Use the spreadsheet
to calculate the temperature rise needed to make the four sheet tetroon
from the book fly. The spreadsheet was written using Microsoft Excel,
but loads perfectly into Gnumeric (the open source spreadsheet
program). Enter the following numbers into the boxes at the top of the
spreadsheet:

sheet short edge length

Measure along the short side of one of the polythene sheets made from a cut up trash bag. Measurement must be in metres.

sheet long edge length

Measure along the short side of one of the polythene sheets made from a cut up trash bag. Measurement must be in metres.

sheet turnover length

Enter
how much you overlap the individual sheets when making joins and how
much of the edge you turn over when making a join at the edge of the
envelope. Enter a value of 0.02 (20mm) when making a taped tetroon, and
0.006 (6mm)when making a welded tetroon. The numbers must be in metres.

tape weight

Weigh
a one metre length of your adhesive tape (scotch tape) and enter the
number in the box. The weight should be in grams per metre.

return tag weight

Weigh the postcard carrying your email address along with the plastic bag cover. Enter the weight in grams into the box.

ambient temperature

Measure
the air temperature in the shade near to where you want to launch the
balloon. Enter the temperature in degrees Celsius into the box.

temperature rise in balloon

Measure
the expected air temperature rise using the solar power meter described
in Chapter 2. Enter the temperature rise in degrees celsius into the
box. You should enter the temperature rise above ambient, not the
expected air temperature inside the balloon. For example if the ambient
temperature is 20 degrees Celsius and the solar power meter predicts an
air temperature inside the balloon of 55 degrees Celsius then your
should enter a temperatre rise of 5520 = 35 degrees Celsius.

You
can use the spreadsheet to explore the effect of different ambient
temperatures, sheet sizes and material weights. You can see by leaving
the temperature rise at a fixed figure and changing the ambient
temperature that a solar balloon can actually work better on a cold day!
