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#Post#: 3847--------------------------------------------------
Re: Rotor Arm Material
By: lynx wind Date: July 13, 2014, 9:46 am
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CG,
I used 1/2" birch plywood and painted with three coats of latex.
This was last fall. Over the winter spring and summer the glue
holding the laminations failed, water crept in and caused the
plywood to become like layers of cardboard.
I know what you are saying, but really it was my material
choice, sealing technique and weather. The 70 mph wind just
revealed the weakening. It wouldn't have mattered if the
turbine was shutdown, shunted through a load or hooked up to a
rectifier.
#Post#: 3915--------------------------------------------------
Re: Rotor Arm Material
By: sut Date: July 19, 2014, 9:06 am
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What if we made a rotor like a wagon wheel with 6 spar spokes
(spar rods for spokes ) the outside rim would be big enough just
to accommodate the wings?
#Post#: 3977--------------------------------------------------
Re: Rotor Arm Material
By: lynx wind Date: July 26, 2014, 9:37 am
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Windspeed is higher for the top blades causing more turning
force. The top blade tries to move forward faster. I have
thought about shortening the top blades slightly to balance
this.
#Post#: 3980--------------------------------------------------
Re: Rotor Arm Material
By: lynx wind Date: July 26, 2014, 12:01 pm
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Countless hours of experimenting and observation.
The problem with shortening is that power in the wind is
logrithmic so knowing how much to adjust is tough. I have
chosen to just strengthen the heck out of the rotor arm and
blades.
#Post#: 3982--------------------------------------------------
Re: Rotor Arm Material
By: lynx wind Date: July 26, 2014, 1:16 pm
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All the VAWTs I have built. (You can probably see it in other
experimenters video as well) It is pretty obvious in higher
winds. If the rotor arms aren't stiff enough they twist badly,
and it can be seen in Video very easy. I have struggled to
overcome this problem. If it develops the blades get crunched
at corners because they don't conform well to parallelogram
shape.
So far I haven't seen a hint of this on the SUT blades with 3/4"
rotor arms. But I haven't seen 40+mph winds either. If it does
develop the aluminum may get wrinkled near the corners.
Nessprojects will probably be able to assess this before I do.
There is a lot of forward torque when winds are high. Just a
bit more on the upper blade. Shortening the upper blade by 1"
may cure this problem. It wont be a factor in low winds, but
will compensate in higher winds.
#Post#: 3985--------------------------------------------------
Re: Rotor Arm Material
By: lynx wind Date: July 27, 2014, 8:53 am
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Its the rotor arm between the steel disk and the blade that
twists. Yes the top blade torques forward from the top so I
guess if the rotor arm is stiff then the blade may either stay
rigid with the rotor arm or wrinkle.
Try your idea and see what happens. The brace is intended to
keep the blade from moving outward so having the brace tie back
should control forward an outward force. Easy enough to move
the brace mount point.
#Post#: 4088--------------------------------------------------
Re: Rotor Arm Material
By: Cartichoke Date: August 7, 2014, 11:47 am
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If you are experiencing plywood failure, perhaps you could make
your own plywood.
Its sounds odd but its actually fairly straight forward. My
brother-in-law had a need for very high
quality, void free, marine grade plywood for use in skim boards
and long boards (he ran summer
camps teaching kids to make skim boards and made long boards for
sale). He is able to make
a much higher quality product by sandwiching the ply layers -
which he just purchased locally
at the lumber yard, albeit a plywood supplier yard. The core
glue is just rolled on by hand
and then the pieces are sandwiched in a press that he made from
2x6 laminated on edge -
screw type press.
The press also has an advantage of being able to provide a
profile of some sort in the
plywood - which was one of the key reasons he made his own ply.
The skim boards
have a rocker and the longboards have compound curves. The
compound curves add
tremendously to the strength.
He also experimented for years with closed cell foam cores
sandwiched between layers
of ply and fiberglassed using vacuum bags. It made stunning,
lightweight, extremely
strong boards but the cost and time were far to high for his
main use - teaching skim
board camps.
Finally, I know that 1/8th inch cedar strip, laminated on edge
and sandwiched between
layers of fiberglass is tremendously strong and lightweight. As
my cedar strip canoe
can attest.
#Post#: 4093--------------------------------------------------
Re: Rotor Arm Material - bamboo?
By: Cartichoke Date: August 7, 2014, 6:33 pm
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I've started to see a lot of laminated bamboo products on the
market. Any thoughts on using a bamboo laminate of some sort? I
believe it has pretty amazing strength to weight ratios.
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