, “. ~ .- ,_ . * -I ' REFERENCE- .? -BBRARY p ;A ~~~ect;~~~vol ...

Wind Pawer S&m
carrying s,par, with a fiberglass skin rivetted
and epoxy-bonded in place around this
spar.This skin was laminated with polyester
resin over a shaped male plug mold-and
removed from the plug after the resin cured.
Ribs were sawed from half-inch-thick ply-+*wood
to close each end. The result was a
Cfootlong blade that weighed 8 pounds.
But the first windmill, tested on the back
of my pickup truck to simulate a wind tunnel,
was a disaster. The fiberglass-bladed rotor
would not spin fast enough to cause a generator-even
with a speed%p transmissionto
kick in and start: charging the batteries.
,
.r
The blade design had too much twist (spiral
turn). In a twisted blade, the airfoil at the root
end (closest to the center of the rotor) points
more into the wind than the airfoil at the tip
ofethe blade. Because of the excessive twist
in my first blades, the root end of each blade
was’acting like a giant air brake and preventing
the rotor from reaching-the
‘i rpm.
necessary
Thedessons learned from that first rotor
design caused me to re-evaluate my bladedesign
equations. The- new equations ,are
the basis for many of the calculations,discussed
iTthis book; they correct the,&vertwist
of my first blades and produce/blade
designs that are efficient and easy to build.
I also tried a different method d,f blade
construction that eliminated the need to mix
resin and laminate .fiberglass. Beta>-e it
offers a smoother surface and less air friction,
1 chose aluminum for the skin of my next
blades. But unfortunatelysheet
a
aluminum
1
.*
4
D
1.
The second in a series of experimental rotb6being readied for a test run. To
lower the air fnctlon, this rotor used sheet alumlnlum Instead of fiberglass for the blade
skins.
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