" A flight to space - or at least getting close! "
July 2008 : Operational again in our new home city.
If you make a big enough black bag it will fly on its own with just the heat from the sun. This is the principle of a solar balloon. By building a balloon out of thin plastic (such as rubbish bags) a solar balloon can be easily built.
But rather than me explain it, look at these websites:
The idea is to let off a solar balloon with a GPS location transmitter attached, and see how high and how far it goes! Future flights could add a camera or even more (a high-altitude glider! - see http://members.shaw.ca/sonde/index.htm )
GPS Location Transmitter
The transmitter will use the amateur radio bands. Due to the distances involved and other factors, the 80m (3.58MHz) band will be used.
Details of the transmitter are located here: DominoEX Transmitter Project
A tetrahedron balloon (often called a tetroon) seems to be the easiest to build. It just requires a rectangular sheet of plastic (ideal ratio is 1:2.3) which is formed into a cylinder and then the cylinder ends sealed perpendicular to each other.
A good explaination of tetroons can be found at http://www.flymetothemoon.com.au/homebuilding/solar.htm
The thickness of the plastic is the key to performance. The easiest material to obtain is thin black plastic rubbish bags, however bags vary in thickness. 14 um (that's micro-metres, or 1/1,000,000 of a metre) seems to be the recommended thickness. To determine the plastic thickness the best method I have found is to weigh the bags and then work out weight per square-metre. The plastic is close to the density of water, so 14g/m2 = 14um material.
These are the bags I've used:
With the end cut off and the bag split they give a sheet 1.5m x 2.2m. They cost $NZ 2.80 for 4 bags. I have also found smaller bags at $NZ 2.00 per 20, but they are only a third of the size and so require more assembly.
I used a soldering iron (25W, with a blunt rounded tip) to weld 6 bags together, giving a final sheet size of 3.1m x 6.7m. The soldering iron cut as well as sealed the plastic sheets together. Working on an MDF base board, I used a wooden guide to press the sheets together and guide the iron. By running the iron along the guide the scrap was cut off and the sheets sealed together. The resulting seams are reasonable strong, and no further strengthening seems necessary.
One corner was cut off and the edge strengthened with tape. This is the bottom of the balloon, and the inflation point.
The balloon was then test inflated using a fan heater (on cold).
12 October 2007
My balloon is now ready for a test flight - on a tether - on the next calm and sunny day (which may be a while given our recent weather!).
26 October 2007
Still waiting for it to stop blowing!
However I have made up an inflation/deflation device (i.e. a fan). I used some PC fans (12V) bolted together. Two of them worked, but one didn't, so the blade was removed and it was used as a duct between the two working fans. Plastic milk bottles were used to form the ducts. Hotmelt glue was used to seal it up. A car lighter plug was connected. For portable operation I power it from an old SLA battery. The unit can be used either way around to either inflate or deflate the balloon. The arrows show the air flow direction.
Now all I need is the chance to use it!
8 November 2007
Well it got tested - but a bit more than I intended! The balloon ripped from its tether and flew part way across town.
Here are the videos:
Unfortunately the balloon didn't have any weight around its neck, so it tumbled, allowing the hot air to escape. I was unable to give chase at the time (kid to manage!) so could only observe it as it flew across town and then dropped from sight after about 5 minutes. Someone will have had a surprise in their back yard!
Some birds took quite an interest in the balloon!
So that's it for this balloon. The concept is proven, but the balloon is lost. As we are moving to Canberra, Australia early next year the balloon projects is going to have to go on hold for a while.
All Go in the New Location
30 July 2008
Back in the air! We finally built a balloon here in Canberra and gave it a flight:
To inflate it I built a fan box using some large computer fans in a wooden box, complete with batteries. Here are my helpers with the fan.