemade Polyethylene helium balloon could stay aloft. At what rate would a balloon lose it’s helium? This is a crucial question, since tomorrow we’ll be building a bunch of balloons. So last night I ran helium dispersion tests through HDPE with four different types of sheeting sitting around my house and a borrowed electronic balance.
Conclusions
The four thicknesses I could find were .315 mil (millionths of an inch) .69 mil, 1 mil, and 3 mil. Two complications to the tests were that the .69 mil was white, meaning it had added pigment, and the balance was only accurate to 1 gram, so I wasn’t able to figure out the rate of loss. I took photos of the balloons every 20 minutes from 10pm to 12pm, and then measured them this morning at 8AM. I then re-filled the .69 mil and 1 mil balloons for a second round of testing, realizing I’d incorrectly filled them the night before.
The conclusion i could draw was that .315 mil loses 1/4 to 1/3 of it’s helium over two hours, which means it probably is a poor choice for helium balloons. Each balloon had around 3 grams of lift.
.315 mil on the left.
.315 mil balloon after 2 hours, partially deflated but still floating.
The unfilled the white .69 mil balloon weighed about 3g. Full, it barely registered on the balance, and this morning the balance still oscillated between 0 and 1g. The 1 mil balloon, which weighed 2g unfilled and registered 1g filled, weighed 2g this morning, with no appreciable loss of gas. I should have noticed immediately that I’d screwed up, but I was distracted and cleaning the kitchen while running the tests. I must have filled the 1 mil and .69 mil balloons with a mixture of air and helium. This is confirmed by re-filling them this morning and watching them float.
So I ran the test again, filling both balloons up. The overnight test, although botched, was confirmed this morning. Over two hours, you can see the 1 mil clear balloon lose lift, while the white balloon remains buoyant.
Why would thicker, clear HDPE lose helium faster than white .69 HDPE? I believe it is the inclusion of metal oxide to tint the white plastic. White pigment is either zinc oxide or titanium dioxide (or lead oxide in really old stuff). This would also explain why the white HDPE is heavier than the thicker clear stuff.