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Forum Index : Windmills : Vawt Height(Physical), not tower height

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screwball3z

Newbie

Joined: 31/07/2009
Location: United States
Posts: 2

Posted: 04:10am 31 Jul 2009

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Hello guys, first time post and i have to say im happy to
have found this forum. The mini mill has actually
answered alot of questions that have been bugging me.
Now onto my actual question/post.

I have been thinking of a VAWT design, as always its a
drag based vawt. my query is do increased height of
blades do anything for the mill. If blades are longer,
they will make it easier to catch wind, but at the same
time the opposite side (drag) will be increased as well.
Also a longer blade would make the mill heavier, and a
little more fragile in my opinion.

I guess i'm really looking for an efficient way to guess
what height would be good, for reference I do not really
plan on putting this VAWT on a post/tower, id like to
keep the design ground/flat rooftop based.

On a side note, i'm guessing that the larger diameter of
the base and vanes is the bigger the better.

Let the conversation begin, and i'll reply back as
needed.Edited by screwball3z 2009-08-01

Don't just think outside the box, burn it down

screwball3z

Newbie

Joined: 31/07/2009
Location: United States
Posts: 2

Posted: 04:33am 31 Jul 2009

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Just to give an idea of what i'm thinking about here's a
rough sketch of what i'm thinking about, the outside vanes
are stationary

31_143329_Vawt_Concept.JPG
Edited by screwball3z 2009-08-07

Don't just think outside the box, burn it down

Roel Bos
Newbie

Joined: 15/08/2009
Location:
Posts: 1

Posted: 06:37pm 14 Aug 2009

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Hey Screwball,

I'm a newbie as well and have a similar idea, cause my neighbours inevitably will complain as I live in the Netherlands.
The idea is to fabricate one VAWT with blades of 1 meter made out PVC pipes, sliced in half in lenght.
It will be like an anemometer with three blades and I'll place it on our shed with a flat roof or just the house roof where it will charge a battery.
I have no doubt it will rotate as I experimented with a smaller one, but the only issue is
The only issues I expect are the speed of it and what kind of motor I should use.

As to your questions: I don't know how to calculate all factors, I'm just going with my instinct.
I think the bigger it gets the slower it rotates, but some gear can overcome that (and reduce the momentum/torque).
The drag will always be present, but the factor between thrust and drag will be the same, according to the shape of the blades.

I made a simple picture(yes, by hand) Hope it can tickle your imagination.

Greetz,

Roel

Edited by Roel Bos 2009-08-16

MacGyver

Guru

Joined: 12/05/2009
Location: United States
Posts: 1329

Posted: 05:39am 19 Aug 2009

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I live in the United States and around here, many business use a small,
flat, wind-driven rotating sign to advertise.

It's merely a flat piece of sheet metal with the left and right side vertical
edges creased in opposite directions. I've seen them at 90 degrees as
well as 45 degrees and they all seem to spin very nicely in any breeze.

You might experiment with something along these lines before building
something high-tech. This type of "windmill" could be built for just a few
bucks (low cost). If you want to increase the thrill of the building process,
learn to "dumpster dive" in your town's manufacturing districts.

If you're worried about your neighbors complaining, paint a butterfly on
each side and tell them it's art. Heck, you can get away with just about
anything if you say it's "art"!

Maybe try building two and use a chain to spin the armature one way and
the stator the other. This would effectively increase your shaft speed and
make manufacturing direct-drive electricity from a d.c. electric motor
more feasible.

If it doesn't work, what the heck? You'll still have "kinetic sculptures" (art)
to tantalize the neighbors, right?

Nothing difficult is ever easy!
Perhaps better stated in the words of Morgan Freeman,
"Where there is no struggle, there is no progress!"
Copeville, Texas

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