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re: darrieus wind turbine
15 jul 2001
jerry knight-rubino   wrote:
>> ...putting a darrieus machine on a tower is not practical, for
>> the simple reason that the darrieus is designed to be a lightweight,
>> towerless turbine design, which keeps it cheap.  the price you pay
>> for the design is reduced aerodynamic efficiency and a large ground
>> footprint of the guy wire attachment points.

the separate guy wire anchors raise the price and interfere with
activities like farming... 
>actually, upon further reflection, i think you could put a 
>darrieus on a tower in a wind farm by attaching the guy wires
>at the top to near the base of the next over darrieus machine.

that could be done with a short tower. one might also connect
machines together with horizontal wires at the peaks, say
in a hexagonal pattern.  

>at the edge of the farm, you'd need a perimeter of anchor points...

sure. like the end of a grape trellis row.
>i've never heard of the double-delta design that nick mentioned.

i noticed a drawing of this in an ieee spectrum issue ca 1980, in an
article by christensen describing designs that had been investigated
by nasa. it's basically a tetrahedron balanced with one point on the
ground and the opposite face in a horizontal plane above that, joined
to the horizontal face of another upside-down tetrahedron above it.
the second tetrahedron has a higher vertex directly over the vertex on
the ground. it rotates on an a vertical axis between these 2 vertices.
the structure looks like a y from above. 

i started building one of these with an automobile wheel at the top
and another wheel "foundation" at the bottom, attached to a 5:1 step-up
auto rear end with the spider gears welded together, as a right-angle
drive for an induction generator that might act as a motor to start
the rotor and a brake to stall it.

i used 6 8' pieces of 1" pvc-covered steel tubing, with 6 thin, low-
solidity dacron sailcloth sailblades (expecting a 6:1 tipspeed ratio)
with leading edges wrapped around the tubing and trailing edges attached
to 6 plastic-covered wires. a tension ring with 3 more horizontal wires
connected the 3 common points of the 2 tetrahedra at the horizontal face
to give the structure vertical support, (with no central column) and 
3 guy wires stabilized the pillow block at the top end.

in a field, the guy wires attached to the top of one of these machines
might connect to the bases of its 3 neighbors, since the straight blades
do not become parallel to the ground near the ground. 


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