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#Post#: 3609--------------------------------------------------
Rotor Arm Material
By: lynx wind Date: July 1, 2014, 11:16 am
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The rotor arm. This is a component of the wind turbine that
bears the brunt of the power and stress.
Problems we have seen is sag, twist and breakage. Last night a
70 mph sustained wind tore through my area. Power is out, trees
down. My neighbor has two large trees laying on his roof. The
Gull 160 turbine suffered a broken rotor arm It was the painted
plywood type. It obviously had a tremendous twisting force and
snapped. It's still attached but broken across the two outer
magnet plate bolts. Think about the force that is required to
twist and snap a 14" wide 3/4" plywood.
To keep costs down I still look for ways to utilize plywood.
Going back to the tried and true method of fiber-glassing the
rotor arms may be the solution. Aluminum bends and is too
heavy. Composites crack and then fly apart.
#Post#: 3615--------------------------------------------------
Re: Rotor Arm Material
By: sut Date: July 1, 2014, 1:13 pm
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Bummer on both accounts neighbors house and windmill ! as long
as no one was hurt everything else can be fixed ! what if you
sandwiched the plywood in between the mag plate and a top plate
made out of aluminum . I think when you tighten up the 3 bolts
it compresses that area and causes a week spot just a thought
and easy to do
#Post#: 3618--------------------------------------------------
Re: Rotor Arm Material
By: lynx wind Date: July 1, 2014, 1:37 pm
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The brakes were on at the time so it wasn't over-speed. My
suggestion is to fiberglass the rotor arms. The production Gull
rotors are aluminum/plywood laminate but it only comes in 1/2".
I think a 3/4" ply fiber-glassed would be quite strong.
I don't talk about it much - but the Gull design has a furling
mechanism built in. You just don't see it. That's partly why
efficiency goes down to 25% at 30+mph.
#Post#: 3620--------------------------------------------------
Re: Rotor Arm Material
By: happygolucky Date: July 1, 2014, 2:07 pm
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i was up all night...sorry.. for your loss....lynx nature is
cruel..an unforgiving i pray no one was injured.. the new
marine board is exactly what your speaking about it is replacing
the now wood marine board with a fiberglass epoxy gel coat..
very strong deck board....
#Post#: 3632--------------------------------------------------
Re: Rotor Arm Material
By: sut Date: July 1, 2014, 9:11 pm
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Its to bad you didn't have a set of my wings in that wind it
would of been a great test for them ! I don't know how much wind
I had because I sleep through everything , I saw yours held up
even though the rotor didn't
#Post#: 3639--------------------------------------------------
Re: Rotor Arm Material
By: lynx wind Date: July 2, 2014, 8:31 am
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Even with the brakes on the VAWT will spin producing dead short
amps. It's extremely hard to turn at more than 2-3 rpm. Think
of putting a shaft in a vice and turning it with a 20 in lever
with 200Lbs of force. It's all torque.
There are lots of ways to add mechanical systems, more rotors,
more bracing, furling, pivots etc... I never say these are bad
ideas and encourage people to explore. My personal quest is for
simple rugged, and low cost performance.
#Post#: 3641--------------------------------------------------
Re: Rotor Arm Material
By: sut Date: July 2, 2014, 8:50 am
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So really then shorting a windmill is just as bad for it stress
wise as letting it spin ? just safer no flying parts to worry
about hitting someone or something
#Post#: 3655--------------------------------------------------
Re: Rotor Arm Material
By: lynx wind Date: July 2, 2014, 6:15 pm
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Upon further investigation the plywood rotor that failed started
de-laminating and lost a lot of strength. Encapsulating in
fiberglass would prevent this. The test rotor arms survived the
autumn, hard winter and spring just painted, and then a 70+ mph
wind. I think fiberglass resin over plywood would survive a
long time, sort of like fiberglass boats.
The circular rotor would work but would be quite big at 40" D -
a lot of extra weight as well. Avoiding extra weight is a good
idea for a lot of reasons.
#Post#: 3656--------------------------------------------------
Re: Rotor Arm Material
By: sut Date: July 2, 2014, 6:34 pm
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Yes it would help a lot the only thing I don't like about that
is when you tighten up the bolts it has a tendency to crack the
resin which can let in water, but you can always silicone around
the fender washer and over bolt to keep that sealed . @CG at one
time also mentioned placing a sleeve in the plywood to keep the
bolt from crushing the plywood when tightened
#Post#: 3662--------------------------------------------------
Re: Rotor Arm Material
By: lynx wind Date: July 2, 2014, 7:58 pm
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Great point SUT. Yes, here's where CG's idea will come in. Tap
some steel inserts in and fiberglass the rotor. Light strong
and wont crush.
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