The blade halves will now be stuck together. The space within the blade will
be filled with expanding foam and the edges joined to finish the blade.
Expanding foam
A two-part expanding polyurethane low density foam was used to fill the air
gaps within the blade. This helps with rigidity and structure.
The foam is initially two liquids which must be mixed in a ratio of 1:1. This will
then expand to 25 times its initial volume.
To estimate the amount of foam required for each blade, the volume of the
blade must be calculated. This was calculated using the water displacement
method. The wooden blade (used to manufacture the mould) was immersed in
a large bucket filled to the brim with water. The water displaced when the
wooden blade was fully immersed was equal to the blade volume. The volume
of water was measured. The volume of the wooden hub at the root was
calculated and subtracted from the full blade volume. This gave an
approximate volume for the space within the blade of around 7 litres. With the
expansion ratio of 25, just 280ml of foam (140ml of each of the two liquids)
was required to fill the inside of the blade.
Note: If there is no access to such foam, this stage might not be necessary.
The process to apply the foam is as follows:
1: Use masking tape to seal all the sides of the blade. This is to ensure that
the foam, when in liquid form, will not flow out of the blade. Small holes must
30