1. Construction of the blade skeleton
Paper stencils of airfoil shapes were
glued onto balsa and cut out using a scalpel. A flat root-guide was made using
tin sheet with a piece steel rod as a round root. The root-guide was
fibreglassed and sanded flat.
Figure
1. The airfoil shapes constructed using balsa (left). The root and guide made
from tin sheet and wire (right).
The
hub for the blade skeleton was made from a piece of wood that was glued onto
the root section. The balsa airfoil shapes were positioned and glued along the
root.
Figure
2. The root section glued to the hub (left). The balsa airfoil shapes glued
along the root (right).
2.
Making a plaster mould
The
blade skeleton was coated in white gelcoat to strengthen it and pieces of clear
plastic sheet were glued on the airfoil shapes to create a wing surface. The
corners and joins were sealed with aluminium tape. A border was made out of
modelling clay to create a mould for the plaster to be poured into.
Figure
3. The gel coated skeleton with plastic sheet glued to the balsa shapes (left).
The final blade skeleton with border made of modelling clay (right).
Plaster and gauze was poured into the
mould. After setting, the process was repeated for the other side to complete
the mould.
Figure 4. Making the plaster and
gauze mould (left). The two completed half moulds (right).
2. Making a fibreglass blade mould.
The plaster mould was waxed then filled
with fibreglass to make a fibreglass wing. After curing, the plaster is removed
and the wing was sanded smooth. A wooden triangle hub piece was glued in place.
Cardboard and foil was used to make a border, then it was filled with fibreglass
and resin to make a fibreglass mould.
Figure
5. The fibreglass blade from the plaster mould (left). Making the fibreglass
mould from the blade (right).
The other side of the mould was
fibreglassed and the border was cut square. The mould opened easily and was
waxed up before use.
Figure
6. Making the fibreglass mould (left) and waxing before use (right).
3. Making the blade.
The half moulds were filled with pre-cut
shapes of fibreglass and Kevlar then the resin was soaked into the glass with a
paintbrush. A wooden hub is inserted at the end of the mould.
Figure
7. Half moulds being filled with glass and soaked in resin (left). A wooden hub
is fitted at the end (right).
The mould halves were pressed together
and tightened using bolts around the border. After the resin cured, the mould
was broken apart using a knife and a screwdriver.
�
Figure
8. A moulded blade ready to be cured (left). Breaking the cured mould apart
(right).
The blade was broken out of the mould
and the edges were cleaned up using a pair of snips. After some sanding and
wrapping in a layer of fibreglass cloth, three blades were fitted together and
reinforced using layers of fibreglass.
Figure
9. Fibreglass blades from the mould (left). The finished 3 blade set (right).
The
finished blades were tested using the generator shown in the 1.8m blade wind
turbine.
The
results are shown below.
4. Testing the wind turbine
Wind turbine was bolted to a trailer,
RPM, Voltage and TSR were measured by connecting the generator to a high power
multi-tap resistor. The turbine was allowed to speed up to an open circuit
voltage of 65v (666rpm) before the resistor load was connected.
5. Measured results for the wind turbine
|
|
25ohm
|
21.5ohm
|
15ohm
|
|
30km/h
|
756
|
|
|
|
40km/h
|
1040
|
844
|
|
|
45km/h
|
1299
|
|
|
|
60km/h
|
1425
|
1143
|
992
|
Rotational
speed (rpm)
|
|
25ohm
|
21.5ohm
|
15ohm
|
|
30km/h
|
177
|
|
|
|
40km/h
|
335
|
249
|
|
|
45km/h
|
521
|
|
|
|
50km/h
|
628
|
457
|
452
|
Power
(watts)
|
|
25ohm
|
21.5ohm
|
15ohm
|
|
30km/h
|
6.6
|
|
|
|
40km/h
|
6.8
|
5.5
|
|
|
45km/h
|
7.5
|
|
|
|
50km/h
|
7.4
|
6.0
|
5.2
|
Tip
speed ratio
Figure
10. Measured power output vs. wind speed
Figure
11. Measured RPM vs. wind speed
Figure
12. Measured efficiency vs. TSR
6. Total cost of the wind turbine
Construction cost (AUD)
Balsa,
glue, tin sheet $10
Gel
coat $40
Plastic
sheet, plaster $25
Modelling
clay $23
Vinyl
ester resin $110
Fibreglass
cloth/mat $80
Total cost $288
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